Wander A, Searle B G, Bailey C L, Harrison N M
CCLRC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD, United Kingdom.
J Phys Chem B. 2005 Dec 8;109(48):22935-8. doi: 10.1021/jp052646p.
Strong Lewis acid catalysts are widely used in a variety of industrial processes including Cl/F exchange reactions. Aluminum 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 surface thermodynamics calculations based on hybrid-exchange density functional theory to predict the composition and structure of the basal plane surface of alpha-AlF3 for the first time. We examine four possible terminations of the alpha-AlF3 (0001) surface and demonstrate that the surface is terminated by a layer containing two fluorine atoms per cell at all realistic fluorine partial pressures. The fluorine ions in the outermost layer of the material reconstruct to mask the Al3+ ion from the external gas phase and consequently we would expect this surface to be inactive as a Lewis acid catalyst in line with experimental observation.
强路易斯酸催化剂广泛应用于包括氯/氟交换反应在内的各种工业过程。氟化铝（AlF₃）在这类反应中具有巨大的应用潜力。尽管表面在催化过程中很重要，但关于AlF₃表面详细的原子尺度结构却知之甚少。在当前的研究中，我们首次采用基于杂化交换密度泛函理论的先进表面热力学计算方法，来预测α-AlF₃基面的组成和结构。我们研究了α-AlF₃（0001）表面的四种可能的终止方式，并证明在所有实际的氟分压下，该表面由每个晶胞包含两个氟原子的一层所终止。材料最外层的氟离子会重构以屏蔽外部气相中的Al³⁺离子，因此我们预计该表面作为路易斯酸催化剂是无活性的，这与实验观察结果一致。
