Acid sites and oxidation center in molybdena supported on tin oxide as studied by solid-state NMRspectroscopy and theoretical calculation

Abstract

Solid-state NMR spectroscopy and density functional theory (DFT) calculations were employed to study the structure and properties, especially the solid acidity, of molybdenum oxide supported on tin oxide. As demonstrated by solid-state NMR experiments, Mo species are mainly dispersed on the surface of SnO₂ support rather than significantly dissolved into the SnO₂ structure and Brønsted as well as Lewis acid sites are present on the MoO₃/SnO₂ catalyst. Acid strength of the supported metal oxide is stronger than those of zeolites, e.g., HY and HZSM-5, though the concentration of acid sites is relatively lower. The DFT calculated ¹³C chemical shift for acetone adsorbed on MoO₃/SnO₂ is in good agreement with the experimental value, which confirms our proposed structure of –Mo–(OH)–Sn– for the Brønsted acid site. Reducibility of the supported metal oxide is also demonstrated by solid-state NMR experiments and an active oxidation center of this catalyst is proposed as well.