Low pgm load diesel oxidation catalyst for exotherm generation

Abstract

A diesel oxidation catalyst includes a monolithic substrate, a first support coating region, a first support coating layer, and a second support coating layer. The first support coating layer extends from the substrate inlet end to a position less than the total axial length L of the substrate, and the second support coating layer extends from the substrate outlet end to a position less than L. The first support coating layer comprises macroporous aluminosilicate zeolite, which includes rings composed of twelve tetrahedral atoms. The first support coating region has a density of 10 g / ft. 3 Up to 40g / ft 3 The total platinum group metal loading has a platinum to palladium weight ratio of 10:1 to 2:1, wherein the axial length of the first carrier coating region is less than the axial length of the second carrier coating layer; the total platinum group metal loading in the first carrier coating region, in g / ft³, is at least twice the total platinum group metal loading in the second carrier coating layer; the total platinum group metal loading on the monolithic substrate is 7 g / ft³. 3 Up to 20g / ft 3 Furthermore, the zeolite loading in the first carrier coating layer is 0.1 g / in. 3 Up to 1.5g / in 3 In the implementation scheme, the first carrier coating area is combined with the first carrier coating layer.

Description

Technical Field

[0001] This invention relates to a diesel oxidation catalyst for use in the exhaust system of a heavy-duty diesel engine, for: oxidizing carbon monoxide (CO) and hydrocarbons (HC) to carbon dioxide (CO2) and water (H2O), particularly exothermic from the generation of HC, for heating a filter substrate in the exhaust system located downstream of the oxidation catalyst; and oxidizing nitric oxide (NO) in the exhaust gas from the heavy-duty diesel engine to nitrogen dioxide (NO2). More specifically, the invention relates to a diesel oxidation catalyst comprising a monolithic substrate, preferably a flow-through substrate having a first (inlet) substrate end and a second (outlet) substrate end and an axial length extending between them; a first carrier coating region comprising both platinum and palladium, extending from the first substrate end to a position less than the axial length of the monolithic substrate; and a second carrier coating layer comprising platinum or both platinum and palladium, extending from the second substrate end to a position less than the axial length of the monolithic substrate. Background Technology

[0002] Internal combustion engines produce substances such as carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx). x Exhaust gases contain pollutants such as particulate matter (PM). Emission standards for pollutants in exhaust gases produced by internal combustion engines, particularly for vehicle engines, are becoming increasingly stringent. There is a need for improved catalysts and exhaust systems that can meet these standards cost-effectively and effectively for treating and removing pollutants from such exhaust gases.

[0003] Exhaust gases from gasoline and diesel engines in automobiles are typically treated with catalysts that: (i) oxidize carbon monoxide (CO) to carbon dioxide (CO2); and (ii) oxidize hydrocarbons (HC) to water (H2O) and carbon dioxide (CO2). Three-way catalysts (TWCs) are commonly used to simultaneously oxidize nitrogen oxides (NOx) in reactions (i) and (ii). x The three-way catalytic converter reduces nitrogen oxides (NOx) in the exhaust gas from gasoline (spark ignition) engines to nitrogen (N2), water (H2O), and carbon dioxide (CO2). Three-way catalytic converters typically include components to promote the reduction of nitrogen oxides (NOx) in the exhaust gas. x Reduced rhodium; and oxygen storage component (OSC), which is typically based on cerium-containing oxides or mixed oxides, used to adsorb and release oxygen from exhaust gases that are slightly lean or slightly richer than the stoichiometric operating conditions of gasoline engines emitting exhaust gases.

[0004] Compared to gasoline engines, exhaust gases from compression ignition engines such as diesel engines are oxygen-rich because the stoichiometric combustion of fuel in the combustion process is lean. Exhaust gases are typically treated with an exhaust gas system containing an oxidation catalyst (often called a diesel oxidation catalyst (DOC)) that performs the oxidation reactions (i) and (ii) described above. Some diesel oxidation catalysts are also designed to oxidize nitric oxide (NO) to nitrogen dioxide (NO2), which can facilitate the removal of NO using additional downstream emission control devices. x The control device is typically a selective catalytic reduction (SCR) catalyst.

[0005] Generally, emission regulations worldwide classify diesel engines based on their duty cycle. Broadly speaking, diesel engines used in passenger vehicles are referred to as "light-duty diesel" vehicles, while those used in trucks and buses are classified as "heavy-duty diesel" engines. Emissions test cycles for light-duty diesel engines typically include a so-called "cold start" test to detect HC emissions; this test is part of, for example, the New European Driving Cycle (NEDC) or serves as the MVEG-B test. Emissions tests for heavy-duty diesel engines do not include this test, primarily because heavy-duty diesel engines emit approximately one-tenth the parts per million (ppm) of hydrocarbons compared to light-duty diesel engines. This difference has led to the inclusion of zeolite components in light-duty diesel oxidation catalysts to adsorb hydrocarbons emitted during "cold starts," which are then desorbed as the catalyst temperature rises as the catalyst as a whole becomes active for HC oxidation (see, for example, WO96 / 040419A1). However, due to the relatively low ppm of hydrocarbons emitted by heavy-duty diesel engines, zeolite is generally not required in heavy-duty diesel oxidation catalyst formulations to meet the required emission standards. Since there are no known technological advantages to including zeolite in heavy-duty diesel oxidation catalysts, and given the relatively high cost of zeolite feedstocks compared to typical catalyst support coating materials such as alumina, commercial heavy-duty diesel oxidation catalyst formulations typically do not contain zeolite.

[0006] Diesel engine exhaust systems include a filter substrate to meet particulate emission standards. Particulate matter trapped on the filter substrate typically needs to be removed through combustion to maintain acceptable back pressure throughout the exhaust system. The process of burning particulate matter on the filter substrate is referred to in the art as "regeneration."

[0007] Regeneration technologies can be broadly categorized into passive, active, and a combination of passive and active methods. In passive systems, the oxidation temperature of particulate matter is reduced to a level at which the filter can automatically regenerate during normal vehicle operation. Examples of such passive systems include catalytic filter media; the addition of catalytic fuel additives so that particulate matter generated by the engine contains a catalyst to promote its auto-ignition; and the generation of nitrogen dioxide (NO2) upstream of the filter to burn the particulate matter retained on the filter: the particulate matter burns in NO2 at a lower temperature than in oxygen. This is known as CRT (Continuous Regeneration Technology). ® Effects (see, for example, EP0341832).

[0008] The active system proactively triggers filter regeneration by raising the temperature of particulate matter trapped in the filter. This can be achieved by burning hydrocarbon fuel already carried on the vehicle and / or by electric heating. Two methods for burning fuel include in-cylinder engine management methods, such as late-cycle injection of additional fuel; or injecting and burning fuel in the exhaust gases, i.e., after the exhaust gases have left the engine cylinders themselves.

[0009] In passive-active systems, compared to non-catalytic active systems, "passive" filters are catalysts or upstream (CRTs) ® Active regeneration catalysts, such as those with enhanced NO oxidation effects, allow for active regeneration at lower exhaust gas temperatures and / or for shorter durations. In either case, the fuel economy losses associated with active regeneration can be minimized: net savings include the additional cost of the catalyst. Regeneration at lower temperatures also reduces thermal stress and increases filter life.

[0010] This invention relates to an oxidation catalyst for generating exothermic compounds from the combustion of hydrocarbons in a passive-active exhaust system.

[0011] The applicant’s WO2014 / 132034A1, WO2020 / 260669A1 and WO2021 / 074605A1 disclose an oxidation catalyst comprising a catalyst layer having a non-uniform distribution of a first noble metal (e.g., palladium) in a direction perpendicular to the surface of a substrate.

[0012] US Patent Publication No. 2012 / 213674A1 discloses a catalyst for purifying exhaust gases from diesel engines, particularly an oxidation catalyst, which is especially suitable for purifying exhaust gases from heavy-duty trucks when an additional exhaust gas purification unit (such as a particulate filter and / or a nitrogen oxide reduction catalyst) is installed downstream of the oxidation catalyst. The catalyst comprises two catalytically active coatings with different compositions, only one of which is in direct contact with the outgoing exhaust gases. The coating (1) in direct contact with the outgoing exhaust gases is platinum-rich and contains a greater total amount of precious metals (platinum and palladium) than the coating (2) which is not in direct contact with the outgoing exhaust gases. The disclosure claims that the platinum-rich coating (1) exhibits extremely high oxidation capacity, particularly in NO oxidation, while the coating (2) not in direct contact with the outgoing exhaust gases ensures good “heating performance” of the catalyst. Embodiments of this disclosure include a monolithic substrate and a second (top) carrier coating, the monolithic substrate being continuously coated with a first carrier coating layer from one end to the other, and the second (top) carrier coating being continuously applied in layers from one end to the other, such that the second carrier coating layer is completely carried by the first (bottom) carrier coating layer.

[0013] US Patent Publication No. 2010 / 00290964A1 discloses a Pd-rich diesel oxidation catalyst and its application as a catalyst for oxidizing CO and HC emissions (including those for exothermic generation) from compression ignition / diesel engines. The catalyst comprises a substrate; and a bottom coating layer containing a refractory oxide support, optional zeolite, optional oxygen storage material, and a main catalytic metal selected from the group consisting of platinum, palladium, iridium, rhodium, ruthenium, alloys thereof, and mixtures thereof; and an outer coating layer containing a refractory oxide support, optional zeolite, optional oxygen storage material, and a main catalytic metal selected from the group consisting of platinum, palladium, iridium, rhodium, ruthenium, alloys thereof, and mixtures thereof, wherein the Pd to Pt ratio of the outer coating layer is greater than that of the bottom coating layer. The catalyst is claimed to be characterized by improved performance and hydrothermal durability, these objectives being achieved through a layered design to eliminate cryogenic catalyst quenching (exothermic loss) caused by toxic HC substances in the exhaust gas stream. Some embodiments are characterized in that a 50% substrate axial length outer coating layer is applied over a 100% substrate axial length undercoat layer.

[0014] WO2010 / 118125A1 discloses an oxidation catalyst composite for treating exhaust gases from a diesel engine. This oxidation catalyst composite comprises at least two support coating layers. The first support coating contains a palladium component, and the second support coating contains platinum, with at least about 50% of the total platinum content located at the rear of the catalyst. Examples include those with a concentration of 110 g / ft. 3Pure platinum carrier coating and 0.25 g / in 3 A complex consisting of a 50% axial length inlet region of H-β zeolite; or a 50% axial length inlet region containing 150 g / ft 3 Platinum and palladium in a 1:2 weight ratio and 0.25 g / in 3 The carrier coating is composed of H-β zeolite. However, WO2010 / 118125A1 does not mention that the disclosed catalyst can be used to generate exothermic or thermal energy from additional hydrocarbons introduced into the exhaust gas, and none of the provided examples illustrate such a use.

[0015] WO2014 / 151677A1 discloses a partitioned diesel oxidation catalyst complex comprising a first carrier coating zone with a Pt / Pd ratio of less than 3:1 and a PGM loading at least twice the PGM loading of a second carrier coating zone. This first carrier coating zone can be used to generate exothermic heat for regenerating a downstream particulate filter. No specific disclosure or embodiment includes any zeolite in either carrier coating zone.

[0016] US Patent Publication No. 2008 / 045405A1 discloses a diesel oxidation catalyst for a light-duty diesel engine comprising two distinct carrier coating layers having two significantly different Pt:Pd ratios, and makes no mention of using the catalyst for exothermic generation or heating of downstream exhaust system components. The catalyst composite in the embodiments comprises a top layer and a bottom layer. One such embodiment comprises a top carrier coating having a content of 55.1 g / ft. 3 The total loading and the 3:1 platinum to palladium weight ratio and 0.4 g / in 3 H-β zeolite; and a bottom layer containing 56 g / ft. 3 The weight ratio of platinum and palladium is 1.4:1. As described, the top and bottom layers can be rearranged such that the top layer is in the upstream region of the substrate and the bottom layer is in the downstream region of the substrate.

[0017] For example, it is known from the applicant’s WO2006 / 056811A1, WO2020 / 260669A1 and WO2021 / 074605A1 that, for the generation of exothermic heat from the combustion of hydrocarbons to heat the downstream filter substrate, the equivalent weight of platinum to palladium or the relatively low weight ratio of palladium-rich platinum is more active than its platinum-rich combination.

[0018] As of the priority date of this application, the “spot price” for palladium was US$1,020 per ounce and the “spot price” for platinum was US$945 per ounce.

[0019] Given the higher price of palladium relative to platinum, there is a general market demand for low-cost heavy-duty diesel oxidation catalysts, i.e., catalysts with a high total platinum to palladium weight ratio that exhibit activity as close as possible to that of Pd-rich oxidation catalysts with a platinum to palladium weight ratio for hydrocarbon generation and retention. There is also a general market demand for reducing the total amount of expensive platinum group metals in such oxidation catalysts while still meeting the desired ability to generate heat. To these purposes, the inventors of the applicant conducted research and, quite surprisingly, discovered that macroporous aluminosilicate zeolites comprising rings of twelve tetrahedral atoms can advantageously contribute to exothermic generation activity, particularly in heavy-duty diesel exhaust, at lower total platinum group metals and a relatively high platinum to palladium weight ratio. This technical effect has not been observed in similar Pd-rich oxidation catalysts. Furthermore, this technical effect differs from the known effect of passively adsorbing (or trapping) hydrocarbons in the zeolite component of light-duty diesel oxidation catalysts at relatively low exhaust temperatures and releasing the adsorbed hydrocarbons at higher exhaust temperatures (see Example 1 below). Summary of the Invention

[0020] In this regard, in a first aspect, the present invention provides a diesel oxidation catalyst for use in the exhaust system of a heavy-duty diesel engine, for: oxidizing carbon monoxide (CO) and hydrocarbons (HC) to carbon dioxide (CO2) and water (H2O), including exothermic generation from HC for heating a filter substrate disposed downstream of the oxidation catalyst in the exhaust system; and oxidizing nitric oxide (NO) in the exhaust gas from the heavy-duty diesel engine to nitrogen dioxide (NO2), the diesel oxidation catalyst comprising:

[0021] (i) A monolithic substrate, preferably a flow-through substrate, having a first substrate end and a second substrate end and an axial length extending between them;

[0022] (ii) A first carrier coating layer, which is at least partially directly supported by the surface of the monolithic substrate and extends from the first substrate end to a position less than the axial length of the monolithic substrate, the first carrier coating layer comprising macroporous aluminosilicate zeolite comprising a ring size consisting of twelve tetrahedral atoms.

[0023] (iii) A first carrier coating region extending from the first substrate end to a position less than the axial length of the monolithic substrate, and comprising both platinum and palladium, as well as particulate refractory metal oxide carrier material, wherein at 10 g / ft 3 Up to 40g / ft 3 With a total platinum group metal loading, the platinum to palladium weight ratio in the first carrier coating region is 10:1 to 2:1; and

[0024] (iv) A second carrier coating layer, which is at least partially directly supported by the surface of the monolithic substrate and extends from the end of the second substrate to a position less than the axial length of the monolithic substrate, the second carrier coating layer having a platinum to palladium weight ratio of 1:0 to 2:1 and a particulate refractory metal oxide material for supporting platinum or both platinum and palladium, wherein the second carrier coating layer is axially adjacent to the first carrier coating layer, the first carrier coating layer overlaps the second carrier coating layer, or the second carrier coating layer overlaps the first carrier coating layer.

[0025] The axial length of the first carrier coating region is less than the axial length of the second carrier coating layer; the first carrier coating region contains g / ft 3 The total platinum group metal loading is at least twice the total platinum group metal loading in the second carrier coating layer; the total platinum group metal loading on the entire substrate is 7 g / ft. 3 Up to 20g / ft 3 Furthermore, the zeolite loading in the first carrier coating layer is 0.1 g / in. 3 Up to 1.5g / in 3 .

[0026] The applicant's inventors discovered a technical effect that has not been recognized in the prior art, in which zeolites are included due to their known hydrocarbon retention properties; and / or zeolites with relatively high g / ft 3 Combination of platinum group metal loading and / or Pt:Pd weight ratio relative to Pd enrichment.

[0027] According to a second aspect, the present invention provides an exhaust system for a heavy-duty diesel engine, the exhaust system comprising a diesel oxidation catalyst according to a first aspect of the present invention and a filter substrate disposed downstream of the diesel oxidation catalyst, wherein a first substrate end of the diesel oxidation catalyst is oriented to the upstream side.

[0028] A third aspect of the invention provides a heavy-duty diesel engine comprising an exhaust system according to a second aspect of the invention.

[0029] According to a fourth aspect, the present invention provides the use of a diesel oxidation catalyst comprising: (i) a monolithic substrate, preferably a flow-through substrate having a first substrate end and a second substrate end and an axial length extending therebetween; (ii) a first carrier coating layer at least partially directly supported by the surface of the monolithic substrate and extending from the first substrate end to a position less than the axial length of the monolithic substrate, the first carrier coating layer comprising macroporous aluminosilicate zeolite comprising a ring size consisting of twelve tetrahedral atoms; and (iii) a first carrier coating region extending from the first substrate end to a position less than the axial length of the monolithic substrate and comprising both platinum and palladium and a particulate refractory metal oxide carrier material, wherein at 10 g / ft 3 Up to 40g / ft 3 Under the total platinum group metal loading, the platinum to palladium weight ratio in the first carrier coating region is 10:1 to 2:1; and (iv) a second carrier coating layer, which is at least partially directly supported by the surface of the monolithic substrate and extends from the end of the second substrate to a position less than the axial length of the monolithic substrate, the second carrier coating layer having a platinum to palladium weight ratio of 1:0 to 2:1 and a particulate refractory metal oxide material for supporting platinum or both platinum and palladium, wherein the second carrier coating layer is axially adjacent to the first carrier coating layer, the first carrier coating layer overlaps with the second carrier coating layer, or the second carrier coating layer overlaps with the first carrier coating layer; wherein the axial length of the first carrier coating region is less than the axial length of the second carrier coating layer; the first carrier coating region contains g / ft 3 The total platinum group metal loading is at least twice the total platinum group metal loading in the second carrier coating layer; the total platinum group metal loading on the entire substrate is 7 g / ft. 3 Up to 20g / ft 3 Furthermore, the zeolite loading in the first carrier coating layer is 0.1 g / in. 3 Up to 1.5g / in 3 It is used to generate exothermic hydrocarbons from the exhaust gas of heavy-duty diesel engines. Attached Figure Description

[0030] Figure 1This is a schematic diagram of a diesel oxidation catalyst 10 according to a first preferred embodiment of a first aspect of the invention. The diagram shows a cross-section of a single channel through a flow-through monolithic substrate (e.g., a cordierite monolithic substrate, also known as a "honeycomb" substrate). In this art, the number of channels in such substrates is typically expressed as pores per square inch (cpsi). The channel walls 12 of the flow-through monolithic substrate are indicated by dashed lines, defining the hollow portions of the channels 14. The channel wall surfaces of the monolithic substrate directly support a first carrier coating layer 16, which in this embodiment comprises a first carrier coating region, and vice versa. The first carrier coating layer 16 is coated over 25% of the axial length of the monolithic substrate. The first carrier coating layer contains barium, 0.7 g / in 3 β or zeolite Y aluminosilicate zeolite, alumina particulate refractory metal oxide carrier material and at 25 g / ft 3 The total platinum group metal loading is 4:1 in weight ratio of platinum and palladium. The first carrier coating layer 16 is oriented upstream, as indicated by the flow direction arrow. The second carrier coating layer 18 comprises alumina particulate refractory metal oxide carrier material, barium, and at a total loading of 4 g / ft... 3 A platinum and palladium layer with a total platinum group metal loading and a weight ratio of 6:1 is positioned downstream of the first carrier coating zone / layer 16 and coated over 75% of the axial length of the bulk substrate, starting from its outlet end. The axial lengths of the first carrier coating zone / layer and the second carrier coating layer are chosen to be adjacent to each other; however, during manufacturing, a relatively small overlap between the first and second carrier coating layers on the other is permissible, provided there is no axial gap between the two layers: axially, the two layers should at least be in contact; and

[0031] Figure 2 This is also a schematic diagram of a diesel oxidation catalyst 19 according to a second preferred embodiment of the first aspect of the invention. A cross-section of a single channel through a flow-through monolithic substrate is shown. Figure 2 and Figure 1 Shared features use the same reference numerals. Figure 2 Contains 1.0g / in 3 A first carrier coating layer 20, containing β- or γ-aluminosilicate zeolite, is applied from its inlet end to 50% of the axial length of the bulk substrate. In this embodiment, the first carrier coating region 22 is composed of a third carrier coating layer 22 (and vice versa), applied on top of the first carrier coating layer from the inlet end of the first carrier coating region to 40% of the axial length of the bulk substrate. The third carrier coating layer 22 comprises barium, alumina particulate refractory metal oxide carrier material doped with 5% by weight of silica, and a loading of 40 g / ft. 3The total platinum group metal loading is 5:1 of platinum and palladium. The second carrier coating layer 24 is applied from the downstream end of the substrate to 60% of the axial length of the substrate. That is, the third carrier coating 24 is intended to be axially adjacent to the third carrier coating layer 22 and overlap the first carrier coating layer below by 10% of the axial length, and some processing overlap is allowed between the third carrier coating layer (20) and the second carrier coating layer (22), that is, the second carrier coating layer is at least adjacent to the third carrier coating layer, so there is no "gap" between them. The second carrier coating layer 22 comprises alumina particulate refractory metal oxide carrier material doped with 5% by weight of silica and at 10 g / ft 3 Platinum and palladium (without barium) in a total platinum group metal loading ratio of 6:1. Detailed Implementation

[0032] The monolithic substrate used in this invention can be a flow-through or so-called "honeycomb" substrate, i.e. a metal or ceramic substrate having axially extending channels open at both ends, or a wall-flow filter, but preferably a flow-through substrate.

[0033] According to a first aspect of the invention, the platinum to palladium weight ratio in the first carrier coating region is preferably from 7:1 to 2.5:1. The preference for this range is illustrated in Example 3 below, which compares a sample according to the invention with comparative sample 13.

[0034] The particulate refractory metal oxide support material in the first support coating region, the first support coating layer, the second support coating layer, or the third support coating layer can each be independently selected from the group consisting of: alumina, magnesium oxide, silicon dioxide, zirconium oxide, titanium dioxide, and composite oxides or mixed oxides consisting of any two or more of them. That is, the support material of each of the first region, the first support coating layer, the second support coating layer, and the third support coating layer can be the same as or different from each other. In principle, any suitable particulate refractory metal oxide support material can be used as a particulate refractory metal oxide support material. However, the inclusion of a dopant can stabilize the particulate 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. Generally speaking, the dopant is different from the refractory metal oxide (i.e., the cation of the refractory metal oxide). Therefore, for example, when the refractory metal oxide is titanium dioxide, the dopant is not titanium or its oxide.

[0035] When a refractory metal oxide support material is doped with a dopant, the refractory metal oxide support material typically contains a total dopant content of 0.1 wt% to 10 wt%. The total dopant content is preferably 0.25 wt% to 7 wt%, more preferably 2.5 wt% to 6.0 wt%. Preferably, the dopant for alumina is silicon dioxide, because oxidation catalysts containing such support materials bonded to platinum group metals and alkaline earth metals (barium or strontium) promote oxidation reactions such as CO and hydrocarbon oxidation.

[0036] The total platinum group metal loading in the first carrier coating zone is preferably 10 g / ft. 3 Up to 30g / ft 3 The basis for this preferred embodiment can be seen from the trends shown in Table 3 of Example 3 regarding the results of Sample 7 and Comparative Sample 6; the results of Sample 9 and Comparative Sample 8; and the results of Comparative Samples 10 and 11. Specifically, it can be seen that as the platinum group metal loading in the front zone (corresponding to the combination of the first carrier coating layer and the first carrier coating zone of the first aspect of the invention) increases, the inlet temperature corresponds to an outlet temperature of ≤500°C; and the inlet temperature corresponding to ≤800 ppm hydrocarbon slip increases for the sample containing zeolite in the front zone compared to the corresponding comparative sample without zeolite in the front zone. Not wishing to be bound by theory, the applicant believes that this phenomenon is likely caused by zeolite “trapping” palladium within the carrier coating layer (even at a Pt:Pd weight ratio such as 3:1 rich in Pt), rather than by allowing palladium to migrate to the exposed surface of the layer during coating drying in the manufacturing process. This effect is described in the applicant’s WO2014 / 132034A1. For similar reasons, the applicant prefers a total platinum group metal loading of 7 g / ft across the entire monolithic substrate. 3 Up to 15g / ft 3 .

[0037] In this regard, preferably, in the diesel oxidation catalyst according to the first aspect of the invention, the first support coating region comprises a catalyst layer having an exposed upper surface and a supported lower surface, and a non-uniform distribution of palladium that decreases from the exposed upper surface to the supported lower surface in a direction perpendicular to the surface of the bulk substrate. The vertical gradient of palladium at the exposed surface and within the layer can be determined by electron probe microscopy (EPMA-WDX) using wavelength dispersive X-ray spectroscopy.

[0038] This was confirmed by samples 1 to 13, 17 and 18 in Examples 2, 3 and 4 below. Figure 1 In the first preferred embodiment illustrated schematically, the first carrier coating region comprises a first carrier coating layer, and the zeolite loading in the first carrier coating layer is 0.1 g / in. 3 Up to 1.0 g / in 3That is, the first carrier coating layer and the first carrier coating region are identical and have the same characteristics. Preferably, the zeolite loading in the first carrier coating layer is 0.3 g / in. 3 Up to 0.8g / in 3 The reason for this preferred option can be seen from the comparison of the results of samples 4 and 5 in Table 3 below, where the zeolite loading ranges from 0.5 g / in 3 Increased to 1.0 g / in 3 No significant improvement was provided in reducing the exothermic generation temperature. In Sample 5, zeolite is a more expensive carrier coating component than alumina carrier material doped with silica, so unless the inclusion of zeolite has functional benefits, producing the catalyst with less zeolite is cheaper overall.

[0039] In a first preferred embodiment, the first carrier coating region may extend from the first substrate end to 15% to 45% of the axial length of the bulk substrate. Comparative examples of samples 7 (33%) and 18 (30%) demonstrate that the objectives of the invention can still be achieved even with this feature altered. In this respect, the first carrier coating region preferably extends from the first substrate end to 20% to 40% of the axial length of the bulk substrate.

[0040] Examples 14 to 16 are shown in Figure 2 In a second preferred embodiment of the first aspect of the invention, schematically illustrated, the first carrier coating region comprises a third carrier coating layer disposed in a layer directly coated on top of the first carrier coating layer, and the zeolite loading in the first carrier coating layer is 0.2 g / in. 3 Up to 1.0 g / in 3 Wherein, as applied, the first carrier coating layer does not contain platinum group metals. "As applied" herein means that platinum group metals are not intentionally contained in the carrier coating slurry forming the first carrier coating layer of this embodiment. However, in the finished product, it cannot be ruled out that some platinum group metals may migrate from the upper third carrier coating layer to the lower first carrier coating layer during processing, for example, by wicking. The advantage of the absence of platinum group metals in the first carrier coating layer is that, at a constant platinum group metal loading, the exothermic generation temperature is advantageously better than the exothermic generation temperature at which platinum group metals transfer from the third carrier coating layer to the first carrier coating (lower) layer. This can be seen from the results of sample 16 in Table 6 below and the comparison of samples 14 and 15.

[0041] As shown in Sample 16, the third carrier coating layer can extend from the first substrate end to 15% to 45% of the axial length of the entire substrate, preferably 20% to 40%.

[0042] Also as shown in sample 16 and as shown in sample 16 Figure 2As shown, the first carrier coating layer can extend at least the axial length of the third carrier coating layer. In fact, as... Figure 2 As shown, preferably, the first carrier coating layer is longer in the axial direction than the third carrier coating layer, and the second carrier coating layer overlaps with the first carrier coating layer. In this respect, the first carrier coating layer may extend 30% to 60% of the axial length of the bulk substrate, and in conjunction with this, the third carrier coating layer extends 15% to 45%, preferably 20% to 40%, of the axial length of the bulk substrate from the end of the first substrate.

[0043] In a first or second preferred embodiment of the first aspect of the invention, the second carrier coating layer may extend from 85% to 55% of the axial length of the bulk substrate, such that the second carrier coating layer is axially adjacent to the first carrier coating layer, and the first carrier coating layer overlaps with the second carrier coating layer or the second carrier coating layer overlaps with the first carrier coating layer. As shown in Sample 16, the second carrier coating layer preferably extends from 80% to 60% of the axial length of the bulk substrate.

[0044] The macroporous aluminosilicate zeolite in the first carrier coating layer can have... BEA, FAU, or MOR skeleton type codes, but preferably... BEA. The preferred FAU zeolite is zeolite Y; and an example of MOR zeolite is mordenite, preferably... BEA zeolite is a β-zeolite. It should be understood that the name " BEA "" indicates zeolite with symbiotic organisms (formerly referred to as "disordered" by the International Zeolite Association). For more information, please see the International Zeolite Association website. https: / / europe.iza- structure.org / IZA-SC / DO_structures / DO_family.php?IFN=Beta .

[0045] When the macroporous aluminosilicate zeolite in the first carrier coating layer is When making a BEA (Best Practices) decision, the preferred option is... BEA's silica to alumina ratio (SAR) is 10 to less than 40, for example 10 to 39, optionally 15 to 35, and preferably 20 to 33. This is because the applicant has discovered that, with... Compared to equivalent catalysts with a SAR of 40 or higher, the present invention contains catalysts with a SAR of less than 40. BEA's aged diesel oxidation catalyst exhibits a better exothermic quenching temperature (as described in Example 5) and is a more active exothermic generation catalyst. Not wishing to be bound by theory, the applicant believes that this technical effect may be due to a lower SAR (e.g., 28.5). BEA is 40 times that of SAR. BEA has relatively better thermal stability.

[0046] In the first and second preferred embodiments, the total carrier coating load in the first carrier coating zone can be 0.5 g / in. 3 Up to 2.5g / in 3 When the first carrier coating region consists of a first carrier coating layer, the total carrier coating loading includes both zeolite loading and particulate refractory metal oxide carrier material. In this respect, the loading of particulate refractory metal oxide carrier material in the first carrier coating region can itself be 0.5 g / in. 3 Up to 2.5g / in 3 For example, zeolite is absent in the first carrier coating region, as in the second preferred embodiment. The loading of the particulate refractory metal oxide carrier material in the first carrier coating region is preferably 0.8 g / in. 3 Up to 2.0g / in 3 See, for example, sample 2 of the first preferred embodiment; and sample 16 of the second preferred embodiment. A higher loading of the particulate refractory metal oxide carrier material ensures sufficient surface area to achieve the desired (i.e., “fresh”) platinum group metal dispersion and reduces platinum group metal sintering during hydrothermal aging, which simulates in-situ aging, i.e., aging during use. However, at relatively low platinum group metal loadings, higher platinum group metal dispersion can reduce mass transfer of gas to the active sites on the elemental platinum group metal particles. Appropriate selection of the loading of the particulate refractory metal oxide carrier material and its hydrothermal aging durability can be determined using conventional optimization methods.

[0047] Preferably, the first carrier coating region contains strontium or barium, more preferably barium. The relevant loading of strontium or barium is 50 g / ft. 3 Up to 175g / ft 3 Preferably 75g / ft 3 Up to 125g / ft 3 As is known from the applicant's WO2020 / 260669A1, the combination of barium and strontium with Pt-rich platinum and palladium can improve exothermic generation.

[0048] Preferably, the second carrier coating layer further comprises strontium or barium, more preferably barium. The preferred loading of strontium or barium is 50 g / ft. 3 Up to 175g / ft 3 Preferably 75g / ft 3 Up to 125g / ft 3 .

[0049] In order to avoid any unintended consequences from catalyst technologies designed for gasoline (spark ignition) engines or sulfur-intolerant diesel oxidation catalysts, the applicant has included two definitions to exclude such catalysts: (i) the diesel oxidation catalyst according to the invention is rhodium-free; and (ii) the diesel oxidation catalyst according to the invention is oxygen-storing components (OSC) as defined below.

[0050] Methods for preparing diesel oxidation catalysts according to the present invention are known in the art and include the applicant's WO 1999 / 047260A1, namely the steps of: (a) positioning a receiving device on top of a monolithic substrate, (b) quantitatively adding a predetermined amount of liquid component to the receiving device (2) in the order of (a) then (b) or (b) then (a), and (c) drawing all said amount of liquid component into at least a portion of the monolithic substrate by applying a vacuum, and retaining substantially all said amount within the monolithic substrate without recirculation. See also WO 2007 / 077462; and WO 2011 / 080525 (for monolithic substrates for coated wall-flow filters). Similarly, conditions for drying and calcining the carrier coating are also well known.

[0051] A method for obtaining the feature “a first carrier coating region comprising a catalyst layer having an exposed upper surface and a carrier lower surface, and a non-uniform distribution of palladium, which decreases from the exposed upper surface to the carrier lower surface in a direction perpendicular to the surface of the bulk substrate” is disclosed in WO2014 / 132034A1, namely: (a) providing an aqueous slurry comprising a first carrier material precursor, a first noble metal component, and a second noble metal component; (b) applying the aqueous slurry onto a substrate to form a coating; and (c) drying and calcining the coating under conditions that allow at least the first noble metal component to flow toward or away from the substrate (refer to Example 1 and Comparative Example 2 therein).

[0052] In the exhaust system of a second aspect of the invention, the system may include an injector for injecting hydrocarbons into exhaust gases flowing downstream of the engine manifold and upstream of a first base end; and a hydrocarbon source for generating exothermic fuels through combustion of the hydrocarbons on an oxidation catalyst. Alternatively, the microprocessor component of the engine control unit may be pre-programmed in a variable manner during use to control fuel injection timing, such as generating multiple injections during an engine cycle. As the name suggests, multiple injections replace a single injection event with multiple discrete injection events. Injection events that occur after the main injection are generally referred to as post-injection events, which allow additional unburned hydrocarbons to be expelled from the engine cylinders to achieve exothermic fuel generation on the diesel oxidation catalyst.

[0053] definition

[0054] The term "oxygen storage component" (OSC) in this document refers to particulate matter having multiple valence states and capable of actively reacting with oxidants (such as oxygen or nitrous oxide) under oxidizing conditions or with reducing agents (such as carbon monoxide (CO) or hydrogen) under reducing conditions. Typically, the OSC will contain one or more reducible oxides of one or more rare earth metals. Examples of suitable OSCs include cerium dioxide itself, zirconium oxide itself, and combinations thereof (such as mixed oxides or composite oxides of cerium dioxide and zirconium oxide). Praseodymium oxide may also be included as an OSC or promoter. The OSC may include one or more promoters or modifiers, such as Y, La, Nd, Sm, Pr, and combinations thereof.

[0055] Heavy-duty diesel engine

[0056] To avoid doubt, the heavy-duty diesel engine according to the third aspect of the invention may use any definitions set forth in the "Background Art" section above. Thus, for example, if the patent application is directed to Japan, the restrictions on heavy-duty diesel vehicles required by Japanese emission standards may be incorporated into the definition of the engine or vehicle claim. The same applies to regulations in Europe or the United States, etc. To further avoid doubt, the heavy-duty diesel engine used in this invention is not designed for normal operation or desulfurization of a lean / rich cycle suitable for lean NOx trap (LNT) catalysts (i.e., catalysts containing relatively high amounts of cerium dioxide, alkaline earth metals, and / or alkali metal carbonates or oxides to adsorb NOx thereon under lean operating conditions). In a preferred arrangement, the exhaust system according to the invention does not include an LNT.

[0057] The heavy-duty diesel engine according to the third aspect of the invention can be a homogeneous charge compression ignition (HCCI) engine, a premixed charge compression ignition (PCCI) engine, or a low-temperature combustion (LTC) engine. Preferably, the diesel engine is a conventional (i.e., traditional) diesel engine, such as a diesel engine employing common rail fuel injection.

[0058] The term "light-duty diesel vehicle (LDV)" is defined in U.S. or EU regulations. In the United States, a light-duty diesel vehicle (LDV) is a diesel vehicle with a gross vehicle weight of ≤8,500 pounds (US lbs).

[0059] In Europe, light-duty diesel vehicles are defined as vehicles with a reference mass of ≤2610 kg (EU5 / 6) in categories M1, M2, N1 and N2.

[0060] In the United States, heavy-duty diesel vehicles (HDVs) are defined in regulations as diesel vehicles with a gross vehicle weight rating of >8,500 pounds (US lbs) within federal jurisdiction and >14,000 pounds in California (models from 1995 onwards).

[0061] In Europe, heavy-duty diesel vehicles are defined as vehicles designed and manufactured for the transport of goods with a maximum mass (i.e., the "technically permissible maximum load capacity") exceeding 3.5 tons (i.e., metric tons) but not exceeding 12 tons (N2 category) or 12 tons (N3 category), i.e., trucks; or vehicles designed and manufactured for the transport of passengers, having more than eight seats in addition to the driver's seat, and having a maximum mass not exceeding 5 tons (M2 category); or, according to EU regulations (Council Directive 2007 / 46 / EC), exceeding 5 tons (M3 category), i.e., buses and coaches. China widely follows the European definition.

[0062] In Japan, HDV is a type of heavy commercial vehicle defined as a vehicle with a gross vehicle weight greater than 7,500 kg.

[0063] In South Korea, emission standards for heavy-duty vehicles are based on European standards, therefore the aforementioned European definitions apply.

[0064] In Brazil, an HDV is a motor vehicle used to transport passengers and / or goods with a maximum gross vehicle weight exceeding 3,856 kg or a curb weight exceeding 2,720 kg.

[0065] In India, an HDV is a vehicle with a gross vehicle weight greater than 3,500 kg.

[0066] The invention may also be defined according to one or more of the following definitions:

[0067] 1. A diesel oxidation catalyst for use in the exhaust system of a heavy-duty diesel engine, for: oxidizing carbon monoxide (CO) and hydrocarbons (HC) to carbon dioxide (CO2) and water (H2O), including exothermic generation from HC for heating a filter substrate disposed downstream of the oxidation catalyst in the exhaust system; and oxidizing nitric oxide (NO) in the exhaust gas from the heavy-duty diesel engine to nitrogen dioxide (NO2), the diesel oxidation catalyst comprising:

[0068] (i) A monolithic substrate, preferably a flow-through substrate, having a first substrate end and a second substrate end and an axial length extending between them;

[0069] (ii) A first carrier coating layer, which is at least partially directly supported by the surface of the monolithic substrate and extends from the first substrate end to a position less than the axial length of the monolithic substrate, the first carrier coating layer comprising macroporous aluminosilicate zeolite comprising a ring size consisting of twelve tetrahedral atoms.

[0070] (iii) A first carrier coating region extending from the first substrate end to a position less than the axial length of the monolithic substrate, and comprising both platinum and palladium, as well as particulate refractory metal oxide carrier material, wherein at 10 g / ft 3 Up to 40g / ft 3 With a total platinum group metal loading, the platinum to palladium weight ratio in the first carrier coating region is 10:1 to 2:1; and

[0071] (iv) A second carrier coating layer, which is at least partially directly supported by the surface of the monolithic substrate and extends from the end of the second substrate to a position less than the axial length of the monolithic substrate, the second carrier coating layer having a platinum to palladium weight ratio of 1:0 to 2:1 and a particulate refractory metal oxide material for supporting platinum or both platinum and palladium, wherein the second carrier coating layer is axially adjacent to the first carrier coating layer, the first carrier coating layer overlaps the second carrier coating layer, or the second carrier coating layer overlaps the first carrier coating layer.

[0072] The axial length of the first carrier coating region is less than the axial length of the second carrier coating layer; the first carrier coating region contains g / ft 3 The total platinum group metal loading is at least twice the total platinum group metal loading in the second carrier coating layer; the total platinum group metal loading on the entire substrate is 7 g / ft. 3 Up to 20g / ft 3 Furthermore, the zeolite loading in the first carrier coating layer is 0.1 g / in. 3 Up to 1.5g / in 3 .

[0073] 2. The diesel oxidation catalyst according to 1, wherein the weight ratio of platinum to palladium in the first support coating region is from 7:1 to 2.5:1.

[0074] 3. The diesel oxidation catalyst according to 1 or 2, wherein the total platinum group metal loading in the first support coating region is 10 g / ft. 3 Up to 30g / ft 3 .

[0075] 4. The diesel oxidation catalyst according to 1, 2 or 3, wherein the total platinum group metal loading on the entire monolithic substrate is 7 g / ft. 3 Up to 15g / ft 3 .

[0076] 5. The diesel oxidation catalyst according to 1, 2, 3 or 4, wherein the first carrier coating region is composed of a first carrier coating layer.

[0077] 6. The diesel oxidation catalyst according to claim 5, wherein the zeolite loading in the first support coating layer is 0.1 g / in.3 Up to 1.0 g / in 3 .

[0078] 7. The diesel oxidation catalyst according to claim 6, wherein the zeolite loading in the first support coating layer is 0.3 g / in. 3 Up to 0.8g / in 3 .

[0079] 8. The diesel oxidation catalyst according to 5, 6 or 7, wherein the first carrier coating region extends from the first substrate end for 15% to 45% of the axial length of the bulk substrate.

[0080] 9. The diesel oxidation catalyst according to 8, wherein the first carrier coating region extends from the first substrate end for 20% to 40% of the axial length of the bulk substrate.

[0081] 10. The diesel oxidation catalyst according to 1, 2, 3 or 4, wherein the first carrier coating region is composed of a third carrier coating layer disposed in a layer directly on top of the first carrier coating layer, wherein, if coated, the first carrier coating layer does not contain platinum group metals.

[0082] 11. The diesel oxidation catalyst according to 10, wherein the zeolite loading in the first support coating layer is 0.2 g / in. 3 Up to 1.0 g / in 3 .

[0083] 12. The diesel oxidation catalyst according to 11, wherein the third carrier coating layer extends from the first substrate end for 15% to 45% of the axial length of the bulk substrate.

[0084] 13. The diesel oxidation catalyst according to 12, wherein the third carrier coating layer extends from the first substrate end for 20% to 40% of the axial length of the bulk substrate.

[0085] 14. The diesel oxidation catalyst according to 10, 11, 12 or 13, wherein the first carrier coating layer extends at least the axial length of the third carrier coating layer.

[0086] 15. The diesel oxidation catalyst according to 14, wherein the first carrier coating layer is longer than the third carrier coating layer in the axial direction, and the second carrier coating layer overlaps with the first carrier coating layer.

[0087] 16. The diesel oxidation catalyst according to 14 or 15, wherein the first carrier coating layer extends 30% to 60% of the axial length of the bulk substrate.

[0088] 17. The diesel oxidation catalyst according to any one of 1 to 16, wherein the second carrier coating layer extends from 85% to 55% of the axial length of the bulk substrate.

[0089] 18. The diesel oxidation catalyst according to 17, wherein the second carrier coating layer extends from 80% to 60% of the axial length of the bulk substrate.

[0090] 19. The diesel oxidation catalyst according to 1 to 18, wherein the macroporous aluminosilicate zeolite has BEA, FAU, or MOR skeleton type is preferred. BEA.

[0091] 20. The diesel oxidation catalyst according to 19, wherein The ratio of silica to alumina in BEA is 10 to less than 40, optionally 15 to 35, and preferably 20 to 33.

[0092] 21. The diesel oxidation catalyst according to any one of 1 to 20, wherein the total carrier coating loading in the first carrier coating zone is 0.5 g / in. 3 Up to 2.5g / in 3 .

[0093] 22. The diesel oxidation catalyst according to any one of 1 to 21, wherein the loading of particulate refractory metal oxide support material in the first support coating region is 0.5 g / in. 3 Up to 2.5g / in 3 .

[0094] 23. The diesel oxidation catalyst according to 22, wherein the loading of particulate refractory metal oxide support material in the first support coating region is 0.8 g / in. 3 Up to 2.0g / in 3 .

[0095] 24. The diesel oxidation catalyst according to any one of 1 to 23, wherein the loading of the particulate refractory metal oxide support material in the second support coating layer is 0.8 g / in. 3 Up to 2.0g / in 3 .

[0096] 25. The diesel oxidation catalyst according to any one of 1 to 24, wherein the first support coating region comprises strontium or barium, preferably barium.

[0097] 26. The diesel oxidation catalyst according to 25, wherein the first support coating zone contains 50 g / ft 3 Up to 175g / ft 3 Strontium or barium, preferably 75 g / ft 3 Up to 125g / ft 3 .

[0098] 27. The diesel oxidation catalyst according to any one of 1 to 26, wherein the second carrier coating layer comprises strontium or barium, preferably barium.

[0099] 28. The diesel oxidation catalyst according to 27, wherein the second support coating layer comprises 50 g / ft 3 Up to 175g / ft 3 Strontium or barium, preferably 75 g / ft 3 Up to 125g / ft 3 .

[0100] 29. The diesel oxidation catalyst according to any one of 1 to 28, wherein the first support coating region comprises a catalyst layer having an exposed upper surface and a support lower surface, and a non-uniform distribution of palladium that decreases from the exposed upper surface to the support lower surface in a direction perpendicular to the surface of the bulk substrate.

[0101] 30. The diesel oxidation catalyst according to any one of 1 to 29, wherein it is rhodium-free.

[0102] 31. The diesel oxidation catalyst according to any one of 1 to 30, wherein it does not contain an oxygen storage component (OSC).

[0103] 32. An exhaust system for a heavy-duty diesel engine, the exhaust system comprising a diesel oxidation catalyst according to any one of 1 to 31 and a filter substrate disposed downstream of the diesel oxidation catalyst, wherein a first substrate end of the diesel oxidation catalyst is oriented to the upstream side.

[0104] 33. The exhaust system of claim 32, the exhaust system comprising an injector for injecting hydrocarbons into exhaust gases flowing in the exhaust system downstream of the engine manifold and upstream of the first base end; and a hydrocarbon source for generating exothermic gases by combustion of hydrocarbons on an oxidation catalyst.

[0105] 34. A heavy-duty diesel engine comprising an exhaust system according to 32 or 33.

[0106] 35. Use of a diesel oxidation catalyst, the diesel oxidation catalyst comprising: (i) a monolithic substrate, preferably a flow-through substrate having a first substrate end and a second substrate end and an axial length extending therebetween; (ii) a first carrier coating layer at least partially directly supported by the surface of the monolithic substrate and extending from the first substrate end to a position less than the axial length of the monolithic substrate, the first carrier coating layer comprising macroporous aluminosilicate zeolite comprising a ring size consisting of twelve tetrahedral atoms; (iii) a first carrier coating region extending from the first substrate end to a position less than the axial length of the monolithic substrate and comprising both platinum and palladium and a particulate refractory metal oxide carrier material, wherein at 10 g / ft 3 Up to 40g / ft 3 Under the total platinum group metal loading, the platinum to palladium weight ratio in the first carrier coating region is 10:1 to 2:1; and (iv) a second carrier coating layer, which is at least partially directly supported by the surface of the monolithic substrate and extends from the end of the second substrate to a position less than the axial length of the monolithic substrate, the second carrier coating layer having a platinum to palladium weight ratio of 1:0 to 2:1 and a particulate refractory metal oxide material for supporting platinum or both platinum and palladium, wherein the second carrier coating layer is axially adjacent to the first carrier coating layer, the first carrier coating layer overlaps with the second carrier coating layer, or the second carrier coating layer overlaps with the first carrier coating layer; wherein the axial length of the first carrier coating region is less than the axial length of the second carrier coating layer; the first carrier coating region contains g / ft 3 The total platinum group metal loading is at least twice the total platinum group metal loading in the second carrier coating layer; the total platinum group metal loading on the entire substrate is 7 g / ft. 3 Up to 20g / ft 3 Furthermore, the zeolite loading in the first carrier coating layer is 0.1 g / in. 3 Up to 1.5g / in 3 It is used to generate exothermic hydrocarbons from the exhaust gas of heavy-duty diesel engines.

[0107] To provide a more complete understanding of the invention, the following embodiments are provided by way of illustration only. The articles disclosed in the embodiments are prepared according to the method disclosed in the applicant's WO 1999 / 047260A1.

[0108] Example

[0109] Example 1 – Evidence of zeolite oxidation activity in the absence of platinum group metals

[0110] β-zeolite was added to an aqueous slurry of milled γ-alumina to obtain a composition of 10% zeolite and 90% alumina. No platinum group metal (PGM) salts were added to the slurry. The carrier coating was mixed and then coated onto a 1.6-liter volume ceramic flow-through substrate, dried, and then calcined. The substrate with the final catalyst coating was hydrothermally aged in air at 750°C for 10 hours.

[0111] Catalyst activity was evaluated by mounting aged catalysts onto a 2.4-liter diesel engine. Low-sulfur diesel fuel was used, and the engine was operated to run a simulated MVEG-B cycle (New European Driving Cycle (NEDC)). See the instructions for the emissions test cycles “ECE 15 + EUDC / NEDC” on DieselNet.com, which are also available at [website address missing]. https: / / dieselnet.com / standards / cycles / ece_eudc.php The emissions were measured at the inlet and outlet locations of the sample substrate. Three consecutive cycles were run, each starting at low temperature conditions (<30°C) and reaching a temperature >315°C inside the catalyst sample substrate during the hottest portion of the test. This temperature was considered sufficiently high to release hydrocarbons adsorbed / stored in the β-zeolite framework and could be demonstrated by simple adsorption and release tests using decane and thermogravimetric analysis equipment.

[0112] The cumulative HC emissions from the engine in the simulated MVEG-B cycle (before the catalyst sample substrate) were 2.0 g.

[0113] Table 1 below shows the percentage reduction in cumulative hydrocarbon emissions after the exhaust gas has passed through the catalyst sample substrate.

[0114] Table 1

[0115]

[0116] When the temperature in the simulated MVEG-B cycle exceeds 300°C, the difference in hydrocarbon emissions between the pre- and post-catalyst positions is not attributed to hydrocarbon storage. Adsorbed / stored hydrocarbons will be released from the β-zeolite in the simulated MVEG-B cycle. Therefore, the inventors attribute the reduction in cumulative hydrocarbon emissions to hydrocarbon conversion (including oxidation), rather than adsorption / storage.

[0117] Example 2 – Sample Preparation

[0118] A cylindrical cordierite flow-through honeycomb substrate (i.e., a channel with openings at both ends) with 400 holes / square inch and dimensions of 4 inches in length × 10.5 inches in diameter was coated from the inlet end to 33% of the substrate's axial length with a first catalyst carrier coating slurry containing aqueous salts of platinum and palladium (in nitrate form), barium acetate, and alumina granular carrier doped with 5 wt% silica. The resulting substrate coated with the first catalyst carrier coating slurry was then dried in a conventional oven at 100°C for 1 hour to remove excess water and other volatile substances. A second catalyst carrier coating slurry was prepared, containing aqueous salts of platinum and palladium (in nitrate form), barium acetate, and alumina granular carrier doped with 5 wt%, and coated from the outlet end to 67% of the substrate's axial length. The resulting substrate, coated with the second catalyst carrier coating slurry, was then dried in a conventional oven at 100°C for 1 hour to remove excess water and other volatile substances. The dried portion was then calcined at 500°C for 1 hour to decompose the platinum and palladium salts and fix the platinum and palladium onto the silica-doped alumina carrier.

[0119] The concentrations of platinum and palladium salts used in the first and second catalyst support coating slurries are selected such that the calcined product has a first catalyst support coating layer and a second catalyst support coating layer, the first and second catalyst support coating layers having the Pt:Pd weight ratio listed in Table 1 below and the total substrate platinum group metal loading (g / ft) as shown in Table 1. 3 The amount of alumina particulate support doped with 5% by weight of silica was selected in the first catalyst support coating slurry, such that the loading of the alumina particulate support doped with 5% by weight of silica in the calcined product was 1.4 g / in. 3 The second catalyst support coating layer has the same loading amount of alumina particulate support doped with 5% by weight of silica as the first catalyst support coating layer. In addition to the loading amount of alumina particulate support doped with 5% by weight of silica, β-zeolite is also added at 0.5 g / in 3 or 1.0g / in 3 The amount of barium acetate added was [amount missing]. In all samples listed in Table 1, the same amount of barium acetate was used in both the first and second catalyst support coating layers. A schematic diagram of the sample construction in Table 1 is shown below. Figure 1 As shown.

[0120] All samples in Table 2 were aged in air at 650°C for 50 hours.

[0121] In Table 2, the first catalyst support coating layer is referred to as the “front zone” or “FZ”, and the second catalyst support coating layer is referred to as the “back zone” or “RZ”.

[0122] Table 2

[0123]

[0124] Example 3 - "Continuous Exothermic" Test

[0125] The aged and comparative samples in Table 2 were subjected to “continuous exothermic” tests using a diesel engine mounted on a laboratory workbench. The engine, running at 2200 rpm with EUVI B7 fuel (7% biofuel) for both engine operation and exhaust hydrocarbon enrichment (exothermic generation), was equipped with an exhaust system comprising an exhaust pipe and a removable canister into which each catalyst sample could be inserted for testing, with the inlet end oriented upstream. The engine was a 7-liter EUV 6-cylinder engine producing 235 kW at 2500 rpm, and the exhaust system included a “7th injector” configured to inject hydrocarbon fuel directly into the exhaust pipe, downstream of the engine manifold and upstream of the catalyst samples being tested. This injector is referred to as the “7th injector” because it complements the six fuel injectors associated with the engine cylinders. For each test sample, thermocouples were located at the substrate sample inlet and outlet. Additionally, a hydrocarbon sensor was located at the substrate sample outlet.

[0126] Each sample substrate was conditioned at an inlet temperature of 490°C for 20 minutes, then rapidly cooled to an inlet temperature of approximately 320°C. The catalyst was introduced into the sample substrate at approximately 320°C and a flow rate of approximately 400 kg / h for 10 minutes. Hydrocarbons were then injected via the 7th injector at a controlled rate to achieve an exothermic reaction at the sample substrate outlet at 600°C. This exothermic reaction was maintained at steady state for 5 minutes. The hydrocarbon oxidation catalyst ignition temperature ramp was then initiated by continuously adjusting the engine load to achieve a temperature decrease of 1°C per minute at the sample substrate inlet at a flow rate of 400 kg / h. The exhaust gas temperature at the sample substrate outlet was recorded when the exhaust gas temperature was 500°C or below. This temperature is also known as the "quenching" temperature, where the exothermic generation is considered "quenched" when the inlet exhaust temperature is equal to or below this temperature. As a means of providing greater resolution for the "quenching" temperature, Table 3 shows the inlet temperature data recorded when 800 ppm or more of hydrocarbons were detected at the sample substrate outlet. This information provides stronger evidence of catalyst activity because the more hydrocarbons slip from the catalyst, the lower the catalyst's activity in burning those slipped hydrocarbons. Therefore, hydrocarbon slip is a measure of the test sample's progress toward exothermic quenching. The results are shown in Table 3 below.

[0127] Table 3

[0128]

[0129] It can be seen that, compared to comparative samples 1, 6, and 8, the inlet temperatures, within the experimental error range, are generally equal to those of the corresponding samples 2, 7, and 9 (according to the invention) when the recorded outlet temperature is ≤500°C, wherein the foreground region contains zeolite. However, in these comparisons, the corresponding inlet temperatures when the detected outlet hydrocarbon slip is ≤800 ppm better reflect the improvements demonstrated by samples 2, 7, and 9 according to the invention, confirming that samples 2, 7, and 9 are better exothermic generation catalysts than their corresponding comparative samples.

[0130] 1 Based on the data provided for this specific comparison, the zeolite loading in the current zone ranges from 0.5 g / in. 3 Increased to 1.0 g / in 3 No additional benefit was observed (comparing the results of samples 4 and 5).

[0131] 2 This catalyst is considered too expensive and not competitive in the market due to its high total platinum group metal content relative to Comparative Sample 8, which contradicts the technical objectives of this invention. Furthermore, at these higher total PGM loadings, the improved exothermic benefits seen at lower total PGM loadings, resulting from the addition of zeolite in the front zone, have been reversed (compare Comparative Samples 10 and 11).

[0132] 3 It should be noted that, compared to the equivalent catalyst according to the invention, comparative samples 12 and 13 have lower inlet temperatures corresponding to outlet temperatures of ≤500°C. However, comparative samples 12 and 13 contain more palladium in the front region, which is more expensive than platinum; and the presence of β-zeolite in the palladium-rich front region is actually detrimental to exothermic generation. This can be seen from the higher inlet temperature of comparative sample 13 compared to comparative sample 12. This effect is thought to be due to the zeolite “trapping” palladium and reducing the contact (mass transfer) between the exhaust gas and the active catalyst sites on the palladium.

[0133] Example 4 – Preparation and Comparison of Double-Layer Inlet Samples

[0134] In the first double-layer sample, referred to herein as Sample 16 (according to the invention), a cylindrical cordierite flow-through honeycomb substrate (i.e., having channels open at both ends) with 400 pores / square inch and dimensions of 4 inches in length × 10.5 inches in diameter was coated with a first carrier coating slurry containing β-zeolite (a platinum group metal salt). The resulting substrate coated with the first carrier coating slurry was then dried in a conventional oven at 100°C for 1 hour to remove excess water and other volatile substances, and the dried portion was then calcined at 500°C for 1 hour. The resulting dried first carrier coating slurry is referred to in Sample 4 as the "first carrier coating layer".

[0135] A second carrier coating slurry was prepared, comprising an aqueous salt of platinum and palladium (in nitrate form), barium acetate, and an alumina particulate carrier doped with 5% by weight of silica. This slurry was coated from the inlet end to 30% of the substrate's axial length, meaning the second carrier coating slurry was entirely supported by the first carrier coating layer. The resulting substrate coated with the second carrier coating slurry was then dried in a conventional oven at 100°C for 1 hour to remove excess water and other volatile substances.

[0136] A third carrier coating slurry was prepared, comprising aqueous salts of platinum and palladium (in nitrate form), barium acetate, and alumina granular carrier doped with 5% by weight of silica. This slurry was coated from the outlet end to 70% of the substrate's axial length, partially covering the first carrier coating layer. The resulting substrate coated with all three carrier coatings was then dried in a conventional oven at 100°C for 1 hour to remove excess water and other volatile substances. The dried portion containing all three carrier coating layers was calcined at 500°C for 1 hour to decompose the platinum and palladium salts and immobilize the platinum and palladium onto the silica-doped alumina carrier. A schematic diagram of the structure of sample 16 is shown below. Figure 2 As shown.

[0137] Comparative samples 14 and 15 were prepared in the same manner as sample 16, except that in comparative sample 14, in addition to β-zeolite, the first carrier coating slurry also contained platinum nitrate (palladium-free), resulting in a loading of 5 g / ft in the first carrier coating layer. 3 Furthermore, in comparative sample 15, in addition to β-zeolite, the first carrier coating slurry also contained palladium nitrate (platinum-free), resulting in a loading of 5 g / ft in the first carrier coating layer. 3 To maintain the total PGM loading on the monolithic substrate relative to sample 16, the total platinum group loading in the second carrier coating layer covering the first carrier coating layer was reduced by 5 g / ft. 3 However, the 6:1 Pt:Pd weight ratio in the second carrier coating layer is maintained (see Table 4 below).

[0138] In all the bilayer samples listed in Table 4 below, the same barium acetate loading was used in both the second and third carrier coating layers.

[0139] The concentrations of platinum and palladium salts used in the second and third carrier coating slurries are selected such that the calcined product has a second carrier coating layer and a third carrier coating layer, the second and third carrier coating layers having the Pt:Pd weight ratios listed in Table 4 below. The amount of alumina particulate support doped with 5% by weight of silica in the second and third carrier coating slurries is selected such that the loading of the alumina particulate support doped with 5% by weight of silica in both the second and third carrier coating layers of the calcined product is 1.4 g / in. 3 .

[0140] For comparison, two monolayer samples were prepared in a manner similar to that of Sample 2, except that the axial length of the inlet (front zone) was 30% and the axial length of the outlet (rear zone) was 70%. The concentrations of platinum and palladium salts used in the first and second catalyst support coating slurries were then selected such that the calcined product had a first catalyst support coating layer and a second catalyst support coating layer, the first and second catalyst support coating layers having the Pt:Pd weight ratio listed in Table 5 below. Sample 17 (without zeolite) is a comparative sample; Sample 18 according to the invention is a reference sample.

[0141] In Table 5, the first catalyst support coating layer is referred to as the “front zone” or “FZ”, and the second catalyst support coating layer is referred to as the “back zone” or “RZ”.

[0142] The total PGM loading on the entire monolithic substrate for all samples in Tables 3 and 4 below is 10 g / ft. 3 .

[0143] All samples in Tables 4 and 5 were aged in air in an oven at 650°C for 50 hours.

[0144] Table 4

[0145]

[0146] Table 5

[0147]

[0148] The aging samples in Tables 4 and 5 were tested according to Example 3. The results are listed in Tables 6 and 7 respectively.

[0149] Table 6

[0150]

[0151] Table 7

[0152]

[0153] Example 5 – Effect of the ratio of zeolite silica to alumina

[0154] Three samples were prepared as follows: A cylindrical cordierite flow-through honeycomb substrate (i.e., a channel open at both ends) with 400 pores / square inch and dimensions of 3.82 inches in length × 5.66 inches in diameter (1.58 liters) was coated from the substrate end marked as the inlet end with a first catalyst carrier coating slurry containing aqueous salts of platinum and palladium (in nitrate form), barium acetate, organic acids such as citric acid and succinic acid, and alumina granular carrier doped with 5% by weight of silica. The coating length was 30% of the axial length from the inlet end to the substrate. In two samples (Examples 5.2 and 5.3), β-zeolite was added to the first catalyst support coating slurry. The first catalyst support coating slurry in the reference sample (Example 5.1) did not contain... β-zeolite. The resulting substrate, coated with the first catalyst support coating slurry, is then dried in a conventional oven at 100°C for 1 hour to remove excess water and other volatile substances. The dried portion is then calcined for 1 hour at a temperature reaching a peak temperature of 500°C over 30 minutes to decompose the platinum and palladium salts and preferentially fix the platinum and palladium onto the silica-doped alumina support. The dried and calcined slurry is referred to hereinafter as the first catalyst support coating layer, which may also be referred to as the "front zone" or "FZ" when applied from the substrate inlet end.

[0155] A second catalyst support coating slurry was prepared, containing only Pt nitrate salt (1:0), organic acid, and a granular alumina support doped with 5% by weight of silica (barium-free). This second slurry was applied to 70% of the axial length of the substrate, starting from the end opposite the substrate end marked as the inlet end, i.e., the outlet end. The resulting substrate coated with the second catalyst support coating slurry was then dried in a conventional oven at 100°C for 1 hour to remove excess water, and the dried portion was then calcined for 1 hour at a temperature reaching a peak temperature of 500°C for 30 minutes to decompose the platinum and palladium salts and fix the platinum and palladium to the silica-doped alumina support. In this embodiment, the dried and calcined slurry is referred to as the "back zone" or "RZ".

[0156] The concentrations of platinum and palladium salts, barium acetate, and β-zeolite used in the first catalyst support coating slurry are selected such that the calcined product has a first catalyst support coating layer, which has a concentration of 36 g / ft. 3 It has a Pt:Pd weight ratio of 5:1 and a weight of 80 g / ft. -3 Barium loading and 0.5 g / in 3 of β-zeolite loading (if present). The PGM loading in each layer is listed in Table 8 below. For all three samples, the total PGM loading on the substrate was 15 g / ft. 3 During the test, the inlet was oriented to the upstream side.

[0157] The concentration of platinum salt used in the second catalyst support coating slurry was selected such that the total platinum loading (1:0 Pt:Pd weight ratio) in the second support coating layer was 6 g / ft. 3 Furthermore, the alumina loading, which is doped with 5% by weight silica, is 1.4 g / in. 3 (Manganese-free).

[0158] Table 8

[0159]

[0160] Prior to testing, the samples were aged for 50 hours at 650°C using air / 10% water (as steam) in a manner similar to that described above.

[0161] Testing – Heavy-duty diesel engine "connection" used to study the suitability of catalysts in filter regeneration mode strategies "Continued heat release" test.

[0162] The aged samples from Example 5 were subjected to a “continuous exothermic” test using a diesel engine mounted on a laboratory workbench. The engine, running at 2200 rpm with EUVI B7 fuel (7% biofuel) for both engine operation and exhaust hydrocarbon enrichment (exothermic generation), was equipped with an exhaust system comprising an upstream 12 kW electrically heated catalyst (EHC) in the exhaust manifold and a removable canister into which each catalyst sample could be inserted for testing, with the inlet end oriented upstream. The engine was a 7-liter EUV 6-cylinder engine producing 235 kW at 2500 rpm, and the exhaust system included a “7th injector” configured to inject hydrocarbon fuel directly into the exhaust manifold downstream of the engine manifold and upstream of the catalyst samples being tested. This injector is referred to as the “7th injector” because it complements the six fuel injectors associated with the engine cylinders. Thermocouples were located at the inlet of the catalyst samples and inserted at various axial locations along the centerline of the substrate bulk for each catalyst sample.

[0163] Each sample was conditioned at an inlet temperature of 490°C for 20 minutes, then rapidly cooled to an inlet temperature of 320°C, at which point the catalyst was held for 10 minutes at a flow rate of approximately 500 kg / h. Hydrocarbons were then injected via the 7th injector at a controlled rate to achieve a detectable exothermic temperature of 600°C at the substrate outlet. This exothermic temperature was maintained at steady state for 5 minutes. The catalyst was then held at the substrate for 56,000 hours by continuously adjusting the engine load. -1 With a constant catalyst sweep volume, an inlet temperature decrease of approximately 1.5°C per minute was achieved, initiating a gradient descent of the hydrocarbon oxidation catalyst ignition temperature. The exhaust temperature at the substrate inlet was recorded when the exhaust temperature at the substrate outlet was equal to or below 425°C. This temperature is also known as the "quenching" temperature; exothermic generation at inlet exhaust temperatures equal to or below this temperature is considered "quenched." Additionally, the exhaust temperature at the substrate inlet was recorded when the hydrocarbon slip detected at the substrate outlet was 1000 ppm C3 or higher. In these tests, a lower "quenching" temperature indicated a better catalyst.

[0164] The results are listed in Table 9.

[0165] Table 9

[0166]

[0167] As can be seen from the results in Table 9, it is usually... Adding β-zeolite to the front zone improved the exothermic quenching temperature; that is, the inlet exhaust gas temperature corresponding to the exothermic temperature detected downstream of the substrate remaining >425°C was relatively low, indicating that the presence of β-zeolite in the front zone... The β-zeolite sample exhibited high oxidation activity at lower inlet exhaust gas temperatures.

[0168] However, it can also be seen that when the SAR of the β-zeolite is 28.5, the catalyst inlet temperature of ≤425°C detected at the substrate outlet is lower than that when the SAR is 40.

[0169] This trend in these results is confirmed by the detection of 1000 ppm C3 HC at the substrate outlet, indicating that the temperature rise at the substrate outlet is caused by the oxidation of the injected hydrocarbons.

[0170] To avoid any doubt, the full text of all recognized references is incorporated herein by reference.

Claims

1. A diesel oxidation catalyst for use in the exhaust system of a heavy-duty diesel engine, for: oxidizing carbon monoxide (CO) and hydrocarbons (HC) to carbon dioxide (CO2) and water (H2O), including exothermic generation from HC for heating a filter substrate disposed downstream of the oxidation catalyst in the exhaust system; and oxidizing nitric oxide (NO) in the exhaust gas from the heavy-duty diesel engine to nitrogen dioxide (NO2), said diesel oxidation catalyst comprising: (i) A monolithic substrate, preferably a flow-through substrate, having a first substrate end and a second substrate end and an axial length extending between them; (ii) A first carrier coating layer, the first carrier coating layer being at least partially directly supported by the surface of the monolithic substrate and extending from the first substrate end to a position less than the axial length of the monolithic substrate, the first carrier coating layer comprising macroporous aluminosilicate zeolite comprising a ring size consisting of twelve tetrahedral atoms. (iii) a first washcoat zone extending from the first substrate end to a position less than the axial length of the monolith substrate and comprising both platinum and palladium and a particulate refractory metal oxide support material, wherein the weight ratio of platinum to palladium in the first washcoat zone is from 10: 1 to 2: 1 at a total platinum group metal loading of from 10 g / ft 3 to 40 g / ft 3 of the monolith substrate; and (iii) a first washcoat zone extending from the first substrate end to a position less than the axial length of the monolith substrate and comprising both platinum and palladium and a particulate refractory metal oxide support material, wherein the weight ratio of platinum to palladium in the first washcoat zone is from 10: 1 to 2: 1 at a total platinum group metal loading of from 10 g / ft 3 to 40 g / ft 3 of the monolith substrate; and and (iv) A second carrier coating layer, the second carrier coating layer being at least partially directly supported by the surface of the monolithic substrate and extending from the end of the second substrate to a position less than the axial length of the monolithic substrate, the second carrier coating layer having a platinum to palladium weight ratio of 1:0 to 2:1 and a particulate refractory metal oxide material for supporting platinum or both platinum and palladium, wherein the second carrier coating layer is axially adjacent to the first carrier coating layer, the first carrier coating layer overlaps with the second carrier coating layer, or the second carrier coating layer overlaps with the first carrier coating layer. The axial length of the first carrier coating region is less than the axial length of the second carrier coating layer; the first carrier coating region contains g / ft 3 The total platinum group metal loading is at least twice the total platinum group metal loading in the second carrier coating layer; the total platinum group metal loading on the entire substrate is 7 g / ft. 3 Up to 20g / ft 3 Furthermore, the zeolite loading in the first carrier coating layer is 0.1 g / in. 3 Up to 1.5g / in 3 .

2. The diesel oxidation catalyst according to claim 1, wherein the first support coating region is composed of the first support coating layer, and the zeolite loading in the first support coating layer is 0.1 g / in. 3 Up to 1.0 g / in 3 .

3. The diesel oxidation catalyst according to claim 2, wherein the first carrier coating region extends from the first substrate end for 15% to 45% of the axial length of the bulk substrate.

4. The diesel oxidation catalyst according to claim 1, wherein the first carrier coating region is composed of a third carrier coating layer, the third carrier coating layer being disposed in a layer directly on top of the first carrier coating layer, wherein, If coated, the first carrier coating layer does not contain platinum group metals.

5. The diesel oxidation catalyst according to claim 4, wherein the third carrier coating layer extends from the first substrate end for 15% to 45% of the axial length of the bulk substrate.

6. The diesel oxidation catalyst according to claim 4 or 5, wherein the first carrier coating layer is longer than the third carrier coating layer in the axial direction, and the second carrier coating layer overlaps with the first carrier coating layer.

7. The diesel oxidation catalyst according to claim 4, 5 or 6, wherein the first carrier coating layer extends 30% to 60% of the axial length of the monolithic substrate.

8. The diesel oxidation catalyst according to any one of the preceding claims, wherein the second carrier coating layer extends from 85% to 55% of the axial length of the monolithic substrate.

9. The diesel oxidation catalyst according to any one of the preceding claims, wherein the macroporous aluminosilicate zeolite has BEA, FAU, or MOR skeleton type is preferred. BEA.

10. The diesel oxidation catalyst according to claim 9, wherein... BEA's silica to alumina ratio is 10 to less than 40, and optionally 15 to 35.

11. The diesel oxidation catalyst according to any one of the preceding claims, wherein the total carrier coating loading in the first carrier coating zone is 0.5 g / in. 3 Up to 2.5g / in 3 .

12. The diesel oxidation catalyst according to any one of the preceding claims, wherein the first support coating region comprises a catalyst layer having an exposed upper surface and a support lower surface, and a non-uniform distribution of palladium, the non-uniform distribution decreasing from the exposed upper surface to the support lower surface in a direction perpendicular to the surface of the bulk substrate.

13. An exhaust system for a heavy-duty diesel engine, the exhaust system comprising a diesel oxidation catalyst according to any one of the preceding claims and a filter substrate disposed downstream of the diesel oxidation catalyst, wherein the first substrate end of the diesel oxidation catalyst is oriented to the upstream side.

14. A heavy-duty diesel engine, the heavy-duty diesel engine comprising the exhaust system according to claim 13.

15. Use of a diesel oxidation catalyst, wherein the diesel oxidation catalyst comprises: (i) A monolithic substrate, preferably a flow-through substrate, having a first substrate end and a second substrate end and an axial length extending between them; (ii) a first carrier coating layer, the first carrier coating layer being at least partially directly supported by the surface of the monolithic substrate and extending from the first substrate end to a position less than the axial length of the monolithic substrate, the first carrier coating layer comprising macroporous aluminosilicate zeolite comprising a ring size consisting of twelve tetrahedral atoms; (iii) a first carrier coating region, the first carrier coating region extending from the first substrate end to a position less than the axial length of the monolithic substrate, and comprising both platinum and palladium and particulate refractory metal oxide carrier material, wherein at 10 g / ft 3 Up to 40g / ft 3 Under the total platinum group metal loading, the platinum to palladium weight ratio in the first carrier coating region is 10:1 to 2:1; and (iv) a second carrier coating layer, the second carrier coating layer being at least partially directly supported by the surface of the monolithic substrate and extending from the end of the second substrate to a position less than the axial length of the monolithic substrate, the second carrier coating layer having a platinum to palladium weight ratio of 1:0 to 2:1 and a particulate refractory metal oxide material for supporting platinum or both platinum and palladium, wherein the second carrier coating layer is axially adjacent to the first carrier coating layer, the first carrier coating layer overlaps with the second carrier coating layer, or the second carrier coating layer overlaps with the first carrier coating layer; wherein the axial length of the first carrier coating region is less than the axial length of the second carrier coating layer; the first carrier coating region contains g / ft 3 The total platinum group metal loading is at least twice the total platinum group metal loading in the second carrier coating layer; the total platinum group metal loading on the entire substrate is 7 g / ft. 3 Up to 20g / ft 3 Furthermore, the zeolite loading in the first carrier coating layer is 0.1 g / in. 3 Up to 1.5g / in 3 It is used to generate exothermic hydrocarbons from the exhaust gas of heavy-duty diesel engines.

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