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Reducibility of Al3+-Modified Co3O4: Influence of Aluminum Distribution
Svetlana V Cherepanova1,2, Egor G Koemets1, Evgeny Yu Gerasimov1,2
1Boreskov Institute of Catalysis SB RAS, Lavrentiev Ave., 5, Novosibirsk 630090, Russia.
Materials (Basel, Switzerland)
|September 28, 2023
Summary
Aluminum (Al3+) doping in cobalt (Co) oxides influences their reduction behavior. The distribution of Al within the Co3O4 lattice significantly alters the reduction pathway and intermediate species formed during hydrogen reduction.
Area of Science:
- Materials Science
- Catalysis
- Inorganic Chemistry
Background:
- Cobalt oxides are crucial in catalysis, but their reduction properties are sensitive to dopants.
- Understanding the role of dopants like aluminum (Al3+) is key to tailoring catalyst performance.
- The preparation method and calcination temperature significantly influence the structure and properties of mixed metal oxides.
Purpose of the Study:
- To investigate the effect of Al3+ doping on the reduction behavior of Co3O4.
- To elucidate the structural changes and cation distribution of Al-doped Co3O4 after calcination.
- To correlate the Al distribution with the reduction pathways and intermediate cobalt oxides.
Main Methods:
- Preparation of Al-doped Co3O4 via coprecipitation followed by calcination at 500 °C and 850 °C.
- In situ X-ray Diffraction (XRD) and Temperature-Programmed Reduction (TPR) to study reduction processes.
- High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) with Energy Dispersive Spectroscopy (EDS) for elemental mapping and cation distribution analysis.
Main Results:
- Al3+ cations incorporated into the Co3O4 lattice, with distribution dependent on calcination temperature.
- Calcination at 500 °C yielded an inhomogeneous (Co,Al)3O4 solid solution.
- Calcination at 850 °C resulted in partial decomposition, forming Al-depleted interiors and Al-enriched surfaces.
- Reduction proceeds via (Co,Al)3O4 → (Co,Al)O → Co, with Al stabilizing intermediate Co(II)-Al(III) oxides.
- Al distribution dictates reduction pathway: homogeneous solid solutions stabilize intermediates, while surface-enriched Al leads to independent reduction of Co and Al species.
Conclusions:
- Al3+ doping significantly modifies the reduction behavior of Co3O4 by influencing cation distribution and stabilizing intermediate oxides.
- The calcination temperature is critical in determining the Al distribution and subsequent reduction characteristics.
- These findings provide insights into the behavior of Co3O4/γ-Al2O3-supported catalysts, impacting active component performance.
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