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 and hydrogen reduction, and characterized by electron paramagnetic resonance (EPR) and hyperfine sublevel correlation experiment (HYSCORE) spectroscopy. Simulations indicate that the cluster contains 12 equivalent platinum atoms. Therefore, the most likely structure is an icosahedral or cuboctahedral magic number Pt-13 cluster with 12 platinum atoms at the surface. One atom in the center possesses only a small spin density. H/D desorption and readsorption experiments monitored via EPR and HYSCORE measurements provide information about the structure of the clusters and about the reversibility of the adsorption/desorption and isotope exchange process. Deuterium desorption experiments result in a value of 2.1 +/- 0.2 eV for the D-2 desorption energy of the Pt-13 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 adsorption on deuterium-covered Pt-13 clusters did not show a vigorous oxyhydrogen reaction. It appears that the reaction is inhibited by the deuterium coverage.