Diatomic nano-catalyst as well as preparation method and application thereof

Abstract

The invention discloses a diatomic nano-catalyst and a preparation method and application thereof, and belongs to the technical field of catalysts.According to the diatomic nano-catalyst, a hexagonal boron nitride material obtained after ball milling serves as a carrier, Co and Cu are loaded on the carrier, the active ingredient is of a CoCu heterojunction structure and is of a core-shell structure, and the nano-particle size is about 10 nm; the apparent activation energy of the catalyst is 23.0 kJ mol < 1 >, the catalyst shows excellent catalytic performance in the aspect of hydrogen production through hydrolysis of ammonia borane, the catalytic performance can reach 28.8 mol H < 2 >. Mol <-1 > metal talmin < 1 >, and compared with a monatomic catalyst Co (at) BN, the performance of the catalyst is improved by nearly 100%, and compared with a monatomic catalyst Cu (at) BN, the performance of the catalyst is improved by 14 times. The catalyst is low in cost and easy to prepare, raw materials are easy to obtain, the diatomic catalyst with the heterojunction structure has universality, and a feasible strategy is provided for designing a high-performance catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a diatomic nanocatalyst and a preparation method and application thereof. Background Art

[0002] With the over-exploitation and use of traditional fossil fuels, people are facing energy crises while also facing environmental problems. The development of clean, green and promising energy carriers is a top priority for future sustainable energy supply and environmental protection. Among many alternative energy sources, hydrogen energy has become one of the cleanest candidate energy sources in the world due to its abundant natural reserves, high energy density and environmental friendliness. However, controllable storage, safe and convenient transportation and efficient production remain challenges for the large-scale application of hydrogen. Recently, liquid hydrogen storage chemicals, such as formic acid, methanol, sodium borohydride and ammonia borane, have been considered as feasible ways to achieve practical applications of hydrogen. Among them, ammonia borane has a hydrogen content of up to 19.6wt%, has good stability, water solubility and non-toxicity, and can release hydrogen through pyrolysis, hydrolysis, alcoholysis and other pathways; the reaction equation for hydrogen production by hydrolysis of ammonia borane is as follows: NH3BH3+ 2H2O → NH4BO2+ 3H2↑ The hydrolysis of ammonia borane can produce 3 molar equivalents of hydrogen, with a large hydrogen production amount. The hydrolysis reaction product is pollution-free and the reaction conditions are mild. It is considered to be a feasible hydrogen production technology. However, the hydrolysis reaction of ammonia borane has a large energy barrier and the hydrogen release rate is extremely slow under normal conditions. It is necessary to use an appropriate catalyst to catalyze the reaction to meet the needs of practical applications. Therefore, people have been committed to studying and discovering efficient, economical and durable ammonia borane hydrolysis catalysts. Pt, Rh, Pd and Ru-based precious metal catalysts are efficient catalysts for hydrogen production by hydrolysis of ammonia borane, but their scarce reserves limit the application of precious metal catalysts. In contrast, non-precious metal catalysts such as Co, Ni, Fe, and Cu are low in cost and have certain catalytic activity, which has aroused widespread interest among researchers. In 2006, Qiang Xu et al. (Catalytic activities of non-noblemetals for hydrogen generation from aqueous ammonia–borane at roomtemperature, Journal of Power Sources, 163 (2006) 364-370.) studied the catalytic effect of supported non-noble metal catalysts on the preparation of hydrogen from aqueous ammonia borane at room temperature. Among the non-noble metals tested, Co and Ni had the best catalytic effect, in which hydrogen was released from aqueous ammonia borane in almost stoichiometric amounts. The catalytic effect of Cu was not as good as that of Co and Ni, while Fe had no catalytic activity for this reaction. However, single-element transition metal-based catalysts are still unsatisfactory due to their low catalytic activity. The construction of bimetallic catalysts is one of the most effective strategies to improve the catalytic performance of ammonia borane hydrolysis. Due to the beneficial synergistic effect between the two different metals, bimetallic catalysts always exhibit excellent catalytic performance. FY Cheng et al. (Ni 1-x Pt x (x=0-0.12) hollow spheres as catalysts for hydrogen generation from ammonia borane, Inorg. Chem, 46 (2007) 788-794.) reported that alloying Pt with secondary metals (such as Ni, Co, and Ag) will bring about a component synergistic effect, thereby changing the surface electronic state of Pt and promoting the cracking of H−OH in H2O, kinetically promoting the adsorption of H atoms of H2O and AB, thereby accelerating the production of H2, but the use of precious metal Pt increases the synthesis cost of the material. Summary of the invention

[0003] The present invention provides a diatomic nanocatalyst and a preparation method and application thereof. Aiming at the problems of high cost and low catalytic activity of existing catalyst materials for ammonia borane hydrolysis reaction, a low-cost and high-activity nanocatalyst for catalyzing the hydrolysis of ammonia borane to produce hydrogen is prepared.

[0004] To achieve the above objectives, the present invention adopts the following technical solutions: A diatomic nanocatalyst uses ball-milled hexagonal boron nitride as a carrier to load Co and Cu. The catalyst has a core-shell structure and is a cobalt-copper bimetallic nanocomposite material with a heterojunction structure. The active component is a Co-Cu heterojunction, and the nanoparticle size is about 10 nm.

[0005] The method for preparing the above-mentioned diatomic nanocatalyst comprises the following steps: (1) Preparation of BN: h-BN hexagonal boron nitride was ball milled at 600 rpm for 10 h using a planetary ball mill to obtain BN; (2) dissolving the BN obtained in step (1), cobalt chloride hexahydrate and anhydrous copper chloride in deionized water and ultrasonicating for 30 minutes; then stirring the solution continuously at room temperature for 30 minutes to obtain a precursor solution; (3) NaBH4 solution (0.36 g NaBH4, 4 mL deionized water) was injected into the precursor solution obtained in step (2) under stirring, and the mixture was stirred at room temperature for 30 minutes. The mixture was centrifuged and then washed three times with anhydrous ethanol. The mixture was dried under vacuum at 50°C to obtain a cobalt-copper diatomic nanocatalyst, denoted as CoCu@BN.

[0006] In the above steps, the amount of BN used is 100 mg, the total mass of cobalt and copper in the cobalt chloride hexahydrate and anhydrous copper chloride is 11.1 mg, the molar ratio of the cobalt chloride hexahydrate to the anhydrous copper chloride is 1-x:x, x=0.1~0.9, and the preferred molar ratio is 0.8:0.2; the volume ratio of the NaBH4 solution to the precursor solution is 1:15, and whether the NaBH4 solution and the precursor solution react fully and completely is the key to whether cobalt and copper can be loaded on the carrier.

[0007] Beneficial effects: The present invention provides a diatomic nanocatalyst and a preparation method and application thereof, which has the following advantages over the prior art: 1. Use ball-milled hexagonal boron nitride as a carrier to load Co and Cu. Co can effectively activate water molecules, while Cu can effectively activate NH3BH3 molecules. The interface between Co and Cu can help Co 1-x Cu x@BN catalyst reduces the activation energy barrier of water and NH3BH3 molecules at the same time, promotes the hydrolysis of NH3BH3, and improves the activity of the catalyst; ball-milled hexagonal boron nitride as a carrier can make the catalyst have more catalytic sites, and then form a Co-Cu heterojunction structure through bimetallic loading, inducing strong electron transfer and changing the electron density, thereby accelerating the cracking of water molecules (the rate-determining step of the hydrolysis reaction of ammonia borane), thereby improving the catalytic performance of the catalytic active sites; 2. The bimetallic loaded cobalt-copper nanocomposite material with a core-shell structure prepared by the present invention is used as a catalyst for the hydrogen production reaction by hydrolysis of ammonia borane and has excellent catalytic performance. The core-shell structure can effectively limit the aggregation between metal particles and expose more catalytic active sites. Characterization results show that the size of the metal particles is between 10 and 14 nm. At the same time, the synergistic effect caused by the bimetallic loading has a very important influence on the catalytic performance of the material. The cobalt-copper diatomic nanocatalyst has excellent catalytic performance. In the hydrolysis reaction of ammonia borane, its catalytic reaction TOF value can reach 28.8 mol H2 mol metal −1 min −1 The apparent activation energy is 23.0 kJ mol −1 , compared with the single-atom pure Co@BN catalyst, its performance is improved by nearly 100%; 3. The bimetallic loading process of the present invention is simple and controllable, and the component ratio can be flexibly adjusted to synthesize a series of Co with different metal loading ratios. 1-x Cu x @BN, provides methods and ideas for the design and synthesis of high-performance catalysts; 4. The catalyst preparation process of the present invention is simple, low-cost, and the raw materials are readily available, easy to operate, and environmentally friendly, and is suitable for large-scale preparation; at the same time, the diatomic nanocatalyst with a heterojunction structure of the present invention is universal and provides a feasible strategy for designing high-performance catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is the Co prepared in the embodiment of the present invention 0.8 Cu 0.2 X-ray diffraction (XRD) patterns of @BN, Co@BN and Cu@BN catalysts.

[0009] Figure 2 is the Co prepared in the embodiment of the present invention 0.8 Cu 0.2 Scanning electron microscope (SEM) image of @BN catalyst.

[0010] Figure 3 is the Co prepared in the embodiment of the present invention 0.8 Cu0.2 Transmission electron microscopy (TEM) image of @BN catalyst.

[0011] Figure 4 is the Co prepared in the embodiment of the present invention 0.8 Cu 0.2 @Elemental analysis (EDS mapping) photo of BN catalyst.

[0012] Figure 5 Co with different loading ratios prepared in the embodiment of the present invention 1-x Cu x @BN catalyst catalyzes the hydrolysis and hydrogenation performance of ammonia borane under room temperature conditions.

[0013] Figure 6 is the Co prepared in the embodiment of the present invention 0.8 Cu 0.2 Arrhenius activation energy calculation diagram of hydrolysis of ammonia borane catalyzed by @BN and Co@BN catalysts at 25℃, 35℃, 45℃ and 55℃.

[0014] Figure 7 is the Co prepared in the embodiment of the present invention 0.8 Cu 0.2 Performance test graph of hydrogen release rate and TOF value of @BN, Co@BN and Cu@BN catalysts catalyzing hydrolysis and hydrogen release of ammonia borane at 25°C. DETAILED DESCRIPTION

[0015] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0016] Core-shell structured bimetallic Co 0.8 Cu 0.2 Preparation of @BN catalyst: (1) Weigh 100 mg h-BN and add it to a ball mill. Set the speed to 600 rpm. Mill for 30 min each time, pause for 15 min, repeat 19 times, and the total milling time is 10 h. The hBN after ball milling is recorded as BN. (2) Weigh 35.32 mg CoCl2·6H2O, 4.99 mg CuCl2 and 100 mg BN into 60 mL deionized water, treat with ultrasound for 30 min, continue stirring for 30 min, inject NaBH4 solution (prepared with 0.36 g NaBH4 and 4 mL deionized water) into the resulting mixed solution under stirring conditions, and continue stirring until the reaction is complete; (amount of substance: 0.1485 mol CoCl2·6H2O, 0.0371 mol CuCl2, 0.8:0.2) (3) The solution obtained in step (2) was centrifuged at a speed of 10000 r / min, and deionized water was added for washing. After repeated centrifugation and washing three times, the collected black solid was vacuum dried at 50° C. for 12 h to obtain Co 0.8 Cu 0.2 @BN.

[0017] The Co prepared in this example 0.8 Cu 0.2 @BN catalyst XRD and electron microscope photos are as follows Figure 1-3 As shown by Figure 1 It can be seen that in Co 0.8 Cu 0.2 In the @BN material, the diffraction peaks of Co (JCPDS NO. 15-0806) and Cu (JCPDS NO. 04-0836) coexist, confirming the existence of a two-phase Co-Cu junction in the synthesized sample. Electron microscope photo Figure 2-3 It shows that the obtained Co 0.8 Cu 0.2 @BN material has a distinct core-shell structure, and the size of the nanoparticles is roughly around 10nm. Figure 4 The elemental analysis results shown also show that Co and Cu elements are successfully loaded on the BN carrier and are evenly distributed in the material. Example 2

[0018] Core-shell structured bimetallic Co 1-x Cu x Preparation of @BN catalyst: The difference from Example 1 is that the molar ratio of CoCl2·6H2O to CuCl2 is different. The other steps are the same. Co 0.9 Cu 0.1 @BN,Co 0.6 Cu 0.4 @BN,Co 0.4 Cu 0.6 @BN,Co 0.2 Cu 0.8 @BN catalyst material.

[0019] Comparative Example 1 Preparation of core-shell structured single metal Co@BN catalyst: The only difference from Example 1 is that the addition of CuCl2 in step (2) is removed, the mass of CoCl2·6H2O is changed to 44.84 mg, and the sample is recorded as Co@BN.

[0020] The XRD pattern of the Co@BN catalyst prepared in this example is shown in Figure 1 As shown, the main phase of the Co@BN material is the Co phase, indicating that Co@BN is successfully synthesized.

[0021] Comparative Example 2 Preparation of core-shell structured single metal Cu@BN catalyst: The only difference from Example 1 is that the addition of CoCl2·6H2O in step (2) is removed, the mass of CuCl2 is changed to 23.51 mg, and the sample is recorded as Cu@BN.

[0022] The XRD pattern of the Cu@BN catalyst prepared in this example is shown in Figure 1 As shown, the main phase of the Cu@BN material is the Cu phase, indicating that Cu@BN is successfully synthesized.

[0023] Ammonia borane hydrolysis hydrogenation experiment under catalyst conditions:

[0024] The catalytic experiment was carried out in a 50mL double-mouthed round-bottom flask. 5mg of catalyst and 5mL of deionized water were added to the round-bottom flask, and the catalyst was evenly dispersed in the water by ultrasound. One port of the flask was connected to a gas micrometer (purchased from Rigamo, Germany) through a rubber tube to record the amount of hydrogen released by the reaction; the other port of the flask was sealed with a rubber stopper. 31.8mg of ammonia borane was dissolved in 5mL of NaOH solution (concentration of 1.0mol / L), and 5mL of alkaline ammonia borane solution was injected into the round-bottom flask through a rubber stopper using a syringe. At this time, the reaction started and the gas micrometer began to record data. During the entire test process, the round-bottom flask was placed in a constant temperature water bath to maintain a constant temperature of 25°C.

[0025] This example tests the Co 1-x Cu x @BN catalyst catalyzes the hydrolysis of ammonia borane. The results are as follows Figure 5 As shown, the rate of hydrogen production by the hydrolysis of ammonia borane catalyzed by the catalyst is Co 1-x Cu x @BN>Co@BN>Cu@BN, and Co 0.8 Cu 0.2 @BN catalyst has the highest hydrogen production rate by catalyzing the hydrolysis of ammonia borane. After forming a heterojunction structure, the catalytic activity of the material is greatly improved. Figure 7 As shown, Co 0.8 Cu 0.2 @BN catalytic hydrogen release rate reached up to 11.8 L H2 min -1 g metal −1 The TOF of the catalytic reaction reached 28.8 min -1 , showing excellent catalytic performance.

[0026] Test of hydrogen release rate and activation energy of catalyst under different temperature conditions:

[0027] By changing the water bath temperature of the round-bottom flask in the above-mentioned ammonia borane hydrolysis dehydrogenation experiment, the samples prepared in Example 1 and Comparative Example 1 were used to test the catalytic ammonia borane hydrolysis dehydrogenation at different temperatures (25°C, 35°C, 45°C and 55°C) according to the method of the above-mentioned ammonia borane hydrolysis dehydrogenation experiment.

[0028] Example 1 Co prepared 0.8 Cu 0.2 The Arrhenius activation energy test diagram of the Co@BN catalyst and the Co@BN catalyst prepared in comparative example 1 at 25°C, 35°C, 45°C and 55°C for catalyzing the hydrolysis and hydrogenation of ammonia borane is shown in the figure below. Figure 6 As shown in the results, the hydrogen release rate is positively correlated with temperature. The higher the temperature, the faster the hydrogen release rate. 0.8 Cu 0.2 The apparent activation energy of the catalytic reaction of Co@BN is 23.0 kJ / mol, and the apparent activation energy of the catalytic reaction of Co@BN is 45.6 kJ / mol, which indicates that the catalytic performance of the diatomic nanocatalyst prepared by the method of the present invention is greatly improved.

[0029] The above description is only a preferred embodiment of the present invention. For ordinary technicians in this technical field, several modifications and improvements can be made without departing from the principle of the present invention. These modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A diatomic nanocatalyst, characterized in that: The catalyst has a core-shell structure, and the active component is a Co-Cu heterojunction.

2. The diatomic nanocatalyst according to claim 1, characterized in that: The catalyst uses ball-milled hexagonal boron nitride as a carrier and loads Co and Cu.

3. The diatomic nanocatalyst according to claim 1 or 2, characterized in that: The catalyst nanoparticle size is 10 nm.

4. A method for preparing a diatomic nanocatalyst, characterized in that: The following steps are involved: S1: ball milling h-BN hexagonal boron nitride to obtain BN; S2: dissolving BN, cobalt chloride hexahydrate and anhydrous copper chloride in deionized water and mixing them evenly to obtain a precursor solution; S3: Add NaBH4 solution to the precursor solution while stirring at room temperature, continue stirring until the reaction is complete, and obtain the cobalt-copper diatomic nanocatalyst after separation, washing and drying.

5. The method for preparing the diatomic nanocatalyst according to claim 4, characterized in that: The amount of BN used is 100 mg, and the total mass of cobalt and copper in the cobalt chloride hexahydrate and anhydrous copper chloride is 11.1 mg.

6. The method for preparing a diatomic nanocatalyst according to claim 4 or 5, characterized in that: The molar ratio of the cobalt chloride hexahydrate to the anhydrous cupric chloride is 1-x:x, where x=0.1-0.

9.

7. The method for preparing a diatomic nanocatalyst according to claim 6, characterized in that: The molar ratio of the cobalt chloride hexahydrate to the anhydrous cupric chloride is 0.8:0.

2.

8. The method for preparing a diatomic nanocatalyst according to claim 4, characterized in that: After adding NaBH4 solution to the precursor solution, stirring was continued for 30 min.

9. The method for preparing a diatomic nanocatalyst according to claim 4 or 8, characterized in that: After the NaBH4 solution and the precursor solution react completely, the solution is centrifuged and then washed three times with anhydrous ethanol; vacuum drying is performed at 50° C. to obtain a cobalt-copper diatomic nanocatalyst.

10. The use of the diatomic nanocatalyst according to any one of claims 1 to 3, characterized in that: The diatomic nanocatalyst is used for producing hydrogen by hydrolyzing ammonia borane.

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