Modification of the redox behaviour of CeO2 induced by structural doping with ZrO2

Reduction/oxidation behaviour of high surface area CeO2 and Ce0.5Zr0.5O2 mixed oxide is compared. It is shown that introduction of ZrO2 into the CeO2 framework with formation of a solid solution strongly modifies the reduction behaviour in comparison to that seen with CeO2 alone. Remarkably, upon repetitive reduction/oxidation processes, the temperature of the reduction of the solid solution decreases from 900 to 700 K. Conversely, in the aged CeO2 sample almost no reduction occurs below 900 K. Textural characterisation shows that the redox process favours a large sintering of both the samples and, unexpectedly, induces formation of a new mesoporosity centered at about 20 nm, The expansion/contraction of the lattice parameter upon, respectively, reduction/oxidation, detected by X-ray diffraction, is suggested to be responsible for the textural modification. The suppression of the redox capacities of CeO2 at moderate temperature is associated with the decrease of the surface area. The sintering process induces a structural modification of Ce0.5Zr0.5O2 which promotes the reduction in the bulk, resulting in a high efficiency of the Ce4+ reversible arrow Ce3+ redox cycle at moderate temperatures. (C) 1996 Academic Press, Inc.