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Preparation and Industrial Production of High-performance Ceria-Zirconia Mixed Oxides

Author: YangJiaFu
Tutor: ZhangZhaoLiang
School: Jinan University
Course: Chemical Engineering
Keywords: Ceria-Zirconia mixed oxides high performance industrialized pilot
CLC: TQ426
Type: Master's thesis
Year: 2013
Downloads: 21
Quote: 0
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Abstract


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.

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CLC: > Industrial Technology > Chemical Industry > Reagents and the production of pure chemicals > Catalyst ( catalyst )
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