Composition for SCR catalysts

Abstract

The present invention relates to a composition comprising a non-zeolitic oxidic material comprising alumina; an 8-membered ring pore zeolitic material comprising one or more of copper and iron, wherein the framework structure of the zeolitic material comprises a tetravalent element Y, a trivalent element X and oxygen, wherein the molar ratio of Y:X, calculated as YO.sub.2X.sub.2O.sub.3, is in the range of from 2:1 to 40:1; wherein at least part of the outer surface of the zeolitic material is covered by a layer comprising the non-zeolitic oxidic material; wherein Y comprises one or more of Si, Sn, Ti, Zr and Ge and X comprises one or more of Al, B, In and Ga.

Claims

1. A composition comprising: (i) a non-zeolitic oxidic material comprising alumina; and (ii) an 8-membered ring pore zeolitic material comprising one or more of copper and iron, wherein a framework structure of the zeolitic material comprises a tetravalent element Y, a trivalent element X and oxygen, wherein the molar ratio of Y:X, calculated as YO.sub.2:X.sub.2O.sub.3, ranges from 2:1 to 40:1; wherein at least part of the outer surface of the zeolitic material according to (ii) is covered by a layer comprising the non-zeolitic oxidic material according to (i); and wherein Y comprises one or more of Si, Sn, Ti, Zr and Ge and X comprises one or more of Al, B, In and Ga; wherein the composition is obtainable or obtained by a process, the process comprising: (a) providing an 8-membered ring pore zeolitic material, comprising one or more of copper and iron, wherein the framework structure of the zeolitic material comprises a tetravalent element Y, a trivalent element X and oxygen, wherein the molar ratio of Y:X, calculated as YO2:X2O3, is in the range of from 2:1 to 40:1; (b) providing a source of a non-zeolitic oxidic material comprising alumina, wherein the source of the non-zeolitic oxidic material is a colloid dispersion comprising particles of the non-zeolitic oxidic material, wherein the particles of the non-zeolitic oxidic material have a Dv50 in the range of from 30 to 200 nm; (c) admixing the zeolitic material obtained in (a) with the source of the non-zeolitic oxidic material comprising alumina obtained in (b), forming a mixture; (d) calcining the mixture obtained in (c) in a gas atmosphere having a temperature in the range of from 400 to 800 C.

2. The composition of claim 1, wherein from 98 weight-% to 100 weight of the non-zeolitic oxidic material according to (i) consist of alumina.

3. The composition of claim 1, wherein the layer comprising the non-zeolitic oxidic material according to (i) has an average thickness ranging from 2 nm to 100 nm.

4. The composition of claim 1, wherein from 99 weight-% to 100 weight-%, of the layer consist of the non-zeolitic oxidic material according to (i).

5. The composition of claim 1, wherein the 8-membered ring pore zeolitic material according to (ii) has a framework type selected from the group consisting of CHA, AEI, RTH, LEV, DDR, KFI, ERI, AFX, LTA, a mixture of two or more thereof and a mixed type of two or more thereof, preferably selected from the group consisting of CHA, AEI, RTH, a mixture of two or more thereof and a mixed type of two or more thereof, more preferably selected from the group consisting of CHA and AEI.

6. The composition of claim 1, wherein from 20% to 100%, of the outer surface of the zeolitic material according to (ii) are covered by the layer comprising the non-zeolitic oxidic material according to (i).

7. A slurry comprising a composition according to claim 1 and a dispersion agent, wherein the dispersion agent is one or more of water, ethanol, acetic acid, nitric acid, lactic acid, and a mixture of two or more thereof.

8. A selective catalytic reduction catalyst for treating an exhaust gas of a combustion engine, the catalyst comprising: (1) a substrate comprising 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; (2) a coating disposed on the substrate (i), the coating comprising a composition according to claim 1.

9. The catalyst of claim 8, wherein the coating (2) further comprises an oxidic binder, wherein the oxidic binder comprises one or more of zirconia, alumina, titania, silica, and a mixed oxide comprising two or more of Zr, Al, Ti, and Si.

10. The catalyst of claim 8, wherein the coating (2) comprises the composition in an amount ranging from 80 weight-% to 100 weight-%, based on the weight of the coating (2).

11. The catalyst of claim 8, wherein the substrate is a wall-flow filter substrate, wherein the plurality of passages comprises inlet passages having an open inlet end and a closed outlet end, and outlet passages having a closed inlet end and an open outlet end.

12. A process for preparing the selective catalytic reduction catalyst for treating an exhaust gas of a combustion engine, the process comprising (A) preparing a mixture comprising water and a composition according to claim 1; (B) disposing the mixture obtained according to (A) on a substrate, the substrate comprising 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, obtaining a mixture-treated substrate; (C) calcining the mixture-treated substrate obtained according to (B), obtaining the substrate having a coating disposed thereon.

13. A process for preparing a composition, the process comprising: (a) providing an 8-membered ring pore zeolitic material, comprising one or more of copper and iron, wherein a framework structure of the zeolitic material comprises a tetravalent element Y, a trivalent element X and oxygen, wherein the molar ratio of Y:X, calculated as YO.sub.2:X.sub.2O.sub.3, ranges from 2:1 to 24:1, wherein the zeolitic material comprises crystals having an average crystal size in the range of from 0.05 micrometers to 5 micrometers; (b) providing a source of a non-zeolitic oxidic material comprising alumina, wherein the source of the non-zeolitic oxidic material is a colloid dispersion comprising particles of the non-zeolitic oxidic material, wherein the particles of the non-zeolitic oxidic material have a Dv50 ranging from 30 nm to 200 nm; (c) admixing the zeolitic material obtained in (a) with the source of the non-zeolitic oxidic material comprising alumina obtained in (b), forming a mixture; and (d) calcining the mixture obtained in (c) in a gas atmosphere having a temperature ranging from 400 C. to 800 C.

14. The process of claim 13, wherein the crystals of the 8-membered ring pore zeolitic material have an average crystal size ranging from 0.06 micrometers to 2 micrometers.

15. The process of claim 13, wherein the 8-membered ring pore zeolitic material comprises particles having a Dv50 ranging from 0.5 micrometers to 4 micrometers.

16. The process of claim 13, wherein the colloid dispersion comprising particles of the non-zeolitic oxidic material provided in (b) is alumina sol.

17. The process of claim 13, wherein the particles of the non-zeolitic oxidic material, the particles of alumina, have a Dv50 ranging from 50 nm to 150 nm.

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 Measurement of the Average Porosity and the Average Pore Size of the Porous Wall-Flow Substrate

(2) The average porosity of the porous wall-flow substrate was determined by mercury intrusion using mercury porosimetry according to DIN 66133 and ISO 15901-1.

Reference Example 3 Determination of the Volume-Based Particle Size Distributions

(3) 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 4 Determination of the Average Thickness of a Layer Comprising a Non-Zeolitic Oxidic Material in a Composition

(4) To determine the thickness of a given layer on the outer surface of a zeoltic material in a composition, said composition was first coated on a substrate, such as the one used in Example 1 or 2, dried at 130 C. for 30 minutes and calcined at 450 C. for 2 hours. Further, at least ten TEM (Transmission Electron Microscopy) images of the coated substrate were generated. The thickness of said given layer was measured on said at least ten TEM images by applying a scale at several parts of the images and averaging over all measurement points at all crystals/particles, examples are given in FIG. 8. FIG. 8.1 or 8.2 shows how the layer thickness was determined on one TEM image.

Reference Example 5 Determination of the Average Crystal Size of a Zeolitic Material

(5) The average crystal size of a zeolitic material was determined by analyzing the zeolitic material powder with TEM images. The size of individual crystals was determined by averaging the crystal size from 20 to 30 individual crystals from at least two TEM images done with a magnification in the range of from 5 000 to 12 000.

Comparative Example 1: Process for Preparing a Selective Catalytic Reduction Catalyst Comprising a Zeolitic Material Comprising Copper not According to the Present Invention

(6) Slurry 1:

(7) A CuO powder having a Dv50 of 33 micrometers was added to water. The amount of CuO was calculated such that the total amount of copper, calculated as CuO, in the coating after calcination was 4.15 weight-% based on the weight of the Chabazite. The resulting mixture was milled using a continuous milling apparatus so that the Dv50 value of the particles was about 2 micrometers and the Dv90 value of the particles was about 5 micrometers. The resulting slurry had a solid content of 8 weight-% based on the weight of said slurry. Acetic acid and an aqueous zirconium acetate solution was added to the CuO-containing mixture forming a slurry. The amount of acetic acid was calculated to be 1.7 weight-% of the Chabazite and the amount of zirconium acetate was calculated such that the amount of zirconia in the coating, calculated as ZrO.sub.2, was 5 weight-% based on the weight of the Chabazite. Separately, a Chabazite (Dv50 of 2.2 micrometers, a Dv90 of 5.2 micrometers, a SiO2:Al.sub.2O.sub.3 of 18, an average crystal size of 0.4 micrometer) was added to water to form a mixture having a solid content of 36 weight-% based on the weight of said mixture. The Cu-Chabazite mixture was mixed to the copper containing slurry. The amount of the Cu-Chabazite was calculated such that the loading of Chabazite after calcination was 84% of the loading of the coating in the catalyst after calcination. The resulting slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 5 micrometers.

(8) Slurry 2:

(9) Separately, an aqueous slurry having a solid content of 12 weight-% based on the weight of said slurry and comprising water and alumina (Al.sub.2O.sub.3 95 weight-% with SiO2 5 weight-% having a BET specific surface area of about 180 m.sup.2/g, a Dv90 of about 5 micrometers) was prepared. The amount of alumina+silica was calculated such that the amount of alumina+silica after calcination was 10 weight-% based on the weight of the Chabazite after calcination.

(10) Subsequently, slurries 1 and 2 were combined, the solid content of the obtained final slurry was of about 31 weight-% based on the total weight of said final slurry. A porous uncoated wall-flow filter substrate, silicon carbide, (an average porosity of 60.5%, a mean pore size of 20 micrometers and 350 CPSI and 0.28 mm (11 mil) wall thickness, diameter: 1.5 inch (38.1 mm)*length: 6 inches (152.4 mm)) was coated twice from the inlet end to the outlet end with the final slurry over 100% of the substrate axial length. To do so, the substrate was dipped in the final slurry from the inlet end until the slurry arrived at the top of the substrate. Further a pressure pulse was applied on the inlet end to distribute the slurry evenly in the substrate. Further, the coated substrate was dried at 130 C. for 30 minutes and calcined at 450 C. for 2 hours. This was repeated once. The final coating loading after calcinations was about 2 g/in.sup.3, including about 1.68 g/in.sup.3 of CHA zeolitic material, 0.17 g/in.sup.3 of alumina+silica, about 0.084 g/in.sup.3 of zirconia and 4.15 weight-% of Cu, calculated as CuO, based on the weight of the CHA zeolitic material.

(11) Characterization:

(12) Analysis of the TEM micrographs (FIG. 1) of the obtained coated substrate demonstrates that no alumina is found around the zeolitic material crystals. Instead, Si-doped-alumina is intermittently dispersed between/among the Chabazite crystals or particles (=agglomerates/aggregates of Chabazite crystals) or independently in separate sections of the sample (not shown on FIG. 1). Without wanted to be bound to any theory, it is believed that it is due to the particle size of the Si-doped-alumina which is significantly higher than that of the chabazite crystals.

Example 1: Process for Preparing a Selective Catalytic Reduction Catalyst Comprising a Zeolitic Material Comprising Copper

(13) In a first step, a zeolitic material having a framework type CHA (Dv50 of 2.2 micrometers, a Dv90 of 5.2 micrometers, a SiO2:Al.sub.2O.sub.3 of 18, an average crystal size of about 0.4 micrometer) was added to an aqueous solution of copper acetate (3.51 weight-% of Cu, calculated as CuO). The aqueous copper acetate solution is provided in a quantity sufficient to fill the pores of the CHA zeolitic material by incipient wetness impregnation to obtain a Cu content, calculated as CuO, of about 4.15 weight-%. After the impregnation, the Cu-containing zeolitic material was calcined in air for 2 hours at 500 C.

(14) In a second step, an alumina sol (boehmite-colloidal dispersion: a solid content 22-25 weight-% and a Dv50 of the particles of alumina in the dispersion of about 90 nm) was dispersed in water and impregnated on the calcined Cu-zeolitic material so that the weight percent of the alumina amounts to 10 weight-% based on the weight of the zeolitic material after calcination. After the impregnation, the Cu-zeolitic material+alumina was calcined in air for 2 hours at 500 C. Subsequently, the calcined Cu-zeolite+alumina was dispersed in water and an aqueous zirconium acetate solution, forming a slurry. The amount of zirconium acetate was calculated such that the amount of zirconia in the coating, calculated as ZrO.sub.2, was 5 weight-% based on the weight of the zeolitic material. Finally, acetic acid (1.7 weight-% based on the weight of the zeolitic material) was added to said slurry. The resulting slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 4 micrometers and the solid content of the obtained slurry was adjusted to 31 weight-% based on the weight of said slurry.

(15) The obtained slurry was coated twice on a porous uncoated wall-flow filter substrate, silicon carbide, (an average porosity of 60.5%, a mean pore size of 20 micrometers and 350 CPSI and 0.33 mm (13 mil) wall thickness, diameter: 1.5 inch (38.1 mm)*length: 6 inches (152.4 mm)) according to the process described in Comparative Example 1 in the foregoing. The final coating loading after calcinations was about 2.1 g/in.sup.3, including about 1.764 g/in.sup.3 of CHA zeolitic material, 0.176 g/in.sup.3 of alumina, about 0.088 g/in.sup.3 of zirconia and 4.15 weight-% of Cu, calculated as CuO, based on the weight of the CHA zeolitic material.

(16) Characterization:

(17) TEM analysis (FIG. 2.1) of the obtained coated substrate shows that about 50-60% of the crystals exhibit some level of alumina coating. While some zeolitic material crystals are without visible alumina layers, other zeolitic material crystals are partially encased in alumina, forming a shell of alumina around the zeolitic material, the core. Only few Chabazite crystals are fully encased by alumina. The average thickness of the alumina layer was about 31 nm determined as in Reference Example 4.

Example 2: Process for Preparing a Selective Catalytic Reduction Catalyst Comprising a Zeolitic Material Comprising Copper

(18) The catalyst of Example 2 was prepared as the catalyst of Example 1 except that the amount of alumina sol was increased such that the weight percent of the alumina amounts to 30 weight-% based on the weight of the zeolitic material after calcination. The final coating loading after calcinations was about 2.1 g/in.sup.3, including about 1.51 g/in.sup.3 of CHA zeolitic material, 0.45 g/in.sup.3 of alumina, about 0.076 g/in.sup.3 of zirconia and 4.15 weight-% of Cu, calculated as CuO, based on the weight of the CHA zeolitic material.

(19) Characterization:

(20) TEM analysis (FIG. 2.2) of the obtained coated substrate clearly demonstrates that a significant fraction of Chabazite crystals are covered by a coating of alumina. While some zeolitic material crystals have little or no coating of alumina (10-20% of said crystals); many zeolitic material crystals are fully encased with alumina, with evidence for alumina morphology on the surface and sides of the primary chabazite crystals. The average thickness of the alumina layer was about 43 nm determined as in Reference Example 4. Hence, it is clear that in the catalyst of Example 2 alumina is forming a shell around the CHA zeolitic material, the core. A recapitulative table is provided in the following.

(21) TABLE-US-00001 TABLE 1 Final Ion- washcoat Zeolitic exchange Oxidic material loadings material method wt.-%* (g/in.sup.3) Comp. Cu-CHA ISIE.sup.a silica-alumina 10 2.0 Ex. 1 (SAR: 18) Ex. 1 Cu-CHA Impregnation alumina sol 10 2.1 (SAR: 18) Cu acetate (nano-dispersed alumina) Ex. 2 Cu-CHA Impregnation alumina sol 30 2.1 (SAR: 18) Cu acetate (nano-dispersed alumina) .sup.aISIE, In-situ ion-exchange of a zeolitic material which is not pre-exchanged. *based on the weight of the zeolitic material. SAR: silica to alumina molar ratio.

Example 3: Testing of the Catalysts of Comparative Example 1, Examples 1 and 2NOx Conversion and Backpressure

(22) 3.1 NOx Conversion

(23) The catalysts were aged in an oven at 800 C. hydrothermally (20% O.sub.2, 10% H.sub.2O in % N.sub.2) for 16 hours prior testing. The NOx conversion of the catalysts at 20 ppm ammonia slip was measured on a laboratory reactor. The reactor was equipped with 3 Fourier-transform infrared spectroscopy apparatus (FTIRs) to measure reactant and product concentrations, the temperature was adjusted with preheaters and a heater around the sample holder. The gas flows were adjusted with several mass flow controllers that allow mixing of different reactant gases. The measurements were done at 200 C. (500 ppm NO, NH.sub.3/NO.sub.x=1.5, 10% O.sub.2, 5% CO.sub.2, 5% H.sub.2O, 80 ppm C.sub.3H.sub.6 (C1 basis)), at a space velocity of 40 k/h and at 600 C. 500 ppm NO, NH.sub.3/NO.sub.x=2.0, 10% O.sub.2, 5% CO.sub.2, 5% H.sub.2O, 80 ppm C.sub.3H.sub.6 (C1 basis)), at a space velocity of 40 k/h and 80 k/h. The results are displayed on FIGS. 3 and 4.

(24) 3.2 Backpressure

(25) The cold flow backpressure data recorded at a volume flow of 27 m.sup.3/h and 293 K was reported on FIG. 5 (Fresh catalysts).

(26) FIGS. 1 to 3 show that the low temperature (200 C.) performance decreases by only about 2% (close to the experimental error) for Example 1 and 6% for Example 2 compared to Comparative Example 1 and the high temperature (600 C.) performance however increases by 8% for Example 1 and 20% for Example 2 compared to the Comparative Example 1. Therefore, Example 3 demonstrates that there is a significant improvement in the high temperature performance while no significant loss in low temperature NOx activity. The catalysts of the present invention also present a reduction in backpressure of about 2.5% (Example 1) and of almost 15% (Example 2). Indeed, the catalyst of Example 2 exhibits a strong advantage in back pressure and high temperature performance, without a significant loss in low temperature NO.sub.x activity. Thus, without wanted to be bound to any particular theory, it is believed that the use of nanodispersed alumina in place of silica-alumina in a selective catalytic reduction catalyst comprising a zeolitic material permits to improve the catalytic performance and stability of the zeolitic material based catalyst and that increasing the amount of nano-dispersed alumina permits to reduce the backpressure and increase the NOx performance at high temperatures after ageing. Furthermore, without wanted to be bound to any particular theory, it is believed that the formation of a coating of alumina which encapsulates the CHA zeolitic material permits to reduce backpressure and increase the NOx performance at high temperatures after hydrothermal aging as it enhances its thermal durability. It is believed that the alumina around the zeolitic material may react with CuO and AlO.sub.x that are formed in an engine or during oven aging.

Comparative Example 2: Process for Preparing a Selective Catalytic Reduction Catalyst Comprising a Zeolitic Material Comprising Copper not According to the Present Invention

(27) The catalyst of Comparative Example 2 is prepared as the catalyst of Comparative Example 1 except that a different wall-flow filter was used, namely a porous uncoated wall-flow filter substrate, silicon carbide, (an average porosity of 60.5%, a mean pore size of 20 micrometers and 350 CPSI and 0.33 mm (13 mil) wall thickness, diameter: 2.28 inch (58 mm)*length: 5.9 inches (150.5 mm)) and that the final washcoat loading was of about 1.8 g/in.sup.3, including 1.512 g/in.sup.3 of CHA zeolitic material, 0.15 g/in.sup.3 of alumina+silica, 0.0756 g/in.sup.3 of zirconia and 4.15 weight-% of Cu, calculated as CuO, based on the weight of the CHA zeolitic material.

Comparative Example 3: Process for Preparing a Selective Catalytic Reduction Catalyst Comprising a Zeolitic Material Comprising Copper not According to the Present Invention

(28) The catalyst of Comparative Example 3 is prepared as the catalyst of Comparative Example 2 except that the amount of silica-alumina was increased to 20 weight-% based on the weight of the Chabazite after calcination. The final washcoat loading was of about 1.8 g/in.sup.3, including 1.394 g/in.sup.3 of CHA zeolitic material, 0.279 g/in.sup.3 of alumina+silica, 0.07 g/in.sup.3 of zirconia and 4.15 weight-% of Cu, calculated as CuO, based on the weight of the CHA zeolitic material.

Example 4: Process for Preparing a Selective Catalytic Reduction Catalyst Comprising a Zeolitic Material Comprising Copper

(29) The catalyst of Example 4 was prepared as the catalyst of Example 1 except that the amount of alumina sol was increased such that the weight percent of the alumina amounts to 20 weight-% based on the weight of the zeolitic material after calcination, that the amount of the CHA zeolitic material was reduced to 77.4 weight-% based on the final coating loading and that a different wall-flow filter was used, namely a porous uncoated wall-flow filter substrate, silicon carbide, (an average porosity of 60.5%, a mean pore size of 20 micrometers and 350 CPSI and 0.33 mm (13 mil) wall thickness, diameter: 2.28 inch (58 mm)*length: 5.9 inches (150.5 mm)). The final coating loading after calcinations was about 1.8 g/in.sup.3, including about 1.394 g/in.sup.3 of CHA zeolitic material, 0.279 g/in.sup.3 of alumina, about 0.07 g/in.sup.3 of zirconia and 4.15 weight-% of Cu, calculated as CuO, based on the weight of the CHA zeolitic material.

Example 5: Testing of the Catalysts of Comparative Examples 2 and 3 and Example 4NOx Conversion and Backpressure

(30) 5.1 NOx Conversion

(31) The catalysts were aged in an oven at 800 C. hydrothermally (20% O.sub.2, 10% H.sub.2O in % N.sub.2) for 16 hours prior testing. The NOx conversion of the catalysts was measured on 2 L, 140 KW, Euro 6 engine at two different temperatures, namely 220 C. and 660 C. At 220 C.: conversion at 20 ppm slip, a volume flow 33 m.sup.3/h, 110 ppm NOx and a NSR (NH.sub.3/NOx) of 1.5. At 660 C.: conversion at maximum ammonia slip, a volume flow 63 m.sup.3/h, 335 ppm NOx and a NSR (NH.sub.3/NOx) of 2. The results are displayed on FIG. 6.

(32) 5.2 Backpressure

(33) The cold flow backpressure data recorded at a volume flow of 65 m.sup.3/h and 293 K was reported in FIG. 7 (Fresh catalysts).

(34) As may be taken from FIGS. 6 and 7, back pressure and NO.sub.x conversion are similar for the catalysts of Comparative Examples 2 and 3, where the increase in silica-alumina content from 10% to 20% does not lead to a strong change in the performance. However, the catalyst of Example 4 shows a strongly reduced back pressure and high temperature NO.sub.x performance is enhanced. These results demonstrate that the catalyst preparation process and the type of alumina used in Example 4 lead to advantages in both backpressure and catalytic performance. Without wanting to be bound by any theory, it is believed that the use of a composition according to the present invention (namely with a zeolitic material covered by a layer of alumina) for preparing a selective catalytic reduction catalyst as the one of Example 4 permits to lower back pressure. Secondly, the encapsulation of the zeolitic material crystals in an alumina layer (shell) seems to improve the durability towards thermal exposure, resulting in the improved high temperature NO.sub.x conversion after ageing compared to the designs where the zeolite particles are not encapsulated in an alumina layer (Comparative Examples 2 and 3).

BRIEF DESCRIPTION OF THE FIGURES

(35) FIG. 1 TEM micrograph of the Cu-Chabazite+alumina-silica used in Comparative Example 1.

(36) FIG. 2 2.1: TEM micrograph of the Cu-Chabazite+alumina used in Example 1. 2.2: TEM micrograph of the Cu-Chabazite+alumina in Example 2. The white arrows show the alumina layer on the outer surface of the zeolitic material. FIG. 3 shows the NOx conversion measured for the catalysts of Comparative Example 1 and of Examples 1 and 2 at 200 C. (SV: 40 k/h).

(37) FIG. 4 shows the NOx conversion measured for the catalysts of Comparative Example 1 and of Examples 1 and 2 at 600 C. (SV: 40 and 80 k/h).

(38) FIG. 5 shows the cold flow backpressure recorded for the catalysts of Comparative Example 1 and of Examples 1 and 2 at a volume flow of 27 m.sup.3/h.

(39) FIG. 6 shows the NOx conversion measured for the catalysts of Comparative Examples 2 and 3 and of Example 4 at 220 C. at 20 ppm NH.sub.3 and at 660 C. at maximum NH.sub.3 slip.

(40) FIG. 7 shows the cold flow backpressure recorded for the catalysts of Comparative Examples 2 and 3 and of Example 4 at a volume flow of 65 m.sup.3/h.

(41) FIG. 8 shows the measurements of the average thickness of a layer comprising a non-zeolitic oxidic material (10 wt. % of alumina based on the weight of the zeolitic materialFIGS. 8.1 and 30 wt. % of alumina based on the weight of the zeolitic materialFIG. 8.2).

CITED LITERATURE

(42) US 2013/0101503 A1 US 2017/7050182 A1 CN 108993579 A WO 2019/225909 A