Morphology-controlled Preparation Of Novel Solid Acid Catalysts And Their Application For The Synthesis Of Alkyl Levulinates

Alkyl levulinates are important organic chemical intermediates and as raw materials widely used in the seasoning and flavor industry as well as transportation fuel. To alleviate the worldwide shortage of energy, the development of conversion of low-cost biomass as raw materials to biomass-derived platform molecule alkyl levulinates is a vital topic of green chemistry. Additionally, the design and preparation of efficient and recyclable solid acid catalyst is one of the key research. At present, for the synthesis of alkyl levulinates, some of the traditional solid acid catalysts possess the disadvantages of poor porosity and small BET surface area, leading to poor accessibility of active sites to reactants and low catalytic activity; meanwhile, the disadvantages of poor surface hydrophobicity, mechanical and thermal stability for these solid acid catalysts, result in the limitation of recycling. Therefore, this thesis is devoted to the morphology controlled preparation of novle solid acid catalyst ?for example, carbon-based or silicon-based materials?, which possess hollow or core-shell structure and controlled surface hydrophobicity by using template-assisted methods and carefully adjusting synthesis conditions. Their acid catalytic activities and stability towards the esterification of levulinic acid and alcoholysis of furfuryl alcohol or D-fructose were investigated.1. A series of arylsulfonic acid functionalized hollow mesoporous carbon spheres ?ArSO₃H-HMCSs? were successfully prepared by chemical bonding ArSO₃H groups to hard template prepared hollow mesoporous carbon spheres via diazonium coupling. The morphology, textural properties, chemical structure and acid site density of as-prepared ArSO₃H-HMCSs were well characterized by TEM, FESEM, nitrogen gas porosimetry measurement, XRD measurement, Raman scattering and FT-IR spectroscopy, XPS surface probe technique, acid-base titration as well as ICP-OES. The influence of arylsulfonic acid loading and hollow spherical morphology as well as inner diameter size on catalytic activity was studied by using esterification of levulinic acid and alcoholysis of furfuryl alcohol as model reactions; meanwhile, the reason of high catalytic activity of ArSO₃H-HMCSs catalysts was analysed carefully. By detecting the relevant products during reaction process using GC-MS technique, possible catalytic reaction mechanism of ArSO₃H-HMCSs catalysts was explored. Additionally, their catalytic stability was evaluated by recycling tests.2. A series of heteropoly acid and ZrO₂ bifunctionalized organosilica nanotubes (PW₁₂/ZrO₂-Si?Et?Si-NTs) were fabricated via a P123 single-micelle-templated sol-gel co-condensation route and carefully adjusted Si-to-Zr molar ratio and acidity in the initial gel mixture. The morphology, textural properties, chemical structure, surface hydrophobicity and acid site denstry or as-preparea PW₁₂/ZrO₂-Si?Et?Si-Nis were well cnaracterizea by IEM, nitrogen gas porosimetry measurement, water vapor adsorption measurement, FT-IR spectroscopy, solid-state NMR spectroscopy, pyridine-adsorbed FT-IR spectroscopy, acid-base titration as well as ICP-AES. The influence of H₃PW₁₂O₄₀ loading, different morphology and surface hydrophobicity on catalytic activity was studied by using esterification of levulinic acid and alcoholysis of furfuryl alcohol as model reactions; meanwhile, the reason of high catalytic activity of PW₁₂/ZrO₂-Si?Et?Si-NTs catalysts was analysed carefully. By detecting the relevant products during reaction process using GC-MS technique, possible catalytic reaction mechanism of PW₁₂/ZrO₂-Si?Et?Si-NTs catalysts was explored. Additionally, their catalytic stability was evaluated by recycling tests.3. A series of arenesulfonic acid and phenyl groups bifunctionalized ethane-bridged organosilica nanotubes ?ArSO₃H-Si?Et?Si-Ph-NTs? were successfully fabricated by one step P123-directed sol-gel co-condensation route combined with hydrothermal treatment and carefully adjusted P123-to-bissilylated organic presursor-to-HCl molar ratio in the starting preparation system. The morphology, textural properties, chemical structure, surface hydrophobicity and acid site density of as-prepared ArSO₃H-Si?Et?Si-Ph-NTs were well characterized by TEM, nitrogen gas porosimetry measurement, water vapor adsorption measurement, solid-state NMR spectroscopy, acid-base titration as well as ICP-OES. The influence of arenesulfonic acid loading, surface hydrophobicity and hollow tubular morphology on catalytic activity was studied by using esterification of levulinic acid and alcoholysis of furfuryl alcohol as model reactions; meanwhile, the reason of high catalytic activity of ArSO₃H-Si?Et?Si-Ph-NTs catalysts was analysed carefully. By detecting the relevant products during reaction process using GC-MS technique, possible catalytic reaction mechanism of ArSO₃H-Si?Et?Si-Ph-NTs catalysts was explored. Additionally, their catalytic stability was evaluated by recycling tests.4. Propylsulfonic acid functionalized micro/mesoporous hydrophilic core/hydrophobic shell silica spheres ?PrSO₃H-MM-SiO₂@Ph/BP/Et? have been successfully fabricated by a CTAB-directed two-step co-condensation route via using inorganic silicon and bridged organosilane respectively as a precursor of core and shell modified by organic sulfonic silane precursor combined with peroxide post-oxidation process. The morphology, textural properties, chemical structure and acid site density of as-prepared PrSO₃H-MM-SiO₂@Ph/BP/Et were well characterized by TEM, nitrogen gas porosimetry measurement, solid-state NMR spectroscopy and acid-base titration. The influence of thickness and organic groups of hydrophobic shell on catalytic activity was studied by using alcoholysis of D-fructose as a model reaction; meanwhile, the reason of high catalytic activity of PrSO₃H-MM-SiO₂@Ph/BP/Et catalysts was analysed carefully. By detecting the relevant products during reaction process using GC-MS and HPLC-MS techniques, possible catalytic reaction mechanism of PrSO₃H-MM-SiO₂@Ph/BP/Et catalysts was explored. Additionally, their catalytic stability was evaluated by recycling tests.