Composite zoned oxidation catalyst for compression ignition internal combustion engines

Abstract

A composite oxidation catalyst for treating exhaust gas generated by a vehicle compression ignition internal combustion engine in an exhaust system, comprising: a substrate having two catalyst carrier coating zones arranged axially in series on and along the substrate surface, wherein the first catalyst carrier coating zone contains a first catalyst carrier coating and has a length of <50% of the axial length L of the substrate, and is defined at one end by the first substrate end and at the second end by the first end of a second catalyst carrier coating zone, the second catalyst carrier coating zone being defined at its second end by the second substrate end and having a length less than L and containing a second catalyst carrier coating; wherein the composite oxidation catalyst comprises a carrier coating covering layer, which extends axially from the first substrate end to >50% to at most 150% of the axial length of the underlying first catalyst carrier coating.

Description

[0001] This application is a divisional application of the invention patent application with application number 202080033284.8 filed on June 26, 2020 and invention name “Composite partitioned oxidation catalyst for compression ignition internal combustion engine”. Technical Field

[0002] The present invention relates to a composite zoned oxidation catalyst for treating exhaust gas generated by a compression ignition internal combustion engine of a vehicle in an exhaust system, preferably for a heavy-duty diesel vehicle and located upstream of a particulate filter in the exhaust system. The present invention also relates to an exhaust system or a vehicle comprising the composite zoned oxidation catalyst. The present invention also relates to the use of the composite zoned oxidation catalyst for generating an exotherm to regenerate a downstream particulate filter; and a method for preparing the composite zoned oxidation catalyst. Background Art

[0003] Internal combustion engines produce pollutants such as carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NO x ) and particulate matter (PM) in exhaust gases. Emission standards for pollutants in exhaust gases produced by internal combustion engines, particularly for vehicle engines, are becoming increasingly stringent. There is a need to provide improved catalysts and exhaust systems for treating and removing pollutants in such exhaust gases that are able to meet these standards and are cost-effective.

[0004] Exhaust gases from gasoline and diesel engines are often treated with a catalyst that can (i) oxidize carbon monoxide (CO) to carbon dioxide (CO2); and (ii) oxidize hydrocarbons (HC) to water (H2O) and carbon dioxide (CO2). A three-way catalyst (TWC) is often used to oxidize nitrogen oxides (NO x ) to nitrogen (N2), water (H2O) and carbon dioxide (CO2). Exhaust from compression ignition engines (such as diesel engines) is often treated with an oxidation catalyst (commonly referred to as a diesel oxidation catalyst (DOC)) that performs oxidation reactions (i) and (ii). Some diesel oxidation catalysts are also capable of oxidizing nitrogen monoxide (NO) to nitrogen dioxide (NO2), which can aid in the removal of NO using additional downstream emission control equipment. x .

[0005] Oxidation catalysts for compression ignition internal combustion engines typically contain one or more platinum group metals. The specific platinum group metal selected for inclusion in the oxidation catalyst will depend on a variety of factors, such as reactivity to specific pollutants and reactivity under different exhaust gas conditions, cost, high temperature durability, chemical compatibility with the support material and any other components of the catalyst, and susceptibility to poisoning by impurities. For example, platinum (Pt) and palladium (Pd) are each capable of oxidizing carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas from a compression ignition engine. Compared to platinum, palladium is more susceptible to poisoning by sulfur in the fuel, but has greater thermal durability.

[0006] When the internal combustion engine is a compression ignition engine, such as a diesel engine, used to power the vehicle, then the vehicle may be a light-duty diesel vehicle or a heavy-duty diesel vehicle.

[0007] The term "Light Duty Diesel Vehicle (LDV)" is defined in US or EU regulations. In the US, a Light Duty Diesel Vehicle (LDV) is a diesel vehicle with a gross vehicle weight ≤ 8,500 pounds (US lbs).

[0008] In Europe, light-duty diesel vehicles are defined as vehicles in the M1, M2, N1 and N2 categories with a reference mass ≤ 2610 kg (EU5 / 6).

[0009] In the United States, a heavy-duty diesel vehicle (HDV) is defined in regulations as a diesel vehicle (model year 1995 and later) with a gross vehicle weight rating >8,500 pounds (US lbs) within federal jurisdiction and greater than 14,000 pounds in California.

[0010] In Europe, according to EU regulations (Council Directive 2007 / 46 / EC), heavy-duty diesel vehicles are vehicles designed and constructed for the transport of goods, with a maximum mass (i.e., the "technically permitted maximum laden mass") exceeding 3.5 tons (i.e., metric tons) but not exceeding 12 tons (N2 category) or exceeding 12 tons (N3 category), i.e., trucks; or vehicles designed and constructed for the transport of passengers, which include more than 8 seats in addition to the driver's seat and have a maximum mass not exceeding 5 tons (M2 category); or exceeding 5 tons (M3 category), i.e., buses and coaches. China broadly follows the European definition.

[0011] In Japan, a HDV is a heavy commercial vehicle, defined as a gross vehicle weight > 7500kg.

[0012] In Russia and South Korea, emission standards for heavy-duty vehicles are based on European standards, so the above European definitions apply.

[0013] In Brazil, an HDV is a motor vehicle used to transport passengers and / or cargo with a maximum gross vehicle weight above 3,856 kg or a curb weight above 2,720 kg.

[0014] In India, HDV is a vehicle with gross vehicle weight > 3,500kg.

[0015] Strategies for meeting current emission standards for heavy-duty diesel engines typically employ an exhaust system architecture that includes a series of catalytic substrates and injectors. In order from upstream to downstream (upstream relative to the engine connected or connectable to the exhaust system), the exhaust system includes a hydrocarbon fuel injector, a diesel oxidation catalyst (DOC), a catalyzed soot filter (CSF, i.e., a catalyzed diesel particulate filter (DPF)), a urea (ammonia precursor) injector, one or more selective catalytic reduction (SCR) catalysts, and an ammonia slip (ASC) catalyst (also known as ammonia oxidation (AMOX)).

[0016] The function of the DOC during normal operation is to control CO and HC emissions, promote the conversion of NO to NO2 for downstream passive filter regeneration (particulate matter held on the filter burns in the exhaust gas at a lower exhaust gas temperature in NO2 than in O2, the so-called effect), and acts as an exothermic generating catalyst during active CSF regeneration via injection of hydrocarbon fuel into the exhaust. For the avoidance of doubt, fuel injection / exothermic generating events do not occur during normal operation: normal operation is considered to be the time interval between fuel injection / exothermic generating events (see the paper by C. Ruehl et al. discussed below). The CSF controls particulate matter (PM) emissions and promotes NO→NO2 conversion to enhance SCR performance. Urea, a precursor to ammonia, is injected downstream of the CSF and mixed with the exhaust. NOx is converted on the SCR catalyst via reaction with ammonia (NH3), and unreacted NH3 is oxidized on an ammonia slip catalyst (ASC).

[0017] SCR catalysts are designed to selectively catalyze the conversion of NO using a nitrogen-containing reductant (usually NH3, which may be derived from an ammonia precursor such as urea). x The reducing agent is injected into the flowing exhaust gas upstream of the SCR catalyst in an amount that promotes the following main NOx reduction reactions:

[0018] (1) 4NH3+4NO+O2→4N2+6H2O;

[0019] (2) 4NH3+2NO2+O2→3N2+6H2O; and

[0020] (3) NO+NO2+2NH3→2N2+ 3 / 2H2O (preferred so-called "fast SCR reaction").

[0021] It will be appreciated that each of reactions (1) to (3) can occur in parallel, but the kinetically fastest reaction will be favored. x In exhaust gases with a ratio of 0.5, the kinetically favorable fast SCR reaction dominates. For most (but not all) applications, some degree of exhaust gas recirculation (EGR) is used to reduce engine-out NOx to a certain level, which can then be further reduced by urea SCR aftertreatment. A DPF is required to reduce the increased engine-out PM emissions caused by the use of EGR, as well as to ensure compliance with the Euro VI particulate matter number emission limits. Using high-efficiency SCR, some Euro VI engines can reduce the use of EGR (for example, through part-time and / or uncooled EGR) or eliminate EGR completely. This leads to three main Euro VI engine strategies:

[0022] 1. Cooled EGR+SCR,

[0023] 2. Hot (uncooled) EGR+SCR, and

[0024] 3. SCR only.

[0025] Using these strategies, emissions from a typical heavy-duty engine are about 60 ppm CO and about 10 ppm unburned hydrocarbon fuel. However, all such systems include a diesel particulate filter. Diesel particulate filter systems for vehicles involve the interaction of filter materials with regeneration technology. "Regeneration" is a selected method of burning diesel particulate matter held on the filter. Regeneration is not performed frequently, but the time interval between regeneration events depends on several factors, including engine design, filtration efficiency during normal operation, engine load during normal operation, etc. According to a recent paper, the empirical regeneration frequency of heavy-duty diesel trucks varies between 3 and 100 hours and 23 and 4078 miles (see C. Ruehl et al., Environ. Sci. Technol, 2018, Vol. 52, No. 10, pp. 5868-5874).

[0026] Regeneration technologies can be broadly divided into the categories of passive, active, and a combination of passive and active. In a passive system, the oxidation temperature of the particulate matter is reduced to a level at which the filter can be automatically regenerated during normal vehicle operation. Examples of such passive systems include catalytic filter media; the addition of a catalyst fuel additive so that the particulate matter on the filter contains a catalyst in its composition that promotes soot combustion; and the generation of nitrogen dioxide (NO2) upstream of the filter for burning the particulate matter held on the filter: the particulate matter burns at a lower temperature in NO2 than in oxygen. This is the so-called effect (see, for example, EP0341832).

[0027] Active systems actively trigger filter regeneration by raising the temperature of particulate matter trapped in the filter. In practice, this can be done onboard the vehicle by burning hydrocarbon fuel already onboard and / or by electrical heating. Two methods for burning the fuel include in-cylinder engine management methods, such as late-cycle injection of additional fuel; or injecting and burning the fuel in the exhaust, i.e. after the exhaust has left the engine cylinders themselves.

[0028] In a passive-active system, the “passive” filter catalyst or upstream ( The invention provides a novel NO oxidation catalyst (e.g., a catalyst that promotes the NO oxidation effect) that allows active regeneration at lower exhaust gas temperatures and / or shorter durations. In either case, the fuel economy penalty associated with active regeneration can be minimized (at the cost of the increased catalyst). Regeneration at lower temperatures can also reduce thermal stress and increase the life of the filter.

[0029] The present invention relates to an active regeneration system or an active-passive regeneration system.

[0030] Applicant's WO 2013 / 088152 A1 discloses a catalytic aftertreatment system for diesel exhaust, the system comprising a diesel oxidation catalyst (DOC) and an aftertreatment device located downstream of the DOC, the aftertreatment device requiring periodic heat treatment, and means for producing a temperature increase within the aftertreatment device, the DOC comprising an upstream zone having a length of 0.5 to 2 inches (12.7 to 50.81 mm) which is more active in oxidizing hydrocarbons (HC) than the remainder of the DOC. The present disclosure explains that during active regeneration of the filter, the exotherm generated when the DOC comes into contact with injected hydrocarbon fuel may surprisingly disappear even when the initially "lit" upstream DOC comes into contact with injected hydrocarbon fuel.

[0031] U.S. patent application publication US2014 / 0271429 A1 discloses an oxidation catalyst composite comprising a zoned-coated diesel oxidation catalyst on a substrate, wherein a first carrier coating zone adjacent to an inlet end of the substrate has a Pt / Pd ratio of less than 3:1 and a PGM loading of at least twice that of a second carrier coating zone adjacent to an outlet end of the substrate, wherein the first carrier coating zone has a shorter length than the second carrier coating zone.

[0032] US Patent Application Publication No. US2009 / 288402 discloses a zoned diesel oxidation catalyst containing a higher precious metal loading in the inlet zone, wherein an outlet zone and an inlet zone of equal or shorter length are described.

[0033] EP 2000639 A1 discloses a method in which the temperature window in which high-concentration hydrocarbons can be burned is considered to be widened, or high-temperature gas is supplied to a rear-stage catalyst more quickly. The method for purifying exhaust gas discharged from an internal combustion engine includes using a catalyst to increase the temperature of the exhaust gas to purify the exhaust gas, and is characterized in that, in the exhaust gas flow, hydrocarbons are introduced into the exhaust passage of the internal combustion engine located on the upstream side of the temperature-raising catalyst in an amount of 1,000-40,000 vol.ppm in terms of methane. That is, if the diesel fuel hydrocarbon compound is a chain of 16 carbon atoms, then according to the definition used in EP'639A1, the hydrocarbon chain represents 16 times the amount of methane (CH4).

[0034] The catalyst in EP'639A1 is obtained by loading a catalytically active component (A) on a refractory inorganic oxide powder (B) and loading the inorganic oxide powder loaded with the catalytically active component on a refractory three-dimensional structure, wherein the catalytically active component consists of (a) platinum; (b) an oxide of at least one metal selected from magnesium, alkaline earth metals and alkali metals, the alkali metal being optionally selected from magnesium, calcium, barium, strontium and potassium; and (c) at least one component selected from palladium and rhodium.

[0035] WO 2015 / 015182 of the applicant discloses an oxidation catalyst for treating exhaust gas from a diesel engine, the oxidation catalyst comprising: a substrate; a first washcoat region disposed on the substrate, wherein the first washcoat region comprises a first platinum group metal and a first support material; a second washcoat region adjacent to the first washcoat region, wherein the second washcoat region comprises a second platinum group metal and a second support material; a third washcoat region disposed on the substrate, wherein the third washcoat region comprises a third platinum group metal and a third support material; and wherein: (i) the third washcoat region is adjacent to the second washcoat region; or (ii) the second washcoat region is disposed on or supported on the third washcoat region. The first washcoat region may or may not comprise an alkaline earth metal.

[0036] WO 2014 / 132034 A1 of the applicant discloses an oxidation catalyst for treating exhaust gas generated by an internal combustion engine, wherein the oxidation catalyst comprises a substrate and a catalyst layer, wherein the catalyst layer comprises: a first support material; a first platinum group metal; and a second platinum group metal; wherein the catalyst layer is disposed on the surface of the substrate, and the catalyst layer has a non-uniform distribution of the first platinum group metal in a direction perpendicular to the surface of the substrate. The oxidation catalyst can be used to oxidize carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) in such exhaust gas.

[0037] WO 2009 / 076574 discloses an emission treatment system and method for remediating nitrogen oxides (NOx), particulate matter and gaseous hydrocarbons present in the exhaust gas flow of a diesel engine. The emission treatment system has an oxidation catalyst upstream of a soot filter upstream of a NOx reduction catalyst. The oxidation catalyst includes an inlet zone having an axial length and an outlet zone having an axial length, the inlet zone containing at least one of platinum and palladium in a first loading amount, the outlet zone containing palladium in a second loading amount, the outlet zone being substantially free of platinum - meaning that platinum is not intentionally provided in the zone, but unintentionally less than about 1% by weight of the metal may contain platinum - the first loading amount is greater than the second loading amount, and the axial length of the inlet zone is less than or equal to the axial length of the outlet zone. The diesel oxidation catalyst contains a catalyst that is effective to produce substantially no additional NO2 in the exhaust gas flow after passing through the diesel oxidation catalyst within about 90% of the diesel oxidation catalyst operating window.

[0038] WO 2006 / 056811 of the applicant discloses an apparatus comprising a compression ignition engine and an exhaust system thereof, the exhaust system comprising at least one exhaust system component for treating exhaust gas and means for generating exotherm to heat said at least one exhaust system component, the exotherm generating means essentially consisting of a catalyst and means for injecting hydrocarbons into the exhaust gas for combustion on the catalyst, the catalyst essentially consisting of both a palladium (Pd) component and a platinum (Pt) component and an optional support material disposed on a substrate monolith.

[0039] The applicant's WO 2014 / 080200 discloses an exhaust system for a compression ignition engine, the exhaust system comprising an oxidation catalyst for treating carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas from the compression ignition engine, wherein the oxidation catalyst comprises: a platinum group metal (PGM) component selected from a platinum (Pt) component, a palladium (Pd) component, and a combination thereof; an alkaline earth metal component; a support material comprising a modified alumina doped with a heteroatom component; and a substrate, wherein the platinum group metal (PGM) component, the alkaline earth metal component, and the support material are disposed on the substrate. The embodiment shows the use of ≥100 g / ft 3 The alkaline earth metal loadings of the light-duty diesel exhaust compositions were tested.

[0040] The applicant's WO 2014 / 080202 discloses a catalyzed soot filter comprising an oxidation catalyst for treating carbon monoxide (CO) and hydrocarbons (HC) in exhaust gas from a compression ignition engine arranged on a filter substrate, wherein the oxidation catalyst comprises: a platinum group metal (PGM) component selected from a platinum (Pt) component, a palladium (Pd) component and a combination thereof; an alkaline earth metal component; a support material comprising modified alumina doped with a heteroatom component.

[0041] Example 8 shows that the oxidation of nitric oxide is affected by the presence of barium oxide in this catalyst formulation.

[0042] WO 2010 / 118125 discloses an oxidation catalyst composite for oxidizing unburned hydrocarbons (HC) and carbon monoxide (CO) and reducing nitrogen oxides (NOx) from a diesel engine, the oxidation catalyst composite comprising at least two carrier coatings, a first carrier coating comprising a palladium component and a second carrier coating comprising platinum, and at least about 50% of the total platinum is located at the rear of the catalyst.

[0043] WO 2015 / 110818 A1 of the applicant discloses an oxidation catalyst for treating exhaust gas from a diesel engine and an exhaust system comprising the oxidation catalyst. The oxidation catalyst comprises: a first carrier coating region for oxidizing carbon monoxide (CO) and hydrocarbons (HC), wherein the first carrier coating region comprises a first platinum group metal (PGM) and a first carrier material; a second carrier coating region for oxidizing nitrogen monoxide (NO), wherein the second carrier coating region comprises platinum (Pt), manganese (Mn) and a second carrier material; and a substrate having an inlet end and an outlet end; wherein the second carrier coating region is arranged at the outlet end of the substrate and contacts the exhaust gas after the exhaust gas contacts the first carrier coating region.

[0044] The applicant's WO 2017 / 093720 discloses an oxidation catalyst for treating exhaust gas generated by a diesel engine, wherein the oxidation catalyst comprises: a substrate; a capture material for capturing at least one phosphorus-containing impurity and / or at least one sulfur-containing impurity in the exhaust gas generated by the diesel engine; and a catalytic region disposed on the substrate; wherein the catalytic region comprises a catalytic material comprising a platinum group metal (PGM) selected from platinum (Pt), palladium (Pd), and a combination of platinum (Pt) and palladium (Pd).

[0045] It is believed that there are two basic mechanisms by which catalysts used to treat exhaust gases from internal combustion engines may be poisoned: (i) selective poisoning, in which contaminants react directly with active sites or catalyst supports, resulting in reduced activity or catastrophic loss of activity; and (ii) non-selective poisoning, which spatially blocks access to active sites or pores in the catalyst support by contaminating (or masking) the surface of the support or active sites, resulting in performance loss. The inventors have found that zinc and (at low temperatures) phosphorus (as phosphoric acid droplets) and the oil droplets themselves (all derived from fuel or lubricant) are non-selective poisons of the exothermic generation function of the oxidation catalyst of the active or active-passive system disclosed in the applicant's WO 2013 / 088152A1. Poisons that chemically react with the catalyst components (mechanism (i)) include phosphorus (at higher temperatures), which can also poison the exothermic generation function of the oxidation catalyst. The main source of phosphorus and zinc in the exhaust gas may come from zinc dialkyl dithiophosphates (ZDDP) additives for mineral-based oils or synthetic oil zinc dithiophosphates (ZDTP). These additives are used to protect the moving parts of the engine, such as the camshaft, from wear during use. Heavy-duty vehicle engine oils have higher concentrations of additives than lubricants used for light-duty vehicle engines (such as those used for passenger cars), so the problem of zinc and phosphorus deactivation is particularly problematic for heavy-duty vehicle engines. Phosphorus and zinc deposits cannot be removed from the catalyst except under conditions that may cause thermal deactivation of the oxidation catalyst component and other catalyst components in the exhaust system (i.e., very high operating temperatures). A review of poisons and poisoning mechanisms, including phosphorus and zinc, can be found, for example, in AJJ Wilkins et al., Platinum Metals Review, 1990, Vol. 34, No. 1: pp. 16-24.

[0046] Platinum group metals as commodities are relatively rare, naturally occurring metallic chemical elements with high economic value relative to industrial base metals (such as copper). Shortly before the filing date of this specification, the spot price of copper at the London Metal Exchange was $5,463 per ton, while the spot price of platinum at the London Bullion Market Association was $845 per ounce, equivalent to $29,806,530 per ton (one metric ton is 35,274 ounces). However, the corresponding spot price of palladium is $1,968 per ounce. That is, by weight, the current cost of palladium is more than twice that of platinum. Therefore, there is a general concern to reduce the amount of palladium in diesel oxidation catalysts relative to platinum, and if possible, to reduce the amount of platinum group metals in diesel oxidation catalysts by appropriately promoting with cheaper metal elements.

[0047] The present invention is based on the active or active-passive system disclosed in the applicant's WO 2013 / 088152 A1, the purpose of which is to generally reduce the amount of total platinum group metals present in a diesel oxidation catalyst, and more specifically to reduce the weight of palladium relative to platinum, and / or to improve the efficiency of active filter regeneration by using less fuel to achieve a desired filter inlet temperature and / or to achieve a higher filter inlet temperature for the same amount of fuel injected upstream of a prior art oxidation catalyst to generate an exotherm therefrom, and / or to enable an exotherm to be generated on the oxidation catalyst from a lower initial exhaust gas temperature at the inlet of the oxidation catalyst. In addition, the inventors have developed a composite oxidation catalyst, i.e. a multifunctional catalyst arrangement on a single substrate, in which one or more of the above objectives can be combined with stable NO2 generation for operation of downstream catalyst functions, including for burning particulate matter on a downstream filter and / or promoting a so-called fast reaction on a selective catalytic reduction (SCR) catalyst. Another advantage of the preferred arrangement is a multifunctional catalyst with improved hydrocarbon slippage control. In a preferred arrangement, in addition to one or more or all of the above advantages, a guard bed feature may be incorporated into the composite oxidation catalyst design to reduce or prevent catalyst poisoning from phosphorus and / or zinc from engine lubricant additives, thereby substantially maintaining catalyst performance, i.e., durability, over a longer period of time. Summary of the invention

[0048] The present inventors have surprisingly discovered that by combining a weight equivalent or preferably platinum-enriched platinum and palladium PGM component with an alkaline earth metal component into a catalyst support coating zone at the inlet end of an oxidation catalyst disposed upstream of a filter substrate in a system for a vehicular compression ignition engine, particularly a vehicular heavy duty diesel engine, one or more desired improvements are obtained.

[0049] According to a first aspect, the present invention provides a composite oxidation catalyst for treating exhaust gas generated by a compression ignition internal combustion engine of a vehicle in an exhaust system, the composite oxidation catalyst preferably being used in a heavy-duty diesel vehicle and being located upstream of a particulate filter in the exhaust system, the composite oxidation catalyst comprising:

[0050] A substrate having a total length L and a longitudinal axis, and having a substrate surface extending axially between a first substrate end portion and a second substrate end portion; and two or more catalyst support coating zones arranged axially in series on the substrate surface, wherein a first catalyst support coating zone having a length L1 is defined at one end by the first substrate end portion, where L1 < L, and at a second end by a first end of a second catalyst support coating zone having a length L2, where L2 < L, wherein the first catalyst support coating zone comprises a first refractory metal oxide support material and two or more platinum group metal components supported thereon, the two or more platinum group metal components including both platinum and palladium, and the weight ratio of platinum to palladium ≥ 1; and the second catalyst support coating zone comprises a second refractory metal oxide support material and one or more platinum group metal components supported thereon, wherein the total platinum group metal loading defined in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) in the first catalyst support coating zone is greater than the total platinum group metal loading in the second catalyst support coating zone, and wherein the first catalyst support coating zone comprises one or more first alkaline earth metal (preferably barium) components supported on the first refractory metal oxide support material.

[0051] The product protected by the claims may also be marked with the following indication: when installed according to any one of the second to fifth inventive aspects described below, the first substrate end portion should be oriented to the upstream side.

[0052] It should be understood that the feature of determining the axial length of the catalyst support coating zone is the platinum group metal loading in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ). Generally, the platinum group metal loading at any point along the axial length of the catalyst support coating zone varies from the average value along the axial length of the zone as a whole by no more than + / -20%, optionally + / -15%, such as + / -10%. The local platinum group metal loading can be determined by X-ray fluorescence (XRF) or electron probe microanalysis (EPMA).

[0053] According to a second aspect, the present invention provides an exhaust system for a vehicle compression ignition engine, the exhaust system comprising a composite oxidation catalyst according to the first inventive aspect and a soot filter substrate disposed downstream of the composite oxidation catalyst, wherein the first substrate end portion of the oxidation catalyst is oriented to the upstream side.

[0054] According to a third aspect, the present invention provides a compression ignition internal combustion engine for a heavy-duty diesel vehicle, the compression ignition internal combustion engine comprising an exhaust system according to the second inventive aspect, wherein the first substrate end portion of the composite oxidation catalyst is oriented to the upstream side.

[0055] According to a fourth aspect, the present invention provides a heavy-duty diesel vehicle, which includes an exhaust system according to the third aspect of the invention, that is, any relevant local definition of a heavy-duty vehicle as set forth in the background section of the above text specification. Thus, for example, if this application is filed in the United States, the definition of a heavy-duty vehicle applicable to the United States in the above background section should be applied. Similarly, if the application is filed with the European Patent Office, the definition of a heavy-duty vehicle in the European Union in the above background section should be applied, and so on.

[0056] According to a fifth aspect, the present invention provides the use of a composite oxidation catalyst according to the first aspect of the invention for heating a soot filter provided downstream of the composite oxidation catalyst in the exhaust system of a vehicle compression ignition engine by bringing the composite oxidation catalyst into contact with an exhaust gas containing an increased concentration of hydrocarbon fuel, and generating exotherm from the increased concentration of hydrocarbon fuel in the exhaust gas flowing in the exhaust system relative to normal operating conditions.

[0057] According to a sixth aspect, the present invention provides a method for preparing a composite oxidation catalyst (optionally, a composite oxidation catalyst according to the first aspect of the invention) for treating exhaust gas generated by a vehicle compression ignition internal combustion engine in an exhaust system, wherein the composite oxidation catalyst includes: a substrate having a total length L and a longitudinal axis and having a substrate surface axially extending between a first base end portion and a second base end portion; and two or more catalyst carrier coating zones axially arranged in series on the substrate surface and along the substrate surface, wherein a first catalyst carrier coating zone having a length L1 is defined by the first base end portion at one end, where L1 < L, and is defined by the first end of a second catalyst carrier coating zone having a length L2 at the second end, where L2 < L, wherein the first catalyst carrier coating zone contains a first refractory metal oxide carrier material and two or more platinum group metal components supported thereon, the two or more platinum group metal components including both platinum and palladium, and the weight ratio of platinum to palladium ≥ 1; and the second catalyst carrier coating zone contains a second refractory metal oxide carrier material and one or more platinum group metal components supported thereon, wherein the total platinum group metal loading defined in terms of grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) in the first catalyst carrier coating zone is greater than the total platinum group metal loading in the second catalyst carrier coating zone, and wherein the first catalyst carrier coating zone contains one or more first alkaline earth metal (preferably barium) components supported on the first refractory metal oxide carrier material, and the method includes the following steps:

[0058] (a) Applying a catalyst carrier coating to the substrate surface, extending from one end of the substrate, the catalyst carrier coating containing a refractory metal oxide carrier material and one or more platinum group metal components; and

[0059] (b) impregnating the catalyst support coating with a solution containing one or more platinum group metals in a zone of length L1 defined at one end by the first substrate end,

[0060] Wherein the one or more alkaline earth metal components are present in the catalyst support coating of step (a) and / or the impregnation solution used in step (b). It should be understood that the catalyst support coating of step (a) may include a platinum component, a palladium component, or both a platinum component and a palladium component, and the solution of step (b) may include platinum, palladium, or both platinum and palladium. As long as the combination of steps (a) and (b) reaches a first catalyst support coating zone having a length L1, the first catalyst support coating zone comprises two or more supported platinum group metal components, the two or more supported platinum group metal components include both platinum and palladium, and the weight ratio of platinum to palladium is ≥1.

[0061] In a seventh aspect, the composite oxidation catalyst according to the present invention may be defined as a product obtained or obtainable by the method according to the sixth inventive aspect.

[0062] More specific features of various aspects of the present invention can improve the durability of the composite oxidation catalyst against phosphorus and / or zinc poisoning from engine lubricants, improve the resistance to downstream processes such as nitrogen oxides (NO x ) by selective catalytic reduction) and reducing costs by limiting the relative amount of palladium to platinum in the composite oxidation catalyst according to the invention.

[0063] The present invention will now be further described. In the following paragraphs, different aspects of the present invention are defined in more detail. Unless there is a clear indication to the contrary, each aspect so defined can be combined with any other one or more aspects. Specifically, any feature indicated as being preferred or advantageous can be combined with any other one or more features indicated as being preferred or advantageous. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1There is shown a composite oxidation catalyst (12) according to the present invention, the composite oxidation catalyst comprising a first catalyst support coating zone (1) provided at an inlet end (I) of a flow-through honeycomb structured substrate monolith (5) having a total length L, and a second catalyst support coating zone (2) adjacent to the first catalyst support coating zone (1) provided at an outlet end (O) of the substrate (5), the first catalyst support coating zone and the second catalyst support coating zone being arranged in series on and along the surface of the substrate. That is, in use, the substrate of the composite oxidation catalyst is oriented such that exhaust gas from the engine first enters the composite oxidation catalyst via the inlet (or upstream) end (I) and exits the composite oxidation catalyst via the outlet (or downstream) end (O), and the exhaust gas flow is in the direction indicated by the arrow at reference numeral 10. This same orientation and sequence of the composite oxidation catalyst in contact with the exhaust gas applies to Figures 1 to 5 all embodiments disclosed in and described herein.

[0065] Figure 1 The composite oxidation catalyst of can be prepared by coating the substrate (5) along the entire axial length L with a first catalyst support coating of an aqueous solution comprising a first refractory metal oxide support material and one or more platinum group metal salts, drying and calcining the coated portion; then impregnating only a portion of the substrate coated with the first catalyst support coating to a length L1, where L1 < L, with an aqueous solution of one or more platinum group metals and optionally one or more alkaline earth metal components at a relatively high concentration to form the first catalyst support coating zone (1), wherein the second catalyst support coating (2) comprises the unimpregnated first catalyst support coating. Alternatively, the first catalyst support coating itself may contain one or more alkaline earth metal components rather than such alkaline earth metal components present in the impregnation medium. Of course, alkaline earth metal components may also be present in both the impregnation medium and the first catalyst support coating. For an explanation of the "impregnation" technique, see below. This arrangement results in a finished product in which the portion of the first catalyst support coating having a length L1 contains two or more supported platinum group metal components containing both platinum and palladium, with a weight ratio of platinum to palladium ≥ 1.

[0066] Alternatively, Figure 1 the composite oxidation catalyst shown can be obtained or obtainable by coating the substrate (5) from a first end thereof in any order as follows: coating to an axial length L1 with a first catalyst support coating (see Figure 19), the first catalyst carrier coating is used to form a first carrier coating catalyst zone and comprises a first refractory metal oxide carrier material, two or more platinum group metal components including both platinum and palladium (for example, platinum and palladium are the only platinum group metal components) and one or more alkaline earth metal components; and coated with a second different catalyst carrier coating comprising a second refractory metal oxide carrier material and one or more second platinum group metals and optionally one or more second alkaline earth metal components to form a second oxidation catalyst zone (see item marked 11) having an axial length L2, so that the second end (13) of the first catalyst carrier coating (9) and the first end (15) of the second catalyst carrier coating (11) are adjacent to each other, and there is substantially no overlap between the first carrier coating and the second carrier coating. In the preparation Figure 1 In the latter method of the implementation scheme, it should be understood that the axial length L1 of the first catalyst carrier coating zone is the same as or substantially the same as the axial length of the first catalyst carrier coating (9); and the axial length L2 of the second catalyst carrier coating zone is the same as or substantially the same as the axial length L2 of the second catalyst carrier coating zone.

[0067] Figure 1 and Figures 2 to 5 Each of the embodiments shown includes the preferred optional feature of a porous washcoat cover layer as a guard bed overlying the first catalyst washcoat zone (1) to reduce or prevent poisoning of the first catalyst washcoat zone by phosphorus and / or zinc deposits derived from lubricant additives such as ZDDP or ZDTP. The optional guard bed feature ("G") is Figures 1 to 5 In each embodiment, the diagram is shown in dashed lines.

[0068] Figure 2 and Figure 3Shows composite oxidation catalysts (14, 16 respectively) according to the present invention based on the same manufacturing principle, that is, a second catalyst carrier coating (7) is applied to the second end of the substrate (5) corresponding to the outlet end (O), and its axial length L4 is less than the total axial length L of the flow-through honeycomb structure substrate blank (5) (i.e., L4 < L). The second catalyst carrier coating contains a second refractory metal oxide carrier material and one or more platinum group metal components and optionally one or more second alkaline earth metal components. Then, the substrate coated with the second catalyst carrier coating (7) is itself coated with a first catalyst carrier coating (6), which is coated from the opposite end of the substrate (5) - corresponding to the inlet or the first base end (I) - to the end of the substrate (5) where the second catalyst carrier coating starts to be coated. The first catalyst carrier coating contains a first refractory metal oxide carrier material and one or more platinum group metal components and optionally one or more first alkaline earth metal components. The axial coating length (L3) of the first catalyst carrier coating (6) is less than the total axial substrate length L, but long enough to overlap with the length (L4) of the second catalyst carrier coating (7), thereby forming a region where the first catalyst carrier coating (6) and the second catalyst carrier coating (7) exist in a two-layer structure: in other words, the "zone". The axial length of the overlapping region of the first carrier coating and the second carrier coating can be defined as "L5", and is shown as "2" in Figure 2 i.e., the second carrier coating catalyst zone; and is shown as "4" in Figure 3 i.e., the fourth carrier coating catalyst zone.

[0069] It can be seen that the zone with an overlapping length of L5 including the first catalyst carrier coating (6) and the second catalyst carrier coating (7) contains the sum of the amounts of one or more platinum group metals and optionally one or more alkaline earth metals present in both the first catalyst carrier coating (6) and the second catalyst carrier coating (7) in the overlapping region. It can also be seen that since the overlapping region of the first catalyst carrier coating (6) and the second catalyst carrier coating (7) represents its own zone, this zone including the single-layer second catalyst carrier coating (7) (marked as 3 in both Figure 2 and Figure 3 ) will have a lower total platinum group metal loading than the immediately adjacent upstream overlapping zones ( Figure 2 zone 2 in; and Figure 3 zone 4 in), this zone is defined by the second (downstream or outlet) end of the overlapping region of the first catalyst carrier coating (6) and the second catalyst carrier coating (7) at the first end (17) and by the second base end (or outlet end (O)) at the second end.

[0070] In Figure 2In the arrangement shown, the overlapping area of ​​the first catalyst support coating (6) and the second catalyst support coating (7) is the second catalyst support coating area (in Figure 2 A portion of the total length of the first catalyst washcoat layer (6) comprises a greater total platinum group metal loading (in g / ft) than the second catalyst washcoat layer zone (2). 3 ), which portion is the first catalyst washcoat zone (labeled 1) and is defined at a first end by the inlet / first substrate end (I), and at a second end by the first (upstream, i.e., closest to the inlet end) end (19) of the second catalyst washcoat zone (2), which point also corresponds to the first or upstream end of the second catalyst washcoat (7). It can also be seen that because Figure 2 The illustrated zone 2 includes an overlap of the first carrier coating (6) and the second carrier coating (7), so the axial length L3 of the first catalyst carrier coating (6) is equal to the sum of the axial lengths of the first catalyst carrier coating zone (1) and the second catalyst carrier coating zone (2). In addition, the length of the first catalyst carrier coating (6) present in the first carrier coating zone (1) is the total length of the catalyst carrier coating 6 minus the length of the first carrier coating present in the overlap zone 2, i.e., L5.

[0071] During the implementation process, Figures 2 to 5 In each of the embodiments shown, this feature of the total platinum group metal loading in the first catalyst support coating zone (1) being greater than the total platinum group metal loading in the second catalyst support coating zone (2) can be obtained by impregnating the desired length (8) (L1) of the underlying first catalyst support coating (6) with a relatively high concentration of a platinum group metal salt (e.g., in an aqueous solution thereof, and optionally also containing an aqueous salt of one or more alkaline earth metals). "Impregnation" is a method known to those skilled in the art and is disclosed, for example, in "Catalytic Air Pollution Control-Commercial Technology", 3rd edition, Ronald M. Heck et al., John Wiley & Sons, Inc. (2009) paragraph 2.3. Figure 2 , the axial length L1 of the first catalyst washcoat zone (labeled 1) is substantially the length of the first catalyst washcoat (6) until the point at which the first catalyst washcoat (6) begins to overlap the second catalyst washcoat (7) at point 19.

[0072] In the case where the support coating used to form the first catalyst support coating (6) does not contain one of platinum and palladium, for example, the impregnation medium should contain a solute salt of palladium or platinum, whichever is not present in the first catalyst support coating (6), so that the desired length (8) (L1) of the first catalyst support coating below contains two or more supported platinum group metal components, the supported platinum group metal components including both platinum and palladium, and the weight ratio of platinum to palladium is ≥1. Of course, in any combination, the first catalyst support coating itself may contain platinum, palladium, or both platinum and palladium; and separately, the impregnation medium may contain platinum, palladium, or both platinum and palladium, that is, the PGM content of the first catalyst support coating and the impregnation medium may be the same or different, as long as the resulting desired length (8) (L1) of the first catalyst support coating below contains two or more supported platinum group metal components containing both platinum and palladium, and the weight ratio of platinum to palladium is ≥1. In the case where the support coating used to form the first catalyst support coating (6) does not contain one or more alkaline earth metal components, for example, the impregnation medium should contain one or more alkaline earth metal salts. Of course, it is also possible that both the washcoat composition and the impregnation medium used to form the first catalyst washcoat (6) contain one or more alkaline earth metals, in which case the one or more or each alkaline earth metal in the washcoat composition and the impregnation medium may be the same or different.

[0073] The third catalyst support coating zone (labeled 3) is defined at its second (or outlet (O)) end by the second substrate end and has an axial length L6. The first end of the third catalyst support coating zone (3), i.e., the end closest to the first substrate (or inlet (I)), is defined as (17) above.

[0074] from Figure 2As can be seen from the arrangement shown, and as described above, each catalyst support coating zone can be partially composed of only a portion of the axial length of the catalyst support coating. Therefore, the refractory metal oxide support material below is located in the catalyst support coating zone of which the catalyst support coating is a part. Therefore, in the case where the catalyst support coating zone includes an overlap of the catalyst support coating, the refractory metal oxide support material in the catalyst support coating zone formed by the overlap includes the refractory metal oxide support present in each catalyst support coating in the overlap. Therefore, in the case where the refractory metal oxide support material in the first catalyst support coating in the overlapping zone is different from the refractory metal oxide support material in the second catalyst support coating, there will be two (or more) refractory metal oxide support materials in the overlapping catalyst support coating zone as a whole. Of course, a single catalyst support coating may also include two or more different refractory metal oxide support materials, in which case the catalyst support coating zone formed by the catalyst support coating of the single layer will contain two or more different refractory metal oxide support materials. Similarly, if the refractory metal oxide support material is the same in each of two catalyst washcoat layers overlapped on a substrate to form a catalyst washcoat zone, then there will be only one refractory metal oxide support material in the overlapping catalyst washcoat layer zone.

[0075] Figure 3 The arrangement shown is similar to Figure 2 The arrangement shown and described above differs in that the first catalyst support coating zone (labeled 1) of axial length L1 is a single layer of the first catalyst support coating (6) formed in a shorter length, for example, by impregnating a substrate (5) coated with a shorter length (8) of the first catalyst support coating (6) with an aqueous solution of one or more platinum group metal salts and optionally one or more alkaline earth metal salts at a relatively high concentration. In this embodiment, the second catalyst support coating zone (labeled 2) is defined at the first end (i.e., closest to the first substrate end or inlet) by the second end (21) of the first catalyst support coating zone 1 (e.g., the impregnation range (8) of the first catalyst support coating (6)), and at the second end by the first end (23) of the overlapping area of ​​the first catalyst support coating (6) with the underlying second catalyst support coating (7) (closest to the inlet end (I)). This feature of a total platinum group metal loading in the first catalyst washcoat zone being greater than the total platinum group metal loading in the second catalyst washcoat zone is satisfied, for example, by impregnating an underlying first catalyst washcoat layer with a relatively high concentration of one or more platinum group metals, the first catalyst washcoat layer comprising one or more platinum group metal components. Such impregnation medium may also comprise an aqueous salt of one or more alkaline earth metals.

[0076] According to the definition of the present invention, the third catalyst support coating (referenced as 3) is defined at its second (or outlet (O)) end by the second substrate end. Figure 3 In the embodiment shown, the zone consisting of the overlap of the first catalyst washcoat layer (6) and the second catalyst washcoat layer (7) - which is axially located between the second catalyst washcoat layer zone (2) and the third catalyst washcoat layer zone (3) - is numbered as the fourth catalyst washcoat layer zone and is Figure 3 It is marked as "4" in the figure. Figure 3 It can be seen that the axial length of the first carrier coating (6) is the sum of the axial lengths of the first catalyst carrier coating zone (1), the second catalyst carrier coating zone (2), and the fourth catalyst carrier coating zone (4). It can also be seen that the axial length of zone 2 is the total axial length L3 of the first catalyst carrier coating (6) minus the axial length in the overlap zone (zone 4) (i.e., equal to L5) and the length L1 of the first catalyst carrier coating zone 1. The axial length of zone 3 is defined at its second (outlet (O) or downstream) end by the second substrate end and has an axial length L6.

[0077] Figure 4 and Figure 5 The arrangements shown (composite oxidation catalysts 18 and 20, respectively) are similar to Figure 2 and Figure 3 The arrangements shown differ in that Figure 4 and Figure 5 In the embodiment shown, a first carrier coating (6) comprising a first refractory metal oxide support material, one or more platinum group metal components and optionally one or more first alkaline earth metal components supported thereon is first applied to a flow-through honeycomb structure substrate monolith (5) from the inlet end (I) to a length L3. Then, the substrate coated with the first catalyst carrier coating (6) is itself coated with a second catalyst carrier coating (7) (i.e., coated to a length of L4<1), the second catalyst carrier coating being applied from the opposite end of the substrate (5) - corresponding to the outlet end (O) - all the way to the end of the substrate (5) where the first catalyst carrier coating (6) is applied. The axial coating length of the second catalyst carrier coating (7) is less than the total axial substrate length L, but is long enough to overlap with the first catalyst carrier coating (6), thereby forming a region where the second catalyst carrier coating (7) and the first catalyst carrier coating (6) exist as a double-layer zone. To avoid repetition, the applicant refers to the explanations given above regarding the axial zone length, zone boundary definition, total zone platinum group metal loading, zone refractory metal oxide support material description, and so on.

[0078] Figure 6is a schematic diagram of a single layer (such as a layer of a first catalyst support coating zone) according to an embodiment of the present invention, which has a uniform or homogeneous distribution of a first platinum group metal (e.g., platinum group metal 1 represented by ρ) and an uneven (i.e., inhomogeneous) distribution of a second platinum group metal (e.g., platinum group metal 2 represented by ○).

[0079] Figure 7 is a schematic diagram showing uniform distribution of two platinum group metals (eg, platinum group metal 1 represented by p and platinum group metal 2 represented by o) in an embodiment of a single-layer catalyst support coating zone of the present invention.

[0080] FIG. 8A to FIG. 8D Various system arrangements including the composite oxidation catalyst according to the first aspect of the present invention are shown, such as Figures 1 to 5 Any one of the composite oxidation catalysts disclosed in each figure of the present invention. DETAILED DESCRIPTION

[0081] For the avoidance of doubt, the composite oxidation catalyst described herein is referred to as an "oxidation catalyst" because it can oxidize pollutants in the exhaust gas during normal lean-burn operation of a compression ignition engine, which produces a lean exhaust gas, primarily carbon monoxide and unburned hydrocarbons. The composite oxidation catalyst can also oxidize nitrogen monoxide in the exhaust gas to nitrogen dioxide to promote downstream catalytic activity such as The invention relates to a composite oxidation catalyst for treating exhaust gases produced by diesel compression ignition engines, wherein the composite oxidation catalyst is preferably used to treat exhaust gases produced by diesel compression ignition engines, and / or promotes selective catalytic reduction reactions, and such NO oxidation activity can be enhanced by using the features of one or more of the attached dependent claims. Since the composite oxidation catalyst is preferably used to treat exhaust gases produced by diesel compression ignition engines, it may also be referred to as a "diesel oxidation catalyst". However, in rare cases, the composite oxidation catalyst according to the invention is intended to generate heat from the additional hydrocarbons introduced into the exhaust gas, thereby heating the downstream particulate filter and thereby regenerating it (i.e., burning the soot trapped thereon (active regeneration)).

[0082] The activity of the composite oxidation catalyst is not limited to oxidation reactions, but the oxidation catalyst should be able to oxidize one or more pollutants in the exhaust gas of a compression ignition engine during normal lean-burn operation. For example, assuming appropriate conditions, the oxidation catalyst is also capable of performing reduction reactions, such as reducing nitrogen oxides (NO x )(So-called poor NO x Catalysis, DeNO x catalytic or hydrocarbon-SCR) and / or capable of temporarily storing one or more pollutants from the exhaust gas, such as NO xFor the further avoidance of doubt, the use of the composite oxidation catalyst to generate exothermic heat from additional hydrocarbon fuel injected into the exhaust is not "normal use" (see discussion of regeneration frequency in the Background section above). That is, "normal lean burn operation" is the time interval between exothermic generating events.

[0083] With respect to NO oxidation activity, preferably, the composite oxidation catalyst as a whole promotes NO oxidation within >10% (such as >20%, >30%, >40% or >50%) of the oxidation catalyst operating window during normal use. This is in stark contrast to the oxidation catalyst disclosed in WO 2009 / 076574 discussed above, in which the diesel oxidation catalyst is effective to produce substantially no additional NO2 in the exhaust gas stream after passing through the diesel oxidation catalyst within about 90% of the diesel oxidation catalyst operating window. The composite oxidation catalyst according to the present invention does this by including at least one zone in the oxidation catalyst, the at least one zone having a weight ratio of platinum to palladium of >1 (such as >1.5:1 or >2:1), optionally with only platinum as the only platinum group metal present in that particular zone, i.e., the weight ratio of platinum to palladium is 1:0 (or "infinity" (∞)). Optionally, for catalyst washcoat zones other than the first catalyst washcoat zone, such other zones may exhibit increased NO oxidation in the presence of lower alkaline earth metal loadings or substantial absence of alkaline earth metals in one or more zones other than the first catalyst washcoat zone.

[0084] According to the first aspect, the second catalyst washcoat zone may be defined at its second end by the second substrate end. That is, the composite oxidation catalyst as a whole includes two catalyst washcoat zones (see, e.g. Figure 1 arrangement shown).

[0085] A method of preparing such a catalyst having two catalyst washcoat zones comprises a method according to the sixth inventive aspect, wherein in step (a), the catalyst washcoat extends along the total length L of the substrate. It will be appreciated that in this method, the first refractory metal oxide support material is the same as the second refractory metal oxide support material. Alternatively, Figure 1 The composite oxidation catalyst shown can be obtained or obtainable by coating the substrate (5) in any order from the first end thereof in the following manner: coating with a first catalyst carrier coating to an axial length L1 (see Figure 1The invention relates to a method for preparing a catalyst layer having an axial length L2 and a first catalyst support coating layer comprising a first refractory metal oxide support material, two or more platinum group metal components including both platinum and palladium, and one or more alkaline earth metal components; and a method for preparing a catalyst layer having an axial length L2 and a second catalyst support coating layer comprising a second refractory metal oxide support material and one or more second platinum group metals and optionally one or more second alkaline earth metal components, so as to form a second oxidation catalyst zone (see item marked 11), so that the second end (13) of the first catalyst support coating layer (9) and the first end (15) of the second catalyst support coating layer (11) are adjacent to each other, and there is substantially no overlap between the first support coating layer and the second support coating layer. Figure 1 In the latter method of the embodiment of the present invention, it should be understood that the axial length L1 of the first catalyst carrier coating zone is the same as or substantially the same as the axial length of the first catalyst carrier coating (9); and the axial length L2 of the second catalyst carrier coating zone is the same as or substantially the same as the axial length L2 of the second catalyst carrier coating zone. More details of the method for preparing the dual-zone composite oxidation catalyst according to the first aspect of the invention are described above in conjunction with Figure 1 Described.

[0086] Alternatively, according to the first aspect, the composite oxidation catalyst may include three or more catalyst support coating zones, wherein a third catalyst support coating zone comprising a third refractory metal oxide support material and one or more platinum group metal components supported thereon is defined at its second end by the second substrate end, and wherein the third catalyst support coating zone has a mass expressed in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) is less than the total platinum group metal loading in the second catalyst support coating zone.

[0087] The composite oxidation catalyst according to the first aspect of the present invention may include four catalyst support coating zones, wherein the fourth catalyst support coating zone is located between the second catalyst support coating zone and the third catalyst support coating zone, the fourth catalyst support coating zone comprises a fourth refractory metal oxide support material and one or more platinum group metal components supported thereon, and is defined at its first end by the second end of the second catalyst support coating zone and at its second end by the first end of the third catalyst support coating zone, and wherein the fourth catalyst support coating zone has a volume in grams of platinum group metal / cubic foot of substrate volume (g / ft 3 ) is greater than the total platinum group metal loading in each of the second catalyst washcoat zone and the third catalyst washcoat zone.

[0088] Preferably, in the composite oxidation catalyst including four catalyst support coating zones according to the first aspect of the present invention, the composite oxidation catalyst includes a first catalyst support coating and a second catalyst support coating, wherein the first catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, having a length L3, where L3 < L, and is defined by a first base end at one end; and the second catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, having a length L4, where L4 < L, and is defined by a second base end at the second end, wherein the fourth catalyst support coating zone includes a double-layer overlapping region of the first catalyst support coating and the second catalyst support coating, and wherein the third catalyst support coating zone includes the second catalyst support coating of a single layer that does not form the overlapping region. The method for preparing such a composite oxidation catalyst is described above with reference to Figure 3 and Figure 5 the embodiments shown and further with reference to Figure 2 and Figure 4 the embodiments shown and their related descriptions.

[0089] The composite oxidation catalyst including three catalyst support coating zones may include a third catalyst support coating zone that is defined by the second end of the second catalyst support coating zone at its first end (see, for example, the arrangement shown in Figure 2 and Figure 4 ).

[0090] Such a composite oxidation catalyst may include a first catalyst support coating and a second catalyst support coating, wherein the first catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, having a length L3, where L3 < L, and is defined by a first base end at one end; and the second catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, having a length L4, where L4 < L, and is defined by a second base end at the second end, wherein the second catalyst support coating zone includes a double-layer overlapping region of the first catalyst support coating and the second catalyst support coating, and wherein the third catalyst support coating zone includes the second catalyst support coating of a single layer that does not form the overlapping region.

[0091] In the three-zone and four-zone arrangements described above, preferably, the one or more platinum group metal components in the third catalyst washcoat zone consist essentially of platinum. It should be understood that where the one or more platinum group metals in the third catalyst washcoat zone consist essentially of platinum, in an arrangement characterized by an overlap of a first catalyst washcoat and a second catalyst washcoat, the second catalyst washcoat forming the third catalyst washcoat zone also consists essentially of platinum.

[0092] It should also be understood that in a composite oxidation catalyst having two zones as described herein, the second catalyst washcoat zone may comprise one or more alkaline earth metals, such as barium and / or strontium, preferably barium.

[0093] It should also be understood that in a composite oxidation catalyst having three zones as described herein, the second catalyst support coating zone, the third catalyst support coating zone, or both the second catalyst support coating zone and the third catalyst support coating zone may each contain one or more alkaline earth metals, such as barium and / or strontium, preferably barium.

[0094] It should also be understood that in a composite oxidation catalyst having four zones as described herein, the second catalyst support coating zone, the third catalyst support coating zone and / or the fourth catalyst support coating zone may each contain one or more alkaline earth metals, such as barium and / or strontium, preferably barium.

[0095] It should also be understood that in a composite oxidation catalyst having three zones or four zones as described herein, the first catalyst support coating, the second catalyst support coating and / or both the first catalyst support coating and the second catalyst support coating may each contain one or more alkaline earth metals, such as barium and / or strontium, preferably barium.

[0096] The method for preparing a three-zone or four-zone composite oxidation catalyst according to the present invention includes a method according to the sixth aspect of the invention, wherein in step (a), the catalyst support coating is a first catalyst support coating, which extends from the end of the first substrate to less than the total length of the substrate, and the method also includes a step (a') before step (a) or after step (a), but in either case it is performed before step (b), in which a second catalyst support coating is applied to the substrate, and the length is from the end of the second substrate to less than the total length of the substrate, so that the first catalyst support coating partially overlaps with the second catalyst support coating or the second catalyst support coating partially overlaps with the first catalyst support coating, wherein the second catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components, and it should be understood that the platinum group metal composition of the support coating catalyst zone comprising two overlapping layers comprises the total platinum group metal present in each layer of the two overlapping layers of the zone.

[0097] Where the above method is used to prepare a composite oxidation catalyst having three or more zones according to the present invention, it will be appreciated that the axial length L1 of the impregnation step may determine the number of catalyst support coating zones present along the axial substrate length. Figure 2 , Figure 3 , Figure 4 and Figure 5 Further explanation.

[0098] Where L1 is less than the axial length between the first substrate end and the first end of the second catalyst carrier coating, indicating the end of the overlapping region of the first catalyst carrier coating and the second catalyst carrier coating that is closest to the first substrate end, the second catalyst carrier coating zone includes a single layer of the first catalyst carrier coating, the second catalyst carrier coating zone is defined at one end by the second end of the first catalyst carrier coating zone L1, and at the second end by the first end of the overlapping region of the first catalyst carrier coating and the second catalyst carrier coating that is closest to the first substrate end. In this case, the fourth catalyst carrier coating zone is defined by the first end of the overlapping region of the first carrier coating and the second carrier coating that is closest to the first substrate end, wherein the platinum group metal loading (g / ft 3 ), the first catalyst support coating zone>the fourth catalyst support coating zone>the second catalyst support coating zone. The third catalyst support coating zone is defined at the second end by the substrate end opposite to the substrate end from which the first catalyst support coating extends, and at the first end by the end of the overlapping region of the first catalyst support coating and the second catalyst support coating that is closest to the end from which the second catalyst support coating extends (i.e., also corresponding to the second end of the fourth catalyst support coating zone). This arrangement is defined in the present invention. Figure 3 and Figure 5 Shown in.

[0099] Wherein L1 is the same length as the axial length of a single layer of the first catalyst carrier coating, and the length extends from the end of the first substrate until the first catalyst carrier coating enters the overlapping area of ​​the second catalyst carrier coating zone. The oxidation catalyst as a whole includes three axially arranged catalyst carrier coating zones, which can be numbered in sequence from the end of the first substrate as the first catalyst carrier coating zone, the second catalyst carrier coating zone and the third catalyst carrier coating zone.

[0100] Alternatively, the oxidation catalyst having three or more catalyst carrier coating zones according to the present invention can be prepared by modifying the method for preparing the oxidation catalyst according to the sixth inventive aspect as follows, wherein the oxidation catalyst has two catalyst carrier coating zones as described above. First, the substrate is coated along its total length L with the first catalyst carrier coating. Second, the second catalyst carrier coating comprising a refractory metal oxide carrier material and one or more platinum group metal components can be coated from the end of the first substrate on top of the first catalyst carrier coating to an axial length less than the total substrate length L, or the first catalyst carrier coating can be impregnated from the end of the first substrate to a length less than the total substrate length L with an impregnation solution comprising one or more platinum group metal salts and optionally one or more alkaline earth metal salts. The second catalyst carrier coating or the impregnated first catalyst carrier coating will partially form the middle or second zone of the three catalyst carrier coating zones arranged axially along the substrate. Third, a third catalyst support coating layer comprising a refractory metal oxide support material and one or more platinum group metal components as the first catalyst support coating layer zone L1 can be coated from the first substrate end on top of the second catalyst support coating layer (or impregnated on the impregnated first support coating layer of zone length L1 corresponding to the first catalyst support coating layer zone) to less than the axial length of the second catalyst support coating layer or the axial length of the first impregnation of the above-mentioned second step. It should be understood that as long as the combination of the layer and the impregnation solution as a whole in L1 contains both platinum and palladium in a weight ratio ≥1, the platinum group metal content of the first catalyst support coating layer zone L1 includes the combination of the platinum group metal compositions of the following first catalyst support coating layer, the second catalyst support coating layer or impregnation solution, and the third catalyst support coating layer or impregnation solution. One or more alkaline earth metal components may be present in the support coating or impregnation step of the first application step, the second application step, and / or the third application step.

[0101] Preferably, at least the third step is carried out as an impregnation to a length L1 corresponding to step (b) of the sixth inventive aspect. This is because the multilayer stack coating reduces the cross-sectional area of ​​the open front area of ​​the substrate for allowing gas to pass through, thereby undesirably increasing the back pressure in the system. Therefore, a composite oxidation catalyst is preferred in which at least one catalyst support coating zone is formed by an impregnation step of the following catalyst support coating, preferably the third step corresponds to forming a first catalyst support coating zone.

[0102] When used in an exhaust system of a compression ignition engine of a vehicle, the first substrate end of the oxidation catalyst according to the first aspect of the present invention, including the first catalyst carrier coating zone, is oriented to the upstream side, i.e., closest to the engine. That is, the first substrate end can be defined as the first upstream inlet substrate end, and the second substrate end can be defined as the second downstream substrate (or outlet) end.

[0103] Platinum group metal loading

[0104] Generally speaking, each catalyst support coating zone in the composite oxidation catalyst according to the present invention comprises one or more, or two or more platinum group metal components selected from platinum, palladium, rhodium, iridium, ruthenium and mixtures or alloys of any two or more thereof, except for the case of the first catalyst support coating zone, which, according to the first aspect of the present invention, comprises both platinum and palladium, with a weight ratio of platinum to palladium ≥ 1. Wherein the catalyst support coating zone - except the first catalyst support coating zone - comprises only one platinum group metal, preferably platinum, i.e., the one or more platinum group metal components consist essentially of platinum or consist of platinum.

[0105] Specifically, the two or more platinum group metal components in the first catalyst washcoat layer zone and / or the first catalyst washcoat layer include both platinum and palladium, for example, the two or more platinum group metal components consist essentially of platinum and palladium or consist of platinum and palladium. Preferably, the only platinum group metals present in the first catalyst washcoat layer zone and / or the first catalyst washcoat layer are platinum and palladium. It should be understood that where the first catalyst washcoat layer comprises both platinum and palladium, any catalyst washcoat layer zone including the first catalyst washcoat layer will also comprise platinum and palladium.

[0106] It is further preferred that the one or more platinum group metal components in the second catalyst washcoat zone include (i.e. intentionally include) platinum, such as both platinum and palladium, or platinum may be the only platinum group metal present in the second catalyst washcoat zone, for example, the one or more platinum group metal components in the second catalyst washcoat zone consist of platinum; or the more than one platinum group metal components in the second catalyst washcoat zone consist of both platinum and palladium. Optionally, the content of platinum in the second catalyst washcoat zone is greater than 1% by weight of the total metals supported on the refractory metal oxide support material in that zone, the total metals including platinum group metals and base metals (e.g. alkaline earth metals). This feature is intended to distinguish the disclosure of WO 2009 / 076574, which is acknowledged in the background section above.

[0107] Preferably, where the substrate comprises three or more catalyst washcoat zones, the third catalyst washcoat zone or the second catalyst washcoat comprises platinum, i.e. intentionally comprises platinum, such as both platinum and palladium, or platinum may be the only platinum group metal present in the third catalyst washcoat zone or the second catalyst washcoat. Optionally, the content of platinum in the third catalyst washcoat zone is greater than 1 wt.% of the total metals supported on the refractory metal oxide support material in that zone, the total metals including platinum group metals and base metals (e.g. alkaline earth metals). This feature is intended to distinguish the disclosure of WO 2009 / 076574, which is acknowledged in the background section above.

[0108] In a preferred arrangement, platinum is the only platinum group metal in the second catalyst washcoat layer, i.e., the one or more platinum group metal components in the second catalyst washcoat layer consist of platinum (Pt:Pd weight ratio of 1:0), because this feature provides more stable NO2 generation for the operation of downstream catalyst functions, especially in arrangements where the second catalyst washcoat layer overlaps the first catalyst washcoat layer, such as Figure 4 and Figure 5 As shown. Therefore, for stable NO2 generation, an arrangement is preferred in which the one or more platinum group metal components in the second catalyst washcoat layer consist of platinum, wherein the second catalyst washcoat layer overlaps the first catalyst washcoat layer. In a preferred arrangement in which platinum is the only platinum group metal present in the third catalyst washcoat layer zone or the second catalyst washcoat layer (i.e., a Pt:Pd weight ratio of 1:0), the third catalyst washcoat layer zone or the second catalyst washcoat layer comprises manganese (see below).

[0109] Preferably, the second catalyst washcoat zone comprises both platinum and palladium, for example, the more than one platinum group metal component in the second catalyst washcoat zone consists of platinum and palladium, because this feature improves hydrocarbon slip control.

[0110] Thus, in general, and to distinguish from the disclosure of WO 2009 / 076574 acknowledged in the background section above, any catalyst support coating zone defined by the second (outlet) end of the substrate at the second end of the catalyst support coating zone intentionally comprises platinum, wherein, optionally, the platinum content in the catalyst support coating zone is greater than 1% by weight of the total metals supported on the refractory metal oxide support material in that zone, the total metals including platinum group metals and base metals (e.g. alkaline earth metals).

[0111] Typically, the total platinum group metal loading (calculated as elemental metal) on the substrate as a whole is from 5 to 60 g / ft 3 , preferably 8 to 50 g / ft 3 , for use in heavy-duty diesel engine exhaust systems.

[0112] The weight ratio of Pt:Pd on the substrate as a whole (calculated as elemental metal) is preferably from 3:2 to 9:1, preferably from 2:1 to 7:1, most preferably from 3:1 to 5:1.

[0113] The platinum group metal loading (calculated as elemental metal) in the first catalyst washcoat zone is preferably less than 100 g / ft 3 , preferably 25-75g / ft 3 , and most preferably 35-65g / ft 3It is understood that the first catalyst washcoat zone may comprise the "underlying" platinum group metal loading in the first catalyst washcoat layer (typically a single layer of the first catalyst washcoat layer) which is subsequently impregnated with a high concentration solution of a platinum group metal salt prior to drying and calcining. Thus, the first catalyst washcoat layer zone is a combination of the platinum group metal loading from both the first catalyst washcoat layer and the impregnation solution.

[0114] The platinum group metal loading in the second catalyst washcoat zone and subsequent catalyst washcoat zones as a whole, i.e., the total platinum group metal (calculated as elemental metal) in the catalyst washcoat zones other than the first catalyst washcoat zone, may depend on the embodiment used. Thus, for example, in an embodiment comprising only two total zones, such as Figure 1 As shown, the total platinum group metal loading in the second catalyst washcoat zone is preferably 1 to 10 g / ft 3 .

[0115] However, in embodiments comprising three catalyst washcoat zones, wherein the second catalyst washcoat zone comprises the overlapping region of the first catalyst washcoat and the second catalyst washcoat (see, e.g., Figure 2 and Figure 4 )-or an embodiment comprising four catalyst washcoat zones, wherein the fourth catalyst washcoat zone comprises an overlapping region of the first catalyst washcoat and the second catalyst washcoat (e.g., see Figure 3 and Figure 5 Embodiment) - the total platinum group metal loading in the second (or fourth) catalyst support coating zone may be 10 to 40 g / ft 3 , preferably 15 to 35 g / ft 3 .

[0116] In a catalyst support comprising three or four zones of coating, such as Figures 2 to 5 In embodiments of the present invention (those shown in any of the Figures of FIG), the total platinum group metal loading in the third catalyst support coating zone may be from 1 to 30 g / ft 3 , preferably 5 to 20 g / ft 3 .

[0117] In an embodiment comprising four catalyst washcoat zones, such as Figure 3 or Figure 5 The total platinum group metal loading in the second catalyst washcoat zone may be from 1 to 30 g / ft 3 , preferably 5 to 20 g / ft 3 However, the total washcoat loading in the second catalyst washcoat zone is always greater than the total washcoat loading in the third catalyst washcoat zone.

[0118] The one or more alkaline earth metal components and / or the one or more platinum group metal components supported on the refractory metal oxide support material may be pre-fixed to the refractory metal oxide support material prior to forming a washcoat with the refractory metal oxide support material, and will therefore be present throughout any washcoat coated with such a washcoat. However, in a preferred method, the solute salt of the one or more platinum group metal components and optionally the solute salt of the one or more first alkaline earth metal components are present in, for example, an aqueous washcoat slurry, which also contains a "fresh" refractory metal oxide material and is applied to a substrate, and after the washcoat slurry is applied to the substrate, the one or more platinum group metal components and the one or more first alkaline earth metal components are fixed to the refractory metal oxide support material by a drying and calcining process. By "fresh refractory metal oxide material" is meant that no platinum group metal component and / or alkaline earth metal component has yet been pre-fixed to the refractory metal oxide component. This method is preferred because it is less energy intensive, i.e., it avoids the two-step process of first preparing a supported pre-fixed refractory metal oxide product and then using the pre-fixed product to prepare a washcoat slurry for coating. Furthermore, the inventors have found that it may be advantageous for the exotherm generation that at least the first catalyst support coating has an inhomogeneous distribution of one or more platinum group metal components and / or one or more alkaline earth metal components throughout its thickness (i.e. the direction perpendicular to the substrate surface represents the thickness of the catalyst layer). This advantageous feature is not obtainable or is not obtainable to the same extent as achieving the desired effect in the case of pre-fixation of the platinum group metal or alkaline earth metal to the refractory metal oxide support material.

[0119] See below for an explanation of this aspect of Applicants' invention.

[0120] According to a sixth inventive aspect, also discussed below, the first catalyst washcoat zone is obtained or obtainable in part by the following steps:

[0121] (a) applying a catalyst washcoat layer to the surface of the substrate in a length extending from one end of the substrate, the catalyst washcoat layer comprising a refractory metal oxide support material and one or more platinum group metal components; and

[0122] (b) impregnating the catalyst support coating with a solution containing one or more platinum group metals in a region of length L1 defined at one end by the first substrate end.

[0123] Thus, it will be appreciated that where a catalyst washcoat (e.g., a first catalyst washcoat comprising one or more platinum group metal components supported on a refractory metal oxide support material) is itself impregnated with a solution comprising one or more platinum group metal components, the platinum group metal composition of the resulting zone is a combination of the underlying catalyst washcoat and the impregnation solution. Thus, for example, the platinum to palladium mass (i.e., weight) ratio in the first catalyst washcoat zone as a whole is derived from the total platinum and palladium derived from both the catalyst washcoat (i.e., the first catalyst washcoat) and the impregnation solution.

[0124] It should also be understood that according to the sixth aspect of the invention, in step (a), the catalyst carrier coating is a first catalyst carrier coating, which extends from the end of the first substrate to less than the total length of the substrate, and the method also includes a step (a') before step (a), but in either case it is performed before step (b), in which a second catalyst carrier coating is applied to the substrate, and the length is extending from the end of the second substrate to less than the total length of the substrate, so that the first catalyst carrier coating partially overlaps with the second catalyst carrier coating or the second catalyst carrier coating partially overlaps with the first catalyst carrier coating, wherein the second catalyst carrier coating comprises a refractory metal oxide carrier material and one or more platinum group metal components.

[0125] As mentioned above about Figure 4 and Figure 5 As discussed, preferably, the first catalyst washcoat layer extends from the first substrate end, and the second catalyst washcoat layer extends from the second substrate end, whereby the second catalyst washcoat layer partially overlaps the first catalyst washcoat layer.

[0126] According to the present invention, the first catalyst carrier coating zone contains both platinum (Pt) and palladium (Pd), and the weight ratio of platinum to palladium is ≥1. Although it is generally desired to reduce the amount of palladium in the composite oxidation catalyst relative to platinum to reduce the total cost of platinum group metals in the catalyst, as can be seen from sample 9.5 in Example 9 below, the applicant's experimental data shows that it is not desirable to completely remove palladium from the first catalyst carrier coating zone without adversely affecting the exothermic generation function of the catalyst during aging. In this regard, sample 9.5 in Example 9 shows that when the following carrier coating with a Pt:Pd weight ratio of 2:1 is impregnated with an impregnation medium that does not contain palladium (i.e., a Pt:Pd weight ratio of 1:0) to form a first catalyst carrier coating zone with a Pt:Pd weight ratio of approximately 47:1, the ability of the resulting catalyst to promote exothermicity is impaired, that is, the first catalyst carrier coating zone is less stable to aging. However, although less preferred, sample 9.5 in Example 9 is still an effective composite oxidation catalyst for the purposes of the present invention.

[0127] However, it is generally preferred that the weight ratio of platinum (Pt) to palladium (Pd) in the first catalyst support coating zone is 10:1≥1:1, preferably 10:1≥1.5:1 or 6:1≥1.5:1, more preferably 4:1≥1.5:1, for example 6:1≥2:1, 4:1≥1.5:1 or 2:1≥1:1, because Example 9 also shows that for the aged composite oxidation catalyst having a first catalyst support coating zone, the exothermic failure temperature (°C) test at an inlet temperature of <500°C is similar, and the first catalyst support coating zone is obtained by impregnating the lower catalyst support coating with a Pt:Pd weight ratio of 2:1 with impregnation media with Pt:Pd weight ratios of 1:1, 2:1, 3:1 and 4:1. It has also been found that, in combination with an alkaline earth metal component, the Pt:Pd ≥ 1:1 weight ratio feature improves the exothermic light-off temperature (light-off temperature is reduced), thereby allowing for increased exothermic heat generation from lower exhaust gas temperatures in active and active-passive regeneration systems.

[0128] It should be understood that further reductions in total platinum group metal cost in a composite oxidation catalyst according to the present invention for equivalent functionality (because the current cost of palladium by weight is significantly greater than the current cost of platinum by weight) may be achieved where the first catalyst carrier coating zone comprises a higher Pt:Pd weight ratio (e.g., ≥1.5:1, such as the preferred 10:1 ≥1.5:1 range, or ≥2:1 when combined with an outlet zone (e.g., a third catalyst carrier coating zone) that is defined at one end by an outlet end of a composite oxidation catalyst substrate comprising a preformed, manganese-doped mixed magnesium aluminum metal oxide. A composite oxidation catalyst having an outlet zone comprising the composition has been shown in Example 8 to improve exothermic performance and may enable the use of a smaller amount of platinum group metal in the outlet zone or in the second catalyst carrier coating that partially forms the outlet (third catalyst carrier coating) zone.

[0129] Preferably, particularly in embodiments comprising three or more catalyst washcoat zones, the one or more platinum group metals in the second catalyst washcoat zone comprise both platinum and palladium. In particularly preferred features, the mass ratio of platinum to palladium in the second catalyst washcoat zone is greater than the mass ratio of platinum to palladium in the first catalyst washcoat zone. An advantage of this Pt:Pd mass ratio in the second catalyst washcoat zone, combined with the platinum group metal loading in the second catalyst washcoat zone, is that the catalyst has improved hydrocarbon slip control, CO oxidation, and NO oxidation.

[0130] In this regard, in an embodiment consisting of two zones, for example, Figure 1As shown - allowing for any overlap with the production methods (see "Definitions" section below) - preferably, the second catalyst support coating zone comprises a Pt-rich PGM composition comprising palladium, preferably in a weight ratio of ≥10:1, ≥5:1, ≥3:1 or ≥2:1. In combination with a first catalyst support coating zone having Pt:Pd ≥1:1, this feature has been found to be advantageous because a second catalyst support coating zone of pure Pt (i.e., a Pt:Pd weight ratio of 1:0) has been found to be detrimental to exothermic light-off and HC slip in an aged catalyst. In this regard, the presence of Pd in ​​addition to Pt in the second catalyst support coating zone can improve the aging stability of the second catalyst support coating zone, i.e., maintain oxidation activity through aging. However, in combination with manganese, a Pt:Pd weight ratio of 1:0 in the second catalyst support coating zone has been found to be beneficial for NO oxidation (see Example 8 and below).

[0131] In the composite oxidation catalyst comprising three catalyst washcoat zones according to the invention, the mass ratio of platinum to palladium preferably increases from the first catalyst washcoat zone to the second catalyst washcoat zone to the third catalyst washcoat zone. This can be achieved, for example, in Figure 2 and Figure 4 In the embodiment shown, it is achieved that the second catalyst support coating (7) has a higher Pt:Pd mass ratio than the first catalyst support coating, preferably a mass ratio of 1:0, i.e., only Pt and substantially free of Pd, so that the single-layer second catalyst support coating in the third catalyst support coating zone (3) has the highest Pt:Pd ratio of any catalyst support coating zone arranged on the substrate. However, the same comments as those described in conjunction with the composite oxidation catalyst comprising only two catalyst support coating zones also apply, i.e., the aging stability of the third catalyst support coating zone can be improved by including some palladium (e.g., ≥10:1, ≥5:1, ≥3:1 or ≥2:1), while still maintaining the preferred arrangement of increasing platinum to palladium mass ratios from the first catalyst support coating zone to the second catalyst support coating zone and then to the third catalyst support coating zone. In the context of the three-zone composite oxidation catalyst, the benefits of also including manganese in the third catalyst support coating zone (3) are also mentioned (see Example 8 and below).

[0132] Furthermore, in a composite oxidation catalyst having four catalyst washcoat zones, the mass ratio of platinum to palladium in each successive catalyst washcoat zone arranged in series along the substrate length L at the inlet end after the first catalyst washcoat zone is greater than the mass ratio of platinum to palladium in the immediately preceding catalyst washcoat zone. This can be achieved, for example, in Figure 3 and Figure 5This is again achieved in the embodiment shown, where the second catalyst support coating (7) has a higher Pt:Pd mass ratio than the first catalyst support coating, preferably a mass ratio of 1:0, i.e., only Pt and essentially free of Pd, so that the single-layer second catalyst support coating in the third catalyst support coating zone (3) has the highest Pt:Pd ratio of any catalyst support coating zone. However, the same comments as those described in conjunction with the composite oxidation catalyst comprising only two catalyst support coating zones also apply, i.e., the aging stability of the third catalyst support coating zone can be improved by including some palladium (e.g., ≥10:1, ≥5:1, ≥3:1 or ≥2:1), while still maintaining the preferred arrangement of increasing platinum to palladium mass ratios from the first catalyst support coating zone to the second catalyst support coating zone and then to the third catalyst support coating zone. In the context of a four-zone composite oxidation catalyst, the benefits of also including manganese in the third catalyst support coating zone (3) are also mentioned (see Example 8 and below).

[0133] It is to be understood that - in the context of the four-zone composite oxidation catalyst according to the present invention - "the feature in each successive catalyst washcoat zone arranged in series along the substrate length L at the inlet end after the first catalyst washcoat zone is greater than the feature in the immediately preceding catalyst washcoat zone" is related to Figure 3 and Figure 5 The catalyst support coating zones in the catalyst support coating are numbered in different order. Figure 3 and Figure 5 , the numbering sequence of the carrier coating catalyst zones starting from the first catalyst carrier coating zone (1) is 1→2→4→3. This is because the third catalyst carrier coating zone (3) is defined at the second end by the second substrate end (or outlet end). However, "the characteristics in each continuous catalyst carrier coating zone arranged in series along the substrate length L at the inlet end after the first catalyst carrier coating zone are greater than the characteristics in the immediately preceding catalyst carrier coating zone" requires, for example, that the mass ratio of Pt:Pd in ​​the fourth catalyst carrier coating zone is greater than the mass ratio of Pt:Pd in ​​the immediately preceding second catalyst carrier coating zone (2), and that the mass ratio of Pt:Pd in ​​the third catalyst carrier coating zone (3) is greater than the mass ratio of Pt:Pd in ​​the immediately preceding fourth catalyst carrier coating zone (4).

[0134] Preferably, the one or more platinum group metals in the second catalyst support coating zone comprise both platinum and palladium, wherein the mass ratio of platinum to palladium is >1:1, preferably 10:1>3:2, such as 5:1>3:2.

[0135] Typically, the first catalyst washcoat zone or first catalyst washcoat does not contain rhodium.

[0136] It may be preferred that the second catalyst washcoat zone or the second catalyst washcoat contains no rhodium.

[0137] The third catalyst washcoat zone or the fourth catalyst washcoat zone may contain no rhodium.

[0138] It may also be preferred that the composite oxidation catalyst according to the present invention is substantially completely free of rhodium.

[0139] The inventors have also discovered that there may be advantages in improving exothermic generation where the one or more platinum group metal components and / or the one or more first alkaline earth metal components are not uniformly distributed in a direction perpendicular to the substrate surface. This will be discussed in more detail under the following headings.

[0140] Alkaline earth metal components

[0141] It should be understood that the purpose of the alkaline earth metal in the composite oxidation catalyst according to the present invention is not to store NO x For later use through the above-mentioned lean NO x The catalytic process releases and reduces NO. This is the result of a specially designed catalyst called lean NO x The purpose of the trap (LNT) is to use a catalyst which may also include alkaline earth metals, platinum group metals and optionally ceria, doped ceria or ceria mixed oxide components, but the LNT must be used in conjunction with a specially programmed engine control unit. The engine control unit is designed to x The lean stoichiometric operating mode and the rich exhaust gas pulse containing additional reducing substances (such as CO and / or hydrocarbons) contact the LNT to desorb the absorbed NO x and through the depleted NO on PGMs x The catalytic reaction reduces it to an operating mode. In the use of LNT, the frequency of lean / rich cycles is about 60 seconds lean and 5 seconds rich. Desulfation of LNT is less frequent, but the rich period can be longer. However, the control of desulfation events also requires a specially programmed engine control unit.

[0142] The composite oxidation catalyst of the present invention can be distinguished from LNT in at least two important respects. First, LNT is not used to treat exhaust from heavy-duty diesel engines, which use SCR catalysts. This is primarily because LNT catalysts for heavy-duty diesel vehicles would need to be so large that the cost of the required platinum group metals would make the cost of the catalyst prohibitively high. Second, preferably, the composite oxidation catalyst of the present invention is substantially free of ceria, doped ceria, or ceria mixed oxide or composite oxide components.

[0143] According to a first inventive aspect, the first catalyst washcoat zone comprises one or more first alkaline earth metal components supported on a first refractory metal oxide support material. The inventors have found that the presence of the alkaline earth metal component, preferably including barium, improves HC conversion for the purpose of generating exothermic heat from hydrocarbon fuels to such an extent that the amount of the one or more platinum group metals in the first catalyst washcoat zone can be reduced by about 7 g / ft 3 and still have the same activity. It is believed that the relatively high platinum group metal loading in the first catalyst washcoat zone quickly initiates and accelerates the exothermic reaction, while the presence of the one or more alkaline earth metals stabilizes the PGM, for example by reducing sintering and improving thermal durability.

[0144] The one or more alkaline earth metal components in the first catalyst washcoat zone are preferably barium (Ba) or strontium (Sr), preferably Ba, for example the one or more first alkaline earth metal components in the first catalyst washcoat zone consist of barium.

[0145] The reasons why barium is preferred over other alkaline earth metals are explained below under the heading "Non-uniform distribution of alkaline earth metal component and / or platinum group metal component in the washcoat layer".

[0146] The total alkaline earth metal component loading in the first catalyst washcoat zone may be in the range of 10-100 g / ft2 calculated as elemental metal. 3 , preferably 20-80g / ft 3 Too much alkaline earth metal component may be detrimental to heat generation. In this regard, the ratio of the total mass of the alkaline earth metal component to the total mass of the platinum group metal (PGM) component may be 1:1 to 1:2, preferably 1:1 to 50:80.

[0147] According to the method of the sixth invention aspect, one or more first alkaline earth metal components may be present in the catalyst support coating applied in step (a) and / or in the impregnation solution of step (b), but preferably in the catalyst support coating (e.g., the first catalyst support coating) of step (a) of the sixth invention aspect. This is because, in the case where alkaline earth metal (e.g., barium) salts are present in the impregnation medium of step (b), it may be more difficult to control the use of platinum group metal salts in the impregnation medium using the preferred pH range, so many alkaline earth metal salts migrate out of the target first catalyst support coating area by wicking. This alternative is preferred because the position of the final alkaline earth metal in the finished product can be better controlled, wherein the alkaline earth metal component is present in the support coating and then dried and calcined after coating.

[0148] It should be understood that where a catalyst support coating (e.g., a first catalyst support coating) comprising one or more alkaline earth metals is applied in step (a) of the sixth aspect of the invention, and where the catalyst support coating itself is impregnated with a solution comprising one or more alkaline earth metal components in step (b) of the sixth aspect of the invention, the composition of the resulting impregnation zone is a combination of the contents of the alkaline earth metal components in the underlying catalyst support coating and the impregnation solution.

[0149] The second catalyst support coating zone may also include one or more alkaline earth metal components, preferably barium. This may be derived from one or more first alkaline earth metal components (preferably barium) present in the catalyst support coating (e.g., the first catalyst support coating) of the sixth invention aspect of step (a), or wherein the composite oxidation catalyst includes a third or fourth catalyst support coating zone, a second catalyst support coating. The one or more alkaline earth metal components present in the second catalyst support coating may be referred to as one or more second alkaline earth metal components in this article. The third and fourth catalyst support coatings may also include one or more second alkaline earth metal components, preferably barium.

[0150] The inventors have also discovered that where one or more platinum group metal components and / or one or more first alkaline earth metal components are not uniformly distributed in a direction perpendicular to the substrate surface, there may be advantages in improving the exothermic generation from at least the first catalyst coating zone. This will be discussed in more detail under the following headings.

[0151] Refractory Metal Oxide Support Materials

[0152] The first, second, third or fourth refractory metal oxide support material of the first and / or second catalyst support coating is each typically selected from alumina, magnesia, silica, zirconia, titania, ceria and composite oxides or mixed oxides of two or more thereof. In principle, any suitable refractory metal oxide support material may be used as the first refractory metal oxide support material. The support material of each of the first, second, third or fourth refractory metal oxide support materials of the first or second catalyst support coating or the refractory metal oxide support material may be the same as or different from each other. However, it should be understood that in Figure 1 The composite oxidation catalyst shown may be a single carrier coating of length L impregnated at the first end to an axial length L1 to define a first catalyst carrier coating zone (1) and a second catalyst carrier coating zone (2), in which case the refractory metal oxide carrier material in the first catalyst carrier coating zone and the second catalyst carrier coating zone will be the same.

[0153] In addition, Figures 2 to 5In the illustrated embodiments comprising three and four catalyst washcoat zones, if the refractory metal oxide support material used in the first catalyst washcoat layer (6) is "X", then because the first, second and (if present) fourth catalyst washcoat layer zones comprise only a portion of the entire length L3 of the first catalyst washcoat layer (6), each of the first, second and (if present) fourth catalyst washcoat layer zones will each comprise the refractory metal oxide support material "X", i.e., the first, second and (if present) fourth refractory metal oxide support materials will be the same. Similarly, in Figures 2 to 5 In the illustrated embodiment, where the second catalyst support coating (7) comprises refractory metal oxide support material "Y", the third catalyst support coating zone and (if present) the second or fourth catalyst support coating zone including the overlapping area only comprise a portion of the entire length L4 of the second catalyst support coating (7), and therefore each of these zones will comprise refractory metal oxide support material "Y".

[0154] Preferably, the refractory metal oxide support material is selected from alumina, silica, zirconia, ceria and composite oxides or mixed oxides of two or more thereof, most preferably selected from alumina, silica and zirconia and composite oxides or mixed oxides of two or more thereof. Mixed oxides or composite oxides include silica-alumina and ceria-zirconia, most preferably silica-alumina. Preferably, the refractory metal oxide support material does not contain ceria or mixed oxides or composite oxides containing ceria. More preferably, the refractory oxide is selected from alumina, silica and silica-alumina. The refractory oxide may be alumina. The refractory oxide may be silica. The refractory oxide may be silica-alumina.

[0155] Because the first catalyst washcoat zone comprises one or more first alkaline earth metal components supported on the first refractory metal oxide support material, preferably, the first catalyst washcoat zone or the first refractory metal oxide support material of the following catalyst washcoat (e.g., the first catalyst washcoat) comprises or consists essentially of alumina doped with heteroatom components. The heteroatom components typically comprise silicon, manganese (see below), magnesium, barium, lanthanum, cerium, titanium or zirconium or a combination of two or more thereof. The heteroatom components may comprise or consist essentially of, or consist of: oxides of silicon, manganese, magnesium, barium, lanthanum, cerium, titanium or zirconium. More preferably, the alumina doped with heteroatom components is alumina doped with silicon dioxide or alumina doped with magnesium oxide or alumina doped with manganese oxide. Even more preferably, the alumina doped with heteroatom components is alumina doped with silicon dioxide. Alumina doped with heteroatom components can be prepared using methods known in the art or, for example, by the method described in US Pat. No. 5,045,519.

[0156] The inclusion of a dopant can stabilize the refractory metal oxide support material or promote the catalytic reaction of the supported platinum group metal. Typically, the dopant can be selected from zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd), barium (Ba) and their oxides. Generally speaking, the dopant is different from the refractory metal oxide (i.e., the cation of the refractory metal oxide). Thus, for example, when the refractory metal oxide is titanium dioxide, the dopant is not titanium or its oxide.

[0157] When the refractory metal oxide support material is doped with a dopant, then typically the refractory metal oxide support material comprises a total amount of 0.1 wt% to 10 wt% of the dopant. The total amount of dopant is preferably 0.25 wt% to 7 wt%, more preferably 2.5 wt% to 6.0 wt%. Preferably, the dopant is silica, because oxidation catalysts comprising such support materials in combination with platinum group metals and alkaline earth metals promote oxidation reactions, such as CO and hydrocarbon oxidation.

[0158] When the refractory metal oxide support material is silica-alumina, then typically the refractory oxide consists essentially of 20 to 95 weight percent alumina and 5 to 80 weight percent silica (e.g., 50 to 95 weight percent alumina and 5 to 50 weight percent silica), preferably 35 to 80 weight percent alumina and 20 to 65 weight percent silica (e.g., 55 to 80 weight percent alumina and 20 to 45 weight percent silica), even more preferably 45 to 75 weight percent alumina and 25 to 55 weight percent silica. Silica-alumina with a higher silica content (e.g., a silica content of about 30 weight percent) can provide greater sulfur tolerance to the composite oxidation catalyst as a whole.

[0159] When the refractory oxide is ceria-zirconia, then typically the ceria-zirconia consists essentially of 20 to 95 wt% ceria and 5 to 80 wt% zirconia (e.g., 50 to 95 wt% ceria and 5 to 50 wt% zirconia), preferably 35 to 80 wt% ceria and 20 to 65 wt% zirconia (e.g., 55 to 80 wt% ceria and 20 to 45 wt% zirconia), even more preferably 45 to 75 wt% ceria and 25 to 55 wt% zirconia.

[0160] Typically, the first and second catalyst washcoats contain 0.1 to 3.5 g in -3 (e.g., 0.25 to 3.0 g in -3 ), preferably 0.3 to 2.5 g in -3 , still more preferably 0.5 to 2.0 g in -3 , and even more preferably 0.6 to 1.75 g in -3 (e.g., 0.75 to 1.5 g in -3 )'s amount of a first refractory metal oxide carrier material.

[0161] Generally, the refractory metal oxide support material used in the present invention is in the form of particles. The first support material may have a D of ≤ 50 μm, preferably ≤ 30 μm, and more preferably ≤ 20 μm. 90 Particle size (as determined by conventional laser diffraction techniques). The particle size distribution of the refractory metal oxide support material is selected to aid adhesion to the substrate. The particles are typically obtained by grinding.

[0162] In addition, each of the first, second, third or fourth refractory metal oxide support materials of the first or second catalyst washcoat layer or the support material or each support material in the refractory metal oxide support material may or may not contain a hydrocarbon adsorbent or consist essentially of a hydrocarbon adsorbent. The hydrocarbon adsorbent may be selected from zeolites, activated carbon, porous graphite and combinations of two or more thereof. If present, it is preferred that the hydrocarbon adsorbent is a zeolite, most preferably an aluminosilicate zeolite.

[0163] When the support material comprises a hydrocarbon adsorbent, then generally the total amount of hydrocarbon adsorbent is from 0.05 to 3.00 g in -3 , specifically 0.10 to 2.00 g in -3 (e.g., 0.2 to 0.8 g in -3 ).

[0164] When the hydrocarbon adsorbent is a zeolite, then preferably each zeolite is a medium pore zeolite (eg, a zeolite having a maximum ring size of ten tetrahedral atoms) or a large pore zeolite (eg, a zeolite having a maximum ring size of twelve tetrahedral atoms).

[0165] Examples of suitable zeolites or zeolite types include faujasite (FAU), clinoptilolite, mordenite, silicalite (MFI), ferrierite, zeolite X (FAU), zeolite Y (FAU), ultrastable zeolite Y (FAU), AEI zeolite, ZSM-5 zeolite, ZSM-12 zeolite (MTW), ZSM-20 zeolite, ZSM-34 zeolite, CHA zeolite, SSZ-13 zeolite, SAPO-5 zeolite (AFI), offretite, beta zeolite or copper CHA zeolite. If present, the zeolite is preferably ZSM-5 (medium pore zeolite), beta zeolite (large pore zeolite) or Y zeolite (large pore zeolite). If present, Y zeolite or beta zeolite is preferred, with beta zeolite being most preferred.

[0166] However, according to the present invention, it is preferred that the oxidation catalyst (excluding any phosphorus and / or zinc guard beds, see below for an explanation of the characteristics thereof) contain no hydrocarbon adsorbents at all, particularly zeolites, since zeolites can undergo hydrothermal degradation during exothermic events, making their inclusion less desirable. The inclusion of hydrocarbon adsorbents in oxidation catalysts for heavy-duty vehicles is also less desirable since the exhaust gas temperature emitted from a heavy-duty diesel engine rarely fluctuates in use below the temperature at which hydrocarbon adsorption is desired to improve overall cycle hydrocarbon conversion.

[0167] Catalyst carrier coating zone length

[0168] In embodiments including only two catalyst washcoat zones, such as Figure 1 As shown, the length of the first catalyst washcoat zone may be <50% of the total substrate length, preferably 20% to 40%.

[0169] However, in a catalyst support comprising three or four catalyst support coating zones (e.g. Figures 2 to 5 In embodiments (those shown in any one of the Figures of ), the length of the first washcoat zone may be from 15% to 35% of the total substrate length (L).

[0170] In a catalyst support comprising three or four zones (e.g. Figures 2 to 5 In any of the embodiments shown in the Figures of FIG. 1 ), the length of the overlapping region of the first and second catalyst support coatings ( 6 , 7 ), ie, Figure 2 and Figure 4 The length of the second catalyst support coating zone in Figure 3 and Figure 5 The length of the fourth catalyst support coating zone in may be 10% to 40%, preferably 10% to 30%, of the total substrate length (L).

[0171] In a catalyst support comprising three or four zones (e.g. Figures 2 to 5 In embodiments (such as those shown in any one of the figures of the present invention), the length of the third catalyst support coating zone may be 10% to 40% of the total substrate length (L), more preferably 15% to 35%, such as 20% to 30%, of the total substrate length (L).

[0172] In a catalyst support coating comprising four zones (e.g., Figure 3 and Figure 5 In the embodiments shown in Figure 3 and Figure 5 The second catalyst washcoat zone in may be 1% to 40%, preferably 5% to 30%, of the total substrate length (L).

[0173] In a particularly preferred embodiment, the inlet catalyst washcoat layer 6 is first applied to the substrate to a length of about 80% L, and then the outlet catalyst washcoat layer 7 is applied to the substrate to a length of about 50% L, i.e., overlapping the catalyst washcoat layer 6 by 30% L. The length of the first washcoat layer zone may be 15% to 35% of the total substrate length (L).

[0174] Because the substrate length can vary, it is often more useful to refer to the length of the first, second, and, if present, third and fourth catalyst washcoat zones by their axial length relative to the total axial substrate length (i.e., as a percentage or fraction). Generally, substrates useful in the present invention have a length of 3 to 6 inches, inclusive, and more typically 4 to 6 inches. Thus, washcoat length or washcoat zone length can be referred to by reference to percent zone length x total substrate length (L).

[0175] Non-uniform distribution of alkaline earth metal components and / or platinum group metal components in the washcoat

[0176] This aspect Figure 6 and Figure 7 , and briefly described above in the description of the drawings.

[0177] In the first inventive aspect, the first catalyst support coating zone may have an uneven distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components in a direction perpendicular to the substrate surface, as determined by electron probe microanalysis (EPMA), wherein the concentration of the one or more platinum group metal components and / or the first alkaline earth metal components decreases in the perpendicular direction toward the substrate surface, as determined by EPMA.

[0178] It has been found that a non-uniform vertical distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components can be achieved within a single layer. Thus, the benefits associated with layering can be obtained by using a single layer or fewer layers to achieve a non-uniform vertical distribution of these components through the catalyst layer.

[0179] In the composite oxidation catalyst of the present invention, the first catalyst carrier coating zone may have an uneven distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components in a direction perpendicular to the substrate surface, optionally present in a single layer, such as a catalyst carrier coating, such as a first catalyst carrier coating (i.e., the catalyst layer does not include multiple layers).

[0180] Preferably, the catalyst support coating has an inhomogeneous distribution of one or more platinum group metal components and / or one or more alkaline earth metal components throughout its thickness (i.e., the direction perpendicular to the substrate surface represents the thickness of the catalyst layer), and most preferably has an inhomogeneous distribution of both one or more platinum group metal components and one or more alkaline earth metal components.

[0181] Typically, the catalyst support coating has a first surface and a second surface. Generally speaking, the first surface is parallel (e.g., substantially parallel) to the second surface (i.e., the plane comprising the first surface is parallel to the plane comprising the second surface). The first surface and the second surface are generally parallel to the surface of the substrate. Therefore, the direction perpendicular to the substrate surface is also perpendicular to the first surface and / or the second surface.

[0182] The vertical distance between the first surface and the second surface is generally the thickness of the catalyst support coating.

[0183] The first surface may be an exposed surface of the catalyst layer, or an additional layer (e.g., a second layer) may be disposed on or supported on the first surface. The first surface is typically on the upper side of the catalyst layer (i.e., it is the top surface). By exposed, it is meant that the first surface is not completely or substantially covered by another material, and typically exhaust gas passing through the catalyst contacts the first surface before the second surface.

[0184] The second surface is not an exposed surface of the catalyst support coating. Generally speaking, the second surface is in direct contact with the surface of the substrate and / or the surface of another layer. Therefore, the second surface is generally the underside of the catalyst support coating (i.e., it is the bottom or lowest surface).

[0185] Preferably, the amount of the one or more platinum group metal components and / or the one or more first alkaline earth metal components decreases in a vertical direction toward the surface of the substrate (i.e., the amount of the one or more platinum group metal components and / or the one or more first alkaline earth metal components decreases from the first surface to the second surface). The amount of the one or more platinum group metal components and / or the one or more first alkaline earth metal components may decrease continuously or discontinuously along the vertical direction toward the surface of the substrate, preferably continuously. Thus, when, for example, the first catalyst support coating zone comprises a single layer (which is a catalyst support coating), then the amount of the one or more platinum group metal components and / or the one or more first alkaline earth metal components decreases from the exposed surface of the catalyst support coating toward the surface of the substrate.

[0186] The catalyst support coating may have a linear or non-linear decreasing rate of the amount of one or more platinum group metal components and / or one or more first alkaline earth metal components in a vertical direction toward the substrate surface (i.e., a linear or non-linear decreasing rate of the amount of the first platinum group metal in a vertical direction from the first surface to the second surface).

[0187] Typically, at least 60% of the total amount of one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., one or more platinum group metal components and / or one or more first alkaline earth metal components of the catalyst support coating) can be distributed between the first surface and a point or plane in the catalyst support coating that is located between the first surface and the second surface (e.g., at 50% of the vertical distance between the first surface and the second surface). The plane is typically parallel to the first surface. Reference to "middle" in this context typically refers to the average middle distance between the first surface and the second surface. Preferably, at least 70%, more preferably at least 75% (such as at least 80%), and even more preferably at least 90% of the total amount of one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., one or more platinum group metal components and / or one or more first alkaline earth metal components of the catalyst support coating) can be distributed between the first surface and a point or plane in the catalyst support coating that is located between the first surface and the second surface.

[0188] Generally speaking, at least 60% of the total amount of one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., one or more platinum group metal components and / or one or more first alkaline earth metal components of the catalyst support coating) can be distributed between the first surface and a point or plane in the catalyst support coating at 25% of the vertical distance from the first surface to the second surface. The plane is generally parallel to the first surface. Preferably, at least 70%, more preferably at least 75% (such as at least 80%), and more preferably at least 90% of the total amount of one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., one or more platinum group metal components and / or one or more first alkaline earth metal components of the catalyst support coating) can be distributed between the first surface and a point or plane in the catalyst support coating at 25% of the vertical distance from the first surface to the second surface.

[0189] At least 60% of the total amount of one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., one or more platinum group metal components and / or one or more first alkaline earth metal components of the catalyst support coating) can be distributed between the first surface and a point or plane in the catalyst support coating at 10% of the vertical distance from the first surface to the second surface. The plane is generally parallel to the first surface. Preferably, at least 70%, more preferably at least 75% (such as at least 80%), and more preferably at least 90% of the total amount of one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., one or more platinum group metal components and / or one or more first alkaline earth metal components of the catalyst support coating) can be distributed between the first surface and a point or plane in the catalyst support coating at 10% of the vertical distance from the first surface to the second surface.

[0190] Generally speaking, the non-uniform distribution of the first platinum group metal in the direction perpendicular to the substrate surface can be a gradient distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components. Alternatively, the non-uniform distribution of the first platinum group metal in the direction perpendicular to the substrate surface can be a stepped distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components.

[0191] The catalyst support coating may have a uniform level distribution or a non-uniform level distribution of the one or more platinum group metal components and / or the one or more first alkaline earth metal components.

[0192] Typically, the distribution of the one or more platinum group metal components and / or the one or more first alkaline earth metal components in the direction parallel to the substrate surface (i.e., the longitudinal plane) and in the direction perpendicular to the central longitudinal axis of the substrate (i.e., the direction parallel to the inlet end face and / or the outlet end face of the substrate) is uniform or non-uniform. Preferably, the distribution of the first platinum group metal in the direction parallel to the substrate surface and perpendicular to the central longitudinal axis of the substrate is uniform.

[0193] Generally speaking, the distribution of the one or more platinum group metal components and / or the one or more first alkaline earth metal components in the direction parallel to the substrate surface (i.e., the longitudinal plane) and in the direction parallel to the central longitudinal axis of the substrate (i.e., the direction perpendicular to the inlet end face and / or the outlet end face of the substrate) can be uniform or non-uniform. Preferably, the distribution of the one or more platinum group metal components and / or the one or more first alkaline earth metal components in the direction parallel to the substrate surface and parallel to the central longitudinal axis of the substrate is uniform.

[0194] A method of obtaining a non-uniform distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components in a direction perpendicular to the substrate surface in the first catalyst support coating zone is to perform conventional thermal drying of a solute salt of one or more platinum group metal components impregnated into a support coating comprising one or more platinum group metals and a first refractory metal oxide support material, wherein the one or more first alkaline earth metal components are present in the support coating and / or as a solute salt in an impregnation medium having a solute salt of one or more platinum group metal components. Preferably, the first alkaline earth metal component is present in the support coating having the one or more platinum group metal components impregnated thereon. Impregnation is a common common sense technique, such as discussed in Chapter 2.3 of Heck et al., "Catalytic Air Pollution Control-Commercial Technology", Third Edition (2009), John Wiley & Sons, Inc. This reference chapter also discusses thermal drying and calcination. The inventors have found that an alternative drying method, freeze drying (see, for example, WO 2009 / 080155), to form well-dispersed alkaline earth metal particles in a direction perpendicular to the substrate surface produces less available exotherm. Further explanation can be found below under the heading "Methods of Preparation".

[0195] It is preferred that the alkaline earth metal is barium. We have found that when non-barium alkaline earth metals are used (e.g., as their acetates), the non-barium alkaline earth metal salts have low fluidity in the drying step and therefore tend not to form uneven distributions like alkaline earth metal salts (such as strontium, calcium or magnesium). The applicant believes that the presence of platinum group metals (particularly palladium and barium) at the upper surface of the catalyst support coating (e.g., in the so-called "shell") is beneficial for the exothermic generation function, which is the main purpose of the composite oxidation catalyst of the present invention. Therefore, it is preferred that, in addition to the uneven distribution of the barium component in the direction perpendicular to the substrate surface as determined by EPMA, if the concentration of the barium component decreases in the vertical direction toward the substrate surface, the concentration of palladium also decreases in the vertical direction toward the substrate surface.

[0196] Phosphorus and / or zinc protection beds

[0197] As explained in the introduction to this specification, lubricants for heavy-duty vehicles have relatively high levels of additives containing zinc and / or phosphorus. Therefore, when used, the catalyst in the exhaust system of a heavy-duty vehicle is exposed to relatively large amounts of zinc and / or phosphorus compounds over the life of the vehicle. The inventors of the applicant analyzed an oxidation catalyst that was a first catalytic substrate arranged in the exhaust system downstream of a Euro 6 heavy-duty diesel engine of the vehicle at the end of the vehicle's life (about 1 million kilometers) and found that 1.0% to 1.5% by weight of phosphorus was present on the oxidation catalyst in the first quarter of the coated substrate measured from the substrate inlet end.

[0198] In the present invention, the first catalyst carrier coating zone has the highest loading of platinum group metals on the substrate and is present in a zone defined at the end of the first substrate, which corresponds to the inlet end when in use. According to the present invention, the highest loading of platinum group metals in the platinum-rich combination of platinum and palladium is a key feature of the composite oxidation catalyst for generating exothermic heat from increased amounts of hydrocarbons present in the exhaust gas. Therefore, the presence of the catalyst causes zinc and / or phosphorus poisoning in the exhaust gas entering the inlet end of the composite oxidation catalyst, which can have a disproportionate effect on reducing the activity of the catalyst in generating exothermic heat from hydrocarbons in the following aspects: additional hydrocarbons are required to achieve the desired exothermic temperature, thereby indirectly reducing vehicle fuel economy; and / or increasing the hydrocarbon ignition temperature, that is, the temperature at which the catalyst is active to begin oxidizing hydrocarbons and thereby generate exothermic heat relative to an oxidation catalyst uniformly coated with the same carrier coating composition (see also Examples 4, 5 and 6 below). Thus, introducing hydrocarbons into the exhaust at relatively lower temperatures that would normally be expected to produce a particular exotherm may result in lower exotherm and increased hydrocarbon slip, leading to higher hydrocarbon emissions to the atmosphere and / or hydrocarbon contamination of downstream exhaust system components or processes and / or on-board diagnostic (OBD) failure modes.

[0199] The inventors of the applicant have studied methods for reducing or preventing the poisoning effects of phosphorus and / or zinc compounds on the function of composite oxidation catalysts, and have found that by providing a carrier coating as a covering layer on a first catalyst carrier coating zone with a sufficient loading (related to the thickness of the carrier coating), optionally wherein the carrier coating comprises a particulate metal oxide of a sufficient average pore diameter and / or the resulting carrier coating has a sufficient average inter-particle pore size, phosphorus and / or zinc compounds can be prevented or reduced from contacting the underlying first catalyst carrier coating zone, and a higher proportion of fresh catalyst activity can be maintained when the catalyst is used, compared to a catalyst not using such additional features, while maintaining a mass transfer path for exhaust gas to the underlying first catalyst coating zone.

[0200] Therefore, in a preferred arrangement, the composite oxidation catalyst according to the first aspect of the invention comprises a washcoat covering layer extending axially from the end of the first substrate for protecting at least a portion of the underlying first catalyst washcoat zone from phosphorus and / or zinc poisoning when in use, the washcoat covering layer comprising ≥ 0.8 g / in 3 of particulate metal oxide loading.

[0201] The applicant's studies have found that the depth of the washcoat coverage appears to be important for achieving the desired function as a protective bed for phosphorus and / or zinc compounds, as 0.5 g / in 3 The relatively low loading of the washcoat cover is not as high as 1.0 g / in 3 The washcoat overlay layer loadings of 100% to 200% were as effective as those of 100% to 200% (see Examples 4, 5 and 6 below).

[0202] The washcoat covering layer may consist essentially of particulate metal oxide, wherein the washcoat covering layer may contain certain binders or additives for aiding processing (e.g., powder flow), washcoat rheology modifiers, etc. That is, while catalyst components (such as barium or one or more platinum group metals) may wick or migrate from the bottom layer into the washcoat layer during the manufacture of the composite oxidation catalyst, the particulate metal oxide is coated in, for example, a washcoat layer that does not contain such metals, and such metals should not enter the washcoat covering layer. In this context, the term "consisting essentially of..." as used above is intended to cover the final product in which any such metals unintentionally migrate into the washcoat covering layer.

[0203] Typically, the washcoat cover has a 0.8 to 3.5 g in -3 , preferably 0.9 to 2.5 g in -3 , still more preferably 1.0 to 2.0 g in -3 , such as 1.1 to 1.75 g in -3 of particulate metal oxide loading.

[0204] Preferably, the washcoat cover layer is applied directly onto the washcoat layer of the first catalyst washcoat zone. However, it is also within the scope of the present invention for one or more washcoats to be present between the preferably arranged first catalyst washcoat zone and the washcoat cover layer.

[0205] It should be understood that the use of the guard bed feature is generally applicable to all embodiments of the present invention and can therefore be easily combined with each embodiment of the present invention, such as Figures 1 to 5 This is specifically shown in the disclosed embodiments, as indicated by the optional dashed feature "G".

[0206] The washcoat cover may include one or more of the following additional optional features:

[0207] (a) the particulate metal oxide in the washcoat covering has an average pore size of ≥10 nm and / or the washcoat covering has an average inter-particle pore size of ≥10 nm;

[0208] (b) the particulate metal oxide in the carrier coating covering layer is selected from alumina, silica, titania, zirconia, ceria, and mixed oxides or composite oxides of any two or more thereof, or aluminosilicate zeolites. Preferably, the particulate metal oxide is alumina doped with silica or alumina having an average pore size of ≥15 nm;

[0209] (c) the particulate metal oxide in the washcoat covering has a diameter of >100 m 2 / g specific surface area;

[0210] (d) the washcoat cover extends axially from the first substrate end to at most 150% of the axial length of the underlying first catalyst washcoat layer to protect it from phosphorus and / or zinc poisoning when used in the exhaust system of a heavy-duty diesel engine, preferably >50% of the axial length of the underlying first catalyst washcoat layer zone, such as >60%, >70%, >80%, >90% or >100% or at most 120% of its axial length; and

[0211] (e) the particulate metal oxide in the washcoat overlayer is loaded with a platinum group metal, the platinum group metal being platinum or a combination of platinum and palladium in a Pt:Pd weight ratio of ≥ 1:1, optionally wherein the platinum group metal loading in the washcoat overlayer is from 1 to 35 gft -3 The platinum group metals are intentionally incorporated into the washcoat covering layer.

[0212] The particulate metal oxide may have one or both of an average pore size and an inter-particle pore size of ≥10 nm. Preferably, the average pore size or the inter-particle pore size is ≥12 nm or ≥15 nm. Applicants have found that certain parameters of the particulate metal oxide may undesirably reduce the hydrocarbon oxidation activity of the underlying first catalyst support coating zone. Therefore, when applicants tested colloidal silica (Ludox TM ) as a possible particulate metal oxide for the washcoat overlayer, it was found that the washcoat had insufficient porosity and permeability to maintain the oxidation function of the underlying first catalyst washcoat. That is, hydrocarbon oxidation in a composite oxidation catalyst comprising colloidal silica as the particulate metal oxide is gas mass transfer limited. Although lower colloidal silica loadings may improve mass transfer, the protective effect of the washcoat overlayer is not expected to be sufficient (reference to the washcoat loading limit of ≥ 0.8 g / in as discussed above). 3 ). Therefore, in order to better maintain the main hydrocarbon oxidation function of the composite oxidation catalyst, the particulate metal oxide has an average pore size of ≥10 nm and / or the carrier coating covering layer has an average inter-particle pore size of ≥10 nm.

[0213] In embodiments characterized by a carrier coating overlay having no supported platinum group metal, applicants' inventors have discovered that certain particulate metal oxides having relatively low average pore sizes (e.g., particulate ceria having a novel average pore size of 8 nm) can be effective in the present invention. Preferably, however, the particulate metal oxide in the carrier coating overlay has an average pore size of ≥10 nm, and / or the carrier coating overlay has an average inter-particle pore size of ≥10 nm, preferably an average pore size of ≥10 nm. That is, particulate metal oxides having an inherently low average pore size (e.g., ceria materials) can be employed in the present invention by appropriate particle size distribution selection (see also below) such that the average inter-particle pore size in the carrier coating is ≥10 nm.

[0214] The average inter-particle pore size of the washcoat covering can be determined by mercury intrusion porosimetry.

[0215] The average pore size of the particulate metal oxide can be determined by N2 adsorption-desorption isotherms using the Barrett-Joyner-Halenda (BJH) method.

[0216] When the particulate metal oxide has a bimodal pore size, the requirement is met where at least one of the two modes is at a particle size above ≥ 10 nm.For the avoidance of doubt, the preferred particulate refractory metal oxide alumina doped with silica satisfies at least the general definition in this paragraph.

[0217] Aluminosilicate zeolites generally do not meet the requirement for an average pore size of ≥10 nm. The characteristic of an inter-particle pore size of ≥10 nm can be obtained by appropriate selection of particle size (i.e., particle size distribution). As explained above in conjunction with colloidal silica, in the case where the particles of the washcoat are too fine, the inter-particle pores are too small to sustain mass transfer of the exhaust gas to the underlying first catalyst washcoat. By appropriate selection of particle size, inter-particle pores can be obtained between particles of appropriate size to meet the preferred condition of an inter-particle pore size of ≥10 nm.

[0218] For example, the particles of the particulate metal oxide may have a D90 of <100 microns. The particles of the particulate metal oxide may preferably have a D90 of <75 microns, such as <50 microns (e.g., <30 microns), and more preferably <20 microns, such as <15 microns. When the refractory oxide has a smaller D90, better filling and adhesion can be obtained.

[0219] As is known in the art, D90 is the particle size value below which 90% of the particles in a distribution have a particle size below this value. For the avoidance of doubt, d90 measurements may be made using a Malvern Mastersizer 2000 TM Obtained by laser diffraction particle size analysis, which is a volume-based technique (i.e., D90 can also be referred to as D V 90 (or D(v,0.90)) and the mathematical Mie theory model was applied to determine the particle size distribution.

[0220] Typically, the particles of the particulate metal oxide have a D90 > 0.1 microns. Preferably, the particles of the particulate metal oxide have a D90 > 1.0 microns, such as > 5.0 microns.

[0221] Particulate metal oxides that meet the required conditions for the guard bed support coating overlay according to the preferred arrangement and have application in the present invention include alumina, silica, titania, zirconia, ceria and mixed oxides or composite oxides of any two or more thereof (such as titania doped with silica, ceria-zirconia mixed oxides, preferably alumina doped with silica) or aluminosilicate zeolites. For example, the particulate metal oxide can be selected from alumina, ceria, alumina doped with silica, titania-alumina, zirconia-alumina, ceria-alumina, ceria-zirconia-alumina, silica-titania, silica-zirconia, zirconia-titania, ceria-zirconia and alumina-magnesia. Preferably, the particulate metal oxide is selected from alumina, silica-doped alumina, titania-alumina, zirconia-alumina, silica-titania, silica-zirconia, zirconia-titania and alumina-magnesia, i.e. the particulate metal oxide does not contain cerium, as discussed above.

[0222] The granular metal oxide may optionally be doped (e.g., doped with a dopant). The dopant may be selected from zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd), and oxides thereof. The inclusion of the dopant may render the granular metal oxide thermally stable. It should be understood that any reference to "doping" in this context refers to a material in which the bulk or host lattice of the granular metal oxide is substitutionally doped or interstitially doped with a dopant. In some cases, a small amount of dopant may be present at the surface of the granular metal oxide. However, the majority of the dopant will generally be present in the bulk of the granular metal oxide.

[0223] When doping a particulate metal oxide, the total amount of dopant is 0.5 wt % to 15 wt %, preferably 1 wt % to 10 wt % (e.g., about 5 wt %) of the particulate metal oxide. A preferred particulate metal oxide is a refractory metal oxide alumina doped with silica, which may meet the requirement of an average pore size of ≥ 10 nm and may also have a pore size of ≥ about 120 nm. 2 / g specific surface area (see below).

[0224] In embodiments where the particulate metal oxide includes an aluminosilicate zeolite, examples of suitable zeolites or zeolite framework types include faujasite, clinoptilolite, mordenite, silicalite, ferrierite, zeolite X, zeolite Y, ultrastable zeolite Y, AEI zeolite, ZSM-5 zeolite, ZSM-12 zeolite, ZSM-20 zeolite, ZSM-34 zeolite, CHA zeolite, SSZ-13 zeolite, offretite, beta zeolite or copper CHA zeolite. The zeolite is preferably ZSM-5, beta zeolite or Y zeolite. The aluminosilicate zeolite may include one or more base metals, such as at least one of copper, iron or manganese. For example, in the case where the aluminosilicate zeolite has a CHA framework type code, CHA may be promoted with copper. Alternatively, the aluminosilicate zeolite may be intended to be free of base metals.

[0225] The particulate metal oxide may be a refractory metal oxide, which term, as defined in this application, excludes aluminosilicate zeolites.

[0226] Particularly preferred particulate metal oxides for use in the present invention are refractory metal oxide silicas doped with alumina in the total amount of silica dopant disclosed above, which refractory metal oxide silicas do not contain the expected noble metals, including platinum group metals. Alumina with an average pore size of ≥ 15 nm is also preferred. Such materials are referred to herein as "wide pore alumina" and are known, for example, from EP1077769A1.

[0227] The specific surface area of ​​the particulate metal oxide is also believed to be important because the higher the specific surface area of ​​the particulate metal oxide component, the greater the expected capacity of the washcoat overlay to adsorb glassy zinc phosphate compounds, such as those derived from lubricant additives.

[0228] The particles of the particulate metal oxide used in the washcoat layer of the novel composite oxidation catalyst according to the present invention have a particle size of ≥ about 100 μm. 2 / g(>about 100m 2 / g), preferably ≥ about 120m 2 / g(>about 120m 2 / g), such as ≥ about 150m 2 / g(>about 150m 2 / g), ≥ about 180m 2 / g(>about 180m 2 / g) or ≥ about 200m 2 / g(>about 200m 2 In general, aluminosilicate zeolites have an average specific surface area (SSA) of ≥ about 200 m 2 / g of SA.

[0229] The average specific surface area (SSA) of the particles of the refractory oxide can be determined by nitrogen physical adsorption using a volumetric method at -196° C. The average SSA is determined using the BET adsorption isotherm equation.

[0230] In a preferred embodiment, the particulate metal oxide in the washcoat overlay supports a platinum group metal that is platinum or a combination of platinum and palladium in a Pt:Pd weight ratio of ≥ 1: 1. It should be understood that a Pt:Pd weight ratio of 1:0 (i.e., Pt only) falls within the range of "≥ 1: 1".

[0231] Preferably, the platinum group metal loading in the washcoat overlay is from 1 to 35 gft -3 , preferably 2.5 to 25 g / ft -3 , such as 5 to 17.5 gft -3 .

[0232] Adding manganese to the outlet catalyst washcoat to improve NO2 management and exothermic behavior

[0233] In the development Figure 5 During research on the four-zone composite oxidation catalyst shown in FIG. 1 , the applicant has discovered that manganese added to the third catalyst washcoat zone defined by the second (i.e., outlet) substrate end at the second end of the third catalyst washcoat zone as part of the second catalyst washcoat (7) applied from the second (outlet) substrate end can advantageously promote the generation of exothermic heat and / or avoid the dissipation of exothermic heat generated during active filter regeneration, enhance the activity of the downstream SCR catalyst to convert nitrogen oxides (NO x ) to N2 and / or improve the nitrogenous reductant injection management for the downstream SCR catalyst. These observations are particularly applicable to the two-zone, three-zone and four-zone composite oxidation catalysts according to the present invention.

[0234] Enhance the downstream SCR catalyst to convert NO x Reduction to N2 activity, as described above, it is known that in exhaust gases containing nitrogen monoxide and nitrogen dioxide, SCR catalysis proceeds via a combination of SCR reactions, the SCR reactions including reactions (1)-(3) (inclusive), all of which reduce NOx to elemental nitrogen (N2).

[0235] The relevant undesirable non-selective side reactions are according to reaction (4):

[0236] 2NH3+2NO2 → N2O+3H2O+N2 (4)

[0237] In practice, reactions (1)-(3) occur simultaneously, with the primary reaction being the one that is particularly favorable based on the kinetics of the reactions and the relative concentrations of the reactants. Kinetically, reaction (2) is relatively slow compared to reaction (1), and reaction (3) is the fastest. Thus, according to this chemistry, the SCR catalysis works most efficiently, with the NO2 / NO2 in the exhaust gas entering the downstream SCR catalyst according to reaction (3). x The ratio is about 0.5, ie the ratio of NO:NO2 is 1:1.

[0238] Applicants' researchers have discovered that by including manganese in Figure 5 The third catalyst support coating zone of the composite oxidation catalyst shown as part of the second catalyst support coating (7) can suppress the peak passive NO oxidation activity, that is, the NO oxidation activity that occurs between active heat release / regeneration events. The "peak passive NO oxidation activity" is shown by the values ​​in the "fresh NO2 / NOx (%) at 300°C" column of Tables 7 and 8.

[0239] By using manganese to suppress the peak oxidation activity, the applicant's researchers found that the NO2 / NO x can be moderated over a large portion of the vehicle’s life to a more stable 0.55 to 0.45, the “sweet spot” for reaction on the downstream SCR catalyst (3), rather than the kinetically slower and less efficient NO x Reduction reaction (2). If the activity of the newly made catalyst in passive oxidation of NO is too high, the peak NO2 / NO x The content can increase to more than 0.65, which not only pushes the exhaust gas composition away from the preferred NO:NO2 ratio of 1:1 for promoting reaction (3) in the downstream SCR catalyst, but also secondarily promotes the slowest reaction (2). In addition, excess NO2 can undesirably lead to the formation of N2O according to reaction (4).

[0240] In improving the management of nitrogenous reductant injection for the downstream SCR catalyst, the applicant's researchers also found that the difference (δ) between the fresh and aged passive NO oxidation activities of the composite oxidation catalyst as a whole was reduced when the third zone contained manganese (see the results given in Tables 7 and 8). That is, the resulting NO2 / NO in the exhaust gas downstream of the composite oxidation catalyst xThe values ​​are more predictable over the life of the vehicle exhaust system because the catalyst starts out fresh and ages steadily during use. In practice, this observation is important because the SCR catalytic reactions typically require the provision of a nitrogenous reductant (see reactions (1) to (3) above). Typically, the nitrogenous reductant is ammonia (NH3), which is carried on the vehicle in the form of a precursor urea for delivery to the flowing exhaust gas via an injector. Upon contact with the hot exhaust gas, urea decomposes into ammonia and water vapor. From reactions (1) to (3), it can be seen that, depending on which reaction is dominant at any particular time, slightly different amounts of ammonia nitrogenous reductant are required to achieve total NO if NH3 slip is to be avoided. x The most effective restoration.

[0241] Another level of complexity is that the ability of an oxidation catalyst to oxidize NO to NO2 typically decreases with age; so-called "aging". This loss of activity over time places an increased burden on the control system designed to deliver the nitrogenous reductant, as the gradual loss of activity will need to be compensated for in the system programming algorithm. However, by reducing the delta between fresh and aged NO oxidation activity, in addition to suppressing the higher NO oxidation activity and thereby converting NO2 / NO2 as described above, x Beyond a “lump” around 0.5, system programming controls to manage nitrogenous reductant injection over the life of the vehicle should be less complex for heavy duty diesel vehicle manufacturers.

[0242] Third, quite surprisingly, as shown below in Example 9, Applicants' researchers have discovered that the inclusion of manganese in the third washcoat zone / second washcoat can beneficially promote exotherm generation and / or avoid exotherm decay generated during active filter regeneration. This observation can allow for the replacement of significantly higher cost platinum group metals with lower cost base metals (i.e., manganese) while maintaining the functionality of the composite oxidation catalyst.

[0243] In exhaust system aftertreatment, manganese can be affected by sulfur poisoning. It is also known that palladium can also be subject to palladium poisoning. For this reason, it may be preferred to avoid including palladium in addition to manganese in the manganese-containing catalyst support coating and / or zone. However, as described above, relatively low levels of palladium can improve the stability of the platinum component in the zone. In this regard, the manganese-containing catalyst support coating and / or zone preferably comprises a platinum-rich weight ratio of Pt:Pd (e.g., ≥10:1), or the one or more platinum group metals in the manganese-containing catalyst support coating and / or zone may be essentially composed of platinum or composed of platinum (e.g., a Pt:Pd weight ratio of 1:0).

[0244] In order to benefit from the technical effects of including manganese, the platinum group metal loading in the manganese-containing catalyst support coating and / or zone is preferably ≥ 2 gft -3 , preferably 5 to 15 gft-3 , such as 7 to 13gft -3 .

[0245] In addition, the applicant has discovered that the technical effect of the "delta" between fresh and aged NO to NO2 oxidation for manganese reduction can be enhanced by appropriately selecting a refractory metal oxide support material in a catalyst support coating zone defined by a second substrate end (e.g., a third catalyst support coating zone) at a second end of the catalyst support coating zone and / or in a second catalyst support coating.

[0246] In this regard, applicants note the beneficial effects of alumina doped with heteroatom support materials, wherein preferably the heteroatom is silicon and / or manganese; or a mixed magnesium aluminum metal oxide. Manganese may be present as a heteroatom itself and / or introduced as a soluble salt in combination with a washcoat refractory metal oxide support material, such as a mixed magnesium aluminum metal oxide or an alumina support material doped with silica, for example as manganese nitrate, and then precipitated onto the support material using a reducing agent, such as using citric acid, tetrabutylammonium hydroxide, formic acid, ascorbic acid, etc. The refractory metal oxide support comprising doped manganese may then be impregnated with additional manganese.

[0247] Thus, the refractory metal oxide support material in the manganese-containing zone or layer may comprise alumina doped with silica, alumina doped with manganese, alumina doped with both silica and manganese, a mixed magnesium aluminum metal oxide, or a "preformed" mixed magnesium aluminum metal oxide doped with manganese. The impregnated manganese component may be supported on the refractory metal oxide support material.

[0248] The mixed magnesium aluminum metal oxide may have a pre-calcined magnesium content of less than or equal to 15 wt%, calculated as Mg, for example, from 0.1 wt% to 12 wt% or from 2.0 wt% to 10 wt%. The calcined support material comprising the mixed magnesium aluminum metal oxide may comprise a magnesium deficient (i.e., non-stoichiometric) spinel. Most preferably, the manganese-containing refractory metal oxide support material is a "preformed" mixed magnesium aluminum metal oxide doped with manganese. The amount of manganese dopant in the manganese aluminum metal oxide doped with manganese may be from 1 wt% to 15 wt%, calculated as MnO2. Example 8 shows that in addition to the NO2 / NO2 ratio between the fresh catalyst and the aged catalyst, the calcined support material may contain ... x In addition to the reduction in "delta", the samples comprising manganese doped magnesium aluminum metal oxides showed a surprising improvement in generating heat release from lower temperatures, as demonstrated by the "continuous heat release" test.

[0249] Substrate

[0250] The substrates used to support the catalyst support coating and catalyst support coating zone components of the composite oxidation catalyst of the present invention are well known in the art. Generally speaking, the substrate is made of ceramic material or metal material.

[0251] Preferably, the substrate is made of or consists of cordierite (SiO2-Al2O3-MgO), silicon carbide (SiC), aluminum titanate (AT), Fe-Cr-Al alloy, Ni-Cr-Al alloy or stainless steel alloy.

[0252] Typically, the substrate is a monolith, ie a monolith substrate. Preferably, the monolith is a flow-through honeycomb structure monolith substrate or a filtration monolith substrate, most preferably a honeycomb structure flow-through monolith substrate.

[0253] Preferably, the composite oxidation catalyst of the present invention is used as a diesel oxidation catalyst (DOC) or a catalytic soot filter (CSF). In practice, the catalyst formulations used in DOC and CSF are similar. However, generally speaking, the main differences between DOC and CSF are the substrate on which the catalyst formulation is coated and the amount of platinum group metal in the coating.

[0254] The flow-through monolith generally comprises a honeycomb structure monolith (e.g., a metal or ceramic honeycomb structure monolith) having a plurality of channels extending therethrough, the channels being open at both ends. When the substrate is a flow-through monolith, the composite oxidation catalyst of the present invention is generally referred to as a diesel oxidation catalyst (DOC) or is used as a diesel oxidation catalyst (DOC).

[0255] When the monolith is a filtering monolith, it is preferred that the filtering monolith is a wall flow filter. In a wall flow filter, each inlet channel is alternately separated from an outlet channel by a wall of a porous structure, and vice versa. Preferably, the inlet channel and the outlet channel have a honeycomb structure arrangement. When there is a honeycomb structure arrangement, it is preferred that the channels vertically and laterally adjacent to the inlet channel are blocked at the upstream end, and vice versa (i.e., the channels vertically and laterally adjacent to the outlet channel are blocked at the downstream end). When viewed from either end, the alternating blocked ends and open ends of the channels present the appearance of a chessboard. When the substrate is a filtering monolith, the oxidation catalyst of the present invention is typically a catalytic soot filter (CSF) or is used as a catalytic soot filter (CSF).

[0256] In principle, the substrate can have any shape or size. However, the shape and size of the substrate are generally selected to optimize the exposure of the catalytically active material in the catalyst to the exhaust gas. The substrate can, for example, have a tubular, fibrous or granular form. Examples of suitable supporting substrates include monolithic honeycomb cordierite-type substrates, monolithic honeycomb SiC-type substrates, layered fiber or knitted fabric-type substrates, foam-type substrates, cross-flow-type substrates, wire mesh-type substrates, metal porous body-type substrates and ceramic granular-type substrates.

[0257] Heavy Duty Engines

[0258] For the avoidance of doubt, the heavy duty engine according to the third aspect of the invention may use any of the definitions set out in the "Background" section above. Thus, for example, if a patent application is for Japan, then the heavy duty diesel vehicle restrictions required by Japanese emission standards may be incorporated into the vehicle claims. The same is true for regulations in Europe or the United States, etc. For the further avoidance of doubt, the heavy duty engine for use with the present invention does not support running a lean / rich cycle for normal operation or desulfurization suitable for an LNT catalyst. In a preferred arrangement, the exhaust system according to the present invention does not include a LNT.

[0259] The heavy duty compression ignition engine according to the third aspect of the invention is preferably a diesel engine, optionally a compressed natural gas (CNG) engine. The heavy duty diesel engine may be a homogeneous charge compression ignition (HCCI) engine, a premixed charge compression ignition (PCCI) engine or a low temperature combustion (LTC) engine. Preferably, the diesel engine is a conventional (i.e. traditional) diesel engine.

[0260] Preparation method

[0261] Methods for preparing the oxidation catalysts of the present invention are known in the art. See, for example, our WO 99 / 47260, WO 2007 / 077462 and WO 2011 / 080525. Similarly, conditions for drying and calcining washcoats are also well known.

[0262] As described above, alternatively, according to the first inventive aspect, the oxidation catalyst may include three or more catalyst washcoat zones, preferably four catalyst washcoat zones.

[0263] The method for preparing such a catalyst is according to the sixth aspect of the invention, wherein in step (a), the catalyst support coating is a first catalyst support coating, which extends from the end of the first substrate to less than the total length of the substrate, and the method also includes a step (a') before step (a) or after step (a), but in either case is performed before step (b), in which a second catalyst support coating is applied to the substrate, having a length extending from the end of the second substrate to less than the total length of the substrate, so that the first catalyst support coating partially overlaps with the second catalyst support coating or the second catalyst support coating partially overlaps with the first catalyst support coating, wherein the second catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components.

[0264] In this regard, preferably, the first catalyst washcoat layer may extend from the first substrate end portion, and the second catalyst washcoat layer extends from the second substrate end portion, whereby the second catalyst washcoat layer partially overlaps the first catalyst washcoat layer.

[0265] In embodiments, this preferred method may produce Figure 4 and Figure 5 Those arrangements shown, i.e., depending on the axial length of the second catalyst support coating applied in step (a'), and therefore depending on the axial length of the overlap of the first catalyst support coating and the second catalyst support coating, the first catalyst support coating zone includes a single layer of the first catalyst support coating loaded on the substrate surface. According to the axial length of L1 applied in step (b), the second or fourth catalyst support coating zone may include an overlap of the first catalyst support coating and the second catalyst support coating. The third catalyst support coating zone includes a single support coating loaded on the substrate surface, which is defined by the second substrate end at its second end, and is defined by the second end of the first catalyst support coating at its first end (i.e., at the point where the second layer extending from the second substrate end in the direction of the first substrate end begins to overlap with the first catalyst support coating). Generally speaking, the first end of the third catalyst support coating zone is the second end of the second or fourth catalyst support coating zone.

[0266] This arrangement is preferred because the exhaust gas entering the oxidation catalyst of the present invention at the end of the first inlet substrate generally contacts the overlapping region catalyst support coating zone before the third catalyst support coating zone. The overlapping region catalyst support coating zone (depending on the embodiment, the second or fourth catalyst support coating zone) acts as a "stabilizer" for the first catalyst support coating zone. The overlapping region catalyst support coating zone acts as a "stabilizer" in the sense that it performs some or all of the oxidation reactions of the first catalyst support coating zone, but the overlapping region catalyst support coating zone may have a higher HC and / or CO light-off temperature than the first catalyst support coating zone.

[0267] It should be understood that in the sixth aspect of the present invention, because the first catalyst support coating zone is obtained in step (b) by impregnating the catalyst support coating applied in step (a), the refractory metal oxide support material in the first catalyst support coating zone may be the same as the refractory metal oxide support material in the catalyst support coating applied in step (a) (e.g., the first catalyst support coating).

[0268] Generally speaking, a first catalyst washcoat zone having a non-uniform distribution of one or more platinum group metal components and optionally one or more first alkaline earth metal components in a direction perpendicular to the substrate surface, as determined by electron probe microanalysis (EPMA), can be obtained by a method in which one or more platinum group metal components and / or one or more first alkaline earth metal components are not rapidly fixed to the refractory metal oxide support material and move within a dried washcoat, wherein the concentration of one or more platinum group metal components and optionally the first alkaline earth metal components decreases in a perpendicular direction toward the substrate surface, as determined by EPMA. A washcoat containing one or more platinum group metal components can be applied to a substrate, and then a thermal drying step and a calcining step are performed using conditions that allow one or more platinum group metal components and optionally one or more first alkaline earth metal components to move within the washcoat before the washcoat is fixed in place. Such conditions are known in the art, particularly because conditions in the prior art are generally selected to rapidly fix the components of the washcoat (i.e., washcoat) to prevent them from moving within the washcoat. That is, if one is aware of the rapid fixation conditions to prevent the platinum group metal salt from moving within the dried washcoat, it means recognizing the conditions that allow such movement.

[0269] Transfer of solutes to or from a wet surface during evaporation is an effect known in other technical fields. The transfer of the first platinum group metal (i.e., platinum group metal salt and / or alkaline earth metal salt) within a wet coating can be represented by the Richards equation:

[0270]

[0271] in:

[0272] t is time (e.g., time before substantial or complete evaporation of the solvent (i.e., water); θ is the solvent (i.e., water) content, typically of the coating; K is the hydraulic conductivity; z is the height; and ψ is the pressure head. The hydraulic conductivity can be approximated by the hydraulic conductivity of the first support material and / or any other support materials that may be present.

[0273] A method for obtaining a catalyst support coating zone having a non-uniform distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components in a direction perpendicular to a substrate surface, the method comprising:

[0274] (a) providing an aqueous slurry comprising a refractory metal oxide support material, one or more platinum group metal components and optionally one or more alkaline earth metal components;

[0275] (b) applying the aqueous slurry to a substrate to form a washcoat; and

[0276] (c) drying and calcining the washcoat layer, wherein the drying conditions at least allow the one or more platinum group metal components and optionally the one or more alkaline earth metal components to flow toward or away from the substrate to obtain a non-uniform distribution of the one or more platinum group metal components and optionally the one or more alkaline earth metal components in a direction perpendicular to the surface of the substrate.

[0277] The washcoat layer may include two or more platinum group metal components, wherein the first platinum group metal component may be referred to as a first platinum group metal component and the second platinum group metal component may be referred to as a second platinum group metal component.

[0278] Typically, at least one of the refractory metal oxide support material, the first platinum group metal component, and the second platinum group metal component is insoluble. However, it should be understood that the slurry may comprise a solution, such as when one or more precursors of the refractory metal oxide support material, the first platinum group metal component, and the second platinum group metal component are all soluble (i.e., dissolved).

[0279] Typically, the refractory metal oxide support material precursor is a compound that undergoes conversion to a refractory metal oxide support material after drying and / or calcining the coating.Such refractory metal oxide support material precursors are well known in the art and include, for example, boehmite as a precursor to gamma-alumina.

[0280] Generally, the first platinum group metal component is a salt of the first platinum group metal or is the first platinum group metal (i.e., it is the first platinum group metal itself). Preferably, the first platinum group metal component is a salt of the first platinum group metal. The salt of the first platinum group metal may be a nitrate of the first platinum group metal, an acetate of the first platinum group metal, or a carboxylate of the first platinum group metal (e.g., a citrate).

[0281] The second platinum group metal component is typically a salt of a second platinum group metal or is the second platinum group metal (i.e., it is the second platinum group metal itself). Preferably, the second platinum group metal component is a salt of a second platinum group metal. The salt of the second platinum group metal may be a nitrate of the second platinum group metal, an acetate of the second platinum group metal, or a carboxylate of the second platinum group metal (e.g., a citrate).

[0282] When two or more different platinum group metals are used (e.g., a first platinum group metal different from a second platinum group metal), there may be differences in the mobility of the first platinum group metal component compared to the second platinum group metal component due to the presence of intermetallic differences that result in a different distribution profile for each platinum group metal relative to the (or each) other platinum group metal in the washcoat (see Figure 6). The same applies to the different mobilities of the alkaline earth metal relative to one or more platinum group metal components present in the catalyst support coating. When the platinum group metal component is a salt of a platinum group metal, the mobility of the platinum group metal component in the catalyst support coating and the preferred vertical flow direction can be changed by selecting appropriate anions. The platinum group metal component may also interact differently with the refractory metal oxide support material and may be selected on this basis. Similarly, the mobility of the alkaline earth metal component in the catalyst support coating can be changed by appropriately selecting a solute salt of the alkaline earth metal component.

[0283] Preferably, the counter anion of the salt of the first platinum group metal is different from the counter anion of the salt of the second platinum group metal. For example, the first platinum group metal component may be palladium nitrate and the second platinum group metal component may be a platinum carboxylate. The nitrate anion is different from the carboxylate anion.

[0284] The mobility of at least one of the platinum group metal components may be altered by supporting it on a support material prior to mixing with the other platinum group metal component (i.e., pre-immobilizing the platinum group metal component). For example, a pre-immobilized first platinum group metal / first refractory metal oxide support material may be mixed with a second refractory metal oxide support material and an aqueous second platinum group metal salt and optionally an aqueous salt of one or more alkaline earth metals.

[0285] One way in which the first platinum group metal component may be supported on the first refractory metal oxide support material precursor is by: (i) mixing the first refractory metal oxide support material precursor with the first platinum group metal component in solution, preferably impregnating the final first refractory metal oxide support material or filling the pores of the final first refractory metal oxide support material; and (ii) drying and / or calcining the aqueous solution to provide the first platinum group metal component (e.g., the first platinum group metal) supported on the first refractory metal oxide support material. Step (i) may be followed by a step (i)(a) of adding a reducing agent to reduce the first platinum group metal component, preferably impregnating the first support material or filling the pores of the first support material. In steps (i) and / or (i)(a), preferably the only platinum group metal component present is the first platinum group metal component.

[0286] Thus, step (a) of the above method may be the following step: (a) providing an aqueous slurry comprising a second platinum group metal component and a first platinum group metal component supported on a first support material precursor.

[0287] With regard to step (b), methods of applying the slurry or washcoat to the substrate are well known in the art (see, for example, Applicant's WO 99 / 47260).

[0288] In one embodiment, step (c) involves drying the coating using drying conditions that allow at least the first platinum group metal component and the second platinum group metal component to flow at different rates from each other in a direction perpendicular to a plane representing the surface of the substrate. In another embodiment, step (c) involves drying the coating using drying conditions that allow only the first platinum group metal component to flow toward or away from the substrate.

[0289] Step (c) determines the point at which the platinum group metal component is typically fixed to the substrate or refractory metal oxide support material. The drying conditions used will depend on the type of material present in the coating (e.g., platinum group metal component, alkaline earth metal component, refractory metal oxide support material, etc.) and the size of the oxidation catalyst (e.g., the size of the substrate, which will vary depending on the application of the catalyst).

[0290] Typically, the drying conditions involve drying the coating for at least 15 minutes, preferably at least 20 minutes. Such conditions can be used to obtain a non-uniform distribution of the first platinum group metal and optional alkaline earth metal. When the drying time is about 5 minutes or less, a uniform distribution tends to be obtained.

[0291] The coating may then be calcined at a temperature of 400°C to 800°C, preferably 450°C to 600°C, more preferably at a temperature of at least 500°C.

[0292] For example, it has been found that when the first catalyst support coating comprises platinum and palladium as two or more platinum group metal components in a first loading amount and weight ratio and one or more alkaline earth metal components are barium, wherein the platinum group metal and barium are both supported on a refractory metal oxide support material, the refractory metal oxide support material being alumina doped with silica at a preferred silica content, and when such a first catalyst support coating is impregnated with an aqueous solution of a relatively high concentration of platinum salt and palladium salt to form a first catalyst support coating zone after applying the above-mentioned drying method, palladium and barium are more likely to migrate to the exposed catalyst support coating surface and are observed as a "shell" under EPMA. In the absence of a pre-fixed refractory metal oxide support material below, the platinum component shows some movement toward the same exposed surface within the cross section of the first catalyst support coating, remaining relatively more evenly distributed than palladium and barium on the cross section of the first catalyst support coating. It has been found that the finished product exhibits beneficial activity to exothermic generation. This effect is also partially shown in Example 2 below.

[0293] Exhaust system

[0294] An exhaust system according to a second aspect of the present invention comprises the composite oxidation catalyst according to the present invention and a soot filter substrate disposed downstream thereof, wherein a first substrate end portion of the composite oxidation catalyst is oriented to the upstream side.

[0295] The soot filter substrate can be - and usually is - coated with a catalyst formulation.

[0296] The catalyst formulation of the soot filter may be suitable for oxidizing: (i) particulate matter (PM) and / or (ii) carbon monoxide (CO) and hydrocarbons (HC). When the catalyst formulation is suitable for oxidizing PM, then the resulting emission control device is referred to as a catalyzed soot filter (CSF). Typically, the catalyst formulation of the CSF comprises a platinum group metal, such as a first platinum group metal and / or a second platinum group metal as defined above.

[0297] SCR catalysts are also well known in the art and may be coated on a flow-through substrate or a filter substrate (such as a wall-flow filter substrate). When the exhaust system of the present invention comprises an SCR catalyst (e.g., coated on a flow-through substrate monolith), the exhaust system may further comprise an injector for injecting a nitrogenous reductant (such as ammonia or urea) into the exhaust gas downstream of a catalyst for oxidizing carbon monoxide (CO) and hydrocarbons (HC) - being a composite oxidation catalyst according to the present invention or a CSF disposed downstream of the composite oxidation catalyst according to the present invention - and upstream of the SCR catalyst. The exhaust system may further comprise an engine management device for enriching the exhaust gas with hydrocarbons so as to contact the composite oxidation catalyst with the hydrocarbons to generate an exotherm, thereby regenerating the downstream soot filter. Alternatively or in addition, hydrocarbon injection may be facilitated via a separate hydrocarbon injector for injecting hydrocarbon fuel into the exhaust gas downstream of the engine manifold but upstream of the composite oxidation catalyst.

[0298] In an alternative to the CSF catalyst formulation, a soot filter substrate (preferably a wall flow filter) may be coated with an SCR catalyst, in which case it is referred to as a SCRF catalyst.

[0299] Generally speaking, SCR catalysts cannot reduce the large amounts of NO in the exhaust gas shortly after a compression ignition engine is started because the exhaust gas temperature (and therefore the temperature of the catalyst) is too low. x For example, lean NO has been used upstream of the SCR catalyst. x Capture catalysts (e.g., NO x adsorbent catalyst) to store NO x , until the SCR catalyst becomes active at higher exhaust gas temperatures. However, when there is a large mass flow of exhaust gas (for example, when the engine is running at a high speed cycle), the lean NO x The capture catalyst is usually not able to store NO sufficiently x .

[0300] According to a second aspect of the present invention, the exhaust system applied to the present invention is attached FIG. 8A to FIG. 8D In the first exhaust system embodiment (see Fig. 8A) in the case of a flow-through honeycomb structure substrate monolith (see Fig. 8A Item 42 in the above) is a composite oxidation catalyst of the present invention, and a selective catalytic reduction filter (SCRF) catalyst. Such an arrangement may be referred to as DOC / SCRF. This embodiment also relates to the use of a combination of a composite oxidation catalyst and a selective catalytic reduction filter (SCRF) catalyst for treating exhaust gas from an internal combustion engine (particularly a compression ignition engine). Preferably, the composite oxidation catalyst is or is used as a diesel oxidation catalyst. The composite oxidation catalyst of the present invention is typically followed by a selective catalytic reduction filter (SCRF) catalyst (e.g., upstream thereof). A nitrogenous reductant injector may be arranged between the composite oxidation catalyst and the selective catalytic reduction filter (SCRF) catalyst. Therefore, the composite oxidation catalyst may be followed by a nitrogenous reductant injector (e.g., upstream thereof), and the nitrogenous reductant injector may be followed by a selective catalytic reduction filter (SCRF) catalyst (e.g., upstream thereof).

[0301] In the second exhaust system embodiment (see Figure 8B ), the exhaust system includes a composite oxidation catalyst of the present invention on a flow-through honeycomb structure substrate monolith and a (uncatalyzed) diesel particulate filter (DPF) or a catalyzed soot filter (CSF). Such an arrangement may be referred to as DOC / DPF or DOC / CSF. This embodiment also relates to the use of a combination of a composite oxidation catalyst with a diesel particulate filter or a catalyzed soot filter for treating exhaust gases from an internal combustion engine (particularly a compression ignition engine). Preferably, the composite oxidation catalyst is or is used as a diesel oxidation catalyst. The composite oxidation catalyst is typically followed by a diesel particulate filter or a catalyzed soot filter (CSF) (e.g., upstream thereof). Thus, for example, the outlet of the composite oxidation catalyst is connected to the inlet of the diesel particulate filter or the catalyzed soot filter.

[0302] Third exhaust system embodiment (see Figure 8C) relates to an exhaust system, which includes a composite oxidation catalyst of the present invention on a flow-through honeycomb structure substrate monolith, a diesel particulate filter or a catalytic soot filter (CSF) and a selective catalytic reduction (SCR) catalyst. Such an arrangement may be referred to as DOC / DPF / SCR or DOC / CSF / SCR. This embodiment also relates to the use of a combination of a composite oxidation catalyst with a diesel particulate filter or a catalytic soot filter (CSF) and a selective catalytic reduction (SCR) catalyst for treating exhaust gas from an internal combustion engine (particularly a compression ignition engine), preferably wherein the oxidation catalyst is or is used as a diesel oxidation catalyst. The composite oxidation catalyst is usually followed by a diesel particulate filter or a catalytic soot filter (CSF) (e.g., upstream thereof). The DPF or CSF is usually followed by a selective catalytic reduction (SCR) catalyst (e.g., upstream thereof). A nitrogenous reductant injector may be arranged between the DPF or CSF and the selective catalytic reduction (SCR) catalyst. Therefore, a nitrogenous reductant injector may be followed by a DPF or CSF (e.g., upstream thereof), and a nitrogenous reductant injector may be followed by a selective catalytic reduction (SCR) catalyst (e.g., upstream thereof).

[0303] Fourth exhaust system implementation scheme (see Fig. 8A ) relates to an exhaust system comprising a wall flow substrate monolith (CSF - see Fig. 8A Item 42 in ), and a selective catalytic reduction (SCR) catalyst of the present invention. This is also a CSF / SCR arrangement. Another aspect of this embodiment relates to the use of a composite oxidation catalyst in combination with a diesel oxidation catalyst (DOC) and a selective catalytic reduction (SCR) catalyst for treating exhaust gases from a compression ignition engine, preferably wherein the composite oxidation catalyst is or is used as a catalytic soot filter (CSF). The diesel oxidation catalyst (DOC) is typically followed by the composite oxidation catalyst of the present invention (e.g., upstream thereof). The composite oxidation catalyst of the present invention is typically followed by a selective catalytic reduction (SCR) catalyst (e.g., upstream thereof). A nitrogenous reductant injector may be arranged between the composite oxidation catalyst and the selective catalytic reduction (SCR) catalyst. Therefore, the composite oxidation catalyst may be followed by a nitrogenous reductant injector (e.g., upstream thereof), and the nitrogenous reductant injector may be followed by a selective catalytic reduction (SCR) catalyst (e.g., upstream thereof).

[0304] In the fifth exhaust system embodiment (see Fig.8D), the exhaust system comprises a composite oxidation catalyst of the invention (preferably a DOC), a selective catalytic reduction (SCR) catalyst and a catalytic soot filter (CSF) or a diesel particulate filter (DPF). The arrangement is DOC / SCR / CSF or DOC / SCR / DPF. This embodiment also relates to the use of a combination of a composite oxidation catalyst with a selective catalytic reduction (SCR) catalyst and a catalytic soot filter (CSF) or a diesel particulate filter (DPF) for treating exhaust gas from an internal combustion engine (particularly a compression ignition engine), preferably wherein the composite oxidation catalyst is or is used as a diesel oxidation catalyst.

[0305] Such arrangements are respectively FIG. 8A to FIG. 8D , wherein item 30 is a heavy-duty diesel engine; item 32 is an exhaust system for a heavy-duty diesel engine; item 34 is a conduit for conveying exhaust gas from the heavy-duty diesel engine to components (42, 44, 50) of the exhaust system or from these components to the atmosphere 36; item 38 is an injector for injecting hydrocarbon fuel into the exhaust gas downstream of the engine manifold 40 and upstream of a composite oxidation catalyst 42 according to the present invention, the composite oxidation catalyst being, for example, Figures 1 to 5 Any of those composite oxidation catalysts shown, in which the first catalyst carrier coating zone 1 is oriented to the upstream side - the substrate of the composite oxidation catalyst can be a flow-through substrate monolith or a wall-flow filter substrate monolith; Item 44 is a diesel particulate filter (DPF) or a catalytic soot filter (CSF); Item 46 is an injector for injecting a nitrogen-containing reductant precursor fluid (e.g., urea) stored in a reservoir 48 into the flowing exhaust gas; Item 50 is a selective catalytic reduction catalyst (SCR) coated on a flow-through substrate monolith or a wall-flow filter substrate monolith (SCRF).

[0306] In addition to the appended claims, the invention may also be defined in accordance with one or more of the following definitions:

[0307] 1. A composite oxidation catalyst for treating exhaust gas generated by a compression ignition internal combustion engine of a vehicle in an exhaust system, the composite oxidation catalyst preferably being used in a heavy-duty diesel vehicle and being located upstream of a particulate filter in the exhaust system, the composite oxidation catalyst comprising:

[0308] a base having an overall length L and a longitudinal axis and having a base surface extending axially between a first base end and a second base end; and

[0309] Two or more catalyst support coating zones arranged axially in series on and along the surface of the substrate, wherein a first catalyst support coating zone having a length L1 is defined at one end by a first base end portion, where L1 < L, and at a second end by a first end of a second catalyst support coating zone having a length L2, where L2 < L, wherein the first catalyst support coating zone comprises a first refractory metal oxide support material and two or more platinum group metal components supported thereon, said two or more platinum group metal components including both platinum and palladium, and the weight ratio of platinum to palladium ≥ 1; and the second catalyst support coating zone comprises a second refractory metal oxide support material and one or more platinum group metal components supported thereon,

[0310] wherein the total platinum group metal loading defined in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) in the first catalyst support coating zone is greater than the total platinum group metal loading in the second catalyst support coating zone, and wherein the first catalyst support coating zone comprises one or more first alkaline earth metal components supported on the first refractory metal oxide support material.

[0311] 2. The composite oxidation catalyst according to 1, wherein the second catalyst support coating zone is defined at its second end by a second base end portion.

[0312] 3. The composite oxidation catalyst according to 1, the composite oxidation catalyst comprising three or more catalyst support coating zones, wherein a third catalyst support coating zone comprising a third refractory metal oxide support material and one or more platinum group metal components supported thereon is defined at its second end by a second base end portion, and wherein the total platinum group metal loading defined in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) in the third catalyst support coating zone is less than the total platinum group metal loading in the second catalyst support coating zone.

[0313] 4. The composite oxidation catalyst according to 3, the composite oxidation catalyst comprising four catalyst support coating zones, wherein a fourth catalyst support coating zone is located between the second catalyst support coating zone and the third catalyst support coating zone, the fourth catalyst support coating zone comprising a fourth refractory metal oxide support material and one or more platinum group metal components supported thereon, and being defined at its first end by the second end of the second catalyst support coating zone and at its second end by the first end of the third catalyst support coating zone, and wherein the total platinum group metal loading defined in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) in the fourth catalyst support coating zone is greater than the total platinum group metal loading in each of the second catalyst support coating zone and the third catalyst support coating zone.

[0314] 5. The composite oxidation catalyst according to 4, wherein the composite oxidation catalyst comprises a first catalyst support coating and a second catalyst support coating, wherein the first catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, having a length L3, where L3 < L, and being defined at one end by a first base end; and the second catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, having a length L4, where

[0315] L4 < L, and being defined at a second end by a second base end, wherein a fourth catalyst support coating region comprises a double-layer overlapping region of the first catalyst support coating and the second catalyst support coating, and wherein a third catalyst support coating region comprises a single layer of the second catalyst support coating that does not form part of the overlapping region.

[0316] 6. The composite oxidation catalyst according to 3, wherein the composite oxidation catalyst comprises three catalyst support coating regions, wherein the third catalyst support coating region is defined at its first end by the second end of the second catalyst support coating region.

[0317] 7. The composite oxidation catalyst according to 6, wherein the composite oxidation catalyst comprises a first catalyst support coating and a second catalyst support coating, wherein the first catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, having a length L3, where L3 < L, and being defined at one end by a first base end; and the second catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, having a length L4, where

[0318] L4 < L, and being defined at a second end by a second base end, wherein a second catalyst support coating region comprises a double-layer overlapping region of the first catalyst support coating and the second catalyst support coating, and wherein a third catalyst support coating region comprises a single layer of the second catalyst support coating that does not form part of the overlapping region.

[0319] 8. The composite oxidation catalyst according to any one of 1 to 7, wherein the weight ratio of platinum to palladium in the first catalyst support coating region is 10:1 ≥ 1.5:1.

[0320] 9. The composite oxidation catalyst according to any one of 2 to 7, wherein the catalyst support coating region defined by the second base end at the second end of the catalyst support coating region comprises manganese and / or the second catalyst support coating comprises manganese.

[0321] 10. A composite oxidation catalyst according to 9, wherein the refractory metal oxide support material in the manganese-containing zone or layer comprises alumina doped with silica, alumina doped with manganese, alumina doped with both silica and manganese, a mixed magnesium aluminum metal oxide, or a mixed magnesium aluminum metal oxide doped with manganese.

[0322] 11. The composite oxidation catalyst according to 9 or 10, wherein the impregnated manganese component is supported on a refractory metal oxide support material.

[0323] 12. The composite oxidation catalyst according to any one of 3 to 11, wherein the one or more platinum group metal components in the second washcoat layer or the third catalyst washcoat layer zone consist essentially of platinum.

[0324] 13. The composite oxidation catalyst according to any one of 5 to 12, wherein the two or more platinum group metal components in the first catalyst support coating layer consist of both platinum and palladium.

[0325] 14. The composite oxidation catalyst according to any one of 1 to 13, wherein the total platinum group metal loading in the first catalyst support coating zone is <100 g / ft2 calculated as elemental metal. 3 .

[0326] 15. The composite oxidation catalyst according to any one of 1 to 14, wherein the one or more platinum group metal components in the second catalyst support coating zone include both platinum and palladium.

[0327] 16. The composite oxidation catalyst according to 15, wherein the mass ratio of platinum to palladium in the second catalyst support coating zone is greater than the mass ratio of platinum to palladium in the first catalyst support coating zone.

[0328] 17. A composite oxidation catalyst according to any one of 4 to 16, wherein after the first catalyst carrier coating zone, the mass ratio of platinum to palladium in each continuous catalyst carrier coating zone arranged in series along the substrate length L is greater than the mass ratio of platinum to palladium in the immediately preceding catalyst carrier coating zone.

[0329] 18. The composite oxidation catalyst according to any one of 1 to 17, wherein L1<50%L.

[0330] 19. The composite oxidation catalyst according to any one of 1 to 18, comprising a total platinum group metal loading on the substrate as a whole of 5 to 60 g / ft2, calculated as elemental metal. 3 .

[0331] 20. The composite oxidation catalyst according to any one of 1 to 19, wherein the total Pt:Pd weight ratio in the composite oxidation catalyst as a whole is 3:2 to 9:1.

[0332] 21. The composite oxidation catalyst according to any one of 1 to 20, wherein

[0333] The total alkaline earth metal loading in the first catalyst support coating zone is 10 to 100 g / ft 3 .

[0334] 22. The composite oxidation catalyst according to any one of 1 to 21, wherein the weight ratio of total alkaline earth metal elements to total platinum group metal elements in the first catalyst support coating zone is <1:1.

[0335] 23. The composite oxidation catalyst according to any one of 1 to 22, wherein the alkaline earth metal in the first catalyst support coating zone comprises barium (Ba) or strontium (Sr), preferably Ba.

[0336] 24. A composite oxidation catalyst according to any one of 1 to 23, wherein the first catalyst carrier coating zone has an uneven distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components in a direction perpendicular to the substrate surface, as determined by electron probe microanalysis (EPMA), wherein the concentration of the one or more platinum group metal components and / or the first alkaline earth metal component decreases in a vertical direction toward the substrate surface.

[0337] 25. The composite oxidation catalyst according to any one of 1 to 24, wherein at least the first refractory

[0338] The metal oxide support material comprises aluminum oxide, preferably silicon dioxide, doped with heteroatoms.

[0339] 26. A composite oxidation catalyst according to any one of 1 to 25, comprising a carrier coating covering layer extending axially from the end of the first substrate for protecting at least a portion of the underlying first catalyst carrier coating zone from phosphorus and / or zinc poisoning when in use, the carrier coating covering layer comprising> 0.8 g / in 3 of particulate metal oxide loading.

[0340] 27. The composite oxidation catalyst according to 26, wherein the particulate metal oxide in the carrier coating covering layer has an average pore size of ≥10 nm, and / or the carrier coating covering layer has an average inter-particle pore size of ≥10 nm.

[0341] 28. A composite oxidation catalyst according to 26 or 27, wherein the particulate metal oxide in the carrier coating covering layer is selected from alumina, silica, titania, zirconia, ceria, and mixed oxides or composite oxides of any two or more thereof or aluminosilicate zeolites.

[0342] 29. The composite oxidation catalyst according to 26, 27 or 28, wherein the particulate metal oxide in the carrier coating covering layer has a diameter of >100 m 2 / g specific surface area;

[0343] 30. The composite oxidation catalyst according to any one of 26 to 29, wherein the particulate metal oxide in the carrier coating layer supports a platinum group metal, and the platinum group metal is platinum or

[0344] Pt:Pd is a combination of platinum and palladium in a weight ratio ≥ 1:1.

[0345] 31. The composite oxidation catalyst according to 30, wherein the platinum group metal loading in the carrier coating covering layer is 1-35 gft -3 .

[0346] 32. The composite oxidation catalyst according to any one of 1 to 31, wherein the substrate is a honeycomb structure flow-through substrate monolith.

[0347] 33. An exhaust system for a vehicle compression ignition engine, the exhaust system comprising

[0348] A composite oxidation catalyst and a soot filter substrate disposed downstream of the oxidation catalyst as described in any one of 32 to 32, wherein the first substrate end of the composite oxidation catalyst is oriented to the upstream side.

[0349] 34. The exhaust system of claim 33, wherein the soot filter substrate is a catalyzed soot filter substrate catalyzed with a platinum group metal catalyst or a selective catalytic reduction catalyst.

[0350] 35. An exhaust system according to 33 or 34, comprising an injector for liquid hydrocarbons connected to a source of liquid hydrocarbons, the injector being arranged to inject the liquid hydrocarbons into exhaust gases flowing in the exhaust system downstream of the engine.

[0351] 36. An exhaust system according to 33, 34 or 35, comprising a substrate disposed downstream of a soot filter substrate catalyzed with a selective catalytic reduction catalyst.

[0352] 37. An exhaust system according to 34, 35 or 36, which includes a selective catalytic reduction catalyst, the system including an injector for a nitrogenous reductant or a precursor thereof, the injector being connected to a source of the nitrogenous reductant or the nitrogenous reductant precursor, the injector being arranged to inject the nitrogenous reductant or the nitrogenous reductant precursor into the flowing exhaust gas downstream of the composite oxidation catalyst and upstream of a substrate including the selective catalytic reduction catalyst.

[0353] 38. A compression ignition internal combustion engine for a heavy-duty diesel vehicle, the compression ignition internal combustion engine comprising an exhaust system according to any one of 33 to 37, wherein a first base end portion of the composite oxidation catalyst is oriented to the upstream side.

[0354] 39. A heavy-duty diesel vehicle, the heavy-duty diesel vehicle comprising a compression ignition internal combustion engine according to 38.

[0355] 40. Use of a composite oxidation catalyst according to any one of 1 to 32 for heating a soot filter disposed downstream of the composite oxidation catalyst in an exhaust system of a vehicle compression ignition internal combustion engine by: causing the oxidation catalyst to contact an exhaust gas containing an increased concentration of a hydrocarbon fuel, and generating heat release from the increased concentration of the hydrocarbon fuel in the exhaust gas flowing in the exhaust system relative to normal operating conditions.

[0356] 41. A method for preparing a composite oxidation catalyst for treating exhaust gas generated by a vehicle compression ignition internal combustion engine in an exhaust system, wherein the composite oxidation catalyst comprises:

[0357] a substrate having a total length L and a longitudinal axis, and having a substrate surface axially extending between a first base end portion and a second base end portion; and

[0358] two or more catalyst carrier coating zones axially arranged in series on and along the substrate surface, wherein a first catalyst carrier coating zone having a length L1 is defined at one end by the first base end portion, wherein L1 < L, and at a second end by a first end of a second catalyst carrier coating zone having a length L2, wherein L2 < L, wherein the first catalyst carrier coating zone comprises a first refractory metal oxide carrier material and two or more platinum group metal components supported thereon, the two or more platinum group metal components including both platinum and palladium, and a weight ratio of platinum to palladium ≥ 1; and

[0359] the second catalyst carrier coating zone comprises a second refractory metal oxide carrier material and one or more platinum group metal components supported thereon,

[0360] wherein a total platinum group metal loading defined in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) in the first catalyst carrier coating zone is greater than the total platinum group metal loading in the second catalyst carrier coating zone, and wherein the first catalyst carrier coating zone comprises one or more first alkaline earth metal

[0361] components supported on the first refractory metal oxide carrier material, the method comprising the steps of:

[0362] (a) applying a catalyst washcoat layer to the surface of the substrate in a length extending from one end of the substrate, the catalyst washcoat layer comprising a refractory metal oxide support material and one or more platinum group metal components; and

[0363] (b) impregnating the catalyst support coating with a solution containing one or more platinum group metals in a zone of length L1 defined at one end by the first substrate end,

[0364] The one or more alkaline earth metal components are present in the catalyst support coating of step (a) and / or the impregnation solution used in step (b).

[0365] 42. The method according to 41, wherein in step (a), the catalyst support coating extends along the total length L of the substrate.

[0366] 43. A method according to 41, wherein in step (a), the catalyst support coating is a first catalyst support coating, which extends from the end of the first substrate to less than the total length of the substrate, and the method also includes a step (a') before step (a) or after step (a), but in either case is performed before step (b), in which a second catalyst support coating is applied to the substrate, having a length extending from the end of the second substrate to less than the total length of the substrate, so that the first catalyst support coating partially overlaps with the second catalyst support coating or the second catalyst support coating partially overlaps with the first catalyst support coating, wherein the second catalyst support coating comprises a refractory metal oxide support material and one or more platinum group metal components.

[0367] 44. The method of claim 43, wherein the first catalyst washcoat layer extends from the first substrate end and the second catalyst washcoat layer extends from the second substrate end, whereby the second catalyst washcoat layer partially overlaps the first catalyst washcoat layer.

[0368] definition

[0369] Any reference to the distribution of a platinum group metal (e.g., a first platinum group metal or a second platinum group metal) in a direction perpendicular to the substrate surface (e.g., a straight line) generally refers to a direction perpendicular to the same surface of the substrate on which a catalyst layer is disposed. For reference purposes, the surface of the substrate is generally in a horizontal (i.e., longitudinal) plane. The direction perpendicular to the substrate surface is generally the direction of a cross-sectional plane (i.e., a cross-sectional plane exposing the thickness of the catalyst layer) passing through the catalyst layer perpendicular to the substrate surface. The cross-sectional plane is generally in a vertical (i.e., transverse) plane. The cross-sectional plane is perpendicular to the surface on which a catalyst layer is disposed. More generally, the cross-sectional plane is substantially parallel to the inlet end face of the substrate and / or the outlet end face of the substrate (i.e., a plane containing the inlet end face and / or a plane containing the outlet end face). Any reference to "substantially parallel" in this context refers to an angle of less than 5°, preferably less than 2.5°, more preferably less than 1° (e.g., less than 0.5°) between the cross-sectional plane and the inlet end face or outlet end face of the substrate.

[0370] Any reference to "the surface of a substrate" typically refers to the surface of the walls of a channel through the substrate.

[0371] As used herein, the term "layer" (e.g., catalyst layer) refers to a thickness of material spread over a surface (such as the surface of a substrate or the surface of another layer), which typically has distinct boundaries or edges (i.e., a first layer can be distinguished from a compositionally different second layer using conventional analytical techniques (e.g., transmission electron microscopy)).

[0372] As used herein, the term "homogeneous" with respect to the distribution of platinum group metals generally refers to a composition (e.g., a layer) wherein the amount of platinum group metal at any point in the composition is within ±20% of the average amount of platinum group metal in the entire composition (e.g., layer). Preferably, the amount of platinum group metal at any point in the composition is within ±10%, more preferably within ±5%, and even more preferably within ±1% of the average amount of platinum group metal in the entire composition (e.g., layer). The average amount of platinum group metal should correspond to the amount of platinum group metal measured during the preparation of the composition. The amount of platinum group metal at any point in the composition can be determined using conventional analytical techniques, such as by EDX analysis using a transmission electron microscope.

[0373] As used herein, the term "mixed oxide" generally refers to a mixture of oxides in a single phase form, as is generally known in the art.

[0374] As used herein, the term "complex oxide" generally refers to a composition of oxides having more than one phase, as is generally known in the art.

[0375] The term "loading" is used to define the amount of concentration of a component, such as a platinum group metal component, an alkaline earth metal component, or a washcoat formulation comprising both one or more platinum group metal components and one or more alkaline earth metal components supported on a refractory metal oxide support material present in a catalyst washcoat zone, in a catalyst washcoat, or as a whole on a substrate. The local concentration of the or each platinum group metal component or the or each alkaline earth metal component can be determined by EPMA or XRF techniques. The units of loading used herein and in the prior art are generally g ft -3 or g in -3 The SI unit equivalents of grams per litre generally relate to the volume of the substrate used. The volume fraction relates to the volume fraction of the substrate to which, for example, a washcoat is applied. Typically, relatively low concentrations of components are expressed in "g ft -3 " so that the amount is meaningful without referring to 1 / 100 or 1 / 1000 of an amount, whereas components with higher concentrations are given as "g in -3 ” is given, such as for the total washcoat applied amount. By common sense convention, the “volume” component of the unit of loading assumes that the substrate is a solid, such as the total volume of a cylinder, and ignores the fact that the substrate has channels extending therethrough defined by walls made of the substrate composition, or that the substrate composition itself is porous.

[0376] The term “comprising” is intended to mean that the stated elements are essential, but other elements may be added and still form a configuration within the scope of the claims.

[0377] As used herein, the expression "consisting essentially of" may be replaced with the broader definition "comprising" and limits the scope of a feature to include the specified materials or steps, as well as any other materials or steps that do not materially affect the basic and novel properties and functions of the feature or the feature in combination with other claim features. In the case where a catalyst support coating zone consists essentially of platinum, this means that it is intended to consist of platinum, but other platinum group metals (e.g., palladium) may be accidentally present in the catalyst support coating zone of the finished product, for example due to migration of palladium into the catalyst support coating zone during manufacturing. In this context, "consisting essentially of" does not exclude the accidental presence of palladium in a catalyst support coating zone that is defined as consisting essentially of platinum. The term "consisting essentially of" encompasses the expression "consisting of" and is interchangeable with "comprising" or "consisting of". The term "consisting of" limits the claim to not including materials other than those listed, except for impurities typically associated therewith.

[0378] With regard to the composite oxidation catalyst according to the present invention, the basic and novel feature of the present invention is at least two catalyst carrier coating zones arranged in series axially on and along the surface of the substrate, wherein the first catalyst carrier coating zone defined at one end by the substrate inlet end comprises a refractory metal oxide carrier material, platinum and palladium with a Pt:Pd weight ratio ≥1, and barium, and the second catalyst carrier coating zone comprises a refractory metal oxide carrier material, and platinum as the only platinum group metal present, or a Pt:Pd weight ratio greater than that of both platinum and palladium in the first catalyst carrier coating zone.

[0379] In the context of stating a "platinum group metal" (e.g., a first platinum group metal or a second platinum group metal), it is understood that it is often difficult to characterize the exact catalytic species in the catalyst, and that the platinum group metal may not be present in elemental metallic form. Any reference to "consisting essentially of a platinum group metal..." encompasses a "platinum group metal portion" in elemental form of a platinum group metal, an alloy comprising a platinum group metal, or a compound comprising a platinum group metal (e.g., an oxide of a platinum group metal). Preferably, any such "platinum group metal portion" is in elemental form of a platinum group metal or an alloy comprising a platinum group metal, more preferably in elemental form of a platinum group metal.

[0380] Reference to claim 2 and Figure 1 Embodiments in which the first catalyst support coating and the second catalyst support coating are adjacent to each other without "substantially any overlap between the first support coating and the second support coating", the term "substantially any overlap" is intended to cover products in which there is no gap between the first catalyst support coating and the second catalyst support coating. In practice, it is actually very difficult to obtain a perfect "gapless" coating without some overlap at the junction between two composite support coatings. Therefore, in practice, the product made by the method covered by the sixth aspect of the invention may have an unintended overlap of from 1-2mm to up to 15% axial length (such as up to 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 8%, 6%, 5%, 4%, 3%, 2% or 1%). Therefore, the composite oxidation catalyst according to the first aspect extends to products with unintended overlap up to this size.

[0381] Example

[0382] The invention will now be illustrated by the following non-limiting examples. For the avoidance of doubt, all coating steps were carried out using the method and apparatus disclosed in the applicant's WO99 / 47260, i.e. the method comprising the steps of: (a) positioning a containment device on top of a substrate, (b) dosing a predetermined amount of a liquid component into said containment device in the order of (a) then (b) or (b) then (a), and (c) by applying a vacuum, sucking the entire amount of the liquid component into at least a portion of the substrate and retaining substantially the entire amount within the substrate without recirculation.

[0383] Example 1 (Comparative)

[0384] A bare cordierite honeycomb structure flow-through substrate monolith with 400 cells per square inch, a wall thickness of 6 thousandths of an inch (6 mils), and a total length of 4 inches was coated with a catalyst washcoat in the following zoned arrangement. A first catalyst washcoat slurry comprising aqueous salts of platinum and palladium (as nitrates) and an alumina support doped with 5 wt% silica was coated onto the substrate monolith from one end marked as the inlet end to an axial length of 75% of the total substrate monolith length. The concentrations of the platinum and palladium salts were selected to achieve a weight ratio of 6.67 Pt:3.33 Pd gft in the coating at a platinum to palladium ratio of 2:1 in the first catalyst washcoat. -3 The inlet coating was then dried in a conventional oven at 100°C for 1 hour to remove excess water and other volatile materials.

[0385] A second catalyst washcoat slurry comprising an aqueous solution of a platinum nitrate salt as the only platinum group metal present and 5 wt% of an alumina support doped with silica was applied to the substrate from the end of the substrate monolith opposite to the end to which the first coating was applied (i.e., the outlet end). The axial length of the second catalyst washcoat coating was 50% of the total substrate length, i.e., 25% of the second washcoat catalyst coating overlapped with the first washcoat catalyst coating. The concentration of the platinum salt used was selected to achieve 2 gft in the 50% axial substrate length coated. -3 Pt loading. The substrate coated with both the first washcoat and the second washcoat was dried in a conventional oven at 100°C for 1 hour, and the dried portion was then calcined at 500°C for 1 hour to decompose the platinum and palladium salts and fix the platinum and palladium to the silica-doped alumina support.

[0386] An aqueous medium containing salts of both platinum nitrate and palladium nitrate in a 1:1 weight ratio was then impregnated onto the coating of the first catalyst support wash to 25% of the axial length of the substrate measured from the inlet end of the substrate. The concentration of the salt was selected to achieve 25 gft of each of platinum and palladium in the substrate over the impregnated length. -3This provides a high PGM loading in the zone at the inlet end, with an additional loading of 50 gft over and above that of the underlying first catalyst washcoat. -3 The impregnated portions were oven dried and calcined as described above.

[0387] All washcoat and impregnation solutions were naturally acidic and no pH adjustment was performed on them.

[0388] The finished product comprises a substrate monolith comprising three catalyst washcoat zones arranged axially in series: a first high loading front zone defined as approximately 25% of the axial length of the substrate monolith measured from the inlet end and having a total platinum group metal loading that is a combination of the following 2Pt:1Pd first catalyst washcoat layer and the impregnated 1:1Pt:Pd; followed by a second catalyst washcoat zone in axial series consisting of the 2Pt:1Pd first catalyst washcoat layer occupying approximately 50% of the axial length of the substrate monolith, the second catalyst washcoat zone having a lower total platinum group metal loading than the first catalyst washcoat zone; and finally a third pure Pt zone at the outlet end consisting of the second catalyst washcoat layer occupying approximately 25% of the axial length of the substrate monolith, the third pure Pt zone having a lower total platinum group metal loading than the first or second catalyst washcoat zones. The total platinum group metal loading on the substrate monolith as a whole is 20 gft -3 , the total Pt:Pd weight ratio is 11.8:4, equivalent to 2.95:1.

[0389] Using EPMA-WDX (electron microprobe analysis-wavelength dispersive X-ray) image analysis, it was found that the first catalyst support coating zone containing high concentrations of both platinum and palladium prepared in this way had an uneven Pd distribution in the direction perpendicular to the substrate surface, that is, the amount of Pd decreased in the vertical direction toward the substrate surface. In other words, the Pd concentration at the upper surface of the support coating in contact with the gas entering the inlet end of the substrate is higher than the Pd concentration in the support coating at the substrate surface. To a lesser extent, platinum was also found to follow the same trend as palladium. However, in the first catalyst support coating zone, the uneven distribution of Pd in ​​the direction perpendicular to the substrate surface is most obvious. This effect is referred to herein as forming a so-called Pd "shell" in the first catalyst support coating zone.

[0390] Example 2

[0391] A product identical to that disclosed in Comparative Example 1 was prepared, except that the first catalyst washcoat slurry contained an aqueous barium acetate salt according to the present invention in addition to the aqueous salts of platinum and palladium. The concentration of barium acetate was selected so that for 75% of the axial length of the first catalyst washcoat the barium loading in the first catalyst washcoat was 80 gft -3 That is, the first catalyst washcoat zone and the second catalyst washcoat zone contain 80 gft -3 The total platinum group metal loading and Pt:Pd weight ratio on the substrate monolith as a whole were the same as in Example 1, i.e. 20 gft -3 .

[0392] Using EPMA-WDX image analysis, it was found that the first catalyst washcoat zone prepared in this manner had a decreasing amount of Pd, and to a lesser extent Pt, in the vertical direction toward the substrate surface, but also had a relatively strong inhomogeneous distribution of barium that decreased in the vertical direction toward the substrate surface. In other words, Pd and Ba (and to a lesser extent Pt) formed a "crust" at the surface of the washcoat that was in contact with the gas entering the inlet end of the substrate.

[0393] Example 3 - Test Method and Results for Comparison of the Presence and Absence of Barium in the Inlet Zone

[0394] Thermal analysis was performed on each composite oxidation catalyst prepared according to Examples 1 and 2 using a laboratory bench mounted diesel engine. The engine was operated at 2200 rpm with EUVI B7 fuel (7% biofuel) as the fuel for engine operation and exhaust hydrocarbon enrichment (exothermic generation) and was equipped with an exhaust system comprising an exhaust pipe and a removable canister into which each composite oxidation catalyst could be inserted for testing, with the inlet end / first catalyst, high load carrier coating zone oriented to the upstream side. The engine was a 7 liter EUV 6 cylinder engine producing 235 kW at 2500 rpm, and the exhaust system included a "7th injector" that was arranged to inject hydrocarbon fuel directly into the exhaust pipe, which was downstream of the engine manifold and upstream of the composite oxidation catalyst to be tested. The injector is referred to as the "7th injector" because it is a supplement to the six fuel injectors associated with the engine cylinders. Thermocouples were located at the inlet of the composite oxidation catalyst and were inserted at various axial positions along the centerline of the substrate monolith of each composite oxidation catalyst.

[0395] Each catalyst was conditioned at an inlet exhaust gas temperature of 490°C with an exhaust gas flow rate of 1000 kg / hr for 10 minutes, followed by a rapid cooling step. The exhaust gas flow rate was then set to 720 kg / hr (corresponding to 120,000 hr -1space velocity of the size and volume of the substrate being tested), while controlling the engine load so that a steady-state set inlet exhaust temperature of about 270° C. is achieved at about 1800 seconds.

[0396] The composite oxidation catalyst was then tested for its ability to generate an exotherm at each stable set temperature by injecting hydrocarbon fuel via a seventh injector, which had a target temperature of 600°C, and generating a stable hydrocarbon "leak" at the outlet of the composite oxidation catalyst substrate via a downstream thermocouple and hydrocarbon sensor. If the hydrocarbon slip measured downstream of the composite oxidation catalyst exceeded 1000 ppm C3, that is, regardless of the hydrocarbon chain length in the detected hydrocarbons - the modal carbon chain length in a typical diesel fuel is C3, the composite oxidation catalyst substrate was ... 16 - In any case, the test will be stopped if the detection is equal to 1000ppm C3. Therefore, if 187.5ppmC is detected, the test will be stopped. 16 , this is equivalent to 1000ppm C3(C 16 Equivalent to 51 / 3x C3 hydrocarbons).

[0397] After testing at a set inlet temperature of about 270°C, the system was preconditioned again at an inlet exhaust temperature of 490°C for 10 minutes at a flow rate of 1000 kg / hour, and then rapidly cooled and tested for heat release at a second set temperature (e.g., about 260°C). This cycle was repeated to test heat release generation at set temperatures of about 250°C, 240°C, and 230°C. The test was stopped when the composite oxidation catalyst failed to generate a stable heat release of 600°C at the end of the composite oxidation catalyst outlet or when the hydrocarbon slip measured at the composite oxidation catalyst outlet exceeded 1000 ppm (C3).

[0398] The results of these tests conducted on Examples 1 and 2 are listed in Table 1 below. It will be appreciated that the lower the inlet temperature at which a stable exotherm can be achieved with acceptable hydrocarbon slip, the more advantageous it is. This is because design flexibility in the system is increased because the filter regeneration event can be initiated from a lower inlet exhaust gas temperature, i.e., there is no need to wait until the exhaust gas temperature under normal operating conditions is high enough to initiate filter regeneration, which may occur less frequently in ordinary operation. In addition, it improves overall fuel economy because not as many hydrocarbons need to be injected in order to achieve the desired exhaust gas temperature at the outlet of the composite oxidation catalyst.

[0399] Table 1

[0400]

[0401] Table 1 shows that the conventional oxidation catalyst (Example 1) cannot achieve stable heat release at an inlet temperature of 250°C or lower, while the composite oxidation catalyst according to the present invention can achieve stable heat release as low as 230°C.

[0402] Example 4 - Evaluation of Guard Beds to Prevent Phosphorus and / or Zinc Poisoning of Catalysts - Sample Preparation

[0403] have Figure 5 The catalyst according to the invention in the configuration shown is used to illustrate the functional principle of the guard bed feature. A cylindrical cordierite flow-through honeycomb monolith substrate having dimensions of 10.5 inches in length by 4 inches in diameter is coated with a first catalyst washcoat (6) and a second washcoat (7), the first catalyst washcoat being coated on the substrate and comprising a 2:1 weight ratio of Pt and Pd supported on an alumina particulate support doped with 5 weight percent silica and 80 gft -3 The first catalyst washcoat zone is obtained by impregnating the first catalyst washcoat layer (6) with a platinum and palladium salt solution sufficient to coat 50 gft / s of the substrate at 50 gft / s. -3 With an additional total PGM loading of 1:1, a Pt to Pd weight ratio of 1:1 was achieved over 25% of the axial length of the substrate. The composite oxidation catalyst as a whole has 21 gft -3 The total platinum group metal loading of Example 4 and a Pt:Pd weight ratio of 7:5 (equivalent to 1.4:1). That is, the first catalyst support coating zone in Example 4 has a Pt:Pd weight ratio of >1:1.

[0404] Three samples were prepared. The first sample was used as a control and no guard bed was used. The second sample had a washcoat of alumina (without platinum group metals) doped with 5 wt% silica - the same alumina doped with silica as used in the first (6) and second (7) catalyst washcoats - at 0.5 gin -3 A washcoat loading of 100% was coated on the first catalyst washcoat zone (1) and a total of 30% of the axial length of the substrate was coated from the inlet end of the substrate (I), i.e. 25% of the axial length of the first catalyst washcoat zone was completely covered by the washcoat cover of the silica-doped alumina "guard bed", i.e. 120% of the axial length of the first catalyst washcoat zone was coated with the washcoat cover. The average pore size of the alumina doped with 5 wt% silica used was about 19 nm.

[0405] The third sample was prepared in the same manner as the second sample, except that the washcoat loading of the alumina "guard bed" doped with 5 wt.% silica was 1.0 gin -3 .

[0406] The three samples were each oven aged at 650°C in air for 50 hours.

[0407] Example 5 - Evaluation of Guard Beds to Prevent Phosphorus and / or Zinc Poisoning of Catalysts - Sample Testing

[0408] Three samples of coated substrates prepared according to Example 4 were canned together in parallel in a proprietary canning arrangement, and the canned substrates were inserted into the exhaust system of a 16-liter heavy-duty diesel engine mounted on a laboratory bench, certified to meet Euro 2 emission standards, using MK1 fuel into which a ZDTP fuel additive had been blended at a concentration of 1750 ppm. The substrates were then engine aged using the following cycle, calculated to expose the canned substrates as a whole to 0.5 g ZDTP / liter of catalyst substrate per cycle:

[0409] (i) "soak" for 30 minutes at a steady-state engine load producing a substrate inlet temperature of 470°C;

[0410] (ii) a 15 minute "soak" at a steady state engine load producing a substrate inlet temperature of 210°C, followed by a 15 minute "soak" at an inlet temperature of 250°C, and finally a 10 minute "soak" at an inlet temperature of 325°C; and

[0411] (iii) repeating steps (i) and (ii) six (6) times.

[0412] The samples were then decanned and each sample was tested in turn using the engine described in Example 3 according to the following procedure.

[0413] The "continuous heat release" test was performed as follows. Each catalyst was conditioned at an inlet temperature of 490°C for 20 minutes and then rapidly cooled to an inlet temperature of 320°C, at which temperature the catalyst was maintained for 10 minutes. Hydrocarbons were then injected via the 7th injector at a rate to achieve a 600°C heat release at the substrate outlet. The heat release was maintained at steady state for 5 minutes. The hydrocarbon oxidation catalyst light-off temperature ramp was then started by continuously adjusting the engine load to achieve an inlet temperature drop of 1°C per minute at a flow rate of 720kg / h. The run was stopped when the temperature at the inlet of the downstream catalytic soot filter was below 425°C or the hydrocarbon slip analyzer limit of 1500ppm C3 was reached.

[0414] The washcoat in the first quarter of the substrate measured from the inlet end of each substrate sample was analyzed using X-ray fluorescence (XRF) to characterize the elemental composition of the washcoat and the poisoning of phosphorus and zinc. The degree of poisoning detected was zeroed against an Omnian multi-element reference standard scan. The results are shown in Table 2 below.

[0415] Table 2

[0416] sample Phosphorus (weight %) Zinc (weight %) Reference example 2.41 0.10 <![CDATA[0.5g / in 3 Guard Bed Sample]]> 2.23 0.11 <![CDATA[1.0g / in 3 Guard Bed Sample]]> 2.29 0.09

[0417] Phosphorus poisoning was consistent in all three fractions, with a maximum difference of approximately 8.0% between any two samples.

[0418] The skilled artisan will appreciate that the phosphorus poisoning achieved using the procedure used in this Example achieves phosphorus poisoning that exceeds what has been reported in the art through normal use (see above, where post-catalyst samples were found to have phosphorus poisoning of 1.0 wt % to 1.5 wt % phosphorus at the end of vehicle life). However, the phosphorus poisoning levels achieved using the procedure described in this Example 5 are comparable to those observed empirically in normal operation at the end of vehicle life.

[0419] The results of the continuous heat release test are listed in Table 3 below.

[0420] Table 3

[0421]

[0422] From these results, it can be seen that the inlet temperature required to obtain an exotherm of ≥ 500° C. was slightly increased by 5.2° C. (2.2%) for both samples including the guard bed feature, compared to the reference catalyst without the guard bed feature. This indicates that there is a small and practically insignificant increase in the inlet temperature at which engine management can initiate an exotherm generating event to regenerate a downstream filter component in an exhaust system according to the present invention, the exhaust system including a composite oxidation catalyst including a guard bed feature.

[0423] It can also be seen that relative to the reference, including 1.0g / in 3 The supported guard bed sample retained significantly more hydrocarbon oxidation activity (only a 13.9% loss in inlet temperature required to achieve a 500°C exotherm compared to a 30.3% loss in inlet temperature for the reference), despite the fact that the same portion of the oxidation catalyst in the reference and the sample according to the invention had similar amounts of poisoning phosphorus present (see Table 3). However, it can also be seen that the inclusion of 0.5 g / in 3 The activity loss of the samples was similar to that of the reference.

[0424] Example 6 - Further Evaluation of Guard Beds to Prevent Phosphorus and / or Zinc Poisoning of Catalyst

[0425] A catalyst having a similar formulation and design to that described in Example 4 was prepared, except that the composite oxidation catalyst as a whole had a 15 gft -3and a Pt:Pd weight ratio of 7.24:5 (equivalent to 1.45:1), but wherein the first catalyst washcoat zone still has a Pt:Pd weight ratio of >1:1.

[0426] The following samples were prepared.

[0427] Table 4

[0428]

[0429] The freshly prepared "gamma alumina" in Examples 6.2 and 6.11 has an inherent average pore size of about 13 nm. The freshly prepared "alumina doped with 5 wt% silica" of Examples 6.3, 6.4 and 6.10 and 6.12-6.14 (including the end values) has an inherent average pore size of 15 nm. The freshly prepared "wide pore alumina" has an inherent average pore size of about 20 nm. The freshly prepared ceria of Example 6.9 has an inherent average pore size of about 8 nm. The AEI aluminosilicate zeolites of Examples 6.7 and 6.8 have a silica to alumina ratio of about 20. The copper loading in the Cu ion-exchanged AEI aluminosilicate zeolite of Example 6.8 is about 3.8 wt%. All particulate metal oxide materials used in this example have a silica to alumina ratio of about 20. 2 / g new specific surface area.

[0430] The particulate metal oxide used in each guard bed example was ground to a D90 < 20 μm and a D50 (average particle size) < 8 μm, a combination that applicants believe produces an average inter-particle pore size of ≥ 10 nm in the guard bed.

[0431] All samples were each oven aged in air at 650°C for 50 hours. The examples were tested in the same manner as described above in Example 5. The results are listed in Table 5 below.

[0432] Table 5

[0433]

[0434] As can be seen from the results shown in Table 5, all of the examples coated with the guard bed had reduced exothermic activity prior to phosphorus aging relative to the control (reference) example 6.1, which had an exothermic failure temperature of 239.0°C. However, all of Examples 6.2-6.14, which included a guard bed, performed better than the reference example after phosphorus aging (285.9°C). The best performing examples were those that had a reasonable balance between performance prior to phosphorus aging (e.g., <252.0°C) and performance after phosphorus aging (e.g., <273.0°C).

[0435] It can also be seen that the higher washcoat loading samples (eg, comparing Examples 6.4 to 6.3) performed better, as did the Examples where the PGM was supported on the particulate oxide material of the guard bed.

[0436] Example 7 - Study of NO Oxidation Between Fresh and Aged Catalysts by Composition Changes in the Outlet Catalyst Support Coating Zone Catalyst activity "δ"

[0437] Catalysts similar to those described in Example 4 were prepared - but No Protective bed - and has Figure 5 A series of catalysts of the configuration shown. The only other difference from the catalyst sample of Example 4 is that the composite oxidation catalyst as a whole has a 30 gft -3 and modifying the formulation of the second washcoat (7) to study the NO oxidation activity of the outlet zone, details of which are listed in Table 7 below. In this Example 7, the total platinum group metal loading of all samples in the second washcoat was 12.5 gft - 3. The second washcoat layer had an equal washcoat loading in all tested samples, and none of the tested second washcoats contained barium. The total Pt:Pd weight ratio in the composite oxidation catalyst as a whole was different from that of the Example 4 sample.

[0438] Each fresh catalyst was inserted into the test exhaust system of a laboratory bench mounted diesel engine as described in Example 3. The fresh catalyst was first "conditioned" for 30 minutes at engine load and speed to produce a catalyst bed temperature of 550°C. The resulting "conditioned" catalyst was then allowed to cool to room temperature. The conditioned fresh catalyst was then tested in a load ramp transient test cycle at a constant 1400 rpm engine speed and increasing air velocity to determine the NO oxidation activity of the composite oxidation catalyst. The NO2 / NO detected in the exhaust gas downstream of the composite oxidation catalyst was recorded relative to the substrate inlet temperature. x The tested catalysts were then cooled, decanned and hydrothermally oven aged at 600°C in air / 10% H2O (steam) for 140 hours to simulate end-of-vehicle oxidation activity. The aged catalysts were then reinstalled into the exhaust system of a laboratory bench mounted diesel engine and reconditioned and retested using the same protocol as described for the fresh catalysts.

[0439] Table 7

[0440]

[0441] Equivalent to 5.0 wt% MnO2 in the calcined material.

[0442] * Impregnation of alumina doped with 5 wt% silica with a manganese nitrate solution of sufficient concentration to obtain the desired calcined weight of manganese.

[0443] Example 8 - Further study of the composition change between fresh and aged catalyst support coating zone NO oxidation catalyst activity "δ"

[0444] Catalysts similar to those described in Example 7 were prepared and had Figure 5 A series of catalysts of the configuration shown. The only difference from the catalyst sample of Example 7 was that the first catalyst washcoat zone was obtained by impregnating the first catalyst washcoat layer (6) with a solution of platinum and palladium salts sufficient to impregnate 25% of the axial length of the substrate, with an additional 35 gft -3 The amount of Pt and Pd (weight ratio of 1:1) makes the composite oxidation catalyst as a whole have 20gft -3 and the total platinum group metal loading of all samples in the second washcoat layer in Example 8 was 7.5 gft -3 The total Pt:Pd weight ratio in the composite oxidation catalyst was 1.9:1.

[0445] Testing was performed in the same manner as described above in Example 7, except that the catalyst was aged differently. In this Example 8, the fresh "conditioned" catalyst was oven aged at 650°C in air for 50 hours.

[0446] Table 8

[0447]

[0448] Equivalent to 5.7 wt% MgO / 94.3 wt% Al2O3. The material is primarily a single cubic phase spinel as determined by X-ray diffraction (XRD). Some excess Al2O3 may be present.

[0449] * 1 Equivalent to 1.0 wt% MnO2.

[0450] * 2 Equivalent to 3.0 wt% MnO2.

[0451] * 3 Equivalent to 5.0 wt% MnO2.

[0452] Additionally, the composite oxidation catalyst of Example 8 was tested according to the "Continuous Exotherm" test described in Example 5, but without ZDTP aging. The results are listed in Table 9 below.

[0453] Table 9

[0454]

[0455] As can be seen from the results shown in Tables 8 and 9, Samples 8.4, 8.5 and 8.6, comprising preformed mixed substoichiometric magnesium aluminum metal oxides doped with manganese, exhibit a surprising and beneficial combination of lower NO oxidation activity and improved exotherm generation between fresh and aged.

[0456] Example 9 - First Catalyst Support Coating Zone Pt:Pd Weight Ratio Study

[0457] The cost of palladium by weight is currently more than twice that of platinum. In this Example 9, the applicant carried out a series of experiments to reduce the total amount of palladium in the composite oxidation catalyst according to the invention.

[0458] Catalysts similar to those described in Example 8 were prepared and had Figure 5 The only difference from the catalyst sample of Example 8 was that the composition of the impregnation solution for the first catalyst washcoat zone was changed enough to -3 At an additional total PGM loading of 15 gft / s, the Pt:Pd weight ratio range listed in Table 10 below is achieved over 25% of the axial length of the substrate from the inlet substrate end, and the composite oxidation catalyst as a whole has 15 gft / s -3 and the only platinum group metal in the second washcoat layer is platinum, i.e., at 2.0 gft -3 At a carrier coating loading of 1:1, the Pt:Pd weight ratio was 1:0.

[0459] Table 10 lists the results of the "Continuous Exotherm" test for catalyst samples aged and tested as described in Example 8.

[0460] Table 10

[0461]

[0462] As can be seen from the results shown in Table 10, the weight ratio of platinum to palladium in the first catalyst washcoat zone can be increased without unduly affecting the ability of the composite oxidation catalyst to generate and maintain its exotherm. However, where the impregnation medium used to obtain the first catalyst washcoat zone contained no palladium (Example 9.5), the degree of exothermic failure was high, and such an arrangement was therefore less preferred. It is therefore preferred that the combined Pt:Pd weight ratio of the impregnation medium and the underlying impregnated catalyst washcoat contain some palladium to stabilize the platinum, e.g., 10:1 ≥ 1:1.

[0463] For the avoidance of any doubt, any and all documents cited herein are hereby incorporated by reference into this application in their entirety.

Claims

1. A composite oxidation catalyst for treating exhaust gas generated by a vehicle compression ignition internal combustion engine in an exhaust system, and the composite oxidation catalyst is located upstream of a particulate filter in the exhaust system, the composite oxidation catalyst comprising: a substrate having a total length L and a longitudinal axis, and having a substrate surface axially extending between a first base end portion and a second base end portion; and two catalyst carrier coating zones axially arranged in series on the substrate surface and along the substrate surface, wherein a first catalyst carrier coating zone having a length L1 and comprising a first catalyst carrier coating is defined at one end by the first base end portion, wherein L1 < L and L1 < 50% L, and at a second end by a first end of a second catalyst carrier coating zone having a length L2 and comprising a second catalyst carrier coating, wherein L2 < L, wherein the first catalyst carrier coating zone comprises a first refractory metal oxide support material and two or more platinum group metal components supported thereon, the two or more platinum group metal components including both platinum and palladium, and the weight ratio of platinum to palladium ≥ 1; and the second catalyst carrier coating zone is defined at its second end by the second base end portion, the second catalyst carrier coating zone comprises a second refractory metal oxide support material and one or more platinum group metal components supported thereon, wherein the first catalyst carrier coating and the second catalyst carrier coating are adjacent to each other, and there is substantially no overlap between the first carrier coating and the second carrier coating, wherein the total platinum group metal loading defined in grams of platinum group metal per liter of substrate volume in the first catalyst carrier coating zone is greater than the total platinum group metal loading in the second catalyst carrier coating zone, and wherein the first catalyst carrier coating zone comprises one or more first alkaline earth metal components supported on the first refractory metal oxide support material, wherein the composite oxidation catalyst comprises a carrier coating overcoat that axially extends from the first base end portion to > 50% to at most 150% of the axial length of the underlying first catalyst carrier coating for protecting at least a portion of the underlying first catalyst carrier coating zone from phosphorus and / or zinc poisoning during use, the carrier coating overcoat comprises a particulate metal oxide loading of > 48.8 g / L and wherein the particulate metal oxide in the carrier coating overcoat has an average pore diameter of ≥ 10 nm and / or the carrier coating overcoat has an average interparticle pore diameter of ≥ 10 nm, wherein the particulate metal oxide in the carrier coating overcoat is loaded with a platinum group metal, which is platinum or a combination of platinum and palladium with a Pt:Pd weight ratio ≥ 1:

1.

2. The composite oxidation catalyst according to claim 1, wherein the composite oxidation catalyst is for a heavy-duty diesel vehicle.

3. The composite oxidation catalyst according to claim 1, wherein the substrate is a honeycomb-structured flow-through substrate monolith.

4. The composite oxidation catalyst according to claim 1, wherein the first alkaline earth metal component is barium (Ba) or strontium (Sr). 5 . The composite oxidation catalyst according to claim 1 , wherein the first alkaline earth metal component is barium. 6 . The composite oxidation catalyst according to claim 1 , wherein a weight ratio of platinum to palladium in the first catalyst support coating zone is 10:1≧1.5:

1.

7. The composite oxidation catalyst according to any one of claims 1 to 6, wherein the catalyst support coating region defined by the second substrate end portion at the second end portion thereof contains manganese.

8. The composite oxidation catalyst according to any one of claims 1 to 6, wherein the total platinum group metal loading in the first catalyst support coating zone is <3.53 g / L calculated as elemental metal.

9. The composite oxidation catalyst according to any one of claims 1 to 6, wherein the one or more platinum group metal components in the second catalyst support coating zone comprise both platinum and palladium.

10. The composite oxidation catalyst according to claim 9, wherein the mass ratio of platinum to palladium in the second catalyst support coating zone is greater than the mass ratio of platinum to palladium in the first catalyst support coating zone.

11. The composite oxidation catalyst according to any one of claims 1 to 6, wherein L1 is 20-40% L.

12. The composite oxidation catalyst according to any one of claims 1 to 6, comprising a total platinum group metal loading on the substrate as a whole of 0.177 to 2.12 g / L calculated as elemental metal. 13 . The composite oxidation catalyst according to claim 12 , wherein a weight ratio of total Pt:Pd in ​​the composite oxidation catalyst as a whole is 3:2 to 9:

1.

14. The composite oxidation catalyst according to any one of claims 1 to 6, wherein the total alkaline earth metal loading in the first catalyst support coating zone is 0.353 - 3.53 g / L calculated as elemental metal.

15. The composite oxidation catalyst according to any one of claims 1 to 6, wherein at least the first refractory metal oxide support material comprises alumina doped with heteroatoms. 16 . The composite oxidation catalyst according to claim 15 , wherein the aluminum oxide doped with heteroatoms is aluminum oxide doped with silicon dioxide.

17. A composite oxidation catalyst according to any one of claims 1 to 6, wherein the particulate metal oxide in the carrier coating covering layer is selected from alumina, silica, titania, zirconia, ceria and mixed oxides or composite oxides of any two or more thereof or aluminosilicate zeolites.

18. The composite oxidation catalyst according to claim 17, wherein the particulate metal oxide in the carrier coating covering layer has a diameter of >100 m 2 / g specific surface area.

19. The composite oxidation catalyst according to any one of claims 1 to 6, wherein the platinum group metal loading in the washcoat layer is 0.035-1.24 g / L.

20. An exhaust system for a vehicle compression ignition engine, the exhaust system comprising a composite oxidation catalyst according to any one of the preceding claims and a soot filter substrate disposed downstream of the oxidation catalyst, wherein the first substrate end of the composite oxidation catalyst is oriented to the upstream side.

21. The exhaust system of claim 20, wherein the soot filter substrate is a catalyzed soot filter substrate catalyzed with a platinum group metal catalyst or a selective catalytic reduction catalyst.

22. An exhaust system according to claim 20, comprising an injector for liquid hydrocarbons connected to a source of liquid hydrocarbons, the injector being arranged to inject the liquid hydrocarbons into exhaust gases flowing in the exhaust system downstream of the engine.

23. An exhaust system according to any one of claims 20-22, comprising a selective catalytic reduction catalyst, the system comprising an injector for a nitrogenous reductant or a precursor thereof, the injector being connected to a source of the nitrogenous reductant or the nitrogenous reductant precursor, the injector being arranged to inject the nitrogenous reductant or the nitrogenous reductant precursor into the flowing exhaust gas downstream of the composite oxidation catalyst and upstream of a substrate comprising the selective catalytic reduction catalyst.

24. A heavy-duty diesel vehicle comprising the exhaust system according to any one of claims 20-23.

25. The use of a composite oxidation catalyst according to any one of claims 1 to 19 for heating a soot filter arranged downstream of the composite oxidation catalyst in an exhaust system of a vehicle compression ignition internal combustion engine by bringing the oxidation catalyst into contact with exhaust gas containing an increased concentration of hydrocarbon fuel, thereby generating heat release from the increased concentration of hydrocarbon fuel in the exhaust gas flowing in the exhaust system relative to normal operating conditions.

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