JP2015500134A - Oxidation catalyst for exhaust gas treatment of internal combustion engines - Google Patents

Abstract

The present invention relates to an exhaust gas purification oxidation catalyst, and more particularly to an oxidation catalyst for purifying exhaust gas discharged from a compression ignition internal combustion engine. The invention further relates to a catalytic substrate monolith having an oxidation catalyst on the substrate monolith for use in treating exhaust gas emitted from a lean burn internal combustion engine. In particular, the present invention relates to a catalyst-based monolith comprising a first washcoat and a second washcoat, the second washcoat being disposed in a layer above the first washcoat. .

Description

  The present invention relates to an exhaust gas purification oxidation catalyst, and more particularly to an oxidation catalyst for purifying exhaust gas discharged from a compression ignition type (specifically, a diesel engine). The invention further relates to a catalytic substrate monolith having an oxidation catalyst on the substrate monolith for use in treating exhaust gas emitted from a lean burn internal combustion engine. In particular, the invention relates to a catalyst-based monolith comprising a first washcoat coating and a second washcoat coating, wherein the second washcoat coating is above the first washcoat coating. Arranged in the layer. The invention also relates to the use of such a catalyst-based monolith in a lean burn internal combustion engine, in particular in an exhaust system of a vehicle lean burn internal combustion engine.

In general, there are four grades of pollutants enacted by intergovernmental organizations throughout the world: carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NO _x ) and particulate matter. (PM).

  Oxidation catalysts have been used to purify hydrocarbons (HC), carbon monoxide (CO), and soluble organic components (SOF) in exhaust gas produced by the combustion of fuel in compression ignition internal combustion engines (Japan) (See Patent Publication No. 9-271474). In recent years, attention has been focused on the processing of particulate matter (PM) generated by combustion of fuel in a compression ignition internal combustion engine, and a filter (diesel particle filter DPF) that can collect PM. In order to improve the PM processing efficiency in the DPF, an oxidation catalyst has been arranged in the upstream part of the DPF (see Japanese Patent Publication No. 2006-272064).

Higher concentration fuels contain a greater proportion of sulfur. In a compression internal combustion engine that uses diesel oil as a fuel, sulfur oxide (SOx) is generated in the combustion and catalytic steps of combustion, and the action of the oxidation catalyst has been reduced by SOx (sulfur poisoning). To counter this problem, an oxidation catalyst resistant to sulfur poisoning has been proposed, which has zeolite as a mixture containing a specific proportion of weight of ZSM-5 and β-zeolite ( (See Japanese Patent Publication No. 2007-229679). In addition, in order to make more efficient the purification of exhaust gases, comprises two different catalyst layers, i.e. NO _x with a NO _x oxidation catalyst layer, a double layer structure comprising a _the NO _x selective reduction catalyst layer A purification catalyst has been proposed (see Japanese Patent Publication No. 2008-279352).

Emission standards for acceptable emissions of pollutants in exhaust gases from vehicle engines are becoming increasingly stringent, and the combination of engine management and a number of catalytic exhaust aftertreatment systems will meet these emission standards. Has been proposed and developed. In the case of an exhaust system that includes a particulate filter, it is used periodically (eg, every 500 km) to raise the temperature within the filter, thereby burning almost all remaining soot retained on the filter. Thus, it is common for engine management to return the system to the baseline level. Such engine-controlled soot combustion events are often referred to as “filter regeneration”. On the other hand, the main focus of filter regeneration is to burn the soot retained on the filter, but one or more catalytic coatings present in the exhaust system, such as a coating on the filter itself (so-called catalytic soot). filter (CSF)), oxidation catalyst (diesel oxidation catalyst (DOC)) or _the NO _x adsorption material catalyst located upstream or downstream of the filter (NAC) (e.g., a diesel particulate filter is followed by a first DOC, thereafter It was an unintended result that the second DOC followed, followed by the SCR catalyst) could be periodically exposed to high exhaust gas temperatures depending on the level of engine management control in the system. Such a situation can also lead to unintentional irregular engine malfunctions or uncontrolled or poorly controlled regeneration situations. However, some diesel engines, especially heavy duty diesel engines that operate at high loads, can even expose the catalyst to significant high temperatures, eg> 600 ° C., under normal operating conditions.

As vehicle manufacturers develop their own engines and engine management systems that meet emissions standards, applicants / assignees provide vehicle manufacturers with catalyst components and catalyst component combinations that support targets that meet emissions standards. It is required to propose. Such components also oxidize DOC, CO, HC, optionally NO, which also oxidizes CO, HC and optionally NO, and oxidize CSF, CO and HC, which capture particulate matter for subsequent combustion. NAC (see below), which oxidizes nitrogen oxide (NO), absorbs it from lean exhaust gas, desorbs adsorbed NO _x and reduces it to N ₂ in rich exhaust gas, and nitrogen reduction A selective catalytic reduction (SCR) catalyst (see below) that reduces NO _x to N ₂ in the presence of an agent, such as ammonia, is included.

  In fact, the catalyst compositions utilized in DOC and CSF are very similar. In general, however, the principal difference between the use of DOC and CSF is the substrate monolith that is coated with the catalyst composition, and in the case of DOC, the substrate monolith typically extends in a row extending through it. Is a flow-through substrate monolith with a metal or ceramic honeycomb monolith having elongated channels, the channels being open at both ends, the CSF substrate monolith having a plurality of inlets arranged in parallel with the plurality of outlet channels A filtering monolith with a channel, for example a porous filter substrate made of ceramic, such as a wall flow filter, where each inlet channel and each outlet channel is by a ceramic wall of porous structure Partially defined, each inlet channel is defined by a porous ceramic wall. Spaced alternately from the outlet channel Te, and vice versa. In other words, the wall-flow filter includes a plurality of first channels blocked at the upstream end and a plurality of second channels blocked at the upstream end but blocked at the downstream end. It is a honeycomb arrangement to define. Channels that are vertically and laterally adjacent to the first channel are plugged at the downstream end. When viewed from either end, the alternating closed and open ends of the channel present a chessboard appearance.

  For example, fairly complex multi-layer catalyst configurations such as DOC and NAC can be coated on the flow-through substrate monolith. Although it is possible to coat certain surfaces of a filter monolith, such as the inlet channel surface of a wall flow filter, with one or more layers of catalyst composition, the problem with coating filtering monoliths is that the filter is filtered by the catalyst washcoat during use. By overloading the monolith and limiting the passage of gas therethrough, avoiding an unnecessarily increased back pressure. Thus, it is impossible to sequentially coat the surface of the filter substrate monolith with one or more different catalyst layers, but any of the areas of the front half and the back half of the filter monolith divided in the axial direction, for example Or by dividing the inlet channel of the wall flow filter substrate monolith with the first catalyst composition and coating the outlet channel with the second catalyst composition. Is more general than for different catalyst compositions. However, in certain embodiments of the invention, the filter inlet is coated with one or more layers, which may be the same or different catalyst compositions. It has also been proposed to apply a NAC composition onto a filtering substrate monolith (see, for example, EP 0 766 993).

In exhaust gas systems comprising multiple catalyst components, each comprising a separate substrate monolith, typically the SCR catalyst is located downstream of DOC and / or CSF and / or NAC because the exhaust gas A ratio of about 1: 1 NO: NO ₂ exiting DOC and / or CSF and / or NAC by oxidizing some of the nitrogen oxide (NO) therein to dinitrogen oxide (NO ₂ ) This is because it is known that downstream SCR reaction is promoted (see below). Further, from EP 341832 (so-called continuous regeneration trap or CRT (registered trademark)), the soot on the downstream filter is passively obtained using NO ₂ generated by oxidizing NO in exhaust gas to NO _2. It is known that it can also be burned. In exhaust gas system configurations where the process of EP 341832 is important, if an SCR catalyst is located upstream of the filter, this will mitigate or prevent the process of burning trapped soot in NO ₂ , which This is because most of the NO _x used to burn soot is probably transferred onto the SCR catalyst.

However, a preferred system configuration for a light duty diesel vehicle is a diesel oxidation catalyst (DOC) followed by a nitrogen reducing agent injector, followed by an SCR catalyst, and finally a catalytic soot filter (CSF). A simple term for such a configuration is “DOC / SCR / CSF”. Such a configuration is preferred for light-duty diesel vehicles because the important issue to consider is that (i) a precursor such as a nitrogen reducing agent, eg ammonia, is injected / decomposed, NO it possible to liberate the ammonia for _x conversion, and (ii) to allow as much as possible high of the NO _x conversion, after the vehicle engine is started, achieving NO _x conversion in as quickly as possible exhaust system It is because it is to do. If a large thermal mass filter is placed upstream of the SCR catalyst, i.e. between the DOC and SCR catalyst ("DOC / CSF / SCR"), the process of (i) and (ii) takes longer to achieve will take, the NO _x conversion of the whole emission standard operation cycle may be reduced. Particle removal can be accomplished using oxygen and forced regeneration of the filter as needed using engine management techniques.

It has also been proposed to coat the SCR catalyst washcoat onto the filter substrate monolith itself (see, for example, WO 2005/01649), in which case the oxidation catalyst is upstream of the SCR coated filter substrate. May be located (whether the oxidation catalyst is a component of DOC, CSF or NAC), thereby modifying the NO / NO ₂ ratio to promote the NO _x reduction action on the SCR catalyst Can do. There are also proposals to place NAC upstream of a placed SCR catalyst on a flow-through substrate monolith, which can be generated in situ during NAC regeneration (see below). Such a proposal is disclosed in GB 2375059.

NAC is, for example, known from Patent US5,473,887, adsorbs NO _x from lean exhaust gas (lambda> 1), when the oxygen concentration in the exhaust gas decreases, is designed to desorb the NO _x . The desorbed NO _x can be reduced to N ₂ using a suitable reducing agent, such as engine fuel, and promoted by the catalytic component located in the NAC itself or downstream of the NAC, such as rhodium. it can. In fact, the management of the oxygen concentration is intermittently can be adjusted to a desired redox composition according to the remaining of the NO _x adsorption force is NAC calculations, for example, a richer than normal engine running operation (but The ratio is still lean, or lambda = 1 composition), ratio or ratio ratio rich (lambda <1), etc. The oxygen concentration can be adjusted by several means, for example, throttling, injecting additional hydrocarbon fuel into the engine cylinder, such as during the exhaust stroke, or exhausting hydrocarbon fuel downstream of the engine manifold. For example, direct injection.

A typical NAC formulation includes a catalytic oxidation component, such as platinum, and a significant amount (ie, a significant amount necessary for use as a promoter, such as a promoter in a three-way catalyst) of a NO _x storage component, such as barium, for example. And a reduction catalyst such as rhodium. One mechanism commonly provided for NO _x storage from lean exhaust gas in the case of such formulations is:
NO + 1 / 2O ₂ → NO _{2 →} (1) and BaO + 2NO ₂ + 1 / 2O ₂ → Ba (NO ₃ ) ₂ (2),
In this case, in reaction (1), nitric oxide reacts with oxygen at the active oxidation position on platinum. Reaction (2) involves the adsorption of NO ₂ by the storage material in the form of inorganic nitrate.

At lower oxygen concentrations and / or elevated temperatures, nitrate species become thermodynamically unstable, decompose and produce NO or NO ₂ according to the following reaction (3). In the presence of a suitable reducing agent, such nitrogen oxides are then reduced to N ₂ by carbon monoxide, hydrogen and hydrocarbons, which can be performed on the reduction catalyst (reaction (4)). See).
Ba (NO ₃ ) ₂ → BaO + 2NO + 3 / 2O ₂ or Ba (NO ₃ ) ₂ → BaO + 2NO ₂ + 1 / 2O ₂ (3) and NO + CO → 1 / 2N ₂ + CO ₂ (4)
(Other reactions are Ba (NO ₃ ) ₂ + 8H ₂ → BaO + 2NH ₃ + 5H ₂ O followed by NH ₃ + NO _x → N ₂ + yH ₂ O or 2NH ₃ + 2O ₂ + CO → N ₂ + 3H ₂ O + CO ₂ ).

  In the reactions (1) to (4) included in the above specification, the reactive barium species is provided as an oxide. However, in the presence of air, it is understood that most barium is in the form of carbonates or, in some cases, hydroxides. A person skilled in the art can adapt the above reaction scheme accordingly to a barium species other than oxide and the sequence of catalyst coating in the exhaust stream.

The oxidation catalyst promotes oxidation of CO to CO ₂ and oxidation of unburned HC to CO ₂ and H ₂ O. Typical oxidation catalysts include platinum and / or palladium on a high surface area support.

Vehicle internal combustion (IC) engine, is well known SCR technology applications for processing NO _x emissions from lean-burn IC engines in detail. Examples of nitrogen reducing agents that can be used in the SCR reaction include compounds such as nitrogen hydrides such as ammonia (NH ₃ ) or hydrazine or NH ₃ precursors.

An NH ₃ precursor is one or more compounds from which NH ₃ can be obtained, for example, by hydrolysis. Degradation of the precursor to ammonia and other by-products may be by hot water or catalytic hydrolysis. The NH ₃ precursor includes urea (CO (NH ₂ ) ₂ ) as an aqueous solution or ammonium carbamate (NH ₂ COONH ₄ ) as a solid. When urea is used as an aqueous solution, a eutectic mixture, such as 32.5% NH ₃ (aqueous solution) is preferred. An additive may be included in the aqueous solution in order to lower the crystallization temperature. Currently, urea is the preferred source of NH ₃ for automotive applications because it is less toxic than NH _3, is easy to transport and handle, is inexpensive, and is generally available. Incomplete hydrolysis of urea can lead to increased PM release in tests to meet the relevant emission test cycle, which means that partially hydrolyzed urea solids or droplets are This is because it is captured by the filter paper used in the test according to the law and is counted as PM mass. Furthermore, the release of certain products of incomplete urea hydrolysis, such as cyanuric acid, is environmentally undesirable.

The SCR has three main reactions (expressed including the following reactions (5) to (7)), which reduce NO _x to elemental nitrogen.
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (ie, 1: 1 NH ₃ : NO) (5)
4NH ₃ + 2NO + 2NO ₂ → 4N ₂ + 6H ₂ O (ie, 1: 1 NH ₃ : NO _x ) (6)
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O (ie, 4: 3NH ₃ : NO _x ) (7)
Related undesirable, non-selective side reactions are
2NH ₃ + 2NO ₂ → N ₂ O + 3H ₂ O + N ₂ (8).

  In fact, reaction (7) is relatively slow compared to reaction (5), and reaction (6) is the fastest of all. For this reason, skilled technicians place an oxidation catalyst element (eg, DOC and / or CSF and / or NAC) upstream of the SCR catalyst when designing an exhaust aftertreatment system for a vehicle. Often likes.

Certain DOCs and / or NACs and / or CSFs are hot when filter regeneration and / or the engine is malfunctioning and / or exposed to high temperatures facing normal hot exhaust gases (in certain heavy duty diesel applications) Low levels of platinum group metal compounds, in particular Pt, allow sufficient time for volatilization from the DOC and / or NAC and / or CSF compounds, after which the platinum group metal is trapped by the downstream SCR catalyst This has become the focus of the applicant / assignee by the applicant / assignee's customers. This leads to a high effect of the presence of Pt on the oxidation of competing non-selective ammonia, such as reaction (9), which leads to the generation of secondary emissions and / or non-productive consumption of NH ₃ . As a result, it can have a rather detrimental effect on the performance of the SCR catalyst.
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O (9)

A vehicle manufacturer reported in SAE paper 2009-01-0627 that he observed such a phenomenon, which is described as ““ Impact and Prevention of Ultra-Low Continuation of Platinum Group Metals on SCR catalysts DU cata For the Fe / zeolite SCR catalyst in contact with the model exhaust gas, which is located in series behind the DOC containing the four purchased platinum group metals (PGM) and flows for 16 hours at 850 ° C. It contains data comparing the NO _x conversion function with respect to temperature. The results presented, 20Pt in PGM entire 70gft ^-3: Pd NO _x conversion action of Fe / zeolite SCR catalyst disposed behind the DOC is more as compared with the evaluation temperature was lowered as a result of Pt is mixed It shows that it changed to negative at the high evaluation temperature. Two 2Pt: Pd DOCs from different suppliers at 105 gft ^-3 of the entire PGM were also tested. In the first 2Pt: Pd DOC, the SCR catalysis was affected to the same extent as the test for 20Pt: Pd DOC, while the SCR catalysis for the second 2Pt: Pd DOC tested was was not only affected to a lesser degree, the second 2Pt: Pd DOC still, if not managed (DOC without simply exposed substrate) nO _x conversion effect were reduced compared to. The author concluded that the second 2Pt: PdDOC supplier that showed a milder NO _x conversion reduction was more successful in establishing 70 gft ⁻³ Pt present with 35 gft ⁻³ Pd. A Pd-only DOC at 150 gft- ³ proved to have no effect on the downstream SCR as compared to the unmanaged case. A previous study of the SAE 2009-01627 writing was published in SAE 2008-01-2488.

  Vehicle manufacturers have begun to require applicants / assignees to take action to resolve the problem of relatively low levels of PGM volatilization from compounds upstream of the SCR catalyst. It would be highly desirable to develop a method to prevent such PGM behavior for downstream SCR catalysts at high temperatures. The inventors have developed several methods to meet these needs.

  US 7,576,031 discloses a Pt-Pd diesel oxidation catalyst with CO / HC ignition and HC storage functions. Specifically, the diesel oxidation catalyst has a washcoat composition comprising two different washcoats. The first (or top) washcoat layer comprises a high surface area support, one or more hydrocarbon storage compounds, and a noble metal catalyst containing platinum (Pt) and palladium (Pd). The second (or bottom) washcoat layer comprises a high surface area support and a noble metal catalyst containing platinum (Pt) and palladium (Pd), wherein the support is a substantially silica-free support. It is a material and does not contain hydrocarbon storage compounds.

  The two layers of diesel oxidation catalyst disclosed in US 7,576,031 have two distinctly different weight ratios of Pt: Pd relative to each other, in which case the first layer (first or first) The Pt: Pd weight ratio in the top washcoat layer) is greater than the Pt: Pd weight ratio in the second layer (second or bottom washcoat layer). For example, the first or top washcoat layer may comprise a Pt: Pd weight ratio of at least 2: 1. Also illustrated are Pt: Pd weight ratios of at least about 2: 1 to about 10: 1, about 3: 1 to about 5: 1, and about 3: 1 to about 4: 1. It is explained that it is important to use a high Pt content in the first or top washcoat layer to enhance sulfur resistance while maintaining some stabilization of the metal phase against sintering. ing. The first or top washcoat layer contains a hydrocarbon (HC) storage compound, such as zeolite, to store HC during the cold start period of the operating cycle. After warming the catalyst, the hydrocarbon (HC) storage compound releases the stored HC, which is then converted to the catalyst. It is important to note that this description continues as hydrocarbon (HC) storage compounds (eg, zeolites) are incorporated into this layer at higher Pt: Pd weight ratios to ensure efficient conversion of released paraffins. It is.

  The second or bottom layer of the diesel oxidation catalyst disclosed in US 7,576,031 includes a lower Pt: Pd weight ratio to replace maximum Pt with Pd for maximum cost reduction reasons To do. The second or bottom washcoat layer has a Pt: Pd weight ratio of less than about 2: 1. Also illustrated are Pt: Pd ratios of less than about 2: 1 to about 1: 2, or less than about 2: 1 to about 1.4: 1 (7: 5). However, a maximum ratio of 1.4: 1 (7: 5) is preferred to ensure sufficient CO / olefin ignition after heat aging.

Japanese Patent Publication No. 9-271474 Japanese Patent Publication No. 2006-272064 Japanese Patent Publication No. 2007-229679 Japanese Patent Publication No. 2008-279352 EP0766693 EP341832 WO2005 / 01649 GB2375059 US 5,473,887 US7,576,031

  Therefore, the development of an oxidation catalyst for an internal combustion engine, in particular a compression ignition internal combustion engine, in which SOF, HC and CO are continuously and effectively purified and preferably almost no sulfur poisoning can be avoided. Now it has become an urgent matter. In recent years, there has been a demand for the development of a catalyst that reduces the amount of expensive and deficient precious metals that have been used so far, while having the same processing capacity as existing exhaust gas purification catalysts.

  The inventors have surprisingly found that HC and CO (especially CO) in the exhaust gas are water-removed especially by the difference between the amount of noble group metal (its load) present in the catalyst layer and the amount of hydrocarbon adsorbent. And conversion to carbon dioxide has been found to produce advantageous catalysis aimed at treating them.

In a first aspect, the present invention provides an oxidation catalyst for oxidizing hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas, the oxidation catalyst comprising a supporting substrate, a supporting substrate, and a supporting substrate. A plurality of catalyst layers supported by a substrate, the plurality of catalyst layers include a washcoat material, an active metal, and a hydrocarbon adsorbent, and one catalyst layer is on the catalyst surface layer side, One or more other catalyst layers are on the lower side of said one catalyst layer;
(A) The amount of the hydrocarbon adsorbent in the one catalyst layer is larger than the amount of the hydrocarbon adsorbent in the one or more other catalyst layers, and the concentration of the active metal in the one catalyst layer is Equal to or less than the concentration of active metal in one or more other catalyst layers, or (b) the amount of hydrocarbon adsorbent in said one catalyst layer is in said one or more other catalyst layers The amount of the active metal in the one catalyst layer is lower than the concentration of the active metal in the one or more other catalyst layers.

  By utilizing the hydrocarbon (HC) adsorption and storage function, the oxidation catalyst of the present invention can efficiently treat carbon monoxide (CO) even at a relatively low temperature. When the exhaust gas temperature rises, the occluded hydrocarbons (HC) are released and are easily affected by the oxidation treatment by the catalyst due to the high temperature. The advantageous exhaust gas purification power of the catalyst of the present invention is related to the dispersion of the hydrocarbon adsorbent and the active metal between the layers. HC adsorption and occlusion functions are given to the “one catalyst layer” on the surface layer on the exhaust gas catalyst side, and the CO oxidation reaction on the “other catalyst layer” on the catalyst surface layer side close to the substrate support is blocked Therefore, when the concentration of noble metal in the “one catalyst layer” on the catalyst surface layer side is low, the formation of CO due to the oxidation of part of the hydrocarbon is prevented when the adsorbed and occluded hydrocarbon is released. It is thought to be done.

  Typically, the oxidation catalyst in the first aspect of the present invention is a catalyst-based monolith and the support substrate is a substrate monolith. One catalyst layer may be a first washcoat coating as defined herein and one of the other catalyst layers is a second washcoat coating as defined herein. It may be.

Therefore, the first aspect of the present invention further relates to a catalyst base monolith for the purpose of oxidizing hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas, the catalyst base monolith being a base monolith. And a first washcoat coating and a second washcoat coating, wherein the second washcoat coating is disposed in a layer above the first washcoat coating, and the first washcoat The coating comprises an active metal and at least one support for the active metal, and the second washcoat coating comprises a hydrocarbon adsorbent;
(A) The amount of hydrocarbon adsorbent in the second washcoat coating is greater than the amount of hydrocarbon adsorbent in the first washcoat coating, and the concentration of active metal in the second washcoat coating is the first Equal to or less than the concentration of active metal in the washcoat coating of
(B) The amount of hydrocarbon adsorbent in the second washcoat coating is the same as the amount of hydrocarbon adsorbent in the first washcoat coating, and the concentration of active metal in the second washcoat coating is Less than the concentration of active metal in one washcoat coating.

  We also have platinum volatilization from PGM-containing catalysts containing both platinum and palladium under extreme temperature conditions when the Pt: Pd weight ratio is about 2: 1 or greater. I found that there was a possibility. Further, when PGM (platinum group metal) is composed of platinum, it is considered that volatilization of platinum may be observed. The inventors have devised a layered PGM catalyst composition for use in combination with a PGM moving from an upstream relatively high load Pt catalyst to a downstream SCR catalyst, particularly a downstream SCR catalyst that avoids or mitigates Pt problems. did.

  A second aspect of the present invention provides a catalyst substrate monolith comprising an oxidation catalyst on a substrate monolith for use in treating exhaust gas emitted from a lean burn internal combustion engine, the catalyst substrate monolith comprising A first washcoat coating (typically having a length L) and a second washcoat coating, wherein the second washcoat coating comprises a first washcoat coating (typically long The first washcoat coating has a catalyst composition comprising platinum and at least one support for platinum, and the second washcoat coating is A second washer comprising a catalyst composition comprising both platinum and palladium, and at least one support for platinum and palladium. The weight ratio of platinum and palladium in the coating coating, ≦ 2, for example, 1.5: 1, such as or example ≦ 1: 1: 1 to about 1, such as. The importance of the latter feature is shown in some examples, and we have preferred Pt: Pd by experimental chemistry compared to similar catalysts with a Pt: Pd weight ratio of 4: 1. The weight ratio was found to be less volatile.

  A third aspect of the present invention provides an exhaust system for a lean burn internal combustion engine, the system comprising a first catalytic substrate monolith according to the present invention, in particular a catalytic substrate according to the second aspect of the present invention. With material monolith.

  According to a fourth aspect of the present invention, there is provided a lean burn internal combustion engine for a vehicle, in particular comprising an exhaust system according to the present invention. A lean-burn internal combustion engine may be a volumetric ignition, typically a spark ignition engine, typically operated with gasoline fuel or a mixture of gasoline fuel and other components such as ethanol, but compression such as a diesel engine. Ignition is preferred. Lean burn internal combustion engines include premixed compression ignition (HCCI) powered by either fuel such as gasoline or diesel fuel.

  A fifth aspect of the present invention is that a selective catalytic reduction (SCR) catalyst in an exhaust system of a lean burn internal combustion engine is exposed to relatively extreme conditions where the catalyst composition comprising platinum includes a relatively high temperature. Volatilized from a first washcoat coating (typically having a length L) comprising platinum disposed on a substrate monolith upstream of the SCR catalyst and at least one support for platinum A method is provided for mitigating or preventing contamination by platinum, the method being disposed in a layer above a first washcoat coating (typically for at least a portion of length L). Trapping volatilized platinum within the second washcoat coating, wherein the second washcoat coating comprises a catalyst comprising both platinum and palladium. And forming, and a platinum and at least one support for the palladium, the weight ratio of platinum and palladium in the second washcoat coating is ≦ 2.

  A sixth aspect of the invention provides an exhaust system for an internal combustion engine, in particular a compression ignition internal combustion engine such as a diesel engine, which system comprises an oxidation catalyst or catalyst-based monolith according to the first aspect of the invention. Is provided.

  A seventh aspect of the present invention provides an internal combustion engine, particularly for a vehicle, according to the sixth aspect of the present invention. The internal combustion engine may be a volumetric ignition, typically a spark ignition engine, typically operated with gasoline fuel or with a mixture of gasoline fuel and other components such as ethanol, but compression ignition such as a diesel engine. preferable.

  A seventh aspect of the present invention provides a vehicle including the engine according to the present invention.

2 is a schematic of a laboratory reactor used to test platinum contamination against the Cu / CHA zeolite SCR catalyst of Example 2 or the Fe / beta zeolite SCR catalyst of Example 6. FIG. 2 is a bar graph comparing the NO _x conversion effects of two heat aged SCR catalyst cores (alpha 0.8, ie NH ₃ : NO _x ) at 500 ° C., each of which is a lab scale exhaust as shown in FIG. A Cu / K containing core samples of the diesel oxidation catalysts of Reference Example 6 and Example 4 each heat aged in the system and heated in a synthetic exhaust gas flowing in a tubular furnace at 900 ° C. for 2 hours and maintained at 300 ° C. It is a bar graph in which the CHA zeolite SCR catalyst core is located downstream. A brand new Fe / beta zeolite SCR catalyst compared to the action of a heat aged Fe / beta zeolite SCR catalyst in the laboratory scale exhaust system shown in FIG. 1 comprising the catalytic soot filter core of Reference Example 7 and Examples 7 and 8 Is a graph that charts the NO _x conversion effect as a function of temperature. FIG. 4 is a bar graph showing the NO _x conversion effect of two different Cu / CHA SCR catalysts, each of which is heat aged downstream of the diesel oxidation catalyst of Example 10 and is 4: 1 and 2 for the SCR catalyst control sample. 1 is a graph having a total Pt: Pd weight ratio of 1: 1. FIG. 4 is a schematic view of an exhaust system according to a first most preferred embodiment according to the third aspect of the present invention. FIG. 6 is a schematic view of an exhaust system according to a second most preferred embodiment according to the third aspect of the present invention. FIG. 6 is a schematic view of an exhaust system according to a third most preferred embodiment according to the third aspect of the present invention.

The oxidation catalyst and the catalyst-based monolith typically each catalyst layer or washcoat coating has an average thickness of 25 to 200 μm, specifically 50 to 150 μm, and more particularly 75 to 125 μm (eg 100 μm). Have. The layer thickness can be measured using an electronic probe microanalyzer.

  The average thickness of each catalyst layer or washcoat coating may be the same or different. In one embodiment of the present invention, the average thickness of at least one of one catalyst layer (eg, second washcoat coating) and the other catalyst layer (first washcoat coating) is approximately the same.

  The oxidation catalyst or catalyst-based monolith of the present invention comprises a plurality of catalyst layers or washcoat coatings. Typically, the oxidation catalyst or catalyst-based monolith is composed of 2, 3, 4 or 5 catalyst layers or washcoat coatings. It is preferred that the oxidation catalyst or catalyst-based monolith is composed of two catalyst layers or washcoat coatings. In the context of the first aspect of the present invention, the present invention relates to “one catalyst layer” and one or more “other catalyst layers” in a plurality of catalyst layers, and “one catalyst layer” in a plurality of catalyst layers. "Is on the catalyst surface layer side, and is positioned as" the other catalyst layer "on the lower side than" one catalyst layer "(on the support substrate side).

In general, a compound that adsorbs hydrocarbons (for example, a hydrocarbon adsorbent or an adsorbent) has a high specific surface area in contact with exhaust gas. Typically, the hydrocarbon adsorbent has a specific surface area of 50 to 1500 m ² / g, preferably 200 to 1000 m ² / g, more preferably 200 to 900 m ² / g. This specific surface area is measured by the BET nitrogen adsorption method using nitrogen as an adsorption-desorption gas.

  Typically, the hydrocarbon adsorbent is selected from zeolite, silica, alumina, titania, zirconia, magnesium oxide, calcium oxide, ceria, niobia, activated carbon, porous graphite and combinations of two or more thereof. Preferably, the hydrocarbon adsorbent is zeolite. Examples of suitable zeolites include natural zeolites such as calcite, chabazite, erionite, sodalite, mordenite, pyroxenite, zeolitic and zeolitic, and type A zeolite type, type Y zeolite, type X zeolite, Synthetic zeolites such as L-type zeolite, erionite, mordenite, beta zeolite and ZSM-5 are included.

  The ratio of the amount of hydrocarbon adsorbent (ie, hydrocarbon adsorber) in the one catalyst layer or second washcoat coating to the one or more other catalyst layers or first washcoat coating is typical. 10: 1 to 1.1: 1, in particular 7.5: 1 to 1.2: 1, more particularly 5: 1 to 1.3: 1, even more particularly 4: 1 to 1.4: 1, and even more particularly 3: 1 to 1.5: 1.

Typically, one catalyst layer or second washcoat coating is 0.05 to 3.00 gin ^-3 , specifically 0.10 to 2.00 gin ^-3 , more particularly 0.25 to 0. A hydrocarbon adsorbent (ie, hydrocarbon adsorber) concentration of .75 gin ^-3 . The amount of hydrocarbon adsorbent present in or throughout a layer is related to the trapping capacity of the oxidation catalyst or catalyst substrate monolith.

  Characteristically, the amount of the hydrocarbon adsorbent present in the “one catalyst layer” is larger than the amount of the hydrocarbon adsorbent present in the “other catalyst layer”, and the above-mentioned amount present in “one catalyst layer” The concentration of the active metal described in the above is lower than the concentration of the active metal present in the “other catalyst layer”, and the catalyst layer may be stacked with “one catalyst layer” and “the other catalyst layer” adjacent to each other. And may have an intermediate catalyst layer (or the other layer, a layer of the same or different composition) inserted between them. Furthermore, the present invention selects any desired two catalyst layers in the plurality of catalyst layers, wherein “one catalyst layer” is on the catalyst surface layer side, and “the other catalyst layer” is the catalyst layer described above. They are positioned so that they are on the lower side of the (supporting substrate side). In this case, when “one catalyst layer” is determined, the other is automatically defined as “the other catalyst layer”.

  One catalyst layer or second washcoat coating is typically 10 to 50% by weight of the layer or washcoat coating, specifically 15 to 40% by weight, more particularly 20 to 30% by weight. It has a concentration of hydrocarbon adsorbent.

  The active metal functions as an active compound catalyzed by an oxidation catalyst or catalyst-based monolith. The active metal is a noble metal, base metal or platinum group metal (PGM).

  Examples of suitable noble metals include platinum, palladium, rhodium, ruthenium, iridium, osmium, gold and silver. If the active metal is a noble metal, then preferably the active metal is platinum, palladium or gold. The noble metal may be used alone or as a mixture of two or more, such as platinum and palladium, or a mixture of platinum, palladium and gold.

  Examples of base metals include nickel, copper, manganese, iron, cobalt and zinc. If the active metal is a base metal, preferably in this case the active metal is nickel, copper, manganese or iron. The base metal can also be used alone or as a mixture of two or more.

  The active metal in one catalyst layer or second washcoat coating may be the same or different from the active metal in the other catalyst layer or first washcoat coating.

  The active metal is preferably a platinum group metal. More preferably, the active metal is platinum, palladium or a mixture thereof.

  If the active metal is present in both one catalyst layer or second washcoat coating and one or more other catalyst layers or first washcoat coating, then the active metal is the same or different There is.

  Typically, the concentration of active metal, such as platinum group metal (PGM), in one of the catalyst layers (or second washcoat coating) and one or more other catalyst layers (or first washcoat). The concentration ratio of the active metal, eg platinum group metal (PGM), in the coating) is from 1:50 to 1: 1.1, in particular from 1:35 to 1: 1.2, more particularly from 1:20. 1: 1.3, more particularly 1:15 to 1: 1.4, and even more particularly 1:10 to 1: 1.5 (eg 1: 5 to 1: 1.5).

Generally, the one or more other catalyst layers (or the first washcoat coating) is 0.05 to 3.5 gin ^-3 , specifically 0.1 to 1.5 gin ^-3 , more specifically 0. active metals .25 from 0.75gin ^-3 (e.g. 0.75Gin ^-3 0.1), for example having a concentration of PGM. The amount of active metal present determines the number of active sites available for the catalyst.

  Typically, one or more of the other catalyst layers (or first washcoat coating) is 0.05 to 7.5 weight percent, specifically 0.5 to 5 weight percent, more particularly 1 From 3 to 3 weight percent of active metal such as PGM.

  One catalyst layer (or second washcoat coating) is typically 0.01 to 5 weight percent, specifically 0.05 to 0.5 weight percent, more particularly 0.1 to 0.00. It has an active metal concentration of 3 weight percent, such as PGM.

  In one embodiment of the present invention, a hydrocarbon adsorbent (ie, a hydrocarbon adsorber) is present in one or more other catalyst layers or the first washcoat coating. In the context of the first aspect of the invention, if there is no hydrocarbon adsorbent present in one or more other catalyst layers or the first washcoat coating, then one catalyst layer or second There may be no active metal present in the washcoat coating, or it is present in a concentration or ratio as defined above.

  If a hydrocarbon adsorbent (ie, a hydrocarbon adsorbent) is present in both one catalyst layer or second washcoat coating and one or more other catalyst layers or first washcoat coating, this Sometimes the hydrocarbon adsorbent may be the same or different. Preferably, the hydrocarbon adsorbent in each catalyst layer or washcoat coating is the same.

  The amount of hydrocarbon adsorbent (ie, hydrocarbon adsorbent) in one catalyst layer or second washcoat coating is such that the hydrocarbon adsorbent in the one or more other catalyst layers or first washcoat coating ( That is, the amount of catalyst in one catalyst layer or the second washcoat coating is typically typically greater than the one or more other catalyst layers or first Less than or approximately the same as the weight of the catalyst in the washcoat coating.

Typically, the washcoat material is a support for the active metal. The support material is, for example, a metal selected from Mg, Si, Ca, Sr, Ba, Al, Ga, In, Sn, transition metal elements, lanthanides, complex oxides thereof, and oxides of a mixture of two or more thereof. It is an oxide. Preferably, the support material is selected from SiO ₂ , Al ₂ O ₃ , CeO ₂ and TiO ₂ , or a composite oxide having SiO ₂ , Al ₂ O ₃ , CeO ₂ or TiO ₂ as a main component. is there.

  The oxidation catalyst or catalyst-based monolith may further comprise a catalyst promoter such as cerium oxide, zirconium oxide or titanium oxide.

  Generally, the support substrate carries a catalyst (for example, an active metal, a hydrocarbon adsorbent, a washcoat material, an accelerator, etc.). The supporting base material may be any material having both durability and reliability without lowering the combustion efficiency of the engine due to a problem with pressure loss or the like.

Typically the support substrate is a ceramic or metallic material. It may be, for example, in a tubular, fibrous or granular form. Examples of suitable supports include monolithic honeycomb cordierite type substrates, monolithic honeycomb SiC type substrates, layered or woven fiber type substrates, foam type substrates, Cross-flow type substrates, metal wire mesh type substrates, metal porous body type substrates and ceramic particle type substrates are included. Supporting substrate, cordierite _{(SiO 2 -Al 2 O 3 -MgO} ), silicon carbide (SiC), Fe-Cr- Al alloy, may be selected from Ni-Cr-Al alloy and stainless steel alloys.

  Preferably, the support substrate is a substrate monolith.

  Typically, the substrate monolith used in the present invention, in particular the substrate monolith used in the second aspect of the present invention, may be a filtering substrate monolith having an inlet surface and an outlet surface, The entrance surface is separated from the exit surface by a porous structure. A particularly preferred filtering substrate monolith is a wall flow filter. However, in a particularly preferred embodiment, the substrate monolith is a flow-through substrate monolith.

  The at least one support of the first washcoat coating or the second washcoat coating (ie, washcoat material) is optionally stabilized alumina, amorphous silica-alumina, optionally stabilized zirconia. , Ceria, titania and optionally stabilized metal oxides selected from the group consisting of ceria-zirconia mixed oxides or molecular sieves or mixtures of any two or more thereof.

  The first washcoat coating can extend substantially the entire length of the channel in the substrate monolith. In the first particular embodiment, the second washcoat coating substantially covers the first washcoat coating. In the second embodiment. The second washcoat coating is disposed in a constant area of generally uniform length at the downstream end of the substrate monolith, which is defined by the outlet end of the substrate monolith itself at the downstream end and upstream. At the end is defined by a specific point that is shorter than the total length of the first washcoat coating. That is, in the second embodiment, the second washcoat coating does not cover the entire first washcoat coating. Methods of making layered coatings of different lengths are known in the art, see for example WO 99/47260 and the following.

  In any of the first, second and third most preferred embodiments of the catalyst-based monolith according to the present invention, the first washcoat coating is in the combined first and second washcoat coatings. 25-75 weight percent of the total platinum group metals present in, for example, 35-65 weight percent. That is, the second washcoat coating can have 75-25 weight percent, for example 65-35 weight percent, of the total platinum group metal present in the combined first and second washcoat coating. . The inventors have found that PGM volatility is generally independent of PGM loading in the washcoat coating layer and depends on the Pt: Pd weight ratio as explained above. Preferably, however, more total PGM is placed in the second washcoat coating because mass transfer is more readily available. Accordingly, it is preferred that> 50 weight percent of the total platinum group metals present in the combined first and second washcoat coatings is present in the second washcoat coating.

One aspect of the catalyst design for total platinum group metal splitting between the first washcoat coating and the second washcoat coating is the washcoat loading in each of the first washcoat coating and the second washcoat coating. is there. In embodiments, the washcoat loading in each of the first washcoat coating and a second washcoat coating is in the range of 0.1-3.5Gin ^-3, for example 0.5-2.5Gin ^-3, for example ≧ Individually selected from 1.5 gin ^-3 , ≧ 2.0 gin ^-3 or ≦ 2.0 gin ^-3 . For example, a higher load is preferred for the NO _x adsorber catalyst. However, using a lower washcoat load in the second washcoat coating than in the first washcoat coating makes the less accessible PGM in the first washcoat coating more accessible for mass transfer. It is possible. That is, in the embodiment, the washcoat load in the first washcoat coating is larger than the washcoat load in the second washcoat load.

  In the second aspect of the invention, the at least one support material (or washcoat material) may comprise one or more molecular sieves, such as aluminosilicate zeolites. The main role of the molecular sieve in the catalyst substrate of the first aspect of the present invention is to occlude hydrocarbons flowing in the cold start or cold phase of the duty cycle, and the associated platinum group metal catalyst compound is more activated for HC conversion. In doing so, the hydrocarbon conversion is improved over a certain duty cycle by releasing hydrocarbons occluded at higher temperatures. See for example EP 0830201. Molecular sieves are typically used in catalyst compositions according to the present invention for light-duty diesel vehicles, while they are rarely used in catalyst compositions in high-load diesel applications because This is because the exhaust gas temperature in the high-load diesel engine means that the hydrocarbon trap function is not necessary. However, when a molecular sieve is present in the catalyst-based monolith according to the present invention, it is highly preferred that at least one of the first washcoat coating and the second washcoat coating comprises a molecular sieve. Most preferably, both the first washcoat coating and the second washcoat coating contain molecular sieves.

  However, molecular sieves such as aluminosilicate zeolites are not particularly good supports for platinum group metals because they are primarily silica, in particular relatively high silica and alumina molecular sieves, Although they are advantageous for increasing the thermal durability of each, they can be degraded by heat during thermal aging, which can cause the molecular sieve structure to collapse and / or PGM is sintered. In order to reduce dissipation, the HC and / or CO conversion action is consequently reduced. Thus, in a preferred embodiment, the first washcoat coating and the second washcoat coating are ≦ 30 weight percent (eg ≦ 25 weight percent, ≦ 20 weight percent, eg ≦ 15 weight percent) of the individual washcoat coating layers. ) Including molecular sieves. The remainder of the support of at least one of the first washcoat coating or the second washcoat coating is optionally stabilized alumina, amorphous silica-alumina, optionally stabilized zirconia, ceria, titania. And optionally stabilized metal oxides selected from the group consisting of ceria-zirconia mixed oxides and any two or more mixtures thereof.

  A preferred molecular sieve for use as a support / hydrocarbon adsorbent is a medium pore zeolite, preferably an aluminosilicate zeolite, i.e. having a maximum ring size of eight tetrahedral atoms and a large pore size. Zeolite (up to 10 tetrahedral atoms), faujasite type, crinotyrosite, mordenite, silicalite crystal, ferrierite, X-type zeolite, Y-type zeolite, Y-type ultrastable zeolite, ZSM-5 Zeolite type zeolite, ZSM-12 type zeolite, SSZ-3 type zeolite, SAPO-5 type zeolite, fluorite type or beta zeolite, preferably natural or synthetic zeolite such as ZSM-5 type, beta and Y type zeolite. Preferred zeolite adsorbents have a high silica to alumina ratio, thereby improving hydrothermal stability. The zeolite is at least about 25/1, preferably at least about 50/1, about 25/1 to 1000/1, 50/1 to 500/1 and about 25/1 to 100/1, 25/1 to 300 /. 1, may have a silica / alumina molecular ratio in the effective range from about 100/1 to 250/1.

The oxidation catalyst in the oxidation catalyst of the first aspect of the present invention or the catalyst-based monolith of the second aspect of the present invention may be a diesel oxidation catalyst or a NO _x adsorbent catalyst. Have the role described. NAC contains a significant amount of alkaline earth metal and / or alkali metal relative to the oxidation catalyst. NACs typically also include ceria or a ceria-containing mixed oxide, such as a mixed oxide of cerium and zirconium, which optionally further includes one or more additional lanthanides or rare earth elements. .

  Methods for making catalyst-based monoliths comprising a single layer washcoat coating and a dual layer configuration (one washcoat coating layer on top of another washcoat coating layer) are known in the art and are described in WO 99 / 47260, i.e. (a) placing a containment means at the top of the substrate monolith, i.e. the first end, and (b) after (a) after (b) or (b) Administering a predetermined amount of a first washcoat coating component to the containment means in any order of (a); and (c) applying the pressure or vacuum to the first washcoat coating. Drawing the ingredients into at least a portion of the substrate monolith and maintaining substantially all of the amount in the substrate monolith. . In the first step, the coating from the first end of the application can be dried, the dried substrate monolith can be flipped 180 degrees, and the same procedure applied to the top of the substrate monolith, ie the second end. The coating from the first end of the substrate monolith and the layer of coating from the second end do not substantially overlap. The resulting coated product is then dried and then fired. This process is repeated for the second washcoat coating component to form the catalyst (double layer) substrate monolith according to the present invention.

  The filtering substrate monolith used in the first or second aspect of the present invention is preferably a wall-flow filter, i.e. a porous ceramic made of a plurality of inlet channels arranged in parallel with a plurality of outlets. A filter substrate, wherein each inlet channel and each outlet channel is defined in part by a ceramic wall of the porous structure, and each inlet channel is separated from the outlet channel by the ceramic wall of the porous structure. Alternatingly spaced, and vice versa. In other words, the wall flow filter defines a plurality of first channels blocked at the upstream end and a plurality of second channels not blocked at the upstream end but blocked at the downstream end. It is a honeycomb arrangement. A channel that is vertically and laterally adjacent to the first channel is plugged at the downstream end. When viewed from either end, the alternating closed and open ends of the channel present a chessboard appearance.

Catalytic filters, preferably wall flow type filters, can be coated using the method disclosed in WO2011 / 080525. That is, a method of coating a honeycomb monolith substrate having a plurality of channels with a liquid containing a catalyst component, the method comprising: (i) holding the honeycomb monolith substrate substantially vertical; Injecting an amount of liquid into the substrate through the open end of the channel at the lower end of the substrate; (iii) maintaining the injected liquid in a sealed manner in the substrate; and (iv) holding Inverting the substrate containing the liquid, and (v) drawing liquid along the substrate channel by applying a vacuum to the open end of the substrate channel at the inverted lower end of the substrate. Consists of steps. The catalyst composition can be coated onto the filter channel from the first end, after which the coated filter can be dried. The use of such a method can be adjusted using, for example, the strength of the vacuum, the duration of the vacuum, the viscosity of the washcoat, the hardness of the washcoat, the coating particle or agglomerate size and the surface tension, so that the catalyst is Most are coated on the inlet surface, but are optionally coated in the porous structure, but also near the inlet surface. Alternatively, the washcoat components may be ground to a specific size, eg D90 <5 μm, so that they “penetrate” into the porous structure of the filter (see WO 2005/016497). The SCR catalyst of the second substrate monolith can have a filtering substrate monolith, preferably a wall flow monolith, or a flow-through substrate monolith. The flow-through substrate monolith can extrude an SCR catalyst or SCR catalyst washcoat against an inert substrate monolith. It is also possible to produce a wall flow type filter from the extruded SCR catalyst (see WO2009 / 093071 and WO2011 / 092521). The SCR catalyst may be selected from the group consisting of at least one of a Group VIII transition metal such as Cu, Hf, La, Au, In, V, lanthanide and lanthanide supported on a refractory oxide or molecular sieve. . Suitable refractory oxides include Al ₂ O ₃ , TiO ₂ , CeO ₂ , SiO ₂ , ZrO ₂ and mixed oxides containing two or more thereof. The catalyst other than zeolite may contain tungsten oxide, for example, V ₂ O ₅ / WO ₃ / TiO ₂ . Preferred metals for a particular subject are selected from the group consisting of Ce, Fe and Cu. Molecular sieves can be ion exchanged with any of the above metals.

  In certain embodiments, the at least one molecular sieve is an aluminosilicate zeolite or SAPO. The at least one molecular sieve may be, for example, a small, medium or large pore molecular sieve. By “small pore molecular sieve” herein is meant a molecular sieve including a maximum ring size of 8 tetrahedral atoms, such as CHA, etc., and by “medium pore molecular sieve” herein, 10 tetrahedral A molecular sieve containing the maximum ring size of the body atoms, such as ZSM-5, is referred to, and a “large pore molecular sieve” herein refers to a molecular sieve including the maximum ring size of 12 tetrahedral atoms, such as beta. Small pore molecular sieves are sometimes advantageous for use with SCR catalysts, see, for example, WO 2008/132252. Molecular sieves for use in SCR catalysts according to the present invention include one or more metals incorporated within the molecular sieve framework, for example, Fe “contains in framework” beta and Cu “contains in framework” CHA Etc.

  Specific molecular sieves with use in the present invention include AEI, including ZSM-34, ZSM-5, ZSM-20, ERI, mordenite, ferrierite, Beta, including Nu-3, Y, CHA, LEV CHA molecular sieves selected from the group consisting of BEA, MCM-22 and EU-1, are currently preferred, especially as a promoter, for example in combination with ion-exchanged CU.

  In one embodiment of the first aspect of the invention, no active metal, such as PGM, is present in one catalyst layer or the second washcoat coating. When no active metal is present in the other catalyst layer or the second washcoat coating, where no hydrocarbon adsorbent is present in the one or more other catalyst layers or the first washcoat coating. Or the hydrocarbon adsorbent may be present at a concentration or ratio as defined above.

  In another embodiment of the first aspect of the present invention, the first washcoat coating comprises a catalyst composition comprising platinum and a support for platinum, and the second washcoat coating comprises platinum and A catalyst composition comprising both palladium and at least one support for platinum and palladium, wherein the weight ratio of platinum to palladium in the second washcoat coating is ≦ 2, for example 1.5: 1 or about 1: 1, such as ≦ 1: 1.

  In one embodiment of the second aspect of the invention, the amount of hydrocarbon adsorbent or adsorbent (eg, zeolite) in the second washcoat coating is the amount of hydrocarbon adsorbent or adsorbent in the first washcoat coating. More than quantity. Preferably, the concentration of active metal in the second washcoat coating is the same as or preferably lower than the concentration of active metal (eg, platinum) in the first washcoat coating. The amount of hydrocarbon adsorbent is as defined above.

  In another embodiment of the second aspect of the present invention, the amount of hydrocarbon adsorbent or adsorbent (eg, zeolite) in the second washcoat coating is the amount of hydrocarbon adsorbent or adsorption in the first washcoat coating. It is the same as the amount of material. Preferably, the concentration of active metals (eg, platinum and palladium) in the second washcoat coating is lower than the concentration of active metals (eg, platinum) in the first washcoat coating.

According to the third and sixth aspects of the exhaust system, the present invention provides an exhaust system for a lean burn internal combustion engine, which system comprises a first catalytic substrate monolith according to the present invention.

In a preferred embodiment, an exhaust system according to the invention, in particular according to the third aspect of the invention, comprises a second catalyst-based monolith having a selective catalytic reduction (SCR) catalyst, this second The catalyst substrate monolith is disposed downstream from the first catalyst substrate monolith. In a preferred embodiment, an exhaust system according to the invention, in particular according to the third aspect of the invention, injects a nitrogen reducing agent into the exhaust gas between the first catalyst substrate monolith and the second catalyst substrate monolith. With an injector. As an alternative (ie, when means for injecting ammonia or a precursor thereof, such as urea, is not disposed between the first catalyst substrate monolith and the second catalyst substrate monolith) or ammonia or a precursor thereof In another embodiment, in addition to the means for injecting the exhaust gas, an engine management means is provided to enrich the exhaust gas, thereby reducing ammonia gas by reducing NO _x in the catalyst composition of the first catalyst substrate monolith. Is generated on the spot.

  Nitrogen reducing agents and precursors used in the present invention include any of those listed above in conjunction with the background art portion, such as ammonia and urea.

In combination with a properly designed and controlled diesel compression ignition engine, an enriched exhaust gas, i.e. an exhaust gas containing increased amounts of carbon monoxide and hydrocarbons relative to the normal lean operating mode, is produced in the first substrate monolith. Contact the catalyst composition. For example, components in NAC such as PGM-promoted ceria or ceria-zirconia can promote the water-gas shift reaction, ie CO _(g) + H ₂ O _(v) → CO _{2 (g))} + H _{2 ( g)} Generate evolved H ₂ . From the footnotes of side reactions to the reactions (3) and (4) described above, NH ₃ is generated in situ from, for example, Ba (NO ₃ ) ₂ + 8H ₂ → BaO + 2NH ₃ + 5H ₂ O, and in the downstream SCR catalyst and it is inserted in the order of the NO _x reduction.

  In a first most preferred embodiment, the exhaust system of the invention, in particular the third aspect of the invention, comprises a third catalyst substrate monolith, in this case the substrate of the first catalyst substrate monolith. The monolith is a flow-through substrate monolith and the third catalyst substrate monolith is a filtering substrate monolith having an inlet surface and an outlet surface, the inlet surface being separated from the outlet surface by a porous structure. The third catalyst substrate monolith includes an oxidation catalyst and is disposed between the first catalyst substrate monolith and the second catalyst substrate monolith, preferably the first catalyst substrate monolith, , Between the first catalyst base monolith and the second catalyst base monolith and between any injectors for injecting a nitrogen reducing agent into the exhaust gas.

  In a second most preferred embodiment, the second catalytic substrate monolith in the exhaust system of the present invention, in particular the third aspect of the present invention, is a filtering substrate monolith having an inlet face and an outlet face. In this case, the inlet face is separated from the outlet face by a porous structure.

  In a third most preferred embodiment, the exhaust system of the present invention, in particular the third aspect of the invention, comprises a third substrate monolith, the third substrate monolith comprising an inlet surface and an outlet surface. Wherein the inlet surface is separated from the outlet surface by a porous structure, and the third substrate monolith is disposed downstream of the second catalyst substrate monolith. The In one particular embodiment, the third substrate monolith includes an oxidation catalyst. That is, in one embodiment, the third substrate monolith does not have any coating.

  In the first, second and third most preferred embodiments of the exhaust system of the present invention, in particular the third aspect of the present invention, the or each filtering substrate monolith is preferably a wall flow filter. is there.

The preferred role of the first catalyst substrate in the second and third embodiments of the present invention, particularly the third aspect of the present invention, differs from that of the first most preferred embodiment. In the second and third most preferred embodiments, the catalyst substrate monolith that follows immediately downstream of the first catalyst substrate monolith is a second substrate monolith comprising an SCR catalyst. In order to promote reaction (6), it is preferred that the first catalyst-based monolith promotes NO oxidation, and at the same time, by volatilization of PGM and subsequent transfer of PGM to the immediately downstream SCR catalyst. It is preferred to avoid reducing the overall NO _x conversion action.

  For this purpose, it is preferred that the Pt: Pd weight ratio of both the first washcoat coating and the second washcoat coating combined is ≧ 2: 1. To avoid volatility problems, the combined Pt: Pd weight ratio of both the first washcoat coating and the second washcoat coating is ≦ 10: 1, such as ≦ 8: 1, ≦ 6: 1 or ≦ Preferably it should be 4: 1. In certain embodiments, preferably the PGM in the first washcoat coating is only Pt, ie substantially free of palladium. In order to trap any platinum that may volatilize from the first washcoat coating, preferably the weight ratio of platinum to palladium in the second washcoat coating is ≦ 2, such as 1.5: 1 or about 1: 1, for example ≦ 1: 1.

  “Substantially palladium free” refers to the fact that no palladium is intentionally provided in the associated layer. However, this material is considered a minor amount (ie, <10%, <9%, <8%, <7%, <6%, <5%, <4%, <3%, <2% of the material) % Or even <1%) may migrate or diffuse from the second washcoat coating to the first washcoat coating.

  The preferred role of the first catalyst substrate in the first most preferred embodiment of the present invention, in particular the third and sixth aspects of the third aspect of the present invention, is the second and third Because the catalytic soot filter (third catalytic substrate monolith) is disposed between the first substrate monolith and the second substrate monolith. . Thus, it is possible to suppress or prevent PGM volatilization from the first catalyst-based monolith and subsequent movement of the PGM to downstream elements, but located downstream from the first catalyst-based monolith. There is a catalytic soot filter, which preferably promotes NO oxidation upstream of the second substrate monolith containing the SCR catalyst for the purpose of promoting reaction (6), for that reason, Due to the fact that it may contain a relatively high platinum content, measures to trap the volatilized PGM can be applied more effectively downstream of the first catalyst substrate monolith. For example, measures for trapping volatilized PGM can be applied to the design aspect of the catalytic soot filter, eg between the filter soot catalyzing the guard bed and the second catalyst substrate monolith, or the second catalyst. It can be placed in the entrance area to the substrate monolith itself. Such measures are referred to as “Catalysed Substrate Monolith”, “Exhaust System for a Lean Burn IC Engineer and Cry Component E and C,” filed under the reference numbers 70050, 70051 and 70053, respectively. a Lean-Burn Internal Combustion Engineering Inclusion SCR Catalyst ", disclosed in the applicant / assignee sister application.

As such, in the context of the first most preferred embodiment of the third and sixth aspects of the present invention, in particular the third aspect of the present invention, the preferred role of the first catalyst-based monolith is one Is to oxidize carbon oxides and unburned hydrocarbons (volatile organic fraction (VOF), also known as soluble organic fraction (SOF)), NO to promote reaction (6) the need not to be oxidized to nO _2.

  Preferably, in the catalyst-based monolith used in the present invention, in particular the first most preferred embodiment of the third and sixth aspects of the third aspect of the invention, the second washcoat coating is The first washcoat coating includes both platinum and palladium, and the first washcoat coating includes platinum and palladium in a weight ratio that is higher than the Pt: Pd weight ratio in the second washcoat coating. That is when the weight ratio of platinum to palladium in the second washcoat coating is ≦ 2, for example 1.5: 1 or about 1: 1, for example ≦ 1: 1 and in the first washcoat coating. The weight ratio is preferably ≧ 1: 2, and most preferably about 2: 1. In certain embodiments, the combined Pt: Pd weight ratio of both the first washcoat coating and the second washcoat coating is ≧ 1: 1.

FIG. 5 is a schematic view of an exhaust system 10 according to a second most preferred embodiment according to the third aspect of the present invention, which is a continuous arrangement from upstream to downstream, coated with a two-layer DCO composition according to the present invention. The flow-through substrate monolith 2 and 100% of its inlet channel supported on granular alumina were coated with 5 gft ^-3 platinum, and 35% of the total length of its outlet channel was supported on granular alumina. 1.75 gft ^-3 palladium coated downstream catalyst wall flow filter substrate monolith 4, ammonia source 6 with injector for ammonia precursor urea, coated with Fe / beta SCR catalyst And a flow-through type substrate monolith 8. Each substrate 2, 4, 8 is placed in a metal container or “can” containing a cone diffuser and is a series of cross-sectional areas smaller than the cross-sectional area of any of the substrate monoliths 2, 4, 8. Connected by a conduit 3. The cone diffuser acts to widen the flow of exhaust gas entering the “canned” substrate monolith housing, so that the exhaust gas as a whole is almost in front of each substrate monolith. Guided across a “plane”. The exhaust gas leaving the substrate monolith 8 is released to the atmosphere at the “tail pipe” 5.

The flow-through substrate monolith 2 coated with a two-layer DOC is designed to promote the oxidation of hydrocarbons, carbon monoxide and nitrogen oxides, with a Pt: Pd weight ratio in the 2: 1 top layer. And a total Pt: Pd weight ratio of 6: 1. The catalyst wall flow-type substrate monolith 4 is described in the applicant / assignee sister patent application filed on the same day as this application, entitled “Catalyzed Substrate Monolith” by reference number 70050, The inventors of the present invention have found that palladium placed at the downstream end of the outlet channel of the wall flow filter is optionally alloyed with palladium from the upstream inlet channel of the wall flow filter, and the palladium volatilized Pt. Reducing the loss of the NO _x conversion effect in the SCR catalyst by the platinum volatilized from the substrate monolith including the platinum-containing catalyst such as DOC upstream from the wall flow type filter going downstream to the SCR catalyst, or I found that I can stop Therefore, the total Pt: Pd weight ratio of the two-layer DOC may be relatively high because there is no concern that platinum volatilizes from the DOC and proceeds directly to the SCR catalyst. However, the ≦ 2: 1 limit for the second washcoat coating limits as much as possible the amount of platinum that can volatilize from the DOC.

  Referring to FIG. 6, there is shown an exhaust system 20 according to a second most preferred embodiment according to the third aspect of the present invention, which is in a sequential order from upstream to downstream and is uniform by layered NAC composition. And a downstream wall flow type substrate monolith 24 whose inlet and outlet channels are coated with CuCHA SCR catalyst. Each substrate monolith 22, 24 is placed in a metal container or “can” containing a cone diffuser and is connected by a series of conduits 3 having a smaller cross-sectional area than either of the substrate monoliths 22, 24. .

Combined with a properly designed and controlled diesel compression ignition engine (not shown) upstream of the substrate monolith, the enriched exhaust gas, i.e. increased amounts of carbon monoxide and hydrocarbons relative to the normal lean mode of operation. The contained exhaust gas comes into contact with NAC. For example, components in NAC such as PGM-promoted ceria or ceria-zirconia can promote water and gas shift reactions, ie CO _(g) + H ₂ O _(v) → CO _{2 (g)} + H _{2 (g )} Generate generated H ₂ . From the footnotes of the side reactions related to the reactions (3) and (4) described above, NH ₃ is generated in situ from, for example, Ba (NO ₃ ) ₂ + 8H ₂ → BaO + 2NH ₃ + 5H ₂ O, and the wall flow type substrate It is occluded for _the NO _x reduction in the downstream SCR catalyst monolith 24. The exhaust gas exiting the substrate monolith 24 is released to the atmosphere at the “tail pipe” 5. The top layer of the layered NAC composition contains both platinum and palladium in a 2: 1 weight ratio, but the total Pt: Pd weight ratio of the NAC composition as a whole is 4: 1 so upstream of the SCR catalyst. Promotes NO oxidation.

  FIG. 7 is a schematic view of an exhaust system 30 according to a third most preferred embodiment according to the third aspect of the present invention, which is uniformly coated with a two-layer DCO composition continuously from upstream to downstream. Flow-through substrate monolith 32, ammonia source 6 with an injector for ammonia precursor urea, downstream flow-through monolith substrate 34 coated with CuCHA SCR catalyst, and wall-flow filter substrate And a downstream catalyst soot filter 36 based on the above. Each substrate monolith 32, 34, 36 is placed in a metal container or “can” containing a cone diffuser, and a series of conduits 3 having a cross-sectional area smaller than the cross-sectional area of any of the substrate monoliths 32, 34, 36. Connected by

  In this embodiment, the flow-through substrate monolith 34 coated with the SCR catalyst is in direct fluid communication with the flow-through substrate monolith comprising DOC. In order to prevent or prevent platinum group metals from volatilizing from the DOC and migrating to the SCR catalyst, the two-layer DOC composition has a Pt: Pd weight ratio of 2: 1 with platinum in the second washcoat coating. Designed to contain both palladium. In order to promote reactions (1) and (6) by promoting NO oxidation, the total Pt: Pd weight ratio is 4: 1.

As explained above, the system of FIG. 7 is a preferred system configuration for light-duty diesel because an important problem is that NO _x conversion is performed in the exhaust system as quickly as possible after the vehicle engine is started. By accomplishing (i) injecting / decomposing a precursor of a nitrogen reducing agent such as ammonia to liberate ammonia for NO _x conversion, and (ii) enabling as high a NO _x conversion as possible Because it is.

Vehicle The present invention is for use in a vehicle exhaust system adapted to an internal combustion engine. Specific examples of vehicles that use internal combustion engines include: cars, buses, heavy trucks, locomotives, motorcycles, electric bicycles and large construction machines, transportation machines, aircraft, forestry and agricultural machinery, plows, Listed are tractors, combines, chainsaw trucks and timber carriers, ships, ships, fishing boats and motorboats, civil engineering machines, cranes, compressors and excavators, and generators. However, the terms are not limited to these.

Definitions As used herein, the expression "oxidation catalyst" refers generally to the combination of a substrate and an oxidation catalyst, such as the oxidation catalyst in the second aspect of the invention, with particular reference to the first aspect of the invention. pointing.

  As used herein, the expression “a plurality of catalyst layers” refers in particular to the first aspect of the invention to “one catalyst layer” and one or more “other catalyst layers”. Including. "One catalyst layer" can be placed directly on top of one or more "other catalyst layers" or placed on top (eg, on top of "other catalyst layers"), One or more intervening layers (eg, a layer that is not a “catalyst layer”) may be disposed between “one catalyst layer” and one or more “other catalyst layers”.

  As used herein, the expression “catalyst surface layer side” refers specifically to the side of the oxidation catalyst that is first exposed to the exhaust gas, usually referring to the first aspect of the invention, and usually the outermost side. The catalyst layer.

  As used herein, the expression “below the one catalyst layer” refers specifically to the oxidation between “one catalyst layer” and the “support substrate”, particularly referring to the first aspect of the invention. Refers to a portion or region of the catalyst.

  As used herein, the expression “a plurality of catalyst layers comprises a washcoat material, an active metal, and a hydrocarbon adsorbent” refers to two or more, particularly referring to the first aspect of the present invention. The combination of all catalyst layers (that is, the entire layer) includes a washcoat material, an active metal, and a hydrocarbon adsorbent. Thus, the washcoat material, active metal and hydrocarbon adsorbent need not be present in each and every catalyst layer. Typically, however, each catalyst layer comprises, consists essentially of or consists of a washcoat material and at least one active metal or hydrocarbon adsorbent. Thus, “one catalyst layer” may comprise, consist essentially of, or consist of a washcoat material and a hydrocarbon adsorbent, and “one or more other catalyst layers” It may comprise, consist essentially of, or consist of a washcoat material and at least one active metal. In general, however, each catalyst layer comprises, consists essentially of, or consists of a washcoat material, an active metal and a hydrocarbon adsorbent.

  As used herein, the expression “amount of hydrocarbon adsorbent” refers to the total amount of hydrocarbon adsorbent present, particularly referring to the first aspect of the invention. Therefore, “amount of hydrocarbon adsorbent in one catalyst layer” refers to the total amount of hydrocarbon adsorbent in “one catalyst layer”. “Amount of hydrocarbon adsorbent in one or more other catalyst layers” refers to the total amount of hydrocarbon adsorbent present in all “other catalyst layers”. Typically, “amount of hydrocarbon adsorbent” is measured as “mass of hydrocarbon adsorbent” (eg, weight of hydrocarbon adsorbent). When two or more types of hydrocarbon adsorbents are present, the “amount” in this case refers to the total amount of all types of hydrocarbons present.

  As used herein, the expression “active metal concentration” refers to the ratio of the weight of active metal to the total weight of each catalyst layer, expressed as weight percent, particularly with respect to the first aspect of the invention. The “concentration of active metal in one catalyst layer” refers to the total concentration of active metal or a plurality of active metals in “one catalyst layer”. “The concentration of the active metal in the one or more other catalyst layers” refers to the total concentration of the active metal or the plurality of active metals in the “other catalyst layer”.

  As used herein, the expression “the concentration of the active metal in the one catalyst layer is the same as the concentration of the active metal in the one or more other catalyst layers” is particularly the first in the present invention. In this embodiment, a concentration is employed that differs by only 1% from the average value, preferably by 0.1% from the average value, more preferably by 0.01% from the average value. Typically, the concentration is the same for all intentions and purposes as measured by standard conventional methods for measuring concentration.

  As used herein, the expression “the amount of the hydrocarbon adsorbent in the one catalyst layer is the same as the amount of the hydrocarbon adsorbent in the one or more other catalyst layers” is particularly With respect to the first aspect of the invention, a concentration is employed that differs by only 1% from the average value, preferably by 0.1% from the average value, more preferably by 0.01% from the average value. Typically, the amount is the same for all intents and purposes when measured by standard conventional methods for measuring the amount.

  As used herein, the expression “the weight of the active metal in the one catalyst layer is the same as the weight of the active metal in the one or more other catalyst layers” is particularly the first in the present invention. In this embodiment, a concentration is employed that differs by only 1% from the average value, preferably by 0.1% from the average value, more preferably by 0.01% from the average value. Typically, the weight is the same for all intents and purposes when measured by standard conventional methods for measuring weight.

  Any reference to “weight of catalyst” as used herein, particularly with reference to the first aspect of the present invention, is a washcoat coating (eg, active metal and hydrocarbon adsorbent) provided on a support substrate. And a washcoat material). Typically, the expression “one catalyst layer” as used herein refers specifically to the first aspect of the invention, the expression “second wash” used in other aspects of the invention. It is synonymous with “coat coating”. Similarly, as used herein, the expression “other catalyst layer” refers specifically to the first aspect of the present invention, typically referring to the expression “first” used in other aspects of the present invention. Is synonymous with "wash coat coating".

  To avoid uncertainty, the term “second washcoat coating, where the second washcoat coating is placed in a layer above the first washcoat coating” refers to the second washcoat The coating can be placed directly on top of the first washcoat coating, or one or more intervening layers can be placed between the first washcoat coating and the second washcoat coating. It points to something. Three-layer catalyst compositions are known in the DOC and NAC fields (see UK Patent Application No. 1021649.7 filed December 21, 2010, respectively in the name of the applicant / assignee).

  As used herein, the phrase “consisting essentially of” substantially refers to the scope of a claim or features in the claim to the specified material or step, as well as to the basic features of the claimed invention. Limited to include any other materials and steps that do not affect. It has an intermediate meaning between the expressions “consisting of” and “comprising”.

EXAMPLES The present invention is illustrated by the following non-limiting examples.

Reference example 1
1) Preparation of one catalyst layer (surface layer side) Pt and Pd (2: 1) as active metals are mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent. A slurry of “one catalyst layer” was prepared. The amount of hydrocarbon adsorbent present was 12 grams per liter of support and the active metal concentration was 0.4 weight percent. The weight of catalyst per liter of support was 50 g (0.2 g active metal).

2) Preparation of the other catalyst layer (support side) Pt and Pd (2: 1) as active metals are mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent, A slurry of “the other catalyst layer” was prepared. The amount of hydrocarbon adsorbent present was 30 g per liter of support and the active metal concentration was 1.7 weight percent. The weight of catalyst per liter of support was 105 g (active metal 1.785 g).

3) Coating to support substrate First, 1.3 liters of honeycomb support substrate of NGK was coated with the slurry of “the other catalyst layer”. Next, firing was performed. Next, the slurry of “one catalyst layer” was coated so as to cover “the other catalyst layer”. Firing is then performed to provide Reference Example 1.

Reference example 2
1) Preparation of one catalyst layer (surface layer side) Pt and Pd (2: 1) as active metals are mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent. A slurry of “one catalyst layer” was prepared. The amount of hydrocarbon adsorbent present was 12 grams per liter of support and the active metal concentration was 2 weight percent. The weight of catalyst per liter of support was 90 g (1.8 g active metal).

2) Preparation of the other catalyst layer (support side) Pt and Pd (2: 1) as active metals are mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent, A slurry of “the other catalyst layer” was prepared. The amount of hydrocarbon adsorbent present was 30 g per liter of support and the active metal concentration was 0.3 weight percent. The weight of catalyst per liter of support was 65 g (0.195 g of active metal).

3) Reference Example 2 for coating on a supporting substrate was obtained as Reference Example 1.

Evaluation test 1
The final catalyst was heat treated in an oven at 800 ° C. for 20 hours and then installed in the exhaust pipe of a four-row diesel engine. Using commercial diesel oil (JIS 2), a temporary action test was performed on the actual exhaust gas to evaluate the catalyst performance.

Test result 1
The results are presented in Table 1. T ₅₀ (which indicates that the catalyst inlet temperature when conversion reaches 50% or more of the catalyst performance is below the T ₅₀ value) is low for Reference Example 2 and the catalytic action of Reference Example 1 However, it is suggested that it is higher than Reference Example 2.

Reference example 3
1) Preparation of one catalyst layer (surface layer side) Pt and Pd (2: 1) as active metals are mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent. A slurry of “one catalyst layer” was prepared. The amount of hydrocarbon adsorbent present was 30 g per liter of support and the active metal concentration was 1.7 weight percent. The weight of catalyst per liter of support was 105 g (active metal 1.785 g).

2) Preparation of the other catalyst layer (support side) Pt and Pd (2: 1) as active metals are mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent, A slurry of “the other catalyst layer” was prepared. The amount of hydrocarbon adsorbent present was 12 grams per liter of support and the active metal concentration was 0.4 weight percent. The weight of catalyst per liter of support was 50 g (0.2 g active metal).

3) Coating Reference Example 3 on the support substrate was obtained as Reference Example 1.

Evaluation test 2
The final catalyst was heat treated in an oven at 800 ° C. for 20 hours and then installed in the exhaust pipe of a four-row diesel engine. Using commercially available diesel oil (JIS 2), a temporary action test was performed on the actual exhaust gas to evaluate the catalyst performance.

Test result 2
The results are presented in Table 2 and suggest that the catalytic action of Reference Example 3 is higher than that of Reference Example 2.

Example 1
1) Preparation of one catalyst layer (surface layer side) Pt as an active metal is mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent, and “one catalyst layer” A slurry of was prepared. The amount of hydrocarbon adsorbent present was 24 grams per liter of support and the active metal concentration was 0.2 weight percent. The weight of catalyst per liter of support was 90 g (active metal 0.18 g).

2) Preparation of the other catalyst layer (support side) Pt as an active metal is mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent, and the “other catalyst layer” A slurry was prepared. The amount of hydrocarbon adsorbent present was 6 grams per liter of support and the active metal concentration was 2.2 weight percent. The weight of catalyst per liter of support was 90 g (active metal 1.98 g).

3) Coating on support substrate Example 1 was obtained using the same method as described in Reference Example 1.

Reference example 4
1) Preparation of one catalyst layer (surface layer side) Pt as an active metal is mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent, and “one catalyst layer” A slurry of was prepared. The amount of hydrocarbon adsorbent present was 15 grams per liter of support and the active metal concentration was 1.2 weight percent. The catalyst weight per liter of support was 90 g (active metal 1.08 g).

2) Preparation of the other catalyst layer (support side) Pt as an active metal is mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent, and the “other catalyst layer” A slurry was prepared. The amount of hydrocarbon adsorbent present was 15 grams per liter of support and the active metal concentration was 1.2 weight percent. The catalyst weight per liter of support was 90 g (active metal 1.08 g).

3) Coating on supporting substrate Reference Example 4 was obtained as Reference Example 1.

Reference example 5
1) Preparation of one catalyst layer (surface layer side) Pt as an active metal is mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent, and “one catalyst layer” A slurry of was prepared. The amount of hydrocarbon adsorbent present was 6 grams per liter of support and the active metal concentration was 2.2 weight percent. The weight of catalyst per liter of support was 90 g (active metal 1.98 g).

2) Preparation of the other catalyst layer (support side) Pt as an active metal is mixed with alumina (Al ₂ O ₃ ) as a washcoat material and zeolite as a hydrocarbon adsorbent, and the “other catalyst layer” A slurry was prepared. The amount of hydrocarbon adsorbent present was 24 g per liter of support and the active metal concentration was 0.2 weight percent. The weight of catalyst per liter of support was 90 g (active metal 0.18 g).

3) Coating on support substrate Reference Example 5 was obtained as Reference Example 1.

Evaluation test 3
The final catalyst was heat treated in an oven at 800 ° C. for 20 hours and then installed in the exhaust pipe of a four-row diesel engine. Using commercial diesel oil (JIS 2), a temporary action test was performed on the actual exhaust gas to evaluate the catalyst performance.

Test result 3
The results are presented in Table 3, suggesting that the catalytic action is clearly higher in Example 1 than in Reference Examples 5 and 5. Therefore, this result shows that the hydrocarbon adsorbent present in one catalyst layer is larger than the concentration present in the other catalyst layer in comparison with the uniform catalyst weight in one catalyst layer and the other catalyst layer, It was pointed out that the CO oxidation action is improved by a catalyst structure in which the concentration of the active metal present in one catalyst layer is lower than the concentration of the active metal present in the other catalyst layer.

Example 2
Preparation of Substrate Monolith Coated with 3 wt% Cu / CHA Zeolite Commercial aluminosilicate CHA zeolite was added to an aqueous solution of Cu (NO ₃ ) ₂ with stirring. The slurry was filtered, then washed and dried. The procedure was repeated to achieve the desired metal loading. The final product was fired. After mixing, a binder and a rheology modifier were added to form a washcoat composition.

  A 400 cpsi cordierite flow-through substrate monolith using the method disclosed in Applicant / assignee's WO 99/4726, (a) placing containment means on top of the support; b) after (a), administering a predetermined amount of liquid component to said containment means in either order of (b) after (b) or (b); and (c) applying pressure or reduced pressure. The liquid component is coated with an aqueous slurry of a 3 wt% Cu / CHA zeolite sample using a method comprising drawing the liquid component into at least a portion of the support and retaining substantially all of the amount in the support. It was. This coated product (coated on one end only) is dried and then baked, and the process is repeated on the other, so that almost the entire substrate monolith is coated and the joint between the two coatings There is a slight overlap in the axial direction. The coated monolith was heat aged in an oven at 500 ° C. for 5 hours. A 1 inch (2.54 cm) diameter X 3 inch long (7.62 cm) core was cut from the finished product.

Example 3
Preparation of Diesel Oxidation Catalyst A Platinum nitrate and palladium nitrate were added to an aqueous slurry of particulate silica-alumina. Beta zeolite is added to the slurry so that it constitutes <30% of the solids content by mass as zeolite and forms a washcoat slurry. The washcoat slurry was administered to a 400 cpsi flow-through substrate monolith using the method disclosed in WO 99/47260. The dosed part was dried and then calcined at 500 ° C. The Pt: Pd weight ratio in the first washcoat coating layer was 2: 1.

A second aqueous washcoat slurry was prepared as described above, but with different amounts of platinum nitrate and palladium nitrate. This second washcoat slurry was dispensed on top of the pre-coated first layer using the same method used to apply the first washcoat coating. The second washcoat coating was dried and then baked at 500 ° C. The Pt: Pd weight ratio in the second washcoat coating layer was 1: 1.6 and the total PGM load in the combined first washcoat coating and the second washcoat coating was 1: 1. It was. The combined first washcoat coating and the second washcoat coating have a total washcoat load of 3.0 gin ^-3 , the combined first washcoat coating and the total platinum of the second washcoat coating. Group metal loading was 120 gft ⁻³ .

  A 1 inch (2.54 cm) diameter x 3 inch (7.62 cm) long core was cut from the finished product. The resulting part is described as “brand new”, ie not heat aged.

Reference example 6
Preparation of Diesel Oxidation Catalyst B Platinum nitrate and palladium nitrate were added to an aqueous slurry of particulate stabilized alumina. Beta zeolite was added to the slurry, making it <30% of the solids content by mass as zeolite. The washcoat slurry was administered to a 400 cpsi flow-through substrate monolith using the same method as in Example 3. The coated part was dried and then fired at 500 ° C. The Pt: Pd weight ratio in the first washcoat coating was 2: 1.

A second aqueous washcoat slurry was prepared by adding platinum nitrate to the granular alumina slurry. Beta zeolite was added to the slurry, making it <30% of the solids content by mass as zeolite. This washcoat slurry was dispensed on top of the pre-coated first layer using the same method as before. The second washcoat coating was then dried and a portion of it was baked at 500 ° C. The Pt: Pd weight ratio in the second washcoat coating layer is 1: 0 and the total PGM load in the combined first washcoat coating and the second washcoat coating is 3.0 gin ^-3 The lower layer has the majority of the washcoat load. The total platinum group metal loading of the first washcoat coating and the second washcoat coating combined was 85 gft- ³ . The Pt: Pd weight ratio of both the first washcoat coating and the second washcoat coating combined was 4: 1. A 1 inch (2.54 cm) diameter x 3 inch (7.62 cm) long core was cut from the finished product. The resulting part may be described as “brand new”, ie not heat aged.

Example 4
Preparation of diesel oxidation catalyst C
Platinum nitrate was added to the aqueous slurry of alumina. Beta zeolite was added to the slurry, making it <30% of the solids content by mass as zeolite. The washcoat slurry was administered to a 400 cpsi flow-through substrate monolith using the same method as in Example 2. The dosed part was dried and then calcined at 500 ° C. This first coating layer has a Pt: Pd weight ratio of 1: 0.

A second aqueous washcoat slurry was prepared by adding platinum nitrate and palladium nitrate to the granular alumina slurry. Beta zeolite was added to the slurry, making it <30% of the solids content by mass as zeolite. This second washcoat slurry was dispensed on top of the pre-coated first layer. The second washcoat coating was dried and then baked at 500 ° C. The Pt: Pd weight ratio in the second washcoat layer was 2: 1. The combined Pt: Pd weight ratio of both the first washcoat coating and the second washcoat coating is 4: 1 and the total platinum group metal loading of both layers combined is 85 gft ^-3. It was. The total washcoat load for both the first and second layers combined is 3.0 gin ^-3 with the majority of the washcoat load being in the second washcoat coating.

  A 1 inch (2.54 cm) diameter x 3 inch (7.62 cm) long core was cut from the finished product. The resulting part may be described as “brand new”, ie not heat aged.

Example 5
System Test A test was conducted on the first synthetic catalytic activity test (SCAT) laboratory reactor shown in FIG. 1, where the thermal aging core of the coated Cu / CHA zeolite SCR catalyst of Example 1 was Diesel oxidation catalyst (DOC) B (according to reference example 6) or C (according to example 4) was placed in a conduit downstream of the core. The syngas mixture passed through the conduit at a rate of 6 liters per minute. A furnace was used to heat the DOC sample at a steady state temperature at a catalyst outlet temperature of 900 ° C. for 2 hours (or “heat aged”). The SCR catalyst is placed downstream of the DOC sample and is maintained at a catalyst temperature of 300 ° C. during the thermal aging process by adjusting the length of the tube between the furnace outlet and the SCR inlet, provided that If so, a water-cooled heat exchanger jacket may be used. The temperature was determined using appropriately positioned thermocouples (T ₁ and T ₂ ). The gas mixture used during heat aging was 40% air, 50% N ₂ and 10% H ₂ O.

Following DOC heat aging, the SCR catalyst was removed from the first catalytic reactor and inserted into a second SCAT reactor, specifically testing the NH ₃ -SCR action of the heat aging sample. The SCR catalyst is then synthesized gas mixture (O ₂ = 10%; H ₂ O = 5%; CO ₂ = 7.5%; CO = 330 ppm; NH ₃ = 400 ppm; NO = 500 ppm; NO ₂ = 0 ppm; N ₂ = balance, ie an α value of 0.8 is used (ratio of NH ₃ : NO _x , so that the maximum possible NO _x conversion available was 80%) Tested for action at 500 ° C., the resulting NO _x conversion was graphed against temperature on the attached bar graph of FIG. This graph basically measures the competition between reaction (9) and reaction (5), so how much NO does reaction (9) depend on the consumption of available NH ₃ required for the SCR reaction (reaction (5))? Measure whether it affects the _x- conversion.

From the results presented in FIG. 2, it can be seen that DOC C (according to Example 6) retains a higher ratio of NO _x conversion than DOC B (according to Reference Example 6). In the conditions used to test this result, the inventors compared Pt to the reverse placement of DOC C (in which case the outer layer has a Pt: Pd weight ratio of 2: 1) It is more volatile from the DOC B outer layer with a Pt: Pd weight ratio of 1: 0, and the total Pt: Pd weight ratio of both layers combined in both cases is equal, i.e. 4: 1 did.

Example 6
Preparation of Substrate Monolith Coated with 5 wt% Fe / Beta Zeolite A commercially available zeta zeolite was added to an aqueous solution of Fe (NO ₃ ) ₃ with stirring. After mixing, a binder and rheology modifier were added to form a washcoat composition.

  A 400 cpsi cordierite flow-through substrate monolith was prepared using the method disclosed in Applicant / assignee WO 99/4726 as described in Example 2 above, using a 5 wt% Fe / beta zeolite sample. Of an aqueous slurry. This coated product (coated at one end only) is dried and then baked, and the process is repeated at the other end to coat almost the entire substrate monolith and between the two coatings. There is a slight overlap in the axial direction at the joint. A 1 inch (2.54 cm) diameter x 3 inch (7.62 cm) long core was cut from the finished product.

Reference example 7
Preparation of a Pt-only catalyst wall flow filter Washcoat composition comprising a mixture of alumina particles, platinum nitrate, binder, and rheology modifier ground to a relatively high particle size distribution in deionized water Was prepared. Aluminum titanate wall flow filter using a method and apparatus disclosed in Applicant / assignee WO 2011/080525, with a final washcoat load of 0.2 g / in ³ and 5 g / ft ⁻³ The first end channel, which is coated with the catalyst composition to the desired total load and intended to be oriented upstream, is 75% of its total length by a washcoat containing platinum nitrate and particulate alumina from its intended upstream end. The coated, opposite end and channel intended to be oriented downstream is coated 25% of its total length with the same washcoat as the inlet channel. That is, the method includes (i) holding the honeycomb monolith substrate substantially vertically; and (ii) pouring a predetermined amount of liquid into the substrate through the open end of the channel at the lower end of the substrate. A step of (iii) holding the charged liquid in a sealed manner in the substrate; (iv) turning over the substrate containing the held liquid; and (v) at the inverted lower end of the substrate. It comprises the step of drawing liquid along the channel of the substrate by applying a vacuum to the open end of the channel of the substrate. The catalyst composition can be coated from the first end to the filter channel, after which the coated filter is dried. The dried filter coated from the first end was then turned over and the process was repeated, coating the same catalyst from the second end to the filter channel, and then dried and calcined.

  A 1 inch (2.54 cm) diameter x 3 inch (7.62 cm) long core was cut from the finished product. The resulting part may be described as "brand new", i.e. not heat aged.

Example 7
Preparation of a catalytic wall flow filter containing a Pt: Pd weight ratio of 1: 3 Reference Example 7 except that the washcoat applied to both the inlet and outlet channels of the filter contains palladium nitrate in addition to platinum nitrate. A coated filter was prepared using the same method. The washcoat load at the inlet and outlet channels is performed so that a 5 g / ft ³ Pt, 5 gf / t ³ Pd load is reached on both the inlet and outlet faces, ie the total PGM load reaches 10 g / ft ^3. It was.

  A 1 inch (2.54 cm) diameter x 3 inch long core was cut from the finished product. The resulting part may be described as "brand new", i.e. not heat aged.

Example 8
Preparation of a catalytic wall flow filter containing a Pt: Pd weight ratio of 5: 1 Reference Example 7 except that the washcoat applied to both the inlet and outlet channels of the filter contains palladium nitrate in addition to platinum nitrate. A coated filter was prepared using the same method. The washcoat loading at the inlet and outlet channels is done so that a 5 g / ft ³ Pt, 1 g / ft ³ Pd load is reached on both the inlet and outlet faces, ie the total PGM load reaches 6 g / ft ^3. It was.

  A 1 inch (2.54 cm) diameter x 3 inch long core was cut from the finished product. The resulting part may be described as "brand new", i.e. not heat aged.

Example 9
System Test A test was performed on the first synthetic catalytic activity test (SCAT) laboratory reactor shown in FIG. 1, where the brand new core of the coated Fe / beta zeolite SCR catalyst of Example 2 was It was placed in a conduit downstream of the core of either the Reference Example 7 or the catalyst wall flow filter of Example 7 or 8. The synthesis gas mixture passed through the conduit with a catalyst stroke volume of 30,000 hr ⁻¹ . Using a furnace, the catalyst wall flow sample was heated at a steady state temperature at a filter inlet temperature of 900 ° C. for 60 minutes (or “heat aged”), during which the inlet SCR catalyst temperature was 300 ° C. It was used. Air (heat exchanger) or water cooling mechanism was used to cause a temperature drop between the filter and the SCR catalyst. The gas mixture during the heat aging action was 10% O ₂ , 6% H ₂ O, 6% CO ₂ , 100 ppm CO, 400 ppm NO, Cl as 100 ppm HC, and the balance N ₂ .

Following heat aging action, SCR catalyst heat aging is removed from the first SCAT reactor, is inserted into the second SCAT reactor, specifically to test the NH ₃ -SCR action of heat aging sample . The heat-aged SCR catalyst is then synthesized gas mixture (O ₂ = 14%; H ₂ O = 7%; CO ₂ = 5%; NH ₃ = 250 ppm; NO = 250 ppm; NO ₂ = 0 ppm; N ₂ = balance ) At 150, 200, 250, 300, 350, 450, 550 and 650 ° C., tested at 500 ° C. for SCR action, and the resulting NO _x conversion is the temperature for each temperature data point in FIG. Was charted against. This graph basically measures the competition between reaction (9) and reaction (5), so how much NO _x depends on the consumption of available NH ₃ required for the SCR reaction (reaction (5)). Measure how it affects the conversion.

This result is graphically represented in FIG. Referring to FIG. 3, the Fe / beta zeolite SCR catalyst heat aged behind a catalytic soot filter with a Pt: Pd weight ratio of 1: 0 (ie Reference Example 7) is a total NO _x compared to a brand new sample. It can be seen that the conversion effect was significantly reduced. The catalyst soot filter of Example 8 has a Pt: Pd weight ratio of 5: 1 and has improved NO _x conversion action compared to Reference Example 7. However, Example 7 can demonstrate that it has a Pt: Pd weight ratio of 1: 1 and has performance similar to that of a non-heat-aged SCR catalyst. There was little loss of action between the brand new Fe / beta catalyst and the Fe / beta catalyst heat aged at 300 ° C. for 1 hour without any catalyst upstream.

Example 10
Alternative Pt: Pd Weight Ratio Studies Two alternative diesel oxidation catalysts were prepared as follows.

Diesel oxidation catalyst D
A single layer DOC was prepared as follows. Platinum nitrate and palladium nitrate were added to the silica-alumina slurry. By adding beta zeolite to the slurry, it comprised <30% of the solids content by mass as zeolite. Using the method of Example 3, a washcoat slurry was administered to a 400 cpsi flow-through substrate. The dosed part was dried and then calcined at 500 ° C. The total platinum group metal loading in the washcoat was 60 gft ⁻³ and the overall Pt: Pd weight ratio was 4: 1.

  A 1 inch (2.54 cm) diameter x 3 inch (7.62 cm) long core was cut from the finished product. The resulting part may be described as "brand new", i.e. not heat aged.

Diesel oxidation catalyst E
A single layer DOC was prepared as follows. Platinum nitrate and palladium nitrate were added to the silica-alumina slurry. By adding beta zeolite to the slurry, it comprised <30% of the solids content by mass as zeolite. Using the same method used for DOC D, the washcoat slurry was dispensed onto a 400 cpsi flow-through substrate. The dosed part was dried and then calcined at 500 ° C. The total PGM loading in the single layer DOC was 120 g / ft 360 gft ⁻³ and the Pt: Pd weight ratio was 2: 1. A 1 inch (2.54 cm) diameter x 3 inch (7.62 cm) long core was cut from the finished product. The resulting part may be described as "brand new", i.e. not heat aged.

  Both catalysts were tested according to the protocol described in Example 5. The results are illustrated in FIG. 4 with reference to a specific control (a heat-aged SCR catalyst that is not further heat-aged downstream of either DOC C or DOC E).

Overall results, the results of Example 9 shown in Figure 3, in conjunction with Examples 7 and 8 and Reference Example 9, 1: 1 to 5: 1 Pt: Pd weight ratio of platinum group metal, mainly It points out that it is advantageous to alleviate the problem of loss of NO _x conversion action due to volatilization of platinum.

The results of Examples 5 and 10 shown in FIG. 4 are 72% for a SCR catalyst heat aged downstream of a DOC with a total Pt: Pd weight ratio of 2: 1 in combination with diesel oxidation catalysts D and E. using the same protocol with NO _x conversion action showing (69% of that loss of the NO _x conversion effect is relatively small in 67% of the NO _x conversion function as compared to the control in NO _x conversion action of SCR catalyst heat aged behind a total of 1: 1 Pt: Pd weight ratio DOC (not described herein). However, when the total Pt: Pd weight ratio increases to 4: 1, the SCR action decreases significantly to 48%.

  Thus, the inventors have concluded that there is a boundary at a Pt: Pd weight ratio of about 2: 1 overall, beyond which Pt volatilization is likely to occur. Thus, by limiting to a total Pt: Pd weight ratio of 2: 1 in the DOC as a whole, and limiting to ≦ 2: 1 Pt: Pd weight ratio in the second washcoat coating layer, Pt in the DOC Is less likely to volatilize and difficult to move to the downstream SCR catalyst.

  The entire contents of any and all references cited herein to avoid any doubt are incorporated into this application by reference.

Claims (36)

An oxidation catalyst for the purpose of oxidizing hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas, comprising a support substrate and a plurality of catalyst layers supported by the support substrate, The plurality of catalyst layers include a washcoat material, an active metal, and a hydrocarbon adsorbent, one catalyst layer is on the catalyst surface layer side, and one or more other catalyst layers are the one On the lower side of the catalyst layer,
(A) The amount of the hydrocarbon adsorbent in the one catalyst layer is larger than the amount of the hydrocarbon adsorbent in the one or more other catalyst layers, and the concentration of the active metal in the one catalyst layer is Equal to or less than the concentration of the active metal in one or more other catalyst layers, or (b) the amount of hydrocarbon adsorbent in the one catalyst layer is the one or more other catalyst layers The oxidation catalyst is the same as the amount of the hydrocarbon adsorbent in, and the concentration of the active metal in the one catalyst layer is lower than the concentration of the active metal in the one or more other catalyst layers.   The oxidation catalyst according to claim 1, comprising two catalyst layers.   The oxidation catalyst according to claim 1 or 2, wherein the hydrocarbon adsorbent is zeolite. The oxidation catalyst according to any one of claims 1 to 3, wherein the one catalyst layer has a hydrocarbon adsorbent concentration of 0.05 to 3.00 gin- ³ .   The ratio of the amount of hydrocarbon adsorbent in the one catalyst layer and the one or more other catalyst layers is from 10: 1 to 1.1: 1. The oxidation catalyst according to 1.   The oxidation catalyst according to any one of claims 1 to 4, wherein no hydrocarbon adsorbent is present in the one or more other catalyst layers.   The oxidation catalyst according to any one of claims 1 to 6, wherein one catalyst layer or the second washcoat coating has a hydrocarbon adsorbent at a concentration of 10 to 50 weight percent of the layer.   The oxidation catalyst according to any one of claims 1 to 7, wherein the active metal is platinum, palladium, or a mixture of platinum and palladium. 9. The oxidation catalyst according to any one of claims 1 to 8, wherein the one or more other catalyst layers have a concentration of active metal of 0.05 to 3.5 gin- ³ .   10. The ratio of the active metal concentration in the one catalyst layer and the one or more other catalyst layers is from 1:50 to 1: 1.1. 11. Oxidation catalyst.   11. An oxidation catalyst according to any one of the preceding claims, wherein the one catalyst layer has an active metal concentration of 0.01 to 5 weight percent. The washcoat material _is a SiO _{2, Al} 2 O 3, support material selected from CeO ₂ and TiO _2, the oxidation catalyst according to any one of claims 1 to 11.   The oxidation catalyst is a catalyst substrate monolith, the support substrate is a substrate monolith, the one catalyst layer is a first washcoat coating, and one of the other catalyst layers is a second washcoat. The oxidation catalyst according to any one of claims 1 to 12, which is a coating.   The first washcoat coating comprises a catalyst composition comprising platinum and at least one support for the platinum, and the second washcoat coating comprises a catalyst composition comprising both platinum and palladium; The oxidation catalyst according to claim 13, comprising the platinum and at least one support for the palladium, wherein the weight ratio of platinum to palladium in the second washcoat coating is ≦ 2.   An oxidation catalyst is provided on a substrate monolith for use in treating exhaust gas emitted from a lean burn internal combustion engine, and includes a first washcoat coating, a second washcoat coating, A catalyst-based monolith disposed in a layer above the first washcoat coating, wherein the first washcoat coating comprises a catalyst composition comprising platinum; and At least one support, wherein the second washcoat coating comprises a catalyst composition comprising both platinum and palladium, and at least one support for the platinum and the palladium; Catalyst base monolith with a platinum to palladium weight ratio of ≦ 2 in the washcoat coating .   The catalyst substrate monolith according to any one of claims 13 to 15, wherein the substrate monolith is a flow-through substrate monolith.   The second washcoat coating comprises both platinum and palladium, and the first washcoat coating is platinum and palladium in a Pt: Pd weight ratio that exceeds the Pt: Pd weight ratio in the second washcoat coating. The catalyst-based monolith according to any one of claims 13 to 16, comprising both of the above.   18. A catalyst-based monolith according to any one of claims 13 to 17, wherein the Pt: Pd weight ratio of both the first washcoat coating and the second washcoat coating is ≧ 1: 1.   19. The catalyst-based monolith of claim 18, wherein the Pt: Pd weight ratio of both the first washcoat coating and the second washcoat coating is ≧ 2: 1.   20. The catalyst-based monolith according to any one of claims 13 to 19, wherein the Pt: Pd weight ratio in both the first washcoat coating and the second washcoat coating is ≦ 10: 1.   21. Any one of claims 13 to 20, wherein the first washcoat coating comprises 25-75 weight percent of the total platinum group metal present in the first washcoat coating and the second washcoat coating. The catalyst-based monolith according to Item.   The at least one support of the first washcoat coating or the second washcoat coating is optionally stabilized alumina, amorphous silica-alumina, optionally stabilized zirconia, ceria, 22. A metal oxide selected from the group consisting of titania and optionally stabilized ceria-zirconia mixed oxide or molecular sieve or any mixture of two or more thereof according to any one of claims 13 to 21. The catalyst-based monolith as described.   23. At least one of the first washcoat coating and the second washcoat coating comprises a molecular sieve at ≦ 30% by weight of the individual washcoat coating layer. Catalyst base monolith. 24. Any of claims 13 to 23, wherein the washcoat load in each of the first washcoat coating and the second washcoat coating is individually selected from the range of 0.1-3.5 gin- ³ . The catalyst-based monolith according to one item. The oxidation catalyst, a diesel oxidation catalyst or _the NO _x adsorption material catalyst, the catalyst substrate monolith according to any one of claims 13 24.   An exhaust system for a lean burn internal combustion engine, wherein the system comprises a first catalyst-based monolith according to any one of claims 13 to 25.   27. A second catalyst substrate monolith comprising a selective catalytic reduction (SCR) catalyst, wherein the second catalyst substrate monolith is disposed downstream from the first catalyst substrate monolith. Exhaust system.   28. The exhaust system of claim 27, comprising an injector for injecting a nitrogen reducing agent into the exhaust gas between the first catalyst substrate monolith and the second catalyst substrate monolith.   A third catalyst substrate monolith, wherein the substrate monolith of the first catalyst substrate monolith is a flow-through substrate monolith, and the third catalyst substrate monolith includes an inlet surface and an outlet surface. The inlet surface is separated from the outlet surface by a porous structure, the third catalyst substrate monolith comprises an oxidation catalyst, and the first catalyst substrate monolith and 29. An exhaust system according to claim 27 or 28, disposed between the second catalyst-based monoliths.   An injector for injecting a nitrogen reducing agent into the exhaust gas between the first catalyst base monolith and the second catalyst base monolith, wherein the injector for injecting the nitrogen reducing agent into the exhaust gas is the third 30. The exhaust system of claim 29, arranged to inject a nitrogen reducing agent into the exhaust gas between a catalyst substrate monolith and the second catalyst substrate monolith.   A third substrate monolith, wherein the third substrate monolith is a filtering substrate monolith having an inlet surface and an outlet surface, the inlet surface being separated from the outlet surface by a porous structure; 29. An exhaust system according to claim 27 or 28, wherein the third substrate monolith is disposed downstream of the second catalyst substrate monolith.   32. The exhaust system of claim 31, wherein the third substrate monolith includes an oxidation catalyst.   33. Any of claims 27 to 32, wherein the second catalyst substrate monolith is a filtering substrate monolith having an inlet surface and an outlet surface, and the inlet surface is separated from the outlet surface by a porous structure. The exhaust system according to one item.   34. An exhaust system according to any one of claims 29 to 33, wherein the filtering substrate monolith is a wall flow filter.   A lean burn internal combustion engine, particularly for a vehicle, comprising an exhaust system according to any one of claims 26 to 34.   When the catalyst composition comprising platinum is exposed to relatively extreme conditions including relatively high temperatures, the catalyst composition comprising platinum and the platinum disposed on the substrate monolith upstream of the SCR catalyst And a platinum that can be volatilized from a first washcoat coating comprising at least one support in a manner that prevents or prevents the selective catalytic reduction (SCR) catalyst in a lean burn internal combustion engine exhaust system from being contaminated. Trapping platinum volatilized in a second washcoat coating disposed in a layer above the first washcoat coating, wherein the second washcoat coating comprises both platinum and palladium. A catalyst composition comprising: and at least one support for the platinum and palladium, How the weight ratio of platinum and palladium in the serial second washcoat coating is ≦ 2.

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