Brønsted acidity of amorphous silica-aluminas for hydrocracking of Fischer-Tropsch wax into diesel fractions

A series of amorphous silica-aluminas were hydrothermally synthesized in the presence of tetraethylammonium hydroxide. Their physicochemical properties were well characterized, and particularly, a facile method of preferentially adsorbing bulky 2, 4, 6-collidine followed by adsorbing pyridine for FTIR was innovatively used to quantitively distinguish the Brønsted acid sites in micropores and on external surfaces. All protonic samples were transformed into hydrocracking catalysts by loading with 0.5 wt% platinum; and the relationship between Brønsted acidity of supports and the catalytic performance was studied by hydrocracking of Fischer-Tropsch wax. The results illustrated that the medium strong Brønsted acid sites located on the external surface play important role on the activity. And the lower the strong Brønsted acid density in micropores, the higher the diesel selectivity. Among the catalysts tested, Pt/SA-10 catalyst exhibited high selectivity to diesel (78.7%) at about 48.8% conversion under reaction conditions close to industrial ones.