The reducibility and oxidation states of oxide-supported rhenium: experimental and theoretical investigations

Abstract

The activity and stability of supported metal catalysts, which exhibit high efficiency and activity, are significantly influenced by the interactions between the metal and the support, that is, metal–support interactions (MSIs). Here, we report an investigation of the MSIs between supported rhenium (Re) and oxide supports such as TiO₂, SiO₂, Al₂O₃, MgO, V₂O₅, and ZrO₂ using experimental and computational approaches. The reducibility of the Re species was found to strongly depend on the oxide support. Experimental studies including temperature-programmed reduction by H₂ as well as Re L₃- and L₁-edge X-ray absorption near edge structure (XANES) analysis revealed that the valency of the Re species started to decrease upon H₂ reduction in the 200–400 °C range, except for Re on MgO, where the shift occurred at temperatures above 500 °C. The dependence of the Re L₃- and L₁-edge XANES spectra of the oxide-supported Re catalysts on the size of Re was also examined.