One-pot synthesis of vanadium-containing silica SBA-3 materials and their catalytic activity for propene oxidation

V-containing silica SBA-3 mesoporous catalysts were prepared by means of one-pot hydrothermal procedure with NH4VO3 or VOSO4 as vanadium precursors under various acidic medium of the reaction mixture (pH < 1, 2.2 or 3.1). The combined spectral techniques (DR UV-vis, FTIR, EPR) as well H-2-TPR allowed to determine the nature of vanadium species in the studied samples. A successful incorporation of vanadium into the structure of silica SBA-3 was attained for the samples with low V content (< 1 wt%), whereas the V-rich samples (i.e. >5 wt%) exhibited the presence of isolated vanadium and also of polynuclear surface species. The resulting V-bearing samples contain the Bronsted and Lewis acidic centres evidenced by FTIR spectra of adsorbed pyridine and by catalytic activity for 2-propanol decomposition and cumene cracking. Ammonia TPD allowed to estimate the number and strength of acid sites in regards to the vanadium content. Propene oxidation with N2O revealed noticeable activity of the synthesised V-SBA-3 samples in epoxidation reaction. On the basis of TOF analysis indicating the activity of particular vanadium ions it seems that not all of the introduced V atoms take part in the formation of mild electrophilic oxygen species responsible for propene oxide formation.