A Fe-N-C supported gamma-Fe2O3 hollow sphere material catalyst, a preparation method and application thereof

Abstract

The application discloses a kind of Fe-N-C loaded gamma-Fe2O3 hollow ball material catalyst and its preparation method and application, the chemical formula of the catalyst is Fe (phen) 3Cl2, wherein, phen in structural formula is 1,10-ortho-phenanthroline ligand;The catalyst structural formula is as follows: the preparation method includes the following steps, and is prepared by pyrolysis of iron-based complex crystal and metal organic framework material ZIF-8, and the iron-based complex crystal is Fe (phen) 3Cl2 complex crystal.The catalyst can be used for the preparation of CO2 at normal temperature and pressure electrocatalytic reduction CO, the catalyst shows excellent CO selectivity in-0.5V~‑1.1V wide potential window, and after 2h continuous electrolysis at-0.6V, current density and CO Faraday efficiency are basically unchanged, and show excellent stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocatalytic reduction of CO2 to prepare CO, and particularly relates to a catalyst of Fe-N-C loaded gamma-Fe2O3 hollow sphere material and a preparation method and application thereof. BACKGROUND

[0002] The consumption of fossil energy leads to the continuous increase of CO2 concentration in the atmosphere, causing a series of environmental problems. The continuous consumption of coal, oil and other non-renewable resources also causes energy crisis. The conversion of CO2 into useful chemicals or fuels through renewable energy technology is an effective means to reduce the concentration of CO2 in the atmosphere and solve the energy crisis, among which, the electrocatalytic technology attracts more and more attention. Fe-N-C material is a kind of CO2-CO electrocatalyst which has been studied more, and has the advantages of low overpotential, high atomic utilization rate, etc. However, due to the hydrogen evolution competition reaction, the existing Fe-N-C has a higher CO Faraday efficiency (FE) at a potential more positive than-0.8V, and the current density is not high, which is not conducive to the further reduction of CO. Secondly, the common preparation method of Fe-N-C is to mix the commercially purchased Fe salt with the ligand, and directly calcine with MOFs. The impurities in the Fe salt and the unreacted ligand will change the structure, composition and proportion of the final product, directly affect the catalytic performance, and easily cause the problem of poor repeatability. SUMMARY

[0003] The purpose of the present application is to provide a catalyst of Fe-N-C loaded gamma-Fe2O3 hollow sphere material and a preparation method and application thereof, which has stable chemical properties and good catalytic performance.

[0004] In one aspect of the present application, a catalyst of Fe-N-C loaded gamma-Fe2O3 hollow sphere material is provided. According to the embodiments of the present application, the chemical formula of the catalyst is Fe(phen)3Cl2, wherein phen in the structural formula is 1,10-phenanthroline ligand.

[0005] The structural formula of the catalyst is as follows:

[0006]

[0007] In another aspect of the present application, a preparation method of the catalyst of Fe-N-C loaded gamma-Fe2O3 hollow sphere material is provided. According to the embodiments of the present application, the preparation method comprises the following steps: preparing by pyrolysis of iron-based complex crystal and metal organic framework material ZIF-8, and the iron-based complex crystal is Fe(phen)3Cl2 complex crystal.

[0008] In addition, the preparation method of the Fe-N-C supported gamma-Fe2O3 hollow sphere material catalyst according to the above embodiment of the application can further have the following additional technical features.

[0009] In some embodiments of the application, the Fe(phen)3Cl2 complex crystals are dissolved in methanol, then ZIF-8 is added thereto, after sufficient stirring, the obtained solid is dried by a rotary evaporator, and then pyrolysis of the solid is performed in a tube furnace under an inert gas, and finally, after acid soaking and filtration, washing is performed until the pH is neutral, and then drying is performed.

[0010] In some embodiments of the application, the mass ratio of the Fe(phen)3Cl2 and ZIF-8 is 1:17.78; the stirring time is 4 h; the inert gas is argon; the pyrolysis temperature is 1050°C, the pyrolysis time is 1 h, and the temperature rising rate is 5°C / min; and the drying temperature is 100°C, and the drying time is 2 h.

[0011] In some embodiments of the application, the Fe(phen)3Cl2 complex crystals are prepared by performing a coordination reaction of 1,10-phenanthroline ligand and FeCl2·4H2O in methanol, and then diffusing the crystals Fe(phen)3Cl2 by ether.

[0012] In some embodiments of the application, the molar ratio of the FeCl2·4H2O and 1,10-phenanthroline is 1:3-1:6, the coordination reaction time is 1-4 h, and after the coordination reaction, filtration is performed, and the filtrate is diffused by ether to obtain the crystals Fe(phen)3Cl2.

[0013] In some embodiments of the application, the ZIF-8 is prepared by performing a coordination reaction of 2-methyl imidazole ligand and Zn(NO3)2·6H2O in methanol to obtain ZIF-8.

[0014] In some embodiments of the application, the ZIF-8 is prepared by performing a coordination reaction of 2-methyl imidazole ligand and Zn(NO3)2·6H2O in methanol to obtain ZIF-8. 2+ In some embodiments of the application, the ZIF-8 is prepared by performing a coordination reaction of 2-methyl imidazole ligand and Zn(NO3)2·6H2O in methanol to obtain ZIF-8. 10 In some embodiments of the application, the ZIF-8 is prepared by performing a coordination reaction of 2-methyl imidazole ligand and Zn(NO3)2·6H2O in methanol to obtain ZIF-8.

[0015] In another aspect of the present application, the present application provides an application of the Fe-N-C supported γ-Fe2O3 hollow sphere material catalyst. According to an embodiment of the present application, the Fe-N-C supported γ-Fe2O3 hollow sphere material catalyst is used for the wide-potential electrocatalytic reduction of CO2 to CO, and the wide-potential is -0.5V to -1.1V.

[0016] In another aspect of the present application, the present application provides a method for electrocatalytic reduction of CO2 to prepare CO. According to an embodiment of the present application, the method comprises the following steps:

[0017] (1) The Fe-N-C supported γ-Fe2O3 hollow sphere material catalyst of claim 1 is uniformly dispersed in isopropyl alcohol by ultrasonic, and then a Nafion solution is added to obtain a catalyst dispersion liquid, which is ready for use under stirring;

[0018] (2) The catalyst dispersion liquid is added dropwise to a gas diffusion electrode in batches, and the working electrode is obtained by drying and ready for use;

[0019] (3) The working electrode obtained is used in a three-electrode system flow cell for electrocatalytic reaction, a nickel mesh is used as the counter electrode, an Ag / AgCl electrode is used as the reference electrode, and a KHCO3 aqueous solution is used as the electrolyte;

[0020] (4) Before the reaction, CO2 is introduced into the cathode cell electrolyte, and air is discharged while the CO2 gas is saturated in the electrolyte, and finally the system is sealed, and the electrolysis reaction is carried out at -0.5V to -1.3V (vs. RHE) to reduce CO2 to CO.

[0021] In addition, the method for electrocatalytic reduction of CO2 to prepare CO according to the above-mentioned embodiments of the present application can also have the following additional technical features:

[0022] In some embodiments of the present application, in the step (1), the mass fraction of the Nafion solution used is 5%; in the step (2), the size of the working electrode is 1.4cm*1.4cm*1mm, and the loading amount of the catalyst on the gas diffusion electrode is 0.45mg to 0.5mg each time, and the geometric area of the working electrode in contact with the electrolyte during electrolysis is 1cm 2 ; in the step (3), the cathode cell and the anode cell in the flow cell are separated by a proton exchange membrane.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] 1) In the present application, the catalyst is Fe-N-C loaded γ-Fe2O3 hollow sphere material, which can catalytically reduce CO2 to obtain CO at normal temperature and pressure through electrocatalysis technology, and the catalyst is stable at normal temperature and pressure and has good catalytic performance. This is because a small amount of γ-Fe2O3 is generated after pyrolysis, which promotes the combination of CO2 and monatomic metal Fe, and H + There is a possibility that more CO can be released by promoting the breaking of C-O in CO2 through protonation reaction.

[0025] 2) The catalyst exhibits excellent CO selectivity (CO Faraday efficiency is greater than 97%) in a wide potential window of-0.5V to-1.1V (vs. reversible hydrogen electrode, vs. RHE), and the current density and CO Faraday efficiency remain basically unchanged after 2h of continuous electrolysis at-0.6V, showing excellent stability. Secondly, -1.1V vs. RHE is the most negative potential for the high-selectivity catalytic reduction of CO2 to CO by Fe-N-C material, which helps to obtain CH4 and other multi-electron reduction products by constructing an efficient series catalytic system.

[0026] 3) The synthesis method of the present application is simple, first Fe(phen)3Cl2 complex crystals are synthesized, then they are mixed and pyrolyzed with ZIF-8 to obtain the catalyst, the yield is high, and the amount of catalyst required for electrocatalytic reaction is less, and the conversion efficiency of the catalyst is high.

[0027] 4) The catalyst of the present application has metal iron as the catalytic site, which belongs to non-noble metal, and the cost of the catalyst is low. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a scanning electron microscope image of the catalyst of Fe-N-C loaded γ-Fe2O3 hollow sphere material in Example 1 of the present application;

[0029] Figure 2 It is a high-resolution transmission electron microscope image of Fe-N-C loaded γ-Fe2O3 in Example 1 of the present application;

[0030] Figure 3 It is a lattice spacing analysis diagram of Fe-N-C loaded γ-Fe2O3 in Example 1 of the present application;

[0031] Figure 4 It is a Faraday efficiency column chart of electrocatalytic CO2 reduction of the catalyst of Fe-N-C loaded γ-Fe2O3 hollow sphere material at different potentials in Example 2 of the present application;

[0032] Figure 5A CO partial current density diagram of the Fe-N-C supported γ-Fe2O3 hollow sphere material catalyst and the NC material in Example 2 of the present application for electrocatalytic reduction of CO2 at different potentials, in which 1 is the Fe-N-C supported γ-Fe2O3 hollow sphere material catalyst, and 2 is the NC material. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0034] Example 1

[0035] A preparation method of a Fe-N-C supported γ-Fe2O3 hollow sphere material catalyst, specifically comprising the following steps:

[0036] (1) 1,10-phenanthroline 0.5410 g is weighed and dissolved in 10 ml of anhydrous methanol, and is marked as solution 1; FeCl2·4H2O 0.1988 g is weighed and dissolved in 5 ml of anhydrous methanol, and is marked as solution 2; solution 2 is slowly added to solution 1, and after being fully stirred for 4 hours, filtration is performed, and the filtrate is diffused by ether to precipitate dark red crystals, which are high-purity Fe(phen)3Cl2. The mass is 0.595 g, and the yield is 80.3%.

[0037] (2) 2.380 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) is weighed and dissolved in 56.66 mL of anhydrous methanol solution, and is marked as solution 1; 5.288 g of 2-methylimidazole is weighed and dissolved in 56.66 mL of anhydrous methanol solution, and is marked as solution 2; then solution 2 is slowly added to solution 1 under stirring, and after being mixed and stirred for 8 hours, the solution becomes milky white, and stirring is stopped. The solution is centrifuged at 10000 r / s for 5 min, and then is washed and centrifuged by ultrasonic oscillation with an anhydrous methanol solution, and the operation is repeated three times. Finally, the obtained wet solid is dried in a vacuum drying box at 60°C for 12 h to obtain white ZIF-8 solid, which is ground into powder with a mortar for standby use;

[0038] (3) Weigh 22.5 mg of Fe(phen)3Cl2 and dissolve it in 10 ml of anhydrous methanol. Weigh 400 mg of ZIF-8 and disperse it in the above solution. After stirring for 4 h, evaporate the solution using a rotary evaporator and then evaporate the resulting solid to dryness. The obtained sample was calcined at 1050 °C for 1 h in a vacuum tube furnace with Ar flowing through it, with a heating rate of 5 °C / min. After pyrolysis, the sample was ground and dispersed in 0.5 M H2SO4 solution and stirred for 12 h. After filtration, washing until neutral, and drying, the Fe-NC supported γ-Fe2O3 hollow sphere catalyst was obtained.

[0039] The catalyst has the following structural formula:

[0040]

[0041] The obtained catalyst was characterized by scanning electron microscopy and high-resolution transmission electron microscopy, and the results are as follows: Figure 1 As shown, the Fe-NC particles are hollow pocket-shaped with a particle size of approximately 3 μm. This open-window structure facilitates the exposure of more active sites, increasing the specific surface area of ​​the catalyst. The particles are interconnected, forming a porous structure, which is beneficial for mass transfer between reactants and products, thus increasing the reaction rate. HR-TEM image ( Figure 2 The image shows a small number of irregular hollow spheres with a diameter of approximately 83 nm dispersed on a carrier containing numerous small pores. The lattice fringe spacing of the hollow sphere walls is 0.25 nm, corresponding to the γ-Fe₂O₃(311) crystal plane. Figure 3 ).

[0042] Example 2

[0043] The catalyst supporting Fe-NC γ-Fe2O3 hollow spheres electrocatalytically reduces CO2 to CO, specifically including the following steps:

[0044] (1) Take 4 mg of the Fe-NC supported γ-Fe2O3 hollow sphere material catalyst prepared in Example 1, add it to isopropanol and sonicate for 30 min to disperse it evenly, then add 30 μL of 5 wt% Nafion solution to obtain the catalyst dispersion, and set it aside under stirring.

[0045] (2) Take 200 μL of the above dispersion and add it dropwise to a 1.4 cm * 1.4 cm * 1 mm gas diffusion electrode. Then dry it in an oven at 50 °C to obtain the working electrode for later use. Weigh the carbon paper before and after drying to ensure that the catalyst loading is between 0.45 mg and 0.5 mg each time.

[0046] (3) The prepared working electrode was used in a three-electrode system flow cell for electrocatalytic reaction, the counter electrode was a nickel mesh, the reference electrode was an Ag / AgCl electrode, and the electrolyte was a 0.5 M KHCO3 aqueous solution. The anode cell and the cathode cell were separated by a proton exchange membrane.

[0047] (4) CO2 was bubbled into the cathode cell electrolyte before the reaction for 30 min until the CO2 gas was saturated in the electrolyte, and air was discharged at the same time. Finally, the system was sealed, CO2 was bubbled into the gas phase chamber at a flow rate of 10 ml / min, and the electrolyte in the anode and cathode chambers was 0.5 mol / L KHCO3 aqueous solution, which was circulated at a flow rate of 6 ml / min. Different potentials (-0.5 V, -0.6 V, -0.7 V, -0.8 V, -0.9 V, -1 V, -1.1 V, -1.2 V, -1.3 V) were applied for the reaction to reduce CO2 to CO, and the reacted gas was introduced into a gas chromatograph for detection.

[0048] The FE value of the gas product was calculated according to the following formula:

[0049]

[0050] In the formula, n is the number of electrons transferred for reducing CO2 or H2O as the target product, F is the Faraday constant (96485 C / mol), ppm is the product concentration analyzed by gas chromatography, G is the gas flow rate; I is the current (unit A), P is the standard atmospheric pressure (1.01 x 10 5 Pa), R = 8.314 J / (mol·K), and T = 273.15 K.

[0051] The total current density is equal to the current divided by the geometric area of the working electrode. The partial current density of CO is equal to the total current density multiplied by the FE CO .

[0052] A comparative material was set, which was a metal-free material, named NC material.

[0053] The preparation method of the NC material was as follows: 11.63 mg of 1,10-phenanthroline was dispersed in 10 mL of anhydrous methanol, and an ultrasonic cleaning machine was used for ultrasonic cleaning for a period of time to make it uniformly dispersed in the methanol. Then, 400 mg of ZIF-8 was slowly poured into the solution, stirred for 4 h, and then dried by a rotary evaporator. The obtained sample was calcined in an Ar-purged vacuum tube furnace at 1050°C for 1 hour, with a heating rate of 5°C / min. After pyrolysis, the sample was ground and dispersed in a 0.5 M H2SO4 solution and stirred for 12 hours. After suction filtration, washing to neutral, and drying, the NC material was obtained.

[0054] As can be seen from Figure 4 and 5 , the maximum FE of the NC material isCO For 48%, the more negative potential, the more serious hydrogen evolution reaction, the highest CO partial current density is only 0.48 mA / cm 2 . And the catalyst prepared in Example 1 has FE CO All more than 97% (such as Figure 4 ), and the highest CO partial current density reaches 25.3 mA / cm 2 (such as Figure 5 ) at-1.1V. It can be seen that the active site of the catalyst for electrocatalytic reduction of CO2 is the Fe component in the material.

[0055] It is worth noting that this potential range is the widest and most negative potential range for the high-selectivity electrocatalytic reduction of CO2 to CO in the Fe-N-C material reported at present, and the maximum CO partial current density is also one of the maximum values in the reported Fe-N-C materials, which is conducive to the construction of a series of catalytic systems and the improvement of the generation efficiency of multi-electron reduction products. Moreover, the catalyst of the application keeps FE CO above 97% and the total current density basically remains unchanged after continuous electrolysis at-0.6V for 2h, indicating that the catalyst of the application has excellent stability.

[0056] The above content is only an example and description of the structure of the application, and those skilled in the art can make various modifications or supplements or use similar ways to replace the described specific embodiments, as long as they do not deviate from the structure of the application or exceed the scope defined by the claims, which shall belong to the protection scope of the application.

Claims

1. A method for preparing a catalyst of Fe-N-C supported γ-Fe2O3 hollow sphere material, characterized in that: Fe(phen)3Cl2 complex crystal is Fe(phen)3Cl2 complex crystal, and phen in the structural formula is 1,10-phenanthroline ligand; The structural formula of the Fe(phen)3Cl2 complex crystal is as follows: 。 2. The method for preparing the catalyst of Fe-NC supported γ-Fe2O3 hollow sphere material according to claim 1, characterized in that, Specifically includes the following steps: dissolving Fe(phen)3Cl2 complex crystal in methanol, then adding ZIF-8 thereto, stirring sufficiently, then rotary evaporation, pyrolysis of the obtained solid in a tube furnace under inert gas, finally acid soaking, filtration, washing to neutral pH, and then drying.

3. The method for preparing the Fe-N-C supported γ-Fe2O3hollow sphere material catalyst according to claim 2, characterized in that: The mass ratio of the Fe(phen)3Cl2 and ZIF-8 is 1:17.78; the stirring time is 4 h; the inert gas is argon; the pyrolysis temperature is 1050 ℃, the pyrolysis time is 1 h, and the heating rate is 5 ℃ / min; and the drying temperature is 100 ℃, and the drying time is 2 h.

4. The method for preparing the Fe-N-C supported γ-Fe2O3hollow sphere material catalyst according to claim 1, characterized in that: The preparation method of the Fe(phen)3Cl2 complex crystal is as follows: 1,10-phenanthroline ligand and FeCl2·4H2O are subjected to coordination reaction in methanol, and then the crystal Fe(phen)3Cl2 is precipitated by ether diffusion.

5. The method for preparing the Fe-N-C supported γ-Fe2O3hollow sphere material catalyst according to claim 4, characterized in that: The molar ratio of the FeCl2·4H2O and 1,10-phenanthroline is 1:3-1:6, the coordination reaction time is 1-4 h, and the crystal Fe(phen)3Cl2 is precipitated by ether diffusion after the coordination reaction.

6. The method for preparing the Fe-N-C supported γ-Fe2O3hollow sphere material catalyst according to claim 1, characterized in that: The preparation method of the ZIF-8 is as follows: 2-methylimidazole ligand and Zn(NO3)2·6H2O are subjected to coordination reaction in methanol to obtain ZIF-8; The molar ratio of the Zn(NO3)2·6H2O and 2-methylimidazole is 1:8; the coordination reaction time is 8 h, and the crystal is centrifuged and washed with anhydrous methanol, and then vacuum dried at 60 ℃ for 12 h.

7. A Fe-N-C loaded γ-Fe2O3 hollow sphere material catalyst prepared by the preparation method of any one of claims 1-6.

8. Use of the catalyst of Fe-N-C supported γ-Fe2O3 hollow sphere material according to claim 7, characterized in that: The Fe-N-C loaded γ-Fe2O3 hollow sphere material catalyst is used for electrocatalytic reduction of CO2 to CO at a wide potential of-0.5 V to-1.1 V.

9. A method for electrocatalytic CO2 reduction to produce CO, characterized in that, The method comprises the following steps: (1) The Fe-N-C loaded γ-Fe2O3 hollow sphere material catalyst of claim 7 is uniformly dispersed in isopropyl alcohol by ultrasonic dispersion, and then a Nafion solution is added to obtain a catalyst dispersion liquid, which is ready for use under stirring; (2) The catalyst dispersion liquid is added dropwise to a gas diffusion electrode in batches, and the working electrode is obtained by drying and ready for use; (3) The prepared working electrode is used in a three-electrode system flow cell for electrocatalytic reaction, a nickel mesh is used as the counter electrode, an Ag / AgCl electrode is used as the reference electrode, and a KHCO3 aqueous solution is used as the electrolyte; (4) Before the reaction, CO2 is bubbled into the cathode cell electrolyte until the CO2 gas is saturated in the electrolyte, while the air is discharged, and finally the system is sealed, and the electrolysis reaction is carried out at -0.5 ~ -1.3 V to reduce CO2 to CO.

10. The method of claim 9, wherein: the step (1) is performed by using a Nafion solution with a mass fraction of 5%, and 7.5 uL of the Nafion solution is used for 1 mg of the catalyst; and the step (3) is performed by separating the cathode cell and the anode cell in the flow cell by a proton exchange membrane.

10. The method of claim 9, wherein: the step (1) is performed by using a Nafion solution with a mass fraction of 5%, and 7.5 uL of the Nafion solution is used for 1 mg of the catalyst; and the step (3) is performed by separating the cathode cell and the anode cell in the flow cell by a proton exchange membrane. The size of the working electrode in step (2) is 1.4 cm*1.4 cm*1 mm, and the loading amount of the catalyst on the gas diffusion electrode is 0.45 mg ~ 0.5 mg each time, and the geometric area of the working electrode in contact with the electrolyte during electrolysis is 1 cm 2 ; ​

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