Water dissociation on K2O-pre-adsorbed transition metals: a systematic theoretical study

Abstract

It is imperative to regulate O–H bond cleavage on metal surfaces with a pre-adsorbed K₂O promoter in heterogeneous catalysis. Density functional theory (DFT) calculations have been performed to explore the adsorption and dissociation of water on K₂O-pre-adsorbed transition metal surfaces (Au, Ag, Cu, Ni, Pt, Rh, Ir, Pd, Ru, Co and Fe) as compared with those on clean and K-pre-adsorbed metal surfaces. The calculation results indicate that the presence of K₂O species significantly promotes water dissociation and the promoting effect depends on the adsorption strength of K₂O, namely, the more strongly K₂O binds to the metal surface, the less promoting effect it has on the water O–H bond cleavage. Based on geometrical and electronic analysis, the stronger promoting effect of K₂O than K on water dissociation on the given metal surfaces can be attributed to stronger attractive electrostatic interactions between OH and the dissociating H of H₂O at the TSs as well as between O of H₂O and K of K₂O at the ISs on K₂O-pre-adsorbed surfaces compared with those on K-pre-covered surfaces. Moreover, the additional hydrogen bond interaction between H and O_ad of K₂O at the ISs on Cu/Ag/Au and Fe/Co/Ni metals would be responsible for the much greater promoting effect of K₂O than K on these metal surfaces, while there is a slightly greater promoting effect of K₂O on the remaining metal surfaces. From the above analysis, we expect our studies can provide profound understanding of the nature of the promoting effect of K₂O on O–H bond scission.