Uncovering the Mechanism of the Hydrogen Poisoning on Ru Nanoparticles via Density Functional Theory Calculations

Abstract

Although hydrogen plays a crucial role in ammonia synthesis, very little is known about its poisoning of Ru catalysts. In this study, density functional theory calculations of H2 and N2 dissociations, and H atom binding on Ru153 were performed to provide a fundamental understanding of hydrogen poisoning. Because of the kinetic dominance of the H2 dissociation over N2 (vertically or horizontally adsorbed) splitting, the dissociated H atoms block the active sites required for horizontal (less energetically demanding dissociation) N2 adsorption to occur either from the gas phase or after its geometrical transformation from being adsorbed vertically. Additionally, the dissociated H atoms withdraw electrons from the surface, which reduces the ability of the neighboring Ru atoms to donate electrons for N2 activation, hindering its dissociation and suppressing ammonia synthesis.