Effects of surface groups on Fe/ZnO catalysts for CO2 hydrogenation to olefin

Abstract

Control of product distribution over CO2-FTO is challenging due to the difficulty in governing the C–C coupling of CHx species. Surface modification to iron catalysts shows potential but its role remains indistinct. Fe/ZnO was used as a model catalyst to investigate the effects of the surface groups on its catalytic performance for CO2-FTO. On hydroxyl group modified Fe/ZnO by H2O2-treatment, at 1000 h–1, 300 °C, and 1 MPa, the CO2 conversion, and the C4+ linear α-olefin selectivity rose to 50.2 % and 48.1 %, respectively. Alkyl group modified Fe/ZnO by stearic acid treatment exhibited higher activity (48.4 %) and the C2=–C3= selectivity (31.0 %). Characterizations showed that decorating the hydroxyl group boosted the formation of Fe5C2 and CHx species, promoting the chain growth for long-chain olefin, whereas the alkyl group modification retarded the activity decline through stabilizing active FeCx phases and forming graphite carbon which was conducive to suppressing secondary hydrogenation.