Mechanism and kinetics of chlorine dioxide reaction with hydrogen peroxide under acidic conditions

The reaction of chlorine dioxide with hydrogen peroxide was studied in a well stirred batch reactor in a pH range of 3.60 to 5.07, which is of interest for commercial chlorine dioxide bleaching of chemical pulp. The reaction rate was determined by following the consumption of chlorine dioxide and hydrogen peroxide and the formation of chlorite. The rate equation was established. It was found that the concentration dependencies of chlorine dioxide, hydrogen peroxide and hydroxide ion were all first-order. A reaction mechanism compatible with the rate equation was proposed. Since it was found in previous work that chlorite in chlorine dioxide solution by the addition of small amount of hydrogen peroxide potentially led to a decrease in the formation of organically bound chlorine during chlorine dioxide bleaching, two methods were suggested to implement this technique in a bleach plant.     

反应介质对氢氧直接合成过氧化氢的影响研究

以超声浸渍法制备的PdO／γ-Al2O3-U为催化剂,考察不同无机酸、不同硫酸浓度对氢氧直接合成过氧化氢的影响。结果表明：酸性介质有利于氢氧直接合成过氧化氢,当反应介质为H2SO4溶液时,氢氧直接合成过氧化氢收率好于其他,其最佳浓度为0．35mol／L。     

双氧水脱除淡盐水中游离氯技术的研究

介绍用双氧水代替亚硫酸钠脱除离子膜电解装置淡盐水中的游离氯,研究了淡盐水的p H值、游离氯含量、双氧水用量与氧化还原电极电位的关系,确定了生产控制方案。结果表明:双氧水脱氯效果良好、成本低,完全可以替代亚硫酸钠。     

双氧水法去除电解盐水中的游离氯

介绍了一种去除电解盐水中游离氯的工业化应用技术——在碱性条件下利用双氧水的氧化性还原电解淡盐水中的游离氯,并总结了该技术去除游离氯的效果。     

Chemical oxidation of anthracite with hydrogen peroxide via the Fenton reaction

Solutions of 30% H₂O₂ ranging from pH = 0 to pH = 11.5 have been used to oxidize anthracite at room temperature. The inorganic impurities, primarily pyrite, catalysed the oxidation and reduction of H₂O₂ (the Fenton reaction) to form the hydroxyl radical; the oxidation of the organic matter was minimal and was observed only in strong acidic solutions (pH < 1.5). After acid demineralization, samples of the same anthracite underwent a significant enhancement of oxidation in both acid and alkaline solutions (pH = 0.4–11.5). As all the iron had been removed from the surface and the reactions were completed in a much shorter time, the oxidation mechanism must have been of a different nature than that for the untreated anthracite. A qualitative model based on the catalytic decomposition of H₂O₂ by activated carbon sites in the coal surface is used to explain the oxidation of the demineralized anthracite.     

过氧化氢环氧化丙烯制环氧丙烷的研究新进展

综述了过氧化氢与丙烯环氧化反应的研究新进展,主要包括商品过氧化氢与丙烯环氧化、过氧化氢制备与丙烯环氧化的集成、氢氧原位一步法丙烯环氧化的研究.并分析了我国环氧丙烷生产面临的挑战,指出我国环氧丙烷清洁生产势在必行,国内研究应立足环境友好新工艺,关键是高活性、高选择性催化剂的开发.     

The electroreduction of oxygen to hydrogen peroxide on fluidized cathodes

The cathodic reduction of oxygen to hydrogen peroxide on fluidized beds of graphite has been studied. The cathodes were fluidized by an oxygen saturated solution of 0.1M NaOH, or by the simultaneous introduction of oxygen gas and hydroxide solution. With increasing current density, the current efficiency always decreased while the product peroxide concentration went through a maximum. In the two-phase system the maximum peroxide concentration increased with bed height. Both current efficiency and the rate of peroxide production generally decreased with catholyte flowrate. For the three-phase fluidized cathode the rate of peroxide production and the current efficiency increased with both catholyte and oxygen flowrate. Possible rate controlling steps are discussed. Current densities for both two phase and three phase fluidized beds were too low to be of commercial use.     

The electroreduction of oxygen to hydrogen peroxide on fluidized cathodes

The cathodic reduction of oxygen to hydrogen peroxide on fluidized beds of graphite has been studied. The cathodes were fluidized by an oxygen saturated solution of 0.1M NaOH, or by the simultaneous introduction of oxygen gas and hydroxide solution. With increasing current density, the current efficiency always decreased while the product peroxide concentration went through a maximum. In the two-phase system the maximum peroxide concentration increased with bed height. Both current efficiency and the rate of peroxide production generally decreased with catholyte flowrate. For the three-phase fluidized cathode the rate of peroxide production and the current efficiency increased with both catholyte and oxygen flowrate. Possible rate controlling steps are discussed. Current densities for both two phase and three phase fluidized beds were too low to be of commercial use.     

氨肟化反应中影响双氧水分解因素浅析

本文对环己酮氨肟化反应体系中引发H2O2分解的因素进行了研究,针对各种影响因素提出控制H2O2分解的优化措施。结果表明：在氨肟化反应体系中,NH3过量导致的碱性环境、H2O2过量加入或H2O2浓度过高以及氨肟化反应不完全,是引起H2O2分解的主要原因;反应温度、反应压力等操作条件的变化也可改变H2O2的分解速度;微量的锰、锌、铜、铁、镍等金属离子的存在,也会大大加速H2O2的分解。控制适当的NH3浓度及酮/H2O2摩尔比、反应条件以及降低金属离子含量有利于提高H2O2的有效利用率,这些结果可以为优化氨肟化反应工艺、降低H2O2消耗提供依据。     

Direct production of hydrogen peroxide from oxygen and hydrogen applying membrane-permeation mechanism

Direct synthesis of hydrogen peroxide is conducted using a palladium membrane reactor. The palladium membrane is prepared on the external surface of the porous α-alumina tubing, by electroless plating (ELP) or chemical vapor deposition (CVD). Thus prepared membrane is immersed into aqueous reaction solution. Hydrogen is supplied from inside of the palladium membrane, while oxygen was bubbled in the reaction solution. Both reacted at the surface of the membrane to produce hydrogen peroxide. Hydrogen peroxide is produced steadily for more than 80 h and the selectivity based on the amount of reacted hydrogen was estimated to be ca. 50%. The reactor performance is investigated in correlation with membrane properties and the hydrogen/oxygen supply pressures.     

The electroreduction of oxygen to hydrogen peroxide on fixed bed cathodes

The production of dilute alkaline peroxide bleaching solutions by electro-reduction of oxygen on fixed beds of graphite particles was investigated. The cell was operated both in the two-phase mode where oxygen saturated 0.1 M NaOH was passed continuously through the bed, and in the three-phase mode where oxygen gas and electrolyte flowed co-currently downward through the cell. Experiments were carried out under oxygen pressures from 1 to 12 atmospheres. The peroxide concentration at the reactor outlet, and the current efficiency dependence on the applied current are reported as functions of electrolyte and oxygen flowrates, oxygen pressure, graphite particle size, fixed bed height and electrolyte pH. Conditions for producing maximum peroxide concentrations are described and possible rate limiting steps in the reaction suggested.     

The electrochemical behaviour of oxygen and hydrogen peroxide on silver electrodes

The reduction of oxygen and the reduction and oxidation of hydrogen peroxide at silver electrodes is examined, with special reference to the side reactions involving the metal and its corrosion products.     

The hydrogen evolution reaction in basic medium on iron electrodeposited with heteropolyacids

Iron was electrodeposited from dilute aqueous solutions of iron sulphate, containing PW₁₂O ₄₀ ^3– , PMo₁₂O ₄₀ ^3– or MoO ₄ ^2– ions. It was shown that improvement in the overpotential and in the exchange current density of the hydrogen evolution reaction (h.e.r.) on the electrodes depends on the nature of the heteropolyacid of the deposition bath. The h.e.r. electrocatalytic activity of the electrodeposits was then analysed and related to their chemical composition. The results show that some active electrocatalysts are produced when combinations of Fe(SiW₁₂) or Fe(PMo₁₂) are formed. The influence of the type of the heteropolyacid in the electrolyte on the electrocatalytic properties of these deposits for the h.e.r. was investigated. The best electrocatalytic properties for the h.e.r. are obtained with electrodes electrodeposited with 2 g dm^–3 of PMo₁₂O ₄₀ ^3– . The effect of [PMoO ₄₀ ^3– ] in the deposition bath on the electrocatalytic properties of the h.e.r. of the electrodes was determined.     

双氧水分解反应放热失控特性及失控判据

双氧水自热分解反应容易引发反应失控。利用泄放小试模拟实验装置,研究了碱性环境下,质量分数10%,15%的双氧水分解反应失控特性,建立了反应失控的临界判据。结果表明:温和反应阶段,系统温度和压力缓和升高,温升速率保持恒定;失控反应阶段,系统温度和压力急剧上升,温升速率出现明显的峰值;质量分数10%双氧水最高失控温度为90.0℃,最大压力为3.07 MPa,最大温升速率为10.7℃/min。质量分数增大,则失控剧烈程度增大。提出采用温度趋势判据和温升速率均值判据作为反应失控的判定准则。对比质量分数10%,15%双氧水分解反应在不同判据下的失控临界点发现,2种判定准则均能实现失控辨别,但精度取决于阈值设定。单一准则下,小的阈值灵敏,但误报率高。     

氢氧直接合成过氧化氢技术的工业化概况

简单介绍了氢氧直接合成过氧化氢(DSHP)技术的优缺点,结合有关专利分别详细介绍了杜邦公司和Evonik–Headwaters公司的DSHP工艺。最后指出,DSHP是一种值得广泛而深入进行研究和开发的、代表过氧化氢合成工艺未来发展方向的绿色合成工艺。     

Epoxidation of propylene and direct synthesis of hydrogen peroxide by hydrogen and oxygen

The autoreduction of palladium–platinum-containing titanium silicalite leads to an effective catalyst for the epoxidation of propylene to propylene oxide by O₂ in the presence of H₂. The one-pot reaction is favoured compared to the two-step reaction path.     

Catalytic reduction of oxygen and hydrogen peroxide by nanoporous gold

Nanoporous gold (NPG) made by dealloying silver/gold alloys is a mesoporous metal combining high surface area and high conductivity. Recently, NPG has been shown to exhibit some of the high catalytic activity previously associated only with supported gold nanoparticles. Here we describe how NPG acts as a catalyst for the oxygen reduction reaction in both gas phase (in fuel cells) and aqueous environments (using rotating disk electrochemistry). NPG was found to reduce oxygen via an effectively 4-four electron route comprised of a first reduction of oxygen to hydrogen peroxide, and then an unusually active further catalytic reduction of hydrogen peroxide to water.     

Influence of Nafion film on oxygen reduction reaction and hydrogen peroxide formation on Pt electrode for proton exchange membrane fuel cell

The influence of Nafion^® film on ORR kinetics and H₂O₂ formation on a Pt electrode was investigated using RRDE in 0.1 M HClO₄. It was found that the Nafion^®-coated Pt system showed lower apparent ORR activity and more H₂O₂ production than the bare Pt electrode system. From the temperature sensitivity, it was revealed that the apparent activation energies of ORR in the Nafion^®-coated Pt system were lower than the bare Pt electrode system, and the H₂O₂ formation was suppressed with the increase of the temperature. In order to analyze the results furthermore, other systems (0.1/1.0 M, HClO₄/CF₃SO₃H) with the bare Pt electrodes were also examined as references. It was exhibited that the ORR kinetic current, the H₂O₂ formation, and the apparent activation energies of 1.0 M CF₃SO₃H system were close to those of the Nafion^®-coated Pt system. We concluded that the orientation of anion species of Nafion^® and CF₃SO₃H to the Pt surface via water molecules, as well as a fluorocarbon polymer network of Nafion^®, might block O₂ adsorption, resulting in the smaller effective surface area of the Pt electrode for ORR, the smaller ORR kinetic current, and the more H₂O₂ production.     

A novel hydrogen peroxide biosensor based on Au-graphene-HRP-chitosan biocomposites

Graphene was prepared successfully by introducing -SO₃⁻ to separate the individual sheets. TEM, EDS and Raman spectroscopy were utilized to characterize the morphology and composition of graphene oxide and graphene. To construct the H₂O₂ biosensor, graphene and horseradish peroxidase (HRP) were co-immobilized into biocompatible polymer chitosan (CS), then a glassy carbon electrode (GCE) was modified by the biocomposite, followed by electrodeposition of Au nanoparticles on the surface to fabricate Au/graphene/HRP/CS/GCE. Cyclic voltammetry demonstrated that the direct electron transfer of HRP was realized, and the biosensor had an excellent performance in terms of electrocatalytic reduction towards H₂O₂. The biosensor showed high sensitivity and fast response upon the addition of H₂O₂, under the conditions of pH 6.5, potential −0.3 V. The time to reach the stable-state current was less than 3 s, and the linear range to H₂O₂ was from 5 × 10⁻⁶ M to 5.13 × 10⁻³ M with a detection limit of 1.7 × 10⁻⁶ M (S/N = 3). Moreover, the biosensor exhibited good reproducibility and long-term stability.     

Direct synthesis of hydrogen peroxide from hydrogen and oxygen over palladium-exchanged insoluble heteropolyacid catalysts

Palladium-exchanged insoluble heteropolyacid (Pd_0.15Cs_xH_2.7?xPW₁₂O₄₀) catalysts were prepared with a variation of cesium content (x = 2.0, 2.2, 2.5, and 2.7), and were applied to the direct synthesis of hydrogen peroxide from hydrogen and oxygen. Pd_0.15Cs_xH_2.7?xPW₁₂O₄₀ showed high catalytic performance even in the absence of H₂SO₄ additive, indicating that Pd_0.15Cs_xH_2.7?xPW₁₂O₄₀ acted as an efficient catalyst and served as an alternate acid source in the reaction. The catalytic performance of Pd_0.15Cs_xH_2.7?xPW₁₂O₄₀ increased with increasing surface acidity of the catalyst. Among the catalysts tested, Pd_0.15Cs_2.5H_0.2PW₁₂O₄₀ catalyst with the largest surface acidity showed the highest yield for hydrogen peroxide.