CN107930697A - A kind of 67 composite materials of Pt/ZIF for being used to be catalyzed ammonia borane hydrolysis hydrogen manufacturing - Google Patents

Abstract

The invention discloses a Pt/ZIF-67 composite material for catalyzing the hydrolysis of ammonia borane to produce hydrogen, which is prepared by a one-step reduction method after mixing chloroplatinic acid and metal organic framework ZIF-67. Its structure retains the ZIF-67 framework structure, the average size of Pt nanoparticles is 1-2 nm, and the distribution is uniform, and there is no obvious Pt metal diffraction characteristic peak detected by XRD. The preparation method includes: step 1) preparation and activation of ZIF-67; step 2) loading of Pt nanoparticles, adding activated ZIF-67 to water for ultrasonic dispersion, then adding chloroplatinic acid, and then adding dropwise NaBH ₄ aqueous solution , and then the product is filtered, washed and dried. As an application to catalyze the hydrolysis of ammonia borane to produce hydrogen, the reaction rate has a turn over frequency (Turn over frequency, TOF) value of 70‑100 mol H ₂ min ^‑1 Pt mol ^‑1 , and an activation energy of 30‑40 kJ mol ^‑1 . The synergistic effect of ZIF-67 and Pt nanoparticles brings better catalytic performance, therefore, the invention has broad application prospects in the field of hydrogen preparation.

Description

A Pt/ZIF-67 Composite Catalytic Hydrogen Production from Ammoniaborane

technical field

The invention belongs to the field of energy technology, in particular to a Pt/ZIF-67 composite material used to catalyze the hydrolysis of ammonia borane to produce hydrogen.

Background technique

Among various chemical hydrogen storage materials, ammonia borane (NH ₃ BH ₃ , AB) has a hydrogen storage capacity as high as 19.6wt%, has high stability in solid state and solution, is non-toxic, and has good solubility. Therefore, it is considered as one of the promising chemical hydrogen storage materials in various applications. The hydrogen stored in ammonia borane can be released by hydrolysis using a suitable catalyst. So far, there have been a variety of catalysts used to catalyze the hydrolysis of ammonia borane, among which noble metal catalysts exhibit fast hydrogen desorption rate and low activation energy during hydrolysis to hydrogen production, and have excellent catalytic performance. However, the high price limits its production and application in practice. In order to reduce the cost, many researchers tend to support noble metal nanoparticles on different substrates (such as carbon materials, polymers, metal organic frameworks), which can not only take advantage of the high catalytic activity of noble metals, but also inhibit the agglomeration of nanoparticles, further Improve catalytic performance. Metal organic frameworks (MOFs) have also attracted much attention due to their unique high specific surface area and porosity properties as well as good chemical stability. Compared with other substrates, MOFs can control the nucleation and growth of noble metal nanoparticles within their framework, thereby preventing their agglomeration. In addition, the pores with high specific surface area and tunable pore size can better disperse noble metal nanoparticles. The researchers found that dispersing noble metal nanoparticles on the surface of MOFs or embedding them in the pores of MOFs can enhance the hydrogen release performance of AB hydrolysis. Cai et al. synthesized Ru/MIL-96 catalyst and used it for the catalytic hydrolysis of ammonia borane, and its activation energy E _a was as high as 47.7 kJ mol ^-1 [Int. J. Hydrogen Energy, 2014, 39, 17129-17135]. Luo et al. immobilized ultrafine Pd nanoparticles in the MIL-101 framework and tested its catalytic performance for the hydrolysis of ammonia borane, but the TOF was low at 45 mol H ₂ min ^-1 Pdmol ^-1 [Int. J. Hydrogen Energy, 2014, 39, 4947-4953]. Wang et al. supported AgPd alloy particles (5-9nm) on UIO-66-NH ₂ , which showed good performance as a catalyst for hydrogen production from ammonia borane hydrolysis, but there was mainly the problem of metal nanoparticles agglomeration [Int. J. Hydrogen Energy, 2016, 41, 944-950].

The catalytic properties of metal nanoparticles are closely related to their surrounding chemical environment. Given the highly tunable nature of the MOF structure, ligands with different functional groups have different interactions with metal nanoparticles, so the catalytic activity of metal nanoparticles is also different. Therefore, selecting appropriate ligands and MOF materials can realize the synergistic effect between MOF materials and metal nanoparticles and bring about better catalytic performance, which is an effective way to solve the above technical problems.

Contents of the invention

The purpose of the present invention is to provide a Pt/ZIF-67 composite material for catalyzing the hydrolysis of ammonia borane to produce hydrogen, which solves the problems of metal nanoparticle agglomeration, low TOF value and high activation energy in the prior art. By using ZIF-67 to combine with Pt, it can provide higher specific surface area and adsorption capacity, so that metal nanoparticles can be more uniformly dispersed on the surface of MOF materials; at the same time, ZIF-67 can be used to achieve synergy with Pt nanoparticles , improve catalytic performance.

In order to realize the foregoing invention object, the technical scheme that the present invention adopts comprises:

The Pt/ZIF-67 composite was prepared by a one-step reduction method after mixing chloroplatinic acid and metal-organic framework ZIF-67, and its structure retained the ZIF-67 framework structure. The average size of Pt nanoparticles is 1-2 nm, and the distribution is uniform, and there is no obvious Pt metal diffraction characteristic peak through XRD detection.

The preparation method of Pt/ZIF-67 composite material, comprises the following steps:

Step 1) Preparation and activation of ZIF-67, adding cobalt acetate tetrahydrate and 2-methylimidazole into water, ultrasonically mixing evenly, then putting them into a high-pressure reactor, putting them in an oven, heating at a constant temperature to initiate the reaction, and waiting for the reaction After the system is slowly cooled to room temperature, the product is taken out, washed and dried to obtain ZIF-67, and the obtained ZIF-67 is activated to obtain activated ZIF-67;

Step 2) Loading of Pt nanoparticles, adding activated ZIF-67 into water, ultrasonically dispersing for 30-60 min to obtain ZIF-67 aqueous solution, and then satisfying the mass ratio of activated ZIF-67 and chloroplatinic acid ( 5-15): 100, add chloroplatinic acid into the ZIF-67 aqueous solution, stir at room temperature for 6-24 h, and then drop the NaBH ₄ aqueous solution with a concentration of 0.01-0.05 mol/L in an ice-water bath while stirring Add it into the solution, continue to stir for 1-6 h, let it stand, then filter the product, wash it repeatedly with absolute ethanol and deionized water, and dry it in vacuum at 60-100 ^o C for 10-20 h to obtain Pt/ZIF-67 composite.

The Pt/ZIF-67 composite material of the present invention is used to catalyze the hydrolysis of ammonia borane to decompose hydrogen, which significantly improves the dehydrogenation performance, and has a higher TOF value of 70-100 mol H ₂ min ^-1 Pt mol ^-1 , and a lower activation energy of 30-40 kJ mol ^-1 .

Compared with the prior art, the present invention has the following advantages:

1. The Pt nanoparticles with an average size of 1-2 nm are uniformly distributed on the surface of metal organic framework ZIF-67, which effectively inhibits the agglomeration of nanoparticles;

2. The Pt/ZIF-67 composite material is used to catalyze the hydrolysis of ammonia borane to decompose hydrogen, showing good catalytic performance, specifically showing a high TOF value of 70-100 mol H ₂ min ^-1 Pt mol ^-1 , and a lower activation energy of 30-40 kJ mol ^-1 .

3. Compared with UIO-66-NH ₂ , ZIF-67 can provide higher specific surface area and better adsorption capacity, which can better disperse metal nanoparticles on the surface of MOF. More importantly, Played the synergistic effect of ZIF-67 and Pt nanoparticles, resulting in better catalytic performance;

4. The hydrogen production material of the present invention is low in cost, environmentally friendly, simple in process, and suitable for mass production.

Therefore, the present invention has broad application prospects in the field of hydrogen production.

Description of drawings:

Fig. 1 is the X-ray diffraction figure of specific embodiment;

Fig. 2 is the transmission electron microscope figure of specific embodiment

Fig. 3 is the particle size distribution figure of the Pt nanoparticle of specific embodiment;

Fig. 4 is the hydrogen release rate figure of specific embodiment catalyzing the hydrolysis of ammonia borane at different temperatures;

Fig. 5 is an Arrhenius curve of a specific embodiment.

Detailed ways

The present invention will be described in further detail through the embodiments in conjunction with the accompanying drawings, but it is not intended to limit the present invention.

Example

The specific operation steps of the Pt/ZIF-67 composite material used to catalyze the hydrolysis of ammonia borane to produce hydrogen are as follows:

Step 1) Preparation and activation of ZIF-67, add 1 mmol of cobalt acetate tetrahydrate and 20 mmol of 2-methylimidazole into 20 mL of water, mix well by ultrasonic, then put into autoclave, put into oven, keep constant temperature The reaction was initiated by heating to 120 ^o C, and the reaction time was 18 h. After the reaction system was slowly cooled to room temperature, the product was taken out, washed repeatedly with absolute ethanol and deionized water, and dried at 80 ^o C to obtain ZIF- 67, and the obtained ZIF-67 was activated under vacuum conditions at 150 ^o C for 12 h to obtain activated ZIF-67;

Step 2) Loading of Pt nanoparticles, 100 mg of activated ZIF-67 was added to 15 mL of water, ultrasonically dispersed for 40 min, then 5 mg of chloroplatinic acid was added to the solution, stirred at room temperature for 18 h, and then placed in an ice-water bath , add 10mL of 0.02 mol/L NaBH ₄ dropwise into the solution while stirring, continue to stir for 4 h, then let it stand, then filter the product, wash it repeatedly with absolute ethanol and deionized water, and put it at 80 ^o C under vacuum for 12 h to obtain the Pt/ZIF-67 composite.

The test results are as follows:

Figure 1 shows the XRD spectra of ZIF-67 and Pt/ZIF-67 composite materials prepared in the present invention. The characteristic peaks at 2θ=7.4˚, 12.7˚, and 16.5˚ correspond to the ZIF-67 crystal planes (011), (112), (013), indicating that the ZIF-67 framework is well preserved during the catalyst preparation process structure. In addition, no obvious Pt metal diffraction characteristic peaks were found from the PXRD pattern of Pt/ZIF-67, which may be due to the good dispersion of metal nanoparticles and low metal loading.

Figure 2 is a transmission electron microscope image of the Pt/ZIF-67 composite material prepared in the present invention. It can be seen from Figure 2 that most of the Pt nanoparticles (black dots) are distributed on the outer surface of ZIF-67, and from Figure 3 that the average size of the Pt nanoparticles is 1-2 nm.

Figure 4 shows the hydrogen desorption rate diagram and Arrhenius curve of the Pt/ZIF-67 composite material prepared in the present invention to catalyze the hydrolysis of ammonia borane at different temperatures. The test results are shown in the figure. The TOF of the Pt/ZIF-67 composite is 72.29 molH ₂ min ^-1 Pt mol ^-1 , and the activation energy is 39.42 kJ mol ^-1 , as shown in Figure 5.

Claims (9)

1. A Pt/ZIF-67 composite material used to catalyze the hydrolysis of ammonia borane to produce hydrogen, characterized in that: after the Pt/ZIF-67 composite material is mixed with chloroplatinic acid and metal organic framework ZIF-67, it is reduced by one step prepared by method. 2. The Pt/ZIF-67 composite material according to claim 1, characterized in that: its structure retains the ZIF-67 frame structure. 3. The Pt/ZIF-67 composite material according to claim 1, characterized in that: the average size of the Pt nanoparticles is 1-2 nm, and the distribution is uniform, and there is no obvious Pt metal diffraction characteristic peak through XRD detection. 4. A method for preparing a Pt/ZIF-67 composite material for catalyzing the hydrolysis of ammonia borane to produce hydrogen according to claim 1, comprising step 1) preparation and activation of ZIF-67, and cobalt acetate tetrahydrate Add 2-methylimidazole and 2-methylimidazole into water, mix evenly by ultrasonic, then put it into a high-pressure reactor, put it in an oven, and heat it at a constant temperature to initiate the reaction. After the reaction system is slowly cooled to room temperature, the product is taken out, washed, and dried to obtain ZIF -67, and the obtained ZIF-67 is activated to obtain activated ZIF-67; it is characterized in that it also includes: step 2) loading of Pt nanoparticles, adding activated ZIF-67 into water, and ultrasonically dispersing to obtain ZIF-67 aqueous solution, then meet a certain mass ratio of activated ZIF-67 and chloroplatinic acid, add chloroplatinic acid into the ZIF-67 aqueous solution, stir at room temperature, and then add a certain concentration of NaBH ₄ The aqueous solution is added dropwise into the solution while stirring, after continuing to stir, stand still, then filter the product, wash repeatedly with absolute ethanol and deionized water, and dry in vacuum to obtain the Pt/ZIF-67 composite material. 5. The preparation method according to claim 4, characterized in that: the mass ratio of activated ZIF-67 and chloroplatinic acid in the step 2) satisfies the relationship of (5-15):100. 6. The preparation method according to claim 4, characterized in that: the concentration of the NaBH ₄ aqueous solution in the step 2) is 0.01-0.05 mol/L. 7. The preparation method according to claim 4, characterized in that: said step 2) the ultrasonic dispersion time is 30-60 min, the stirring time at room temperature is 6-24 h, and the stirring time in ice-water bath is 1-6 h, the condition of vacuum drying is that the drying temperature is 60-100°C and the drying time is 10-20 h. 8. According to the application of the Pt/ZIF-67 composite material described in claim 1 as the hydrogen production by catalyzing the hydrolysis of ammonia borane, it is characterized in that: catalyzing the hydrolysis of ammonia borane to decompose hydrogen, obviously improving the dehydrogenation performance, representing its reaction rate The turnover frequency value (Turnover frequency, TOF) reaches 70-100 mol H ₂ min ^-1 Pt mol ^-1 . 9. The application of the Pt/ZIF-67 composite material according to claim 1 as catalyzing the hydrolysis of ammonia borane to produce hydrogen, characterized in that: the activation energy of catalyzing the hydrolysis of ammonia borane to decompose hydrogen is 30-40 kJ mol ^-1 .