Pt nanoparticles breathe and reversibly detach from Al₂O₃ in hydrogen

The dynamic behavior of supported metal nanoparticles under reaction conditions is a key factor in their catalytic performance. Pt nanoparticles are particularly susceptible to structural relaxation induced by adsorbed CO and H₂. In a hydrogenated state, theoretical models predict the reshaping of Pt nanoparticles, but also their shift away from the support. Here, we examine the dynamic structural behavior of well-dispersed 1-3 nm diameter Pt nanoparticles under hydrogenation conditions. Using time-resolved X-ray diffraction and pair distribution function analysis allied to a modulated excitation approach, we provide experimental evidence of the simultaneous "breathing" of the Pt nanoparticles and their detachment from the Al₂O₃ support under H₂. These effects appear size-dependent, reversible, and occur in both gas-phase (150 °C) and liquid-phase (cyclohexane, 70 °C) conditions. Achieving direct evidence of the behavior of supported metal nanoparticles towards structural deformation in reactive chemical environments is a groundbreaking step towards precise structural control of catalysts under reaction conditions.