Effects of zinc on χ-Fe5C2 for carbon dioxide hydrogenation to olefins: Insights from experimental and density function theory calculations

Abstract

Production of light olefins from CO 2 , the primary greenhouse gases, is of great importance to mitigate the adverse effects of CO 2 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 CO 2 . 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-Fe 5 C 2 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 H 2 O and the desorption of H 2 O, which reduces the possibility of surface carbide being oxidized by the chemisorbed oxygen.