Fischer-Tropsch Synthesis: Reaction mechanisms for iron catalysts

The reaction mechanism for the Fischer-Tropsch synthesis with iron catalysts under low-temperature conditions is described. Our data are considered to support an oxygenate intermediate. The structure of the chain initiating species is considered to be, or closely resembles, the formate species responsible of the water-gas shift reaction. Chain propagation is considered to involve a different species that is either CO ora species derived from CO. The growing chain is considered to lose the final oxygen during the chain termination step. The structure of the stable low-temperature iron catalyst is considered to consist of a core that is Fe(3)O(4) with the core surrounded by a layer of iron carbide. The data show that iron carbide is the active phase and that there is a synergistic interaction between the alkali and structural promoter that maintains an adequate iron carbide layer. (c) 2008 Elsevier B.V. All rights reserved.