Sulfur loading on a sulfated zirconia catalyst was studied as a function of H2SO4 concentration. The resulting catalytic activity was tested using the isomerization of n -butane as a reaction probe at 200degreesC. Optimum catalytic activity was observed for a catalyst prepared using 0.5 N H2SO4 . The amount of carbon required to completely deactivate the catalyst was determined using a TGA/FTIR technique. For all of the catalysts synthesized in this study it was found that two active sulfate sites were poisoned by a single deposited carbon atom. Using this information, an active site composed of two coupled sulfate sites, perhaps a surface pyrosulfate site, is suggested. Using a TGA/FTIR technique it was found that the number of catalytically active sulfate sites never exceeded 14% of the total sulfate loading. These results were also supported by calorimetric studies.