The n-butane isomerization reaction on Al-promoted zirconia catalysts modified by persulfate was studied both at low temperature in the absence of hydrogen and at high temperature in the presence of hydrogen. The addition of Al shows a significant enhancement in the activity and stability of the samples for n-butane isomerization at 250 degrees C. After running on stream for 200 h, the n-butane conversion on the catalyst containing 3 mol% Al2O3 remains steady at 72% of its equilibrium conversion and no observable trend of further deactivation has been observed. The different behavior of the with or without Al-promoted catalysts at low temperature and high temperature is probably associated with a change of reaction mechanism from bimolecular to monomolecular. Microcalorimetric measurements of ammonia adsorption on catalysts reveal that the remarkable activity and stability of the Al-promoted catalysts are caused by an appropriate distribution of acid site strengths and an enhancement in the number of acid sites with intermediate acid strengths effective for the n-butane isomerization reaction.