Effect of vanadium dispersion and of support properties on the catalytic activity of V-containing silicas

Two V-SBA-15 and V-MCF materials (containing about 2.5 wt.% vanadium) were prepared by direct synthesis and tested as catalysts in the decomposition of the most stable chlorinated-alkane, dichloromethane (a total oxidation reaction) and in the oxidative dehydrogenation (ODH) of propane (a partial oxidation reaction). Comparison was made with: (i) two V-SBA-15 and V-MCF materials prepared by “traditional” impregnation method and (ii) a non-porous V-SiO2 catalyst prepared by flame pyrolysis. All catalysts tested had a vanadium content of about 2.5 wt.%. Samples properties were investigated by means of complementary techniques (TEM, IR and DR UV–vis spectroscopies, N2 sorption at −196 °C) in order to find possible correlations between catalytic properties of the studied materials and their different physico-chemical features. It is shown that direct synthesis allows a better vanadium dispersion to be achieved, a feature that positively affects catalytic performances in both total and partial oxidations. The different porous networks of the SBA-15 and MCF supports also play an important role on catalytic activity: both V-SBA-15 samples gave better results in dichloromethane decomposition, whereas both V-MCF samples were more selective in propane ODH. The latter findings are ascribed to different molecules diffusion and residence time inside the channels of either SBA-15 or MCF networks.

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► V-SBA-15 and V-MCF prepared direct synthesis were tested as catalysts for oxidation reactions.
► Direct synthesis gives rise to better vanadium dispersion, with a beneficial effect on the catalytic properties.
► The different mesoporous networks of SBA-15 and MCF play a prominent role on catalytic activity.
► SBA-15 monodimensional mesoporous channels favour longer residence times of molecules, finally promoting their total oxidation.
► 3-D ultra-large pores of MCF favour diffusion, improving the propene selectivity in propane ODH.