SELECTIVE CATALYTIC REDUCTION CATALYST

Abstract

A selective catalytic reduction catalyst composition for converting oxides of nitrogen (NO.sub.x) in an exhaust gas using a nitrogenous reductant comprises a mixture of a first component and a second component, wherein the first component is an admixture of the H-form of an aluminosilicate mordenite zeolite (MOR) and an iron-promoted aluminosilicate MFI zeolite; and the second component is a vanadium oxide supported on a metal oxide support, which is titania, silica-stabilized titania or a mixture of both titania and silica-stabilized titania, wherein the weight ratio of the first component to the second component is 10:90 to 25:75.

Claims

1. A selective catalytic reduction catalyst composition for converting oxides of nitrogen (NO.sub.x) in an exhaust gas using a nitrogenous reductant, which catalyst composition comprising a mixture of a first component and a second component, wherein the first component is an admixture of the H-form of an aluminosilicate mordenite zeolite (MOR) and an iron-promoted aluminosilicate MFI zeolite; and the second component is a vanadium oxide supported on a metal oxide support, which is titania, silica-stabilized titania or a mixture of both titania and silica-stabilized titania, wherein the weight ratio of the first component to the second component is 10:90 to 25:75.

2. A catalyst composition according to claim 1, wherein the weight ratio of the H-form of the aluminosilicate mordenite zeolite (MOR) to the iron-promoted aluminosilicate MFI zeolite is from 3:1 to 3:5, preferably 1:1 to 3:5.

3. A catalyst composition according to claim 1, wherein the weight ratio of the first component to the second component is 15:85 to 20:80.

4. A catalyst composition according to claim 1, comprising one or more binder component, wherein the weight ratio of the combined weight of the first and second components to the combined weight of the one or more binder component is from 80:20 to 95:5, preferably 90:10 to 85:15.

5. A catalyst composition according to claim 4, wherein the one or more binder component is a clay, alumina and/or glass fibers.

6. A catalyst composition according to claim 4, wherein the metal oxide support of the second component comprises tungsten oxide.

7. A catalyst composition according to claim 4, wherein the vanadium oxide of the second component comprises iron vanadate.

8. A catalyst composition according to claim 4, wherein the mixture comprises 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.

9. A catalytic washcoat comprising a catalyst composition according to claim 4, comprising one or more fillers, binders, processing aids, water and dopants.

10. A catalyst article comprising a substrate monolith coated with a catalytic washcoat according to claim 9, wherein the substrate is a metal flow-through substrate, a ceramic flow-through substrate, a wall-flow filter, a sintered metal filter or a partial filter.

11. A catalyst article according to claim 9 in the form of an extruded substrate, preferably a honeycomb monolith.

12. A catalyst article according to claim 10, comprising a second catalyst composition in the form of a washcoat for selectively reducing NO.sub.x using a nitrogenous reductant and/or for oxidizing NH.sub.3, which second catalyst composition is: (a) a catalyst mixture according to any of claims 1 to 9; (b) a transition metal promoted molecular sieve; (c) a platinum group metal supported on a metal oxide; or (d) a catalyst comprising vanadium oxide supported on titania.

13. A catalyst article according to claim 12, wherein the substrate comprises an ammonia slip catalyst (ASC) comprising a first layer of (c) for oxidizing ammonia and a second layer comprising the catalyst according to any of claims 1 to 8, wherein the first layer is disposed directly on the substrate and the second layer overlies the first layer.

14. An exhaust system for treating exhaust gas comprising a selective catalytic reduction (SCR) catalyst disposed upstream from an ammonia slip catalyst (ASC), wherein at least one of the SCR and the ASC catalyst comprises a catalyst according to claim 9.

15. An exhaust system according to claim 14, comprising an oxidation catalyst comprising a platinum group metal supported in a metal oxide coated on a substrate monolith and disposed upstream of the SCR catalyst composition.

16. An automotive vehicular lean burn internal combustion engine comprising an exhaust system according to claim 14.

17. An automotive vehicle comprising an engine according to claim 16.

18. A method for treating an exhaust gas, which optionally comprises a ratio of NO to NO.sub.2 from about 4:1 to about 1:3 by volume, which method comprising the steps of: (i) contacting an exhaust gas stream containing NO.sub.x and NH.sub.3 with a catalyst according to claim 9; 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 NH.sub.3 to at least one of N.sub.2 and NO.sub.2.

19. A method for treating an exhaust gas, which optionally comprises a ratio of NO to NO.sub.2 from about 4:1 to about 1:3 by volume, which method comprising the steps of: (i) contacting an exhaust gas stream containing NO.sub.x and NH.sub.3 with a catalyst according to claim 11; 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 NH.sub.3 to at least one of N.sub.2 and NO.sub.2.

Description

EXAMPLES

Example 1: Preparation of Extruded Honeycomb Substrate

[0041] An extruded honeycomb substrate catalyst according to WO 2014/027207 A1 was prepared by firstly mixing a powdered commercially available MFI aluminosilicate zeolite that has been ion-exchanged with >1 wt. % iron, a commercially available powdered H-form of mordenite or a mixture of both the powdered >1 wt. % Fe/MFI aluminosilicate zeolite and the powdered H-form of mordenite with 2 wt. % V.sub.2O.sub.5-10 wt. % WO.sub.3/TiO.sub.2 balance with inorganic auxiliaries to improve rheology for extrusion and increase mechanical strength of the extrudate. Suitable organic auxiliaries were added to facilitate mixing to form a homogeneous extrudable mass. The extrudable mass was extruded to form a 1-inch diameter70 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.

[0042] The appropriate proportions of the zeolites, V.sub.2O.sub.5-WO.sub.3/TiO.sub.2, inorganic auxiliaries were selected so thatfollowing removal of the organic auxiliaries by calcinationthe extruded substrates had the wt. % compositions set out in Table 1 below.

TABLE-US-00001 TABLE 1 V.sub.2O.sub.5- Inorganic WO.sub.3/TiO.sub.2 auxiliaries Fe-MFI H-MOR Example (wt. %) (wt. %) (wt. %) (wt. %) 1 71.4 12.6 10.0 6.0 2 71.4 12.6 8.0 8.0 3 71.4 12.6 4.0 12.0 Comparative 71.4 12.6 16.0 0.0 1 Comparative 71.4 12.6 0.0 16.0 2

Example 2: Extruded Honeycomb Substrate Ageing

[0043] The extruded catalyst honeycomb substrates resulting from Example 1 were thermally aged (no water added) in an accelerated ageing step either by heating them in an oven in air at above 600 C. for 2 hours (referred to herein as fresh) or at 650 C. for 100 hours (referred to herein as aged) to simulate the expected exposure of the honeycomb substrates to automotive vehicular exhaust gases over a vehicle end-of-life, according to European emission standard legislation.

Example 3: Catalyst Performance

[0044] The fresh and aged substrates were each exposed to a simulated diesel engine exhaust gas at a space velocity of about 120,000/hour. The simulated exhaust gas contained about 9.3 wt. % O.sub.2, about 7.0 wt. % H.sub.2O, about 300 ppm NO.sub.x (NO only) about 300 ppm NH.sub.3, and the balance N.sub.2. The activity of the fresh and aged catalyst substrates to convert NO.sub.x was determined at temperatures of 180, 215, 250, 300 and 400 C. The results for the % NO.sub.x conversion data are presented in Tables 2 and 3 (the higher values the better).

[0045] The N.sub.2O selectivity of the aged catalyst substrate samples at 500 C. is shown in Table 3 (the lower values the better). N.sub.2O selectivity is determined by the equation:

SN.sub.2O=2*(N.sub.2O-out minus N.sub.2O-in)/(NO.sub.x-in minus NO.sub.x-out)*100.

TABLE-US-00002 TABLE 2 % NOx conversion for Fresh Catalyst Substrate Samples % difference between Example 2 Compar- Compar- and Temp ative Exam- Exam- Exam- ative Comparative ( C.) Example 1 ple 1 ple 2 ple 3 Example 2 Example 2 180 22.9 22.2 19.0 17.1 18.5 0.5 215 47.0 48.0 42.0 39.0 41.4 0.6 250 67.7 69.2 62.7 60.3 62.2 0.5 300 83.6 84.8 79.6 78.5 79.0 0.6 400 91.5 93.0 89.4 89.4 89.2 0.2 500 82.0 87.7 83.3 83.2 82.8 0.5

TABLE-US-00003 TABLE 3 % NOx conversion for Aged Catalyst Substrate Samples % difference between Example 2 Compar- Compar- and Temp ative Exam- Exam- Exam- ative Comparative ( C.) Example 1 ple 1 ple 2 ple 3 Example 2 Example 2 180 4.1 9.1 9.2 N/A 8.7 0.5 215 9.5 21.6 22.5 22.2 21.3 1.2 250 18.5 40.4 42.0 41.8 40.5 1.5 300 36.0 65.8 67.6 67.7 65.9 1.7 400 56.3 80.5 82.5 82.8 82.6 0.1 500 24.4 58.6 63.3 66.3 68.0 4.7

TABLE-US-00004 TABLE 4 N.sub.2O Selectivity by Aged Catalyst Substrates at 500 C. Comparative Example Example Example Comparative Example 1 1 2 3 Example 2 N.sub.2O 26.8 13.0 10.4 selectivity

[0046] It can be seen from the data presented in Tables 2, 3 and 4 that the fresh NO.sub.x conversion activity for Examples 2 and 3 is similar to Comparative Example 2, whereas Example 1 is better than Comparative Example 2 and similar to Comparative Example 1. The aged NO.sub.x conversion activity of all Examples are better than Comparative Example 1 and are better than (Example 2, particularly at <400 C.) or similar to Comparative Example 2. The N.sub.2O selectivity data in Table 4 show that Example 2 has similar N.sub.2O selectivity than Comparative Example 2 and a better N.sub.2O selectivity than Comparative Example 1.

[0047] Overall, these data show an order of preference of Example 2>Example 1>Example 3.

[0048] The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

[0049] For the avoidance of doubt, the entire contents of all documents acknowledged herein are incorporated herein by reference.