Functionalized mesoporous metal oxide spheres as catalysts for efficient conversion of carbohydrates into 5-hydroxymethylfurfural

© 2018 Dr. Seyed Farshad MotevalizadehFossil fuels currently provide more than 90% of global energy needs and feedstocks for the chemical industry. One of the most critical challenges facing mankind is reducing emissions of carbon dioxide. Biomass is a globally accessible resource that could provide an alternative feedstock for synthesizing chemical building blocks. 5-(Hydroxymethyl)furfural (5-HMF) is a commercially useful platform molecule that can be synthesized from biomass. Solid acid catalysts such as metal oxides and modified oxides fill an important role in biomass conversion, due to advantages like carrying both Lewis and Brønsted-acid sites, where the catalytic activity occurs, as well as thermal stability and low cost. The research focus is the preparation, surface modification and characterization of zirconium oxide and binary titanium zirconium oxides spheres as solid-acid catalysts for the conversion of biomass-derived carbohydrates to 5-HMF. In Chapter 2, mesoporous zirconia was functionalized with common di-carboxylic acids and amino acids (i.e. terephthalic acid, 2-amino terephthalic acid, adipic acid, aspartic acid, succinic acid and glutamic acid) to prepare a multifunctional acidic catalyst for conversion of carbohydrates (fructose, glucose, sucrose, cellulose and starch) to 5-HMF. A green and versatile method was utilized to introduce the functional groups on the surface of the zirconia. The final catalyst, which was grafted with terephthalic acid, exhibited acceptable activity towards the dehydration conversion of fructose to 5-HMF with a yield of 42% after 2 h in dimethyl sulfoxide (DMSO) at 150 °C, with negligible loss of activity over five consecutive catalytic recycles. In Chapter 3, mesoporous titanium zirconium oxide spheres were prepared via sol-gel chemistry and templating using a solvothermal and calcination process with varied pore diameters (2.3-10.7 nm), surface areas (76-420 m2 g-1), and surface hydroxyl group densities (4.8-7.0 nm-2). Spheres with high surface area, large pore diameter and high surface hydroxyl density were functionalized with nitrilotri(methylphosphonic acid) via a green and simple method, then used as solid-acid catalysts to produce 5-HMF through the dehydration of carbohydrates. The impact of time, temperature, solvent and amount of catalyst on the yield of 5-HMF was systematically investigated. The recyclability of the catalyst was tested across five consecutive runs. In Chapter 4, sulfated, mesoporous zirconium titanium oxide spheres were synthesized for the catalytic dehydration of carbohydrate to 5-HMF. Five factors affected the sulfate loading: zirconia content, solvothermal temperature, sulfuric acid concentration, duration of the acid treatment, and the post-sulfate grafting calcination temperature. After optimization, the leading catalyst had a maximum sulfate loading of 10.7 wt%, and a total surface acidity of 0.62 mmol g-1. This solid-acid catalyst demonstrated excellent results in the dehydration of fructose to 5-HMF, with a yield of 80% after 1 h in DMSO at 150 °C, and 93% after 6 h. The catalyst was reused in five consecutive cycles with only a 3% loss of activity. Modified zirconia and mesoporous zirconium titanium binary oxide can be considered as promising solid acid catalysts to produce high-value chemicals from biomass feedstocks