Theoretical investigation on the Au-anchor site in phosphate-doped Au/Al2O3 catalysts

Abstract

In order to clarify the Au-anchor site in phosphate-doped Al2O3 and investigate the mechanism of Au-stabilization by phosphate, density functional theory (DFT) calculations were carried out. We calculated Au atom adsorption onto three model surfaces, such as sAl2O3 (a stoichiometric Al2O3 surface), fPO-Al2O3 (an Al2O3 surface fully covered by phosphate), and pPO-Al2O3 (an Al2O3 surface partially covered by phosphate). The calculated results showed that the order of stability for Au atom adsorption onto these three model surfaces is Au/fPO-Al2O3 > Au/pPO-Al2O3 > Au/sAl2O3. When Au atom adsorbs to a phosphate-phosphate bridge site of fPO-Al2O3 surface, the stabilization of Au adsorption onto the surface is especially large (the adsorption energy of Au is -3.16 eV). This high stability of Au at the phosphate-phosphate bridge site is due to negative charge transfer from Au to Al2O3 surface, which makes Au-O bond more stable. Hence, we have concluded that "phosphate-phosphate bridge sites" anchor Au.