MgO活化甲烷碳氢键的密度泛函研究

A DFT Study on Methane Activation by MgO

在B3LYP/ 6 311+G(2d ,2p)水平上计算了MgO +CH4 →Mg +CH3 OH反应的单态势能曲线 .结果发现MgO和CH4 发生相互作用 ,首先形成两种类型的分子 -分子复合物 (MgOCH4 和OMgCH4 ) ;分子 -分子复合物OMgCH4 能发生进一步转化 ,即MgO插入到CH4 的C—H键中 ,产生中间体HOMgCH3 ,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MgCH3 OH ,但其活化能太高 ,为 2 99.8kJ·mol-1,是整个反应的速率控制步骤 ;最后一步是MgCH3 OH放出CH3 OH分子 ,整个反应放热 146 .1kJ·mol-1.

The reaction of CH4 + MgO-->Mg + CH3OH 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 OMgCH4 and MgOCH4. OMgCH4 could undergo oxidative addition, cleaving a C-H bond and yielding the insertion product HOMgCH3. The third step is a reductive elimination, leading to an atom-molecule complex MgCH3OH, 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 HOMgCH3 is predicted to be the energetically preferred configuration in the reaction. The overall reaction is exothermic by 146.1 kJ.mol(-1).