V. O. Kazak

Mechanistic Aspects of the Activation of Silica-Supported Iron Catalysts for Fischer–Tropsch Synthesis in Carbon Monoxide and Syngas

The mechanism of activation of silica‐supported iron catalysts for Fischer–Tropsch synthesis was investigated in syngas or carbon monoxide under transient and isothermal conditions using the in situ magnetic method. The catalyst activation proceeds in two steps and involves reduction of hematite into magnetite and magnetite carbidisation into Hägg carbide. Smaller supported iron particles exhibit higher rates of hematite reduction and magnetite carbidisation than the larger counterparts. The reduction of hematite to magnetite proceeds with similar rates in syngas and pure carbon monoxide, while magnetite can be carbidised more rapidly in carbon monoxide. The concentration of iron carbide was approximately 3 times higher after activation in CO relative to the activation in syngas.

Cobalt and iron oxides dispersed onto activated carbons: The size effect

The effect the nature of activated carbons prepared from natural renewable resources has on the metal particle size in cobalt- and iron-containing systems that can be used as catalysts in Fischer-Tropsch synthesis (FTS) is studied. The highest dispersity is observed for the Co3O4-WS (wood sawdust) system. The average particle size is 9.5 nm.

Dynamics of carbide formation in iron-supported catalysts of the Fischer–Tropsch process promoted by copper and potassium

The kinetics of the formation of iron carbides during the activation of iron-coated catalyst for Fischer–Tropsch synthesis promoted by copper and potassium, and by carbon monoxide and syngas, is studied. It is established that the presence of copper lowers the initial temperature of hematite reduction to magnetite and leads to the formation of carbide in both CO and СО/Н2. Potassium slows the rate of magnetite formation, but it accelerates the formation of iron oxide. It is shown that the rate of carbide formation during magnetite reduction for catalysts is half that in the reaction of hematite reduction to magnetite in both CO and СО/Н2.

Dynamics of topochemical reactions in supported iron Fischer–Tropsch synthesis catalysts during their reduction in flowing CO and CO + H2

The reduction of Fe2O3/SiO2 catalysts in flowing CO and CO + H2 in the temperature-programmed and isothermal modes has been investigated by in situ magnetization measurements. The process takes place in two steps, successively yielding magnetite and Hägg carbide. The carbide concentration in the case of reduction with CO is higher than in the case of reduction with the CO + H2. This is assumed to be due to the formation of Fe2SiO4 in the reduction of the catalysts with CO + H2.

Effect of a carrier’s nature on the activation of supported iron catalysts

The effect a carrier’s nature has on the activation of supported iron catalysts in a stream of pure carbon monoxide CO is investigated. It is shown that iron is mainly present in the form of magnetite Fe3O4 in case of carbon supports and in the form of hematite Fe2O3 for silica gel supports. It is shown that all activated samples are chiefly made up of the Hägg carbide χ-Fe5C2, but its concentration is higher for the carbon supports.

Effect of Potassium Promotion on the Formation of a Fe/C act Catalyst in the Course of Reduction in CO and CO/H 2

The process of formation of a Fe/C catalyst was considered as a sequence of topochemical reactions. It was demonstrated that potassium promotion accelerated the formation of magnetite at the stage of catalyst calcination in a flow of argon. The particle size of iron oxides decreased with the concentration of potassium. Potassium promotion also led to an increase in the concentration of Hägg carbide in the course of catalyst reduction by synthesis gas.

Effect of external magnetic field on the Co3O4 reduction kinetics

The effect of external magnetic field on the kinetics of reduction of bulk Co3O4 and silica-supported cobalt oxide (Co3O4/SiO2) with hydrogen has been investigated. The magnetic field exerts an effect on the apparent activation energy of reduction of the bulk oxide and has no effect on the activation energy of reduction of Co3O4/SiO2. It is hypothesized that the changes in the kinetic parameters are due to the effect of the external magnetic field on the structure defects in the solid.