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, NH 3, H 2 O, CO 2, and N 2 O have been investigated using FT-ICR mass spectrometry. It is found that Pt 2 + is unique in efficiently activating NH 3 whereas the other clusters simply add this reactant in the primary reactions. The consecutive products Pt 4 (NH 3 ) 3 + and Pt 5 NH 3 +, however, also induce dehydrogenation of further NH 3 . Reactions of Pt n + with N 2 O effect O transfer, those with O 2 lead to degradation of the platinum clusters by loss of neutral PtO 2 . Only Pt 5 + is observed to add H 2 and H 2 O with low efficiencies whereas no reactions at all occur with CO 2 . In addition, the reactions between Pt n + and CH 4 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.