Selective catalytic reduction catalyst and a process for preparing a selective catalytic reduction catalyst

Abstract

The present invention relates to a process for preparing a catalyst for the selective catalytic reduction of nitrogen oxide comprising, among other steps, preparing a second aqueous mixture comprising water and an iron salt; and disposing the second mixture on the substrate obtained according to (ii), comprising a coating comprising a zeolitic material comprising copper, over y % of the substrate axial length from the inlet end to the outlet end of the substrate, wherein y is in the range of from 10 to x, obtaining a substrate comprising, in a first zone, the coating comprising a zeolitic material comprising copper and over y % of the substrate axial length an iron salt; and, if x>y, in a second zone extending from y % to x % of the substrate axial length from the inlet end to the outlet end, the coating comprising a zeolitic material comprising copper.

Claims

1. A process for preparing a catalyst for a selective catalytic reduction of nitrogen oxide comprising a coating comprising iron and a zeolitic material comprising copper, the process comprising: (i) preparing a first aqueous mixture comprising water and a zeolitic material comprising copper; (ii) disposing the first aqueous mixture obtained according to (i) to a substrate, wherein the substrate comprises an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end and a plurality of passages defined by internal walls of the substrate extending therethrough, and over x % of the substrate axial length from the inlet end to the outlet end of the substrate, wherein x ranges from 80 to 100; calcining the substrate having the first aqueous mixture disposed thereon, obtaining a substrate comprising a coating comprising a zeolitic material comprising copper; (iii) preparing a second aqueous mixture comprising only water and an iron salt; (iv) disposing only the second aqueous mixture obtained according to (iii) on the substrate obtained according to (ii) over y % of the substrate axial length from the inlet end to the outlet end of the substrate, wherein y ranges from 10 to x, obtaining a substrate comprising, in a first zone, the coating comprising a zeolitic material comprising copper and over y of the substrate axial length the iron salt; and, if x>y, in a second zone extending from y % to x of the substrate axial length from the inlet end to the outlet end, the coating comprising the zeolitic material comprising copper, wherein the iron salt is one or more of iron (III) nitrate, iron (II) acetate, ammonium iron (III) citrate, iron (II) sulfate, and iron (II) oxalate, wherein (iv) is performed by dipping the substrate obtained according to (ii) into the second aqueous mixture prepared in (iii); and (v) calcining the substrate obtained according to (iv).

2. The process of claim 1, wherein the zeolitic material comprising copper in the first aqueous mixture prepared according to (i) has a framework type selected from the group consisting of CHA, AEI, RTH, LEV, DDR, KFI, ERI, AFX, a mixture of two or more thereof, and a mixed type of two or more thereof.

3. The process of claim 1, wherein the zeolitic material comprising copper in the aqueous mixture prepared according to (i) has a framework type selected from the group consisting of FER, BEA, MFI, FAU, MOR, a mixture of two or more thereof, and a mixed type of two or more thereof.

4. The process of claim 1, wherein the first aqueous mixture prepared according to (i) comprises at most 1000 ppm of iron, calculated as elemental iron.

5. The process of claim 1, wherein calcining the substrate having the first aqueous mixture disposed thereon according to (ii) is performed in a gas atmosphere having a temperature ranging from 400 C. to 800 C.

6. The process of claim 1, wherein the substrate comprising the coating comprising a zeolitic material comprising copper obtained according to (ii) has a water adsorption, expressed in weight of H.sub.2O relative to the volume of the coating, ranging from 1 g/in.sup.3 to 5 g/in.sup.3.

7. The process of claim 1, wherein the second aqueous mixture prepared according to (iii) comprises the iron salt in an amount, calculated as Fe.sub.2C>3, which ranges from 4 weight-% to 40 weight-%, based on the weight of the second aqueous mixture prepared according to (iii).

8. The process of claim 1, wherein y ranges from 20 to x.

9. The process of claim 1, wherein (iv) is performed by dipping the substrate obtained according to (ii) into the second aqueous mixture prepared in (iii) for 5-120 seconds.

10. A catalyst for a selective catalytic reduction of nitrogen oxide prepared by the process of claim 1.

11. The catalyst of claim 10, wherein the zeolitic material comprising copper in the coating has a framework type selected from the group consisting of CHA, AEI, RTH, LEV, DDR, KR, ERI, AFX, a mixture of two or more thereof, and a mixed type of two or more thereof; or wherein the zeolitic material comprising copper has a framework type selected from the group consisting of FER, BEA, MF, FAU, MOR, a mixture of two or more thereof, and a mixed type of two or more thereof.

12. The catalyst of claim 10, wherein the amount of copper, calculated as CuO, comprised in the zeolitic material in the coating ranges from 1.5 weight-% to 15 weight-%, based on the weight of the zeolitic material comprised in the coating.

13. The catalyst of claim 10, wherein the coating comprised in the first zone comprises the iron salt in an amount ranging from 0.5 weight-% to 3.5 weight-%, based on the weight of the zeolitic material.

14. The catalyst of claim 10, wherein x>y.

15. An exhaust gas treatment system for the treatment of exhaust gas exiting from an internal combustion engine, the system comprising: a catalyst for a selective catalytic reduction of nitrogen oxide according to claim 10 and one or more of a diesel oxidation catalyst, an ammonia oxidation catalyst, a selective catalytic reduction catalyst, a catalyzed soot filter, and a SCR/AMOx catalyst.

16. An exhaust gas treatment catalyst comprising: an ammonia oxidation catalyst disposed over z % of the substrate axial length, from the outlet end to the inlet end of the substrate, wherein z ranges from 5 to 100; and the catalyst for a selective catalytic reduction of nitrogen oxide prepared by the process of claim 1.

17. The catalyst of claim 16, wherein z ranges from 8 to 50.

18. The catalyst of claim 16, wherein the ammonia oxidation catalyst comprises a platinum group metal component, wherein the platinum group metal component is one or more of platinum, palladium, rhodium, osmium, and iridium.

Description

EXAMPLES

Reference Example 1 Measurement of the BET Specific Surface Area

(1) The BET specific surface area was determined according to DIN 66131 or DIN-ISO 9277 using liquid nitrogen.

Reference Example 2 Determination of the Volume-Based Particle Size Distributions

(2) The particle size distributions were determined by a static light scattering method using Sympatec HELOS (3200) & QUIXEL equipment, wherein the optical concentration of the sample was in the range of from 6 to 10%.

Reference Example 3 Cu-Chabazite Prepared According to Usual Liquid Phase Ion-Exchange (LPIE) Process

(3) The zeolitic materials having the framework structure type CHA comprising Cu and used in some of the examples herein were prepared essentially as disclosed in U.S. Pat. No. 8,293,199 B2. Particular reference is made to Inventive Example 2 of U.S. Pat. No. 8,293,199 B2, column 15, lines 26 to 52.

Reference Example 4 General Coating Method

(4) In order to coat a flow-through substrate with a coating, the flow-through substrate was immersed vertically in a portion of a given slurry for a specific length of the substrate which was equal to the targeted length of the coating to be applied. In this manner, the washcoat contacted the walls of the substrate. The sample was left in the slurry for a specific period of time, usually for 1-10 seconds. The substrate was then removed from the slurry, and excess slurry was removed from the substrate by allowing it to drain from the substrate, then by blowing with compressed air (against the direction of slurry penetration).

Reference Example 5 Determination of the Water Adsorption of a Cu-CHA Catalyst

(5) 1) A catalyst, which has been previously dried and calcined, comprising a core sample (for example with 1 inch3 inches core) coated with a catalytic coating (Cu-CHA)in the present case, the catalyst of Comparative Example 1is weighted under ambient conditions (room temperature with no additional pre-drying or pre-calcining before weighting). The weight A is noted. 2) Then, the catalyst is immerged completely in water for 30 seconds and slightly moved back and forth to release gas bubbles. 3) The catalyst is removed from water and drained. 4) The catalyst is again weighted under the same ambient conditions used for 1). The weight B is noted. The water adsorption of the catalyst is obtained by calculating the difference between the weight B and the weight A.

Comparative Example 1 Preparation of a Selective Catalytic Reduction Catalyst (Cu-SCR)

(6) An aqueous solution of zirconyl acetate was mixed with 1692 g of Cu-CHA zeolite with a Cu content, calculated as CuO, of 5.1 weight-% based on the weight of Cu-CHA (a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of about 18:1, a BET specific surface area of 5 m.sup.2/g), prepared as described in Reference Example 3, and deionized water to form a slurry. The obtained slurry was then dispersed by high shear mixing until the resulting D.sub.v90 determined as described in Reference Example 2 herewith was 10 micrometers. The slurry was then disposed over the full length of an uncoated flow-through honeycomb cordierite monolith substrate (diameter 2.54 cm (1 inch) x length: 76.2 cm (3 inches) cylindrically shaped substrate with 400/(2.54).sup.2 cells per square centimeter and 0.1016 millimeter (4 mil) wall thickness). Said substrate was coated according to the method described in Reference Example 4. Afterwards, the substrate was dried at 120 C. for 60 minutes and then calcined at 590 C. for 60 minutes. The washcoat loading after calcination was of about 128.15 g/l (2.1 g/in.sup.3), including about 121.44 g/l (1.99 g/in.sup.3) of Cu-CHA and about 6.71 g/l (0.11 g/in.sup.3) of zirconia.

Example 1 Preparation of a Selective Catalytic Reduction Catalyst (Fe/Cu-SCR)

(7) Iron Impregnation

(8) The water adsorption of the Cu-SCR catalyst prepared according to Comparative Example 1 was determined as described in Reference Example 5 and said water adsorption was of 176.97 g/l (2.9 g/in.sup.3) by weight/volume. The iron impregnation was performed under the same ambient conditions defined in 1) of Reference Example 5. An aqueous solution of 100 g deionized water and 17.85 g iron nitrate nonahydrate (Fe(III)NO.sub.3 9H.sub.2O) was prepared. The Cu-SCR catalyst prepared according to Comparative Example 1 was then dipped into the aqueous iron nitrate solution at a desired zone length (ranging from 33% to 100%see Table 1 below) for 30 seconds before being removed from the solution. Each catalyst was subsequently dried in air for 1 h at 120 C. to remove the excess water and subsequently calcined for 1 h at 590 C.

(9) TABLE-US-00001 TABLE 1 Cu Fe Fe zone Total wash- content Zeolitic content length coat loading (wt.-%*) material (wt.-%**) (%) (g/in.sup.3) Example 1.1 5.1 CHA 1.35 33 2.13 (SAR: 18:1) Example 1.2 5.1 CHA 2.47 50 2.15 (SAR: 18:1) Example 1.3 5.1 CHA 3.14 100 2.16 (SAR: 18:1) *Cu content, calculated as CuO, in weight-% based on the weight of the zeolitic material. **Fe content, calculated as Fe.sub.2O.sub.3, in weight-% based on the weight of the zeolitic material.

Example 2 Testing of the Catalysts of Example 1 and of Comparative Example 1 NOx Conversion and N.SUB.2.O Formation

(10) The catalysts of Examples 1.1, 1.2, 1.3 and of Comparative Example 1 were further aged under hydrothermal conditions (10% O.sub.2/10% H.sub.2O) at 650 C. for 50 hours prior to measurement.

(11) SCR Testing Conditions:

(12) Space velocity (SV)=60 k h.sup.1, Temperatures: 250 C., 200 C. Standard SCR Gas feed: 550 ppm NH.sub.3, 500 ppm NO, 10% H.sub.2O, 10% O.sub.2 Fast SCR Gas feed: 550 ppm NH.sub.3, 250 ppm NO, 250 ppm NO.sub.2, 10% H.sub.2O, 10% O.sub.2

(13) The results were displayed in FIGS. 1a/1b and 2a/2b. FIGS. 1a and 2a summarize the results obtained under the standard SCR gas feed conditions, while FIGS. 1b and 2b summarize the results obtained under the fast SCR gas feed conditions, both described above. As may be taken from FIG. 1a, the NOx conversion level of the comparative example 1 was of 74% at 200 C. and of 99% at 250 C. While the NOx conversion at 250 C. is already very high for all samples, the performance of Examples 1.1 to 1.3 is on the same level as measured with the comparative example 1. Therefore, to distinguish the samples in NOx conversion, we must take a look at the 200 C. test point. Example 1.1 and 1.2 are equal to close to the comparative example in NOx conversion at 200 C. under the standard SCR feed gas conditions (FIG. 1a), only the Example 1.3 with the 100% Fe-zone length is significantly lower in NOx conversion. However, the advantage of the examples will be seen in the N.sub.2O make in FIG. 2a. The N.sub.2O make at 200 C. of the comparative example can be decreased from 11 to 3 ppm, and considering approximately identical NOx conversion from 11 to 7 ppm (Example 1.2 vs. Comparative Example 1). The advantage of the lower N.sub.2O make of the Examples 1.1 to 1.3 can be seen at the 250 C. test point as well.

(14) As may be taken from FIGS. 1b and 2b, generally due to the fast SCR reaction occurring, the NOx conversion level is higher compared with to the results obtained using the standard SCR feed gas conditions. However, only the 100% Fe-zone length sample was measured with 87% NOx conversion at 200 C. compared to 91 to 93% NOx conversion of the comparative example and Examples 1.1 and 1.2. Even under the fast SCR feed gas conditions, the advantage of Example 1.1 to 1.3 can be seen in the significantly lower N.sub.2O make compared to comparative example 1. At 200 C. the N.sub.2O make was decreased by 6 to 7 ppm coming from 20 ppm. At 250 C., the decrease was with 3 to 4 ppm detectable, but less pronounced.

(15) In summary, the new catalyst manufacturing concept has shown that flexible Fe containing zones are possible and that the advantage of adding Fe to the comparative example 1 will lead to a significant decrease in N.sub.2O make, while maintaining the NOx conversion level under both standard SCR and fast SCR gas feed conditions.

Reference Example 6 Preparation of Cu-FER and Cu-BEA

(16) The Cu-zeolitic materials having a framework type FER and BEA, respectively, were prepared with a target Cu content of 3.42 weight-% based on the weight of the zeolitic material as described in the following. An aqueous mixture of Cu(NO.sub.3).sub.2 was prepared by mixing water with Cu(NO.sub.3).sub.2 for 20 minutes at 20 C. The zeolitic material was impregnated with said aqueous Cu(NO.sub.3).sub.2 mixture for 35 minutes under stirring at ambient conditions. The Cu-impregnated zeolitic material was collected by filtration and was dried over night at 120 C. The dried material was then calcined at 700 C. in air for 2 hours, obtaining a powder of Cu-containing zeolitic material.

Comparative Example 2 Preparation of a Selective Catalytic Reduction Catalyst (Cu-SCR)

(17) An aqueous solution of zirconyl acetate (ZrO.sub.2: 5 weight-% of based on the zeolite) was mixed with Cu-FER zeolite with a Cu content, calculated as CuO, of 3.42 weight-% based on the weight of Cu-FER (a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of about 20:1, a BET specific surface area of 400 m.sup.2/g), prepared as described in Reference Example 6, and deionized water to form a slurry. The obtained slurry was then dispersed by high shear mixing until the resulting D.sub.v90 determined as described in Reference Example 2 herewith was 7.5 micrometers. The pH of the slurry was adjusted to about 5 (target pH) and said slurry had a solid content of about 35 weight-%. The slurry was then disposed over the full length of an uncoated flow-through honeycomb cordierite monolith substrate (diameter 2.54 cm (1 inch) x length: 76.2 cm (3 inches) cylindrically shaped substrate with 400/(2.54).sup.2 cells per square centimeter and 0.1016 millimeter (4 mil) wall thickness). Said substrate was coated according to the method described in Reference Example 4. Afterwards, the substrate was dried at 120 C. for 60 minutes and then calcined at 590 C. for 60 minutes. The washcoat loading after calcination was of about 2.1 g/in.sup.3, including 1.99 g/in.sup.3 of Cu-FER and 0.1 g/in.sup.3 of zirconia.

Example 2 Preparation of a Selective Catalytic Reduction Catalyst (Fe/Cu-SCR)

(18) Iron Impregnation

(19) The water adsorption of the Cu-SCR catalyst prepared according to Comparative Example 2 was determined as described in Reference Example 5 and said water adsorption was of 2.6 g/in.sup.3 by weight/volume. The iron impregnation was performed under the same ambient conditions defined in 1) of Reference Example 5. An aqueous solution of 100 g deionized water and 17.85 g iron nitrate nonahydrate (Fe(III)NO.sub.3 9H.sub.2O) was prepared. The Cu-SCR catalyst prepared according to Comparative Example 2 was then dipped into the aqueous iron nitrate solution at a desired zone length (33% and 100%see Table 2 below) for 30 seconds before being removed from the solution. Each catalyst was subsequently dried in air for 1 h at 120 C. to remove the excess water and subsequently calcined for 1 h at 590 C.

(20) TABLE-US-00002 TABLE 2 Fe Total wash- Cu Fe zone coat content Zeolitic content length loading (wt.-%*) material (wt.-%**) (%) (g/in.sup.3) Example 2.1 3.42 FER 1.3 33 2.12 (SAR: 20:1) Example 2.2 3.42 FER 1.9 100 2.13 (SAR: 20:1) *Cu content, calculated as CuO, in weight-% based on the weight of the zeolitic material. **Fe content, calculated as Fe.sub.2O.sub.3, in weight-% based on the weight of the zeolitic material.

Comparative Example 3 Preparation of a Selective Catalytic Reduction Catalyst (Cu-SCR)

(21) An aqueous solution of zirconyl acetate (ZrO.sub.2: 5 weight-% of based on the zeolite) was mixed with Cu-BEA zeolite with a Cu content, calculated as CuO, of 3.42 weight-% based on the weight of Cu-BEA (a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of about 26:1, a BET specific surface area of 700 m.sup.2/g), prepared as described in Reference Example 6, and deionized water to form a slurry. The obtained slurry was then dispersed by high shear mixing until the resulting D.sub.v90 determined as described in Reference Example 2 herewith was 7.5 micrometers. The pH of the slurry was adjusted to about 5 (target pH) and said slurry had a solid content of about 35 weight-%. The slurry was then disposed over the full length of an uncoated flow-through honeycomb cordierite monolith substrate (diameter 2.54 cm (1 inch) x length: 76.2 cm (3 inches) cylindrically shaped substrate with 400/(2.54).sup.2 cells per square centimeter and 0.1016 millimeter (4 mil) wall thickness). Said substrate was coated according to the method described in Reference Example 4. Afterwards, the substrate was dried at 120 C. for 60 minutes and then calcined at 590 C. for 60 minutes. The washcoat loading after calcination was of 2.1 g/in.sup.3, including 1.99 g/in.sup.3 of Cu-BEA and 0.1 g/in.sup.3 of zirconia.

Example 3 Preparation of a Selective Catalytic Reduction Catalyst (Fe/Cu-SCR)

(22) Iron Impregnation

(23) The water adsorption of the Cu-SCR catalyst prepared according to Comparative Example 3 was determined as described in Reference Example 5 and said water adsorption was of 2.6 g/in.sup.3 by weight/volume. The iron impregnation was performed under the same ambient conditions defined in 1) of Reference Example 5. An aqueous solution of 100 g deionized water and 17.85 g iron nitrate nonahydrate (Fe(III)NO.sub.3 9H.sub.2O) was prepared. The Cu-SCR catalyst prepared according to Comparative Example 3 was then dipped into the aqueous iron nitrate solution at a desired zone length (33% and 100%see Table 2 below) for 30 seconds before being removed from the solution. Each catalyst was subsequently dried in air for 1 h at 120 C. to remove the excess water and subsequently calcined for 1 h at 590 C.

(24) TABLE-US-00003 TABLE 3 Fe Total wash- Cu Fe zone coat content Zeolitic content length loading (wt.-%*) material (wt.-%**) (%) (g/in.sup.3) Example 3.1 3.42 BEA 1.1 33 2.11 (SAR: 26:1) Example 3.2 3.42 BEA 1.63 100 2.12 (SAR: 26:1) *Cu content, calculated as CuO, in weight-% based on the weight of the zeolitic material. **Fe content, calculated as Fe.sub.2O.sub.3, in weight-% based on the weight of the zeolitic material.

Example 4 Testing of the Catalysts of Examples 2 and 3 and of Comparative Examples 2 and 3NOx Conversion and N.SUB.2.O Formation

(25) a) Fe/Cu-SCRFER

(26) The catalysts of Examples 2.1 and 2.2 and of Comparative Example 2 were tested under fresh conditions.

(27) SCR Testing Conditions:

(28) Space velocity (SV)=80 k h.sup.1, Temperatures: 500 C. Standard SCR Gas feed: 900 ppm NH.sub.3, 750 ppm NO, 10% H.sub.2O, 10% O.sub.2

(29) The results were displayed in FIGS. 4 and 5. FIG. 4 summarize the results obtained under the standard SCR gas feed conditions. As may be taken from FIG. 4, the NOx conversion level of the comparative example 2 was of about 90% at 500 C., while the NOx conversion the performance of Examples 2.1 and 2.2 is better, namely with a NOx conversion of about 92-93% at the same temperature. Further, as may be taken from FIG. 5, the catalysts of Examples 2.1 and 2.2 also exhibits lower nitrous oxide formation compared to the catalyst of the comparative example. Indeed, such formation is at least reduced by a factor 2. Thus, it is clear from said results that the new catalyst manufacturing concept has shown that flexible Fe containing zones are possible and that the advantage of adding Fe to the comparative example 2 will lead to an improvement in NOx conversion, in particular at high temperatures, and significant decrease in N.sub.2O make.

(30) b) Fe/Cu-SCRBEA

(31) The catalysts of Examples 3.1 and 3.2 and of Comparative Example 3 were tested under fresh conditions.

(32) SCR Testing Conditions:

(33) Space velocity (SV)=80 k h.sup.1, Temperatures: 250, 500 C. Standard SCR Gas feed: 900 ppm NH.sub.3, 750 ppm NO, 10% H.sub.2O, 10% O.sub.2

(34) The results were displayed in FIGS. 6 and 7. FIG. 6 summarize the results obtained under the standard SCR gas feed conditions at 250 and 500 C. As may be taken from FIG. 6, the NOx conversion level of the comparative example 3 was of about 91% at 250 C. and of about 91% at 500 C., while the NOx conversion the performance of Examples 3.1 and 2.2 is better at 500 C. and of about 85-88.5% at 250 C. Further, as may be taken from FIG. 7, the catalysts of Examples 3.1 and 3.2 also exhibits lower nitrous oxide formation, ranging from 24-30 ppm compared to the catalyst of the comparative example (34 ppm). Thus, it is clear from said results that the new catalyst manufacturing concept has shown that flexible Fe containing zones are possible and that the advantage of adding Fe to the comparative example 3 will lead to improved or similar NOx conversion and significant decrease in N.sub.2O make.

BRIEF DESCRIPTION OF THE FIGURES

(35) FIG. 1a shows the NOx conversions obtained with the catalysts of Examples 1.1, 1.2, 1.3 and Comparative Example 1 under the standard SCR feed conditions.

(36) FIG. 1b shows the NOx conversions obtained with the catalysts of Examples 1.1, 1.2, 1.3 and Comparative Example 1 under the fast SCR feed conditions.

(37) FIG. 2a shows the N.sub.2O formation obtained with the catalysts of Examples 1.1, 1.2, 1.3 and Comparative Example 1 under the standard SCR feed conditions.

(38) FIG. 2b shows the N.sub.2O formation obtained with the catalysts of Examples 1.1, 1.2, 1.3 and Comparative Example 1 under the fast SCR feed conditions.

(39) FIG. 3 shows a schematic representation of an exhaust gas treatment catalyst according to the second set of embodiments. The represented catalyst comprises a substrate 1, preferably a flow-through substrate, coated by a first coating 2, an ammonia oxidation coating, preferably comprising platinum on alumina, and by a second coating 3 (3a+3b), wherein the portion 3a comprises a zeolitic material comprising copper and the portion 3b comprises iron and a zeolitic material comprising copper. The portion 3b forms a first zone of the catalyst and a second zone of the catalyst comprises the portion 3a. The first coating is within the second zone.

(40) FIG. 4 shows the NOx conversions obtained with the catalysts of Examples 2.1, 2.2 and of Comparative Example 2 under the standard SCR feed conditions.

(41) FIG. 5 shows the N.sub.2O formation obtained with the catalysts of Examples 2.1, 2.2 and of Comparative Example 2 under the standard SCR feed conditions.

(42) FIG. 6 shows the NOx conversions obtained with the catalysts of Examples 3.1, 3.2 and of Comparative Example 3 under the standard SCR feed conditions.

(43) FIG. 7 shows the N.sub.2O formation obtained with the catalysts of Examples 3.1, 3.2 and of Comparative Example 3 under the standard SCR feed conditions.

CITED LITERATURE

(44) US 2011/0305614 A1 WO 2016/070090 A1 WO 2017/153894 A1