A comparative study of the activity and deactivation of alumina supported tungsten and molybdenum oxides was performed. The catalysts were prepared by impregnation on gamma- and alpha-thetaAl(2)O(3) and their activity, selectivity and deactivation during skeletal isomerization of 1-butene (380 degreesC, atmospheric pressure) was assessed. The catalysts were further characterized by means of temperature programmed reduction (TPR), X-ray diffraction (XRD), sortometry and laser Raman spectroscopy. The amount and nature of coke deposits produced during the reaction were determined by temperature programmed oxidation (TPO) and laser Raman spectroscopy.Best activity and selectivity values for both catalysts were obtained at intermediate W and Mo loadings which seemingly corresponded to an optimum concentration of surface tetrahedrally coordinated species. Tungsten supported catalysts performed better than molybdenum ones. When the support was alpha-thetaAl(2)O(3) the amount of coke was low but high calcination temperatures were needed to bum it off, because of its aromatic or pregraphitic nature. (C) 2003 Elsevier B.V. All rights reserved.