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.     

The effect of carbon black mixture composition on the structural and electrochemical characteristics of gas diffusion electrodes for electrosynthesis of hydrogen peroxide

Gas-diffusion electrodes containing polytetrafluoroethylene, acetylene black A437E and its mixtures with two types of furnace black (P702 and P268E) with different size of particles are studied. The electrode capacitance, the average diameter and volume of pores and their surface area are investigated as a function of the electrode composition. The kinetic characteristics of electrodes in the oxygen electroreduction are assessed. The slope of polarization curves in Tafel coordinates and the transfer coefficient value are shown to be virtually independent of the electrode composition. The preparative synthesis of Н₂О₂ is carried out.     

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.     

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.     

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.     

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.