Impact of in situ MAS NMR techniques to the understanding of the mechanisms of zeolite catalyzed reactions

The in situ MAS NMR studies of the mechanisms of zeolite catalyzed reactions are reviewed. The first part of the critical review contains brief information on the different experimental approaches used for the in situ MAS NMR studies under batch and flow conditions. In the second part, a cross reference index between the reactions studied, the catalysts used, the mechanistic information obtained and the corresponding literature sources is established. Finally, in the last part the most widely studied areas are discussed in more detail. In particular, the impact of in situ MAS NMR to unravel the mechanisms of olefin, alcohol and alkanes transformations over zeolite catalysts is analyzed (232 references).     

Graphitized carbon materials for electrosynthesis of Н<Subscript>2</Subscript>О<Subscript>2</Subscript> from О<Subscript>2</Subscript> in gas-diffusion electrodes

New graphitized carbon materials: technical carbon N220, С140, and СН85 (Omsktekhuglerod) were studied as catalysts of electrosynthesis of alkaline solutions of hydrogen peroxide from oxygen in gasdiffusion electrodes (GDEs). The kinetic parameters of oxygen reduction in alkaline solution and the capacity of gas-diffusion electrodes based on technical carbon N220, С140, and СН85 were determined. Data on the kinetics of hydrogen peroxide accumulation were obtained at different current densities. The fraction of current γ spent on the reduction of oxygen to hydrogen peroxide was determined. The rate constants of hydrogen peroxide decomposition under the given conditions were calculated.     

Pilot laboratory electrolyzer for electrosynthesis of hydrogen peroxide in acid and alkaline solutions

Results of a preparative electrosynthesis of hydrogen peroxide by cathodic reduction of oxygen in a carbon black gas-diffusion electrode in acid and alkaline electrolyte solutions in a versatile pilot laboratory three-chamber electrolyzer are presented.     

Effects of the composition of acid solutions and the presence of organic acids on oxygen electroreduction to hydrogen peroxide in a carbon black gas-diffusion electrode

This paper reports on the effects of the K₂SO₄, H₂SO₄, NaCl, HCl, and tetrabutylammonium bromide concentrations (0.01–0.0002 M) and the presence of formic, acetic, and butyric acids in the electrolyte on the kinetic characteristics of oxygen reduction to H₂O₂ in a carbon black gas-diffusion electrode (GDE) and on the H₂O₂ accumulation kinetics in electrolyte at current densities of 30–100 mA/cm². The introduction of K₂SO₄ and tetrabutylammonium bromide in the electrolyte led to an increase in the transfer coefficient α and a decrease in the coefficients in the Tafel equation. The concentration and the current efficiency of H₂O₂ decreased with the salt to acid concentration ratio. The organic acids reduced the current efficiency of H₂O₂ and increased the electrode polarization. Peracids with a current efficiency of up to 0.27% and concentration of up to 7.5 mM were obtained. Solutions of H₂O₂ with concentrations of 0.6–3.3 M and current efficiencies of 17–75% were obtained at current densities of 30–100 mA/cm² in electrolytes with salt and inorganic acid concentrations of 0.9–40 g/l and in the presence of organic acids.     

Kinetics of Hydrogen Peroxide Accumulation in Electrosynthesis from Oxygen in Gas-Diffusion Electrode in Acidic and Alkaline Solutions

Accumulation of H₂O₂ in aqueous solutions with various pH values in electroreduction of oxygen in carbon-black gas-diffusion hydrophobized electrodes was studied. The effect of various parameters of the process on its electrochemical component and decomposition rate of the H₂O₂ formed was analyzed.     

Reactivity of a phosphonate layer grafted onto a surface of dispersed hydroxyapatite

The reactivity of a grafted layer contained on the surface of hydroxyapatite modified with diethyl butylphosphonate is studied. Modified hydroxyapatite is shown to interact with nucleophilic agents. The composition of reaction products depends on the nature of the latter.     

Investigation of the influence of technological factors on quality of basic brands of HPPE

The comparative analysis of the molecular mass distribution, temperatures and heat effect of phase transitions, degree of crystallinity of defect materials and matrix polyethylene film were carried out. Possible reasons of deterioration of the quality of polyethylene on stages of its synthesis, transportation, storage, and processing were determined.     

Impregnation of Acetylene Black Electrodes with a Polytetrafluoroethylene Binder with an Aqueous Solution and Evaluation of Its Specific Double Layer Capacity

The effect of (0.05 M) tetraalkylammonium salt additions in aqueous 0.5 M KOH on the rate of impregnation of carbon black electrodes with a polytetrafluoroethylene binder (5–20 wt % PTFE) at hydrogen evolution potentials was studied. It was shown that tetraalkylammonium salts facilitate the fast filling of electrodes with electrolyte, and their effect increases with the molecular mass of the cation. Tetramethylammonium bromide showed the weakest effect. In solutions with tetrabutylammonium bromide, the electrodes were completely flooded with 5 wt % PTFE within 15 min. Diethyldibenzylammonium bromide had a similar effect. The influence of the PTFE concentration in the electrodes on their capacity was studied. The specific capacity of acetylene black in acid and alkaline aqueous solutions was evaluated from the electrode surface area determined by low-temperature nitrogen adsorption (BET).     

Effect of trialkylammonium salts and current density on the electrosynthesis of hydrogen peroxide from oxygen in a gas-diffusion electrode in acid solutions

The influence exerted by the nature of cation of a supporting electrolyte and by the current density on the electroreduction of oxygen to hydrogen peroxide in acid K₂SO₄ solutions (pH 0.9–1.4) in gas-diffusion hydrophobized carbon black electrodes with varied electrolyte porosity was studied.