Pd1+AuPd / CeO2 synergistic catalyst and its application in oxidation reaction of 5-hydroxymethylfurfural

Abstract

This invention relates to a Pd1+AuPd / CeO2 synergistic catalyst and its application in the oxidation of 5-hydroxymethylfurfural, specifically a Pd1+AuPd / CeO2 synergistic catalyst with spatially separated dual active sites and its application in the oxidation of 5-hydroxymethylfurfural. This catalytic system simultaneously constructs Pd1-O2 on a cerium oxide support. v The -Ce single-atom sites and AuPd alloy particle sites, the former for efficiently activating molecular oxygen and the latter for promoting the hydroxymethyl dehydrogenation reaction, are spatially separated but functionally synergistic, significantly reducing the reaction energy barrier and accelerating the reaction kinetics. This catalytic system achieves high conversion and high selectivity of FDCA generation under mild conditions, and maintains good stability and applicability under high substrate concentration, scale-up, and continuous flow conditions.

Description

Technical Field

[0001] This invention relates to a Pd1+AuPd / CeO2 synergistic catalyst and its application in the oxidation of 5-hydroxymethylfurfural. Specifically, it is a Pd1+AuPd / CeO2 synergistic catalyst with spatially separated dual active sites and its application in the oxidation of 5-hydroxymethylfurfural, belonging to the field of heterogeneous catalyst design and high-value utilization of biomass platform molecules. Background Technology

[0002] With the increasing demand for high-value utilization of biomass resources, biomass platform molecules, represented by 5-hydroxymethylfurfural (HMF), have attracted widespread attention due to their wide availability and highly tunable structure. 2,5-Furfurandicarboxylic acid (FDCA), as an important target product of 5-hydroxymethylfurfural oxidation, can be used to prepare bio-based polyesters and functional materials, showing promising application prospects. Therefore, developing efficient and stable 5-hydroxymethylfurfural oxidation catalytic systems has become one of the research hotspots in this field.

[0003] In existing technologies, the oxidation of 5-hydroxymethylfurfural typically employs supported noble metal catalysts, such as Au, Pd, and their alloys, often supported on cerium oxide, titanium oxide, or carbon materials. For example, the AuPd / CeO2 system exhibits certain advantages in molecular oxygen activation due to CeO2's oxygen storage and migration capabilities. However, these catalysts are usually prepared through impregnation, co-deposition, or reduction methods, resulting in the noble metal components being randomly dispersed or partially alloyed on the support surface. The different metal active sites are highly mixed spatially, making precise structural control difficult.

[0004] The HMF oxidation reaction is a multi-step tandem oxidation process involving several key steps, including alcohol hydroxyl oxidation, aldehyde oxidation, and oxygen activation. Different reaction steps have different requirements for the properties of the active sites. Traditional mixed AuPd / CeO2 catalysts suffer from the following technical problems: 1) Unclear functional division of active sites: Different metal sites come into random contact, making it difficult to selectively regulate different reaction steps; 2) Mutual influence or shielding of active sites: In mixed or alloy structures, one metal may cover or change the surface electronic structure of another metal, thereby affecting the progress of key reaction steps; 3) Uncontrollable synergistic interface: The intermetallic interface structure is reconstructed with changes in preparation and reaction conditions, resulting in insufficient stability of the synergistic effect; 4) Stability decreases under high substrate concentration or continuous flow conditions: Noble metal particles may migrate, agglomerate or rearrange at the interface, resulting in activity degradation.

[0005] To improve the utilization efficiency of precious metals, single-atom catalysts have gradually attracted attention. By anchoring single-atom metal species to defect sites or oxygen vacancies on the surface of a support, the activation ability of molecular oxygen can be enhanced to some extent. However, since single-atom active sites can usually only provide a single type of reaction function, in oxidation systems involving multi-step or cascade reactions, it is difficult to simultaneously address key reaction steps such as molecular oxygen activation and organic substrate dehydrogenation, thus limiting the overall reaction kinetics.

[0006] Furthermore, while some existing technologies introduce multiple active components through co-loading or physical mixing, the lack of effective spatial regulation and synergistic mechanisms between different active sites often makes it difficult to achieve stable and controllable synergistic catalytic effects. Additionally, these technologies still have shortcomings in terms of catalyst structural stability and reusability. Therefore, it remains necessary to develop a catalytic system with a well-defined structure, controllable distribution of active sites, and the ability to achieve synergistic effects across multiple reactions to meet the high activity, high selectivity, and high stability requirements of the 5-hydroxymethylfurfural oxidation reaction. Summary of the Invention

[0007] The purpose of this invention is to provide a Pd1+AuPd / CeO2 synergistic catalyst and its application in the oxidation of 5-hydroxymethylfurfural (HMF), overcoming the shortcomings of existing technologies, namely, the single-function active sites, insufficient synergistic effect, and difficulty in balancing reaction rate and stability in HMF oxidation catalysts. Specifically, this invention relates to a Pd1+AuPd / CeO2 synergistic catalyst with spatially separated dual active sites and its application in the oxidation of 5-hydroxymethylfurfural. The key lies in simultaneously constructing Pd single-atom sites and AuPd alloy particle sites on a cerium oxide support, forming a spatially separated dual-active-site synergistic catalysis. By constructing a functionally complementary and controllably distributed active site structure on the same support surface, the synergistic process of molecular oxygen activation and organic substrate dehydrogenation is achieved, thereby improving the efficiency and selectivity of the HMF oxidation reaction and enhancing the catalyst's applicability under scale-up and continuous reaction conditions.

[0008] Furthermore, compared with traditional AuPd / CeO2 supported catalysts, this invention, through its spatially separated dual active site configuration, makes the Pd single-atom sites and AuPd alloy particle sites structurally independent, reducing direct shielding and interference between active centers. This helps maintain their respective functional characteristics and achieves synergistic effects through oxygen migration or electronic regulation on the support surface, thereby improving overall catalytic efficiency and reaction selectivity.

[0009] This invention provides a Pd1+AuPd / CeO2 dual-active-site synergistic catalyst, which uses cubic cerium oxide as a support. The support surface simultaneously possesses Pd single-atom active sites and AuPd alloy particle active sites, wherein the Pd single atoms form stable Pd1-O sites with oxygen vacancies on the support surface. v -Ce coordination structure, AuPd alloy is dispersed in nanoparticle form on the carrier surface, Pd1-O v -Ce single-atom active sites and AuPd alloy nanoparticle active sites are spatially separated and form a synergistic effect during the reaction.

[0010] Cerium oxide has reversible Ce 4+ / Ce 3+ It exhibits high conversion ability and readily forms oxygen vacancy structures during heat treatment. These oxygen vacancies strongly anchor Pd species, causing some Pd to be stably dispersed as single atoms on the support surface, forming Pd1-O. v -Ce single-atom sites. Meanwhile, during the hydrothermal process, due to the certain lattice matching and negative mixing enthalpy between Au and Pd, under appropriate temperature conditions, Pd and Au atoms undergo surface diffusion and rearrangement, resulting in alloying and forming stable AuPd alloy nanoparticle sites.

[0011] The total metal loading of Au and Pd is 0.5 to 5 mol% based on the carrier, preferably 2 mol%.

[0012] The molar ratio of Au to Pd is 2-8:2-8; preferably, the molar ratio of Au to Pd is 6:4.

[0013] This invention provides an Au x Pd 10-x The preparation method of / CeO2 and Pd1+AuPd / CeO2 dual active site synergistic catalysts includes the following steps: 1) Add cerium nitrate, potassium chloropalladate, and chloroauric acid to deionized water according to the measured amount, and sonicate for 5-10 minutes to obtain the precursor solution.

[0014] 2) Then pour the above precursor solution into a 6-12 mol / L sodium hydroxide aqueous solution and stir for 20-60 min.

[0015] 3) Transfer the mixture to a polytetrafluoroethylene-lined autoclave and carry out a hydrothermal reaction at 150–200 °C for 18–30 h.

[0016] 4) The product was washed repeatedly with deionized water 3-4 times until the pH was neutral, and then vacuum dried at 40-80℃ for 8-14 h to obtain a solid catalyst sample, named Au. x Pd10-x / CeO2, x is 2, 4, 6, 8; where x=6 corresponds to the Pd1+AuPd / CeO2 catalyst.

[0017] The molar ratio of Au to Pd in ​​step 1) is 2-8: 2-8, preferably 6:4.

[0018] The total metal loading of Au and Pd in ​​step 1) is 0.5–5 mol based on the carrier.

[0019] The gold salt mentioned in step 1) is selected from chloroauric acid and its hydrates (trihydrate or tetrahydrate), preferably tetrachloroauric acid trihydrate.

[0020] This invention provides the application of the Pd1+AuPd / CeO2 synergistic catalyst in the oxidation reaction of 5-hydroxymethylfurfural, and the specific application method involves the following steps: 1) The synergistic catalyst was packed into a fixed-bed reactor, and a 5-hydroxymethylfurfural (HMF) aqueous solution was used as the reaction raw material to construct a reaction system mixture. Continuous catalytic oxidation reaction was carried out under the condition of oxygen introduction to prepare 2,5-furandicarboxylic acid; The reaction system mixture includes HMF, an alkaline substance, a catalyst, and water; the concentration of the 5-hydroxymethylfurfural aqueous solution is 0.02–0.8 mol / L, the oxygen flow rate is 1–10 mL / min, preferably 2 mL / min; the reaction temperature is 25–120 °C, preferably 85 °C; the alkaline substance is sodium carbonate, and its dosage is 0.08–3.2 mol / L; the catalyst dosage is 0.8–2 g, preferably 1000 mg, and its particle size is 40–60 mesh.

[0021] 2) After continuous operation for 0.2 to 1.0 h, the reaction system reaches a stable state. The reaction liquid product is periodically collected at the reactor outlet and the composition of the liquid product is analyzed to evaluate the conversion rate of HMF and the formation of the target oxidation product.

[0022] Before the reaction begins, the HMF aqueous solution is continuously introduced into the reactor at a flow rate of 0.01–1.0 mL / min to fully wet the catalyst bed, preferably at a flow rate of 0.2 mL / min. After the catalyst bed is fully wetted, oxygen is introduced into the reaction system at a flow rate of 1–10 mL / min, preferably 2.0 mL / min, and the reaction temperature is controlled at 25–120 °C, preferably 85 °C.

[0023] Compared with the prior art, the present invention has the following advantages: 1) This invention simultaneously introduces specifically coordinated Pd1-O on the surface of a cerium oxide support. vBy constructing a spatially separated and functionally complementary dual-active-site structure, the -Ce sites and AuPd alloy nanoparticle sites achieve highly efficient synergy between molecular oxygen activation and organic substrate dehydrogenation reactions. This effectively avoids the problem of single or mutually interfering active site functions, enabling multi-step oxidation reaction processes to proceed synergistically, thereby improving the formation efficiency and selectivity of the target product FDCA.

[0024] 2) The synergistic catalyst described in this invention achieves stable anchoring of active species through support confinement and metal-support interaction. It exhibits good HMF oxidation performance and stability under both batch reaction and continuous flow fixed-bed reaction conditions. It effectively overcomes the problems of deactivation and decreased selectivity of noble metal catalysts under high substrate concentration or continuous operation conditions in the prior art, and is suitable for continuous and large-scale application of HMF oxidation reaction. Attached Figure Description

[0025] Figure 1 The images show the XRD patterns of the catalysts prepared in Examples 1-6.

[0026] Figure 2 These are TEM images of the catalysts prepared in Examples 1-6.

[0027] Figure 3 The image shows the HAADF-STEM image of the catalyst prepared in Example 4.

[0028] Figure 4 The graph shows the HMF oxidation performance of the catalyst prepared in Example 9 in a batch reactor.

[0029] Figure 5 The HMF oxidation performance and stability of the catalyst prepared in Example 10 in a continuous flow reactor were analyzed. Detailed Implementation

[0030] The features of the present invention are further described below through embodiments, but the present invention is not limited to the following examples. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions and conditions described in the manual, or under conditions recommended by the manufacturer; the general equipment, materials, reagents, etc. used are commercially available unless otherwise specified.

[0031] This invention provides a method for preparing a synergistic catalyst with spatially separated dual active sites. Specific steps for catalyst preparation are detailed in Examples 1-8. The catalytic performance of the catalyst in the catalytic oxidation of HMF to FDCA was evaluated using both batch and continuous flow reactors, as shown in Examples 7 and 8-10, respectively.

[0032] Example 1: Preparation of Pd / CeO2 catalyst Pd / CeO2 (total Pd loading of 2 mol%) was prepared by hydrothermal method.

[0033] 0.868 g of Ce(NO3)3·6H2O and 0.016 g of K2PdCl6 were added to 5 mL of deionized water and ultrasonically mixed to form a precursor solution. This solution was then poured into 9.6 g of NaOH aqueous solution (6 M) and stirred for 30 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and reacted at 180 °C for 24 h. After the reaction, the mixture was repeatedly washed with deionized water until neutral and then vacuum dried at 50 °C for 12 h to obtain the target catalyst.

[0034] Example 2: Preparation of Au2Pd8 / CeO2 catalyst The Au2Pd8 / CeO2 catalyst (Au:Pd = 2:8) was prepared using the same method as in Example 1.

[0035] The catalyst was obtained by using 0.01 g of K2PdCl6 and 0.8 mL (10 mM) of HAuCl4·3H2O, while keeping the other conditions unchanged.

[0036] Example 3: Preparation of Au4Pd6 / CeO2 catalyst The Au4Pd6 / CeO2 catalyst (Au:Pd = 4:6) was prepared using the same method as in Example 2.

[0037] The catalyst was obtained by using 0.008 g of K2PdCl6 and 1.6 mL (10 mM) of HAuCl4·3H2O, while keeping the other conditions unchanged.

[0038] Example 4: Preparation of Pd1+AuPd / CeO2 synergistic catalyst A hydrothermal method was used to prepare an Au6Pd4 / CeO2 synergistic catalyst (Au:Pd = 6:4, total AuPd loading of 2 mol%), and the sample was designated as Pd1+AuPd / CeO2.

[0039] 0.868 g of Ce(NO3)3·6H2O, 0.006 g of K2PdCl6, and 2.4 mL of HAuCl4·3H2O (10 mM) were added to 2.6 mL of deionized water and ultrasonically mixed to form a precursor solution. This solution was then poured into 9.6 g of NaOH aqueous solution (6 M) and stirred for 30 min. The resulting mixture was subjected to hydrothermal reaction at 180 °C for 24 h, washed, and vacuum dried at 50 °C for 12 h to obtain the catalyst.

[0040] Example 5: Preparation of Au8Pd2 / CeO2 catalyst The Au4Pd6 / CeO2 catalyst (Au:Pd = 8:2) was prepared using the same method as in Example 4.

[0041] The catalyst was obtained by using 0.003 g of K2PdCl6 and 3.2 mL (10 mM) of HAuCl4·3H2O, while keeping the other conditions unchanged.

[0042] Example 6: Preparation of Au / CeO2 catalyst The Au / CeO2 catalyst (total Au loading of 2 mol%) was prepared using the same method as in Example 5.

[0043] The amount of HAuCl4·3H2O used was 4 mL (10 mM), and the other conditions remained unchanged to obtain the Au / CeO2 catalyst.

[0044] Example 7: Preparation of AuPd / CeO2 control catalyst This embodiment provides an AuPd / CeO2 alloy catalyst, used as a comparative catalyst. (Total AuPd loading is 2 mol%) (1) Add PdCl2 solution (0.9 mL, 10 mM) and HAuCl4·3H2O solution (1.4 mL, 10 mM) to 100 mL of deionized water and stir until homogeneous.

[0045] (2) Add 1 wt% polyvinyl alcohol (PVA) aqueous solution to control the total mass ratio of PVA to Au+Pd to be 1.2:1.

[0046] (3) Add freshly prepared NaBH4 solution (0.1 mol / L) dropwise, control the total molar ratio of NaBH4 to Au+Pd to be 5:1, and continue stirring for 30 min to obtain AuPd colloidal solution.

[0047] (4) Add 0.2 g CeO2 carrier to the above solution, adjust the pH to 1-2 with dilute sulfuric acid under stirring, and continue stirring for 2 h.

[0048] (5) Filter, wash with water until neutral, and dry overnight at 120 °C.

[0049] (6) The obtained sample was reduced at 300 °C for 3 h in H2 atmosphere to obtain AuPd / CeO2 control catalyst.

[0050] Example 8: Preparation of Pd1 / CeO2 control catalyst In this embodiment, based on the Pd1+AuPd / CeO2 catalyst, a single-atom Pd1 / CeO2 control catalyst was further constructed through an oxidation-induced dispersion mechanism.

[0051] First, a Pd1+AuPd / CeO2 catalyst was prepared as a precursor according to the method described in Example 4 above. The obtained Pd1+AuPd / CeO2 catalyst was placed in a tube furnace and calcined at high temperature under an oxygen atmosphere. Specifically, the temperature was increased to 800 °C at a rate of 5 °C / min under an oxygen flow (volume fraction ≥80%), and held at this temperature for 12 h. After calcination, the catalyst was naturally cooled to room temperature to obtain the Pd1 / CeO2 catalyst.

[0052] Under the aforementioned high-temperature oxidizing atmosphere, the original AuPd alloy particles undergo oxidation-induced dispersion, and some metal species transform from particulate state to highly dispersed single-atom form, anchoring to oxygen vacancies or defect sites on the CeO2 support surface, thereby forming a single-atom structure.

[0053] Example 9: Application of catalyst in the catalytic oxidation of HMF in a batch reaction system A reaction mixture containing 0.252 g HMF, 0.868 g sodium carbonate, 40 mg catalyst, and 10 mL deionized water was placed in a 25 mL three-necked flask equipped with a condenser. Oxygen was introduced into the reaction system at a flow rate of 80 mL / min under continuous stirring, and the actual reaction temperature was controlled at 85 °C to carry out the catalytic oxidation reaction. After reacting for a certain period of time under the above conditions, the reaction product was obtained and analyzed to evaluate the conversion of HMF and the formation of the target oxidation product.

[0054] Under the same reaction system conditions, the catalytic performance of different catalysts in the HMF oxidation reaction was compared and tested, and the results are shown in Table 1.

[0055] As shown in Table 1, the Pd1+AuPd / CeO2 catalyst constructed in this invention achieves 100% HMF conversion within 40 min, with an FDCA yield of 99.9% and a corresponding turnover time (TOF) of 659.97 min⁻¹. In contrast, although the traditional AuPd / CeO2 alloy catalyst can achieve 100% conversion within 4 h of reaction time, its FDCA yield is only 78.7%, and its TOF is only 15.51 min⁻¹, indicating a significantly lower reaction rate.

[0056] Meanwhile, although Au4Pd6 / CeO2, Au8Pd2 / CeO2, and Au2Pd8 / CeO2 catalysts with different Au / Pd ratios achieved high FDCA yields under 4 h conditions, their TOF was significantly lower than that of the Pd1+AuPd / CeO2 catalyst, indicating that the synergistic efficiency of active sites in a single alloy structure is limited. The Pd1 / CeO2 single-atom catalyst achieved only 28.1% FDCA yield within 4 h, indicating that a single type of active site is insufficient to efficiently complete a multi-step tandem oxidation process.

[0057] This invention constructs a spatially separated dual-active-site structure, allowing the Pd1 single-atom sites and AuPd alloy sites to undertake different reaction functions. This ensures effective activation of molecular oxygen and improves the conversion efficiency of organic substrates, forming a stable and controllable synergistic interface. Its TOF is increased by more than an order of magnitude compared to traditional AuPd alloy catalysts, demonstrating the significant performance advantages of the dual-site synergistic catalytic system over traditional AuPd alloy catalysts.

[0058] TOF = (HMF conversion (%) * (nHMF / nPt)) / (10min * Pt dispersion), where nHMF and nPt are the moles of HMF and platinum, respectively. Calculate the TOF value after 1 min of reaction.

[0059]

[0060] Example 10: Application of Pd1+AuPd / CeO2 catalyst in catalytic oxidation of HMF in a continuous flow reaction system 1000 mg of Pd1+AuPd / CeO2 catalyst (particle size 40-60 mesh) was packed into a fixed-bed reactor to construct a continuous flow reaction system. An aqueous solution of HMF at a concentration of 0.02 mol / L was continuously introduced into the reactor at a flow rate of 0.2 mL / min before the reaction began to fully wet the catalyst bed. Oxygen was then introduced into the reaction system at a flow rate of 2.0 mL / min, and the reaction temperature was controlled at 85 °C. After running under these conditions for 30 min, the reaction system reached a steady state. The liquid product was collected at the reactor outlet and analyzed to evaluate the HMF conversion rate and the formation of oxidation products.

[0061] Example 11: Application of Pd1+AuPd / CeO2 catalyst in catalytic oxidation of HMF in a continuous flow reaction system 1000 mg of Pd1+AuPd / CeO2 catalyst (particle size 40–60 mesh) was packed into a fixed-bed reactor to construct a continuous flow reaction system. An aqueous solution of HMF (hydrogen fluoride) at a concentration of 0.4 mol / L was continuously introduced into the reactor at a flow rate of 0.2 mL / min before the reaction began to fully wet the catalyst bed. Oxygen was then introduced into the reaction system at a flow rate of 2.0 mL / min, and the reaction temperature was controlled at 85 °C. After running under these conditions for 30 min, the reaction system reached a steady state. The liquid product was collected at the reactor outlet and analyzed to evaluate the HMF conversion rate and the formation of oxidation products.

[0062] Example 12: Application of Pd1+AuPd / CeO2 catalyst in catalytic oxidation of HMF in a continuous flow reaction system 1000 mg of Pd1+AuPd / CeO2 catalyst (particle size 40–60 mesh) was packed into a fixed-bed reactor to construct a continuous flow reaction system. An aqueous solution of HMF (hydrogen fluoride) at a concentration of 0.8 mol / L was continuously introduced into the reactor at a flow rate of 0.2 mL / min before the reaction began to fully wet the catalyst bed. Oxygen was then introduced into the reaction system at a flow rate of 2.0 mL / min, and the reaction temperature was controlled at 85 °C. After running under these conditions for 30 min, the reaction system reached a steady state. The liquid product was collected at the reactor outlet and analyzed to evaluate the HMF conversion rate and the formation of oxidation products.

Claims

1. A Pd1+AuPd / CeO2 dual-active-site synergistic catalyst, characterized in that... It uses cubic cerium oxide as a support, and the surface of the support simultaneously has Pd single-atom active sites and AuPd alloy particle active sites. Among them, the Pd single atoms form stable Pd1-O with oxygen vacancies on the support surface. v -Ce(O v The AuPd alloy, with its oxygen vacancy coordination structure, is dispersed as nanoparticles on the carrier surface. v -Ce single-atom active sites and AuPd alloy nanoparticle active sites are spatially separated and form a synergistic effect during the reaction process; The total metal loading of Au and Pd is 0.5–5 mol% based on the carrier. The molar ratio of Au to Pd is 2-8:2-8; The preparation method involves the following steps: dissolving cerium source, palladium source and gold source in water to form a precursor solution; adding the precursor solution to an alkaline solution with a concentration of 6-12 mol / L and stirring; and then hydrothermally reacting at 150-200°C for 18-30 h to allow Pd single atoms to form synchronously with AuPd alloy; and finally washing and drying to obtain the catalyst.

2. The synergistic catalyst according to claim 1, characterized in that: The total metal loading of Au and Pd is 2 mol based on the carrier.

3. The synergistic catalyst according to claim 1, characterized in that: The molar ratio of Au to Pd in ​​the Pd1+AuPd / CeO2 catalyst is 6:

4.

4. The preparation method of the Pd1+AuPd / CeO2 dual-active-site synergistic catalyst according to claim 1, characterized in that... Includes the following steps: 1) Add cerium nitrate, potassium chloropalladate, and chloroauric acid to deionized water according to the measured amount, and sonicate for 5-10 minutes to obtain the precursor solution; 2) Pour the above precursor solution into a 6-12 mol / L sodium hydroxide aqueous solution and stir for 20-60 min; 3) Transfer the mixture to a polytetrafluoroethylene-lined autoclave and carry out a hydrothermal reaction at 150–200 °C for 18–30 h; 4) The product was washed repeatedly with deionized water 3-4 times until the pH was neutral, and then vacuum dried at 40-80℃ for 8-14 h to obtain a solid catalyst sample, named Au. x Pd 10-x / CeO2, x is 2, 4, 6, 8; where x=6 corresponds to the Pd1+AuPd / CeO2 catalyst.

5. The preparation method according to claim 4, characterized in that... The chloroauric acid mentioned in step 1) is tetrachloroauric acid trihydrate.

6. The application of the Pd1+AuPd / CeO2 dual-active-site synergistic catalyst according to claim 1 in the oxidation reaction of 5-hydroxymethylfurfural.

7. The application according to claim 6, characterized in that... The specific application method involves the following steps: 1) The synergistic catalyst is packed into a fixed-bed reactor, and a 5-hydroxymethylfurfural (HMF) aqueous solution is used as the reaction raw material to construct a reaction system mixture, and a continuous catalytic oxidation reaction is carried out under the condition of oxygen introduction; The reaction system mixture includes HMF, an alkaline substance, a catalyst, and water; the concentration of the 5-hydroxymethylfurfural aqueous solution is 0.02–1.0 mol / L, and the oxygen flow rate is 1–10 mL / min; the reaction temperature is 25–120 °C; the alkaline substance is sodium carbonate, and its dosage is 0.08–3.2 mol / L; the amount of the catalyst is 0.8–2 g, and its particle size is 40–60 mesh. 2) After continuous operation for 0.2 to 1.0 h, the reaction system reaches a stable state. The reaction liquid product is periodically collected at the reactor outlet and the composition of the liquid product is analyzed to evaluate the conversion rate of HMF and the formation of the target oxidation product.

8. The application according to claim 7, characterized in that... Before the start of the continuous catalytic oxidation reaction, the HMF aqueous solution is continuously introduced into the reactor at a flow rate of 0.01 to 1 mL / min to fully wet the catalyst bed. After the catalyst bed is fully wetted, oxygen is introduced into the reaction system at a flow rate of 2.0 mL / min, and the reaction temperature is controlled at 85°C.

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