Imaging N <sub>2</sub>-K, a Haber-Bosch Catalysis Precursor, at the Atomic Scale

Abstract

The low ionization potentials make alkali atoms obliging electron donors in reduction chemistry in important industrial chemical processes, where they act as cocatalysts. Interaction between potassium atoms and nitrogen molecules co-adsorbed on metal surfaces is of interest as a model of catalytic promotion of dissociation of a reluctant precursor, N2, which is considered to be the rate-limiting step in the Haber-Bosch ammonia synthesis. Although the atomic scale insight into the co-adsorption of K and N2 on metals is fundamentally important for understanding the alkali promotion chemistry, the high mobility of K atoms, the weak chemisorption of N2, and the extreme pressure and temperature conditions in the Haber-Bosch process obstruct investigation of their interactions at the atomic scale. By scanning tunneling microscopy and density functional theory, here we characterize the N2 adsorption, collective interactions, and tunneling electron-induced desorption on K/Ag(111) surface. Our study reveals the fundamental collective interactions of alkali promoters with the N2 molecular feedstock of consequence to heterogeneous catalysis.