Strong Lewis acid catalysts are used in a variety of industrial processes. High surface area AlF3 has great potential as a heterogeneous catalyst for such applications. Recently much progress has been made in modelling the surfaces of this material in the presence of HF and H2O together with the adsorption of small molecules (H2O, NH3 and CO) on the surfaces. This work will be briefly reviewed.
These studies have now been extended to investigate the role of charged defects in the surface chemistry. Fluorine vacancies in the bulk of both alpha and beta AlF3 are shown to give rise to the formation of localised colour centres which can act as charge reservoirs for surface chemistry. The stability, geometry and electronic structure of these vacancies will be discussed together with their role in surface chemistry.
The beta surface is known to have two very low energy terminations. Consequently, real systems can be expected to show large numbers of steps between these two surfaces. The structure of these steps will also be discussed. This extends are earlier work on periodic crystalline samples by explicitly examining the role of defects in determining the surface chemistry.
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