Dynamic structural changes of ensemble and single supported Pt particles during ammonia oxidation

Platinum and its alloys remain the state-of-the-art catalysts for selective nitric oxide production via ammonia oxidation. Yet improving efficiency, selectivity, and stability is a century-old challenge. Operando diffraction techniques are combined with mass spectrometry to investigate structural dynamics of ensemble and single α -Al 2 O 3 -supported Pt crystalline particles under realistic reaction conditions. Only by switching from ensemble averaging methods such as surface X-ray diffraction to single-particle sensitive Bragg coherent diffraction imaging can we identify distinct strain and morphology responses between particle types. Large and elongated particles exhibit annealing-induced misfit strain and a stable morphology during the reaction, while smaller, round, and low-strain particles display surface roughening and defect evolution at 400 °C, coinciding with enhanced NO selectivity. Notably, NH 3 exposure at 600 °C reverses facet strain. These findings highlight the critical role of nanoscale strain and morphology in catalyst performance and demonstrate the power of multi-techniques operando approaches to guide the design of next-generation catalytic materials. • Operando BCDI tracks strain evolution in single Pt nanoparticles during NH 3 oxidation. • Oxygen-rich and ammonia-rich regimes induce distinct defect and strain behaviors. • Structural response varies across particles, highlighting heterogeneity. • Strain in Pt nanoparticles evolve during NH 3 exposure at 600 °C. • Defect formation correlates with catalytic selectivity between NO and N 2 .