Toolbox for atomic layer deposition process development on high surface area powders

Tuning catalysis by surface-deposition of elements on oxidation catalysts via atomic layer deposition

This study on surface-modifications of bulk oxidation catalysts with sub-monolayers of POx, BOx and MnOxvia atomic layer deposition demonstrates this method to be a powerful tool for tuning the performance in selective oxidations of light alkanes.

Modelling atomic layer deposition overcoating formation on a porous heterogeneous catalyst

Atomic layer deposition (ALD) was used to deposit a protective overcoating (Al₂O₃) on an industrially relevant Co-based Fischer-Tropsch catalyst. A trimethylaluminium/water (TMA/H₂O) ALD process was used to prepare ∼0.7-2.2 nm overcoatings on an incipient wetness impregnated Co-Pt/TiO₂ catalyst. A diffusion-reaction differential equation model was used to predict precursor transport and the resulting deposited overcoating surface coverage inside a catalyst particle. The model was validated against transmission electron (TEM) and scanning electron (SEM) microscopy studies. The prepared model utilised catalyst physical properties and ALD process parameters to estimate achieved overcoating thickness for 20 and 30 deposition cycles (1.36 and 2.04 nm respectively). The TEM analysis supported these estimates, with 1.29 ± 0.16 and 2.15 ± 0.29 nm average layer thicknesses. In addition to layer thickness estimation, the model was used to predict overcoating penetration into the porous catalyst. The model estimated a penetration depth of ∼19 μm, and cross-sectional scanning electron microscopy supported the prediction with a deepest penetration of 15-18 μm. The model successfully estimated the deepest penetration, however, the microscopy study showed penetration depth fluctuation between 0-18 μm, having an average of 9.6 μm.

Synthesis of High Surface Area-Group 13-Metal Oxides via Atomic Layer Deposition on Mesoporous Silica

The atomic layer deposition of gallium and indium oxide was investigated on mesoporous silica powder and compared to the related aluminum oxide process. The respective oxide (GaO_x, InO_x) was deposited using sequential dosing of trimethylgallium or trimethylindium and water at 150 °C. In-situ thermogravimetry provided direct insight into the growth rates and deposition behavior. The highly amorphous and well-dispersed nature of the oxides was shown by XRD and STEM EDX-mappings. N₂ sorption analysis revealed that both ALD processes resulted in high specific surface areas while maintaining the pore structure. The stoichiometry of GaO_x and InO_x was suggested by thermogravimetry and confirmed by XPS. FTIR and solid-state NMR were conducted to investigate the ligand deposition behavior and thermogravimetric data helped estimate the layer thicknesses. Finally, this study provides a deeper understanding of ALD on powder substrates and enables the precise synthesis of high surface area metal oxides for catalytic applications.