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Methane Oxidation over Cu2+/[CuOH]+ Pairs and Site-Specific Kinetics in Copper Mordenite Revealed by Operando Electron Paramagnetic Resonance and UV/Visible Spectroscopy |
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| Authors: | Jörg Wolfram Anselm Fischer Andreas Brenig Dr Daniel Klose Prof Dr Jeroen Anton van Bokhoven Dr Vitaly L Sushkevich Prof Dr Gunnar Jeschke |
| Institution: | 1. Institute for Molecular Physical Science, ETH Zurich, Vladimir-Prelog-Weg 1–5/10, 8093 Zurich, Switzerland;2. Institute for Chemical and Bioengineering, ETH Zurich, Vladimir-Prelog-Weg 1–5/10, 8093 Zurich, Switzerland;3. Laboratory for Catalysis and Sustainable Chemistry, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen, Switzerland |
| Abstract: | Cu-exchanged mordenite (MOR) is a promising material for partial CH4 oxidation. The structural diversity of Cu species within MOR makes it difficult to identify the active Cu sites and to determine their redox and kinetic properties. In this study, the Cu speciation in Cu-MOR materials with different Cu loadings has been determined using operando electron paramagnetic resonance (EPR) and operando ultraviolet-visible (UV/Vis) spectroscopy as well as in situ photoluminescence (PL) and Fourier-transform infrared (FTIR) spectroscopy. A novel pathway for CH4 oxidation involving paired CuOH]+ and bare Cu2+ species has been identified. The reduction of bare Cu2+ ions facilitated by adjacent CuOH]+ demonstrates that the frequently reported assumption of redox-inert Cu2+ centers does not generally apply. The measured site-specific reaction kinetics show that dimeric Cu species exhibit a faster reaction rate and a higher apparent activation energy than monomeric Cu2+ active sites highlighting their difference in the CH4 oxidation potential. |
| Keywords: | Copper heterogeneous catalysis methane to methanol operando spectroscopy zeolites |