Catalyst Co2P-NC as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ammonia borane hydrolysis hydrogen production, and discloses a catalyst Co2P-NC and a preparation method and application thereof. The catalyst is Co2P modified NC (nitrocellulose). The preparation method comprises the following steps: (1) preparing nitrogen and phosphorus doped lignin carbon NPC; (2) modifying Co2P: dissolving cobalt acetate and zinc acetate in ethanol according to a molar ratio of cobalt to zinc of 1: 1 to prepare a mixed solution; adding NPC, and uniformly stirring; after stirring, evaporating the obtained turbid liquid to dryness the solvent, and then drying to obtain a solid; and grinding the obtained solid into powder, heating to 800-900 DEG C in an inert atmosphere, preserving heat and calcining for 2-2.5 hours, naturally cooling to room temperature, passivating a sample by using ethanol, and drying after the ethanol volatilizes until the sample does not flow any more, thereby obtaining the target product Co2P-NC. The catalyst Co2P-NC prepared by the preparation method disclosed by the invention has very high activity in ammonia borane hydrolysis hydrogen desorption, and the rB value reaches 2205mL. Min <-1 >. GCo <-1 >; after 6 times of cycle tests, the rB value is 2052 mL.min <-1 >. GCo <-1 >, the performance is only reduced by 7%, and the catalyst has good catalytic stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen production by hydrolysis of ammonia borane, and particularly relates to a catalyst Co2P@NC, a preparation method thereof and an application thereof. Background Art

[0002] With the rapid development of human society and the overuse of traditional fossil fuels, as well as the current imperfect energy structure and relatively backward energy use technologies, the energy problem and environmental pollution problem are constantly intensifying. For example, energy sources such as coal and oil are becoming increasingly depleted, and the greenhouse effect caused by acid rain and excessive emissions of CO2. These problems affect the sustainable development of human society on the one hand, and at the same time hinder the pace of the world's social and economic development towards a higher level. Therefore, developing clean, efficient and sustainable secondary energy to replace the current dependence on limited fossil fuel resources is the trend of future development. Among many clean energies, hydrogen energy is considered to be one of the ideal green clean energies that can replace non-renewable energy due to its good combustion performance, environmentally friendly combustion products, high specific heat value and being unaffected by regions. However, the efficient and safe storage and release of hydrogen are still a huge barrier in its practical application. Researchers have explored several physical hydrogen storage methods, such as compression, liquefaction and physical adsorption in solid materials. However, these physical hydrogen storage methods have inevitable disadvantages such as the need for a large amount of energy input, continuous boiling, logistics obstacles and low adsorption capacity, which are not conducive to the establishment of hydrogen energy in practical applications. Among all hydrogen storage methods, chemical hydrogen storage stores hydrogen in the form of chemical bonds, has good safety, convenience and high efficiency, and has the greatest development potential. Ammonia borane (AB) is considered to be an excellent hydrogen storage material due to its high hydrogen content (19.6 wt%), high stability in aqueous solution and non-toxicity. Research shows that noble metal-based catalysts Pt, Pd, Rh, Ru usually show high efficiency for the hydrolysis of AB. However, high cost and scarcity have hindered their wide application. There is an urgent need to develop alternative catalysts based on cheap non-precious metal elements to achieve efficient hydrolysis of AB. Non-precious metal nickel-based, cobalt-based, iron-based, copper-based and other catalysts can also greatly increase the rate of hydrogen production by hydrolysis of ammonia borane, especially Co-based catalysts have the most practical prospects. However, only metal particle catalysts are generally prone to agglomeration, have a small specific surface area, reduce active sites and reduce the catalytic effect. Therefore, selecting a suitable carrier to load the metal is one of the hotspots in the current research field of hydrogen production by hydrolysis of ammonia borane, and the carriers of most catalysts affect the evaluation of their catalytic activity. Carbon materials are considered to be excellent precursors for metal catalysts due to their good chemical stability, long service life, high metal loading capacity, low cost and other advantages. Heteroatom (nitrogen, sulfur, phosphorus, etc.) doped carbon materials can effectively avoid lattice mismatch, improve the surface electron density and electron transport rate of carbon materials, provide more active centers, and further improve the catalytic performance. Summary of the Invention

[0003] To solve the following problems existing in the prior art: ① The noble metal-based catalyst is costly and scarce; ② Only the metal particle catalyst is prone to agglomeration, reducing the catalyst effect; ③ Lattice mismatch, the purpose of the present invention is to provide a catalyst Co2P@NC and its preparation method and application.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows: A catalyst Co2P@NC, which is Co2P-modified NC; wherein, Co2P represents cobalt phosphide, and NC represents nitrogen-doped lignin carbon.

[0005] The preparation method of the catalyst Co2P@NC is as follows: (1) Preparation of nitrogen and phosphorus-doped lignin carbon: Dissolve the nitrogen and phosphorus-rich precursor and lignin in water and stir evenly; after stirring, evaporate the solvent of the obtained turbid liquid and then dry it to obtain a solid; grind the obtained solid into powder, calcine it under air isolation conditions, and naturally cool it to room temperature to obtain a powder; wash the obtained powder with hydrochloric acid first, then wash it with water until neutral, and dry it to obtain nitrogen and phosphorus-doped lignin carbon, named NPC. (2) Co2P modification: Dissolve cobalt acetate and zinc acetate in ethanol according to the molar ratio of cobalt:zinc = 1:1 to prepare a mixed solution; add the NPC prepared in step (1) and stir evenly; after stirring, evaporate the solvent of the obtained turbid liquid and then dry it to obtain a solid; grind the obtained solid into powder, heat it to 800-900 °C in an inert atmosphere and keep it calcined for 2-2.5 h, naturally cool it to room temperature, passivate the sample with ethanol, and dry it after the ethanol volatilizes until the sample no longer flows to obtain the target product Co2P@NC.

[0006] Preferably, in step (1), the nitrogen and phosphorus-rich precursor is (NH4)3PO3·3H2O, the calcination temperature is 800-900 °C, and the calcination time is 2-2.5 h.

[0007] Preferably, in step (1), the raw material dosage ratio is (NH4)3PO3·3H2O:lignin:water = (10.0000-12.0084) g:(5.0000-6.0023) g:(65-80) mL.

[0008] Preferably, in step (1), the concentration of hydrochloric acid is 0.01-0.02 M.

[0009] Preferably, in step (2), the raw material dosage ratio is cobalt acetate:ethanol:NPC = (0.6-0.75) mmol:(20-25) mL:(0.2-0.25) g.

[0010] Preferably, in step (2), when passivating with ethanol, the amount of ethanol used should ensure complete coverage of the sample.

[0011] Preferably, in steps (1) and (2), the time for uniform stirring is 6 - 7 h, the temperature for evaporating the solvent is 60 - 75 °C, and the drying temperature is 40 - 60 °C.

[0012] Preferably, in steps (1) and (2), during calcination, the temperature is raised to the corresponding temperature at a rate of 3 - 5 °C / min.

[0013] Application of the catalyst Co2P@NC in hydrogen production by hydrolysis of ammonia borane.

[0014] In the present invention, zinc acetate and cobalt acetate compete differently for active sites, and zinc volatilizes at about 900 °C. The role of adding zinc acetate is to adjust the number of active sites, prevent the agglomeration of active sites, and improve the catalytic activity.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The catalyst Co2P@NC prepared by the present invention has high activity in hydrogen production by hydrolysis of ammonia borane; the incorporation of two heteroatoms, nitrogen and phosphorus, makes the catalyst reaction have more active sites, further improving the catalytic performance, and the r B value reaches 2205 mL·min -1 ·g Co -1 ; after 6 cyclic tests of the Co2P@NC catalyst, the r B value is 2052 mL·min -1 ·g Co -1 , and the performance only decreases by 7%, showing good catalytic stability; (2) The present invention creatively designs a cobalt phosphide - modified lignin - based carbon catalyst Co2P@NC. The presence of N, P - doped lignin - based carbon can effectively avoid lattice mismatch, increase the surface electron density and electron transport rate of the carbon material, provide more active centers, and further improve the catalytic performance; (3) The present invention uses cobalt phosphide - modified lignin - based carbon, reducing the catalyst cost and improving the catalytic performance. Description of the Drawings

[0016] Figure 1 : X - ray diffraction patterns (XRD) of the catalysts Co2P@NC - 1, Co2P@NC - 0, Co2P@NC - 2, and Co2P@NC - 3 prepared in Example 1 and Comparative Examples 1 - 3.

[0017] Figure 2: XPS spectra of C1s, N1s, Co 2p and P 2p of the catalyst Co2P@NC-1 prepared in Example 1.

[0018] Figure 3 : HRTEM of the catalyst Co2P@NC-1 prepared in Example 1.

[0019] Figure 4 : Hydrolysis reaction process of ammonia borane of the catalysts Co2P@NC-1, Co2P@NC-0, Co2P@NC-2, Co2P@NC-3 prepared in Example 1 and Comparative Examples 1-3.

[0020] Figure 5 : 6-cycle stability test of the catalyst Co2P@NC-1 prepared in Example 1. Detailed implementation manners

[0021] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the described embodiments, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention.

[0022] Example 1

[0023] A preparation method of a catalyst, the steps are as follows: (1), Prepare nitrogen and phosphorus doped lignin carbon: Dissolve (NH4)3PO3·3H2O (12.0084 g) and lignin (6.0023 g) in 80 mL of ultrapure water and stir for 6 h; after stirring, place the obtained turbid liquid in a water bath at 60 °C until the water is evaporated, and then place it in an oven at 60 °C to dry to obtain a brown solid; grind the obtained solid into powder and put it into a crucible, and heat it in a muffle furnace under an inert atmosphere (cover a layer of coconut shell charcoal, that is, carbonized coconut shell, on the solid powder, then cover the lid of the crucible, and cover the crucible as tightly as possible) at a heating rate of 5 °C / min to 800 °C and keep it calcined for 2 h, and then cool it naturally to room temperature to obtain a powder; wash the obtained powder with 0.01 M hydrochloric acid first, and then wash it with deionized water until neutral, and dry it in a vacuum drying oven at 60 °C to obtain nitrogen and phosphorus doped lignin carbon, named NPC; (2), Co2P modification: Dissolve CH3COO)2Co·4H2O (0.1492 g) and (CH3COO)2Zn in 20 mL of absolute ethanol according to the molar ratio of Co∶Zn = 1∶1 to prepare a mixed solution; add the NPC prepared in step (1) (0.2000 g), and stir for 6 h; after stirring, place the obtained turbid liquid in a water bath at 60 °C until the absolute ethanol is evaporated, and then place it in a vacuum oven at 40 °C to dry it to obtain a solid; grind the obtained solid into powder and put it into a porcelain boat, and in a N2 atmosphere in a tubular furnace, heat it to 900 °C at a heating rate of 5 °C / min and keep it calcined for 2 h. After the tubular furnace calcination is completed, wait for it to cool naturally to room temperature. When disassembling the tubular furnace, quickly pull out the porcelain boat, quickly add absolute ethanol to cover the entire sample for passivation, and after the absolute ethanol evaporates until the sample in the porcelain boat no longer flows, place it in a vacuum drying oven at 40 °C to dry it to obtain the target product, named Co2P@NC-1.

[0024] Comparative Example 1 The difference from Example 1 is that in step (2), under the condition that the dosage of CH3COO)2Co·4H2O remains unchanged, adjust the dosage of (CH3COO)2Zn so that the molar ratio of CH3COO)2Co·4H2O to (CH3COO)2Zn is Co∶Zn = 1∶0; the others are the same as in Example 1.

[0025] The obtained product is named Co2P@NC-0.

[0026] Comparative Example 2 The difference from Example 1 is that in step (2), under the condition that the dosage of CH3COO)2Co·4H2O remains unchanged, adjust the dosage of (CH3COO)2Zn so that the molar ratio of CH3COO)2Co·4H2O to (CH3COO)2Zn is Co∶Zn = 1∶2; the others are the same as in Example 1.

[0027] The obtained product is named Co2P@NC-2.

[0028] Comparative Example 3 The difference from Example 1 is that in step (2), under the condition that the dosage of CH3COO)2Co·4H2O remains unchanged, adjust the dosage of (CH3COO)2Zn so that the molar ratio of CH3COO)2Co·4H2O to (CH3COO)2Zn is Co∶Zn = 1∶3; the others are the same as in Example 1.

[0029] The obtained product is named Co2P@NC-3.

[0030] Catalyst structure characterization Figure 1XRD patterns of the catalysts Co2P@NC-1, Co2P@NC-0, Co2P@NC-2, and Co2P@NC-3 prepared in Example 1 and Comparative Examples 1-3. It can be seen from the XRD patterns that all the catalysts correspond to the PDF standard card (32-0306) of Co2P, indicating that Co2P has been successfully incorporated into the catalysts.

[0031] Figure 2 XPS spectra of C 1s, N 1s, Co 2p, and P 2p of the catalyst Co2P@NC-1 prepared in Example 1, demonstrating the successful preparation of the catalyst Co2P@NC-1.

[0032] Figure 3 HRTEM of the catalyst Co2P@NC-1 prepared in Example 1. From Figure 3 it can be seen that the measured lattice spacing is approximately 0.29 nm, which is in good agreement with the crystal interplanar spacing of Co2P (120) (32-0306).

[0033] Catalyst performance test The catalysts Co2P@NC-1, Co2P@NC-0, Co2P@NC-2, and Co2P@NC-3 prepared in Example 1 and Comparative Examples 1-3 were used for hydrogen production from ammonia borane. The experimental procedure was as follows: (1) Weigh 0.2000 g of sodium hydroxide and dissolve it completely in 5 mL of ultrapure water to prepare an aqueous NaOH solution. Place it in a water bath at 30 °C for heat preservation and reserve it. (2) Add 10 mg of the catalyst and 2.5 mL of the NaOH aqueous solution prepared in step (1) to a 25 mL round-bottom flask. Place the flask in an ultrasonic cleaner and oscillate the solution for 2 min. After the ultrasonic treatment, place the round-bottom flask in a constant temperature water bath at 30 °C and stir magnetically, with the rotation speed maintained at 500 r·min -1 ; (3) Weigh 44 mg of ammonia borane and pour it into the remaining 2.5 mL of the NaOH aqueous solution in step (1). After the ammonia borane is completely dissolved, quickly suck it out with a dropper and squeeze it into the round-bottom flask in step (2). Quickly connect the rubber tube and start timing. After the reaction starts, record the time every time 5 mL of hydrogen is produced until the reading no longer changes. Calculate the hydrogen production rate, and the rate of the catalytic reaction of the catalyst is measured by r B (the average hydrogen production rate of the catalyst for catalyzing ammonia borane).

[0034] Figure 4 Hydrolysis reaction process of ammonia borane for the catalysts Co2P@NC-1, Co2P@NC-0, Co2P@NC-2, and Co2P@NC-3 prepared in Example 1 and Comparative Examples 1-3. From Figure 4It can be seen that the r value of Co2P@NC-1 is 2205 mL·min B ·g -1 ·g Co -1 、the r value of Co2P@NC-0 is 1116 mL·min B ·g -1 ·g Co -1 、the r value of Co2P@NC-2 is 1488 mL·min B ·g -1 ·g Co -1 ,and the r value of Co2P@NC-3 is 864 mL·min B ·g -1 ·g Co -1 。This is because: the proportion of (CH3COO)2Zn added is different, and the competition between (CH3COO)2Co and (CH3COO)2Zn for active sites is different. Only when the proportion of (CH3COO)2Co and (CH3COO)2Zn is just right, the competitive effect of (CH3COO)2Zn on active sites is appropriate, and the number and dispersion of formed active sites are both optimal, the catalytic activity is optimal, and the hydrogen production rate of ammonia borane is optimal.

[0035] Figure 5 is the 6-cycle stability test of the catalyst Co2P@NC-1 prepared in Example 1. It can be seen from Figure 5 that after 6-cycle tests of the Co2P@NC-1 catalyst, the r value is 2052 mL·min B ·g -1 ·g Co -1 ,and the performance only decreases by 7%, showing good catalytic stability.

Claims

1. A catalyst Co2P@NC, characterized in that: The catalyst is Co2P modified NC; where Co2P represents cobalt phosphide and NC represents nitrogen-doped lignin carbon.

2. A preparation method of the catalyst Co2P@NC as described in claim 1, characterized in that, The steps are as follows: (1) Preparation of nitrogen and phosphorus co-doped lignin carbon: Dissolve the nitrogen and phosphorus-rich precursor and lignin in water and stir evenly; after stirring, evaporate the solvent of the obtained turbid liquid and then dry it to obtain a solid; grind the obtained solid into powder, calcine it under air isolation conditions, and cool it naturally to room temperature to obtain a powder; wash the obtained powder with hydrochloric acid first, then wash it with water until neutral, and dry it to obtain nitrogen and phosphorus co-doped lignin carbon, named NPC. (2) Co2P modification: Dissolve cobalt acetate and zinc acetate in ethanol according to the molar ratio of cobalt:zinc = 1:1 to prepare a mixed solution; add the NPC prepared in step (1) and stir evenly; after stirring, evaporate the solvent of the obtained turbid liquid and then dry it to obtain a solid; grind the obtained solid into powder, heat it to 800 - 900 °C in an inert atmosphere and keep it calcined for 2 - 2.5 h, cool it naturally to room temperature, passivate the sample with ethanol, and dry it after the ethanol volatilizes until the sample no longer flows to obtain the target product Co2P@NC.

3. The preparation method of the catalyst Co2P@NC according to claim 2, characterized in that: In step (1), the nitrogen and phosphorus-rich precursor is (NH4)3PO3·3H2O, the calcination temperature is 800 - 900 °C, and the calcination time is 2 - 2.5 h.

4. The preparation method of the catalyst Co2P@NC according to claim 3, characterized in that: In step (1), the raw material dosage ratio is (NH4)3PO3·3H2O∶lignin∶water = (10.0000 - 12.0084) g∶(5.0000 - 6.0023) g∶(65 - 80) mL.

5. The preparation method of the catalyst Co2P@NC according to claim 2, characterized in that: In step (1), the concentration of hydrochloric acid is 0.01 - 0.02 M.

6. The preparation method of the catalyst Co2P@NC according to claim 2, characterized in that: In step (2), the raw material dosage ratio is cobalt acetate∶ethanol∶NPC = (0.6 - 0.75) mmol∶(20 - 25) mL∶(0.2 - 0.25) g.

7. The preparation method of the catalyst Co2P@NC according to claim 2, characterized in that: In step (2), when passivating with ethanol, the amount of ethanol used should ensure complete coverage of the sample.

8. The preparation method of the catalyst Co2P@NC according to claim 2, characterized in that: In steps (1) and (2), the stirring time is 6 - 7 h, the solvent evaporation temperature is 60 - 75 °C, and the drying temperature is 40 - 60 °C.

9. The preparation method of the catalyst Co2P@NC according to claim 2, characterized in that: In steps (1) and (2), during calcination, heat up to the corresponding temperature at a rate of 3 - 5 °C / min.

10. Application of the catalyst Co2P@NC as described in claim 1 in the hydrolysis of ammonia borane for hydrogen production.

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