NO Reduction by H2 on the Rh(111) and Rh(221) Surfaces: A Mechanistic and Kinetic Study

Periodic density functional theory (DFT) was used to investigate the selective catalytic reduction of NO by H-2 (H-2 SCR) on Rh(111) and stepped Rh(221) surfaces. The stepped Rh(221) surface exhibits a higher reactivity for NO reduction than the Rh(111) surface. NO dissociation on the Rh(221) surface exhibits almost no effect in the presence of H-2, whereas predosed H atoms slightly inhibit NO dissociation on Rh(111). Microkinetic calculations further predicted the product selectivity for H-2 SCR at different temperatures and pressures. It was found that, under ultrahigh-vacuum (UHV) conditions, NH3 is the only N-containing product on Rh(111), consistent with the experimental observations, whereas on the Rh(221) surface, N2O formation is predominant at low temperatures, and N-2 becomes main product above 480 K. Under near-atmospheric-pressure conditions, the product selectivity on the Rh(111) surface exhibits almost no change, whereas N2O is the dominant product on Rh(221) throughout the whole temperature range. The present study indicates that the NO dissociation activity and product selectivity are strongly dependent on both the Rh surface structure and the experimental conditions.