A Study On In-situ Hydrogenation Of 5-hydroxymethylfurfural To 2,5-dimethylfuran Over Non-noble Metal Catalyst

The increasingly severe energy crisis spur the development of renewable and green sources.Biomass,an abundant sustainable resource,can be converted into many value-added chemicals and fuels.5-Hydroxymethylfurfural（5-HMF）,an important degradation product of lignocellulose,is regarded as one of the most promising biomass-based platform feedstocks.Among its various derivatives,2,5-dimethylfuran（DMF）recevied extensive attention and was considered as an ideal liquid fuel due to its good physical and chemical properties.The selective catalytic reducuction of 5-HMF to DMF has been widely studied.However,the current reports are still focused on noble metal catalyst under molecular H₂ as the hydrogen donor.To achieve a more economical and green catalytic system,the in-situ hydrogenation of 5-HMF over non-noble metal catalysts with alcohol as hydrogen donor has became more and more interested in recent years.In this work,5-HMF was chosen as substrate for the preperation of DMF by in-situ hydrogenation over non-noble metal catalysts,and methanol and ethanol were selected as hydrogen donors.Basically,the process of H₂ production from hydrogen donor and hydrodeoxygenation of 5-HMF were investigated.The main work is summarized as follows:The production of DMF by in-situ hydrogenation of 5-HMF with methanol as hydrogen donor over different Cu-based catalysts were investigated.The hydrogen production from methanol and hydrodeoxygenation of 5-HMF was explored over Cu/Al₂O₃,Cu/ZnO,Cu/CeO₂,Cu/Co₃O₄ and Cu/ZrO₂.X-ray diffraction（XRD）,temperature programmed reduction（H₂-TPR）,temperature programmed desorption（NH₃-TPD）were performed to characterize the catalysts.The effect of reaction conditions on the preparation of DMF was further investigated and the reuse performance of catalysts was studied.The experimental results showed that different supports in Cu-based catalysts significantly influenced the activity of hydrogen production from methanol and hydrodeoxygenation of 5-HMF.Cu/Al₂O₃ catalyst showed the best catalytic activity,which can be attribute to the smaller Cu crystallite size,suitable acidity on the surface and the highest hydrogen content from methanol.Cu/ZnO exhibited higher utilization rate of hydrogen in the system.And the hydrogen content produced from methanol was directly related to temperature,lower temperature results in the decrease of hydrogen production,which may affect the DMF yield.Besides,except for CU/Co₃O₄ and Cu/ZrO₂,the reusing performance of other catalysts was poor.The production of DMF by in-situ hydrogenation of 5-HMF with ethanol as hydrogen donor over Cu/ZnO/CoO_x catalyst was investigated.XRD,inductively coupled plasma-optical emission spectroscopy（ICP-OES）,H₂-TPR,energy transmission electron microscopy（TEM）and dispersive X-ray spectroscopy（EDS-mapping）were performed to analyze the components and structure of catalysts.The effects of different components in the Cu/ZnO/CoO,on the H₂ production from ethanol and DMF prodcution from 5-HMF were investigated.The intermediate products were analyzed and the effects of catalyst loading,reaction temperature et al.on the production of DMF were observed.And the reuse performance of the catalyst was studied.The experimental results showed 100%conversion of 5-HMF and 99%yield of DMF was obtained at 210 ℃ for 5 h,and Cu/ZnO/CoO_x can still keep high activity after reused for six times.The hydrogen production from ethanol was mainly accomplished in the existence of CoOX,which was necessary for Cu/ZnO/CoO_x being used as an efficient catalyst.Cu was the main active site for the in-situ hydrogenation of 5-HMF,the interaction between Cu and Co further enhanced the selectivity to DMF,and the addition of ZnO would promote the hydrogenation of-CHO in 5-HMF to-CH₂OH.The synergistic catalysis between three components would be the reason for the high catalytic activity of Cu/ZnO/CoO_x.