Cobalt-based catalyst as well as preparation method and application thereof

Abstract

The invention discloses a cobalt-based catalyst and a preparation method and application thereof, the cobalt-based catalyst is obtained by at least taking a cobalt-based precursor and an organic nitrogen source as raw materials through in-situ carbonization treatment; wherein the raw materials of the cobalt-based precursor at least comprise a cobalt salt, a zinc salt and an imidazole organic ligand. The preparation method comprises the following steps: dissolving cobalt salt and zinc salt in water to obtain a metal salt aqueous solution; the preparation method comprises the following steps: dissolving an imidazole organic ligand in water to obtain an imidazole organic ligand aqueous solution; the preparation method comprises the following steps: mixing a metal salt aqueous solution and an imidazole organic ligand aqueous solution, heating, aging, collecting a solid product, washing and drying to obtain a catalyst precursor; and mixing the catalyst precursor with an organic nitrogen source, and carrying out in-situ carbonization treatment to obtain the catalyst. The cobalt-based catalyst shows excellent catalytic activity and selectivity in the methanol oxidative carbonylation reaction, has good reaction stability, can still keep high methanol conversion rate and DMC selectivity after being recycled for five times, and has good industrial application potential.

Description

Technical Field

[0001] This invention belongs to the field of industrial catalysis technology, specifically relating to a cobalt-based catalyst, its preparation method, and its application. Background Technology

[0002] Dimethyl carbonate (DMC), as an environmentally friendly green chemical raw material, can be synthesized through various methods, including methanol hydrogenation, alcoholysis, ethylene carbonate / propylene carbonate transesterification, direct CO2 synthesis, and methanol oxidative carbonylation. Among these, methanol oxidative carbonylation has become a research hotspot due to its advantages such as high atom economy, favorable thermodynamics, and the fact that water is the only byproduct. Copper-based catalysts have been extensively studied in the methanol oxidative carbonylation synthesis of DMC, but achieving a balance between activity and selectivity remains challenging. While industrially used CuCl catalysts exhibit some catalytic effect, the easy conversion of chlorine to HCl during the reaction leads to chlorine loss, corrosion of reaction equipment, and catalyst deactivation. Although various chlorine-free copper-based catalysts have been developed, they still have limitations in improving DMC selectivity and methanol conversion.

[0003] Zeolite-like imidazolium ester framework materials (ZIFs) possess the ordered crystal structure, large specific surface area, and tunable pore size characteristic of general MOFs. The metal-imidazolium-metal bond angles in ZIFs are similar to the Si-O-Si bond angles in silica-based zeolites. This characteristic also makes the ZIF series more inclined towards a zeolite-type topology, allowing ZIFs to inherit the advantages of zeolite structure and the tunability and multifunctionality of MOFs. Studies have shown that ZIF materials, with their tunable structure, pore size, and high surface area, are widely used in gas storage and separation, catalysis, and electrochemical sensors.

[0004] ZIF-67 is a typical cobalt-containing catalyst, but the Co-promoted organic ligands decompose rapidly during high-temperature carbonation, leading to the collapse of the ZIF structure and a sharp decrease in specific surface area. This results in the aggregation of Co nanoparticles and a reduction in catalytic activity. Therefore, although cobalt-based catalysts exhibit a high selectivity of up to 99% for DMC in the methanol oxidative carbonylation reaction, significantly outperforming copper-based catalysts, homogeneous cobalt catalysts face difficulties in recycling, while heterogeneous cobalt-based catalysts generally suffer from low methanol conversion rates and limited reaction stability, restricting their practical application. Wang et al. (Appl. Organomet. Chem., 2024, 3) synthesized core-shell structured ZIFs materials, effectively inhibiting the aggregation of Co nanoparticles and reducing the catalyst deactivation rate. However, the reaction activity still significantly decreased after five cycles, indicating a considerable gap between the current state and the industrial application requirements of cobalt-based catalysts in the methanol carbonylation synthesis of dimethyl carbonate.

[0005] Therefore, developing heterogeneous cobalt-based catalysts with high methanol conversion rate and high reaction stability to achieve efficient and selective conversion of methanol to DMC has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a cobalt-based catalyst, its preparation method and application, which has high selectivity and high reaction stability.

[0007] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0008] A cobalt-based catalyst, wherein the cobalt-based catalyst is obtained by in-situ carbonization treatment using at least a cobalt-based precursor and an organic nitrogen source as raw materials;

[0009] The raw materials for the cobalt-based precursor include at least cobalt salt, zinc salt, and imidazole organic ligand.

[0010] In one or more embodiments of the present invention, the ratio of the number of cobalt atoms to the sum of the number of cobalt atoms and zinc atoms in the cobalt-based catalyst is 8%-80%.

[0011] In one or more embodiments of the present invention, the cobalt salt is at least one of cobalt chloride hexahydrate and cobalt nitrate hexahydrate; and / or,

[0012] The zinc salt is at least one of zinc nitrate hexahydrate and zinc acetate; and / or,

[0013] The imidazole organic ligand is at least one of 2-methylimidazolium and 1-methylimidazolium; and / or,

[0014] The organic nitrogen source is at least one of urea and melamine.

[0015] Another specific embodiment of the present invention provides the following technical solution:

[0016] A method for preparing a cobalt-based catalyst, the method comprising the following steps:

[0017] Cobalt salts and zinc salts are dissolved in water to obtain an aqueous solution of the metal salts;

[0018] The imidazole organic ligand was dissolved in water to obtain an aqueous solution of the imidazole organic ligand.

[0019] A mixture of an aqueous solution of a metal salt and an aqueous solution of an imidazole organic ligand was heated and aged. The solid product was collected, washed, and dried to obtain the catalyst precursor.

[0020] The catalyst precursor and organic nitrogen source were mixed and subjected to in-situ carbonization to obtain a cobalt-based catalyst.

[0021] In one or more embodiments of the present invention, the cobalt salt and zinc salt are mixed in a ratio of 8% to 80% of the total number of cobalt atoms and the sum of the number of cobalt atoms and zinc atoms; and / or,

[0022] The molar ratio of the sum of the molar amounts of cobalt and zinc atoms to the organic ligand is 1:(1-5); and / or,

[0023] The mass ratio of the catalyst precursor to the organic nitrogen source is 3:(0.5-3).

[0024] In one or more embodiments of the present invention, the concentration of the aqueous metal salt solution is 0.001 g / mL to 0.02 g / mL; and / or,

[0025] The concentration of the aqueous solution of the imidazole organic ligand is 0.01 g / mL to 0.03 g / mL.

[0026] In one or more embodiments of the present invention, the aqueous solution of the metal salt and the aqueous solution of the imidazole organic ligand are mixed and stirred at 25°C-60°C for 0.5h-4h, and then allowed to stand for precipitation and aging for 1h-24h; and / or,

[0027] The drying temperature is 60℃-100℃, and the time is 8h-12h.

[0028] In one or more embodiments of the present invention, the in-situ carbonization treatment is performed as follows: under an inert atmosphere, the temperature is increased to 600℃-900℃ at a heating rate of 2℃ / min-10℃ / min, and the treatment time is 0.5h-5h.

[0029] Another specific embodiment of the present invention provides the following technical solution:

[0030] The application of a cobalt-based catalyst or a cobalt-based catalyst prepared by a method for preparing cobalt-based catalysts in the catalytic oxidative carbonylation of methanol to synthesize dimethyl carbonate.

[0031] In one or more embodiments of the present invention, the cobalt-based catalyst and methanol are mixed, with a ratio of 0.1g-0.5g of cobalt-based catalyst per 25mL of methanol.

[0032] After the air is vented, the system is pressurized with a raw material gas at a pressure of 2.0 MPa to 4.0 MPa; the raw material gas is composed of CO and O2 with a partial pressure ratio of (30-2):1.

[0033] Under continuous stirring, the reaction was carried out at 100℃-140℃ for 0.5h-4h.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The cobalt-based catalyst prepared by this invention has higher selectivity than traditional copper-based catalysts, which can increase the selectivity of DMC from 95.0% to over 99.0%, and at the same time has a high methanol conversion rate, which is beneficial to reducing the purification and separation cost of the product DMC.

[0036] 2. The cobalt-based catalyst prepared in this invention exhibits significantly better reaction stability compared to similar cobalt-based catalysts reported in the literature. After five cycles of reuse, it still maintains high methanol conversion, DMC selectivity, and DMC space-time yield, demonstrating good potential for industrial application.

[0037] 3. The cobalt-based catalyst prepared by this invention is a solid catalyst. In the methanol liquid-phase oxidative carbonylation synthesis of DMC, the catalyst after the reaction is easy to separate. It can be separated by plate and frame filtration, centrifugation and other methods, which reduces the subsequent separation cost. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 The image shows the XRD pattern of the cobalt-based catalyst in Example 4 of this invention.

[0040] Figure 2 This is a TEM image of the cobalt-based catalyst in Example 4 of the present invention;

[0041] Figure 3 The N2 physical adsorption-desorption curves of the cobalt-based catalyst in Example 4 of this invention are shown. Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0043] To address the limitations of existing homogeneous copper-based catalysts, such as insufficient activity and separation difficulties, and heterogeneous cobalt-based catalysts, which exhibit low activity, this invention synthesizes a ZIF-67 precursor followed by pyrolysis to prepare a mesoporous carbon-based catalyst with highly dispersed cobalt nanoparticles. Based on this, the influence of the cobalt-based catalyst preparation process on its precursor structure and final catalytic performance is systematically investigated. A method for synthesizing ZIF-derived cobalt-based catalysts using inexpensive metals as raw materials, exhibiting both high selectivity and high reaction stability, is proposed.

[0044] The preparation method of the cobalt-based catalyst of the present invention involves dissolving cobalt salt, zinc salt, and organic ligands in an aqueous solvent, respectively, and complexing them with the organic ligands by changing the atomic ratio of the metals to form ZIF-67 with different metal atomic ratios. After drying the ZIF-67, it is physically mixed with an organic nitrogen source and then subjected to in-situ carbonization treatment at 600℃-900℃ for 0.5h-5h to obtain the catalyst. N2 physical adsorption-desorption curves, XRD patterns, and TEM characterization results show that the cobalt-based catalyst provided by the present invention has a hierarchical porous structure and highly dispersed cobalt nanoparticles.

[0045] One specific embodiment of the present invention provides a cobalt-based catalyst, which is obtained by in-situ carbonization treatment using at least a cobalt-based precursor and an organic nitrogen source as raw materials; wherein, the raw materials of the cobalt-based precursor include at least a cobalt salt, a zinc salt and an imidazole organic ligand.

[0046] Furthermore, the ratio of the number of cobalt atoms to the sum of the number of cobalt and zinc atoms is 8%-80%, the cobalt salt is at least one of cobalt chloride hexahydrate and cobalt nitrate hexahydrate, the zinc salt is at least one of zinc nitrate hexahydrate and zinc acetate, the imidazole organic ligand is at least one of 2-methylimidazole and 1-methylimidazole, and the organic nitrogen source is at least one of urea and melamine.

[0047] Specifically, this invention optimizes the particle size and structural characteristics of cobalt by controlling the cobalt-zinc atomic ratio and in-situ carbonization conditions, thereby improving the catalytic performance of the cobalt-based catalyst. Compared with traditional copper-based catalysts, the cobalt-based catalyst prepared by this invention exhibits excellent catalytic activity and selectivity in the methanol oxidative carbonylation reaction, with a DMC selectivity exceeding 99%, and good reaction stability. After five cycles of use, the catalyst still maintains a high methanol conversion rate and DMC selectivity, demonstrating good potential for industrial application.

[0048] Another specific embodiment of the present invention provides a method for preparing a cobalt-based catalyst, which specifically includes the following steps:

[0049] Step 1: Prepare an aqueous solution of the metal salt.

[0050] Specifically, a certain volume of water is measured, and according to the atomic ratio of Co / (Co+Zn) of 8%-80%, a certain amount of cobalt salt and zinc salt are weighed out and then dissolved in an aqueous solvent to obtain a metal salt aqueous solution with a concentration of 0.001g / mL-0.02g / mL.

[0051] Step 2: Prepare an aqueous solution of imidazole organic ligand.

[0052] Specifically, a certain volume of water is measured, and a certain amount of organic ligand is weighed according to the molar ratio of Co+Zn to organic ligand of 1:1-1:5. The organic ligand is then dissolved in an aqueous solvent to obtain an aqueous solution of imidazole organic ligand with a concentration of 0.01 g / mL-0.03 g / mL.

[0053] Step 3: Mix the aqueous solution of metal salt and the aqueous solution of imidazole organic ligand, heat and age the mixture, collect the solid product, and dry it to obtain the catalyst precursor.

[0054] Specifically, the metal salt aqueous solution is added to the imidazole organic ligand aqueous solution, stirred at 30℃-60℃ for 0.5h-4h, allowed to stand for precipitation and aging for 1h-24h, the solid product is collected by centrifugation, the solid product is washed with water solvent, and the washed solid product is placed in a vacuum oven at 60℃-100℃ for 8h-12h to obtain the catalyst precursor.

[0055] Step 4: Mix the catalyst precursor and the organic nitrogen source and perform in-situ carbonization to obtain the cobalt-based catalyst.

[0056] Specifically, the catalyst precursor and organic nitrogen source are physically mixed at a mass ratio of 3:(0.5-3), ground for 0.5-30 min, and then subjected to in-situ carbonization treatment at 600-900℃ under an inert atmosphere with a heating rate of 2-10℃ / min for 0.5-5 h to obtain a cobalt catalyst based on a carbon support with a hierarchical porous structure. The high-temperature reactor used in this step is a tubular furnace.

[0057] In this step, before the catalyst precursor is pyrolyzed, an organic nitrogen source is introduced to physically mix with the catalyst precursor to anchor cobalt species, inhibit agglomeration, and achieve high catalyst stability.

[0058] This invention optimizes the dispersion, particle size, and texture properties of cobalt species by precisely controlling the atomic ratio of cobalt and zinc and the amount of organic nitrogen source added, achieving a DMC selectivity of over 99% while maintaining excellent reaction stability (minimal decline in activity and selectivity after five cycles).

[0059] Another specific embodiment of the present invention provides the application of a cobalt-based catalyst in the catalytic oxidative carbonylation of methanol to synthesize dimethyl carbonate.

[0060] Specifically, the cobalt-based catalyst catalyzes the oxidative carbonylation of methanol to synthesize dimethyl carbonate (DMC). This process is suitable for a slurry bed reactor. The reaction conditions are as follows: 0.1g-0.5g of cobalt-based catalyst is used per 25mL of methanol; the cobalt-based catalyst and methanol are mixed; after the slurry bed reactor is sealed and the air is purged, it is pressurized with a feed gas at a total pressure of 2.0MPa-4.0MPa; the feed gas consists of CO and O2 with a partial pressure ratio of 30:1-2:1; under continuous stirring, the reaction is carried out at 100℃-140℃ for 0.5h-4h.

[0061] The present invention will be further described in detail below with reference to specific embodiments.

[0062] Example 1

[0063] The preparation method of the cobalt-based catalyst in this embodiment is as follows:

[0064] (1) 2.4643 g of 2-methylimidazole was weighed and dissolved in 100 mL of water to prepare a transparent solution A. Then, 1.6484 g of zinc nitrate hexahydrate and 0.1344 g of cobalt nitrate hexahydrate were weighed and dissolved in 100 mL of water to form solution B. Under vigorous stirring, solution B was rapidly pumped into solution A, and the reaction was stirred at room temperature for 1 h. After standing and aging for 24 h, the solid obtained by centrifugation and water washing was dried under vacuum at 60 °C for 12 h to obtain the catalyst precursor Zn / Co-ZIF.

[0065] (2) Weigh 3 g Zn / Co-ZIF and 1.0 g urea, physically mix and grind for 0.5 min, then carbonize in an inert atmosphere of argon at 800℃ for 2 h with a heating rate of 10℃ / min. Finally, collect the solid product obtained after carbonization to obtain the cobalt-based catalyst, labeled as 8%Co-N@C-1.0N.

[0066] The performance testing process for the catalytic carbonylation synthesis of dimethyl carbonate from methanol is as follows:

[0067] The activity of the catalyst was evaluated in the liquid-phase methanol oxidative carbonylation reaction, and the results are shown in Table 1. The evaluation conditions were as follows: 25 mL of methanol, 0.5 g of biphenyl, and 0.25 g of the prepared 8% Co-N@C-1.0N catalyst were added to a 100 mL high-pressure reactor. After sealing and purging the air, the reactor was pressurized to a total pressure of 3 MPa, with a CO / O2 molar ratio of 2:1, and reacted at 110 °C for 2 h with stirring. The liquid products after the reaction were analyzed by liquid chromatography. The evaluation results are shown in Table 1.

[0068] Example 2

[0069] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that in Example 1. The difference is that the amount of zinc nitrate hexahydrate used in step (1) is 1.0989 g, the Zn / Co atomic ratio in the obtained cobalt-based catalyst is 10%, and the obtained cobalt-based catalyst is labeled as 10%Co-N@C-1.0N.

[0070] The obtained catalyst was evaluated and analyzed in the methanol oxidative carbonylation reaction under the operating conditions of Example 1. The evaluation results are shown in Table 1.

[0071] Example 3

[0072] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that in Example 1. The difference is that the amount of zinc nitrate hexahydrate used in step (1) is 0.5495 g, the Zn / Co atomic ratio in the obtained cobalt-based catalyst is 20%, and the obtained cobalt-based catalyst is labeled as 20%Co-N@C-1.0N.

[0073] The obtained catalyst was evaluated and analyzed in the methanol oxidative carbonylation reaction under the operating conditions of Example 1. The evaluation results are shown in Table 1.

[0074] Example 4

[0075] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that in Example 1. The difference is that the amount of zinc nitrate hexahydrate used in step (1) is 0.2060 g, the Zn / Co atomic ratio in the obtained cobalt-based catalyst is 40%, and the obtained cobalt-based catalyst is labeled as 40%Co-N@C-1.0N.

[0076] The obtained catalyst was evaluated and analyzed in the methanol oxidative carbonylation reaction under the operating conditions of Example 1. The evaluation results are shown in Table 1.

[0077] Example 5

[0078] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that in Example 1. The difference is that the amount of zinc nitrate hexahydrate used in step (1) is 0.0343 g, the Zn / Co atomic ratio in the obtained cobalt-based catalyst is 80%, and the obtained cobalt-based catalyst is labeled as 80%Co-N@C-1.0N.

[0079] The obtained catalyst was evaluated and analyzed in the methanol oxidative carbonylation reaction under the operating conditions of Example 1. The evaluation results are shown in Table 1.

[0080] Example 6

[0081] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that in Example 4. The difference is that the amount of urea used in step (2) is 3 g, and the resulting cobalt-based catalyst is labeled as 40%Co-N@C-3.0N.

[0082] The obtained catalyst was evaluated and analyzed in the methanol oxidative carbonylation reaction under the operating conditions of Example 1. The evaluation results are shown in Table 1.

[0083] Example 7

[0084] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that in Example 4. The difference is that the amount of urea used in step (2) is 0.75 g, and the resulting cobalt-based catalyst is labeled as 40%Co-N@C-0.75N.

[0085] The obtained catalyst was evaluated and analyzed in the methanol oxidative carbonylation reaction under the operating conditions of Example 1. The evaluation results are shown in Table 1.

[0086] Example 8

[0087] The preparation method of the cobalt-based catalyst in this embodiment is basically the same as that in Example 4. The difference is that the amount of urea used in step (2) is 0.6 g, and the resulting cobalt-based catalyst is labeled as 40%Co-N@C-0.60N.

[0088] Example 9

[0089] The catalyst evaluated in Example 4 was completely separated by centrifugation and vacuum dried at 60°C for 12 hours to completely remove the liquid feedstock and product. The dried catalyst was then evaluated cyclically according to the conditions of Example 1. The above steps were repeated five times. The obtained catalyst was evaluated and analyzed in the methanol oxidative carbonylation reaction under the operating conditions of Example 1. The results of the fifth cycle evaluation are shown in Table 1.

[0090] Comparative Example 1

[0091] The preparation method of the catalyst in this comparative example is basically the same as that in Example 1. The difference is that only 1.747 g of zinc nitrate hexahydrate was used in step (1) to prepare a pure zinc catalyst, which is labeled as Zn-N@C.

[0092] The obtained catalyst was evaluated and analyzed in the methanol oxidative carbonylation reaction under the operating conditions of Example 1. The evaluation results are shown in Table 1.

[0093] Comparative Example 2

[0094] The preparation method of the catalyst in this comparative example is basically the same as that in Example 1. The difference is that only 1.786 g of cobalt nitrate hexahydrate was used in step (1) to prepare a pure cobalt catalyst, which is labeled as Co-N@C.

[0095] The obtained catalyst was evaluated and analyzed in the methanol oxidative carbonylation reaction under the operating conditions of Example 1. The evaluation results are shown in Table 1.

[0096] Performance testing

[0097] 1. Morphology and structural characterization of catalysts

[0098] 1.1 Crystal structure properties of cobalt-based catalysts before and after reaction

[0099] The crystal structure of 40% Co-N@C-1.0N in Example 4 of this invention was characterized using a Rigaku-Smartlab X-ray diffractometer manufactured by Rigaku Corporation of Japan. Figure 1 Wide-angle X-ray diffraction patterns of the PDF standard card for Co and the Co-based catalyst prepared in Example 4 of this invention. From Figure 1 As can be seen, the Co materials prepared in Example 4 all exhibited strong characteristic diffraction peaks of Co metal, indicating the presence of highly crystalline elemental Co in the products. Among them, 44.2°, 51.5°, and 75.8° correspond to the crystal planes of elemental Co (1 1 1), (2 0 0), and (2 2 0), respectively.

[0100] 1.2 Microstructural properties of cobalt-based catalysts before and after reaction

[0101] The crystal structure of the cobalt-based catalyst prepared in Example 4 of this invention was characterized using a JEOL field emission transmission electron microscope (JEM-F200). The results are as follows: Figure 2 As shown. The prepared 40% Co-N@C-1.0N uses carbon material formed by ZIF-67 calcination as a carrier to load uniform cobalt nanoparticles.

[0102] 1.3, N2 adsorption-desorption curves before and after the reaction of the cobalt-based catalyst

[0103] The crystal structure of the cobalt-based catalyst prepared in Example 4 of this invention was characterized using autosorb iQ fully automated gas adsorption, and the results are as follows: Figure 3 As shown in the figure, the sample exhibits a rapid increase in gas adsorption in the low relative pressure region, reaching saturation after a certain pressure. This indicates that both the 40% Co-N@C-1.0N sample before and after the reaction have a large number of microporous structures, and the isotherm shows a distinct hysteresis loop, suggesting the presence of slit-like mesoporous structures induced by intergranular stacking or defects in the material, which promotes the diffusion of reactant molecules.

[0104] Table 1 Catalyst performance evaluation results

[0105]

[0106] In Examples 1-5, the zinc-cobalt ratio was controlled. As shown in Table 1, adjusting the molar ratio of Zn / Co controls the catalyst activity and STY. A low cobalt content results in insufficient effective active sites in the catalyst, leading to a decrease in its ability to catalyze methanol conversion; the pure zinc catalyst is completely unable to achieve the carbonylation synthesis of dimethyl carbonate from methanol. Conversely, an excessively high cobalt content easily causes the agglomeration of cobalt nanoparticles during calcination, thereby reducing its effective specific surface area, decreasing the available active surface for reaction, and ultimately affecting the overall performance of the catalyst. The cobalt-based catalyst shown in Example 4 exhibits excellent DMC selectivity and good catalytic activity.

[0107] In Examples 4 and 6-8, the amount of organic nitrogen source added was adjusted. The results showed that adjusting the amount of organic nitrogen source (urea) added effectively improved the catalytic activity and DMC space-time yield of the catalyst. Appropriate urea addition can supplement nitrogen to the carbon framework during calcination and coordinate with cobalt species, thus anchoring the cobalt particles. However, excessive urea addition will generate an additional carbon layer on the surface of the cobalt nanoparticles during calcination, covering some active sites and reducing the effective reaction surface area of ​​the catalyst, thereby affecting its overall catalytic performance.

[0108] Example 9 tested the catalytic performance of the cobalt-based catalyst after five reaction cycles. The results showed that even after the fifth cycle, the catalyst maintained high DMC selectivity and DMC space-time yield. This confirms that the addition of urea during the preparation process can effectively anchor cobalt species, inhibiting their aggregation, migration, or loss during the reaction, thereby significantly improving the catalyst's reaction stability and reusability, providing a good foundation for its further industrial application.

[0109] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of this disclosure. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this disclosure.

[0110] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A cobalt-based catalyst, characterized in that, The cobalt-based catalyst is obtained by in-situ carbonization of at least a cobalt-based precursor and an organic nitrogen source. The raw materials for the cobalt-based precursor include at least cobalt salt, zinc salt, and imidazole organic ligand.

2. The cobalt-based catalyst according to claim 1, characterized in that, In the cobalt-based catalyst, the ratio of the number of cobalt atoms to the sum of the number of cobalt atoms and zinc atoms is 8%-80%.

3. The cobalt-based catalyst according to claim 1, characterized in that, The cobalt salt is at least one of cobalt chloride hexahydrate and cobalt nitrate hexahydrate; and / or, The zinc salt is at least one of zinc nitrate hexahydrate and zinc acetate; and / or, The imidazole organic ligand is at least one of 2-methylimidazolium and 1-methylimidazolium; and / or, The organic nitrogen source is at least one of urea and melamine.

4. A method for preparing the cobalt-based catalyst according to claim 1, characterized in that, The preparation method includes the following steps: Cobalt salts and zinc salts are dissolved in water to obtain an aqueous solution of the metal salts; The imidazole organic ligand was dissolved in water to obtain an aqueous solution of the imidazole organic ligand. A mixture of an aqueous solution of a metal salt and an aqueous solution of an imidazole organic ligand was heated and aged. The solid product was collected, washed, and dried to obtain the catalyst precursor. The catalyst precursor and organic nitrogen source were mixed and subjected to in-situ carbonization to obtain a cobalt-based catalyst.

5. The method for preparing the cobalt-based catalyst according to claim 4, characterized in that, The cobalt salt and zinc salt are mixed in a ratio of 8% to 80% of the total number of cobalt atoms and zinc atoms; and / or, The molar ratio of the sum of the molar amounts of cobalt and zinc atoms to the organic ligand is 1:(1-5); and / or, The mass ratio of the catalyst precursor to the organic nitrogen source is 3:(0.5-3).

6. The method for preparing the cobalt-based catalyst according to claim 4, characterized in that, The concentration of the aqueous solution of the metal salt is 0.001 g / mL to 0.02 g / mL; and / or, The concentration of the aqueous solution of the imidazole organic ligand is 0.01 g / mL to 0.03 g / mL.

7. The method for preparing the cobalt-based catalyst according to claim 4, characterized in that, The aqueous solutions of the metal salt and the imidazole organic ligand are mixed and stirred at 25℃-60℃ for 0.5h-4h, then allowed to stand for precipitation and aging for 1h-24h; and / or, The drying temperature is 60℃-100℃, and the time is 8h-12h.

8. The method for preparing the cobalt-based catalyst according to claim 4, characterized in that, The in-situ carbonization process is as follows: under an inert atmosphere, the temperature is increased to 600℃-900℃ at a heating rate of 2℃ / min-10℃ / min, and the treatment time is 0.5h-5h.

9. The application of the cobalt-based catalyst of claim 1 or the cobalt-based catalyst prepared by the method of claim 4 in the catalytic reaction of methanol oxidative carbonylation to synthesize dimethyl carbonate.

10. The application according to claim 9, characterized in that, Based on the use of 0.1g-0.5g of cobalt-based catalyst per 25mL of methanol, the cobalt-based catalyst and methanol are mixed. After the air is vented, the system is pressurized with a raw material gas at a pressure of 2.0 MPa to 4.0 MPa; the raw material gas is composed of CO and O2 with a partial pressure ratio of (30-2):

1. Under continuous stirring, the reaction was carried out at 100℃-140℃ for 0.5h-4h.

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