Catalytic hydroxylation of benzene over vanadium-containing molecular sieves

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. (C) 2000 Elsevier Science B.V. All rights reserved.