NiHZSM-5 Brønsted acid catalyst, its composite system with LiBH4, and preparation method for hydrogen storage materials.

Abstract

The application relates to a preparation method of a NiHZSM-5 Bronsted acid catalyst and a hydrogen storage material of a LiBH4 composite system. The NiHZSM-5 Bronsted acid catalyst is prepared by the following method: step one: adding nickel nitrate hexahydrate, deionized water and diethylenetriamine into a reaction kettle, then adding sodium metaaluminate, n-propyl ammonium hydroxide and deionized water in sequence, finally adding tetraethyl orthosilicate, stirring and aging, and carrying out hydrothermal reaction to obtain a reactant; step two: washing, drying and calcining the reactant to obtain NiZSM-5 powder; and step three: carrying out ammonium nitrate solution exchange and reduction on the NiZSM-5 powder to prepare the NiHZSM-5 Bronsted acid catalyst. The hydrogen storage material is prepared by the following steps: mixing the NiHZSM-5 Bronsted acid catalyst and LiBH4 in a glove box, and ball milling to obtain the hydrogen storage material. The NiHZSM-5 Bronsted acid catalyst provided by the application is simple in synthesis and short in period. The hydrogen storage performance of LiBH4 can be effectively improved, and the hydrogen release capacity reaches 5.9 wt% and 6.8 wt% at 320 DEG C and 380 DEG C isothermally for 200 min.

Description

Technical Field

[0001] This invention relates to the field of solid hydrogen storage materials and their preparation technology, specifically to a NiHZSM-5 Brønsted acid catalyst and its composite hydrogen storage material with LiBH4, and its preparation method. Background Technology

[0002] Energy is a crucial guarantee for the sustainable development of human society and a vital material foundation for human survival. With the continuous progress and development of human society, the demand and consumption of energy are constantly increasing, making the development of efficient, clean, safe, and inexpensive new energy sources extremely important and urgent. Hydrogen, with its high energy density, high calorific value, water as a combustion product, clean and pollution-free nature, abundant reserves, and wide availability, has become an ideal secondary energy source. Safe and efficient hydrogen storage is a crucial and key technology for realizing the large-scale application of hydrogen energy. Currently, hydrogen storage methods include high-pressure gaseous hydrogen storage, liquid hydrogen storage, and solid-state hydrogen storage. Among these, solid-state hydrogen storage is considered the most promising technology due to its high volumetric and gravimetric hydrogen storage densities and good safety. Among numerous solid hydrogen storage materials, the light metal borohydride LiBH4 possesses a high gravimetric hydrogen storage density of 18.5 wt% and a volumetric density of 121 kg / m³. 3 It is considered one of the most promising solid-state hydrogen storage materials. However, its hydrogen storage performance has been less than ideal.

[0003] In recent years, cation and anion substitution has been a major method to improve the hydrogen storage performance and high hydrogen release temperature of LiBH4. The thermodynamic stability of metal borohydrides is related to the electronegativity of the central ion. Based on this principle, it is concluded that the thermodynamic stability of metal borohydrides decreases as the electronegativity of the metal cation increases. The higher the electronegativity of the cation, the less likely it is to lose electrons, and the less likely it is to convert to [BH4]. - The transfer weakened Li + and [BH4] -The strength of the ionic bonds between them. For example, Fang et al. {The Journal of Physical Chemistry C, 2010, 114(51): 22736-22741} ball-milled LiBH4 and Ca(BH4)2 to form a bimetallic ion composite system LiCa(BH4)3, which achieved hydrogen release at 250-360 °C. Pavnsbaek et al. {Physical Chemistry Chemical Physics, 2013, 15: 19774-19789} found that the hydrogen release temperature of the composite hydrogen storage system formed by LiBH4 with NaBH4, Mg(BH4)2, Mn(BH4)2, and Na(BH4) is lower than that of the single system. Rude et al. {Journal of Alloys and Compounds, 2011, 509(33): 8299-8305} prepared a LiBH4-LiI composite system by mechanical ball milling of LiBH4 and LiI. Their research showed that I... - It replaced part of [BH4]. - h-Li[BH4] was formed. 1-x I x However, the hydrogen storage performance of this substitution system was not improved compared to LiBH4. Fang et al. {The Journal of Physical Chemistry C, 2011, 115(27): 13528-13533} found through theoretical calculations and experimental studies on the LiBH4-MnF2 and LiBH4-MnCl2 composite systems that F - It can partially replace H - Formation [BH 4-x F x ], while Cl - It will not replace [BH4] - H in - However, the following problems still exist: 1) Although cation and anion substitution can lower the hydrogen decomposition temperature of LiBH4, the initial hydrogen decomposition temperature remains very high. A major reason for the high hydrogen decomposition temperature is the large number of electrons between the BH bonds. These electrons interact with each other, requiring higher energy to break the BH bonds during decomposition.

[0004] 2) Metal borohydrides, as candidates for ion substitution, are expensive and difficult to prepare.

[0005] 3) It is difficult to maintain the characteristics of lattice substitution by anion and cation substitution, and the hydrogen release capacity is not ideal. Summary of the Invention

[0006] This invention aims to provide a method for preparing NiHZSM-5 Brønsted acid catalyst and its composite hydrogen storage material with LiBH4, thereby overcoming the problems of high hydrogen release temperature, high price, difficult preparation, and insufficient hydrogen release capacity in existing technologies.

[0007] To achieve the objectives of this invention, the technical solution provided by this invention is as follows: Part 1 provides a NiHZSM-5 Brønsted acid catalyst, which is prepared by the following method: Step 1: First, add nickel nitrate hexahydrate, deionized water, and diethylenetriamine to the reaction vessel and stir for 20-40 minutes. Then, add sodium aluminate, tetrapropylammonium hydroxide, and deionized water to the reaction vessel in sequence and stir at 70-80 ℃ for 2-3 hours. Next, add tetraethyl orthosilicate and continue stirring at 80-90 ℃ for 2-3 hours to age the product and obtain a gel. Finally, transfer the product to a forced-air drying oven and keep it at 160-180 ℃ for 48-52 hours for hydrothermal reaction to obtain the reactants.

[0008] Step 2: The reactants are centrifuged, washed and dried, and then calcined in a muffle furnace to remove the organic template, thereby obtaining NiZSM-5 powder; Step 3: NiZSM-5 powder is exchanged and reduced with ammonium nitrate solution to prepare NiHZSM-5 Brønsted acid catalyst.

[0009] In step one above, the mass ratio of nickel nitrate hexahydrate, deionized water, and diethylenetriamine is 0.5-0.7g: 20-22g: 0.5-0.7g.

[0010] In step one above, the mass ratio of sodium aluminate, tetrapropylammonium hydroxide, and deionized water is 0.17-0.33g: 19-21g: 20-22g.

[0011] In step one above, the mass of tetraethyl orthosilicate is 20.6-21g.

[0012] Preferably, the Si / Al molar ratio is 25-50:1.

[0013] In step three above, the exchange process is as follows: First, 1 g of NiHZSM-5 is added to 20 g of ammonium nitrate solution (1 mol / L), stirred at 80-90℃ for 1-2 h, and the exchange is repeated several times; then, the sample is dried and calcined in a muffle furnace to remove the organic template; finally, the sample is reduced in a tube furnace; the reduction process is as follows: a mixed gas with a volume percentage of 10% H2 + 90% Ar is introduced into the tube furnace, and the temperature is maintained at 400-500℃ for 1-2 h, and then the temperature is raised to 500-550℃ and maintained for 4-5 h.

[0014] The second part provides a method for preparing the above-mentioned NiHZSM-5 Brønsted acid catalyst and LiBH4 composite system hydrogen storage material, including the following steps: Step 1: Vacuum dry the NiHZSM-5 Brønsted acid catalyst and keep it at 300-350℃ for 10-12 h.

[0015] Step 2: In a glove box, mix NiHZSM-5 Brønsted acid catalyst and LiBH4 in a mass ratio of 25-50:50-75, place the mixture in a ball mill jar, and purge with Ar gas as a protective gas. The ball milling speed is 400-500 rpm / min, and the milling time is 1-2 h. After the ball milling is completed, collect the product.

[0016] Preferably, in step two above, the mass ratio of NiHZSM-5 Brønsted acid catalyst to LiBH4 is 40:60.

[0017] In step two above, the ball-to-material ratio is 100:1, and the grinding beads are selected as carbide beads with a diameter of 6mm.

[0018] The third part provides a composite hydrogen storage material prepared by the above method.

[0019] Compared with the prior art, the advantages of the present invention are as follows: 1. Currently, the preparation of NiHZSM-5 Brønsted acid catalysts with supported metallic Ni mostly employs ion exchange. However, exchanging metal cations reduces the Brønsted acidity of the catalyst, resulting in weaker acidity and a decrease in the number of -OH groups on the molecular sieve framework, making it unsuitable as a catalyst for weakening the electron cloud density of BH bonds in LiBH4. Furthermore, the ion exchange process is complex, time-consuming, and prone to incomplete exchange.

[0020] The preparation method provided by this invention first introduces single-atom nickel in situ during the synthesis process, unlike ion exchange. Then, the NiHZSM-5 Brønsted acid catalyst is synthesized by exchanging the nickel with ammonium nitrate solution. In this process, the traditional ion exchange method for loading nickel is omitted, effectively avoiding the reduction of -OH groups on the molecular skeleton. Therefore, NiZHSM-5 with abundant Brønsted acid sites can be synthesized, giving it strong acidity. Simultaneously, the number of Brønsted acid sites can be effectively controlled by changing the Si / Al ratio during the preparation process; the smaller the Si / Al ratio, the stronger the acidity of the resulting NiZHSM-5 Brønsted acid catalyst. Because the nickel is directly added during the synthesis process, avoiding the ion exchange process, the NiHZSM-5 Brønsted acid catalyst provided by this invention uses inexpensive raw materials, is simple to synthesize, and has a short cycle time.

[0021] 2. This invention utilizes the abundant Brønsted acid in the NiHZSM-5 Brønsted acid catalyst prepared by the method of this invention to improve the hydrogen storage material LiBH4. The Brønsted acid catalyst is introduced into the hydrogen storage material as an additive, and the -OH on the catalyst framework is a proton H. + , and [BH4] in LiBH4 - H in - Coupling occurs (H) + +H - =H2), thus weakening the electron cloud density between BH bonds in LiBH4, causing structural instability of LiBH4. NiHZSM-5 Brønsted acid catalyst, as a destabilizing agent, interacts with LiBH4. When reducing the hydrogen desorption temperature, it does not need to maintain lattice integrity as with anion and cation substitution, thus effectively improving the hydrogen storage performance of LiBH4.

[0022] 3. This invention uses the NiHZSM-5 Brønsted acid catalyst prepared by the method of this invention as an additive to prepare composite hydrogen storage materials. Therefore, the composite hydrogen storage materials can be prepared by a simple ball milling process. The metal single atom introduced in this invention can also act as a destabilizing agent, reducing the hydrogen desorption temperature of LiBH4. The composite system composed of LiBH4 and NiHZSM-5 has a 110 °C lower initial hydrogen desorption temperature than the original LiBH4, and the hydrogen desorption capacity can reach 7 wt% at 400 °C. Isothermal performance tests show that the composite hydrogen storage material provided by this invention can achieve hydrogen desorption capacities of 5.9 wt% and 6.8 wt% after isothermal testing at 320 °C and 380 °C for 200 min, respectively. Attached Figure Description

[0023] Figure 1 This is the Xrd characterization diagram of NiHZSM-5 (Si / Al=25, 200).

[0024] Figure 2 These are the Brønsted acid spectra of NiHZSM-5 (Si / Al=25, 200) at different temperatures, obtained by qualitative analysis of infrared pyridine absorption spectra.

[0025] Figure 3 This is a SEM characterization image of NiHZSM-5 (Si / Al=25).

[0026] Figure 4 This is a diagram of non-equivalent dehydrogenation in the 6LiBH4-4NiHZSM-5 composite system.

[0027] Figure 5 The graph shows the hydrogen release of 6LiBH4-4NiHZSM-5 at 320 ℃ and 380 ℃. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] Example 1: Preparation of NiHZSM-5 (Si / Al=25) Brønsted acid catalyst, the specific steps are as follows: Step 1: Weigh 0.582 g of nickel nitrate hexahydrate, 0.168 g of diethylenetriamine, and 20.376 g of deionized water into a 100 ml hydrothermal reactor and stir at room temperature for 30 min. Then, weigh 0.328 g of sodium aluminate and 20.336 g of tetrapropylammonium hydroxide into the reactor and stir at 80 ℃ for 2 h. Subsequently, add 20.838 g of tetraethyl orthosilicate and stir at 80 ℃ for 3 h to age the product and obtain a gel. After aging, transfer the gel to a forced-air drying oven and maintain the temperature at 180 ℃ for a hydrothermal reaction for 48 h to obtain the reactant.

[0030] Step 2: Centrifuge the reactants and wash them with deionized water at least three times to obtain a neutral sample. Place the sample in a crucible and dry it at 100 °C for 10 h. After drying, place it in a muffle furnace and calcine it at 550 °C (heating rate 2 °C / min) for 4 h to remove the organic template. The resulting NiZSM-5 (Si / Al=25) catalyst sample can be obtained.

[0031] Step 3: NiZSM-5 (Si / Al=25) was ion-exchanged with ammonium nitrate solution (1 mol / L) to obtain NiHZSM-5 (Si / Al=25). During the ion exchange, the solid-to-liquid mass ratio was 20:1. The mixture was stirred at 80 °C for 2 hours, and the exchange was repeated three times. Then, the sample was dried at 100 °C for 8 hours. Finally, it was calcined in a muffle furnace at 550 °C (heating rate 2 °C / min) for 4 hours to remove the organic template. The sample was then reduced in a tube furnace with a hydrogen-argon mixture (10% H2 + 90% Ar) at 400 °C for 2 hours, followed by heating to 550 °C and holding for 4 hours. After the tube furnace cooled naturally, the sample was collected to obtain NiHZSM-5 (Si / Al=25).

[0032] Examples 2-5: The preparation method of NiHZSM-5 (Si / Al=50, 100, 200, 300) Brønsted acid catalyst is the same as that in Example 1, except that the Si / Al ratio is different, which is achieved by changing the amount of sodium aluminate added.

[0033] The amount of raw materials added in each embodiment is shown in Table 1:

[0034] See Figure 1As can be seen, NiHZSM-5 (Si / Al=25, 200) exhibits a typical MFI crystal structure, belonging to the orthorhombic crystal system. The characteristic peaks at 2θ are located at 7.9°, 8.8°, 23.1°, 23.9°, and 24.4°. The introduction of the single Ni atom does not change the crystal structure.

[0035] Table 2 shows the infrared semi-quantitative analysis of pyridine for two different Si / Al (Si / Al=25, 200) ratio NiHZSM-5 Brønsted acid catalysts prepared in Examples 1 and 4. As can be seen from Table 2, Si / Al=25 has more Brønsted acid sites.

[0036]

[0037] See Figure 2 The spectrum shows that Si / Al=25 has a stronger Brønsted acid, which means it contains more Brønsted acid.

[0038] See Figure 3 As can be seen from the figure, NiHZSM-5 exhibits irregular particles mixed with many crystals of different sizes. Each particle is small in size and has a high specific surface area, which can expose more active sites.

[0039] Example 1 in the above embodiments is the best embodiment.

[0040] Example 6: The NiHZSM-5 (Si / Al=25) Brønsted acid catalyst prepared in Example 1 was used to prepare 6LiBH4-4NiHZSM-5 (Si / Al=25) hydrogen storage material. The steps are as follows: Step 1: Before adding the NiHZSM-5 (Si / Al=25) Brønsted acid catalyst, vacuum dry it and keep it at 300℃ for 12 h to remove water and gaseous impurities adsorbed by the catalyst.

[0041] Step 2: Weigh 0.6 g of LiBH4 and 0.4 g of NiHZSM-5 (Si / Al=25) Brønsted acid catalyst in a glove box and place them in a 220 ml ball mill jar. Add 6 mm diameter carbide beads to the ball mill jar, with a ball-to-material ratio of 100:1. Then, purge the ball mill jar with argon gas as a protective gas, place the ball mill jar in a ball mill, set the bidirectional mode, the speed to 400 rpm, and run the mill in both directions for 30 minutes each, with a 6-minute time interval, for a total of 2 runs.

[0042] Samples were collected to obtain a composite hydrogen storage material of 6LiBH4-4NiHZSM-5 (Si / Al=25).

[0043] The prepared 6LiBH4-4NiHZSM-5 (Si / Al=25) composite hydrogen storage system was subjected to non-isothermal testing. The non-isothermal performance testing instrument was a Sieverts-type gas-solid reaction device made by Zhejiang University.

[0044] Each test uses a 50 mg sample, which is connected to the instrument. A vacuum is then created, and the non-isothermal test program can be set up simultaneously. After vacuuming, wait 10 minutes before performing the non-isothermal test.

[0045] See Figure 4 The figure shows the initial hydrogen release temperature and hydrogen release capacity. It can be seen that the hydrogen storage performance of the composite hydrogen storage system 6LiBH4-4NiHZSM-5 (Si / Al=25) prepared by this invention is significantly improved compared with the original LiBH4. The initial hydrogen release temperature of the original LiBH4 is reduced by 110 °C, while the initial hydrogen release temperature of the original LiBH4 is around 310 °C. The hydrogen release capacity of 6LiBH4-4NiHZSM-5 (Si / Al=25) can reach 7 wt% at 400 °C.

[0046] This invention conducted isothermal tests at 320 °C and 380 °C on the prepared 6LiBH4-4NiHZSM-5 (Si / Al=25) composite hydrogen storage system. Each test involved 50 mg of sample connected to a large instrument. A vacuum was drawn, and the isothermal test program could be set simultaneously with the vacuuming process. After vacuuming, the isothermal test was performed after 10 minutes.

[0047] See Figure 5 As we can see, the hydrogen release capacity can reach 5.9 wt% and 6.8 wt% respectively when isothermally heated at 320 ℃ and 380 ℃ for 200 min (including the heating time, from room temperature to the target temperature at 10 ℃ / min). The hydrogen release of the composite system is basically over.

[0048] Example 7: The NiHZSM-5 (Si / Al=50) Brønsted acid catalyst prepared in Example 2 was used to prepare 6LiBH4-4NiHZSM-5 (Si / Al=50) hydrogen storage material. The steps are as follows: Step 1: Before adding the NiHZSM-5 (Si / Al=50) Brønsted acid catalyst, vacuum dry it and keep it at 350℃ for 10 hours to remove water and gaseous impurities adsorbed by the catalyst.

[0049] Step 2: Weigh 0.6 g of LiBH4 and 0.4 g of NiHZSM-5 (Si / Al=50) Brønsted acid catalyst in a glove box and place them in a 220 ml ball mill jar. Add 6 mm diameter carbide beads to the ball mill jar, with a ball-to-material ratio of 100:1. Then, purge the ball mill jar with argon gas as a protective gas, place the ball mill jar in a ball mill, set the bidirectional mode, the speed to 500 rpm, and run the mill in both directions for 15 minutes each, with a 6-minute time interval, for a total of 2 runs.

[0050] Samples were collected to obtain a composite hydrogen storage material of 6LiBH4-4NiHZSM-5 (Si / Al=50).

[0051] Non-isothermal tests were conducted on the prepared 6LiBH4-4NiHZSM-5 (Si / Al=50) composite hydrogen storage system. Its initial hydrogen release temperature was 110 °C lower than that of the original LiBH4, which is around 310 °C. The hydrogen release capacity of 6LiBH4-4NiHZSM-5 (Si / Al=50) can reach 7 wt% at 400 °C.

[0052] The prepared 6LiBH4-4NiHZSM-5 (Si / Al=50) composite hydrogen storage system was tested at 320 °C and 380 °C. The hydrogen release capacity reached 5.7 wt% and 6.6 wt% after being isothermally tested at 320 °C and 380 °C for 200 min, respectively.

[0053] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the embodiments described above. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a hydrogen storage material based on a NiHZSM-5 Brønsted acid catalyst and a LiBH4 composite system, comprising the following steps: Step 1: Vacuum dry the NiHZSM-5 Brønsted acid catalyst and keep it at 300-350℃ for 10-12 h; Step 2: In a glove box, mix NiHZSM-5 Brønsted acid catalyst and LiBH4 in a mass ratio of 25-50:50-75, place the mixture in a ball mill jar, and purge with Ar gas as a protective gas. The ball milling speed is 400-500 rpm, and the ball milling time is 1-2 h. After the ball milling is completed, collect the product. The NiHZSM-5 Brønsted acid catalyst was prepared by the following method: Step (1): First, add nickel nitrate hexahydrate, deionized water, and diethylenetriamine to the reaction vessel and stir for 20-40 min; then add sodium aluminate, tetrapropylammonium hydroxide, and deionized water to the reaction vessel in sequence and stir at 70-80 ℃ for 2-3 h; then add tetraethyl orthosilicate and continue stirring at 80-90 ℃ for 2-3 h for aging to obtain a gel; finally, transfer it to a forced-air drying oven and keep it at 160-180 ℃ for 48-52 h for hydrothermal reaction to obtain the reactants; Step (2): The reactants were centrifuged, washed and dried, and then calcined in a muffle furnace to remove the organic template, thereby obtaining NiZSM-5 powder; Step (3): NiZSM-5 powder is exchanged and reduced with ammonium nitrate solution to prepare NiHZSM-5 Brønsted acid catalyst; in step (1), the mass ratio of nickel nitrate hexahydrate, deionized water and diethylenetriamine is 0.5-0.7g:20-22g:0.5-0.7g; in step (1), the mass ratio of sodium aluminate, tetrapropylammonium hydroxide and deionized water is 0.17-0.33g:19-21g:20-22g.

2. The method for preparing a hydrogen storage material based on a NiHZSM-5 Brønsted acid catalyst and a LiBH4 composite system according to claim 1, characterized in that, In step (1), the mass of tetraethyl orthosilicate is 20.6-21g.

3. The method for preparing a hydrogen storage material based on a NiHZSM-5 Brønsted acid catalyst and a LiBH4 composite system according to claim 1 or 2, characterized in that, The Si / Al molar ratio is 25-50:

1.

4. The method for preparing a hydrogen storage material based on a NiHZSM-5 Brønsted acid catalyst and a LiBH4 composite system according to claim 3, characterized in that, In step (3), the exchange process is as follows: First, 1g of NiZSM-5 is added to 20g of ammonium nitrate solution with a concentration of 1mol / L, and stirred at 80-90℃ for 1-2h, and the exchange is repeated several times; then it is dried and calcined in a muffle furnace to remove the organic template to obtain the sample; Finally, the sample was reduced in a tube furnace. The reduction process was as follows: a mixed gas of 10% H2 and 90% Ar by volume was introduced into the tube furnace, and the temperature was maintained at 400-500℃ for 1-2 hours, and then the temperature was raised to 500-550℃ and maintained for 4-5 hours.

5. The method for preparing a hydrogen storage material based on a NiHZSM-5 Brønsted acid catalyst and a LiBH4 composite system according to claim 1, characterized in that, In step two, the mass ratio of NiHZSM-5 Brønsted acid catalyst to LiBH4 is 40:

60.

6. A method for preparing a hydrogen storage material based on a NiHZSM-5 Brønsted acid catalyst and a LiBH4 composite system according to claim 1 or 5, characterized in that, In step two, the ball-to-material ratio is 100:1, and the grinding beads are selected as carbide beads with a diameter of 6mm.

7. The hydrogen storage material of the NiHZSM-5 Brønsted acid catalyst and LiBH4 composite system prepared by the preparation method according to claim 1.

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