Chemical properties of mass-selected coinage metal cluster anions: Towards obtaining molecular-level understanding of nanocatalysis

The catalytic activity of metal clusters often shows an interesting cluster size selectivity, e.g., metals which are inert in bulk form can become extraordinarily catalytically active with reduced cluster sizes. To shed light on elementary steps of catalytic processes on nanoclusters, the chemisorption properties of mass-selected coinage metal cluster anions in the gas phase were studies using time-of-flight (TOF) mass-spectrometry and ultraviolet photoelectron spectroscopy (UPS). In surface chemistry, it is generally accepted that O ₂ dissociates at room temperature; however, on coinage metal cluster anions, di-oxygen species can be found, implying that di-oxygen species on coinage metal clusters are important reaction intermediates for the catalytic CO-oxidation and partial oxidation of hydrocarbons. For H adsorption on Au cluster anions, H acts as a one-electron donor like Au does. The implication of this result on heterogeneous catalysis of nanoclusters is discussed.