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Towards Rational Zeolite Design

Final Activity Report Summary - TORAZEDE (Towards Rational Zeolite Design)

Microporous crystals, such as zeolites, are an important and fascinating class of materials which contain regular nanometre-sized pores and channels. They are used in many applications, from washing powder to petroleum cracking and from radionuclide clean-up to lost-cost refrigeration. Such materials are also being increasingly investigated for gas adsorption applications such as CO2 capture and hydrogen storage. Despite their wide usage and the many different types of chemistry which they can exhibit, the zeolites all share a unique structural feature. They possess a microscopic framework based on tetrahedra of atoms, which can be linked together in many different ways. Recently, advances in mathematics and computing enabled us to explore this enormous structural richness as never before and to discover that there are possibly many thousands of framework architectures which might exist, in case a way was found to manufacture them chemically. However, this manufacture process is still only understood at a very empirical level, with a 'hit and miss' synthetic approach still largely being the only available.

Two key unanswered questions therefore are:
1. to find some way of understanding the crystal architectures of these materials so as to be able to predict which types of chemistry are suited to particular structure; and
2. to identify what type of synthetic process would be most suitable to creating a given material in the laboratory.

In this project we developed and extended our theoretical understanding of this area by combining mathematical analysis of topology and geometry with computational chemistry methods such as molecular modelling.

Our main scientific achievement was to show that we could use the concept of tetrahedral distortion to predict which topologies were more likely to form as aluminosilicates and to show that more distorted structures could instead form more easily as sulphides. In fact, we showed for the first time that the 'energy landscape' which determined which crystal structures were more likely to exist than others was radically different for sulphides than it was for aluminosilicates and indeed for other compositions such as imide. Another key result was that we also categorically disproved a widely-held belief that there was a maximum size to the pores which could exist within such materials. We showed that there existed energetically-feasible classes of material which, in principle, were capable of accommodating an infinite range of pore diameters.