Jones, Andrew
(2025)
Defect-stabilised Pt catalysts on UiO-66(NH2).
PhD thesis, University of Nottingham.
Abstract
This thesis broadly explores the use of the metal organic framework (MOF) UiO-66(NH2) as a support material for photocatalytic hydrogen generation.
Hydrogen generation is an important reaction in sustainable catalysis, with the potential to create hydrogen fuel using sunlight energy, improving upon the current methods such as steam reforming, which produce CO2 emissions during hydrogen generation. Hydrogen is an ideal candidate for an energy carrier in a net-zero fuel economy, and its production using sunlight is a highly promising prospect to contribute to the global effort of circumventing CO2 emissions and reducing anthropogenic global warming.
UiO-66(NH2) is an analogue of the highly popular MOF UiO-66, where UiO-66(NH2) is composed of Zr6O4(OH)4 zirconium-oxo clusters and linkers of 2-amino terephtalate. These building units co-ordinate into extended macromolecules developing a crystal structure with networks of high porosity. UiO-66, and its analogues exhibit relatively high thermal and chemical stability, an essential trait for catalyst supports. These MOFs also display a very high tunability, with the ability to replace the metal and organic components with certain candidates, while maintaining the crystal structure. UiO-66 family MOFs are perhaps most distinguished by their ability to form defects, which have been observed to present in a variety of ways, with the possibility for both cluster and linker vacancies, and phases of the material which naturally incorporate defects.
This research aims to use UiO-66(NH2) catalysts to create more sustainable catalysts, by reducing sintering during catalysis. Sintering is a significant cause for loss of catalyst activity for catalysts where an active site is immobilised upon a support material. Agglomeration of the catalyst particles reduces the surface proportion of atoms, and therefore the proportion of catalytically active atoms.
Chapter 4 presents a body of work in which I introduce missing linker defects to UiO-66(NH2) in varying quantities, measuring the physical properties of the MOF using PXRD and SEM, and quantifying the missing linker concentrations by TGA. I explore the effects of missing linkers on catalytic activity towards photocatalytic hydrogen generation, and conduct post mortem analysis to measure nanoparticle sintering to assess the efficacy for missing linker defects introducing ‘anchor sites’ at which to stabilise catalyst nanoparticles.
Chapter 5 presents work which occurred in parallel with Chapter 4, developing and optimising a photocatalytic reactor cell to maximise the observed hydrogen generation from UiO-66(NH2) photocatalysts. This chapter investiagtes key design parameters in a photocatalytic reactor, and achieves large increases in the observed rate of photocatalysis by applying the same catalyst to a new reactor. The development of this reactor was key to highlight changes in rate of H2 generation in both Chapters 4 and 6.
Chapter 6 Investigates another approach to sustainable heterogeneous catalysis. Instead of stabilising Pt catalysts, I implemment Nickel and Nickel/ Platinum mixed metal catalysts, with the aim of using cheaper, more earth-abundant metals for photocatalysis.
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