Gheorghi P. Vissokov

Catalyst preparation using plasma technologies

This paper discusses catalyst preparation using thermal and cold plasmas. In general, there are three main trends in preparing catalysts using plasma technologies: (1) plasma chemical synthesis of ultrafine particle catalysts; (2) plasma assisted deposition of catalytically active compounds on various carriers, especially plasma spraying for the preparation of supported catalysts; (3) plasma enhanced preparation or plasma modification of catalysts. Compared to conventional catalyst preparation, there are several advantages of using plasmas, including: (1) a highly distributed active species; (2) reduced energy requirements; (3) enhanced catalyst activation, selectivity, and lifetime; (4) shortened preparation time. These advantages are leading to many potential applications of plasma prepared catalysts.

Experimental studies on the plasma-chemical synthesis of a catalyst for natural gas reforming

Abstract We designed and built equipment for plasma-chemical synthesis and/or regeneration of spent catalyst for natural gas reforming. Under the conditions of an electric-arc low-temperature plasma, we studied the Ni–O–Al system and performed a comprehensive physico-chemical analysis of the ultra-dispersed product obtained. We found that the plasma-chemically synthesized samples were reduced 3–4 times as fast as the conventional G56A catalyst.

Plasma-Chemical Synthesis of Nanosized Powders – Nitrides, Carbides, Oxides, Carbon Nanotubes and Fullerenes

In this article the plasma-chemical synthesis of nanosized powders (nitrides, carbides, oxides, carbon nanotubes and fullerenes) is reviewed. Nanosized powders - nitrides, carbides, oxides, carbon nanotubes and fullerenes have been successfully produced using different techniques, technological apparatuses and conditions for their plasma-chemical synthesis.

Nanodispersed Oxides-Plasma-Chemical Synthesis and Properties

We discuss the plasma-chemical synthesis and the properties of transition metals oxides, Al2O3, SiO2, rare-earth oxides, oxides for ceramics and metal-ceramics, and oxides used as catalysts. Bearing in mind the indisputable advantages of using plasma-chemically synthesized nanodispersed oxides for the needs of various industrial fields, we set out to review the articles published in the past few years devoted to the problems of plasma-chemical synthesis and characterization of nanodispersed oxides.

Synthesis and Characterization of Ultra-Fine Si3N4 by Electric Arc Plasma

Under conditions of electric-arc low-temperature plasma (LTP), ultra-finely dispersed Si3N4 particles have been synthesized by using silicon powder and nitrogen as raw materials. The prepared samples are characterized by x-ray diffraction (XRD), scanning electron spectroscopy (SEM), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The result indicates that the basic phase in Si3N4 produced is α- and β-Si3N4. The particle size of Si3N4 sample is in the range of 30-500 nm.

The Role of Nanodispersed Nitrides in the Sintering of Silicon Nitride Ceramics

The synthesis of ceramics based on silicon nitride using nanopowders of TiN and Si3N4 as additives was studied. The ceramic compositions were pressurelessly sintered under nitrogen atmosphere at different temperatures (1550°C, 1650°C and 1750°C) with a heating rate of 10°C/min and a holding time of 2 h. The nanodispersed nitrides (NDN) were produced by electric-arc plasma synthesis and characterized. The ceramic composites obtained with nanoparticles of 1 wt% to 5 wt% TiN and 20 wt% Si3N4 were characterized by scanning electron microscopy (SEM), atom force microscopy (AFM) and energy-dispersive spectrometry (EDX). The effect of the addition of nanodispersed powders on the mechanical properties and microstructure of Si3N4 ceramics was investigated.

Study of Nanodispersed Iron Oxides Produced in Steel Drilling by Contracted Electric-Arc Air Plasma Torch

The optimal conditions on the plasma-forming gas flowrate, discharge current and voltage, distance between the plasma-torch nozzle and the metal plate surface for the process of penetration in and vaporization of steel plates by the contracted electric-arc air plasma torch accompanied by water quenching, were determined. The X-ray structural and phase studies as well as Mossbauer and electron microscope studies on the samples treated were performed. It was demonstrated that the vaporized elemental iron was oxidized by the oxygen present in the air plasma jet to form iron oxides (wustite, magnetite, hematite), which, depending on their mass ratios, determined the color of the iron oxide pigments, namely, beginning from light yellow, through deep yellow, light brown, deep brown, violet, red-violet, to black. A high degree of dispersity of the iron oxides is thus produced, with an averaged diameter of the particles below 500 nm, and their defective crystal structure form the basis of their potential application as components of iron-containing catalysts and pigments.

Electric-Arc Plasma Installation for Preparing Nanodispersed Carbon Structures

An electric-arc plasma installation operated in the hidden anode arrangement is constructed and used for the preparation of carbon nanostructures. A contracted plasma arc generated by a plasma torch using an inert gas is used as heat source. The average mass temperature of arc is higher than 104 K, while its power density, which is directly transferred onto the electrode (anode), is ~ 2 kW/mm2. The anode contact area formed on the electrode moves against the arc by way of shifting the electrode and is hidden completely in the interior of plasma gas stream moving towards it. As a result of both the direct plasma attack and the opposite movement of streams in the hidden anode contact area, a temperature higher than 6000 K is reached. Thus, intensive vaporization takes place, which forms a saturated plasma-gas-aerosol phase of the initial material of electrode (anode). This gas phase is mixed in and carried by the plasma stream. Over that mixed plasma stream, a controlled process of quenching (fixation) is carried out by twisted turbulent fluid streams. After the fixation, the resultant carbon nano-structures are caught by a filter and collected in a bunker.

Complex physico-chemical characterization and kinetic studies on the reduction and activity of catalyst for ammonia synthesis regenerated by electric-arc plasma

Abstract A comprehensive physico-chemical characterization is carried out and the reduction kinetic and activity are studied of samples of CA-1-type catalyst for ammonia synthesis regenerated in quasi-equilibrium electric-arc low-temperature plasma. The experimental conditions are described for the plasma-chemical regeneration of a spent catalyst for ammonia synthesis. The samples regenerated are characterized by means of determining: the specific surface (using the Klyatchko-Gurvich technique); the size of the finely-dispersed particles (electron microscope analysis); and the phase content (X-ray phase analysis, Moessbauer spectroscopy, chemical analysis, derivatographic analysis). A mechanism is proposed for the plasma-chemical regeneration of the samples. The reduction process is studied and the activity, the relative degree of transformation, the activation energies, the rate constants, the relative activity and the degree of thermal deactivation of the regenerated samples are determined. It is found that the samples are reduced three to five times as fast as the standard ones. The increased reduction rate and the high catalytic activity are due to the increased pre-exponent factor in the Arrhenius equation at constant activation energy. The causes for the high activity and thermal stability of the samples are explained. The advantages of the plasma-chemical technique are outlined as compared with the conventional methods for activation of spent catalysts for ammonia synthesis.