Carbon black and propylene oxidation over Ru/CoxMgyAl2Oz catalysts

The effects of Co_xMg_yAl₂O_z mixed oxides composition and ruthenium addition on the oxidation of propylene and carbon black (CB) were investigated. Different reactive cobalt and ruthenium oxide species were formed following calcination at 600 °C. The addition of ruthenium was beneficial for the CB oxidation under “loose contact” conditions and for propylene oxidation when the cobalt content was intermediate to low. The calculated activation energy for CB oxidation was decreased from 151 kJ mol⁻¹ for the uncatalyzed reaction to 111 kJ mol⁻¹ over the best catalyst.     

Thermal and photochemical production of chromate(VI) ions from some complexes containing the “CrNO”2+ group

Results are reported for the oxidation of complexes of the type [Cr(CN)_5?x(H₂O)_xNO]^x?3 by molecular oxygen in alkaline medium. In the case of the [Cr(CN)₅NO]^3? complex the reaction proceeded photochemically, whereas in othe cases the thermal oxidation was also observed. The influence of pH, CN^? concentration and energy of radiation was investigated.     

Tuning the crystallinity of MnO2 oxidant to achieve highly efficient pollutant degradation

Manganese dioxide (MnO₂), a commonly find oxidant in both natural environment and industrial application, plays a crucial role for various organic compound degradation. Tuning the MnO₂ crystal structure is a cost-effective strategy to boost the oxidation reactions, where the challenge remains due to lacking in-depth investigation of the crystal properties. Herein, MnO₂ with different crystalline structures (x-MnO₂) including α-, β- and δ- was prepared through the hydrothermal synthesis for a typical organic pollutant removal. The structural and degradation analysis indicated that the oxidation capacity was originated from Mn³⁺ and oxygen vacancies (OVs). The intrinsic relationships between oxidation performance and other physiochemical properties such as morphology and electrochemistry were thoroughly discussed, and positive correlations between oxidation capacity and electrochemical properties were found which eventually led to excellent oxidation performance via modulating the above-mentioned properties. Moreover, the K⁺ content was determined to be the most crucial role in manipulating the structure properties. This work offers a crystal-level insight into the relationship between the crystal structure and oxidative property, promoting rational design of highly efficient oxidant.     

N,N-Ethylene-bridged flavinium salts derived from l-valinol: synthesis and catalytic activity in H2O2 oxidations

Three chiral N¹,N¹⁰-ethylene-bridged flavinium salts with a stereogenic centre derived from l-valinol are prepared and investigated as oxidation catalysts. These salts efficiently catalyse chemoselective H₂O₂ oxidation of sulfides to sulfoxides and the oxidation of 3-phenylcyclobutanone to the corresponding lactone at room temperature. The flavinium salts react with hydrogen peroxide to form flavin-10a-hydroperoxide, which is the agent responsible for oxidation of the substrate.     

Preparative syntheses of bis(4-tert-butylphenyl)aminoxyl

Bis(4-tert-butylphenyl)aminoxyl was obtained in 80 and 95% yield by oxidation of the corresponding amine and hydroxylamine with H₂O₂/WO ₄ ^2? in methanol at 65°C. The oxidation of bis(4-tert-butylphenyl)hydroxylamine to bis(4-tert-butylphenyl)aminoxyl was catalyzed by Cu⁺ and Ag⁺ ions which also catalyzed disproportionation of the former to bis(4-tert-butylphenyl)amine and bis(4-tert-butylphenyl)aminoxyl. Mechanisms of the catalytic oxidation of the amine and hydroxylamine and disproportionation of the latter were proposed.     

Catalytic oxidation of benzoin and p-substituted benzhydrol by p-benzoquinone or air in the presence of [FeII(SPh)4]2− and [FeII(SePh)4]2−

[Fe^II(SPh)₄]²⁻ (1) and [Fe^II(SePh)₄]²⁻ (2) exhibit high catalytic activity in the oxidation of benzoin with p-benzoquinone or air and of p-substituted benzhydrol with air under mild conditions (1 atm, 25 °C). p-Substitution of benzhydrols shows a trend in the oxidation rate: 4-Cl>H>4-OMe. Furthermore, the observed isotope effect of k_H/k_D = 4.0 (catalyzed by [Fe(Sph)₄]²⁻ (1)) and 3.3 (catalyzed by [Fe(SePh)₄]²⁻ (2)) in the p-benzoquinone oxidation of benzoin indicates that the methine hydrogen of benzoin and benzhydrol is released as a proton in the rate-determining step.     

Investigation on electro-catalytic oxidation properties of carbon nanotube–Ce-modified PbO2 electrode and its application for degradation of m-nitrophenol

In this work a carbon nanotube–Ce-modified PbO₂ (CNT–Ce–PbO₂) electrode was prepared by electrodeposition method, and compared with pure PbO₂, Ce–PbO₂, and CNT–PbO₂ electrodes. The direct and indirect oxidation capacities of prepared electrodes in electro-catalytic oxidation processes were investigated by cyclic voltammetry and hydroxyl radical production tests, respectively. The electro-catalytic activity of electrodes was examined by electro-catalytic oxidation of a model pollutant of m-nitrophenol (m-NP). Besides, high-performance liquid chromatography (HPLC) was also employed to identify the products resulting from the electro-catalytic oxidation of m-NP and the degradation mechanism of m-NP was proposed. Results show that the CNT–Ce–PbO₂ anode has higher direct and indirect oxidation capacities than pure PbO₂, Ce–PbO₂, and CNT–PbO₂ anodes. In the electro-catalytic oxidation of m-NP, the m-NP can be oxidized and degraded at all anodes, and the oxidation reactions of m-NP follow first-order kinetics. m-NP and TOC removal efficiencies are about 0.987 and 0.622 after electrolysis of 120 min and a maximum first-order rate constant of 0.036 min⁻¹ is achieved at the CNT–Ce–PbO₂ anode, which are obviously higher than those of the other three kinds of anodes.     

通过CeOx修饰提高金纳米颗粒在CO氧化反应中的催化活性和耐久性

CO催化氧化是一个重要的经典反应,与许多应用息息相关,包括痕量CO气体检测、汽车尾气净化和安全防护等,吸引了人们广泛的研究兴趣.负载型Au纳米颗粒在CO氧化等许多反应中有着与众不同的催化活性,具有广泛的应用前景,但依然存在着稳定性差、易团聚失活的问题.人们通过应用多孔载体隔离Au纳米颗粒,在Au纳米颗粒表面覆盖金属氧化物、二氧化硅或碳,以及对Au纳米粒子进行封装等方法解决这些问题.尤其是利用金属氧化物与Au纳米粒子间的强相互作用对其进行覆盖或封装,有效地提高了Au催化材料的稳定性.但以上策略操作流程复杂,不利于应用.本文发展了一种简单有效的方法,通过EDTA的络合作用引入CeOx对Au纳米粒子进行修饰,得到的CeOx@Au/SiO2催化剂活性和耐久性明显提升.采用X射线衍射(XRD)和高分辨透射电子显微镜(HRTEM)证明了CeOx成功地修饰在Au纳米颗粒上.且通过EDTA引入CeOx所制备的CeOx@Au/SiO2催化剂结构明显不同于直接加入纳米CeO2所得到的CeOx-Au/SiO2的结构.EDTA的络合作用能有效地连结Ce与Au物种,经焙烧消除EDTA后,加强了CeOx与Au间相互作用,最终在Au纳米粒子表面形成丰富的CeOx颗粒与原子级厚度的CeOx层.进一步应用X射线光电子能谱(XPS)和氢气程序升温还原(H2-TPR)等手段研究了CeOx修饰对Au纳米粒子的影响.XPS结果表明,CeOx@Au/SiO2催化剂带正电的Au+和Au3+的浓度明显高于一般的Au/SiO2和直接加入CeO2制备得到的CeOx-Au/SiO2催化剂.H2-TPR同样表明,CeOx修饰调变了Au纳米粒子的氧化还原性.这些均对其在CO催化氧化反应中的催化活性具有重要影响将CeOx@Au/SiO2催化剂用于CO催化氧化反应中,160°C时,CO转化率达98.8％,至180°C后实现了CO的完全转化.而一般的Au/SiO2催化剂在160°C时CO转化率仅为4.0％,CO的完全转化则需340°C.直接加入纳米CeO2所得到的CeOx-Au/SiO2催化剂,其催化活性略有提升,CO完全转化所需的温度为300°C.这充分证明了通过CeOx修饰Au纳米粒子,能有效提升其催化活性.原位漫反射红外光谱(DRIFT)结果表明,CeOx修饰促进了CO在Au表面的吸附,并能形成[Au(CO)2]δ+物种;同时还观察到大量的单齿CO32? 物种信号,反映了CeOx@Au/SiO2催化剂表面存在丰富的活性氧物种.通入O2后,观察到了大量CO32?物种信号和气相CO2,印证了催化剂表面发生的CO催化氧化过程,也表明其具有非常高的催化活性.考察了CeOx@Au/SiO2催化剂的耐久性,发现经50 h CO氧化反应,催化剂依然能有效保持活性.相比之下,Au/SiO2催化剂经10 h反应后,开始明显失活.由此可见,CeOx@Au/SiO2催化剂具有相当高的耐久性.在600°C将催化剂焙烧3 h,发现Au/SiO2催化剂中Au纳米粒子存在明显团聚现象,而CeOx@Au/SiO2催化剂的Au纳米粒子依然均匀分布在载体表面,且粒径未发生明显变化.     

Kinetics and mechanism of the oxidation of acrylic acid and methyl methacrylate

The kinetics of the initiated oxidation of acrylic acid and methyl methacrylate in the liquid phase were studied volumetrically by measuring oxygen uptake during the reaction. Both processes proceed via the chain mechanism with quadratic-law chain termination. The oxidation rate is described by the equation w = k ₂/(2k ₆)^1/2[monomer]w _i ^1/2 , where w _i is the initiation rate and k ₂ and k ₆ are the rate constants of chain propagation and termination. The parameter k ₂/(2k ₆)^1/2 is 7.58 × 10^?4 (l mol^?1 s^?1)^1/2 for acrylic acid oxidation and 2.09 × 10^?3 (l mol^?1 s^?1)^1/2 for the oxidation of methyl methacrylate (T = 333 K). For the oxidation of acrylic acid, k ₂ = 2.84 l mol^?1 s^?1 (T = 333 K) and the activation energy is E ₂ = 54.5 kJ/mol; for methyl methacrylate oxidation, k ₂ = 2.96 l mol^?1 s^?1 (T = 333 K) and E ₂ = 54.4 kJ/mol. The enthalpies of the reactions of RO ₂ ^? with acrylic acid and methyl methacrylate were calculated, and their activation energies were determined by the intersecting parabolas method. The contribution from the polar interaction to the activation energy was determined by comparing experimental and calculated E ₂ values: ΔE _μ = 5.7 kJ/mol for the reaction of RO ₂ ^? with acrylic acid and ΔE _μ = 0.9 kJ/mol for the reaction of RO ₂ ^? with methyl methacrylate. Experiments on the spontaneous oxidation of acrylic acid provided an estimate of the rate of chain initiation via the reaction of oxygen with the monomer: w _i,0 = (3.51 ± 0.85) × 10^?11 mol l^?1 s^?1 (T = 333 K).     

Kinetics of oxidation of cysteine and captopril via Cs3[Mo(CN)8] and Cs3[W(CN)8]

The kinetics of the oxidation of cysteine and captopril via octacyanomolybdate(V) and octacyanotungstate(V) in a buffered acidic media (pH range 2.20–4.80) have been studied spectrophotometrically. The rate law for the oxidation is: Rate = k [RSH] [Ox] [H⁺]⁻¹, where RSH is cysteine or captopril and Ox is Cs₃[Mo(CN)₈] or Cs₃[W(CN)₈]. The activation parameters (E_a, ΔH^#, ΔG^#, ΔS^#) for the oxidation of cysteine and captopril via Cs₃[Mo(CN)₈] or Cs₃[W(CN)₈] have been determined. The results indicate that Cs₃[Mo(CN)₈] is more reactive than Cs₃[W(CN)₈] as an oxidizing agent. Effects of pH, ionic strength, temperature, dielectric constant of the reaction medium and copper(II) ions on the oxidation rate have been studied. Mechanisms for the oxidation of cysteine to cystine and captopril to the corresponding disulfide have been proposed.     

P NMR study of the valence stability of tin in its 1-hydroxyethylene-diphosphonate (HEDP) and N,N′,N′-trimethylenephosphonate-polyethyleneimine (PEI-MP) complexes

The valence stability of tin in its complexes with 1-hydroxyethylene-diphosphonate (HEDP) and with N,N′,N′-trimethylenephosphonate-polyethyleneimine (PEI-MP) was investigated. With particular interest in the possible interconversion between Sn²⁺ and Sn⁴⁺, the complexes were monitored with the aid of ³¹P NMR spectroscopy. The extent of complex formation with both ligands was evaluated for systems with tin in their respective oxidation states. The Sn²⁺-complexes underwent initial, but limited oxidation upon preparation, and beyond which were rather stable, irrespective of pH or time. Both Sn²⁺- and Sn⁴⁺-complexes were found to exist in solution without change. Oxidation of Sn²⁺ was achieved by addition of hydrogen-peroxide and was partially reversed by the addition of glutathione (GSH). The amount of H₂O₂ needed for complete oxidation of the Sn²⁺- into Sn⁴⁺-complexes was determined for both ligands, as well as the time taken for that oxidation.     

Oxidation of cyclopentane-1,2-dione: a study with O labeled reagents

The asymmetric oxidation of 3-alkyl-cyclopentane-1,2-diones with the Ti(OⁱPr)₄/tartaric ester/t-BuOOH complex, which gives, in a cascade process, highly enantiomerically enriched γ-lactone acids, was studied by ¹⁸O isotopic labeling in the substrate and in the oxidant. The path of the labeled atoms was followed by ¹³C NMR spectroscopy. It was found that the oxidative ring cleavage of 1,2-dione proceeds via a Baeyer-Villiger-type oxidation mechanism.     

Pd-Cu-Clx/Al2O3催化剂对CO氧化的稳定性

CO催化氧化广泛应用于空气净化、机动车尾气治理和CO气体传感器中.在CO氧化催化剂设计与制备过程中,催化剂与使用环境密切相关.例如工业和机动车尾气净化需要在高温(200–600°C)下进行,而对于半密闭空间(隧道或者地下停车场)空气净化需要在室温和高相对湿度下进行.频繁冷启动导致半密闭空间CO浓度累积而超过排放控制标准,因此制备室温、高相对湿度下CO氧化催化剂是面临的重要问题之一.负载型Wacker催化剂对于CO低温催化氧化的研究一直受到广泛关注.环境中少量水的存在会促进负载型Wacker催化剂对CO的低温氧化性能,但随着水沉积量的增加,活性位点将被覆盖,并且Pd和Cu活性组分之间的紧密结构被破坏,从而导致催化剂的失活,即催化剂的稳定性变差.因此,为了提高催化剂在高相对湿度下的稳定性,利用二乙氧基二甲基硅烷对Al2O3载体进行硅烷化处理,以增加载体的疏水性,考察载体疏水改性对CO低温氧化过程中催化剂稳定性的影响.催化剂的稳定性测试结果表明,在0°C,100%相对湿度条件下,未改性催化剂在约20 h内CO转化率由81%下降到50%;载体硅烷化后制备的催化剂在反应进行150 h后,CO转化率仍保持在78%,即反应活性未见降低.由此表明催化剂载体经有机硅烷改性后,可显著增强催化剂在低温、高相对湿度下的稳定性.N2吸附/脱附和水吸附实验结果表明,载体硅烷化改性并未对催化剂的比表面积产生影响,但显著降低了催化剂上水沉积速度和沉积量,未改性催化剂的初始吸水速度是改性后催化剂的4倍,但改性后催化剂的饱和吸水率仅占未改性催化剂的1/3.X射线衍射结果表明,载体预处理后活性物种Cu2(OH)3Cl晶粒尺寸有所增加.氢气程序升温还原、X射线光电子能谱结果表明,载体硅烷化预处理改善了催化剂中Cu和Pd物种的化学分布及接触状态,增加了与Pd物种紧密接触的Cu物种的量,从而促进了Cu物种的还原.与此同时,载体硅烷化显著降低了催化剂表面Cl离子的浓度,从而影响到对CO吸附.为了进一步研究水与催化剂稳定性之间的关系,采用原位红外漫反射(In situ DRIFT)对催化剂进行表征.负载型Wacker催化剂对CO氧化反应机理为:Pd是CO氧化反应的活性中心,通过Pd和Cu物种之间的氧化还原循环来实现CO氧化,且Pd+比Pd2+具有更高的CO氧化性能.反应气氛中水的存在,有利于CO在Pd+上氧化、以及金属态Pd被Cu2+物种再氧化的过程,同时水也显著促进了催化剂表面碳酸盐的生成以及抑制了活性物种Pd+生成.与表面碳酸盐累积相比,水对于活性物种Pd+生成的抑制作用是导致催化剂活性降低的主要原因.     

Thermal oxidative degradation of polypropylene-containing pro-oxidants

The thermal degradation of polypropylene-containing pro-oxidants was studied by determining the oxidation induction time (OIT) and by assessing the activation energy (E _a) estimated from thermogravimetric analysis. Polypropylene (PP) was prepared with different concentrations of two pro-oxidants, polyacetal (POM) and d₂w^®. The pro-oxidants accelerated the oxidation process of oxidation of PP in the presence of oxygen; however, there is little change in the values of the OIT in compositions with different concentrations of d₂w^®. For PP/POM blends, the volatile low molecular mass compounds, primarily from POM-derived formaldehyde, accounted for the decrease in E _a with the increasing POM concentration.     

CO oxidation on the heterodinuclear tantalum-nickel monoxide carbonyl complex anions

The series of heterodinuclear metal oxide carbonyls in the form of TaNiO(CO)_n(n=5-8) are generated in the pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectroscopy.During the consecutive CO adsorption,the μ~2-O-bent structure initially is the most favorable for TaNiO(CO)_5,and subsequently both μ~2-O-bent and μ~2-O-linear structures are degenerate for TaNiO(CO)_6,then the μ~2-O-linear structure is most preferential for TaNiO(CO)_7,and finally theη_2-CO_2-tagged structure is the most ene rgetically competitive one for TaNiO(CO)_8,i.e., the CO oxidation occurs at n=8.ln contrast to the literature reported CO oxidation on heteronuclear metal oxide complexes generally proceeding via Langmuir-Hinshelwood-like mechanism,complementary theo retical calculations suggest that both Langmuir-Hinshelwood-like and Eley-Rideal-like mechanisms prevail for the CO oxidation reaction on TaNiO(CO)_8 complex.Our findings provide new insight into the composition-selective mechanism of CO oxidation on heteronuclear metal complexes,of which the composition be tailored to fulfill the desired chemical behaviors.     

Application of Box-Behnken design with response surface methodology for modeling and optimizing ultrasonic oxidation of arsenite with H2O2

A combined ultrasound (US)/H₂O₂ process was used to oxidize arsenite to arsenate, yielding a synergistic effect value of 1.26. This showed that the combined process could be an effective method of oxidizing arsenite, instead of using either ultrasonic or H₂O₂ oxidation processes. This combined process was successfully modeled and optimized using a Box-Behnken design with response surface methodology (RSM). The effects of the US power density, the initial concentration of arsenite, and the H₂O₂ concentration on the sonochemical oxidation efficiency of arsenite were investigated. Analysis of variance indicated that the proposed quadratic model successfully interpreted the experimental data with coefficients of determination of R ² = 0.95 and adjusted R ² = 0.91. Through this model, we can predict and control the oxidation efficiency under different conditions. Furthermore, the optimal conditions for the oxidation of arsenite were found to be a US power density of 233.26 W L^?1, an initial arsenite concentration of 0.5 mg L^?1, and an H₂O₂ concentration of 74.29 mg L^?1. The predicted oxidation efficiency obtained from the RSM under the optimal conditions was 88.95%. A confirmation test of the optimal conditions verified the validity of the model, yielding an oxidation efficiency of 90.1%.      

The surface oxidation behavior of Ni–45.16%Ti shape memory alloys at different temperatures

The isothermal oxidation behavior of Ni–45.16%Ti (composition in atomic percent) alloy was investigated by thermogravimetric analysis, and differential scanning calorimeter (DSC) methods. It was found that Ni-rich NiTi alloy exhibits a different oxidation behavior at temperatures above 400 °C in oxygen atmosphere. The alloy was exposed to oxygen atmosphere isothermally, i.e., between 400 and 800 °C, for 1 h. A gravimetric method was used to determine the oxidation kinetics and it was seen that the oxidation constant increases significantly with isothermal temperature. The activation energy of oxidation reaction for NiTi alloy was determined to be 65.47 kJ mol^?1. According to DSC measurements, the transformation temperature of alloy (M _s, M _f, A _s and A _f) was increased and also R phase disappeared above 500 °C. The formal oxides were determined by means of SEM–EDX measurements and obtained oxides are TiO and TiO₂ oxides.     

Study of oxidation properties and decomposition kinetics of three-dimensional (3-D) braided carbon fiber

The XRD, SEM, isothermal oxidation-weight loss and non-isothermal thermogravimetry (TG)-differential thermogravimetry (DTG) were used to study the oxidation properties and oxidation decomposition kinetics of three-dimensional (3-D) braided carbon fiber (abbreviated as fiber). The results showed that the non-isothermal oxidation process of fiber exhibited self-catalytic characteristic. The kinetic parameters and oxidation mechanism of fiber were studied through analyzing the TG and DTG data by differential and integral methods. The oxidation mechanism was random nucleation, the kinetic parameters were: lg A=10.299 min⁻¹; E_a=156.29 kJ mol⁻¹.     

The Oxidation of Phenylhydrazine by Tyrosinase

Tyrosinase was found to catalyze the oxidation of phenylhydrazine to phenol in a reaction that did not resemble those typically performed by tyrosinase. The kinetics of this reaction was investigated by measuring the initial velocity of the formation of phenol (25 °C). The values of k _cat and K _M for the oxidation of phenylhydrazine were obtained as 11.0 s^?1 and 0.30 mM, respectively. The generation of superoxides during the oxidation of phenylhydrazine by tyrosinase was monitored by nitroblue tetrazolium (NBT) assay. In the phenylhydrazine-tyrosinase reaction, 1 mol O₂ was required for the production of 1 mol phenol and 1/6 mol superoxide. The decomposition of superoxide by superoxide dismutase enhanced the rate constant of the oxidation of phenylhydrazine. Phenol formed in the oxidation of phenylhydrazine by tyrosinase was further oxidized by tyrosinase to an o-quinone, after the oxidation of phenylhydrazine by tyrosinase was almost completed.     

Mechanistic studies of oxidation of maltose and lactose by [H2OBr]+ in presence of chloro-complex of Rh(III) as homogeneous catalyst

Kinetic studies in homogeneously Rh(III)-catalyzed oxidation of reducing sugars, i.e. maltose and lactose, by N-bromoacetamide (NBA) in the presence of perchloric acid have been made at 40 °C using mercuric acetate as Br⁻ ion scavenger. The results obtained for the oxidation of both reducing sugars show first-order dependence of the reactions on NBA at its low concentrations, which shifts towards zero-order at its higher concentrations. First-order kinetics in [Rh(III)] and zero-order kinetics in [reducing sugar] were observed. Positive effect of [Cl⁻] was observed in the oxidation of both maltose and lactose. Order of reaction was found to be one and half (1.5) throughout the variation of [H⁺] in the oxidation of both maltose and lactose. An increase in the rate of reaction with the decrease in [Hg(OAc)₂] and [NHA] was observed for both the redox systems. The rate of oxidation is unaffected by the change in ionic strength (μ) of the medium. The main oxidation products of the reactions were identified as formic acid and arabinonic acid in the case of maltose and formic acid, arabinonic acid and lyxonic acid in the case of lactose. A common mechanism for the oxidation of both maltose and lactose, showing the formation of most reactive activated complex, [RhCl₄(H₃O)H₂OBr]⁺, and an unreactive complex, [RhCl₄(H₂O)(H₂OBrHg)]²⁺, has been proposed. Various activation parameters have also been calculated and on the basis of these parameters, a suitable explanation for the reaction mechanism has been given.