SCR Zeolite Catalysts for Reduced N2O Formation

Abstract

The present invention discloses a crystalline aluminosilicate small-pore zeolite having a maximum ring size of eight tetrahedral atoms, wherein the zeolite comprises copper, wherein the Cu:Al atomic ratio is between 0.12 and 0.55; and a metal M1, which is calcium, magnesium, or strontium, wherein the M1:Cu atomic ratio is between 0.05 and 0.95; and a metal M2, wherein M2 is selected from magnesium, calcium, barium, strontium, yttrium, titanium, zirconium, niobium, iron, zinc, silver, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and mixtures thereof, and wherein M1 and M2 are different from one another, and wherein the M2:Cu atomic ratio is between 0.05 and 0.80; and wherein the sum of the atomic ratios of copper, metal M1 and metal M2 to aluminum, (Cu+M1+M2):Al, is between 0.20 and 0.80; and wherein the zeolite comprises at least 2.5 wt.-% of copper, calculated as CuO and based on the total weight of the zeolite. Catalyst substrate monoliths comprising the crystalline aluminosilicate zeolite are also disclosed. These catalyst substrate monoliths can be used in a process for the removal of nitrogen oxides from combustion exhaust gases, and they can be part of emissions treatment systems.

Claims

1. A crystalline aluminosilicate small-pore zeolite having a maximum ring size of eight tetrahedral atoms, wherein the zeolite comprises copper, wherein the Cu:Al atomic ratio is between 0.12 and 0.55; an a metal M1, wherein M1 is calcium, magnesium or strontium, and wherein the M1:Cu atomic ratio is between 0.10 and 0.95; and a metal M2, wherein M2 is selected from magnesium, calcium, barium, strontium, yttrium, titanium, zirconium, niobium, iron, zinc, silver, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and mixtures thereof, and wherein the M2:Cu atomic ratio is between 0.05 and 0.80; and wherein M1 and M2 are different from one another, and wherein the sum of the atomic ratios of copper, metal M1 and metal M2 to aluminum, (Cu+M1+M2):Al, is between 0.20 and 0.80; and wherein the zeolite comprises at least 2.5 wt.-% of copper, calculated as CuO and based on the total weight of the zeolite.

2. The crystalline aluminosilicate small-pore zeolite having a maximum ring size of eight tetrahedral atoms according to claim 1, wherein the zeolite is selected from ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, BIK, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, ESV, ETL, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON, and mixtures and intergrowths thereof.

3. The crystalline aluminosilicate small-pore zeolite having a maximum ring size of eight tetrahedral atoms according to claim 1, wherein the zeolite is selected from AEI, CHA, AFX, and LEV.

4. The crystalline aluminosilicate small-pore zeolite according to claim 1, wherein the zeolite has a SAR value of 5 to 50.

5. The crystalline aluminosilicate small-pore zeolite according to claim 1, wherein M1 is calcium or magnesium, and M2 is selected from iron, cerium, zirconium, yttrium, samarium, strontium, lanthanum, or barium.

6. A process for the removal of NOx from automotive combustion exhaust gases, wherein a crystalline aluminosilicate zeolite according to claim 1 is used as the SCR catalytically active composition for the conversion of NOx.

7. A catalysed substrate monolith comprising an SCR catalytically active composition for the conversion of NOx for use in treating automotive combustion exhaust gases, wherein said SCR catalytically active composition for the conversion of NO.sub.x is a crystalline aluminosilicate zeolite according to claim 1.

8. The catalysed substrate monolith according to claim 7, wherein the crystalline aluminosilicate zeolite is present in the form of a washcoat on a carrier substrate.

9. The catalysed substrate monolith according to claim 8, wherein the carrier substrate is a honeycomb flow-through substrate, a honeycomb wall-flow filter, a corrugated substrate, a wound or packed fiber filter, an open cell foam, or a sintered metal filter.

10. The catalysed substrate monolith according to claim 7, wherein the catalysed substrate monolith is an extruded catalysed substrate monolith.

11. The catalysed substrate monolith according to claim 9, wherein the monolith is a flow-through monolith coated with a bottom layer comprising an oxidation catalyst and a top layer comprising the crystalline aluminosilicate zeolite.

12. An emissions treatment system for the removal of NOx emissions from exhaust gases of internal combustion engines, and optionally also for the removal of particulate matter, the system comprising, in the following order, from upstream to downstream: a) means for injecting ammonia or an ammonia precursor solution into the exhaust gas stream, b) a catalysed substrate monolith comprising an SCR-catalytically active composition for the conversion of NOx in automotive combustion exhaust gases, wherein said SCR catalytically active compositions for the conversion of NOx is a crystalline aluminosilicate zeolite according to claim 1, and wherein the substrate monolith is selected from honeycomb flow-through substrates, honeycomb wall-flow filters, corrugated substrates, wound or packed fiber filters, open cell foams, sintered metal filters, and extruded catalysed substrate monoliths.

13. The emissions treatment system according to claim 12, wherein said emissions treatment system is arranged in a close-coupled position.

14. The emissions treatment system according to claim 12, wherein said emissions treatment system is arranged in an underfloor position.

15. A method for the removal of NOx emissions from exhaust gases of internal combustion engines, and optionally also for the removal of particulate matter, the method comprising, in the following order, from upstream to downstream: a) injecting ammonia or an ammonia precursor solution into the exhaust gas stream, b) introducing the exhaust gas from step a) into a catalysed substrate monolith comprising an SCR-catalytically active composition for the conversion of NOx in automotive combustion exhaust gases, wherein said SCR catalytically active compositions for the conversion of NOx is a crystalline aluminosilicate zeolite according to claim 1, and wherein the substrate monolith is selected from honeycomb flow-through substrates, honeycomb wall-flow filters, corrugated substrates, wound or packed fiber filters, open cell foams, sintered metal filters, and extruded catalysed substrate monoliths.

16. The method according to claim 15, wherein the internal combustion engine is selected from gasoline, diesel, and hydrogen internal combustion engines (H.sub.2 ICE).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0152] FIG. 1 shows the NO.sub.x conversion at 175 C. and the N.sub.2O reduction at 400 C., each in percent, for CE1, CE4, Ex1, Ex3 and Ex5 in the aged state under NO only conditions.

[0153] FIG. 2 shows the NO.sub.x conversion at 175 C. and the N.sub.2O reduction at 400 C., each in percent, for CE1, Ex1, Ex3 and Ex5 in the aged state at 175 C. and 400 C. under 25% NO.sub.2 conditions.

[0154] FIG. 3 shows the NO.sub.x conversion at 175 C. and the N.sub.2O reduction at 400 C., each in percent, for CE6, CE7, Ex5, Ex6, Ex12, Ex14 and Ex15 in the aged state at 175 C. and 400 C. under 25% NO.sub.2 conditions.

[0155] FIG. 4 shows the NO.sub.x conversion at 175 C. and the N.sub.2O reduction at 400 C., each in percent, for CE8, CE9, CE10, Ex3, Ex4, Ex7, Ex8, Ex9, Ex10 and Ex16 in the aged state at 175 C. and 400 C. under 25% NO.sub.2 conditions.

EMBODIMENTS

Comparative Example 1 (CE1): CuCHA

[0156] 11.5 g of copper (II) acetylacetonate (24.4% by weight Cu, ex Aldrich) was coarsely mixed with 96.5 g of CHA (SAR 13.4) in a sealable plastic bottle of 250 mL capacity. Next 10 g Y-stabilised ZrO.sub.2 beads, (5 mm diameter), were added. The bottle was sealed and locked into a paint shaker (Olbrich Model RM 500, 0.55 KW) and homogenised by vibration for 5 minutes. The bottle was then unlocked from the paint shaker and the mixture passed through a coarse sieve to remove the beads. Finally the mixed powders were transferred to a calcination vessel and heated in static air to 600 C. (at a ramp rate of 5 C./min) and for a period of 2 hours.

[0157] The CHA thus obtained had a Cu:Al molar ratio of 0.21 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Comparative Example 2 (CE2): CuCHA

[0158] 20.4 g of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O crystals were dissolved under stirring in 40 g of de-ionised water. The solution thus produced was added dropwise to 93.0 g of CHA (SAR 13.4) with constant stirring over 15 minutes. The powder obtained was further dried in air at 80 C. for 4 h following by calcination for 2 hours at 600 C. in air.

[0159] The CHA thus obtained had a Cu:Al molar ratio of 0.43 and a Cu content of 7.0 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Comparative Example 3 (CE3): CuCHA

[0160] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 12.5 g of copper (II) acetylacetonate and 96.2 g of CHA (SAR 13.4).

[0161] The CHA thus obtained had a Cu:Al molar ratio of 0.23 and a Cu content of 3.8 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Comparative Example 4 (CE4): CuCaCHA

[0162] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 11.5 g of copper (II) acetylacetonate, 11.3 g of Ca (II) acetylacetonate hydrate and 94.0 g of CHA (SAR 13.4).

[0163] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Cu:Ca molar ratio of 1.0, a (Cu+Ca):Al molar ratio of 0.42 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Comparative Example 5 (CE5): CuCaCHA

[0164] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 21.3 g of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O, 3.1 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O, and 95.7 g of CHA (SAR 13.4).

[0165] The CHA thus obtained had a Cu:Al molar ratio of 0.43, a Ca:Cu molar ratio of 0.15, a (Cu+Ca):Al molar ratio of 0.49 and a Cu content of 7.0 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Comparative Example 6 (CE 6): CuCaCHA

[0166] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 7.6 g of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O, 4.2 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O and 96.5 g of CHA (SAR 23.8).

[0167] The CHA thus obtained had a Cu:Al molar ratio of 0.25, a Ca:Al molar ratio of 0.14, and a Cu content of 2.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Comparative Example 7 (CE 7): CuCaCHA

[0168] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 7.6 g of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O, 6.5 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O and 96.5 g of CHA (SAR 17.5).

[0169] The CHA thus obtained had a Cu:Al molar ratio of 0.18, a Ca:Al molar ratio of 0.16, and a Cu content of 2.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Comparative Example 8 (CE 8): CuFeKCHA

[0170] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 9.1 g of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O, 2.6 g of Fe(NO.sub.3).sub.3.Math.9H.sub.2O, 0.6 g of KNO.sub.3 and 96.2 g of CHA (SAR 13.4).

[0171] The CHA thus obtained had a Cu:Al molar ratio of 0.18, a Fe:Al molar ratio of 0.03, a (Cu+Fe):K molar ratio of 7, and a Cu content of 3.0 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Comparative Example 9 (CE 9): CuFeKCHA

[0172] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 10.6 g of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O, 1.8 g of Fe(NO.sub.3).sub.3.Math.9H.sub.2O, 0.7 g of KNO.sub.3 and 95.8 g of CHA (SAR 13.4).

[0173] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Fe:Al molar ratio of 0.02, a (Cu+Fe):K molar ratio of 7, and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Comparative Example 10 (CE 10): CuFeNaCHA

[0174] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 9.1 g of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O, 2.6 g of Fe(NO.sub.3).sub.3.Math.9H.sub.2O, 0.5 g of NaNO.sub.3 and 95.8 g of CHA (SAR 13.4).

[0175] The CHA thus obtained had a Cu:Al molar ratio of 0.18, a Fe:Al molar ratio of 0.03, a (Cu+Fe):Na molar ratio of 7, and a Cu content of 3.0 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 1 (Ex1): CuCaBaCHA

[0176] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 11.5 g of copper (II) acetylacetonate, 5.6 g of Ca (II) acetylacetonate, 7.8 g of Ba (II) acetylacetonate, and 93.6 g of CHA (SAR 13.4).

[0177] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.50, a Ba:Cu molar ratio of 0.50, a (Cu+Ca+Ba):Al molar ratio of 0.42 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 2 (Ex2): CuCaBaCHA

[0178] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 11.5 g of copper (II) acetylacetonate, 3.4 g of Ca (II) acetylacetonate, 4.7 g of Ba (II) acetylacetonate, and 93.7 g of CHA (SAR 13.4).

[0179] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.30, a Ba:Cu molar ratio of 0.30, a (Cu+Ca+Ba):Al molar ratio of 0.34 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 3 (Ex3): CuCaFeCHA

[0180] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 11.5 g of copper (II) acetylacetonate, 5.6 g of Ca (II) acetylacetonate, 7.8 g of Fe (III) acetylacetonate, and 95.3 g of CHA (SAR 13.4).

[0181] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.50, a Fe:Cu molar ratio of 0.50, a (Cu+Ca+Fe):Al molar ratio of 0.42 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 4 (Ex4): CuCaFeCHA

[0182] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 11.5 g of copper (II) acetylacetonate, 3.4 g of Ca (II) acetylacetonate, 4.6 g of Fe (III) acetylacetonate, and 94.7 g of CHA (SAR 13.4).

[0183] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.30, a Fe:Cu molar ratio of 0.30, a (Cu+Ca+Fe):Al molar ratio of 0.34 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 5 (Ex5): CuCaSmCHA

[0184] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 11.5 g of copper (II) acetylacetonate, 5.6 g of Ca (II) acetylacetonate, 10.2 g of Sm (III) acetylacetonate, and 94.8 g of CHA (SAR 13.4).

[0185] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.50, a Sm:Cu molar ratio of 0.50, a (Cu+Ca+Sm):Al molar ratio of 0.42 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 6 (Ex6): CuCaSmCHA

[0186] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 11.5 g of copper (II) acetylacetonate, 3.4 g of Ca (II) acetylacetonate, 6.1 g of Sm (III) acetylacetonate, and 93.4 g of CHA (SAR 13.4).

[0187] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.30, a Sm:Cu molar ratio of 0.30, a (Cu+Ca+Sm):Al molar ratio of 0.34 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 7 (Ex7): CuCaFeCHA

[0188] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 21.3 g of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O, 5.2 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O, 8.9 g of Fe(NO.sub.3).sub.3.Math.9H.sub.2O, and 93.5 g of CHA (SAR 13.4).

[0189] The CHA thus obtained had a Cu:Al molar ratio of 0.43, a Ca:Cu molar ratio of 0.25, a Fe:Cu molar ratio of 0.25, a (Cu+Ca+Fe):Al molar ratio of 0.65 and a Cu content of 7.0 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 8 (Ex8): CuCaFeCHA

[0190] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 21.3 g of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O, 3.1 g of Ca(NO).sub.2.Math.4H.sub.2O, 5.3 g of Fe(NO.sub.3).sub.3.Math.9H.sub.2O, and 94.7 g of CHA (SAR 13.4).

[0191] The CHA thus obtained had a Cu:Al molar ratio of 0.43, a Ca:Cu molar ratio of 0.15, a Fe:Cu molar ratio of 0.15, a (Cu+Ca+Fe):Al molar ratio of 0.56 and a Cu content of 7.0 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 9 (Ex9): CuCaFeCHA

[0192] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 12.5 g of copper (II) acetylacetonate, 6.1 g of Ca (II) acetylacetonate, 8.4 g of iron (III) acetylacetonate, and 91.0 g of CHA (SAR 13.4).

[0193] The CHA thus obtained had a Cu:Al molar ratio of 0.23, a Ca:Cu molar ratio of 0.50, a Fe:Cu molar ratio of 0.50, a (Cu+Ca+Fe):Al molar ratio of 0.46 and a Cu content of 3.8 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 10 (Ex10): CuCaFeCHA

[0194] This material was prepared following the method described in Comparative Example 1, with the exception that the mixture comprised 12.5 g of copper (II) acetylacetonate, 8.6 g of Ca (II) acetylacetonate, 5.1 g of iron (III) acetylacetonate, and 93.2 g of CHA (SAR 13.4).

[0195] The CHA thus obtained had a Cu:Al molar ratio of 0.23, a Ca:Cu molar ratio of 0.70, a Fe:Cu molar ratio of 0.30, a (Cu+Ca+Fe):Al molar ratio of 0.46 and a Cu content of 3.8 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 11 (Ex11): CuSrCaCHA

[0196] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 10.6 g of Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 5.2 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O, 4.6 g of Sr(NO.sub.3).sub.2, and 93.0 g of CHA (SAR 13.4).

[0197] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.5, a Sr:Cu molar ratio of 0.5, a (Cu+Ca+Sr):Al molar ratio of 0.42 and a Cu content of 3.5 wt. %, calculated as CuO and based on the total weight of the zeolite.

Example 12 (Ex12): CuCaCeCHA

[0198] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 10.6 g of Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 7.3 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O, 5.7 g of Ce(NO.sub.3).sub.3.Math.6H.sub.2O, and 92.5 g of CHA (SAR 13.4).

[0199] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.7, a Ce:Cu molar ratio of 0.3, a (Cu+Ca+Ce):Al molar ratio of 0.42 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 13 (Ex13): CuCaZrCHA

[0200] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 10.6 g of Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 7.3 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O, 3.3 g of ZrO(NO.sub.3).sub.2, and 92.5 g of CHA (SAR 13.4).

[0201] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.7, a Zr:Cu molar ratio of 0.3, a (Cu+Zr+Ce):Al molar ratio of 0.42 and a Cu content of 3.5 wt. %, calculated as CuO and based on the total weight of the zeolite.

Example 14 (Ex14): CuCaYCHA

[0202] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 10.6 g of Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 7.3 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O, 5.1 g of Y(NO.sub.3).sub.3.Math.6H.sub.2O, and 92.5 g of CHA (SAR 13.4).

[0203] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.7, a Y:Cu molar ratio of 0.3, a (Cu+Ca+Y):Al molar ratio of 0.42 and a Cu content of 3.5 wt. %, calculated as CuO and based on the total weight of the zeolite.

Example 15 (Ex15): CuCaLaCHA

[0204] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 10.6 g of Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 7.3 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O, 5.7 g of La(NO.sub.3).sub.3.Math.6H.sub.2O, and 92.6 g of CHA (SAR 13.4).

[0205] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Ca:Cu molar ratio of 0.7, a La:Cu molar ratio of 0.3, a (Cu+Ca+La):Al molar ratio of 0.42 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 16 (Ex16): CuMgFeCHA

[0206] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 10.6 g of Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 7.9 g of Mg(NO.sub.3).sub.2.Math.6H.sub.2O, 5.3 g of Fe(NO.sub.3).sub.3.Math.9H.sub.2O, and 92.5 g of CHA (SAR 13.4).

[0207] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Mg:Cu molar ratio of 0.7, a Fe:Cu molar ratio of 0.3, a (Cu+Mg+Fe):Al molar ratio of 0.42 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Example 17 (Ex17): CuMgCaCHA

[0208] This material was prepared following the method described in Comparative Example 2, with the exception that the mixture comprised 10.6 g of Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 5.6 g of Mg(NO.sub.3).sub.2.Math.6H.sub.2O, 5.2 g of Ca(NO.sub.3).sub.2.Math.4H.sub.2O, and 94.3 g of CHA (SAR 13.4).

[0209] The CHA thus obtained had a Cu:Al molar ratio of 0.21, a Mg:Cu molar ratio of 0.5, a Ca:Cu molar ratio of 0.5, a (Cu+Mg+Ca):Al molar ratio of 0.42 and a Cu content of 3.5 wt.-%, calculated as CuO and based on the total weight of the zeolite.

Measurement of NOx Conversion and N.SUB.2.O Reduction

[0210] The Comparative Examples and Examples according to the present invention, as listed above, were tested for their reaction behavior in NO.sub.x conversion and N.sub.2O reduction. The Examples according to the present invention were compared with zeolites comprising copper only, or only copper and calcium as metal M1, but no metal M2. These comparative tests illustrate the low temperature performance and durability benefits of the present invention for SCR application. The measurements were performed using a conventional plug flow model. In these measurements gas streams, simulating lean burn exhaust gas from the engine, were passed over and through meshed particles of test samples under conditions of varying temperature and the effectiveness of the sample in NOx reduction was determined by means of on-line FTIR (Fourier Transform Infra-Red) spectrometer. Two different testing conditions were carried out with NO only and NO.sub.2/NO.sub.x=25% to simulate the close-coupled and underfloor SCR catalyst position, respectively.

[0211] Table 1 below details the full experimental parameters employed in the generation of the data included herein.

TABLE-US-00001 TABLE 1 Model Gas testing conditions Component/ Concentration/ Concentration/ Parameter Setting (NO only) Setting (25% NO.sub.2) NH.sub.3 750 ppm 750 ppm NO 500 ppm 375 ppm NO.sub.2 125 ppm H.sub.2O 4% 4% O.sub.2 5% 5% Temperature Ramp 600 to 100 C. @ 2 C./min Sample mass 180 mg Particle size of sample 300-500 m GHSV 250,000 h.sup.1

TABLE-US-00002 TABLE 2 NO.sub.x conversion rates and N.sub.2O reduction after hydrothermal aging at 650 C. for 100 hours of Comparative Examples 1 to 5 and Examples 1 to 17. 650 C., 100 h, hydrothermally aged NO only 25% NO.sub.2 NOx % N.sub.2O % NOx % N.sub.2O % Name 175 C. 400 C. 175 C. 400 C. CE 1 25.91 1.32 57.71 3.39 CE 2 61.00 2.30 74.73 3.73 CE 3 31.58 1.38 61.49 3.48 CE 4 48.15 1.32 CE 5 62.79 2.39 3.18 CE 6 34.59 1.63 56.38 2.19 CE 7 35.38 1.10 58.14 1.64 CE 8 27.25 1.28 57.46 2.81 CE 9 34.24 1.50 60.94 3.16 CE 10 26.09 1.44 68.31 3.06 Ex 1 44.60 0.54 63.23 1.40 Ex 2 44.95 0.85 65.49 2.11 Ex 3 52.17 0.87 71.12 2.06 Ex 4 46.79 1.10 68.54 2.46 Ex 5 48.29 0.64 69.04 1.59 Ex 6 44.88 0.86 68.17 2.04 Ex 7 60.19 1.84 72.75 2.61 Ex 8 66.11 1.85 77.08 2.87 Ex 9 58.24 0.87 73.69 1.94 Ex 10 57.54 0.68 72.75 1.61 Ex11 47.99 0.81 67.77 1.68 Ex12 53.34 0.84 73.09 1.44 Ex13 50.76 0.95 67.67 1.65 Ex14 52.95 0.82 74.30 1.24 Ex15 51.71 0.64 68.76 1.22 Ex16 50.18 0.78 68.75 1.65 Ex17 49.84 0.77 68.31 1.40

[0212] The data above show that calcium alone works as a good promoter for the stabilization of copper. However, the N.sub.2O selectivity in percent is still quite high for zeolites that are promoted with copper and calcium only (CE1 to CE7). By introducing a second element such as iron, cerium, zirconium, yttrium, or lanthanum (Ex3, Ex12, Ex13, Ex14, Ex15), the N.sub.2O selectivity in percent can be considerably lowered. Besides, additional benefit for NO.sub.x conversion in percent at 175 C. was also observed.

[0213] FIG. 3 shows the NO.sub.x conversion at 175 C. and the N.sub.2O reduction at 400 C., each in percent, for CE6, CE7, Ex5, Ex6, Ex12, Ex14 and Ex15 in the aged state at 175 C. and 400 C. under 25% NO.sub.2 conditions. CE6 and CE7 are promoted with copper and calcium, but no third promoter metal. Ex5, Ex6, Ex12, Ex 14 and Ex15 each additional comprise a third promoter metal, which is a rare earth metal. These five examples according to the present invention show a significantly better NO.sub.x conversion under both NO only and 25% NO.sub.2 conditions and a lower N.sub.2O selectivity at 400 C. under NO only conditions. The N.sub.2O selectivity of Ex5 at 400 C. under 25% NO.sub.2 conditions is in the same range as that of CE6, whereas Ex6, Ex12, Ex14 and Ex15 show a significantly lower N.sub.2O selectivity than both comparative examples.

[0214] FIG. 4 shows the NO.sub.x conversion at 175 C. and the N.sub.2O reduction at 400 C., each in percent, for CE8, CE9, CE10, Ex3, Ex4, Ex7, Ex8, Ex9, Ex10 and Ex16 in the aged state at 175 C. and 400 C. under 25% NO.sub.2 conditions. CE8 and CE9 are promoted with copper, iron and potassium, and CE10 is promoted with copper, iron and sodium. By contrast, the examples according to the present invention are all promoted with copper, an alkaline earth metal and iron, and they only differ in their SAR values and/or in their amounts of copper, iron and/or the alkaline earth metal. The alkaline earth metal in Ex3, Ex4 and Ex7 to Ex10 is calcium, and in Ex16, it is magnesium. All examples promoted with copper, iron and an alkaline earth metal calcium show significantly better NO.sub.x conversions both under NO only and under 25% NO.sub.2 conditions than the comparative examples, wherein the zeolite is promoted with copper, iron and an alkali metal which is potassium or sodium. The N.sub.2O selectivity of Ex7 and Ex8 is comparable with that of CE8, CE9 and CE10 under both NO only and 25 NO.sub.2 conditions, whereas it is significantly lower for the other examples according to the present invention.