浆态F-T合成反应的Raney Fe催化剂制备动力学(英文)

在一搅拌反应器中,通过对在RaneyFe－Al合金抽滤过程中一定温度和浓度下Al生成量的分析,研究了其抽滤动力学,得到了各种参数对抽滤速率和比例的影响规律。这些参数包括抽滤温度、碱液浓度、RaneyFe－Al合金粒度和搅拌速度等。结果表明,抽滤过程第一阶段的动力学数据满足表达式：1－（1－x）1/3=kt,而后一阶段则可以用log（x/（1－x））=α·log（t／β）来表示,其中x是抽滤过程中的Al生成量,t是抽滤时间,参数α和β是常量。这里的反应动力学数据和活化能以初始反应速率为基础。结果还表明,在抽滤过程中生成的一部分Al存留在最后固体的内孔表面上。     

制备条件对Raney铁结构与性能的影响

描述新型Ｒａｎｅｙ铁催化剂在制备时的抽滤工艺、抽滤温度、碱液浓度及合金组成等因素对其结构参数和浆态相Ｆ－Ｔ合成反应性能的影响规律，得到了较优化的催化剂制备参数；采用常规的制备途径，合金铝铁比为４，抽滤温度为８５℃，碱液浓度为２５％ＮａＯＨ所制备的Ｒａｎｅｙ铁催化剂Ｆ－Ｔ活性可以达到催化剂的水平。     

Size-dependent morphology of dealloyed bimetallic catalysts: linking the nano to the macro scale

Chemical dealloying of Pt binary alloy precursors has emerged as a novel and important preparation process for highly active fuel cell catalysts. Dealloying is a selective (electro)chemical leaching of a less noble metal M from a M rich Pt alloy precursor material and has been a familiar subject of macroscale corrosion technology for decades. The atomic processes occurring during the dealloying of nanoscale materials, however, are virtually unexplored and hence poorly understood. Here, we have investigated how the morphology and intraparticle composition depend on the particle size of dealloyed Pt-Co and Pt-Cu alloy nanoparticle precursor catalysts. To examine the size-morphology-composition relation, we used a combination of high-resolutionscanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), electron energy loss (EEL) spectroscopy, energy-dispersive X-ray spectroscopy (EDS), and surface-sensitive cycling voltammetry. Our results indicate the existence of three distinctly different size-dependent morphology regimes in dealloyed Pt-Co and Pt-Cu particle ensembles: (i) The arrangement of Pt shell surrounding a single alloy core ("single core-shell nanoparticles") is exclusively formed by dealloying of particles below a characteristic diameter d(multiple cores) of 10-15 nm. (ii) Above d(multiple cores), nonporous bimetallic core-shell particles dominate and show structures with irregular shaped multiple Co/Cu rich cores ("multiple cores-shell nanoparticles"). (iii) Above the second characteristic diameter d(pores) of about 30 nm, the dealloyed Pt-Co and Pt-Cu particles start to show surface pits and nanoscale pores next to multiple Co/Cu rich cores. This structure prevails up to macroscopic bulklike dealloyed particles with diameter of more than 100 nm. The size-morphology-composition relationships link the nano to the macro scale and provide an insight into the existing material gap of dealloyed nanoparticles and highly porous bulklike bimetallic particles in corrosion science.     

Electrochemical Behavior of Dental Ni‐Cr Wirolloy Coated with Eco‐friendly Films in Artificial Saliva

The electrochemical corrosion behavior of the non‐precious Ni‐Cr Wirolloy, being used in dentistry, was investigated before and after applying of two types of eco‐friendly coatings, polyvinyl silsesquioxane (PVS) and nano‐hydroxyapatite (nHAP) separately in artificial saliva solution at 37 °C for 14 d of immersion. The study aimed to investigate the effectiveness of the introduced coating films in enhancing the corrosion resistance of the alloy, and in decreasing the leaching of the toxic Ni ions from the alloy into the environment. The electrochemical corrosion investigation methods used are; open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The evaluated results revealed that the electrochemically coated alloy with PVS. prepared at cathodic potential showed higher corrosion resistance and more stable film compared to that prepared by conventional dip‐coating method. At the same time, the nHAP electrochemically coated film provided the best anti‐corrosion properties over all examined time intervals. The obtained results were confirmed via surface analysis, which assured the formation of the prepared coatings on the alloy surface. Chemical analysis of the corrosion product/solutions showed that the effect of electrochemically deposited nHAP and PVS. polymer films in suppression of Ni ions leaching is similar and slightly higher than that of the chemically coated PVS. one; however, all of them are efficient in decreasing the leaching of the risky Ni ions into the solution.     

原始合金制备方法对RaneyNi催化剂结构及加氢活性的影响

骨架镍催化剂由纳米级镍晶粒、未转变的ＮｉＡｌ３和Ｎｉ２Ａｌ３母相及其界面区组成。Ｘ射线衍射及高分辨电子显微观察发现，脱铝过程中ＮｉＡｌ３晶粒碎裂成纳米级尺寸，而Ｎｉ２Ａｌ３相则不出现碎裂现象。     

新型固定床Raney Ni制备过程中晶相结构的转化

以拟薄水铝石制备粘结剂，加入镍铝合金粉和田菁粉捏合、成型，在空气中高温焙烧，然后用苛性碱溶液充分浸取，制备出可应用于固定床加氢的活性Raney Ni催化剂。采用XRD和TG-DTA分析了催化剂制备过程中晶相结构的转化，结果表明，成型合金焙烧过程中，富铝合金相（如Al₃Ni-Al和Al₃Ni）逐渐转变为贫铝合金相（如Al₃Ni₂和AlNi），释放出的金属铝依次发生氧化，同时抑制金属镍的氧化；在高于1 123～1 133K焙烧时金属铝氧化生成α-Al₂O₃，使催化剂获得较高的颗粒强度。苯加氢活性评价结果表明，该新型固定床Raney Ni催化剂活性高于负载型镍催化剂，也高于参照专利方法制备的有机聚合物粘结的同类型催化剂，并且具有较好的低温加氢活性。     

Leaching studies over immobilized a-amylase. importance of the nature of enzyme attachment

The enzyme α-amylase was immobilized on montmorillonite K-10 via adsorption and covalent bonding. These two modes of attachment play a vital role in the leaching of enzyme. Covalent bonding retains most of the enzyme even at high loadings. The significance of temperature has also been established. Higher temperatures lead to severe leaching in case of adsorbed enzyme. Covalent linkage, being of higher strength, does not yield to enzyme leaching even at high temperatures. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of γ-dose on the crystal structure and leaching behavior of TiO<Subscript>2</Subscript> matrix labeled with <Superscript>181</Superscript>Hf/<Superscript>181</Superscript>Ta tracer

A new method for the possible incorporation of nuclear wastes has been attempted here by using ceramic matrix of TiO₂ as a host precursor for confinement. Hafnium is used as a simulant for actinide high-level waste. After incorporating ¹⁸¹Hf tracer into TiO₂ matrix, the leaching property of the resulting matrix was studied in water, sodium chloride and humic acid solutions. The leaching was measured in each of the case by following the radioactivity of ¹⁸¹Hf. TiO₂ matrix has also been exposed to γ-radiation in order to simulate the radiation field for nuclear waste. It has been investigated with a nuclear technique called time differential perturbed Angular Correlation (TDPAC) that the lattice structure of titania remains undisturbed even under a strong radiation field. The leaching of ¹⁸¹Hf has also been studied after irradiating the TiO₂ matrix with γ-radiation and the leaching behavior was observed not to change from that before irradiation.     

β-沸石骨架铝化改性的红外光谱

β沸石是以有机胺为模板剂合成的高硅沸石．为在孔道中进行吸附和催化反应,通常是在空气中 (５５０℃ )进行焙烧,将有机胺脱除并使质子酸中心形成．但这种脱模板剂方法,会造成骨架脱铝［１ -４］,使质子酸中心显著减少．β沸石固有结构中存在着孔道位错和结构空穴,空气中焙烧脱有机胺可能会进一步损伤沸石的骨架结构［４,５］．沸石骨架改性已发展了多种铝化方法［６ -８］．有的研究工作表明,通常用红外光谱和ＭＡＳＮＭＲ表征的非骨架铝,在温和的条件下,例如回馏温度下的离子交换或者在较低温度下 (１００℃或室温 )与碱反应就可…     

Phosphate rock treatment with citric acid for the rapid potentiometric determination of fluoride with ion-selective electrode

A fast method for sample treatment of phosphate rock has been developed for the purpose of quantitative leaching (98-100%) of fluoride but less of the interfering cations such as iron and aluminum. Citric acid (0.5 M) was used to extract fluoride in 15-45 min. Leaching of iron and aluminum is minimal, and these ions are complexed with citric acid. The leaching method was optimized with respect to sample size, citric acid concentration, leaching time and temperature. The analysis was completed by the rapid determination of fluoride with ion-selective electrode. The proposed treatment method was applied to phosphate rock samples from Jordan and Morocco and yielded accurate results as compared to the standard steam distillation from strong acid solution followed by thorium nitrate titration.     

Geochemical association of plutonium in sediments of the Trombay coastal environment

Geochemical association of plutonium in the coastal environment of Trombay has been studied. A sequential leaching method was employed for chemical partitioning of plutonium in sediments. The results show that 95±15% of plutonium was extracted by different leaching reagents out of which 85±14% was associated with organic matter and hydrous oxide and 9±4% with residual fraction.The presence of significant fraction of Pu bound with organic matter of the sediment is an important factor in determining the extent to which an element becomes available to bottom feeding biota and so enters the aquatic food chain.     

Ultrasound-assisted extraction and silylation prior to gas chromatography-mass spectrometry for the characterization of the triterpenic fraction in olive leaves

One of the most important fractions of bioactive compounds isolated from plants is that formed by triterpenic compounds, which have proved to be anti-bacterial, antifungal, anti-inflammatory, cytotoxic and anti-tumour. A method for leaching and determination of the main triterpenic compounds (oleanolic acid, ursolic acid, uvaol, erythrodiol) in olive leaves is here presented. Quantitative leaching was obtained with ethanol as leachant and ultrasonic assistance for 20 min, a very short time as compared to conventional procedures by maceration, which usually requires at least 5 h. After isolation, an aliquot of the ethanolic leachate was silylated to derivatize the analytes prior to gas chromatography-mass spectrometry analysis. Silylation reaction was also assisted with ultrasound in order to accelerate the derivatization step, which only required 5 min--a dramatic shortening in comparison to conventional silylation of terpenic compounds with derivatization times ranging from 30 min to 3 h. The proposed method has demonstrated to be useful for isolation and characterization of the triterpenic fraction in plants; the capability of ultrasound to assist sample preparation (acceleration of leaching and derivatization) has also been proved.     

High stability three-dimensional porous PtSn nano-catalyst for ethanol electro-oxidation reaction

In addition to the theoretical research, direct ethanol fuel cells have great potential in practical applications. The performance of direct ethanol fuel cells largely depends on the electrocatalysts. Pt-based electrocatalysts have been promising candidates for advancing direct ethanol fuel cells for its high catalytic activity and great durability. Here, a PtSn catalyst with unique three-dimensional porous nanostructure has been designed and synthesized via a two-step liquid phase reduction reaction. Sn formed a self-supporting framework in PtSn alloy particles (∼3.5 nm). In ethanol electro-oxidation reaction, the PtSn catalyst exhibited high mass activity and excellent recycling time compared with that of Pt/C. After the morphology characterization before and after potential cycling, the PtSn alloy-based nano-catalyst showed good stability. The PtSn catalysts effectively avoid structural instability due to the external carriers, and prolong the leaching time of Sn. In addition, the introduction of a certain amount of Sn can also solve the poisoning phenomenon of active sites on Pt surface. The design strategy of porous alloy nano-catalyst sheds light on its applications in direct ethanol fuel cells.     

Activation of the Surface of Polymetallic Carriers by the Formation of Intermediate Intermetallic Phases

A method for the conversion of a surface layer of monolithic polymetallic carriers into highly active catalytic phases with a high specific surface area, which contain nanosized formations, was developed. An intermetallide layer was formed in the course of the high-temperature aluminum coating of the carrier surface; this layer was transformed into an active form by leaching and stabilization. A method was proposed for the enrichment of the aluminized layer in alloy additives. The microstructure of the intermetallide layer and the distribution of elements in it were studied with the use of chrome-nickel stainless steel gauze as an example. The physicochemical characteristics of the active phase were examined using a BET method, scanning electron microscopy, and X-ray diffraction analysis. The catalytic properties of the samples were studied in the processes of the deep oxidation of CO and propane and the hydrogenation of CO₂.     

Effect of storage time on the pressure oxidation enthalpy of pyrite

The information on heat of oxidation?Creduction reactions is important for the heat balance and optimization of the autoclave design in the hydrometallurgical industry in ore processing. Pyrite (FeS₂) is a gangue mineral that presents with nickel-containing pentlandite, and copper-containing chalcopyrite minerals. The presence of pyrite impacts to the overall heat of leaching process. This study has been performed on a differential scanning calorimeter (DSC80, Setaram) with a commercial mixing cell to study the thermal behaviour of pure pyrite FeS₂ (Valdenegrillos, Spain) mineral particles during oxidative pressure leaching at 150?°C and partial oxygen pressure of 3.4?MPa. A calorimetric method for determining the enthalpy of leaching of sulphide minerals at high temperatures and oxygen pressures has been used to evaluate the enthalpies of oxidation of freshly ground pyrite and pyrite stored for a year in contact with air (stored pyrite) under conditions relevant to pressure oxidation operations. Ground pyrite stored over time has long since been known to result in greater heat evolution during oxidative leaching. A likely mechanism for this phenomenon was uncovered: formation of ferrous sulphate and sulphuric acid during storage in contact with air influencing greater heat evolution at the outset of the reaction. Two mass loss steps on TG curve of stored pyrite, attributed to the elimination of atmospheric moisture and H₂O molecule from FeSO₄·H₂O, is absent on TG curve of freshly ground pyrite.     

The effect of unsaturation on the reaction of aqueous alkyl bromides with brass foil

Brass (a zinc/copper alloy) foil reacts with mixtures of water and alkyl bromides to give dissolution of zinc and copper. The relative rates of leaching depend on the bromide used: saturated bromides favor dissolution of zinc, whereas unsaturated bromides favor dissolution of copper. This difference is attributed to the formation of π-complexes between the unsaturated linkages and the copper atoms.     

Investigation of the leaching behavior of components of the magnesium potassium phosphate matrix after high salt radioactive waste immobilization

The samples of the magnesium potassium phosphate (MPP) matrix have been synthesized during solidification of the simulator of acid intermediate level waste. The main phase of the obtained samples corresponds to MgK_1?x(NH₄)_xPO₄ × 6H₂O. The behavior of the matrix components during leaching with bidistilled water according to the semi-dynamic test GOST R 52126-2003 has been studied. The high hydrolytic stability of the MPP matrix to leaching of ¹³⁷Cs, ⁹⁰Sr, ²³⁹Pu and ²⁴¹Am exceeding the stability of the cement matrix has been shown. It has been found that the components leaching process is controlled by various mechanisms due to the formation of the salts with different solubility.     

Pt-表层限域的表面FeOx结构用于低温CO氧化反应

通过简单的浸渍-还原并随后在酸性溶液中处理制备了Pt-Cu双金属催化剂. 利用电感耦合等离子体发射光谱、X射线衍射和X射线光电子能谱对不同处理条件下的Pt-Cu纳米粒子的结构和组成进行了表征. 研究发现, Pt-Cu催化剂在高温H₂中还原形成了PtCu₃合金结构, 酸洗处理后形成了包含Pt-骨架(Pt-skeleton)的表面结构和PtCu₃合金核的纳米粒子. 而Pt-骨架结构又可通过在H₂中退火转变为规整的Pt-表层(Pt-skin)结构. Pt-表层表面修饰Fe氧化物后在CO选择氧化反应中表现出较好的催化性能. 通过此方法制备的三金属Pt-Cu-Fe催化剂可达到与Pt-Fe相近的高活性, 并且催化剂中Pt的用量大大降低.     

Voltammetric methods for the determination of heavy metals in domestic waste and compost produced from it

Methods of sampling an preparation of waste and compost samples for analysis are described. A voltammetric method has been used for the determination of the contents of toxic heavy metals (one of the most important criterion for compost quality evaluation) in domestic waste and in compost produced from it. A novel method was proposed for the UV mineralisation of water extracts obtained during leaching of waste and compost samples. Copper, lead, zinc and cadmium were determined in wet-digested samples of domestic waste, compost and its extracts by anodic stripping voltammetry. Nickel and cobalt were determined by adsorption voltammetry. The determination of five metals in one sample over a wide range of concentrations and the low cost of the apparatus used are the main advantages of the analytical method described. This has been shown by the determination of the metals in fractions of domestic waste, in compost produced of that waste and in compost mixed with sewage sludge. Special attention has been paid to investigations of the mobilisation of metals from waste and compost during the leaching test.     

新型有机荧光染料嵌合的核壳荧光纳米材料的研制

采用油包水的反相微乳液方法,首次以羊抗人免疫球蛋白(IgG)标记的异硫氰酸荧光素(FITC)为核材料,成功地制备了FITC的核壳荧光纳米颗粒,克服了采用传统方法制备核壳荧光纳米颗粒中存在的荧光染料泄露的问题.制备的这种核壳荧光纳米颗粒比细胞小很多,且具有生物亲和性,可为纳米生物传感器件提供新型材料.基于该核壳荧光纳米颗粒的标记方法也为生物医学提供了一种新型的非同位素分析方法.