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In Situ EPR Study of the Redox Properties of CuO–CeO 2 Catalysts for Preferential CO Oxidation (PROX)

DOI: 10.1021/acscatal.6b00589 DOI Help

Authors: Feng Wang (Max-Planck-Institut für Kohlenforschung) , Robert Büchel (Department of Mechanical and Process Engineering, ETH Zürich) , Anton Savitsky (Max-Planck-Institut für Chemische Energiekonversion) , Michal Zalibera (Max-Planck-Institut für Chemische Energiekonversion) , Daniel Widmann (Ulm University, Institute of Surface Chemistry & Catalysis) , Sotiris E. Pratsinis (Department of Mechanical and Process Engineering, ETH Zürich) , Wolfgang Lubitz (Max-Planck-Institut für Chemische Energiekonversion) , Ferdi Schüth (Max-Planck-Institut für Kohlenforschung)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Catalysis , VOL 6 , PAGES 3520 - 3530

State: Published (Approved)
Published: June 2016
Diamond Proposal Number(s): 10306

Abstract: Understanding the redox properties of metal oxide based catalysts is a major task in catalysis research. In situ electron paramagnetic resonance (EPR) spectroscopy is capable of monitoring the change of metal ion valences and formation of active sites during redox reactions, allowing for the identification of ongoing redox pathways. Here in situ EPR spectroscopy combined with online gas analysis, supported by ex situ X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), temporal analysis of product (TAP), and mass spectrometry (MS) studies, was utilized to study the redox behavior of CuO–CeO2 catalysts under PROX conditions (preferential oxidation of carbon monoxide in hydrogen). Two redox mechanisms are revealed: (i) a synergetic mechanism that involves the redox pair Ce4+/Ce3+ during oxidation of Cu0/Cu+ species to Cu2+ and (ii) a direct mechanism that bypasses the redox pair Ce4+/Ce3+. In addition, EPR experiments with isotopically enriched 17O2 established the synergetic mechanism as the major redox reaction pathway. The results emphasize the importance of the interactions between Cu and Ce atoms for catalyst performance. With the guidance of these results, an optimized CuO–CeO2 catalyst could be designed. A rather wide temperature operation window of 11 K (from 377 to 388 K), with 99% conversion efficiency and 99% selectivity, was achieved for the preferential oxidation of CO in a H2 feed.

Journal Keywords: CuO−CeO2 catalyst; EPR; in situ spectroscopy; preferential CO oxidation; redox mechanism

Subject Areas: Chemistry

Instruments: B18-Core EXAFS