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The structure and catalytic properties of Rh-doped CeO2 catalysts
E A Derevyannikova1, T Yu Kardash, L S Kibis
1Boreskov Institute of Catalysis SB RAS, Prosp. Akad. Lavrentieva, 5, Novosibirsk, 630090, Russia.
Physical Chemistry Chemical Physics : PCCP
|November 28, 2017
Summary
Rhodium-doped ceria catalysts exhibit high activity for low-temperature carbon monoxide oxidation. Their stability and performance depend on nanocrystalline structure, with decomposition and reduced activity observed at higher temperatures.
Area of Science:
- Materials Science
- Catalysis
- Nanotechnology
Background:
- Ceria (CeO2) based materials are crucial in catalysis.
- Doping ceria with transition metals like Rhodium (Rh) can enhance its catalytic properties.
- Understanding the structural and chemical state of dopants is key to optimizing catalyst performance.
Purpose of the Study:
- To investigate the structural and local atomic arrangements of nanocrystalline Rh-doped CeO2 catalysts.
- To correlate the structural properties with catalytic activity in low-temperature CO oxidation.
- To determine the stability and decomposition pathways of Rh-doped CeO2 under thermal treatment.
Main Methods:
- Co-precipitation method for catalyst synthesis.
- Pair Distribution Function (PDF) analysis for average and local structure.
- High-Resolution Transmission Electron Microscopy (HRTEM) for morphology.
- X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) for phase identification and electronic state.
- Raman spectroscopy for vibrational properties.
Main Results:
- Homogeneous solid solutions of Rh3+ substituting Ce4+ in the fluorite structure were formed for Rh content < 10 wt% and calcination at 450 °C.
- Oxygen vacancies were created to maintain charge neutrality upon Rh doping.
- The Rh-doped CeO2 solid solution showed high catalytic activity for low-temperature CO oxidation.
- Catalytic activity decreased upon thermal treatment above 450 °C due to Rh association and structural distortion.
- Alpha-Rh2O3 nanoparticles formed at 800 °C, with XRD-detectable Rh oxide phases at 1000 °C, though some subsurface solid solution retained activity.
Conclusions:
- Nanocrystalline Rh-doped CeO2 forms a stable solid solution with Rh3+ substituting Ce4+ and creating oxygen vacancies.
- High catalytic activity for low-temperature CO oxidation is achieved in this solid solution.
- Thermal instability above 450 °C leads to decomposition and reduced activity, but residual subsurface solid solution maintains some catalytic function.
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