Preparation Of Niobium-based Solid Acid/SBA-15 And Catalytic Glucose Dehydration To 5-HMF

As effective substitute for fossil energy,biomass is an environment-friendly and renewable resource that hasmany advantages such as abundant and priceless.The effective preparation of 5-HMF with high added value from biomass is one of the important ways of utilization of biomass.At present,the 5-HMF selectivity of glucose dehydration by solid acid is low.The main reason is that the two step reaction of glucose isomerization to fructose and fructose dehydration to 5-HMF require different surface acid sites.And the internal structure of catalyst has a great influence on selectivity of reaction.Therefore,the key to realize one step method of preparing 5-HMF from glucose is the regulation of internal structure and the surface acidity of the catalyst.However,in the process of dehydration of hexose to 5-HMF,most of the reaction solvent is the organic solvent with high boiling point.In this system,it is difficult to separate the 5-HMF and solvent.This thesis started with the preparation of a niobium solid acid for catalytic hexose to 5-HMF in water solvent system.The dehydration of the fructose and glucose to 5HMF was investigated in detail.Nb/SBA-15 was prepared via incipient wetness impregnation using self-made SBA-15 as support.The catalyst preparation was optimized.By further treatment with phosphoric acid,a highly effective and efficient catalyst Nb-P/SBA-15 was obtained.Characterization by SEM,TEM,BET and XRD showed that Nb/SBA-15 preserved the microscopic structure of SBA-15 very well,with a diameter of internal channel of about 10 nm,and that the niobic species highly dispersed on the surface of the channels while the wall of channels became thinner after impregnation and treatment with phosphoric acid.With the treatment of phosphoric acid,P atom could insert into the skeleton of Nd-O and as a result generated medium and strong acidic sites,which enables Nb-P/SBA-15 more effective and efficient than Nb/SBA-15 as a catalyst in conversion of fructose to 5-HMF.Under the catalysis of Nb-P/SBA-15,the 5-HMF yield could be reached up to 92.6% with fructose conversion of 96.1% after reacting at 160 oC for 1.5 h when using water/MIBK(V/V=1:2)as the reaction media.Even after four times of successive recycling,Nb-P/SBA-15 could still demonstrate high catalytic activity and 5-HMF selectivity,suggesting it is a stable catalyst.To further improve catalytic glucose dehydration to 5-HMF,NbAl/SBA-15 was prepared by doping Al as the seconddactive component into Nb/SBA-15.The results suggested that the reaction activity of NbAl/SBA-15 was superior to the other catalysts at the same reaction condition.NbAl/SBA-15-x was prepared through regulating the molar ratio of two active components.Characterization by SEM,TEM,BET and XRD showed that NbAl/SBA-15 preserved the microscopic structure of SBA-15 very well.With the increase of Al ratio,pore size and surface area were diminishing and the wall of channel was thickening.Characterization by py-IR and NH3-TPD showed that NbAl/SBA-15-x combined the Br?nsted acid and Lewis acid.The NbAl/SBA-15-1.5 has a higher total acidity and acid strength,which enables NbAl/SBA-15-1.5 more effective and efficient than others as a catalyst in conversion of glucose to 5-HMF.Under the catalysis of NbAl/SBA-15-1.5,the 5-HMF yield could be reached up to 48.1% with fructose conversion of 93.4% after reacting at 170 oC for 10 h when using water/MIBK(V/V=1:2)as the reaction media.Even after four times of successive recycling,NbAl/SBA-15-1.5 could still demonstrate high catalytic activity and 5-HMF selectivity,suggesting it is a stable catalyst.