CN116281854B - Method for catalyzing ammonia borane pyrolysis dehydrogenation by eutectic solvent - Google Patents

Abstract

The scheme relates to a method for catalyzing ammonia borane to be pyrolyzed and dehydrogenated by using a eutectic solvent, which takes ammonia borane as a raw material, takes potassium tert-butoxide or potassium hydroxide as an additive, and carries out pyrolysis and dehydrogenation reaction on the ammonia borane in an organic solvent through the catalysis of the eutectic solvent; the eutectic solvent comprises a hydrogen bond acceptor and a hydrogen bond donor in a mass ratio of 3:1-1:6. The invention provides a method for efficiently catalyzing pyrolytic dehydrogenation of ammonia borane by using a eutectic solvent, which has the advantages of simple preparation process, high catalytic efficiency, mild reaction condition, large hydrogen release amount and recycling, and a hydrogen bond donor-acceptor can play a role in synergistic catalysis.

Description

A method for thermal dehydrogenation of ammonia borane catalyzed by a deep eutectic solvent

Technical Field

The invention relates to the field of dehydrogenation catalytic reaction, and in particular to a method for thermal dehydrogenation of ammonia borane catalyzed by a low eutectic solvent.

Background Art

After entering the 21st century, how to rationally develop and utilize new energy has gradually become a research hotspot. Ammonia borane (NH ₃ BH ₃ ) is considered to be a chemical hydrogen production material with great application prospects because of its extremely high hydrogen content (19.6wt%), high stability, safety and non-toxicity. The dehydrogenation methods of ammonia borane are generally divided into hydrolysis dehydrogenation and thermal dehydrogenation. The hydrolysis dehydrogenation reaction conditions are mild, and the dehydrogenation rate is extremely fast and the amount of hydrogen released is large. Therefore, most of the current research focuses on hydrolysis dehydrogenation, and many literatures and patents have reported it, for example: Applied Catalysis A, General 595 (2020) 117511, ACSSustainable Chem. Eng. 2020, 8, 8256-8266, CN115608375A, CN115121271A.

However, hydrolysis dehydrogenation will bring in oxygen atoms, and the final product is borate. If you want to regenerate ammonia borane, you need to break the B-O bond in the borate, which is difficult to achieve in actual operation. The boron-nitrogen polymer produced by pyrolysis dehydrogenation only needs a suitable reducing agent to obtain regenerated ammonia borane, which is more conducive to sustainable development. The pyrolysis dehydrogenation of ammonia borane is divided into two cases with or without solvent. When there is no solvent involved, the first molecule of hydrogen is released at 97°C to 110°C, and the second step occurs between 110°C and 150°C, but the third step completely removes the last molecule of hydrogen. It requires extremely high temperature, even reaching 1400°C. It is relatively easy to carry out pyrolysis dehydrogenation of ammonia borane in organic solutions (pyridine, diethylene glycol dimethyl ether, tetrahydrofuran, etc.), but a suitable catalyst is still needed to reduce the activation energy of the reaction. At present, there is still relatively little research on the pyrolysis dehydrogenation of ammonia borane, and the prior art still lacks ammonia borane pyrolysis dehydrogenation method with mild reaction conditions and large hydrogen release.

Summary of the invention

In view of the shortcomings in the prior art, the present invention proposes a method for efficiently catalyzing the thermal dehydrogenation of ammonia borane by using a low eutectic solvent. Compared with traditional catalysts, the present invention avoids expensive organic ligands and complicated production processes, and utilizes the bond energy between hydrogen bond donors and acceptors to stabilize the metal center, thereby achieving a synergistic catalytic effect. It has the advantages of simple preparation process, high catalytic efficiency, mild reaction conditions, large hydrogen release amount, and recyclability.

To achieve the above object, the present invention provides the following technical solutions:

A method for thermal dehydrogenation of ammonia borane catalyzed by a low eutectic solvent comprises taking ammonia borane as a raw material and potassium tert-butoxide or potassium hydroxide as an additive, and carrying out a thermal dehydrogenation reaction of ammonia borane in an organic solvent through the catalytic effect of the low eutectic solvent; the low eutectic solvent comprises a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 3:1 to 1:6.

Furthermore, the dosage of the additive is 0.5wt% to 3wt% of the mass of ammonia borane.

Furthermore, the organic solvent is one of tetrahydrofuran and diethylene glycol dimethyl ether or a mixture of the two.

Furthermore, the organic solvent is a mixture of tetrahydrofuran and diethylene glycol dimethyl ether in a mass ratio of 1:10 to 10:1.

Furthermore, the mass ratio of the organic solvent to ammonia borane is 20:1 to 80:1.

Furthermore, the hydrogen bond acceptor of the low eutectic solvent is iridium trichloride, and the hydrogen bond donor is one of acetamide, methyl urea and 1,3-dimethyl urea.

Furthermore, the amount of the low eutectic solvent used is 1 wt% to 10 wt% of the mass of ammonia borane.

Furthermore, the thermal dehydrogenation reaction temperature is 30°C to 100°C, and the reaction time is 5min to 60min.

In the thermal decomposition catalytic process of ammonia borane, the metal active center M first attacks the B-H bond to form an active intermediate of M-H. Then the first hydrogen molecule is removed, and the process is continuously repeated to gradually remove all hydrogen. Therefore, it is particularly important to be able to efficiently and stably form metal hydrogen active intermediates. In this case, the low eutectic solvent can be used as a catalyst in the dehydrogenation reaction of ammonia borane, and the bond energy between the hydrogen bond donor and acceptor is used to stabilize the metal center. The precious metal iridium is used as the active center and hydrogen bond acceptor. At the same time, the hydrogen bond donor can play a synergistic catalytic role, which has the advantages of simple preparation process, high catalytic efficiency, mild reaction conditions, large hydrogen release, and recyclable use.

Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a method for efficiently catalyzing the thermal dehydrogenation of ammonia borane using a low eutectic solvent, and the hydrogen bond donor and acceptor can play a synergistic catalytic role, which has the advantages of simple catalyst preparation process, high catalytic efficiency, mild reaction conditions, large hydrogen release amount, and recyclability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydrogen nuclear magnetic spectrum of [IrCl ₃ ] ₁ [acetamide] ₂ in Example 1. FIG.

FIG. 2 is the NMR carbon spectrum of [IrCl ₃ ] ₁ [acetamide] ₂ in Example 1. FIG.

FIG3 is a hydrogen NMR spectrum of [IrCl ₃ ] ₂ [methylurea] ₁ in Example 1. FIG.

FIG. 4 is the NMR carbon spectrum of [IrCl ₃ ] ₂ [methylurea] ₁ in Example 1. FIG.

FIG. 5 is a hydrogen NMR spectrum of [IrCl ₃ ] ₁ [1,3-dimethylurea] ₁ in Example 1. FIG.

FIG6 is the NMR carbon spectrum of [IrCl ₃ ] ₁ [1,3-dimethylurea] ₁ in Example 1.

FIG. 7 is a NMR boron spectrum of the product of thermal dehydrogenation of ammonia borane in the present invention.

DETAILED DESCRIPTION

The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

Example 1: Preparation of a deep eutectic solvent catalyst, the steps are as follows

8.1 g of iridium trichloride as a hydrogen bond acceptor and 3.3 g of acetamide as a hydrogen bond donor were placed in a 100 mL single-necked flask at a mass ratio of 1:2, and reacted at 80° C. with closed stirring for 6 h. After the reaction, a transparent homogeneous solution was formed as a eutectic catalyst [IrCl ₃ ] ₁ [acetamide] ₂ , which was recorded as sample 1, and no purification step was required. The specific NMR carbon hydrogen spectrum of the catalyst in this example is shown in Figures 1-2.

By adopting the above method, the hydrogen bond donors are acetamide, methyl urea, and 1,3-dimethyl urea. By changing the molar ratio of the hydrogen bond donor and acceptor used, another 7 deep eutectic solvent catalysts with different compositions can be prepared: [IrCl ₃ ] ₃ [acetamide] ₁ , [IrCl ₃ ] ₁ [acetamide] ₁ , [IrCl ₃ ] ₁ [acetamide] ₆ , [IrCl ₃ ] ₂ [methyl urea] ₁ , [IrCl ₃ ] ₁ [methyl urea] ₄ , [IrCl ₃ ] ₁ [1,3-dimethyl urea] ₁ , [IrCl ₃ ] ₁ [1,3-dimethyl urea] ₅ (the subscripts are the molar ratios), which are respectively recorded as samples 2 to 8. For specific NMR carbon hydrogen spectra of the catalysts [IrCl ₃ ] ₂ [methylurea] ₁ and [IrCl ₃ ] ₁ [1,3-dimethylurea] ₁ in this example, please refer to Figures 3-6.

Example 2: Thermal dehydrogenation of ammonia borane, the steps are as follows

Weigh 0.5g of ammonia borane and place it in a 50mL two-mouth pressure bottle. Seal one mouth with a rubber stopper and connect the other mouth with a leather tube to collect hydrogen. Weigh 5wt% of the catalyst of ammonia borane and 1wt% of the potassium tert-butoxide of ammonia borane, and disperse them in 20g of tetrahydrofuran and diethylene glycol dimethyl ether mixed solution (mass ratio 1:4). Inject into the reaction bottle with a syringe, start timing, keep heating and stirring at 50℃, and record the volume of hydrogen collected after 5 minutes of reaction.

The present invention uses the water displacement method to obtain the amount of hydrogen released by ammonia borane under normal pressure, and _nH2 is calculated according to _VH2 / _Vm . Each ammonia borane molecule can produce 3 hydrogen molecules after complete reaction. The value of _nH2 / _nAB is used to measure the reaction progress. When the ratio is 3, it means that ammonia borane has completely released all hydrogen.

Wherein, V _H2 represents the volume of hydrogen collected in the experiment, in L; V _m represents the molar volume of the _gas , which is approximately 24.5 L/mol at 25°C and normal pressure; n _H2 represents the amount of hydrogen released, in mol; and n _AB represents the amount of ammonia borane initially added, in mol.

Example 2-1. Effect of different deep eutectic solvents on thermal dehydrogenation of ammonia borane

Table 1

From the above table, it can be seen that the catalyst sample 1, i.e. [IrCl3]1[acetamide]2, has better results as the catalyst. The NMR boron spectrum after the catalytic reaction is shown in Figure 7, indicating that ammonia borane was successfully catalytically decomposed.

Example 2-2. Effect of Catalyst Amount and Additive Amount on Thermal Dehydrogenation of Ammonia Borane

The method of Example 2 was adopted, the following conditions were changed, and the rest remained unchanged. The results are shown in Table 2.

Table 2

As can be seen from Table 2, increasing the amount of catalyst and additive can accelerate the process of ammonia borane dehydrogenation reaction, wherein the amount of catalyst has a more significant effect on the result, and potassium tert-butoxide has a better effect as an additive. Considering the product consumption, when the amount of catalyst is 5wt% and the additive is potassium tert-butoxide and the amount is 1wt%, the effect is better.

Example 2-3: Effect of solvent dosage and mixing ratio on thermal dehydrogenation of ammonia borane

The method of Example 2 was adopted, the catalyst was Sample 1, the mass ratio of the organic solvent to ammonia borane (m ₁ ) and the mass ratio of the organic solvent mixing ratio of tetrahydrofuran to diethylene glycol (m ₂ ) were changed, and the other conditions remained unchanged. The results are shown in Table 3.

Table 3

Example 2-4: Effect of reaction temperature and reaction time on thermal dehydrogenation of ammonia borane

The method of Example 2 was adopted, the catalyst was Sample 1, and the corresponding conditions were changed. The results are shown in Table 4.

Table 4

It can be seen from Table 4 that increasing the reaction temperature or extending the reaction time is beneficial to the progress of the ammonia borane dehydrogenation reaction. Considering the energy consumption cost, the reaction time of 20 min at 50 ° C is the best result.

Example 3-5: Recycling of catalyst in ammonia borane dehydrogenation reaction

In combination with Examples 2-1 to 2-4, it can be found that a better structure can be obtained by adopting the method in Example 2, wherein the catalyst is sample 1, the reaction temperature is 50°C, the reaction time is 20 min, and the other conditions remain unchanged.

After the reaction was completed, the filtrate was collected by filtration and re-injected into new ammonia borane for catalyst circulation experiment. The results are shown in Table 5:

Table 5

It can be seen from Table 5 that after multiple cycles of use, the catalytic activity of the catalyst for the thermal dehydrogenation reaction of ammonia borane decreased slightly, but generally maintained a good catalytic effect.

Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims (6)

1. A method for catalyzing ammonia borane to be pyrolyzed and dehydrogenated by using a eutectic solvent is characterized in that ammonia borane is taken as a raw material, potassium tert-butoxide or potassium hydroxide is taken as an additive, and the ammonia borane is pyrolyzed and dehydrogenated in an organic solvent through the catalysis of the eutectic solvent; the eutectic solvent comprises a hydrogen bond acceptor and a hydrogen bond donor in a mass ratio of 3:1-1:6; the hydrogen bond acceptor is iridium trichloride, and the hydrogen bond donor is one of acetamide, methyl urea and 1, 3-dimethyl urea; the pyrolysis dehydrogenation reaction temperature is 30-50 ℃ and the reaction time is 5-60 min.

2. A method of the eutectic solvent catalyzed pyrolytic dehydrogenation of ammonia borane according to claim 1, wherein the amount of the additive is 0.5wt% to 3wt% of the ammonia borane mass.

3. The method for the pyrolytic dehydrogenation of ammonia borane catalyzed by a eutectic solvent according to claim 1, wherein the organic solvent is one or a mixture of tetrahydrofuran and diethylene glycol dimethyl ether.

4. A method for the pyrolytic dehydrogenation of ammonia borane catalyzed by a eutectic solvent according to claim 3, wherein the organic solvent is a mixture of tetrahydrofuran and diethylene glycol dimethyl ether, and the mass ratio is 1:10-10:1.

5. The method for the pyrolytic dehydrogenation of ammonia borane catalyzed by a eutectic solvent according to claim 1, wherein the mass ratio of the organic solvent to ammonia borane is 20:1-80:1.

6. A method of ammonia borane pyrolysis dehydrogenation catalyzed by a eutectic solvent according to claim 1 wherein the eutectic solvent is used in an amount of 1wt% to 10wt% of ammonia borane mass.