CO₂ Hydrogenation over Unsupported Fe-Co Nanoalloy Catalysts

The thermo-catalytic synthesis of hydrocarbons from CO₂ and H₂ is of great interest for the conversion of CO₂ into valuable chemicals and fuels. In this work, we aim to contribute to the fundamental understanding of the effect of alloying on the reaction yield and selectivity to a specific product. For this purpose, Fe-Co alloy nanoparticles (nanoalloys) with 30, 50 and 76 wt% Co content are synthesized via the Inert Gas Condensation method. The nanoalloys show a uniform composition and a size distribution between 10 and 25 nm, determined by means of X-ray diffraction and electron microscopy. The catalytic activity for CO₂ hydrogenation is investigated in a plug flow reactor coupled with a mass spectrometer, carrying out the reaction as a function of temperature (393-823 K) at ambient pressure. The Fe-Co nanoalloys prove to be more active and more selective to CO than elemental Fe and Co nanoparticles prepared by the same method. Furthermore, the Fe-Co nanoalloys catalyze the formation of C₂-C₅ hydrocarbon products, while Co and Fe nanoparticles yield only CH₄ and CO, respectively. We explain this synergistic effect by the simultaneous variation in CO₂ binding energy and decomposition barrier as the Fe/Co ratio in the nanoalloy changes. With increasing Fe content, increased activation temperatures for the formation of CH₄ (from 440 K to 560 K) and C₂-C₅ hydrocarbons (from 460 K to 560 K) are observed.