SCR catalyst for the treatment of an exhaust gas of a diesel engine

Abstract

An SCR catalyst for treating diesel exhaust gas has: a flow-through substrate with 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 flow through substrate extending therethrough; a first coating disposed on the internal wall surface of the substrate, the surface defining the interface between the internal walls and passages, the first coating extending over 40 to 100% of the substrate axial length, the first coating having an 8-membered ring pore zeolitic material with copper and/or iron; a second coating extending over 20 to 100% of the substrate axial length, the second coating having a first oxidic material with titania, wherein at least 75 wt. % of the second coating is titania, calculated as TiO.sub.2, and 0 to 0.01 wt. % of the second coating is vanadium oxides, calculated as V.sub.2O.sub.5.

Claims

1. A selective catalytic reduction catalyst suitable for treating an exhaust gas of a diesel engine, the catalyst comprising: (i) a flow through 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 flow through substrate extending therethrough; (ii) a first coating disposed on a surface of the internal walls of the substrate, the surface defining an interface between the internal walls and the passages, the first coating extending over 40 to 100% of the substrate axial length, and comprising an 8-membered ring pore zeolitic material comprising copper and/or iron; (iii) a second coating extending over 20 to 100% of the substrate axial length, the second coating comprising a first oxidic material comprising titania, the second coating comprising at least 75 wt. % titania, calculated as TiO.sub.2, and from 0 to 0.01 wt. % vanadium oxide(s), calculated as V.sub.2O.sub.5, wherein in the catalyst, the first coating has a total loading (L1) and the second coating has a total loading (L2), wherein the ratio of the total loading of the first coating relative to the total loading of the second coating, (L1): (L2), is in the range of from 0.5:1 to 5:1.

2. The catalyst of claim 1, wherein the first coating extends over 75 to 100% of the substrate axial length.

3. The catalyst of claim 1, wherein the second coating extends over 75 to 100% of the substrate axial length.

4. The catalyst of claim 1, wherein the second coating disposed on the first coating.

5. The catalyst of claim 1, wherein the 8-membered ring pore zeolitic material in the first coating has a CHA, AEI, RTH, LEV, DDR, KFI, ERI, and/or AFX framework type.

6. The catalyst of claim 1, wherein the zeolitic material in the first coating comprises copper.

7. The catalyst of claim 1, wherein in the framework structure of the zeolitic material in the first coating, the molar ratio of Si to Al, calculated as molar SiO.sub.2:Al.sub.2O.sub.3, is in a range of from 2:1 to 50:1.

8. The catalyst of claim 1, wherein the first coating further comprises an oxidic binder.

9. The catalyst of claim 1, wherein from 0 to 0.01 wt. %, of the first coating is titania.

10. The catalyst of claim 1, wherein the titania in the first oxidic material of the second coating has a tetragonal crystal system and/or an orthorhombic crystal system.

11. The catalyst of claim 1, wherein the first oxidic material of the second coating further comprises cerium oxide, magnesium oxide, niobium oxide, silicon oxide, and/or tungsten oxide.

12. The catalyst of claim 1, wherein the second coating further comprises a second oxidic material comprising silica, alumina, zirconia, and/or ceria.

13. The catalyst of claim 1, wherein the first coating extends over 75 to 100% of the substrate axial length, from the inlet end toward the outlet end of the substrate.

14. The catalyst of claim 1, wherein the first coating extends over 75 to 100% of the substrate axial length, from the outlet end toward the inlet end of the substrate.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1: shows the SCR inlet and outlet temperatures and exhaust mass flows operated for 30 minutes in the WHTC test cycle (world harmonized test cyclehot phase) at which the converted NOx and the N.sub.2O make for the catalysts of Example 1 and Comparative Examples 1 and 2 have been measured and calculated.

(2) FIG. 2: shows the NOx converted and N.sub.2O formation (in g/kWh) obtained with the catalysts of Example 1 (fresh and aged), Comparative Example 1 (fresh) and Comparative Example 2 (aged), respectively, under transient test cycle conditions (WHTCworld harmonized test cyclehot phase) under real exhaust gas conditions.

(3) FIG. 3: shows the SCR inlet and outlet temperatures and exhaust mass flows operated for 30 minutes in the WHTC test cycle (world harmonized test cyclehot phase) at which the converted NOx and the N.sub.2O make for the catalysts of Example 3 and Comparative Examples 3 and 4 have been measured and calculated.

CITED LITERATURE

(4) Yisun Cheng et al., Sulfur tolerance and DeSO.sub.x studies on diesel SCR catalysts, SAE International Journal Fuels and Lubricants 1(1), pages 471-476, 2008

(5) Krishna Kamasamudram et al., N.sub.2O formation and mitigation in diesel after-treatment systems, Cummins Inc., SAE International Journal Engines 5(2), pages 688-698, 2012

(6) Ashok Kumar et al., Effect of transition metal ion properties on the catalytic functions and sulfation behavior of zeolite-based SCR catalysts, SAE International Journal Engines 10(4), pages 1604-1612, 2017

(7) U.S. Pat. No. 8,293,199 B2

(8) U.S. Pat. No. 5,047,378 B

(9) CN 105 944 755 A