Influence of Pr ions on the properties of Pd supported on ultradispersed diamond and graphite from organometallic precursors

Abstract

The formation, dispersion, state of components, adsorption and catalytic properties of (Pd+Pr)/C catalysts obtained by anchoring (iso-C 3H 7C 5H 4) 3Pr and C 3H 5PdC 5H 5, on the surface of oxidized graphite and diamond have been studied by FTIR, TEM and XPS. According to FTIR evidence, the interaction of (iso-C 3H 7C 5H 4) 3Pr with the diamond surface proceeds with the participation of carboxyl groups of the support, while subsequently-supported C 3H 5PdC 5H 5 coordinates with the anchored Pr ions. As follows from XPS and TEM data, in (Pd + Pr)/C catalysts reduced in H 2 at 300 δC, Pr cations are observed together with metallic Pd particles of 20 Å size on graphite and less than 10 Å on diamond. The stability of the metallic particles towards sintering is higher on diamond than on graphite. The presence of Pr ions in (Pd + Pr)/diamond catalyst leads to the appearance of a new absorption band at 1600–1620 cm −1 in the spectrum of adsorbed CO, to an order of magnitude increase in activity in CH 3OH synthesis, but a several-fold decrease in activity in benzene hydrogenation. These effects are similar to those observed earlier for (Pd + Pr)/SiO 2 and Pd/Pr 4O 7 catalysts, and are probably due to the formation of hetero-atomic Pd-Pr active sites in these systems.