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Catalysts design for biomass conversion

Morteo Flores, Fabian 2022. Catalysts design for biomass conversion. PhD Thesis, Cardiff University.
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Abstract

The strong dependency on fossil fuels has generated environmental problems due to greenhouse gas emissions, causing a rise in average global temperature and governments' attention to using renewable energies to reduce the net carbon to zero. The study of biomass conversion as a renewable source fuel into bio-oil has increased in recent years due to its energy-efficient and widely available feedstock being one alternative in replacing fossil fuels and gas. However, using bio-oil as a fuel has significant disadvantages due to the high amount of oxygenated compounds present in the mixture, which causes an increase in viscosity and challenges the ignition in the engines. Therefore, a bio-oil upgrade must be used to remove the oxygen compounds before being used as a fuel. One option is the hydrodeoxygenation process, which requires high temperatures, hydrogen, and catalysts to remove oxygen in the form of water and produce free-oxygen fuel. This thesis aims to study the selection of hydrodeoxygenation (HDO) catalysts, such as transition metals (TMs) and oxide supports, using DFT calculations. First, studies were carried out to explore the relationship between the electronic properties of thirteen TMs, Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, Ag, W, Ir, Pt and Au and their hydrogen/oxygen affinity. The results helped to create scaling relationships to select the most suitable metal catalysts to bind the biomass-derived compounds and break the C–O bonds. Second, the acid-base properties of five pristine and hydroxylated oxide surfaces, γ-Al2O3, CeO2, MgO, β-SiO2 and anatase-TiO2, were investigated. This includes the interaction with model compounds derived from lignin, such as guaiacol, phenol, anisole, and catechol. Third, the guaiacol’s HDO mechanism is analysed on six TM catalysts based on the intermediate hydrogen/oxygen affinity, Fe (110), Co (0001), Ni (111), Cu (111), Pd (111) and Pt (111). Three first main pathways were proposed to convert guaiacol to anisole (dihydroxylation), phenol (demethoxylation) and catechol (demethylation). The results confirmed that the demethylation pathway is the most accessible on Co, Ni, Cu, Pd, and Pt, following the route guaiacol → catechol → phenol → benzene. In contrast, IV Fe (110) preferred the dehydroxylation (DHY) reaction pathway, following the guaiacol → anisole → benzene route. Finally, a microkinetic study was implemented to understand the catalytic process of the guaiacol HDO conversion on five metal surfaces, Co, Ni, Cu, Pd, and Pt. The study includes temperature-programmed reaction and rate order simulations. The results showed that Ni exhibits a fast-kinetic rate at 573 K and performs well in the deoxygenation and hydrogenation reactions compared to the other TM surfaces. The impact of the results in this thesis provides a better understanding of the guaiacol HDO process. Moreover, the use of DFT calculations in the selection of metal catalysts, reaction mechanisms and microkinetic studies is a step forward to closing the gap between the theoretical and experimental studies, giving insight into the metal catalysts design from an atomistic perspective. This will help to understand the catalysts’ performance and design of new materials promoting a circular and sustainable economy

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 13 September 2022
Last Modified: 14 Sep 2022 09:57
URI: https://orca.cardiff.ac.uk/id/eprint/152539

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