Tungsten catalysts supported on activated carbon were used in the isomerization reaction of 1-butene. The results obtained were compared with those of other tungsten catalysts supported on Al2O3, SiO2, and TiO2. When the catalysts supported on activated carbon were pretreated in He flow, at either 623 or 748 K, the activity to produce isobutene increased linearly with the surface acidity of the catalysts, and the specific activity after pretreatment at 623 K was higher than that after pretreatment 748 K. The activity to produce isobutene did not decrease with reaction time and no dimerization by-products were obtained. After the pretreatments at 973 and 1223 K, there was a loss of activity with reaction time, and by-products from the dimerization of butenes appeared. The presence of water vapor in the reaction mixture was also studied. The catalysts supported on Al2O3, SiO2, and TiO2 and pretreated under the same conditions, at both 623 and 748 K, showed a decrease in activity to produce isobutene with reaction time and the catalyst supported on Al2O3 was the most active. Results show the importance of the support in these kinds of catalysts and seem to indicate that the activated carbon, due to its surface basicity, moderates the surface acidity of the tungsten oxide particles. Therefore, with a lower surface acidity of the catalyst it has an activity similar to that found with the Al2O3-W catalysts but without deactivation. (C) 2000 Academic Press.