Patent ID: 7454900
Filing Date: 2008-11-25
Classification: B01D,F01N,F02D,Y02A,Y02T

Abstract:
1. Catalyst recovery method comprising: a rich step of bringing an exhaust gas flowing into an NOx storage reduction catalyst installed on an exhaust passage of a lean-burn internal combustion engine into a reducing atmosphere thereby to raise the temperature of said NOx storage reduction catalyst and to release sulfur oxides occluded in said NOx storage reduction catalyst; a lean step of bringing said exhaust gas flowing into said NOx storage reduction catalyst into an oxidative atmosphere thereby to lower the temperature of said NOx storage reduction catalyst; and a recovery step of executing said rich step and said lean step in an alternate manner thereby to recover sulfur poisoning of said NOx storage reduction catalyst; wherein the air fuel ratio of said exhaust gas flowing into said NOx storage reduction catalyst in at least one of said rich step and said lean step is controlled based on the length of at least one of said rich step and said lean step; and wherein the air fuel ratio of said exhaust gas flowing into said NOx storage reduction catalyst in said rich step is made lower than a predetermined rich air fuel ratio when the length of said rich step decreases.