清洁及氧修饰Cu(100)表面上CO_2加氢制甲醇反应的能量学

Reaction Energetics for Methanol Synthesis from CO_2/H_2 over the Clean and the Oxygen-Modified Cu(100) Surfaces

分别以清洁及氧修饰Cu（100）表面作为金属态铜和部分氧化态铜的表面模拟，用键级守恒-Morse势法研究了两种表面上CO2加氢制甲醇反应的能量学．计算结果表明：在两种表面上，CO2加氢制甲醇反应的优势反应途径均为“CO2，s→HCOOs→H2COs→CH3Os→CH3OHs”；与清洁铜表面上的相应基元步骤相比，在CU（100）-p（2X2）O表面上甲醇合成反应各基元步骤具有更低的活化能；HCOOs是合碳产物CH3OH、CO共同的前驱中间体，甲醇选择性由HCOOs的氢解反应与其解离生成COs及OHs竞争反应的相对速率决定；在清洁铜表面上，HCOOs的氢解反应与其解离生成COs及OHs竞争反应具有相似的活化能，而在氧修饰铜表面上，前者的活化能显著低于后者．因此，从反应能量学角度看，甲醇合成反应在部分氧化态铜表面上比在金属态铜表面上更有利．

Clean and oxygen-modified Cu(100) surfaces have been used to model the metallicand the partially oxidized copper surfaces respectively. Activati0n energies for elementary re-actions involved in the methanol synthesis from CO2/H2 over Cu (100) and Cu (1O0)-p(2 X 2)O surfaces have been calculated using bond order conservation-Morse potential approach.The following conclusions have been obtained: the main pathway for methanol formation canbe expressed as 'CO2,s→HCOO3→H2CO3→CH3O3→CH3OHs'; In comparison withthat over the clean Cu(100) surface, each elementary reaction involved in methanol synthesishas a lower activation energy over the oxygen-modified Cu(100) surface;HCOOs is the com-mon precursor intermediate for methanol and CO formations and the selectivity of methanolis governed by the relative reaction rate of hydrogenolysis of formate to the dissociation offormate (to COs+ OHs); Over the clean Cu(100) surface, the activation energy for formatehydrogenolysis is similar to that for formate dissociation to COs and OHs, while the former ismuch lower than the latter over the oxygen-modified Cu (100) surface- Judging by the activa-tion energies, we conclude that methanol synthesis from CO2/H2 is more favorable over thepartially oxidized copper surface than that over the metallic copper surface.