Feasibility of Pure Silica Zeolites

For an investigation of thermodynamic synthesis feasibility of pure silica zeolites, we applied computer simulations with two force fields BS and SLC. The recently developed BS force field excellently fits experimental enthalpies of pure silica zeolites with respect to quartz. On the basis of calculations with the BS force field, two empirical criteria may be adopted to assess thermodynamic feasibility. First, it was found that the upper energetic limit for synthesized pure silica zeolites is ca. 16 kJ/mol SiO2 above α-quartz and, second, the density of excess energy of pure silica zeolites lies in the region where ΔE/V < 0.5 kJ/cm3. We show how total energies and van der Waals, electrostatic, and three-body interactions correlate with the molar volume and topology of frameworks. The thermodynamic feasibility was not only studied from the structural viewpoint, but also the presence of organic templates and water was considered. We select a case study and propose a possible route for the synthesis of an MSO as-made material. An organic template that provides a large energetic stabilization is proposed. It is also determined that the influence of water on the material stability depends on the positions of molecules in the MSO framework. An effect of maximum stabilization is reached when d6r and mso cages are filled by water molecules. A comparison between solid water and crystalline silica structures stimulated us to put forward a hypothesis about stabilization of zeolite frameworks by high pressure applied during the zeolite synthesis.