PREPARATION AND PROPERTIES OF HIGHLY FLUORINATED ALUMINA PREPARED FROM BOEHMITE AEROGELS OR COMMERCIAL GAMMA-AI(2)O(3)

Pellets of alumina-based aerogels, doped with chromium or chromium and titanium, have been prepared according to a proposed preparation proc edure from preformed and partly dried aqueous gels precipitated from m etal chloride solutions. After supercritical drying, low density and h igh surface area (> 300 m(2) g(-1)) aerogel pellets were obtained, con sisting of ca. 5 nm boehmite crystals. Fluorination of such aerogels w ith CHF3 resulted in high conversion to fluoride with the formation of mainly alpha-AIF(3) and some beta/gamma-AIF(3). Substantial crystal g rowth was observed with uniform pellet shrinkage and a large decrease in surface area. in contrast to fluorinated materials prepared from co mmercial gamma-Al2O3 by fluorination with HF1 fluorinated aerogels hav e a much more expanded and heterogeneous structure with a broad distri bution of size/shape of particles and pores. Fluorinated aerogels show catalytic activity in trichloroethene hydrofluorination to CF3CH2Cl. By the fluorination of alumina-based aerogels, very porous, high surfa ce area and catalytically active fluorides can be prepared. Such highl y dispersed materials are believed to be very useful in studying heter ogeneous catalytic reactions of technically important fluoro-derivativ es of lower halogenated hydrocarbons.