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

2. The catalyst composition according to claim 1, wherein the first component is an admixture of the H-form of the aluminosilicate mordenite zeolite (MOR) and the H-form of the aluminosilicate chabazite zeolite (CHA) and the weight ratio of the H-form of the aluminosilicate mordenite zeolite (MOR) to the H-form of an aluminosilicate chabazite zeolite (CHA) is from 5:3 to 3:5.

3. The 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. The 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.

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

6. The catalyst composition according to claim 1, wherein the metal oxide support of the second component comprises tungsten oxide.

7. The catalyst composition according to claim 1, wherein the vanadium oxide of the second component comprises iron vanadate.

8. The catalyst composition according to claim 1, wherein the mixture comprises 0.5 to 5.0 weight percent vanadium calculated as V.sub.2O.sub.5, based on the total weight of the catalyst composition as a whole.

9. A catalytic washcoat comprising the catalyst composition according to claim 1, comprising one or more fillers, binders, processing aids, water and dopants.

10. A catalyst article comprising a substrate monolith coated with the 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. The catalyst article according to claim 10, further 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 mixture of a first component and a second component, wherein the first component is the H-form of an aluminosilicate chabazite zeolite (CHA); or an admixture of the H-form of an aluminosilicate mordenite zeolite (MOR) and the H-form of an aluminosilicate chabazite zeolite (CHA); and the second component is a vanadium oxide supported on a metal oxide support, which is titania, silica-stabilized titania or a mixture of titania and silica-stabilized titania, wherein the weight ratio of the first component to the second component is 10:90 to 25:75; (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.

12. A catalyst article according to claim 1 in the form of an extruded substrate.

13. The catalyst article according to claim 12, 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 mixture of a first component and a second component, wherein the first component is the H-form of an aluminosilicate chabazite zeolite (CHA); or an admixture of the H-form of an aluminosilicate mordenite zeolite (MOR) and the H-form of an aluminosilicate chabazite zeolite (CHA); and the second component is a vanadium oxide supported on a metal oxide support, which is titania, silica-stabilized titania or a mixture of titania and silica-stabilized titania, wherein the weight ratio of the first component to the second component is 10:90 to 25:75; (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.

14. 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 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 NH.sub.3 to at least one of N.sub.2 and NO.sub.2.

Description

EXAMPLES

Example 1: Preparation of Extruded Honeycomb Substrate

(1) An extruded honeycomb substrate catalyst according to WO 2014/027207 A1 was prepared by firstly mixing a powdered commercially available H-form of aluminosilicate CHA, a commercially available powdered H-form of aluminosilicate mordenite or a mixture of both the powdered H-form of aluminosilicate CHA and the powdered H-form of aluminosilicate 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. All zeolites were synthetic and selected from within the preferred SAR ranges. 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.

(2) The appropriate proportions of the zeolites, V.sub.2O.sub.5WO.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.

(3) TABLE-US-00001 TABLE 1 V.sub.2O.sub.5 Inorganic WO.sub.3/TiO.sub.2 auxiliaries FeMFI HCHA HMOR Example (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) 1 71.4 12.6 0.0 8.0 8.0 2 71.4 12.6 0.0 16.0 0.0 3 77.4 12.6 0.0 10.0 0.0 Comparative 71.4 12.6 16.0 0.0 0.0 1 Comparative 71.4 12.6 0.0 0.0 16.0 2

Example 2: Extruded Honeycomb Substrate Ageing

(4) 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

(5) 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 both 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 % NOx conversion data are presented in Tables 2 and 3 (the higher values the better).

(6) TABLE-US-00002 TABLE 2 % NOx conversion for Fresh Catalyst Substrate Samples Comparative Example 1 Example Example Comparative Example 1 (16 wt. % 2 3 Example 4 Temp (16 wt. % 50 HCHA: (16 wt. % (10 wt. % (16 wt. % ( C.) FeMFI) 50 HMOR) HCHA) HCHA) HMOR) 180 21.0 19.4 23.0 22.9 18.5 215 44.4 41.4 49.1 48.0 41.4 250 63.0 61.0 70.6 69.4 62.2 300 79.6 77.7 85.9 85.3 79.0 400 88.1 88.3 92.9 92.6 89.2 500 80.5 81.1 82.3 80.6 82.8

(7) TABLE-US-00003 TABLE 3 % NOx conversion for Aged Catalyst Substrate Samples Comparative Example 1 Example Example Comparative Example 1 16 wt. % 2 3 Example 4 Temp 16 wt. % 50 HCHA: 16 wt. % 10 wt. % 16 wt. % ( C.) FeMFI 50 HMOR HCHA HCHA HMOR 180 4.1 9.4 4.4 9.1 8.7 215 9.5 21.8 10.5 21.3 21.3 250 18.5 40.5 21.4 39.3 40.5 300 36.0 67.0 40.4 64.2 65.9 400 56.3 85.0 64.1 81.9 82.6 500 24.4 73.8 22.0 54.2 68.0

(8) The N.sub.2O ppm generated over the aged catalyst substrate samples at 500 C. is shown in Table 4 (the lower values the better).

(9) TABLE-US-00004 TABLE 4 ppm N.sub.2O Generated by Aged Catalyst Substrates at 500 C. Com- Com- parative Example 1 Example Example parative Example 1 16 wt. % 2 3 Example 4 16 wt. % 50 HCHA: 16 wt. % 10 wt. % 16 wt. % FeMFI 50 HMOR HCHA HCHA HMOR N.sub.2O 9.8 9.6 15.6 16.8 10.6 Generated (ppm)

(10) It can be seen from the data presented in Tables 2, 3 and 4 that the fresh NOx conversion activity for Example 1 is comparable to both Comparative Examples, whereas Examples 2 and 3 are better than both Comparative Examples. The aged NOx conversion activity for Example 1 is better than either Comparative Example, Example 3 is comparable to the activity of Comparative Example 2 and Example 2 is Comparative Example 1. The N.sub.2O slip data in Table 4 show that Example 1 has a lower N.sub.2O generation than Comparative Example 2 and a comparable N.sub.2O generation to Comparative Example 1. Both Examples 2 and 3 generate moderately more N.sub.2O than the Comparative Examples.

(11) Overall, these data show an order of preference of Example 1>>Example 3>Example 2.

(12) 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.

(13) For the avoidance of doubt, the entire contents of all documents acknowledged herein are incorporated herein by reference.