Multizoned oxidation catalysts for compression-ignition internal combustion engines.

Abstract

To provide a compression ignition internal combustion engine for a heavy-duty diesel vehicle provided with a composite oxidation catalyst capable of reducing or preventing catalyst contamination due to phosphorus and / or zinc and substantially maintaining durability for a longer period of time.SOLUTION: A composite oxidation catalyst included upstream of the soot filter substrate has a substrate 5 with length L and a first catalytic washcoat zone 1 with length LI<L where one end is defined by the inlet end I and the second end is defined by the first end 15 of the second catalytic washcoat zone 2 with length L2<L. The second end is defined by the outlet end O and extends in an axial direction from the inlet end I and comprises a washcoat coating layer G comprising particulate metallic oxides having a loading of greater than 48.8 g / l, wherein a total platinum group metal loading in the first catalyst washcoat zone is greater than a total platinum group metal loading in the second catalyst washcoat zone 2 and wherein the first catalyst washcoat zone comprises one or more alkaline earth metal components supported on the first refractory metal oxide support material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-zoned oxidation catalyst for use in an exhaust system to treat exhaust gases produced by a compression-ignition internal combustion engine for a vehicle, preferably a heavy-duty diesel vehicle, and upstream of a particulate filter in the exhaust system. The present invention further relates to an exhaust system or vehicle comprising the multi-zoned oxidation catalyst. The present invention also relates to the use of the multi-zoned oxidation catalyst to generate heat for regenerating a downstream particulate filter, and to a method for preparing the multi-zoned oxidation catalyst. [Background technology]

[0002] Combustion engines emit carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NO x Combustion engines, particularly those for vehicle engines, produce exhaust gases containing pollutants such as carbon monoxide (CO2), carbon dioxide (CO3), and particulate matter (PM). Emission standards for pollutants in exhaust gases produced by combustion engines, particularly those 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 can meet these standards and are cost-effective.

[0003] Exhaust gases from gasoline and diesel engines are usually treated with catalysts capable of oxidizing (i) carbon monoxide (CO) to carbon dioxide (CO2), and (ii) hydrocarbons (HC) to water (HO) and carbon dioxide (CO2). Three-way catalysts (TWCs) typically oxidize nitrogen oxides (NO2) simultaneously with the oxidation reactions (i) and (ii). x ) to nitrogen (N2), water (HO), and carbon dioxide (CO2). The exhaust gases of compression-ignition engines, such as diesel engines, are typically 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 can also oxidize nitric oxide (NO) to nitrogen dioxide (NO2), which can be used to treat the exhaust gases of gasoline engines by reducing NO ...) using additional downstream emissions control devices. xcan assist in the removal of

[0004] Oxidation catalysts for compression-ignition internal combustion engines typically contain one or more platinum group metals. The particular platinum group metal selected for inclusion in the oxidation catalyst depends on various factors, such as the target reactivity with specific pollutants and different exhaust gas conditions, cost, durability at high temperatures, chemical compatibility with the support material and any other components of the catalyst, and susceptibility to contamination by impurities. For example, platinum (Pt) and palladium (Pd) can oxidize carbon monoxide (CO) and hydrocarbons (HC), respectively, in the exhaust gas of a compression-ignition engine. Palladium is more susceptible to contamination by sulfur in the fuel than platinum, but has higher thermal durability.

[0005] Where the internal combustion engine is a compression ignition engine for powering a vehicle, such as a diesel engine, the vehicle may be a light duty diesel vehicle or a heavy duty diesel vehicle.

[0006] The term "light-duty diesel vehicle (LDV)" is defined by U.S. or European legislation. In the United States, a light-duty diesel vehicle (LDV) refers to a diesel vehicle having a gross weight of ≦8,500 pounds (US pounds).

[0007] In Europe, light duty diesel vehicles are defined as vehicles of categories M1, M2, N1 and N2, with a reference mass (EU5 / 6) of ≦2610 kg.

[0008] In the United States, a heavy-duty diesel vehicle (HDV) is defined by statute as a diesel vehicle with a rated gross vehicle weight of >8,500 pounds (US pounds) in federal jurisdictions and >14,000 pounds (1995 and later models) in California.

[0009] In Europe, according to EU legislation (Council Directive 2007 / 46 / EC), heavy diesel vehicles are vehicles designed and constructed for the transport of goods and have a maximum mass (i.e., "maximum technically permissible payload") of more than 3.5 tonnes (i.e., metric tonnes) but not more than 12 tonnes (N2 category) or more than 12 tonnes (N3 category), i.e., trucks; or vehicles designed and constructed for the carriage of passengers, with more than eight seats in addition to the driver's seat, and with a maximum mass of either not more than 5 tonnes (M2 category) or more than 5 tonnes (M3 category), i.e., buses and coaches. China broadly follows the European definition.

[0010] In Japan, an HDV is a heavy commercial vehicle defined as having a gross vehicle weight >7500 kg.

[0011] In Russia and South Korea, the emission standards for heavy vehicles are based on European standards, so the above European definition applies.

[0012] In Brazil, an HDV is a motor vehicle used to transport passengers and / or goods with a maximum gross weight exceeding 3,856 kg or an unladen weight exceeding 2,720 kg.

[0013] In India, HDVs are vehicles with a gross vehicle weight > 3,500 kg.

[0014] Efforts to meet current emissions standards for heavy-duty diesel engines typically employ an exhaust system configuration comprising a series of catalyzed substrate and fuel injectors. From upstream to downstream (upstream relative to the engine connected or connectable to the exhaust system), the exhaust system comprises: 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).

[0015] The functions of the DOC during normal operation are to control CO and HC emissions, promote the conversion of NO to NO for downstream passive filter regeneration (combustion of filter-retained particulate matter in NO at exhaust gas temperatures lower than O in the exhaust, i.e., the so-called CRT® effect), and act as an exothermic catalyst during active CSF regeneration, which is achieved via injection of hydrocarbon fuel into the exhaust. For the avoidance of doubt, fuel injection / exothermic events do not occur during normal operation; normal operation is considered to be the period between fuel injection / exothermic events (described below (see C. Ruehl et al.)). The CSF controls particulate matter (PM) emissions and promotes NO → NO conversion, improving SCR performance. Urea, a precursor to ammonia, is injected downstream of the CSF and mixed with the exhaust gas. NO is converted via reaction with ammonia (NH) on the SCR catalyst, and unreacted NH is oxidized on the ammonia slip catalyst (ASC).

[0016] SCR catalysts selectively use a nitrogen-based reductant, typically NH3, which can be derived from an ammonia precursor such as urea, to produce NO x The reductant is injected into the flowing exhaust gas upstream of the SCR catalyst in an amount that promotes the following key NOx reduction reactions: (1) 4NH3+4NO+O2→4N2+6H2O, (2) 4NH3 + 2NO2 + O2 → 3N2 + 6H2O, and (3) NO + NO2 + 2NH3 → 2N2+ 3 / 2H2O (preferably the so-called "fast SCR reaction").

[0017] It will be appreciated that although reactions (1) to (3) can occur in parallel, the kinetically fastest reaction is favored. xIn exhaust gases with a ratio of 0.5, the kinetically favorable fast SCR reaction dominates. Most, if not all, applications use some degree of exhaust gas recirculation (EGR) to reduce engine-exit NOx to a level that can then be further reduced by urea-SCR aftertreatment. A DPF is required to reduce the increase in engine-exit PM resulting from the use of EGR and to ensure compliance with Euro VI particulate number emission limits. With the use of high-efficiency SCR, some Euro VI engines can reduce EGR use, for example, by using transient and / or uncooled EGR, or even eliminate EGR entirely. This has led to three main Euro VI engine strategies: 1.Cooled EGR+SCR, 2. High temperature (uncooled) EGR + SCR, and 3.SCR only.

[0018] Using these strategies, emissions from a typical heavy-duty engine are approximately 60 ppm CO and 10 ppm unburned hydrocarbon fuel. However, all such systems include a diesel particulate filter. Vehicle diesel particulate filter systems involve the interaction of filter material with regeneration technology. "Regeneration" is the selected method of burning off diesel particulate matter retained in the filter. Regeneration occurs infrequently, and the duration between regeneration events depends on several factors, including engine design, filtration efficiency during normal operation, and engine load during normal operation. According to a recent paper, empirical regeneration frequencies for heavy-duty diesel trucks vary from 3 to 100 hours and from 23 to 4,078 miles (see C. Ruehl et al., Environ. Sci. Technol., 2018, 52(10), pp. 5868-5874).

[0019] Regeneration technologies can be broadly divided into passive, active, and a combination of both passive and active. In passive systems, the oxidation temperature of particulate matter is reduced to a level that allows the filter to automatically regenerate during normal vehicle operation. An example of a passive system includes catalyzing the filter material, adding a catalytic fuel additive so that the particulate matter on the filter is contained in a catalyst composition for promoting soot combustion, and generating nitrogen dioxide (NO2) upstream of the filter to combust the particulate matter retained on the filter, where the particulate matter burns at a lower temperature in NO2 than in oxygen. This is the so-called CRT (registered trademark) effect (see, for example, European Patent No. 0341832).

[0020] Active systems actively induce filter regeneration by increasing the temperature of the particulate matter trapped in the filter. In practice, this can be done on the vehicle by burning hydrocarbon fuel already present in the vehicle and / or by electrical heating. Two methods for burning fuel include late-cycle injection of additional fuel, or in-cylinder engine management methods such as injection and combustion of fuel in the exhaust, i.e., after the exhaust gases have left the engine cylinder itself.

[0021] In passive-active systems, active regeneration can occur at lower exhaust gas temperatures and / or in shorter times compared to non-catalytic systems, such as through a "passive" filter catalyst or an upstream (CRT® effect-enhancing) NO oxidation catalyst. In either case, the fuel economy penalty associated with active regeneration can be minimized (at the added cost of the catalyst). Regeneration at lower temperatures can also reduce thermal stress and extend the useful life of the filter.

[0022] The present invention relates to an active or active-passive regeneration system.

[0023] Applicant's WO 2013 / 088152 A1 discloses a catalytic aftertreatment system for diesel engine exhaust gases, the system comprising a diesel oxidation catalyst (DOC), an aftertreatment device located downstream of the DOC, the aftertreatment device requiring periodic heat treatment, and means for creating a temperature increase within the aftertreatment device, the DOC including an upstream zone 0.5 to 2 inches (12.7 to 50.81 mm) long that has a higher oxidation activity toward hydrocarbons (HC) than the remainder of the DOC. The disclosure explains that during active filter regeneration, the heat generated while the upstream DOC is initially "lit" and in contact with injected hydrocarbon fuel can surprisingly be extinguished even while the DOC is in contact with the injected hydrocarbon fuel.

[0024] EP 2000639(A1) discloses a method for purifying exhaust gases from an internal combustion engine, which is said to broaden the temperature range at which high hydrocarbon concentrations can be combusted, or to allow hot gases to be fed more rapidly to a post-catalyst. The method includes using a catalyst to raise the temperature of the exhaust gases and purify the exhaust gases, and is characterized in that the hydrocarbons are introduced into the exhaust gas passage of the internal combustion engine upstream of the temperature-raising catalyst in the exhaust gas stream in an amount of 1,000 to 40,000 vol. ppm of the exhaust gas relative to the amount of methane. That is, according to the definition used in EP '639(A1), if a diesel fuel hydrocarbon compound is a chain of 16 carbon atoms, this hydrocarbon chain represents 16 times the amount of methane (CH4).

[0025] The catalyst of EP '639(A1) is obtained by supporting a catalytically active component (A) on a heat-resistant three-dimensional structure, the catalytically active component (A) being composed of (a) platinum, (b) an oxide of at least one metal selected from the group consisting of magnesium, alkaline earth metals, and alkali metals arbitrarily selected from the group consisting of magnesium, calcium, barium, strontium, and potassium, and (c) at least one member selected from the group consisting of palladium and rhodium, and supporting an inorganic oxide powder having the catalytically active component supported on top of the inorganic oxide powder (B).

[0026] Applicant's WO 2015 / 015182 discloses an oxidation catalyst for treating diesel engine exhaust gases, comprising: a substrate; a first washcoat region disposed on the substrate, the first washcoat region comprising a first platinum group metal and a first support material; a second washcoat region adjacent to the first washcoat region, the second washcoat region comprising a second platinum group metal and a second support material; and a third washcoat region disposed on the substrate, the third washcoat region comprising a third platinum group metal and a third support material, where (i) the third washcoat region is adjacent to the second washcoat region or (ii) the second washcoat region is disposed on or supported by the third washcoat region. The first washcoat region may or may not comprise an alkaline earth metal.

[0027] Applicant's WO 2014 / 132034 A1 discloses an oxidation catalyst for treating exhaust gases produced by a combustion engine, the oxidation catalyst comprising a substrate and a catalyst layer, the catalyst layer comprising a first support material, a first platinum group metal, and a second platinum group metal, the catalyst layer being disposed on a surface of the substrate, the catalyst layer having a non-uniform distribution of the first platinum group metal in a direction perpendicular to the surface of the substrate. The oxidation catalyst can also be used to oxidize carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) in such exhaust gases.

[0028] WO 2009 / 076574 discloses an exhaust treatment system and a method for remediating nitrogen oxides (NOx), particulate matter, and gaseous hydrocarbons present in a diesel engine exhaust stream. The exhaust treatment system includes 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 a discharge zone having an axial length. The inlet zone includes at least one of platinum and palladium in a first loading, and the discharge zone includes palladium in a second loading. The discharge zone is substantially free of platinum, meaning that platinum is not intentionally provided in the zone but may unintentionally include less than about 1% platinum by weight of the metal. The first loading is greater than the second loading, and the axial length of the inlet zone is equal to or less than the axial length of the discharge zone. The diesel oxidation catalyst contains an effective catalyst that does not produce substantially additional NO2 in the exhaust gas stream after passing through the diesel oxidation catalyst at about 90% of the operating range of the diesel oxidation catalyst.

[0029] Applicant's WO 2006 / 056811 discloses an apparatus comprising: a compression ignition engine; an exhaust system for the compression ignition engine including at least one exhaust system component for treating the exhaust gas; means for producing heat for heating the at least one exhaust system component, the heat generating means consisting essentially of a catalyst and means for injecting hydrocarbons into the exhaust gas for combustion over the catalyst, the catalyst consisting essentially of both a palladium (Pd) component and a platinum (Pt) component; and an optional support material disposed on a substrate monolith.

[0030] Applicant's WO 2014 / 080200 discloses an exhaust system for a compression ignition engine, including an oxidation catalyst for treating carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas of the compression ignition engine, the oxidation catalyst including a platinum group metal (PGM) component selected from the group consisting of a platinum (Pt) component, a palladium (Pd) component, and combinations thereof, an alkaline earth metal component, a support material including modified alumina incorporating a heteroatom component, and a substrate, wherein the platinum group metal (PGM) component, alkaline earth metal component, and support material are disposed on the substrate. In an embodiment, the oxidation catalyst has a metal monoxide concentration of ≧100 g / ft 3 Tests performed on a light-duty diesel exhaust gas composition using alkaline earth metal loadings of 1000 .mu.m or less are shown.

[0031] Applicant's WO 2014 / 080202 discloses a catalytic soot filter comprising an oxidation catalyst for treating carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas of a compression-ignition engine, the oxidation catalyst being disposed on a filtering substrate, the oxidation catalyst comprising a platinum group metal (PGM) component selected from the group consisting of a platinum (Pt) component, a palladium (Pd) component, and combinations thereof, an alkaline earth metal component, and a support material comprising modified alumina incorporating a heteroatom component. Example 8 demonstrates that the oxidation of nitric oxide is affected by the presence of barium oxide in such a catalyst formulation.

[0032] WO 2010 / 118125 discloses an oxidation catalyst composite for the oxidation of unburned hydrocarbons (HC) and carbon monoxide (CO) and the reduction of nitrogen oxides (NOx) in diesel engines, comprising at least two washcoat layers, a first washcoat containing a palladium component and a second washcoat containing platinum, with at least about 50% of the total platinum being on the rear side of the catalyst.

[0033] Applicant's WO 2015 / 110818 A1 discloses an oxidation catalyst for treating exhaust gas from a diesel engine, and an exhaust system including the oxidation catalyst. The oxidation catalyst includes a first washcoat region for oxidizing carbon monoxide (CO) and hydrocarbons (HC), the first washcoat region including a first platinum group metal (PGM) and a first support material, a second washcoat region for oxidizing nitrogen oxides (NO), the second washcoat region including platinum (Pt), manganese (Mn), and a second support material, and a substrate having an intake end and a discharge end, the second washcoat region being positioned such that the exhaust gas contacts the discharge end of the substrate after contacting the first washcoat region.

[0034] Applicant's WO 2017 / 093720 discloses an oxidation catalyst for treating exhaust gases produced by a diesel engine, the oxidation catalyst comprising a substrate, a capture material for capturing at least one phosphorus-containing impurity and / or at least one sulfur-containing impurity in the exhaust gases produced by the diesel engine, and a catalytic region disposed on the substrate, the catalytic region comprising a catalytic material comprising a platinum group metal (PGM) selected from the group consisting of platinum (Pt), palladium (Pd), and a combination of platinum (Pt) and palladium (Pd).

[0035] WO 2014 / 151677 A1 discloses an oxidation catalyst composite comprising a zone-coated diesel oxidation catalyst on a substrate having a Pt / Pd ratio of less than 3:1 and a first washcoat zone adjacent the substrate intake end of the substrate and at least twice the PGM loading of a second washcoat zone adjacent the substrate discharge end, wherein the first washcoat zone has a shorter length than the second washcoat zone.

[0036] European Patent No. 3170553 (A2) discloses an exhaust article (catalyst) coated on a single monolithic honeycomb substrate having a plurality of channels along its axial length. Different washcoat compositions are deposited along the length of the channel walls of the substrate starting from either the axial inlet end or the axial outlet end of the substrate, forming an inlet catalyst layer and an outlet catalyst layer, respectively. In the coating process described, the channel walls are coated with a catalyst washcoat composition such that they have a length shorter than the axial length of the substrate. The so-called "structure" of the resulting catalyst layer is said to define a plurality of zones along the length of the substrate.

[0037] European Patent Application No. 19182733.6 filed on June 26, 2019 by the applicant entitled "Composite, Zoned Oxidation Catalyst for a Compression Ignition Internal Combustion Engine" discloses a composite oxidation catalyst for use in an exhaust system to treat exhaust gases generated by a large compression ignition internal combustion engine for vehicles and upstream of a particulate matter filter in the exhaust system. The composite oxidation catalyst has an overall length L and a longitudinal axis and a substrate having a substrate surface extending axially between a first substrate end and a second substrate end, and two or more catalyst washcoat zones arranged in series axially on and along the substrate surface. The first catalyst washcoat zone has a length L1, where L1 < L, and at one end is defined by the first substrate end and at the second end is defined by the first end of a second catalyst washcoat zone having a length L2, where L2 < L. The first catalyst washcoat zone includes a first heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, including both platinum and palladium with a weight ratio of platinum to palladium of 1 or more. The second catalyst washcoat zone includes a second heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, and two or more catalyst washcoat zones, and the grams of platinum group metal per cubic foot of substrate volume (g / ft 3) is greater than the total platinum group metal loading in the second catalytic washcoat zone, and the first catalytic washcoat zone comprises one or more first alkaline earth metal components, preferably barium, supported on a first refractory metal oxide support material.

[0038] There are believed to be two basic mechanisms by which catalysts for treating exhaust gases from internal combustion engines can be contaminated: (i) selective contamination, in which the contaminant reacts directly with the active sites or catalyst support, causing a reduction or catastrophic loss of activity, and (ii) non-selective contamination, in which the surface of the support or active sites is fouled (or masked), thereby sterically blocking access to the active sites or pores in the catalyst support, causing a loss of performance. The present inventors have found that zinc and (cold) phosphorus (as phosphoric acid droplets) and their own oil droplets (all from the fuel or lubricant) are non-selective contaminants of the heat-generating function of the oxidation catalyst in the active or active-passive systems disclosed in applicant's WO 2013 / 088152 A1. Contaminants that chemically react with catalyst components (mechanism (i)) include (hot) phosphorus, which may also impair the heat-generating function of the oxidation catalyst. The primary source of phosphorus and zinc in exhaust gases likely comes from the additive zinc dialkyldithiophosphate (ZDDP) used in mineral-based oils or synthetic oils, zinc dithiophosphate (ZDTP). These additives are used to protect moving engine parts, such as camshafts, from wear during use. Zinc and phosphorus deactivation is particularly problematic for heavy-duty engines because heavy-duty engine oils have higher concentrations of additives than lubricants used in light-duty engines, such as those used in passenger cars. Phosphorus and zinc deposits cannot be removed from the catalyst except under conditions (i.e., very high operating temperatures) that can cause thermal deactivation of oxidation catalysts and other catalytic components in the exhaust system. A review of fouling and fouling mechanisms involving phosphorus and zinc can be found, for example, in A.J.J. Wilkins et al., Platinum Metals Review, 1990, 34(1) 16-24.

[0039] European Patent No. 2051799 (A1) discloses a system for minimizing the adverse effects of petroleum-derived and / or gasoline fuel additive compounds on automotive exhaust gas treatment systems. To mitigate the adverse effects of engine oil and / or gasoline fuel additive contamination, the document describes a catalyst comprising a 100% overcoat layer comprising one or more base metal oxides coated on a porous refractory oxide and one or more precious metal-containing washcoat layers. The overcoat is intended to prevent phosphorus and other contaminant deposits from fouling or negatively interacting with the underlying precious metal-containing washcoat. In an alternative embodiment, the invention provides partial coating of the upstream end of the catalyst member with an overcoat layer, thereby forming an upstream pollutant capture zone. The disclosure is exemplified by a uniformly coated three-way catalyst comprising a 100% or partial overcoat layer.

[0040] The present invention builds on the active or active-passive systems disclosed in Applicant's WO 2013 / 088152 A1, which aim to generally reduce the total amount of platinum group metals present in diesel oxidation catalysts, more specifically, reduce the weight ratio of platinum to palladium, and / or improve the efficiency of active filter regeneration by using a lower amount of fuel to achieve a desired filter inlet temperature, and / or achieve a higher filter inlet temperature for the same amount of fuel injected upstream of a prior art oxidation catalyst to generate heat therefrom, and / or enable heat generation over the oxidation catalyst from a lower initial exhaust temperature at the oxidation catalyst inlet. Furthermore, the inventors have developed a composite oxidation catalyst on a single substrate, i.e., a multifunctional catalyst configuration, which can combine one or more of the above goals with stable NO production for the operation of downstream catalytic functions, including the CRT effect on particulate matter combustion on the downstream filter and / or promotion of so-called fast reactions for selective catalytic reduction (SCR) catalysts. A further advantage of the preferred configuration is a multifunctional catalyst with improved hydrocarbon slip control. In addition to one or more or all of the above benefits, the preferred configuration incorporates guard bed features into the dual oxidation catalyst design to reduce or prevent catalyst poisoning by phosphorus and / or zinc from engine lubricity additives, thereby substantially maintaining catalyst performance, i.e., durability, over a longer period of time. Summary of the Invention

[0041] The present inventors have surprisingly found that one or more of the desired improvements can be obtained by combining a platinum and palladium PGM component, rich in palladium by weight, with an alkaline earth metal component in a catalyst washcoat zone at the intake end of an oxidation catalyst located upstream of a filter substrate in a vehicular compression ignition engine, particularly a heavy-duty vehicular diesel engine, system.

[0042] According to a first aspect, the present invention provides a composite oxidation catalyst for use in an exhaust system for treating exhaust gas generated by a compression ignition internal combustion engine for a vehicle, preferably a heavy-duty diesel vehicle, upstream of a particulate matter filter in the exhaust system, the composite oxidation catalyst comprising a substrate having an overall length L and a longitudinal axis and having a substrate surface extending axially between a first substrate end and a second substrate end, and two or more catalyst washcoat zones arranged in series axially on and along the substrate surface, the first catalyst washcoat zone having a length L1, where L1 < L, being defined at one end by the first substrate end and at the second end by the first end of a second catalyst washcoat zone having a length L2, where L2 < L, the first catalyst washcoat zone comprising a first heat-resistant metal oxide support material and two or more platinum group metal components supported thereon, both platinum and palladium having a weight ratio of less than 1, the second catalyst washcoat zone comprising a second heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, the two catalyst washcoat zones, the total platinum group metal loading in the first catalyst washcoat zone defined in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) being greater than the total platinum group metal loading in the second catalyst washcoat zone, the first catalyst washcoat zone comprising two or more catalyst washcoat zones comprising one or more first alkaline earth metal components, preferably barium, supported on the first heat-resistant metal oxide support material.

[0043] That is, in order to distinguish the invention by the applicant disclosed in European Patent Application No. 19182733.6 by the applicant, in the composite oxidation catalyst according to the present invention, the weight ratio of platinum to palladium in the first catalyst washcoat zone is not 1 or more.

[0044] The claimed product may also be labeled with an indication that the first substrate end should be oriented upstream when adapted to any of the second through fifth inventive aspects described below.

[0045] The characteristic that determines the axial length of the catalytic washcoat zone is the grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) is understood to be the platinum group metal loading at any point along the axial length of the catalytic washcoat zone. Typically, the platinum group metal loading at any point along the axial length of the zone as a whole will vary within + / - 20%, optionally + / - 15%, for example + / - 10%, of the average along the axial length of the zone as a whole. Localized platinum group metal loading can be determined by X-ray fluorescence (XRF) or electron probe microanalysis (EPMA).

[0046] According to a second aspect, the present invention provides an exhaust system for a compression-ignition engine for a vehicle, comprising a composite oxidation catalyst according to the first inventive aspect and a soot filter substrate arranged downstream of the composite oxidation catalyst, with a first substrate end of the oxidation catalyst facing upstream.

[0047] According to a third aspect, the present invention provides a compression-ignition internal combustion engine for heavy-duty diesel vehicles, comprising an exhaust system according to the second inventive aspect, wherein a first substrate end of the composite oxidation catalyst is oriented upstream.

[0048] According to a fourth aspect, the present invention provides a heavy-duty diesel vehicle, i.e., a heavy-duty vehicle according to any relevant regional definition set out in the Background section of this specification above, comprising an exhaust system according to the third inventive aspect. Thus, for example, if this application is being prosecuted in the United States, the definition of a heavy-duty vehicle according to the United States in the Background section of this specification shall apply. Similarly, if this application is being prosecuted in the European Patent Office, the definition of a heavy-duty vehicle for the EU in the Background section of this specification above shall apply.

[0049] According to a fifth aspect, the present invention provides for the use of a composite oxidation catalyst in an exhaust system of a compression ignition engine for a vehicle, by contacting the composite oxidation catalyst with an exhaust gas containing a high concentration of hydrocarbon fuel, so that heat is generated from the high concentration of hydrocarbon fuel in the exhaust gas flowing in the exhaust system under normal operating conditions, thereby heating a soot filter disposed downstream of the composite oxidation catalyst.

[0050] According to a sixth aspect, the present invention provides a composite oxidation catalyst for use in an exhaust system for treating exhaust gas generated by a compression ignition internal combustion engine for a vehicle, optionally, a method for manufacturing the composite oxidation catalyst according to a first aspect of the invention. The composite oxidation catalyst has a total length L and a longitudinal axis, and has a substrate surface extending axially between a first substrate end and a second substrate end. Two or more catalyst washcoat zones are arranged in series axially on and along the substrate surface. The first catalyst washcoat zone has a length L1, where L1 < L. At one end, it is defined by the first substrate end, and at the second end, it is defined by the first end of a second catalyst washcoat zone having a length L2, where L2 < L. The first catalyst washcoat zone includes a first heat-resistant metal oxide support material and two or more platinum group metal components supported thereon, including both platinum and palladium with a weight ratio of platinum to palladium less than 1. The second catalyst washcoat zone includes a second heat-resistant metal oxide support material and one or more platinum group metal components supported thereon. The two or more catalyst washcoat zones include a first catalyst washcoat zone defined by the number of grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) The total platinum group metal loading in the first catalyst washcoat zone is greater than the total platinum group metal loading in the second catalyst washcoat zone. The first catalyst washcoat zone includes one or more first alkaline earth metal components, preferably barium, supported on the first heat-resistant metal oxide support material. This method (a) applying a catalytic washcoat layer to a surface of a substrate a length extending from one end of the substrate, the catalytic washcoat layer comprising a refractory metal oxide support material and one or more platinum group metal components; (b) impregnating the catalytic washcoat layer within a zone of length L1 defined at one end by a first substrate edge with a solution containing one or more platinum group metals; One or more alkaline earth metal components are present in the catalytic washcoat layer of step (a) and / or in the impregnation solution used in step (b). It is understood that the catalytic washcoat layer of step (a) comprises a platinum component, a palladium component, or both platinum and palladium components, and the solution of step (b) comprises platinum, palladium, or both platinum and palladium, so long as the combination of steps (a) and (b) results in a first catalytic washcoat zone having a length L1 with two or more supported platinum group metal components comprising both platinum and palladium, with the platinum to palladium weight ratio being less than 1.

[0051] In a seventh aspect, a composite oxidation catalyst according to the present invention may be defined as a product obtained or obtainable by a method according to the sixth inventive aspect.

[0052] A more particular feature of this embodiment of the present invention is that it can improve the durability of composite oxidation catalysts to withstand phosphorus and / or zinc contamination from engine lubricants, and reduce nitrogen oxides (NO x This allows for improved management of NO oxidation in downstream processes such as the selective catalytic reduction of NO.

[0053] The present invention will now be further described. In the following sections, different aspects of the invention are defined in more detail. Each aspect so defined can be combined with any other aspect or aspects, unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous can be combined with any other feature or features indicated as being preferred or advantageous. [Brief explanation of the drawings]

[0054] [Figure 1] FIG. 1 shows a preferred composite oxidation catalyst (12) according to the present invention, comprising a first catalytic washcoat zone (1) disposed at the intake end (I) of a flow-through honeycomb substrate monolith (5) having an overall length L, and a second catalytic washcoat zone (2) disposed at the discharge end (O) of the substrate (5) adjacent to the first catalytic washcoat zone (1), with the first and second catalytic washcoat zones disposed in series on and along the surface of the substrate. That is, during use, the substrate of the composite oxidation catalyst is oriented such that engine exhaust gases first enter the composite oxidation catalyst through the intake (or upstream) end (I) and exit the composite oxidation catalyst through the discharge (or downstream) end (O), with the exhaust gas flow in the direction indicated by the arrows at reference numeral 10. This same orientation and sequence of contacting the composite oxidation catalyst with the exhaust gas applies to all embodiments disclosed in FIGS. 1-5 and described herein.

[0055] The composite oxide catalyst of FIG. 1 can be produced by coating a substrate (5) along its entire axial length L with a first heat-resistant metal oxide support material and an aqueous solution of one or more platinum group metal salts, drying and firing the coated portion, and then impregnating only a portion of the substrate coated with the first catalyst washcoat layer up to a length L1 (L1 < L) with an aqueous solution of one or more platinum group metals at a relatively high concentration and optionally one or more alkaline earth metal components to form a first catalyst washcoat zone (1). The second catalyst washcoat (2) includes the unimpregnated first catalyst washcoat layer. Alternatively, instead of the alkaline earth metal component present in the impregnation medium, the first catalyst washcoat layer itself may contain one or more alkaline earth metal components. Of course, the alkaline earth metal component may be present in both the impregnation medium and the first catalyst washcoat layer. For an explanation of the "impregnation" technique, see below. This configuration results in a final product in which the portion of the first catalyst washcoat layer having a length L1 contains two or more supported platinum group metal components including both platinum and palladium with a weight ratio of platinum to palladium less than 1.

[0056] Alternatively, the composite oxidation catalyst shown in FIG. 1 may comprise a substrate (5) having, from a first end thereof, a first catalyst washcoat layer having an axial length L1 (see item labeled 9 in FIG. 1 ) for forming a first washcoat catalytic zone and including a first refractory metal oxide support material, two or more platinum group metal components including both platinum and palladium (e.g., platinum and palladium are the only platinum group metal components), and one or more alkaline earth metal components, and a second refractory metal oxide support material and one or more alkaline earth metal components for forming a second oxidation catalytic zone. 1 embodiment, the first catalytic washcoat zone (9) may have an axial length L1 that is the same as or substantially the same as the axial length of the first catalytic washcoat layer (9), and the second catalytic washcoat zone (11) may have an axial length L2 that is the same as or substantially the same as the axial length of the first catalytic washcoat layer (9), and the second catalytic washcoat zone (12) may have an axial length L2 that is the same as or substantially the same as the axial length of the second catalytic washcoat zone (12).

[0057] Each of the embodiments shown in Figures 1 and 2-5 includes a preferred optional feature of a porous washcoat coating layer overlying the first catalytic washcoat zone (1) as a guard bed to reduce or prevent contamination of the first catalytic washcoat zone with phosphorus and / or zinc deposits from lubricity additives such as ZDDP or ZDTP. The optional guard bed feature ("G") is shown in dotted lines in each of the embodiments of Figures 1-5.

[0058] [Figure 2]Shown is a composite oxidation catalyst according to the invention based on the same manufacturing principle (14, 16 respectively), i.e., the second catalyst washcoat layer (7) is applied from the second end of the substrate (corresponding to the discharge end (O)) for an axial length L4 less than the total axial length L of the flow-through honeycomb substrate monolith (5), i.e., L4 < L. The second catalyst washcoat layer comprises a second heat-resistant metal oxide support material, one or more platinum group metal components, and optionally one or more second alkaline earth metal components. The substrate coated with the second catalyst washcoat layer (7) is then itself coated with the first catalyst washcoat layer (6) from the opposite end of the substrate (the suction end, i.e., corresponding to the end (I) of the first substrate) to the location where the coating of the second catalyst washcoat layer on the substrate (5) began. The first catalyst washcoat layer comprises a first heat-resistant metal oxide support material, 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 washcoat layer (6) is shorter than the total axial length L of the substrate, but is long enough to overlap with the length (L4) of the second catalyst washcoat layer (7), forming a region, i.e., a "zone", where the first catalyst washcoat layer (6) and the second catalyst washcoat layer (7) exist in a two-layer structure. The axial length of the overlapping zone of the first washcoat layer and the second washcoat layer can be defined as "L5", shown as "2" in Figure 2, i.e., the second washcoat catalyst zone, and "4" in Figure 3, i.e., the fourth washcoat catalyst zone. [Figure 3]Shows the composite oxidation catalyst according to the invention (14, 16 respectively) based on the same manufacturing principle, i.e., the second catalyst washcoat layer (7) is applied from the second end of the substrate (corresponding to the discharge end (O)) for an axial length L4 less than the total axial length L of the flow-through honeycomb substrate monolith (5), i.e., L4 < L. The second catalyst washcoat layer comprises a second heat-resistant metal oxide support material, 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 washcoat layer (7) is itself coated with the first catalyst washcoat layer (6) from the opposite end of the substrate (the suction end, i.e., corresponding to the end (I) of the first substrate) to the location where the coating of the second catalyst washcoat layer on the substrate (5) started. The first catalyst washcoat layer comprises a first heat-resistant metal oxide support material, 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 washcoat layer (6) is shorter than the total axial length L of the substrate but is long enough to overlap with the length (L4) of the second catalyst washcoat layer (7), forming a region where the first catalyst washcoat layer (6) and the second catalyst washcoat layer (7) exist in a two-layer structure, i.e., a "zone". The axial length of the overlapping zone of the first washcoat layer and the second washcoat layer can be defined as "L5" and is shown as "2" in Figure 2, i.e., the second washcoat catalyst zone, and "4" in Figure 3, i.e., the fourth washcoat catalyst zone.

[0059] The zone of length L5 comprising the overlap of the first catalytic washcoat layer (6) and the second catalytic washcoat layer (7) may be understood to include 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 catalytic washcoat layer (6) and the second catalytic washcoat layer (7) within the overlapping region. It may also be understood that, because the overlap region of the first catalytic washcoat layer (6) and the second catalytic washcoat layer (7) represents its own zone, the zone (labeled 3 in both Figures 2 and 3) comprising a single layer of the second catalytic washcoat layer (7) bounded at its first end (17) by the second (downstream, or discharge, side) end of the overlap region of the first catalytic washcoat layer (6) and the second catalytic washcoat layer (7) and at its second end by the second substrate end (i.e., discharge end (O)) has a lower total platinum group metal loading than the immediately adjacent upstream overlap zone (zone 2 in Figure 2 and zone 4 in Figure 3).

[0060] In the configuration shown in FIG. 2, the overlap zone of the first catalytic washcoat layer (6) and the second catalytic washcoat layer (7) is the second catalytic washcoat zone (labeled 2 in FIG. 2). The first catalytic washcoat zone (labeled 1), which is bounded at its first end by the inlet / first substrate end (I) and at its second end by the first (upstream, i.e., closest to the inlet end) end (19) of the second catalytic washcoat zone (2) (which also corresponds to the first, or upstream, end of the second catalytic washcoat layer (7)), has a higher total platinum group metal loading (g / ft ) than the second catalytic washcoat zone (2). 32 includes the overlap of the first washcoat layer (6) and the second washcoat layer (7). Therefore, it can be understood that the axial length L3 of the first catalytic washcoat layer (6) is equal to the sum of the axial lengths of the first catalytic washcoat zone (1) and the second catalytic washcoat zone (2). Furthermore, the length of the first catalytic washcoat layer (6) present in the first washcoat zone (1) is the total length of the catalytic washcoat layer 6 minus the length of the first washcoat layer present in the overlap zone 2, i.e., L5.

[0061] In practice, in each of the embodiments shown in Figures 2-5, the feature of a greater total platinum group metal loading in the first catalytic washcoat zone (1) than in the second catalytic washcoat zone (2) can be achieved by impregnating the desired length (8) (L1) of the underlying first catalytic washcoat layer (6) with a relatively high concentration of a platinum group metal salt in its aqueous solution, 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 described, for example, in "Catalytic Air Pollution Control - Commercial Technology," 3 rd Edition, Ronald M. Heck et al., John Wiley & Sons, Inc. (2009) at paragraph 2.3. In Figure 2, the axial length L1 of the first catalytic washcoat zone (labeled 1) is essentially the length of the first catalytic washcoat layer (6) up to the point where it begins to overlap the second catalytic washcoat layer (7) at point 19.

[0062] If the washcoat for forming the first catalytic washcoat layer (6) does not include one of platinum and palladium, for example, the impregnation medium should contain a solute salt of palladium or platinum, neither of which is present in the first catalytic washcoat layer (6), and the desired length (8) (L1) of the underlying first catalytic washcoat layer includes two or more supported platinum group metal components comprising both platinum and palladium, with the platinum to palladium weight ratio being less than 1. Of course, the first catalytic washcoat layer itself can comprise platinum, palladium, or both platinum and palladium, in any combination, and separately the impregnation medium can comprise platinum, palladium, or both platinum and palladium; that is, the PGM content of the first catalytic washcoat layer and the impregnation medium can be the same or different, so long as the resulting desired length (8) (L1) of the underlying first catalytic washcoat layer comprises two or more supported platinum group metal components including both platinum and palladium, with the platinum to palladium weight ratio being less than 1.

[0063] If the washcoat for forming the first catalytic washcoat layer (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, both the washcoat for forming the first catalytic washcoat layer (6) and the impregnation medium can contain one or more alkaline earth metals, in which case the alkaline earth metal or metals in the washcoat composition and the impregnation medium, respectively, can be the same or different.

[0064] The third catalytic washcoat zone (labeled 3) is defined at the second (i.e., discharge (O)) end by the second substrate end and has an axial length L6. The first end of the third catalytic washcoat zone (3), i.e., the end closest to the first substrate (i.e., inlet (I)) end, is defined as (17) above.

[0065] From the configuration shown in FIG. 2 and described above, it can be understood that each catalytic washcoat zone can be made up in part from only a portion of the axial length of a catalytic washcoat layer. Thus, the refractory metal oxide of the underlying layer supports the material in the catalytic washcoat zone where the catalytic washcoat layer is partial. As a result, when a catalytic washcoat zone includes an overlap of catalytic washcoat layers, the refractory metal oxide support material in the catalytic washcoat zone formed from the overlap will include a refractory metal oxide support material in each of the catalytic washcoat layers present in the overlap. Thus, when the refractory metal oxide support material in a first catalytic washcoat layer in the overlap zone is different from the refractory metal oxide support material in a second catalytic washcoat layer, there will be two (or more) refractory metal oxide support materials in the overlapping catalytic washcoat zone as a whole. Of course, an individual catalytic washcoat layer can include two or more different refractory metal oxide support materials, in which case a catalytic washcoat zone formed from a single catalytic washcoat 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 catalytic washcoat layers that overlap to form a catalytic washcoat zone on a substrate, then only one refractory metal oxide support material will be present in the overlapping catalytic washcoat zone.

[0066] The configuration shown in FIG. 3 is similar to that shown in FIG. 2 and described above, except that the axial length L1 of the first catalytic washcoat zone (labeled 1) is shorter than the length of a single layer of the first catalytic washcoat layer (6), for example, formed by impregnating a shorter length (8) of substrate (5) coated with the first catalytic washcoat layer (6) with a relatively high concentration of aqueous one or more platinum group metal salts, and optionally also one or more alkaline earth metal salts. In this embodiment, the second catalytic washcoat zone (labeled 2) is defined at its first end, i.e., the end closest to the first substrate end or inlet, by the second end (21) of the extent of impregnation (8) of the first catalytic washcoat zone 1, e.g., the first catalytic washcoat layer (6), and at its second end by the first end (23) of the overlap region of the first catalytic washcoat layer (6) with the underlying second catalytic washcoat layer (7) closest to the inlet end (I). The characteristic of a total platinum group metal loading in the first catalytic washcoat zone being greater than the total platinum group metal loading in the second catalytic washcoat zone is satisfied, for example, by impregnating an underlying first catalytic washcoat layer containing one or more platinum group metal components with a relatively high concentration of one or more platinum group metals. Such impregnation media may also include aqueous salts of one or more alkaline earth metals.

[0067] According to the present definition, the third catalytic washcoat layer (labeled 3) is defined at its second (i.e., outlet (O)) end by the second substrate edge. Thus, in the embodiment shown in FIG. 3, the zone consisting of the overlap of the first catalytic washcoat layer (6) and the second catalytic washcoat layer (7) is axially disposed between the second catalytic washcoat zone (2) and the third catalytic washcoat zone (3), and is numbered as the fourth catalytic washcoat zone, labeled "4" in FIG. 3. From FIG. 3, it can be seen that the axial length of the first washcoat layer (6) is the sum of the axial lengths of the first (1), second (2), and fourth (4) catalytic washcoat zones. It can also be seen that the axial length of Zone 2 is the total axial length L3 of the first catalytic washcoat layer (6) minus the axial lengths of both the overlap zone, i.e., Zone 4, which is equal to L5, and the length L1 of the first catalytic washcoat zone 1. The axial length of Zone 3 is defined at the second (discharge (O), or downstream end) by the second substrate end and has an axial length L6.

[0068] [Figure 4]The configurations shown in Figure 4 (composite oxidation catalysts 18 and 20, respectively) are similar to those shown in Figures 2 and 3, respectively, except that in the embodiments shown in Figures 4 and 5, a first washcoat layer (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 on the upper surface thereof is first coated onto a flow-through honeycomb substrate monolith (5) from the inlet end (I) to a length L3. The substrate coated with the first catalyst washcoat layer (6) is then itself coated with a second catalyst washcoat layer (7) (i.e., to a length where L4<1) from the opposite end (corresponding to the discharge end (O)) of the substrate (5) to the point where coating of the first catalyst washcoat layer (6) onto the substrate (5) began. The axial coating length of the second catalytic washcoat layer (7) is less than the overall axial length L of the substrate, but is long enough to overlap the first catalytic washcoat layer (6), forming an area where the second catalytic washcoat layer (7) and the first catalytic washcoat layer (6) exist in two zones. To avoid repetition, applicants, by analogy, refer the reader to the above discussion for descriptions of axial zone lengths, zone boundary definitions, total zone platinum group metal loadings, descriptions of zone refractory metal oxide support materials, etc. [Figure 5]The configurations shown in Figure 5 (composite oxidation catalysts 18 and 20, respectively) are similar to those shown in Figures 2 and 3, respectively, except that in the embodiments shown in Figures 4 and 5, a first washcoat layer (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 on the upper surface thereof is first coated onto a flow-through honeycomb substrate monolith (5) from the inlet end (I) to a length L3. The substrate coated with the first catalyst washcoat layer (6) is then itself coated with a second catalyst washcoat layer (7) (i.e., to a length where L4<1) from the opposite end (corresponding to the discharge end (O)) of the substrate (5) to the point where coating of the first catalyst washcoat layer (6) onto the substrate (5) began. The axial coating length of the second catalytic washcoat layer (7) is less than the overall axial length L of the substrate, but is long enough to overlap the first catalytic washcoat layer (6), forming an area where the second catalytic washcoat layer (7) and the first catalytic washcoat layer (6) exist in two zones. To avoid repetition, applicants, by analogy, refer the reader to the above discussion for descriptions of axial zone lengths, zone boundary definitions, total zone platinum group metal loadings, descriptions of zone refractory metal oxide support materials, etc.

[0069] [Figure 6] 1 is a schematic representation of a single layer, such as a layer of a first catalytic washcoat zone, having a uniform or homogeneous distribution of a first platinum group metal (e.g., platinum group metal 1, represented by Δ) and a non-uniform (i.e., heterogeneous) distribution of a second platinum group metal (e.g., platinum group metal 2, represented by ○), according to an embodiment of the present invention.

[0070] [Figure 7] FIG. 2 is a schematic diagram illustrating the uniform distribution of two platinum group metals (e.g., platinum group metal 1, represented by Δ, and platinum group metal 2, represented by ○) in an embodiment of a single layer catalyst washcoat zone of the present invention.

[0071] [Figure 8A] 1 shows various system configurations including a composite oxidation catalyst according to a first embodiment of the present invention, for example, any of those disclosed in each of FIGS. 1 to 5. FIG. [Figure 8B] 1 shows various system configurations including a composite oxidation catalyst according to a first embodiment of the present invention, for example, any of those disclosed in each of FIGS. 1 to 5. FIG. [Figure 8C] 1 shows various system configurations including a composite oxidation catalyst according to a first embodiment of the present invention, for example, any of those disclosed in each of FIGS. 1 to 5. FIG. [Figure 8D] 1 shows various system configurations including a composite oxidation catalyst according to a first embodiment of the present invention, for example, any of those disclosed in each of FIGS. 1 to 5. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0072] For the avoidance of doubt, the composite oxidation catalyst described herein is referred to as an "oxidation catalyst" because it is capable of oxidizing pollutants in the exhaust gas during normal lean-burn operation of a compression-ignition engine, producing lean exhaust gas, primarily carbon monoxide and unburned hydrocarbons. The composite oxidation catalyst can also oxidize nitric oxide in the exhaust gas to nitrogen dioxide, promoting downstream catalytic activity such as the CRT® effect and / or promoting selective catalytic reduction reactions, and such NO oxidation activity can be improved by employing one or more features of the dependent claims appended hereto. Because it is preferably used to treat exhaust gas 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 present invention is intended to generate heat from additional hydrocarbons introduced into the exhaust gas, thereby heating and thereby regenerating a downstream particulate filter (i.e., combusting soot collected on its upper surface (active regeneration)).

[0073] Although the activity of a composite oxidation catalyst is not limited to oxidation reactions, the oxidation catalyst must be capable of oxidizing one or more pollutants in the exhaust gas of a compression ignition engine during normal lean-burn operation. For example, assuming appropriate conditions, an oxidation catalyst can oxidize one or more pollutants in the exhaust gas by a reduction reaction, e.g., to nitrogen oxides (NO), using hydrocarbons in the exhaust gas as reducing agents. x ) reduction (so-called lean NO x Catalysis, DeNO x may additionally be used for catalytic or hydrocarbon-SCR) and / or NO x and / or temporary adsorption of hydrocarbons, etc., to temporarily store one or more pollutants from the exhaust. Further, for the avoidance of doubt, use of a composite oxidation catalyst to generate 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 between heat-generating events.

[0074] With respect to NO oxidation activity, preferably, the composite oxidation catalyst as a whole promotes NO oxidation over more than 10%, e.g., more than 20%, more than 30%, more than 40%, or more than 50% of the operating range of the oxidation catalyst during normal use. This is in stark contrast to the oxidation catalysts disclosed in WO 2009 / 076574, in which the diesel oxidation catalyst is effective to produce substantially no additional NO in the exhaust gas stream after passing through the diesel oxidation catalyst over about 90% of the operating range of the diesel oxidation catalyst. The composite oxidation catalyst according to the present invention achieves this by including at least one zone in the oxidation catalyst having a platinum to palladium weight ratio of >1, e.g., >1.5:1 or >2:1, optionally with only platinum when only platinum group metal is present in that particular zone, i.e., a platinum to palladium weight ratio of 1:0 (or "infinite" (∞)). Optionally, for catalytic washcoat zones other than the first catalytic washcoat zone, such other zones may exhibit increased NO oxidation when low alkaline earth metal loading or substantially no alkaline earth metal is present in the zones other than the first catalytic washcoat zone.

[0075] According to the first aspect, the second catalytic washcoat zone may preferably be defined at its second end by a second substrate edge, i.e., the combined oxidation catalyst as a whole comprises two catalytic washcoat zones (see, for example, the configuration shown in FIG. 1).

[0076] A preferred method for producing a catalyst having two catalytic washcoat zones includes a method according to a sixth inventive embodiment, in which in step (a) the catalytic washcoat extends along the entire length L of the substrate. It will be understood that in this method, the first refractory metal oxide support material is the same as the second refractory metal oxide support material. Alternatively, the composite oxidation catalyst shown in FIG. 1 comprises a substrate (5) having, from its first end, a first catalytic washcoat layer, along an axial length L1 (see item labeled 9 in FIG. 1 ), for forming a first washcoat catalytic zone and including 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 second refractory metal oxide support material, one or more second platinum group metal components, for forming a second oxidation catalytic zone. The catalyst may be, or may be obtainable by coating, in either order, a second, different catalytic washcoat layer (see item labeled 11), optionally including one or more second alkaline earth metal components, over an axial length L2 such that the second end (13) of the first catalytic washcoat layer (9) and the first end (15) of the second (11) catalytic washcoat layer abut one another without substantial overlap between the first and second washcoat layers. In the latter method of making the embodiment of FIG. 1 , it will be understood that the axial length L1 of the first catalytic washcoat zone is the same as or substantially the same as the axial length of the first catalytic washcoat layer (9), and the axial length L2 of the second catalytic washcoat zone is the same as or substantially the same as the axial length of the second catalytic washcoat zone L2. Further details of the method of making the two-zone composite oxidation catalyst according to the first inventive aspect are described above in connection with FIG. 1 .

[0077] Alternatively, according to the first aspect, the composite oxidation catalyst may include three or more catalytic washcoat zones, the third catalytic washcoat zone comprising a third refractory metal oxide support material and one or more platinum group metal components supported on an upper surface thereof, the third catalytic washcoat zone being bounded at its second end by a second substrate edge and having a platinum group metal content in grams per cubic foot of substrate volume (g / ft 3 The total platinum group metal loading in the third catalytic washcoat zone, as defined by (Pt / Pt), is less than the total platinum group metal loading in the second catalytic washcoat zone.

[0078] The composite oxidation catalyst according to the first aspect of the present invention may comprise four catalytic washcoat zones, a fourth catalytic washcoat zone disposed between the second catalytic washcoat zone and the third catalytic washcoat zone, the fourth catalytic washcoat zone comprising a fourth refractory metal oxide support material and one or more platinum group metal components supported on an upper surface thereof, the fourth catalytic washcoat zone being bounded at a first end thereof by the second end of the second catalytic washcoat zone and at a second end thereof by the first end of the third catalytic washcoat zone, and having a mass fraction of the fourth catalytic washcoat zone in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 The total platinum group metal loading in the fourth catalytic washcoat zone, as defined by (a) above, is greater than the total platinum group metal loading in each of the second catalytic washcoat zone and the third catalytic washcoat zone.

[0079] Preferably, in the composite oxidation catalyst according to the first aspect of the present invention including four catalyst washcoat zones, the composite oxidation catalyst includes a first catalyst washcoat layer and a second catalyst washcoat layer. The first catalyst washcoat layer includes a heat-resistant metal oxide support material and one or more platinum group metal components supported on the upper surface, has a length L3, where L3 < L at this time, and is defined at one end by the first substrate end. The second catalyst washcoat layer includes a heat-resistant metal oxide support material and one or more platinum group metal components supported on the upper surface, has a length L4, where L4 < L at this time, and is defined at the second end by the second substrate end. The fourth catalyst washcoat zone includes a two-layer overlapping region of the first catalyst washcoat layer and the second catalyst washcoat layer, and the third catalyst washcoat zone includes a single layer of the second catalyst washcoat layer not included in the overlapping region. A method for manufacturing such a composite oxidation catalyst has been described above with reference to the embodiments shown in FIGS. 3 and 5, and further with reference to the embodiments shown in FIGS. 2 and 4 and their related descriptions.

[0080] The composite oxidation catalyst including three catalyst washcoat zones may include a third catalyst washcoat zone defined at its first end by the second end of the second catalyst washcoat zone (for example, refer to the configurations shown in FIGS. 2 and 4).

[0081] Such a composite oxidation catalyst includes a first catalyst washcoat layer and a second catalyst washcoat layer. The first catalyst washcoat layer includes a heat-resistant metal oxide support material and one or more platinum group metal components supported on the upper surface, has a length L3, where L3 < L, and is defined at one end by the first substrate end. The second catalyst washcoat layer includes a heat-resistant metal oxide support material and one or more platinum group metal components supported on the upper surface, has a length L4, where L4 < L, and is defined at the second end by the second substrate end. The second catalyst washcoat zone includes a two-layer overlapping region of the first catalyst washcoat layer and the second catalyst washcoat layer, and the third catalyst washcoat zone may include a single layer of the second catalyst washcoat layer not included in the overlapping region.

[0082] In the above three-zone and four-zone configurations, preferably, one or more platinum group metal components in the third catalyst washcoat zone consist essentially of platinum. In a configuration characterized by the overlap of the first and second catalyst washcoat layers, when one or more platinum group metals in the third catalyst washcoat zone consist essentially of platinum, it will be understood that the second catalyst washcoat layer forming the third catalyst washcoat zone also consists essentially of platinum.

[0083] In a preferred composite oxidation catalyst having two zones described herein, it is further understood that the second catalyst washcoat zone may include one or more alkaline earth metals, such as barium and / or strontium, preferably barium.

[0084] Also, in a composite oxidation catalyst having three zones described herein, it will be understood that the second catalyst washcoat zone, the third catalyst washcoat zone, or both the second catalyst washcoat zone and the third catalyst washcoat zone may each include one or more alkaline earth metals, such as barium and / or strontium, preferably barium.

[0085] It will further be understood that in the four-zone composite oxidation catalyst described herein, the second catalytic washcoat zone, the third catalytic washcoat zone, and / or the fourth catalytic washcoat zone may each comprise one or more alkaline earth metals, such as barium and / or strontium, preferably barium.

[0086] It will further be understood that in the three or four zone composite oxidation catalysts described herein, the first catalytic washcoat layer, the second catalytic washcoat layer, and / or both the first catalytic washcoat layer and the second catalytic washcoat layer may each comprise one or more alkaline earth metals, such as barium and / or strontium, preferably barium.

[0087] Methods for producing a three or four zone composite oxidation catalyst according to the present invention include methods according to a sixth inventive aspect, wherein in step (a) the catalytic washcoat layer is a first catalytic washcoat layer extending from a first substrate edge to less than the entire length of the substrate, and the method further comprises step (a') of applying a second catalytic washcoat layer to the substrate before step (a) or after step (a), but in either case before step (b), with a length extending from a second substrate edge to less than the entire length of the substrate, such that the first catalytic washcoat layer partially overlaps the second catalytic washcoat layer, or the second catalytic washcoat layer partially overlaps the first catalytic washcoat layer, wherein the second catalytic washcoat layer comprises a refractory metal oxide support material and one or more platinum group metal components, and it is understood that the platinum group metal composition of a washcoat catalytic zone comprising two overlapping layers comprises the total platinum group metal present in each of the two overlapping layers of the zone.

[0088] It will be appreciated that when the above method is used to prepare a composite oxidation catalyst according to the present invention having three or more zones, the axial length L1 of the impregnation step can determine the number of catalyst washcoat zones present along the axial substrate length, as will be further explained with reference to Figures 2, 3, 4 and 5 herein.

[0089] If L1 is less than the axial length between the first substrate edge and the first end of the second catalytic washcoat, which represents the end of the overlap region between the first catalytic washcoat layer and the second catalytic washcoat layer closest to the first substrate edge, the second catalytic washcoat zone includes a single layer of the first catalytic washcoat layer, bounded at one end by the second end of the first catalytic washcoat zone L1 and at a second end by the first end of the overlap region of the first catalytic washcoat layer and the second catalytic washcoat layer closest to the first substrate edge. In this case, the fourth catalytic washcoat zone is defined by the first end of the overlap region of the first and second washcoat layers closest to the first substrate edge, and has a platinum group metal loading (g / ft 3 ) is first catalytic washcoat zone > fourth catalytic washcoat zone > second catalytic washcoat zone. The third catalytic washcoat zone is defined at its second end by the substrate edge opposite the substrate edge where the first catalytic washcoat layer begins to extend, and at its first end by the edge of the overlap region between the first catalytic washcoat layer and the second catalytic washcoat layer closest to the edge where the second catalytic washcoat layer begins to extend, i.e., also corresponds to the second end of the fourth catalytic washcoat zone. This configuration is shown in Figures 3 and 5 herein.

[0090] If L1 is equal to the axial length of a single layer of the first catalytic washcoat layer extending from the first substrate end until the first catalytic washcoat layer enters the overlap region of the second catalytic washcoat zone, then the oxidation catalyst as a whole comprises three axially arranged catalytic washcoat zones, which can be numbered sequentially from the first substrate end as first, second, and third catalytic washcoat zones.

[0091] Alternatively, an oxidation catalyst having three or more catalytic washcoat zones according to the present invention can be prepared in accordance with the method for producing an oxidation catalyst having two catalytic washcoat zones according to the sixth aspect of the present invention, as follows: First, a substrate is coated with a first catalytic washcoat layer along its entire length L. Second, a second catalytic washcoat layer containing a refractory metal oxide support material and one or more platinum group metal components can be coated on the top surface of the first catalytic washcoat layer from the first substrate end to an axial length less than the entire substrate length L. Alternatively, the first catalytic washcoat layer can be impregnated with an impregnation solution containing one or more platinum group metal salts and optionally one or more alkaline earth metal salts from the first substrate end to a length less than the entire substrate length L. The second catalytic washcoat layer or the impregnated first catalytic washcoat layer partially forms the center or second portion of the three catalytic washcoat zones axially arranged along the substrate. Third, a third catalytic washcoat layer comprising a refractory metal oxide support material and one or more platinum group metal components, designated as a first catalytic washcoat zone L1, can be coated on top of the second catalytic washcoat layer from the first substrate edge to an axial length shorter than the axial length of the second catalytic washcoat layer or the first impregnation in the second step (or impregnated onto the impregnated first washcoat layer for a zone length L1 corresponding to the first catalytic washcoat zone). The platinum group metal content of the first catalytic washcoat zone L1 includes the combination of the platinum group metal compositions of the underlying first catalytic washcoat layer, the second catalytic washcoat layer or impregnation solution, and the third catalytic washcoat layer or impregnation solution, but this is understood to be limited to the case where the combination of the layers and impregnation solutions as a whole in L1 includes both platinum and palladium in a weight ratio less than 1. One or more alkaline earth metal components may be present in the washcoat or impregnation steps of the first, second, and / or third application steps.

[0092] At least the third step is preferably carried out as an impregnation up to a length L1, which corresponds to step (b) of the sixth aspect of the invention. This is because coating on multiple layers reduces the cross-sectional area of ​​the open frontal area of ​​the substrate that allows gas passage, thereby unnecessarily increasing back pressure in the system. Therefore, a composite oxidation catalyst in which at least one catalyst washcoat zone is formed from the impregnation step of an underlying catalyst washcoat layer, preferably the third step corresponding to the formation of the first catalyst washcoat zone, is preferred.

[0093] In use in the exhaust system of a vehicle compression ignition engine, the first substrate end of the oxidation catalyst according to the first aspect of the present invention, including the first catalytic washcoat zone, is oriented upstream, i.e., nearest the engine, i.e., the first substrate end may be defined as the first, upstream intake substrate end, and the second substrate end may be defined as the second, downstream substrate (or discharge) end.

[0094] Platinum group metal loading Typically, each catalytic washcoat zone of the composite oxidation catalyst according to the present invention, other than the first catalytic washcoat zone, comprises one or more platinum group metal components selected from the group consisting of platinum, palladium, rhodium, iridium, ruthenium, and mixtures or alloys of any two or more thereof, and according to the first aspect of the present invention, comprises both platinum and palladium, with the platinum to palladium weight ratio being less than 1. As can be seen from Examples 1 to 4 below, the Pt:Pd weight ratio in the first catalytic washcoat zone is preferably 3:1 or greater. When a catalytic washcoat zone (other than the first catalytic washcoat zone) comprises only one platinum group metal, it is preferably platinum, i.e., the one or more platinum group metal components consist essentially of or consist of platinum.

[0095] Specifically, the two or more platinum group metal components in the first catalytic washcoat zone and / or first catalytic washcoat layer include both platinum and palladium, with the platinum to palladium weight ratio being less than 1; for example, the two or more platinum group metal components consist essentially of or consist of platinum and palladium. Preferably, the only platinum group metals present in the first catalytic washcoat zone and / or first catalytic washcoat layer are platinum and palladium. As can be seen from Examples 1-4 below, the Pt:Pd weight ratio in the first catalytic washcoat zone is preferably 3:1 or greater. When the first catalytic washcoat layer includes both platinum and palladium, it will be understood that any catalytic washcoat zone including the first catalytic washcoat layer also includes both platinum and palladium.

[0096] More preferably, one or more platinum group metal components in the second catalytic washcoat zone comprise, i.e., intentionally comprise, platinum, such as both platinum and palladium, or platinum can be the only platinum group metal present in the second catalytic washcoat zone, e.g., one or more platinum group metal components of the second catalytic washcoat zone consist of platinum, or the plurality of platinum group metal components of the second catalytic washcoat zone consist of both platinum and palladium. Optionally, the content of platinum in the second catalytic washcoat zone is greater than 1 wt. % of the total metals, including platinum group metals and base metals (e.g., alkaline earth metals), supported on the refractory metal oxide support material in the zone. This feature is intended to distinguish it from the disclosure of WO 2009 / 076574, identified in the Background section above.

[0097] Preferably, when the substrate includes three or more catalytic washcoat zones, the third catalytic washcoat zone or the second catalytic washcoat layer includes, or intentionally includes, platinum, such as both platinum and palladium, or platinum can be the only platinum group metal present in the third catalytic washcoat zone or the second catalytic washcoat layer. Optionally, the platinum content in the third catalytic washcoat zone is greater than 1 wt. % of the total metals, including platinum group metals and base metals (e.g., alkaline earth metals), supported on the refractory metal oxide support material in the zone. This feature is intended to distinguish it from the disclosure of WO 2009 / 076574, identified in the Background section above.

[0098] In a preferred configuration, platinum is the only platinum group metal in the second catalytic washcoat layer, i.e., the one or more platinum group metal components in the second catalytic washcoat layer consist of platinum (Pt:Pd weight ratio 1:0). As shown in Figures 4 and 5, this feature provides more stable NO production for downstream catalytic operation, particularly in configurations where the second catalytic washcoat layer overlaps the first catalytic washcoat layer. Therefore, for stable NO production, a configuration where the one or more platinum group metal components in the second catalytic washcoat layer consist of platinum is preferred, when the second catalytic washcoat layer overlaps the first catalytic washcoat layer. In a preferred configuration where platinum is the only platinum group metal present in the third catalytic washcoat zone or second catalytic washcoat layer, i.e., the Pt:Pd weight ratio is 1:0, the third catalytic washcoat zone or second catalytic washcoat layer contains manganese (see below).

[0099] Preferably, the second catalytic washcoat zone comprises both platinum and palladium, for example, the two or more platinum group metal components in the second catalytic washcoat zone consist of platinum and palladium, as this feature improves hydrocarbon slip control.

[0100] Thus, generally, and to distinguish from the disclosure of WO 2009 / 076574 identified in the Background section of this specification above, any catalytic washcoat zone defined by and at the second (discharge) end of the substrate intentionally comprises platinum, and optionally the content of platinum in the catalytic washcoat zone exceeds 1 wt. % of the total metals, including platinum group metals and base metals (e.g., alkaline earth metals), supported on the refractory metal oxide support material in the zone.

[0101] Typically, the total platinum group metal loading on the substrate for heavy-duty diesel engine exhaust system applications is between 5 and 60 g / ft overall (calculated as elemental metal). 3 , preferably 8 to 50 g / ft 3 is.

[0102] The platinum group metal loading (calculated as elemental metal) of the first catalytic washcoat zone is preferably 100 g / ft 3 Less than 25-75g / ft 3 , most preferably 35 to 65 g / ft 3 It will be understood that the first catalytic washcoat zone may comprise an "underlying" platinum group metal loading within a first catalytic washcoat layer, typically a single first catalytic washcoat layer, which is then impregnated with a concentrated solution of a platinum group metal salt before being dried and calcined. As a result, the first catalytic washcoat zone is a combination of the platinum group metal loadings from both the first catalytic washcoat layer and the impregnation solution.

[0103] The overall platinum group metal loading in the second and subsequent catalytic washcoat zones, i.e., the total platinum group metal (calculated as elemental metal) in the catalytic washcoat zones other than the first catalytic washcoat zone, may depend on the embodiment used. Thus, for example, in an embodiment including only two total zones, such as that shown in FIG. 1, the total platinum group metal loading in the second catalytic washcoat zone is preferably 1 to 10 g / ft. 3 is.

[0104] However, in embodiments including three catalytic washcoat zones, where the second catalytic washcoat zone comprises an overlapping region of the first and second catalytic washcoat layers (see, e.g., the embodiments of Figures 2 and 4), or four catalytic washcoat zones, where the fourth catalytic washcoat zone comprises an overlapping region of the first and second catalytic washcoat layers (see, e.g., the embodiments of Figures 3 and 5), the total platinum group metal loading in the second (or fourth) catalytic washcoat zone is between 10 and 40 g / ft 3 , preferably 15 to 35 g / ft 3 It could be.

[0105] In embodiments including three or four catalytic washcoat zones, such as those shown in any one of Figures 2-5, the total platinum group metal loading in the third catalytic washcoat zone is between 1 and 30 g / ft 3 , preferably 5 to 20 g / ft 3 It could be.

[0106] In embodiments including four catalytic washcoat zones, such as those shown in FIG. 3 or FIG. 5, the total platinum group metal loading in the second catalytic washcoat zone is from 1 to 30 g / ft 3 , preferably 5 to 20 g / ft 3 However, the total washcoat amount in the second catalytic washcoat zone is always greater than that in the third catalytic washcoat zone.

[0107] The one or more platinum group metal components and / or one or more alkaline earth metal components supported on the refractory metal oxide support material can be pre-immobilized on the refractory metal oxide support material prior to forming a washcoat layer therewith, and thus are present throughout any washcoat layer coated with such a washcoat coating. However, in a preferred method, the solute salts of the one or more platinum group metal components, and optionally the solute salts of the one or more first alkaline earth metal components, are present in, for example, an aqueous washcoat slurry that also contains a "fresh" refractory metal oxide material, and are applied to the substrate, and the one or more platinum group metal components and the one or more first alkaline earth metal components are immobilized on the refractory metal oxide support material through a drying and calcination process after coating the washcoat slurry on the substrate. By "fresh refractory metal oxide material," it is meant that the platinum group metal components and / or alkaline earth metal components are not pre-immobilized on the refractory metal oxide component. This method is preferred because it is less energy consuming, i.e., it avoids the two-step process of first preparing a supported, pre-immobilized refractory metal oxide product and then using this pre-immobilized product to prepare a washcoat slurry for coating. Furthermore, the inventors have discovered that it can be advantageous for exotherm generation for at least the first catalytic washcoat layer to have a non-uniform 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 surface of the substrate represents the thickness of the catalytic layer). This advantageous feature cannot be utilized to achieve, or to the same extent as, the desired effect of pre-immobilizing the platinum group metal or alkaline earth metal on a refractory metal oxide support material.

[0108] For a description of this aspect of Applicants' invention, see below.

[0109] According to a sixth aspect of the invention, also described below, the first catalytic washcoat zone comprises, in part: (a) applying a catalytic washcoat layer to a surface of a substrate a length extending from one end of the substrate, the catalytic washcoat layer comprising a refractory metal oxide support material and one or more platinum group metal components; (b) impregnating the catalytic washcoat layer within a zone of length L1 defined at one end by the first substrate edge with a solution containing one or more platinum group metals.

[0110] It will thus be understood that a catalytic washcoat layer, e.g., a first catalytic washcoat layer 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, and the platinum group metal composition of the resulting zone is a combination of the underlying catalytic washcoat layer and the impregnation solution. Thus, for example, the platinum to palladium mass (i.e., weight) ratio in the first catalytic washcoat zone as a whole is derived from the sum of the platinum and palladium from both the catalytic washcoat layer, i.e., the first catalytic washcoat layer, and the impregnation solution.

[0111] It will be further understood that according to a sixth aspect of the invention, in step (a), the catalytic washcoat layer is a first catalytic washcoat layer extending from a first substrate end to less than the entire length of the substrate, and the method further comprises step (a') prior to step (a) but before step (b) of applying a second catalytic washcoat layer to the substrate over a length extending from a second substrate end to less than the entire length of the substrate, in either case so that the first catalytic washcoat layer partially overlaps the second catalytic washcoat layer, or so that the second catalytic washcoat layer partially overlaps the first catalytic washcoat layer, wherein the second catalytic washcoat layer comprises a refractory metal oxide support material and one or more platinum group metal components.

[0112] As described above with respect to Figures 4 and 5, preferably, the first catalytic washcoat layer extends from the first substrate end and the second catalytic washcoat layer extends from the second substrate end, whereby the second catalytic washcoat layer partially overlaps the first catalytic washcoat layer.

[0113] In accordance with the present invention, the first catalytic washcoat zone comprises both platinum (Pt) and palladium (Pd) with a weight ratio of platinum (Pt) to palladium (Pd) of less than 1. This feature is preferred because, when combined with an alkaline earth metal component, it has been found to improve (lower) the light-off temperature of the exotherm, allowing for increased exotherm production from lower exhaust gas temperatures in active and active passive regeneration systems.

[0114] Preferably, particularly in embodiments including three or more catalytic washcoat zones, the one or more platinum group metals in the second catalytic washcoat zone include both platinum and palladium. In a particularly preferred aspect, the weight ratio of platinum to palladium in the second catalytic washcoat zone is greater than the weight ratio of platinum to palladium in the first catalytic washcoat zone. When combined with the platinum group metal loading of the second catalytic washcoat zone, the benefit of this Pt:Pd weight ratio in the second catalytic washcoat zone is that the catalyst improves hydrocarbon slip control, CO oxidation, and NO oxidation.

[0115] In this regard, for example, in a preferred two-zone embodiment as shown in Figure 1, allowing for any overlap due to manufacturing methods (see the "Definitions" section below), the second catalytic washcoat zone preferably comprises a Pt-rich PGM composition, preferably containing palladium in a weight ratio of 10:1 or greater, 5:1 or greater, 3:1 or greater, or 2:1 or greater. When combined with a first catalytic washcoat zone containing Pt:Pd less than 1:1, this feature has been found to be advantageous since a second catalytic washcoat zone containing only Pt (i.e., a Pt:Pd weight ratio of 1:0) has been found to be detrimental to exothermic light-off and HC slip of aged catalysts. In this regard, the presence of Pd in ​​addition to Pt in the second catalytic washcoat zone can improve the aging stability of the second catalytic washcoat zone, i.e., maintain oxidation activity during aging. However, in combination with manganese, a Pt:Pd weight ratio of 1:0 in the second catalytic washcoat zone was found to be beneficial for NO oxidation (see Example 12 and below).

[0116] In a combined oxidation catalyst according to the invention comprising three catalytic washcoat zones, the platinum to palladium mass ratio preferably increases from the first catalytic washcoat zone to the second catalytic washcoat zone to the third catalytic washcoat zone. This can be done, for example, in the embodiment shown in Figures 2 and 4, where the second catalytic washcoat layer (7) has a higher Pt:Pd mass ratio than the first catalytic washcoat layer, preferably a mass ratio of 1:0, i.e., only Pt and substantially no Pd, so that the single layer of the second catalytic washcoat layer in the third catalytic washcoat zone (3) has the highest Pt:Pd ratio of any of the catalytic washcoat zones disposed on the substrate. However, the same comments as those made in connection with a combined oxidation catalyst comprising only two catalytic washcoat zones apply. That is, by including some palladium, for example ≧10:1, ≧5:1, ≧3:1 or ≧2:1, the stability of the third catalytic washcoat zone over time can be improved while still maintaining the preferred arrangement of increasing platinum to palladium mass ratios from the first catalytic washcoat zone to the second catalytic washcoat zone to the third catalytic washcoat zone. In the context of three-zone composite oxidation catalysts, the benefit of also including manganese in the third catalytic washcoat zone (3) is also noted (see Example 12 and below).

[0117] Furthermore, in a combined oxidation catalyst having four catalytic washcoat zones, after the first catalytic washcoat zone, the mass ratio of platinum to palladium in each successive catalytic washcoat zone at the inlet end arranged in series along the substrate length L is greater than that of the immediately preceding catalytic washcoat zone. This can be achieved, for example, in the embodiments shown in Figures 3 and 5, in which the second catalytic washcoat layer (7) has a greater Pt:Pd mass ratio than the first catalytic washcoat layer, preferably a mass ratio of 1:0, i.e., only Pt and substantially no Pd, so that the single layer of the second catalytic washcoat layer in the third catalytic washcoat zone (3) has the highest Pt:Pd ratio of any of the catalytic washcoat zones. However, the same comments as those made in connection with a combined oxidation catalyst including only two catalytic washcoat zones apply. That is, by including some palladium, for example ≧10:1, ≧5:1, ≧3:1 or ≧2:1, the stability of the third catalytic washcoat zone over time can be improved while still maintaining the preferred arrangement of increasing platinum to palladium mass ratios from the first catalytic washcoat zone to the second catalytic washcoat zone to the third catalytic washcoat zone. In the context of four-zone composite oxidation catalysts, the benefit of also including manganese in the third catalytic washcoat zone (3) is also noted (see Example 8 and below).

[0118] In the context of a four-zone composite oxidation catalyst according to the present invention, it should be understood that the feature "in each successive catalytic washcoat zone arranged in series along the substrate length L after the first catalytic washcoat zone at the intake end, the catalytic washcoat zone is greater than the immediately preceding catalytic washcoat zone" refers to a different order of numbering of the catalytic washcoat zones than in Figures 3 and 5. That is, in Figures 3 and 5, the order of numbering of the washcoat catalytic zones from the first catalytic washcoat zone (1) is 1 → 2 → 4 → 3. This is because the third catalytic washcoat zone (3) is defined at the second end by the second substrate end (or discharge end). However, the feature "in each successive catalytic washcoat zone arranged in series along the substrate length L after the first catalytic washcoat zone at the intake end, the Pt:Pd mass ratio is greater than that of the immediately preceding catalytic washcoat zone" requires, for example, that the Pt:Pd mass ratio of the fourth catalytic washcoat zone be greater than that of the immediately preceding second catalytic washcoat zone (2), and that the Pt:Pd mass ratio of the third catalytic washcoat zone (3) be greater than that of the immediately preceding fourth catalytic washcoat zone (4).

[0119] Preferably, the one or more platinum group metals in the second catalytic washcoat zone include both platinum and palladium, and the mass ratio of platinum to palladium is >1:1, preferably 10:1 > 3:2, for example 5:1 > 3:2.

[0120] Typically, the first catalytic washcoat zone or first catalytic washcoat layer does not contain rhodium.

[0121] It may be preferred that the second catalytic washcoat zone or second catalytic washcoat layer be rhodium-free.

[0122] The third or fourth catalytic washcoat zone may be free of rhodium.

[0123] It may be further preferred that the composite oxidation catalyst according to the present invention is substantially free of rhodium.

[0124] The inventors have also found that there can be improved heat generation advantages when a non-uniform distribution of the one or more platinum group metal components and / or the one or more first alkaline earth metal components is present in a direction perpendicular to the surface of the substrate, as will be explained in more detail under the following headings.

[0125] alkaline earth metal components The purpose of the alkaline earth metal in the composite oxidation catalyst of the present invention is to x NO for subsequent release and reduction by catalytic processes x It will be understood that this is because the lean NOx is not stored in the electrolyte. This may also include alkaline earth metals, platinum group metals, and optionally ceria, doped ceria, or ceria mixed oxide components. x The purpose of this is a specially designed catalytic converter called a Lean-Nutrition-Trapping (LNT), which must be used in conjunction with a specially programmed engine control unit that operates in a lean, stoichiometric operating mode while trapping NO x is absorbed in the LNT, and in the operating mode, a pulse of rich exhaust gas containing additional reducing species such as CO and / or hydrocarbons contacts the LNT, thereby reducing the absorbed NO x Desorbing and oxidizing lean NO on platinum group metals x The reduction occurs via a catalytic reaction. In LNT operation, the lean / rich cycle is approximately 60 seconds lean, followed by 5 seconds rich. Desulfation in LNTs occurs less frequently, but the periods of richness can be longer. However, controlling the desulfation event also requires a specially programmed engine control unit.

[0126] The composite oxidation catalyst of the present invention can be distinguished from LNT for at least two significant reasons. First, LNT is not used to treat exhaust gas from heavy-duty diesel engines, which instead use SCR catalysts. This is primarily because LNT catalysts for heavy-duty diesel vehicles would require such large quantities that the cost of the required platinum group metals would make the catalyst prohibitive. 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.

[0127] According to a first inventive aspect, the first catalytic washcoat zone comprises one or more first alkaline earth metal components supported on a first refractory metal oxide support material. The present inventors have determined that, for purposes of generating heat from a hydrocarbon fuel, the presence of the alkaline earth metal component, preferably comprising barium, is sufficient to maintain the amount of one or more platinum group metals in the first catalytic washcoat zone at about 7 g / ft. 3 It has been found that the relatively high platinum group metal loading in the first catalyst washcoat zone rapidly initiates and promotes the exothermic reaction, while the presence of one or more alkaline earth metals stabilizes the PGMs, for example, by reducing sintering and improving thermal durability.

[0128] The one or more alkaline earth metal components in the first catalytic 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 catalytic washcoat zone comprise barium.

[0129] The reason for the preference of barium over other alkaline earth metals is explained below under the heading "Non-uniform distribution of alkaline earth metal and / or platinum group metal components in the washcoat layer."

[0130] Calculated as elemental metal, the total alkaline earth metal component loading in the first catalyst washcoat zone is between 10 and 100 g / ft 3, preferably 20 to 80 g / ft 3 An excessively large amount of alkaline earth metal components may be detrimental to heat generation. In this regard, the ratio of the total mass of alkaline earth metal components to the total mass of platinum group metal (PGM) components may be 1:1 to 1:2, preferably 1:1 to 50:80.

[0131] According to the method of the sixth inventive aspect, one or more first alkaline earth metal components can be present in the catalytic washcoat layer applied in step (a) and / or in the impregnation solution of step (b), but are preferably present in the catalytic washcoat layer of step (a) of the sixth inventive aspect, e.g., the first catalytic washcoat layer. This is because when an alkaline earth metal salt, e.g., a barium salt, is present in the impregnation medium of step (b), it can be more difficult to control using the preferred pH range for the platinum group metal salt in the impregnation medium, and therefore, many migrate by wicking away from the targeted first catalytic washcoat zone. This alternative is preferred because the alkaline earth metal component is present in the washcoat, which allows for more control over the final location of the alkaline earth metal in the final product, which is then dried and calcined after coating.

[0132] It will be appreciated that when a catalytic washcoat layer comprising one or more alkaline earth metals, e.g., a first catalytic washcoat layer, is applied in step (a) of the sixth invention embodiment, and the catalytic washcoat layer is impregnated with a solution in step (b) of the sixth invention embodiment that itself comprises one or more alkaline earth metal components, the composition of the resulting impregnated zone will be a combination of the content of the alkaline earth metal components in the underlying catalytic washcoat layer and the impregnation solution.

[0133] The second catalytic washcoat zone may also contain 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 catalytic washcoat layer of the sixth inventive aspect of step (a), e.g., the first catalytic washcoat layer, or, if the composite oxidation catalyst includes a third or fourth catalytic washcoat zone, the second catalytic washcoat layer. The one or more alkaline earth metal components present in the second catalytic washcoat layer may be referred to herein as one or more second alkaline earth metal components. The third and fourth catalytic washcoat layers may also contain one or more second alkaline earth metal components, preferably barium.

[0134] The inventors have also found that there can be an advantage of improved exotherm production from at least the first catalytic washcoat zone when a non-uniform distribution of the one or more platinum group metal components and / or the one or more first alkaline earth metal components is present in a direction perpendicular to the surface of the substrate, as will be described in more detail under the following headings.

[0135] Heat resistant metal oxide support material The first, second, third, or fourth refractory metal oxide support material, or the refractory metal oxide support material of the first and / or second catalytic washcoat layers, respectively, is generally selected from the group consisting of 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 can be used as the first refractory metal oxide support material. The support materials of the first, second, third, or fourth refractory metal oxide support material, or the refractory metal oxide support materials of the first or second catalytic washcoat layers, respectively, can be the same as or different from each other. However, it will be understood that if the composite oxidation catalyst shown in FIG. 1 can be a single washcoat layer of length L impregnated at a first end to an axial length L1 to define a first catalytic washcoat zone (1) and a second catalytic washcoat zone (2), the refractory metal oxide support material in the first and second catalytic washcoat zones is the same.

[0136] Furthermore, in the embodiments including three and four catalytic washcoat zones shown in Figures 2-5, if the refractory metal oxide support material used in the first catalytic washcoat (6) is "X," then the first, second, and (if present) fourth catalytic washcoat zones each include the refractory metal oxide support material "X," i.e., the first, second, and (if present) fourth refractory metal oxide support materials are the same, because the first, second, and (if present) fourth catalytic washcoat zones include only a portion of the total length L3 of the first catalytic washcoat layer (6). Similarly, when the second catalytic washcoat layer (7) in the embodiment shown in Figures 2-5 comprises the refractory metal oxide support material "Y", the third catalytic washcoat zone, and if present, the second or fourth catalytic washcoat zones including the overlapping region, comprise only a portion of the total length L4 of the second catalytic washcoat layer (7), so that each of these zones comprises the refractory metal oxide support material "Y".

[0137] Preferably, the refractory metal oxide support material is selected from the group consisting of alumina, silica, zirconia, ceria, and composite oxides or mixed oxides of two or more thereof, most preferably selected from the group consisting of alumina, silica, and zirconia, and composite oxides or mixed oxides of two or more thereof. The mixed oxides or composite oxides include silica-alumina and ceria-zirconia, most preferably silica-alumina. Preferably, the refractory metal oxide support material does not include ceria or mixed oxides or composite oxides containing ceria. More preferably, the refractory oxide is selected from the group consisting of alumina, silica, and silica-alumina. The refractory oxide may be alumina. The refractory oxide may be silica. The refractory oxide may be silica-alumina.

[0138] Because the first catalytic washcoat zone comprises one or more first alkaline earth metal components supported on a first refractory metal oxide support material, preferably the first catalytic washcoat zone or underlying catalytic washcoat, e.g., the first refractory metal oxide support material of the first catalytic washcoat, comprises or consists essentially of alumina doped with a heteroatom component. The heteroatom component typically comprises silicon, manganese (see below), magnesium, barium, lanthanum, cerium, titanium, or zirconium, or a combination of two or more thereof. The heteroatom component may comprise, consist essentially of, or consist of silicon oxide, manganese oxide, magnesium oxide, barium oxide, lanthanum oxide, cerium oxide, titanium oxide, or zirconium oxide. More preferably, the heteroatom component-doped alumina is silica-doped alumina, magnesium oxide-doped alumina, or manganese oxide-doped alumina. Even more preferably, the heteroatom-doped alumina is silica-doped alumina. Heteroatom-doped alumina can be prepared using methods known in the art or by the methods described, for example, in U.S. Pat. No. 5,045,519.

[0139] 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 the group consisting of zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd), barium (Ba), and their oxides. In general, the dopant is different from the refractory metal oxide (i.e., the cation of the refractory metal oxide). Thus, for example, if the refractory metal oxide is titania, the dopant is not titanium or its oxide.

[0140] When the refractory metal oxide support material is doped with a dopant, the refractory metal oxide support material typically comprises a total amount of dopant of 0.1 to 10 wt. %. Preferably, the total amount of dopant is 0.25 to 7 wt. %, more preferably 2.5 to 6.0 wt. Preferably, the dopant is silica, since 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.

[0141] When the refractory metal oxide support material is silica-alumina, the refractory oxide typically consists essentially of 20-95 wt. % alumina and 5-80 wt. % silica (e.g., 50-95 wt. % alumina and 5-50 wt. % silica), preferably 35-80 wt. % alumina and 20-65 wt. % silica (e.g., 55-80 wt. % alumina and 20-45 wt. % silica), and even more preferably 45-75 wt. % alumina and 25-55 wt. % silica. Silica-aluminas with higher silica contents, for example, about 30 wt. %, can provide higher sulfur tolerance to the overall composite oxidation catalyst.

[0142] When the heat-resistant oxide is ceria-zirconia, the heat-resistant oxide typically 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), and even more preferably 45 to 75 wt. % ceria and 25 to 55 wt. % zirconia.

[0143] Typically, the first and second catalytic washcoat layers are 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 , and even more preferably 0.5 to 2.0 g in -3 , and even more preferably 0.6 to 1.75 g in -3 (e.g. 0.75-1.5g in -3 ) an amount of the first refractory metal oxide support material.

[0144] Generally, the refractory metal oxide support material used in the present invention is in particulate form. The first support material has a D of ≦50 μm, preferably ≦30 μm, and more preferably ≦20 μm. 90 The refractory metal oxide support material may have a particle size (determined by conventional laser diffraction methods). The particle size distribution of the refractory metal oxide support material is selected to aid adhesion to the substrate. The particles are generally obtained by milling.

[0145] Additionally, each support material in each of the first, second, third, or fourth refractory metal oxide support materials and / or the refractory metal oxide support materials of the first or second catalytic washcoats may or may not include, or may or may not 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. When present, preferably the hydrocarbon adsorbent is a zeolite, most preferably an aluminosilicate zeolite.

[0146] When the support material includes a hydrocarbon adsorbent, typically the total amount of hydrocarbon adsorbent is between 0.05 and 3.00 g in -3 , especially 0.10 to 2.00 g in -3 (e.g., 0.2 to 0.8 g in -3 )

[0147] When the hydrocarbon adsorbent is a zeolite, preferably each zeolite is a medium pore zeolite (e.g., a zeolite having a ring size of up to 10 tetrahedral atoms) or a large pore zeolite (e.g., a zeolite having a ring size of up to 12 tetrahedral atoms).

[0148] Examples of suitable zeolites or types of zeolites include faujasite (FAU), clinoptilolite, mordenite, silicalite (MFI), ferrierite, X zeolite (FAU), Y zeolite (FAU), ultrastable Y zeolite (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. When present, the zeolite is preferably ZSM-5 (medium pore zeolite), beta zeolite (large pore zeolite), or Y zeolite (large pore zeolite). When present, Y or beta zeolite is preferred, with beta zeolite being most preferred.

[0149] However, in accordance with the present invention, it is preferred that the oxidation catalyst (without any phosphorus and / or zinc guard bed layers, see below for a description of this feature) be completely free of hydrocarbon adsorbents, particularly zeolites, since zeolites can be hydrothermally decomposed during an exothermic event, making their inclusion undesirable. There is also little need to include hydrocarbon adsorbents in oxidation catalysts for heavy-duty vehicles, since the exhaust gas temperatures emitted from heavy-duty diesel engines rarely fluctuate during use below temperatures at which hydrocarbon adsorption is desirable to improve overall cycle hydrocarbon conversion.

[0150] Catalyst washcoat zone length In embodiments including only two catalytic washcoat zones, such as that shown in FIG. 1, the length of the first catalytic washcoat zone may be less than 50%, preferably 20-40%, of the total substrate length.

[0151] However, in embodiments including three or four catalyst washcoat zones, for example, those shown in any one of Figures 2-5, the length of the first washcoat zone can be 15-35% of the total substrate length (L).

[0152] In embodiments including three or four catalytic washcoat zones, such as those shown in any one of Figures 2-5, the length of the overlap region of the first catalytic washcoat layer (6) and the second catalytic washcoat layer (7), i.e., the length of the second catalytic washcoat zone in Figures 2 and 4, or the length of the fourth catalytic washcoat zone in Figures 3 and 5, can be 10-40%, preferably 10-30%, of the total substrate length (L).

[0153] In embodiments including three or four catalytic washcoat zones, such as those shown in any one of Figures 2-5, the length of the third catalytic washcoat zone can be 10-40% of the total substrate length (L), more preferably 15-35%, such as 20-30% of the total substrate length (L).

[0154] In embodiments including four catalytic washcoat zones, such as those shown in Figures 3 and 5, the second catalytic washcoat zone in Figures 3 and 5 can be 1 to 40%, preferably 5 to 30%, of the total substrate length (L).

[0155] In a particularly preferred embodiment, the inlet catalyst washcoat layer 6 is first coated onto the substrate to a length of about 80% of L, and then the outlet catalyst washcoat layer 7 is coated onto the substrate to a length of about 50% of L, i.e., the catalyst washcoat layers 6 overlap by 30% of L. The length of the first washcoat zone can be 15-35% of the total substrate length (L).

[0156] Because the length of the substrate can vary, it is more useful to refer to the lengths of the first, second, and, if present, third and fourth catalytic washcoat zones as axial lengths relative to the total axial substrate length, i.e., as percentages or proportions. Generally, substrates having application in the present invention are 3 to 6 inches in length, more typically 4 to 6 inches in length. Thus, it is possible to refer to the length of a washcoat layer or the length of a washcoat zone by referring to the percentage of the zone length times the total substrate length (L).

[0157] Non-uniform distribution of alkaline earth metal and / or platinum group metal components in the washcoat layer This embodiment is illustrated in Figures 6 and 7 and is briefly described in the Brief Description of the Figures herein.

[0158] In a first invention aspect, the first catalytic washcoat zone can have 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 surface of the substrate as determined by electron probe microanalysis (EPMA), wherein the concentrations of the one or more platinum group metal components and / or the first alkaline earth metal components decrease in a direction perpendicular to the surface of the substrate as determined by EPMA.

[0159] It has been discovered 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, and therefore the benefits associated with layering to achieve a non-uniform vertical distribution of these components through the layers of catalyst can be obtained by using a single layer or fewer layers.

[0160] In the composite oxidation catalyst of the present invention, the first catalytic washcoat zone may have 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 surface of the substrate, optionally in a single layer, e.g., a catalytic washcoat layer such as the first catalytic washcoat layer (i.e., the catalytic layer does not include multiple layers).

[0161] Preferably, the catalytic washcoat layer has a non-uniform distribution of one or more platinum group metal components and / or one or more alkaline earth metal components, most preferably both one or more platinum group metal components and one or more alkaline earth metal components, throughout its thickness (i.e., the direction perpendicular to the surface of the substrate represents the thickness of the catalytic layer).

[0162] Typically, the catalytic washcoat layer has a first surface and a second surface. Generally, the first surface is parallel (e.g., substantially parallel) to the second surface (i.e., the plane containing the first surface is parallel to the plane containing the second surface). The first surface and the second surface are typically parallel to the surface of the substrate. Thus, a direction normal to the surface of the substrate is also normal to the first surface and / or the second surface.

[0163] The vertical distance between the first surface and the second surface is generally the thickness of the catalytic washcoat layer.

[0164] The first surface may be the 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 generally the upper side (i.e., the top surface) of the catalyst layer. By exposed, we mean that the first surface is not completely or substantially covered by another material, and that exhaust gases passing through the catalyst typically contact the first surface before the second surface.

[0165] The second surface is not an exposed surface of the catalytic washcoat layer. Generally, the second surface is in direct contact with the surface of the substrate and / or the surface of another layer. Thus, the second surface is generally below (i.e., the bottom or lowermost surface of) the catalytic washcoat layer.

[0166] Preferably, the amount of the one or more platinum group metal components and / or 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 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 one or more first alkaline earth metal components may decrease continuously or discontinuously, preferably continuously, in a vertical direction toward the surface of the substrate. Thus, for example, if the first catalytic washcoat zone includes a single layer that is a catalytic washcoat layer, the amount of the one or more platinum group metal components and / or one or more first alkaline earth metal components decreases from the exposed surface of the catalytic washcoat layer toward the surface of the substrate.

[0167] The catalytic washcoat layer may have a linear or non-linear decrease in the amount of one or more platinum group metal components and / or one or more first alkaline earth metal components in a direction perpendicular to the surface of the substrate (i.e., a linear or non-linear decrease in the amount of the first platinum group metal in a direction perpendicular to the first surface to the second surface).

[0168] Typically, at least 60% of the total amount of the one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., of the catalytic washcoat layer) can be distributed between the first surface and a midpoint or midplane in the catalytic washcoat layer between the first and second surfaces (e.g., 50% of the perpendicular distance between the first and second surfaces). The plane is typically parallel to the first surface. Reference to "midpoint" in this context generally refers to the average midpoint distance between the first and second surfaces. Preferably, at least 70%, more preferably at least 75%, e.g., at least 80%, and even more preferably at least 90% of the total amount of the one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., of the catalytic washcoat layer) can be distributed between the first surface and a midpoint or midplane in the catalytic washcoat layer between the first and second surfaces.

[0169] Generally, at least 60% of the total amount of the one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., of the catalytic washcoat layer) can be distributed between the first surface and a point or plane in the catalytic washcoat layer that is 25% of the perpendicular distance from the first surface to the second surface. The plane is typically parallel to the first surface. Preferably, at least 70%, more preferably at least 75%, e.g., at least 80%, and even more preferably at least 90% of the total amount of the one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., of the catalytic washcoat layer) can be distributed between the first surface and a point or plane in the catalytic washcoat layer that is 25% of the perpendicular distance from the first surface to the second surface.

[0170] At least 60% of the total amount of the one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., of the catalytic washcoat layer) can be distributed between the first surface and a point or plane in the catalytic washcoat layer that is 10% of the perpendicular distance from the first surface to the second surface. The plane is typically parallel to the first surface. Preferably, at least 70%, more preferably at least 75%, e.g., at least 80%, and even more preferably at least 90% of the total amount of the one or more platinum group metal components and / or one or more first alkaline earth metal components (e.g., of the catalytic washcoat layer) can be distributed between the first surface and a point or plane in the catalytic washcoat layer that is 10% of the perpendicular distance from the first surface to the second surface.

[0171] The non-uniform distribution of the first platinum group metal in a direction perpendicular to the surface of the substrate may generally be a stepwise 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 a direction perpendicular to the surface of the substrate may be a stepwise distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components.

[0172] The catalytic washcoat layer can have a uniform or non-uniform horizontal distribution of the one or more platinum group metal components and / or the one or more first alkaline earth metal components.

[0173] Typically, the distribution of the one or more platinum group metal components and / or the one or more first alkaline earth metal components parallel to the surface of the substrate (i.e., the longitudinal plane) and perpendicular to the central longitudinal axis of the substrate (i.e., parallel to the inlet end and / or outlet end faces of the substrate) may be uniform or non-uniform. Preferably, the distribution of the first platinum group metal is uniform parallel to the surface of the substrate and perpendicular to the central longitudinal axis of the substrate.

[0174] Generally, the distribution of the one or more platinum group metal components and / or the one or more first alkaline earth metal components parallel to the surface of the substrate (i.e., the longitudinal plane) and parallel to the central longitudinal axis of the substrate (i.e., perpendicular to the inlet end and / or outlet end faces 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 parallel to the surface of the substrate and parallel to the central longitudinal axis of the substrate is uniform.

[0175] A method for achieving a non-uniform distribution of one or more platinum group metal components and / or one or more first alkaline earth metal components in the first catalytic washcoat zone perpendicular to the substrate surface is conventional baking of solute salts of one or more platinum group metal components impregnated into a washcoat 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 as solute salts in the washcoat coating and / or in an impregnation medium having solute salts of the one or more platinum group metal components. Preferably, the first alkaline earth metal components are present in the washcoat coating that impregnates the one or more platinum group metal components. Impregnation is a common general knowledge technique, for example, as described 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 baking and calcination. The inventors have found that an alternative drying method, freeze-drying (see, for example, WO 2009 / 080155), produces alkaline earth metal particles that are sufficiently well dispersed in the direction perpendicular to the surface of the substrate and generates less useful heat. Further discussion can be found below under the heading "Method of Production."

[0176] Preferably, the alkaline earth metal is barium. The present inventors have found that when an alkaline earth metal other than barium is used, for example, as an acetate, the salt of the alkaline earth metal other than barium has low mobility during the drying process and therefore tends not to form the non-uniform distribution that occurs in the case of alkaline earth metal salts such as strontium, calcium, or magnesium. The applicants believe that the presence of platinum group metals, particularly palladium, and barium, for example, on the upper surface of the catalytic washcoat layer in the so-called "crust," is beneficial to the heat generation function, which is the primary purpose of the composite oxidation catalyst of the present invention. Therefore, preferably, in addition to the non-uniform distribution of the barium component in a direction perpendicular to the surface of the substrate, the concentration of the palladium component also decreases in a direction perpendicular to the surface of the substrate, as measured by EPMA, when the barium component decreases in a direction perpendicular to the surface of the substrate.

[0177] Phosphorus and / or zinc protection bed As explained in the introduction to this specification, heavy-duty lubricants have relatively high contents of additives containing zinc and / or phosphorus. As a result, in use, over the life of the vehicle, catalysts in the exhaust systems of heavy-duty vehicles are exposed to relatively large amounts of zinc and / or phosphorus compounds. Applicant's inventors analyzed an oxidation catalyst that was the first catalyst substrate disposed in the exhaust system downstream of a Euro 6 heavy-duty diesel engine at the end of the vehicle life (approximately 1,000,000 kilometers) and found that 1.0 to 1.5 wt. % phosphorus was present on the oxidation catalyst in the first quarter of the coated substrate, measured from the substrate intake end.

[0178] In the present invention, the first catalyst washcoat zone has the highest platinum group metal loading on the substrate and is located within a zone defined by the first substrate end, which corresponds to the intake end in use. According to the present invention, the highest platinum group metal loading in the palladium-rich platinum / palladium combination is a key feature of the composite oxidation catalyst for generating exotherms from increased amounts of hydrocarbons present in the exhaust gas. Therefore, the presence of catalyst-contaminating zinc and / or phosphorus in the exhaust gas entering the intake end of the composite oxidation catalyst can have a disproportionate effect on the catalyst's activity for generating exotherms from hydrocarbons by indirectly reducing vehicle fuel economy by requiring additional hydrocarbons to achieve the desired exotherm temperature and / or by increasing the hydrocarbon light-off temperature, i.e., the temperature at which the catalyst becomes active to begin oxidizing hydrocarbons, thereby generating an exotherm relative to an oxidation catalyst uniformly coated with the same washcoat composition (see also Examples 8, 9, and 10, below). Thus, hydrocarbons introduced into the exhaust gas at relatively low temperatures where a specific heat generation would normally be expected may result in lower heat generation and increased hydrocarbon slip, resulting in 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.

[0179] Through their work, applicants' inventors also found that palladium-rich catalysts can suffer from more severe contamination by phosphorus and / or zinc compounds than platinum-rich catalysts of similar total platinum group metal loading.

[0180] Applicant's inventors have investigated ways to reduce or prevent the poisoning effects of phosphorus and / or zinc compounds on the combined oxidation catalyst function and have found that by disposing a washcoat layer as a coating layer on the first catalyst washcoat zone at a sufficient loading (corresponding to the thickness of the washcoat layer) (optionally, the washcoat contains particulate metal oxides of a sufficient average pore size and / or the resulting washcoat has a sufficient average inter-particle pore size), contact between the underlying first catalyst washcoat zone and the phosphorus and / or zinc compounds can be prevented or reduced, maintaining a higher percentage of the initial catalytic activity retained during use than catalysts not employing such additional features, while maintaining exhaust gas mass transfer access to the underlying first catalyst washcoat zone.

[0181]

[0013] Thus, in a preferred arrangement, the composite oxidation catalyst according to the first aspect of the present invention comprises a washcoat coating layer extending axially from the first substrate end to protect at least a portion of the underlying first catalyst washcoat zone from phosphorus and / or zinc contamination in use, the washcoat coating layer having a concentration of at least 0.8 g / in 3 The amount of particulate metal oxide supported is as above.

[0182] Applicant's research has shown that 0.5 g / in 3 The relatively low loading of the washcoat coating is 1.0 g / in 3 It has been found that the depth of the washcoat coating appears to be important for achieving the desired function as a guard bed for the phosphorus and / or zinc compounds, since washcoat coating loadings of 0.1 to 1.5 wt. % are not found to be as effective as washcoat coating loadings of 0.1 to 1.5 wt. % (see Examples 8, 9 and 10 below).

[0183] The washcoat coating layer may consist essentially of a particulate metal oxide, and the washcoat coating layer may contain certain binders or additives to aid processing, such as powder flow, washcoat rheology modifiers, etc. That is, although catalytic components such as barium or one or more platinum group metals may be wicked up or migrate from an underlying layer into the washcoat coating layer during the preparation of the composite oxidation catalyst, the particulate metal oxide may, for example, be coated in a washcoat that is free of such metals, and it is not intended that such metals should enter the washcoat coating layer. In this context, the term "consisting essentially of," as used herein, is intended to encompass end products in which any such metals have unintentionally migrated into the washcoat coating layer.

[0184] Typically, the washcoat coating is 0.8 to 3.5 g in -3 , preferably 0.9 to 2.5 g in -3 , and even more preferably 1.0 to 2.0 g in -3 , e.g., 1.1 to 1.75 g in -3 The amount of particulate metal oxide carried is

[0185] Preferably, the washcoat coating layer is coated directly onto the washcoat of the first catalytic washcoat zone, however, it is within the scope of the present invention for one or more washcoat layers to be present between the first catalytic washcoat zone and the washcoat coating layer in the preferred arrangement.

[0186] It will be understood that the application of the protective floor feature is generally applicable to all embodiments of the present invention and, therefore, is readily combinable with each and every embodiment of the present invention, as indicated by the optional dotted feature "G," and particularly as shown in the embodiments disclosed in Figures 1-5.

[0187] The washcoat coating may include one or more of the following additional optional features: (a) The particulate metal oxide in the washcoat coating has an average pore size of ≧10 nm, and / or the washcoat coating has an average interparticle pore size of ≧10 nm. (b) The particulate metal oxide of the washcoat coating layer is selected from the group consisting of alumina, silica, titania, zirconia, ceria, a mixed oxide or composite oxide of any two or more of these, or an aluminosilicate zeolite. Preferably, the particulate metal oxide is silica-doped alumina or alumina having an average pore size of ≥ 15 nm. (c) Particulate metal oxides in the washcoat coating are >100 m 2 / g specific surface area. (d) The washcoat coating layer extends axially from the first substrate end up to 150% of the axial length of the underlying first catalytic washcoat layer, preferably more than 50% of the axial length of the underlying first catalytic washcoat zone, e.g., more than 60%, 70%, 80%, 90%, or 100%, or up to 120% of its axial length, to protect against phosphorus and / or zinc contamination when used in the exhaust system of a heavy-duty diesel engine. (e) the particulate metal oxide in the washcoat coating layer supports a platinum group metal that is platinum or a combination of platinum and palladium in a Pt:Pd weight ratio of 1:1 or greater, and optionally, the platinum group metal loading in the washcoat coating layer is 1 to 35 gft -3 The platinum group metal is intentionally incorporated into the washcoat coating.

[0188] The particulate metal oxide can have one or both of an average pore size and an interparticle pore size of ≥ 10 nm. Preferably, the average pore size or the interparticle pore size is ≥ 12 nm or ≥ 15 nm. Applicant has found that certain parameters of the particulate metal oxide can unnecessarily reduce the hydrocarbon oxidation activity of the underlying first catalytic washcoat zone. Thus, when Applicant tested colloidal silica (Ludox™) as a possible particulate metal oxide for use in the washcoat coating layer, it was found that the washcoat layer was insufficiently porous and permeable to maintain the oxidation function of the underlying first catalytic washcoat layer. That is, hydrocarbon oxidation in a composite oxidation catalyst containing colloidal silica as the particulate metal oxide was gas mass transfer limited. While lowering the colloidal silica loading can improve mass transfer, the protective effect of the washcoat coating layer was expected to be insufficient (above ≥ 0.8 g / in). 3 (See washcoat load limit in ). Therefore, in order to better maintain the primary hydrocarbon oxidation function of the composite oxidation catalyst, the particulate metal oxide has an average pore size of ≥ 10 nm and / or the washcoat coating layer has an average interparticle pore size of ≥ 10 nm.

[0189] In embodiments featuring a washcoat coating layer without a supported platinum group metal, Applicant's inventors have found that certain particulate metal oxides having a relatively low average pore size, such as particulate ceria having an initial average pore size of 8 nm, can be effective in the present invention. However, preferably, the particulate metal oxide in the washcoat coating layer has an average pore size of ≥ 10 nm, and / or the washcoat coating layer has an average interparticle pore size of ≥ 10 nm, preferably an average pore size of ≥ 10 nm. That is, particulate metal oxides, such as ceria materials, having an inherently low average pore size can be applied in the present invention by selecting an appropriate particle size distribution (see also below) so that the average interparticle pore size in the washcoat layer is ≥ 10 nm.

[0190] The average interparticle pore size of the washcoat coating layer can be measured by mercury porosimetry.

[0191] The average pore size of the particulate metal oxide can be determined by N2 moisture absorption / desorption isothermal curves using the Barrett-Joyner-Halenda (BJH) method.

[0192] Where the particulate metal oxide has a bimodal pore size, the requirement is met if at least one of the two modes exceeds a particle size of ≥ 10 nm. For the avoidance of doubt, preferred particulate refractory metal oxide alumina doped with silica will at least meet the general definition in this paragraph.

[0193] Aluminosilicate zeolites generally do not meet the requirement of an average pore size of ≥ 10 nm. The characteristic of an interparticle pore size of ≥ 10 nm can be achieved by appropriate selection of particle size, i.e., particle size distribution. As discussed above with respect to colloidal silica, if the washcoat particles are too small, the interparticle pores will be too small to support exhaust gas mass transfer through the underlying first catalyst washcoat layer. By appropriate selection of particle size, it is possible to obtain interparticle pores of the appropriate size between particles to meet the preferred condition of an interparticle pore size of ≥ 10 nm.

[0194] For example, the particulate metal oxide particles may have a D90 of <100 micrometers. The particulate metal oxide particles may preferably have a D90 of <75 micrometers, such as <50 micrometers (e.g., <30 micrometers), more preferably <20 micrometers, such as <15 micrometers. If the refractory oxide has a smaller D90, better packing and adhesion can be obtained.

[0195] 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. For the avoidance of doubt, d90 measurements can be obtained by laser diffraction particle size analysis using a Malvern Mastersizer 2000™, which is a volume-based technique (i.e., D90 is the D V 90 (or may be referred to as D(v,0.90)), the mathematical Mie theory model is applied to determine the particle size distribution.

[0196] Typically, the particulate metal oxide particles have a D90 of >0.1 micrometers. Preferably, the particulate metal oxide particles have a D90 of >1.0 micrometers, for example >5.0 micrometers.

[0197] Particulate metal oxides that meet the requirements for use in protective bed washcoat coatings according to preferred configurations 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 silica-doped titania and ceria-zirconia mixed oxides, with silica-doped alumina or aluminosilicate zeolites being preferred. For example, the particulate metal oxide may be selected from the group consisting of alumina, ceria, silica-doped alumina, titania-alumina, zirconia-alumina, ceria-alumina, ceria-zirconia-alumina, silica-titania, silica-zirconia, zirconia-titania, ceria-zirconia, and alumina-magnesium oxide. Preferably, the particulate metal oxide is selected from the group consisting of alumina, silica-doped alumina, titania-alumina, zirconia-alumina, silica-titania, silica-zirconia, zirconia-titania, and alumina-magnesium oxide, i.e., the particulate metal oxide is cerium-free as described above.

[0198] The particulate metal oxide may optionally be doped (e.g., with a dopant). The dopant may be selected from the group consisting of zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd), and their oxides. The inclusion of a dopant can thermally stabilize the particulate metal oxide. Any reference to "doped" in this context should be understood to refer to a material in which the bulk or host lattice of the particulate metal oxide is substitutionally or interstitially doped with a dopant. In some cases, a small amount of dopant may be present on the surface of the particulate metal oxide. However, the majority of the dopant is generally present in the bulk of the particulate metal oxide.

[0199] When the particulate metal oxide is doped, the total amount of dopant is 0.5 to 15% by weight of the particulate metal oxide, preferably 1 to 10% by weight (e.g., about 5% by weight). A preferred particulate metal oxide is a refractory metal oxide alumina doped with silica, which can meet the requirement of having an average pore size of 10 nm or more and has an average pore size of about 120 nm. 2 / g or more (see below).

[0200] In embodiments in which the particulate metal oxide comprises an aluminosilicate zeolite, examples of suitable zeolites or zeolite framework types include faujasite, clinoptilolite, mordenite, silicalite, ferrierite, X-type zeolite, Y-type zeolite, ultrastable Y-type zeolite, 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-type zeolite. The aluminosilicate zeolite may contain one or more base metals, such as at least one of copper, iron, or manganese. For example, if the aluminosilicate zeolite has a CHA framework type code, the CHA may be promoted with copper. Alternatively, the aluminosilicate zeolite may be intended to be free of base metals.

[0201] The particulate metal oxide may be a refractory metal oxide, which term, as defined in this application, excludes aluminosilicate zeolites.

[0202] Particularly preferred particulate metal oxides for use in the present invention are refractory metal oxide silicas doped with alumina within the total amount of silica dopants disclosed herein, which are intentionally free of precious metals, including platinum group metals. Alumina having 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 EP 1077769 (A1).

[0203] 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 higher the predicted adsorption capacity of the washcoat coating layer for, for example, glassy zinc phosphate compounds derived from lubricity additives.

[0204] The particulate metal oxide particles for use in the washcoat coating layer of the new composite oxidation catalyst of the present invention have a particle size of ≥ about 100 m2 / g(>about 100m 2 / g), preferably ≥ about 120m 2 / g(>about 120m 2 / g), e.g., ≥ approx. 150m 2 / g(>about 150m 2 / g), ≧approx. 180m 2 / g(>about 180m 2 / g), or ≧ 200m 2 / g(>about 200m 2 Generally, aluminosilicate zeolites have an average specific surface area (SSA) of ≥ about 200 m 2 / g or more SSA.

[0205] The average specific surface area (SSA) of refractory oxide particles can be determined by nitrogen physisorption at −196° C. using the volumetric method. The average SSA is determined using the BET adsorption isotherm.

[0206] In a preferred embodiment, the particulate metal oxide in the washcoat coating layer carries a platinum group metal that is platinum or a combination of platinum and palladium in a Pt:Pd weight ratio of 1:1 or greater, with a Pt:Pd weight ratio of 1:0, i.e., Pt alone, being understood to be within the "1:1 or greater" range.

[0207] Preferably, the amount of platinum group metal carried in the washcoat coating layer is 1 to 35 gft -3 , preferably 2.5 to 25 g / ft -3 , for example, 5 to 17.5 gft -3 is.

[0208] Addition of manganese to the exhaust catalyst washcoat layer for improved NO2 management and exothermic behavior During research into the development of the four-zone composite oxidation catalyst shown in FIG. 5, Applicant has found that adding magnesium to the third catalyst washcoat zone defined at its second end by the second (i.e., outlet) substrate end as part of a second catalyst washcoat layer (7) applied from the second (i.e., outlet) substrate end advantageously promotes exotherm production and / or avoids exotherm dissipation during active filter regeneration, and improves the activity of the downstream SCR catalyst to reduce nitrogen oxides (NO x ) to N and / or improve nitrogenous reductant injection management for use in a downstream SCR catalyst. These observations are equally applicable to, among others, two-, three-, and four-zone combined oxidation catalysts according to the present invention.

[0209] As mentioned above, improving the activity of the downstream SCR catalyst reduces NO x Regarding the reduction of NOx to elemental nitrogen (N2), in exhaust gases containing both nitric oxide and nitrogen dioxide, SCR catalysis is known to proceed via a combination of SCR reactions, including reactions (1)-(3), all of which reduce NOx to elemental nitrogen (N2).

[0210] A related undesired and non-selective side reaction follows reaction (4). 2NH3+2NO2→N2O+3H2O+N2(4)

[0211] In practice, reactions (1)-(3) occur simultaneously, with the dominant reaction being favored depending, among other things, 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 of all. Thus, according to this chemistry, the SCR catalyst is able to balance the NO2 / NO2 ratio in the exhaust gas entering the downstream SCR catalyst. x It works most efficiently when the ratio is about 0.5, i.e., a 1:1 ratio of NO:NO2 according to reaction (3).

[0212] Applicant's researchers have found that the inclusion of manganese in the third catalytic washcoat zone of the combined oxidation catalyst shown in Figure 5 as part of the second catalytic washcoat layer (7) can suppress peak passive NO oxidation activity, i.e., the NO oxidation activity that occurs during an active exotherm / regeneration event. "Peak passive NO oxidation activity" is indicated by the value in the "Initial NO2 / NOx (%) at 300°C" column in Tables 7 and 8.

[0213] By using manganese to suppress the peak oxidation activity, applicant researchers were able to determine the NO2 / NO2 ratio of the "initial" and "aged" composite oxidation catalysts. x However, for a significant portion of the vehicle's lifespan, the NOx emissions are more stable at 0.55-0.45, i.e., the downstream SCR catalyst is kinetically slower and less efficient. x We found that we could dial down the "sweet spot" to perform reaction (3) instead of reduction reaction (2). If the initial catalyst activity to passively oxidize NO is too high, the peak NO / NO ratio in the exhaust gas would be too high. x The NO content can be increased beyond 0.65, not only shifting the exhaust gas composition away from the preferred 1:1 NO ratio to promote reaction (3) in the downstream SCR catalyst, but secondarily promoting the slowest reaction (2). Furthermore, excess NO can undesirably result in the production of N2O via reaction (4).

[0214] By improving the nitrogenous reductant injection management for use in the downstream SCR catalyst, Applicant's researchers also found that when the third zone contained manganese, the difference (Δ) between the initial and aging passive NO oxidation activity of the entire combined oxidation catalyst was reduced (see results shown in Tables 7 and 8). That is, the resulting NO2 / NO2 ratio in the exhaust gas downstream of the combined oxidation catalyst was xThe values ​​were more predictable over the life of the vehicle exhaust system because the catalyst starts fresh and ages steadily through use. This observation is important because, in practice, SCR catalytic reactions generally require the provision of a nitrogenous reductant (see reactions (1)-(3) above). Typically, this nitrogenous reductant is ammonia (NH3), which is carried on the vehicle in the form of a precursor, urea, for delivery into the exhaust gases flowing through the injectors. Upon contact with the hot exhaust gases, urea decomposes into ammonia and water vapor. From reactions (1)-(3), depending on which reaction is dominant at any particular time, it can be seen that if NH3 slip is avoided, NO x It can be seen that slightly different amounts of ammonia nitrogen reductant are required to achieve the most efficient overall reduction.

[0215] To further complicate matters, the ability of oxidation catalysts to oxidize NO to NO2 typically diminishes over time through use (so-called "aging"). This loss of activity over time places an increased burden on the design of control systems for delivering nitrogenous reductants, as system program algorithms must compensate for the gradually diminishing activity. However, by suppressing higher NO oxidation activity, the NO2 / NO2 ratio can be reduced, as described above in this specification. x By "centering" the Δ between initial and aged oxidation activity in addition to "centering" the Δ to about 0.5, managing system programming control of nitrogenous reductant injection over the life of the vehicle should be less complicated for manufacturers of heavy-duty diesel vehicles.

[0216] Third, and quite surprisingly, Applicant's researchers discovered that including manganese in the third washcoat zone / second washcoat layer can advantageously enhance exotherm generation and / or avoid exotherm dissipation during active filter regeneration, as shown in Example 11 below. This observation allowed for the replacement of very high-cost platinum group metals with a low-cost base metal, i.e., manganese, while maintaining the functionality of the composite oxidation catalyst.

[0217] In exhaust system aftertreatment, manganese can be affected by sulfur contamination. Palladium is also known to suffer from palladium contamination. For this reason, it may be preferable to avoid including palladium in addition to manganese in the manganese-containing catalytic washcoat layer and / or zone. However, as noted above, a relatively low content of palladium can improve the stability of the platinum component in the zone. In this regard, it is preferred that the manganese-containing catalytic washcoat layer and / or zone include a platinum-rich Pt:Pd weight ratio (e.g., 10:1 or greater), or that one or more platinum group metals in the manganese-containing catalytic washcoat layer and / or zone consist essentially of or can consist of platinum (e.g., a Pt:Pd weight ratio of 1:0).

[0218] To benefit from the described technical effects of containing manganese, the platinum group metal loading in the manganese-containing catalytic washcoat layer and / or zone is preferably 2 g / ft -3 or more, preferably 5 to 15 gft -3 , for example 7 to 13 gft -3 is.

[0219] Furthermore, Applicant has discovered that the technical effect of manganese-decreased NO oxidation "Δ" to NO over time can be enhanced by appropriate selection of a refractory metal oxide support material in the catalytic washcoat zone defined at the second substrate end, e.g., by the third catalytic washcoat zone, and / or in the second catalytic washcoat layer.

[0220] In this regard, applicants point out the benefits of alumina doped heteroatom support materials, where the heteroatoms are preferably silicon and / or manganese, or mixed magnesium aluminum metal oxides. Manganese can be present as such a heteroatom and / or introduced as a soluble salt, e.g., manganese nitrate, in combination with a washcoat refractory metal oxide support material, such as a mixed magnesium aluminum metal oxide or silica-doped alumina support material, and then precipitated onto the support material using a reducing agent, e.g., citric acid, tetrabutylammonium hydroxide, formic acid, ascorbic acid, etc. The doped manganese-containing refractory metal oxide support can then be impregnated with additional manganese.

[0221] Thus, the refractory metal oxide support material in the manganese-containing zone or layer can comprise silica-doped alumina, manganese-doped alumina, alumina doped with both silica and manganese, a mixed magnesium aluminum metal oxide, or a manganese-doped "preformed" mixed magnesium aluminum metal oxide. The impregnated manganese component can be supported on the refractory metal oxide support material.

[0222] The mixed magnesium aluminum metal oxide can have a pre-calcined magnesium content, calculated as Mg, of 15 wt.% or less, e.g., 0.1-12 wt.%, or 2.0-10 wt.%. The calcined support material comprising the mixed magnesium aluminum metal oxide can comprise a magnesium-deficient, i.e., non-stoichiometric, spinel. Most preferably, the manganese-containing refractory metal oxide support material is a manganese-doped "preformed" mixed magnesium aluminum metal oxide. The amount of manganese dopant in the manganese-doped magnesium aluminum metal oxide can be 1-15 wt.%, calculated as MnO2. Example 8 demonstrates that samples comprising the manganese-doped magnesium aluminum metal oxide exhibit a reduced NO2 / NO2 ratio between the initial catalyst and the aged catalyst. xIn addition to the "Δ", it shows a surprising improvement in heat generation from lower temperatures as demonstrated by the "continuous heat release" test.

[0223] Base material Substrates for supporting the catalytic washcoat layer and catalytic washcoat zone components of the composite oxidation catalyst of the present invention are well known in the art. Typically, the substrates are made from ceramic or metallic materials.

[0224] The substrate is preferably 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.

[0225] Typically, the substrate is a monolith, i.e., a monolith substrate. Preferably, the monolith is a flow-through honeycomb monolith substrate or a filtering monolith substrate, most preferably a honeycomb flow-through monolith substrate.

[0226] The composite oxidation catalyst of the present invention is preferably 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, in general, the principal difference between DOC and CSF is the substrate on which the catalyst formulation is coated and the amount of platinum group metal in the coating.

[0227] Typically, a flow-through monolith comprises a honeycomb monolith (e.g., a metal or ceramic honeycomb 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 typically referred to as or used as a diesel oxidation catalyst (DOC).

[0228] When the monolith is a filtering monolith, the filtering monolith is preferably a wall-flow filter. In a wall-flow filter, each inlet channel is alternately separated from an outlet channel by a wall of porous structure, and vice versa. The inlet and outlet channels preferably have a honeycomb arrangement. When a honeycomb arrangement is present, the channels vertically and laterally adjacent to the inlet channel are preferably blocked at their upstream ends, and vice versa (i.e., the channels vertically and laterally adjacent to the outlet channel are blocked at their downstream ends). When viewed from either end, the alternating blocked and open ends of the channels form a checkerboard appearance. 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).

[0229] In principle, the substrate may be of any shape or size. However, the shape and size of the substrate are typically selected to optimize the exposure of the catalytically active materials in the catalyst to the exhaust gas. The substrate may have, for example, a tubular, fibrous, or particulate form. Examples of suitable support 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, metal wire mesh-type substrates, metal porous body-type substrates, and ceramic particle-type substrates.

[0230] Heavy engine For the avoidance of doubt, a heavy-duty engine according to the third aspect of the present invention may use any of the definitions set out in the "Background" section of this specification above. Thus, for example, in a patent application for Japan, the heavy-duty diesel vehicle limitations required by Japanese emissions standards may be incorporated into the patent claims for the vehicle. Similar regulations apply to European or U.S. regulations, etc. For the further avoidance of doubt, a heavy-duty engine for use in the present invention is not managed to operate a lean / rich cycle suitable for normal operation of an LNT catalyst or for desulfation. In a preferred configuration, an exhaust system according to the present invention does not include an LNT.

[0231] 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., conventional) diesel engine.

[0232] Manufacturing method Methods for preparing the oxidation catalyst of the present invention are known in the art (see, for example, WO 99 / 47260, WO 2007 / 077462, and WO 2011 / 080525), as are the conditions for drying and calcining the washcoat.

[0233] As mentioned above, or according to the first inventive aspect, the oxidation catalyst may comprise three or more catalytic washcoat zones, preferably four catalytic washcoat zones.

[0234] A method of producing such a catalyst is according to a sixth aspect of the invention, wherein in step (a), the catalyst washcoat layer is a first catalyst washcoat layer extending from a first substrate edge to less than the entire length of the substrate, and the method further comprises step (a') of applying a second catalyst washcoat layer to the substrate before step (a) or after step (a), but in either case before step (b), with a length extending from a second substrate edge to less than the entire length of the substrate, such that the first catalyst washcoat layer partially overlaps the second catalyst washcoat layer, or such that the second catalyst washcoat layer partially overlaps the first catalyst washcoat layer, wherein the second catalyst washcoat layer comprises a refractory metal oxide support material and one or more platinum group metal components.

[0235] In this regard, preferably, the first catalytic washcoat layer can extend from the first substrate end and the second catalytic washcoat layer can extend from the second substrate end, whereby the second catalytic washcoat layer partially overlaps the first catalytic washcoat layer.

[0236] In embodiments, this preferred method can result in configurations such as those shown in Figures 4 and 5, where the first catalyst washcoat zone comprises a single layer of the first catalyst washcoat supported on the substrate surface, depending on the axial length of application of the second catalyst washcoat layer in step (a') and, therefore, the axial length of the overlap between the first and second catalyst washcoat layers. Depending on the axial length of application L1 in step (b), the second or fourth catalyst washcoat zone can comprise an overlap between the first and second catalyst washcoat layers. The third catalyst washcoat zone comprises a single washcoat layer supported on the substrate surface bounded at its second end by the second substrate edge and at its first end by the second end of the first catalyst washcoat layer, i.e., at the point where the second layer, extending in a direction from the second substrate edge to the first substrate edge, begins to overlap the first catalyst washcoat layer. Generally, the first end of the third catalytic washcoat zone is the second end of the second or fourth catalytic washcoat zone.

[0237] This configuration is preferred because exhaust gas entering the oxidation catalyst of the present invention at the first intake substrate end generally contacts the overlapping region catalyst washcoat zone before the third catalyst washcoat zone. The overlapping region catalyst washcoat zone (either the second or fourth catalyst washcoat zone, depending on the embodiment) acts as a "stabilizer" for the first catalyst washcoat zone. Although the overlapping region catalyst washcoat zone functions as a "stabilizer" in the sense that it performs some or all of the oxidation reactions of the first catalyst washcoat zone, the overlapping region catalyst washcoat zone may have a higher light-off temperature for HC and / or CO than that of the first catalyst washcoat zone.

[0238] In the sixth aspect of the present invention, since the first catalytic washcoat zone is obtained in step (b) by impregnation with the catalytic washcoat applied in step (a), it will be appreciated that the refractory metal oxide support material in the first catalytic washcoat zone can be the same refractory metal oxide support material in the catalytic washcoat, e.g., the first catalytic washcoat layer applied in step (a).

[0239] A first catalytic 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 surface of the substrate as determined by electron probe microanalysis (EPMA), wherein the concentrations of the one or more platinum group metal components and optional first alkaline earth metal components decrease in a direction perpendicular to the surface of the substrate as determined by EPMA, can generally be obtained by a process in which the 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 but are mobile within the washcoat during drying. A washcoat containing one or more platinum group metal components can be applied to a substrate, followed by thermal drying and calcination steps using conditions that allow for the migration of the one or more platinum group metal components and optional one or more first alkaline earth metal components in the coating, and then fixed in place. Such conditions are known in the art, particularly since conditions in the prior art are generally selected to rapidly fix components of the coating (i.e., washcoat coating) to prevent migration within the coating, i.e., by impregnation, what are recognized as rapid fixation conditions to avoid migration of platinum group metal salts within the washcoat during drying are recognized as conditions that allow such migration.

[0240] The migration of solutes toward or away from a wet surface during evaporation is an effect known in other arts. The migration 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:

[0241]

number

[0242] A method for achieving a catalytic washcoat 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 the surface of a substrate comprises: (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; (b) applying the aqueous slurry onto a substrate to form a washcoating; (c) drying and calcining the washcoating, the drying conditions allowing at least one or more platinum group metal components and, optionally, one or more alkaline earth metal components to flow towards or away from the substrate, e.g., to obtain a non-uniform distribution of the one or more platinum group metal components and, optionally, one or more alkaline earth metal components in a direction perpendicular to the surface of the substrate.

[0243] The washcoating may include two or more platinum group metal components, where a first platinum group metal component may be referred to as the first platinum group metal component and a second platinum group metal component may be referred to as the second platinum group metal component.

[0244] 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, for example, if precursors of one or more 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).

[0245] Typically, the refractory metal oxide support material precursor is a compound that undergoes conversion to the 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 γ-alumina.

[0246] 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., 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 (e.g., a citrate) of the first platinum group metal.

[0247] The second platinum group metal component is typically a salt of the second platinum group metal or is the second platinum group metal (i.e., the second platinum group metal itself). Preferably, the second platinum group metal component is a salt of the 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 (e.g., a citrate) of the second platinum group metal.

[0248] When two or more different platinum group metals are used (e.g., a first platinum group metal is different from a second platinum group metal), there may be differences in the mobility of the first platinum group metal component relative to the second platinum group metal component resulting from the differences in the metals present, resulting in different distribution profiles of each platinum group metal relative to the other (or each other) platinum group metals in the washcoat layer (see Figure 6). The same applies to differences in the mobility of alkaline earth metals relative to one or more platinum group metal components present in the catalytic washcoat layer. By selecting an appropriate anion when the platinum group metal component is a platinum group metal salt, the mobility of the platinum group metal component within the catalytic washcoat layer, and also the preferred vertical flow, can be altered. Platinum group metal components may also interact differently with the refractory metal oxide support material and may be selected based on this. Similarly, the mobility of alkaline earth metal components within the catalytic washcoat layer can be altered by appropriate selection of their solute salts.

[0249] 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.

[0250] The mobility of at least one of the platinum group metal components can be modified by supporting it on a support material (i.e., pre-immobilizing the platinum group metal component) prior to mixing with the other platinum group metal components. 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.

[0251] One way in which a first platinum group metal component can be supported on a first refractory metal oxide support material precursor is by (i) mixing the first refractory metal oxide support material precursor and the first platinum group metal component in solution, preferably impregnating 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 step (i)(a) of adding a reducing agent to reduce the first platinum group metal component and preferably impregnate or fill the pores of the first support material. In steps (i) and / or (i)(a), it is preferred that the only platinum group metal component present is the first platinum group metal component.

[0252] Thus, step (a) of the above method may be: (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.

[0253] With respect to step (b), methods for applying a slurry or washcoat to a substrate are well known in the art (see, for example, applicant's WO 99 / 47260).

[0254] In one embodiment, step (c) comprises drying the coating using drying conditions that allow at least the first and second platinum group metal components to flow at different rates in a direction perpendicular to a plane representing the substrate surface, hi another embodiment, step (c) comprises drying the coating using drying conditions that allow only the first platinum group metal component to flow toward or away from the substrate.

[0255] Step (c) determines the point at which the platinum group metal component is immobilized, usually on a substrate or refractory metal oxide support material. The drying conditions used depend on the identity of the materials 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 varies depending on the application of the catalyst).

[0256] Typically, the drying conditions include drying the coating for at least 15 minutes, preferably at least 20 minutes. A uniform distribution of the first platinum group metal and optional alkaline earth metal can be obtained using such conditions. A uniform distribution tends to be obtained when the drying time is about 5 minutes or less.

[0257] The coating may then be fired at a temperature of 400-800°C, preferably 450-600°C, more preferably at a temperature of at least 500°C.

[0258] As an example, when a first catalytic washcoat layer includes a first loading and a weight ratio of platinum and palladium as the two or more platinum group metal components, and one or more alkaline earth metal components is barium, both the platinum group metal and barium are supported on a refractory metal oxide support material, which is silica-doped alumina with a preferred silica content. Such a first catalytic washcoat layer is impregnated with a relatively high concentration aqueous solution of platinum and palladium salts to form a first catalytic washcoat zone after application of the drying method described above. It has been found that the palladium and barium migrate more readily to the exposed catalytic washcoat layer surface, which is observed as a "crust" by EPMA. When not previously fixed to the underlying refractory metal oxide support material, the platinum component exhibits some mobility toward the same exposed surface within the cross-section of the first catalytic washcoat layer, and remains relatively more uniformly distributed across the cross-section of the first catalytic washcoat layer compared to the palladium and barium. The finished product has been found to demonstrate beneficial activity for heat generation. This effect is also partially demonstrated in Examples 1, 2, 3, 5 and 6 below.

[0259] Exhaust system An exhaust system according to a second aspect of the present invention comprises a composite oxidation catalyst according to the present invention and a soot filter substrate arranged downstream thereof, with a first substrate end of the composite oxidation catalyst facing upstream.

[0260] The soot filter substrate may be, and typically is coated with, a catalytic formulation.

[0261] The catalytic formulation of the soot filter may be suitable for the oxidation of (i) particulate matter (PM) and / or (ii) carbon monoxide (CO) and hydrocarbons (HC). When the catalytic formulation is suitable for the oxidation of PM, the resulting emission control device is known as a catalytic soot filter (CSF). Typically, the catalytic formulation of a CSF comprises a platinum group metal, such as a first platinum group metal and / or a second platinum group metal, as defined above.

[0262] SCR catalysts are also well known in the art and can be coated on a filter substrate, such as a flow-through substrate or a wall-flow filter substrate. When the exhaust system of the present invention includes an SCR catalyst coated on a flow-through substrate monolith, for example, the exhaust system may further include an injector for injecting a nitrogen-based reductant, such as ammonia or urea, into the exhaust gas downstream of the catalyst for oxidizing carbon monoxide (CO) and hydrocarbons (HC) (the combined oxidation catalyst of the present invention or a CSF disposed downstream of the combined oxidation catalyst of the present invention) and upstream of the SCR catalyst. The exhaust system may further include engine management means for mixing hydrocarbons into the exhaust gas to contact the combined oxidation catalyst with the hydrocarbons and generate heat for regenerating the downstream soot filter. Alternatively, or in addition, hydrocarbon injection may be facilitated via a stand-alone hydrocarbon injector for injecting hydrocarbon fuel into the exhaust gas downstream from the engine manifold but upstream of the combined oxidation catalyst.

[0263] Instead of a CSF catalyst formulation, the soot filter substrate, preferably a wall-flow filter, can be coated with an SCR catalyst, in which case it is referred to as an SCRF catalyst.

[0264] Generally, SCR catalysts are designed to suppress the release of a significant amount of NO in the exhaust gas immediately after starting a compression ignition engine because the exhaust gas temperature (i.e., the catalyst temperature) is too low. x It is not possible to reduce lean NO x Trap catalyst (e.g., NO x Adsorption catalysts (e.g., adsorption catalysts) are used upstream of SCR catalysts, and do not absorb NO until the SCR catalyst becomes active at higher exhaust gas temperatures. x However, lean NO x Trap catalysts often reduce NO when the exhaust gas flow rate is high (e.g., when the engine is operated at high speeds). x cannot store enough.

[0265] According to a second aspect of the present invention, an exhaust system applicable to the present invention is shown in the accompanying Figures 8A-D. The first exhaust system embodiment (see Figure 8A) includes a composite oxidation catalyst of the present invention on a flow-through honeycomb substrate monolith (see item 42 in Figure 8A) and a selective catalytic reduction filter (SCRF) catalyst. Such a configuration may be referred to as a DOC / SCRF. This embodiment also relates to the use of the composite oxidation catalyst in combination with a selective catalytic reduction filter (SCRF) catalyst for treating exhaust gases from a combustion engine, particularly a compression-ignition engine. Preferably, the composite oxidation catalyst is or is used as a diesel oxidation catalyst. Typically, the composite oxidation catalyst of the present invention is followed by a selective catalytic reduction filter (SCRF) catalyst (e.g., the composite oxidation catalyst is upstream). A nitrogen-based reductant injection device may be located between the composite oxidation catalyst and the selective catalytic reduction filter (SCR) catalyst. Thus, the combined oxidation catalyst may be followed by a nitrogenous reductant injector (e.g., the combined oxidation catalyst is upstream), or the nitrogenous reductant injector may be followed by a selective catalytic reduction filter (SCRF) catalyst (e.g., the nitrogenous reductant injector is upstream).

[0266] In a second exhaust system embodiment (see FIG. 8B ), the exhaust system includes a composite oxidation catalyst of the present invention on a flow-through honeycomb substrate monolith and one of a (non-catalyzed) diesel particulate filter (DPF) or a catalyzed soot filter (CSF). Such a configuration may be referred to as a DOC / DPF or DOC / CSF. This embodiment also relates to the use of the composite oxidation catalyst in combination with a diesel particulate filter or a catalyzed soot filter for treating exhaust gases from a 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., the composite oxidation catalyst is upstream). 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.

[0267] A third exhaust system embodiment (see FIG. 8C ) relates to an exhaust system including a composite oxidation catalyst of the present invention on a flow-through honeycomb substrate monolith, a diesel particulate filter or catalytic soot filter (CSF), and a selective catalytic reduction (SCR) catalyst. Such a configuration may be referred to as DOC / DPF / SCR or DOC / CSF / SCR. This embodiment also relates to the use of the composite oxidation catalyst for treating exhaust gases from a combustion engine, particularly a compression-ignition engine, in combination with either a diesel particulate filter or catalytic soot filter (CSF) and a selective catalytic reduction (SCR) catalyst, preferably where the oxidation catalyst is or is used as a diesel oxidation catalyst. The composite oxidation catalyst is typically followed by the diesel particulate filter or catalytic soot filter (CSF) (e.g., the composite oxidation catalyst is upstream). The DPF or CSF is typically followed by the selective catalytic reduction (SCR) catalyst (e.g., the DPF or CSF is upstream). The nitrogenous reductant injector may be located between the DPF or CSF and the selective catalytic reduction (SCR) catalyst. Thus, the DPF or CSF may be followed by the nitrogenous reductant injector (e.g., upstream), or the nitrogenous reductant injector may be followed by the selective catalytic reduction (SCR) catalyst (e.g., upstream).

[0268] A fourth exhaust system embodiment (see FIG. 8A ) relates to an exhaust system including a combined oxidation catalyst (CSF, see item 42 in FIG. 8A ) of the present invention on a wall-flow substrate monolith and a selective catalytic reduction (SCR) catalyst. This is also a CSF / SCR configuration. A further aspect of this embodiment relates to the use of the combined oxidation catalyst for treating exhaust gases from a compression-ignition engine in combination with a diesel oxidation catalyst (DOC) and a selective catalytic reduction (SCR) catalyst, preferably the combined oxidation catalyst being a catalytic soot filter (CSF) or used as a CSF. The diesel oxidation catalyst (DOC) is typically followed by the combined oxidation catalyst of the present invention (e.g., the diesel oxidation catalyst (DOC) is upstream). The combined oxidation catalyst of the present invention is typically followed by a selective catalytic reduction (SCR) catalyst (e.g., the combined oxidation catalyst is upstream). A nitrogen-based reductant injection device may be positioned between the combined oxidation catalyst and the selective catalytic reduction (SCR) catalyst. Thus, the combined oxidation catalyst may be followed by a nitrogenous reductant injector (e.g., the combined oxidation catalyst is upstream), or the nitrogenous reductant injector may be followed by a selective catalytic reduction (SCR) catalyst (e.g., the nitrogenous reductant injector is upstream).

[0269] In a fifth exhaust system embodiment (see FIG. 8D ), the exhaust system comprises a composite oxidation catalyst of the present invention, preferably as a DOC, a selective catalytic reduction (SCR) catalyst, and either a catalyzed soot filter (CSF) or a diesel particulate filter (DPF). The configuration is either DOC / SCR / CSF or DOC / SCR / DPF. This embodiment also relates to the use of the composite oxidation catalyst for treating exhaust gases from a combustion engine, in particular a compression-ignition engine, in combination with a selective catalytic reduction (SCR) catalyst and either a catalyzed soot filter (CSF) or a diesel particulate filter (DPF), preferably wherein the composite oxidation catalyst is or is used as a diesel oxidation catalyst.

[0270] Such a configuration is shown in Figures 8A-8D, respectively, in which item 30 is a heavy-duty diesel engine, item 32 is an exhaust system for the heavy-duty diesel engine, item 34 is a pipe for conveying exhaust gases from the heavy-duty diesel engine to components of the exhaust system (42, 44, 50) or from the exhaust system to the atmosphere 36, and item 38 is an injector for injecting hydrocarbon fuel into the exhaust gases downstream of the engine manifold 40 and upstream of a composite oxidation catalyst 42 according to the present invention (e.g., any one of the composite oxidation catalysts illustrated in Figures 1-5). wherein the first catalyst washcoat zone 1 is oriented upstream, 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 catalyzed soot filter (CSF), item 46 is an injector for injecting a nitrogen-based reductant precursor fluid, such as urea, held in a reservoir 48 into the flowing exhaust gas, and item 50 is a selective catalytic reduction catalyst (SCR) coated on the flow-through substrate monolith or wall-flow filter substrate monolith (SCRF).

[0271] Definition of Alternative Invention The present invention may also be defined according to one or more of the following definitions. 1. A composite oxidation catalyst for use in an exhaust system to treat exhaust gases produced by a compression-ignition internal combustion engine for a vehicle, preferably a heavy-duty diesel vehicle, and upstream of a particulate matter filter in the exhaust system, the composite oxidation catalyst comprising: a substrate having an overall length L and a longitudinal axis, the substrate having a substrate surface extending axially between a first substrate end and a second substrate end; Two or more catalyst washcoat zones arranged in series axially on and along the surface of a substrate, wherein the first catalyst washcoat zone has a length L1, L1 < L, and at one end is defined by a first substrate end, and at the second end is defined by the first end of a second catalyst washcoat zone having a length L2, L2 < L, the first catalyst washcoat zone includes a first heat-resistant metal oxide support material and two or more platinum group metal components supported thereon, including both platinum and palladium with a weight ratio of less than 1, and the second catalyst washcoat zone includes a second heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, including two or more catalyst washcoat zones. Gram of platinum group metal per cubic foot of substrate volume (g / ft 3 ) The total platinum group metal loading in the first catalyst washcoat zone, defined by, is greater than the total platinum group metal loading in the second catalyst washcoat zone. The first catalyst washcoat zone includes a composite oxidation catalyst containing one or more first alkaline earth metal components supported on the first heat-resistant metal oxide support material. 2. The compression ignition internal combustion engine according to 1, wherein the weight ratio of platinum to palladium in the first catalyst washcoat zone (1) is less than 1:1 to 1:3 or more. 3. The compression ignition internal combustion engine according to 1 or 2, wherein the second catalyst washcoat zone is defined by a second substrate end at its second end. 4. A third catalyst washcoat zone including three or more catalyst washcoat zones, including a third heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, is defined by a second substrate end at its second end, and the total platinum group metal loading in the third catalyst washcoat zone defined by 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 washcoat zone. The composite oxidation catalyst according to 1 or 2. 5. Comprising four catalyst washcoat zones, the fourth catalyst washcoat zone being disposed between the second catalyst washcoat zone and the third catalyst washcoat zone, the fourth catalyst washcoat zone comprising a fourth heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, at its first end being defined by the second end of the second catalyst washcoat, and at its second end being defined by the first end of the third catalyst washcoat zone, the total platinum group metal loading in the fourth catalyst washcoat zone defined in grams of platinum group metal per cubic foot of substrate volume (g / ft 3 ) being greater than the total platinum group metal loadings in each of the second catalyst washcoat zone and the third catalyst washcoat zone, the composite oxidation catalyst according to 4. 6. Comprising a first catalyst washcoat layer and a second catalyst washcoat layer, the first catalyst washcoat layer comprising a heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, having a length L3, where L3 < L, at one end being defined by the first substrate end, the second catalyst washcoat layer comprising a heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, having a length L4, where L4 < L, at its second end being defined by the second substrate end, the fourth catalyst washcoat zone comprising a two-layer overlap region of the first catalyst washcoat layer and the second catalyst washcoat layer, the third catalyst washcoat zone comprising a single layer of the second catalyst washcoat layer not included in the overlap region, the composite oxidation catalyst according to 5. 7. Comprising three catalyst washcoat zones, the third catalyst washcoat zone being defined at its first end by the second end of the second catalyst washcoat zone, the composite oxidation catalyst according to 4. 8. It includes a first catalyst washcoat layer and a second catalyst washcoat layer. The first catalyst washcoat layer includes a heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, has a length L3, where L3 < L, and at one end, it is defined by the first substrate end. The second catalyst washcoat layer includes a heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, has a length L4, where L4 < L, and at the second end, it is defined by the second substrate end. The second catalyst washcoat zone includes a two-layer overlapping region of the first catalyst washcoat layer and the second catalyst washcoat layer. The third catalyst washcoat zone includes a single layer of the second catalyst washcoat layer not included in the overlapping region. The composite oxidation catalyst according to 7. 9. The catalyst washcoat zone is defined by the second substrate end at its second end, contains manganese, and / or the second catalyst washcoat layer contains manganese. The composite oxidation catalyst according to any one of 2 to 8. 10. The heat-resistant metal oxide support material in the manganese-containing zone or layer includes alumina doped with silica, alumina doped with manganese, alumina doped with both silica and manganese, mixed magnesium aluminum metal oxide, or mixed magnesium aluminum metal oxide doped with manganese. The composite oxidation catalyst according to 9. 11. The impregnated manganese component is supported on the heat-resistant metal oxide support material. The composite oxidation catalyst according to 9 or 10. 12. One or more platinum group metal components of the second washcoat layer or the third catalyst washcoat zone consist essentially of platinum. The composite oxidation catalyst according to any one of 4 to 11. 13. One or more platinum group metal components of the first catalyst washcoat layer consist of both platinum and palladium. The composite oxidation catalyst according to any one of 6 to 12. 14. The total platinum group metal loading amount in the first catalyst washcoat zone is less than 100 g / ft calculated as elemental metal. The composite oxidation catalyst according to any one of 1 to 13. 3 The composite oxidation catalyst according to any one of 1 to 13. 15. The composite oxidation catalyst according to any one of 1 to 14, wherein the one or more platinum group metal components of the second catalytic washcoat zone include both platinum and palladium. 16. The composite oxidation catalyst according to 15, wherein the mass ratio of platinum to palladium in the second catalytic washcoat zone is greater than the mass ratio of platinum to palladium in the first catalytic washcoat zone. 17. A composite oxidation catalyst according to any one of 5 to 16, wherein the mass ratio of platinum to palladium in each successive catalytic washcoat zone arranged in series along the substrate length L after the first catalytic washcoat zone is greater than that in the immediately preceding catalytic washcoat zone. 18. The composite oxidation catalyst according to any one of 1 to 17, wherein L1 is less than 50% of L. 19. Calculated as elemental metal, 5-60 g / ft 3 19. The composite oxidation catalyst according to any one of 1 to 18, wherein the total amount of platinum group metal supported on the substrate is: 20. The total alkali metal loading in the first catalyst washcoat zone, calculated as elemental metal, is 10-100 g / ft 3 20. The composite oxidation catalyst according to any one of 1 to 19, wherein 21. The composite oxidation catalyst according to any one of 1 to 20, wherein the weight ratio of total elemental alkaline earth metals to total elemental platinum group metals in the first catalytic washcoat zone is less than 1:1. 22. The composite oxidation catalyst according to any one of 1 to 21, wherein the alkaline earth metal of the first catalytic washcoat zone comprises barium (Ba) or strontium (Sr), preferably Ba. 23. The composite oxidation catalyst according to any one of 1 to 22, wherein the first catalytic washcoat zone has a non-uniform distribution of the one or more platinum group metal components and / or the 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 concentrations of the one or more platinum group metal components and / or the first alkaline earth metal component decrease in a direction perpendicular to the substrate surface. 24. The composite oxidation catalyst according to any one of 1 to 23, wherein at least the first refractory metal oxide support material comprises alumina doped with heteroatoms, preferably silica. 25. A washcoat coating layer extending axially from a first substrate end to protect at least a portion of an underlying first catalytic washcoat zone from phosphorus and / or zinc contamination in use, the washcoat coating layer having a 0.8 g / in 3 25. The composite oxidation catalyst according to any one of 1 to 24, comprising a particulate metal oxide supported in an amount exceeding 1. 26. The composite oxidation catalyst according to 25, wherein the particulate metal oxide in the washcoat coating layer has an average pore size of 10 nm or more, and / or the washcoat coating layer has an average interparticle pore size of 10 nm or more. 27. The composite oxidation catalyst according to 25 or 26, wherein the particulate metal oxide in the washcoat coating layer is selected from the group consisting of alumina, silica, titania, zirconia, ceria, and mixed oxides or composite oxides of any two or more thereof, or aluminosilicate zeolites. 28. The particulate metal oxide in the washcoat coating layer is 100m 2 28. The composite oxidation catalyst according to 25, 26 or 27, having a specific surface area of ​​more than 1 / g. 29. The composite oxidation catalyst according to any one of 25 to 28, wherein the particulate metal oxide in the washcoat coating layer supports a platinum group metal which is platinum or a combination of platinum and palladium in a Pt:Pd weight ratio of 1:1 or more. 30. The platinum group metal loading of the washcoat layer is 1 to 35 gft -3 30. The composite oxidation catalyst according to 29, wherein 31. The composite oxidation catalyst according to any one of 1 to 30, wherein the substrate is a honeycomb flow-through substrate monolith. 32. An exhaust system for a compression ignition engine for a vehicle, comprising a composite oxidation catalyst according to any one of 1 to 31 and a soot filter substrate arranged downstream of the oxidation catalyst, with a first substrate end of the composite oxidation catalyst facing upstream. 33. The exhaust system of claim 32, wherein the soot filter substrate is a catalyzed soot filter substrate catalyzed with a platinum group metal catalyst or a selective catalytic reduction catalyst. 34. An exhaust system as described in 32 or 33, including an injector for liquid hydrocarbons connected to a liquid hydrocarbon source, the injector being arranged to inject the liquid hydrocarbons into exhaust gases flowing in the exhaust system downstream of the engine. 35. An exhaust system as described in 32, 33 or 34, including a substrate positioned downstream of the soot filter substrate catalyzed with a selective catalytic reduction catalyst. 36. An exhaust system according to 33, 34 or 35, including a selective catalytic reduction catalyst, wherein the system includes an injector for a nitrogen-based reductant or a precursor thereof connected to a source of nitrogen-based reductant or a nitrogen-based reductant precursor, the injector being arranged to inject the nitrogen-based reductant or nitrogen-based reductant precursor into exhaust gases flowing downstream of the composite oxidation catalyst and upstream of the substrate comprising the selective catalytic reduction catalyst. 37. A compression-ignition internal combustion engine for a heavy-duty diesel vehicle comprising an exhaust system according to any one of 32 to 36, wherein the first substrate end of the composite oxidation catalyst is directed upstream. 38.37 Heavy-duty diesel vehicles containing a compression-ignition internal combustion engine. 39. Use of a composite oxidation catalyst according to any one of 1 to 31 for heating a soot filter located downstream of the composite oxidation catalyst in the exhaust system of a compression-ignition internal combustion engine for a vehicle by contacting the oxidation catalyst with exhaust gas containing a high concentration of hydrocarbon fuel, thereby generating heat from the high concentration of hydrocarbon fuel in the exhaust gas flowing through the exhaust system under normal operating conditions. 40. A method for producing a composite oxidation catalyst for use in an exhaust system for treating exhaust gases produced by a compression-ignition internal combustion engine for a vehicle, the composite oxidation catalyst comprising: a substrate having an overall length L and a longitudinal axis, the substrate surface extending axially between a first substrate end and a second substrate end; Two or more catalyst washcoat zones arranged in series axially on and along the surface of a substrate, wherein the first catalyst washcoat zone has a length L1, L1 < L, and at one end is defined by the first substrate end, and at the second end is defined by the first end of a second catalyst washcoat zone having a length L2, L2 < L, the first catalyst washcoat zone includes a first heat-resistant metal oxide support material and two or more platinum group metal components supported thereon, including both platinum and palladium with a weight ratio of platinum to palladium less than 1, and the second catalyst washcoat zone includes a second heat-resistant metal oxide support material and one or more platinum group metal components supported thereon, the catalyst washcoat zone, and Gram of platinum group metal per cubic foot of substrate volume (g / ft 3 ) The total platinum group metal loading in the first catalyst washcoat zone, defined as, is greater than the total platinum group metal loading in the second catalyst washcoat zone, and the first catalyst washcoat zone includes one or more first alkaline earth metal components supported on the first heat-resistant metal oxide support material, and the method is (a) Applying a catalyst washcoat layer to the surface of the substrate for a length extending from one end of the substrate, the catalyst washcoat layer including a heat-resistant metal oxide support material and one or more platinum group metal components, the step and (b) Impregnating the catalyst washcoat layer in a zone of length L1 defined by the first substrate end at one end with a solution containing one or more platinum group metals, and including One or more alkaline earth metal components are present in the catalyst washcoat layer of step (a) and / or the impregnation solution used in step (b), the method. 41. The method according to 40, wherein in step (a), the catalyst washcoat extends along the entire length L of the substrate. 42. The method of claim 40, wherein in step (a), the catalytic washcoat layer is a first catalytic washcoat layer that extends from a first substrate end to less than the entire length of the substrate, and the method further comprises step (a') of applying a second catalytic washcoat layer to the substrate before step (a) or after step (a), but in either case before step (b), with a length that extends from a second substrate end to less than the entire length of the substrate, such that the first catalytic washcoat layer partially overlaps the second catalytic washcoat layer, or such that the second catalytic washcoat layer partially overlaps the first catalytic washcoat layer, and wherein the second catalytic washcoat layer comprises a refractory metal oxide support material and one or more platinum group metal components. 43. The method of claim 42, wherein a first catalytic washcoat layer extends from a first substrate end and a second catalytic washcoat layer extends from a second substrate end, whereby the second catalytic washcoat layer partially overlaps the first catalytic washcoat layer.

[0272] definition 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 surface of the substrate (e.g., in a straight line) generally refers to a direction perpendicular to the same surface of the substrate on which the catalyst layer is disposed. For reference purposes, the surface of the substrate generally lies in a horizontal (i.e., longitudinal) plane. A direction perpendicular to the surface of the substrate is typically a direction in a cross-sectional plane passing through the catalyst layer (i.e., a cross-sectional plane exposing the thickness of the catalyst layer) perpendicular to the surface of the substrate. The cross-sectional plane is generally a vertical (i.e., transverse) plane. The cross-sectional plane is perpendicular to the surface on which the catalyst layer is disposed. More typically, the cross-sectional plane is substantially parallel to the inlet end face of the substrate and / or the discharge end face of the substrate (i.e., a plane containing the inlet end face and / or a plane containing the discharge end face). Any reference to "substantially parallel" in this context refers to an angle of less than 5°, preferably less than 2.5°, and more preferably less than 1° (e.g., less than 0.5°) between the cross-sectional plane of the substrate and the inlet end face or the discharge end face.

[0273] Any reference to a "surface of the substrate" generally refers to the surface of the walls of a channel through the substrate.

[0274] As used herein, the term "layer" (e.g., catalyst layer) refers to a thickness of material extending over a surface, such as the surface of a substrate or the surface of another layer, and typically has a distinct boundary or edge (i.e., it is possible to distinguish a first layer from a compositionally different second layer using conventional analytical techniques (e.g., transmission electron microscopy)).

[0275] The term "uniform," as used herein with respect to the distribution of platinum group metals, generally refers to a composition (e.g., a layer) in which 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., a layer). Preferably, the amount of platinum group metal at any point in the composition is within ±10%, more preferably ±5%, and even more preferably ±1% of the average amount of platinum group metal in the entire composition (e.g., a layer). The average amount of platinum group metal should correspond to the amount of platinum group metal measured during 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 EDX analysis using a transmission electron microscope.

[0276] The term "mixed oxide" as used herein generally refers to a mixture of oxides in a single phase, as conventionally known in the art.

[0277] The term "complex oxide" as used herein generally refers to an oxide composition having two or more phases, as conventionally known in the art.

[0278] 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 containing 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 catalytic washcoat zone, a catalytic washcoat layer, or on a substrate as a whole. EPMA or XRF techniques can be used to determine the local concentration of each platinum group metal component or each alkaline earth metal component. The units of loading used herein and in the prior art are generally g ft, which roughly relate to the volume of substrate used. -3 Or g in -3 or their SI unit equivalents, grams / liter. The volume fraction relates to the volume fraction of the substrate to which, for example, the washcoat layer is applied. Typically, components at relatively low concentrations are expressed in terms of "g ft" to make the amount meaningful without needing to refer to hundredths or thousandths of a quantity. -3 " and higher concentrations, such as total washcoat application, are given as "g in -3 By common technical convention, the "volume" component of the loading unit assumes that the substrate is solid, e.g., the total volume of a cylinder, and ignores the fact that the substrate has channels extending therethrough defined by walls made from the substrate composition, or that the substrate composition is porous in nature.

[0279] The term "comprising" is intended to mean that the specified elements are essential, but other elements may be added and still form a component within the scope of the claim.

[0280] As used herein, the phrase "consisting essentially of" can be substituted for the broader "comprising" and limits the scope of a feature to include the specified materials or steps and any other materials or steps that do not materially affect the basic and novel properties and function of that feature or that feature in combination with other claimed features. When a catalytic washcoat zone consists essentially of platinum, this means that although it is intended to consist of platinum, other platinum group metals, such as palladium, may be unintentionally present in the catalytic washcoat zone of the final product, for example, due to palladium migrating to the catalytic washcoat zone during production. In this context, "consisting essentially of" does not exclude the unintentional presence of palladium in a catalytic washcoat zone defined as consisting essentially of platinum. The term "consisting essentially of" encompasses the phrase "consisting of" and is interchangeable with either "comprising" or "consisting of." "Consisting of" closes a claim to the inclusion of materials other than those listed, except for impurities normally associated therewith.

[0281] With respect to the composite oxidation catalyst of the present invention, a basic and novel feature of the present invention is a substrate having at least two catalytic washcoat zones axially disposed in series on and along the substrate surface, wherein at one end, a first catalytic washcoat zone defined by the inlet end of the substrate comprises a refractory metal oxide support material, both platinum and palladium in a Pt:Pd weight ratio of less than 1, and barium, and a second catalytic washcoat zone comprises a refractory metal oxide support material, both platinum and palladium in a platinum-rich Pt:Pd ratio of greater than 3:2.

[0282] In the context of the phrase "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 a catalyst, and that the platinum group metal may not be present in elemental metal form. Any reference to "consisting essentially of a platinum group metal" encompasses the elemental form of a platinum group metal, an alloy including a platinum group metal, or the "platinum group metal portion" of a compound including a platinum group metal (e.g., an oxide of a platinum group metal). Preferably, any such "platinum group metal portion" is the elemental form of a platinum group metal or an alloy containing a platinum group metal, more preferably the elemental form of a platinum group metal.

[0283] Referring to the embodiment of the statement of Invention 3 above and FIG. 1 , the first and second catalytic washcoat layers abut one another without "substantially overlapping between the first and second washcoat layers," the term "substantially overlapping" being intended to include a product in which there are no gaps between the first and second catalytic washcoat coatings. In practice, it is extremely difficult to achieve a completely "gap-free" coating between two composite washcoat layers without some overlap at the junction between them. Thus, actual products made by the method encompassed by the sixth aspect of the present invention may have unintentional overlaps of 1-2 mm up to 15% of their axial length, e.g., up to 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 8%, 6%, 5%, 4%, 3%, 2%, or 1%. The composite oxidation catalyst according to the first aspect therefore extends to products with unintentional overlap up to this dimension. [Example]

[0284] 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 Applicant's WO 99 / 47260, namely, comprising the steps of: (a) placing a containing means over a substrate; (b) introducing predetermined amounts of liquid components into said containing means in the order of either (a) then (b) or (b) then (a); and (c) applying a vacuum to draw the entire amount of liquid components into at least a portion of the substrate and retain substantially all of said amount within the substrate without recycling.

[0285] Example 1 (Comparative Example) A bare cordierite honeycomb flow-through substrate monolith having 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 catalytic washcoat in the following zone configuration: First, a catalytic washcoat slurry (corresponding to a second catalytic washcoat according to the fifth inventive embodiment) comprising an aqueous solution of platinum and palladium nitrates and a 5 wt. % silica-doped alumina support was coated onto the substrate monolith from one end labeled as the discharge end to an axial length of 70% of the total length of the substrate monolith, and the coated substrate monolith was dried in a conventional oven at 100°C for 1 hour. The weight ratio of platinum to palladium in the second catalytic washcoat coating was 8 gft. -3 The total platinum group metal loading was 5:1. No barium was present in the second catalytic washcoat coating.

[0286] Next, another catalytic washcoat slurry (corresponding to a first catalytic washcoat according to the fifth invention embodiment) comprising an aqueous solution of platinum, palladium, and barium acetate nitrate salts and a 5 wt. % silica-doped alumina support was coated onto the substrate monolith from the inlet end to an axial length of 30% of the total length of the substrate monolith. The coating process was controlled so that the axial length of the first catalytic washcoat coating substantially avoided a gap between the first and second catalytic washcoat coatings and achieved a targeted minimum 2 mm overlap of the first washcoat coating with the second washcoat coating. The platinum to palladium weight ratio of the first catalytic washcoat coating was 50 gft. -3 The total platinum group metal loading in the first catalytic washcoat coating was 1:1. The barium loading in the first catalytic washcoat coating was 80 gft -3 The resulting product coated with the first washcoat coating and the second washcoat coating was dried in a conventional oven at 100°C for 1 hour and calcined at 500°C for 1 hour.

[0287] The final product comprises a substrate monolith containing two catalyst washcoat zones arranged axially in series, with a first, high loading front zone at the intake end corresponding to the length of the first catalyst washcoat coating and containing 50 gft of 1Pt:1Pd. -3 of total platinum group metal loading and 80gft -3 The substrate monolith was defined as approximately 30% of the axial length of the substrate monolith with barium, corresponding to the second catalyst washcoat coating length, and 8 gft of 5Pt:1Pd. -3 This was followed axially in series by a second catalyst washcoat zone of approximately 70% of the axial length of the substrate monolith having a total platinum group metal loading of 20 g ft for an overall Pt:Pd weight ratio of 11.8:4, which corresponds to 2.95:1. -3 It was.

[0288] Using EPMA-WDX image analysis, the first catalyst washcoat zone thus prepared was found to have a relatively strong non-uniform distribution of Pd, and to a lesser extent Pt, as well as barium, which decreased vertically toward the surface of the substrate. In other words, both Pd and Ba (to a lesser extent relative to Pt) formed a "crust" on the surface of the washcoat layer upon contact with the gas entering the inlet end of the substrate.

[0289] Example 2 The weight ratio of platinum to palladium in the first catalytic washcoat coating is 50 gft -3 An identical product was made to that disclosed in Example 1, except that the total platinum group metal loading in the first catalytic washcoat coating was 1:2. Using EPMA-WDX image analysis, "crusts" of Pd, Ba, and to a lesser extent Pt were observed.

[0290] Example 3 The first catalytic washcoat coating has a platinum to palladium weight ratio of 50 gft -3 An identical product was made to that disclosed in Example 1, except that the total platinum group metal loading in the first catalytic washcoat coating was 1:3. Using EPMA-WDX image analysis, "crusts" of Pd, Ba, and to a lesser extent Pt were observed.

[0291] Example 4 - Test Method and Results for Exothermic Generation Comparison of the Catalysts of Examples 1-3 Thermal analysis of each of the composite oxidation catalysts prepared according to Examples 1 and 2 was performed using a bench-mounted diesel engine. The engine was operated at 2200 rpm with EUVI B7 fuel (7% biofuel) injected for both engine operation and exhaust gas hydrocarbon enrichment (exothermic production). It was equipped with an exhaust system containing exhaust piping and removable canning into which each of the composite oxidation catalysts could be inserted for testing, with the intake end / first catalyst, high-loading washcoat zone oriented upstream. The engine was a 7-liter EUV 6-cylinder engine producing 235 kW at 2500 rpm. The exhaust system included a "seventh injector" positioned to inject hydrocarbon fuel directly from the engine manifold into the exhaust piping downstream and upstream of the composite oxidation catalyst being tested. This fuel injector is named "seventh injector" because it is in addition to the six fuel injectors associated with the engine's cylinders. Thermocouples were located at the intake to the composite oxidation catalyst and inserted at various axial positions along the centerline of each composite oxidation catalyst's substrate monolith.

[0292] 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 reduced to 720 kg / hr (120,000 hours for the size and volume of the substrate tested). -1 The engine load was controlled so that the set intake exhaust gas temperature was stably maintained at approximately 270°C for approximately 1800 seconds.

[0293] The combined oxidation catalyst was then tested for its ability to generate an exotherm at a stable set temperature by injecting hydrocarbon fuel through a seventh injector that targeted both 600°C and a stable hydrocarbon "slip" at the discharge of the combined oxidation catalyst substrate using a downstream thermocouple and hydrocarbon sensor. The test was stopped when the hydrocarbon slip measured downstream of the combined oxidation catalyst exceeded 1000 ppm C3, regardless of the hydrocarbon chain length in the detected hydrocarbons (the formal carbon chain length in typical diesel fuel is C3). 16The test was stopped when the equivalent of 1000 ppm C3 was detected. 16 If detected, this is 1000 ppm C3(C 16 is equivalent to 5 1 / 3 × C3 hydrocarbons).

[0294] Following the test at an inlet temperature set at approximately 270°C, the system was again preconditioned at an inlet exhaust gas temperature of 490°C for 10 minutes at a flow rate of 1000 kg / hr, followed by rapid cooling and an exotherm test at a second set temperature, e.g., approximately 260°C. This cycle was repeated to test exotherm generation at set temperatures of approximately 250°C, 240°C, and 230°C. The test was stopped either when the combined oxidation catalyst was unable to generate a stable exotherm of 600°C at the combined oxidation catalyst outlet, or when the hydrocarbon slip measured at the combined oxidation catalyst outlet exceeded 1000 ppm(C3).

[0295] The results of the tests conducted on Comparative Example 1 and Examples 2 and 3 are shown in Table 1 below. It will be appreciated that the lower the intake temperature at which stable exotherm can be achieved with acceptable hydrocarbon slip, the more advantageous it is. This is because it increases the design flexibility of the system in that a filter regeneration event can be initiated by a lower intake exhaust gas temperature, i.e., without having to wait until the exhaust gas temperature under normal operating conditions is high enough to initiate filter regeneration, which occurs infrequently under normal operating conditions. Also, overall fuel economy is improved because more hydrocarbons do not need to be injected to achieve the desired exhaust gas temperature at the discharge of the combined oxidation catalyst.

[0296] [Table 1]

[0297] Table 1 shows that the composite oxidation catalysts of Examples 2 and 3 according to the present invention achieve lower and more stable heat generation at inlet temperatures of 272°C and 265°C, and further achieve stable heat generation up to 255°C, compared with the comparative composite oxidation catalyst of Example 1 and the composite oxidation catalyst of Example 2.

[0298] Example 5 Using the same bare substrate monolith as used in Example 2, the first catalytic washcoat coating had a barium loading of 40 gft -3 An identical oxidation catalyst according to the invention was prepared, except that: Using EPMA-WDX imaging, "crusts" of Pd, Ba, and to a lesser extent Pt were observed.

[0299] Example 6 The first catalytic washcoat coating had a barium loading of 120 gft -3 A product identical to that disclosed in Example 2 was prepared, except that: Using EPMA-WDX imaging, "crusts" of Pd, Ba, and to a lesser extent Pt were observed.

[0300] Example 7 - Test method and results for barium loading investigation The oxidation catalysts of Examples 5, 2, and 6 were each tested in the same manner as described above for Example 4. The testing of this Example 7 was performed on a different date than the testing performed for Example 2 reported in Table 1. While the test results of this Example 7 show some differences from the results of Example 2, these are within expected tolerances, and the trends observed and reported in this Example 7 were the same as those seen in all tests performed on the combined oxidation catalysts of the present invention and the comparative catalysts.

[0301] [Table 2]

[0302] A "fail" number is a slip of 1000 ppm C3HC or more. If the normalized value for Example 5 or Example 6 is greater than 1, the result is understood to be better than Example 2; that is, at that inlet temperature, the catalyst slip is less C3HC than Example 2. However, for a normalized result less than 1 for Example 5 or 6, Example 2 is better than the catalyst of Example 5 or 6 at that inlet temperature point.

[0303] As can be seen from the results shown in Table 2, the activity of the catalyst for oxidizing hydrocarbons, as indicated by the amount of slipped hydrocarbons detected downstream of the tested catalyst, varies with barium loading. Furthermore, increasing barium loading did not reduce hydrocarbon slip at all temperatures. This is in contrast to the alkaline earth metal loadings exemplified for use in treating exhaust gases from light-duty diesel engines (see Applicant's WO 2014 / 080200, supra), and these results suggest that the alkaline earth metal concentration for HC oxidation should be increased to approximately 80 gft. -3 The results show that there is no benefit to increasing the amount of barium above 1.6, corresponding to a total PGM to barium mass ratio of 1.6, or a barium to Pt mass ratio of 3.3. In this regard, it is noted from Applicant's WO 2014 / 080200 that NO oxidation can also be affected by increasing the amount of alkaline earth metal in the catalyst composition. Applicant's records show that the barium loading in Example 5-1 of WO 2014 / 080200 is 150 gft -3 Furthermore, the addition of alkaline earth metals in excess of that required to achieve the desired function increases the overall cost of the catalyst by including excess raw materials.

[0304] Next, those skilled in the art will understand that HC oxidation activity over the widest intake temperature range is important because it allows for exothermic generation over the widest available exhaust gas temperature operating range. That is, if engine management can only trigger exothermic generation to regenerate the downstream filter through HC oxidation when the intake exhaust gas temperature is 260°C or higher, this is less desirable than a situation where the trigger temperature is 250°C or higher. In this regard, those skilled in the art will understand that the results of Example 2 are, on balance, the best results of Examples 2, 5, and 6 in this Example 7, because although the higher barium loading catalyst of Example 6 is more active for HC oxidation than Example 2 at higher temperatures (as evidenced by less slipped HC), the result that Example 2 achieves sub-failure HC oxidation / HC slip at the lowest temperature point (250°C) indicates that Example 2 is technically the best oxidation catalyst for the intended purpose / function of the three catalysts tested.

[0305] Example 8 - Evaluation of Guard Beds to Prevent Phosphorus and / or Zinc Contamination of Catalysts (Reference) - Sample Preparation Although not in accordance with the present invention, a catalyst having the structure shown in Figure 5 was used to demonstrate the functional principle of the guard bed feature. A cylindrical cordierite flow-through honeycomb monolith substrate having dimensions of 10.5 inches long by 4 inches diameter was filled with Pt and Pd in ​​a 2:1 weight ratio supported on a 5 wt% silica-doped alumina particulate support, and 80 gft -3 The first catalytic washcoat zone was coated with a first catalytic washcoat layer (6) containing 50 gft of barium on the substrate for 75% of the axial coating length from the intake end (I), and a second washcoat layer (7) containing only Pt supported on a 5 wt. % silica-doped alumina particulate support (no barium) coated for 50% of the axial length of the substrate from the discharge end (O). The first catalytic washcoat zone was coated with 50 gft of barium on the first catalytic washcoat layer (6). -3The composite oxidation catalyst was obtained by impregnating the substrate with a solution of platinum and palladium salts sufficient to achieve a 1:1 weight ratio of Pt to Pd over 25% of the axial length with an additional total PGM loading of 21 gft. -3 had a Pt:Pd weight ratio of 7:5, corresponding to a total platinum group metal loading of 1.4:1. That is, the first catalyst washcoat zone of this Example 8 had a Pt:Pd weight ratio of greater than 1:1.

[0306] Three samples were prepared. The first sample was used as a control without any protective bedding applied. The second sample was used with 0.5 gin -3 The first catalytic washcoat zone (1) had a washcoat of 5 wt. % silica-doped alumina (containing no platinum group metals) (the same silica-doped alumina used in the first catalytic washcoat layer (6) and the second catalytic washcoat layer (7)) coated over a total of 30% of the substrate's axial length from the inlet end of the substrate (I) with a washcoat loading of 1000 Wt. %, i.e., 25% of the axial length of the first catalytic washcoat zone was completely covered with a washcoat coating layer of silica-doped alumina "guard bed," i.e., 120% of the axial length of the first catalytic washcoat zone was covered with a washcoat coating layer. The average pore size of the 5 wt. % silica-doped alumina used was approximately 19 nm.

[0307] 5 wt% silica-doped alumina "guard bed" washcoat loading 1.0g -3 A third sample was prepared similarly to the second sample, except that:

[0308] Each of the three samples was aged in an oven at 650°C in air for 50 hours.

[0309] Example 9 - Evaluation of Guard Beds to Prevent Phosphorus and / or Zinc Contamination of Catalysts (Reference) - Sample Testing Three coated substrate samples prepared according to Example 8 were canned simultaneously in parallel in a unique canning configuration, and the canned substrates were inserted into the exhaust system of a bench-mounted, Euro 2 emission-certified 16-liter diesel engine running on MK1 fuel blended with ZDTP fuel additive to a concentration of 1750 ppm. The substrates were then aged through the engine using the following cycles, calculated to expose the canned substrates overall to 0.5 g of ZDTP per liter of catalyst substrate per cycle: (i) 30 minute "soak" at engine load resulting in a steady state substrate inlet temperature of 470°C. (ii) A 15 minute "soak" at engine load resulting in a steady state substrate inlet temperature of 210°C, followed by 15 minutes at an inlet temperature of 250°C and finally 10 minutes at an inlet temperature of 325°C. (iii) Steps (i) and (ii) were repeated six times.

[0310] The samples were then opened and each sample was tested using the engine described in Example 4 according to the following procedure.

[0311] A "continuous exotherm" test was performed as follows: Each catalyst was conditioned at an inlet temperature of 490°C for 20 minutes, then rapidly cooled to an inlet temperature of 320°C, where the catalyst was held for 10 minutes. Hydrocarbon injection through the seventh injector was then initiated at a rate that resulted in an exotherm of 600°C at the substrate discharge. This exotherm was maintained at steady state for 5 minutes. The hydrocarbon oxidation catalyst digester temperature was then ramped down by continuously adjusting the engine load to achieve an inlet temperature drop of 1°C per minute at a flow rate of 720 kg / h. Operation was terminated when the downstream catalyzed soot filter inlet temperature fell below 425°C or when the hydrocarbon slip analysis limit of 1500 ppm C3 was reached.

[0312] The washcoat coating of the first quarter of the substrate, measured from the intake end of each substrate sample, was analyzed using X-ray fluorescence (XRF) to characterize the washcoat's elemental composition and phosphorus and zinc contamination. The degree of contamination detected was zeroed against an Omnian multi-element reference standard scan. The results are shown in Table 3 below.

[0313] [Table 3]

[0314] Phosphorus contamination was consistent across all three parts, with a maximum difference of approximately 8.0% between any two samples.

[0315] Those skilled in the art will appreciate that the phosphorus contamination achieved using the procedure used in this example is higher than reported in the art through normal use (see above, where post-catalyst samples were found to have 1.0-1.5 wt. % phosphorus contamination at the end of a vehicle's life), but the levels of phosphorus contamination obtained using the procedure described in this Example 9 were comparable to those empirically seen in normal operation at the end of a vehicle's life.

[0316] The results of the continuous heat release test are shown in Table 4 below.

[0317] [Table 4]

[0318] As can be seen from these results, there was only a 5.2°C (2.2%) increase in the inlet temperature required to obtain an exotherm of 500°C or greater for the two samples containing guard bed features compared to the reference catalyst without guard bed features. This indicates that there is a small and substantially insignificant increase in inlet temperature at which engine management can initiate an exotherm-generating event for regeneration of downstream filter components in an exhaust system according to the present invention that includes a composite oxidation catalyst that includes a guard bed feature.

[0319] Also, although identical segments of the oxidation catalyst in the reference and inventive samples have comparable amounts of contaminating phosphorus present, the 1.0 g / in 3 It can also be seen that the sample containing the guard bed with a loading of 0.5 g / in retained significantly higher hydrocarbon oxidation activity compared to the reference (only a 13.9% loss in inlet temperature was required to achieve the 500°C exotherm compared to a 30.3% loss in inlet temperature for the reference sample) (see Table 3). However, the washcoat coating with 0.5 g / in 3 It can also be seen that the samples containing α-tocopherol undergo a similar loss of activity relative to the reference.

[0320] Overall, these results indicate that the 1.0 gin -3 While one skilled in the art would expect that a loading of silica-doped alumina feature applied to the washcoat coating from the intake end of the underlayer comprising the first catalytic washcoat zone of the composite oxidation catalyst according to the first embodiment of the present invention would perform a similar function of preserving the hydrocarbon oxidation activity of the oxidation catalyst, the catalyst tested in this example demonstrates a Pt:Pd weight ratio of 1:1 or greater in the first catalytic washcoat zone, i.e., the function of the guard bed feature is not dependent on the catalytic activity of the underlayer.

[0321] Example 10 - Further evaluation of guard beds to prevent phosphorus and / or zinc contamination of catalysts (reference) The combined oxidation catalyst is 15gft in total. -3 A catalyst was made having a similar formulation and design to the catalyst described in Example 8 (i.e., not in accordance with the present invention), except that the first catalyst washcoat zone still had a Pt:Pd weight ratio greater than 1:1, with a total platinum group metal loading of 7.24:5, corresponding to 1.45:1, but the first catalyst washcoat zone still had a Pt:Pd weight ratio greater than 1:1.

[0322] The following samples were prepared:

[0323] [Table 5]

[0324] The fresh "γ-alumina" of Examples 10.2 and 10.11 had a characteristic average pore diameter of about 13 nm. The fresh "5 wt. % silica-doped alumina" of Examples 10.3, 10.4, 10.10, and 10.12-10.14 had a characteristic average pore diameter of 15 nm. The fresh "wide pore alumina" had a characteristic average pore diameter of about 20 nm. The fresh ceria of Example 10.9 had a characteristic average pore diameter of about 8 nm. The AEI aluminosilicate zeolites of Examples 10.7 and 10.8 had a silica-alumina ratio of about 20. The copper loading in the Cu ion-exchanged AEI aluminosilicate zeolite of Example 10.8 was about 3.8 wt. %. All particulate metal oxide materials used in this example were measured at 100 m 2 The initial specific surface area was over 1 / g.

[0325] The particulate metal oxide used in each guard bed example was milled to have a D90 of less than 20 μm and a D50 (average particle size) of less than 8 μm, a combination that the applicant believes results in an average interparticle pore size within the guard bed that is 10 nm or greater.

[0326] All samples were oven aged for 50 hours in air at 650° C. The examples were tested in the same manner as described above in Example 9. The results are shown in Table 6 below.

[0327] [Table 6]

[0328] As can be seen from the results shown in Table 6, all of the guard bed coated Examples exhibit reduced exothermic activity before phosphorus aging compared to the control (reference) Example 10.1, which has an exothermic failure temperature of 239.0°C. However, Examples 10.2-10.14, which include a guard bed, all performed better than the post-phosphorus aging benchmark (285.9°C). The best performing Examples were those with a reasonable balance of performance between pre-phosphorus aging, e.g., below 252.0°C, and post-phosphorus aging, e.g., below 273.0°C.

[0329] It can also be seen that samples with higher washcoat loadings (eg compare Example 10.4 with 10.3) performed better, as did the examples where the PGMs were supported on a particulate oxide material in a guard bed.

[0330] Those skilled in the art will believe that the guard bed tested in this Example 10, when used in combination with a composite oxidation catalyst according to the first aspect of the present invention, would be expected to provide the same trend in protection against phosphorus contamination observed in this Example 10.

[0331] Example 11 - Investigation of Initial vs. Aging "Δ" NO Oxidation Catalyst Activity with Composition Changes to the Outlet Catalyst Washcoat Zone (Reference) A series of catalysts similar to those described in Example 9, but without a guard bed, were prepared having the structure shown in Figure 5. The only other difference from the catalyst samples of Example 9 was that the composite oxidation catalyst was loaded with a total of 30 gft -3 The second washcoat layer (7) formulation was modified to investigate discharge zone NO oxidation activity, details of which are set forth in Table 7 below. The total platinum group metal loading in all samples in the second washcoat layer of this Example 11 was 12.5 g ft -3 The washcoat loading of the second washcoat layer in all tested samples was equivalent, and the tested second washcoat layer did not contain barium. The total Pt:Pd weight ratio of the entire composite oxidation catalyst was different from the total Pt:Pd weight ratio of the sample in Example 9.

[0332] Each new catalyst was inserted into the test exhaust system of the bench-mounted diesel engine described in Example 4. First, the new catalyst was "conditioned" for 30 minutes at an engine load and speed that produced a catalyst bed temperature of 550°C. The resulting "conditioned" catalyst was then allowed to cool to room temperature. The conditioned initial catalyst was then tested in a load ramp transient test cycle at a constant engine speed of 1400 rpm and increasing space velocity to determine the NO oxidation activity of the combined oxidation catalyst. The NO2 / NO2 ratio detected in the exhaust gas downstream of the combined oxidation catalyst was x was recorded versus the substrate inlet temperature. The tested catalysts were then cooled, opened, and hydrothermally oven-aged at 600°C in air / 10% HO for 140 hours to simulate end-of-life oxidation activity in a vehicle. The aged catalysts were then reinstalled in the exhaust system of a bench-mounted diesel engine, reconditioned, and retested using the same protocol as described for the fresh catalysts.

[0333] [Table 7] †Equivalent to 5.0 wt% MnO2 in the calcined material. * Alumina doped with 5 wt. % silica was impregnated with manganese nitrate solution at a concentration sufficient to achieve the desired calcined manganese weight.

[0334] Example 12 - Further investigation of initial vs. aging "Δ" NO oxidation catalyst activity with compositional changes to the outlet catalyst washcoat zone (reference) A series of catalysts similar to those described in Example 11 and having the structure shown in Figure 5 were prepared. The only difference from the catalyst samples of Example 11 was that the first catalyst washcoat layer (6) contained a total of 20 gft of composite oxidation catalyst. -3 an additional 35 gft -3The first catalytic washcoat zone was obtained by impregnating the substrate with a solution of platinum and palladium salts sufficient to impregnate 25% of the axial length of the substrate, having a 1:1 weight ratio of Pt and Pd. The total platinum group metal loading in all samples in the second washcoat layer of this Example 12 was 7.5 g ft -3 The total Pt:Pd weight ratio of the composite oxidation catalyst was 1.9:1.

[0335] Testing was carried out in the same manner as described above in Example 11, except for the aging of the catalyst. In this Example 12, a fresh "conditioned" catalyst was aged in an oven at 650°C in air for 50 hours.

[0336] [Table 8] †Equivalent to 5.7 wt% MgO / 94.3 wt% Al2O3. As determined by X-ray diffraction (XRD), this material is predominantly single-phase cubic spinel. Some excess Al2O3 may be present. *1 Equivalent to 1.0 wt% MnO2. *2 Equivalent to 3.0 wt% MnO2. *3 Equivalent to 5.0 wt% MnO2.

[0337] Additionally, the composite oxidation catalyst of Example 12 was tested according to the "continuous exotherm" test described in Example 9, but without the ZDTP aging treatment. The results are shown in Table 9 below.

[0338] [Table 9]

[0339] The results shown in Tables 8 and 9 demonstrate that Samples 12.4, 12.5, and 12.6, which comprise preformed manganese-doped substoichiometric mixed magnesium aluminum metal oxides, exhibit a surprising and beneficial combination of reduced NO oxidation activity and improved exotherm production initially versus after aging.

[0340] For the avoidance of any doubt, all documents and the entire contents of all documents cited herein are incorporated by reference into this application.

Claims

1. 1. A composite oxidation catalyst (14, 16, 18, 20) for use in an exhaust system for treating exhaust gases produced by a compression-ignition internal combustion engine (30) for a vehicle, upstream of a particulate matter filter (44, 50) in the exhaust system, the composite oxidation catalyst comprising: a substrate (5) having an overall length L and a longitudinal axis, and having a substrate surface extending axially between a first substrate end (I) and a second substrate end (O); Three or more catalytic washcoat zones (1, 2, 3; or 1, 2, 3, 4) arranged in series on the substrate surface and axially along the substrate surface, １ <Length L that satisfies L １ The first catalytic washcoat zone (1) is defined at one end by a first substrate edge and at its second end by L ２ <Length L that satisfies L ２ the first catalytic washcoat zone (1) comprises a first refractory metal oxide support material and, supported thereon, two or more platinum group metal components comprising both platinum and palladium in a platinum / palladium weight ratio of less than 1; the second catalytic washcoat zone (2) comprises a second refractory metal oxide support material and, supported thereon, one or more platinum group metal components; and the third catalytic washcoat zone (3) comprises a third refractory metal oxide support material and, supported thereon, one or more platinum group metal components; and at its second end, three or more catalytic washcoat zones (1, 2, 3; or 1, 2, 3, 4) defined by the second substrate end (O); Including, a total platinum group metal loading in the first catalytic washcoat zone (1), defined in grams of platinum group metal per liter of substrate volume (g / L), greater than a total platinum group metal loading in the second catalytic washcoat zone (2); a total platinum group metal loading in the third catalytic washcoat zone (3), defined in grams of platinum group metal per liter of substrate volume (g / L), less than a total platinum group metal loading in the second catalytic washcoat zone; and the first catalytic washcoat zone (1) comprising one or more first alkaline earth metal components supported on a first refractory metal oxide support material. Composite oxidation catalyst.

2. comprising four catalytic washcoat zones (1, 2, 3, 4); a fourth catalytic washcoat zone (4) located between the second catalytic washcoat zone (2) and the third catalytic washcoat zone (3); the fourth catalytic washcoat zone (4) comprises a fourth refractory metal oxide support material and one or more platinum group metal components supported thereon, and is bounded at its first end (23) by the second end of the second catalytic washcoat zone and at its second end (17) by the first end of the third catalytic washcoat zone (3), and a total platinum group metal loading in the fourth catalytic washcoat zone (4), defined in grams of platinum group metal per liter of substrate volume (g / L), is greater than the total platinum group metal loading in each of the second catalytic washcoat zone (2) and the third catalytic washcoat zone (3); The composite oxidation catalyst according to claim 1.

3. a first catalytic washcoat layer (6) and a second catalytic washcoat layer (7); The first catalytic washcoat layer (6) comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, ３ <Length L that satisfies L ３ and defined at one end by the first substrate end (I), The second catalytic washcoat layer (7) comprises a refractory metal oxide support material and one or more platinum group metal components supported thereon, ４ <Length L that satisfies L ４ and at its second end is defined by the second substrate end (O), The fourth catalytic washcoat zone includes a two-layer overlap region of the first catalytic washcoat layer and the second catalytic washcoat layer (7), and the third catalytic washcoat zone includes a single layer of the second catalytic washcoat layer (7) that does not constitute the two-layer overlap region. The composite oxidation catalyst according to claim 2.

4. The total platinum group metal loading supported in the first catalytic washcoat zone, calculated as elemental metals, is less than 3.53 g / l (100 g / ft ３ less than The composite oxidation catalyst according to any one of claims 1 to 3.

5. the weight ratio of platinum to palladium in the first catalytic washcoat zone (1) is greater than or equal to 1:3 and less than 1:1; The composite oxidation catalyst according to any one of claims 1 to 4.

6. in each successive catalytic washcoat zone disposed in series along the substrate length L after the first catalytic washcoat zone, the mass ratio of platinum to palladium is greater than that of the immediately preceding catalytic washcoat zone; The composite oxidation catalyst according to any one of claims 1 to 5.

7. Calculated as elemental metal, the total amount of metal on the substrate (5) is 0.18-2.12 g / L (5-60 g / ft ３ ) including the total platinum group metal loading, The composite oxidation catalyst according to any one of claims 1 to 6.

8. the ratio of the total mass of the alkaline earth metal component to the total mass of the platinum group metal component in the first catalytic washcoat zone (1) is less than 1:1; The composite oxidation catalyst according to any one of claims 1 to 7.

9. the first catalytic washcoat zone (1) has 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 surface of the substrate (5) 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 direction perpendicular to the surface of the substrate; The composite oxidation catalyst according to any one of claims 1 to 8.

10. at least the first refractory metal oxide support material comprises heteroatom-doped alumina; The composite oxidation catalyst according to any one of claims 1 to 9.

11. 11. The composite oxidation catalyst of claim 10, wherein the heteroatom-doped alumina is silica-doped alumina.

12. the third catalytic washcoat zone (3) comprises manganese and / or the second catalytic washcoat layer (7) comprises manganese; The composite oxidation catalyst according to any one of claims 1 to 11.

13. a washcoat coating layer (G) extending axially from the first substrate end (I) for protecting at least a portion of the underlying first catalytic washcoat zone from phosphorus and / or zinc contamination in use, the washcoat coating layer (G) having a phosphorus content of 48.8 g / L (0.8 g / in ３ ) a particulate metal oxide loading of more than The composite oxidation catalyst according to any one of claims 1 to 12.

14. 14. The composite oxidation catalyst according to claim 13, wherein said washcoat coating layer (G) supports a platinum group metal.

15. A composite oxidation catalyst according to any one of the preceding claims, wherein the compression ignition internal combustion engine (30) is a compression ignition internal combustion engine for heavy duty diesel vehicles.

16. The composite oxidation catalyst according to any one of claims 1 to 15, wherein the substrate (5) is a honeycomb flow-through substrate monolith.

17. 17. A compression-ignition internal combustion engine (30) for a heavy-duty diesel vehicle, comprising an exhaust system (32), the exhaust system comprising a composite oxidation catalyst according to any one of claims 1 to 16, and a soot filter substrate (44, 50) located downstream of the oxidation catalyst, the first substrate end of the composite oxidation catalyst being oriented upstream.

18. 17. Use of a composite oxidation catalyst (14, 16, 18, 20) according to any one of claims 1 to 16, for heating a soot filter (44, 50) located downstream of the composite oxidation catalyst in an exhaust system (32) of a compression-ignition internal combustion engine for a vehicle, by contacting the oxidation catalyst with exhaust gas containing an increased concentration of hydrocarbon fuel, thereby generating heat from the increased concentration of hydrocarbon fuel in the exhaust gas flowing through the exhaust system relative to normal operating conditions.

19. 1. A method for producing a composite oxidation catalyst, comprising: (a) applying a first catalytic washcoat layer (6) to a surface of a substrate (5) from one end (I, O) of the substrate over a length extending less than the entire length of the substrate, the catalytic washcoat layer (6) comprising a refractory metal oxide support material and one or more platinum group metal components; and (b) a length L defined at one end by a first substrate end (I); １ impregnating said catalytic washcoat layer (6) with a solution containing one or more platinum group metals in a zone one or more alkaline earth metal components are present in said catalytic washcoat layer (6) of step (a) and / or in the impregnation solution used in step (b); The method further comprises the step (a') of applying a second catalytic washcoat layer to the substrate before step (a) or after step (a), but in either case before step (b), wherein the second catalytic washcoat layer is applied to the substrate over a length extending from a second substrate end to less than the entire length of the substrate such that the first catalytic washcoat layer partially overlaps the second catalytic washcoat layer or the second catalytic washcoat layer partially overlaps the first catalytic washcoat layer. The second catalytic washcoat layer comprises a refractory metal oxide support material and one or more platinum group metal components, and the length L of the first catalytic washcoat layer (6) to be impregnated with a solution containing the one or more platinum group metals is １ the zone of formula (I) comprises two or more platinum group metal components comprising both platinum and palladium in a platinum to palladium weight ratio of less than 1; Method for producing a composite oxidation catalyst.

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