Amino-modified copper-silicon catalysts, methods for their preparation and use

Abstract

This invention provides an amino-modified copper-silicon catalyst, its preparation method, and its application, belonging to the field of catalyst technology. The copper oxide particles in the copper-silicon catalyst provided by this invention have a small particle size and high dispersibility on the silica surface, which can significantly improve the catalytic activity of the copper-silicon catalyst, thereby improving the selectivity of ethanol in the hydrogenation of diethyl oxalate. Example results show that, at 180℃ and a hydrogen-to-ester ratio of 25, the copper-silicon catalyst provided by this invention achieves a diethyl oxalate conversion rate of 96.66% and an ethanol selectivity of 84.72% for diethyl oxalate. Furthermore, after 270 hours of stable reaction, the diethyl oxalate conversion rate still reaches 94.7%, and the ethanol selectivity still reaches 66.29%, indicating that the copper-silicon catalyst does not show significant deactivation.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to an amino-modified copper-silicon catalyst, its preparation method, and its application. Background Technology

[0002] Ethanol, as a key basic organic chemical raw material, solvent and clean energy, has applications in the fields of medicine, food, chemical industry and energy. Its traditional production route is mainly based on petroleum and is achieved through the ethylene hydration method. However, this route has significant economic bottlenecks. Petroleum is a non-renewable resource with limited global reserves and high costs, making it difficult to meet the needs of industrial upgrading and green development.

[0003] Diethyl oxalate (DEO) hydrogenation, as a typical non-petroleum route, enables the efficient conversion of resources such as coal, providing a feasible alternative to petroleum-based ethanol production. In the DEO hydrogenation process, catalysts effectively activate hydrogen molecules and ester functional groups, lowering the activation energy and precisely controlling the reaction pathway to suppress side reactions, thereby improving DEO conversion and ethanol selectivity. Currently, diethyl oxalate hydrogenation catalysts are mainly divided into noble metal catalysts and copper-based catalysts. While noble metal catalysts have high activity, they are expensive and prone to over-hydrogenation; while copper-based catalysts are low-cost, they generally suffer from low ethanol selectivity. For example, a copper-silicon catalyst modified with a tertiary amine silane coupling agent only achieved a maximum ethanol selectivity of 2.8% in the ester hydrogenation reaction. Summary of the Invention

[0004] The purpose of this invention is to provide an amino-modified copper-silicon catalyst, its preparation method, and its application. The copper-silicon catalyst provided by this invention exhibits good selectivity for ethanol in the hydrogenation of diethyl oxalate.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: An amino-modified copper-silicon catalyst comprises mesoporous silica and copper oxide supported on the surface of the mesoporous silica; the copper oxide has a particle size of 2-4 nm. The specific surface area of ​​the copper-silicon catalyst is 259.40~371.87 m². 2 / g; the average pore volume of the copper-silicon catalyst is 0.27~0.43cm³. 3 / g; the average pore size of the copper-silicon catalyst is 4.18~4.35nm; The copper-silicon catalyst contains 13.18 to 42.23 wt% copper oxide.

[0006] This invention also provides a method for preparing the copper-silicon catalyst described in the above technical solution, comprising the following steps: Modified mesoporous silica is obtained by mixing mesoporous silica with an aminosilane coupling agent and an organic solvent. The modified mesoporous silica was mixed with copper salt, water and ammonia water, and then subjected to ammonia stripping and water removal in sequence to obtain the precursor. The precursor was calcined to obtain a copper-silicon catalyst.

[0007] Preferably, the mass ratio of the mesoporous silica to the aminosilane coupling agent is 1:(2.25~3).

[0008] Preferably, the aminosilane coupling agent includes 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, or γ-ureopropyltriethoxysilane.

[0009] Preferably, the modification temperature is 90~105℃, and the modification time is 12~24h.

[0010] Preferably, the mass ratio of the modified mesoporous silica to the copper ions in the copper salt is 100:(10~46).

[0011] Preferably, the copper salt comprises copper nitrate or copper acetate.

[0012] Preferably, the temperature for ammonia stripping is 80~100℃, and the time for ammonia stripping is 1~2h.

[0013] Preferably, the roasting temperature is 450~550℃ and the roasting time is 4~6h.

[0014] The present invention also provides the application of the copper-silicon catalyst described in the above technical solution or the copper-silicon catalyst prepared by the preparation method described in the above technical solution in the hydrogenation of diethyl oxalate.

[0015] This invention provides an amino-modified copper-silicon catalyst, comprising mesoporous silica and copper oxide supported on the surface of the mesoporous silica; the copper oxide has a particle size of 2-4 nm; and the copper-silicon catalyst has an average pore volume of 0.27-0.43 cm³. 3 / g; the average pore size of the copper-silicon catalyst is 4.18~4.35nm; the mass fraction of copper in the copper-silicon catalyst is 13.18~42.23wt%. The copper oxide particles in the copper-silicon catalyst provided by this invention have small size and high dispersibility on the silica surface, which can significantly improve the catalytic activity of the copper-silicon catalyst, thereby improving the selectivity of ethanol in the hydrogenation of diethyl oxalate. Example results show that, at 180℃ and a hydrogen-to-ester ratio of 25, the copper-silicon catalyst provided by this invention can achieve a diethyl oxalate conversion rate of 96.66% and an ethanol selectivity of 84.72% for diethyl oxalate. Furthermore, after 270h of stable reaction, the diethyl oxalate conversion rate still reaches 94.6%, and the ethanol selectivity still reaches 66.38%, indicating that the copper-silicon catalyst did not show significant deactivation. Attached Figure Description

[0016] Figure 1 TEM images of the copper-silicon catalysts in Example 1 and Comparative Example 1; Figure 2 Infrared absorption spectra of copper-silicon catalyst precursors in Examples 1 and 2 and Comparative Examples 1 and 2; Figure 3 The N2 adsorption isotherms of the copper-silicon catalysts in Example 1 and Comparative Example 1 are shown below. Figure 4 The pore size distribution diagrams are for the copper-silicon catalysts of Example 1 and Comparative Example 1. Figure 5 The diagram shows the catalytic performance of the copper-silicon catalysts in Example 1 and Comparative Example 1. Figure 6 The graphs show the catalytic performance of the copper-silicon catalysts in Example 2 and Comparative Example 2. Figure 7 The images show the XRD patterns of copper-silicon catalysts after reduction in Examples 1 and 2 and Comparative Examples 1 and 2. Figure 8 The chromatogram of the product synthesized by hydrogenation of diethyl oxalate using a copper-silicon catalyst in Example 1 is shown. Detailed Implementation

[0017] This invention provides an amino-modified copper-silicon catalyst, comprising mesoporous silica and copper oxide supported on the surface of the mesoporous silica; the copper oxide has a particle size of 2-4 nm; The specific surface area of ​​the copper-silicon catalyst is 259.40~371.87 m². 2 / g; the average pore volume of the copper-silicon catalyst is 0.27~0.43cm³. 3 / g; the average pore size of the copper-silicon catalyst is 4.18~4.35nm; The copper-silicon catalyst contains 13.18 to 42.23 wt% copper oxide.

[0018] The copper-silicon catalyst provided by this invention comprises mesoporous silica. By employing mesoporous silica as a support, this invention leverages its high specific surface area and well-defined mesoporous channels to achieve a high degree of dispersion of the copper active component. Simultaneously, the pore confinement effect inhibits copper particle sintering, enhances mass transfer between reactants and products, thereby improving the catalyst's catalytic activity, ethanol selectivity, and operational stability. In one embodiment of this invention, the specific surface area of ​​the mesoporous silica can be 254~289 m². 2 / g, the pore volume of the mesoporous silica can be 0.3~0.5cm. 3 / g, wherein the pore size of the mesoporous silica can be 4~6nm.

[0019] As one embodiment of the present invention, the method for preparing the mesoporous silica can be as follows: A mesoporous silica precursor was obtained by mixing polyoxypropylene-polyoxyethylene copolymer, tetraethyl orthosilicate, hydrochloric acid and water and carrying out a hydrothermal reaction. The mesoporous silica precursor was calcined to obtain mesoporous silica.

[0020] As one embodiment of the present invention, polyoxypropylene-polyoxyethylene copolymer, tetraethyl orthosilicate, hydrochloric acid and water can be mixed and subjected to a hydrothermal reaction to obtain a mesoporous silica precursor.

[0021] In one embodiment of the present invention, the mass fraction of HCl in the hydrochloric acid can be 37%.

[0022] In one embodiment of the present invention, the molar ratio of tetraethyl orthosilicate: polyoxypropylene-polyoxyethylene copolymer: HCl in hydrochloric acid: water can be 1:(0.016~0.018):(5.6~6.0):(130~150), or 1:0.017:5.88:136. The present invention does not impose any particular limitation on the mixing of the polyoxypropylene-polyoxyethylene copolymer, tetraethyl orthosilicate, hydrochloric acid, and water; any mixing method well known in the art can be used.

[0023] In one embodiment of the present invention, the temperature of the hydrothermal reaction can be 80~160℃ or 100~120℃; the time of the hydrothermal reaction can be 8~48h, 10~36h or 12~24h.

[0024] In one embodiment of the present invention, after the hydrothermal reaction is completed, the product of the hydrothermal reaction can be subjected to solid-liquid separation, washing, and drying sequentially to obtain a mesoporous silica precursor. The present invention does not have a specific limitation on the solid-liquid separation; any solid-liquid separation method well-known in the art can be used to separate the solid and liquid to obtain a solid. In one embodiment of the present invention, the washing can be performed by washing the solid obtained from the solid-liquid separation with deionized water and ethanol sequentially; the number of times the deionized water is washed can be 3 to 6 times, and the number of times the ethanol is washed can be 1 to 3 times. The present invention does not have a specific limitation on the drying; any drying method well-known in the art can be used to remove water and ethanol from the washed product.

[0025] In one embodiment of the present invention, after obtaining the mesoporous silica precursor, the mesoporous silica precursor can be calcined to obtain mesoporous silica. In one embodiment of the present invention, the calcination temperature can be 450~550℃, the calcination heating rate can be 2℃ / min, and the calcination time can be 5~8h or 6~7h.

[0026] The copper-silicon catalyst provided by the present invention further includes copper oxide supported on the surface of the mesoporous silica.

[0027] In one embodiment of the present invention, the particle size of the copper oxide can be 2-4 nm or 2.5-3.5 nm. The present invention ensures that the copper oxide has a small particle size, a large specific surface area, faster diffusion of reactants and products, a more uniform concentration distribution within the pores, higher catalytic efficiency for the hydrogenation of diethyl oxalate, and better selectivity for ethanol by limiting the particle size of the copper oxide.

[0028] In one embodiment of the present invention, the mass fraction of copper oxide in the copper-silicon catalyst can be 13.18~42.23 wt%, 20~40 wt%, or 25~35 wt%. The present invention ensures sufficient active sites and high catalytic activity during the hydrogenation catalysis of diethyl oxalate by limiting the copper loading in the copper-silicon catalyst.

[0029] In one embodiment of the present invention, the particle size of the copper-silicon catalyst can be 40-60 mesh.

[0030] The copper oxide in the copper-silicon catalyst provided by this invention has a small particle size and high dispersibility on the surface of silica, which can significantly improve the catalytic activity of the copper-silicon catalyst and thus improve the selectivity of ethanol in the hydrogenation of diethyl oxalate.

[0031] This invention also provides a method for preparing the copper-silicon catalyst described in the above technical solution, comprising the following steps: Modified mesoporous silica is obtained by mixing mesoporous silica with an aminosilane coupling agent and an organic solvent. The modified mesoporous silica was mixed with copper salt, water and ammonia water, and then subjected to ammonia stripping and water removal in sequence to obtain the precursor. The precursor was calcined to obtain a copper-silicon catalyst.

[0032] This invention modifies mesoporous silica by mixing it with an aminosilane coupling agent and an organic solvent to obtain modified mesoporous silica.

[0033] In one embodiment of the present invention, the aminosilane coupling agent may include 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, or γ-ureopropyltriethoxysilane. The present invention modifies a silica support by using a specific aminosilane coupling agent. The silanol generated by the hydrolysis of the aminosilane coupling agent reacts with a large number of hydroxyl groups (isolated hydroxyl, ortho-hydroxyl, bridging hydroxyl) present on the silica support surface to generate Si-O-Si, which is then grafted onto the silica surface. This exposes the terminal amino groups on the silica support surface, allowing them to coordinate with copper ions in the subsequent copper-ammonia complex formed by the copper salt and ammonia water, forming stable coordination bonds. This results in a high dispersion of copper on the silica support surface, while simultaneously reducing the particle size of copper, improving the catalytic activity of the copper-silicon catalyst, and thus enhancing the selectivity of ethanol in the hydrogenation of diethyl oxalate.

[0034] In one embodiment of the present invention, the mass ratio of the mesoporous silica to the aminosilane coupling agent can be 1:(2.25~3) or 1:(2.5~2.75). The present invention ensures that the aminosilane coupling agent reacts more fully with the hydroxyl groups in the mesoporous silica by limiting the mass ratio of the mesoporous silica to the aminosilane coupling agent.

[0035] In one embodiment of the present invention, the organic solvent may be toluene. In another embodiment of the present invention, the mass ratio of the mesoporous silica to the organic solvent may be 1:(15~40). The present invention ensures more complete dissolution of the mesoporous silica and the aminosilane coupling agent by limiting the mass ratio of the mesoporous silica to the organic solvent.

[0036] The present invention does not have any particular limitation on the mixing of the mesoporous silica with the aminosilane coupling agent and the organic solvent; any mixing method well known in the art can be used.

[0037] In one embodiment of the present invention, during the modification process, the silanol generated by the hydrolysis of the aminosilane coupling agent reacts with a large number of hydroxyl groups (isolated hydroxyl groups, ortho-hydroxyl groups, and bridging hydroxyl groups) present on the surface of the mesoporous silica support to generate Si-O-Si, which is then grafted onto the surface of the mesoporous silica. In another embodiment of the present invention, the modification temperature can be 90~105℃ or 95~100℃; the modification time can be 12~24h or 15~20h. The present invention limits the modification temperature and time to ensure that the aminosilane coupling agent reacts more fully with the hydroxyl groups in the mesoporous silica.

[0038] As one embodiment of the present invention, after the modification is completed, the modified product can be subjected to solid-liquid separation, washing and drying in sequence to obtain modified mesoporous silica.

[0039] This invention does not impose any particular limitation on the solid-liquid separation; any solid-liquid separation method well-known in the art can be used to separate the solid and liquid to obtain a solid. In one embodiment of this invention, the washing may involve washing the solid obtained from the solid-liquid separation sequentially with toluene and ethanol; the toluene washing may be performed 1-2 times, and the ethanol washing may be performed 2-3 times. This invention does not impose any particular limitation on the drying; any drying method well-known in the art can be used to remove residual solvent.

[0040] After obtaining the modified mesoporous silica, the present invention mixes the modified mesoporous silica with copper salt, water and ammonia, and then performs ammonia stripping and dehydration sequentially to obtain the precursor.

[0041] In one embodiment of the present invention, the copper salt may include copper nitrate or copper acetate. In another embodiment, the mass ratio of the modified mesoporous silica to copper ions in the copper salt is 100:(10~46), or it may be 100:(20~30). The present invention ensures effective control of the loading and dispersion state of the copper active component by limiting the molar ratio of the modified mesoporous silica to the copper ions in the copper salt, allowing copper ions to be highly dispersed on the surface of the modified mesoporous silica and form a stable anchoring structure. In another embodiment, the mass ratio of the copper salt to water may be 1:(10~40). The present invention ensures more complete dissolution of the copper salt by limiting the mass ratio of the copper salt to water.

[0042] This invention does not impose any particular limitations on the concentration and amount of ammonia added. A concentration and amount of ammonia well-known in the art can be used to ensure the pH of the solution system is 10-11. In one embodiment of this invention, the mixing of the modified mesoporous silica with copper salt, water, and ammonia can be performed by first mixing the modified mesoporous silica, copper salt, and water, and then adding ammonia for a second mixing. The second mixing is carried out under dropping conditions, and the dropping rate can be 2-5 mL / min. In another embodiment of this invention, both the first and second mixing are carried out under stirring. This invention does not impose any particular limitations on the stirring method; a stirring method well-known in the art can be used to mix the modified mesoporous silica with copper salt, water, and ammonia until homogeneous. The stirring time for the second mixing can be 0.5-3 hours.

[0043] In one embodiment of the present invention, during the ammonia stripping process, a copper-ammonia complex is formed by the copper salt and ammonia water. Then, the copper ions in the copper-ammonia complex coordinate with the amino groups on the surface of the modified mesoporous silica, forming stable coordinate bonds. In another embodiment of the present invention, the ammonia stripping temperature can be 80-100°C, and the stripping time can be 1-2 hours.

[0044] In one embodiment of the present invention, the water removal can be achieved by sequentially performing solid-liquid separation and drying on the product after ammonia stripping to obtain the precursor. The present invention does not impose any particular limitation on the solid-liquid separation and drying; any method well-known in the art can be used to remove the water.

[0045] After obtaining the precursor, the present invention calcines the precursor to obtain a copper-silicon catalyst.

[0046] In one embodiment of the present invention, during the calcination process, the framework of the aminosilane coupling agent in the dehydrated product is removed, copper hydroxide is converted into copper oxide, organic matter and impurities in the product are removed, the mesoporous silica framework structure is stabilized, and the copper-silica interaction is enhanced while controlling the dispersion and particle size of copper oxide. In another embodiment of the present invention, the calcination temperature can be 450~550℃, and the calcination time can be 4~6 hours. The present invention ensures sufficient stabilization of the mesoporous silica framework structure by limiting the calcination temperature and time, while simultaneously enhancing the copper-silica interaction and controlling the dispersion and particle size of copper oxide.

[0047] In one embodiment of the present invention, the particle size of the copper-silicon catalyst can be 40-60 mesh. When the particle size of the copper-silicon catalyst is not within the above range, the present invention can crush and sieve the copper-silicon catalyst.

[0048] This invention uses an aminosilane coupling agent to modify a silica support. The silanol generated by the hydrolysis of the aminosilane coupling agent reacts with a large number of hydroxyl groups (isolated hydroxyl, ortho-hydroxyl, and bridging hydroxyl) on the surface of the silica support to generate Si-O-Si, which is then grafted onto the silica surface, exposing the terminal amino groups on the silica support surface. Then, through the coordination of copper ions in the copper-ammonia complex generated by ammonia stripping and copper salt and ammonia water, stable coordination bonds are formed, making it highly dispersed on the silica support surface. Finally, calcination further stabilizes the mesoporous silica framework structure, while enhancing the copper-silica interaction and regulating the dispersion and particle size of copper oxide, thereby improving the selectivity of ethanol in the hydrogenation of diethyl oxalate.

[0049] The present invention also provides the application of the copper-silicon catalyst described in the above technical solution or the copper-silicon catalyst prepared by the preparation method described in the above technical solution in the hydrogenation of diethyl oxalate.

[0050] As one embodiment of the present invention, the method of applying the copper-silicon catalyst in the hydrogenation of diethyl oxalate may include: The copper-silicon catalyst is pretreated, and then diethyl oxalate and hydrogen are introduced to carry out a hydrogenation reaction to obtain ethanol; the pretreatment includes: mixing the copper-silicon catalyst with H2 and then carrying out a reduction reaction.

[0051] The present invention does not impose any special limitations on the mixing of the copper-silicon catalyst and H2; the copper-silicon catalyst and H2 can be mixed using a mixing method well known in the art.

[0052] In one embodiment of the present invention, the reduction temperature can be 170~300℃, and the reduction time can be 3~6 hours. After the reduction reaction is completed, the product of the reduction reaction can be cooled to the hydrogenation reaction temperature.

[0053] In one embodiment of the present invention, the pressure of the hydrogenation reaction can be 2~2.5 MPa, the temperature of the hydrogenation reaction can be 180~240°C, the hydrogen-ester ratio of the hydrogenation reaction can be 20~100, and the space velocity of the hydrogenation reaction can be 0.5~1.0 h⁻¹. -1 .

[0054] The copper-silicon catalyst provided by this invention, when applied to the hydrogenation of diethyl oxalate, results in a high conversion rate of diethyl oxalate and good selectivity for ethanol.

[0055] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0056] Example 1 An amino-modified copper-silicon catalyst is composed of mesoporous silica and copper oxide supported on the surface of the mesoporous silica; the copper oxide has a particle size of 2-4 nm. The specific surface area of ​​the copper-silicon catalyst is 288.56 m². 2 / g; the average pore volume of the copper-silicon catalyst is 0.30 cm³. 3 / g; the average pore size of the copper-silicon catalyst is 4.27nm; The copper-silicon catalyst has a copper oxide loading of 34.71 wt%.

[0057] The preparation method of the above copper-silicon catalyst is as follows: 360g of deionized water and 12g of polyoxypropylene-polyoxyethylene copolymer (P123) were added sequentially to a beaker and stirred at 35°C until a clear, transparent solution was formed. Then, 72g of 37% hydrochloric acid was added, and stirring continued for 20 minutes to ensure homogeneity. The mixture was then stirred at 300 rpm, and 25.5g of tetraethyl orthosilicate (TEOS) was added at a rate of 1 mL / min. The mixture was stirred at 35°C for 24 hours to obtain a white suspension. The white suspension was then transferred to… In a hydrothermal reactor, crystallization was carried out at 100℃ for 24 hours, followed by natural cooling to room temperature. The product in the reactor was washed three times by centrifugation with deionized water and ethanol solution, and then dried in an oven at 90℃ for 6 hours to obtain a white powder. The powder was then placed in a muffle furnace and heated to 550℃ at a rate of 1℃ / min, held for 6 hours, and then naturally cooled to room temperature to obtain mesoporous silica. The molar ratio of tetraethyl orthosilicate:polyoxypropylene-polyoxyethylene copolymer:HCl in hydrochloric acid:water was 2.125:1:2.22:30. 6 g of mesoporous silica was mixed with 15 mL of 3-aminopropyltriethoxysilane and 185 mL of toluene, and refluxed at 100 °C for 18 h to obtain amino-modified mesoporous silica; the mass ratio of the mesoporous silica to the aminosilane coupling agent was 1:2.375; the mass ratio of the mesoporous silica to toluene was 1:30. Take 5g of modified mesoporous silica and add it to 300mL of aqueous solution containing 8.14g Cu(NO3)2·3H2O under stirring. Add ammonia water dropwise at a rate of 3mL / min until pH=11. After stirring for 12h, transfer it to a 90℃ water bath and heat for 1h until pH=7. Centrifuge to obtain precipitate, dry at 110℃ for 6h, and then calcine in a muffle furnace at 450℃ for 4h to obtain copper-silicon catalyst. The mass ratio of the modified mesoporous silica to copper ions in the copper salt is 100:40.24; the mass ratio of Cu(NO3)2·3H2O to water is 1:36.85.

[0058] Example 2 The difference between this embodiment and Example 1 is that the amount of Cu(NO3)2·3H2O is replaced from 8.14g to 4.75g; the mass ratio of the amino-modified mesoporous silica to the copper ions in the copper salt is 100:24.8; the mass ratio of Cu(NO3)2·3H2O to water is 1:25; the rest is the same as in Example 1, and a copper-silicon catalyst is obtained; the copper oxide loading in the copper-silicon catalyst is 23.72wt%; the particle size of the copper oxide is 2~4nm. The specific surface area of ​​the copper-silicon catalyst is 317.84 m². 2 / g; the average pore volume of the copper-silicon catalyst is 0.37 cm³. 3 / g; the average pore size of the copper-silicon catalyst is 4.46nm.

[0059] Example 3 The difference between this embodiment and Example 1 is that 3-aminopropyltriethoxysilane is replaced with γ-ureopropyltriethoxysilane, the amount of Cu(NO3)2·3H2O is changed from 8.14g to 8.67g, the mass ratio of the modified mesoporous silica to copper ions in the copper salt is 100:45.2, and the mass ratio of Cu(NO3)2·3H2O to water is 1:15; the rest is the same as in Example 1, resulting in a copper-silicon catalyst; the particle size of the copper oxide is 3~5nm; and the specific surface area of ​​the copper-silicon catalyst is 259.40m². 2 / g; the average pore volume of the copper-silicon catalyst is 0.28 cm³. 3 / g; the average pore size of the copper-silicon catalyst is 4.18nm; the copper oxide loading in the copper-silicon catalyst is 39.78wt%.

[0060] Example 4 The difference between this embodiment and Example 1 is that 3-aminopropyltriethoxysilane is replaced with 3-aminopropyltrimethoxysilane, the amount of Cu(NO3)2·3H2O is replaced from 8.14g to 2.32g, the mass ratio of the modified mesoporous silica to copper ions in the copper salt is 100:12, and the mass ratio of Cu(NO3)2·3H2O to water is 1:15; the rest is the same as in Example 1, resulting in a copper-silicon catalyst; the particle size of the copper oxide is 2~3nm; and the specific surface area of ​​the copper-silicon catalyst is 286.69m². 2 / g; the average pore volume of the copper-silicon catalyst is 0.4319 cm³. 3 / g; the average pore size of the copper-silicon catalyst is 4.35nm; the mass fraction of copper oxide in the copper-silicon catalyst is 13.18wt%.

[0061] Comparative Example 1 The difference between this comparative example and Example 1 is that the step of mixing mesoporous silica with 3-aminopropyltriethoxysilane and toluene and refluxing at 100°C for 18 hours to obtain modified mesoporous silica is omitted; the rest is the same as in Example 1. A copper-silicon catalyst is obtained; the particle size of the copper oxide is 4-5 nm; and the specific surface area of ​​the copper-silicon catalyst is 281.16 m². 2 / g; the average pore volume of the copper-silicon catalyst is 0.32 cm³. 3 / g; the average pore size of the copper-silicon catalyst is 4.35nm; the mass fraction of copper oxide in the copper-silicon catalyst is 34.71wt%.

[0062] Comparative Example 2 The difference between this comparative example and Example 2 is that the step of mixing mesoporous silica with 3-aminopropyltriethoxysilane and toluene and refluxing at 100°C for 18 hours to obtain modified mesoporous silica is omitted; the rest is the same as in Example 1. A copper-silicon catalyst is obtained; the particle size of the copper oxide is 3.5~4.5 nm; the specific surface area of ​​the copper-silicon catalyst is 371.89 m². 2 / g; the average pore volume of the copper-silicon catalyst is 0.45 cm³. 3 / g; the average pore size of the copper-silicon catalyst is 4.54nm; the mass fraction of copper oxide in the copper-silicon catalyst is 23.72wt%.

[0063] The steps for evaluating reaction performance are as follows: The copper-silicon catalysts prepared in Examples 1-4 and Comparative Examples 1-2 were crushed and sieved to obtain copper-silicon catalyst particles of 40-60 mesh for later use. Test 1: 2g of 40-60 mesh copper-silicon catalyst particles obtained in Examples 1-4 and Comparative Examples 1-2 were respectively loaded into a stainless steel reactor along with quartz sand. H2 was introduced and the reactor was reduced in situ at 300°C for 4 hours. After the reactor temperature was lowered, diethyl oxalate and H2 were introduced. Then, the reactor was subjected to a reaction at a pressure of 2.0 MPa, a reaction temperature of 180°C, a hydrogen-to-ester ratio of 50, a catalyst loading of 1.20g, and a reaction space velocity of 0.50 h⁻¹. -1 Under the reaction conditions, hydrogenation of diethyl oxalate was carried out, and the reaction results are shown in Table 1. Test 2: The difference between this test and Test 1 is that 2g of 40-60 mesh copper-silicon catalyst particles obtained in Examples 1-4 were used; the reaction temperature was changed from 180℃ to 190℃, 210℃, 220℃ and 240℃ respectively, and the reaction results are shown in Table 1. Test 3: The difference between this test and Test 1 is that 2g of 40-60 mesh copper-silicon catalyst particles obtained in Examples 1-4 were taken; the hydrogen-ester ratio was replaced by 25, 40, and 100 respectively, and the reaction was carried out. The reaction results are shown in Table 1. Test 4: The difference between this test and Test 1 is that 2g of 40-60 mesh copper-silicon catalyst particles obtained from Example 1 and Comparative Examples 1-2 were taken; the reaction temperature was changed from 180℃ to 240℃ and the hydrogen-ester ratio was changed from 50 to 100, and the reaction was carried out. The reaction results are shown in Table 1. Table 1. Catalytic performance of copper-silicon catalysts prepared in Examples 1-4 and Comparative Examples 1-2

[0064] As shown in Table 1, the copper-silicon catalysts of Examples 1-4 of this invention, at a reaction temperature of 180℃ and a hydrogen-to-ester ratio of 50, catalyzed the hydrogenation of diethyl oxalate, achieving a diethyl oxalate conversion rate of 95.48-99.64% and an ethanol selectivity of 80.95-82.03%. In contrast, the copper-silicon catalysts of Comparative Examples 1-2, at the same reaction temperature of 180℃ and a hydrogen-to-ester ratio of 50, achieved a diethyl oxalate conversion rate of 82.71-83.81% and an ethanol selectivity of 60.32-65.47%. Therefore, Examples 1-4 of this invention exhibit highly efficient catalytic hydrogenation performance, achieving high ethanol selectivity and high catalytic stability under mild conditions of 180℃ and a hydrogen-to-ester ratio of 50. In Example 1 of this invention, the copper-silicon catalyst was used to catalyze the hydrogenation of diethyl oxalate at hydrogen-to-ester ratios of 25, 40, and 100. It was found that the conversion rate of diethyl oxalate and the selectivity of ethanol did not change significantly with the increase of the hydrogen-to-ester ratio, indicating that the catalyst has good catalytic performance at a low hydrogen-to-ester ratio. In the present invention, the copper-silicon catalysts of Examples 1, 1, and 2 were used to catalyze the hydrogenation of diethyl oxalate at a reaction temperature of 240°C and a hydrogen-to-ester ratio of 100. It was found that the copper-silicon catalyst of Example 1, at a reaction temperature of 240°C and a hydrogen-to-ester ratio of 100, exhibited higher diethyl oxalate conversion and ethanol selectivity than those of Comparative Examples 1 and 2.

[0065] The copper oxide in the copper-silicon catalysts of Example 1 and Comparative Example 1 was characterized using transmission electron microscopy, and the results are as follows: Figure 1 As shown in the figure, the copper oxide particle size in the copper-silicon catalyst of Example 1 is between 2 and 4 nm; while the copper oxide particle size in the copper-silicon catalyst of Comparative Example 1 is between 3 and 6 nm. The copper oxide particle size in the copper-silicon catalyst of Example 1 of this invention is smaller and the dispersion is better.

[0066] The structures of the copper-silicon catalyst precursors in Examples 1 and 2 and Comparative Examples 1 and 2 were characterized using infrared spectroscopy, and the results are as follows: Figure 2As shown in the figure. It can be seen from the figure that there is no 673cm in Examples 1 and 2. -1 The absorption peak at the point indicates that the amino group was successfully bound to the surface of the silicon-based support, thus preventing the formation of copper silicate.

[0067] The N2 adsorption and desorption of the copper-silicon catalysts in Example 1 and Comparative Example 1 were tested using a Micrometrics ASAP 2420 physical adsorption analyzer. The results are as follows: Figure 3 As shown in the figure, the N2 adsorption and desorption curves of the copper-silicon catalysts in Example 1 and Comparative Example 1 are approximately the same. And according to... Figure 3 The data calculation yielded an aperture distribution map, such as... Figure 4 As shown in the figure, the pore size distribution of the copper-silicon catalysts in Example 1 and Comparative Example 1 is approximately the same, indicating that the pore size distribution of the catalyst prepared by modifying mesoporous silica with an aminosilane coupling agent in Example 1 of this invention has not changed.

[0068] A fixed-bed tubular flow reactor was used to test the copper-silicon catalysts of Example 1 and Comparative Example 1 at a pressure of 2.0 MPa, a reaction temperature of 180 °C, a hydrogen-to-ester ratio of 100, and a reaction space velocity of 0.50 h⁻¹. -1 Under the reaction conditions, hydrogenation of diethyl oxalate was carried out, and the results were as follows: Figure 5 As shown in the figure, in Example 1, with the copper-silicon catalyst at a reaction temperature of 180℃ and a hydrogen-to-ester ratio of 100, the diethyl oxalate conversion rate was almost 100%, the ethanol selectivity was >80%, and the reaction was stable for 276 h without significant deactivation. In contrast, under the same conditions, the diethyl oxalate conversion rate of the copper-silicon catalyst in Comparative Example 1 decreased to 42.3% after 108 h, and the ethanol selectivity decreased to 67.73% after 100 h, indicating poor stability.

[0069] A fixed-bed tubular flow reactor was used to test the copper-silicon catalysts of Example 2 and Comparative Example 2 at a pressure of 2.0 MPa, a reaction temperature of 180 °C, a hydrogen-to-ester ratio of 100, and a reaction space velocity of 0.50 h⁻¹. -1 Under the reaction conditions, hydrogenation of diethyl oxalate was carried out, and the results were as follows: Figure 6 As shown in the figure, in Example 2, with the copper-silicon catalyst at a reaction temperature of 180℃ and a hydrogen-to-ester ratio of 100, the diethyl oxalate conversion rate was almost 100%, the ethanol selectivity was >80%, and the reaction was stable for 96 h without significant deactivation. In contrast, under the same conditions, the diethyl oxalate conversion rate of the copper-silicon catalyst in Comparative Example 2 decreased from 86.84% to 41.73% after 96 h, and the ethanol selectivity decreased from 59.65% to 39.18% after 96 h, indicating poor stability.

[0070] The phases after reduction of copper-silicon catalysts in Examples 1 and 2 and Comparative Examples 1 and 2 were characterized using X-ray diffraction, and the results are as follows: Figure 7As shown in the figure, a characteristic peak of Cu₂O (111) at 36.4° and characteristic peaks of metallic Cu at 43.3° (111) and 50.4° (200) are observed. The peak positions remain consistent after amine modification, indicating that no significant metal agglomeration has occurred, while the relatively weak and broad peak shape suggests that the copper species has high dispersibility.

[0071] The product synthesized by hydrogenation of diethyl oxalate using the copper-silicon catalyst in Example 1 was detected by gas chromatography, and the results are as follows: Figure 8 As shown in the figure, the product of the hydrogenation synthesis of diethyl oxalate is mostly ethanol, with only a very small amount of ethylene glycol. Ethyl glycolate and diethyl oxalate were not detected.

[0072] In summary, the copper-silicon catalyst provided by this invention, when applied to the hydrogenation of diethyl oxalate, can achieve high diethyl oxalate conversion and high ethanol selectivity at low temperature and low hydrogen-to-ester ratio.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An amino-modified copper-silicon catalyst, comprising mesoporous silica and copper oxide supported on the surface of the mesoporous silica; wherein the copper oxide has a particle size of 2-4 nm; The specific surface area of the copper-silicon catalyst is 259.40-371.87 m 2 / g; the average pore volume of the copper-silicon catalyst is 0.27-0.43 cm 3 / g; and the average pore diameter of the copper-silicon catalyst is 4.18-4.35 nm. The copper-silicon catalyst contains 13.18 to 42.23 wt% copper oxide.

2. The method for preparing the copper-silicon catalyst according to claim 1, comprising the following steps: Modified mesoporous silica is obtained by mixing mesoporous silica with an aminosilane coupling agent and an organic solvent. The modified mesoporous silica was mixed with copper salt, water and ammonia water, and then subjected to ammonia stripping and water removal in sequence to obtain the precursor. The precursor was calcined to obtain a copper-silicon catalyst.

3. The production method according to claim 2, characterized by, The mass ratio of the mesoporous silica to the aminosilane coupling agent is 1:(2.25~3).

4. The production method according to claim 2 or 3, characterized by, The aminosilane coupling agent includes 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, or γ-ureopropyltriethoxysilane.

5. The preparation method according to claim 2, characterized in that, The modification temperature is 90~105℃, and the modification time is 12~24h.

6. The preparation method according to claim 2, characterized in that, The mass ratio of the modified mesoporous silica to the copper ions in the copper salt is 100:(10~46).

7. The preparation method according to claim 2 or 6, characterized in that, The copper salt includes copper nitrate trihydrate or copper acetate.

8. The preparation method according to claim 2, characterized in that, The ammonia stripping temperature is 80~100℃, and the ammonia stripping time is 1~2h.

9. The preparation method according to claim 2, characterized in that, The roasting temperature is 450~550℃, and the roasting time is 4~6h.

10. The application of the copper-silicon catalyst of claim 1 or the copper-silicon catalyst prepared by any one of claims 2 to 9 in the hydrogenation of diethyl oxalate.

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