Predicting Structural Feasibility of Silica and Germania Zeolites

Abstract

High throughput experimental techniques for zeolite synthesis, combined with the introduction of germanium in the synthesis gel, have allowed an increase in the number of new zeolites, especially of those containing large and extralarge pores. Zeolite phases containing Si/Ge as tetrahedral atoms stabilize certain unique topologies. One particular feature of Ge-containing zeolites is the stabilization of small TOT (T = Si, Ge) angles compared to their silica counterparts. This study employs computational chemistry techniques to calculate and rationalize the relative stability of zeolite phases as silicates and germanates. Atomistic force fields are used to simulate the structural properties of experimentally synthesized Si/Ge-containing zeolites, and an ab initio Hartree−Fock methodology is used to estimate the energetics of TOT angles. It is shown that each particular topology is only compatible with certain ranges of TOT angles, and, depending on the chemical composition, this induces stability or strain. A calculation of the energetic penalty associated with TOT angles for the different chemical compositions at each topology allows an estimate of their feasibility. The results are in agreement with experiments and allow one to make predictions about feasibility of new SiO2 or GeO2 zeolite structures