A modified copper-based catalyst, a preparation method and application in selective hydrogenation

Abstract

This invention belongs to the field of catalytic chemical technology, disclosing a modified copper-based catalyst, its preparation method, and its application in selective hydrogenation. The modified copper-based catalyst is either an AgCu / SiO2 catalyst or a Cu / AgCuMgAl-LDO catalyst. The AgCu / SiO2 catalyst is prepared by a deposition precipitation method, while the Cu / AgCuMgAl-LDO catalyst is prepared by a co-precipitation method. Silver-modified copper-based catalysts can significantly improve the hydrogenation activity, target intermediate selectivity, and fixed-bed continuous operation stability of copper-based catalysts. The AgCu / SiO2 catalyst can effectively improve the yield of dimethyl oxalate hydrogenation to methyl glycolate, while the Cu / AgCuMgAl-LDO catalyst can significantly improve quinoline conversion and enhance long-term operational stability while maintaining high 1,2,3,4-tetrahydroquinoline selectivity.

Description

Technical Field

[0001] This invention belongs to the field of catalytic chemical technology, and relates to a modified copper-based catalyst, its preparation method, and its application in selective hydrogenation. Background Technology

[0002] Selective hydrogenation is an important reaction type for the preparation of fine chemicals, pharmaceutical intermediates, and other chemicals. In a series hydrogenation reaction system, how to control the depth of hydrogenation while ensuring reactivity, improve the selectivity of the target intermediate, and avoid excessive hydrogenation leading to increased byproducts and waste of raw materials is a crucial technical challenge in the field of catalysis.

[0003] Quinoline (py-THQ) hydrogenation and dimethyl oxalate (DMO) hydrogenation are two representative selective hydrogenation reactions. The intermediate 1,2,3,4-tetrahydroquinoline (THQ) from quinoline (py-THQ) hydrogenation is a key intermediate in the synthesis of various pharmaceuticals and pesticides. However, quinoline is prone to over-hydrogenation during hydrogenation to form decahydroquinoline (DHQ), and may even undergo other ring-opening side reactions, leading to a decrease in the yield of the target product THQ. Methyl glycolate (MG), an intermediate from dimethyl oxalate (DMO) hydrogenation, is an important precursor in the synthesis of biodegradable plastic polyglycolic acid (PGA). However, in actual production, methyl glycolate readily undergoes further hydrogenation to form ethylene glycol (EG) and even ethanol. Therefore, developing a highly efficient catalyst capable of precisely controlling the depth of hydrogenation is of great significance for improving industrial economic efficiency.

[0004] Copper-based catalysts have been widely used in the hydrogenation reactions of esters and nitrogen-containing heterocyclic compounds due to their low cost and relatively mild hydrogenation activity. However, in actual industrial production, copper-based catalysts still face some challenges: firstly, it is difficult to balance high activity and high selectivity, and the adsorption-desorption balance of intermediates (such as THQ and MG) at copper active sites cannot be efficiently controlled; secondly, copper nanoparticles are prone to agglomeration and sintering, resulting in a short catalyst lifespan. Therefore, developing a modification scheme that can control the selective hydrogenation behavior of copper-based catalysts and is suitable for fixed-bed continuous reactions is crucial for improving the hydrogenation process of quinoline and dimethyl oxalate. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying a silver-modified copper-based catalyst, in order to solve the problems of insufficient activity, low selectivity of target intermediate products, and poor stability in continuous fixed-bed operation of existing copper-based catalysts in the selective hydrogenation of quinoline and dimethyl oxalate.

[0006] The technical solution of the present invention: A silver-modified copper-based catalyst exhibits electronic properties of surface active centers, dispersion state, and adsorption / desorption behavior of substrates and intermediates.

[0007] The silver-modified copper-based catalysts include AgCu / SiO2 catalysts and Cu / AgCuMgAl-LDO catalysts.

[0008] A method for preparing an AgCu / SiO2 catalyst, which is prepared by a deposition precipitation method, includes the following steps: S1. Dissolve AgNO3 and Cu(NO3)2·3H2O in deionized water to prepare solution A; take 1 / 3 volume of solution A, add urea and nitric acid to it to prepare solution B; add carrier gaseous SiO2 to the remaining 2 / 3 volume of solution A to form suspension C; add solution B dropwise to suspension C, and obtain catalyst precursor by stirring, drying and calcining. S2. The catalyst precursor is reduced under a hydrogen atmosphere to obtain the AgCu / SiO2 catalyst.

[0009] AgNO3, as a silver additive, regulates the surface properties of active sites and the adsorption behavior of reactants. The two work synergistically to significantly improve the hydrogenation activity of the catalyst and the selectivity of the target product.

[0010] In step S1, the mass ratio of AgNO3 to Cu(NO3)2·3H2O is 1:4, and the concentration of AgNO3 in solution A is 0.014 mol / L.

[0011] In step S1, the mass ratio of urea to nitric acid is 15:1, and the mass percentage concentration of nitric acid in solution B is 68%.

[0012] In step S1, the concentration of carrier gas phase SiO2 in suspension C is 0.25 mol / L.

[0013] In step S1, the volume ratio of solution B to suspension C is 1:2.

[0014] In step S1, the stirring temperature is 90°C. o C.

[0015] In step S1, the drying conditions are: vacuum drying at 110 °C for 12 h.

[0016] In step S1, the calcination conditions are: calcination temperature 450 ℃, calcination time 4 h.

[0017] In step S2, the reduction conditions are: reduction temperature is 350°C. o C, reduction time 4 hours.

[0018] A method for preparing a Cu / AgCuMgAl-LDO catalyst, which is prepared by co-precipitation, includes the following steps: S1. Dissolve AgNO3, Cu(NO3)2·3H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O in deionized water to obtain solution D; dissolve sodium hydroxide and anhydrous sodium carbonate in deionized water to obtain solution E; under stirring conditions, add 60... o Solution D and solution E were added dropwise to deionized water of C, and the pH was maintained between 9 and 10 during the dropwise addition. After the dropwise addition was completed, the mixture was stirred for 2-3 hours, and then filtered, washed, dried and calcined to obtain the catalyst precursor. S2. The catalyst precursor is reduced under a hydrogen atmosphere to obtain the Cu / AgCuMgAl-LDO catalyst.

[0019] AgNO3, as a silver additive, modulates the surface properties of active sites and the adsorption behavior of reactants, significantly improving the hydrogenation activity and target product selectivity of the catalyst.

[0020] In step S1, the molar ratio of AgNO3, Cu(NO3)2·3H2O, Mg(NO3)2·6H2O and Al(NO3)3·9H2O is 0.25:0.75:2:1, and the concentration of AgNO3 in solution D is 0.1 mol / L.

[0021] In step S1, the mass ratio of sodium hydroxide to anhydrous sodium carbonate is 1:2; In step S1, the drying conditions are: vacuum drying at 120 °C for 10 h.

[0022] In step S1, the calcination conditions are: calcination temperature 500 ℃, calcination time 4 h.

[0023] In step S2, the reduction conditions are: reduction temperature is 350°C. o C, reduction time 2 h.

[0024] A silver-modified copper-based catalyst is used for a selective hydrogenation reaction, wherein the selective hydrogenation reaction comprises at least one of the following: (1) Selective hydrogenation of dimethyl oxalate to prepare methyl glycolate; AgCu / SiO2 catalyst was used for the hydrogenation reaction of dimethyl oxalate. The steps are as follows: AgCu / SiO2 catalyst was packed into a fixed-bed reactor, and a 10wt% dimethyl oxalate-methanol solution was introduced. The temperature was 185-200 °C, the pressure was 1.5-3 MPa, and the hydrogen-to-oil molar ratio was 80.

[0025] (2) Selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline; The Cu / AgCuMgAl-LDO catalyst is used for the hydrogenation reaction of quinoline. The steps are as follows: the Cu / AgCuMgAl-LDO catalyst is packed into a fixed-bed reactor, and a 5wt% quinoline-ethanol solution is introduced. The temperature is 80-100 °C, the pressure is 1-3 MPa, and the hydrogen-to-oil volume ratio is 400.

[0026] The beneficial effects of this invention are: 1. This invention proposes a modification scheme for copper-based catalysts modified with silver additives. All of them use copper as the main active component and silver as the additive component. The silver additive is used to improve the dispersion of copper and the adsorption behavior of substrates and intermediate products, thereby achieving the technical effect of balancing activity and selectivity of target intermediate products in selective hydrogenation reactions.

[0027] 2. The preparation method of AgCu / SiO2 catalyst described in this invention is simple and suitable for the selective hydrogenation of dimethyl oxalate to prepare methyl glycolate, and can effectively suppress deep hydrogenation.

[0028] 3. The Cu / AgCuMgAl-LDO catalyst of the present invention has a simple preparation process, can be used for quinoline hydrogenation in a continuous flow system, and has high activity, 1,2,3,4-tetrahydroquinoline selectivity and stability.

[0029] 4. This invention describes the unique modification advantages and application value of silver additives in selective hydrogenation reactions. Compared with non-precious metal additives such as nickel and zinc, the introduction of trace amounts of silver can achieve a synergistic improvement in catalyst hydrogenation activity, target product selectivity, and resistance to deactivation. Firstly, through the electron transfer effect, the introduction of silver additives can precisely control the Cu content. + / (Cu + +Cu 0 To achieve Cu at the optimal ratio 0 Dissociation of activated hydrogen and Cu + The highly efficient synergistic adsorption and activation of the substrate, along with the targeted regulation of the adsorption-desorption behavior of the substrate and intermediate products, precisely controls the depth of hydrogenation, solving the problem of balancing activity and selectivity in traditional copper-based catalysts. Secondly, the silver promoter anchors copper particles, effectively inhibiting their migration and aggregation, achieving high dispersion of copper particles and improving catalytic stability. In the selective hydrogenation reactions of dimethyl oxalate and quinoline, the silver-modified copper-based catalyst achieved high reactant conversion and high selectivity for the target product, while maintaining excellent catalytic stability, meeting the requirements of continuous industrial production. Attached Figure Description

[0030] Figure 1 This is a TEM image of the AgCu / SiO2 catalyst prepared in Example 1.

[0031] Figure 2 This is a TEM image of the CuNi / SiO2 catalyst in Comparative Example 1.

[0032] Figure 3 This is a TEM image of the CuSiO2 catalyst in Comparative Example 2.

[0033] Figure 4 This is a TEM image of the Cu / AgCuMgAl-LDO catalyst prepared in Example 2.

[0034] Figure 5 This is a TEM image of the Cu / CuMgAl-LDO catalyst prepared in Comparative Example 3.

[0035] Figure 6 This is a TEM image of the Cu / CuZnMgAl-LDO catalyst prepared in Comparative Example 4. Detailed Implementation

[0036] The specific embodiments of the present invention will be further described below in conjunction with the technical solutions and accompanying drawings.

[0037] Preparation Example 1 AgCu / SiO2 catalysts were prepared by a deposition-precipitation method.

[0038] (1) Precursor preparation: Weigh 0.943 g Cu(NO3)2·3H2O and 0.242 g AgNO3 and dissolve them in deionized water to prepare 100 mL of mixed metal salt solution A. Take 1 / 3 volume of solution A and add 3.78 g urea and 0.3 g nitric acid to prepare solution B. Add 1 g of carrier gaseous SiO2 to the remaining 2 / 3 volume of solution A to form suspension C. Pour suspension C into a three-necked flask, stir and heat to 70 °C, add solution B dropwise at a rate of one drop every five seconds, and heat to 90 °C and react for 4 h. After the reaction is completed, filter the mixture obtained from the reaction with deionized water until neutral. Take the filter cake and dry it at 110 °C for 12 h. After drying, calcine at 450 °C for 4 h to obtain AgCu / SiO2 catalyst precursor.

[0039] (2) Precursor reduction: The catalyst precursor prepared in (1) was placed in a fixed-bed reactor for in-situ reduction. Under the protection of a hydrogen atmosphere of 150 mL / min, the temperature was increased to 350℃ for 4 h at a rate of 10 ℃ / min. After the program was completed, the temperature was lowered to room temperature. The resulting catalyst was denoted as AgCu / SiO2.

[0040] Figure 1 The image shows the TEM spectrum of AgCu / SiO2. Cu particles are uniformly distributed on the surface of the support, with an average particle size of 3.10 nm.

[0041] Example 1 The AgCu / SiO2 catalyst prepared in Example 1 was reacted at different temperatures.

[0042] Reaction Procedure: The catalyst was loaded into the isothermal zone of a fixed-bed reactor, the apparatus was sealed and leak-tested, and the performance of the in-situ reduced catalyst was evaluated under the reaction conditions. The reactant conversion and product selectivity were investigated. The obtained products were analyzed in an Aglient 6890 N-type gas chromatograph using a commercially available HP-Innowax capillary column and a flame ionization detector.

[0043] Reaction conditions: Catalyst loading mass 0.2 g, reaction temperature 185–205 °C o C, mass hourly space velocity is 1.5 h. -1 The reaction pressure was 2 MPa, and a 10 wt% dimethyl oxalate-methanol solution was pumped in. The hydrogenation reaction was carried out under conditions of a hydrogen-to-oil molar ratio of 80. The reaction results are shown in Table 1.

[0044] Table 1 Experimental results of AgCu / SiO2 catalyst at different reaction temperatures

[0045] Table 1 shows that the reaction temperature (185–205 °C) significantly affects the performance of the hydrogenation of dimethyl oxalate to methyl glycolate. As the reaction temperature increases from 185 °C to 195 °C, the conversion rate increases from 59.8% to 88.1%, and the selectivity of methyl glycolate increases from 58.6% to 89.7%. When the temperature is further increased to 205 °C, the conversion rate of dimethyl oxalate rapidly rises to 98.9%, while the selectivity of methyl glycolate drops to 1.6%. This is because the excessively high reaction temperature leads to over-hydrogenation of dimethyl oxalate, generating the byproduct ethylene glycol. At a reaction temperature of 195 °C, the yield of methyl glycolate is optimal, reaching 79.0%.

[0046] Example 2 The AgCu / SiO2 catalyst prepared in Example 1 was reacted under different pressures.

[0047] Reaction conditions: Catalyst loading mass 0.2 g, reaction temperature 195 °C o C, mass hourly space velocity is 1.5 h. -1 A 10 wt% dimethyl oxalate-methanol solution was pumped in, and a hydrogenation reaction was carried out under a hydrogen-to-oil molar ratio of 80. The reaction results are shown in Table 2.

[0048] Table 2 Experimental results of AgCu / SiO2 catalyst under different reaction pressures

[0049] Table 2 shows that the reaction pressure (1.5–3 MPa) significantly affects the performance of the hydrogenation of dimethyl oxalate to methyl glycolate. When the reaction pressure increases from 1.5 MPa to 3 MPa, the conversion rate increases from 68.9% to 94.7%, and the selectivity of methyl glycolate initially increases and then decreases. At excessively high pressures, the selectivity of methyl glycolate decreases rapidly, because the excessively high reaction pressure leads to over-hydrogenation of dimethyl oxalate, generating byproducts such as ethylene glycol. The best methyl glycolate yield, reaching 81.0%, is achieved at a reaction pressure of 2.5 MPa.

[0050] Comparative Example 1 CuNi / SiO2 catalysts were prepared by a deposition-precipitation method.

[0051] (1) Precursor preparation: Weigh 0.943 g Cu(NO3)2·3H2O and 0.261 g Ni(NO3)2·6H2O and dissolve them in deionized water to prepare 100 mL of mixed metal salt solution A. Take 1 / 3 volume of solution A and add 3.78 g urea and 0.3 g nitric acid to prepare solution B. Add 1 g of carrier gaseous SiO2 to the remaining 2 / 3 volume of solution A to form suspension C. Pour suspension C into a three-necked flask, stir and heat to 70 °C, add solution B dropwise at a rate of one drop every five seconds, and heat to 90 °C and react for 4 h. After the reaction is completed, filter the mixture obtained from the reaction with deionized water until neutral. Take the filter cake and dry it at 110 °C for 12 h. After drying, calcine at 450 °C for 4 h to obtain CuNi / SiO2 catalyst precursor.

[0052] (2) Precursor reduction: The catalyst precursor prepared in (1) was placed in a fixed-bed reactor for in-situ reduction. Under the protection of a hydrogen atmosphere of 150 mL / min, the temperature was increased to 400℃ at a rate of 10℃ / min for 4 h. After the program was completed, the temperature was lowered to room temperature. The resulting catalyst was denoted as CuNi / SiO2.

[0053] Figure 2 The image shows the TEM spectrum of CuNi / SiO2, with an average particle size of 3.31 nm, which is slightly less dispersed than the sample prepared in Example 1.

[0054] Comparative Example 1 The CuNi / SiO2 catalyst of Comparative Example 1 was used to react at different temperatures.

[0055] Reaction conditions: Except for the type of catalyst used, the conditions were the same as in Example 1. The reaction results are shown in Table 3.

[0056] Table 3 Experimental results of CuNi / SiO2 catalyst at different reaction temperatures

[0057] As shown in Table 3, under the same reaction conditions, the performance of the CuNi / SiO2 catalyst is far inferior to that of the AgCu / SiO2 catalyst with silver additive in Example 1. At 195 °C, the conversion rate of dimethyl oxalate under CuNi / SiO2 catalysis is 75.4%, which is 12.7% lower than that of the AgCu / SiO2 catalyst, and the selectivity of methyl glycolate is only 24.1%, which is 65.6% lower than that of the AgCu / SiO2 catalyst. The comparative results indicate that the nickel additive has excessive hydrogenation activity and cannot suppress side reactions such as over-hydrogenation, thus failing to achieve the modification effect of silver additive in achieving both high activity and high selectivity.

[0058] Comparative Example 2 CuSiO2 catalyst was prepared by deposition precipitation method.

[0059] Except for the absence of AgNO3, the other conditions were the same as in Preparation Example 1, and the reaction was used for the hydrogenation of dimethyl oxalate.

[0060] Figure 3 The image shows the TEM spectrum of Cu / SiO2, with an average particle size of 3.50 nm, which is less dispersed than the sample prepared in Example 1.

[0061] Comparative Example 2 Reactions were carried out using the Cu / SiO2 catalyst of Comparative Example 1 above under different pressures.

[0062] Reaction conditions: Except for the type of catalyst used, the conditions were the same as in Example 1. The reaction results are shown in Table 4.

[0063] Table 4 Experimental results of Cu / SiO2 catalyst at different reaction temperatures

[0064] As shown in Table 4, within the temperature range of 185–205 °C, although the Cu / SiO2 catalyst without silver additive exhibits some hydrogenation activity, its overall reaction performance is significantly lower than that of the AgCu / SiO2 catalyst in Example 1. At 195 °C, although the Cu / SiO2 catalyst achieves a selectivity of 89.7% for methyl glycolate, the conversion rate of dimethyl oxalate is only 50.2%, 37.9% lower than that of the AgCu / SiO2 catalyst, and the yield of the target product is only 45%, lower than the 60% yield of the AgCu / SiO2 catalyst. The comparative results directly demonstrate that the introduction of silver additive can significantly improve the hydrogenation activity of copper-based catalysts without sacrificing the selectivity of the target product, achieving a synergistic improvement in both activity and selectivity, while pure copper-based catalysts cannot achieve both simultaneously.

[0065] Preparation Example 2 Cu / AgCuMgAl-LDO catalyst was prepared by co-precipitation method.

[0066] (1) Preparation of precursors: Weigh 0.84 g AgNO3, 3.6 g Cu(NO3)2·3H2O, 10.3 g Mg(NO3)2·6H2O and 7.5 g Al(NO3)3·9H2O and dissolve them together in 50 mL of deionized water to prepare solution A. Dissolve 5.6 g NaOH and 10.6 g Na2CO3 together in 60 mL of deionized water to prepare solution B. Place a three-necked flask in an oil bath and place a serpentine condenser for reflux. Add 10 mL of deionized water to the three-necked flask. When the liquid in the three-necked flask reaches 60 °C, add a magnetic stirrer and stir vigorously. Then add solutions A and B dropwise to the three-necked flask simultaneously, keeping the pH between 9 and 10 during the dropwise addition. After solution A is used up, maintain the temperature at 60 °C and stir continuously for 2.5 h. After stirring, filter and wash with deionized water until the filtrate is neutral. The solid obtained by vacuum filtration was dried in a vacuum oven at 120 °C for 10 h to obtain AgCuMgAl-LDH precursor (n Ag :n Cu :n Mg :n Al =0.25:0.75:2:1). The prepared AgCuMgAl-LDH precursor was placed in a muffle furnace and heated to 500 °C at a rate of 10 °C / min, held for 4 h, and then cooled to room temperature to obtain the mixed metal oxide AgCuMgAl-LDO precursor.

[0067] (2) Precursor reduction: The catalyst precursor prepared in (1) was placed in a fixed-bed reactor for in-situ reduction. Under the protection of a hydrogen atmosphere of 150 mL / min, the temperature was increased to 350 °C for 2 h at a rate of 10 °C / min. After the program was completed, the temperature was lowered to room temperature. The resulting catalyst was denoted as Cu / AgCuMgAl-LDO catalyst.

[0068] Figure 4 The TEM spectrum of Cu / AgCuMgAl-LDO shows that Cu particles are uniformly distributed on the support surface, with an average particle size of 2.96 nm. N₂O titration of the sample revealed a Cu species dispersion of 23.9%, indicating good dispersion. The chemical valence state of the copper component in the catalyst was investigated using XPS spectroscopy and X-ray induced Auger electron spectroscopy (AES). + / (Cu + +Cu 0 The figure was 72.7%, which is at a relatively high level.

[0069] Example 3 The Cu / AgCuMgAl-LDO catalyst prepared in Example 2 was reacted at different temperatures.

[0070] Reaction Procedure: The catalyst was loaded into the isothermal zone of a fixed-bed reactor, the apparatus was sealed and leak-tested, and the performance of the in-situ reduced catalyst was evaluated under the reaction conditions. The reactant conversion and product selectivity were investigated. The obtained products were analyzed in an Aglient 6890 N-type gas chromatograph using a commercially available HP-Innowax capillary column and a flame ionization detector.

[0071] Reaction conditions: Catalyst loading mass 0.2 g, reaction temperature 80–100 °C o C, mass hourly space velocity is 3 h -1 The reaction was carried out at a pressure of 3 MPa, with a quinoline-ethanol solution of 5 wt% pumped in, and a hydrogen-to-oil volume ratio of 400. The reaction results are shown in Table 5.

[0072] Table 5 Experimental results of Cu / AgCuMgAl-LDO catalyst at different reaction temperatures

[0073] Table 5 shows that the Cu / AgCuMgAl-LDO catalyst maintains high catalytic activity and selectivity for 1,2,3,4-tetrahydroquinoline across the entire reaction temperature range, indicating that the silver promoter also promotes the selective hydrogenation of nitrogen-containing heterocyclic substrates. Reaction temperature has a certain impact on the performance of quinoline hydrogenation to 1,2,3,4-tetrahydroquinoline. Increasing the reaction temperature from 80 ℃ to 100 ℃ increases the conversion rate from 89.3% to 99.2%, while maintaining the selectivity at 99.9%.

[0074] Example 4 The Cu / AgCuMgAl-LDO catalyst prepared in Example 2 was reacted under different pressures.

[0075] Reaction conditions: Catalyst loading mass 0.2 g, reaction temperature 100 °C o C, mass hourly space velocity is 3 h -1 A quinoline-ethanol solution with a mass concentration of 5 wt% was pumped in, and a hydrogenation reaction was carried out under a hydrogen-to-oil volume ratio of 400. The reaction results are shown in Table 6.

[0076] Table 6 Experimental results of Cu / AgCuMgAl-LDO catalyst under different reaction pressures

[0077] As shown in Table 6, within the range of 1–3 MPa, the quinoline conversion on the Cu / AgCuMgAl-LDO catalyst significantly increased with increasing reaction pressure, while the selectivity for 1,2,3,4-tetrahydroquinoline remained consistently at a high level of 99.9%. This indicates that reaction pressure has a significant impact on quinoline conversion; increasing the hydrogen pressure is beneficial for improving the hydrogenation conversion of quinoline, while the selectivity for the target product, 1,2,3,4-tetrahydroquinoline, remains at an extremely high level. Therefore, the Cu / AgCuMgAl-LDO catalyst can maintain excellent selectivity for the target product over a wide pressure range.

[0078] Example 5 The stability of the Cu / AgCuMgAl-LDO catalyst prepared in Example 2 above was tested.

[0079] Reaction conditions: Catalyst loading mass 0.2 g, reaction temperature 100 °C o C, the reaction pressure is 3 MPa, and the mass hourly space velocity is 3 h⁻¹. -1 A quinoline-ethanol solution with a mass concentration of 5 wt% was pumped in, and a hydrogenation reaction was carried out under the condition of a hydrogen-to-oil volume ratio of 400.

[0080] Table 7. Stability test results of Cu / AgCuMgAl-LDO catalyst

[0081] As shown in Table 7, after 100 h of continuous reaction, the quinoline conversion rate remained at 88.9%, and the selectivity for 1,2,3,4-tetrahydroquinoline remained at 99.9%. This indicates that the Cu / AgCuMgAl-LDO catalyst can maintain high activity under long-term fixed-bed operation conditions, while the selectivity of the target product remains essentially unchanged. The Cu / AgCuMgAl-LDO catalyst can not only efficiently catalyze the selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline, but also exhibits good stability and resistance to deactivation.

[0082] Comparative Example 3 CuMgAl-LDO catalyst was prepared by coprecipitation method.

[0083] (1) Precursor preparation: Weigh 4.8 g Cu(NO3)2·3H2O, 10.3 g Mg(NO3)2·6H2O and 7.5 g Al(NO3)3·9H2O and dissolve them together in 50 mL of deionized water to prepare solution A. Dissolve 5.6 g NaOH and 10.6 g Na2CO3 together in 60 mL of deionized water to prepare solution B. Place a three-necked flask in an oil bath and place a serpentine condenser for reflux condensation. Add 10 mL of deionized water to the three-necked flask. When the liquid in the three-necked flask reaches 60 °C, add a magnetic stirrer and stir vigorously. Then, add solutions A and B dropwise to the three-necked flask simultaneously, keeping the pH between 9 and 10 during the dropwise addition. After solution A is used up, maintain the temperature at 60 °C and stir continuously for 2.5 h. After stirring, filter under vacuum and wash with deionized water until the filtrate is neutral. The solid obtained by vacuum filtration was dried in a vacuum oven at 120 °C for 10 h to obtain CuMgAl-LDH precursor (n Cu :n Mg :n Al =1:2:1). The prepared CuMgAl-LDH precursor was placed in a muffle furnace and heated to 500 °C at a rate of 10 °C / min, held for 4 h, and then cooled to room temperature to obtain the mixed metal oxide CuMgAl-LDO precursor.

[0084] (2) Precursor reduction: The catalyst precursor prepared in (1) was placed in a fixed-bed reactor for in-situ reduction. Under the protection of a hydrogen atmosphere of 150 mL / min, the temperature was increased to 350 °C for 2 h at a rate of 10 °C / min. After the program was completed, the temperature was lowered to room temperature. The resulting catalyst was denoted as Cu / CuMgAl-LDO catalyst.

[0085] Figure 5 The TEM spectrum of CuMgAl-LDO shows an average particle size of 3.28 nm, slightly larger than that of Cu / AgCuMgAl-LDO catalysts. N₂O titration analysis revealed a Cu species dispersion of 20.1%, indicating low dispersion. The chemical valence states of the copper component in the catalyst were investigated using XPS spectroscopy and X-ray induced Auger electron spectroscopy (AES). + / (Cu + +Cu 0 The concentration was 67.3%, which is lower than that of Cu / AgCuMgAl-LDO catalyst.

[0086] Comparative Example 2 The CuMgAl-LDO catalyst of Comparative Example 3 was used for the reaction under different pressures.

[0087] Reaction conditions: Except for the type of catalyst used, the conditions were the same as in Example 4. The reaction results are shown in Table 8.

[0088] Table 8 Experimental results of Cu / CuMgAl-LDO catalyst at different reaction pressures

[0089] As shown in Table 8, the Cu / CuMgAl-LDO catalyst without silver additive, under the same reaction conditions as in Example 4, maintained 99.9% selectivity for 1,2,3,4-tetrahydroquinoline, but its hydrogenation activity was significantly lower than that of the Cu / AgCuMgAl-LDO catalyst with silver additive. Under the same reaction pressure, the quinoline conversion of the Cu / CuMgAl-LDO catalyst was significantly lower: only 90.4% at 3 MPa, 8.8% lower than that of the Cu / AgCuMgAl-LDO catalyst. The comparative results indicate that the introduction of the additive significantly improved the hydrogenation activity of the copper-based catalyst for quinoline, enabling the catalyst to achieve a higher quinoline conversion while maintaining high selectivity for 1,2,3,4-tetrahydroquinoline.

[0090] Comparative Example 3 The stability of the CuMgAl-LDO catalyst in Comparative Example 3 was tested.

[0091] Reaction conditions: Catalyst loading mass 0.2 g, reaction temperature 100 °C o C, the reaction pressure is 3 MPa, and the mass hourly space velocity is 3 h⁻¹. -1 A quinoline-ethanol solution with a mass concentration of 5 wt% was pumped in, and a hydrogenation reaction was carried out under a hydrogen-to-oil volume ratio of 400. The results are shown in Table 8.

[0092] Table 9. Stability test results of Cu / CuMgAl-LDO catalyst

[0093] As shown in Table 9, the stability of the Cu / CuMgAl-LDO catalyst without silver additive is far inferior to that of the Cu / AgCuMgAl-LDO catalyst in Example 5 of this invention. After 100 h of continuous reaction, the quinoline conversion rate of the catalyst without silver additive dropped to 41.8%, while the conversion rate of the Cu / AgCuMgAl-LDO catalyst with silver additive remained at 88.9% after 100 h of continuous reaction. The comparative results directly demonstrate that the introduction of silver additive can improve the deactivation resistance of copper-based catalysts and ensure continuous operation stability, while catalysts without silver modification cannot meet the requirements of long-term operation.

[0094] Comparative Example 4 CuZnMgAl-LDO catalyst was prepared by co-precipitation method.

[0095] (1) Precursor preparation: Weigh 3.6 g Cu(NO3)2·3H2O, 1.5 g Zn(NO3)2·6H2O, 10.3 g Mg(NO3)2·6H2O and 7.5 g Al(NO3)3·9H2O and dissolve them together in 50 mL of deionized water to prepare solution A. Dissolve 5.6 g NaOH and 10.6 g Na2CO3 together in 60 mL of deionized water to prepare solution B. Place a three-necked flask in an oil bath and place a serpentine condenser for reflux condensation. Add 10 mL of deionized water to the three-necked flask. After the liquid in the three-necked flask reaches 60 °C, add a magnetic stirrer and stir vigorously. Then add solutions A and B dropwise to the three-necked flask simultaneously, keeping the pH between 9 and 10 during the dropwise addition. After solution A is used up, maintain the temperature at 60 °C and stir continuously for 2.5 h. After stirring, the mixture was filtered and washed with deionized water until the filtrate was neutral. The solid obtained by filtration was placed in a vacuum oven and dried at 120 °C for 10 h to obtain CuZnMgAl-LDH precursor (n Cu :n Zn :n Mg :n Al =0.75:0.25:2:1). The prepared CuZnMgAl-LDH precursor was placed in a muffle furnace and heated to 500 °C at a rate of 10 °C / min, held for 4 h, and then cooled to room temperature to obtain the mixed metal oxide CuZnMgAl-LDO precursor.

[0096] (2) Precursor reduction: The catalyst precursor prepared in (1) was placed in a fixed-bed reactor for in-situ reduction. Under the protection of a hydrogen atmosphere of 150 mL / min, the temperature was increased to 350 °C for 2 h at a rate of 10 °C / min. After the program was completed, the temperature was lowered to room temperature. The resulting catalyst was denoted as Cu / CuZnMgAl-LDO catalyst.

[0097] Figure 6 The TEM spectrum of Cu / CuZnMgAl-LDO shows an average particle size of 4.87 nm, indicating a relatively large particle size. N₂O titration of the sample revealed a Cu species dispersion of 17.5%, indicating poor dispersion. The chemical valence state of the copper component in the catalyst was investigated using XPS spectroscopy and X-ray induced Auger electron spectroscopy (AES). + / (Cu + + Cu 0 The concentration was 64.2%, which is lower than that of Cu / AgCuMgAl-LDO catalyst.

[0098] Comparative Example 4 The stability of the Cu / CuZnMgAl-LDO catalyst in Comparative Example 4 was tested.

[0099] Reaction conditions: Catalyst loading mass 0.2 g, reaction temperature 100 °C o C, the reaction pressure is 3 MPa, and the mass hourly space velocity is 3 h⁻¹. -1 A quinoline-ethanol solution with a mass concentration of 5 wt% was pumped in, and a hydrogenation reaction was carried out under conditions of a hydrogen-to-oil volume ratio of 400. The results are shown in Table 10.

[0100] Table 10 Stability test results of Cu / CuZnMgAl-LDO catalyst

[0101] As shown in Table 10, the activity and stability of the Cu / CuZnMgAl-LDO catalyst modified with zinc (Zn) as an additive are far inferior to those of the silver-modified catalyst in Example 5 of this invention. In the initial stage, the quinoline conversion rate of this catalyst was only 84.3%, 14.9% lower than that of the Cu / AgCuMgAl-LDO catalyst. After 100 h of continuous reaction, its conversion rate dropped to 45.6%, significantly lower than the 88.9% of the silver-modified Cu / AgCuMgAl-LDO catalyst. These results clearly demonstrate that, compared to non-precious metal additives such as zinc, silver additives possess unique modification advantages, simultaneously achieving a dual improvement in the activity and stability of copper-based catalysts.

[0102] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A modified copper-based catalyst, characterized in that, The modified copper-based catalyst is an AgCu / SiO2 catalyst.

2. A method for preparing an AgCu / SiO2 catalyst, characterized in that, Prepared by deposition precipitation method, including the following steps: S1. Dissolve AgNO3 and Cu(NO3)2·3H2O in deionized water to prepare solution A; take 1 / 3 volume of solution A, add urea and nitric acid to it to prepare solution B; add carrier gaseous SiO2 to the remaining 2 / 3 volume of solution A to form suspension C. Solution B was added dropwise to suspension C, and the catalyst precursor was obtained by stirring, drying and calcining. S2. The catalyst precursor is reduced under a hydrogen atmosphere to obtain the AgCu / SiO2 catalyst.

3. The preparation method according to claim 2, characterized in that, In step S1, The mass ratio of AgNO3 to Cu(NO3)2·3H2O is 1:4, and the concentration of AgNO3 in solution A is 0.014 mol / L; The mass ratio of urea to nitric acid is 15:1, and the mass percentage concentration of nitric acid in solution B is 68%. The concentration of the carrier gaseous SiO2 in suspension C is 0.25 mol / L; The volume ratio of solution B to suspension C is 1:2; The stirring temperature is 90°C. o C; The drying conditions were: vacuum drying at 110 °C for 12 h; The calcination conditions were: calcination temperature 450 ℃, calcination time 4 h.

4. The preparation method according to claim 2, characterized in that, In step S2, The reduction conditions are: reduction temperature 350°C. o C, reduction time 4 hours.

5. A silver-modified copper-based catalyst for selective hydrogenation reactions, characterized in that, The selective hydrogenation reaction includes at least one of the following: (1) Selective hydrogenation of dimethyl oxalate to prepare methyl glycolate; AgCu / SiO2 catalyst was used for the hydrogenation reaction of dimethyl oxalate. The steps are as follows: AgCu / SiO2 catalyst was packed into a fixed-bed reactor, and a 10wt% dimethyl oxalate-methanol solution was introduced. The temperature was 185-200 °C, the pressure was 1.5-3 MPa, and the hydrogen-to-oil molar ratio was 80. (2) Preparation of 1,2,3,4-tetrahydroquinoline by selective hydrogenation of quinoline; AgCu / SiO2 catalyst is used for the hydrogenation reaction of quinoline. The steps are as follows: Cu / AgCuMgAl-LDO catalyst is packed into a fixed bed reactor, and 5wt% quinoline-ethanol solution is introduced. The temperature is 80-100 °C, the pressure is 1-3 MPa, and the hydrogen-to-oil volume ratio is 400.

6. The silver-modified copper-based catalyst according to claim 5 for selective hydrogenation reaction, characterized in that, The AgCu / SiO2 catalyst was replaced with a Cu / AgCuMgAl-LDO catalyst.

7. The silver-modified copper-based catalyst according to claim 6 for selective hydrogenation reactions, characterized in that, The Cu / AgCuMgAl-LDO catalyst is prepared by a co-precipitation method, comprising the following steps: S1. Dissolve AgNO3, Cu(NO3)2·3H2O, Mg(NO3)2·6H2O and Al(NO3)3·9H2O in deionized water to obtain solution D. Dissolve sodium hydroxide and anhydrous sodium carbonate in deionized water to obtain solution E. Under stirring conditions, to 60 o Solution D and solution E were added dropwise to deionized water of C, and the pH was maintained between 9 and 10 during the dropwise addition. After the dropwise addition was completed, the mixture was stirred for 2-3 hours, and then filtered, washed, dried and calcined to obtain the catalyst precursor. S2. The catalyst precursor is reduced under a hydrogen atmosphere to obtain the Cu / AgCuMgAl-LDO catalyst.

8. The silver-modified copper-based catalyst according to claim 7 for selective hydrogenation reaction, characterized in that, In step S1, The molar ratio of AgNO3, Cu(NO3)2·3H2O, Mg(NO3)2·6H2O and Al(NO3)3·9H2O is 0.25:0.75:2:1, and the concentration of AgNO3 in solution D is 0.1 mol / L; The mass ratio of sodium hydroxide to anhydrous sodium carbonate is 1:2; The drying conditions were: vacuum drying at 120 °C for 10 h; The calcination conditions were: calcination temperature 500 ℃, calcination time 4 h.

9. The silver-modified copper-based catalyst according to claim 7 for selective hydrogenation reaction, characterized in that, In step S2, The reduction conditions are: reduction temperature 350°C. o C, reduction time 2 h.

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