Physicochemical and catalytic properties of systems based on CeO<Subscript>2</Subscript>

The effect of synthesis conditions, the nature of components, and the ratio between the components on the phase composition, the texture, and the redox and catalytic properties of the Ce-Zr-O, Ce-Zr-M₁-O (M₁ = Mn, Ni, Cu, Y, La, Pr, or Nd), N/Ce-Zr-O (N = Rh, Pd, or Pt), and Pd/Ce-Zr-M₂-O/Al₂O₃ (M₂ = Mg, Ca, Sr, Ba, Y, La, Pr, Nd, or Sm) was considered. A cubic solid solution with the fluorite structure was formed on the introduction of <50 mol % zirconium into CeO₂, and the stability of this solid solution depended on preparation procedure and treatment conditions. The presence of transition or rare earth elements in certain concentrations extended the range of compositions with the retained fluorite structure. The texture of the Ce-Zr-O system mainly depended on treatment temperature. An increase in this temperature resulted in a decrease in the specific surface area of the samples. The total pore volume varied over the range of 0.2–0.3 cm³/g and depended on the Ce/Zr ratio. The presence of transition or rare earth elements either increased the specific surface area of the system or made it more stable to thermal treatment. The introduction of the isovalent cation Zr⁴⁺ into CeO₂ increased the number of lattice defects both on the surface and in the bulk to increase the mobility of oxygen and facilitate its diffusion in the Ce_{1 − x} Zr _x O₂ lattice. The catalytic properties of the Ce-Zr-M₁-O or N/Ce-Zr-M₂-O systems were due to the presence of anion vacancies and the easy transitions Ce⁴⁺ ai Ce³⁺, M₁²ⁿ⁺ ai M₁ ⁿ⁺, and N ^δ+ → N ⁰ in the case of noble metals.     

Ce4+替代Pu4+的模拟固化体(Gd1-xCex)2Zr2O7+x的合成及结构演变

Gd₂Zr₂O₇中Gd具有很大的中子吸收截面, 其烧绿石结构-缺陷萤石结构的转变能较低, 使其成为理想的核废料固化基材. 使用硝酸盐为原料, 添加少量NaF作助熔剂, 在较低温度下(和传统高温固相反应相比), 合成了烧绿石型Gd₂Zr₂O₇. 以Ce⁴⁺模拟Pu⁴⁺, 研究了Gd₂Zr₂O₇对锕系核素的固化, 并合成了系列模拟固化体(Gd_1-xCe_x)₂Zr₂O_7+x (0≤x≤0.6). 采用粉末X射线衍射(XRD)对系列样品进行了表征. 结果表明: 随着x值的增大,样品从烧绿石结构向缺陷萤石结构转变, 且晶胞大小基本保持恒定, 但当x=0.6时, 衍射峰明显宽化, 晶格畸变比较严重, 晶格稳定性降低. 当x=1时, 即用Ce⁴⁺完全取代Gd³⁺进行合成, 不能得到Ce₂Zr₂O₈, 产物发生了相分离, 为四方结构的(Zr_0.88Ce_0.12)O₂和萤石结构的(Ce_0.75Zr_0.25)O₂的混合物. 模拟固化体的浸出率测试表明: 当x≤0.2时, 各元素浸出率均很低, 但当x≥0.4时, 各元素的浸出率明显升高, 说明以Gd₂Zr₂O₇作为固化Pu⁴⁺的基材, Pu⁴⁺掺入量不宜高于40%.     

Mesoporous mesocrystal Ce1−xZrxO2 with enhanced catalytic property for CO conversion

Novel mesoporous mesocrystal Ce_1−xZr_xO₂ was synthesized using acetate salt as inorganic species and P123 as surfactant. Transmission electron microscopy reveals that the wall framework consists of a single phase based on the face-centered cubic CeO₂ and the nanocrystals are highly oriented with the crystal axis [001] parallel to the pore channel if the Zr⁴⁺ molar fraction x is 0.3 or less. However, when the Zr⁴⁺ molar fraction is larger than 0.3, a mixture of cubic and tetragonal phases forms and the preferential crystal orientation disappears as revealed by XRD and Raman measurements. The formation mechanism is ascribed to the oriented attachment following the manner of coherent interface. The single phase solid solution at Zr⁴⁺ molar fraction 0.3 demonstrates the best catalytic performance for CO conversion due to the unique mesoporous mesocrystal structure with dominant exposure of highly active {200} planes and an enhanced redox property caused by adequate Zr⁴⁺ incorporation.     

XRD and UV-Vis diffuse reflectance analysis of CeO2-ZrO2 solid solutions synthesized by combustion method

A series of ceria-incorporated zirconia (Ce_1−xZr_xO₂,x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route. The products were characterized by XRD and UV-Vis-NIR diffuse reflectance spectroscopy. The materials are crystalline in nature and the lattice parameters of the solid solution series follow Vegard’s law. Diffuse reflectance spectra of the solid solutions in the UV region show two intense bands at 250 and 297 nm which are assigned respectively to Ce³⁺ ← O²⁻and Ce⁴⁺ ← O²⁻ charge transfer transitions. The two vibrational bands in 6960 cm⁻¹ and 5168 cm⁻¹ in the NIR region indicate the presence of surface hydroxyl groups on these materials.     

Effect of Transition Metals (Cu, Co and Fe) on the Autothermal Reforming of Methane over Ni/Ce0.2Zr0.1Al0.7Oδ Catalyst

The transition metals (Cu, Co, and Fe) were applied to modify Ni/Ce0.2Zr0.1 Al0.7Oδcatalyst. The effects of transition metals on the catalytic properties of Ni/Ce0.2Zr0.1 Al0.7Oδautothermal reforming of methane were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS. Tests in autothermal reforming of methane to hydrogen showed that the addition of transition metals (Cu and Co) significantly increased the activity of catalyst under the conditions of lower reaction temperature, and Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδwas found to have the highest conversion of CH4 among all catalysts in the operation temperatures ranging from 923 K to 1023 K. TPR, XRD and XPS measurements indicated that the cubic phases of CexZr1-xO2 solid solution were formed in the preparation process of catalysts. Strong interaction was found to exist between NiO and CexZr1-xO2 solid solution. The addition of Cu improved the dispersion of NiO, inhibited the formation of NiAl2O4, and thus significantly promoted the activity of the catalyst Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ.     

Catalytic properties of the VO<Subscript><Emphasis Type="Italic">х</Emphasis></Subscript>/Ce<Subscript>0.46</Subscript>Zr<Subscript>0.54</Subscript>O<Subscript>2</Subscript> oxide system in the oxidative dehydrogenation of propane

Ce_0.46Zr_0.54O₂ solid solution prepared using a cellulose template was employed as a carrier for vanadium catalysts of the oxidative dehydrogenation of propane. The properties of VO _х /Ce_0.46Zr_0.54O₂ catalyst (5 wt % vanadium) are compared with the properties of the neat support. The carrier and catalyst are studied by means of BET, SEM, DTA, XRD, and Raman spectroscopy. It is shown that the CeVO₄ phase responsible for the ODH process is formed upon interaction between vanadate ions and cerium ions on the surface of the solid solution. The catalytic properties of the catalyst and the support are studied in the propane oxidation reaction at temperatures of 450 and 500°C with pulse feeding of the reagent. It is found that the complete oxidation of propane occurs on the support with formation of CO₂ and H₂O. Three products (propene, CO₂, and H₂O) form in the presence of the vanadium catalyst. It is suggested that there are two types of catalytic centers on the catalyst’s surface. It is concluded that the centers responsible for the complete oxidation of propane are concentrated mainly on the carrier, while the centers responsible for propane ODH are on the CeVO₄.     

Further improvements in the 2,4-xylenol spectrophotometric method for nitrate

Improvements are described for the 2,4-xylenol spectrophotometric method for nitrate that reduce the elapsed and working time. Diluted (22 + 3) sulfuric acid is added quickly to the sample solution while the flask is immersed in tap water. 2,4-xylenol solution is added, the 6-nitro-2,4-xylenol formed is steam-distilled into a composite ammonia—isopropanol reagent, and the absorbance of the ammonium salt of 6-nitro-2,4-xylenol is measured. Further possible interferences are described. Br₂, I₂, ClO^-, CIO₃^-, BrO₃^-, and I0₄^-, cause low results by deactivating or destroying the 2,4-xylenol. Azide, hydrazine, and elemental carbon cause low results by reducing the nitrate in the strong sulfuric acid solution. Se⁺ causes low results because 2,4-xylenol is consumed in reducing Se⁴⁺ to the element. Pt⁴⁺ and Os⁸⁺ cause high results. Interferences from Br₂, I₂, ClO^-, ClO₃^- lO₃^-, and I0₄^- can be eliminated by reduction to the halide with sulfurous acid and precipitation with silver sulfate. Sulfurous acid reduction also eliminates interferences from V⁵⁺. Mn⁷⁺, Cr⁶⁺, S₂O₈^2-, and H₂0₂. Interferences from N₃^-, Br₂, I₂, and S₂0₈^2- are eliminated merely by boiling a 0.5% sulfuric acid solution for 30 min (and precipitating any residual halide with silver sulfate).     

Zur Modifizierung hochreaktiver Aluminiumoxidübergangsformen

Modification of Highly Reactive Transition Aluminas By combination of mechanical pretreatment of coarse-dispersed gibbsite, α-Al(OH)₃, with the shock calcination of these treated particles partial crystalline transition aluminas can be obtained. The products are characterized among other things by a high portion of 5-fold coordinated Al³⁺ ions (²⁷Al MAS NMR), remarkable differences in the RDF and a high solid state reactivity. The same properties can be produced by direct shock calcination of highly dispersed gibbsite of uniform morphological structure. In the course of subsequent rehydration – simultaneously by presence of promoting components (La³⁺, Y³⁺, Ce⁴⁺, Zr⁴⁺) – the conversion of the solid particles into a fibrillar boehmite, AlOOH, containing the promotor ions occurs. The calcination of this modified boehmite causes the formation of highly dispersed, phase- and thermostabilized γ-Al₂O₃.     

Structure and surface properties of ZrO<Subscript>2</Subscript>, CeO<Subscript>2</Subscript>, and Zr<Subscript>0.5</Subscript>Ce<Subscript>0.5</Subscript>O<Subscript>2</Subscript> prepared by a microemulsion method according to X-ray diffraction,TPR, and EPR data

It was established by X-ray diffraction, TPR, and EPR that microemulsion (m.e.) synthesis yields the binary oxides ZrO₂(m.e.) and CeO₂(m.e.) and the mixed oxide Zr_0.5Ce_0.5O₂(m.e.) in the form of a tetragonal, cubic, and pseudocubic phase, respectively, having crystallite sizes of 5–6 nm. The bond energy of surface oxygen in the (m.e.) samples is lower than in their analogues prepared by pyrolysis. Hydrogen oxidation on the oxides under study occurs at higher temperatures than CO oxidation. ZrO₂(m.e.) and CeO₂(m.e.) are active in O₂⁻ formation during NO + O₂ adsorption, while CeO₂ is active during CO + O₂ adsorption, too. However, its amount here is one-half to one-third its amount in the pyrolysis-prepared samples, signifying a reduced number of active sites, which are Zr⁴⁺ and Ce⁴⁺ coordinatively unsaturated cations and Me⁴⁺-O²⁻ pairs. O₂⁻ radical anions are stabilized in the coordination sphere of Zr⁴⁺ coordinatively unsaturated cations via ionic bonding, and in the sphere of Ce⁴⁺ cations, via covalent bonding. Ionic bonds are stronger than ionic-covalent bonds and do not depend on the ZrO₂ phase composition. Zr_0.5Ce_0.5O₂ is inactive in these reactions because of the strong interaction of Zr and Ce cations. It is suggested that Ce^{(4 + β)+} coordinatively unsaturated cations exist on its surface, and their acid strength is lower than that of Zr⁴⁺ and Ce⁴⁺ cations in ZrO₂ and CeO₂, according to the order ZrO₂ > CeO₂ ≥ Zr_0.5Ce_0.5O₂. Neither TPR nor adsorption of probe molecules revealed Zr cations on the surface of the mixed oxide.     

Pt/Ce0.6Zr0.4O2催化剂催化氧化碳烟过程中活性氧对NO-NO2循环及表面含氧物种的分解作用简

通过在Ce_0.6Zr_0.4O₂载体上浸渍Pt（NO₃）₂制得Pt/Ce_0.6Zr_0.4O₂催化剂,该催化剂在松散接触条件下,于NO+O₂或O₂气氛中均表现出比Pt/Al₂O₃更好的碳烟氧化性能. 进一步研究表明,Pt/Ce_0.6Zr_0.4O₂催化剂中的Pt 与Ce_0.6Zr_0.4O₂存在相互作用,使得催化剂在一定温度范围内对活性氧的利用率大为提高,从而促进了气氛中NO↔NO₂的循环,乃至碳烟与NO₂的反应和碳烟表面含氧中间物种的生成;更重要的是,这部分活性氧本身可加速含氧中间物种的分解. 因此,在NO + O₂的气氛中,Pt/Ce_0.6Zr_0.4O₂催化剂的碳烟起燃温度比Pt/Al₂O₃降低了34 ℃.     

Caracterisation De Catalyseurs ZrxCe1–xO2 et Etude De Leur Reactivite Dans L'Oxydation Des Suies Par ATD/ATG

Thermal analysis has been used to investigate the crystallization of Zr_xCe_1-xO₂ mixed oxides, prepared by co-precipitation of corresponding hydroxides. For x≤0.5, small crystals of CeO₂, were formed at low temperatures (373 K). For x>0.5an exothermic peak at 420°C (693 K) was observed after calcination under a flow of air ofhydroxide samples. This peak was associated with the formation of a Zr_xCe_1-xO₂ solid solution (XRD) in a tetragonal phase (Raman). The solids calcined at 700°C (973 K) present a reactivity towards the carbon black oxidation. The thermal analysis coupled with a gas chromatograph (GC) were used to follow this reactivity. Simultaneous study of the activity (thermal analysis) and the selectivity (GC) in CO or CO₂ of the different catalysts revealed an important parameter: acatalyst-soot particle contact. We also obtained a more precise comparison of Zr_xCe_1-xO₂ oxides in the catalytic soot combustion. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study on the mechanism of removing fluoride from wastewater by oxalic acid modified aluminum ash-carbon slag-carbon black doped composite

In this study, SAA@CS-CB(aluminum-ash carbide slag carbon black doped composite) was prepared by sintering method and modified by impregnation with oxalic acid to obtain SAA@CS-CB_oa. Fluoride adsorption experiments were carried out using this composite as adsorbent. With increasing pH values, the adsorption amount of fluoride decreases in the range of 2–11. The pseudo second order equation and Langmuir model were fit to the experimental data, and the adsorption of fluoride by SAA@CS-CB_oa exhibited spontaneous and endothermic characteristics. When PO₄^3-, CO₃^2–, SO₄^2-, Cl^-, NO₃^–, Br^- and HCO₃^– anions were individually or combined in solution, the adsorbents exhibited higher fluoride selectivity and sensitivity, while PO₄^3-and CO₃^2– weakened the adsorption of fluoride in solution in the same way regardless of the presence of the other 5 anions. The results of SEM, EDS, XRD and FTIR characterizations showed that the mechanism of fluoride adsorption and removal by SAA@CS-CB_oa included the combined effects of electrostatic attraction, surface coordination precipitation and ion exchange. SAA@CS-CB_oa is an effective composite material for water adsorption of fluoride, and still has an excellent performance of cyclic regeneration after 10 times adsorption desorption. This study provides a new approach for the utilization of fluoride removal resources for industrial solid waste resource recycling.     

掺杂Zr4+对纳米Au/TiO2催化剂结构和性能的影响

采用氨水反滴加沉淀法合成了Zr4+掺杂的系列TiO2载体,以尿素溶液为沉淀剂,用沉积-沉淀法制备负载金催化剂。运用N2吸附-脱附(BET)、X射线衍射(XRD)、X射线荧光(XRF)、高分辨电镜(HR-TEM)和氨吸附红外光谱(NH3-IR)等技术对催化剂的结构与形貌进行了表征,并在色谱-微反应装置上考察了催化剂对CO氧化反应的活性。结果表明:(1)少量的Zr4+掺杂可形成锐钛矿型固溶体,且载体的比表面积增大;随着Zr4+掺杂量增加至10%以上,载体逐渐向无定形转变,同时比表面积急剧增大。(2)保持规整锐钛矿晶相的Zr4+掺杂载体,其表面Lewis酸位占有率较高,且具备结构缺陷,而无定形载体表面的Lewis酸位占有率大幅度降低。(3)载体表面的Lewis酸位以及结构缺陷有利于增强载体对Au颗粒的锚定作用,从而减弱焙烧过程中的颗粒聚集。(4)少量Zr4+掺杂入TiO2载体中,可以提高Au颗粒的抗烧结能力,焙烧所得的Au颗粒尺寸较小(3.63 nm),且表现出优异的催化活性,在常温下就可以将CO完全氧化。     

Selective Amperometric Determination of Thorium by Ethyl Cyanoglyoxalate Phenyl-2-Carboxylic Acid Hydrazone

Abstract

The reagent ethyl cyanoglyoxalate phenyl-2-carboxyllc acid hydrazone has been developed for the selective amperometric determination of thorium. Commonly associated ions like UO²⁺ ₂, Pe³⁺, La³⁺, Ce⁴⁺, and Zr⁴⁺ do not interfere even when present in ten fold molar excess. 23μg to 4.6mg thorium can be determined within an error of ±1.5 percent.     

Syntheses and Characterization of Novel Perovskite-Type LaScO3-Based Lithium Ionic Conductors

Perovskite-type lithium ionic conductors were explored in the (Li_xLa_1−x/3)ScO₃ system following their syntheses via a high-pressure solid-state reaction. Phase identification indicated that a solid solution with a perovskite-type structure was formed in the range 0 ≤ x < 0.6. When x = 0.45, (Li_0.45La_0.85)ScO₃ exhibited the highest ionic conductivity and a low activation energy. Increasing the loading of lithium as an ionic diffusion carrier expanded the unit cell volume and contributed to the higher ionic conductivity and lower activation energy. Cations with higher oxidation numbers were introduced into the A/B sites to improve the ionic conductivity. Ce⁴⁺ and Zr⁴⁺ or Nb⁵⁺ dopants partially substituted the A-site (La/Li) and B-site Sc, respectively. Although B-site doping produced a lower ionic conductivity, A-site Ce⁴⁺ doping improved the conductive properties. A perovskite-type single phase was obtained for (Li_0.45La_0.78Ce_0.05)ScO₃ upon Ce⁴⁺ doping, providing a higher ionic conductivity than (Li_0.45La_0.85)ScO₃. Compositional analysis and crystal-structure refinement of (Li_0.45La_0.85)ScO₃ and (Li_0.45La_0.78Ce_0.05)ScO₃ revealed increased lithium contents and expansion of the unit cell upon Ce⁴⁺ co-doping. The highest ionic conductivity of 1.1 × 10⁻³ S cm⁻¹ at 623 K was confirmed for (Li_0.4Ce_0.15La_0.67)ScO₃, which is more than one order of magnitude higher than that of the (Li_xLa_1−x/3)ScO₃ system.     

Highly Dispersed Ce x Zr1−x O2 Nano-Oxides Over Alumina, Silica and Titania Supports for Catalytic Applications

We have been exploring the utilization of supported ceria and ceria–zirconia nano-oxides for different catalytic applications. In this comprehensive investigation, a series of Ce _x Zr_1−x O₂/Al₂O₃, Ce _x Zr_1−x O₂/SiO₂ and Ce _x Zr_1−x O₂/TiO₂ composite oxide catalysts were synthesized and subjected to thermal treatments from 773 to 1073 K to examine the influence of support on thermal stability, textural properties and catalytic activity of the ceria–zirconia solid solutions. The physicochemical characterization studies were performed using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HREM), thermogravimetry and BET surface area methods. To evaluate the catalytic properties, oxygen storage/release capacity (OSC) and CO oxidation activity measurements were carried out. The XRD analyses revealed the formation of Ce_0.75Zr_0.25O₂, Ce_0.6Zr_0.4O₂, Ce_0.16Zr_0.84O₂ and Ce_0.5Zr_0.5O₂ phases depending on the nature of support and calcination temperature employed. Raman spectroscopy measurements in corroboration with XRD results suggested enrichment of zirconium in the Ce _x Zr_1−x O₂ solid solutions with increasing calcination temperature thereby resulting in the formation of oxygen vacancies, lattice defects and oxygen ion displacement from the ideal cubic lattice positions. The HREM results indicated a well-dispersed cubic Ce _x Zr_1−x O₂ phase of the size around 5 nm over all supports at 773 K and there was no appreciable increase in the size after treatment at 1073 K. The XPS studies revealed the presence of cerium in both Ce⁴⁺ and Ce³⁺ oxidation states in different proportions depending on the nature of support and the treatment temperature applied. All characterization techniques indicated absence of pure ZrO₂ and crystalline inactive phases between Ce–Al, Ce–Si and Ce–Ti oxides. Among the three supports employed, silica was found to stabilize more effectively the nanosized Ce _x Zr_1−x O₂ oxides by retarding the sintering phenomenon during high temperature treatments, followed by alumina and titania. Interestingly, the alumina supported samples exhibited highest OSC and CO oxidation activity followed by titania and silica. Details of these findings are consolidated in this review.     

Spectrophotometric determination of thorium(IV) using 3-nitroso-4-hydroxycoumarin

Summary 3-Nitroso-4-hydroxycoumarin is suggested as a new reagent for the spectrophotometric determination of 125 g to 0.50 mg Th(IV) in 3: 1 dioxan: water medium as 1: 1 complex having orange red colour with absorption maximum at 419 nm, at pH 4.5–6.0. For the estimation of9.6 ppm Th(IV) 100-folds acetate, citrate, tartrate; 50 ppm UO₂ ²⁺, 75 ppm Ce³⁺, La³⁺, Gd³⁺; 4.5 ppm Ce⁴⁺; 25 ppm Tm³⁺, Zr⁴⁺; and 100 ppm Ti⁴⁺, V⁵⁺, MoO₄ ^2– and WO₄ ^2– do not interfere.

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Zusammenfassung 3-Nitroso-4-hydroxycoumarin wird als neues Reagens für die spektrophotometrische Bestimmung von 125 g bis 0,50 mg Th(IV) in Dioxan: Wasser = 3: 1 als 1: 1-Komplex mit orange-roter Farbe mit einem Absorptionsmaximum bei 419 nm bei pH 4,5–6,0 empfohlen. Bei einem Einsatz von 9,6 ppm Th(IV) stört die hundertfache Menge Acetat, Citrat, Tartrat nicht. Auch 50 ppm UO₂ ²⁺, 75 ppm Ce³⁺, La³⁺, Gd³⁺, 4,5 ppm Ce⁴⁺, 25 ppm Tm³⁺, Zr⁴⁺, 100 ppm Ti⁴⁺, V⁵⁺, MoO₄ ^2– bzw. WO₄ ^2– stören nicht.

     

Ceria–Zirconia Nanoparticles as an Enhanced Multi‐Antioxidant for Sepsis Treatment

The two oxidation states of ceria nanoparticles, Ce³⁺ and Ce⁴⁺, play a pivotal role in scavenging reactive oxygen species (ROS). In particular, Ce³⁺ is largely responsible for removing O₂⁻ and ^.OH that are associated with inflammatory response and cell death. The synthesis is reported of 2 nm ceria–zirconia nanoparticles (CZ NPs) that possess a higher Ce³⁺/Ce⁴⁺ ratio and faster conversion from Ce⁴⁺ to Ce³⁺ than those exhibited by ceria nanoparticles. The obtained Ce_0.7Zr_0.3O₂ (7CZ) NPs greatly improve ROS scavenging performance, thus regulating inflammatory cells in a very low dose. Moreover, 7CZ NPs are demonstrated to be effective in reducing mortality and systemic inflammation in two representative sepsis models. These findings suggest that 7CZ NPs have the potential as a therapeutic nanomedicine for treating ROS‐related inflammatory diseases.     

Crystallization kinetics of calcium carbonate at a stoichiometric ratio of components

The formal kinetics of calcium carbonate crystallization in aqueous solutions is studied at a stoichiometric ratio of Ca²⁺ and CO₃^2- ions. The kinetics of the process was monitored by convenient and reliable methods (complexometric analysis for calcium in an aqueous solution and energy dispersive and microscopic measurement of solid particle sizes). The effect the temperature and degree of supersaturation have on the periods of induction and mass crystallization and the equilibrium concentration of calcium ions in solution is estimated at continuously controlled pH and solution ionic strength. The kinetic parameters (n, k, τ_1/2, E_a) of calcium carbonate crystallization are calculated. It is shown that calcium carbonate with a calcite structure formed at a stoichiometric ratio of reagents, and changes in the temperature (25–45°C) and the solution’s degree of supersaturation (2–6) within the considered range had no effect on the characteristics of the solid phase.     

纳米CexFe1-xO2固溶体的模板法制备及其乙醇水蒸气重整催化性能

以超高比表面炭材料为模板,硝酸盐为氧化物前体,通过改进的模板路线制备了具有较高比表面积的纳米CexFe1-xO2固溶体.采用X射线衍射、拉曼光谱、物理吸附和透射电镜对制备的样品进行了表征.结果表明,α-Fe2O3,CexFe1-xO2固溶体和CeO2的粒子尺寸为5~15nm,CeO2中部分Ce4 离子被Fe3 离子取代,从而形成了CexFe1-xO2固溶体.乙醇水蒸气重整反应结果显示,CexFe1-xO2固溶体比相应的α-Fe2O3和CeO2具有更高的催化活性和对氢气的选择性.