Imaging a Haber-Bosch catalysis precursor at the atomic scale

Abstract

The low ionization potentials make alkali atoms obliging electron donors in industrial reduction chemistry as important, general 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, N 2 , which is considered the rate-limiting step in the Haber-Bosch ammonia synthesis. Although the atomic-scale insight into the co-adsorption of K and N 2 on metals is fundamentally important for understanding the alkali promotion chemistry, the high mobility of K atoms, the weak chemisorption of N 2 , and the extreme pressures and temperatures in the Haber-Bosch process obstruct investigation of their atomic-scale interactions. By scanning tunneling microscopy and density functional theory, we characterize the N 2 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 N 2 feedstock of consequence to heterogeneous catalysis. • Electrostatic interactions of K Haber-Bosch co-catalyst with N 2 molecules • STM measurements detect K atom displacement by N 2 adsorption • Collective K-N 2 molecule interactions are evident • DFT theory characterizes the N 2 chemisorption on K/Ag(111) surface The low ionization potentials make alkali atoms obliging electron donors in reduction chemistry in important industrial catalytic processes, such as ammonia synthesis. Zhang et al. investigate the co-adsorption of N 2 molecules and K atoms on Ag(111) surface and their collective interactions by scanning tunneling microscopy and density functional theory.