Different ratios of phosphomolybdic acid PMA supported on silica gel (1-30 wt%) and promoted with alkali metal hydroxide have been prepared by an impregnation method and calcinated at 350 degrees C for 4 h. The catalysts were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray diffraction, FT-IR spectroscopy and N-2 adsorption measurements. The surface acidity and basicity of the catalysts were determined by adsorption of pyridine and the dehydration-dehydrogenation of 2-propanol. The gas-phase esterification of acetic acid by ethanol was carried out in a conventional flow bed reactor. The results clearly revealed that among the PMA loading, the use of 10 wt% catalyst showed maximum yield of ethyl acetate. This catalyst also improved on addition of Na or K-hydroxide. These results were correlated with the structure and the acid-base properties of the prepared catalysts. (c) 2005 Elsevier B.V. All rights reserved.