Reactant-driven structural and chemical dynamics of Fe clusters for promoting hydrocarbon formation over a Na/FeZn catalyst

Abstract

This study unravels gas-driven structural and chemical dynamics of Fe clusters in a Fe-Zn catalyst during the hydrogenation of CO₂, using kinetics, chemical titration, and in-situ spectroscopic characterizations. The gas-driven dynamics of iron clusters lead to a promotion in formation rates of C₂₊ hydrocarbons and C₂₊ olefins by almost one magnitude, in response to the changes in reactants. These rates are single-valued functions of the ${{\mathrm{P}}_{\mathrm{C}\mathrm{O}}}^2/{\mathrm{P}}_{{\mathrm{C}\mathrm{O}}_2}$ ratio which determines the carbon chemical potential at the catalyst surface and influences the thermodynamic tendency for carbon deposition and carbonization of iron species. As the ratio increases, both the quantities of carbon species and iron carbides rise, however, crystalline graphite grows faster and covers part of iron carbide species at higher ${{\mathrm{P}}_{\mathrm{C}\mathrm{O}}}^2/{\mathrm{P}}_{{\mathrm{C}\mathrm{O}}_2}$ ratios. These gas-driven structural dynamics allow the maximum formation of exposed iron carbide species for the formation of C₂₊ hydrocarbons and result in a volcano-type relationship between these formation rates and the ${{\mathrm{P}}_{\mathrm{C}\mathrm{O}}}^2/{\mathrm{P}}_{{\mathrm{C}\mathrm{O}}_2}$ ratio.