Journal of Molecular Catalysis A-Chemical, Vol.279, No.1, 104-111, 2008
Hydroxylation of phenol over molybdovanadophosphoric acid modified zirconia
Molybdovanadophosphoric acid (MVPA) supported zirconia was synthesized by an incipient wetness impregnation method taking zirconium hydroxide and MVPA as the precursors. The neat and supported catalysts were calcined at 500 degrees C and characterized by nitrogen adsorption-desorption, X-ray powder diffraction, FTIR, UV-vis DRS, temperature programmed reduction (TPR) and Raman spectroscopy techniques. The 15 wt.% MVPA stabilizes the tetragonal phase of zirconia, which leads to an increase in surface area. The Keggin structure of MVPA remains unaltered up to 500 degrees C. The catalytic activities were evaluated for hydroxylation of phenol using H2O2 as the oxidant. Among all the promoted catalysts, 15 wt.% molybdovanadophosphoric acid supported zirconia exhibits highest catalytic activity in phenol hydroxylation, giving 49% conversion having 61% para selectivity. (c) 2007 Elsevier B.V. All rights reserved.