Microwave-assisted heterogeneous catalysis of propene selective oxidation

Sun, Jia 2022. Microwave-assisted heterogeneous catalysis of propene selective oxidation. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Compared with traditional heating methods, microwave heating has the advantages of uniform and fast heating of substrates, selective heating of components in a mixture, easily switching on and off, and a sensitive response to changes in input power. As an energy source, it has been widely used in chemistry, especially in organic synthesis and material processing. However, the application of microwaves in gas-phase heterogeneous catalysis is somewhat limited because microwaves are not sufficient to break chemical bonds to initiate chemical reactions, and gases cannot be heated by microwaves. In this doctoral thesis, the selective oxidation of propene was selected as the target reaction to investigate the feasibility and potential of microwave-assisted gas-phase catalysis. Bismuth molybdate, a material that performs well for this reaction in traditional catalysis, was selected as the main catalyst in this study. Different synthesis methods such as hydrothermal synthesis, sol-gel synthesis, and a sol-gel deposition method were used to synthesize and modify the supported bismuth molybdate samples. Whether a material can be heated in a microwave electric field is governed by their dielectric properties. The dielectric properties of a range of materials were analysed and the results compared to their performance as catalysts for propene oxidation. It has been proposed that bismuth-based composite metal oxides have good dielectric properties and can be heated to suitable temperatures under microwave conditions. The results of these studies found that bismuth molybdate samples synthesized under certain conditions also showed good performance in microwave-assisted heterogeneous catalysis. The dielectric loss factor of the material will vary depending on the synthesis method and it was found that catalysts synthesized by a hydrothermal method had a higher dielectric loss factor II than materials prepared using a sol-gel method, so they were easier to heat in the microwave, and performed better in the microwave-assisted catalysis process. Modifying standard bismuth molybdate materials was also investigated. Replacing molybdenum with vanadium in bismuth molybdate increases defects in the material, making it more easily heated by microwave radiation. The use of silicon carbide as a support was also found to improve the microwave-absorbing ability of the catalyst, giving a uniform catalyst bed temperature, and increasing the conversion rate of propene, the yield of acrolein and the stability of the catalyst. The chemical and physical properties of the catalysts used in this work were characterized by several different techniques including X-ray diffraction (XRD), Raman spectroscopy (Raman), Inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS) , dielectric perturbations, to elucidate structure activity relationships for the different catalysts. Insights gained in this study provide new information on the role of catalysts in microwave assisted catalysis for gas-phase selective oxidation with potential applications in greenhouse gas conversion

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Date of First Compliant Deposit:	1 December 2022
Last Modified:	06 Jan 2024 04:36
URI:	https://orca.cardiff.ac.uk/id/eprint/154607

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