Enhancing CO2 hydrogenation to light olefins over Fe-Zr catalysts derived from MOF-808: Effect of thermal treatment conditions

The utilization of metal-organic frameworks (MOF) as a precursor for the synthesis of Fe-based catalysts for CO 2 hydrogenation has currently received significant attention due to the inherent benefits associated with the formation of highly dispersed iron nanoparticles. In this study, a series of Fe-Zr catalysts derived from the Zr-based MOF (MOF-808) for CO 2 hydrogenation to light olefins was synthesized without and with K promotion and thermally treated under various conditions through calcination or pyrolysis processes. The physicochemical properties and catalytic performance of the catalysts were comprehensively assessed, revealing the distinct behaviors of calcined and pyrolyzed ones. The calcined catalysts exhibited an increased adsorption of CO 2 and a decreased affinity for H 2 at elevated temperatures, leading to an enhanced selectivity to CO concomitantly with a decrease in CH 4 selectivity. Meanwhile, the pyrolyzed catalysts displayed the opposite trend, which outperformed the calcined ones because the cohabitation of carbon and ZrO 2 facilitated the formation of iron carbide and oxygen vacancy sites. This consequently promoted the adsorption of CO 2 and inhibited the dissociation of H 2 , thereby leading to an increased conversion of CO 2 to olefins. In addition, density functional theory-based calculations confirmed the positive effect of doping carbon onto the ZrO 2 surface on the oxygen vacancy formation, resulting in an increasing number of active sites available for CO 2 adsorption and activation. The pyrolyzed K-promoted Fe-Zr catalyst with 60 % Fe loading exhibited outstanding light olefin yields, compared with state-of-the-art catalysts at similar GHSV ranges, highlighting its potential for advanced CO 2 hydrogenation applications. • K-promoted Fe-Zr catalysts were synthesized from MOF-808 for CO 2 hydrogenation. • The pyrolyzed catalysts with active carbon species outperformed the calcined ones. • The pyrolyzed one had higher light olefin yield than the state-of-the-art catalysts. • DFT calculations emphasized enhanced CO 2 adsorption by carbon-doped active sites.