A mesoporous cobalt-zinc bimetallic single-atom catalyst, its preparation method and application

Abstract

This invention discloses a mesoporous cobalt-zinc bimetallic single-atom catalyst, its preparation method, and its application, belonging to the field of catalyst material technology. The method includes the following steps: S1, zinc nitrate hexahydrate and 2-methylimidazole are added to methanol and mixed to obtain solution A and solution B. Solution A is then added to solution B and mixed. The mixture is stirred at room temperature, and after centrifugation, washing, drying, and grinding, ZIF-8 powder is obtained. S2, cobalt nitrate hexahydrate and 1,10-phenanthroline monohydrate are added to methanol and mixed. Then, ZIF-8 powder is added, and the mixture is stirred at 50°C. After centrifugation, washing, drying, and grinding, Co-phen / ZIF-8 powder is obtained. S3, the Co-phen / ZIF-8 powder is calcined to obtain the mesoporous cobalt-zinc bimetallic single-atom catalyst. The catalyst prepared by this invention exhibits excellent performance in the catalytic synthesis of cyclic carbonates.

Description

Technical Field

[0001] This invention belongs to the field of catalyst materials technology, specifically relating to a mesoporous cobalt-zinc bimetallic single-atom catalyst, its preparation method, and its application. Background Technology

[0002] The increasing combustion of fossil fuels in recent years has led to climate and environmental changes, with carbon dioxide (CO2) being the most significant greenhouse gas. The high-value industrial utilization of carbon dioxide is currently a popular research direction. Carbon dioxide can be used to produce fine chemical products such as organic carbonates, urea derivatives, formic acid, and cyclic carbonates, thereby increasing its industrial value. However, the thermodynamic stability and inertness of carbon dioxide mean that converting it into cyclic carbonates under mild reaction conditions remains a considerable challenge.

[0003] Existing technologies use ionic liquids as solvents to improve the synthesis of cyclic carbonates. The anionic moiety in the ionic liquid promotes the ring-opening step in the synthesis of cyclic carbonates, thereby improving the selectivity and catalytic yield of the reaction. However, since ionic liquids are easily miscible with water, they cannot be directly recycled through simple treatment, resulting in poor economic efficiency.

[0004] Using nitrogen-doped carbon as a framework and anchoring metal single atoms thereon, metal single-atom catalysts that are not easily leached or sintered under harsh conditions are formed. Nitrogen-doped carbon-supported metal single-atom catalysts exhibit excellent catalytic performance in various organic reactions such as hydrogenation, oxidation, hydroformylation, and carbon-carbon coupling reactions. However, the pore size of the nitrogen-doped carbon framework is limited, and the catalytic performance of a single metal single atom is also limited. When used to catalyze the synthesis of cyclic carbonate compounds, the conversion rate is low, which cannot meet current production needs.

[0005] Therefore, how to develop a catalyst with high catalytic activity and conversion rate and apply it to the cycloaddition reaction of carbon dioxide and epoxides is a technical problem that needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a mesoporous cobalt-zinc bimetallic single-atom catalyst, its preparation method, and its application, in order to solve the problems in the background art.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A method for preparing a mesoporous cobalt-zinc bimetallic single-atom catalyst includes the following steps:

[0009] Step S1: Add zinc nitrate hexahydrate and 2-methylimidazole to methanol and mix ultrasonically to obtain solution A and solution B. Then add solution A to solution B and mix ultrasonically for 10 min. Stir and react at room temperature for 12 h. After the reaction is complete, centrifuge at 8000 r / min for 3-5 min to separate. Wash with methanol 3-5 times. Then dry in a vacuum oven at 50℃ for 12 h. After grinding, obtain ZIF-8 powder.

[0010] Step S2: Cobalt nitrate hexahydrate and 1,10-phenanthroline monohydrate were added to methanol and ultrasonically mixed until homogeneous. Then ZIF-8 powder was added, and the mixture was stirred at 50°C for 12 h. After centrifugation at 8000 r / min for 3-5 min, the mixture was washed with methanol 3-5 times and then dried in a vacuum oven at 50°C for 12 h. After grinding, Co-phen / ZIF-8 powder was obtained.

[0011] Step S3: Under a nitrogen atmosphere, calcine Co-phen / ZIF-8 powder at 800-1000℃ for 2 hours to obtain a mesoporous cobalt-zinc bimetallic single-atom catalyst.

[0012] Furthermore, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:4; the amount of methanol used is not specifically required, as long as it is sufficient to dissolve the appropriate amount of zinc nitrate hexahydrate and 2-methylimidazole.

[0013] Furthermore, the mass ratio of cobalt nitrate hexahydrate, 1,10-phenanthroline monohydrate, and ZIF-8 powder is 1:4-6:25; the amount of methanol used is not specifically required, as long as it is sufficient to dissolve the appropriate amount of zinc nitrate hexahydrate and 2-methylimidazole.

[0014] A mesoporous cobalt-zinc bimetallic single-atom catalyst was prepared by the above method.

[0015] The application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates includes the following steps:

[0016] A mesoporous cobalt-zinc bimetallic single-atom catalyst was added to an epoxide and N,N-dimethylformamide, followed by the addition of tetrabutylammonium bromide. Carbon dioxide was continuously introduced while heating and stirring to carry out a cycloaddition reaction for 8-10 hours, yielding a cyclic carbonate.

[0017] Furthermore, the ratio of the mesoporous cobalt-zinc bimetallic single-atom catalyst, epoxide, N,N-dimethylformamide, and tetrabutylammonium bromide is 30 mg: 1-30 mmol: 0-3 mL: 50-300 mg. When the amount of epoxide is sufficient to disperse the catalyst and tetrabutylammonium bromide, no additional solvent such as N,N-dimethylformamide is required; when the amount of epoxide is insufficient to completely disperse the catalyst and tetrabutylammonium bromide, an appropriate amount of N,N-dimethylformamide needs to be added to ensure that the reaction proceeds fully.

[0018] Furthermore, the epoxide is any one of styrene oxide, propylene oxide, butane oxide, butene oxide, epichlorohydrin, and bromopropylidene; the purity of the epoxide is ≥98%.

[0019] Furthermore, the heating temperature is 100-120℃; within this temperature range, the conversion rate of the reaction can be maintained at a high level, while below this temperature range, the conversion rate of the reaction will be greatly reduced; the stirring speed is 1000 r / min.

[0020] Beneficial effects:

[0021] This invention first uses zinc nitrate hexahydrate to coordinate with 2-methylimidazolium to form ZIF-8 powder, then uses cobalt nitrate hexahydrate to coordinate with 1,10-phenanthroline monohydrate and coats it on the surface of ZIF-8 to obtain Co-phen / ZIF-8 powder. Finally, the Co-phen / ZIF-8 powder is calcined and pyrolyzed at high temperature to obtain a mesoporous cobalt-zinc bimetallic single-atom catalyst. This invention uses inexpensive raw materials, and the preparation method is simple, safe, and environmentally friendly. The obtained mesoporous cobalt-zinc bimetallic single-atom catalyst is not only low in cost but also has a unique mesoporous structure on its surface. When used to catalyze the cycloaddition reaction of epoxides and carbon dioxide, it has an absolute advantage under mild conditions and can significantly improve the conversion rate of cyclic carbonate products.

[0022] The mesoporous bimetallic single-atom catalyst prepared by this invention contains graphitized nitrogen-doped carbon, the channel structure of ZIF-8, and a surface mesoporous structure. First, the graphitized nitrogen-doped carbon can coordinate with the metal as a Lewis acid-base pair, which is conducive to catalyzing cycloaddition reactions. The original channel structure of ZIF-8 is retained in the catalyst, which can promote medium transfer and product escape, and has good conductivity, enabling rapid electron transfer, thereby improving catalytic activity. Most importantly, by incorporating 1,10-phenanthroline monohydrate, a large number of irregular mesoporous structures can be formed on the catalyst surface, increasing the surface area of ​​the catalyst. This makes the catalytic activity for cycloaddition significantly better than that of the bimetallic single-atom catalyst prepared without 1,10-phenanthroline monohydrate, showing significant progress. Attached Figure Description

[0023] The invention will now be further described with reference to the accompanying drawings.

[0024] Figure 1 This is a high-resolution transmission image of the mesoporous cobalt-zinc bimetallic single-atom catalyst prepared in Example 2 of this invention;

[0025] Figure 2 This is a high-resolution transmission image of the cobalt-zinc bimetallic single-atom catalyst prepared in Comparative Example 3 of this invention.

[0026] Figure 3 These are the XRD patterns of the catalysts prepared in Example 2 and Comparative Example 2 of this invention. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment provides a mesoporous bimetallic single-atom catalyst, which is prepared by the following method:

[0030] Step S1: Add 13.39 g (0.045 mol) zinc nitrate hexahydrate to 375 mL methanol and dissolve by sonication to obtain solution A; add 14.78 g (0.18 mol) 2-methylimidazole to 375 mL methanol and dissolve by sonication to obtain solution B; add solution A to solution B and sonicate for 10 min, then stir and react at room temperature for 12 h. After the reaction is complete, centrifuge at 8000 r / min for 3 min to separate, wash 3 times with methanol, then dry in a vacuum oven at 50 °C for 12 h, and grind to obtain white ZIF-8 powder;

[0031] Step S2: Add 40 mg of cobalt nitrate hexahydrate and 160 mg of 1,10-phenanthroline monohydrate to 50 mL of methanol and sonicate for 10 min. Then add 1 g of ZIF-8 powder and stir at 50 °C for 12 h. Separate by centrifugation at 8000 r / min for 3 min. Wash three times with methanol and dry in a vacuum oven at 50 °C for 12 h. After grinding, obtain purple Co-phen / ZIF-8 powder.

[0032] Step S3: Calcine Co-phen / ZIF-8 powder for 2 hours under a nitrogen atmosphere and at 800°C to obtain a mesoporous cobalt-zinc bimetallic single-atom catalyst, designated m-CoZn-NC1.

[0033] Example 2

[0034] This embodiment provides a mesoporous bimetallic single-atom catalyst, which is prepared by the following method:

[0035] Step S1: Add 13.39g of zinc nitrate hexahydrate to 375mL of methanol and dissolve by sonication to obtain solution A; add 14.78g of 2-methylimidazole to 375mL of methanol and dissolve by sonication to obtain solution B; add solution A to solution B and sonicate for 10min, then stir and react at room temperature for 12h. After the reaction is complete, centrifuge at 8000r / min for 4min to separate, wash 4 times with methanol, then dry in a vacuum oven at 50℃ for 12h, and grind to obtain white ZIF-8 powder;

[0036] Step S2: Add 40 mg of cobalt nitrate hexahydrate and 200 mg of 1,10-phenanthroline monohydrate to 50 mL of methanol and sonicate for 10 min. Then add 1 g of ZIF-8 powder and stir at 50 °C for 12 h. Separate by centrifugation at 8000 r / min for 4 min. Wash with methanol 4 times and dry in a vacuum oven at 50 °C for 12 h. After grinding, obtain purple Co-phen / ZIF-8 powder.

[0037] Step S3: Under a nitrogen atmosphere and at 900°C, Co-phen / ZIF-8 powder was calcined for 2 hours to obtain a mesoporous cobalt-zinc bimetallic single-atom catalyst, designated as m-CoZn-NC2.

[0038] like Figure 1 As shown, the mesoporous cobalt-zinc bimetallic single-atom catalyst prepared in this embodiment is octahedral and has a special mesoporous structure on its surface.

[0039] Example 3

[0040] This embodiment provides a mesoporous bimetallic single-atom catalyst, which is prepared by the following method:

[0041] Step S1: Add 13.39g of zinc nitrate hexahydrate to 375mL of methanol and dissolve by sonication to obtain solution A; add 14.78g of 2-methylimidazole to 375mL of methanol and dissolve by sonication to obtain solution B; add solution A to solution B and sonicate for 10min, then stir and react at room temperature for 12h. After the reaction is complete, centrifuge at 8000r / min for 5min to separate, wash 5 times with methanol, and then dry in a vacuum oven at 50℃ for 12h. After grinding, white ZIF-8 powder is obtained.

[0042] Step S2: Add 40 mg of cobalt nitrate hexahydrate and 240 mg of 1,10-phenanthroline monohydrate to 50 mL of methanol and sonicate for 10 min. Then add 1 g of ZIF-8 powder and stir at 50 °C for 12 h. Separate by centrifugation at 8000 r / min for 5 min. Wash with methanol 5 times and dry in a vacuum oven at 50 °C for 12 h. After grinding, obtain purple Co-phen / ZIF-8 powder.

[0043] Step S3: Under a nitrogen atmosphere and at 1000℃, Co-phen / ZIF-8 powder was calcined for 2 hours to obtain a mesoporous cobalt-zinc bimetallic single-atom catalyst, designated as m-CoZn-NC3.

[0044] Comparative Example 1

[0045] The difference between this comparative example and Example 2 is that cobalt nitrate hexahydrate is not added in step S2, while the other raw materials and steps are the same, resulting in a mesoporous zinc single-atom catalyst, designated m-Zn-NC.

[0046] Comparative Example 2

[0047] The difference between this comparative example and Example 2 is that 1,10-phenanthroline monohydrate is not added in step S2, while the other raw materials and steps are the same, resulting in a cobalt-zinc bimetallic single-atom catalyst, designated CoZn-NC.

[0048] like Figure 2 As shown, the cobalt-zinc bimetallic single-atom catalyst prepared in this comparative example retains only the original octahedral and pore structure of ZIF-8, but its surface does not contain mesoporous structure.

[0049] like Figure 3 As shown, the catalysts prepared in Example 2 and Comparative Example 2 both showed only peaks of graphitized carbon, while cobalt and zinc existed in the form of single atoms.

[0050] Comparative Example 3

[0051] The difference between this comparative example and Example 2 is that step S2 is not performed, while the other raw materials and steps are the same, resulting in a zinc single-atom catalyst, designated Zn-NC.

[0052] Example 4

[0053] This embodiment provides an application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates, including the following steps:

[0054] 30 mg of the m-CoZn-NC1 catalyst prepared in Example 1, 30 mmol of styrene oxide and 300 mg of tetrabutylammonium bromide were added to the reaction tube. Then, carbon dioxide with a purity of 99.999% was continuously introduced into the reaction tube. The reaction was carried out under heating and stirring at 100 °C and 1000 rpm for 10 h. After cooling to room temperature, cyclic carbonates were obtained.

[0055] Example 5

[0056] This embodiment provides an application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates, including the following steps:

[0057] 30 mg of the m-CoZn-NC2 catalyst prepared in Example 2, 30 mmol of styrene oxide and 300 mg of tetrabutylammonium bromide were added to the reaction tube. Then, carbon dioxide with a purity of 99.999% was continuously introduced into the reaction tube. The reaction was carried out under heating and stirring at 120 °C and 1000 rpm for 8 h. After cooling to room temperature, cyclic carbonates were obtained.

[0058] Example 6

[0059] This embodiment provides an application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates, including the following steps:

[0060] 30 mg of the m-CoZn-NC3 catalyst prepared in Example 3, 30 mmol of styrene oxide and 300 mg of tetrabutylammonium bromide were added to the reaction tube. Then, carbon dioxide with a purity of 99.999% was continuously introduced into the reaction tube. The reaction was carried out at 110 °C and 1000 rpm for 9 h with heating and stirring. After cooling to room temperature, cyclic carbonate was obtained.

[0061] Example 7

[0062] This embodiment provides an application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates, including the following steps:

[0063] 30 mg of the m-CoZn-NC1 catalyst prepared in Example 1, 30 mmol of styrene oxide and 300 mg of tetrabutylammonium bromide were added to the reaction tube. Then, carbon dioxide with a purity of 99.999% was continuously introduced into the reaction tube. The reaction was carried out under heating and stirring at 100 °C and 1000 rpm for 8 h. After cooling to room temperature, cyclic carbonates were obtained.

[0064] Example 8

[0065] This embodiment provides an application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates, including the following steps:

[0066] 30 mg of the m-CoZn-NC2 catalyst prepared in Example 2, 1 mmol of propylene oxide, 3 mL of N,N-dimethylformamide and 50 mg of tetrabutylammonium bromide were added to a reaction tube. Then, carbon dioxide with a purity of 99.999% was continuously introduced into the reaction tube. The reaction was carried out at 120 °C and 1000 rpm with stirring for 8 h. After cooling to room temperature, cyclic carbonates were obtained.

[0067] Example 9

[0068] This embodiment provides an application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates, including the following steps:

[0069] 30 mg of the m-CoZn-NC2 catalyst prepared in Example 2, 1 mmol of epoxide, 3 mL of N,N-dimethylformamide and 50 mg of tetrabutylammonium bromide were added to a reaction tube. Then, carbon dioxide with a purity of 99.999% was continuously introduced into the reaction tube. The reaction was carried out at 120 °C and 1000 rpm with stirring for 8 h. After cooling to room temperature, cyclic carbonates were obtained.

[0070] Example 10

[0071] This embodiment provides an application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates, including the following steps:

[0072] 30 mg of the m-CoZn-NC2 catalyst prepared in Example 2, 1 mmol of epoxide, 3 mL of N,N-dimethylformamide and 50 mg of tetrabutylammonium bromide were added to a reaction tube. Then, carbon dioxide with a purity of 99.999% was continuously introduced into the reaction tube. The reaction was carried out at 120 °C and 1000 rpm with stirring for 10 h. After cooling to room temperature, cyclic carbonate was obtained.

[0073] Example 11

[0074] This embodiment provides an application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates, including the following steps:

[0075] 30 mg of the m-CoZn-NC2 catalyst prepared in Example 2, 1 mmol of epichlorohydrin, 3 mL of N,N-dimethylformamide and 50 mg of tetrabutylammonium bromide were added to a reaction tube. Then, carbon dioxide with a purity of 99.999% was continuously introduced into the reaction tube. The reaction was carried out at 120 °C and 1000 rpm with stirring for 10 h. After cooling to room temperature, cyclic carbonates were obtained.

[0076] Example 12

[0077] This embodiment provides an application of a mesoporous cobalt-zinc bimetallic single-atom catalyst in the catalytic synthesis of cyclic carbonates, including the following steps:

[0078] 30 mg of the m-CoZn-NC2 catalyst prepared in Example 2, 1 mmol of epichlorohydrin, 3 mL of N,N-dimethylformamide and 50 mg of tetrabutylammonium bromide were added to the reaction tube. Then, carbon dioxide with a purity of 99.999% was continuously introduced into the reaction tube. The reaction was carried out at 120 °C and 1000 rpm with stirring for 8 h. After cooling to room temperature, cyclic carbonates were obtained.

[0079] Comparative Example 4

[0080] The difference between this comparative example and Example 5 is that the reaction temperature is 80°C, while the other steps and parameters are the same.

[0081] Comparative Example 5

[0082] The difference between this comparative example and Example 5 is that the catalyst was replaced in equal amounts with the m-Zn-NC catalyst prepared in Comparative Example 1, while the other raw materials and step parameters were the same.

[0083] Comparative Example 6

[0084] The difference between this comparative example and Example 5 is that the catalyst was replaced in equal amounts with the CoZn-NC catalyst prepared in Comparative Example 2, while the other raw materials and step parameters were the same.

[0085] Comparative Example 7

[0086] The difference between this comparative example and Example 5 is that the catalyst was replaced in equal amounts with the Zn-NC catalyst prepared in Comparative Example 3, while the other raw materials and step parameters were the same.

[0087] The products obtained from Examples 4-12 and Comparative Examples 4-7 were detected using a TRACE1300 series gas chromatograph, and the product conversion rates were recorded. The results are shown in Table 1.

[0088] Table 1

[0089]

[0090] As can be seen from the data in Table 1, the conversion rates of Examples 4-12 are relatively high, and they can be applied to different epoxide substrates. As can be seen from Comparative Example 4, the conversion rate of cyclic carbonates will decrease significantly when the reaction temperature is lower than that set in this application. The conversion rates of Comparative Examples 5-7 are all lower than that of Example 5, indicating that the mesoporous cobalt-zinc bimetallic single-atom catalyst prepared by this invention has superior catalytic performance.

[0091] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0092] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. The application of a mesoporous cobalt-zinc bimetallic single-atom catalyst, characterized in that, Includes the following steps: Mesoporous cobalt-zinc bimetallic single-atom catalyst was added to epoxide and N,N-dimethylformamide, then tetrabutylammonium bromide was added, and carbon dioxide was continuously introduced while heating and stirring for 8-10 hours to obtain cyclic carbonate. The preparation method of the mesoporous cobalt-zinc bimetallic single-atom catalyst includes the following steps: Step S1: Add zinc nitrate hexahydrate and 2-methylimidazole to methanol and mix ultrasonically to obtain solution A and solution B. Then add solution A to solution B and mix ultrasonically until homogeneous. Stir and react at room temperature for 12 hours. After the reaction is complete, centrifuge, wash, dry and grind to obtain ZIF-8 powder. Step S2: Cobalt nitrate hexahydrate and 1,10-phenanthroline monohydrate were added to methanol and ultrasonically mixed until homogeneous. Then, ZIF-8 powder was added, and the mixture was stirred at 50°C for 12 hours. After centrifugation, washing, drying, and grinding, Co-phen / ZIF-8 powder was obtained. The mass ratio of cobalt nitrate hexahydrate, 1,10-phenanthroline monohydrate, and ZIF-8 powder was 1:4-6:

25. Step S3: Calcine Co-phen / ZIF-8 powder for 2 hours under a nitrogen atmosphere and at 800-1000℃ to obtain a mesoporous cobalt-zinc bimetallic single-atom catalyst.

2. The application of the mesoporous cobalt-zinc bimetallic single-atom catalyst according to claim 1, characterized in that, The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:

4.

3. The application of the mesoporous cobalt-zinc bimetallic single-atom catalyst according to claim 1, characterized in that, The ratio of the mesoporous cobalt-zinc bimetallic single-atom catalyst, epoxide, N,N-dimethylformamide and tetrabutylammonium bromide is 30 mg: 1-30 mmol: 0-3 mL: 50-300 mg.

4. The application of the mesoporous cobalt-zinc bimetallic single-atom catalyst according to claim 1, characterized in that, The epoxide is any one of styrene oxide, propylene oxide, butane oxide, butene oxide, epichlorohydrin, and bromopropane oxide.

5. The application of the mesoporous cobalt-zinc bimetallic single-atom catalyst according to claim 1, characterized in that, The heating temperature is 100-120℃; the stirring speed is 1000 r / min.

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