阅读说明：本技术 一种负载型钴单原子催化剂及其制备方法和应用 (Supported cobalt monoatomic catalyst and preparation method and application thereof ) 是由 唐智勇 高燕 乐天 邱雪英 于 2020-05-11 设计创作，主要内容包括：本发明提供一种负载型钴单原子催化剂及其制备方法和应用,所述制备方法包括如下步骤：(1)尿素进行热聚合反应,得到石墨化氮化碳；(2)将步骤(1)得到的石墨化氮化碳与钴盐进行反应,得到钴与石墨化氮化碳的复合物；(3)将步骤(2)得到的复合物与次磷酸盐进行热处理,得到所述负载型钴单原子催化剂。所述制备方法简单、原料来源广泛、收率高,具有规模化应用的前景。所述负载型钴单原子催化剂为磷掺杂石墨化氮化碳负载的钴单原子催化剂,具有带隙可调、催化活性好和选择性高的特点,能够实现高转化率的光催化下的选择性氧化,尤其适用于将醇类化合物通过光氧化催化反应转化为醛类化合物或酮类化合物。(The invention provides a supported cobalt monoatomic catalyst, a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) carrying out thermal polymerization reaction on urea to obtain graphitized carbon nitride; (2) reacting the graphitized carbon nitride obtained in the step (1) with cobalt salt to obtain a compound of cobalt and graphitized carbon nitride; (3) and (3) carrying out heat treatment on the compound obtained in the step (2) and hypophosphite to obtain the supported cobalt single-atom catalyst. The preparation method is simple, wide in raw material source and high in yield, and has a large-scale application prospect. The supported cobalt monoatomic catalyst is a phosphorus-doped graphitized carbon nitride-supported cobalt monoatomic catalyst, has the characteristics of adjustable band gap, good catalytic activity and high selectivity, can realize selective oxidation under photocatalysis with high conversion rate, and is particularly suitable for converting alcohol compounds into aldehyde compounds or ketone compounds through a photo-oxidation catalytic reaction.)

1. A preparation method of a supported cobalt monoatomic catalyst is characterized by comprising the following steps:

(1) carrying out thermal polymerization reaction on urea to obtain graphitized carbon nitride;

(2) reacting the graphitized carbon nitride obtained in the step (1) with cobalt salt to obtain a compound of cobalt and graphitized carbon nitride;

(3) and (3) carrying out heat treatment on the compound obtained in the step (2) and hypophosphite to obtain the supported cobalt single-atom catalyst.

2. The method according to claim 1, wherein the temperature of the thermal polymerization in the step (1) is 400 to 650 ℃;

preferably, the time of the thermal polymerization reaction in the step (1) is 2-4 h;

preferably, the temperature rise process of the thermal polymerization reaction in the step (1) is constant temperature rise;

preferably, the temperature rise rate of the uniform temperature rise is 2-10 ℃/min;

preferably, the step (1) of thermal polymerization further comprises the step of post-treatment of the product after the thermal polymerization reaction is completed;

preferably, the post-treatment comprises washing and drying;

preferably, the wash liquor comprises water;

preferably, the washing is ultrasonic cleaning;

preferably, the drying temperature is 40-80 ℃.

3. The method according to claim 1 or 2, wherein the cobalt salt of step (2) comprises any one or a combination of at least two of cobalt nitrate, cobalt chloride or cobalt acetate, preferably cobalt nitrate;

preferably, the mass ratio of the graphitized carbon nitride to the cobalt salt in the step (2) is (20-200): 1, and more preferably (30-80): 1;

preferably, the reaction of step (2) is carried out in a solvent;

preferably, the solvent is water;

preferably, the amount of the solvent is 50-3000 mL based on 1g of the graphitized carbon nitride;

preferably, the temperature of the reaction in the step (2) is 60-100 ℃;

preferably, the reaction time in the step (2) is 6-24 h;

preferably, the reaction of step (2) is carried out under stirring conditions;

preferably, the reaction of the step (2) is completed and then the post-treatment of the product is included;

preferably, the post-treatment comprises solvent removal and annealing;

preferably, the annealing temperature is 300-600 ℃;

preferably, the annealing time is 1-4 h;

preferably, the annealing is performed in a protective atmosphere, preferably argon.

4. The method according to any one of claims 1 to 3, wherein the hypophosphite of step (3) comprises any one or a combination of at least two of sodium hypophosphite, potassium hypophosphite or ammonium hypophosphite, preferably sodium hypophosphite;

preferably, the mass ratio of the compound to the hypophosphite in the step (3) is 1 (0.5-10), and more preferably 1 (1-5);

preferably, the compound in the step (3) is uniformly mixed with hypophosphite and then is subjected to heat treatment;

preferably, the method for uniformly mixing is grinding;

preferably, the temperature of the heat treatment in the step (3) is 250-400 ℃;

preferably, the temperature rise process of the heat treatment in the step (3) is constant temperature rise;

preferably, the temperature rise rate of the uniform temperature rise is 1-5 ℃/min;

preferably, the time of the heat treatment in the step (3) is 1-4 h;

preferably, the heat treatment of step (3) is performed in a protective atmosphere, preferably argon;

preferably, the heat treatment in the step (3) is completed and then the post-treatment of the product is included;

preferably, the post-treatment comprises washing and drying;

preferably, the wash liquor comprises water and/or ethanol;

preferably, the drying temperature is 40-80 ℃.

5. The preparation method according to any one of claims 1 to 4, characterized by specifically comprising the steps of:

(1) heating urea to 400-650 ℃ at a constant speed of 2-10 ℃/min, and carrying out thermal polymerization for 2-4 h to obtain graphitized carbon nitride;

(2) stirring and reacting the graphitized carbon nitride obtained in the step (1) and cobalt salt in water at 60-100 ℃ for 6-24 hours, removing a solvent after the reaction is finished, and annealing the obtained solid-phase product in a protective atmosphere at 300-600 ℃ for 1-4 hours to obtain a compound of cobalt and graphitized carbon nitride; the mass ratio of the graphitized carbon nitride to the cobalt salt is (20-200) to 1;

(3) mixing and grinding the compound obtained in the step (2) and hypophosphite, and then carrying out heat treatment for 1-4 h at 250-400 ℃ in a protective atmosphere to obtain the supported cobalt monoatomic catalyst; the mass ratio of the compound to the hypophosphite is 1 (0.5-10).

6. A supported cobalt monatomic catalyst, wherein the supported cobalt monatomic catalyst is obtained by the production method according to any one of claims 1 to 5;

the supported cobalt monatomic catalyst is a phosphorus-doped graphitized carbon nitride supported cobalt monatomic catalyst.

7. Use of a supported cobalt monatomic catalyst according to claim 6 in the preparation of aldehyde compounds or ketone compounds by photocatalytic oxidation.

8. The use according to claim 7, wherein the starting material for preparing aldehyde compounds or ketone compounds by photocatalytic oxidation is alcohol compounds;

preferably, the aldehyde compound includes an aromatic aldehyde;

preferably, the aromatic aldehyde comprises benzaldehyde.

9. A synthetic method of benzaldehyde is characterized by comprising the following steps: taking benzyl alcohol as a raw material, and carrying out photocatalytic oxidation reaction under the catalysis of the supported cobalt monoatomic catalyst of claim 6 to obtain the benzaldehyde.

10. The synthesis method according to claim 9, wherein the amount of the supported cobalt monatomic catalyst is 10 to 30mg, based on 1mmol of the benzyl alcohol;

preferably, the oxidant of the photocatalytic oxidation reaction is oxygen;

preferably, the photocatalytic oxidation reaction is carried out in a solvent;

preferably, the solvent comprises acetonitrile;

preferably, the time of the photocatalytic oxidation reaction is 4-8 h.

Technical Field

The invention belongs to the technical field of catalytic materials, and particularly relates to a supported cobalt monoatomic catalyst and a preparation method and application thereof.

Background

The aldehyde ketone compounds are important intermediates in fine chemical industry and pharmaceutical industry, wherein aromatic aldehydes are used as important raw materials for preparing medicines and fine chemicals and are widely applied to pesticides, spices, dyes and pharmaceutical industry. Benzaldehyde is a representative compound in aromatic aldehyde series, and the development and optimization of the preparation process are research hotspots in the chemical field. In industry, toluene or benzene is usually used as a starting material and reacts with oxidant such as permanganate or dichromate under high temperature and high pressure conditions to generate benzaldehyde; however, the oxidant in the preparation process is a harmful reagent, and the reaction conditions are harsh, the energy consumption is high, and the development requirement of environmental protection cannot be met. Therefore, the development of a preparation process of the aldehyde compound with environment-friendly raw materials and mild reaction process has very important significance.

Researches show that the method for oxidizing alcohol compounds into aldehyde ketone compounds by utilizing the photocatalytic technology is a synthesis idea with good development prospect, and selective green oxidation of the alcohol compounds by taking molecular oxygen as an oxidant and water as a unique byproduct under mild reaction conditions is widely concerned in recent years. In the photocatalytic oxidation reaction of alcohol compounds, the key to realizing green alcohol oxidation is the use of an environment-friendly catalyst of nontoxic metal. Semiconductor catalyst materials commonly used in the art include CeO₂CdS and TiO₂Etc.; in which CeO is present₂The energy gap is wider, the light energy utilization rate is not high, and the photocatalytic activity is not ideal; CdS is a semiconductor material with narrow band gap energy, but is easily corroded by light to generate toxic Cd, so that the environment is damaged; TiO 2₂Has good photocatalytic activity, but is resistant to violetThe external light is more sensitive, the utilization rate of visible light is lower, and the wide application of the catalyst in catalytic materials is limited.

In order to solve the problems of catalytic activity and light energy utilization of the catalyst, a number of heterogeneous catalysts have also been developed one after another. Among them, noble metal catalysts, especially palladium-based and ruthenium-based catalysts, have great advantages due to good catalytic activity and selectivity. For example, CN109621953A discloses a three-dimensionally ordered macroporous bismuth vanadate supported ruthenium catalyst for photocatalytic oxidation of benzyl alcohol with high efficiency, wherein the catalyst is BiVO (three-dimensionally ordered macroporous (3DOM)₄xRu/3DOM BiVO formed by loading ruthenium nano particles₄The composite photocatalyst has good photocatalytic activity and selectivity for the oxidation of the phenylcarbinol. CN109012662A discloses a preparation method of a photocatalytic benzyl alcohol oxidation catalyst, wherein the catalyst takes Pd as an active center and takes one-dimensional H₂Ti₃O₇The nano-wire is prepared by loading a carrier, wherein the loading amount of Pd is 0.1-5%; said H₂Ti₃O₇The nanowire-supported Pd catalyst can be used in the reaction of preparing benzaldehyde by photocatalytic methanol solvent-free liquid phase oxidation, and can obtain higher benzaldehyde yield. CN109331819A discloses a titanium dioxide supported Pt-Pd bimetallic photocatalyst, a preparation method and an application thereof, wherein the particle size of the catalyst is 3-7 nm, the Pt loading is 0.5-2 wt%, and the Pd loading is 0.5-2 wt%, and the catalyst is used in the reaction of preparing benzaldehyde by photocatalytic benzyl alcohol solvent-free liquid phase oxidation, and has the characteristics of high activity, high selectivity and the like. However, the high cost and scarcity of noble metal catalysts limits their large-scale application.

Therefore, the development of a catalyst with high activity, high selectivity, high stability and low cost for the green light catalytic oxidation of alcohol compounds is a problem to be solved in the field.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a supported cobalt monatomic catalyst, a preparation method and application thereof, wherein the supported cobalt monatomic catalyst is a phosphorus-doped graphitized carbon nitride supported cobalt monatomic catalyst, has the characteristics of adjustable band gap, good catalytic activity and high selectivity, can realize selective oxidation under photocatalysis with high conversion rate, and has the advantages of simple preparation method, wide raw material source, high yield and wide application prospect.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a preparation method of a supported cobalt monatomic catalyst, comprising the steps of:

(1) carrying out thermal polymerization reaction on urea to obtain graphitized carbon nitride;

(2) reacting the graphitized carbon nitride obtained in the step (1) with cobalt salt to obtain a compound of cobalt and graphitized carbon nitride;

(3) and (3) carrying out heat treatment on the compound obtained in the step (2) and hypophosphite to obtain the supported cobalt single-atom catalyst.

The preparation method provided by the invention mainly comprises three steps, namely, firstly, carrying out thermal polymerization on urea to obtain graphitized carbon nitride (g-C)₃N₄) And further converting g-C₃N₄Reacting with cobalt salt to obtain a compound (Co) of cobalt and graphitized carbon nitride₁/C₃N₄) Finally, the supported cobalt single-atom catalyst, namely Co, is obtained by phosphorizing the catalyst through hypophosphite₁a/PCN catalyst. The preparation method has the advantages of rich raw material sources, low cost, simple process route, no need of complex and expensive experimental instruments and high yield, and the obtained supported cobalt monoatomic catalyst is a phosphorus-doped graphitized carbon nitride-supported cobalt monoatomic catalyst and can realize the selective oxidation of alcohol compounds under photocatalysis.

Preferably, the temperature of the thermal polymerization reaction in step (1) is 400-650 ℃, such as 420 ℃, 440 ℃, 450 ℃, 470 ℃, 490 ℃, 500 ℃, 520 ℃, 540 ℃, 550 ℃, 570 ℃, 590 ℃, 600 ℃, 620 ℃ or 640 ℃, and the specific values therebetween are limited by space and for the sake of brevity, and the invention is not exhaustive.

Preferably, the thermal polymerization reaction time in step (1) is 2-4 h, such as 2.2h, 2.4h, 2.5h, 2.7h, 2.9h, 3h, 3.2h, 3.4h, 3.5h, 3.7h or 3.9h, and the specific values therebetween are limited by space and for the sake of brevity, and the invention is not exhaustive list of the specific values included in the range.

Preferably, the temperature rise process of the thermal polymerization reaction in the step (1) is constant temperature rise.

Preferably, the temperature raising rate of the uniform temperature raising is 2-10 ℃/min, such as 2.5 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min or 9.5 ℃/min, and the specific values between the above values are limited by space and for the sake of brevity, the invention is not exhaustive list of the specific values included in the range.

Preferably, the thermal polymerization reaction in step (1) is completed and then the post-treatment of the product is included.

Preferably, the post-treatment comprises washing and drying.

Preferably, the wash liquor comprises water.

Preferably, the washing is ultrasonic cleaning.

Preferably, the drying temperature is 40-80 ℃, such as 42 ℃, 45 ℃, 48 ℃, 50 ℃, 52 ℃, 55 ℃, 58 ℃, 60 ℃, 62 ℃, 65 ℃, 68 ℃, 70 ℃, 72 ℃, 75 ℃ or 78 ℃, and the specific values therebetween, which are not limited by the space and for the sake of brevity, the invention is not exhaustive of the specific values included in the scope.

Preferably, the cobalt salt in step (2) comprises any one or a combination of at least two of cobalt nitrate, cobalt chloride and cobalt acetate, and is further preferably cobalt nitrate.

Preferably, the mass ratio of the graphitized carbon nitride to the cobalt salt in the step (2) is (20-200): 1, for example, 25:1, 30:1, 35:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 110:1, 120:1, 130:1, 140:1, 150:1, 160:1, 170:1, 180:1 or 190:1, and more preferably (30-80): 1.

Preferably, the reaction of step (2) is carried out in a solvent.

Preferably, the solvent is water; the reaction in the step (2) is preferably an impregnation reaction of an aqueous solution of graphitized carbon nitride and an aqueous solution of cobalt salt.

Preferably, the amount of the solvent is 50 to 3000mL, such as 70mL, 90mL, 100mL, 150mL, 200mL, 250mL, 300mL, 400mL, 450mL, 600mL, 700mL, 800mL, 900mL, 1000mL, 1200mL, 1500mL, 1800mL, 2000mL, 2200mL, 2500mL, 2700mL or 2900mL, based on 1g of the graphitized carbon nitride, and specific values therebetween are not limited by space and are not exhaustive, and the invention is not intended to list the specific values included in the range for simplicity.

Preferably, the reaction temperature in the step (2) is 60 to 100 ℃, for example, 62 ℃, 65 ℃, 68 ℃, 70 ℃, 72 ℃, 75 ℃, 78 ℃, 80 ℃, 82 ℃, 85 ℃, 88 ℃, 90 ℃, 92 ℃, 95 ℃ or 98 ℃, and the specific values therebetween are limited by space and for the sake of brevity, and the invention is not exhaustive of the specific values included in the range.

Preferably, the reaction time in step (2) is 6-24 h, such as 7h, 8h, 9h, 10h, 12h, 14h, 15h, 17h, 19h, 20h, 21h or 23h, and the specific values therebetween are limited by space and for the sake of brevity, and the invention is not exhaustive.

Preferably, the reaction of step (2) is carried out under stirring conditions.

Preferably, the reaction in step (2) is completed and then the post-treatment of the product is included.

Preferably, the post-treatment comprises solvent removal and annealing.

Preferably, the annealing temperature is 300-600 ℃, such as 310 ℃, 330 ℃, 350 ℃, 370 ℃, 390 ℃, 400 ℃, 420 ℃, 440 ℃, 450 ℃, 480 ℃, 500 ℃, 520 ℃, 550 ℃, 570 ℃ or 590 ℃, and the specific values therebetween are limited by space and for the sake of brevity, and the invention is not exhaustive of the specific values included in the range.

Preferably, the annealing time is 1 to 4 hours, such as 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.5 hours, 2.7 hours, 2.9 hours, 3 hours, 3.2 hours, 3.4 hours, 3.5 hours, 3.7 hours, or 3.9 hours, and specific point values therebetween are limited to space and for brevity, and the invention is not exhaustive of the specific point values included in the range.

Preferably, the annealing is performed in a protective atmosphere, preferably argon.

Preferably, the hypophosphite of step (3) comprises any one or a combination of at least two of sodium hypophosphite, potassium hypophosphite or ammonium hypophosphite, and further preferably sodium hypophosphite.

Preferably, the mass ratio of the compound in the step (3) to the hypophosphite is 1 (0.5-10), such as 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, 1:3.2, 1:3.5, 1:3.8, 1:4, 1:4.2, 1:4.5, 1:4.8, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9 or 1:9.5, and the like, and further preferably 1 (1: 1-5).

Preferably, the compound of step (3) is mixed with hypophosphite uniformly and then is subjected to heat treatment.

Preferably, the method for uniformly mixing is grinding.

Preferably, the temperature of the heat treatment in the step (3) is 250-400 ℃, for example, 260 ℃, 270 ℃, 280 ℃, 290 ℃, 300 ℃, 310 ℃, 320 ℃, 330 ℃, 340 ℃, 350 ℃, 360 ℃, 370 ℃, 380 ℃ or 390 ℃, and the specific values therebetween are limited by space and for the sake of brevity, and the invention is not exhaustive enumeration of the specific values included in the range.

Preferably, the temperature rise process of the heat treatment in the step (3) is constant temperature rise.

Preferably, the temperature raising rate of the uniform temperature raising is 1-5 ℃/min, such as 1.2 ℃/min, 1.5 ℃/min, 1.8 ℃/min, 2 ℃/min, 2.2 ℃/min, 2.5 ℃/min, 2.8 ℃/min, 3 ℃/min, 3.2 ℃/min, 3.5 ℃/min, 3.8 ℃/min, 4 ℃/min, 4.2 ℃/min, 4.5 ℃/min or 4.8 ℃/min, and the specific point values between the above point values are limited to space and for the sake of brevity, and the specific point values included in the range are not exhaustive.

Preferably, the heat treatment time in step (3) is 1 to 4 hours, such as 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.5 hours, 2.7 hours, 2.9 hours, 3 hours, 3.2 hours, 3.4 hours, 3.5 hours, 3.7 hours or 3.9 hours, and the specific points between the above points are limited by space and for brevity, the invention is not exhaustive of the specific points included in the range.

Preferably, the heat treatment of step (3) is performed in a protective atmosphere, preferably argon.

Preferably, the heat treatment in step (3) is completed and then the product is post-treated.

Preferably, the post-treatment comprises washing and drying.

Preferably, the washing liquid comprises water and/or ethanol.

Preferably, the drying temperature is 40-80 ℃, such as 42 ℃, 45 ℃, 48 ℃, 50 ℃, 52 ℃, 55 ℃, 58 ℃, 60 ℃, 62 ℃, 65 ℃, 68 ℃, 70 ℃, 72 ℃, 75 ℃ or 78 ℃, and the specific values therebetween, which are not limited by the space and for the sake of brevity, the invention is not exhaustive of the specific values included in the scope.

Preferably, the preparation method specifically comprises the following steps:

(1) heating urea to 400-650 ℃ at a constant speed of 2-10 ℃/min, and carrying out thermal polymerization for 2-4 h to obtain graphitized carbon nitride (g-C)₃N₄)；

(2) Stirring and reacting the graphitized carbon nitride obtained in the step (1) with cobalt salt in water at 60-100 ℃ for 6-24 h, removing the solvent after the reaction is finished, and annealing the obtained solid-phase product in a protective atmosphere at 300-600 ℃ for 1-4 h to obtain a cobalt-graphitized carbon nitride compound (Co and graphitized carbon nitride compound)₁/C₃N₄) (ii) a The mass ratio of the graphitized carbon nitride to the cobalt salt is (20-200) to 1;

(3) the compound (Co) obtained in the step (2)₁/C₃N₄) Mixing and grinding the mixture with hypophosphite, and carrying out heat treatment for 1-4 h at 250-400 ℃ in a protective atmosphere to obtain the supported cobalt monoatomic catalyst, namely Co₁a/PCN catalyst; the complex and hypophosphorous acidThe mass ratio of the salt is 1 (0.5-10).

In another aspect, the present invention provides a supported cobalt monoatomic catalyst obtained by the preparation method as described above; the supported cobalt monatomic catalyst is a phosphorus-doped graphitized carbon nitride supported cobalt monatomic catalyst.

The invention provides a supported cobalt monatomic catalyst, namely Co₁catalyst/PCN with monoatomic anchoring of cobalt to graphitized carbon nitride g-C₃N₄On a support, providing maximum atomic efficiency and catalytic activity; g-C₃N₄The metal cobalt composite material is an ideal carrier for coordinating unsaturated metal sites due to the characteristics of larger specific surface area, lone pair electrons of nitrogen and the like, is beneficial to stabilizing metal cobalt dispersed at an atomic level, and the chemical bond formed between the cobalt and the carrier can further improve the stability of a cobalt single atom; in addition, the supported cobalt monoatomic catalyst is also doped with phosphorus, and phosphorus atoms prevent the polymerization of metal centers by forming an additional bond, so that metal sites in the catalyst are not aggregated into larger metal nanoparticles or metal clusters under the irradiation of light. Therefore, the invention provides Co₁the/PCN catalyst has the characteristics of adjustable band gap, good catalytic activity and high selectivity, can realize selective oxidation under photocatalysis with high conversion rate, and is particularly suitable for converting alcohol compounds into aldehyde compounds or ketone compounds through a photo-oxidation catalytic reaction.

In another aspect, the invention provides an application of the supported cobalt monatomic catalyst in preparing aldehyde compounds or ketone compounds by photocatalytic oxidation.

Preferably, the starting material for preparing the aldehyde compound or the ketone compound by photocatalytic oxidation is an alcohol compound.

Preferably, the aldehyde compound includes an aromatic aldehyde.

Preferably, the aromatic aldehyde comprises benzaldehyde.

On the other hand, the invention provides a synthetic method of benzaldehyde, which comprises the following steps: taking benzyl alcohol as a raw material, and carrying out photocatalytic oxidation reaction under the catalysis of the supported cobalt monoatomic catalyst to obtain the benzaldehyde.

Preferably, the amount of the supported cobalt monatomic catalyst is 10 to 30mg, for example, 12mg, 14mg, 15mg, 17mg, 19mg, 20mg, 22mg, 24mg, 25mg, 27mg or 29mg, based on 1mmol of the benzyl alcohol, and specific values therebetween are not exhaustive, and for the sake of brevity and clarity, and the invention is not intended to be exhaustive.

Preferably, the oxidant for the photocatalytic oxidation reaction is oxygen.

Preferably, the photocatalytic oxidation reaction is carried out in a solvent.

Preferably, the solvent comprises acetonitrile.

Preferably, the photocatalytic oxidation reaction time is 4-8 h, such as 4.2h, 4.5h, 4.8h, 5h, 5.2h, 5.5h, 5.8h, 6h, 6.2h, 6.5h, 6.8h, 7h, 7.2h, 7.5h, 7.7h or 7.9h, and the specific values therebetween are limited by space and for the sake of brevity, and the invention is not exhaustive and the specific values included in the range are not included.

Compared with the prior art, the invention has the following beneficial effects:

(1) the preparation method provided by the invention takes urea, cobalt salt and hypophosphite as raw materials, and obtains the phosphorus-doped graphitized carbon nitride supported cobalt monatomic catalyst through thermal polymerization of urea, impregnation and compounding of graphitized carbon nitride and cobalt salt, and thermal treatment and phosphorization; the preparation method has the advantages of rich raw material sources, low cost, simple process route, mild conditions, high preparation efficiency, no need of complex and expensive experimental instruments, high yield of the supported cobalt monatomic catalyst and capability of realizing large-scale preparation.

(2) The supported cobalt monoatomic catalyst allows metal atoms to be doped on the surface of the catalyst without aggregation, has the characteristics of adjustable band gap, good catalytic activity and high selectivity, and metal sites in the supported cobalt monoatomic catalyst cannot be polymerized into particles or clusters with larger particle sizes under the irradiation of light, can realize selective oxidation under the photocatalysis of high conversion rate, and is particularly suitable for converting alcohol compounds into aldehyde compounds or ketone compounds through the photo-oxidation catalytic reaction.

(3) The supported cobalt monoatomic catalyst is used for preparing benzaldehyde, and can be used for carrying out selective photocatalytic oxidation on benzyl alcohol under mild reaction conditions to obtain benzaldehyde, wherein the reaction conversion rate reaches 67-97%, the selectivity reaches 80-89%, so that the benzyl alcohol is selectively oxidized efficiently and in an environment-friendly manner, and a new idea is provided for green industrial preparation of aldehyde compounds.

Drawings

FIG. 1 is a transmission electron micrograph of a supported cobalt monatomic catalyst prepared in example 1;

FIG. 2 is a high angle annular dark field imaging plot of the supported cobalt monatomic catalyst prepared in example 1;

FIG. 3 is an elemental analysis chart of the supported cobalt monatomic catalyst prepared in example 1, wherein (a) is a C element, (b) is an N element, (C) is a P element, and (d) is a Co element;

FIG. 4 is the X-ray photoelectron spectrum of cobalt element in the supported cobalt monatomic catalyst prepared in example 1;

FIG. 5 is a phosphorus X-ray photoelectron spectrum of the supported cobalt monatomic catalyst prepared in example 1;

fig. 6 is a transmission electron micrograph of the supported cobalt monatomic catalyst prepared in example 1 after four catalytic cycles.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

A preparation method of a supported cobalt monoatomic catalyst specifically comprises the following steps:

(1) graphitized carbon nitride (g-C)₃N₄) The preparation of (1): placing 10g of urea in a crucible with a cover, transferring the urea into a muffle furnace, heating the muffle furnace from room temperature to 600 ℃ at the speed of 5 ℃/min, keeping the temperature for 2h, naturally cooling, and placing the powder in the crucibleUltrasonic washing in deionized water, centrifuging, and vacuum drying at 60 deg.C to obtain solid powder g-C₃N₄；

(2) Composite of cobalt and graphitized carbon nitride (Co)₁/C₃N₄) The preparation of (1): 160mg of g-C obtained in step (1)₃N₄Mixing with 50mL of deionized water, uniformly dispersing by ultrasonic, and transferring to an oil bath at 80 ℃; mixing 3mg of cobalt nitrate and 1.5mL of deionized water to prepare a solution, and mixing the solution with g-C₃N₄Mixing the aqueous dispersions, stirring and reacting for 18 hours in an oil bath at the temperature of 80 ℃; after the reaction is finished, the solvent is removed by rotary evaporation, the obtained dry powder is placed in a tubular furnace, and annealing treatment is carried out for 2 hours at 400 ℃ in the argon atmosphere to obtain Co₁/C₃N₄；

(3) 30mg of Co obtained in step (2)₁/C₃N₄Mixing with 60mg of sodium hypophosphite, grinding uniformly, placing in a tube furnace, heating to 300 ℃ at the speed of 5 ℃/min in the argon atmosphere, and carrying out heat treatment for 2 h; washing the obtained solid phase with water and ethanol for 3 times, and vacuum drying at 60 ℃ to obtain the supported cobalt single-atom catalyst, namely Co₁a/PCN catalyst; in g-C₃N₄Calculating Co as a reference₁The mass yield of the/PCN catalyst was 96%.

The morphology of the supported cobalt monatomic catalyst obtained in this example was tested by a transmission electron microscope (TEM, Tecnai G2F 20S-TWIN), and the transmission electron micrograph obtained is shown in FIG. 1.

The supported cobalt monatomic catalyst obtained in the example was subjected to structure and composition analysis by a transmission electron microscope (TEM, Tecnai G2F 20S-TWIN), and the obtained high-angle annular dark field imaging graph is shown in fig. 2, and the bright part in fig. 2 is cobalt atoms, so that it can be seen that the distribution of cobalt atoms on the substrate is very uniform, and no agglomeration occurs, thereby proving that the catalyst obtained in the example is a monatomic catalyst.

The supported cobalt monatomic catalyst obtained in this example was further subjected to elemental analysis, and the elemental analysis chart thereof was shown in fig. 3, in which (a) is a C element, (b) is an N element, (C) is a P element, and (d) is a Co element; the light spots in the figure represent the corresponding elements.

The supported cobalt monatomic catalyst obtained in the present example was tested by an X-ray photoelectron spectrometer (XPS, ESCALAB 20X), and the obtained X-ray photoelectron energy spectrum is shown in fig. 4 and 5; wherein FIG. 4 shows cobalt element, FIG. 5 shows phosphorus element, phosphorus 2P_1/2The state representing a combination of phosphorus and nitrogen, phosphorus 2P_3/2The state represents the combination of phosphorus and cobalt.

Example 2

A preparation method of a supported cobalt monoatomic catalyst specifically comprises the following steps:

(1) graphitized carbon nitride (g-C)₃N₄) The preparation of (1): putting 10g of urea into a crucible with a cover, transferring the crucible into a muffle furnace, heating the muffle furnace from room temperature to 450 ℃ at the speed of 2 ℃/min, keeping the temperature for 4 hours, naturally cooling, putting the powder in the crucible into deionized water, ultrasonically washing, centrifuging, and drying at 80 ℃ in vacuum to obtain solid powder, namely g-C₃N₄；

(2) Composite of cobalt and graphitized carbon nitride (Co)₁/C₃N₄) The preparation of (1): 50mg of g-C obtained in step (1)₃N₄Mixing with 100mL of deionized water, uniformly dispersing by ultrasonic, and transferring to an oil bath at 100 ℃; 2.5mg of cobalt acetate and 30mL of deionized water are mixed to prepare a solution, and the solution is mixed with g-C₃N₄Mixing the aqueous dispersions, stirring and reacting for 10 hours in an oil bath at 100 ℃; after the reaction is finished, the solvent is removed by rotary evaporation, the obtained dry powder is placed in a tubular furnace, and annealing treatment is carried out for 4 hours at 300 ℃ in the argon atmosphere to obtain Co₁/C₃N₄；

(3) 30mg of Co obtained in step (2)₁/C₃N₄Mixing with 16mg of sodium hypophosphite, grinding uniformly, placing in a tube furnace, heating to 250 ℃ at the speed of 1.5 ℃/min under the argon atmosphere, and carrying out heat treatment for 4 h; washing the obtained solid phase with water and ethanol for 3 times, and vacuum drying to obtain the supported cobalt monatomic catalyst, namely Co₁a/PCN catalyst.

Example 3

A preparation method of a supported cobalt monoatomic catalyst specifically comprises the following steps:

(1) graphitized carbon nitride (g-C)₃N₄) The preparation of (1): putting 10g of urea into a crucible with a cover, transferring the crucible into a muffle furnace, heating the muffle furnace from room temperature to 650 ℃ at the speed of 10 ℃/min, keeping the temperature for 2.5 hours, naturally cooling, putting the powder in the crucible into deionized water, ultrasonically washing, centrifuging, and drying at 50 ℃ in vacuum to obtain solid powder, namely g-C₃N₄；

(2) Composite of cobalt and graphitized carbon nitride (Co)₁/C₃N₄) The preparation of (1): 500mg of g-C obtained in step (1)₃N₄Mixing with 100mL of deionized water, uniformly dispersing by ultrasonic, and transferring to an oil bath at 60 ℃; 5mg of cobalt chloride and 5mL of deionized water are mixed to prepare a solution, and the solution is mixed with g-C₃N₄Mixing the aqueous dispersions, stirring and reacting for 24 hours in an oil bath at the temperature of 60 ℃; after the reaction is finished, the solvent is removed by rotary evaporation, the obtained dry powder is placed in a tubular furnace, and annealing treatment is carried out for 1.5h at 600 ℃ in the argon atmosphere to obtain Co₁/C₃N₄；

(3) 30mg of Co obtained in step (2)₁/C₃N₄Mixing with 150mg of sodium hypophosphite, uniformly grinding, placing in a tubular furnace, heating to 400 ℃ at the speed of 5 ℃/min in the argon atmosphere, and carrying out heat treatment for 1 h; washing the obtained solid phase with water and ethanol for 3 times, and vacuum drying to obtain the supported cobalt monatomic catalyst, namely Co₁a/PCN catalyst.

Example 4

A preparation method of a supported cobalt monoatomic catalyst specifically comprises the following steps:

(1) graphitized carbon nitride (g-C)₃N₄) The preparation of (1): putting 10g of urea into a crucible with a cover, transferring the crucible into a muffle furnace, heating the muffle furnace from room temperature to 550 ℃ at the speed of 10 ℃/min, keeping the temperature for 3 hours, naturally cooling, putting the powder in the crucible into deionized water, ultrasonically washing, centrifuging, and drying at 60 ℃ in vacuum to obtain solid powder, namely g-C₃N₄；

(2) Composite of cobalt and graphitized carbon nitride (Co)₁/C₃N₄) The preparation of (1): 400mg of g-C obtained in step (1)₃N₄Mixing with 160mL of deionized water, uniformly dispersing by ultrasonic, and transferring to an oil bath at 60 ℃; 2mg of cobalt nitrate and 20mL of deionized water are mixed to prepare a solution, and the solution is mixed with g-C₃N₄Mixing the aqueous dispersions, stirring and reacting for 24 hours in an oil bath at the temperature of 60 ℃; after the reaction is finished, the solvent is removed by rotary evaporation, the obtained dry powder is placed in a tubular furnace, and annealing treatment is carried out for 1.5h at 600 ℃ in the argon atmosphere to obtain Co₁/C₃N₄；

(3) 30mg of Co obtained in step (2)₁/C₃N₄Mixing with 300mg of sodium hypophosphite, grinding uniformly, placing in a tube furnace, heating to 300 ℃ at the speed of 3 ℃/min in the argon atmosphere, and carrying out heat treatment for 2 h; washing the obtained solid phase with water and ethanol for 3 times, and vacuum drying to obtain the supported cobalt monatomic catalyst, namely Co₁a/PCN catalyst.

Comparative example 1

g-C₃N₄The preparation method of the catalyst comprises the following steps:

putting 10g of urea into a crucible with a cover, transferring the crucible into a muffle furnace, heating the muffle furnace from room temperature to 600 ℃ at the speed of 5 ℃/min, keeping the temperature for 2h, naturally cooling, putting the powder in the crucible into deionized water, ultrasonically washing, centrifuging, and vacuum-drying at 60 ℃ to obtain solid powder, namely g-C₃N₄。

Comparative example 2

Supported cobalt monoatomic catalyst Co₁/C₃N₄The preparation method specifically comprises the following steps:

(1)g-C₃N₄the preparation of (1): putting 10g of urea into a crucible with a cover, transferring the crucible into a muffle furnace, heating the muffle furnace from room temperature to 600 ℃ at the speed of 5 ℃/min, keeping the temperature for 2h, naturally cooling, putting the powder in the crucible into deionized water, ultrasonically washing, centrifuging, and vacuum-drying at 60 ℃ to obtain solid powder, namely g-C₃N₄；

(2) Supported cobalt monoatomic catalyst Co₁/C₃N₄The preparation of (1): 160mg of g-C obtained in step (1)₃N₄Detached from 50mLMixing the seed water, uniformly dispersing by ultrasonic, and transferring to an oil bath at 80 ℃; mixing 3mg of cobalt nitrate and 1.5mL of deionized water to prepare a solution, and mixing the solution with g-C₃N₄Mixing the aqueous dispersions, stirring and reacting for 18 hours in an oil bath at the temperature of 80 ℃; after the reaction is finished, the solvent is removed by rotary evaporation, the obtained dry powder is placed in a tubular furnace, and annealing treatment is carried out for 2 hours at 400 ℃ in the argon atmosphere to obtain Co₁/C₃N₄。

Application example 1

A method for synthesizing benzaldehyde comprises the following steps: 20mg of the supported cobalt monatomic catalyst Co obtained in example 1₁dispersing/PCN and 0.1mol of benzyl alcohol in 2mL of acetonitrile solvent; introducing 0.1MPa oxygen into the reaction solution, and irradiating for 5 hours under an LED light source of 455 nm; and centrifuging the reaction solution after the irradiation is finished, and collecting supernatant to obtain the benzaldehyde.

The supernatant was analyzed by gas chromatography-mass spectrometer (GC-MS, Thermo Fisher Scientific Trace DSQ) under the following chromatographic conditions: the initial temperature is 50 ℃, the temperature is kept for 10min, the temperature is increased to 220 ℃ at the heating rate of 10 ℃/min, the temperature is kept for 2min, the substrate and the product are determined according to the mass spectra corresponding to different peak-out times, and the reaction conversion rate and the selectivity are obtained according to the peak area ratio of the product to the substrate; reaction conversion is the product peak area/(product peak area + substrate peak area), selectivity is the target product (benzaldehyde) peak area (benzaldehyde)/(target product peak area + other product peak area).

Application example 2

The present application example differs from application example 1 only in that the catalysts are supported cobalt monoatomic catalysts prepared in example 2, respectively.

Application example 3

The present application example differs from application example 1 only in that the catalysts are supported cobalt monoatomic catalysts prepared in example 3, respectively.

Application example 4

The present application example differs from application example 1 only in that the catalysts were each the supported cobalt monoatomic catalyst prepared in example 4.

Comparative application example 1

This comparative application example differs from application example 1 only in that the catalyst was g-C prepared in comparative example 1₃N₄A catalyst.

Comparative application example 2

The comparative application example differs from application example 1 only in that the catalyst was Co prepared in comparative example 2₁/C₃N₄A catalyst.

The conversion rate and selectivity data of the benzyl alcohol photocatalytic oxidation synthesized into benzaldehyde in application examples 1-4 and comparative application examples 1-2 are shown in table 1.

TABLE 1

As can be seen from the data in Table 1, the supported cobalt monoatomic catalyst prepared by the preparation method of the present invention shows excellent photocatalytic benzyl alcohol oxidation characteristics, wherein Co prepared under the conditions of example 1₁the/PCN single-atom catalyst has the highest photocatalytic benzyl alcohol oxidation conversion rate and selectivity. In addition, the catalytic results of the comparative application example 1 and the comparative application example 2 further prove that the load of the cobalt monoatomic atoms and the phosphorus doping can be synergized, the activity and the selectivity of the catalyst are effectively improved, and the Co is further proved₁Successful preparation of a/PCN monatomic catalyst.

Application example 5

The supported cobalt monoatomic catalyst obtained in the example 1 is used for catalytic synthesis of benzaldehyde, and the synthesis method is the same as that in the application example 1; after the reaction is finished, the supported cobalt monoatomic catalyst is recovered for recycling, namely, the supported cobalt monoatomic catalyst is reused for synthesizing benzaldehyde, and the catalyst is recycled for 4 times; GC-MS is adopted to monitor the reaction conversion rate and the selectivity, the reaction conversion rate of each synthesis is more than or equal to 91%, and the selectivity is more than or equal to 83%, so that the supported cobalt monatomic catalyst obtained by the invention can be recycled, and the catalytic performance cannot be greatly attenuated along with the prolonging of the use times or the use time.

The supported cobalt monatomic catalyst after 4 catalytic cycles was tested by a transmission electron microscope (TEM, Tecnai G2F 20S-TWIN), and the transmission electron micrograph obtained is shown in FIG. 6, and it can be seen from FIG. 6 that the supported cobalt monatomic catalyst Co monatomic catalyst is shown in FIG. 6₁The metals of the/PCN are not aggregated in the circulating catalysis process, which proves that the metal sites in the supported cobalt monoatomic catalyst obtained by the invention are not polymerized into larger particles or clusters under long-time light irradiation, and the supported cobalt monoatomic catalyst can be repeatedly used for realizing selective oxidation under photocatalysis with high conversion rate.

The applicant states that the present invention is illustrated by the above examples to describe a supported cobalt monatomic catalyst, a preparation method and applications thereof, but the present invention is not limited to the above process steps, i.e., it is not meant that the present invention must rely on the above process steps to be carried out. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.