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

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 50 wt.% 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 50 wt.%. 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.

Impregnation of H3+xPMo12−xVxO40 heteropolyacids (HPAs) with x = 0–3 on mesoporous HMS support leads to a good dispersion of HPAs species without destruction of the Keggin structure. The stabilization of polyanions by the support is caused by the formation of (SiOH2+)(H2+xPMo12−xVxO40−) surface species.Figure optionsDownload as PowerPoint slideHighlights
► HMS supported 20–50 wt.% H3+xPMo12−xVxO40H3+xPMo12−xVxO40 (x = 0–3) heteropolyacids (HPAs).
► Profound change in the morphology of HMS for a acid percentage above 30 wt.%.
► The breakdown of HPAs can be prevented at a pH <2 using the dry impregnation method.
► HPAs form (SiOH2+)(H2+xPMo12−xVxO40−) surface species finely dispersed on a support.
► In propene oxidation, supported HPAs provide better activity than the bulk HPAs.