NH3与BeH2反应机理的密度泛函理论研究

金属-N-H体系储氢材料在放氢反应过程中往往伴随着NH_3的释放,且NH_3会对材料的储放氢性能产生重要影响.采用密度泛函理论当中的杂化密度泛函(B3LYP)方法,6-311G(d,p)基组水平上对NH_3与BeH_2的微观反应机理进行了理论计算分析,对得到的中间体和过渡态进行频率计算和内禀反应坐标(IRC)分析,以判断中间体和过渡态的正确性和相互连接关系.使用QCISD方法在6-311G(d,p)基组水平对各驻点的单点能进行计算,给出能量信息.计算结果表明:BeH_2与NH_3主要以摩尔比为1:2进行反应,分两步氢取代过程,生成产物Be(NH_2)_2和2H_2.反应所释放的H_2中两个H原子分别来源于BeH_2和NH_3,反应的关键是脱氢,主要在于克服N—H键断裂所需能量.相比较而言从NH_3中脱氢比从—NH_2中脱氢较易.

Theoretical study on the reaction between NH3 and BeH2

There are often have NH3 during the reaction of hydrogen release by Metal-N-H system hydrogen storage materials, and NH3 have an important influence to the materials. The reaction mechanism between NH3 and BeH2 has been investigated by a B3LYP method of density functional theory at the 6-311G(d,p) level. Vibration analysis and intrinsic reaction coordinates (IRC) calculation at the same level have been applied to validate the connection of the stationary points. The single point energy of each station is calculated using the QCISD method at the 6-311G (d, p) level, to get the energy information.The results indicate that the reaction between NH3 and BeH2 are mainly reacted at a molar ratio of 1:2, has two hydrogen substitution reactions, the reaction products are Be(NH2)2 and H2. The two released hydrogen atoms in H2 come from NH3 and BeH2 respectively. The sticking point of the dehydrogenation is overcome to break the bond of N-H. In contrast, dehydrogenation from NH3 is easier to dehydrogenate from -NH2.