Identification of possible Lewis acid sites on the β-AlF3(100) surface: an ab initio total energy study

Abstract

Strong Lewis acid catalysts are widely used in a variety of industrial processes including Cl/F exchange reactions. Aluminium fluorides (AlF₃) have great potential for use in such reactions. Despite the importance of the surface in the catalytic process little is known about the detailed atomic scale structure of AlF₃ surfaces. In the current study we employ state of the art total energy calculations based on hybrid-exchange density functional theory to predict the composition and structure of the (100) surface of β-AlF₃ for the first time. We examine six possible terminations of the β-AlF₃ (100) surface and demonstrate that there are two relatively low energy terminations that result in the formation of under co-ordinated Al³⁺ ions at the surface. Such under co-ordinated ions are expected to be strong Lewis acid sites. This is the first ab initio determination of the atomic scale structure of such sites on the surface of β-AlF₃.