Toward decorrelation of surface oxygen groups from metal dispersion effects in Pd/C hydrogenation catalysts

Abstract

Carbon-supported Pd-based catalysts have found wide applications in hydrogenation of specific functional groups. Surface modification of the support, via the introduction of oxygen functional groups, modulates the metal dispersion and the interaction of reactant(s) with the catalyst surface, consequently tuning its catalytic properties. However, it is difficult to decorrelate the effect of surface oxygen groups from that of the dispersion of the metallic phase. This study aims at decorrelating these effects on the catalytic performance for phenylacetylene hydrogenation by using preformed monodispersed Pd nanoparticles deposited on carbon supports presenting different densities of surface oxygen groups. X-ray photoelectron spectroscopy, temperature-programmed decomposition experiments and transmission electron microscopy were used to analyze the dispersion and oxidation state of Pd and the concentration of surface oxygen groups. The results reveal that such decorrelation is not an easy task, particularly since spillover of the nanoparticles' native capping ligand (oleylamine) occurs during Pd particle deposition. This phenomenon, which depends on the density of oxygen functional groups and the size of Pd particles, impacts the Pd(0)/Pd2+ ratio and the surface Pd/N atomic ratio. These two last parameters, which seem to be interconnected, significantly impact the catalytic performance.