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oxygen storage capacity of Pt-, Pd-, Rh/CeO_2-Based Oxide Catalyst

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Journal of Rare Earths 2007年第1期25卷 6-10页

作者：李凯王学中周泽兴吴晓东翁端 Laboratory of Advanced Materials Department of Materials Science and Engineering Tsinghua UniversityBeijing 100084 China Chinese Research Academy of Environmental Sciences Beijing 100012 China Chinese Research Academy of Environmental Sciences Beijing 100012 China

CZO （CeO2-ZrO2） and CZYO （CeO2-ZrO2-Y2O3） series of mixed oxides were prepared by coprecipitaion, and a part of these oxides were loaded with precious metals （PM）. XRD, BET, and oxygen storage capacity （OSC） investigations were performed on samples aged at 750, 900, and 1050 ℃. It was observed that BET surface area and OSC showed a marked decrease in CeO2 aged at high temperature, and the erystallite size showed an obvious increase. The CZO samples consist of cubic- and tetragonal crvstal phases, and their crystallite size increase rapidly when aged at high temperature. The CZYO samples consist of single crystal phase when the content of Y exceeds 0.15 mol, and their erystallite size increases slowly during high-temperature aging. It is concluded that additive Y can stabilize the performance of CZYO oxides. In the aged CZO and CZYO mixed-oxide systems, addition of a small amount of precious metals （Pt, Pd, Rh） increased the rate of reduction and led to an obvious improvement in OSC. OSC of CZO and CZYO with precious metals are related to their composition and the type of precious metal.

关键词： CeO2 CZO CZYO rare earths oxygen storage capacity precious metal

Synthesis and characterization of Nd^(3+)-doped Ce_(0.6)Zr_(0.4)O_(2) and its doping significance on oxygen storage capacity

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Rare Metals 2021年第1期40卷 231-236页

作者： Natesan Shanmuga Priya Chandramohan Somayaji S.Kanagaraj Siddaganga Institute of Technology TumkurKarnataka 572103India Indian institute of Technology Guwahati 781039India

Cerium and cerium-based oxides are found to be an important element in three-way catalytic converter(TWC).The effective utilization of TWC is found to be reduced due to thermal loading which results in structural deformation of ceria,Doping Zr^(4+)into the rare earth element can increase the oxygen storage capacity and thermal ***,an attempt was made to study the oxygen storage capacity and thermal stability of ceria by doping Zr^(4+)and Nd^(3+).Cerium-based nanocrystallite in the composition of Ce_(0.6)Zr_(0.4-x)Nd_(1.3)xO_(2)(0≤x≤0.4)was prepared by sol-gel synthesize technique with citric acid as a gel-forming agent.X-ray diffraction(XRD)result shows that doping Nd^(3+)into ceria lattice forms homogenous solid solution of cubic fluorite structure up to 25%of substitute *** higher amount of Nd^(3+)into ceria lattice leads to the formation of Nd_(2)O_(3).Raman spectrum study confirms that oxygen storage capacity band is present in Ce_(0.6)Zr_(0.4)O2 and Ce_(0.6)Zr_(0.3)Nd_(0.13)O_(2).The oxygen storage capacity was calculated through weight loss of the sample during the second heating cycle with cyclic heating from30 to 800℃in thermogravimetric analysis(TGA).The TGA study reveals that the oxygen storage capacity of Ce_(0.6)Zr_(0.4)O2 decreases after the substitution of Nd^(3+),which is due to the larger ionic radius of Nd^(3+)compared with that of Zr4+and CeO2.

关键词： Cerium oxide Sol-gel technique Thermogravimetric analysis Ionic radius Homogeneous solid solution oxygen storage capacity

Fabrication and characterization of Ce_(0.7)Zr_( 0.3)O_2 nanorods having high specific surface area and large oxygen storage capacity

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Particuology 2011年第1期9卷 63-68页

作者： Yucheng Du Shuli Shi Hong He Hongxing Dai Key Laboratory of Advanced Functional Materials Ministry of Education Beijing University of Technology Beijing 100124 China Department of Chemistry and Chemical Engineering College of Environmental and Energy Engineering Beijing University ofTechnology Beijing 100124 China

Nanorod-like Ce0.7Zr0.3O2 solid solutions were synthesized by a sodium dodecyl sulfate-assisted precipitation method. The samples were characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and specific surface area measurement. Typical Ce0.7Zr0.3O2 nanorods were 40 nm in average diameter and 450 nm in length, with specific surface area and oxygen storage capacity of 194 m2/g and 374 μmol/g, respectively.

关键词： Cerium–zirconium solid solution oxygen storage capacity Nanorod

Structure and oxygen storage capacity of Pd/Pr/CeO_2-ZrO_2 catalyst:effects of impregnated praseodymia

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Journal of Rare Earths 2014年第2期32卷 108-116页

作者：冉锐张宏伟吴晓东樊俊翁端 Key Laboratory of Advanced Materials(MOE) School of Materials Science and EngineeringTsinghua University The Administrative Centre for China's Agenda 21

Praseodymium （Pr） was impregnated to CeO2-ZrO2 solid solution by an impregnation method. The as-obtained Pr modi- fied CeO2-ZrO2 was impregnated with 1 wt.% Pd to prepare the catalysts. The structure and reducibility of the fresh and hydrother- really aged catalysts were characterized by X-ray diffraction （XRD）, Raman, X-ray photoelectron spectroscopy （XPS）, CO chemi- sorption and H2 temperature-programmed reduction （H2-TPR）. The oxygen storage capacity （OSC） was evaluated with CO serving as probe gas. Effects of impregnated Pr on the structure and oxygen storage capacity of catalysts were investigated. The results showed that the aged Pr-impregnated samples had much higher OSC and better reducibility than the unmodified ones. The scheme of structural evolutions of the catalysts with and without Pr was also established. Partial of the impregnated Pr diffused into the bulk of CeO2-ZrO2 during ageing, which inhibited the sintering, and increased the amount of oxygen vacancies in CeO2-ZrO2 support. Furthermore, those impregnated Pr species which covered on the surface of the support obstructed the strong metal-support interaction between Pd and Ce so as to reduce the encapsulation of Pd as well as the back spill-over of the oxygen during the catalytic process.

关键词： CeO2-ZrO2 praseodymia sintering covering oxygen storage capacity rare earths

Dynamic oxygen storage capacity Measurements on Ceria-Based Material

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Journal of Rare Earths 2007年第1期25卷 48-52页

作者：沈美庆王欣全安源翁端赵敏伟王军 School of Chemical Engineering & Technology Key Laboratory for Green Chemical Technology of State Education Ministry Tianjin UniversityTianjin 300072 ChinaState Key Laboratory of Engine Tianjin UniversityTianjin 300072 China School of Chemical Engineering & Technology Key Laboratory for Green Chemical Technology of State Education Ministry Tianjin UniversityTianjin 300072 China Department of Material Science & Engineering Tsinghua UniversityBeijing 100086 China

Dynamic oxygen storage and release capability （OSC） measurement apparatus was designed to evaluate the OSC performance of ceria-based oxygen storage material. The optimum measurement condition was at a frequency of 0.1 Hz with the inlet gas-flow sequence CO （5S）→O2（5S）→CO→O2 and a flow rate of 300 ml·min^-1. Under this condition, similar regular square wave in the inlet and outlet of the reactor was obtained to guarantee the reliability of the dynamic OSC results. The dynamic OSC performance of the CeO2 and Ce0.67Zr0.33O2 mixed oxide prepared using the citric sol-gel method was studied at the optimum measurement condition with focus on both quantitative and qualitative analyses, The results reveal distinctly that Ce0.67Zr0.33O2 had better dynamic OSC performance because of its higher oxygen migration rate than CeO2. Under dynamic conditions, two CO2 production peaks occurred corresponding to the CO pulse and the O2 pulse, respectively, during the entire cycle. The intensity and ratio between the two CO2 productions were highly influenced by temperature and frequency indicating complex surface phenomena during the oxygen storage/release process, As a result, this set-up can be applied to the evaluation of ceria-based material on the OSC performance.

关键词： oxygen storage capacity ceria-based oxygen storage material dynamic OSC measurement rare earths

Structure and oxygen storage capacity of Pr-doped Ce_(0.26)Zr_(0.74)O_2 mixed oxides

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Journal of Rare Earths 2011年第11期29卷 1053-1059页

作者：冉锐翁端吴晓东樊俊王蕾吴筱笛 Laboratory of Advanced Materials Department of Materials Science and EngineeringTsinghua University The Administrative Center for China's Agenda 21

Binary Ce-Zr（CZ）,Pr-Zr（PZ） and ternary Ce-Zr-Pr（CZP） mixed oxides were prepared by an ammonia-aided co-precipitation method,and were aged in a steam/air flow at 1050 °C.X-ray diffraction（XRD）,Raman spectra,X-photon spectra（XPS） and CO temperature programmed reduction（TPR） were carried out to characterize the micro-structure and reducibility of *** oxygen storage capacity（OSC） was evaluated with CO serving as probe *** results showed that a pseudo cubic structure was formed for the Zr-rich ceria-zirconia mixed oxides with Pr *** insertion of Pr prevented the phase segregation of the mixed oxides during the hydrothermal *** Pr doped samples showed better redox performances in comparison with CZ,and the sample doped with 5 wt.% Pr showed the most remarkably promoted dynamic oxygen storage *** phenomenon was closely related to both the reducibility and oxygen mobility of the mixed *** introduction of praseodymium into ceria-zirconia could accelerate the oxygen migration by increasing the amount of oxygen vacancies,although it was difficult for Pr3＋ ions themselves to participate in the oxygen exchange process.

关键词： ceria-zirconia Zr-rich praseodymium oxygen storage capacity rare earths

Structures and oxygen storage capacities of CeO_2-ZrO_2-Al_2O_3 ternary oxides prepared by a green route:supercritical anti-solvent precipitation

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Journal of Rare Earths 2012年第6期30卷 524-528页

作者：黄盼姜浩锡张敏华 Key Laboratory for Green Chemical Technology of Ministry of Education R&D Center for Petrochemical TechnologyTianjin University

CeO2-ZrO2-Al2O3 ternary oxides were successfully prepared by a green route of supercritical anti-solvent precipitation with supercritical CO2 as anti-solvent and methanol as solvent. The structures and oxygen storage capacities of these ternary oxides were characterized by XRD, Raman spectra and oxygen storage capacity measurements. It was found that Al3＋ and Zr4＋ inserted into CeO2 lattice, forming CeO2-ZrO2-Al2O3 solid solution. The concentration of aluminium isopropoxide in the solution affected the concentration of oxygen vacancy and the distortion of oxygen sublattice which were responsible for the oxygen storage capacity. The rapidest oxygen uptake/release rate and maximum total oxygen storage capacity （122.0 mmolO2/molCeO2） were obtained with the aluminitun isopropoxide concentration at 0.2 wt.% in the solution.

关键词： CeO2-ZrO2-Al2O3 solid solution supercritical anti-solvent precipitation oxygen storage capacity rare earths

Role of Surface Adsorption in Fast oxygen storage/Release of CeO_2-ZrO_2 Mixed Oxides

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Journal of Rare Earths 2007年第4期25卷 416-421页

作者：吴晓东梁清吴筱笛翁端 Laboratory of Advanced Materials Department of Materials Science and Engineering Tsinghua University

Four kinds of CeO2-ZrO2 mixed oxides, i.e., a physical mixture of ceria and zirconia （CZP）, zirconia-coated ceria （ZCC）, ceria-coated zirconia （CCZ） and a chemical mixture of celia and zirconia （CZC）, were prepared. The oxygen storage capacity （OSC） measurements at 500℃ were performed under transient and stationary reaction conditions. All the curves of CO2 evolution during CO-O2 cycles presented a bimodal shape. The fast peak was primarily the result of the reaction of CO with the oxygen from the oxides, which was mainly determined by the nature of the material The sec- ond peak was mostly related to the CO2 adsorption behavior and was highly influenced by the surface area and the number of surface active sites. As a result, OSC activity of the samples followed in the order of CZC 〉 CCZ 〉 ZCC=CZP.

关键词： CeO2-ZrO2 microstructure surface properties oxygen storage capacity rare earths

Preparation of Ce_(0.65)Zr_(0.35)O_2 by co-precipitation: The role of hydrogen peroxide

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Journal of Rare Earths 2013年第5期31卷 461-469页

作者：黄利华陈山虎朱艺龚茂初陈耀强 Department of Architecture and Environment Sichuan University Insititute of Environment and Resources Southwest University of Science and Technology Key Laboratory of Green Chemistry & Technology of the Ministry of Education

The effect of H2O2 on the properties of Ce0.65Zr0.35O2 a mixed aqueous solution of ammonia and was explored by treating cerium nitrate and zirconium nitrate with in the presence/absence of H2O2. The resultant products were characterized by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, nitrogen adsorption/desorption, oxygen storage capacity （OSC） and H2- reduction （H2-TPR）. The presence of H2O2 was found to have profound effect on powder properties such as surface area, crystallite size of the samples. It was also shown that the addition of H2O2 favored the incorporation of Zr4＋ into CeO2 lattice, which facilitated the formation of CeO2-ZrO2 solid solution, and enhanced the thermal stability of the samples. OSC and H2-TPR studies indicated that the use of H2O2 enhanced the OSC and redox properties. Catalytic activity tests showed that as a support, the Ce0.65Zr0.35O2 prepared in the presence of H2O2 was more suitable for three-way catalyst. The corresponding Pd-only three-way catalyst demonstrated outstanding performance： wide air to fuel operation window, low light-off and total conversion temperature for the conversion of C3H8, NO and CO.

关键词： solid solution H2O2 oxygen storage capacity three-way catalysts Ce0.65Zr0.35O2 rare earths