Affiliation:
1. Institute for Chemical and Bioengineering ETH Zurich Vladimir-Prelog-Weg 1–5/10 8093 Zurich Switzerland
2. Laboratory for Catalysis and Sustainable Chemistry Paul Scherrer Institute Forschungsstrasse 111 5232 Villigen Switzerland
3. Institute for Molecular Physical Science ETH Zurich Vladimir-Prelog-Weg 1–5/10 8093 Zurich Switzerland
Abstract
AbstractThe CH4 oxidation performance of Cu‐chabazite zeolites characterized by distinct Si/Al ratios and Cu loadings has been studied and the observed variations in reactivity have been correlated to the differences in the nature of the formed active centers. Plug flow reactor tests, in situ Fourier‐transform infrared, and X‐ray absorption spectroscopy demonstrate that a decrease in Cu loading shifts the reactivity/redox profile to higher temperatures and increases the CH3OH selectivity and Cu‐efficiency. In situ electron paramagnetic resonance, Raman, ultraviolet‐visible, Fourier‐transform infrared, and photoluminescence spectroscopies reveal that this behavior is associated with the presence of monomeric Cu active sites, including bare Cu2+ and [CuOH]+ present at low Si/Al ratio and Cu loading. Formation of two distinct [Cu2(μ‐O)]2+ moieties at higher Si/Al ratio or Cu loading forces these trends into the opposite direction. Operando electron paramagnetic resonance and ultraviolet‐visible spectroscopy show that the apparent activation energy of monomeric Cu active species decreases with increasing Si/Al ratio, whereas the one of dimeric centers is unaffected.