Correlations of WO 3 species and structure with the catalytic performance of the selective oxidation of cyclopentene to glutaraldehyde on WO 3/TiO 2 catalysts

Abstract

A series of WO 3/TiO 2 catalysts were synthesized by ultrasonic impregnation method using as-prepared TiO 2 microspheres as support as a function of tungsten oxide species loading. The crystalline structure, molecular structure and the interaction with the support of the supported tungsten oxide phase were characterized by various techniques (scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and specific surface areas (BET)), and their effects on the catalytic performance in selective oxidation of cyclopentene to glutaraldehyde were investigated. It was found that highly dispersed WO 3 species were obtained on the surface of TiO 2, and only W(VI) oxidation state was present on the support. The WO 3/TiO 2 catalysts showed high catalytic activity for selective oxidation of cyclopentene to glutaraldehyde. The catalytic activity increased with the WO 3 loading, and reached maximum on the catalysts with the WO 3 loading of 15–20 wt%. The molecular structures of calcinated tungsten oxide phase were determined to be tetrahedral surface tungsten oxide species with the WO 3 loading below 20 wt%, and both Brönsted acid sites and Lewis acid sites were present on the surface of the catalysts. The strong support effect on the dispersion and molecular structure of WO 3 as well as the Brönsted acid observed in the present work may have important catalytic implication. Further increasing the WO 3 loading resulted in the decrease of catalytic performance of the catalyst, meanwhile the crystalline WO 3 nanoparticles were present on the surface of the support. These reactivity trends showed the influence of molecular structure of WO 3 on the surface of TiO 2 support on the selective oxidation activity of cyclopentene to glutaraldehyde.