The fluorolytic sol–gel reaction of aluminium alkoxides: a multinuclear MAS NMR study of structural influences of the synthesis parameters

The fluorolytic sol–gel reaction between aluminium alkoxides and non-aqueous HF leads, after drying in vacuum, to xerogels. These can be seen as intermediates for the preparation of aluminium fluorides with large surface areas having a great potential for application in diverse fields of heterogeneous catalysis. This work reports about a comprehensive systematic study of the involved local structures of the aluminium alkoxide fluorides and their changes provoked by (a) the variation of sol gel synthesis parameters, (b) a subsequent drying and (c) the exposure of the materials to different atmospheres. The main analytical tools are solid state MAS NMR investigations of the naturally abundant nuclei in these kinds of materials, namely 27Al, 19F for probing the Al- and F-environments and 1H and 13C for probing the organic moieties. The results of previous studies become more comprehensive and were underlined by the findings reported here.