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 °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 °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.

Molybdovanadophosphoric acids supported zirconia (ZMVPA) is an efficient catalyst for phenol oxidation to hydroquinone and catechol. H2O2 reacts with ZMVPA to give hydroxyl radical through a redox mechanism, which attacks phenol ring to give hydroquinone and catechol as major products.Figure optionsDownload as PowerPoint slide