Study on Catalytic and Electronic Properties of Deposited Alloy Clusters onto a Substrate

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This study has been focused on adsorption reactivity and electronic property of alloy clusters as a microscopic model of catalytic activity, because finite system of metal/alloy clusters having 2-100 atoms can be regarded as a minimum catalytic site. A couple of binary clusters were chosen in the viewpoint of useful catalytic activity ; (a) alloy clusters of niobium (Nb)-aluminum (Al), gold (Au)-palladium (Pd), and gold (Au)-zinc (Zn), (b) semiconductor clusters of lanthanide/transition-metal-silicon (Si), and (c) metal oxides of vanadium oxide and cobalt oxide. Furthermore, the soft-landing technique was successfully established to design catalytic surface with the deposition of alloy clusters synthesized in gas phase.The binary clusters were generated by the two-rod laser vaporization, and their electronic properties were studied with photoelectron spectroscopy. The results summarized as follows ; (a) Adsorption reactivity of the alloy clusters was correlated well with geometries rather than electronic structures. In Au-Pd clusters, interestingly, an electron promotion occurs from 4d to 5s orbital in the Pd atom. (b) In semiconductor binary clusters, adsorption reactivity provides the information on reaction sites, and metal-encapsulated silicon clusters were discovered. (c) In metal oxide clusters, geometric phase transition was drastically induced by the mixing of oxygen atoms into metal clusters, although oxygen atoms having less than 10% concentration could be treated as impurity atoms. Photoelectron spectroscopy and mass spectrometry for reactivity have revealed fundamental insight on composite effects in alloy/binary clusters, of which the principles can lead to design new catalyst with the soft-landing technique.