Reduction behavior of nanoparticles of Ce0.8Zr0.2O2 produced by different approaches

High surface area ceria–zirconia solid solutions with nominal composition Ce0.8Zr0.2O2 were prepared by co-precipitation and microemulsion techniques. The samples were characterized by XRD, temperature programmed reduction and N2 physisorption after various calcination treatments. Both syntheses led to the formation of a single cubic phase. The reduction kinetics of Ce0.8Zr0.2O2 was studied by static volumetric hydrogen adsorption. A change in the rate-controlling regime was observed with the temperature increase. The apparent activation energies determined between 473 and 523 K were 83 and 70kJmol-1 for the Ce0.8Zr0.2O2 produced by co-precipitation and microemulsion, respectively. In the high temperature range (523–673 K) both samples showed an apparent activation energy of 30kJmol-1. Considering the relatively high hydrogen pressure used during the volumetric measurements and the high reduction degree reached, the reduction rate of Ce0.8Zr0.2O2 can be interpreted as bulk diffusion limited at 673 K, whereas at 473 K the process is surface step controlled.