CO(2) Hydrogenation over Unsupported Fe-Co Nanoalloy Catalysts

The thermo-catalytic synthesis of hydrocarbons from CO(2) and H(2) is of great interest for the conversion of CO(2) 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 CO(2) 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 C(2)-C(5) hydrocarbon products, while Co and Fe nanoparticles yield only CH(4) and CO, respectively. We explain this synergistic effect by the simultaneous variation in CO(2) 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 CH(4) (from 440 K to 560 K) and C(2)-C(5) hydrocarbons (from 460 K to 560 K) are observed.