Charge polarization induced site preferences phenomena of ethylene hydrogenation via electronic metal support interactions

Abstract

The catalytic activity of supported catalyst is closely related to the electronic metal-support interactions (EMSI). In this paper, first principles density functional theory study was conducted to understand the EMSI between Pd clusters (Pd4, Pd7, Pd10) and CeO2 substrate. When Pd was loaded on CeO2 surface, the electrons of Pd would transfer to the CeO2 substrate via Pd-O bonding interactions. Moreover, the charge redistribution on the Pd cluster leads to significant polarization of electron density. Consequently, the Pd atoms located at the metal-support interface (IF site) are positively charged, while the Pd atoms at the topmost (T site) are negatively charged. The H2 dissociation and ethylene hydrogenation at these sites were calculated with both low and high hydrogen coverage. It was found that the two types of sites should collaborate synergically to promote the hydrogenation of ethylene. In particular, the IF sites exhibit relatively high activity for H2 dissociation, while the T sites show superior catalytic efficiency for ethylene hydrogenation. Therefore, the EMSI induced charge polarization can tune the electronic structure and charge state of supported metal catalysts, which further determines the performance of different region on the catalyst.