A series of catalysts based on combinations between copper and cerium oxides, in which the former has been modified by doping with Co, Zn and Sn, have been prepared by a microemulsion method and characterized by XRD and S-BET measurements. Their catalytic activity as well as details of redox processes taking place during the course of the reaction has been examined by means of operando-DRIFTS-MS under CO-PROX conditions. The results reveal differences in the characteristics of carbonyl species formed through a reductive process during the course of the reaction which are employed to rationalize catalytic properties of the systems. (C) 2009 Elsevier B.V. All rights reserved.