The improvement in the performance of the NOx storage-reduction (NSR) catalyst with a direct-injection gasoline engine has been examined.

It has been clarified that H₂ has the ability to act as a higher reducing agent than CO for improve-ment of the NOx reduction efficiency by analyz-ing the relationship between the after-treatment configuration and NOx reduction. To produce H₂ on the NSR catalyst, the promotion of the water gas shift reaction (H₂O+CO = CO₂+ H₂) using ceria (CeO₂) was attempted. An increase in the ceria content in the NSR catalyst caused enhance-ment of the oxygen storage capacity (OSC).

The OSC-enhanced NSR catalyst during a rich spike period showed the characteristic of the production of high heat release and the generation of H₂. It was postulated that the high heat release would contribute to the activation of the precious metals on the catalyst.

This OSC-enhanced NSR catalyst showed that the NOx conversion was improved by 30% compared to the standard NSR catalyst by optimizing the rich spike conditions. With the combination of the OSC-enhanced NSR catalyst and the rich spike combustion, the desulfation was more significantly promoted by a rapid catalyst temperature rise.