The activity of the Pt-promoted systems prepared on the basis of Keggin H3PW12O40 (HPW) and H3PW11Zr (HPW11Zr), and Dawson H6P2W18O62 (HP2W18) and H6P2W21O71 (HP2W21) heteropoly acids supported on zirconia in the isomerization of n-hexane was studied. The Pt/HPW/ZrO2 catalytic system shows high activity in n-hexane isomerization. The yield of isohexanes was close to 80% and the selectivity was 96-98% at 190degreesC. The DTA and FTIR spectroscopic studies allowed us that partially distorted grafted Keggin ions are responsible for the catalytic activity. However, these species cannot be formed by dispersion of HP2Wn and HPW11Zr heteropoly acids because of their insufficient stability. The support of these systems on ZrO2 is accompanied by significant structural transformations. The Pt/HP2Wn/ZrO2 or HPW11Zr/ZrO2 catalytic systems shows the best performance (yield is close to 80%) at higher temperatures (30-40degreesC) than Pt/HPW/ZrO2. However, these systems show higher selectivity due to lower density of active sites and inhibition of bimolecular alkylation-cracking side reactions. (C) 2003 Elsevier B.V. All rights reserved.