Preparation method of amorphous vanadium-doped carbon nitride catalyst

Abstract

The invention relates to an amorphous vanadium-doped carbon nitride catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: selecting amino-rich carbon nitride as a catalyst carrier, taking vanadyl acetylacetonate as a vanadium source, carrying out acid treatment on the vanadium source and the carbon nitride, and then carrying out heat treatment at high temperature to form the amorphous V / g-C3N4 composite catalyst. In the preparation process, due to strong interaction between metal and the carbon nitride carrier, agglomeration of vanadium species nanoparticles can be inhibited, and high dispersity of the V species on the carbon nitride carrier is achieved. The V / g-C3N4 composite catalyst disclosed by the invention shows good catalytic performance in a reaction for synthesizing phenol through benzene hydroxylation. Meanwhile, the preparation process of the catalyst is simple, convenient and rapid; synthesis raw materials are low in cost; no secondary pollution is generated; the development concept of green chemistry is met.

Description

Technical Field

[0001] The present invention belongs to the field of heterogeneous catalysts, and particularly relates to a preparation method of an amorphous vanadium-doped carbon nitride catalyst. Background Art

[0002] Phenol is an important chemical organic intermediate, which is widely used in the synthesis of polymer materials, chemical products, pesticides, fertilizers, paints, textiles, etc., and has important uses especially in the medical, agricultural, biological and dye industries. The cumene process for producing phenol is a mature technology that has been used for nearly 80 years. After continuous improvement, it is widely used in large-scale continuous production of phenol in various countries in the world. However, this method has multiple limitations such as high separation energy consumption, environmental pollution, safety risks, complex process, equipment corrosion, market demand fluctuations and environmental protection restrictions. For this reason, researchers have developed a process for directly hydroxylation of benzene to synthesize phenol in a hydrogen peroxide system. Therefore, developing a catalyst with high activity, high selectivity, high economic benefits and environmental friendliness is the research focus for synthesizing phenol from benzene in a hydrogen peroxide system.

[0003] Graphitic carbon nitride (g-C3N4) is an inorganic polymer material with a two-dimensional stacked structure of π-conjugated planar layers, which is composed of basic structural units of triazine rings and 3-s-triazine rings. The highly condensed carbon nitride material has high thermal stability and chemical stability. The g-C3N4 material shows potential catalytic activity in benzene-related reactions, including Friedel-Crafts acylation of benzene, alkylation reaction of benzene, selective oxidation of benzene, etc. In the reaction system for directly hydroxylation of benzene to synthesize phenol, the catalytic activity achieved on the g-C3N4 material is quite limited, and usually this reaction is carried out under visible light irradiation or conditions of loading active metal catalysts. For example, the patent with the patent number CN104624239A discloses a synthesis method of a catalyst for hydroxylation of benzene to synthesize phenol. This method synthesizes a series of M / g-C3N4 catalysts by loading different metal acetylacetonates onto a carbon nitride carrier, and obtains a phenol yield of 22%. However, the preparation cycle of this catalyst is long, and a large amount of organic solvents such as toluene and acetone are used in the preparation, resulting in high preparation cost of the catalyst.

[0004] In order to produce phenol more efficiently in the benzene hydroxylation system, the present invention provides a preparation method of a highly dispersed vanadium-doped carbon nitride catalyst material. By acid treatment, vanadium is introduced into g-C3N4 to prepare a supported catalyst. This method not only increases the dispersion of vanadium species on carbon nitride, but also forms V-N bonds between vanadium species and nitrogen elements on the carbon nitride carrier, increasing the stability of the catalyst. The synthesis process has a short cycle, does not use organic solvents such as toluene, and has a simple preparation process. At present, there is no report on such an efficient and green preparation method of V / g-C3N4 catalyst material in the benzene hydroxylation system. Summary of the Invention

[0005] The object of the present invention is to provide an amorphous vanadium-doped carbon nitride catalyst material, a preparation method and an application thereof, and to use the same in the reaction of benzene hydroxylation to synthesize phenol, so as to solve the problems existing in the prior art.

[0006] A preparation method of an amorphous vanadium-doped carbon nitride catalyst material includes the following steps: (1) Adding a carbon nitride support and vanadyl acetylacetonate to a solvent, stirring, and heating to evaporate the solvent to obtain a catalyst precursor; (2) Performing high-temperature treatment on the catalyst precursor obtained in step (1) at 200-500 °C.

[0007] Further, the preparation of the carbon nitride catalyst support includes: placing melamine in a muffle furnace, raising the temperature to 550 °C at a heating rate of 2 °C / min, maintaining for 3-6 h, cooling to room temperature, and grinding the obtained solid to obtain a carbon nitride catalyst support.

[0008] Further, the mass ratio of vanadyl acetylacetonate to carbon nitride is 1:10-1:100.

[0009] Further, the solvent in step (1) includes one or more of deionized water, citric acid solution, oxalic acid solution, and acetic acid solution.

[0010] Further, the temperature for heating and evaporating to dryness in step (1) is 60-90 °C.

[0011] Further, the calcination temperature in step (2) is 200-500 °C.

[0012] The amorphous vanadium-doped carbon nitride catalyst obtained by the above preparation method.

[0013] The application of the above amorphous vanadium-doped carbon nitride catalysis is used in the reaction of benzene hydroxylation to synthesize phenol.

[0014] The present invention uses a carbon nitride material rich in amino groups as a catalyst support, and uses vanadyl acetylacetonate as a source of vanadium element. By adding an acid solution and heat treatment means to remove the coordination groups of the vanadium precursor, an amorphous V / g-C3N4 composite catalyst material is prepared. In the preparation process, there is a strong interaction between the metal and carbon nitride, effectively preventing the aggregation of vanadium species nanoparticles and ensuring the high dispersion of V on carbon nitride. The V / g-C3N4 composite catalyst of the present invention exhibits excellent catalytic activity in the reaction of benzene hydroxylation to phenol and has good recycling ability.

[0015] Compared with the prior art, the present invention has the following advantages: (1) The g-C3N4 support used in the present invention is made from melamine, which is widely available, easy to prepare, low in cost, and has good stability.

[0016] (2) Based on the strong interaction between the metal and the support, an amorphous vanadium-doped carbon nitride catalyst material was designed and synthesized. The acid-treated flaky carbon nitride as the support forms a strong metal-support interaction with vanadyl acetylacetonate, inducing the uniform dispersion of vanadium species on the carbon nitride support, inhibiting the agglomeration of vanadium species on the carbon nitride support, exposing more metal active sites, and further improving the catalytic activity.

[0017] (3) The V / g-C3N4 catalyst prepared in the present invention exhibits good catalytic performance in the reaction of benzene hydroxylation to synthesize phenol. At the same time, the preparation process of this catalyst is simple and no organic solvent is used, which conforms to the concept of green development. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the XRD characterization spectrum of the catalyst of the present invention.

[0019] Figure 2 It is the TEM and mapping characterization spectra of the catalyst of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] In order to make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments. However, the implementation of the present invention is not limited thereto. EXAMPLE

[0021] (1) Take 3.0 g of melamine powder and place it in a crucible with a lid. Then place the crucible in a muffle furnace under an air atmosphere. The muffle furnace is heated to 550 °C at a heating rate of 2 °C / min and maintained at this temperature for 4 h. When the temperature drops to room temperature, pour the yellow solid into a mortar and grind it until there is no granular feeling to obtain the yellow catalyst support g-C3N4. Weigh 0.0156 g of vanadyl acetylacetonate and 0.3 g of the catalyst support g-C3N4 powder and disperse them in a wide-mouth bottle. Then add 10 ml of 0.6 mol / L acetic acid solution and ultrasonically assist the dispersion at room temperature for 30 min. Then place it on a magnetic stirrer and stir at room temperature for 2 h. Then evaporate to dryness in an oil bath at 80 °C. Grind the obtained catalyst precursor evenly, and then transfer the ground powder to a crucible with a lid and calcine it in a muffle furnace at 300 °C for 2 h, with the heating rate set at 2 °C / min. When the temperature drops to room temperature, obtain the catalyst 1%V / g-C3N4.

[0022] (2) Take 50 mg of the above-mentioned 1% V / g-C3N4 catalyst, 5 mmol of benzene, 4 ml of acetic acid, and 1 ml of acetonitrile. Then, place them in an oil bath at 60 °C for condensation reflux, turn on magnetic stirring, and slowly add 20 mmol of H2O2 using a peristaltic pump (completed in about 30 minutes). The reaction time is 6 h. After the reaction is completed, wait for it to cool to room temperature. After the obtained mixed solution is centrifuged, take the supernatant for analysis. The phenol yield is 8.9%, and the phenol selectivity is 97.2%. Example

[0023] (1) Take 3.0 g of melamine powder and place it in a crucible with a lid. Then, place the crucible in a muffle furnace in an air atmosphere. The muffle furnace is heated to 550 °C at a heating rate of 2 °C / min and maintained at this temperature for 4 h. When the temperature drops to room temperature, pour the yellow solid into a mortar and grind it until there is no granular feeling to obtain the yellow catalyst support g-C3N4. Weigh 0.0312 of vanadyl acetylacetonate and 0.3 g of the catalyst support g-C3N4 powder and disperse them in a wide-mouth bottle. Then add 10 ml of 0.6 mol / L acetic acid solution and ultrasonically assist in dispersing for 30 min at room temperature. Then place it on a magnetic stirrer and stir at room temperature for 2 h. Then evaporate to dryness in an oil bath at 80 °C. Grind the obtained catalyst precursor evenly, and then transfer the ground powder to a crucible with a lid and calcine it in a muffle furnace at 300 °C for 2 h with a heating rate set at 2 °C / min. When the temperature drops to room temperature, obtain the catalyst 2% V / g-C3N4.

[0024] (2) Take 50 mg of the above-mentioned 2% V / g-C3N4 catalyst for the hydroxylation of benzene to synthesize phenol. The reaction conditions are the same as those in Example 1. The phenol yield is 14.5%, and the phenol selectivity is 96.5%. Example

[0025] (1) Place 3.0 g of melamine powder in a crucible with a lid, and then place the crucible in a muffle furnace under an air atmosphere. The muffle furnace is heated to 550 °C at a heating rate of 2 °C / min and maintained at this temperature for 4 h. When the temperature drops to room temperature, pour the yellow solid into a mortar and grind it until there is no granular feeling to obtain the yellow catalyst support g-C3N4. Weigh 0.0468 of vanadyl acetylacetonate and 0.3 g of the catalyst support g-C3N4 powder and disperse them in a wide-mouth bottle. Then add 10 ml of 0.6 mol / L acetic acid solution and ultrasonically assist the dispersion at room temperature for 30 min. Then place it on a magnetic stirrer and stir at room temperature for 2 h. Then evaporate to dryness in an oil bath at 80 °C. Grind the obtained catalyst precursor evenly, and then transfer the ground powder to a crucible with a lid and calcine it in a muffle furnace at 300 °C for 2 h, with the heating rate set at 2 °C / min. When the temperature drops to room temperature, obtain the catalyst 3%V / g-C3N4.

[0026] (2) Take 50 mg of the above 3%V / g-C3N4 catalyst for the synthesis of phenol by benzene hydroxylation. The reaction conditions are the same as those in Example 1. The phenol yield is 17.3%, and the phenol selectivity is 96.3%. Example

[0027] (1) Place 3.0 g of melamine powder in a crucible with a lid, and then place the crucible in a muffle furnace under an air atmosphere. The muffle furnace is heated to 550 °C at a heating rate of 2 °C / min and maintained at this temperature for 4 h. When the temperature drops to room temperature, pour the yellow solid into a mortar and grind it until there is no granular feeling to obtain the yellow catalyst support g-C3N4. Weigh 0.0624 of vanadyl acetylacetonate and 0.3 g of the catalyst support g-C3N4 powder and disperse them in a wide-mouth bottle. Then add 10 ml of 0.6 mol / L acetic acid solution and ultrasonically assist the dispersion at room temperature for 30 min. Then place it on a magnetic stirrer and stir at room temperature for 2 h. Then evaporate to dryness in an oil bath at 80 °C. Grind the obtained catalyst precursor evenly, and then transfer the ground powder to a crucible with a lid and calcine it in a muffle furnace at 300 °C for 2 h, with the heating rate set at 2 °C / min. When the temperature drops to room temperature, obtain the catalyst 4%V / g-C3N4.

[0028] (2) Take 50 mg of the above 4%V / g-C3N4 catalyst for the synthesis of phenol by benzene hydroxylation. The reaction conditions are the same as those in Example 1. The phenol yield is 19.1%, and the phenol selectivity is 97.1%. Example

[0029] (1) Place 3.0 g of melamine powder in a crucible with a lid, and then place the crucible in a muffle furnace under an air atmosphere. The muffle furnace is heated to 550 °C at a heating rate of 2 °C / min and held at this temperature for 4 h. When the temperature drops to room temperature, pour the yellow solid into a mortar and grind it until there is no granular feeling to obtain the yellow catalyst support g-C3N4. Weigh 0.0624 of vanadyl acetylacetonate and 0.3 g of the catalyst support g-C3N4 powder and disperse them in a wide-mouth bottle. Then add 10 ml of 0.6 mol / L oxalic acid solution and ultrasonically assist the dispersion at room temperature for 30 min. Then place it on a magnetic stirrer and stir at room temperature for 2 h. Then evaporate to dryness in an oil bath at 80 °C. Grind the obtained catalyst precursor evenly, and then transfer the ground powder to a crucible with a lid and calcine it in a muffle furnace at 300 °C for 2 h, with the heating rate set at 2 °C / min. When the temperature drops to room temperature, obtain the catalyst 4%V / g-C3N4.

[0030] (2) Take 50 mg of the above 4%V / g-C3N4 catalyst for the synthesis of phenol by benzene hydroxylation. The reaction conditions are the same as those in Example 1. The phenol yield is 17.6%, and the phenol selectivity is 96.4%. Example

[0031] (1) Place 3.0 g of melamine powder in a crucible with a lid, and then place the crucible in a muffle furnace under an air atmosphere. The muffle furnace is heated to 550 °C at a heating rate of 2 °C / min and held at this temperature for 4 h. When the temperature drops to room temperature, pour the yellow solid into a mortar and grind it until there is no granular feeling to obtain the yellow catalyst support g-C3N4. Weigh 0.0642 of vanadyl acetylacetonate and 0.3 g of the catalyst support g-C3N4 powder and disperse them in a wide-mouth bottle. Then add 10 ml of 0.6 mol / L citric acid solution and ultrasonically assist the dispersion at room temperature for 30 min. Then place it on a magnetic stirrer and stir at 40 °C for 2 h. Then evaporate to dryness in an oil bath at 80 °C. Grind the obtained catalyst precursor evenly, and then transfer the ground powder to a crucible with a lid and calcine it in a muffle furnace at 300 °C for 2 h, with the heating rate set at 2 °C / min. When the temperature drops to room temperature, obtain the catalyst 4%V / g-C3N4.

[0032] (2) Take 50 mg of the above 4%V / g-C3N4 catalyst for the synthesis of phenol by benzene hydroxylation. The reaction conditions are the same as those in Example 1. The phenol yield is 17.2%, and the phenol selectivity is 95.8%. Example

[0033] (1) Take 3.0 g of melamine powder and place it in a crucible with a lid. Then, place the crucible in a muffle furnace under an air atmosphere. The muffle furnace is heated to 550 °C at a heating rate of 2 °C / min and maintained at this temperature for 4 h. When the temperature drops to room temperature, pour the yellow solid into a mortar and grind it until there is no granular feeling to obtain the yellow catalyst support g-C3N4. Weigh 0.0642 of vanadyl acetylacetonate and 0.3 g of the catalyst support g-C3N4 powder and disperse them in a wide-mouth bottle. Then, add 5 ml of 0.6 mol / L acetic acid solution and 5 ml of 0.6 mol / L oxalic acid solution, and ultrasonically assist the dispersion at room temperature for 30 min. Then, place it on a magnetic stirrer and stir at 40 °C for 2 h. Then, evaporate to dryness in an oil bath at 80 °C. Grind the obtained catalyst precursor evenly, and then transfer the ground powder to a crucible with a lid and calcine it in a muffle furnace at 300 °C for 2 h, with the heating rate set at 2 °C / min. When the temperature drops to room temperature, obtain the catalyst 4%V / g-C3N4.

[0034] (2) Take 50 mg of the above 4%V / g-C3N4 catalyst for the synthesis of phenol by benzene hydroxylation. The reaction conditions are the same as those in Example 1. The phenol yield is 17.6%, and the phenol selectivity is 96.8%. Example

[0035] (1) Take 3.0 g of melamine powder and place it in a crucible with a lid. Then, place the crucible in a muffle furnace under an air atmosphere. The muffle furnace is heated to 550 °C at a heating rate of 2 °C / min and maintained at this temperature for 4 h. When the temperature drops to room temperature, pour the yellow solid into a mortar and grind it until there is no granular feeling to obtain the yellow catalyst support g-C3N4. Weigh 0.0642 of vanadyl acetylacetonate and 0.3 g of the catalyst support g-C3N4 powder and disperse them in a wide-mouth bottle. Then, add 10 ml of deionized water, and ultrasonically assist the dispersion at room temperature for 30 min. Then, place it on a magnetic stirrer and stir at 40 °C for 2 h. Then, evaporate to dryness in an oil bath at 80 °C. Grind the obtained catalyst precursor evenly, and then transfer the ground powder to a crucible with a lid and calcine it in a muffle furnace at 300 °C for 2 h, with the heating rate set at 2 °C / min. When the temperature drops to room temperature, obtain the catalyst 4%V / g-C3N4.

[0036] (2) Take 50 mg of the above 4%V / g-C3N4 catalyst for the synthesis of phenol by benzene hydroxylation. The reaction conditions are the same as those in Example 1. The phenol yield is 14.3%, and the phenol selectivity is 91.6%.

[0037] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A preparation method of an amorphous vanadium-doped carbon nitride catalyst, characterized in that, It includes the following steps: (1) Add carbon nitride support and vanadyl acetylacetonate into a solvent, stir at a temperature of 30-60 °C, heat to evaporate the solvent to obtain a catalyst precursor; (2) Calcinate the catalyst precursor obtained in step (1) at a high temperature in a muffle furnace under an air atmosphere.

2. The preparation method according to claim 1, wherein The preparation of the carbon nitride catalyst support includes: placing melamine in a muffle furnace under an air atmosphere, heating to 550 °C at a heating rate of 2-5 °C / min, holding for 3-6 h, cooling to room temperature, and grinding the obtained solid to obtain the carbon nitride catalyst support.

3. The preparation method according to claim 1, wherein The mass ratio of vanadyl acetylacetonate to carbon nitride is 1:10-1:

100.

4. The preparation method according to claim 1, wherein, The solvent in step (1) includes one or more of deionized water, oxalic acid, citric acid, and acetic acid solution.

5. The preparation method according to claim 1, characterized in that, The temperature for heating and evaporating to dryness in step (1) is 60-90 °C.

6. The preparation method according to claim 1, wherein The calcination temperature in step (2) is 200-500 °C.

7. An amorphous vanadium-doped carbon nitride catalyst obtained by the preparation method according to any one of claims 1-6. The weight of vanadium in the catalyst accounts for 1-10% of the weight of the catalyst support.

8. Use of the amorphous vanadium-doped carbon nitride catalyst according to claim 7, characterized in that, It is applied to the reaction of benzene hydroxylation to synthesize phenol in a hydrogen peroxide system.

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