Highly active and stable catalyst for synthesizing methacrylonitrile, its preparation method and application thereof

Abstract

The application discloses a high-activity and high-stability catalyst for synthesizing methacrylonitrile and a preparation method and application thereof, and has the technical scheme that (1) manganese dioxide powder is added into an acid solution and placed in an oven, and the manganese dioxide powder is pickled at 120-150 DEG C for 10-24h; the pickling solution is filtered, washed, dried and calcined to obtain a pickling-treated catalyst carrier; (2) a ruthenium precursor is added into a solvent and fully dissolved to obtain a ruthenium solution; the pickling-treated catalyst carrier is added into the ruthenium solution and loaded under ultrasonic, and then the solution is filtered, washed, dried and calcined to obtain a ruthenium monatomic catalyst. The method is simple, the reaction condition is mild, the production cost is low, raw materials are easy to obtain, the conversion rate of methacrolein is high, the yield of methacrylonitrile is high, and the stability is good.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalytic ammonia oxidation, and particularly relates to a ruthenium monatomic catalyst for synthesizing methacrylonitrile, a preparation method and application of the catalyst. BACKGROUND

[0002] Methacrylonitrile is a colorless liquid and an important chemical raw material, which can be used as an intermediate product to produce methyl methacrylimide (PMI) foam and methyl methacrylate, etc. At present, the most important use is to produce PMI foam. PMI foam is a high-performance lightweight high-strength polymer material, which has been widely used in aerospace, automobile lightweight, rail transportation and many other military and civilian fields due to its excellent performance.

[0003] At present, one of the main reasons restricting the development of PMI foam is the high price of raw material methacrylonitrile. The processes for producing methacrylonitrile mainly include isobutylene one-step method, isobutylene two-step method, mixed carbon four direct ammonia oxidation method, methacrylamide dehydration method and acetone cyanohydrin method. Among them, the acetone cyanohydrin dehydration method is the earliest application, and the advantage of this process is low production cost, but due to the toxic raw material, the environmental protection problem is prominent, which limits its development. Japan Asahi Kasei Company and the United States Sohio Company adopt isobutylene one-step ammonia oxidation method, which belongs to high-temperature gas-solid phase reaction, and the advantage is low investment, and the raw material isobutene can be obtained from petroleum cracking, but there are problems such as many reaction by-products, low methacrylonitrile yield and generation of toxic by-product hydrogen cyanide.

[0004] Patent No. 201911122322.2 discloses a catalyst for preparing methacrylonitrile and a method for preparing methacrylonitrile. The catalyst is a supported catalyst, which comprises a carrier and an active component supported on the carrier, wherein the chemical formula of the active component is as follows: MgaNibFecKdMoeBifXgYhOz. Compared with the same kind of catalyst for preparing methacrylonitrile, the catalyst has the characteristics of high conversion rate of isobutene, high selectivity of methacrylonitrile, etc. However, due to the more active components supported, there are problems such as complex preparation method, poor reproducibility of catalyst preparation, harsh requirements in preparation process, high production cost, etc.

[0005] Therefore, researchers have been committed to developing a simple method, low production cost, more efficient, energy saving and environmentally friendly methacrylonitrile production process. SUMMARY

[0006] The purpose of the present application is to solve the problems in the background art, and to provide a preparation method of a high-activity and high-stability catalyst for synthesizing methacrylonitrile, which has the advantages of simple method, mild reaction condition, low production cost, easy-to-obtain raw material, high methacrylaldehyde conversion rate, high methacrylonitrile yield and good stability.

[0007] The application further provides the high-activity and high-stability catalyst prepared by the method.

[0008] The application further provides the application of the high-activity and high-stability catalyst.

[0009] The application further provides the preparation method of the high-activity and high-stability catalyst for synthesizing methacrylonitrile.

[0010] (1) adding manganese dioxide powder into an acid solution and placing the acid solution in an oven, and treating the acid solution at 120-150 DEG C for 10-24 hours to perform acid washing on the manganese dioxide powder; filtering, washing, drying and calcining the acid washing solution to obtain an acid washing treated catalyst carrier;

[0011] (2) adding a ruthenium precursor into a solvent to sufficiently dissolve the ruthenium precursor, and obtaining a ruthenium solution; adding the acid washing treated catalyst carrier into the ruthenium solution and performing loading under ultrasonic, and then filtering, washing, drying and calcining the solution to obtain a ruthenium monatomic catalyst.

[0012] In the step (1), the acid solution is at least one of a hydrochloric acid solution, a nitric acid solution, a sulfuric acid solution, a phosphoric acid solution, an acetic acid solution and a citric acid solution.

[0013] The concentration of the acid in the acid solution is 0.1-5 mmol / L, and more preferably 0.2-1 mmol / L.

[0014] In the step (1), the mass ratio of the manganese dioxide powder to the acid solution is 1:(5-50).

[0015] In the step (1) and the step (2), the washing solvent used in the washing step is at least one of deionized water, ultrapure water, methanol, ethanol, isopropanol, acetonitrile, acetone and tetrahydrofuran.

[0016] In the step (1), the drying condition is 60-80 DEG C in the oven for 5-12 hours.

[0017] In the step (1), the calcining condition is 200-300 DEG C in a muffle furnace for 2-12 hours.

[0018] In the step (2), the ruthenium precursor is at least one of ruthenium chloride, ruthenium acetylacetonate, ruthenium iodide, ruthenium nitrosyl nitrate and ruthenium carbonyl.

[0019] In the step (2), the mass fraction of the ruthenium precursor in the ruthenium solution is 0.005-1%, and more preferably 0.01-0.5%.

[0020] The solvent for dissolving the ruthenium precursor in the step (2) is at least one of deionized water, ultrapure water, acetylacetone, tetrahydrofuran, toluene, N,N-dimethylformamide, dimethyl sulfoxide.

[0021] The ultrasonic condition in the step (2) is 20-50Hz ultrasonic for 10-60min under 50-80℃ water bath.

[0022] The drying condition in the step (2) is 60-80℃ drying for 5-12h in an oven.

[0023] The calcination condition in the step (2) is 300-380℃ calcination for 2-8h in a muffle furnace.

[0024] The weight percentage of ruthenium in the prepared ruthenium monatomic catalyst in the step (2) is 0.01-0.5wt%, more preferably 0.02-0.3wt%.

[0025] The catalyst is prepared by the above method.

[0026] The application of the catalyst in the reaction of synthesizing methacrylonitrile from methacrolein and ammonia.

[0027] The catalyst carrier disclosed in the application is manganese dioxide powder, and industrial manganese dioxide powder can be used to further reduce the production cost of the catalyst. Here, the manganese dioxide is subjected to hydrothermal acid washing with a very low concentration of dilute acid, which can effectively etch and activate the relatively inert surface of the manganese dioxide to produce active independent manganese vacancies, facilitate the subsequent loading of ruthenium monatomic and reaction, and at the same time, the acid washing can also remove the impurities remaining and / or adsorbed on the surface of the manganese dioxide to avoid the occurrence of side reactions during the reaction. The concentration of the acid in the acid solution is preferably 0.1-5mmol / L, more preferably 0.2-1mmol / L. A too high concentration will cause unnecessary loss of the carrier and generate adjacent manganese vacancies, and a too low concentration will result in too few manganese vacancies on the manganese dioxide after acid washing, which will limit the mass fraction of the loaded ruthenium or cause part of the ruthenium to be unanchored on the manganese vacancies during loading, and generate nanoparticles.

[0028] When the catalyst is loaded, a low-concentration ruthenium solution is used, and ultrasonic vibration is used to effectively anchor the ruthenium monatomic atom in the manganese vacancy of the acid washing carrier. The ruthenium atom is connected to the manganese atom through an oxygen bridge, and the property is stable and not prone to migration, aggregation or loss of ruthenium, thereby ensuring the performance of the catalyst and realizing low loading of ruthenium. Preferably, the mass fraction of the ruthenium precursor in the ruthenium solution is 0.005-1%. More preferably, the mass fraction is 0.01-0.5%. If the concentration is too high, excess ruthenium will be loaded on the carrier, causing aggregation to form nanoparticles. If the concentration is too low, the loading amount of ruthenium in the catalyst will be too low, which will affect the reaction activity. The final ruthenium monatomic catalyst has a ruthenium content of 0.01-0.5wt%, and more preferably, the content is 0.02-0.3wt%.

[0029] The ruthenium monatomic atoms in the prepared catalyst have similar physical and chemical environments, and the surrounding carrier can provide active oxygen, which is conducive to the ammoxidation of methylacrolein and the efficient generation of a single product, methacrylonitrile. At the same time, low loading of ruthenium can greatly reduce the cost of industrial production.

[0030] The ruthenium monatomic catalyst prepared by the application can be used as a catalyst for the ammoxidation of methylacrolein to synthesize methacrylonitrile. The reaction can be a slurry bed tank reaction or a trickle bed reaction.

[0031] When the reaction is a slurry bed tank reaction, the specific reaction conditions include: adding the ruthenium monatomic catalyst, the raw material methylacrolein and the organic solvent into the reaction kettle, respectively, introducing ammonia gas as the ammonia source and air as the oxygen source into the system, and performing the ammoxidation reaction under mechanical stirring or magnetic stirring to obtain the target product, methacrylonitrile.

[0032] The slurry bed reaction pressure is 1-6MPa, the temperature is 10-30℃, and the reaction time is 2-20min. The organic solvent is one or more of methanol, ethanol, acetonitrile, ethyl acetate, butyl acetate, dimethyl sulfoxide, acetone, carbon tetrachloride, tetrahydrofuran, N,N-dimethylformamide, chloroform, 1,2-dichloroethane, cyclohexane and toluene. The mass ratio of the ruthenium monatomic catalyst to the raw material methylacrolein to the organic solvent is 1:(10-30):(100-200). The molar ratio of the raw material methylacrolein to ammonia to the oxygen in the air is 1:(0.5-10):(0.5-10), and preferably 1:(1-2):(1-2).

[0033] When the reaction is a trickle bed reaction, the specific reaction conditions include: the prepared catalyst is granulated, the size is controlled to be 20-40 mesh, and is filled into the middle section of the reaction tube; before the reaction, a certain amount of raw material methacrolein is weighed, added into an organic solvent, and uniformly mixed, and the mass fraction of methacrolein in the obtained solution is 3-20 %; during the reaction, the methacrolein solution, ammonia and air are synchronously fed through different pipelines, respectively, pass through the catalyst for catalysis, and the product methacrylonitrile is prepared.

[0034] The trickle bed reaction temperature is 10-30 DEG C, and the reaction pressure is 1-6 MPa. The organic solvent is one or two or more of methanol, ethanol, acetonitrile, ethyl acetate, butyl acetate, dimethyl sulfoxide, acetone, carbon tetrachloride, tetrahydrofuran, N, N-dimethylformamide, chloroform, 1, 2-dichloroethane, cyclohexane and toluene. The liquid hourly space velocity of methacrolein is 0.05-1.0 h -1 The molar ratio of methacrolein, ammonia and oxygen contained in the air is 1: (0.5-10) : (0.5-10), preferably 1: (1-2) : (1-2).

[0035] The ruthenium single-atom catalyst synthesized by the method has the following advantages for the synthesis of methacrylonitrile compared with the prior art:

[0036] (1) The carrier manganese dioxide used for preparing the ruthenium single-atom catalyst is cheap and easy to obtain, and industrial products can be used, the ruthenium loading in the catalyst is low, the preparation cost is low, the synthesis method is simple and easy to operate, and the industrialized preparation and production are facilitated.

[0037] (2) The active manganese vacancies are obtained by acid washing, and the ruthenium single atoms are anchored by ultrasonic assisted loading, so that the high-activity ruthenium single-atom catalyst for ammonia oxidation is prepared, the catalyst has a single active site, which is helpful for the generation of a single product, the conversion rate of methacrolein is close to 100 %, and the yield of methacrylonitrile can reach more than 90 %.

[0038] (3) The ruthenium single-atom catalyst prepared by the method is anchored in the active manganese vacancies, and is not easy to migrate, aggregate or lose, so that good stability can be maintained. For the slurry bed reaction, the catalyst can be reused by simple filtration, and the activity does not decrease obviously after twenty regeneration experiments; for the trickle bed reaction, the activity does not decrease obviously after 100 h of reaction. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1XRD pattern of the industrial MnO2 support, the acid-washed MnO2 support and the Ru single-atom catalyst prepared in Example 3 of the method described in the present application. As can be seen from the XRD pattern, after acid washing, the crystal phase of the MnO2 support did not change significantly, indicating that acid washing only etched and activated the surface of the MnO2; no characteristic diffraction peak of Ru species appeared in the Ru single-atom catalyst, indicating that Ru existed in the form of small size (the detection limit of X-ray is about 3 nm).

[0040] Figure 2 The spherical aberration electron microscopy pattern of the Ru single-atom catalyst prepared in Example 3 of the method described in the present application. As can be seen from the figure, Ru exists in the form of single atom (dashed circle in the figure), and Ru occupies the Mn vacancy position.

[0041] Figure 3 The long-period activity reaction result curve of the Ru single-atom catalyst prepared in Example 3 of the method described in the present application applied to a trickle bed reactor for catalyzing the preparation of methacrylonitrile from methacrolein ammoxidation. As can be seen from the figure, the Ru single-atom catalyst prepared in the present application exhibits good reaction activity and stability. DETAILED DESCRIPTION

[0042] The present application will be described in more detail with reference to the following specific examples, which are for illustrative purposes only and should not be construed as limiting the scope of the present application.

[0043] Example 1

[0044] Preparation of 0.02wt% Ru / MnO2 single-atom catalyst

[0045] 20 g of self-made MnO2 powder was weighed, and 500 mL of dilute hydrochloric acid solution with a concentration of 0.5 mmol / L was added, and the mixed solution was transferred to a crystallization kettle with a polytetrafluoroethylene lining, and the crystallization kettle was placed in an oven, and treated at 125℃ for 15 h. The kettle was opened, and the acid-washed solution was filtered, and the filter cake solid was washed with 100 mL of deionized water, and the washing was repeated twice, and the solid sample was dried in an oven at 80℃ for 10 h, and finally the sample was placed in a muffle furnace and calcined at 200℃ for 12 h, to prepare an acid-washed MnO2 support.

[0046] Take 6.2 mg of ruthenium trichloride solid into a beaker, add 100 mL of ultrapure water to dissolve thoroughly, and prepare a solution with a mass fraction of 0.0062% of ruthenium precursor. Add 15 g of the acid-washed manganese dioxide carrier to the above solution for loading, and place the beaker into a heatable ultrasonic cleaner. Ultrasonic treatment is performed at 60°C water bath, 30 Hz ultrasonic wave, and for 10 min. Filter the solution, wash the filter cake with 75 mL of ultrapure water for 2 times, dry the solid sample in an oven at 80°C for 10 h, and finally calcine the sample in a muffle furnace at 380°C for 4 h, to prepare a 0.02wt% Ru / MnO2 monatomic catalyst.

[0047] Example 2

[0048] Preparation of 0.2wt% Ru / MnO2 monatomic catalyst

[0049] Take 50 g of industrial manganese dioxide powder, add 1500 mL of dilute phosphoric acid solution with an acid concentration of 0.3 mmol / L, transfer the mixed solution into a crystallization kettle with a polytetrafluoroethylene liner, and place the crystallization kettle into an oven for treatment at 130°C for 20 h. Open the kettle, filter the acid-washed solution, wash the filter cake with 250 mL of tetrahydrofuran for 3 times, dry the solid sample in an oven at 60°C for 6 h, and finally calcine the sample in a muffle furnace at 230°C for 3 h, to prepare an acid-washed manganese dioxide carrier.

[0050] Take 0.316 g of ruthenium acetylacetonate solid into a beaker, add 200 mL of acetylacetone to dissolve thoroughly, and prepare a solution with a mass fraction of 0.162% of ruthenium precursor. Add 40 g of the acid-washed manganese dioxide carrier to the above solution for loading, and place the beaker into a heatable ultrasonic cleaner. Ultrasonic treatment is performed at 50°C water bath, 20 Hz ultrasonic wave, and for 50 min. Filter the solution, wash the filter cake with 200 mL of tetrahydrofuran for 3 times, dry the solid sample in an oven at 60°C for 5 h, and finally calcine the sample in a muffle furnace at 350°C for 2 h, to prepare a 0.2wt% Ru / MnO2 monatomic catalyst.

[0051] Example 3

[0052] Preparation of 0.1wt% Ru / MnO2 monatomic catalyst

[0053] Take 50 g of industrial manganese dioxide powder, add 2000 mL of dilute nitric acid solution with an acid concentration of 0.3 mmol / L, transfer the mixed solution to a crystallization kettle with a polytetrafluoroethylene lining, and put the crystallization kettle into an oven, 150°C for 10 h. Open the kettle, filter the acid-washed solution, wash the filter cake solids with 250 mL of methanol, wash 3 times, dry the solid sample in an oven at 60°C for 12 h, and finally put the sample into a muffle furnace at 250°C for 3 h to prepare the acid-washed manganese dioxide carrier.

[0054] Take 92.4 mg of ruthenium trichloride solid into a beaker, add 500 mL of ultrapure water to dissolve thoroughly, and prepare a solution with a ruthenium precursor mass fraction of 0.0185%. Add 45 g of the acid-washed manganese dioxide carrier to the above solution for loading, and put the beaker into a heatable ultrasonic cleaner, 70°C water bath, 50 Hz ultrasonic wave, ultrasonic for 20 min. Filter the solution, wash the filter cake solids with 200 mL of methanol, wash 3 times, dry the solid sample in an oven at 60°C for 10 h, and finally put the sample into a muffle furnace at 300°C for 8 h to prepare a 0.1wt% Ru / MnO2 monatomic catalyst.

[0055] Example 4

[0056] Preparation of kilogram-level 0.1wt% Ru / MnO2 monatomic catalyst

[0057] Take 1.5 kg of industrial manganese dioxide powder, add 60 L of dilute nitric acid solution with an acid concentration of 0.3 mmol / L, transfer the mixed solution to a crystallization kettle with a polytetrafluoroethylene lining, and heat the crystallization kettle with heat conducting oil, 150°C for 10 h. Open the kettle, filter the acid-washed solution, wash the filter cake solids with 6 L of methanol, wash 3 times, dry the solid sample in an oven at 60°C for 12 h, and finally put the sample into a muffle furnace at 250°C for 3 h to prepare the acid-washed manganese dioxide carrier.

[0058] Take 2.772 g of ruthenium trichloride solid into a stainless steel container, add 15 L of deionized water to dissolve thoroughly, and prepare a solution with a ruthenium precursor mass fraction of 0.0185%. Add 1.35 kg of the acid-washed manganese dioxide carrier to the above solution for loading, and put the stainless steel container into a heatable industrial ultrasonic cleaner, 70°C water bath, 50 Hz ultrasonic wave, ultrasonic for 20 min. Filter the solution, wash the filter cake solids with 5 L of methanol, wash 3 times, dry the solid sample in an oven at 60°C for 10 h, and finally put the sample into a muffle furnace at 360°C for 8 h to prepare a kilogram-level 0.1wt% Ru / MnO2 monatomic catalyst.

[0059] Example 5

[0060] 0.01wt% Ru / MnO2 monatomic catalyst preparation

[0061] Take 10 g of industrial manganese dioxide powder, add 500 mL of dilute hydrochloric acid solution with an acid concentration of 0.1 mmol / L, transfer the mixed solution to a crystallization kettle with a polytetrafluoroethylene lining, and put the crystallization kettle into an oven, 120°C for 24 h. Open the kettle, filter the acid-washed solution, wash the filter cake solids with 70 mL of deionized water, wash twice, dry the solid sample in a 70°C oven for 5 h, and finally put the sample into a muffle furnace at 300°C for 2 h to prepare the acid-washed manganese dioxide carrier.

[0062] Take 1.55 mg of ruthenium trichloride solid into a beaker, add 31 mL of ultrapure water to dissolve thoroughly, and prepare a solution with a ruthenium precursor mass fraction of 0.005%. Add 7.5 g of the acid-washed manganese dioxide carrier to the above solution for loading, and put the beaker into a heatable ultrasonic cleaner, 60°C water bath, 50 Hz ultrasonic wave, ultrasonic for 20 min. Filter the solution, wash the filter cake solids with 50 mL of ultrapure water, wash twice, dry the solid sample in a 70°C oven for 10 h, and finally put the sample into a muffle furnace at 380°C for 4 h to prepare a 0.01wt% Ru / MnO2 monatomic catalyst.

[0063] Example 6

[0064] 0.5wt% Ru / MnO2 monatomic catalyst preparation

[0065] Take 20 g of self-made manganese dioxide powder, add 100 mL of dilute nitric acid solution with an acid concentration of 5 mmol / L, transfer the mixed solution to a crystallization kettle with a polytetrafluoroethylene lining, and put the crystallization kettle into an oven, 120°C for 10 h. Open the kettle, filter the acid-washed solution, wash the filter cake solids with 120 mL of deionized water, wash twice, dry the solid sample in an 80°C oven for 10 h, and finally put the sample into a muffle furnace at 300°C for 3 h to prepare the acid-washed manganese dioxide carrier.

[0066] Take 0.164 g of ruthenium trichloride solid into a beaker, add 16.2 mL of ultrapure water to dissolve thoroughly, and prepare a solution with a ruthenium precursor mass fraction of 1%. Add 16 g of the acid-washed manganese dioxide carrier to the above solution for loading, and put the beaker into a heatable ultrasonic cleaner, 80°C water bath, 50 Hz ultrasonic wave, ultrasonic for 60 min. Filter the solution, wash the filter cake solids with 100 mL of ultrapure water, wash twice, dry the solid sample in an 80°C oven for 12 h, and finally put the sample into a muffle furnace at 330°C for 5 h to prepare a 0.5wt% Ru / MnO2 monatomic catalyst.

[0067] Comparative Example 1

[0068] Preparation of 0.1 wt% Ru / MnO2 - no acid wash - ultrasound assisted catalyst

[0069] The industrial manganese dioxide powder was used directly as the catalyst support without acid washing.

[0070] A 92.4 mg of ruthenium trichloride solid was weighed into a beaker and dissolved in 500 mL of ultrapure water to make a solution with a ruthenium precursor mass fraction of 0.0185%. The above solution was loaded with 45 g of the acid washed manganese dioxide support and the beaker was placed in a heated ultrasonic cleaner at 70 °C water bath, 50 Hz ultrasound for 20 min. The solution was filtered and the filter cake solids were washed with 200 mL of methanol, washed 3 times and the solid sample was dried in a 60 °C oven for 10 h and finally the sample was calcined in a muffle furnace at 360 °C for 8 h to make the 0.1 wt% Ru / MnO2 - acid wash - no ultrasound assisted catalyst.

[0071] Comparative Example 2

[0072] Preparation of 0.1 wt% Ru / MnO2 - acid wash - no ultrasound assisted catalyst

[0073] The acid washed industrial manganese dioxide was used as the catalyst support and the loading method was changed from ultrasound assisted to magnetic stirring.

[0074] The acid wash step of the industrial manganese dioxide was kept the same as in Example 3.

[0075] A 92.4 mg of ruthenium trichloride solid was weighed into a beaker and dissolved in 500 mL of ultrapure water to make a solution with a ruthenium precursor mass fraction of 0.0185%. The above solution was loaded with 45 g of the acid washed manganese dioxide support and the beaker was placed in a 70 °C water bath with magnetic stirring for 20 min. The solution was filtered and the filter cake solids were washed with 200 mL of methanol, washed 3 times and the solid sample was dried in a 60 °C oven for 10 h and finally the sample was calcined in a muffle furnace at 360 °C for 8 h to make the 0.1 wt% Ru / MnO2 - acid wash - no ultrasound assisted catalyst.

[0076] Experimental Example 1: Methylacrylonitrile production from methylacrolein ammoxidation using the catalysts prepared in the above examples and comparative examples (slurry phase)

[0077] The ruthenium single-atom catalysts prepared in Examples 1-4 were used to investigate the performance of the catalysts in the catalytic oxidation of methylacrolein to methacrylonitrile in a slurry reactor, with the catalysts prepared in Comparative Examples 1-2 as a comparison. At the same time, the catalytic cycle stability of the catalysts prepared in Example 3 and Comparative Example 2 was investigated.

[0078] A 0.2 g catalyst, 4 g of raw material methylacrolein and 30 g of solvent acetonitrile were added to a reaction kettle, the reaction kettle was sealed, 0.97 g of ammonia and 5 MPa of air (oxygen content about 2.20 g) were filled, mechanical stirring was started at room temperature (temperature ~ 15°C), and reaction was carried out for 5 min. After the reaction was completed, the gas was slowly released to normal pressure, the kettle was opened, and the obtained solution was analyzed by chromatography to analyze the conversion rate of methylacrolein, the selectivity and yield of methacrylonitrile.

[0079] As shown in Table 1, the ruthenium single-atom catalysts prepared in the application exhibit excellent catalytic activity in the ammonia oxidation reaction, the conversion rate of methylacrolein is more than 91%, and the yield of methacrylonitrile can reach 93%. At the same time, the kilogram-level single-atom catalyst prepared in Example 4 obtained by scaling up the production of Example 3 also exhibits good activity, and is similar to the catalytic results of Example 3, indicating that the catalyst preparation is easy to scale up. As a comparison, the prepared comparative catalysts (0.1wt% Ru / MnO2- not acid washed- ultrasonic assisted catalyst and 0.1wt% Ru / MnO2- acid washed- not ultrasonic assisted catalyst) have significantly lower catalytic activity. In particular, the catalyst prepared using an unacid-washed carrier has a methylacrolein conversion rate of less than 50% and a methacrylonitrile selectivity of only ~ 30%. The relatively inert surface of industrial manganese dioxide makes it difficult to completely load the ruthenium species subsequently, and the loaded ruthenium species is prone to migration, agglomeration or loss during the preparation and calcination process and the ammonia oxidation reaction process, resulting in a decrease in activity.

[0080] Table 1

[0081]

[0082]

[0083] The ruthenium single-atom catalyst prepared in Example 3 and the 0.1wt% Ru / MnO2- acid washed- not ultrasonic assisted catalyst prepared in Comparative Example 2 were subjected to catalytic cycle stability tests.

[0084] The reaction solution was filtered, and the catalyst solids were directly added to the reaction kettle for the next reaction test.

[0085] As shown in Table 2, the ruthenium single-atom catalyst prepared in this invention exhibits excellent catalytic activity and stability for ammonia oxidation, with no significant decrease in activity after twenty regeneration experiments. In contrast, the prepared 0.1 wt% Ru / MnO2-acid-washed-unultrasonic-assisted catalyst showed a significant decrease in activity after one regeneration, and the conversion rate of methacrolein dropped below 40% after two regenerations. Using magnetic stirring for loading resulted in weak interactions between ruthenium species and the support, leading to easy loss or migration and aggregation of ruthenium species during the reaction, thus reducing catalyst activity.

[0086] Table 2

[0087]

[0088]

[0089]

[0090]

[0091] Experimental Example 2: Catalytic ammoxidation of methacrylaldehyde to methacrylonitrile using the catalyst prepared in the above examples (trickling bed)

[0092] The ruthenium single-atom catalyst prepared in Example 3 was used to investigate its performance and stability in catalyzing the ammoxidation of methacrylaldehyde to methacrylonitrile in a trickle bed reactor.

[0093] A trickle-bed reactor was used. The prepared catalyst was granulated to a size controlled at 20-40 mesh, and 5g was weighed and filled into the middle section of the reaction tube. A certain amount of the raw material, methacrolein, was weighed and mixed with ethyl acetate until homogeneous. The mass fraction of methacrolein in the resulting solution was 5%. During the reaction, the methacrolein solution, ammonia, and air were simultaneously injected through different pipelines. After catalysis by the catalyst, the product methacrylonitrile was obtained. The reaction temperature was 30℃, the reaction pressure was 5MPa, the molar ratio of methacrolein to ammonia to oxygen in the air was 1:1.2:1.5, and the liquid hourly space velocity of methacrolein was 0.2h⁻¹. -1 The reaction solution was collected periodically for chromatographic analysis to determine the conversion rate of methacrylaldehyde, the selectivity of methacrylonitrile, and the yield.

[0094] like Figure 3 As shown, the ruthenium single-atom catalyst prepared by this invention exhibits good catalytic activity and stability in ammonia oxidation. In a 100-h lifetime experiment, the conversion rate of methacrolein can be maintained above 97.5%, and the yield of methacrylonitrile can be maintained above 89.0%.

Claims

1. A method for preparing a high-activity and high-stability catalyst for synthesizing methacrylonitrile, characterized in that, (1) manganese dioxide powder is added into an acid solution, the concentration of the acid in the acid solution is 0.1-5 mmol / L, the mass ratio of the manganese dioxide powder to the acid solution is 1: (5-50), the mixed solution is transferred into a crystallization kettle with a polytetrafluoroethylene lining, and the crystallization kettle is placed in an oven for treatment at 120-150 ℃ for 10-24 h to perform pickling on the manganese dioxide powder; the pickling solution is filtered, washed, dried, and calcined to obtain a pickling-treated catalyst carrier; (2) a ruthenium precursor is added into a solvent to be fully dissolved to obtain a ruthenium solution, the mass fraction of the ruthenium precursor in the ruthenium solution is 0.005-1%; the pickling-treated catalyst carrier is added into the above-mentioned ruthenium solution to be loaded under ultrasonic conditions, the ultrasonic conditions are as follows: 50-80 ℃ water bath, 20-50 Hz ultrasonic for 10-60 min, and then the solution is filtered, washed, dried, and calcined to obtain a ruthenium monatomic catalyst, the weight percentage content of ruthenium in the obtained ruthenium monatomic catalyst is 0.01-0.5 wt%. In the step (1), the acid solution is at least one of a hydrochloric acid solution, a nitric acid solution, a sulfuric acid solution, a phosphoric acid solution, an acetic acid solution, and a citric acid solution. In the steps (1) and (2), the washing solvent used in the washing step is at least one of deionized water, ultrapure water, methanol, ethanol, isopropanol, acetonitrile, acetone, and tetrahydrofuran.

2. The method for preparing a high-activity and high-stability catalyst for synthesizing methacrylonitrile according to claim 1, characterized by, In the step (1), the calcination conditions are as follows: calcination at 200-300 ℃ in a muffle furnace for 2-12 h; in the step (2), the calcination conditions are as follows: calcination at 300-380 ℃ in a muffle furnace for 2-8 h.

3. The method for preparing a high-activity and high-stability catalyst for synthesizing methacrylonitrile according to claim 1, characterized by, In the step (2), the ruthenium precursor is at least one of ruthenium chloride, ruthenium acetylacetonate, ruthenium iodide, ruthenium nitrosyl nitrate, and ruthenium carbonyl.

4. The method for preparing a high-activity and high-stability catalyst for synthesizing methacrolein according to claim 1, characterized by, In the step (2), the solvent for dissolving the ruthenium precursor is at least one of deionized water, ultrapure water, acetylacetone, tetrahydrofuran, toluene, N, N-dimethylformamide, and dimethyl sulfoxide.

5. The method for preparing a high-activity and high-stability catalyst for synthesizing methacrolein according to claim 1, characterized by, Prepared by the method of any one of claims 1-6.

6. The method for preparing a high-activity and high-stability catalyst for synthesizing methacrolein according to claim 1, characterized by, Application of the catalyst in a reaction of synthesizing methacrylonitrile from methacrolein and ammonia.

7. A highly active and highly stable catalyst for the synthesis of methacrylonitrile, characterized in that, ​ 8. Use of a catalyst as claimed in claim 7, characterized in that ​

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