Characterization of Pd/MgO catalysts: Role of organometallic precursor-surface interactions

Pd(acac)(2) was supported on a highly dehydroxylated and decarbonated magne sium oxide surface (MgO500), on an untreated MgO surface (MgOAIR), and on a silica (SiO2450). EXAFS and DRIFT data indicate that the organopalladium c omplex is adsorbed intact on all the surfaces, but its dispersion is depend ent on the nature of the surface. On MgO500, dispersion at the molecular le vel occurs, in contrast to the formation of islands of multilayers on MgOAI R and SiO2450. The final properties of the metal phase, formed by H-2 treat ment at 500 degreesC, are dependent on precursor-surface interactions. HRTE M analysis shows a narrow distribution of the metal particles centered at 0 .6 nn on MgO500, and a wide diameter distribution around 6.1 and 9.9 nm on MgOAIR and SiO2450, respectively. In the n-heptane dehydrocyclization at 50 0 degreesC, the highest selectivity is shown by Pd/MgO500 catalysts and it is consistent with a predominant fraction of very small particles in close contact with surface basic sites. (C) 2001 Academic Press.