Molecular Beam Study of the Oxidation of Carbon Monoxide on a Regular Array of Palladium Clusters on Alumina

Abstract

For the first time, CO oxidation has been studied by molecular beam methods on a regular array of metal clusters with a very narrow size distribution. The use of a regular array of clusters offers the possibility to quantify the effect of the reverse spillover of CO, which increases the flux of CO adsorbing on the metal clusters. The reverse spillover of CO is studied on a hexagonal array of Pd clusters grown on an alumina ultrathin film on Ni3Al(111). Comparing the adsorption rate of CO with an analytical model describing exactly the CO adsorption on the supported cluster array, the adsorption probability and the difference between the adsorption energy and the diffusion energy of a CO molecule on the alumina substrate are determined. The turnover frequency (TOF) for the CO oxidation reaction is measured as a function of temperature. After correction from the reverse spillover effect, the TOF measured on the Pd clusters with an average size of 181 atoms is compared with TOF values previously obtained on ...