Co_3O_4纳米晶催化氧化甲烷的理论研究:C–H键活化的晶面效应及活性中心(英文)

Theoretical study of the crystal plane effect and ion-pair active center for C–H bond activation by Co_3O_4 nanocrystals

甲烷是一种在自然界中大量存在的原材料，在取代原油和合成重要化工产品等许多领域具有潜在的应用价值.然而，由于CH4中C-H键的键能特别大（约-4.5 eV），如何实现甲烷的绿色有效转化在化学化工领域仍然是一个挑战.本文采用密度泛函理论对Co3O4（001）和（011）晶面活化甲烷C-H键的机理进行了理论研究，得到了如下结论：（1） CH4的C-H键在Co3O4晶面的解离具有很高的活性，只需要克服大约1 eV的能垒；（2）与Co2＋相连的Co-O离子对是CH4活化的活性位点，其中两个带正负电荷的离子对C-H解离起着协同作用，帮助产生Co-CH3和O-H物种；（3）（011）面的反应活性明显大于（001）面，与实验的观察一致.本文的计算结果表明， Co3O4纳米晶面对CH4中C-H键的活化表现出明显的晶面效应和结构敏感效应， Co-O离子对活性中心对于活化惰性的C-H键发挥了关键作用.

Methane has attracted extensive interest in recent years due to its potential application as a re-placement of oil and a feedstock for valuable chemicals. Due to the large C-H bond energy, the con-version of methane into useful products has been a challenge. In the present study, density func-tional theory （DFT） calculations were performed to study the activation of the C-H bond of methane on the （001） and （011） planes of Co3O4, which showed that CH4 activation on Co3O4 nanocrystals was fairly easy with only small energy barriers （less than 1.1 eV）. Surface Co-O ion pairs are the active site for C-H bond activation, where the two ions provide a synergistic effect for the activation of the strong C-H bond and yield surface Co-CH3 and O-H species. The Co3O4（011） surface is shown to be more reactive for C-H bond activation than the Co3O4（001） surface, which is consistent with previous experimental results. Our results suggest that methane oxidation on Co3O4 nanocrystals has strong crystal plane effect and structure sensitivity and the ion-pair active center plays a signif-icant role in activating the strong C-H bond.