Multi-function catalyst article for treating both CO and NOx in stationary emission source exhaust gas

Abstract

A multi-function catalyst article for treating both NO and carbon monoxide emissions in a flow of a combustion exhaust gas from a stationary emission source comprises a honeycomb monolith substrate comprising one or more channels which are open at both ends and extend along an axial length thereof and through which, in use, a combustion exhaust gas flows, which catalyst article comprising a catalyst composition comprising a combination of a first, vanadium-containing SCR catalyst component and a second component which is a compound of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof and optionally a third, crystalline molecular sieve component.

Claims

1. A multi-function catalyst article for treating both NO.sub.x and carbon monoxide emissions in a flow of a combustion exhaust gas from a stationary emission source, the article comprising a honeycomb monolith substrate comprising one or more channels which are open at both ends and extend along an axial length thereof and through which, in use, a combustion exhaust gas flows, which catalyst article comprising a catalyst composition comprising a combination of a first, vanadium-containing SCR catalyst component and a second component, wherein the second component is a mixed oxide comprising manganese, magnesium, aluminium and lanthanum (MnMgAlLaOx).

2. The multi-function catalyst article according to claim 1, which does not comprise any precious metals.

3. The multi-function catalyst article according to claim 1, wherein the catalyst composition is impregnated with palladium as an only precious metal present in the multi-function catalyst article.

4. The multi-function catalyst article according to claim 1, wherein the catalyst composition comprises palladium as an only precious metal present in the multi-function catalyst article which has been pre-fixed onto a refractory metal oxide support material.

5. The multi-function catalyst article according to claim 3, wherein the second component is a compound of a transition metal further comprising any one or more of copper, cobalt, molybdenum, nickel or cerium.

6. The multi-function catalyst article according to claim 1, wherein the catalyst comprises a third, crystalline molecular sieve component.

7. The multi-function catalyst article according to claim 6, wherein the third, crystalline molecular sieve component is ion-exchanged with a transition metal being iron, copper, nickel, cobalt or zinc or a combination of any two or more thereof.

8. The multi-function catalyst article according to claim 7, wherein all transition metals present in second component are different from the transition metal ion-exchanged in the third, crystalline molecular sieve component.

9. The multi-function catalyst article according to claim 1, wherein the catalyst composition does not comprise a crystalline molecular sieve.

10. An exhaust system for selectively catalysing the reduction of oxides of nitrogen (NO.sub.x) including nitrogen monoxide and carbon monoxide in an exhaust gas of a stationary source of combined NO.sub.x and CO emissions, which system comprising an injector for introducing a nitrogenous reductant into the exhaust gas located downstream from the oxidation catalyst; and a catalyst article according to claim 1 located downstream of the injector.

11. An exhaust system according to claim 10 comprising a heat recovery steam generator (HRSG).

12. A stationary source of NO.sub.x and carbon monoxide emissions, which is a power station, an industrial heater, a cogeneration power plant, a combined cycle power generation plant, a wood-fired boiler, a stationary diesel engine, a stationary natural gas-fired engine, a marine propulsion engine, a diesel locomotive engine, an industrial waste incinerator, a municipal waste incinerator, a chemical plant, a glass manufacturing plant, a steel manufacturing plant or a cement manufacturing plant comprising an exhaust system according to claim 10.

13. A method for treating an exhaust gas comprising NO.sub.x, which optionally comprises a ratio of NO to NO.sub.2 from about 4:1 to about 1:3 by volume, and carbon monoxide, which method comprising the steps of: (i) contacting an exhaust gas stream containing NO.sub.x and NH.sub.3 with a catalyst article according to claim 1; and (ii) converting at least a portion of the NO.sub.x to N.sub.2 and/or converting at least a portion of the CO to CO.sub.2.

14. The multi-function catalyst article according to claim 7, wherein one or more transition metal in the second component is the same as the transition metal ion-exchanged in the third, crystalline molecular sieve component, wherein the quantity of the metal present in the catalyst composition is in excess of the ion-exchange capacity of the third, crystalline molecular sieve component.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present disclosure will now be described further. In the following passages different aspects/embodiments of the disclosure are defined in more detail. Each aspect/embodiment so defined may be combined with any other aspect/embodiment or aspects/embodiments unless clearly indicated to the contrary. 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. It is intended that the features disclosed in relation to the product may be combined with those disclosed in relation to the method and vice versa.

(2) Furthermore, the term “comprising” as used herein can be exchanged for the definitions “consisting essentially of” or “consisting of”. The term “comprising” is intended to mean that the named elements are essential, but other elements may be added and still form a construct within the scope of the claim. The term “consisting essentially of” limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claimed invention. The term “consisting of” closes the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith.

(3) The invention provides a multi-function catalyst article for treating both NO.sub.x and carbon monoxide emissions in a flow of a combustion exhaust gas from a stationary emission source, the article comprising a honeycomb monolith substrate comprising one or more channels which are open at both ends and extend along an axial length thereof and through which, in use, a combustion exhaust gas flows, which catalyst article comprising a catalyst composition comprising a combination of a first, vanadium-containing SCR catalyst component and a second component which is a compound of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof and optionally a third, crystalline molecular sieve component.

(4) That is, the basic and novel characteristics of the invention consist essentially of a catalyst article comprising a catalyst composition which—aside from fillers, binders etc which substantially do not contribute to catalyst activity—is a combination of two catalytic components: a first, vanadium-containing SCR catalyst component and a second component which is a compound of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof.

(5) There are a number of ways in which the second component can be combined with the first component. In one method, the first component can be physically mixed or blended with particles comprising the second component. This physical mixture can be in the form of a washcoat for coating onto an inert substrate monolith; a paste for pressing into a perforated metal gauze for use in a metal plate-type honeycomb monolith substrate; or as an extrudeable mass for extruding into a honeycomb monolith substrate form.

(6) In a second method, the first component is washcoated onto an inert substrate monolith; or a paste comprising the first component is pressed into a perforated metal gauze for use in a metal plate-type honeycomb monolith substrate; or a composition comprising the first component is extruded into a honeycomb monolith substrate form; and then the second component is combined with the first component by impregnating the washcoat, paste or extrudate comprising the first component with an aqueous solution of a compound of the second component.

(7) Such methods are defined according to the third, fourth, sixth and seventh aspects of the present invention.

(8) Catalyst compositions for use in connection with the third aspect of the invention are defined according to the second aspect of the invention; and catalyst compositions for use in connection with the fifth aspect of the invention are defined according to the fourth aspect of the invention.

(9) Furthermore, the multi-function catalyst article can be precious metal free, i.e. it does not comprise any precious metals; or palladium as the sole precious metal can be combined with at least the first component either by impregnating the washcoat, paste or extrudate with palladium; or by including palladium which has been pre-fixed onto a refractory metal oxide support material in the washcoat, paste or extrudeable mass mixture itself.

(10) The above features are defined in various specific modes of the methods according to the invention, as follows:

(11) The method according to the third aspect can be further specified as including the step of impregnating the coated catalyst composition on the inert honeycomb monolith substrate with an aqueous salt of a palladium compound and drying and calcining the resulting impregnated coated honeycomb monolith substrate.

(12) The method according to the fourth aspect can be further specified as including the step of including palladium as an only precious metal present in the catalyst composition, which has been pre-fixed onto a refractory metal oxide support material; or by impregnating the coated catalyst composition on the inert honeycomb monolith substrate with an aqueous salt of a palladium compound and drying and calcining the impregnated coated inert honeycomb monolith substrate, wherein the aqueous salt of the palladium compound is present in a mixture with the aqueous salt of a compound of a transition metal selected from the group consisting of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof; or the step of impregnating channel walls of a calcined coated inert honeycomb monolith substrate with an aqueous salt of a palladium compound and drying and calcining the impregnated coated inert honeycomb monolith substrate is performed either before or after the step of impregnating channel walls of the calcined coated inert honeycomb monolith substrate with an aqueous salt of a compound of a transition metal selected from the group consisting of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof and drying and calcining the impregnated coated inert honeycomb monolith substrate.

(13) In the method according to the fourth aspect including the impregnation step, the inert honeycomb monolith substrate coated with the catalytic washcoat has an axial length L, wherein the step of impregnating channel walls with any one or more of (i) only the aqueous salt of a compound of a transition metal selected from the group consisting of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof; (ii) the mixture of aqueous salts of a compound of a transition metal selected from the group consisting of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof and the aqueous salt of a palladium compound; or (iii) only the aqueous salt of a palladium compound, can comprise impregnating less than the axial length L of the coated inert honeycomb monolith substrate, optionally ≤0.5 L.

(14) In methods wherein an inert honeycomb monolith substrate is coated with a paste, the inert honeycomb monolith substrate is preferably a metal plate-type substrate comprising layers of perforated metal gauze.

(15) The method of the sixth aspect of the invention can be further specified by the step of impregnating channel walls of the calcined extruded honeycomb monolith substrate with an aqueous salt of a palladium compound and drying and calcining the impregnated extruded honeycomb monolith substrate.

(16) The method according to the seventh aspect can be further specified as including the step of including palladium as an only precious metal present in the catalyst composition, which has been pre-fixed onto a refractory metal oxide support material; or by including the step of impregnating the honeycomb monolith substrate comprising the extruded catalyst composition with an aqueous salt of a palladium compound and drying and calcining the impregnated honeycomb monolith substrate, wherein the aqueous salt of the palladium compound is present in a mixture with the aqueous salt of a compound of a transition metal selected from the group consisting of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof; or the step of impregnating channel walls of the calcined honeycomb monolith substrate with an aqueous salt of a palladium compound and drying and calcining the impregnated calcined honeycomb monolith substrate is performed either before or after the step of impregnating channel walls of the calcined honeycomb monolith substrate with an aqueous salt of a compound of a transition metal selected from the group consisting of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof and drying and calcining the impregnated honeycomb monolith substrate.

(17) In the method according to the seventh aspect including the impregnation step, the honeycomb monolith substrate comprising the extruded catalyst composition has an axial length L, wherein the step of impregnating channel walls with any one or more of (i) only the aqueous salt of a compound of a transition metal selected from the group consisting of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof; (ii) the mixture of aqueous salts of a compound of a transition metal selected from the group consisting of a transition metal comprising copper, manganese, cobalt, molybdenum, nickel or cerium or a mixture of any two or more thereof and the aqueous salt of a palladium compound; or (iii) only the aqueous salt of a palladium compound can comprise impregnating less than the axial length L of the honeycomb monolith substrate, optionally ≤0.5 L.

(18) For some applications, the honeycomb flow-through monolith preferably has a high cell density, for example about 600 to 800 cells per square inch, and/or an average internal wall thickness of about 0.18-0.35 mm, preferably about 0.20-0.25 mm. For certain other applications, the honeycomb flow-through monolith preferably has a low cell density of about 150-600 cells per square inch, more preferably about 200-400 cells per square inch. Preferably, the honeycomb monoliths are porous.

(19) Aspects of the multi-function catalyst article according to the first aspect of the invention can be defined as follows:

(20) In one embodiment, the multi-function catalyst does not comprise any precious metals.

(21) In a preferred embodiment, the catalyst composition comprises palladium as an only precious metal present in the multi-function catalyst article. In one arrangement the catalyst composition is impregnated with the palladium. In another arrangement, the palladium is pre-fixed onto a refractory metal oxide support material and combined with at least the first component.

(22) In the embodiment comprising the palladium, the palladium loading can be about 0.5 to about 350 gft.sup.−3. A palladium loading of about 3 to about 20 gft.sup.−3 is preferred for use with stationary sources which are power plants, e.g. cogeneration plants including gas turbines. Palladium loadings at about 20<about 350 gft.sup.−3 are useful for Compressed Natural Gas (CNG) engine applications.

(23) Preferably, the second component comprises copper, manganese, cobalt, cerium or a mixture of any two or more thereof. In this regard, Applicant has found that including a ceria-zirconia mixed oxide (CeZrOx) in the washcoat, paste or extrudeable mass mixtures and then impregnating the resulting composition with copper and manganese has provided beneficial results. In a particular embodiment, the second component is a mixed oxide comprising manganese, magnesium, aluminium and lanthanum (MnMgAlLaOx), which is included in the mixture of the washcoat, paste or extrudeable mass.

(24) Methods of making the first, vanadium-containing SCR catalyst component are known. Preferably, the first, vanadium-containing SCR catalyst component comprises a vanadium oxide—often quoted as V.sub.2O.sub.5—supported on a metal oxide support, which is titania, silica-stabilized titania or a mixture of titania and silica-stabilized titania. Where present, the titania is preferably anatase because it has a higher surface area. The silica-titania mixed oxide, where present, may be characterised by a silica to titania balance. Preferably, the silica-titania mixed oxide contains less than 50 wt % silica, preferably from 5 to 25 wt % and more preferably from 7 to 15 wt % silica.

(25) Most preferably, the metal oxide support of the first, vanadium-containing SCR catalyst component comprises tungsten oxide as this improves the stability of the vanadium oxide and improves overall catalyst activity.

(26) The vanadium oxide of the first, vanadium-containing SCR catalyst component can be provided in the form of an iron vanadate.

(27) The vanadium present in the catalyst composition of the final product can comprise 0.5 to 5.0 weight percent vanadium calculated as V.sub.2O.sub.5, preferably 1.0 to 3.0 wt. %, based on the total weight of the catalyst composition as a whole.

(28) The multi-function catalyst according to the present invention extends to embodiments including the first and second components only, i.e. the catalyst composition does not comprise a crystalline molecular sieve. Examples of extruded vanadium-containing substrates are provided in WO 2011/092521, WO 2009/093071 and WO 2013/017873. However, in an alternative component, the catalyst composition comprises the third, crystalline molecular sieve component, which is optionally ion-exchanged with the transition metal iron, copper, nickel, cobalt or zinc or a combination of any two or more thereof. Details of catalyst compositions comprising the first and third components can be found in Applicant's WO 2014/027207.

(29) The third, crystalline molecular sieve can be a ferrosilicate molecular sieve (also known as an amorphous iron molecular sieve); or a non-zeolite molecular sieve (silicoaluminophophate). The crystalline molecular sieve can be promoted with a transition metal or it can be present as in the H.sup.+ form. The crystalline molecular sieve can also have the MFI, BEA or FER framework type or be any isotype thereof. However, in order to further distinguish Applicant's WO 2014/027207, any one or more of the features in this paragraph can be disclaimed from the definitions of any one or more of the first to tenth aspects according to the invention.

(30) Preferably, where present, the third, crystalline molecular sieve for use in the present invention is an aluminosilicate zeolite. A zeolite is a microporous aluminosilicate having any one of the framework structures listed in the Database of Zeolite Structures published by the International Zeolite Association (LZA). Preferred framework structures for use in the present invention include, but are not limited to those of the CHA, FAU, BEA, MFI, MOR types. Non-limiting examples of zeolites having these structures include chabazite, faujasite, zeolite Y, ultrastable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X, and ZSM-5. Zeolites can be categorised by pore size, e.g. a maximum number of tetrahedral atoms present in a zeolite's framework. As defined herein, a small pore zeolite, such as CHA, contains a maximum ring size of eight tetrahedral atoms, whereas a medium pore zeolite, e.g. MFI, contains a maximum ring size of ten tetrahedral atoms and a large pore zeolite, such as BEA, contains a maximum ring size of twelve tetrahedral atoms. Meso pore zeolites are also known, but they have a maximum ring size of greater than twelve tetrahedral atoms. Most preferred zeolite frameworks for the SCR catalyst compositions for use in layers of the present invention are the small pore zeolites, particularly those having the framework type AEI, AFX, CHA, DDR, ERI, ITE, LEV, LTA, STI or SFW, or which CHA or AEI are particularly preferred.

(31) Aluminosilicate zeolites can have a silica/alumina molar ratio (SAR) defined as SiO.sub.2/Al.sub.2O.sub.3) from at least about 5, preferably at least about 20, with useful ranges of from about 10 to 200. Most preferably, the aluminosilicate SAR range is 10 to 30, which provides a balance between activity, i.e. the ability to ion-exchange to anionic sites provided by alumina, and thermal durability provided by the silica content.

(32) It will be appreciated that the transition metals of the second component overlap with the transition metals disclosed for ion-exchange in the zeolites of the compositions disclosed in WO 2014/027207. Therefore, to distinguish the compositions disclosed in WO 2014/027207, either (i) all transition metals present in second component can different from the transition metal ion-exchanged in the third, crystalline molecular sieve component; or (ii) one or more transition metal in the second component is the same as the metal ion-exchanged in the third, crystalline molecular sieve component, and the quantity of the metal present in the catalyst composition is in excess of the ion-exchange capacity of the third, crystalline molecular sieve component. In this regard, the quantity of the metal present in the catalyst composition according to the first aspect of the invention can be in excess of the ion-exchange capacity of the third, crystalline molecular sieve component can be at least twice the ion-exchange capacity of the third, crystalline molecular sieve component, such as at least three time (×3), at least ×4, at least ×5, at least ×6, at least ×7, at least ×8, at least ×9 or at least ×10 that of the ion-exchange capacity of the third, crystalline molecular sieve component.

(33) Where present, a weight ratio of the first, vanadium-containing SCR catalyst component to the third, crystalline molecular sieve component in the catalyst composition can be 95:5 to 60:40.

(34) The multi-function catalyst according to the invention can take a number of forms. In one arrangement, the honeycomb monolith substrate is inert, e.g. it is made of a ceramic such as cordierite, and the channels are defined at least in part by surfaces of the honeycomb monolith substrate channel walls and wherein the catalyst composition is disposed on the channel walls of the honeycomb monolith substrate as a washcoat. Alternatively, the honeycomb monolith substrate is an inert metal plate-type substrate comprising layers of perforated metal gauze and the catalyst composition is pressed into the gauze as a paste-consistency.

(35) Alternatively, the catalyst composition is extruded as a honeycomb monolith substrate. In this case, the catalyst composition typically comprises one or more binder component, which is a clay, alumina and/or glass fibres.

(36) In the exhaust system according to the eighth aspect of the invention, the exhaust system according can comprise a heat recovery steam generator (HRSG).

(37) The nitrogenous reductant for use in the exhaust system according to the eighth aspect of the present invention can be ammonia per se, hydrazine or an ammonia precursor selected from the group consisting of urea ((NH.sub.2).sub.2CO), ammonium carbonate, ammonium carbamate, ammonium hydrogen carbonate and ammonium formate. Ammonia is most preferred.

(38) The stationary source according to the ninth aspect of the invention can be a cogeneration plant, preferably a stationary natural gas-fired engine, wherein the exhaust system comprises a heat recovery steam generator (HRSG).

(39) According to the method of the tenth aspect of the invention, the kNO.sub.x of the honeycomb substrate monolith or the plate-type substrate comprising the catalyst can be less than or equal to about 300 m/hr.

(40) Preferably, the kNOx of the honeycomb substrate monolith or the plate-type substrate comprising the catalyst is about 90<kNOx<about 300 m/h between about 300 and about 400° C.

(41) The catalyst for converting ammonia in exhaust gas also containing oxygen to nitrogen and water preferably converts about 70% NH.sub.3 at above 250° C., more preferably >about 80% NH.sub.3 at above about 300° C.

(42) The catalyst for converting ammonia in exhaust gas also containing oxygen to nitrogen and water preferably has an sNOx=NOx out divided by (NH.sub.3 in minus NH.sub.3 out)<about 20% below about 400° C., more preferably an sNOx<about 10% below about 350° C., wherein the sNOx is determined using the same conditions defined for determining kNO.sub.x hereinabove.

(43) The space velocity at which the exhaust gas contacts the catalyst for converting ammonia in exhaust gas also containing oxygen to nitrogen and water can be from 50,000 to 500,000 h.sup.−1, such as 100,000 to 400,000 h.sup.−1 or 150,000 h.sup.−1 to 350,000 h.sup.−1.

Definitions

(44) As defined herein “precious metals” include the platinum group metals, i.e. platinum, palladium, rhodium, ruthenium, osmium and iridium; and the metal elements silver and gold.

(45) SCR Catalyst NOx Activity can be defined by the kNO.sub.x of a catalyst. The term “k-value” is used to express the SCR catalyst activity. In order to determine the “k-value”, catalyst samples are tested in a laboratory reactor where the NO.sub.x conversion rate is measured under defined conditions, intended to match the actual flue gas conditions of the unit.

(46) To describe the catalyst deactivation trend versus time, the term “k.sub.t/k.sub.0” or relative catalyst activity is used. The value k.sub.t/k.sub.0 provides a measure of the relative activity remaining in the catalysts at the sampling time (e g—a k.sub.t/k.sub.0 value of 0.90 means that 90% of the original catalyst activity remains at the time of sampling). k.sub.t is the activity value at a given time after flue gas exposure, k.sub.0 is the activity of the fresh catalyst.

(47) The following calculations are used in the determination of NO.sub.x activity in the test reactor.

(48) NO.sub.x conversion equation:

(49) ${\eta }_{\mathrm{NOx}}=\frac{c_0^{\left(\mathrm{NOx}\right)}-c^{\left(\mathrm{NOx}\right)}}{c_0^{\left(\mathrm{NOx}\right)}}*100\%$
where:
η.sub.NOx is the NO.sub.x conversion through the catalyst sample—in %
c.sub.0(NO.sub.x) is the NO.sub.x concentration at the inlet of the test reactor—in ppmvd
c(NO.sub.x) is the NO.sub.x concentration at the outlet of the test reactor—in ppmvd
ppmvd is parts per million, volume based, dry gas
NO.sub.x activity constant equation:

(50) $k\left(\mathrm{NO}x\right)=-AV*\ln \left(1-\frac{{\eta }_{NOx}}{100\%}\right)$
where:
k(NO.sub.x) is the NO.sub.x activity constant for the catalyst sample—in m/h
AV is the area velocity through the catalyst sample—in m/h

(51) $AV=\frac{\mathrm{Exhaust}\mathrm{Gas}\mathrm{Flow}\mathrm{Rate}\left[m^3/h\right]}{\mathrm{Exposed}\mathrm{Outer}\mathrm{Catalyst}\mathrm{Surface}\mathrm{Area}\left[m^2\right]}$

(52) Oxidation Catalyst Light-Off is the measure of CO conversion through the oxidation catalyst vs temperature. The light-off performance is determined in a laboratory-scale reactor by flowing synthetic exhaust gas through a catalyst sample and measuring CO conversion while ramping the gas temperature from low to high. CO conversion at a given temperature is calculated per the following equation:

(53) $\mathrm{CO}\mathrm{Conversion}=\frac{{\left[\mathrm{CO}\right]}_{\mathrm{in}}-{\left[\mathrm{CO}\right]}_{\mathrm{out}}}{{\left[\mathrm{CO}\right]}_{\mathrm{in}}}\times 100\%$
where [CO].sub.in is the CO concentration at the sample inlet and [CO].sub.out is the CO concentration at the sample outlet.

(54) The present disclosure will now be further described with reference to the following non-limiting Examples.

EXAMPLES

Example 1: Preparation of Base Extruded Honeycomb Substrate

(55) An extruded honeycomb substrate catalyst according to WO 2014/027207 A1 was prepared by firstly mixing a MFI aluminosilicate zeolite that has been ion-exchanged with >1 wt. % iron with 2 wt. % V.sub.2O.sub.5—WO.sub.3/TiO.sub.2 balance components with inorganic auxiliaries including glass fibres to improve rheology for extrusion and increase mechanical strength of the extrudate. Suitable organic auxiliaries such as extrusion lubricants and plasticisers can be added to facilitate mixing to form an homogeneous extrudable mass. The organic auxiliaries may include cellulose, water soluble resins such as polyethylene glycol and are burnt out from the final substrate during calcination. The appropriate proportions of the zeolite, V.sub.2O.sub.5—WO.sub.3/TiO.sub.2, inorganic auxiliaries were selected so that—following removal of the organic auxiliaries—the substrate comprised 16 wt. % of the Fe/zeolite component, 72 wt. % of the V.sub.2O.sub.5— WO.sub.3/TiO.sub.2 component, 12 wt. % of the inorganic auxiliaries. The extrudable mass was extruded to form a 1-inch diameter×70 mm long cylindrical honeycomb body in the flow-through configuration (i.e. cells open at both ends) having a cell density of 400 cells per square inch and having honeycomb cell wall thicknesses of 11 thousandths of an inch (mil). The extruded honeycomb substrates so formed were then dried and calcined to form the finished product.

Example 2: Impregnation of Substrate Samples

(56) Following an analysis of the water uptake of the porous extruded honeycomb substrate prepared according to Example 1, the whole of an extruded honeycomb substrate prepared according to Example 1 was dipped in an aqueous solution of copper acetate at a concentration calculated from the water uptake step to achieve a copper loading of 1.2 wt %. This sample was labelled “Example 2A”.

(57) Separately, a second extruded honeycomb substrate prepared according to Example 1 was dipped in an aqueous solution of copper acetate and manganese acetate at concentrations calculated from the water uptake step to achieve a copper loading of 4.4 wt % and a manganese loading of 4.4 wt %. This sample was labelled “Example 2B”.

(58) Separately, a third extruded honeycomb substrate prepared according to Example 1 was dipped in an aqueous solution of copper acetate, manganese acetate and CeZrO.sub.4 at concentrations calculated from the water uptake step to achieve a copper loading of 1.2 wt % and a manganese loading of 0.1 wt % and a Ce—Zr loading of 10 wt %. This sample was labelled “Example 2C”.

(59) The resulting impregnated parts were dried and calcined. The resulting products are defined as being “fresh” catalysts, i.e. freshly prepared, un-aged.

Example 3: Sample Testing

(60) The samples prepared according to Example 2 were each loaded into a synthetic catalytic activity test (SCAT) laboratory apparatus to test each sample's ability to reduce NOx and to oxidise carbon monoxide. The test gas mixture used was 50 ppm CO, 24 ppm NO, 6 ppm NO.sub.2, 30 pm NH.sub.3, 15% O.sub.2, 8% water, 3% CO.sub.2, and balanced by N.sub.2 at a flow rate such that the Gas Hourly Space Velocity (GHSV) was 75,000 hr.sup.−1. CO, NOx, and NH.sub.3 conversions were measured with the reactor held at steady state temperature points. The results are set out in the following Tables. A catalyst prepared according to Example 1 was tested as a control.

(61) TABLE-US-00001 Example 1 SCR Inlet T Conversion (%) (° C.) NOx CO 200 46.3 0 250 51.8 0 300 57.8 0 350 59.7 0 400 57.3 0 450 48.0 0

(62) TABLE-US-00002 Example 2A SCR + 1.2% CuOx Inlet T Conversion (%) (° C.) NOx CO 200 37.1 1.1 250 50.7 2.2 300 58.9 5.7 350 59.0 13.4 400 49.7 26.5 450 22.6 40.4

(63) TABLE-US-00003 Example 2B SCR + 4.4% CuOx + 4.4% MnOx Inlet T Conversion (%) (° C.) NOx CO 250 48.3 7.1 300 54.2 14.1 350 55.1 26.7 400 47.9 40.4

(64) TABLE-US-00004 Example 2C SCR + 1.2% CuOx + 0.1% MnOx + 10% Ce—Zr Inlet T Conversion (%) (° C.) NOx CO 200 44.9 0.5 250 52.2 0.7 300 59.4 3.1 350 61.6 6.4 400 59.0 13.2 450 52.3 23.3

Example 4: Preparation of Extruded Honeycomb Substrate Containing MnOx

(65) Using the recipe of Example 1 as a base, three further samples were prepared each having different proportions of the base 72 wt. % of the V.sub.2O.sub.5—WO.sub.3/TiO.sub.2 component removed and exchanged for commercially available manganese oxide. In a first sample (Example 4A) 10 wt % of the V.sub.2O.sub.5—WO.sub.3/TiO.sub.2 component was removed and replaced with the MnOx component. In a second sample (Example 4B), 15 wt % was replaced by MnOx; and in a third sample (Example 4C) 20 wt % was replaced by MnOx. It will be appreciated that by removing some of the V.sub.2O.sub.5—WO.sub.3/TiO.sub.2 component, the weight ratio of the first, vanadium-containing SCR catalyst component to the third, crystalline molecular sieve component in the catalyst composition decreased. The resulting samples were dried and calcined.

Example 5: Sample Testing

(66) The samples prepared according to Example 4 were tested in the same way as Example 3 and the results are set out in the following Tables. The results of the control (Example 1) are those in the Table reported in Example 3 hereinabove.

(67) TABLE-US-00005 Example 4A SCR + 10% MnOx Inlet T Conversion (%) (° C.) NOx CO 200 57.3 1.2 250 55.3 0.7 300 63.6 1.7 350 66.5 4.6 400 66.4 7.7

(68) TABLE-US-00006 Example 4B SCR + 15% MnOx Inlet T Conversion (%) (° C.) NOx CO 200 47.0 0.5 250 61.7 1.4 300 68.2 3.6 350 67.9 7.8 400 66.2 12.7

(69) TABLE-US-00007 Example 4C SCR + 20% MnOx Inlet T Conversion (%) (° C.) NOx CO 200 56.7 2.4 250 61.4 6.4 300 67.2 13.8 350 68.4 21.6 400 62.6 26.9

Example 6: Preparation of Extruded Honeycomb Substrate Containing Impregnated Palladium

(70) Three samples prepared according to Example 1 were impregnated with aqueous palladium nitrate similarly to the method described in Example 2 in such a way that palladium loadings of 5 g/ft.sup.3, 10 g/ft.sup.3 and 20 g/ft.sup.3 were obtained. The resulting samples were dried and calcined.

Example 7: Sample Testing

(71) The samples prepared according to Example 5 were tested in the same way as Example 3, except in that a space velocity of 120,000 hr.sup.−1 was used. The results are set out in the following Tables, but are presented as kNOx and kCO instead of absolute NOx % conversion and absolute CO % conversion reported in Examples 3 and 5. The results of the control are those of the base catalyst of Example 1.

(72) Example 8 with a flow rate such that the Gas Hourly Space Velocity (GHSV) was 120,000 hr.sup.−1.

(73) TABLE-US-00008 Example 1 SCR Inlet T kNOx kCO (° C.) (m/hr) (m/hr) 200 22.3 0.5 250 38.7 0.3 300 56.0 0.4 350 64.7 0.8 400 66.5 0.9 450 57.6 0.5

(74) TABLE-US-00009 Example 7A SCR + 5 g/ft.sup.3 Pd Inlet T kNOx kCO (° C.) (m/hr) (m/hr) 200 17.8 0.9 250 38.3 9.5 300 53.4 64.5 350 60.5 106.2 400 58.3 125.4 450 46.0 134.0

(75) TABLE-US-00010 Example 7B SCR + 10 g/ft.sup.3 Pd Inlet T kNOx kCO (° C.) (m/hr) (m/hr) 200 18.7 1.4 250 35.1 13.4 300 48.3 63.5 350 56.0 99.4 400 50.0 117.7 450 36.8 128.4

(76) TABLE-US-00011 Example 7C SCR + 20 g/ft.sup.3 Pd Inlet T kNOx kCO (° C.) (m/hr) (m/hr) 200 15.6 1.3 250 35.7 15.2 300 54.0 74.8 350 63.2 109.6 400 55.5 128.1 450 39.4 139.6

(77) For the avoidance of any doubt, the entire contents of all documents cited herein are incorporated into the description by reference.