System for treating exhaust gases

Abstract

A system for treating exhaust gases from a vehicle lean-burn internal combustion engine comprises, in the following order: (i) a first means for injecting a nitrogen-based reducing agent; (ii) a first selective catalytic reduction (SCR) catalyst; (iii) a catalytic soot filter (CSF) containing a filter substrate; and (iv) a second selective catalytic reduction (SCR) catalyst, wherein the CSF contains palladium and optionally platinum, the weight ratio of palladium to platinum in the CSF is greater than 1:1, and the total platinum group metal content of the CSF is 0.3-2 gft -3 That is the case.

Description

Technical Field

[0001] The present invention relates to a system for treating exhaust gas to achieve low NOx, NH3, and N2O emissions without the need for separate ammonia slip catalyst components. As a result, a system with reduced complexity and / or reduced platinum group metal loading requirements can be manufactured while achieving the same or better performance.

Background Art

[0002] Combustion engines produce exhaust gases containing pollutants such as carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). In particular, the emission standards for pollutants in the exhaust gases generated by combustion engines for vehicle engines are becoming increasingly strict. There is a need to provide improved catalysts and exhaust systems for treating and removing such pollutants in exhaust gases that can meet these standards and are cost-effective. It is particularly desirable for these catalysts to exhibit consistent performance over their lifespan.

[0003] Exhaust gases from gasoline engines and diesel engines are generally treated with various catalysts to address different components of the exhaust system. Some of these catalysts contain one or more platinum group metals. The specific platinum group metal(s) (PGM) selected for inclusion in the catalyst depends on various factors such as the reactivity towards specific pollutants, different exhaust gas conditions, cost, durability at high temperatures, support materials, and chemical compatibility with any other components of the catalyst, as well as susceptibility to contamination by impurities.

[0004] To meet current emission standards for large and small diesel engines, a typical approach involves employing an exhaust system architecture comprising a series of catalytic substrates and injectors. From upstream to downstream (for engines where the upstream is connected to or can be connected to the exhaust system), the exhaust system comprises, in the following order: a hydrocarbon fuel injector, a diesel oxidation catalyst (DOC), a catalytic soot filter (CSF, i.e., a catalytic diesel particulate filter (DPF)), a urea (ammonia precursor, nitrogen-based reducing agent) injector, one or more selective catalytic reduction (SCR) catalysts, and an ammonia slip (ASC) catalyst. Providing each of these components is cost-related, particularly when significant loading of PGMs is required.

[0005] A diesel oxidation catalyst (DOC) carries out oxidation reactions by (i) oxidizing carbon monoxide (CO) to carbon dioxide (CO2), (ii) oxidizing hydrocarbons (HC) to water (H2O) and carbon dioxide (CO2), and oxidizing nitric oxide (NO) to nitrogen dioxide (NO2).

[0006] Ammonia slip catalysts (ASCs), also known in the art as ammonia oxidation (AMOx) catalysts, are designed to oxidize ammonia that has passed through an upstream SCR catalyst without converting, for example, NOx to N2 and residual water (H2O).

[0007] Vehicle diesel particulate matter filter systems capture and accumulate small particles in the form of soot. The filter must incorporate some form of regeneration technology. “Regeneration” is a chosen method for burning the diesel particulate matter held in the filter. Regeneration technologies can be broadly categorized into passive, active, and combinations of both. In passive systems, the oxidation temperature of the particulate matter is reduced to a level at which the filter can be automatically regenerated during normal vehicle operation. An example of such a passive system is catalytic soot filtering (a so-called catalytic soot filter, or “CSF”), where a catalytic fuel additive is added so that the particulate matter on the filter is contained in a compositional catalyst to promote soot combustion, generating NO2 upstream of the filter to burn the particulate matter held on the filter, and the particulate matter burns in NO2 at a lower temperature than in oxygen. This is the so-called CRT® effect (see, for example, EP0341832). The rate of passive regeneration depends on the exhaust gas temperature within the system, which in turn can be influenced by several factors, including engine design, filter efficiency during normal operation, and engine load during normal operation.

[0008] SCR catalysts are designed to catalyze the reduction of NOx by selectively using nitrogen-based reducing agents, typically those that can be derived from ammonia precursors such as urea. The reducing agent is injected in a certain amount into the fluid exhaust gas upstream of the SCR catalyst to promote the following main NOx reduction reactions: (1) 4NH3 + 4NO + O2 → 4N2 + 6H2O; (2) 4NH3 + 2NO2 + O2 → 3N2 + 6H2O; and (3) NO + NO2 + 2NH3 → 2N2 + 3H2O (preferably the so-called "fast SCR reaction").

[0009] U.S. Patent Application No. 2004 / 098973 discloses a system for effective NOx and particulate matter control in diesel or other lean-burn internal combustion engines. The system includes a urea-based SCR catalyst, which comprises an oxidation catalyst coupled upstream and a particulate filter coupled downstream of the SCR catalyst. This system configuration results in improved NOx conversion due to rapid SCR catalyst warm-up and higher operating temperatures. Furthermore, by placing the particulate filter last in this system configuration, ammonia emissions in the exhaust pipe are reduced and thermal damage to the SCR catalyst due to particulate filter regeneration is prevented. The filter components may be coated with PGM, but the focus is on the Pt-containing catalyst.

[0010] European Patent No. 3134624 discloses an exhaust gas treatment system comprising: (i) a first dispensing device (371) arranged to supply a first additive to the exhaust flow; (ii) a first reduction catalyst device (331) located downstream of the first dispensing device for reducing nitrogen oxides (NOx) through the use of the additive; (iii) a particulate filter (320) located downstream of the first reduction catalyst device (331) and comprising at least a catalytic oxidation coating; (iv) a second dispensing device (372) located downstream of the particulate filter (320) and arranged to supply a second additive to the exhaust flow; and (v) a second reduction catalyst device (332) located downstream of the second dispensing device (372) and arranged to reduce nitrogen oxides in the exhaust flow through the use of at least one of the first and second additives.

[0011] International Publication No. 03 / 054364 discloses a method for selectively catalyzing the reduction of NOx in exhaust gas flowing through the exhaust system of an internal combustion engine, comprising a filter (40) for particulate matter, which comprises a second catalyst capable of selectively catalyzing the reduction of NOx using a reducing agent, the method comprising introducing a reducing agent or its precursor into the exhaust gas and contacting the resulting gas with a filter. Figure 1 shows an exhaust system comprising a tightly coupled SCR catalyst (12) and an underbody SCR catalyst (14).

[0012] International Publication No. 2019 / 159151 discloses a system for processing exhaust gas flow from an engine, the system comprising an upstream selective catalytic reduction (SCR) catalyst that receives the exhaust gas flow without the interposition of a catalyst; a diesel oxidation catalyst (DOC) located downstream thereof; a catalytic soot filter (CSF) located downstream of the diesel oxidation catalyst; a second SCR catalyst located downstream of the catalytic soot filter; and an ammonia oxidation (AMOx) catalyst. [Overview of the project]

[0013] Therefore, an object of the present invention is to provide a system for treating exhaust gas that can avoid the need for a dedicated ammonia slip catalyst, or at least solve the related problems in the prior art, or provide a commercially viable alternative.

[0014] According to a first aspect, the present invention is a system for processing exhaust gas from a vehicle lean-burn internal combustion engine, the system comprising the following steps: (i) A first means for injecting a nitrogen-based reducing agent, (ii) A first selective catalytic reduction (SCR) catalyst, (iii) A catalytic soot filter (CSF) containing a filter substrate, (iv) comprising a second selective catalytic reduction (SCR) catalyst, CSF contains palladium and optionally platinum, with a weight ratio of palladium to platinum greater than 1:1, and a total platinum group metal content of 0.3-2 gft in CSF. -3 It provides a system.

[0015] Herein lies a further explanation of this disclosure. Different aspects / embodiments of this disclosure are defined in more detail in the following sections. Each of the aspects / embodiments defined in this way may be combined with any other aspects / embodiments or more aspects / embodiments unless otherwise expressly indicated. In particular, any feature shown as preferred or advantageous may be combined with any other or more features shown as preferred or advantageous. Features disclosed in relation to a product may be combined with features disclosed in relation to a method, and vice versa.

[0016] In the following, CSF containing palladium and optionally platinum, where the weight ratio of palladium to platinum in the CSF is greater than 1:1, will be abbreviated as "Pd-rich".

[0017] In systems with nitrogen injectors and SCRs, ammonia slip can be present. This can be addressed with an ASC, but the ASC is an expensive additional component to include, not only due to its PGM content but also because of the additional volume it occupies in the system and the additional system complexity that results in onboard diagnostics that need to be designed around this component. In addition to all other components in the exhaust system, the presence of an ASC undesirably generates additional back pressure within the system.

[0018] The inventors have recognized that CSF can perform not only the function of CSF (i.e., oxidizing CO and HC to CO2 and H2O) but also the function of an ammonia slip catalyst (ASC). This is desirable because the filter components are usually present in the exhaust system anyway, and therefore the associated additional costs, volume, and back pressure are limited. In other words, the present invention proposes the use of existing CSF components that partially function as an ammonia slip catalyst without incorporating a dedicated / additional ASC catalyst, due to a similar PGM composition.

[0019] However, the inventors have further found that CSF needs to be Pd-only, or at least Pd-rich, because these are more selective for the oxidation of NH3 to N2 (than for the oxidation of NH3 to NOx and N2O). As a result, there is less NOx regeneration (i.e., NOx is produced after engine power NOx is reduced by SCR) and less N2O production (N2O is a powerful "greenhouse" gas with a "global warming potential" ("GWP") 273 times that of CO2 over a 100-year timescale, according to the U.S. Environmental Protection Agency). Engine power typically does not contain more than trace amounts of N2O. It is also true that, unlike Pt-containing CSF, Pd-only CSF does not produce any NO2 at all.

[0020] The use of Pd-rich CSF generates less N2O, but it also consumes less NH3. Therefore, an exhaust system configuration with an SCR downstream of the CSF can utilize the slipped NH3. This means that a second nitrogen dosing device may not be required, or may be used to a lesser extent, resulting in better utilization of nitrogen-based reducing agents in the system. Furthermore, the amount of PGM required in a Pd-only configuration is significantly reduced while achieving the same CO and HC conversions.

[0021] Overall NOx conversion across the system is significantly higher for Pd-only CSF in test cycles such as the US06 cycle compared to those containing Pt (in this cycle, due to the increase in inlet temperature across the components, NH3 slip occurs from the first SCR catalyst downstream of the CSF). Without being bound by theory, this is believed to be due to more selective NH3 oxidation across the Pd-only CSF, and thus resulting in less NOx regeneration.

[0022] Therefore, the inventors have found a specific combination of a more specific CSF that can act as a highly selective ASC alternative (one less component) to avoid N2O and NO2 generation, and a system configuration (also referred to herein as "system architecture", i.e., the serial order of components) that can process the slipped NH3 or even benefit from the slipped NH3. The HC and CO conversion of the CSF is generally not impaired.

[0023] Compared to US Patent Application No. 2004 / 098973, the present system requires a Pd-rich, preferably Pd-only CSF, and a downstream SCR component. The instruction in US Patent Application No. 2004 / 098973 to use a Pt-only CSF means that NH3 exposed to the CSF can cause significant NOx regeneration and higher N2O generation. This nullifies the good operation of the system up to after the SCR, as found by the inventors.

[0024] The DPF can be coated with a noble metal, but only Pt is specifically disclosed. Compared with European Patent No. 3134624, the present system requires a Pd-rich or Pd-only CSF component. Each SCR catalyst herein has its own NH3 injector, but it is not essential for the second SCR catalyst of the present invention to have this. Further, the system structure of European Patent No. 3134624 includes the provision of two ammonia slip catalyst components. The present system avoids these requirements, which results in significant cost reduction and leads to simplified on-board diagnosis (OBD) and control system complexity.

[0025] Compared with International Publication No. 03 / 054364, the system described therein includes a DPF (40), but this is coated with an SCR catalyst rather than Pd. Further, the DPF is not immediately downstream of the close-coupled (cc) SCR catalyst, and there is an oxidation catalyst (38) therebetween.

[0026] Summarizing the advantages of the system of the present disclosure, by providing a coated filter component that is Pd-rich or Pd-only and is disposed between two SCR components: - Elimination of the need for a dedicated ammonia slip catalyst in the system (reduction of system cost and complexity) due to additional functionality to the CSF with selective NH3 oxidation, and - Reduction of NOx regeneration and N2O generation (from increased NH3 oxidation selectivity), and - The main function of the CSF to reduce CO / HC emissions while being maintained (without penalty), and - Reduction of the PGM loading / cost in the catalyst components, and - Reduction of the burden / load on the second means for injecting the nitrogen-based reducing agent are enabled.

[0027] The present invention provides a system for processing exhaust gases from a vehicle lean-burn internal combustion engine. Vehicle lean-burn internal combustion engines are well known in the art and include at least all known configurations of diesel engines. The exhaust system used to process the exhaust gases is also of a well known structure, extending from the engine's exhaust manifold, which receives the exhaust gases to be processed, to a tailpipe, through which the processed gases are released into the atmosphere.

[0028] This system comprises numerous different catalyst components, all of which are well known in the art. The forms and structures of components such as SCR and DOC are well known in the art. These will be described in more detail below, but will be immediately familiar to those skilled in the art. While the CSF component is conventionally Pt-rich, those skilled in the art will not have difficulty providing equivalent Pd-rich or Pd-only components according to the teachings provided herein.

[0029] This system proceeds in the following order: (i) A first means for injecting a nitrogen-based reducing agent, (ii) A first selective catalytic reduction (SCR) catalyst, (iii) Catalytic soot filter (CSF), and (iv) comprising a second selective catalytic reduction (SCR) catalyst.

[0030] Preferably, the components are provided without the interposition of further catalysts or filter articles, or without the interposition of further injection means. This preferably means that no such components are provided between the first means for injecting a nitrogen-based reducing agent and the first selective catalytic reduction (SCR) catalyst, or between the first selective catalytic reduction (SCR) catalyst and a catalytic soot filter (CSF), or between the catalytic soot filter (CSF) and, if present, a second means for injecting a nitrogen-based reducing agent, or, if the second means for injecting a nitrogen-based reducing agent is not present, between the catalytic soot filter (CSF) and the second selective catalytic reduction (SCR) catalyst. This does not preclude the presence of upstream components, such as a DOC upstream of the first means for injecting a nitrogen-based reducing agent; in fact, preferably, these are also present. This does not preclude the presence of downstream components, such as further SCR components downstream of the second selective catalytic reduction (SCR) catalyst.

[0031] injection means Means for injecting nitrogen-based reducing agents are well-known components. This helps in metering and supplying the appropriate amount of nitrogen-based reducing agent into the exhaust system. The nitrogen-based reducing agent may be ammonia itself, hydrazine, anhydrous ammonia, aqueous ammonia, or an ammonia precursor selected from the group consisting of urea ((NH2)2CO), ammonium carbonate, ammonium carbamate, ammonium bicarbonate, and ammonium formate. Pure anhydrous ammonia is toxic and difficult to store safely, but does not require further conversion to react with an SCR catalyst. Urea (typically in the form of a solution with water) is the safest to store, but requires conversion to ammonia by thermal decomposition to be used as an effective reducing agent.

[0032] As in conventional systems, the injector is controlled by a controller that monitors numerous engine and exhaust parameters to determine the appropriate amount of nitrogen-based reducing agent to inject. Such parameters include, for example, exhaust gas NOx concentration, exhaust gas temperature, catalyst bed temperature, accelerator position, exhaust gas mass flow rate in the system, manifold vacuum, ignition timing, engine speed, exhaust gas lambda value, amount of fuel injected into the engine, exhaust gas recirculation (EGR) valve position, and the resulting EGR and boost pressure levels.

[0033] The injector can continuously, periodically, or intermittently introduce a reducing agent into the exhaust gas in a dose effective for optimizing the downstream SCR reaction. The injector is in fluid communication with the exhaust gas flow and may be attached to, connected to, and / or integrated with conduits such as pipes to guide the exhaust through at least a portion of the exhaust gas system. The injector may also be in fluid communication with a reducing agent supply tank to provide repeated injections of the reducing agent.

[0034] The amount of nitrogen-based reducing agent introduced into the system can be controlled according to the amount of nitrogen oxides in the exhaust gas. The amount of reducing agent can be determined directly (using a suitable NOx sensor) or indirectly by using a pre-correlated lookup table or map stored in a control system that correlates any measurement indicating the engine condition with the predicted NOx content of the exhaust gas.

[0035] Controlling metering involves limiting the introduction of nitrogen-based reducing agents into the flowing exhaust gas only when it is determined that the SCR catalyst can catalyze NOx reduction at an efficiency greater than the desired level. Metering may be assisted by one or more suitable sensor inputs indicating engine conditions, selected from the group consisting of exhaust gas temperature, catalyst bed temperature, accelerator position, exhaust gas mass flow rate in the system, manifold vacuum, ignition timing, engine speed, exhaust gas lambda value, amount of fuel injected into the engine, exhaust gas recirculation (EGR) valve position, and the resulting EGR and boost pressure amounts.

[0036] In this system, there is at least a first means for injecting a nitrogen-based reducing agent upstream of the first selective catalytic reduction (SCR) catalyst. In some embodiments, there may be a second means for injecting a nitrogen-based reducing agent upstream of the second selective catalytic reduction (SCR) catalyst. In each case, this means is preferably located immediately upstream of the corresponding SCR catalyst, but this does not preclude the presence of components such as a static mixer for mixing the reducing agent into the exhaust gas. In some embodiments, preferably, there is no second means for injecting a nitrogen-based reducing agent upstream of the second selective catalytic reduction (SCR) catalyst. This is because the use of certain Pd-rich CSFs may avoid the need to include this second injector. This is advantageous as it further reduces system complexity and cost.

[0037] SCR catalyst SCR catalysts are also well known. The forms of the first and second SCR catalysts are discussed below. Each of the SCR catalysts can be independently formulated from the types described below. Furthermore, one or both of the first and second SCR catalysts may be divided over two or more adjacent substrates. In this case, the adjacent substrates do not need to have the same composition. Thus, for example, the second SCR catalyst may be provided from two series SCR components (2A and 2B). The exact composition of the SCR catalyst is not important if it is selected and sized for its intended application.

[0038] The two most common designs for the shape of SCR catalysts used are honeycomb and plate. The honeycomb form is typically an extruded ceramic, either uniformly applied across a ceramic support or coated onto a substrate. Plate-type catalysts have a smaller pressure drop, are less prone to clogging and fouling than honeycomb types, but plate configurations are much larger and more expensive. Honeycomb configurations are smaller than plate types but have a greater pressure drop and are more prone to clogging. These supports serve to hold the SCR catalyst composition in place.

[0039] SCR catalyst compositions generally include base metals, oxides of base metals, metals supported on mixed oxides, molecular sieves, metal-containing molecular sieves, or mixtures thereof. The base metals may be selected from the group consisting of cerium (Ce), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), tungsten (W), vanadium (V), and mixtures thereof.

[0040] SCR compositions consisting of vanadium supported on heat-resistant metal oxide surfaces such as alumina, silica, zirconia, titania, ceria, and combinations thereof are well known and widely used commercially in automotive applications. Typical compositions are described in U.S. Patents 4,010,238 and 4,085,193. In particular, compositions commercially used in automotive applications include TiO2, on which WO3 and V2O5 are dispersed at concentrations ranging from 5 to 20% by weight and 0.5 to 6% by weight, respectively. These catalysts may contain other inorganic substances such as SiO2 and ZrO2, which act as binders and accelerators.

[0041] SCR catalysts include molecular sieves or metal-containing molecular sieves. As used herein, “molecular sieve” is understood to mean a metastable substance containing small pores of precise and uniform size that can be used as an adsorbent for gases or liquids. Molecules small enough to pass through the pores are adsorbed, while larger molecules are not. As used herein, “metal-containing molecular sieve” means a metal-exchanged or metal-substituted molecular sieve. SCR catalysts may include aluminosilicate molecular sieves, aluminophosphate molecular sieves, silicoaluminophosphate molecular sieves, metal-containing aluminosilicate molecular sieves, metal-containing aluminophosphate molecular sieves, or metal-containing silicoaluminophosphate molecular sieves.

[0042] A preferred SCR catalyst composition comprises molecular sieves, preferably containing at least silicon and aluminum, and optionally phosphorus, and having an 8-membered ring pore opening structure. Preferably, the molecular sieves have one or more of the following skeleton types as defined by the Structural Committee of the International Zeolite Society: AEI, AFX, CHA, LEV, LTA. Preferably, the skeleton type is CHA, or CHA combined with one or more different skeleton types, such as AEI-CHA intercrystals.

[0043] Aluminosilicate zeolites can have a silica / alumina molar ratio (SAR) defined as iO2 / Al2O3, which ranges from at least about 5, preferably at least about 20, with a useful range of about 10 to 200.

[0044] In addition to molecular sieves, SCR catalysts include transition metals embedded in the sieves. Suitable transition metals include, for example, Cr, Mn, Fe, Co, Ce, Ni, Cu, Zn, Ga, Mo, Ag, In, Sn, Re, Ir, Au, Pr, Nd, W, Bi, and Os. Preferably, the transition metal is Cu, Fe, or a combination thereof. In one embodiment, the amount of transition metal loaded is about 0.3% to about 5% by weight of the catalyst composition. The type and concentration of the transition metal may vary depending on the sieve and its application.

[0045] CSF CSF is a filter component and therefore based on a filter catalyst substrate. A suitable substrate is the so-called wall-flow filter.

[0046] Suitable filter bodies include nonwoven fiber filters, as well as metal or cordierite honeycomb and other types of diesel particulate filters. Preferably, the filter substrate is a monolith having a so-called honeycomb shape, comprising a plurality of adjacent parallel channels, each channel typically having a square, round, hexagonal, or triangular cross-section. The honeycomb shape provides a large catalyst surface area with a minimum overall size and pressure drop. Other substrates include sheets or screens that can be zoned in any suitable manner, including stacking, winding, or arranging around a central axis. Other substrates include packed beds that can be formed of adsorbent pellets, preferably held together with a binder or sintered to form aggregates.

[0047] Filters for use in the present invention can be manufactured using a variety of materials, including sintered metals, ceramics, or metal fibers. A preferred type of filter is a so-called "wall flow" filter made from porous ceramic or other material in the form of a monolithic array of many small channels that extend substantially parallel over most of the length of the filter body, the channels being capped at alternating ends in a checkerboard pattern. Specific building materials for wall flow monoliths include cordierite, α-alumina, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia, or zirconium silicate, ceramic composite fibers, or porous refractory metals. Preferred materials include cordierite, silicon carbide, and aluminatitanate.

[0048] By capping or plugging the alternating ends of the channels in the wall-flow filter, exhaust gases pass through the porous ceramic channel walls. These walls are porous, but prevent most particles from passing through. That is, exhaust gases that have not been processed by the catalytic filter flow into the substrate channel (i.e., the filter inlet), where they come into contact with the upstream side of the substrate wall. During engine operation, a pressure difference exists between the inlet and outlet surfaces of the substrate (higher pressure at the inlet than at the outlet), and therefore a pressure difference also exists between the upstream and downstream sides of the substrate wall. This pressure difference, along with the gas permeability of the wall, allows exhaust gases flowing into the channel opening at the inlet surface to pass from the upstream side of the porous wall to the downstream side of that wall, and then enter the adjacent channel (i.e., the filter outlet) opening into the downstream section of the exhaust system. A wall-flow filter useful in this invention has up to approximately 700 channels (cells) per square inch of cross-section. A wall flow filter may contain approximately 100 to 400 cells ("cpsi") per square inch.

[0049] During normal operation of the exhaust system, soot and other particulate matter accumulate upstream or inlet of the filter, leading to an increase in back pressure. To mitigate this increase in back pressure, the filter substrate is regenerated continuously, i.e. passively, or periodically (i.e., actively), by burning the accumulated soot. The combustion process is facilitated by a catalyst provided on the filter substrate, thereby producing CSF (Computer-Splitting Fluid).

[0050] Pd-rich catalyst compositions can be incorporated into or on the filter by any practical means. For example, a washcoat containing the catalyst can be applied to the inlet side (face) of the filter. The application method and the properties of the washcoat can be modified using techniques known to those skilled in the art, such as the application of pressure or vacuum. After applying the washcoat, it is dried and then calcined. The temperature and duration used for calcination may vary depending on the specific soot catalyst used. Calcination can be carried out at a temperature of about 400°C to about 600°C for about 1 to about 3 hours. In some combinations of soot catalyst and SCR catalyst, the catalyst coating can be activated, preferably at a temperature of about 100°C to about 300°C for about 1 to about 3 hours.

[0051] CSF contains palladium and optionally platinum, with a weight ratio of palladium to platinum greater than 1:1. When CSF contains only Pd as the PGM component (this is the most preferred embodiment), it is referred to herein as Pd-only. When CSF contains a certain amount of Pt, but less by weight than the amount of Pd, the CSF is referred to as Pd-rich. For comparative examples containing Pt ≥ Pd, these are referred to herein as Pt-rich.

[0052] Preferably, the weight ratio of palladium to platinum in the CSF is greater than 2:1, preferably greater than 3:1, preferably greater than 5:1, and preferably greater than 6:1. Since the presence of Pt can cause the regeneration of NOx and the formation of N2O, it is preferable to minimize the amount of Pt present. It is preferable that Pt is substantially absent, and most preferably that the CSF consists only of Pd, i.e., that Pd is the only platinum group metal present in the CSF.

[0053] Preferably, the total platinum group metal content of CSF consists of palladium and optionally platinum, and preferably consists of palladium. According to the present invention, CSF is 0.3 to 2 gft -3It has a total platinum group metal load. These loads are typically lower than the total platinum group metal content of conventional Pt-containing CSF components. Preferably, the Pd content is 0.3 to 2 gft. -3 That is the case.

[0054] Preferably, the CSF filter substrate is coated on the inlet and / or outlet as a single-layer catalyst composition. This is quite different from conventional ASC compositions, which are generally offered as a two-layer catalyst structure with an SCR composition on top of a PGM-containing composition.

[0055] Preferably, the system does not include an ammonia slip catalyst (ASC) upstream of the CSF. Preferably, the system does not include an ammonia slip catalyst (ASC), i.e., does not include one at all.

[0056] To avoid any ambiguity, ASC is typically a two-layer coating (e.g., an NH3 oxidation underlayer with PGM on a support, and a NOx reduction top layer with Cu / Fe on a zeolite, or a blend of NOx reduction and NH3 oxidation catalysts). In conventional ASC, both layers each contain 1.5–3.5 g / in 3 While the CSF of the present invention has a high wash coat loading capacity, the CSF of the present invention preferably has an extremely low wash coat loading capacity (preferably 0.1 to 0.3 g / in). 3 The inventors recognized that the disadvantage of back pressure in the system is mitigated by the use of CSF alone, which has an NH3 oxidizing functional group, compared to incorporating a separate ASC, which has a significantly higher washcoat load.

[0057] Preferably, palladium, and if present, platinum, is provided on a heat-resistant metal support applied to the substrate. Preferably, the platinum group metals may be supported on a high surface area washcoat component such as alumina, zeolites such as aluminosilicate zeolites, silica, non-zeolite silica alumina, ceria, zirconia, titania, or a mixture or composite oxide containing both ceria and zirconia.

[0058] Preferably, the CSF is the only filter in the system. This is desirable because the filter components act as a considerable heat sink, and this can lower the observed operating temperature and impair the effectiveness of the system, especially if there is another filter upstream of the CSF.

[0059] DOC In some embodiments, a diesel oxidation catalyst (DOC) is further provided upstream of the first means for injecting a nitrogen-based reducing agent. The diesel oxidation catalyst (DOC) is for oxidizing the hydrocarbon-soluble organic fraction (SOF) and carbon monoxide content of the diesel exhaust by simple oxidation: CO + 1 / 2O2 → CO2 [HC] + O2 → CO2 + H2O

[0060] DOC can also function to oxidize NO to NO2, which can then be used to oxidize particulate matter in CSF. Furthermore, DOC may play a role in reducing particulate matter (PM) in exhaust gases.

[0061] The oxidation catalyst can be adapted such that the gas flowing into the SCR zeolite catalyst is generated with an NO to NO2 volume ratio of approximately 4:1 to approximately 1:3 at exhaust gas temperatures of 250°C to 450°C at the oxidation catalyst inlet.

[0062] DOC may contain at least one platinum group metal (or a combination of two or more of these metals), such as platinum, palladium, or rhodium, coated on a flow-through monolith substrate. Other metal catalysts that can be used in DOC include aluminum, barium, cerium, alkali metals, alkaline earth metals, rare earth metals, or a combination of two or more of these. The at least one platinum group metal may be platinum, palladium, or a combination of both platinum and palladium. The platinum group metal can be supported on a high-surface-area washcoat component such as alumina, zeolites such as aluminosilicate zeolites, silica, non-zeolite silica alumina, ceria, zirconia, titania, or a mixture or composite oxide containing both ceria and zirconia. The diesel oxidation catalyst composition is dispersed on a high-surface-area, refractory oxide support (e.g., γ-alumina) at a concentration of about 10-120 g / ft. 3 It may contain platinum group metals (e.g., platinum, palladium, or rhodium).

[0063] Purpose In a further embodiment, a vehicle is provided comprising a lean-burn internal combustion engine and an exhaust system as described herein. Preferably, the engine is a diesel engine. Preferably, components (i) to (iii) are tightly coupled to the engine, and component (iv) is located in an underfloor position. Placing components (i) to (iii) in close proximity to the engine (i.e., not in an underfloor position) helps ensure that the CSF operates at a temperature high enough to achieve optimal performance. The optimal benefit is observed under a warm-up test cycle, as shown in the following embodiments.

[0064] In a further embodiment, a method is provided for treating exhaust gases from a vehicle lean-burn internal combustion engine, the method comprising passing the exhaust gases through a system described herein.

[0065] definition As used herein, the singular forms "a," "an," and "the" refer to multiple objects unless the context clearly indicates otherwise.

[0066] The use of the term “comprising” is intended to be interpreted as including such features but not excluding other features, and also intended to include a selection of features that are necessarily limited to those described. In other words, the term also includes the limitations of “essentially consisting of” (intended to mean that certain further components may exist on the condition that they do not substantially affect the essential nature of the described feature) and “consisting of” (intended to mean that if the components are expressed as percentages by their proportions, these together make up 100%, while explaining any unavoidable impurities, but not including any other features).

[0067] As used herein, the term “above” is intended to mean “directly above,” such that there is no intervening layer between one material and another. Spatially relative terms such as “below,” “beneath,” “lower,” “above,” and “upper” may be used herein to facilitate descriptions of the relationship between one element or feature and another. It will be understood that spatially relative terms are intended to encompass different orientations of the catalyst in use or operation, in addition to the orientation shown in the figures.

[0068] The US06 test cycle (officially, the US06 Supplemental Federal Test Procedure (SFTP)) is a test cycle intended to represent aggressive, high-speed, and / or high-acceleration driving behavior, rapid speed changes, and post-start driving behavior. Details of the US06 test cycle can be found at the following link on DieselNet.com: https: / / dieselnet.com / standards / cycles / ftp_us06.php.

[0069] The US06 test cycle is performed immediately after the completion of FTP-75 (Federal Test Procedure-75), and includes three stages: the first cold start stage, the second stabilization stage, and the third warm start stage. Details of the FTP-75 test cycle can be found at the following link on DieselNet.com: https: / / dieselnet.com / standards / cycles / ftp75.php. References to emissions from the FTP-75 test cycle herein refer to emissions detected only during that FTP-75 test cycle and do not include any emissions detected during any stage following the FTP-75 test cycle, such as the US06 test cycle.

[0070] The US06 test cycle is sometimes referred to as the "fourth stage" of FTP-75. The US06 test cycle, which is the "fourth stage" of FTP-75, i.e., the US06 test cycle performed immediately after the completion of the FTP-75 test cycle, is referred to herein as the "standard US06 test cycle," and any reference to emissions during the "standard US06 test cycle" refers only to emissions detected during that "standard US06 test cycle," and does not include any emissions detected during the preceding FTP-75 stage or any test cycles performed after the completion of the "standard US06 test cycle."

[0071] In this specification, a “warm-up US06 test cycle” is defined as an additional US06 test cycle that is initiated immediately after the completion of a preceding “standard US06 test cycle,” that is, while the engine is still hot. References to emissions from a “warm-up US06 test cycle” refer only to emissions detected during that “warm-up US06 test cycle,” and do not include any emissions detected during a preceding “standard US06 test cycle,” or any test cycles after the completion of the “warm-up US06 test cycle.” [Brief explanation of the drawing]

[0072] Here, the present invention will be further explained in the following figures. [Figure 1] An exemplary system is shown in accordance with the disclosures of this specification. [Figure 2] The Pd-only CSF is compared to the Pt-rich Pt / Pd CSF (2:1). The plots show the measured levels of NH3 at the inlet and outlet of these CSFs. The solid line represents the inlet value, and the dashed line represents the outlet value. The line for the Pd-only CSF is higher in both cases. The test was performed using the "Warm US06" cycle. [Figure 3] The Pd-only CSF is compared to the Pt-rich Pt / Pd CSF (2:1). The plots show the measured NOx levels at the inlet and outlet of these CSFs. The solid line represents the inlet value, and the dashed line represents the outlet value. The inlet lines for both CSFs completely overlap. The outlet line is generally lower for the Pd-only CSF in all cases. The test was conducted using the "Warm US06" cycle. [Figure 4a] We compare Pd-only CSF with Pt-rich Pt / Pd CSF (2:1). The plots show the measured levels of N2O at the inlet (Figure 4a) and outlet (Figure 4b) of these CSFs. The solid line represents the inlet value, and the dashed line represents the outlet value. The line for Pd-only CSF is substantially identical at the inlet and outlet. The line for Pt-containing CSF is substantially higher at the outlet. The test was conducted using the "Warm US06" cycle. [Figure 4b] We compare Pd-only CSF with Pt-rich Pt / Pd CSF (2:1). The plots show the measured levels of N2O at the inlet (Figure 4a) and outlet (Figure 4b) of these CSFs. The solid line represents the inlet value, and the dashed line represents the outlet value. The line for Pd-only CSF is substantially identical at the inlet and outlet. The line for Pt-containing CSF is substantially higher at the outlet. The test was conducted using the "Warm US06" cycle. [Figure 5a] We compare Pd-only CSF with Pt-rich Pt / Pd CSF (2:1). The plots show the measured levels of NO2 at the inlet (Figure 5a) and outlet (Figure 5b) of these CSFs. The solid line represents the inlet value, and the dashed line represents the outlet value. The only line that is not substantially zero is the line for Pt-containing CSF that produces a significant level of NO2. The experiment was conducted using the "Warm US06" cycle. [Figure 5b]We compare Pd-only CSF with Pt-rich Pt / Pd CSF (2:1). The plots show the measured levels of NO2 at the inlet (Figure 5a) and outlet (Figure 5b) of these CSFs. The solid line represents the inlet value, and the dashed line represents the outlet value. The only line that is not substantially zero is the line for Pt-containing CSF that produces a significant level of NO2. The experiment was conducted using the "Warm US06" cycle. [Figure 6a] The Pd-only CSF is compared to the Pt-rich Pt / Pd CSF (2:1). The plots show the measured CO levels at the inlet (Figure 6a) and outlet (Figure 6b) of these CSFs. The solid line represents the inlet value, and the dashed line represents the outlet value. The lines show substantially identical CO conversion for both CSFs. The test was conducted using the "Warm US06" cycle. [Figure 6b] The Pd-only CSF is compared to the Pt-rich Pt / Pd CSF (2:1). The plots show the measured CO levels at the inlet (Figure 6a) and outlet (Figure 6b) of these CSFs. The solid line represents the inlet value, and the dashed line represents the outlet value. The lines show substantially identical CO conversion for both CSFs. The test was conducted using the "Warm US06" cycle. [Figure 7] The Pd-only CSF is compared to the Pt-rich Pt / Pd CSF (2:1). The plot shows the measured levels of HC at the inlet and outlet of these CSFs. The solid line represents the inlet value, and the dashed line represents the outlet value. The inlet line is substantially identical and has a height, while the outlet line shows the HC being processed. The line for the Pd-only CSF shows an increase in HC slip compared to the Pt-containing CSF. The test was conducted using the "Warm US06" cycle. [Figure 8a] The NOx, CO, and total HC conversions are shown across three test cycles: FTP-75, standard US06, and warmed-up US06. In each case, the left column shows Pt-containing CSF, and the right column shows Pd-only CSF. [Figure 8b] The NOx, CO, and total HC conversions are shown across three test cycles: FTP-75, standard US06, and warmed-up US06. In each case, the left column shows Pt-containing CSF, and the right column shows Pd-only CSF. [Figure 8c] The NOx, CO, and total HC conversions are shown across three test cycles: FTP-75, standard US06, and warmed-up US06. In each case, the left column shows Pt-containing CSF, and the right column shows Pd-only CSF. [Figure 9a] Three test cycles are shown, each representing NH3 slip across FTP-75, standard US06, and "warmed-up US06". In each case, the left column is Pt-containing CSF, and the right column is Pd-only CSF. [Figure 9b] Three test cycles are shown, each representing NH3 slip across FTP-75, standard US06, and "warmed-up US06". In each case, the left column is Pt-containing CSF, and the right column is Pd-only CSF. [Figure 9c] Three test cycles are shown, each representing NH3 slip across FTP-75, standard US06, and "warmed-up US06". In each case, the left column is Pt-containing CSF, and the right column is Pd-only CSF. [Modes for carrying out the invention]

[0073] According to the system shown in Figure 1, the engine that produces the exhaust gas to be treated is supplied in the following order: tightly coupled DOC, first nitrogen injector (urea injector 1), first SCR component (SCR1), Pd-rich or Pd-only CSF (CSF), second nitrogen injector (urea injector 2), second SCR component (SCR2), optionally a third SCR component (SCR3), after which the treated exhaust gas is released into the atmosphere. [Examples]

[0074] The present invention will now be further described with respect to the following non-limiting embodiments.

[0075] Two systems were set up for testing. The system was prepared using a sub-7L 2011 diesel engine. This system had the following components in the following order: 1. Aged DOC tightly coupled to the engine, 2. First nitrogen-based reducing agent injector, 3. The first aged SCR, 4.2gft -3 With a loading capacity of 0.67 gft, aged CSF containing Pt and Pd in ​​a 2:1 ratio, or 0.67 gft -3 With the loading amount, either of the aged CSFs has only Pd, and therefore both CSFs have the same Pd load, 5. Second nitrogen-based reducing agent injector, 6. The second aged SCR, 7. The third aged SCR.

[0076] The tests conducted utilized standard test protocols, including the chilled FTP-75, standard US06, and a "warmed-up" US06 performed immediately after the standard US06 without a cooling period.

[0077] The test results are shown in Figures 2-9.

[0078] As shown in Figure 2, Pd-only CSF converts less ammonia than Pt-rich (Pt / Pd), calculated to be 97% (Pt-rich CSF) vs. 73% (Pd-only CSF) over a warm-up US06 cycle. As shown in Figure 3, with similar inlet NOx levels, Pd-only CSF releases lower levels of NOx at the outlet, which indicates less NOx regeneration due to more selective oxidation of NH3.

[0079] As shown in Figures 4a-b, Pd-only CSF does not produce significant levels of N2O compared to Pt-rich (Pt / Pd)CSF.

[0080] As shown in Figures 5a-b, Pd-only CSF does not produce significant levels of NO2 compared to Pt-rich (Pt / Pd) CSF.

[0081] As shown in Figures 6a and 6b, the CO performance is not impaired by changes in CSF.

[0082] As shown in Figure 7, the Pd-only CSF slipped a slightly increased amount of HC, which did not affect the overall conversion due to the low levels of the detected concentrations.

[0083] As shown in Figures 8a-c, CO and HC performance were substantially similar across tests for both CSFs, but NOx conversion was significantly higher under the US06 test cycle using Pd-only CSF.

[0084] As shown in Figures 9a-c, Pd-only CSF selectively converts less NH3 to N2O and NOx compared to Pt-rich (Pt / Pd)CSF, and further significantly reduces NH3 slip under high-temperature conditions. The slipped NH3 can be used in the downstream SCR component.

[0085] The following table summarizes the CSF inlet temperature of the Pt-only CSF of the present invention compared to the Pt-rich (Pt / Pd) CSF of a comparative example. The greatest advantage of the present invention is shown in the warm-up US06 cycle, where the inlet temperature is highest.

[0086] [Table 1]

[0087] The detailed description above is provided for illustrative and illustrative purposes only and is not intended to limit the scope of the appended claims. Many modifications of the currently preferred embodiments shown herein will be obvious to those skilled in the art and remain within the scope of the appended claims and their equivalents.

[0088] To avoid any ambiguity, the entire contents of all documents found herein are incorporated herein by reference.

Claims

1. A system for processing exhaust gas from a vehicle lean-burn internal combustion engine, wherein the system operates in the following order: (i) A first means for injecting a nitrogen-based reducing agent, (ii) A first selective catalytic reduction (SCR) catalyst, (iii) A catalytic soot filter (CSF) containing a filter substrate, (iv) comprising a second selective catalytic reduction (SCR) catalyst, The CSF contains palladium and optionally platinum, the weight ratio of palladium to platinum in the CSF is greater than 1:1, and the total platinum group metal content of the CSF is 0.3 to 2 gft. －３ That is the system.

2. (v) The system according to claim 1, further comprising a second means for injecting a nitrogen-based reducing agent, disposed between the CSF and the second SCR catalyst.

3. The system according to claim 1 or 2, wherein the components are provided without the interposition of further catalysts or filter articles, or without the interposition of further injection means.

4. The system according to any one of claims 1 to 3, wherein the weight ratio of palladium to platinum in the CSF is greater than 2:1, preferably greater than 5:

1.

5. The system according to any one of claims 1 to 4, wherein the total platinum group metal content of the CSF consists of palladium and optionally platinum, preferably consisting of palladium.

6. The system according to any one of claims 1 to 5, wherein the palladium and optionally platinum are supported on a high-surface-area washcoat component of alumina, silica, non-zeolite silica-alumina, zirconia, or titania.

7. The system according to any one of claims 1 to 6, wherein the filter substrate of the CSF is coated on the inlet and / or outlet as a single-layer catalyst composition, and / or palladium and optionally platinum are provided on a heat-resistant metal support.

8. The system according to claim 1 or 2, wherein the system does not contain an ammonia slip catalyst (ASC) upstream of the CSF, and preferably the system does not contain an ammonia slip catalyst (ASC).

9. The system according to claim 1 or 2, wherein a diesel oxidation catalyst (DOC) is further provided upstream of the first means for injecting the nitrogen-based reducing agent.

10. The system according to claim 1 or 2, wherein the CSF is the only filter in the system.

11. The system according to any one of claims 1 to 10, wherein the filter substrate of the CSF is a wall flow filter.

12. A vehicle comprising a lean-burn internal combustion engine and an exhaust system as described in any one of claims 1 to 11, wherein components (i) to (iii) are tightly coupled to the engine, and component (iv) is positioned under the floor.

13. A method for treating exhaust gases from a lean-burn internal combustion engine of a vehicle, wherein the method comprises passing the exhaust gases through a system according to any one of claims 1 to 11.

14. The method according to claim 13, wherein the overall NOx conversion across the system is higher in the US06 test cycle compared to the same system, except that the CSF contains Pt to Pd in ​​a ratio of 1:1 or greater with the same total CSF PGM load.

15. The method according to claim 14, wherein the US06 test cycle is a warm-up US06 test cycle.

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