The catalytic activity of Pt/SO42-/ZrO2 in the benzene hydrogenation and isomerization reaction at 250 degreesC is superior to that of other Pt/conventional solid acid catalysts such as Pt/MY-zeolite and Pt/H-mordenite. The catalytic activity of SO42-/ZrO2 for cyclohexane isomerization to methylcyclopentane at 250 degreesC is higher than that of KY-zeolite and H-mordenite. SO42-/ZrO2 and HM10 have more Bronsted acid sites of the highest strength and show a higher percentage of isomerization conversion. In contrast, ZrO2, which contains almost no Bronsted acid sites, and HY5.6, which contains almost no Bronsted acid sites of the highest strength, show a lower conversion percentage. Consequently, Bronsted acid sites of the highest strength are active sites responsible for cyclohexane isomerization. However, the isomerization conversion percentage does not completely correlate with the number of highest-strength Bronsted acid sites, suggesting that not all of these sites contribute to the reaction nor do only Bronsted acid sites influence cyclohexane isomerization. Neither the total number nor the number of highest-strength Lewis acid sites correlates with the isomerization conversion rate, indicating that Lewis acid sites are not responsible for cyclohexane isomerization.