A copper-nickel single-atom catalyst based on an MXene support, its preparation method and application

Abstract

The present invention discloses a copper-nickel single-atom catalyst based on an MXene support, its preparation method and application, belonging to the technical field of catalysts, including: an MXene support, on which a copper-nickel single-atom active component is loaded and coated with a nitrogen-doped carbon layer; wherein, the content of the copper-nickel single-atom active component is 0.2~1.5 wt%, and the molar ratio of copper to nickel in the copper-nickel single-atom active component is 1:0.3~1:1.2; the content of the nitrogen-doped carbon coating layer is 7~10 wt%. The copper-nickel single-atom catalyst of the present invention does not contain toxic chromium metal. It adopts a ternary composite system of MXene / copper-nickel single-atom / nitrogen-doped carbon layer. The few-layer MXene support provides rich surface active sites to anchor the copper-nickel single-atom active component through chemical adsorption. The dehydrogenation active center of copper atoms and the cyclization active center of nickel atoms act synergistically, and the antioxidant property and stability of the catalyst are significantly improved by coating with a nitrogen-doped carbon layer, overcoming the technical bottlenecks of low activity, short lifespan and heavy pollution of traditional catalysts, and providing an efficient solution for the green synthesis of lactones.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts. More specifically, the present invention relates to a copper-nickel single-atom catalyst based on an MXene support, a preparation method thereof, and an application thereof. Background Art

[0002] Lactones refer to cyclic esters with the functional group -COO-. They are an important class of organic compounds and intermediates, and are widely used in the fields of medicine, pesticides, and polymer materials. The chemical synthesis methods of lactones mainly include, fundamentally speaking, the catalytic dehydrogenation method of diols, the hydrogenation method of maleic anhydride, the direct cyclization method of unsaturated acids, the Baeyer-villiger oxidation method, and the intramolecular esterification method, etc. Among them, the catalytic dehydrogenation method of diols has become a lactone synthesis method with industrial production value due to its advantages such as simple process, mild reaction conditions, and easy separation of by-products.

[0003] Kangnian et al. prepared a series of Au-based catalysts supported on SnO2 by the deposition-precipitation method for the reaction of dehydrogenating 1,4-butanediol to prepare γ-butyrolactone. At 300 o °C and 2 MPa, the reaction was carried out for 10 h, and the yield of γ-butyrolactone was only 88%. Liu et al. used a CuO / Cr2O3 / Al2O3 catalyst to catalytically dehydrogenate 1,6-hexanediol in the gas phase to prepare ε-caprolactone. At a reaction temperature of 300 °C, a space velocity of 0.08 h -1 , a hydrogen-to-alcohol molar ratio of 8:2, the conversion rate of 1,6-hexanediol reached 100%, but the yield of ε-caprolactone was only 66.2% (Modern Chemical Industry, Vol. 27, No. 10, P41). US Patent US Pat.2,807,629 set the chromium content in the copper / chromium compound catalyst to 10% - 50% to dehydrogenate diethylene glycol in the liquid phase and distill and purify it to obtain the target product, and the maximum yield was only increased to 81%. Zhao et al. prepared a series of Cu-Cr catalysts using ammonia water as a precipitating agent and used them in the dehydrogenation reaction of 1,4-butanediol. Under the conditions of 200 °C, 0.1 MPa, and a liquid volume space velocity of 0.3 h -1 , the highest yield of γ-butyrolactone could reach 94.1%. Patent CN112473675A prepared a catalyst with copper oxide and silicon oxide as active components by the coprecipitation method. Under the conditions of normal pressure, 260 °C, a gas space velocity of 240 h -1 , and a liquid space velocity of 0.3 h -1 , the conversion rate of diethylene glycol was 88.56%, and the selectivity to dioxane-2-one was 92.22%.

[0004] It is not difficult to see from the prior art publicly available at home and abroad that in the preparation of corresponding lactones by the catalytic dehydrogenation method of diols, traditional catalysts such as Cu / Cr and Au / SnO2 have very low diol conversion rates, high reaction condition requirements or contain toxic chromium components. In addition, due to their low specific surface area and poor conductivity, Al2O3 and SiO2 supports often cause the metal active components to sinter and deactivate easily, resulting in a short catalyst life. In short, existing catalysts are difficult to achieve high conversion rate, high selectivity and long life at the same time, and the preparation process is complex and costly. Summary of the Invention

[0005] One object of the present invention is to solve the above problems and / or deficiencies and provide the advantages described hereinafter.

[0006] To achieve these objects and other advantages of the present invention, there is provided a preparation method of a copper-nickel single-atom catalyst based on an MXene support, comprising the following steps:

[0007] S1. Add citric acid and ammonium chloride to water in sequence and stir until dissolved, adjust the pH to prepare an electrolyte; mix Ti3AlC2 powder with a binder, coat it on a titanium foil, dry it and then place it in the electrolyte, control the temperature and voltage for electrolysis to obtain an MXene support; place the MXene support in deionized water, and prepare a suspension by ultrasonic dispersion;

[0008] S2. Dissolve copper compounds and nickel compounds in a mixed solution of water and ethanol, add it to the suspension, stir and impregnate, and obtain an MXene support loaded with copper-nickel single atoms through drying, calcination and reduction;

[0009] S3. Dissolve glucose and melamine in deionized water, add the MXene support loaded with copper-nickel single atoms, mix evenly, transfer it to a reaction kettle, perform hydrothermal reaction, then centrifuge, wash and dry, and perform low-temperature carbonization in a tubular furnace to obtain a copper-nickel single-atom catalyst based on an MXene support coated with a nitrogen-doped carbon coating;

[0010] Wherein, the content of copper-nickel single atoms is 0.2-1.5 wt%, and the molar ratio of copper to nickel in the copper-nickel single atoms is 1:0.3-1:1.2; the content of the nitrogen-doped carbon coating is 7-10 wt%.

[0011] Preferably, in the S1, the pH of the electrolyte is 3-5, the electrolysis temperature is 20-60 °C, and the voltage is 0.2-0.6 V;

[0012] The MXene support is few-layer Ti3C2Tx nanosheets with 2-5 layers;

[0013] The specific surface area of the MXene support > 250 m² / g, and the conductivity > 6×10 5 S / m;

[0014] The binder is polyvinylidene fluoride, and the mass ratio of Ti3AlC2 powder to polyvinylidene fluoride is 9:1;

[0015] The method for adjusting the pH value is to add a pH regulator, and the pH regulator includes any one or a combination of at least two of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonia water, sodium hydroxide, potassium hydroxide, nitric acid, hydrochloric acid, sulfuric acid, acetic acid.

[0016] Preferably, in the S2, the molar ratio of copper in the copper compound to nickel in the nickel compound is 1:0.3 to 1:1.2, and the ratio of the total mass of the copper compound and the nickel compound to the amount of the mixed solution used is 1 g:10 mL to 1 g:13 mL;

[0017] The copper compound includes any one or a combination of at least two of copper nitrate, copper carbonate, copper acetate, copper chloride, copper hydroxide, or copper sulfate;

[0018] The nickel compound includes any one or a combination of at least two of nickel nitrate, nickel sulfate, nickel chloride, nickel phthalocyanine, nickel acetate, nickel citrate, nickel hydroxide;

[0019] The method of calcination is to heat in segments at a temperature of 250 to 500 °C for 3 to 8 h;

[0020] The treatment method of reduction is to heat at a temperature of 200 to 400 °C for 1 to 4 h in an atmosphere of one gas or a mixed gas of hydrogen, carbon monoxide, or nitrogen.

[0021] Preferably, in the S3, the hydrothermal reaction conditions are to react at a temperature of 150 to 220 °C for 6 to 24 h;

[0022] The method of low-temperature carbonization treatment is to heat at a temperature of 300 to 500 °C for 1 to 7 h;

[0023] The mass ratio of glucose to melamine is 1:1 to 3:1, and the ratio of the total mass of glucose and melamine to the amount of deionized water used is 1 g:80 mL to 1 g:150 mL;

[0024] The content of the nitrogen-doped carbon layer is 7 to 10 wt%, and the layer thickness is 1 to 3 nm.

[0025] A copper-nickel single-atom catalyst based on an MXene support, which is prepared by the preparation method of the copper-nickel single-atom catalyst based on the MXene support described above.

[0026] An application of a copper-nickel single-atom catalyst based on an MXene support, and the copper-nickel single-atom catalyst based on the MXene support is applied to catalyze the dehydrogenative cyclization reaction of diol to prepare lactone.

[0027] Preferably, the diol includes any one or a combination of at least two of diethylene glycol, 1,6 - hexanediol, 1,5 - hexanediol, 1,4 - hexanediol, 1,5 - pentanediol, 1,4 - pentanediol, 1,4 - butanediol, or 1,3 - propanediol and their derivatives.

[0028] Preferably, the diol includes any one or a combination of at least two of 1,4 - butanediol, 1,5 - pentanediol, 1,6 - hexanediol, or diethylene glycol and their derivatives.

[0029] Preferably, the raw material for the dehydrogenative cyclization reaction of the diol is the diol, and the process of the dehydrogenative cyclization reaction of the diol is a mixed gasification dehydrogenative cyclization reaction of the diol with a mixed gas of hydrogen and nitrogen to generate the corresponding lactone.

[0030] Preferably, the temperature of the dehydrogenative cyclization reaction of the diol is 200 - 300 °C; the mass space velocity of the dehydrogenative cyclization reaction of the diol is 0.1 - 10 h -1 ; the molar ratio of hydrogen to nitrogen is 0.5:1 - 12:1; the molar ratio of the diol to the mixed gas of hydrogen and nitrogen is 1:1 - 10:1.

[0031] The present invention has at least the following beneficial effects:

[0032] 1. The copper - nickel single - atom catalyst based on the MXene support provided by the present invention adopts a ternary composite system of MXene / copper - nickel single - atom / nitrogen - doped carbon layer. The MXene support provides abundant surface active sites, anchors copper - nickel single - atoms through chemical adsorption to ensure atomic - level dispersion; the dehydrogenation active center of copper atoms and the cyclization active center of nickel atoms act synergistically, and the high conductivity of the support accelerates electron transfer, reduces the activation energy of the reaction, and achieves a double breakthrough of conversion rate > 99% and selectivity > 99%.

[0033] 2. For the copper - nickel single - atom catalyst based on the MXene support provided by the present invention, the surface functional groups (-OH) of the MXene support form covalent bonds of Ti - O - M (M = Cu / Ni) with copper - nickel single - atoms, effectively inhibiting metal migration and agglomeration at high temperatures. The coated nitrogen - doped carbon layer forms a C - Ti bonding interaction with MXene, significantly improving the antioxidant property, avoiding the inactivation of active sites, and the catalyst life exceeds 2000 hours.

[0034] 3. The copper - nickel single - atom catalyst based on the MXene support provided by the present invention can be used in the dehydrogenative cyclization reaction of diols to generate the corresponding lactones, with strong universality. By precisely controlling the structure and electronic properties of the catalyst, high selectivity for the products of the dehydrogenative cyclization reaction of diols is achieved. The reaction by - product is high - purity hydrogen, which can be directly used in the hydrogenation process to realize resource recycling.

[0035] 4. The copper-nickel single-atom catalyst based on the MXene support provided by the present invention does not involve toxic chromium metal throughout the process, overcoming the technical bottlenecks of low activity, short lifespan, and heavy pollution of traditional catalysts, providing an efficient solution for the green synthesis of lactones, and having remarkable technological advancement and commercial potential. Description of the Drawings

[0036] Figure 1 Figure showing the change of conversion rate with time for the catalytic dehydrogenation cyclization reaction of diethylene glycol by catalyst B prepared in Example 2;

[0037] Figure 2 Figure showing the change of selectivity for the formation of p-dicyclohexanone with time for the catalytic dehydrogenation cyclization reaction of diethylene glycol by catalyst B prepared in Example 2. Detailed Embodiments

[0038] The following further describes the present invention in detail with reference to the drawings, so that those skilled in the art can implement it according to the text of the specification.

[0039] It should be understood that the terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0040] Example 1

[0041] S1. Add 9.8 g of citric acid and 5.5 g of ammonium chloride to deionized water in sequence, stir until completely dissolved, add hydrochloric acid to adjust the pH to 3.0, and make up to the mark with a 200 mL volumetric flask to prepare the electrolyte for standby; Mix 9 g of Ti3AlC2 powder with 1 g of polyvinylidene fluoride (PVDF) binder, coat it on the titanium foil, dry it, and place it in the electrolyte. The solid-liquid ratio for electrolytic delamination is 1 g:100 ml, electrolyze at a voltage of 0.4 V for 4 h. After the electrolysis is completed, perform ultrasonic treatment, and centrifuge and wash with deionized water until neutral to obtain dry few-layer Ti3C2Tx nanosheet powder, that is, the MXene support. Disperse 1 g of Ti3C2Tx nanosheet powder in 100 mL of deionized water, and perform ultrasonic treatment for 10 min to prepare a suspension;

[0042] S2. Weigh 7.25 g of copper nitrate trihydrate and 4.24 g of nickel nitrate hexahydrate, dissolve them in a mixed solution of 60 mL of deionized water and 60 mL of ethanol, add them to the suspension, stir and impregnate at room temperature for 2 h, perform centrifugal separation, wash with deionized water, dry at 60 °C for 12 h, calcine in a muffle furnace at 350 °C for 2 h, and reduce with hydrogen at 300 °C for 2 h to obtain Ti3C2Tx powder loaded with copper-nickel single atoms;

[0043] S3. Dissolve 3 g of glucose and 2 g of melamine in 500 mL of deionized water. Add the Ti3C2Tx powder loaded with copper and nickel single atoms, disperse it by ultrasonic treatment, transfer it to a reaction kettle, and carry out hydrothermal reaction at 180 °C for 12 h. Then, carry out centrifugation, washing, and drying, and carbonize it in a tubular furnace under an Ar atmosphere at 500 °C for 2 h to obtain catalyst A (copper-nickel single-atom catalyst based on MXene support).

[0044] Under atmospheric pressure, adjust the temperature to 220 °C. Mix the mixed gas of hydrogen and nitrogen with a molar ratio of 10:1 with diethylene glycol and continuously pass it through a vaporization superheater for vaporization, and then introduce it into a fixed-bed tubular reactor filled with 5 g of catalyst A (copper-nickel single-atom catalyst based on MXene support) for contact reaction. The effluent after the reaction is condensed and separated to obtain the product. The liquid hourly space velocity of diethylene glycol is 0.5 h -1 , and the conversion rate of diethylene glycol is measured to be 99.1% and the selectivity for dioxane is 99.3% by using a gas chromatograph equipped with a packed column GDX-102 for the reaction product. The service life of the catalyst can reach 180 days.

[0045] Example 2

[0046] S1. Add 9.8 g of citric acid and 5.5 g of ammonium chloride to deionized water in sequence and stir until completely dissolved. Dropwise add hydrochloric acid to adjust the pH to 3.0, and make up the volume to 200 mL with a volumetric flask to prepare the electrolyte for standby; Mix 9 g of Ti3AlC2 powder with 1 g of PVDF binder, coat it on a titanium foil, dry it, and place it in the electrolyte. The solid-liquid ratio for electrolytic exfoliation is 1 g:80 ml, and electrolyze at a voltage of 0.4 V for 3 h. After the electrolysis is completed, carry out ultrasonic treatment for 20 min, and centrifuge and wash it with deionized water until neutral to obtain dry few-layer Ti3C2Tx nanosheet powder; Disperse 1 g of Ti3C2Tx nanosheet powder in 100 mL of deionized water and carry out ultrasonic treatment for 10 min to prepare a suspension;

[0047] S2. Weigh 6.04 g of copper nitrate trihydrate and 3.64 g of nickel nitrate hexahydrate, dissolve them in 100 mL of deionized water, add them to the suspension, stir and impregnate at room temperature for 2 h, carry out centrifugal separation, wash with deionized water, dry at 60 °C for 12 h, calcine in a muffle furnace at 400 °C for 2 h, and reduce with hydrogen at 300 °C for 2 h to obtain the Ti3C2Tx powder loaded with copper and nickel single atoms;

[0048] S3. Dissolve 2 g of glucose and 1 g of melamine in 360 mL of deionized water. Add the Ti3C2Tx powder loaded with copper and nickel single atoms, disperse it by ultrasonic treatment, transfer it to a reaction kettle, and carry out hydrothermal reaction at 180 °C for 12 h. Then, carry out centrifugation, washing, and drying, and carbonize it in a tubular furnace under an Ar atmosphere at 500 °C for 2 h to obtain catalyst B.

[0049] At atmospheric pressure, the temperature is adjusted to 230 °C. A mixed gas of hydrogen and nitrogen with a molar ratio of 10:1 is mixed with diethylene glycol and continuously vaporized through a vaporization superheater, and then introduced into a fixed-bed tubular reactor containing 6.5 g of catalyst B for contact reaction. The effluent after the reaction is condensed and separated to obtain the product. The liquid hourly space velocity of diethylene glycol is 0.8 h -1 , and the reaction product is analyzed using a gas chromatograph equipped with a packed column GDX-102, as shown in Figure 1 and Figure 2 . During 180 days of continuous catalytic reaction, the conversion rate of diethylene glycol is measured to be greater than 99.9%, and the selectivity for dicyclohexanone is greater than 99.5%. This not only shows that catalyst B has a high conversion rate of diethylene glycol and selectivity for dicyclohexanone, but also maintains extremely high conversion and selectivity during the 180-day continuous catalytic process, indicating that the service life of catalyst B can reach 180 days.

[0050] Example 3

[0051] S1. 9.8 g of citric acid and 5.5 g of ammonium chloride are successively added to deionized water and stirred until completely dissolved. Hydrochloric acid is added dropwise to adjust the pH to 3.0, and the solution is made up to the mark in a 200 mL volumetric flask to prepare the electrolyte for use. 8 g of Ti3AlC2 powder is mixed with 1 g of PVDF binder, coated on a titanium foil, dried, and placed in the electrolyte. Electrolysis is carried out at a voltage of 0.4 V for 4 h. After the electrolysis is completed, ultrasonic treatment is performed, and the mixture is centrifuged and washed with deionized water until neutral to obtain dry few-layer Ti3C2Tx nanosheet powder;

[0052] S2. 7.25 g of copper nitrate trihydrate and 2.73 g of nickel nitrate hexahydrate are dissolved in a mixed solution of 80 mL of deionized water and 50 mL of ethanol. 2 g of Ti3C2Tx nanosheet powder is added, and the mixture is ultrasonically dispersed for 15 min, stirred and impregnated at room temperature for 4 h, centrifuged and separated, washed with deionized water, dried at 60 °C for 12 h, calcined in a muffle furnace at 350 °C for 2 h, and reduced with hydrogen at 300 °C for 2 h to obtain Ti3C2Tx powder loaded with copper and nickel single atoms.

[0053] S3. 1 g of glucose and 1 g of melamine are dissolved in 260 mL of deionized water. The Ti3C2Tx powder loaded with copper and nickel single atoms is added, and the mixture is ultrasonically dispersed, transferred to a reaction kettle, and hydrothermally reacted at 180 °C for 14 h. After centrifugation, washing, and drying, it is carbonized in a tubular furnace under an Ar atmosphere at 500 °C for 2 h to obtain catalyst C.

[0054] At atmospheric pressure, the temperature is adjusted to 230 °C. A mixed gas of hydrogen and nitrogen with a molar ratio of 8:1 is mixed with diethylene glycol and continuously vaporized through a vaporization superheater, and then introduced into a fixed-bed tubular reactor containing 4 g of catalyst C for contact reaction. The effluent after the reaction is condensed and separated to obtain the product. The liquid hourly space velocity of diethylene glycol is 0.5 h -1, the reaction product was measured by a gas chromatograph equipped with a packed column GDX-102. The conversion rate of diethylene glycol was 99.4%, the selectivity for dicyclohexanone was 98.3%, and the service life of the catalyst could reach 180 days.

[0055] Example 4

[0056] S1. 9.8 g of citric acid and 5.5 g of ammonium chloride were successively added to deionized water and stirred until completely dissolved. Hydrochloric acid was added dropwise to adjust the pH to 3.0, and the solution was made up to the mark in a 200 mL volumetric flask to obtain the electrolyte for standby. 8 g of Ti3AlC2 powder was mixed with 1 g of PVDF binder, coated on a titanium foil, dried, and then placed in the electrolyte. The solid-liquid ratio for electrolytic delamination was 2 g:80 ml, and electrolysis was carried out at a voltage of 0.5 V for 4 h. After electrolysis, ultrasonic treatment was performed, and it was centrifuged and washed with deionized water until neutral to obtain dry few-layer Ti3C2Tx nanosheet powder. 1 g of Ti3C2Tx nanosheet powder was dispersed in 100 mL of deionized water, and ultrasonic treatment was carried out for 10 min to prepare a suspension;

[0057] S2. 7.25 g of copper nitrate trihydrate and 2.42 g of nickel nitrate hexahydrate were dissolved in a mixed solution of 50 mL of water and 50 mL of ethanol, added to the suspension, stirred and impregnated at room temperature for 2 h, centrifuged and separated, washed with deionized water, dried at 60 °C for 12 h, calcined in a muffle furnace at 350 °C for 2 h, and reduced with hydrogen at 300 °C for 2 h to obtain Ti3C2Tx powder loaded with copper and nickel single atoms;

[0058] S3. 3 g of glucose and 1 g of melamine were dissolved in 320 mL of deionized water, added with Ti3C2Tx powder loaded with copper and nickel single atoms, ultrasonically dispersed, transferred to a reaction kettle, and hydrothermally reacted at 180 °C for 12 h. After that, it was centrifuged, washed, and dried, and carbonized in a tubular furnace under an Ar atmosphere at 500 °C for 3 h to obtain the catalyst D of this example.

[0059] The system pressure was adjusted to 0.3 Mpa and the temperature to 275 °C. A mixed gas of hydrogen and nitrogen with a molar ratio of 8:1 was mixed with 1,6-hexanediol and continuously vaporized through a vaporization superheater, and then introduced into a fixed-bed tubular reactor containing 6.5 g of catalyst D for catalytic reaction. The effluent after the reaction was condensed and separated to obtain a liquid product. The liquid hourly space velocity of 1,6-hexanediol was 0.8 h -1 , and the reaction product was measured by a gas chromatograph equipped with a capillary column OV-1. The conversion rate of 1,6-hexanediol was 99.2%, and the selectivity for ε-caprolactone was 97.9%. The service life of the catalyst D prepared in this example could reach 180 days.

[0060] Example 5

[0061] S1. Add 9.8 g of citric acid and 5.5 g of ammonium chloride to deionized water in sequence, stir until completely dissolved, add hydrochloric acid dropwise to adjust the pH to 3.0, and make up the volume to 200 mL with a volumetric flask to prepare the electrolyte for standby; Mix 9 g of Ti3AlC2 powder with 1 g of PVDF binder, coat it on a titanium foil, dry it, and place it in the electrolyte. The solid-liquid ratio of electrolytic stripping is 1 g:80 ml, electrolyze at a voltage of 0.4 V for 3 h. After the electrolysis is completed, perform ultrasonic treatment, centrifuge and wash with deionized water until neutral to obtain dry few-layer Ti3C2Tx nanosheet powder. Disperse 1 g of Ti3C2Tx nanosheet powder in 100 mL of deionized water and perform ultrasonic treatment for 10 min to prepare a suspension;

[0062] S2. Weigh 6.04 g of copper nitrate trihydrate and 3.64 g of nickel nitrate hexahydrate, dissolve them in 100 mL of deionized water, add them to the suspension, stir and impregnate at room temperature for 2 h, centrifuge and separate, wash with deionized water, dry at 60 °C for 12 h, calcine in a muffle furnace at 400 °C for 2 h, and reduce with hydrogen at 300 °C for 2 h to obtain Ti3C2Tx powder loaded with copper and nickel single atoms;

[0063] S3. Dissolve 2 g of glucose and 1.2 g of melamine in 380 mL of deionized water, add the Ti3C2Tx powder loaded with copper and nickel single atoms, perform ultrasonic dispersion, transfer to a reaction kettle, carry out hydrothermal reaction at 180 °C for 12 h, and then centrifuge, wash and dry, and carbonize in a tubular furnace under Ar atmosphere at 500 °C for 2 h to obtain catalyst E.

[0064] Adjust the temperature to 250 °C. Mix a mixed gas of hydrogen and nitrogen with a molar ratio of 10:1 and 1,6-hexanediol with a molar ratio of 1:1, continuously vaporize them through a vaporization superheater, and then introduce them into a fixed-bed tubular reactor containing 7.5 g of catalyst E for contact reaction. The liquid product is obtained by condensing and separating the effluent after the reaction. The liquid hourly space velocity of 1,6-hexanediol is 1 h -1 . The conversion rate of 1,6-hexanediol is measured to be 99.5% by a gas chromatograph equipped with a capillary column OV-1, and the selectivity of ε-caprolactone is 99.2%. The service life of catalyst E prepared in this example can reach 180 days.

[0065] Comparative Example 1

[0066] S1. Disperse 1 g of graphene powder in 100 mL of deionized water and perform ultrasonic treatment for 10 min to prepare a suspension;

[0067] S2. Weigh 6.04 g of copper nitrate trihydrate and 3.64 g of nickel nitrate hexahydrate, dissolve them in 200 mL of deionized water, add them to the graphene suspension, stir and impregnate at room temperature for 2 h, centrifuge and separate, wash with deionized water, dry at 60 °C for 12 h, calcine in a muffle furnace at 400 °C for 2 h, and reduce with hydrogen at 300 °C for 2 h to obtain Comparative Catalyst 1 (graphene powder loaded with copper and nickel single atoms);

[0068] S3. Dissolve 2 g of glucose and 1 g of melamine in 360 mL of deionized water, add the graphene powder loaded with copper and nickel single atoms, disperse by ultrasonic wave, transfer to a reaction kettle, carry out hydrothermal reaction at 180 °C for 12 h, then centrifuge, wash and dry, and carbonize in a tube furnace under Ar atmosphere at 500 °C for 2 h to obtain Comparative Catalyst B1.

[0069] Under atmospheric pressure, adjust the temperature to 230 °C. Mix a mixed gas of hydrogen and nitrogen with a molar ratio of 10:1 with diethylene glycol and continuously pass it through a vaporization superheater for vaporization, and then introduce it into a fixed-bed tubular reactor filled with 6.5 g of Comparative Catalyst B1 for contact reaction. The effluent after the reaction is condensed and separated to obtain the product. The liquid hourly space velocity of diethylene glycol is 0.8 h -1 , and the conversion rate of diethylene glycol is measured to be 76.5% and the selectivity to dicyclohexanone is 80.4% by using a gas chromatograph equipped with a packed column GDX-102 for the reaction product.

[0070] Comparative Example 2

[0071] S1. Disperse 1 g of MoS2 powder in 100 mL of deionized water and prepare a suspension by ultrasonic treatment for 10 min.

[0072] S2. Weigh 6.04 g of copper nitrate trihydrate and 3.64 g of nickel nitrate hexahydrate, dissolve them in 200 mL of deionized water, add them to the graphene suspension, stir and impregnate at room temperature for 2 h, centrifuge and separate, wash with deionized water, dry at 60 °C for 12 h, calcine in a muffle furnace at 400 °C for 2 h, and reduce with hydrogen at 300 °C for 2 h to obtain Comparative Catalyst C1.

[0073] Under atmospheric pressure, adjust the temperature to 230 °C. Mix a mixed gas of hydrogen and nitrogen with a molar ratio of 8:1 with diethylene glycol and continuously pass it through a vaporization superheater for vaporization, and then introduce it into a fixed-bed tubular reactor filled with 4 g of Comparative Catalyst C1 for contact reaction. The effluent after the reaction is condensed and separated to obtain the product. The liquid hourly space velocity of diethylene glycol is 0.5 h -1 , and the conversion rate of diethylene glycol is measured to be 64.7% and the selectivity to dicyclohexanone is 73.8% by using a gas chromatograph equipped with a packed column GDX-102 for the reaction product, and the service life of the catalyst is 380 hours.

[0074] Comparative Example 3

[0075] Prepare a mixed solution containing copper nitrate, chromium nitrate and aluminum nitrate (molar ratio 2:2:1). While stirring at 70 °C, dropwise add the Na2CO3 solution into the above mixed solution. The obtained precipitate is centrifuged, washed, dried at 100 °C for 24 h, then calcined for 3 h, and tableted. The catalyst CuO / Cr2O3 / Al2O3 reported in the literature (Modern Chemical Industry, Vol. 27, No. 10, P41).

[0076] Adjust the temperature to 250 °C. Mix a mixed gas of hydrogen and nitrogen with a molar ratio of 10:1 and 1,6-hexanediol with a molar ratio of 1:1, continuously vaporize them through a vaporization superheater, and then introduce them into a fixed-bed tubular reactor containing 6.5 g of the catalyst CuO / Cr2O3 / Al2O3 for a contact reaction. The effluent after the reaction is condensed and separated to obtain a liquid product. The liquid hourly space velocity of 1,6-hexanediol is 1 h -1 , and the conversion rate of 1,6-hexanediol is measured to be 85.7% by a gas chromatograph equipped with a capillary column OV-1, and the selectivity of ε-caprolactone is 52.3%.

[0077] The equipment quantities and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be apparent to those skilled in the art.

[0078] Although the embodiments of the present invention have been disclosed as above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrated and described examples here.

Claims

1. A preparation method of a copper-nickel single-atom catalyst based on an MXene support, characterized in that, It includes the following steps: S1. Add citric acid and ammonium chloride into water in sequence and stir until dissolved, adjust the pH to prepare an electrolyte solution; Mix Ti3AlC2 powder with a binder, coat it on a titanium foil, dry it, and then place it in the electrolyte solution. Control the temperature and voltage for electrolysis to obtain an MXene support; Place the MXene support in deionized water and disperse it by ultrasonic treatment to prepare a suspension; S2. Dissolve a copper compound and a nickel compound in a mixed solution of water and ethanol, add it to the suspension, stir and impregnate, and obtain an MXene support loaded with copper-nickel single atoms through drying, calcination, and reduction; S3. Dissolve glucose and melamine in deionized water, add the MXene support loaded with copper-nickel single atoms, mix evenly, transfer it to a reaction kettle, carry out a hydrothermal reaction, and then through centrifugation, washing, and drying, and low-temperature carbonization in a tubular furnace to obtain a copper-nickel single-atom catalyst based on an MXene support coated with a nitrogen-doped carbon coating; Among them, the content of copper-nickel single atoms is 0.2-1.5 wt%, and the molar ratio of copper to nickel in the copper-nickel single atoms is 1:0.3-1:1.2; The content of the nitrogen-doped carbon coating is 7-10 wt%.

2. The preparation method of the copper-nickel single-atom catalyst based on the MXene support according to claim 1, characterized in that, In the above S1, the pH of the electrolyte solution is 3-5, the electrolysis temperature is 20-60 °C, and the voltage is 0.2-0.6 V; The MXene support is few-layer Ti3C2Tx nanosheets with 2-5 layers; The specific surface area of the MXene support is > 250 m² / g, and the conductivity is > 6×10 5 S / m; The binder is polyvinylidene fluoride, and the mass ratio of Ti3AlC2 powder to polyvinylidene fluoride is 9:1; The method for adjusting the pH value is to add a pH regulator, and the pH regulator includes any one or a combination of at least two of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonia water, sodium hydroxide, potassium hydroxide, nitric acid, hydrochloric acid, sulfuric acid, and acetic acid.

3. The preparation method of the copper-nickel single-atom catalyst based on the MXene support according to claim 1, wherein, In the above S2, the molar ratio of copper in the copper compound to nickel in the nickel compound is 1:0.3-1:1.2, and the ratio of the total mass of the copper compound and the nickel compound to the amount of the mixed solution used is 1 g:10 mL to 1 g:13 mL; The copper compound includes any one or a combination of at least two of copper nitrate, copper carbonate, copper acetate, copper chloride, copper hydroxide, or copper sulfate; The nickel compound includes any one or a combination of at least two of nickel nitrate, nickel sulfate, nickel chloride, nickel phthalocyanine, nickel acetate, nickel citrate, or nickel hydroxide; The calcination method is to heat in segments at a temperature of 250-500 °C for 3-8 h; The reduction treatment method is to heat at a temperature of 200-400 °C for 1-4 h in an atmosphere of one gas or a mixed gas of hydrogen, carbon monoxide, or nitrogen.

4. The preparation method of the copper-nickel single-atom catalyst based on the MXene support according to claim 1, characterized in that, In the above S3, the hydrothermal reaction conditions are to react at a temperature of 150-220 °C for 6-24 h; The low-temperature carbonization treatment method is to heat at a temperature of 300-500 °C for 1-7 h; The mass ratio of glucose to melamine is 1:1-3:1, and the ratio of the total mass of glucose and melamine to the amount of deionized water used is 1 g:80 mL-1 g:150 mL; The content of the nitrogen-doped carbon coating is 7-10 wt%, and the layer thickness is 1-3 nm.

5. A copper-nickel single-atom catalyst based on an MXene support, characterized in that, The copper-nickel single-atom catalyst based on the MXene support is prepared by the preparation method of the copper-nickel single-atom catalyst based on the MXene support according to any one of claims 1-4.

6. Use of the copper-nickel single-atom catalyst based on MXene support according to claim 5, characterized in that, The copper-nickel single-atom catalyst based on the MXene support is applied to the catalytic dehydrogenation cyclization reaction of diols to prepare lactones.

7. Use of the copper-nickel single-atom catalyst based on MXene support according to claim 6, characterized in that, The diols include any one or a combination of at least two of diethylene glycol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 1,5-pentanediol, 1,4-pentanediol, 1,4-butanediol or 1,3-propanediol.

8. The application of the copper-nickel single-atom catalyst based on the MXene support according to claim 6, characterized in that, The diols include any one or a combination of at least two of 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol or diethylene glycol.

9. Use of the copper-nickel single-atom catalyst based on the MXene support according to claim 6 or 7, characterized in that The raw material of the dehydrogenation cyclization reaction of the diol is the diol, and the process of the dehydrogenation cyclization reaction of the diol is the mixed gasification dehydrogenation cyclization reaction of the diol with a mixed gas of hydrogen and nitrogen to generate the corresponding lactone.

10. Use of the copper-nickel single-atom catalyst based on MXene support according to claim 9, characterized in that, The temperature of the diol dehydrogenation cyclization reaction is 200~300 °C; the mass space velocity of the diol dehydrogenation cyclization reaction is 0.1~10 h -1 ; the molar ratio of hydrogen to nitrogen is 0.5:1~12:1; the molar ratio of diol to the mixed gas of hydrogen and nitrogen is 1:1~10:1.

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