Catalytic conversion of biorenewable-carbohydrate sources to 5-Hydroxymethylfurfural: a platform molecule for future chemical and energy

Abstract

Cellulosic biomass provides renewable alternatives to fossil-fuel resources for the sustainable production of liquid fuels and valuable chemicals. The challenge for the effective utilization of biomass resources is to develop cost-effective processing methods for the transformation of carbohydrates into value-added chemicals. Carbohydrates, predominantly cellulose, represent the largest fraction of biomass, and various strategies for their efficient use as a commercial chemical feedstock are currently being established with the aim to supplement and ultimately replace fossil fuels. To achieve this goal, it is pivotal to develop more efficient and environmental-friendly methods to convert cellulose into useful chemicals. One possible conversion route of cellulose is through the synthesis of 5-hydroxymethyfurfural (HMF), which the US Department of Energy has classified as one of the most promising renewable molecules.This thesis is aimed at advancing the potential application of heterogeneous catalysis and waterorganic biphase system for the synthesis of HMF directly from solid biomass. Firstly, we undertook a literature survey of the current strategies employed for HMF production with more attention on solid catalysis.Secondly, we explored the catalytic potential of non-toxic TiO 2 nanoparticle prepared by sol-gel technique on glucose conversion into HMF in an aqueous reaction system. Catalytic performance of TiO 2 was modified by introducing a second metal oxide (ZrO 2 ) to form binary oxides. Compared to pure TiO 2 , the binary oxide displayed better activity in terms of HMF yield, which was attributed to optimum balance of basic and acid sites for the tandem isomerization-dehydration reactions.Solvent effect was also studied in order to promote the reaction preferentially towards target product. Consequently, a biphase system of water-organic solvent mix was utilized and in combination with TiO 2 -ZrO 2 /Amberlyst 70 catalyst system, a remarkable yield of HMF can be produced from glucose Thirdly, catalytic properties of TiO 2 nanoparticle were fine-tuned to develop a single solid acid bifunctional (Lewis and Brønsted acidity) catalyst. To achieve this goal, TiO 2 was modified with phosphate anion and evaluated as catalysts for the conversion of glucose to HMF in a water-butanol biphasic system. Catalyst synthesis protocol was optimized by varying loading amount of phosphate anion and calcination temperature. X-ray spectroscopic analysis confirmed phosphorus incorporation into the TiO 2 framework giving rise to small-sized nanocrystals with high surface acidity. Pyridine-infrared (Py-IR) spectroscopy on the TiO 2 catalyst confirmed the presence of bifunctional Lewis and Brønsted acid sites as compared to pure TiO 2 with only Lewis acidity. The ii phosphate modified TiO 2 demonstrated excellent catalytic performance in terms of both activity and selectivity, as well as good recyclability.Fourthly, the robustness of phosphated TiO 2 catalyst to transform a variety of sugar moieties ranging from simple to ...