The one-step synthesis of MIBK from acetone in gas phase was studied over palladium catalysts on NaX zeolite (1 and 3 wt% of Pd). A greater selectivity to MIBK was observed for a H-2/acetone ratio of 6.2. Although increasing the reaction temperature caused an increase of the selectivity to condensation products, the temperature for which the selectivity to MIBK was maximum was the lower one (523 K). Decreasing the reduction temperature from 633 to 573 K for PdNaX enhanced the hydrogenation activity and decreased MIBK selectivity. Selectivities to MIBK as high as 80% were obtained. (C) 2009 Elsevier B.V. All rights reserved.