Morphology Controlled Preparation And Performance Of Both Heteropoly Acid And Bridged Organosilica Units Bifunctionalized Organic-Inorganic Hybrid Catalysts

Recently, the development of eco-friendly and high-efficiency catalysts is a vital topic ofgreen chemistry. Heteropolyacids (HPAs) have attracted extensive attention in the fields ofacid catalysis, photocatalysis and oxidation catalysis, due to their inherent propertiesincluding strong Br nsted acidity and discrete ionic structure. However, the disadvantages ofHPAs such as small BET surface area (<10m2g1), low thermal stability, high solubility inpolar media and hard to reuse limit their application in catalytic fields. In this dissertation, aseries of organic-inorganic hybrid materials with tunable pore structural ordering andmorphology functionalized by Keggin-type heteropoly acid, alkyl-bridged organosilicamoieties and ZrO2were prepared. The acid catalytic activities towards the esterification oflevulinic acid and biodiesel production from the low-cost non-edible oil (eruca sativa gars(ESG) oli and yellow horn oil) were investigated.1. A series of3D wormhole-like H3PW12O40/ZrO2–Si(Et)Si with different percentages ofethane-bridged organosilica goups were prepared through one-step sol-gelco-condensation–hydrothermal treatment in the presence of a triblock copolymer surfactantF127. The structural composition, pore morphology and porosity of the hybrid catalysts werecharacterized by FT-IR,31P MAS NMR,13C CP-MAS NMR and29Si MAS NMR,transmission electron microscopy (TEM) and nitrogen porosimetry measurement. The acidcatalytic performances of the hybrid catalysts were evaluated by the transesterification ofESG oil under the mild conditons, and the influences of the contents of functionalcomponents and hydrophobicity on the catalytic activity were investigated systematically.Additionally, the improved catalytic activity of H3PW12O40/ZrO2–Si(Et)Si hybrid catalystswas analyzed in detail. After three recyclings, acid catalytic activity and textural properties ofhybrid materials were unchanged, moreover, the leaching of H3PW12O40was not detectedduring the catalytic process.2. A series of mesostructured H3PW12O40/ZrO2–Si(R)Si and H3PW12O40/ZrO2–Si(R)(R=–CH2CH2–?–C6H4–or–C6H5) hybrid catalysts with controlled pore geometries andstructural orderings were produced through one-step sol-gel co-condensation–hydrothermaltreatment with a aid of P123.2D hexagonal (H3PW12O40/ZrO2–Si(Ph)Si) and3Dwormhole-like (H3PW12O40/ZrO2–Si(Et)Si and H3PW12O40/ZrO2–Si(Ph)) pore morphologywere obtained by adjusting the structure of the organosilica groups and initial Si/Zr molarratio. The structural composition, pore morphology, porosity and interaction of functionalcomponents and support were characterized by FT-IR,31P MAS NMR,13C CP-MAS NMRand29Si MAS NMR, TEM and nitrogen porosimetry measurement. Additionally, the acid capacity and the type of acid sites were determined by acid-base titration and pyridine-FTIR.The results suggest that H3PW12O40exists in the pore channel via Zr–O–W covalent linkedwith ZrO2, while the organosilica groups were introduced into the ZrO2farmework through–Zr–O–Si–R–Si–O–/–Zr–O–Si–R(R=–CH2CH2–?–C6H4–or–C6H5)linkages. The stronginteraction of the active component and support can facilitate the delocalization of negativecharge, ultimately leading to the enhanced Br nsted acidity. The effects of alcohol to acidmolar ratio, structural orderings and pore geometries as well as the type of alcohol werestudied through the esterification of levulinic acid with various alcohols (methanol, ethanoland n-butanol) under mild conditions. Based on the above results, the mechanism ofesterification of levulinic acid catalyzed by different types of acid sites was proposed. Theacid catalytic activity and stability of hybrid catalysts were evaluated through threeconsecutive cycles.3. Single-micelle-templated preparation of heteropoly acid and ZrO2bifunctionalizedorganosilica hollow nanospheres (H3PW12O40/ZrO2-Et-HNS) was developed by co-hydrolysisand-condensation of bissilylated organic precursor,1,2-bis(trimethoxysilyl)ethane (BTMSE),with zirconium source (Zr(n-OBu)4) in the presence of H3PW12O40, triblock copolymersurfactant F127and1,3,5-trimethylbenzene (TMB) followed by boiling ethanol washing.Through tuning the molar ratio of BTMSE/Zr(n-OBu)4in the initial gel mixture, themorphology transformation from3D interconnected mesostructure to the hollow sphericalnanostructure was realized. The inner diameter of the H3PW12O40/ZrO2-Et-HNS materials isin the range of612nm, and their shell thickness is ca.2nm. As the novel organic-inorganichybrid catalysts, the catalytic activity of H3PW12O40/ZrO2-Et-HNS was evaluated by themodel reactions of esterification of levulinic acid with methanol to methyl levulinate andtransesterification of yellow horn seed oil with methanol to biodiesel under refluxingtemperature (65oC) and atmospheric pressure. The obtained excellent heterogeneous acidcatalytic activity of H3PW12O40/ZrO2-Et-HNS is explained in terms of their strong Br nstedand Lewis acid acidity, unique hollow nanospherical morphology and hydrophobic surface.Finally, the recyclability of the hybrid catalysts was tested through three consecutive catalyticruns.