A cobalt metal catalyst and its preparation method and application

Abstract

The present invention provides a cobalt metal catalyst, a preparation method and an application thereof. The preparation method uses a cobalt-based metal organic framework as a precursor and alkali metal and / or alkaline earth metal salts as pore-forming agents for pyrolysis. During the high-temperature pyrolysis process, the alkali metal and / or alkaline earth metal salts are thermally decomposed into alkaline earth metal oxides and gases such as carbon dioxide, so that the amorphous carbon obtained by the high-temperature pyrolysis of the metal organic framework is converted into porous carbon, thereby increasing the specific surface area of the catalyst. At the same time, the catalyst is modified with an alkali to increase the concentration of active oxygen such as hydroxyl groups on the catalyst surface, thereby significantly improving the catalytic activity.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a cobalt metal catalyst and a preparation method and application thereof. Background Art

[0002] Formaldehyde is the most serious pollutant from furniture and decoration materials and has been identified by the World Health Organization as a carcinogen and teratogen. The release of formaldehyde from furniture and decoration materials is characterized by low concentration and long release period. Long-term exposure to low doses (<1mg / m 3 Formaldehyde can cause chronic respiratory diseases, nasopharyngeal cancer, nuclear gene mutations, leukemia, and other diseases. Since people spend most of their time indoors in modern life, eliminating the negative impacts of low-concentration formaldehyde on the environment and human health is essential. Among the many methods currently available for formaldehyde removal, catalytic oxidation has garnered widespread attention from researchers due to its advantages, including room temperature operation, the absence of heat and light sources, and the lack of secondary pollution.

[0003] However, the existing catalysts of this method are mostly used for the catalytic purification of high-concentration formaldehyde, and there are few studies on the catalytic purification of low-concentration formaldehyde, which is closer to the actual situation. At the same time, the catalytic oxidation of low-concentration, high-flux formaldehyde is also a difficulty in the research of catalysts for this system. Precious metal catalysts show excellent room-temperature catalytic activity in the catalytic oxidation of low-concentration, high-flux formaldehyde due to their excellent low-temperature catalytic activity, but their scarcity and high cost limit further application. In recent years, many research efforts have focused on the development of transition metal oxide catalysts, among which Co3O4 is considered to be one of the most promising catalysts in the field of formaldehyde catalytic purification due to its high catalytic activity and stability, environmental friendliness, and excellent redox properties. However, many studies are still focused on high-concentration formaldehyde, and the catalytic elimination of low-concentration formaldehyde (<1mg / m 3 ) research remains rare. Related technologies have produced highly active cobalt oxide catalysts, but they still require the addition of precious metals or other transition metal oxides as additives. Other related technologies have produced highly defective cobalt tetroxide catalysts through acid etching or reduction modification, but these still target high concentrations of formaldehyde (>50 ppm) and are ineffective at catalytic purification of lower concentrations. Therefore, catalytic purification of low-concentration formaldehyde using transition metal oxide catalysts at room temperature remains a significant challenge. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the first aspect of the present invention provides a method for preparing a cobalt metal catalyst.

[0005] The second aspect of the present invention provides a cobalt metal catalyst prepared by the preparation method of the cobalt metal catalyst.

[0006] The third aspect of the present invention provides an application of the cobalt metal catalyst.

[0007] According to a first aspect of the present invention, a method for preparing a cobalt metal catalyst is provided, comprising the following steps:

[0008] S1: Cobalt salt and organic ligand are mixed in a solvent and subjected to a solvothermal reaction to prepare a metal-organic framework precursor;

[0009] S2: Under an inert atmosphere, the metal organic framework precursor and the alkali metal salt and / or alkaline earth metal salt are pyrolyzed to generate gas to obtain the cobalt metal catalyst.

[0010] In the present invention, a cobalt-based metal-organic framework is used as a precursor and alkali metal and / or alkaline earth metal salts are used as pore-forming agents for pyrolysis. During the high-temperature pyrolysis process, the alkali metal and / or alkaline earth metal salts are thermally decomposed into alkaline earth metal oxides and gases such as carbon dioxide, so that the amorphous carbon obtained by the high-temperature pyrolysis of the metal-organic framework is converted into porous carbon, thereby increasing the specific surface area of the catalyst. At the same time, the catalyst is modified with an alkali to increase the concentration of active oxygen such as hydroxyl groups on the catalyst surface, thereby significantly improving the catalytic activity.

[0011] In some embodiments of the present invention, in the method for preparing the cobalt metal catalyst, S1: mixing a cobalt salt, an organic ligand, and a base in a solvent and then conducting a solvothermal reaction to obtain a metal organic framework precursor; preferably, the base includes at least one of sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide; further preferably, the molar ratio of the base to the organic ligand is 1: (1 to 1.5).

[0012] In some preferred embodiments of the present invention, the mass ratio of the metal organic framework precursor to the alkali metal salt and / or alkaline earth metal salt is 1:(10-100).

[0013] In some more preferred embodiments of the present invention, in S1, the temperature of the solvent thermal reaction is 0°C to 200°C, and the time is 6h to 48h; preferably, the temperature of the solvent thermal reaction is 20°C to 150°C, and the time is 6h to 24h.

[0014] In some more preferred embodiments of the present invention, in S2, the pyrolysis temperature is 800°C to 1000°C; preferably, the pyrolysis time is 2h to 5h.

[0015] In some more preferred embodiments of the present invention, the cobalt salt comprises at least one of nitrate, acetate, sulfate, halide or perhalide of metallic cobalt.

[0016] In some more preferred embodiments of the present invention, the organic ligand includes at least one of terephthalic acid, 2-aminoterephthalic acid, 2-nitroterephthalic acid, 2-haloterephthalic acid, 2,5-dihydroxyterephthalic acid, 1,3,5-trimellitic acid, triethylenediamine, 2,4,6-tris(4-pyridyl)-1,3,5-triazine, imidazole, 2-methylimidazole, 2-ethylimidazole, 2-nitroimidazole, 2-aminoimidazole, 2-imidazolecarboxaldehyde or benzimidazole.

[0017] In some more preferred embodiments of the present invention, in S1, the solvent includes at least one of water, methanol, ethanol, propanol, isopropanol, ether, acetone, N,N-dimethylformamide, tetrahydrofuran or dimethyl sulfoxide.

[0018] In some more preferred embodiments of the present invention, the alkali metal salt includes at least one of alkali metal carbonate, bicarbonate, and nitrate.

[0019] In some more preferred embodiments of the present invention, the alkaline earth metal salt includes at least one of carbonate, bicarbonate, and nitrate of an alkaline earth metal.

[0020] In some more preferred embodiments of the present invention, the inert atmosphere comprises at least one of nitrogen, argon or helium atmosphere.

[0021] According to a second aspect of the present invention, a cobalt metal catalyst prepared by the method for preparing the cobalt metal catalyst is provided.

[0022] According to a third aspect of the present invention, a use of the cobalt metal catalyst in catalytic purification of formaldehyde is proposed.

[0023] In some embodiments of the present invention, the temperature of the catalytic purification is 0°C to 45°C; preferably 10°C to 35°C.

[0024] The beneficial effects of the present invention are:

[0025] 1) The present invention uses a cobalt-based metal organic framework as a precursor and an alkali metal and / or alkaline earth metal salt as a pore-forming agent for pyrolysis. During the high-temperature pyrolysis process, the alkali metal and / or alkaline earth metal salt is thermally decomposed into alkaline earth metal oxides and gases such as carbon dioxide, so that the amorphous carbon obtained by the high-temperature pyrolysis of the metal organic framework is converted into porous carbon, thereby increasing the specific surface area of the catalyst and overcoming the problem of low formaldehyde concentration and difficulty in enrichment and conversion in the catalytic purification of low-concentration formaldehyde.

[0026] 2) The present invention utilizes the fluidity generated by the melting of alkali metal salts during high-temperature pyrolysis to perform alkali modification on the catalyst, thereby increasing the concentration of active oxygen such as hydroxyl groups on the catalyst surface, thereby significantly improving the catalytic activity.

[0027] 3) The cobalt metal catalyst for catalytically purifying formaldehyde at room temperature of the present invention can catalytically oxidize formaldehyde into harmless CO2 and H2O at room temperature without the aid of external energy such as light, electricity, and heat, and has the characteristics of low cost, high activity, and long life. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0029] Figure 1 The XRD patterns of the catalysts of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention are shown.

[0030] Figure 2 TEM images of the catalysts of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention, wherein (a) is the TEM image of the catalyst in Example 1; (b) is the TEM image of the catalyst in Comparative Example 1; and (c) is the TEM image of the catalyst in Comparative Example 2. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0032] Example 1

[0033] This example prepares a cobalt metal catalyst, and the specific process is as follows:

[0034] Dissolve 0.45g of cobalt nitrate in 3mL of water and 5.5g of 2-methylimidazole in 20mL of water. Mix the two solutions thoroughly and react at room temperature for 6h. Filter, wash, and dry to obtain a purple powder. Mix 0.1g of the powder with 2g of sodium carbonate and 6g of magnesium carbonate. Calcinate at 860°C for 4h under a helium atmosphere. Soak in 0.01M dilute hydrochloric acid for 6h. Filter, wash, and dry to obtain the cobalt metal catalyst.

[0035] Example 2

[0036] This example prepares a cobalt metal catalyst, and the specific process is as follows:

[0037] Dissolve 1.6g of cobalt acetate in a mixture of 3mL of water and 3mL of ethanol. Dissolve 0.33g of 2,5-dihydroxyterephthalic acid and 0.16g of potassium hydroxide in 45mL of N,N-dimethylformamide. Mix the two solutions thoroughly, react at 135°C for 24h, filter, wash, and dry to obtain reddish-brown crystals. Mix 0.1g of the crystals with 4g of potassium carbonate and 6g of calcium carbonate, calcinate at 900°C for 3h under a nitrogen atmosphere, soak in 0.01M dilute hydrochloric acid for 6h, filter, wash, and dry to obtain the cobalt metal catalyst.

[0038] Example 3

[0039] This example prepares a cobalt metal catalyst, and the specific process is as follows:

[0040] Dissolve 1.6g of cobalt acetate in a mixture of 3mL of water and 3mL of ethanol. Dissolve 0.33g of 2,5-dihydroxyterephthalic acid and 0.16g of potassium hydroxide in 45mL of N,N-dimethylformamide. Mix the two solutions thoroughly, react at 135°C for 24h, filter, wash, and dry to obtain reddish-brown crystals. Mix 0.1g of the crystals with 4g of potassium carbonate and 6g of calcium carbonate, calcinate at 900°C for 3h under a nitrogen atmosphere, soak in 0.01M dilute hydrochloric acid for 6h, filter, wash, and dry to obtain the cobalt metal catalyst.

[0041] Example 4

[0042] This example prepares a cobalt metal catalyst, and the specific process is as follows:

[0043] 0.4 g of cobalt nitrate and 0.23 g of terephthalic acid were placed in a 25 mL Shrek tube, and a mixed solution of 10 mL of DMF and 2.5 mL of anhydrous ethanol was added. The air in the tube was then replaced with nitrogen and sealed. The temperature was raised to 100°C and maintained for 15 hours. The mixture was filtered, washed, and dried to obtain purple-red crystals. 0.1 g of the crystals was mixed with 2.4 g of sodium bicarbonate and 5 g of magnesium carbonate, calcined at 850°C for 3 hours under a nitrogen atmosphere, and soaked in 0.01 M dilute hydrochloric acid for 6 hours. The mixture was then filtered, washed, and dried to obtain the cobalt metal catalyst.

[0044] Example 5

[0045] This example prepares a cobalt metal catalyst, and the specific process is as follows:

[0046] 0.46g of cobalt nitrate, 0.13g of 2,4,6-tris(4-pyridyl)-1,3,5-triazine, and 0.17g of 1,3,5-trimesic acid were dissolved in 48mL of a mixed solvent of N,N-dimethylformamide, ethanol, and water (the volume ratio of N,N-dimethylformamide, ethanol, and water was 1:1:1). The mixture was reacted at 100°C for 24h, filtered, washed, and dried to obtain red crystals. 0.1g of the crystals was mixed with 1g of sodium carbonate, 1g of potassium carbonate, and 4g of magnesium carbonate, calcined at 875°C for 3h under an argon atmosphere, and soaked in 0.01M dilute hydrochloric acid for 6h. The mixture was filtered, washed, and dried to obtain the cobalt metal catalyst.

[0047] Example 6

[0048] This example prepares a cobalt metal catalyst, and the specific process is as follows:

[0049] Dissolve 0.8g of cobalt nitrate, 0.5g of terephthalic acid, and 0.16g of triethylenediamine in 20mL of N,N-dimethylformamide, react at 120°C for 48h, filter, wash, and dry to obtain a purple-red powder. Mix 0.1g of the powder with 4g of cesium carbonate and 6g of magnesium carbonate, calcine at 880°C for 4h under a helium atmosphere, soak in 0.01M dilute hydrochloric acid for 6h, filter, wash, and dry to obtain the cobalt metal catalyst.

[0050] Example 7

[0051] This example prepares a cobalt metal catalyst, and the specific process is as follows:

[0052] 0.46g of cobalt nitrate and 0.34g of 1,3,5-trimesic acid were dissolved in 48mL of a mixed solvent of N,N-dimethylformamide, ethanol, and water (volume ratio of N,N-dimethylformamide, ethanol, and water was 1:1:1). The mixture was reacted at 100°C for 24h, filtered, washed, and dried to obtain purple crystals. 0.1g of the crystals was mixed with 2g of sodium carbonate and 6g of calcium carbonate, calcined at 1000°C for 2h under an argon atmosphere, and soaked in 0.01M dilute hydrochloric acid for 6h. The mixture was then filtered, washed, and dried to obtain the cobalt metal catalyst.

[0053] Example 8

[0054] This comparative example prepared a cobalt metal catalyst, and the specific process was as follows:

[0055] Dissolve 3.6g of cobalt chloride in 50mL of water, 1.67g of terephthalic acid and 0.8g of sodium hydroxide in 250mL of water, and add the cobalt nitrate solution dropwise to the terephthalic acid and sodium hydroxide solution while stirring. After the addition is complete, the mixed solution is allowed to react at room temperature for 12 hours, filtered, washed, and dried to obtain a pink powder. 0.1g of the powder is mixed with 3g of rubidium carbonate, calcined at 900°C for 2 hours under an argon atmosphere, and soaked in 0.01M dilute hydrochloric acid for 6 hours. Filter, wash, and dry to obtain the cobalt metal catalyst.

[0056] Example 9

[0057] This comparative example prepared a cobalt metal catalyst, and the specific process was as follows:

[0058] 0.4g of cobalt nitrate and 0.23g of terephthalic acid were placed in a 25mL Shrek tube, and a mixed solution of 10mL of DMF and 2.5mL of anhydrous ethanol was added. The air in the tube was then replaced with nitrogen and sealed. The temperature was raised to 100°C and maintained for 15 hours. The mixture was then filtered, washed, and dried to obtain purple-red crystals. 0.1g of the crystals was mixed evenly with 5g of magnesium carbonate, calcined at 850°C for 3 hours under a nitrogen atmosphere, and soaked in 0.01M dilute hydrochloric acid for 6 hours. The mixture was then filtered, washed, and dried to obtain the cobalt metal catalyst.

[0059] Comparative Example 1

[0060] This comparative example prepared a catalyst, and the specific process was as follows:

[0061] Dissolve 0.45g of cobalt nitrate in 3mL of water and 5.5g of 2-methylimidazole in 20mL of water. Mix the two solutions thoroughly and react at room temperature for 6h. Filter, wash, and dry to obtain a purple powder. Mix 0.1g of the powder with 2g of sodium carbonate and 6g of magnesium carbonate. Calcinate at 600°C under a helium atmosphere for 4h. Soak in 0.01M dilute hydrochloric acid for 6h. Filter, wash, and dry to obtain the catalyst.

[0062] Comparative Example 2

[0063] This comparative example prepared a catalyst, and the specific process was as follows:

[0064] Dissolve 0.45g of cobalt nitrate in 3mL of water and 5.5g of 2-methylimidazole in 20mL of water. Mix the two solutions thoroughly and react at room temperature for 6h. Filter, wash, and dry to obtain a purple powder. Calcine 0.1g of the powder at 860°C under a helium atmosphere for 4h, soak in 0.01M dilute hydrochloric acid for 6h, filter, wash, and dry to obtain the catalyst.

[0065] Test Example 1

[0066] In this test example, XRD and TEM tests were performed on the catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0067] Figure 1 The XRD patterns of the catalysts of Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. Figure 1 As can be seen from the figure, the diffraction peaks corresponding to Example 1, Comparative Example 1, and Comparative Example 2 are concentrated at 44.2°, 51.5°, and 75.9°, corresponding to the (111), (200), and (220) crystal planes of elemental cobalt, indicating that elemental cobalt nanoparticles were generated. In Example 1, a distinct broad diffraction peak was observed in the 10-30° range, indicating that a graphitic carbon structure was generated.

[0068] Figure 2 TEM images of the catalysts prepared in Example 1(a), Comparative Example 1(b) and Comparative Example 2(c) of the present invention. Figure 2 It can be seen that the catalysts in Comparative Examples 1 and 2 do not exhibit a hierarchical pore structure, while the catalyst in Example 1 exhibits a distinct hierarchical pore structure. Furthermore, the cobalt nanoparticles have a small particle size. Even when pyrolyzed at 860°C, the nanoparticle size is still comparable to that of the catalyst prepared at 600°C in Comparative Example 1. This indicates that the addition of alkali metal salts and alkaline earth metal salts during pyrolysis not only generates hierarchical pores but also effectively prevents agglomeration of cobalt nanoparticles, thereby improving their dispersion.

[0069] Test Example 2

[0070] This test example tests the specific surface area and formaldehyde purification performance of the catalysts prepared in the examples and comparative examples. The specific process is as follows:

[0071] Specific surface area test: The catalysts prepared in Example 1 and Comparative Examples 1-2 were subjected to nitrogen adsorption and desorption tests at 77K liquid nitrogen using a Micromeritics ASAP2460 specific surface area analyzer to determine the specific surface area of the samples. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. The specific surface area of the cobalt metal catalyst in Example 1 was 656 m 2 / g, while the specific surface areas of the catalysts in Comparative Example 1 and Comparative Example 2 were 315m 2 / g and 274m 2 / g, which was reduced by nearly half.

[0072] Performance test of formaldehyde purification: The room temperature catalytic formaldehyde purification catalysts prepared in Examples 1 to 9 and Comparative Examples 1 to 2 were tested for performance. The test conditions were: the initial formaldehyde concentration was 1 mg / m 3The test method was as follows: At room temperature (25°C), formaldehyde from a formaldehyde solution was bubbled through a quartz tube containing a room-temperature formaldehyde oxidation catalyst using air. Gas samples were taken before and after passing through the quartz tube to calculate the formaldehyde conversion rate. The test results are shown in Table 1.

[0073] Table 1 Room temperature catalytic formaldehyde purification performance test of the catalysts of Examples 1 to 9 and Comparative Examples 1 to 2

[0074]

[0075]

[0076] It can be seen from Table 1 that the room temperature catalytic purification of formaldehyde by the cobalt metal catalyst prepared by the method of the present invention has a high efficiency at an initial formaldehyde concentration of 1 mg / m 3 Under the conditions of 10000mL / g / h and 120000mL / g / h air velocity, the formaldehyde conversion rate at room temperature is better than that of the catalyst in the comparative example.

[0077] From the test results and characterization results of Comparative Example 1 ( Figure 2 (b) It can be found that the low-temperature heat treatment method cannot make the alkaline earth metal salt thermally decompose to generate gas to form pores during the pyrolysis process, nor can it make the alkali metal salt melt to modify the catalyst, thereby resulting in a decrease in catalytic activity. From the test results and characterization results of Comparative Example 2 ( Figure 2 (c) As can be seen, without the addition of alkali metal salts and alkaline earth metal salts during the high-temperature pyrolysis process, the catalyst prepared is similar to Comparative Example 1, lacking a multi-level pore structure and having a lower specific surface area than Example 1, resulting in weaker formaldehyde adsorption and enrichment capabilities and lower catalytic activity. Comparing the effects of the cobalt metal catalysts of Examples 1-7 with those of Examples 8 and 9, it can be seen that the introduction of either alkali metal salts or alkaline earth metal salts alone during the pyrolysis process can improve the catalyst activity to a certain extent, while the simultaneous use of alkali metal salts and alkaline earth metal salts can produce a synergistic effect on the modification of the cobalt metal catalyst, resulting in even better catalytic activity for the resulting cobalt metal catalyst.

[0078] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A method for preparing a cobalt metal catalyst, characterized in that: The following steps are involved: S1: Cobalt salt and organic ligand are mixed in a solvent and subjected to a solvothermal reaction to prepare a metal-organic framework precursor; S2: Under an inert atmosphere, pyrolyzing the metal organic framework precursor and an alkali metal salt and / or an alkaline earth metal salt to generate gas and performing base modification to obtain the cobalt metal catalyst; During the pyrolysis and gas production process, the metal organic framework is transformed from amorphous carbon to porous carbon; the porous carbon has a multi-level pore structure; The organic ligand includes at least one of terephthalic acid, 2-aminoterephthalic acid, 2-nitroterephthalic acid, 2-halogenated terephthalic acid, 2,5-dihydroxyterephthalic acid, 1,3,5-trimellitic acid, triethylenediamine, 2,4,6-tris(4-pyridyl)-1,3,5-triazine, imidazole, 2-methylimidazole, 2-ethylimidazole, 2-nitroimidazole, 2-aminoimidazole, 2-imidazolecarboxaldehyde or benzimidazole; The alkali metal salt includes at least one of a carbonate and a bicarbonate of an alkali metal; The alkaline earth metal salt includes at least one of a carbonate and a bicarbonate of an alkaline earth metal; In S2, the pyrolysis temperature is 800°C to 1000°C; the pyrolysis time is 2h to 4h; The mass ratio of the metal organic framework precursor to the alkali metal salt and / or alkaline earth metal salt is 1:(10-100).

2. The method for preparing a cobalt metal catalyst according to claim 1, wherein: S1: mixing a cobalt salt, an organic ligand, and a base in a solvent and performing a solvothermal reaction to obtain a metal organic framework precursor; the base comprises at least one of sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide.

3. The method for preparing a cobalt metal catalyst according to claim 1, wherein: The cobalt salt includes at least one of nitrate, acetate, sulfate, halide or perhalide of metallic cobalt.

4. The method for preparing a cobalt metal catalyst according to claim 1, wherein: In S1, the solvent includes at least one of water, methanol, ethanol, propanol, isopropanol, ether, acetone, N,N-dimethylformamide, tetrahydrofuran or dimethyl sulfoxide.

5. The method for preparing a cobalt metal catalyst according to claim 1, wherein: In S1, the temperature of the solvent thermal reaction is 20° C. to 150° C., and the time is 6 h to 48 h.

6. A cobalt metal catalyst obtained by the method for preparing a cobalt metal catalyst according to any one of claims 1 to 5.

7. Use of the cobalt metal catalyst according to any one of claim 6 in catalytic purification of formaldehyde.

8. The use according to claim 7, characterized in that: The temperature of the catalytic purification is 0°C to 45°C.

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