Potassium-promoted molybdenum oxide/alumina-zirconia catalysts were prepared by the sol-gel method. The catalysts were characterized by nitrogen physisorption, X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and Fourier transform spectroscopy measurements. It was observed that potassium addition did not drastically disturb the textural properties and led to a redispersion of the molybdenum oxides composed both of octahedral and tetrahedral structures. Molybdenum oxide mainly led to the formation of Bronsted acid centers while alumina-zirconia support contained Lewis acid centers. Potassium led to a decrease in the number of Bronsted acid centers rather than that of Lewis centers. (C) 2004 Elsevier B.V. All rights reserved.