Characterization of CeO2-ZrO2 mixed oxides prepared by two different co-precipitation methods

A series of cerium zirconium mixed oxides were prepared by two co-precipitation methods using magnesium hydrogen carbonate(MHC)and mixed ammonia-ammonia hydrogen carbonate(AAHC)as precipitant respectively.The crystal structure,BET surface area and morphology of the produced cerium zirconium mixed oxides were characterized by X-ray diffraction(XRD),Brumauer-Emmett-Teller(BET)and scanning electron microscopy(SEM)techniques.The reduction-oxidation behavior and oxygen storage capacity(OSC)performance were also studied by temperature programmed reduction(TPR)and oxygen pulse chemical adsorption methods.The XRD results demonstrated that the cerium zirconium mixed oxides obtained by both methods possessed structure of cubic solid solution phase.The fresh surface area calcinated at 600℃,aged surface area after 1000℃ and OSC at 500 ℃ of cerium zirconium mixed oxides were determined to be 89.337,34.784 m2/g,and 567 μmol O2/g for MHC method and 122.010,46.307 m2/g,and 665 μmol O2/g for AAHC method,respectively.     

Effects of precursor moisture and inert N_2 atmosphere calcinations on structure and properties of alumina modified CeZrLaNd mixed oxides

CeO_2-ZrO_2 mixed oxides are widely used in the three-way catalysts due to their unique reversible oxygen storage and release capacity. Large surface area, high oxygen storage capacity and good thermal stability of cerium zirconium mixed oxides are the key properties for the automotive catalysts so as to meet the strict emission regulations. In this work, alumina modified CeZrLaNd mixed oxides were prepared by a co-precipitation method. The effects of moisture in precursor and inert N2 atmosphere during calcinations on the structure and properties were investigated by Brunauer-Emmett-Teller(BET) surface area measurements, X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), hydrogen temperature-programmed reduction(H_2-TPR), oxygen storage capacity(OSC), Raman spectroscopy, and X-ray photoelectron spectroscopy(XPS). The results show that the moisture in precursor during calcinations increases the crystal grain size of the cerium zirconium mixed oxides, improving the thermal stability. And the aged surface area of sample after being calcined at1000 ℃ for 4 h reaches 68.8 m~2/g(5.7% increase compared with the common sample). The inert N2 atmosphere endows a great pore-enlarging effect, which leads to high fresh surface area of 148.9 m2/g(13.5% increase compared with the common sample) and big pore volume of 0.5705 mL/g. The redox and oxygen storage capacity are also improved by inert N2 atmosphere with high OSC value of 241.06μmolO_2/g(41.3% increase compared with the common calcination), due to the abundant formation of the crystal defects and oxygen vacancies.     

Effects of ammonia concentration in hydrothermal treatment on structure and redox properties of cerium zirconium solid solution

Cerium zirconium solid solution is a key washcoat material for automotive three-way catalysts(TWCs).However,improving the redox ability and high temperature thermal stability of cerium zirconium solid solution is still a challenge.In this paper,the cerium zirconium solid solution was prepared by a coprecipitation-hydrothermal method,and the effects of the ammonia concentration on their structures and redox properties were investigated.The results show that when the ammonia concentration is 0.8 mol/L,the aged sample(1100℃/10 h)of cerium zirconium solid solution has the highest specific surface area of 23.01 m²/g.Additionally,the increase of ammonia concentration improves the uniformity of phase compositions and increases the oxygen vacancies.When the ammonia concentration reaches 0.4 mol/L,the cerium zirconium solid solution exhibits the best redox activity,with the lowest reduction temperature of 565℃.Therefore,increasing ammonia concentration in the hydrothermal treatment is beneficial to the thermal stability and redox performance of cerium zirconium solid solution.     

Preparation and characteristics of nano-crystalline Cu-Ce-Zr-O composite oxides via a green route: supercritical anti-solvent process

The nano-crystalline Cu-Ce-Zr-O composite oxides were successfully prepared by the supercritical anti-solvent (SAS) process. The physicochemical properties and catalytic performances were investigated by X-ray diffraction (XRD), Raman spectroscopy, H2 temperature-programmed reduction (H2 -TPR), oxygen storage capacity (OSC) measurement and catalytic activity evaluation. It was found that Cu2+ ions incorporated into CeO2 -ZrO2 lattice to form Cu-Ce-Zr-O solid solution associated with the formation of oxygen vacancies. The Cu-Ce-Zr-O catalysts prepared via the SAS process with the Cu content 2.63 mol.% showed the highest OSC index of 636.9 μmol/g. Compared with the samples prepared by impregnation method, Cu doping using SAS process could improve the dispersion of Cu2+ in the composite oxide, enhance the interaction between Cu2+ and CeO2-ZrO2 , improve the reducibility of catalyst, and thus improve the OSC performance and increase the catalytic activity for CO oxidation at low temperature.     

Study on Catalysts with Rhodium Loading on Different Cerium-Zirconium Mixed Oxides

The catalysts with Rh loading on different cerium-zirconium mixed oxides were characterized by BET, H2-TPR and OSC. The effects of different cerium-zirconium mixed oxides on catalytic performance and thermal stability of Rh loaded catalyst were studied. The results show that: (1) Rh can enhance cerium-zirconium mixed oxides OSC and catalytic reaction rates; (2) cerium-zirconium mixed oxides with high Ce contents and low Zr contents are more favorable to the stability of catalysts. Moreover, the contents of CeO2 have important effect on catalysts characteristics, and the addition of some rare earth components, such as La, Pr and Nd also have some influences.     

Effect of CuO species and oxygen vacancies over CuO/CeO2 catalysts on low-temperature oxidation of ethyl acetate

The catalytic oxidation of ethyl acetate(EA) was studied over CuO/CeO₂ catalysts which were prepared by ball milling with different precursors(copper oxide,cerium acetate,cerium dioxide,copper acetate and cerium hydroxide).The CuO/CeO₂ catalyst(O-A) prepared with copper oxide and cerium acetate as precursors shows very high catalytic activity that 100% EA conversion is achieved at low temperature of 220℃.It is found that specific surface area(112.8 m²/g),particle...     

Effect of grain size on thermal stability and oxygen storage capacity of Ce0.17Zr0.73La0.02Nd0.04Y0.04O2 solid solutions

Nanostructured CeO_2-ZrO_2 materials are an irreplaceable constituent in catalytic systems for automobile exhaust purification due to their unique oxygen storage capacity(OSC). However, traditional CeO_2-ZrO_2 materials are easy to sinter at high temperature, which causes a sharp decrease of OSC. In this paper,La~(3+) , Nd~(3+) and Y~(3+) are chosen as dopants for CeO_2-ZrO_2 to improve anti-sintering and OSC properties.The Ce_(0.17) Zr_(0.73) La_(0.02) Nd_(0.04) Y_(0.04) O_2 powders(CZLNY) were prepared by co-precipitation method. The effects of grain sizes with different mixed chlorinated solution concentrations on performances were investigated. X-ray diffraction(XRD) and transmission electron micrograph(TEM) were performed to calculate the grain sizes of CZLNY. The specific surfaces, OSC and redox properties were investigated by N_2 adsorption/desorption and temperature programmed reduction(H2-TPR). The results show that introducing La~(3+) , Nd~(3+) and Y~(3+) into CeO_2-ZrO_2 lattice can improve the stability of phase structure and anti-sintering ability. Moreover, low concentration of mixed chlorinated solution remarkably improves structural and textural properties of CZLNY. Relatively large fresh grain exhibits superior thermal stability and OSC under the condition of being calcined at 800℃ for 3 h. The specific surface and OSC are42.37 m~2/g and 333.13 mmol/g after calcining at 1000℃ for 10 h, respectively. This is owing to the low sintered driving force of large grain and long-range migration energy of large pores during the sintering process, which are beneficial to the stability of structure in CZLNY materials.     

Preparation of Ce0.65Zr0.35O2 by co-precipitation： The role of hydrogen peroxide

The effect of H2O2 on the properties of Ce0.65Zr0.35O2 was explored by treating cerium nitrate and zirconium nitrate with a mixed aqueous solution of ammonia and ammonia-carbonate 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-temperature-programmed 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.     

Influence of [La(EDTA)]− on pore structure of activated alumina carrier at high-temperature

The activated alumina as a catalyst carrier were widely used in automotive exhaust catalysts under high temperature, such as, petroleum refining catalysts, hydrogenation and hydrodesulfurization catalyst carrier in China and abroad. γ-Al₂O₃ was the catalyst carrier that was the most widely used and the best carrier of improved specific surface area . However, the activation of the coating consisted of γ-Al₂O₃ were usually transformed into α-Al₂O₃ at 800 °C, causing increased density, reduced specific surface area, and the collapse result of pore structure. While the temperature reached 1200 °C, activation of coating detached from the carrier, the resistance of flowing gas increased, catalytic activity decreased. Addition of La₂O₃ stabilized the γ-Al₂O₃ crystal structure, which would keep the activation stability of coating at a high temperature and inhibit activity loss. The activated alumina carrier treated with the solid-pore-expanding agent containing [La(EDTA)]^? that synthesized using solid and solid-hybrid approach with the thermal stabilizer lanthana and EDTA at the high-temperature had a 10-30 μm large pore porous network-like structure, after alumina was calcined at 1200 °C for 1 h. The specific surface area of four specimen were beyond 120 m²/g, while the sample specific surface area of x([La(EDTA)]^?)=1% was up to 150.36 m²/g.     

乙二醇辅助聚乙烯醇制备花状氧化铈探索

利用浓硝酸和双氧水将不规则形貌氧化铈溶解，生成硝酸铈.采用水作为溶剂或水和乙二醇共同作为溶剂，聚乙烯醇作为分散剂，草酸铵作为沉淀剂，通过直接沉淀法合成草酸铈前驱体，在高温反应炉中按照8 ℃/min的升温程序，600 ℃保温2 h，得到氧化铈.结果表明，以水为溶剂，聚乙烯醇为分散剂时，所得氧化铈易碎，呈尺寸不均匀片状，厚度在100 nm左右，长度和宽度尺寸约3~10 μm和1~2 μm，比表面积为14.9 m2/g.以水和乙二醇共同为溶剂，聚乙烯醇为分散剂时，所得氧化铈具有花状结构，由表面光滑、尺寸均匀的纳米片组成，片状氧化铈的厚度、长度和宽度分别约100 nm、4 μm和1.5 μm，形成直径约2~5 μm的氧化铈花状团簇，比表面积为21.45 m2/g.利用乙二醇辅助聚乙烯醇制备花状氧化铈，有望应用于调节具有花状形貌的稀土氧化物.      

Preparation of fine copper powders from organic media by reaction with hydrogen under pressure: Part I. Experimental study

In this work, a novel method of preparing copper powder having the required properties for thick film applications was investigated. This method involves the precipitation of copper powder by hydrogen reduction under pressure from Kelex 100-decanol-Versatic 10-kerosene media. The parameters studied were temperature (453 to 573 K), hydrogen pressure (1.03 to 3.79 MPa) time, use of additives, solvent composition,etc. Powders with the following excellent properties were produced:d ₅₀ = 1 μm; 80 pct spread ?1.3 + 0.7 μm; specific surface area = 1 ±0.2 m²/g, spheroidal shape; and 0.056 wt pct oxygen content.     

Deoxidation of the tantalum powder produced by self-propagating high-temperature synthesis

The possibility of removal of oxygen and magnesium from the products of the magnesium reduction of tantalum pentoxide under self-propagating high-temperature synthesis conditions that contain 30 wt % Mg₄Ta₂O₉ is studied. Additional reduction of this material can decrease the magnesium content to <0.01%. The oxygen content in the fabricated tantalum powder does not exceed its amount in the surface oxide (3 × 10^?3 g/m²). The specific surface area of the powder is an order of magnitude higher than that of the initial material, which can result from the formation of a tantalum powder with a specific surface area >30 m²/g during the reduction of Mg₄Ta₂O₉.     

Hydrothermal synthesis of nanocrystalline powders in the ZrO2-Y2O3-CeO2 system

The paper examines the properties of the nanocrystalline powder 95 mole% ZrO₂-2 mole% CeO₂-3 mole% Y₂O₃, synthesized using a combination of two methods: coprecipitation and hydrothermal decomposition. It is established that coprecipitation produces an x-ray amorphous gel consisting of hard agglomerates from 5 to 10 μm and having a specific surface area of 120 m²/g and a bottle density of 2.94 g/cm³. Hydrothermal synthesis results in a low-temperature metastable cubic solid solution based on ZrO₂ (F-ZrO₂). Its specific surface area is 101.6 m²/g and bottle density is 4.65 g/cm³. Soft agglomerates (0.5–10 μm) consist of primary particles with sizes to 10 nm. The change in hydrothermal suspension processing steps results in soft agglomerates with branched internal porosity. This method allows synthesizing powders of needed compositions in the ZrO₂-CeO₂-Y₂O₃ system. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 23–30, 2007.     

Influence of cooling rate and addition of lanthanum and cerium on formation of nanoporous copper by chemical dealloying of CUlsAIss alloy

The influence of cooling rate and addition of La and Ce on the formation of nanoporous copper by chemical dealloying of Cu15Al85 alloy was studied. The components and microstructures of nanoporous copper were characterized by utilizing X-ray diffrac-tion, field emission scanning electron microscopy and energy dispersive X-ray analysis. N2 adsorption/desorption experiments were used to evaluate specific surface areas of samples. The results showed that, with the increase of cooling rate, phase composition of precursor alloy almost had no change, the ligament size of nanoporous copper had a decrease trend, and specific surface area in-creased gradually. And it was found that the specific surface area of the nanoporous copper obtained by Cu15Al85 alloy containing La and Ce was 63.258 m2/g, which was more than 11.739 m2/g compared with the nanoporous copper dealloying by Cu15Al85 alloy without La and Ce under the same conditions.     

The effect of hydrogen peroxide on properties of Ce_(0.35)Zr_(0.55)La_(0.055)Pr_(0.045)O_2 oxides and the catalytic performance used on Pd supported three-way catalyst

In this study,two series of cerium zirconium mixed oxides Ce_(0.35)Zr_(0.55)La_(0.055)Pr_(0.045)O_2 were prepared under traditional co-precipitation and oxidation co-precipitation methods respectively. The physicochemical properties of the samples were compared under these two methods and assessed by XRD,Raman,BET,TEM,H_2 TPR,OSC,XPS and catalysts measurements. The formation of homogeneity phase structure can be facilitated by changing the precipitating properties of Ce3+ under oxidation coprecipitation method, which is helpful to enhance the homogeneity of Ce and Zr at atomic level.What's more, it is conducive to remove impurities Na~+ and Cl~-by oxidation co-precipitation with hydrogen peroxide. The catalysts activities are related to both the redox properties and the textural properties of mixed oxides. The Pd-only TWCs supported on the CZLP-H-F exhibits better catalytic performance and thermal stability with wider air/fuel ratio operation window, lower light-off and full conversion temperatures of C_3 H_8 and NO. The homogeneity of phase structure for cerium zirconium mixed oxide can be predicted and deduced from detecting the atomic distribution uniformity of its precursor. So this work not only provides insights into the mechanisms for phase segregation of cerium zirconium mixed oxide, but also provides a guidance to improve homogeneity of cerium zirconium mixed oxide by adding additives.     

Enhanced thermal stability of Ce_(0.33)Zr_(0.55)(LaNdY)_(0.12)O_2 mixed oxides prepared by sulfate-aided coprecipitation method

Ceria-zirconia based mixed oxides(CZs) have been applied in three-way catalysts(TWCs) for their high surface area and oxygen storage capacity(OSC).In this work,enhanced thermal stability of Ce_(0.33)Zr_(0.55)(LaNdY)_(0.12)O_2 mixed oxides was realized via a facile and scalable approach,namely,sulfateaided coprecipitation method was labelled as CZ-S.Sulfate ion(SO_4~(2-)) was added into raw solution in the form of sulfuric acid and acted as coordination agent.The control sample was prepared by conventional coprecipitation method without sulfuric acid added and labelled as CZ.The promotion effect of sulfate ion was analyzed systematically by X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),N_2 adsorption-desorption,Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),OSC and hydrogen temperatureprogrammed reduction(H_2-TPR) analysis.XRD and high resolution TEM results reveal that CZ-S have homogeneous distributions of elements.TEM and SEM images show that fresh samples of CZ-S have narrower distributions of grain sizes and larger pore sizes than those of CZ.Through cross analysis of structure and morphology of CZ and CZ-S,we find that the introduction of sulfate ions results in uniform distributions of elements,narrows distributions of grain sizes,and enables the formation of secondary loose packing of sub-particles,which lead to enhanced thermal stability of the samples of CZ-S upon aging process at high temperature.After aging treatment at 1100℃ for 10 h,aged samples of CZ-S present larger specific surface areas and pore volumes than the aged sample prepared by conventional coprecipitation method without sulfate ions added.Furthermore,the aged sample of CZ-S2(SO_4~(2-)/Zr=1)possesses the highest specific surface area of 21.9 m2/g and the biggest pore volume of 0.035 mL/g among all aged samples.     

Effects of loading transition metal(Mn,Cr,Fe,Cu) oxides on oxygen storage/release properties of CeO_2-ZrO_2 solid solution

Cerium zirconium-based(CZ) oxygen storage materials(OSMs) play a crucial role in three-way catalysts(TWCs),while CZ needs to be modified to satisfy more rigorous emission standard.In this study,transition metal(TMs=Mn,Cr,Fe,Cu) oxides modified CZ were prepared by incipient wetness impregnation method to improve the oxygen storage capacity of CZ-based materials.To clearly illustrate the influence of TM oxides,N_2 adsorption-desorption,X-ray diffraction(XRD),oxygen storage capacity(OSC),temperature programmed reduction by H_2(H_2-TPR) and X-ray photoelectron spectroscopy(XPS) were used to characterize the physical and chemical properties of samples.It is found that,all modified CZ have higher OSC,lower reduction temperatures than those of pristine CZ.Interaction between TMOs and CZ take precedence over specific surface to influence OSC.Notably,FeO_x/CZ has the highest OSC,which is about 1.9 times that of CZ and it could be attributed to synergistic effect between FeO_x and CZ;CuO_x/CZ has the lowest reduction temperature which is 168℃lower than that of CZ,and it can be explained by hydrogen spillover effect.     

Effect of ferrite powder fineness on the structure and properties of ceramic materials

Comprehensive study of the structure and properties of ferrite materials prepared from powders with different specific surface (0.4 m²/g<S_sp<1.2 m²/g) shows that the optimum specific surface of manganese—zinc ferrite powders is about 0.6 m²/g. With an increase in the specific surface of nickel—zinc and barium ferrite powders the porous crystalline structure of sintered specimens and most of the main electromagnetic properties of ferrite articles are improved.     

静态离子交换分离-硫酸钡比浊法测定高铈化合物中SO42-

将静态离子交换技术与比浊法相结合建立了测定高铈稀土化合物中硫酸根含量方法。研究了离子交换分离条件(R-SO₃H树脂用量、萃取时间、萃取酸度)和比浊测定条件（分析波长、酸度、稳定剂用量、BaCl₂浓度等）对测量结果的影响。结果表明, 在H⁺浓度为0.18mol/LHCl介质中15g强酸性苯乙烯系阳离子交换树脂与试液混匀, 静置1h后以中速滤纸过滤, 可以富集SO₄^2-, 并与大量基体元素铈分离。分离后的滤液在2.4mmol/LHCl中和一定量的稳定剂存在下, BaCl₂质量浓度为20g/L时, SO₄^2-和Ba²⁺生成稳定的胶态悬浮体, 在430nm波长处溶液的吸光度随着SO₄^2-浓度增加而线性增加, 其增加值ΔA_430nm与SO₄^2-质量浓度在0.80～6.00μg/mL范围内呈良好的线性关系, 其线性相关系数为0.9997, 检测下限为0.010%（质量分数）。本法用于高铈化合物中SO₄^2-的测定, 测定结果与电感耦合等离子体原子发射光谱法相符。     

Preparation of Zirconia-Ceria Powders with High Specific Surface Area

Zirconia-ceria mixed oxide powders were prepared by high temperature aging method.The effects of the temperature and the time of aging, cerium content and calcination on powder performance were studied.The result shows that high temperature aging is an efficient way of preparation of ZrO2-CeO2 mixed oxide powders with high specific surface area and good thermal stability, and that addition of a small amount of cerium to hydrous zirconia can promote the preparation of high specific surface area powders.