Nitrogen-doped porous carbon sphere supported palladium-based catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of phenol hydrogenation catalysis, and discloses a nitrogen-doped porous carbon sphere loaded palladium-based catalyst as well as a preparation method and application thereof in order to solve the problems that active components of an existing catalyst are difficult to highly disperse, the reaction condition is harsh and the stability is poor. The nitrogen-doped porous carbon spheres derived from the nitrogen-doped polymer are used as carriers to load Pd, and high dispersion of Pd is promoted by N sites on the nitrogen-doped porous carbon spheres, so that the number of active centers is increased, and cyclohexanone can be prepared through phenol hydrogenation under mild conditions; and the interaction between the N site and the Pd metal hinders the loss of the active component, so that the high stability of the catalyst is realized. In addition, N sites on the nitrogen-doped porous carbon spheres can promote vertical adsorption of phenol molecules, so that high-selectivity preparation of cyclohexanone is realized.

Description

Technical Field

[0001] The invention relates to a phenol hydrogenation catalyst, in particular to a nitrogen-doped porous carbon sphere-supported palladium-based catalyst and a preparation method and application thereof, belonging to the technical field of phenol catalytic hydrogenation. Background Art

[0002] The efficient hydrogenation of phenol to produce cyclohexanone is a cutting-edge topic in the field of catalytic hydrogenation. This is because cyclohexanone is an important type of fine chemical product and basic chemical raw material, and is usually used to synthesize adipic acid, nylon 66 and caprolactam. In recent years, there are three main methods for producing cyclohexanone: cyclohexene hydration, cyclohexane oxidation and phenol one-step hydrogenation. However, cyclohexene hydration and cyclohexane oxidation have problems such as high cost and harsh reaction conditions, which do not conform to the concept of green catalysis. On the contrary, the one-step hydrogenation method of renewable phenol to prepare cyclohexanol is more economical and environmentally friendly; at the same time, less three wastes are produced, the reaction products are easy to separate, and the reaction conditions are mild.

[0003] In recent years, the one-step hydrogenation of phenol to prepare cyclohexanone is mainly based on precious metal catalysts. You Chenjia et al. (CN110563564A) of Sinopec disclosed a γ-Al2O3-loaded Pd catalyst for the hydrogenation reaction with phenol, which obtained a phenol conversion rate of nearly 100% at 160°C, but there were problems such as harsh reaction conditions and easy agglomeration of active components. Yongjun Gao's group (ACS Sustainable Chem. Eng. 2020, 8, 32, 12304–12312) reported a Pd–chitin catalyst that used HCOONa as a hydrogen source to achieve transfer hydrogenation of phenol to prepare cyclohexanone. Due to the additional addition of HCOONa, the separation cost of the reaction product was increased. Therefore, it is of great significance to develop a catalyst for the hydrogenation of phenol to prepare cyclohexanone with high activity, high selectivity, high stability and mild reaction conditions. Summary of the invention

[0004] In view of the problems in the prior art of preparing cyclohexanone by the existing one-step hydrogenation method of phenol, such as easy agglomeration of active components of the catalyst, low catalytic efficiency, harsh reaction conditions and poor catalytic stability, the present invention provides a nitrogen-doped porous carbon sphere-supported palladium-based catalyst and its preparation method and use. By using nitrogen-doped porous carbon spheres derived from nitrogen-doped polymers as carriers to load Pd, the N sites on the nitrogen-doped porous carbon spheres are used to promote the high dispersion of Pd, thereby increasing the number of active centers, and realizing the hydrogenation of phenol to prepare cyclohexanone under mild conditions; and the interaction between the N sites and the Pd metal hinders the loss of active components, thereby achieving high stability of the catalyst. In addition, the N sites on the nitrogen-doped porous carbon spheres can also promote the vertical adsorption of phenol molecules, thereby achieving highly selective preparation of cyclohexanone.

[0005] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows: According to a first embodiment of the present invention, there is provided a method for preparing a nitrogen-doped porous carbon sphere-supported palladium-based catalyst: A method for preparing a nitrogen-doped porous carbon sphere-supported palladium-based catalyst, the method comprising the following steps: 1) Using aldehyde compounds, aldehyde acid compounds, phenolic compounds and long-chain amine compounds as raw materials, nitrogen-doped porous carbon spheres are obtained after mixing reaction and calcination treatment in sequence.

[0006] 2) The nitrogen-doped porous carbon spheres obtained in step 1) are added to a palladium-containing precursor solution for impregnation treatment, and then heat-treated to obtain nitrogen-doped porous carbon spheres loaded with palladium-based catalysts.

[0007] Preferably, the aldehyde compound is a C1-C10 aldehyde compound, preferably one or more of formaldehyde, acetaldehyde, propionaldehyde, and isopropionaldehyde.

[0008] Preferably, the aldehyde acid compound is a C2-C8 aldehyde acid compound, preferably one or more of glyoxylic acid and its hydrate.

[0009] Preferably, the phenolic compound includes at least one of phenol, catechol, pyrogallol, resorcinol and phloroglucinol, and is preferably a mixture of resorcinol and phloroglucinol.

[0010] Preferably, the phenolic compound is a mixture of phloroglucinol and resorcinol in a mass ratio of 0.5 to 2.5:1, preferably a mixture in a mass ratio of 1 to 2:1.

[0011] Preferably, the long-chain amine compound is a C4-C20 chain amine compound, preferably one or more of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0012] Preferably, in step 1), the mass ratio of aldehyde compounds, aldehyde acid compounds, phenolic compounds and long-chain amine compounds is 1:0.3-2:1-1.5:0.4-1.2, preferably 1:0.8-1.5:1.1-1.3:0.5-1.

[0013] Preferably, in step 1), the mixing reaction is specifically as follows: firstly, the aldehyde compound, the aldehyde acid compound, the phenolic compound and water are stirred and mixed uniformly, and then the long-chain amine compound is added and allowed to stand for treatment, and then the solid-liquid separation is performed and the solid is washed with a mixed solution of acetone and water, and finally the solid is freeze-dried.

[0014] Preferably, in step 1), the calcination treatment is specifically: calcining the solid product obtained after the mixed reaction at 600-1000° C. for 0.5-3 h in an inert atmosphere.

[0015] Preferably, in step 2), the palladium-containing precursor is palladium acetate.

[0016] Preferably, in step 2), the mass ratio of the nitrogen-doped porous carbon spheres to the palladium-containing precursor is 1000:1-30, preferably 1000:3-20.

[0017] Preferably, in step 2), the impregnation treatment is specifically: subjecting the mixed system of nitrogen-doped porous carbon spheres and palladium-containing precursor solution to ultrasonic dispersion treatment first, and then to freeze-drying treatment.

[0018] Preferably, in step 2), the heat treatment is specifically: calcining the solid product obtained by the impregnation treatment in a reducing atmosphere (eg, a hydrogen atmosphere) at 250-400° C. for 0.5-3 h.

[0019] According to a second embodiment of the present invention, a nitrogen-doped porous carbon sphere-supported palladium-based catalyst is provided: A nitrogen-doped porous carbon sphere-supported palladium-based catalyst is prepared by the method described in the first embodiment.

[0020] Preferably, the palladium loading in the nitrogen-doped porous carbon sphere-supported palladium-based catalyst is 0.1-3.0 wt %, preferably 0.2-2.0 wt %, preferably 0.3-1.5 wt % (all based on the total mass of the catalyst).

[0021] According to a third embodiment of the present invention, there is provided a use of a nitrogen-doped porous carbon sphere-supported palladium-based catalyst: A use of a nitrogen-doped porous carbon sphere-supported palladium-based catalyst, characterized in that the nitrogen-doped porous carbon sphere-supported palladium-based catalyst prepared by the method described in the first embodiment is used as a hydrogenation catalyst, preferably as a hydrogenation catalyst for hydrogenating phenol to prepare cyclohexanone.

[0022] Preferably, when the nitrogen-doped porous carbon sphere-supported palladium-based catalyst is used as a hydrogenation catalyst for preparing cyclohexanone by hydrogenation of phenol: the mass ratio of phenol to water is 1 to 5:100 (preferably 1.5 to 3:100, for example 2:100). The pressure of hydrogen in the hydrogenation reactor is 0.5 to 5 MPa (preferably 0.8 to 2 MPa, for example 1 MPa). The reaction temperature of the hydrogenation reaction is 50 to 100°C (preferably 60 to 80°C, for example 70°C), and the reaction time is 1 to 6 h (preferably 2 to 3.5 h). The stirring speed in the hydrogenation reactor is 100 to 500 rpm (preferably 200 to 400 rpm, for example 300 rpm).

[0023] In the present invention, nitrogen-doped porous carbon spheres derived from nitrogen-doped polymers are used as carriers, and the N sites on the nitrogen-doped porous carbon spheres are utilized to promote high dispersion of Pd, thereby increasing the number of active centers; and the interaction between the N sites on the nitrogen-doped porous carbon spheres and the Pd metal hinders the loss of active components, thereby achieving high stability of the catalyst. In addition, the N sites on the nitrogen-doped porous carbon spheres can also promote vertical adsorption of phenol molecules, thereby achieving highly selective preparation of cyclohexanone.

[0024] In the present invention, nitrogen-doped porous carbon spheres are prepared by a solvothermal method using an organic carbon source and an organic nitrogen source as raw materials. The organic carbon source includes aldehyde compounds, aldehyde acid compounds, phenolic compounds, and the like. The organic nitrogen source is a long-chain amine compound. It should be noted that, among the organic carbon sources, the aldehyde compound is preferably one or more of formaldehyde, acetaldehyde, propionaldehyde, and isopropionaldehyde, the aldehyde acid compound is preferably glyoxylic acid and its hydrate (e.g., glyoxylic acid monohydrate), and the phenolic compound is preferably at least one of phenol, catechol, pyrogallol, resorcinol, and pyrogallol.

[0025] In the present invention, by adding aldehyde compounds to the organic carbon source, the aldehyde compounds, in addition to serving as carbon sources, can also undergo condensation polymerization with phenolic compounds to form phenolic microspheres, thereby playing a role in morphology control.

[0026] In the present invention, by adding aldehyde acid compounds to the organic carbon source, the aldehyde acid compounds can introduce some functional groups in addition to being a carbon source. For example, when glyoxylic acid is used, functional groups such as carboxyl groups can be introduced on the surface of the carbon spheres during the preparation process, and these functional groups can further improve the hydrophilicity of the carbon spheres. When phenol is hydrogenated to prepare cyclohexanone, the hydroxyl group (-OH) of phenol can form hydrogen bonds with water molecules, thereby showing a certain hydrophilicity; therefore, the hydroxyl group (-OH) of phenol can be preferentially adsorbed on the catalyst surface to participate in the reaction. In addition, the product cyclohexanone is hydrophobic, so when phenol is hydrogenated to produce cyclohexanone, it can immediately detach from the catalyst surface, thereby avoiding excessive hydrogenation to produce cyclohexanol.

[0027] It should be noted that in the present invention, it is found through research that the ratio between the aldehyde compound and the aldehyde acid compound can affect the selectivity of the catalyst in the catalytic hydrogenation of phenol to obtain cyclohexanone. When the ratio of the aldehyde compound to the aldehyde acid compound is too large, the hydrophilicity of the catalyst surface will be reduced, resulting in excessive hydrogenation of cyclohexanone to cyclohexanol; when the ratio of the aldehyde compound to the aldehyde acid compound is too small, the pore structure and specific surface area of ​​the carbon sphere will be reduced, and the selectivity of cyclohexanone will also be affected. For example, when the aldehyde compound is formaldehyde and the aldehyde acid compound is glyoxylic acid monohydrate, the mass ratio of formaldehyde to glyoxylic acid monohydrate is preferably between 0.3 and 2:1 (preferably 0.8 to 1.5:1). Exceeding or falling below this ratio will reduce the selectivity when synthesizing cyclohexanone.

[0028] In the present invention, by adding phenolic compounds to the organic carbon source, the phenolic compounds, in addition to being used as carbon sources, can also undergo polymerization or cross-linking reactions with aldehyde compounds to form a three-dimensional network structure, which is crucial for forming carbon balls with a stable structure.

[0029] In the present invention, the organic nitrogen source is an amine compound with a long chain structure, such as triethylenetetramine. The long chain structure is conducive to exposing more amine groups. Amine groups have strong coordination ability and can form coordination complexes with Pd (palladium), thereby achieving anchoring and fixation of Pd metal. By introducing long-chain amine groups on carbon spheres, more Pd active sites can be exposed, thereby improving catalytic performance.

[0030] Compared with the prior art, the beneficial technical effects of the present invention are as follows: 1: The nitrogen-doped porous carbon sphere-supported palladium-based catalyst prepared by the present invention uses nitrogen-doped porous carbon spheres derived from nitrogen-doped polymers as carriers to support Pd, and has the advantages of high activity, high selectivity, high stability and mild reaction conditions.

[0031] 2: The raw materials for preparing the nitrogen-doped porous carbon sphere-loaded palladium-based catalyst in the present invention are easily available, the preparation process is simple, and it is easy to implement and apply industrially, and has broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a TEM image of the nitrogen-doped porous carbon sphere-supported palladium-based catalyst prepared in Example 1 of the present invention.

[0033] Figure 2 This is a TEM image of the nitrogen-doped porous carbon sphere-supported palladium-based catalyst prepared in Example 1 of the present invention after being recycled 15 times. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is illustrated below by way of example, and the scope of protection requested by the present invention includes but is not limited to the following embodiments. Example 1

[0035] 1.32 g of phloroglucinol, 0.88 g of resorcinol, 1.0 g of glyoxylic acid monohydrate, and 1.0 g of formaldehyde were added to 40 ml of distilled water and stirred at 25°C for 30 min to obtain a mixed solution; then 1.0 g of triethylenetetramine was weighed and placed in the above mixed solution and allowed to stand at 25°C for 12 h. After the standing period, the supernatant was removed and the solid was washed three times with an acetone / water mixed solution (volume ratio of 1:1), and then the washed solid was placed in a low-temperature refrigerator (below freezing point) and frozen for 24 h and then moved to a freeze dryer for freeze drying for 48 h; finally, the freeze-dried solid was calcined at 800°C in an argon atmosphere for 1 h to obtain nitrogen-doped porous carbon spheres.

[0036] Palladium acetate and nitrogen-doped porous carbon spheres were weighed in a mass ratio of 15:1000 and dispersed in 50 ml of distilled water to obtain a mixed solution. The mixed solution was then placed in an ultrasonic disperser and ultrasonically dispersed for 1 hour and then freeze-dried for 48 hours. Finally, the freeze-dried solid was calcined at 300°C in a hydrogen atmosphere for 1 hour to obtain a nitrogen-doped porous carbon sphere-loaded palladium-based catalyst (the palladium loading was about 15wt%).

[0037] Weigh 0.1g of the above-prepared nitrogen-doped porous carbon sphere-supported palladium-based catalyst and place it in a 100ml polytetrafluoroethylene liner, then add 25ml water and 0.5ml phenol; then place the polytetrafluoroethylene liner in a high-pressure reactor, first replace the air in the reactor with hydrogen through a vacuum pump, and then introduce 1.0MPa of H2 after three replacements, and stir (300rpm) at 70℃ for 3h. After the reaction is completed, cool naturally to room temperature, take out the reaction liquid for analysis, and its phenol conversion rate is 33.7%, and the selectivity of cyclohexanone is 90.6%. Example 2

[0038] Example 1 was repeated except that the amount of phloroglucinol used was 1.47 g and the amount of resorcinol used was 0.73 g. Example 3

[0039] Example 1 was repeated except that the amount of phloroglucinol used was 1.57 g and the amount of resorcinol used was 0.63 g. Example 4

[0040] Example 1 was repeated except that the amount of phloroglucinol used was 2.2 g and the amount of resorcinol used was 0 g. Example 5

[0041] Example 1 was repeated except that the amount of phloroglucinol used was 1.1 g and the amount of resorcinol used was 1.1 g. Example 6

[0042] Example 1 was repeated except that the amount of phloroglucinol used was 0.73 g and the amount of resorcinol used was 1.47 g. Example 7

[0043] Example 1 was repeated except that the amount of phloroglucinol was 0 g and the amount of resorcinol was 2.2 g. Example 8

[0044] Example 1 was repeated except that the amount of glyoxylic acid monohydrate used was 1.2 g and the amount of formaldehyde used was 0.8 g. Example 9

[0045] Example 1 was repeated except that the amount of glyoxylic acid monohydrate used was 1.33 g and the amount of formaldehyde used was 0.67 g. Example 10

[0046] Example 1 was repeated except that the amount of glyoxylic acid monohydrate used was 2.0 g and the amount of formaldehyde used was 0 g. Embodiment 11

[0047] Example 1 was repeated except that the amount of glyoxylic acid monohydrate used was 0.89 g and the amount of formaldehyde used was 1.11 g. Example 12

[0048] Example 1 was repeated except that the amount of glyoxylic acid monohydrate used was 0.57 g and the amount of formaldehyde used was 1.43 g. Embodiment 13

[0049] Example 1 was repeated except that the amount of glyoxylic acid monohydrate used was 0 g and the amount of formaldehyde used was 2.0 g. Embodiment 14

[0050] Example 1 was repeated except that the amount of triethylenetetramine used was 0.8 g. Embodiment 15

[0051] Example 1 was repeated except that the amount of triethylenetetramine used was 0.5 g. Example 16

[0052] Example 1 was repeated except that the amount of triethylenetetramine used was 0.3 g. Embodiment 17

[0053] Example 1 was repeated except that triethylenetetramine was replaced by diethylenetriamine. Embodiment 18

[0054] Example 1 was repeated, except that the mass ratio of palladium acetate to nitrogen-doped porous carbon spheres was 10:1000. Embodiment 19

[0055] Example 1 was repeated, except that the mass ratio of palladium acetate to nitrogen-doped porous carbon spheres was 20:1000. Embodiment 20

[0056] Example 1 was repeated, except that the mass ratio of palladium acetate to nitrogen-doped porous carbon spheres was 5:1000. Embodiment 21

[0057] Example 1 was repeated except that 0.5 MPa of H2 was introduced into the autoclave. Embodiment 22

[0058] Example 1 was repeated except that 2.0 MPa of H2 was introduced into the autoclave. Embodiment 23

[0059] Example 1 was repeated except that the stirring reaction time at 70°C was 2 h. Embodiment 24

[0060] Example 1 was repeated except that the reaction time was 4 h at 70°C. Embodiment 25

[0061] Example 1 was repeated except that the reaction was stirred (300 rpm) at 60°C for 3 h. Embodiment 26

[0062] Example 1 was repeated except that the reaction was stirred (300 rpm) at 80°C for 3 h.

[0063] Comparative Example 1 Palladium acetate and activated carbon were weighed in a mass ratio of 15:1000, dispersed in 50 ml of distilled water and placed in an ultrasonic disperser for 1 hour, and then freeze-dried for 48 hours; finally, the freeze-dried solid was calcined at 300°C in a hydrogen atmosphere for 1 hour to obtain an activated carbon-supported Pd-based catalyst.

[0064] Weigh 0.1g of the above-prepared activated carbon supported Pd-based catalyst and place it in a 100ml polytetrafluoroethylene liner, then add 25ml water and 0.5ml phenol; then place the polytetrafluoroethylene liner in a high-pressure reactor, first replace the air in the reactor with hydrogen through a vacuum pump, and then introduce 1.0MPa of H2 after three replacements, and stir (300rpm) at 70℃ for 3h. After the reaction is completed, cool naturally to room temperature, take out the reaction liquid for analysis, and its phenol conversion rate is 20.1%, and the selectivity of cyclohexanone is 93.5%.

[0065] Comparative Example 2 Palladium acetate and carbon nanotubes were weighed in a mass ratio of 15:1000, dispersed in 50 ml of distilled water and placed in an ultrasonic disperser for 1 hour, and then freeze-dried for 48 hours; finally, the freeze-dried solid was calcined at 300°C in a hydrogen atmosphere for 1 hour to obtain a carbon nanotube-loaded Pd-based catalyst.

[0066] Weigh 0.1g of the carbon nanotube-supported Pd-based catalyst prepared above and place it in a 100ml polytetrafluoroethylene liner, then add 25ml of water and 0.5ml of phenol; then place the polytetrafluoroethylene liner in a high-pressure reactor, first replace the air in the reactor with hydrogen through a vacuum pump, and then introduce 1.0MPa of H2 after three replacements, and stir (300rpm) at 70℃ for 3h. After the reaction is completed, naturally cool to room temperature, take out the reaction liquid for analysis, and its phenol conversion rate is 33.7%, and the selectivity of cyclohexanone is 90.6%.

[0067] Table 1 below is a comparison table of phenol conversion and cyclohexanone selectivity data for each embodiment and comparative example:

[0068] Cyclic stability test: The nitrogen-doped porous carbon sphere-supported palladium-based catalysts prepared in Examples 1 to 17 were subjected to 100 cycles of catalytic tests according to the process flow of preparing cyclohexanone by hydrogenation of phenol in Example 1. The results of the 100th catalytic test are shown in Table 2 below:

[0069] It can be seen from the above table that the catalyst of the present invention has good cycle stability. Figure 1 It can be seen from the TEM spectrum of the fresh catalyst prepared in Example 1 that the Pd nanoparticles are evenly dispersed on the porous carbon spheres derived from the nitrogen-doped polymer, and the average particle size of Pd is small and highly dispersed. This also explains why the catalyst has high activity. In addition, Figure 2 (TEM spectrum of the catalyst prepared in Example 1 after being recycled 15 times). Compared with the fresh catalyst, the Pd nanoparticles did not agglomerate, and the dispersion degree and average particle size of Pd were consistent with those of the fresh catalyst, which also explains why it has high stability.

Claims

1. A method for preparing nitrogen-doped porous carbon spheres supported on a palladium-based catalyst, characterized in that: The method comprises the following steps: 1) Using aldehyde compounds, aldehyde acid compounds, phenolic compounds and long-chain amine compounds as raw materials, nitrogen-doped porous carbon spheres are obtained after mixing reaction and calcination treatment in sequence; 2) The nitrogen-doped porous carbon spheres obtained in step 1) are added to a palladium-containing precursor solution for impregnation treatment, and then heat-treated to obtain nitrogen-doped porous carbon spheres loaded with palladium-based catalysts.

2. The method according to claim 1, characterized in that: The aldehyde compound is a C1-C10 aldehyde compound, preferably one or more of formaldehyde, acetaldehyde, propionaldehyde, isopropionaldehyde; and / or The aldehyde acid compound is a C2-C8 aldehyde acid compound, preferably one or more of glyoxylic acid and its hydrate.

3. The method according to claim 1 or 2, characterized in that: The phenolic compound comprises at least one of phenol, catechol, pyrogallol, resorcinol and phloroglucinol, preferably a mixture of resorcinol and phloroglucinol; Preferably, the phenolic compound is a mixture of phloroglucinol and resorcinol in a mass ratio of 0.5 to 2.5:1, preferably a mixture in a mass ratio of 1 to 2:

1.

4. The method according to any one of claims 1 to 3, characterized in that: The long-chain amine compound is a C4-C20 chain amine compound, preferably one or more of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

5. The method according to any one of claims 1 to 4, characterized in that: In step 1), the mass ratio of aldehyde compounds, aldehyde acid compounds, phenolic compounds and long-chain amine compounds is 1:0.3-2:1-1.5:0.4-1.2, preferably 1:0.8-1.5:1.1-1.3:0.5-1.

6. The method according to any one of claims 1 to 5, characterized in that: In step 1), the mixing reaction is specifically: firstly, the aldehyde compound, the aldehyde acid compound, the phenol compound and water are stirred and mixed uniformly, then the long-chain amine compound is added and allowed to stand, then the solid-liquid separation is performed and the solid is washed with a mixed solution of acetone and water, and finally the solid is freeze-dried; and / or In step 1), the calcination treatment is specifically: calcining the solid product obtained after the mixed reaction at 600-1000° C. for 0.5-3 h in an inert atmosphere.

7. The method according to any one of claims 1 to 6, characterized in that: In step 2), the palladium-containing precursor is palladium acetate; and / or In step 2), the mass ratio of the nitrogen-doped porous carbon spheres to the palladium-containing precursor is 1000:1-30, preferably 1000:3-20.

8. The method according to any one of claims 1 to 7, characterized in that: In step 2), the impregnation treatment is specifically: subjecting the mixed system of nitrogen-doped porous carbon spheres and palladium-containing precursor solution to ultrasonic dispersion treatment first, and then to freeze-drying treatment; and / or In step 2), the heat treatment is specifically: calcining the solid product after the impregnation treatment at 250-400° C. for 0.5-3 h in a reducing atmosphere (such as a hydrogen atmosphere).

9. A nitrogen-doped porous carbon sphere supported palladium-based catalyst, characterized in that: The nitrogen-doped porous carbon sphere-supported palladium-based catalyst is prepared by the method described in any one of claims 1 to 8.

10. A use of nitrogen-doped porous carbon spheres supporting a palladium-based catalyst, characterized in that: The nitrogen-doped porous carbon sphere-supported palladium-based catalyst prepared by the method of any one of claims 1 to 8 is used as a hydrogenation catalyst, preferably as a hydrogenation catalyst for hydrogenating phenol to prepare cyclohexanone.

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