Electrical Conductivity of Hydrophobized Electrodes Fabricated from Thermally Expanded Graphite and Their Activity in Electroreduction of Oxygen

Intercalation compounds of GT-1 and GAK-3 graphites were electrically synthesized in concentrated sulfuric and nitric acids. Porous composite samples based on thermally expanded graphite produced from electrochemically synthesized GT-1 graphite hydrosulfate, chemically synthesized GSM-1 graphite nitrate, and fluoroplastic-4D (1–15 wt %), with a volume density of 650–1090 g l^?2, were fabricated and studied.     

Electrosynthesis of hydrogen peroxide in solutions of salts that form molecular addition products (peroxo solvates) with it

The possibility of electrosynthesis of hydrogen peroxide in the electroreduction of oxygen in a gas-diffusion electrode in solutions of salts that form the molecular addition products (peroxo solvates) with H₂O₂ was studied. In KF and potassium and sodium phosphate solutions, H₂O₂ was obtained at concentrations of 2.3–3.6 M at current densities of 0.1–0.15 A/cm² and current efficiencies of 75–92%. The resulting solutions were concentrated to 11–27 M to give solid peroxo solvates with high hydrogen peroxide contents (22–50%). These results demonstrate that the application of gas-diffusion electrodes for electrosynthesis of inorganic products can be significantly expanded.     

Solid-state NMR spectroscopic study of the structure of grafted layers of phosphonic acid ester-modified hydroxyapatite

Interaction of hydroxyapatite (HAP) surface with phosphonic acid esters is studied under different conditions. The urgency of the study is due to the fact that HAP is one of the main components of bone tissue and is widely applied in the production of materials designed for filling bone defects. Modification of the surface properties of HAP may result in the development of materials with increased biocompatibility. It is revealed that, in the absence of solvents or in the medium of an aprotic solvent, phosphonic acid esters interact with HAP surface to yield pyrophosphate groups. The interaction with the surface does not take place in the presence of protic solvents.     

Iron(III) chloride supported on MCM-41 molecular sieve as a catalyst for the liquid-phase oxidation of phenol

FeCl₃ was supported on MCM-41 mesoporous molecular sieve via adsorption or coordination bonding and by embedding as an anionic constituent of covalently immobilized imidazolium ionic liquid (IL). The synthesized materials were characterized by N₂-BET, SEM, TEM, FT-IR, ¹H, ¹³C, and ²⁹Si NMR, and DSC-TG. All of the catalysts were shown to be active for the liquid-phase oxidation of phenol by hydrogen peroxide. Supported FeCl₃ species present as tetrachloroferrate counterions of immobilized IL are the most resistant to iron leaching.     

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.     

New accelerated method of impregnation by aqueous electrolyte of carbon black gas-diffusion electrodes to study their structural and electrochemical characteristics

A new method of fast impregnation of carbon black gas-diffusion hydrophobized electrodes is suggested under their cathodic polarization in an alkaline aqueous solution of tetrabutylammonium bromide (TBAB) at the potentials of hydrogen evolution. As dependent on the quantitative content of polytetrafluoroethylene (PTFE) in the electrode, current density, time, TBAB concentration, various degree of electrode wetting is observed, up to nearly complete electrode flooding in just several hours. When electrodes are stored, their original electrolyte porosity is not recovered. the electrode with 8 wt % of PTFE was used to show the effect of the electrode flooding degree on the double layer capacity, average diameter of electrolyte pores, their surface area and activity in the case of oxygen reduction. This method may be used for simulation of the process of flooding of gas-diffusion electrodes by electrolyte in the course of their prolonged operation.     

1H and 13C MAS NMR studies of light alkanes activation over MFI zeolite modified by Zn vapour

The early stages of methane, ethane and propane conversion were studied by in situ ¹H and ¹³C MAS NMR techniques over fully exchanged Zn²⁺/MFI catalyst obtained by the reaction with zinc vapour. The in situ techniques revealed strong interaction of alkanes with Zn²⁺ cations evidenced by significant shift of the corresponding NMR lines. Besides that, the formation of methyl zinc, ethyl zinc and n-propyl zinc species along with bridging and silanol surface OH-groups was detected already at the ambient temperature. These results pointed to dissociative adsorption of alkanes over (ZO)–Zn²⁺–(OZ) and (ZO)–Zn²⁺–(OSi) active sites of the catalyst. The dissociative adsorption was shown to be a dead-end surface reaction in the case of methane starting reactant, while in the case of ethane and propane, it appeared to be responsible for the initiation of the catalytic cycle leading to alkenes and dihydrogen formation and regeneration of zinc containing catalytic sites.     

Electrosynthesis of Н<Subscript>2</Subscript>О<Subscript>2</Subscript> from О<Subscript>2</Subscript> in Gas Diffusion Electrodes Based on Black СН600

Furnace black СН600 was studied as a catalyst for electrosynthesis of Н₂О₂ from О₂ in a gas diffusion electrode in alkaline and acidic solutions. The texture properties of the starting black СН600 and gas diffusion electrodes (GDEs) based on it were determined by the low-temperature nitrogen adsorption (LTNA) method. The rate constants of Н₂О₂ decomposition on black and its mixtures with fluoroplast-4D in acidic and alkaline solutions of electrolyte were calculated. The process selectivity γ (the current fraction spent on the two-electron reduction of oxygen), kinetic parameters of oxygen reduction, and double-layer capacity of the СН600-based GDE were determined. Data on the kinetics of hydrogen peroxide accumulation during electrosynthesis from oxygen in СН600-based GDE in acidic and alkaline solutions were obtained.     

Catalytic activity of in situ synthesized MoWNi sulfides in hydrogenation of aromatic hydrocarbons

MoWNi–sulfide catalysts were obtained in situ by thermal decomposition of metal–polymer precursors based on the copolymers of polymaleic anhydride in a hydrocarbon raw material. The activity of the synthesized catalysts in hydrogenation of bicyclic aromatic hydrocarbons was studied, and the composition and structure of active phase nanoparticles were determined.