Core-shell structure zinc-cobalt double-monatomic catalyst as well as preparation method and application thereof

Abstract

The invention discloses a core-shell structure zinc-cobalt double-monatomic catalyst and a preparation method and application thereof, and belongs to the technical field of catalyst materials.The preparation method comprises the following steps that ZIF-67 and zinc nitrate hexahydrate are added into methyl alcohol to be evenly mixed, then a methanol solution of 2-methylimidazole is added, stirring and mixing are conducted for 12 h at the normal temperature, centrifugal separation and precipitation are conducted, washing is conducted with methyl alcohol, and a core-shell structure zinc-cobalt double-monatomic catalyst is obtained; drying to obtain a precursor; and calcining the precursor at 850-950 DEG C for 2 hours to obtain the zinc-cobalt double-monatomic catalyst with the core-shell structure, the application comprises the following steps: stirring and mixing the core-shell structure zinc-cobalt double-monatomic catalyst, nitrobenzene, formic acid and a non-polar organic solvent, then introducing nitrogen, and stirring and reacting at 90 DEG C for 1-2 hours to obtain formanilide; the preparation method disclosed by the invention is simple, low in cost, green and safe, and shows excellent catalytic activity and selectivity in N-formylation reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst materials, and specifically relates to a core-shell structure zinc-cobalt double single-atom catalyst and a preparation method and application thereof. Background Art

[0002] N-phenylformamide has another name called formanilide, is a kind of chemical raw material commonly used and important chemical reagent, can be used as the intermediate of synthesizing some optical materials, spices, dyestuff, medicine.The traditional method of synthesizing formanilide is to utilize aniline and formic acid to carry out back flow reaction, and the reaction time is long, and the product yield has only about 60%.Also in the prior art, use aniline and carbonic acid gas and reductive agent (such as hydrogen, borane etc.) as raw material, in the presence of noble metal catalyst (such as Pt, Pd, Au, Rh etc.), use carbonic acid gas as carbonyl source, carry out the method for N-formylation reaction synthesis formanilide, but need to carry out under the harsh conditions such as high temperature and high pressure, inevitably produce by product, the cost of catalyst is also higher, causes production cost to remain high.

[0003] Single-atom catalysts with non-noble metal-N coordination structures show comparable or even better catalytic performance than noble metal catalysts in many aspects. In recent years, nitrogen-doped carbon catalysts (Zn-NC) loaded with zinc single atoms or nitrogen-doped carbon catalysts (Co-NC) loaded with cobalt single atoms derived from zeolitic imidazolate framework (ZIF) materials have excellent catalytic effects in the reduction and N-formylation of nitrobenzene to synthesize formanilide, but still require higher reaction temperatures, longer reaction times, and even higher pressures.

[0004] Therefore, how to prepare a single-atom site catalyst and apply it to the reduction and N-formylation reaction of nitrobenzene to synthesize formanilide, so as to achieve the purpose of easy and cheap raw materials, mild and safe reaction conditions, and high yield of target products, is a technical problem that needs to be solved at present. Summary of the invention

[0005] The purpose of the present invention is to provide a core-shell structure zinc-cobalt double single-atom catalyst and a preparation method and application thereof, so as to solve the problems in the background technology.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing a core-shell structured zinc-cobalt double single-atom catalyst comprises the following steps:

[0008] Step A1, dissolving cobalt nitrate hexahydrate in methanol by ultrasonic wave to obtain a cobalt nitrate solution; then dissolving 2-methylimidazole in methanol by ultrasonic wave, adding the cobalt nitrate solution at room temperature and stirring for 24 hours, separating the precipitate by centrifugation and washing it with methanol, and drying it at 60° C. overnight to obtain ZIF-67;

[0009] Step A2, adding ZIF-67 and zinc nitrate hexahydrate into methanol and mixing them evenly, then adding a methanol solution of 2-methylimidazole, stirring and mixing at room temperature for 12 hours, centrifuging and separating the precipitate, washing with methanol, and drying to obtain a precursor; the precursor uses ZIF-67 as the central core site for growing ZIF-8, thereby fixing zinc ions on the surface of ZIF-67, and the ZIF-8 formed by epitaxial growth is anchored on the surface of ZIF-67, forming a core-shell structure of ZIF-67@ZIF-8;

[0010] Step A3, calcining the precursor at 850-950° C. for 2 h to obtain a core-shell structured zinc-cobalt double single-atom catalyst.

[0011] Furthermore, the usage ratio of the cobalt nitrate hexahydrate to methanol is 5 mmol:100 mL; and the usage ratio of the 2-methylimidazole to methanol is 40 mmol:100 mL.

[0012] Furthermore, the dosage ratio of ZIF-67, zinc nitrate hexahydrate, methanol, and 2-methylimidazole methanol solution is 0.3-0.5 g: 14 g: 400 mL: 320 mL; the concentration of the 2-methylimidazole methanol solution is 0.6 M. If the dosage of ZIF-67 is too low, the cobalt content in the catalyst will be reduced, resulting in a reduction in catalytic active sites, thereby affecting the catalytic performance of the core-shell structure zinc-cobalt double single-atom catalyst; if the dosage of ZIF-67 is too high, the cobalt in the catalyst will form cobalt nanoclusters, which will reduce the catalytic effect.

[0013] A core-shell structured zinc-cobalt double single-atom catalyst is prepared by the above preparation method.

[0014] Furthermore, the core-shell structure zinc-cobalt double single-atom catalyst is a core-shell structure zinc-cobalt double single-atom catalyst formed by using a nitrogen-doped carbon material loaded with a cobalt single atom as a core and a nitrogen-doped carbon material loaded with a zinc single atom as a shell. The catalyst has a rhombic dodecahedral structure, and the catalyst surface has obvious wrinkles and microporous structures. Such a structure improves the mass transfer effect, thereby improving the conversion rate.

[0015] Application of a core-shell structured zinc-cobalt double single-atom catalyst in catalyzing the reduction and N-formylation of nitrobenzene to prepare formanilide, specifically comprising the following steps:

[0016] Add a core-shell structure zinc-cobalt double single-atom catalyst, nitrobenzene, formic acid and a non-polar organic solvent into a reaction tube and stir to mix. Then, introduce nitrogen into the reaction tube and stir to react at 90° C. and a rotation speed of 1500 r / min for 1-2 hours.

[0017] The reaction process is as follows:

[0018]

[0019] Furthermore, the usage ratio of the core-shell structure zinc-cobalt double single-atom catalyst, nitrobenzene, formic acid and non-polar organic solvent is 20 mg: 0.5 mmol: 6-7.5 mmol: 5 mL; the formic acid used in the present invention is reagent-grade formic acid with a content of 88%.

[0020] Furthermore, the non-polar organic solvent is any one of toluene and 1,4-dioxane; preferably, the organic solvent is toluene. According to the principle of like dissolves like, toluene is more suitable for the reductive formylation reaction of nitrobenzene of the present invention.

[0021] Beneficial effects:

[0022] The present invention uses a metal organic framework material ZIF-67 as a core, and a metal organic framework material ZIF-8 as an outer shell coated on the surface of the ZIF-67 core to form a precursor, which is then calcined at a high temperature in a nitrogen atmosphere to obtain a zinc-cobalt double single-atom site catalyst with a core-shell structure, and the cobalt atom is located in the inner core and is not easy to agglomerate or escape during the catalytic reaction. The preparation process of the present invention is simple and fast, low in cost, and green and safe.

[0023] The invention is based on the unique structure of a core-shell structure zinc-cobalt double single-atom catalyst, and applies it to a reduction and N-formylation reaction in which nitrobenzene is used as a substrate and formic acid is used as a reducing agent and a formylation agent at the same time, thereby showing unique catalytic advantages and performances, generating a product formanilide with a conversion rate of more than 95% and a selectivity of more than 93%, and exhibiting excellent catalytic activity and selectivity; and the reaction conditions are mild, and the reaction can be carried out under normal pressure, and the reaction rate is fast, the reaction time is short, and the yield of the product is high, thereby providing a new reference route for the low-cost and high-quality industrial synthesis of formanilide. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below in conjunction with the accompanying drawings.

[0025] Figure 1 This is a transmission electron microscope image of the core-shell structure zinc-cobalt double single-atom catalyst prepared in Example 2 of the present invention at a scale of 100 nm;

[0026] Figure 2 This is a transmission electron microscope image of the core-shell structure zinc-cobalt double single-atom catalyst prepared in Example 2 of the present invention at a scale of 10 nm;

[0027] Figure 3 This is a spherical aberration electron microscope image of the core-shell structure zinc-cobalt double single-atom catalyst prepared in Example 2 of the present invention;

[0028] Figure 4This is the X-ray powder diffraction pattern of the core-shell structure zinc-cobalt double single-atom catalyst prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] A core-shell structured zinc-cobalt double single-atom catalyst is prepared by the following steps:

[0032] Step A1, dissolving 1.43 g (5 mmol) of cobalt nitrate hexahydrate in 100 mL of methanol by ultrasonication to obtain a cobalt nitrate solution; then dissolving 3.24 g (40 mmol) of 2-methylimidazole in 100 mL of methanol by ultrasonication, adding the above cobalt nitrate solution at room temperature, stirring and mixing for 24 hours, separating the precipitate by centrifugation, washing it with methanol, and drying it at 60° C. overnight to obtain ZIF-67;

[0033] Step A2, 0.3 g ZIF-67 and 14 g zinc nitrate hexahydrate were added to 400 mL methanol and mixed evenly, and then 320 mL of 0.6 M 2-methylimidazole methanol solution was added, and the mixture was stirred and mixed at room temperature for 12 h, and the precipitate was separated by centrifugation and washed with methanol, and dried at 60 ° C overnight to obtain a precursor;

[0034] Step A3, calcining the precursor at 850° C. for 2 h to obtain a core-shell structured zinc-cobalt double single-atom catalyst, code-named ZnCo / NC-850.

[0035] Example 2

[0036] A core-shell structured zinc-cobalt double single-atom catalyst is prepared by the following steps:

[0037] Step A1, dissolving 1.43 g of cobalt nitrate hexahydrate in 100 mL of methanol by ultrasonication to obtain a cobalt nitrate solution; then dissolving 3.24 g of 2-methylimidazole in 100 mL of methanol by ultrasonication, adding the above cobalt nitrate solution at room temperature, stirring and mixing for 24 hours, centrifuging and separating the precipitate, washing it with methanol, and drying it at 60° C. overnight to obtain ZIF-67;

[0038] Step A2, 0.4 g ZIF-67 and 14 g zinc nitrate hexahydrate were added to 400 mL methanol and mixed evenly, and then 320 mL of 0.6 M 2-methylimidazole methanol solution was added, and the mixture was stirred and mixed at room temperature for 12 h, and the precipitate was separated by centrifugation and washed with methanol, and dried at 60 ° C overnight to obtain a precursor;

[0039] Step A3: calcining the precursor at 900° C. for 2 h to obtain a core-shell structured zinc-cobalt double single-atom catalyst, code-named ZnCo / NC-900.

[0040] Depend on Figure 1 It can be seen that the core-shell structure zinc-cobalt double single-atom catalyst prepared in this embodiment has a rhombic dodecahedron structure; Figure 2 Obvious wrinkles and microporous structures can be seen; Figure 3 Many bright spots at the atomic level can be seen, proving that the cobalt element in the catalyst is distributed in a single atom; Figure 4 The main characteristic peaks of graphitized carbon are shown in the graphite sample, and no characteristic peaks of cobalt nanoparticles are found, which proves that cobalt is distributed in the form of single atoms and no particle agglomeration occurs.

[0041] Example 3

[0042] A core-shell structured zinc-cobalt double single-atom catalyst is prepared by the following steps:

[0043] Step A1, dissolving 1.43 g of cobalt nitrate hexahydrate in 100 mL of methanol by ultrasonication to obtain a cobalt nitrate solution; then dissolving 3.24 g of 2-methylimidazole in 100 mL of methanol by ultrasonication, adding the above cobalt nitrate solution at room temperature, stirring and mixing for 24 hours, centrifuging and separating the precipitate, washing it with methanol, and drying it at 60° C. overnight to obtain ZIF-67;

[0044] Step A2, 0.5 g ZIF-67 and 14 g zinc nitrate hexahydrate (297.49 47 mmol) were added to 400 mL methanol and mixed evenly, and then 320 mL of 0.6 M 2-methylimidazole methanol solution was added, and the mixture was stirred and mixed at room temperature for 12 h, and the precipitate was separated by centrifugation and washed with methanol, and dried at 60 ° C overnight to obtain a precursor;

[0045] Step A3, calcining the precursor at 950° C. for 2 h to obtain a core-shell structured zinc-cobalt double single-atom catalyst, code-named ZnCo / NC-950.

[0046] Comparative Example 1

[0047] Compared with Example 2, this comparative example is different in that the calcination temperature in step A3 is 800° C., and the other raw materials and steps are the same, thereby obtaining a core-shell structure zinc-cobalt double single-atom catalyst, code-named ZnCo / NC-800.

[0048] Comparative Example 2

[0049] Compared with Example 2, this comparative example is different in that the calcination temperature in step A3 is 1000° C., and the other raw materials and steps are the same, thereby obtaining a core-shell structure zinc-cobalt double single-atom catalyst, code-named ZnCo / NC-1000.

[0050] Comparative Example 3

[0051] Compared with Example 2, the difference between this comparative example is that in step A1, "1.43 g (5 mmol) of cobalt nitrate hexahydrate" is replaced by "1.49 g (5 mmol) of zinc nitrate hexahydrate", and in step A2, "14 g (47 mmol) of zinc nitrate hexahydrate" is replaced by "13.7 g (47 mmol) of cobalt nitrate hexahydrate", that is, the cobalt nitrate hexahydrate and the zinc nitrate hexahydrate in step A1 and step A2 are replaced by equal molar amounts, and the other raw materials and steps are the same, to obtain a core-shell structured cobalt-zinc dual single-atom catalyst, code-named CoZn / NC-900.

[0052] Comparative Example 4

[0053] The difference between this comparative example and Example 2 is that step A1 and step A2 are combined, 1.43 g of cobalt nitrate hexahydrate, 14 g of zinc nitrate hexahydrate and 19 g of 2-methylimidazole are added to 1 L of methanol and stirred for 24 hours, the precipitate is separated by centrifugation and washed with methanol, and dried at 60°C overnight to obtain a precursor; the remaining raw materials and steps are the same to obtain a cobalt-zinc double single-atom catalyst code-named Co / Zn / NC-900.

[0054] Example 4

[0055] Application of a core-shell structured zinc-cobalt double single-atom catalyst in catalyzing the reduction and N-formylation of nitrobenzene to prepare formanilide, specifically comprising the following steps:

[0056] 20 mg of the core-shell structure zinc-cobalt double single-atom catalyst prepared in Example 1, 0.5 mmol of nitrobenzene, 7.5 mmol of formic acid and 5 mL of 1,4-dioxane were added to the reaction tube and stirred to mix. Then nitrogen was introduced into the reaction tube, and the reaction was stirred at 90° C. and 1500 r / min for 2 h.

[0057] Example 5

[0058] Application of a core-shell structured zinc-cobalt double single-atom catalyst in catalyzing the reduction and N-formylation of nitrobenzene to prepare formanilide, specifically comprising the following steps:

[0059] 20 mg of the core-shell structure zinc-cobalt double single-atom catalyst prepared in Example 2, 0.5 mmol of nitrobenzene, 7.5 mmol of formic acid and 5 mL of toluene were added to the reaction tube and stirred to mix. Then nitrogen was introduced into the reaction tube, and the reaction was stirred at 90° C. and 1500 r / min for 2 h.

[0060] Example 6

[0061] Application of a core-shell structured zinc-cobalt double single-atom catalyst in catalyzing the reduction and N-formylation of nitrobenzene to prepare formanilide, specifically comprising the following steps:

[0062] 20 mg of the core-shell structure zinc-cobalt double single-atom catalyst prepared in Example 3, 0.5 mmol of nitrobenzene, 6 mmol of formic acid and 5 mL of toluene were added to the reaction tube and stirred to mix. Then nitrogen was introduced into the reaction tube, and the reaction was stirred at 90° C. and 1500 r / min for 2 h.

[0063] Example 7

[0064] Application of a core-shell structured zinc-cobalt double single-atom catalyst in catalyzing the reduction and N-formylation of nitrobenzene to prepare formanilide, specifically comprising the following steps:

[0065] 20 mg of the core-shell structure zinc-cobalt double single-atom catalyst prepared in Example 2, 0.5 mmol of nitrobenzene, 7.5 mmol of formic acid and 5 mL of toluene were added to the reaction tube and stirred to mix. Then nitrogen was introduced into the reaction tube, and the reaction was stirred at 90° C. and 1500 r / min for 1 h.

[0066] Comparative Example 5

[0067] The difference between this comparative example and Example 5 is that the catalyst prepared in Comparative Example 1 is used to replace the catalyst prepared in Example 2 in equal amount, and the other raw materials and steps are the same.

[0068] Comparative Example 6

[0069] The difference between this comparative example and Example 5 is that the catalyst prepared in Comparative Example 2 is used to replace the catalyst prepared in Example 2 in equal amount, and the other raw materials and steps are the same.

[0070] Comparative Example 7

[0071] The difference between this comparative example and Example 5 is that the catalyst prepared in Comparative Example 3 is used to replace the catalyst prepared in Example 2 in equal amount, and the other raw materials and steps are the same.

[0072] Comparative Example 8

[0073] The difference between this comparative example and Example 5 is that the catalyst prepared in Comparative Example 4 is used to replace the catalyst prepared in Example 2 in equal amount, and the other raw materials and steps are the same.

[0074] Comparative Example 9

[0075] The difference between this comparative example and Example 5 is that the amount of formic acid is reduced from 7.5 mmol to 5 mmol, and the amounts of other raw materials and steps are the same.

[0076] Comparative Example 10

[0077] This comparative example is compared with Example 5, except that an equal amount of toluene is replaced by tetrahydrofuran, and the other raw materials and steps are the same.

[0078] Comparative Example 11

[0079] This comparative example is different from Example 5 in that an equal amount of toluene is replaced by N,N-dimethylformamide, and the other raw materials and steps are the same.

[0080] Comparative Example 12

[0081] The difference between this comparative example and Example 5 is that the reaction temperature is reduced from 90° C. to 80° C., and the remaining raw material amounts and steps are the same.

[0082] Comparative Example 13

[0083] The difference between this comparative example and Example 5 is that the reaction time is reduced from 2 h to 0.5 h, and the remaining raw material amounts and steps are the same.

[0084] The reaction results of Example 4 to Example 7 and Comparative Example 5 to Comparative Example 13 were detected using a TRACE1300 series gas chromatograph, and the product conversion rate and reaction selectivity were recorded. The results are shown in Table 1:

[0085] Table 1

[0086]

[0087]

[0088] It can be seen from the data in Table 1 that the core-shell structured zinc-cobalt double single-atom catalysts prepared in Examples 1 to 3 exhibit excellent catalytic performance in the process of catalyzing the reduction of nitrobenzene and N-formylation to synthesize formanilide; at the same time, the solvent type, reaction temperature and reaction time have a great influence on the conversion rate and selectivity of the above reaction, and a high conversion rate and selectivity can be maintained under the reaction conditions specified in the present invention.

[0089] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0090] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a core-shell structure zinc-cobalt double single-atom catalyst, characterized in that: The steps include: Step A1, dissolving cobalt nitrate hexahydrate in methanol by ultrasonic wave to obtain a cobalt nitrate solution; then dissolving 2-methylimidazole in methanol by ultrasonic wave, adding the cobalt nitrate solution at room temperature, stirring and mixing for 24 hours, centrifuging and separating the precipitate, washing, and drying to obtain ZIF-67; Step A2, adding ZIF-67 and zinc nitrate hexahydrate into methanol and mixing them evenly, then adding a methanol solution of 2-methylimidazole, stirring and mixing at room temperature for 12 hours, centrifuging and separating the precipitate, washing with methanol, and drying to obtain a precursor; Step A3, calcining the precursor at 850-950° C. for 2 h to obtain a core-shell structured zinc-cobalt double single-atom catalyst.

2. The method for preparing a core-shell structure zinc-cobalt double single-atom catalyst according to claim 1, characterized in that: The usage ratio of the cobalt nitrate hexahydrate to methanol is 5 mmol:100 mL; the usage ratio of the 2-methylimidazole to methanol is 40 mmol:100 mL.

3. The method for preparing a core-shell structure zinc-cobalt double single-atom catalyst according to claim 1, characterized in that: The dosage ratio of the ZIF-67, zinc nitrate hexahydrate, methanol, and the methanol solution of 2-methylimidazole is 0.3-0.5 g: 14 g: 400 mL: 320 mL; the concentration of the methanol solution of 2-methylimidazole is 0.6M.

4. A core-shell structure zinc-cobalt double single-atom catalyst, characterized in that: Prepared by the preparation method according to any one of claims 1 to 3.

5. A core-shell structure zinc-cobalt double single-atom catalyst according to claim 4, characterized in that: The core-shell structure has a nitrogen-doped carbon material carrying a single cobalt atom as a core and a nitrogen-doped carbon material carrying a single zinc atom as a shell.

6. Application of a core-shell structure zinc-cobalt double single-atom catalyst, characterized in that: The following steps are involved: Add a core-shell structure zinc-cobalt double single-atom catalyst, nitrobenzene, formic acid and a non-polar organic solvent into a reaction tube and stir to mix. Then, introduce nitrogen into the reaction tube and stir to react at 90° C. for 1-2 hours.

7. The use of a core-shell structure zinc-cobalt double single-atom catalyst according to claim 6, characterized in that: The usage ratio of the core-shell structure zinc-cobalt double single-atom catalyst, nitrobenzene, formic acid and non-polar organic solvent is 20 mg: 0.5 mmol: 6-7.5 mmol: 5 mL.

8. The use of a core-shell structure zinc-cobalt double single-atom catalyst according to claim 6, characterized in that: The non-polar organic solvent is any one of toluene and 1,4-dioxane.

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