Understanding the Role of Potassium Addition on the Active Centers and Reaction Pathway of MoS2 Catalysts for Water Gas Shift Reaction

MoS2 is a promising sulfur-resistant candidate for water-gas shift (WGS) reaction, and its catalytic efficiency can be promoted by alkali metal. In this work, a series of K-modified MoS2/Al2O3 catalysts with variable K/Mo ratios were prepared to elucidate the promotion role of potassium through IR spectroscopy studies. CO adsorption followed by IR spectroscopy shows that after potassium addition the number of accessible edge sites of MoS2 slabs is decreased. Meanwhile, the downward shift of v(CO/MoS2) indicates that the presence of potassium increases the electronic density of Mo atoms. This electronic effect activates terminal S atoms, favoring their reaction with CO to form COS at lower temperature than in absence of K. Additionally, conversely to the case of MoS2/Al2O3 catalysts, little or even no formate species are observed on K-modified MoS2 catalysts during IR operando studies, implying a change of the WGS reaction route that would explain the beneficial effect of K on MoS2 edge site activity.