JP2006051473A - Hydrogen storing/releasing catalyst and hydrogen storing compound material using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storing/releasing catalyst capable of accelerating the hydrogen storing/releasing speed of a hydrogen storage material and lowering the hydrogen storing/releasing temperature of the hydrogen storage material and to provide a hydrogen storing/releasing compound material capable of storing/releasing a large quantity of hydrogen at a lower temperature. <P>SOLUTION: This hydrogen storing/releasing catalyst is composed of a carrier composed of at least one of an inorganic oxide or a carbon material and a metal particle deposited on the carrier. This hydrogen storing/releasing compound material is obtained by compounding this hydrogen storing/releasing catalyst in the hydrogen storage material in a highly dispersed state. Since this hydrogen storing/releasing catalyst improves the hydrogen storing/releasing characteristic of the hydrogen storage material, the hydrogen storing/releasing catalyst-compounded hydrogen storing/releasing compound material can store/release a large quantity of hydrogen at the lower temperature. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrogen storage / release catalyst that improves the hydrogen storage / release characteristics of a hydrogen storage material, and a hydrogen storage composite material using the same.

  In recent years, hydrogen energy has attracted attention as a clean alternative energy due to environmental problems such as global warming caused by carbon dioxide emissions and energy problems such as exhaustion of petroleum resources. For the practical application of hydrogen energy, it is important to develop technology for safely storing and transporting hydrogen. There are several candidates for the hydrogen storage method, and among them, a method using a hydrogen storage material capable of reversibly storing and releasing hydrogen is promising. As hydrogen storage materials, carbon materials such as activated carbon, fullerene, and nanotubes and various metal hydrides are known.

For example, magnesium (Mg) reacts with hydrogen to produce a hydride MgH ₂ . Magnesium is attracting attention as one of the hydrogen storage materials because it is lightweight and has a large hydrogen storage capacity. However, it requires a high temperature of about 300 ° C. for storage and release of hydrogen, and the storage and release speed of hydrogen is extremely slow. For this reason, attempts have been made to use catalysts such as metals in order to improve the hydrogen storage / release characteristics of magnesium. For example, Non-Patent Document 1 discloses an attempt to perform a mechanical pulverization treatment by adding a transition metal such as nickel (Ni) to MgH ₂ . Patent Document 1 discloses hydrogen storage alloy particles having catalytic metal particles such as Ni on the surface and inside of Mg particles.
G. Liang and four others, “Catalytic effect of transition metals on hydrogen sorption in nanocrystalline ball milled MgH2-Tm (Tm = Ti, V, Mn, Fe and Ni)”, “Journal of Alloys and Compounds”, 1999, vol.292, p.247-252 JP 2003-166024 A

Non-Patent Document 1 shows hydrogen release characteristics at 235 to 300 ° C. of MgH ₂ —Tm (Tm: Ti, V, Mn, Fe, Ni) obtained by mechanical pulverization. According to the same literature, when hydrogen is occluded at 29 ° C., MgH ₂ —Ni added with Ni hardly occludes hydrogen like MgH ₂ . On the other hand, Patent Document 1 only shows the hydrogen storage / release characteristics at 310 ° C., and the hydrogen storage / release temperature is not lowered. Thus, the hydrogen storage / release characteristics of magnesium-based materials are still not sufficient for practical use.

  The present invention has been made in view of such a situation, and provides a hydrogen storage / release catalyst capable of increasing the hydrogen storage / release speed of the hydrogen storage material and realizing the reduction of the hydrogen storage / release temperature. This is the issue. Another object of the present invention is to provide a hydrogen storage composite material capable of storing and releasing a large amount of hydrogen at a lower temperature by using this hydrogen storage / release catalyst.

  The hydrogen storage / release catalyst of the present invention comprises a carrier composed of at least one of an inorganic oxide and a carbon material and metal particles supported on the carrier, and is characterized by improving the hydrogen storage / release characteristics of the hydrogen storage material. To do.

  The hydrogen storage / release catalyst of the present invention has a structure in which metal particles are supported on a carrier. In such a support structure, the metal particles are uniformly dispersed in the carrier. Therefore, by adopting the supporting structure, when the hydrogen storage / release catalyst of the present invention is combined with the hydrogen storage material, fine metal particles can be dispersed almost uniformly in the hydrogen storage material. In the hydrogen storage / release catalyst of the present invention, the metal particles mainly serve as a catalyst for increasing the hydrogen storage / release rate. On the other hand, inorganic oxides and carbon materials serving as carriers also have a catalytic ability to increase the rate of hydrogen storage and release. For this reason, the hydrogen storage / release catalyst of the present invention has high catalytic ability to increase the hydrogen storage / release speed of the hydrogen storage material. Therefore, according to the hydrogen storage / release catalyst of the present invention, the hydrogen storage / release speed of the hydrogen storage material is increased, and the hydrogen storage / release temperature can be lowered.

  Further, the hydrogen storage composite material of the present invention is characterized in that the hydrogen storage / release catalyst of the present invention is combined with a hydrogen storage material in a highly dispersed state. As described above, the hydrogen storage / release catalyst of the present invention has high catalytic ability to increase the hydrogen storage / release speed of the hydrogen storage material. Further, when the hydrogen storage / release catalyst of the present invention is combined with the hydrogen storage material, fine metal particles are combined with the hydrogen storage material in a substantially uniform state, that is, in a highly dispersed state. Thereby, the hydrogen molecules adsorbed on the surface of the hydrogen storage material are easily dissociated, and the dissociated hydrogen atoms are easily diffused inside. Therefore, the hydrogen storage composite material of the present invention can store and release a large amount of hydrogen at a lower temperature.

  The hydrogen storage / release catalyst of the present invention comprises a support composed of at least one of an inorganic oxide and a carbon material, and metal particles supported on the support. According to the hydrogen storage / release catalyst of the present invention, the hydrogen storage / release speed of the hydrogen storage material can be increased, and the hydrogen storage / release temperature can be lowered. Further, the hydrogen storage composite material of the present invention is formed by combining the hydrogen storage material with the hydrogen storage / release catalyst of the present invention in a highly dispersed state. The hydrogen storage / release rate is increased by the hydrogen storage / release catalyst of the present invention, and the hydrogen storage composite material of the present invention can store and release a large amount of hydrogen at a lower temperature.

  Hereinafter, the hydrogen storage / release catalyst and the hydrogen storage composite material of the present invention will be described in detail. The hydrogen storage / release catalyst and the hydrogen storage composite material of the present invention are not limited to the following embodiments, and various modifications and improvements that can be made by those skilled in the art without departing from the scope of the present invention. It can implement with the form of.

<Hydrogen storage and release catalyst>
The hydrogen storage / release catalyst of the present invention comprises a support composed of at least one of an inorganic oxide and a carbon material, and metal particles supported on the support. A support | carrier may be comprised only with an inorganic oxide and may be comprised only with a carbon material. Moreover, you may comprise with both an inorganic oxide and a carbon material. When an inorganic oxide is used, the dispersibility of the metal particles is improved. When a carbon material is used, in addition to suppressing aggregation of metal particles, reduction treatment can be performed at a relatively low temperature in the production of the hydrogen storage / release catalyst of the present invention. Therefore, it is preferable that the carrier is composed of both the inorganic oxide and the carbon material because the amount of the supported metal particles can be increased.

  As the inorganic oxide, alumina, silica gel, silica / alumina, zeolite, titania, zirconia, or the like may be used. Among these, alumina is preferable because the metal particles are easily dispersed. As the carbon material, graphite, activated carbon, carbon nanotube, graphite nanofiber, fullerene, carbon black, or the like may be used. It is desirable that the specific surface area be as large as possible. Among these inorganic oxides and carbon materials, one kind may be used alone, or two or more kinds may be mixed and used.

  It is desirable that the metal particles supported on the carrier have high activity with respect to hydrogen. For example, it is desirable that the metal particles include one or more elements selected from Group 4 to 10 elements of the periodic table. In this specification, an element is specified based on the periodic table of IUPAC (1989). That is, Group 4 elements are Ti, Zr, Hf, Group 5 elements are V, Nb, Ta, Group 6 elements are Cr, Mo, W, Group 7 elements are Mn, Tc, Re, Group 8 elements are Fe, Ru, Os, Group 9 elements are Co, Rh, Ir, and Group 10 elements are Ni, Pd, Pt. Among these elements, Ni, V, and Ti have high catalytic ability to increase the hydrogen storage / release rate. Therefore, the metal particles are preferably composed of one or more elements selected from Ni, V, and Ti. The metal particles may be one type or two or more types.

  From the viewpoint of increasing the catalytic activity, it is desirable that the particle diameter of the metal particles be as small as possible. For example, the average particle diameter of the metal particles is preferably 100 nm or less. More preferably, it is 50 nm or less. The average particle diameter of the metal particles can be determined, for example, by the powder X-ray diffraction method shown below.

First, a wide angle X-ray diffraction intensity curve of the hydrogen storage / release catalyst of the present invention is measured by a reflection diffractometer method using CuΚα rays monochromatized by a graphite monochromator. Next, the half-value width β _klm (radian) of the diffraction peak on the crystal plane (klm) is obtained from the obtained diffraction intensity curve. Then, an average value D _klm (Å) of crystallite diameters in a direction perpendicular to the (klm) crystal plane of the metal particles is calculated by Scherrer's equation [D _klm = Kλ / β _klm cos θ _klm ]. Here, the constant K is 0.90, λ is the X-ray wavelength (Å), and θ _klm is the diffraction angle (°). In this specification, the calculated value of D _klm (Å) is adopted as the average particle diameter of the metal particles. For example, when the metal particles are Ni particles, the average particle diameter D ₀₁₁ (Å) in the direction perpendicular to the (011) crystal plane is the average particle diameter.

  The content of the metal particles in the hydrogen storage / release catalyst of the present invention is desirably 5 wt% or more when the total weight of the catalyst is 100 wt%. If it is less than 5 wt%, a sufficient catalytic effect cannot be obtained. More preferably, it is 10 wt% or more. On the other hand, it is desirable to set it to 95 wt% or less for the reason of suppressing the coarsening of the metal particles. More preferably, it is 90 wt% or less, and further 50 wt% or less.

  The method for producing the hydrogen storage / release catalyst of the present invention is not particularly limited. It can be produced using a known precipitation method, impregnation method, ion exchange method or the like. For example, an inorganic acid salt such as a metal nitrate or sulfate used as a metal particle, or an aqueous solution of an organic acid salt such as acetate, oxalate or formate, and an inorganic oxide or carbon material as a carrier What is necessary is just to carry. And after baking at predetermined | prescribed temperature, it can reduce and process as needed.

  Firing may be performed at a temperature of about 350 to 800 ° C. in a nitrogen atmosphere or in air. The firing time is preferably about 1 to 10 hours. The particle diameter of the metal particles varies depending on the firing temperature. For example, when the firing temperature is high, the particle size of the metal particles increases. On the other hand, when the firing temperature is low, the particle size of the metal particles becomes small. Therefore, it is desirable to control the firing temperature so as to obtain a desired particle size. In order to obtain nanometer-sized metal particles, firing at 500 ° C. or lower is desirable.

  When metals other than noble metals such as Pt, Pd, and Rh are used as metal particles, the metal particles are oxidized by firing. Therefore, in this case, it is desirable that the hydrogen storage / release catalyst after calcination is subjected to reduction treatment by heating and holding at a predetermined temperature in a hydrogen atmosphere. The reduction treatment may be performed at a temperature of about 300 to 500 ° C. for about 1 to 2 hours.

<Hydrogen storage composite material>
The hydrogen storage composite material of the present invention is formed by combining a hydrogen storage material with the hydrogen storage / release catalyst of the present invention in a highly dispersed state. As the hydrogen storage material, an ion-bonded hydride having a low hydrogen storage / release rate may be used. For example, a relatively lightweight hydrogen storage _{materials, MgH 2, Mg (NH 2} ) 2, CaNH, Ca 2 NH, LiH, NaH, KH, CaH 2, NaBH 4, NaAlH 4, LiBH 4, LiAlH 4, KBH 4 , KAlH ₄ , Mg (BH ₄ ) ₂ , CaNH, Ca ₂ NH, Ca (BH ₄ ) ₂ , Ba (BH ₄ ) ₂ , Sr (BH ₄ ) ₂ , Fe (BH ₄ ) ₂ , Mg (AlH ₄ ) ₂ , Mn (AlH ₄ ) ₂ , In (AlH ₄ ) ₃ , Ga (AlH ₄ ) ₃ , Fe (AlH ₄ ) ₂ , CuAlH ₄ , Ce (AlH ₄ ) ₃ , Ca (AlH ₄ ) ₂ , Be (AlH ₄ ) ₂ , AgAlH ₄ , AgBH ₄ , Na ₃ AlH ₆ , Sn (AlH ₄ ) ₄ , Ti (AlH ₄ ) ₄ , Ti (AlH ₄ ) ₃ , Zr (AlH ₄ ) ₄ , Al (BH ₄ ) ₃ , _{Ba (BH 4) 2, Be} (BH 4) 2, Ca (B _{4) 2, Co (BH 4} ) 2, Cs (BH 4) 2, CuBH 4, Fe (BH 4) 2, Hf (BH 4) 2, Sn (BH 4) 2, TiBH 4, Th (BH 4) ₄ , Ti (BH ₄ ) ₃ , Zn (BH ₄ ) ₂ , Zr (BH ₄ ) ₄ , Li ₂ NH, LiNH ₂ , Ca (NH ₂ ) ₂ , Li ₂ Mg (NH ₂ ) _{2 and the} like. One kind of these may be used alone, or two or more kinds may be mixed and used. Among them, MgH ₂ having a large theoretical hydrogen storage amount of 7.6 wt% is preferable at low cost.

In addition, although metal hydride was mentioned here as a hydrogen storage material, the hydrogen storage material which comprises the hydrogen storage composite material of this invention is a concept also including the state from which the said metal hydride discharge | released hydrogen. For example, if the hydrogen storage material is MgH _2, consisting of hydrogen is released from MgH ₂ and MgH ₂ → Mg. At this time, the hydrogen storage composite material of the present invention is in a state where the hydrogen storage catalyst of the present invention is combined with the material (Mg) after releasing hydrogen. That is, the hydrogen storage material constituting the hydrogen storage composite material of the present invention includes both a metal hydride that has stored hydrogen and a material from which hydrogen has been released.

  The content of the hydrogen storage / release catalyst of the present invention in the hydrogen storage composite material of the present invention is preferably 0.1 wt% or more when the total weight of the hydrogen storage composite material is 100 wt%. When the amount is less than 0.1 wt%, the catalytic effect of increasing the hydrogen storage / release rate cannot be obtained sufficiently. More preferably, it is 2 wt% or more. On the other hand, considering the hydrogen storage amount, it is desirable to set it to 50 wt% or less. More preferably, it is 20 wt% or less.

As an aspect in which the hydrogen storage material and the hydrogen storage / release catalyst of the present invention are combined, for example, an aspect in which the particles of the hydrogen storage / release catalyst of the present invention adhere to the particle surface of the hydrogen storage material, or a finely pulverized hydrogen storage material And the hydrogen storage / release catalyst of the present invention may be mixed. In the former embodiment, for example, a mixture obtained by mixing a metal hydride and the hydrogen storage / release catalyst of the present invention can be produced by mechanical pulverization. In the latter embodiment, for example, the metal hydride powder that has been mechanically pulverized can be mixed with the hydrogen storage / release catalyst powder of the present invention. In any production method, the metal hydride is mechanically pulverized and refined. For this reason, the diffusion distance of hydrogen is shortened, which is effective for improving the hydrogen storage / release rate. In addition, by dispersing the nanometer-sized hydrogen storage / release catalyst of the present invention on the surface of the refined metal hydride, the catalytic effect of the catalyst can be sufficiently exerted. In the above production method, a metal hydride is used as a raw material. For example, MgH ₂ is harder than Mg. Therefore, when a metal hydride such as MgH ₂ is used as a raw material, there is an advantage that mechanical pulverization can be easily performed.

  The particles of the hydrogen storage / release catalyst of the present invention are reduced by being pulverized and refined by being mixed with a metal hydride by mechanical pulverization or the like. Therefore, in a state where the hydrogen storage / release catalyst of the present invention and the hydrogen storage material are combined, the average particle diameter of the metal particles in the catalyst is smaller than that in the case where the catalyst exists alone. Thus, in the hydrogen storage composite material of the present invention, it is desirable that the average particle diameter of the metal particles in the hydrogen storage / release catalyst of the present invention is 50 nm or less. It is more preferable that it is 15 nm or less.

  The mechanical pulverization process may be performed in a predetermined atmosphere by storing a raw material such as a metal hydride in a processing apparatus. The mechanical pulverization treatment is desirably performed in an atmosphere free of oxygen and moisture, such as an inert gas atmosphere, a hydrogen atmosphere, or a vacuum atmosphere. The mechanical pulverization treatment may be performed at room temperature and atmospheric pressure.

  The type of the mechanical pulverization process is not particularly limited, and a process that uses an already known injection pressure or collision force may be used. For example, a mechanical gliding process, a mechanical milling process, a mechanical alloying process, etc. are mentioned. In particular, a mechanical gliding process is suitable. The mechanical pulverization process is desirably performed by a dry method. Specifically, for example, a planetary ball mill, a vibration ball mill, a jet mill, a hammer mill or the like may be used. There are no particular limitations on the materials for the container for containing the raw materials and the balls for grinding. For example, a container made of structural alloy steel such as chrome steel, nickel chrome steel, nickel chrome molybdenum steel, chrome molybdenum steel, a ball for pulverization, or the like may be used.

  Various conditions for the mechanical pulverization treatment may be appropriately determined according to the apparatus to be used and in consideration of the amount of raw material to be treated. For example, the grinding energy is desirably 5 times (5G) or more of the gravitational acceleration. The treatment time may be appropriately determined in consideration of the obtained hydrogen storage composite material, the particle size of the metal hydride, and the like. For example, the treatment may be performed for about 5 to 50 hours.

  Based on the above embodiment, two types of hydrogen storage / release catalysts of the present invention were manufactured, and eight types of hydrogen storage composite materials serving as examples of the present invention were manufactured using them. Moreover, the catalyst etc. were changed and 12 types of hydrogen storage composite materials used as a comparative example were manufactured. Hydrogen was released and stored in each produced hydrogen storage composite material, and their hydrogen storage / release characteristics were investigated. Hereinafter, the manufacture of the hydrogen storage composite material and the hydrogen storage / release characteristics of the manufactured hydrogen storage composite material will be described.

(1) Production of hydrogen storage composite material (a) Hydrogen storage composite materials # 1 to # 4 (Examples)
First, a hydrogen storage / release catalyst was produced. Activated carbon (3000 m ² / g) was added to an aqueous solution in which nickel nitrate and aluminum nitrate were dissolved in water and stirred. A sodium carbonate aqueous solution was dropped into this aqueous solution to deposit nickel hydroxide and aluminum hydroxide on the activated carbon surface. This aqueous solution was put into a dryer, dried overnight, and then calcined in air at 450 ° C. for 3 hours. After calcination, reduction treatment was performed at 500 ° C. in a hydrogen atmosphere for 3 hours, and a hydrogen storage / release catalyst in which nickel particles are supported on alumina and carbon (in Tables 1 and 3 below, indicated as “Ni / Al ₂ O ₃ / C”). ) The hydrogen storage / release catalyst has a Ni content of 46 wt%, an Al ₂ O ₃ content of 8 wt%, and a C content of 46 wt%. This hydrogen storage / release catalyst was used as the catalyst of Example 1.

Next, the hydrogen storage composite material of the present invention was manufactured using the catalyst of Example 1 above. MgH ₂ (manufactured by Aldrich) having a purity of 90 wt% was used as the metal hydride. A mixture was prepared by blending the catalyst of Example 1 in various proportions with MgH ₂ . 5 g of each prepared mixture is put into a chrome steel container (volume: 300 ml) together with 40 chrome steel balls (outer diameter 9.5 mm), and mechanical gliding is performed by planetary ball mill P-5 (manufactured by FRITSCH). Processing (hereinafter referred to as “MG processing”). The MG treatment was performed for 24 hours under a vacuum atmosphere, room temperature, and 0.1 MPa with a grinding energy of 6G. The obtained hydrogen storage composite materials were numbered # 1 to # 4 according to the mixing ratio of the catalyst of Example 1. The composition and the like of the # 1 to # 4 hydrogen storage composite materials are summarized in Table 1 below.

(B) Hydrogen storage composite materials of # 5 and # 6 (Example)
The hydrogen storage composite material of the present invention was produced using the catalyst of Example 1 in the same manner as (a) above. MgH ₂ (manufactured by Aldrich) having a purity of 90 wt% was used as the metal hydride. 5 g of MgH ₂ was placed in a chrome steel container (volume: 300 ml) together with 40 chrome steel balls (outer diameter 9.5 mm), and subjected to MG treatment with a planetary ball mill P-5 (manufactured by FRITSCH). The conditions for the MG treatment were the same as the above (a). The MG-treated MgH ₂ was mixed with the catalyst of Example 1 at a predetermined ratio and mixed using a mortar. The obtained hydrogen storage composite materials were numbered # 5 and # 6 according to the blending ratio of the catalyst of Example 1. The composition and the like of the hydrogen storage composite materials # 5 and # 6 are summarized in Table 1 below.

(C) Hydrogen storage composite materials of # 7 and # 8 (Example)
First, a hydrogen storage / release catalyst was produced. Nickel nitrate and aluminum nitrate were dissolved in water. A sodium carbonate aqueous solution was dropped into this aqueous solution to precipitate nickel hydroxide and aluminum hydroxide. This aqueous solution was put into a dryer, dried overnight, and then calcined in air at 450 ° C. for 3 hours. After firing, reduction treatment was performed at 500 ° C. for 3 hours in a hydrogen atmosphere to obtain a hydrogen storage / release catalyst (shown as “Ni / Al ₂ O ₃ ” in Tables 1 and 3 below) in which nickel particles were supported on alumina. . The hydrogen storage / release catalyst has a Ni content of 85 wt% and an Al ₂ O ₃ content of 15 wt%. This hydrogen storage / release catalyst was used as the catalyst of Example 2.

Next, the hydrogen storage composite material of the present invention was manufactured using the catalyst of Example 2 above. As the metal hydride, MgH ₂ having a purity of 90 wt% containing 10 wt% MgO was used. A mixture was prepared by blending the catalyst of Example 2 in a predetermined ratio with MgH ₂ . 5 g of each prepared mixture was treated with MG in the same manner as in the above (a). The obtained hydrogen storage composite materials were numbered # 7 and # 8 according to the mixing ratio of the catalyst of Example 2. The composition and the like of the hydrogen storage composite materials # 7 and # 8 are summarized in Table 1 below.

(D) Hydrogen storage composite material of # 51 to # 54 (comparative example)
A hydrogen storage composite material of a comparative example was manufactured using MgH ₂ similar to the above as the metal hydride and Ni as the catalyst. A mixture was prepared by blending Ni powder (manufactured by Soekawa Rikagaku Co., Ltd., average particle size 0.8 μm) at a predetermined ratio with MgH ₂ . 5 g of each prepared mixture was treated with MG in the same manner as in the above (a). The obtained hydrogen storage composite materials were numbered as # 51 to # 54 according to the mixing ratio of Ni. The composition and the like of the hydrogen storage composite materials # 51 to # 54 are summarized in Table 2 below.

(E) Hydrogen storage composite material of # 55 and # 56 (comparative example)
A comparative hydrogen storage composite material was produced using MgH ₂ as the metal hydride and Ni as the catalyst. Similarly to the above (b), 5 g of MgH ₂ was treated with MG. Ni powder (manufactured by Soekawa Rikagaku Co., Ltd., average particle size 0.8 μm) was blended in a predetermined ratio to MG-treated MgH ₂ and mixed using a mortar. The obtained hydrogen storage composite materials were numbered as # 55 and # 56 according to the mixing ratio of Ni. The composition and the like of the hydrogen storage composite materials of # 55 and # 56 are summarized in Table 2 below.

(F) Hydrogen storage composite material of # 57 to # 62 (comparative example)
Hydrogen of the comparative example using MgH ₂ similar to the above as the metal hydride and using various metal oxides, Ti (manufactured by Nippon Kogyo Chemical Co., Ltd.), and super activated carbon (manufactured by Kansai Thermal Chemical Co., Ltd.) as the catalyst. An occluded composite material was produced. Each catalyst was blended with MgH ₂ at a weight ratio of 95: 5 to prepare a mixture. 5 g of each prepared mixture was treated with MG in the same manner as in the above (a). The obtained hydrogen storage composite materials were numbered # 57 to # 62 depending on the type of catalyst. The composition and the like of the hydrogen storage composite materials # 57 to # 62 are summarized in Table 2 below.

(2) Hydrogen storage / release characteristics (a) A hydrogen release test was conducted as a first test. That is, each produced hydrogen storage composite material of the Example and the comparative example was hold | maintained for 6 hours in the argon gas atmosphere of 200 degreeC and 0.1 Mpa, respectively, and hydrogen was discharge | released from each hydrogen storage composite material. Then, the hydrogen release amount of each hydrogen storage composite material was determined by a thermal desorption method. Tables 1 and ₂ show the composition of each hydrogen storage composite material, the mixing ratio (weight ratio) of the metal hydride (MgH ₂ ) and the catalyst, the production method, the average particle diameter of the metal particles (Ni), and the hydrogen release amount. Show. Table 1 shows each hydrogen storage composite material of the example, and Table 2 shows each hydrogen storage composite material of the comparative example.

  As shown in Table 1, in the hydrogen storage composite material of the example, the average particle diameter of the metal particles (Ni) was 10 nm or less. Further, the hydrogen release amount was as large as 4.1 to 6.0 wt%. That is, the hydrogen storage composite material of the present invention using the hydrogen storage release catalyst of the present invention can release a large amount of hydrogen even at a relatively low temperature of about 200 ° C.

For example, when the hydrogen storage composite materials # 1 to # 4 were compared, the hydrogen release amount increased when the blending ratio of the catalyst increased from 2 to 5, and 10 wt%. However, in # 4 where the blending ratio of the catalyst was 20 wt%, the amount of released hydrogen was slightly reduced compared with # 2 and # 3 where the ratio was 5, 10 wt%. In addition, comparing the hydrogen storage composite materials # 2 and # 7, and # 4 and # 8, which have the same catalyst mixing ratio and different types, respectively, the hydrogen storage composite materials # 2 and # 4 containing carbon materials However, the hydrogen release amount has increased. In addition, when comparing the # 2 and # 5 and # 3 and # 6 hydrogen storage composite materials, which differ only in the manufacturing method, respectively, the hydrogen storage of # 2 and # 3 manufactured by MG treatment of both MgH ₂ and the catalyst The amount of hydrogen released from the composite material was larger.

  On the other hand, as shown in Table 2, the hydrogen release amount of the hydrogen storage composite material of the comparative example was 2.8 wt% at the maximum. In particular, the # 55 and # 56 hydrogen storage composite materials manufactured by mortar mixing and the # 57 to # 62 hydrogen storage composite materials using a catalyst other than Ni released almost no hydrogen.

  (B) A hydrogen storage test was performed as a second test. First, each produced hydrogen storage composite material of the example and the comparative example is accommodated in a predetermined container, and the inside of the container is evacuated at 250 ° C. to 0.2 Pa or less, so that hydrogen is extracted from each hydrogen storage composite material. Released. Separately from this, the temperature was changed, and the hydrogen storage composite material was evacuated at 450 ° C. to 0.2 Pa or less to release hydrogen from each hydrogen storage composite material. Next, for each hydrogen storage composite material from which hydrogen was released under each condition, hydrogen was stored at room temperature (23 ° C.) under a hydrogen pressure of 9 MPa. And the hydrogen storage amount 6 hours after the hydrogen storage start was calculated | required using the PCT characteristic measuring apparatus (made by Suzuki Shokan). Tables 3 and 4 show the hydrogen storage amount of each hydrogen storage composite material according to the hydrogen release temperature. Table 3 shows each hydrogen storage composite material of the example, and Table 4 shows each hydrogen storage composite material of the comparative example.

  As shown in Table 3, the hydrogen storage composite materials of the Examples stored hydrogen even at room temperature, although there were differences depending on the hydrogen release temperature. In particular, when hydrogen was released at 250 ° C., the hydrogen storage amount increased. This is presumably because the release of hydrogen at a low temperature made it difficult for the Mg crystals to grow and the coarsening of the Mg crystals was suppressed. In addition, as with the release of hydrogen, the amount of hydrogen occlusion changed depending on the blending ratio of the catalyst and the type of catalyst.

  On the other hand, as shown in Table 4, the hydrogen storage amount of the hydrogen storage composite material of the comparative example was 3.7 wt% at the maximum even when the hydrogen release temperature was 250 ° C. Here, the hydrogen storage composite material of # 57 to # 61 using only metal oxide or super activated carbon as a catalyst could hardly release hydrogen at 250 ° C., and therefore could not store hydrogen at room temperature.

  In summary, the hydrogen storage composite material of the present invention has a higher hydrogen storage / release rate due to the hydrogen storage / release catalyst of the present invention, so that it can release hydrogen at a relatively low temperature of about 200 ° C. and store hydrogen at room temperature. be able to.

  In this hydrogen storage test, the hydrogen storage amount of the hydrogen storage composite material (# 51 to # 54) using only Ni as a catalyst is relatively large at 3.0 to 3.7 wt%. This is because in this hydrogen storage test, hydrogen was stored under a high pressure of 9 MPa. Until now, it was common to occlude hydrogen under hydrogen pressure of about 1 MPa. Under such a low pressure, the hydrogen storage amount of the hydrogen storage composite material using only Ni as a catalyst is only about 0.4 wt%. That is, it can be seen from the results of this hydrogen storage test that the hydrogen storage amount can be increased by increasing the pressure. Recently, it has become possible to occlude hydrogen under a high pressure of 35 MPa or more. Therefore, it is considered that the hydrogen storage composite material of the present invention can store a large amount of hydrogen in a shorter time at room temperature by increasing the hydrogen pressure during storage of hydrogen to 35 to 70 MPa.

  For example, in a hydrogen vehicle, waste heat from a hydrogen engine can be used. The hydrogen storage composite material of the present invention releases about 5 wt% of hydrogen by holding at a temperature of about 200 ° C. for 4 hours. Therefore, if the hydrogen storage composite material of the present invention is used as a hydrogen storage source, hydrogen can be sufficiently supplied to the hydrogen engine using waste heat of about 200 ° C. Thus, the hydrogen storage composite material of the present invention is useful as a hydrogen supply source for hydrogen engines, fuel cells, and the like.

Claims (9)

  A hydrogen storage / release catalyst comprising a support made of at least one of an inorganic oxide and a carbon material and metal particles supported on the support, and improving the hydrogen storage / release characteristics of the hydrogen storage material.   The hydrogen storage / release catalyst according to claim 1, wherein an average particle diameter of the metal particles is 100 nm or less.   The hydrogen storage / release catalyst according to claim 1, wherein the metal particles include one or more elements selected from Group 4 to 10 elements.   2. The hydrogen storage / release catalyst according to claim 1, wherein the content of the metal particles is 5 wt% or more and 95 wt% or less when the total weight of the hydrogen storage / release catalyst is 100 wt%.   A hydrogen storage composite material obtained by combining the hydrogen storage material according to claim 1 in a highly dispersed state with a hydrogen storage material.   6. The hydrogen storage composite material according to claim 5, wherein the content of the hydrogen storage / release catalyst is 0.1 wt% or more and 50 wt% or less when the total weight of the hydrogen storage composite material is 100 wt%.   The hydrogen storage composite material according to claim 5, wherein an average particle diameter of the metal particles in the hydrogen storage / release catalyst is 50 nm or less.   The hydrogen storage composite material according to claim 5, which is produced by mechanically pulverizing a mixture obtained by mixing a metal hydride and the hydrogen storage / release catalyst according to claim 1.   The hydrogen storage composite material according to claim 5, which is produced by mixing the metal hydride subjected to mechanical grinding with the hydrogen storage / release catalyst according to claim 1.