Method for preparing 5-methylfurfural from 5-hydroxymethylfurfural and catalyst used therein

Abstract

Disclosed in the present invention is a method for preparing 5-methylfurfural from 5-hydroxymethylfurfural by directly and selectively hydrogenating a C-OH structure. The method comprises: adding 5-hydroxymethylfurfural, a nickel / niobium pentoxide (Ni-TT-Nb2O5) catalyst and tetrahydrofuran at a ratio of (0.06-0.25 g):(0.025-0.075 g):10 mL to a reactor, replacing air with hydrogen, and catalyzing 5-hydroxymethylfurfural to selectively synthesize 5-methylfurfural. The reaction conditions are as follows: the reaction temperature is 100-160ºC, the hydrogen pressure is 0.1-3 MPa, the stirring speed is 400-800 rpm, and the reaction time is 1-4 hours. In the present invention, the nickel / niobium pentoxide, which contains oxygen vacancies, is used as the catalyst, and the catalyst is not only simple in terms of preparation method, low in terms of price and high in terms of catalytic activity and stability, but can also effectively and selectively hydrogenate 5-hydroxymethylfurfural to directly prepare a single product, i.e., 5-methylfurfural.

Description

A method for preparing 5-methylfurfural using 5-hydroxymethylfurfural and its catalyst

[0001] This application claims priority based on a Chinese patent application filed with the State Intellectual Property Office of China on August 25, 2023, with application number: 2023110818097, and the name of the invention: "A method for preparing 5-methylfurfural using 5-hydroxymethylfurfural". The disclosed content of the Chinese patent application is hereby introduced as a whole into the text of this application. Technical Field

[0002] The invention belongs to the technical field of 5-methylfurfural preparation, and particularly relates to a method for preparing 5-methylfurfural by utilizing the selective hydrogenation of 5-hydroxymethylfurfural. Background Art

[0003] 5-Methylfurfural (MF), a direct hydrogenation product of 5-hydroxymethylfurfural, is a very useful chemical that can be used as a food additive and an intermediate in the synthesis of other chemicals.

[0004] At present, the system for preparing 5-methylfurfural by catalytic direct hydrogenation of 5-hydroxymethylfurfural is extremely difficult, mainly because in the process of 5-hydroxymethylfurfural hydrogenation, compared with C-OH structure, C=O structure is easier to hydrogenate both from a kinetic point of view and from a thermodynamic point of view (ACS Catalysis, 2013, 2655-2668, Journal of Catalysis, 2016, 248-260), which undoubtedly causes great difficulties for the preparation of 5-methylfurfural. At present, only precious metal catalysts (Pt, Au, etc.) can achieve the preparation of 5-hydroxymethylfurfural to 5-methylfurfural, but the high cost and complicated preparation method limit the application of catalysts (Nature Communications, 2021, 12 (1); Applied Catalysis B: Environmental, 2023, 122893). In addition, the low product yield, poor selectivity, and harsh reaction conditions in the preparation of 5-methylfurfural from 5-hydroxymethylfurfural also pose great challenges to the preparation of 5-methylfurfural (Applied Catalysis B: Environmental, 2023, 122893). Therefore, it is urgent to develop and research a non-precious metal with mild reaction conditions, simple preparation method, low cost, and high activity for this reaction system.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to realize the one-step preparation of 5-methylfurfural from 5-hydroxymethylfurfural. The present invention loads metallic nickel onto pseudo-hexagonal niobium pentoxide (TT-Nb2O5) to prepare a Ni-TT-Nb2O5 catalyst. The catalyst can selectively hydrogenate the C-OH structure of 5-hydroxymethylfurfural alone, so that 5-hydroxymethylfurfural is completely converted into 5-methylfurfural with a high yield. The catalyst used in the present invention can be obtained by a hydrothermal calcination method, and the preparation method is simple. In addition, during the reaction process, the catalyst has the advantages of mild reaction conditions, high substrate conversion rate, strong catalyst selectivity, and high product yield. In addition, the catalyst is a non-precious metal catalyst, which fills an industry gap for the one-step preparation of 5-methylfurfural from 5-hydroxymethylfurfural.

[0007] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0008] The present invention provides a method for preparing a nickel / niobium pentoxide catalyst (Ni-TT-Nb2O5), which comprises the following steps:

[0009] S1: First, urea is dissolved in a beaker containing deionized water, and then Ni(NO3)2·6H2O is added to the mixed solution. Then, a pseudo-hexagonal niobium pentoxide support is poured into the mixed solution and sonicated. Finally, the beaker is placed in a 95°C oil bath and stirred for 12 hours until the mixture is completely dry. A light green solid powder is collected.

[0010] S2 then calcined the solid powder in a tube furnace in an N2 / H2 atmosphere. After the tube furnace cooled to room temperature, the black solid was collected, which was the nickel / niobium pentoxide catalyst.

[0011] The preparation method of the pseudo-hexagonal niobium pentoxide (TT-Nb2O5) carrier is as follows:

[0012] a. Add ammonium niobium oxalate to a mixed solution containing deionized water and hydrogen peroxide, stir magnetically for 30 minutes, pour the mixed solution into a polytetrafluoroethylene liner, and react at 175°C;

[0013] b. After the reaction is complete, the reactor is cooled to room temperature, the product is collected, and the product is washed repeatedly with deionized water and anhydrous ethanol;

[0014] c. The niobium pentoxide precursor was then placed in a vacuum drying oven at 60°C and dried overnight;

[0015] d. The dried niobium pentoxide precursor was then placed in a muffle furnace and calcined at 380° C. for 2 h to obtain a pseudo-hexagonal niobium pentoxide carrier.

[0016] Preferably, in step S1, the mass ratio of Ni(NO3)2·6H2O and the pseudohexagonal niobium pentoxide carrier is 1:20 to 1:5, preferably the mass ratio of Ni(NO3)2·6H2O and the pseudohexagonal niobium pentoxide carrier is 1:10.

[0017] In step S2, the solid powder is calcined in a tube furnace, specifically by heating to 300-600° C. at a rate of 2-5° C. / min in an N 2 / H 2 (10%) atmosphere and keeping the temperature for 2 h.

[0018] Additionally, preferably, in step a, the hydrogen peroxide is 30% by mass, the volumes of deionized water and hydrogen peroxide are 65 mL to 100 mL and 15 mL to 20 mL, respectively, with a volume ratio of 4:1 to 5:1; the amount of ammonium niobium oxalate added is 5.2 g to 6.9 g, and the molar ratio of hydrogen peroxide to niobium is 10:1; in step b, the reaction is carried out at 175° C. for 12-18 hours; and the mixture is washed alternately with deionized water and ethanol 3-8 times; in step c, the residue is placed in a vacuum drying oven and dried at 60-80° C. for 12-24 hours; and in step d, the specific operation of calcination is to heat the mixture in a muffle furnace at 4-6° C. / min to 300-400° C. and then keep the temperature for 1-3 hours;

[0019] The present invention provides a Ni-TT-Nb2O5 catalyst obtained by the preparation method.

[0020] To reveal the high activity and selectivity of Ni-TT-Nb2O5 for the hydrogenolysis of HMF to MF, the surface structure and elemental valence of Ni-TT-Nb2O5 were studied and analyzed. TEM analysis (Figures 5a-d) shows that rod-shaped TT-Nb2O5 was synthesized, with a lattice spacing of 0.39 nm on its surface, corresponding to the (001) crystal plane of Nb2O5. In addition, TEM also reveals the presence of a certain number of Ni nanoparticles on the catalyst surface. These nanoparticles are 4 to 6 nm in size, with a primary lattice spacing of 0.20 nm, corresponding to the (111) crystal plane of Ni0. At the same time, HAADF-STEM images (Figure 5e) show that there are clearly clustered and luminescent spots. These spots were identified as Ni by EDS-mapping (Figures 5f-h). These results indicate that the Ni element on the surface of TT-Nb2O5 exists as Ni0 nanoparticles. Subsequently, in order to further explore the main components of the catalyst surface, the XRD patterns of TT-Nb2O5 and Ni-TT-Nb2O5 were studied (Figure 6a). The results showed that there were some obvious diffraction peaks in the XRD patterns of TT-Nb2O5 and Ni-TT-Nb2O5, mainly located at 2θ = 22.6°, 28.6°, 46.2° and 55.2°. These diffraction peaks were mainly attributed to the pseudo-hexagonal Nb2O5 (TT-Nb2O5) (PDF#28-0317). In addition, additional diffraction peaks were also found in the XRD pattern of Ni-TT-Nb2O5, which were mainly located at 2θ = 44.4°, 51.7° and 76.4°. These peaks were attributed to Ni 0 In order to further explore the elemental valence state of the surface composition of Ni-TT-Nb2O5, its XPS spectrum was studied. As shown in Figure 6b, the Ni 2p XPS spectrum was fitted into three characteristic peaks at 852.3, 856.3 and 861.6 eV, respectively. These three peaks are attributed to Ni 0 、Ni 2+ and Ni 0 This result further indicates that there is Ni on the surface of Ni-TT-Nb2O5 0 The presence of Ni is consistent with the results of TEM and XRD analysis. However, compared with the XRD analysis results, the XPS spectrum shows that Ni 2+ This may be due to the presence of Ni on the catalyst surface. 0O1s XPS spectrum (Figure 6c) can be fitted into two peaks, corresponding to oxygen vacancies (Ov) (530.3eV) and Ni-O bonds (531.3eV). At the same time, the Nb 3d XPS spectrum (Figure 6d) was analyzed and fitted with three main characteristic peaks. Among them, the characteristic peak at 206.1eV is Nb 4+ , the characteristic peak at 207.4eV is Nb 5+ Based on the above results, it is shown that the supported nanocatalyst Ni-TT-Nb2O5 with rod-shaped TT-Nb2O5 as the carrier and Ni nanoparticles as the main active sites was successfully prepared by static precipitation method and hydrogen reduction method.

[0021] The present invention further provides a method for preparing 5-methylfurfural by selectively hydrogenating the C-OH structure of 5-hydroxymethylfurfural, which comprises the following steps: adding 5-hydroxymethylfurfural, the Ni-TT-Nb2O5 catalyst prepared by the above method, and tetrahydrofuran into a closed reactor, replacing air with hydrogen, and causing a catalytic reaction to generate 5-methylfurfural.

[0022] Preferably, the conditions of the catalytic reaction are: reaction temperature 100-160°C, hydrogen pressure 0.1-4 MPa, preferably 1-3 MPa, stirring speed 400-1000 rpm, preferably 500-800 rpm, reaction time 1h-8h, preferably 3-6h.

[0023] More preferably, the conditions of the catalytic reaction are: reaction temperature 160° C., hydrogen pressure 2 MPa, stirring speed 600 rpm, and reaction time 4 h.

[0024] In a specific embodiment, the ratio of the 5-hydroxymethylfurfural, Ni-TT-Nb2O5 catalyst and tetrahydrofuran is 0.06-0.25 g:0.025~0.075:10 mL; preferably, the ratio of the 5-hydroxymethylfurfural, Ni-TT-Nb2O5 catalyst and tetrahydrofuran is 0.126 g:0.05 g:10 mL.

[0025] Preferably, the closed reactor is a stainless steel closed reactor.

[0026] The present invention has the beneficial effect of selectively hydrogenating the C-OH structure of 5-hydroxymethylfurfural to produce 5-methylfurfural by constructing a non-precious metal catalyst, Ni-TT-Nb2O5. Using the Ni-TT-Nb2O5 catalyst not only simplifies the preparation method and reduces production costs, but also exhibits strong adsorption capacity for the C-OH structure of 5-hydroxymethylfurfural, enabling complete conversion of 5-hydroxymethylfurfural to produce a high yield of 5-methylfurfural. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a gas chromatogram of 5-hydroxymethylfurfural and 5-methylfurfural obtained in Example 2 of the present invention in the absence of a catalyst.

[0028] FIG2 is a gas chromatogram of 5-hydroxymethylfurfural and 5-methylfurfural obtained when the catalyst is TT-Nb2O5 in Example 2 of the present invention.

[0029] FIG3 is a gas chromatogram of 5-hydroxymethylfurfural and 5-methylfurfural obtained when the catalyst is Ni-TT-Nb2O5 500 according to Example 2 of the present invention.

[0030] FIG4 is a gas chromatogram of 5-hydroxymethylfurfural and 5-methylfurfural obtained in Example 7 of the present invention, when the dosage of 5-hydroxymethylfurfural is 0.126 g.

[0031] Figure 5.ad is the TEM image of Ni-TT-Nb2O5; e is the HAADF-STEM image of Ni-TT-Nb2O5; fh are the EDS-mapping images of Ni-TT-Nb2O5.

[0032] Figure 6.a is the XRD patterns of TT-Nb2O5 and Ni-TT-Nb2O5; bd are the Ni 2p XPS spectrum, O 1s XPS spectrum and Nb 3d XPS spectrum of Ni-TT-Nb2O5, respectively. DETAILED DESCRIPTION

[0033] The technical solutions of the present invention are clearly and completely described in conjunction with the embodiments. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0034] Example 1: Preparation of different catalysts

[0035] The specific operations of the preparation experiments of different catalysts are as follows:

[0036] First, urea was dissolved in a beaker containing deionized water, and then Ni(NO3)2·6H2O was added to the mixed solution; then, a pseudo-hexagonal niobium pentoxide support was poured into the mixed solution and sonicated. Finally, the beaker was placed in a 95°C oil bath and stirred for 12 hours to completely dry the mixture, and a light green solid powder was collected; then, the mixture was calcined in a N2 / H2 atmosphere at 400, 500, and 600°C, respectively. After the tube furnace was cooled to room temperature, black solid powders were collected and named Ni-TT-Nb2O5 400, Ni-TT-Nb2O5 500, and Ni-TT-Nb2O5600, respectively.

[0037] The mass ratio of Ni(NO3)2·6H2O to the pseudo-hexagonal niobium pentoxide carrier is 1:10.

[0038] Example 2: Effect of different catalysts on 5-methylfurfural yield

[0039] The specific steps of the comparative experiment of different catalysts are as follows:

[0040] 0.126 g of 5-hydroxymethylfurfural, various catalysts, and 10 mL of tetrahydrofuran were added to a sealed stainless steel reactor, filled with 2 MPa of H₂, and reacted at 130°C for 4 h with a stirring speed of 600 rpm. After completion of the reaction, the mixture was cooled to room temperature. Solid-liquid separation was performed using a centrifuge (8000 rpm, 5 min), and quantitative analysis was performed using a gas chromatograph (Agilent 7890A). Gas chromatographic analysis was used to calculate the conversion of 5-hydroxymethylfurfural, the molar yield of 5-methylfurfural, and the selectivity, and to further explore the effects of the catalyst on the yield and selectivity of 5-methylfurfural.

[0041] As can be seen from Table 1, the addition of no catalyst and the addition of TT-Nb2O5 have no effect on the conversion rate of 5-hydroxymethylfurfural, and no corresponding 5-methylfurfural is generated. The gas chromatograms are shown in Figures 1 and 2. Although the Ni-TT-Nb2O5 catalyst calcined at different temperatures can convert 5-hydroxymethylfurfural into 5-methylfurfural, the calcination temperature is 500℃, and the 5-hydroxymethylfurfural conversion rate is the highest and the selectivity of 5-methylfurfural is the best. The gas chromatogram is shown in Figure 3.

[0042] Table 1 Effect of different catalysts on 5-methylfurfural yield

[0043] Example 3: Effect of different reaction temperatures on 5-methylfurfural yield

[0044] The specific operation steps of the comparative experiment of different reaction temperatures are as follows:

[0045] Referring to Example 2, 0.05 g of Ni-TT-Nb2O5 500 was selected as the catalyst and the reaction was carried out at different temperatures. Gas chromatography analysis was used to calculate the conversion of 5-hydroxymethylfurfural, the molar yield of 5-methylfurfural, and the selectivity. The effect of the catalyst on the yield and selectivity of 5-methylfurfural was further explored.

[0046] As shown in Table 2, with the increase of reaction temperature, the conversion rate of 5-hydroxymethylfurfural gradually increased and eventually reached complete conversion; the yield and selectivity of 5-methylfurfural first increased and then decreased with the increase of reaction temperature. When the reaction temperature was 160°C, the yield (98%) and selectivity (98%) were the highest.

[0047] Table 2 Effect of different reaction temperatures on 5-methylfurfural yield

[0048] Example 4: Effect of different hydrogen pressures on 5-methylfurfural yield

[0049] The specific steps of the comparative experiment of different hydrogen pressures are as follows:

[0050] Referring to Example 3, the reaction was conducted under different hydrogen pressures and at 160°C for 4 hours with stirring at 600 rpm. Gas chromatography analysis was used to calculate the conversion of 5-hydroxymethylfurfural, the molar yield of 5-methylfurfural, and the selectivity. The effects of the catalyst on the yield and selectivity of 5-methylfurfural were further investigated.

[0051] As can be seen from Table 3, with the increase of hydrogen pressure, the conversion rate of 5-hydroxymethylfurfural gradually increased and eventually reached complete conversion; the yield of 5-methylfurfural showed an increasing trend with the increase of hydrogen pressure, reaching the best at 2 MPa, while the selectivity of 5-methylfurfural did not change with the change of hydrogen pressure.

[0052] Table 3 Effect of different hydrogen pressures on 5-methylfurfural yield

[0053] Example 5: Effect of different stirring speeds on 5-methylfurfural yield

[0054] The specific steps of the comparative experiment of different stirring speeds are as follows:

[0055] Referring to Example 4, a hydrogen pressure of 2 MPa was selected, and the reaction was carried out under different stirring speeds. Gas chromatography analysis was performed to calculate the conversion of 5-hydroxymethylfurfural, the molar yield and selectivity of 5-methylfurfural, and to further explore the effect of the catalyst on the yield and selectivity of 5-methylfurfural.

[0056] As shown in Table 4, the conversion rate of 5-hydroxymethylfurfural gradually increased with the increase of stirring speed, and finally reached complete conversion; the yield and selectivity of 5-methylfurfural increased with the increase of stirring speed, and reached the best at 600 rpm.

[0057] Table 4 Effect of different stirring speeds on 5-methylfurfural yield

[0058] Example 6: Effect of different Ni-TT-Nb2O5 500 dosages on 5-methylfurfural yield

[0059] The specific operation steps of the comparative experiment of different catalyst dosages are as follows:

[0060] Referring to Example 5, the reaction was conducted at a stirring speed of 600 rpm with varying Ni-TT-Nb2O5 dosages. Gas chromatography analysis was used to calculate the conversion of 5-hydroxymethylfurfural, the molar yield of 5-methylfurfural, and the selectivity. The effects of the catalyst on the yield and selectivity of 5-methylfurfural were further explored.

[0061] As can be seen from Table 5, with the increase of Ni-TT-Nb2O5 500 dosage, the conversion rate of 5-hydroxymethylfurfural gradually increased and finally reached complete conversion; the yield of 5-methylfurfural showed an increasing trend with the increase of Ni-TT-Nb2O5 500 dosage, and reached the best under the condition of 0.05g; in addition, with the increase of Ni-TT-Nb2O5 500 dosage, the selectivity of 5-methylfurfural remained unchanged.

[0062] Table 5 Effect of different Ni-TT-Nb2O5 500 dosage on 5-methylfurfural yield

[0063] Example 7: Effect of different 5-hydroxymethylfurfural dosages on 5-methylfurfural yield

[0064] The specific operation steps of the comparative experiment of different 5-hydroxymethylfurfural dosages are as follows:

[0065] Referring to Example 4, the reaction was conducted with a dosage of 0.05 g of Ni-TT-Nb2O5 500 at various 5-hydroxymethylfurfural dosages. Gas chromatography analysis was used to calculate the conversion of 5-hydroxymethylfurfural, the molar yield of 5-methylfurfural, and the selectivity. The effects of the catalyst on the yield and selectivity of 5-methylfurfural were further explored.

[0066] As can be seen from Table 6, the conversion rate of 5-hydroxymethylfurfural decreases with the increase of the dosage of 5-hydroxymethylfurfural; the yield of 5-methylfurfural decreases with the increase of the dosage of 5-hydroxymethylfurfural, but has no effect on the selectivity of 5-methylfurfural. In view of the conversion of the substrate, the yield of the product and the cost, the dosage of 5-hydroxymethylfurfural is selected as 0.126 g, and the results are shown in Figure 4.

[0067] Table 6 Effect of different 5-hydroxymethylfurfural dosage on 5-methylfurfural yield

[0068] Further optimization and screening in the examples revealed that, at 160°C, a reaction time of 4 hours, 2 MPa of H₂, and 600 rpm, 0.05 g of Ni-TT-Nb₂O₅500 catalyst could completely hydrogenate 0.126 g of 5-hydroxymethylfurfural to 5-methylfurfural with a yield of 98%. Under these reaction conditions, the selectivity for 5-methylfurfural was 98%.

[0069] The specific embodiments of the present invention are only for illustrative purposes and do not limit the scope of protection of the present invention in any way. Those skilled in the art may make changes or modifications based on the above description, and these improvements and modifications should fall within the scope of protection of the claims attached to the present invention. Industrial Applicability

[0070] The present invention discloses a method for preparing 5-methylfurfural by directly and selectively hydrogenating the C-OH structure of 5-hydroxymethylfurfural. 5-hydroxymethylfurfural, a nickel / niobium pentoxide (Ni-TT-Nb2O5) catalyst, and tetrahydrofuran (TEF) are added to a reactor in a ratio of 0.06-0.25 g:0.025-0.075 g:10 mL. The air is replaced by hydrogen to catalyze the selective conversion of 5-hydroxymethylfurfural to 5-methylfurfural. The reaction conditions are: a reaction temperature of 100-160°C, a hydrogen pressure of 0.1-3 MPa, a stirring speed of 400-800 rpm, and a reaction time of 1-4 hours. The present invention utilizes a nickel / niobium pentoxide catalyst containing oxygen vacancies. This catalyst is simple to prepare, inexpensive, and possesses high catalytic activity and stability. Furthermore, it can effectively and selectively hydrogenate 5-hydroxymethylfurfural to directly produce the single product, 5-methylfurfural, demonstrating industrial applicability.

Claims

1. A method for preparing a nickel / niobium pentoxide Ni-TT-Nb2O5 catalyst, characterized in that: The steps include: S1: First, urea is dissolved in a beaker containing a deionized water solution, and then Ni(NO3)2·6H2O is added to the mixed solution; then, a pseudo-hexagonal niobium pentoxide carrier is poured into the mixed solution and ultrasonicated, and finally, the beaker is placed in an oil bath at 90-100°C (preferably 95°C) and stirred for 8-16h (preferably 10-14h, more specifically 12h) until the mixed solution is completely dry, and a light green solid powder is collected; S2 then calcined the solid powder in a tube furnace in a N2 / H2 atmosphere, and after the tube furnace cooled to room temperature, collected the black solid, which was the nickel / niobium pentoxide catalyst; Wherein, the preparation method of the pseudo-hexagonal niobium pentoxide (TT-Nb2O5) carrier is as follows: a. Adding ammonium niobium oxalate to a mixed solution containing deionized water and hydrogen peroxide, mixing by magnetic stirring, pouring the mixed solution into a polytetrafluoroethylene liner, and reacting at 160-190°C, preferably 170-180°C, more specifically 175°C; b. After the reaction is completed, the reactor is cooled to room temperature, the product is collected, and repeatedly washed with deionized water and anhydrous ethanol; c. The niobium pentoxide precursor is then placed in a vacuum drying oven at 40-80°C, preferably 50-70°C, specifically 60°C, and dried overnight; d. The dried niobium pentoxide precursor is then placed in a muffle furnace and calcined to obtain a pseudo-hexagonal niobium pentoxide carrier, preferably at 350-400° C., preferably 370-390° C., specifically 380° C. for 2 h.

2. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of Ni(NO3)2·6H2O to the pseudo-hexagonal niobium pentoxide carrier is 1:20 to 1:5, preferably the mass ratio of Ni(NO3)2·6H2O to the pseudo-hexagonal niobium pentoxide carrier is 1:

10.

3. The preparation method according to claim 1, characterized in that: In step S2, the solid powder is calcined in a tube furnace, specifically by heating the temperature to 300-600°C at 2-5°C / min in a N2 / H2 (10%) atmosphere and keeping the temperature for 2 hours.

4. The preparation method according to claim 1, characterized in that: In step a, the hydrogen peroxide is 30% by mass, the volumes of deionized water and hydrogen peroxide are 65 mL to 100 mL and 15 mL to 20 mL, respectively, and the volume ratio of the two is 4:1 to 5:1; the amount of ammonium niobium oxalate added is 5.2 g to 6.9 g, and the molar ratio of hydrogen peroxide to niobium is 10:1; In step b, the reaction is carried out at 175° C. for 12-18 hours; and washing is performed alternately with deionized water and ethanol for 3-8 times; In step c, the residual material is placed in a vacuum drying oven and dried at 60-80°C for 12-24h; In step d, the specific operation of calcination is to heat the mixture to 300-400°C at 4-6°C / min in a muffle furnace and then keep the temperature for 1-3h; 5. The Ni-TT-Nb2O5 catalyst obtained by the preparation method according to any one of claims 1 to 4.

6. A method for preparing 5-methylfurfural by selectively hydrogenating the C-OH structure of 5-hydroxymethylfurfural, characterized in that: The method comprises the following steps: adding 5-hydroxymethylfurfural, the Ni-TT-Nb2O5 catalyst as claimed in claim 5 and tetrahydrofuran into a closed reactor, replacing air with hydrogen, and causing a catalytic reaction to generate 5-methylfurfural.

7. The method according to claim 6, characterized in that The conditions of the catalytic reaction are: reaction temperature 100-160° C., hydrogen pressure 0.1-4 MPa, preferably 1-2 MPa, stirring speed 400-1000 rpm, preferably 500-800 rpm, reaction time 1 h-8 h, preferably 3-6 h.

8. The method according to claim 7, characterized in that The conditions of the catalytic reaction are: reaction temperature 160° C., hydrogen pressure 2 MPa, stirring speed 600 rpm, and reaction time 4 h.

9. The method according to claim 6, characterized in that The ratio of the 5-hydroxymethylfurfural, Ni-TT-Nb2O5 catalyst and tetrahydrofuran is 1-4.17:1-3; preferably, the ratio of the 5-hydroxymethylfurfural, Ni-TT-Nb2O5 catalyst and tetrahydrofuran is 1 g:0.416 g:83 mL.

10. A method for preparing a nickel / niobium pentoxide Ni-TT-Nb2O5 catalyst, characterized in that: The steps include: S1: Dissolve urea in a deionized water solution, add Ni(NO3)2·6H2O to the mixed solution; then pour the pseudo-hexagonal niobium pentoxide carrier into the mixed solution and ultrasonicate, place the beaker in an oil bath at 90-100°C and stir for 8-16h until the mixed solution is completely dry, and collect the light green solid powder; S2: calcining the solid powder in a tube furnace in a N2 / H2 atmosphere at 400, 500, and 600°C. After the tube furnace is cooled to room temperature, the black solid is collected, which is the nickel / niobium pentoxide catalyst. In the step S1, the mass ratio of Ni(NO3)2·6H2O to the pseudo-hexagonal niobium pentoxide carrier is 1:20 to 1:

5.

11. A catalyst for the selective hydrogenation of 5-hydroxymethylfurfural to prepare 5-methylfurfural, which is a nickel / niobium pentoxide catalyst having a structure of a supported nanocatalyst Ni-TT-Nb2O5 with rod-shaped TT-Nb2O5 as a carrier and Ni nanoparticles as the main active sites.

12. A method for preparing 5-methylfurfural by selectively hydrogenating the C-OH structure of 5-hydroxymethylfurfural, characterized in that: The method comprises the following steps: adding 5-hydroxymethylfurfural, the Ni-TT-Nb2O5 catalyst according to claim 11 and tetrahydrofuran into a closed reactor, charging with hydrogen, and preparing 5-methylfurfural at a stirring speed of 400-1000 and a reaction temperature of 100-160°C.

13. The method according to claim 12, characterized in that The conditions of the catalytic reaction are: reaction temperature 160° C., hydrogen pressure 2 MPa, stirring speed 600 rpm, and reaction time 4 h.

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