Abstract:
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 Pt13 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 D2
desorption 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
adsorption on deuterium covered Pt13 clusters did not show a vigorous oxyhydrogen reaction. It
appears that the reaction is inhibited by the deuterium coverage.
