Tolerance of platinum clusters to CO poisoning induced by molybdenum doping

Abstract

The influence of a single Mo dopant atom on the CO adsorption on isolated cationic platinum clusters in the gas phase, Ptn+ (13≤n≤24), has been investigated. The sticking probability of the first CO molecule to bare Ptn+ clusters is estimated to be close to unity and is not notably changed upon Mo doping. The adsorption probability of the second CO molecule, however, shows a significant reduction for Ptn−1Mo+ compared to Ptn+, reaching a maximal reduction of as much as 80% for Pt19Mo+. As a result, the average number of CO molecules adsorbed on Ptn+ with 19≤n≤24, and surviving on the time scale of the experiment, decreases by about 10–15% upon substitution of a single Pt atom by a single Mo atom. A statistical analysis of the unimolecular dissociation of the cluster CO complexes suggests that the lower sticking probability for the second CO molecule for Mo-doped species is related to a reduction of the CO chemisorption energy. Electron transfer from Mo to Pt resulting in a lowering of the Pt 5d vacancies and a downshift of the 5d-center is likely responsible for this reduced CO binding energy.