Hydroxyl Group Modification Improves the Selectivity of Metal Single Atom on Poly(Heptazine Imide) for Electrocatalytic Acetylene Semi-Hydrogenation

Abstract

Electrocatalytic semi-hydrogenation of acetylene to ethylene has recently attracted attention as a process for removing acetylene from ethylene-rich gas streams due to its mild conditions and energy-saving advantages. However, developing catalysts with low cost and high selectivity for acetylene semi-hydrogenation remains a huge challenge. In this work, we investigated the selectivity of acetylene semi-hydrogenation with or without hydroxyl group modified metal single atom catalyst supported by poly(heptazine imide) (PHI) through density functional theory calculations. The results show that the hydroxyl group as ligand not only increases the steric resistance of acetylene adsorption, but also acted as electron-withdrawing group, which makes the metal atoms present a higher oxidation state. Thus the adsorption of acetylene and its subsequent intermediates was weakened, facilitating the desorption of ethylene and avoiding over-hydrogenation. The Ni-OH/PHI and Fe-2OH/PHI are capable of achieving the selective hydrogenation of acetylene to ethylene and have good thermodynamic stability, which can be used as ideal catalysts for the electrocatalytic semi-hydrogenation of acetylene to selectively generate ethylene. This study provides theoretical guidance for the rational design of electrocatalysts for the selective semi-hydrogenation of acetylene.

Keywords: metal single atom, Poly(heptazine imide), acetylene semi-hydrogenation, hydroxyl group, density functional theory calculations