羟基氧化铟团簇与二氧化碳和甲烷作用的密度泛函理论研究

二氧化碳(CO₂)和化石能源气体燃料甲烷(CH₄)均是化学稳定、 温室效应较大的分子, 因而对其活化、 转化和利用的研究具有显著的理论和实际意义. 本文采用密度泛函理论方法, 计算研究了羟基氧化铟团簇与CO₂, CH₄和(CO₂+CH₄)的作用. 结果表明, 氧化铟团簇通过其活性位点—In—O(桥氧)—对CO₂和CH₄分子进行2+2]加成活化, 而羟基的引入调变了氧化铟团簇活性位点上的局部电荷, 显著降低了其与CO₂和CH₄分子作用的活化自由能垒, 使得CO₂和CH₄分子的活化变得容易进行. 活性位点—In—O(桥氧)—中的In, O上的局部电荷差值(q_In－q_O)越大, 其对CO₂和CH₄分子作用的活化自由能垒越低. 羟基氧化铟与CO₂和CH₄分子作用时, 电子由羟基氧化铟流向CO₂和CH₄分子(亲核活化); 而羟基引入前的氧化铟与CO₂和CH₄分子作用时, 电子则由CO₂和CH₄分子流向氧化铟(亲电活化).

Density-functional Theoretical Study on the Interaction of Indium Oxyhydroxide Clusters with Carbon Dioxide and Methane

Both carbon dioxide（CO₂） and methane（CH₄） as fossil energy gas fuel are chemically stable molecules with a large greenhouse effect， so it is theoretical and practical significance to investigate their activation， transformation and utilization. The density functional theory（DFT） method were used to investigate computationally the interaction of indium oxide clusters with CO₂， CH₄ and CO₂+CH₄. The results show that， indium oxide clusters activate CO₂ and CH₄via —In—O（bridge）— with ［2+2］ addition mode， and the presence of hydroxyl changes the local charge of the active site of indium oxide clusters， leading to significantly decrease of activation free barrier for their interaction with CO₂ and CH₄， and then making the activation be easily proceeded. Interestingly， the difference of local charges between In and O（q_In－q_O） of the active site —In—O— correlates well with the activation of CO₂ and CH₄， i.e.， the greater the q_In－q_O， the lowest the activation free barrier for their interaction with CO₂ and CH₄. For activation of CO₂ and CH₄ by indium oxyhydroxide clusters， electrons transfer to CO₂ and CH₄ from the clusters（nucleophilic activation）， and for that by indium oxide clusters without hydroxyl， the opposite transfer of electrons occurs（electrophilic activation）.