The promotional effects of carbon nanotube on Fe5C2-ZnO catalysts for CO2 hydrogenation to heavy olefins

The multi-walled carbon nanotubes (MWNTs) supported Fe-based catalysts, including FeZnNa/MWNTs, FeZnK/MWNTs, and FeZnRb/MWNTs were synthesized through co-precipitation, and incipient wetness impregnation approaches. The physicochemical results demonstrated that the addition of MWNTs had significantly influenced the morphology, reduction, phase structure, adsorption behavior of Fe-based catalysts, and consequently, the reactivity of CO2 hydrogenation to olefins. Furthermore, adding MWNTs to the alkali metal-promoted FeZn catalysts inhibits the synthesis of CH4 and CO and favors an improved selectivity for olefins. With the incorporation of MWNTs, the heavy olefins (C5-C8=) selectivity over FeZnNa, FeZnK, and FeZnRb catalysts increased from 27.1 to 32.2, 27.0–31.1, and 24.2–28.6 %, respectively. The results proved that the superior selectivity of heavy olefin over the MWNTs-supported catalysts might be accomplished by the electron-donating ability of the MWNTs surface, the presence of extra Hägg carbide, and higher adsorption strength with light olefins. In addition, the catalyst supported by MWNTs demonstrated exceptional stability throughout the 100-hour test at 593 K.