| AVS 66th International Symposium & Exhibition | |
| Frontiers of New Light Sources Applied to Materials, Interfaces, and Processing Focus Topic | Thursday Sessions |
| Session LS+AC+HC+SS-ThA |
| Session: | Emerging Methods with New Coherent Light Sources |
| Presenter: | Heath Kersell, Lawrence Berkeley National Laboratory |
| Authors: | H. Kersell, Lawrence Berkeley National Laboratory B. Eren, Lawrence Berkeley National Laboratory C.H. Wu, Lawrence Berkeley National Laboratory I. Waluyo, Brookhaven National Laboratory A. Hunt, Brookhaven National Laboratory G.A. Somorjai, Lawrence Berkeley National Laboratory M.B. Salmeron, Lawrence Berkeley National Laboratory |
| Correspondent: | Click to Email |
X-ray based spectroscopies routinely yield detailed elemental, chemical, electronic, and magnetic information on a wide array of physically and chemically diverse samples. However, the spatial resolution of these techniques is limited, frequently by the size of the X-ray spot. Conversely, certain structural probes readily resolve sample topography with nanoscale- or even atomic-resolution. The union of X-ray based spectroscopies with nanoscale structural probes enables the acquisition of spectroscopic information at unprecedented length scales. We will demonstrate the combination of X-ray based spectroscopies (e.g. X-ray photoelectron spectroscopy {XPS}) with scanning tunneling microscopy (STM), and its application to CO adsorption and oxidation on model catalyst surfaces.
CO adsorption on various crystal surfaces plays a critical role in numerous chemical processes, including for example CO oxidation, the water gas shift reaction, and methanol oxidation. CO oxidation is widely used as a prototype reaction for studies of fundamental catalytic phenomena and is crucial in exhaust gas processing for automobiles and stationary CO sources. Recent studies demonstrate strikingly high activity for CO oxidation by Pt nanoparticles supported on cobalt oxide (CoOx) as compared to either of the constituent materials. In the further development of these catalysts, a deeper understanding of the active sites and their deactivation is crucial. Using a combination of operando high pressure STM (HP-STM) and ambient pressure XPS (AP-XPS), we investigate the nature of catalytically active sites for CO oxidation on CoO-Pt catalysts at CO and O2 pressures up to 130 mTorr. Our experiments showed very different behavior for the lattice oxygen (Olat) in CoO between fully oxidized and sub-stoichiometric cobalt oxides. At RT, fully oxidized Co films adsorbed CO in the form of stable surface carbonate species, poisoning the reaction until reaching higher temperatures where they decomposed. On sub-stoichiometric CoOx the CO oxidation reaction proceeded at RT, reducing the oxide to the metallic state. We discuss these results in the context of structural transformations observed in-situ via HP-STM, and demonstrate the behavior of surface sites under relevant gas mixtures.
As an outlook, we will discuss various in-situ multi-modal approaches which enhance the spatial resolution of X-ray based spectroscopies toward the nano- or even single atom scales. Such a union of spectroscopic and structural probes will provide a more accurate and complete picture of operating devices in the near future.