Preparation method and application of nano-copper-based catalyst with controllable grain size

Abstract

The invention discloses a preparation method and application of a nano copper-based catalyst with a controllable grain size, and belongs to the technical field of catalyst preparation. The preparation method comprises the following steps: dissolving a mild organic reducing agent in water to obtain a reducing agent solution; dissolving PVP in a reducing agent solution to obtain a solution A; dissolving a copper salt or a composition of the copper salt and other metal salts and PVP in water to obtain a solution B; slowly dropwise adding the solution B into the solution A; alkali liquor is added in the dropwise adding process, the reaction liquid is suspension liquid, and the pH of the suspension liquid is adjusted to be alkaline; after dropwise adding, reacting for a period of time, changing the color of the suspension liquid, finally turning into dark red, stopping the reaction, centrifuging, washing the solid, and carrying out ultrasonic treatment to obtain the nano-copper composition; the nano-copper composition and liquid paraffin are subjected to temperature rise and heating reaction under the protection of inert gas to obtain the pasty nano-copper-based catalyst. The catalyst prepared by the invention shows good catalytic activity and excellent stability in a reaction for preparing ethanol from synthesis gas.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, and particularly relates to a method for preparing and applying a nano-copper-based catalyst with controllable grain size. Background Technology

[0002] The catalytic conversion of syngas (CO + H2) is a core process in C1 chemistry. Producing high-value liquid fuels (such as ethanol and other C2+ alcohols) is a key pathway to achieving clean and efficient utilization of coal and the resource recovery of carbon dioxide, possessing significant strategic and economic importance. Among numerous catalytic systems, copper-based catalysts have attracted considerable attention due to their unique catalytic activity and selectivity towards alcohols, particularly ethanol. Currently, the industrial application of this technology still faces significant challenges, the core issue being the difficulty in simultaneously achieving catalyst stability and selectivity.

[0003] Currently, the key factor limiting the performance of copper-based catalysts lies in the size stability of their active centers—metallic copper nanocrystals. Under harsh reaction conditions of high temperature and high pressure, copper nanoparticles, due to their high surface energy, are prone to sintering and migration, leading to rapid growth and deactivation of active grains and a sharp shortening of catalyst lifetime. Simultaneously, the selectivity of catalytic reactions heavily depends on the exposure of copper crystal faces and the size effect. Studies have shown that smaller copper nanoparticles are favorable for reactions such as methanol synthesis, while larger particles tend to favor C2+ alcohols such as ethanol. Therefore, how to precisely control and stabilize the size of copper nanocrystals has become a core scientific problem and technical challenge in overcoming the bottlenecks in syngas-to-ethanol technology.

[0004] Patent CN102500374A discloses a copper-based multimetal nanocatalyst for the synthesis of higher alcohols from syngas, which promotes carbon chain growth by introducing multiple Fischer-Tropsch metal components such as ruthenium, iron, cobalt, and nickel. While this type of catalyst exhibits some activity in the synthesis of higher alcohols, its complex multimetallic system leads to cumbersome preparation processes and high costs, and it generally suffers from low selectivity for the target product ethanol. Furthermore, this technology fails to provide an effective method for precise and continuous control of the catalyst nanocrystal size, resulting in unpredictable catalyst performance design and challenges in reproducibility and stability.

[0005] In existing technologies, methods for controlling metal grain size mainly fall into two categories: First, using different types of supports (such as ZnO, SiO2) or adding a second metal promoter (such as Fe, Co) (e.g., the copper-based multimetal nanocatalyst disclosed in CN102500374A) to suppress sintering through metal-support interactions or alloy formation. However, these methods are complex, and the introduced heterogeneous components may cover active sites or unpredictably affect intrinsic reaction pathways, hindering in-depth research on the size effect of copper itself. Second, liquid-phase reduction methods are used to prepare nano-copper, but these methods either focus on obtaining small-sized nanoparticles themselves or are limited by specific equipment (such as ultrasound), failing to reveal the universal law that the continuous and precise controllable size of nano-copper grains can be achieved by simply adjusting a single chemical parameter (such as the concentration of the reducing agent). In particular, there is a lack of in-depth research that systematically correlates this size effect with the selectivity of the specific reaction of syngas to ethanol and demonstrates its advantages over complex catalyst systems.

[0006] Therefore, developing a new strategy that does not rely on complex carriers or auxiliaries, has a simple process, can achieve precise and controllable preparation of copper grains by adjusting key synthesis parameters, and can be directly applied to the synthesis of ethanol from syngas while exhibiting excellent selectivity and stability has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a method for controlling the grain size of a syngas-to-ethanol catalyst (nano-copper based catalyst). This method has the advantages of simple preparation, low cost, and suitability for industrial production. Addressing the bottleneck problems in existing syngas-to-ethanol copper-based catalyst preparation technologies, this invention provides a method for constructing a pure copper catalytic system with controllable size by simply adjusting core preparation parameters. The resulting series of nano-copper catalysts exhibit good activity and stability in the syngas-to-ethanol reaction, providing a reliable material basis and preparation route for advancing the application of this technology.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for controlling the grain size of a syngas-to-ethanol catalyst (nano-copper) includes the following steps: S1. Dissolve a mild organic reducing agent in water to obtain a reducing agent solution; S2. Dissolve polyvinylpyrrolidone (PVP) in the reducing agent solution in S1 to obtain solution A; S3. Dissolve copper salt or a combination of copper salt and other metal salts with PVP in water in a certain proportion to obtain solution B; S4. Heat solution A to a certain temperature and adjust solution A to be alkaline. Slowly add solution B to solution A. The reaction solution is a suspension. During the addition process, control the reaction solution to be alkaline. S5. After the addition is complete and the reaction has continued for a period of time, the color of the suspension changes and eventually turns dark red. The reaction is stopped, the solid is centrifuged, washed, and sonicated to obtain nano-copper or nano-copper-based bimetal. S6. A slurry-like nano-copper catalyst is obtained by heating nano-copper or nano-copper-based bimetal and liquid paraffin under inert gas protection.

[0009] Furthermore, the mild organic reducing agent includes glucose, ascorbic acid, and sodium citrate, and the concentration of the reducing agent solution is 0.1~0.6 mol / L.

[0010] Furthermore, the mass ratio of PVP to mild organic reducing agent in solution A is 1:0.4~3.6.

[0011] Furthermore, the copper salt mentioned in step S3 includes copper nitrate and copper sulfate, and the other metal salts are selected from one of iron salts or cobalt salts. The iron salts include ferric nitrate and ferric sulfate, and the cobalt salts include cobalt nitrate and cobalt sulfate.

[0012] Furthermore, the mass ratio of copper salt to PVP in solution B is 7:3~6, the mass ratio of copper salt to iron salt or cobalt salt is 2~5:1, the volume ratio of solution B to solution A is 1:1, and solution A is heated to 80~100℃ in step S3.

[0013] Further, the alkaline solution in step S4 is an aqueous solution of alkali metal hydroxide, including sodium hydroxide solution and potassium hydroxide solution, and the concentration of the alkaline solution is 4-6 mol / L.

[0014] Furthermore, in step S4, the dropping rate of solution B is 1.8~2.0 ml / min, and the pH of the reaction solution is controlled at 8~10.

[0015] Furthermore, in step S5, the reaction time is 1-2 hours, the centrifugation conditions are 8500-10000 rpm, the centrifugation time is 8-10 minutes, the heating rate in step S6 is 5-10 °C / min, the final heating temperature is 260-280 °C, and the holding time is 7-9 hours.

[0016] Another objective of this application is to provide the application of nano-copper catalysts for the catalytic synthesis of ethanol from syngas under high pressure.

[0017] Furthermore, the method for preparing ethanol from syngas is as follows: a mixture of H2 and CO is introduced into a reactor containing a slurry of nano-copper catalyst. The pressure inside the reactor is slowly increased to 3.5~4.0 MPa. The reaction temperature is increased to 260~280℃ at a heating rate of 8~10℃ / min. After the temperature stabilizes, the flow rate of the reaction gas is set to 100~150 mL / min, and the volume ratio of H2 to CO is 2:1.

[0018] Due to the adoption of the above technical solution, the technical effects achieved by the present invention are as follows: This invention provides a novel, simple, and efficient strategy for controlling the size of copper nanocrystals. By cleverly utilizing the relationship between the concentration of a mild organic reducing agent and reduction kinetics, precise control over the initial copper nucleus generation rate and growth process is achieved. This method eliminates the need for exogenous supports or metal promoters, avoiding the masking of active sites or interference with reaction pathways by heterogeneous components, thus maximizing the preservation of the intrinsic catalytic activity of copper and providing a pure model catalytic system for studying size-dependent catalytic performance. Furthermore, this preparation process exhibits excellent reproducibility and scalability.

[0019] The parameters specified in this application, such as the concentration of the mild organic reducing agent, pH value, and temperature, are easily and precisely controlled, ensuring a high degree of consistency in the performance of different batches of catalysts. This application overcomes the technical bottleneck of traditional methods, which suffer from difficulty in precisely controlling crystal size and poor reproducibility, by directly linking the final crystallite size to a single variable (the concentration of the mild organic reducing agent), thus achieving designability of catalyst performance. More importantly, the catalyst prepared in this application has a stable crystallite structure, ensuring the long-term operational stability of the catalyst.

[0020] The method described in this application uses readily available and inexpensive raw materials and is environmentally friendly, providing a new technical route for developing high-performance, long-life industrial catalysts for syngas to ethanol production, and has great potential for industrial application. Attached Figure Description

[0021] Figure 1 These are TEM images of the series of catalysts prepared in Example 1; Figure 2 These are the X-ray diffraction (XRD) patterns of the series of catalysts prepared in Example 1. Detailed Implementation

[0022] The technical solution of this application will be described in detail below with reference to specific implementation methods.

[0023] Example 1: Preparation of nano-Cu precursor by glucose reduction method Five 29.52g PVP solutions were dissolved in 450ml of glucose solutions of different concentrations to obtain solution A. The glucose solution concentrations were 0.2, 0.3, 0.4, 0.5, and 0.6 mol / L, respectively. At 90℃, five 450ml solutions containing 16.89g copper nitrate (0.20mol / L) and 29.52g PVP were slowly added dropwise to solution A. Sodium hydroxide (5mol / L) solution was added before and during the synthesis to adjust the pH of the suspension to 10. After complete addition, the reaction was allowed to proceed for 1 hour. When the suspension changed from yellow, orange, and red to dark red, it indicated copper formation. The samples were centrifuged (10000rpm, 10min), washed five times with ultrapure water, sonicated for 20min, and then stored to obtain a series of nano-copper samples.

[0024] 300 ml of liquid paraffin was added to each of the aforementioned different nano-coppers, and the mixture was stirred under a N2 atmosphere and slowly heated to 280 °C and maintained for 9 h to obtain slurry-like nano-copper catalysts. The obtained catalysts were named Cu2, Cu3, Cu4, Cu5, and Cu6, respectively.

[0025] The prepared series of nano-copper catalysts were subjected to TEM and X-ray diffraction. The results are as follows: Figure 1 , 2 As shown.

[0026] Figure 1 The images show TEM images of the series of catalysts prepared in Example 1. As can be seen from the images, the external morphology of the copper nanoparticles is irregular and loose; the particle surface is smooth. The particle size of the copper nanoparticles decreases with the increase of glucose concentration, which indicates that glucose plays the role of a structure guiding agent in the formation of nanoparticles.

[0027] Figure 2 The X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1 is shown. Three distinct diffraction peaks were observed at 2θ values ​​of 43.1, 51.1, and 74.5, corresponding to the (111), (200), and (220) crystal planes of metallic copper, respectively. The formation of the Cu0 species can be attributed to the thermal decomposition of liquid paraffin during the thermal reduction of the catalyst. Furthermore, the grain size of the nano-copper particles was calculated using the Scherrer equation (D=K*λ / β*cosθ), where β represents the full width at half maximum (FWHM) of the strongest diffraction peak. As shown in Table 1, the calculation results indicate a negative correlation between grain size and the increase in glucose concentration in the precursor solution, consistent with the TEM results.

[0028] Table 1. Grain sizes of Cu series catalysts (glucose reduction method)

[0029] The particle size distribution and average particle size of the nano-copper catalyst prepared in Example 1 were detected using a laser particle size analyzer. The results are shown in Table 2. The results indicate that the particle size is negatively correlated with the increase of glucose concentration in the precursor solution, which is consistent with the TEM and XRD results.

[0030] Table 2. Grain sizes of Cu series catalysts (glucose reduction method)

[0031] The prepared slurry-like copper nanocatalyst was placed in a 500 mL slurry bed reactor. The stirring speed was 500 r / min, and a mixture of H2 and CO was introduced to slowly raise the pressure inside the reactor to 4.0 MPa. The reaction temperature was then raised to 280 °C at a heating rate of 10 °C / min. After the temperature stabilized, the reaction gas flow rate was set to 150 mL / min (v(H2) / v(CO)=2). The reactor was allowed to run stably for 24 h before the catalyst activity was evaluated. The generated tail gas was separated into gas and liquid phases by a condenser. The gas phase product was analyzed online using a GC-950 and then discharged via a wet gas flow meter. The liquid phase product was collected every 24 h and analyzed manually offline. The results of the catalyst-catalyzed synthesis gas to ethanol production in Example 1 are shown in Table 3.

[0032] Table 3 Results of syngas-to-ethanol reaction using Cu series catalysts (glucose reduction method)

[0033] Example 2: Preparation of a series of nano-Cu precursors using the ascorbic acid reduction method 12.32 g, 24.63 g, 30.79 g, 36.95 g, and 48 g of L-ascorbic acid and 29.52 g of PVP (K30) were dissolved in 450 ml of ultrapure water to obtain solution A, with L-ascorbic acid concentrations of 0.156, 0.606, 0.311, 0.389, 0.467, and 0.606 mol / L, respectively.

[0034] Five 450 ml aliquots (solution B) containing 16.89 g copper nitrate (Cu(NO3)2·3H2O) and 29.52 g PVP were simultaneously and slowly added dropwise to solution A at the same rate (1.5 ml / min) using a peristaltic pump under constant temperature and vigorous stirring in a 60℃ water bath. Sodium hydroxide aqueous solution (5 mol / L) was added dropwise before and during the synthesis to precisely adjust and maintain the pH of the reaction system at 8.0. After the solution was completely added, the reaction was continued at 60℃ for 1 h. During the reaction, the suspension color rapidly changed from light blue to orange-yellow, and finally to a stable reddish-brown, indicating the formation of copper nanoparticles. After the reaction, the mixture was cooled to room temperature, centrifuged (10000 rpm, 10 min) to collect the solid product, and washed six times with ultrapure water to thoroughly remove residual ions and byproducts. Finally, the product was stored in a vacuum bag to obtain a series of copper nanoparticles.

[0035] 300 ml of liquid paraffin was added to each flask containing the aforementioned nano-copper, and the mixture was stirred under a N2 atmosphere and slowly heated to 280 °C and maintained for 9 h to obtain a slurry catalyst. The obtained catalysts were named Cu12, Cu18, Cu24, Cu30, and Cu36, respectively.

[0036] The nano-copper catalyst prepared in Example 2 was analyzed for particle size distribution and average particle size using a laser particle size analyzer. The results are shown in Table 4. Table 4. Grain sizes of Cu series catalysts (ascorbic acid reduction method)

[0037] The prepared catalyst was placed in a 500 mL slurry bed reactor with a stirring speed of 500 r / min. A mixture of H2 and CO was introduced to slowly increase the pressure inside the reactor to 4.0 MPa. The reaction temperature was then raised to 280 °C at a heating rate of 10 °C / min. After the temperature stabilized, the reaction gas flow rate was set to 150 mL / min (v(H2) / v(CO)=2). The catalyst activity was evaluated after the reactor had been running stably for 24 h. The generated tail gas was separated into gas and liquid phases by a condenser. The gas phase product was analyzed online by a GC-950 and then discharged through a wet gas flow meter. The liquid phase product was collected every 24 h and analyzed manually offline. The results of the catalytic synthesis of ethanol using the catalyst prepared in Example 2 are shown in Table 5.

[0038] Table 5 Results of syngas-to-methanol reaction using Cu series catalysts (ascorbic acid reduction method)

[0039] Example 3: Preparation of nano-copper precursors using sodium citrate reduction method: First, five 29.52g portions of PVP (K30) were dissolved in 450ml of sodium citrate aqueous solutions of different concentrations (0.1, 0.2, 0.3, 0.4, 0.5mol / L) and magnetically stirred until completely dissolved, preparing a series of solutions A. Simultaneously, 16.89g of copper nitrate (Cu(NO3)2·3H2O) was dissolved together with 29.52g of PVP in 450ml of ultrapure water and magnetically stirred for 30 minutes to form solution B. Under a constant temperature water bath at 90°C and mechanical stirring at 500rpm, solution A was preheated for 10 minutes, and then solution B was slowly added dropwise at a rate of 2.0ml / min using a peristaltic pump. Throughout the process, the pH of the system was precisely controlled at approximately 10.0 by adding sodium hydroxide aqueous solution (5mol / L). During the reaction, the solution color changed from blue to yellow, then orange-red, and finally to dark reddish-brown, indicating the gradual formation of copper nanoparticles. After solution B was completely added, the reaction was continued at this temperature for 2 hours to ensure complete reaction. After the reaction was completed, the mixture was immediately cooled to room temperature in an ice-water bath. The resulting suspension was centrifuged at 10,000 rpm for 10 minutes to collect the solid product, which was then washed 6 times with ultrapure water. Finally, the product was ultrasonically treated and vacuum dried to obtain nano-copper, which was then sealed and stored for later use.

[0040] 300 ml of liquid paraffin was added to each of the three-necked flasks containing the aforementioned nano-copper. The mixture was stirred under a nitrogen atmosphere and slowly heated to 280 °C and maintained for 9 h to obtain a slurry catalyst. The obtained catalysts were named Cu0.1, Cu0.2, Cu0.3, Cu0.4, and Cu0.5, respectively.

[0041] The nano-copper catalyst prepared in this embodiment was analyzed for particle size distribution and average particle size using a laser particle size analyzer. The results are shown in Table 6 below: Table 6. Grain sizes of Cu series catalysts (sodium citrate reduction method)

[0042] The prepared catalyst was placed in a 500 mL slurry bed reactor with a stirring speed of 500 r / min. A mixture of H2 and CO was introduced to slowly increase the pressure inside the reactor to 4.0 MPa. The reaction temperature was then raised to 280 °C at a heating rate of 10 °C / min. After the temperature stabilized, the reaction gas flow rate was set to 150 mL / min (v(H2) / v(CO)=2). The catalyst activity was evaluated after the reactor had been running stably for 24 h. The generated tail gas was separated into gas and liquid phases by a condenser. The gas phase product was analyzed online by a GC-950 and then discharged through a wet gas flow meter. The liquid phase product was collected every 24 h and analyzed manually offline. The results of the catalytic synthesis of ethanol using the catalyst prepared in Example 3 are shown in Table 7.

[0043] Table 7 Results of syngas-to-methanol reaction using Cu series catalysts (sodium citrate reduction method)

[0044] Example 4: Preparation of nano-CuZn precursor by glucose reduction method Five 29.52 g PVP solutions were dissolved in 450 ml of glucose solutions of different concentrations (0.1, 0.2, 0.3, 0.4, 0.5 mol / L), respectively, to obtain solution A. At 90 °C, five 450 ml solutions containing 16.89 g copper nitrate (0.20 mol / L), 3.2 g zinc nitrate, and 29.52 g PVP were slowly added dropwise to solution A. Sodium hydroxide (6 mol / L) was added before and during synthesis to adjust the pH of the suspension to 10. After complete addition, the reaction was allowed to proceed for 1 h. When the suspension changed from yellow, orange, and red to dark red, it indicated the formation of copper-zinc. The samples were centrifuged (10000 rpm, 10 min), washed five times with ultrapure water, sonicated for 20 min, and then stored to obtain nano-copper-zinc.

[0045] 300 ml of liquid paraffin was added to each of the flasks containing nano-copper and zinc, and the mixture was stirred under a nitrogen atmosphere and slowly heated to 280 °C and maintained for 9 h to obtain a slurry catalyst. The obtained catalysts were named Cu2Zn, Cu3Zn, Cu4Zn, Cu5Zn, and Cu6Zn, respectively.

[0046] The nano-copper catalyst prepared in Example 4 was analyzed for particle size distribution and average particle size using a laser particle size analyzer. The results are shown in Table 8 below: Table 8. Grain Sizes of CuZn Series Catalysts

[0047] The prepared catalyst was placed in a 500 mL slurry bed reactor with a stirring speed of 500 r / min. A mixture of H2 and CO was introduced to slowly increase the pressure inside the reactor to 4.0 MPa. The reaction temperature was then raised to 280 °C at a heating rate of 10 °C / min. After the temperature stabilized, the reaction gas flow rate was set to 150 mL / min (v(H2) / v(CO)=2). The catalyst activity was evaluated after the reactor had been running stably for 24 h. The generated tail gas was separated into gas and liquid phases by a condenser. The gas phase product was analyzed online by a GC-950 and then discharged through a wet gas flow meter. The liquid phase product was collected every 24 h and analyzed manually offline. The results of catalytic synthesis of ethanol using the catalyst prepared in this example are shown in Table 9.

[0048] Table 9 Results of syngas-to-methanol reaction using CuZn series catalysts (sodium citrate reduction method)

[0049] Comparative Example The nano-copper catalyst prepared in Example 1 was placed in a quartz tube and loaded into a fixed-bed reactor to evaluate its catalytic performance. The reaction conditions, steps and product detection were the same as those in the slurry bed in Example 1. The results of the catalyst catalyzing the synthesis of ethanol from syngas are shown in Table 10. As can be seen from the table, the ethanol selectivity was the highest at 17.37%, which was lower than the 22.52% of the slurry bed.

[0050] Table 10 Results of syngas-to-ethanol reaction using Cu series catalysts (glucose reduction method)

[0051] This invention successfully achieved continuous and precise control over the crystallite size of copper nanocatalysts, ranging from tens to over thirty nanometers, by using the concentration of a mild organic reducing agent as a single control variable. This preparation method does not rely on complex additives such as precious metals, and is simple, low-cost, and highly reproducible. The catalyst prepared in Example 4 exhibits significantly improved catalytic performance in the syngas-to-ethanol reaction, particularly with an ethanol selectivity exceeding 52.68%, far superior to the copper-based multi-metal nanocatalysts and other multi-metal catalyst systems disclosed in CN102500374A for the syngas-to-higher alcohols reaction, demonstrating considerable potential for industrial application.

Claims

1. A method for preparing a copper-based nanocatalyst with controllable grain size, characterized in that, Includes the following steps: S1. Dissolve a mild organic reducing agent in water to obtain a reducing agent solution; S2. Dissolve PVP in the reducing agent solution in S1 to obtain solution A; S3. Dissolve copper salt or a combination of copper salt and other metal salts with PVP in water in a certain proportion to obtain solution B; S4. Heat solution A to a certain temperature and adjust solution A to be alkaline. Slowly add solution B to solution A. The reaction solution is a suspension. During the addition process, control the reaction solution to be alkaline. S5. After the addition is complete and the reaction has continued for a period of time, the color of the suspension changes and eventually turns dark red. The reaction is stopped, the solid is centrifuged, washed, and sonicated to obtain nano-copper or nano-copper-based bimetal. S6. A slurry-like nano-copper catalyst is obtained by heating nano-copper or nano-copper-based bimetal and liquid paraffin under inert gas protection.

2. The method for preparing a controllable grain size copper-based nanocatalyst according to claim 1, characterized in that: The mild organic reducing agent includes glucose, ascorbic acid, and sodium citrate, and the concentration of the reducing agent solution is 0.1~0.6 mol / L.

3. The method for preparing a controllable grain size nano-copper-based catalyst according to claim 2, characterized in that: The mass ratio of PVP to mild organic reducing agent in solution A is 1:0.4~3.

6.

4. The method for preparing a controllable grain size nano-copper-based catalyst according to claim 1, characterized in that: The copper salts mentioned in step S3 include copper nitrate and copper sulfate. Other metal salts are selected from iron salts or cobalt salts. Iron salts include ferric nitrate and ferric sulfate, and cobalt salts include cobalt nitrate and cobalt sulfate.

5. The method for preparing a controllable grain size nano-copper-based catalyst according to claim 4, characterized in that: In solution B, the mass ratio of copper salt to PVP is 7:3~6, the mass ratio of copper salt to iron salt or cobalt salt is 2~5:1, the volume ratio of solution B to solution A is 1:1, and in step S3, solution A is heated to 80~100℃.

6. The method for preparing a controllable grain size nano-copper-based catalyst according to claim 1, characterized in that: The alkaline solution in step S4 is an aqueous solution of alkali metal hydroxides, including sodium hydroxide solution and potassium hydroxide solution, and the concentration of the alkaline solution is 4-6 mol / L.

7. The method for preparing a controllable grain size nano-copper-based catalyst according to claim 1, characterized in that: In step S4, the dropping rate of solution B is 1.8~2.0 ml / min, and the pH of the reaction solution is controlled at 8~10.

8. The method for preparing a controllable grain size nano-copper-based catalyst according to claim 1, characterized in that: In step S5, the reaction time is 1-2 hours, the centrifugation conditions are 8500-10000 rpm, the centrifugation time is 8-10 minutes, the heating rate in step S6 is 5-10℃ / min, the final heating temperature is 260-280℃, and the holding time is 7-9 hours.

9. The application of the nano-copper-based catalyst according to any one of claims 1-8, characterized in that: Used for catalytic synthesis of ethanol from syngas under high pressure.

10. The application of the nano-copper-based catalyst according to claim 9, characterized in that: The method for preparing ethanol from syngas is as follows: H2 and CO mixture is introduced into a reactor containing a slurry of nano-copper catalyst. The pressure inside the reactor is slowly increased to 3.5~4.0 MPa. The reaction temperature is increased to 260~280℃ at a heating rate of 8~10℃ / min. After the temperature stabilizes, the flow rate of the reaction gas is set to 100~150 mL / min, and the volume ratio of H2 to CO is 2:1.

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