Alkali-metal fluorides supported on γ-alumina. Surface reactions involving¹⁸F- and³⁵S-labelled sulphur tetrafluoride and thionyl fluoride,³⁵S-labelled sulphur dioxide,¹⁸F- and¹⁴C-labelled carbonyl fluoride and¹⁴C-labelled carbon dioxide

Abstract

Reactions between the Lewis acids, SF4, F2SO, F2CO and CO2, radiolabelled with 14C, 18F and 35S as appropriate, and CsF or KF supported on γ-alumina have been studied under heterogeneous conditions at room temperature. Fluorine-containing Lewis acids react in two ways, with surface F– anions to form Lewis acid–base complexes and to fluorinate surface hydroxyl groups. Maximum surface F– anion activity occurs at a metal fluoride loading of 5.5 mmol g–1. The reaction between CsF or KF and γ-alumina to give hexafluoroaluminate salts, which occurs during the impregnation process, becomes more important as the metal fluoride loading increases over the range 0.6–20.0 mmol g–1. This reaction is accompanied by dehydroxylation of the surface of the support, but there is no evidence for the presence of free hydroxide anions.