Water-Gas Shift Reaction on K/Cu(111) and Cu/K/TiO2(110) Surfaces: Alkali Promotion of Water Dissociation and Production of H2

Abstract

The addition of potassium atoms to Cu(111) and Cu/TiO2(110) surfaces substantially enhances the rate for water dissociation and the production of hydrogen through the water-gas shift reaction (WGS, CO + H2O → H2 + CO2). In the range of temperatures investigated, 550-625 K, Cu/K/TiO2(110) exhibits a WGS activity substantially higher than those of K/Cu(111), Cu(111), and Cu/ZnO(0001̄) systems used to model an industrial Cu/ZnO catalyst. The apparent activation energy for the WGS drops from 18 Kcal/mol on Cu(111) to 12 Kcal/mol on K/Cu(111) and 6 Kcal/mol on Cu/K/TiO2(110). The results of density functional calculations show that K adatoms favor the thermochemistry for water dissociation on Cu(111) and Cu/TiO2(110) with the cleavage of an O-H bond occurring at room temperature. Furthermore, at the Cu/K/TiO2 interface, there is a synergy, and this system has a unique ability to dissociate the water molecule and catalyze hydrogen production through the WGS process. Therefore, when optimizing a regular catalyst, it is essential to consider mainly the effects of an alkali promoter on the metal-oxide interface.