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Modelling atomic layer deposition overcoating formation on a porous heterogeneous catalyst
Niko Heikkinen1, Juha Lehtonen1, Laura Keskiväli1
1VTT Technical Research Centre of Finland, P.O.Box 1000, FIN-02044 VTT, Espoo, Finland. niko.heikkinen@vtt.fi.
Physical Chemistry Chemical Physics : PCCP
|August 22, 2022
Summary
Atomic layer deposition (ALD) created protective aluminum oxide (Al2O3) coatings on cobalt catalysts. A diffusion-reaction model accurately predicted coating thickness and penetration into the catalyst pores.
Area of Science:
- Materials Science
- Chemical Engineering
- Catalysis
Background:
- Industrially relevant cobalt-based Fischer-Tropsch catalysts require protective overcoatings to enhance stability and performance.
- Atomic Layer Deposition (ALD) offers precise control over thin film deposition, making it suitable for modifying catalyst surfaces.
Purpose of the Study:
- To deposit protective aluminum oxide (Al2O3) overcoatings on a Co-Pt/TiO2 Fischer-Tropsch catalyst using ALD.
- To develop and validate a diffusion-reaction model for predicting precursor transport, overcoating thickness, and penetration depth within catalyst particles.
- To correlate model predictions with experimental microscopy data.
Main Methods:
- Atomic Layer Deposition (ALD) using trimethylaluminium (TMA) and water (H2O) to create Al2O3 overcoatings on a Co-Pt/TiO2 catalyst.
- Development of a diffusion-reaction differential equation model to simulate precursor transport and coating formation.
- Validation of the model using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) for overcoating thickness and penetration depth analysis.
Main Results:
- ALD successfully deposited Al2O3 overcoatings with thicknesses ranging from approximately 0.7 to 2.2 nm.
- The diffusion-reaction model accurately predicted overcoating thicknesses (e.g., 1.36-2.04 nm predicted vs. 1.29-2.15 nm measured by TEM).
- The model predicted a penetration depth of ~19 μm, with SEM confirming deep penetration (15-18 μm), though experimental data showed variable penetration (0-18 μm average 9.6 μm).
Conclusions:
- ALD is an effective method for applying protective Al2O3 overcoatings to Co-based Fischer-Tropsch catalysts.
- The developed diffusion-reaction model provides a reliable tool for predicting ALD overcoating characteristics within catalyst particles.
- The model aids in understanding and optimizing the ALD process for enhanced catalyst design and performance.
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