Method for preparing high metal content carbon-based catalyst using liquid oligomer and its application
The preparation of high metal content carbon-based catalysts through the liquid oligomer method solves the problem of agglomeration of metal nanoparticles, and realizes simple, environmentally friendly and efficient preparation of acetophenone for ethylbenzene oxidation, which is suitable for large-scale production.
Patent Information
- Application Number
- CN202310685470.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-12
- Publication Date
- 2025-08-19
- Estimated Expiration
- 2043-06-12
AI Technical Summary
During the preparation of existing carbon-based metal catalysts, metal nanoparticles are prone to agglomeration, resulting in a decrease in catalytic activity. The traditional methods are complex and costly, making it difficult to improve the ethylbenzene oxidation efficiency under low energy consumption and environmental protection conditions.
The liquid oligomer method is used to dissolve the metal salt and organic ligand small molecules in glycerol and self-assemble to form metal oligomers. A high-metal content carbon-based catalyst is prepared by high-temperature pyrolysis, and a self-sacrificing template is formed by using glycerol-ligand-metal ion interaction to ensure uniform dispersion of metal precursors and thermal stability of organic ligands.
It has achieved simple preparation of carbon-based catalysts with high metal content, and the catalytic ethylbenzene oxidation reaction shows excellent selectivity and conversion rate. The catalytic system is environmentally friendly and efficient, and is suitable for large-scale production.
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Figure CN116726930B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of carbon material preparation, and in particular relates to a method for preparing a high-metal-content carbon-based catalyst by using a liquid oligomer and an application thereof in catalytic oxidation. Background Art
[0002] The selective oxidation of ethylbenzene to produce acetophenone is an important chemical reaction. Aromatic ketones are important chemical products with widespread applications in the synthesis of fine chemicals, dyes, and pharmaceuticals. However, current preparation methods primarily utilize Lewis acid catalysts to convert aromatic hydrocarbons into aromatic ketones via a Friedel-Crafts acylation reaction. During post-processing, the hydrolysis of the Lewis acid generates large amounts of acidic wastewater, which not only pollutes the environment but also corrodes equipment. Furthermore, the preparation of aromatic ketones via the Friedel-Crafts acylation reaction is also affected by the groups on the aromatic benzene ring. While acetophenone can also be obtained via distillation, the yield is relatively low. Therefore, it is of great significance to improve acetophenone selectivity under catalytic oxidation reaction conditions with low pollution and energy consumption, and to find a high-efficiency catalyst that enhances the efficiency of ethylbenzene oxidation.
[0003] Carbon nanomaterials have been widely used in the field of catalysis due to their excellent chemical stability and unique microstructure and other physical properties. Carbon-supported metal catalysts are an important type of catalyst in the field of industrial catalysis. Johnson Matthey, a world-renowned catalyst company, has listed 69 organic catalytic reactions, of which 9 catalysts are supported by carbon. However, the preparation of traditional carbon-based metal catalysts relies heavily on complex procedures and specific precursors. At the same time, during the pyrolysis process, due to the instability of the precursor structure, the supported metals tend to agglomerate into large nanoparticles, resulting in a significant decrease in catalytic activity. At the same time, oxidation reactions, as an important type of catalytic reaction, have long been a research hotspot. It is very important to find a catalyst material with stable performance. In order to better meet actual needs, it is urgent to develop carbon-based metal catalysts that are simple to prepare and low-cost.
[0004] Template methods, as one of the main preparation strategies for carbon-based metal catalysts, can generally be divided into hard template methods and soft template methods. The soft template method mainly obtains nanomaterials with specific structures by processing soft templates such as various ordered polymers and self-organized structures of macromolecules. Due to the diverse morphological structures and easy construction characteristics of soft templates, the soft template method has received increasing attention and research. For example, Liang et al. successfully synthesized functional carbon materials through transition metal-assisted carbonization of conventional organic small molecules (Science Advances, DOI: 10.1126 / sciadv.aat0788), and Han et al. used a unified solution carbonization preparation method to synthesize 37 single-atom catalysts (Nature Materials, DOI: 10.1038 / s41563-022-01252-y). Both methods use solvent carbonization to prepare a series of nanomaterials with specific structures, but the catalyst materials prepared by these two methods are difficult to have a high metal content while ensuring a small metal nanoparticle size. Summary of the Invention
[0005] In order to resolve the contradiction between high metal content and small nanoparticle size during the preparation process, as well as the problem that the catalytic components are difficult to control, the present invention provides a method for preparing a high-metal content carbon-based catalyst using a liquid oligomer. This method is carried out by placing an organic ligand small molecule and a metal salt in propylene glycol and stirring them at room temperature to self-assemble. Before thermal decomposition, a metal oligomer structure is formed through the interaction of propylene glycol-ligand molecule-metal ion. This structure not only ensures the stable and uniform dispersion of the metal precursor solution, but also effectively avoids the sublimation of the organic ligand small molecule during the thermal decomposition process, improves the thermal stability of the organic ligand small molecule, and ensures the successful preparation of highly dispersible carbon-based metal materials. The universality of this liquid oligomer is generally applicable to a variety of metals and organic ligands. At the same time, by selecting and adding different ligands, the particle size and catalytic performance of the metal nanoparticles can be controlled. The prepared carbon-based metal material exhibits excellent catalytic performance in the selective oxidation reaction of ethylbenzene, showing great application potential in heterogeneous catalysis.
[0006] The method of the present invention is to dissolve metal salt and organic ligand small molecules in glycerol solvent to prepare liquid oligomers, directly pyrolyze and carbonize the liquid oligomers at a high temperature of 400-1000°C in an inert atmosphere, and obtain a high-metal content carbon-based catalyst after cooling.
[0007] The metal salts include but are not limited to iron salts, cobalt salts, nickel salts, copper salts, zinc salts, palladium salts, platinum salts, and ruthenium salts; the organic ligand small molecules include but are not limited to nitrogen-containing organic compounds and carboxyl-containing organic compounds; the molar ratio of the metal salt to the organic ligand small molecule is 1:0.01 to 100.
[0008] Nitrogen-containing organic compounds include but are not limited to melamine, triethylenediamine, and urea, and carboxyl-containing organic compounds include but are not limited to fumaric acid, oxalic acid, and malonic acid.
[0009] The inert atmosphere includes nitrogen and argon, the gas flow rate is 1 mL / min-20 mL / min, and the carbonization time is 1 to 8 hours.
[0010] Another object of the present invention is to use the high-metal content carbon-based catalyst prepared by the above method in the catalytic oxidation of ethylbenzene to prepare acetophenone. Specifically, 5 mg to 100 mg of the high-metal content carbon-based catalyst is placed in an autoclave reactor, 5 mL to 15 mL of ethylbenzene is added, 1 atm to 10 atm of oxygen is introduced, and the reaction is stirred at 100 to 150° C. for 5 to 8 hours to prepare acetophenone.
[0011] Advantages and technical effects of the present invention:
[0012] The method of the present invention forms a liquid oligomer through the interaction of glycerol, ligand molecules, and metal ions before pyrolysis. This self-sacrificial template allows for the simple preparation of a carbon-based catalyst with a high metal content and a small size while maintaining metal dispersion. The catalyst can also be recycled and reused, thus having practical significance. The catalytic material is used to catalyze the oxidation of ethylbenzene to produce acetophenone in an oxygen atmosphere. The catalytic system is efficient, environmentally friendly, and has high conversion rate and selectivity.
[0013] The synthesis method of the present invention greatly reduces the preparation cost of the catalyst and has a large degree of freedom in adjusting the added components, and is suitable for the large-scale preparation of catalytic materials with different applications. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 is a transmission electron microscope image of the catalyst material of Example 1;
[0015] Figure 2 is a particle size distribution diagram of metal nanoparticles on the catalyst material of Example 1;
[0016] Figure 3 is an X-ray diffraction pattern of the catalyst material of Example 1;
[0017] Figure 4 This is a high-resolution electron microscope image of the catalyst material of Example 1;
[0018] Figure 5 This is a transmission electron microscope image of the catalyst material of Example 2;
[0019] Figure 6 This is a particle size distribution diagram of metal nanoparticles of the catalyst material of Example 2;
[0020] Figure 7is a transmission electron microscope image of the catalyst material of Example 3;
[0021] Figure 8 This is a particle size distribution diagram of metal nanoparticles on the catalyst material of Example 3;
[0022] Figure 9 is a transmission electron microscope image of the catalyst material of Example 4;
[0023] Figure 10 This is a diagram showing the particle size distribution of metal nanoparticles on the catalyst material of Example 4;
[0024] Figure 11 is a transmission electron microscope image of the catalyst material of Example 5;
[0025] Figure 12 This is a particle size distribution diagram of metal nanoparticles on the catalyst material of Example 5;
[0026] Figure 13 is a transmission electron microscope image of the catalyst material of Example 6;
[0027] Figure 14 This is a diagram showing the particle size distribution of metal nanoparticles on the catalyst material of Example 6;
[0028] Figure 15 is a transmission electron microscope image of the catalyst material of Example 7;
[0029] Figure 16 This is a particle size distribution diagram of metal nanoparticles on the catalyst material of Example 7;
[0030] Figure 17 is a transmission electron microscope image of the catalyst material of Example 8;
[0031] Figure 18 This is the particle size distribution diagram of the metal nanoparticles on the catalyst material of Example 8. DETAILED DESCRIPTION
[0032] The following examples clearly and completely describe the technical solutions of the present invention. Obviously, the examples described are only part of the embodiments of the present invention, not all of them. Based on the examples of the present invention, all other examples obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0033] In the following examples, the Co loading was obtained by ICP-OES testing;
[0034] Example 1:
[0035] 1. Preparation of high Co content carbon-based catalyst
[0036] 5 mmol of cobalt nitrate hexahydrate and 5 mmol of L-alanine were dissolved in 55 mL of glycerol. The solution was then placed in a tube furnace and carbonized at 600 ° C for 2 h under a nitrogen atmosphere (nitrogen flow rate of 15 mL / min). After cooling to room temperature, a carbon-based catalyst Co@CN-G with a Co content of 68.3% was obtained. The transmission electron microscopy image of the catalyst material is shown in FIG. Figure 1 The particle size distribution of Co metal nanoparticles on the catalyst material is shown in Figure 2 , the average particle size is 5.20nm; X-ray diffraction pattern is shown in Figure 3 The diffraction peak at 44.2° is attributed to the (111) face of face-centered cubic (fcc) Co, which indicates the formation of metallic Co. The high-resolution electron microscopy of the catalyst material shows Figure 4 A typical lattice spacing of 0.204 nm attributed to the Co(111) crystal plane was observed in the Co NPs in the catalyst, further proving the generation of metallic Co.
[0037] 2. Preparation of acetophenone from ethylbenzene using high Co content carbon-based catalyst
[0038] (1) 50 mg of high-Co content carbon-based catalyst Co@CN-G was placed in a 25 mL autoclave reactor, 10 mL of ethylbenzene was added, 8 atm of oxygen was introduced, and the reaction was stirred at 120 °C for 5 h. After the reaction was completed, gas chromatography was used to detect the ethylbenzene conversion rate of 32.7% and the acetophenone selectivity of 96.5%.
[0039] (2) The reaction solution was filtered, and the recovered high-Co content carbon-based catalyst Co@CN-G was washed three times with ethylbenzene and then used again in the catalytic oxidation reaction. 10 mL of ethylbenzene was added, and the reaction conditions were the same as in step (1). Gas chromatography detection showed that the ethylbenzene conversion rate was 32.1% and the acetophenone selectivity was 95.9%.
[0040] Example 2
[0041] 1. Preparation of high Co content carbon-based catalyst
[0042] 5 mmol of cobalt nitrate hexahydrate and 5 mmol of fumaric acid were dissolved in 55 mL of glycerol, and then the solution was placed in a tube furnace and carbonized at 600 ° C for 2 h under an argon atmosphere with a gas flow rate of 15 mL / min. After the reaction was completed, it was cooled to room temperature to obtain a carbon-based catalyst with a Co content of 59.8%. The transmission electron micrograph of the catalyst material is shown in FIG. Figure 5 The particle size distribution of metal nanoparticles on the catalyst is shown in Figure 6 , the average particle size is 5.16nm.
[0043] 2. Oxidation of ethylbenzene to acetophenone over high-Co content carbon-based catalysts
[0044] (1) 50 mg of a high-Co content carbon-based catalyst was placed in a 25 mL autoclave reactor, 10 mL of ethylbenzene was added, 8 atm of oxygen was introduced, and the mixture was stirred at 140°C for 8 h. After the reaction, gas chromatography showed that the ethylbenzene conversion was 20.7% and the acetophenone selectivity was 71.5%.
[0045] (2) The reaction liquid was filtered, and the recovered high-Co content carbon-based catalyst was washed three times with ethylbenzene and used again in the catalytic oxidation reaction. 10 mL of ethylbenzene was added, and the reaction conditions were the same as those in step (1). The ethylbenzene conversion rate was 21.1%, and the acetophenone selectivity was 70.9% by gas chromatography.
[0046] Example 3
[0047] 1. Preparation of carbon-based catalysts with high Co metal content
[0048] 5 mmol of cobalt nitrate hexahydrate and 5 mmol of oxalic acid were dissolved in 55 mL of glycerol, and then the solution was placed in a tube furnace and carbonized at 600 ° C for 2 h under a nitrogen atmosphere with a gas flow rate of 15 mL / min. After the reaction was completed, it was cooled to room temperature to obtain a carbon-based catalyst with a Co content of 60.1%. The transmission electron micrograph of the catalyst material is shown in FIG. Figure 7 The particle size distribution of the metal nanoparticles on the catalyst material is shown in Figure 8 , the average particle size is 4.71nm.
[0049] 2. Oxidation of ethylbenzene to acetophenone over high-Co content carbon-based catalysts
[0050] (1) 50 mg of a high-Co content carbon-based catalyst was placed in a 25 mL autoclave reactor, 10 mL of ethylbenzene was added, 8 atm of oxygen was introduced, and the mixture was stirred at 140°C for 8 h. After the reaction, gas chromatography showed that the ethylbenzene conversion was 21.0% and the acetophenone selectivity was 75.5%.
[0051] (2) The reaction solution was filtered, and the recovered high-Co metal content carbon-based catalyst was washed three times with ethylbenzene and used again in the catalytic oxidation reaction. 10 mL of ethylbenzene was added, and the reaction conditions were the same as those in step (1). The ethylbenzene conversion rate was 21.2%, and the acetophenone selectivity was 74.9%.
[0052] Example 4
[0053] 1. Preparation of high Co content carbon-based catalyst
[0054] 5mmol of cobalt nitrate hexahydrate and 5mmol of malonic acid were dissolved in 55mL of glycerol, and then the solution was placed in a tube furnace and carbonized at 600℃ for 2h under nitrogen atmosphere with a gas flow rate of 15mL / min. After the reaction was completed, it was cooled to room temperature to obtain a carbon-based catalyst with a Co content of 57.6%. The transmission electron micrograph of the catalyst material is shown in FIG. Figure 9 The particle size distribution of the metal nanoparticles on the catalyst material is shown in Figure 10 , the average particle size is 6.14nm.
[0055] 2. Oxidation of ethylbenzene to acetophenone over high Co metal content carbon-based catalysts
[0056] (1) 50 mg of a high-Co content carbon-based catalyst was placed in a 25 mL autoclave reactor, 10 mL of ethylbenzene was added, 8 atm of oxygen was introduced, and the mixture was stirred at 140°C for 8 h. After the reaction, gas chromatography showed that the ethylbenzene conversion was 20.1% and the acetophenone selectivity was 73.5%.
[0057] (2) The reaction solution was filtered, and the recovered high-Co metal content carbon-based catalyst was washed three times with ethylbenzene and used again in the catalytic oxidation reaction. 10 mL of ethylbenzene was added, and the reaction conditions were the same as those in step (1). The ethylbenzene conversion rate was 19.9%, and the acetophenone selectivity was 73.1%.
[0058] Example 5
[0059] 1. Preparation of carbon-based catalysts with high Co metal content
[0060] 5 mmol of cobalt nitrate hexahydrate and 5 mmol of urea were dissolved in 55 mL of glycerol, and then the solution was placed in a tube furnace and carbonized at 600 ° C for 2 h under a nitrogen atmosphere with a gas flow rate of 15 mL / min. After the reaction was completed, it was cooled to room temperature to obtain a carbon-based catalyst with a Co content of 73.0%. The transmission electron micrograph of the catalyst material is shown in FIG. Figure 11 The particle size distribution of the metal nanoparticles on the catalyst material is shown in Figure 12 , the average particle size is 58.35nm.
[0061] 2. Oxidation of ethylbenzene to acetophenone over high-Co content carbon-based catalysts
[0062] (1) 50 mg of high-Co content carbon-based catalyst was placed in a 25 mL autoclave reactor, 10 mL of ethylbenzene was added, 8 atm of oxygen was introduced, and the reaction was stirred at 140 ° C for 8 h. After the reaction was completed, the ethylbenzene conversion rate was 25.5% and the acetophenone selectivity was 83.7%.
[0063] (2) The reaction liquid was filtered, and the recovered high-Co metal content carbon-based catalyst was washed three times with ethylbenzene and used again in the catalytic oxidation reaction. 10 mL of ethylbenzene was added, and the reaction conditions were the same as those in step (1). The ethylbenzene conversion rate was 25.1%, and the acetophenone selectivity was 84.2% by gas chromatography.
[0064] Example 6
[0065] 1. Preparation of carbon-based catalysts with high Co metal content
[0066] 5mmol of cobalt nitrate hexahydrate and 5mmol of triethylenediamine were dissolved in 55mL of glycerol, and then the solution was placed in a tube furnace and carbonized at 600℃ for 2h under nitrogen atmosphere with a gas flow rate of 15mL / min. After the reaction was completed, it was cooled to room temperature to obtain a carbon-based catalyst with a Co content of 73.4%. The transmission electron micrograph of the catalyst material is shown in FIG. Figure 13 The particle size distribution of the metal nanoparticles on the catalyst material is shown in Figure 14 , the average particle size is 48.78nm.
[0067] 2. Oxidation of ethylbenzene to acetophenone over high-Co content carbon-based catalysts
[0068] (1) 50 mg of a high-Co content carbon-based catalyst was placed in a 25 mL autoclave reactor, 10 mL of ethylbenzene was added, 8 atm of oxygen was introduced, and the mixture was stirred at 140°C for 8 h. After the reaction, gas chromatography showed that the ethylbenzene conversion was 26.1% and the acetophenone selectivity was 84.5%.
[0069] (2) The reaction solution was filtered, and the recovered high-Co metal content carbon-based catalyst was washed three times with ethylbenzene and used again in the catalytic oxidation reaction. 10 mL of ethylbenzene was added, and the reaction conditions were the same as in step (1). The ethylbenzene conversion rate was 25.9%, and the acetophenone selectivity was 85.1%.
[0070] Example 7
[0071] 1. Preparation of carbon-based catalysts with high Co metal content
[0072] 5 mmol of cobalt nitrate hexahydrate and 5 mmol of melamine were dissolved in 55 mL of glycerol, and then the solution was placed in a tube furnace and carbonized at 600 ° C for 2 h under a nitrogen atmosphere with a gas flow rate of 15 mL / min. After the reaction was completed, it was cooled to room temperature to obtain a carbon-based catalyst with a Co content of 74.1%. The transmission electron micrograph of the catalyst material is shown in FIG. Figure 15 The particle size distribution of the metal nanoparticles on the catalyst material is shown in Figure 16 , the average particle size is 57.71nm.
[0073] 2. Oxidation of ethylbenzene to acetophenone over high-Co content carbon-based catalysts
[0074] (1) 50 mg of a high-Co metal content carbon-based catalyst was placed in a 25 mL autoclave reactor, 10 mL of ethylbenzene was added, 8 atm of oxygen was introduced, and the mixture was stirred at 140°C for 8 h. After the reaction, gas chromatography showed that the ethylbenzene conversion was 26.1% and the acetophenone selectivity was 86.5%.
[0075] (2) The reaction liquid was filtered, and the recovered high-Co metal content carbon-based catalyst was washed three times with ethylbenzene and used again in the catalytic oxidation reaction. 10 mL of ethylbenzene was added, and the reaction conditions were the same as those in step (1). The ethylbenzene conversion rate was 26.3%, and the acetophenone selectivity was 86.9% by gas chromatography.
[0076] Example 8
[0077] 1. Preparation of carbon-based catalysts with high Co metal content
[0078] 5mmol of cobalt nitrate hexahydrate, 5mmol of fumaric acid, and 5mmol of urea were dissolved in 55mL of glycerol, and then the solution was placed in a tube furnace and carbonized at 600℃ for 2h under nitrogen atmosphere with a gas flow rate of 15mL / min. After the reaction was completed, it was cooled to room temperature to obtain a carbon-based catalyst with a Co content of 56.9%. The transmission electron micrograph of the catalyst material is shown in FIG. Figure 17 The particle size distribution of the metal nanoparticles on the catalyst material is shown in Figure 18 , the average particle size is 3.59nm.
[0079] 2. Oxidation of ethylbenzene to acetophenone over high-Co content carbon-based catalysts
[0080] (1) 50 mg of a high-Co content carbon-based catalyst was placed in a 25 mL autoclave reactor, 10 mL of ethylbenzene was added, 8 atm of oxygen was introduced, and the mixture was stirred at 120°C for 5 h. After the reaction, gas chromatography showed that the ethylbenzene conversion was 32.7% and the acetophenone selectivity was 95.5%.
[0081] (2) The reaction liquid was filtered, and the recovered high-Co metal content carbon-based catalyst was washed three times with ethylbenzene and used again in the catalytic oxidation reaction. 10 mL of ethylbenzene was added, and the reaction conditions were the same as those in step (1). The ethylbenzene conversion rate was 32.9%, and the acetophenone selectivity was 95.9% by gas chromatography.
[0082] From the above examples, it can be seen that compared with the carboxyl ligand, the average particle size of the material prepared with the nitrogen-containing ligand is significantly increased by nearly 10 times. This shows that the material prepared with the carboxyl ligand has better dispersibility and smaller metal nanoparticle size, which may be due to the stronger coordination ability of the oxygen atoms in the carboxyl ligand with the metal ions. This makes the metal in an interval state during the pyrolysis process, and it is not easy for metal sintering to occur, which will produce smaller metal NPs. However, the selected nitrogen-containing ligand has poor thermal stability and is easy to volatilize or sublime during the pyrolysis process, so it is difficult to maintain the restriction effect on the metal ions and obtain a uniform carbon material, resulting in the formation of large-sized metal NPs. It is worth noting that the average particle size of the material prepared with L-alanine containing both nitrogen and carboxyl groups is 5.20nm. This shows that the mixture of different ligands may affect the size of the material, so the size of the catalyst metal nanoparticles can be regulated by changing the ligand.
[0083] The preparation method of the high-metal-content carbon-based catalyst in the present invention first generates a liquid oligomer structure before the calcination process. Thanks to the formation of this oligomer system, the thermal stability of the organic ligand small molecules is greatly improved. While maintaining the metal dispersion, the high-metal-content carbon-based catalyst is easily prepared, and it also has the advantage of a simple reaction system that is easy to expand.
Claims
1. Use of a high-metal content carbon-based catalyst prepared from a liquid oligomer in catalyzing the oxidation of ethylbenzene to produce acetophenone, characterized in that: The high metal content carbon-based catalyst prepared by using liquid oligomer is prepared by dissolving metal salt and organic ligand small molecules in glycerol solvent to prepare liquid oligomer. The liquid oligomer is directly pyrolyzed and carbonized at a high temperature of 400-1000°C in an inert atmosphere and then cooled. The organic ligand small molecule is selected from nitrogen-containing organic compounds and carboxyl-containing organic compounds; the nitrogen-containing organic compound is selected from melamine, triethylenediamine, urea, and alanine, and the carboxyl-containing organic compound is selected from fumaric acid, oxalic acid, and malonic acid.
2. The use according to claim 1, characterized in that: The metal salt is selected from iron salts, cobalt salts, nickel salts, copper salts, zinc salts, palladium salts, platinum salts, and ruthenium salts.
3. The use according to claim 1, characterized in that: The molar ratio of the metal salt to the organic ligand small molecule is 1:0.01~100.
4. The use according to claim 1, characterized in that: The pyrolysis time is 1~8h.