Self-supporting cobalt nanosheet catalytic electrode and preparation method and application thereof

Abstract

The application discloses a self-supporting cobalt nanosheet catalytic electrode and a preparation method and application thereof, the active component of the catalytic electrode is a Co nanosheet structure grown on a carrier foam nickel, the corrugated Co nanosheet loaded on the substrate is uniformly distributed, so that the catalyst has a larger specific surface area and an electrochemical active area, the porous nanosheet structure contributes more active sites, promotes the diffusion of active substances and is also helpful to the transmission of protons in electrolyte, thereby improving the hydrogenation performance of electrocatalytic reaction; the catalytic electrode is used in electrocatalytic hydrogenation of quinoline to synthesize 1,2,3,4-tetrahydroquinoline, and has the characteristics of green environmental protection and mild high efficiency; the Co nanomaterial electrolytic reaction efficiency of the application is relatively high, and can reach more than 80% in the first hour, which indicates that the Co nanomaterial has good application potential in many chemical reactions, and the selectivity and conversion rate are also relatively ideal.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic electrocatalytic materials, and particularly relates to a cobalt nanosheet catalytic electrode loaded on a nickel foam and a preparation method thereof, and application in electrocatalytic hydrogenation of quinoline to synthesize 1,2,3,4-tetrahydroquinoline. BACKGROUND

[0002] Nitrogen-containing heterocyclic compounds are quite important in pharmaceuticals and fine chemicals. Among them, quinoline and its derivatives are important components of nitrogen-containing heterocyclic compounds. They are mostly natural products and can also be artificially synthesized by various methods, and are widely used in the development and research of active drug molecules. One of the hydrogenation products of quinoline, 1,2,3,4-tetrahydroquinoline, is widely used as a pharmaceutical intermediate in the synthesis of drugs with antibacterial activity, neuroprotective agents, immunomodulators, and active drugs for treating Alzheimer's disease. In addition, the 1,2,3,4-tetrahydroquinoline structure also has a good electron-donating chromophore, which can be used as an intermediate for the synthesis of dyes. As an electron donor, the dye has the advantages of bright color and large extinction coefficient. Therefore, the research on 1,2,3,4-tetrahydroquinoline compounds has always been of great concern to scientists.

[0003] In industry, 1,2,3,4-tetrahydroquinoline is mainly prepared by chemical catalytic quinoline hydrogenation process. This process requires an external hydrogen source and is carried out under high temperature and high pressure conditions. In addition, the chemical catalytic quinoline hydrogenation reaction is usually not one-way, and there are many side reactions, poor product selectivity, low conversion rate, and low yield. In view of this, compared with the chemical hydrogenation method, electrochemical reduction hydrogenation is a very promising method, which is more environmentally friendly in nature. By adjusting the electrochemical parameters, the occurrence of side reactions can be reduced, the selectivity of the product can be improved, and the conversion rate and yield can be improved. In particular, the use of high-temperature and high-pressure containers is avoided in traditional chemical methods.

[0004] Currently, some patent documents, such as CN113735767B, report the use of Ni@NC catalysts for thermal catalytic reduction of quinoline to generate 1,2,3,4-tetrahydroquinoline, with a maximum yield of 98%. However, the preparation of this electrode is not easy and the reaction must be carried out under high temperature and high pressure conditions. Considering the complexity of this process, we envisage synthesizing a new material that can effectively promote the activation of quinoline and water, and using electrochemical methods to improve the activity and selectivity of the quinoline hydrogenation reaction.

[0005] Electrode materials play a crucial role in electrochemical conversion reactions. In the field of organic electrochemical synthesis, transition metals exhibit a variety of unique characteristics. Co-based catalysts are widely studied in nitrate and electrolytic water due to their low cost and high stability, which can achieve efficient electron transfer in electrochemical reactions and promote the progress of the reaction. Moreover, reduced-state catalysts are generally beneficial to electrochemical hydrogenation reactions, which may be due to the fact that low-valence metals are more likely to achieve active hydrogen adsorption and transfer processes. In the process of electrochemical hydrogenation reaction, adsorbed hydrogen is an important reaction intermediate, and by attacking another reaction intermediate such as a small molecule adsorbed on the interface through highly active adsorbed hydrogen, a reduction hydrogenation reaction can be completed. Compared with ordinary thermal chemical methods, electrochemical synthesis methods have the advantages of easy separation of products, safe operation of equipment, simple process flow, environmental friendliness and other advantages, and are an important part of "green chemical synthesis".

[0006] Based on the study of the mechanism of such electrochemical quinoline hydrogenation reaction, the present application designs a low-valence cobalt material catalytic electrode, which utilizes electrode materials, reaction microenvironment and different organic additive solvents to control the selectivity and conversion rate of the reaction. At present, there are not many related studies on the use of such high-activity Co-based materials in quinoline electrochemical selective hydrogenation conversion systems. SUMMARY

[0007] In view of the problems of low yield, poor selectivity and harsh conditions in the synthesis of 1,2,3,4-tetrahydroquinoline in the prior art, the present application provides a self-supporting cobalt nanosheet catalytic electrode and a preparation method thereof, and application of the self-supporting cobalt nanosheet catalytic electrode as a cathode electrode in electrocatalytic hydrogenation of quinoline to synthesize 1,2,3,4-tetrahydroquinoline.

[0008] The technical scheme of the present application is as follows:

[0009] A preparation method of a self-supporting cobalt nanosheet catalytic electrode, comprising:

[0010] (1) Immersing a nickel foam (NF) substrate in an electrodeposition solution, and performing an electrodeposition reaction under a single-tank three-electrode system, and then washing and drying to obtain a catalytic electrode precursor;

[0011] The nickel foam is pretreated as follows before use: sequentially ultrasonicating the nickel foam in acetone, 3M hydrochloric acid solution, deionized water and ethanol for 15 minutes each, and drying for standby use.

[0012] The electrodeposition solution is obtained by dissolving cobalt nitrate hexahydrate in deionized water, and the concentration of the cobalt nitrate hexahydrate is 0.04-0.08 mol / L, preferably 0.05 mol / L;

[0013] The three-electrode system takes the foamed nickel as a working electrode, a Hg / HgO electrode as a reference electrode, and a Pt sheet as a counter electrode; the conditions of the electrodeposition reaction are as follows: the current setting is -0.02 to -0.05 A, preferably -0.04 A; the electrodeposition time is 6 to 9 min, preferably 8 min;

[0014] (2) taking the catalytic electrode precursor obtained in step (1) as a working electrode, performing an electro-reduction reaction in a three-electrode system (electrode distribution reference Figure 2 ) of an H-type electrolytic cell to obtain a self-supporting cobalt nanosheet catalytic electrode;

[0015] Similarly, the three-electrode system takes a Hg / HgO electrode as a reference electrode, and a Pt sheet as a counter electrode;

[0016] Preferably, the conditions of the electro-reduction reaction are as follows: the electrolyte is a 1M KOH solution, the voltage setting is -1.1 to -1.3 V, and the electro-reduction time is 2 to 6 h.

[0017] The present application relates to the self-supporting cobalt nanosheet catalytic electrode prepared by the above preparation method. The obtained catalytic electrode has Co nanosheet structures grown on the carrier NF as active ingredients; the corrugated Co nanosheets loaded on the substrate are uniformly distributed, so that the catalyst has a larger specific surface area and electrochemical active area, the porous nanostructure contributes more active sites, which promotes the diffusion of active substances and also helps the transmission of protons in the electrolyte, thereby improving the performance of the electrocatalytic reaction hydrogenation.

[0018] The self-supporting cobalt nanosheet catalytic electrode can be used in the electrocatalytic hydrogenation of quinoline to synthesize 1,2,3,4-tetrahydroquinoline. The specific application method is as follows:

[0019] The electrocatalytic reaction device adopts an H-type electrolytic cell (as shown in Figure 2 ), a platinum electrode is used as an anode, and the self-supporting cobalt nanosheet catalytic electrode of the present application is used as a cathode; an N117 cation membrane is used to separate the electrolyte between the anode and the cathode; the electrocatalytic reaction is carried out in a constant voltage electrolysis mode under the conditions of stirring and constant temperature;

[0020] The reaction equation is shown in Figure 1 ;

[0021] The electrolyte in the anode reaction tank is a 1M KOH solution;

[0022] The electrolyte in the cathode reaction tank is a 1M KOH mixed solution containing quinoline and organic additives, wherein the concentration of quinoline is 10 to 20 mmol / L, and the volume ratio of the organic additives is 3 to 14%; the organic additives are selected from isopropyl alcohol or n-propanol;

[0023] The conditions of the electrocatalytic reaction are as follows: the temperature is 25-55 DEG C, the temperature regulation adopts constant temperature water bath method; the constant voltage is set to -1.1--1.3V; and the electrolysis time is 0.5-2.5h.

[0024] Compared with the prior art, the present application has the advantages of:

[0025] The electrochemical method for synthesizing 1,2,3,4-tetrahydroquinoline is green, environment-friendly, mild and efficient compared with the thermal catalytic method. The electrocatalytic selective hydrogenation reduction of quinoline is realized by using the relatively cheap organic additive liquid isopropyl alcohol to replace the traditional electrochemical organic additive liquid 1,4-dioxane in the cathode liquid, and satisfactory conversion rate and selectivity are achieved.

[0026] Compared with other materials reported previously, the Co nanomaterial preparation method of the present application is simple, environment-friendly, and the metal is cheap and easy to obtain, and the synthesis process is pollution-free to the environment, and has good industrial application prospect. At the same time, the Co nanomaterial electrolysis reaction efficiency of the present application is higher, which can reach more than 80% in the first hour, indicating that it has good application potential in many chemical reactions, and the selectivity and conversion rate are also ideal. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The reaction equation of synthesizing 1,2,3,4-tetrahydroquinoline by electrocatalytic hydrogenation of quinoline.

[0028] Figure 2 The electrolytic cell device for synthesizing 1,2,3,4-tetrahydroquinoline by electrocatalytic hydrogenation of quinoline.

[0029] Figure 3 The SEM and TEM images of the Co nanosheet prepared in Example 1.

[0030] Figure 4 The XRD image of the Co nanosheet prepared in Example 1. DETAILED DESCRIPTION

[0031] In order to facilitate the understanding of the present application, the specific content of the present application is further described in combination with specific examples, and these examples are only used to illustrate the present application and do not limit the scope of the present application. The professional terms used are only for the purpose of describing the specific examples, and are not intended to limit the protection scope of the present application.

[0032] Example 1

[0033] 1. Preparation of Co nanosheet material grown on NF. NF (Cyber Electrochemical Materials net 1.5mm*200mm*250mm) was immersed in 80 mL of cobalt nitrate hexahydrate solution (concentration 0.05 mol / L), and constant current (current setting -0.04 A) electrodeposition was carried out at room temperature for 480 seconds, then washed with water and ethanol, vacuum dried, and after that, the material was used as the working electrode, and in a H-type electrolytic cell three-electrode system, 1M KOH solution at -1.2V vs. Hg / HgO was electro-reduced for 4 hours, to obtain the Co nanosheet material, and the morphology and XRD of the material are shown in Figure 3 and Figure 4

[0034] 2. Electro-catalytic hydrogenation of quinoline using Co nanosheet grown on NF as cathode. H-type electrolytic reaction tank was used, N117 cation exchange membrane was used to separate the anolyte and catholyte, platinum electrode was used as anode, and Hg / HgO was used as reference electrode. The electrolyte in the anode reaction tank was 1 mol / L potassium hydroxide solution (30 mL, same below); the catholyte was 1M KOH mixed solution containing 14.14 mmol / L quinoline and 3.33% (volume fraction) isopropanol (30 mL, same below), and the electrolysis potential was controlled at -1.2V, and the electrolysis was carried out at room temperature (25℃, same below) with constant speed stirring at 500 r / min for 2.5 hours. High performance liquid chromatography was used for detection, and the results showed that the selectivity of 1,2,3,4-tetrahydroquinoline was 99.99%, and the yield was 95.36%.

[0035] Example Two

[0036] 1. The material was prepared as in Example One.

[0037] 2. Electro-catalytic hydrogenation of quinoline using Co nanosheet grown on NF as cathode. H-type electrolytic reaction tank was used, N117 cation exchange membrane was used to separate the anolyte and catholyte, platinum electrode was used as anode, and Hg / HgO was used as reference electrode. The electrolyte in the anode reaction tank was 1 mol / L potassium hydroxide solution; the catholyte was 1M KOH mixed solution containing 14.14 mmol / L quinoline and 6.67% (volume fraction) isopropanol, and the electrolysis potential was controlled at -1.2V, and the electrolysis was carried out at room temperature with constant speed stirring for 2.5 hours. High performance liquid chromatography was used for detection, and the results showed that the selectivity of 1,2,3,4-tetrahydroquinoline was 99.99%, and the yield was 98.28%.

[0038] Example Three

[0039] 1. The material was prepared as in Example One.

[0040] ​2. Co nanosheets grown on NF were used as cathode to electrocatalytically hydrogenate quinoline. H-type electrolysis cell was used, N117 cation exchange membrane was used to separate the electrolyte of anode and cathode. Pt electrode was used as anode, Hg / HgO was used as reference electrode. The electrolyte in anode cell was 1 mol / L KOH solution, the electrolyte in cathode cell was 1 M KOH solution containing 14.14 mmol / L quinoline and 10% isopropanol. The electrolysis potential was controlled at -1.2 V, and the electrolysis was carried out at room temperature for 2.5 hours with constant stirring. The results were detected by HPLC, the selectivity of 1,2,3,4-tetrahydroquinoline was 99.99%, and the yield was 99.61%.

[0041] Example Four

[0042] 1. The material was prepared as in Example One.

[0043] 2. Co nanosheets grown on NF were used as cathode to electrocatalytically hydrogenate quinoline. H-type electrolysis cell was used, N117 cation exchange membrane was used to separate the electrolyte of anode and cathode. Pt electrode was used as anode, Hg / HgO was used as reference electrode. The electrolyte in anode cell was 1 mol / L KOH solution, the electrolyte in cathode cell was 1 M KOH solution containing 14.14 mmol / L quinoline and 10% isopropanol. The electrolysis potential was controlled at -1.2 V, and the electrolysis was carried out at room temperature for 2.5 hours with constant stirring. The results were detected by HPLC, the selectivity of 1,2,3,4-tetrahydroquinoline was 99.99%, and the yield was 99.61%.

[0044] Table 1. Influence of different organic solvents on the hydrogenation reduction of quinoline

[0045]

[0046] All experiments in Table 1 were the same as Example Four except that the organic additive was different.

[0047] Table 2. Influence of different quinoline concentrations on the hydrogenation reduction of quinoline

[0048]

[0049] All experiments in Table 2 were the same as Example Three except that the quinoline concentration was different.

[0050] Table 3. Influence of different reaction temperatures (constant temperature water bath) on the hydrogenation reduction of quinoline

[0051]

[0052] All experiments in Table 3 were the same as Example Three except that the reaction temperature was different.

Claims

1. Use of a self-supported cobalt nanosheet catalytic electrode in the electrocatalytic hydrogenation of quinoline to synthesize 1,2,3,4-tetrahydroquinoline; The self-supported cobalt nanosheet catalytic electrode is prepared as follows: (1) Submerge the nickel foam substrate in an electrodeposition solution and perform an electrodeposition reaction under a single-tank three-electrode system, and then wash and dry to obtain a catalytic electrode precursor; The electrodeposition solution is obtained by dissolving cobalt nitrate hexahydrate in deionized water; The three-electrode system uses nickel foam as the working electrode, a Hg / HgO electrode as the reference electrode, and a Pt sheet as the counter electrode; the electrodeposition reaction conditions are as follows: current setting -0.02~-0.05 A, electrodeposition time 6~9 min; (2) Use the catalytic electrode precursor obtained in step (1) as the working electrode and perform an electroreduction reaction under a three-electrode system in an H-type electrolytic tank to obtain a self-supported cobalt nanosheet catalytic electrode; The three-electrode system uses the catalytic electrode precursor as the working electrode, a Hg / HgO electrode as the reference electrode, and a Pt sheet as the counter electrode; the electroreduction reaction conditions are as follows: electrolyte is 1M KOH solution, voltage setting -1.1~-1.3 V, electroreduction time 2~6 h.

2. Use according to claim 1, wherein In step (1) of the preparation method of the self-supported cobalt nanosheet catalytic electrode, the concentration of cobalt nitrate hexahydrate in the electrodeposition solution is 0.04~0.08 mol / L.

3. The use according to claim 1, wherein The application method is as follows: The electrocatalytic reaction device uses an H-type electrolytic tank, the anode uses a platinum electrode, the cathode uses a self-supported cobalt nanosheet catalytic electrode, and an N117 cation membrane is used to separate the electrolyte between the anode and cathode reaction tanks, and the electrocatalytic reaction is performed under constant voltage electrolysis with stirring and constant temperature; The electrolyte in the anode reaction tank is 1M KOH solution; The electrolyte in the cathode reaction tank is a 1M KOH mixed solution containing quinoline and organic additives, wherein the concentration of quinoline is 10~20 mmol / L, and the volume fraction of organic additives is 3~14%; the organic additives are selected from isopropyl alcohol or n-propanol; The electrocatalytic reaction conditions are as follows: temperature is 25~55℃, temperature adjustment uses a constant temperature water bath method; constant voltage setting is -1.1~-1.3 V; electrolysis time is 0.5~2.5 h.

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