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Title: Sugar conversion to hydroxymethylfurfural and aromatics over niobium oxides and modified zeolites
Author: Kreissl, Hannah T.
ISNI:       0000 0004 6501 1624
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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Research in the field of renewable energies is becoming ever more important due to the depletion of fossil fuels and increasing environmental concerns. The upgrading of biomass to commodity and fine chemicals in order to substitute conventional fossil-fuel derived products is a major topic in the area, particularly the upgrading of sugars as the main biomass component. Glucose derived from cellulose is the most abundant sugar and its acid catalysed dehydration yields the platform molecule hydroxymethylfurfural (HMF), a promising precursor for plastics, solvents, fuels and fine chemicals. In this work the conversion of sugars to HMF is studied in water over niobium oxides as solid acid catalysts, presenting an environmentally- and separation-friendly conversion route. An emphasis is put on the reaction mechanistic details and the analysis of catalyst structure in relation to acidity and catalytic performance, as these are key factors in the development of targeted synthesis and improved catalysts. For example, the efficient conversion of glucose to HMF requires the presence of both Lewis acid (LA) and Brønsted acid (BA) sites on the niobium oxides. Large quantities of both LA (exposed Nb centres) and BA (acidic surface hydroxyl) sites are found prominently on the nano-structured niobium oxides compared to their bulk analogues. This results from the large surface areas and structural flexibility of the nano-materials, where LA sites appear to arise from distortions and oxygen defects. Amorphous mesoporous Nb2O5*ub>nH2O shows the best catalytic performance due to the presence of both LA and comparably weak BA sites, where weaker BA sites are formed by protons of terminal surface hydroxyl groups. In addition to sugar conversion to HMF, the conversion of HMF to aromatic hydrocarbons has been addressed, using a two-step reaction route via dimethylfuran (DMF) over modified zeolite catalysts. Although there is room for yield improvements, the significant advantage of this route is the use of ethanol as common solvent and sacrificial reagent for both reaction steps, facilitating the combination into a one-batch-process in the future. Aromatics are important fuel additives and precursors for polymers, resins and solvents and are currently fossil-fuel derived, raising the need for such alternative production pathways.
Supervisor: Tsang, S. C. Edman Sponsor: Sinopec China ; Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available