Potassium(K)is known to enhance the catalytic performance of Fe-based catalysts in the reverse water-gas shift(rWGS)reaction,which is highly relevant during Fischer-Tropsch(FT)synthesis of CO_(2)-H_(2) mixtures.To elu...Potassium(K)is known to enhance the catalytic performance of Fe-based catalysts in the reverse water-gas shift(rWGS)reaction,which is highly relevant during Fischer-Tropsch(FT)synthesis of CO_(2)-H_(2) mixtures.To elucidate the mechanistic role of K promoter,we employed density functional theory(DFT)calculations in conjunction with microkinetic modelling for two representative surface terminations of Hägg carbide(χ-Fe_(5)C_(2)),i.e.,(010)and(510).K_(2)O results in stronger adsorption of CO_(2)and H_(2) on Hägg carbide and promotes C–O bond dissociation of adsorbed CO_(2)by increasing the electron density on Fe atoms close to the promoter oxide.The increased electron density of the surface Fe atoms results in an increased electron-electron repulsion with bonding orbitals of adsorbed CO_(2).Microkinetics simulations predict that K_(2)O increases the CO_(2)conversion during CO_(2)-FT synthesis.K_(2)O also enhances CO adsorption and dissociation,facilitating the formation of methane,used here as a proxy for hydrocarbons formation during CO_(2)-FT synthesis.CO dissociation and O removal via H_(2)O compete as the rate-controlling steps in CO_(2)-FT.展开更多
文摘Potassium(K)is known to enhance the catalytic performance of Fe-based catalysts in the reverse water-gas shift(rWGS)reaction,which is highly relevant during Fischer-Tropsch(FT)synthesis of CO_(2)-H_(2) mixtures.To elucidate the mechanistic role of K promoter,we employed density functional theory(DFT)calculations in conjunction with microkinetic modelling for two representative surface terminations of Hägg carbide(χ-Fe_(5)C_(2)),i.e.,(010)and(510).K_(2)O results in stronger adsorption of CO_(2)and H_(2) on Hägg carbide and promotes C–O bond dissociation of adsorbed CO_(2)by increasing the electron density on Fe atoms close to the promoter oxide.The increased electron density of the surface Fe atoms results in an increased electron-electron repulsion with bonding orbitals of adsorbed CO_(2).Microkinetics simulations predict that K_(2)O increases the CO_(2)conversion during CO_(2)-FT synthesis.K_(2)O also enhances CO adsorption and dissociation,facilitating the formation of methane,used here as a proxy for hydrocarbons formation during CO_(2)-FT synthesis.CO dissociation and O removal via H_(2)O compete as the rate-controlling steps in CO_(2)-FT.
