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应用密度泛函理论(DFT)反应能计算及最小能量路径分析研究了CO2在气相和电化学环境中于Cu(111)单晶表面的还原过程.气相CO2还原为碳氢化合物的反应路径可能为:CO2(g)+H*→COOH*→(CO+OH)*→CHO*;CHO+H*→CH2O*→(CH2+O)*;CH2*+2H*→CH4或2CH2*→C2H4.整个反应由CO2(g)+H*→COOH*→(CO+OH)*,(CO+H)*→CHO*和CH2O*→(CH2+O)*等几个步骤联合控制.在-0.50 V(vs.RHE)以正的电势下,CO2在Cu(111)表面电化学还原主要形成HCOO-和CO吸附物;随着电势逐渐负移,CO2加氢解离形成CO的反应越来越容易,CO成为主要产物;随电势进一步变负,形成碳氢化合物的趋势逐渐变强.与CO2的气相化学还原不同的是,电化学环境下CO质子化形成的CHO中间体倾向于解离形成CH,而在气相中CHO中间体则倾向于进一步质子化形成CH2O中间体.
The reduction process of CO2 on the Cu (111) single crystal surface in gas phase and in electrochemical environment was studied by using density functional theory (DFT) reaction calculations and minimum energy path analysis. The reaction pathway for the reduction of gaseous CO2 to hydrocarbon may be : CO2 (g) + H * → COOH * → (CO + OH) * → CHO *; CHO + H * → CH2O * → (CH2 + O) *; CH2 * + 2H * → CH4 or 2CH2 * → C2H4. The whole reaction is controlled in several steps such as CO2 (g) + H * → COOH * → (CO + OH) *, (CO + H) * → CHO * and CH2O * → (CH2 + O) At the positive potential of V (vs. RHE), the electrochemical reduction of CO 2 on the Cu (111) surface mainly formed HCOO- and CO adsorbates. As the potential gradually shifted negatively, the reaction of CO 2 dissociation by CO 2 hydrogenation became more and more CO becomes the main product easily.With the potential further negative, the tendency to form hydrocarbons gradually becomes stronger.Compared with the gas phase chemical reduction of CO2, the CHO intermediates formed by CO protonation in electrochemical environment tend to dissociate CH, whereas in the gas phase CHO intermediates tend to further protonate to form CH2O intermediates.