Theoretical Studies of Catalytic Reactions on Transition-Metal and Metal-Oxide Surfaces

• Main Authors: Chang, Ming-Wen, 張銘文
• Other Authors: Sheu, Wen-Shyan
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/94048599325904922859

博士 === 輔仁大學 === 化學系 === 104 === The composition of gases and the oxidation state of metal atoms were reported to significantly influence catalytic ability for metal nanoparticles supported on metal oxide surfaces. The major goal of this thesis is to obtain a deep understanding of the influences of catalysts on the water-gas-shift (WGS) reaction and the CO oxidation reaction. Using periodic-density-functional-theory calculations, we explore the mechanism for the CO oxidation reaction in the presence of trace amounts of water on Ag(111) and the effect of the Au charge on the WGS reaction on gold-substituted Ce1-xO2(111) surfaces in the presence of multiple oxygen vacancies. Regarding the oxidation of CO in the presence of trace amounts of water on Ag(111), it is found that water not only stabilizes the adsorbed oxygen molecules on Ag(111), but also directly participates in the reaction as a catalyst. The oxidation of CO on Ag(111) is enhanced via the reaction intermediate of HO2*, which is produced by transferring a hydrogen atom from a water molecule to an oxygen molecule. The overall reaction barrier is calculated to be as low as 0.20 eV. Therefore, it is expected to be operative at low temperatures. The implications of the findings for experimental results are also discussed. As for the WGS reaction on gold-substituted Ce1-xO2(111) surfaces, we find that, for a gold atom adsorbed on a cerium vacancy site of CeO2(111), the charge state of the Au atom is influenced by the number and configuration of oxygen vacancies around the Au. It can be varied from a highly positively charged state to a highly negatively charged state. However, only the Au atom in a modestly charged state is found to be responsible for the WGS-catalytic activity. The physical origin of the charge variation and the role of the Au charge in the WGS reaction are also discussed.