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.
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