Intrinsic Metal Size Effect on Adsorption of Organic Molecules on Platinum

Abstract

Di-σ adsorbed ethene, bridge(30) adsorbed benzene (with four di-σ-type and two π-type interactions), and η1 and η2 adsorbed acetone on nanosized platinum clusters consisting of 19 to 38 Pt atoms were studied theoretically by density functional theory (DFT) calculations with general gradient approximation (GGA) utilizing plane wave and local basis sets. The cluster results were compared to plane wave calculations employed with periodic boundary conditions. It was found that the geometries obtained with different methods are very similar but the adsorption energy depends prominently on the cluster size. Adsorption was strongest on the 22- and 26-atom clusters and weakest on the 35- and 38-atom clusters. No correlation between the d-band center of the clusters and the adsorption energy was observed. The relative amount of adsorbed active and spectator species of an organic molecule may depend on the cluster size as exemplified by the η1 and η2 adsorption modes of acetone. It is also feasible that the reaction energies are size-dependent adhering to the Brønsted−Evans−Polanyi relationship. This indicates that the catalytic activity of Pt nanoparticles can be increased by carefully controlling their size.