Catalyst for producing hydrogen and method for producing hydrogen

Abstract

A metal-supporting catalyst for decomposing ammonia into hydrogen and nitrogen. The catalyst shows a high performance with a low cost and being advantageous from the viewpoint of resources, and an efficient method for producing hydrogen using the catalyst. The catalyst catalytically decomposes ammonia gas to generate hydrogen. The hydrogen generation catalyst includes, as a support, a mayenite type compound having oxygen ions enclosed therein or a mayenite type compound having 10.sup.15 cm.sup.3 or more of conduction electrons or hydrogen anions enclosed therein, and metal grains for decomposing ammonia are supported on the surface of the support. Hydrogen is produced by continuously supplying 0.1-100 vol % of ammonia gas to a catalyst layer that comprises the aforesaid catalyst, and reacting the same at a reaction pressure of 0.01-1.0 MPa, at a reaction temperature of 300-800 C. and at a weight hourly space velocity (WHSV) of 500/mlg.sup.1h.sup.1 or higher.

Claims

1. A method for producing hydrogen comprising: continuously supplying an ammonia gas with a volume fraction of 0.1 to 100% to a catalyst layer comprising supported metal catalyst packed in a reactor; and performing contact decomposition reaction at a reaction temperature of 350 C. to 800 C., wherein the supported metal catalyst comprises a support comprising a mayenite-type compound which includes 10.sup.15 cm.sup.3 or more of conduction electrons or hydrogen anions, and particles of catalytically active metal for ammonia decomposition which are supported on a surface of the support, wherein the contact decomposition reaction is performed at a weight hourly space velocity (WHSV) of 500 /mlg.sup.1h.sup.1 or more.

2. The method for producing hydrogen according to claim 1, wherein the contact decomposition reaction is performed at a pressure of 0.01 MPa to 1.0 MPa.

3. The method for producing hydrogen according to claim 1, wherein the catalytically active metal comprises at least one selected from the metal elements of Groups VIII, IX, and X.

4. The method for producing hydrogen according to claim 1, wherein the supported metal catalyst includes the catalytically active metal at an amount of 0.01 wt % to 30 wt % of the mayenite-type compound.

5. The method for producing hydrogen according to claim 1, wherein the supported metal catalyst has a BET specific surface area of 1 to 100 m.sup.2g.sup.1.

6. A method for producing hydrogen comprising: continuously supplying an ammonia gas with a volume fraction of 0.1 to 100% to a catalyst layer comprising supported metal catalyst packed in a reactor; and performing contact decomposition reaction at a reaction temperature of 350 C. to 800 C., wherein the supported metal catalyst comprises a support comprising a mayenite-type compound which includes oxygen ions which has not been made to include 10.sup.15 cm.sup.3 or more of conduction electrons or hydrogen anions, and particles of catalytically active metal for ammonia decomposition which are supported on a surface of the support, wherein the contact decomposition reaction is performed at a weight hourly space velocity (WHSV) of 500 /mlg.sup.1h.sup.1 or more.

7. The method for producing hydrogen according to claim 6, wherein the contact decomposition reaction is performed at a pressure of 0.01 MPa to 1.0 MPa.

8. The method for producing hydrogen according to claim 6, wherein the catalytically active metal comprises at least one selected from the metal elements of Groups VIII, IX, and X.

9. The method for producing hydrogen according to claim 6, wherein the supported metal catalyst includes the catalytically active metal at an amount of 0.01 wt % to 30 wt % of the mayenite-type compound.

10. The method for producing hydrogen according to claim 6, wherein the supported metal catalyst has a BET specific surface area of 1 to 100 m.sup.2g.sup.1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic drawing of a reaction line used for NH.sub.3 decomposition shown in Examples 1 to 8 and Comparative Examples 1 and 2.

DESCRIPTION OF EMBODIMENTS

(2) The structure of a hydrogen-producing catalyst of the present invention, a method for producing the catalyst, and a method for producing hydrogen by ammonia decomposition using the catalyst are described in detail below.

(3) <Production of Mayenite-Type Compound Base Material>

(4) C12A7 which is a typical composition of a mayenite-type compound is described in detail below, but the present invention is not limited to C12A7 and can be applied to all mayenite-type compounds having the same crystal structure as C12A7, such as 12SrO.7Al.sub.2O.sub.3 or the like in which Ca is substituted with Sr. A base material composed of C12A7 and used as a starting material of a method of producing a catalyst of the present invention may be a powder or a compact such as a porous body, a solid sintered body, a thin film, a solid single crystal, or the like, and the compact may have any shape. In addition, C12A7 supported on a support composed of another material may be used as the base material. The base material functions as a support for catalytically active metal particles.

(5) A raw material of C12A7 is synthesized by a solid-phase method, a hydrothermal method, or the like. Hydrothermal reaction is a reaction involving water at a high temperature and high pressure of 100 C. or more and 5 MPa or more, and a ceramic powder can be synthesized by reaction at a low temperature within a short time. By using a hydrothermal synthesis method, a C12A7 powder with a large specific surface area (about 20 to 60 m.sup.2g.sup.1) can be produced. For example, Ca.sub.3Al.sub.2(OH).sub.12 which is a hydroxide used as a precursor of C12A7 can be produced by mixing water, calcium hydroxide, and aluminum hydroxide with a stoichiometric composition, and then heating the resultant mixture, for example, at 150 C. for about 6 hours. The adsorbed water, surface hydroxyl groups, OH.sup. in the cages, etc. can be removed by vacuum evacuation treatment of the powder at 750 C. to 900 C., thereby preventing deactivation of a reducing agent in the step of injecting electrons.

(6) <Step of Including Conduction Electrons or Hydrogen Anions in C12A7 Base Material>

(7) In producing a C12A7 powder including conduction electrons, a raw material powder of C12A7 with the stoichiometric composition may be heated in a reducing atmosphere. For a porous body or solid sintered body of C12A7 including conduction electrons, a raw material powder of C12A7 with the stoichiometric composition may be molded and then heated with Ca, CaH.sub.2, or the like in a reducing atmosphere. The C12A7 base material including conduction electrons other than a thin film and a solid single crystal can be produced directly from a raw material without passing through the production of a C12A7 base material not containing conduction electrons. Similarly, a powder, a porous body, or a solid sintered body of the the C12A7 base material containing hydrogen anions can also be synthesized by heating in a hydrogen stream or heating with Ca or the like in a reducing atmosphere.

(8) A thin film of C12A7 containing conduction electrons can be produced by forming a thin film of C12A7 on a substrate of MgO, Y.sub.3Al.sub.5O.sub.12, or the like by a pulsed laser deposition (PLD) method, a sputtering method, a plasma spraying method, or the like using a C12A7 solid sintered body as a target and again depositing a C12A7 thin film by the PLD method under heating at 500 C. or more to integrate these thin films. In the second PLD method, plasmanized C12A7 functions as a reducing agent, and thus conduction electrons are included in the thin film. A thin film of C12A7 containing hydrogen anions can also be synthesized by the same method.

(9) A solid single crystal of C12A7 containing conduction electrons may be produced by pulling up a melt (CZ method) prepared by melting a C12A7 raw material powder at about 1600 C. to form a C12A7 single crystal, sealing the single crystal in a vacuum glass tube together with a metal Ca powder or Ti powder, or the like, and heating the single crystal in a reducing atmosphere to include conduction electrons into the solid single crystal. A solid single crystal of C12A7 including hydrogen anions can also be synthesized by the same method.

(10) The solid sintered body or soil single crystal of C12A7 including conduction electrons or hydrogen anions can be processed into a powder. Processing into a powder can be performed by grinding in a mortar, grinding by a jet mill, or the like. The size of the powder is not particularly limited, but particles having a distribution of particle diameters in a range of about 100 nm to 1 mm can be produced by the this method. In addition, C12A7 including 110.sup.15 cm.sup.3 or more of conduction electrons or hydrogen anions can be produced by the method.

(11) Regardless of a power, a porous body, a solid sintered body, a thin film, and a solid single crystal, conduction electrons may be removed from a surface portion of the base material according to the production method. In this case, it is preferred to include 110.sup.15 cm.sup.3 or more of conduction electrons up to the uppermost surface of the base material by heating at 500 C. or more to less than the melting point (1250 C.) of the compound in vacuum, inert gas, or a reducing atmosphere.

(12) <Step of Supporting Active Metal Component>

(13) The ammonia decomposition of the present invention can be performed by using as the catalytically active metal a transition metal element selected from the Group VIII, Group IX, or Group X in the long-period periodic table. However, a Group VIII element selected from Fe, Ru, and Os, a Group IX element selected from Co, Rh, and Ir, and a Group X element selected from Ni, Pd, and Pt are particularly preferably used alone or in combination.

(14) When the C12A7 powder or porous body is used as the base material, the C12A7:e.sup.1 powder or porous body containing 110.sup.15 cm.sup.3 or more of conduction electrons produced in the above-described steps is mixed with a compound of the catalytically active metal by any one of various methods, for example, a CVD method (chemical vapor deposition method) and an impregnation method. When the solid sintered body, the thin film, the solid single crystal, or the like is used, like the powder or porous body, a compound of the catalytically active metal is deposited on the surface of the base material by the impregnation method, the CVD method, or the sputtering method, and the compound of the catalytically active metal is thermally decomposed in a reducing atmosphere, preferably, at a temperature of 150 C. to 800 C. to deposit and adhere the catalytically active metal to the surface of the base material. When the compound of the catalytically active metal is used, for example, a method can be used, in which each of the metal raw materials is deposited on C12A7 by the CVD method or the like, thermally decomposed, and then nitrided with ammonia gas.

(15) Examples of the compound of the catalytically active metal include, but are not particularly limited to, easily thermally decomposable inorganic metal compounds or organic metal complexes, such as triruthenium dodecacarbonyl [Ru.sub.3(CO).sub.12], dichlorotetrakis(triphenylphosphine) ruthenium(II) [RuCl.sub.2(PPh.sub.3).sub.4], dichlorotris(triphenylphosphine) ruthenium(II) [RuCl.sub.2(PPh.sub.3).sub.3], tris(acetylacetonate) ruthenium(III) [Ru(acac).sub.3], ruthenocene [Ru(C.sub.5H.sub.5)], ruthenium chloride [RuCl.sub.3], pentacarbonyl iron [Fe(CO).sub.5], tetracarbonyl iron iodide [Fe(CO).sub.4I.sub.2], iron chloride [FeCl.sub.3], ferrocene [Fe(C.sub.5H.sub.5).sub.2], tris(acetylacetonate) iron(III) [Fe(acac).sub.3], dodecacarbonyl triiron [Fe.sub.3(CO).sub.12], cobalt chloride [CoCl.sub.3], tris(acetylacetonate) cobalt(III) [Co(acac).sub.3], cobalt(II) acetylacetonate [Co(acac).sub.2], cobaltoctacarbonyl [Co.sub.2(CO).sub.3], cobaltocene [Co(C.sub.5H.sub.5).sub.2], triosmium dodecacarbonyl [Os.sub.3(CO).sub.12], acetylacetonate nickel (II) dihydrate [C.sub.10H.sub.14NiO.sub.4.xH.sub.2O], and the like.

(16) The impregnation method can use the following steps. For example, a support powder is dispersed in a solution of the compound of the catalytically active metal (for example, a hexane solution of Ru carbonyl complex) and the resultant dispersion is stirred. In this case, the amount of the compound of the catalytically active metal is 0.01 to 40 wt %, preferably 0.02 to 30 wt %, and more preferably 0.05 to 20 wt % relative to the support powder. Then, the solvent is evaporated to dryness by heating in an inert gas stream, such as nitrogen, argon, helium, or the like, or under vacuum at 50 C. to 200 C. for 30 minutes to 5 hours. Next, a catalyst precursor composed of the dried compound of the catalytically active metal is reduced. These steps can yield a supported metal catalyst in which the catalytically active metal is highly dispersed as fine particles having a diameter of several nm to several hundred nm and strongly adheres to the surface of the support powder. If required, the catalyst of the present invention may use an accelerator as an additive.

(17) The supported metal catalyst including the 12CaO.7Al.sub.2O.sub.3 powder as a support has a BET specific surface area of about 1 to 100 m.sup.2g.sup.1, and the amount of the catalytically active metal is 0.01 to 30 wt %, preferably 0.02 to 20 wt %, and more preferably 0.05 to 10 wt % relative to the support powder. The amount of less than 0.01 wt % is ineffective because of an excessively small number of active points, and the amount of over 30 wt % is undesired for cost because of little increase in catalytic activity.

(18) Instead of the method described above, a supported metal catalyst having the same form as described above can be produced by mixing, in a solid phase, a C12A7 powder containing 110.sup.15 cm.sup.3 or more of conduction electrons and a compound powder of the catalytically active metal by a physical mixing method under the same conditions as described above, and then reducing the mixture by heating.

(19) Also, the supported metal catalyst can be used as a compact by using a general molding technique. Examples of a shape include a granular shape, a spherical shape, a tablet shape, a ring shape, a macaroni-like shape, a four-leaf shape, a dice shape, a honeycomb shape, and the like. The support coated with the supported metal catalyst can also be used.

(20) <Decomposition of Ammonia>

(21) Ammonia decomposition is a reaction represented by formula 1 below, in which a reactor is filled with the supported metal catalyst to form a catalyst layer, and ammonia gas as a raw material is continuously supplied at a reaction temperature of 350 C. to 800 C. and is brought into contact with the catalyst layer, thereby producing hydrogen and nitrogen.
2NH.sub.3.fwdarw.3H.sub.2+N.sub.2(Formula 1)

(22) The ammonia decomposition reaction is an equilibrium reaction and is also an endothermic reaction and a volume-increasing reaction, and thus high temperature-low pressure conditions are advantageous. When the catalyst of the present invention is used, the reaction pressure is preferably in a range of 0.01 Mpa to 1.0 MPa, and the temperature is preferably in a range of 300 C. to 800 C. The reaction pressure of less than 0.1 MPa allows the decomposition reaction to efficiency proceeds but is disadvantageous in view of cost because of the need for a pressure deducing equipment. The reaction pressure of 0.10 MPa (atmospheric pressure) is preferred in view of equipment. On the other hand, the reaction pressure over 1.0 MPa causes an equilibrium advantageous to the raw material side and thus cannot exhibit a satisfactory decomposition rate. The reaction temperature of less than 300 C. is unpractical because of a low reaction rate. On the other hand, the temperature over 800 C. causes a high decomposition rate but is undesired because of the need for an expensive heat-resistant apparatus and the influence on the catalyst life. The reaction temperature is more preferably 400 C. to 750 C., and the temperature for a Ru catalyst is more preferably 400 C. to 600 C., and the temperature for a Ni or Co catalyst is more preferably 500 C. to 750 C. The C12A7 has a melting point of 1250 C. and is not sintered at about 800 C.

(23) The method of the present invention can use, as the raw material, either ammonia gas diluted with a balance gas or ammonia alone, that is, ammonia gas with a volume fraction of 0.1% to 100% can be used. When hydrogen is produced by ammonia decomposition reaction, it is necessary to separate between the produced hydrogen and nitrogen, and thus the volume fraction of ammonia is preferably as high as possible. The suitable volume fraction is 5% or more, preferably 20% or more, and more preferably 70% or more. The decomposition reaction at a weight hourly space velocity (WHSV) of 500 mlg.sup.1h.sup.1 or more can exhibit a high NH.sub.3 conversion rate.

(24) The gas produced by the ammonia decomposition method of the present invention theoretically contains hydrogen and nitrogen at a molar ratio of 3:1, and can be used as gas, for example, for bright annealing finish of stainless steel, nickel steel, nickel, nickel-copper or nickel-chromium alloy, or the like. Further, hydrogen produced in the present invention do not contain CO and CO.sub.2 which are harmful to fuel cells, and thus the produced hydrogen separated from nitrogen and purified can be used as, for example, hydrogen for fuel cells.

(25) The ammonia decomposition reaction can be performed by using a general gas-solid phase contact reaction apparatus using a corrosion-resistant material such as stainless steel or the like. The reaction system may be any one of a batch reaction system, a closed circulating reaction system, and a flow reaction system, but the flow reaction system is most preferred from a practical viewpoint. Since the reaction is an endothermic reaction, it is advantageous to perform the reaction while supplying reaction heat, and various industrial designs for supplying reaction heat are considered for increasing the yield. For example, a method is proposed, in which ammonia decomposition reaction is performed while combustion heat is obtained by oxidizing a portion of an ammonia raw material with air.

(26) In the present invention, like in a usual method, the ammonia decomposition reaction can be performed by using a single reactor filled with the catalyst or a plurality of reactors. Also, any one of a method of connecting a plurality of reactors and a method of using a reactor including a plurality of reaction layers formed therein can be used. The catalyst used may be any one of the catalyst of the present invention alone, a combination of two or more catalysts selected from the catalysts of the present invention, or a combination of the catalyst of the present invention and a known catalyst. In view of improvement in conversion rate, the catalytic metal is preferably activated by exposing the catalyst to a reducing gas atmosphere of hydrogen or the like at 300 C. to 700 C. for about 30 minutes to 2 hours before the ammonia decomposition reaction.

(27) The present invention is described in further detail below based on examples. An atmospheric pressure fixed-bed flow reactor (FIG. 1) was used, and an ammonia decomposition rate was determined by gas-chromatographic quantitative determination of an amount of NH.sub.3 produced to evaluate ammonia decomposition activity. The conversion rate a (%) was determined according to a formula below. In the formula, P.sub.NH3 and P.sub.NH3 represent ammonia partial pressures before and after the reaction, respectively.
NH.sub.3 conversion rate: a (%)=100P.sub.NH3(P.sub.NH3P.sub.NH3)/(P.sub.NH3+P.sub.NH3)

(28) FIG. 1 shows the outlines of an apparatus used in experiments. A quartz reactor 1 (inner diameter: 6 mm, length: 24 cm, inner volume: 6.8 ml) was filled with a supported metal catalyst prepared in each of examples and comparative examples described below. Then, the supported metal catalyst was previously reduced by flowing H.sub.2 to the reactor 1 from a cylinder 3. Then, NH.sub.3 was flowed to the reactor 1 from a cylinder 4. When H.sub.2 was diluted, a predetermined amount of He was supplied from a cylinder 2 and mixed with H.sub.2. The ammonia flow rate was controlled by a ball flow meter 5 so as to be a predetermined weight hourly space velocity. Then, the reaction system was heated to a predetermined temperature, and an activity test was conducted. The reaction product flowing out from the reactor 1 was discharged through an exhaust port 6 (vent), and a part of the product was collected in a measuring tube 7 (Sampling loop) and analyzed by a gas chromatograph 9 (On-line TCD-GC) with a thermal conductive detector to which a carrier gas was supplied from a carrier gas inlet 8 (carrier in) of the gas chromatograph.

EXAMPLE 1

(29) <Preparation of C12A7 Base Material Containing Oxygen Ions>

(30) Powders of Ca(OH).sub.2 (Shuzui Hikotaro Shoten, 23.1 g) and Al(OH).sub.3 (Kojundo Chemical Laboratory Co., Ltd., 28.4 g) were mixed so that a Ca/Al molar ratio was 12:14, and 449 ml of water was added to the resultant mixture, followed by hydrothermal treatment in an autoclave at 150 C. over 5 hours. The resultant powder was filtered, washed with 500 ml of water, dried at 150 C., fired in an oxygen stream at 800 C. for 2 hours, and then ground to prepare a C12A7 (referred to as C12A7:O hereinafter) powder having a specific surface area of 40 m.sup.2g.sup.1 and a particle diameter of 0.1 mm to 0.5 mm and containing oxygen ions but not containing conduction electrons and hydrogen anions.

(31) <Preparation of C12A7 Base Material Containing Conduction Electrons>

(32) The C12A7:O powder prepared by the method described above was inserted into a silica glass tube and pre-treated by vacuum-heating at 800 C. for 15 hours in a vacuum of 110.sup.4 Pa. Then, 2.5 g of the resultant powder was inserted, together with 0.1 g of a Ca metal powder, in a silica glass tube and heated at 700 C. for 15 hours to prepare a C12A7:e.sup. (hereinafter referred to as C12A7:e) powder having a conduction electron concentration of 1.510.sup.21 cm.sup.3. The prepared powder had a smaller specific surface area of 14 m.sup.2g.sup.1 (particle diameter: 0.2 mm to 1 mm).

(33) <Preparation of C12A7 Base Material Containing Hydrogen Anions>

(34) The C12A7:O powder prepared by the method described above was inserted into a silica glass tube and pre-treated by vacuum-heating at 750 C. for 15 hours in a vacuum of 110.sup.4 Pa. Then, 1.5 g of the resultant powder was inserted, together with 45 mg of a Ca metal powder, in a silica glass tube and heated at 700 C. for 15 hours to prepare a C12A7:H.sup. (hereinafter referred to as C12A7:H) powder having a hydrogen anion concentration of 2.510.sup.20 cm.sup.3. Inclusion of hydrogen anions was confirmed by .sup.1H NMR and iodometry. The prepared powder had a smaller specific surface area of 16 m.sup.2g.sup.1 (particle diameter: 0.2 mm to 1 mm).

(35) <Supporting of Ru on Support Powder>

(36) First, 1 g of the resultant C12A7:e powder was inserted, together with 45 mg of Ru.sub.3(CO).sub.12, in a silica glass tube, and then Ru.sub.3(CO).sub.12 was reduced by heating at 400 C. for 2 hours to adhere Ru particles to the surface of the C12A7:e powder by chemical vapor deposition. As a result, a supported metal catalyst (2 wt % Ru/C12A7:e) including an electride powder on which 2% by weight of Ru metal was supported was produced. The specific surface area was measured by a fully automatic BET surface area measurement device. The particle diameter was determined from the results of measurement of CO dispersibility. The Ru metal after hydrogen reduction had a particle diameter of 15 nm, and the dispersibility determined based on CO adsorption was 8.6%.

(37) <Ammonia Decomposition Reaction>

(38) A quartz reaction tube was packed with 60 to 100 mg of the Ru-supported catalyst produced by the method described above to form a catalyst layer, and ammonia decomposition reaction was carried out by using an ammonia decomposition apparatus shown in FIG. 1. Before the decomposition reaction, Ru was activated by reducing the Ru-supported catalyst in a hydrogen steam for 2 hours in the quartz reaction tube heated to 400 C. to 450 C. Then, the temperature in the quartz reaction tube was adjusted to 350 C. to 700 C., and ammonia gas with an ammonia volume fraction of 100% was flowed through the catalyst layer at 5 to 100 ml.Math.min.sup.1. The reaction results are shown in Table 1. The NH.sub.3 conversion rates at 350 C., 440 C., and 700 C. are 51.9%, 79.8%, and 99.8%, respectively, and the NH.sub.3 decomposition rates at 350 C., 440 C., and 700 C. are 1.11, 8.2, and 82.3 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1), respectively. The weight hourly space velocities are 3000, 15000, and 120000 mlg.sup.1h.sup.1, respectively.

EXAMPLE 2

(39) A 5 wt % Ru/C12A7:e powder was prepared by the same method as in Example 1 except that the amount of Ru supported was 5 wt %, and ammonia decomposition reaction was carried out. The results are shown in Table 1. The NH.sub.3 conversion rate at 440 C. was 67.2%, and the NH.sub.3 decomposition rate at 440 C. was 6.9 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1).

EXAMPLE 3

(40) A 2 wt % Ru/C12A7:H powder was prepared by the same method as in Example 1 except that C12A7:H was used as a support, and ammonia decomposition reaction was carried out. The results are shown in Table 1. The NH.sub.3 conversion rate at 440 C. was 76.5%, and the NH.sub.3 decomposition rate at 440 C. was 7.9 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1).

EXAMPLE 4

(41) The same catalyst as tested in Example 1 was used and tested at an ammonia volume fraction (V.sub.NH3) of 1.7% (He balance) and a total gas flow rate of 180 ml/min (WHSV: 216000 mlg.sup.1h.sup.1). The results are shown in Table 1. The NH.sub.3 conversion rate at 440 C. was 100%, and the NH.sub.3 decomposition rate at 440 C. was 2.1 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1).

EXAMPLE 5

(42) A 2 wt % Ru/C12A7:O powder was prepared by the same method as in Example 1 except that a C12A7:O powder containing oxygen ions but not containing conduction electrons was used instead of the C12A7:e powder, and ammonia decomposition activity was examined. The results are shown in Table 1. The NH.sub.3 conversion rate at 440 C. was 54.3%, and the NH.sub.3 decomposition rate at 440 C. was 5.6 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1).

COMPARATIVE EXAMPLE 1

(43) A 2 wt % Ru/CaO powder was prepared by the same method as in Example 1 except that a CaO powder (Kojundo Chemical Laboratory Co., Ltd., particle diameter: 5 mm to 10 mm) was used instead of the C12A7:e powder, and ammonia decomposition activity was examined.

(44) The particle diameter of Ru metal after hydrogen reduction was 4 nm, and dispersibility determined by CO adsorption was 40%. The results are shown in Table 1. The NH.sub.3 conversion rate at 440 C. was 42.1%, and the NH.sub.3 decomposition rate at 440 C. was 4.3 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1).

COMPARATIVE EXAMPLE 2

(45) A 6 wt % Ru/-Al.sub.2O.sub.3 powder was prepared by the same method as in Example 1 except that a -Al.sub.2O.sub.3 powder (Kojundo Chemical Laboratory Co., Ltd., particle diameter: 0.1 mm to 0.5 mm) was used instead of the C12A7:e powder, and ammonia decomposition activity was examined. The particle diameter of Ru metal after hydrogen reduction was 11 nm, and dispersibility determined by CO adsorption was 13%. The results are shown in Table 1. The NH.sub.3 conversion rate at 440 C. was 31.9%, and the NH.sub.3 decomposition rate at 440 C. was 3.3 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1).

(46) TABLE-US-00001 TABLE 1 NH.sub.3 Electron H- Amount decom- concen- concen- Ru Temper- of NH.sub.3 flow NH.sub.3 position S.sub.BET/ tration/ tration/ amount/ ature/ catalyst/ rate/ WHSV/ conversion rate/ Support m.sup.2g.sup.1 cm.sup.3 cm.sup.3 wt % C. mg mlmin.sup.1 V.sub.NH3/% mlg.sup.1h.sup.1 rate/% kgkg.sup.1h.sup.1 Example 1 C12A7:e 14 1.5 10.sup.21 No 2 350 100 5 100 3000 51.9 1.1 14 1.5 10.sup.21 No 2 440 60 15 100 15000 79.8 8.2 14 1.5 10.sup.21 No 2 700 60 100 100 120000 99.8 82.3 Example 2 C12A7:e 14 1.5 10.sup.21 No 5 440 60 15 100 15000 67.2 6.9 Example 3 C12A7:H 16 No 2.5 10.sup.2 2 440 60 15 100 15000 76.5 7.9 Example 4 C12A7:e 14 1.5 10.sup.21 No 2 440 60 3 1.7 216000 100.0 2.1 Example 5 C12A7:O 40 No No 2 440 60 15 100 15000 54.3 5.6 Comparative CaO 3 No No 2 440 60 15 100 15000 42.1 4.3 Example 1 Comparative Al2O3 170 No No 6 440 60 15 100 15000 31.9 3.3 Example 2

EXAMPLE 6

(47) A 5 wt % Co/C12A7:e powder was prepared by the same chemical vapor deposition method as for Ru using a C12A7:e powder described in Example 1 and using a Co.sub.4(CO).sub.12 raw material instead of Ru.sub.3(CO).sub.12. The results are shown in Table 2. The NH.sub.3 conversion rate at 600 C. was 54.6%, and the NH.sub.3 decomposition rate at 600 C. was 5.6 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1).

EXAMPLE 7

(48) A 5 wt % Co/C12A7:O powder was prepared by the same method as in Example 6 except that a C12A7:O powder containing oxygen ions but not containing conduction electrons was used instead of the C12A7:e powder, and ammonia decomposition activity was examined. The results are shown in Table 2. The NH.sub.3 conversion rate at 600 C. was 28.0%, and the NH.sub.3 decomposition rate at 600 C. was 2.9 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1).

EXAMPLE 8

(49) A 5 wt % Ni/C12A7:e powder was prepared by the same chemical vapor deposition method as for Ru using a C12A7:e powder described in Example 1 and using acetylacetonate nickel (II) dihydrate [C.sub.10H.sub.14NiO.sub.4.xH.sub.2O] instead of Ru.sub.3 (CO).sub.12, and ammonia decomposition activity was examined. The results are shown in Table 2. The NH.sub.3 conversion rate at 600 C. was 86.4%, and the NH.sub.3 decomposition rate at 600 C. was 8.9 (kg.sub.NH3kg.sub.cat.sup.1h.sup.1).

(50) TABLE-US-00002 TABLE 2 Electron H- Amount NH.sub.3 concen- concen- Metal of NH.sub.3 flow NH.sub.3 decomposition S.sub.BET/ tration/ tration/ amount/ Temperature/ catalyst/ rate/ WHSV/ conversion rate/ Support m.sup.2g.sup.1 cm.sup.3 cm.sup.3 wt % C. mg mlmin.sup.1 P.sub.NH3/% mlg.sup.1h.sup.1 rate/% kgkg.sup.1h.sup.1 Example 6 C12A7:e 14 1.5 10.sup.21 No Co 5 600 60 15 100 15000 54.6 5.6 Example 7 C12A7:O 40 No No Co 5 600 60 15 100 15000 28.0 2.9 Example 8 C12A7:e 14 1.5 10.sup.21 No Ni 5 600 60 15 100 15000 86.4 8.9

INDUSTRIAL APPLICABILITY

(51) A contact decomposition method using a hydrogen producing catalyst of the present invention can produce, with a high conversion rate, hydrogen by decomposing ammonia with a low volume fraction to a high volume fraction at about the atmospheric pressure within a wide reaction temperature range of 350 C. to 800 C., and thus the method is considered as a preferred method in view of reduction of energy consumption. Also, hydrogen can be produced by decomposing ammonia with a very high efficiency using inexpensive materials as compared with usual Ru supported catalysts.