Encapsulated catalysts, methods of making and using same, and selective hydrogenation of butadiene-acrylonitrile rubber

Abstract

The application relates to the field of catalyst preparation, and discloses a packaging type catalyst, a preparation method and application thereof, and a nitrile rubber selective hydrogenation method. The packaging type catalyst contains a silicon dioxide carrier, a cheap metal element, a noble metal element and a carbon coating layer wrapping the silicon dioxide carrier, the cheap metal element and the noble metal element; wherein, the content of the silicon dioxide carrier is 75-90% by weight, the content of the cheap metal element is 5-15% by weight, the content of the noble metal element is 0.5-5% by weight, and the content of the carbon is 3-10% by weight, based on the total weight of the catalyst. The packaging type catalyst has stable properties, is applied to a hydrogenated nitrile rubber reaction for preparing hydrogenated nitrile rubber through nitrile rubber selective hydrogenation, has excellent catalytic activity, and can realize high reactant conversion rate and high product selectivity.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, specifically to an encapsulated catalyst, its preparation method, application, and a selective hydrogenation method for nitrile rubber. Background Technology

[0002] Hydrogenated nitrile butadiene rubber (HNBR) is produced by selectively hydrogenating the butadiene units in the nitrile butadiene rubber (NBR) molecular chain. HNBR not only possesses the oil resistance and abrasion resistance of NBR, but also exhibits superior resistance to oxidation and chemical corrosion, making it an important type of specialty rubber.

[0003] Currently, the preparation of commercial HNBR mainly adopts the solution hydrogenation method, and its core technology is the hydrogenation catalyst. The catalysts currently used have defects such as high price, difficult synthesis, and easy deactivation, which seriously hinder the industrialization process of HNBR. The most commonly used homogeneous catalysts for NBR hydrogenation are mainly rhodium-based and ruthenium-based catalysts. These catalysts have high hydrogenation activity, but they are sensitive to air and easily deactivated, expensive, and difficult to recover. Commonly used heterogeneous catalysts are made by loading nano-metal particles such as Ru, Rh, and Pd onto supports such as activated carbon, SiO2, and some porous mesoporous materials. Heterogeneous catalysts have the characteristics of easy separation and recovery, but there are still some problems that need to be solved, mainly: (1) Low catalyst activity: Due to the large steric hindrance of polymer chains, there is a serious mass transfer resistance in the hydrogenation process; (2) Easy catalyst deactivation: Due to the strong adsorption of nitrile groups in HNBR at the active sites, they cannot be completely desorbed after the reaction, so the active sites of the catalyst cannot be recovered during the reaction. Therefore, it is urgent to develop and synthesize a green, inexpensive, simple, efficient, and highly stable catalyst. Summary of the Invention

[0004] To overcome the problems of easy catalyst deactivation and the need for further improvement in catalyst activity in existing technologies, this invention provides an encapsulated catalyst, its preparation method, application, and a method for selective hydrogenation of nitrile rubber. The encapsulated catalyst of this invention is stable and exhibits excellent catalytic activity in the selective hydrogenation of nitrile rubber to prepare hydrogenated nitrile rubber, achieving high reactant conversion and high product selectivity.

[0005] To achieve the above objectives, the present invention provides an encapsulated catalyst, wherein the catalyst comprises a silica support, an inexpensive metal element, a noble metal element, and a carbon coating layer encapsulating the silica support, the inexpensive metal element, and the noble metal element;

[0006] Based on the total weight of the catalyst, the content of silica support is 75-90% by weight, the content of inexpensive metal elements is 5-15% by weight, the content of precious metal elements is 0.5-5% by weight, and the content of carbon is 3-10% by weight.

[0007] A second aspect of this invention provides a method for preparing an encapsulated catalyst, the method comprising the following steps:

[0008] (1) Introduce a cheap metal precursor into silica to obtain a solid product;

[0009] (2) The solid product obtained in step (1) is mixed with a carbon source and then calcined under a protective gas atmosphere to obtain a calcined product with a carbon layer coating structure.

[0010] (3) The calcined product obtained in step (2) is reacted with a noble metal precursor to obtain an encapsulated catalyst.

[0011] The third aspect of this invention provides the application of the encapsulated catalyst described in the first aspect or the encapsulated catalyst prepared by the preparation method described in the second aspect in the selective hydrogenation reaction of nitrile rubber.

[0012] The fourth aspect of the present invention provides a method for selective hydrogenation of nitrile rubber, the method comprising: reacting nitrile rubber, hydrogen gas and an encapsulated bimetallic catalyst in the presence of a solvent, wherein the encapsulated catalyst is the encapsulated catalyst described in the first aspect or the encapsulated catalyst prepared by the preparation method described in the second aspect.

[0013] The beneficial effects of this invention include:

[0014] (1) The encapsulated catalyst of the present invention can block the direct contact between the nitrile group and the active site in the hydrogenated nitrile rubber, and at the same time inhibit the loss of active components in the catalyst, thereby improving the activity of the catalyst.

[0015] (2) When using the encapsulated catalyst of the present invention to catalyze the hydrogenation of nitrile rubber to prepare hydrogenated nitrile rubber, the selectivity of hydrogenated nitrile rubber is greater than 99%.

[0016] (3) The encapsulated catalyst provided by the present invention has stable properties and can be regenerated and reused multiple times, up to 5 times, which greatly improves cycle stability and service life.

[0017] (4) The preparation method of the encapsulated catalyst of the present invention has the advantages of simple operation, green and economical operation. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the overall morphology of the catalyst prepared in Example 1;

[0019] Figure 2 High-resolution transmission electron microscope image (left) of the carbon coating structure of the catalyst prepared in Example 1 and particle size distribution map of inexpensive metal particles (right);

[0020] Figure 3 High-resolution transmission electron microscope image (left) of the catalyst sandwich-coated structure prepared in Example 1 and particle size distribution map of noble metal particles (right). Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] In one aspect, the present invention provides an encapsulated catalyst, wherein the catalyst comprises a silica support, an inexpensive metal element, a noble metal element, and a carbon coating layer encapsulating the silica support, the inexpensive metal element, and the noble metal element;

[0023] Based on the total weight of the catalyst, the content of silica support is 75-90% by weight, the content of inexpensive metal elements is 5-15% by weight, the content of precious metal elements is 0.5-5% by weight, and the content of carbon is 3-10% by weight.

[0024] According to the present invention, preferably, based on the total weight of the catalyst, the content of silica support is 75-85% by weight, the content of inexpensive metal elements is 5-12% by weight, the content of precious metal elements is 0.5-3% by weight, and the content of carbon is 5-10% by weight.

[0025] The total content of all components in the catalyst of this invention is 100%.

[0026] The content of each component in the catalyst of the present invention was determined by ICP and thermogravimetric methods.

[0027] According to the present invention, preferably, the weight ratio of the inexpensive metal element to the precious metal element is 4-30:1, more preferably 5-20:1. By adopting this preferred embodiment, the synergistic effect of the inexpensive metal and the precious metal is beneficial to improving the catalytic activity of the catalyst, thereby promoting the reaction, while reducing the amount of precious metal used and lowering the cost of the catalyst.

[0028] According to the present invention, preferably, the inexpensive metal element and the noble metal element are present between the silica support and the carbon coating layer, and the catalyst has a sandwich-type coating structure. This preferred embodiment avoids direct contact between the catalyst active site and the reactants, which is beneficial to improving the catalyst's cycle stability.

[0029] According to the present invention, preferably, the carbon coating layer is a nitrogen-doped carbon coating layer. This preferred embodiment can suppress the loss and aggregation of active metals, and the introduction of nitrogen can further anchor the metals, which is beneficial to maintaining the catalyst activity and stability.

[0030] According to the present invention, preferably, the nitrogen content is 0.5-2% by weight, based on the total weight of the catalyst.

[0031] In existing technologies, the average particle size of inexpensive metal particles with high loading in catalysts is relatively high, generally between 50-100 nm. The average particle size of inexpensive metal particles in the encapsulated catalyst of this invention is significantly reduced, which is beneficial for the exposure and full utilization of active sites. According to this invention, preferably, the average particle size of the inexpensive metal particles is 1-50 nm, more preferably 10-30 nm.

[0032] According to the present invention, preferably, the average particle size of the noble metal particles is 1-10 nm, more preferably 1-5 nm.

[0033] The average particle size of the silica carrier, inexpensive metal particles, and noble metal particles described in this invention was measured using high-resolution transmission electron microscopy.

[0034] According to the present invention, preferably, the inexpensive metal particles and noble metal particles in the catalyst have uniform particle size. The particle size distribution of the inexpensive metal particles and noble metal particles in the catalyst can be observed by scanning electron microscopy. Figure 2 (right) and Figure 3 (Right) For example, it can be seen that the average particle size of the inexpensive metal in the encapsulated catalyst prepared in Example 1 is about 10 nm, and the average particle size of the noble metal is about 2.6 nm.

[0035] The present invention has a wide range of choices for the inexpensive metals. Preferably, the inexpensive metals are selected from at least one of the group IVB, VIB and VIII metal elements.

[0036] According to the present invention, preferably, the inexpensive metal is selected from at least one of Ti, Zr, Cr, Mo, Fe, Co and Ni.

[0037] According to the present invention, more preferably, the inexpensive metal is selected from at least one of Fe, Co and Ni, and more preferably Ni.

[0038] The present invention allows for a wide range of choices of the precious metal, and any precious metal commonly used in the art can be used. Preferably, the precious metal is selected from at least one of Pt, Pd, and Ru, and more preferably Pd.

[0039] A second aspect of this invention provides a method for preparing an encapsulated catalyst, the method comprising the following steps:

[0040] (1) Introduce a cheap metal precursor into silica to obtain a solid product;

[0041] (2) The solid product obtained in step (1) is mixed with a carbon source and then calcined under a protective gas atmosphere to obtain a calcined product with a carbon layer coating structure.

[0042] (3) The calcined product obtained in step (2) is reacted with a noble metal precursor to obtain an encapsulated catalyst.

[0043] According to the present invention, preferably, the amounts of silica, carbon source, inexpensive metal precursor and noble metal precursor are such that, based on the total weight of the catalyst, the content of silica support is 75-90% by weight, the content of inexpensive metal element is 5-15% by weight, the content of noble metal element is 0.5-5% by weight, and the content of carbon is 3-10% by weight.

[0044] According to the present invention, preferably, the amounts of silica, carbon source, inexpensive metal precursor and noble metal precursor are such that, based on the total weight of the catalyst, the content of silica support is 75-85% by weight, the content of inexpensive metal element is 5-12% by weight, the content of noble metal element is 0.5-3% by weight, and the content of carbon is 5-10% by weight.

[0045] According to the present invention, preferably, the ratio of the inexpensive metal precursor to the noble metal precursor is such that the weight ratio of the inexpensive metal element to the noble metal element in the prepared encapsulated catalyst is 4-30:1, more preferably 5-20:1.

[0046] According to the present invention, the source of the silica is wide-ranging, and it can be commercially available or prepared in-house. Preferably, step (1) includes: mixing ethanol, ammonia, water and a silicon source to obtain a mixture containing silica microspheres, and then introducing an inexpensive metal precursor.

[0047] The method of introducing the inexpensive metal precursor in step (1) of this invention can also be prepared using conventional techniques in the art, such as impregnation. Specifically, silicon dioxide can be impregnated with an impregnation solution containing the inexpensive metal precursor, and then dried. The drying conditions can be carried out under conventional conditions, which will not be elaborated here.

[0048] During the research process, the inventors discovered that directly introducing inexpensive metal precursors into a mixture containing silica microspheres facilitates closer contact between the inexpensive metals and the silica microspheres, thereby resulting in a more uniform metal distribution in the synthesized catalyst.

[0049] Preferably, the introduction of the inexpensive metal precursor in step (1) is carried out under stirring conditions. The present invention does not impose any particular limitation on the stirring conditions, which can be appropriately selected according to specific circumstances.

[0050] This invention uses silica microspheres as a carrier, which is more stable, and the abundant hydroxyl groups on its surface are conducive to the adsorption of active metal precursors.

[0051] According to the present invention, preferably, the average particle size of the silica microspheres is 300-400 nm.

[0052] According to the present invention, preferably, the average pore size of the silica microspheres is 5-30 nm.

[0053] The average particle size of the silica microspheres described in this invention was measured by transmission electron microscopy.

[0054] The average pore size of the silica microspheres described in this invention was measured by a nitrogen isothermal adsorption-desorption method.

[0055] According to the present invention, preferably, the mass ratio of ethanol, ammonia, water and silicon source is 50:(0.1-10):(5-10):(1-10), more preferably 50:(0.5-4.5):(5-8):(2-5).

[0056] This invention allows for a wide range of silicon source selection, including commonly used silicon sources in the field. In this embodiment, tetraethyl orthosilicate is used as an example.

[0057] In the method provided by the present invention, the selection range of the inexpensive metal and the precious metal can be the same as the selection range described in the first aspect above, and will not be repeated here.

[0058] The present invention allows for a wide range of selection for the inexpensive metal precursor, as long as the aforementioned metals are available. Preferably, the inexpensive metal precursor is an organic salt of an inexpensive metal, preferably selected from at least one of Fe(C2H3O2)2, Ni(C2H3O2)2, and Co(C2H3O2)2. This preferred embodiment facilitates pore formation in biomass during the roasting process, further promoting the formation of a porous carbon coating layer.

[0059] In a preferred embodiment, the silica containing the inexpensive metal precursor is subjected to filtration and drying to obtain a solid product. The filtration and drying conditions can be performed under conventional conditions, which will not be described in detail here.

[0060] This invention allows for a wide range of carbon source selection, as long as a carbon coating layer can be obtained subsequently. Preferably, the carbon source is a biomass compound, preferably selected from at least one of glucose, cellulose, and chitin, and more preferably chitin. In this preferred embodiment, the amino groups in chitin are tightly bonded to the hydroxyl groups on the surface of silica via hydrogen bonds, which is beneficial for the formation of the carbon layer and the generation of the coating structure.

[0061] The present invention does not impose any particular limitation on the mixing conditions, which can be appropriately selected according to the specific circumstances, as long as the purpose of uniform mixing can be achieved.

[0062] According to the present invention, preferably, the calcination conditions in step (2) include: a temperature of 500-900℃, preferably 600-800℃; and a time of 1-6h, preferably 2-4h.

[0063] The calcined product obtained in step (2) has a carbon layer coating structure. During the calcination process, the carbon source adsorbed on the surface of the silica microspheres undergoes condensation oligomerization at low temperature (100-300℃). As the temperature rises, the oligomers gradually deoxygenate and carbonize, eventually forming a porous carbon skeleton.

[0064] According to the present invention, the protective gas atmosphere can be a conventional choice in the art, but for economic reasons, nitrogen is preferred.

[0065] This invention allows for a wide range of choices for the noble metal precursor, as long as the aforementioned noble metal is available. According to this invention, preferably, the noble metal precursor is a soluble salt of a noble metal, preferably selected from at least one of K₂PdCl₄, K₂PtCl₄, and RuCl₃. These substances are all conventional choices in the art and are commercially available.

[0066] Preferably, the noble metal precursor is provided in solution form. The present invention does not have particular requirements for the choice of solvent; any solvent capable of dissolving the noble metal precursor can be used. In this invention, water is preferably used as the solvent.

[0067] The reaction described in this invention is a redox reaction between a high-valent noble metal in a noble metal precursor and a zero-valent inexpensive metal in a calcination product. Using this preferred embodiment avoids the use of a reducing agent, making the process green and efficient. Furthermore, the catalyst obtained by this method exhibits close contact between the noble and inexpensive metals, enhancing their interaction.

[0068] The carbon layer described in this invention has a porous structure, allowing noble metal ions to easily pass through the carbon layer and come into contact with inexpensive metals, thereby undergoing a spontaneous redox reaction to generate an elemental state.

[0069] According to the present invention, preferably, the reaction conditions in step (3) include: a temperature of 10-100℃, preferably 20-80℃; and a time of 1-24h, preferably 2-12h.

[0070] Preferably, the reaction in step (3) is carried out under stirring conditions. The present invention does not impose any particular limitation on the stirring conditions, which can be appropriately selected according to specific circumstances, as long as the purpose of achieving a complete reaction is achieved.

[0071] The third aspect of this invention provides the application of the encapsulated catalyst described in the first aspect or the encapsulated catalyst prepared by the preparation method described in the second aspect in the selective hydrogenation reaction of nitrile rubber.

[0072] The fourth aspect of the present invention provides a method for selective hydrogenation of nitrile rubber, the method comprising: reacting nitrile rubber, hydrogen gas and an encapsulated catalyst in the presence of a solvent, wherein the encapsulated catalyst is the encapsulated catalyst described in the first aspect or the encapsulated catalyst prepared by the preparation method described in the second aspect.

[0073] According to the present invention, preferably, the conditions for selective hydrogenation of the nitrile rubber include: a temperature of 60-150°C, preferably 80-130°C; and a reaction pressure of 1-5 MPa, preferably 2-4 MPa.

[0074] According to the present invention, preferably, the amount of catalyst used is 20-60 parts by weight, more preferably 40-50 parts by weight, relative to 100 parts by weight of nitrile rubber.

[0075] According to the present invention, the solvent can be any existing organic substance capable of serving as a reaction medium. Preferably, the solvent is selected from at least one of isopropanol, ethanol, acetonitrile, toluene, dichloromethane, ethyl acetate, N,N-dimethylformamide, acetone, N-methylpyrrolidone, and cyclohexanone, more preferably acetone and / or ethanol.

[0076] According to the present invention, preferably, the amount of solvent used is 10-100 parts by weight, more preferably 60-90 parts by weight, relative to 1 part by weight of nitrile rubber.

[0077] The encapsulated catalyst provided by this invention can be regenerated and reused multiple times. This invention does not particularly limit the regeneration method; methods commonly used in the art can be employed. Preferably, this invention involves washing and drying the encapsulated catalyst.

[0078] Preferably, in this invention, the washing conditions are such that, upon infrared spectroscopy detection, no polymer peaks are found in the washing liquid.

[0079] Preferably, the detergent is selected from at least one of isopropanol, ethanol, acetonitrile, toluene, dichloromethane, ethyl acetate, N,N-dimethylformamide, acetone, N-methylpyrrolidone, and cyclohexanone.

[0080] In a preferred embodiment, the detergent is the same as the solvent described above.

[0081] Preferably, the washing conditions include a temperature of 25-100°C.

[0082] The present invention does not impose any particular limitation on the drying conditions, and can refer to the methods commonly used in the field, as long as the drying purpose can be achieved.

[0083] The present invention will be described in detail below through embodiments.

[0084] In the following embodiments, the encapsulated catalyst with a carbon coating structure was observed using high-resolution transmission electron microscopy.

[0085] The encapsulated catalyst with a sandwich-like structure was observed using high-resolution transmission electron microscopy.

[0086] All reagents used in the following examples are commercially available and of analytical grade.

[0087] Preparation Example 1

[0088] This preparation example is used to prepare silica microspheres.

[0089] Add 60 mL of ethanol, 6 mL of deionized water and 2 mL of ammonia to a 100 mL round-bottom flask. Stir at room temperature for 30 min, then add 3 mL of tetraethyl orthosilicate dropwise and stir for 2 h to obtain a mixture containing silica microspheres. After centrifugation, washing and drying, silica microspheres are obtained.

[0090] The silica microspheres have an average particle size of 350 nm and an average pore size of 6 nm.

[0091] Example 1

[0092] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. Nickel acetate was added, and the mixture was stirred for 2 h. The mixture was then filtered and dried to obtain a solid product. The solid product was mixed with chitin and calcined at 800 °C for 2 h under a nitrogen atmosphere to obtain a calcined product with a carbon-coated structure. The calcined product was reacted with an aqueous solution of K₂PdCl₄ at 25 °C with stirring for 4 h to obtain an encapsulated catalyst. The specific composition is shown in Table 1.

[0093] The overall morphology of the catalyst is as follows Figure 1 As shown.

[0094] Encapsulated catalysts with carbon coating structures and sandwich coating structures, such as Figure 2 (Left), Figure 3 As shown in the left image, SiO2 is spherical with nano-metals attached to its exterior, which are then coated with a carbon layer.

[0095] Example 2

[0096] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. Nickel acetate was added, and the mixture was stirred for 2 h. The mixture was then filtered and dried to obtain a solid product. The solid product was mixed with chitin and calcined at 600 °C for 2 h under a nitrogen atmosphere to obtain a calcined product with a carbon-coated structure. The calcined product was reacted with an aqueous solution of K₂PdCl₄ at 40 °C with stirring for 12 h to obtain an encapsulated catalyst. The specific composition is shown in Table 1.

[0097] Example 3

[0098] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. Nickel acetate was added, and the mixture was stirred for 2 h. The mixture was then filtered and dried to obtain a solid product. The solid product was mixed with chitin and calcined at 700 °C for 2 h under a nitrogen atmosphere to obtain a calcined product with a carbon-coated structure. The calcined product was reacted with an aqueous solution of K₂PdCl₄ at 80 °C with stirring for 2 h to obtain an encapsulated catalyst. The specific composition is shown in Table 1.

[0099] Example 4

[0100] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. Nickel acetate was added, and the mixture was stirred for 2 h. The mixture was then filtered and dried to obtain a solid product. The solid product was mixed with glucose and then calcined at 800 °C for 2 h under a nitrogen atmosphere to obtain a calcined product with a carbon-coated structure. The calcined product was reacted with an aqueous solution of K₂PdCl₄ at 25 °C with stirring for 4 h to obtain an encapsulated catalyst. The specific composition is shown in Table 1.

[0101] Example 5

[0102] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. Nickel acetate was added, and the mixture was stirred for 2 h. The mixture was then filtered and dried to obtain a solid product. The solid product was mixed with cellulose and calcined at 800 °C for 2 h under a nitrogen atmosphere to obtain a calcined product with a carbon-coated structure. The calcined product was reacted with an aqueous solution of K₂PdCl₄ at 25 °C with stirring for 4 h to obtain an encapsulated catalyst. The specific composition is shown in Table 1.

[0103] Example 6

[0104] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. Ferrous acetate was added, and the mixture was stirred for 2 h. The mixture was then filtered and dried to obtain a solid product. The solid product was mixed with 0.5 g of cellulose and calcined at 800 °C for 2 h under a nitrogen atmosphere to obtain a calcined product with a carbon-coated structure. The calcined product was reacted with an aqueous solution of K₂PdCl₄ at 25 °C with stirring for 4 h to obtain an encapsulated catalyst. The specific composition is shown in Table 1.

[0105] Example 7

[0106] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. Cobalt acetate was added, and the mixture was stirred for 2 h, filtered, and dried to obtain a solid product. The solid product was mixed with chitin and then calcined at 800 °C for 2 h under a nitrogen atmosphere to obtain a calcined product with a carbon-coated structure. The calcined product was reacted with an aqueous solution of K₂PdCl₄ at 25 °C with stirring for 4 h to obtain an encapsulated catalyst. The specific composition is shown in Table 1.

[0107] Example 8

[0108] The method of Example 1 was followed, except that an equal mass of nickel chloride was added to obtain an encapsulated catalyst, the specific composition of which is shown in Table 1.

[0109] Comparative Example 1

[0110] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. K₂PdCl₄ aqueous solution was added, and the mixture was stirred for 2 h, filtered, and dried to obtain a solid product. The solid product was mixed with chitin and then calcined at 800 °C for 2 h under a nitrogen atmosphere to obtain an encapsulated catalyst.

[0111] Comparative Example 2

[0112] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. Nickel acetate was added, and the mixture was stirred for 2 h, filtered, and dried to obtain a solid product. The solid product was mixed with chitin and then calcined at 800 °C for 2 h under a nitrogen atmosphere to obtain an encapsulated catalyst.

[0113] Comparative Example 3

[0114] In a 100 mL round-bottom flask, 60 mL of ethanol, 6 mL of deionized water, and 2 mL of ammonia were added. After stirring at room temperature for 30 min, 3 mL of tetraethyl orthosilicate was added dropwise, and the mixture was stirred for 2 h to obtain a mixture containing 0.8 g of silica microspheres. Nickel acetate and K₂PdCl₄ aqueous solution were added, and the mixture was stirred for 2 h. The mixture was then filtered and dried to obtain a solid product. The solid product was calcined at 400 °C for 2 h under a hydrogen atmosphere to obtain a catalyst.

[0115] Table 1

[0116]

[0117] Test Example 1

[0118] 500 mg of the catalyst prepared in the examples and comparative examples, 1000 mg of NBR, and 80 mL of acetone were added to a 500 mL stainless steel autoclave. The autoclave was then purged three times with hydrogen (i.e., the air inside the autoclave was replaced with hydrogen to purge it). The pressure was increased to 2 MPa and the autoclave was sealed. The reaction temperature was 120 °C, and the autoclave was mechanically stirred for selective hydrogenation for 10 h. After the reaction was stopped, the residual hydrogen in the autoclave was removed, and the reaction solution was taken out. The heterogeneous catalyst and reaction solution were separated by centrifugation. The reaction solution was analyzed by infrared spectroscopy and nuclear magnetic resonance. The results are shown in Table 2.

[0119] Table 2

[0120] Example 1 96 100 Example 2 88 100 Example 3 85 100 Example 4 86 100 Example 5 87 100 Example 6 81 100 Example 7 82 100 Example 8 80 100 Comparative Example 1 24 100 Comparative Example 2 10 100 Comparative Example 3 52 100

[0121] Test Example 2

[0122] This test is used to illustrate the cycle stability of the encapsulated catalyst of this invention.

[0123] 500 mg of the catalyst from Example 1 (after reaction in Test Example 1), washed and dried at 60°C (labeled as Catalyst-2), 1000 mg of NBR, and 80 mL of acetone were added to a 500 mL stainless steel autoclave. The autoclave was then purged with hydrogen three times, followed by purging to 2 MPa and sealing. The reaction was carried out at 120°C with mechanical stirring for selective hydrogenation for 10 hours. After the reaction was stopped, the residual hydrogen in the autoclave was released, and the reaction solution was removed. The heterogeneous catalyst and reaction solution were separated by centrifugation. The reaction solution was analyzed by infrared spectroscopy and nuclear magnetic resonance. The calculated conversion rate of NBR was 86%, and the selectivity of HNBR was 100%. The catalyst obtained after centrifugation, washing at 60°C, and drying (labeled catalyst-3) was used in the next reaction, and the calculated conversion rate of NBR was 81%, and the selectivity of HNBR was 100%. The catalyst obtained after centrifugation, washing at 60°C, and drying (labeled catalyst-4) was used in the next reaction, and the calculated conversion rate of NBR was 77%, and the selectivity of HNBR was 100%. The catalyst obtained after centrifugation, washing at 60°C, and drying (labeled catalyst-5) was used in the next reaction, and the calculated conversion rate of NBR was 70%, and the selectivity of HNBR was 100%.

[0124] Test Example 3

[0125] 500 mg of catalyst from Comparative Example 3 (after reaction in Test Example 1), washed and dried at 60°C (labeled Catalyst-2), 1000 mg of NBR, and 80 mL of acetone were added to a 500 mL stainless steel autoclave. The autoclave was then purged with hydrogen three times, followed by purging to 2 MPa and sealing. The reaction was carried out at 120°C with mechanical stirring for selective hydrogenation for 10 h. After stopping the reaction, the residual hydrogen in the autoclave was removed, and the reaction solution was taken out. The heterogeneous catalyst and reaction solution were separated by centrifugation. The reaction solution was analyzed by infrared spectroscopy and nuclear magnetic resonance, and the calculated conversion rate of NBR was 6%, and the selectivity of HNBR was 100%. Further, the centrifuged, washed, and dried catalyst at 100°C (labeled Catalyst-3) was used in the next reaction, and the calculated conversion rate of NBR was 7%, and the selectivity of HNBR was 100%.

[0126] The test results show that when the encapsulated catalyst of the present invention is used to catalyze the hydrogenation of NBR to prepare HNBR, the conversion rate of NBR can reach up to 96%, and the selectivity of HNBR is greater than 99%. This indicates that the encapsulated catalyst of the present invention can prevent direct contact between the nitrile groups and the active sites in HNBR, while inhibiting the loss of active components in the catalyst, thereby improving the activity of the catalyst.

[0127] Moreover, the encapsulated catalyst provided by this invention can be regenerated and reused multiple times, up to 5 times, which greatly improves cycle stability and service life. In contrast, the catalyst with the non-encapsulated structure (without carbon coating) prepared in Comparative Example 3 is easily deactivated, and its cycle stability is greatly reduced. Even after regeneration, its activity cannot be restored, thus proving the importance of the encapsulation structure.

[0128] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An encapsulated catalyst, characterized in that, The catalyst contains a silica support, inexpensive metal elements, precious metal elements, and a carbon coating layer that encapsulates the silica support, inexpensive metal elements, and precious metal elements. Based on the total weight of the catalyst, the content of silica support is 75-90% by weight, the content of inexpensive metal elements is 5-15% by weight, the content of precious metal elements is 0.5-5% by weight, and the content of carbon is 3-10% by weight. The method for preparing the encapsulated catalyst includes the following steps: (1) Introduce a cheap metal precursor into silica to obtain a solid product; (2) The solid product obtained in step (1) is mixed with a carbon source and then calcined under a protective gas atmosphere to obtain a calcined product with a carbon layer coating structure; wherein the carbon source is a biomass compound. (3) The calcined product obtained in step (2) is reacted with a noble metal precursor to obtain an encapsulated catalyst.

2. The catalyst according to claim 1, wherein, Based on the total weight of the catalyst, the content of silica support is 75-85% by weight, the content of inexpensive metal elements is 5-12% by weight, the content of precious metal elements is 0.5-3% by weight, and the content of carbon is 5-10% by weight.

3. The catalyst according to claim 1, wherein, The weight ratio of the inexpensive metal element to the precious metal element is 4-30:

1.

4. The catalyst according to claim 3, wherein, The weight ratio of the inexpensive metal element to the precious metal element is 5-20:

1.

5. The catalyst according to any one of claims 1-4, wherein, The inexpensive and precious metal elements are present between the silica support and the carbon coating layer, and the catalyst has a sandwich-type coating structure.

6. The catalyst according to any one of claims 1-4, wherein, The carbon coating layer is a nitrogen-doped carbon coating layer; Based on the total weight of the catalyst, the nitrogen content is 0.5-2% by weight.

7. The catalyst according to any one of claims 1-4, wherein, The average particle size of inexpensive metal particles is 1-50 nm; The average particle size of the noble metal particles is 1-10 nm.

8. The catalyst according to claim 7, wherein, The average particle size of inexpensive metal particles is 10-30 nm. The average particle size of the noble metal particles is 1-5 nm.

9. The catalyst according to any one of claims 1-4, wherein, The low-cost metal is selected from at least one of Group IVB, VIB and VIII metal elements; The precious metal is selected from at least one of Pt, Pd and Ru.

10. The catalyst according to claim 9, wherein, The inexpensive metal is selected from at least one of Fe, Co, and Ni; The precious metal is Pd.

11. A method for preparing an encapsulated catalyst, the method comprising the following steps: (1) Introduce a cheap metal precursor into silica to obtain a solid product; (2) The solid product obtained in step (1) is mixed with a carbon source and then calcined under a protective gas atmosphere to obtain a calcined product with a carbon layer coating structure; wherein the carbon source is a biomass compound. (3) The calcined product obtained in step (2) is reacted with a noble metal precursor to obtain an encapsulated catalyst.

12. The method according to claim 11, wherein, The amounts of silica, carbon source, inexpensive metal precursor, and noble metal precursor used in the prepared encapsulated catalyst are such that, based on the total weight of the catalyst, the silica support content is 75-90% by weight, the inexpensive metal element content is 5-15% by weight, the noble metal element content is 0.5-5% by weight, and the carbon content is 3-10% by weight.

13. The method according to claim 12, wherein, The amounts of silica, carbon source, inexpensive metal precursor, and noble metal precursor used in the prepared encapsulated catalyst are such that, based on the total weight of the catalyst, the silica support content is 75-85% by weight, the inexpensive metal element content is 5-12% by weight, the noble metal element content is 0.5-3% by weight, and the carbon content is 5-10% by weight.

14. The method according to claim 11, wherein, The ratio of the inexpensive metal precursor to the noble metal precursor is such that the weight ratio of the inexpensive metal element to the noble metal element in the prepared encapsulated catalyst is 4-30:

1.

15. The method according to claim 14, wherein, The ratio of the inexpensive metal precursor to the noble metal precursor is such that the weight ratio of the inexpensive metal element to the noble metal element in the prepared encapsulated catalyst is 5-20:

1.

16. The method according to claim 11, wherein, Step (1) includes: mixing ethanol, ammonia, water and silicon source to obtain a mixture containing silica microspheres, and then introducing a low-cost metal precursor; The average particle size of the silica microspheres is 300-400 nm. And / or, the average pore size of the silica microspheres is 5-30 nm.

17. The method according to claim 16, wherein, The mass ratio of the ethanol, ammonia, water and silicon source is 50:(0.1-10):(5-10):(1-10).

18. The method according to claim 17, wherein, The mass ratio of the ethanol, ammonia, water and silicon source is 50:(0.5-4.5):(5-8):(2-5).

19. The method according to claim 11, wherein, The inexpensive metal is selected from at least one of the group IVB, VIB and VIII metal elements.

20. The method according to claim 19, wherein, The inexpensive metal is selected from at least one of Fe, Co, and Ni.

21. The method according to any one of claims 11-20, wherein, The carbon source is selected from at least one of glucose, cellulose and chitin.

22. The method according to claim 21, wherein, The carbon source is chitin.

23. The method according to any one of claims 11-20, wherein, The roasting conditions in step (2) include: a temperature of 500-900℃ and a time of 1-6.

24. The method according to claim 23, wherein, The roasting conditions in step (2) include: a temperature of 600-800℃ and a time of 2-4h.

25. The method according to any one of claims 11-20, wherein, The precious metal is selected from at least one of Pt, Pd and Ru.

26. The method of claim 25, wherein, The precious metal is Pd.

27. The method according to any one of claims 11-20, wherein, The reaction conditions in step (3) include: temperature of 10-100℃ and time of 1-24h.

28. The method according to claim 27, wherein, The reaction conditions in step (3) include: temperature of 20-80℃ and time of 2-12h.

29. The application of an encapsulated catalyst according to any one of claims 1-10 or an encapsulated catalyst prepared by any one of claims 11-28 in the selective hydrogenation reaction of nitrile rubber.

30. A method for selective hydrogenation of nitrile rubber, characterized in that, The method includes: reacting nitrile rubber, hydrogen, and an encapsulated bimetallic catalyst in the presence of a solvent, wherein the encapsulated bimetallic catalyst is the encapsulated catalyst according to any one of claims 1-10 or the encapsulated catalyst prepared by the preparation method according to any one of claims 11-28.

31. The method according to claim 30, wherein, The conditions for selective hydrogenation of the nitrile rubber include: a temperature of 60-150℃ and a reaction pressure of 1-5MPa; The amount of catalyst used is 20-60 parts by weight relative to 100 parts by weight of nitrile rubber.

32. The method according to claim 31, wherein, The conditions for selective hydrogenation of the nitrile rubber include: a temperature of 80-130℃ and a reaction pressure of 2-4 MPa; The amount of the catalyst is 40-50 parts by weight relative to 100 parts by weight of nitrile rubber.

33. The method according to claim 30, wherein, The solvent is selected from at least one of isopropanol, ethanol, acetonitrile, toluene, dichloromethane, ethyl acetate, N,N-dimethylformamide, acetone, N-methylpyrrolidone, and cyclohexanone.

34. The method according to claim 33, wherein, The solvent is acetone and / or ethanol.

35. The method according to claim 30, wherein, The amount of solvent used is 10-100 parts by weight relative to 1 part by weight of nitrile rubber.

36. The method according to claim 35, wherein, The amount of solvent used is 60-90 parts by weight relative to 1 part by weight of nitrile rubber.

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