A copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent, and a method for preparing and use thereof

Abstract

The application discloses a copper-silicon catalyst silanized by a nitrogen-containing silane coupling agent, which comprises a copper species, silica and silica silanized by a nitrogen-containing silane coupling agent; the copper species accounts for 10-30 wt.% of the weight of the copper-silicon catalyst, the silica accounts for 60-85 wt.% of the weight of the copper-silicon catalyst, and the nitrogen element in the silica silanized by the nitrogen-containing silane coupling agent accounts for 0.1-2 wt.% of the weight of the copper-silicon catalyst. The application further discloses a preparation method of the catalyst and the use of the catalyst in the preparation of ethylene glycol from dimethyl oxalate by hydrogenation. In the copper-silicon catalyst, the silicon hydroxyl groups are covered by the nitrogen-containing silane coupling agent, thereby promoting the desorption of methyl glycolate, improving the stability of the catalyst under harsh conditions, and meanwhile, the alkalinity of the catalyst is weakened, thereby inhibiting the generation of by-products. The doping of the nitrogen element in the catalyst improves the activity of the catalyst, the electron-donating effect of the nitrogen element makes the active copper species have more excellent hydrogenation activity, and the conversion rate of the catalyst is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to a gas-phase ester hydrogenation catalyst, particularly a copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent, its preparation method, and its uses. Background Technology

[0002] Ethylene glycol (EG) is a widely used essential chemical product, used as a solvent, antifreeze, and PET raw material. Compared to petroleum-derived routes, the production of EG from coal has become increasingly attractive. This process involves three steps: pressurized coal gasification to generate syngas, carbon monoxide undergoing a catalytic coupling reaction to obtain dimethyl oxalate (DMO), and the hydrogenation of DMO to produce EG. Due to abundant syngas resources, a short process flow, and low cost, this process has become one of the main development directions of my country's coal chemical industry. The hydrogenation reaction of DMO, as a key step in this process, has received widespread attention both domestically and internationally.

[0003] Copper-silicon catalysts are widely used in the hydrogenation reaction of dimethyl oxalate due to their excellent selective hydrogenation performance of carbon-oxygen double bonds. Currently, there are a series of methods for preparing copper-silicon catalysts, such as the ammonia stripping method (AE), sol-gel method, deposition-precipitation method, impregnation method, and ion exchange method. Among these, the ammonia stripping method is beneficial for the formation of layered copper silicate, promotes the high dispersion of active copper species on the silica support, and enhances the strong interaction between the metal and the support. Therefore, it has become a commonly used method for preparing copper-silicon catalysts and is applied in industrial production.

[0004] However, the catalyst still has the following problems that need to be solved. First, the silanol groups on the surface of the copper-silicon catalyst have a certain degree of basicity, and the Guerbet reaction generates byproducts containing three or four carbon atoms (also referred to as C in the following text) at the basic sites. 3,4 -OH indicates, for example, 1,2-butanediol and 1,2-propanediol. The reaction byproducts 1,2-butanediol and ethylene glycol have similar boiling points, which greatly increases the separation cost and energy consumption. Secondly, the initial hydrogenation product methyl glycolate is easily adsorbed and polymerized on the isolated silanol groups on the catalyst surface, which leads to catalyst coking and deactivation. In addition, the silanol groups on the catalyst surface may also react with the product methanol to generate tetramethoxysilane. With long-term use, the silica support of the catalyst will be gradually corroded, causing copper species to agglomerate and the catalyst to deactivate.

[0005] To address the above problems, this invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent for ester hydrogenation reaction. The copper-silicon catalyst modified by the nitrogen-containing silane coupling agent not only improves the reaction activity and stability, but also reduces the selectivity of reaction byproducts.

[0007] The first aspect of this invention provides a copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent, comprising a copper species, silica, and silica modified by silanization with a nitrogen-containing silane coupling agent; the copper species accounts for 10-30 wt.% of the weight of the copper-silicon catalyst, the silica accounts for 60-85 wt.% of the weight of the copper-silicon catalyst, and the nitrogen element in the silica modified by silanization with a nitrogen-containing silane coupling agent accounts for 0.1-2 wt.% of the weight of the copper-silicon catalyst; preferably, the nitrogen element in the silica modified by silanization with a nitrogen-containing silane coupling agent accounts for 0.5-1.7 wt.% of the weight of the copper-silicon catalyst; more preferably, the nitrogen element in the silica modified by silanization with a nitrogen-containing silane coupling agent accounts for 0.54-1.65 wt.% of the weight of the copper-silicon catalyst. All the above mass percentages are based on the silanized copper-silicon catalyst product.

[0008] Preferably, the copper species particle size in the copper-silicon catalyst is 1.5-4.5 nm, and the specific surface area of ​​the copper-silicon catalyst is 200-500 m². 2 / g, with an average pore volume of 0.4-0.9cm³. 3 / g, with an average pore size of 5-12nm.

[0009] Preferably, the nitrogen-containing silane coupling agent is selected from 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or diethylenetriaminopropyltrimethoxysilane.

[0010] A second aspect of the present invention provides a method for preparing the copper-silicon catalyst described in the first aspect of the present invention, comprising the following steps:

[0011] (1) After stirring the mixed solution of copper salt and ammonia, add silicon source and stir at room temperature to obtain the first mixed solution;

[0012] (2) Heat the first mixed solution obtained in step (1) and perform ammonia stripping until the pH value is 6-7. Then stop the ammonia stripping and obtain the second mixed solution.

[0013] (3) The second mixed solution obtained in step (2) is filtered, washed, dried, and calcined to obtain the copper-silicon catalyst obtained by the ammonia stripping method;

[0014] (4) The copper-silicon catalyst obtained in step (3) by ammonia stripping is mixed and stirred with a nitrogen-containing silane coupling agent in an organic solvent, followed by filtration and washing or centrifugation washing, and drying to obtain a copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent. Preferably, centrifugation washing is performed. The organic solvent is selected from anhydrous methanol, anhydrous ethanol, isopropanol, toluene, etc., preferably anhydrous methanol.

[0015] Preferably, in step (1), the copper salt is copper nitrate, copper acetate, or copper chloride; the silicon source is silica sol, sodium silicate solution, tetraethyl orthosilicate, or propyl orthosilicate; the silicon source is added dropwise at a rate of one drop every 1-3 seconds, and the stirring time after adding the silicon source is 0.5-24 hours. The amount of copper salt and silicon source added is determined based on the copper metal loading in the copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent, wherein the copper metal loading is preferably 20 wt.%.

[0016] Preferably, in step (2), the first mixed solution obtained in step (1) is heated to 70-90°C to evaporate ammonia.

[0017] Preferably, in step (3), the second mixed solution obtained in step (2) is first filtered and washed directly, or the second mixed solution is first cooled to room temperature and then filtered and washed. The calcination temperature is 350-450℃ and the calcination time is 4-6h.

[0018] Preferably, in step (4), the copper-silicon catalyst obtained in step (3) via ammonia stripping is mixed and stirred with a nitrogen-containing silane coupling agent in an organic solvent, heated to 70-100°C, and refluxed and stirred for 4-8 hours; the nitrogen-containing silane coupling agent is selected from 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, or diethylenetriaminopropyltrimethoxysilane. The organic solvent is selected from anhydrous methanol, anhydrous ethanol, isopropanol, toluene, etc., preferably anhydrous methanol.

[0019] The third aspect of the present invention provides the use of the copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent as described in the first aspect of the present invention for ester hydrogenation reactions.

[0020] Preferably, the copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent is used in the hydrogenation of dimethyl oxalate to ethylene glycol to reduce by-product formation and improve the selectivity, catalyst activity and stability of the main product ethylene glycol.

[0021] Preferably, the copper-silicon catalyst, after being reduced by hydrogen, is used in the hydrogenation of dimethyl oxalate to ethylene glycol. First, the copper-silicon catalyst is loaded into the isothermal section of a fixed-bed reactor, and hydrogen is introduced at a pressure of 2-3 MPa for programmed temperature increase. After reduction at 220-350°C for 2-6 hours, the temperature is lowered to the reaction temperature of 180-220°C, and then dimethyl oxalate is introduced for reaction. The reaction pressure is 2-3 MPa, and the hydrogen-to-ester ratio is 70-100.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The copper-silicon catalyst modified by nitrogen-containing silane coupling agent of the present invention uses copper species as the active component, and has the characteristics of mild reaction conditions, excellent catalytic reaction performance, simple preparation process and low cost.

[0024] 2. When used in the heterogeneous hydrogenation reaction of dimethyl oxalate, compared with the unmodified copper-silicon catalyst, the copper-silicon catalyst modified by the nitrogen-containing silane coupling agent of this invention exhibits superior reactivity, as well as excellent high selectivity and high stability. Furthermore, compared with traditional noble metal catalysts, the nitrogen-containing silane-modified copper-silicon catalyst of this invention achieves excellent reactivity, high selectivity, and high stability while ensuring economic cost and environmental friendliness.

[0025] 3. In this invention, the silanol groups in the copper-silicon catalyst modified by the nitrogen-containing silane coupling agent are covered by the nitrogen-containing silane coupling agent, which promotes the desorption of methyl glycolate, thereby improving the stability of the catalyst under harsh conditions. At the same time, the basicity of the catalyst is reduced, inhibiting the formation of byproducts such as 1,2-butanediol and 1,2-propanediol, which contain three or four carbon atoms, thereby reducing the selectivity of byproducts. Industrially, this can further reduce the energy consumption and cost of separating byproducts 1,2-butanediol and ethylene glycol.

[0026] 4. The doping of nitrogen in the catalyst of the present invention improves the activity of the catalyst, and the electron-donating effect of nitrogen makes the active copper species have better hydrogenation activity and higher conversion frequency.

[0027] 5. In addition to the hydrogenation reaction of dimethyl oxalate, the catalyst involved in this invention can also be applied to other ester hydrogenation reactions. Attached Figure Description

[0028] Figure 1 The infrared spectra of the copper-silicon catalyst after reduction in this invention include catalyst samples 20Cu / SiO2, 20Cu / SiO2-4.6CH3, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2.

[0029] Figure 2 The X-ray diffraction (XRD) patterns of the copper-silicon catalyst after reduction in this invention include catalyst samples 20Cu / SiO2, 20Cu / SiO2-4.6CH3, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2.

[0030] Figure 3The images show temperature-programmed desorption mass spectra (MG-TPD-MS) of methyl glycolate after reduction by copper-silicon catalysts modified with different types and contents of silane coupling agents in this invention, including catalyst samples 20Cu / SiO2, 20Cu / SiO2-4.6CH3, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2.

[0031] Figure 4 The figures show the CO2 temperature-programmed desorption (CO2-TPD) diagrams of copper-silicon catalysts modified with different types and contents of silane coupling agents in this invention, including catalyst samples 20Cu / SiO2, 20Cu / SiO2-4.6CH3, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2;

[0032] Figure 5 The byproduct selectivity results of copper-silicon catalysts modified with different types and contents of silane coupling agents in this invention include catalyst samples 20Cu / SiO2, 20Cu / SiO2-4.6CH3, and 20Cu / SiO2-0.95NH2;

[0033] Figure 6 The stability results of copper-silicon catalysts modified with different types and contents of silane coupling agents in this invention are shown, including catalyst samples 20Cu / SiO2, 20Cu / SiO2-4.6CH3, and 20Cu / SiO2-0.95NH2;

[0034] Figure 7 The byproduct selectivity results of copper-silicon catalysts modified with different contents of nitrogen-containing silane coupling agents in this invention include catalyst samples 20Cu / SiO2, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2;

[0035] Figure 8 The structure and name of the silane coupling agent used in the modification of the copper-silicon catalyst in this invention are shown. Detailed Implementation

[0036] The present invention will be further illustrated below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions, conditions described in manuals, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified. The raw materials used in the following embodiments and comparative examples are all commercially available. Copper nitrate, ammonia, and nitrogen-containing silane coupling agents are all commercially purchased products.

[0037] The methods for evaluating the online reduction and catalytic effect of the catalyst in this embodiment and the comparative example are as follows:

[0038] In this invention, the hydrogenation reaction of dimethyl oxalate is carried out in a fixed-bed reactor. 0.5 g of catalyst is loaded, and reduction is performed at 300 °C in a pure H2 atmosphere at 2.5 MPa, with a gas flow rate of 80 mL / min, maintained for 4 h. The temperature is then lowered to the reaction temperature of 200 °C, and the dimethyl oxalate is vaporized and mixed with hydrogen before entering the reaction system. The mass hourly space velocity (HSV) of dimethyl oxalate is 0.5–7 h⁻¹. -1 The hydrogenation reaction was carried out at 2.5 MPa. The products were analyzed by gas chromatography, and the conversion of dimethyl oxalate and the selectivity of methyl glycolate, ethylene glycol, ethanol, and byproducts were calculated. The copper species conversion frequency was determined at a liquid hourly space velocity (LHSV) of 7 h⁻¹. -1 The stability was calculated under the following conditions: reaction temperature was 190℃, and dimethyl oxalate and methyl glycolate were mixed and fed in a 1:1 ratio.

[0039] Comparative Examples 1-3: 10Cu / SiO2, 20Cu / SiO2, 30Cu / SiO2

[0040] Comparative Examples 1-3 represent the preparation of 10Cu / SiO2, 20Cu / SiO2, and 30Cu / SiO2, where 10Cu / SiO2 refers to a copper metal loading of 10 wt.% in the copper-silicon catalyst produced by the ammonia stripping method, and the copper metal loadings in 20Cu / SiO2 and 30Cu / SiO2 are 20 wt.% and 30 wt.%, respectively.

[0041] The specific preparation method is as follows: Weigh 7.9140g, 15.2259g, and 18.1920g of copper nitrate respectively and dissolve them in 100ml of distilled water. Add 52ml of ammonia water and stir for a period of time. Then, add 45ml of silica sol dropwise at a rate of one drop every 2-3 seconds. After the addition is complete, stir at room temperature for a certain period of time. Raise the temperature to 80℃, open the stopper, and evaporate ammonia. The initial pH is 11-12. Continue evaporating ammonia until the pH reaches 6-7. The ammonia evaporation is then completed. Cool the solution to room temperature, filter and wash it. The pH will decrease slightly. Place the filter cake in an oven for drying. Place the dried sample in a muffle furnace and calcine it in air for 4 hours at a temperature controlled at around 400℃. Press the catalyst into tablets, sieve them, and obtain 40-60 mesh particles, which are the ammonia evaporation catalysts 10Cu / SiO2, 20Cu / SiO2, and 30Cu / SiO2.

[0042] The online reduction and catalytic effect evaluation of the catalyst are described above, and the catalyst performance evaluation results are shown in Table 1.

[0043] Comparative Example 4: 20Cu / SiO2-4.6CH3

[0044] Comparative Example 4 describes the preparation of 20Cu / SiO2-4.6CH3, in which the copper metal loading is 20 wt.%, the silane coupling agent is 0.0605 g, and the carbon element accounts for 4.6 wt.% of the catalyst weight.

[0045] The specific preparation method is as follows: Weigh 1g of 20Cu / SiO2 and dissolve it in 125ml of anhydrous methanol. Add 0.0605g of n-propyltrimethoxysilane dropwise at 30℃. After the addition is complete, raise the temperature to 80℃ and reflux for 6h. Centrifuge and wash the cooled solution, then dry it overnight at 80℃ to obtain the alkylsilane-modified copper-silicon catalyst. Compress the catalyst into tablets, sieve them, and obtain 40-60 mesh particles, which is the alkylsilane coupling agent-modified copper-silicon catalyst 20Cu / SiO2-4.6CH3.

[0046] The online reduction and catalytic effect evaluation of the catalyst are described above, and the catalyst performance evaluation results are shown in Table 2.

[0047] Examples 1-3: 10Cu / SiO2-0.95NH2, 20Cu / SiO2-0.95NH2, 30Cu / SiO2-0.95NH2

[0048] Examples 1-3 describe the preparation of 10Cu / SiO2-0.95NH2, 20Cu / SiO2-0.95NH2, and 30Cu / SiO2-0.95NH2 catalysts. In 10Cu / SiO2-0.95NH2, the copper metal loading in the ammonia stripping copper-silicon catalyst is 10 wt.%, and the nitrogen element accounts for 0.95 wt.% of the catalyst weight. In 20Cu / SiO2-0.95NH2 and 30Cu / SiO2-0.95NH2, the copper metal loading is 20 wt.% and 30 wt.%, respectively, and the nitrogen element accounts for 0.95 wt.% of the catalyst weight in both cases. The copper loading and nitrogen content of the active species in the catalysts of this invention were characterized using inductively coupled plasma atomic emission spectrometry and elemental analysis.

[0049] The specific preparation method is as follows: 1g of 10Cu / SiO2, 20Cu / SiO2, and 30Cu / SiO2 were weighed and dissolved in 125mL of anhydrous methanol. 0.0660g of 3-aminopropyltrimethoxysilane was added dropwise at 30℃. After the addition was complete, the temperature was raised to 80℃ and stirred under reflux for 6 hours. The cooled solutions were centrifuged, washed, and dried overnight at 80℃ to obtain copper-silicon catalysts modified with nitrogen-containing silane coupling agents. The catalysts were pressed into tablets, sieved, and 40-60 mesh particles were obtained, which are the copper-silicon catalysts 10Cu / SiO2-0.95NH2, 20Cu / SiO2-0.95NH2, and 30Cu / SiO2-0.95NH2 modified with nitrogen-containing silane coupling agents.

[0050] The online reduction and catalytic effect evaluation of the catalyst are described above, and the catalyst performance evaluation results are shown in Table 1.

[0051] Examples 4-5: 20Cu / SiO2-0.54NH2, 20Cu / SiO2-1.29NH2

[0052] Examples 4-5 describe the preparation of 20Cu / SiO2-0.54NH2 and 20Cu / SiO2-1.29NH2. 20Cu / SiO2-0.54NH2 refers to a copper-silicon catalyst prepared by the ammonia stripping method with a copper metal loading of 20 wt.% and a nitrogen element content of 0.54 wt.% of the catalyst weight. 20Cu / SiO2-1.29NH2 also has a copper metal loading of 20 wt.% and a nitrogen element content of 1.29 wt.% of the catalyst weight.

[0053] The specific preparation method is as follows: 1 g of 20Cu / SiO2 is dissolved in 125 ml of anhydrous methanol. 0.0132 g and 0.1320 g of 3-aminopropyltrimethoxysilane are added dropwise at 30 °C. After the addition is complete, the temperature is raised to 80 °C and stirred under reflux for 6 h. The cooled solution is centrifuged, washed, and dried overnight at 80 °C to obtain a copper-silicon catalyst modified with a nitrogen-containing silane coupling agent. The catalyst is pressed into tablets, sieved, and 40-60 mesh particles are obtained, which are the silanized copper-silicon catalysts 20Cu / SiO2-0.54NH2 and 20Cu / SiO2-1.29NH2 modified with a nitrogen-containing silane coupling agent.

[0054] In-situ infrared spectroscopy was used to characterize the reduced 20Cu / SiO2, 20Cu / SiO2-4.6CH3, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2 catalysts to investigate the coverage of silanol groups on the catalyst surface before and after silane coupling agent modification. The results are shown in the appendix. Figure 1 As shown. 3740cm -1The peak (I1) is attributed to the stretching vibration peak of isolated silanol groups on the surface of the copper-silicon catalyst, at 3675 cm⁻¹. -1 The peak (I2) is attributed to the stretching vibration peak of the silanol groups within the silica support, 2860-2960 cm⁻¹. -1 and 1391cm -1 The peak at 3740 cm⁻¹ is attributed to the CH vibration. A distinct CH peak can be observed after silane coupling agent modification, indicating the introduction of propyl side chains and alkyl groups. Furthermore, the four catalysts modified with silane coupling agent show a peak at 3740 cm⁻¹. -1 The intensity of the isolated silanol peak decreased significantly, indicating that the silane coupling agent was successfully grafted onto the catalyst surface and effectively covered the silanol groups. Furthermore, compared to the catalyst modified with alkyl silanizing agents (20Cu / SiO2-4.6CH3), the three catalysts modified with nitrogen-containing silane coupling agents showed a significantly lower peak intensity at 1588 cm⁻¹. -1 The presence of distinct shoulder peaks near the catalyst surface, attributed to NH bond vibrations, further confirms the successful modification of the catalyst by the nitrogen-containing silane coupling agent. The I1 / I2 ratio in the infrared spectrum represents the relative content of isolated silanol groups on the catalyst surface. Using the unmodified copper-silicon catalyst as a standard, the silanol coverage of different catalyst surfaces can be obtained. After verification, the silanol coverage of the catalyst sample with 4.6 wt.% carbon (20Cu / SiO2-4.6CH3) and the catalyst sample with 0.95 wt.% nitrogen (20Cu / SiO2-0.95NH2) was consistent. Furthermore, the relative peak intensity of the silanol gradually decreased with increasing amounts of nitrogen-containing silane coupling agent, confirming a gradual increase in silanol coverage.

[0055] The reduced compounds 20Cu / SiO2, 20Cu / SiO2-4.6CH3, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2 of this invention were characterized by XRD, and the results are attached. Figure 2 As shown, the characteristic diffraction peak at 2θ of 43.3° is a diffraction peak of metallic copper (JCPDS 65-9743), while the characteristic peak at 2θ of 36.4° belongs to the characteristic diffraction peak of cuprous oxide (JCPDS 05-0667). This indicates that the active species after reduction by different catalysts of the present invention are mainly metallic copper and monovalent copper species, and the particle size range calculated according to the Scherrer formula is about 1.5-4.5 nm.

[0056] MG-TPD-MS was used to investigate the desorption capacity of 20Cu / SiO2 and its surface-modified compounds 20Cu / SiO2-4.6CH3, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2 for methyl glycolate. The results are shown in the attached figure. Figure 3 As shown. (From the appendix) Figure 3 It can be seen that: 1. Compared with the ammonia stripping method copper-silicon catalyst 20Cu / SiO2, the desorption temperatures of methyl glycolate for copper-silicon catalysts modified with different functional groups, 20Cu / SiO2-4.6CH3 and 20Cu / SiO2-0.95NH2, are all lower, indicating that covering silanol groups can promote the desorption of methyl glycolate; 2. The desorption temperatures of methyl glycolate for copper-silicon catalysts modified with different amounts of nitrogen-containing silane coupling agents are all lower than those for the ammonia stripping method, indicating that covering silanol groups through modification with nitrogen-containing silane coupling agents is beneficial for the desorption of methyl glycolate from the catalyst surface. Furthermore, with the increase of the amount of nitrogen-containing silane coupling agent added, the degree of silanol coverage increases, and the desorption temperature of methyl glycolate for the catalyst gradually decreases, indicating that the methyl glycolate desorption capacity of the modified catalyst gradually increases with the increase of silanol coverage.

[0057] CO2-TPD was used to investigate the number and intensity of basic sites on the surface of 20Cu / SiO2 catalysts and their surface-modified catalysts 20Cu / SiO2-4.6CH3, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2. The results are shown in the attached figure. Figure 4 From the appendix Figure 4 It can be seen that: 1. The peak areas of copper-silicon catalysts modified with different functional groups are all smaller than those of copper-silicon catalysts produced by the ammonia stripping method, confirming that silane coupling agents with amino and alkyl terminals can reduce the number of basic sites on the catalyst surface, and that covering silanol groups can reduce the basicity of the catalyst; 2. The copper-silicon catalyst produced by the ammonia stripping method has a significant carbon dioxide desorption peak at high temperatures, corresponding to the presence of medium-to-strong basic sites, while the catalyst modified with nitrogen-containing silane coupling agents does not have a significant desorption peak at high temperatures, only showing weak or medium-strength basic sites. This indicates that the basicity of the catalyst is reduced after modification with nitrogen-containing silane coupling agents, thereby reducing the formation of by-products. Furthermore, with the increase of the amount of nitrogen-containing silane coupling agent added, the coverage of silanol groups increases, the basicity of the catalyst gradually weakens, and the selectivity of by-products gradually decreases.

[0058] After BET characterization analysis, the specific surface area of ​​the copper-silicon catalyst was found to be 200-500 m². 2 / g, with an average pore volume of 0.4-0.9cm³. 3 / g, with an average pore size of 5-12nm.

[0059] The online reduction and catalytic effects of 10Cu / SiO2, 20Cu / SiO2, 30Cu / SiO2, 10Cu / SiO2-0.95NH2, 20Cu / SiO2-0.95NH2, and 30Cu / SiO2-0.95NH2 were evaluated as described above. The performance evaluation results of the catalysts are shown in Table 1. The reaction conditions were set as follows: reaction temperature 200℃, reaction pressure 2.5MPa, hydrogen-ester ratio 80, and liquid hourly space velocity 1.5h⁻¹. -1 .

[0060] Table 1 Performance evaluation of different catalyst samples for the hydrogenation reaction of dimethyl oxalate

[0061]

[0062]

[0063] Table 1 shows that the copper-silicon catalysts modified with nitrogen-containing silane coupling agents all exhibited inhibitory effects on byproducts, indicating that passivation of silanol groups can suppress side reactions. Furthermore, the catalytic activity was best when the copper metal loading was 20 wt.%. The byproducts mentioned in this paper refer to alcohols containing three or four carbon atoms (C...). 3,4 -OH), specifically 1,2-butanediol and 1,2-propanediol.

[0064] The online reduction and catalytic performance evaluation of the 20Cu / SiO2, 20Cu / SiO2-4.6CH3, 20Cu / SiO2-0.54NH2, 20Cu / SiO2-0.95NH2, and 20Cu / SiO2-1.29NH2 catalysts are as described above. The selectivity of the byproducts of 20Cu / SiO2, 20Cu / SiO2-4.6CH3, and 20Cu / SiO2-0.95NH2 is shown in the appendix. Figure 5 The stability results of the catalyst are shown in the appendix. Figure 6 The performance evaluation results of other catalysts are shown in Table 2, and the selectivity of byproducts is shown in Appendix 2. Figure 7 The reaction conditions were set as follows: reaction temperature 200℃, reaction pressure 2.5MPa, hydrogen-to-ester ratio 80, and liquid hourly space velocity 1.5h⁻¹. -1 Additionally, the switching frequency is at a liquid hourly space velocity of 7 h⁻¹. -1 The results were calculated under the following conditions. Stability tests were conducted at a reaction temperature of 190°C with a 1:1 mixture of dimethyl oxalate and methyl glycolate as feed.

[0065] Table 2 Performance evaluation of different catalyst samples for the hydrogenation reaction of dimethyl oxalate

[0066]

[0067]

[0068] From Table 2 and Appendix Figure 7 It can be seen that the copper-silicon catalysts modified with silane coupling agents with alkyl or amino terminal groups exhibit significantly reduced selectivity for byproducts compared to the ammonia stripping method catalyst. Furthermore, with increasing amounts of nitrogen-containing silane coupling agents, the degree of silanol coverage gradually increases, while the catalyst's selectivity for byproducts gradually decreases, indicating that silanol coverage can suppress side reactions, and the degree of suppression of side reactions gradually increases with increasing silanol coverage. Simultaneously, the catalysts modified with nitrogen-containing silane coupling agents show a higher catalytic conversion frequency per active site compared to the ammonia stripping method catalyst, and the activity gradually increases with increasing amounts of nitrogen-containing silane coupling agents, indicating that the introduction of nitrogen enhances the activity of the hydrogenation reaction. (See attached...) Figure 6 It can be seen that the stability of copper-silicon catalysts modified by silanization is improved. In particular, the copper-silicon catalyst modified by nitrogen-containing silanization coupling agent has the best stability. The ethylene glycol selectivity of the 20Cu / SiO2 catalyst begins to decrease after 20 hours of reaction, while the decrease in activity and ethylene glycol selectivity of the 20Cu / SiO2-4.6CH3 catalyst is significantly weakened in the same time period. The activity and ethylene glycol selectivity of the 20Cu / SiO2-0.95NH2 catalyst hardly decrease in the same time period. Modification of copper-silicon catalysts by nitrogen-containing silanization coupling agent can significantly improve their stability.

[0069] And from the appendix Figure 4 and attached Figure 5 It can be seen that the catalyst modified with nitrogen-containing silane coupling agents has a slightly higher byproduct selectivity and a slightly lower ethylene glycol selectivity compared with the catalyst modified with alkyl silane coupling agents. This is because the number of basic sites at medium-strong bases is slightly higher in the nitrogen-containing silane coupling agent-modified catalyst compared with the alkyl-modified catalyst. However, the catalyst modified with nitrogen-containing silane coupling agents has a higher conversion frequency and better activity, indicating that the catalyst with nitrogen element has a promoting effect on the hydrogenation of dimethyl oxalate.

[0070] Examples 6-7: 20Cu / SiO2-1.41NH2-2N, 20Cu / SiO2-1.65NH2-3N

[0071] Examples 6-7 describe the preparation of 20Cu / SiO2-1.41NH2-2N and 20Cu / SiO2-1.65NH2-3N. 20Cu / SiO2-1.41NH2-2N refers to a copper-silicon catalyst prepared by the ammonia stripping method, in which the copper metal loading is 20 wt.%, nitrogen element accounts for 1.41 wt.% of the catalyst weight, and the number of nitrogen atoms in the functional group branches is 2. 20Cu / SiO2-3N-NH2 also has a copper metal loading of 20 wt.%, nitrogen element accounts for 1.65 wt.% of the catalyst weight, and the number of nitrogen atoms in the functional group branches is 3.

[0072] The specific preparation method is as follows: 1 g of 20Cu / SiO2 is dissolved in 125 mL of anhydrous methanol. At 30 °C, 0.0819 g of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or 0.0977 g of diethylenetriaminopropyltrimethoxysilane is added dropwise. After the addition is complete, the temperature is raised to 80 °C and stirred under reflux for 6 h. The cooled solution is centrifuged, washed, and dried overnight at 80 °C to obtain a copper-silicon catalyst modified with a nitrogen-containing silane coupling agent. The catalyst is pressed into tablets, sieved, and 40-60 mesh particles are obtained, which are the silanized copper-silicon catalysts 20Cu / SiO2-1.41NH2-2N and 20Cu / SiO2-1.65NH2-3N modified with a nitrogen-containing silane coupling agent.

[0073] After verification, the silanol coverage in the catalyst samples 20Cu / SiO2-0.95NH2, 20Cu / SiO2-1.41NH2-2N, and 20Cu / SiO2-1.65NH2-3N was consistent.

[0074] The online reduction and catalytic effect evaluation of the catalyst were described above, and the performance evaluation results of the catalyst are shown in Table 3. The reaction conditions were set as follows: reaction temperature 200℃, reaction pressure 2.5MPa, hydrogen-ester ratio 80, and liquid hourly space velocity 7h⁻¹. -1 .

[0075] Table 3 Performance evaluation of different catalyst samples for the hydrogenation reaction of dimethyl oxalate

[0076]

[0077] As shown in Table 3, at high space velocities, the catalysts modified with nitrogen-containing silane coupling agents exhibit significantly improved activity compared to the ammonia stripping method catalysts. With the increase in the number of nitrogen atoms in the functional group branches, the catalyst activity shows a volcano-like trend of first increasing and then decreasing, confirming that the catalyst activity improves with increasing nitrogen content. However, when the functional group branches are too long, the active species of the catalyst may be partially covered, leading to a decrease in catalyst activity.

[0078] The catalyst evaluation results are shown in Tables 1, 2, and 3. It can be seen that the surface-modified copper-silicon catalyst of this invention, when applied to the hydrogenation reaction of dimethyl oxalate, exhibits higher dimethyl oxalate conversion and ethylene glycol selectivity under the same conditions. Specifically, the 20Cu / SiO2-1.41NH2-2N catalyst performs particularly well under conditions of a hydrogen-to-ester ratio of 80 and a space velocity of 7 h⁻¹. -1 At that time, the conversion rate of dimethyl oxalate can reach 98.8%, which is much higher than the 68.2% conversion rate of 20Cu / SiO2.

[0079] The catalyst of this invention was characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES) and elemental analysis, respectively, for the loading of active copper species and nitrogen content. The results are shown in Table 4. With the increase of nitrogen-containing silane coupling agent, the nitrogen content gradually increased, while the loading of active copper species remained almost unchanged.

[0080] Table 4. Copper loading and nitrogen content of active species in different catalyst samples

[0081]

[0082] Besides the hydrogenation reaction of dimethyl oxalate, the catalyst involved in this invention can also be applied to other ester hydrogenation reactions, such as the hydrogenation reaction of ethylene carbonate and diethyl oxalate. For example, in the hydrogenation reaction of ethylene carbonate, the silanol groups on the surface of the copper-silicon catalyst promote side reactions, resulting in high selectivity for byproducts such as 1,2-butanediol. After modification with a silane coupling agent, the selectivity of the catalyst for byproducts is significantly reduced, indicating that covering the silanol groups inhibits byproduct production. Furthermore, modification of the copper-silicon catalyst with a nitrogen-containing silane coupling agent can significantly improve its stability, and the doping of nitrogen element improves the catalyst activity. The electron-donating effect of nitrogen element gives copper species superior hydrogenation activity, greatly improving the catalyst conversion rate. The catalyst modified with a nitrogen-containing silane coupling agent has a higher conversion frequency and better activity.

[0083] The present invention has been described above by way of example. It should be noted that, without departing from the core of the present invention, any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort fall within the protection scope of the present invention.

Claims

1. The use of a copper-silicon catalyst modified with a nitrogen-containing silane coupling agent for ester hydrogenation reactions, wherein the catalyst comprises a copper species, silica, and silica modified with a nitrogen-containing silane coupling agent; the copper species constitutes 10-30 wt.% of the weight of the copper-silicon catalyst, the silica constitutes 60-85 wt.% of the weight of the copper-silicon catalyst, and the nitrogen element in the silica modified with the nitrogen-containing silane coupling agent constitutes 0.95-2 wt.% of the weight of the copper-silicon catalyst, characterized in that... The copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent is used in the hydrogenation of dimethyl oxalate to ethylene glycol to reduce the formation of byproducts 1,2-butanediol and 1,2-propanediol, and to improve the selectivity, catalyst activity and stability of the main product ethylene glycol. The nitrogen-containing silane coupling agent is selected from 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or diethylenetriaminopropyltrimethoxysilane.

2. The use according to claim 1, characterized in that, The copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent is used in the hydrogenation reaction of dimethyl oxalate to ethylene glycol after reduction with hydrogen. First, the copper-silicon catalyst is loaded into the isothermal section of a fixed-bed reactor. Hydrogen is introduced at a pressure of 2-3 MPa for programmed temperature increase. After reduction at 220-350℃ for 2-6 hours, the temperature is lowered to the reaction temperature of 180-220℃. Then, dimethyl oxalate is introduced to carry out the reaction at a pressure of 2-3 MPa and a hydrogen-to-ester ratio of 70-100.

3. The use according to claim 1, characterized in that, The copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent has a copper species particle size of 1.5-4.5 nm and a specific surface area of ​​200-500 m². 2 / g, with an average pore volume of 0.4-0.9 cm³. 3 / g, with an average pore size of 5-12 nm.

4. The use according to claim 1, characterized in that, The preparation of the copper-silicon catalyst modified by nitrogen-containing silane coupling agent includes the following steps: (1) After stirring the mixed solution of copper salt and ammonia, add silicon source and stir at room temperature to obtain the first mixed solution; (2) Heat the first mixed solution obtained in step (1) and perform ammonia stripping until the pH value is 6-7. Then stop the ammonia stripping to obtain the second mixed solution. (3) The second mixed solution obtained in step (2) is filtered, washed, dried, and calcined to obtain the copper-silicon catalyst obtained by the ammonia stripping method; (4) The copper-silicon catalyst obtained in step (3) by ammonia stripping is mixed and stirred with a nitrogen-containing silane coupling agent in an organic solvent, then washed and dried to obtain a copper-silicon catalyst modified by silanization with a nitrogen-containing silane coupling agent.

5. The use according to claim 4, characterized in that, In step (1), the copper salt is copper nitrate, copper acetate, or copper chloride; the silicon source is silica sol, sodium silicate solution, tetraethyl orthosilicate, or propyl orthosilicate; the silicon source is added by dropping, with a dropping rate of one drop every 1-3 seconds, and the stirring time after adding the silicon source is 0.5-24 hours.

6. The use according to claim 4, characterized in that, In step (2), the first mixed solution obtained in step (1) is heated to 70-90°C to evaporate ammonia.

7. The use according to claim 4, characterized in that, In step (3), the second mixed solution obtained in step (2) is first filtered and washed, and the calcination temperature is 350-450℃ and the calcination time is 4-6h.

8. The use according to claim 4, characterized in that, In step (4), the copper-silicon catalyst obtained in step (3) by ammonia stripping is mixed and stirred in an organic solvent, heated to 70-100℃, and refluxed and stirred for 4-8 hours; the nitrogen-containing silane coupling agent is selected from 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or diethylenetriaminopropyltrimethoxysilane.

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