Fe-Zn catalysts for the production of high-calorie synthetic natural gas

Abstract In this study, Fe-Zn catalysts were applied in a methanation reaction, where the C₂-C₄ hydrocarbon selectivity was controlled in order to increase the heating value of the synthetic gas product. Fe-Zn catalysts were prepared by the co-precipitation method and were activated via two different pretreatments: carburization (using synthesis gas) and reduction (using diluted hydrogen). The active species within the carburized Fe-Zn catalysts primarily consisted of iron carbides, while magnetite was the dominant species in the reduced Fe-Zn catalysts. The carburized Fe-Zn catalysts exhibited a higher CO conversion between 95.9% and 98.2% compared to the reduced Fe-Zn catalysts with same composition (81.7-89.9%) due to stronger interactions with CO and a higher BET area. The carbon chain growth on both catalysts was nearly identical (0.18-0.23), but reduced Fe-Zn catalysts exhibited higher paraffin-to-olefin ratio up to 4.30, while the carburized catalysts achieved relatively low ratio between 1.95 and 2.76, because magnetite was more efficient in olefin hydrogenation than the iron carbides. The carburized and reduced Fe-Zn catalysts produced high-calorie synthetic natural gas with a heating value of over 56 MJ/Nm³.