Preparation and characterization of Mesopoous VO x/SBA-16 and their application for the direct catalytic hydroxylation of benzene to phenol

Abstract

Vanadium oxide supported on mesoporous SBA-16 (VO x /SBA-16) catalysts have been prepared by the impregnation method and characterized by small-angle XRD, wide-angle XRD, TEM, N 2-physisorption, DRUV–vis, Raman spectrum and H 2-TPR. The VO x /SBA-16 catalysts retained the cubic cage-like pore structure of SBA-16. The dispersion and the nature of the vanadium species depend strongly on the V amount. At V loading of less than 3.6 wt%, isolated tetrahedral VO 4 is the main existence species that is highly dispersed in the pores of the support SBA-16. With the increase in V loading, the aggregation of isolated tetrahedral VO 4 species occurred to form polymerized VO 4 units. When the V loading was above 5.5 wt%, nanostructured V 2O 5 crystallites were formed besides aggregation of polymerized VO 4 units. VO x /SBA-16 with 7.3 wt% V showed excellent activity for the hydroxylation of benzene. The effect of reaction time, temperature and the amount of catalyst was investigated over VO x /SBA-16 (7.3 wt%) catalyst. The highest phenol yield and turnover number were 13.8% and 32.4, respectively, which were attributed to the formation of highly dispersed VO 4 species and polymerized VO 4 units. The TON and yield of phenol also increase in the presence of the V 2O 5 crystallites but its selectivity decreases.