过渡金属氧化物(M2O5)+m=1,2(M=V, Nb, Ta)与C2H4气相反应机理的密度泛函研究

采用密度泛函理论研究了过渡金属钒族氧化物阳离子团簇(M2O5)+m=1,2(M=V, Nb, Ta)与C2H4气相反应机理. 反应为(M2O5)m++C2H4→(M2O5)m-1M2O4++C2H4O, 反应物先化合生成C—O键相连的化合物, 经过过渡态后M—O键断裂, 从而发生氧原子转移到碳氢化合物上的反应. 对于V2O5+与C2H4的反应, 存在经顺式和反式两种过渡态结构路径, 从能量上看, 经反式过渡态结构的路径更有利. 计算结果表明, 发生反应时C2H4与钒氧化物阳离子反应大量放热, 而与铌、钽氧化物阳离子反应却放热较少甚至不放热, 这与实验结果一致. 钒、铌、钽氧化物阳离子团簇发生氧转移反应活性不同的原因是金属-氧键的强弱不同所致.

DFT Studies on Gas-phase Reactions Mechanism of (M2O5)+m=1,2 (M=V, Nb, Ta) and C2H4

The reaction mechanisms of group V transition metal oxide cations (M2O5)+m=1,2(M=V, Nb, Ta) with ethylene were studied by density functional theory with BP86 method. For the reaction (M2O5)m++C2H4→(M2O5)m-1M2O4++C2H4O, the bond V—O was broken after the transition state and the oxygen transfer happened. It has both cis and trans transition structures for the reaction of V2O5+ and C2H4, the path with the trans transition structure was energetically favorable. The calculation results show that when it reacted with C2H4, the (V2O5)m+ was highly exothermic, but the (M2O5)m+(M=Nb, Ta) were slightly or even not exothermic. This is well in line with the experimental results. The different reactivity of the group V transition metal oxide cluster ions is attributed to the different bond strength of the metal-oxygen bonds.