The electrochemical behaviour of cobalt in alkaline nitrate melts at different temperatures

The electrochemical behaviour of cobalt in molten alkali nitrates in the temperature range from 141 to 321°C has been investigated. At lower temperatures the metal dissolves as Co(II); the oxidation product at higher temperatures is Co₃O₄. Nitrogen oxides are also formed. Passivation and localized corrosion occur under definite anode potential, Co(II) concentration and temperature conditions. These effects have been studied by non-stationary measurements. Co(II) dissolved in the melt can be electrodeposited either on cobalt or platinum cathodes.     

Investigation of factors influencing sodium sulfide oxidation in the presence of polymeric heterogeneous catalysts of transition metal oxides

The activity of heterogeneous catalysts of transition metal oxides and their mixtures deposited on the polymeric matrix in the oxidation of sodium sulfide was investigated. It is shown that mixtures of manganese oxide and other transition metal oxides have high catalytic activity. It was evident that the positive synergistic effect occurred in the combined action of two or more catalytically active transition metal oxides, and the maximum effect was observed in the mixture of three catalytic agents of transition metal oxides. Catalytic mechanism of transition metal oxides for sulfide oxidation was studied. The kinetics of formation of products of sodium sulfide oxidation was studied in the presence of heterogeneous catalysts based on phthalocyanine cobalt and transition metal oxides. The dependence of the rate of formation of products of sodium sulfide oxidation on alkali concentration was investigated. Some factors influencing the oxidation rate such as sulfide, oxygen and alkaline concentrations, antioxidant and oxidation products were investigated.     

钼铋复合金属氧化物催化低碳烯烃选择氧化制备醛类研究进展

低碳烯烃选择氧化制备醛类等含氧化合物是生产有机化工中间体及产品的关键步骤,钼铋复合金属氧化物因其优异的催化性能在相关工业界和学术界受到广泛关注,然而目前关于该催化剂上选择氧化反应机制和催化反应本质等科学问题的认识尚未形成统一理论。本文系统综述了钼铋复合金属氧化物在催化低碳烯烃选择氧化制备醛类反应中的研究进展,包括催化剂微观结构的三种调控手段,即主组分钼酸铋物相结构、助剂及载体等对反应性能的影响,并对反应机理进行了深入讨论与总结。最后展望了钼铋复合金属氧化物在该选择氧化反应中的发展前景,为钼铋复合金属氧化物修饰改性及开发高效低碳烯烃选择氧化制含氧化合物催化剂提供思路。     

Adhesion and Wetting Hysteresis of a Metal (Mercury) on an Oxide Glass in Air and Nitrogen

In general, oxygen can considerably change the wetting behavior of oxides by molten metals. This work is a basic illustration of the oxidation effect on the wetting behavior of glass by a liquid metal. Taking mercury as a model of a metal, the importance of the metal oxidation in the glass/metal interaction has been observed by measuring wetting contact angles of mercury on glass and the ability of calibrated mercury drops to slide down, under gravitation, on an inclined glass plate in air or in nitrogen. It is believed that the highest force of detachment by sliding of the mercury drop in air results from the metal oxidation which can be interpreted by a higher contact angle hysteresis when the metal is exposed to air.     

Adhesion and Wetting Hysteresis of a Metal (Mercury) on an Oxide Glass in Air and Nitrogen

In general, oxygen can considerably change the wetting behavior of oxides by molten metals. This work is a basic illustration of the oxidation effect on the wetting behavior of glass by a liquid metal. Taking mercury as a model of a metal, the importance of the metal oxidation in the glass/metal interaction has been observed by measuring wetting contact angles of mercury on glass and the ability of calibrated mercury drops to slide down, under gravitation, on an inclined glass plate in air or in nitrogen. It is believed that the highest force of detachment by sliding of the mercury drop in air results from the metal oxidation which can be interpreted by a higher contact angle hysteresis when the metal is exposed to air.     

Ionic crosslinking of carboxyl-terminated liquid rubbers with metal oxides

Ionic crosslinking of carboxyl-terminated liquid rubbers with metal oxides and metal carbonates, mainly with the former, were investigated. The liquid rubbers used were a polymer of butadiene (Hycar CTB 2000X162) and a copolymer of butadiene–acrylonitrile (Hycar CTBN 1300X8). The CTBN ionically crosslinked rubbers obtained showed higher tensile strength than the CTB series, due to the polarity effect of the nitrile groups. The ionic rubbers cured with MgO and CaO were studied in detail, and it was found that their tensile strength increased markedly with increase in the metal oxides used, and in addition white carbon and carbon black showed remarkable reinforcing effects. The properties such as tensile strength, elongation, Shore A hardness, and melt index are influenced by humidity. It is characteristic of these ionically crosslinked rubbers that they can be successfully reprocessed.     

Interface Properties of Dielectric Oxides

Chemical and electronic properties of dielectric oxide interfaces as obtained using photoelectron spectroscopy are presented and discussed. Interface preparation includes the deposition of metals onto dielectrics and vice versa as well as the effect of postdeposition treatments. Most interfaces are not abrupt as either reduction in the oxide surface occurs during metal deposition or oxidation of the metal substrate is induced by oxide deposition. The Schottky barrier heights at these interfaces are strongly affected by the interface chemistry. Reactive interfaces exhibit a strong Fermi level pinning due to defect formation. Nonreactive interfaces, which are obtained by depositing metallic oxide electrodes, exhibit an unpinned Schottky–Mott‐like barrier formation. Barrier heights can therefore be modified by more than 1 eV with suitable electrode material and processing. Postdeposition oxidation and reduction treatments and ferroelectric polarization can lead to comparable changes of barrier height. Interface studies between dielectric oxides reveal the dependence of valence band maximum and conduction band minimum energies. Due to transitivity of band alignment, these can be arranged on an absolute energy scale. The range of Fermi level positions in dielectric oxides, which can also be obtained from photoelectron spectroscopy and which is limited by intrinsic defect formation, is comparable when the oxides aligned on the energy scale determined by the photoemission experiments. The band alignment therefore indicates if a material can be made n‐type or p‐type by donor or acceptor doping. The range of Fermi levels in the oxides corresponds also with the range of the Fermi levels at oxide/metal interfaces.     

Preparation and Application of Perovskite Catalysts for Diesel Soot Emissions Control: An Overview

The diesel engines are energy efficient (1), but their particulate matter (soot) emissions are still a matter of concern even though major advances in their control are being made. For soot abatement, catalytic diesel particulate filter (DPF) technique is widely employed to trap and burn the soot. Many types of catalysts have been investigated for the soot combustion i.e. platinum group metal (PGM) based, perovskite-type oxides, spinel-type oxides, rare earth metal oxides, and mixed transient metal oxides etc. The cost of PGM catalysts is high and their availability is questionable. Further they are susceptible to poisoning and have low thermal stability. On the other hand perovskite catalysts show potential as effective soot oxidation catalyst for the DPF because of their low cost, high thermal stability and tailoring flexibility. Many papers related to soot oxidation over perovskite catalysts have been published but no review paper appears in the literature that is dedicated to soot oxidation. Thus, this article provides a summary of published information regarding pure and substituted perovskite catalyst, preparation methods, properties, and their application for diesel soot emission control.     

非贵金属催化剂催化氧化甲醛的研究进展

室内装修装饰材料释放出的甲醛是一级致癌物质,严重危害人类的身体健康。催化氧化法在较为温和的条件下可以将甲醛转化为无毒的CO₂和H₂O,是一种非常有效的消除甲醛技术。其中该技术采用的非贵金属催化剂因资源丰富,价格低廉,目前研究的最为广泛。本文综述了近年来非贵金属催化剂的研究进展,主要介绍了单一金属氧化物和复合金属氧化物的研发情况;对这些催化剂的合成、结构及甲醛催化氧化性能进行了分析,并总结了一部分甲醛催化氧化的反应机理。另外还对非贵金属催化剂未来的研究发展方向进行了展望：通过各种制备方法调控金属氧化物的结构、形貌、比表面积,进而暴露大面积活性面和丰富优化活性位来提高催化性能;同时借助一些先进的表征技术和理论计算方法探索非贵金属催化剂结构和催化性能之间的关系,深入探讨甲醛催化氧化反应机理等基础问题。     

Ni-Cr-Co氧化物纳米催化剂对甲醇阳极氧化的电催化性能研究

采用了热分解法合成Ni-Cr-Co氧化物纳米粒子,并用作直接甲醇燃料电池(DMFC)的阳极电催化剂。通过X射线衍射(XRD)、透射电子显微镜(TEM)和扫描电子显微镜(SEM)对催化剂进行表征,制得的纳米催化剂均匀分散,且粒径为25~50 nm。利用循环伏安法(CV)对不同金属摩尔比和焙烧温度下的催化剂在甲醇氧化反应中的活性进行了研究。结果表明,Ni-Cr-Co(摩尔比为1∶1∶1.5)的纳米氧化物对甲醇氧化反应的起始电位、峰值氧化电流密度和If/Ib分别为0.38 V,19.3 mA/cm2和1.72,表现了很好的电催化性能。     

Tailor-made nanomaterials designed by electrochemical methods

We have developed different electrochemical procedures for the production of nanostructured bulk metals, catalyst particles and metal oxides with variable crystallite sizes. The crystallite size of the nanoparticles can be controlled by the variation of the physical and chemical process parameters. Efficient and inexpensive catalyst layers for polymer electrolyte fuel cells were prepared using pulsed electrodeposition (PED) and DC-plating procedures. The advantage of these techniques is the site-selective deposition of Pt and PtRu catalysts on the carbon support. Large amounts of nanostructured metal oxides with different crystallite sizes can be prepared with our EDOC process (electrochemical deposition under oxidizing conditions) which is based on the reduction of metal ions generated from the anodic dissolution of a sacrificial anode with subsequent oxidation of the formed metal clusters. For these nanomaterials we also discuss the physical properties (e.g. thermal stability, catalytic activity).     

Catalytic oxidation of saturated hydrocarbons on multicomponent Au/Al2O3 catalysts: Effect of various promoters

The performance of unpromoted and MO_x-(M: alkali (earth), transition metal and cerium) promoted Au/Al₂O₃ catalysts have been studied for combustion of the saturated hydrocarbons methane and propane. As expected, higher temperatures are required to oxidize CH₄ (above 400 °C), compared with C₃H₈ (above 250 °C). The addition of various MO_x to Au/Al₂O₃ improves the catalytic activity in both methane and propane oxidation. For methane oxidation, the most efficient promoters to enhance the catalytic performance of Au/Al₂O₃ are FeO_x and MnO_x. For C₃H₈ oxidation a direct relationship is found between the catalytic performance and the average size of the gold particles in the presence of alkali (earth) metal oxides. The effect of the gold particle size becomes less important for additives of the type of transition metal oxides and ceria. The results suggest that the role of the alkali (earth) metal oxides is related to the stabilization of the gold nanoparticles, whereas transition metal oxide and ceria additives may be involved in oxygen activation.     

金的催化作用

用共沉淀法和沉积-沉淀法可以制备高度分散的金负载氧化物催化剂。当负载的金粒子的直径小于5nm时，该类催化剂对许多化学反应具有优良的活性。概括地介绍了近期发表的关于金负载催化剂成功地用于催化CO氧化，乙炔氢氯化，丁烯醛选择加氢，水煤气转换和氮氧化物还原等反应的例子。     

Catalysis and inhibition of the combustion of ammonium perchlorate based solid propellants

Results of studies of the combustion of a composite solid propellant based on ammonium perchlorate are presented. The effect of additives of metal oxides is studied for the high and low-temperature decompositions, linear pyrolysis, and combustion of ammonium perchlorate, the decomposition of HClO₄, isobutylene oxidation by oxygen and perchloric acid, and the combustion of propellants with various organic combustibles. It is shown that the efficiency of metal oxides in the reactions of oxidation of isobutylene and propellant combustion is related to the energy of the Me—O bond in the surface oxide layer or the enthalpy of formation of this bond. The extremal nature of the catalytic effect of metal oxides on the burning rate of the propellant is due to the small time of residence of the oxide particles in the zone of intense oxidation-reduction reactions. For this reason, the same additives of metal oxides has different effects on the combustion of the propellant with different organic, combustibles, and the most efficient catalyst can be chosen by a simplified algorithm. The potentials for affecting the composite solid propellant via gas-phase oxidation-reduction reactions is indicated by the effect of additives of organic sources of active species—amines and halides. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 76–90, November–December 1999.     

含氯挥发性有机物的催化氧化研究进展

催化氧化是控制挥发性有机污染物排放的有效途径之一,但传统催化剂在氧化消除含氯挥发性有机物(CVOCs)时易中毒而失活,因此,研发新型、高效、稳定的催化剂对其工业应用具有重要意义。简要综述近年来稀土及过渡金属氧化物、分子筛和负载贵金属催化剂对CVOCs氧化的催化性能和催化反应机理,剖析CVOCs氧化反应副产物的形成和催化剂失活的原因,并展望CVOCs催化氧化技术的未来发展趋势。     

多孔复合金属氧化物的制备及其在消除挥发性有机物中的应用

挥发性有机物(Volatile Organic Compounds,VOCs)是一类大气环境污染物,危害人身健康,必须严格控制其排放。在消除VOCs的方法中,催化氧化被认为是最有效的方法之一,其消除效果取决于催化剂的性能。简要综述近年来多孔复合金属氧化物(包括钙钛矿型氧化物、类钙钛矿型氧化物、尖晶石型氧化物和六铝酸盐)及其负载过渡金属氧化物和贵金属(合金)催化剂的制备及其氧化消除VOCs的催化性能。比表面积、孔结构、粒子分散度、粒径、吸附氧物种浓度、低温还原性、反应物活化能力或过渡金属氧化物或贵金属(合金)与载体之间的相互作用等是影响催化剂活性的主要因素。此外,就此类研究工作的未来发展趋势还进行了展望。     

异丙苯催化氧化催化剂研究进展

异丙苯氧化反应是石油化学工业中重要的反应过程,传统的异丙苯氧化工艺是以少量的氧化产物过氧化氢异丙苯作为引发剂的无催化氧化工艺,存在效率低和安全性差等缺陷。几十年来,研究者对异丙苯催化氧化工艺进行了广泛研究,开发的催化剂类型主要有碱金属或碱土金属催化剂、金属氧化催化剂、过渡金属离子有机络合物催化剂、N-羟基邻苯二甲酰亚胺类催化剂、负载型催化剂、金属及合金催化剂和中孔分子筛催化剂等。其中,改性MgO催化剂、Ag及Ag-Au合金催化剂和负载过渡金属杂原子的中孔分子筛催化剂表现出较优越的催化性能,具有较好的开发前景。但迄今为止报道的各类催化体系还不能彻底解决传统氧化工艺的固有问题,开发具有高活性、高选择性和高稳定性的环境友好催化体系是今后研究的重点。     

Role of potassium in the aerobic oxidation of aromatic alcohols over K+-promoted Mn/C catalysts

The aerobic oxidation of aromatic alcohol on alkali metal promoted Mn/C catalysts has been investigated. A dramatic improvement of the oxidation activity can be observed when the Mn/C catalyst is modified with potassium ions. Characterizations of Raman and X-ray absorption fine structure (XAFS) evidence that potassium ions induce a large local distortion to Mn–O octahedrons in supported manganese oxides with coexistence of Mn²⁺ and Mn³⁺, which has been suggested to be a vital factor to enhance the activation of O₂ for the oxidation of benzylic alcohol.     

Heterogeneous Catalyzed Ozonation using Cu-Ni-Co Oxides for Degradation of Dichlorophenol

The ozone initiated oxidation of dichlorophenol (DCP) in aqueous medium, catalyzed by various loadings of Cu, Ni and Co oxides supported on γ-Al₂O₃ was studied, as function of ozonation time and pH. Ternary catalyst materials synthesized by a wet-impregnation were fully characterized. The XRD results showed metal oxides were well incorporated within the alumina phase. Microscope images illustrated that metal oxide particles are dispersed on the surface of the support. Dihydroxyfumaric acid and oxalic acid were, respectively, found to be major and minor oxidation products. The oxidation products were characterized by FT-IR, ¹H NMR, and mass spectral data.     

挥发性有机化合物催化氧化技术

基于环境友好,对使用催化氧化法去除挥发性有机化合物(VOCs)的原理、特点以及催化剂、工艺流程等研究进行综述。挥发性有机化合物完全催化氧化机理分为:Mars-van Krevelen(MVK)模型、Langmuir-Hinshelwood(L-H)模型和Eley-Rideal(E-R)模型。复合金属氧化物催化剂是研究的热点,去除VOCs的核心是使反应温度降低,即具有低温和高活性的催化剂。延长催化剂寿命、提高去除效率也可以带来良好的节能效果和降低投资成本。对于低浓度和大体积VOCs排放,可通过吸附+催化混合法先进技术实现去除,且成功应用于实践。