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

由于具有2-100个原子的金属/合金团簇的有限体系可视为最小催化中心，因此本研究主要关注合金团簇的吸附反应性和电子性质作为催化活性的微观模型。从有效催化活性的角度选择了几个二元簇合物：(A)Nb(Nb)-Al(Al)、Au(Au)-Pd(Pd)和Au(Au)-Pd(Pd)的合金簇合物，(B)稀土/过渡金属硅(Si)的半导体簇合物，以及(C)金属氧化物的钒氧化物和钴氧化物。在此基础上，成功地建立了利用气相沉积合金团簇进行催化表面设计的软着陆技术，并用光电子能谱对其电子性质进行了研究。主要研究结果如下：(A)合金团簇的吸附活性与几何构型相关，而与电子结构相关。有趣的是，在Au-Pd团簇中，Pd原子的电子促进作用发生在4d至5s轨道上。(B)在半导体二元团簇中，吸附反应性提供了关于反应位置的信息，发现了金属包裹的硅团簇。(C)在金属氧化物团簇中，氧原子与金属团簇的混合导致了几何相变，尽管浓度小于10%的氧原子可以被视为杂质原子。反应活性的光电子能谱和质谱学揭示了合金/二元团簇中复合效应的基本原理，这些原理可以指导使用软着陆技术设计新的催化剂。

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.