Three-dimensional porous pt / n-mxene catalysts and methods of making the same

Abstract

The application discloses a preparation method of a three-dimensional porous Pt / N-MXene catalyst, and specifically comprises the following steps: step 1, preparing a sheet MXene; step 2, preparing a three-dimensional porous N-MXene carrier according to the product obtained in step 1; and step 3, preparing a three-dimensional porous Pt / N-MXene catalyst according to the product obtained in step 3. The application further discloses the three-dimensional porous Pt / N-MXene catalyst. The catalyst prepared by the application can optimize the loading amount and cluster size of platinum, ensure that the platinum exists in a zero-valence form with a high content (more than 80 %), and significantly enhance the stability and activity of the catalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalyst preparation, and relates to a three-dimensional porous Pt / N-MXene catalyst, and further relates to a preparation method of the three-dimensional porous Pt / N-MXene catalyst. BACKGROUND

[0002] Organic liquid hydrogen carrier (LOHC) provides an alternative solution for safe hydrogen storage and transportation, and the key to its development lies in optimizing the dehydrogenation process. Methylcyclohexane (MCH) is stable at room temperature and pressure, compatible with existing infrastructure, has high hydrogen storage density and low transportation loss, and is a typical choice. Its catalytic dehydrogenation is a gas-solid heterogeneous reaction, and the efficiency can be improved by prolonging the residence time in the catalytic bed. Compared with traditional zero-dimensional catalysts, three-dimensional structure catalysts have more abundant pore structures, which promote the diffusion and heat transfer of reactants and products, thereby improving the reaction efficiency. Among various active metals (such as Pt, Pd, Rh, Re, Ni and Cu), Pt catalysts exhibit good potential and C-H selectivity in LOHC dehydrogenation, but their high cost and rarity limit large-scale application. To overcome this bottleneck, reducing the amount of platinum and optimizing the carrier to improve its utilization efficiency and catalytic performance is a feasible strategy.

[0003] MXene is a new type of two-dimensional (2D) transition metal carbide with high specific surface area, and there are abundant defects (such as -O, -OH and -F) on the surface after etching. These defects can serve as anchoring sites for noble metal atoms, and oxygen sites are particularly effective for the adsorption of platinum cations. However, MXene nanosheets are prone to self-accumulation due to high surface energy and strong interlayer van der Waals forces, which affects the interface charge and microstructure, hindering the effective exposure of anchoring sites. In addition, Pt with oxygen coordination tends to form larger particles, resulting in the existence of a large amount of low-activity Pt (IV), which greatly affects its catalytic effect. How to finely control the microstructure and active sites, and conduct structure design and controllable construction of Pt sub-nanoclusters, is still a great challenge currently. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a three-dimensional porous Pt / N-MXene catalyst, which ensures the existence of platinum in a high content (more than 80%) of zero-valent form by optimizing the loading amount and cluster size of platinum, and improves the stability and activity of the catalyst.

[0005] Another purpose of the present application is to provide a three-dimensional porous Pt / N-MXene catalyst.

[0006] The first technical solution adopted by the present application is a preparation method of a three-dimensional porous Pt / N-MXene catalyst, which specifically comprises the following steps:

[0007] Step 1, preparing a layered MXene;

[0008] Step 2, preparing a three-dimensional porous N-MXene carrier according to the product obtained in step 1;

[0009] Step 3, preparing a three-dimensional porous Pt / N-MXene catalyst according to the product obtained in step 3.

[0010] The first technical solution of the present application is also characterized in that:

[0011] The specific process of step 1 is:

[0012] Step 1.1, preparing a LiF / HCl mixed solution;

[0013] Step 1.2, preparing a sheet MXene according to the product obtained in step 1.1 and step 1.

[0014] The specific process of step 1.1 is:

[0015] Weigh 1.6-2.4 g of lithium fluoride powder, measure 15-30 mL of concentrated hydrochloric acid and 5-10 mL of deionized water, pour the lithium fluoride powder, concentrated hydrochloric acid and deionized water into a polytetrafluoroethylene bottle, use a magnetic stirrer to heat at 45-65°C, and make the lithium fluoride powder fully dissolve in the hydrochloric acid to obtain a LiF / HCl mixed solution.

[0016] The specific process of step 1.2 is:

[0017] Add 1-1.5 g of Ti3AlC2 MAX phase powder to the LiF / HCl mixed solution, stir at a speed of 350-650 rpm, etch for 24-48 h, after the reaction is completed, pour the reaction liquid into a plastic centrifuge tube, wash with deionized water, centrifuge at a speed of 3500-5500 rpm for 5-15 min, pour off the supernatant, add deionized water and centrifuge again, repeat the washing until the supernatant is neutral, discard the supernatant, disperse the precipitate in 100-200 mL of deionized water, ultrasonic treat in an ice water bath for 2-3 h, then centrifuge the dispersion, take the dark green supernatant, which is the single-layer MXene dispersion, freeze-dry the MXene dispersion for 24-48 h to obtain the sheet MXene.

[0018] The specific process of step 2 is:

[0019] Step 2.1, protonating melamine;

[0020] Step 2.2, preparing a MXene suspension according to the product obtained in step 1;

[0021] Step 2.3, after the melamine is protonated in step 2.1, the melamine is dispersed in deionized water, and then added to the MXene suspension prepared in step 2.2, after ultrasonic stirring, the suspension is flocculated and precipitated, and then the mixed solution is freeze-dried for 24-48 h to obtain an N-MXene precursor;

[0022] Step 2.4, the freeze-dried N-MXene precursor is placed in a tube furnace, H2 / Ar mixed gas is introduced, heated from room temperature to 350 DEG C, and kept for 10-30 min, then continuously heated to 550 DEG C and kept for 2-3 h, the heating rate is 5-10 DEG C·min -1 , to obtain a three-dimensional porous N-MXene carrier.

[0023] The specific process of step 2.1 is: 2-4 g of melamine is dispersed in 30-60 mL of anhydrous alcohol, stirred vigorously for 1.5-2 h, then 6 mL of concentrated hydrochloric acid is added, mixed and stirred for 2-4 h, then washed with water and ethanol by centrifugation 2-5 times, and dried in a vacuum drying oven at 60 DEG C, finally, the solid is ground into powder to obtain protonated melamine powder.

[0024] The specific process of step 3 is: 0.3-0.5 g of solid N-MXene carrier is taken, 20-40 mL of water is added, 4-8 mg of H2PtCl6 6H2O is added, mixed and ultrasonically stirred for 30-60 min, dried at 60 DEG C-80 DEG C for 12-24 h, and then placed in a tube furnace for reduction reaction, H2 / Ar mixed gas is introduced, the reduction temperature is 200-500 DEG C, the reduction time is 3-5 h, and the reduction pressure is 0.1-0.13 MPa, to obtain a three-dimensional porous Pt / N-MXene catalyst.

[0025] The second technical solution adopted by the present application is a three-dimensional porous Pt / N-MXene catalyst, which is prepared by the above-mentioned method.

[0026] The beneficial effects of the present application are: the present application prepares high-dispersed sub-nanometer platinum clusters on a nitrogen-doped three-dimensional MXene substrate by a simple impregnation method. The doping element is introduced by a non-in-situ doping-pyrolysis method to control the active site, and the MXene is designed in a three-dimensional structure. The Pt / N-MXene platinum-based catalyst is obtained by freeze-drying, calcination, impregnation and high-temperature annealing reduction. Not only the atomic utilization rate of platinum is effectively improved, but also the stability and activity of the catalyst are significantly enhanced. By optimizing the platinum loading and cluster size, platinum exists in a high content (more than 80%) of zero-valent form. The fixed bed catalytic conversion rate is increased to more than 80%, and the hydrogen release rate reaches 600 mmol·g Pt-1 · min -1 Above, there is no obvious decrease in conversion rate (decrease rate is less than 1.11%) for a reaction time of up to 72 h. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 SEM image of the Pt / N-MXene catalyst sample obtained for the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application, Example 1;

[0028] Figure 2 HRTEM image of the Pt / N-MXene catalyst sample obtained for the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application, Example 1;

[0029] Figure 3 HRTEM image of the Pt / N-MXene catalyst sample obtained for the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application, Example 1; Pt particle size distribution chart;

[0030] Figure 4 Pt 4f XPS chart of the Pt / N-MXene catalyst sample obtained for the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application, Example 1; f Figure;

[0031] Figure 5 Performance chart of the Pt / N-MXene catalyst obtained for the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application, Example 1, for catalyzing MCH dehydrogenation;

[0032] Figure 6 XRD chart of the Pt / N-MXene catalyst obtained for the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application, Example 1, before and after catalyzing MCH dehydrogenation;

[0033] Figure 7 Raman chart of the Pt / N-MXene catalyst obtained for the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application, Example 1, before and after catalyzing MCH dehydrogenation. DETAILED DESCRIPTION

[0034] The present application will be described in detail below in conjunction with the drawings and specific embodiments.

[0035] The preparation method of the three-dimensional porous Pt / N-MXene of the present application comprises the following steps:

[0036] Step 1, obtain MXene with a sheet layer;

[0037] Take 1.6-2.4 g of lithium fluoride powder, measure 15-30 mL of concentrated hydrochloric acid, 5-10 mL of deionized water. Pour the lithium fluoride powder, concentrated hydrochloric acid, and deionized water into a polytetrafluoroethylene bottle, heat to 45-65°C using a magnetic stirrer, and stir for 5-10 min to fully dissolve the lithium fluoride powder in the hydrochloric acid to obtain a LiF / HCl mixed solution;

[0038] Slowly (add for 3-5 min) add 1-1.5 g of Ti3AlC2 MAX phase powder (200-400 mesh) to the LiF / HCl mixed solution, and observe a large amount of bubbles rising from the liquid, indicating that the reaction has started. Stir at a speed of 350-650 rpm for 24-48 h. After the reaction is complete, pour the reaction liquid into a plastic centrifuge tube, wash with deionized water, and centrifuge at high speed (3500-5500 rpm) for 5-15 min. Discard the supernatant, add deionized water, and centrifuge again. Repeat the washing until the supernatant is neutral, and then discard the supernatant. Disperse the precipitate in 100-200 mL of deionized water, and ultrasonicate (200-300 W) in an ice water bath for 2-3 h. Centrifuge the dispersion. Take the dark green supernatant, which is the single-layer MXene dispersion. Freeze-dry the dispersion for 24-48 h to obtain the MXene with a layered structure.

[0039] Step 2, preparation of three-dimensional porous N-MXene carrier;

[0040] Protonated melamine preparation: Disperse 2-4 g of melamine in 30-60 mL of anhydrous alcohol, and stir vigorously for 1.5-2 h. Then add 6 mL of concentrated hydrochloric acid. Further stir the mixture for 2-4 h, then wash with water and ethanol for 2-5 times, and dry in a vacuum drying oven at 60°C. Finally, grind the solid into powder to obtain protonated melamine;

[0041] Disperse a certain amount of protonated melamine in deionized water, and then add it to the prepared MXene suspension (the mass ratio of MXene to protonated melamine is 1:0.5-3). After ultrasonic stirring, the suspension appears flocculation and precipitation. Then freeze-dry the mixed solution for 24-48 h to obtain N-MXene precursor. Place the freeze-dried N-MXene precursor in a tube furnace, and pass H2 / Ar mixed gas. Heat from room temperature to 350°C, and keep for 10-30 min. Then continue to heat to 550°C for 2-3 h at a heating rate of 5-10°C⋅min -1 to obtain a three-dimensional porous N-MXene carrier;

[0042] Step 3, preparation of three-dimensional porous Pt / N-MXene catalyst, the specific process is as follows:

[0043] Take 0.3-0.5 g of solid N-MXene carrier, add 20-40 mL of water, and add 4-8 mg of H2PtCl6 6H2O, mix and ultrasonic for 30-60 min, dry at 60-80℃ for 12-24 h, put the dried product into a tube furnace for reduction reaction, pass in H2 / Ar mixed gas, reduction temperature is 200-500℃, reduction time is 3-5 h, reduction pressure is 0.1-0.13 MPa, to obtain three-dimensional porous Pt / N-MXene catalyst;

[0044] The three-dimensional porous Pt / N-MXene catalyst is used to catalyze the MCH dehydrogenation process: in a fixed bed reactor, the dehydrogenation reaction conditions of methylcyclopropane are as follows: the dehydrogenation reaction temperature is 280-380℃, the dehydrogenation reaction pressure is 0.1-0.5 MPa, and the dehydrogenation reaction space velocity is 5-10 h -1 .

[0045] Example 1

[0046] Take 2.2 g of lithium fluoride powder, measure 30 mL of concentrated hydrochloric acid and 10 mL of deionized water. Pour the LiF powder, concentrated hydrochloric acid and deionized water into a polytetrafluoroethylene bottle, heat to 55℃ using a magnetic stirrer, and fully dissolve the LiF powder in the hydrochloric acid (after stirring for 5 min), to obtain a LiF / HCl mixed solution; slowly add 1.3 g of Ti3AlC2 MAX phase powder (400 mesh) to the LiF / HCl mixed solution (addition process 3 min), and observe that a large amount of bubbles are generated in the liquid, indicating that the reaction has started. Stir at a speed of (350 rpm) for 24 h. After the reaction is completed, pour the reaction liquid into a plastic centrifuge tube, wash with deionized water, centrifuge at high speed (3500 rpm) for 5 min, pour off the supernatant, and add deionized water again and centrifuge. Repeat the washing until the supernatant is neutral, and discard the supernatant. Disperse the precipitate in 100 mL of deionized water, ultrasonic treat (200 W) in an ice water bath for 2 h, and then centrifuge (5000 rpm) the dispersion for 1 h. Take the dark green upper dispersion, and freeze dry for 24 h to obtain a layered MXene.

[0047] Disperse 3 g of melamine in 40 mL of anhydrous alcohol, stir vigorously for 1.8 h, then add 6 mL of concentrated hydrochloric acid. The obtained mixture is further stirred for 3 h, then washed with water and ethanol for 3 times, and dried in a vacuum drying oven at 60℃. Finally, the solid is ground into powder to obtain protonated melamine;

[0048] 0.3 g of protonated melamine was dispersed in deionized water (mass ratio of MXene to protonated melamine was 1:1), and then added to the MXene suspension (MXene and deionized water were prepared into a suspension), and flocculation and precipitation occurred. Then the mixed solution was freeze-dried for 24 h to obtain N-MXene precursor, and the N-MXene precursor was placed in a tube furnace, H2 / Ar mixed gas was introduced into the tube furnace, heated to 350℃, and kept for 30 min, and then continuously heated to 550℃ and kept for 2 h. The heating rate was 5℃⋅min -1 , to obtain a three-dimensional porous N-MXene carrier.

[0049] 0.3 g of solid N-MXene carrier was taken, 20 mL of water was added, 4 mg of H2PtCl6 6H2O was added, and ultrasonic treatment was performed for 30 min, and then dried at 60℃ for 12 h, and the dried product was placed in a tube furnace for reduction reaction, H2 / Ar mixed gas was introduced, the reduction temperature was 350℃, the reduction time was 3 h, and the reduction pressure was 0.1 MPa, to obtain a Pt / N-MXene catalyst. In a fixed bed reactor, the conditions for the dehydrogenation reaction of methylcyclopropane were as follows: the dehydrogenation reaction temperature was 350℃, the dehydrogenation reaction pressure was 0.32 MPa, and the dehydrogenation reaction weight hourly space velocity was 7.7 h -1 .

[0050] Figure 1 SEM image of the Pt / N-MXene catalyst sample obtained in Example 1 of the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application. The obvious three-dimensional porous structure can be seen, which confirms the success of the structure design.

[0051] Figure 2 HRTEM image of the Pt / N-MXene catalyst sample obtained in Example 1 of the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application. The Pt particles are small and uniformly dispersed.

[0052] Figure 3 Pt particle size distribution diagram of the HRTEM image of the Pt / N-MXene catalyst sample obtained in Example 1 of the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application. The average Pt particle size is 1.22 nm after fitting analysis. This indicates that the active site design is successful, the platinum clusters formed are highly dispersed, and the size is small.

[0053] Figure 4 Pt 4 fFigure. The valence state distribution of Pt sub-nanoclusters obtained by peak fitting analysis is mainly Pt(0) of 80.78%, which is much better than the results reported in the known literature. This is also the main reason for the good effect of MCH dehydrogenation.

[0054] Figure 5 The Pt / N-MXene catalyst obtained by the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application in Example 1 has the performance graph of catalyzing MCH dehydrogenation. It can be seen that in the reaction for up to 72 h, the catalyst maintains good stability and activity, the conversion rate remains at 80% until the end of the reaction, and the activity only decreases by 1.1%. The hydrogen release rate reaches a maximum of 636.30 mmol·g Pt -1 ·min -1 , and is always lower than 600 mmol·g Pt -1 ·min -1 . This also shows that the structural design of the catalyst and the controllable construction of the Pt sub-nanoclusters are very important to improve the catalytic activity of MCH.

[0055] Figure 6 The XRD graphs of the Pt / N-MXene catalyst obtained by the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application in Example 1 before and after catalyzing MCH dehydrogenation. According to the graph analysis, the characteristic peaks do not shift or have other peaks, which shows that the Pt / N-MXene catalyst is very stable in the long-term reaction process.

[0056] Figure 7 The Raman graphs of the Pt / N-MXene catalyst obtained by the preparation method of the three-dimensional porous Pt / N-MXene catalyst of the present application in Example 1 before and after catalyzing MCH dehydrogenation. According to the graph analysis, for carbon structural materials, the D peak and the G peak are characteristic peaks of C atom crystals, and the Pt / N-MXene catalyst has characteristic peaks at 1358 cm -1 and 1575 cm -1 , which correspond to amorphous carbon and graphite carbon, respectively. Their intensity ratio I D / I G to some extent reflects the defect degree of the C material, and the intensity ratio before and after the use of the catalyst does not change, and no carbon deposition appears on the surface. This is consistent with the experimental results, which shows that Pt / N-MXene is an excellent catalyst for long-term stable catalytic dehydrogenation of MCH.

[0057] Comparative Example 1 (when preparing the MXene sheet, less than 15 mL of concentrated hydrochloric acid is taken)

[0058] Take 1.6 g of lithium fluoride powder, 10 mL of concentrated hydrochloric acid, 5 mL of deionized water. Pour the LiF powder and hydrochloric acid solution into a polytetrafluoroethylene bottle, heat to 55°C with a magnetic stirrer, and fully dissolve the LiF powder in the hydrochloric acid (after stirring for 5 min). Slowly add 1.0 g of Ti3AlC2 MAX phase powder (400 mesh) to the LiF / HCl mixed solution (addition process 3 min), and observe a large amount of bubbles in the liquid, indicating that the reaction has started. Stir at a speed of (350 rpm) for 24 h. After the reaction is completed, pour the reaction liquid into a plastic centrifuge tube, wash with deionized water, centrifuge at high speed (3500 rpm) for 5 min, pour off the supernatant, and add deionized water again and centrifuge. Repeat the washing until the supernatant is neutral, and discard the supernatant. Disperse the precipitate in 100 mL of deionized water, ultrasonic (200W) in an ice water bath for 2 h, and then centrifuge (5000 rpm) the dispersion for 1 h. Take the dark green upper dispersion, and freeze-dry for 24 h to obtain MXene sheets.

[0059] Disperse 3 g of melamine in 40 mL of anhydrous alcohol, stir vigorously for 1.8 h, then add 6 mL of concentrated hydrochloric acid. The resulting mixture is further stirred for 3 h, then washed with water and ethanol 3 times, and dried in a vacuum drying oven at 60°C. Finally, the solid is ground into powder to obtain protonated melamine;

[0060] Disperse 0.3 g of protonated melamine in deionized water (mass ratio of MXene to protonated melamine is 1:1), then add to the MXene suspension (MXene and deionized water are prepared into a suspension), and flocculation and precipitation occur. Then freeze-dry the mixed solution for 24 h. The obtained N-MXene precursor is heated to 350°C in a tube furnace with H2 / Ar mixed gas for 30 min, and then continuously heated to 550°C for 2 h. The heating rate is 5°C⋅min -1 , and a three-dimensional porous N-MXene carrier is obtained.

[0061] Take 0.3 g of solid N-MXene carrier, add 20 mL of water, and add 4 mg of H2PtCl6 6H2O, ultrasonic for 30 min, 60°C drying for 12 h, H2 / Ar mixed gas reduction temperature 350°C, reduction time 3 h, reduction pressure 0.1 MPa, to obtain Pt / N-MXene catalyst. In a fixed bed reactor, the conditions for the dehydrogenation reaction of methylcyclopropane are as follows: dehydrogenation reaction temperature 350°C, dehydrogenation reaction pressure 0.32 MPa, and dehydrogenation reaction weight hourly space velocity 7.7 h -1 .

[0062] Comparative Example 2 (mass ratio of MXene to melamine is greater than 1:3)

[0063] Take 2.2 g of lithium fluoride powder, 30 mL of concentrated hydrochloric acid, and 10 mL of deionized water. Pour the LiF powder and hydrochloric acid solution into a polytetrafluoroethylene bottle, heat to 55°C using a magnetic stirrer, and fully dissolve the LiF powder in the hydrochloric acid (after stirring for 5 min). Slowly add 1.3 g of Ti3AlC2 MAX phase powder (400 mesh) to the LiF / HCl mixed solution (addition process for 3 min), and observe a large amount of bubbles rising from the liquid, indicating that the reaction has started. Stir at a speed of 350 rpm for 24 h. After the reaction is complete, pour the reaction liquid into a plastic centrifuge tube, wash with deionized water, centrifuge at high speed (3500 rpm) for 5 min, pour off the supernatant, and add deionized water again and centrifuge. Repeat the washing until the supernatant is neutral, and discard the supernatant. Disperse the precipitate in 100 mL of deionized water, ultrasonic treat (200 W) in an ice water bath for 2 h, and then centrifuge (5000 rpm) the dispersion for 1 h. Take the dark green supernatant dispersion, and freeze dry for 24 h to obtain a layered MXene.

[0064] Disperse 3 g of melamine in 40 mL of anhydrous alcohol, stir vigorously for 1.8 h, then add 6 mL of concentrated hydrochloric acid. The resulting mixture is further stirred for 3 h, then washed with water and ethanol 3 times, and dried in a vacuum drying oven at 60°C. Finally, the solid is ground into powder to obtain protonated melamine;

[0065] Disperse 0.3 g of protonated melamine in deionized water (mass ratio of MXene to protonated melamine is 1:5, respectively), then add to the MXene suspension, and flocculation and precipitation occur. Then freeze dry the mixed solution for 24 h, and obtain the N-MXene precursor. Heat the N-MXene precursor to 350°C in a tube furnace with H2 / Ar mixed gas for 30 min, then continue to heat to 550°C for 2 h. The heating rate is 5°C⋅min -1 , and obtain a three-dimensional porous N-MXene carrier. Take 0.3 g of solid N-MXene carrier, add 20 mL of water, add 4 mg of H2PtCl6⋅6H2O, ultrasonic treat for 30 min, dry at 60°C for 12 h, reduce at 350°C with H2 / Ar mixed gas for 3 h, and reduce at a pressure of 0.1 MPa to obtain a Pt / N-MXene catalyst. In a fixed bed reactor, the conditions for the dehydrogenation reaction of methylcyclopropane are as follows: dehydrogenation reaction temperature is 350°C, dehydrogenation reaction pressure is 0.32 MPa, and dehydrogenation reaction weight hourly space velocity is 7.7 h -1 .

[0066] Comparative Example 3 (N-MXene precursor in a tube furnace, N2inlet)

[0067] Take 2.2 g of lithium fluoride powder, 30 mL of concentrated hydrochloric acid, 10 mL of deionized water. Pour the LiF powder and hydrochloric acid solution into a polytetrafluoroethylene bottle, heat to 55°C using a magnetic stirrer, and fully dissolve the LiF powder in the hydrochloric acid (after stirring for 5 min). Slowly add 1.3 g of Ti3AlC2MAX phase powder (400 mesh) to the LiF / HCl mixed solution (addition process 3 min), and observe a large amount of bubbles in the liquid, indicating that the reaction has started. Stir at a speed of (350 rpm) for 24 h. After the reaction is completed, pour the reaction liquid into a plastic centrifuge tube, wash with deionized water, centrifuge at high speed (3500 rpm) for 5 min, pour off the supernatant, and add deionized water again and centrifuge. Repeat the washing until the supernatant is neutral, and discard the supernatant. Disperse the precipitate in 100 mL of deionized water, ultrasonic treat (200W) in an ice water bath for 2 h, and then centrifuge (5000 rpm) the dispersion for 1 h. Take the dark green supernatant dispersion, and freeze-dry for 24 h to obtain the MXene sheet.

[0068] Disperse 3 g of melamine in 40 mL of anhydrous alcohol, stir vigorously for 1.8 h, then add 6 mL of concentrated hydrochloric acid. The resulting mixture is further stirred for 3 h, then washed with water and ethanol 3 times, and dried in a vacuum drying oven at 60°C. Finally, the solid is ground into powder to obtain protonated melamine;

[0069] Disperse 0.3 g of protonated melamine in deionized water (mass ratio of MXene to protonated melamine is 1:1), then add to the MXene suspension, and flocculation and precipitation occur. Then freeze-dry the mixed solution for 24 h, and the obtained sample is heated to 350°C in a tube furnace, N2gas, for 30 min, then continue to heat to 550°C for 2 h. The heating rate is 5°C⋅min -1 After annealing, a three-dimensional porous N-MXene carrier is obtained. Take 0.3 g of solid N-MXene carrier, add 20 mL of water, add 4 mg of H2PtCl6⋅6H2O, ultrasonic treat for 30 min, and dry at 60°C for 12 h. The reduction temperature of the H2 / Ar mixed gas is 350°C, the reduction time is 3 h, and the reduction pressure is 0.1 MPa, to obtain a Pt / N-MXene catalyst. In a fixed bed reactor, the conditions for the methylcyclopropane dehydrogenation reaction are as follows: the dehydrogenation reaction temperature is 350°C, the dehydrogenation reaction pressure is 0.32 MPa, and the dehydrogenation reaction weight hourly space velocity is 7.7 h -1 .

[0070] Comparative Example 4 (Sodium borohydride reduction method used in preparation of three-dimensional porous Pt / N-MXene catalyst)

[0071] Take 2.2 g of lithium fluoride powder, 30 mL of concentrated hydrochloric acid, 10 mL of deionized water. Pour the LiF powder and hydrochloric acid solution into a polytetrafluoroethylene bottle, heat to 55°C using a magnetic stirrer, and fully dissolve the LiF powder in the hydrochloric acid (after stirring for 5 min). Slowly add 1.3 g of Ti3AlC2 MAX phase powder (400 mesh) to the LiF / HCl mixed solution (addition process 3 min), and observe a large amount of bubbles in the liquid, indicating that the reaction has started. Stir at a speed of (350 rpm) for 24 h. After the reaction is completed, pour the reaction liquid into a plastic centrifuge tube, wash with deionized water, centrifuge at high speed (3500 rpm) for 5 min, pour off the supernatant, and add deionized water again and centrifuge. Repeat the washing until the supernatant is neutral, and discard the supernatant. Disperse the precipitate in 100 mL of deionized water, ultrasonic (200W) in an ice water bath for 2 h, and then centrifuge (5000 rpm) the dispersion for 1 h. Take the dark green supernatant dispersion, and freeze-dry for 24 h to obtain the MXene sheet.

[0072] Disperse 3 g of melamine in 40 mL of anhydrous alcohol, stir vigorously for 1.8 h, then add 6 mL of concentrated hydrochloric acid. The resulting mixture is further stirred for 3 h, then washed with water and ethanol 3 times, and dried in a vacuum drying oven at 60°C. Finally, the solid is ground into powder to obtain protonated melamine;

[0073] Disperse 0.3 g of protonated melamine in deionized water (mass ratio of MXene to protonated melamine is 1:1), then add to the MXene suspension, and flocculation and precipitation occur. Then freeze-dry the mixed solution for 24 h, and heat the obtained sample to 350°C in a tube furnace with H2 / Ar mixed gas for 30 min, then continue to heat to 550°C for 2 h. The heating rate is 5°C⋅min -1 . After annealing, a three-dimensional porous N-MXene carrier is obtained. Take 0.3 g of solid N-MXene carrier, add 20 mL of water, add 4 mg of H2PtCl6⋅6H2O, ultrasonic for 30 min, and reduce with sodium borohydride to obtain a Pt / N-MXene catalyst. In a fixed bed reactor, the conditions for the dehydrogenation of methylcyclopropane are as follows: the dehydrogenation temperature is 350°C, the dehydrogenation pressure is 0.32 MPa, and the dehydrogenation weight hourly space velocity is 7.7 h -1 .

[0074] Table 1 Comparison of dehydrogenation effects of catalysts under different conditions

[0075]

[0076] As shown in Table 1, the Pt / N-MXene catalyst obtained in Example 1 has the best catalytic effect on the dehydrogenation of MCH. In Comparative Example 1, the low concentration of hydrochloric acid may lead to incomplete etching of the MXene layers, resulting in fewer active sites, which cannot be further regulated, so the activity is the lowest. In Comparative Example 2, the amount of melamine introduced is larger, which means that the N doping is more. N has weaker electron-accepting ability than O, which leads to a decrease in the ability of active sites to compete for Pt adsorption, resulting in larger Pt clusters and more high-valence Pt, and the catalytic activity decreases. In Comparative Example 3, H2 / Ar mixed gas is not used in the preparation of N-MXene precursor. Under high-temperature annealing conditions, most of the active sites are not retained, so the activity of the Pt clusters obtained subsequently is not as good as that under the H2 / Ar condition. However, according to the selectivity of the catalyst, it can be found that they are all higher than 99%, which is because Pt has excellent C-H selectivity.

[0077] Example 2

[0078] 1.6 g of lithium fluoride powder was weighed, 15 mL of concentrated hydrochloric acid and 5 mL of deionized water were measured, and the LiF powder, concentrated hydrochloric acid and deionized water were poured into a polytetrafluoroethylene bottle. A magnetic stirrer was used to heat at 45°C, so that the LiF powder was fully dissolved in the hydrochloric acid (after stirring for 8 min), and a LiF / HCl mixed solution was obtained;

[0079] 1 g of Ti3AlC2MAX phase powder (200 mesh) was slowly added (the addition process took 4 min) to the LiF / HCl mixed solution, and a large amount of bubbles was observed to come out of the liquid, indicating that the reaction started. Stirring was carried out at a speed of (450 rpm) for 36 h. After the reaction was completed, the reaction liquid was poured into a plastic centrifuge tube, washed with deionized water, and centrifuged at high speed (4500 rpm) for 10 min. The supernatant was poured out, and deionized water was added again for centrifugation. The supernatant was repeatedly washed until the pH of the supernatant was neutral, and the supernatant was discarded. The precipitate was dispersed in 150 mL of deionized water, ultrasonicated (260 W) in an ice water bath for 2.5 h, and then the dispersion was centrifuged (5000 rpm) for 1 h. The dark green upper dispersion was taken, and freeze-dried for 36 h to obtain layered MXene.

[0080] 2 g of melamine was dispersed in 30 mL of anhydrous alcohol, and stirred vigorously for 1.5 h, and then 6 mL of concentrated hydrochloric acid was added. The obtained mixture was further stirred for 2 h, and then washed with water and ethanol twice, and dried in a vacuum drying box at 60°C; finally, the solid was ground into powder to obtain protonated melamine;

[0081] 0.3 g of protonated melamine was dispersed in deionized water (MXene to melamine mass ratio of 1:0.5) and then added to the MXene suspension, causing flocculation and precipitation. The mixed solution was then freeze-dried for 36 hours to obtain the N-MXene precursor. The N-MXene precursor was placed in a tube furnace and heated to 350°C with a H2 / Ar mixture. The mixture was held for 10 minutes and then heated to 550°C for 2.5 hours at a heating rate of 8°C / min. -1 , and a three-dimensional porous N-MXene support was obtained.

[0082] Take 0.4 g of solid N-MXene support, add 30 mL of water, add 6 mg of H2PtCl6⋅6H2O, ultrasonicate for 40 minutes, dry at 70℃ for 16 hours, and place the dried product in a tube furnace for reduction reaction. A H2 / Ar mixed gas is introduced at a reduction temperature of 200℃, a reduction time of 4 hours, and a reduction pressure of 0.11 MPa to obtain a Pt / N-MXene catalyst. The conditions for the dehydrogenation of methylcyclomethane in a fixed-bed reactor are: a dehydrogenation temperature of 280℃, a dehydrogenation pressure of 0.1 MPa, and a weight hourly space velocity of 5 h. -1 .

[0083] Example 3

[0084] Weigh 2.4 g of lithium fluoride powder, add 20 mL of concentrated hydrochloric acid, and 8 mL of deionized water. Pour the LiF powder, concentrated hydrochloric acid, and deionized water into a polytetrafluoroethylene bottle. Heat at 65°C using a magnetic stirrer to fully dissolve the LiF powder in the hydrochloric acid (after stirring for 10 minutes) to obtain a LiF / HCl mixed solution.

[0085] 1.5 g of Ti3AlC2MAX phase powder (300 mesh) was slowly added (over a 5-minute addition period) to a LiF / HCl mixture. Bubbles were observed in the solution, indicating the onset of the reaction. The mixture was stirred at 650 rpm and etched for 48 hours. After the reaction was complete, the reaction solution was poured into a plastic centrifuge tube, washed with deionized water, and centrifuged at high speed (5500 rpm) for 15 minutes. The supernatant was discarded, deionized water was added, and centrifugation was repeated. Washing was repeated until the pH of the supernatant was neutral, at which point the supernatant was discarded. The precipitate was dispersed in 200 mL of deionized water and sonicated (300 W) in an ice-water bath for 3 hours. The dispersion was then centrifuged (5000 rpm) for 1 hour. The dark green supernatant was then freeze-dried for 48 hours to yield flaky MXene.

[0086] 4 g of melamine was dispersed in 60 mL of anhydrous alcohol, stirred vigorously for 2 h, and then 6 mL of concentrated hydrochloric acid was added. The obtained mixture was further stirred for 4 h, then washed with water and ethanol by centrifugation for 5 times, and dried in a vacuum drying oven at 60℃; finally, the solid was ground into powder to obtain protonated melamine;

[0087] 0.3 g of protonated melamine was dispersed in deionized water (the mass ratio of MXene to melamine was 1:3), then added to the MXene suspension, and flocculation and precipitation occurred. Then the mixed solution was freeze-dried for 48 h to obtain N-MXene precursor, and the N-MXene precursor was placed in a tube furnace, and H2 / Ar mixed gas was introduced into the tube furnace to heat to 350℃, and kept for 20 min, then continued to heat to 550℃ and kept for 3 h, the heating rate was 10℃⋅min -1 , to obtain a three-dimensional porous N-MXene carrier.

[0088] 0.5 g of solid N-MXene carrier was taken, 40 mL of water was added, 8 mg of H2PtCl6⋅6H2O was added, ultrasonic was performed for 60 min, and 80℃ drying was performed for 24 h. The dried product was placed in a tube furnace for reduction reaction, H2 / Ar mixed gas was introduced, the reduction temperature was 500℃, the reduction time was 5 h, and the reduction pressure was 0.13 MPa, to obtain a Pt / N-MXene catalyst. In a fixed bed reactor, the conditions for the dehydrogenation reaction of methylcyclopropane were as follows: the dehydrogenation reaction temperature was 380℃, the dehydrogenation reaction pressure was 0.5 MPa, and the dehydrogenation reaction weight hourly space velocity was 10 h -1 .

[0089] Example 4

[0090] Compared with Example 1, in step 1, the amount of concentrated hydrochloric acid added was 25 mL, and the remaining steps were the same as Example 1.

[0091] Example 5

[0092] Compared with Example 1, in step 2, the mass ratio of MXene to protonated melamine was 1:2, and the remaining steps were the same as Example 1.

[0093] Example 6

[0094] Compared with Example 1, in step 3, the reduction temperature in the tube furnace was 450℃, and the remaining steps were the same as Example 1.

Claims

1. A method for preparing a three-dimensional porous Pt / N-MXene catalyst, characterized by: The specific steps include: Step 1: Prepare MXene sheets. The specific process of step 1 is as follows: Step 1.1, preparing a LiF / HCl mixed solution; the specific process of step 1.1 is: Weigh 1.6-2.4 g of lithium fluoride powder, add 15-30 mL of concentrated hydrochloric acid, and 5-10 mL of deionized water. Pour the lithium fluoride powder, concentrated hydrochloric acid, and deionized water into a polytetrafluoroethylene bottle. Heat the solution at 45-65°C using a magnetic stirrer to fully dissolve the lithium fluoride powder in the hydrochloric acid to obtain a LiF / HCl mixed solution. Step 1.2, preparing a sheet MXene according to step 1.1 and the product obtained in step 1; Step 2, preparing a three-dimensional porous N-MXene support according to the product obtained in step 1; The specific process of step 2 is as follows: step 2.1, protonating melamine; The specific process of step 2.1 is as follows: 2-4 g of melamine is dispersed in 30-60 mL of anhydrous alcohol, and the mixture is vigorously stirred for 1.5-2 h. Then, 6 mL of concentrated hydrochloric acid is added, and the mixture is mixed and stirred for 2-4 h. Then, the mixture is centrifuged and washed 2-5 times with water and ethanol, and dried in a vacuum drying oven at 60° C. Finally, the solid is ground into powder to obtain protonated melamine powder. Step 2.2, preparing a MXene suspension according to the product obtained in step 1; In step 2.3, the protonated melamine obtained in step 2.1 is dispersed in deionized water and then added to the MXene suspension prepared in step 2.

2. After ultrasonic stirring, the suspension flocculates and precipitates. The mixed solution is then freeze-dried for 24 to 48 hours to obtain an N-MXene precursor. In step 2.4, the freeze-dried N-MXene precursor was placed in a tube furnace, and H2 / Ar mixed gas was introduced. The mixture was heated from room temperature to 350 °C and kept for 10 to 30 min. Then, the mixture was heated to 550 °C and kept for 2 to 3 h. The heating rate was , to obtain a three-dimensional porous N-MXene support; Step 3, preparing a three-dimensional porous Pt / N-MXene catalyst according to the product obtained in step 3; The specific process of step 3 is as follows: take 0.3-0.5 g of solid N-MXene support, add 20-40 mL of water, add 4-8 mg of After mixing, ultrasonic treatment was performed for 30 to 60 minutes and drying was performed at 60 to 80 degrees Celsius for 12 to 24 hours. The dried product was placed in a tube furnace for reduction reaction, and H2 / Ar mixed gas was introduced. The reduction temperature was 200 to 500 degrees Celsius; the reduction time was 3 to 5 hours; and the reduction pressure was 0.1 to 0.13 MPa to obtain a three-dimensional porous Pt / N-MXene catalyst.

2. The method for preparing a three-dimensional porous Pt / N-MXene catalyst according to claim 1, wherein: The specific process of step 1.2 is as follows: 1-1.5 g Ti3AlC2 MAX phase powder was added to a LiF / HCl mixed solution, stirred at 350 rpm-650 rpm, and etched for 24-48 h. After the reaction was completed, the reaction solution was poured into a plastic centrifuge tube, washed with deionized water, and centrifuged at 3500 rpm-5500 rpm for 5-15 min. The supernatant was discarded, deionized water was added, and centrifugation was performed again. The washing was repeated until the pH of the supernatant was neutral. The supernatant was discarded, and the precipitate was dispersed in 100 mL-200 mL deionized water and ultrasonically treated in an ice water bath for 2-3 h. The dispersion was then centrifuged and the dark green supernatant was taken, which was the monolayer MXene dispersion. The MXene dispersion was then freeze-dried for 24-48 h to obtain lamellar MXene.

3. A three-dimensional porous Pt / N-MXene catalyst, prepared by the preparation method of the three-dimensional porous Pt / N-MXene catalyst according to any one of claims 1 to 2.

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