Nanophase Fluorite-Structured CeO2–ZrO2Catalysts Prepared by High-Energy Mechanical Milling☆

The utilization of mechanical milling for the preparation of catalysts based on ceria structurally modified with zirconia is presented. It is shown that room-temperature high-energy ball milling is an effective tool for the synthesis of nanophase CeO2–ZrO2solid solution in a wide composition range. The use of combined X-ray diffraction analysis, Raman spectroscopy, and electron microscopy indicate that the milling process induces the formation of true solid solutions with a contraction of thecell parameter for cubic ceria following the introduction of Zr into the lattice. This, in turn, remarkably enhances the oxygen storage/transport and redox capacity compared to pure ceria and zirconia or to a simple mixture thereof. An unusual resistance to high-temperature cycling was also evidenced. These features were analyzed by the study of the reduction profile of dopedceria carried out by temperature-programmed reduction at different milling times. The oxygen storage capacity (OSC) of the catalysts was also evaluated;both the total and the kinetic accessible OSC indicated that the best composition is CexZr1−xO2withx > 0.5. This was correlated to the structural features and to the presence of a high concentration of ions with redox character (i.e., Ce4+ions) which favor oxygen mobility.