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: 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.

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 has a total loading (L1) and the second coating has a total loading (L2), wherein a (L1):(L2) ratio of total loading of the first coating relative to the total loading of the second coating is in a range of from 0.5:1 to 5:1.

14. An exhaust gas treatment system configured for treating an exhaust gas stream exiting a diesel engine, the exhaust gas treatment system having an upstream end for introducing the exhaust gas stream into the exhaust gas treatment system, the system comprising: (A) a diesel oxidation catalyst comprising a coating disposed on a substrate; (B) the selective catalytic reduction catalyst of claim 1; wherein the diesel oxidation catalyst (A) is located upstream of the selective catalytic reduction catalysts (B), and optionally, a filter, located downstream of the diesel oxidation catalyst (A) and upstream of the selective catalytic reduction catalyst (B).

15. An exhaust gas treatment system configured for treating an exhaust gas stream exiting a diesel engine, the exhaust gas treatment system having an upstream end for introducing the exhaust gas stream into the exhaust gas treatment system, the system comprising: the catalyst of claim 1 as a first selective catalytic reduction catalyst, and a diesel oxidation catalyst, a second selective catalytic reduction catalyst; and wherein the diesel oxidation catalyst, a second selective catalytic reduction catalyst, an ammonia oxidation catalyst and/or a filter are located downstream of the first selective catalytic reduction.

16. A process for preparing a selective catalytic reduction catalyst, the process comprising: (a) preparing a first slurry comprising a source of a 8-membered ring pore zeolitic material, comprising copper and/or iron, and water; (b) disposing the first slurry on surface of a internal walls of a flow through substrate, the 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 substrate extending therethrough, the surface defining and interface between the internal walls and the passages, over 40 to 100% of the substrate axial length, to obtain a slurry-treated substrate; (c) drying the slurry-treated substrate to obtain a substrate comprising a first coating disposed thereon; (d) optionally, calcining the substrate comprising a first coating disposed thereon; (e) preparing a second slurry comprising a first oxidic material comprising titania, and water, the first oxidic material optionally comprising cerium oxide, magnesium oxide, niobium oxide, silicon oxide, and/or tungsten oxide; (f) disposing, over 20 to 100% of the substrate axial length, the second slurry on the substrate comprising a first coating disposed thereon to obtain a slurry-treated substrate; (g) drying the slurry-treated substrate, to obtain substrate comprising a first coating and a second coating disposed thereon; (h) calcining the substrate comprising the first coating and second coating thereon, the second coating comprises from 0 to 0.01 wt. % of vanadium oxide(s), calculated as V.sub.2O.sub.5, and at least 75 wt. % of titania, calculated as TiO.sub.2, to obtain the selective catalytic reduction catalyst.

17. The process of claim 16, wherein the preparing (a) comprises: (a.1) mixing an oxidic binder, with a 8-membered ring pore zeolitic material, comprising the copper and/or iron, and water, to obtain a first slurry; (a.2) milling the first slurry to a particle size Dv90 in a range of from 3 to 15 micrometers.

18. The process of claim 16, wherein the preparing (e) comprises: (e.1) mixing a first oxidic material comprising (i) titania, and optionally (ii) cerium oxide, magnesium oxide, niobium oxide, silicon oxide, and/or tungsten oxide, an organic dispersant, and water; (e.2) adjusting the pH, comprising adding an ammonium hydroxide solution, to a value in a range of from 3.0 to 7.0.

19. 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.

20. 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

[0302] 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 cycle—hot 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.

[0303] 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 (WHTC—world harmonized test cycle—hot phase) under real exhaust gas conditions.

[0304] 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 cycle—hot 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

[0305] 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

[0306] 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

[0307] 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

[0308] U.S. Pat. No. 8,293,199 B2

[0309] U.S. Pat. No. 5,047,378 B

[0310] CN 105 944 755 A