Preparation method of cobalt diatom and cobalt cluster catalyst and application of cobalt diatom and cobalt cluster catalyst in cyclohexane oxidation

Abstract

The invention provides a preparation method of a cobalt diatom and cobalt cluster catalyst and application of the cobalt diatom and cobalt cluster catalyst in cyclohexane oxidation. The cobalt-based catalyst has a coordination structure of Co-O and Co-Co, and the cobalt-based catalyst is mainly composed of diatomic cobalt and Co clusters. The cobalt-based metal of the material is relatively dispersed, so that adsorption and activation of cyclohexane are facilitated. The cobalt diatom and cobalt cluster catalyst prepared by the invention has better performance of thermocatalytic cyclohexane oxidation reaction. The conversion rate of cyclohexane is 9.4%, and the selectivity of KA oil is 94.1%. The material has the advantages that synthesis is controllable, cyclohexane oxidation is promoted under the mild condition, the product KA oil has high selectivity, and a feasible thought is provided for industrial large-scale preparation of the KA oil.

Description

Technical Field

[0001] The present invention relates to the application of a dispersed cobalt-based catalyst in cyclohexane oxidation, specifically to the synthesis of a dispersed cobalt-based catalyst and the application of the catalyst in the preparation of cyclohexanol and cyclohexanone through cyclohexane oxidation. Background Art

[0002] Cyclohexane is selectively oxidized to cyclohexanol (C6H 10 O) and cyclohexanone (C6H 11 OH), which is of great significance in industrial production. At the same time, the generated KA oil (K is C6H 10 O and A are C6H 11 OH) is an important precursor for the preparation of adipic acid and caprolactam. In addition, the generated adipic acid is a precursor for the preparation of nylon-6 and nylon-66 [J.Catal.2022,411,135-148.]. However, alkane molecules have a relatively high symmetric structure and a high dissociation energy of the C-H bond [Joule,2019,3(7),1606-1636.]. Therefore, the activation of cyclohexane requires harsh reaction conditions such as high energy input and high-pressure reaction environment [Nat.Commun.2015,6(1),8446.]. Such conditions result in low cyclohexane conversion and product selectivity.

[0003] In addition, compared to thermal catalysis, light as a clean energy source has been used to activate cyclohexane under mild conditions. For example, the team of Academician Fu Xianzhi and others applied chlorine-modified BiOBr / TiO2 to photocatalytic cyclohexane oxidation, achieving a cyclohexane conversion rate of 0.47% and a KA oil selectivity of 82.8% [Angew.Chem.Int.Ed.2013,52(3):1035-1039.]. Similarly, photocatalysts with different components, such as Bi-based catalysts [Appl.Catal.B 2019,251:17-24.], carbon materials [ACS Catal.2014,4(1):328-336.], metal sulfides [ACS SustainableChem.Eng.2020,8(17):6622-6633.], etc. have been applied to the activation of cyclohexane. However, under the optimized reaction conditions, the conversion rate of cyclohexane is still low [ACS Catal. 2017, 7(1): 293-300.], and the conversion rate is less than 1%, which makes it difficult to meet the industrial demand for the expansion of KA oil.

[0004] Photothermal catalysis has the advantages of high reaction activity under mild reaction conditions [Angew.Chem.Int.Ed.2021,60(9):4872-4878.], tunable reaction pathway [Nat.Commun.2017,8(1),14542.], excellent catalyst stability [Angew.Chem.Int.Ed.2020,59(31),12909-12916.], simple catalyst pretreatment process [Chem.Soc.Rev.2021,50(3),2173-2210.] and instantaneous control of the reaction [Nat.Commun.2018,9(1),3027.], etc., which has attracted widespread attention in recent years. Moreover, since the first preparation of Pt1 / FeO by the team of Academician Zhang Tao in 2011, the research progress has been greatly improved. XSingle atom, the concept of single atom catalysis was formally proposed for the first time [Nat.Chem.2011,3(8),634-641.], and single atom catalysts are developing rapidly. In addition, single atom catalysts have advantages such as higher surface free energy [Acc.Chem.Res.2013,46(8),1740-1748.], active valence electrons [Energy Environ.Sci.2020,13(6),1658-1693.], and low unsaturated coordination environment [Angew.Chem.Int.Ed.2020,59(37),15849-15854.], which are conducive to the adsorption of molecules and the effective transfer of charge between metals and supports, as well as further improving reaction performance. However, single atom catalysts cannot break the correlation between adsorption energies in multi-step reactions. The diatomic catalyst not only inherits the advantages of the single-atom catalyst, but also has electronic effects and synergistic effects, and provides redundant sites for the adsorption of multiple intermediates [Acc.Mater.Res.2022,3(6),584-596.], which will help promote the activation of cyclohexane in thermal reactions and photothermal reactions. In addition, according to reports in some literature, single-atom or cluster catalysts dispersed by transition metals such as Co / SBA-15[Mater.Chem.Phys.2020,246:122814.], Co1 / C3N4[Nano Res.2022,15(10),8791-8803.], and CuO@SAPO-34[Angew.Chem.Int.Ed.2020,59(7),2606-2611.] have been used for the oxidation of cyclohexane. Furthermore, some Co single-atom catalysts [Chem 2023, 9, 1017-1035.] and Co diatomic catalysts [Nat. Commun. 2022, 13, 1375.] have also been used for the oxidation of alkanes and methane to methanol. Therefore, inspired by these previous studies, we designed and synthesized Co diatomic and Co cluster catalysts and applied them to the photothermal oxidation of cyclohexane. Summary of the Invention

[0005] The present invention provides a cobalt diatomic and cobalt cluster catalyst for catalyzing the oxidation of cyclohexane to produce KA oil, and applies the catalyst to photothermal catalytic cyclohexane oxidation.

[0006] The preparation method of the cobalt diatomic and cobalt cluster catalyst provided by the present invention comprises the following steps:

[0007] 1) Weigh an appropriate amount of cobalt chloride hexahydrate (CoCl2·6H2O) and dissolve it in a certain volume of deionized water. Separately, weigh an equimolar amount of 2,2′-bipyridine and dissolve it in a suitable volume of methanol. Furthermore, weigh an appropriate amount of oxalic acid (H2C2O4) and dissolve it in a suitable volume of deionized water. The molar ratio of CoCl2·6H2O to 2,2′-bipyridine and H2C2O4 is 1:1:0.5.

[0008] 2) Under magnetic stirring, add the 2,2′-bipyridine solution and the oxalic acid solution dropwise to the cobalt chloride aqueous solution, and then continue stirring for 1 hour;

[0009] 3) The mixed solution obtained in the previous step is centrifuged and washed with deionized water and methanol, and the obtained solid is placed in a vacuum drying oven for drying to finally obtain a light pink solid, which is a cobalt dimer complex compound;

[0010] 4) Weighing an appropriate amount of urea into a 50 mL crucible, covering it, and placing it in a muffle furnace at a temperature of 520-550° C. for pyrolysis for 3-8 hours to finally prepare a carbon material;

[0011] 5) Weighing an appropriate amount of a cobalt dimer complex compound and dispersing it in an appropriate volume of methanol. Separately, weighing an appropriate amount of a carbon material and dispersing it in a certain volume of methanol. Under magnetic stirring, the methanol solution of the cobalt dimer complex compound is added dropwise to the methanol solution of the carbon material.

[0012] 6) drying the mixed solution on a hot plate at 25-80°C for 5-36 hours to obtain a carbon material;

[0013] 7) Place the carbon material obtained in the previous step in a tube furnace in an air atmosphere at a temperature of 200-280°C and an air flow rate of 5-100 mL min -1 The pyrolysis is carried out within a range of 2 to 15 hours.

[0014] Based on the above preparation method, the cobalt-based catalyst obtained in the present invention has a coordination structure of Co—O and Co—Co, and the cobalt-based catalyst is mainly composed of diatomic cobalt and Co clusters.

[0015] Furthermore, the present invention provides the use of the cobalt diatomic and cobalt cluster catalysts obtained by the above preparation method in cyclohexane oxidation. The method comprises the following steps:

[0016] 1) Weigh an appropriate amount of the catalytic material prepared in the previous step and place it in a 220 mL reactor. Then, add a magnetic particle and 20 mL of cyclohexane (containing a 0.1 M internal standard chlorobenzene solution). Finally, seal the reactor.

[0017] 2) Then, at room temperature, the reactor was charged with 25% O2 / N2 three times, and then charged with 25% O2 / N2 at 5-50 MPa, and the temperature was set at 100-150°C and the reaction time was set at 0.5-15 hours;

[0018] 3) After the reaction is completed, the reactor is cooled to room temperature, the gas is discharged, and then the liquid is filtered using a 0.45 μm filter membrane. The filtered liquid is placed in a refrigerator for subsequent gas chromatography testing.

[0019] The present invention provides the synthesis and application of cobalt diatomic and cobalt cluster catalysts. The present invention focuses on the application of cobalt diatomic and cobalt cluster catalysts in cyclohexane oxidation and focuses on the discussion of the synthesis of the catalysts and the study of their application effect in catalyzing cyclohexane oxidation to produce KA oil.

[0020] The present invention uses cobalt diatomic and cobalt cluster catalysts to catalyze the oxidation of cyclohexane to produce KA oil. The reaction temperature is set at 100-160°C and the oxygen pressure is 0.25-1.25 MPa. Furthermore, at a temperature of 120°C, the catalyst achieved a 9.4% conversion rate and 94.1% KA oil selectivity, achieving high cyclohexane oxidation reaction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Energy dispersive spectra and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images of cobalt diatomic and cobalt cluster catalysts.

[0022] Figure 2 X-ray absorption near-edge structure maps and Fourier transform extended X-ray absorption fine structure maps.

[0023] Figure 3 The X-ray powder diffraction patterns of cobalt diatomic and cobalt cluster catalysts.

[0024] Figure 4 Figure 2 shows the reactivity of cobalt diatomic and cobalt cluster catalysts in cyclohexane oxidation. DETAILED DESCRIPTION

[0025] The following content will provide a detailed description of the specific embodiments of the present invention, which is used to illustrate and explain the present invention, but is not intended to limit the present invention in any way.

[0026] Experimental methods without specific conditions specified in the examples are generally performed according to conventional conditions and conditions described in the manual, or according to conditions recommended by the manufacturer; the general equipment, materials, reagents, etc. used are all commercially available unless otherwise specified.

[0027] Example 1

[0028] 1) Weigh a certain amount of CoCl2·6H2O (CuCl2·2H2O and NiCl2·2H2O) and dissolve it in an appropriate volume of deionized water. Separately, weigh a certain amount of 2,2′-bipyridine and dissolve it in an appropriate volume of methanol. Also, weigh a suitable volume of oxalic acid and dissolve it in an appropriate volume of water. The molar ratio of the three compounds, CoCl2·6H2O, 2,2′-bipyridine, and H2C2O4, is 1:1:0.5.

[0029] 2) Under magnetic stirring, 2,2′-bipyridine and oxalic acid were added dropwise to the cobalt chloride hexahydrate solution, and then stirred at room temperature for 1 h to finally prepare a light pink solid.

[0030] 3) The prepared light pink solid is placed in a vacuum drying oven and dried at room temperature for 5-36 hours to obtain a cobalt complex compound.

[0031] 4) Weigh an appropriate amount of urea into a crucible and cover it. Place the crucible in a muffle furnace and pyrolyze at 520-550°C for 3-8 hours. Finally, a light yellow C3N4 carbon material is produced.

[0032] 5) Weigh an appropriate amount of the light pink solid and disperse it in methanol. Separately, weigh a certain amount of C3N4 and disperse it in methanol. While magnetically stirring, add the light pink solid / methanol mixture dropwise to the C3N4 mixture. Dry at 25-80°C.

[0033] 6) The prepared solid was heated at a temperature of 200-280°C in an air atmosphere at an air flow rate of 5-100 mL / min -1 The pyrolysis was carried out in an air atmosphere for 2-15 hours. The powder was characterized by transmission electron microscopy. Figure 1 a-1d shows that Co is evenly distributed on the carbon and nitrogen carrier. In addition, the sample was characterized by aberration-corrected high-angle annular dark field scanning transmission electron microscopy to explore the existence state of the Co element. Figure 1 e shows that Co exists mainly in the form of diatoms (region 1) and clusters (region 2) on the carbon-nitrogen material. X-ray absorption near-edge structure and Fourier transform extended X-ray absorption fine structure tests were performed on the prepared samples to detect the valence state and coordination structure of cobalt. Figure 2 a It can be seen that the valence of cobalt is +2 and Figure 2 b It can be seen that the cobalt diatomic and cobalt cluster catalysts have Co-Co and Co-O(N) bonds. At the same time, the powder was tested by X-ray powder diffraction. Figure 3It can be seen that the carbon-nitrogen framework material was successfully prepared and cobalt oxide was not formed.

[0034] 7) Weigh 5-100 mg of the catalytic material prepared in the previous step and place it in a 220 mL reactor. Add a magnet and an appropriate amount of cyclohexane, then seal the reactor. Inflate and deflate the reactor three times with 25% O₂ / N₂. Set the reactor pressure to 5-50 MPa, the reaction temperature to 100-150°C, the reaction time to 0.5-15 h, and the stirring speed to 50-900 rpm.

[0035] 8) After the reaction is completed, the reactor is cooled to room temperature, and the liquid after the reaction is filtered using a 0.45 μm PTFE filter membrane. The filtered liquid is placed in a refrigerator for subsequent testing.

[0036] 9) Performing GC-Mass testing on the liquid after the reaction to perform qualitative analysis on the sample. Also, performing gas chromatography testing on the liquid after the reaction to achieve the purpose of quantitative analysis on the liquid after the reaction.

[0037] Table 1

[0038]

[0039] Example 2

[0040] The process is carried out in the same manner as in Example 1, except that the pyrolysis temperature in step 6) is 200°C.

[0041] Example 3

[0042] The process was carried out in the same manner as in Example 1, except that the pyrolysis temperature in step 6) was 210°C.

[0043] Example 4

[0044] The process is carried out in the same manner as in Example 1, except that the pyrolysis temperature in step 6) is 220°C.

[0045] Example 5

[0046] The process was carried out in the same manner as in Example 1, except that the pyrolysis temperature in step 6) was 230°C.

[0047] Example 6

[0048] The process is carried out in the same manner as in Example 1, except that the pyrolysis temperature in step 6) is 240°C.

[0049] Example 7

[0050] The process is carried out in the same manner as in Example 1, except that the pyrolysis temperature in step 6) is 250°C.

[0051] Example 8

[0052] The process was carried out in the same manner as in Example 1, except that the pyrolysis temperature in step 6) was 260°C.

[0053] Example 9

[0054] The process is carried out in the same manner as in Example 1, except that the pyrolysis temperature in step 6) is 270°C.

[0055] Example 10

[0056] The process is carried out in the same manner as in Example 1, except that the pyrolysis temperature in step 6) is 280°C.

[0057] Example 11

[0058] The process was carried out in the same manner as in Example 1, except that the air flow rate in step 6) was set to 5 mL min -1 .

[0059] Example 12

[0060] The method of Example 1 was followed, except that the air flow rate in step 6) was set to 10 mL / min. -1 .

[0061] Example 13

[0062] The process was carried out in the same manner as in Example 1, except that the air flow rate in step 6) was set to 20 mL / min. -1 .

[0063] Example 14

[0064] The process was carried out in the same manner as in Example 1, except that the air flow rate in step 6) was set to 30 mL / min. -1 .

[0065] Example 15

[0066] The method of Example 1 was followed, except that the air flow rate in step 6) was set to 40 mL / min. -1 .

[0067] Example 16

[0068] The process was carried out in the same manner as in Example 1, except that the air flow rate in step 6) was set to 50 mL / min. -1 .

[0069] Example 17

[0070] The process was carried out in the same manner as in Example 1, except that the air flow rate in step 6) was set to 60 mL / min. -1 .

[0071] Example 18

[0072] The process was carried out in the same manner as in Example 1, except that the air flow rate in step 6) was set to 70 mL / min. -1 .

[0073] Example 19

[0074] The process was carried out in the same manner as in Example 1, except that the air flow rate in step 6) was set to 80 mL / min. -1 .

[0075] Example 20

[0076] The process was carried out in the same manner as in Example 1, except that the air flow rate in step 6) was set to 90 mL / min. -1 .

[0077] Example 21

[0078] The process was carried out in the same manner as in Example 1, except that the air flow rate in step 6) was set to 100 mL / min. -1 .

[0079] Example 22

[0080] The process was carried out in the same manner as in Example 1, except that the pyrolysis time in step 6) was 2 h.

[0081] Example 23

[0082] The process was carried out in the same manner as in Example 1, except that the pyrolysis time in step 6) was 4 h.

[0083] Example 24

[0084] The process was carried out in the same manner as in Example 1, except that the pyrolysis time in step 6) was 6 h.

[0085] Example 25

[0086] The process was carried out in the same manner as in Example 1, except that the pyrolysis time in step 6) was 8 h.

[0087] Example 26

[0088] The process was carried out in the same manner as in Example 1, except that the pyrolysis time in step 6) was 10 h.

[0089] Example 27

[0090] The process was carried out in the same manner as in Example 1, except that the pyrolysis time in step 6) was 12 h.

[0091] Example 28

[0092] The process was carried out in the same manner as in Example 1, except that the pyrolysis time in step 6) was 14 h.

[0093] Example 29

[0094] The process was carried out in the same manner as in Example 1, except that the pyrolysis time in step 6) was 15 h.

[0095] Example 30

[0096] The method of Example 1 was followed, except that a single factor variable analysis was performed and the type of metal input in step 1) was changed from CoCl2·6H2O to CuCl2·2H2O and NiCl2·2H2O.

[0097] Example 31

[0098] The procedure was carried out in the same manner as in Example 1, except that a single factor variance analysis was performed and the mass of the catalytic material used in step 7) was 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 mg.

[0099] Example 32

[0100] The procedure of Example 1 was followed, except that a single factor analysis was performed on the 25% O2 / N2 pressure in step 7), where the pressures of 25% O2 / N2 were 5, 10, 20, 30, 40, and 50 MPa.

[0101] Example 33

[0102] The process was carried out in the same manner as in Example 1, except that a single factor variable analysis was performed and the reaction temperature in step 7) was 100, 110, 120, 130, 140 and 150°C.

[0103] Example 34

[0104] The procedure of Example 1 was followed, except that a single factor analysis was performed on the reaction time in step 7), where the reaction time was 0.5, 1, 3, 6, 9, 12, and 15 h.

[0105] Example 35

[0106] The method of Example 1 was followed, except that a single factor variance analysis was performed and the stirring speed in step 7) was 50, 100, 200, 300, 400, 500, 600, 700, 800 and 900 rpm.

[0107] The factors such as the type of metal precursor, the quality of the catalytic material, the O2 pressure, the reaction temperature, the reaction time, and the stirring speed were optimized in Examples 30-35. Therefore, the optimal reaction conditions were found to obtain the best catalytic effect of the cyclohexane oxidation reaction catalyzed by the cobalt diatomic and cobalt cluster catalysts. As shown in Table 1 and Figure 4 As shown in the figure, under the optimized reaction conditions, the best performance of the cobalt diatomic and cobalt cluster catalysts in the cyclohexane oxidation reaction was achieved. Among them, the catalytic material achieved a cyclohexane conversion rate of 9.4% and a KA oil selectivity of 94.1%.

[0108] The above content describes in detail the preferred embodiments of the present invention, but the present invention is not limited to the specific details of the above-mentioned implementation steps. Without violating the overall concept of the present invention, those skilled in the art may reasonably improve and regulate the implementation scheme, and these simple improvements and modifications also fall within the scope of protection of the present invention. In particular, the present invention is not limited to cobalt diatomic and cobalt cluster catalysts, and can also be extended to other atomically dispersed catalysts such as single-atom catalysts and diatomic catalysts, which also fall within the scope of protection of the present invention.

[0109] In addition, it should be noted that, in the absence of conflicts, the technical features of each part in the above-mentioned embodiments can be reorganized in an appropriate manner. In order to avoid repetition, the present invention will not further explain the possible reorganization methods. As long as they do not violate the technical concept of the present invention, they should also be regarded as the contents disclosed by the present invention and should also fall within the scope of protection of the present invention.

Claims

1. A method for preparing cobalt diatomic and cobalt cluster catalysts, characterized in that Here are the steps: 1) Weigh an appropriate amount of cobalt chloride hexahydrate CoCl2·6H2O and dissolve it in appropriate deionized water, then weigh an equimolar amount of 2,2′-bipyridine and dissolve it in an appropriate amount of methanol solvent, then weigh an appropriate amount of oxalic acid and dissolve it in appropriate deionized water; 2) While stirring, add the 2,2′-bipyridine solution and the oxalic acid solution dropwise into the cobalt chloride aqueous solution, and after a large amount of precipitate is generated, continue stirring the mixture for 1 hour; 3) The precipitate generated in the previous step is placed in a vacuum drying oven for drying, and finally a light pink solid is obtained, which is a cobalt dimer complex compound; 4) Weigh 20 g of urea into a 50 mL crucible, cover it, and place it in a muffle furnace at 520-550° C. for pyrolysis for 3-8 h to prepare a C3N4 material; 5) Weigh an appropriate amount of the light pink solid and disperse it in the methanol solution. At the same time, weigh an appropriate amount of the C3N4 material prepared in the previous step and disperse it in methanol. Then, under stirring, add the methanol mixture of the light pink solid dropwise to the C3N4 mixture; 6) The powder prepared in the previous step is placed in a tubular furnace and heated at a rate of 2°C / min. The sample is pyrolyzed at a temperature of 200-280°C and an air flow of 5-100 mL in an air atmosphere. The pyrolysis time is set to 2-15 h, and a cobalt-based catalyst is finally prepared.

2. The method for preparing the cobalt diatomic and cobalt cluster catalyst according to claim 1, characterized in that: In step 1), the molar ratio of CoCl2·6H2O, 2,2′-bipyridine and oxalic acid is 1:1:0.

5.

3. The method for preparing the cobalt diatomic and cobalt cluster catalyst according to claim 1, characterized in that: In step 5), the mixed solution is stirred and dried on a hot plate at 25-80°C.

4. Cobalt diatomic and cobalt cluster catalysts prepared by the method according to any one of claims 1 to 3, characterized in that: Cobalt-based catalysts have Co-O and Co-Co coordination structures, and are mainly composed of diatomic cobalt and Co clusters.

5. Use of the cobalt diatomic and cobalt cluster catalysts obtained by the preparation method according to any one of claims 1 to 3 in cyclohexane oxidation.

6. Use of the cobalt diatomic and cobalt cluster catalysts in cyclohexane oxidation according to claim 5, characterized in that The following steps are involved: 1) Weigh an appropriate amount of catalyst and put it into a reactor, add a magnet, add an appropriate cyclohexane solution containing 0.1M chlorobenzene, and seal the reactor; 2) Using 25% O2 / N2, the reactor was charged and discharged three times, and 5-50MPa 25% O2 / N2 was charged. Then, the outlet valve of the reactor was closed. In addition, the reaction temperature of the reactor was set to 100-150°C and the reaction time was set to 0.5-15h to carry out the reaction; 3) After the reaction is completed, the reactor is cooled to room temperature, excess gas is removed, the liquid after the reaction is filtered using a 0.45 μm polytetrafluoroethylene filter membrane, and the filtered liquid is placed in a refrigerator for freezing and storage for subsequent testing; 4) The generated products were quantitatively analyzed by GC-Mass and qualitatively analyzed by gas chromatography.

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