Characterization of H3+xPMo12−xVxO40 heteropolyacids supported on HMS mesoporous molecular sieve and their catalytic performance in propene oxidation

Abstract

Materials, consisting of H3+xPMo12−xVxO40 heteropolyacids (HPAs) with x=0–3, supported on a HMS mesoporous pure-silica molecular sieve, have been prepared by means of dry impregnation method and characterized by elemental analysis, X-ray diffraction, transmission and diffuse reflectance (DR) FT-IR, Raman and X-ray photoelectron spectroscopies, nitrogen physisorption and thermal analysis (TG–DTA). The HPA/HMS compositions with HPA loadings from 10 to 50wt.% display uniformly sized mesopores. HPA retains the Keggin structure on the HMS surface and forms finely dispersed HPA species over the whole range of HPA loadings, crystal phases being absent even at 50wt.%. Results demonstrate that HPA/HMS exhibit a higher catalytic activity than bulk heteropolyacids in propene oxidation by molecular oxygen. Furthermore, the supported species allow for an enhanced oxidation catalytic activity (formation of acrolein, acetaldehyde and acetic acid) compared to the mother catalysts. The catalytic performance exhibited by H3+xPMo12−xVxO40/HMS catalysts was attributed to the fine dispersion of H3+xPMo12−xVxO40 species on the HMS mesoporous material via physical adsorption. The HPA/HMS systems, with strong acid sites, high redox power and a regular mesoporous distribution, are promising catalysts for the oxidative reactions.