Magnetic field separable catalyst for partial hydrogenation of benzene to cyclohexene and preparation method thereof

Abstract

This invention discloses a magnetically separable catalyst for the partial hydrogenation of benzene to cyclohexene and its preparation method. The catalyst employs a composite structure design of a ferromagnetic core, an intermediate coating layer, and an outer Ru active component. The ferromagnetic core is selected from transition metals such as iron, cobalt, and nickel, and their alloys. The intermediate coating layer is ZrO2 or carbon material, and the promoter is selected from one or more of Zn, Fe, Co, and Ni. The preparation method involves preparing the ferromagnetic core via a co-precipitation / hydrothermal method, followed by coating modification to obtain a coated ferromagnetic metal core substrate. Then, liquid-phase atomic layer deposition (L-ALD) technology is used to sequentially deposit the Ru active component and the promoter, forming a Ru-promoter interface coupling structure. Finally, the target catalyst is obtained by vacuum drying. This invention offers strong process controllability and excellent repeatability, low equipment investment costs, and efficient separation and recovery via magnetic field sedimentation, significantly reducing catalyst loss during the reaction process, making it suitable for industrial-scale applications.

Description

Technical Field

[0001] This invention belongs to the field of catalytic chemistry and organic synthesis technology, specifically relating to a magnetically separable catalyst for the partial hydrogenation of benzene to cyclohexene and its preparation method. Background Technology

[0002] Cyclohexene is a key intermediate in the synthesis of important chemical products such as nylon 6, nylon 66, adipic acid, and cyclohexanone. With the rapid development of downstream industries, its market demand continues to rise. The partial hydrogenation of benzene has become the mainstream industrial process for cyclohexene production due to its advantages such as the wide availability of benzene as a raw material, its environmentally friendly reaction process, and high atom utilization. The core technological bottleneck of this process lies in the development of high-performance catalysts that simultaneously meet the requirements of high benzene conversion, high cyclohexene selectivity, long-term cycle stability, and easy separation and recovery.

[0003] Existing benzene partial hydrogenation catalysts mostly use Ru as the core active component, supplemented by Zn, Fe, Co, Ni and other auxiliary agents, and the support is mainly selected from oxide materials such as ZrO2, SiO2, and Al2O3. Traditional catalyst preparation methods include impregnation, co-precipitation, sol-gel and other methods, but there are many technical defects: (1) The particle size of the active component Ru is difficult to control precisely, and it is easy to agglomerate and form large particles (the particle size is usually >10nm), resulting in low cyclohexene selectivity (generally <80%); (2) The dispersion uniformity of the auxiliary agent and Ru active component is poor, the interfacial synergy is weak, and the active component is easy to fall off and be lost during the recycling process of the catalyst, requiring frequent replenishment of new catalyst, which increases the cost of industrial production; (3) The separation of the catalyst from the reaction system is difficult. Conventional separation methods such as filtration and sedimentation are complicated to operate, have high energy consumption, and are easy to cause catalyst loss. Existing magnetic response catalysts have not yet achieved efficient adaptation to magnetic field sedimentation, and the loss rate control is still not ideal.

[0004] Liquid-phase atomic layer deposition (L-ALD) technology, based on the self-limiting reaction characteristics of the gas-liquid interface, enables atomically precise deposition of active components on the surface of a coated ferromagnetic core substrate. This allows for effective control of the particle size, dispersibility, and interaction with the support of the active components, making it more suitable for large-scale applications of liquid precursors compared to vapor-phase atomic layer deposition (ALD). However, current technologies have not fully integrated the magnetic field sedimentation adaptability of the ferromagnetic core with L-ALD technology, failing to fully utilize the rapid separation advantage of magnetic field sedimentation to solve the catalyst loss problem. Furthermore, the lack of precise control over the electronic effects at the active component-promoter interface results in significant room for improvement in the overall catalyst performance. Therefore, developing a magnetically separable catalyst based on a ferromagnetic core and L-ALD technology, achieving efficient separation through magnetic field sedimentation, and addressing the core problems of high loss rates and difficult separation in traditional catalysts, has significant industrial application value. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a magnetically separable catalyst for the partial hydrogenation of benzene to cyclohexene and its preparation method. Through a composite structure design of "ferromagnetic core – intermediate coating layer – Ru active component," combined with the atomic-level control advantages of L-ALD technology, the interfacial synergistic effect between the active component and the promoter is enhanced. Simultaneously, the magnetic response characteristics of the ferromagnetic core are utilized to achieve rapid separation of the catalyst via magnetic field sedimentation, significantly reducing the catalyst loss rate during the reaction process. Ultimately, a benzene partial hydrogenation catalyst to cyclohexene exhibits high selectivity, high stability, and easy magnetic field separation.

[0006] catalyst structure

[0007] The magnetically separable benzene fraction hydrogenation catalyst for cyclohexene production provided by this invention employs a ferromagnetic core-intermediate coating layer-active layer composite structure, specifically comprising:

[0008] a. Ferromagnetic core: Selected from one or more ferromagnetic materials such as transition metals iron, cobalt, nickel and their alloys, to impart the magnetic response performance required for magnetic field sedimentation of the catalyst, preferably with a particle size of 4-50 nm to ensure rapid sedimentation under magnetic field;

[0009] b. Intermediate Coating Layer: This layer is made of ZrO2 or carbon material, serving to protect the ferromagnetic core from oxidation and corrosion, while providing a stable loading substrate for the Ru active component. Its high specific surface area and suitable pore size structure facilitate mass transfer between reactants and products. The preferred ZrO2 coating layer is monoclinic or tetragonal, with a thickness of 4–30 nm and a specific surface area of ​​10–120 m². 2 / g, pore size 15–40 nm; carbon coating layer is amorphous carbon or graphitized carbon, thickness 4–30 nm, specific surface area 50–300 m² / g. 2 / g, pore size 20-50nm;

[0010] c.Ru active component: Atomic-level dispersion is achieved through L-ALD technology, with the optimal particle size precisely controlled at 3-6 nm and the loading at 5-20 wt%, providing highly efficient hydrogenation active sites;

[0011] d. Additives: selected from one or more of Zn, Fe, Co, and Ni, preferably a Zn and Ni composite system (composite mass ratio 1:0.3-0.8), with a loading of 0.1-5 wt%, forming a composite active site with interfacial electronic coupling with Ru, which significantly improves the selectivity of cyclohexene and the stability of the catalyst.

[0012] Preparation method

[0013] The method for preparing the catalyst includes the following steps:

[0014] 1. Preparation of ferromagnetic core: Ferromagnetic core materials are prepared by co-precipitation or hydrothermal methods;

[0015] a. Coprecipitation method: A solution of transition metal salt (such as ferric chloride, cobalt chloride, nickel chloride, etc.) is mixed with an alkaline solution (such as sodium hydroxide or potassium hydroxide solution) at a molar ratio of 1:1.5 to 1:3. The mixture is stirred at 30 to 60°C for 2 to 4 hours to generate hydroxide precipitate. The precipitate is washed with deionized water until neutral, filtered, and then reduced at 200 to 400°C under a hydrogen atmosphere for 2 to 5 hours to obtain a ferromagnetic core.

[0016] b. Hydrothermal method: A transition metal salt solution is mixed with an organic amine complexing agent (such as ethylenediamine or triethylenetetramine) at a volume ratio of 1:0.5 to 1:2, and the mixture is transferred to a hydrothermal reactor. The reaction is carried out at 120 to 200°C for 6 to 12 hours. After washing and drying, the product is reduced at 300 to 500°C under a hydrogen atmosphere for 3 to 6 hours to obtain a ferromagnetic core.

[0017] 2. Liquid Phase Atomic Layer Deposition Apparatus Setup: This liquid phase atomic layer deposition apparatus uses a dual-pulse reactor as the core reaction unit, integrating a precursor supply system, a washing and purification system, an inert gas purging system, a constant temperature control system, and supporting fluid control and sealing units to form a closed-loop atomic layer deposition reaction system. It can achieve precise delivery of precursors and controllable reaction process, and is suitable for atomic layer thin film deposition on various types of substrates. It solves the technical pain points of traditional deposition such as uneven film thickness, component mixing, and weak interfacial bonding, while taking into account the practicality and scalability of the apparatus.

[0018] 3. Preparation of the intermediate coating layer: The liquid phase atomic layer deposition apparatus is started to perform ZrO2 coating or carbon coating on the ferromagnetic core. ZrO2 coating involves mixing the ferromagnetic core with a 0.05–0.5 mol / L zirconium source aqueous solution at a solid-liquid ratio (mass ratio) of 1:10–1:25, stirring at 40–70℃ for 4–8 h, drying at 80–120℃ for 4–6 h, and then calcining in air at 500–700℃ for 3–6 h. Carbon coating involves mixing the ferromagnetic core with a 0.5–2 mol / L carbon source solution at a solid-liquid ratio (mass ratio) of 1:8–1:20, hydrothermally carbonizing at 80–160℃ for 8–24 h, followed by calcination in nitrogen at 600–900℃ for 2–5 h. The carbon source is selected from glucose, sucrose, fructose, and phenolic resin.

[0019] 4. Ru active component deposition (first deposition cycle):

[0020] a. Precursor pulse: The coated ferromagnetic core substrate is added to the reactor, and a 0.015-0.045 mol / L solution of ruthenium(III) acetylacetone in ethylene glycol is injected, with the liquid level covering the coated ferromagnetic core substrate. The mixture is stirred and adsorbed at 35-55℃ for 35-65 min. The Ru precursor is adsorbed on the surface of the coated ferromagnetic core substrate by utilizing the self-limiting reaction characteristics of L-ALD.

[0021] b. Washing and desorption: Drain the precursor solution and wash with anhydrous ethanol 4 to 6 times. Each time, the amount of washing solution is 5 to 10 times the mass of the coated ferromagnetic core substrate to completely remove the physically adsorbed Ru precursor.

[0022] c. Reduction reaction: Introduce a mixed gas of H2 / N2 (H2 volume fraction 5-20%), heat to 200-450℃, and hold for 2.5-4.5 h to reduce the adsorbed Ru precursor to the active component of metallic Ru;

[0023] d. Nitrogen purging: Stop the H2 / N2 mixed gas flow and continue to purge with nitrogen until room temperature, completing one Ru deposition cycle;

[0024] e. Repeat the cycle: Repeat steps a to d 20 to 50 times, controlling the Ru load at 5 to 20 wt%;

[0025] 5. Additive deposition (second deposition cycle):

[0026] a. Precursor pulse: A 0.012–0.028 mol / L precursor solution was injected into the Ru-deposited catalyst, and the mixture was stirred and adsorbed at 45–65 °C for 25–45 min; the precursor for the Zn and Ni composite additive was a mixed aqueous solution of Zn(Ac)2 and Ni(NO3)2, with a Zn to Ni mass ratio of 1:0.3–0.8;

[0027] b. Washing and desorption: Drain the precursor solution and wash with deionized water 4 to 6 times to remove the physically adsorbed auxiliary precursor;

[0028] c. Precipitant pulse: Inject 0.02-0.04 mol / L NaOH aqueous solution into the washed coated ferromagnetic core substrate, stir at 45-65℃ for 2.5-3.5 h, and precipitate the auxiliary precursor into the form of metal hydroxide, forming an interfacial coupling structure with Ru;

[0029] d. Repeat the cycle: Repeat steps a to c 5 to 30 times, controlling the total loading of the additives to be 0.5 to 5 wt%;

[0030] 6. Post-treatment: The deposited catalyst is vacuum dried at 80-125℃ for 4.5-6.5h to remove residual moisture and impurities, thus obtaining the target magnetic field separable catalyst (denoted as Ru-M-MC, where M is the promoter and MC is the coated ferromagnetic core substrate).

[0031] The preferred Ru precursor solution in step 4) is a 0.015-0.045 mol / L ruthenium(III) acetylacetone ethylene glycol solution.

[0032] The preferred step 5) is a mixed aqueous solution of Zn(Ac)2 and Ni(NO3)2 at a concentration of 0.012 to 0.028 mol / L, with a mass ratio of Zn to Ni of 1:0.3 to 0.8.

[0033] In the preferred step 3), the zirconium source for ZrO2 coating is selected from zirconium chloride and zirconium nitrate; the carbon source for carbon coating is selected from glucose, sucrose, fructose, and phenolic resin.

[0034] The preferred method for preparing the intermediate coating layer includes: preparation of precursor and reactant: prepare a zirconium source precursor solution, using a 0.05-0.3 mol / L zirconium oxychloride (ZrOCl2・8H2O) aqueous solution or a 0.05-0.2 mol / L zirconium nitrate aqueous solution, and simultaneously prepare a 0.1-0.5 mol / L ammonia aqueous solution as a reactant. Both solutions are ultrasonically degassed for 30 min to ensure system homogeneity and reactivity.

[0035] Ferromagnetic core dispersion: The ferromagnetic cores are added to a mixed solvent of deionized water and anhydrous ethanol (volume ratio 1:1) at a solid-liquid ratio (mass ratio) of 1:15-1:30. The mixture is ultrasonically dispersed for 40-60 min, and mechanically stirred at 300-500 r / min to form a stable core suspension without agglomeration, which lays the foundation for subsequent uniform deposition.

[0036] Liquid-phase atomic layer deposition cycle: The suspension is heated to 30-60 ℃, and the L-ALD alternating deposition cycle is started. The single cycle process is as follows: ① Precursor adsorption: The zirconium source precursor solution is injected, and adsorption is carried out by stirring for 15-30 min, using Zr 4+ Chemical interaction with the hydroxyl groups on the surface of the ferromagnetic core to achieve Zr 4+ ① Self-limited monolayer saturated adsorption on particle surface; ② Solvent washing: Inject mixed solvent, stir and wash for 10-15 min to quickly remove unadsorbed free precursors and byproducts; ③ Reaction agent reaction: Inject ammonia solution, stir and react for 15-30 min to allow the adsorbed Zr to saturate. 4+The ZrO2 precursor film is generated by in-situ reaction with OH- to form a zirconium hydroxide (Zr(OH)4) monolayer precursor film; ④ Secondary washing: The mixed solvent is injected again for 5-10 min to remove unreacted ammonia and reaction byproducts, completing one deposition cycle. Depending on the target coating thickness (1-20 nm), the deposition cycle is repeated 5-50 times to achieve layer-by-layer controllable growth of the ZrO2 precursor layer. After deposition, the product is centrifuged, washed alternately with deionized water and anhydrous ethanol 3-5 times, vacuum dried at 80-120℃ for 4-6 h, and then calcined in air at 500-700℃ for 3-6 h to completely transform the Zr(OH)4 precursor layer into a crystalline ZrO2 coating layer, while removing residual solvent and organic matter, resulting in a uniformly coated ferromagnetic core of ZrO2.

[0037] Preparation of carbon coating layer: Preparation of carbon source precursor and reactant: Select organic carbon source precursor, prepare 0.1-1 mol / L glucose aqueous solution, 0.05-0.5 mol / L phenolic resin ethanol solution or 0.2-1.5 mol / L sucrose aqueous solution, and at the same time prepare 0.05-0.3 mol / L formaldehyde aqueous solution as crosslinking reactant. All solutions are filtered through a 0.22 μm filter membrane and then ultrasonically degassed for later use.

[0038] Ferromagnetic core dispersion: Add the ferromagnetic core to anhydrous ethanol at a solid-liquid ratio (mass ratio) of 1:10-1:25, ultrasonically disperse for 20-40 min, and stir at a low speed of 200-400 r / min to avoid particle collision and agglomeration and maintain the stability of the suspension.

[0039] Liquid-phase atomic layer deposition (L-ALD) cycle: The suspension is heated to 40-80℃ for alternating L-ALD deposition of carbon layers. A single cycle consists of: ① Carbon source adsorption: Injecting a carbon source precursor solution and stirring for 20-40 min to allow organic carbon source molecules to achieve self-confined monolayer adsorption on the ferromagnetic core surface via hydrogen bonds and van der Waals forces; ② Solvent washing: Injecting anhydrous ethanol and stirring for 10-20 min to wash away unadsorbed free carbon source; ③ Crosslinking reaction: Injecting formaldehyde as a reactant and stirring for 25-50 min to allow in-situ crosslinking polymerization of adsorbed carbon source molecules, forming a stable organic carbon monolayer film; ④ Secondary washing: Injecting anhydrous ethanol and washing for 5-15 min to remove unreacted crosslinking agents and small molecule byproducts, completing one deposition cycle. Depending on the target carbon layer thickness (0.5-10 nm), the deposition cycle is repeated 3-30 times to achieve precise layer-by-layer deposition of the carbon precursor layer. The deposited product was centrifuged, washed 3-5 times with anhydrous ethanol, vacuum dried at 60-100 ℃ for 3-5 h, and then calcined at 600-900 ℃ under a nitrogen atmosphere for 2-5 h to carbonize the organic carbon precursor layer into an amorphous / graphitized carbon coating layer while maintaining the density and uniformity of the carbon layer, thus obtaining a carbon-coated ferromagnetic core.

[0040] Preferably, step 4)e is repeated 30 times from steps a to d, and step 5)d is repeated 10 times from steps a to c. At this point, the Ru loading is 12.5 wt%, and the total Zn-Ni loading is 1.2 wt%, resulting in optimal catalyst magnetic field settling performance and catalytic performance. The preferred catalyst, under an applied magnetic field of 0.2–0.3 T, exhibits a settling separation time ≤ 3 min, a single reaction catalyst loss rate < 0.1%, and a cumulative loss rate < 0.5% after 5 cycles.

[0041] Beneficial effects

[0042] The catalyst provided by this invention has the following beneficial effects:

[0043] 1. The ferromagnetic core endows the catalyst with excellent magnetic field settling performance. Under an applied magnetic field (0.2~0.3T), the settling separation time is ≤3min, the catalyst loss rate in a single reaction is <0.1%, and the cumulative loss rate after 5 cycles is <0.5%. High-efficiency recovery is achieved through magnetic field settling, which significantly reduces catalyst loss and production costs, and solves the core problems of difficult separation and high loss rate of traditional catalysts.

[0044] 2. The intermediate coating layer effectively protects the ferromagnetic core from corrosion by the reaction system, while its high specific surface area and suitable pore size structure provide a guarantee for the loading and mass transfer process of Ru active components, thus enhancing the structural stability of the catalyst.

[0045] 3. L-ALD technology achieves atomic-level dispersion of Ru active components with precise particle size control of 3-6 nm, avoiding the problem of active component agglomeration in traditional methods and significantly improving the utilization rate of active sites; at the same time, by precisely controlling the number of deposition cycles, the loading can be precisely controlled, resulting in excellent process repeatability.

[0046] 4. The additive forms a composite active site with interfacial electronic coupling with Ru, which synergistically enhances the selectivity of benzene partial hydrogenation, with the cyclohexene selectivity reaching up to 92%. After 5 cycles, the benzene conversion rate still remains >38%, and the catalytic stability is significantly better than that of traditional catalysts.

[0047] 5. The preparation process is mild, requires no high vacuum equipment, has low equipment investment costs, and the preparation of the coated ferromagnetic metal core substrate and the L-ALD deposition process are easy to scale up. In addition, the magnetic field sedimentation separation operation is simple and energy-efficient, making it suitable for industrial applications. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 This is a schematic diagram of the structure of the catalyst of the present invention;

[0050] Figure 2 This is a transmission electron microscope (TEM) image of the Fe-Ni alloy ferromagnetic core prepared in Example 1 of the present invention;

[0051] Figure 3 TEM image of the Ru-Zn-Ni / Fe-Ni@ZrO2 catalyst prepared in Example 1 of this invention;

[0052] Figure 4 This is a comparison chart of the recycling performance of the catalysts in Example 1 and the comparative example of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Unless otherwise stated, the materials and reagents used in the embodiments and comparative examples of this invention are commercially available products.

[0054] Example 1: Preparation of Ru~Zn~Ni / Fe~Ni@ZrO2 catalyst

[0055] The preparation method includes the following steps:

[0056] 1. Preparation of ferromagnetic core: A co-precipitation method was used. A mixed aqueous solution of 0.2 mol / L FeCl3 and NiCl2 (Fe to Ni molar ratio 1:1) was mixed with 0.5 mol / L NaOH solution at a volume ratio of 1:2. The mixture was stirred at 45°C for 3 h. The precipitate was washed with deionized water until neutral, filtered, and then reduced at 300°C under a hydrogen atmosphere for 4 h to obtain Fe-Ni alloy ferromagnetic core (particle size 7 nm).

[0057] 2. L-ALD apparatus setup: A 500mL dual-pulse reactor is used, integrating a precursor supply system, a washing and purification system, an inert gas purging system, a constant temperature control system, and a matching fluid control and sealing unit to form a closed-loop atomic layer deposition reaction system.

[0058] 3. Preparation of the intermediate coating layer: The liquid phase atomic layer deposition apparatus was started, and the Fe-Ni ferromagnetic core was mixed with a 0.3 mol / L zirconium chloride aqueous solution at a solid-liquid ratio (mass ratio) of 1:15. The mixture was stirred at 55°C for 6 hours, dried at 90°C for 5 hours, and then calcined at 600°C in air for 4 hours to obtain a ZrO2-coated ferromagnetic metal core substrate (ZrO2 layer thickness 8 nm, specific surface area 48 m²). 2 / g);

[0059] 4. Ru active component deposition:

[0060] a. Precursor pulse: The coated ferromagnetic core substrate is added to the reactor, and 200 mL of 0.03 mol / L ruthenium(III) acetylacetone glycol solution is injected. The mixture is stirred and adsorbed at 45 °C for 50 min.

[0061] b. Washing: Drain the solution and wash 5 times with anhydrous ethanol (100 mL each time).

[0062] c. Reduction: Introduce a H2 / N2 mixture with a hydrogen integral of 10%, heat to 300℃, and hold at that temperature for 3.5 hours;

[0063] d. Purging: Purge with nitrogen to room temperature, completing one cycle;

[0064] e. Repeat the cycle: Repeat steps a to d 30 times, with Ru loading of 12.5 wt% (particle size 3.5 nm).

[0065] 5. Additive deposition:

[0066] a. Precursor pulse: 200 mL of a 0.02 mol / L mixed aqueous solution of Zn(Ac)2 and Ni(NO3)2 (Zn to Ni molar ratio 1:0.5) was injected into the Ru-deposited catalyst, and the mixture was stirred at 55 °C for 35 min for adsorption.

[0067] b. Washing and desorption: Drain the solution and wash 5 times with deionized water (100 mL each time).

[0068] c. Precipitating agent pulse: Inject 0.03 mol / L NaOH aqueous solution and stir at 55℃ for 3 h;

[0069] d. Repeat the cycle: Repeat steps a to c 10 times, with a total loading of Zn to Ni of 1.2 wt%;

[0070] 6. Post-treatment: After the catalyst has been deposited, it is washed and dried under vacuum at 110℃ for 5.5h to obtain Ru~Zn~Ni / Fe~Ni@ZrO2 catalyst.

[0071] Performance testing

[0072] Reaction conditions: 100 mL benzene, 200 mL deionized water, 33.2 g zinc sulfate heptahydrate, and 13.6 g of the catalyst prepared in this example were added to a high-pressure reactor. The reactor was stirred at 150 °C and 5 MPa H2 pressure, with a rotation speed of 1500 r / min.

[0073] Single reaction test results: benzene conversion rate 39.8%, cyclohexene selectivity 89.3%, after the reaction was completed, an external magnetic field (0.2-0.3T) was applied, the catalyst sedimentation separation time was 2 min, and the loss rate was 0.08%.

[0074] Cyclic performance test: After repeating the above reaction conditions for 5 cycles, the benzene conversion rate was 38.2%, the cyclohexene selectivity was 88.7%, and the cumulative loss rate was 0.4%.

[0075] Example 2: Preparation of Ru-Fe / Co@C catalyst

[0076] 1. Preparation of ferromagnetic cores: A hydrothermal method was used to mix 0.15 mol / L CoCl2 aqueous solution with ethylenediamine at a volume ratio of 1:1, transfer the mixture to a hydrothermal reactor, and react at 160℃ for 8 h. After washing and drying, the product was reduced at 400℃ under a hydrogen atmosphere for 4 h to obtain Co ferromagnetic cores (particle size 15 nm).

[0077] 2. L-ALD device setup: Same as in Example 1;

[0078] 3. Preparation of the intermediate coating layer: The liquid phase atomic layer deposition apparatus was started, and the Co ferromagnetic core was mixed with a 1 mol / L glucose aqueous solution at a solid-liquid ratio (mass ratio) of 1:12. The mixture was hydrothermally carbonized at 100℃ for 12 h, followed by calcination at 700℃ under a nitrogen atmosphere for 3 h, yielding a carbon-coated ferromagnetic metal core support (carbon layer thickness 10 nm, specific surface area 180 m²). 2 / g, pore size 35nm);

[0079] 4. Ru active component deposition: Repeat steps 4a to d of Example 1 for 23 cycles, with a Ru loading of 11.2 wt% (particle size 4.2 nm).

[0080] 5. Additive deposition:

[0081] a. Precursor pulse: 200 mL of 0.02 mol / L Fe(NO3)3 aqueous solution was injected into the Ru-deposited catalyst, and the mixture was stirred and adsorbed at 55 °C for 35 min;

[0082] b. Washing and desorption: Wash 5 times with deionized water (100 mL each time);

[0083] c. Precipitating agent pulse: Inject 0.03 mol / L NaOH aqueous solution and stir at 55℃ for 3 h;

[0084] d. Repeat the cycle: Repeat steps a to c 13 times, with an Fe loading of 1.8 wt%;

[0085] 6. Post-processing: Same as in Example 1, to obtain Ru~Fe / Co@C catalyst.

[0086] Performance testing

[0087] The reaction conditions were the same as in Example 1. The test results were as follows: the benzene conversion rate was 37.5% and the cyclohexene selectivity was 91.2% in a single reaction. With an external magnetic field applied (0.2-0.3T), the catalyst sedimentation and separation time was 1.5 min and the loss rate was 0.06%. After 5 cycles, the benzene conversion rate was 36.1% and the cyclohexene selectivity was 90.5%, with a cumulative loss rate of 0.3%.

[0088] Example 3: Effect of different ferromagnetic core materials on catalyst performance

[0089] Referring to Example 1, and under the same conditions, Ru~Zn~Ni / Fe@ZrO2 and Ru~Zn~Ni / Ni@ZrO2 catalysts with Fe and Ni as ferromagnetic cores, respectively, were prepared. Performance tests were conducted according to the method in Example 1, and the results are shown in the table below:

[0090]

[0091] Comparative Example: Preparation of Ru-Zn-Ni / ZrO2 Catalysts (without Ferromagnetic Core) by Traditional Impregnation Method

[0092] Take 10g of ZrO2 support and add 200mL of a mixed aqueous solution containing 12.5wt% Ru (ruthenium(III) acetylacetone·3H2O) and 1.2wt% Zn~Ni (Zn(Ac)2·2H2O and Ni(NO3)2·6H2O, molar ratio 1:0.5). Impregnate at room temperature for 24h; evaporate and dry at 80℃, calcine in air at 550℃ for 4h, and reduce with pure H2 at 350℃ for 3h to obtain a non-magnetic catalyst.

[0093] Performance testing

[0094] The reaction conditions were the same as in Example 1. The test results were as follows: the benzene conversion rate was 59.1% and the cyclohexene selectivity was 74.5% in a single reaction; the catalyst loss rate was 3.8% after centrifugation (8000 r / min, 10 min); after 5 cycles, the benzene conversion rate was 30.2%, the cyclohexene selectivity was 68.7%, and the cumulative loss rate was 15.4%.

[0095] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a magnetically separable catalyst for the hydrogenation of benzene to cyclohexene, characterized in that, The catalyst consists of a ferromagnetic core, an intermediate coating layer, a Ru active component, and an additive. The ferromagnetic core is selected from one or more of the transition metals iron, cobalt, nickel, and their alloys. The intermediate coating layer is ZrO2 or a carbon material. The additive is selected from one or more of Zn, Fe, Co, and Ni. The preparation method includes the following steps: 1) Preparation of ferromagnetic cores: The cores are prepared by co-precipitation or hydrothermal methods. The co-precipitation method involves mixing a transition metal salt solution with an alkaline solution at a molar ratio of 1:1.5 to 1:3 and stirring at 30 to 60°C for 2 to 4 hours to generate a hydroxide precipitate. After washing and filtration, the precipitate is reduced at 200 to 400°C under a hydrogen atmosphere for 2 to 5 hours. The hydrothermal method involves mixing a transition metal salt solution with an organic amine complexing agent at a volume ratio of 1:0.5 to 1:2 and reacting hydrothermally at 120 to 200°C for 6 to 12 hours. After washing and drying, the product is reduced at 300 to 500°C under a hydrogen atmosphere for 3 to 6 hours. 2) Construction of liquid phase atomic layer deposition apparatus: The double-pulse reactor is used as the core reaction unit, integrating a precursor supply system, a washing and purification system, an inert gas purging system, a constant temperature control system, and a supporting fluid control and sealing unit to form a closed-loop atomic layer deposition reaction system. 3) Preparation of intermediate coating layer: Start the liquid phase atomic layer deposition device to perform ZrO2 coating or carbon coating on the ferromagnetic core. ZrO2 coating is performed by mixing the ferromagnetic core with a 0.05-0.5 mol / L zirconium source aqueous solution at a solid-liquid ratio of 1:10-1:25, stirring at 40-70℃ for 4-8 h, drying at 80-120℃ for 4-6 h, and then calcining in air at 500-700℃ for 3-6 h. Carbon coating is performed by mixing the ferromagnetic core with a 0.5-2 mol / L carbon source solution at a solid-liquid ratio of 1:8-1:20, hydrothermally carbonizing at 80-160℃ for 8-24 h, and then calcining in nitrogen at 600-900℃ for 2-5 h. 4) Deposition of Ru active components: The ferromagnetic core substrate to be coated is added to the reactor, Ru precursor solution is injected, and the mixture is stirred and adsorbed at 35-55℃ for 35-65 min. It is washed 4-6 times with anhydrous ethanol, and a mixed gas of H2 / N2 with a hydrogen integral of 5-20% is introduced. The mixture is reduced at 200-450℃ for 2.5-4.5 h, and then purged with nitrogen to room temperature. This cycle is repeated 20-50 times. 5) Additive deposition: Inject a 0.012-0.028 mol / L additive precursor solution into the Ru-deposited catalyst, stir and adsorb at 45-65℃ for 25-45 min, wash with deionized water 4-6 times, inject a 0.02-0.04 mol / L NaOH aqueous solution, stir at 45-65℃ for 2.5-3.5 h, and repeat this cycle 5-30 times; 6) Post-treatment: After the catalyst has been deposited, it is washed and then vacuum dried at 80-125℃ for 4.5-6.5h to obtain a magnetically separable catalyst.

2. The method for preparing the magnetically separable benzene fraction hydrogenation catalyst to cyclohexene according to claim 1, characterized in that, The ferromagnetic core has a particle size of 4–50 nm.

3. The method for preparing the magnetically separable benzene fraction hydrogenation catalyst to cyclohexene according to claim 1, characterized in that, The thickness of the intermediate coating layer is 4–30 nm; wherein the ZrO2 coating layer is a monoclinic or tetragonal phase with a specific surface area of ​​10–120 m². 2 / g, pore size 15–40 nm; carbon coating layer is amorphous carbon or graphitized carbon, specific surface area 50–300 m² / g. 2 / g, pore size 20~50nm.

4. The method for preparing the magnetically separable benzene fraction hydrogenation catalyst to cyclohexene according to claim 1, characterized in that, The Ru active component has a particle size of 3-6 nm and a loading of 5-20 wt%.

5. The method for preparing the magnetically separable benzene fraction hydrogenation catalyst to cyclohexene according to claim 1, characterized in that, The additive is a Zn and Ni compound with a mass ratio of 1:0.3 to 0.8 and a loading of 0.1 to 5 wt%, forming a composite active site with Ru through interfacial electronic coupling.

6. The method for preparing the magnetically separable benzene fraction hydrogenation catalyst to cyclohexene according to claim 1, characterized in that, The Ru precursor solution in step 4) is a 0.015–0.045 mol / L ruthenium(III) acetylacetone ethylene glycol solution.

7. The method for preparing the magnetically separable benzene fraction hydrogenation catalyst to cyclohexene according to claim 1, characterized in that, The precursor solution of the auxiliary agent in step 5) is a mixed aqueous solution of Zn(Ac)2 and Ni(NO3)2 with a concentration of 0.012 to 0.028 mol / L, and the mass ratio of Zn to Ni is 1:0.3 to 0.

8.

8. The method for preparing the magnetically separable benzene fraction hydrogenation catalyst to cyclohexene according to claim 1, characterized in that, In step 3), the zirconium source for ZrO2 coating is selected from zirconium chloride and zirconium nitrate; the carbon source for carbon coating is selected from glucose, sucrose, fructose, and phenolic resin.

9. The method for preparing the magnetically separable benzene fraction hydrogenation catalyst to cyclohexene according to claim 1, characterized in that, The deposition cycle in step 4) is repeated 30 times, and the deposition cycle in step 5) is repeated 10 times. At this time, the Ru loading is 12.5 wt% and the total Zn-Ni loading is 1.2 wt%.

10. The method for preparing the magnetically separable benzene moiety hydrogenation catalyst to cyclohexene according to claim 1, characterized in that, The catalyst, under an external magnetic field of 0.2–0.3T, has a sedimentation separation time of ≤3 min, a single reaction catalyst loss rate of <0.1%, and a cumulative loss rate of <0.5% after 5 cycles.

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