A computational study of K promotion of CO dissociation on Hägg carbide

Abstract

The dissociation of CO is a critical step in producing long-chain hydrocarbons in the Fischer–Tropsch (FT) synthesis reaction. Although potassium (K) is known to enhance CO conversion and the selectivity to olefins of Fe-carbide FT catalysts, its precise mechanistic role remains unclear. In this work, we used density functional theory to show that K₂O facilitates C–O bond dissociation in CO, HCO, and COH by increasing the electron density of the Fe surface atoms of Hägg carbide (χ-Fe₅C₂) that bind these surface intermediates. This leads to a higher electron density in anti-bonding orbitals and enhanced electron–electron repulsion between the bonding orbitals of the CO, COH, and HCO intermediates and the Fe atoms. Effective promotion of C–O bond dissociation requires K to be adjacent to the active site on the χ-Fe₅C₂ surface.