Conversion Of Biomass-derived Furans And Their Derivatives Through Multiple Catalytic Systems

With increasing demands for the renewable chemicals and fuels,biomass has attracted great attention as an alternative feedstock.In the past few decades,extensive researches on the biomass valorization have been motivated.Lignocellulose,a key part of biomass,is composed of cellulose,hemicellulose and lignin.Starting from lignocellulose,a lot of valuable platform chemicals can be obtained.Furans（furfural,5-hydromethylfurfural and 2,5-furandicarboxylic acid）and their derivates（levulinic acid）belong to the family of Top 12 valuable platform molecules.On the basis of furans and their derivates,a lot of valuable fuels and chemicals can be obtained through catalytic conversion routes.Firstly,the tandem Diels-Alder and dehydration reactions of furan derivatives with ethylene were catalyzed by a series of haloacetic acids and rare-earth metal triflates.With the carefully selected catalysts and solvent,a quasi-homogeneous reaction system can be formed,where accurate kinetic studies could be performed.Haloacetic acids exhibit considerable activity in the Diels-Alder and dehydration reactions with a similar apparent activity energy value of～8.4 kcal/mol,and CF₂ClCOOH with a proper Br?nsted acidity is optimized for the reaction.Rare-earth metal triflates also exhibit considerable activity in the Diels-Alder and dehydration reactions with a similar apparent activity energy value of～13.0 kcal/mol,and Sc（OTf）₃ with the highest Lewis acidity is optimized.On the basis of kinetic analysis results,the impacts of acidity on the performance of catalysts are discussed in detail and the reaction network is proposed.Besides,the substrate scope of furan derivatives for the Diels-Alder and dehydration reactions with ethylene is investigated using CF₂ClCOOH and Sc（OTf）₃ as catalysts for possible extensions of the reaction.Secondly,Meso-Zr-Al-beta zeolites are successfully prepared through a multiple-step post-synthesis strategy composed of controlled dealumination,desilicication and metal incorporation.The presence of both Br?nsted and Lewis acid sites with a certain extent of strength in Meso-Zr-Al-beta is demonstrated by NH₃-TPD and FTIR spectroscopy with pyridine adsorption/desorption.The creation of mesopores via desilicication through alkaline treatment is confirmed by N₂ adsorption/desorption isotherms.Meso-Zr-Al-beta,with Br?nsted acid sites,Lewis acid sites and mesopores,is applied as a zeolite catalyst for the cascade conversion of biomass platform molecule furfural toγ-valerolactone.Owing to the presence of multiple functional sites and their mutual compatibility,remarkable activity forγ-valerolactone production and catalyst recyclability could be achieved with a single Meso-Zr-Al-beta,which appears to be a better catalyst than the commonly-employedcombinationcatalystsystems.Themultifunctional Meso-Zr-Al-beta zeolite is also applied as a promising catalyst in other cascade reactions in biomass valorization,i.e.glucose conversion to 5-hydromethylfurfural and trioses conversion to ethyl lactate.Similar zeolite catalysts containing multiple functional sites could be prepared via similar routes,and the number of acid sites and their strength can be adjusted to some extent to derive an optimized catalyst by changing the preparation parameters.Finally,a non-precious metal catalyst Ni/NiO is developed for the efficient hydrogenation of furan derivates levulinic acid toγ-valerolactone under mild conditions.Treating nickel oxide in hydrogen at controlled temperature of 473-573 K results in its partial reduction to metallic nickel and the formation of Ni/NiO heterojunctions,as indicated by the characterization results from in situ XRD,XPS and TEM.The as-prepared Ni/NiO catalyst exhibits remarkable activity in levulinic acid hydrogenation with a high mass activity of 14.1 mmol/h/g at 393 K,being over18 times higher than NiO and 10 times higher than metallic Ni.Besides,Ni/NiO shows very good stability and recyclability during the reaction,making it a promising catalyst for practical levulinic acid hydrogenation.The formation of Ni/NiO heterojunctions is crucial for the remarkable activity of Ni/NiO composite catalyst and a cooperative Langmuir-Hinshelwood mechanism is proposed for levulinic acid hydrogenation on the basis of kinetic analysis and theoretical calculations.The concept of cooperative catalysis on metal/oxide heterojunctions can be expanded to other hydrogenation reactions.