Interplay of water, extra-framework cations and framework atoms in the structure of low-silicazeolites: the case of the natural zeolite Goosecreekite as studied by computer simulation

Abstract

Computational methods are described that model accurately the structure of hydrated Ca-bearing zeolites. Using Goosecreekite as a model system we probe the influence of framework ordering, cation siting and hydration of pores on the structure and its stability. We develop a methodology which allows the location of Al within the framework to be determined together with the position of extra-framework cations, in a stepwise fashion, progressing from an anhydrous model, via a dielectric continuum model, to finally, a fully atomistic model of the water in the intrazeolite pore space. Our methods reveal the complex interplay of short- and long-range interactions on the optimal structure of such materials.

Screening heteroatom distributions in zeotype materials using an effective Hamiltonian approach: the case of aluminogermanate PKU-9

“…goosecreekite, 41 edingtonite, 42 thomsonite, 43 or yugawaralite, 44 and partial ordering in many others, such as brewsterite, 45 HEU-topology clinoptilolite 46 and heulandite, 47 epistilbite, 48 and levyne. 49 Computational modelling have successfully shown the preferential ordering in goosecreekite 28,29 and partial ordering in HEU-type zeolites 26,49,50 in agreement with experimental results. On the other hand, the limitation of computational studies in the calculation of heteroatom distributions based on T site energetics becomes important in cases like ZSM-5 (MFI), with low aluminium content, where calculations reveal 31 that there are only small energy differences between configurations.…”

“…[15][16][17][18][19] A large body of experimental and computational work exists aimed at identifying and attempting to explain the distribution of Al in aluminosilicate materials. [20][21][22][23][24][25][26][27][28][29][30][31] In aluminogermanates the scenario is different, and computer modelling offers a valuable tool for identifying preferred siting of heteroatoms, as evidenced by previous successful applications to the investigation of Si-Al [24][25][26][27][28][29][30][31] and Si-Ge distribution in zeolites. 12,[32][33][34][35] Heteroatoms can be distributed over the framework of zeolites with varying degrees of order, from full ordering in some cases to completely random distribution in others.…”

“…Alternatively, symmetry considerations can be used to explore heteroatom distribution in a larger configurational space. [26][27][28][29]31,70 However, in zeolites with high concentrations of heteroatoms even with the use of symmetry and of some ad hoc structurerelated constraints, the number of independent configurations is larger than what is tractable by fully atomistic simulations. Our selection of the aluminogermanate PKU-9 zeolite, will provide here an example on how the structural information regarding the location of the Al atoms will vary according to the approach used as the composition changes from that found experimentally to higher Ge/Al.…”

Understanding Nanopore Window Distortions in the Reversible Molecular Valve Zeolite RHO

“…The symmetry also changes from the centric to the acentric space group. The decrease of the charge of the cations could be regarded as an increase in water content, and is accompanied by a reduction of cation-oxygen interactions, and consequently by larger interatomic distances [37]. This can cause the migration of cations, which indeed moved from Site I to Site II.…”

“…The methodology used here for the realistic structural modeling of zeolite RHO is inspired by the experience in modeling massively defective ionic solids [23,24], in which large structural deformations occur. Since one of the results of this research has been the development of the new methodology, it is presented in the next section, along with the rest of the results.…”