Chemisorption of carbon monoxide on carburized polycrystalline tungsten

Desorption spectra of CO chemisorbed on clean and carburized W at room temperature were measured in the temperature range from 300 to 1900 K and coverage versus exposure plots were constructed. The partial conservation of the β state on carburized W is discussed.     

Formic acid regeneration by electromembrane processes

Waters containing low amounts of sodium formate and sodium hydroxide were processed in order to regenerate formic acid. The treatment was performed in three steps: wastewaters neutralization, sodium formate concentration by conventional electrodialysis (ED), and sodium formate splitting into formic acid and sodium hydroxide by bipolar membrane electrodialysis (BMED). A coupling of these processes was performed. ED was carried out with a current efficiency of 90% and sodium formate concentration up to 2 mol dm⁻³. BMED was performed in a three-compartment cell configuration. Formic acid solution up to 30% was obtained with current efficiency of 80% under a current density of 500 A m⁻². Diffusion of molecular formic acid explains the current efficiency loss. The current efficiency varies with acid concentration and current density. Diffusion is more important through the anion-exchange membrane than through the bipolar membrane (2.5-fold).

Depleted salt produced in BMED was recycled to the neutralisation step.     

Suitability of nitric-sulphuric acid decomposition for the determination of tungsten and molybdenum in geochemical exploration

A mixture of nitric and sulphuric acids is used for the decomposition of geochemical samples for the estimation of tungsten. In the resulting sample solution tungsten is determined colorimetrically by the dithiol method. The decomposition procedure suggested works well for scheelite mineral. However wolframite is only partially decomposed. The same sample solution is used for estimation of molybdenum by the thiocyanate method. The method is suitable for batch analysis and results in a high throughput.     

Formic acid oxidation by iridium single-atom catalysts on nitrogen-doped carbon

正The challenge of the depletion of traditional fossil fuels forces researchers to develop sustainable and highly effective energy storage and conversion technologies. Direct formic acid fuel cells (DFAFCs) exhibit great potential applications in small, lightweight and long-lasting portable power sources, due to the inherent advantages of formic acid,e.g., safer and easier to store and handle than hydrogen,faster electro-oxidation kinetics than ethanol and lower fuel crossover through the Nafion membrane than methanol [1].     

Ammonia decomposition on polycrystalline Pt at pressures between 1.3 and 93 kPa

The kinetics of ammonia decomposition on polycrystalline Pt at temperatures between 600 and 1700 K and at pressures between 1.3 and 93 kPa were measured and correlated with a Langmuir-Hinshelwood unimolecular reaction rate expression. This rate expression had previously been shown to fit data in the same temperature range for pressures between 2 and 1400 Pa.

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Pt 600–1700 1,3 93 , - . , , , 2 1400 .

     

Mechanism of the decomposition of the surface oxide film on polycrystalline palladium

The decomposition of thin surface oxide films on polycrystalline palladium Pd(poly) at 500–1300 K was investigated by mathematical modeling. This process was analyzed in terms of a model including O₂ desorption from the chemisorbed oxygen layer (O_ads) and the passage of oxygen inserted under the surface layer of the metal (O_abs) and oxygen dissolved in metal subsurface layers (O_dis) to the surface. O₂ desorption was modeled on a surface with a square lattice of adsorption sites, with account taken of the energy of the lateral repulsive interactions between adjacent O_ads atoms (ε_aa). At ε_aa = 10 kJ/mol and when the activation energy of O₂ desorption for a chemisorbed-oxygen surface coverage of θ ≈ 0 is E_des⁰ = 230 kJ/mol, the calculated spectra are in agreement with the oxygen temperature-programmed desorption (TPD) spectra obtained for Pd(poly) at θ ≤ 0.5. The passage of O_abs and O_dis atoms to the surface was calculated using a first-order equation, with account taken of the activation energy for these atoms coming out to the surface (E₂ and E₃, respectively). As the oxide film is heated, O₂ desorption is accompanied by the passage of O_abs and then O_dis to the surface, which leads to an increase in the O_ads surface coverage and, accordingly, to a buildup of lateral surroundings in the adsorbed layer. Owing to this fact and to the repulsive interactions between O_ads atoms, the bonds between O_ads and the surface weaken and E_des decreases. As a consequence, the O₂ desorption rate increases and a low-temperature peak with T_max ≈ 710 K, which is due to the passage of O_abs atoms to the surface, and then a high-temperature peak with T_max ≈ 770 K, which is due to the passage of O_dis atoms to the surface, appear in the TPD spectrum. At ε_aa = 10 kJ/mol, E_des⁰ = 230 kJ/mol, E₂ = 145 kJ/mol, and E₃ = 160 kJ/mol and when the number of inserted oxygen monolayers is θ_abs ≤ 0.3 and the number of oxygen monolayers dissolved in subsurface layers is θ_dis ≤ 10, the TPD spectra calculated for the given model are in agreement with the O₂ TPD spectra that are observed for Pd(poly) and are due to the decomposition of surface oxide films.     

Photoelectron spectra of the decomposition of ethylene on (110) tungsten

Photoelectron spectra, LEED patterns, and work function changes were obtained for ethylene adsorbed on (110) tungsten at room temperature, and with subsequent heat treatment. For saturated adsorption of C₂H₄ on (110) W at room temperature, features in the photoelectron spectrum were observed which are believed to be due to the C, HCC, and Cmetal bonds in an adsorbed species of the form C₂H₂. The work function decreased by 1.2 eV at saturation, but LEED showed no change from the clean surface pattern. Upon heating to ≈ 500 K, where hydrogen is known to desorb, the CH bond was broken, whereas the CC and Cmetal bonds remained. The work function increased, from saturation, by ≈ 0.6 eV and the LEED pattern exhibited a large diffuse background with no new spots. Upon heating to ≈ 1100 K the CC bond broke and the LEED pattern ordered into the characteristics carbon contamination pattern.     

XPS and factor analysis study of initial stages of cerium oxide growth on polycrystalline tungsten

The initial stages of growth of the nanostructured cerium oxide deposited on the polycrystalline tungsten surface by pulsed laser deposition are studied using XPS technique. The population of Ce (III) and Ce (IV) oxidation states in the deposited CeO_2?x layers is determined applying factor analysis method. Tungsten atoms react with oxygen from the cerium oxide nanoparticles already at the room temperature, and a layer of tungsten trioxide is formed at the interface. Gradual heating of the samples up to 900 K leads to the increase of the thickness of WO₃ oxide layer and a partial reduction of Ce (IV) to Ce (III). The spectra of O (1s) photoelectrons are composed from a signal originating from metal oxides and a signal of surface superoxide and hydroxyl groups. Factor analysis was performed on the spectra of Ce (3d) photoelectrons to determine the position, shape, and intensity of the spectral components belonging to Ce (III) and Ce (IV) oxidation states. We propose a new simple method to generate components of the spectroscopic meaning. The basic idea of our method consists in the use of the slightly positive values instead of zeros to the needle test vector. Two components are required to reproduce the original data within the experimental errors. Copyright © 2015 John Wiley & Sons, Ltd.     

Insights into the enhanced tolerance to carbon monoxide on model tungsten trioxide-decorated polycrystalline platinum electrode

Polycrystalline platinum decorated by WO₃ nanoparticles (WO₃/Pt_pc) is used as a model electrode to gain insights into the enhanced tolerance to carbon monoxide (CO) observed on such composite materials. Bifunctional-type reactions involving WO₃ and Pt active sites are observed, such as hydrogen spill-over or the electrooxidation of CO molecules adsorbed on Pt sites neighboring the WO₃ nanoparticles. The resulting CO_ad-free Pt sites are active for the hydrogen oxidation reaction (HOR), thereby enhancing the HOR activity for WO₃/Pt_pc electrode relatively to bare Pt_pc in 300 ppm CO/H₂ saturated HClO₄ electrolyte. However, this bifunctional effect occurs exclusively for CO molecules weakly adsorbed on Pt, i.e. only for a small fraction of the CO_ad fully covering the Pt surface.     

Formic acid reduction—XVII : Kinetic studies on the formic acid reduction of N-benzylideneaniline

The formic acid reduction of azomethine which has been reported² to proceed nearly quantitatively by the use of the formate reagent, 5HCO₂H·2NEt₃, was kinetically investigated by the carbon dioxide trapping and UV spectroscopic methods, using N-benzylideneaniline as a representative. Rate data gave the rate equation, v = (k + k′ [NEt₃])[N-benzylideneaniline][HCO₂H], indicating two-path mechanism. By the technique of using deuterated formic acids, it was found that the hydrogen bound to the carbon of formic acid is transferred as hydride to the carbon of the CN double bond in the rate determining step. The reaction is facilitated by the electron-releasing substituents of the two benzene rings of N-benzylideneaniline. On the bases of these results a possible mechanism is proposed.     

Electrochemical reduction of mesoxalic acid on polycrystalline platinum surfaces

The electrochemical reduction of mesoxalic acid on polycristalline platinum surfaces has been studied in acid medium. The reaction proceeds through the interaction with adsorbed hydrogen atoms. Malonic acid is proposed as final reaction product.

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Elektrochemische Reduktion von Mesoxalsäure auf polykristallinen Platinoberflächen

Zusammenfassung Die elektrochemische Reduktion von Mesoxalsäure auf polykristallinen Platinoberflächen wurde in saurem Medium untersucht. Die Reaktion verläuft über die Wechselwirkung mit adsorbierten Wasserstoffatomen, wobei als Endprodukt Malonsäure entsteht.

     

Effect of traces of water vapor on the rate of ammonia decomposition on polycrystalline platinum

The influence of small (lower than 0.02) molar fractions of water on the rate of ammonia decomposition on platinum wires was studied for ammonia pressures varying between 6.7 and 93.3 kPa and temperatures between 800 and 1700 K. The presence of water strongly inhibited the rate of reaction in all experiments.

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( 0,02) , 6,7 93,3 , 800 1700 K. .

     

Formic acid electrooxidation on Pd in acidic solutions studied by surface-enhanced infrared absorption spectroscopy

A mechanistic study of electrocatalytic oxidation of formic acid on Pd in sulfuric and perchloric acids is reported. Surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS) shows the adsorption of CO, bridge-bonded formate, bicarbonate, and supporting anions on the electrode surface. Poisoning of the Pd surface by CO, formed by dehydration of formic acid, is very slow and scarcely affects formic acid oxidation. The anions are adsorbed more strongly in the order of (bi)sulfate > bicarbonate > perchlorate, among which the most strongly adsorbed (bi)sulfate considerably suppresses formic acid oxidation in the double layer region. The oxidation is suppressed also at higher potentials in both acids by the oxidation of the Pd surface. Adsorbed formate is detected only when formic acid oxidation is suppressed. The results show that formate is a short-lived reactive intermediate in formic acid oxidation and is hence detected when its decomposition yielding CO(2) is suppressed. The high electrocatalytic activity of Pd can be ascribed to the high tolerance to CO contamination and also high catalytic activity toward formate decomposition.     

Autocatalytic decomposition of carbonic acid

Long held to be unstable or metastable in the gas phase, carbonic acid has successfully been produced and identified in its gaseous form in recent decades. Theoretical studies have indicated that isolated carbonic acid in the gas phase may in fact be quite stable, its decomposition attributable to the catalytic effect of water molecules, either present or produced in a chain reaction by an initially slow decomposition. In this study, a previously unreported autocatalytic decomposition route is studied using high‐accuracy ab initio quantum chemical methods. Results indicate that a carbonic acid dimer may react and decompose in a single‐step, highly concerted reaction. The transition state of this reaction was characterized, and the reaction pathway was found to have significantly lower activation energy than the uncatalyzed decomposition, and comparable or lower energy than the water‐catalyzed reaction. The results indicate that gaseous carbonic acid should be unstable even in the absence of water. © 2013 Wiley Periodicals, Inc.     

甲酸－异丙醇体系分离蛋白质时甲酸的作用研究

本文在反相高效液相色谱上，用甲酸－异丙醇体系作流动相，研究了甲酸浓度变化对蛋白质分离的影响。结果表明当甲酸浓度增加时，蛋白质的保留时间减小和计量置换模型之值的降低反映了甲酸在这个体系中具有洗脱剂的作用。甲酸使蛋白质在流动相中的溶解度增大，具有离子对试剂的作用。在这个体系中甲酸还具有破坏蛋白质结构的功能。