Atomic and Electronic Structures of Au/TiO 2 Catalyst - First-Principle Calculations
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Atomic and Electronic Structures of Au/TiO2 Catalyst – First-Principle Calculations – Kazuyuki Okazaki1, Yoshitada Morikawa2, Shingo Tanaka (SWING)1,2, Satoshi Ichikawa1, Koji Tanaka1, and Masanori Kohyama1,2 1 Interface Science Research Group, Special Division for Green Life Technology, AIST Kansai, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda 563-8577, Japan. 2 Quantum Modeling Research Group, Research Institute for Computational Science, AIST Tsukuba, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 2, 1-1-1 Umezono, Tsukuba 305-8567, Japan. ABSTRACT The atomic and electronic structures of Au/TiO2(110) systems have been theoretically investigated based on the density functional theory. We have examined Au adsorption on the stoichiometric TiO2(110) surface and on the Ti-rich surface formed by the removal of bridging-oxygen atoms (VOB surface) and the O-rich surface formed by the removal of 6-fold titanium and bridging-oxygen atoms (VTi6OB surface). For the stoichiometric surface, the stable site for the Au adatom is the hollow site of one bridging-oxygen and two in-plane oxygen atoms or the on-top site above 5-fold titanium atom. For the Ti-rich VOB surface, the bridging site of 6-fold titanium atoms along [001] direction is the most stable. In addition, the vacant site of 6-fold titanium atom is the most stable for the O-rich VTi6OB surface. The adhesive energies between the Au adlayer and the TiO2 surface are larger for the non-stoichiometric surfaces than that for the stoichiometric surface. The charge transfer between the Au adatom and the substrate is small for stoichiometric surface. For the Ti-rich VOB surface, the electron transfer occurs from the 6-fold Ti to the Au, while from the Au to the in-plane oxygen for the O-rich VTi6OB surface. It can be said that the TiO2 surface conditions such as defects or non-stoichiometry strongly affect the adsorption energy and electron structure of the Au adsorbed system. This point should be closely related the catalytic property of the Au/TiO2 system. INTRODUCTION Haruta and co-workers [1] found that gold has catalytic activity when gold is deposited as nano-size particles on several kinds of metal oxides such as TiO2. Au/TiO2 systems can act as a catalyst for the room-temperature oxidation of CO and the epoxidation of propylene in a gas containing oxygen and hydrogen [2-5]. It is quite interesting that chemically stable gold is involved in the catalytic activity. Goodman and co-workers [6-9] have investigated in details the structure and catalytic properties of Au on TiO2 and concluded that CO oxidation on the Au/TiO2(110) system is structure sensitive and the activity of the Au is likely due to quantum size effects in the highly dispersed Au clusters. Akita and co-workers [10] have carried out the
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analytical high-resolution transmission electron microscope (HRTEM) observation for Au deposited on TiO2 (anatase and rutile) to obtain a structural insight into the un
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