Catalytic hydroxylation of benzene over vanadium-containing molecular sieves

Abstract

Vanadium-containing molecular sieves with mesopore structures such as MCM-41 and MCM-48, and micropore structures such as BEA and MFI were synthesized by hydrothermal method. XRD, FT-IR, UV–Vis DRS, EPR and XANES were used to characterize their structure, electronic states, and active sites of vanadium species. All the vanadium containing molecular sieves exhibit a pre-edge peak in the V K-edge XANES. The charge transfer transition bands appear at 250 and 340 nm are attributed to the [V VO] 3+ species in the tetrahedral framework position and in the surface wall, respectively. Upon calcining the as-synthesized vanadium-containing samples in the air, V IV species are oxidized to V V which is EPR silent. V V is reduced reversibly by dehydration at 723 K. As for catalytic hydroxylation of benzene, V-MCM-41 shows the highest activity where the turnover number is 64 h −1 at 343 K. Under the higher temperature and the higher acidic conditions, respectively, the catalytic activity is enhanced.