Close-coupled scr system

Patent metadata

Field	Value
Publication number	US-2016166990-A1
Application number	US-201314436811-A
Country	US
Kind code	A1
Filing date	Oct 17, 2013
Priority date	Oct 18, 2012
Publication date	Jun 16, 2016
Grant date	—

Abstract

A system for treating exhaust gases from a combustion engine and a method for using the same results in improved NO x conversion during engine startup. The system includes a compact SCR flow-through monolith installed upstream of a close-coupled SCR wall-flow filter, wherein the compact SCR flow-through monolith may be extruded or made of a thin-walled substrate, such that the SCR flow-through monolith has a smaller volume with lower heat capacity and higher catalyst loading relative to the SCR wall-flow filter.

First claim

What is claimed:

1 . A system for treating exhaust gases containing NO x from an engine, said system comprising:
a flow-through monolith having a first catalytic composition for selective catalytic reduction of NO x and having a first volume; a close-coupled particulate matter filter having a second catalytic composition for reduction of particulate matter and selective catalytic reduction of NO x and having a second volume; and a volume ratio of the first volume to the second volume of less than about 1:2, wherein said flow-through monolith is in fluid communication with, and incorporated upstream of, said particulate matter filter.

2 . The system of claim 1 , wherein the volume ratio is about 1:10 to about 1:2.

3 . The system of claim 1 , wherein the volume ratio is about 1:6 to about 1:4.

4 . The system of claim 1 , wherein said flow-through monolith is an extruded catalyst brick.

5 . The system of claim 4 , wherein said particulate matter filter is an inert substrate coated and/or impregnated with said second catalytic composition.

6 . The system of claim 5 , wherein said substrate is made primarily of either cordierite or metal.

7 . The system of claim 1 , wherein said flow-through monolith has a lower heat capacity relative to said particulate matter filter.

8 . The system of claim 1 , wherein said flow-through monolith has a lower specific heat capacity relative to said particulate matter filter.

9 . The system of claim 8 , wherein said flow-through monolith has a specific heat that is about 20 to about 80% of the specific heat capacity of said particulate matter filter.

10 . The system of claim 9 , wherein said flow-through monolith has a specific heat that is about 35 to about 65% of the specific heat capacity of said particulate matter filter.

11 . The system of claim 1 , wherein said first and second catalytic compositions comprise a base-metal promoted aluminosilicate or silioaluminophosphate molecular sieve.

12 . The system of claim 11 , wherein said flow-through monolith has an SCR catalyst loading greater than an SCR catalyst loading on said particulate matter filter.

13 . The system of claim 12 , wherein said flow-through monolith has an SCR catalyst loading of about 3 to 15 g/in 3 .

14 . The system of claim 1 , wherein said first and second catalytic compositions are different, provided that at least one of said first and second catalytic compositions comprise a base-metal promoted aluminosilicate or silioaluminophosphate molecular sieve.

15 . The system of claim 1 , wherein said second catalytic composition for selective catalytic reduction of NO is coated and/or impregnated on a downstream side of said particulate matter filter.

16 . The system of claim 1 , wherein said second catalytic composition for selective catalytic reduction of NO is coated and/or impregnated on an upstream side of said particulate matter filter.

17 . The system of claim 1 , wherein said particulate matter filter is about 0.01 to about 0.25 meters downstream of the flow-through monolith.

18 . The system of claim 17 , further comprising a source of reductant injection, in fluid communication with and disposed between said flow-through monolith and said particulate matter filter.

19 . A method for treating an engine exhaust gas stream containing NO x and soot comprising:
contacting said exhaust gas stream, in the presence of a reductant, with a flow-through monolith having a first SCR catalytic composition loading and a first volume to produce an intermediate gas stream wherein a first portion of said NO x has been converted to N 2 and O 2 ; contacting said intermediate gas stream with a close-coupled catalytic particulate matter filter having a second SCR catalytic composition loading and a second volume, wherein said second volume is at least about twice the first volume, to trap a portion of the soot and produce a clean gas stream wherein a second portion of said NO x has been converted to N 2 and O 2 ; oxidizing said portion of the soot at a soot oxidation temperature to regenerate the catalytic particulate matter filter; heating said catalytic close-coupled flow-through monolith to an SCR light off temperature before heating said catalytic particulate matter filter to an SCR light off temperature; and maintaining, under low load conditions, said soot oxidation temperature of the catalytic particulate matter filter for a longer period of time as compared to a catalytic particulate matter filter having a volume equal to said first and second volumes combined.

20 . The method of claim 19 , wherein said steps of contacting said exhaust gas stream and said contacting said intermediate gas stream have a higher conversion of said NO x as compared to a catalytic particulate matter filter having a volume equal to said first and second volumes combined and an SCR catalyst loading equal to said first and second loadings.

Assignees

• Johnson Matthey Plc

Inventors

• Phillips Paul Richard
• Wylie James Alexander

Classifications

• B01D2255/915

  Catalyst supported on particulate filters · CPC title

• F01N13/02

  having two or more separate silencers in series · CPC title

• F01N2330/06

  Ceramic, e.g. monoliths · CPC title

• F01N3/0222

  the structure being monolithic, e.g. honeycombs · CPC title

• F01N2610/02

  the substance being ammonia or urea · CPC title