Preparation method and application of Pt nanocatalyst supported by carbon nanotubes

Abstract

The present invention provides a preparation method and application of a Pt nanocatalyst supported on carbon nanotubes. During the preparation process, good dispersion is achieved through simple stirring, and sodium borohydride as a reducing agent is rapidly added under the condition of 30 °C, thereby forming a Pt / CNT nanocatalyst. The synthesis method requires simple equipment, has a simple process, and does not need to add any stabilizers during the preparation process, which is a simple and green synthesis method. The Pt nanoparticles have good catalytic selectivity for the reaction of diboron tetrahydroxide (B2(OH)4) to release hydrogen, and at the same time have good recyclability and can be used as a good economical catalyst.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage catalysis, and in particular relates to a preparation method and application of a Pt nanocatalyst loaded with carbon nanotubes. Background Art

[0002] Fossil energy is the main energy consumed in the world, but with the continuous exploitation by humans, the depletion of fossil energy is inevitable. Therefore, finding a new sustainable and environmentally friendly new energy source has become the key to research.

[0003] At present, new clean energy sources include solar energy, tidal energy and wind energy, but these energy sources have certain discontinuities. Hydrogen energy is a secondary energy source with abundant sources, green and low carbon, and wide applications. It is of great significance to achieve the goals of carbon peak and carbon neutrality. Hydrogen energy is considered by many researchers to be the most promising carbon-free, clean and sustainable energy in the future. It can release higher energy and has a larger hydrogen storage density. At the same time, hydrogen and oxygen combine to form water. The combustion products are environmentally friendly and are widely stored in chemical hydrogen storage materials.

[0004] Common chemical hydrogen storage materials include cycloalkanes, methanol, ammonia borane, hydrazine hydrate and other substances. The hydrogen content of cycloalkanes is 14.3 wt%, the hydrogen content of methanol is 12.5 wt%, and the hydrogen storage capacity of ammonia borane is as high as 19.8 wt%. Ammonia borane can release hydrogen under the conditions of catalyst and room temperature. It is one of the hydrogen storage materials with great development potential, but the price is relatively high.

[0005] Tetrahydroxydiboron B2(OH)4 is not a hydrogen storage material. It is relatively stable at room temperature, but it can produce hydrogen (H2) at room temperature after adding a catalyst. Considering H2 as a green and clean new energy source, there are studies on using B2(OH)4 as a hydrogen source for hydrogen production. At present, the hydrolysis research of tetrahydroxydiboron as a hydrogen source tends to be in water, but it is difficult to achieve low-temperature reactions in the water phase, and freezing at low temperatures prevents the reaction from proceeding. Summary of the invention

[0006] The invention provides a preparation method of a carbon nanotube-loaded Pt nanocatalyst and application thereof. The carbon nanotube-loaded Pt nanocatalyst is prepared by a simple chemical reduction method for hydrogen production reaction of tetrahydroxydiboron in a methanol solvent.

[0007] The technical solution of the present invention is a method for preparing a carbon nanotube-supported Pt nanocatalyst, comprising the following steps:

[0008] Step 1: Configure Pt 4+ The aqueous solution of ions is dispersed by ultrasonic and then used for later use; the carbon nanotubes and water are mixed and then used for later use;

[0009] Step 2: Place the Pt 4+ The aqueous solution of ions is added to the carbon nanotube water mixture, firstly ultrasonically mixed, then mechanically stirred and heated, and then NaBH4 solution is added to mix.

[0010] Step 3: The material obtained in step 2 is allowed to settle, filtered, washed and then dried to obtain a carbon nanotube-loaded Pt nanocatalyst.

[0011] Furthermore, Pt 4+ Pt in aqueous solution 4+ The ion concentration is 0.01-0.05mmol / mL.

[0012] Furthermore, in step 2, Pt 4+ The dosage ratio of ions to carbon nanotubes is 1:2~40.

[0013] Furthermore, in step 2, the ultrasonic mixing time is 0-20 min, and the mechanical stirring and heating adopts a heat-collecting constant temperature heating magnetic stirrer, stirring for 5-20 min, the temperature is set at 30° C., and the rotation speed is 10-30 r.

[0014] Furthermore, the mass ratio of sodium borohydride to carbon nanotubes is 1-8:5-10, and the NaBH4 solution is quickly added and stirred for 10 minutes.

[0015] Furthermore, in step 3, washing is first performed with water and then with ethanol.

[0016] Furthermore, the carbon nanotubes are replaced with CoFe2O4, Fe3O4, ZnO, ZrO2, CeO2 or NiO to obtain Pt / CoFe2O4, Pt / Fe3O4, Pt / ZnO, Pt / ZrO2, Pt / CeO2 or Pt / NiO catalysts, respectively.

[0017] The invention also relates to a catalyst obtained by the preparation method.

[0018] The present invention also relates to the application of the catalyst in the B2(OH)4 hydrogen production reaction.

[0019] Furthermore, after the catalyst is mixed with B2(OH)4, anhydrous methanol is added to carry out hydrogen production reaction.

[0020] The present invention has the following beneficial effects:

[0021] In the catalyst preparation process of the present invention, good dispersion is achieved through simple stirring, and the reducing agent sodium borohydride is quickly added at 30° C. The carbon nanotubes have certain pores, and the metal ions enter the carbon nanotubes, are reduced to metal nanoparticles through in-situ reduction, and are encapsulated in the pores by the carbon nanotubes, thereby forming a Pt nanocatalyst.

[0022] The Pt nanocatalyst provided by the inventor is used for the reaction of tetrahydroxydiboron (B2(OH)4) in an alcohol solvent to produce hydrogen. When preparing the catalyst, it is necessary to avoid adding an organic solvent as a stabilizer, otherwise during the reduction reaction, the organic solvent remaining in the catalyst may be miscible with the alcohol solvent added later, affecting the effect of the reaction. The present invention does not add any organic stabilizer during the catalyst preparation process, and its preparation process is simple, fast, and low-cost.

[0023] The Pt nanoparticles prepared by the present invention have good catalytic selectivity for the reaction of tetrahydroxydiboron (B2(OH)4) releasing hydrogen. By combining carbon nanotubes of carbon materials with metal nanomaterials Pt, the carbon nanotubes have good stabilization effect, can protect the metal nanomaterials, and prevent agglomeration. In addition, the catalyst also has good recyclability and is an economical catalyst; when used for the reaction of tetrahydroxydiboron in anhydrous methanol, low-temperature hydrogen production can be achieved, and the reaction performance is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD pattern of the Pt / CNT nanocatalyst obtained in Example 1.

[0025] Figure 2 This is the image and particle size distribution of the Pt / CNT nanocatalyst obtained in Example 1.

[0026] Figure 3 This is a hydrogen production diagram of the Pt / CNT nanocatalyst used to change the amount of tetrahydroxydiboron B2(OH)4 in Example 2.

[0027] Figure 4 This is a graph showing the effect of changing the amount of Pt / CNT catalyst on hydrogen production from tetrahydroxydiboron B2(OH)4 in Example 3.

[0028] Figure 5 This is a graph showing hydrogen production of tetrahydroxydiboron B2(OH)4 by the Pt / CNT catalyst at different temperatures in Example 4.

[0029] Figure 6 This is the hydrogen production diagram of tetrahydroxydiboron B2(OH)4 over the Pt / CNT catalyst at 263 K in Example 4.

[0030] Figure 7The Pt / CNT nanocatalyst in Example 5 is used for the cyclic hydrogen production of tetrahydroxydiboron B2(OH)4.

[0031] Figure 8 This is a diagram of hydrogen production when Pt nanoparticles are loaded on different carriers in Example 6. DETAILED DESCRIPTION

[0032] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0033] Embodiment 1:

[0034] A method for preparing a Pt / CNT nanocatalyst, comprising the following specific steps:

[0035] Step 1: Dissolve the metal salt containing PtCl4 ions (0.01mmol / ml) in deionized water to obtain 0.01mmol / mL Pt 4+ Ionic aqueous solution;

[0036] Step 2: Weigh 100 mg of CNT into a round-bottom flask and add 15 mL of deionized water;

[0037] Step 3: Take 2.5ml of Pt 4+ The ion aqueous solution was added to step 2, and after ultrasonic treatment for 10 min, it was placed in a heat-collecting constant temperature heating magnetic stirrer and stirred for 10 min at a temperature of 30 °C and a speed of 20 r.

[0038] Step 4: Rapidly add 2 mL of NaBH4 (19.5 mmol / mL) solution to step 3 and stir for 15 min;

[0039] Step 5: Wash the precipitate obtained in step 4, wash it with water and ethanol several times, and then dry it to prepare the Pt / CNT catalyst.

[0040] The XRD pattern of the catalyst is shown in Figure 1 As can be seen from Figure 1, its characteristic diffraction peaks are consistent with the target product, and the characteristic peaks of the (002) crystal plane of C and the diffraction peaks of (111) and (200) of Pt appear, indicating that the synthesis method successfully loads Pt on carbon nanotubes. We further characterized by TEM and found that fine Pt nanoparticles were indeed formed. The image and particle size distribution of the catalyst are shown in Figure 2 .like Figure 2 It can be seen that the Pt nanoparticles are loaded on the carbon nanotubes, and the average particle size is 3.97 nm.

[0041] Embodiment 2:

[0042] The Pt / CNT nanocatalyst obtained in Example 1 is used to change the mass production of hydrogen from tetrahydroxydiboron B2(OH)4, and the specific steps are as follows:

[0043] Step 1: Weigh 16.8 mg of the dried Pt / CNT nanocatalyst and 91.5 mg (1 mmol), 137.2 mg (1.5 mmol), 182.9 mg (2 mmol), and 228.7 mg (2.5 mmol) of tetrahydroxydiboron B2(OH)4, respectively, and place them in the corresponding hydrogen production reactor, add a stirrer to disperse them, and seal the reactor; the temperature is 30 °C and the rotation speed is 30 r;

[0044] Step 2: Use a microsyringe to draw 2 ml of anhydrous methanol solution and quickly inject it into the reactor in step 1. Start timing at the same time; record the hydrogen volume at the corresponding time every 15 seconds;

[0045] like Figure 3 As shown, the fitting slope of the hydrogen production reaction of B2(OH)4 is close to 1, indicating that the reaction of Pt / CNT nanocatalyst for hydrogen production by tetrahydroxydiboron B2(OH)4 is a first-order reaction.

[0046] Embodiment 3:

[0047] The Pt / CNT nanocatalyst obtained in Example 1 was used for hydrogen production from B2(OH)4, and the specific steps were as follows:

[0048] Step 1: Weigh 2 mmol B2(OH)4 and Pt / CNT nanocatalysts (0.2 mmol% (8.4 mg), 0.3 mmol% (12.6 mg), 0.4 mmol% (16.8 mg), 0.5 mmol% (21 mg)) and place them in a hydrogen production reactor, add a stirrer to disperse them, and seal the reactor; the temperature is 30 °C and the rotation speed is 30 r;

[0049] Step 2: Use a microsyringe to draw 2 ml of anhydrous methanol solution and quickly inject it into the reactor in step 1, and start timing at the same time;

[0050] Step 3: Record the volume of hydrogen at the corresponding time every 15 s;

[0051] like Figure 4 As shown, the fitting slope of the hydrogen release reaction of B2(OH)4 is close to 1, indicating that the relationship between its hydrogen production reaction and the concentration of Pt / CNT nanocatalyst is a first-order reaction.

[0052] Embodiment 4:

[0053] Effect of Pt / CNT nanocatalyst on hydrogen production of B2(OH)4 at different temperatures:

[0054] Step 1: Weigh 16.8 mg of Pt / CNT nanocatalyst and 2 mmol of tetrahydroxydiboron and place them in a hydrogen production reactor, add a stirrer for dispersion, set the temperature at 303, 293, 283, 273, and 263 K, and seal the reactor; the rotation speed is 30 r;

[0055] Step 2: Use a microsyringe to draw 2 ml of methanol solution and quickly inject it into the reactor in step 1, and start timing at the same time;

[0056] Step 3: Record the volume of hydrogen at the corresponding time every 15 s;

[0057] like Figure 5 and Figure 6 The figure shows the hydrogen production of tetrahydroxydiboron B2(OH)4 by the Pt / CNT catalyst at different temperatures. In a methanol environment, when the temperature is 263K, the fitting slope of the hydrogen production reaction of B2(OH)4 is close to 1, indicating that the reaction of Pt / CNT nanocatalyst for the hydrogen production of tetrahydroxydiboron B2(OH)4 is a first-order reaction, and its activation energy can be calculated to be 19.47 kJ / mol.

[0058] Embodiment 5:

[0059] The effect of the amount of Pt / CNT nanocatalyst on hydrogen production from B2(OH)4 is as follows:

[0060] Step 1: Weigh five portions of the catalyst of Example 1: 16.8 mg Pt / CNT nanocatalyst and 2 mmol tetrahydroxydiboron were placed in five hydrogen production reactors, and the reactors were sealed; the temperature was 30 ° C, the speed was 30 r;

[0061] Step 2: Use a microsyringe to draw 2 ml of anhydrous methanol solution and quickly inject it into the hydrogen production reactor in step 1, and start timing at the same time;

[0062] Step 3: Record the volume of hydrogen at the corresponding time every 15 seconds to obtain a mixed solution, thus completing the first cycle;

[0063] Step 4: Add 2 ml of NaOH (0.5 mmol / ml) aqueous solution to the mixed solution in step 3, centrifuge, wash with deionized water until neutral, and dry overnight (50 °C);

[0064] Step 5: Weigh 16.8 mg of the Pt / CNT catalyst dried in step 4 and place it in a hydrogen production reactor, add 2 mmol of tetrahydroxydiboron to each reactor, produce hydrogen as in step 3, and then obtain a mixed solution. That is, the second cycle is completed, and then NaOH solution is added to the mixed solution for centrifugation, washed with deionized water until neutral, and then dried overnight;

[0065] Step 6: Weigh 16.8 mg of the Pt / CNT catalyst dried in step 5 in three portions respectively and place them in hydrogen production reactors, add 2 mmol of tetrahydroxydiboron to each reactor, and produce hydrogen as in step 3 to obtain a mixed solution, that is, complete the third cycle, and after the mixed catalyst is washed with NaOH solution and centrifuged, it is washed with deionized water and dried;

[0066] Step 7: Weigh 16.8 mg of two portions of the dried Pt / CNT catalyst in step 6 and place them in hydrogen production reactors respectively. Add 2 mmol of tetrahydroxydiboron to each reactor, and produce hydrogen as in step 3. Then, a mixed solution is obtained, that is, the fourth cycle is completed. Then, NaOH solution is added to the mixed solution, centrifuged, washed with deionized water until neutral, and dried overnight.

[0067] Step 8: Weigh 16.8 mg of the Pt / CNT catalyst dried in step 7 and place them in two hydrogen production reactors, and add 2 mmol of tetrahydroxydiboron to each reactor to produce hydrogen, thus completing the fifth cycle experiment;

[0068] like Figure 7 As shown in the figure, the cyclic hydrogen production performance of B2(OH)4 is shown in the figure. As the catalytic times increase, the hydrogen production rate slows down slightly, but it still has a high catalytic activity. The Pt / CNT nanocatalyst has good cyclic performance.

[0069] Embodiment 6:

[0070] The production of hydrogen by Pt nanoparticles loaded on different carriers includes the following steps:

[0071] Step 1: Prepare 0.01 mmol / mL PtCl4 metal salt aqueous solution, disperse it by ultrasonication and set aside;

[0072] Step 2: Weigh 100 mg of carriers (CoFe2O4, Fe3O4, ZnO, ZrO2, CeO2, NiO, CNT) respectively and place them in different round-bottom flasks, and add 15 mL of deionized water;

[0073] Step 3: Take 2.5 ml of Pt 4+The ionic aqueous solution was added to Step 2. After ultrasonic treatment for 10 min, it was placed in a thermostatic heating magnetic stirrer with a collecting head and stirred for 10 min. The temperature was set at 30 °C and the speed was 20 r;

[0074] Step 4: Then, 2 mL of NaBH4 (19.5 mmol / mL) solution was quickly added to Step 3 and stirred for 15 min

[0075] Step 5: The precipitate obtained in Step 4 was washed, washed several times with water and ethanol, and then dried to prepare the Pt / CNT catalyst. The same method can be used to prepare Pt nanoparticles supported on CoFe2O4, Fe3O4, ZnO, ZrO2, CeO2, and NiO respectively; they are denoted as Pt / CoFe2O4, Pt / Fe3O4, Pt / ZnO, Pt / ZrO2, Pt / CeO2, and Pt / NiO respectively;

[0076] Step 6: Weigh 16.8 mg of the dried Pt / CNT nanocatalyst in Step 5 and 2 mmol of B2(OH)4 and place them in a hydrogen production reactor. Add a magnetic stir bar for dispersion and seal the reactor; the temperature is 30 °C and the rotation speed is 30 r;

[0077] Step 7: Use a syringe to draw 2 ml of methanol solution and quickly inject it into the hydrogen production reactor in Step 6, and start timing at the same time;

[0078] As Figure 8 shown, the support is of great significance to Pt nanoparticles. The catalytic activities of different supports can be seen as Pt / CoFe2O4 = Pt / Fe3O4 = Pt / ZnO < Pt / NiO < Pt / ZrO2 < Pt / CeO2 < Pt / CNT. Among them, Pt / CNT has the highest catalytic activity, and the main reason can be attributed to the strong interaction between the support and Pt nanoparticles.

[0079] The above embodiments are only used to illustrate the technical idea and characteristics of the present invention. The above content is only the preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Within the technical scope disclosed by the present invention, equivalent changes or improvements made according to the technical solution and inventive concept of the present invention should all be covered within the protection scope of the present invention.

Claims

1. Application of a carbon nanotube-supported Pt nanocatalyst in a hydrogen production reaction of B2(OH)4. After the catalyst is mixed with B2(OH)4, anhydrous methanol is added to produce hydrogen at a reaction temperature of 263K~303K. The preparation method of the catalyst comprises the following steps: Step 1: Configure Pt 4+ The aqueous solution of ions is dispersed by ultrasonic and then used for later use; the carbon nanotubes and water are mixed and then used for later use; Step 2: Place the Pt 4+ The aqueous solution of ions is added to the carbon nanotube water mixture, firstly ultrasonically mixed, then mechanically stirred and heated, and then NaBH4 solution is added to mix. Step 3: The material obtained in step 2 is allowed to settle, filtered, washed and then dried to obtain a carbon nanotube-loaded Pt nanocatalyst.

2. The use according to claim 1, characterized in that: Contains Pt 4+ Pt in aqueous solution 4+ The ion concentration is 0.01- 0.05 mmol / mL.

3. The use according to claim 1, characterized in that: Step 2 Pt 4+ The mass ratio of ions to carbon nanotubes is 1:2~40.

4. The use according to claim 1, characterized in that: In step 2, the ultrasonic mixing time is 0-20 min, and the mechanical stirring and heating adopts a heat-collecting constant temperature heating magnetic stirrer, stirring for 5-20 min, and the temperature is set at 30° C. and 10-30 r.

5. The use according to claim 1, characterized in that: The mass ratio of sodium borohydride to carbon nanotubes is 1-8:5-10, and the NaBH4 solution is added and stirred for 5-20 min.

6. The use according to claim 1, characterized in that: In step 3, water and ethanol are used for washing in sequence.

7. The use according to any one of claims 1 to 6, characterized in that: Replace carbon nanotubes with CoFe2O4, Fe3O4, ZnO, ZrO2, CeO2 or NiO to obtain Pt / CoFe2O4, Pt / Fe3O4, Pt / ZnO, Pt / ZrO2, Pt / CeO2 or Pt / NiO catalysts respectively.

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