关键词:
分子筛,
密度泛函理论计算,
镧离子,
离子水合,
团簇
Abstract: As one kind of acid and shape-selective catalyst, zeolites Y have been widely used in the fields of drying and clean filtration, adsorption and separation because of its neat and uniform pore structures. The production of rare earth (RE) zeolites generally utilized RE ion aqueous to replace in NaY zeolites by Na-RE ion exchange reaction. However, the structures of RE ion hydration and the microscopic mechanism of the clusters crossing the pores of zeolites were still unclear. This work mainly focused on the structural prosperities of La3+ hydration and different valent hydration clusters based on density functional theory (DFT) calculations at M06-2X-D3/def2-SVP (LANL2DZ for La3+) and SMD=water implicit solvent level. The dimensions of the clusters, Mulliken charges, binding energies, and energy decomposition had been analyzed in this work. It could be found that the structures of clusters were flexible, it was not greater than a certain hydration number of the clusters to pass through the pores of zeolites. With the expanding number of hydration in clusters, the average radius of La-O(H2O) would increase. From the analysis of binding energy, the La3+ tended to be a more stable structure with high hydration in aqueous solution. In addition, the binding energies of La-O(OH-) were stronger than that of La-O(H2O). When n≤9 in the [La(H2O)n]3+ clusters, the electrostatic interaction occupied the dominant proportion, and the following items were induction, exchange repulsion and dispersion energy in the system based on the energy decomposition. When n＞9 in the [La(H2O)n]3+ clusters, the proportion of electrostatic interaction would decrease, the induction item would increase at the same time. The proportion changes of exchange repulsion and dispersion energy were not obvious with the increasing numbers of hydration. This work would provide some guidance for understanding the structure of La3+ hydration and basic aid for production of the RE zeolites.
Key words:
molecular sieve,
DFT calculations,
lanthanum ion,
ion hydration,
clusters