Mechanical Activation of α-AlF3: Changes in Structure and Reactivity

Abstract

α-AlF3, the thermodynamically stable rhombohedral phase of aluminum fluoride, was used as starting material to produce nanostructured powders by high-energy ball milling. Both the polycrystalline and the nanostructured powders were studied by XRD, TEM, and 27Al and 19F MAS NMR. Thermally programmed desorption of NH3 and IR spectroscopy of adsorbed CO probe molecules unambiguously demonstrate the formation of Lewis acid and Brønsted acid sites as a consequence of the mechanical impact. Catalytic test reactions using milled α-AlF3 as solid catalyst proved experimentally the theoretically suggested catalytic activity of nanosized AlF3 particles as a result of high structural distortion brought into the solid by milling.