Reactivity of small cationic platinum clusters

The gas-phase reactions between Pt-n(+) clusters (n = 1-5) and the inorganic substrates H-2, O-2, NH3, H2O, CO2, and N2O have been investigated using FT-ICR mass spectrometry. It is found that Pt-2(+) is unique in efficiently activating NH3 whereas the other clusters simply add this reactant in the primary reactions. The consecutive products Pt-4(NH3)(3)(+) and Pt5NH3+, however, also induce dehydrogenation of further NH3. Reactions of Pt-n(+) with N2O effect O transfer, those with O-2 lead to degradation of the platinum clusters by loss of neutral PtO2. Only Pt-5(+) is observed to add H-2 and H2O with low efficiencies whereas no reactions at all occur with CO2. In addition, the reactions between Pt-n(+) and CH4 have been reinvestigated. Besides confirming the results previously reported, evidence is found that thermodynamics accounts for the anomalously low reactivity Of Pt-4(+). Comparing the reactivity of Pt-n(+) clusters with that of Pt surfaces shows distinct similarities and, thus, encourages use of the former in the development of gas-phase models for heterogeneous catalysis.