Formation of high‐molecular hydrocarbons by CO‐based Fischer‐Tropsch synthesis using Na‐promoted Fe catalysts

The present study deals with the CO conversion to high‐molecular hydrocarbons using the Fischer‐Tropsch (FT) synthesis. Fe2O3 samples with Na surface contents between 0 and 10 wt.% were prepared, carbidized and characterized using X‐ray photoelectron spectroscopy, X‐ray diffraction, Mössbauer spectroscopy, Raman spectroscopy, temperature‐programmed reduction by H2 and N2 physisorption. The correlation of catalytic FT activity‐selectivity and physical‐chemical properties of the samples showed that the Na promoter electronically activated the Fe sites enhancing the CO adsorption and carbon coverage. As a result, the Na‐doped catalysts revealed a very high chain growth probability (α = 0.95) substantiating the pronounced formation of long‐chain hydrocarbons. FT investigations with different catalyst bed lengths evidenced that the carbon chain propagation mainly occurred in the inlet area referred to the increasing transformation of the active Fe carbides into FT‐inactive Fe3O4 along the bed. Additionally, with the decreasing proportion of Fe carbides, bulk carbon and wax deposits formed. Moreover, the activation energies of CO conversion (33 kJ/mol) and CH4 formation (54 kJ/mol) were estimated using Arrhenius plots.