分子筛合成过程中三聚铝硅酸盐生成机理的DFT研究

采用密度泛函理论研究了在分子筛合成的碱性环境中铝硅酸盐三聚体的生成机理.在B3LYP/6-31 G(d,p)计算水平上对反应物、过渡态和产物分别进行了几何结构的全优化和频率计算,通过内禀反应坐标的方法验证了反应路径,并计算了反应的活化能.采用COSMO-RS模型考虑了溶剂效应.结果表明,二聚硅酸分子SiOSi(OH)6和单体铝酸根离子Al(OH)**的缩聚反应可以按照协同方式进行,SiO-Al桥键的形成与水分子的脱除同时发生,最终生成铝硅酸盐的三聚体.计算得到的缩聚反应活化能为80.1 kJ/mol.

DFT study on the formation of aluminosilicate trimer in zeolite synthesis

The condensation of silicate dimer with aluminate in alkaline environment of zeolite synthesis is studied using density-func- tional theory at the B3LYP/6-31 G(d,p)level.The solvent effect is included by the COSMO-RS model.The study involves the complete geometry optimization and frequency calculation of the reactants,transition state and products,as well as the activation energy estimation.The intrinsic reaction coordinate method is used to verify the reactants and products connected by the transition state.The calculated results show that the Si-O-Al linkage formation can proceed via a single-step reaction path,in which SiO-Al bond formation and water removal are synergetic,with the activation energy of 80.1 kJ/mol.This result is comparable to the activation energy of the silica condensation.