基于量子化学计算的BH_4^-水解制氢反应机理研究  

Reaction Mechanism of Hydrogen Generation from Hydrolysis of BH_4^-:Quantum Chemistry Computing

作　　者：张应[1] 李明涛[1] 杨伯伦[1] 

机构地区：[1]西安交通大学化学工程系动力工程多相流国家重点实验室,西安710049

出　　处：《化学学报》2013年第5期769-776,共8页Acta Chimica Sinica

基　　金：国家"973计划"(No.2009CB219906);国家自然科学基金(No.21276203);高等学校博士学科点专项科研基金(No.20110201130002)资助~~

摘　　要：采用密度泛函理论(DFT)和二阶微扰理论(MP2)对BH-4与两分子水反应制氢的微观机理进行了研究.在B3PW91/6-311++G(2df,2p)和MP2(full)/6-311++G(2df,2p)水平上优化了反应体系中所有反应物、中间体、过渡态和产物的几何构型,通过振动频率分析和内禀反应坐标(IRC)跟踪验证了过渡态的正确性.计算结果表明,反应生成氢气的过程是分四步进行,并存在两种可能的反应路径:路径1中,两分子的水分别在第一步、第三步参加反应;而路径2中,两分子的水分别在第一步、第二步参加反应;其中路径2的势垒比路径1低应为主反应路径.此外,两种反应路径都是强放热过程,且MP2法所得焓变值与所报道的实验值更接近.Borohydrides are considered to be one of the most promising hydrogen storage materials due to their high theo- retical hydrogen storage gravimetric capacity. The recognition of reaction mechanism that the borohydrides generate hydro- gen by hydrolysis can provide effective help for seeking the optimal reaction conditions. In this study, the mechanism for hydrogen evolution reaction between BH4 and two molecules of water has been investigated in detail by using the density functional theory （DFT） and the second-order Moller-Plesset perturbation theory （MP2）. At the B3PW91/6-311 q- q-G（2df, 2p） and MP2（full）/6-311 q-＋G（2df, 2p） level of theory, the geometries of all species in the reaction system （reactants, iso- mers, transition states and products） were optimized. The transition states were validated by the vibrational frequency analy- sis and the calculations of the internal reaction coordinate （IRC）. The computational results show that hydrogen is formed by a hydridic B--H hydrogen and a protic O--H hydrogen and that the reaction includes four steps in two possible reaction paths. In the first path, the water participates with the reaction in the first step and the third step, respectively; in the second path, the water participates with the reaction in the first step and the second step, respectively. Meanwhile, since the reaction barrier of each step is very high, the reaction is not easy to proceed spontaneously. The reaction barrier of the first step reac- tion is 252.0 kJomo1-1 （in MP2 method） which is the highest in full steps, so that the first step is the control step of the reac- tion. In addition, both reaction paths are strong exothermic reaction process. The enthalpy change values obtained in MP2 method （--200.3 kJ·mo1-1） is closer to the experimental observations （-216.7 kJ·mol-1）. And during the reaction process, the hybridization of the center atom boron changes from sp3 hybrid to sp2 hybrid and then to sp hybrid.

关 键 词：BH4- 反应机理 密度泛函理论 二阶微扰理论 

分 类 号：O643.12[理学—物理化学]