Abstract: Production of light olefins from CO₂, the primary greenhouse gases, is of great importance to mitigate the adverse effects of CO₂ emission on environment and to supply the value-added products from non-petroleum resource. However, development of robust catalyst with controllable selectivity and stability remains a challenge. Herein, we report that Zn-promoted Fe catalyst can boost the stable and selective production of light olefins from CO₂. Specifically, the Zn-promoted Fe exhibits a highly stable activity and olefin selectivity over 200 h time-on-stream compared to the unpromoted Fe catalyst, primarily owing to the preservation of active χ-Fe₅C₂ phase. Structural characterizations of the spent catalysts suggest that Zn substantially regulates the content of iron carbide on the surface and suppresses the re-oxidation of bulk iron carbide during the reaction. DFT calculations confirm that adsorption of surface carbon atoms and graphene-like carbonaceous species are not thermochemically favored on Zn-promoted Fe catalyst. Carbon deposition by C-C coupling reactions of two surface carbon atoms and dehydrogenation of CH intermediate are also inhibited. Furthermore, the effects of Zn on antioxidation of iron carbide were also investigated. Zn favored the hydrogenation of surface adsorbed oxygen atoms to H₂O and the desorption of H₂O, which reduces the possibility of surface carbide being oxidized by the chemisorbed oxygen.

Key words: Reaction engineering, χ-Fe₅C₂, Zn promoter, Carbon dioxide, Hydrogenation, Density function theory

摘要： Production of light olefins from CO₂, the primary greenhouse gases, is of great importance to mitigate the adverse effects of CO₂ emission on environment and to supply the value-added products from non-petroleum resource. However, development of robust catalyst with controllable selectivity and stability remains a challenge. Herein, we report that Zn-promoted Fe catalyst can boost the stable and selective production of light olefins from CO₂. Specifically, the Zn-promoted Fe exhibits a highly stable activity and olefin selectivity over 200 h time-on-stream compared to the unpromoted Fe catalyst, primarily owing to the preservation of active χ-Fe₅C₂ phase. Structural characterizations of the spent catalysts suggest that Zn substantially regulates the content of iron carbide on the surface and suppresses the re-oxidation of bulk iron carbide during the reaction. DFT calculations confirm that adsorption of surface carbon atoms and graphene-like carbonaceous species are not thermochemically favored on Zn-promoted Fe catalyst. Carbon deposition by C-C coupling reactions of two surface carbon atoms and dehydrogenation of CH intermediate are also inhibited. Furthermore, the effects of Zn on antioxidation of iron carbide were also investigated. Zn favored the hydrogenation of surface adsorbed oxygen atoms to H₂O and the desorption of H₂O, which reduces the possibility of surface carbide being oxidized by the chemisorbed oxygen.

关键词: Reaction engineering, χ-Fe₅C₂, Zn promoter, Carbon dioxide, Hydrogenation, Density function theory