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Catalytic conversion of biomass

Guadix Montero, Susana 2019. Catalytic conversion of biomass. PhD Thesis, Cardiff University.
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There is a global need to deal with the growing chemical and energy demands without compromising the environment. The conversion of different biomass-derivate feedstock still needs to improve to accomplish a biorefinery able to compete with the conventional refineries. The work presented in this thesis investigates two different catalytic approaches to selectively cleave the C-O bond over the C-C bond and vice versa for bio-derived feedstock molecules. In the industrial biodiesel production, the by-product obtained in large proportion – glycerol –requires to be converted into more valuable products, such as propanediols. Therefore, the design of heterogeneous catalyst for the selective scission of the C-O bond in the presence of the C-C bond of glycerol is one of the objectives of this thesis. Another kind of biomass is lignocellulosic biomass (waste biomass). Depolymerisation of lignin requires the breaking of C-C bond over the C-O bond. In this context, the second objective is to develop a catalytic system that selectively cleaves C-C bond for lignin model compounds, aiming at lignin depolymerisation. The first part of the thesis reports the synthesis, catalytic activity, and characterisation of monometallic Pd, Ru, Pt and bimetallic PdRu, RuPt nanoparticles supported on TiO2 for the hydrogenolysis of glycerol at relatively low temperatures (165 °C) using gaseous H2. All these catalysts were found to be active but showing different products distributions. It was found that the incorporation of a second metal to monometallic Pt and Pd catalysts resulted in a compromise between conversion and selectivity towards C3 products via C-O bond cleavage. Detailed characterisation using XPS, SEM-EDX, STEM, TGA and computational modelling was employed to rationalise the difference in the catalytic properties of monometallic and bimetallic catalysts. The data revealed the important correlation between metal oxidation state, nanostructure and their catalytic properties. Among all the catalysts tested, PdRu over TiO2 catalysts presented good conversion, selectivity and reusability upon glycerol hydrogenolysis. For glycerol hydrogenolysis reaction, the role of support was investigated using the best PdRu bimetallic combination. Several metal oxides and zeolites with diverse framework structure types were employed for the study. The textural properties of these catalysts were analysed (BET surface area and pore size distribution) and their elemental and structural properties were further characterised using XPS, MP-AES, SEM, and TEM. Furthermore, the hydrothermal stability of the zeolite-based catalyst was investigated. Finally, the relative acid site density of the samples was determined by NH3-TPD for all the catalysts. Pyridine DRIFT of the most significant catalysts was also performed. The effect of the catalyst acidity was found to correlate with the bifunctional catalyst activity, showing an optimum value within a volcano plot. In the next part of the thesis, the study of lignin model compounds bearing similar linkages and functionalities, present in native lignin, are used to investigate lignin depolymerisation research. This thesis reports the catalytic bond cleavage of different inter-unit linkages present in lignin model compounds. Ruthenium ion catalysed oxidation, known as RICO reaction, is an effective method to disrupt the most recalcitrant inter-unit linkages in lignin, such as β-5 and 5-5’, at room temperature and atmospheric pressure. Oxidation of simple model compounds and degradation of a polymeric model as β-O-4 polymer and a hexamer model compound, closer to the lignin structure, was accomplished at rapid reaction times. Several techniques, namely, FT-IR, 1H, 13C, HSQC, HMBC and 31P NMR, were used to characterise the materials and monitor the reactions. A detailed description of the methodology employed for the estimation of the potential bond cleavage of the inter-unit linkages is detailed in this thesis. From the data reported, RuO4 could play an important role in the oxidative depolymerisation of technical and native lignin via the opening of aromatic rings to form carboxylic acids and aldehydes. Finally, a summary of all the results and potential ideas for future research in the areas of bimetallic catalysts for glycerol hydrogenolysis and RICO for oxidative depolymerisation of lignin are presented.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 24 September 2019
Last Modified: 26 Mar 2021 16:49

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