A single-atom catalyst for synthesizing methylacrylonitrile and a preparation method thereof

Abstract

The present invention discloses a single-atom catalyst for synthesizing methylacrylonitrile and a preparation method thereof. A manganese precursor is added to a solvent and stirred to dissolve to obtain solution A. The active component manganese element is loaded on a carrier by the equal-volume impregnation method, the excess impregnation method or the deposition-precipitation method, and dried at room temperature for 2 to 24 hours; then dried at 60 to 150 °C for 2 to 24 hours, and finally calcined at 300 to 600 °C for 2 to 72 hours in an air or oxygen atmosphere to obtain the single-atom catalyst. The prepared single-atom catalyst has a low manganese loading amount (<1 wt%), a 100% atomic utilization rate, can rapidly catalyze the synthesis of methylacrylonitrile, the product yield can reach up to ~99% at most, has excellent catalytic performance and reaction stability, and can effectively reduce the cost of manganese raw materials.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly to a single-atom catalyst for synthesizing methacrylonitrile and a preparation method thereof. Background Art

[0002] Methacrylonitrile (MAN) is an important chemical raw material, which is easy to polymerize with acrylonitrile, butadiene, styrene, acrylic acid and its esters, and methacrylic acid and its esters to prepare polymers, copolymers, elastomers and other polymer materials. At present, its main use is to polymerize with methacrylic acid to produce polymethacrylimide (PMI) foam. PMI foam is a lightweight and high-strength foam with a 100% closed-cell structure. Its uniformly cross-linked pore wall structure endows it with outstanding structural stability and excellent mechanical properties. It is an ideal core material for sandwich structure composite materials and has broad application prospects.

[0003] At present, the methods for producing methacrylonitrile mainly include isobutene one-step method, mixed C4 direct ammoxidation method, isobutene two-step method, acetone cyanohydrin method and methacrylamide method, etc. Among them, the acetone cyanohydrin dehydration method was first used by Röhm GmbH in Germany. Its main advantage is low production cost, but its raw materials are highly toxic, difficult to obtain, and the environmental protection problem is prominent. The isobutene one-step ammoxidation method is used by Asahi Kasei in Japan and Sohio in the United States. It has low investment and easy access to raw materials, but there are problems such as low selectivity, many by-products and difficult treatment.

[0004] Preparing methacrylonitrile by ammoxidation of methacrolein is a green, environmentally friendly, mild-condition and low-by-product route. Usually, manganese-based materials are used as catalysts, but the manganese content in these catalysts is relatively high, and manganese exists in the form of nano-oxides or even micro-oxides. This results in that most of the manganese does not participate in the reaction, and the atomic utilization rate is very low, causing waste and increased cost. Summary of the Invention

[0005] The present invention is to overcome the above technical problems, and provides a single-atom catalyst for synthesizing methacrylonitrile with low loading, high atomic utilization rate, good activity and stability, and a preparation method thereof.

[0006] To achieve the above object, the present invention provides a preparation method of a single-atom catalyst for synthesizing methacrylonitrile, including the following steps:

[0007] Adding a manganese precursor to a solvent and stirring to dissolve it to obtain solution A. Using the equal-volume impregnation method, adding solution A to the carrier powder to make the carrier powder completely absorb solution A, and drying at room temperature for 2 to 24 hours; then drying at 60 to 150 °C for 2 to 24 hours, and finally calcining in an air or oxygen atmosphere at 300 to 600 °C for 2 to 72 hours to obtain a single-atom catalyst;

[0008] Alternatively, dissolve the manganese precursor in a solvent with stirring to obtain Solution A. Add Solution A to the carrier powder by the incipient wetness impregnation method, stir at room temperature for 6 to 24 hours, and then perform suction filtration to obtain a filter cake. Then dry the filter cake at 60 to 150 °C for 2 to 24 hours, and finally calcine it at 300 to 600 °C in an air or oxygen atmosphere for 2 to 72 hours to obtain the single-atom catalyst.

[0009] Alternatively, dissolve the manganese precursor in a solvent with stirring to obtain Solution A. Heat Solution A to 40 to 80 °C using a water bath. Then, with stirring, add the carrier powder to Solution A by the deposition precipitation method, and continuously stir for 1 to 4 hours to obtain a mixture B. Add an alkaline solution dropwise to mixture B to adjust the pH to 9 to 10. Stir for another 1 to 4 hours and then perform suction filtration to obtain a filter cake. Finally, dry the filter cake at 60 to 150 °C for 2 to 24 hours and calcine it at 300 to 600 °C in an air or oxygen atmosphere for 2 to 72 hours to obtain the single-atom catalyst.

[0010] Further, the weight percentage of manganese in the single-atom catalyst is 0.01 to 1 wt%.

[0011] Further, the weight percentage of manganese in the single-atom catalyst is 0.05 to 0.5 wt%.

[0012] Further, the molar concentration of manganese ions in Solution A is 0.0001 to 0.03 mol / L.

[0013] Further, the mass fraction of the solute in the alkaline solution is 0.1 to 30%.

[0014] Further, the manganese precursor is one or more of potassium permanganate, manganese sulfate, manganese nitrate, manganese acetate, manganese chloride, manganese carbonate, or manganese perchlorate.

[0015] Further, the solvent is one or more of deionized water, methanol, ethanol, acetonitrile, ethyl acetate, ethylene glycol, or glycerol.

[0016] Further, the carrier powder is one or more of aluminum oxide, titanium dioxide, zinc oxide, magnesium oxide, silicon dioxide, magnesium-aluminum hydrotalcite, magnesium-aluminum spinel, magnesium-aluminum-iron spinel, activated carbon, or graphene.

[0017] Further, the alkaline solution is one or more of potassium hydroxide solution, sodium hydroxide solution, potassium carbonate solution, sodium carbonate solution, potassium bicarbonate solution, sodium bicarbonate solution, urea solution, or ammonia water.

[0018] There is also provided a single-atom catalyst for synthesizing methacrylonitrile, which is prepared by the above preparation method.

[0019] The single-atom catalyst prepared by the present invention can be applied to the ammoxidation of methacrolein to prepare methacrylonitrile. The specific process is as follows:

[0020] Add the single-atom catalyst, organic solvent and raw material methacrolein into the reaction kettle, introduce ammonia gas as the ammonia source, and introduce oxygen and / or air as the oxygen source. Under magnetic stirring or mechanical stirring, carry out the ammoxidation reaction to obtain the product methacrylonitrile. The reaction pressure is 0.5 - 6 MPa, and the temperature is -10 - 60 °C (preferably 0 - 30 °C).

[0021] In the above methacrylonitrile synthesis reaction, the organic solvent is one or more of methanol, ethanol, acetonitrile, ethyl acetate, butyl acetate, ethylene glycol, glycerol, acetone, tetrahydrofuran, carbon tetrachloride, toluene, N,N-dimethylformamide, dimethyl sulfoxide, 1,2-dichloroethane, chloroform or cyclohexane.

[0022] In the above methacrylonitrile synthesis reaction, the mass ratio of the raw material methacrolein to the single-atom catalyst is 1:0.01 - 0.5 (preferably 1:0.05 - 0.3).

[0023] In the above methacrylonitrile synthesis reaction, the molar ratio of the raw material methacrolein to ammonia to oxygen or the oxygen contained in air is 1:(1 - 8):(0.5 - 6), preferably 1:(2 - 5):(1 - 3).

[0024] Under the catalysis of the single-atom catalyst, the raw material methacrolein can react with oxygen (or air) and ammonia to generate methacrylonitrile. This process is green and environmentally friendly, the reaction conditions are mild, and the yield of the target product can reach up to ~99%. The active component of the catalyst disclosed in the present invention is manganese element. On the surface of the carrier, manganese exists in the form of single atoms and does not form nanoparticles. Since all manganese elements exist in the form of single atoms, the chemical environment is basically similar, which helps the formation of a single product. At the same time, the manganese single atoms have weak adsorption to the product, which helps the desorption of the generated product and promotes the progress of the reaction.

[0025] Advantages of the single-atom catalyst synthesized by the method of the present invention for methacrylonitrile synthesis compared with the prior art:

[0026] 1) The single-atom catalyst prepared by the present invention has a low manganese loading amount (<1 wt%), 100% atomic utilization rate, can quickly catalyze the synthesis of methacrylonitrile, the product yield can reach up to ~99%, has excellent catalytic performance and reaction stability, and can effectively reduce the cost of manganese raw materials;

[0027] 2) The preparation method of the single-atom catalyst of the present invention is simple and easy to operate, without particularly complex processes, and can be produced on a large scale;

[0028] 3) The single-atom catalyst prepared by the present invention has good stability while ensuring excellent activity. After multiple regeneration experiments, the yield of methacrylonitrile can be maintained above 98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 FIG. 6 is a high-resolution electron microscopy photograph of the 0.05 wt% Mn / Al2O3-500 °C-3 h single-atom catalyst prepared in Example 2. There are no manganese species nanoparticles in this catalyst, and they all exist in the form of manganese single atoms.

[0030] Figure 2 FIG. 10 is a high-resolution electron microscopy photograph of the 0.07 wt% Mn / TiO2-450 °C-5 h single-atom catalyst prepared in Example 5. There are no manganese species nanoparticles in this catalyst, and they all exist in the form of manganese single atoms. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be described in more detail below with reference to the following specific examples. This is for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0032] Example 1

[0033] Preparation of 0.3 wt% Mn / MgAl2O4-600 °C-10 h single-atom catalyst. Weigh 0.137 g of manganese nitrate tetrahydrate solid, add 20 mL of deionized water, stir to dissolve, add 10.0 g of MgAl2O4 magnesium aluminate spinel powder, stir evenly, i.e., equal-volume impregnation. Dry at room temperature for 12 h, then dry in an oven at 100 °C for 12 h, and finally calcine in a tube furnace at 600 °C for 10 h in an oxygen atmosphere to obtain a 0.3 wt% Mn / MgAl2O4-600 °C-10 h manganese single-atom catalyst.

[0034] Example 2

[0035] Preparation of 0.05 wt% Mn / Al2O3-500 °C-3 h single-atom catalyst. Weigh 0.0446 g of manganese acetate tetrahydrate solid, add 100 mL of acetonitrile, stir to dissolve, and add 20.0 g of alumina powder to the solution by the method of excess impregnation. Stir at room temperature for 8 h, filter by suction, then dry the catalyst in an oven at 80 °C for 24 h, and finally calcine in a muffle furnace at 500 °C for 3 h to obtain a 0.05 wt% Mn / Al2O3-500 °C-3 h single-atom catalyst. As Figure 1 shown, there are no manganese species nanoparticles in this catalyst, and they all exist in the form of manganese single atoms.

[0036] Example 3

[0037] Preparation of 0.1 wt% Mn / MgO-400 °C-50 h single-atom catalyst. Weigh 0.134 g of manganese acetate tetrahydrate solid, add 500 mL of glycerol, stir to dissolve, add 30.0 g of magnesium oxide powder to the solution, stir at room temperature for 10 h, filter by suction, then place the catalyst in an oven and dry at 130 °C for 20 h, and finally calcine in a muffle furnace at 400 °C for 50 h to obtain 0.1 wt% Mn / MgO-400 °C-50 h single-atom catalyst.

[0038] Example 4

[0039] Preparation of 0.02 wt% Mn / graphene-300 °C-30 h single-atom catalyst. Weigh 0.0042 g of manganese carbonate solid, add 200 mL of deionized water, stir to dissolve, heat the solution to 60 °C using a water bath, add 10.0 g of graphene powder to the solution, stir for 2 h, then add ammonia water to the solution until the pH is 9, stir for 2 h, filter by suction, then place the catalyst in an oven and dry at 90 °C for 6 h, and finally calcine in a muffle furnace at 300 °C for 30 h to obtain 0.02 wt% Mn / graphene-300 °C-30 h single-atom catalyst.

[0040] Example 5

[0041] Preparation of 0.07 wt% Mn / TiO2-450 °C-5 h single-atom catalyst. Weigh 0.0427 g of manganese sulfate tetrahydrate solid, add 500 mL of deionized water, stir to dissolve, heat the solution to 80 °C using a water bath, add 15.0 g of titanium dioxide powder to the solution, stir for 1 h, then add 0.1 mol / L sodium hydroxide solution to the solution until the pH is 10, stir for 1 h, filter by suction, then place the catalyst in an oven and dry at 120 °C for 3 h, and finally calcine in a muffle furnace at 450 °C for 5 h to obtain 0.07 wt% Mn / TiO2-450 °C-5 h single-atom catalyst. As Figure 2 shown, there are no manganese species nanoparticles in this catalyst, and they all exist in the form of manganese single atoms.

[0042] Use the catalysts prepared in the above examples to catalyze the ammoxidation of methacrolein to methacrylonitrile. Use the single-atom catalysts prepared in Examples 1-5 as catalysts to investigate their performance in the ammoxidation of methacrolein to methacrylonitrile.

[0043] Use a stirred autoclave reactor. Add 0.5 g of single-atom catalyst, 50 g of solvent ethyl acetate, and 2 g of raw material methacrolein to the reactor in sequence, seal the reactor, charge 1.0 g of ammonia and 2.2 g of oxygen, with a pressure of about 1.5 MPa. Start magnetic stirring in a 20 °C constant temperature bath and react for 5 min. After the reaction, slowly release the gas to atmospheric pressure, open the reactor, and perform chromatographic analysis on the obtained solution to analyze the conversion rate of methacrolein, the selectivity of methacrylonitrile, and the yield.

[0044] As shown in Table 1, the single-atom catalyst prepared in the present invention exhibits excellent catalytic activity for ammonia oxidation of methacrolein, with the selectivity of methacrylonitrile being above 98% and the highest yield of methacrylonitrile reaching up to ~99.5%.

[0045] Table 1

[0046]

[0047] The regeneration experiment of the catalyst prepared in the above example for the catalytic ammoxidation of methacrolein to methacrylonitrile was investigated; the single-atom catalyst prepared in Example 5 was used as the catalyst to investigate the cyclic stability of the catalyst for the catalytic ammoxidation of methacrolein to methacrylonitrile.

[0048] A batch reactor was used. First, 0.6 g of the single-atom catalyst, 100 g of the solvent acetonitrile, and 3 g of the raw material methacrolein were added to the reactor in sequence. The reactor was sealed, 3.0 g of ammonia gas and 5 g of oxygen gas were charged, and the pressure was about 3.5 MPa. Magnetic stirring was started in a constant temperature bath at 10 °C, and the reaction was carried out for 6 min. After the reaction was completed, the gas was slowly released to atmospheric pressure, the reactor was opened, and the obtained solution was analyzed by chromatography to analyze the conversion rate of methacrolein, the selectivity of methacrylonitrile, and the yield. The catalyst was recycled and regenerated, and the above experiment was repeated more than ten times.

[0049] As shown in Table 2, the single-atom catalyst prepared in the present invention exhibits excellent catalytic stability. After ten recycling experiments, the yield of methacrylonitrile can still be maintained above 98%.

[0050] Table 2

[0051]

Claims

1. A preparation method of a single-atom catalyst for synthesizing methylacrylonitrile, characterized in that, It includes the following steps: Add the manganese precursor into a solvent and stir to dissolve it to obtain solution A. Add solution A to the carrier powder by the equal-volume impregnation method, and dry at room temperature for 2 to 24 hours; then dry at 60 to 150 °C for 2 to 24 hours, and finally calcine in an air or oxygen atmosphere at 300 to 600 °C for 2 to 72 hours to obtain the single-atom catalyst; Or, add the manganese precursor into a solvent and stir to dissolve it to obtain solution A. Add solution A to the carrier powder by the excess impregnation method, stir at room temperature for 6 to 24 hours and then filter to obtain the filter cake; then dry the filter cake at 60 to 150 °C for 2 to 24 hours, and finally calcine in an air or oxygen atmosphere at 300 to 600 °C for 2 to 72 hours to obtain the single-atom catalyst; Or, add the manganese precursor into a solvent and stir to dissolve it to obtain solution A. Heat solution A to 40 to 80 °C using a water bath; then, under stirring, add the carrier powder to solution A by the deposition-precipitation method and continuously stir for 1 to 4 hours to obtain the mixed solution B. Add an alkaline solution to the mixed solution B to adjust the pH to 9 to 10; stir for another 1 to 4 hours and then filter to obtain the filter cake; finally, dry the filter cake at 60 to 150 °C for 2 to 24 hours and calcine in an air or oxygen atmosphere at 300 to 600 °C for 2 to 72 hours to obtain the single-atom catalyst; The weight percentage content of manganese in the single-atom catalyst is 0.01 to 1 wt%, and the molar concentration of manganese ions in solution A is 0.0001 to 0.03 mol / L.

2. The preparation method of the single-atom catalyst for synthesizing methacrylonitrile according to claim 1, characterized in that, The weight percentage content of manganese in the single-atom catalyst is 0.05 to 0.5 wt%.

3. The preparation method of the single-atom catalyst for synthesizing methacrylonitrile according to claim 1, characterized in that, The mass fraction of the solute in the alkaline solution is 0.1 to 30%.

4. The preparation method of the single-atom catalyst for synthesizing methacrylonitrile according to claim 1, characterized in that, The manganese precursor is one or more of potassium permanganate, manganese sulfate, manganese nitrate, manganese acetate, manganese chloride, manganese carbonate or manganese perchlorate.

5. The preparation method of the single-atom catalyst for synthesizing methacrylonitrile according to claim 1, characterized in that, The solvent is one or more of deionized water, methanol, ethanol, acetonitrile, ethyl acetate, ethylene glycol or glycerol.

6. The preparation method of the single-atom catalyst for synthesizing methacrylonitrile according to claim 1, characterized in that, The carrier powder is one or more of aluminum oxide, titanium dioxide, zinc oxide, magnesium oxide, silicon dioxide, magnesium-aluminum hydrotalcite, magnesium-aluminum spinel, magnesium-aluminum-iron spinel, activated carbon or graphene.

7. The preparation method of the single-atom catalyst for synthesizing methacrylonitrile according to claim 1, wherein, The alkaline solution is one or more of potassium hydroxide solution, sodium hydroxide solution, potassium carbonate solution, sodium carbonate solution, potassium bicarbonate solution, sodium bicarbonate solution, urea solution or ammonia water.

8. A single-atom catalyst for synthesizing methacrylonitrile, characterized in that, The single-atom catalyst for synthesizing methacrylonitrile is prepared by the preparation method according to any one of claims 1 to 7.

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