Exhaust Gas Treatment Systems

Abstract

The exhaust gas treatment system, in turn, includes an intake for receiving exhaust gas from a lean-burn combustion engine, an injector for providing a nitrogenous reductant, a proximal-coupled vanadium-containing SCR catalyst composition, and one or more downstream PGM-containing oxidation catalyst compositions, wherein the proximal-coupled vanadium-containing SCR catalyst composition includes cerium in a Ce:V molar ratio greater than 0.3.

Description

[Technical field]

[0001] The present invention relates to exhaust gas treatment systems and methods for treating exhaust gases, and in particular to those that employ close-coupled vanadium-containing SCR compositions that have high SCR activity without compromising the activity of downstream PGM-containing oxidation compositions that may additionally contain Cu-zeolite. [Background technology]

[0002] Emissions regulations due to come into force in Europe from 2025 (Euro 7) will require stricter control of NOx and N2O emissions.

[0003] To meet the requirements of the Euro 7 regulation, it is desirable to use vanadium-containing SCR catalysts because of their low selectivity to NO compared to copper zeolites. In particular, it would be desirable to place vanadium-containing SCR catalysts in a close-coupled position that allows them to be rapidly heated by the exhaust gas after switching on (i.e. after engine start), thereby allowing the catalyst to rapidly reach its light-off temperature. The use of a larger amount of vanadium in such catalysts improves their SCR activity. In particular, the use of a larger amount of vanadium in such catalysts improves their NO reduction activity. This is particularly important when vanadium-containing SCR catalysts are placed in a close-coupled position where there is little NO2 present and therefore most of their performance is related to the reduction of NO. In known arrangements, the catalyst support material may be stabilized to allow a higher amount of vanadium to be employed. In some cases, antimony is used to stabilize titania-based support materials. However, increasing the vanadium content makes it more likely that vanadium will volatilize and subsequently lose from the SCR catalyst during use, especially when the SCR catalyst is in a high-temperature close-coupled position. Loss of vanadium from the close-coupled SCR catalyst is particularly problematic for downstream PGM-containing oxidation catalysts such as DOC or ASC, especially those that also contain copper-zeolite, which become poisoned by the released vanadium, thereby reducing their activity.

[0004] There is therefore a need to provide an improved exhaust gas treatment system that employs a close-coupled SCR catalyst composition together with a downstream PGM-containing oxidation catalyst composition that demonstrates high NO activity and low NO selectivity without compromising oxidation activity such that the requirements of Euro 7 legislation may be met. It is an object of the present invention to address this problem and address the shortcomings associated with the prior art, or at least provide a commercially useful alternative thereto. Summary of the Invention

[0005] According to one particular aspect of the present invention, an exhaust gas treatment system includes, in sequence: an intake for receiving exhaust gases from a lean-burn combustion engine; an injector for providing a nitrogen reductant; a proximal linked vanadium-containing SCR catalyst composition; and one or more downstream PGM-containing oxidation catalyst compositions, The proximal linked vanadium-containing SCR catalyst composition comprises cerium in a Ce:V molar ratio greater than 0.3.

[0006] In some embodiments, vanadium is present in the proximal-linked vanadium-containing SCR catalyst composition in an amount of at least 2 wt.%, or from 2 to 6 wt.%, based on V2O5. The proximal-linked vanadium-containing SCR catalyst composition may further include antimony in a Sb:V molar ratio greater than 0.5, or from 0.6 to 0.9. Cerium may be present in the proximal-linked vanadium-containing SCR catalyst composition in a Ce:V molar ratio of 0.3 to 0.7, or from 0.4 to 0.6.

[0007] In some embodiments, the proximal-linked vanadium-containing SCR catalyst composition is provided as an extruded porous substrate or a washcoat on a porous substrate. The extruded porous substrate or porous substrate can be a honeycomb monolith substrate.

[0008] In some embodiments, the close-coupled vanadium-containing SCR catalyst composition comprises a titania-based catalyst support material.

[0009] In certain embodiments, the downstream PGM-containing oxidation catalyst composition is provided as an extruded porous substrate or a washcoat on a substrate.

[0010] In some embodiments, the one or more downstream PGM-containing oxidation catalyst compositions are provided on and / or in the same substrate as the proximal-linked vanadium-containing SCR catalyst composition forming a single catalyst article, the substrate having an inlet end, an outlet end, and an axial length. The proximal-linked vanadium-containing SCR catalyst composition may be disposed in a first region and the one or more downstream PGM-containing oxidation catalyst compositions are disposed in a second region, the first region being spaced apart from the second region. In some embodiments, the first region extends from the inlet end and the second region extends from the outlet end, optionally, the first region extends along 10%-90% of the axial length of the substrate, 25-85% of the axial length of the substrate, and the second region extends along 10%-90% of the axial length of the substrate, 10-60% of the axial length of the substrate. In certain embodiments, the first region and the second region do not overlap such that a gap exists along the axial length of the substrate between the first region and the second region, and optionally, the first region is a first layer and the second region is a second layer.

[0011] The system may further include a coating layer extending from the outlet end over at least a portion of the second region, optionally the coating layer comprising the SCR catalyst composition. In some embodiments, the first region is a first layer and the second region is a second layer, the first region and the second region being separated from one another by an intervening layer extending between the first layer and the second layer, optionally the intervening layer comprising the SCR catalyst composition. In some embodiments, the first layer overlaps the second layer.

[0012] In certain embodiments, the proximal-linked vanadium-containing SCR catalyst composition and the one or more PGM-containing oxidation catalyst compositions are provided on separate substrates, thereby forming a proximal-linked vanadium-containing SCR catalyst article and one or more PGM-containing oxidation catalyst articles, optionally, the proximal-linked vanadium-containing SCR catalyst article being spaced apart from the one or more PGM-containing oxidation catalyst articles.

[0013] In some embodiments, the downstream PGM-containing oxidation catalyst composition comprises an ASC composition and a DOC composition, and the ASC composition is upstream of the DOC composition.

[0014] In certain embodiments, the system further comprises a downstream SCR catalyst composition downstream of the one or more PGM-containing oxidation catalyst compositions, optionally, the one or more PGM-containing oxidation catalyst compositions and the downstream SCR catalyst composition are in an SCRT® configuration.

[0015] In some embodiments, the one or more downstream PGM-containing oxidation catalyst compositions further comprise a Cu-zeolite, where the Cu-zeolite is a small pore zeolite, preferably the Cu-zeolite has a CHA or AEI type framework structure.

[0016] According to some aspects of the present invention, a combustion and emissions treatment system includes: Lean-burn combustion engines; and an exhaust gas treatment system as described herein.

[0017] According to some aspects of the present invention, a method for the treatment of exhaust gas includes treating the exhaust gas in an exhaust gas treatment system as described herein.

[0018] According to one particular embodiment, the invention involves the use of cerium to reduce vanadium loss from a close-coupled vanadium-containing SCR catalyst composition, the close-coupled vanadium-containing SCR catalyst composition comprising cerium in a Ce:V molar ratio greater than 0.3. [Brief description of the drawings]

[0019] [Figure 1] 1 illustrates a first exemplary configuration of a catalyst article according to the present invention. [Diagram 2] 3 illustrates a second exemplary configuration of a catalyst article according to the present invention. [Diagram 3] 3 illustrates a third exemplary configuration of a catalyst article according to the present invention. [Figure 4] FIG. 2 is a schematic diagram of the setup employed to test vanadium loss from the vanadium-containing SCR catalysts of Examples 1-27. [Diagram 5] 5 is a graph demonstrating the reduction in vanadium loss from a vanadium-containing SCR due to the presence of cerium in the catalyst provided as a washcoat on a substrate. The data shown in the graph of FIG. 5 is normalized. [Figure 6] 1 is a graph demonstrating the maintenance of NOx activity achieved despite the presence of cerium in a vanadium-containing SCR catalyst provided as a washcoat on a substrate. [Figure 7] 1 is a graph demonstrating the effect of cerium loading on vanadium loss from an extruded vanadium-containing SCR catalyst and from a vanadium-containing catalyst formed as a washcoat on a substrate, with the data for Examples 7-14 normalized to the data for Example 7 and the data for Examples 15-18 normalized to the data for Example 15. [Figure 8] 1 is a graph of vanadium loading of vanadium-containing SCR catalyst versus vanadium-containing SCR catalyst, demonstrating reduced vanadium loss at different vanadium loadings due to the presence of cerium in the catalyst. [Figure 9] Different representations of the data used in the graph of Figure 5. In Figure 6, the graph is vanadium loss from a vanadium-containing SCR catalyst versus the molar ratio of added metal:vanadium when the added metal is cerium, tungsten, or niobium. [Figure 10] 1 is a graph demonstrating the improved fresh NOx activity at 225° C. achieved at higher vanadium loadings despite the presence of cerium in the vanadium-containing SCR catalyst. [Figure 11] 1 is a graph demonstrating the improved aging NOx activity at 225° C. achieved at higher vanadium loadings despite the presence of cerium in the vanadium-containing SCR catalyst. [Figure 12]1 is a graph demonstrating improved fresh NOx activity at 500° C. with higher vanadium loading achieved despite the presence of cerium in a vanadium-containing SCR catalyst. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] According to a first aspect, there is provided an exhaust gas treatment system comprising, in sequence: an intake for receiving exhaust gases from a lean-burn combustion engine; an injector for providing a nitrogen reductant; a proximal linked vanadium-containing SCR catalyst composition; and one or more downstream PGM-containing oxidation catalyst compositions, An exhaust gas treatment system is provided in which the close-coupled vanadium-containing SCR catalyst composition comprises cerium in a Ce:V molar ratio greater than 0.3.

[0021] In the following passages, different aspects / embodiments are defined in more detail. Each aspect / embodiment so defined may be combined with any other aspect(s) / embodiment(s), unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0022] As discussed above, to meet the requirements of the Euro 7 regulations, it would be desirable to use a close-coupled vanadium-containing SCR catalyst to reduce NOx and NO emissions due to its lower light-off temperature. The use of higher amounts of vanadium in such catalysts is desirable for improving SCR activity, but results in greater volatilization and subsequent loss of vanadium during use, especially when placed in a high temperature close-coupled location. Loss of vanadium from the close-coupled SCR catalyst causes poisoning of downstream PGM-containing oxidation catalysts, thereby reducing their activity. The present invention relates to an exhaust gas treatment system that includes both a close-coupled vanadium-containing SCR catalyst composition and one or more downstream PGM-containing oxidation catalyst compositions, where the close-coupled vanadium-containing SCR catalyst composition includes cerium at a Ce:V molar ratio greater than 0.3. The inventors of the present invention have surprisingly found that the presence of such an amount of cerium surprisingly reduces vanadium volatilization without impairing the performance of the SCR catalyst. The reduced volatilization allows for greater loading of vanadium, which is desirable for improving the efficiency of the SCR catalyst. Reduced volatilization also results in reduced poisoning of downstream PGM-containing oxidation catalysts, such that oxidation catalysts that are smaller in size or have lower PGM loading may be employed while still maintaining sufficient oxidation activity.

[0023] The present invention relates to an exhaust gas treatment system. The exhaust gas treatment system is a system suitable for treating exhaust gas from a lean-burn combustion engine. That is, the exhaust gas treatment system can be used to treat exhaust gas derived from a combustion process in a lean-burn combustion engine, which may be mobile or stationary. The exhaust gas treatment system, in turn, comprises an inlet for receiving exhaust gas from the lean-burn combustion engine, an injector for providing a nitrogen reductant, a close-coupled vanadium-containing SCR catalyst composition, and one or more downstream PGM-containing oxidation catalyst compositions. In other words, the inlet is upstream of the injector, and the injector is upstream of the close-coupled vanadium-containing SCR catalyst composition. The close-coupled vanadium-containing SCR catalyst is upstream of the one or more PGM-containing oxidation catalyst compositions. The exhaust gas treatment system may optionally include further components for treating exhaust gas downstream of the close-coupled vanadium-containing SCR catalyst, such as a particulate filter, which may optionally contain one or more PGMs.

[0024] The injector may be any means for injecting the nitrogenous reductant into the exhaust gas. The injector may include a nozzle. The injector may optionally include a valve. The nitrogenous reductant may include ammonia. The injector is located upstream of the close-coupled vanadium-containing SCR catalyst composition. The catalyst composition of the present invention is for catalytic treatment of exhaust gas from a lean-burn combustion engine to convert or transform components of the gas prior to releasing them into the atmosphere to meet exhaust gas regulations.

[0025] The SCR catalyst composition stores NH3 and selectively reduces NOx with NH3 in the presence of oxygen. The SCR catalyst composition is disposed in a close-coupled position, i.e., located near the intake for receiving exhaust gas from the engine, and is therefore referred to as a close-coupled SCR catalyst composition. In the close-coupled position, the SCR catalyst composition is rapidly heated by the exhaust gas after switching on (i.e., engine start), thereby allowing the SCR catalyst composition to rapidly reach its light-off temperature.

[0026] The proximal-linked SCR catalyst composition contains vanadium and is therefore referred to as a proximal-linked vanadium-containing SCR catalyst composition. The presence of vanadium in the SCR catalyst composition achieves good SCR activity. The vanadium is preferably present in the proximal-linked vanadium-containing SCR catalyst composition as vanadium oxide. Preferably, the proximal-linked vanadium-containing SCR catalyst composition contains at least 2 wt. % vanadium, more preferably 2-6 wt. % vanadium, based on V2O5 (i.e., preferably, the proximal-linked vanadium-containing SCR catalyst composition contains at least 2 wt. %, preferably 2-6 wt. % V2O5). Such levels are suitable for high SCR activity.

[0027] The proximal-linked vanadium-containing SCR catalyst composition may be provided as an extruded porous substrate, or as a washcoat on a substrate, which may be porous, or may be impregnated into a substrate, thereby forming a catalyst article. The substrate includes an inlet end (upstream end) and an outlet end (downstream end) and has an axial length L.

[0028] Catalytic articles are suitable components for use in exhaust gas systems. Typically, such articles are honeycomb monoliths, sometimes referred to as "bricks". They have a high surface area configuration suitable for contacting the gas to be treated with the catalytic material to effect conversion or transformation of the exhaust gas components. Other forms of catalytic articles are known, including plate configurations, as well as wrapped metal catalytic substrates. The catalytic articles described herein are suitable for use in all of these known forms, but are particularly preferred in the form of honeycomb monoliths, as they offer a good performance-to-volume ratio.

[0029] The catalyst article of the present invention is for the catalytic treatment of exhaust gases from lean-burn combustion engines to convert or transform components of the gases prior to their release into the atmosphere to meet exhaust gas regulations.

[0030] The proximal-linked vanadium-containing SCR catalyst composition may be extruded to form an extruded porous substrate, or may be applied to a substrate as a washcoat, or may be impregnated into a porous substrate. The substrate may optionally be formed from a metallic or ceramic material. Thus, the catalyst article containing the proximal-linked vanadium-containing SCR catalyst composition may be an extruded substrate, a washcoated substrate, or an impregnated substrate. Preferably, when the catalyst article is provided as an extruded substrate, a washcoated substrate, or an impregnated porous substrate, the porous substrate is a honeycomb monolith substrate. This is typically a flow-through substrate, as it facilitates the passage of gases in and out of the structure. The substrate may be a filtration substrate. When the proximal-linked vanadium-containing SCR catalyst composition is disposed on a filtration substrate, it forms a selective catalytic reduction filter catalyst, referred to herein by the abbreviation "SCRF®".

[0031] The substrate may be cordierite-based so that it can withstand the environment encountered at the proximal connection location, especially high temperatures. Other suitable substrate materials include ceramic-like materials such as alpha-alumina, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica magnesia, or zirconium silicate, or porous refractory metals. When the proximal connection vanadium-containing SCR catalyst composition is provided as a washcoat on a substrate or impregnated into a porous substrate, the substrate is preferably formed from a ceramic-like material, more preferably cordierite. When the proximal connection vanadium-containing SCR catalyst composition is provided as an extruded porous substrate, the substrate may include titania and one or more fibers and / or binders. The proximal connection vanadium-containing SCR catalyst composition may include a titania-based catalyst support material.

[0032] The proximal linked vanadium-containing SCR catalyst composition includes cerium having a cerium to vanadium molar ratio greater than 0.3, preferably 0.3 to 0.7, more preferably 0.4 to 0.6. By employing cerium and vanadium in such ratios, the volatilization of vanadium is reduced without reducing the activity of the proximal linked vanadium-containing SCR catalyst composition. The reduced volatilization allows for a higher loading of vanadium, which is desirable for improving the efficiency of the SCR catalyst. The reduced volatilization also results in reduced poisoning of downstream PGM-containing oxidation catalysts, such that oxidation catalysts that are smaller in size or have lower PGM loadings may be employed while still maintaining sufficient oxidation activity. By way of example, the proximal linked vanadium-containing SCR catalyst composition may include vanadium in an amount of 2 to 6 wt. %, preferably 3 to 5 wt. %, based on V2O5, and cerium in an amount of 1 to 10 wt. %, preferably 2 to 5 wt. %, based on CeO2. The close-coupled vanadium-containing SCR catalyst composition may include 2-6 wt. %, preferably 3-5 wt. %, V2O5, and 1-10 wt. %, preferably 2-5 wt. %, CeO2.

[0033] The close-coupled vanadium-containing SCR catalyst composition may additionally include antimony. As discussed above, antimony is sometimes used to stabilize titania-based support materials so that greater amounts of vanadium can be used in the close-coupled vanadium-containing SCR catalyst composition. However, as shown by the data in FIG. 2 of the present application, antimony does not substantially reduce the volatilization of vanadium. Antimony may be present in an amount such that the molar ratio of antimony to vanadium is greater than 0.5, preferably 0.6-0.9, more preferably 0.7-0.8. Antimony may be present as Sb2O5. By way of example, the close-coupled vanadium-containing SCR catalyst composition may include 2-6 wt.% V2O5, 2-6 wt.% CeO2, and 3-8 wt.% Sb2O5.

[0034] The proximal linked vanadium-containing SCR catalyst composition may additionally comprise SiO2. SiO2 may be present in an amount of at least 1 wt%, preferably at least 3 wt%. SiO2 may be either doped onto a support, which may be titania, or may function as a binder. When SiO2 is used as a binder (e.g., silica sol), it may be present in an amount of up to 25 wt%. For example, when used as a binder, SiO2 may be present in an amount of 1-20 wt%, preferably 5-20 wt%, more preferably 10-18 wt%. When used as a dopant, such as a titania dopant, SiO2 may be present in an amount of 1-6 wt%, preferably 2-4 wt%. When used as both a dopant, such as a titania dopant, and a binder, SiO2 may be present in an amount of 2-26 wt%, preferably 7-24 wt%, more preferably 12-22 wt%. By way of example, a close-coupled vanadium-containing SCR catalyst composition may include 2-6 wt. % V2O5, 2-6 wt. % CeO2, 3-8 wt. % Sb2O5, 1-20 wt. % SiO2, and the balance TiO2.

[0035] One or more downstream platinum group metal (PGM)-containing oxidation catalyst compositions are disposed downstream of the proximal-linked vanadium-containing SCR catalyst composition. As a result, the exhaust gas passes through the proximal-linked vanadium-containing SCR catalyst composition before passing through the one or more downstream platinum group metal (PGM)-containing oxidation catalyst compositions. The one or more downstream PGM-containing oxidation catalyst compositions oxidize components of the exhaust gas before they are released into the atmosphere. In the exhaust system of the present invention, the cerium present in the upstream SCR catalyst composition reduces vanadium loss therefrom. This reduces vanadium poisoning of the downstream PGM-containing oxidation composition, so that its oxidation activity can be substantially maintained. As a result, the PGM-containing oxidation catalyst can be reduced in size or employ a lower loading of PGM while still maintaining sufficient oxidation activity, thereby reducing costs.

[0036] The one or more downstream PGM-containing oxidation catalyst compositions contain one or more platinum group metals which may be supported on a support material. The one or more platinum group metals (PGMs) present in the PGM-containing oxidation catalyst compositions may be selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, and mixtures of two or more thereof. The one or more downstream PGM-containing oxidation catalyst compositions may contain at least 0.05 wt.% of one or more PGMs.

[0037] The one or more downstream PGM-containing oxidation catalyst compositions may additionally comprise one or more Cu-zeolites (i.e., copper-containing zeolites) in addition to the one or more PGMs. Additionally or alternatively, one or more Cu-zeolites may be provided in addition to the one or more downstream PGM-containing oxidation catalyst compositions. For example, one or more Cu-zeolites may be provided between the proximal-linked vanadium-containing SCR catalyst composition and the one or more PGM-containing oxidation catalyst compositions (i.e., downstream of the proximal-linked vanadium-containing SCR catalyst composition and upstream of the one or more PGM-containing oxidation catalyst compositions).

[0038] Zeolites are constructed of repeating SiO4, AlO4, and tetrahedral units, e.g., linked together in rings, to form a framework with regular intracrystalline cavities and channels of molecular dimensions. A particular arrangement of tetrahedral units (ring members) gives rise to the framework of a zeolite, and by convention, each unique framework is assigned a unique three-letter code (e.g., "CHA") by the International Zeolite Association (IZA). Zeolites can also be classified by pore size, e.g., the maximum number of tetrahedral atoms present in the framework of the zeolite. As defined herein, "small pore" molecular sieves, such as CHA, contain a maximum ring size of 8 tetrahedral atoms, while "medium pore" molecular sieves, e.g., MFI, contain a maximum ring size of 10 tetrahedral atoms, and "large pore" molecular sieves, such as BEA, contain a maximum ring size of 12 tetrahedral atoms.

[0039] The Cu-zeolite can be a copper-containing large pore zeolite, a medium pore zeolite, or a small pore zeolite.

[0040] Most preferably, the Cu-zeolite is a small pore zeolite. Preferably, the small pore zeolite has a framework structure selected from the group consisting of AEI, AFT, AFV, AFX, AVL, CHA, EMT, GME, KFI, LEV, LTN, and SFW (including mixtures of two or more thereof). It is particularly preferred that the Cu-zeolite has a CHA or AEI type framework structure.

[0041] In particular, one of the downstream PGM-containing oxidation catalyst compositions may be an ammonia slip catalyst composition (ASC) (also known as an ammonia oxidation catalyst), which removes ammonia from the exhaust gas by converting it to nitrogen. This is advantageous because the ammonia oxidation catalyst composition selectively oxidizes ammonia to N2 and NOx, which would otherwise slip to less selective further downstream components such as DOC or CSF, resulting in the production of N2O. In the present invention, the vanadium-containing SCR catalyst of the system is in a close-coupled position with no upstream catalyst acting as a heat sink / buffer. As a result, the close-coupled vanadium-containing SCR catalyst is most exposed to sudden temperature spikes from the engine, which can result in ammonia desorption from the storage sites of the vanadium-containing SCR catalyst and the resulting ammonia slip. Thus, employing a downstream ammonia oxidation catalyst in the exhaust system of the present invention is particularly advantageous in reducing ammonia slip and the resulting production of N2O.

[0042] One of the downstream PGM-containing oxidation catalyst compositions may be a diesel oxidation catalyst that oxidizes one or more of NO, CO, and / or hydrocarbons present in the exhaust gas. In an exemplary arrangement, the downstream PGM-containing oxidation catalyst composition includes an ASC and a DOC, with the ASC being upstream of the DOC. In a further exemplary arrangement, the exhaust gas treatment system may further include a downstream SCR catalyst composition downstream of the one or more downstream PGM-containing oxidation catalyst compositions, optionally with the one or more downstream PGM-containing oxidation catalyst compositions and the downstream SCR catalyst composition being in an SCRT® configuration. The SCRT® configuration contains, in order, a DOC, a continuously regenerating particulate trap, a source of reductant fluid, an SCR catalyst, and optionally also an ASC.

[0043] One or more of the downstream PGM-containing oxidation catalyst compositions may be provided as a washcoat on one or more substrates, or impregnated into one or more porous substrates, or provided as one or more extruded porous substrates to form one or more catalyst articles. In other words, one or more of the downstream PGM-containing oxidation catalyst compositions may be washcoated onto one or more substrates, or impregnated into one or more substrates, or extruded to form one or more extruded porous substrates.

[0044] The one or more downstream PGM-containing oxidation catalyst compositions may be provided on and / or in one or more substrates separate from the substrate on which the close-linked vanadium-containing SCR catalyst composition is provided. Such an arrangement would thus provide a vanadium-containing SCR catalyst article upstream of the one or more PGM-containing oxidation catalyst articles. The substrate of the close-linked vanadium-containing SCR catalyst article may be adjacent to or spaced apart from the substrate of the one or more downstream PGM-containing oxidation catalyst articles. The substrate of the close-linked vanadium-containing SCR catalyst may be referred to as a first substrate and the substrate of the one or more PGM-containing oxidation catalyst articles may be referred to as a second substrate.

[0045] Alternatively, one or more of the downstream PGM-containing oxidation catalyst compositions may be present on and / or in the same substrate as the proximal-linked vanadium-containing SCR catalyst composition, thereby forming a single catalyst article.Various configurations of catalyst compositions may be employed, provided that at least a portion of the proximal-linked vanadium-containing SCR catalyst composition is disposed upstream of at least a portion of the one or more PGM-containing oxidation catalyst compositions.

[0046] The area of ​​the unitary catalyst article containing the proximal-linked vanadium-containing SCR catalyst composition may be referred to as a first region of the unitary catalyst article, and the area of ​​the catalyst article containing one or more PGM-containing oxidation catalyst compositions may be referred to as a second region of the unitary catalyst article. The first region and the second region are disposed / located / supported on the same substrate. As discussed below, the first region and / or the second region may be disposed / located / supported directly on the same substrate (i.e., the regions are in direct contact with a surface of the substrate).

[0047] The first region can extend from an inlet end of the substrate and the second region can extend from an outlet end of the substrate.

[0048] The first region may extend along 10% to 90% of the axial length of the substrate, preferably 25 to 85% of the axial length of the substrate, and the second region may extend along 10% to 90% of the axial length of the substrate, preferably 10 to 60% of the axial length of the substrate.

[0049] The first region containing the proximal-linked vanadium-containing SCR catalyst composition and the second region containing the PGM-containing oxidation catalyst composition may overlap. Preferably, in the overlapping area, the proximal-linked vanadium-containing SCR catalyst composition is disposed above the PGM-containing oxidation catalyst composition. The overlapping area will contain both the proximal-linked vanadium-containing SCR catalyst composition and one or more PGM-containing oxidation catalyst compositions. Thus, the overlapping area may form an ASC zone (ammonia slip catalyst zone) between the SCR zone and the oxidation zone.

[0050] Alternatively, the first region containing the proximal linked vanadium-containing SCR catalyst composition and the second region containing the one or more PGM-containing oxidation catalyst compositions may be non-overlapping.

[0051] The first region and the second region may be impregnated areas of the substrate and / or may be washcoat layers on the substrate.

[0052] For example, the proximal-linked vanadium-containing SCR catalyst composition may be provided as a washcoat on or impregnated into a substrate, and one or more downstream PGM-containing oxidation catalysts may also be provided as washcoats on or impregnated into the same substrate. In other words, the first region may be a washcoat layer or impregnated area containing the proximal-linked vanadium-containing SCR catalyst composition, and the second region may be a washcoat layer or impregnated area containing one or more PGM-containing oxidation catalyst compositions. In an arrangement in which both the first region and the second region are formed as washcoat layers, at least a portion of the washcoat containing the proximal-linked vanadium-containing SCR catalyst composition is upstream of the washcoat containing one or more downstream PGM-containing oxidation catalyst compositions. The washcoat containing one or more downstream PGM-containing oxidation catalyst compositions may be applied and dried separately from the washcoat containing the proximal-linked vanadium-containing SCR catalyst composition. The washcoat containing one or more downstream PGM-containing oxidation catalysts may or may not overlap with the washcoat containing the proximal linked vanadium-containing SCR catalyst composition.

[0053] The first region may be spaced apart from the second region, where "spaced apart" means that the first region does not contact the second region, i.e., the proximal-coupled vanadium-containing SCR catalyst composition does not contact one or more downstream PGM-containing oxidation catalyst compositions.

[0054] In an exemplary arrangement, the first region and the second region may both be disposed directly on / in the substrate (i.e., in direct contact with the substrate). The first region may be spaced from the second region along the length of the substrate, thereby forming a gap between the first and second regions, the gap extending along the axial length of the substrate. The gap may extend along at least 10% of the length of the substrate, preferably 20-50% of the axial length of the substrate.

[0055] The catalyst article may further include a coating region comprising the SCR catalyst composition. The coating region may be disposed on at least a portion of the second region. The coating region may be a layer extending from the outlet end over at least a portion of the second region. The coating region may extend over a gap formed between the first region and the second region. The coating region is preferably substantially free of vanadium. Thus, the SCR catalyst composition of the coating region is preferably substantially free of vanadium. The SCR catalyst composition of the coating region may include a zeolite. As used herein with respect to a material, the term "substantially free" means that the material may be present in small amounts, e.g., ≦5 wt.%, preferably ≦2 wt.%, more preferably ≦1 wt. The term "substantially free" encompasses the term "free". The SCR catalyst composition of the coating region may include a zeolite.

[0056] In addition to or as an alternative to an arrangement in which the first region is spaced apart from the second region along the axial length of the substrate, the first region may alternatively or additionally be spaced apart from the second region by an intervening layer extending at least partially therebetween (i.e., an intervening layer extending between the first region and the second region). In such an arrangement, the first region may be the first layer and the second region may be the second layer. The intervening layer at least partially overlaps both the first region and the second region. The intervening layer preferably overlaps at least a downstream portion of the first layer and at least an upstream portion of the second layer. That is, the intervening layer preferably overlaps at least a portion of the second layer side of the first layer and overlaps at least a portion of the first layer side of the second layer. The first layer may be disposed directly on at least a portion of the intervening layer. The intervening layer may be disposed directly on at least a portion of the second layer. Thus, the intermediate layer may be in direct contact with the first layer and the second layer.

[0057] The intervening layer may include an SCR catalyst composition. The intervening layer is preferably substantially free of vanadium. Thus, the SCR catalyst composition present in the intervening layer may be substantially free of vanadium. As used herein with respect to a material, the term "substantially free" means that the material may be present in small amounts, e.g., ≦5 wt%, preferably ≦2 wt%, more preferably ≦1 wt%. The term "substantially free" encompasses the term "free". The SCR catalyst composition of the intervening layer may include a zeolite.

[0058] The intermediate layer may extend from the outlet end of the substrate along 10-90% of the axial length of the substrate, preferably along 20-80% of the axial length of the substrate. Preferably, the first layer extends from the inlet end along 25-85% of the axial length of the substrate, the second layer extends from the outlet end along 10-60% of the axial length of the substrate, and the third layer extends from the outlet end along 20-80% of the axial length of the substrate. Preferably, the length of the second layer extending from the outlet end is shorter than the length of the intermediate layer also extending from the outlet end. Preferably, the sum of the length of the intermediate layer and the length of the first layer is equal to or greater than 100% of the axial length L of the substrate.

[0059] Preferably, the sum of the length of the first layer and the length of the second layer is less than 100% of the axial length L of the substrate, i.e., preferably, the first layer does not overlap the second layer. However, in an arrangement in which the first and second layers optionally overlap, the first and second layers may be spaced apart from each other in the overlapping area by an intervening layer. In other words, the first and second layers may be spaced apart from each other transversely to the axial length of the substrate in the overlapping area by an intervening layer. The first and second layers may overlap over 10-50% of the axial length of the substrate.

[0060] In an exemplary arrangement, the catalyst article may further include a third layer extending from the inlet end and including the proximal-linked vanadium-containing SCR catalyst composition. The third layer may extend less than the entire axial length L of the substrate. The intervening layer may extend at least partially between the third layer and the first layer, and between the first layer and the second layer. The third layer may be spaced apart from the second layer along the length of the substrate, thereby forming a gap between the first region and the second region, the gap extending along the axial length of the substrate. The gap may extend along at least 10% of the length of the substrate, preferably 20-50% of the axial length of the substrate.

[0061] In an arrangement including an intervening or coating layer that includes the SCR catalyst composition and extends from the outlet end, the intervening or coating layer forms an ASC zone with the second region, and thus the resulting catalyst article can have an ASC zone extending from the outlet end of the substrate and an SCR zone extending from the inlet end of the substrate.

[0062] In all of these configurations, poisoning of the one or more PGM-containing oxidation catalyst compositions by the vanadium of the close-coupled vanadium-containing SCR catalyst composition can be further reduced by avoiding contact between the close-coupled vanadium-containing SCR catalyst composition and the one or more PGM-containing oxidation catalyst compositions.

[0063] In an exemplary arrangement, a proximal-linked vanadium-containing SCR catalyst composition can be extruded to form an extruded porous substrate, and one or more PGM-containing oxidation catalyst compositions can be washcoated onto or impregnated within a downstream portion of the extruded porous substrate containing the proximal-linked vanadium-containing SCR catalyst composition.

[0064] The present invention also relates to a combustion and exhaust gas treatment system comprising a lean-burn combustion engine and an exhaust gas treatment system as described above. The exhaust gas treatment system has an inlet for receiving exhaust gas from the lean-burn combustion engine. The lean-burn combustion engine may be mobile or stationary. In the lean-burn combustion engine, combustion occurs at an air-fuel ratio higher than the stoichiometric air-fuel ratio. The lean-burn combustion engine may be an internal combustion engine such as a diesel engine, a lean-burn gasoline engine, an H2-fueled internal combustion engine, or a hybrid of the two.

[0065] According to a further aspect, there is provided a method for the treatment of exhaust gases, comprising treating the exhaust gases in an exhaust gas treatment system as described above. Thus, all features described for the system equally apply to the method aspect. The method typically comprises contacting a close-coupled vanadium-containing SCR catalyst composition, followed by a downstream PGM-containing oxidation catalyst composition, with exhaust gases received from a lean-burn combustion engine.

[0066] According to a further aspect, there is provided a use of cerium to reduce vanadium loss from a close-coupled vanadium-containing SCR catalyst composition, the close-coupled vanadium-containing SCR catalyst composition comprising cerium in a Ce:V molar ratio greater than 0.3.

[0067] Preferably, the use described in this aspect can be applied to the methods and systems described herein, and therefore all features described as preferred for the systems and methods apply equally to the use aspect.

[0068] According to a further aspect, there is provided an exhaust gas treatment system comprising, in sequence: an intake for receiving exhaust gases from a lean-burn combustion engine; an injector for providing a nitrogen reductant; a proximal linked vanadium-containing SCR catalyst composition; and one or more downstream catalyst compositions comprising a copper-containing zeolite; An exhaust gas treatment system is provided in which the close-coupled vanadium-containing SCR catalyst composition comprises cerium in a Ce:V molar ratio greater than 0.3.

[0069] The exhaust gas system discussion above applies equally to this embodiment requiring one or more downstream catalyst compositions comprising a copper-containing zeolite. For example, the discussion of the proximal linked vanadium-containing SCR catalyst composition above applies equally to this embodiment. The discussion of the configuration of one or more downstream PGM-containing oxidation catalyst compositions above applies equally to the configuration of one or more downstream catalyst compositions comprising a copper-containing zeolite required by this embodiment.

[0070] It is noted that in the above embodiments, the one or more downstream PGM-containing oxidation catalyst compositions may additionally comprise a copper-containing zeolite (Cu-zeolite). The descriptions of the copper-containing zeolite that may be present in the downstream PGM-containing oxidation catalyst composition in the above embodiments apply equally to the copper-containing zeolite of this embodiment that may be present without the downstream PGM-containing oxidation catalyst composition.

[0071] FIG. 1 shows a schematic diagram of a first exemplary catalyst article of the present invention having a substrate having a first region (1), a second region (2), and an intervening layer (3) disposed thereon. The substrate has an inlet (upstream) end 4a and an outlet (downstream) end 4b, and an axial length L. The arrows in FIG. 1 indicate from which end of the substrate each region / layer is applied (the first region (1) is applied from the inlet end 4a, and the second region (2) and the intervening layer (3) are applied from the outlet end 4b). In use, exhaust gas to be treated enters the catalyst article through the inlet end 4a and exits the catalyst article through the outlet end 4b. The first region (1) is a first layer and contains a proximal linked vanadium-containing SCR catalyst composition. The first layer extends from the inlet end 4a over less than the entire axial length L of the substrate. The second region (2) is a second layer and contains a PGM-containing oxidation catalyst composition. The second layer extends from the outlet end 4b over less than the entire axial length (L) of the substrate. The second layer (2) is disposed directly on the substrate (4). The first and second layers (1), (2) do not overlap. The intervening layer (3) is disposed on the second layer (2) and extends from the outlet end 4b over less than the entire axial length (L) of the substrate. The intervening layer has a longer length than the second layer. The intervening layer (3) extends at least partially between the first layer (1) and the second layer (2). The intervening layer overlaps the downstream portion of the first layer (1) and the entire second layer (2). The upstream portion of the first layer (1) is disposed directly on the substrate, and the downstream portion of the first layer (1) is disposed directly on the upstream portion of the intervening layer (3). The intervening layer (3) contains an SCR catalyst composition and is substantially free of vanadium. The SCR catalyst composition of the intervening layer (3) comprises a zeolite, and the presence of the intervening layer (3) increases the size of the gap along the length of the substrate (4) between the portion of the first layer (1) that is in direct contact with the substrate and the second layer (2).

[0072] FIG. 2 shows a schematic diagram of a second exemplary catalyst article of the present invention having a substrate with a first region (1), a second region (2), and a coating layer (5) disposed on the substrate (4). The substrate has an inlet (upstream) end 4a and an outlet (downstream) end 4b, and an axial length L. The arrows in FIG. 2 indicate from which end of the substrate each region / layer is applied (the first region (1) is applied from the inlet end 4a, and the second region (2) and coating layer (5) are applied from the outlet end 4b). In use, exhaust gas to be treated enters the catalyst article via the inlet end 4a and exits the catalyst article through the outlet end 4b. The first region (1) is a first layer and contains a vanadium-containing SCR catalyst composition. The first layer (1) extends from the inlet end 4a over less than the entire axial length L of the substrate. The second region (2) is a second layer and contains a PGM-containing oxidation catalyst composition. The second layer (2) extends from the outlet end 4b over less than the entire axial length L of the substrate. The first layer (1) and the second layer (2) are disposed directly on (i.e., in direct contact with) the substrate (4). The first layer and the second layer (1), (2) do not overlap, i.e., the total length of the first layer and the second layer is less than 100% of the entire axial length L of the substrate. Thus, a gap (G) is formed between the first layer and the second layer along the axial length L of the substrate. The gap extends between the downstream end of the first layer (1) and the upstream end of the second layer (2). The covering layer (5) extends from the outlet end over less than the entire axial length L of the substrate (4). The covering layer (5) is disposed directly on the first layer (1) and the second layer (2) and covers the gap (G). The covering layer (5) has a length greater than that of the second layer (2). The coating layer (5) overlaps the first layer (1) and the second layer (2). More specifically, the coating layer (5) overlaps a downstream portion of the first layer (1) and the entire second layer (2). The coating layer (5) contains an SCR catalyst composition and is substantially free of vanadium. The SCR catalyst composition of the coating layer (5) comprises a zeolite. In this arrangement, contact between the first layer (1) and the second layer (2) is avoided, thereby reducing poisoning of the PGM-containing oxidation catalyst composition of the second layer (2). An ASC zone is provided extending from the outlet without poisoning of the PGM-containing oxidation catalyst composition.

[0073] FIG. 3 shows a schematic diagram of a third exemplary catalyst article of the present invention having a substrate (4) on which a first region (1), a second region (2), an intervening layer (3), and a third layer (6) are disposed. The substrate has an inlet (upstream) end 4a and an outlet (downstream) end 4b and an axial length L. The arrows in FIG. 1 indicate from which end of the substrate each region / layer is applied (the first region (1) and the third layer (6) are applied from the inlet end 4a, and the second region (2) and the intervening layer (3) are applied from the outlet end 4b). In use, exhaust gas to be treated enters the catalyst article through the inlet end 4a and exits the catalyst article through the outlet end 4b. The first region (1) is the first layer and contains a vanadium-containing SCR catalyst composition. The first layer (1) extends from the inlet end 4a over less than the entire axial length L of the substrate. The second region (2) is a second layer and contains a PGM-containing oxidation catalyst composition. The second layer (2) extends from the outlet end 4b over less than the entire axial length L of the substrate. The second layer (2) is disposed directly on the substrate (4). The first and second layers (1), (2) do not overlap. The intervening layer (3) is disposed on the second layer (2) and extends from the outlet end 4b over less than the entire axial length (L) of the substrate. The intervening layer (3) has a longer length than the second layer (2). The intervening layer (3) extends at least partially between the first layer (1) and the second layer (2). The intervening layer (3) overlaps a downstream portion of the first layer (1) and the entire second layer (2). The upstream portion of the first layer (1) is disposed directly on the third layer (6), and the downstream portion of the first layer (1) is disposed directly on the upstream portion of the intervening layer (3). The intervening layer (3) contains an SCR catalyst composition and is substantially free of vanadium. The SCR catalyst composition of the intervening layer (3) includes a zeolite. The third layer (6) extends from the inlet end (4a) over less than the entire axial length of the substrate (4) and is disposed directly on the substrate (4). Like the first layer (1), the third layer (6) also contains a proximal-linked vanadium-containing SCR catalyst composition. The intervening layer (3) extends at least partially between the first layer and the third layer. The third layer (6) and the first layer (1) have the same length. Thus, the third layer and the second layer (6,2) do not overlap. EXAMPLES

[0074] The invention will now be further described with reference to the following non-limiting examples.

[0075] Examples 1 to 6 Examples 1 to 4 and 6 are comparative examples. Example 5 is according to the present invention.

[0076] The catalyst of Example 1 has a molecular weight of 130 g / ft 3 Vanadium, 3.0g / in 3 of TiO2 (and 1.0 g / in 3 It is a washcoat catalyst having SiO2.

[0077] Vanadium was present as vanadium oxide supported on titania in Example 1. The vanadium loading in the catalyst of Example 1 as V2O5 is 3.3 wt%.

[0078] The catalyst was prepared by forming an aqueous slurry including vanadyl oxalate, high surface area titania powder, and an aqueous dispersion of colloidal silica. Specifically, the high surface area titania powder employed was DT-51d obtained from Tronox®, and the aqueous dispersion of colloidal silica employed was Ludox® AS-40 from Grace. The aqueous slurry had a final pH of 5-8 and was deposited on a substrate, a cordierite flow-through monolith, by a suction process, followed by drying and calcination. The catalyst was dried at 100° C. for about 15 minutes, followed by calcination at 500° C. for about 10 minutes.

[0079] The catalysts of Examples 2 to 6 also had a molecular weight of 130 g / ft 3 Vanadium, 3.0g / in 3 of TiO2, and 1.0 g / in 3Each of the catalysts of Examples 2-6 differs from the catalyst of Example 1 in that the catalysts of Examples 2-6 also contain an additional metal present as an oxide, which metal is referred to herein as the "additive metal", and the molar ratio of the added metal to vanadium is 0.4. The added metal and associated amounts present in the catalysts of Examples 2-6 are shown in Table 1 below.

[0080] Vanadium was present as vanadium oxide supported on titania in Examples 2 to 6. The vanadium loading in the catalysts of Examples 2 to 6 as V2O5 is 3.2 wt %.

[0081] Similar to Example 1, the catalysts of Examples 2-6 were prepared by forming an aqueous slurry containing vanadyl oxalate, high surface area titania powder, an aqueous dispersion of colloidal silica, and precursors of the added metals as shown in the table below. Specifically, the high surface area titania powder employed was DT-51d obtained from Tronox®, and the aqueous dispersion of colloidal silica employed was Ludox® AS-40 from Grace. The aqueous slurry had a final pH of 5-8 and was deposited on the catalyst monolith by a suction process, followed by drying and calcination. The catalyst was dried at 100° C. for about 15 minutes, followed by calcination at 500° C. for about 10 minutes.

[0082] [Table 1]

[0083] Each of the catalysts of Examples 1-6 was formed as a washcoat on a substrate core (brick) formed from cordierite (cordierite flow-through monolith) having a size of 1 inch by 3 inches 300 / 5, and each was loaded into a respective holder as shown in FIG. 4. The catalysts were aged in parallel on the engine behind the DOC+CSF with urea dosing upstream of the holder at ANR 1.05, at about 26K SV, for 100 hours at a core holder inlet temperature of 560° C. (+ / - 10° C.). The H2O level during aging was about 9-10%. As shown in FIG. 4, an alumina coated substrate core (labeled as Core 2: Alumina Coated Capture Core in FIG. 4) was positioned downstream (i.e., behind) each of the catalysts of Examples 1-6 (labeled as Core 1: V-SCR in FIG. 4) in the holder to capture volatilized vanadium. The arrows in FIG. 4 indicate the direction of exhaust gas passing through them.

[0084] The first / front inch of each alumina coated substrate core was analyzed by XRF for vanadium and titania content to determine vanadium loss from the vanadium-containing SCR catalyst of Examples 1-6 upstream of each alumina coated substrate core. Results were corrected for any washcoat loss by comparing the measured titania to a baseline level. The baseline vanadium content in each alumina coated substrate core brick was also subtracted, which was about 49 ppm from the cordierite. The results are shown in the graph of FIG. 5 and are also provided in Table 2 below.

[0085] [Table 2]

[0086] Fresh NOx conversion activity at both 225 and 500°C for Examples 1-6 was measured by flowing a syngas mixture over the catalysts of Examples 1-6 on a laboratory flow-through reactor. The syngas mixture had a 60K SV and contained 500ppm NO, 525ppm NH, 8% CO, 10% O, 0.035% CO, 5% H2O, and the balance N2. The results are shown in the graph of Figure 6. For each Example, the NOx conversion activity was lower at 225°C than at 500°C.

[0087] As can be seen from the graph of Figure 5, vanadium-containing SCR catalysts employing cerium demonstrated significantly less vanadium loss compared to vanadium-containing SCR catalysts without added metals (Example 1) and compared to vanadium-containing SCR catalysts employing other metals such as W, Sb, or Nb (Examples 2, 3, and 4). Indeed, it can be seen that the presence of antimony does not substantially affect vanadium loss (Example 4), while the presence of W or Nb actually increases vanadium loss compared to the vanadium-containing SCR catalyst without added metals (Example 1).

[0088] FIG. 5 shows that the vanadium-containing catalyst containing erbium (Example 6) achieved slightly less vanadium loss than the vanadium-containing catalyst containing cerium (Example 5). However, as shown in the graph of FIG. 5, the presence of erbium significantly impacts low-temperature NOx conversion. In fact, the NOx conversion at 225° C. dropped from 45% to 25% due to the presence of erbium, as shown by comparing the NOx conversion achieved for Example 1 with the NOx conversion achieved for Example 6. Thus, while the presence of erbium in the SCR catalyst reduced vanadium loss, it also reduced low-temperature NOx conversion activity. In contrast, the vanadium-containing catalyst employing cerium demonstrated substantially the same NOx conversion at 225° C. and slightly higher NOx conversion at 500° C. compared to the vanadium-containing catalyst without added metal. Thus, the presence of cerium in the vanadium-containing catalyst reduced vanadium loss from the SCR catalyst without affecting its NOx conversion activity.

[0089] Examples 7 to 18 Examples 8 to 14 and 16 to 18 are according to the present invention. Examples 7 and 15 are comparative examples.

[0090] Examples 7-14 were formed as washcoats on a substrate. Examples 15-18 were formed as extrudates. The compositions of Examples 7-14 are shown in Table 3 provided below. The compositions of Examples 15-18 are shown in Table 4 provided below.

[0091] The washcoated vanadium-containing catalysts (Examples 7-14) contained V2O5 in an amount of 4.5 wt%, Sb2O5 in an amount of 5.6 wt%, SiO2 in an amount shown in Table 3 below, optionally CeO2 as shown in Table 3 below, and the balance TiO2. As shown in Table 3 below, the washcoated vanadium-containing catalyst without ceria (Example 7) contained 18.73% SiO2. For the washcoated vanadium-containing catalysts that also contained ceria (Examples 8-14), the SiO2 content was reduced to compensate for the added CeO2, thus keeping the total washcoat loading and V and Sb content constant for all of Examples 7-14.

[0092] [Table 3]

[0093] Each of the washcoat catalysts (Examples 7-14) was prepared by forming an aqueous slurry including vanadyl oxalate, high surface area titania powder, an aqueous dispersion of colloidal dalceria, and an aqueous dispersion of colloidal silica. Specifically, the high surface area titania powder employed was DT-51d obtained from Tronox®, and the aqueous dispersion of colloidal silica employed was Ludox® AS-40 from Grace. The aqueous dispersion of colloidal dalceria employed was JMA702 from Solvay. The aqueous slurry had a final pH of 5-8 and was deposited on the catalyst monolith by a suction process, followed by drying and calcination. The catalyst was dried at 100° C. for about 15 minutes, followed by calcination at 500° C. for about 10 minutes.

[0094] The extruded vanadium-containing catalyst contained V2O5 in an amount of 4.5 wt%, antimony pentoxide in an amount of 6.7 wt%, 14.5 wt% binder, and the balance titania containing silica.

[0095] Each of the extruded catalysts (Examples 15-18) was prepared by mixing commercially available silica-containing titania (anatase with a nominal SiO2 content of 3.5 wt%) with ammonium metavanadate to achieve the desired V2O5 equivalent. CeO2 was added as disclosed in Table 4 to reduce the titania silica content accordingly. 8 wt% glass fiber and 6.4 wt% low alkali content clay were added as binder / strength improving components. Approximately 1-2 wt% cellulose, 1-2 wt% polyethylene oxide and ammonia solution were blended in the next step to prepare a well plasticized moldable paste with a pH of 5-7 by using a kneader. The paste was extruded into a flow-through honeycomb body with continuous channels and a circular cross section exhibiting a cell density of 400 cpsi. The catalyst bodies were then freeze-dried at 2 mbar for 1 hour and calcined at a temperature of 580° C. to form solid catalyst bodies according to the method described in WO 2009 / 080155, which is incorporated herein by reference. A general method for the preparation of these catalysts is described in WO 002013017873(A1), which is incorporated herein by reference.

[0096] [Table 4]

[0097] Each of the catalysts of Examples 7-14 was provided as a washcoat on a substrate core (brick) formed from cordierite having a size of 1 inch by 3 inches 300 / 5, and each of the catalysts of Examples 15-18 was provided as an extrudate formed as a core / brick having a size of 1 inch by 3 inches 400 / 11. Each of the cores / bricks of Examples 7-18 was loaded into a respective holder as shown in FIG. 4. The catalysts were aged in parallel on the engine behind the DOC+CSF at a core holder inlet temperature of 560° C. (+ / - 10° C.) for 100 hours, at about 26 K SV, and with urea dosed upstream of the holder at ANR 1.05. H2O levels during aging were about 9-10%. As shown in FIG. 4, an alumina coated substrate core was positioned downstream (i.e., behind) each of the catalysts of Examples 7-14(a),(b) in the holder to capture volatilized vanadium.

[0098] The first / front inch of each alumina coated substrate core was analyzed by XRF for vanadium and titania content to determine vanadium loss from the vanadium-containing SCR catalyst of Examples 7-18 upstream of each alumina coated substrate core. Results were corrected for any washcoat loss by comparing the measured titania to a baseline level. The baseline vanadium content in each alumina coated substrate core brick was also subtracted, which was about 49 ppm from the cordierite. The results are shown in the graph of FIG. 7. Thus, FIG. 7 is a graph demonstrating the effect of cerium loading on vanadium loss from washcoated vanadium-containing SCR catalysts and extruded vanadium-containing SCR catalysts.

[0099] As shown by the graph in Figure 7, the presence of ceria in vanadium-containing SCR catalysts demonstrates a reduction in vanadium loss at all loadings of ceria tested (i.e., 1 wt% to 14 wt%) compared to vanadium-containing SCR catalysts without ceria. Ceria loadings equal to a cerium:vanadium molar ratio of 0.3 or greater result in approximately a 50% reduction in vanadium loss. As shown in Figure 6, no further reduction in vanadium loss is achieved for molar ratios of Ce:V greater than 0.7.

[0100] Examples 19 to 27 The catalysts of Examples 19 to 27 had a melting point of 3.81 g / in 3 of TiO2, 1.0 g / in 3 SiO2, vanadium in the amounts shown in Table 5, and 389 g / ft 3 Each of the catalysts in Examples 19-21 contained 389 g / ft cerium. 3 The catalysts of Examples 19-21 contained cerium:vanadium in amounts of 389 g / ft 2, but with different amounts of vanadium present, as shown in Table 5 below. For the catalysts of Examples 19-21, the molar ratio of cerium:vanadium ranged from 0.55 to 0.85. The catalysts of Examples 22-24 contained 389 g / ft 2 3 The alloys contain tungsten in an amount of 389 g / ft 2, but differ in the amount of vanadium present, as shown in Table 5 below. Examples 25-27 contain 389 g / ft 2 3 The alloys contain niobium in amounts of 0.1 to 100% by weight, but differ in the amount of vanadium present, as shown in Table 5 below.

[0101] The vanadium was present as vanadium oxide supported on titania in Examples 19-27.

[0102] The catalysts of Examples 19-27 were prepared by forming an aqueous slurry containing vanadyl oxalate, high surface area titania powder, an aqueous dispersion of colloidal silica, and precursors of the added metals as shown in Table 5 below. Specifically, the high surface area titania powder employed was DT-51d obtained from Tronox®, and the aqueous dispersion of colloidal silica employed was Ludox® AS-40 from Grace. The aqueous slurry had a final pH of 5-8 and was deposited on the catalyst monolith by a suction process, followed by drying and calcination. The catalyst was dried at 100° C. for about 15 minutes, followed by calcination at 500° C. for about 10 minutes.

[0103] [Table 5]

[0104] Each of the catalysts of Examples 19-27 was formed as a washcoat on a substrate core (brick) formed from cordierite (cordierite flow-through monolith) having a size of 1 inch by 3 inches 300 / 5, and each was loaded into a respective holder as shown in FIG. 4. The catalysts were aged in parallel on the engine behind the DOC+CSF at a core holder inlet temperature of 560° C. (+ / - 10° C.) for 100 hours, at about 26K SV, and with urea dosed upstream of the holder at ANR 1.05. H2O levels during aging were about 9-10%. As shown in FIG. 4, an alumina coated substrate core was positioned downstream (i.e., behind) each of the catalysts of Examples 19-27 in the holder to capture volatilized vanadium.

[0105] The first / front inch of each alumina coated substrate core was analyzed by XRF for vanadium and titania content to determine vanadium loss from the vanadium-containing SCR catalyst of Examples 19-27 upstream of each alumina coated substrate core. Results were corrected for any washcoat loss by comparing the measured titania to a baseline level. The baseline vanadium content in each alumina coated substrate core brick was also subtracted, which was about 49 ppm from the cordierite. The results are shown in the graphs of Figures 8 and 9. Figure 8 is a graph of vanadium loading of catalyst versus vanadium loss from the catalyst of Examples 19-27 and Figure 9 is a graph of molar ratio of added metal:vanadium of catalyst versus vanadium loss from the catalyst of Examples 19-27. The data shown by dashed crosses relate to Examples 19-21, the data shown by solid black circles relate to Examples 22-24, and the data shown by solid grey squares relate to Examples 25-27.

[0106] As shown in Figures 8 and 9, the presence of cerium significantly reduced volatility at all three vanadium loadings tested, down to about 250 ppm, which corresponds to a molar ratio of cerium:vanadium of about 0.55 to 0.85. In contrast, the 389 g / ft 3 The presence of the same amounts of niobium or tungsten demonstrated high vanadium losses that increased with vanadium loading (vanadium losses of 1400-3900 ppm for Examples 22-27).

[0107] Fresh NOx conversion activity at both 225°C and 500°C and aged NOx conversion activity at 225°C for Examples 19-27 were measured by flowing a syngas mixture over the catalysts of Examples 19-27 in a laboratory flow-through reactor. The syngas mixture had a 60K SV and contained 500 ppm NO, 525 ppm NH3, 8% CO2, 10% O2, 0.035% CO, 5% H2O, and the balance N2. The results are shown in the graphs of Figure 10 (fresh NOx activity at 225°C), Figure 11 (aged NOx activity at 225°C), and Figure 12 (fresh NOx activity at 500°C). Data shown as dashed crosses are for Examples 19-21, data shown as solid black circles are for Examples 22-24, and data shown as solid grey squares are for Examples 25-27.

[0108] As shown in Figures 10, 11, and 12, lower NOx conversion was demonstrated for the fresh and aged cerium-containing examples (Examples 19 and 20) with lower vanadium loadings compared to the tungsten or niobium-containing examples (Examples 21, 22, 24, and 25) with the same lower vanadium loadings. However, the presence of cerium allows for increased vanadium loadings to result in increased NOx conversion at 225°C and 500°C, as demonstrated by Example 21. This increase in NOx conversion is achieved without compromising vanadium volatility, as demonstrated by the data shown in Figures 8 and 9. Thus, Figures 8 and 9, together with Figures 10, 11, and 12, demonstrate that the presence of cerium in a vanadium-containing SCR catalyst reduced vanadium loss from the catalyst, even at high vanadium loadings, without affecting its fresh NOx conversion activity at both 225°C and 500°C and aged NOx conversion activity at 225°C.

[0109] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Use of the term "comprising" is intended to be interpreted as including such features but not excluding other features, and is intended to include options of features that are necessarily limited to those recited. In other words, this term also includes the limitations "consisting essentially of" (intended to mean that certain additional components may be present provided they do not materially affect the essential properties of the recited feature) and "consisting of" (intended to mean that when components are expressed as percentages by their proportions, they add up to 100%, while accounting for any unavoidable impurities, but that other features may not be included), unless the context clearly dictates otherwise.

[0110] As used herein, the term "region" refers to an area of ​​a washcoat or impregnated catalyst composition on a substrate. A "region" can be disposed or supported on the substrate as, for example, a "layer" or a "zone." The area or location of the catalyst composition on the substrate is generally controlled during the process of applying the washcoat to the substrate or impregnating the substrate with the catalyst composition. A "region" typically has a distinct boundary or edge (i.e., it is possible to distinguish one region from another using conventional analytical techniques).

[0111] The term "washcoat" is well known in the art and typically refers to an adherent coating that is applied to a substrate during the production of a catalyst.

[0112] Typically, a "region" has a substantially uniform length. Reference to a "substantially uniform length" in this context refers to a length that does not deviate from its average value by more than 10% (e.g., the difference between the maximum and minimum length), preferably does not deviate by more than 5%, and more preferably does not deviate by more than 1%.

[0113] Each "region" preferably has a substantially uniform composition (i.e., there is no substantial difference in the composition of the washcoat when comparing one portion of the region to another portion of the region). Substantially uniform composition in this context refers to a material (e.g., region) that has a compositional difference of 10% or less, usually 5% or less, and most commonly 2.5% or less when comparing one portion of the region to another portion of the region.

[0114] The overall length of a substrate is the distance between its inlet end and its outlet end (eg, both ends of the substrate).

[0115] The term "substantially free," as used herein with respect to a material, typically means a small amount of material, such as 5% by weight or less, preferably 2% by weight or less, more preferably 1% by weight or less, in relation to the contents of a region, layer, or zone. The term "substantially free" encompasses the term "free."

[0116] Terms such as "first", "second", and the like may be used herein to describe various elements, layers, and / or portions, but it is understood that the elements, layers, and / or portions should not be limited by these terms. These terms are used only to distinguish one element, layer, or portion from another or further element, layer, or portion. Spatially relative terms such as "under", "below", "beneath", "lower", "over", "above", "upper", and the like may be used herein for ease of description to describe the relationship of one element or feature to another element or feature. It will be understood that the spatially relative terms are intended to encompass different orientations of the system during use or operation in addition to the orientation shown in the drawings. For example, if a catalytic article or system described herein were turned over, an element described as "under" or "below" another element or feature would be oriented "above" or "above" the other element or feature. Thus, the exemplary term "below" can encompass both an orientation of above and below. The catalytic article or system may be otherwise oriented, and the spatially relative descriptive terms used herein are interpreted accordingly.

[0117] The foregoing detailed description has been provided for purposes of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments described herein will be apparent to those of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. An exhaust gas treatment system, in order, An intake port for receiving exhaust gases from a lean-burn combustion engine, An injector for supplying nitrogen reducing agents, A proximal-linked vanadium-containing SCR catalyst composition, comprising one or more downstream PGM-containing oxidation catalyst compositions, An exhaust gas treatment system wherein the proximal-linked vanadium-containing SCR catalyst composition contains cerium in a Ce:V molar ratio greater than 0.

3.

2. Vanadium is present in the proximal-linked vanadium-containing SCR catalyst composition. ２ O ５ The exhaust gas treatment system according to claim 1, wherein the exhaust gas is present in an amount of at least 2% by weight, preferably 2 to 6% by weight, as a standard.

3. The exhaust gas treatment system according to claim 1, wherein the proximal-linked vanadium-containing SCR catalyst composition further contains antimony in an Sb:V molar ratio greater than 0.5, preferably 0.6 to 0.

9.

4. The exhaust gas treatment system according to claim 1, wherein cerium is present in the proximal-linked vanadium-containing SCR catalyst composition in a Ce:V molar ratio of 0.3 to 0.7, preferably 0.4 to 0.

6.

5. The exhaust gas treatment system according to claim 1, wherein the proximal-linked vanadium-containing SCR catalyst composition is provided as an extruded porous substrate or a wash coat on a porous substrate.

6. The exhaust gas treatment system according to claim 5, wherein the extruded porous substrate or the porous substrate is a honeycomb monolith substrate.

7. The exhaust gas treatment system according to claim 1, wherein the proximal-linked vanadium-containing SCR catalyst composition comprises a titania-based catalyst support material.

8. The exhaust gas treatment system according to claim 1, wherein the one or more downstream PGM-containing oxidation catalyst compositions are provided as an extruded porous substrate or a wash coat on a substrate.

9. The exhaust gas treatment system according to claim 1, wherein the one or more downstream PGM-containing oxidation catalyst compositions are provided on and / or in the same substrate as the proximal-linked vanadium-containing SCR catalyst compositions forming a single catalyst article, and the substrate has an inlet end, an outlet end, and an axial length.

10. The exhaust gas treatment system according to claim 9, wherein the proximal-linked vanadium-containing SCR catalyst composition is arranged in a first region, and one or more downstream PGM-containing oxidation catalyst compositions are arranged in a second region, and the first region is spaced apart from the second region.

11. The exhaust gas treatment system according to claim 9, wherein the first region extends from the inlet end, the second region extends from the outlet end, and optionally, the first region extends along 10% to 90% of the axial length of the substrate, preferably 25% to 85% of the axial length of the substrate, and the second region extends along 10% to 90% of the axial length of the substrate, preferably 10% to 60% of the axial length of the substrate.

12. The exhaust gas treatment system according to claim 9, wherein the first region and the second region do not overlap, and the first region is the first layer and the second region is the second layer, with the first region being the first layer and the second region being the second layer, respectively, with the first region being the first layer and the second region being the second layer, respectively.

13. The exhaust gas treatment system according to claim 12, further comprising a coating layer extending from the outlet end over at least a portion of the second region, wherein the coating layer optionally comprises an SCR catalyst composition.

14. The exhaust gas treatment system according to claim 9, wherein the first region is a first layer, the second region is a second layer, the first region and the second region are separated from each other by an intervening layer extending between the first layer and the second layer, and optionally the intervening layer comprises an SCR catalyst composition.

15. The exhaust gas treatment system according to claim 14, wherein the first layer overlaps with the second layer.

16. The exhaust gas treatment system according to claim 1, wherein the proximal-linked vanadium-containing SCR catalyst composition and one or more PGM-containing oxidation catalyst compositions are provided on separate substrates, thereby forming a proximal-linked vanadium-containing SCR catalyst article and one or more PGM-containing oxidation catalyst articles, and optionally the proximal-linked vanadium-containing SCR catalyst article is spaced apart from the one or more PGM-containing oxidation catalyst articles.

17. The exhaust gas treatment system according to claim 1, wherein the downstream PGM-containing oxidation catalyst composition comprises an ASC composition and a DOC composition, and the ASC composition is located upstream of the DOC composition.

18. The exhaust gas treatment system according to claim 1, further comprising a downstream SCR catalyst composition downstream of the one or more PGM-containing oxidation catalyst compositions, wherein the one or more PGM-containing oxidation catalyst compositions and the downstream SCR catalyst composition are optionally in an SCRT (registered trademark) configuration.

19. The exhaust gas treatment system according to claim 1, wherein the one or more downstream PGM-containing oxidation catalyst compositions further comprises Cu-zeolite, wherein the Cu-zeolite is a small-pore zeolite, and preferably the Cu-zeolite has a CHA or AEI type skeletal structure.

20. A combustion and exhaust treatment system, Lean burn combustion engine, A combustion and exhaust gas treatment system comprising the exhaust gas treatment system described in claim 1.

21. A method for treating exhaust gas, comprising treating the exhaust gas in the exhaust gas treatment system according to claim 1.

22. Use of cerium to reduce vanadium loss from a proximal-linked vanadium-containing SCR catalyst composition, wherein the proximal-linked vanadium-containing SCR catalyst composition contains cerium in a Ce:V molar ratio greater than 0.3.

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