Natural Sciences, Physical Sciences, Atom and Molecular Physics and Optics, Naturvetenskap, Fysik, Atom- och molekylfysik och optik (Här ingår: Kemisk fysik, kvantoptik), Chemical Sciences, Inorganic Chemistry, Kemi, Oorganisk kemi

We present an operando study where Ambient-Pressure X-ray Photoelectron Spectroscopy (AP-XPS), Polarization Modulation-InfraRed Reflection Absorption Spectroscopy (PM-IRRAS) and Mass Spectrometry (MS) were employed simultaneously with sub-minute time resolution to monitor the CO oxidation and NO reduction reactions on Rh(111). AP-XPS is a powerful tool to follow reactions at the surface-gas interface at near-ambient pressures, yet with challenges at sub-minute time resolutions. PM-IRRAS allows to identify molecular adsorbate sites with sub-minute resolution. Therefore, PM-IRRAS can serve as complementary tool alongside dynamic AP-XPS measurements, when the interpretation of photoemission spectra is limited by overlapping contributions and low statistics. This multi-modal setup simultaneously monitors individual adsorption sites of molecular adsorbates, the build-up of surface atomic species and oxides, and the effect of the surface chemical species on the catalyst reactivity. To demonstrate the combined setup, model reactions (CO oxidation, NO reduction) were studied on Rh(111) in the mbar range of pressures. For CO oxidation, a decrease of the surface activity towards CO2 production is observed as the Rh surface oxide develops. For NO reduction, a steady N2/CO2 production and an O-free active stage of the reaction are shown. The presented setup provides valuable insights into surface chemical reactions with sub-minute time resolution.