Effects of surface oxidation of Rh on CO-NO light-off process in three-way catalysts: A phenomenological oxide film formation and destruction model

The full-hybrid system with a spark ignition engine is essential for the future powertrain systems in passenger cars. However, many aspects of three-way catalysts remain unclear, necessitating urgent clarification. Simultaneously, modeling the phenomenon and establishing numerical prediction technology are required. The effect of surface oxidation after exposure in abundant O 2 surroundings encountered during not only fuel cut-off at deceleration, but also engine stop of HEV on the purification performance of Rh, which is one of the highest performing precious metals supported on three-way catalysts, was investigated by CO-O 2 light-off test and XPS analysis in the previous research. The light-off curve started to rise at higher temperature in the case of pretreatment in the lean atmosphere than in the rich atmosphere, and the results of XPS analysis showed that the reversible oxide film was formed in the lean atmosphere. In this study, the CO-NO light-off test was repeated twice after lean atmosphere pretreatment. The rise of the second light-off curve was significantly faster and almost coincided with the light-off curve after hydrogen reduction treatment, suggesting that the oxide film formed in the lean atmosphere may be decomposed during the CO-NO light-off test. By adding the reactions that describe the decomposition of oxide film by carbon and nitrogen adsorbed on the surface to the detailed surface reaction model developed in the previous research, CO-NO light-off on Rh surface were simulated and could reasonably reproduce the result of experimental results. Through this research, the phenomenological model of oxide film formation and decomposition on Rh surface and the effect of Rh oxidation to the purification performance have been proposed.