Synthesis and Surface acidity of Amorphous Fluorine-Containing Aluminium Borates

A series of fluorine-containing aluminium borate samples with Al2O3/B2O3 = 3 and HF/B2O3 = 0.05-0.50 molar ratios has been synthesized by an impregnation method using NH4F. The materials obtained are amorphous up to 840-1130 K. Their thermal transformations were investigated by DTAand MSA. There are Lewis and Brönsted acid sites present in these samples. The very strong Lewis sites are due to formation of trigonal B3+, bonded with F- on the surface of fluorine-containing aluminium borates. Dehydration of isopropyl alcohol was used as a probe reaction to measure the acidity. The results of measurements have shown that these materials were more acidic and catalytically active than the starting aluminium borate.