| It has important application and scientific study value onhighly-efficient production of chemicals from biomass resources by means of catalytic system from theviewpoint of green chemistry and sustainable development.Base-metal catalysts with high performance can greatly reduce the production cost and promotelarge-scale biomass conversions.Furfuralderived from hemicelluloseshas been selectedas the promising renewable platform,which canconvert to methylfuroatevia oxidative esterification reactionwith molecular oxygen in methanol and thereforehas provided anew non-petroleum basedsynthetic routeto producemethylfuroate.However,in many previous reports,stoichiometric basic additives are generally needed in noble or non-noble metal catalysts to achieve high performance,resulting in the problem such as high energy-consumption,leaching,side reaction,which hindersits widespread application.Owing to its low-cost and unique property in electrocatalysisand organic reactions,metal-containing N_doped carbon catalyst has beenselected as an alternative for noblemetal catalysts.Up to now,various cobalt-nitrogen-doped carbon catalysts have been synthesized by pyrolysis of nitrogen-rich metal complexes or mixtures of metal salts and N-containing ligands on supports under nitrogen atmosphere.Single Co atom bonded to N atom within graphitic sheets has been used as active center in aerobic oxidative cross-coupling and hydrogenative coupling reactions.Basic additives such as LiOH or NaOH have been found to be indispensible for Co-N-C catalyst in these reactions.According to previous study,we have usedcobalt-nitrogen-doped carbon supported on basic carrier to realize high oxidation efficiency of furfural under basic additive-free condition.The Co-N-C/MgO catalyst was synthesized by direct pyrolyzation ofCo-1,10-phenanthroline on MgO(prepared by impregnation method)at 800 ? in N2.Transmission electron microscopy9X-ray diffraction,X_ray photoelectron spectroscopy,and ICP results have showedthat cobalt-nitrogen-doped carbon might existed in Co-N-C/MgOcatalyst.In the oxidative esterification reaction of furfural to methylfuroate,the conversion and selectivity of Co-N-C/MgO catalyst have achieved 93.0% and 98.5% respectively to methylfuroate under 0.5 MPa O2 at 100 ? for 12 h without basic additives,which are much higher than thoseof cobalt catalysts by pyrolyzation of Co-1,10-phenanthroline on activated carbon and typical basic supports including NaX5 NaY,and CaO.The high performance of Co-N-C/MgO catalyst in the production of methylfuroate under mild conditions without any basic additiveswas due to its high ability for dehydrogenation.In addition,oxygen pressure has negligible effect on the oxidative esterification of fixrfural with Co-N-C/MgO in the range of 0.3 MPa-1.0 MPa.To further investigate the catalytic performance of cobalt-nitrogen containing carbon species,C?-N-C(HC1)(0.05 mmol Co)was synthesized by means of removal of MgO with HC1,and utilized as catalyst in the oxidative esterification of furfural in methanol under 0.5MPa O2 at 100 0C for 5 h.Interestingly,using Co-N-C(HCl)as catalyst has leaded to large-scale generation of byproduct of acetal[2-(dimethoxymethyl)furan] formed by condensation of furfural and methanol.However,when introducingMgO,the majority of furfural converted to methylfuroate under the same condition.Therefore,the condensation of furfural with methanol to acetal and the oxidative esterification of fiirfural to methylfuroate are two competitive pathways5 the dominant pathway decides the main product.Our study hasalsoconfirmedthe conclusion oQ)ervious researchers that M-N-C catalyst isinvolved in the catalysis mechanismand specific anions including CP remarkably influence its performance via coordination or competition with O2 for active metal centers.Our workhas provided a useful process foroxidative esterification of biomass-derived aldehyde compounds and thedesign of non-noblemetal catalyst. |
PDF Full Text Request