Chromium oxide supported on zirconia was prepared by dry impregnation of powdered Zr(OH)(4) with an aqueous solution of (NH4)(2)CrO4 followed by calcining in air. Upon the addition of only a small amount of chromium oxide (1 wt% Cr) to ZrO2, both the acidity and acid strength of the catalyst increased remarkably. The redox and catalytic behaviors of the samples were investigated through XPS and the reaction of cumene using a pulse technique. It was found that Cr6+ species existing on the surface of catalyst were responsible for the formation of strong acid sites and the catalytic activity for cracking of cumene. However, the Cr6+ species were easily reduced to Cr3+ species during the catalytic reaction of cumene and the reduced Cr3+ species were active for a-methylstyrene formation due to the dehydrogenation of cumene. The reduced Cr3+ species could be reoxidized by treatment with O-2 and subsequently the reoxidized catalyst exhibited catalytic activity for the cracking reaction of cumene.