Low temperature selective catalytic reduction catalyst and associated systems and methods

• US 8,491,845 B2
• Filed: 09/10/2010
• Issued: 07/23/2013
• Est. Priority Date: 09/10/2009
• Status: Active Grant

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Ettireddy, Padmanabha Reddy, Henrichsen, Matthew
• Primary Examiner(s): Duong, Tom
• Application Number:
  US12/879,776
• Publication Number:
  US 20110058999A1
• Time in Patent Office: 1,047 Days
• Field of Search: 422/177, 422/180
• US Class Current: 422/177
• CPC Class Codes: B01D 2251/206 Ammonium compounds
• CPC Class Codes: B01D 2255/2073 Manganese
• CPC Class Codes: B01D 2255/20761 Copper
• CPC Class Codes: B01D 2255/20784 Chromium
• CPC Class Codes: B01D 53/9418 for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• CPC Class Codes: B01D 53/9477 with catalysts positioned on separate bricks, e.g. exhaust systems
• CPC Class Codes: B01J 23/20 Vanadium, niobium or tantalum
• CPC Class Codes: B01J 23/24 Chromium, molybdenum or tungsten
• CPC Class Codes: B01J 23/34 Manganese
• CPC Class Codes: B01J 23/50 Silver
• CPC Class Codes: B01J 23/72 Copper
• CPC Class Codes: B01J 23/74 Iron group metals
• CPC Class Codes: B01J 37/0215 Coating
• CPC Class Codes: B01J 37/0244 Coatings comprising several layers
• CPC Class Codes: F01N 13/0093 the purifying devices are of the same type
• CPC Class Codes: F01N 2560/06 the means being a temperature sensor
• CPC Class Codes: F01N 3/035 with catalytic reactors , e.g. catalysed diesel particulate filters
• CPC Class Codes: F01N 3/2053 By-passing catalytic reactors, e.g. to prevent overheating
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: F01N 9/00 Electrical control of exhaust gas treating apparatus monitoring or diagnostic devices for exhaust-gas treatment apparatus F01N11/00; conjoint electrical control of two or more combustion engine functions F02D43/00
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 : Engine management systems

Abstract

According to one embodiment, described herein is an exhaust gas after-treatment system that is coupleable in exhaust gas stream receiving communication with an internal combustion engine. The exhaust gas after-treatment system includes a low temperature SCR catalyst configured to reduce NO_x in exhaust gas having a temperature below a temperature threshold. The system also includes a normal-to-high temperature SCR catalyst configured to reduce NO_x in exhaust gas having a temperature above the temperature threshold.

Claims

1. An exhaust gas after-treatment system coupleable in exhaust gas stream receiving communication with an internal combustion engine, comprising:

a low temperature selective catalytic reduction (SCR) catalyst configured to reduce NO_x in exhaust gas having a temperature below a temperature threshold;

a normal-to-high temperature SCR catalyst configured to reduce NO_x in exhaust gas having a temperature above the temperature threshold; and

an exhaust bypass valve configured to direct at least a portion of an exhaust gas stream through the low temperature SCR catalyst if a temperature of the exhaust gas stream is below the temperature threshold, and direct all of the exhaust gas stream through the normal-to-high temperature SCR catalyst if the temperature of the exhaust gas stream is above the temperature threshold.

2. The exhaust gas after-treatment system of claim 1, wherein the bypass valve is configured to direct all of the exhaust gas stream through the low temperature SCR catalyst if a temperature of the exhaust gas stream is below a minimum operating temperature of the normal-to-high temperature SCR catalyst, wherein the minimum operating temperature is lower than the temperature threshold.

3. The exhaust gas after-treatment system of claim 2, wherein the bypass valve is configured to incrementally decrease the amount of the exhaust gas stream flowing into the low temperature SCR catalyst from 100% to 0% of the exhaust gas stream as the temperature of the exhaust gas stream correspondingly increases from the minimum operating temperature to the temperature threshold.

4. The exhaust gas after-treatment system of claim 2, wherein the bypass valve is configured to incrementally decrease the amount of the exhaust gas stream flowing into the low temperature SCR catalyst from 0% to 100% of the exhaust gas stream as the temperature of the exhaust gas stream correspondingly decreases from the temperature threshold to the minimum operating temperature.

5. The exhaust gas after-treatment system of claim 1, wherein the temperature threshold comprises a degradation temperature of the low temperature SCR catalyst.

6. The exhaust gas after-treatment system of claim 1, wherein the bypass valve is positioned upstream of the low and normal-to-high temperature SCR catalysts, and wherein the low temperature SCR catalyst is positioned upstream of the normal-to-high temperature SCR catalyst.

7. The exhaust gas after-treatment system of claim 1, wherein the normal-to-high temperature SCR catalyst is positioned downstream of the low temperature SCR catalyst and receives all of the exhaust gas that flows through the low temperature SCR catalyst.

8. The exhaust gas after-treatment system of claim 1, wherein the low temperature SCR catalyst is positioned downstream of the normal-to-high temperature SCR catalyst and receives all of the exhaust gas that flows through the normal-to-high temperature SCR catalyst.

9. The exhaust gas after-treatment system of claim 1, wherein the temperature threshold is between about 150°

C. and about 250°

C.

10. The exhaust gas after-treatment system of claim 1, wherein the low temperature SCR catalyst comprises:

a carrier layer made from a material selected from the group consisting of TiO₂, Al₂O₃, SiO₂, ZrO₂, GaO₂, TiO₂—

Al₂O₃, TiO₂—

SiO₂, TiO₂—

GaO₂, TiO₂—

ZrO₂, CeO₂, CeO₂—

ZrO₂, Al₂O₃—

SiO₂, Al₂O₃—

ZrO₂, TiO₂—

SiO₂—

ZrO₂, and TiO₂—

Al₂O₃—

SiO₂; and

a catalytic layer coupled to the carrier layer, the catalytic layer being made from a material selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag, Ge, and Nb.

11. The exhaust gas after-treatment system of claim 10, wherein the combined carrier layer and catalytic layer are configured to reduce NO_x in an exhaust gas stream at an exhaust temperature between about 60°

C. and about 250°

C.

12. The exhaust gas after-treatment system of claim 10, wherein the carrier layer is made from TiO₂ and the catalytic layer is made from one of Mn, Cr, Cu, Co, Fe, V, and Ni.

13. The exhaust gas after-treatment system of claim 10, carrier layer is made from TiO₂ and the catalytic layer is made from Mn.

14. The exhaust gas after-treatment system of claim 10, wherein the carrier layer is made from TiO₂ and the catalytic layer is made from Cr.

15. The exhaust gas after-treatment system of claim 10, wherein the carrier layer is made from TiO₂ and the catalytic layer is made from Cu.

16. The exhaust gas after-treatment system of claim 10, wherein the combined carrier layer and catalytic layer are configured to reduce 100% of NO_x in an exhaust stream at an exhaust temperature less than about 175°

C.