Unraveling Strain Effects on Ammonia Synthesis over Ruthenium Catalysts via Density Functional Theory and Microkinetic Analysis

Strain engineering has emerged as a promising strategy for tuning heterogeneous catalyst performance, yet its specific influence on ammonia synthesis over ruthenium remains unclear due to concurrent support-induced effects. Here, density functional theory calculations combined with mean-field microkinetic modeling are used to examine the impact of ±5% biaxial strain on terrace Ru(0001) and stepped Ru(101̅0) surfaces. Tensile strain strengthens adsorption while compressive strain weakens it, with these trends governed by systematic shifts in d-band width. Because the stepped surface relaxes more readily, strain produces smaller energetic changes on Ru(101̅0) than on Ru(0001). Activation barriers follow Brønsted–Evans–Polanyi relationships: tensile strain lowers the barriers for N2 and H2 dissociation but raises those for NHx hydrogenation. Microkinetic analysis shows that N2 dissociation remains rate limiting on Ru(0001), whereas the RDS on Ru(101̅0) varies between NH2 hydrogenation and N2 dissociation depending on reaction conditions, leading to opposite TOF responses to strain across the two facets. When combined to represent a realistic 2– 4 nm Ru nanoparticle, overall activity follows the order pristine > tensile > compressive, indicating that unstrained surfaces yield the highest ammonia production. These results clarify how strain modifies reaction energetics and kinetics on Ru catalysts and provide a quantitative basis for evaluating strain engineering in ammonia synthesis.