The optimisation of heterogeneous catalysis in continuous flow has the potential
to deliver significant benefits to fine chemical manufacturing. However, many
promising industrial heterogeneous catalyst candidates, such as metal-organic
frameworks (MOFs), exist as powders which are unsuitable for use in flow
reactors. This thesis explores an approach to exploiting MOFs for heterogeneous
catalysis in continuous flow by combining them with scalable, industrially
implementable polymer-based spherical activated carbon (PBSAC) supports. A
novel heterogeneous catalyst consisting of the Lewis acidic MOF MIL-100(Sc)
immobilised onto PBSAC spheres, termed MIL-100(Sc)@PBSAC, was
developed and studied in continuous flow.
Firstly, following in-depth characterisation (i.e. PXRD, TGA, FT-IR, N2 adsorption,
SEM-EDX, DLS and XPS), the Lewis acidic catalytic properties of MIL-100(Sc)
(in powder form) towards an industrially important reaction (intramolecular
cyclisation of citronellal) were studied via design-of-experiments (DoE) and
kinetic modelling approaches (Chapter 2). Statistically significant DoE models
were generated when studying the initial rate and catalytic efficiency. Upon kinetic
model generation, a Langmuir-Hinshelwood mechanism was found to adequately
describe the reaction mechanism. Next, novel MIL-100(Sc)@PBSAC composites
were reproducibly synthesised by a reflux approach and thoroughly characterised
(i.e. FIB-SEM-EDX, PXRD, N2 adsorption, TGA, AAS, XPS, DLS and crush
testing) (Chapter 3). MIL-100(Sc) was found to reside primarily in the pores and
cracks on the surface of PBSAC spheres. The MIL-100(Sc)@PBSAC composite
was then successfully applied in continuous flow for industrially relevant Lewis
acid-catalysed reactions, including both intramolecular cyclisation of citronellal
and cannabidiol synthesis (Chapter 4). Finally, initial work regarding the
development of a new catalytic system, Cu@UiO-67-BPY@PBSAC,
incorporating a postsynthetic modification step, for application in 3-phase
(liquid-solid-gas) continuous flow heterogeneous catalysis, is discussed (Chapter
5).
Overall, this research demonstrates the potential for MOF-based heterogeneous
catalysis in continuous flow for fine chemical synthesis. Adding a new dimension
in the form of MOF@PBSAC composites to the broader trend from catalysis in
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batch to catalysis in flow, this work outlines a generalisable approach to exploit
the versatility of MOF- and other coordination polymer-based catalysts in
continuous manufacturing.
