Water-Gas Shift Reaction over Au(111): The Effect of Potassium from a First-Principles-Based Microkinetic Model Analysis

The water-gas shift reaction over Au(111) and K/Au(111) was studied by density functional theory combined with mean-field microkinetic modeling to explore the effect of the potassium promoter on the catalytic activity. It was shown that the addition of the K adatom can enhance the adsorption strength of oxygen-containing species such as H2O and COOH*(HCOO*) through the Coulomb interaction and thus promote the water dissociation (H2O*-* OH* + H*), leading to higher catalytic activity. Importantly, the high promotion effect of K can be attributed to the strong direct space interaction between K and the adsorbate through the induced electric field and thus can stabilize the transition states of water dissociation. By comparison with other alkali atoms, the water adsorption strength becomes weaker from Li to Cs, but the alkali additive promotion effect follows the order Na > K > Li > Rb approximate to Cs, and sodium is the best promoter due to its moderate stabilization for water adsorption. By examining the effect of the potassium loading (at 1/9 to 4/9 ML potassium coverage) on the catalytic properties, it was shown that 2/9 ML potassium coverage displays the strongest adsorption behavior of the water molecule and thus has the best catalytic activity. Among the different metal catalysts, K promotes H2O dissociation on Au (or Cu) more significantly than on Pt(or Ni), and hence, a higher promotion effect on Au (or Cu) might be observed as compared to that of Pt (or Ni). Microkinetic model analysis indicated that the carboxyl mechanism is the dominant mechanism of the whole reaction processes, followed by the redox mechanism and formate mechanism. It is hoped that the present work may extend to other water-gas shift reaction catalysts including Au catalysts with a lower coordination number like corner atoms or reduced metal oxide-supported Au clusters.

Automated summary

The effect of potassium promoter on the water-gas shift reaction over Au(111) and K/Au(111) was studied. It was found that the addition of potassium can enhance the adsorption strength of oxygen-containing species, leading to higher catalytic activity. Among different metal catalysts, sodium is the best promoter. The microkinetic model analysis indicated that the carboxyl mechanism is the dominant mechanism of the whole reaction processes.