The effects of ZrO2 content on the CO oxidation activity in a series of CuOx/CexZr1-xO2 (x = 0, 0. 15, 0.5, 0.7 and 1) catalysts were investigated, both in the absence and in the presence of H-2, i.e. preferential CO oxidation-PROX. The investigation was performed under light-off conditions to focus the effects of transients and shut-down/start-up cycles on the performance; such phenomena are expected to affect the activity of PROX catalysts in small/delocalised fuel reformers. Evidence has been obtained for a transition from an "oxidized" towards a "reduced" state of the catalyst under the simulated PROX reaction Conditions as a function of the reaction temperature, leading to different active species under the reaction conditions. Both CO oxidation activity and PROX selectivity appear to be affected by this process. IR characterisation of the surface copper species suggests an important role of reduced cerium sites in close contact with copper clusters on the CO oxidation activity at low temperatures.
