Subnanometer Tracking of the Oxidation State on Co₃O₄ Nanoparticles by Identical Location Imaging and Spectroscopy

Understanding a catalytic reaction requires tools that elucidate the structure of the catalyst surface and subsurface, ideally at atomic resolution and under reaction conditions. Operando electron microscopy meets this requirement in some cases, but fails in others where the required reaction conditions cannot be reached or lead to an unwanted influence of the electron beam on the reactant and catalyst. We introduce ILIAS (identical location imaging and spectroscopy) in combination with a quasi in situ approach to disentangle the effect of heat and gas on the surface of nanoparticles from the effect of the electron beam. With this approach we allow high temperatures and pressures in any gaseous environment on the one hand, and atomic resolution imaging and spectroscopy on the other. As a proof of concept, we resolve the structural evolution of a Co₃O₄ spinel catalyst using ILIAS and track the oxidation state across the surface before and after heating in a reductive or oxidative environment. We then titrate the surface of the catalyst using CO as a probe molecule to remove highly active oxygen species formed during the thermal treatment, providing unprecedented insight into the interplay between pretreatment and surface reactivity of Co₃O₄ nanoparticles.