Study Of Conversion Of Biomass Into High-valued Chemicals Assisted By Low-temperature Plasma

Glucose,a cost-inefficient biomass platform compound,was highly economical as a reactant for conversion to 5-hydroxymethylfurfural（HMF）.Glucose could isomerize to fructose on Lewis acid or base catalyst,and fructose could dehydrate to HMF on Br（?）nsted acid.The isomerization of glucose to fructose was the rate control step.A variety of by-products were usually generated during fructose dehydration to HMF.The regulation of Br（?）nsted-Lewis acid sites in the catalyst and their acidic strength played an important role in the generation of HMF from glucose.Metal-organic frameworks（MOFs）had open Lewis acid sites.The Cr metal sites in Cr-MOFs could minimize the time of variable spin equilibrium betweenα-andβ-glucopyranose isomers and promote the isomerization reaction of glucose to fructose.However,the yield of HMF was not high due to the single Lewis acid site of Cr-MOFs.Therefore,it’s necessary to develop a method to regulate the acid sites of Cr-MOFs.As an unconventional means,dielectric barrier discharge（DBD）low-temperature plasma played an important role in assisting glucose conversion and catalyst preparation.In this paper,DBD plasma assisted the preparation of catalyst to regulate glucose conversion,and the glucose conversion with DBD plasma was studied.Amberlyst-15and zirconium oxide were used to regulate the acid sites of Cr-MOFs based catalysts,in which zirconium oxide（ZrO₂-D）was obtained by calcination of Zr-MOFs material（Zr-MOFs-D）synthesized with DBD plasma.Using Cr（NO₃）₃·9H₂O as metal source and terephthalic acid（PTA）as ligand,adding Amberlyst-15 ion exchange resin,Cr-MOFs/Cr（OH）₃-[Amb x%]catalyst for for glucose catalytic conversion was successfully prepared by one-pot hydrothermal method.The study found that the strong Br（?）nsted acid sites determined the conversion of glucose to HMF,while weak Br（?）nsted acid sites could lead to the formation of FA.When the glucose concentration was 5 g/L in DMF,the reaction condition was 150℃for 2 h,98%of glucose conversion and 31.2%of HMF yield were obtained with 0.01wt%Cr-MOFs/Cr（OH）₃-[Amb 2%]（the molar concentration of Amberlyst-15 was 2mol%）under N₂atmosphere.Using DBD low-temperature plasma to synthesize Zr-MOFs-D and calcined to obtain ZrO₂-D,Cr-MOFs/Cr（OH）₃@ZrO₂-D was obtained by using ZrO₂-D compounded with Cr-MOFs based catalysts.The strong electric field on the catalyst surface formed by low-temperature plasma was beneficial to format strong metal oxide-support interaction（SMOSI）.SMOSI accompanied with the encapsulation of Zr metal nanoparticles.The SMOSI stabilized the metal nanoparticles could change the encapsulation of metal nanoparticles.Which could modulate the acidic sites of the catalyst.When the reaction condition was 150℃for 2 h,the glucose concentration was 3 g/L in DMF,97.9%of glucose conversion and 38.0%of HMF yield was obtained with 0.01 wt%Cr-MOFs/Cr（OH）₃-ZrO₂-D-3h（the calcination time of ZrO₂-D was 3 h）under N₂atmosphere.Using DBD low-temperature plasma to convert glucose without catalyst.When glucose concentration of 3 g/L in DMF solvent,discharge voltage of 10.2 k V for 2 h,the glucose conversion reached 77.6%while the fructose yield was 18.5%.However,the HMF production was trace.By combining DBD low-temperature plasma with 0.01 wt%Cr-MOFs/Cr（OH）₃@ZrO₂-3h catalyst,discharge voltage of 10.2 k V for 1 h.The glucose conversion reached 80.9%,the fructose yield reached 22.6%,and the HMF yield reached 7.13%.In conclusion,the use of low-temperature plasma could effectively assist the catalytic conversion of glucose to high-value chemical products.