Support
Effects on Hydrogen Desorption, Isotope Exchange,
Chemical Reactivity, and Magnetism of Platinum Nanoclusters in KL
Zeolite
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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 Pt<sub>13</sub> 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<sub>2</sub> desorption energy of the Pt<sub>13</sub> 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<sub>13</sub> clusters did not show a vigorous oxyhydrogen reaction. It appears
that the reaction is inhibited by the deuterium coverage