Method for catalyzing one-step oxidation of cyclohexane into adipic acid by using monatomic cobalt catalyst

Abstract

The invention discloses a method for catalyzing one-step oxidation of cyclohexane into adipic acid by using a monatomic cobalt catalyst, and aims to provide a method for one-step oxidation of cyclohexane into adipic acid, with high selectivity and mild reaction conditions. A monatomic cobalt catalyst is adopted to catalyze one-step oxidation of cyclohexane in a solvent to obtain adipic acid; the monatomic cobalt catalyst comprises a functional carrier and monatomic cobalt active sites loaded on the functional carrier; the loading capacity of the monatomic cobalt is 0.1 to 2 weight percent; belongs to the technical field of chemical synthesis and catalysis.

Description

Technical Field

[0001] The invention relates to a method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst, and belongs to the technical field of chemical synthesis. Background Art

[0002] Adipic acid, also known as adipic acid, is an important organic dicarboxylic acid widely used in chemical production, organic synthesis, pharmaceuticals, lubricant manufacturing, and other fields. Its main uses include the production of nylon 66, polyurethane, food additives, high-efficiency lubricants, and plasticizers.

[0003] The traditional cyclohexane oxidation process typically uses a two-step process. In the first step, cyclohexane is oxidized to KA oil using air or oxygen; in the second step, KA oil is further oxidized to adipic acid using nitric acid. This process is mature and dominates adipic acid production. The byproducts are primarily succinic acid and glutaric acid, which are easily separated, resulting in a relatively pure product. However, this process has some significant drawbacks. During the KA oil to adipic acid oxidation stage, nitric acid is used as the oxidant, which consumes a large amount of nitric acid and produces a large amount of harmful nitrogen oxides, which have significant negative impacts on both equipment and the environment. Therefore, the development of efficient and environmentally friendly catalyst systems has become a research hotspot in this field.

[0004] Currently, a variety of catalysts have been used for cyclohexane oxidation, including homogeneous catalysts (such as transition metal complexes) and heterogeneous catalysts (such as supported metal oxides). However, existing catalysts generally suffer from low selectivity, prone to forming intermediates such as cyclohexanone and cyclohexanol, which reduces the yield of adipic acid. Furthermore, the catalysts are prone to deactivation under high temperature and pressure conditions, resulting in a short service life. Summary of the Invention

[0005] In response to the above problems, the purpose of the present invention is to provide a method for the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst. This method has high selectivity, mild reaction conditions, and greatly reduces energy consumption and operational risks.

[0006] To this end, the technical solution provided by the present invention is as follows: A method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst, wherein the one-step oxidation of cyclohexane to adipic acid is catalyzed by the single-atom cobalt catalyst in a solvent in the presence of oxygen or air; The single-atom cobalt catalyst comprises a functionalized support and single-atom cobalt active sites supported on the functionalized support; The loading amount of the single atomic cobalt is 0.1 to 2 wt %.

[0007] Furthermore, the method for catalyzing the one-step oxidation of cyclohexane to adipic acid using the above-mentioned single-atom cobalt catalyst comprises adding cyclohexane, a solvent, and a single-atom cobalt catalyst into a reactor, introducing air or oxygen into the reactor under sealed conditions until the pressure in the reactor reaches 0.3 to 10.0 MPa, stirring and heating to 80 to 200° C., and reacting for 6 to 30 hours; The mass ratio of cyclohexane to solvent is 100:1 to 1:10; The mass ratio of the catalyst to cyclohexane is 1:10 to 1:100; Furthermore, in the method for catalyzing the one-step oxidation of cyclohexane to adipic acid using the above-mentioned single-atom cobalt catalyst, the solvent is at least one of acetic acid, acetone, acetonitrile, cyclohexanone and cyclohexanol.

[0008] Furthermore, the method of catalyzing the one-step oxidation of cyclohexane to adipic acid using the above-mentioned single-atom cobalt catalyst is as follows: cyclohexane, a solvent and a single-atom cobalt catalyst are added to a reactor. The reaction conditions are as follows: under sealed conditions, air or oxygen is introduced until the pressure in the reactor reaches 0.5 to 5.0 MPa, and the reactor is heated to 100 to 150° C. with stirring and reacting for 6 to 24 hours.

[0009] Furthermore, the single-atom cobalt catalyst is used to catalyze the one-step oxidation of cyclohexane to adipic acid, wherein the single-atom cobalt catalyst is prepared by the following steps: 1) Preparation of functionalized carriers; 2) mixing the functionalized support prepared in step 1) with a cobalt salt solution to obtain a mixed solution; 3) aging the mixed solution prepared in step 2), centrifuging, washing, and drying to obtain a catalyst precursor; 4) calcining the catalyst precursor prepared in step 3) at 550-700° C. for 2-4 hours to obtain a single-atom cobalt catalyst.

[0010] Furthermore, in the method for catalyzing the one-step oxidation of cyclohexane to adipic acid using the above-mentioned single-atom cobalt catalyst, the cobalt salt is selected from cobalt nitrate or cobalt chloride.

[0011] Furthermore, in the method for catalyzing the one-step oxidation of cyclohexane to adipic acid using the above-mentioned single-atom cobalt catalyst, the functionalized carrier is at least one of functionalized silica, functionalized alumina, and functionalized ceria.

[0012] Furthermore, the above-mentioned single-atom cobalt catalyst catalyzes the one-step oxidation of cyclohexane to adipic acid: The functionalized silica is prepared by the following steps: tetraethoxysilane, ethanol, concentrated hydrochloric acid and deionized water are mixed and stirred in a mass ratio of 20:17.66:0.035:6.92 to form a sol; the sol is aged and dried to obtain the functionalized silica; The functionalized cerium dioxide is prepared by the following steps: co-precipitating a cerium nitrate hexahydrate solution with a sodium hydroxide solution, washing until neutral, and collecting the precipitate; and drying the precipitate to obtain the functionalized cerium dioxide; The functionalized alumina is prepared by the following steps: aluminum nitrate solution and ammonia water are co-precipitated to generate Al(OH)3, and the functionalized alumina is obtained after centrifugal washing and drying.

[0013] Furthermore, in the method for catalyzing the one-step oxidation of cyclohexane to adipic acid using the above-mentioned single-atom cobalt catalyst, the mass ratio of the cobalt ions in the cobalt salt to the mass ratio of the carrier is 0.001-0.02:1.

[0014] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages: The single-atom Co catalyst provided by the present invention can realize the efficient catalytic oxidation of cyclohexane to produce adipic acid, has a high cyclohexane conversion rate and adipic acid yield, and avoids the environmental pollution problem of nitrogen oxides in the traditional two-step oxidation method. It is green and friendly to the environment and has no harmful gas emissions. DETAILED DESCRIPTION

[0015] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these specific embodiments. Any person skilled in the art who is familiar with the present invention can make equivalent substitutions or changes based on the technical solutions and inventive concepts of the present invention within the technical scope disclosed in the present invention, and these changes should be included in the scope of protection of the present invention.

[0016] The technical solutions provided in the embodiments of the present application, which do not explicitly limit the temperature, are all carried out under room temperature conditions.

[0017] Example 1

[0018] This embodiment provides a method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst. In a 100mL stainless steel autoclave equipped with magnetic stirring, electric heating, a thermocouple, and a pressure display, 0.5g of catalyst 1wt% Co@SiO2, 10.0g of cyclohexane, and 10.0g of acetone were added in sequence. The stainless steel autoclave was sealed, stirred, heated, and the reaction temperature was controlled to 130°C. O2 was introduced to achieve a reaction pressure of 3MPa, and the reaction was continued for 10h. The conversion of cyclohexane was finally quantitatively obtained to be 74.8%, and the selectivity of adipic acid was 80.3%.

[0019] The catalyst 1wt% Co@SiO2 is prepared by the following steps: 1) Preparation of functionalized silica carrier 20.0 g of tetraethoxysilane, 17.66 g of ethanol, 0.0350 g of concentrated hydrochloric acid, and 6.92 g of deionized water were weighed and mixed in appropriate proportions. The mixture was magnetically stirred for 2 hours to obtain a homogeneous, transparent sol. The sol was then aged in a 40°C water bath for 24 hours. The aged sample was then dried in a 120°C oven for 12 hours to obtain a functionalized silica support.

[0020] 2) Preparation of single-atom Co catalysts 2.1) Weigh 0.1977 g of Co(NO3)2·6H2O and dissolve it in 20.0 mL of deionized water to prepare a cobalt nitrate solution; weigh the functionalized silica support prepared in step 1) 4.0 g was dispersed in 40.0 ml of deionized water to form a uniform SiO2 suspension; 2.2) Adding the entire cobalt nitrate solution prepared in step 2.1) dropwise to the SiO2 suspension prepared in step 2.1) to uniformly load the cobalt on the surface of the SiO2 support; stirring was continued for 1 hour after the addition was complete to obtain a mixed solution; 2.3) The mixed solution prepared in step 2.2) was allowed to stand for aging for 12 hours, and then centrifuged to obtain a precipitate; the precipitate was repeatedly washed with deionized water, and the washed precipitate was placed in an oven and dried at 80°C for 12 hours to obtain a Co@SiO2 precursor; 2.4) The Co@SiO2 precursor was transferred to a muffle furnace and calcined at 550°C for 4 hours to obtain a 1 wt% Co@SiO2 single-atom cobalt catalyst.

[0021] Example 2

[0022] This embodiment provides a method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst. In a 100mL stainless steel autoclave with magnetic stirring, electric heating, a thermocouple, and a pressure display, 0.5g of catalyst 1wt% Co@CeO2, 10.0g of cyclohexane, and 10.0g of acetone are added in sequence. The stainless steel autoclave is closed, stirred, heated, and the reaction temperature is controlled to 130°C. O2 is introduced so that the reaction pressure reaches 3MPa, and the reaction is continued for 10h. The conversion rate of cyclohexane is finally quantitatively obtained to be 48.9%, and the selectivity of adipic acid is 73.7%.

[0023] The catalyst 1wt% Co@CeO2 was prepared by the following steps: 1) Preparation of functionalized cerium oxide support Weigh 15.0 g of cerium nitrate hexahydrate and dissolve it in 50 mL of deionized water. Then weigh 7.0 g of NaOH and dissolve it in 20 mL of deionized water. Then, add the sodium hydroxide solution dropwise to the cerium nitrate solution under stirring. After complete addition, continue stirring with magnetic stirring for 12 hours. Then, filter and wash the precipitate until it is neutral. Finally, dry the precipitate in an oven at 80°C for 2 hours to obtain a functionalized cerium oxide support.

[0024] 2) Preparation of single-atom Co catalysts 2.1) Weigh 0.1615 g of CoCl2·6H2O and dissolve it in 20.0 mL of deionized water to prepare a cobalt chloride solution; weigh the functionalized cerium oxide support prepared in step 1) 4.0 g was dispersed in 40.0 ml of deionized water to form a uniform CeO2 suspension; 2.2) Adding the entire cobalt chloride solution prepared in step 2.1) dropwise to the CeO2 suspension prepared in step 2.1) to uniformly load the cobalt on the support surface; after the addition is complete, stirring is continued for 1 hour to obtain a mixed solution; 2.3) The mixed solution prepared in step 2.2) was allowed to stand for aging for 12 hours, followed by centrifugation to obtain a precipitate; the precipitate was repeatedly washed with deionized water; and the washed precipitate was dried in an oven at 80° C. for 12 hours to obtain a Co@CeO2 precursor; 2.4) The Co@CeO2 precursor prepared in step 2.3) was transferred to a muffle furnace and calcined at 700°C for 2 hours to obtain a 1 wt% Co@CeO2 single-atom cobalt catalyst.

[0025] Example 3

[0026] This embodiment provides a method for the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst. 0.5g of catalyst 1wt% Co@Al2O3, 10.0g of cyclohexane, and 10.0g of acetone are added sequentially into a 75mL stainless steel autoclave with magnetic stirring, electric heating, a thermocouple, and a pressure display. The stainless steel autoclave is sealed, stirred, heated, and the reaction temperature is controlled to 130°C. O2 is introduced to achieve a reaction pressure of 3MPa, and the reaction is continued for 10 hours. The conversion of cyclohexane is finally quantitatively obtained to be 33.7%, and the selectivity of adipic acid is 65.0%.

[0027] The catalyst 1wt% Co@Al2O3 was prepared by the following steps: 1) Preparation of functionalized Al2O3 support 1.1) Weigh 20.0 g of Al(NO₃)₃·9H₂O and dissolve it in 100 ml of deionized water to form a uniform ionic solution. Add 160 mL of 1 mol / L ammonia dropwise with stirring. Continue stirring for 1 hour after the addition is complete. Reflux at 60°C for 6 hours to form an Al(OH)₃ precipitate. Centrifuge and wash the solution to remove surface-adsorbed impurities and unreacted precipitant. 1.2) The washed precipitate was placed in an oven and dried at 80°C for 12 hours to obtain a functionalized Al2O3 precursor.

[0028] 2) Preparation of single-atom Co catalysts 2.1) Weigh 0.1977 g of Co(NO₃)₂·6H₂O and dissolve it in 20 mL of deionized water to prepare a cobalt nitrate solution. Weigh 4.0 g of the functionalized Al₂O₃ support prepared in step 1) and disperse it in 40.0 mL of deionized water to form a uniform Al₂O₃ suspension. 2.2) Adding the entire cobalt nitrate solution prepared in step 2.1) dropwise to the Al2O3 suspension prepared in step 2.1) and stirring for 1 hour after the addition is complete to obtain a mixed solution; 2.3) The mixed solution prepared in step 2.2) was allowed to stand for 12 hours, and then centrifuged to obtain a precipitate. The precipitate was repeatedly washed with deionized water and dried in an oven at 80°C for 12 hours to obtain a Co@Al2O3 precursor. 2.4) The Co@Al2O3 precursor was transferred to a muffle furnace and calcined at 550°C for 4 hours to obtain a 1 wt% Co@Al2O3 single-atom cobalt catalyst.

[0029] Example 4

[0030] This embodiment provides a method for the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst. 0.5g of 2wt% Co@Al2O3 catalyst, 10.0g of cyclohexane, and 10.0g of acetone were added sequentially into a 75mL stainless steel autoclave equipped with magnetic stirring, electric heating, a thermocouple, and a pressure display. The stainless steel autoclave was sealed, stirred, heated, and the reaction temperature was controlled to 130°C. O2 was introduced to achieve a reaction pressure of 3MPa, and the reaction was continued for 10h. The conversion of cyclohexane was finally quantitatively obtained to be 53.3%, and the selectivity of adipic acid was 55.0%.

[0031] The preparation steps and parameters of the catalyst 2wt% Co@Al2O3 are basically the same as those of the catalyst 1wt% Co@Al2O3 described in Example 3, with the only difference being that the amount of Co(NO3)2·6H2O used in the preparation step 2.1) is 0.3954 g.

[0032] Example 5

[0033] This embodiment provides a method for the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst. 0.5 g of the catalyst 0.1 wt% Co@Al2O3 prepared in Example 5, 10.0 g of cyclohexane, and 10.0 g of acetone were added sequentially into a 75 mL stainless steel autoclave equipped with magnetic stirring, electric heating, a thermocouple, and a pressure display. The stainless steel autoclave was sealed, stirred, heated, and the reaction temperature was controlled to 130°C. O2 was introduced to achieve a reaction pressure of 3 MPa, and the reaction was continued for 10 hours. The conversion of cyclohexane was finally quantitatively obtained to be 10.2%, and the selectivity of adipic acid was 75.4%.

[0034] The preparation steps and parameters of the catalyst 0.1wt%Co@Al2O3 are basically the same as those of the catalyst 1wt%Co@Al2O3 described in Example 3, with the only difference being that the amount of Co(NO3)2·6H2O used in the preparation step 2.1) is 0.01977 g.

[0035] Example 6

[0036] To a 100 mL stainless steel autoclave equipped with magnetic stirring, electric heating, a thermocouple, and a pressure display, 0.5 g of the 1 wt% Co@SiO2 catalyst prepared in Example 3, 10.0 g of cyclohexane, and the solvents listed in Table 1 were added in sequence. The autoclave was sealed, stirred, heated, and the reaction temperature was controlled at 130°C. O2 was introduced to a pressure of 3 MPa, and the reaction was continued for 10 hours. The relationship between the cyclohexane conversion and adipic acid selectivity of this example and the quality and type of the solvents is shown in Table 1.

[0037] Table 1

[0038] Comparative Example 1 In a 75 mL stainless steel autoclave equipped with magnetic stirring, electric heating, a thermocouple, and a pressure display, 0.5 g of the Co₂O₃-SiO₂ supported catalyst, 10.0 g of cyclohexane, and 10.0 g of acetone were added sequentially. The autoclave was sealed, stirred, and heated at 100°C. O₂ was introduced to a pressure of 1 MPa, and the reaction was continued for 10 hours. The cyclohexane conversion was 10.6%, and the selectivity for adipic acid was 42.4%.

[0039] The Co2O3-SiO2 supported catalyst is prepared by the following steps in sequence: 1) Weigh 1.620 g of Co(NO3)2·6H2O and dissolve it in 40.0 mL of deionized water. Weigh 4.0 g of fumed SiO2 and disperse it in 40.0 mL of deionized water to form a uniform SiO2 suspension.

[0040] 2) Add the entire cobalt salt solution prepared in step 1) dropwise to the SiO2 suspension while stirring continuously. Add sodium hydroxide solution dropwise to adjust the pH to 9 and continue stirring for 2 hours to ensure that the precipitate is evenly distributed on the SiO2 surface, yielding a mixed solution.

[0041] 3) The mixed solution prepared in step 2) was transferred to an autoclave, sealed, and placed in an oven at 150° C. for reaction for 18 hours; the resulting mixture was then centrifuged, washed, and vacuum-dried at 60° C. for 12 hours to obtain a precursor.

[0042] 4) The dried precursor was transferred to a muffle furnace and calcined at 600° C. for 4 hours to obtain a Co2O3-SiO2 supported catalyst, wherein the Co3O4 loading was 10 wt%.

[0043] It can be seen from the above examples and comparative examples that the conversion rate and selectivity of the single-atom cobalt catalyst provided in the examples when catalyzing the one-step oxidation of cyclohexane to adipic acid are significantly higher than the conversion rate and selectivity of the Co2O3-SiO2 supported catalyst used in comparative example 1 when catalyzing the one-step oxidation of cyclohexane to adipic acid.

[0044] The above is merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A method for the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst, characterized in that: In the presence of oxygen or air, a single-atom cobalt catalyst is used to catalyze the one-step oxidation of cyclohexane to adipic acid in a solvent. The single-atom cobalt catalyst comprises a functionalized support and single-atom cobalt active sites supported on the functionalized support; The loading amount of the single atomic cobalt is 0.1 to 2 wt %.

2. The method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst according to claim 1, characterized in that: Add cyclohexane, solvent and single-atom cobalt catalyst into the reactor, and under sealed conditions, introduce air or oxygen until the pressure in the reactor reaches 0.3-10.0 MPa, stir and heat to 80-200° C., and react for 6-30 hours; The mass ratio of cyclohexane to solvent is 100:1 to 1:10; The mass ratio of the catalyst to cyclohexane is 1:10 to 1:

100.

3. The method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst according to claim 1 or 2, characterized in that: The solvent is at least one of acetic acid, acetone, acetonitrile, cyclohexanone and cyclohexanol.

4. The method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst according to claim 2, characterized in that: Add cyclohexane, solvent and single-atom cobalt catalyst into the reactor, and under sealed conditions, introduce air or oxygen until the pressure in the reactor reaches 0.5-5.0 MPa. Stir and heat to 100-150° C. and react for 6-24 hours.

5. The method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst according to claim 1 or 2, characterized in that: The single-atom cobalt catalyst is prepared by the following steps: 1) Preparation of functionalized carriers; 2) mixing the functionalized support prepared in step 1) with a cobalt salt solution to obtain a mixed solution; 3) aging the mixed solution prepared in step 2), centrifuging, washing, and drying to obtain a catalyst precursor; 4) calcining the catalyst precursor prepared in step 3) at 550-700° C. for 2-4 hours to obtain a single-atom cobalt catalyst.

6. The method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst according to claim 5, characterized in that: The cobalt salt is selected from cobalt nitrate or cobalt chloride.

7. The method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst according to claim 5, characterized in that: The functionalized carrier is at least one of functionalized silicon dioxide, functionalized aluminum oxide, and functionalized ceria.

8. The method for the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst according to claim 7, wherein: The functionalized silica is prepared by the following steps: tetraethoxysilane, ethanol, concentrated hydrochloric acid and deionized water are mixed and stirred in a mass ratio of 20:17.66:0.035:6.92 to form a sol; the sol is aged and dried to obtain the functionalized silica; The functionalized cerium dioxide is prepared by the following steps: co-precipitating a cerium nitrate hexahydrate solution with a sodium hydroxide solution, washing until neutral, and collecting the precipitate; and drying the precipitate to obtain the functionalized cerium dioxide; The functionalized alumina is prepared by the following steps: aluminum nitrate solution and ammonia water are co-precipitated to generate Al(OH)3, and the functionalized alumina is obtained after centrifugal washing and drying.

9. The method for catalyzing the one-step oxidation of cyclohexane to adipic acid using a single-atom cobalt catalyst according to claim 5, characterized in that: The mass ratio of the cobalt ions in the cobalt salt to the carrier is 0.001-0.02:1.

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