The liquid-phase acylation of anisole using acetic anhydride was performed over 12 heteropoly acid of tungsten and molybdenum (PWM) modified zirconia (ZPWM). Catalysts with different PWM loadings (3-20 wt.%) were prepared by the incipient wetness impregnation method using mesoporous zirconia and 12-heteropolyacid of W and Mo. The samples calcined at 500 degrees C were characterized by chemical analysis, nitrogen adsorption-desorption, surface acid sites, powder X-ray diffraction patterns, Fourier transform infrared spectroscopy, UV-vis diffuse reflectance spectroscopy, P-31 nuclear magnetic resonance spectroscopy and electron probe microanalysis The sample promoted by 15 wt.% PWM was found to be the most active in the acylation reaction giving 89% conversion with 97% para-selectivity. The effect of temperature, molar ratio and catalyst amount on the conversion of acetic anhydride and anisole were studied in detail to optimize the process parameters. Reusability of the catalyst was also appraised. (C) 2008 Elsevier B.V. All rights reserved,