Copper cha zeolite catalysts

TECHNICAL FIELD [0001] Embodiments of the invention relate to zeolites that have a CHA crystal structure, methods for their preparation, and catalysts containing such zeolites. In particular, embodiments of the invention relate to copper-zeolite CHA catalysts and methods for their preparation and use in exhaust gas purification systems.

BACKGROUND ART [0002] Zeolites are aluminosilicate crystalline materials with fairly uniform pore sizes, which, depending on the type of zeolite and the type and amount of cations contained in the zeolite crystal network, usually have a diameter ranging from about 3 to 10 Angstroms. Both synthetic and natural zeolites and their use to support certain reactions, including the selective reduction of nitrogen oxides with ammonia in the presence of oxygen, are well known in the art. US 6,709,644 B2 relates to zeolites with a chabazite crystal structure (CHA) of low crystallite size, methods of using CHA with small crystallites as a catalyst, and gas separation processes using CHA with small crystallites. US 2006/115 403 A1 discloses a method for reducing oxides in a gas stream (e.g. in car exhaust), which uses a catalyst comprising a molecular sieve with a CHA crystal structure and having a molar ratio greater than 50 to 1500 (1) oxide selected from silicon oxide , germanium oxide or mixtures thereof to (2) an oxide selected from alumina, iron oxide, titanium oxide, gallium oxide and mixtures thereof.

[0003] Metal-promoted zeolite catalysts including, but not limited to, iron-promoted and copper-promoted zeolite catalysts for the selective catalytic reduction of nitrogen oxides with ammonia. Iron-promoted zeolite beta was an efficient catalyst for the selective reduction of nitrogen oxides with ammonia. Unfortunately, it was found that under severe hydrothermal conditions, such as reduction of NOx from flue gas at a temperature exceeding 500 ° C, the activity of many metal-promoted zeolites begins to decrease. It is believed that this decrease in activity occurs due to zeolite destabilization, such as as a result of de-alumination, and therefore a reduction in the number of metal-containing catalytic centers in the zeolite. In order to maintain the total NOx reduction activity, increased concentrations of iron-promoted zeolite catalyst should be provided. As the zeolite catalyst concentrations are increased to ensure adequate NOx removal, it is obvious that the cost-effectiveness of the NOx removal process is diminished as catalyst costs increase.

[0004] There is a need to produce materials that provide SCR (selective catalytic reduction) activity at low temperature and / or increased hydrothermal strength compared to existing zeolites, for example catalytic materials that are stable at temperatures up to at least about 650 ° C and higher .

SUMMARY [0005] Aspects of the invention relate to zeolites that have a CHA crystal structure (which is defined by the International Zeolite Association), to catalysts containing such zeolites, and to exhaust gas purification processes using such catalysts. The catalyst may be part of an exhaust gas purification system used for purifying exhaust gas streams, particularly those emitted from gasoline or diesel engines.

[0006] One embodiment of the present invention relates to copper-CHA catalysts and their use in flue gas systems, such as those intended for the reduction of nitrogen oxides. In certain embodiments, new copper-metabolite catalysts are provided that exhibit increased SCR NOx using NH3. Copper-chabazite catalysts manufactured in accordance with one or more embodiments of the present invention provide a catalytic material that exhibits excellent hydrothermal stability and high catalytic activity over a wide temperature range. Compared with other zeolite catalysts that are used in this field, such as Fe Beta zeolites, copper-CHA catalytic materials in accordance with the embodiment of the present invention provide increased low temperature activity and hydrothermal stability.

[0007] One embodiment of the invention relates to a catalyst comprising a zeolite with a CHA crystal structure and a silica to alumina molar ratio greater than about 15 and a copper to aluminum atomic ratio greater than about 0.25. In a specific embodiment, the molar ratio of silica to alumina is from about 15 to about 256, and the atomic ratio of copper to aluminum is from about 0.25 to about 0.50. In a more specific embodiment, the molar ratio of silica to alumina is from about 25 to about 40. In an even more specific embodiment, the molar ratio of silica to alumina is about 30. In a specific embodiment, the atomic ratio of copper to aluminum is from about 0.30 to about 0 50. In a specific embodiment, the copper-aluminum atomic ratio is about 0.40. In a specific embodiment, the molar ratio of silica to alumina is from about 25 to about 40, and the atomic ratio of copper to aluminum is from about 0.30 to about 0.50. In another particular embodiment, the silica to alumina ratio is about 30 and the copper to alumina atomic ratio is about 0.40.

[0008] In a particular embodiment, the catalyst contains ion-exchanged copper and some non-exchangeable copper, sufficient to maintain the catalyst efficiency in NOx conversion in the exhaust gas stream containing nitrogen oxides, after hydrothermal aging of the catalyst. In one embodiment, the catalyst efficiency in NOx conversion at about 200 ° C, after aging, is at least 90% of the catalyst efficiency in NOx conversion, at about 200 ° C, before aging. In a particular embodiment, the catalyst contains at least about 2.00 weight percent copper oxide.

[0009] In at least one embodiment, the catalyst is supported on a honeycomb structure. In one or more forms, the honeycomb structured body comprises a wall flow medium. In other embodiments, the honeycomb structured body comprises a flow medium. In some embodiments, at least a portion of the flow substrate is coated with CuCHA adapted to reduce nitrogen oxides contained in the gas stream flowing through the substrate. In a specific embodiment, at least part of the flow medium is coated with Pt and CuCHA adapted to oxidize ammonia in the flue gas stream.

[0010] In embodiments that utilize a wall flow substrate, at least a portion of the wall flow substrate is coated with CuCHA adapted to reduce the nitrogen oxides contained in the gas flow flowing through the substrate. In other embodiments, at least a portion of the wall flow substrate is coated with Pt and CuCHA adapted to oxidize ammonia in the flue gas stream.

[0011] In a specific embodiment, the catalyst product comprises a honeycomb structured body comprising a CHA zeolite crystalline matrix supported on a medium in which the zeolite has a silica to alumina molar ratio greater than about 15 and a copper to aluminum atomic ratio greater than about 0.25, and which contains more free copper than ion-exchanged copper. In one embodiment, the free copper is present in an amount sufficient to prevent hydrothermal degradation of the catalyst for nitric oxide conversion. In one or more forms, free copper prevents hydrothermal degradation of the catalyst for the conversion of nitric oxide after hydrothermal aging. The catalyst may further comprise a binder. In specific embodiments, the ion-exchanged copper is exchanged using copper acetate.

[0012] Other aspects of the invention relate to exhaust gas purification systems containing catalysts of the type described above. Still other aspects relate to a method for reducing nitrogen oxides contained in a gas stream in the presence of oxygen, said method comprising contacting the gas stream with the catalyst described above.

[0013] Another aspect relates to an exhaust gas purification system comprising an NOx-containing exhaust gas stream and a catalyst as described above effective in the selective catalytic reduction of at least one NOx component in an exhaust gas stream. Yet another aspect relates to an exhaust gas purification system comprising an exhaust gas stream comprising ammonia and a catalyst as described above, effective in decomposing at least a portion of the ammonia in the exhaust gas stream.

BRIEF DESCRIPTION OF THE DRAWINGS [0014]

Fig. 1 is a graph showing nitrogen oxide removal efficiency (%), ammonia consumption (%) and N2O produced (ppm) using a CuCHA catalyst as a function of reaction temperature for CuCHA produced according to the methods of Example 1; Fig. 1A is a graph showing nitrogen oxide removal efficiency (%), ammonia consumption (%) and N2O produced (ppm) using a CuCHA catalyst as a function of reaction temperature for CuCHA produced according to the methods of Examples 1 and 1A;

Fig. 2 is a graph showing nitrogen oxide removal efficiency (%), ammonia consumption (%) and N2O produced (ppm) using a CuCHA catalyst as a function of reaction temperature for CuCHA produced according to the methods of Example 2; Fig. 3 is a graph showing nitrogen oxide removal efficiency (%), ammonia consumption (%) and N2O produced (ppm) using a CuCHA catalyst as a function of reaction temperature for CuCHA produced according to the methods of Example 3; FIG. 4 is a graph showing nitrogen oxides removal efficiency (%), ammonia consumption (%) and N2O produced (ppm) using a CuCHA catalyst as a function of reaction temperature for CuCHA produced according to the methods of Example 4; Fig. 5 is a graph showing the effect of CO, propene, n-octane and water on SCR CuCHA activity at various temperatures;

Fig. 5A is a graph showing the amounts of HC that are stored, released, deposited as coke and coke burned for a test sample according to Example 12A; Fig. 5B is a bar diagram showing the efficiency of CuCHA relative to hydrocarbon compared to the CuY and Fe beta zeolites of Example 12A;

Fig. 6 is a graph showing the emissions of NH3, NOx (= NO + NO2), N2O and N2 from the outlet of an AMOX catalyst, given as ppm relative to the nitrogen atom produced and aged according to the method of Examples 13 and 14;

Fig. 7 is a graph showing nitrogen oxide removal efficiency (%), ammonia consumption (%) and N2O produced (ppm) using a CuCHA catalyst as a function of reaction temperature for CuCHA produced according to the methods of Example 16; Fig. 8 is a graph showing nitrogen oxide removal efficiency (%), ammonia consumption (%) and N2O produced (ppm) using a CuCHA catalyst as a function of reaction temperature for CuCHA produced according to the methods of Example 17; FIG. 9 is a graph showing nitrogen oxides removal efficiency (%), ammonia consumption (%) and N2O produced (ppm) using a CuCHA catalyst as a function of reaction temperature for CuCHA produced according to the methods of Example 18; Figures 10A, 10B and 10C are schematic representations of three exemplary embodiments of the system according to the invention for purifying emissions;

Fig. 11 shows the UV / VIS spectrum of Examples 22 and 22A; and Fig. 12 shows the spectrum²⁷Al MAS NMR of Examples 22 and 22A, compared to CHA and aged CHA samples.

DETAILED DESCRIPTION.

[0015] Before describing several exemplary embodiments of the invention, it should be understood that the invention is not limited to the structural details or to the process steps described herein. The invention allows other forms and various ways of implementation or guidance.

[0016] In one embodiment of the invention, zeolites with a CHA structure, such as chabazite, are provided. In one or more forms, a zeolite with a CHA crystal structure and a silica to alumina molar ratio greater than about 15 and a copper to aluminum atomic ratio greater than about 0.25 is provided. In certain embodiments, the molar ratio of silica to alumina is about 30 and the atomic ratio of copper to aluminum is about 0.40. Other zeolites with the CHA structure include, but are not limited to, SSZ-13, LZ-218, Linde D, Linde R, Phi, ZK-14 and ZYT-6.

[0017] The synthesis of zeolites with a CHA structure can be carried out according to various techniques known in the art. For example, in a typical SSZ-13 synthesis, the silica source, alumina source, and organic targeting agent are mixed together under aqueous alkaline conditions. Typical silica sources include various types of fumed silica, precipitated silica and colloidal silica, as well as silicon alkoxides. Typical sources of alumina include bohemes, pseudo-demites, aluminum hydroxides, aluminum salts such as aluminum sulfate and aluminum alcoholates. Sodium hydroxide is usually added to the reaction mixture, but this is not required. A typical targeting agent for this synthesis is adamantyltrimethylammonium hydroxide, although other amines and / or quaternary ammonium salts may be substitutes or be added to the latter targeting agent. The reaction mixture is heated in a pressure vessel with stirring to produce the crystalline product SSZ-13. Typical reaction temperatures are 150 to 180 ° C. Typical response time is 1 to 5 days.

[0018] After completion of the reaction, the product is filtered off and washed with water. Alternatively, the product can be centrifuged. Organic additives can be used to aid in the handling and isolation of the solid product. Spray drying is an optional step in the processing of the product. The solid product is heat treated in an air or nitrogen atmosphere. Alternatively, each gas treatment may be carried out in a different order or gas mixtures may be used. Typical calcination temperature is in the range of 400 ° C to 700 ° C.

[0019] CuCHA zeolite catalysts in accordance with one or more embodiments of the invention may be used in catalytic processes that include oxidation and / or hydrothermal conditions, for example at a temperature exceeding about 600 ° C, for example higher than about 800 ° C and in the presence of about 10% water vapor. In particular, it was found that CuCHA zeolite catalysts that were prepared according to embodiments of the invention have increased hydrothermal stability compared to CuY and CuBeta zeolites. CuCHA zeolite catalysts produced in accordance with embodiments of the invention show increased activity in the selective catalytic reduction of NOx by ammonia, especially when operating at high temperatures of at least about 600 ° C, for example about 800 ° C and higher, and in an environment with a high water vapor content of about 10 % or more. CuCHA has a high specific activity, which allows the use of smaller amounts of catalytic material, which in turn should reduce the back pressure of honeycomb substrates coated with intermediate layers of CuCHA catalysts. In one or more forms, hydrothermal aging refers to subjecting the catalyst to a temperature of about 800 ° C in an environment with a high water vapor content of about 10% or more, for at least about 5 to about 25 hours, and in certain specific embodiments to about 50 hours.

[0020] Embodiments of the present invention also relate to a method of reducing NOx in the exhaust gas stream generated by an internal combustion engine using CuCHA zeolite catalysts with a silica to alumina molar ratio greater than about 15 and a copper to aluminum atomic ratio greater than about 0.25. Other embodiments relate to SCR catalysts comprising a CuCHA zeolite catalyst with a silica to alumina molar ratio greater than about 15 and a copper to aluminum atomic ratio greater than about 0.25, and an exhaust gas purification system comprising CuCHA zeolite catalysts. Still other embodiments relate to catalysts (AMOX) for the oxidation of ammonia and exhaust gas purification systems containing an AMOX catalyst comprising a CuCHA zeolite catalyst with a silica to alumina molar ratio greater than about 15 and a copper to aluminum atomic ratio greater than about 0.25. According to one or more embodiments, the catalysts and systems use CuCHA catalysts containing ion-exchanged copper and a sufficient excess of free copper to prevent thermal decomposition of the catalysts when operating at high temperatures of at least about 600 ° C, for example about 800 ° C and higher , and in an environment with a high water vapor content of about 10% or more.

[0021] Experiments have shown that the increased efficiency of the catalysts according to embodiments of the invention is related to the Cu load. Although Cu can be exchanged, it has been found that in order to increase the level of Cu associated with the exchange sites in the zeolite structure, it is preferable to leave Cu not listed as a salt, for example as CuSO4 in a zeolite catalyst. As a result of calcining, the copper salt decomposes into CuO, which may be referred to herein as "free copper" or "soluble copper." According to one or more forms, this free Cu is both active and selective, resulting in the formation of small amounts of N2O when used to purify a gas stream containing nitrogen oxides. It has been surprisingly found that this "free" Cu gives greater stability to catalysts subjected to thermal aging at temperatures up to about 800 ° C.

[0022] Although the embodiments of the invention are not intended to be bound by a particular base, it is believed that relatively small channel openings in CHA do not allow high molecular weight hydrocarbons (HC), typical of diesel, to enter and adsorb in the CuCHA structure . Unlike other zeolites, such as Beta or ZSM5, CHA catalysts manufactured according to embodiments of the invention have relatively low affinity for adsorbing these high molecular weight HC components. This is the preferred property to be used in selective catalytic reduction (SCR) catalysts.

[0023] In systems that use SCR downstream of a diesel oxidation catalyst (DOC), the properties of CuCHA catalysts provide one or more favorable results in accordance with embodiments of the invention. During start-up and prolonged operation at low temperature, only SCR or diesel oxidation catalyst (DOC) or DOC and catalyzed soot filter (CSF) before the SCR CuCHA catalyst are not fully activated for HC oxidation. According to one or more forms, because HC at low temperature does not affect the CuCHA SCR catalyst, it remains active over a wide range of low operating range temperatures. According to one or more embodiments, low temperatures refer to temperatures of about 250 ° C and lower.

[0024] According to one or more embodiments, the CuCHA catalysts operate at low temperatures. With the passage of time, the exhaust gas purification system containing the DOC precatalyst after the engine, followed by the SCR and CSF catalyst or the DOC precatalyst before CSF and SCR, DOC tends to both activate the thermal catalyst at low temperature and burn HC fuel. It is advantageous if in such systems the SCR catalyst can maintain its ability to operate at low temperatures. Because oxidation catalysts lose their ability to oxidize NO to NO2, it is useful to provide an SCR catalyst that can convert NO as efficiently as NO2. CuCHA catalysts made according to embodiments of the invention have the ability to reduce NO using NH3 at low temperatures. This feature can be enhanced by adding non-specified Cu to the zeolite catalyst. [0025] According to embodiments of the invention, the SCR catalyst may be in the form of self-supporting catalytic particles or as a honeycomb monolith made from an SCR catalyst composition. However, in one or more embodiments of the invention, the SCR catalyst composition is deposited as an intermediate layer or as a combination of intermediate layers on a ceramic or metallic substrate, for example on a honeycomb flow substrate.

[0026] In a specific embodiment of the emission purification system, the SCR catalyst is produced from a CHA zeolite material with Cu exchange, which contains free copper in addition to ion exchange copper.

[0027] When depositing on monolithic honeycomb substrates, such SCR catalyst compositions are deposited at a concentration of at least about 0.5 g / inch³ (0.0305 g / cm³), for example about 1.3 g / inch³ (0.0793 g / cm³), about 2.4 g / inch³ (0.1464 g / cm³) or greater to ensure that the desired NOx reduction is achieved and to ensure adequate catalyst durability over extended periods of use.

[0028] The term "SCR" catalyst is used in the broad sense herein and means selective catalytic reduction in which the catalyzed reaction of nitrogen oxides with a reducing agent occurs to reduce nitrogen oxides. The terms "reducing agent" or "reducing agent" are also used extensively throughout this specification and mean any chemical agent or compound that tends to reduce NOx at elevated temperatures. In certain embodiments, the reducing agent is ammonia, in particular an ammonia precursor, i.e. urea, and SCR is a nitrogen reducing SCR. However, according to the broader scope of the invention, the reducer may include fuel, especially diesel oil and its fractions, as well as any hydrocarbon and oxidised hydrocarbons, collectively referred to as the HC reducer.

SUBSTRATES [0029] The catalyst compositions are deposited on the substrate. The substrate may be any of those materials usually used for the preparation of catalysts, and usually includes a ceramic or metal honeycomb structure. Any suitable substrate may be used, such as a monolithic substrate of the type comprising fine, parallel gas flow channels passing through it extending from the cross section of the inlet or outlet of the substrate so that the channels are open to the fluid flowing through them (referred to as flow media honeycomb). The channels, which are essentially straight paths from their fluid inlet to their fluid outlet, are defined by walls on which the catalytic material is deposited as an intermediate layer, so that the gases flowing through the channels contact the catalytic material. Flow channels in a monolithic substrate are thin-walled channels that can have any suitable shape and cross-sectional size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, etc. Such structures may contain from about 60 to about 400 or more gas (or cells) inlet holes per square inch (from about 9.3 to about 62.0 or more gas (or cells) inlet holes per square centimeter ) cross section.

[0030] The substrate may also be a wall flow filter substrate in which the channels are alternately blocked, which allows the gas stream to enter the channels from one direction (inlet direction), flow through the wall of the channels and exit the channels from another direction (direction outlet). The AMOX and / or SCR catalyst composition can be applied to the flow filter or wall flow. If a substrate with flow through the wall is used, the resulting system will be able to remove solid particles along with gaseous pollutants. Wall-flow filter media can be made of materials commonly known in the art, such as cordierite, aluminum titanate or silicon carbide. It should be understood that the load of the catalytic composition on a wall-flow substrate will depend on the properties of the substrate, such as porosity and wall thickness, and will typically be less than the load on the flow substrate.

[0031] The ceramic substrate can be made of any refractory material, for example, cordierite, cordierite-alumina, silicon nitride, zirconium mullite, spodumene, alumina-silica-magnesium oxide, zirconium silicate, silimanite, magnesium silicate, zirconium, petalite, alpha alumina, aluminosilicate and the like.

[0032] Substrates useful for the catalysts of the embodiments of the present invention may also be of a metallic nature and consist of one or more metals or metal alloys. Metallic substrates of various shapes can be used, such as corrugated steel or monolithic form. Suitable metallic substrates include heat-resistant metals and metal alloys, such as titanium and stainless steel, as well as other alloys in which iron is a significant or major component. Such alloys may contain one or more of nickel, chromium and / or aluminum components, and the total amount of these metals may preferably be at least 15 wt. alloy, for example 10-25 wt. chromium, 3-8 wt. aluminum and up to 20 wt. nickel. The alloys may also contain small or trace amounts of one or more other metals, such as manganese, copper, vanadium, titanium and the like. The surface of metal substrates can be oxidized at high temperatures, for example at 1000 ° C and higher, to increase the corrosion resistance of the alloy as a result of the formation of an oxide layer on the surface of the substrates. Such high temperature oxidation may increase the adhesion to the substrate of components in the form of a refractory support of metal oxide and catalytically promoting metal components.

[0033] In alternative embodiments, one or both of the CuCHA catalyst compositions may be deposited on an open cell foam substrate. Such substrates are well known in the art and are usually made of refractory ceramic or metal materials.

Preparation of an intermediate layer [0034] According to one or more embodiments, intermediate layers of CuCHA can be produced using a binder. According to one or more embodiments, ZrO2 is used as the binder, derived from a suitable precursor such as zirconyl acetate or any other suitable zirconium precursor such as zirconyl nitrate. In one embodiment, zirconyl acetate as a binder provides a catalytic coating that remains homogeneous and intact after thermal aging, for example when the catalyst is subjected to high temperatures, at least about 600 ° C, for example about 800 ° C and above, and in an environment with high water vapor content of about 10% or more. Keeping the intermediate layer intact is advantageous because a loose or loose coating could clog the back of the CSF causing an increase in back pressure.

[0035] According to one or more embodiments, CuCHA catalysts can be used as an ammonia oxidation catalyst. Such AMOX catalysts are useful for an exhaust gas purification system, including an SCR catalyst. As described in U.S. Patent No. 5,516,497 to the same Applicant, a gaseous stream containing oxygen, nitrogen oxides and ammonia may pass sequentially through the first and second catalysts, a first catalyst to reduce nitrogen oxides, and a second catalyst to promote oxidation or other excess decomposition. ammonia. As described in U.S. Patent No. 5,516,497, the first catalyst may be a zeolite-containing SCR catalyst and the second catalyst may be a zeolite-containing AMOX catalyst.

[0036] As known in the art, to reduce nitrogen oxide emissions from exhaust and exhaust gases, ammonia is added to the gas stream containing nitrogen oxides, and then the gas stream is contacted with a suitable catalyst at an elevated temperature to catalyze the reduction of nitrogen oxides ammonia. Such gas streams, for example the products of combustion of an internal combustion engine or gas-fueled or diesel-fueled turbine engine, often also contain inherently significant amounts of oxygen. Typical exhaust gases from a turbine engine contain from about 2 to 15 volume percent oxygen and from about 20 to 500 volume parts per million nitrogen oxides, the latter typically consisting of a mixture of NO and NO2. Usually, there is enough oxygen in the gaseous stream to oxidize residual ammonia, even if the excess over the stoichiometric amount of ammonia required to reduce all nitrogen oxides is used. However, in cases where a very large excess of ammonia is used over the stoichiometric amount or when the gas stream to be purified does not contain or is low in oxygen, the oxygen-containing gas, usually air, may be introduced between the first catalyst zone and the second catalyst zone , to ensure that the right amount of oxygen is in the zone of the second catalyst to oxidize residue or excess ammonia.

[0037] Metal-promoted zeolites are used to promote the reaction of ammonia with nitrogen oxides to form nitrogen and H2O, selectively over the competing reaction of oxygen and ammonia. Therefore, sometimes the catalyzed reaction of ammonia and nitrogen oxides is referred to as selective catalytic reduction ("SCR") of nitrogen oxides or sometimes in the present description simply as the "SCR process". Theoretically, it would be desirable to supply ammonia in excess of the stoichiometric amount required to completely react with the nitrogen oxides present in the SCR process, both to promote reaction completion and to help overcome inadequate mixing of ammonia in the gas stream. However, in fact, there is usually no significant excess of ammonia above the stoichiometric amount, since simply discharging unreacted ammonia from the catalyst into the atmosphere would create a problem with air pollution. This discharge of unreacted ammonia can occur even in cases where ammonia is present only in stoichiometric or sub-stoichiometric amount, as a result of unreacted reaction and / or poor mixing of ammonia in the gas stream, which leads to the formation of channels with high ammonia concentration. This channel formation is of particular importance when catalysts containing monolithic honeycomb carriers containing refractory materials with many fine, parallel gas flow paths through them are used, because, unlike the case with particulate catalysts, it is not possible to mix gas between channels.

[0038] According to embodiments of the present invention, CuCHA catalysts can be formulated to promote either (1) the SCR process, i.e. reduction of nitrogen oxides with ammonia to form nitrogen and H2O, or (2) oxidation of ammonia with oxygen to form nitrogen and H2O, with selectivity the catalyst is adjusted by controlling the Cu content in zeolite. U.S. Patent No. 5,516,497 discloses iron and copper loading levels on zeolites other than copper-CHA to achieve selectivity in the SCR reaction and selectivity of the catalyst for oxidizing ammonia with oxygen at the expense of the SCR process, thereby increasing the removal of ammonia. In accordance with embodiments of the invention, the CuCHA copper load can be adjusted to obtain selectivity for SCR and for oxidation of ammonia by oxygen, and to provide an exhaust gas purification system using both types of catalyst.

[0039] The above principles are utilized by providing a stepwise or dual zone catalyst in which the first zone of a zeolite copper-bearing catalyst that promotes SCR is followed by a second zone of the catalyst comprising a copper-laden zeolite and / or a precious metal component that promotes ammonia oxidation. Thus, the resulting catalyst composition comprises a first zone (in the front) that promotes the reduction of nitrogen oxides with ammonia and a second zone (in the rear) that promotes the oxidation of ammonia. In this way, when ammonia is present in excess of the stoichiometric amount, regardless of whether in the entire cross-section of the gas stream flow that is being treated or in localized channels with a high concentration of ammonia, oxidation of residual ammonia by oxygen the rear part, i.e. the second catalyst zone, favors. The amount of ammonia in the gaseous stream discharged from the catalyst is thus reduced or removed. The first zone and the second zone may be on a single catalyst support or be separate supports.

[0040] An intermediate layer of the CuCHA catalyst comprising a precious metal, for example Pt, has been shown to provide an AMOX catalyst. Not only ammonia is expected to be broken down in the gas flowing through the catalyst, but there is continuous removal of NOx as a result of conversion to N2. In a specific embodiment, the SiO2 / Al2O3 ratio in zeolite is from about 15 to about 256, and the Al / M ratio between 2 and 10, where M is the total Cu and precious metal content. In one embodiment, the precious metal is platinum and the platinum content is between 0.02% and 1.0% by weight of the catalyst, and the component load is from about 0.5 to about 5 g / inch³ (from about 0.0305 to about 0.3050 g / cm³).

[0041] According to one or more embodiments of the invention, the SCCH CuCHA catalysts may be deposited on a flow-through filter or on a catalyzed soot filter. Intermediate layers of the CuCHA catalyst can be coated on a porous filter to ensure soot combustion and perform SCR and AMOX functions.

[0042] In one or more embodiments of the present invention, the catalyst comprises a noble metal component, i.e. a metal component from the platinum group. For example, as mentioned above, AMOX catalysts usually contain a platinum component. Suitable components in the form of precious metals include platinum, palladium, rhodium and mixtures thereof. The individual components (e.g. CuCHA and the noble metal component) of the catalyst material can be applied to the refractory support element, i.e. to the substrate, as a mixture of two or more components or as separate components in subsequent steps in a manner that will be readily understood by specialists in the field of catalyst production. As described above and in the examples, a typical method for producing catalysts in accordance with an embodiment of the present invention involves providing the catalytic material as a coating or intermediate layer on the walls of the gas flow channels in a suitable support element. This can be achieved by soaking the refractory metal oxide support material in the form of fine particles, for example gamma alumina, with one or more components in the form of a catalytic metal, such as a precious metal, i.e. from the platinum group, a chemical compound or other precious metal or metal base, drying and roasting the soaked ground particles and forming an aqueous suspension of these particles. Copper-chabazite catalyst particles present in bulk can be contained in the suspension. Activated alumina can be thermally stabilized before the catalytic components are dispersed therein, as is well known in the art, by soaking it with, for example, a solution of soluble barium, lanthanum, zirconium, rare earth metal or other suitable stabilizer precursor, followed by drying ( for example at 110 ° C for one hour) and calcining (for example at 550 ° C for one hour) soaked, activated alumina to form a stabilizing metal oxide dispersed on alumina. Base metal catalysts may also optionally be impregnated with activated alumina, for example by impregnating with a base metal nitrate solution on alumina particles and calcining to provide a base metal oxide dispersed in alumina particles.

[0043] The carrier may then be immersed in a slurry of impregnated, activated alumina, and excess slurry removed to provide a thin coating from the slurry on the walls of the gas flow channels in the carrier. The coated support is then dried and calcined to obtain an adherent coating of a catalytic component and optionally of copper-CHA material for the walls of its channels. One or more additional layers may be placed on the support. After each layer has been applied, or after applying many desired layers, the support is then dried and calcined to provide a finished catalyst element in accordance with one embodiment of the present invention.

[0044] Alternatively, alumina or other substrate particles impregnated with a precious metal or base metal component may be mixed with loose or embedded particles of copper-chabazite material in an aqueous suspension, and this mixed suspension of particles of the catalytic component and of particles of copper-chabiteite may be applied as coating on the walls of the flow channels for gas in the carrier.

[0045] The used flue gas stream may be contacted with a catalyst produced in accordance with embodiments of the present invention. For example, CuCHA catalysts manufactured in accordance with embodiments of the present invention are well suited for the purification of exhaust gases from engines, including diesel engines.

[0046] Without intending to limit the invention in any way, embodiments of the present invention will be described in more detail in the following examples.

EXAMPLE 1 [0047] CuCHA powder catalyst was prepared by mixing 100 g CHA in the form of NH4⁺, with a silica / alumina molar ratio of 30, with 400 ml of a 1.0 M copper (II) sulfate solution. The pH was adjusted to 3.5 with nitric acid. The ion exchange reaction between the NH4 form⁺ CHA and copper ions were carried out by stirring the suspension at 80 ° C for 1 hour. The resulting mixture was then filtered off, washed with 800 ml of deionized water in three portions until the filtrate became clear and colorless, indicating that substantially no soluble or free copper remained in the sample and the washed sample was dried at 90 ° C. The above process, including ion exchange, filtration, washing and drying, was repeated once.

[0048] Then the obtained product in the form of CuCHA was calcined at 640 ° C in an atmosphere of air for 6 hours. The resulting CuCHA catalyst contained 2.41 wt% CuO as determined by ICP analysis. A CuCHA suspension was prepared by mixing 90 g of CuCHA described above with 215 ml of deionized water. The mixture was ground in a ball mill. To the suspension, 15.8 g of zirconium acetate in diluted acetic acid (containing 30% ZrO2) was added to the suspension.

[0049] The suspension was applied to 1 "Dx3" L cellular ceramic cores with a cell density of 400 cpsi (cells per square inch) (62 cells per square centimeter) and a wall thickness of 6.5 mils. The coated cores were dried at 110 ° C for 3 hours and calcined at 400 ° C for 1 hour. The coating process was repeated once to obtain a target load of intermediate layer 2.4 g / inch³ (0.1464 g / cm³).

[0050] The selective catalytic reduction (SCR) efficiency of nitrogen oxides and the selectivity of the fresh catalyst core were measured by feeding a feed gas mixture of 500 ppm NO, 500 ppm NH3, 10% O2, 5% H2O, and N2 as a supplement to the steady state reactor containing a 1 "D x 3" L catalyst core. The reaction was carried out at a volume speed of 80,000 hours^-1 in the temperature range 150 ° C to 460 ° C.

[0051] Hydrothermal stability of the catalyst was measured by hydrothermal aging of the catalyst core in the presence of 10% H2O at 800 ° C for 50 hours, followed by measurement of the SCR efficiency of nitrogen oxides and selectivity in the same process as described above for the SCR assessment on a fresh catalyst core.

[0052] Figure 1 is a graph showing NOx conversion and production or formation of N2O as a function of temperature for this sample. These results are summarized in the Table

1. This sample, which did not contain soluble copper before calcination, as shown by the color of the filtrate described above, did not show increased resistance to thermal aging.

EXAMPLE 1A [0053] Copper sulfate pentahydrate was added to the coating suspension of Example 1 to increase the total CuO content to 3.2%. The suspension was applied to the monolith and aged and tested for the presence of SCR NOx as described above in Example 1, except that the monolith was calcined at 640 ° C. Catalytic efficiency was compared to Example 1 in Figure 1A. The addition of copper sulfate to the coating suspension significantly improved hydrothermal stability and activity at low temperature.

EXAMPLE 2 [0054] CuCHA powder catalyst was prepared by mixing 17 kg CHA in the form of NH4⁺, with a silica / alumina molar ratio of 30, with a 68 L 1.0 M copper (II) sulfate solution. The pH was adjusted to 3.5 with nitric acid. The ion exchange reaction between the NH4 form⁺-CHA and copper ions were carried out by stirring the suspension at 80 ° C for 1 hour. The resulting mixture was then filtered off and air dried. The above process, including ion exchange and filtration, was repeated once. The wet cake was then resuspended in 40 L of deionized water, then filtered off and dried at 90 ° C. The resulting CuCHA product was then calcined at 640 ° C in air for 6 hours. The resulting CuCHA catalyst contained 2.75 wt% CuO.

[0055] Slurry preparation, coating and SCR NOx evaluation was carried out in the same manner as described above in Example 1. The product of this example contained free copper and showed increased hydrothermal stability compared to Example 1.

EXAMPLE 3 [0056] A CuCHA catalyst containing 3.36% by weight of CuO was prepared using the same process as in Example 2, followed by impregnation by the first humidity method. [0057] Using the procedure of Example 2, 134 grams of CuCHA with a CuO content of 3.11% by weight were prepared. Copper sulfate solution containing 1.64 g of copper sulfate pentahydrate and 105 ml of deionized water was added to this material. The impregnated sample was dried at 90 ° C and calcined at 640 ° C for 6 hours.

[0058] Slurry preparation, coating and SCR NOx assessment was carried out in the same manner as described above in Example 1. As shown in Figure 3, the sample containing more non-listed copper exhibited, in addition to hydrothermal stability, higher activity at low temperature.

EXAMPLE 4 [0059] A CuCHA catalyst containing 3.85% by weight of CuO was produced only as a result of the impregnation process by the first humidity method. A solution of copper sulfate containing 18.3 g of copper sulfate pentahydrate and 168 ml of deionized water was impregnated with 140 g of CHA in the form of NH4⁺, with a silica / alumina molar ratio of 30. The impregnated sample was then dried at 90 ° C and calcined at 640 ° C for 6 hours.

[0060] Slurry preparation, coating and SCR NOx assessment was carried out in the same manner as described above in Example 1. As shown in Fig. 4, the product of Example 4 showed a decrease in efficiency at temperatures between 350 ° C and 450 ° C, after hydrothermal aging.

EXAMPLE 5 [0061] A CuCHA catalyst containing 1.94% by weight of CuO was prepared using the same process as in Example 1, except that this sample was prepared by a single ion exchange.

[0062] Slurry preparation, coating and SCR NOx assessment was carried out in the same manner as described above in Example 1, except that hydrothermal stability was not measured. EXAMPLE 6 [0063] A CuCHA powder catalyst was prepared by mixing 0.2 g CHA in the form of NH4⁺, with a silica / alumina molar ratio of 15, with 16 ml of a 25 mM copper (II) sulfate solution. Ion exchange reaction between CHA in the form of NH4⁺ and copper ions were carried out by stirring the suspension at 80 ° C for 1 hour. The resulting mixture was then filtered off, washed with deionized water and dried at 90 ° C. The above process, including ion exchange, filtration, washing and drying, was repeated once. The resulting CuCHA product was then calcined at 540 ° C in air for 16 hours. The resulting CuCHA catalyst contained 4.57 wt% CuO.

[0064] The powder catalyst was subjected to hydrothermal aging in the presence of 10% H2O at 800 ° C for 50 hours, and then the SCR efficiency of nitrogen oxides was measured. [0065] The efficiency of the catalyst was evaluated using a micro-channel catalytic converter containing a bed of about 12.6 mm³ catalyst. The flow rate (under standard temperature and pressure conditions) was 500 ml / min for reagents with the composition 500 ppm NOx, 500 ppm NH3, 10% O2, 5% H2O, supplemented with He, and 25 ml / min of steam was passed through various beds temperatures (200, 250, 300, 350, 400, 450 and 500 ° C) to determine the reactivity of the catalyst. The NOx conversion was determined as 100 * (NOx on supply - NOx on outlet) / (NOx on supply) using a mass spectrum analyzer. EXAMPLE 7 [0066] A CuCHA powder catalyst containing 2.94% by weight CuO was prepared using the same process as in Example 6, including ion exchange, filtration, washing, drying, calcination and hydrothermal aging, except that the molar ratio silica / alumina was 30, and the ion exchange process was repeated 4 times.

[0067] The SCR NOx rating is the same as described above for Example 6.

EXAMPLE 8 [0068] A CuCHA powder catalyst containing 0.45 wt.% CuO was prepared using the same process as in Example 6, including ion exchange, filtration, washing, drying, calcining and hydrothermal aging except that the silica molar ratio / alumina was 50.

[0069] The SCR NOx rating is the same as described above for Example 6

EXAMPLE 9 [0070] A CuCHA powder catalyst was prepared by mixing 15.0 g CHA in the form of NH4⁺, with a silica / alumina molar ratio of 256, with 61 ml of 0.64 M copper (II) sulfate solution. Ion exchange reaction between CHA in the form of NH4⁺and copper ions were carried out by stirring the suspension at 80 ° C for 1 hour. The resulting mixture was then filtered off, washed with deionized water and dried at 90 ° C. The above process, including ion exchange, filtration, washing and drying, was repeated 4 times. The resulting CuCHA product was then calcined at 540 ° C in air for 16 hours. The resulting CuCHA catalyst contained 2.63 wt% CuO.

[0071] Hydrothermal aging and SCR NOx evaluation were the same as described above for Example 6.

COMPARATIVE EXAMPLE 10 [0072] A Cu / Y zeolite powder catalyst with a silica / alumina molar ratio of 5 was prepared, as further described below.

[0073] A Cu / Y powder catalyst was prepared by mixing 500 g Zeolite Y in the form of NH4⁺, with a silica / alumina molar ratio of ~ 5, with 2500 ml of a 0.1 M copper (II) sulfate solution. The pH was between 2.9 and 3.3. Ion exchange reaction between zeolite Y in the form of NH4⁺ and copper ions were carried out by stirring the suspension at 80 ° C for 1 hour. The resulting mixture was then filtered off, washed with deionized water and dried at 90 ° C. The above process, including ion exchange, filtration, washing and drying, was repeated for a total of 5 exchanges, with the pH value similar to the above. The resulting product in the form of the zeolite Cu / Y was then calcined at 640 ° C under an atmosphere of air for 16 hours. The resulting Cu / Y zeolite catalyst contained 4.60% by weight CuO [0074] A Cu / Y suspension was prepared by mixing 200 g Cu / Y, which was described above, with 400 ml deionized water. The mixture was milled by passing it through the Eigermill apparatus twice to obtain a suspension that contained 90% of particles smaller than 8 μm. To this suspension, 8.7 g of zirconium acetate in dilute acetic acid (containing 30% ZrO2) was added to this suspension with stirring.

[0075] The suspension was applied to 1 "Dx3" L cellular ceramic cores with a cell density of 400 cpsi (cells per square inch) (62 cells per square centimeter) and a wall thickness of 6.5 mils (0.1651 mm). Two coatings were required to obtain a target intermediate layer load of 1.6 g / inch³ (0.0976 g / cm³). The coated cores were dried at 90 ° C for 3 hours and the cores were calcined at 450 ° C for 1 hour after the second drying step.

[0076] Hydrothermal aging and SCR assessment were the same as described in Example 1, except that they were carried out at 750 ° C for 25 hours.

COMPARATIVE EXAMPLE 11.

[0077] A Cu / Beta powder catalyst was prepared with a silica / alumina molar ratio of 35 using a procedure similar to the sample prepared in EXAMPLE 10. The hydrothermal aging and SCR rating are the same as described in Example 1.

[0078] The summary of data for Examples 1-5 and Comparative Examples 10-11 is given in Table 1 below.

Table 1

<td rowspan="2">Example</td><td rowspan="2">Ratio atomic Cu / Al</td><td rowspan="2">CuO %</td><td colspan="4">NOx conversion (%)</td><td colspan="2">Produced N2O, ppm</td>

<td>210 ° C fresh</td><td>210 ° C after aging</td><td>460 ° C fresh</td><td>460 ° C after aging</td><td>460 ° C fresh</td><td>460 ° C after aging</td>

<td> 1</td><td> 0,30</td><td> 2,4 1</td><td> 75</td><td> 43</td><td> 95</td><td> 82</td><td> 0,8</td><td> 5,3</td>

<td> 2</td><td> 0,33</td><td> 2,7 5</td><td> 62</td><td> 59</td><td> 90</td><td> 83</td><td> 3,1</td><td> 9,3</td>

<td rowspan="2">Example</td><td rowspan="2">Ratio atomic Cu / Al</td><td rowspan="2">CuO %</td><td colspan="4">NOx conversion (%)</td><td colspan="2">Produced N2O, ppm</td>

<td>210 ° C fresh</td><td>210 ° C after aging</td><td>460 ° C fresh</td><td>460 ° C after aging</td><td>460 ° C fresh</td><td>460 ° C after aging</td>

<td> 3</td><td> 0,38</td><td> 3,3 6</td><td> 74</td><td> 70</td><td> 91</td><td> 81</td><td> 2,7</td><td> 10,5</td>

<td> 4</td><td> 0,44</td><td> 3,8 5</td><td> 76</td><td> 60</td><td> 88</td><td> 72</td><td> 3,5</td><td> 14,2</td>

<td> 5</td><td> 0,24</td><td> 1,9 4</td><td> 50</td><td> 30</td><td> 95</td><td> 75</td><td> 0,2</td><td> 5,0</td>

<td> 10</td><td> 0,23</td><td> 4,6</td><td> 43</td><td> 42</td><td> 99</td><td> 96</td><td> 26</td><td> 51</td>

<td> 11</td><td> 0,36</td><td> 2,5</td><td> 92</td><td> 23</td><td> 84</td><td> 53</td><td> 10</td><td> 9,4</td>

<td> 12</td><td> 0,46</td><td> 3,7</td><td> 75</td><td> 78</td><td> 89</td><td> 80</td><td> 5,4</td><td> 11,7</td>

<td>1A</td><td> 0,40</td><td> 3,2</td><td></td><td> 61</td><td></td><td> 82</td><td></td><td> 11,3</td>

[0079] Table 1 indicates that in Example 3 the best combination of low temperature activity, high temperature activity and slight deterioration due to hydrothermal aging was obtained.

[0080] Table 2 shows the normalized NOx conversion for Examples 6-9, with different SiO2 / Al2O3 molar ratios and Cu / Al atomic ratios. In Example 7, the best efficiency was achieved. Although the performance of Examples 6, 8 and 9 was not optimal, it should be noted that in each of these Examples, aging was performed at a relatively high temperature of 800 ° C. Not all catalysts will be exposed to such high temperatures, and it is believed that samples aged at lower temperatures should exhibit acceptable performance over a wider range of acceptable silica / alumina ratios. For example, in an exhaust gas purification system comprising an SCR catalyst downstream of a catalyzed soot filter, SCR is usually exposed to high temperatures, for example exceeding about 700 ° C. If the SCR is deposited on CSF, the SCR may be exposed to temperatures as high as about 800 ° C or higher. According to embodiments of the present invention, greater flexibility in the placement of a catalyst, such as an SCR catalyst, in an exhaust gas purification system is provided due to CuCHA catalysts that exhibit increased hydrothermal stability compared to other types of zeolite materials. It would be expected that samples with a silica to aluminum oxide ratio in the range between about 15 and 256 that are exposed to operating temperatures below about 800 ° C, provide acceptable NOx conversion at low temperature. Thus, in accordance with embodiments of the invention, silica to alumina ratios from about 15 to about 256 are within the scope of the invention, however, narrower ranges having a lower limit point of about 10, 20, about 25 and about 30, and a higher limit point of about 150, 100 , 75, 50 and 40 are within the scope of the invention.

Table 2

<td rowspan="2">Example</td><td rowspan="2">Ratio molar SiO2 / Al2O3</td><td rowspan="2">CuO %</td><td rowspan="2">Ratio atomic Cu / Al</td><td colspan="3">NOx conversion, aged, normalized</td>

<td>200 ° C</td><td>250 ° C</td><td>300 ° C</td>

<td> 6</td><td> 15</td><td> 4,57</td><td> 0,30</td><td> 0,34</td><td> 0,61</td><td> 0,81</td>

<td rowspan="2">Example</td><td rowspan="2">Ratio molar SiO2 / Al2O3</td><td rowspan="2">CuO %</td><td rowspan="2">Ratio atomic Cu / Al</td><td colspan="3">NOx conversion, aged, normalized</td>

<td>200 ° C</td><td>250 ° C</td><td>300 ° C</td>

<td> 7</td><td> 30</td><td> 2,94</td><td> 0,36</td><td> 1,00</td><td> 1.00</td><td> 0,98</td>

<td> 8</td><td> 50</td><td> 0,45</td><td> 0,089</td><td> 0,39</td><td> 0,54</td><td> 1,00</td>

<td> 9</td><td> 256</td><td> 2,63</td><td> 2,6</td><td> 0,10</td><td> 0,70</td><td> 0,88</td>

EXAMPLE 12. CUFF INHIBITION TEST:

[0081] The samples tested in this Example were prepared as follows. A CuCHA powder catalyst was prepared by mixing 250 g CHA in the form of NH4⁺, with a silica / alumina molar ratio of 30, with a 2.0 L 0.1 M copper (II) sulfate solution. The pH was adjusted to 3.0-3.4 with nitric acid. Ion exchange reaction between CHA in the form of NH4⁺ and copper ions were carried out by stirring the suspension at 80 ° C for 1 hour. The resulting mixture was then filtered off, washed with deionized water and dried at 90 ° C. The above process, including ion exchange, filtration, washing and drying, was repeated a total of 5 times. The resulting CuCHA product was then calcined at 640 ° C in air for 16 hours. The resulting CuCHA catalyst contained 3.68 wt% CuO.

[0082] The effect of CO, propene, n-octane and water on SCR CuCHA activity at 170, 200, 250, 300 and 350 ° C was investigated. The catalyst cores were tested in a simulated mixture of exhaust gases from a diesel engine. The main gas concentrations were: 500 ppm NO, 500 ppm NH3, 10% CO2, 10% O2. The following ingredients were added sequentially to study their effect on NOx conversion: 5% H2O, 300 ppm C3H6 as C1, 600 ppm C3H6 as C1, 100 ppm octane as C1 and 500 ppm CO. The volumetric rate in the experiments was set to 142,000 hours^-1. The reaction was allowed to reach equilibrium at the following temperature points: 170 ° C, 200 ° C, 250 ° C, 300 ° C and 350 ° C, and then the conversion and interaction of the components were recorded. Gas analysis of NO, NO2, N2O, NH3, CO2, CO, C3H6 and H2O was carried out using the MKS 2030 MultiGas FTIR device operating at a resolution of 0.5 cm^-1.

[0083] The results are summarized in Figure 5. At low temperatures of 170 ° C and 200 ° C, water was the main inhibitor, a high level of 200 ppm propene (600 ppm C1) exerted a slight inhibitory effect at 200 ° C, 100 ppm propene (300 ppm C1 ), CO and n-octane had no effect. At temperatures higher than 250 ° C the effect of water as a promoter is clearly visible. None of the tested components inhibited NOx conversion at 250 ° C, on the contrary, they were all promoters. At 300 ° C CO and n-octane supported SCR NOx, while 600 ppm of propene as C1 inhibited the reaction. At 350 ° C, only 600 ppm of propene as C1 had a slight inhibitory effect, and all other components had a beneficial effect. It is believed that this performance is better than that of other Cu-promoted SCR catalysts that use medium and large pore zeolites, for example beta zeolites. SCR catalysts are known to be susceptible to short-term poisoning by long-chain hydrocarbons that can fill pores with coke. These studies show that CuCHA zeolite with small pores does not show this problem.

EXAMPLE 12A

HC COLLECTION / RELEASE TEST:

GASES AND DEVICE:

[0084] A CuCHA catalyst core applied to a ceramic monolith (400 cpsi (62 cells per square centimeter) / 6 mils (0.1524 mm)) having a cross section of

144 open cells and 1 inch in length, first aged for 50 hours at 800 ° C, in 10% H2O, 10% O2, supplemented with nitrogen. The catalyst was then placed in a laboratory reactor. The catalyst was treated with a gas mixture containing 4% H2O, 14% O2, 100 ppm NO, supplemented with N2, and heated to 100 ° C. After the temperature stabilized at 100 ° C, a mixture of toluene and octane was added through a mass flow regulator to achieve a target concentration of 100 ppm C1 as octane and 100 ppm C1 as toluene, at a total volume rate of 104 kh^-1. The waste gas was directed through an afterburner, which contained an oxidation catalyst based on Pt / alumina and was kept at a constant temperature of 600 ° C. Any hydrocarbon emissions, including partial oxidation and CO products that may have been generated over the CuCHA catalyst, will be oxidized to CO2 as it passes through the afterburner. The exhaust CO2 from the afterburner is monitored by an IR analyzer for CO2. In parallel, the part of the exhaust stream from the CuCHA catalyst passing past the afterburner is analyzed by the FID-HC analyzer.

RESEARCH PROTOCOL:

[0085] After stabilizing the CuCHA catalyst at 100 ° C in a mixture of 4% H2O, 14% O2, 100 ppm NO, supplemented with N2, a hydrocarbon mixture of octane and toluene was introduced. The catalyst temperature was kept at 100 ° C for 10 minutes. During this time, HC is accumulated over the catalyst, which leads to a CO2 signal from the afterburner below the HC inlet concentration. After the collection period, the temperature rises linearly from 100 ° C to 600 ° C at a rate of 20 ° C / min. The afterburner CO2 signal increases rapidly due to the release of accumulated HC from the catalyst. After desorption, the CO2 signal returns to its original value (which = concentration in the feed gas). With the increase in temperature, a small decrease in the CO2 signal from the afterburner, below the level in the feed gas, indicates a second type of HC removal, caused by the deposition of carbonaceous deposits, produced from toluene and octane on the catalyst. As the temperature increases further, any carbon deposits generated burn out and cause an elevated CO2 signal from the afterburner. After burning out carbon deposits, the afterburner CO2 signal returns to its initial value.

DATA ANALYSIS:

[0086] The CO2 signal from the afterburner was quantified to determine the amount of HC that is accumulated, released, deposited as coke and spent coke. Corresponding intersection points of the CO2 signal at the afterburner output shown in Fig. 5A, with HC concentration in the feed gas were used as integration limits. For example, for CuCHA, these integration limits were approximately between 0 and 800 s for storage, between 800 s and 1000 s for release, between 1000 s and 1400 s for coking, respectively. The amounts of HC that have been collected, released, deposited as coke, and then fired are expressed in mg HC, based on the average C: H ratio in the HC feed stream.

RESULTS:

[0087] This study was conducted with SCR catalysts, Cu-Y (after aging for 25 h at 750 ° C, in 10% H2O, 10% O2, supplemented with N2) and Fe-Beta (after aging for 50 h at 800 ° C, in 10% H2O, 10% O2, supplemented with N2) of the same volume under the same conditions. It turned out that in the case of CuCHA very little coking occurs and therefore there is no visible firing signal. The results are shown in Fig. 5B. It is clear that the CuCHA catalyst accumulates the smallest amount of HC, most of which is released as HC and little is deposited as coke. In contrast, the Cu-Y catalyst does not produce a significant amount of carbonaceous deposits in the temperature range from about 200 ° C to 450 ° C. Part of the accumulated coke is then fired at higher temperatures.

EXAMPLE 13. MANUFACTURE OF AMOX CATALYST.

[0088] An ammonia oxidation catalyst was prepared containing CuCHA, as in Example 12, with a copper content of 3.68%, measured as CuO and a SiO2 / Al2O3 ratio of 30. This material was applied to a standard monolithic substrate from cordierite with a square cell geometry of 400 cells / inch³to ensure a total load of 2.40 g / inch³ (0.1464 g / cm³) based on the bulk volume of the monolith. This precoated monolith was then immersed in a solution of the precursor containing platinum (a complex of platinum with hydroxyamine) to distribute the platinum precursor completely and evenly on this element. The element was dried at 110 ° C and then calcined at 450 ° C for one hour. A platinum load of 4.3 g / ft was thus obtained on this element³ (0.1518 g / l), based on the bulk volume of the monolith. Thus, the catalyst had the following composition: 3.68% CuO + 0.10% Pt supported on a CuCHA carrier, applied to a 400/6 standard cordierite substrate with a total load of approximately 2.4 g / inch³ (0.1464 g / cm³). The Al: Cu: Pt atomic ratio in this catalyst is about 190: 90: 1. The ratio Al / M (M = Cu + Pt) is about 2.1. EXAMPLE 14-TESTING OF SAMPLES IN EXAMPLE 13.

[0089] Ammonia removal efficiency and oxidation selectivity of the product for the hydrothermal aged AMOX catalyst core, prepared as described in Example 13, was measured by feeding a feed gas mixture of 500 ppm NH3, 10% O2, 5% H2O, supplemented with N2 (as air ), to a steady state reactor containing a 3.0-inch (7.62 cm) square-cylindrical catalyst core with a frontal section containing 144 open cells. The reaction was carried out at a volumetric speed of 100,000 h^-1 in the temperature range 150 ° C to 460 ° C. Hydrothermal aging conditions were as follows: 10 hours at 700 ° C with 10% H2O in an air atmosphere. Figure 6 is a graph showing emissions compared to those of a hydrothermal aged CuCHA sample. The data show 1) a very selective conversion of NH3 to N2, catalyzed by a CuCHA catalyst without Pt impregnation and 2) that the NH3 conversion can be significantly increased by the inclusion of a platinum-containing component, without compromising the high N2 selectivity. The latter is important because the prior art shows that platinum in the form of a metal mesh or deposited on other oxides or zeolite supports is essentially selective for the production of N2O or NOx.

EXAMPLE 15 [0090] Comparison of the composition of CuCHA on a flow substrate and a filter with wall flow at comparable loads. The wall-flow filter was coated with the same catalyst as the flow-through catalyst of Example 3 and measured on two samples to compare their catalytic activity.

[0091] A CuCHA suspension was prepared by mixing 90 g of CuCHA, which was described above, with 215 ml of deionized water. The mixture was ground in a ball mill for 11 hours to obtain a suspension which contained 90% of particles smaller than 10 μm. To the suspension, 15.8 g of zirconium acetate in diluted acetic acid (containing 30% ZrO2) was added to the suspension.

[0092] The suspension was applied to cellular ceramic filter cores with a 1 "Dx6" L wall flow with a cell density of 300 cpsi (cells per square inch) (46.5 cells per square centimeter) and a wall thickness of 12 mils (0.3048 mm) . The coated cores were dried at 120 ° C for 3 hours and calcined at 540 ° C for 1 hour. The coating process was repeated once to obtain a target intermediate layer load of 2.0 g / inch³ (0.1220 g / cm³).

[0093] The selective catalytic reduction (SCR) efficiency of nitrogen oxides and the selectivity of the fresh catalyst core were measured by feeding a mixture of feed gas with 500 ppm NO, 500 ppm NH3, 10% O2, 5% H2O, supplemented with N2, to a steady-state reactor containing a core 1 "D x 6" L catalyst. The reaction was carried out at a volume speed of 40,000 h^-1 in the temperature range 150 ° C to 400 ° C.

[0094] Hydrothermal stability of the catalyst was measured by hydrothermal aging of the catalyst core in the presence of 10% H2O at 750 ° C for 25 hours, followed by measuring the SCR yield of nitrogen oxides and selectivity by the same method as described above for the assessment of SCR on a fresh catalyst core.

[0095] Table 3 below provides a comparison of the SCR efficiency of a hydrothermal aged CuCHA applied to a filter versus CuCHA applied to a flow catalyst support.

Table 3: Comparison of SCR efficiency (% conversion) for filtration and flow media.

<td>WELL</td><td>NO2</td><td>NOx</td><td>NH3</td><td>N2O production (ppm)</td><td>Sample temperature (degrees C)</td>

<td colspan="3">CuCHA on the ground</td><td colspan="3">flow, aged for 50 h at 800 ° C w / 10% water</td>

<td> 74,6</td><td> 83,5</td><td> 75,0</td><td> 76,9</td><td> 8,4</td><td> 211</td>

<td> 96,3</td><td> 95,6</td><td> 96,2</td><td> 93,9</td><td> 9,2</td><td> 255</td>

<td> 97,6</td><td> 97,5</td><td> 97,6</td><td> 97,3</td><td> 7,6</td><td> 309</td>

<td> 82,7</td><td> 36,5</td><td> 81,0</td><td> 98,1</td><td> 12,3</td><td> 441</td>

<td colspan="6">CuCHA on the filter, aged for 25 h at 750 ° C w / 10% water</td>

<td> 74,7</td><td> 81,5</td><td> 75,1</td><td> 76,0</td><td> 8,8</td><td> 207</td>

<td> 96,4</td><td> 96,1</td><td> 96,4</td><td> 96,5</td><td> 9,9</td><td> 255</td>

<td> 98,6</td><td> 97,7</td><td> 98,5</td><td> 96,8</td><td> 8,7</td><td> 304</td>

<td> 96,2</td><td> 90,7</td><td> 95,9</td><td> 98,7</td><td> 8,2</td><td> 352</td>

<td> 91,1</td><td> 62,4</td><td> 89,8</td><td> 99,4</td><td> 11,7</td><td> 400</td>

[0096] Despite some differences in the exact details of the experiment, the comparison clearly confirms the equivalence of CuCHA catalytic efficiency on the filter core and on the monolithic flow catalyst.

EXAMPLE 16 [0097] NH4 suspension was prepared⁺-CHA by mixing 608 g NH4⁺-CHA with a silica / alumina molar ratio of 30 with 796 ml of deionized water. The mixture was ground using a Netzsch Mill to obtain a slurry that contained 90% of particles smaller than 8.4 Pm. 106 g zirconium acetate in dilute acetic acid (containing 30% ZrO2) was added to the suspension while stirring.

[0098] The suspension was applied to 1 "Dx3" L ceramic cell cores with a cell density of 400 cpsi (62 cells per square centimeter) and a wall thickness of 6.5 mils (0.1651 mm). The coated cores were dried at 110 ° C for 3 hours. The coating process was repeated once to obtain a target intermediate layer load of 2.4 g / inch³ (0.1464 g / cm³).

[0099] This precoated monolith was then immersed in a 0.25 M copper acetate solution for 5 minutes at room temperature. The core was gently blown with an air gun and dried at 110 ° C for 3 hours, then calcined at 400 ° C for 1 hour. This ensured a CuO load on CHA of 2.72 wt.%, Relative to the weight of CHA on the monolith.

[0100] The SCR NOx rating of the fresh catalyst was the same as that described for Example 1. The hydrothermal stability of the catalyst was measured by the hydrothermal aging of the catalyst core in the presence of 10% water vapor at 850 ° C for 6 h and then by measuring the SCR NOx yield, which has been described for fresh catalyst.

[0101] Figure 7 is a graph showing NOx conversion and N2O formation as a function of temperature for this sample.

EXAMPLE 17 [0102] 12.1 g copper acetate monohydrate was dissolved in 420 g deionized water, then 141 g NH4 was added⁺-CHA with a silica / alumina molar ratio of 30. The mixture was milled in a Netzsch Mill to obtain a suspension that contained 90% of particles smaller than 3.5 Pm.

[0103] The suspension was applied to 1 "Dx3" L cellular ceramic cores with a cell density of 400 cpsi (62 cells per square centimeter) and a wall thickness of 6.5 mils (0.1651 mm). The coated cores were dried at 110 ° C for 3 hours. The coating process was repeated twice to obtain the target intermediate layer load

2.4 g / inch³ (0.1464 g / cm³). The coated cores were then calcined at 400 ° C for 1 hour. This provided a 3.3% wt CuO on CHA.

[0104] The SCR NOx rating of the fresh catalyst was the same as that described for Example 1. The hydrothermal stability of the catalyst was measured by hydrothermal aging of the catalyst core in the presence of 10% water vapor at 850 ° C for 6 hours, followed by measuring the SCR NOx yield, which described for fresh catalyst.

[0105] Figure 8 is a graph showing NOx conversion and N2O formation as a function of temperature for this sample.

EXAMPLE 18 [0106] A CuCHA powder catalyst was prepared by ion exchange with copper acetate. A 0.40 M copper (II) acetate monohydrate solution was prepared by dissolution

89.8 g of copper salt in 1.125 l of deionized water at 70 ° C. Then 300 g CHA in the form of NH4 was added to this solution⁺. Ion exchange reaction between CHA in the form of NH4⁺ and copper ions were carried out by stirring the suspension at 70 ° C for 1 hour. During the reaction, the pH was between 4.8 and 4.5. The resulting mixture was then filtered off, washed until the filtrate had a conductivity &lt;200 μScm^-1which indicated that essentially no soluble or free copper remained in the sample and the washed sample was dried at 90 ° C. The resulting CuCHA catalyst contained 3.06 wt.% CuO and 140 ppm Na2O.

[0107] The suspension preparation, coating and SCR NOx evaluation was the same as described above for Example 1. As shown in Fig. 7, Example 18 showed the same SCR efficiency as Example 3, which was produced by exchanging ions with copper sulfate twice and impregnation by the initial moisture method.

EXAMPLE 19 [0108] A CuCHA catalyst containing 2.99% by weight of CuO was prepared using the same process as in Example 18, except that this sample was prepared in 0.30 M Cu solution.

EXAMPLE 20 [0109] A CuCHA catalyst containing 2.69 wt.% CuO was prepared using the same process as in Example 18 except that the ion exchange process was carried out at 45 ° C.

EXAMPLE 21 [0110] A CuCHA catalyst was prepared containing 2.51% by weight of CuO using the same process as in Example 19 except that the ion exchange process was carried out at 45 ° C.

[0111] In Table 4, the Cu loads of Examples 18-21 were compared with those of Example 5 1. It can be seen that copper acetate is more effective than copper sulfate in providing the desired Cu load using a low copper concentration solution at a lower reaction temperature .

Table 4

<td>Example</td><td>Cu salt</td><td>Cu concentration²+, M</td><td>Reaction temperature, ° C</td><td>CuO, wt.%</td>

<td> 1</td><td>Cu sulfate</td><td> 1,0</td><td> 80</td><td> 2,41</td>

<td> 18</td><td>Cu acetate</td><td> 0,40</td><td> 70</td><td> 3,06</td>

<td> 19</td><td>Cu acetate</td><td> 0,30</td><td> 70</td><td> 2,99</td>

<td> 20</td><td>Cu acetate</td><td> 0,40</td><td> 45</td><td> 2,69</td>

<td> 21</td><td>Cu acetate</td><td> 0,30</td><td> 45</td><td> 2,51</td>

EXAMPLE 22- Hydrothermal aging and chemical analysis of Example 2 [0112] The Cu / CHA powder prepared in Example 2 was subjected to hydrothermal aging in the presence of 10% H2O in an air atmosphere at 800 ° C for 48 hours. The analyzed material of Example 2 is designated as Example 22 in Figures 11 and 12 and in Tables 5 and 6. The hydrothermal aged sample is designated as Example 22A in Tables 5 and 6 and in Figures 11 and 12.

[0113] X-ray powder diffraction patterns were made using standard techniques. The generator was set at 45 kV and 40 mA. The diffractometer optics consist of a variable divergence gap, Soller slots of the incident beam, a receiving slot, a graphite monochromator and a scintillation counter using Bragg-Brentano para-focusing geometry. Distances d were calculated from the parameters of the crystal lattice, a = 13.58 and c = 14.76 A for Example 22, and a = 13.56 and c = 14.75 A for Example

22A. The crystal lattice parameters were determined by scanning the sample with a LaB6 instrument mixed in as an internal standard. The data range was 15-38.5 degrees two theta, using step size 0.01 and pulses for 5 seconds. The obtained diffractogram was processed by profile cleaning in a JADE computer program. The LaB6 network parameters were kept constant at 5.169 A to compensate for errors due to sample shifts. Table 5 shows the X-ray powder diffraction lines for Example 22 and Example 22A. The CHA crystal structure was preserved after aging with steam for 48 hours at 800 ° C.

Table 5

<td colspan="3">Example 22</td><td colspan="3">Example 22A</td>

<td>2-Theta</td><td>d (A)</td><td>AND(%)</td><td>2-Theta</td><td>d (A)</td><td>AND(%)</td>

<td> 9,63</td><td> 9,201</td><td> 100%</td><td> 9,62</td><td> 9,189</td><td> 100%</td>

<td> 13,02</td><td> 6,793</td><td> 37%</td><td> 13,04</td><td> 6,782</td><td> 36%</td>

<td> 14,15</td><td> 6,252</td><td> 8%</td><td> 14,17</td><td> 6,247</td><td> 7%</td>

<td> 16,21</td><td> 5,465</td><td> 28%</td><td> 16,23</td><td> 5,457</td><td> 26%</td>

<td> 18,01</td><td> 4,921</td><td> 32%</td><td> 18,03</td><td> 4,917</td><td> 30%</td>

<td> 19,28</td><td> 4,600</td><td> 3%</td><td> 19,30</td><td> 4,595</td><td> 3%</td>

<td> 20,85</td><td> 4,258</td><td> 89%</td><td> 20,88</td><td> 4,251</td><td> 82%</td>

<td colspan="3">Example 22</td><td colspan="3">Example 22A</td>

<td> 22,29</td><td> 3,985</td><td> 4%</td><td> 22,31</td><td> 3,981</td><td> 4%</td>

<td> 22,65</td><td> 3,922</td><td> 5%</td><td> 22,69</td><td> 3,916</td><td> 4%</td>

<td> 23,33</td><td> 3,809</td><td> 8%</td><td> 23,37</td><td> 3,804</td><td> 7%</td>

<td> 25,27</td><td> 3,521</td><td> 41%</td><td> 25,29</td><td> 3,519</td><td> 38%</td>

<td> 26,22</td><td> 3,397</td><td> 24%</td><td> 26,26</td><td> 3,391</td><td> 23%</td>

<td> 27,98</td><td> 3,186</td><td> 5%</td><td> 28,03</td><td> 3,181</td><td> 5%</td>

<td> 28,53</td><td> 3,126</td><td> 6%</td><td> 28,56</td><td> 3,123</td><td> 5%</td>

<td> 29,91</td><td> 2,985</td><td> 3%</td><td> 29,96</td><td> 2,980</td><td> 3%</td>

<td> 30,98</td><td> 2,885</td><td> 57%</td><td> 31,03</td><td> 2,880</td><td> 53%</td>

<td> 31,21</td><td> 2,864</td><td> 17%</td><td> 31,23</td><td> 2,862</td><td> 17%</td>

<td> 31,48</td><td> 2,840</td><td> 28%</td><td> 31,51</td><td> 2,837</td><td> 26%</td>

<td> 31,99</td><td> 2,795</td><td> 4%</td><td> 32,04</td><td> 2,792</td><td> 4%</td>

<td> 32,75</td><td> 2,733</td><td> 3%</td><td> 32,80</td><td> 2,728</td><td> 3%</td>

<td> 33,73</td><td> 2,655</td><td> 2%</td><td> 33,78</td><td> 2,651</td><td> 2%</td>

<td> 33,95</td><td> 2,639</td><td> 4%</td><td> 33,98</td><td> 2,637</td><td> 4%</td>

<td> 34,92</td><td> 2,568</td><td> 13%</td><td> 34,98</td><td> 2,563</td><td> 12%</td>

<td> 35,38</td><td> 2,535</td><td> 3%</td><td> 35,43</td><td> 2,531</td><td> 2%</td>

<td> 36,50</td><td> 2,460</td><td> 9%</td><td> 36,54</td><td> 2,457</td><td> 8%</td>

<td> 38,72</td><td> 2,324</td><td> 2%</td><td> 38,78</td><td> 2,320</td><td> 1%</td>

<td> 38,90</td><td> 2,313</td><td> 1%</td><td> 38,93</td><td> 2,312</td><td> 1%</td>

<td> 39,13</td><td> 2,300</td><td> 2%</td><td> 39,18</td><td> 2,297</td><td> 2%</td>

<td> 39,56</td><td> 2,276</td><td> 1%</td><td> 39,62</td><td> 2,273</td><td> 1%</td>

<td> 39,78</td><td> 2,264</td><td> 2%</td><td> 39,84</td><td> 2,261</td><td> 2%</td>

[0114] UV / VIS diffuse reflection spectra expressed by F (R) were acquired using an integrating reflection diffusion adapter and a BaSO4 coated reference inside a Cary 300 UV-Vis spectrometer. The UV / VIS of Examples 22 and 22A are shown in Figure 11.

[0115] Table 6 summarizes the data regarding ²⁹Si MAS NMR and calculated range of the Si / Al atomic ratio of Examples 22 and 22A. For comparison, data on CHA and CHA aged with 10% water vapor for 48 hours at 800 ° C are also included. These data indicate that a certain degree of de-gelling occurs after aging of both CHA and Cu / CHA samples. However, the Cu / CHA sample is de-glazed to a much lesser degree after aging. It was also observed that the Cu exchange process itself slightly changes the range of the Si / Al atomic ratio from 15 to 17.

[0116] Figure 12 shows spectra ²⁷Al (Nuclear Magnetic Resonance Imaging) from Examples 22 and 22A, as well as aged CHA and CHA samples. These spectra indicate that some Al tetrahedral forms are converted into penta- and octa-coordinated forms as a result of Cu exchange. The spectra clearly confirm that after aging, the Cu / CHA sample is de-glazed to a much lesser degree than the CHA sample.

Table 6

<td rowspan="2">A sample</td><td colspan="4">Intensity%</td><td rowspan="2">Si / Al</td>

<td>Si (0Al) - 114 PP^m</td><td>Si (0Al) - 111 PP^m</td><td>Si (1Al) - 105 PP^m</td><td>Si (1Al) - 101 PP^m</td>

<td>CHA</td><td> 2</td><td> 71</td><td> 16</td><td> 11</td><td> 15</td>

<td>CHAs aged</td><td> 0</td><td> 95</td><td> 1</td><td> 4</td><td> 82</td>

<td>Example 22</td><td> 2</td><td> 75</td><td> 19</td><td> 5</td><td> 17</td>

<td>Example 22A</td><td> 4</td><td> 85</td><td> 11</td><td> &lt;1</td><td> 34</td>

[0117] Exemplary forms of emission treatment systems are shown in Figures 10A, 10B and 10C. One embodiment of the emission treatment system according to the invention designated 11A is schematically shown in FIG. 10A. The exhaust gas containing gaseous pollutants (including unburned hydrocarbons, carbon monoxide and NOx) and solid particles are sent from the engine 19 to a place at the rear of the exhaust system, in which a reducing agent, i.e. ammonia or an ammonia precursor, is added to the exhaust gas stream. The reducer is injected as a mist through a nozzle (not shown) into the exhaust stream. The aqueous urea solution shown on line 25 can serve as an ammonia precursor that can be mixed with air on another line 26 in a mixing station 24. The valve 23 can be used to accurately dose the amount of aqueous urea solution that is converted into ammonia in the exhaust stream.

[0118] The exhaust stream with added ammonia is sent to SCR catalyst substrate 12 (also referred to herein as the "first substrate" herein) containing CuCHA in one or more forms. Passing through the first substrate 12, the NOx component in the exhaust stream is converted by selective NOx catalytic reduction using NH3 to N2 and H2O. In addition, the excess NH3 that exits the inlet zone can be converted by oxidation in the rear by an ammonia oxidation catalyst (not shown) also containing CuCHA to convert ammonia to N2 and H2O. The first substrate is usually a flow monolithic substrate.

[0119] An alternative embodiment of the emission treatment system, designated 11B, is shown in FIG. 10B, which includes a second substrate 27 sandwiched between the NH3 injector and the first substrate 12. In this embodiment, the second substrate is coated with an SCR catalyst composition that can be the same as the composition used to coat the first substrate 12 or another composition. The advantage of this embodiment is that the SCR catalyst compositions that are used to coat the substrate can be selected in such a way as to optimize the NOx conversion to the operating conditions characteristic at a given location along the exhaust system. For example, the second substrate may be coated with an SCR catalyst composition that is better suited to the higher temperatures that occur in the front segments of the exhaust system, while another SCR composition may be used to coat the first substrate (i.e., the inlet zone of the first substrate) which is better suited to the lower temperature of the exhaust gases that occur at the rear of the exhaust system.

[0120] In the embodiment shown in FIG. 10B, the second substrate 27 may be a honeycomb flow substrate, an open cell foam substrate or a honeycomb substrate with wall flow. In embodiments of this form in which the second substrate is a wall flow substrate or a high efficiency foam cell with open cells, the system can remove more than 80% of the solid particles, including soot and SOF fractions. SCR coated wall flow substrate and its suitability for reducing NOx and particulate matter are described, for example, in US Patent Application Serial No. 10/634 659 filed August 5, 2003.

[0121] In some applications, it may be advantageous to add an oxidation catalyst upstream of the ammonia / ammonia precursor injection site. For example, in the form shown in FIG. 10C an oxidation catalyst is supported on catalyst bed 34. The emission purification system 11C comprises a first substrate 12 and optionally includes a second substrate 27. In this form, the exhaust stream is first directed to the catalyst substrate 34, where at least some of the gaseous hydrocarbons, CO and solid particles are burned to harmless components. In addition, a significant proportion of the NOx from the exhaust gas component is converted to NO2. Higher shares of NO2 in the NOx component facilitate the reduction of NOx to N2 and H2O on the SCR catalyst (s) downstream. It should be noted that in the form shown in Fig. 10C, the first substrate 12 may be a catalyzed soot filter and the SCR catalyst may be supported on a catalyzed soot filter. In an alternative embodiment, the second substrate 27 containing the SCR catalyst may be located in front of the catalyst substrate 34.