Combined spatially resolved operando spectroscopy: New insights into kinetic oscillations of CO oxidation on Pd/Γ-Al 2 O 3

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    • Ellie K. Dann
    • Emma K. Gibson
    • C. Richard A. Catlow
    • Veronica Celorrio
    • Paul Collier
    • Tugce Eralp
    • Monica Amboage
    • Christopher Hardacre
    • Cristina Stere
    • Anna Kroner
    • Agnes Raj
    • Scott Rogers
    • Alexandre Goguet
    • Peter P. Wells

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    Spatially resolved, combined energy dispersive EXAFS (EDE) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements have been performed over a fixed catalyst bed of Pd/γ-Al 2 O 3 during kinetic oscillations of CO oxidation. The kinetic oscillations of CO oxidation over Pd (or for that matter Pt or Rh) catalysts are a complicated phenomenon that require characterisation techniques with high time resolution and spatial resolution in order to make links between catalyst structure and surface reactivity. By measuring the extent of Pd oxidation at the nanoparticle surface, from Pd K-edge EDE, and matching this with the CO coverage, from DRIFTS spectra, at multiple positions of the fixed bed reactor it is found that the majority of the catalyst undergoes a sharp transition from the CO poisoned catalyst to the highly active, oxidised Pd surface. This transition occurs initially at the end of the catalyst bed, nearest the outlet, and propagates upstream with increasing temperature of the reactor. The oscillations in Pd surface oxide formation and CO coverage are observed only in the first ∼1 mm of the bed, which gives rise to oscillations in CO 2 and O 2 concentrations observed by end-pipe mass spectrometry after the light-off temperature. The catalyst initially exists as less active, CO poisoned metallic Pd nanoparticles before light-off which transition to a highly active state after light-off when the Pd nanoparticle surface becomes dominated by chemisorbed oxygen. Kinetic oscillations only occur at the front of the catalyst bed where there is sufficient concentration of CO in the gas phase to compete with O 2 for adsorption sites at the catalyst surface. We demonstrate the complex nature of the evolving catalyst structure and surface reactivity during catalytic operation and the need for spatially resolved operando methods for understanding and optimising catalyst technologies.

    Documents

    DOI

    Original languageEnglish
    Number of pages8
    Pages (from-to)201-208
    JournalJournal of Catalysis
    Journal publication date01 May 2019
    Volume373
    Early online date08 Apr 2019
    DOIs
    Publication statusPublished - 01 May 2019

      Research areas

    • CO oxidation, DRIFTS, Operando spectroscopy, Pd/Al O, XAFS

    ID: 175525675