在鉑奈米金屬團簇/氧化石墨烯表面進行:(1)甲烷轉換為甲醇及(2)一氧化碳轉換為二氧化碳之理論計算研究

Abstract

本篇文章藉由密度泛函理論研究在鉑原子氧化石墨烯表面上進行之兩個反應：(1) 純甲烷之氧化反應以及 (2) 一氧化碳和氧氣氧化反應。鉑金屬團簇氧化石墨烯表面上對於甲烷、氧氣具有之吸附能分別為 -0.35、和 -1.53 eV。首先在甲烷與氧氣的轉換反應中，O2先行吸附在表面，吸附能為 -1.56 eV並斷鍵形成兩個O原子於表面，此步驟須跨過 0.49 eV的反應能障，CH4靠近吸附於鉑金屬團簇上並經過0.94 eV的反應能障打斷C-H鍵結，形成CH3基與OH基在表面，最後經由0.25 eV的能障形成第一個CH3OH。接著加入第二個CH4至催化表面，其吸附能為0.55 eV，且只需要跨越0.08 eV的反應能障即可斷鍵生成CH3與H，接著經0.80 eV屏障形成CH3O甲醇基，最後以越過0.75 eV的位能障礙形成第二個CH3OH。 我們同時也考慮氧化不完全之微量的CO若於O2斷鍵後進入反應，將會透過0.22~0.29 eV的能障並走Eley–Rideal反應途徑氧化產生CO2並回到初始表面。該結果可以應用於甲醇燃料電池中，防止CO毒化催化劑進而使其失去催化活性。Based on density functional theory study, we studied two reaction mechanisms: (1) conversion of CH4 into CH3OH, and (2) oxidation of CO into CO2, on graphene oxide supported sub-nano Pt cluster. First, the O2 was adsorbed on the surface, then it crosses 0.49 eV of barrier to dissociate its O-O bond and form two O atoms. Second, CH4 was added and then broke its C-H bond to produce CH3 and OH, and the CH3 and OH coupled together to form a methanol, with the barriers of 0.94 and 0.25 eV, respectively. By adding the other CH4 with the adsobtion energy of 0.55 eV, and the C-H scission barrier 0.08 eV, the formation of CH3O and finally CH3OH are possible with the barriers of 0.80 and 0.75 eV, respectively. We also consider the CO oxidation into CO2 in which CO will be oxidized with O atom and produce CO2 through 0.22~0.29 eV barrier by Eley–Rideal (E.-R.) mechanism. This result could be applied in the fuel cell system to prevent the Pt electrode from being poisoned by the CO.