To reduce the occurrence of cracking reactions and obtain high activity for n-heptane isomerization, we performed this study, aimed at improvements of the Al-promoted Pt/SO42-/ZrO2 (Pt/SZ) catalyst. The effect of sulfur content was studied and it was found that lowering sulfate content in the Al-promoted Pt/SZ resulted in remarkably enhanced selectivity towards iso-C-7 formation from 25% up to 83% compared with Pt/SZ without a loss of activity. The results of catalyst characterizations revealed that the tetragonal phase of ZrO2 and its acidity were responsible for the higher activity, and that aluminum helped to stabilize the tetragonal phase in Al-promoted Pt/SZ and hence maintained catalytic activity at low sulfate content, while the low acidity and high Pt dispersion resulted in a high ratio of metal sites to acid sites ;and hence benefited a higher selectivity for iso-C-7. (C) 2010 Elsevier B.V. All rights reserved.