Adsorptive and Catalytic Properties of Alumina-Supported Pd–Mo Catalysts

The adsorption properties of ethanol, CO, and NO on Pd, Mo, and Pd–20Mo/Al2O3 catalysts were studied using TPD and IR techniques as well as the reactions of NO+CO and ethanol+NO. The presence of Pd favored decomposition and dehydrogenation of ethanol, while Mo presented activity for oxidative dehydrogenation. The Pd–Mo catalyst showed better formation of N2 on TPD of NO, probably due to the NO adsorption on partially reduced molybdenum oxide. DRIFT results for the NO+CO reaction on the Pd–20Mo catalyst exhibited bands which correspond to nitrate or nitrous complexes and hydroxyl groups besides NCO species. MoO3 addition to a Pd/Al2O3 catalyst favored the formation of acetaldehyde at lower temperatures. A redox mechanism was proposed to explain the molybdenum promotional effect on Pd in the CO+NO reaction, evidencing Mo as promoter when the reducible oxide reacts with NO. However, molybdenum oxide does not promote the ethanol+NO reaction and this may be due to different reaction mechanisms.