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

本研究的重点是作为催化活性微观模型的合金团簇的吸附反应性和电子性质，因为具有2-100个原子的金属/合金团簇的有限系统可以被视为最小催化位点。从有用的催化活性的角度选择了一对二元簇;（a）铌（Nb）-铝（Al）、金（Au）-钯（Pd）和金（Au）-锌（Zn）的合金簇，（B）镧系元素/过渡金属-硅（Si）的半导体簇，和（c）氧化钒和氧化钴的金属氧化物。在此基础上，成功地建立了软着陆技术，利用双棒激光蒸发法制备了二元合金团簇，并利用光电子能谱研究了其电子性质。结果表明：（a）合金团簇的吸附活性与几何结构而非电子结构相关。在Au-Pd团簇中，有趣的是，Pd原子中的电子从4d到5s轨道发生促进。(b)在半导体二元团簇中，吸附反应性提供了反应位点的信息，并发现了金属包裹的硅团簇。(c)在金属氧化物团簇中，尽管浓度小于10%的氧原子可以被视为杂质原子，但氧原子混合到金属团簇中会引起几何相变。光电子能谱和质谱反应性研究揭示了合金/二元团簇复合效应的基本原理，为软着陆技术设计新型催化剂提供了理论依据。

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.