MgO活化甲烷碳氢键的密度泛函研究

在B3LYP/6-311 + G（2d, 2p）水平上计算了MgO + CH_4 → Mg+CH_3OH反应的 单态势能曲线。结果发现MgO和CH_4发生相互作用，首先形成两种类型的分子-分子 复合物（MgOCH_4和OMgCH_4）；分子-分子复合物OMgCH_4能发生进一步转化，即 MgO插入到CH_4的C-H键中，产生中间体HOMgCH_3，此中间体在本反应中是能量上最 稳定的构型；它还有可能进一步发生反应，产生原子-分子复合物MgCH_3OH，但其 活化能太高，为299.8kJ·mol~(-1)，是整个反应的速率控制步骤；最后一步是 MgCH_3OH放出CH_3OH分子，整个反应放热146.1 kJ·mol~(-1)。

A DFT Study on Methane activation by MgO

The reaction of CH_4 + MgO → Mg + CH_3OH has been studied on a singlet state potential energy curve at B3LYP/6-311 + G (2d, 2p) level. The reaction path in which the intermediates transfer from one to another via transition states has been rationalized by their structure, natural bond orbital (NBO) and vibrational frequency analysis. In the first step, the reactants give molecule-molecule complexes OMgCH_4 and MgOCH_4. OMgCH_4 could undergo oxidative addition, cleaving a C-H bond and yielding the insertion product HOMgCH_3. The third step is a reductive elimination, leading to an atom-molecule complex MgCH_3OH, and this step is the rate-determination step in the whole reaction path; the final step is the release of methanol molecule leaving magnesium atom behind. The complex HOMgCH_3 is predicted to be the energetically preferred configuration in the reaction. The overall reaction is exothermic by 146.1 kJ ·mol~(-1).