Design Of Sulfonic Acid Functionalized Organosilica Hollow Nanospheres And Their Catalytic Performance In The Furfuralalcohol Alcoholysis To Ethyl Levulinate

Recently, from the view of green, one of the important research direction of chemistry field is the utilization of eco-friendly and high-efficiency catalysts. Porous organosulfonic acid functionalized silica catalysts generally possess large surface areas, uniform pore sizes and high pore volumes, leading to them excellent catalytic activity in the reaction of esterification, transesterification, hydrolysis and dehydration. However, their long pore channels may lead to the lengthened diffusion distance of reactants and products, which can limit their catalytic activity to some extent. Moreover, most of biomass conversion-related processes perform under hydrothermal(or solvothermal) conditions. It often leads to the anchored sulfonic acid groups being unstable and leaching into the reaction media; meanwhile, accumulation of carbonaceous materials on the catalyst surface always happens. For the purpose of further improvement of the heterogeneous acid catalytic activity and stability of the catalysts, a series of organosulfonic acid functionalized ethane- or benzene-bridged organosilica hollow nanospheres(Pr/Ar SO3H-Et/Ph-HNS) were prepared. The catalytic activity was evaluated by alcoholysis of furfural alcohol to produce ethyl levulinate.1. A series of propylsulfonic acid functionalized ethane-bridged organosilica hollow nanospheres(Pr SO3H-Et-HNS) with different sulfonic acid group loadings were demonstrated by one-step co-hydrolysis and-condensation method of 1,2-bis(trimethoxysilyl)ethane(BTMSE) and 3-mercaptopropyltrimethoxysilane(MPTMS) combined with in-situ H2O2 oxidation using nonionic surfactant F127(EO106PO70EO106) as the soft template and 1,3,5-trimethylbenzene(TMB) as the micelle expanding agent. The morphology, porosity properties, chemical structure and thermal stability of the hybrid catalysts were well characterized by high resolusion transmission electron microscopy(TEM), nitrogen porosimetry measurement, 29 Si MAS NMR, 13 C CP-MAS NMR and TGA. And the acid property of the hybrid catalysts was determined by acid-base titration and ICP-OES method. To evaluate the influence of sulfonic acid group loading on the catalytic activity of Pr SO3H-Et-HNS, we selected the alcoholysis of furfural alcohol to produce ethyl levulinate as the model reaction. It showed that the yield of ethyl levulinate increased gradually for the Pr SO3H-Et-HNS5.4-, Pr SO3H-Et-HNS9.0- and Pr SO3H-Et-HNS12.5-catalyzed ethanolysis reaction; as for the Pr SO3H-Et-HNS15.8- and Pr SO3H-Et-HNS17.0-catalyzed ethanolysis reaction, the yield of ethyl levulinate decreased slightly as compared to Pr SO3H-Et-HNS12.5. For example, after the reaction proceeded for 60 min, the yield of ethyl levulinate reached 52.5%(Pr SO3H-Et-HNS5.4), 60.3%(Pr SO3H-Et-HNS9.0), 74.3%(Pr SO3H-Et-HNS12.5), 73.3%(Pr SO3H-Et-HNS15.8) and 72.0%(Pr SO3H-Et-HNS17.0), respectively. The excellent catalytic activity of as-prepared Pr SO3H-Et-HNS was explained in terms of Br?nsted acidity, unique hollow nanosphere morphology, excellent porosity properties and surface hydrophobicity. Also, after four successive catalytic recyclings, the used catalyst was characterized. It indicated that the physicochemical properties of the fourth time used catalyst were retained and the leaching of ?SO3H group into the reaction medium was trace. Finally, the possible mechanism of synthesis of ethyl levulinate from alcoholysis of furfural alcohol was put forward. Therefore, these hybrid materials worked effectively as recyclable solid acid catalysts in the alcoholysis of furfural alcohol to yield ethyl levulinate;2. A series of hybid materials with different morphologies were prepared by one-step co-hydrolysis and-condensation method combined with hydrothermal treatment technique using nonionic surfactant F127 as the soft template, 1,3,5-trimethylbenzene(TMB) as the micelle expanding agent, 1,2-bis(trimethoxysilyl)ethane(BTMSE) or 1,4-bis(triethoxysilyl)benzene(BTESB) as the silica precursor and 3-mercaptopropyltrimethoxysilane(MPTMS) or 2-(4-chlorosulfonylphenyl)ethyl trimethoxysilane(CSPTMS) as the organosulfonic acid precursor. The different morphologies including hollow nanosphere, 3D interconnected and cubic mesostructures were obtained by adjusting suitable molar ratios of total Si to F127 in the initial gel mixture. The morphology, textual properties and thermal stability of the hybrid catalysts were well characterized by high resolusion transmission electron microscopy(TEM), nitrogen porosimetry measurement and TGA. And the acid property of the hybrid catalysts was determined by acid-base titration and ICP-OES method. The influence of different morphologies on catalytic activity of catalylsts was evaluated by the alcoholysis of furfural alcohol to produce ethyl levulinate. It showed that hollow nanospherical hybrids showed higher activity with respect to their mesostructured counterparts. For example, for the Ar SO3H-Et-HNS7.4-, Pr SO3H-Ph-HNS5.9-, Pr SO3H-Et-3Dint5.8- and Pr SO3H-Et-3Dcub5.3-catalyzed reaction, the yield of ethyl levulinate reached 69.0%, 52.8%, 46.0% and 39.1%, respectively, over period of 60 min. It can be explained in terms of Br?nsted acidity, morphology and porosity properties. In order to evaluate the influence of morphologies on the catalytic activity more accurately, yield of ethyl levulinate per acid site(i.e. TOF, h?1) was presented. For comparison, commercially available Amberlyst-15 and H-ZSM-5 were also given under the same conditions.