Method for preparing PdH (at) mC core-shell catalyst and method for catalyzing phenol to prepare cyclohexanone

Abstract

The invention discloses a method for preparing a PdH-coated mC core-shell catalyst and catalyzing phenol to prepare cyclohexanone, which comprises the following steps: S1, dissolving xylose in deionized water, stirring, adding K2PdCl4, and carrying out ultrasonic treatment to obtain a mixed solution; s2, putting the mixed solution in the S1 into a hydrothermal reaction kettle, putting the hydrothermal reaction kettle into a drying oven for hydrothermal reaction, and after the hydrothermal reaction is finished, taking out the hydrothermal reaction kettle and cooling the hydrothermal reaction kettle to room temperature; s3, the solution in the hydrothermal reaction kettle in the S2 is poured out, vacuum drying is performed after centrifugal washing, and the PdH (at) mC core-shell type catalyst is obtained. The catalyst has high catalytic activity and selectivity when used for catalyzing phenol to prepare cyclohexanone, few byproducts are obtained and are easy to treat, the catalyst does not need follow-up treatment, the catalyst can be directly and repeatedly used, and the recycling effect is good. The preparation method disclosed by the invention is simple, and the synthesized core-shell type catalyst is regular in morphology and has relatively good catalyst stability, catalytic activity and reusability.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a method for preparing a PdH@mC core-shell catalyst and catalyzing phenol to prepare cyclohexanone. Background Art

[0002] As an important organic chemical intermediate, cyclohexanone is widely used in the chemical industry. In industry, cyclohexanone is often used to produce chemicals such as caprolactam and nylon, and is then widely used in textiles, electronics, machinery, daily necessities and other fields. Due to its excellent performance (high solubility, low volatility, and low toxicity), it is used as a solvent in paints, fuels, dyes, plastics and other industries. In addition, cyclohexanone can be used to prepare medical products such as coumarin, cyclohexeneethylamine, and cyclohexanone peroxide through a series of reactions, which broadens the application of cyclohexanone in the medical field. Cyclohexanone downstream products can be used as coating dispersants, ink brighteners, resin curing agents, plasticizers and inducers, and flavoring agents for tobacco and spices. The traditional preparation process for producing cyclohexanone has the disadvantages of high energy consumption and low yield. With the development of the concept of green chemistry, phenol hydrogenation is considered to be the most promising synthetic route in the production of cyclohexanone. The process has the advantages of high selectivity, low energy consumption, and high atom economy.

[0003] Palladium (Pd) is an efficient catalytic material for many important reactions, including those related to selective hydrogenation and CC coupling, as well as in the fields of catalytic conversion and fuel cells. In particular, Pd has been shown to be one of the best monometallic catalysts for the hydrogenation of phenol to cyclohexanone. The performance of Pd-based phenol catalysts has been extensively studied both theoretically and experimentally. In addition to their intrinsic material properties, previous studies involving density functional theory (DFT) calculations and in situ reaction kinetics have determined that the phenol hydrogenation activity on Pd surfaces decreases in the order Pd(111)>Pd(100)>Pd(110). Despite significant progress in this field, the limited supply and rising price of Pd call for the development of new strategies to further improve the performance of catalysts without modifying this scarce metal. Reported strategies include modifying the catalyst with SnO2, introducing CeO2 supports with specific surface structures, removing adsorbed capping agents, forming thin layers or metal compound structures, and transforming the crystal structure of pristine Pd into Pd hydride (PdHx).

[0004] Since Pd is one of the few metals that can form metal hydrides, synthetic strategies involving PdHx are rare. The formation of PdHx not only plays a crucial role in a series of catalytic reactions, but also receives extensive attention in many basic research. This is because the introduction of H elements into Pd hydrides expands the Pd lattice, effectively optimizes the electronic structure of Pd, and increases the adsorption free energy of reaction intermediates on Pd catalytic sites, thereby significantly improving the catalytic performance. The volume and surface properties of the Pd group can be adjusted by adjusting the stoichiometry of H atoms in the Pd lattice (i.e., x in PdHx). Most of the basic research reported in the literature involves the use of hydrogen as the source of hydrogen atoms. Some alternative sources of hydrogen atoms have also been reported, among which famous examples include dimethylformamide (DMF), sodium borohydride (NaBH4), formaldehyde (HCHO), hydrazine hydrate (N2H4) and amines (-NH2). The exploration of biomass sugars as hydrogenation agents and their hydrogenation mechanisms have not been reported. However, most strategies for preparing PdHx usually require stringent preparation conditions, and the surfaces of PdHx produced using these methods are often contaminated by these organic compounds or their derived chemicals. Therefore, it is urgent to develop a green and environmentally friendly sample synthesis strategy to obtain pure PdH without contamination. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing a PdH@mC core-shell catalyst and catalyzing phenol to prepare cyclohexanone.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing a PdH@mC core-shell catalyst comprises the following steps:

[0008] S1, dissolving xylose in deionized water, adding K2PdCl4 after stirring, and performing ultrasound to obtain a mixed solution;

[0009] S2, placing the mixed solution in S1 in a hydrothermal reaction kettle, placing it in an oven for hydrothermal reaction, and after the hydrothermal reaction is completed, taking out the hydrothermal reaction kettle and cooling it to room temperature;

[0010] S3, pouring out the solution in the hydrothermal reaction kettle of S2, washing by centrifugation and then vacuum drying to obtain a PdH@mC core-shell catalyst.

[0011] Preferably, in S1, the amount of xylose added is 0.0083 mol, the amount of deionized water added is 2.78 mol, and the amount of K2PdCl4 added is 0.00004 mol.

[0012] Preferably, in S1, the stirring time is 30 min.

[0013] Preferably, in S1, the ultrasonic power is 100 Hz and the ultrasonic time is 30 minutes.

[0014] Preferably, in S2, the hydrothermal reaction kettle is 150 mL of polytetrafluoroethylene.

[0015] Preferably, in S2, the temperature of the hydrothermal reaction is 180° C., and the time of the hydrothermal reaction is 3 to 4 hours.

[0016] Preferably, in S3, the product is washed with deionized water and ethanol for 3-5 times, and then dried in a vacuum oven at 40°C.

[0017] A method for preparing cyclohexanone by catalyzing phenol with a PdH@mC core-shell catalyst comprises the following steps:

[0018] S4: First, N2 is used to replace the air in the autoclave, and then H2 is introduced to replace the air in the autoclave. The H2 pressure in the autoclave is maintained at 1-2 MPa, and the autoclave is heated and stirred to perform a catalytic hydrogenation reaction;

[0019] S5: After the reaction is completed, the product cyclohexanone is obtained by centrifugal separation, and the PdH@mC core-shell catalyst is recovered at the same time.

[0020] Preferably, in S4, N2 is used to replace the air in the kettle for 3 to 5 times, and H2 is introduced to replace the air in the kettle for 2 to 3 times.

[0021] Preferably, in S5, the centrifugal speed is 300-800 r / min, and the H content in the PdH@mC core-shell catalyst is 0.25-0.47.

[0022] Compared with the prior art, the present invention has achieved the following technical effects:

[0023] (1) The core-shell catalyst PdH@mC provided by the present invention has high catalytic activity and selectivity when catalyzing the hydrogenation of phenol to prepare cyclohexanone; less by-products are obtained after the reaction, and the post-treatment of the product is simple; after the phenol hydrogenation reaction is completed, the catalyst and the product can be separated simply and efficiently by centrifugation, and the catalyst does not need post-treatment and can be directly reused. After being reused for 5 times, the catalytic performance has not been significantly reduced, and its core-shell structure has not been significantly changed, and the recycling effect is good;

[0024] (2) The preparation method of the core-shell catalyst PdH@mC provided by the present invention is simple. The core-shell alloy catalyst synthesized by the method provided by the present invention has a regular morphology and good dispersibility. The catalyst catalyzes phenol hydrogenation to prepare cyclohexanone and has high catalyst stability, catalytic activity and reusability.

[0025] (3) The introduction of H element into Pd hydride in the present invention will expand the Pd lattice, and H atoms will enter the vacancies of face-centered cubic Pd to form a regular PdH unit cell, which effectively optimizes the electronic structure of Pd and increases the adsorption free energy of reaction intermediates on the Pd catalytic site; the volume and surface properties of Pd can be adjusted by adjusting the stoichiometry of H atoms in the Pd lattice (i.e., the x in PdHx); PdH acts as a hydrogen transfer medium to store hydrogen in biomass sugar during the hydrothermal synthesis process and release it as an additional hydrogen source to participate in hydrogenation, which is in the subsequent H2-free process. The results of the experiment showed that the PdH phase in the catalyst was 0.38 (PdH@mC-0.38), and the phenol hydrogenation activity increased by 1.14 times. The reaction kinetics and density functional theory (DFT) confirmed that this was due to the enhanced adsorption of H2 and phenol by PdH. In addition, H2 molecules are more easily and stably adsorbed on PdH, and the adsorption of H2 molecules helps to release a large number of H atoms in PdH. PdH can be stored as a hydrogen source in the system, providing a large amount of additional hydrogen in PdH for the hydrogenation reaction, thereby significantly improving the catalytic performance.

[0026] (4) This invention provides a feasible strategy for enhancing the reaction performance of Pd-based catalysts without changing this rare metal; in addition, it also deepens the understanding of the utilization of hydrogen energy in biomass. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the synthesis of a core-shell catalyst PdH@mC in a method for preparing a PdH@mC core-shell catalyst and catalyzing phenol to prepare cyclohexanone according to the present invention;

[0028] Figure 2 A synthesis mechanism diagram of a core-shell catalyst PdH@mC for preparing a PdH@mC core-shell catalyst and a method for catalyzing phenol to prepare cyclohexanone according to the present invention;

[0029] Figure 3 TEM image and particle size distribution diagram of a core-shell catalyst PdH@mC in a method for preparing a PdH@mC core-shell catalyst and catalyzing phenol to prepare cyclohexanone according to the present invention;

[0030] (ac) are TEM images of core-shell catalysts; (df) are particle size distribution diagrams; (a) PdH@mC-0.25, (b) PdH@mC-0.38, (c) PdH@mC-0.47; (d) PdH@mC-0.25, (e) PdH@mC-0.38, (f) PdH@mC-0.47;

[0031] Figure 4The XRD diagram of the core-shell catalyst PdH@mC in the method for preparing the PdH@mC core-shell catalyst and catalyzing phenol to prepare cyclohexanone is shown in the figure. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Embodiment 1:

[0034] Synthesis of PdH@mC-0.25 core-shell catalyst and method for hydrogenating phenol to cyclohexanone

[0035] S1. Dissolve 0.0083 mol of xylose in 2.78 mol of deionized water, stir magnetically for 30 min, then add 0.00004 mol of K2PdCl4 solid, and disperse the mixture by ultrasonication at a power of 100 Hz for 30 min to obtain a mixed solution;

[0036] S2, transferring the obtained mixed solution into a 150 mL polytetrafluoroethylene hydrothermal reactor and sealing it, and then performing a hydrothermal reaction in an oven at 180° C. for 3 h;

[0037] S3. After the above process is completed, the hydrothermal reactor is slowly cooled to room temperature, the solid product is centrifuged and washed with deionized water and ethanol for 3-5 times, and then dried in a vacuum oven at 40°C to finally obtain a PdH@mC core-shell catalyst;

[0038] S4, 0.1g phenol, 0.05g PdH@mC-0.25, 5mL dichloromethane and high temperature magnetron were placed in a 75mL autoclave, the air in the autoclave was replaced with nitrogen 3 times, and hydrogen 2 times, the pressure in the autoclave was maintained at 2MPa, and heated and stirred at 150℃ for 3h;

[0039] S5. After the reaction is completed, the mixture is allowed to stand and cool to room temperature, and the product cyclohexanone is obtained by centrifugal separation, and the PdH@mC-0.25 core-shell catalyst is recovered.

[0040] The phenol conversion rate was 93.7%, and the cyclohexanone yield was 98.4%.

[0041] The calculation formulas for phenol conversion and cyclohexanone yield are as follows:

[0042]

[0043] Y=S*X

[0044] Wherein, Y is the yield of cyclohexanone; X is the conversion rate of phenol; S is the selectivity of cyclohexanone; n initial is the amount of phenol added; n final is the amount of remaining phenol substance; n product is the amount of substance of the product cyclohexanone.

[0045] Embodiment 2:

[0046] Synthesis of PdH@mC-0.38 core-shell catalyst and method for hydrogenating phenol to cyclohexanone

[0047] S1. Dissolve 0.0083 mol of xylose in 2.78 mol of deionized water, stir magnetically for 30 min, then add 0.00004 mol of K2PdCl4 solid, and disperse the mixture by ultrasonication at a power of 100 Hz for 30 min to obtain a mixed solution;

[0048] S2, transferring the obtained mixed solution into a 150 mL polytetrafluoroethylene hydrothermal reactor and sealing it, and then performing a hydrothermal reaction in an oven at 180° C. for 3.5 h;

[0049] S3. After the above process is completed, the hydrothermal reactor is slowly cooled to room temperature, the solid product is centrifuged and washed with deionized water and ethanol for 3-5 times, and then dried in a vacuum oven at 40°C to finally obtain a PdH@mC core-shell catalyst;

[0050] S4, 0.1g phenol, 0.05g PdH@mC-0.38, 5mL dichloromethane and high temperature magnetron were placed in a 75mL autoclave, the air in the autoclave was replaced with nitrogen 3 times, and hydrogen 2 times, the pressure in the autoclave was maintained at 2MPa, and heated and stirred at 150℃ for 3h;

[0051] S5. After the reaction is completed, the mixture is allowed to stand and cool to room temperature, and the product cyclohexanone is obtained by centrifugal separation, and the PdH@mC-0.38 core-shell catalyst is recovered.

[0052] The phenol conversion rate was 98.9%, and the cyclohexanone yield was 99.9%.

[0053] Embodiment 3:

[0054] Synthesis of PdH@mC-0.47 core-shell catalyst and method for hydrogenating phenol to cyclohexanone

[0055] S1. Dissolve 0.0083 mol of xylose in 2.78 mol of deionized water, stir magnetically for 30 min, then add 0.00004 mol of K2PdCl4 solid, and disperse the mixture by ultrasonication at a power of 100 Hz for 30 min to obtain a mixed solution;

[0056] S2, transferring the obtained mixed solution into a 150 mL polytetrafluoroethylene hydrothermal reactor and sealing it, and then performing a hydrothermal reaction in an oven at 180° C. for 4 h;

[0057] S3. After the above process is completed, the hydrothermal reactor is slowly cooled to room temperature, the solid product is centrifuged and washed with deionized water and ethanol for 3-5 times, and then dried in a vacuum oven at 40°C. After drying, the PdH@mC core-shell catalyst is finally obtained.

[0058] S4, 0.1g phenol, 0.05g PdH@mC-0.47, 5mL dichloromethane and high temperature magnetron were placed in a 75mL autoclave, the air in the autoclave was replaced with nitrogen 3 times, and hydrogen 2 times, the pressure in the autoclave was maintained at 2MPa, and heated and stirred at 150℃ for 3h;

[0059] S5. After the reaction is completed, the mixture is allowed to stand and cool to room temperature, and the product cyclohexanone is obtained by centrifugal separation, and the PdH@mC-0.47 core-shell catalyst is recovered.

[0060] The phenol conversion rate was 99.9%, and the cyclohexanone yield was 98.7%.

[0061] Embodiment 4:

[0062] Synthesis of PdH@mC-0.38 core-shell catalyst and method for hydrogenation of phenol to cyclohexanone without hydrogen source

[0063] S1. Dissolve 0.0083 mol of xylose in 2.78 mol of deionized water, stir magnetically for 30 min, then add 0.00004 mol of K2PdCl4 solid, and disperse the mixture by ultrasonication at a power of 100 Hz for 30 min to obtain a mixed solution;

[0064] S2, transferring the obtained mixed solution into a 150 mL polytetrafluoroethylene hydrothermal reactor and sealing it, and then performing a hydrothermal reaction in an oven at 180° C. for 3.5 h;

[0065] S3. After the above process is completed, the hydrothermal reactor is slowly cooled to room temperature, the solid product is centrifuged and washed with deionized water and ethanol for 3-5 times, and then dried in a vacuum oven at 40°C to finally obtain a PdH@mC core-shell catalyst;

[0066] S4, 0.1g phenol, 0.05g PdH@mC-0.38, 5mL dichloromethane and high temperature magnetron were placed in a 75mL autoclave, the air in the autoclave was replaced with nitrogen three times to keep the pressure in the autoclave at 2MPa, and heated and stirred at 150℃ for 3h;

[0067] S5. After the reaction is completed, the mixture is allowed to stand and cool to room temperature, and the product cyclohexanone is obtained by centrifugal separation, and the PdH@mC-0.47 core-shell catalyst is recovered.

[0068] The phenol conversion was 2.1% and the cyclohexanone selectivity was 99.9%.

[0069] Embodiment 5:

[0070] Catalytic performance testing of catalysts after repeated use

[0071] The experimental conditions and steps were the same as those in Example 1, except that the catalyst was replaced with the catalyst recovered in Example 1. The experiment was repeated five times. After five times of repeated use, the phenol conversion rate was 99.3% and the cyclohexanone selectivity was 96.8%.

[0072] like Figure 1 As shown, the synthesis process of the PdH@mC core-shell catalyst provided by the present invention is as follows:

[0073] 0.0083 mol of xylose was dissolved in 2.78 mol of deionized water and magnetically stirred for 30 minutes. Then, 0.00004 mol of K2PdCl4 solid was added, and the mixture was ultrasonically dispersed at a power of 100 Hz for 30 minutes to obtain a mixed solution. The obtained mixed solution was then transferred to a 150 mL polytetrafluoroethylene hydrothermal reactor and sealed, and then a hydrothermal reaction was carried out in an oven at 180°C. After the above process was completed, the hydrothermal reactor was slowly cooled to room temperature, the solid product was centrifuged and washed with deionized water and ethanol for 3-5 times, and then dried in a vacuum oven at 40°C. After drying, the PdH@mC core-shell catalyst was finally obtained.

[0074] like Figure 2 As shown, it is a schematic diagram of the synthesis mechanism of the PdH@mC core-shell catalyst provided by the present invention, specifically:

[0075] 1) Formation of Pd particles and PdH cores by H doping; 2) Xylose conversion to carbon shell coating (mC). 2+ The PdH@mC core-shell catalyst was prepared by solution hydrothermal method. By adjusting the hydrothermal time, PdH@mC samples with different PdH contents were successfully obtained. 2+ The redox reaction with the aldehyde group in xylose results in Pd 2+The reduction forms a Pd0 cluster, while the aldehyde group (R-CHO) is oxidized to form a carboxylic acid (R-COOH). 0 The hydrogen is further converted into substances such as CO2, releasing H2. The hydrothermal reactor provides good thermodynamic and kinetic conditions for hydrogen doping into Pd metal. As the hydrothermal time increases, different contents of PdH are obtained. In addition, xylose undergoes dehydration, hydrolysis, polymerization and aromatization reactions during the hydrothermal process to generate carbon oligomers, which are then matured and grown into a carbon shell with a certain thickness with PdH particles as the core using hydrothermal methods.

[0076] like Figure 3 As shown, it is a TEM image of the PdH@mC core-shell catalyst provided by the present invention; wherein, (a) PdH@mC-0.25, (b) PdH@mC-0.38, (c) PdH@mC-0.47. It can be seen from the figure that the synthesized PdH@mC core-shell catalyst has a distinct core-shell structure. The results in the figure show that there are significant differences in Pd nanoparticles (NPs) (shaded part), which is related to the formation of PdHx under different H doping contents; Figure 3 (d-f) show the size distribution of Pd metal particles in different PdH@mC core-shell catalysts. The size of metal particles increases with the increase of PdHx content, which may be related to the expansion of metal lattice caused by H doping.

[0077] like Figure 4 As shown in the figure, it is the XRD pattern of the PdH@mC core-shell catalyst provided by the present invention. It can be seen that the characteristic peaks of all samples are located at 40°, 46°, 66° and 79°, respectively, belonging to the (111), (200), (220) and (311) crystal planes of Pd metal, respectively. It is worth noting that a new peak (2θ=38.9°, JCPDS No.18-0951) appears next to the Pd (111) peak (2θ=40.1°, JCPDS No.46-1043), indicating the appearance of the PdH phase. The lattice constants of the Pd phase and the PdH phase in the samples obtained under different reaction conditions can be calculated using the JADE software. It is calculated that when the H doping amount is low (x=0.25), the lattice constant of the PdH phase Slightly larger than the lattice constant of the Pd phase Pd and PdH phases coexist, forming a broad characteristic peak. As the H doping concentration increases (x = 0.38), the lattice constant of the PdH phase increases to The characteristic peak dominated by the PdH phase becomes clearer. When the H doping amount increases to 0.47, the lattice constant of the PdH phase increases to The entire metal particle transforms into the PdH phase, and the characteristic peak further shifts to 38.9°. Obviously, the content of PdH in each nanoparticle can be controlled by adjusting the reaction.

[0078] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a PdH@mC core-shell catalyst, characterized in that: The following steps are involved: S1, dissolving xylose in deionized water, adding K2PdCl4 after stirring, and performing ultrasound to obtain a mixed solution; S2, placing the mixed solution in S1 in a hydrothermal reaction kettle, placing it in an oven for hydrothermal reaction, and after the hydrothermal reaction is completed, taking out the hydrothermal reaction kettle and cooling it to room temperature; S3, pouring out the solution in the hydrothermal reaction kettle of S2, washing by centrifugation and then vacuum drying to obtain a PdH@mC core-shell catalyst.

2. A method for preparing a PdH@mC core-shell catalyst according to claim 1, characterized in that: In the S1, the added amount of xylose is 0.0083 mol, the added amount of deionized water is 2.78 mol, and the added amount of K2PdCl4 is 0.00004 mol.

3. A method for preparing a PdH@mC core-shell catalyst according to claim 1, characterized in that: In S1, the stirring time is 30 min.

4. A method for preparing a PdH@mC core-shell catalyst according to claim 1, characterized in that: In S1, the ultrasonic power is 100 Hz and the ultrasonic time is 30 minutes.

5. A method for preparing a PdH@mC core-shell catalyst according to claim 1, characterized in that: In S2, the hydrothermal reaction kettle is 150 mL of polytetrafluoroethylene.

6. A method for preparing a PdH@mC core-shell catalyst according to claim 1, characterized in that: In S2, the temperature of the hydrothermal reaction is 180° C., and the time of the hydrothermal reaction is 3 to 4 hours.

7. A method for preparing a PdH@mC core-shell catalyst according to claim 1, characterized in that: In S3, the sample was washed with deionized water and ethanol for 3-5 times, and then dried in a vacuum oven at 40°C.

8. A method for preparing cyclohexanone from phenol using a PdH@mC core-shell catalyst, characterized in that: The following steps are involved: S4: First, N2 is used to replace the air in the autoclave, and then H2 is introduced to replace the air in the autoclave. The H2 pressure in the autoclave is maintained at 1-2 MPa, and the autoclave is heated and stirred to perform a catalytic hydrogenation reaction; S5: After the reaction is completed, the product cyclohexanone is obtained by centrifugal separation, and the PdH@mC core-shell catalyst is recovered at the same time.

9. The method for preparing cyclohexanone from phenol using a PdH@mC core-shell catalyst according to claim 8, characterized in that: In S4, N2 is used to replace the air in the kettle for 3 to 5 times, and H2 is introduced to replace the air in the kettle for 2 to 3 times.

10. The method for preparing cyclohexanone from phenol using a PdH@mC core-shell catalyst according to claim 9, characterized in that: In the S5, the centrifugal speed is 300-800 r / min, and the H content in the PdH@mC core-shell catalyst is 0.25-0.47.

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