Preparation Of Solid Acid And Nickel-based Catalysts And Their Catalytic Activities For Furan Platform Molecular Conversion Of Biomass

Energy crisis threatens the survival of human beings.It is urgent to seek renewable green energy.Biomass is the only renewable carbon source,which can be transformed into high value-added compounds through a variety of means.Efficient utilization of biomass resources can alleviate the energy crisis.Furan derivatives are the bridge between biomass and alternative carbon source chemicals.It is of great significance to develop cost-effective catalysts for the conversion of furan derivatives.In this paper,a series of low-cost solid acid catalysts and Ni based catalysts were synthesized for the conversion of furan compounds to high value-added chemicals.The effects of the types of catalyst supports,the acidity and basicity of the catalyst surface and the active sites on the catalyst activity were investigated.The main contents are as follows:1.In this study,clay based solid acid catalyst was prepared by using sulfuric acid as sulfonating agent and ordinary clay as support.The effects of sulfuric acid concentration and calcination temperature on physiochemical properties,interaction of sulfur species with the oxides in clay,distribution of Br（?）nsted acid sites and Lewis acid sites,and catalytic performances of conversion of furfuryl alcohol（FA）to ethyl levulinate（EL）in ethanol were investigated.The results showed that sulfuric acid reacted with alumina in clay to form Al₂（SO₄）₃,thus changing structure and crystal phase of the catalyst.Increasing calcination temperature enhanced the interaction between sulfate species and clay,the retaining of sulfur on clay surface and the formation of more Br（?）nsted acid sites while less Lewis acid sites.In addition,balanced distribution of the acidic sites was crucial for selective conversion of FA to EL.Over the clay catalyst impregnated with 4 M H₂SO₄ and calcined at 300℃,the yield of EL could reach 90%.The catalyst was not stable in polar solvent like ethanol due to leaching of sulfur species,while in aprotic solvent like dimethyl sulfoxide,the catalyst maintained a good catalytic stability.2.Attapulgite（ATTP）is an abundant natural magnesium aluminosilicate mineral that can be used as support for manufacturing cost-effective solid acid catalysts.This study mainly focuses on structural change of ATTP and the formation of Br（?）nsted and Lewis acid sites during sulfonation in H₂SO₄.The results indicate that the sulfonation leads to the drastic change of the crystal phases as sulfuric acid not only plays the roles of grafting the sulfur species but also reacts with the Ca O,Mg O,Al₂O₃ and Fe₂O₃ or their salts in ATTP to form the sulfates,resulting in the substantial change of the porous structure of ATTP.In such a process,the Br（?）nsted acidic sites,which are the main active sites for the conversion of furfuryl alcohol（FA）to ethyl levulinate（EL）,are introduced,while the abundance/strength of the Lewis acid sites are enhanced.The yield of EL up to 95.4%is achieved over the H₂SO₄/ATTP catalyst.The Fe₂（SO₄）₃ and Mg SO₄ in the catalyst leaches in ethanol but does not affect the catalytic stability.The formed polymer also does not affect much the catalytic activity after their removal via the calcination in air.3.In this study,ordinary clay was activated with sodium hydroxide and a nickel-based catalyst was prepared.The results showed that the treatment with Na OH drastically modified the structures and the performances of the catalyst in the hydrogenation of furfural in ethanol.The treatment significantly enhanced abundance of the mesopores,benefiting for the dispersion of Ni and formation of abundant alkaline sites.The presence of the alkaline sites suppressed the acetalization and etherification in the conversion of either furfural or vanillin in ethanol,making hydrogenation as the dominate reaction route.Further to this,the alkaline sites with the electron-rich nature also suppressed the further hydrogenation of the furan ring in furfuryl alcohol with ethanol as the reaction medium.The nickel catalyst with the un-treated clay as support did not have such effect and the abundant acidic sites made the acetalization/etherification as the competitive reactions of hydrogenation.The results herein demonstrated that the acidic/basic properties of the Ni/clay before and after the pretreatment with Na OH significantly impacted the reaction network in the hydrogenation reactions.4.In this study,the influence of the abundance of active metals on the catalytic hydrogenation selectivity of furfural was investigated.The conversion of furfural to cyclopentanone involves multiple hydrogenation steps.Not only the type of metal sites,but also the abundance of metal sites may affect the formation of reaction intermediates,thus affecting the selectivity of the product.In this study,we found that,during the hydrogenation,the carbonyl and the furan ring functionalities in furfural showed the different response to the number of nickel sites on Ni/Si O₂ catalyst.The hydrogenation of the C=O in furfural could take place effectively with the nickel loading below 1 wt%to form firstly furfuryl alcohol（FA）and then to CPO with the selectivity as high as 98.2%.In comparison,the higher nickel loading favored the hydrogenation of the furan ring in furfural or FA to form tetrahydrofurfuryl alcohol（THFA）,formation of which eliminated the chance for the formation of CPO.The hydrogenation of the carbonyl functionality and furan ring in furfural proceeded via distinct orientations of adsorption and the involvement of the varied number of metal sites.Controlling the number of exposed metallic nickel sites could thus tailor the selectivity of the products in hydrogenation of furfural.