A magnetic carrier catalyst, its preparation method and application thereof

Abstract

The application discloses a magnetic carrier catalyst, a preparation method and application thereof. The magnetic carrier catalyst comprises a magnetic core, a dense PDA coating layer coated on the magnetic core, and an active component supported on the dense PDA coating layer; and the dense PDA coating layer is formed by coating and densification treatment of polydopamine (PDA). The application prepares a dense coating layer on the surface of the magnetic core. Compared with a traditional porous structure and a porous carrier, when the active component is supported, the active component is not wrapped into the inside of the channel, but is only supported on the surface, so that the loading amount of the noble metal catalyst is reduced by several times or orders of magnitude, the catalyst still has high activity even when the loading amount of the active component is very low, and the hydrogenation degree can reach more than 90%. Because the active component is several to tens of nanometers in size and structure, the hydrogenation activity is high, and the catalyst can be fully recovered by magnetic force, so that the use cost of the catalyst is low.

Description

Technical Field

[0001] This invention relates to the field of industrial catalysis technology, specifically to a magnetically supported catalyst, its preparation method, and its application. Background Technology

[0002] Synthetic rubber, plastics, and chemical fibers are the three traditional synthetic materials in the petrochemical industry and are crucial pillar materials in modern industrial production. Nitrile rubber (NBR) is a copolymer of butadiene and acrylonitrile. With its excellent airtightness, water resistance, oil resistance, temperature resistance, and abrasion resistance, it is widely used in the automotive, aerospace, marine, and oil extraction industries. The polymer chain structure of NBR contains C=C and C≡N bonds. The presence of C≡N gives the rubber excellent properties such as oil resistance, high tensile strength, and high modulus, while the presence of C=C double bonds can lead to potential problems in aging resistance and chemical corrosion resistance.

[0003] To improve the performance and application range of nitrile rubber, hydrogenation is often used to eliminate C=C double bonds. However, removing the precious metal catalyst after hydrogenation and purifying the hydrogenated product requires a combination of one or more methods such as centrifugation, filtration, and extraction. The process is quite cumbersome and it is difficult to remove the catalyst completely. How to achieve this goal efficiently has always been one of the hot topics in this technology research.

[0004] CN101703936A discloses a magnetically supported catalyst on which magnetic supports and active components are loaded onto a long-chain organic polymer and its preparation method. From the preparation process, it can be seen that a large amount of active components are encapsulated inside the polymer, resulting in the loss of active components and increasing the cost of the catalyst.

[0005] CN112023939A discloses a magnetic core-shell hydrogenation catalyst and method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, wherein the catalyst is represented as Fe3O4@S / M; wherein Fe3O4 is the core layer, S is the shell support, and M is the main active metal and / or auxiliary metal supported on the shell support; the active metal is one or more of Ru, Ni, Ir, Pd, and Pt, and the loading is 1-50 wt% of the catalyst; the auxiliary metal is one or more of Cu, Fe, Co, Zn, and Sn, and the molar ratio of the auxiliary metal to the main active metal is 0.1-10:1. The catalyst prepared by this method has a porous structure and a large loading of active components. However, in a high-viscosity system like nitrile rubber with a large molecular weight, the active components entering the pores are quickly blocked by the nitrile rubber and cannot function.

[0006] CN104785301A discloses a magnetically supported palladium composite catalyst, its preparation method, and its uses. The magnetic palladium composite catalyst uses superparamagnetic Fe3O4@SiO2 microspheres as a support, and the surface is covalently modified with loaded amino Pd(II) particles. The process involves sequentially preparing Fe3O4 nanoparticles, core-shell structured magnetic nanospheres Fe3O4@SiO2, Fe3O4@SiO2@APTES, and finally loading Pd(II) particles to obtain the Fe3O4@SiO2@APTES@Pd catalyst. The final catalyst has a porous surface structure.

[0007] KR102436881B1 discloses a magnetically supported Fe3O4 / PDA / Pd catalyst for Suzuki-Miyaura coupling, Sonogashira coupling, and Heck coupling reactions, and its preparation method. The preparation method includes the following steps: preparing a hydrophobic compound, polydopamine (PDA), for introducing hydrophobic alkyl groups; preparing a magnetic base support; reacting the hydrophobic compound with the base support; introducing hydrophobic alkyl groups onto the base support; and loading metal nanoparticles onto the base support containing the introduced hydrophobic alkyl groups. Summary of the Invention

[0008] One object of the present invention is to provide a magnetically supported catalyst and a method for preparing the same, specifically a magnetically supported catalyst with a magnetic core@PDA@active hydrogenation component that can be used in the hydrogenation process of unsaturated polymer latex, liquid, or viscous solution.

[0009] Another object of the present invention is to provide the application of the magnetically supported catalyst in the hydrogenation process of polymers containing unsaturated olefin double bonds, especially in the hydrogenation of nitrile rubber.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] The present invention provides a magnetically supported catalyst, particularly a magnetically supported catalyst for hydrogenation of nitrile rubber; the magnetically supported catalyst includes a magnetic core, a dense PDA coating layer coated on the magnetic core, and an active component supported on the dense PDA coating layer;

[0012] The dense PDA coating layer is formed by coating and densifying polydopamine (PDA);

[0013] The active component is selected from at least one of Pd, Rh, Ru, Ni, and Mo.

[0014] In some preferred embodiments of the present invention, the densification treatment is a heat treatment at 180–500°C under a protective gas atmosphere. The protective gas used in the present invention can be nitrogen or an inert gas, such as argon.

[0015] This invention employs polydopamine (PDA) to coat the magnetic core. Due to PDA's excellent adhesiveness, it can firmly bind to almost all inorganic and organic substances. The adhesion mechanism can be explained in two ways: first, PDA contains thiol and amino groups that readily form covalent bonds, thus easily forming covalent bonds with other molecules; second, PDA contains thiol and amino groups that readily form ion coordination and chelation. Therefore, selecting PDA as the coating material for the magnetic core reliably integrates the magnetic core with the active component into a unified whole. After surface densification treatment, this facilitates separation from the reaction system after hydrogenation. Furthermore, the number of PDA coating layers can be controlled according to the required catalyst particle size and bulk density, coating at least one or more layers to form a dense surface, ultimately resulting in a final catalyst morphology with controllable particle size, bulk density, and specific surface area.

[0016] The coating method for polydopamine (PDA) can employ common methods such as dopamine hydrochloride hydrolysis and layered assembly, with dopamine hydrochloride hydrolysis being the preferred method.

[0017] In some preferred embodiments of the present invention, the magnetically supported catalyst has a particle size of 70 nm to 600 nm and a specific surface area of ​​45 m². 2 / g~91m 2 / g, bulk density is 0.6g / cm³ 3 ~1.25g / cm 3 .

[0018] In some preferred embodiments of the present invention, the particle size of the magnetically supported catalyst is 70 nm to 300 nm, more preferably 80 nm to 250 nm.

[0019] In some preferred embodiments of the present invention, the specific surface area of ​​the magnetically supported catalyst is 50 m². 2 / g~90m 2 / g, more preferably 60m 2 / g~80m 2 / g.

[0020] In some preferred embodiments of the present invention, the packing density of the magnetically supported catalyst is 0.7 g / cm³. 3 ~1.0g / cm 3 .

[0021] In some preferred embodiments of the present invention, the active component is selected from at least one of Pd, Rh, and Ru.

[0022] In some preferred embodiments of the present invention, the active component is more preferably Pd element.

[0023] In some preferred embodiments of the present invention, the loading of the active component accounts for 0.01 wt% to 6 wt% of the catalyst.

[0024] In some preferred embodiments of the present invention, the loading of the active component accounts for 0.02 wt% to 1 wt% of the catalyst.

[0025] In some preferred embodiments of the present invention, the loading of the active component accounts for 0.05 wt% to 0.5 wt% of the catalyst.

[0026] In some preferred embodiments of the present invention, the active component is loaded by impregnation or in-situ synthesis. The in-situ synthesis method includes different preparation methods such as titration and in-situ reduction. The present invention does not impose any particular limitation. Any preparation method that can ultimately form active sites of several nanometers to tens of nanometers on the surface of the dense coating layer can be adopted. Titration and in-situ reduction are preferred.

[0027] In some preferred embodiments of the present invention, the magnetic core is selected from at least one of magnetic nanopowders with ferromagnetism, such as at least one of Fe3O4, Fe3S4 and FeNi; the magnetic core can be commercially available or prepared in the laboratory.

[0028] In some preferred embodiments of the present invention, the particle size of the magnetic core is 50 nm to 500 nm.

[0029] In some preferred embodiments of the present invention, the magnetic core is selected from Fe3O4 magnetic nanopowder with a particle size of 50nm to 300nm.

[0030] In some preferred embodiments of the present invention, the magnetic core is selected from Fe3O4 magnetic nanopowder with a particle size of 50nm to 150nm.

[0031] Another aspect of the present invention provides a method for preparing the above-described magnetically supported catalyst, wherein the preparation method includes the following steps:

[0032] The coating of the magnetic core with polydopamine (PDA) was completed by the hydrolysis reaction of dopamine hydrochloride, resulting in magnetic microspheres coated with polydopamine (PDA), namely magnetic core@PDA.

[0033] Magnetic microspheres coated with polydopamine (PDA) are heat-treated at 180–500°C for 1–4 hours in a protective atmosphere to form the dense PDA coating layer; when the catalyst particle size and density cannot meet the hydrogenation requirements, the coating is repeated multiple times to form multiple layers of the dense PDA coating layer.

[0034] By supporting the active component, the magnetically supported catalyst, namely magnetic core@PDA@active component, is obtained.

[0035] The thickness of the dense coating layer outside the magnetic core in this invention can be controlled by adjusting the thickness and number of times the polydopamine (PDA) coating is applied. If the final particle size and packing density are not satisfactory, the polydopamine (PDA) coating process can be repeated one or more times for adjustment until a satisfactory result is achieved, ultimately forming a structure with a dense specific surface area and suitable particle size.

[0036] Since the magnetically supported catalyst of this invention targets a high-viscosity rubber system, the purpose of coating the magnetic core is not to prepare a porous system, but to form a dense surface structure by coating polydopamine (PDA) and densifying it. This surface densification reduces the loading of the active component while maintaining hydrogenation activity in the high-viscosity system; it also reduces the adhesion between the catalyst surface and the high-viscosity system, facilitating catalyst separation and recovery. Furthermore, for high-viscosity systems with varying viscosities, the particle size, bulk density, and specific surface area of ​​the final catalyst can be adaptively adjusted by controlling the number of PDA coating layers, facilitating magnetic separation and reuse of the catalyst (for high-viscosity systems, excessively small catalyst particle size makes separation difficult).

[0037] In some preferred embodiments of the present invention, the coating process of the magnetic core includes:

[0038] The magnetic nucleus was added to a buffer solution, followed by the addition of dopamine hydrochloride. The mixture was stirred at 12–35°C for 4–12 hours. After the reaction was completed, the precipitate was separated and recovered using a magnet. The precipitate was then washed and dried to obtain the magnetic nucleus@PDA.

[0039] In some preferred embodiments of the present invention, the drying can be performed by freeze drying, oven drying, or other methods, wherein the drying temperature does not exceed 60°C. The washing is performed sequentially using water and ethanol. The buffer solution is preferably a Tris buffer solution, more preferably a Tris buffer solution with a pH of 8-9.

[0040] In some preferred embodiments of the invention, the dopamine hydrochloride is added in excess, and the mass ratio of the magnetic core to dopamine hydrochloride is 1:(0.5-6.0). The coating thickness of the PDA layer can be controlled by adjusting the amount of dopamine hydrochloride and buffer solution, as well as the hydrolysis time.

[0041] In some preferred embodiments of the present invention, the loading process of the active component includes:

[0042] The magnetic core coated with a dense PDA layer is dispersed in a solvent, and the precursor of the active component is added to react. After the reaction is completed, the solid is separated and recovered by a magnet, washed and dried, and the resulting solid powder is the magnetically supported catalyst, namely magnetic core@PDA@active component.

[0043] The precursor of the active component is generally added in excess. In some preferred embodiments of the present invention, the mass ratio of the magnetic core coated with a dense PDA coating to the precursor of the active component is 1:(0.02 to 1.03).

[0044] In some preferred embodiments of the present invention, the precursor of the active component is selected from at least one of noble metal elements such as palladium, rhodium, and ruthenium, and acetates, halides, and ammonium salts of nickel and molybdenum. Except for rhodium and ruthenium-based noble metals, the catalysts prepared by the present invention should be activated by hydrogen reduction at 200–400°C before use.

[0045] In some preferred embodiments of the present invention, the solvent used in the loading process of the active component is water.

[0046] The magnetic nuclei of this invention can be commercially available or prepared in a laboratory; the particle size can be between 50 and 500 nm, and the closer the shape is to spherical, the better, which is related to the evaluation device and method used in this invention. In this embodiment, a slurry bed evaluation device is used. The final particle size of the catalyst cannot be too large because the magnetic nucleus density is relatively high, for example, Fe3O4 reaches 5.18 g / cm³. 3 If the particle size is too large, it will settle and cannot be well dispersed in the colloidal solution. Therefore, the sedimentation problem of the catalyst can be solved by controlling the appropriate coating thickness and ultimately by controlling the particle size of the catalyst.

[0047] For example, Fe3O4 magnetic microspheres can be prepared as magnetic cores using a solvothermal method. Specifically, they can be prepared by thermal reaction of iron salts and reducing agents. Organic sodium salts, polyethylene glycol, and caustic sodas can also be added during the preparation process.

[0048] Specifically, the preparation methods of Fe3O4 magnetic microspheres include:

[0049] The reducing agent, iron salt, organic sodium salt, polyethylene glycol, and caustic alkali are added to the reactor in a mass ratio and mixed evenly at 10–45°C to prepare the initial reaction mixture. The mixture is then added to the reaction vessel and heated at 80–220°C for 12–24 hours to obtain a mixture of Fe3O4 magnetic microspheres and reaction solvent. The mixture is cooled to 12–35°C, then separated and recovered using a magnet, washed, freeze-dried, and stored for later use.

[0050] The reducing agent can be an organic alcohol, preferably ethylene glycol and / or propylene glycol. The iron salt can be ferric chloride and / or ferrous chloride. The organic sodium salt can be at least one of sodium acetate, sodium stearate, and sodium benzoate. The polyethylene glycol can be a commercially available product, such as polyethylene glycol 6000; this invention does not specifically limit the type of polyethylene glycol. The caustic alkali can be at least one of sodium hydroxide, potassium hydroxide, and ammonia.

[0051] The preferred mass ratio of the reducing agent, iron salt, organic sodium salt, polyethylene glycol, and caustic alkali is (5-20):1:(1-5):(4-10):(0.1-0.5), more preferably (6-18):1:(2-4):(3-9):(0.15-0.45).

[0052] The particle size of the prepared Fe3O4 magnetic microspheres can be controlled by adjusting the material ratio, reaction time, and reaction temperature.

[0053] In another aspect, the present invention provides the application of any one of the above magnetically supported catalysts in the hydrogenation process of polymers containing unsaturated olefin double bonds, especially the hydrogenation of nitrile rubber.

[0054] The magnetically supported catalyst of this invention can meet the different requirements of NBR rubber, SBR rubber and other latex systems for catalyst systems. By utilizing different formulations and catalyst particle sizes, it can achieve highly selective hydrogenation of unsaturated double bonds, while also enabling efficient separation and reuse of the catalyst through an external magnetic field. It is a convenient method for using magnetically supported noble metal catalysts to hydrogenate NBR to prepare HNBR and to perform hydrogenation saturation treatment of different latexes.

[0055] In some preferred embodiments of the present invention, the organic solvent in the hydrogenation process is selected from at least one of ethers, chlorinated aromatics and ketones; more preferably, it is one of the ketones, such as acetone or butanone; the weight ratio of nitrile rubber to magnetic catalyst is (1-2):1, and even more preferably (1-1.5):1.

[0056] In some preferred embodiments of the present invention, hydrogenation is carried out in a stirred tank or a slurry tank, preferably in a stirred tank; the hydrogenation temperature is 70–120°C, preferably 70–110°C, more preferably 70–100°C; the hydrogen pressure is 2–16 MPa, preferably 2–10 MPa, more preferably 4–8 MPa; the reaction time is 2–10 hours, more preferably 4–8 hours. The reaction is carried out under stirring conditions, with a stirring speed preferably 180–600 rpm, more preferably 200–450 rpm; after the reaction, the original NBR can be converted into HNBR with a hydrogenation degree greater than 95%.

[0057] The magnetically supported catalyst of this invention can be recovered and separated after use by applying an external electromagnetic field or a permanent magnetic field, preferably using a permanent magnet. The catalyst recovery efficiency is not less than 98%, and the recovered catalyst can be reused after solvent washing.

[0058] The magnetically supported catalyst of this invention can achieve highly selective hydrogenation of double bonds in olefins such as nitrile rubber, latex, or emulsion, while having low catalyst cost, low active component content in HNBR, and long service life. It can also efficiently separate the catalyst by an external magnetic field, with high separation efficiency and simple operation. It is a convenient method for preparing HNBR by hydrogenation of NBR using magnetically supported noble metal catalysts.

[0059] The beneficial effects of this invention include:

[0060] 1) The method for preparing magnetically supported catalysts in this invention is simple and the preparation cost is low; the active component loading of the prepared magnetically supported catalyst is low, which can greatly reduce the cost of catalyst use. The catalyst prepared by this invention has a dense surface structure. Since the catalyst bulk phase is not a conventional porous structure, i.e., the bulk phase has no channels, the catalyst efficiency is high; however, since the catalyst particle size is at the nanoscale, the hydrogenation effect is close to that of homogeneous catalysts, and the hydrogenation effect can be guaranteed.

[0061] 2) Using the magnetically supported catalyst of the present invention in the hydrogenation of NBR to prepare HNBR can improve the separation efficiency of the catalyst, extend the service life of the catalyst, and improve the final performance of HNBR products.

[0062] Compared to existing homogeneous methods, this invention eliminates the need for complex separation processes such as extraction or ion exchange of the catalyst after hydrogenation. Compared to existing heterogeneous methods, this invention eliminates the need for time-consuming catalyst centrifugation and sedimentation processes, enabling magnetic recovery of the catalyst. Furthermore, the recovered catalyst, after washing to remove surface-adhered HNBR gum, can be reused, resulting in a long catalyst lifespan. Therefore, this invention offers advantages in terms of catalyst usage cost, separation efficiency, and significantly reduced final catalyst residue in HNBR processes. Detailed Implementation

[0063] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0064] The key to this invention lies in densifying the magnetic core coating layer, making its surface distinct from conventional porous structures and channels. When the active hydrogenation component is supported on this dense coating layer, it is prevented from being trapped inside the channels; instead, the active component is supported only on the surface. This significantly reduces the loading of the noble metal catalyst, maintaining high activity even at very low loading levels, with a hydrogenation degree exceeding 90%. Because the active component has a structure at the nanometer to tens of nanometer scale, it exhibits high hydrogenation activity and can be completely magnetically recovered, resulting in low catalyst usage costs. Furthermore, the magnetic catalyst of this invention can be controlled by adjusting the number of dense PDA layers to achieve a final morphology with a dense surface and controllable particle size and specific surface area. The magnetically supported catalyst prepared by this invention not only exhibits high hydrogenation activity for nitrile rubber, making it suitable for the harsh hydrogenation environment of nitrile rubber, but also, due to its superparamagnetic nature, allows for efficient recovery and reuse using an external magnetic field, reducing hydrogenation costs.

[0065] The magnetically supported catalyst of the present invention comprises a magnetic core, a dense PDA coating layer coated on the magnetic core, and an active component supported on the dense PDA coating layer;

[0066] The dense PDA coating layer is formed by coating and densifying polydopamine (PDA);

[0067] The active component is selected from at least one or more elements among the noble metals Pd, Rh, and Ru, and elements with high hydrogenation activity such as Ni and Mo, preferably at least one of the noble metals palladium and Ni and Mo with high hydrogenation activity.

[0068] The densification treatment is a heat treatment at 180–500°C, preferably 220–380°C, under a protective gas atmosphere. The protective gas used in this invention can be nitrogen or other inert gases, such as argon.

[0069] The magnetically supported catalyst was prepared through the following steps:

[0070] The coating of the magnetic core with polydopamine (PDA) was completed by the hydrolysis reaction of dopamine hydrochloride, resulting in magnetic microspheres coated with polydopamine (PDA), namely magnetic core@PDA.

[0071] Magnetic microspheres coated with polydopamine (PDA) are heat-treated at 180–500°C for 1–4 hours in a protective atmosphere to form the dense PDA coating layer; when the catalyst particle size and density cannot meet the hydrogenation requirements, the coating is repeated multiple times to form multiple layers of the dense PDA coating layer.

[0072] By supporting the active component, the magnetically supported catalyst, namely magnetic core@PDA@active component, is obtained.

[0073] The magnetically supported catalyst prepared by this invention has a particle size of 70 nm to 600 nm, preferably 70 nm to 300 nm, and more preferably 80 nm to 250 nm; its specific surface area is 45 m². 2 / g~91m 2 / g, preferably 50m 2 / g~90m 2 / g, more preferably 60m 2 / g~80m 2 / g; bulk density is 0.6g / cm³ 3 ~1.25g / cm 3 0.7g / cm 3 ~1.0g / cm 3 The active component is supported on the catalyst at a rate of 0.01 wt% to 6 wt%, preferably 0.02 wt% to 1 wt%, and more preferably 0.05 wt% to 0.5 wt%.

[0074] The magnetic core is compositely coated with at least one or more dense PDA layers to form a final morphology with a dense surface and controllable catalyst particle size and specific surface area. The final support surface is dense rather than a traditional porous form, with a specific surface area of ​​45 m². 2 / g~91m 2 / g, far lower than the 80m² of conventional porous surfaces. 2 / g~600m 2 / g; bulk density is 0.6g / cm³ 3 ~1.25g / cm 3 It is far higher than the 0.4 g / cm³ of traditional conventional catalysts. 3 ~0.6g / cm 3 The active component loading ranges from 0.01 wt% to 6 wt% of the catalyst, which is significantly wider than the 1 wt% to 5 wt% loading of conventional catalysts. This allows for flexible adjustment of the catalyst concentration in different concentrations of colloidal solutions, depending on actual needs. Furthermore, due to the nanoscale particle size, the hydrogenation effect is close to that of homogeneous catalysts. Since the active component can be completely recovered, the catalyst cost is low while maintaining the same hydrogenation activity.

[0075] The active component is loaded using either impregnation or in-situ synthesis. The in-situ synthesis method includes different preparation methods such as titration and in-situ reduction. This invention does not impose any particular limitation on these methods. Any preparation method that can ultimately form active sites of several to tens of nanometers on the surface of the dense coating layer is acceptable. Titration and in-situ reduction are preferred.

[0076] The magnetic core is selected from at least one of ferromagnetic magnetic nanopowders, such as at least one selected from Fe3O4, Fe3S4, and FeNi; the magnetic core can be commercially available or prepared in the laboratory. The particle size of the magnetic core should be between 50 nm and 500 nm. Preferably, the magnetic core is a low-cost, commercially available or laboratory-synthesized Fe3O4 magnetic nanopowder with a particle size of 50 nm to 300 nm, more preferably a Fe3O4 magnetic nanopowder with a particle size of 50 nm to 150 nm.

[0077] The magnetic nuclei of this invention can be commercially available or prepared in a laboratory; the particle size can be between 50 and 500 nm, and the closer the shape is to spherical, the better, which is related to the evaluation device and method used in this invention. In this embodiment, a slurry bed evaluation device is used. The final particle size of the catalyst cannot be too large because the magnetic nucleus density is relatively high, for example, Fe3O4 reaches 5.18 g / cm³. 3 If the particle size is too large, it will settle and cannot be well dispersed in the colloidal solution. Therefore, the sedimentation problem of the catalyst can be solved by controlling the appropriate coating thickness and ultimately by controlling the particle size of the catalyst.

[0078] For example, Fe3O4 magnetic microspheres can be prepared as magnetic cores using a solvothermal method. Specifically, they can be prepared by thermal reaction of iron salts and reducing agents. Organic sodium salts, polyethylene glycol, and caustic sodas can also be added during the preparation process.

[0079] Specifically, the preparation methods of Fe3O4 magnetic microspheres include:

[0080] The reducing agent, iron salt, organic sodium salt, polyethylene glycol, and caustic alkali are added to the reactor in a mass ratio and mixed evenly at 10–45°C to prepare the initial reaction mixture. The mixture is then added to the reaction vessel and heated at 80–220°C for 12–24 hours to obtain a mixture of Fe3O4 magnetic microspheres and reaction solvent. The mixture is cooled to 12–35°C, then separated and recovered using a magnet, washed, freeze-dried, and stored for later use.

[0081] The reducing agent can be an organic alcohol, preferably ethylene glycol and / or propylene glycol. The iron salt can be ferric chloride and / or ferrous chloride. The organic sodium salt can be at least one of sodium acetate, sodium stearate, and sodium benzoate. The polyethylene glycol can be a commercially available product, such as polyethylene glycol 6000; this invention does not specifically limit the type of polyethylene glycol. The caustic alkali can be at least one of sodium hydroxide, potassium hydroxide, and ammonia.

[0082] The preferred mass ratio of the reducing agent, iron salt, organic sodium salt, polyethylene glycol, and caustic alkali is (5-20):1:(1-5):(4-10):(0.1-0.5), more preferably (6-18):1:(2-4):(3-9):(0.15-0.45).

[0083] The particle size of the prepared Fe3O4 magnetic microspheres can be controlled by adjusting the material ratio, reaction time, and reaction temperature.

[0084] In some specific embodiments of the present invention, the coating process of the magnetic core includes:

[0085] The magnetic core was added to a buffer solution, followed by dopamine hydrochloride, and stirred at 12–35°C for 4–12 hours. After the reaction was complete, the precipitate was separated and recovered using a magnet, washed, and dried to obtain the magnetic core@PDA. The magnetic core@PDA was then densified.

[0086] The drying process can be performed using methods such as freeze drying or oven drying, wherein the drying temperature does not exceed 60°C. The washing process involves sequentially adding water and ethanol. A general excess of dopamine hydrochloride is typically used, preferably with a mass ratio of the magnetic core to dopamine hydrochloride of 1:(0.5–6.0). The coating thickness of the PDA layer can be controlled by adjusting the amounts of dopamine hydrochloride and the buffer solution, as well as the coating time. The buffer solution is preferably a Tris (tris(hydroxymethyl)aminomethane) buffer solution, more preferably a Tris buffer solution with a pH of 8–9, such as a Tris buffer solution with a pH of approximately 8.5.

[0087] The thickness of the dense coating layer outside the magnetic core in this invention can also be controlled by adjusting the thickness and number of times the polydopamine (PDA) coating is applied. If the final particle size and packing density are not satisfactory, the polydopamine (PDA) coating process can be repeated one or more times for adjustment until a satisfactory effect is achieved, ultimately forming a structure with a dense specific surface area and suitable particle size.

[0088] Since the magnetically supported catalyst of this invention targets a high-viscosity rubber system, the purpose of coating the magnetic core is not to prepare a porous system, but to form a dense surface structure by coating polydopamine (PDA) and densifying it. This surface densification reduces the loading of the active component while maintaining hydrogenation activity in the high-viscosity system; it also reduces the adhesion between the catalyst surface and the high-viscosity system, facilitating catalyst separation and recovery. Furthermore, for high-viscosity systems with varying viscosities, the particle size, bulk density, and specific surface area of ​​the final catalyst can be adaptively adjusted by controlling the number of PDA coating layers, facilitating magnetic separation and reuse of the catalyst (for high-viscosity systems, excessively small catalyst particle size makes separation difficult).

[0089] In some preferred embodiments of the present invention, the coating process of the magnetic core includes:

[0090] Tris was added to deionized water to prepare a Tris buffer solution with pH = 8.5. Fe3O4 was then added and dispersed evenly. Dopamine hydrochloride was then added to form a mixed solution, and the mixture was stirred at room temperature for 4–12 hours. After the reaction was completed, the solution and solid were separated using a magnet. The resulting black solid was washed successively with deionized water and ethanol, and then freeze-dried to obtain Fe3O4@PDA.

[0091] In some specific embodiments of the present invention, the loading process of the active component includes:

[0092] The magnetic core coated with a dense PDA layer is dispersed in a solvent (preferably distilled water or ethanol), and the precursor of the active component is added to carry out the reaction. After the reaction is completed, the solid is separated and recovered by a magnet, washed and dried, and the resulting solid powder is the magnetically supported catalyst, namely magnetic core@PDA@active component.

[0093] The precursor of the active component is selected from at least one of noble metal elements such as palladium, rhodium, and ruthenium, and acetates, halides, and ammonium salts of nickel and molybdenum. Except for rhodium and ruthenium-based noble metals, the catalysts prepared in this invention should be activated by hydrogen reduction at 200–400°C before use.

[0094] The precursor of the active component is generally added in excess. Preferably, the mass ratio of the magnetic core coated with a dense PDA coating to the precursor of the active component is 1:(0.02-1.03).

[0095] The reaction temperature during the active component loading process is generally 25–120°C, and the reaction time is generally 4–10 hours. In the case of a heated reaction, after cooling to 12–35°C (room temperature) after the reaction is complete, the solid can be separated and recovered using a magnet. The washing process includes washing with deionized water and washing with ethanol.

[0096] The magnetically supported catalyst prepared by this invention can be used in the hydrogenation process of NBR rubber, SBR rubber, latex, and other materials containing unsaturated olefin double bonds. The NBR hydrogenation process is preferred. The organic solvents used in the hydrogenation process include ethers, chlorinated aromatics, and ketones, with chlorinated aromatics and ketones being preferred, and ketones such as acetone and butanone being even more preferred. The weight ratio of the rubber to the catalyst is (1-2):1, and even more preferably (1-1.5):1.

[0097] In some specific embodiments of the present invention, hydrogenation is carried out in a stirred tank or a slurry tank, preferably in a stirred tank; the hydrogenation temperature is 70–120°C, preferably 70–110°C, more preferably 70–100°C; the hydrogen pressure is 2–16 MPa, preferably 2–10 MPa, more preferably 4–8 MPa; the reaction time is 2–10 hours, more preferably 4–8 hours. The reaction is carried out under stirring conditions, with a stirring speed preferably 180–600 rpm, more preferably 200–450 rpm; after the reaction, the original NBR can be converted into HNBR with a hydrogenation degree greater than 95%.

[0098] The magnetically supported catalyst of this invention can be recovered and separated after use by applying an external electromagnetic field or a permanent magnetic field, preferably using a permanent magnet. The catalyst recovery efficiency is not less than 98%, and the recovered catalyst can be reused after solvent washing.

[0099] The magnetically supported catalyst of this invention can achieve highly selective hydrogenation of double bonds in olefins such as nitrile rubber, latex, or emulsion, while having low catalyst cost, low active component content in HNBR, and long service life. It can also efficiently separate the catalyst by an external magnetic field, with high separation efficiency and simple operation. It is a convenient method for preparing HNBR by hydrogenation of NBR using magnetically supported noble metal catalysts.

[0100] The following provides some specific embodiments for more detailed illustration, wherein all numerical specifications (e.g., temperature, time, concentration, and weight, including ranges for each) are generally approximate values ​​that may be changed in increments of 0.1 or 1.0 (+) or (-). All numerical specifications are to be understood as being preceded by the term "about".

[0101] Example 1

[0102] This embodiment prepares a magnetically supported catalyst, including the following process:

[0103] 1) Preparation of Fe3O4 nanoparticles:

[0104] Add 500 mL of ethylene glycol to a reaction vessel, then add 32 g of FeCl3·6H2O, 63 g of anhydrous sodium acetate, 138 g of polyethylene glycol-6000, and 6.3 g of sodium hydroxide. Stir the mixture at 25 °C until homogeneous, then transfer it to a reaction vessel and heat it at 200 °C for 15 hours to obtain 150 nm Fe3O4 nanoparticles. Cool the mixture to 25 °C, and after the reaction is complete, separate and recover the nanoparticles using a magnet, wash them, and freeze-dry them.

[0105] 2) Preparation of Fe3O4 / PDA magnetic nanoparticles:

[0106] 1.2 g of Tris was weighed and dissolved in 600 mL of deionized water to prepare a pH 8.5 buffer solution. Then, 1.5 g of Fe3O4 nanoparticles with a particle size of 150 nm were added and dispersed evenly. Then, 50 mL of 15% dopamine hydrochloride aqueous solution was added dropwise over 10 minutes. The mixture was stirred at 25 °C for 12 hours to prepare Fe3O4 / PDA magnetic nanoparticles with a coating thickness of 10 nm. After the reaction, the nanoparticles were separated and recovered using a magnet, washed successively with deionized water and ethanol, and then freeze-dried. The particle size was characterized by a laser particle size analyzer and a transmission electron microscope.

[0107] 3) Densification treatment:

[0108] The dried Fe3O4 / PDA magnetic nanoparticles were densified at 280℃ for 1 hour under nitrogen protection.

[0109] 4) Loaded active components:

[0110] Then, 1g of densely coated magnetic nanoparticles were weighed and dispersed again in 350mL of distilled water. Then, 0.02g of palladium chloride (PdCl2·2H2O) was added and stirred evenly. The mixed reactants were then added to the reaction vessel and stirred at 25℃ for 6 hours. After the reaction was completed, the reactants were separated and recovered by a magnet, washed, and freeze-dried to obtain the Fe3O4 / PDA / Pd magnetic catalyst.

[0111] 5) Hydrogenation reduction:

[0112] The obtained Fe3O4 / PDA / Pd magnetically supported catalyst was reduced with hydrogen at 380℃ for 2 h. Finally, a supported Fe3O4@PDA@Pd catalyst with hydrogenation activity was obtained.

[0113] The catalyst was found to have a particle size of 170 nm, contain 0.01 wt% Pd, and have a specific surface area of ​​86 m². 2 / g; bulk density is 0.82g / cm³ 3 .

[0114] The final catalyst loading can be obtained by digesting the prepared catalyst or by analyzing the palladium content in the catalyst precursor residue. This invention uses a digestion reaction to obtain the loading.

[0115] 6) Evaluation of hydrogenation degree:

[0116] Weigh 1.02 g of NBR (grade 3304) and add it to 200 g of acetone solution. Stir thoroughly until completely dissolved, then transfer the solution to a high-pressure reactor. Add 0.51 g of Fe3O4@PDA@Pd magnetically supported catalyst to the reactor. Purge the reactor with nitrogen three times to replace the air, then purge with H2 twice. Heat to 120 °C, increase the hydrogen pressure to 4 MPa at this temperature, and react for 6 h at a stirring rate of 400 r / min. After the reaction, cool the reactor to room temperature, slowly vent, and after the hydrogen gas is exhausted, open the reactor and take a sample. Separate the solid catalyst from the reaction solution using magnetic precipitation, and the catalyst recovery rate was found to be 99.1%. Collect the solution in a reagent bottle to obtain a mixture of HNBR and acetone. The degree of hydrogenation of HNBR was determined to be 91.2 using infrared spectroscopy. See Table 1.

[0117] Example 2

[0118] This embodiment prepares a magnetically supported catalyst, including the following process:

[0119] 1) Preparation of Fe3O4 / PDA magnetic nanoparticles:

[0120] 1.2 g of Tris was weighed and dissolved in 600 mL of deionized water to prepare a pH 9.0 buffer solution. Then, 1.8 g of commercially available Fe3O4 magnetic core with a particle size of 200 nm was added and dispersed evenly. Then, 70 mL of 15% dopamine hydrochloride aqueous solution was added dropwise over 10 minutes. The mixture was stirred at 25 °C for 12 hours to prepare Fe3O4 / PDA magnetic nanoparticles with a coating thickness of 15 nm. After the reaction, the nanoparticles were separated and recovered using a magnet, washed successively with deionized water and ethanol, and then freeze-dried. The particle size was characterized by a laser particle size analyzer and a transmission electron microscope.

[0121] 2) Densification treatment:

[0122] The dried Fe3O4 / PDA magnetic nanoparticles were densified at 300℃ for 3 hours under nitrogen protection.

[0123] 3) Loaded active components:

[0124] Then, 1g of densely coated magnetic nanoparticles were weighed and dispersed again in 350mL of distilled water. Then, 0.78g of rhodium chloride (RhCl3·3H2O) was added and stirred evenly. The mixed reactants were then added to the reaction vessel and stirred at 30℃ for 4 hours. After the reaction, the reactants were separated and recovered by a magnet, washed, and freeze-dried to obtain the Fe3O4 / PDA / Rh magnetic catalyst.

[0125] The catalyst has a particle size of 230 nm, a Rh content of 0.1 wt%, and a specific surface area of ​​74 m². 2 / g; bulk density is 0.91g / cm³ 3 .

[0126] 4) Evaluation of hydrogenation degree:

[0127] 1.01 g of 3604 NBR was added to 200 g of acetone solution and stirred thoroughly until completely dissolved. Then, it was added together with 1.0 g of Fe3O4@PDA@Rh to a high-pressure reactor, along with 10 mL of a 1 mol / L triphenylphosphine acetone solution. The reactor was purged three times with 0.4 MPa nitrogen and twice with 2 MPa H2. The temperature was raised to 70 °C, the hydrogen pressure was 16 MPa, and the stirring rate was 380 r / min. The reaction was carried out for 2 h. The catalyst recovery rate and degree of hydrogenation are shown in Table 1.

[0128] Example 3

[0129] This embodiment prepares a magnetically supported catalyst, including the following process:

[0130] 1) Preparation of Fe3S4@PDA magnetic nanoparticles:

[0131] 1.2 g of Tris was weighed and dissolved in 600 mL of deionized water to prepare a buffer solution with pH = 8.25. Then, 1 g of commercially available Fe3S4 with a particle size of 50 nm was added and dispersed evenly. Then, 70 mL of 15% dopamine hydrochloride aqueous solution was added dropwise over 10 minutes. The mixture was stirred at 15 °C for 8 hours to prepare Fe3S4 / PDA magnetic nanoparticles with a coating thickness of 10 nm. After the reaction, the nanoparticles were separated and recovered using a magnet, washed successively with deionized water and ethanol, and then freeze-dried. The particle size was characterized by a laser particle size analyzer and a transmission electron microscope.

[0132] 2) Densification treatment:

[0133] The dried Fe3S4 / PDA magnetic nanoparticles were densified at 250°C for 3 hours under nitrogen protection.

[0134] 3) Loaded active components:

[0135] Then, 1g of densely coated magnetic nanoparticles were weighed and dispersed again in 350mL of distilled water. Then, 0.02g of palladium chloride (PdCl2·2H2O) and 1.24g of nickel chloride (NiCl2·2H2O) were added and stirred evenly. The mixed reactants were then added to the reaction vessel and stirred at 25℃ for 4 hours. After the reaction was completed, the reactants were separated and recovered by a magnet, washed, and freeze-dried to obtain the Fe3S4@PDA@Pd+Ni magnetic catalyst.

[0136] 4) Hydrogenation reduction:

[0137] The obtained Fe3S4@PDA@Pd+Ni magnetically supported catalyst was reduced with hydrogen at 200℃ for 6 h. Finally, a supported Fe3S4@PDA@Pd+Ni catalyst with hydrogenation activity was obtained.

[0138] The catalyst has a particle size of 70 nm, a Pd content of 0.01 wt%, a Ni content of 0.3%, and a specific surface area of ​​95 nm. 2 / g; bulk density is 0.6g / cm³ 3 .

[0139] 5) Evaluation of hydrogenation degree:

[0140] Weigh 1.0 g of NBR (grade 3304) and add it to 201 g of acetone solution. Stir thoroughly to completely dissolve the NBR, then transfer the solution to a high-pressure reactor. Add 1 g of Fe3S4@PDA@Pd+Ni magnetically supported catalyst to the reactor. Purify the reactor three times with 0.4 MPa nitrogen and twice with 2 MPa H2. React at 90 °C, hydrogen pressure of 12 MPa, and stirring rate of 389 r / min for 10 h. Catalyst recovery and degree of hydrogenation are shown in Table 1.

[0141] Example 4

[0142] This embodiment prepares a magnetically supported catalyst with 1g of commercially available 500nm Fe3O4 as the magnetic core. Due to the large particle size of the magnetic core, it underwent three coating and heat treatment processes to obtain a suitable density, resulting in a final coating thickness of 50nm. The coating process involved first coating 10nm and then heat-treating at 250℃; then coating 20nm and heat-treating at 270℃; and finally coating another 20nm and heat-treating at 350℃. This was done to obtain a suitable final catalyst density. The specific processes included are as follows:

[0143] 1) One-time coating and densification treatment:

[0144] 1.2 g of Tris was weighed and dissolved in 600 mL of deionized water to prepare a buffer solution with pH = 8.5-8.0. Then, 1 g of commercially available Fe3O4 magnetic core with a particle size of 500 nm was added and dispersed evenly. Then, 70 mL of 15% dopamine hydrochloride aqueous solution was added dropwise over 10 minutes. The mixture was stirred at 25 °C for 6 hours to prepare Fe3O4 / PDA magnetic nanoparticles with a coating thickness of 10 nm. After the reaction, the nanoparticles were separated and recovered using a magnet, washed successively with deionized water and ethanol, and then freeze-dried. The dried Fe3O4 / PDA magnetic nanoparticles were then densified at 250 °C for 1 hour under nitrogen protection.

[0145] 2) Secondary coating and densification treatment:

[0146] The magnetic core processed in step 1) was coated with a 20nm PDA layer again using the same method, and then subjected to densification treatment at 270℃ for 2 hours.

[0147] 3) Three-stage coating and densification treatment:

[0148] The magnetic core processed in step 2) was coated with a 20nm PDA layer again using the same method, and then subjected to densification treatment at 350℃ for 1 hour.

[0149] 4) Loaded active components:

[0150] Weigh more than 1g of the three-time densely coated magnetic nanoparticles and disperse them again in 350mL of 25% ethanol aqueous solution. Then add 0.39g of rhodium chloride (RhCl3·3H2O) and 0.64g of ruthenium chloride (RuCl3·3H2O). After stirring evenly, add the evenly mixed reactants to the reaction vessel and stir at 25℃ for 5 hours. After the reaction is completed, separate and recover the reactants with a magnet, wash them, and freeze-dry them to obtain the Fe3S4@PDA@Rh+Ru magnetic catalyst.

[0151] The catalyst has a particle size of 600 nm, contains 0.1 wt% Rh and 0.3 wt% Ru, and has a specific surface area of ​​45 m². 2 / g; bulk density is 1.25g / cm³ 3 .

[0152] 5) Evaluation of hydrogenation degree:

[0153] 1.06 g of 3604 NBR was added to 203 g of acetone solution and stirred thoroughly until completely dissolved. Then, it was added together with 1.05 g of Fe3O4@PDA@Rh+Ru into a high-pressure reactor, along with 10 mL of a 1 mol / L triphenylphosphine acetone solution. The reactor was purged three times with 0.4 MPa nitrogen and twice with 2 MPa H2. The reaction was carried out at 100 °C, with a hydrogen pressure of 2 MPa and a stirring rate of 401 r / min for 8 h. The catalyst recovery rate and degree of hydrogenation are shown in Table 1.

[0154] Example 5

[0155] This embodiment prepares a magnetically supported catalyst. The magnetic core is a commercially available 300nm Fe3O4. Due to the relatively large particle size of the magnetic core, in order to obtain a suitable density, the magnetic core is coated with 20nm particles twice and subjected to heat treatment at temperatures of 220℃ and 380℃, respectively. The specific process includes the following:

[0156] 1) One-time coating and densification treatment:

[0157] 1.2 g of Tris was weighed and dissolved in 600 mL of deionized water to prepare a buffer solution with pH = 8.75. Then, 1 g of commercially available Fe3O4 magnetic core with a particle size of 300 nm was added and dispersed evenly. Then, 70 mL of 15% dopamine hydrochloride aqueous solution was added dropwise over 10 minutes. The mixture was stirred at 12 °C for 12 hours to prepare Fe3O4 / PDA magnetic nanoparticles with a coating thickness of 20 nm. After the reaction, the nanoparticles were separated and recovered using a magnet, washed with deionized water and ethanol in sequence, and freeze-dried. The dried Fe3O4 / PDA magnetic nanoparticles were then densified at 220 °C for 2.5 hours under nitrogen protection.

[0158] 2) Secondary coating and densification treatment:

[0159] The magnetic core processed in step 1) was coated with a 20nm PDA layer again using the same method, and then subjected to densification treatment at 380℃ for 1 hour.

[0160] 3) Loaded active components:

[0161] Weigh more than 1g of the twice densely coated magnetic nanoparticles and disperse them again in 350mL of distilled water. Then add 0.11g of palladium chloride (PdCl2·2H2O), stir evenly, and add the evenly mixed reactants into a reaction vessel. Stir at 25℃ for 5 hours. After the reaction, separate and recover the reactants with a magnet, wash them, and freeze dry them to obtain the Fe3O4@PDA@Pd magnetic catalyst.

[0162] 4) Hydrogenation reduction:

[0163] The obtained Fe3O4 / PDA / Pd magnetic catalyst was reduced with hydrogen at 370℃ for 1.5 h. Finally, a supported Fe3O4@PDA@Pd catalyst with hydrogenation activity was obtained.

[0164] The catalyst has a particle size of 380 nm, a Pd content of 6 wt%, and a specific surface area of ​​66 m². 2 / g; bulk density is 0.97g / cm³ 3 .

[0165] 5) Evaluation of hydrogenation degree:

[0166] Weigh 1.02 g of NBR (grade 3304) and add it to 201 g of acetone solution. Stir thoroughly to completely dissolve the NBR, then transfer the solution to a high-pressure reactor. Add 1 g of Fe3O4@PDA@Pd magnetic catalyst to the reactor. Purify the reactor three times with 0.4 MPa nitrogen and twice with 2 MPa H2. React at 85 °C, hydrogen pressure of 6 MPa, and stirring rate of 503 r / min for 4 h. Catalyst recovery and degree of hydrogenation are shown in Table 1.

[0167] Example 6

[0168] This embodiment prepares a magnetically supported catalyst, including the following process:

[0169] 1) Preparation of FeNi@PDA magnetic nanoparticles:

[0170] 1.2 g of Tris was weighed and dissolved in 600 mL of deionized water to prepare a pH 8.5 buffer solution. Then, 1 g of commercially available FeNi with a particle size of 100 nm was added and dispersed evenly. Then, 70 mL of 15% dopamine hydrochloride aqueous solution was added dropwise over 10 minutes. The mixture was stirred at 23 °C for 7 hours to prepare FeNi / PDA magnetic nanoparticles with a coating thickness of 10 nm. After the reaction, the nanoparticles were separated and recovered using a magnet, washed with deionized water and ethanol in sequence, and then freeze-dried. The particle size was characterized by a laser particle size analyzer and a transmission electron microscope.

[0171] 2) Densification treatment:

[0172] The dried FeNi / PDA magnetic nanoparticles were densified at 500℃ for 1 hour under nitrogen protection.

[0173] 3) Loaded active components:

[0174] Then, 1g of densely coated magnetic nanoparticles were weighed and dispersed again in 350mL of distilled water. Then, 0.02g of palladium chloride (PdCl2·2H2O) and 0.99g of ammonium molybdate (NH4)2MoO4 were added and stirred evenly. The mixed reactants were then added to the reaction vessel and stirred at 20℃ for 5.5 hours. After the reaction was completed, the reactants were separated and recovered by a magnet, washed, and freeze-dried to obtain the Fe3O4@PDA@Pd+Mo magnetic catalyst.

[0175] 4) Hydrogenation reduction:

[0176] The obtained Fe3O4@PDA@Pd+Mo magnetically supported catalyst was reduced with hydrogen at 400℃ for 1.5 h. Finally, a supported Fe3O4@PDA@Pd+Mo catalyst with hydrogenation activity was obtained.

[0177] The catalyst has a particle size of 120 nm, contains 0.01 wt% Pd and 0.5 wt% Mo, and has a specific surface area of ​​91 m². 2 / g; bulk density is 0.73g / cm³ 3 .

[0178] 5) Evaluation of hydrogenation degree:

[0179] Weigh 1.02 g of NBR (grade 3304) and add it to 201 g of acetone solution. Stir thoroughly to completely dissolve the NBR, then transfer the solution to a high-pressure reactor. Add 1.01 g of FeNi@PDA@Pd+Mo magnetically supported catalyst to the reactor. Purify the reactor three times with 0.4 MPa nitrogen and twice with 2 MPa H2. React at 90 °C, hydrogen pressure of 6 MPa, and stirring rate of 380 r / min for 10 h. Catalyst recovery and degree of hydrogenation are shown in Table 1.

[0180] Example 7

[0181] This embodiment prepares a magnetically supported catalyst, including the following process:

[0182] 1) Preparation of FeNi@PDA magnetic nanoparticles:

[0183] 1.2 g of Tris was weighed and dissolved in 600 mL of deionized water to prepare a buffer solution with pH = 8.5. Then, 1 g of commercially available FeNi with a particle size of 200 nm was added and dispersed evenly. Then, 70 mL of 15% dopamine hydrochloride aqueous solution was added dropwise over 10 minutes. The mixture was stirred at 35 °C for 4 hours to prepare FeNi / PDA magnetic nanoparticles with a coating thickness of 10 nm. After the reaction, the nanoparticles were separated and recovered using a magnet, washed with deionized water and ethanol in sequence, and then freeze-dried. The particle size was characterized by a laser particle size analyzer and a transmission electron microscope.

[0184] 2) Densification treatment:

[0185] The dried FeNi / PDA magnetic nanoparticles were densified at 180°C for 4 hours under nitrogen protection.

[0186] 3) Loaded active components:

[0187] Then, 1g of densely coated magnetic nanoparticles were weighed and dispersed again in 350mL of distilled water. Then, 0.033g of palladium chloride (PdCl2·2H2O) was added and stirred evenly. The mixed reactants were then added to the reaction vessel and stirred at 25℃ for 4 hours. After the reaction was completed, the reactants were separated and recovered by a magnet, washed, and freeze-dried to obtain the FeNi@PDA@Pd magnetic catalyst.

[0188] 4) Hydrogenation reduction:

[0189] The obtained FeNi@PDA@Pd magnetically supported catalyst was reduced with hydrogen at 370℃ for 2 hours. Finally, a supported FeNi@PDA@Pd catalyst with hydrogenation activity was obtained.

[0190] The catalyst has a particle size of 220 nm, a Pd content of 2.0 wt%, and a specific surface area of ​​67 m². 2 / g; bulk density is 0.97g / cm³ 3 .

[0191] 5) Evaluation of hydrogenation degree:

[0192] Weigh 1g of NBR (grade 3304) and add it to 200g of acetone solution. Stir thoroughly until completely dissolved. Then, add 1g of FeNi@PDA@Pd to a high-pressure reactor. Replace the reactor three times with 0.4MPa nitrogen and twice with 2MPa H2. Heat to 80℃, maintain a hydrogen pressure of 2MPa, and react for 2 hours at a stirring rate of 380r / min. Catalyst recovery and degree of hydrogenation are shown in Table 1.

[0193] Comparative Example 1

[0194] Commercially available 200nm Fe3O4 was used, then directly impregnated with 5wt% palladium acetate, followed by hydrogen reduction at 280°C. The magnetically supported catalyst obtained using this method had a Pd loading of 3.1wt%, significantly higher than the 0.01wt% Pd loading in Example 1. Used for 3304NBR hydrogenation, under the same catalyst and solution addition amounts and hydrogenation conditions, the hydrogenation activity was acceptable, reaching 98.7%. However, further testing showed that 49.9wt% Pd detached from the Fe3O4 surface and entered the solution after hydrogenation, requiring extremely complex separation steps. This indicates that the method of directly impregnating Fe3O4 nanoparticles causes active component detachment during hydrogenation, contaminating the final HNBR product. The magnetically supported catalyst with a magnetic core surface coated according to this invention solves this problem.

[0195] Comparative Example 2

[0196] This comparative example attempted to prepare a Fe3O4@PDA@Pd type magnetically supported catalyst using the same method as in Example 1. The only difference was that the surface of this catalyst was not densified after coating the Fe3O4, resulting in a high Pd loading of 3wt%. Despite this high loading, the hydrogenation activity during 3304NBR hydrogenation was only 88.3%, and 27.5% of the active component detached and entered the gel. Analysis showed that approximately 68.1% of the active component entered the coating layer, and this portion was completely blocked by the gel, failing to perform its intended function. Therefore, despite the high nominal loading, the hydrogenation effect was poor.

[0197] Comparative Example 3

[0198] This comparative example attempted to prepare a Fe3O4@PDA@Pd type magnetic catalyst using the same method as in Example 1, but with Fe3O4 magnetic cores of average particle size of 20 nm. For the 3304NBR high-viscosity system, the hydrogenation activity was 99.5%, but the catalyst recovery rate after use was only 80%. Even after several recovery attempts, it only reached 91%. This is because some magnetic core particles were too small and remained in the viscous solution, ultimately leading to a low catalyst recovery rate.

[0199] Table 1. Results of hydrogenation and magnetic separation in the examples and comparative examples.

[0200]

[0201] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A magnetically supported catalyst, wherein, The magnetically supported catalyst includes a magnetic core, a dense PDA coating layer on the magnetic core, and an active component supported on the dense PDA coating layer; The dense PDA coating layer is formed by polydopamine coating and densification treatment; The densification process is a heat treatment at 180-500°C under a protective atmosphere.

2. The magnetically supported catalyst according to claim 1, wherein, The magnetically supported catalyst has a particle size of 70 nm to 600 nm and a specific surface area of ​​45 m². 2 / g ~ 91 m 2 / g, with a bulk density of 0.6 g / cm³. 3 ~ 1.25 g / cm 3 .

3. The magnetically supported catalyst according to claim 1, wherein, The active component is supported at a rate of 0.01 wt% to 6 wt% of the catalyst.

4. The magnetically supported catalyst according to claim 1, wherein, The active component is selected from at least one of Pd, Rh, Ru, Ni, and Mo.

5. The magnetically supported catalyst according to claim 1, wherein, The magnetic core is selected from at least one of Fe3O4, Fe3S4 and FeNi.

6. The magnetically supported catalyst according to claim 1, wherein, The particle size of the magnetic core is 50 nm to 500 nm.

7. A method for preparing the magnetically supported catalyst according to any one of claims 1-6, wherein, The preparation method includes the following steps: Polydopamine was used to coat the magnetic core with polydopamine to obtain polydopamine-coated magnetic microspheres. Magnetic microspheres coated with polydopamine are heat-treated at 180-500°C for 1-4 hours in a protective atmosphere to form the dense PDA coating layer; when the catalyst particle size and density cannot meet the hydrogenation requirements, the coating is repeated multiple times to form multiple layers of the dense PDA coating layer. The active component is supported to obtain the magnetically supported catalyst.

8. The preparation method according to claim 7, wherein, The coating process of the magnetic core includes: The magnetic core was added to a buffer solution, followed by the addition of dopamine hydrochloride. The mixture was stirred at 12-35°C for 4-12 hours. After the reaction was completed, the precipitate was separated and recovered using a magnet. The precipitate was then washed and dried to obtain polydopamine-coated magnetic microspheres.

9. The preparation method according to claim 8, wherein, The buffer solution is a Tris buffer solution with pH = 8~9.

10. The preparation method according to claim 7, wherein, The loading process of the active component includes: The magnetic core coated with a dense PDA coating is dispersed in a solvent, and the precursor of the active component is added to carry out the reaction. After the reaction is completed, the solid is separated and recovered by a magnet, washed and dried, and the resulting solid powder is the magnetically supported catalyst.

11. The preparation method according to claim 10, wherein, The precursor of the active component is selected from at least one of the following: acetate, halide, and ammonium salt of palladium, rhodium, ruthenium, nickel, and molybdenum.

12. The use of the magnetically supported catalyst according to any one of claims 1-6 in the hydrogenation process of polymers containing unsaturated olefin double bonds.

13. The application according to claim 12, wherein, The magnetically supported catalyst was used in the hydrogenation of nitrile rubber.

14. The application according to claim 13, wherein, The weight ratio of nitrile rubber to magnetically supported catalyst is (1~2):

1.

15. The application according to claim 13, wherein, The hydrogenation is carried out in a stirred tank or a slurry tank; the hydrogenation temperature is 70~120℃, the hydrogen pressure is 2~16 MPa, and the reaction time is 2~10 h.

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