The properties of CrO3-ZrO2 and Pt/CrO3-ZrO2 were studied by IR and ESR spectroscopy to elucidate the active sites in n-heptane isomerization and cumene cracking. Surface analyses showed the presence of cubic, monoclinic and tetragonal phases of ZrO2 with a BET specific surface area of about 150 m(2)/g for both catalysts. 2,6-Lutidine adsorbed IR confirmed the presence of treble doublet bands at 1675 + 1660, 1650 + 1625 and 1640 + 1630 cm(-1) corresponding to Bronsted acid sites and quartet doublet bands at 1604 + 1580, 1595 + 1580, 1590 + 1580 and 1570 + 1560 cm(-1) corresponding to Lewis acid sites. The presence of Pt enhanced the activity of CrO3-ZrO2 in cumene hydrocracking, in which Pt facilitated the formation of protonic acid sites at 1675 + 1660 and 1650 + 1625 cm(-1) through a hydrogen spillover mechanism. The IR study verified that the Lewis acidic center at 1570 + 1560 cm(-1) was involved in the formation of protons by trapping electrons. Meanwhile, neither CrO3-ZrO2 nor Pt/CrO3-ZrO2 was active in n-heptane hydroisomerization. (c) 2013 Elsevier B.V. All rights reserved.