A Systematic Theoretical Study of Water Gas Shift Reaction on Cu(111) and Cu(110): Potassium Effect

• Published in: ACS catalysis 2019-03, Vol.9 (3), p.2261-2274
• Main Authors: Wang, Yan-Xin, Wang, Gui-Chang
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.8b04427

It is crucial to probe the effect of the alkali metal additives on the forward and reverse water–gas shift reaction (WGSR and RWGSR). Density functional theory (DFT) calculations were performed to investigate the reaction mechanism and activity of WGSR on clean and K-modified Cu(111) and Cu(110) surfaces. The calculation results indicate that the K adatom greatly stabilizes the adsorption of all oxygenate intermediates but rarely affects the binding strength of other species (e.g., H, H2). More importantly, it is found that the K adatom can improve the reactivity of WGSR and RWGSR on Cu catalysts by favoring their rate-limiting steps of H2O and CO2 dissociation and reducing the apparent activation energy of the whole reaction. On the basis of energetic and electronic analysis, the promoting effect of K on H2O and CO2 dissociation can be attributed to the direct bonding forming between the atomic K and O of oxygenate species at the TSs, and more, stronger K–O bonding on Cu(111) than on Cu(110) contributes to the stronger promoting effect of K on WGSR and RWGSR on the (111) surface. The effects of other alkali metals (Na, Rb, and Cs) on H2O and CO2 dissociation were also explored, and the different promoting effects are due to different electronegativities of alkali metals, which induce different work function changes and surface dipole moments; the lower the work function or the higher the surface dipole moment, the stronger the promoting effect of alkali metal.