A preparation method and application of a catalyst for directly dehydrogenating ethanol to acetaldehyde

Abstract

This invention relates to a method for preparing and applying a catalyst for the direct dehydrogenation of ethanol to acetaldehyde. The method utilizes the principle of hydroxymethylation, employing different organic amines as nitrogen sources to react with formaldehyde, thereby achieving nitrogen doping. The resulting nitrogen-doped carbon support enriches ethanol while promoting acetaldehyde desorption, which helps reduce side reactions of acetaldehyde and improves acetaldehyde selectivity and catalyst stability. The catalyst obtained by this invention features uniformly dispersed active sites, high catalyst activity, resistance to deactivation, high mechanical strength, and high thermal stability. In the direct dehydrogenation of ethanol to acetaldehyde, the catalyst exhibits advantages such as high activity, high selectivity, and high stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing a Cu / Si@NC catalyst for direct dehydrogenation of ethanol. Background Technology

[0002] Acetaldehyde, an important organic chemical, is a crucial intermediate in the synthesis of pharmaceuticals and food additives, possessing extremely high industrial application value. Downstream products of acetaldehyde include acetate esters, sorbic acid, pyridine compounds, and crotonaldehyde, which have wide applications in the chemical industry. With the development of the chemical industry, my country is currently the world's largest consumer of acetaldehyde. Traditional methods for synthesizing acetaldehyde mainly include ethylene oxidation, acetylene hydration, acetic acid reduction, and ethane oxidation. These traditional methods suffer from drawbacks such as high energy consumption and numerous byproducts. With the advancement of science and technology, ethanol dehydrogenation has received increasing attention. Ethanol dehydrogenation includes oxidative dehydrogenation and direct dehydrogenation. Ethanol oxidative dehydrogenation is an exothermic reaction; therefore, industrial direct oxidative dehydrogenation requires high-temperature conditions, resulting in high energy consumption. Simultaneously, water is generated during the reaction, making acetaldehyde separation and purification difficult and increasing production costs. Furthermore, byproducts such as formic acid and acetic acid pose serious corrosion problems during product condensation and recovery. The direct dehydrogenation of ethanol to synthesize acetaldehyde can effectively reduce energy consumption in the production process, and the product H2 is a clean and renewable energy source. Therefore, ethanol can not only synthesize the widely used acetaldehyde, but also serve as an effective carrier for hydrogen storage.

[0003] Currently, direct dehydrogenation of ethanol can be divided into homogeneous catalysis and heterogeneous catalysis. Although homogeneous catalysis has been proven to have excellent catalytic performance, its dependence on precious metals and the high cost of ligands limit its large-scale practical application. Compared with homogeneous catalysis, heterogeneous catalysts are easier to recover and can exhibit superior catalytic performance. Non-precious metal supported Cu-based catalysts exhibit excellent catalytic activity in heterogeneous catalysis, with high ethanol conversion and high selectivity for acetaldehyde.

[0004] The design and development of highly active, selective, and stable non-precious metal catalysts has become a bottleneck problem for this reaction. However, copper-based catalysts have been extensively studied in the ethanol dehydrogenation reaction and have proven to be the most commercially promising catalysts. CN116060098A discloses a Cu-based MFI molecular sieve single-atom catalyst prepared using an ammonia stripping method and an acid treatment strategy. The ammonia stripping method can change the pore structure of the molecular sieve and improve the anchoring effect between copper and the molecular sieve, which helps to improve the stability of the catalyst. However, the acid treatment significantly reduces the copper loading. Although single-atom dispersion of copper is achieved, the overall activity of the catalyst is greatly reduced. CN117225423A discloses a catalyst for the dehydrogenation of ethanol to acetaldehyde, using silica as a support, copper as the active component, and nickel and zinc as promoters. The loading of the three metals is achieved through an ammonia stripping method and a post-impregnation method. The catalyst preparation process is cumbersome and greatly increases the production cost of the catalyst. This patented study found that carbon carriers play an important role in enriching ethanol. At the same time, using nitrogen-doped carbon materials as carriers is beneficial to promoting acetaldehyde desorption, thereby reducing side reactions of acetaldehyde and improving acetaldehyde selectivity. Summary of the Invention

[0005] The purpose of this invention is to address the limitations of current technologies by providing a method for preparing and applying a catalyst for the dehydrogenation of ethanol to acetaldehyde. This method uses different organic amines as nitrogen sources, and then achieves nitrogen doping through a hydroxymethylation reaction with formaldehyde (formalin). The catalyst obtained by this invention has the characteristics of uniformly dispersed active sites, high catalyst activity, low deactivation rate, high mechanical strength, and high thermal stability. In the direct dehydrogenation of ethanol to acetaldehyde, the catalyst exhibits advantages such as high activity, high selectivity, and high stability.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing a catalyst for the direct dehydrogenation of ethanol to acetaldehyde, the method comprising the following steps:

[0008] (1) Weigh anhydrous sodium carbonate, resorcinol and formalin and put them into deionized water. Dissolve them by sonication to obtain solution A. The mass ratio of anhydrous sodium carbonate, resorcinol and formalin to water is 0.1~1:10~100:10~50:30.

[0009] (2) Weigh out organic amine and formalin, place them in deionized water, and dissolve them by sonication to obtain solution B.

[0010] The mass ratio of organic amine to formalin is 1:2 to 5.

[0011] The organic amine is one or more of aniline, diphenylamine, phenylenediamine, melamine, ethylenediamine, and urea;

[0012] The formaldehyde concentration in the formalin in steps (1) and (2) ranges from 35% to 40%.

[0013] (3) Add solutions A and B to the silica sol with stirring within 3-30 minutes to obtain mixture C;

[0014] For every 50–150 mL of silica sol, add 10–50 mL of solution A and 10–50 mL of solution B.

[0015] The concentration of the silica sol is 30 wt%; the particle size of the silica is 8-15 nm.

[0016] (4) Mixture C is heated and solidified in a water bath at 35-55°C for 3-8 hours under a sealed environment to obtain solid D;

[0017] (5) Dry and grind solid D, and then calcine it at 600-1000℃ for 1-8 hours in an inert atmosphere to obtain solid E;

[0018] (6) Solid E is placed in sodium hydroxide solution, heated and stirred in a water bath at 40-70°C for 1-5 hours, and after filtration, washing and vacuum drying, carrier F is obtained;

[0019] The mass ratio of solid E to sodium hydroxide is 1–10:5–20.

[0020] The concentration of sodium hydroxide solution is 0.1-4 mol / L.

[0021] (7) Weigh out copper source, water and ammonia water and put them into a container. Seal and stir at room temperature to dissolve all the solids to obtain solution G;

[0022] The mass ratio of copper, water, and ammonia in the copper source is 0.01–0.5:100:50.

[0023] The concentration of the ammonia solution is 20-30 wt%.

[0024] (8) Add carrier F to solution G, stir for 4-10 hours, raise the temperature to 60-80℃, keep the liquid level basically unchanged, and evaporate ammonia until the solution pH = 7-9. After filtration, washing, vacuum drying and calcination, the desired catalyst is obtained.

[0025] In this case, 0.5–4 g of carrier F is added to every 200 mL of solution G;

[0026] In step (5), the drying temperature is 80-12℃ and the drying time is 42-96h.

[0027] In step (5), the inert atmosphere is one of nitrogen, argon, or a nitrogen-argon mixture.

[0028] In step (6), the vacuum drying temperature is 60-90℃ and the vacuum drying time is 4-12h.

[0029] In step (7), the copper source is one or more of copper nitrate trihydrate, copper sulfate and copper chloride.

[0030] In step (8), the vacuum drying temperature is 60-90℃ and the vacuum drying time is 4-12h.

[0031] In step (8), the roasting atmosphere is argon, the roasting temperature is 250-500℃, and the roasting time is 1-5h.

[0032] The catalyst used in the preparation method is applied to the direct dehydrogenation reaction of ethanol.

[0033] Specifically, the following steps are included:

[0034] (1) The reaction gas is introduced into a fixed-bed reactor filled with catalyst after the N2 gas is vented, and the reaction is carried out at atmospheric pressure and 240-350℃ to obtain the catalytic performance of direct dehydrogenation of ethanol to acetaldehyde.

[0035] The reactant gas is a mixture of ethanol and nitrogen, with ethanol accounting for 2–20% of the reactant gas; the space velocity is 0.5–3 h⁻¹. -1 .

[0036] The essential features of this invention are:

[0037] The core innovation of this invention lies in the discovery that nitrogen-doped carbon supports prepared using different nitrogen sources can enrich ethanol and promote acetaldehyde desorption, thereby improving the activity of the catalyst, reducing side reactions of acetaldehyde, and improving the selectivity of acetaldehyde and the stability of the catalyst.

[0038] In current technology, copper is supported on silicon-carbon composite material as a catalyst by the ammonia stripping method. Active metallic copper is introduced through the ammonia stripping method to obtain a catalyst with fatty acid ester hydrogenation performance.

[0039] This invention utilizes the principle of hydroxymethylation reaction, employing different organic amines as nitrogen sources to react with formaldehyde and achieve nitrogen doping. The resulting nitrogen-doped carbon support enriches ethanol while promoting acetaldehyde desorption, which helps reduce side reactions of acetaldehyde, improves acetaldehyde selectivity and catalyst stability, and thus warrants a patent application for a catalyst preparation method for the direct dehydrogenation of ethanol to acetaldehyde.

[0040] The beneficial effects of this invention are as follows:

[0041] (1) A hard template method was adopted, using SiO2 as a hard template agent, phenolic resin as a carbon precursor, and organic amine as a nitrogen source. After carbonization and partial removal of the template agent, a mesoporous silica-coated nitrogen-carbon composite material was obtained. The preparation method is simple and low-cost. The pore size of the obtained catalyst is controllable and mainly distributed in the mesoporous range, which can fully realize the internal and external diffusion and adsorption-desorption of reactants and products in the pores during the ethanol dehydrogenation reaction. Within 1.5 h -1 At a space velocity and 300℃, an ethanol conversion rate of 90.5% and an acetaldehyde selectivity of 92% were achieved, and the reaction remained basically stable after 600 hours.

[0042] (2) The method uses phenolic resin with mature preparation process as carbon precursor, organic amine as nitrogen source and silica sol as hard template agent. The synthesis method has the advantages of abundant raw materials, simple preparation process, adjustable material structure, high repeatability and easy to realize large-scale preparation, and has broad industrial application prospects.

[0043] (3) The mesoporous silica-coated nitrogen-carbon composite material has an enrichment effect on ethanol. Simultaneously, acetaldehyde has a low low-temperature desorption barrier (300°C), allowing it to rapidly detach from the catalyst surface after formation, reducing side reactions and improving acetaldehyde selectivity. Compared to the undoped nitrogen catalyst, the nitrogen-doped catalyst exhibits better ethanol enrichment at 1.5 h. -1 At space velocity and 300°C, the ethanol conversion rate increases by nearly 30%, and the acetaldehyde selectivity increases by nearly 20%.

[0044] (4) Cu is loaded onto silicon-coated nitrogen-carbon composite material by ammonia stripping method. The copper is more uniformly dispersed and smaller in particle size. The active material and the support have stronger interaction forces and are less likely to be deactivated due to the aggregation of active centers in the catalytic reaction. Attached Figure Description

[0045] Figure 1 The pore size distribution diagrams are for the catalysts prepared in Examples 1, 7, 10 and Comparative Example 1.

[0046] Figure 2 The graph shows the changes in conversion and selectivity of the catalyst prepared in Example 1 during the ethanol dehydrogenation reaction in a fixed-bed reactor.

[0047] Figure 3 The image shows a SEM image of the catalyst prepared in Example 1. Detailed Implementation

[0048] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0049] Example 1

[0050] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0051] (1) Weigh 0.15g of anhydrous sodium carbonate, 10g of resorcinol and 10g of formalin (concentration of 37%) and put them into 6g of deionized water. Sonicate until completely dissolved to obtain solution A.

[0052] (2) Weigh 5g of melamine and 10g of formalin and put them into deionized water. Dissolve them by sonication to obtain solution B.

[0053] (3) Measure 90 mL of silica sol (SiO2 mass concentration of 30 wt%, silica particle size of 8-15 nm) and put it into a beaker. During the stirring process, slowly add solution A and solution B at a rate of 5 mL / min. After the addition is completed, mixture C is obtained.

[0054] (4) Seal the mouth of the beaker with plastic wrap and solidify the mixture C under a water bath heating condition of 38°C for 4 hours to obtain solid D.

[0055] (5) Crush solid D with a spatula, dry it at 80°C for 36 hours, grind the solid until the particles are ≤200 mesh, and carbonize it at 800°C for 2 hours under an argon atmosphere to obtain solid E.

[0056] (6) Weigh 600 mL of water, 6.74 g of sodium hydroxide (0.17 mol) and 5.73 g of solid E carrier and put them into a beaker. Heat and stir in a water bath at 50 °C for 2 h. Filter to obtain solid. Wash with deionized water until the filtrate is neutral. Dry under vacuum at 80 °C for 8 h to obtain carrier F.

[0057] (7) Weigh 0.81g of copper nitrate trihydrate (containing 0.22g of copper element), 100mL of deionized water, and 50mL of ammonia water (concentration 25-28wt%) and put them into a flask. Seal and stir in a water bath at 38℃ for 30min to obtain solution G.

[0058] (8) Add 1g of carrier F to solution G, stir for 6h, and then heat to 80℃ to start ammonia evaporation. Mark the liquid level on the outside of the three-necked flask with a pen, keep the liquid level in the flask unchanged, and continue ammonia evaporation until the solution pH=7. Filter to obtain solid, wash with deionized water until the filtrate pH=7, vacuum dry the filter cake at 80℃ for 8h, and calcine at 350℃ for 2h under argon atmosphere to obtain the desired catalyst, denoted as Cu / Si@NC-1.

[0059] The evaluation process and conditions for catalysts are as follows:

[0060] (1) The catalysts Cu / Si@NC-1~15 and Cu / Si@C-16 prepared by the above method were respectively loaded into a fixed bed reactor with an inner diameter of 8 mm, and N2 gas was continuously introduced for 4 h to remove impurity gases in the system.

[0061] (2) Introduce 10% ethanol gas at a space velocity of 1.5 h⁻¹. -1 The carrier gas is nitrogen, the total flow rate of the mixed gas is 98 mL / min, the reaction temperature is 300℃, and the reaction is carried out at atmospheric pressure.

[0062] (3) After the reaction stabilizes, online chromatography is used to analyze the reaction raw materials and products.

[0063] Product analysis methods:

[0064] The product mainly consists of ethanol, acetaldehyde, diethyl ether, acetic acid, ethylene, ethyl formate, and ethyl acetate. Online analysis of the products was performed using an Anhui GC5190E chromatograph equipped with FID and TCD detectors. The product analysis employed the internal standard method, using ethanol as the internal standard, and the relative molar correction factors of each component relative to ethanol were calculated according to Formula 1.

[0065] Formula 1: f2 / f1=(A1m2M1) / (A2m1M2); where f1 – molar correction factor for ethanol, set to 1; f2 – molar correction factor for the substance to be determined; A1 – peak area of ​​ethanol; A2 – peak area of ​​the substance to be determined; m1 – mass of ethanol; m2 – mass of the substance to be determined; M1 – molecular weight of ethanol; M2 – molecular weight of the substance to be determined. From this, the corresponding conversion rate and selectivity can be calculated.

[0066] The evaluation effect of the catalyst prepared in Example 1 on the ethanol dehydrogenation reaction is as follows: Figure 1 As shown, the products of the catalytic reaction fluctuated in the early stage of catalysis, but quickly stabilized. During the 600-hour activity and stability evaluation, the conversion rate of ethanol remained stable above 90%, and the selectivity of the main product acetaldehyde reached over 92.5%, exhibiting long-term stability. The main byproducts of the catalytic reaction were ethylene, diethyl ether, ethyl formate, ethyl acetate, and acetic acid, with selectivity for byproducts generally below 3%. After 600 hours of activity evaluation, the catalyst showed no significant deactivation, and the stability and activity of the catalytic reaction remained stable over a long period, indicating that the catalyst has high industrial application value.

[0067] Example 2

[0068] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0069] Other conditions are the same as in Example 1, except that the amount of anhydrous sodium carbonate added in step (1) is changed: the amount of anhydrous sodium carbonate added is 0.24g, and the resulting catalyst is denoted as Cu / Si@NC-2.

[0070] Example 3

[0071] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0072] Other conditions are the same as in Example 1, except that the type of organic amine in step (2) is changed: melamine is replaced with aniline, and the resulting catalyst is denoted as Cu / Si@NC-3.

[0073] Example 4

[0074] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0075] Other conditions are the same as in Example 1, except that the dropping rates of solution A and solution B in step (3) are changed: the dropping rate is 20 mL / min, and the resulting catalyst is denoted as Cu / Si@NC-4.

[0076] Example 5

[0077] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0078] Other conditions are the same as in Example 1, except that the water bath temperature in step (4) is changed: the water bath temperature is 55°C, and the resulting catalyst is denoted as Cu / Si@NC-5.

[0079] Example 6

[0080] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0081] Other conditions are the same as in Example 1, except that the calcination procedure in step (5) is changed: calcination is carried out at 600°C for 4 hours under a nitrogen atmosphere, and the resulting catalyst is denoted as Cu / Si@NC-6.

[0082] Example 7

[0083] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0084] Other conditions are the same as in Example 1, except that the amount of sodium hydroxide added in step (6) is changed: the amount of sodium hydroxide added is 8.26g, and the resulting catalyst is denoted as Cu / Si@NC-7.

[0085] Example 8

[0086] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0087] Other conditions are the same as in Example 1, except that the water bath conditions in step (6) are changed: the water bath is heated and stirred at 70°C for 5 hours, and the resulting catalyst is denoted as Cu / Si@NC-8.

[0088] Example 9

[0089] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0090] Other conditions are the same as in Example 1, except that the copper source in step (7) is changed from copper nitrate trihydrate to copper sulfate, and the resulting catalyst is denoted as Cu / Si@NC-9.

[0091] Example 10

[0092] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0093] Other conditions are the same as in Example 1, except that the amount of copper nitrate trihydrate added in step (7) is changed: 3.26g of copper nitrate trihydrate ammonia water is added, and the resulting catalyst is denoted as Cu / Si@NC-10.

[0094] Example 11

[0095] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0096] Other conditions are the same as in Example 1, except that the amount of support added in step (8) is changed: 1.5g of support is added, and the resulting catalyst is denoted as Cu / Si@NC-11.

[0097] Example 12

[0098] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0099] Other conditions are the same as in Example 1, except that the ammonia distillation temperature in the water bath in step (8) is changed to 60°C. The resulting catalyst is denoted as Cu / Si@NC-12.

[0100] Example 13

[0101] The preparation steps of the mesoporous Cu / Si@NC catalyst for ethanol dehydrogenation are as follows:

[0102] Other conditions are the same as in Example 1, except that the calcination procedure in step (8) is changed: calcination at 500°C for 3 hours, and the resulting catalyst is denoted as Cu / Si@NC-13.

[0103] Comparative Example 1

[0104] The Cu / Si@NC catalyst was prepared using an equal-volume impregnation method. The specific preparation steps are as follows:

[0105] (1) The preparation steps of Si@NC carrier are the same as steps (1) to (7) in Example 1.

[0106] (2) Weigh 1.63g of copper nitrate trihydrate and dissolve it in deionized water. Stir for 30 minutes to obtain the impregnation solution.

[0107] (3) The impregnation solution was added dropwise onto the support Si@NC, dried at room temperature for 4 hours, and then dried under vacuum at 80°C for 8 hours. The catalyst was then calcined at 350°C for 2 hours under an argon atmosphere to obtain the desired catalyst, which is denoted as Cu / Si@NC-14.

[0108] Comparative Example 2

[0109] The purpose is to compare with Example 1 to illustrate the effect of the sodium hydroxide dissolution step on catalytic activity.

[0110] The preparation steps of the mesoporous Cu / Si@NC catalyst are as follows:

[0111] (1) Weigh 0.12g of anhydrous sodium carbonate, 9g of resorcinol and 13.27g of formalin and put them into 3.68g of deionized water. Sonicate until completely dissolved to obtain solution A.

[0112] (2) Weigh 5g of melamine and 10g of formalin and put them into deionized water. Dissolve them by sonication to obtain solution B.

[0113] (3) Measure 90 ml of silica sol and put it into a beaker. While stirring, slowly add solution A and solution B at a rate of 5 mL / min. After the addition is complete, mixture C is obtained.

[0114] (3) Seal the mouth of the beaker with plastic wrap and solidify the mixture C under a water bath heating condition of 38°C for 4 hours to obtain solid D.

[0115] (4) Crush solid D with a spatula, dry it at 80°C for 36 hours, grind the solid until the particles are ≤200 mesh, and carbonize it at 800°C for 2 hours under an argon atmosphere to obtain solid E.

[0116] (5) Weigh 1.63g of copper nitrate trihydrate, 100mL of deionized water and 50mL of ammonia into a flask, seal and stir in a water bath at 38℃ for 30min to obtain solution F.

[0117] (6) Add 1g of carrier E to solution F, stir for 6h, and then heat to 80℃ to start ammonia evaporation. Mark the liquid level on the outside of the three-necked flask with a pen, keep the liquid level in the flask unchanged, and continue evaporating ammonia until the solution pH=7. Filter to obtain solid, wash with deionized water until the filtrate pH=7, vacuum dry the filter cake at 80℃ for 8h, and calcine at 350℃ for 2h under argon atmosphere to obtain the desired catalyst, denoted as Cu / Si@NC-15.

[0118] Comparative Example 3

[0119] The purpose is to compare with Example 1 to illustrate the effect of N doping on catalytic activity.

[0120] (1) Weigh 0.15g of anhydrous sodium carbonate, 10g of resorcinol and 15.38g of formalin and put them into 5.87g of deionized water. Sonicate until completely dissolved to obtain solution A.

[0121] (2) Measure 90 ml of silica sol and put it into a beaker. During the stirring process, slowly add solution A at a rate of 5 mL / min. After the addition is complete, mixture B is obtained.

[0122] (3) Seal the mouth of the beaker with plastic wrap and solidify the mixture B under a water bath heating condition of 38°C for 4 hours to obtain solid C.

[0123] (4) Crush solid C with a spatula, dry it in a forced-air dryer at 80°C for 36 hours, grind the solid until the particles are ≤200 mesh, and carbonize it at 800°C for 2 hours under an argon atmosphere to obtain solid D.

[0124] (5) Weigh 600 mL of water, 6.74 g of sodium hydroxide and 5.73 g of solid D carrier and put them into a beaker. Heat and stir in a water bath at 50 °C for 2 h. Filter to obtain solid. Wash with deionized water until the filtrate is neutral. Dry under vacuum at 80 °C for 8 h to obtain carrier E.

[0125] (6) Weigh 0.81g of copper nitrate trihydrate, 100mL of deionized water and 50mL of ammonia into a flask, seal and stir in a water bath at 38℃ for 30min to obtain solution F.

[0126] (7) Add 1g of carrier E to solution F, stir for 6h, and then heat to 80℃ to start ammonia evaporation. Mark the liquid level on the outside of the three-necked flask with a pen, keep the liquid level in the flask unchanged, and continue evaporating ammonia until the solution pH=7. Filter to obtain solid, wash with deionized water until the filtrate pH=7, vacuum dry the filter cake at 80℃ for 8h, and calcine at 350℃ for 2h under argon atmosphere to obtain the desired catalyst, denoted as Cu / Si@C-16.

[0127] The reaction performance of the catalysts prepared in Examples 1-13 and Comparative Examples 1-3 is shown in Table 1. All data results are stable results after 50 h of reaction.

[0128] Table 1

[0129] Catalyst X (ethanol) / % S (acetaldehyde) / % Catalyst X (ethanol) / % S (acetaldehyde) / % Cu / Si@NC-1 90.5 92.2 Cu / Si@NC-9 63.4 73.2 Cu / Si@NC-2 87.6 89.4 Cu / Si@NC-10 88.4 90.5 Cu / Si@NC-3 84.3 94.6 Cu / Si@NC-11 76.8 91.5 Cu / Si@NC-4 85.4 90.4 Cu / Si@NC-12 65.2 88.3 Cu / Si@NC-5 78.6 91.5 Cu / Si@NC-13 56.4 76.8 Cu / Si@NC-6 75.2 82.4 Cu / Si@NC-14 25.8 85.6 Cu / Si@NC-7 75.3 87.2 Cu / Si@NC-15 68.4 87.6 Cu / Si@NC-8 86.5 90.3 Cu / Si@C-16 61.2 72.3

[0130] The pore size distribution diagrams of the catalysts prepared in Examples 1, 7, 10 and Comparative Example 1 are shown below. Figure 1As shown, the catalyst prepared in Example 1 has a pore size mainly distributed in the mesoporous range of 11–30 nm; in Example 7, due to the increased addition of sodium hydroxide, the amount of dissolved silica increased, resulting in some pores in the catalyst becoming macropores, with the pore size mainly distributed in the range of 12–70 nm; in Example 10, due to the increased addition of Cu, some pores were blocked by Cu, resulting in smaller pores in the catalyst, but the pore size of the catalyst was still within the mesoporous range, with the pore size mainly distributed in the range of 6–15 nm; in Comparative Example 1, due to the use of impregnation method to load Cu, Cu is more likely to form large particles, so the pore size of the catalyst is reduced significantly, with the pore size mainly distributed in the range of 2–9 nm. Comparative Example 2 mainly involves loading without removing the template agent, which prevents the catalyst from generating suitable pores, thus affecting the reaction activity and selectivity; Comparative Example 3 mainly involves preparing the catalyst support without nitrogen doping, thereby reducing the amount of ethanol adsorption and acetaldehyde desorption at low temperatures (below 300 °C), thus reducing the catalyst activity and selectivity.

[0131] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

[0132] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a catalyst for the direct dehydrogenation of ethanol to acetaldehyde, characterized in that, The method includes the following steps: (1) Weigh anhydrous sodium carbonate, resorcinol, and formalin and dissolve them in deionized water by sonication to obtain solution A. The mass ratio of anhydrous sodium carbonate, resorcinol, formalin and deionized water is 0.1~1:10~100:10~50:30; (2) Weigh out organic amine and formalin, place them in deionized water, and dissolve them by sonication to obtain solution B. The mass ratio of organic amine to formalin is 1:2~5; The organic amine is one or more of aniline, phenylenediamine, melamine, and ethylenediamine; (3) Add solutions A and B to the silica sol with stirring within 3-30 minutes to obtain mixture C; For every 50-150 mL of silica sol, add 10-50 mL of solution A and 10-50 mL of solution B. (4) The mixture C is heated and solidified in a water bath at 35~55℃ for 3~8h under a sealed environment to obtain solid D; (5) Dry and grind solid D, and then calcine it at 600~1000℃ for 1~8h in an inert atmosphere to obtain solid E; (6) Place solid E in sodium hydroxide solution, heat and stir in a water bath at 40~70℃ for 1~5h, and after filtration, washing and vacuum drying, the carrier F is obtained; The mass ratio of solid E to sodium hydroxide is 1~10:5~20; (7) Weigh out copper source, water and ammonia water and put them into a container. Seal and stir at room temperature to dissolve all the solids to obtain solution G; The mass ratio of copper, water, and ammonia in the copper source is 0.01~0.5:100:

50. (8) Add carrier F to solution G, stir for 4-10 h, raise the temperature to 60-80℃, keep the liquid level constant and evaporate ammonia until the solution pH=7-9. After filtration, washing, vacuum drying and calcination, the desired catalyst is obtained. For every 200 mL of solution G, add 0.5–4 g of carrier F.

2. The method for preparing the catalyst for the direct dehydrogenation of ethanol to acetaldehyde as described in claim 1, characterized in that, The formaldehyde concentration in formalin in steps (1) and (2) ranges from 35% to 40%, the concentration of silica sol in step (3) is 30 wt%, and the particle size of silica is 8-15 nm.

3. The method for preparing the catalyst for the direct dehydrogenation of ethanol to acetaldehyde as described in claim 1, characterized in that, In step (5), the drying temperature is 80°C and the drying time is 42~96h.

4. The method for preparing the catalyst for the direct dehydrogenation of ethanol to acetaldehyde as described in claim 1, characterized in that, In step (5), the inert atmosphere is one of nitrogen, argon, or a nitrogen-argon mixture.

5. The method for preparing the catalyst for the direct dehydrogenation of ethanol to acetaldehyde as described in claim 1, characterized in that, In step (6), the vacuum drying temperature is 60~90℃, the vacuum drying time is 4~12h, and the sodium hydroxide solution concentration is 0.1-4mol / L.

6. The method for preparing the catalyst for the direct dehydrogenation of ethanol to acetaldehyde as described in claim 1, characterized in that, In step (7), the copper source is one or more of copper nitrate trihydrate, copper sulfate and copper chloride; the concentration of the ammonia water is 20-30 wt%.

7. The method for preparing the catalyst for the direct dehydrogenation of ethanol to acetaldehyde as described in claim 1, characterized in that, In step (8), the vacuum drying temperature is 60~90℃ and the vacuum drying time is 4~12h; the calcination atmosphere is argon, the calcination temperature is 250~500℃ and the calcination time is 1~5h.

8. The application of the catalyst prepared by the method described in claim 1 in the direct dehydrogenation of ethanol to acetaldehyde.

9. The application as described in claim 8, characterized in that, Includes the following steps: (1) The reaction gas is introduced into a fixed-bed reactor filled with catalyst after N2 is vented, and the reaction is carried out at atmospheric pressure and 240~350℃ to obtain the catalytic performance of direct dehydrogenation of ethanol to acetaldehyde. The reactant gas is a mixture of ethanol and nitrogen, with ethanol accounting for 2-20% of the reactant gas; the space velocity is 0.5-3 h⁻¹. -1 .

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