Development of SO2–O2 system as an oxidant at uranium leaching processes

The oxidation of Fe²⁺ in uranium leaching solutions with gaseous mixture of SO₂ and air has been studied. The variables studied include H₂SO₄ concentration, temperature, SO₂ concentration and time. The oxidation rate was founded to increase greatly with an increase in the solution temperature. The almost total oxidation of Fe²⁺ is readily achieved at 95 °C. By appropriately adjusting the temperature of solution and SO₂/O₂ in the gas, oxidation of ferrous ion and generation of sulphuric acid can be carried out. It was founded that solutions produced by such oxidation processing are very suitable for the uranium ore leaching.     

Gas Sensing Properties of In2O3and Au-doped In2O3Films for Detecting Carbon Monoxide in Air

Catalytic and sensing properties of several metal oxides in the reaction of CO oxidation and in the sensor detection of CO in air have been studied and compared to each other. Indium oxide has been found to be the most sensitive and possessing a relatively low catalytic activity in the oxidation of CO. Possible reasons for the high activity of the indium oxide sensor matrix are discussed. The promoting effect of Au and Pd doping of In₂O₃in the detection of CO in air has been studied, and a mechanism explaining the enhanced sensor response of Au-doped In₂O₃has been proposed. A change in humidity has no significant effect on the sensor response of Au-doped In₂O₃in the detection of CO in air.     

Hydrogenation of Cinnamaldehyde on Ir/γ-Al2O3 Catalysts. Influence of the Surface Acidity

The oxidation of methane has been studied in a flow system as a function of the chemical composition of zeolite catalyst using nitrous oxide as oxidant. It is concluded that methanol is a primary oxidation product which may undergo further oxidation to formaldehyde and to carbon oxides. However, it may also undergo conversion over the acidic catalyst to higher hydrocarbons. Reaction with nitrous oxide resulted in the production of carbon oxides, methanol, formaldehyde, C₂ - C₄ , C₅ - C₇ nonaromatics, and aromatics. The effect of Fe₂ O₃ and Al₂ O₃ , with or without, over HZSM5 on products was studied.     

Characteristics of the Oxidation of Carbon Monoxide on Platinum and Palladium Acetylacetonates Immobilized on a Silica Surface

Characteristics of the kinetics of the oxidation of carbon monoxide on acetylacetonates of palladium and platinum immobilized on a silica surface have been studied. The bound metal complexes show no hysteresis in the dependence of the rate of reaction on the concentration of CO and O₂ and have a higher catalytic activity than Pt/SiO₂ and Pd/SiO₂. A mechanism is proposed for the oxidation of carbon monoxide on platinum and palladium complexes bound to a SiO₂ surface.     

The reduction of CeO2 in the ketonization of ch3cooh

Summary The decomposition of CH₃COOH on various samples of CeO₂ has been studied. The reduction of Ce to Ce⁺³ with the simultaneous oxidation of the CH₃COOH has been detected.     

Effect of valence state of vanadium on stereoblock polymerization of methyl methacrylate with VOCl3–AlEt2Br catalyst system

The polymerization of methyl methacrylate with the VOCL₃–ALEt₂Br catalyst system in n-hexane has been studied. The first-order dependence of rate of polymerization on catalyst and monomer concentrations, activation energy of 6.67 kcal/mole, and NMR spectra of polymer lend support to a coordinate anionic mechanism of polymerization. It has been shown that the vanadium in V⁺² oxidation state is less active than V⁺³ oxidation state of active complex.     

The vapor phase oxidation of 2-ethylhexanal over oxide catalysts

The vapor phase oxidation of 2-ethylhexanal over a series of oxide catalysts has been studied at 373–623 K. Monolayer vanadia supported on SiO₂ and TiO₂, molybdena and tungstenia supported on SiO₂, and SnO₂ were used as the catalysts. In contrast to the liquid phase process, resulting in 2-ethylhexanoic acid, the main observed reaction was reactant combustion. The partial oxidation products were 3-heptanone, 3-heptyl formate, and heptene. No traces of 2-ethylhexanoic acid were detected in any of the transformations performed.     

Studies on the role of oxidation states of the platinum surface in electrocatalytic oxidation of small primary alcohols

The role of the oxidation state of a platinum polycrystalline surface in the electrocatalytic oxidation of C₁ to C₄ primary alcohols has been studied by using electrochemical techniques, in situ FTIR spectroscopy and X-ray photoelectron spectroscopy. The results revealed that the oxidation state of the Pt surface plays a key role in the oxidation of primary alcohols, and demonstrated that the oxidation of C₁ to C₄ primary alcohols on a Pt electrode is controlled by the formation of surface oxides on the Pt electrode at different potentials. It was found that the dependence of the reaction process on the oxidation states of the platinum surface yielded similar features in the cyclic voltammogram for oxidation of different primary alcohols at a Pt electrode. According to the effects in the oxidation of primary alcohols, the surface oxides of platinum may be classified as active and poison species. The Pt surface oxides of higher oxidation states (Pt(OH)₃ and PtO₂) formed at potentials above 1.0 V (SCE) were identified as poison species, while other lower oxidation states of Pt surface oxides such as PtOH, Pt(OH)₂ and PtO may be identified as the possible active species for primary alcohol oxidation.     

Specific features of oxidation of ferrocenylmethanol with hydrogen peroxide in acidic media

Two types of transformations (the metal complex protonation and oxidation) have been revealed in the ferrocenylmethanol–Н₂О₂–НХ system (HX = HClO₄, CF₃COOH) by means of electronic spectroscopy. The efficiency of protonation has been determined from the intensity of the FcCH₂⁺ carbocation absorption band (λ_max = 600 nm); it depends on the acid strength and relative concentration as well as the solvent nature. Kinetics of ferrocenylmethanol oxidation in dioxane has been studied in the presence of trifluoroacetic acid. Two alternative reaction mechanisms have been proposed, differing in the coordination type of the reagents.     

Effect of anions and pH on the adsorption and oxidation of methanol on a platinum electrode

The influence of various anions and pH on methanol oxidation as well as its products of chemisorption on platinum has been studied by voltammetric and radiometric methods. It was found that the rate of methanol oxidation from the bulk solution was lowest for Na₂CO₃ and highest for NaOH solutions. The influence of anions on the chemisorbed species of methanol on a platinum electrode has also been investigated.     

Inner-sphere oxidation of 2-aminomethylpyridinecobalt(II) complex by N-bromosuccinimide

The kinetics of the oxidation of the 2-aminomethylpyridineCo^II complex by N-bromosuccinimide (NBS), have been studied in aqueous solutions under various conditions, and obey the following rate law:Rate = [NBS][Co(L)(H₂O)₂]²⁺[k₂₊k₃/[H⁺]]An inner-sphere mechanism is proposed for the oxidation pathway for both protonated and deprotonated complex species, with the formation of an intermediate, which is slowly converted into the final oxidation products. The reaction rate is increased by increasing the pH, T, [complex], and decreased by increasing ionic strength over the range studied.     

A kinetic study of the oxidation of hydroxamic acids by compounds I and II of horseradish peroxidase: Effect of transition metal ions

Abstract

Oxidation of hydroxamic acids (HXs) generates HNO, and it is not clear whether it is formed also in the presence of metal ions. The kinetics of the oxidation of HXs, such as acetohydroxamic acid, suberohydroxamic acid, and suberoylanilide hydroxamic acid (SAHA), by compounds I and II of horseradish peroxidase (HRP) at pH 7.0 and 25?°C have been studied using rapid-mixing stopped-flow. The kinetics of these reactions were compared to those observed in the presence of Cu(ClO₄)₂, NiSO₄, or ZnSO₄. The rates decrease upon increasing [Cu^II] at constant [HXs], and no oxidation of HX occurs when [HX]/[Cu^II] ≈ 2, implying that HX oxidation in the presence of Cu^II proceeds through the free ligand since the predominant complex is CuX₂. In the case of Ni^II, the oxidation rate decreases upon increasing the ratio [Ni^II]/[HX] beyond 1, where the predominant complex is Ni^IIX⁺, implying that its oxidation is feasible. The effect of Zn^II could be studied only on the rate of HXs oxidation by compound II demonstrating similar behavior to that of Ni^II. HXs were also oxidized catalytically by HRP/H₂O₂ at pH 7.0, demonstrating that metal ions facilitate the formation of HNO while hardly affecting its yield and the extent of HX oxidation.     

Kinetics and mechanism of oxidation of malonic acid by permanganate and manganese dioxide in acid perchlorate medium

Summary The kinetics of oxidation of malonic acid by both [MnO₄]^– and MnO₂ have been studied in an HClO₄ medium. The oxidation product of the organic acid was found to be glyoxylic acid. A reaction mechanism assuming complexation between MnO₂ and malonic acid is suggested. The rate is independent of [H⁺].     

Oxidation of chromium carbide

The oxidation of chromium carbide has been studied gravimetrically. Products of reaction have been examined by gas sorption analysis and X-ray diffraction. Changes in phase composition, crystallinity and crystallite size are correlated with the reaction conditions.Chromium carbide, Cr₃C₂, differs from most of the transitional metal carbides in that it forms stable films of metal oxide (Cr₂O₃) around the remaining carbide particles, inhibiting further oxidation. Thus chromium carbide additive inhibits oxidation of interstitial zirconium carbide, ZrC, by forming some chromic oxide which stabilises the zirconia (ZrO₂) layer around the remaining carbide crystallites.     

Thermooxidative stability of polymethyl methacrylate containing nanoparticles of silica/titania and silica/zirconia

The influence of silica/titania and silica/zirconia nanoparticles on thermooxidative degradation of PMMA was studied by non-isothermal thermogravimetry. Kinetic parameters describing the length of the oxidation induction periods were obtained from the treatment of the dependence of oxidation onset temperature on heating rate. Using these parameters, the protection factors of nanoparticles have been calculated. It was found that SiO₂/TiO₂ nanoparticles increase the thermooxidation stability of PMMA where the stabilizing effect, expressed as the protection factor, depends on temperature only slightly. The stabilizing effect of SiO₂/ZrO₂ is much stronger than that of SiO₂/TiO₂ and decreases with increasing temperature.     

Effect of the calcination temperature on the properties of Fe2O3/SiO2 catalysts for oxidation of hydrogen sulfide

The effect of the calcination temperature on the properties of supported iron oxide catalysts for hydrogen sulfide oxidation prepared by impregnation of silica with iron(III) nitrate has been studied. An increase in the calcination temperature was found to diminish the catalytic activity of the Fe₂O₃/SiO₂ catalysts in hydrogen sulfide oxidation. This behavior can be explained by the agglomeration of iron oxide particles and by a decrease in the surface concentration of active sites. It has been shown that an increase in the calcination temperature makes the catalyst more stable towards the sulfidation of the active component (Fe₂O₃) to the iron disulfide phase.     

Surface area development of three cokes in relation to the zinc–lead blast furnace

The development of surface area on burn-off for three metallurgical cokes has been studied and correlated with rates of oxidation in carbon dioxide. The role of boric oxide, B₂O₃, as inhibitor of oxidation is discussed. The effect of ash build-up in the later stages of coke burn-off is evaluated in relation to surface area changes.     

VOCs and carbonaceous particles removal assisted by NOx on alkali0.15/ZrO2 and Csx–M0.1/ZrO2 catalysts (M = Cu or Co)

The effect of alkali metals on the physicochemical characteristics of zirconium oxide and the properties of alkali metals in the oxidation of toluene and/or carbonaceous particles and/or conversion of nitrogen oxides have been studied. We observed that they had an effect on the structural and textural properties of ZrO₂. These solids were tested first in the oxidation of toluene and carbonaceous particles separately and secondly with both pollutants. Whatever the experiments, the sample Cs_0.15/ZrO₂ was found to be the catalyst the most active. The simultaneous removal of toluene and soot shows that the presence of toluene leads to a decrease in the temperature of the maximum soot oxidation rate, particularly with catalysts impregnated of Cs and Cu. The effect of the Cs/Co ratio on NO_x conversion and toluene oxidation was also studied. It was found that the oxidizing properties of NO_x can increase the conversion of toluene. This phenomenon occurs especially in the presence of catalysts with a low amount of alkali metal. For the oxidation of carbonaceous particles on the samples Cs/ZrO₂ impregnated with transition metals, the best performance is obtained for copper, although a decrease of the ratio Cs/Cu leads to a slower oxidation and a shift to higher temperatures.     

Evidence of protonation during the oxidation of some aryl alcohols by permanganate in perchloric acid medium and mechanism of the oxidation processes

The oxidation of benzyl alcohol and methoxy-, chloro-, and nitro- substituted benzyl alcohols by permanganate has been studied in aqueous and acetic acid medium in presence of perchloric acid. The reaction is first-order in [MnO₄^?] and [XC₆H₄CH₂OH], but the order is complex with respect to [H⁺]. Different thermodynamic parameters have been evaluated. The reaction occurs through the protonation of alcohol in a fast preequilibrium followed by a slow rate-determining oxidation step. A two-electron transfer oxidation step has been suggested for benzyl alcohol and chloro- and nitro- substituted alcohols, while the oxidation of methoxy compounds involves a one-electron transfer via a free-radical mechanism. © 1995 John Wiley & Sons, Inc.     

Catalytic Systems for the H<Subscript>2</Subscript>S Wet Oxidation at room Temperature

The catalytic wet oxidation process is the most attractive process for small-scale hydrogen sulfide (H₂S) removal from natural gas. The catalytic wet oxidation process is anticipated to be cost effective and simple so that it can be used for treating sour gases containing small amounts of H₂S and can be easily operated even in isolated sites. The development of effective catalyst is the key technology in the wet catalytic oxidation of H₂S. The scale of operation for the process has to be flexible so its use will not be limited by the flow rates of the gas to be treated. The heterogeneous catalytic wet oxidation of H₂S has been attempted on activated carbons, but the H₂S removal capacity still shows the low removal efficiency. The catalytic wet oxidation of H₂S was studied over Fe/MgO for an effective removal of H₂S. In order to develop a sulfur removal technology, one has to know what surface species of catalyst are the most active. This article discusses the following systematic studies: (i) the catalytic preparation to disperse Fe metal well on MgO support for enhancing H₂S removal capacity, (ii) the effect of the catalytic morphology on the activity of Fe/MgO for the H₂S wet oxidation, (iii) the influence of precursor and support on the activity of Fe/MgO for catalytic wet oxidation of H₂S to sulfur.