Promotion Effect of Pt-Substituted Rh55 Cluster Toward NO Adsorption and Dissociation: A First-Principles Study

Abstract

NO adsorption and dissociation on cuboctahedral RhnPt55-n clusters, e.g. Rh55, Rh13@Pt12Rh30, and Rh13@Pt24Rh18, have been investigated using density functional theory. Our results indicated that the most stable site of NO adsorption on Rh55 cluster is the hcp threefold hollow site, while on Pt55, NO adsorption on the bridge site is favorable. For RhnPt55-n clusters, NO prefers to adsorb on the Rh atoms; when Pt atoms distribute around the Rh, the adsorption will be enhanced. The N–O bond of adsorbed NO was elongated, and the hollow site has a larger elongation, which origins to the great down-shift of 4σ orbital and up-shift of 1π orbital of adsorbed NO. NO dissociation on hcp site (H1) of Rh55 cluster needs to overcome an energy barrier of 1.36 eV. The dissociation on bridge site (B2) of Rh55 is much easier, whose energy barriers are 0.59 eV for direct dissociation and 0.56 eV for two-step reaction. When Pt atoms substituted the (100) terrace sites of Rh55, the energy barriers have decreased by 0.23 and 0.08 eV, respectively. While when Pt atoms substituted the edge sites, it needs to overcome higher energy barriers of 0.61 and 0.63 eV.