Support Effects on Hydrogen Desorption, Isotope Exchange, Chemical Reactivity, and Magnetism of Platinum Nanoclusters in KL Zeolite

Platinum clusters were prepared by ion exchange of a KL zeolite, followed by oxygen calcination \nand hydrogen reduction, and characterized by electron paramagnetic resonance (EPR) and \nhyperfine sublevel correlation experiment (HYSCORE) spectroscopy. Simulations indicate that \nthe cluster contains 12 equivalent platinum atoms. Therefore, the most likely structure is an \nicosahedral or cuboctahedral magic number Pt13 cluster with 12 platinum atoms at the surface. \nOne atom in the center possesses only a small spin density. H/D desorption and readsorption \nexperiments monitored via EPR and HYSCORE measurements provide information about the \nstructure of the clusters and about the reversibility of the adsorption/desorption and isotope \nexchange process. Deuterium desorption experiments result in a value of 2.1±0.2 eV for the D2 \ndesorption energy of the Pt13 clusters dispersed in KL zeolite. This is more than double of the value for a (111) Pt single-crystal surface, revealing a finite size and/or support effect. Oxygen \nadsorption on deuterium covered Pt13 clusters did not show a vigorous oxyhydrogen reaction. It \nappears that the reaction is inhibited by the deuterium coverage.