CHARACTERIZATION AND SELECTIVE POISONING OF ACID SITES ON SULFATED ZIRCONIA

Microcalorimetric measurements and infrared spectroscopy of ammonia ad sorption were used to characterize the acidic properties of sulfated z irconia catalysts. Reaction kinetic measurements for n-butane isomeriz ation were conducted over catalysts that were selectively poisoned wit h controlled amounts of ammonia. Initial heats of ammonia adsorption o n the strong acid sites of sulfated zirconia were 150-165 kJ/mol, and these sites contain Bronsted acid and possibly Lewis acid centers. Sul fated zirconia samples that show high activity for the isomerization o f n-butane possess Bronsted acid sites of intermediate strength, with differential heats of ammonia adsorption between 125 and 140 kJ/mol. T he results of selective poisoning of sulfated zirconia with ammonia co nfirm 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.