Correlative Tomography: Three Dimensional Multiscale Imaging and Modelling of Hierarchical Porous Materials
Author(s)
Tariq, Farid
Type
Thesis
Abstract
Heterogeneous catalyst based pellets typify a material where functionality is dependant on
hierarchical pore structures spanning many orders of magnitude from nanometers up to tens
of microns. The total activity, selectivity and lifetime of catalyst based pellets depends on
the ability of molecules to flow through a large pellet bed (m), into the pellets (mm) and
their pore structure (μm-nm) to/from the active sites. Three dimensional imaging
techniques such as tomography allow for the direct characterisation and quantification of
pore structures. However, the field of view in tomography decreases as resolution increases.
This work circumvents this issue with multiscale tomography (MT) combining x-ray
microtomography (XMT), dual beam focused ion beam tomography (DB-FIB) and electron
tomography (ET) to probe porous pellet based catalysts.
The results show MT as a viable method that offers new insights into the
quantification and behaviour of pellet based catalysts across large length scales, all in three
dimensions (3D), that no single tomographic technique can adequately capture. MT was
successfully used in the characterising of pore sizes, distributions, structures and spatial
relationships and this was compared to existing multiscale characterisation techniques to
illustrate the new insights that can be obtained. The pore structures were meshed and
modeled using MT data to provide results for understanding the transport properties scaled
up from the nanometre length scale to the packed bed, through pellet based catalysts
produced under different manufacturing conditions. The results show the very strong
dependence on the calcining temperature which is important for designing better catalysts
in future. The tomography data was also used to determine thermal/mechanical stresses at both a pellet and pellet bed level. Although many stresses are compressive; the packing of the pellets creates local tensile stresses and a potential cause for pellet failure through
internal flaws at relatively low loads.
In summary, multiscale tomography was demonstrated to be a viable method for
obtaining new insights for the development of pellet based catalysts by both improved
quantification and allows for the first time direct 3D multiscale simulation of transport and
mechanical properties across multiple scales from nanometers to metres to catalyst pellets
in beds.
hierarchical pore structures spanning many orders of magnitude from nanometers up to tens
of microns. The total activity, selectivity and lifetime of catalyst based pellets depends on
the ability of molecules to flow through a large pellet bed (m), into the pellets (mm) and
their pore structure (μm-nm) to/from the active sites. Three dimensional imaging
techniques such as tomography allow for the direct characterisation and quantification of
pore structures. However, the field of view in tomography decreases as resolution increases.
This work circumvents this issue with multiscale tomography (MT) combining x-ray
microtomography (XMT), dual beam focused ion beam tomography (DB-FIB) and electron
tomography (ET) to probe porous pellet based catalysts.
The results show MT as a viable method that offers new insights into the
quantification and behaviour of pellet based catalysts across large length scales, all in three
dimensions (3D), that no single tomographic technique can adequately capture. MT was
successfully used in the characterising of pore sizes, distributions, structures and spatial
relationships and this was compared to existing multiscale characterisation techniques to
illustrate the new insights that can be obtained. The pore structures were meshed and
modeled using MT data to provide results for understanding the transport properties scaled
up from the nanometre length scale to the packed bed, through pellet based catalysts
produced under different manufacturing conditions. The results show the very strong
dependence on the calcining temperature which is important for designing better catalysts
in future. The tomography data was also used to determine thermal/mechanical stresses at both a pellet and pellet bed level. Although many stresses are compressive; the packing of the pellets creates local tensile stresses and a potential cause for pellet failure through
internal flaws at relatively low loads.
In summary, multiscale tomography was demonstrated to be a viable method for
obtaining new insights for the development of pellet based catalysts by both improved
quantification and allows for the first time direct 3D multiscale simulation of transport and
mechanical properties across multiple scales from nanometers to metres to catalyst pellets
in beds.
Date Issued
2011
Date Awarded
2011-02
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
McComb, David
Lee, Peter
Sponsor
Shell Global Solutions International B.V.
Creator
Tariq, Farid
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)