NANOPHASE FLUORITE-STRUCTURED CEO2-ZRO2 CATALYSTS PREPARED BY HIGH-ENERGY MECHANICAL MILLING - ANALYSIS OF LOW-TEMPERATURE REDOX ACTIVITY AND OXYGEN STORAGE CAPACITY

The utilization of mechanical milling for the preparation of catalysts based on ceria structurally modified with zirconia is presented. It i s shown that room-temperature high-energy hall milling is an effective tool for the synthesis of nanophase CeO2-ZrO2 solid solution in a wid e composition range, The use of combined X-ray diffraction analysis, R aman spectroscopy, and electron microscopy indicate that the milling p rocess induces the formation of true solid solutions with a contractio n of the cell parameter for cubic ceria following the introduction of Zr into the lattice, This, in turn, remarkably enhances the oxygen sto rage/transport and redox capacity compared to pure ceria and zirconia or to a simple mixture thereof. An unusual resistance to high-temperat ure cycling was also evidenced, These features were analyzed by the st udy of the reduction profile of doped ceria carried out by temperature -programmed reduction at different milling times, The oxygen storage c apacity (OSC) of the catalysts was also evaluated; both the total and the kinetic accessible OSC indicated that the best composition is CexZ r1-xO2 with x > 0.5. This was correlated to the structural features an d to the presence of a high concentration of ions with redox character (i.e., Ce4+ ions) which favor oxygen mobility. (C) 1997 Academic Pres s.