Selective catalytic reduction catalyst on a filter substrate

Abstract

A selective catalytic reduction catalyst for the treatment of an exhaust gas stream of a passive ignition engine, the catalyst comprising a porous wall-flow filter substrate comprising an inlet end, an outlet end, a substrate axial length (w) 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 catalyst further comprises a first coating, said first coating extending over x % of the substrate axial length from the inlet end toward the outlet end of the substrate, x being in the range of from 10 to 100, wherein the first coating comprises copper and an 8-membered ring pore zeolitic material; wherein the catalyst further comprises a second coating, the second coating extending over y % of the substrate axial length from the outlet end toward the inlet end of the substrate, y being in the range of from 20 to 90, wherein the second coating comprises copper, and optionally an 8-membered ring pore zeolitic material; wherein the catalyst optionally further comprises a third coating; wherein x+y is at least 90; wherein y % of w from the outlet end toward the inlet end of the substrate define the outlet zone of the coated substrate and (100−y) % of w from the inlet end toward the outlet end of the substrate define the inlet zone of the coated substrate; wherein the ratio of the loading of copper in the inlet zone, Cu(in), calculated as CuO, relative to the loading of copper in the outlet zone, Cu(out), calculated as CuO, Cu(in):Cu(out), is less than 1:1.

Claims

1. A selective catalytic reduction catalyst for the treatment of an exhaust gas stream of a passive ignition engine, the catalyst comprising: a porous wall-flow filter substrate comprising an inlet end, an outlet end, a substrate axial length w 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 internal walls; wherein the catalyst further comprises a first coating, the first coating extending over x % of the substrate axial length from the inlet end toward the outlet end of the substrate, x ranges from 10 to 100, wherein the first coating comprises copper and an 8-membered ring pore zeolitic material; wherein the catalyst further comprises a second coating, the second coating extending over y % of the substrate axial length from the outlet end toward the inlet end of the substrate, y ranges from 20 to 90, wherein the second coating comprises copper, and optionally an 8-membered ring pore zeolitic material; wherein the catalyst optionally further comprises a third coating, at least 90 weight-% of thereof being comprised in the pores of the internal walls, the third coating extending over z % of the substrate axial length, z ranges from 95 to 100, wherein the third coating comprises copper and an 8-membered ring pore zeolitic material; wherein x+y is at least 90; wherein y % of w from the outlet end toward the inlet end of the substrate define the outlet zone of the coated substrate and (100−y) % of w from the inlet end toward the outlet end of the substrate define the inlet zone of the coated substrate; and wherein a ratio of the loading of copper in the inlet zone, Cu(in), calculated as CuO, relative to the loading of copper in the outlet zone, Cu(out), calculated as CuO, Cu(in):Cu(out), is less than 1:1.

2. The selective catalytic reduction catalyst of claim 1, wherein there is a gap between the first coating and the second coating, and wherein the gap extends over g % of the substrate axial length, g at most 10, wherein x+y+g=100.

3. The selective catalytic reduction catalyst of claim 1, wherein x+y=100, and wherein there is no gap between the first coating and the second coating.

4. The selective reduction catalyst of claim 1, wherein x ranges from 95 to 100 and wherein y ranges from 20 to 50, wherein x+y>100, or wherein there is an overlap of the first coating and the second coating over q % of the substrate axial length, q at most 50, wherein x+y−q=100.

5. The selective catalytic reduction catalyst of claim 1, wherein the zeolitic material contained in the first coating has a framework type chosen from CHA, AEI, RTH, LEV, DDR, KFI, ERI, AFX, a mixture of two or more thereof and a mixed type of two or more thereof; and wherein from 95 weight-% to 100 weight % of the framework structure of the zeolitic material consists of Si, Al, and O, wherein in the framework structure, the molar ratio of Si to Al, calculated as molar SiO.sub.2:Al.sub.2O.sub.3, ranges from 2:1 to 50:1, wherein %, of.

6. The selective catalytic reduction catalyst of claim 1, wherein the first coating further comprises a non-zeolitic oxidic material, wherein the non-zeolitic oxidic material comprises one or more of alumina, titania, silica, zirconia, ceria, and iron oxide; and wherein the first coating comprises the zeolitic material at a loading (I1)/(g/in.sup.3) and the non-zeolitic oxidic material at a loading (I2)/(g/in.sup.3), wherein the ratio of (I1) to (I2), (I1):(I2), ranges from 2:1 to 18:1.

7. The selective catalytic reduction catalyst of claim 1, wherein the first coating comprises copper in an amount, calculated as CuO, ranging from 0.5 weight-% to 7 weight-%, based on the weight of the zeolitic material of the first coating.

8. The selective catalytic reduction catalyst of claim 1, wherein the second coating comprises an 8-membered ring pore zeolitic material, wherein the zeolitic material has a framework type chosen from CHA, AEI, RTH, LEV, DDR, KFI, ERI, AFX, a mixture of two or more thereof and a mixed type of two or more thereof.

9. The selective catalytic reduction catalyst of claim 8, wherein the second coating further comprises a non-zeolitic oxidic material, and wherein the non-zeolitic oxidic material of the second coating comprises one or more of alumina, titania, silica, zirconia, ceria, and iron oxide.

10. The selective catalytic reduction catalyst of claim 8, wherein the second coating comprises copper in an amount, calculated as CuO, ranging from 2.5 weight-% to 15 weight-%, based on the weight of the zeolitic material of the second coating.

11. The selective catalytic reduction catalyst of claim 1, wherein from 98 weight-% to 100 weight % of the second coating consists of CuO.

12. The selective catalytic reduction catalyst of claim 1, wherein the second coating further comprises a non-zeolitic oxidic material, wherein the non-zeolitic oxidic material of the second coating comprises one or more of alumina, titania, silica, zirconia, ceria, and iron oxide; and wherein the weight ratio of the non-zeolitic oxidic material of the second coating to copper comprised in the second coating ranges from 0.1:1 to 5:1.

13. The selective catalytic reduction catalyst of claim 1, wherein the third coating extends over z % of the substrate axial length from the inlet end toward the outlet end or from the outlet end toward the inlet end.

14. The selective catalytic reduction catalyst of claim 13, wherein the zeolitic material of the third coating has a framework type chosen from CHA, AEI, RTH, LEV, DDR, KFI, ERI, AFX, a mixture of two or more thereof and a mixed type of two or more thereof; wherein the third coating further comprises an oxidic material; and wherein the third coating comprises the oxidic material at a loading ranging from 0.01 g/in.sup.3 to 0.4 g/in.sup.3.

15. The selective catalytic reduction catalyst of claim 13, wherein the third coating further comprises a non-zeolitic oxidic material, wherein the non-zeolitic oxidic material comprises one or more of alumina, titania, silica, zirconia, ceria, and iron oxide; and wherein the third coating comprises the zeolitic material at a loading (I1″)/(g/in.sup.3) and the non-zeolitic oxidic material at a loading (I2″)/(g/in.sup.3), wherein the ratio of (I1″) to (I2″), (I1″):(I2″), ranges from 2:1 to 18:1.

16. The selective catalytic reduction catalyst of claim 13, wherein the third coating comprises copper in an amount, calculated as CuO, ranging from 0.5 weight-% to 7 weight-%, based on the weight of the zeolitic material of the third coating.

17. The selective catalytic reduction catalyst of claim 1, wherein the ratio of the loading of copper in the inlet zone, Cu(in), calculated as CuO, relative to the loading of copper in the outlet zone, Cu(out), calculated as CuO, Cu(in):Cu(out), ranges from 0.30:1 to 0.95:1.

18. The selective catalytic reduction catalyst of claim 1, wherein the ratio of the loading of the zeolitic material in the outlet zone, I(out)/(g/in.sup.3), relative to the loading of the zeolitic material in the inlet zone, I(in)/(g/in.sup.3), I(out)/I(in), ranges from 0.9:1 to 1.1:1.

19. A process for preparing the selective catalytic reduction catalyst, comprising (a) providing an uncoated porous wall-flow filter substrate comprising an inlet end, an outlet end, a substrate axial length w 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 internal walls; (b) optionally providing an aqueous mixture comprising water, a source of copper and an 8-membered ring pore zeolitic material, disposing the mixture on the substrate provided in (a), over z % of the substrate axial length, with z ranging from 95 to 100, calcining the substrate comprising the mixture disposed thereon, obtaining the substrate comprising a third coating, wherein at least 90 weight-% of the coating are comprised in the pores of the internal walls of the substrate; (c) providing an aqueous mixture comprising water, a source of copper and an 8-membered ring pore zeolitic material, disposing the mixture on the substrate provided in (a), or on the substrate comprising a third coating obtained in (b), over x % of the substrate axial length from the inlet end toward the outlet end of the substrate, with x ranging from 10 to 100, calcining the substrate comprising the mixture disposed thereon, obtaining the substrate comprising a first coating, and optionally a third coating; (d) providing an aqueous mixture comprising water, a source of copper, and optionally an 8-membered ring pore zeolitic material, disposing the mixture on the substrate provided in (c), over y % of the substrate axial length from the outlet end toward the inlet end of the substrate, with y ranging from 20 to 90, calcining the substrate comprising the mixture disposed thereon, obtaining the substrate comprising a first coating, a second coating, and optionally a third coating; wherein x+y is at least 90; wherein y % of w from the outlet end toward the inlet end of the substrate define the outlet zone of the coated substrate and (100−y) % of w from the inlet end toward the outlet end of the substrate define the inlet zone of the coated substrate; wherein the ratio of the loading of copper in the inlet zone, Cu(in), calculated as CuO, relative to the loading of copper in the outlet zone, Cu(out), calculated as CuO, Cu(in):Cu(out), is less than 1:1.

20. An exhaust gas treatment system for treating an exhaust gas stream exiting a passive ignition engine, the exhaust gas treatment system having an upstream end for introducing the exhaust gas stream into the exhaust gas treatment system, wherein the exhaust gas treatment system comprises a selective catalytic reduction catalyst according to claim 1, and one or more of a diesel oxidation catalyst, a selective catalytic reduction catalyst, an ammonia oxidation catalyst, a NOx trap, and a particulate filter.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the NOx conversions obtained with the catalysts of Example 1 and of Comparative Example 1 at 200, 600 and 650° C.

(2) FIG. 2 shows the NH.sub.3 storage obtained with the catalysts of Example 1 and of Comparative Example 1 at 200° C.

(3) FIG. 3 shows the NOx conversions obtained with the catalysts of Examples 7 and 8 and of Comparative Example 3 at 200, 230, 600 and 650° C.

(4) FIG. 4 shows the NOx conversions obtained with the catalysts of Examples 10 to 12 and of Comparative Example 1 at 230° C.

(5) FIG. 5 shows the NOx conversions obtained with the catalysts of Example 10 and of Comparative Example 1 at 650° C.

CITED LITERATURE

(6) US 2015/0098870 A1

(7) WO 2017/178576 A1

(8) US 2018/0296979 A1