CN116237077B - Method for synthesizing metal single-atom catalyst by using metal phthalocyanine compound - Google Patents

Abstract

The application provides a method for synthesizing a metal monoatomic catalyst by using a metal phthalocyanine compound, which belongs to the technical field of catalysts, wherein the metal monoatomic catalyst is obtained by taking the metal phthalocyanine compound and ammonium salt as raw materials and then pyrolyzing under the protection of inert gas.

Description

A method for synthesizing metal single-atom catalysts from metal phthalocyanine compounds

Technical field

The invention belongs to the technical field of catalysts, and in particular relates to a method for synthesizing a metal single-atom catalyst from a metal phthalocyanine compound.

Background technique

Single-atom catalysts are catalysts in which isolated single metal atoms are dispersed on a carrier material, with the isolated metal atoms serving as active centers. As an advanced new type of catalyst, single-atom catalysts have the advantages of clear structure, high catalytic reaction activity, and high selectivity, and have great application prospects in industrial production such as petroleum, chemical industry, and biomedicine. Among the preparation methods of single-atom materials, compared with methods such as atomic layer deposition, impregnation, and photochemical reduction, the high-temperature pyrolysis method is to combine metal-organic ligands, carbon, template carriers, etc. at high temperatures (600 to 1000°C) in an inert atmosphere. ) cracking carbonization, metal atoms coordinate with N, P and other heteroatoms in carbon materials to form an isolated M-N-C (M refers to metal atom) structural active center, which is currently the most important method for the preparation of single-atom catalysts. However, there are still many problems that need to be solved during the preparation process, such as the low content of metal active centers (generally less than 1.5wt%), the easy aggregation of metal atoms to form metal nanoparticles, and the difficulty in large-scale preparation, etc., which restrict the practical use of single-atom catalysts. application.

Patent CN115672375A discloses a method for preparing a tungsten or molybdenum-loaded nitrogen-doped carbon single-atom catalyst. The tungsten or molybdenum oxide and ZIF-8 are placed in the same porcelain boat without contact, and metal single atoms are formed through high-temperature atomic migration. Atomic catalyst. The prepared single-atom catalyst has high activity in electrocatalytic reactions such as oxygen reduction and hydrogen evolution; however, the loading capacity of metal atoms in the product is low and the product needs to be washed with dilute sulfuric acid, which is not conducive to scale-up production. Patent CN111905794B provides another method for preparing high-density iron single-atom catalysts, which pre-reacts iron salts, sucrose, melamine and pore-forming agents to form a precursor, and then carbonizes it through high-temperature heat treatment to form an iron single-atom catalyst, using high-concentration Sodium hydroxide removes the pore-forming agent, and the metal content of the resulting catalyst Fe-N ₄ is 5wt% to 12wt%. In the later stage of this patent, high-concentration sodium hydroxide is required, which causes serious pollution.

Contents of the invention

In order to solve the above technical problems, the present invention proposes a method for synthesizing metal single-atom catalysts from metal phthalocyanine compounds, specifically involving the synthesis of metal single-atom supported nitrogen-doped carbon catalysts such as iron, cobalt, manganese, nickel, copper and zinc. method.

In order to achieve the above object, the present invention provides a method for synthesizing a metal single-atom catalyst from a metal phthalocyanine compound, which includes the following steps:

(1) Mix the metal phthalocyanine compound and the ammonium salt and grind them to obtain a mixture;

(2) The mixture is subjected to high-temperature pyrolysis, and the resulting product is washed and dried to obtain a metal single-atom catalyst.

Metal phthalocyanine compounds have high chemical stability and bright colors and are widely used in the printing and dyeing industry. In their chemical structure, metal atoms coordinate with the nitrogen atoms in the phthalocyanine and are located in the center of the phthalocyanine molecule, interacting with single-atom catalysts. Similar active centers have similar structures and are excellent precursors for preparing high-loading metal single-atom catalysts. In the present invention, during the pyrolysis process of the metal phthalocyanine compound, some metal atoms will migrate and aggregate into metal nanoparticles. The present invention uses the hydrogen halide gas generated by the decomposition of the ammonium salt to react with the migrated metal atoms to generate the corresponding metal salt. (metal chloride or metal bromide), etching metal nanoparticles in situ or inhibiting the formation of metal nanoparticles, and finally washing with water to remove the generated metal salt, thereby obtaining a metal single atom supported nitrogen-doped carbon catalyst (metal single atom catalyst ).

Furthermore, the mass ratio of the metal phthalocyanine compound to the ammonium salt is 1:1 to 1:10. If the ammonium salt is too little, the ammonium salt will be completely decomposed and sublimated before rising to the specified temperature; if it is too much, the ammonium salt will be wasted and the product will be harvested. rate decreases.

Further, the metal phthalocyanine compound includes one of iron phthalocyanine, copper phthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, zinc phthalocyanine and manganese phthalocyanine.

Further, the ammonium salt is ammonium chloride, ammonium bromide or a mixture thereof. The ammonium salt decomposes at high temperature to produce hydrogen halide gas (hydrogen chloride, hydrogen bromide), which can in-situ etch metal atoms that migrate due to high temperature to generate Metal halides to avoid the formation of metal nanoparticles.

Further, the high-temperature pyrolysis is performed under the protection of an inert gas, and the inert gas is nitrogen or argon.

Further, the temperature of the high-temperature pyrolysis is 550-700°C, the time is 2-4h, and the temperature rise rate is 1-10°C/min, preferably 2-5°C/min.

A metal single atom catalyst is synthesized according to the above synthesis method.

Application of the metal single atom catalyst in catalytic oxidation and catalytic reduction.

Compared with the existing technology, the present invention has the following advantages and technical effects:

The present invention uses the above synthesis method to convert metal phthalocyanine compounds into metal single-atom supported nitrogen-doped carbon catalysts, including iron, cobalt, nickel, copper, manganese, zinc and other metal single-atom catalysts. The metal phthalocyanine compounds are very easy to use as industrial products. Obtained; there is no formation of metal nanoparticles in the prepared product, no need for strong acid washing, the method is simple, and can achieve macro-preparation of metal single-atom catalysts; the ammonium salt used can be recycled and reused (after a very small amount of hydrogen halide reacts with the metal , the metal salt generated remains in the sample, and the remaining ammonium salt decomposes at high temperature to generate hydrogen halide and ammonia gas, which are combined again in the low temperature area to form ammonium salt and condensed in the low temperature area, the recovery rate is nearly 90%), and it is environmentally friendly.

Description of the drawings

The drawings that form a part of this application are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an improper limitation of this application. In the attached picture:

Figure 1 is a spherical aberration corrected scanning transmission electron microscope image of the iron single atom catalyst prepared in Example 1;

Figure 2 is an EDS spectrum of the iron single atom catalyst prepared in Example 1;

Figure 3 is a synchrotron radiation analysis diagram of the iron single atom catalyst prepared in Example 1, where A is the Fe K edge X-ray absorption near-edge spectrum, and B is the Fourier transform spectrum Fe K edge extended X-ray absorption fine structure spectrum ;

Figure 4 is an X-ray diffraction pattern of the iron single atom catalyst prepared in Example 3;

Figure 5 is a transmission electron microscope image of the supported iron catalyst prepared in Example 5;

Figure 6 is a magnetic comparison diagram of the iron catalysts prepared in Example 1 and Example 5;

Figure 7 shows the color change of the solution before and after the reduction of 4-nitrophenol catalyzed by the iron single atom catalyst obtained in Example 1;

Figure 8 is the absorption curve of the solution before and after the iron single atom catalyst catalyzes 4-nitrophenol obtained in Example 1;

Figure 9 is the UV-visible absorption spectrum of the iron single-atom catalyst obtained in Example 1 when catalytically oxidizing 3,3',5,5'-tetramethylbenzidine (TMB). In the left illustration, from left to right These are pictures of TMB solution, TMB+H ₂ O ₂ solution and TMB+H ₂ O ₂ + iron single atom catalyst reaction solution after reacting for 5 minutes.

Detailed ways

Various exemplary embodiments of the invention will now be described in detail. This detailed description should not be construed as limitations of the invention, but rather as a more detailed description of certain aspects, features and embodiments of the invention.

It should be understood that the terms used in the present invention are only used to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges in the present invention, it should be understood that every intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or value intermediate within a stated range, and any other stated value or value intermediate within a stated range, is also included within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded from the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only the preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and/or materials in connection with which the documents relate. In the event of conflict with any incorporated document, the contents of this specification shall prevail.

It will be apparent to those skilled in the art that various modifications and changes can be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to the skilled person from the description of the invention. The specification and examples of the present invention are exemplary only.

The words "includes", "includes", "has", "contains", etc. used in this article are all open terms, which mean including but not limited to.

The room temperature in the present invention refers to 25±2°C.

Example 1

This embodiment provides a method for preparing an iron single atom supported nitrogen-doped carbon catalyst, which is specifically prepared by the following steps:

Weigh 10g of iron phthalocyanine and 50g of ammonium bromide respectively into a mortar, grind and mix, put into a quartz bottle, transfer to a vacuum tube furnace, set the heating rate to 2°C/min, under argon protection Raise the temperature to 650°C and keep it for 4 hours. After naturally cooling to room temperature, the product is washed with pure water until there is no bromide ion (the silver nitrate test solution acidified with nitric acid detects that there is no bromide ion in the washed water), and finally dried to obtain 8.2 g black iron single atom catalyst.

The spherical aberration-corrected scanning transmission electron microscope image of the iron single-atom catalyst prepared in this example is shown in Figure 1. The white highlights in Figure 1 represent iron atoms. It can be observed that in the iron single-atom catalyst prepared in Example 1, iron is in the form of single atoms. Distributed in nitrogen-doped carbon, the EDS energy spectrum is shown in Figure 2, and the EDS test loading is 9.6%, which proves that the iron single-atom catalyst can be successfully prepared using the solution of Example 1. The synchrotron radiation analysis of the iron single-atom catalyst obtained in this example is shown in Figure 3. It can be seen that iron exists in the catalyst in the form of Fe-N-C and does not exist in the form of Fe-Fe or Fe-O, indicating the formation of single-atom active sites.

Example 2

This embodiment provides a method for preparing a cobalt single atom supported nitrogen-doped carbon catalyst, which is specifically prepared by the following steps:

Weigh 1g of cobalt phthalocyanine and 10g of ammonium chloride respectively into the mortar, grind and mix, put into a quartz bottle, transfer to a vacuum tube furnace, set the heating rate to 5°C/min, and raise the temperature under nitrogen protection to 620°C and kept for 2 hours. After natural cooling to room temperature, the resulting product is washed with pure water until there is no chloride ion (nitric acid acidified silver nitrate test solution detects that there is no chloride ion in the washed water), and finally dried to obtain black cobalt. Single atom catalyst.

Example 3

This embodiment provides a method for preparing an iron single atom supported nitrogen-doped carbon catalyst, which is specifically prepared by the following steps:

Weigh 3.0g of iron phthalocyanine and 15g of ammonium chloride respectively into a mortar, grind and mix, put into a quartz bottle, transfer to a vacuum tube furnace, set the heating rate to 5°C/min, and under nitrogen protection Raise the temperature to 700°C, keep it warm for 2 hours, and after naturally cooling to room temperature, wash the resulting product with pure water until it is free of chloride ions, and finally dry it to obtain a black iron single-atom catalyst.

The X-ray diffraction pattern of the black iron single atom catalyst prepared in this example is shown in Figure 4. It can be seen that the X-ray diffraction pattern of the iron single atom and the phthalocyanine iron raw material has changed significantly, and there is no trace of metallic iron or iron oxide. X-ray diffraction peaks indicate that there are no iron nanoparticles and iron oxide particles in the prepared iron single atom catalyst.

Example 4

This embodiment provides a method for preparing a zinc single atom supported nitrogen-doped carbon catalyst, which is specifically prepared by the following steps:

Weigh 4g of zinc phthalocyanine and 20g of ammonium chloride respectively into a mortar, grind and mix, put into a quartz bottle, transfer to a vacuum tube furnace, set the heating rate to 10°C/min, and raise the temperature under nitrogen protection to 700°C, kept for 2 hours, and after naturally cooling to room temperature, the resulting product was washed with pure water until it was free of chloride ions, and finally dried to obtain a zinc single-atom catalyst.

Example 5

For comparison, this example does not add ammonium salt in the process of preparing the iron single-atom catalyst. The other methods are the same as Example 3. The specific method is: weigh 3.0g of iron phthalocyanine, add it to a mortar, grind it, and transfer it to a vacuum tube furnace. , set the heating rate to 5°C/min, raise the temperature to 700°C under nitrogen protection, keep it warm for 2 hours, and then naturally cool to room temperature to obtain a black catalyst (supported iron catalyst). The transmission electron microscope image of the supported iron catalyst prepared in this example is shown in Figure 5. It can be seen that the iron catalyst obtained by direct pyrolysis of iron phthalocyanine in the absence of ammonium salt can clearly observe the presence of iron nanoparticles.

The magnetic comparison diagram of the iron catalyst prepared in Example 1 and Example 5 is shown in Figure 6. It can be seen that the iron single-atom catalyst prepared in Example 1 cannot be adsorbed by the magnet at all and has no magnetism, indicating that an iron single-atom material is formed. The iron catalyst obtained in Example 5 has strong magnetism and is easily adsorbed by magnets, indicating the presence of iron nanoparticles.

Application example 1

Application of the iron single atom catalyst obtained in Example 1 in catalytic reduction (taking the catalytic reduction of sodium borohydride as an example).

In 25mL 4-nitrophenol (0.1mmol/L) solution, add 30mg sodium borohydride, the solution turns bright yellow, add 2mg iron single atom catalysis, after 30 minutes of reaction, the solution turns colorless (Figure 7), explain 4-Nitrophenol is reduced to 4-aminophenol. As a comparison, in the absence of iron single-atom catalyst, the reaction is difficult to proceed and the color of the solution does not change. The catalytic effect of the iron single-atom catalyst on the catalytic hydrogenation reduction reaction of 4-nitrophenol was further confirmed by UV-visible absorption spectroscopy. After the catalytic reaction, the absorption peak of 4-nitrophenol disappeared, and the absorption of 4-aminophenol appeared at the same time. peak (Figure 8); while in the comparative experiment without adding a catalyst, the UV-visible absorption curve had no significant change.

Application example 2

Application of the iron single atom catalyst obtained in Example 1 in catalytic oxidation (taking the catalytic oxidation of 3,3’,5,5’-tetramethylbenzidine as an example).

3,3’,5,5’-Tetramethylbenzidine (TMB) changes from colorless to blue after being oxidized. This reaction is difficult to carry out without a catalyst and can be used to test the catalytic activity of the catalyst. Take 0.5mL sodium dihydrogen phosphate-sodium phosphate buffer solution (pH=4) in a 1.5mL centrifuge tube, add 10μL TMB solution, 10μL hydrogen peroxide (20mmol/L) and 10μL iron single atom catalyst dispersion (0.5mg/mL) , shake well and leave it for 5 minutes, you can see that the reaction solution changes from colorless to blue, and its UV-visible absorption spectrum shows a maximum absorption peak at 652nm (Figure 9). TMB solution will not be oxidized in the buffer solution; after adding hydrogen peroxide solution, the oxidation reaction of TMB is still difficult to proceed, the solution is still colorless, and its UV-visible absorption spectrum has no obvious change compared with TMB; it can be seen that the iron single-atom catalyst can effectively catalyze Progress of TMB oxidation reaction.

The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any person familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application. All are covered by the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

Claims (6)

1. A method for synthesizing a metal single-atom catalyst from a metal phthalocyanine compound, which is characterized in that it includes the following steps: (1) Mix and grind a metal phthalocyanine compound and an ammonium salt to obtain a mixture. The ammonium salt is ammonium chloride, ammonium bromide or a mixture thereof; (2) The mixture is subjected to high-temperature pyrolysis, and the resulting product is washed and dried to obtain a metal single-atom catalyst. The temperature of the high-temperature pyrolysis is 550~700°C, the time is 2~4h, and the temperature rise rate is 1~10°C. /min. 2. A method for synthesizing a metal single-atom catalyst from a metal phthalocyanine compound according to claim 1, characterized in that the mass ratio of the metal phthalocyanine compound to the ammonium salt is 1:1 to 1:10. 3. A method for synthesizing a metal single atom catalyst from a metal phthalocyanine compound according to claim 2, characterized in that the metal phthalocyanine compound includes iron phthalocyanine, copper phthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, phthalocyanine nickel, One of zinc cyanine and manganese phthalocyanine. 4. A method for synthesizing a metal single-atom catalyst from a metal phthalocyanine compound according to claim 1, characterized in that the high-temperature pyrolysis is carried out under the protection of an inert gas. 5. A metal single atom catalyst, characterized in that it is synthesized according to the method described in any one of claims 1 to 4. 6. Application of the metal single atom catalyst of claim 5 in catalytic oxidation and catalytic reduction.