Study on selective oxidation of isobutane over V2O5/SiO2 catalyst

V2O5/SiO2 catalyst samples were prepared by impregnation and sol-gel method, respectively. The surface composition, structure, chemisorbility and activity of V2O5/SiO2 were systematically studied by using XRD, IR, TPD and micro-reactor. The results showed that there exist Lewis base sites (V = O and V-O-V) and Lewis acid sites (V5+) on the surface of the catalyst. Isobutane can be chemisorbed on the terminal oxygen of Lewis base sites V = O bonds by one or two H atoms in -CH3. Isobutene can be chemisorbed on the terminal oxygen of Lewis base sites V = O and on the bridging oxygen in V-O-V bonds by two H atoms and one C atom in -CH3, or chemisorbed on Lewis acid sites V5+ by C = C bond. The main products of the selective oxidation of isobutane are isobutene, methylacrolein, methylacrylic acid and COx on the catalyst. The reaction of intermediate product isobutene adsorbed on Lewis acid sites V5+ with the adsorbed active oxygen on the same sites is the main reason for the formation of deeply oxidative product COx.