Cobalt phthalocyanine supported carbon nanotube catalyst suitable for electrochemical methanol preparation and preparation method and application thereof

Abstract

The invention discloses a cobalt phthalocyanine supported carbon nanotube catalyst suitable for electrochemical methanol preparation and a preparation method and application thereof. The preparation method of the catalyst comprises the following steps: mixing 4-nitrophthalonitrile, cobalt chloride hexahydrate and N, N-dimethylformamide, then adding 1, 8-diazacyclo [5, 4, 0] undecylene-7, and carrying out hydrothermal reaction to obtain nitrated cobalt phthalocyanine; introducing carboxyl on the surface of the carbon nano tube by acidification to obtain a carboxylated carbon nano tube; and dispersing and loading nitrated cobalt phthalocyanine on the carboxylated carbon nanotube to obtain the cobalt phthalocyanine loaded carboxylated carbon nanotube catalyst. Carboxyl is introduced to the carbon nanotubes, so that the polarity of the surface of the catalyst is improved; carboxyl is used as a coordination site to stabilize a reaction transition state, so that the activity of the catalyst can be improved. When the cobalt phthalocyanine supported carboxylated carbon nanotube catalyst is applied to electroreduction of CO2, the catalytic activity and reaction stability of the catalyst can be further improved, and the capacity of the catalyst for preparing methanol through electroreduction of CO2 is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electro-reduction of CO2 and relates to a cobalt phthalocyanine-loaded carbon nanotube catalyst suitable for electrochemical production of methanol and a preparation method and application thereof. Background Art

[0002] Due to the instability of wind power generation, wind energy resources have not been fully utilized. Electrocatalytic CO2 reduction technology can convert unstable wind power into methanol that is easy to store. This can not only alleviate the problem of absorbing new energy electricity, but also provide energy storage and peak load regulation solutions for the power system.

[0003] The electroreduction of CO2 to methanol faces the challenges of high chemical stability and multiple electron transfer steps, and requires efficient electrocatalysts to achieve highly selective conversion. Cobalt phthalocyanine (CoPc) is a molecular catalyst with high CO2 catalytic activity. Studies have shown that loading CoPc on carbon nanotubes (CNTs) can enhance its adsorption capacity for CO and promote the highly selective reduction of CO2 to methanol through molecular interactions between CNTs and CoPc. However, the physical binding force between CoPc and CNTs is weak. Under wind power fluctuation conditions, there are a series of energy and mass transfer mismatches such as electrolyte ion migration, CO2 gas diffusion, and catalyst charge transfer. Especially in liquid flow batteries, the flow rate of the electrolyte significantly affects the microenvironment of the adsorbed intermediates on the catalyst surface. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a cobalt phthalocyanine loaded carboxylated carbon nanotube catalyst suitable for electrochemical production of methanol and its preparation method and application, wherein carboxyl groups are introduced on carbon nanotubes to increase the polarity of the catalyst surface; the carboxyl groups are used as coordination sites to stabilize the reaction transition state, thereby improving the catalyst activity; when the cobalt phthalocyanine loaded carboxylated carbon nanotube catalyst is applied to the electroreduction of CO2, the carboxylated carbon nanotubes can further improve its catalytic activity and reaction stability by changing the coordination environment of the metal center, thereby effectively improving the catalyst's ability to electroreducing CO2 to produce methanol.

[0005] To this end, the present invention adopts the following technical solution.

[0006] In a first aspect, the present invention provides a method for preparing a cobalt phthalocyanine-supported carboxylated carbon nanotube catalyst suitable for electrochemical methanol production, comprising:

[0007] 4-nitrophthalonitrile, cobalt chloride hexahydrate and N,N-dimethylformamide are mixed, and then 1,8-diazacyclo[5,4,0]undecene-7 is added to prepare nitrated cobalt phthalocyanine through a hydrothermal reaction;

[0008] Carboxyl groups are introduced on the surface of carbon nanotubes by acidification to obtain carboxylated carbon nanotubes;

[0009] The nitrated cobalt phthalocyanine is dispersed and loaded on the carboxylated carbon nanotubes to obtain a cobalt phthalocyanine loaded carboxylated carbon nanotube catalyst.

[0010] The present invention has found that the introduction of carboxyl groups on carbon nanotubes (CNTs) can increase the polarity of the catalyst surface and provide additional interaction sites (such as hydrogen bonds and coordination bonds), enhance the interfacial bonding between carbon nanotubes (CNTs) and cobalt phthalocyanine (CoPc), and stabilize the adsorption transition state of CO* reaction intermediates. Therefore, cobalt phthalocyanine-supported carboxylated carbon nanotube-based catalysts can effectively improve the ability of CO2 electrocatalysis to produce methanol.

[0011] The present invention disperses and loads nitrated cobalt phthalocyanine on carboxylated carbon nanotubes, realizes stable loading through the π-π interaction between cobalt phthalocyanine and carbon nanotubes, and avoids aggregation between nitrated cobalt phthalocyanine through electrostatic repulsion, realizes monodisperse loading of nitrated cobalt phthalocyanine on carbon nanotubes, fully exposes cobalt active sites, and enables stable adsorption of *CHO key intermediates, thereby realizing one-step electroreduction of CO2 to produce methanol.

[0012] Furthermore, the method of introducing carboxyl groups on the surface of carbon nanotubes by acidification to obtain carboxylated carbon nanotubes is specifically as follows: adding carbon nanotubes to H2O2 and stirring the reaction to obtain carboxylated carbon nanotubes.

[0013] Furthermore, after 4-nitrophthalonitrile, cobalt chloride hexahydrate and N,N-dimethylformamide are mixed and before 1,8-diazacyclo[5,4,0]undecene-7 is added, the following operation is performed: the obtained mixed solution is stirred to form a uniform solution, and nitrogen gas is introduced.

[0014] Furthermore, the temperature of the hydrothermal reaction is 170-190° C., and the time is 2-3 hours.

[0015] Furthermore, the specific process of loading the nitrated cobalt phthalocyanine on the carboxylated carbon nanotubes is as follows:

[0016] The carboxylated multi-walled carbon nanotubes and polyvinyl pyrrolidone are added to N,N-dimethylformamide and uniformly dispersed by ultrasound to obtain solution A;

[0017] The nitrated cobalt phthalocyanine is added into N,N-dimethylformamide and dispersed by ultrasound to obtain solution B;

[0018] The solution B is added dropwise to the solution A, and stirred at room temperature. Finally, the product is collected by vacuum filtration to obtain a cobalt phthalocyanine-supported carboxylated carbon nanotube catalyst.

[0019] Furthermore, in the solution B, the concentration of nitroated cobalt phthalocyanine is 2-50 g / L, most preferably 10 g / L.

[0020] In a second aspect, the present invention provides a cobalt phthalocyanine-supported carboxylated carbon nanotube catalyst suitable for electrochemical production of methanol, which is prepared by the above-mentioned preparation method.

[0021] In a third aspect, the present invention provides an application of a cobalt phthalocyanine-supported carboxylated carbon nanotube catalyst suitable for electrochemical production of methanol, wherein the catalyst is prepared by the above-mentioned preparation method, and the catalyst electro-reduces CO2 to produce methanol.

[0022] Furthermore, the specific steps of producing methanol by electro-reduction of CO2 by the catalyst include:

[0023] Cobalt phthalocyanine supported carboxylated carbon nanotube catalyst, deionized water, isopropanol and Nafion solution were mixed evenly by ultrasonic treatment, sprayed on carbon paper, and then dried in a vacuum oven to prepare a cathode electrode;

[0024] A flowable electrolyzer is used as a reactor, the cathode electrode and the reference electrode are installed on one side, and an IrO2 catalyst is used as an anode electrode on the other side. The reactor is sealed and connected by nails and separated by an anion exchange membrane in the middle; the cathode electrode, the anion exchange membrane and the anode electrode are positioned and clamped by a polytetrafluoroethylene gasket, and connected to the electrode clamp by a conductive copper tape to form an external circuit;

[0025] CO2 is introduced into the cathode electrolytic cell and the flow rate is controlled by a flow meter. Then, the cathode electrolyte containing dissolved CO2 is transported to the electrolysis chamber by a peristaltic pump, and the electroreduction reaction is carried out by chronoamperometry.

[0026] Furthermore, KHCO3 is used as the anode and cathode electrolyte respectively, and the flow rates of the cathode and anode electrolytes are set to 2-15 rpm, preferably 4-6 rpm (rpm), and most preferably 5 rpm; the flow meter controls the CO2 flow rate to preferably 6-10 sccm, and most preferably 8 sccm.

[0027] Furthermore, the mass concentration of the Nafion solution is preferably 4-6%, and most preferably 5%.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The cobalt phthalocyanine-loaded carboxylated carbon nanotubes of the present invention have abundant negatively charged functional groups, excellent electrical conductivity and high stability, making them an efficient cathode catalyst. In the CO2 reduction reaction (CO2RR), the carboxylated carbon nanotubes can further improve their catalytic activity and reaction stability by changing the coordination environment of the metal center. The carboxyl group acts as a coordination site to stabilize the reaction transition state and improve the catalyst activity; since the carboxyl group carries a negative charge, it promotes electron transfer by adjusting the surface charge distribution; provides protons to achieve proton-coupled electron transfer; forms hydrogen bonds or weak interactions with reactants to enhance adsorption and reaction efficiency, and improves the interaction between the material and the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a process flow chart of the method for producing methanol by electroreduction of CO2 using a cobalt phthalocyanine-supported carboxylated multi-walled carbon nanotube catalyst. DETAILED DESCRIPTION

[0031] The 4-nitrophthalonitrile, cobalt chloride hexahydrate, NN-dimethylformamide, multi-walled carbon nanotubes, polyvinyl pyrrolidone, 1,8-diazacyclo[5,4,0]undecene-7, potassium bicarbonate, sulfuric acid (98%), hydrogen peroxide (30%), ethanol, hydrochloric acid solution (37%), Nafion solution and anion ion membrane used in the present invention are all purchased from commercial products.

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments may enable professionals and technicians in this field to understand the present invention more comprehensively, but do not limit the present invention in any way.

[0033] like Figure 1 As shown, the method for electro-reducing CO2 with a cobalt phthalocyanine-supported carboxylated multi-walled carbon nanotube catalyst specifically comprises the following steps:

[0034] (1) First, take 4-nitrophthalonitrile and cobalt chloride hexahydrate, add them to DMF, stir to form a uniform solution, and pass high-purity nitrogen. Then add DBU (1,8-diazacyclo[5,4,0]undecene-7), continue stirring for 25-35 minutes, transfer to a polytetrafluoroethylene liner, hydrothermally react at 170-190°C for 2-3 hours, and cool naturally to room temperature. Then the resulting product is collected by centrifugation, washed 3 times with 1M HCl, deionized water and anhydrous ethanol, and finally freeze-dried to obtain a CoPc sample (i.e., nitrocobalt phthalocyanine), which is stored at low temperature for later use.

[0035] (2) Take multi-walled carbon nanotubes, add H2O2 (30% wt.), and stir at 75-85°C for 11-13h to introduce polar functional groups carboxyl (-COOH) on the surface of the carbon nanotubes. Then collect the obtained product by centrifugation, wash it with deionized water and anhydrous ethanol three times each, and finally freeze-dry to obtain a carboxylated multi-walled carbon nanotube sample, which is stored at low temperature for future use.

[0036] (3) Take the carboxylated multi-walled carbon nanotubes and polyvinyl pyrrolidone (PVP) in step (2), add them to the DMF solution and ultrasonicate for 25-35 minutes to make them uniformly dispersed, and set it as solution A. Take the CoPc prepared in step (1), add it to the DMF solution and ultrasonicate for 25-35 minutes to make it uniformly dispersed, and set it as solution B. Then add solution B dropwise to solution A and stir at room temperature for 23-25h. Finally, vacuum filtration collects the product, and washes it with deionized water and ethanol three times respectively, and dries it at 55-65°C for 11-13h to obtain a cobalt phthalocyanine-supported carboxylated multi-walled carbon nanotube sample, which is recorded as CoPc@CNT catalyst and stored at low temperature for standby use.

[0037] (4) The CoPc@CNT catalyst, deionized water, isopropanol, and Nafion solution obtained in step (3) are mixed evenly by ultrasonic treatment, sprayed on carbon paper, and then placed in a vacuum oven at 35-45° C. and dried for 11-13 hours to obtain a cathode electrode.

[0038] (5) Use a flowable electrolytic cell as a reactor. Install the 1 cm 2 The cathode electrode and the reference electrode (Ag / AgCl electrode (1M KCl)) are 1 cm 2 Commercial IrO2 catalyst is used as the anode electrode, and the double-cell reactor is sealed and connected by nails and separated by an anion exchange membrane in the middle; the prepared cathode, anion exchange membrane and IrO2 anode are positioned and clamped together by polytetrafluoroethylene gaskets, and connected to the electrode clamps through conductive copper tapes to form an external circuit.

[0039] (6) KHCO3 was used as the anode and cathode electrolyte, and the flow rate of the cathode and anode electrolyte was set to 2-15 rpm. CO2 was introduced into the cathode chamber and the flow rate was controlled by a flowmeter. Then, the cathode electrolyte dissolved with CO2 was transferred to the electrolysis chamber by means of a peristaltic pump, and the anode electrolyte was also transferred by a peristaltic pump, and the electroreduction reaction was carried out by chronoamperometry. During the CO2 reduction reaction, the carboxyl groups on the multi-walled carbon nanotubes combined with the CoPc molecules by forming Co-N / Co-O axial coordination, thereby improving the stability of CoPc and reducing the activation energy of COOH* formation. In addition, the carboxyl groups can form hydrogen bonds or other weak interactions with CO2, significantly improving the adsorption of CO2; at the same time, they can provide protons to help achieve proton-coupled electron transfer and accelerate the reduction of CO2.

[0040] (7) During the electrolysis reaction, the gas phase products were analyzed in real time using an Agilent gas chromatograph (8860, Agilent). The electrolyte was collected after each electrolysis reaction, and the liquid products were detected using a nuclear magnetic resonance spectrometer (NMR, Bruker AVIII HD 600). 1H pressurized water NMR quantitative analysis was performed using dimethyl sulfoxide (DMSO) as the internal standard.

[0041] The methanol Faraday efficiency in the liquid product obtained by the above method is 43-62%.

[0042] Example 1

[0043] A method for electroreduction of CO2 using a cobalt phthalocyanine-supported carboxylated multi-walled carbon nanotube catalyst, comprising the following specific steps:

[0044] Step (1): Take 3.46g of 4-nitrophthalonitrile and 1.665g of cobalt chloride hexahydrate, add them to 100ml of DMF, stir for 30 minutes to form a uniform solution, and pass high-purity nitrogen. Then add 0.445ml of DBU (1,8-diazacyclo[5,4,0]undecene-7), continue stirring for 30 minutes, transfer to a polytetrafluoroethylene liner, hydrothermally react at 180°C for 2.5 hours, and cool naturally to room temperature. Then the resulting product is collected by centrifugation, washed 3 times with 1M HCl, deionized water and anhydrous ethanol, and finally freeze-dried to obtain a CoPc sample, which is stored at low temperature for later use.

[0045] Step (2): 0.2 g of multi-walled carbon nanotubes were added to 100 ml of H2O2 (30% wt.), and stirred at 80°C for 12 h, thereby introducing polar functional groups of carboxyl (-COOH) on the surface of the carbon nanotubes. The resulting product was then collected by centrifugation, washed with deionized water and anhydrous ethanol three times each, and finally freeze-dried to obtain a carboxylated multi-walled carbon nanotube sample, which was stored at low temperature for future use.

[0046] Step (3): Take 0.1g of the carboxylated multi-walled carbon nanotubes in step (2) and 15mg of polyvinyl pyrrolidone (PVP), add them to 100ml of DMF solution and ultrasonicate for 30 minutes to make them uniformly dispersed, set as solution A. Take 10mg of the CoPc prepared in step (1), add them to 10ml of DMF solution and ultrasonicate for 30 minutes to make them uniformly dispersed, set as solution B. Then, solution B is added dropwise to solution A at a rate of 0.05ml / s, and stirred at room temperature for 24h. Finally, the product is collected by vacuum filtration, washed with deionized water and ethanol three times respectively, and dried at 60°C for 12h to obtain a cobalt phthalocyanine-loaded carboxylated multi-walled carbon nanotube sample, recorded as CoPc@CNT, and stored at low temperature for standby use.

[0047] Step (4): Take 5 mg of the CoPc@CNT catalyst obtained in step (3), 1000 μL of deionized water, 1000 μL of isopropanol, and 20 μL of 5% Nafion solution, mix them evenly by ultrasonic treatment, and then spray them on a 5×5 cm 2 The cathode electrode was prepared by placing the film on carbon paper and then drying it in a vacuum oven at 40°C for 12 hours.

[0048] Step (5): Use a flowable electrolyzer as a reactor. Install the 1 cm 2 The cathode electrode and the reference electrode (Ag / AgCl electrode (1M KCl)) are 1 cm 2 Commercial IrO2 catalyst is used as the anode electrode, and the double-cell reactor is sealed and connected by nails and separated by an anion exchange membrane in the middle; the prepared cathode, anion exchange membrane and IrO2 anode are positioned and clamped together by polytetrafluoroethylene gaskets, and connected to the electrode clamps through conductive copper tapes to form an external circuit.

[0049] Step (6): 0.5M KHCO3 is used as the anode and cathode electrolyte, and the flow rate of the cathode and anode electrolyte is set to 5 rpm. CO2 is introduced into the cathode chamber and the flow rate is controlled to 8 sccm by a flowmeter. The electroreduction reaction is carried out by chronoamperometry. During the CO2 reduction reaction, the carboxyl groups on the multi-walled carbon nanotubes combine with the CoPc molecules by forming Co-N / Co-O axial coordination, thereby improving the stability of CoPc and reducing the activation energy of COOH* formation. In addition, the carboxyl groups can form hydrogen bonds or other weak interactions with CO2, significantly improving the adsorption of CO2. At the same time, protons can be provided to help achieve proton-coupled electron transfer and accelerate the reduction of CO2.

[0050] Step (7): During the electrolysis reaction, the gas phase product was analyzed in real time using an Agilent gas chromatograph (8860, Agilent), the electrolyte was collected after each electrolysis reaction, the liquid product was detected using a nuclear magnetic resonance spectrometer (NMR, Bruker AVIII HD 600), and 1H pressurized water NMR quantitative analysis was performed using dimethyl sulfoxide (DMSO) as an internal standard. The Faraday efficiency of methanol in the liquid product was 62%.

[0051] Example 2

[0052] The difference between Example 2 and Example 1 is that the flow rate of the cathode and anode electrolytes is set to 2 revolutions per minute (2 rpm), and the methanol Faradaic efficiency in the liquid product is 51%.

[0053] Example 3

[0054] The difference between Example 3 and Example 1 is that the flow rate of the cathode and anode electrolytes is set to 10 revolutions per minute (10 rpm), and the methanol Faradaic efficiency in the liquid product is 49%.

[0055] Example 4

[0056] The difference between Example 4 and Example 1 is that the flow rate of the cathode and anode electrolytes is set to 15 revolutions per minute (15 rpm), and the methanol Faradaic efficiency in the liquid product is 43%.

[0057] It can be seen from Examples 1-4 that the selectivity of the CoPc@CNT-10 catalyst for methanol in the CO2 reduction reaction process at an electrolyte flow rate of 5 rpm was increased by 11%, 13% and 19% respectively compared with 2 rpm, 10 rpm and 15 rpm.

[0058] Example 5

[0059] A method for electroreduction of CO2 using a cobalt phthalocyanine-supported carboxylated multi-walled carbon nanotube catalyst, comprising the following specific steps:

[0060] Step (1): Take 3.46g of 4-nitrophthalonitrile and 1.665g of cobalt chloride hexahydrate, add them to 100ml of DMF, stir for 30 minutes to form a uniform solution, and pass high-purity nitrogen. Then add 0.445ml of DBU (1,8-diazacyclo[5,4,0]undecene-7), continue stirring for 30 minutes, transfer to a polytetrafluoroethylene liner, hydrothermally react at 170°C for 2 hours, and cool naturally to room temperature. Then the resulting product is collected by centrifugation, washed 3 times with 1M HCl, deionized water and anhydrous ethanol, and finally freeze-dried to obtain a CoPc sample, which is stored at low temperature for later use.

[0061] Step (2): 0.2 g of multi-walled carbon nanotubes were added to 100 ml of H2O2 (30% wt.), and stirred at 60°C for 12 h, thereby introducing polar functional groups of carboxyl (-COOH) on the surface of the carbon nanotubes. The resulting product was then collected by centrifugation, washed with deionized water and anhydrous ethanol three times each, and finally freeze-dried to obtain a carboxylated multi-walled carbon nanotube sample, which was stored at low temperature for future use.

[0062] Step (3): Take 0.1g of the carboxylated multi-walled carbon nanotubes in step (2) and 15mg of polyvinyl pyrrolidone (PVP), add them to 100ml of DMF solution and ultrasonicate for 30 minutes to make them uniformly dispersed, set as solution A. Take 10mg of the CoPc prepared in step (1), add them to 10ml of DMF solution and ultrasonicate for 30 minutes to make them uniformly dispersed, set as solution B. Then, solution B is added dropwise to solution A at a rate of 0.1ml / s, and stirred at room temperature for 24h. Finally, the product is collected by vacuum filtration, washed with deionized water and ethanol three times respectively, and dried at 60°C for 12h to obtain a cobalt phthalocyanine-loaded carboxylated multi-walled carbon nanotube sample, recorded as CoPc@CNT, and stored at low temperature for standby use.

[0063] Step (4): Take 5 mg of the CoPc@CNT catalyst obtained in step (3), 1000 μL of deionized water, 1000 μL of isopropanol, and 20 μL of 4% Nafion solution, mix them evenly by ultrasonic treatment, and then spray them on a 5×5 cm 2 The cathode electrode was prepared by placing the film on carbon paper and then drying it in a vacuum oven at 40°C for 12 hours.

[0064] Step (5): Use a flowable electrolyzer as a reactor. Install the 1 cm 2 The cathode electrode and the reference electrode (Ag / AgCl electrode (1M KCl)) are 1 cm 2 Commercial IrO2 catalyst is used as the anode electrode, and the double-cell reactor is sealed and connected by nails and separated by an anion exchange membrane in the middle; the prepared cathode, anion exchange membrane and IrO2 anode are positioned and clamped together by polytetrafluoroethylene gaskets, and connected to the electrode clamps through conductive copper tapes to form an external circuit.

[0065] Step (6): 0.5M KHCO3 is used as the anode and cathode electrolyte, and the flow rate of the cathode and anode electrolyte is set to 5 rpm. CO2 is introduced into the cathode chamber and the flow rate is controlled to 6 sccm by a flowmeter. The electroreduction reaction is carried out by chronoamperometry. During the CO2 reduction reaction, the carboxyl groups on the multi-walled carbon nanotubes combine with the CoPc molecules by forming Co-N / Co-O axial coordination, thereby improving the stability of CoPc and reducing the activation energy of COOH* formation. In addition, the carboxyl groups can form hydrogen bonds or other weak interactions with CO2, significantly improving the adsorption of CO2. At the same time, protons can be provided to help achieve proton-coupled electron transfer and accelerate the reduction of CO2.

[0066] Step (7): During the electrolysis reaction, the gas phase product was analyzed in real time using an Agilent gas chromatograph (8860, Agilent), the electrolyte was collected after each electrolysis reaction, the liquid product was detected using a nuclear magnetic resonance spectrometer (NMR, Bruker AVIII HD 600), and 1H pressurized water NMR quantitative analysis was performed using dimethyl sulfoxide (DMSO) as an internal standard. The Faraday efficiency of methanol in the liquid product was 49%.

[0067] The difference between Example 5 and Example 1 is that: hydrothermal reaction was carried out at 170°C for 2 hours and cooled naturally to room temperature; 0.2g of multi-walled carbon nanotubes was added to 100ml of H2O2 (30%wt.) and stirred at 60°C for 12h; then solution B was added dropwise to solution A at a rate of 0.1ml / s and stirred at room temperature for 24h; 20μL of 4% Nafion solution was taken. CO2 was introduced into the cathode cavity and the flow rate was controlled to 6sccm by a flowmeter, and the methanol Faraday efficiency in the obtained liquid product reached 49%.

[0068] Example 6

[0069] The difference between Example 6 and Example 1 is that: hydrothermal reaction is carried out at 170°C for 2 hours; 0.2g of multi-walled carbon nanotubes are added to 100ml of H2O2 (30%wt.), and stirred at 60°C for 12h; then solution B is added dropwise to solution A at a rate of 0.1ml / s, and stirred at room temperature for 24h; 20μL of 4% Nafion solution is taken. CO2 is introduced into the cathode cavity and the flow rate is controlled to 10sccm by a flowmeter, and the methanol Faraday efficiency in the obtained liquid product reaches 42%.

[0070] It can be seen from Examples 1, 5-6 that, compared with 6 sccm and 10 sccm, the selectivity of CoPc@CNT-10 catalyst for methanol in the CO2 reduction reaction process at a CO2 flow rate of 8 sccm is increased by 13% and 20%, respectively.

[0071] Example 7

[0072] A method for electroreduction of CO2 using a cobalt phthalocyanine-supported carboxylated multi-walled carbon nanotube catalyst, comprising the following specific steps:

[0073] Step (1): Take 3.46g of 4-nitrophthalonitrile and 1.665g of cobalt chloride hexahydrate, add them to 100ml of DMF, stir for 30 minutes to form a uniform solution, and pass high-purity nitrogen. Then add 0.445ml of DBU (1,8-diazacyclo[5,4,0]undecene-7), continue stirring for 30 minutes, transfer to a polytetrafluoroethylene liner, hydrothermally react at 190°C for 3 hours, and cool naturally to room temperature. Then the resulting product is collected by centrifugation, washed 3 times with 1M HCl, deionized water and anhydrous ethanol, and finally freeze-dried to obtain a CoPc sample, which is stored at low temperature for future use.

[0074] Step (2): 0.2 g of multi-walled carbon nanotubes were added to 100 ml of H2O2 (30% wt.), and stirred at 100° C. for 12 h, thereby introducing polar functional groups of carboxyl (-COOH) on the surface of the carbon nanotubes. The resulting product was then collected by centrifugation, washed with deionized water and anhydrous ethanol three times each, and finally freeze-dried to obtain a carboxylated multi-walled carbon nanotube sample, which was stored at low temperature for later use.

[0075] Step (3): Take 0.1g of the carboxylated multi-walled carbon nanotubes in step (2) and 15mg of polyvinyl pyrrolidone (PVP), add them to 100ml of DMF solution and ultrasonicate for 30 minutes to make them uniformly dispersed, set as solution A. Take 2mg of the CoPc prepared in step (1), add them to 10ml of DMF solution and ultrasonicate for 30 minutes to make them uniformly dispersed, set as solution B. Then, solution B is added dropwise to solution A at a rate of 0.05ml / s, and stirred at room temperature for 24h. Finally, the product is collected by vacuum filtration, washed with deionized water and ethanol three times respectively, and dried at 60°C for 12h to obtain a cobalt phthalocyanine-loaded carboxylated multi-walled carbon nanotube sample, recorded as CoPc@CNT, and stored at low temperature for standby use.

[0076] Step (4): Take 5 mg of the CoPc@CNT catalyst obtained in step (3), 1000 μL of deionized water, 1000 μL of isopropanol, and 20 μL of 6% Nafion solution, mix them evenly by ultrasonic treatment, and then spray them on a 5×5 cm 2 The cathode electrode was prepared by placing the film on carbon paper and then drying it in a vacuum oven at 40°C for 12 hours.

[0077] Step (5): Use a flowable electrolyzer as a reactor. Install the 1 cm 2The cathode electrode and the reference electrode (Ag / AgCl electrode (1M KCl)) are 1 cm 2 Commercial IrO2 catalyst is used as the anode electrode, and the double-cell reactor is sealed and connected by nails and separated by an anion exchange membrane in the middle; the prepared cathode, anion exchange membrane and IrO2 anode are positioned and clamped together by polytetrafluoroethylene gaskets, and connected to the electrode clamps through conductive copper tapes to form an external circuit.

[0078] Step (6): 0.5M KHCO3 is used as the anode and cathode electrolyte, and the flow rate of the cathode and anode electrolyte is set to 5 rpm. CO2 is introduced into the cathode chamber and the flow rate is controlled to 8 sccm by a flowmeter. The electroreduction reaction is carried out by chronoamperometry. During the CO2 reduction reaction, the carboxyl groups on the multi-walled carbon nanotubes combine with the CoPc molecules by forming Co-N / Co-O axial coordination, thereby improving the stability of CoPc and reducing the activation energy of COOH* formation. In addition, the carboxyl groups can form hydrogen bonds or other weak interactions with CO2, significantly improving the adsorption of CO2. At the same time, protons can be provided to help achieve proton-coupled electron transfer and accelerate the reduction of CO2.

[0079] Step (7): During the electrolysis reaction, the gas phase product was analyzed in real time using an Agilent gas chromatograph (8860, Agilent), the electrolyte was collected after each electrolysis reaction, the liquid product was detected using a nuclear magnetic resonance spectrometer (NMR, Bruker AVIII HD 600), and 1H pressurized water NMR quantitative analysis was performed using dimethyl sulfoxide (DMSO) as an internal standard. The Faraday efficiency of methanol in the liquid product was found to be 28%.

[0080] The difference between Example 7 and Example 1 is that: the hydrothermal reaction was carried out at 190°C for 3 hours and the mixture was naturally cooled to room temperature; 0.2 g of multi-walled carbon nanotubes was added to 100 ml of H2O2 (30% wt.) and stirred at 100°C for 12 hours; 20 μL of 6% Nafion solution was taken; 2 mg of CoPc prepared in step (1) was added to 10 ml of DMF solution and ultrasonicated for 30 minutes to make it uniformly dispersed, which was referred to as solution B. The methanol Faraday efficiency of the obtained liquid product reached 28%.

[0081] Example 8

[0082] The difference between Example 8 and Example 1 is that: the hydrothermal reaction is carried out at 190°C for 3 hours and cooled naturally to room temperature; 0.2g of multi-walled carbon nanotubes are added to 100ml of H2O2 (30%wt.) and stirred at 100°C for 12h; 20μL of 6% Nafion solution is taken; 50mg of CoPc prepared in step (1) are taken and added to 10ml of DMF solution and ultrasonicated for 30 minutes to make it uniformly dispersed, which is referred to as solution B. The methanol Faraday efficiency of the obtained liquid product is 8%.

[0083] It can be seen from Examples 1, 7-8 that compared with 2 mg and 50 mg, the CoPc@CNT catalyst prepared with 10 mg CoPc has the best ability to electro-reduce CO2 to methanol, and the selectivity of methanol in the CO2 reduction reaction process is increased by 34% and 54%, respectively.

[0084] Finally, it should be noted that the above examples are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples, and many variations are possible. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for preparing a cobalt phthalocyanine-supported carbon nanotube catalyst suitable for electrochemical methanol production, characterized in that: include: 4-nitrophthalonitrile, cobalt chloride hexahydrate and N,N-dimethylformamide are mixed, and then 1,8-diazacyclo[5,4,0]undecene-7 is added to prepare nitrated cobalt phthalocyanine through a hydrothermal reaction; Carboxyl groups are introduced on the surface of carbon nanotubes by acidification to obtain carboxylated carbon nanotubes; The nitrated cobalt phthalocyanine is dispersed and loaded on the carboxylated carbon nanotubes to obtain a cobalt phthalocyanine loaded carboxylated carbon nanotube catalyst.

2. The preparation method according to claim 1, characterized in that: The method of introducing carboxyl groups on the surface of carbon nanotubes by acidification to obtain carboxylated carbon nanotubes is specifically as follows: adding carbon nanotubes to H2O2 and stirring the reaction to obtain carboxylated carbon nanotubes.

3. The preparation method according to claim 1, characterized in that: After 4-nitrophthalonitrile, cobalt chloride hexahydrate and N,N-dimethylformamide were mixed, and before 1,8-diazacyclo[5,4,0]undecene-7 was added, the following operation was performed: the obtained mixed solution was stirred to form a uniform solution, and nitrogen was introduced.

4. The preparation method according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 170-190° C. and the time is 2-3 hours.

5. The preparation method according to claim 1, characterized in that: The specific process of dispersing and loading the nitrated cobalt phthalocyanine on the carboxylated carbon nanotubes is as follows: The carboxylated multi-walled carbon nanotubes and polyvinyl pyrrolidone are added to N,N-dimethylformamide and uniformly dispersed by ultrasound to obtain solution A; The nitrated cobalt phthalocyanine is added into N,N-dimethylformamide and dispersed by ultrasound to obtain solution B; The solution B is added dropwise to the solution A, and stirred at room temperature. Finally, the product is collected by vacuum filtration to obtain a cobalt phthalocyanine-supported carboxylated carbon nanotube catalyst.

6. A cobalt phthalocyanine supported carbon nanotube catalyst suitable for electroreduction of CO2 to methanol, characterized in that: The method is prepared by any one of claims 1 to 5.

7. An application of a cobalt phthalocyanine-supported carbon nanotube catalyst suitable for electrochemical methanol production, wherein the catalyst is prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The catalyst electro-reduces CO2 to produce methanol.

8. The use according to claim 7, characterized in that: The specific steps of preparing methanol by electro-reduction of CO2 by the catalyst include: Cobalt phthalocyanine supported carboxylated carbon nanotube catalyst, deionized water, isopropanol and Nafion solution were mixed evenly by ultrasonic treatment, sprayed on carbon paper, and then dried in a vacuum oven to prepare a cathode electrode; A flowable electrolyzer is used as a reactor, the cathode electrode and the reference electrode are installed on one side, and an IrO2 catalyst is used as an anode electrode on the other side. The reactor is sealed and connected by nails and separated by an anion exchange membrane in the middle; the cathode electrode, the anion exchange membrane and the anode electrode are positioned and clamped by a polytetrafluoroethylene gasket, and connected to the electrode clamp by a conductive copper tape to form an external circuit; CO2 is introduced into the cathode electrolytic cell and the flow rate is controlled by a flow meter. Then, the cathode electrolyte containing dissolved CO2 is transported to the electrolysis chamber by a peristaltic pump, and the electroreduction reaction is carried out by chronoamperometry.

9. The use according to claim 8, characterized in that: KHCO3 was used as the anode and cathode electrolytes, respectively. The flow rates of the cathode and anode electrolytes were set to 4-6 rpm, and the flow meter controlled the CO2 flow rate to 6-10 sccm.

10. The use according to claim 8, characterized in that: The mass concentration of the Nafion solution is 4-6%.

Images