阅读说明：本技术 Fe-N-C催化剂，制备方法及其用途 (Fe-N-C catalyst, preparation method and application thereof ) 是由 胡喜乐 顾均 于 2019-02-12 设计创作，主要内容包括：本发明涉及用于电化学还原二氧化碳的单原子铁催化剂,及其制备方法和用途。特别地,本发明涉及一种Fe(II)掺杂的Zn-ZIF前体材料的制备方法及其在催化剂的制备中的用途,该催化剂包含Fe单原子,在N掺杂的碳基质上,自这种Fe(II)掺杂的Zn-ZIF前体材料的热解获得。(The invention relates to a monatomic iron catalyst for electrochemical reduction of carbon dioxide, a preparation method and application thereof. In particular, the present invention relates to a process for the preparation of an Fe (ii) -doped Zn-ZIF precursor material and its use in the preparation of a catalyst comprising Fe single atoms, obtained from the pyrolysis of such Fe (ii) -doped Zn-ZIF precursor material, on an N-doped carbon substrate.)

1. Use of a catalytic material containing iron single atoms on an N-doped carbon matrix prepared from an Fe (II) -doped Zn-Zeolithium Imidazole Framework (ZIF) for the conversion of CO₂Electro-reduction to CO.

2. A method of making a catalytic material comprising the steps of:

a) providing an fe (ii) -doped Zn-Zeolitic Imidazole Framework (ZIF) in dry form under an inert atmosphere;

b) the fe (ii) doped Zn-ZIF is pyrolyzed under an inert atmosphere for about 2 to about 24 hours, typically 3 hours;

c) the pyrolysis product obtained was collected as catalytic material.

3. The method of claim 2, wherein said pyrolyzing of step b) is carried out at a temperature between about 800 and 950 ℃.

4. The process of claim 2 or 3, wherein said pyrolyzing of step b) is carried out at a temperature of about 3 to 10 ℃ for min^-1Is increased at a rate of (3).

5. A method of preparing an fe (ii) -doped Zn-ZIF material, comprising the steps of:

(i) providing an imidazole or imidazole derivative precursor;

(ii) in the prevention of Fe²⁺Dissolving the imidazole or imidazole derivative precursor in a degassed polar solvent in a reducing atmosphere of cationic oxidation to obtain a solution A;

(iii) dissolving an iron (II) precursor and a zinc salt in a degassed polar solvent to obtain a solution B;

(iv) adding the solution B into the solution A;

(v) collecting and washing the precipitate;

(vi) drying the washed precipitate at room temperature to obtain fe (ii) -doped Zn-Zeolitic Imidazole Framework (ZIF) in dry powder form, wherein steps (ii) to (vi) are carried out under stirring under inert atmosphere.

6. The process of claim 5, wherein in step (iv), solution B is added dropwise to solution A with stirring for about 1 hour.

7. The process according to any one of claims 5 to 6, wherein the reaction mixture from step (iv) is kept under stirring under an inert atmosphere for about 1 day after the addition of solution B is complete.

8. The method of any one of claims 5 to 7, wherein the imidazole precursor is 2-methylimidazole.

9. The method of any one of claims 5 to 8, wherein the iron (II) precursor is FeCl₂。

10. The method of any one of claims 2 to 9, wherein the inert atmosphere consists of N₂The stream is provided.

11. The method of any one of claims 5 to 10, wherein the precipitate is collected in step (v) by centrifugation under an inert atmosphere or ambient pressure filtration.

12. The method according to any of claims 2 to 4, wherein the provided Fe (II) -doped Zn-Zeolitic Imidazolate Framework (ZIF) is obtained according to the method of any of claims 5 to 11.

13. A catalyst comprising Fe single atoms on an N-doped carbon substrate obtained from the method of any one of claims 2 to 4 or 12.

14. Use according to claim 1, wherein the catalytic material is obtained by pyrolysis of fe (ii) -doped Zn-ZIF-8.

15. Use according to claim 1 or 14, wherein the catalytic material is a material according to claim 13.

16. The use of claim 1, wherein the fe (ii) -doped Zn-ZIF has a crystalline structure of Zn-ZIF-8, wherein some of the Zn (ii) ions are replaced by fe (ii) ions.

17. The method of any of claims 2 to 4 or 10, wherein the fe (ii) -doped Zn-ZIF has a crystalline structure of Zn-ZIF-8, wherein some Zn (ii) ions are substituted by fe (ii) ions.

18. For electrochemical reduction of CO₂Comprising a catalytic material prepared from a fe (ii) -doped Zn-Zeolitic Imidazole Framework (ZIF).

19. A kit for the preparation of catalytic material according to the invention, comprising at least one container containing the fe (ii) -doped Zn-Zeolitic Imidazolate Framework (ZIF) in dry form and under an inert atmosphere.

20. The kit of claim 19, wherein the fe (ii) -doped Zn-ZIF has a crystalline structure of Zn-ZIF-8, wherein some of the Zn (ii) ions are replaced with fe (ii) ions.

21. A kit for the preparation of an fe (ii) -doped Zn-Zeolitic Imidazole Framework (ZIF), said kit comprising, in separate compartments or containers:

a) imidazole or an imidazole derivative precursor;

b) iron (II) precursors, e.g. FeCl₂Or Fe (CH)₃COO)₂；

c) Zinc salts, e.g. Zn (NO)₃)₂Or ZnCl₂(ii) a And

d) optionally, a reducing agent to prevent Fe²⁺Oxidation of ions, for example iodide derivatives, such as potassium iodide, sodium iodide or ammonium iodide.

Technical Field

The present invention relates generally to the field of electrochemical reduction of carbon dioxide, in particular for CO₂An electro-reduced catalyst.

Background

Atmospheric carbon dioxide (CO)₂) The rise in levels has attracted global attention and anticipates a range of environmental consequences, including damaging climate change, that may impact modern civilization. Due to CO produced over the last fifty years₂The number of them is considerable, and therefore various methods are required to reduce the number thereof. Among them, the synthesis of CO has been developed₂Methods for electrochemical reduction to useful chemicals, including carbon monoxide (CO), formic acid, methane and ethylene (Jhong et al, 2013, a modern point of view in chemical engineering, 2(2), 191-199).

Thus, CO in the aqueous electrolyte₂Electrolytic reduction to CO is considered to be the reduction of CO₂And conversion of electrical power to CO and O₂Promising technology of immobilizing CO₂While valuable chemicals are produced and waste CO can be recycled₂The recycle is utilized to the "carbon neutralization" cycle. Electrochemical reduction of CO₂To form carbon-based fuels and chemicals are widely proposed for storage and utilization of intermittent renewable energy sources such as solar and wind (Zhu et al, 2016, Adv mater, 28(18), 3423-52). However, there are two major drawbacks to CO rejection₂Electrolytic reduction has evolved into a viable technology: energy inefficiency due to large overpotentials, and poor selectivity leading to separation problems. If CO is CO₂The only product of the reduction can then be reduced by reacting the appropriate CO: h₂Proportional addition of H₂The product is directly used for the synthesis of hydrocarbons (Fischer-Tropsch synthesis), methanol and aldehyde.

In the past thirty yearsThe work has focused primarily on screening different metal catalysts and the various products that can be formed using these metals. Unfortunately, at overpotentials below 400mV, the conversion is usually very low (<20mA/cm²) And the selectivity to the desired product is also low.

For use up to now from CO₂The most active catalysts for the electrolytic reduction to CO are gold and silver based nanomaterials (Chen et al, 2012, J.S.Chem., 134, 19969-19972; Zhu et al, 2014, J.S.Chem., 136, 16132-16135; Lu et al, 2014, Nature communications, 5, 3242) and have so far been used for the electrochemical reduction from CO₂The two most active catalysts for the electrolytic reduction to CO are (1) oxide-derived gold (Chen et al, 2012, supra): the CO generation rate was 8mA cm at-0.4V relative Reversible Hydrogen Electrode (RHE)^-2(ii) a (2) Gold needle electrode (Liu et al, 2016, nature, 537, 328): at-0.35V versus RHE, CO forms a current density of about 14mA cm^-2. However, the high cost of such catalysts limits their use on a large scale. Most non-noble metal catalysts (e.g., copper and zinc) have much poorer performance (Li et al, 2012, J. Am. chem., 134, 7231-. Catalysts comprising earth-rich metals such as iron, cobalt, nickel have been developed, but the partial current density is still lower than for catalysts based on gold and silver. In particular, a commercially available Zeolitic Imidazolate Framework (ZIF), ZIF-8, iron (II) acetate (Fe (Ac))₂) And phenanthroline (phen) as a precursor, mixed by ball milling prior to pyrolysis, to produce catalytic materials of various properties, but all achieved a much lower rate of CO formation than gold catalysts, i.e., about 2mA cm at-0.4V^-2(Huang et al, 2017, ACS Catal., 7, 1520). The iron, cobalt and nitrogen Co-doped carbon catalyst was prepared by pyrolysis of an fe (ii) doped Co-ZIF precursor prepared from 2-methylimidazolium cobalt (ZIF-67) (CN 107086313). The resulting catalyst is said to be useful in the fuel cell and metal-air cell fields and is superior to the commercial catalyst Pt/C.

Ye Yifan et alThe catalyst for the oxygen reduction reaction is obtained from a precursor consisting of ZIF-8 functionalized by ammonium iron salt (AFC) ((II))ZIF-8) followed by a two-step pyrolysis (Ye Yifan et al, 2017, Proc. Energ Chem., 26(6), 1174-1180). The second pyrolysis is said to improve the mesoporous area and the formation of undesirable iron nanoparticles. Precursor for pyrolysis (

ZIF-8) was prepared from AFC without addition of a reducing agent, so the precursor was fe (iii) -doped Zn-ZIF.

CO thus produced by catalytic processes in a selective and efficient manner₂Conversion is of interest and there is a high demand for high performance catalysts capable of achieving cost-effective selective carbon dioxide conversion.

Disclosure of Invention

It is an object of the present invention to provide a catalytic material useful for the conversion of CO in an aqueous electrolyte₂Electro-reduction to CO.

It would be advantageous to provide a catalytic material with high catalytic activity that is capable of increasing CO₂While maintaining a high selectivity for CO formation.

It would be advantageous to provide a catalytic material having production costs that allow for large-scale use.

It would be advantageous to provide a catalytic material that is stable during use, thereby limiting the amount of catalytic material used per reduction process, avoiding the need for expensive catalyst regeneration, which would reduce CO₂The overall production cost of the electro-reduction product.

It would be advantageous to provide a catalyst made from a rich metal that allows for large scale use.

It would be advantageous to provide a cost-effective process for preparing a catalyst for the conversion of CO in an aqueous electrolyte₂An efficient catalytic material for electro-reduction to CO.

It would be advantageous to provide a cost-effective method for preparing an effective catalytic material that exhibits a discrete distribution of Fe and Zn atoms within the structure of the catalyst.

It is advantageous to prepare the catalyst from readily available chemical reagents.

It is an object of the present invention to provide a method for the conversion of CO in an aqueous electrolyte₂Selective and cost-effective process for electro-reduction to CO.

The object of the invention is achieved by providing a use according to claim 1, a method according to claim 2 and a catalytic material according to claim 13.

According to a first aspect of the present invention, there is disclosed the use of a catalytic material prepared from a fe (ii) -doped Zn-Zeolitic Imidazolate Framework (ZIF) for the conversion of CO₂Electro-reduction to CO, the catalytic material comprising Fe single atoms on an N-doped carbon matrix.

According to a second aspect of the present invention, there is disclosed herein a method of preparing a catalytic material comprising the steps of:

a) providing an fe (ii) -doped Zn-Zeolitic Imidazole Framework (ZIF) in dry form under an inert atmosphere;

b) pyrolyzing the Fe (II) -doped Zn-ZIF under an inert atmosphere for about 2 to about 24 hours, typically 3 hours;

c) the pyrolysis product obtained was collected as catalytic material.

The method may advantageously comprise providing fe (ii) -doped Zn ZIF, obtained by a method comprising the steps of:

(i) providing an imidazole or imidazole derivative precursor;

(ii) in the prevention of Fe²⁺Dissolving the imidazole or imidazole derivative precursor in a degassed polar solvent (e.g. methanol or ethanol) in a reducing environment of cationic oxidation, for example in an iodide derivative (e.g. potassium iodide KI, sodium iodide NaI or ammonium iodide NH₄I) In the presence of (a) to obtain a solution A;

(iii) by addition of iron (II) precursors, e.g. FeCl₂、FeCl₂·4H₂O、Fe(CH₃COO)₂And zinc salts such asZn(NO₃)₂Or ZnCl₂Dissolving in degassed methanol and degassed polar solvent such as methanol or ethanol to obtain solution B;

(iv) adding the solution B into the solution A;

(v) collecting and washing the precipitate;

(vi) drying the washed precipitate at room temperature to obtain a fe (ii) -doped Zn-Zeolitic Imidazolate Framework (ZIF) in the form of a dry powder, wherein steps (ii) to (vi) are carried out under stirring under an inert atmosphere;

(vii) collecting Zn-Zeolitic Imidazole Frameworks (ZIFs) doped with Fe (II) in the form of a dry powder under an inert atmosphere.

According to a third aspect of the present invention, there is disclosed a catalytic material comprising iron single atoms on N-doped base carbon, obtained by pyrolysis of fe (ii) -doped Zn-ZIF.

According to another aspect of the present invention, there is disclosed herein the use of a catalyst material for the conversion of CO₂Electro-reduction to CO, the catalytic material comprising iron single atoms on N-doped base carbon, obtained by pyrolysis of fe (ii) -doped Zn-ZIF.

According to another aspect of the present invention, there is disclosed herein a method for electrochemically reducing carbon dioxide to CO, the method comprising the steps of:

-providing for CO₂An electroreduction system for electrochemical reduction;

-providing a catalytic material according to the invention comprising Fe single atoms on N-doped host carbon;

-contacting the catalytic material with a working electrode of an electroreduction system;

-carrying out CO₂Generating CO through an electroreduction reaction;

collecting the released gas, which contains carbon monoxide, small amounts of H₂And unreacted CO₂。

In accordance with another aspect of the present invention, disclosed herein is a method for electrochemical reduction of CO₂Or a part of an electro-reduction system (e.g. a support electrode), CO comprising the catalytic material of the invention₂。

According to another aspect of the present invention, there is disclosed herein a method for electroreduction of CO₂A kit comprising the catalytic material of the invention.

According to another aspect of the present invention, there is disclosed herein a kit for preparing the catalytic material of the present invention, the kit comprising a container comprising an fe (ii) -Zn doped Zeolitic Imidazole Framework (ZIF) in dry form and under an inert atmosphere.

According to another aspect of the present invention, there is disclosed herein a kit for preparing an fe (ii) -doped Zn-Zeolitic Imidazole Framework (ZIF) suitable for preparing the catalytic material of the present invention, comprising, in separate compartments or containers:

a) imidazole or an imidazole derivative precursor;

b) iodide derivatives, e.g. potassium iodide, sodium iodide or ammonium iodide (KI or NaI or NH)₄I)；

c) Iron (II) precursors, e.g. FeCl₂Or Fe (CH)₃COO)₂(ii) a And

d) zinc salts, e.g. Zn (NO)₃)₂Or ZnCl₂。

Other features and advantages of the invention will be apparent from the claims, the detailed description, and the drawings.

Brief description of the drawings

Fig. 1 shows a method (a) of obtaining a catalytic material (Fe-N-c (ii)) comprising Fe single atoms on an N-doped carbon matrix according to the invention, and a method (B) of obtaining an Fe (ii) doped Zn-ZIF-8 precursor according to the invention for such a catalytic material.

Fig. 2 provides X-ray diffraction patterns of fe (ii) doped Zn-ZIF-8 precursor (top) and undoped Zn-ZIF-8 precursor (bottom) before pyrolysis for precursor (a) and corresponding pyrolysis product (b), and a graphical comparison of fe (ii) doped Co-ZIF-8 precursor (top) and fe (ii) doped Zn-ZIF-8 precursor of the invention (bottom) before pyrolysis (c) and after pyrolysis (d), as described in example 3.

Figure 3 provides electron microscopy characterization of catalytic materials of the invention by (a) Transmission Electron Microscopy (TEM) and (b) High Resolution Transmission Electron Microscopy (HRTEM) imaging and (c) Energy Dispersive Spectroscopy (EDS) imaging as described in example 3. Fe. The distribution of N and Zn is shown in c2, c3 and c4, respectively.

Figure 4 provides an electron microscopy characterization of the catalytic material of the invention by Scanning Electron Microscopy (SEM) imaging as described in example 3. a and b: fe (ii) doped Zn-ZIF-8 precursor prior to pyrolysis; c. d and e: a pyrolysis product obtained from an fe (ii) doped ZIF-8 precursor; f: particle size distribution plots of Fe (II) doped Zn-ZIF-8 (light color) and pyrolysis product (dark color) prior to pyrolysis.

Fig. 5 provides an electron microscopy characterization of comparative material (Fe-N-c (iii)) prepared by pyrolysis of Fe (iii) -doped ZIF-8 as described in example 3 by Scanning Electron Microscopy (SEM) imaging. a and b: pyrolyzing the comparative fe (iii) doped ZIF-8 precursor prior to; c and d: fe (iii) doped ZIF-8 precursor pyrolysis product; e: particle size distribution plots of fe (iii) -doped ZIF-8 (light color) and pyrolysis product (dark color) prior to pyrolysis.

FIG. 6 shows the use of 0.5M KHCO as described in example 4₃Electrochemical characterization of the performance of the catalytic material of the invention obtained as described in example 2 in comparison with other materials in an electrolytic test as electrolyte. a: in the electrochemical reduction of CO₂A schematic diagram of the electrolytic tests carried out in the electrochemical reduction system of (1), which comprises a working electrode (WE, carbon cloth, the surface of which is deposited by drop casting a catalytic material, as described in example 4), a counter electrode (RE, platinum wire) and a reference electrode (RE, Ag/AgCl, saturated KCl solution electrode); b: the Fe-N-C (II) material and the undoped ZIF-8 material of the invention are used in CO₂(solid line) and N₂(dotted line) the pyrolysis products in the saturated electrolyte obtained stable Cyclic Voltammetry (CV) curves; c: the catalytic material of the invention is 'Fe-N-C (II)' in CO₂Chronoamperometric curve at-0.37V versus RHE in saturated electrolyte. The dots show the faradaic efficiency of the CO. d: Fe-N-C (II) material with CO (bottom) and H at different applied potentials₂Faradaic efficiency (top). Faradaic efficiencies (e) and (e) of CO on Fe-N-C (II) materials (solid line) and other catalysts (dashed line) at different applied potentialsComparison of the partial current densities (f). (1): 0.6mg/cm²The Fe-N-C (II) material of the present invention was prepared by dispersing 3mg of the catalyst in 1mL of ethanol and dropping 200. mu.L of the dispersion on a carbon cloth electrode of 1cm × 1cm (2): 1mg/cm²Comparative material Fe-N-C material (Fe 0.5d) (from huang et al, 2017, supra): 1mg of the catalyst was dispersed to 200. mu.L and dropped on 1cm²On the carbon paper electrode; (3): 0.4mg/cm²CoPc/CNT (from Zhang et al, 2017, Nature communications, 8, 14675): CoPc/CNT were prepared by adsorbing Co phthalocyanine molecules on multi-walled carbon nanotubes in DMF. 2mg of the catalyst was dispersed in 1mL, and 100. mu.L of the dispersion was dropped to 0.5cm²Porous Ag (from Lu et al, 2014, supra) prepared by acid etching α -Al (Ag) alloy synthesized at 546 ℃, and (5) oxide-derived (OD) Au (from Chen et al, 2012, supra) prepared by acid etching at 0.5M H₂SO₄Applying a symmetrical 1kHz square wave pulse of 2.70V to 0.70V on an Au foil for 60min in an electrolyte to prepare an OD Au electrode; Fe-N-C (II) material (squares) and other comparative Fe doped ZIF materials (dots: Fe (II) doped Co ZIFs from CN 107086313; triangles: Fe (III) doped ZIFs, CO (solid line) and H on Ye Yifan et al, 2017, supra) at different applied potentials₂Faradaic efficiency (g) and partial current density (h) of CO (dashed line).

FIG. 7 provides a characterization of the Fe-N-C (II) catalyst of the present invention as described in example 3 (a) by high angle annular dark field scanning Transmission Electron microscopy (HAADF-STEM) and (b) by energy dispersive X-ray Spectroscopy (EDS) for the areas indicated by white squares; (c) characterization of faradaic efficiency by measuring Fe-N-c (ii) total current density (curve) and CO (point) of the invention in different electrolytes by chronoamperometry at-0.37V versus RHE: (1) ultrapure K₂CO₃(99.999%) and deionized water (18.2 M.OMEGA.cm), (2) KHCO having the purity of the analytical reagent₃(99.7%) and deionized water, and (3) KHCO having the purity of the analytical reagent₃And tap water.

Figure 8 provides electron microscopy characterization of the material of the invention after electrolysis by (a) Transmission Electron Microscopy (TEM) and (b) High Resolution Transmission Electron Microscopy (HRTEM) imaging, and (c) EDS imaging as described in example 5. Fe. The distribution of N and Zn is shown at c2, c3 and c4, respectively, and (d) the EDS spectra of the Fe-N-C (II) material before (top) and after (bottom) electrolysis.

FIG. 9 provides a characterization of the precursors Fe (II) doped Zn-ZIF material (a-c) and the catalytic material Fe-N-C (II) obtained by pyrolysis of Fe (II) doped Zn-ZIF by X-ray absorption Spectroscopy (XAS) as described in example 3. a: with Fe foil (black dotted line), Fe (II) (phen)₃SO₄(black dots) and Fe₂O₃(solid gray line) Fe K-boundary XANES spectra compared to Fe (ii) doped Zn-ZIF of the present invention (solid black line); b: fe (ii) K-boundary EXAFS spectra of Fe (lll) doped Zn-ZIF precursors of the invention. Black curve: fitting a crystal structure of ZIF-8, wherein the positions of Zn (II) ions are occupied by Fe (II) ions; c: schematic representation of structures used as an EXAFS fitting model, in particular the area around ZIF-8 cell metals; d: fe K-boundary EXAFS spectra of the catalytic material of the present invention Fe-N-c (ii) obtained from pyrolysis of Fe (ii) doped Zn-ZIF precursor.

Detailed Description

Zeolitic Imidazolate Frameworks (ZIFs) are a subfamily of Metal Organic Frameworks (MOFs) that can be synthesized by solvothermal/hydrothermal and microwave-assisted reactions at a temperature range of 298-423K. ZIFs employ a porous crystalline structure composed of metal ions and an organic linker, arranged in a manner similar to the arrangement of silicon and oxygen in zeolites. Tetrahedral metal centres [ e.g. M ═ Zn (II)]Only the nitrogen atoms in the 1, 3-positions of the imidazolate bridging ligands coordinate to provide an overall neutral backbone. Imidazole ester ligands are generally obtained via phenyl (benzimidazole ester (PhIM)) or methyl (2-methylimidazolium ester (MeIM)) groups (Park et al, 2006, Proc. Natl. Acad. Sci. USA (PNAS), 103(7), 10186-. ZIF-8, which is easily synthesized at room temperature and stable in water, is a tetrahedrally coordinated zinc metal and 2-methylimidazolium ring (Zn (MeIM)₂) Has a sodalite topology (SOD) exhibiting a 3D structure, has a cavity with a diameter of 11.6A, accessible through a window of 3.4A. The zinc sites in ZIF may be substituted with other ones having fourDivalent metal cations in a coordination mode (e.g. Fe)²⁺And Co²⁺) Instead, the internal space of the ZIF may accommodate other metal cations (e.g., Fe)³⁺、Ni²⁺And Cu²⁺) The complex of (1). In the framework of the present invention, it was surprisingly found that by using Fe²⁺Doped Zeolitic Imidazolate Frameworks (ZIFs), in particular ZIF-8, as precursor material for the pyrolysis carried out according to the process of the present invention, it is possible to obtain catalytic materials containing Fe single atoms on an N-doped carbon matrix, with a CO similar to that of an oxide-derived Au catalyst₂And (4) electroreduction performance.

The performance of the catalyst can be measured by Faradaic Efficiency (FE), the fractional current density and stability of CO formation (Jones et al 2014, isr.j.chem., 54, 1451-. Typically, the faradaic efficiency is greater than 80% for applied potentials greater than-0.6V versus RHE, and the fractional current density for CO formation is greater than 10mA cm^-2(this indicates that the rate of CO production is higher than 3.3 mL. multidot.h^-1·cm^-2) The catalyst of (a) is considered to be a very effective catalyst.

The expression "imidazole or imidazole derivative precursor" refers to precursors of imidazole precursors capable of forming an imidazole bridge with a tetrahedral metal ion within the zeolitic imidazolate framework. Examples of imidazole precursors are described in Han et al, 2009, reports of chemical research, 43(1), 58-67 and Park et al, 2006, supra. In particular, imidazole or imidazole derivative precursors include 2-ethylimidazole, 2-methylimidazole, 4-nitroimidazole, 4, 5-dichloronitroimidazole, imidazole ester-2-carboxaldehyde, 4-cyanoimidazole, benzimidazole, methylbenzimidazole, 4-azabenzimidazole, 5-azabenzimidazole, and purine.

The expression "iodide derivative" includes potassium iodide, sodium iodide, ammonium iodide, tetramethylammonium iodide, tetraethylammonium iodide and tetrabutylammonium iodide.

The expression "iron (II) precursor" refers to any iron (II) containing precursor suitable for doping ZIFs. Examples of iron (II) precursors according to the invention include FeCl₂、FeSO₄、(NH₄)₂Fe(SO₄)₂·6H₂O、Fe(CH₃COO)₂And removal of iron (II) acetylacetonateWater or a hydrate.

The expression "zinc salt" refers to any zinc-containing salt suitable for use in preparing the zeolitic imidazolate framework. Examples of zinc salts according to the invention include Zn (NO)₃)₂、ZnCl₂、ZnSO₄、Zn(ClO₄)₂、ZnBr₂、Zn(CH₃COO)₂And dehydrated or hydrated forms of zinc acetylacetonate.

The expression "preventing Fe²⁺The reducing environment for cation oxidation "includes the introduction of reducing agents, including Na₂SO₃、K₂SO₃Ascorbic acid and formaldehyde.

Referring to the drawings, and in particular initially to FIG. 1A, there is provided an illustration of a method for preparing a catalytic material comprising Fe single atoms on an N-doped substrate, the method comprising the steps of:

a) providing an fe (ii) doped zinc-Zeolitic Imidazolate Framework (ZIF), for example in dry form under an inert atmosphere (ii) doped ZIF-8 (7);

b) (ii) when the fe (ii) -doped Zn-ZIF-8 is pyrolyzed under an inert atmosphere from about 2 to about 24;

c) the pyrolysis product obtained was collected as catalytic material.

In one embodiment, the fe (ii) -doped Zn-Zeolitic Imidazolate Framework (ZIF) is in dry form on N₂Provided in an atmosphere or immersed in hexane. Generally, the fe (ii) -doped Zn-Zeolitic Imidazolate Frameworks (ZIFs) according to the present invention are stable under inert atmosphere.

According to another further embodiment, the fe (ii) -doped Zn-Zeolitic Imidazolate Framework (ZIF) is placed on a support under an inert atmosphere and the pyrolysis in step b) is carried out directly on said support.

In one embodiment, the pyrolysis of step b) is carried out for about 3 hours.

In an embodiment, the pyrolysis of step b) is carried out at a temperature of between about 800 and 950 ℃, typically 900 ℃.

In another embodiment, the pyrolysis of step b) is carried out at about 2 to 10 ℃ for min^-1At a rate of, for example, 5 ℃ for min^-1。

In another embodiment, the inert atmosphere consists of N₂The stream is supplied, for example, at 50 to 150mL min^-1The flow rate of (c).

In another embodiment, the fe (ii) -doped Zn-ZIF material according to the present invention adopts a crystal structure of Zn ZIF-8 having some Zn (ii) ions substituted by fe (ii) ions.

In another embodiment, the method of preparing a catalytic material according to the present invention may advantageously comprise providing an fe (ii) doped ZIF material obtained by the method according to the present invention.

Referring to fig. 1B, a schematic representation of a specific embodiment of the steps of a process for the preparation of fe (ii) -doped Zn-ZIF is provided, obtained by a process comprising the steps of:

(i) providing an imidazole precursor, in particular a 2-methylimidazole precursor (1);

(ii) dissolving the imidazole precursor in the presence of an iodide derivative such as potassium iodide (KI) (3) in a degassed polar solvent such as methanol (2) to give a solution a;

(iii) by addition of iron (II) precursors, e.g. FeCl₂(4) And zinc salts such as Zn (NO)₃)₂·6H₂Dissolving O (5) in a degassed polar solvent such as methanol (6) to give solution B;

(iv) adding the solution B into the solution A;

(v) collecting and washing the precipitate;

(vi) drying the washed precipitate at room temperature to obtain fe (ii) -doped ZIF-8(8) in the form of a dry powder, wherein steps (ii) to (vi) are carried out under stirring under an inert atmosphere;

(vii) collecting the fe (ii) -doped Zn-Zeolitic Imidazole Framework (ZIF) in dry powder form under an inert atmosphere.

In another embodiment, the method of preparing Fe (II) -doped Zn-ZIF comprises dissolving an iron (II) precursor and a zinc salt in step (iii) to obtain solution B such that the molar ratio of Fe to Zn is from about 1: 20 to about 1: 4, preferably not higher than 1: 9.

In another embodiment, the method of preparing the fe (ii) -doped Zn-ZIF comprises adding solution B dropwise to solution a over about 1 hour with stirring.

In another embodiment, the method of preparing fe (ii) -doped Zn-ZIF comprises maintaining the reaction mixture obtained in step (iv) under inert atmosphere stirring for about one day after completing the addition of solution B.

In another embodiment, the method of preparing fe (ii) -doped Zn-ZIF comprises collecting the precipitate in step (v) by centrifugation under inert atmosphere or filtration at ambient pressure.

In another embodiment, the method of preparing fe (ii) -doped Zn-ZIF comprises washing the precipitate in step (v) by washing the collected precipitate in a solvent sequence. According to another particular embodiment, said washing is carried out according to a solvent sequence comprising a washing with N, N-Dimethylformamide (DMF) and a washing twice with methanol.

In another embodiment, the inert atmosphere consists of a closed reaction space (e.g., filled with N) under an inert atmosphere₂Glove box of (d).

According to another embodiment, the fe (ii) -doped Zn-Zeolitic Imidazolate Frameworks (ZIFs) of the present invention collected in step (vii) in dry form may be subjected to an atmosphere of protective air (e.g. under N) before being subjected to pyrolysis₂Under atmosphere or immersed in hexane) for about 1 week.

In another embodiment, the method of preparing fe (ii) -doped Zn-ZIF further comprises the step of (viii) dispersing the dried precipitate obtained in step (vii) in hexane before it is pyrolyzed so as to be stored in an air-protecting atmosphere.

In a particular embodiment, the fe (ii) -doped Zn-ZIFs according to the invention are obtained or deposited directly on a support, for example on a support electrode (e.g. carbon cloth or carbon fiber paper).

According to a particular aspect, the process of the invention for the preparation of fe (ii) -doped Zn-ZIF precursors advantageously allows doping of fe (ii) ions during the formation of ZIF structures (in step (iv)), which allows catalysts obtained after pyrolysis such as Huan et al, 2017, supra, described catalysts obtained from precursors obtained only by mixing ZIF-8 and fe (ii)Has better CO₂Reduction performance. In a particular embodiment, catalytic materials containing Fe single atoms on an N-doped carbon matrix prepared from Fe (ii) -doped Zn-Zeolitic Imidazolate Frameworks (ZIFs) according to the present invention may be used for the CO oxidation₂In the process of electro-reduction to CO, and may be useful as an electrochemical reduction of CO₂And/or for the electro-reduction of CO₂The kit of (1).

According to a particular embodiment, the catalytic material according to the invention may be deposited on the surface of the working electrode of an electroreduction system.

According to another particular embodiment, the catalytic material of the invention can be deposited on the surface by spin coating, drop casting or by dip coating, spray coating. According to a particular embodiment, the catalytic material according to the invention may be mixed with a binder such as a resin or polymer to adhere to the surface of use. Carbon nanotubes or carbon fibers may be added to the mixture to increase the strength of the deposit. For example, deposition may be achieved by drying a solution of the catalyst, binder, and optionally carbon nanotubes or carbon fibers onto the desired surface.

According to another embodiment, the catalytic material according to the invention can be coated or deposited on the surface used, in particular on the surface of an electrode for an electrical reduction system or of an electrical reduction system. More particularly, a mixture of catalytic material and binder may be pressed into a membrane electrode for an electroreduction system.

Alternatively, according to another further embodiment, the catalytic material of the present invention may be prepared by pyrolysis of Fe (II) -doped Zn-ZIF-8 grown or deposited directly on a support, for example on a support electrode (such as carbon cloth or carbon fiber paper).

According to another aspect of the invention, is a method for electroreduction of CO₂A kit comprising the catalytic material of the invention. For example, the kit comprises the catalyst in dry form in a container (e.g., vial, cartridge, etc.) or deposited on a surface, such as a support electrode.

According to a particular embodiment, there is provided a method of operating a motor vehicleFor electrochemical reduction of CO₂Comprising the catalytic material of the present invention, e.g., the catalytic material is present in a dry form in a container (e.g., vial, cartridge, etc.) or deposited on a surface, e.g., on a support electrode of an electro-reduction system.

According to a particular embodiment, the electroreduction system according to the invention is a three-electrode system (working, counter and reference electrode) using KHCO₃Or NaHCO₃The aqueous solution is used as electrolyte, and is mixed with CO under 1atm₂And (4) saturation.

According to a particular embodiment, the working electrode of the electroreduction system is a carbon cloth.

Having described the invention, the following examples are illustrative only and not limiting.

Examples