Study On HMF Transfer Hydrogenation Catalyzed By New Copper-silicon Catalys

In recent years,due to the increasing depletion of fossil fuels and the problems of Greenhouse Effect and environmental pollution caused by the extensive use of fossil fuels,biomass fuels have attracted much attention because of their wide range of raw material sources,environment-friendly and renewable.5-hydroxymethylfurfural（HMF）,obtained from lignocellulose by hydrolysis,is an important biomass platform compound,which can be used to prepare high performance liquid fuel 2,5-dimethylfuran（DMF）by catalytic hydrogenation.Traditional hydrogenation methods usually use hydrogen as hydrogen source for hydrogenation,but there are some problems such as high cost of hydrogen transportation and storage.Therefore,the selection of liquid hydrogen source instead of hydrogen for transfer hydrogenation has important practical significance and application prospects.Based on this,a series of new copper-silicon catalysts were carried out to catalyze the transfer hydrogenation of 5-hydroxymethylfurfural to 2-dimethylfuran.The main work is summarized as follows:Firstly,a series of copper-silicon nanotube catalysts（Cu_x-Si_y-NT）with different ratios of copper to silicon were prepared by hydrothermal method,and the effects of the ratio of copper to silicon on the structure and performance of the catalysts were studied.The catalyst activity test results show that Cu/Sihas the highest catalytic activity when the reaction temperature is1:1,the reaction time is 1 h,the nitrogen pressure is 2 MPa,and isopropanol is used as the solvent to provide hydrogen source.The conversion of HMF is 100%,and the selectivity of the main product DMF is 74.7%.After 5 cycles,the activity of Cu-Si-NT catalyst did not decrease obviously,which indicated that the catalyst had good stability.Through a series of characterization methods such as X-ray diffraction,scanning,transmission electron microscope and temperature programmed reduction,it was found that the catalyst was nanotube-like structure and layer copper silicate structure.The reduction catalyst formed the composite structure of Cu⁰/Cu⁺and improved the hydrogenation activity.Secondly,the copper-silicon catalyst based on MOFs was studied.Cu-MOFs@SiO₂ was prepared by silicon coating on the basis of Cu-MOFs,and then Cu/C@SiO₂ catalyst was prepared by pyrolysis and carbonization.The effects of Cu-MOFs type（Cu-BTC and Cu-BDC）and Cu/Siratio on the structure and performance of the catalyst were investigated.The activity test results show that Cu/C@SiO₂ with Cu-BTC as MOF source has the highest activity.At the reaction temperature of 180℃,the partial pressure of nitrogen is 3 MPa,isopropanol is used as hydrogen source,the conversion of HMF is 100%and the selectivity is 99%.After 5 cycles,the activity of the catalyst does not decrease obviously and shows good stability.The activity of transfer hydrogenation of copper-based catalysts is higher than that of all copper-based catalysts at present.By means of X-ray diffraction,X-ray photoelectron spectroscopy,inductively coupled plasma emission spectroscopy,electron microscopy and temperature programmed desorption,it is found that there is layered copper silicate in the catalyst,Cu coexists in the mixed valence state of Cu⁺/Cu⁰,and the catalyst contains strong Lewis acid sites,which is the key reason for the high activity of the catalyst.