Trace nickel-doped nickel-cobalt oxide magnetic catalyst as well as preparation method and application thereof

Abstract

The invention relates to a trace nickel-doped nickel-cobalt oxide catalyst and application of the trace nickel-doped nickel-cobalt oxide catalyst in catalytic hydrogenation of 5-hydroxymethylfurfural to preparation of 2, 5-dimethylfuran. Chitosan rich in a nitrogen source is chelated with metal nickel (trace) and metal cobalt, a catalyst precursor is obtained after freeze drying, and the NiCo-C magnetic catalyst can be obtained by calcining the catalyst precursor at a high temperature in a nitrogen atmosphere. The NiCo-C catalyst is simple in preparation method, low in cost, high in cycling stability and high in catalytic activity and product selectivity, and has industrial economic practicability. The catalyst can realize 100% conversion of 5-hydroxymethylfurfural under relatively mild reaction conditions, and the yield of generated 2, 5-dimethylfuran is as high as 96.9%. The catalyst is separated and recovered by adopting a simple magnetic method, and the method is suitable for industrial large-scale application.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic conversion of biomass-based platform compounds, and particularly relates to a method for preparing a trace nickel-cobalt oxide magnetic catalyst doped with nickel, and application of the catalyst in the selective hydrogenation of 5-hydroxymethylfurfural to prepare 2,5-dimethylfuran. Background Art

[0002] As a natural resource of abundant and renewable organic carbon and hydrogen, lignocellulosic biomass can be converted into high-value-added chemicals and liquid fuels to reduce dependence on fossil resources and achieve goals. Cellulose-derived 5-hydroxymethylfurfural is an important biomass-based platform compound that can be used to prepare liquid fuels, chemicals, etc. through a variety of reaction pathways. In particular, the selective catalytic hydrogenolysis of 5-hydroxymethylfurfural to 2,5-dimethylfuran has attracted widespread attention from researchers. 2,5-dimethylfuran has a high energy density (30 kJ / cm 3 ), high octane number, suitable boiling point, and good miscibility with gasoline make it one of the most promising new liquid biofuels. Furthermore, 2,5-dimethylfuran can be used to prepare chemicals such as p-xylene, making it a very versatile material. Because 5-hydroxymethylfurfural contains a rich set of functional groups, including aldehydes, hydroxymethyl groups, and furan rings, it readily forms ring hydrogenation byproducts during catalytic hydrogenation, such as 2,5-dihydroxymethyltetrahydrofuran, tetrahydro-5-methyl-2-furanmethanol, and 2,5-dimethyltetrahydrofuran. Therefore, developing a highly selective catalyst for the efficient hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran is of great research value.

[0003] Currently, efficient catalytic hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran can be achieved based on precious metal catalysts such as Ru, Pd, Pt, and Au. Patent CN113292519A discloses an Au-Co / CoOx bimetallic catalyst that catalyzes the hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran in tetrahydrofuran solvent at 160°C, 1MPa H2, for 2h, to produce a high yield of 2,5-dimethylfuran. However, this catalytic system uses the precious metal Au. Currently, precious metals have problems such as scarce reserves, high cost, and easy leaching and sintering, which severely limit their application in actual large-scale industrialization. Therefore, the development of inexpensive metal catalysts has great advantages. Reference (Fuel, 2020, 274, 117853) reports that a Ni / ZSM-5 catalyst reacted at 180°C, 0.25 MPa H₂, and tetrahydrofuran solvent for 7 h, resulting in a yield of only 87.7% for 2,5-dimethylfuran. After five catalytic cycles, the conversion of 5-hydroxymethylfurfural and the selectivity for 2,5-dimethylfuran decreased to 70% and 60.7%, respectively, accompanied by the formation of byproducts and poor cyclic stability. Studies have shown that oxophilic Co-based catalysts have high catalytic activity for C=O bonds, facilitating the selective hydrogenation of C=O bonds. However, the catalytic activity of metallic Co for CO bonds is limited, making the efficient hydrogenation of 5-hydroxymethylfurfural using a single, inexpensive metal catalyst challenging. The literature (Chem. Eng. J., 2025, 503, 158336) reported a carbon layer constrained and nitrogen anchored CoNi alloy catalyst (Co2Ni1@NC), with metal Co and Ni contents of 36.12wt% and 18.73wt%, respectively. Under relatively mild conditions (150℃, 1MPa H2, 3h, tetrahydrofuran solvent), the yield of 2,5-dimethylfuran was 98.9%. The results showed that the good catalytic activity of the catalytic system was attributed to the interaction between the CoNi alloy and the Co-N x The synergistic effect of the sites prioritizes C=O hydrogenation and C-OH hydrogenolysis; however, the catalyst has a relatively high Ni loading, and the preparation process requires an additional nitrogen source, dicyanamide, resulting in a cumbersome process and unfavorable environmental sustainability. Patent CN115501898A discloses a two-step catalytic hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran using a cobalt-molybdenum bimetallic catalyst (CoMo@NC). Although the cobalt-molybdenum bimetallic catalyst has a low Co content, the invention first utilizes nano-Al2O3 to catalyze the hydrogenation of 5-hydroxymethylfurfural to 2,5-furan dimethanol in an n-propanol solvent (170°C, 0.5MPa N2, for 4 hours). Subsequently, CoMo@NC is used to catalyze the deoxygenation of 2,5-furan dimethanol to produce 2,5-dimethylfuran (with a yield of 92%) at 170°C, 1.5MPa H2, for 2 hours. This catalytic system has a high reaction temperature and requires two catalytic hydrogenation steps, making it impossible to obtain the target product in a single pot.

[0004] The second active metal (Ni, Zn, etc.) can effectively adjust the electronic structure and oxygen vacancies on the surface of Co-based metal catalysts. At the same time, CoOx rich in oxygen vacancies can not only promote the heterolytic splitting of substrate molecules, but also split H2 into highly reactive H δ- Therefore, designing a cobalt-based metal catalyst with a simple preparation process, low cost, and trace nickel doping for the selective hydrogenation of 5-hydroxymethylfurfural has important practical application significance. Summary of the Invention

[0005] The main purpose of the present invention is to overcome the problems of the prior art, such as the cumbersome preparation process of cheap metal catalysts, low catalytic hydrogenolysis efficiency, harsh reaction conditions, and poor cyclic stability. The present invention provides a nickel-cobalt oxide magnetic catalyst doped with trace nickel and a preparation method thereof, which can achieve high yield and high selectivity conversion of 5-hydroxymethylfurfural to 2,5-dimethylfuran under relatively mild conditions. The catalyst uses a low-cost biomass-based carbon source compound and a metal salt to react in an acidic aqueous solution, followed by freeze drying and high-temperature pyrolysis in a nitrogen atmosphere to obtain a nickel-cobalt oxide magnetic catalyst (NiCo@C). , overcoming the disadvantage of high metal loading of bimetallic catalysts, only a trace amount of metal Ni (<0.4wt%) is required, and the synergistic catalytic effect with metal Co improves its hydrogenolysis efficiency; at the same time, the doping of appropriate metal Ni can effectively reduce the oxygen vacancy formation energy in cobalt oxide through charge compensation, which is conducive to the generation of surface oxygen vacancies; and after high-temperature calcination, the catalyst has rich pores, and the CoOx containing oxygen vacancies has a strong adsorption effect on H2, which reduces the H2 cracking energy barrier and promotes the efficient catalytic hydrogenolysis of 5-hydroxymethylfurfural to 2,5-dimethylfuran, and still maintains excellent catalytic performance after multiple cycles.

[0006] In order to solve the above technical problems, the present invention is achieved through the following technical solutions.

[0007] The first aspect of the present invention provides a method for preparing a trace nickel-doped nickel-cobalt oxide magnetic catalyst, comprising the following steps:

[0008] (1) adding a carbon source, a cobalt salt, and a nickel salt to an aqueous solution to form a mixed solution, adding an acidic solution dropwise to adjust the pH, and stirring the mixed solution uniformly under heating conditions;

[0009] (2) pre-freezing the reaction mixture and then freeze-drying it in a vacuum to obtain a catalyst precursor;

[0010] (3) The catalyst precursor is calcined at high temperature under a protective gas atmosphere.

[0011] Preferably, the carbon source in step (1) is selected from one or more of chitosan, chitin, carboxymethyl cellulose, bacterial cellulose, microcrystalline cellulose, and nanocellulose; more preferably, the carbon source is selected from chitosan, which is rich in nitrogen and has a strong anchoring effect on metal ions, thereby improving the stability of the catalyst.

[0012] Preferably, the cobalt salt in step (1) is selected from one or more of cobalt acetate, cobalt nitrate, and cobalt chloride; more preferably, the cobalt salt is selected from one of cobalt acetate and cobalt chloride.

[0013] Preferably, the nickel salt in step (1) is selected from one or more of nickel acetate, nickel nitrate, and nickel chloride; more preferably, the nickel salt is selected from one of nickel acetate and nickel chloride.

[0014] Preferably, the concentration of the carbon source in the mixed solution in step (1) is 12 to 20 mg / mL; more preferably, the concentration of the carbon source in the mixed solution is 15 to 20 mg / mL.

[0015] Preferably, the molar ratio of the cobalt element in the cobalt salt to the nickel element in the nickel salt in step (1) is 65-180:1; more preferably, the molar ratio of the cobalt element in the cobalt salt to the nickel element in the nickel salt is 105-120:1.

[0016] Preferably, the mixing and stirring temperature in step (1) is 55 to 75° C., and the reaction time is 14 to 24 hours.

[0017] Preferably, the pH value in step (1) is adjusted to 2.5-3.

[0018] Preferably, the pre-freezing temperature in step (2) is selected from one of -50 to -18°C and liquid nitrogen freezing, and the pre-freezing time is 24 to 30 hours; the freeze-vacuum drying temperature is selected from one of -50 to -18°C and liquid nitrogen freezing, and the freeze-vacuum drying time is 24 to 72 hours; more preferably, the pre-freezing temperature is selected from -35 to -20°C; the freeze-vacuum drying temperature is selected from -35 to -20°C.

[0019] Preferably, the protective gas in step (3) is selected from one or more of nitrogen, carbon dioxide, helium and hydrogen.

[0020] Preferably, the procedure of the high-temperature calcination in step (3) is: increasing the temperature to 350°C at a heating rate of 1-3°C / min, then increasing the temperature to 800-950°C at a heating rate of 5-8°C / min, maintaining for 2-4 hours, and cooling to room temperature at a cooling rate of 10°C / min; more preferably, the procedure of the high-temperature calcination is: increasing the temperature to 350°C at a heating rate of 2°C / min, then increasing the temperature to 880-950°C at a heating rate of 5-8°C / min, maintaining for 3.5 hours, and cooling to room temperature at a cooling rate of 10°C / min.

[0021] The second aspect of the present invention provides a nickel-cobalt oxide magnetic catalyst doped with trace amounts of nickel prepared according to the above preparation method.

[0022] Preferably, the average particle size of the trace nickel-doped nickel-cobalt oxide magnetic catalyst is 21 to 23 nm.

[0023] Preferably, the nickel-cobalt oxide magnetic catalyst doped with trace nickel has a flower-ball-like morphology after staged high-temperature calcination, with continuous three-dimensional coral-like protrusions on the surface. The flower-ball-like morphology has a size of 455 to 565 nm, which is beneficial to increasing the specific surface area of ​​the catalyst, promoting the contact between the reaction substrate and the catalytic active sites, and improving the efficiency of the catalytic reaction.

[0024] Preferably, the Co content in the trace nickel-doped nickel-cobalt oxide magnetic catalyst is 54.5-65.5 wt%, and the Ni content is 0.21-0.59 wt%. Adding a trace amount of metallic Ni can effectively regulate the electronic structure of the cobalt oxide, capture the lattice oxygen of the adjacent cobalt oxide, generate surface oxygen vacancies, and improve the cobalt oxide's ability to hydrogenate C=O and hydrogenolyze C-OH.

[0025] Preferably, the nickel-cobalt oxide magnetic catalyst precursor doped with trace nickel can retain the porous network structure to the maximum extent after medium-speed pre-freeze drying, and presents a mesoporous structure after high-temperature calcination with an average pore size of 2 to 3 nm; the specific surface area of ​​the nickel-cobalt bimetallic magnetic catalyst doped with trace nickel is 105 to 210 m 2 / g; The mesoporous structure can provide diffusion channels for reaction substrates and products, reduce internal diffusion limitations, and promote material transport.

[0026] The third aspect of the present invention provides the use of a trace nickel-doped nickel-cobalt oxide magnetic catalyst prepared according to the above preparation method in the catalytic hydrogenation reaction of 5-hydroxymethylfurfural.

[0027] A fourth aspect of the present invention provides a method for preparing 2,5-dimethylfuran by catalytic hydrogenation of 5-hydroxymethylfurfural, comprising the following steps:

[0028] (1) placing a trace nickel-doped nickel-cobalt oxide magnetic catalyst prepared according to the above preparation method, 5-hydroxymethylfurfural, and a solvent in a container, evacuating the air in the container with nitrogen at room temperature, and then filling the container with hydrogen to carry out a heating reaction;

[0029] (2) After the reaction is completed, the nickel-cobalt oxide magnetic catalyst doped with trace nickel is separated and recovered by using a magnet, and the remaining product is filtered.

[0030] Preferably, the mass ratio of the trace nickel-doped nickel-cobalt oxide magnetic catalyst to 5-hydroxymethylfurfural in step (1) is 1:2.5-10; more preferably, the mass ratio of the trace nickel-doped nickel-cobalt oxide magnetic catalyst to 5-hydroxymethylfurfural is 1:2.5-5.

[0031] Preferably, the solvent in step (1) is selected from one or more of tetrahydrofuran, methanol, and isopropanol; more preferably, the solvent is selected from tetrahydrofuran.

[0032] Preferably, the mass ratio of 5-hydroxymethylfurfural to the solvent in step (1) is 1:25-55; more preferably, the mass ratio of 5-hydroxymethylfurfural to the solvent is 1:30-45.

[0033] Preferably, the pressure of the hydrogen gas charged in step (1) is 0.5 to 2 MPa; more preferably, the pressure of the hydrogen gas charged is 0.5 to 1 MPa.

[0034] Preferably, the temperature of the heating reaction in step (1) is 110-160° C., and the time is 0.5-5 h; more preferably, the temperature of the heating reaction is 140-150° C., and the time is 3-5 h.

[0035] Preferably, the nickel-cobalt oxide magnetic catalyst doped with trace nickel in step (2) can be optionally rinsed with deionized water 2 to 4 times after being separated and recovered by a magnet, and then dried for use in a circulation test.

[0036] Preferably, the drying temperature is 60°C.

[0037] Preferably, in step (2), 0.2-0.4 μm organic filter membrane is used for filtration.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The present invention can effectively regulate the electronic structure of CoOx by doping with trace metal Ni. On the one hand, the potential energy barrier for the formation of oxygen vacancies in cobalt oxide is reduced; on the other hand, metal Ni can act as a reduction site to capture the lattice oxygen of the adjacent cobalt oxide, producing CoOx modified with oxygen vacancies, thereby promoting the homolytic and heterolytic scission of hydrogen, and improving the adsorption and activation of 5-hydroxymethylfurfural; at the same time, the active metals Co and Ni are anchored on the carbon support in the form of nanoparticles, Co as the main active site component, and trace Ni as a synergistic effect component. The synergistic effect of nickel and cobalt metals promotes the selective hydrogenation of the C=O bond and the hydrogenolysis of C-OH, and the complete conversion of 5-hydroxymethylfurfural can be achieved under low catalyst dosage conditions to generate 2,5-dimethylfuran products with high yield and high selectivity.

[0040] (2) The present invention uses chitosan, which is abundant in nature and rich in nitrogen sources, as a carbon precursor, and chelates cheap metal ions through a simple preparation method, which has low economic cost and is easy to apply industrially; at the same time, nitrogen has a strong anchoring effect on metal ions, and the catalyst has good cyclic stability.

[0041] (3) The catalyst prepared by the present invention has strong magnetism and can be efficiently separated by a magnet, thereby reducing the difficulty and cost of catalyst recovery, avoiding environmental pollution caused by the use of chemical reagents, and complying with the concept of green and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a scanning electron microscope image of the NiCo@C catalyst prepared in Example 1.

[0043] Figure 2 This is a high-resolution transmission electron microscopy image of the NiCo@C catalyst prepared in Example 1 ( Figure 2 ac), metal nanoparticle size distribution diagram ( Figure 2 d) and the element mapping diagram ( Figure 2 e).

[0044] Figure 3 This is the X-ray diffraction spectrum of the NiCo@C catalyst prepared in Example 1.

[0045] Figure 4 This is the Raman spectrum of the NiCo@C catalyst prepared in Example 1.

[0046] Figure 5 N2 adsorption-desorption isotherm of NiCo@C catalyst prepared in Example 1 ( Figure 5 a) and pore size distribution curve ( Figure 5 b).

[0047] Figure 6 This is the X-ray electron energy spectrum of the NiCo@C catalyst prepared in Example 1 ( Figure 6 a), Co 2p( Figure 6 b), Ni 2p( Figure 6 c) and O1s( Figure 6 d) High-resolution X-ray electron spectrum.

[0048] Figure 7 This is a diagram of the recovery and separation of the NiCo@C catalyst prepared in Example 1. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the following examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0050] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0051] Example 1

[0052] First, the nickel-cobalt bimetallic magnetic catalyst (NiCo@C catalyst) is prepared, which specifically includes the following steps:

[0053] (1) 1 g of chitosan, 1.08 g of Co(OAc)2·4H2O, and 10 mg of Ni(OAc)2·4H2O were placed in water to form a mixed solution. Acetic acid aqueous solution (2 wt%) was added dropwise to adjust the pH to 2.7, and the mixture was mixed under magnetic stirring at 60°C for 24 h.

[0054] (2) The reaction mixture was pre-frozen at -30°C for 24 hours, and then freeze-dried in a vacuum at -30°C for 72 hours to obtain a catalyst precursor.

[0055] (3) The catalyst precursor was placed in a tubular furnace and calcined at high temperature under a nitrogen atmosphere. The calcination procedure was as follows: heating to 350°C at a rate of 2°C / min, then to 950°C at a rate of 5°C / min, holding for 3.5 hours, and finally cooling to room temperature at a rate of 10°C / min to obtain a magnetic NiCo@C catalyst. ICP-AES analysis revealed that the Ni content in the NiCo@C catalyst was 0.36 wt% and the Co content was 58.3 wt%.

[0056] Subsequently, 5-hydroxymethylfurfural is catalytically hydrogenated to produce 2,5-dimethylfuran using the NiCo@C catalyst prepared above, which specifically includes the following steps:

[0057] (1) 60 mg of NiCo@C catalyst, 150 mg of 5-hydroxymethylfurfural, and 5 mL of tetrahydrofuran were placed in a glass-lined autoclave. After the autoclave was sealed, the air in the container was evacuated with nitrogen at room temperature, and then hydrogen was introduced to a pressure of 1 MPa. The reaction was heated at 150°C for 4 h.

[0058] (2) After the reaction, the reactor was cooled to room temperature, and the NiCo@C catalyst was separated from the liquid product using a magnet. The recovered NiCo@C catalyst was rinsed three times with deionized water, dried in an oven at 60°C, and used for the next cycle test. The liquid product was filtered through a 0.22 μm organic filter, and the 5-hydroxyfurfural conversion rate and 2,5-dimethylfuran yield were analyzed using GC-MS and GC instruments, respectively. The 5-hydroxymethylfurfural conversion rate and 2,5-dimethylfuran yield were calculated according to the following formula:

[0059] The conversion rate of 5-hydroxymethylfurfural and the yield of 2,5-dimethylfuran were calculated according to the following formula:

[0060]

[0061] The results of the test showed that the conversion rate of 5-hydroxymethylfurfural in this embodiment was 100%, and the yield of 2,5-dimethylfuran was 96.9%.

[0062] Furthermore, the morphology, crystal form, defect level and chemical coordination of the NiCo@C catalyst prepared in Example 1 were characterized in detail. The results showed that the NiCo@C catalyst had a flower ball-like morphology with coral-like protrusions on the surface. The flower ball size was about 500 nm (see Figure 1 High-resolution transmission electron microscopy revealed that metallic Co and Ni were uniformly dispersed on the carbon support in the form of nanoparticles. The average particle size of the metal nanoparticles was about 21.5 nm, with clear lattice fringes and interplanar spacings of 0.204 nm and 0.247 nm, belonging to the Co(111) and CoO(111) planes, respectively. A distorted graphitic carbon lattice structure (0.34 nm) was present at the edge of the structure, but no metallic Ni lattice structure was found, possibly due to the low Ni content. Elemental mapping revealed that the elements Co, Ni, C, O, and N were uniformly dispersed in the catalyst (see Figure 2 ). The X-ray diffraction spectrum of NiCo@C catalyst is shown in Figure 3As shown in the figure, the diffraction peaks of metallic Co appear at 44.3°, 51.6° and 75.9°, and the characteristic peaks at 36.6°, 42.5°, 61.6°, 73.7° and 77.6° are attributed to CoO. The Co element exists in two forms: zero-valent and oxidized. No characteristic diffraction peaks of metallic Ni are observed, which may be due to the high dispersion of metallic Ni nanoparticles. Co-O and Ni-O related signal peaks appear in the Raman spectrum of NiCo@C catalyst (100-750cm -1 ), at 1342.4cm -1 、1578.9cm -1 The signal peaks at the displacement are attributed to the D peak and the G peak, respectively. D / I G The value is about 0.8, indicating that the NiCo@C catalyst has a carbon support with a graphite structure (see Figure 4 The specific surface area of ​​NiCo@C catalyst is 195.5m 2 / g, there is no obvious N2 adsorption in the low pressure region (P / P0<0.1), and a typical H2 type hysteresis loop appears in the high pressure region (P / P0>0.4), indicating that there is a mesoporous structure in the NiCo@C catalyst, with an average pore size of about 2.2nm (see Figure 5 In the full XPS spectrum of NiCo@C catalyst, the signal peaks of C1s, N 1s, O 1s, Co 2p and Ni 2p were observed; in the high-resolution spectrum of Co 2p, the characteristic peaks at 779.5eV and 794.2eV were attributed to Co 0 Species, the characteristic peaks at 780.9eV and 795.7eV are Co 2+ Species, the element Co satellite characteristic peaks are located at 786.7eV and 803.4eV; Ni was observed from the Ni 2p spectrum 0 (852.2eV, 870.1eV), Ni 2+ (854.8eV, 873.0eV) and satellite peaks (860.5eV, 879.7eV); in the O1s spectrum, there are characteristic peaks of O-Co / O-Ni (529.7eV), OC (531.2eV) and OC=O (532.4eV); XPS analysis results show that the metal Co and Ni in the NiCo@C catalyst exist in the form of zero valence and oxide (see Figure 6 ).

[0063] Example 2

[0064] A NiCo@C catalyst was prepared according to the method described in Example 1 and used to catalyze the hydrogenation of 5-hydroxymethylfurfural to produce 2,5-dimethylfuran. The effects of different reaction solvent systems on the hydrogenation performance of 5-hydroxymethylfurfural were investigated. The catalytic reaction steps and conditions were the same as in Example 1, except that different reaction solvents were used. The reaction results are shown in Table 1. The results showed that the yields of 2,5-dimethylfuran were relatively low in methanol and isopropanol solvents, at 38.8% and 65.9%, respectively. In alcohol solvents, 2,5-furan dimethanol and 5-methyl-2-furanmethanol served as reaction intermediates, generating cyclohydrogenation byproducts such as tetrahydro-5-methyl-2-furanmethanol and 2,5-dimethyltetrahydrofuran. The high presence of the intermediate 5-methyl-2-furanmethanol may be due to the co-adsorption of hydroxyl groups in the alcohol solvent and the reaction intermediate on the catalyst surface, thereby hindering the conversion to 2,5-dimethylfuran. Different reaction solvents have a certain influence on the hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran catalyzed by CoNi / NC, and tetrahydrofuran has the best catalytic effect.

[0065] Table 1

[0066]

[0067] Example 3

[0068] According to the method in Example 1, the NiCo@C catalyst was prepared and used to catalyze the hydrogenation of 5-hydroxymethylfurfural to prepare 2,5-dimethylfuran. The effect of different reaction times on the hydrogenation performance of 5-hydroxymethylfurfural was studied. The catalytic reaction steps and conditions were the same as in Example 1, except that the catalytic reaction time was different. The reaction results are shown in Table 2. The results showed that when the reaction time was 0.5h, the conversion rate of 5-hydroxymethylfurfural reached 100%, the yield of 2,5-dimethylfuran was 58.2%, the intermediate product 5-methyl-2-furanmethanol (33.3%) was detected, and no 5-methylfurfural was detected; as the reaction time was extended to 4h, the yield of 2,5-dimethylfuran increased to 96.9%; when the reaction time was 5h, the yield of 2,5-dimethylfuran decreased, and a cyclohydrogenation byproduct was generated.

[0069] Table 2

[0070]

[0071] Example 4

[0072] A NiCo@C catalyst was prepared according to the method described in Example 1 and used to catalyze the hydrogenation of 5-hydroxymethylfurfural to produce 2,5-dimethylfuran. The effect of different reaction temperatures on the hydrogenation performance of 5-hydroxymethylfurfural was investigated. The catalytic reaction steps and conditions were the same as in Example 1, except for the different reaction temperatures. The reaction results are shown in Table 3. The results show that at a reaction temperature of 110°C, the 5-hydroxymethylfurfural conversion and 2,5-dimethylfuran yield were low, at 30.1% and 5.3%, respectively. As the reaction temperature increased to 140°C, the 5-hydroxymethylfurfural conversion reached 100%, and the 2,5-dimethylfuran yield increased to 60.7%. At a reaction temperature of 150°C, the 2,5-dimethylfuran yield reached its maximum (96.9%). Further increasing the temperature to 160°C resulted in a decrease in the 2,5-dimethylfuran yield, with further hydrogenation of the furan ring to form byproducts.

[0073] Table 3

[0074]

[0075]

[0076] Example 5

[0077] A NiCo@C catalyst was prepared according to the method described in Example 1 and used to catalyze the hydrogenation of 5-hydroxymethylfurfural to produce 2,5-dimethylfuran. The effects of different reaction pressures on the hydrogenation performance of 5-hydroxymethylfurfural were investigated. The catalytic reaction steps and conditions were the same as in Example 1, except that the hydrogen pressure was varied. The reaction results are shown in Table 4. The results show that a high yield of 2,5-dimethylfuran was obtained at a hydrogen pressure of 1 MPa. A small amount of 5-methylfurfural (4%) was detected at 0.1 MPa of H₂. When the hydrogen pressure was increased to 0.5 MPa, 5-methylfurfural disappeared, and the yield of 2,5-dimethylfuran reached 80.7%. These results demonstrate that the NiCo@C catalyst exhibits efficient catalytic hydrogenation of C₂O and C=O bonds under relatively low hydrogen pressures.

[0078] Table 4

[0079]

[0080] Example 6

[0081] According to the method in Example 1, a NiCo@C catalyst was prepared and used to catalyze the hydrogenation of 5-hydroxymethylfurfural to produce 2,5-dimethylfuran. The effect of different catalyst dosages on the hydrogenation performance of 5-hydroxymethylfurfural was studied. The catalytic reaction steps and conditions were the same as in Example 1, except that the catalyst dosage was different (wherein the catalyst dosage refers to the percentage of the catalyst mass to the mass of 5-hydroxymethylfurfural). The reaction results are shown in Table 5. The results show that when the catalyst dosage was 10wt%, the 5-hydroxymethylfurfural conversion rate was 100% and the 2,5-dimethylfuran yield was 52.7%; as the catalyst dosage increased, the 2,5-dimethylfuran yield showed a positive correlation with the catalyst dosage, with the highest yield being 96.9%.

[0082] Table 5

[0083]

[0084] Example 7

[0085] The NiCo@C catalyst was prepared according to the method in Example 1 and used to catalyze the hydrogenation of 5-hydroxymethylfurfural to produce 2,5-dimethylfuran. The effect of different catalyst recycling times on the hydrogenation performance of 5-hydroxymethylfurfural was studied. The catalytic reaction steps and conditions were the same as those in Example 1, except that after the catalytic reaction, the catalyst was separated by a magnet, rinsed with water, dried, and then used in the recycling experiment. The recovery and separation diagram is shown in FIG. Figure 7 The reaction results are shown in Table 6. The results show that after five cycles, the metal Co and Ni contents in the NiCo@C catalyst were 56.9wt% and 0.35wt%, respectively; the specific surface area was about 104.9m 2 / g, with an average pore size of 2.1nm, and still maintaining a mesoporous structure. There is no significant difference in the structure of the NiCo@C catalyst recycled five times and the newly prepared catalyst.

[0086] Table 6

[0087]

[0088]

[0089] Comparative Example 1

[0090] First, the Co@C catalyst is prepared, which specifically includes the following steps:

[0091] (1) 1 g of chitosan and 1.08 g of Co(OAc)2·4H2O were placed in water to form a mixed solution, and an acetic acid aqueous solution (2 wt%) was added dropwise to adjust the pH value to 2.7. The mixture was mixed under magnetic stirring at 60°C for 24 h.

[0092] (2) The reaction mixture was pre-frozen at -30°C for 24 hours, and then freeze-dried in a vacuum at -30°C for 72 hours to obtain a catalyst precursor.

[0093] (3) The catalyst precursor was placed in a tubular furnace and calcined at high temperature under a nitrogen atmosphere; the high temperature calcination procedure was as follows: heating to 350°C at a rate of 2°C / min, then heating to 950°C at a rate of 5°C / min, keeping the temperature for 3.5 hours, and finally cooling to room temperature at a rate of 10°C / min to obtain a Co@C magnetic catalyst. The Co@C catalyst exhibited a mesoporous structure with a specific surface area of ​​182.7 m 2 / g; ICP-AES measured the Co content in the Co@C catalyst to be 58.1wt%.

[0094] Subsequently, the Co@C catalyst prepared above was used to carry out catalytic hydrogenation of 5-hydroxymethylfurfural to prepare 2,5-dimethylfuran according to the catalytic conditions in Example 1. The conversion rate of 5-hydroxymethylfurfural was 85%, and the yield of 2,5-dimethylfuran was 81.5%.

[0095] Comparative Example 2

[0096] Ni prepared in Comparative Example 2 L The operation steps of Co@C magnetic catalyst are the same as those in Example 1, except that the added Ni(OAc)2·4H2O mass is 6 mg, and Ni L The Co@C catalyst has a mesoporous structure and a specific surface area of ​​189.3 m 2 / g; Ni was measured by ICP-AES L The Ni content in the Co@C catalyst is 0.21wt% and the Co content is 58.3wt%. Compared with the Co@C catalyst system without metal Ni doping in Comparative Example 1, the Ni L The low content of metallic Ni in the Co@C catalytic system increases CoOx defects and oxygen vacancies, and synergistically catalyzes the conversion of 5-hydroxymethylfurfural and improves the yield of 2,5-dimethylfuran. The conversion of 5-hydroxymethylfurfural is 91%, and the yield of 2,5-dimethylfuran is 88.9%.

[0097] Comparative Example 3

[0098] Ni prepared in Comparative Example 3 H The operation steps of Co@C magnetic catalyst are the same as those in Example 1, except that the added Ni(OAc)2·4H2O mass is 18 mg, and Ni H The Co@C catalyst has a mesoporous structure and a specific surface area of ​​204.7 m 2 / g; Ni was measured by ICP-AES LThe Ni content in the Co@C catalyst is 0.59wt% and the Co content is 58.3wt%. Compared with the NiCo@C catalyst in Example 1, the Ni@C catalyst with a higher content of metallic Ni is H The Co@C catalytic system achieved 100% conversion of 5-hydroxymethylfurfural, while the yield of 2,5-dimethylfuran decreased slightly to 95.7%, with a small amount of 2,5-dimethyltetrahydrofuran detected. This is due to excessive C=C hydrogenation in a hydrogen atmosphere at high Ni content, which can easily form cyclohydrogenation byproducts.

[0099] Comparative Example 4

[0100] The NiCo@C-LN magnetic catalyst prepared in Comparative Example 4 was prepared using the same procedures as in Example 1, except that it was pre-frozen in liquid nitrogen for 4 hours and then freeze-dried in a vacuum at -30°C for 72 hours. ICP-AES analysis revealed that the Ni content in the NiCo@C-LN catalyst was 0.37 wt% and the Co content was 59.6 wt%. After rapid freezing in liquid nitrogen and calcination at high temperature, the NiCo@C-LN catalyst exhibited a microporous structure with a specific surface area of ​​126.3 m 2 Compared to mesoporous structures, the smaller pore size of microporous structures hinders the diffusion of reaction substrates and products, and the long diffusion paths reduce the transport rate. The conversion rate of 5-hydroxymethylfurfural and the yield of 2,5-dimethylfuran decreased slightly to 93% and 90.2%, respectively.

[0101] Comparative Example 5

[0102] The NiCo@C-850 magnetic catalyst prepared in Comparative Example 5 was prepared using the same procedures as in Example 1, except that the maximum calcination temperature was 850°C and the temperature was maintained for 2 hours. ICP-AES analysis revealed that the Ni content in the NiCo@C-850 catalyst was 0.36 wt% and the Co content was 58.1 wt%. After calcination at 850°C for 2 hours, the NiCo@C-850 catalyst had a mesoporous structure, and the specific surface area was reduced to 153.7 m 2 The low-temperature, short-term calcination process resulted in insufficient pore collapse and incomplete exposure of the metal active sites, which reduced the effective contact between the reactants and the active metal sites. The 5-hydroxymethylfurfural conversion rate was 96%, and the 2,5-dimethylfuran yield was 93.5%.

[0103] The above detailed description of the technical solutions involved in the present invention is provided in detail. It should be noted that the above description is intended only to help those skilled in the art better understand the methods and concepts of the present invention, and is not intended to limit the relevant content. Without departing from the principles of the present invention, those skilled in the art may also make appropriate adjustments or modifications to the present invention, and such adjustments and modifications shall also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a trace nickel-cobalt oxide magnetic catalyst doped with nickel, characterized in that: The steps include: (1) adding a carbon source, a cobalt salt, and a nickel salt to an aqueous solution to form a mixed solution, adding an acidic solution dropwise to adjust the pH, and stirring the mixed solution uniformly under heating conditions; (2) pre-freezing the reaction mixture, and then freeze-drying it in a vacuum to obtain a catalyst precursor; (3) The catalyst precursor is calcined at high temperature under a protective gas atmosphere.

2. The preparation method according to claim 1, characterized in that The carbon source in step (1) is selected from any one of chitosan, chitin, carboxymethyl cellulose, bacterial cellulose, microcrystalline cellulose, and nanocellulose; the cobalt salt is selected from any one of cobalt acetate, cobalt nitrate, and cobalt chloride; and the nickel salt is selected from any one of nickel acetate, nickel nitrate, and nickel chloride.

3. The preparation method according to claim 1, characterized in that The molar ratio of the cobalt element in the cobalt salt to the nickel element in the nickel salt in step (1) is 65 to 180:

1.

4. The preparation method according to claim 1, characterized in that In step (1), the pH value is adjusted to 2.5-3.

5. The preparation method according to claim 1, characterized in that The pre-freezing temperature in step (2) is selected from one of -50 to -18°C and liquid nitrogen freezing, and the pre-freezing time is 24 to 30 hours; the freeze-vacuum drying temperature is selected from one of -50 to -18°C and liquid nitrogen freezing, and the freeze-vacuum drying time is 24 to 72 hours.

6. The preparation method according to claim 1, characterized in that The procedure of high temperature calcination in step (3) is as follows: heating to 350°C at a rate of 1-3°C / min, then heating to 800-950°C at a rate of 5-8°C / min, maintaining for 2-4 hours, and cooling to room temperature at a rate of 10°C / min.

7. A nickel-cobalt oxide magnetic catalyst doped with trace nickel prepared according to the preparation method according to any one of claims 1 to 6.

8. The nickel-cobalt oxide magnetic catalyst doped with trace nickel according to claim 7, characterized in that: The average particle size of the trace nickel-doped nickel-cobalt oxide magnetic catalyst is 21 to 23 nm; the trace nickel-doped nickel-cobalt oxide magnetic catalyst has a flower ball-like morphology, with continuous three-dimensional coral-like protrusions on the surface, and the flower ball morphology size is 455 to 565 nm; the Co content of the trace nickel-doped nickel-cobalt oxide magnetic catalyst is 54.5 to 65.5 wt%, and the Ni content is 0.21 to 0.59 wt%; the trace nickel-doped nickel-cobalt oxide magnetic catalyst has a mesoporous structure with an average pore size of 2 to 3 nm; the specific surface area of ​​the trace nickel-doped nickel-cobalt oxide magnetic catalyst is 105 to 210 m 2 / g.

9. A method for preparing 2,5-dimethylfuran by catalytic hydrogenation of 5-hydroxymethylfurfural, characterized in that: The steps include: (1) placing a trace nickel-doped nickel-cobalt oxide magnetic catalyst prepared by the preparation method according to any one of claims 1 to 6, 5-hydroxymethylfurfural, and a solvent in a container, evacuating the air in the container with nitrogen at room temperature, then filling the container with 0.1-2 MPa hydrogen, and heating the reaction at a temperature of 110-160° C. for 0.5-5 h; (2) After the reaction is completed, the nickel-cobalt oxide magnetic catalyst doped with trace nickel is separated and recovered by using a magnet, and the remaining product is filtered.

10. The method according to claim 9, characterized in that The mass ratio of the nickel-cobalt bimetallic magnetic catalyst to 5-hydroxymethylfurfural in step (1) is 1:2.5-10.

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