Structural and electronic feature evolution of Au-Pd bimetallic catalysts supported on graphene and SiO2 in H2 and O2

Abstract

The structure and electronic feature evolution of graphene (Gr)- and SiO2-supported Au-Pd bimetallic nanoparticles (NPs) in H2 and O2 at different temperatures were investigated with a series of techniques and DFT calculation method. It was found that a uniform Au-Pd alloy nanostructure was formed on Gr, while a Au@Pd core-shell structure was generated on SiO2. The formation of Au-Pd alloy nanostructure on Gr originates from a strong s-p-d hybridization among Au 5d6s, Pd 4d and Gr C 2p, which greatly facilitates the electron transfer among Au, Pd and Gr and enhances the reduction of palladium species. The higher stability of the geometric and electronic structures of Au-Pd NPs on Gr than on SiO2 in both H2 and O2 atmospheres below 100 °C results from the fact that Gr could timely supplement the electrons transferring to O2 from metallic species in O2-treatment process, but play a contrary role in H2-treatment process. Such unique geometric and electronic structures endow Au-Pd/Gr show higher catalytic activity than Au-Pd/SiO2 in selective oxidation of methanol to methyl formate. A further investigation of catalytic mechanism reveals that the activation of O2 is dominated by the methanol-assisted way on Au and Au-Pd alloy NPs, whereas the direct dissociation of O2 mainly occurs on Pd and Au@Pd NPs.