Preparation and characterization of mesoporous Ag/VO(x)-TiO2 employed for catalytic hydroxylation of benzene.

The V-based complex oxides were found to exhibit good catalytic reactivity for the selective oxidation of benzene to phenol. In order to understand the effect of the catalyst on the reaction, a series of Ag/VO(x)-TiO2 catalysts with different Ag loadings were prepared. Data from the X-ray diffraction (XRD), N2-adsorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS) showed the formation of complex oxides with phases of silver and vanadates, and the increased redox ability of vanadium species. The results from H2-TPR revealed that the addition of Ag promoted the reduction of vanadium species in the complex catalysts. The presence of Ag and Ag+ ions at the catalyst surface were proved independently by XPS measurements. The Ag and Ag+ ions also effectively strengthened the thermostability of the Ag/VO(x)-TiO2 catalyst, and the Ag species also made a strong contribution to the monodispersion of vanadium on the surface of the TiO2 carrier. The reactivity for the selective oxidation of benzene was evaluated by using a liquid-phase reaction unit, and was correlated with the surface redox property of the catalysts.