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

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 H-2 as well as Re L-3- and L-1-edge X-ray absorption near edge structure (XANES) analysis revealed that the valency of the Re species started to decrease upon H-2 reduction in the 200-400 degrees C range, except for Re on MgO, where the shift occurred at temperatures above 500 degrees C. The dependence of the Re L-3- and L-1-edge XANES spectra of the oxide-supported Re catalysts on the size of Re was also examined.