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    題名: Conversion of CO to Formaldehyde Catalyzed by BeO: A Theoretical Study
    作者: 黃德彥;Hwang, Der-yan;Mebel, Alexander M.
    貢獻者: 淡江大學化學學系
    日期: 2001-11-15
    上傳時間: 2009-12-01
    出版者: American Chemical Society (ACS)
    摘要: Ab initio calculations at the G2M(MP2)//MP2/6-31G** level have been performed to investigate the potential energy surface for various reaction mechanisms in the BeO/CO/H2 system. The results show that the conversion of carbon monoxide to formaldehyde can be catalyzed by beryllium oxide in the gas phase. Two different reaction mechanisms have been suggested. In the first one, BeO + CO + H2 → OBeOC + H2 → OBeOCH2 → BeO + H2CO, BeO first reacts with CO to form the OBeOC complex (bound by 20.2 kcal/mol), which interacts with H2 to give the complex between BeO and H2CO via a barrier of 53.1 kcal/mol relative to the initial reactants, and OBeOCH2 decomposes to BeO + formaldehyde without an exit barrier but with endothermicity of 44.9 kcal/mol. In the second mechanism, BeO + H2 + CO → HBeOH + CO → t-HCOBeOH → OBeOCH2 → BeO + H2CO, the initial step is the reaction of BeO with molecular hydrogen exothermic by 88.3 kcal/mol. Then, CO inserts into the Be−H bond of HBeOH to form the HCOBeOH intermediate, 80.2 kcal/mol below the reactants, which undergoes a 1,3-hydrogen shift from carbon to oxygen yielding the OBeOCH2 complex and the latter decomposes to the final products. On this pathway, the highest barrier is found for the t-HCOBeOH → OBeOCH2 hydrogen shift step with a transition state lying only 5.4 kcal/mol above BeO + H2 + CO, thus making the gas-phase reaction possible even at low temperatures. The reverse reaction of the H2CO decomposition to H2 + CO can be also catalyzed by BeO in the gas phase, since the barrier decreases from ∼80 kcal/mol for the unimolecular dissociation to only 2.0 kcal/mol for the reaction in the presence of BeO.
    關聯: Journal of physical chemistry A 105(45), pp.10433-10438
    DOI: 10.1021/jp0122171
    顯示於類別:[化學學系暨研究所] 期刊論文

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