Modern Concepts of the Ways of Forming the Active State in Cobalt Catalysts of the Fisher-Tropsch Synthesis

Abstract

One of the technologies for obtaining hydrocarbons from natural gas is the gas-to-liquid (GTL) technology, based on the catalytic Fischer-Tropsch synthesis (FTS). Cobalt-supported catalysts, in particular Co/Al₂O₃, are used to synthesize predominantly linear high-molecular hydrocarbons at low temperatures and pressures. The active component of the catalyst is metal particles with sizes from 6 to 10 nm, formed during the reduction of the oxide precursor of the catalyst in a hydrogen-containing environment. The temperature of the reductive activation depends on the degree of interaction of cobalt with the oxide carrier. In the case of Al₂O₃, the interaction of the carrier with cobalt cations leads to the formation of joint Co-Al oxides, which are reduced at a temperature of 500 °C and above. Such a high temperature of reductive activation creates significant difficulties in the industrial use of these catalysts. On the other hand, some interaction between the support and the metal is welcomed, as it ensures high particle dispersion by fixing the active component, preventing migration and sintering during FTS, and thus contributes to high catalyst activity and stability. It is possible to lower the activation temperature by introducing structural modifiers into the carrier, in particular oxide compounds of Zr and P, which help to reduce the degree of interaction during catalyst preparation, or by introducing a small amount of noble metals (promoters), in particular Ru, into the finished catalyst. The relevance of the work lies in the need to conduct comprehensive studies of the influence of the chemical composition, methods of obtaining and activating Co- Al₂O₃ catalysts of the SFT on the nature and character of the formation of the active state of the catalyst surface.