Catalyst system for gasoline combustion engines, having three-way catalysts and SCR catalyst

Patent metadata

Field	Value
Publication number	US-10022672-B2
Application number	US-201515124481-A
Country	US
Kind code	B2
Filing date	Mar 11, 2015
Priority date	Mar 13, 2014
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

The present invention is directed to a catalyst system for the reduction of the harmful exhaust-gas constituents hydrocarbons (THC), carbon monoxide (CO), nitrogen oxides (NOx), and the environmentally detrimental secondary emissions ammonia (NH3) and nitrous oxide (N2O) of combustion engines operated using gasoline and to a corresponding method for exhaust-gas purification. The system is characterized by a particular arrangement of catalysts and is used in the case of engines which are operated with predominantly, on average, stoichiometric air/fuel mixtures. Here, a three-way catalyst produced in accordance with the current prior art is preferably installed in a close-coupled position. In the underfloor position, there is situated an SCR catalyst produced in accordance with the current prior art, followed by a further three-way catalyst produced in accordance with the current prior art. The three-way catalyst in the underfloor region furthermore has a lower oxygen-storing capacity than the close-coupled three-way catalyst.

First claim

The invention claimed is:

1. A catalyst system for reducing harmful exhaust gases from a vehicle having a gasoline combustion engine that is operated predominantly, on average, stoichiometrically, having, in the following sequence:
i) a three-way catalyst arranged close to the engine,
ii) an SCR catalyst arranged in the underfloor of the vehicle, the SCR catalyst having an NH 3 -storing capacity, and
iii) an additional three-way catalyst arranged downstream of the SCR catalyst,
wherein the additional three-way catalyst arranged downstream of the SCR catalyst has less oxygen-storing capacity in mg per liter of catalyst volume than an oxygen-storing capacity of the three-way catalyst close to the engine.

2. The catalyst system according to claim 1 , wherein
the three-way catalyst arranged downstream of the SCR catalyst comprises two different catalytic coatings lying one on top of the other.

3. The catalyst system according to claim 2 , wherein
a base catalytic coating of the three-way catalyst arranged downstream of the SCR catalyst has no oxygen-storing material.

4. The catalyst system according to claim 3 , wherein
the base catalytic coating has only palladium as a catalytically active metal.

5. The catalyst system according to claim 4 , wherein
a top catalytic coating of the three-way catalyst arranged downstream of the SCR catalyst has palladium and rhodium as the only catalytically active metals, and oxygen-storing material.

6. The catalyst system according to claim 1 , wherein
the SCR catalyst has no oxygen-storing material.

7. The catalyst system according to claim 1 , wherein
the SCR catalyst is positioned downstream of the three-way catalyst close to the engine by such a distance that, during a driving operation, a temperature of the SCR catalyst is 300° C. to 400° C.

8. A process for reducing harmful exhaust gases from a vehicle having a gasoline combustion engine that is operated predominantly, on average, stoichiometrically, comprising
passing the exhaust gas over a catalyst system according to claim 1 during a driving operation.

9. The catalyst system according to claim 1 , wherein
the oxygen-storing capacity of the three-way catalyst close to the engine makes up >50% of the oxygen-storing capacity of the catalyst system.

10. The catalyst system according to claim 1 , wherein
the oxygen-storing capacity of the three-way catalyst close to the engine makes up ≥60% of the oxygen-storing capacity of the catalyst system.

11. The catalyst system according to claim 1 , wherein
the oxygen-storing capacity of the three-way catalyst close to the engine makes up ≥70% of the oxygen-storing capacity of the catalyst system.

12. The catalyst system according to claim 1 , wherein
a ratio of the oxygen-storing capacity of the three-way catalyst arranged downstream of the SCR catalyst to the oxygen-storing capacity of the three-way catalyst arranged close to the engine is from 1:2 to 1:12.

13. The catalyst system according to claim 1 , wherein
a ratio of the oxygen-storing capacity of the three-way catalyst arranged downstream of the SCR catalyst to the oxygen-storing capacity of the three-way catalyst arranged close to the engine is from 1:2 to 1:7.

14. The catalyst system according to claim 1 , wherein
a ratio of the oxygen-storing capacity of the three-way catalyst arranged downstream of the SCR catalyst to the oxygen-storing capacity of the three-way catalyst arranged close to the engine is from 1:7 to 1:12.

Assignees

• Umicore Ag & Co Kg

Inventors

• Schoenhaber Jan
• Schmidt Marcus
• Adam Frank

Classifications

• B01D53/945

  characterised by a specific catalyst · CPC title

• B01J23/464

  Rhodium · CPC title

• Y02C20/10

  of nitrous oxide (N2O) · CPC title

• B01D2255/1023

  Palladium · CPC title

• B01D53/9409

  Nitrogen oxides · CPC title