Acetylation of anisole on TPA/ZrO2

摘要

Zirconia loaded with 5-20 wt% of tungstophosphoric acid (TPA) were prepared by suspending solid hydrous zirconia in methanolic TPA solution followed by evaporation of methanol and calcination at 400°C for 4 h.The product were characterized by X-ray diffraction,photoacoustic FTIR spectroscopy,and NH3-TPD.XRD results show the formation of single tetragonal phase of ZrO2 only for the sample loaded with 5wt% of TPA (5-TPA/Z1O2),whereas the samples loaded with 10,15 and 20wt% of TPA show two separate phases;cubic phase of hydrogen tungsten phosphate hydrate and tetragonal phase of ZrO2.The photoacoustic FTIR-spectra of pyridine chemisorbed catalysts show the existence of both Bronsted (BC) and Lewis (LC) acid sites.The intensity of Bronsted acid sites band (at 1535 cm~(-1)) and the intensity ratios of Bronsted to Lewis acid site bands increase with increased loading of TPA from 5 to 15 wt% and decrease with 20 wt% loading of TPA.This is correlating with catalytic yields (4-and 2-methoxy acetophenone) obtained for catalysts loaded with 5-20 wt% of TPA for the acetylation of anisole reaction with acetic anhydride.The results suggest that only the Bronsted acid sites of catalyst take part in the acetylation of anisole reaction.The NH3-TPD curves of above catalysts show that the 'strong' acid sites which are in the >450°C region participate in the reaction.