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

DFT Studies on Gas-phase Reactions Mechanism of(M_2O_5)_(m=1,2)^+(M=V,Nb,Ta) and C_2H_4

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.

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-1 M2O4 ＋ C2H4 O, 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 C2 H4, 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=1,2^＋（M=V,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.