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Catalysts 2017, 7(9), 279; doi:10.3390/catal7090279

Surface Oxidation of Supported Ni Particles and Its Impact on the Catalytic Performance during Dynamically Operated Methanation of CO2

1
Institute for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany
2
Institute of Catalysis Research and Technology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
3
Paul Scherrer Institute (PSI), CH-5232 Villigen, Switzerland
4
Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany
5
Stanford Synchrotron Radiation Lightsource (SSRL), SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
6
Laboratory of Industrial Chemistry, Ruhr-University Bochum, D-44801 Bochum, Germany
*
Author to whom correspondence should be addressed.
Received: 1 August 2017 / Revised: 25 August 2017 / Accepted: 5 September 2017 / Published: 18 September 2017
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Abstract

The methanation of CO2 within the power-to-gas concept was investigated under fluctuating reaction conditions to gather detailed insight into the structural dynamics of the catalyst. A 10 wt % Ni/Al2O3 catalyst with uniform 3.7 nm metal particles and a dispersion of 21% suitable to investigate structural changes also in a surface-sensitive way was prepared and characterized in detail. Operando quick-scanning X-ray absorption spectroscopy (XAS/QEXAFS) studies were performed to analyze the influence of 30 s and 300 s H2 interruptions during the methanation of CO2 in the presence of O2 impurities (technical CO2). These conditions represent the fluctuating supply of H2 from renewable energies for the decentralized methanation. Short-term H2 interruptions led to oxidation of the most reactive low-coordinated metallic Ni sites, which could not be re-reduced fully during the subsequent methanation cycle and accordingly caused deactivation. Detailed evaluation of the extended X-ray absorption fine structure (EXAFS) spectra showed surface oxidation/reduction processes, whereas the core of the Ni particles remained reduced. The 300-s H2 interruptions resulted in bulk oxidation already after the first cycle and a more pronounced deactivation. These results clearly show the importance and opportunities of investigating the structural dynamics of catalysts to identify their mechanism, especially in power-to-chemicals processes using renewable H2. View Full-Text
Keywords: CO2 methanation; dynamic reaction conditions; operando XAS; quick-EXAFS; surface oxidation-reduction; H2 dropout CO2 methanation; dynamic reaction conditions; operando XAS; quick-EXAFS; surface oxidation-reduction; H2 dropout
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MDPI and ACS Style

Mutz, B.; Gänzler, A.M.; Nachtegaal, M.; Müller, O.; Frahm, R.; Kleist, W.; Grunwaldt, J.-D. Surface Oxidation of Supported Ni Particles and Its Impact on the Catalytic Performance during Dynamically Operated Methanation of CO2. Catalysts 2017, 7, 279.

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