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 and disordering induced by adsorbed CO and H ₂ . In a hydrogenated state, theoretical models have predicted not only the reshaping of Pt nanoparticles, but also their shift away from the surface of their metal oxide support. In this work we examined the dynamic 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 direct experimental evidence of the simultaneous “breathing” of the Pt nanoparticles and their detachment from the Al ₂ O ₃ support under H ₂ atmosphere. These dynamic structural changes are shown to be size-dependent, to occur in both gas phase (150°C) and liquid phase (cyclohexane, 70°C), and to be reversible, thus ensuring the stability of the catalyst under hydrogenation conditions. Gaining direct structural evidence of the ductile behavior of supported metal nanoparticles in reactive chemical environments is a groundbreaking step towards precise structural control of catalysts under reaction conditions.