A study on the oxidation activity of cobalt (Co) catalysts ion-exchanged and impregnated on NaY and NaUSY (ultra stable Y) zeolites and their alkali metal added counterpart, and the nature of the active supported Co species was carried out using the gas-phase catalytic oxidation of benzyl alcohol. The main oxidation products over the supported Co catalysts used in this study were benzaldehyde and CO2. The partial oxidation activity increased with increasing the amount of Co in the Co catalyst (Co/NaUSYimp) impregnated on NaUSY zeolite, although the degree of the increase in the benzaldehyde yield tended to decrease in the region of the higher amount of Co. The yield of benzaldehyde over the Co catalyst (Co/NaYimp) impregnated on NaY zeolite had a maximum at a comparatively lower amount of Co. The addition of an alkali metal to the impregnated and ion-exchanged Co catalysts with a low amount of Co (1 wt.%) effectively promoted the partial oxidation activity. The redox property of the supported Co catalysts was investigated using UV-vis diffuse reflectance (DR) spectra. The role of the added alkali metal was inferred to be assistance for Co-2, to be oxidized to Co3+ to form Co3O4 [Co2+(Co3+)(2)O-4] which was assumed to be active species for the partial oxidation of benzyl alcohol. (c) 2006 Elsevier B.V. All rights reserved.