Oxidation of p-methoxyphenol on SnO2–Sb2O5 electrodes: Effects of electrode potential and concentration on the mineralization efficiency

The oxidation of p-methoxyphenol in aqueous solution on antimony-doped tin oxide has been studied, and the effects of applied potential and initial PMP concentration upon the oxidation rate have been identified. The concentration decay of PMP during its electrooxidation follows first-order reaction kinetics. Analysis solution during electrolysis using UV–Vis spectroscopy revealed that under some experimental conditions partial oxidation of PMP occurs. The principal products were p-benzoquinone and aliphatic (maleic and oxalic) acids. The Faradaic efficiencies for oxidation at different applied potentials were determined from the UV–Vis spectra obtained. It is shown that production of CO₂ was very low at potentials below 2.3 V with respect to the saturated calomel electrode, and that at more positive potentials mineralization to CO₂ decreased as the concentration of PMP in solution increased.     

Electrooxidation of Cyanide on Cobalt Oxide Anodes

Oxidation of cyanide ions at a Ti/Co₃O₄ electrode in aqueous base solution has been investigated. The cyclic voltammetric curve for the oxidation of cyanide at Ti/Co₃O₄ shows a well formed wave prior to oxygen evolution at a potential where the spinel surface itself undergoes oxidation. Using a flow cell it is confirmed that the conversion of cyanide (CN^–) to cyanate (CNO^–) can be achieved galvanostatically with a reasonable current efficiency. As an example, at a current density of 100 A m^–2, CN^– concentration can be lowered from 10 to 0.2 mM with an electric energy consumption of about 18 kWh kg^–1 of CN^– oxidized and a global current efficiency of 28.5%. The oxide coating appears to be quite stable during repeated electrolyses.     

Competitive electrochemical oxidation of p-chlorophenol and p-nitrophenol on Bi-doped PbO2

The initial stages of oxidation of aqueous solutions of p-chlorophenol (pcp) and p-nitrophenol (pnp) on Bi-doped PbO₂ electrodes have been studied. From deconvolution and analysis of UV-Vis spectra of the solutions obtained during electrochemical oxidation, benzoquinone and aliphatic acids were identified as the primary oxidation intermediates; oxidation of benzoquinone was found to be the slow step during the early stages of the electrochemical combustion process. The effect of competing adsorption of pcp and pnp on Bi-PbO₂ was also examined, and the presence of pnp in solution was found to inhibit the rate of oxidation of pcp during concurrent oxidation of both phenols.     

Study of the oxidation of solutions of p-chlorophenol and p-nitrophenol on Bi-doped PbO2 electrodes by UV-Vis and FTIR in situ spectroscopy

The oxidation of p-chlorophenol (pcp) and p-nitrophenol (pnp) was studied at Bi-doped PbO₂ (Bi-PbO₂) electrodes. The mass balance between solution composition and flowing charge was obtained from deconvolution of UV-Vis spectra recorded during electrolysis at constant potential. It is shown that the time-dependent production of CO₂ is different for the oxidation of pcp and pnp, indicating different reaction mechanisms for the oxidation of each of these compounds. The reaction kinetics was also followed under thin layer conditions by SNIFTIRS; the similarly increasing signals associated to the generation of CO₂ obtained during oxidation of both compounds indicates that under conditions of restricted mass transfer the mineralization rates of pcp and pnp are similar. The results show that benzoquinone (bq) formed from oxidation of phenols desorbs prior to further oxidation to yield maleic acid (ma), in turn oxidizing further to CO₂.     

Electrochemical Oxidation of Ferulic Acid in Aqueous Solutions at Gold Oxide and Lead Dioxide Electrodes

A kinetic study of the electrochemical oxidation of ferulic acid (3-methoxy-4-hydroxycinnamic acid) by direct electron transfer at treated gold disk was combined with results of electrolyses in order to produce total degradation into CO₂ and H₂O at Ta/PbO₂ anode. The oxidation of ferulic acid at gold electrode was studied by cyclic voltammetry. At low concentration, ferulic acid shows one irreversible anodic peak. The peak current shows adsorption characteristics. For ferulic acid concentrations higher than 0.02 mmol dm⁻³, the voltammogram shows two anodic peaks. The effect of experimental conditions on the ratio of these two peaks was examined. The proposed mechanism is based on the hypothesis of two-electron oxidation of ferulic acid molecule involving a three intermediate cation mesomers. Hydrolysis of these mesomers leads to the formation of caffeic acid, methoxyhydroquinone and 3,4-dihydroxy-5-methoxycinnamic acid. Then ferulic acid was quantitatively oxidised by electrolysis on lead dioxide to produce, via intermediate aromatic compounds, maleic acid, oxalic acid and formic acid whose oxidation leads to carbon dioxide.     

不同金属氧化物阳极上甲基橙的电化学氧化降解

分别以Ti/SnO2+Sb2O3和Ti/SnO2+Sb2O3/PbO2电极为阳极进行甲基橙的电化学氧化,研究了两种金属氧化物阳极上甲基橙氧化降解过程的反应速率、电流效率及COD的变化.结果表明,两种金属氧化物阳极都能有效氧化降解甲基橙,氧化反应符合一级反应动力学规律,在Ti/SnO2+Sb2O3和Ti/SnO2+Sb2O3/PbO2电极上甲基橙氧化降解过程的表观速率常数分别为0.148和2.43×10-2 min-1. 以Ti/SnO2+Sb2O3为阳极电解30 min,甲基橙的浓度从初始时的0.305 mmol/L降至4.89×10-3 mmol/L,甲基橙的转化率达98.4%;在Ti/SnO2+Sb2O3/PbO2电极上,相同电解时间下甲基橙的浓度只降至0.14 mmol/L,转化率为55.0%. 对不同电极上甲基橙电化学氧化过程电流效率的研究表明,Ti/SnO2+Sb2O3电极的电流效率明显高于Ti/SnO2+Sb2O3/PbO2电极. Ti/SnO2+Sb2O3电极的反应速率大、电流效率高主要源于其较高的析氧电位.     

多层水系流延和共烧法制备具有阳极功能层固体氧化物燃料电池

采用多层水系流延和共烧方法制备具有阳极功能层的单电池。阳极基底、阳极功能层、电解质层和阴极层分别为Ni-YSZ、Ni-ScSZ、YSZ和LSM-ScSZ。在H2/空气气氛中,分别在700、750、800℃测试具有阳极功能层的单电池,其最大功率密度分别为：0.30、0.55W/cm2和0.8W/cm2;其对应的电池欧姆电阻（R0）分别为0.39、0.30cm2和0.19cm2。电池的极化电阻则分别为1.28、0.91cm2和0.62cm2。采用相同工艺制备无阳极功能层的单电池,其在700、750、800℃的最大功率密度分别为0.21、0.31W/cm2和0.56W/cm2,对应的R0为0.41、0.39cm2和0.28cm2。电池的极化电阻为1.40、1.27cm2和0.91cm2。这说明采用的多层水系流延和共烧法制备的固体氧化物燃料电池的阳极功能层能有效减小电池的活化极化,从而提高单电池的电化学性能。     

金属支撑固体氧化物燃料电池研究进展

与传统全陶瓷结构的燃料电池不同,金属支撑固体氧化物燃料电池利用多孔金属来支撑功能阳极层–电解质层–阴极层,具有结构稳定性高、抗热快速热循环能力强,电堆组装简单,材料成本低等优势。本文分析了金属支撑固体氧化物燃料电池(SOFC)材料的选择和电池制备过程中的关键问题,并概述了金属支撑SOFC技术的研究进展。     

A Mechanistic Study of Low Temperature CO Oxidation over Cobalt Oxide

The CO oxidation over Co₃O₄ and Co₃O₄/Al₂O₃ has been investigated using flow reactor and in situ FTIR studies. Cobalt oxide shows very high activity even at room temperature. However, a gradual deactivation takes place during reaction. The deactivated catalyst shows the presence of two different carbonate species and one graphite-like species. A possible mechanism for the deactivation is discussed.     

Stability of ruthenium catalysts supported on TiO2 or ZrO2 in catalytic wet air oxidation

The stability of ruthenium catalysts supported on TiO₂ and ZrO₂ were studied in the wet air oxidation of aqueous solution of succinic and p-hydroxybenzoic acids taken as model effluent and on real effluents from the paper-pulp industry. Catalyst recycling experiments were conducted in batch reactor and long-term stability tests were conducted in trickle-bed reactor. In all experiments, ruthenium and support materials were perfectly stable to leaching, sintering and fouling. Ruthenium catalysts experienced a weak deactivation as they were exposed to air, e.g., in recycling experiments however the loss of activity occurred only after the first exposure and was completely reversible upon catalyst reduction. The deactivation was attributed to an over-oxidation of the catalyst surface particularly noticeable in the case of very small Ru-clusters (1 nm).     

Molecular Engineering of Supported Vanadium Oxide Catalysts Through Support Modification

Highly dispersed, multilayered surface metal oxide catalysts (V₂O₅/MO _x /SiO₂, M = Ti(IV), Zr(IV) or Al(III)) were successfully synthesized by taking into account various factors that govern the maximum dispersion of metal oxide species on silica. The characterization results revealed that the molecular structures of the surface vanadium oxide species on the modified supports are a strong function of environmental conditions. The surface vanadium oxide species under dehydrated conditions are predominantly isolated VO₄ units, similar to the dehydrated V₂O₅/SiO₂ catalysts. Upon hydration, the surface vanadium oxide species on the modified supports consist of polymerized VO₅/VO₆ units and/or less polymerized (VO₃) _n species, which depend on the vanadia content and the specific second metal oxide loading. The surface V cations are found to preferentially interact with the surface metal (Ti, Zr or Al) oxide species on silica. The V(V) cations in the dehydrated state appear to possess both oxygenated ligands of Si(IV)–O^– and M–O^–. Consequently, the reducibility and catalytic properties of the surface vanadium oxide species are significantly altered. The turnover frequencies of the surface VO₄ species on these modified supports for methanol oxidation to redox products (predominantly formaldehyde) increase by more than an order of magnitude relative to the unmodified V₂O₅/SiO₂ catalysts. These reactivity enhancements are associated with the substitution of Si(IV)–O^– oxygenated ligands by less electronegative M–O^– ligands in the O=V(–O–support)₃ structure, which strongly suggests that the bridging V–O–support bonds play a key role in determining the reactivity of the surface vanadium oxide species on oxide supports.     

Performance of sol–gel Titanium Mixed Metal Oxide electrodes for electro-catalytic oxidation of phenol

Mixed metal oxides SnO₂–RuO₂–IrO₂, Ta₂O₅–IrO₂ and RhO₂–IrO₂ were immobilised on a Ti substrate using sol–gel techniques. The Ti mixed metal oxides were characterized in terms of morphology using scanning electron microscopy. Cyclic voltammetric responses of phenol at Ti/SnO₂–RuO₂–IrO₂, Ti/Ta₂O₅–IrO₂ and Ti/RhO₂–IrO₂ electrodes were evaluated and showed significantly low potentials for Ti/Ta₂O₅–IrO₂ (+100 mV), Ti/SnO₂–RuO₂–IrO₂ (+200 mV) and Ti/RhO₂–IrO₂ (−100 mV). The degradation of phenol in aqueous solution and its intermediates were investigated by bulk electrolysis and quantitatively assessed by HPLC analysis to elucidate the decomposition pathways and to develop a kinetic model for the electro-catalytic oxidation of phenol over Ti mixed metal oxides. Ring compounds, benzoquinone/hydroquinone, catechol, and short chain organics, carboxylic acids, have been identified as intermediate products for the electro-catalytic oxidation of phenol. Fundamental kinetic data were obtained for the conversion of phenol at these electrodes and was found to proceed in accordance with the pseudo-first-order kinetics with respect to the phenol concentration.     

Comparative Study of Electrocoagulation and Electrooxidation Processes for the Degradation of Ellagic Acid From Aqueous Solution

A comparative study of electrocoagulation and electrooxidation processes for the degradation of ellagic acid from aqueous solution was carried out. For the electrocoagulation process, metallic iron was used as electrodes whereas graphite and RuO₂/IrO₂/TaO₂ coated titanium electrodes were used for the electrooxidation processes. The effect of the process variables such as initial pH, concentration of the supporting electrolyte, applied current density, electrolysis time, and anode materials on COD removal were systematically examined and discussed. Maximum COD removal of 93% was obtained at optimum conditions by electrocoagultion using an iron electrode. The ellagic acid was degraded completely by electrooxidation using graphite electrodes under the optimum conditions. During electrooxidation, the chloride ion concentration was estimated and the effect of the Cl^? ion was discussed. The finding of this study shows that an increase in the applied current density, NaCl concentration, and electrolysis time enhanced the COD removal efficiency. The UV–Vis spectra analysis confirms the degradation of ellagic acid from aqueous solution.     

金属氧化物催化剂上H_2S选择性催化氧化研究进展

选择性催化氧化法作为一种新型的脱除H_2S尾气技术,重点是开发具有高活性和多种性能特点的催化剂形成系列产品。总结了金属氧化物催化剂上H_2S选择性催化氧化反应的研究进展。重点介绍了不同载体、活性组分和助剂对催化剂活性的影响;阐述了H_2S选择性催化氧化的反应机理和失活机理,并对金属氧化物催化剂的未来发展方向上进行了展望。     

Effect of Lead Oxide on Niobium-Doped Titania Varistors

The effect of PbO on Nb-doped TiO₂ varistors was investigated. It was found that the PbO dopant had significant effect on the varistor properties of Nb-doped TiO₂ ceramics. There existed an optimal range of PbO starting from 0.25 to 1 mol% for the nonlinear I–V characteristics of the 0.25 at.% Nb-doped TiO₂ ceramics. Within this PbO range, an effective boundary energy barrier of about 0.70 eV was created which yielded nonlinear I–V characteristics with α= 7.6. In contrast, α values of the samples containing PbO dopant outside this optimal range are only about 2 to 3. The effect of PbO on TiO₂ varistors was analyzed by impedance spectroscopy, C–V and dielectric measurements, and X-ray diffraction, as well as scanning electron microscopy. The results are discussed in the text.     

Mycorrhizal Colonization and Plant Growth Affected by Aqueous Extract of Artemisia princeps var. orientalis and Two Phenolic Compounds

The effects of an aqueous extract of Artemisia princeps var. orientalis and two phenolic compounds on mycorrhizal colonization and plant growth have been investigated. Greenhouse studies showed that the inhibitory effect of the extract on mycorrhizal colonization and plant growth increased in proportion to the concentration of the extract. When the mycorrhizal test plants were treated with an increasing concentration of phenolic compounds, the mycorrhizal colonization in roots of the test plant and the plant growth were decreased. There were strong indications that mycorrhizal fungi mitigated the inhibitory influence of shoot extract of A. princeps var. orientalis and phenolic compounds.     

Unprecedented Selective Oxidation of Styrene Derivatives using a Supported Iron Oxide Nanocatalyst in Aqueous Medium

Iron oxide nanoparticles supported on mesoporous silica‐type materials have been successfully utilized in the aqueous selective oxidation of alkenes under mild conditions using hydrogen peroxide as green oxidant. The supported catalyst could be easily recovered after completion of the reaction and reused several times without any loss in activity (no metal leaching observed during the reaction), constituting a facile and straightforward example of aqueous oxidation chemistry promoted by iron‐based heterogeneous systems.     

Isotopic Studies of Sn-Cr Binary Oxide Catalysts for Methane Total Oxidation

A series of Sn-Cr binary oxide catalysts were prepared by a co-current co-precipitation method and tested for methane total oxidation. The binary oxide catalysts have much higher surface areas and catalytic activities for methane oxidation than pure SnO₂. CrO _x /SnO₂ with a Cr/Sn atomic ratio of 3:7 displays the highest activity. Selected samples were subjected to temperature-programmed ¹⁸O isotope-exchange measurements. Both complete and partial heteromolecular ¹⁸O isotope exchange, as well as oxygen release, was observed for all catalysts. Reaction between CH₄ and ¹⁸O₂ under static conditions was performed to investigate the reaction mechanism and it was found that the total oxidation of methane over Sn-Cr binary oxide catalysts occurs via a redox cycle with the chromium ion in a high oxidation state as the active center. Oxygen mobility of the catalyst plays an important role in the total oxidation of methane, but too high a mobility leads to very high oxygen release and a reduction of the surface reoxidability. This causes a decrease in the catalytic oxidation activity.     

利用空气氧化NO的技术探讨

本文针对工业废气中NOx治理技术,对氧化NO的方法进行了论述,比较了各种方法的主要技术特征,着重分析了用空气作为氧化剂的可行性,得出了用空气氧化NO有较好的经济性、应用前景广阔的结论。     

Ru-Ir-Sn-Ti/Ti氧化物涂层阳极的性能研究

采用热分解法,在钛基体上制备了具有不同中间层及不同金属元素配比的Ru–Ir–Sn–Ti氧化物涂层阳极,通过扫描电子显微镜、X射线衍射、极化曲线、强化电解寿命和循环伏安曲线,研究了该氧化物涂层阳极的物理性能和电化学性能,并与Ru–Ir–Ti氧化物涂层阳极进行了比较。结果表明,以IrO2·SnO2为中间层的Ru–Ir–Sn–Ti(摩尔比16∶16∶4∶64)氧化物涂层阳极有较好的电催化性能,其强化寿命达432h。