DFT Investigation on the Competition of the Water–Gas Shift Reaction Versus Methanation on Clean and Potassium‐Modified Nickel(1 1 1) 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(1 1 1) surface. On clean Ni(1 1 1), 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(1 1 1) 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., H 2 O, 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.