Electrochemical oxidation of nitrite on nanodiamond powder electrode

Nanodiamond (ND) powder electrodes were fabricated and the electrochemical properties were investigated in the solution containing nitrite in this article. This electrode exhibits substantial catalytic ability toward the oxidation of nitrite anions. The electrochemical oxidation mechanism of nitrite on the ND powder electrode is discussed. The oxidation of NaNO₂ is a two-electron transfer process. The electrode reaction rate constant k is estimated to be 2.013 × 10⁻⁴ cm/s and (1 − α)n_α is 0.1643. The peak current increases linearly with the rising of the concentration of NaNO₂.     

Highly sensitive electrochemical determination of nitric oxide using fused spherical gold nanoparticles modified ITO electrode

This paper describes the highly sensitive electrochemical determination of nitric oxide (NO) using the fused spherical gold nanoparticles (FAuNPs) modified ITO electrode. The FAuNPs were self-assembled on a (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel film, which was preassembled on ITO electrode. The attachment of FAuNPs on MPTS sol-gel film was confirmed by UV-vis absorption spectroscopy, atomic force microscopy (AFM) and cyclic voltammetry (CV). The AFM image shows that the AuNPs retain their fused morphology after immobilized on MPTS sol-gel film. The FAuNPs modified ITO electrode shows an excellent electrocatalytic activity towards the oxidation of NO. Using FAuNPs modified electrode, the detection of 12 nM NO was achieved for the first time by amperometry method. Further, the current response was increased linearly with increasing NO concentration in the range of 1.2 × 10⁻⁸ to 7 × 10⁻⁴ M and the detection limit was found to be 3.1 × 10⁻¹⁰ M (S/N = 3). The FAuNPs modified ITO electrode displays an excellent selectivity towards the determination of 12 nM NO even in the presence of 1000-fold excess common interfering agents.     

Reduction of nitric oxide to nitrous oxide by cobalt porphyrins and corrins

The reduction of nitric oxide (NO) to nitrous oxide (N₂O) by dithiothreitol in the presence of cobalt-centered corrin and porphyrin are presented. Reactions were monitored directly using Fourier transform infrared (FTIR) spectroscopy of vapor phase spectra. Reaction rates were two-fold faster for cobalt corrin than cobalt-centered porphyrins. The stoichiometry showed loss of two NO molecules per N₂O generation.     

Promoting effect of water vapor on catalytic oxidation of methane over cobalt/manganese mixed oxides

Methane oxidation was conducted in a fixed bed quartz tubular reactor on a series of mixed oxides of cobalt/manganese prepared by a sol–gel method. A unique promoting effect of water vapor on methane conversion was observed for the first time on these cobalt/manganese mixed oxides calcined at 450 or 600 °C. However, these mixed catalysts lost their catalytic activities after being calcined at 850 °C. The catalytic activity of methane oxidation was significantly improved by supporting the cobalt/manganese mixed species onto the high surface area SiO₂ or Al₂O₃–SiO₂ materials. It was noteworthy that the water enhancement effect was retained on these supported catalysts.     

Complete oxidation of acetone over manganese oxide catalysts supported on alumina- and zirconia-pillared clays

The complete oxidation of acetone has been studied over a series of manganese oxide catalysts supported on the unpillared and the Al- and Zr-pillared forms of two natural clays of the smectite class (a montmorillonite and a saponite). The temperatures required for total combustion of acetone over the several catalysts ranged from 610 to 660 K at the relatively low W_Mn/F_in ratio of 0.40 g_Mn min mmol_acetone⁻¹ used. A significant influence of the clay supports characteristics on the catalytic performance has been found. According to the general behaviour of the various catalysts throughout the light-off tests, the following order of improving catalytic performance can be established with respect to the pillars composition: Al-pillared clays2O₃, MnO₂, Al₂O₃ and ZrO₂, as well as physical mixtures of ZrO₂ with the unpillared clays. The effect on the catalytic performance of the possible competition between the acetone combustion and aldol condensation processes has also been considered.     

Electrochemical supercapacitor material based on manganese oxide: preparation and characterization

A novel class of electrochemical supercapacitor electrode material has been electrochemically synthesized from a manganese halide complex in water-containing acetonitrile electrolyte at room temperature. This material has been physically and chemically characterized by scanning electron microscopy, X-ray photoelectron microscopy (XPS), FT-Raman microscopy and cyclic voltammetry. XPS and FT-Raman characterization suggest that this material is composed of manganese oxide with a chemical composition of Mn₃O₄ and containing a moderate amount of carbon. Cyclic voltammetric characterization indicates that this material has higher electronic conductivity than usually seen for manganese oxide and that it shows fast kinetics for the charge-discharge process in both aqueous and acetonitrile electrolytes. The material provides a large pseudocapacitance over a potential window of about 1 V in aqueous electrolyte and about 2 V in acetonitrile electrolyte. It is therefore a good candidate as a material for an electrochemical supercapacitor electrode.     

Preparation of copper-containing mesoporous manganese oxides and their catalytic performance for CO oxidation

Copper-containing mesoporous manganese oxides were prepared by the sol–gel method. The samples obtained were characterized by XRD, N₂ adsorption–desorption, ICP, CO-TPD, redox measurement and XPS. After calcination at 300 °C, amorphous structure was shown by XRD for all the samples. All the samples had mesopores of about 6 nm and high surface areas of 170–230 m² g⁻¹. Using these samples as catalysts, CO oxidation was carried out as a model reaction. Copper-containing mesoporous manganese oxide prepared by the sol–gel method showed a very high activity. On the other hand, copper-supported manganese oxide prepared by the impregnation method using copper sulfate showed a low activity. Differences in activities were correlated with the mobility of lattice oxygen.     

Electrochemical characteristics of dopamine oxidation at palladium hexacyanoferrate film, electroless plated on aluminum electrode

A novel electrode material was obtained at an aluminum electrode (Al) by a simple electroless method including two consecutive procedures: (i) the electroless deposition of metallic palladium on the Al electrode surface from PdCl₂ + 25% ammonia solution and (ii) the chemical transformation of deposited palladium to the palladium hexacyanoferrate (PdHCF) films in a solution containing 0.5 M K₃[Fe(CN)₆]. The modified Al electrode demonstrated a well-behaved redox couple due to the redox reaction of the PdHCF film. The PdHCF film showed an excellent electrocatalytic activity toward the oxidation of dopamine (DA). The effect of solution pH on the voltammetric response of DA has been investigated. A linear calibration graph was obtained over the DA concentration range 2-51 mM. The rate constant k and transfer coefficient α for the catalytic reaction and the diffusion coefficient of DA in the solution D, were found to be 4.67 × 10² M⁻¹ s⁻¹, 0.63 and 2.5 × 10⁻⁶ cm² s⁻¹, respectively. The interference of ascorbic acid was investigated and greatly reduced using a thin film of Nafion on the modified electrode. The modified electrode indicated reproducible behavior and a high level stability during electrochemical experiments, making it particularly suitable for the analytical purposes.     

Effect of the nature and structure of pillared clays in the catalytic behaviour of supported manganese oxide

In the present work, the complete oxidation of acetone has been studied over a series of supported manganese oxide catalysts on the unpillared and the Al- and Zr-pillared forms of two natural clays, a montmorillonite and a saponite. A significant influence of the clay supports characteristics on the catalytic performance has been found. The following order of improving catalytic performance is established with respect to the pillars composition: Al-pillared clays < unpillared clays < Zr-pillared clays.     

Supramolecular assembly of porphyrin bound DNA and its catalytic behavior for nitric oxide reduction

A stable Fe(4-TMPyP)-DNA-PADDA (FePyDP) film was prepared on pyrolytic graphite electrode (PGE) through the supramolecular interaction between water-soluble iron(III) meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(4-TMPyP)) and DNA template, where PADDA (poly(acrylamide-co-diallyldimethylammonium chloride)) is employed as a co-immobilizing polymer. Electronic absorption spectral and quartz crystal microbalance measurements revealed that Fe(4-TMPyP) interacted with DNA to generate a species with the molar ratio of 1:5 for Fe(4-TMPyP):DNA phosphate. Cyclic voltammetry of FePyDP film showed a pair of stable and reversible peaks corresponding to Fe^III/Fe^II redox potential of −0.13 V versus Ag|AgCl in pH 7.4 PBS. The electron transfer was expected across the double-strand of DNA by an “electron tunneling” mechanism. The modified electrode displayed an excellent catalytic activity for NO reduction at −0.61 V versus Ag|AgCl. The catalytic current was enhanced at lower pH. Chronoamperometric experiments demonstrated a rapid response to the reduction of NO with a linear range from 0.1 to 90 μM. The detection limit was 30 nM at a signal-to-noise ratio of 3.     

Inhibiting and deactivating effects of water on the selective catalytic reduction of nitric oxide with ammonia over MnOx/Al2O3

The effect of water on the selective catalytic reduction (SCR) of nitric oxide with ammonia over alumina supported with 2–15 wt.-% manganese oxide was investigated in the temperature range 385–600 K, with the emphasis on the low side of this temperature window. Studies on the effect of 1–5 vol.-% water vapour on the SCR reaction rate and selectivity were combined with TPD experiments to reveal the influence of water on the adsorption of the single SCR reactants. It turned out that the activity decrease due to water addition can be divided into a reversible inhibition and an irreversible deactivation. Inhibition is caused by molecular adsorption of water. TPD studies showed that water can adsorb competitively with both ammonia and nitric oxide. Additional kinetic experiments revealed that adsorbed ammonia is present in excess on the catalyst surface, even in the presence of water. Reduced nitric oxide adsorption is responsible for the observed reversible decrease in the reaction rate; the fractional reaction order changes from 0.79 in the absence of water to 1.07 in its presence. Deactivation is probably due to the dissociative adsorption of water, resulting in the formation of additional surface hydroxyls. As the amount of surface hydroxyls formed is limited to a saturation level, the deactivating effect on the catalyst is limited too. The additional hydroxyls condense and desorb in the temperature range 525–775 K, resulting in a lower degree of deactivation at higher temperature. A high temperature treatment at 775 K results in a complete regeneration. The amount of surface hydroxyls formed per unit surface area decreases at increasing MnO_x-loading. The selectivity to the production of nitrogen is enhanced significantly by the presence of gas phase water.     

Destruction of carbon tetrachloride in the presence of hydrogen-supplying compounds with ionisation and catalytic oxidation: Part 2. Methane as hydrogen font

The performance of methane (CH₄) as hydrogen donor molecule for the deep and clean oxidation of tetracloromethane (CCl₄) has been experimented. The oxidation of CCl₄–CH₄ admixtures were performed by catalytic combustion with and without pre-catalytic actions (i.e. ionisation/ozonisation) over manganese oxide based catalyst. The extent of CCl₄ and CH₄ combustion was controlled by quantitative determinations of both CO₂ and HCl formed and of CCl₄ and CH₄ converted. Experiments were performed in the 100–500 °C reaction interval in a continuous reaction line at laboratory scale. Fixed CCl₄ concentration (2000 ppmv) with/without CH₄ addition to air constituted the feed. Methane was added to the feedstream in variable concentration (1000–3000 ppmv), the obtained organic mixtures had H/Cl atomic ratios (R_H/Cl) from 0.5 to 1.5. Comparing the tests of ionisation/ozonisation (I/O) of pure CCl₄ streams and CCl₄–CH₄ admixtures, the efficiency of the hydrogen donor role of CH₄ was evidenced. The residue CH₄ concentration was not affected by the residence time (14–42 s) in the ionisation reactor while the residue concentration of CCl₄ decreased by increasing it. A first-order rate equation in CCl₄ concentration was found to represent the ionisation process both in the absence and in the presence of hydrocarbon. On the manganese oxide catalyst, CCl₄ catalytic combustion (CC) was not remarkably influenced by CH₄ presence. CCl₄ destruction by catalytic combustion assisted with ionisation (IOCC) gave rise to higher HCl yield in comparison with conventional combustion. The HCl formation increased with increasing the R_H/Cl value both in the I/O and IOCC experiments, while the CO₂ formation lightly decreased for high R_H/Cl in the CC and IOCC experiments due to incomplete oxidation of CH₄.     

A carbon nanotube/polyvanillin composite film as an electrocatalyst for the electrochemical oxidation of nitrite and its application as a nitrite sensor

We report a simple method for the stable dispersion of multi-walled carbon nanotubes (MWNTs) in water by vanillin and controllable surface addition onto carbon fiber microelectrodes (CFE) via electropolymerization. We have characterized these polyvanillin-carbon nanotube (PVN-MWNT) composite films with techniques including scanning electron microscopy (SEM), infrared spectroscopy (IR) and voltammetry. These investigations showed that the films have a uniform porous nanostructure with a large surface area. This PVN-MWNT composite-modified CFE (PVN-MWNT/CFE) exhibited a sensitive response to the electrochemical oxidation of nitrite. Under optimal working conditions, the oxidation peak current of nitrite linearly increased with its concentration in the range of 0.2 μM-3.1 mM, with the system exhibiting a lower detection limit of 50 nM (S/N = 3). We successfully applied the PVN-MWNT/CFE system to the determination of nitrite from lake water. The efficient recovery of nitrite indicated that this electrode was able to detect nitrite in real samples.     

Catalytic oxidation of nitric oxide over modified carbide slag: Experimental and theoretical studies

In this work, experimental and theoretical methods were used to investigate the catalytic effect of K₂O on NO oxidation. Experimental results indicated that K₂O was the main active component. It enhanced the removal of NO and decreased the reaction temperature. Theoretical results indicated that the K₂O (001)-O surface was more suitable for the adsorption of NO and O₂. Also, NO and O₂ on the Ca(OH)₂ surface may migrate to the K₂O surface for reaction. NO₂ was formed via the interaction of (NO)₂ and O atoms. The formation of ON NO was the key step for NO oxidation, which was more conducive to the subsequent oxidation of NO.     

Effect of microwave absorption properties and morphology of manganese dioxide on catalytic oxidation of toluene under microwave irradiation

A large number of studies had shown that the morphology of the sample had a significant effect on the microwave absorption properties and catalytic activity of the sample. Manganese dioxide with different morphologies was synthesized by hydrothermal method through different precursors. The effects of sample morphology and microwave absorption properties on the catalytic activity of the sample in conventional thermal and microwave fields were studied. The results indicated that compared with the conventional thermal field, the catalytic activity of the samples in microwave field were obviously improved, and the activation energy of the reaction were decreased. Compared with the conventional thermal field, the conversion of toluene in microwave thermal field of MnO₂(Ac), MnO₂(S) and MnO₂(N) increased by 59%, 42% and 12%, and the mineralization rate increased by 36%,11% and 2%, respectively, when the catalytic temperature was 150 °C. Compared with the traditional thermal field, the activation energy of the sample MnO₂(Ac) in the microwave field was reduced by 88.3 KJ. A series of characterization results showed that the sample MnO₂(Ac) had good catalytic activity in the microwave field was due to: MnO₂(Ac) had proper microwave absorption properties, large amount of surface functional groups, large specific surface area and rich pore structure. The analysis results of electromagnetic parameters showed that: the reason that the sample MnO₂(Ac) had good microwave absorption performance was that the MnO₂(Ac) had proper impedance matching, high attenuation constant and Debye dipole relaxation effect.     

Pillared clay and zirconia-based monolithic catalysts for selective catalytic reduction of nitric oxide by methane

New monolithic catalysts based on zirconia and pillared clays (PILC) have been studied for NO_x removal by CH₄ in the presence of oxygen. A comparative study of the influence of ZrO₂ from various commercial sources for the system Pd–ZrO₂ and the effect of the noble metal chosen for the system NM–PILC was carried out, trying to correlate the catalytic activity with the physico-chemical properties of these catalysts. The obtained results indicate that structure and surface acidity of the support plays an important role on the selectivity to NO_x reduction, although properties such as the surface area or pore volume could also determine the overall activity of the monolithic catalysts.     

Electrochemical oxidation of 1,3,5-trimethoxybenzene in aqueous solutions at gold oxide and lead dioxide electrodes

A kinetic study of the electrochemical oxidation of 1,3,5-trimethoxybenzene (TMB) by direct electron transfer at treated gold disk was combined with results of electrolysis in order to produce total degradation into CO₂ and H₂O at Ta/PbO₂ anode. The oxidation of TMB at gold electrode was studied by cyclic voltammetry. The cyclic voltammogram shows one irreversible anodic peak (I) corresponding to the oxidation of adsorbed TMB molecules. The proposed mechanism is based on the hypothesis of two-electron oxidation of TMB molecule leading, via intermediate of a radical cation, to the formation of the 2,4,6-trimethoxyphenol (TMP) and an adsorbed polymeric film. The TMP molecule undergoes a rapid oxidation leading to the formation of 2,6-dimethoxy-p-benzoquinone (DMBQ) as a major product. Degradation of TMB was studied by galvanostatic electrolysis using Ta/PbO₂ anode. The influence of initial TMB concentration and applied current density was investigated. Measurement of total organic carbon (TOC) and analysis by HPLC were used to follow this degradation. The experimental data indicated that the removal of TMB follows a pseudo first-order kinetic. The efficiency of the electrochemical process increases at lower current density and higher TMB initial concentration while it decreases with the TOC removal progress.     

925银电极上同步电化学还原NO2-与CO2合成尿素

引言煤炭、石油等化石燃料燃烧的同时会产生大量氮氧化物(NOx)和二氧化碳(CO2),导致地球的生态系统遭受严重破坏[1]。NOx是导致酸雨、光化学烟雾的主要污染物,而CO2是主要的温室气体。目前国内外使用比较广泛的NOx废气处理方法可分为干法和湿法两大类,其中干法可以分为选择性催     

钛基氧化物电极导致的H_2O_2分解及其对苯胺氧化的影响

The decomposition of H₂O₂ at the Ti-based oxide electrode coated with IrO₂, RuO₂ and TiO₂ (Ti/ IrO₂/RuO₂/TiO₂) prepared by thermal decomposition, was investigated in the electrolysis system of constant potential and the non-electrolysis system respectively. Additionally, the influence of the decomposition of H₂O₂ caused by Ti-based oxide electrode on the oxidation of aniline was also investigated. The results showed that both higher loading of oxides and higher pH were able to accelerate the decomposition of H₂O₂ in the non-electrolysis system and in this case the decay of H₂O₂ was mainly caused by the catalytic action of the oxides coating. In the electrolysis system with Ti-based oxides electrode as anode, the decay rate of H₂O₂ increased with increasing anodic potential. In this case, the decay of H₂O₂ involved two mechanisms: catalytic decomposition and electrochemical oxidation. It was also found that the catalytic decomposition of H₂O₂ at the oxides electrode was useless to the oxidation of aniline while the electrochemical oxidation of H₂O₂ was only slightly helpful to the oxidation of aniline. This work suggested that using the appropriate anodes of less H₂O₂ decomposition as well as reasonable potential in the electro-Fenton process could achieve high chemical efficiency of H₂O₂.     

Effect of KOH on the continuous synthesis of cobalt oxide and manganese oxide nanoparticles in supercritical water

The effects of KOH on the supercritical hydrothermal synthesis of cobalt oxide and manganese oxide particles are investigated using a continuous-flow reactor. Significant changes in morphology, particle size, and oxidation state are observed by adding KOH. The spinel Co₃O₄ phase is transformed to a rocksalt CoO phase and the pyrolusite MnO₂ phase is transformed to a hausmannite Mn₃O₄ phase in the presence of 0.5 M KOH. The average particle size of the metal oxides decreased with an addition of KOH. The OH⁻ ions of KOH may act as a reducing agent as well as a supersaturation enhancing agent under supercritical water conditions.