Characterization of Pd/MgO Catalysts: Role of Organometallic Precursor-Surface Interactions

Abstract Pd(acac) 2 was supported on a highly dehydroxylated and decarbonated magnesium oxide surface (MgO 500 ), on an untreated MgO surface (MgO AIR ), and on a silica (SiO 2 450 ). EXAFS and DRIFT data indicate that the organopalladium complex is adsorbed intact on all the surfaces, but its dispersion is dependent on the nature of the surface. On MgO 500 , dispersion at the molecular level occurs, in contrast to the formation of islands of multilayers on MgO AIR and SiO 2 450 . The final properties of the metal phase, formed by H 2 treatment at 500°C, are dependent on precursor–surface interactions. HRTEM analysis shows a narrow distribution of the metal particles centered at 0.6 nm on MgO 500 , and a wide diameter distribution around 6.1 and 9.9 nm on MgO AIR and SiO 2 450 , respectively. In the n -heptane dehydrocyclization at 500°C, the highest selectivity is shown by Pd/MgO 500 catalysts and it is consistent with a predominant fraction of very small particles in close contact with surface basic sites.