Acetylation of anisole on TPA/ZrO2

Abstract

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 methnol and calcination at 400 degrees 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/ZrO2), whereas the samples loaded with 10, 15 and 20wt% of TPA show two seperate phases; cubic phase of hydrogen tungsten phosphate hydrate and tetragonal phase of ZiO(2). 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 degrees C region participate in the reaction.