Sławomir Jodzis

Thermally modified active carbon as a support for catalysts for NH3 synthesis

The effect of thermal treatment of a typical active carbon at 1300 °C and 1900 °C on its structural properties was investigated. It has been found that only a high-temperature heating (1900 °C) produced substantial changes in the structure of the carbon used: a disappearance of a considerable part of open micropores and formation of a turbostratic structure. The prepared materials were used as a support in catalysts for NH3 synthesis. The precursor of the active phase was Fe(NO3)3 · 9H2O. The iron nitrate deposited on the raw amorphous carbon decomposes to finely dispersed, hardly reducible iron oxides on heating to 470 °C in a H2 + N2 mixture. Even if reduced to more than 33%, iron is inactive in NH3 synthesis (400–470 °C, p = 10MPa). When deposited on the turbostratic, low-surface area carbon, iron forms, however, well developed crystallites (~60 nm), and is active in ammonia synthesis. Potassium activates strongly the surface of Fe, and, in the case of the amorphous support, it stimulates the reduction of iron oxides.

Studies on kinetics of ammonia synthesis over ruthenium catalyst supported on active carbon

Abstract The rate of ammonia synthesis was measured for ruthenium and iron catalysts under high (100 bar) and under atmospheric pressures. The effect of ammonia concentration in the gas phase on reaction rate was measured at 400, 430, and 470°C for p = 100bar at 370 and 400°C for p = 1bar . It was found that ruthenium is less sensitive than iron to the increase of ammonia pressure in the gas phase. It is also much less sensitive to changes in the total pressure (for p H 2 :p N 2 =const. ). At relatively high conversion degrees the ruthenium catalyst used was several times more active than the fused iron catalyst at 100 bar and 25–40 times more active under atmospheric pressure.

Effect of Silica Packing on Ozone Synthesis from Oxygen-Nitrogen Mixtures

The effect of silica packing in an ozone generator fed with oxygen-nitrogen mixtures has been studied. The measurements were carried out in an ozone generator with a double-sided cooled discharge gap, in which silica packing has been placed. In the presence of the packing considerably higher ozone concentrations were achieved than in the ozone generator without packing. An especially clear effect of silica packing was observed in air-fed conditions. It has been found that the increase in the concentration of the obtained ozone coincides with the increase of N2O in the post-reaction gas.

Ozone Synthesis Under Surface Discharges in Oxygen: Application of a Concentric Actuator

The results of studies on the ozone synthesis under discharges generated on the surface of the ceramic actuator built as the concentric-strip electrode system are presented. Experiments were carried out in pure oxygen. The ozonizer, in which the gas flows with variable linear velocity, was used. The ozone concentrations and the process energy efficiencies show the possibility of effective ozone generation in the reactors with nonconventionally organized discharge space.

Effective Ozone Generation in Oxygen Using a Mesh Electrode in an Ozonizer with Variable Linear Velocity

Results of studies on ozone synthesis under discharges proceeding in a metal mesh-ceramic dielectric system have been presented. The experiments were carried out in the reactor with unique reaction space geometry, in which the reacting gas flew with consequently increasing linear velocity. The high voltage electrode was made of a metal mesh, which caused intensification of the gas mixing in the reaction space. Using a simple reactor with one-side cooling of the reaction space, high ozone maximum concentrations (100 g/Nm3) and energy efficiencies (180–200 g/kWh) were obtained at 25 °C.

Kinetic and Energetic Analysis of the Ozone Synthesis Process in Oxygen-fed DBD Reactor. Effect of Power Density, Gap Volume and Residence Time

ABSTRACT The analysis of measurements of ozone synthesis process rate in pure oxygen with the use of the unique plasma reactor was presented. The kinetic measurements have been made using the integral and the differential method. The effect of energy stream delivered (i.e., power) and gas residence time in a discharge gap on the rate and energy efficiency of the process carried out in dielectric barrier discharge was shown. It was presented how the process rate and energy efficiency change along a discharge gap and the way they depend on both power density and a residence time.

Activity and thermoresistance of fused iron catalysts for ammonia synthesis

Abstract The activity and thermoresistance of five industrial catalysts were examined. Kinetic measurements were carried out in an isothermal, flow differential reactor under 10.0 MPa in the 400–520°C temperature range. In thermoresistance tests, overheating of the catalysts was carried out at 650°C for 24 h, or at 620°C for 24 to 192 h. The relationships obtained during both experimental tests were similar, with 24-h operating at 650°C giving a similar activity decrease as ageing for 192 h at 620°C. The chemical composition of the catalysts (XRF) was determined.

Influence of aluminium and potassium on activity and texture of fused iron Catalysts for ammonia synthesis

Abstract BET, scanning electron microscopy and X-ray diffraction were used to investigate the texture of fused iron Catalysts which had been previously reduced and passivated, and into which potassium hydroxide was introduced by impregnation or aluminium removed by extraction. Activity tests were carried out under 10.0 MPa in the 400–520 °C temperature range. Investigations were performed on the doubly promoted (Al, Ca) and industrial, triply promoted (K, Al, Ca) Catalysts. Introduction of potassium hydroxide into the doubly promoted Catalyst increases the process rate by about 15–20 times per unit surface area. Sintering and recrystallization are observed in the Catalyst, proving that interaction takes place during the process between the potassium hydroxide introduced and the alumina present on the iron surface. Partial removal of aluminium from the surface of the doubly and triply promoted Catalysts also leads to sintering and recrystallization under ammonia synthesis conditions. This shows that the presence of alumina on the surface, and not within the iron, is responsible for textural promotion. Loss of Catalysts activity is proportional to reduction in total surface area.

Catalytic activity of silica in ozone formation in electrical discharges

The catalytic action of granular silica packing on ozone formation has been observed under discharge conditions. Using a glass ozonizer with a metal high-voltage electrode, at a frequency of 400 Hz it was possible to obtain much higher ozone concentrations in the presence q( silica than without packing, with the same total energy consumption. The dependence between ozone production and energy efficiency is considered, and conditions of the optimum ozonizer run are discussed. It is shown that in the all-glass ozonizer with a narrow discharge gap, the ozone concentration may be as high as 6.5% (ca. 130g O3/m3) when silica packing is applied.

Gas Temperature in an Ozonizer. The Computer Modeling of an Actual Discharge System

Dielectric barrier discharges are commonly used for ozone synthesis. The main reactions of this process proceed in the microdischarge channels in which the variable temperature occurs. The temperature in the discharge gap was modeled. The dynamics of a gas temperature inside the discharge gap changes were presented.