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Electron microscopy studies of novel catalysts based on amorphous materials

Hewes, Daniel 2023. Electron microscopy studies of novel catalysts based on amorphous materials. PhD Thesis, Cardiff University.
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Heterogeneous catalysis development is a key building block towards a sustainable future due to its involvement in such a significant proportion of chemical and energy industries. The characterisation of novel heterogeneous catalysts is an important step in the development process. Characterisation allows for the identification of unique characteristics within the catalyst materials, which, when compared with catalytic testing data, can be attributed to structure-activity relationships which drive the development towards new, more active, stable, or cost-efficient catalysts. Alongside many standard characterisation techniques, this thesis puts an emphasis on the use of advanced characterisation techniques, such as electron microscopy and its related technologies, and X-ray absorption spectroscopy. These techniques are very powerful for the characterisation of novel heterogeneous catalysts, however, it is their use in conjunction with many other techniques and technologies which paints a full picture of the material and its capabilities. A series of catalytic materials were characterised and tested herein. The three main areas of study surrounded AlSiOx, CeZrOx, and FeMoOx materials. All three of these materials showed activity for the propane dehydrogenation reaction under different reaction conditions. The initial focus was on the development of a bespoke characterisation technique, known as stopstart microscopy, whereby a material could be characterised in a quasi-in situ manner via repeated removal from the microscope for heating steps. This method was shown to be a cost-effective and simpler alternative to real in situ microscopy. The stop-start method was tested on both the CeZrOx materials and the FeMoOx materials. Little was gained from the CeZrOx materials due to the prevalence of beam damage on the sample, whereas some valuable insights into the structural changes of FeMoOx during calcination were obtained. All three catalysts were characterised and tested for the propane dehydrogenation reaction. The AlSiOx materials were loaded with Pt and tested under direct dehydrogenation conditions, without the presence of oxygen in the feed gas. The CeZrOx materials were also loaded with Pt and tested for both the soft-oxidative dehydrogenation of propane in the presence of CO2, and the CO2 hydrogenation reaction, where the effect of Zr in a CeO2 material was tested. The FeMoOx materials were characterised for the effect of calcination on the structure with the intent for use in the oxidative dehydrogenation of propane in the presence of oxygen. The preparation method of each of the three catalysts was varied, with focus on the supercritical antisolvent (SAS) precipitation method, and the flame spray pyrolysis (FSP) method. Both methods iii were shown to have an effect on the structure or activity of the materials. The SAS method was shown to produce characteristic hollow spheres which appear after calcination of the materials, however, this did not appear to have a significant effect on the surface area of the material. In the case of Pt/AlSiOx, the SAS preparation method produced significantly higher initial propene productivity compared to the FSP, or more conventional sol gel preparation methods, however, these catalysts were shown to be unstable. The FSP materials were shown to produce highly stable Pt/AlSiOx catalysts, which were tested for the propane dehydrogenation reaction at higher weight loadings. The addition of Zr to well-reported Pt/CeO2 catalysts was shown to be detrimental to the reverse water gas shift reaction (RWGS) due to a slight decrease in selectivity to CO, however appeared to be beneficial to the methanol synthesis reaction due to higher selectivity to methanol.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 8 April 2024
Last Modified: 08 Apr 2024 11:38

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