Production of high-calorie synthetic natural gas using copper-impregnated iron catalysts

Fe-Cu catalysts were applied in the production of high-calorie synthetic natural gas (HC-SNG), wherein a proper level of C₂–C₄ hydrocarbon selectivity must be secured. The Fe-Cu catalysts were activated by reduction under diluted CO gas before the reaction, and their catalytically active Fe phases changed according to the reduction temperature: Fe₃O₄ formed when reduced at 300 °C, carbon-deficient FeC_x at 400 °C and Fe₃C at 500 °C. Iron carbide catalysts achieved stronger CO adsorption and higher BET surface area than Fe₃O₄ catalysts, which resulted in higher CO conversion. The carbon-deficient FeC_x was metal-like in its electron structure due to the low number of bonded carbons, and it was attributed to the highest CO and H₂ conversion of FC15-400R by providing H₂ activation ability. The C_n (n ≥ 2) selectivity or carbon chain growth of the hydrocarbons increased as the carburization degree of the active Fe phase increased, which was associated with an increase in the CO chemisorption strength. The impregnated Cu exerted little influence on the product selectivity, but it promoted hydrogen adsorption, thereby improving the paraffin-to-olefin ratio of the produced hydrocarbons.