Removal of dibenzothiophene in diesel oil by oxidation over a promoted activated carbon catalyst

Oxidative removal of dibenzothiophene (DBT) in n-octane solution by H₂O₂ on a promoted activated carbon (AC) catalyst was studied. DBT adsorption and catalytic behaviors on AC were examined. Effects of pH in aqueous phase, amounts of AC and formic acid (HCOOH) for promotion as well as initial molar H₂O₂/S ratio were investigated. Experimental results led to conclusion that DBT was readily oxidized by H₂O₂ over an AC catalyst promoted by HCOOH. Suitable amount of AC can improve the activity of H₂O₂ resulting in a deeper extent of sulfur removal. A 100% conversion of DBT in an octane solution by H₂O₂ oxidation was attained on the HCOOH-H₂O₂/AC catalyst at 80°C for a reaction time of 30 min.     

Direct Synthesis of H2O2 by a H2/O2 Fuel Cell

Direct synthesis of H₂O₂ solutions by a fuel cell method was reviewed. The fuel cell reactor of [O₂, gas-diffusion cathode electrolyte solutions Nafion membrane electrolyte solutions gas-diffusion anode, H₂] is very effective for formation of H₂O₂. The three-phase boundary (O₂(g)–electrode(s)–electrolyte(l)) in the gas-diffusion cathode is essential for efficient formation of H₂O₂. Fast diffusion processes of O₂ to the active surface and of H₂O₂ to the bulk electrolyte solutions are essential for H₂O₂ accumulation. The maxima H₂O₂ concentrations of 1.2 M (3.5 wt%) and 2.4 M (7.0 wt%) were accomplished by the heat-treated Mn-OEP/AC electrocatalyst with H₂SO₄ electrolyte and by the VGCF electrocatalyst with NaOH electrolyte, respectively, under short circuit conditions.     

Enthalpic characterisation of activated carbon monoliths obtained from lignocellulosic materials

In this study, energetic interactions between activated carbon monoliths and various liquids were evaluated by determining immersion enthalpies in C₆H₆, H₂O and aqueous solutions of NaOH and HCl. Immersion enthalpies depend on both the surface chemistry and the interactions between specific groups, and were compared with results from volumetric titrations. Immersion enthalpies of activated carbon monoliths were between ?95.85 and ?176.5 J g^?1 for C₆H₆ and between ?11.19 and ?68.31 J g^?1 for H₂O; whereas immersion enthalpies in NaOH and HCl solutions were between ?20.36 and ?82.25 J g^?1 and ?18.81 and ?96.16 J g^?1, respectively. In support of these results, a high level of acidic groups was found on the surface of the activated carbon monoliths by Boehm volumetric titrations, with values between 719 and 1,290 g mol^?1, in agreement with the higher immersion enthalpies observed in NaOH. Correlations were established between immersion enthalpies in the liquids and the surface chemistry properties of the activated carbon monoliths determined by volumetric titrations, demonstrating that immersion enthalpy is a useful parameter for characterisation of these materials in specific liquids.     

Electrosynthesis of hydrogen peroxide from oxygen in a gas-diffusion electrode in solutions of mineralized exometabolites

The electrosynthesis of H₂O₂ in aqueous solutions (pH 1–9) of mineralized liquid and solid bio-wastes (exometabolites) for their processing in closed life-support systems was studied. It was shown that H₂O₂ can be obtained in these solutions by electrochemical reduction of oxygen in carbon black gas diffuse electrodes to concentrations of over 2 M with current efficiency 80%. The composition of the solution was found to affect the accumulation of H₂O₂ during the synthesis. The solutions can be concentrated further to 19 M H₂O₂. The results showed that the electrolytic method is promising for preparing H₂O₂ for closed life-support systems.     

Photocatalytic activities of TiO2 loaded with NiO

A pretreated NiO-TiO₂ powder system is an active catalyst for photocatalytic decomposition of H₂O into H₂ and O₂ in aqueous alkaline solution (3 N NaOH) as well as under NaOH coating conditions.     

Effect of solvent media and condensed benzene rings on thermochemical behaviour of dibenzo-18-crown-6 in solution

The specific and non-specific interactions of twelve activated carbon cloth samples prepared from commercial cotton fabric, and that present different activation degrees are studied through the determination of immersion enthalpies in CCl₄ and H₂O, and in aqueous solutions of NaOH and HCl. The immersion enthalpies found for the solvents CCl₄ and H₂O are in a range of 5.49–45.84 and 1.77–7.76 J g⁻¹, respectively. The enthalpic values for the materials in aqueous solutions of NaOH and HCl, allow characterizing the chemical surface of these materials, which are in a range of 6.63 and 21.49 J g⁻¹, finding through them important relations in company with other characterizing techniques used in the study of these materials.     

原位化学沉积法制备碳/聚苯胺复合材料作为超级电容器材料的研究

Polyaniline （PA） film was chemically deposited onto the surface of activated carbon （AC） uniformly. Chemical deposition was carried out in 0.1 mol/L aniline plus 0.5 mol/L H2SO4 solution adopting V2O5·nH2O coated on the surface of activated carbon as oxidant. The surface morphologies and structures of the composite materials were characterized by scanning electron microscopy and FT-IR spectra. The electrochemical properties of the composite material electrodes were studied by cyclic voltammetry and constant current charge/discharge tests in 1 molFL H2SO4 solutions. The specific capacitance of composite materials was exhibited as high as 237.5 F/g at a current density of 1.0 A/g compared with a value of 120 F/g for pure carbon electrode. Good power characteristic and good stability of composite electrodes were also demonstrated.     

Surface structure of γ-Alumina-Supported Ruthenium Catalysts for ammonia synthesis

Ruthenium supported catalysts were prepared by impregnation of RuCl₃ · 3 H₂O and K₄[Ru(CN)₆] · 3 H₂O aqueous acetone solutions upon several acid(base)-modified γ-Al₂O₃ samples. Characterization of the catalysts was carried out by CO chemisorption and kinetics of hydrogen reduction, correlating the particle size and dispersion of the metallic phase with the previous acid modification of the γ-Al₂O₃, as well as with the type of precursor and solvent used. The surface properties were also correlated with their catalytic activities for ammonia synthesis at atmospheric pressure and 583 K (N₂/H₂ ? 1/3).     

Preparation of Cu<Subscript>2</Subscript>O/AC photocatalysts and their photocatalytic activity in degradation of pyrocatechol

Cu₂O on active carbon (Cu₂O/AC) catalysts were prepared by impregnation of support with aqueous solutions of CuSO₄ in various concentrations and then treated with a mixture of glucose and NaOH. Photocatalytic activity of the prepared catalysts was investigated in the photocatalytic degradation of pyrocatechol. The catalyst prepared by dipping of 0.5 g of AC into 25 ml of 0.04 mol/l CuSO₄ was found to exhibit the best activity. The effects of the reaction time and the amount of catalyst on the photocatalytic degradation of pyrocatechol were also studied.     

Interaction between hydrogen peroxide and cobalt(II) acetylacetonate in the system of reverse micelles of triton X-100 nonionic surfactant in cyclohexane

The yield of free radicals upon the decomposition of hydrogen peroxide catalyzed by cobalt acetylacetonate (Co(acac)₂) in the systems of reverse micelles of TX-100/n-hexanol and AOT in cyclohexane at 37°C was studied with the inhibitor method using a stable nitroxyl radical as a spin trap. It is shown that, in micellar AOT solutions in cyclohexane as well as in n-decane, H₂O₂ and Co(acac)₂ in practice do not react, because H₂O₂ is localized in a micelle water pool and Co(acac)₂, in the organic phase. Therefore, the generation of radicals is not observed in AOT solutions in cyclohexane, whereas, in aqueous solution, Co(acac)₂ catalyzes the radical decomposition of H₂O₂. In the system of mixed reverse micelles of TX-100 and n-hexanol in cyclohexane, at equal overall concentrations of H₂O₂ and Co(acac)₂, the rate of radical formation is much higher than in aqueous solution; i.e., the micellar catalysis of the radical decomposition of H₂O₂ takes place. It follows from measurements of UV and ESR spectra and the kinetics of changes in the content of peroxides in the reaction mixture that TX-100 and n-hexanol react with free radicals formed upon H₂O₂ decomposition and with atmospheric oxygen.     

Electrochemically reactive matrices based on electron-ion conducting and adsorption-active tissues

A review of methods for the synthesis of new composite materials—electroactive and adsorption-active tissues, their electrochemical properties, and potential applications is presented. These are cellulose or asbestos fibers with porous layers linked to their surface, which consist of cyclam derivatives of PVC filled with active carbon, providing electric conductivity. The H⁺ or OH^– ion conductivity is provided by the H₂SO₄ or NaOH aqua complexes with aza-crown groups in the pore walls. The high rate of ion transport was demonstrated in air, hexane, benzene, and their vapors. When the current is passed, H₂ or O₂ is evoluted, or redox transformations of the adsorbed substances occur on the carbon particles. The dependence of the characteristics of the material on its composition and adsorption equilibrium conditions was analyzed. The mechanism of its functioning was suggested. The material was shown to be promising for use in the production of H₂ or O₂ and acid–base or redox transformations of substances adsorbed from gaseous media or nonaqueous solutions.     

Liquid phase benzylation of toluene using benzyl alcohol over iron promoted sulfated zirconia

Concentrated (0.2 M) aqueous solutions of HP-acids, such as H_3+x+mPV^IV _mV^V _x-mMo_12-xO₄₀ and their analogues with an excess VO²⁺ cation, are oxidized by dioxygen at 343 K and atmospheric pressure through intermediate active complexes (IAC) [H_x+m-1PV^IV _mV^V _x-mMo_12-xO₄₀ ^{4 -}] · [VO²⁺]_y · O₂, where m + y ≥ 3. The electron transfer to the coordinated O₂ molecule inside AC is the limiting stage at high m. At low m, the formation of IAC becomes the limiting stage that results in a sharp decrease in the oxidation rate. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the mechanism of H2O2 reduction at Prussian Blue modified electrodes

Prussian Blue deposited on the electrode surface under certain conditions is known to be a selective electrocatalyst of hydrogen peroxide (H₂O₂) reduction in the presence of O₂. The electrocatalyst was stabilized at cathodic potentials preventing its loss from the electrode surface. Hydrodynamic voltammograms of H₂O₂ reduction indicated the transfer of two electrons per catalytic cycle. The operational stability of Prussian Blue in H₂O₂ reduction was highly dependent on the buffer capacity of the supporting electrolyte. Since Prussian Blue is known to be dissolved in alkaline solution, it was confirmed that in neutral aqueous solutions the product of H₂O₂ electrocatalytic reduction is OH⁻.     

Studies on oscillating chemical reaction in Cu(II)‐catalyzed thiocyanate–hydrogen peroxide–NaOH system using pulsating sensor

We present a novel measurement technique to study an oscillating chemical reaction using a new class of sensor, viz. a pulsating sensor developed in‐house. A halogen‐free oscillating chemical reaction in the Cu(II)‐catalyzed H₂O₂‐KSCN–NaOH system reported by Orban was chosen to examine the performance of this technique. Shift in potential during the oscillating reaction was captured online with high precision and excellent resolution using this simple but high‐performance pulsating potentiometric measurement technique. In this work, the influence of bath temperature and flow rate of reagents on the Cu(II)‐catalyzed H₂O₂–KSCN–NaOH oscillating chemical reaction is investigated to optimize the conditions for rapid oscillations. This, in turn, helps to evolve analyte pulse perturbation techniques for rapid assay of hydrazine, uranium(VI), and sodium thiosulfate in aqueous solutions using the above oscillating reaction. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 19–29, 2013     

Photosynthesis of a cyanocomplex containing molybdenum(IV) and molybdenum(VI): Photosynthesis of K6[Mo2Mo(CN)8O6]2H2O

A photochemical method for the preparation of K₆[Mo₆[Mo₂^IVMo^IV(CN)₈O₆]2H₂O is discussed. The synthesis of this complex was achieved by photolysing aqueous solutions of K₄Mo(CN)₈ in contact with atmospheric oxygen.     

Formation of peracids from corresponding organic acids under oxygen electroreduction in gas-diffusion electrode

The effect of conditions of electrolysis in aqueous solutions of (K₂SO₄ + H₂SO₄) electrolytes was studied in the presence of formic, acetic, and butyric acids on the formation of the corresponding peracids under oxygen electroreduction in carbon black gas-diffusion electrodes. In the presence of organic acids with the concentration of 1.5–4.7 M, as dependent in the electrolysis conditions, the current efficiency of H₂O₂ formation decreases from 70 to 13 % and its concentration drops from 2.3 to 0.4 M. Electrolysis under constant current (50–100 mA/cm²) results in formation of peracids with the concentration of up to 7.5 mM. No direct dependence of the concentration of peracids on the concentration of the obtained H₂O₂ is observed. The presence of tetrabutylammonium bromide in the solution inhibits significantly peracid formation. It is assumed that synthesis of peracids occurs partly on the surface of carbon black through activation of the adsorbed acid by a hydrogen cation and further interaction with the active form of oxygen obtained under oxygen reduction or decomposition of H₂O₂.     

Simple Electrodeposition of Dendritic Pd Without Supporting Electrolyte and Its Electrocatalytic Activity Toward Oxygen Reduction and H2O2 Sensing

Metallic palladium (Pd) electrocatalysts for oxygen reduction and hydrogen peroxide (H₂O₂) oxidation/reduction are prepared via electroplating on a gold metal substrate from dilute (5 to 50 mM) aqueous K₂PdCl₄ solution. The best Pd catalyst layer possessing dendritic nanostructures is formed on the Au substrate surface from 50 mM Pd precursor solution (denoted as Pd‐50) without any additional salt, acid or Pd templating chemical species. The Pd‐50 consisted of nanostructured dendrites of polycrystalline Pd metal and micropores within the dendrites which provide high catalyst surface area and further facilitate reactant mass transport to the catalyst surface. The electrocatalytic activity of Pd‐50 proved to be better than that of a commercial Pt (Pt/C) in terms of lower overpotential for the onset and half‐wave potentials and a greater number of electrons (n) transferred. Furthermore, amperometric i–t curves of Pd‐50 for H₂O₂ electrochemical reaction show high sensitivities (822.2 and ?851.9 µA mM^?1 cm^?2) and low detection limits (1.1 and 7.91 µM) based on H₂O₂ oxidation H₂O₂ reduction, respectively, along with a fast response (<1 s).     

Flow Injection Determination of Hydrogen Peroxide Using a Carbon Paste Electrode Modified with a Manganese Dioxide Film

Abstract

A manganese dioxide film modified carbon paste electrode was developed for use as an amperometric sensor for the determination of hydrogen peroxide (H₂O₂) in ammoniacal aqueous solutions. The electrode showed a stable response towards H₂O₂ after electrochemical activation. Effects of flow rate, operating potential, concentration, injection volume and interferences were investigated. A linear response towards H₂O₂ from 5 μg.l^?1 to 450 mg.l^?1 and a detection limit (3 signal-to-noise ratio) of 4.7 μg.l^?1 was found. The method was employed for the determination of H₂O₂ in rain water samples.     

Preparation of Hydrated Strontium Silicates from Silica Hydrogel Isolated from Serpentines and Their Thermal Transformations

Interaction between silica hydrogel isolated from serpentines (Mg(Fe))₆[Si₄O₁₀](OH)₈, sodium hydroxide NaOH, and strontium chloride SrCl₂ in aqueous medium was studied by DTA and X-ray powder diffraction (XRD). Stirring of the boiling aqueous suspension prepared from these reagents under the atmospheric pressure for 2 h yields hydrated strontium silicate species: Sr₃Si₂O₇ · 4H₂O and Sr₃Si₂O₇ · 3H₂O or their mixtures, whose heating to 810–825°C is accompanied by some phase transformations: strontium metasilicate Sr₃Si₃O₉ or strontium orthosilicate Sr₂SiO₄ is formed after bound water is removed in the range 250–350°C, and strontium silicate SrSiO₃ is formed at higher temperatures. Sr₂SiO₄ single phase is observed upon heat treatment to 700–750°C. The optimal molar ratio of the reagents was found to favor Sr₂SiO₄ formation.