清洁及氧修饰Cu(100)表面上CO₂ 加氢制甲醇反应的能量学

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→HCOO_s→H₂CO_s→CH₃O_s→CH₃OH_s”;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;HCOO_s是合碳产物CH₃OH、CO共同的前驱中间体，甲醇选择性由HCOO_s的氢解反应与其解离生成CO_s及OH_s竞争反应的相对速率决定;在清洁铜表面上，HCOO_s的氢解反应与其解离生成CO_s及OH_s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 metallic and the partially oxidized copper surfaces respectively. Activation energies for elementary reactions involved in the methanol synthesis from CO₂/H₂ over Cu(100) and Cu(100)-p(2×2) O surfaces have been calculated using bond order conservation-Morse potential approach. The following conclusions have been obtained : the main pathway for methanol formation can be expressed as "CO_2,5→ HCOO_s→H₂CO_s→ CH₃O_s→ CH₃OH_s"; In comparison with that over the clean Cu(100) surface, each elementary reaction involved in methanol synthesis has a lower activation energy over the oxygen-modified Cu(100) surface; HCOO, is the common precursor intermediate for methanol and CO formations and the selectivity of methanol is governed by the relative reaction rate of hydrogenolysis of formate to the dissociation of formate (to CO_s+ OH_s); Over the clean Cu(100) surface, the activation energy for formate hydrogenolysis is similar to that for formate dissociation to CO_s and OH_s, while the former is much lower than the latter over the oxygen-modified Cu(100) surface. Judging by the activation energies, we conclude that methanol synthesis from CO₂/H₂ is more favorable over the partially oxidized copper surface than that over the metallic copper surface.