A SELECTIVE CATALYTIC REDUCTION CATALYST ON A FILTER

Abstract

The present invention relates to a selective catalytic reduction catalyst comprising a porous wall-flow filter substrate; wherein in the pores of the porous internal walls and on the surface of the porous internal walls, the catalyst comprises a selective catalytic reduction coating comprising a selective catalytic reduction component comprising a zeolitic material comprising one or more of copper and iron. The present invention further relates to a process for preparing a selective catalytic reduction catalyst using particles of a carbon-containing additive and an aqueous mixture comprising said particles of a carbon-containing additive.

Claims

1. A selective catalytic reduction catalyst comprising a porous wall-flow filter substrate comprising an inlet end, an outlet end, a substrate axial length extending between the inlet end and the outlet end, and a plurality of passages defined by porous internal walls of the porous wall-flow filter substrate, wherein the plurality of passages comprise 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, wherein an interface between the passages and the porous internal walls is defined by a surface of the porous internal walls; and wherein in the pores of the porous internal walls and on the surface of the porous internal walls, the catalyst comprises a selective catalytic reduction coating comprising a selective catalytic reduction component comprising a zeolitic material comprising one or more of copper and iron; wherein in the pores of the porous internal walls, the selective catalytic reduction catalytic coating is present as in-wall-coating, and on the surface of the porous internal walls, the selective catalytic reduction catalytic coating is present as on-wall-coating; and wherein in addition to the selective catalytic reduction catalytic coating, the catalyst comprises no further coating in the pores of the porous internal walls and no further coating on the surface of the porous internal walls; and wherein the selective catalytic reduction coating is present at a total loading, I(total), which is the sum of the loading of the in-wall coating, I(in-wall coating), and the loading of the on-wall coating, I(on-wall coating), wherein in the catalyst, a loading ratio, defined as the loading of the on-wall coating, I(on-wall coating), relative to the loading of the in-wall coating, I(in-wall coating), the loading ratio, being defined as I(on-wall coating):I(in-wall coating), ranges from 17:83 to 80:20.

2. The catalyst of claim 1, wherein the loading ratio, I(on-wall coating):I(in-wall coating), ranges from 20:80 to 60:40; wherein the total loading, I(total), of the selective catalytic reduction coating in the catalyst ranges from 1.3 g/in.sup.3 to 6 g/in.sup.3.

3. The catalyst of claim 1, wherein the zeolitic material comprised in the selective catalytic reduction component comprised in the selective catalytic reduction coating is a 8-membered ring pore zeolitic material; wherein the zeolitic material comprised in the selective catalytic reduction component of the selective catalytic reduction coating comprises copper in an amount, calculated as CuO, ranging from 1 wt-% to 15 wt-%, based on the weight of the zeolitic material comprised in the selective catalytic reduction coating.

4. The catalyst of claim 1, wherein the porous internal walls of the porous wall-flow filter substrate comprising the in-wall coating have a relative average porosity ranging from 15% to 60%, wherein the relative average porosity is defined as the average porosity of the internal walls comprising the in-wall coating relative to the average porosity of the internal walls not comprising the in-wall coating; and wherein the total loading of the selective catalytic coating, I(total), ranges from 1.8 g/in.sup.3 to 4.5 g/in.sup.3; and wherein the average porosity of the internal walls not comprising the in-wall coating ranges from 30% to 75%.

5. The catalyst of claim 1, wherein the porous internal walls of the porous wall-flow filter substrate comprising the in-wall coating have an average pore size ranging from 5 micrometers to 30 micrometers.

6. The catalyst of claim 1, wherein the in-wall coating comprises pores, wherein at least 15%, of the pores of the in-wall coating have a mean pore size ranging from 0.5 micrometer to 18 micrometers.

7. The catalyst of claim 1, wherein the in-wall coating comprises pores, wherein from 3% to 12%, of the pores of the in-wall coating have a mean pore size in the range of 0.005 micrometer to 2 micrometers.

8. A process for preparing a selective catalytic reduction catalyst according to claim 1, the process comprising (i) providing a porous wall-flow filter substrate comprising an inlet end, an outlet end, a substrate axial length extending between the inlet end and the outlet end, and a plurality of passages defined by porous internal walls of the porous wall-flow filter substrate, wherein the plurality of passages comprise 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, wherein the interface between the passages and the porous internal walls is defined by the surface of the porous internal walls; (ii) preparing an aqueous mixture comprising water, particles of a carbon-containing additive, and a source of a selective catalytic reduction component comprising a zeolitic material and a source-of one or more of copper and iron, wherein the carbon-containing additive has a removal temperature ranging from 120° C. to 900° C.; (iii) disposing the mixture obtained in (ii) on the surface of the internal walls of the porous substrate provided in (i), and optionally drying the substrate comprising the mixture disposed thereon; and (iv) calcining the substrate obtained in (iii) in a gas atmosphere having a temperature ranging from 500° C. to 1000° C., to obtain a porous wall-flow filter substrate comprising a selective catalytic reduction coating; wherein the particles of the carbon-containing additive contained in the aqueous mixture prepared in (ii) have a Dv50 ranging from 0.5 micrometers to 40 micrometers.

9. The process of claim 8, wherein the carbon-containing additive contained in the aqueous mixture prepared in (ii) is one or more of graphite, synthetic graphite, carbon black, graphene, diamond, fullerene, carbon nanotubes and amorphous carbon; and wherein the carbon-containing additive has a removal temperature ranging from 400° C. to 850° C.

10. The process of claim 9, wherein the carbon-containing additive is one or more of graphite, synthetic graphite, graphene, fullerene, carbon nanotubes and amorphous carbon; or wherein the carbon-containing additive is carbon black; wherein carbon black has a BET specific surface area ranging from 5 m.sup.2/g to 30 m.sup.2/g.

11. The process of claim 8, wherein the carbon-containing additive is one or more of polyacrylate, microcrystalline cellulose, corn starch, styrene, poly(methyl methacrylate-co-ethylene glycol), polymethylurea, and polymethyl methacrylate; wherein the carbon-containing additive has a removal temperature ranging from 150° C. to 550° C.

12. The process of claim 8, wherein (ii) further comprises (ii.1) preparing a first mixture comprising water and a zeolitic material comprising one or more of copper and iron, wherein the zeolitic material is a 8-membered ring pore zeolitic material, and wherein the zeolitic material has a framework type chosen from CHA, AEI, RTH, AFX, a mixture of two or more thereof and a mixed type of two or more thereof; (ii.2) milling the first mixture; (ii.3) preparing a second mixture comprising water, and a non-zeolitic oxidic material; (ii.4) admixing the first mixture obtained in (ii.1), with the second mixture obtained in (ii.3); (ii.5) preparing a suspension comprising water and the particles of the carbon-containing additive; (ii.6) admixing the mixture obtained in (ii.4) and the suspension obtained in (ii.5); wherein (ii) further comprises (ii.1′) preparing a first mixture comprising water, a source of one or more of copper and iron, and a zeolitic material, wherein the zeolitic material is a 8-membered ring pore zeolitic material, and wherein the zeolitic material has a framework type chosen from CHA, AEI, RTH, AFX, a mixture of two or more thereof and a mixed type of two or more thereof (ii.2′) milling the first mixture; (ii.3′) preparing a second mixture comprising water, and a non-zeolitic oxidic material; (ii.4′) admixing the first mixture obtained in (ii.1′), with the second mixture obtained in (ii.3′); (ii.5′) preparing a suspension comprising water and the particles of the carbon-containing additive; (ii.6′) admixing the mixture obtained in (ii.4′) and the suspension obtained in (ii.5′).

13. The process of claim 8, wherein the aqueous mixture prepared in (ii) comprises the particles of the carbon-containing additive in an amount ranging from 2 wt.-% to 40 wt-%, based on the weight of the zeolitic material and of the non-zeolitic oxidic material in the aqueous mixture prepared in (ii).

14. (canceled)

15. An aqueous mixture, comprising water, particles of a carbon-containing additive, and a source of a selective catalytic reduction component comprising a zeolitic material, and a source-of one or more of copper and iron, wherein the particles of the carbon-containing additive contained in the aqueous mixture have a Dv50 ranging from 0.5 micrometer to 40 micrometers and wherein the carbon-containing additive has a removal temperature ranging from 120° C. to 900° C.

16. A selective catalytic reduction catalyst comprising a porous wall-flow filter substrate comprising an inlet end, an outlet end, a substrate axial length extending between the inlet end and the outlet end, and a plurality of passages defined by porous internal walls of the porous wall-flow filter substrate, wherein the plurality of passages comprise 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, and wherein a interface between the passages and the porous internal walls is defined by the surface of the porous internal walls; the catalyst further comprising (i) a first coating, in the pores of the porous internal walls, wherein the first coating comprising a first selective catalytic reduction component comprising a first zeolitic material comprising one or more of copper and iron; and (ii) a second coating, in the pores of the porous internal walls and coated onto the first coating, wherein the second coating comprising a second selective catalytic reduction component comprising a second zeolitic material comprising one or more of copper and iron; wherein the pores of the porous internal walls comprise the first coating at a loading I(1) and the second coating at a loading I(2), wherein the loading ratio I(1):I(2) ranges from 3:1 to 25:1.

Description

EXAMPLES

Reference Example 1 Determination of the Volume-Based Particle Size Distributions (Dv10, Dv50, Dv90 and Dv99)

[0577] 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 below 10%.

Reference Example 2 Measurement of the BET Specific Surface Area

[0578] The BET specific surface area of the alumina was determined according to DIN 66131 or DIN-ISO 9277 using liquid nitrogen.

Reference Example 3 Collection of SEM Images

[0579] The SEM images were collected with a Carl Zeiss Table Top Electron Microscope: EHT: 18.00 kV, Signal A: HDBSD, WD: 9.00 mm

Reference Example 4 Measurement of the Average Porosity, the Average/Mean Pore Size of the Internal Walls of the Porous Wall-Flow Substrate

[0580] The average porosity of the internal walls of the porous wall-flow substrate was determined by mercury intrusion using mercury porosimetry according to DIN 66133. The reported data has been collected with the instrument AutoPore V in the range 0.1-61000 psia with a HG temperature of 23-25° C.

Reference Example 5 Determination of the Fraction of In-Wall Coating and of On-Wall Coating in a Given Catalyst

[0581] To determine the fraction of coating that is disposed within the internal walls of a given substrate (in-wall coating) and the fraction of coating that is disposed on the surface of the internal walls of the given substrate (on-wall coating), SEM images such as the ones in FIGS. 4 a-b and FIGS. 5a-b, respectively, are quantitatively evaluated. As the amount of in-wall coating and on-wall coating can be clearly distinguished in such images, the respective areas of on-wall coating, as well as in-wall coating, are analysed from several SEM images (at least two images) with an appropriate software program.

Comparative Example 1 Preparation of a Selective Catalytic Reduction Catalyst not According to the Present Invention

[0582] Slurry 1:

[0583] A Cu-Chabazite with a Cu content of 3.33 weight-%, calculated as CuO, based on the weight of the Cu-zeolite (Dv50 of 20 micrometers and a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 25, primary crystallite size of less than 0.5 micrometer and a BET specific surface area of about 600 m.sup.2/g) was dispersed in water forming a slurry. The solid content of the obtained slurry was adjusted to 37 weight-%. The resulting slurry was milled using a continuous milling apparatus so that the Dv50 value of the particles was of about 5 micrometers.

[0584] Slurry 2:

[0585] An aqueous slurry having a solid content of 30 weight-% and comprising alumina (Al.sub.2O.sub.3 94 weight-% with SiO.sub.2 6 weight-% having a BET specific surface area of 173 m.sup.2/g, a Dv90 of about 5 micrometers) was prepared. The amount of alumina+silica was calculated such that it was 10 weight-% based on the weight of the Cu-zeolite. Tartaric acid was added to the aqueous slurry. The amount of tartaric acid was calculated such that it was 0.7 weight-% based on the weight of the alumina-silica.

[0586] Subsequently, slurries 1 and 2 were combined obtaining a final slurry. The solid content of the final slurry was adjusted to 34 weight-%. The final slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 4 micrometers. The final slurry was further diluted. A porous uncoated wall-flow filter substrate, silicon carbide, (an average porosity of 63%, a mean pore size of 20 micrometers and 350 CPSI and 0.28 mm wall thickness, diameter: 58 mm*length: 140.5 mm, dimension (or cross section) inlet passages larger than those of outlet passages: asymmetry factor of about 1.35) was coated from the inlet end to the outlet end with the final slurry over 100% of the substrate axial length and a second time from 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 and a second time from the outlet end with the final slurry over 100% of the substrate axial length. Further a pressure pulse was applied on the inlet end to shoot out the slurry and distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 minutes and calcined at 450° C. for 2 hours (first coat). This was repeated once (second coat). The obtained coated substrate was then subjected to a final calcination at 600° C. for 30 minutes. The first coat loading represented 60% of the total catalyst loading after the final calcination and the second coat loading represented 40% of the total catalyst loading after the final calcination. The final coating loading after calcinations in the catalyst was of 1.95 g/in.sup.3, including 1.71 g/in.sup.3 of Chabazite, 0.059 g/in.sup.3 of copper calculated as CuO, and 0.18 g/in.sup.3 of silica+alumina.

Comparative Example 2 Preparation of a Selective Catalytic Reduction Catalyst not According to the Present Invention Using Sucrose

[0587] Slurry 1:

[0588] It was prepared as slurry 1 of Comparative Example 1.

[0589] Slurry 2:

[0590] It was prepared as slurry 2 of Comparative Example 1.

[0591] Subsequently, slurries 1 and 2 were combined. A powder of sucrose was added and dissolved in the obtained slurry, obtaining a final slurry. The solid content of the final slurry was adjusted to 34 weight-%. The final slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 4 micrometers. The final slurry was further diluted. A porous uncoated wall-flow filter substrate, silicon carbide, (an average porosity of 63%, a mean pore size of 20 micrometers and 350 CPSI and 0.28 mm wall thickness, diameter: 58 mm*length: 140.5 mm, dimension (or cross section) inlet passages larger than those of outlet passages: asymmetry factor of about 1.35) was coated from the inlet end to the outlet end and a second time from 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 and the second time the substrate was dipped in the final slurry from the outlet end until the slurry arrived at the inlet side of the substrate. Further a pressure pulse was applied on the inlet end to shoot out the slurry and distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 minutes and calcined at 450° C. for 2 hours (first coat). This was repeated once (second coat). The obtained coated substrate was then subjected to a final calcination at 600° C. for 30 minutes. The first coat loading represented 60% of the total catalyst loading after the final calcination and the second coat loading represented 40% of the total catalyst loading after the final calcination. The final coating loading after calcinations in the catalyst was of 1.95 g/in.sup.3, including 1.71 g/in.sup.3 of Chabazite, 0.059 g/in.sup.3 of copper calculated as CuO, and 0.18 g/in.sup.3 of alumina+silica.

Example 1 Preparation of a Selective Catalytic Reduction Catalyst with In-Wall Coating and On-Wall Coating Using Particles of Carbon Black

[0592] Slurry 1:

[0593] It was prepared as slurry 1 in Comparative Example 1.

[0594] Slurry 2:

[0595] It was prepared as slurry 2 in Comparative Example 1.

[0596] Slurry 3:

[0597] A powder of carbon black (with a Dv10 of about 0.4 micrometers, a Dv50 of about 1.45 micrometers, a Dv90 of about 5.1 micrometers and a Dv99 of about 15.7 micrometers, a BET specific surface area of about 7-12 m.sup.2/g) was dispersed in deionized water for 30 minutes forming an aqueous slurry having a solid content of 35 weight-%. The amount of carbon black was calculated such that it was 10 weight-% based on the weight of the Cu-Chabazite+alumina-silica.

[0598] Subsequently, slurries 1 and 2 were combined. Finally, slurry 3 was added. The solid content of the obtained slurry was adjusted to 37 weight-% and was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 4 micrometers. Subsequently, acetic acid was added to the obtained slurry. The amount of acetic acid was calculated such that it was 1 weight-% based on the weight of the Cu-Chabazite. The solid content of the final slurry was adjusted to 34 weight-%. The final slurry was further diluted. A porous uncoated wall-flow filter substrate, silicon carbide, (an average porosity of 63%, a mean pore size of 20 micrometers and 350 CPSI and 0.28 mm wall thickness, diameter: 58 mm*length: 140.5 mm, dimension (or cross section) inlet passages larger than those of outlet passages: asymmetry factor of about 1.35) was coated from the inlet end to the outlet end and a second time from 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 and the second time the substrate was dipped in the final slurry from the outlet end until the slurry arrived at the inlet side of the substrate. Further a pressure pulse was applied on the inlet end to shoot out the slurry and distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 minutes and calcined at 450° C. for 2 hours (first coat). This was repeated once (second coat). The obtained coated substrate was then subjected to a final calcination at 600° C. for 30 minutes (in order to burn off the carbon black completely). The first coat loading represented 60% of the total catalyst loading after the final calcination and the second coat loading represented 40% of the total catalyst loading after the final calcination. The final coating loading after calcinations in the catalyst was of 1.95 g/in.sup.3, including 1.71 g/in.sup.3 of Chabazite, 0.059 g/in.sup.3 of copper calculated as CuO and 0.18 g/in.sup.3 of silica+alumina.

Example 2 Backpressure Evaluation

[0599] The backpressure of the catalysts obtained in Comparative Examples 1 and 2 and Example 1 was measured on a Superflow device that was adapted for the measurements of cores with 58 mm in diameter. The backpressure data was recorded at a volume flow of 100 m.sup.3/h and reported in FIG. 1. As may be taken from FIG. 1, the backpressure obtained with the catalyst of Example 1 was of about 98 mbar while the backpressures obtained with the catalysts of Comparative Examples 1 and 2 were of about 101 mbar and of about 103 mbar, respectively. The lower back pressure of the catalyst prepared according to Example 1 compared to the catalyst prepared according to Comparative Example 1 showed that the presence of carbon black lowers the backpressure of a coated diesel particle filter. Taking the enhanced backpressure of the catalyst prepared according to Comparative Example 2 into account allows to conclude that this effect cannot be reached with an organic substance that dissolves in the slurry. Thus, Example 2 demonstrates that the presence of particles of carbon black during the preparation of the catalytic coating permits to decrease the backpressure of the obtained catalyst.

Example 3 Preparation of Selective Catalytic Reduction Catalysts with In-Wall and On-Wall Coatings Using Particles of Synthetic Graphite

[0600] Slurry 1:

[0601] 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 in the coating after calcination was of 3.5 weight-%, calculated as CuO, 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 2.5 micrometers and the Dv90 value of the particles was about 9 micrometers. The resulting slurry had a solid content of 5 weight-%. An aqueous zirconium acetate solution was added to the CuO-containing mixture 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 Chabazite. Separately, a Cu-Chabazite with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite (Dv50 of 20 micrometers, a SiO.sub.2:Al.sub.2O.sub.3 of 25, a primary crystallite size of less than 0.5 micrometer and a BET specific surface area of about 600 m.sup.2/g) was added to water to form a mixture having a solid content of 34 weight-%. 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 84.5% of the loading of the coating after calcination. The resulting slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 3.5 micrometers.

[0602] Slurry 2:

[0603] Separately, an aqueous slurry having a solid content of 30 weight-% and comprising alumina (Al.sub.2O.sub.3 94 weight-% with SiO.sub.2 6 weight-% having a BET specific surface area of 173 m.sup.2/g, a Dv90 of about 18 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 Cu-Chabazite. Tartaric acid was added to the aqueous slurry. The amount of tartaric acid was calculated such that it was 0.7 weight-% based on the weight of the alumina-silica.

[0604] Slurry 3:

[0605] For each catalyst (3a-3e), a powder of synthetic graphite was dispersed in deionized water for 30 minutes forming an aqueous slurry having a solid content of 35 weight-%. The amount of synthetic graphite was calculated such that it was from 10 to 20 weight-% based on the weight of the starting Cu-Chabazite (with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite)+alumina-silica (see Table 1 below).

TABLE-US-00001 TABLE 1 Dv10 Dv50 Dv90 Particles Particles (microme- (microme- (microme- Catalysts of (wt.-%*) ters) ters) ters) 3 a Synthetic 10 3.3 7.7 14.9 graphite 3 b Synthetic 20 3.3 7.7 14.9 graphite 3 c Synthetic 10 5.1 16.6 42.6 graphite 3 d Synthetic 20 5.1 16.6 42.6 graphite 3 e Synthetic 15 3.5 11 27.2 graphite *based on wt. of the starting Cu-Chabazite + silica-alumina.

[0606] Subsequently, slurry 1 and slurry 2 were combined. Finally, slurry 3 was added. The obtained slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about Dv90 of 8 micrometers. Subsequently, acetic acid was added to the obtained slurry. The amount of acetic acid was calculated such that it was 2.9 weight-% based on the weight of the starting Cu-Chabazite (with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite). The solid content of the final slurry was adjusted to 34 weight-%. The final slurry was further diluted. 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 wall thickness, diameter: 36.6 mm*length: 150.5 mm, dimension (or cross section) inlet passages larger than those of outlet passages: asymmetry factor about 1.25) 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 shoot out the slurry and distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 minutes and calcined at 450° C. for 2 hours (first coat). This was repeated once (second coat). The obtained coated substrate was then subjected to a final calcination at 750° C. for 30 minutes (in order to burn off the synthetic graphite completely). The final coating loading in the catalyst after calcination was 2.2 g/in.sup.3. The first coat loading represented 60% of the total catalyst loading after the final calcination and the second loading 40% of the total catalyst loading after the final calcination.

[0607] The SEM images were collected as described in Reference Example 3 herein and are displayed in FIGS. 4a-b and 5a-b. As may be taken from the SEM images, the catalytic coating of the catalyst of Examples 3b and 3d was disposed as in-wall coating and as on-wall-coating. The SEM images were analyzed, it was calculated that for sample 3a, there were about 40% of the coating onto the surface of the porous internal walls. Thus, the I(on-wall coating):I(in-wall coating) ratio is of about 40:60. For sample 3b, it was calculated that there were about 32% of the coating onto the surface of the porous internal walls. Thus, the ratio I(on-wall coating):I(in-wall coating) ratio is of about 32:68. Finally, for sample 3d, it was calculated that there were about 37% of the coating onto the surface of the porous internal walls. Thus, the ratio I(on-wall coating):I(in-wall coating) ratio is of about 37:63. In view of the SEM images and FIG. 10 (Hg intrusion), without wanting to be bound to any theory, it is believed that the particles of synthetic graphite used according to the present invention block the pores of the porous internal walls of the wall-flow filter substrate to a large extent so that the catalytic coating may not enter completely within the porous internal walls and the remainder of said catalytic coating is deposited on the surface of the porous internal walls. The fractions of on-wall coating and in-wall coating were determined as defined in Reference Example 5 in order to calculate the I(on-wall coating):I(in-wall coating) ratios.

[0608] According to Hg intrusion as determined in Reference Example 4 herein above, it was calculated that for the catalyst of Example 3b, 25.6% of the pores of the in-wall coating of said catalyst had a mean pore size in the range of from 1 to 16 micrometers and that 6.0% of the pores of the in-wall coating of said catalyst had a mean pore size in the range of from 0.01 to 1 micrometer. It was also calculated that for the catalyst of Example 3b, 20.6% of the pores of the in-wall coating of said catalyst had a mean pore size in the range of from 1 to 16 micrometers.

Comparative Example 3 Preparation of a Selective Catalytic Reduction Catalyst not According to the Present Invention without Using Particles of a Carbon-Containing Additive

[0609] Slurry 1:

[0610] It was prepared as slurry 1 in Example 3.

[0611] Slurry 2:

[0612] It was prepared as slurry 2 in Example 3.

[0613] Subsequently, slurries 1 and 2 were combined obtaining a final slurry. The solid content of the final slurry was adjusted to 34 weight-%. Subsequently, acetic acid was added to the obtained slurry. The amount of acetic acid was calculated such that it was 2.9 weight-% based on the weight of the starting Cu-Chabazite (with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite). The final slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 8 micrometers. The final slurry was further diluted. 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 wall thickness, diameter: 36.6 mm*length: 150.5 mm, dimension (or cross section) inlet passages larger than those of outlet passages: asymmetry factor of about 1.25) 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 shoot out the slurry and distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 min and calcined at 450° C. for 2 hours (first coat). This was repeated once (second coat). The obtained coated substrate was then subjected to a final calcination at 800° C. for 30 minutes. The final coating loading in the catalyst after calcinations was 2.2 g/in.sup.3. The first coat loading represented 60% of the total catalyst loading after the final calcination and the second loading 40% of the total catalyst loading after the final calcination.

Example 4 Backpressure Evaluation—Porosity Evaluation

[0614] The backpressure of the fresh catalysts 3a-3e obtained according to Example 3 was measured on an in-house constructed device. The catalytic filters are mounted in a holder that is adapted individually for each filter diameter and sealed air tight. Air-is pumped with a compressor (K04-MS MOR IE2) through the sample, the air flow is adjusted with a vacuum valve. The pressure drop is measured with a pressure sensor (SD8000). The backpressure data recorded at a volume flow of 27 m.sup.3/h was reported in FIG. 2.

[0615] As may be taken from FIG. 2, the catalysts 3a-3e of Example 3 according to the present invention prepared by using particles of synthetic graphite permit to reduce the backpressure compared to the catalyst of Comparative Example 3 which was prepared without particles of synthetic graphite. In particular, reduction of the backpressure was observed for the catalysts with a Dv50 of 7.7 micrometers and 16.6 micrometers but was stronger for the catalysts containing particles with a Dv50 of 16.6 micrometers. Furthermore the backpressure was reduced when using catalysts according to the present invention, wherein the particles of a carbon-containing additive were present in an amount of 10 weight-% and 20 weight-% based on the weight of Cu-zeolite+alumina-silica in said catalysts. Thus, this demonstrates that the catalysts according to the present invention permits to reduce the backpressure. The porosity of the fresh catalysts 3a-3e obtained according to Example 3 was measured with Hg intrusion with an AutoPore V instrument in the range 0.1-61000 psia with a Hg temperature of 23-25° C. The results are displayed on FIG. 3. The data plotted on the y axis of FIG. 3 showed the cumulated Hg intrusion in the range of 3 micrometers to 30 micrometers. As may be taken from FIG. 3, the porosimetry data shows that the Hg intrusion increases with poreformer content.

Comparative Example 4 Preparation of a Selective Catalytic Reduction Catalyst not According to the Present Invention without Using Particles of a Carbon-Containing Additive

[0616] The catalyst of Comparative Example 4 was prepared as the catalyst of Comparative Example 3, except that the final coating loading in the catalyst after calcinations was of 1.8 g/in.sup.3. The SEM images were collected as described in Reference Example 3 herein and are displayed in FIGS. 6a-6b. According to said images, the catalytic coating of the selective catalytic reduction catalyst of Comparative Example 3 is almost completely within the porous internal walls of the substrate.

Example 5 Preparation of a Selective Catalytic Reduction Catalyst with In-Wall Coating and On-Wall Coating Using Particles of Synthetic Graphite

[0617] The catalyst of Example 5 was prepared as the catalyst of Example 3a, except that the final coating loading in the catalyst after calcinations was of 1.8 g/in.sup.3. The SEM images were collected as described in Reference Example 3 herein and are displayed in FIGS. 7a-7b. According to said figures, the catalytic coating of the selective catalytic reduction catalyst of Example 5 is present as in-wall coating and as on-wall coating. The SEM images were analyzed, it was calculated that about 21% of the coating was onto the surface of the porous internal walls. Thus, the I(on-wall coating):I(in-wall coating) ratio is of about 21:79.

Comparative Example 5 Preparation of a Selective Catalytic Reduction Catalyst not According to the Present Invention without Using Particles of a Carbon-Containing Additive

[0618] Slurry 1:

[0619] 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 after calcination was of 3.5 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 2.5 micrometers and the Dv90 value of the particles was about 9 micrometers. The resulting slurry had a solid content of 5 weight-%. An aqueous zirconium acetate solution was added to the CuO-containing mixture 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 Chabazite. Separately, a Cu-Chabazite with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite (Dv50 of 20 micrometers, a SiO.sub.2:Al.sub.2O.sub.3 of 25, a primary crystallite size of less than 0.5 micrometer and a BET specific surface area of about 600 m.sup.2/g) was added to water to form a mixture having a solid content of 34 weight-%. 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 84.5% of the loading of the coating after calcination. The resulting slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 3.5 micrometers.

[0620] Slurry 2:

[0621] Separately, an aqueous slurry having a solid content of 30 weight-% and comprising alumina (Al.sub.2O.sub.3 94 weight-% with SiO.sub.2 6 weight-% having a BET specific surface area of 173 m.sup.2/g, a Dv90 of about 18 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 Cu-Chabazite. Tartaric acid was added to the aqueous slurry. The amount of tartaric acid was calculated such that it was 0.7 weight-% based on the weight of the alumina-silica.

[0622] Subsequently, slurries 1 and 2 were combined obtaining a final slurry. The solid content of the final slurry was adjusted to 34 weight-%. The final slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 8 micrometers. The final slurry was further diluted. 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 wall thickness, diameter 58 mm*length: 150.5 mm, dimension (or cross section) inlet passages larger than those of outlet passages: asymmetry factor of about 1.25) 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 outlet end to shoot out the slurry and a further pressure pulse was applied on the inlet end to distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 minutes and calcined at 450° C. for 2 hours (first coat). This was repeated once (second coat). The obtained coated substrate was then subjected to a final calcination at 800° C. for 30 minutes. The final coating loading after calcinations in the catalyst was 2.2 g/in.sup.3. The first coat loading represented 60% of the total catalyst loading after the final calcination and the second loading 40% of the total catalyst loading after the final calcination.

Example 6 Preparation of a Selective Catalytic Reduction Catalyst with In-Wall and On-Wall Coatings Using Particles of Polymethylurea

[0623] Slurry 1:

[0624] It was prepared as slurry 1 of Comparative Example 5.

[0625] Slurry 2:

[0626] It was prepared as slurry 2 of Comparative Example 5.

[0627] Slurry 3:

[0628] Separately, a powder of polymethylurea (having a Dv50 of 11 micrometers, a Dv90 of 19 micrometers, density 1.18 g/cm.sup.3, flame point 160° C. (melting) and ignition temperature 200° C. (boiling)) was dispersed in deionized water for 30 minutes forming an aqueous slurry having a solid content of 35 weight-%. The amount of polymethylurea was calculated such that it was 6.2 weight-% based on the weight of the starting Cu-Chabazite (with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite)+alumina-silica.

[0629] Subsequently, slurry 1 and slurry 2 were combined. Finally, slurry 3 was added. The obtained slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 8 micrometers. Subsequently, acetic acid was added to the obtained slurry. The amount of acetic acid was calculated such that it was 3 weight-% based on the weight of the starting Cu-Chabazite (with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite). The solid content of the final slurry was adjusted to 31 weight-%. The final slurry was further diluted. 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 wall thickness, diameter: 58 mm*length: 150.5 mm, dimension (or cross section) inlet passages larger than those of outlet passages: asymmetry factor of about 1.25) 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 outlet end to shoot out the slurry and a further pressure pulse was applied on the inlet end to distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 minutes (first coat). The coating was repeated once, the obtained coated substrate was dried at 110° C. for 30 minutes, then heated to 170° C. with a heating rate of 300° C./h and subsequently heated to 590° C. with a heating rate of 60° C./h. Lastly, the catalyst was calcined at 590° C. for 1 hour (second coat) such that the polymethylurea was removed. The final coating loading after calcinations in the catalyst was 2.2 g/in.sup.3. The first coat loading represented 60% of the total catalyst loading after the final calcination and the second loading 40% of the total catalyst loading after the final calcination.

[0630] The SEM images were collected as described in Reference Example 3 herein and are displayed in FIGS. 8a-8b. These images were analyzed and it was calculated that there were about 21% of the coating onto the surface of the porous internal walls. Thus, the I(on-wall coating):I(in-wall coating) ratio was of about 21:79.

Example 7 Preparation of a Selective Catalytic Reduction Catalyst with In-Wall and On-Wall Coatings Using Particles of Polymethyl Methacrylate

[0631] Slurry 1:

[0632] It was prepared as slurry 1 of Comparative Example 5.

[0633] Slurry 2:

[0634] It was prepared as slurry 2 of Comparative Example 5.

[0635] Slurry 3:

[0636] Separately, a powder of polymethyl methacrylate (PMMA) (Dv10 of 10.04 micrometers, Dv50 of 10.3 micrometers, Dv90 of 10.56 micrometers, density 1.2 g/cm.sup.3, flame point 280° C. and ignition temperature 450° C.) was dispersed in deionized water for 30 minutes forming an aqueous slurry having a solid content of 35 weight-%. The amount of PMMA was calculated such that it was 10 weight-% based on the weight of the starting Cu-Chabazite (with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite)+alumina-silica. Subsequently, slurry 1 and slurry 2 were combined. Finally, slurry 3 was added. The obtained slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 8 micrometers. Subsequently, acetic acid was added to the obtained slurry. The amount of acetic acid was calculated such that it was 3 weight-% based on the weight of the starting Cu-Chabazite (with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite). The solid content of the final slurry was adjusted to 31 weight-%. The final slurry was further diluted. 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 wall thickness, diameter: 58 mm*length: 150.5 mm, dimension (or cross section) of inlet passages larger than those of outlet passages: asymmetry factor about 1.25) 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 outlet end to shoot out the slurry and a further pressure pulse was applied on the inlet end to distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 minutes (first coat). The coating was repeated once, the obtained coated substrate was dried at 110° C. for 30 minutes, then heated to 170° C. with a heating rate of 300° C./h and subsequently heated to 590° C. with a heating rate of 60° C./h. Lastly, the catalyst was calcined at 590° C. for 1 hour (second coat) such that the PMMA was removed. The final coating loading after calcinations in the catalyst was 2.2 g/in.sup.3. The first coat loading represented 60% of the total catalyst loading after the final calcination and the second loading 40% of the total catalyst loading after the final calcination.

[0637] According to Hg intrusion as determined in Reference Example 4 herein above, it was calculated that 25% of the pores of the in-wall coating had a mean pore size in the range of from 1 to 16 micrometers and that 6.0% of the pores of the in-wall coating of said catalyst had a mean pore size in the range of from 0.01 to 1 micrometer.

Example 8 Backpressure Evaluation

[0638] The backpressure of the fresh catalysts of Examples 6, 7 and of Comparative Example 5 was measured on an engine bench with a VW MLB 140 kW Euro 6 engine, under the following conditions: V.sub.I=40 m.sup.3/h at 215° C., V.sub.I=45 m.sup.3/h at 540° C. and 75 m.sup.3/h at 650° C. The results are displayed in FIG. 9. As may be taken from FIG. 9, the catalyst of Example 6, prepared by a process using particles of polymethylurea, exhibits a backpressure of 92 mbar at 215° C., of 181 mbar at 540° C. and of 298 mbar at 600° C. and the catalyst of Example 7, prepared by a process using particles of polymethyl methacrylate (PMMA), exhibits a backpressure of 83 mbar at 215° C., of 168 mbar at 540° C. and of 283 mbar at 600° C. In contrast thereto, the catalyst of Comparative Example 5 exhibits higher backpressures, namely backpressures of 94 mbar, 90 mbar and 318 mbar at 215, 540 and 600° C., respectively. Thus, Example 8 demonstrates that the use of particles of a carbon-containing polymer in a process for preparing a selective catalytic reduction catalyst on a filter permits to reduce the backpressure of a coated filter.

Comparative Example 6 Preparation of a Selective Catalytic Reduction Catalyst not According to the Present Invention

[0639] The catalyst of Comparative Example 6 was prepared as the catalyst of Comparative Example 1 except that the filter substrate was a porous uncoated wall-flow filter substrate, silicon carbide, (an average porosity of 63%, a mean pore size of 20 micrometers, 350 cpsi and 0.28 mm wall thickness, diameter: 38.1 mm x length: 140.5 mm).

Example 9 Preparation of Selective Catalytic Reduction Catalysts Comprising Two Coatings

[0640] First Coating:

[0641] Slurry 1:

[0642] A Cu-Chabazite with a Cu content of 3.3 weight-%, calculated as CuO, based on the weight of the Chabazite (Dv50 of 20 micrometers and a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 25, primary crystallite size of less than 0.5 micrometer and a BET specific surface area of about 600 m.sup.2/g) was added to and water forming a slurry. The solid content of the obtained slurry was adjusted to 40 weight-%. The resulting slurry was milled using a continuous milling apparatus so that the Dv50 value of the particles was about of about 5 micrometers.

[0643] Slurry 2:

[0644] An aqueous slurry having a solid content of 30 weight-% and comprising alumina (Al.sub.2O.sub.3 94 weight-% with SiO.sub.2 6 weight-% having a BET specific surface area of 173 m.sup.2/g, a Dv90 of about 5 micrometers) was prepared. The amount of alumina+silica was calculated such that it was 10 weight-% based on the weight of the Cu-Chabazite. Tartaric acid was added to the aqueous slurry. The amount of tartaric acid was calculated such that it was 0.7 weight-% based on the weight of the alumina-silica.

[0645] Subsequently, slurries 1 and 2 were combined obtaining a final slurry. The solid content of the final slurry was adjusted to 34 weight-%. The final slurry was milled using a continuous milling apparatus so that the Dv90 value of the particles was of about 4 micrometers. The final slurry was further diluted. A porous uncoated wall-flow filter substrate, silicon carbide, (an average porosity of 63%, a mean pore size of 20 micrometers, 350 cpsi and 11 mil (0.28 mm) wall thickness, diameter: 38.1 mm x length: 140.5 mm, dimension (or cross section) of inlet passages larger than those of outlet passages: asymmetry factor about 1.35) was coated from the inlet end to the outlet end of the substrate 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 shoot out the slurry and distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 minutes and calcined at 450° C. for 2 hours (first coat loading representing 60% of the first coating loading after calcination). The obtained substrate was coated from the outlet end to the inlet end over 100% of the substrate axial length with the method described above, dried at 130° C. for 30 minutes and calcined at 450° C. for 2 hours (second coat loading representing 40% of the first coating loading after calcination). The final loading of the first coating (first+second coats) after calcinations in the catalyst was of about 1.95 g/in.sup.3, including 1.77 g/in.sup.3 of Cu-Chabazite, 0.177 g/in.sup.3 of alumina-silica.

[0646] Second Coating:

[0647] Slurry 1: Slurry 1 of the second coating was prepared as slurry 1 of Example 3.

[0648] Slurry 2: Slurry 2 of the second coating was prepared as slurry 2 of Example 3.

[0649] Slurry 3:

[0650] For each catalyst (9a-9e), a powder of synthetic graphite was dispersed in deionized water for 30 minutes forming an aqueous slurry having a solid content of 35 weight-%. The amount of synthetic graphite was calculated such that it was from 20 to 50 weight-% based on the weight of the starting Cu-Chabazite (with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite)+alumina-silica depending on the catalyst (see Table 2 below).

TABLE-US-00002 TABLE 2 Dv10 Dv50 Dv90 Particles (microme- (microme- (microme- Catalysts Type Wt.-%* ters) ters) ters) 9a Synthetic 50 5.1 16.6 42.6 graphite 9b Synthetic 20 5.1 16.6 42.6 graphite 9c Synthetic 50 5.1 16.6 42.6 graphite 9d Synthetic 35 3.5 11 27.2 graphite 9e Synthetic 50 3.3 7.7 14.9 graphite 9f Synthetic 20 3.3 7.7 14.9 graphite *based on the weight of the starting Cu-Chabazite + alumina-silica.

[0651] Subsequently, slurry 1 and slurry 2 were combined. Finally, slurry 3 was added. The obtained slurry was milled with a continuous milling apparatus so that the Dv90 value of the particles was of about 8 micrometers. Subsequently, acetic acid was added to the obtained slurry. The amount of acetic acid was calculated such that it was 1 weight-% based on the weight of the starting Cu-Chabazite (with a Cu content of 1.25 weight-%, calculated as CuO, based on the weight of the Chabazite). The solid content of the final slurry was adjusted to 31 weight-%. The substrate coated with the first coating was then coated from the outlet end to the inlet end of the substrate over 100% of the substrate axial length. To do so, the substrate was dipped in the final slurry for the second coating, which was beforehand further diluted, from the outlet end until the slurry arrived at the top of the substrate. Further a pressure pulse was applied on the outlet end to shoot out the slurry and distribute it evenly in the substrate. Further, the coated substrate was dried at 130° C. for 30 minutes and calcined at 450° C. for 1 hour. Further, it was calcined at 750° C. for 30 minutes (to burn off completely the particles of synthetic graphite). The final loading of the second coating after calcination was from 0.1 to 0.3 g/in.sup.3 depending on the catalyst (9a-9e), the loadings are displayed in Table 3 below.

TABLE-US-00003 TABLE 3 Loading of the second Examples coating (g/in.sup.3) 9a 0.1 9b 0.3 9c 0.3 9d 0.2 9e 0.1 9f 0.3

[0652] The final coating loading after calcinations in the catalyst was from 2.05 to 2.25 g/in.sup.3.

Example 10 Performance Evaluation of the Catalysts of Example 9 and of the Catalyst of Comparative Example 6—NOx Conversion

[0653] The catalysts of Example 9 (9a-9e) and the catalyst of Comparative Example 6 were aged for 16 hours at 800° C. (10% H.sub.2O, 20% O.sub.2, 70% N.sub.2). The NOx conversion was measured in a reactor at 500 ppm NO, with a NH.sub.3/NOx ratio of 1.5, 10% O.sub.2, 5% CO.sub.2, 5% CO.sub.2, 5% H.sub.2O and 80 ppm CH.sub.3 at a temperature of 200° C. at two different space velocities, namely 40 k and 80 k, in 500 ppm NO with an NSR=1.5 (NH.sub.3 to NOx ratio), 10% O.sub.2, 5% CO.sub.2, 5% H.sub.2O, 80 ppm C.sub.3H.sub.6. The results are displayed on FIG. 12. As may be taken from FIG. 12, the NOx conversions of the catalysts 9a-9e according to the present invention are in the range of from 71.5 to 83% while the NOx conversion of the catalyst of Comparative Example 6 is 67.8%. In particular, the catalyst 9d which as a total coating loading of 2.05 g/in.sup.3 exhibits a NOx conversion of 83% which is more than 15% higher than the NOx conversion of the catalyst of Comparative Example 6. Thus, Example 10 demonstrates that the use of a carbon-containing additive when preparing a selective catalytic reduction catalyst on a filter permits to obtained catalysts exhibiting improved NOx conversion compared to catalysts prepared without such an additive.

BRIEF DESCRIPTION OF THE FIGURES

[0654] FIG. 1 shows the backpressure obtained with the catalysts of Example 1 and of Comparative Examples 1 and 2.

[0655] FIG. 2 shows the backpressure obtained with the catalysts 3a-3e of Example 3.

[0656] FIG. 3 shows the porosimetry via Hg intrusion in the range 3 μm-30 μm with the catalysts of Example 3.

[0657] FIG. 4a shows SEM image of the selective catalytic reduction catalyst of Example 3b (Magnification: 50×) obtained as described in Reference Example 3.

[0658] FIG. 4b shows SEM image of the selective catalytic reduction catalyst of Example 3b (Magnification: 300×) obtained as described in Reference Example 3.

[0659] FIG. 5a shows SEM image of the selective catalytic reduction catalyst of Example 3d (Magnification: 50×) obtained as described in Reference Example 3.

[0660] FIG. 5b shows SEM image of the selective catalytic reduction catalyst of Example 3d (Magnification: 500×) obtained as described in Reference Example 3.

[0661] FIG. 6a shows SEM image of the selective catalytic reduction catalyst of Comparative Example 4 (Magnification: 50×) obtained as described in Reference Example 3.

[0662] FIG. 6b shows SEM image of the selective catalytic reduction catalyst of Comparative Example 4 (Magnification: 300×) obtained as described in Reference Example 3.

[0663] FIG. 7a shows SEM image of the selective catalytic reduction catalyst of Example 5 (Magnification: 50×) obtained as described in Reference Example 3.

[0664] FIG. 7b shows SEM image of the selective catalytic reduction catalyst of Example 5 (Magnification: 500×) obtained as described in Reference Example 3.

[0665] FIG. 8a shows SEM image of the selective catalytic reduction catalyst of Example 6 (Magnification: 120×) obtained as described in Reference Example 3.

[0666] FIG. 8b shows SEM image of the selective catalytic reduction catalyst of Example 6 (Magnification: 500×) obtained as described in Reference Example 3.

[0667] FIG. 9 shows the backpressure obtained with the catalysts of Examples 6, 7 and of Comparative Example 5.

[0668] FIG. 10 shows the cumulative Hg intrusion measured for the catalysts of Examples 3b, 3d, 3e and 5 and of Comparative Example 3. The mercury intrusion in the range of 3 to 30 micrometers was strongly enhanced for the catalysts according to the present invention prepared with carbon graphite particles compared to the catalyst not according to the present invention prepared without such carbon graphite particles. The effect was observed for catalysts prepared with carbon graphite particles of three different particles size (a Dv50 of 7.7 micrometers, 11 micrometers and 16.6 micrometers) and with different washcoat loadings of 2 g/in.sup.3 and 2.2 g/in.sup.3.

[0669] FIG. 11 shows the cumulative Hg intrusion measured at the inlet end and at the middle of the substrate for the catalysts of Examples 6 and 7 and of Comparative Example 5. Similarly as for the catalysts according to the present invention prepared with carbon graphite particles, the mercury intrusion in the range of 3 to 30 micrometers was enhanced the catalysts according to the present invention prepared with particles of carbon containing organic polymers (PMMA and polymethylurea) compared to the catalyst not according to the present invention prepared without such particles. Further, for the catalyst prepared with PMMA, the mercury Intrusion in the range 0.2 micrometer to 10 micrometers was enhanced as well.

[0670] FIG. 12 shows the NOx conversions of the catalysts 9a-9e of Example 9 and of the catalyst of Comparative Example 6 at 200° C.