Chemical and structural properties of Na decorated Fe5C2-ZnO catalysts during hydrogenation of CO2 to linear α-olefins

[Display omitted] •RWGS reaction was chemically equilibrated during CO2 hydrogenation on Fe5C2-ZnO-xNa catalysts.•Decorating Na suppressed the subsequent hydrogenation route for forming paraffins.•Phase oxidation of iron carbides was inhibited by adding Na during CO2 hydrogenation.•More CH* species existed during CO2 hydrogenation on Fe5C2-ZnO-xNa catalysts decorated with Na. This work unravels the chemical and structural properties of Fe5C2-ZnO catalysts decorated with sodium (Na) during CO2 hydrogenation to linear α-olefins, determined by rate assessments and series of in-situ characterizations. Reaction network remains as a combination of reverse water-gas-shift (RWGS) and CO hydrogenation, but their relative contributions vary. The RWGS reaction is chemically equilibrated, thus CO2 conversion is determined solely by the thermodynamic constraint. However, Na addition alleviates the formation rates of paraffins from the subsequent CO hydrogenation and reactions of olefins with hydrogen. Na additive does not alter the structures of Fe5C2-ZnO, but improves largely the stability of Fe5C2 by preventing the phase oxidation during the reaction. Na modifies the surface properties of catalyst, thus facilitates reaction of CO* and H* and the CC bond formation. The dual role of Na leads more effective olefins turnovers and provides new insights to the design of novel catalysts for CO2 utilization.