JP2011031215A - Catalyst for hydrogen generation, and hydrogen generation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for highly efficiently generating hydrogen with good selectivity in a hydrogen generation method using hydrazine decomposition reaction. <P>SOLUTION: The catalyst for hydrogen generation includes a composite metal of rhodium and nickel for generating hydrogen by decomposition reaction of at least one kind of a compound selected from the group consisting of hydrazine and its hydrates, and the hydrogen generation method includes bringing the catalyst into contact with at least one kind of a compound selected from the group consisting of hydrazine and its hydrates. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hydrogen generation catalyst and a hydrogen generation method.

  Hydrogen gas supplied to the fuel cell can be generated by electrolyzing water; reacting metal with acid; reacting water with metal hydride; reforming methyl alcohol or natural gas with steam Methods: Various methods are known, such as a method of releasing hydrogen from a hydrogen storage material such as a hydrogen storage alloy, activated carbon, carbon nanotube, or lithium-nitrogen material. However, these methods have drawbacks such as requiring a large amount of energy to generate hydrogen, a small amount of hydrogen generation with respect to the raw materials used, and a large-scale facility. For this reason, these methods can be used for production of hydrogen on a factory scale or generation of hydrogen to the extent that it can be used in laboratories. However, the required amount of hydrogen fuel can be continuously supplied and the size can be reduced. It is unsuitable as a hydrogen supply method for required fuel cells for automobiles; portable fuel cells for mobile phones, personal computers, and the like.

On the other hand, metal hydrides such as LiAlH ₄ and NaBH ₄ are used in laboratories as hydrogenation reagents, but when they come into contact with water, a large amount of hydrogen is temporarily generated to cause an explosive phenomenon. It must be handled with care and is also unsuitable as a hydrogen source for the fuel cell described above.

Tetrahydroborate such as NaBH ₄ (see Patent Documents 1 and 2 and Non-Patent Documents 1 and 2 below) and borane / ammonia represented by the chemical formula: NH ₃ BH ₃ (Patent Document 3 and Non-Patent Documents 3 and 3 below) 4), the method of releasing hydrogen using a hydrolysis reaction has also been reported. However, these methods have problems in terms of recovery and regeneration of a boric acid compound as a product.

Hydrazine (H ₂ NNH ₂ ) is a liquid at room temperature and has a high hydrogen content (12.5 wt%) and is considered to be a promising hydrogen source. It can be decomposed into nitrogen and hydrogen by catalytic reaction. Has been. For example, Patent Document 4 below discloses a method of generating hydrogen by bringing hydrazine and its derivatives into contact with a metal having a hydrogen generation catalytic ability such as nickel, cobalt, iron, copper, palladium, platinum or the like. However, for these metal catalysts, the hydrogen generation catalytic ability in the hydrazine decomposition reaction was examined, and a sufficient amount of hydrogen generation was not necessarily obtained (see Non-Patent Document 5 below).

  Patent Document 5 discloses a hydrogen production apparatus including a decomposer that uses ammonia or hydrazine as a hydrogen source, decomposes it into nitrogen and hydrogen, and supplies the fuel cell. However, Patent Document 5 does not specifically disclose a method for decomposing hydrazine to generate hydrogen.

  Patent Documents 6 and 7 disclose a method of generating hydrogen by bringing a catalyst in which rhodium is supported on a support containing alumina or silica and an aqueous hydrazine solution into contact with each other. However, in these methods, the hydrogen generation rate from hydrazine is low, and a sufficient amount of hydrogen generation is not obtained.

Japanese Patent Laid-Open No. 2001-19401 JP 2002-241102 A JP 2006-213563 A Japanese Patent Laid-Open No. 2004-244251 JP 2003-40602 A JP 2007-269514 A JP 2007-269529 A

S. C. Amendola et al., International Journal of Hydrogen Energy, 25 (2000), 969-975 ; Z. P. Li et al., Journal of Power Source, 126 (2004) 28-33 M. Chandra, Q. Xu, Journal of Power Sources 156 (2006) 190-194. Q. Xu, M. Chandra, Journal of Power Sources 163 (2006) 364-370. Sanjay Kumar Singh, Xin-Bo Zhang, Qiang Xu, J. Am. Chem. Soc., 131 (2009) 9894-9895.

  The present invention has been made in view of the above-described problems of the prior art, and its main object is to generate hydrogen with high selectivity and high efficiency in a hydrogen generation method utilizing a decomposition reaction of hydrazine. It is to provide a way that can be done.

  The present inventor has intensively studied to achieve the above-described object. As a result, when hydrazine or its hydrate is used as a hydrogen generation source, by using a composite metal of rhodium and nickel as a catalyst, the selection is very high compared to the case of using a conventionally known metal catalyst. It has been found that hydrogen can be efficiently generated at a high rate, and the present invention has been completed here.

That is, the present invention provides the following hydrogen generation catalyst and hydrogen generation method.
1. A catalyst for hydrogen generation by a decomposition reaction of at least one compound selected from the group consisting of hydrazine and hydrates thereof composed of a composite metal of rhodium and nickel.
2. Item 2. The hydrogen generation catalyst according to Item 1, wherein the rhodium-nickel composite metal is an alloy, intermetallic compound, or solid solution of rhodium and nickel.
3. Item 3. The hydrogen generation catalyst according to Item 1 or 2, wherein the rhodium and nickel ratio in the rhodium and nickel composite metal is in the range of Rh: Ni (atomic ratio) = 100: 1 to 1:50.
4). 4. A hydrogen generation method, wherein the hydrogen generation catalyst according to any one of Items 1 to 3 is contacted with at least one compound selected from the group consisting of hydrazine and hydrates thereof.
5). A method for supplying hydrogen to a fuel cell, comprising supplying hydrogen generated by the method of item 4 above as a hydrogen source for the fuel cell.

  Hereinafter, the present invention will be specifically described.

In the hydrogen generation method of the present invention, at least one compound selected from the group consisting of hydrazine represented by the chemical formula: H ₂ NNH ₂ and hydrates thereof is used as the hydrogen generation source. Hydrazine (anhydride and monohydrate) is a known compound and is liquid at room temperature.

  In general, a hydrazine-catalyzed decomposition reaction involves a hydrazine complete decomposition reaction in which hydrogen and nitrogen represented by the following formula (1) are generated, or a hydrazine partial decomposition reaction in which ammonia and nitrogen are represented by formula (2) It is considered to be.

N ₂ H ₄ → N ₂ + 2H ₂ (1)
3N ₂ H ₄ → N ₂ + 4NH ₃ (2)
Non-Patent Document 5 described above describes the decomposition reaction of hydrazine in the presence of a rhodium catalyst. When rhodium metal is used as a catalyst, the hydrazine complete decomposition reaction represented by the formula (1) is more effective. It is disclosed that the hydrazine partial decomposition reaction represented by (2) proceeds preferentially to produce a large amount of ammonia. As for other metal catalysts, when a metal such as nickel, copper, or iron is used as a catalyst, the decomposition reaction of hydrazine does not proceed. When the catalyst is a cobalt metal, the decomposition reaction of hydrazine proceeds. However, in addition to the complete decomposition reaction, the partial decomposition reaction proceeds to produce a large amount of ammonia. Furthermore, according to the research of the present inventors, when a rhodium-copper composite metal, a rhodium-iron composite metal, a rhodium-cobalt composite metal or the like is used as a catalyst, the selectivity of the hydrogen generation reaction by complete decomposition is reduced. There is no improvement.

  On the other hand, when the rhodium-nickel composite metal used in the present invention is used as a catalyst, the partial decomposition reaction in which ammonia is generated is suppressed, and the complete decomposition reaction in which hydrogen is generated selectively proceeds.

  Hereinafter, the rhodium-nickel composite metal catalyst used in the present invention and the hydrogen generation method using the catalyst will be specifically described.

Rhodium-nickel composite metal catalyst The rhodium-nickel composite metal catalyst used in the hydrogen generation method of the present invention is not a mixture of rhodium and nickel, but must be a composite metal in which rhodium and nickel are closely related to each other. is there. Specific examples of such composite metals include alloys, intermetallic compounds, and solid solutions.

  As described above, when rhodium metal is used alone as a catalyst, the hydrazine partial decomposition reaction represented by the above formula (2) proceeds to produce a large amount of ammonia. Further, when nickel metal is used alone as a catalyst, the decomposition reaction of hydrazine does not proceed.

  On the other hand, when a metal catalyst in which rhodium and nickel are combined is used, surprisingly, the complete decomposition reaction of hydrazine represented by the above formula (1) proceeds with good selectivity and is very efficient. Hydrogen can be generated.

  The ratio of rhodium to nickel in the rhodium and nickel composite metal is preferably about Rh: Ni (atomic ratio) = 100: 1 to 1:50, more preferably about 8: 1 to 1: 4. Preferably, it is about 4: 1 to 3: 1.

The method for producing the rhodium-nickel composite metal catalyst is not particularly limited. For example, by adding a reducing agent to an aqueous solution containing a rhodium compound and a nickel compound, the rhodium ion and the nickel ion are reduced and metallized. The target rhodium and nickel composite metal can be obtained. In addition, after reducing the rhodium ion by adding a reducing agent to an aqueous solution containing a rhodium compound, the nickel ion is reduced by adding a nickel compound to the aqueous solution containing the nickel compound. Then, a method of reducing by adding a rhodium compound can also be adopted. In particular, according to a method of reducing rhodium ions and nickel ions by adding a reducing agent to an aqueous solution containing a rhodium compound and a nickel compound, a metal catalyst having excellent uniformity can be obtained. The rhodium compound and nickel compound used in these methods are not particularly limited, but may be any compound that is soluble in a solvent. For example, metal salts such as rhodium or nickel chloride, nitrate, sulfate, and various metal complexes Can be used.

  The reducing agent used for reducing these rhodium compounds and nickel compounds is not particularly limited, and is not particularly limited as long as it can reduce rhodium compounds and nickel compounds, such as sodium tetrahydroborate and hydrazine itself. Available.

  The size of the composite metal of rhodium and nickel is not particularly limited. For example, a composite metal in an ultrafine particle state having a particle size of about 1 to 100 nm is advantageous in that it has high activity. In this case, the particle diameter of the composite metal is a value measured by an electron microscope.

  The rhodium-nickel composite metal may be further compounded with other metals within a range that does not adversely affect the catalytic activity.

  The complex metal of rhodium and nickel may be used as a supported catalyst supported on a support such as silica, alumina, zirconia, activated carbon and the like. The method for producing such a supported catalyst is not particularly limited. For example, it can be obtained by reducing the rhodium compound and the nickel compound in a state where the carrier is dispersed in a solution containing the rhodium compound and the nickel compound. Can do. The amount supported is not particularly limited. For example, the amount of the composite metal is preferably about 0.1 to 20% by weight on the basis of the total amount of the composite metal of rhodium and nickel and the carrier. More preferably, it is about 10 to 10 weight%, More preferably, it is about 1 to 5 weight%.

Hydrogen Generation Method In the hydrogen generation method of the present invention, at least one compound selected from the group consisting of hydrazine and hydrates thereof is used as the hydrogen generation source. There is no limitation in particular about the kind of hydrazine and its hydrate, What is generally marketed can be used as it is. Further, other components may be included at the same time as long as there is no adverse effect on the hydrogen generation.

Among these compounds, when anhydrous hydrazine (H ₂ NNH ₂ ) is used as a raw material, hydrogen generation efficiency is high because 12.5% by weight of hydrogen is generated with respect to hydrazine. Because there is a problem with safety. On the other hand, in the case of hydrazine monohydrate _{(H 2 NNH 2 · H 2} O) and hydrogen source, since hydrogen is generated by the 7.9% by weight relative to hydrazine monohydrate, an anhydride Although the hydrogen generation efficiency is somewhat inferior to that of the raw material, the hydrogen generation efficiency is still high and the safety is improved. For this reason, in consideration of safety, hydrazine monohydrate or an aqueous solution obtained by further diluting water may be used. In the present invention, it is particularly preferable to use an aqueous solution having a hydrazine concentration of about 40 to 60% by weight in consideration of both safety and hydrogen generation efficiency.

  In the hydrogen generation method of the present invention, at least one compound selected from the group consisting of hydrazine and hydrates thereof is used as a hydrogen generation source, and this is brought into contact with the above-described catalyst composed of a composite metal of rhodium and nickel. Good. A specific method is not particularly limited, and for example, a method of adding hydrazine and a catalyst in a reaction vessel and mixing them can be employed. Moreover, the method of introduce | transducing hydrazine aqueous solution to the reactor filled with the catalyst, and letting it pass a catalyst layer is also employable.

The amount of the catalyst composed of the rhodium-nickel composite metal is not particularly limited. The rhodium-nickel composite metal is used per 1 mol of at least one compound selected from the group consisting of hydrazine and hydrates thereof. Can be selected from a wide range of about 0.0001 to 10 mol. In particular, considering the balance of reaction rate, catalyst cost, and the like, for example, the amount of the composite metal is 0.01 to 0.00 with respect to 1 mol of at least one compound selected from the group consisting of hydrazine and hydrates thereof. It is preferably about 5 moles. In the method of passing through the catalyst layer, the catalyst amount of the catalyst layer may be determined in consideration of the flow rate of hydrazine or its hydrate solution and the contact time.

  The reaction temperature of the hydrogen generation reaction is not particularly limited, but is preferably about 0 ° C to 80 ° C, and more preferably about 10 to 50 ° C.

  There is no limitation in particular about the pressure and atmosphere in the reaction system at the time of reaction, and it can select suitably.

Method for Utilizing Generated Hydrogen According to the method of the present invention, hydrogen generation reaction by decomposition of hydrazine proceeds with good selectivity, and hydrogen can be generated efficiently.

  The generated hydrogen can be directly supplied to the fuel cell as fuel for the fuel cell, for example. In particular, the hydrogen generation method of the present invention can generate hydrogen at a temperature near room temperature, and can control the hydrogen generation rate, generation amount, etc., so that it is a fuel cell for automobiles; This method is highly useful as a hydrogen supply method for computers and other portable fuel cells.

  The generated hydrogen can be collected and stored in a container filled with a hydrogen storage alloy, for example. It is also possible to control the internal pressure of the generated hydrogen by using a hydrogen storage alloy and adjusting the temperature according to the equilibrium pressure-temperature relationship.

  According to the hydrogen generation method of the present invention, hydrogen gas can be efficiently generated under controllable conditions without heating to a high temperature.

  The hydrogen gas generated by the method of the present invention is highly useful as a fuel for, for example, a fuel cell for automobiles and a portable fuel cell.

The graph which shows the relationship between the amount of hydrogen discharge | release measured in Example 1, the comparative example 1, and the comparative example 2, and reaction time. The graph which shows the relationship between the hydrogen release amount and reaction time which were measured in Examples 1-4.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1
RhCl ₃ · 3H ₂ O (0.053 g), NiCl ₂ · 6H ₂ O (0.012 g), hexadecyltrimethylammonium bromide (CTAB, 95%) (0.105 g), and water in a 30 ml two-necked flask (2.5 mL) and ultrasonically stirred for 5 minutes, then add NaBH ₄ (0.010 g) aqueous solution (1.5 mL), shake vigorously for 2 minutes, and Rh ₄ Ni nanoparticles with a particle size of about 3 nm. A catalyst was formed.

Then, the two-necked flask hydrazine monohydrate in a syringe _{(H 2 NNH 2 · H 2} O, 99%) (0.1 mL, 1.97 mmol) were charged, and stirring was continued at room temperature. The released gas passed through a trap containing 1.0 M hydrochloric acid to absorb ammonia, and then only hydrogen and nitrogen were introduced into the gas burette, and the released amount was measured. Outgassing of 16 ml 5 minutes after the start of stirring, 26 ml after 10 minutes, 42 ml after 20 minutes, 76 ml after 50 minutes, 119 ml after 100 minutes, 144 ml after 150 minutes, and 146 ml after 190 minutes was observed.

  As a result of mass spectrometry (MS), it was confirmed that the released gas was hydrogen and nitrogen. The amount of hydrogen released was 3 times the mol of hydrazine used as a raw material. This hydrogen release amount corresponds to a hydrogen production selectivity of 100%.

  In addition, it was confirmed that the hydrogen gas generated by the above-described method was introduced into the solid polymer fuel cell as it was to operate the fuel cell.

Comparative Example 1
Place RhCl ₃ 3H ₂ O (0.053 g), hexadecyltrimethylammonium bromide (CTAB, 95%) (0.105 g), and water (2.5 mL) into a 30 ml two-necked flask for 5 minutes. After stirring, an aqueous NaBH ₄ (0.010 g) solution (1.5 mL) was added, and the reaction vessel was vigorously shaken for 2 minutes to form an Rh nanoparticle catalyst.

Then, the two-necked flask hydrazine monohydrate in a syringe _{(H 2 NNH 2 · H 2} O, 99%) (0.1 mL, 1.97 mmol) were charged, and stirring was continued at room temperature. The released gas passed through a trap containing 1.0 M hydrochloric acid to absorb ammonia, and then only hydrogen and nitrogen were introduced into the gas burette, and the released amount was measured. Gas release of 11 ml was observed 5 minutes after the start of stirring, 27 ml after 10 minutes, 50 ml after 20 minutes, 67 ml after 40 minutes, 70 ml after 50 minutes, and 71 ml after 60 minutes.

As a result of mass spectrometry (MS), it was confirmed that the released gas was hydrogen and nitrogen. The amount of hydrogen released was 1.5 times the mol of hydrazine used as a raw material. This hydrogen release amount corresponds to a hydrogen production selectivity of 44%, which is inferior to the case where Rh ₄ Ni nanoparticles are used as a catalyst.

Comparative Example 2
NiCl ₂ · 6H ₂ O (0.012 g), hexadecyltrimethylammonium bromide (CTAB, 95%) (0.105 g), and water (2.5 mL) are placed in a 30 ml two-necked flask and ultrasonicated for 5 minutes. After stirring, an aqueous NaBH ₄ (0.010 g) solution (1.5 mL) was added, and the reaction vessel was vigorously shaken for 2 minutes to form a Ni nanoparticle catalyst.

The two-necked flask hydrazine monohydrate in a syringe _{(H 2 NNH 2 · H 2} O, 99%) (0.1 mL, 1.97 mmol) were charged, was stirred 80 minutes at room temperature, outgassing observed It was.

Example 2
RhCl ₃ · 3H ₂ O (0.040 g), NiCl ₂ · 6H ₂ O (0.012 g), hexadecyltrimethylammonium bromide (CTAB, 95%) (0.105 g), and water in a 30 ml two-necked flask (2.5 mL) and ultrasonically stirred for 5 minutes, then add NaBH ₄ (0.010 g) aqueous solution (1.5 mL), shake the reaction vessel vigorously for 2 minutes, and Rh ₃ Ni nanoparticles with a particle size of about 3 nm. A catalyst was formed.

The two-necked flask hydrazine monohydrate in a syringe _{(H 2 NNH 2 · H 2} O, 99%) (0.1 mL, 1.97 mmol) were charged, and stirring was continued at room temperature. The released gas passed through a trap containing 1.0 M hydrochloric acid and absorbed ammonia, and then only hydrogen and nitrogen were introduced into the gas burette, and the released amount was measured. 10 ml after 10 minutes, 17 ml after 20 minutes, 27 ml after 20 minutes, 58 ml after 50 minutes, 103 ml after 100 minutes, 135 ml after 150 minutes, 140 ml after 180 minutes, and 140 ml after 200 minutes.

  As a result of mass spectrometry (MS), it was confirmed that the released gas was hydrogen and nitrogen. The amount of hydrogen released was 2.9 times mol of hydrazine used as a raw material. This hydrogen release amount corresponds to a hydrogen production selectivity of 96%.

  In addition, it was confirmed that the hydrogen gas generated by the above-described method was introduced into the solid polymer fuel cell as it was to operate the fuel cell.

Example 3
RhCl ₃ · 3H ₂ O (0.027 g), NiCl ₂ · 6H ₂ O (0.024 g), hexadecyltrimethylammonium bromide (CTAB, 95%) (0.105 g), and water in a 30 ml two-necked flask (2.5 mL) and ultrasonically stir for 5 minutes, then add NaBH ₄ (0.010 g) aqueous solution (1.5 mL), vigorously shake the reaction vessel for 2 minutes, Formed.

Hydrazine monohydrate syringe double neck flask _{(H 2 NNH 2 · H 2} O, 99%) (0.1 mL, 1.97 mmol) were charged, and stirring was continued at room temperature. The released gas passed through a trap containing 1.0 M hydrochloric acid to absorb ammonia, and then only hydrogen and nitrogen were introduced into the gas burette, and the released amount was measured. 10 ml after 10 minutes from the start of stirring, 30 ml after 50 minutes, 53 ml after 100 minutes, 76 ml after 150 minutes, 94 ml after 200 minutes, 122 ml after 300 minutes, 129 ml after 350 minutes, and 130 ml after 420 minutes.

  As a result of mass spectrometry (MS), it was confirmed that the released gas was hydrogen and nitrogen. The amount of hydrogen released was 2.7 times mol of hydrazine used as a raw material. This hydrogen release amount corresponds to a hydrogen production selectivity of 86%.

  In addition, it was confirmed that the hydrogen gas generated by the above-described method was introduced into the solid polymer fuel cell as it was to operate the fuel cell.

Example 4
RhCl ₃ · 3H ₂ O (0.013 g), NiCl ₂ · 6H ₂ O (0.047 g), hexadecyltrimethylammonium bromide (CTAB, 95%) (0.105 g) and filled with water (2.5 mL), followed by ultrasonic agitation for 5 minutes, NaBH ₄ placed (0.010 g) aqueous solution (1.5 mL), 2 minutes shaken vigorously reaction vessel, a particle size of about 3 nm RhNi ₄ nano A particle catalyst was formed.

The two-necked flask hydrazine monohydrate in a syringe _{(H 2 NNH 2 · H 2} O, 99%) (0.1 mL, 1.97 mmol) were charged, and stirring was continued at room temperature. The released gas passed through a trap containing 1.0 M hydrochloric acid and absorbed ammonia, and then only hydrogen and nitrogen were introduced into the gas burette, and the released amount was measured. Outgassing of 4 ml 10 minutes after the start of stirring, 13 ml after 50 minutes, 26 ml after 100 minutes, 57 ml after 200 minutes, 86 ml after 300 minutes, 104 ml after 405 minutes, 107 ml after 490 minutes was observed.

  As a result of mass spectrometry (MS), it was confirmed that the released gas was hydrogen and nitrogen. The amount of hydrogen released was 2.2 times the mol of hydrazine used as a raw material. This hydrogen release amount corresponds to a hydrogen generation selectivity of 71%.

  In addition, it was confirmed that the hydrogen gas generated by the above-described method was introduced into the solid polymer fuel cell as it was to operate the fuel cell.

Claims (5)

A catalyst for hydrogen generation by a decomposition reaction of at least one compound selected from the group consisting of hydrazine and hydrates thereof composed of a composite metal of rhodium and nickel. The catalyst for hydrogen generation according to claim 1, wherein the composite metal of rhodium and nickel is an alloy of rhodium and nickel, an intermetallic compound or a solid solution. The catalyst for hydrogen generation according to claim 1 or 2, wherein a ratio of rhodium to nickel in the composite metal of rhodium and nickel is in a range of Rh: Ni (atomic ratio) = 100: 1 to 1:50. A method for generating hydrogen, comprising contacting the hydrogen generating catalyst according to any one of claims 1 to 3 with at least one compound selected from the group consisting of hydrazine and hydrates thereof. A method for supplying hydrogen to a fuel cell, comprising supplying hydrogen generated by the method of claim 4 as a hydrogen source for the fuel cell.

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