Changes in the surface structure of sulfated zirconia prepared by sol-gel method were studied using nitrogen adsorption, XRD, TGA and in situ DRIFTS. These studies were performed following deactivation and regeneration of the catalyst. The physical properties of sulfated sol-gel zirconia were unchanged as a result of reaction and catalyst regeneration. The isomerization of n-butane was used as a probe reaction. Both Bronsted and Lewis acid sites as determined using pyridine adsorption at 100 degrees C were observed on sulfated zirconia. Only Lewis acid sites were observed on non-sulfated zirconia. The ratio of Bronsted to Lewis acid sites was found to be strongly dependent on catalyst pre-treatment temperature prior to reaction. The Bronsted to Lewis acid ratio was observed to decrease from a value of 0.466 to 0.127 following the removal of the catalytically active surface sulfur. The total catalyst acidity was observed to decrease only slightly following removal of this surface sulfur species. An infrared band, centered at 1370 cm(-1), was observed for the catalytically active material. This band appeared following activation in N-2 at 375 degrees C and was assigned to S=O. A Bronsted/Lewis acid site ratio of approximately 0.5 was found to be optimum for the isomerization of n-butane.