Method for carbon nanotube supported noble metal electrochemical conversion of co2 in molten salt

Abstract

The application provides a method for CO2 molten salt electro-conversion of carbon nanotube supported noble metal, which comprises the following steps: firstly, uniformly mixing a beneficial component with an inorganic salt solvent to obtain a mixture, placing the mixture in a crucible, and heating and keeping the dried furnace charge in a closed vertical tube furnace under the protection of inert atmosphere in a vacuum drying oven; after the furnace charge is completely melted to form a liquid molten salt, CO2 is introduced into the liquid molten salt, and constant tank voltage electrolysis is continuously carried out; after the electrolysis is completed, the cathode product is separated from the electrode, and is repeatedly cleaned in dilute hydrochloric acid and deionized water under ultrasonic waves to obtain a carbon nanotube supported noble metal composite material. The method directly converts CO2 into high-value carbon nanotube supported materials, has the advantages of low operation difficulty, less green emission in the process, stable structure of the carbon nanotube supported noble metal, and the like, fully realizes effective conversion of gas, liquid and solid three phases, achieves the purpose of one-step short process preparation of waste gas into high-value materials, and meets the current circular green economic development planning.

Description

TECHNICAL FIELD

[0001] The patent relates to a method for preparing carbon nanotube supported noble metal by CO2 molten salt electrochemical conversion, belonging to the field of energy and chemical industry, and particularly to the field of CO2 molten salt capture and electrochemical conversion. BACKGROUND

[0002] Carbon nanotube is a coaxial tube composed of carbon hexagons. Due to its unique one-dimensional structure, it exhibits excellent thermal, electrical, mechanical and quantum properties, and has great application prospects in various fields such as nanoelectronic devices, catalytic supports, quantum conductors and hydrogen storage materials. It has become one of the most cutting-edge research fields, and researchers around the world have shown great interest in it.

[0003] Carbon nanotubes with unique tubular structure exhibit unique support properties in the field of catalytic supports. Planeitx. J. M. et al. mixed carbon nanotubes with metal salt solution by impregnation method, evaporated the solvent after impregnation, and then heated the metal salt to decompose it under hydrogen reduction atmosphere to prepare carbon nanotube-metal composite material with metal deposited on the surface of carbon nanotube (J. Am. Chem. Soc. 1994. 116: 7935). The feature of this carbon nanotube-metal composite is that the metal can cover the surface of the carbon nanotube, but there are often problems such as uneven coverage and serious agglomeration. In addition, Chinese patent 200410008326.5 discloses a method for preparing carbon nanotube supported platinum by chemical deposition. In the field of pollutant treatment, noble metal catalysts also exhibit irreplaceable catalytic activity and selectivity. For example, in the treatment of copper and chromium wastewater, heavy metal ions such as tetravalent chromium and divalent copper can be reduced to low valence ions for removal by noble metal catalysis. However, the catalysts often cannot avoid deactivation during use, and the catalytic effect gradually deteriorates with the progress of the catalytic reaction. The main reasons for deactivation include: detachment of active components from the support, poisoning of active components, agglomeration of active components, and sintering deactivation. To weaken this deactivation phenomenon, patents (CN 108970608 A, CN 107282082 B) disclose a kind of carbon nanotube composite material coated with noble metal; the main content is to coat a layer of nitrogen-doped carbon layer obtained by carbonization of dopamine on the surface of carbon nanotube material loaded with noble metal Pt, thereby improving the deactivation phenomenon. However, this process requires complex organic precursors, and the formation of a carbon tube-noble metal-carbon layer three-layer structure is difficult to prepare, and the demand for raw materials is strict, which is not conducive to mass production. Therefore, the present patent proposes to directly use greenhouse gas CO2 as a carbon source from the raw material source, and discloses a method for directly preparing a carbon nanotube coated with noble metal by molten salt electrolysis in a green and pollution-free manner. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method for CO2 molten salt electro-conversion of carbon nanotubes loaded with noble metals, aiming at solving the above-mentioned problems of the prior art.

[0005] To solve the above-mentioned technical problem, the technical solution adopted by the present application is as follows: a method for CO2 molten salt electro-conversion of carbon nanotubes loaded with noble metals, characterized in that the method comprises the following steps:

[0006] Step one: uniformly mixing beneficial components and inorganic salt flux to obtain a mixture, and then placing the mixture in a corundum crucible and heat treating at 150-200 DEG C in a vacuum drying box for more than 12 hours to obtain dried charge;

[0007] Step two: heating the dried charge obtained in step one to 600-1000 DEG C in a closed vertical tube furnace, and continuously heat treating until the charge is completely melted to form a liquid molten salt, then slowly lowering the cathode electrode and the anode electrode from the top of the closed vertical tube furnace to a fixed position below the liquid level of the liquid molten salt and fixing them, clamping the negative pole and the positive pole of a constant potential instrument at the upper end of the cathode electrode and the anode electrode respectively, directly passing CO2 into the molten salt system through a corundum tube for 5-30 minutes to stabilize, and continuously electrolyzing at a constant cell voltage of 1.0-5.0 V for not less than 2 hours, after the electrolysis is completed, separating the cathode electrode and the anode electrode from the molten salt system, and taking out the cathode electrode product after the temperature of the furnace body is cooled to room temperature to obtain carbon nanotubes loaded with noble metals; the electrolysis process is carried out in an inert atmosphere; the process of taking out the cathode electrode product is as follows: after the cathode product is separated from the electrode, it is placed in dilute hydrochloric acid and deionized water, and ultrasonic cleaning is repeatedly carried out for not less than 3 times and not less than 5 hours each time, and then drying is carried out in a vacuum drying box.

[0008] The method for CO2 molten salt electro-conversion of carbon nanotubes loaded with noble metals is characterized in that, in step one, the content of the beneficial components in the mixture is 1-5% of the amount of the inorganic salt flux.

[0009] The method for CO2 molten salt electro-conversion of carbon nanotubes loaded with noble metals is characterized in that, in step one, the inorganic salt flux is one or more than two of LiCl, NaCl, KCl, CsCl, CaCl2, MgCl2, BaCl2, Na2CO3, K2CO3, Li2CO3, Cs2CO3, BaCO3, CaO, MgO, Li2O, and BaO.

[0010] The above-mentioned method for CO2 molten salt electroconversion of carbon nanotubes loaded with noble metals is characterized in that the beneficial component in step one is one of AgCl, RuCl3, Na2[PtCl6]·6H2O, RuCl3*nH2O, RuI3, K2RuCl5·nH2O, RuO2*nH2O, and IrCl3*3H2O.

[0011] The above-mentioned method for CO2 molten salt electroconversion of carbon nanotubes loaded with noble metals is characterized in that the continuous holding temperature in step two is 700℃~900℃; the constant cell voltage is 1.5V~4.0V; the electrolysis time is not less than 4h; and the CO2 flow rate is 10mL·min. -1 ~50mL·min -1 .

[0012] The above-mentioned method for CO2 molten salt electroconversion of carbon nanotubes loaded with noble metals is characterized in that, in step two, the anode electrode is a NiFe2O4-based, TiB2-based, SnO2, or RuO2*TiO2 inert anode, and the cathode electrode is a copper sheet, nickel sheet, titanium sheet, or stainless steel sheet.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. This invention directly uses greenhouse gas CO2 as raw material, based on molten salt electrolysis technology, using inexpensive, readily available, and reusable molten salt as electrolyte, adding beneficial components, and exerting an in-situ catalytic conversion and reduction effect on CO2. Carbon nanotube-loaded noble metal composite materials are obtained at the cathode through constant voltage electrolysis. The continuous feeding and electrode rotation methods enable continuous preparation, which has the advantages of low operation difficulty, wide range of molten salt preparation, green and sustainable overall process, and stable carbon nanotube-loaded noble metal structure.

[0015] 2. The beneficial components of this invention are salts containing precious metal elements, which can achieve beneficial effects while enabling the precious metals to be electroreduced and loaded or filled into carbon nanotubes without the introduction of other impurities, thus facilitating the direct utilization of CO2 electroconversion products.

[0016] 3. This invention fully realizes the effective conversion of gas, liquid and solid phases, achieving the goal of preparing high-value-added materials from waste gas in a one-step short process.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 The image shows the XRD pattern of the carbon nanotubes loaded with the noble metal ruthenium prepared in Example 1 of this invention.

[0019] Figure 2This is a SEM image of the carbon nanotubes loaded with the noble metal ruthenium prepared in Example 1 of the present invention.

[0020] Figure 3 This is a TEM image of carbon nanotubes loaded with the noble metal ruthenium, prepared in Example 1 of the present invention.

[0021] Figure 4 This is a high-angle annular dark field (HAADF) image of carbon nanotubes loaded with the noble metal ruthenium prepared in Example 1 of the present invention. Detailed Implementation

[0022] Example 1

[0023] This embodiment includes the following steps:

[0024] Step 1: Mix 1.5g of RuCl3*nH2O with 60.54g of NaCl, 89.46g of Na2CO3 and 3.0g of CaO salt flux to obtain a mixture. Then place the mixture in a corundum crucible and keep it at 150℃ for 12h in a vacuum drying oven to obtain the dried furnace charge.

[0025] Step 2: Heat the dried charge obtained in Step 1 to 750℃ in a sealed vertical tubular electric furnace and maintain the temperature continuously until the charge completely melts into liquid molten salt. Then, slowly lower the cathode and anode electrodes from the top of the furnace to a fixed position below the surface of the liquid molten salt and fix them in place. Clamp the negative and positive terminals of the potentiostat to the upper ends of the cathode and anode electrodes, respectively. CO2 is continuously injected directly through the corundum tube at a rate of 10 mL / min. -1 After the flow rate was stabilized in the molten salt system for 20 minutes, electrolysis was continued for 6 hours at a constant cell voltage of 2.0V. After electrolysis, the cathode and anode electrodes were removed from the molten salt system. After the furnace body temperature was cooled to room temperature, the cathode electrode product was taken out. The cathode product was separated from the electrode and placed in dilute hydrochloric acid and deionized water for repeated ultrasonic cleaning at least 3 times and each time for at least 5 hours. Then it was dried in a vacuum drying oven to obtain ruthenium-loaded carbon nanotubes.

[0026] In addition to "NaCl, Na2CO3 and CaO", the embodiments are not limited to one or more of LiCl, KCl, CsCl, CaCl2, MgCl2, BaCl2, K2CO3, Li2CO3, Cs2CO3, BaCO3, MgO, Li2O and BaO.

[0027] In addition to RuCl3*nH2O, the beneficial component in the embodiments may also be one of AgCl, RuCl3, Na2[PtCl6]·6H2O, RuCl3*nH2O, RuI3, K2RuCl5·nH2O, RuO2*nH2O, and IrCl3*3H2O.

[0028] Figure 1 The image shows the XRD pattern of the ruthenium-loaded carbon nanotubes prepared in this embodiment. Figure 1 As can be seen from the above, the carbon nanotubes loaded with the noble metal ruthenium prepared in this embodiment are mainly composed of carbon and the noble metal ruthenium.

[0029] Figure 2 SEM image of carbon nanotubes loaded with the noble metal ruthenium, prepared in this embodiment; Figure 3 TEM image of carbon nanotubes loaded with the noble metal ruthenium, prepared in this embodiment; Figure 4 High-angle annular dark-field (HAADF) image of the ruthenium-loaded carbon nanotubes prepared in this embodiment. Figures 2 to 4 As can be seen from the above, in the carbon nanotubes loaded with the noble metal ruthenium prepared in this embodiment, the noble metal ruthenium is encapsulated inside the carbon nanotubes.

[0030] Example 2

[0031] This embodiment includes the following steps:

[0032] Step 1: Mix 7.5g of AgCl, 82.5g of NaCl, and 67.5g of LiCl salt flux evenly to obtain a mixture. Then place the mixture in a corundum crucible and keep it at 200℃ for 15 hours in a vacuum drying oven to obtain the dried furnace charge.

[0033] Step 2: Heat the dried charge obtained in Step 1 to 600℃ in a sealed vertical tubular electric furnace and maintain the temperature continuously until the charge completely melts into liquid molten salt. Then, slowly lower the cathode and anode electrodes from the top of the furnace to a fixed position below the surface of the liquid molten salt and fix them in place. Clamp the negative and positive terminals of the potentiostat to the upper ends of the cathode and anode electrodes, respectively. CO2 is continuously injected directly through the corundum tube at a rate of 30 mL / min. -1 After the flow rate was stabilized in the molten salt system for 20 minutes, electrolysis was continued for 6 hours at a constant cell voltage of 1.0V. After electrolysis, the cathode and anode electrodes were removed from the molten salt system. After the furnace body temperature was cooled to room temperature, the cathode electrode product was taken out. The cathode product was separated from the electrode and placed in dilute hydrochloric acid and deionized water for repeated ultrasonic cleaning at least 3 times and each time for at least 5 hours. Then it was dried in a vacuum drying oven to obtain silver-loaded carbon nanotubes.

[0034] Example 3

[0035] This embodiment includes the following steps:

[0036] Step 1: Mix 4.5g of IrCl3*3H2O with 59.32g of NaCl, 87.67g of Na2CO3 and 3.0g of CaO salt flux evenly to obtain a mixture. Then place the mixture in a corundum crucible and keep it at 150℃ for 12h in a vacuum drying oven to obtain the dried furnace charge.

[0037] Step 2: Heat the dried charge obtained in Step 1 to 800℃ in a sealed vertical tubular electric furnace and maintain the temperature continuously until the charge is completely melted into liquid molten salt. Then, slowly lower the cathode and anode electrodes from the top of the furnace to a fixed position below the surface of the liquid molten salt and fix them in place. Clamp the negative and positive terminals of the potentiostat to the upper ends of the cathode and anode electrodes, respectively. CO2 is continuously injected directly through the corundum tube at a rate of 50 mL / min. -1 After the flow rate was stabilized in the molten salt system for 20 minutes, electrolysis was continued for 8 hours at a constant cell voltage of 2.5V. After electrolysis, the cathode and anode electrodes were removed from the molten salt system. After the furnace body temperature was cooled to room temperature, the cathode electrode product was taken out. The cathode product was separated from the electrode and placed in dilute hydrochloric acid and deionized water for repeated ultrasonic cleaning at least 3 times and each time for at least 5 hours. Then it was dried in a vacuum drying oven to obtain iridium-loaded carbon nanotube powder.

[0038] Example 4

[0039] This embodiment includes the following steps:

[0040] Step 1: Mix 5.0g of RuCl3*nH2O with 194.17g of CaCl2 and 5.83g of CaO salt flux evenly to obtain a mixture. Then place the mixture in a corundum crucible and keep it at 200℃ for 12h in a vacuum drying oven to obtain the dried furnace charge.

[0041] Step 2: Heat the dried charge obtained in Step 1 to 1000℃ in a sealed vertical tubular electric furnace and maintain the temperature continuously until the charge is completely melted into liquid molten salt. Then, slowly lower the cathode and anode electrodes from the top of the furnace to a fixed position below the surface of the liquid molten salt and fix them in place. Clamp the negative and positive terminals of the potentiostat to the upper ends of the cathode and anode electrodes, respectively. CO2 is continuously injected directly through the corundum tube at a rate of 30 mL / min. -1 After the flow rate was stabilized in the molten salt system for 30 minutes, electrolysis was continued for 8 hours at a constant cell voltage of 3.0V. After electrolysis, the cathode and anode electrodes were removed from the molten salt system. After the furnace body temperature was cooled to room temperature, the cathode electrode product was taken out. The cathode product was separated from the electrode and placed in dilute hydrochloric acid and deionized water for repeated ultrasonic cleaning at least 3 times and each time for at least 5 hours. Then it was dried in a vacuum drying oven to obtain ruthenium-loaded carbon nanotubes.

[0042] Example 5

[0043] This embodiment includes the following steps:

[0044] Step 1: Mix 3.0g of RuCl3*nH2O with 51.8g of K2CO3, 50.0g of Na2CO3 and 48.2g of Li2CO3 salt flux evenly to obtain a mixture. Then place the mixture in a corundum crucible and keep it at 180℃ for 24h in a vacuum drying oven to obtain the dried furnace charge.

[0045] Step 2: Heat the dried charge obtained in Step 1 to 600℃ in a sealed vertical tubular electric furnace and maintain the temperature continuously until the charge completely melts into liquid molten salt. Then, slowly lower the cathode and anode electrodes from the top of the furnace to a fixed position below the surface of the liquid molten salt and fix them in place. Clamp the negative and positive terminals of the potentiostat to the upper ends of the cathode and anode electrodes, respectively. CO2 is continuously injected directly through the corundum tube at a rate of 10 mL / min. -1 After the flow rate was stabilized in the molten salt system for 5 minutes, electrolysis was continued for 6 hours at a constant tank voltage of 5.0V. After electrolysis, the cathode and anode electrodes were removed from the molten salt system. After the furnace body temperature was cooled to room temperature, the cathode electrode product was taken out. The cathode product was separated from the electrode and placed in dilute hydrochloric acid and deionized water for repeated ultrasonic cleaning at least 3 times and each time for at least 5 hours. Then it was dried in a vacuum drying oven to obtain ruthenium-loaded carbon nanotubes.

[0046] Example 6

[0047] The difference between this embodiment and embodiment 5 is that the temperature for continuous heat preservation in step two is 700℃; and the voltage of the constant tank is 1.5V.

[0048] Example 7

[0049] The difference between this embodiment and embodiment 5 is that the temperature for continuous heat preservation in step two is 900℃; and the voltage of the constant tank is 4V.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for CO2 molten salt electroconversion of carbon nanotubes loaded with noble metals, characterized in that, The method includes the following steps: Step 1: Mix the beneficial components with the inorganic salt flux evenly to obtain a mixture. Then, place the mixture in a corundum crucible and keep it at 150℃~200℃ for more than 12 hours in a vacuum drying oven to obtain the dried furnace charge. The beneficial components are one of AgCl, RuCl3, Na2[PtCl6]·6H2O, and IrCl3·3H2O. Step 2: In a sealed vertical tubular electric furnace, heat the dried furnace charge obtained in Step 1 to 600℃~1000℃ and maintain the temperature continuously until the furnace charge is completely melted to form liquid molten salt. Slowly lower the cathode electrode and anode electrode from the top of the sealed vertical tubular electric furnace to a fixed position below the liquid surface of the liquid molten salt and fix them in place. Clamp the negative and positive electrodes of the potentiostat to the upper ends of the cathode electrode and anode electrode, respectively. After CO2 is directly introduced into the molten salt system through the corundum tube for 5min~30min and stabilized, electrolyze continuously at a constant tank voltage of 1.0V~5.0V for no less than 2h. After electrolysis, remove the cathode electrode and anode electrode from the molten salt system. After the furnace body temperature is cooled to room temperature, take out the cathode electrode product to obtain carbon nanotubes loaded with noble metal. The electrolysis process is carried out under an inert atmosphere. The process of taking out the cathode electrode product is as follows: after peeling the cathode product from the electrode, place it in dilute hydrochloric acid and deionized water and ultrasonically clean it repeatedly for no less than 3 times, each time for no less than 5h, and then dry it in a vacuum drying oven.

2. The method for CO2 molten salt electroconversion of carbon nanotubes loaded with noble metals according to claim 1, characterized in that, The content of beneficial components in the mixture described in step one is 1% to 5% of the inorganic salt flux, by mass fraction.

3. The method for CO2 molten salt electroconversion of carbon nanotubes loaded with noble metals according to claim 1, characterized in that, The inorganic salt flux mentioned in step one is one or more of the following: LiCl, NaCl, KCl, CsCl, CaCl2, MgCl2, BaCl2, Na2CO3, K2CO3, Li2CO3, Cs2CO3, BaCO3, CaO, MgO, Li2O, and BaO.

4. The method for CO2 molten salt electroconversion of carbon nanotubes loaded with noble metals according to claim 1, characterized in that, The beneficial component mentioned in step one may also be one of RuCl3·nH2O, RuI3, or K2RuCl5·nH2O.

5. The method for CO2 molten salt electroconversion of carbon nanotubes loaded with noble metals according to claim 1, characterized in that, In step two, the continuous heat preservation temperature is 700℃~900℃; the constant cell voltage is 1.5V~4.0V; the electrolysis time is not less than 4 hours; and the CO2 flow rate is 10mL·min. -1 ~50mL·min -1 .

6. The method for CO2 molten salt electroconversion of carbon nanotubes loaded with noble metals according to claim 1, characterized in that, The anode electrode in step two is a NiFe2O4-based, TiB2-based, SnO2, or RuO2·TiO2 inert anode, and the cathode electrode is a copper sheet, nickel sheet, titanium sheet, or stainless steel sheet.

Images