A nanoparticulate CeO2 catalyst is presented that is able to oxidize cyclohexane to K/A-oil (a mixture of cyclohexanone and cyclohexanol) using hydroperoxides as oxidizing species. The improvement in selectivity with decreasing particle size suggests the existence of a structure-activity relationship in this process, and points to a preferential activation of cyclohexane at defective corner or edge sites. A detailed theoretical study of the reaction mechanism over three different CeO2 catalyst models shows that cyclohexane is preferentially activated by bicoordinated oxygen atoms present at the edges of small particles, following a Mars van Krevelen mechanism which has been confirmed by in situ IR spectroscopy and O-18/O-16 isotopic exchange experiments. The process is fully heterogeneous, and the catalyst can be reused without loss of activity up to four cycles. (C) 2016 Elsevier Inc. All rights reserved.