A copper-based catalyst, its preparation method, and its application in ester hydrogenation.

Abstract

This invention discloses a multi-layer core-shell catalyst prepared through a multi-step controllable process of "induction-assembly-coating," comprising a hollow carbon sphere core, a copper-silicon composite as the intermediate phase, and a carbon-nitrogen-silicon-oxygen hybrid armor layer, as well as its preparation method and applications. The catalyst's microscopic particles have hollow carbon sphere diameters of 0.8 µm to 1.2 µm, copper-silicon composite layer thicknesses of 80 nm to 200 nm, and carbon-nitrogen-silicon-oxygen hybrid armor layer thicknesses of 1 nm to 5 nm. The catalyst contains 21.6% to 35.6% Cu by mass, 3.1% to 6.9% C by mass, 0.3% to 0.9% N by mass, 0.5% to 1.3% alkaline earth metals by mass, with the remainder being SiO2. The catalyst exhibits a hierarchical pore distribution and a specific surface area of ​​160 m². 2 / g~245 m 2 / g, pore volume 0.31 cm 3 / g~0.42 cm 3 The catalyst exhibits a pore size distribution in two ranges: 2 nm to 5 nm and 30 nm to 80 nm. This structure effectively inhibits the sintering, carbon deposition, and loss of active species of the active components, thereby improving the activity and selectivity of ester hydrogenation while extending the catalyst's lifespan.

Description

Technical Field

[0001] This invention belongs to the field of ester hydrogenation catalyst preparation, specifically relating to a multi-layer core-shell structure catalyst with a hollow carbon sphere core, a copper-silicon composite as the intermediate phase, and a carbon-nitrogen-silicon-oxygen hybrid armor layer, as well as its preparation method and application. Background Technology

[0002] The core of ester hydrogenation is the reduction of the carbonyl group in the ester molecule by hydrogen gas under the action of a catalyst, producing the corresponding alcohol. The general reaction formula is as follows: R-COO-R' + 2H2 → R-CH2OH + R'-OH R and R' represent alkyl groups or hydrogen atoms. Depending on their differences, reactions can be classified into different types.

[0003] Ester hydrogenation is a core bridge connecting basic raw materials and high-value products. It is not only applicable to the current large-scale production of bulk chemicals, but also has received widespread attention as one of the key technologies for future green chemistry and carbon circular economy (Table 1).

[0004] Table 1 Common types of industrial reactions for ester hydrogenation reaction type Examples of main reactants Target product Major industrial application areas Oxalate hydrogenation Dimethyl oxalate (DMO) Ethylene glycol (EG) Coal / syngas to ethylene glycol Methyl glycolate (MG) Fine chemical intermediates Hydrogenation of fatty acid esters Methyl stearate, oils Long-chain fatty alcohols Surfactants, lubricants, cosmetics Acetate hydrogenation Methyl acetate ethanol Coal / syngas to ethanol Carbonate hydrogenation Ethylene carbonate Methanol, ethylene glycol Indirect conversion and utilization of carbon dioxide Hydrogenation of bio-oil-derived esters Esters in the light components of bio-oil Alcohol ester fuels Biomass energy upgrading Hydrogenation of acetylacetate Ethyl levulinate γ-Valactone (GVL) Biomass platform molecular transformation Take the hydrogenation of dimethyl oxalate to ethylene glycol as an example. Ethylene glycol (EG), a basic chemical raw material with a global production capacity of over 40 million tons, is the core monomer of the polyester industry chain. Its downstream derivatives cover three major pillar areas: polyester fiber accounts for 82% of the synthetic fiber market, PET packaging materials have an annual demand growth rate of over 6%, and automotive antifreeze accounts for 90% of the global market share. With the explosive growth of the new energy industry, the demand for EG in lithium battery electrolyte solvents, such as in the synthesis of ethylene carbonate and polyester separator coatings, is further increasing, driving my country's consumption to grow at an average annual rate of 4.5%.

[0005] Dimethyl oxalate (DMO) hydrogenation, as a key step in the coal-based route, has become a core technology in my country's "coal-to-oil" strategy due to its wide adaptability of raw materials, low carbon emission intensity (30% lower than the petroleum route), and other advantages. Copper-based catalysts are widely used in DMO hydrogenation due to their high ester hydrogenation activity. Previous patents have reported copper-based catalysts supported on different supports such as SiO2, Al2O3, and molecular sieves (CN119175096A, CN113797931B, CN101411990B, CN118304893A). Among them, the SiO2-supported Cu-based catalyst exhibits excellent performance in DMO hydrogenation due to its suitable surface properties and specific Cu species states, becoming a typical catalyst for current industrial applications (Applied Catalysis A: General, 2013, 468: 296-304, Journal of Catalysis, 2022, 407: 241-252).

[0006] However, copper-based catalysts supported on SiO2 still face serious deactivation problems when used for ester hydrogenation. First, the operating temperature of ester hydrogenation is typically above 200 °C, and the highly exothermic nature of hydrogenation results in even higher temperatures at the catalyst's active sites, far exceeding the Hüttig temperature of metallic copper (approximately 134 °C). This makes it highly susceptible to the aggregation and growth of metallic CuO, leading to catalyst deactivation. Second, the diffusion restriction of the catalyst channels and the presence of acidic sites on the surface prevent the generated alcohols from rapidly diffusing out of the channels, easily leading to the formation of polymers such as polyethers, polyesters, and long-chain alkanes. This exacerbates carbon deposition and further deactivates the catalyst. Third, SiO2 reacts with the reaction product alcohol to form alkoxysilanes, causing the loss of Si species. This not only leads to the migration and aggregation of active components but also results in a decrease in overall strength, severe catalyst pulverization, increased bed pressure drop, and ultimately irreversible catalyst deactivation (Applied Surface Science, 2025, 701: 163248, Applied Catalysis A: General, 2016, 509:66-74, Chemical Communications, 2013, 49(45): 5195-5197). In summary, inhibiting the sintering and aggregation of metallic CuO and reducing carbon deposition and Si species loss are key to improving catalyst stability and extending service life; however, existing literature has not provided an effective solution. Summary of the Invention

[0007] The purpose of this invention is to provide a multi-layer core-shell structure catalyst (“hollow carbon@copper silicon@carbon nitrogen-silicon oxygen hybrid armor layer” catalyst) with a hollow carbon sphere as the core, a copper-silicon composite as the intermediate phase, and a carbon-nitrogen-silicon-oxygen hybrid armor layer as the coating, as well as its preparation method and application, which effectively solves the problems of easy coking and deactivation of existing copper-based catalysts and loss of silicon species in the reaction of ester hydrogenation to the corresponding alcohol.

[0008] To address the aforementioned problems, according to one aspect of the present invention, a multilayer core-shell structure catalyst is provided, consisting of hollow carbon spheres as the core, a copper-silicon composite as the mesophase, and an outer layer of carbon-nitrogen-silicon-oxygen hybrid armor. The catalyst's microparticles have hollow carbon spheres with a diameter of 0.8 µm to 1.2 µm, a copper-silicon composite layer thickness of 80 nm to 200 nm, and a carbon-nitrogen-silicon-oxygen hybrid armor layer thickness of 1 nm to 5 nm. The catalyst contains 21.6% to 35.6% Cu by mass, 3.1% to 6.9% C by mass, 0.3% to 0.9% N by mass, 0.5% to 1.3% alkaline earth metals by mass, with the remainder being SiO2. The catalyst's texture parameters were obtained based on N2 physical adsorption data. Figure 3 As shown in Table 7, the catalyst exhibits a hierarchical pore distribution with a specific surface area of ​​160 m². 2 / g~245 m 2 / g, pore volume 0.31 cm 3 / g~ 0.42 cm 3 The catalyst exhibits a pore size distribution in two ranges: 2 nm to 5 nm and 30 nm to 80 nm. After compression, the catalyst forms a columnar shape with dimensions of 3 mm to 5 mm in height and 3 mm to 5 mm in diameter, and a radial strength >300 N. This structure effectively inhibits sintering, carbon deposition, and loss of active species. It effectively improves the activity and selectivity of ester hydrogenation while extending the catalyst's lifespan.

[0009] According to another aspect of the present invention, a method for preparing a multilayer core-shell structure catalyst with a hollow carbon sphere as the core, a copper-silicon composite as the intermediate phase, and an outer layer of carbon-nitrogen-silicon-oxygen hybrid armor is provided, comprising: Step 1: Under N2 protection, methyl methacrylate (MMA) was added to a certain amount of methanol-water mixed solvent to prepare an MMA-methanol-water mixed solution. The temperature was raised to 65℃~75℃, and potassium persulfate (KPS) was added. After polymerization for 5 h~10 h, a methacryloyloxyethyltrimethylammonium chloride (DMC) solution was added at a uniform rate, with the addition time controlled at 45 min~75 min. After the addition was completed, the reaction continued for 1 h~2 h. Subsequently, the mixture was rapidly cooled with ice water, and the precipitate phase was obtained by centrifugation and washing. After drying, PMMA-DMC microspheres were obtained.

[0010] Step 2: Under strong stirring, dissolve an appropriate amount of copper nitrate trihydrate in an appropriate amount of deionized water, add ammonia water, and stir thoroughly to form a copper ammonia solution.

[0011] Step 3: Take a certain amount of PMMA-DMC microspheres, add them to the silica sol, mix them thoroughly, and then add them to the copper ammonia solution prepared in Step 2. Stir thoroughly and heat to 65 ℃~105 ℃, and treat with ammonia stripping for 10 h~28 h.

[0012] Step 4: After ammonia stripping, the mixture is centrifuged, the precipitate is washed with distilled water, and dried at 80 ℃~150 ℃ for 10 h~24 h to obtain the copper-silicon composite precursor.

[0013] Step 5: Take an appropriate amount of the copper-silicon composite precursor prepared in Step 4 and mix it evenly with an appropriate amount of amino acids, silane coupling agents, alcohols, adhesives, and alkaline earth metal oxides. Under an inert atmosphere, microwave-assisted carbonize at 250 ℃~550 ℃ for 3 h~6 h to obtain catalyst powder.

[0014] Step 6: Add carbon fiber, graphite powder, and graphene to the catalyst powder obtained in step 5, mix evenly, and then compress into tablets.

[0015] Step 7: The tableted catalyst obtained in Step 6 is loaded into an atmosphere furnace, and H2 / Ar mixed gas is introduced to raise the temperature and reduce it to obtain the final C@copper silicon@carbon nitrogen-silicon oxygen hybrid armor layer catalyst.

[0016] In step one, the MMA-methanol-water mixture is prepared with an MMA mass concentration of 25 g / L to 35 g / L.

[0017] In step one, the volume ratio of methanol to water is 1.5:1 to 4:1, preferably 2:1 to 3:1.

[0018] In step one, the concentration of KPS in the MMA-methanol-water mixed solution is 0.2 g / L to 0.35 g / L.

[0019] In step one, the amount of DMC added is 2.8 wt% to 3.2 wt% of the mass of MMA.

[0020] In step one, the concentration of the added methacryloyloxyethyltrimethylammonium chloride (DMC) solution is 2.5 g / L to 3.1 g / L.

[0021] In step two, the amount of copper nitrate trihydrate used is calculated as 82 g to 120 g of copper nitrate trihydrate added to 1 L of deionized water.

[0022] In step two, the concentration of ammonia water used is 26%~28%, and the amount of ammonia water used is calculated as 0.25 L~0.5 L of ammonia water added to 1 L of deionized water.

[0023] In step three, the SiO2 concentration in the silica sol used is 28%~30%, and the amount of silica sol used is calculated as 180 g~240 g of silica sol added to 1L of deionized water in step two.

[0024] In step three, the mass of the PMMA-DMC microspheres used is calculated as 3% to 8% of the mass of the silica sol.

[0025] In step three, the preferred ammonia stripping temperature is 75 ℃ to 95 ℃.

[0026] In step four, the preferred drying conditions are drying at 110 ℃ to 130 ℃ for 10 h to 14 h.

[0027] In step five, the mass fractions of amino acids, silane coupling agents, alcohols, adhesives, and alkaline earth metal oxides in the catalyst powder are 1%~10%, 1%~5%, 1%~5%, 1%~5%, and 1%~3%, respectively. The amino acid is at least one of tryptophan, serine, and glutamic acid; the silane coupling agent is at least one of γ-aminopropyltriethoxysilane, N-trimethylsilane, and γ-glycidoxypropyltrimethoxysilane; the alcohol is at least one of ethanol, n-propanol, and n-butanol; the adhesive is at least one of epoxy resin adhesives, acrylate adhesives, and polyurethane adhesives; and the alkaline earth metal oxide is one or both of MgO and CaO. The inert atmosphere is one of N2, He, and Ar.

[0028] In step six, carbon fiber, graphite powder, and graphene account for 0.1%~0.3%, 1%~3%, and 0.1%~0.2% of the mass fraction of the catalyst powder, respectively. After tableting, the catalyst is columnar with a height × diameter of 3mm × 3mm, 4mm × 4mm, or 5mm × 5mm.

[0029] In step seven, the volume fraction of H2 in the H2 / Ar mixture is 0.5%~10%, the reduction temperature is 200 ℃~450 ℃, and the time is 1 h~12 h, preferably 3 h~8 h.

[0030] According to one aspect of the present invention, a multilayer core-shell structure catalyst is provided, consisting of a hollow carbon sphere as the core, a copper-silicon composite as the mesophase, and a carbon-nitrogen-silicon-oxygen hybrid armor layer. This catalyst is suitable for the hydrogenation of dimethyl oxalate to ethylene glycol in a fixed-bed reactor at a reaction temperature of 150 °C–220 °C, a reaction pressure of 1.5 MPa–2.6 MPa, a hydrogen to dimethyl oxalate molar ratio of 50–200, and a dimethyl oxalate liquid hourly space velocity of 0.5 h⁻¹.-1 ~0.76 h -1 Dimethyl oxalate single-pass conversion rate ≥99.9%, ethylene glycol selectivity ≥97.3%.

[0031] According to one aspect of the present invention, a multilayer core-shell structure catalyst is provided, consisting of a hollow carbon sphere as the core, a copper-silicon composite as the intermediate phase, and a carbon-nitrogen-silicon-oxygen hybrid armor layer. This catalyst is also applicable to the hydrogenation of other esters to corresponding alcohols, such as the hydrogenation of methyl stearate and oils to long-chain fatty alcohols, the hydrogenation of methyl acetate to ethanol, and the hydrogenation of ethylene carbonate to methanol and ethylene glycol.

[0032] This invention utilizes a multi-step, controllable process of "induction-assembly-coating" to construct a unique multi-layered core-shell catalyst with a hollow carbon sphere core, a copper-silicon composite as the intermediate phase, and a carbon-nitrogen-silicon-oxygen hybrid armor layer. First, a positively charged PMMA@DMC micron-sized template is prepared. Then, through electrostatic interaction, a negatively charged copper-silicon composite is uniformly deposited on its surface, forming a highly dispersed copper-silicon composite layer. Finally, under microwave assistance, an ultrathin, chemically bonded carbon-nitrogen-silicon-oxygen hybrid armor layer is constructed in situ by carbonizing a catalyst precursor incorporating amino acids and silane coupling agents. Compared with existing catalysts, this invention offers the following advantages: (1) The PMMA-DMC template undergoes melting and pyrolysis during carbonization, which leads to the enrichment of carbon species inside the copper-silicon composite layer, thus forming hollow carbon spheres with their outer edges tightly bonded to the copper-silicon composite layer. The internal cavity can buffer the thermal stress caused by temperature changes during the reaction, thereby significantly improving the mechanical stability and structural thermal stability of the catalyst.

[0033] (2) During carbonization, hydrocarbons generated by the pyrolysis of the PMMA-DMC template escape outward along the mesoporous structure of the copper-silicon composite layer and deposit in the mesoporous structure of the copper-silicon composite layer to form a carbon layer. Step 5 introduces appropriate amounts of amino acids, silane coupling agents, alcohols, adhesives, etc. into the prepared copper-silicon composite precursor. These substances form a carbon-nitrogen-silicon-oxygen hybrid armor layer on the outer surface of the copper-silicon composite layer during carbonization. Through the action of these two modification layers, a hydrophobic surface is constructed, enabling the catalyst to form a good gas-liquid-solid three-phase contact interface. The special hydrophobic structure creates a local microenvironment with a high concentration of hydrogen around the active site by selectively adsorbing and enriching hydrogen molecules in the reaction system. A high-concentration hydrogen atmosphere is formed around the active Cu site, which directly improves the chemical adsorption and dissociation rate of H2 on the Cu surface. This solves the problem that ester groups on the catalyst surface are easily adsorbed, but the adsorbed hydrogen concentration is insufficient. This effectively matches the concentrations of ester and hydrogen molecules on the catalyst surface, improving the hydrogenation activity.

[0034] (3) The ammonia stripping process and the addition of the template agent result in a pore structure of 2 nm to 5 nm in the copper-silicon composite layer. Micron-sized primary particles accumulate during the molding process to form a larger pore structure of 30 nm to 80 nm. The emergence of the hierarchical pore structure not only maintains high intrinsic activity but also greatly enhances the mass transfer efficiency of the reaction system and indirectly inhibits catalyst deactivation, thus achieving a dual breakthrough in activity and stability. The 2 nm to 5 nm mesopores provide a high specific surface area to load a large number of active sites, ensuring high initial activity. The uniformly distributed mesopores ensure the high dispersion of active centers, maximizing the exposure of the active interface. On the other hand, the ability of reactants to quickly reach internal active sites and the ability of products to leave in a timely manner are key factors in determining the overall apparent activity and selectivity. The interconnected macropores of 30 nm to 80 nm inside this catalyst act as "highways" to ensure that reactants and products can enter and exit quickly. This not only makes the catalyst exhibit high hydrogenation activity, but more importantly, it effectively eliminates the problems of insufficient utilization of internal active sites and aggravated side reactions caused by micropore diffusion limitations in traditional catalysts. It fundamentally reduces the formation of high molecular weight carbon deposits caused by side reactions such as polymerization and dehydration due to the failure of intermediates such as alcohols and aldehydes to desorb in time, thus significantly improving the service life of the catalyst.

[0035] (4) The introduction of alkaline earth metals Mg / Ca, along with the carbon layer and the encapsulating carbon-nitrogen-silicon-oxygen hybrid armor layer, forms a multi-layered chemical protection mechanism, stabilizing the catalyst support structure. The first layer of protection, Mg... 2+ / Ca 2+ Through strong electrostatic interactions, it combines with the silanol groups (Si-OH) in the SiO2 network to form stable Mg. 2+ -O-Si bond or Ca 2+ -O-Si bonds significantly reduce the rate of alcoholysis reaction with alcohol products to generate volatile alkoxysilanes. Simultaneously, the in-situ generated carbon layer and the encapsulating carbon-nitrogen-silicon-oxygen hybrid armor layer act as a nanoscale "armor," not only physically preventing direct contact between the reaction medium and the core Cu-SiO2, but also further suppressing the loss of silicon species from the catalyst due to their stable Si-OC and Si-NC covalent networks. The combined effect of these two aspects significantly inhibits the dissolution and collapse of the support framework, solving the catalyst deactivation caused by the loss of Si species. The second layer of protection, Mg... 2+ / Ca 2+Furthermore, the introduction of an N-containing armor layer reduces the acidic sites on the catalyst surface, inhibiting the polymerization of esters, alcohols, and other reactive molecules caused by the presence of acidic sites, thus solving the activity decline caused by carbon accumulation on the catalyst surface. The third layer of protection, based on the increased interaction between alkaline earth metal Mg / Ca modified SiO2 and Cu, and the spatial confinement effect of the carbon layer and the encapsulating carbon-nitrogen-silicon-oxygen hybrid armor layer, inhibits the migration and aggregation of Cu species, solving the problem of irreversible catalyst deactivation caused by the aggregation of active components during long-term operation. These three layers of protection significantly improve the catalyst's lifespan.

[0036] Due to its multiple structural advantages, the catalyst exhibits excellent activity, selectivity and lifetime in the hydrogenation of dimethyl oxalate. Attached Figure Description

[0037] Figure 1 High-resolution electron microscope images of samples at different preparation stages; Figure 2 The image shows the XRD pattern of the catalyst. Figure 3 The N2 adsorption-desorption isotherm (left) and pore size distribution diagram (right) of the catalyst. Detailed Implementation

[0038] The present invention will be further described below with reference to embodiments. The following embodiments are only used to illustrate the performance of the present invention more clearly, and should not be limited to the embodiments described below.

[0039] Example 1: According to the data in Table 2, under N2 protection, 1 L of methanol-water mixed solvent with a volume ratio of 1.5 (methanol:water) was taken, and 25 g of MMA was added to prepare an MMA-methanol-water mixed solution with a mass concentration of 25 g / L. The temperature was raised to 65℃, and 0.2 g of KPS (KPS concentration of 0.2 g / L) was added. After polymerization for 5 h, 2.5 g / L of DMC aqueous solution (DMC added amount of 0.7 g) was added at a uniform rate over a period of 45 min. After the addition was completed, the reaction was continued for 1 h. Subsequently, the mixture was rapidly cooled with ice water, and the precipitate phase was obtained by centrifugation, washing, and drying to obtain PMMA-DMC microspheres.

[0040] Based on the data in Table 3, 120 g of copper nitrate trihydrate was added to 1 L of deionized water, dissolved, and stirred thoroughly. Then, 0.25 L of ammonia solution with a concentration of 26%-28% was added to form a copper-ammonia solution. 180 g of silica sol with a SiO2 concentration of 28%-30% was taken, and 5.4 g of PMMA-DMC microspheres were added and mixed thoroughly. The silica sol with added PMMA-DMC microspheres was added to the aforementioned copper-ammonia solution, stirred thoroughly, and heated to 65 ℃ for ammonia removal treatment for 10 h. After ammonia removal, the mixture was centrifuged, the resulting precipitate was washed with distilled water, and dried at 80 ℃ for 10 h to obtain the copper-silicon composite precursor.

[0041] Take 100 g of copper-silicon composite precursor, add 1 g of tryptophan, 1 g of γ-aminopropyltriethoxysilane, 1 g of ethanol, 1 g of epoxy resin adhesive, and 1 g of MgO. The mixed materials are then microwave-assisted carbonized at 250 ℃ for 6 h under an inert N2 atmosphere to obtain catalyst powder.

[0042] Weigh 100 g of the prepared catalyst powder, add 0.1 g of carbon fiber, 1 g of graphite powder and 0.1 g of graphene according to the specific conditions listed in Table 6, mix evenly and then compress into tablets. The catalyst tablets are columnar with a height × diameter of 3 mm × 3 mm.

[0043] Example 2: According to the data in Table 2, under N2 protection, 1 L of methanol-water mixed solvent with a volume ratio of 3:1 (methanol:water) was taken, and 30 g of MMA was added to prepare an MMA-methanol-water mixed solution with a mass concentration of 30 g / L. The temperature was raised to 72℃, and 0.25 g of KPS (KPS concentration of 0.25 g / L) was added. After 8 h of polymerization, 3 g / L of DMC aqueous solution (DMC added amount of 0.94 g) was added at a uniform rate over a period of 60 min. After the addition was completed, the reaction was continued for 2 h. Subsequently, the mixture was rapidly cooled with ice water, and the precipitate phase was obtained by centrifugation, washing, and drying to obtain PMMA-DMC microspheres.

[0044] Based on the data in Table 3, 108 g of copper nitrate trihydrate was added to 1 L of deionized water, dissolved, and stirred thoroughly. Then, 0.32 L of ammonia solution with a concentration of 26%–28% was added to form a copper-ammonia solution. 195 g of silica sol with a SiO2 concentration of 28%–30% was taken, and 7.8 g of PMMA-DMC microspheres were added and mixed thoroughly. The silica sol with added PMMA-DMC microspheres was added to the aforementioned copper-ammonia solution, stirred thoroughly, and heated to 80 °C for ammonia removal treatment for 16 h. After ammonia removal, the mixture was centrifuged, the resulting precipitate was washed with distilled water, and dried at 90 °C for 12 h to obtain the copper-silicon composite precursor.

[0045] Take 100 g of copper-silicon composite precursor, add 3 g of serine, 3 g of N-trimethylsilane, 3 g of n-propanol, 3 g of acrylate adhesive, 1 g of MgO, and 1 g of CaO. The mixed materials are then microwave-assisted carbonized at 300 °C for 5.5 h under an inert N2 atmosphere to obtain catalyst powder.

[0046] Weigh 100 g of the prepared catalyst powder, add 0.2 g of carbon fiber, 2 g of graphite powder and 0.2 g of graphene according to the specific conditions listed in Table 6, mix evenly and then compress into tablets. The catalyst tablets are columnar with a height × diameter of 4 mm × 4 mm.

[0047] Example 3: According to the data in Table 2, under N2 protection, 1 L of methanol-water mixed solvent with a volume ratio of 3.5:1 was taken, and 35 g of MMA was added to prepare an MMA-methanol-water mixed solution with a mass concentration of 35 g / L. The temperature was raised to 66℃, and 0.28 g of KPS (KPS concentration of 0.28 g / L) was added. After polymerization for 7 h, 2.9 g / L of DMC aqueous solution (DMC added amount of 0.98 g) was added at a uniform rate over a time controlled at 55 min. After the addition was completed, the reaction was continued for 1.5 h. Subsequently, the mixture was rapidly cooled with ice water, and the precipitate phase was obtained by centrifugation, washing, and drying to obtain PMMA-DMC microspheres.

[0048] Based on the data in Table 3, 100 g of copper nitrate trihydrate was added to 1 L of deionized water, dissolved, and stirred thoroughly. Then, 0.36 L of ammonia solution with a concentration of 26%–28% was added to form a copper-ammonia solution. 210 g of silica sol with a SiO2 concentration of 28%–30% was taken, and 10.5 g of PMMA-DMC microspheres were added and mixed thoroughly. The silica sol with added PMMA-DMC microspheres was added to the aforementioned copper-ammonia solution, stirred thoroughly, and heated to 90 °C for ammonia removal treatment for 20 h. After ammonia removal, the mixture was centrifuged, the resulting precipitate was washed with distilled water, and dried at 110 °C for 14 h to obtain the copper-silicon composite precursor.

[0049] Take 100 g of copper-silicon composite precursor, add 10 g of glutamic acid, 5 g of γ-glycidyl etheroxypropyltrimethoxysilane, 5 g of n-butanol, 5 g of polyurethane adhesive, and 2 g of CaO. The mixed materials are then microwave-assisted carbonized at 350 °C for 5 h under an inert He atmosphere to obtain catalyst powder.

[0050] Weigh 100 g of the prepared catalyst powder, add 0.3 g of carbon fiber, 3 g of graphite powder and 0.1 g of graphene according to the specific conditions listed in Table 6, mix evenly and then compress into tablets. The catalyst tablets are columnar with a height × diameter of 5 mm × 5 mm.

[0051] Example 4: According to the data in Table 2, under N2 protection, 1 L of methanol-water mixed solvent with a volume ratio of 2:1 (methanol:water) was taken, and 28 g of MMA was added to prepare an MMA-methanol-water mixed solution with a mass concentration of 28 g / L. The temperature was raised to 70℃, and 0.3 g of KPS (KPS concentration of 0.3 g / L) was added. After 8 h of polymerization, 2.8 g / L of DMC aqueous solution (DMC added amount of 0.9 g) was added at a uniform rate over a period of 60 min. After the addition was completed, the reaction continued for 1.5 h. Subsequently, the mixture was rapidly cooled with ice water, and the precipitate phase was obtained by centrifugation, washing, and drying to obtain PMMA-DMC microspheres.

[0052] Based on the data in Table 3, 92 g of copper nitrate trihydrate was added to 1 L of deionized water, dissolved, and stirred thoroughly. Then, 0.4 L of ammonia solution with a concentration of 26%–28% was added to form a copper-ammonia solution. 220 g of silica sol with a SiO2 concentration of 28%–30% was taken, and 13.5 g of PMMA-DMC microspheres were added and mixed thoroughly. The silica sol with added PMMA-DMC microspheres was added to the aforementioned copper-ammonia solution, stirred thoroughly, and heated to 95 °C for ammonia removal treatment for 24 h. After ammonia removal, the mixture was centrifuged, the resulting precipitate was washed with distilled water, and dried at 125 °C for 16 h to obtain the copper-silicon composite precursor.

[0053] Take 100 g of copper-silicon composite precursor, add 2 g of glutamic acid, 2 g of tryptophan, 1 g of γ-aminopropyltriethoxysilane, 2 g of n-propanol, 2 g of ethanol, 2 g of epoxy resin adhesive, and 3 g of MgO. The mixed materials are then microwave-assisted carbonized at 400 ℃ for 4 h under an inert He atmosphere to obtain catalyst powder.

[0054] Weigh 100 g of the prepared catalyst powder, add 0.1 g of carbon fiber, 3 g of graphite powder and 0.2 g of graphene according to the specific conditions listed in Table 6, mix evenly and then compress into tablets. The catalyst tablets are columnar with a height × diameter of 3 mm × 4 mm.

[0055] Example 5: According to the data in Table 2, under N2 protection, 1 L of methanol-water mixed solvent with a volume ratio of 4:1 was taken, and 32 g of MMA was added to prepare an MMA-methanol-water mixed solution with a mass concentration of 32 g / L. The temperature was raised to 75℃, and 0.35 g of KPS (KPS concentration of 0.35 g / L) was added. After polymerization for 10 h, 3.1 g / L of DMC aqueous solution (DMC added amount of 0.95 g) was added at a uniform rate over a period of 75 min. After the addition was completed, the reaction was continued for 2 h. Subsequently, the mixture was rapidly cooled with ice water, and the precipitate phase was obtained by centrifugation, washing, and drying to obtain PMMA-DMC microspheres.

[0056] Based on the data in Table 3, 88 g of copper nitrate trihydrate was added to 1 L of deionized water, dissolved, and stirred thoroughly. Then, 0.48 L of ammonia solution with a concentration of 26%–28% was added to form a copper-ammonia solution. 230 g of silica sol with a SiO2 concentration of 28%–30% was taken, and 16.1 g of PMMA-DMC microspheres were added and mixed thoroughly. The silica sol with added PMMA-DMC microspheres was added to the aforementioned copper-ammonia solution, stirred thoroughly, and heated to 100℃ for ammonia removal treatment for 26 h. After ammonia removal, the mixture was centrifuged, the resulting precipitate was washed with distilled water, and dried at 140℃ for 20 h to obtain the copper-silicon composite precursor.

[0057] Take 100 g of copper-silicon composite precursor, and add 4 g of serine, 6 g of glutamic acid, 3 g of N-trimethylsilane, 1 g of γ-aminopropyltriethoxysilane, 2 g of n-propanol, 3 g of n-butanol, 2 g of acrylate adhesive, and 2 g of CaO. The mixed materials are then microwave-assisted carbonized at 450 °C for 3.5 h under an inert Ar atmosphere to obtain catalyst powder.

[0058] Weigh 100 g of the prepared catalyst powder, add 0.3 g of carbon fiber, 1 g of graphite powder and 0.2 g of graphene according to the specific conditions listed in Table 6, mix evenly and then compress into tablets. The catalyst tablets are columnar with a height × diameter of 4 mm × 5 mm.

[0059] Example 6: According to the data in Table 2, under N2 protection, 1 L of methanol-water mixed solvent with a volume ratio of 2.5:1 was taken, and 34 g of MMA was added to prepare an MMA-methanol-water mixed solution with a mass concentration of 34 g / L. The temperature was raised to 68℃, and 0.22 g of KPS (KPS concentration of 0.22 g / L) was added. After 6 h of polymerization, 2.6 g / L of DMC aqueous solution (DMC added amount of 1.09 g) was added at a uniform rate over a period of 50 min. After the addition was completed, the reaction was continued for 1 h. Subsequently, the mixture was rapidly cooled with ice water, and the precipitate phase was obtained by centrifugation, washing, and drying to obtain PMMA-DMC microspheres.

[0060] Based on the data in Table 3, 82 g of copper nitrate trihydrate was added to 1 L of deionized water, dissolved, and stirred thoroughly. Then, 0.48 L of ammonia solution with a concentration of 26%–28% was added to form a copper-ammonia solution. 240 g of silica sol with a SiO2 concentration of 28%–30% was taken, and 19.2 g of PMMA-DMC microspheres were added and mixed thoroughly. The silica sol with added PMMA-DMC microspheres was added to the aforementioned copper-ammonia solution, stirred thoroughly, and heated to 105 °C for ammonia removal treatment for 28 h. The mixture was centrifuged, and the resulting precipitate was washed with distilled water and dried at 150 °C for 24 h to obtain the copper-silicon composite precursor.

[0061] Take 100 g of copper-silicon composite precursor, and add 2 g of tryptophan, 8 g of glutamic acid, 5 g of γ-aminopropyltriethoxysilane, 4 g of ethanol, 1 g of n-butanol, 2 g of polyurethane adhesive, 3 g of epoxy resin adhesive, 2 g of MgO, and 2 g of CaO. The mixed materials are then microwave-assisted carbonized at 550 °C for 3 h under an inert Ar atmosphere to obtain catalyst powder.

[0062] Weigh 100 g of the prepared catalyst powder, add 0.2 g of carbon fiber, 2 g of graphite powder and 0.1 g of graphene according to the specific conditions listed in Table 6, mix evenly and then compress into tablets. The catalyst tablets are columnar with a height × diameter of 5 mm × 5 mm.

[0063] Table 2 Preparation conditions of PMMA-DMC microspheres PMMA-DMC microspheres numbering V methanol : V water MMA / g KPS / g Polymerization temperature / °C Aggregation time / h DMC concentration / g / L DMC dosage / g DMC addition time / min Reaction time after DMC addition / h 1 1.5:1 25 0.20 65 5 2.5 0.70 45 1.0 2 2.0:1 28 0.30 70 8 2.8 0.9 60 1.5 3 3.0:1 30 0.25 72 8 3.0 0.94 60 2.0 4 4.0:1 32 0.35 75 10 3.1 0.95 75 2.0 5 2.5:1 34 0.22 68 6 2.6 1.09 50 1.0 6 3.5:1 35 0.28 66 7 2.9 0.98 55 1.5 Table 3. Preparation conditions of copper-silicon composite precursors Table 4 Catalyst Powder Preparation Conditions-1 Table 5 Catalyst Powder Preparation Conditions - 2 Table 6 Catalyst Forming Conditions Catalyst number 1# 2# 3# 4# 5# 6# carbon fiber mass / g 0.1 0.2 0.3 0.1 0.3 0.2 Graphite powder mass / g 1 2 3 3 1 2 Graphene mass / g 0.1 0.2 0.1 0.2 0.2 0.1 Height x Diameter / mm 3×3 4×4 5×5 3×4 4×5 5×5 High-resolution electron microscopy characterization was performed on samples from different preparation stages (e.g. Figure 1 As can be seen from step one, PMMA-DMC microspheres with a size of 0.8 µm to 1 µm were obtained. Due to the DMC modification, the surface of the microspheres carries a positive charge. Through steps two, three, and four, the negatively charged copper silicate phase grows around the surface of the PMMA-DMC microspheres based on the principle of electrostatic self-assembly, forming a copper-silicon composite layer. Then, in step five, appropriate amounts of amino acids, silane coupling agents, alcohols, adhesives, alkaline earth metal oxides, etc., are introduced to roughen the surface of the microspheres. Under an inert atmosphere, microwave-assisted carbonization at 250 ℃ to 550 ℃ for 3 h to 6 h yields catalyst powder. Due to the decomposition and carbonization of PMMA-DMC microspheres, a carbon layer is formed inside the copper-silicon composite layer, while the amino acids, silane coupling agents, alcohols, adhesives, alkaline earth metal oxides, etc. on the outside carbonize to form a carbon-nitrogen-silicon-oxygen hybrid armor layer. The resulting catalyst had a multilayer core-shell structure with hollow carbon spheres as the core, a copper-silicon composite as the intermediate phase, and a carbon-nitrogen-silicon-oxygen hybrid armor layer. The microscopic particles of the catalyst had hollow carbon spheres with a diameter of 0.8 µm to 1.2 µm, a copper-silicon composite layer thickness of 80 nm to 200 nm, and a carbon-nitrogen-silicon-oxygen hybrid armor layer thickness of 1 nm to 5 nm.

[0064] The prepared catalyst powder (sample before molding) was characterized by XRD, such as... Figure 2 As shown, only extremely diffuse characteristic peaks of copper folinic silicate were observed. XRF characterization confirmed the content of each element in the catalyst, as shown in Table 7. The mass fraction of Cu in the catalyst was 21.6%–35.6%, the mass fraction of C was 3.1%–6.9%, the mass fraction of N was 0.3%–0.9%, the mass fraction of alkaline earth metals was 0.5%–1.3%, and the remainder was SiO2. The texture parameters of the catalyst were obtained based on N2 physisorption data. Figure 3 As shown in Table 7, the catalyst exhibits a hierarchical pore distribution with a specific surface area of ​​160 m². 2 / g~245 m 2 / g, pore volume 0.31 cm 3 / g~ 0.42cm 3 / g, exhibiting two pore size distributions: 2 nm to 5 nm and 30 nm to 80 nm.

[0065] Table 7 Catalyst Composition and Physicochemical Properties Catalyst number 1# 2# 3# 4# 5# 6# Cu mass fraction / % 35.6 30.2 27.8 25.7 23.2 21.6 Alkaline earth metal mass fraction / % 0.5 0.7 0.8 1.2 0.7 1.3 C quality fraction / % 3.1 5.0 6.5 6.9 4.9 5.4 N mass fraction / % 0.3 0.5 0.9 0.8 0.6 0.4 <![CDATA[Specific surface area / m 2 / g]]> 245 231 220 182 175 160 <![CDATA[Pore volume / cm 3 / g]]> 0.31 0.35 0.36 0.39 0.41 0.42 Average pore size / nm 3.1 3.3 3.5 3.7 4.0 4.2 Performance testing: The performance of the catalyst was evaluated in a fixed-bed reactor, and the results are shown in Table 8. After the catalyst was loaded into a stainless steel fixed-bed reactor with an inner diameter of 30 mm (catalyst bed height 1000 mm), reduction was carried out in an H2 / Ar mixture with a volume fraction of 0.5%–10% H2, with the temperature increased to 200–450 °C at a rate of 0.5–5 °C / min controlled by electric heating, and the reaction was carried out for 1–12 h. The reaction temperature was then adjusted to 150–220 °C, the reaction pressure to 1.5–2.6 MPa, the molar ratio of hydrogen to dimethyl oxalate to be 50–200, and the liquid hourly space velocity (LISH) of dimethyl oxalate to be 0.5 h⁻¹. -1 ~0.76 h -1 Dimethyl oxalate single-pass conversion rate ≥99.9%, ethylene glycol selectivity ≥97.3%.

[0066] Table 8. Reduction and evaluation results of each catalyst Note: a represents the temperature range at different locations in the bed during the isothermal reduction process; b represents the temperature range at different locations in the bed during the reaction process.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a copper-based catalyst, characterized in that, Includes the following steps: Step 1: Under N2 protection, methyl methacrylate (MMA) was added to a certain amount of methanol-water mixed solvent to prepare an MMA-methanol-water mixed solution. The temperature was raised to 65℃~75℃, potassium persulfate (KPS) was added, and after polymerization for 5 h~10 h, a methacryloyloxyethyltrimethylammonium chloride (DMC) solution was added at a uniform rate, with the addition time controlled at 45 min~75 min. After the addition was completed, the reaction continued for 1 h~2 h, and then the mixture was quickly cooled with ice water. The precipitate phase was obtained by centrifugation and washing, and then dried to obtain PMMA-DMC microspheres. Step 2: Under strong stirring, dissolve an appropriate amount of copper nitrate trihydrate in an appropriate amount of deionized water, add ammonia water, and stir thoroughly to form a copper ammonia solution; Step 3: Take a certain amount of PMMA-DMC microspheres, add them to the silica sol, mix them thoroughly, and then add them to the copper ammonia solution prepared in Step 2. Stir thoroughly and heat to 65 ℃~105 ℃, and treat with ammonia stripping for 10 h~28 h. Step 4: After ammonia stripping, the mixture is centrifuged, the precipitate is washed with distilled water, and dried at 80 ℃~150 ℃ for 10 h~24 h to obtain the copper-silicon composite precursor. Step 5: Take an appropriate amount of the copper-silicon composite precursor prepared in Step 4 and mix it evenly with an appropriate amount of amino acids, silane coupling agents, alcohols, adhesives, and alkaline earth metal oxides. Under an inert atmosphere, microwave-assisted carbonize at 250 ℃~550 ℃ for 3 h~6 h to obtain catalyst powder.

2. The preparation method according to claim 1, characterized in that, In step one, the prepared MMA-methanol-water mixed solution has an MMA mass concentration of 25 g / L to 35 g / L, a methanol:water volume ratio of 1.5:1 to 4:1, preferably 2:1 to 3:1, a KPS concentration of 0.2 g / L to 0.35 g / L, a DMC addition amount of 2.8 wt% to 3.2 wt% of the MMA mass, and a DMC solution concentration of 2.5 g / L to 3.1 g / L. In step two, copper nitrate trihydrate is added at a concentration of 82 g to 120 g per L of deionized water, and the ammonia solution used has a concentration of 26% to 28%, with 0.25 L to 0.5 L added per L of deionized water. In step three, the SiO2 concentration in the silica sol used is 28%~30%, and the amount of silica sol used is 180 g~240 g of silica sol added to 1 L of deionized water used in step two. The mass of PMMA-DMC microspheres used is 3%~8% of the silica sol mass. The ammonia stripping temperature is 75 ℃~95 ℃. In step four, the drying conditions are drying at 110 ℃~130 ℃ for 10 h~14 h. h, in step five, the amino acids, silane coupling agents, alcohols, adhesives, and alkaline earth metal oxides account for 1%~10%, 1%~5%, 1%~5%, 1%~5%, and 1%~3% of the mass fraction of the catalyst powder, respectively. The amino acid is at least one of tryptophan, serine, and glutamic acid. The silane coupling agent is at least one of γ-aminopropyltriethoxysilane, N-trimethylsilane, and γ-glycidoxypropyltrimethoxysilane. The alcohol is at least one of ethanol, n-propanol, and n-butanol. The adhesive is at least one of epoxy resin adhesives, acrylate adhesives, and polyurethane adhesives. The alkaline earth metal oxide is one or two of MgO and CaO. The inert atmosphere is one of N2, He, and Ar.

3. The preparation method according to claim 1, characterized in that, It also includes the following steps: Step Six: Add carbon fiber, graphite powder, and graphene to the catalyst powder obtained in Step Five, mix evenly, and then compress into tablets; Step 7: The tableted catalyst obtained in Step 6 is loaded into an atmosphere furnace, and H2 / Ar mixed gas is introduced to raise the temperature and reduce it to obtain C@copper-silicon@carbon-nitrogen-silicon-oxygen hybrid armor layer catalyst.

4. The preparation method according to claim 1, characterized in that, In step six, the carbon fiber, graphite powder, and graphene account for 0.1%~0.3%, 1%~3%, and 0.1%~0.2% of the catalyst powder by mass, respectively. After tableting, the catalyst is columnar with a height × diameter of 3mm×3mm, 4mm×4mm, or 5mm×5mm. In step seven, the volume fraction of H2 in the H2 / Ar mixture is 0.5%~10%, the reduction temperature is 200℃~450℃, and the time is 1 h~12 h, preferably 3 h~8 h.

5. The copper-based catalyst obtained by the preparation method according to claim 1 or 2, wherein the copper-based catalyst is a multi-layer core-shell structure catalyst with hollow carbon spheres as the core, copper-silicon composite as the intermediate phase, and a carbon-nitrogen-silicon-oxygen hybrid armor layer on the outside.

6. The copper-based catalyst according to claim 5, characterized in that, The catalyst has hollow carbon spheres with a diameter of 0.8 µm to 1.2 µm, a copper-silicon composite layer thickness of 80 nm to 200 nm, and a carbon-nitrogen-silicon-oxygen hybrid armor layer thickness of 1 nm to 5 nm. The catalyst contains 21.6% to 35.6% Cu, 3.1% to 6.9% C, 0.3% to 0.9% N, 0.5% to 1.3% alkaline earth metals, and the remainder is SiO2. The catalyst exhibits a hierarchical porous distribution and a specific surface area of ​​160 m². 2 / g~245 m 2 / g, pore volume 0.31 cm 3 / g~ 0.42 cm 3 / g, exhibiting two pore size distributions: 2 nm to 5 nm and 30 nm to 80 nm.

7. The copper-based catalyst obtained by the preparation method according to claim 3 or 4, wherein the catalyst is columnar with a height × diameter of 3 mm to 5 mm × 3 mm to 5 mm and a radial strength > 300 N.

8. The use of the copper-based catalyst according to any one of claims 5-7 in the hydrogenation of dioxalate to ethylene glycol, wherein, In a fixed-bed reactor, the reaction temperature was 150 ℃~220 ℃, the reaction pressure was 1.5 MPa~2.6 MPa, the molar ratio of hydrogen to dimethyl oxalate was 50~200, and the liquid hourly space velocity of dimethyl oxalate was 0.5 h⁻¹. -1 ~0.76 h -1 .

9. The application of the copper-based catalyst according to any one of claims 5-7 in the hydrogenation of esters to the corresponding alcohols, wherein the hydrogenation of esters to the corresponding alcohols includes methyl stearate, hydrogenation of oils to long-chain fatty alcohols, hydrogenation of methyl acetate to ethanol, and hydrogenation of ethylene carbonate to methanol and ethylene glycol.

10. The copper-based catalyst obtained by the preparation method according to any one of claims 1-4 is used in the hydrogenation of esters to the corresponding alcohols, wherein the hydrogenation of esters to the corresponding alcohols includes methyl stearate, hydrogenation of oils to long-chain fatty alcohols, hydrogenation of methyl acetate to ethanol, and hydrogenation of ethylene carbonate to methanol and ethylene glycol.

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