Reshaping Dynamics of Gold Nanoparticles under H2 and O2 at Atmospheric Pressure

Despite intensive research efforts, the nature of the active sites for O-2 and H-2 adsorption/dissociation by supported gold nanoparticles (NPs) is still an unresolved issue in heterogeneous catalysis. This stems from the absence of a clear picture of the structural evolution of Au NPs at near reaction conditions, i.e., at high pressures and high temperatures. We hereby report real-space observations of the equilibrium shapes of titania-supported Au NPs under O-2 and H-2 at atmospheric pressure using gas transmission electron microscopy. In situ TEM observations show instantaneous changes in the equilibrium shape of Au NPs during cooling under O-2 from 400 degrees C to room temperature. In comparison, no instant change in equilibrium shape is observed under a H-2 environment. To interpret these experimental observations, the equilibrium shape of Au NPs under O-2 atomic oxygen, and H-2 is predicted using a multiscale structure reconstruction model. Excellent agreement between TEM observations and theoretical modeling of Au NPs under O-2 provides strong evidence for the molecular adsorption of oxygen on the Au NPs below 120 degrees C on specific Au facets, which are identified in this work. In the case of H-2, theoretical modeling predicts no interaction with gold atoms that explain their high morphological stability under this gas. This work provides atomic structural information for the fundamental understanding of the O-2 and H-2 adsorption properties of Au NPs under real working conditions and shows a way to identify the active sites of heterogeneous nanocatalysts under reaction conditions by monitoring the structure reconstruction.