Zirconium dioxide based catalysts were synthesized by mechanical mixing method and evaluated for the direct synthesis of isobutene and isobutane (i-C-4) from CO hydrogenation. The experiments of temperature-programmed desorption of ammonia and carbon dioxide indicated that both the amount of acid-base sites and the strength of acid and base of the catalysts varied with the incorporation of promoters including various calcium salts, Al2O3 and KOH in ZrO2. The test results indicated that the activity and selectivity of the zirconia based catalysts depended on the acid-base properties of the catalysts. An appropriate amount of moderately strong acid-base sites and ratio of basic to acidic sites on the catalysts are significant for an active catalyst to selectively produce isobutene and isobutane from CO hydrogenation. (C) 2002 Elsevier Science Ltd. All rights reserved.