Investigating acidity of metal fluoride surfaces by spectroscopic and chemical methods

Recent investigations into the surface acidity of some aluminium and magnesium fluorides and their derivatives are reviewed with emphases on relative acidities and accessibilities of surface sites. The high specific surface areas of the materials are ideal for their study, either by FTIR spectroscopy using various probe molecules that have different basicity and steric requirements or by carrying out probe reactions that are catalysed by acidic surfaces. Context for some of the recent work is provided by a summary of the commercial catalyst, fluorinated chromia and the related, fluorinated aluminas; a particular emphasis in these sections is their catalysis of reactions that involve carbon–halogen species. For the high surface area metal fluorides and their derivatives, room temperature dehydrochlorination of tert-butyl chloride, employing chlorine-36 labelling to detect surface adsorbed species, enables comparative studies of surface acidity to be undertaken.