Reversible Structure Transformation of Antimony Oxides on SiO2Relevant to Selective Catalytic Oxidation of Ethanol

Abstract

Sb/SiO2 catalysts were prepared by chemical vapor deposition of Sb(OEt)3 on a SiO2 surface followed by water vapor admission and calcination. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectra, and X-ray absorption fine structure and by catalytic performance for selective oxidation of ethanol. At low loadings (2−4 wt %) Sb(OEt)3 reacted with surface OH groups on the SiO2 surface to form surface-attached Sb(III) species. At high Sb loadings (>5 wt %), in addition to the attached Sb(III) species, crystalline Sb2O3 species were formed after exposure to water vapor. The amount of crystalline Sb2O3 species increased with Sb loading, and 30−50% of Sb species existed as crystalline Sb2O3 at 7−12 wt %. Most of the Sb(III) species remained trivalent after calcination. On the other hand, the crystalline Sb2O3 was oxidized to Sb(V) and spread on the SiO2 surface. The spread antimony oxide species were active for selective catalytic oxidation of ethanol through a redox mechanism. When ...