A Curvature-Induced Pentagonal Oxide Motif Governs Ethylene Epoxidation Selectivity on Silver Nanoparticles

Silver-catalyzed ethylene epoxidation is a cornerstone of the chemical industry, yet the operando surface structure of Ag nanoparticles and the identity of selectivity-governing active sites remain elusive. Here, we integrate machine learning potentials, stochastic surface walking global optimization, molecular dynamics simulation, and statistical analysis to resolve the surface landscape of Ag nanoparticles approaching experimentally relevant sizes under reaction conditions. Oxygen-induced reconstruction transforms pristine Ag facets into a globally amorphous oxide layer composed of three types of locally ordered ring motifs interspersed with structural defects. A pentagonal motif (ring5), topologically required to accommodate nanoparticle curvature and absent in conventional slab models, dominates the surface across all investigated particle sizes. Its recessed central Ag atom acts as an electronic charge buffer that weakens the critical C–Ag bond in the oxametallacycle intermediate, conferring high intrinsic ethylene oxide selectivity. Microkinetic analyses confirm that the oxygen species of ring5 regulate ethylene oxide yield, peaking at a nanoparticle oxidation degree of O/Ag ≈ 0.3–0.4. This work establishes a statistical paradigm for decoding active phases on realistic catalyst surfaces through dynamic structural ensembles.