Influence of preparation methods on CuO-CeO2 catalysts in the preferential oxidation of CO in excess hydrogen

Influence of three different preparation methods, i.e. impregnation, coprecipitation, and inverse coprecipitation, on the preferential oxidation of CO in excess hydrogen （PROX） over CuO-CeO2 catalysts has been investigated and CuO-CeO2 catalysts are characterized using BET, XPS, XRD, UV Raman, and TPR techniques. The results show that the catalysts prepared by coprecipitation have smaller particle sizes, well-dispersed CuOx species, more oxygen vacancies, and are more active in the PROX than those prepared by the other methods. However. the inverse coprecipitation depresses the catalytic performance of CuO-CeO2 catalysts and causes the growth of CuO-CeO2 because of different pH value in the precipitation process.     

Influence of some metal ions on the coprecipitation of Am(III) and Pu(IV) with BiPO4

The influence of increasing concentration of Na, Cs, Ca, Zn, Ni, Cr(III), La, Fe(III) and Al on coprecipitation of Am(III) and Pu(IV) with BiPO₄ has been studied. The coprecipitation of Am(III) decreases with increasing concentration of La, Fe(III) and Al and the coprecipitation of Pu(IV) decreases with increasing concentration of Cs, Fe(III) and Al. The other elements studied did not influence the coprecipitation of Am(III) and Pu(IV) with BiPO₄.     

Growth of carbon nanotubes on the novel FeCo-Al_2O_3 catalyst prepared by ultrasonic coprecipitation

FeCo-Al2O3 catalyst was prepared by an ultrasonic coprecipitation (UC) method for the growth of carbon nanotubes (CNTs) from catalytic decomposition of methane.Its catalytic performance was compared with that of the FeCo-Al2O3 catalyst counterparts prepared by stepwise impregnation (I) and conventional coprecipitation (C) methods,respectively.The structure and properties of the catalysts and the CNTs as produced thereon were investigated by means of XRD,XPS,TEM and N2 adsorption techniques.It was found that the catalyst prepared by the ultrasonic coprecipitation method was more active,and the yield and purity of the synthesized CNTs were promoted evidently.The XPS results revealed that there were more active components on the surface of the catalyst prepared by the ultrasonic coprecipitation method.On the other hand,N2 adsorption demonstrated that the catalyst prepared by the ultrasonic coprecipitation method conferred larger specific surface area,which was beneficial to dispersion of active components.TEM images further confirmed its higher dispersion.These factors could be responsible for its higher activity for the growth of CNTs from catalytic decomposition of methane.     

Growth of carbon nanotubes on the novel FeCo-Al2O3 catalyst prepared by ultrasonic coprecipitation

FeCo-Al_2O_3 catalyst was prepared by an ultrasonic coprecipitation (UC) method for the growth of carbon nanotubes (CNTs) from catalytic decomposition of methane. Its catalytic performance was compared with that of the FeCo-Al_2O_3 catalyst counterparts prepared by stepwise impregnation (I) and conventional coprecipitation (C) methods, respectively. The structure and properties of the catalysts and the CNTs as produced thereon were investigated by means of XRD, XPS, TEM and N_2 adsorption techniques. It was found that the catalyst prepared by the ultrasonic coprecipitation method was more active, and the yield and purity of the synthesized CNTs were promoted evidently. The XPS results revealed that there were more active components on the surface of the catalyst prepared by the ultrasonic coprecipitation method. On the other hand, N_2 adsorption demonstrated that the catalyst prepared by the ultrasonic coprecipitation method conferred larger specific surface area, which was beneficial to dispersion of active components. TEM images further confirmed its higher dispersion. These factors could be responsible for its higher activity for the growth of CNTs from catalytic decomposition of methane.     

Comparative Coprecipitation of Phosphate and Arsenate with Yttrium and the Rare Earths: The Influence of Solution Complexation

Coprecipitation of yttrium (Y) and rare earth elements (REEs) with phosphate and arsenate removes these elements from solution in variable proportions. During both phosphate and arsenate Coprecipitation, middle REEs (Sm and Eu) are progressively depleted in solution relative to heavier and lighter elements. Solution complexation by oxalate (Ox ^2-) influences Y and REE removal patterns by strongly enhancing the retention of Y and the heaviest REEs in solution. The extent of this enhancement is well described by a quantitative account of the comparative solution complexation of Y and REEs as M(Ox)⁺ and M(Ox) . The comparative behavior of phosphate and arsenate coprecipitation exhibits both similarities and differences. During arsenate coprecipitation the light REEs are retained in solution, relative to the heavy REEs, to a greater extent than is the case for phosphate coprecipitation. Notable irregularities are observed in the comparative coprecipitation behavior of nearest-neighbor elements (e.g., Eu–Gd–Tb and Tm–Yb–Lu). Such irregularities are very similar for phosphate and arsenate coprecipitation in the absence and in the presence of solution complexation.     

The effect of morphological changes on the coprecipitation of strontium by calcium phosphate

The coprecipitation of strontium by a calcium phosphate phase formed at an elevated pH 10.8 was investigated. The first phase obtained under these conditions in the amorphous calcium phosphate (ACP) which is transformed into crystalline hydroxyapatite (HA) after the induction period. Is has been shown that this transformation together with morphological changes of the precipitated solid phase, influences the amount of the sorbed strontium significantly. The possible consequences of this finding on practical application of coprecipitation of strontium by calcium phosphate have been discussed.     

Urine radiobioassay intercomparison results from the Intercomparison Studies Program at Oak Ridge National Laboratory

The concentrations of As(III) and As(V) in natural hot spring and river waters collected in the Kusatsu-Shirane volcano area, Gunma, Japan, were determined by neutron activation analysis (NAA) preceded by the pyrrolidinedithiocarbamate (PDC) coprecipitation. The PDC coprecipitation technique using Pb(PDC)₂ as a collector of As(III) was applicable to the determination of As(III) at μg/L to mg/L levels. It was found important that the sufficient amount of PDC must be added to sample waters to accomplish the quantitative coprecipitation of As(III), taking the amounts of coexisting metal ions into consideration.     

Determination of the lanthanoids in a neutral hot spring water by neutron activation analysis

Determination of the lanthanoids in a neutral hot spring water has been studied by menas of neutron activation analysis. The aluminium coprecipitation process, which used aluminium as the collector of the lanthanoids, was incorporated in the preparation of a sample for irradiation. Nine lanthanoids, La, Ce, Nd, Sm, Eu, Tb, Tm, Yb and Lu, were determined at ppt levels with satisfactory precision, indicating the effectiveness of aluminium coprecipitation.     

影响Fe3O4超微粒子性能因素的研究

超微Fe_3O_4粒子正在广泛地应用到磁流体和催化等领域。化学共沉淀法制备Fe_3O_4是将碱液滴入一定温度的Fe~(2+)、Fe~(3+)混合液中。反应式为Fe~(2+)+2Fe~(3+)+8OH~-=Fe_3O_4+4H_2O。本文研究了Fe_3O_4超微粒子的磁性、粒度与工艺条件的关系。 1 实验 配制一定浓度的FeCl_2和FeCl_3溶液,按一定比例混合并置于三颈瓶中恒温。搅拌后,缓     

Sequential separation of neptunium,plutonium, americium and curium using coprecipitation with bismuth phosphate

The reaction of neptunium, plutonium and americium with oxidizing or reducing agents in phosphoric acid solution has been studied to design a separation procedure of the actinide elements using coprecipitation with bismuth phosphate. In the presence of uranium, successive separation of neptunium, plutonium, americium and curium was accomplished by combining the coprecipitation and redox reaction of the elements. The coprecipitation behaviour of fission products during the course of sequential separation of the actinide elements on bismuth phosphate was also discussed.     

采用基于乙醇体系的一步草酸共沉淀法制备层状富锂锰基正极材料

首次报道了一种新颖的基于乙醇溶液的一步草酸共沉淀法合成富锂锰基正极材料的方法。在这种方法中,包括锂元素在内的所有元素均能在共沉淀反应步骤发生沉淀反应,以此实现更为均匀的元素混合。此外,相比传统的草酸铵共沉淀法,该法省略了前驱体初烧的步骤,节约了合成的时间和成本。通过X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学测试等检测手段表征了所得样品的晶体结构与电化学性能,研究了两种方法所制备的富锂锰基正极材料的结构、形貌与电化学性能。结果表明,一步草酸共沉淀法合成的富锂材料,拥有更好的结晶性、更大的层间距;材料的颗粒更为均匀和细小。这些晶体结构与形貌上的优势,使得该法制备的富锂材料展现出了更高的放电比容量、更好的循环性能和倍率性能。这些结果均展示了我们所提出的一步草酸共沉淀法的可行性与优势。这种新颖而简便的共沉淀法,可推广于其他层状材料的合成与设计。     

喷射共沉淀法制备纳米ZnFe_2O_4及其结构表征

对化学共沉淀法加以改进称为喷射共沉淀法。采用喷射共沉淀法制备了ZnFe2O4纳米粉末材料。采用XRD、SEM和TEM进行结构分析结果表明喷射共沉淀法制备的ZnFe2O4纳米粉末颗粒细小均匀形状完整。由于纳米尺寸效应的存在纳米ZnFe2O4粉末材料具有铁磁性。从流体力学角度分析了喷射共沉淀法中物质的输运和反应过程并解释了试验结果。认为喷射共沉淀法是一种较好的制备氧化物纳米粉末材料的方法。     

Interfacial coprecipitation to prepare magnetite nanoparticles: Concentration and temperature dependence

A novel interfacial coprecipitation method to prepare magnetite nanoparticles was proposed by us recently, which possesses advantages such as facility, Gram-scale synthesis and surface functionality. In this paper, the effects of precursors concentration and reaction temperature in interfacial coprecipitation method were systematically studied to evaluate the differences between classical and interfacial coprecipitation. It was found for first time that in both interfacial and classical coprecipitation there is a critical region of ferrous ion concentration to obtain magnetite at different amine concentrations, in which a phase of two-line ferrihydrite was considered to be an intermediate. Meanwhile, although the size of nanoparticles was not obviously varied by adjusting the reaction temperature, their dispersibility and saturation magnetization can be tailored. Besides, by comparing with classical coprecipitation, the mechanism in the interfacial coprecipitation was elucidated.     

Zn添加剂的添加方式对镍电极性能的影响

Zn元素;Zn添加剂的添加方式对镍电极性能的影响     

Influence of the synthesis conditions on the particle size and morphology of yttrium orthoferrite obtained from aqueous solutions

The size and morphology of yttrium orthoferrite nanoparticles were examined in relation to the synthesis conditions. The chemical composition of the crystalline phases resulted from heat treatment of the samples at 650°C varies with the procedure of coprecipitation of yttrium and iron(III) hydroxides. At the same time, heat treatment at 750°C leads to formation of yttrium orthoferrite solely. The size of the YFeO₃ crystals is weakly dependent on the initial composition preparation procedure, and the size and shape of their agglomerates are sensitive to the conditions of coprecipitation of the hydroxides.     

The separation of241Am from bones by coprecipitation with bismuth phosphate

The conditions of²⁴¹Am separation from bone by coprecipitation with BiPO₄ were studied. It was found that by coprecipitation with BiPO₄ ²⁴¹Am can be separated with high yield from different amount of bone. The main condition of the achievement of a high yield is a low Fe/III/ concentration in solution at americium coprecipitation.     

Synthesis of calcium metaniobate by thermal decomposition of a coprecipitation product

The paper presents a new, nonconventional method, based upon coprecipitation, for the synthesis of niobium oxidic compounds. The coprecipitation product of niobic acid with calcium oxalate was used as precursor. Calcium metaniobate was obtained by appropriate thermal treatment of the coprecipitate. The coprecipitation mechanism was studied and the optimal conditions for quantitative precipitation of niobium and calcium were established. The mechanism of thermal decomposition of the coprecipitate was investigated by means of differential thermal analysis and X-ray powder diagrams. The final product of thermal decomposition, calcium metaniobate, is formed at 730°C.     

Microdetermination of Lead in Water Samples,Preconcentration by Coprecipitation Followed by its Atomic Absorption Spectrophotometric Determination

Abstract

The method incorporates coprecipitation of lead on zirconium hydroxide and its quantitative spectrophotometric determination in natural, polluted and synthetic water samples. The method incorporates coprecipitation of lead on zirconium hydroxide and its quantitative determination by AAS using 283.3 nm wavelength.     

Kinetic effect in the size-control of CdS nanoparticles

A new method of size control for CdS nanoparticles, called common cation coprecipitation, is reported. In the course of coprecipitation, both CdS and CdSt_2(cadmium stearate) formations are diffusion-controlled and their rates are quite different. The size of CdS nanoparticles depends on the ratio of initial concentrations of S~(2-) to St~- (stearate ion). Characterized by UV-Vis absorption, XRD, TEM, fluorescence and XPS, the results obtained show that the coprecipitate is a composite, i. e. CdS particle inserts in the CdSt_2 molecular layers to form a sandwich-like structure. The method reported for size control of CdS nanoparticles might be called kinetic self-assembling.     

Synthesis of Zn/Al mixed-oxide catalyst for carbonylation of glycerol with urea

Zn/Al mixed oxide was prepared by the coprecipitation or the hydrothermal method under different conditions and used as catalyst for synthesis of glycerol carbonate by carbonylation of glycerol with urea. The physical properties of the prepared Zn/Al mixed oxide particles were investigated, as well as their activity as catalyst in the mentioned synthesis. The dried Zn/Al mixed-oxide particles prepared by the coprecipitation method showed higher activity in synthesis of glycerol carbonate than those prepared by the hydrothermal method. The Zn/Al mixed oxide prepared by the coprecipitation method without NaNO₃ showed the highest catalytic activity in synthesis of glycerol carbonate.