Two sulfated zirconia catalysts were prepared via sulfation and calcination of zirconium hydroxide at 873 K; the zirconium hydroxide had been aged at room temperature for 1 h (SZ-1) or aged at 373 K for 24 h (SZ-2). SZ-1 was active for n-butane isomerization at 373 K; SZ-2 reached a similar performance level only at 473 K. Both materials contained about 9 wt% sulfate and were tetragonal. Because of a lower BET surface area (105 vs. 148 m(2)/g) SZ-1 featured a higher sulfate density, and XRD and EXAFS analysis showed larger (ca. 10 nm) and more well ordered crystals than for SZ-2. n-Butane TPD on SZ-1 showed a butene desorption peak at low temperature, whereas no obvious butene desorption was observed with SZ-2. suggesting that SZ-1 has a higher oxidizing power at low temperature than SZ-2. The number of sites capable of dehydrogenation are less than 5 mumol/g, because the differential heats of n-butane adsorption as measured by microcalorimetry were 45-60 kJ/mol for higher coverages, indicating weak and reversible interaction. TAP experiments describe the adsorption and desorption behavior of n-butane at different activity states and are the basis for a simple adsorption model. Reactant pulses and purge experiments show that the active species, presumably formed in an oxidative dehydrogenation step, are stable at the surface under reaction conditions. (C) 2004 Elsevier Inc. All rights reserved.