High surface aluminium fluoride, HS-AlF₃, and aluminium chlorofluoride, ACF, (AlCl_xF_3−x, x = 0.05…0.3) are amorphous solids with an extraordinary high Lewis acidity, which play an increasingly important role in heterogeneous catalysis. After a historic introduction, an overview of the different experimental and theoretical methods for understanding the nature of these catalysts is provided. Special attention is given to the theoretical modelling of the surface centres and the comparison with experimental results. A classification of these solid Lewis acids among well-known molecular Lewis acids is achieved using various methods. Several fascinating catalytic reactions involving C–H and C–F bond activation are presented in the second part of the review. This includes H/D exchange between alkanes (and not only arenes), hydroarylation even with deactivated aromatic compounds, activation of fluoromethanes due to hydrodefluorination, and finally, selective dehydrohalogenation reactions of hydrochlorofluoro-alkanes.

Amorphous materials—magnesium oxide fluoride with hydroxy groups—of high surface area were prepared for the first time by a soft sol–gel method involving initial fluorination and subsequent hydrolysis of the fluorinated gel. Their structural properties were studied with XRD, FTIR, XPS, and ¹⁹F MAS NMR. The magnesium oxide fluorides with hydroxy groups were also tested as heterogeneous catalysts in Michael additions. The incorporation of F into the MgO network led to diverse fluorine coordinations and high surface areas. The introduction of F into the framework enables a tuning of the base properties of the materials and leads to varied catalytic activities and selectivities. A weaker basicity can be obtained by the bridging of isolated OH groups in the MgF₂ network with increasing fluorine content. The sample prepared with an F : Mg molar ratio of 1.6 exhibited a catalytic activity similar to that of calcined Mg–Al hydrotalcites and selectively produced Michael addition products in high yields.