Exhaust gas purifying catalyst for internal combustion engine

An exhaust gas purifying system for an internal combustion engine, comprising:

• an exhaust gas purifying catalyst disposed in an exhaust gas passage of the engine to remove an exhaust gas component, the exhaust gas purifying catalyst being a NOx trap catalyst of a type wherein NOx is adsorbed in an oxidation atmosphere and released in a reduction atmosphere;
• a concentration sensor disposed in the exhaust gas passage downstream of the exhaust gas purifying catalyst to detect a concentration of the exhaust gas component, the concentration sensor being a NOx sensor for detecting a concentration of NOx;
• and
• a control unit programmed to carry out
• detecting an activity transition time at which the exhaust gas purifying catalyst changes from an inactive state to an active state, in accordance with the concentration of the exhaust gas component detected by the concentration sensor, and
• judging a deterioration of the exhaust gas purifying catalyst at the activity transition time,
• accomplishing a compulsory sulfur poisoning releasing processing for the NOx trap catalyst after an initial judgment of the deterioration of the NOx trap catalyst,
• judging as to whether the NOx trap catalyst is subjected to a sulfur poisoning after a second judgment of the deterioration of the NOx trap catalyst and after the sulfur poisoning releasing processing, and
• generating a warning when the NOx trap catalyst is judged not to be subjected to the sulfur poisoning.

An exhaust gas purifying system for an internal combustion engine, comprising:

• an exhaust gas purifying catalyst disposed in an exhaust gas passage of the engine to remove an exhaust gas component;
• means for detecting a concentration of the exhaust gas component in the exhaust gas passage downstream of the exhaust gas purifying catalyst;
• means for detecting an activity transition time at which the exhaust gas purifying catalyst changes from an inactive state to an active state, based on the concentration of the exhaust gas component detected by the concentration detecting means;
• and
• means for judging a deterioration of the exhaust gas purifying catalyst at the activity transition time.

A method of purifying exhaust gas discharged from an internal combustion engine provided with an exhaust gas purifying catalyst disposed in an exhaust gas passage of the engine to remove an exhaust gas component, the exhaust gas purifying method comprising:

• detecting a concentration of the exhaust gas component in the exhaust gas passage downstream of the exhaust gas purifying catalyst;
• detecting an activity transition time at which the exhaust gas purifying catalyst changes from an inactive state to an active state, based on the detected concentration of the exhaust gas component;
• and
• judging a deterioration of the exhaust gas purifying catalyst at the activity transition time.