Exhaust Gas Treatment Systems

Abstract

A method and system relating to an exhaust gas treatment system, comprising the following, in order: (i) a first exhaust gas treatment system; (i) a first means for injecting a nitrogenous reductant; (ii) a first selective catalytic reduction catalyst (SCR catalyst); (iii) an ammonia slip catalyst (ASC), and (iv) a second selective catalytic reduction catalyst (SCR catalyst) The ASC comprises an SCR catalyst and a supported palladium (Pd) component.

Description

[Technical Field]

[0001] The present invention relates to an improved exhaust gas treatment system that provides improved NOx treatment and reduced ammonia slip. In particular, the present invention relates to the use of a palladium-containing Ammonia Slip Catalyst (ASC) that is configured to allow for more aggressive ammonia injection (or dosage) for NOx removal without increasing the expected ammonia slip. [Background technology]

[0002] Combustion of hydrocarbon fuels produces engine exhaust or flue gases, which mostly contain relatively benign nitrogen (N2), water vapor (H2O), and carbon dioxide (CO2). However, exhaust gases also contain relatively small amounts of harmful and / or toxic substances, such as carbon monoxide (CO) (from incomplete combustion), hydrocarbons (HC) (from unburned fuel), nitrogen oxides (NOx) (from excessive combustion temperatures), and particulate matter (mostly soot). In order to reduce the environmental impact of exhaust gases emitted (or released or released) into the atmosphere, it is desirable to eliminate or reduce the amount of undesirable constituents (or components), preferably by a process that does not, in turn, generate other harmful or toxic substances.

[0003] NOx (which includes nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O)) is a difficult component to remove from exhaust gases produced by lean-burn engines. The reduction of NOx to N2 is particularly problematic in lean-burn exhaust gases because such exhaust gases contain sufficient oxygen to favor oxidation reactions instead of reduction reactions. Nevertheless, NOx can be reduced by a process commonly known as Selective Catalytic Reduction (SCR). The SCR process involves the conversion of NOx into elemental nitrogen (N2) and water in the presence of a catalyst and with the aid of a nitrogenous reducing agent (e.g., ammonia). In the SCR process, a gaseous reductant (e.g., ammonia) is added to the exhaust gas stream, which is then brought into contact with an SCR catalyst. A reducing agent (or reductant) is adsorbed (or absorbed) on the catalyst, and the reduction of NO proceeds as the gas is passed through or over the catalyzed substrate. The chemical equation for a stoichiometric SCR reaction with ammonia is:

[0004] 4NO+4NH3+O2→4N2+6H2O

[0005] 2NO2+4NH3+O2→3N2+6H2O

[0006] NO + NO2 + 2NH3 → 2N2 + 3H2O

[0007] To maximize the conversion (or transformation or conversion or conversion) of NOx, some SCR processes utilize ammonia in excess of the stoichiometric amount. Unreacted ammonia passing through the SCR process (sometimes referred to as "ammonia slip") is undesirable because the slipped ammonia gas can react with other combustion species and / or can have adverse atmospheric effects if released (or vented) into the atmosphere. To reduce ammonia slip, SCR systems may include an ammonia oxidation catalyst (AMOX) (also known as an ammonia slip catalyst (ASC)) downstream of the SCR catalyst.

[0008] Catalysts are known for oxidizing excess ammonia in exhaust gases. For example, U.S. Pat. No. 7,393,511 describes an ammonia oxidation catalyst comprising a precious metal (e.g., platinum, palladium, rhodium, or gold) on a support (titania, alumina, silica, zirconia, etc.). Such catalysts oxidize NH3 to produce (or give) N2 and / or secondary NOx (or secondary NOx) + H2O, as follows:

[0009] 4NH3+7O2→4NO2+6H2O

[0010] 4NH3+5O2→4NO+6H2O

[0011] 2NH3+2O2→N2O+3H2O

[0012] 4NH3+3O2→2N2+6H2O

[0013] To combat this secondary NOx (or secondary NOx) generation (or formation), a typical ASC comprises a top catalyst layer (or upper catalyst layer or upper catalyst layer or upper catalyst layer) and a bottom catalyst layer (or lower catalyst layer or lower catalyst layer or lower catalyst layer). The top catalyst layer comprises a conventional SCR catalyst. The bottom catalyst layer comprises an ammonia oxidation catalyst (or ammonia oxidation catalyst). The exhaust gas (containing slipped NH3 and little or no NOx) passes through the top SCR layer of the ASC, where the SCR catalyst stores (or stores) a portion of the NH3. Another portion of the NH3 continues to permeate the catalyst until it reaches the bottom layer, where it is oxidized to secondary NOx (or secondary NOx) and H2O. The secondary NOx (or secondary NOx) permeates back to the top layer where it reacts with absorbed NH3 to produce N2 and H2O.

[0014] The top and bottom layers of the ASC are separated (or segregated) to inhibit (or prevent) the rapid oxidation of NH3, which can result in the formation of untreated secondary NOx (or secondary NOx) in the exhaust stream. This is because the top layer of an ASC generally does not contain precious metals (e.g., platinum group metals (PGMs)). Furthermore, the bottom layer (the layer containing the PGM-based oxidation catalyst) is completely coated (or covered) by the top layer, which inhibits (or prevents) untreated secondary NOx (or secondary NOx) from entering the exhaust stream.

[0015] The configuration and composition of ammonia slip catalysts are well known in the art. The ASC is generally placed at the end of the exhaust system and acts as a gatekeeper to ammonia slip from the system, as explained above.

[0016] Traditionally, Pt has been used in ammonia slip catalysts (ASC). The light-off temperature of Pt (approximately 250°C) is lower than that of Pd (approximately 400°C). This means that Pt is preferred over Pd in ​​ASCs at the end of the exhaust system because Pt can achieve lower levels of NH3 slip at lower temperatures than Pd. Pt is most useful in the ASC for exhaust emission cleanup during cold starts, after which the SCR temperature rises and ammonia is used to convert NOx.

[0017] Pt ASC is commercially available, but palladium-containing ASCs are also contemplated. For example, US20150037233 discloses the provision of a palladium-containing ASC component. Summary of the Invention [Problem to be solved by the invention]

[0018] It is an object of the present invention to provide an improved exhaust gas treatment system, which addresses problems associated with the prior art and / or at least provides a commercially viable alternative thereto. [Means for solving the problem]

[0019] Accordingly, the present invention provides an exhaust gas treatment system, which comprises the following items (i) to (iv) in this order: (i) a first means for injecting a nitrogenous reductant; (ii) a first selective catalytic reduction (SCR) catalyst (SCR catalyst); (iii) an ammonia slip catalyst (ASC), and (iv) a second selective catalytic reduction (SCR) catalyst (SCR catalyst) The ASC described above comprises an SCR catalyst and a supported palladium (Pd) component.

[0020] The present disclosure will now be further described. In the following passages (or sections), various aspects / embodiments of the present disclosure are described (or defined or specified) in more detail. Each aspect / embodiment so described (or defined or specified) may be combined with any other aspect(s) / embodiment(s) unless expressly stated to the contrary. In particular, any feature or features described as being preferred or advantageous may be combined with any other feature or features described as being preferred or advantageous.

[0021] The inventors have now discovered that the exhaust system of the present disclosure can be operated in a manner different from conventional ASC-based methods. Rather than being used as a clean-up catalyst at the end of the system for occasional use (cold start and high temperature ammonia slip), the ASC is used continuously as a damper, regulating (or managing or controlling) the ammonia feed to the second SCR. That is, the system does not have an additional injector upstream of the second SCR, but the ASC acts as a damper to manage the ammonia that is seen by the second SCR. This system can operate with lower NOx emissions and lower NH3 slip despite more aggressive ANR (ANR targeted upstream of the first SCR).

[0022] In particular, a single injector upstream of an SCR / ASC / SCR configuration is actively operated with an ammonia to NOx ratio (ANR) > 1 (more ammonia than stoichiometric). This means that the NOx reduction in the first SCR component can be very high. However, this results in increased NH3 slip from the first SCR component, which needs to be mitigated. In this case, such NH3 slip is mitigated by ASC containing Pd (or ASC containing Pd or Pd-containing ASC).

[0023] To operate the ASC in this manner, it is necessary to use a Pd ASC (ie, not a Pt ASC). Pd ASC is highly selective for N2 relative to NOx. This means that in an operating window above 400°C (above the NH3 oxidation light-off temperature observed in Pd ASCs), the Pd ASC can handle intentional ammonia slip without excessive NOx regeneration. If NOx is regenerated (or remade) to a high degree, this would argue for a higher conversion of NOx with SCR. Because the Pt ASC is less selective for N production (i.e., results in greater NO regeneration) at high temperatures (when exposed to intentional NH slip via an aggressive dose strategy), it will regenerate NO significantly, negating the high NO reduction achieved with SCR and resulting in increased NO emissions.

[0024] For the new continuous use approach, Pd (which is more selective for the production (or formation) of N2) would be ideal. Furthermore, it is incorrect for such components to be at the end of the system (see traditional ASC), where they would encounter conditions closer to optimal operating conditions for Pd.

[0025] The present disclosure relates to exhaust gas treatment systems. An exhaust gas treatment system is a conventional arrangement of catalytic components provided in a gas-tight flow path. The system extends from the exhaust manifold, which is the source (or origin or source) of the exhaust gases, to the outlet (or release) for emitting (or opening or releasing) the treated exhaust gases to the atmosphere. Typically the exhaust manifold is the exhaust manifold from an engine (e.g. a diesel car engine). The exhaust gas from a diesel engine comprises hydrocarbons (HS), carbon monoxide (CO), and nitrogen oxides (NOx). These gaseous components must be treated and transformed before they can be released into the atmosphere.

[0026] The exhaust gas treatment systems described in this disclosure are based on providing elements (or parts or members or components) of known exhaust gas systems in novel configurations. That is, an ASC containing Pd (or an ASC containing Pd or a Pd-containing ASC) is unusual, while not described in the SCR / ASC / SCR configuration (as described in this disclosure). The additional ingredients (or parts or members or components) (including, for example, ingredients (or parts or members or components) of the DOC, SCR, and CSF) may all take on a range of different forms and configurations and are not intended to be unduly limited. All such elements (or parts or members or components) would be within the purview of one skilled in the art and may be selected and configured as required for the final configured system.

[0027] A system comprises a number (or plurality) of elements (or parts or members or components) in order. That is, such elements (or parts or members or components) are fluidly connected (or fluidly connected) to one another and arranged (or arranged) so that exhaust gases passing through the exhaust gas treatment system come into contact with each element (or part or member or component) in sequence (the order in which they are listed). For example, exhaust gases to be treated must first pass through an SCR and then through an ASC.

[0028] The system comprises a first means for injecting a nitrogenous reductant (or nitrogenous reductant or nitrogen-based reductant). Such means are typically spray injectors (or spray injectors). The nitrogen reducing agent is typically urea or ammonia, although other precursor chemicals that decompose in situ to provide ammonia may also be injected. For brevity, this disclosure generally refers to ammonia, which is shorthand for ammonia equivalent in those embodiments (embodiments in which the nitrogenous reductant is not ammonia itself). Preferably, the nitrogen reducing agent is ammonia.

[0029] Preferably, the first means for injecting a nitrogenous reductant (or nitrogen-containing or nitrogen-based reductant) is configured to administer (or dose) the nitrogenous reductant at an ANR greater than 1, preferably an ANR of 1.1 to 1.5. ANR (ie, ammonia to NOx ratio) is well known in the art. In conventional systems, this is generally the case when configuring the ANR such that the target's ANR=1. That is, the stoichiometric ratio of ammonia (or ammonia equivalent (or ammonia equivalent or ammonia equivalent)) to NOx is 1. Such a configuration may be based on measurements by a first sensor to determine the NOx level in the exhaust gas.

[0030] Preferably, the system further comprises a first sensor for determining (or measuring) the NOx level in the exhaust gas. The first sensor may be a NOx measuring sensor, the NOx measuring sensor being located (or arranged) downstream of the first means for injecting (or injecting) a nitrogenous reductant. Preferably, if the first sensor is a NOx sensor, the NOx sensor is downstream of the first SCR catalyst. In this manner, feedback can be provided based on the NOx passing through the first SCR to determine (or measure) the nitrogenous dosing required to achieve the desired ANR. Alternatively, the first sensor is one or more of a temperature sensor, an engine speed sensor (or an engine speed sensor), and an engine load sensor (or an engine load sensor). Based on such measurements, a look-up table can be used to determine (or measure) the approximate NOx level in the exhaust gas.

[0031] The system comprises a first selective catalytic reduction catalyst (SCR catalyst). SCR catalysts are well known in the art. The SCR catalyst of the present invention is not particularly limited, provided that the SCR catalyst of the present invention is capable of selectively reducing NOx in the presence of a reducing agent in an oxidizing environment. Preferably, the first SCR catalyst comprises a Cu or Fe doped zeolite component.

[0032] SCR catalysts preferably comprise at least one promoter metal on a high surface area support, such as refractory metal oxides and molecular sieves (e.g., aluminosilicates (zeolites), silico-aluminophosphates (SAPOs), or aluminophosphates (AIPOs)). In certain embodiments, the SCR catalyst has little or no NH3 oxidation capacity (or NH3 oxidative capacity), but can store and release NH3 as a function of temperature, lean or rich environment, or both. As used in this disclosure, the term "lean environment" refers to exhaust gases produced by combustion of a fuel in excess of the stoichiometric amount of an air-fuel mixture (e.g., excess air), or exhaust gases containing oxygen in amounts at least equal to that of a lean-burn exhaust gas. As used in this disclosure, the term "rich environment" refers to exhaust gases produced by combustion of a rich air-fuel mixture.

[0033] Preferred promoter metals are selected from the group consisting of V, Cr, Co, Cu, Fe, Hf, La, Ce, In, V, Mn, Ni, Zn, and Ga, or any combination thereof. The promoter metal may be a free metal or a metal ion and may be incorporated onto or into the support by a variety of techniques, including ion exchange, incipient wetness, and direct coating. Alternatively, it may be incorporated in situ during synthesis of the support material. Preferred promoter metals include Cu and Fe, especially when the promoter metal is loaded on top of the molecular sieve (preferably a small pore zeolite) and / or inside the molecular sieve (preferably a small pore zeolite).

[0034] The promoter metal oxide may be vanadium, for example, free vanadium, vanadium ions, or an oxide of vanadium or a derivative thereof. Preferably, the form (or shape or form) of the vanadium is vanadia (V2O5). In addition to vanadium, the promoter metal oxide may include other catalytically active metal oxides (e.g., tungsten oxide and / or molybdenum oxide). As used in this disclosure, a "catalytically active" metal oxide is one that directly participates as a molecular component in the catalytic reduction of NOx and / or the oxidation of NH3 or other nitrogen-based SCR reductants. In certain embodiments, the SCR catalyst is V2O5 / WO3 / TiO2, optionally comprising MoO3.

[0035] Preferred molecular sieve supports include zeolites and SAPOs having a framework selected from the group consisting of AEI, AFX, CHA, KFI, LEV, ERI, DDR, UEI, RHO, EAB, PAU, MER, GOO, YUG, GIS, UFI, VIN, AEI / CHA intergrowths, BEA, MFI, MOR, and FER. In certain embodiments, the framework is selected from AEI, CHA and intergrowths thereof. The silica-to-alumina ratio of the preferred aluminosilicate molecular sieves is from about 10 to about 50, preferably from about 15 to about 25.

[0036] Particularly preferred SCR catalysts include the following: V2O5 / WO3 / TiO2, optionally containing MoO3; Cu loaded onto an aluminosilicate molecular sieve having a framework selected from AEI, CHA, or a combination thereof or an intergrowth. Fe loaded (or added) onto an aluminosilicate molecular sieve having a framework (or structure or skeleton structure) selected from BEA and FER

[0037] The system comprises an Ammonia Slip Catalyst (ASC). The ASC comprises an SCR catalyst and a supported palladium (Pd) component. The SCR catalyst component may be any of the SCR catalysts described above.

[0038] Supported palladium component means that the palladium is supported on a support material. Such materials are well known in the art. There is no particular restriction on the type of support for palladium, except that it must be a particle with a large surface area, be inert, and be suitable for use in an after-treatment system. Examples of support materials include refractory metal oxides (e.g., alumina, silica, zirconia, titania, ceria, and physical mixtures or composites thereof). Alumina is particularly preferred. Ceria is also particularly preferred. In certain embodiments, the support comprises wide pores (eg, 100-350 Å (angstroms)) or both wide and narrow pores. In certain embodiments, the BET surface area of ​​the support is at least 50 m 2 / g, preferably about 50 to 500m 2 / g, more preferably about 50 to 300m 2 / g or approximately 150-250m 2 / g. The pore volume of the refractory (or heat-resistant) metal oxide support is preferably about 0.1 to 0.5 g / cc, for example about 0.2 to 0.4 g / cc, preferably as measured by mercury intrusion porosimetry.

[0039] Other palladium supports for the second oxidation catalyst include molecular sieves (e.g., aluminosilicates, silicoaluminophosphates, and aluminophosphates) that have a zeolite-type framework (e.g., AEI, AFX, CHA, KFI, LEV, ERI, DDR, UEI, RHO, EAB, PAU, MER, GOO, YUG, GIS, UFI, VIN, AEI / CHA intergrowth, BEA, MFI, MOR, and FER). Preferably, the palladium component is supported on a granular metal oxide or zeolite (preferably alumina).

[0040] Preferably, the ASC is substantially free of (or substantially free of) Pt. The presence of low selectivity Pt in an exhaust system can result in the production (or formation or evolution) of undesirable NOx. Therefore, its content should be minimized. Preferably, the ASC comprises less than 10 wt.%, preferably less than 2 wt.%, preferably less than 1 wt.% Pt, based on the total weight of PGMs in the ASC. Preferably, it does not contain Pt (or is Pt-free).

[0041] Although it is known to provide an ASC element (or ASC component) comprising a mixture of Pt and an SCR catalyst, it is preferred that the ASC for the current system have a layered structure. That is, the Pd is preferably provided in a layer separate from the SCR catalyst. Preferably, in such a layered structure, the upper layer comprises the SCR catalyst and the lower layer comprises a supported palladium (Pd) component. The SCR catalyst incorporated in the ASC is used to treat secondary NOx (or secondary NOx) and, more generally, is physically separate and distinct from the SCR catalysts (first, second, and third SCR catalysts) (as described in this disclosure) to treat NOx produced (or formed or generated) by the combustion of fuel.

[0042] The system comprises a second selective catalytic reduction catalyst (SCR catalyst). The component of the SCR catalyst (or SCR catalyst component) may be any of the SCR catalysts described above. Preferably, the second SCR catalyst comprises a Cu or Fe doped zeolite component.

[0043] Preferably, after the first SCR, there is no additional means for injecting nitrogenous reductant. That is, the Pd-ASC provides all of the ammonia management (or management or control) required for the second SCR catalyst required in this system.

[0044] In one embodiment, the first selective catalytic reduction catalyst (SCR catalyst) and the ammonia slip catalyst (ASC) share a common substrate. In another embodiment, the ammonia slip catalyst (ASC) and the second selective catalytic reduction catalyst (SCR catalyst) share a common substrate. Alternatively, all three may be provided on separate substrates. Providing one or more components on a common substrate provides space and volume efficiency in the exhaust system.

[0045] If they share a common substrate, preferably the ASC occupies less than 50%, more preferably 10-40%, of the axial length of the shared substrate. An SCR catalyst (first or second SCR catalyst) is then provided on the remainder (or remainder) of the axial length of the shared substrate.

[0046] The exhaust gas treatment preferably comprises, upstream of the first means for injecting a nitrogen reductant, in the following order: Second means for injecting nitrogenous reductant a third selective catalytic reduction catalyst (SCR catalyst), and Catalyzed soot filter (CSF) further comprising: The third SCR catalyst can be any of the materials described above for the SCR catalyst.

[0047] A catalyzed soot filter is a component known in the art. In particular, this is a catalyst coated diesel particulate filter (DPF). It catalyzes the oxidation of gaseous emissions, converting carbon monoxide and hydrocarbons into carbon dioxide and water, due to the presence of precious metals (e.g., Pt and Pd) coated on the wall-flow monolith. This also provides sufficient NO2 and a sufficient NO2 / NOx ratio downstream of the SCR for passive regeneration of soot by oxidation of NO to NO2. Wall flow form (or foam) means that when the filter is regenerated (or regenerated), it also filters out particulate matter (or granules) that can be broken down under hot conditions (or heat conditions).

[0048] If the exhaust system includes a CSF, it is undesirable to have ammonia slipping thereon, as the PGMs there will oxidize the ammonia and further produce (or form or generate) NOx. It is therefore desirable to have a system comprising a CSF such that an upstream SCR operates with an underdose of ammonia (wherein the third SCR catalyst is the upstream or "front" SCR of the system). This means that the likelihood of slip is significantly reduced, while still allowing a satisfactory amount of NOx reduction to proceed with the SCR.

[0049] In use, the system has a front SCR (or front SCR) (third SCR) that is fully operational during cold start conditions. However, due to the temperature dependency of the SCR reaction, its performance decreases under higher temperature conditions. The first and second SCRs are in slower, cooler positions, and can take over the required SCR performance when the engine is under high load (all hot). Therefore, the catalyst configurations described in this disclosure enable a new approach to ammonia management, whereby ammonia is reduced in the upstream injectors and increased in the downstream injectors, with the goal of utilizing ammonia most efficiently. Thus, in this disclosure, an aspect of the invention is controlling or varying the injection (or administration or dose) between the two injectors based on the temperature conditions throughout the exhaust system (at the front (cooler) and then towards the back (warmer)).

[0050] Preferably, the exhaust system further comprises a diesel oxidation catalyst upstream of the second means for injecting a nitrogen reductant or between the third SCR catalyst and the CSF. Diesel oxidation catalysts are well known in the art. A Diesel Oxidation Catalyst (DOC) is a catalytic converter specifically designed for diesel engines and equipment to reduce emissions of Carbon Monoxide (CO), Hydrocarbons (HC), and Particulate Matter (PM). They also oxidize NO to NO2 to provide a sufficient NO2 / NOx ratio downstream of the SCR. Modern catalytic converters typically comprise a monolithic honeycomb substrate (or flow-through substrate) coated with a platinum group metal catalyst. The honeycomb structure has many small parallel channels, providing a large catalytic contact area for the exhaust gases. When hot gases come into contact with the catalyst, some exhaust pollutants are converted into harmless substances (carbon dioxide and water).

[0051] Preferably, the exhaust gas treatment system further comprises a second sensor for determining (or measuring) NOx levels in the exhaust gas, and the second means for injecting (or administering) a nitrogenous reductant is configured (or configured) to administer (or dose) the nitrogenous reductant at an ANR of less than 1, preferably an ANR of 0.5 to 0.9, based on a measurement (or measurement) by such second sensor. Like the first sensor, the second sensor may be a NOx measuring sensor, such NOx measuring sensor being located (or arranged) downstream of the second means for injecting nitrogenous reductant, preferably downstream of the third SCR catalyst. Alternatively, the second sensor is one or more of a temperature sensor, an engine speed sensor (or an engine speed sensor), and an engine load sensor (or an engine load sensor). In this second alternative use, such other sensors may be used alone or in combination with a look-up table to estimate NOx levels and thus arrive at a desired ANR dose.

[0052] In a preferred embodiment, the system further comprises a CSF, or a DOC and a CSF, in sequence, downstream of the second SCR.

[0053] In a preferred embodiment, the system does not include any catalytic component downstream of the second SCR.

[0054] In this disclosure, several preferred embodiments of the exhaust system (or exhaust system) according to the present invention are described. In the following embodiments only, the component numbers (or numerical labels) have been renumbered to provide a more logical ascending numbering order from the front (or front side or front) to the rear (or rear side or back) of the exhaust system (or exhaust system). Therefore, in the following embodiments (where there are two means for injecting nitrogenous reductant), the labels for "first" and "second" have been revised. Similarly, in the following embodiment (in which three SCR catalysts are present), the first, second, and third SCR catalysts correspond to the third, first, and second SCR catalysts described above, respectively. In all of these embodiments, the ASC is as described in this disclosure (ie, Pd-based (or Pd-based)).

[0055] According to a preferred embodiment (the embodiment shown in FIG. 3), the exhaust system (or exhaust system) comprises the following in order: (i) a first exhaust port; (i) a first means for injecting a nitrogenous reductant; (ii) a first selective catalytic reduction catalyst (SCR catalyst); (iii) catalyzed soot filter (CSF), (iv) a second means for injecting a nitrogenous reductant; (v) a second selective catalytic reduction catalyst (SCR catalyst); (vi) an ammonia slip catalyst (ASC), and (vii) a third selective catalytic reduction catalyst (SCR catalyst)

[0056] According to a preferred embodiment (the embodiment shown in FIG. 4), the exhaust system comprises the following in order: (i) a first exhaust pipe; (i) diesel oxidation catalyst (or diesel oxidation catalyst), (ii) Catalyzed Soot Filter (CSF); (iii) a first means for injecting a nitrogenous reductant; (ii) a first selective catalytic reduction catalyst (SCR catalyst); (vi) an ammonia slip catalyst (ASC), and (vii) a second selective catalytic reduction catalyst (SCR catalyst)

[0057] According to a preferred embodiment (the embodiment shown in FIG. 5), the exhaust system comprises the following in order: (i) a first exhaust pipe; (i) diesel oxidation catalyst; (ii) a first means for injecting a nitrogenous reductant; (iii) a first selective catalytic reduction catalyst (SCR catalyst); (iv) catalyzed soot filters (CSFs); (v) a second means for injecting a nitrogenous reductant; (vi) a second selective catalytic reduction catalyst (SCR catalyst); (vii) an ammonia slip catalyst (ASC), and (viii) a third selective catalytic reduction catalyst (SCR catalyst)

[0058] According to a preferred embodiment (the embodiment shown in FIG. 6), the exhaust system comprises the following in order: (i) a first exhaust pipe; (i) a first means for injecting a nitrogenous reductant; (ii) a first selective catalytic reduction catalyst (SCR catalyst); (iii) diesel oxidation catalyst; (iv) catalyzed soot filters (CSFs); (v) a second means for injecting a nitrogenous reductant; (vi) a second selective catalytic reduction catalyst (SCR catalyst); (vii) an ammonia slip catalyst (ASC), and (viii) a third selective catalytic reduction catalyst (SCR catalyst)

[0059] According to a preferred embodiment (the embodiment shown in FIG. 7), the exhaust system comprises the following in order: (i) a first exhaust pipe; (i) a first means for injecting a nitrogenous reductant; (ii) a first selective catalytic reduction catalyst (SCR catalyst) (closely connected (i.e., connected within 100 cm, preferably within 50 cm, of the engine manifold)); (iii) diesel oxidation catalyst; (iv) catalyzed soot filters (CSFs); (v) a second means for injecting a nitrogenous reductant; (vi) a second selective catalytic reduction catalyst (SCR catalyst); (vii) an ammonia slip catalyst (ASC), and (viii) a third selective catalytic reduction catalyst (SCR catalyst)

[0060] According to a preferred embodiment (the embodiment shown in FIG. 8), the exhaust system comprises the following in order: (i) a first exhaust pipe; (i) diesel oxidation catalyst; (ii) a first means for injecting a nitrogenous reductant; (iii) a first selective catalytic reduction catalyst (SCR catalyst); (iv) an ammonia slip catalyst (ASC), and (v) a second selective catalytic reduction catalyst (SCR catalyst); (vi) Catalyzed Soot Filter (CSF)

[0061] According to a preferred embodiment (the embodiment shown in FIG. 9), the exhaust system comprises the following in order: (i) a first exhaust pipe; (i) a first diesel oxidation catalyst; (ii) a first means for injecting a nitrogenous reductant; (iii) a first selective catalytic reduction catalyst (SCR catalyst); (iv) an ammonia slip catalyst (ASC), and (v) a second selective catalytic reduction catalyst (SCR catalyst); (vi) a second diesel oxidation catalyst; (vii) Catalyzed Soot Filter (CSF)

[0062] Each of the above examples may further include an (additional) catalyzed soot filter (CSF) downstream of the final selective catalytic reduction catalyst (SCR catalyst), or may further include a further DOC and an (additional) CSF.

[0063] According to a further aspect, there is provided a diesel combustion and exhaust gas treatment system comprising a diesel engine and an exhaust gas treatment system, as described herein, positioned (or arranged or arranged) to treat exhaust gas generated by the diesel engine.

[0064] According to a further aspect, there is provided a method for treating exhaust gases of a diesel engine, the method comprising passing the exhaust gases through an exhaust gas treatment system described herein.

[0065] (definition) As used in this disclosure, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[0066] Use of the term "comprising" is intended to be interpreted as including such feature(s) but not excluding other feature(s), and is intended to include any feature (not necessarily limited to the features listed). In other words, the term, in the absence of context clearly dictating otherwise, also encompasses the limitations "consisting essentially of" (intended to mean that specified additional ingredients (or components) (but which do not materially affect the essential characteristics of the stated feature) may be present) as well as "consisting of" (intended to mean that no other characteristics may be included, such that ingredients (or components) by their proportions, when expressed as a percentage (%), add up to 100%, while taking into account any unavoidable impurities).

[0067] As used in this disclosure, the term "on" is intended to mean "directly on," such that there is no intervening layer between the material said to be "on" and another material. Spatially relative terms, such as "below," "beneath," "lower," "above," "upper," etc., may be used in this disclosure for ease of description to describe the relationship of one element or feature to another element(s) or feature(s). It will be understood that spatially relative terms are intended to include various orientations in addition to the orientation depicted in the figures when the catalyst is in use or operation.

[0068] (drawing) The present invention is further described in this disclosure with reference to the following non-limiting figures. [Brief explanation of the drawings]

[0069] [Figure 1] FIG. 1 shows the basic components of the exhaust system described in this disclosure. [Figure 2] FIG. 2 shows a preferred embodiment of the exhaust system (or exhaust system) described in this disclosure. [Figure 3] FIG. 3 shows a preferred embodiment of the exhaust system (or exhaust system) described in this disclosure. [Figure 4] FIG. 4 shows a preferred embodiment of the exhaust system (or exhaust system) described in this disclosure. [Figure 5] FIG. 5 shows a preferred embodiment of the exhaust system (or exhaust system) described in this disclosure. [Figure 6] FIG. 6 shows a preferred embodiment of the exhaust system (or exhaust system) described in this disclosure. [Figure 7] FIG. 7 shows a preferred embodiment of the exhaust system (or exhaust system) described in this disclosure. [Figure 8] FIG. 8 shows a preferred embodiment of the exhaust system (or exhaust system) described in this disclosure. [Figure 9] FIG. 9 shows a preferred embodiment of the exhaust system described in this disclosure. [Figure 10A]FIG. 10A shows a comparison of NOx conversion for Pd and Pt ASC components in a conventional SCR / ASC configuration. [Figure 10B] FIG. 10B shows a comparison of N2O production for Pd and Pt ASC components in a conventional SCR / ASC configuration. [Figure 11A] FIG. 11A shows a comparison of NH3 conversion for Pt and Pd containing parts in a conventional SCR / ASC configuration. [Figure 11B] FIG. 11B shows a comparison of slip for Pt and Pd containing parts in a conventional SCR / ASC configuration. [Figure 12A] FIG. 12A shows NH conversion (or NH conversion or NH conversion or NO conversion) (FIG. 12 shows the performance of a conventional SCR / SCR / ASC arrangement compared to the SCR / ASC / SCR configuration described in this disclosure). [Figure 12B] FIG. 12B shows slip (FIG. 12 shows the performance of a conventional SCR / SCR / ASC arrangement compared to the SCR / ASC / SCR configuration described in this disclosure). [Figure 13A] FIG. 13A shows the NOx conversion (or NOx conversion or NOx conversion or NOx conversion) performance of a conventional SCR / SCR / ASC arrangement compared to the SCR / ASC / SCR configuration described in this disclosure. [Figure 13B] FIG. 13B shows NO production (or NO make) (FIG. 13 shows the performance of a conventional SCR / SCR / ASC configuration compared to the SCR / ASC / SCR configuration described in this disclosure). [Figure 14A]Figure 14A shows the data obtained when testing the exhaust configuration on an engine. [Figure 14B] Figure 14B shows the data obtained when the exhaust configuration was tested on the engine. DETAILED DESCRIPTION OF THE INVENTION

[0070] As shown in FIG. 1 , an exhaust gas treatment system 1 is provided comprising, in the following order, from an engine 5 to an exhaust (or emission outlet) 10: a first means for injecting a nitrogenous reductant (or nitrogen-containing or nitrogen-based reductant) 15; a first selective catalytic reduction catalyst (SCR catalyst) 20; an ammonia slip catalyst (ASC) 25; and a second selective catalytic reduction catalyst (SCR catalyst) 30. The system further comprises a NOx sensor 31 .

[0071] The ASC 25 comprises a layer 35 of SCR catalyst that overlies a layer 40 containing supported palladium (Pd).

[0072] In use, the first means for injecting nitrogenous reductant 15 is actively operated at an ANR ratio (or ANR ratio) greater than one. This allows the SCR reaction to proceed thoroughly on the first selective catalytic reduction catalyst (SCR catalyst) 20. The first means for injecting 15 nitrogenous reductant controls (or manages or controls) the injection (or administration or dose) of nitrogenous reductant based on measurements taken by the NOx sensor 31 .

[0073] The ammonia slip catalyst (ASC) 25 serves to regulate the ammonia sent to the second selective catalytic reduction catalyst (SCR catalyst) 30 . This ensures that there is no ammonia slip and that NOx emissions (or liberation or release) are minimized. The location of the ammonia slip catalyst (ASC) 25 in the exhaust gas treatment system 1 means that it operates under optimal conditions for the palladium component, making it highly selective for NOx.

[0074] As shown in FIG. 2, the exhaust gas treatment system 1 of FIG. 1 includes a second means for injecting an upstream nitrogen reductant (or a nitrogen-containing or nitrogen-based reductant) 45, a third selective catalytic reduction catalyst (SCR catalyst) 50, and a catalyzed soot filter (CSF) 55. The system further comprises an additional NOx sensor 51 .

[0075] In use, the second means for injecting nitrogenous reductant 45 operates at an ANR of less than 1. This ensures that there is no (or minimal) ammonia slip into the CSF 55. Any ammonia passing through the system is treated downstream by the SCR catalyst 20 . The ANR of the second means for injecting nitrogenous reductant 45 may be controlled (or managed or controlled) based on measurements taken by the additional NOx sensor 51 .

[0076] At cold start, the third selective catalytic reduction catalyst (SCR catalyst) 50 handles the majority (or bulk) of the required SCR reactions. However, as the temperature of the exhaust gas increases, the performance of the upstream third selective catalytic reduction catalyst (SCR catalyst) 50 that is too hot decreases. Thus, ammonia can be saved (or reduced) by shifting the balance of ammonia input (or ammonia dosing) from the second means for injecting nitrogenous reductant 45 (which is upstream and hot) to the first means for injecting nitrogenous reductant 15 (which is cooler and downstream). This means that the performance of the system can be improved by using less nitrogenous reductant.

[0077] 3 to 9, the same elements (or parts or components) as those in FIGS. 1 and 2 above are designated by the same symbols (or reference numerals). Additional ingredients (or parts or components) are shown by their conventional abbreviations (as explained in this disclosure). [Example]

[0078] (Example) The present invention will now be further described with reference to the following non-limiting examples.

[0079] An exhaust gas system was prepared and tested as described below.

[0080] (Reactor Test (or Reactor Test))

[0081] The test reactor was operated with the following settings:

[0082] High Temperature (HT) aging: 650℃ / 264 h / 10% H2O / Air SV across ASC :210,000h -1

[0083] Feed gas: 350 ppm NO, 500 ppm NH, 10% O, 6.5% H, 7% CO, balance N

[0084] ASC (test): 2g / ft 3 Pt or Pd, or 5g / ft 3 Pd, PGM, Al2O3 based bottom layer (0.35g / in 3 WCL excl. PGM), Cu.CHA based top layer (3.33 wt% Cu 2.4g / in 3 WCL)

[0085] SCR (test): Cu.CHA system (3.33 wt% Cu, 2.4 g / in 3 WCL)

[0086] Temperature: 500°C / 30 min. Preconditioning in basic gas was performed, followed by a temperature ramp to 200°C, at which point the flow of NO / NH3 was initiated and emissions were measured from the temperature ramp to 600°C (5°C / min).

[0087] 10A and 10B show the results for NOx conversion (or NOx conversion or NOx conversion or NOx conversion) and NO2 production (or NO2 make) (comparison of Pt and Pd ASC components). Some of them were subjected to high temperature aging (650°C, 264 hours, 10% H2O / Air). These were tested in a feed gas (containing 350 ppm NO, 500 ppm NH, 10% O, 6.5% H, O, 7% CO, balance N) using a reactor rig (as described above).

[0088] 10A shows the improvement in NOx conversion at high temperatures (for two Pd-containing ASCs). The labels on this chart correspond to the three lines at 550° C. in order (top to bottom). FIG. 10B shows the reduction in NO production for Pd-containing ASC. At 550°C, the lowest line (or lines) is at 2 g / ft 3 ) ASC. At 250°C, the highest line (or lines) is Pt ASC.

[0089] 11A and 11B show the results of NH3 conversion and NH3 slip (comparison of the ASC components of Pt and Pd). As can be seen, the Pd ASC exhibits a slower NH3 light-off, but approaches a similar conversion as the Pt ASC in the high temperature regime. In FIG. 11A, the order of the lines (or rays) at 550° C. is the reverse of their order listed in the figure. In FIG. 11B, the order of the lines (or rays) at 550° C. corresponds to their order listed in FIG. 8A.

[0090] FIG. 12A shows the improvement in NH3 conversion at high temperatures (SCR / ASC / SCR configuration described in this disclosure). FIG. 12B shows the reduction in NH3 slip at high temperatures (SCR / ASC / SCR configuration described in this disclosure).

[0091] FIG. 13A shows the improvement in NOx conversion at high temperatures (SCR / ASC / SCR configuration described herein). FIG. 13B shows the reduction in NO production at temperatures below about 500° C. (SCR / ASC / SCR configurations described herein (performance equivalent to that described above)).

[0092] As shown in Figures 10-13, the Pd ASC exhibits higher NOx conversion in the high temperature regime compared to the Pt ASC, where NH3 conversion approaches that of the Pt ASC. In the low temperature region (or low temperature regime), significantly lower N2O production is observed with the Pd ASC compared to the Pt ASC. The ASC configuration of the present disclosure (Pd ASC) exhibits higher NOx conversion and slightly higher NO production in the high temperature regime compared to the conventional configuration (Pt ASC).

[0093] 14A and 14B show engine performance data for an exhaust system configured as described in this disclosure. As shown, the upstream SCR allows for higher NOx emissions with slight variability in ammonia input, yet increases NOx conversion and results in lower NOx emissions. FIG. 14A shows that NH3 slip is reduced (i.e., essentially zero (0)).

[0094] (Example of engine test)

[0095] DOC + inj (ANR 0.9) + SCR1 + CSF + inj (ANR 1.2) + SCR2 (with / without Pd ASC) + SCR3

[0096] DOC (Ba promoter, PGM. SiO2 / Al2O3 system, 2.6g / in 3 WCL) SCR(4.25wt% Cu,Cu.CHA-based, 2.4g / in 3 (WCL, ASC not included) CSF (PGM.Al2O3 system, 0.2g / in 3 WCL) SCR2 (3.33wt% Cu,Cu.CHA-based, 2.4g / in 3 WCL), 5L Pd ASC with or without (0:1 / 2) SCR3 (same as SCR2) (no ASC)

[0097] The above configuration was tested and demonstrated a reduction in NOx emissions (mg / mi) while running the US06 cycle on a 6.6L light duty diesel engine, along with an increase in NOx conversion.

[0098] The above detailed description is provided by way of example and is not intended to limit the scope of the appended claims. Many modifications (or variations) of the presently preferred embodiments set forth in this disclosure will be obvious to those skilled in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. An exhaust gas treatment system, the exhaust gas treatment system comprises the following (i) to (iv): (i) A first means for injecting a nitrogen reducing agent, (ii) First selective catalytic reduction catalyst (SCR catalyst), (iii) Ammonia slip catalyst (ASC), and (iv) Second selective catalytic reduction catalyst (SCR catalyst) An exhaust gas treatment system comprising the following in order, wherein the ASC comprises an SCR catalyst and a supported palladium (Pd) component.

2. The exhaust gas treatment system according to claim 1, wherein the ASC has a layered structure, the upper layer comprises the SCR catalyst, and the lower layer comprises the supported palladium (Pd) component.

3. The exhaust gas treatment system according to claim 1, further comprising a first sensor for determining the NOx level in the exhaust gas, comprising a first means for injecting the nitrogen reducing agent to introduce the nitrogen reducing agent at an ANR greater than 1, preferably 1.1 to 1.5, based on the measurement value from the first sensor.

4. The exhaust gas treatment system according to claim 3, wherein the first sensor is a NOx measuring sensor located downstream of the first means for injecting the nitrogen reducing agent, preferably downstream of the first SCR catalyst, or the first sensor is one or more of a temperature sensor, an engine speed sensor, and an engine load sensor.

5. Upstream of the first means for injecting the nitrogen reducing agent, in the following order: A second means for injecting a nitrogen reducing agent, Third selective catalytic reduction catalyst (SCR catalyst), Catalytic soot filter (CSF) The exhaust gas treatment system according to claim 1, further comprising the following:

6. The exhaust gas treatment system according to claim 5, further comprising a diesel oxidation catalyst upstream of the second means for injecting the nitrogen reducing agent, or between the third SCR catalyst and the CSF.

7. The exhaust gas treatment system according to claim 5, further comprising a second sensor for determining the NOx level in the exhaust gas, comprising a second means for injecting the nitrogen reducing agent to introduce the nitrogen reducing agent at an ANR of less than 1, preferably 0.5 to 0.9, based on the measurement value from the second sensor.

8. The exhaust gas treatment system according to claim 1, wherein the first selective catalytic reduction catalyst (SCR catalyst) and the ammonia slip catalyst (ASC) share a common substrate, or the ammonia slip catalyst (ASC) and the second selective catalytic reduction catalyst (SCR catalyst) share a common substrate.

9. The exhaust gas treatment system according to claim 1, wherein the first SCR catalyst and / or the second SCR catalyst comprises a zeolite component doped with Cu or Fe.

10. The exhaust gas treatment system according to claim 1, wherein the ASC substantially does not contain Pt.

11. The exhaust gas treatment system according to claim 1, wherein the palladium component is supported by granular metal oxide or zeolite, preferably alumina.

12. The exhaust gas treatment system according to claim 1, further comprising CSF, or DOC and CSF in sequence, downstream of the second SCR, or not comprising any catalyst components downstream of the second SCR.

13. A diesel combustion and exhaust gas treatment system comprising a diesel engine and an exhaust gas treatment system according to any one of claims 1 to 12, which is arranged for treating the exhaust gas generated from the diesel engine.

14. A method for treating exhaust gas from a diesel engine, comprising passing the exhaust gas through an exhaust gas treatment system according to any one of claims 1 to 12.

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