Multiscale multimodal imaging of nanoporous catalyst
Publication Date
December 13, 2022
Creator
Abstract
This thesis is dedicated to the study of the structure-transport relationship in disordered porous materials such as heterogeneous catalyst systems. Integrated mercury porosimetry and gas adsorption experiments, including the gas overcondensation method, have been applied to probe the relative importance of particular sub-sets of pores to mass transport rates within various disordered catalyst pellets. This was achieved by examining the relative rates of low-pressure gas uptake into a network before and after a known set of pores was filled with frozen, entrapped mercury. The multi-scale data from porosimetry was combined with multi-modal imaging, including low and high-resolution CXT and FIB-SEM, to spatially locate the specific pore sizes that entrapped mercury and study their impact on the mass transport in the pellets.
The first part of this thesis investigates fresh, reduced, and spent methanol synthesis catalyst pellets made using spray-dried (SD) or roll compacted (RC) feed materials. It examined how the different pellet fabrication processes affected the pore structure of the fresh catalyst by studying both the starting feed particles and the finished tablets. The impact on mass transfer of the controlled modifications to the void space, achieved through mercury porosimetry, was modelled with a random pore-bond network using characteristic parameters obtained from percolation analysis of the overcondensation data. This revealed the differential importance to mass transfer of particular sets of pores associated with certain pellet structural features and the impact on tortuosity of pellet fabrication parameters such as particle feed size. The effectiveness of the reduced and spent methanol synthesis pellets, and the impacts of cracks on the random pore-bond model, were also investigated. It was found that a random pore-bond percolation model accurately captures the macroscopic structure of the reduced and spent SD pellets but not the reduced and spent RC pellets.
In the second part of this thesis, i) the entrapment of non-wetting fluids in high-temperature shift catalyst pellets made via precipitation was investigated using the combined indirect characterisation and X-ray imaging methods. This technique was used to identify the specific pore sizes that entrapped mercury and their impact on the mass transport rates, ii) A novel thermoporometry by DSC method was introduced that uses three separate probe liquids (nitrogen, water and mercury) to validate pore space characterisations obtained through indirect methods. This hybrid experiment permits the comparison of data from multiple techniques for the same sample, allowing parameter calibration and phase transition mode selection to be performed. It was found that the dual-probe experiment overcomes the critical drawbacks and assumptions made when applying the indirect pore characterisation methods to disordered porous materials.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Subjects (LC)
Associated Schools / Departments
Faculty of Engineering
eprints ID
71865
UoN Repository URI
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Suleiman_Corrected thesis.pdf
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Examined. Multiscale Multimodal Imaging of Nanoporous Catalyst
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Suleiman_Corrections.pdf
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Examined. Corrections list
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