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Tracking Chromium Evolution on Ceria from Particles to Single Atoms: A Catalyst Regeneration Strategy for Ammonia
Ivan Surin1, Mikhail Agrachev2, Frank Krumeich3
1Institute of Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland.
Chromium catalysts on reducible oxides can regenerate via redispersion under oxidative conditions. This process converts Cr2O3 into mobile Cr6+ species, restoring catalyst performance and structure.
Area of Science:
- Heterogeneous Catalysis
- Materials Science
- Surface Chemistry
Background:
- Supported chromium catalysts are widely used but their behavior on reducible oxides is not fully understood.
- Previous work showed CeO2-supported Cr single atoms are effective for NH3 oxidation but deactivate via Cr2O3 agglomeration.
Purpose of the Study:
- To investigate the evolution of chromium species on CeO2 supports under various reactive conditions.
- To understand the mechanism of catalyst deactivation and explore regeneration strategies.
Main Methods:
- Utilized advanced microscopy, in situ Raman, UV-vis, electron paramagnetic resonance, and X-ray absorption spectroscopies.
- Studied chromium species transformation on different reducible oxide supports (CeO2, ZrO2, TiO2, Al2O3, Nb2O5).
Main Results:
- Oxidative conditions induced redispersion of Cr2O3, transforming it into isolated chromium species (Cr6+, Cr5+).
- Redispersion rate correlated with support reducibility, being faster on CeO2 and slower on ZrO2 and TiO2.
- This redispersion effectively regenerated catalyst structure and performance.
Conclusions:
- Redox-active supports facilitate reversible changes in metal nanostructure, enabling catalyst regeneration.
- Controlling support properties is key to tuning chromium speciation and generating active Cr6+ sites from Cr2O3.
- This offers a promising strategy for designing and regenerating catalysts for various applications.
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