Increasing activity for the conversion of n-hexadecane is observed for 0.6% Pt-SO42--ZrO2 catalysts with increasing time of activation in air at 500 degrees C (773 K). XPS analysis suggests that, rather than a change in the crystal phase, this increase is due to a loss of water and/or an increase in surface concentration of SO42-. It is noted that there is a reasonably good correlation between the relative surface sulfate concentration and relative conversion of n-hexadecane with increasing heating time, although there are minor differences. In spite of the many assumptions that were made to generate the two curves showing the relative XPS peak area and the catalytic activity, there is surprising agreement between the two. It is therefore inviting to relate the catalytic activity for n-hexadecane conversion to that of the sulfate group. Furthermore, it appears that the active site related to the sulfate group is not one that contains water in its make-up.