Few-layer V2AlC MAX phase material and preparation method and application thereof

Abstract

The invention provides a few-layer V2AlC MAX phase material and also provides a preparation method and application of the material, and the preparation method comprises the following steps: grinding and uniformly mixing vanadium powder, aluminum powder and graphite powder, and tabletting the mixed powder to obtain a solid A; roasting and grinding the solid A to obtain powder B; mixing sodium hydroxide, potassium hydroxide and the powder B, and performing high-temperature treatment to obtain powder C; the powder C is washed, subjected to suction filtration and dried and then mixed with isopropanol, nitrogen is introduced for heating treatment, and turbid liquid is obtained; and carrying out ultrasonic treatment on the turbid liquid, standing, centrifuging supernatant, washing and drying to obtain the few-layer V2AlC MAX phase material. The few-layer V2AlC MAX phase material with high catalytic activity is synthesized by using the molten alkali and the intercalator, the conversion rate of the few-layer V2AlC MAX phase material used for solvent-free catalysis of toluene reaches 20.83%, the selectivity of benzoic acid reaches 70.02%, and chlorine is not introduced into the obtained benzoic acid, so that the few-layer V2AlC MAX phase material can be applied to food and medicines.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a few-layer V2AlC MAX phase material and a preparation method and application thereof. Background Art

[0002] Benzoic acid is the simplest and most important aromatic acid. It has a wide range of applications in the industrial field and is a key fine chemical product and a core intermediate in organic synthesis. However, the process cost of extracting benzoic acid from natural raw materials is relatively high, and the output is not enough to meet market demand. Therefore, producing benzoic acid through chemical processes is the main choice for obtaining this type of organic intermediate. At present, the main methods for producing benzoic acid in the chemical industry are toluene chlorination hydrolysis and toluene direct oxidation. The production of benzoic acid by toluene chlorination hydrolysis has many problems such as complex process, serious pollution, and difficulty in catalyst recovery, which does not meet the requirements of green chemical development. Benzoic acid produced by toluene chlorination hydrolysis contains chlorine, which is prohibited from use in many industries. At the same time, wastewater treatment is difficult and corrosion is serious in the process. The toluene oxidation process solves the problem of chlorine in benzoic acid products.

[0003] MAX phase (Mn+1AXn, n=1, 2 or 3, M is an early transition metal, A is a main group element, and X is carbon or nitrogen) is a new type of ternary metal carbide or nitride. MAX phase successfully combines the important properties of both metal and ceramic materials, such as low density, high electrical and thermal conductivity, corrosion resistance, oxidation resistance, good mechanical strength, etc., among which electrical, thermal and mechanical properties have been widely studied. As a new material, MAX phase has also been gradually applied to traditional catalysis. However, the layered materials of MAX phase are tightly combined and have a small specific surface area. Therefore, the development of a new process for peeling off the MAX phase has great application prospects.

[0004] The invention patent with publication number CN119263267A discloses a method for preparing three-dimensional graphene. This method has problems such as long preparation time, high difficulty in peeling, lack of stability, etc., and cannot be applied to the preparation of few-layer MAX phase. Summary of the invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the background technology, the first purpose of the present invention is to disclose a few-layer V2AlC MAX phase material;

[0006] The second object is to disclose a method for preparing the above-mentioned few-layer V2AlC MAX phase material;

[0007] The third purpose is to disclose the use of the above-mentioned few-layer V2AlC MAX phase material as a catalyst for catalyzing the oxidation of toluene to produce benzoic acid.

[0008] Technical solution: The few-layer V2AlC MAX phase material disclosed in the present invention has a specific surface area of ​​5-10m2 / g.

[0009] Correspondingly, a method for preparing the above-mentioned few-layer V2AlC MAX phase material is also disclosed, comprising the following steps:

[0010] S1. Grind and mix vanadium powder, aluminum powder and graphite powder evenly, and press the mixed powder into tablets to obtain solid A;

[0011] S2, roasting solid A, cooling, and grinding to obtain powder B;

[0012] S3, mixing sodium hydroxide, potassium hydroxide and powder B, and treating at high temperature to obtain powder C;

[0013] S4, washing, filtering and drying the powder C, mixing it with isopropanol, introducing nitrogen and heating it to obtain a suspension;

[0014] S5. Ultrasonicate the suspension, let it stand, centrifuge the upper liquid, wash, and dry to obtain a thin layer of V2AlC MAX phase material.

[0015] Among them, in S1: in the mixed powder, the molar ratio of vanadium, aluminum and carbon is 2:1:1.

[0016] Furthermore, the calcination treatment conditions in S2 are: heating to 1500° C. at a heating rate of 5° C. / min in an argon atmosphere and calcining for 2 h.

[0017] Furthermore, in S3, the mass ratio of sodium hydroxide, potassium hydroxide and powder B is 3:4:1.

[0018] Furthermore, the high temperature treatment condition in S3 is: standing at 200° C. in a hydrothermal reactor for 24 hours.

[0019] Furthermore, the conditions for the heating treatment in S4 are: the nitrogen pressure in the reactor is 1 MPa, and the treatment is performed at 80-160° C. for 24 h; and the mass ratio of isopropanol to powder C is 40:1.

[0020] Furthermore, the conditions for ultrasonic treatment in S5 are: ultrasonic treatment at room temperature for 8 hours; and standing time for 24 hours.

[0021] Correspondingly, the application of the above-mentioned few-layer V2AlC MAX phase material is also disclosed, and the few-layer V2AlC MAX phase material is used as a catalyst to catalyze the oxidation of toluene to produce benzoic acid.

[0022] Furthermore, the few-layer V2AlC MAX phase is used in a reactor to catalyze the selective oxidation of toluene to prepare benzoic acid. The conditions of the catalytic reaction are: a mass ratio of catalyst to toluene is 1:20-60, a reaction temperature is 170°C, a reaction time is 24h, and a reaction pressure is 3MPa.

[0023] Reaction mechanism: When vanadium powder, aluminum powder and graphite powder are calcined at a certain temperature, a layered ternary carbide MAX phase will be obtained. Mix NaOH and KOH, and the mixed molten alkali obtained by increasing the temperature can etch the surface of the V2AlC MAX phase to form holes, which is conducive to the entry of the intercalation agent. Isopropanol is used as the intercalation agent, and the temperature is increased and stirred continuously to make it diffuse evenly. Nitrogen is introduced to prevent the powder from being oxidized and to ensure the safety of the experiment. Afterwards, under the action of ultrasound, the V2AlC MAX phase is peeled off into a few layers of V2AlC. After standing, the upper liquid is centrifuged, washed, and dried to obtain a few-layer V2AlC MAX phase material.

[0024] Beneficial effects: Compared with the prior art, the advantages of the present invention are:

[0025] (1) The catalyst composition and preparation method are relatively simple, the reaction raw materials are cheap and easy to obtain, the reaction conditions are easy to control, and the requirements for the reaction device are relatively low;

[0026] (2) The surface defects of MAX phase were successfully created, and after adding intercalation agent, a few-layer MAX phase was obtained, and the specific surface area was significantly increased;

[0027] (3) In the process of catalytic oxidation of toluene to prepare benzoic acid, no chlorine element is introduced, and the high-quality benzoic acid obtained can be used in food and medicine;

[0028] (4) The catalyst is used in the reaction of toluene oxidation to prepare benzoic acid. The toluene conversion rate reaches 20.83% and the selectivity of benzoic acid reaches 70.02%, showing good activity and selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 XRD patterns of MAX phase materials prepared in Examples 1 to 3 of the present invention;

[0030] Figure 2 XRD diagram of the recovered few-layer V2AlC MAX phase material and the fresh catalyst in Example 2 of the present invention;

[0031] Figure 3 XRD patterns of the few-layer V2AlC MAX phase materials prepared in Comparative Example 1, Comparative Example 2 and Example 2 of the present invention;

[0032] Figure 4 SEM images of the MAX phase materials of Comparative Examples 2 and 3 of the present invention and TEM images of the few-layer V2AlC MAX phase material of Example 2. DETAILED DESCRIPTION

[0033] The following is a detailed description with reference to specific examples and accompanying drawings.

[0034] Example 1

[0035] A few-layer V2AlC MAX phase material with a specific surface area of ​​4.98 m 2 / g.

[0036] Prepared by the following steps:

[0037] S1. Mix vanadium powder, aluminum powder and graphite powder and grind for 2 hours, and press the mixed powder into tablets to obtain solid A. The molar ratio of V:Al:C is 2:1:1.

[0038] S2. The solid A in S1 was heated to 1500°C in an argon atmosphere at a heating rate of 5°C / min for 2 h, and then cooled to room temperature at a cooling rate of 3°C / min. The argon flow rate was maintained at 50 mL / min. After grinding for 1 h, powder B was obtained.

[0039] S3. Place powder B in S2 in a 100 mL polytetrafluoroethylene liner tube, then add the mixed powder of sodium hydroxide and potassium hydroxide, place it in a 200°C hydrothermal autoclave and let it stand for 24 hours to obtain powder C, in which the mass ratio of sodium hydroxide, potassium hydroxide and powder B is 3:4:1.

[0040] S4. Wash the powder C obtained in S3 with distilled water for multiple times and filter it, and dry the obtained solid at 60°C for 12 hours; place the dried solid in a reactor, add isopropanol, and the mass ratio of isopropanol to powder C is 40:1; introduce nitrogen into the reactor, heat it to 80°C and stir it magnetically for 24 hours, wherein the nitrogen pressure is 1MPa.

[0041] S5. The suspension obtained in S4 was ultrasonicated for 8 h, and after standing for 24 h, the upper liquid was centrifuged at a rate of 5000 rpm for 5 min and washed with anhydrous ethanol. After repeated multiple times, the obtained solid was dried at 60°C for 12 h to obtain a few-layer V2AlC MAX phase material, which was recorded as V2AlC-80.

[0042] Application Example 1

[0043] The V2AlC-80MAX phase material prepared in Example 1 is used as a catalyst in catalyzing toluene oxidation to produce benzoic acid, and the method is as follows:

[0044] Catalyst V2AlC-80MAX phase material (0.2 g) and toluene (8.6 g) were added to a kettle reactor with a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0045] Example 2

[0046] A few-layer V2AlC MAX phase material with a specific surface area of ​​7.24 m 2 / g.

[0047] Prepared by the following steps:

[0048] S1. Mix vanadium powder, aluminum powder and graphite powder and grind for 2 hours, and press the mixed powder into tablets to obtain solid A. The molar ratio of V:Al:C is 2:1:1.

[0049] S2. The solid A in S1 was heated to 1500°C in an argon atmosphere at a heating rate of 5°C / min for 2 h, and then cooled to room temperature at a cooling rate of 3°C / min. The argon flow rate was maintained at 50 mL / min. After grinding for 1 h, powder B was obtained.

[0050] S3. Place powder B in S2 in a 100 mL polytetrafluoroethylene liner tube, then add the mixed powder of sodium hydroxide and potassium hydroxide, place it in a 200°C hydrothermal autoclave and let it stand for 24 hours to obtain powder C, in which the mass ratio of sodium hydroxide, potassium hydroxide and powder B is 3:4:1.

[0051] S4. Wash the powder C obtained in S3 with distilled water for multiple times and filter it, and dry the obtained solid at 60°C for 12 hours; place the dried solid in a reactor, add isopropanol, and the mass ratio of isopropanol to powder C is 40:1; introduce nitrogen into the reactor, heat it to 120°C and stir it magnetically for 24 hours, wherein the nitrogen pressure is 1MPa.

[0052] S5. The suspension obtained in S4 was ultrasonicated for 8 h, and after standing for 24 h, the upper liquid was centrifuged at a rate of 5000 rpm for 5 min and washed with anhydrous ethanol. After repeated multiple times, the obtained solid was dried at 60°C for 12 h to obtain a few-layer V2AlC MAX phase material, which was recorded as V2AlC-120.

[0053] Application Example 2

[0054] The V2AlC-120MAX phase material prepared in Example 2 is used as a catalyst in catalyzing toluene oxidation to produce benzoic acid, and the method is as follows:

[0055] Catalyst V2AlC-80MAX phase material (0.2 g) and toluene (8.6 g) were added to a kettle reactor with a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0056] Example 3

[0057] A few-layer V2AlC MAX phase material with a specific surface area of ​​10.12 m 2 / g.

[0058] Prepared by the following steps:

[0059] S1. Mix vanadium powder, aluminum powder and graphite powder and grind for 2 hours, and press the mixed powder into tablets to obtain solid A. The molar ratio of V:Al:C is 2:1:1.

[0060] S2. The solid A in S1 was heated to 1500°C in an argon atmosphere at a heating rate of 5°C / min for 2 h, and then cooled to room temperature at a cooling rate of 3°C / min. The argon flow rate was maintained at 50 mL / min. After grinding for 1 h, powder B was obtained.

[0061] S3. Place powder B in S2 in a 100 mL polytetrafluoroethylene liner tube, then add the mixed powder of sodium hydroxide and potassium hydroxide, place it in a 200°C hydrothermal autoclave and let it stand for 24 hours to obtain powder C, in which the mass ratio of sodium hydroxide, potassium hydroxide and powder B is 3:4:1.

[0062] S4. Wash the powder C obtained in S3 with distilled water for multiple times and filter it, and dry the obtained solid at 60°C for 12 hours; place the dried solid in a reactor, add isopropanol, and the mass ratio of isopropanol to powder C is 40:1; introduce nitrogen into the reactor, heat it to 160°C and stir it magnetically for 24 hours, wherein the nitrogen pressure is 1MPa.

[0063] S5. The suspension obtained in S4 was ultrasonicated for 8 h, and after standing for 24 h, the upper liquid was centrifuged at a rate of 5000 rpm for 5 min and washed with anhydrous ethanol. After repeated multiple times, the obtained solid was dried at 60°C for 12 h to obtain a few-layer V2AlC MAX phase material, which was recorded as V2AlC-160.

[0064] Application Example 3

[0065] The V2AlC-160MAX phase material prepared in Example 3 is used as a catalyst in catalyzing toluene oxidation to produce benzoic acid, and the method is as follows:

[0066] Catalyst V2AlC-80MAX phase material (0.2 g) and toluene (8.6 g) were added to a kettle reactor with a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0067] The XRD test of the few-layer V2AlC MAX phase material prepared in Example 1 to Example 3 was carried out on an X-ray diffractometer. The XRD results are as follows: Figure 1 As shown. Figure 1 The figure shows the few-layer V2AlC MAX phase material after exfoliation at different temperatures during isopropanol treatment. When the temperature is low, the isopropanol dispersion effect is poor, the degree of mixing with the MAX phase material is small, and the intercalation effect is poor; when the temperature is too high, the V2AlC material is easily oxidized, and the purity cannot be guaranteed due to excessive impurities.

[0068] The results of the determination of the reaction activity of the catalysts in Application Examples 1 to 3 for catalyzing the oxidation of toluene to produce benzoic acid are shown in Table 1, and it can be seen that the catalyst in Example 2 has good catalytic activity. Using isopropanol as an intercalation agent at an appropriate temperature is conducive to transforming the MAX phase into a few-layer ternary carbide, increasing the specific surface area and making the catalyst have higher activity.

[0069] Table 1 Reaction activity of Application Example 1 to Application Example 3 for catalytic oxidation of toluene to produce benzoic acid

[0070]

[0071] Application Example 4

[0072] The solvent-free molecular oxygen oxidation experiment of toluene with the catalyst was carried out at a reaction temperature of 170°C, a reaction pressure of 3 MPa and a reaction time of 24 h.

[0073] Application Example 2 (0.2 g) and toluene (4.0 g) were added to a kettle reactor, and the reaction was carried out under the conditions of a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0074] Application Example 5

[0075] The solvent-free molecular oxygen oxidation experiment of toluene with the catalyst was carried out at a reaction temperature of 170°C, a reaction pressure of 3 MPa and a reaction time of 24 h.

[0076] Application Example 2 (0.2 g) and toluene (12.0 g) were added to a kettle reactor, and the reaction was carried out under the conditions of a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0077] Table 2 Reaction activity of catalytic oxidation of toluene to produce benzoic acid in Application Example 2, Application Example 4 and Application Example 5

[0078]

[0079] The results of the determination of the reaction activity of catalyzing the oxidation of toluene to produce benzoic acid in Application Example 2, Application Example 4, and Application Example 5 are shown in Table 2. It can be seen from Table 2 that when the amount of catalyst in Application Example 5 is too low, it may be because the active sites provided by it are too few, and the number of active sites required for the reaction cannot be met. Too much catalyst may have excessive adsorption on toluene, and the conversion rate is only slightly improved. In terms of comprehensive conversion rate and economic benefits, Application Example 2 is the most suitable catalyst-to-oil ratio.

[0080] Application Example 6

[0081] The catalyst activity stability experiment was carried out at a reaction temperature of 170°C, a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0082] The MAX phase material recovered after 24 hours of reaction in Application Example 2 was filtered 5 times with anhydrous ethanol through a No. 4 sand core funnel, and after washing away the reaction liquid, it was dried in an oven at 60° C. for 12 hours to obtain a recovered catalyst R1.

[0083] The recovered catalyst R1 (0.2 g) and toluene (8.6 g) were added into a kettle reactor, and the reaction was carried out under the conditions of a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0084] Application Example 7

[0085] The MAX phase material recovered after 24 hours of reaction in Application Example 6 was filtered 5 times with anhydrous ethanol through a No. 4 sand core funnel, and after washing away the reaction liquid, it was dried in an oven at 60° C. for 12 hours to obtain a recovered catalyst R2.

[0086] The recovered catalyst R2 (0.2 g) and toluene (8.6 g) were added into a kettle reactor, and the reaction was carried out under the conditions of a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0087] Application Example 8

[0088] The MAX phase material recovered after 24 hours of reaction in Application Example 7 was filtered 5 times with anhydrous ethanol through a No. 4 sand core funnel, and after washing away the reaction liquid, it was dried in an oven at 60° C. for 12 hours to obtain a recovered catalyst R3.

[0089] The recovered catalyst R3 (0.2 g) and toluene (8.6 g) were added to a kettle reactor, and the reaction was carried out under the conditions of a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0090] Application Example 9

[0091] The MAX phase material recovered after reacting for 24 hours in Application Example 8 was filtered five times with anhydrous ethanol through a No. 4 sand core funnel, and after washing away the reaction liquid, it was dried in an oven at 60° C. for 12 hours to obtain a recovered catalyst R4.

[0092] Recovered catalyst R4 (0.2 g) and toluene (8.6 g) were added to a kettle reactor, and the reaction was carried out under the conditions of a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0093] Application Example 10

[0094] The MAX phase material recovered after reacting for 24 hours in Application Example 9 was filtered five times with anhydrous ethanol through a No. 4 sand core funnel, and after washing away the reaction liquid, it was dried in an oven at 60° C. for 12 hours to obtain a recovered catalyst R5.

[0095] Recovered catalyst R5 catalyst (0.2 g) and toluene (8.6 g) were added to a kettle reactor, and the reaction was carried out under the conditions of a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0096] The results of the determination of the reaction activity of catalyzing toluene oxidation to produce benzoic acid in Application Examples 2, 6 to 10 are shown in Table 3. It can be seen from Table 3 that the catalytic activity of the few-layer V2AlC MAX phase in the toluene oxidation reaction and the selectivity for the target product benzoic acid remain relatively stable after 6 cycles of evaluation, with a toluene conversion rate (20.5%) and a benzoic acid selectivity (70.53%).

[0097] Table 3 Reaction activity of catalytic oxidation of toluene to produce benzoic acid in Application Examples 2, 6 to 10

[0098]

[0099]

[0100] The MAX phase material recovered after 24 hours of reaction in Application Example 10 was filtered 5 times with anhydrous ethanol through a No. 4 sand core funnel, and after washing away the reaction liquid, it was dried in an oven at 60°C for 12 hours to obtain a recovered catalyst R6, recorded as V2AlC-R6.

[0101] The XRD test of the sixth recycling of the few-layer V2AlC MAX phase material and the fresh catalyst was carried out on an X-ray diffractometer. The XRD results are shown in Figure 2 As shown. Figure 2 It can be seen that after 6 reactions of catalytic performance evaluation, the few-layer V2AlC MAX phase catalyst treated with delamination remains relatively stable. After multiple reactions and washings, the intensity of the diffraction peak of the recycled catalyst XRD results is reduced. The stability test results show that the few-layer V2AlC MAX phase treated with delamination still has good stability and recyclability.

[0102] Application Comparative Example 1

[0103] Toluene (8.6 g) was added into a kettle reactor, and the reaction was carried out under the conditions of a stirring speed of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0104] Comparative Example 2

[0105] The V2AlC MAX phase material provided in this comparative example has a molar ratio of V, Al, and C of 2:1:1.

[0106] The preparation method of the above MAX phase material comprises the following steps:

[0107] (1) Vanadium powder, aluminum powder and graphite powder are mixed and ground for 2 hours, and the mixed powder is pressed into tablets to obtain solid A.

[0108] (2) The solid A in step (1) was heated to 1500°C in an argon atmosphere at a heating rate of 5°C / min and calcined for 2 h, and then cooled to room temperature at a cooling rate of 3°C / min, with the argon flow rate maintained at 50 mL / min. After grinding for 1 h, a powder was obtained, which was recorded as V2AlC.

[0109] Application Comparative Example 2

[0110] The V2AlC MAX phase material prepared in Comparative Example 2 was used as a catalyst in the oxidation of toluene to produce benzoic acid, and the method was as follows:

[0111] Toluene (8.6 g) was added into a kettle reactor, and the reaction was carried out under the conditions of a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa, and a reaction time of 24 h.

[0112] Comparative Example 3

[0113] In the few-layer V2AlC MAX phase material provided in this embodiment, the molar ratio of V, Al and C is 2:1:1.

[0114] The method for preparing the above-mentioned few-layer V2AlC material comprises the following steps:

[0115] (1) Vanadium powder, aluminum powder and graphite powder are mixed and ground for 2 hours, and the mixed powder is pressed into tablets to obtain solid A.

[0116] (2) The solid A in step (1) was heated to 1500°C in an argon atmosphere at a heating rate of 5°C / min for 2 h, and then cooled to room temperature at a cooling rate of 3°C / min, with the argon flow rate maintained at 50 mL / min. After grinding for 1 h, powder B was obtained.

[0117] (3) Powder B in step (2) is placed in a 100 mL polytetrafluoroethylene liner tube, and then a mixed powder of sodium hydroxide and potassium hydroxide is added, and the mixture is allowed to stand at 200° C. for 24 h to obtain powder C, wherein the mass ratio of sodium hydroxide, potassium hydroxide and powder B is 3:4:1.

[0118] (4) The powder C obtained in step (3) was washed with distilled water for multiple times and filtered, and the obtained solid was dried at 60°C for 12 hours; the dried solid was placed in a reactor, and isopropanol was added, and the mass ratio of isopropanol to powder C was 40:1; nitrogen was introduced into the reactor, and the temperature was raised to 120°C and magnetically stirred for 24 hours, wherein the nitrogen pressure was 1 MPa. This was recorded as V2AlC-E.

[0119] Application Comparative Example 3

[0120] The V2AlC-E MAX phase material prepared in Comparative Example 3 was used as a catalyst in catalyzing toluene oxidation to produce benzoic acid, and the method was as follows:

[0121] Catalyst V2AlC-E MAX phase material (0.2 g) and toluene (8.6 g) were added into a kettle reactor with a stirring rate of 700 rpm, a reaction temperature of 170° C., a reaction pressure of 3 MPa and a reaction time of 24 h.

[0122] The XRD tests of Comparative Example 2, Comparative Example 3 and Example 2 were carried out on an X-ray diffractometer. The XRD results are shown in Figure 3 As shown. Figure 3 It can be seen that after alkaline etching and isopropanol stripping, the material phase has not changed significantly. The diffraction peak intensity has slightly decreased, which may be because the grain size has decreased after treatment, the diffraction peak intensity has become lower; the porosity has increased, which has increased the diffraction and absorption of X-rays; the sample thickness has become thinner, and the total amount of substances involved in diffraction has decreased. This is conducive to increasing the specific surface area of ​​the material, exposing more active sites, and improving the material's toluene solvent-free molecular oxygen oxidation performance.

[0123] The results of the determination of the reaction activity of catalytic oxidation of toluene to produce benzoic acid in Application Comparative Examples 1 to Application Comparative Examples 3 are shown in Table 4.

[0124] As shown in Table 4, it can be seen from Application Comparative Example 1 and Application Example 2 that the autocatalytic oxidation process is difficult during the toluene oxidation reaction. It can be seen from Application Comparative Example 2 and Application Example 2 that the catalytic effect of V2AlC after peeling is better. Compared with the traditional ternary layered MAX phase, the few-layer V2AlC has a larger specific surface area and a better effect as a catalyst. It can be seen from Application Comparative Example 3 and Application Example 2 that when isopropanol is used as an intercalation agent, when the temperature is low, the isopropanol dispersion effect is not good, the degree of mixing with the MAX phase material is small, and the intercalation effect is not good; when the temperature is too high, the V2AlC material is easily oxidized, and there are too many impurities to ensure purity. Using isopropanol as an intercalation agent at an appropriate temperature is conducive to converting the MAX phase into a few-layer ternary carbide, increasing the specific surface area and making the catalyst more active.

[0125] Table 4 Reaction activity of catalytic oxidation of toluene to produce benzoic acid in Comparative Example 1-Comparative Example 3

[0126]

[0127]

[0128] Table 5. Crystallite size, elemental composition and textural properties of the catalysts.

[0129]

[0130] a Using the Scherrer equation, b Determined by BET method.

[0131] As shown in Table 5, the grain size of V2AlC and V2AlC-120 catalysts was calculated by Scherrer formula. The grain size of V2AlC was 33.4 nm, and the grain size of the catalyst V2AlC-120 after exfoliation was 22.0 nm. This indicates that the addition of mixed alkali and intercalation agent is conducive to the formation of holes on the surface of V2AlC catalyst, causing defects on the surface of MAX phase. Ultrasound at different temperatures causes isopropanol to play an intercalation role, resulting in a smaller grain size and an increased specific surface area, from 1.80 m 2 / g increased to 7.24m 2 / g, which can provide more possible active sites for catalytic reactions. However, in V2AlC-160 (Example 3), the specific surface area increases to 10.12 m 2 / g, but produced a small amount of oxide impurities, which could not guarantee the purity of the MAX phase material.

[0132] like Figure 4 As shown, a is the SEM image of application comparative example 2, which has typical ternary layered MAX phase characteristics, and it can be seen that it is tightly stacked. b is the SEM image of application comparative example 3, that is, the V2AlC MAX phase after being treated with sodium hydroxide and potassium hydroxide, and its surface is damaged and holes appear, which is conducive to the entry of the intercalation agent. c is the TEM image of application example 2, which becomes a 3-5 layer V2AlC MAX phase material after being treated with isopropanol and ultrasound.

Claims

1. A few-layer V2AlC MAX phase material, characterized in that: Specific surface area is 5-10m 2 / g.

2. The method for preparing the few-layer V2AlC MAX phase material according to claim 1, characterized in that: The following steps are involved: S1. Grind and mix vanadium powder, aluminum powder and graphite powder evenly, and press the mixed powder into tablets to obtain solid A; S2, roasting solid A, cooling, and grinding to obtain powder B; S3, mixing sodium hydroxide, potassium hydroxide and powder B, and treating at high temperature to obtain powder C; S4, washing, filtering and drying the powder C, mixing it with isopropanol, introducing nitrogen and heating it to obtain a suspension; S5. Ultrasonicate the suspension, let it stand, centrifuge the upper liquid, wash, and dry to obtain a thin layer of V2AlC MAX phase material.

3. The method for preparing a few-layer V2AlC MAX phase material according to claim 2, characterized in that: In S1: In the mixed powder, the molar ratio of vanadium, aluminum and carbon is 2:1:

1.

4. The method for preparing a few-layer V2AlC MAX phase material according to claim 2, characterized in that: The calcination conditions in S2 are: heating to 1500° C. at a heating rate of 5° C. / min in an argon atmosphere and calcining for 2 h.

5. The method for preparing a few-layer V2AlC MAX phase material according to claim 2, characterized in that: In S3: the mass ratio of sodium hydroxide, potassium hydroxide and powder B is 3:4:

1.

6. The method for preparing a few-layer V2AlC MAX phase material according to claim 2, characterized in that: The conditions for high temperature treatment in S3 are: standing at 200°C in a hydrothermal reactor for 24 hours.

7. The method for preparing a few-layer V2AlC MAX phase material according to claim 2, characterized in that: The conditions for the heating treatment in S4 are: the nitrogen pressure in the reactor is 1 MPa, the treatment is performed at 80-160° C. for 24 h; and the mass ratio of isopropanol to powder C is 40:

1.

8. The method for preparing a few-layer V2AlC MAX phase material according to claim 2, characterized in that: The conditions of ultrasonic treatment in S5 are: ultrasonic treatment at room temperature for 8 h; and standing time for 24 h.

9. The use of the few-layer V2AlC MAX phase material according to claim 1, characterized in that: Few-layer V2AlC MAX phase material is used as a catalyst to catalyze the oxidation of toluene to produce benzoic acid.

10. The use of the few-layer V2AlC MAX phase material according to claim 9, characterized in that: The few-layer V2AlC MAX phase is used in a reactor to catalyze the selective oxidation of toluene to prepare benzoic acid. The conditions of the catalytic reaction are: a mass ratio of catalyst to toluene is 1:20-60, a reaction temperature is 170°C, a reaction time is 24h, and a reaction pressure is 3MPa.

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