CHARACTERIZATION AND SELECTIVE POISONING OF ACID SITES ON SULFATED ZIRCONIA

Microcalorimetric measurements and infrared spectroscopy of ammonia adsorption were used to characterize the acidic properties of sulfated zirconia catalysts. Reaction kinetic measurements for n-butane isomerization were conducted over catalysts that were selectively poisoned with controlled amounts of ammonia. Initial heats of ammonia adsorption on the strong acid sites of sulfated zirconia were 150-165 kJ/mol, and these sites contain Bronsted acid and possibly Lewis acid centers. Sulfated zirconia samples that show high activity for the isomerization of n-butane possess Bronsted acid sites of intermediate strength, with differential heats of ammonia adsorption between 125 and 140 kJ/mol. The results of selective poisoning of sulfated zirconia with ammonia confirm that Bronsted acid sites of intermediate strength are active for n-butane isomerization at 423 K while not discounting a possible role of the stronger acid sites.