Study On The Preparation Of Furan-based Platform Compounds From Biomass Catalyzed By Bifunctional Acid Catalysts

Furfural and 5-hydroxymethylfurfural(HMF),as two multi-functional furan compounds,play an extremely critical role as a“transit station”in the conversion utilization of biomass.Relying on furfural and 5-hydroxymethylfurfural as a"transit platform",biomass can be further processed and transformed into a variety of high value-added terminal chemicals including aviation fuel,pharmaceutical intermediates,and basic chemical raw materials.Therefore,achieving high efficiency conversion of furanyl platform compounds from biomass or its derived raw materials has become an important factor affecting the high-value utilization of biomass energy.In this paper,based on the formation mechanism of furfural and 5-hydroxymethylfurfural,a series of bifunctional solid acidic catalysts with suitable physicochemical properties were designed and prepared,which achieved the high-efficiency formation of furan-based platform compounds from biomass materials through catalytic driving.While screening to determine the optimal process parameters of the catalytic system used,a detailed study of possible catalytic paths,active centers,and catalyst deactivation mechanisms was also conducted.The main research conclusions obtained are summarized as follows:(1)The HfP/SiO₂ solid acid catalyst with high catalytic performance was successfully synthesized by the preparation method of introducing active HfP in-situ in the SiO₂ carrier.The catalyst drives the hydrolysis conversion process of xylan(hemicellulose)to achieve a furfural yield of up to 85%,and the catalytic performance and physicochemical properties of the catalyst are maintained after seven consecutive cycles.The preparation and application of HfP/SiO₂ catalysts have further broadened the family of acidic metal phosphide catalysts.(2)The discovery and application of the CrPO₄ catalyst solves the problem that the active phosphide component needs to rely on the carrier to express high activity,and simplifies the preparation process of the phosphide catalyst.Under optimal reaction conditions,CrPO₄ catalyzed the dehydration conversion of xylose to achieve a furfural yield of 88%.Moreover,when virgin wheat straw was used as the reaction substrate,solid CrPO₄ also exhabited considerable catalytic performance,achieving 67%furfural yield and 34%5-hydroxymethylfurfural yield,respectively.By analyzing the solubility of the catalyst and the distribution of the products,the high catalytic performance of the CrPO₄ catalyst was confirmed to be due to its temperature-controlled phase transfer characteristics.That is,as the reaction temperature increases,part of the catalyst undergoes dissolution,ionization,and hydrolysis processes in sequence to form Lewis acidic metal hydroxy compound[Cr(H₂O)₅OH]²⁺and Br(?)nsted acidic H⁺,both of which act as active centers to efficiently catalyze xylan hydrolysis,xylose isomerization and xylulose dehydration.(3)By sequentially introducing-H₂PO₃ functional group and Cr³⁺ion into the surface of mesoporous SBA-15,a series of dual-function(x)Cr³⁺/P-SBA-15 catalysts with stepped acidity difference were successfully prepared.Among them,the(0.25)Cr³⁺/P-SBA-15 catalyst showed the best catalytic performance due to the combination of appropriate total active sites and acid ratio.The catalyst can achieve a furfural yield of up to 91%with xylose as a substrate under optimal reaction conditions,and a furfural yield of 58%with hemicellulose as a substrate.Moreover,the catalyst still has the ability to exhibit excellent catalytic activity and structural stability after repeated cycles.Its well-developed pore structure can accommodate sufficient active components and thus has the ability to resist the negative effects caused by carbon deposition blockage and loss of active sites.(4)Through the impregnation preparation method,the beneficial catalytic effects of both Crelement and H-?zeolite carrier can be perfectly combined in the form of Cr/?catalyst.Under the evaluation of the probe reaction(glucose conversion to prepare HMF),the excellent catalytic performance of the Cr/?solid acid catalyst was verified(achieved a high HMF yield of 72%and a product selectivity of 83%).The high activity of the catalyst stems from the Lewis and Br(?)nsted acid sites with the appropriate quantity,strength and ratio.In addition,through the substrate expansion experiment,the wide catalytic compatibility of the Cr/?zeolite catalyst was also confirmed,indicating that the catalyst has the practical application ability to drive a variety of biomass-derived substrates to prepare furan-based platform compounds.(5)By using Lewis acid salt SnCl₂ and Br(?)nsted acidic solid phosphotungstic acid(PTA)to gradually modify H-?zeolite,(x)SnCl₂-PTA/?series catalysts with high acid density were successfully prepared.Because of its high strength acid density,suitable acid ratio and suitable pore structure,this series of catalysts showed excellent catalytic performance in the process of catalytic conversion of wheat straw.Under the optimal reaction conditions,furfural and HMF yields of up to 71%and 30%,respectively,were obtained.After repeated cycles of use,the catalyst exhibited loss of active components and collapse of pores,resulting in a partial decrease in the catalytic activity of the catalyst after cycling.However,due to the developed mesoporous structure of the catalyst,partial restoration of the catalytic activity of the catalyst can be achieved by simple impregnation of SnCl₂ and PTA active components.