Unraveling the Structural Dynamics in Ammonia Synthesis over the Strontium Fluoride-Supported Ruthenium Catalyst

The catalytic synthesis of ammonia (NH3) is a cornerstone of the chemical industry. However, to date, direct visualization of the reactant-support interaction and the structural dynamics of catalyst surface/interfaces during efficient NH3 synthesis remain scarce. Herein, this article elucidates the dynamic structural evolution of a previously unreported catalyst Ru/SrF2 by utilizing multiple in situ techniques. The in situ environmental transmission electron microscopy technique not only visualizes the N2/H2 exposure-induced reversible surface rearrangement of SrF2 from (100) to (111) with lamellar nanostructures but also unravels the reaction-driven cyclic reconstruction of the Ru/SrF2 surface-interface under the N2-H2 mixture. The catalytically-active sites are identified mainly as the fluorine vacancy (VF)-centered Ru0-VF-Srγ+ perimeter sites. These sites are abundantly generated due to the recurring surface-interface reconstruction over Ru/SrF2 and underlie the catalyst's exceptional performance under mild conditions. This work may inspire more advanced operando studies for understanding catalytic mechanisms and developing practical catalysts.