Catalytic consequences of the decoration of sodium and zinc atoms during CO2 hydrogenation to olefins over iron-based catalyst

This study unravels the effects of Na decoration and/or ZnO addition on the structures of Fe based catalysts, and the reaction pathways and the rate dependencies on both the composition of reactants and reaction temperature for CO2 hydrogenation to olefins, using kinetics and structure characterization by Raman spectroscopy, X-ray diffraction, and temperature-programmed CO reduction techniques. CO2 hydrogenation over Fe based catalysts occurs as a combination of the primary reverse water-gas-shift reaction to form CO and the subsequent CO hydrogenations to produce olefins and paraffins. Adding ZnO into Fe catalysts enhanced the rates of CO2 hydrogenation to all carbon containing products because ZnO facilitated the generation of iron carbide, as an active phase in Fe based catalysts, however, the relative rates among primary RWGS reactions, secondary CO hydrogenation to olefins and to paraffins were insensitive to the addition of Zn. Decoration of Na into Fe catalysts altered significantly the rate dependencies on both reactants and reaction temperature for olefins formation, which might be the results of the modification of the reducibility and surface identities of Fe catalysts by Na atoms, thus changed the rate ratios of paraffins and olefins. As results of decoration of Na and addition of Zn, the modified Fe based catalyst exhibits optimal performance for CO2 hydrogenation to olefins, which shows a CO2 conversion of 43 % with a selectivity of 54.1 % to high olefins, and a high olefins-to-paraffins ratio of 7.3.