Study On Preparation Of 5-hydroxymethylfurfural And 2,5-furandicarboxymoxylic Acid

Catalytic preparation of biomass-based chemicals from abundant and renewable biomass-based hexose is of great significance for accelerating the development and utilization of biomass energy,alleviating the energy crisis,and responding to global climate change.5-Hydroxymethylfurfural（HMF）is an important platform compound linking biomass resources and petrochemistry,and its oxidation-produced 2,5-furandicarboxylic acid（FDCA）is a petroleum-based the most potential biomass-based substitute for phthalic acid.The preparation of HMF catalyzed by hexose requires a multi-step transformation process,and HMF is chemically active and prone to side reactions.The multiple functional groups need to be oxidized in the reaction process of oxidation for HMF to FDCA,the reaction steps are complicated,and the activation of oxidant O₂ is difficult.Therefore,designing a high-efficiency and high-selectivity catalytic system has become the key to realizing the efficient preparation of HMF from hexose and oxidation of HMF to FDCA,which is of great significance for promoting biomass to replace traditional fossil energy and petrochemical products.In this paper,a series of multi-active site heterogeneous catalysts were designed and controllably prepared to catalyze multi-step reactions such as isomerization and dehydration of hexose to HMF in one pot,and to explore the synergy of multi-active sites in the catalytic process and means of suppressing side effects.A series of Ce O₂-supported noble metal catalysts were prepared with the goal of achieving high-efficiency oxidation of HMF to FDCA.The concentration of oxygen vacancy（V_O）on the surface of the support and its regulation method,promoting the electron transport of Au-Pd-Ce O₂ and changing the support structure were studied.The structure-activity relationship of oxidative capacity and the possible catalytic mechanism were analyzed.The main research work of this paper is as follows:1.Construction of multi-active-site catalysts for catalytic conversion of hexose to HMF in different solvent systems（1）The conversion of biomass-based hexose to HMF often requires multi-step transformations such as converting aldose to ketose,and then removing three molecules of water.Sulfonic acid groups（-SO₃H）and Cr ions were modified on the surface of Halloysite（HNTs）,and a bifunctional catalyst was prepared to regulate the active sites of Br（?）nsted acid and Lewis acid,which was used to catalyze the continuous conversion of mannose to HMF.Catalytic experiments showed that the Lewis acid active site promoted the stereoisomerization of mannose to glucose and glucose to fructose,and the Br（?）nsted acid active site catalyzed the dehydration of fructose to HMF.And the hydrophobic alkane chain was introduced to increase the hydrophobicity of the catalyst,which promoted the extraction of the generated HMF into the stable MIBK phase in a two-phase solvent of saturated sodium chloride aqueous solution and methyl isobutyl ketone（MIBK）,and inhibited the formation of by-products from the hydration of HMF.The mannose conversion of 95.0%and highest HMF yield of 48.1%can be obtain under the optimak conditions（130℃,18.0 h）.（2）It is more cost-effective to catalyze the preparation of HMF from cellulose,which accounts for the largest proportion of plant biomass.Macroporous Br（?）nsted acid-base bifunctional polymer-based（Poly-Px）catalysts were prepared by thermal polymerization using acid-base metal-organic frameworks（MOFs）-stabilized Pickering high internal phase emulsions as templates,which was used to catalyze the conversion of cellulose to HMF by one-pot.By adjusting the emulsion parameters and the ratio of acid and base MOFs,the catalyst pore structure and acid and base density were optimized.The results showed that the Br（?）nsted acid active site catalyzed the depolymerization of cellulose to monosaccharide glucose and the dehydration of fructose to HMF,and the Br（?）nsted base active site promoted the isomerization of glucose to fructose,and the synergistic effect improved the catalytic properformance.And the pore structure played a key role in the mass transfer and transformation of macromolecular cellulose.When the acid density was 1.99 mmol·g^-1,the base density was 1.13 mmol·g^-1,and the pore size was 53.3±11.3μm,the highest HMF yield of40.5%.2.Construction of Au/Ce O2 supported catalysts for catalytic oxidation of HMF to FDCA（1）Heterogeneous catalysts are crucial for the adsorption and enrichment of reaction substrates to exert their catalytic ability.A multi-component catalyst was prepared by combining natural nitrogen-containing biomass chitosan derived nitrogen-doped carbon（N-PC）and Bi element-doped Ce O₂ to oxide HMF to FDCA.The adsorption experiments showed that N-PC effectively enhanced the adsorption capacity of the catalyst for HMF.And EPR resuls showed that Bi doping increased the V_Oconcentration of the catalyst and enhanced the oxidation performance of the catalyst.The catalyst Au/Bi-Ce O₂/N-PC was prepared by loading Au nanoparticles（Nano-particles,NPs）,which synergized the advantages of Bi-Ce O₂ and N-PC to effectively promote the enrichment and conversion of reactant HMF on the catalyst surface,improving the yield of target product FDCA.The highest FDCA yield of 92.8%was obtained at 110℃and 12.0 h.（2）From the previous experiment,it can be concluded that V_O can be used as an active site to participate in the oxidation of HMF by Ce O₂-based catalysts.How to increase the concentration of V_O becomes a key factor to improve the oxidation ability of the catalyst.Au/Ce O₂ catalysts with different exposed crystal planes were prepared by co-precipitation method to prepare three Au NPs supported on Ce O₂ supports with different morphologies.Raman and EPR results indicated that rod-Ce O₂（100）had higher V_O concentration than cube-Ce O₂（110）and oct-Ce O₂（111）,making the catalyst Au/rod-Ce O₂（100）exhibited stronger O₂ adsorption and activation capacity.The experimental results showed that the catalyst Au/rod-Ce O₂（100）exhibited the best catalytic performance for the conversion of HMF to FDCA compared with the catalysts Au/cube-Ce O₂（110）and Au/oct-Ce O₂（111）.The highest FDCA yield of 95.6%was obtained at 120℃and 12.0 h.3.Construction of Au-Pd/Ce O2 supported catalysts for catalytic oxidation of HMF and BHMF to FDCA（1）Based on the results of the previous experiment,the optimal exposed crystal face rod-Ce O₂（100）was selected as the research object,the V_O concentration of Ce O₂was further increased by acid treatment,and Au and Pd NPs were loaded on Ce O₂ by combining chemical reduction and photoreduction to prepare bimetals catalyst of Au_xPd_y/A_t-Ce O₂.XPS and density function theory results exhibited that there was a strong charge effect between Au-Pd in the catalyst,which promoted electron transport between Au-Pd and Au-Pd-Ce O₂.The advantages of synergistic V_O and strong electron transport enhanced the adsorption of O₂,accelerated the oxygen conversion rate and the generation efficiency of reactive oxygen species.And the adsorption and conversion ability of the catalyst to HMF was strengthened,so that the high-efficiency conversion of HMF to FDCA can be realized under mild reaction conditions.The HMF conversion of 99.9%and highest FDCA yield of 99.0%can be obtain under the optimak conditions（80℃,40.0 min）.（2）The surface of Ce O₂ has both acid and base sites,which are related to the oxidation performance of Ce O₂-based catalysts.The bimetal catalyst Au_xPd_y/P_T-Ce O₂was prepared by two times of hydrothermal synthesis of high Ce ions and porous rod-like Ce O₂ support with a certain V_O concentration supporting both Au and Pd NPs.The EPR results exhibited that adjusting the secondary hydrothermal temperature can realize the controllable adjustment of the Ce ion concentration in the Ce O₂.The results of NH₃-TPD and catalysis showed that high concentration of Ce ions enhanced the acid density of the catalyst and accelerateed the catalytic ability of the catalyst to convert aldehyde groups into carboxyl groups.Converting 2,5-furandimethanol（BHMF）to FDCA with more stable catalytic physicochemical properties,a high-efficiency conversion of BHMF and a high yield of FDCA can be achieved.The BHMF conversion of 99.9%and highest FDCA yield of 98.4%can be obtain under the optimak conditions（80℃,60.0 min）.