Heats of adsorption of organic bases on aerosilogels containing small quantities of aluminium

Calorimetric heats of adsorption of the organic bases triethylamine and benzene on aerosilogels have been measured. The aerosilogels were prepared from industrial aerosils and dehydroxylated in vacuo at temperatures up to 1150°C. One sample of aerosilogel, which contained 0.4 % by weight of aluminium impurity, produced very active surface sites, which were characterized by a high initial heat of adsorption—about 50 kcal mol–1(209 kJ mol–1) for triethylamine and 20 kcal mol–1(84 kJ mol–1) for benzene. Other samples containing less than 0.02 % aluminium did not show this activity. Aluminium was artificially introduced into a pure sample of aerosilogel using aluminium nitrate solution. The adsorption properties of this sample were similar to those of the aerosilogel prepared from the impure aerosil containing 0.4 % aluminium.