Electrochemical regeneration of Ce(iv) for oxidation of p-methoxytoluene

The development of the electrochemical oxidation of aromatic compounds on an industrial scale is hindered by the deactivation of the electrode occurring under anodic polarization. This paper presents some results on the indirect oxidation of p-methoxy toluene by ceric sulfate electrochemically regenerated on a platinized titanium electrode. A technique that reactivates the fouled electrode on the one hand and avoids the passivation of the electrode during electrolysis on the other hand is proposed. Methylene chloride is used to extract the organic products from the aqueous phase before electrolysis. The preparative electrolysis of anisaldehyde is performed on the laboratory scale and the results show an overall (chemical and electrochemical) yield close to 80%.     

A study of the Ce(III)/Ce(IV) redox couple for redox flow battery application

In this study, the electrochemical behavior of the Ce(III)/Ce(IV) redox couple in sulfuric acid medium with various concentrations and the influence of the operating temperature were investigated. A change of the concentration of sulfuric acid mainly produced the following two results. (1) With an increase of the concentration of sulfuric acid the redox peak currents decreased. (2) The peak potential separation for the redox reactions increased with rising concentration of sulfuric acid from 0.1 to 2 M and then decreased with further increase of the concentration. Elevated temperature was electrochemically favorable for Ce(III)/Ce(IV) couple, which caused an increase of the peak currents for the redox reactions and a decrease of the peak potentials separation. Constant-current electrolysis shows that the current efficiency was 73% for the oxidation process of Ce(III) and 78% for the reduction process at 298 K, and could be improved by elevating the temperature. The open-circuit voltage of the Ce-V cell, after full charging, remained constant at 1.870±0.005 V for more than 48 h, and is about 29% higher than that of the all-vanadium batteries. The coulombic efficiency was approximately 87%, showing that self-discharge of the Ce-V battery was small. The preliminary exploration shows that the Ce(III)/Ce(IV) couple is electrochemically promising for redox flow battery (RFB) application.     

Use of the Nasicon/Na2SO4 couple in a solid state sensor for SO x (x=2,3)

The e.m.f. of a concentration cell for SO _x (x=2,3)-O₂ incorporating Nasicon as the main solid electrolyte has been measured in the temperature range 720 to 1080 K. The cell arrangement can be represented as, $$Pt, O'_2 + SO'_2 + SO'_3 \left| {Na_2 SO_4 \left\| {\left. {Nasicon} \right\|} \right.} \right.\left. {Na_2 SO_4 } \right|SO''_3 + SO''_2 + O''_2 , Pt$$ The Na₂SO₄ acts both as an auxiliary electrode, converting chemical potentials of SO _x and O₂ to equivalent sodium potentials, and as an electrolyte. The presence of Na₂SO₄ provides partial protection of Nasicon from chemical reaction with gas mixtures containing SO _x . The open circuit e.m.f. of the cell is in close agreement with values given by the Nernst equation. For certain fixed inlet gas compositions of SO₂+O₂, the e.m.f. varies non-linearly with temperature. The intrinsic response time of the cell to step changes in gas composition is estimated to vary from ～2.0 ksec at 723K to ～ 0.2 ksec at 1077K. The cell functions well for large differences in partial pressures of SO₃(p″_{SO 3}/p′_{SO 3}≈10⁴) at the electrodes.     

铈镁铝混合氧化物同时吸附NO、SO2的研究

用共沉淀法制备了二氧化铈和镁铝水滑石混合物,考察了催化剂的制备条件：晶化时间、焙烧温度、铈含量对该混合氧化物在富氧条件下同时吸附SO2,NO的性能影响。结果表明,本实验室制备的铈镁铝混合氧化物对SO2,NO具有同时吸附的性能。     

Electrocatalysis of the charge-transfer process for the Sb(III)/Sb(V) couple at a platinum electrode in concentrated HCl

Electrocatalysis of the electrochemical oxidation and reduction of Sb(V) and Sb(III) by adsorbed I⁻ and I₂ at a rotating Pt disc electrode was investigated in 12 M HCl. The heterogeneous rate constant in the absence of adsorbed halogen was increased by 200x for a maximum surface coverage by halogen. This large rate increase cannot be predicted on the basis of an electrostatic argument and a mechanism based on electron-transfer bridging is proposed.     

稀土固体超强酸SO_4~(2-)/TiO_2/Ce(IV)催化合成环己酮1,2-丙二醇缩酮

以环己酮与1,2-丙二醇为原料,稀土固体超强酸SO42-/TiO2/Ce(IV)为催化剂,合成了环己酮1,2-丙二醇缩酮,考察了影响反应的因素。结果表明,在n(酮)n∶(醇)=1 1∶.5、催化剂用量占反应物总质量的1.7%、带水剂环己烷用量占反应物总质量的30%、反应时间1h的优化条件下,环己酮1,2-丙二醇缩酮收率可达84.28%。     

Influence of aromatic reactants and products involved in the two stage electrochemical oxidation on the voltammetric behaviour of Ce(IV)/Ce(III) redox couple

The redox behaviour of the Ce(IV)/Ce(III) couple in 1.0 M nitric acid, 1.0 M sulfuric acid, 1.0 M perchloric acid and in different concentrations of methane sulfonic acid was investigated on a glassy carbon electrode using cyclic voltammetry. Quasi reversible redox behaviour with low E _p value of 200 mV and below were observed in 1.0 M sulfuric acid and high concentrations of methane sulfonic acid. Anionic complexes apparently exist in this media. The reactants and products involved in the indirect oxidations are found to influence cerous/ceric redox behaviour in 2.0 M methane sulfonic acid in three distinct ways: (i) in the presence of cerous methane sulfonate organic compounds such as toluene, benzaldehyde and naphthaquinone do not exhibit substantial inhibitive effects; (ii) compounds such as p-xylene and p-tolualdehyde exhibit some inhibitive effect at higher concentrations; and (iii) compounds like naphthalene, p-ethoxy toluene and p-ethoxy benzaldehyde exhibit a fairly high level of inhibitive effect.     

载硫酸高铈凹凸棒石的制备及其性能研究

现阶段已经发现多种类型催化剂可以催化制备苯甲醛缩乙二醇,它是一种非常重要的精细化工中间体,被广泛应用于化工、医药等研究领域.以酸化凹凸棒石为初始原材料,采用浸渍法制备了负载硫酸高铈凹凸棒石催化剂Ce(SO4)2/ATP,并利用比表面积和孔隙度分析仪、傅里叶红外光谱等技术手段对催化剂进行了表征,同时考察了该催化剂催化制备...     

硅胶负载硫酸铈催化合成苯乙醛缩乙二醇

以苯乙醛和乙二醇为原料,以硅胶负载硫酸铈(Ce2(SO4)3/S iO2)为催化剂,合成了苯乙醛缩乙二醇,考察了醛醇摩尔比、反应时间、催化剂用量及其稳定性等因素对收率的影响。实验结果表明,较优反应条件为:苯乙醛0.1 mol,n(苯乙醛)∶n(乙二醇)=1.0∶1.5,催化剂用量0.2 g,带水剂环己烷12 mL,回流反应2.0 h,苯乙醛缩乙二醇的产率可达96.0%以上。     

Investigation on the electrode process of the Mn(II)/Mn(III) couple in redox flow battery

The Mn(II)/Mn(III) couple has been recognized as a potential anode for redox flow batteries to take the place of the V(IV)/V(V) in all-vanadium redox battery (VRB) and the Br₂/Br⁻ in sodium polysulfide/bromine (PSB) because it has higher standard electrode potential. In this study, the electrochemical behavior of the Mn(II)/Mn(III) couple on carbon felt and spectral pure graphite were investigated by cyclic voltammetry, steady polarization curve, electrochemical impedance spectroscopy, transient potential-step experiment, X-ray diffraction and charge-discharge experiments. Results show that the Mn(III) disproportionation reaction phenomena is obvious on the carbon felt electrode while it is weak on the graphite electrode owing to its fewer active sites. The reaction mechanism on carbon felt was discussed in detail. The reversibility of Mn(II)/Mn(III) is best when the sulfuric acid concentration is 5 M on the graphite electrode. Performance of a RFB employing Mn(II)/Mn(III) couple as anolyte active species and V(III)/V(II) as catholyte ones was evaluated with constant-current charge-discharge tests. The average columbic efficiency is 69.4% and the voltage efficiency is 90.4% at a current density of 20 mA cm⁻². The whole energy efficiency is 62.7% close to that of the all-vanadium battery and the average discharge voltage is about 14% higher than that of an all-vanadium battery. The preliminary exploration shows that the Mn(II)/Mn(III) couple is electrochemically promising for redox flow battery.     

A sustainable mediated electrochemical process for the abatement of NOx from simulated flue gas by using Ag(I)/Ag(II) redox mediators

Electrochemical removal of NO and NO₂ by using Ag(I)/Ag(II) redox mediator system in nitric acid medium by two-stage scrubbing process was investigated. Experiments were carried out for the complete removal of NO and NO₂ from the stimulated flue gas at room temperature and atmospheric pressure. The process parameters like current density, Ag(I) concentration, HNO₃ concentration, initial concentration of NO, Ag(I) concentration and temperature were studied and optimized. A removal efficiency of >99% was achieved using this sustainable redox process. Ag(II)/Ag(I) can be regenerated and reused for the scrubbing of waste gases continuously and there is no other gases emission during scrubbing.     

A study of the Ag(s)/Ag2 SO4+Na2 SO4(l)1102 reference electrode

The high temperature electrode Ag(s)/Ag₄SO₄+Na₂SO₂(l) contained in a mullite membrane is a suitable reference electrode for measuring sodium activities in Na₂SO₄ melts. Several Na concentration cells have been studied at 900° C to establish the thermodynamic basis for the Ag(s)/10 mol% Ag₂SO₄ + Na₂SO₄ electrode. Part of this work involved the determination of the ratio of activity coefficients of Ag₂SO₄ and Na₂SO₄ in melts that were dilute in Ag₂SO₄. When the non-ideal solution behaviour was taken into account, very good agreement was obtained between predicted and measured cell voltages for acidic Na₂SO₄ melts.     

Experimental study of the SO2 removal over a NOx trap catalyst

The NO_x storage capacity of a NO_x trap catalyst is affected by SO₂ poisoning. When the extent of poisoning is low (less than 30% of BaO involved in sulphate formation), it is possible to regenerate the catalyst under reducing conditions and the initial storage capacity can be recovered, even in the presence of some remaining sulphates. When the extent of poisoning is very high, it is more difficult to regenerate the material and the initial NO_x storage capacity cannot be recovered, even after long regeneration duration.     

Electrochemical behaviour of the Cr(II)/Cr(III) couple on silver,silver amalgam and silver-based mercury film electrodes

The electrocatalytic activity of silver, mercury, silver-based mercury films, and silver amalgam electrodes for the reduction of Cr(III) ions in acidic solutions is analysed. An enhancement in the activity of the last two electrodes is observed when they are pretreated with high cathodic current polarization or ultrasonic waves. These effects can be explained by the formation of an unstable highly reactive amalgam. The electrocatalytic enhancement is not observed when the same electrode pretreatments are applied to sitting-drop mercury or silver electrodes.     

Ce(III)/Ce(IV) in methanesulfonic acid as the positive half cell of a redox flow battery

The characteristics of the Ce(III)/Ce(IV) redox couple in methanesulfonic acid were studied at a platinum disk electrode (0.125 cm²) over a wide range of electrolyte compositions and temperatures: cerium (III) methanesulfonate (0.1–1.2 mol dm⁻³), methanesulfonic acid (0.1–5.0 mol dm⁻³) and electrolyte temperatures (295–333 K). The cyclic voltammetry experiments indicated that the diffusion coefficient of Ce(III) ions was 0.5 × 10⁻⁶ cm² s⁻¹ and that the electrochemical kinetics for the oxidation of Ce(III) and the reduction of Ce(IV) was slow. The reversibility of the redox reaction depended on the electrolyte composition and improved at higher electrolyte temperatures. At higher methanesulfonic acid concentrations, the degree of oxygen evolution decreased by up to 50% when the acid concentration increased from 2 to 5 mol dm⁻³. The oxidation of Ce(III) and reduction of Ce(IV) were also investigated during a constant current batch electrolysis in a parallel plate zinc–cerium flow cell with a 3-dimensional platinised titanium mesh electrode. The current efficiencies over 4.5 h of the process Ce(III) to Ce(IV) and 3.3 h electrolysis of the reverse reaction Ce(IV) to Ce(III) were 94.0 and 97.6%, respectively. With a 2-dimensional, planar platinised titanium electrode (9 cm² area), the redox reaction of the Ce(III)/Ce(IV) system was under mass-transport control, while the reaction on the 3-dimensional mesh electrode was initially under charge-transfer control but became mass-transport controlled after 2.5–3 h of electrolysis. The effect of the side reactions (hydrogen and oxygen evolution) on the current efficiencies and the conversion of Ce(III) and Ce(IV) are discussed.     

Electrochemical behaviour of the β(II)-Ni(OH)2/β(III)-NiOOH redox couple upon potentiodynamic cycling conditions

The electrochemical behaviour of pure and Co-doped Ni(OH)₂ powders is investigated under potentiodynamic cycling conditions. Evolution of some β-Ni(OH)₂ physical properties as a function of the oxidation state is followed by ex situ Surface Enhanced μ-Raman Spectroscopy and in situ Ellipsometry. Effects related to the first and second reduction steps, as well as to the sweeping rate, are qualitatively studied. When compared to the results that have been recently obtained under galvanostatic conditions [S. Deabate, F. Henn, Electrochim. Acta 50 (2005) 2823], the present work confirms that the second reduction process is strongly associated to the occurrence of a reduced phase, i.e. NiO₂H_2−?, with 0 < ? < ∼0.3, at the surface of the active mass grains. This reduced phase exhibits spectroscopic features very similar to the initial hydroxide which is known to be highly insulating in regards to both electrons and protons transfer.     

NOx storage capacity,SO2 resistance and regeneration of Pt/(Ba)/CeZr model catalysts for NOx-trap system

NOx storage capacity, sulphur resistance and regeneration of 1wt%Pt/Ce_0.7Zr_0.3O₂ (Pt/CeZr) and 1wt%Pt/10wt%BaO/Ce_0.7Zr_0.3O₂ (Pt/Ba/CeZr) catalysts were studied and compared to a 1wt%Pt/10wt%BaO/Al₂O₃ (Pt/Ba/Al) model catalyst submitted to the same treatments. Pt/Ba/CeZr presents the best NOx storage capacity at 400 °C in accordance with basicity measurements by CO₂ TPD and Pt/CeZr shows the better performance at 200 °C mainly due to a low sensitivity to CO₂ at this temperature. For all samples, sulphating induces a detrimental effect on NOx storage capacity but regeneration at 550 °C under rich conditions generally leads to the total recovery of catalytic performance. However, the nearly complete sulphur elimination is only observed on Pt/CeZr. Moreover, an oxidizing treatment at 800 °C leads to partial sulphates elimination on the Pt/CeZr catalyst whereas a stabilization of sulphates on Ba containing species is observed.     

高抗硫性的铜钒钛低温SCR脱硝催化剂的制备表征及催化活性

采用浸渍法制备了Cu-V/TiO2系列催化剂,考察了催化剂的低温脱硝活性,并通过N2低温吸附-脱附、X射线衍射、红外光谱、热重、NH3程序升温脱附等手段对催化剂进行了表征。结果显示,当Cu/V摩尔比为1:4,反应温度为180℃时,催化剂对NOx的转化率可达90%以上,当烟气中含有0.01%(体积比)SO2时,催化剂Cu1-V4/TiO2的活性能够保持在90%左右。铜离子的加入使得VOx在载体TiO2表面分散更均匀。催化剂Cu1-V4/TiO2具有最高的比表面积,且其表面弱酸量增加,有利于催化活性的提高;抗硫测试后,Cu1-V4/TiO2催化剂表面仅有少量的硫酸铵盐及硫酸铜的形成与沉积,催化剂表现出强抗硫性。     

Novel method for removal of NO x and SO2 by sustainable electrochemical process using Ag(I)/Ag(II) redox mediator

The objective of this work was to develop a process for removal of industrial waste gases like NO, NO₂ and SO₂ by electrochemically generated Ag(I)/Ag(II) redox mediator system in aqueous nitric acid medium. 100% removal efficiencies were achieved in these studies for removal of NO _x and SO₂ with Ag(II) ions in room temperature and atmospheric pressure. This Ag(I)/Ag(II) redox mediator system can be regenerated continuously during the scrubbing process.     

Electrochemical cell current requirements for toxic organic waste destruction in Ce(IV)-mediated electrochemical oxidation process

The electrochemical cell for cerium oxidation and reactor for organic destruction are the most important operation units for the successful working mediated electrochemical oxidation (MEO) process. In this study, electrochemical cells with DSA electrodes of two types, single stack and double stack connected in series, were used. The performances towards the electrochemical generation of Ce(IV) in nitric acid media at 80 °C were studied. The current-voltage curves and cerium electrolysis kinetics showed the dependence on number of cell stacks needed to be connected in series for the destruction of a given quantity of organic pollutant. The presence of an optimum region for Ce(III) oxidation with a contribution of oxygen evolution, especially at low Ce(III) concentration (high conversion ratios), was found. The cells were applied for the Ce(IV) regeneration during the organic destruction. The cell and reactor processes were fitted in a simple model proposed and used to calculate the current needed in terms of Ce(III) oxidation rate and the number of cell stacks required for maintaining Ce(IV)/Ce(III) ratio at the same level during the organic destruction. This consideration was based on the kinetic model previously developed by us for the organic destruction in the MEO process.