This work is concerned with the interaction between platinum and molybdenum oxide for Pt-MoO3/gamma-Al2O3 catalysts. Two types of characterization techniques were used: thermal analysis; and NO and H-2 desorption at programmed temperature. The results of thermal analysis as well as those of hydrogen desorption suggest bronze formation for catalysts with Mo. The NO desorption data show that Mo is the main responsible for the N-2 selectivity. The activity of the catalysts was evaluated with reduction of nitric oxide by carbon monoxide. A synergic behavior was observed between Pt and Mo. Product selectivity of the NO reduction by CO is function of the prevailing treatment and reaction conditions and suggests significant changes of surface sites during the reaction. (C) 2003 Elsevier B.V. All rights reserved.