本文利用論計算的方法，來研究在純Pt (111)及Pt/Pt (111) 表面上進行甲醇裂解反應以及一氧化碳氧化反應。首先甲醇吸附於表面上進行脫氫反應，是經由O-H鍵裂解形成甲氧基分子，或者是經由C-H鍵裂解產生CH2OH吸附於表面上。由DFT的計算結果發現，甲醇裂解反應先經由脫O-H鍵上的氫之後，在連續脫C-H鍵上的氫，形成一氧化碳是比較容易發生的路徑。其中，水的裂解反應也扮演著非常重要的角色。在純Pt (111)表面上，水裂解反應其能障均較高於Pt/Pt (111)表面，然而考慮水雙體的裂解反應，利用水分子間的質子傳遞路徑，計算出的反應能障都較水單體裂解能障低。利用水於表面裂解所產生的氫氧基，與COtop或 CObri結合產生COOH，這兩個路徑的反應能障都為0.43 eV，此氧化反應生成CO2之能障為0.94 eV，為此反應機制之速率決定步驟。另外由COOH與OH共吸附時，反應而形成CO2，反應能障降低至0.53 eV，可見OH有利於COOH的氧化。最後我們亦考慮CO 和O氧化形成CO2的計算，其反應能障降易亦很低。
關鍵字：Pt (111)、甲醇裂解反應、一氧化碳氧化反應、水分解

Periodic, self-consistent, Density Functional Theory (PAW-GGA) calculations are used to study competitive paths for the dehydrogenation of methanol on Pt (111) surfaces (clean and defective Pt (111) surface). Pathway proceeding through initial O-H scission event in methanol is considered to compare pathway proceeding through an opening C-H bond scission event. My calculated results suggest that methanol dehydrogenation via CH3O and either CH2O intermediates is a kinetically feasible route; C-H bond scission to CH2OH, followed by sequential dehydrogenation, may be another realistic route. The reaction barrier via initial O-H bond scission to form the CH3O intermediate was found to be 0.1 eV lower than C-H bond scission to form CH2OH intermediate. All the reaction barriers of C-H and O-H bond scission are lower than 0.85 eV. The most favorable reaction path on Pt (111) surface involves the O-H bond breaking in CH3OH and the further dehydrogenation of the resulting CH3O species to CO and H. However, the dissociation of H2O to form OH plays a crucial role in oxidative removal of poisoning CO (CO + OH COOH CO2 + H). Therefore, the H2O dissociation to OH and CO oxidation with OH on Pt (111) surface is also investigated. The calculated results indicate that the reaction barrier of H2O dimer dissociation was found to be 0.14 eV lower than that to H2O monomer dissociation over clean Pt (111) surface. On defective Pt (111) surface, reaction barrier for H2O dimer dissociation was smaller by at least 0.15 eV than the H2O monomer dissociation. Many possible elementary steps involved in CO oxidation on clean Pt (111) surface have been investigated. First, CO can react with OH to form COOH, I find that the reaction barriers of COtop + OH  COOHcis and CObri + OH  COOHtrans (0.43 eV) are lower than that of other CO + OH oxidation reactions, indicating the both reactions are favorable to allow. Second, CO2 formation from COOH (COOH  CO2 + H) is relatively (0.94 eV). Third, the calculated results demonstrate that COOH oxidation with OH helps to markedly lower the reaction barrier. In addition, showing the reaction barrier of CO oxidation with O can be significantly reduced.
Key Point: methanol dehydrogenation, water, CO oxidation, Pt (111) surface

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