Heterogeneous environmental catalysis – a gentle art: CeO2–ZrO2 mixed oxides as a case history

Current status and perspectives of rare earth catalytic materials and catalysis

Structure, synthesis, and catalytic properties of nanosize cerium-zirconium-based solid solutions in environmental catalysis

Differences in surface and structural properties, thermal stability and oxygen storage capability (OSC) were investigated from different interactions between Ce0.7Zr0.3O2 and Al2O3 in mixed ceria−zirconia−alumina oxides. Physical techniques such as X-ray diffraction (XRD), BET and pore volume measurement, electron spin resonance (EPR), and mass spectrometry with CO−O2 transient pulses/CO pulses were used for sample characterization. With incorporation of Al3+ into the lattices of Ce0.7Zr0.3O2 at different degrees, which indicates the essential interaction between Ce0.7Zr0.3O2 and Al2O3, we found that mixed oxides have various structural properties. The sample of which most Al3+ incorporated into Ce0.7Zr0.3O2 lattices has intimate interaction, the smallest crystallites, and the highest surface area confirmed through BET and XRD measurements. Meanwhile, EPR detected increasing Ce3+ and OSC is obviously enhanced by the intimate interaction between ceria−zircona and alumina. The results show that the intimate...

Effect of Interaction between Ce0.7Zr0.3O2 and Al2O3 on Structural Characteristics, Thermal Stability, and Oxygen Storage Capacity

A series of nonplatinic ceria-based oxides supported catalysts LaCoO3/K2CO3/S (S=CeO2, Ce0.75Zr0.25O2 or 5%Y/Ce0.75Zr0.25O2) were prepared by successive impregnation and employed for lean-burn NOx trapping. It is found that the doping of Zr or YZr into CeO2 facilitates the formation of CeZrO binary or YCeZrO ternary solid solutions, increasing the specific surface area and improving the redox property of ceria. The results of EXAFS and H2-TPR reveal that the LaCoO3 in the solid solution supported catalysts possesses higher dispersion and better reducibility than that in CeO2 supported one. The result of O2-TPD shows that the surface active oxygen species are remarkably increased after loading LaCoO3 on the supports. The YCeZrO ternary solid solution supported catalyst containing 5 wt % K2CO3 exhibits the best performance for NO oxidation and reduction at 350 °C, showing a high NO-to-NO2 conversion (66.5%) at lean condition, and a very high NOx reduction percentage (98.2%) and an extremely high NOx-to-N2 s...

YCeZrO Ternary Oxide Solid Solution Supported Nonplatinic Lean-Burn NOx Trap Catalysts Using LaCoO3 Perovskite as Active Phase

Car manufacturers use close coupled three way catalysts to reduce cold start emissions. These close coupled catalysts must show long term durability and thermal stability at temperatures higher than 1000 °C. Thus, during the past 10 years, a significant amount of attention has been paid to the design of CeO2-ZrO2 OSC materials with improved surface area, phase and OSC stability. Solid solutions of Ce/Zr mixed oxides are now commonly available on industrial scale. Recent studies have demonstrated that the introduction of rare earth oxides promoters such as La, Pr, Nd, Y, Sm [ENGELHARD WO patent o2 30546; OMG-DMC2 EP Patent 1 181 970; DAIHATSU EP Patent 1 174 174; DELPHI US Patent 6 387 338; ENGELHARD WO Patent 02 22242] or aluminium oxide [TOYOTA EP Patent 1 172 139; Kanzawa et al. SAE Technical Paper 2003-01- 0811] in the Ce/Zr matrix is a very good way to improve the thermal stability and the redox properties of these materials. Positive interactions between PGM and these ‘promoters’ are also claimed. Nevertheless, not only the composition but the optimization of the manufacturing processes is a key factor to obtain both high thermal stability (expressed as surface area and XRD phase purity) and OSC. To meet the increasingly stringent emission limits, Rhodia has developed a new generation of CeZr based mixed oxides. These materials show phase stability and thermal stability at temperatures higher than 1100 °C in a wide composition range: from Zr-rich to Ce-rich mixed oxides. These characteristics have been obtained with a new manufacturing process which leads to highly porous materials. The controlled morphology at microscopic and macroscopic scale prevents particle sintering under severe ageing conditions. Such materials are preferred PGM supports for cost effective catalysts with low PGM loadings.

From Zr-rich to Ce-rich: thermal stability of OSC materials on the whole range of composition

Innovative Materials with High Stability, High OSC, and Low Light-Off for Low PGM Technology

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From Zr-rich to Ce-rich: thermal stability of OSC materials on the whole range of composition

Innovative Materials with High Stability, High OSC, and Low Light-Off for Low PGM Technology