Preparation method and application of copper-cobalt composite catalyst

Abstract

This invention relates to a method for preparing a copper-cobalt composite catalyst, comprising the following steps: mixing a soluble copper salt, citrate, and water to obtain solution A; adding a cobalt cyanide compound to water to obtain solution B; adding solution B to solution A, stirring to obtain a mixed solution, allowing it to stand for aging, washing and drying to obtain a Prussian blue analog; calcining the Prussian blue analog at 350℃~800℃ in an inert gas or nitrogen atmosphere to obtain the copper-cobalt composite catalyst. This catalyst preparation method is simple, catalyzes the oxidation of cyclohexane with air to obtain adipic acid in one step, is reusable, and has low cost, solving the problems of low yield and poor selectivity of existing catalysts.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalysis and relates to a method for preparing a copper-cobalt composite catalyst and its application. Background Technology

[0002] Adipic acid (AA) is an important chemical raw material for the production of nylon-6,6 polyamide, polyurethane resins, coatings, synthetic fibers, plastics, lubricants, and plasticizers. Global annual AA production exceeds 3.5 million tons, ranking second among all dicarboxylic acids. The two-step oxidation process for AA from cyclohexane is the most traditional and widely used process in industry. First, homogeneous Co salts are used to catalyze the oxidation of cyclohexane to obtain KA oil (a mixture of cyclohexanone and cyclohexanol); then, concentrated nitric acid is used to oxidize the KA oil to obtain adipic acid. This process has low conversion rates, poor selectivity, and very low energy efficiency. Furthermore, the strong oxidizing properties of nitric acid itself not only severely corrode equipment but also generate large amounts of waste acid and waste gas, causing serious environmental pollution and contradicting the principles of green chemistry.

[0003] One-step oxidation to adipic acid is an effective method to overcome the shortcomings of existing cyclohexane oxidation to adipic acid. Currently, homogeneous catalysts, such as porphyrins and metal complexes, are the most studied. However, these catalysts are difficult to separate and recover, and they affect product purity. Heterogeneous catalysts, due to their simple preparation and ease of separation from reactants, are a promising candidate for one-step cyclohexane oxidation to adipic acid. Currently, the types of heterogeneous catalysts used for one-step cyclohexane oxidation to adipic acid include supported molecular sieves, nano-metal oxides, and supported carbon materials. Supported molecular sieves mostly use noble metal components, resulting in high preparation costs; nano-metal oxides have unsatisfactory catalytic effects; and carbon materials are small in size and difficult to recover, thus exhibiting poor recyclability and unsuitability for industrial production. Therefore, there is an urgent need for efficient and recyclable catalysts to achieve industrial catalytic oxidation of cyclohexane to adipic acid. Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, the purpose of this invention is to provide a method for preparing copper-cobalt composite catalysts and their applications.

[0005] This invention provides a method for preparing a copper-cobalt composite catalyst, which includes the following steps:

[0006] A solution A is obtained by mixing a soluble copper salt, a citrate, and water.

[0007] Adding the cobalt cyanide compound to water yields solution B;

[0008] Solution B was added to solution A, stirred to obtain a mixed solution, allowed to stand and age, washed and dried to obtain a Prussian blue analogue;

[0009] The Prussian blue analogue was calcined at 350°C to 800°C in an inert gas or nitrogen atmosphere to obtain the copper-cobalt composite catalyst.

[0010] The present invention also provides the application of the copper-cobalt composite catalyst obtained by the above method in the catalytic oxidation of cyclohexane to prepare adipic acid.

[0011] Compared with existing technologies, the present invention has the following beneficial effects:

[0012] (1) This invention uses a copper-cobalt Prussian blue analogue as a precursor, which is calcined at high temperature under an inert atmosphere or nitrogen to obtain a carbon-nitrogen-doped copper-cobalt composite catalyst. Utilizing the cyano carbon and nitrogen elements within the Prussian blue analogue framework, carbides and nitrides are generated in situ to form the carbon-nitrogen-doped copper-cobalt composite. This overcomes the shortcomings of traditional copper-based catalysts, such as easy metal leaching and low recycling efficiency during use, and meets the requirements of green chemistry development.

[0013] (2) The method of the present invention utilizes in-situ derivatization of Prussian blue to prepare a carbon-nitrogen-doped copper-cobalt composite catalyst, and applies it to the catalytic oxidation of cyclohexane with oxygen to prepare adipic acid. The copper and cobalt metal sites in this method have a synergistic catalytic effect. The cobalt metal species activates oxygen and breaks the CH bond in the cyclohexane conversion to generate cyclohexanone and cyclohexanol; due to its excellent electronegativity, copper metal induces the expression of electrophilic sites, mainly adsorbing and oxidizing the oxygen-containing species cyclohexanone and cyclohexanol, and lowering the reaction energy barrier to further generate adipic acid.

[0014] (3) The Prussian blue derivative used in this invention to prepare the copper-cobalt composite is simple to synthesize, can be separated from the reactants by centrifugation, and can be reused, exhibiting good cycle stability. Compared with traditional methods for preparing nanocomposite metal oxides, the method of this invention simplifies the catalyst preparation process, is low in cost, simple to operate, and suitable for industrial production. Attached Figure Description

[0015] Figure 1 This is a scanning electron microscope image of the Prussian blue analogue obtained in Example 1 of the present invention;

[0016] Figure 2 This is a scanning electron microscope image of the copper-cobalt composite catalyst obtained in Example 1 of the present invention;

[0017] Figure 3 This is a scanning electron microscope image of the copper-cobalt composite catalyst obtained in Example 2 of the present invention;

[0018] Figure 4 This is a scanning electron microscope image of the copper-cobalt composite obtained in Example 3 of the present invention;

[0019] Figure 5This is a scanning electron microscope image of the copper-cobalt composite obtained in Example 4 of the present invention;

[0020] Figure 6 This is a scanning electron microscope image of the copper-cobalt oxide obtained in Comparative Example 1 of the present invention;

[0021] Figure 7 The images show the XRD phase diagrams of the copper-cobalt composites and oxide catalysts obtained in Examples 1-4 and Comparative Example 1 of this invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] This invention provides a method for preparing a copper-cobalt composite catalyst, which includes the following steps:

[0024] S01: Mix soluble copper salt, citrate and water to obtain solution A;

[0025] SO2: Add cobalt cyanide compound to water to obtain solution B;

[0026] S03: Add solution B to solution A, stir to obtain a mixed solution, let stand and age, wash and dry to obtain a Prussian blue analogue;

[0027] S04: The Prussian blue analogue is calcined at 350°C to 800°C in an inert gas or nitrogen atmosphere to obtain the copper-cobalt composite catalyst.

[0028] Specifically, in step S01, the copper salt is a copper ion-containing metal salt containing water of crystallization, such as copper nitrate, copper sulfate, copper chloride, and copper acetate, or copper nitrate containing water of crystallization. The copper-containing metal salts are not limited to those listed above; other commonly used copper-containing metal salts in the art can also be used in this invention. The molar ratio of copper ions in the citrate and soluble copper salt is (0.5–2):1. The citrate can be sodium citrate, potassium citrate, or other citrates.

[0029] Specifically, in step S02, the cobalt cyanide compound is potassium cobalt cyanide or sodium cobalt cyanide. Preferably, the cobalt cyanide compound is potassium cobalt cyanide. The molar ratio of copper to cobalt in the soluble copper salt to cobalt in the cobalt cyanide compound is (1-2):1, for example, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, or 2:1, etc. Preferably, the molar ratio of copper to cobalt in the soluble copper salt to cobalt in the cobalt cyanide compound is (1.3-1.7):1. The concentration of the cobalt cyanide compound in solution B is 5-30 mmol / L.

[0030] In step S03, solution B is added to solution A and stirred to obtain a mixed solution. The volume ratio of solution B to solution A is 1:(0.5~2).

[0031] The stirring can be magnetic stirring; the stirring speed is 300–1000 rpm; the stirring time is 3–10 min. The aging temperature is 20–80℃, for example 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, or 80℃, preferably 20℃–30℃. The aging time is 6–24 h, for example 6 h, 8 h, 12 h, 14 h, 16 h, 20 h, or 24 h, preferably 16 h–24 h.

[0032] Specifically, the aged product is washed three times by alternating washing with ethanol and water and centrifugation at a speed of 6000–8000 rpm for 3–10 min. The centrifuged product is then heat-dried at 80°C with forced air for 6–12 h.

[0033] In step S04, preferably, the calcination atmosphere is argon. The calcination temperature is 350℃~800℃, for example 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, or 700℃. The calcination time is 1h~4h, for example 1h, 2h, 3h, or 4h. After calcination in an inert gas or nitrogen atmosphere, the metal will form low-valence metal oxides, metal carbides, or elemental metals with in-situ doped C and N atoms, which facilitates electron transfer and redox valence state changes.

[0034] Furthermore, this invention provides the application of the copper-cobalt composite catalyst obtained by the above-described method for preparing the copper-cobalt composite catalyst in the catalytic oxidation of cyclohexane to adipic acid.

[0035] In the cyclohexane oxidation reaction, the mass ratio of cyclohexane to copper-cobalt composite catalyst is (100-1000):1, the reaction temperature is 130-160℃, the reaction time is 4-24h, the reaction pressure is 1.0-2.0MPa, the added solvent is acetonitrile, and the mass ratio of acetonitrile to cyclohexane is 8:1.5.

[0036] The following specific examples illustrate the preparation method of the copper-cobalt composite catalyst and its application in the catalytic oxidation of cyclohexane to adipic acid. The copper-cobalt composite catalysts in the following examples can be prepared directly using existing methods; of course, they can also be purchased directly from the market in other examples, and are not limited thereto.

[0037] Example 1 :

[0038] Preparation of copper-cobalt composite catalysts:

[0039] Weigh 0.288g Cu(NO3)2·3H2O and place it in a 200mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0040] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0041] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 24 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain a Prussian blue analogue.

[0042] The Prussian blue analogue was calcined in a tube furnace under argon atmosphere from room temperature to 500°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt composite catalyst.

[0043] Cyclohexane oxidation:

[0044] 0.005 g of the copper-cobalt composite catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 12 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 15.95%, and the selectivity for adipic acid was 65%.

[0045] Example 2 :

[0046] Preparation of copper-cobalt composite catalysts:

[0047] Weigh 0.288g Cu(NO3)2·3H2O and place it in a 200mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0048] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0049] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 24 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain a Prussian blue analogue.

[0050] The Prussian blue analogue was calcined in a tube furnace under argon atmosphere from room temperature to 400°C at a heating rate of 2.5°C / min for 2 hours to obtain the copper-cobalt composite catalyst.

[0051] Cyclohexane oxidation:

[0052] 0.005 g of the copper-cobalt composite catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 12 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 13.25%, and the selectivity of adipic acid was 62.9%.

[0053] Example 3 :

[0054] Preparation of copper-cobalt composite catalysts:

[0055] Weigh 0.288g Cu(NO3)2·3H2O and place it in a 100mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0056] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0057] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 24 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain a Prussian blue analogue.

[0058] The Prussian blue analogue was calcined in a tube furnace under argon atmosphere from room temperature to 600°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt composite catalyst.

[0059] Cyclohexane oxidation:

[0060] 0.005 g of the copper-cobalt composite catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 12 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 13.05%, and the selectivity of adipic acid was 62.4%.

[0061] Example 4 :

[0062] Preparation of copper-cobalt composite catalysts:

[0063] Weigh 0.288g Cu(NO3)2·3H2O and place it in a 100mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0064] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0065] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 24 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain a Prussian blue analogue.

[0066] The Prussian blue analogue was calcined in a tube furnace under argon atmosphere from room temperature to 700°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt composite catalyst.

[0067] Cyclohexane oxidation:

[0068] 0.005 g of the copper-cobalt composite catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 12 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 12.6%, and the selectivity for adipic acid was 61%.

[0069] Example 5 :

[0070] Preparation of copper-cobalt composite catalysts:

[0071] Weigh 0.288g Cu(NO3)2·3H2O and place it in a 100mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0072] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0073] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 12 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain a Prussian blue analogue.

[0074] The Prussian blue was calcined in a tube furnace under an argon atmosphere from room temperature to 500°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt composite catalyst.

[0075] Cyclohexane oxidation:

[0076] 0.005 g of the copper-cobalt composite catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 12 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 12.24%, and the selectivity of adipic acid was 58.6%.

[0077] Example 6:

[0078] Preparation of copper-cobalt composite catalysts:

[0079] Weigh 0.288g Cu(NO3)2·3H2O and place it in a 100mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0080] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0081] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 12 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain a Prussian blue analogue.

[0082] The Prussian blue analogue was calcined in a tube furnace under argon atmosphere from room temperature to 500°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt composite catalyst.

[0083] Cyclohexane oxidation:

[0084] 0.005 g of the copper-cobalt composite catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 2 MPa, and the reaction time was 24 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 14.24%, and the selectivity of adipic acid was 54.6%.

[0085] Example 7:

[0086] Preparation of copper-cobalt composite catalysts:

[0087] Weigh 0.218g Cu(NO3)2·3H2O and place it in a 100mL container. Add 0.395g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0088] 0.2g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0089] Solution B was added dropwise to solution A, aged at room temperature (30°C) for 24 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain a Prussian blue analogue.

[0090] The Prussian blue analogue was calcined in a tube furnace under argon atmosphere from room temperature to 500°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt composite catalyst.

[0091] Cyclohexane oxidation:

[0092] 0.005 g of the copper-cobalt composite catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 24 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 15.14%, and the selectivity for adipic acid was 58.6%.

[0093] Example 8:

[0094] Preparation of copper-cobalt composite catalysts:

[0095] Weigh 0.362g Cu(NO3)2·6H2O and place it in a 100mL container. Add 0.658g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0096] 0.332g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0097] Solution B was added dropwise to solution A, aged at room temperature (35°C) for 8 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain the Prussian blue analogue.

[0098] The Prussian blue analogue was calcined in a tube furnace under argon atmosphere from room temperature to 500°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt composite catalyst.

[0099] Cyclohexane oxidation:

[0100] 0.005 g of the copper-cobalt composite catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 24 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 14.94%, and the selectivity of adipic acid was 64.6%.

[0101] Comparative Example 1 :

[0102] Preparation of copper-cobalt oxide:

[0103] Weigh 0.288g Cu(NO3)3·3H2O and place it in a 100mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0104] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0105] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 24 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain a Prussian blue analogue.

[0106] The Prussian blue analogue was calcined in an air atmosphere in a muffle furnace from room temperature to 500°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt oxide catalyst.

[0107] Cyclohexane oxidation:

[0108] 0.005 g of the copper-cobalt oxide catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 12 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 12.27%, and the selectivity for adipic acid was 52.4%.

[0109] Comparative Example 2 :

[0110] Preparation of copper cobalt cyanide compounds:

[0111] Weigh 0.288g Cu(NO3)3·3H2O and place it in a 100mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0112] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0113] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 24 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain the copper cobalt cyanide compound.

[0114] Cyclohexane oxidation:

[0115] 0.005 g of the copper cobalt cyanide catalyst was weighed, and 1.5 g of cyclohexane and 8 g of acetonitrile were added. The mixture was placed in a high-pressure reactor lined with 50 mL of polytetrafluoroethylene for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 12 h. After the reaction was complete, the products were analyzed by gas chromatography, revealing a cyclohexane conversion rate of 14.36% and an adipic acid selectivity of 45%. Some of the catalyst dissolved during the high-temperature and high-pressure reaction, resulting in a significant reduction in mass and poor recyclability.

[0116] Comparative Example 3:

[0117] Preparation of copper-cobalt composite catalysts:

[0118] Weigh 0.288g Cu(NO3)2·3H2O and place it in a 100mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0119] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0120] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 24 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain the Prussian blue analogue.

[0121] The Prussian blue analogue was calcined in a tube furnace under argon atmosphere from room temperature to 500°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt composite catalyst.

[0122] Cyclohexane oxidation:

[0123] 0.005 g of the copper-cobalt composite catalyst was weighed, and 4 g of cyclohexane and 4 g of acetone were added. The mixture was placed in a high-pressure reactor with a 50 mL polytetrafluoroethylene liner for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 12 h. After the reaction was completed, the products were analyzed by gas chromatography, and the conversion rate of cyclohexane was 10.6%, and the selectivity for adipic acid was 25.8%.

[0124] Comparative Example 4:

[0125] Preparation of copper-cobalt composite catalysts:

[0126] Weigh 0.288g Cu(NO3)2·3H2O and place it in a 100mL container. Add 0.5g sodium citrate and 40mL water, and stir until well mixed to form solution A.

[0127] 0.266g K3[Co(CN)6] was dissolved in 40mL of deionized water to obtain solution B;

[0128] Solution B was added dropwise to solution A, aged at room temperature (25°C) for 24 hours, centrifuged, washed alternately with ethanol and deionized water, and dried in air at 80°C for 24 hours to obtain the Prussian blue analogue.

[0129] The Prussian blue analogue was calcined in a tube furnace under argon atmosphere from room temperature to 500°C for 2 hours at a heating rate of 2.5°C / min to obtain the copper-cobalt composite catalyst.

[0130] Cyclohexane oxidation:

[0131] 0.005 g of the copper-cobalt composite catalyst was weighed and added to 4 g of cyclohexane. The mixture was placed in a high-pressure reactor lined with 50 mL of polytetrafluoroethylene for catalyst performance evaluation. The reaction temperature was 135 °C, the reaction pressure was 1.5 MPa, and the reaction time was 12 h. After the reaction was completed, the products were analyzed by gas chromatography, and the cyclohexane conversion rate was 21%, and the selectivity for adipic acid was 37.6%.

[0132] Depend on Figures 2-5 It can be seen that the copper-cobalt composite catalysts obtained by calcination under an inert atmosphere at different temperatures have different morphologies than those obtained by calcination without calcination and calcination in air. Calcination at 400℃ and 500℃ in an inert atmosphere results in a hollow cage-like cubic structure. As the calcination temperature further increases to 600℃ and 700℃, the cubic shape changes to a plate-like shape and a spindle-shaped shape, respectively. Experimental results demonstrate that the cage-like structure is beneficial for the adsorption of cyclohexane and the desorption of the product. Figure 7 It can be seen that the copper-cobalt composite formed in Example 1 mainly consists of Cu, CoCx, Co, CuO, and CoO in its crystal phase composition. With increasing calcination temperature, the carbides disappear, and the crystal phase composition becomes Cu, Co, CuO, and CoO. Observing the crystal phase composition of Comparative Example 1, calcination in air resulted in a mixture of cobalt tetroxide and copper oxide. Calcination of cyanide at 500°C in an inert atmosphere resulted in the in-situ formation of a metal compound doped with carbon and nitrogen atoms. These heteroatoms play a crucial role in electron transfer and changes in metal valence state. As shown in Table 1 of the XPS energy dispersive spectroscopy data, the copper-cobalt composite obtained in Example 1 has a higher content of pyridine nitrogen and carbon-oxygen bonds compared to the composite metal oxide. This indicates that in-situ doping in an inert atmosphere can increase the number of active species and oxygen activation capacity of the carbon-nitrogen composite metal compound, thereby improving its oxidation performance.

[0133] Table 1

[0134] catalyst pyridine nitrogen % Carbon oxygen % Example 1 70 55 Comparative Example 1 0 42

[0135] In Example 1, the highly active carbon-nitrogen-doped copper-cobalt composite obtained by calcining the prepared copper-cobalt Prussian blue at 500°C was separated and recovered after the reaction. Under the same oxidation performance conditions, the cyclohexane conversion rate remained above 15%, and the adipic acid selectivity was 64-66%, indicating that the derived composite has excellent cyclic stability.

[0136] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. The application of a copper-cobalt composite catalyst in the catalytic oxidation of cyclohexane to adipic acid, wherein the preparation method of the copper-cobalt composite catalyst includes the following steps: A solution A is obtained by mixing a soluble copper salt, a citrate, and water. Adding the cobalt cyanide compound to water yields solution B; Add solution B to solution A, stir to obtain a mixed solution, let stand for 16-24 h, wash and dry to obtain a Prussian blue analogue; The Prussian blue analogue was placed in an inert gas or nitrogen atmosphere at 350°C. o C~800 o The copper-cobalt composite catalyst was obtained by C calcination. The copper-cobalt composite catalyst catalyzes the oxidation of cyclohexane with oxygen to prepare adipic acid. The mass ratio of cyclohexane to the copper-cobalt composite catalyst is (100~1000):1, and the reaction temperature is 130~160°C. o C, the reaction time is 4~24 h, the solvent added is acetonitrile, and the mass ratio of acetonitrile to cyclohexane is 8:1.

5.

2. The application according to claim 1, characterized in that, The soluble copper salt is at least one of copper nitrate, copper sulfate, copper chloride, and copper acetate.

3. The application according to claim 1, characterized in that, The cobalt cyanide compound is potassium cobalt cyanide or sodium cobalt cyanide.

4. The application according to claim 1, characterized in that, The molar ratio of copper in the soluble copper salt to cobalt in the cobalt cyanide compound is (1~2):

1.

5. The application according to claim 1 or 4, characterized in that, The molar ratio of copper to cobalt in the soluble copper salt to cobalt in the cobalt cyanide compound is (1.3~1.7):

1.

6. The application according to claim 1, characterized in that, The concentration of cobalt cyanide in solution B is 5-30 mmol / L.

7. The application according to claim 1, characterized in that, The volume ratio of solution B to solution A is 1:(0.5~2).

8. The application according to claim 1, characterized in that, The roasting atmosphere is argon.

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