DFT Investigation on the Competition of the Water-Gas Shift Reaction Versus Methanation on Clean and Potassium-Modified Nickel(111) Surfaces

We used periodic DFT calculations to investigate the effect of alkali promoter on the selectivity of the water-gas shift reaction (WGSR) explicitly on the Ni(111) surface. On clean Ni(111), the WGSR redox and carboxyl pathways are both kinetically competitive. The selectivity of the WGSR can be affected by methanation on Ni, in which the C-O bond cleavage pathway of CHO is the most competitive. A Ni(111) surface modified with K adatoms was used to further understand the promoter effects on the WGSR selectivity. A combined energetic and kinetic analysis from DFT calculations indicates that the K adatom stabilizes certain reactive intermediates (e.g., H2O, CO) thermodynamically but is energetically neutral or even repulsive toward other intermediates. As a result, WGSR pathways benefit from the presence of K adatoms compared to the competing methanation pathway. This study thus confirmed the promoting effects of alkali metals on the WGSR with DFT-based mechanistic insights.