Selective hydroxylation of benzene using dioxygen activated by vanadium-copper oxide catalysts supported on SBA-15

The vanadium and copper oxide species supported catalyst, VO_x/CuSBA-15, was synthesized to catalyze the hydroxylation reaction of benzene to form phenol using molecular dioxygen in the presence of ascorbic acid. A high yield of phenol was achieved at ca. 27% with the selectivity of nearly 100%. The VO_x/CuSBA-15 has two characteristics that it can selectively activate dioxygen molecules rather than H₂O₂, and it can selectively catalyze benzene hydroxylation to form phenol, but can hardly catalyze phenol for further oxidation under the same reaction conditions. Both copper and vanadium oxide species supported on a mesoporous silicate has a prominent catalytic performance toward the benzene hydroxylation reaction comparing to the other bi-transition metal oxides or monometallic catalysts on the same support. The results suggest that there might be a synergy between copper and vanadium oxide species on the support. It is believed that benzene hydroxylation over the VO_x/CuSBA-15 catalyst occurs through the hydroxyl radical pathway, and the catalytic activation of molecular oxygen to form hydroxyl radical would be a rate determining step.