Preparation And Industrial Production Of High-performance Ceria-Zirconia Mixed Oxides

Environmental pollution caused by the exhaust from vehicles has attracted more andmore attention nowadays. Three-way catalytic purification technology （TWCs） is the mosteffective way to control pollutions discharged from gasoline engine powered vehicles. Asoxygen storage materials and key part of three-way catalysts, ceria-zirconia mixed oxidesexhibited significant effects on broadening the window of air/fuel ratio and stabilizing theperformance of catalyst. For the sake of reducing the exhaust pollution effectively, the workingtemperature in TWC converter can rise even above1000-1100℃. Although excellent coldstart performance can be fulfilled in this practical process, the problems of the sintering ofceria-zirconia mixed oxides and the loss of oxygen storage capacity （OSC） still exist, leadingto the lowering of activities of TWC catalysts. Therefore, improvement of high thermalstability in ceria-zirconia mixed oxides is very important to develop TWCs with high catalyticperformance.In the laboratory test, CZPN was synthesized by coprecipitation method, coprecipitation-supercritical drying method （ethanol or CO₂） and coprecipitation-hydrothermal method. Thetextural-structural property, specific surface area and redox property of catalysts were tested byX-ray diffraction （XRD）, N2-adsorption/desorption （BET）, temprerature-programmedreduction （H₂-TPR） technique. The results of BET show that CZPN prepared bycoprecipitation method has the specific surface area of30.24m²/g and the pore volume of0.12cm³/g after aging at1000℃for12h. However, CZPN prepared by coprecipitation-CO₂supercritical drying technique possess the highest specific surface area （54.2m²/g） andmaximum pore volume （0.491cm³/g） with wide mesopore-size distribution （10-100nm） afteraging at1000℃for12h. The specific surface area and pore volume are41.1m²/g and0.21cm³/g respectively for CZPN prepared by coprecipitation-hydrothermal method. XRD resultssuggest that all the samples prepared by these three methods present CeO₂cubic phase.H₂-TPR results of CZPN obtained by coprecipitation-hydrothermal method exhibits the largesthydrogen consumption （23.7μmol/g）.Due to the limits for the status of co-enterprise and the cost, coprecipitation-hydrothermal method was chosen to prepare CZPN and CZLY in the industrialization pilot scale. The crystal structure and specific surface area as well as the pore size distribution werecharacterized using X-ray diffraction and N2-adsorption/desorption. Furthermore, the oxygenstorage capacity （OSC） of the as-synthesized samples was also tested. XRD results show thatCZPN and CZLY samples were still CeO₂cubic phase in pilot scale. The specific surface areasof fresh CZPN and CZLY samples were127.83m²/g and125.68m²/g with the pore sizedistribution range of4-10nm and2-7nm, and average pore size were7.09nm and4.72nm,respectively. Compared with the fresh samples, the specific surface areas of both CZPN andCZLY were decreased to30.55m²/g and24.61m²/g after aging at1000℃. The results ofOSC test showed that oxygen storage capacities of aged CZPN and CZLY were92.14μmol/gand75.16μmol/g, respectively, indicating that the aged samples possessed excellent oxygenstorage performance.