Foster, Martin David; (2003) Computational studies of the topologies and properties of zeolites. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Computational chemistry techniques are used to study the structural and chemical properties of zeolites. In this work we present results of three main topics; structural properties of Fe enhanced ZSM-5, acidic properties of Al and B substituted zeolites beta, ZSM-12 and ZSM-48 and the evaluation and characterisation of hypothetical zeolite structures derived from new tiling theory results. Calculations have been performed using classical interatomic potential methods, quantum mechanical density functional theory methods and embedded cluster techniques. The first main topic investigates Fe substituted ZSM-5 via a cluster model approximation to examine structural properties and vibrational frequencies. We present results from calculations using a variety of different density functional schemes and levels of detail. These results are in good agreement with previous experimental and computational studies. Alternative suggestions to those foimd in current literature are presented for the structures of extra-framework Fe species. The second topic investigates Al and B substituted beta zeolites, ZSM-12 and ZSM-48 and their acidic properties. Results are presented of classical interatomic potential calculations for the Al substituted zeolite systems. Hybrid QM/MM calculations and periodic Density Functional calculations were performed on Al and B substituted beta C zeolite. However, the results thus far do not suggest a reason for the differences observed in catalytic activity of these zeolites. Finally, the third topic, which represents the larger part of this thesis, is the characterisation and evaluation of hypothetical zeolite structures. Following on from recent advances in mathematical tiling theory, over 900 systematically enumerated zeolite structures have been investigated using classical interatomic potential methods. We report the minimised structures for uninodal, binodal and trinodal structures. In the case of the uninodal structures this is the complete set of possible structures. Additionally we report correlations between calculated energetics and structural properties of known and hypothetical zeolite topologies. Finally a short discussion of the use of a novel template prediction program is presented with initial suggestions for template molecules for some of the feasible candidate structures.

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