Optimization of activity and selectivity for syngas-to-ethanol conversion on metal-based catalysts via the first-principles microkinetic simulations

Abstract

Achieving high selectivity in converting syngas to ethanol has long been a challenging task, requiring identification of key factors favoring ethanol production over other by-products such as methane, methanol, and acetaldehyde. Herein, we perform systematic density functional theory (DFT) calculations and microkinetic simulations to shed light on the activity and selectivity trends of ethanol relative to three competing by-products in syngas conversion, which quantitatively unveils the key determining factors on the transition metal-based catalysts. The scaling relations involved are revealed as functions of the adsorption energies of C and O species (EC and EO), and the three-dimensional activity and selectivity surfaces are constructed quantitatively, indicating that the optimal condition (peak position) correspond to EC = -6.10 eV and EO = -5.70 eV. Furthermore, we find that ethanol activity at the peak is primarily constrained by the kinetic barriers of CH3O dissociation and the coupling reaction of CH3 and CO, while its selectivity can be enhanced by increasing the energy barrier of CH3 hydrogenation and strengthening the adsorption of CH3CHO. More significantly, following these rules, the single-atom metal alloy catalysts (i.e., Cu1Co, Cu1Ni) are identified that could serve as promising candidates for ethanol synthesis, which are superior to the common alloy-type catalysts. We believe that these insights further deepen the understanding of theoretical design of metal alloy catalysts in ethanol production.