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Combined spatially resolved operando spectroscopy: New insights into kinetic oscillations of CO oxidation on Pd/γ-Al2O3

DOI: 10.1016/j.jcat.2019.03.037 DOI Help

Authors: Ellie K. Dann (University College London; UK Catalysis Hub, Research Complex at Harwell) , Emma K. Gibson (UK Catalysis Hub, Research Complex at Harwell; University of Glasgow) , C. Richard A. Catlow (University College London; UK Catalysis Hub, Research Complex at Harwell; Cardiff University) , Veronica Celorrio (University College London; UK Catalysis Hub, Research Complex at Harwell) , Paul Collier (Johnson Matthey Technology Centre) , Tugce Eralp (Johnson Matthey Technology Centre) , Monica Amboage (Diamond Light Source) , Christopher Hardacre (UK Catalysis Hub, Research Complex at Harwell; The University of Manchester) , Cristina Stere (UK Catalysis Hub, Research Complex at Harwell; The University of Manchester) , Anna Kroner (Diamond Light Source) , Agnes Raj (Johnson Matthey Technology Centre) , Scott Rogers (University College London (UCL); UK Catalysis Hub, Research Complex at Harwell) , Alexandre Goguet (UK Catalysis Hub, Research Complex at Harwell; Queen's University Belfast) , Peter P. Wells (UK Catalysis Hub, Research Complex at Harwell; Diamond Light Source; University of Southampton)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Journal Of Catalysis , VOL 373 , PAGES 201 - 208

State: Published (Approved)
Published: May 2019
Diamond Proposal Number(s): 17340 , 17725

Open Access Open Access

Abstract: 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-Al2O3 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 CO2 and O2 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 O2 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.

Journal Keywords: XAFS; DRIFTS; CO oxidation; Pd/Al2O3; Operando spectroscopy

Subject Areas: Chemistry


Instruments: B18-Core EXAFS , I20-EDE-Energy Dispersive EXAFS (EDE)

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