Linking Changes in Reaction Kinetics and Atomic-Level Surface Structures on a Supported Ru Catalyst for CO Oxidation

A fundamental scientific challenge in heterogeneous catalysis is understanding the relationship between surface structure and reactivity. Catalytically relevant surface motifs may form only under reaction conditions, but inactive spectator structures can also form, complicating interpretation of the observed structures. Operando approaches, correlating observed structures with reaction kinetics are thus valuable to differentiate active and spectator structures. Here, we describe an atomic resolution operando approach by mass spectrometry, electron energy loss spectroscopy, and atomic resolution imaging in an environmental transmission electron microscope. Specifically, this approach is applied to the oxidation of carbon monoxide over a supported ruthenium catalyst, a system where the surface structure responsible for high activity has been the subject of debate for several decades. We find that RuO2 layers formed under some reaction conditions and once thought to be the source of ruthenium catalysts' high activity, are effective spectator species, which diminish the activity of the catalyst by reducing the surface area available for more active surface structures.