Catalysts And Catalytic Mechanism For Selective Hydrogenation Of Furfural And Its Derivatives

The conversion of biomass to produce high-value chcmicals is an important topic in the field of green chemistry and energy chemistry currently.As a bulk biomass platform molecule,the catalytic conversion of furfural and its derivatives have received wide attention.Furfural itself is chemically active and contains carbonyl,diene and cyclic ether functional groups within the molecule,it can produce a variety of C4 and C5 molecules through selective hydrogenation/hydrogenolysis.The development of efficient catalysts for the catalytic conversion of furfural and its derivatives to high value-added products is significant in the basic fundamental research and practical applications.In this dissertation,the research objective is focused on the catalytic conversion of furfural and its derivatives to high value-added small molecules,specifically,focused on the basic scientific problems in biomass hydrogenolysis and multi-phase catalysis.,Herein,the Pd/TiH2,NiPrOx/Al2O3 and Ni/Eu2O3 catalysts have been designed for the efficient conversion of furfural and tetrahydrofurfurfuryl alcohol,respectively.The main purpose is to design and prepare efficient selective hydrogenation catalysts;to establish the structure-activity relationship between active metal electronic structure,the surface defect sites/interfacial sites with the catalytic performances;to explore the competitive adsorption behaviors on the catalyst surface and elucidate the catalytic mechanisms.The main research contents and innovative findings are as follows:(1)The Pd/TiH2 catalysts have been prepared by impregnation method for the selective hydrogenation of furfural to investigate the factors affecting the catalytic performance and discuss the related catalytic hydrogenation mechanism.TiH2 exhibits a unique crystal structure and abundant surface defects,and is thus was selected to prepare Pd-based catalysts for promoting the adsorption and activation of C=O bonds on the active metal Pd.The structural characterization by TEM,XRD,TPR,TPD and Raman showed that the Pd nanoparticles were uniformly dispersed on the surface of catalysts;the TiH2 support surface had abundant defect sites and contained competitive processes of hydrogen storage-release.Combined with the experimental data and the characterization results of the catalyst active center and substrate adsorption behaviors analyzed by XPS and in situ DRIFTS,the conformational relationships have been established for Pd dispersion,electronic state and surface defects of the catalyst with catalytic activity and selectivity in furfural hydrogenation.(2)Designed and prepared praseodymium oxide(PrOx)modified Ni/Al2O3 catalyst,and discussed its catalytic performances in tetrahydrofurfurfuryl alcohol hydrogenolysis reaction.It was demonstrated that the catalytic activity and selectivity of the catalysts had a significant dependence on the Pr/Ni ratio.The optimal catalyst was obtained on a catalyst with Pr/Ni ratio of 1.2,and the selectivity of 1,5-pentanediol was up to 88.4%at 79.2%conversion.The presence of Ni could promote the reduction of praseodymium oxide,resulting in the formation of defect-rich PrOx and the formation of Ni-PrOx interfacial sites with Ni nanoparticles;while γ-Al2O3 plays a role in improving the dispersion and the stability of Ni-PrOx active sites.It was confirmed by in situ DRIFTS and control experiments that:the metal Ni0 sites adsorbed and activated H2 to generate active hydrogen;the introduction of PrOx in nickel-based catalysts facilitated the adsorption of tetrahydrofurfuryl alcohol;the synergistic effect between the defect-rich PrOx and adjacent active Ni species played a key role in the selective cleavage of C-O bond in tetrahydrofurfuryl alcohol.(3)Europium oxide(Eu2O3)supported nickel-based catalysts exhibited remarkable catalytic performance in the tetrahydrofurfuryl alcohol hydrogenolysis with a selectivity to1,5-pentanediol higher than 95%.The effects of the metal as well as the structure and electronic state of the interfacial sites on the catalytic performance were investigated by varying active metal,the loading of metal Ni and the reduction temperature.Compared with Eu2O3 supported Cu-,Ru-,and Rh catalysts,the Ni/Eu2O3 catalyst presented the significant higher reaction rate of THFA hydrogenolysis and the selectivity to 1,5-pentanediol.The characterized results of XRD,H2-TPR,H2-TPD,TEM,XPS showed the synergistic effect between Ni and Eu2O3.In situ DRIFTS combined with catalyst surface structure analysis demonstrated that the interfacial region of the Ni and Eu2O3 is the active center for tetrahydrofurfuryl alcohol adsorption,while the active hydrogen species spillovered to the surface of Eu2O3 has facilitating effect on the hydrogenolysis reaction.