Extruded honeycomb catalyst

Abstract

An extruded honeycomb catalyst for nitrogen oxide reduction according to the selective catalytic reduction (SCR) method in exhaust gases from motor vehicles includes an extruded active carrier in honeycomb form having a first SCR catalytically active component and with a plurality of channels through which the exhaust gas flows during operation, and a washcoat coating having a second SCR catalytically active component being applied to the extruded body, wherein the first SCR catalytically active component and the second SCR catalytically active component are each independently one of: (i) vanadium catalyst with vanadium as catalytically active component; (ii) mixed-oxide catalyst with one or more oxides, in particular those of transition metals or lanthanides as catalytically active component; and (iii) an Fe- or a Cu-zeolite catalyst.

Claims

1. A set of various different extruded honeycomb catalysts for nitrogen oxide reduction according to the selective catalytic reduction (SCR) method in exhaust gases from motor vehicles, each extruded honeycomb catalyst comprising an extruded catalyst carrier in honeycomb form comprising a first SCR catalytically active component and with a plurality of channels through which the exhaust gas flows during operation, and a washcoat coating comprising a second SCR catalytically active component, the washcoat coating being in the form of a layer applied to the extruded catalyst carrier, wherein the first SCR catalytically active component and the second SCR catalytically active component are each independently selected from the group consisting of: (i) vanadium catalyst with vanadium as catalytically active component; (ii) mixed-oxide catalyst with one or more oxides, in particular those of transition metals or lanthanides as catalytically active component; and (iii) a metal zeolite catalyst comprising a Cu-CHA catalyst; wherein all the honeycomb catalysts in the set have an identical carrier.

2. The set of extruded honeycomb catalysts according to claim 1, wherein the washcoat coating, at least in a frontal area of the carrierin relation to a direction of flow of the exhaust gas during operationis free from noble metals.

3. The set of extruded honeycomb catalysts according to claim 1, wherein the carrier has a rear areain relation to a direction of flow of the exhaust gas during operationon which there is a noble metal coating to prevent ammonia slip.

4. The set of extruded honeycomb catalysts according to claim 3, wherein the washcoat coating extends over the entire length of the carrier and also covers the noble metal coating in the rear area of the carrier.

5. The set of extruded honeycomb catalysts according to claim 1, wherein the washcoat coating and the carrier have a BET surface area in the range of about 40-80 m.sup.2/g.

6. The set of extruded honeycomb catalysts according to claim 1, wherein the layer thickness of the washcoat coating lies in the range of 30 to 100 ?m.

7. The set of extruded honeycomb catalysts according to claim 1, wherein the honeycomb form has webs and the web width is 150 to 220 ?m.

8. The set of extruded honeycomb catalysts according to claim 1, wherein the extruded catalyst carrier is a mixed oxide catalyst and the washcoat coating is a Cu-CHA catalyst.

9. The set of extruded honeycomb catalysts according to claim 1, wherein the extruded catalyst carrier is a mixed oxide catalyst and the washcoat coating is a vanadium catalyst.

10. The set of extruded honeycomb catalysts according to claim 1, wherein at least one of the extruded catalyst carrier and the washcoat coating is a Cu-CHA catalyst.

11. The set of extruded honeycomb catalysts according to claim 1, wherein the extruded catalyst carrier is a Cu-CHA catalyst.

12. The set of extruded honeycomb catalysts according to claim 1, wherein the extruded catalyst carrier is a Cu-CHA catalyst and the washcoat coating is a vanadium catalyst.

13. The set of extruded honeycomb catalysts according to claim 1, wherein the extruded catalyst carrier and the washcoat coating are formed from a Cu-CHA catalyst.

14. The set of extruded honeycomb catalysts according to claim 1, wherein the extruded catalyst carrier and the washcoat coating are formed from a vanadium catalyst.

15. The set of extruded honeycomb catalysts according to claim 1, wherein the extruded catalyst carrier and the washcoat coating are formed from the same mixed-oxide with one or more of cerium oxide, zirconium oxide, and tungsten oxide as catalytically active component.

16. The set of extruded honeycomb catalysts according to claim 1, wherein the carrier is a vanadium catalyst and the washcoat coating is a Cu-CHA catalyst.

17. An exhaust system for a vehicular lean burn internal combustion engine comprising a set of extruded honeycomb catalysts according to claim 1 disposed in a flow conduit thereof.

18. An exhaust system according to claim 17, comprising means for injecting a nitrogenous reductant or a precursor thereof into the exhaust gas upstream of the set of extruded honeycomb catalysts.

19. A lean burn internal combustion engine comprising an exhaust system according to claim 17 comprising a catalyst for generating NH.sub.3 in situ in exhaust gas upstream of the set of extruded honeycomb catalysts and control means for changing an exhaust gas composition to a composition which promotes in situ NH.sub.3 on the catalyst for generating NH.sub.3 in situ.

20. A lean burn internal combustion engine according to claim 19, wherein the catalyst for generating NH.sub.3 in situ in exhaust gas upstream of the extruded honeycomb catalyst is a diesel oxidation catalyst or a NOx absorber catalyst.

21. A vehicle comprising an exhaust system according to claim 17.

22. The set of extruded honeycomb catalysts according to claim 1, wherein the extruded catalyst carrier comprises a neutral component.

23. The set of extruded honeycomb catalysts according to claim 22, wherein the neutral component is selected from the group consisting of a clay, aluminum oxide, and kaolin.

24. Method for producing honeycomb catalysts according to claim 1, wherein identically carriers are provided and coated with different washcoats.

25. The set of extruded honeycomb catalysts according to claim 1, wherein the vanadium catalyst contains as main components vanadium oxide, titanium oxide, and tungsten oxide.

26. The set of extruded honeycomb catalysts according to claim 1, wherein the metal zeolite catalyst contains a Cu-CHA catalyst in a proportion by volume of 10 to 70%.

27. The set of extruded honeycomb catalysts according to claim 1, wherein the extruded catalyst carrier further comprises at least one of a binder, a filler and a glass fiber.

Description

(1) In order that the present invention may be more fully understood, the following Examples are provided by way of illustration only and with reference to the accompanying drawings, wherein:

(2) FIG. 1 is a graph showing the NO.sub.x conversion activity at various temperatures for an extruded honeycomb catalyst according to the present invention comprising an extruded active carrier comprising a V.sub.2O.sub.5/WO.sub.3/TiO.sub.2 or Fe-ZSM-5 (MFI) zeolite first SCR catalyst washcoated with a WO.sub.3/CeO.sub.2ZrO.sub.2 second SCR catalyst compared with the second SCR catalyst coated on an inert cordierite honeycomb and the extruded active carriers without the second SCR catalyst coating;

(3) FIG. 2 is a graph showing the NO.sub.x conversion activity at various temperatures for an extruded honeycomb catalyst according to the present invention comprising an extruded active carrier comprising a Fe-ZSM-5 (MFI) zeolite first SCR catalyst washcoated with a Cu-SAPO-34 (CHA) second SCR catalyst compared with the second SCR catalyst coated on an inert cordierite honeycomb and the extruded active carrier without the second SCR catalyst coating;

(4) FIG. 3 is a graph showing the NO.sub.x conversion activity at various temperatures for an extruded honeycomb catalyst according to the present invention comprising an extruded active carrier comprising a Fe-Beta zeolite first SCR catalyst washcoated with a Cu-SSZ-13 (CHA) second SCR catalyst at two different washcoat loadings compared with the same loadings of the second SCR catalyst coaxed on an inert cordierite honeycomb and the extruded active carrier without the second SCR catalyst coating; and

(5) FIG. 4 is a graph showing the NO.sub.x conversion activity at various temperatures for an extruded honeycomb catalyst according to the present invention comprising an extruded active carrier comprising a V.sub.2O.sub.5/WO.sub.3/TiO.sub.2 first SCR catalyst washcoated with a Cu-SSZ-13 (CHA) second SCR catalyst at two different washcoat loadings compared with the same loadings of the second SCR catalyst coated on an inert cordierite honeycomb and the extruded active carrier without the second SCR catalyst coating.

EXAMPLES

Example 1

Preparation of Extruded Active Carrier in Honeycomb Form Comprising First SCR Catalyst

Example 1A

Extruded Active Carrier Containing Fe-Beta Zeolite

(6) Powdered commercially available Beta zeolite in hydrogen form is mixed with iron oxide (Fe.sub.2O.sub.3), glass fibres, Kaolin, powdered synthetic boehmite and the plasticisers polyethylene oxide (2.25 wt. %) and oleic acid (1.62 wt. %) (both based on 100% of the total inorganic solids content) and is processed in an aqueous solution with a pH-value of 5-6 into a shapeable and flowable slip. When the mixture is well plasticised, cellulose is added at 2.25 wt % based on 100% of the total inorganic solids content. The quantitative proportions of the starting materials are selected in such a way that the active material of the finished solid catalyst body contains 70.34% by weight of zeolite, iron and iron compounds; 2.76% by weight of the Kaolin; 15.94% by weight of ?-Al.sub.2O.sub.3; and 4.84% by weight of glass fibers. The shapeable mixture is extruded into a flow-through honeycomb catalyst body, i.e. with continuous channels and with a circular cross-section exhibiting a cell density of 400 cpsi (cells per square inch). Subsequently, the catalyst body is freeze dried for 1 hour at 2 mbar according to the method described in WO 2009/080155 (the entire contents of which is incorporated herein by reference) and calcined at a temperature of 580? C. to form a solid catalyst body. It is found that by using the method described that at least some of the iron introduced into the mixture becomes ion-exchanged with the zeolite.

Example 1B

Extruded Active Carrier Containing V2O5/WO3/TiO2

(7) Powdered commercially available tungsten-containing TiO.sub.2 at 10 wt. % tungsten is mixed with glass fibres, Kaolin, a low alkaline clay filler and powdered synthetic boehmite Ammonium metavanadate: 1.88 wt. %; 2-Aminoethanol: 1.5 liters; Lactic acid 90%: 0.48 wt %; Ammonia 25%: 8.97 wt % and the plastieisers polyethylene oxide (0.86 wt. %) and oleic acid (0.14 wt. %) (all based on 100% of the total inorganic solids content) and is processed in an aqueous solution with a pH-value of 5-6 into a shapeable and flowable slip. When the mixture is well plasticised, cellulose is added at 0.86 wt % based on 100% of the total inorganic solids content. The quantitative proportions of the starting materials are selected in such a way that the active material of the finished solid catalyst body contains approximately 72 wt % V.sub.2O.sub.5/WO.sub.3/TiO.sub.2; silica 1.20 wt %; Kaolin 2.85 wt %; clay 2.85 wt. %; and glass fibres 6.93 wt. %. The shapeable mixture is extruded into a flow-through honeycomb catalyst body, i.e. with continuous channels and with a circular cross-section exhibiting a cell density of 400 epsi (ceils per square inch). Subsequently, the catalyst body is freeze dried for 1 hour at 2 mbar according to the method described in WO 2009/080155 (the entire contents of which is incorporated herein by reference) and calcined at a temperature of 580? C. to form a solid catalyst body.

Example 1C

Extruded Active Carrier Containing Fe-ZSM-5 (MFI) Zeolite

(8) An ion-exchanged, synthetic ZSM-5 zeolite, the active material of which contains 5% by weight of iron, is selected as zeolite. The powdered ZSM-5 zeolite is mixed with glass fibers and powdered synthetic boehmite and is processed in an acetous aqueous solution with a pH-value of 3.5 into a shapeable and flowable slip by admixture of cellulose, and oleic acid and polyethylene glycol plasticizers. The quantitative proportions of the starting materials are selected in such a way that the active material of the finished solid catalyst body contains 75% by weight of zeolite containing the iron and iron compounds; 11.8% by weight of ?-Al.sub.2O.sub.3 and 8% by weight of glass fibers. The shapeable mixture is extruded into a honeycomb catalyst body with continuous channels and with a round cross-section exhibiting a cell density of 400 cpsi (cells per square inch). Subsequently, the catalyst body is dried at a temperature of 90? C. and calcined to form a solid catalyst body at a temperature of 600? C.

Example 2

Preparation of Washcoat Compositions Comprising Second SCR Catalyst

Method of Making Fresh 3 wt % Cu/Zeolites (Examples 2A and 2B)

(9) Commercially available SAPO-34 (CHA) (Example 2A) and SSZ-13 (CHA) (Example 2B) were NH.sub.4.sup.? ion exchanged in a solution of NH.sub.4NO.sub.2, then filtered. The resulting materials were added to an aqueous solution of Cu(NO.sub.2).sub.2 with stirring. The slurry was filtered, then washed and dried. The procedure can be repeated to achieve a desired metal loading. The final product was calcined.

Example 2C

Method of Making WOx/CeO2ZrO2

(10) A catalyst comprising 15 wt % tungsten supported on a ceria-zireonia mixed oxide comprising 50:50 weight % of ceria and zirconia was prepared by an incipient wetness impregnation method comprising dissolving sufficient ammonium metatungstate to give the desired 15 wt % W loadings in deionised H.sub.2O. The total volume of solution was equivalent to the pore volume of the support sample (incipient wetness technique). The solution was added to the mixed oxide support material and the resultant mixture was dried overnight at 105? C. and then calcined at 700? C. for 3 hours.

Example 3

Preparation of Extruded Honeycomb Catalysts

(11) Extruded active carriers of Example 1 were coated with a washcoat comprising the second SCR catalyst of Example 2 using the method disclosed in WO 99/47260, i.e. comprising the steps of (a) locating a containment means on top of a extruded active carrier support, (b) dosing a pre-determined quantity of a liquid component into said containment means, either in the order (a) then (b) or (b) then (a), and (c) by applying pressure or vacuum, drawing said liquid component into at least a portion of the extruded active carrier support, and retaining substantially all of said quantity within the extruded active carrier support. The coated extruded active carriers were then dried in air at 100? C. for 1 hour and calcined at 500? C. for 2 hours.

(12) The following combinations of extruded active carrier and washcoat were prepared.

(13) TABLE-US-00001 TABLE 1 Extruded Catalyst Washcoat Extruded Honeycomb Carrier Example Example Washcoat Catalyst Example No. Component Component Loading (g/in.sup.3) 3A 1B 2C 3.1 3B 1C 2C 3.1 3C 1C 2A 1.8 3D1 1A 2B 1.5 3D2 1A 2B 0.5 3E1 1B 2B 0.5 3E2 1B 2B 1.5

Example 5

Synthetic Catalytic Activity Tests

(14) A 2.54 cm?14 cm core was cut from each of the extruded honeycomb catalysts of Example 3 and the catalysts were tested at steady state at the following temperature points; 180? C., 215? C., 250? C., 300? C., 400? C. and 500? C. in a synthetic catalytic activity test laboratory apparatus using the following synthetic gas mixture: O.sub.2 9.3%; H.sub.2O 7.0%; NO.sub.x 100 ppm (NO only); NH.sub.3 100 ppm; Balance N.sub.2 (Swept Volume: 60.000 liters/hr).

(15) The results including comparative data are shown in FIGS. 1 to 4.

(16) FIG. 1 shows the results for Examples 3A and 3B compared with an identical washcoat composition (i.e. Example 2C) coated on an inert cordierite honeycomb carrier at 400 cpsi at 3.4 g/in.sup.3 loading; and the extruded catalyst carriers of Examples 1B and 1C per se. As can be seen from the results, Examples 3A and 3B show increased NO.sub.x conversion performance across the full temperature range.

(17) FIG. 2 shows the results for Example 3C compared with an identical washcoat composition (i.e. Example 2 A) coated on an inert cordierite honeycomb carrier at 400 cpsi at 1.8 g/in.sup.3 loading; and the extruded catalyst carrier of Example 1C per se. As can be seen from the results, there is a positive effect in the 200-500? C. temperature range tested.

(18) FIG. 3 shows the results for Examples 3D1 and 3D2 compared with identical washcoat compositions (i.e. Example 2B) coated on an inert cordierite honeycomb carrier at 400 cpsi at 1.5 g/in.sup.3 and 0.5 g/in.sup.3 loadings; and the extruded catalyst carrier of Example 1A per se. As can be seen from the results, Examples 3D1 and 3D2 show increased NO.sub.x conversion performance at <300? C. and >400? C.,

(19) FIG. 4 shows the results for Examples 3E1 and 3E2 compared with identical washcoat compositions (i.e. Example 2B) coated on an inert cordierite honeycomb carrier at 400 cpsi at 1.5 g/in.sup.3 and 0.5 g/in.sup.3 loadings; and the extruded catalyst carrier of Example 1B per se. As can be seen from the results, Examples 3E1 and 3E2 show increased NO.sub.x conversion performance at >400? C.

(20) For the avoidance of any doubt the entire contents of all documents cited herein are incorporated herein by reference in their entirety.