WO2019188219A1

WO2019188219A1 - Ammonia decomposition catalyst and method for producing same, and method for producing hydrogen gas

Info

Publication number: WO2019188219A1
Application number: PCT/JP2019/009788
Authority: WO
Inventors: 裕貴三浦; 孝美大江; 圭一中村
Original assignee: 昭和電工株式会社
Priority date: 2018-03-26
Filing date: 2019-03-11
Publication date: 2019-10-03
Also published as: JP7264154B2; JP2023076661A; JPWO2019188219A1

Abstract

Provided are: an ammonia decomposition catalyst which can exhibit a high activity even at a lower temperature in an ammonia decomposition reaction; a method for producing the ammonia decomposition catalyst; and a method for producing a hydrogen gas using the ammonia decomposition catalyst. An ammonia decomposition catalyst in which ruthenium and a rare earth oxide are carried on a carrier composed of a metal oxide other than a rare earth oxide and the content of the rare earth oxide is 0.1 to 30.0% by mass can be produced through step 1 and step 2, wherein the step 1 comprises allowing the rare earth oxide to be carried on the carrier and step 2 comprises allowing the ruthenium to be carried on the carrier produced in step 1 and having the rare earth oxide carried thereon. A hydrogen gas can be produced by decomposing ammonia using the ammonia decomposition catalyst.

Description

Ammonia decomposition catalyst, method for producing the same, and method for producing hydrogen gas

The present invention relates to an ammonia decomposition catalyst for promoting a reaction for decomposing ammonia into hydrogen gas and nitrogen gas, a method for producing the same, and a method for producing hydrogen gas using the ammonia catalyst.

Hydrogen produces water by combustion and does not produce carbon dioxide, which is a greenhouse gas like general fossil fuels. Therefore, hydrogen has attracted attention as a clean energy. In recent years, fuel cells using hydrogen as a fuel have been put to practical use. It has become.
However, hydrogen has a problem that it is very light in a gaseous state, difficult to transport, and requires a large amount of energy to be liquefied, resulting in a high transport cost.

For this, ammonia containing 1.5 molecules of hydrogen per molecule is used as a hydrogen carrier, hydrogen gas and nitrogen gas are generated by catalytic decomposition of ammonia, and the hydrogen gas is taken out and used as an energy source. The technology to do is known. And in order to produce hydrogen gas more efficiently, research and development of a catalyst that promotes the decomposition reaction of ammonia at a low temperature of 600 ° C. or less has been advanced.

For example, Patent Document 1 describes an ammonia decomposition catalyst in which ruthenium is supported on an inorganic carrier such as α-alumina.
Patent Document 2 describes that the ammonia decomposition rate can be improved by supporting ruthenium and an alkali metal or alkaline earth metal as a promoter on a support such as alumina.
Patent Document 3 includes ammonia containing ruthenium and a rare earth oxide such as cerium oxide, and further containing 1 to 50 parts by mass of a refractory inorganic oxide such as aluminum oxide with respect to 100 parts by mass of the rare earth oxide. A cracking catalyst is described.

JP-A-8-84910 JP 2011-78888 A JP 2013-237045 A

However, the catalysts described in Patent Documents 1 to 3 cannot be said to have sufficient activity for decomposing ammonia at a low temperature. Further, as described in Patent Document 3, catalytic activity is not sufficient. If the content of the rare earth oxide is increased in order to increase the catalyst, the catalyst becomes expensive and the cost of ammonia decomposition increases.

The present invention has been made to solve the above-described problems. An ammonia decomposition catalyst exhibiting high activity even at a low temperature in a decomposition reaction of ammonia, a method for producing the same, and hydrogen gas using the ammonia decomposition catalyst An object of the present invention is to provide a manufacturing method.

The present invention is based on the finding that in a catalyst using ruthenium as an active metal, the catalytic activity in the ammonia decomposition reaction is improved by supporting a rare earth oxide in addition to ruthenium on a support.

That is, the present invention provides the following [1] to [16].
[1] An ammonia decomposition catalyst, in which ruthenium and a rare earth oxide are supported on a carrier made of a metal oxide other than the rare earth oxide, and the content of the rare earth oxide is 0.1 to 30.0 mass%.
[2] The ammonia decomposition catalyst according to the above [1], wherein the metal oxide is one or more selected from alumina, zirconia, and titania.
[3] The ammonia decomposition catalyst according to [1] or [2], wherein the metal oxide is alumina.
[4] The ammonia decomposition catalyst according to the above [2] or [3], wherein the alumina is α-alumina.
[5] The ammonia decomposition catalyst according to any one of the above [1] to [4], wherein the rare earth oxide is one or more selected from lanthanum oxide, cerium oxide, neodymium oxide, and samarium oxide. .
[6] The ammonia decomposition catalyst according to any one of the above [1] to [5], wherein the rare earth oxide is neodymium oxide.
[7] The ammonia decomposition catalyst according to any one of the above [1] to [6], wherein the ruthenium content is 0.1 to 10.0% by mass.
[8] The ammonia decomposition according to any one of the above [1] to [7], wherein the carrier further carries one or more metals selected from alkali metals and alkaline earth metals catalyst.
[9] The ammonia decomposition catalyst according to the above [8], wherein the metal content is 0.1 to 10.0 mol with respect to 1 mol of the ruthenium.
[10] The ammonia decomposition catalyst according to any one of [1] to [9], wherein the ruthenium is supported in an egg shell type.
[11] The ammonia decomposition catalyst according to [10], wherein in the egg shell type, the thickness of the shell part, which is a ruthenium distribution region, is 10 to 300 μm.
[12] The ammonia decomposition catalyst according to the above [11], wherein the concentration of ruthenium in the shell part is 0.1 to 15.0% by mass with respect to 100% by mass of the constituent atoms of the shell part.

[13] A method for producing an ammonia decomposition catalyst as described in any one of [1] to [12] above, obtained by the step 1 of supporting the rare earth oxide on the carrier and the step 1 And a step 2 of supporting the ruthenium on a carrier on which the rare earth oxide is supported.
[14] The ammonia decomposing catalyst according to the above [13], wherein the step 2 includes a step of immersing the carrier carrying the rare earth oxide in an aqueous solution of ruthenium salt and then contacting with a basic aqueous solution. Manufacturing method.
[15] The alkali metal obtained in the step 1 on which the rare earth oxide is supported or the carrier obtained in the step 2 on which the rare earth oxide and ruthenium are supported is further added to an alkali metal. And the method for producing an ammonia decomposition catalyst according to the above [13] or [14], comprising a step of supporting one or more metals selected from alkaline earth metals.
[16] A method for producing hydrogen gas, wherein ammonia is decomposed to produce hydrogen gas in the presence of the ammonia decomposition catalyst according to any one of [1] to [12].

According to the present invention, it is possible to provide an ammonia decomposition catalyst with improved catalytic activity in the ammonia decomposition reaction. Therefore, by using the ammonia decomposition catalyst of the present invention, the ammonia decomposition reaction can be promoted even at a low temperature, and hydrogen gas can be produced at low cost.

Hereinafter, the ammonia decomposition catalyst of the present invention, a method for producing the same, and a method for producing hydrogen gas using the ammonia decomposition catalyst will be described in detail.
[Ammonia decomposition catalyst]
The ammonia decomposition catalyst of the present invention (hereinafter also simply referred to as “catalyst”) has ruthenium and a rare earth oxide supported on a carrier made of a metal oxide other than the rare earth oxide, and the content of the rare earth oxide is 0. .1 to 30.0% by mass.
The catalyst of the present invention exhibits high activity even at low temperatures in an ammonia decomposition reaction while suppressing the amount of expensive rare earth metal used, and by using this, ammonia can be decomposed at low cost.

(Carrier)
The carrier in the present invention supports ruthenium and a rare earth oxide, and is made of a metal oxide other than the rare earth oxide.
As the metal oxide, a metal oxide used as a general catalyst carrier can be used. Examples thereof include alumina, silica, titania, zirconia, magnesia, iron oxide, zinc oxide, and tin oxide. The said metal oxide may be used individually by 1 type, or may use 2 or more types together. Of these, preferred is alumina, zirconia or titania, and more preferred is alumina. The kind of alumina is not particularly limited, and examples thereof include α alumina, θ alumina, γ alumina, and the like, and preferably α alumina. Since α-alumina has a smaller specific surface area than other types of alumina, the surface of the support can be coated even with a small amount of rare earth oxide supported on the support, and high catalytic activity can be maintained in the ammonia decomposition reaction. it can.

Here, α-alumina means a corundum type crystal structure among the crystal phases of alumina. θ-alumina has a monoclinic crystal system, and γ-alumina has a defect spinel type crystal structure.
The presence of the metal oxide in the catalyst can be confirmed by powder X-ray diffraction analysis (XRD).

The carrier is the main component contained most in the constituent components of the catalyst of the present invention, and the content in the constituent components is preferably larger than the amount of the rare earth oxide to be supported, preferably 50% by mass. As mentioned above, More preferably, it is 60 mass% or more, More preferably, it is 65 mass% or more. The upper limit of the content of the carrier is not particularly limited, but is preferably 99% by mass or less, more preferably 97% by mass or less in consideration of the amount of ruthenium to be supported.
The content of the carrier can be calculated from the analysis of the component composition of the catalyst as described in the examples described later, or can be estimated by calculating from the charged amounts of other components of the catalyst.

The carrier preferably has an average pore diameter of 5 nm or more, more preferably 8 to 200 nm, still more preferably 10 to 180 nm, from the viewpoint of suppressing a reduction in catalytic action due to diffusion of ammonia gas in the pores.
The average pore diameter can be determined by a gas adsorption method, and is determined from the total pore volume and BET specific surface area measured by a specific surface area pore distribution measuring device. The average pore diameter in the present specification is a value determined by the measurement method described in Examples described later.

Further, the shape and size of the carrier are appropriately determined according to the specifications of the apparatus for performing the ammonia decomposition reaction, operating conditions, and the like. The shape is, for example, powder, granule, sphere, pellet or the like. The size is 1 μm to 3 mm, more preferably 2 μm to 2.5 mm, still more preferably 3 μm to 2.5 mm in terms of the pressure loss of ammonia gas to be decomposed and the contact area with the catalyst. .
In addition, the particle size of the carrier in this specification is determined as a volume average particle size D50 by a laser diffraction particle size distribution meter. The values in the following examples are catalog values.

(Rare earth oxide)
Examples of the rare earth oxide supported on the carrier include yttrium oxide, lanthanum oxide, cerium oxide, neodymium oxide, samarium oxide, gadolinium oxide, and ytterbium oxide. The rare earth oxides may be used alone or in combination of two or more. Among these, from the viewpoint of improving the catalytic activity, those having a basicity at 500 ° C. of more than 600 μmol / g are preferable, and specifically, lanthanum oxide, cerium oxide, neodymium oxide or samarium oxide is preferable, and more preferable. Is neodymium oxide.
The basicity can be measured by a temperature programmed desorption method using carbon dioxide as an acid probe molecule. For the basicity of the rare earth oxide, for example, the values described in “Applied Catalysis A: General”, vol. 356, 2009, p. 57-63 can be referred to.

The content of the rare earth oxide in the catalyst of the present invention is 0.1 to 30.0% by mass, preferably 1.0 to 30.0% by mass, more preferably 3.0 to 29.0% by mass. %, More preferably 8.0 to 28.0% by mass, particularly preferably 13.0 to 27.0% by mass. If the content is 0.1% by mass or more, it is sufficient to coat the support, and the catalytic activity in the ammonia decomposition reaction can be improved. Moreover, if it is 30.0 mass% or less, the specific surface area of the support | carrier by coating with rare earth oxide will not fall significantly, and the fall of catalyst activity will be suppressed.
The content of the rare earth oxide in the catalyst is preferably 0.3 to 20.0% by mass, more preferably 0.5 to 10% when the metal oxide of the support is α-alumina. 0% by mass. When the metal oxide is θ-alumina, the content is preferably 10.0 to 25.0% by mass, more preferably 12.0 to 21.0% by mass. When the metal oxide is γ-alumina, the content is preferably 10.0 to 30.0% by mass, more preferably 14.0 to 28.0% by mass.

The rare earth oxide is preferably distributed only on the surface of the support from the viewpoint of easily contributing to the ammonia decomposition reaction.
When the impregnation method as described later is used as a catalyst preparation method, the rare earth oxide is supported so as to cover the surface of the support, so that the component uniformity in the catalyst as obtained by a coprecipitation method or the like is obtained. Unlike the high one, the rare earth oxide is substantially present only on the surface of the support.

(ruthenium)
Ruthenium is a metal species as an active component of the ammonia decomposition catalyst of the present invention, and is supported on the carrier together with a rare earth oxide. By supporting ruthenium in such a manner, the catalytic activity in the ammonia decomposition reaction can be improved.
The ruthenium content in the catalyst is preferably such that a sufficiently high catalytic activity is obtained, and is preferably 0.1 to 10.0% by mass in consideration of the cost of ammonia decomposition. Is 0.5 to 8.0 mass%, more preferably 1.0 to 7.0 mass%.
The presence of metal ruthenium in the catalyst can be confirmed with a transmission electron microscope (TEM).

As a typical mode of supporting the active component of the catalyst, it is classified into modes called a uniform type, egg shell type, egg yoke type, egg white type, and the like. The uniform type is an aspect in which the active ingredient is uniformly distributed with respect to the carrier. The egg shell type is also called an outer layer carrying type, and is an aspect in which active ingredients are distributed with a predetermined thickness from the surface of the carrier to the inside like an egg shell. The egg yoke type is an embodiment in which the active ingredient is distributed in the core part of the carrier, such as egg yolk. The egg white type is an aspect in which active ingredients are distributed within a predetermined depth inside the carrier surface, such as egg white.

In the catalyst of the present invention, the support mode of ruthenium, which is an active component, may be any of the above, but preferably from the viewpoint of suppressing the diffusion of ammonia gas into the carrier pores from the reaction rate limiting. Egg shell type.
The egg shell type catalyst preferably has a region in which ruthenium is distributed at a predetermined concentration from the surface to the inside of the support, that is, a shell portion, and the thickness of the shell portion is preferably 10 to 300 μm. More preferably, the thickness is 20 to 250 μm, and still more preferably 50 to 200 μm. Even if ruthenium is contained in a portion other than the shell portion, it is difficult to contribute to the ammonia decomposition reaction. Therefore, it is preferable that the region other than the shell portion, that is, the region inside the shell portion does not contain ruthenium.
The concentration of ruthenium in the shell part is preferably 0.1 to 15.0% by mass, more preferably 0.5 to 10.0% by mass, and still more preferably 100% by mass of the constituent atoms of the shell part. Is 1.0 to 8.0% by mass.

Note that the thickness of the shell portion and the ruthenium concentration in the shell portion of the egg shell type catalyst are determined by electron beam microanalyzer (EPMA) or scanning electron microscope / energy dispersive X-ray spectroscopic analysis (SEM). / EDX) can be obtained by measurement using an apparatus. In this invention, it is set as the value calculated | required with the measuring method as described in the Example mentioned later.

(Alkali metals and alkaline earth metals)
The carrier may further carry one or more metals selected from alkali metals and alkaline earth metals. These metals act as promoters for further promoting the ammonia decomposition reaction in the catalyst of the present invention.
Examples of the alkali metal include sodium, potassium, cesium and the like. Examples of the alkaline earth metal include calcium and barium. These metals may be used individually by 1 type, or may use 2 or more types together. Of these, sodium, potassium or cesium is preferable, and potassium is more preferable.

When the metal is contained in the catalyst, the content of the metal is preferably 0.1 to 10.0 mol, more preferably 0.2 to 8. mol per 1 mol of the ruthenium. The amount is 0 mol, more preferably 0.5 to 5.0 mol.

In addition, the component composition of a catalyst can be calculated | required with the general analysis method of a metal, a metal oxide, and a metal salt. For example, an aqueous solution in which the catalyst is completely dissolved using an acid or base can be prepared, and quantitative analysis of each metal element can be performed with an ICP (high frequency inductively coupled plasma) emission spectroscopic analyzer. In addition, as a simple method, the residual components in the container used for loading a predetermined substance are dissolved, the metal element is quantified by ICP emission spectroscopic analysis, and the contained metal element in the raw material for loading is determined. The component composition of the catalyst can also be determined from the difference from the amount. The component composition of the catalyst in the present invention is a value obtained by the analysis method described in Examples described later.

[Method for producing ammonia decomposition catalyst]
The catalyst comprises: a step 1 for supporting the rare earth oxide on the carrier; and a step 2 for supporting the ruthenium on the carrier obtained by supporting the rare earth oxide obtained in the step 1. Can be manufactured.

(Process 1)
In step 1, a rare earth oxide is supported on the carrier made of a metal oxide other than the rare earth oxide. This step can be performed using a general catalyst preparation method for supporting a metal oxide. For example, it is possible to use an impregnation method in which a rare earth compound solution is impregnated in the carrier, and then dried and fired.

The rare earth compound is a precursor of a rare earth oxide and is not particularly limited, and examples thereof include salts such as nitrates, carbonates, and chlorides. Preferably, it is a water-soluble nitrate.

The specific method of the impregnation method is not particularly limited, and can be performed by, for example, a pore filling method, an evaporation to dryness method, or the like.
For example, when an aqueous solution of rare earth nitrate is used, first, a considerable amount of rare earth nitrate corresponding to the amount of rare earth oxide to be supported is obtained based on the constituent rare earth metal.
In the pore filling method, the equivalent amount of rare earth nitrate is dissolved in water equal to or less than the water absorption amount of the carrier measured in advance to prepare an aqueous solution, and the carrier is impregnated with the whole amount of the aqueous solution and then dried. Let The water absorption amount of the carrier can be determined by subtracting the mass of the dried carrier from the mass of the absorbed carrier. The mass of the water-absorbed carrier is a state in which water (supernatant) adhering to the surface of the carrier is separated using a sieve or a filter paper after the entire dried carrier is sufficiently immersed in water.
In the evaporation to dryness method, an aqueous solution is prepared by dissolving the corresponding amount of rare earth nitrate in a predetermined amount of water, and the entire amount of the aqueous solution is added to the carrier while heating to evaporate the water, A rare earth oxide precursor is supported.

Also, a method is used in which a carrier is impregnated with an aqueous solution of rare earth nitrate, rare earth chloride, etc., and then a basic aqueous solution is added to form a water-insoluble rare earth hydroxide, followed by firing to carry the rare earth oxide on the carrier. You can also.

In the impregnation method, drying and calcination can be performed under the general conditions in the catalyst preparation method.
The drying method is not particularly limited as long as the liquid can be sufficiently volatilized as a pretreatment for baking. For example, when the aqueous solution is impregnated, the carrier can be dried by heating to 80 to 130 ° C., preferably 90 to 120 ° C., more preferably 100 to 110 ° C. under atmospheric pressure and atmospheric pressure. it can.
The firing method is not particularly limited as long as the rare earth oxide precursor can be oxidized into the rare earth oxide. For example, when a rare earth nitrate is used, it is fired at 450 to 800 ° C., preferably 470 to 700 ° C., more preferably 480 to 600 ° C. under normal pressure, thereby obtaining a rare earth oxide in which the rare earth nitrate is thermally decomposed. be able to.

(Process 2)
In step 2, ruthenium is supported on the carrier obtained in step 1 on which the rare earth oxide is supported. This step can be performed using a general method for preparing a metal-supported catalyst.
For example, the ruthenium compound solution is impregnated in a carrier on which the rare earth oxide is supported, dried, and then reduced, whereby the ruthenium supporting form is a uniform type, and the rare earth oxide and ruthenium are supported. An ammonia decomposition catalyst can be prepared.
In addition, for example, after impregnating a carrier on which the rare earth oxide is supported with an aqueous solution of a ruthenium salt such as ruthenium chloride or nitrosyl ruthenium nitrate, a basic aqueous solution such as sodium carbonate, sodium metasilicate, potassium carbonate, You may make it contact with aqueous solutions, such as barium hydroxide. The carrier is dried, and the surface of the carrier on which the rare earth oxide is supported is supported with water-insoluble ruthenium oxide, and then reduced, whereby the ruthenium is supported in an egg shell type. And an ammonia decomposition catalyst carrying ruthenium can be prepared.

The ruthenium compound is a ruthenium precursor to be supported, and is not particularly limited. For example, the ruthenium compound has a water-soluble salt such as ruthenium chloride and an organic ligand such as tris (acetylacetonato) ruthenium. A compound or the like can be used. A water-soluble salt is preferable, and ruthenium chloride is more preferable.

The drying method can be performed in the same manner as the drying method in step 1 above.
The reduction method is not particularly limited. For example, a gas phase reduction using a gas containing a reducing gas such as hydrogen gas or ammonia gas, a liquid using a solution containing a reducing agent such as sodium borohydride, or the like. Examples of the method include phase reduction.
In the case of gas phase reduction, the temperature is preferably 200 ° C. or higher, more preferably 200 to 600 ° C., and further preferably 250 to 550 ° C. The reduction time is not particularly limited, but is preferably 1 to 24 hours, more preferably 1 to 10 hours, and further preferably 1.5 to 5 hours. From the viewpoint of sufficient reaction progress, it is also preferable to raise the reduction temperature stepwise.
Note that the gas phase reduction as described above may be performed, for example, in a state where the ammonia decomposition apparatus is filled before the ammonia decomposition reaction.

(Supporting alkali metal and / or alkaline earth metal)
When preparing a catalyst in which ruthenium and a rare earth oxide are supported on the support and further an alkali metal and / or alkaline earth metal is supported, in addition to the steps 1 and 2, an alkali metal and / or an alkali is prepared. Through a process of supporting an earth metal.
This step can also be performed using a general catalyst preparation method for supporting a metal. For example, it is possible to use a method in which an alkali metal salt and / or alkaline earth metal salt solution is impregnated in the support, dried, and then reduced.
The drying method can be performed in the same manner as the drying method in step 1 above.
Further, the reduction method can be performed under the same conditions as in Step 2 above.

The step of supporting the alkali metal and / or alkaline earth metal on the carrier may be before or after the step 1 or after the step 2. Preferably, after step 1 or 2. That is, the carrier obtained by supporting the rare earth oxide obtained in the step 1 or the carrier obtained by supporting the rare earth oxide and ruthenium obtained by the step 2, and an alkali metal and It is preferable to support an alkaline earth metal.
More preferably, an alkali metal and / or an alkaline earth metal is supported on the support obtained in Step 2 on which the rare earth oxide and ruthenium are supported.

[Method for producing hydrogen gas]
In the method for producing hydrogen gas of the present invention, ammonia is decomposed to generate hydrogen gas in the presence of the above-described ammonia decomposition catalyst of the present invention. By using the catalyst of the present invention, the ammonia decomposition reaction can be promoted even at a low temperature, and hydrogen gas can be produced at a low cost.

The ammonia decomposition reaction is basically a reaction in which 1.5 mol of hydrogen gas and 0.5 mol of nitrogen gas are generated from 1 mol of ammonia by contacting an ammonia-containing gas with a catalyst. This reaction can be carried out in a general gas phase-solid contact reactor. Examples of the reaction system include a batch system and a circulation system, and a fixed bed system and a fluidized bed system are not particularly limited, but a circulation system and a fixed bed system are preferable.

The reaction temperature of the ammonia decomposition reaction is preferably 300 to 700 ° C., more preferably 400 to 600 ° C., and still more preferably 400 to 500 ° C. from the viewpoint of the decomposition rate of ammonia and the equipment cost.
Space velocity in the reactor of the ammonia-containing gas is from the same viewpoint as described above, preferably from 50 ~ 30000h ^-1, more preferably 50 ~ 20000h ^-1, more preferably from 100 ~ 15000h ^-1.
The reaction pressure is not particularly limited, but the absolute pressure is preferably 0.1 to 0.6 MPa, more preferably 0.1 to 0.5 MPa, and still more preferably 0.1 to 0.3 MPa. It is.

The hydrogen gas generated by the ammonia decomposition reaction is subjected to a treatment for separation from nitrogen gas and removal of residual ammonia and other trace impurities using a known purification method. For example, pressure swing adsorption (PSA) method that varies the pressure and temperature swing that varies the temperature as a method that uses the adsorbent such as zeolite and activated carbon and uses the difference in gas adsorption characteristics depending on the pressure and temperature. Adsorption (TSA: Thermal Swing Adsorption) method and the like. Further, a palladium alloy membrane permeation method, a cryogenic separation method, or the like can be used.

The amount of generated gas in the decomposition reaction of ammonia is determined by, for example, quantifying hydrogen gas with a gas component analyzer such as a gas chromatograph, It is obtained by a method such as quantifying ammonia gas and calculating from the amount of decomposed ammonia gas.

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.

[Analysis evaluation method]
Various analysis evaluation methods in this example are shown below.

(Average pore diameter of metal oxide)
About 0.1 g of a metal oxide sample, the total pore volume was determined with a specific surface area pore distribution measuring device ("BELSORP-max" manufactured by Microtrack Bell Co., Ltd., adsorbed gas: nitrogen), and this was BET The average pore diameter was determined from the specific surface area by a single point method.

(Water absorption of θ alumina)
The mass m ₁ [g] of a dried sample of θ alumina dried at 110 ° C. for 6 hours was measured. After the dried sample was immersed in water for 2 hours to absorb water, the surface water (supernatant) not absorbed by the carrier was removed with a stainless sieve (mesh 710 μm), and the mass m ₂ [g] of the water-absorbed sample was measured. . From the mass obtained by subtracting the weight of the dry sample from the mass of the water sample _{_{m 2 [g] m 1 [}} g], the specific gravity of water is regarded as a 1 g / mL, determined water absorption volume, which in the mass m ₁ of dry sample The divided value {(m ₂ −m ₁ ) [g] / 1 [g / mL]} / m ₁ [g] was calculated as the amount of water absorption (per gram of carrier) [mL / g].

(Catalyst component composition)
In preparing the catalyst, hydrochloric acid is added to each of the container used for supporting the rare earth oxide, the container used for supporting the ruthenium, and the container used for supporting the alkali metal to dissolve the residue. In addition, the ICP emission spectroscopic analyzer (“ICPS-8100” manufactured by Shimadzu Corporation) was used to quantify the metal elements in the residue, and from the difference from the amount of each metal element contained in the raw material used, the catalyst The component composition of was calculated.

(Analysis of egg shell type catalyst)
The prepared egg shell type catalyst is embedded in a resin using an automatic hydraulic embedding machine, and then ground with a polishing machine to produce a catalyst particle cross-section sample. SEM / EDX (scanning electron microscope / energy dispersive type) The X-ray spectroscopy apparatus was used to observe and measure the cross section of the catalyst particles to determine the thickness of the shell portion and the concentration of ruthenium other than the shell portion or the shell portion. The thickness of the shell part is defined as a distance in which the ruthenium concentration is 0.1% by mass or more with respect to 100% by mass of the constituent atoms of the shell part on a straight line from the outer periphery to the center of the particle in the observation image of the catalyst particle cross section. Asked.
In addition, the measured values of the two arbitrary catalyst particle samples of the eggshell catalyst obtained in Example 12 and Comparative Example 9 below are shown in Table 2 as representative examples. Table 2 also shows the measured values of any three catalyst particle samples of the uniform type catalyst obtained in Comparative Example 8 as a reference.
As shown in Table 2, since the thickness of the shell portion for each catalyst particle sample of Example 12 and Comparative Example 9 below was 100 to 200 μm, the ruthenium concentration of the shell portion was the depth from the particle surface. The ruthenium concentration in the range of 0-100 μm was measured. Further, as the ruthenium concentration other than the shell portion, the ruthenium concentration in the range from 200 μm to the center from the particle surface was measured.

(Ammonia decomposition rate)
The recovered gas after the ammonia decomposition reaction was circulated through a Fourier transform infrared spectrophotometer (FT-IR spectrophotometer, manufactured by Thermo Fisher Scientific Co., Ltd.), and the absorption peak intensity at a wave number of 3333 cm ⁻¹ was measured. A residual ammonia concentration (x [%]) was determined from a calibration curve using a gas (ammonia: manufactured by Taiyo Nippon Sanso Corporation, dilution gas: nitrogen), and a decomposition rate was calculated by the following formula.
Ammonia decomposition rate [%] = {(100−x) / (100 + x)} × 100
In the recovered gas, except for ammonia, it was considered that only nitrogen gas and hydrogen gas generated by decomposition of ammonia were included.

[Preparation of ammonia decomposition catalyst]
Details of the raw materials used for the preparation of the ammonia decomposition catalysts of the following Examples and Comparative Examples are as follows. In addition, the value of the particle size of each raw material is a catalog value.
<Ruthenium raw material>
Ruthenium chloride: Ruthenium (III) chloride hydrate (RuCl ₃ · nH ₂ O), manufactured by Furuya Metal Co., Ltd. <Rare earth oxide raw material>
・ Neodymium nitrate hexahydrate: manufactured by Strem Chemicals ・ Lantan nitrate: manufactured by Strem Chemicals ・ Cerium nitrate: manufactured by Strem Chemicals ・ Samarium nitrate: manufactured by Strem Chemicals ・ Cerium oxide: 1st rare element chemical industry Made by Co., Ltd., average pore diameter 7.4 nm, pore volume 0.21 mL / g, particle size 4 μm
<Support (metal oxide)>
Γ-alumina (1): Sigma-Aldrich, average pore size 20 nm, pore volume 0.74 mL / g, particle size 0.5 mm
Zirconia: manufactured by Daiichi Rare Element Chemical Industries, Ltd., average pore diameter 17 nm, pore volume 0.35 mL / g, particle size 4 μm
-Titania: manufactured by Saint-Gobain, average pore size 28 nm, pore volume 0.3 mL / g, particle size 0.5 mm
Α-alumina (1): manufactured by Sasol, average pore diameter 170.5 nm, pore volume 0.1243 mL / g, particle diameter 1 mm
.Theta. Alumina: manufactured by Sasol, average pore size 14 nm, pore volume 0.398 mL / g, particle size 1 mm, water absorption 0.4 mL / g
Α-alumina (2): manufactured by Kanto Chemical Co., Inc., particle size 42 nm
Γ alumina (2): manufactured by Sasol, average pore diameter 10.9 nm, pore volume 0.529 mL / g, particle diameter 1 mm
<Metal (alkali metal) raw material>
・ Potassium carbonate: Wako Pure Chemical Industries, Ltd. ・ Potassium nitrate: Wako Pure Chemical Industries, Ltd. ・ Sodium carbonate: Wako Pure Chemical Industries, Ltd. ・ Cesium carbonate: Wako Pure Chemical Industries, Ltd.

Example 1
1.9 mL of neodymium nitrate aqueous solution prepared using 2.11 g of neodymium nitrate hexahydrate while mixing 2.10 g of γ-alumina (1) carrier in an evaporating dish and about 1 mL with Pasteur pipette By repeating the operation of dropping and drying, the whole amount was added to obtain a γ-alumina carrier (Nd (NO ₃ ) ₃ / γAl ₂ O ₃ ) on which neodymium nitrate was supported. This carrier was dried at 100 to 110 ° C. in an air atmosphere and then calcined at 500 ° C. for 2 hours to obtain a γ-alumina carrier (Nd ₂ O ₃ / γAl ₂ O ₃ ) carrying neodymium oxide. .
After the carrier is cooled to room temperature, the whole amount is added by repeating the operation of dripping about 1 mL of a ruthenium chloride aqueous solution (containing 0.09 g of ruthenium content) with a Pasteur pipette and drying the mixture while mixing with a shaker. Then, it was dried at 100 to 110 ° C. in an air atmosphere to obtain an ammonia decomposition catalyst precursor (RuCl ₃ / Nd ₂ O ₃ / γAl ₂ O ₃ ) carrying ruthenium chloride and neodymium oxide. 3 mL of this precursor was charged into a flow-through and fixed bed reactor and reduced in a mixed gas stream of hydrogen gas and nitrogen gas for 1 hour at 300 ° C. and further for 1 hour at 500 ° C. to form a γ-alumina carrier. A uniform type ammonia decomposition catalyst (Ru / Nd ₂ O ₃ / γAl ₂ O ₃ ) carrying ruthenium and neodymium oxide was obtained.

(Examples 2-6, Comparative Examples 1-4, 7 and 8)
Each of the ammonia decomposition catalysts was prepared in the same manner as in Example 1 except that the blending raw materials were changed so as to have the component composition of the catalyst shown in Table 1 below.

(Example 7)
In Example 1, the amount of the γ-alumina (1) support was changed to 2.01 g, and other than that, in the same manner as in Example 1, an ammonia decomposition catalyst (Ru / Nd ₂ ) on which ruthenium and neodymium oxide were supported. O ₃ / γAl ₂ O ₃ ) was prepared.
While mixing this catalyst with a cartridge, 3.7 mL of an aqueous solution of 0.16 g of potassium carbonate (amount of potassium contained in 2.6 mol of 1 mol of ruthenium) is dropped by a Pasteur pipette and dried. After repeating the operation and adding the entire amount, drying is performed at 100 to 110 ° C. in an air atmosphere, and a potassium carbonate-treated ammonia decomposition catalyst precursor (K ₂ ) on which potassium carbonate is supported and ruthenium and neodymium oxide are supported. CO ₃ / Ru / Nd ₂ O ₃ / γAl ₂ O ₃ ) was obtained. 3 mL of this precursor was reduced in the same manner as in Example 1, and a uniform type potassium-treated ammonia decomposition catalyst (K / Ru / Nd ₂ O ₃₎ in which potassium, ruthenium, and neodymium oxide were supported on a γ-alumina support. / ΓAl ₂ O ₃ ).

(Example 8)
2.81 g of α-alumina (1) support was added to 0.35 mL of an aqueous neodymium nitrate solution prepared using 0.27 g of neodymium nitrate hexahydrate, dried at 100 to 110 ° C. in an air atmosphere, and then at 500 ° C. Firing for 2 hours gave an α-alumina carrier (Nd ₂ O ₃ / αAl ₂ O ₃ ) on which neodymium oxide was supported.
This carrier is cooled to room temperature, then added to 0.30 mL of ruthenium chloride aqueous solution (containing 0.09 g of ruthenium), and dried at 100 to 110 ° C. in an air atmosphere to decompose ammonia carrying ruthenium chloride and neodymium oxide. A catalyst precursor (RuCl ₃ / Nd ₂ O ₃ / αAl ₂ O ₃ ) was obtained. 3 mL of this precursor was reduced in the same manner as in Example 1, and a uniform type ammonia decomposition catalyst (Ru / Nd ₂ O ₃ / αAl ₂ O ₃ ) in which ruthenium and neodymium oxide were supported on an α alumina support. Obtained.

Example 9
In Example 8, the amount of α-alumina (1) support was changed to 2.67 g, and neodymium nitrate hexahydrate was changed to 0.63 g. Otherwise, in the same manner as in Example 8, ruthenium was added to the α-alumina support. And a uniform type ammonia decomposition catalyst (Ru / Nd ₂ O ₃ / αAl ₂ O ₃ ) carrying neodymium oxide.

(Example 10)
2.46 g of θ alumina support was added to 0.88 mL of an aqueous neodymium nitrate solution prepared using 1.17 g of neodymium nitrate hexahydrate, dried at 100 to 110 ° C. in an air atmosphere, and then calcined at 500 ° C. for 2 hours. Thus, a θ-alumina support (Nd ₂ O ₃ / θAl ₂ O ₃ ) on which neodymium oxide was supported was obtained.
The carrier is cooled to room temperature, then added to 0.80 mL of a ruthenium chloride aqueous solution (containing 0.09 g of ruthenium), dried in an air atmosphere at 100 to 110 ° C., and an ammonia decomposition catalyst carrying ruthenium chloride and neodymium oxide. A precursor (RuCl ₃ / Nd ₂ O ₃ / θAl ₂ O ₃ ) was obtained. 3 mL of this precursor was reduced in the same manner as in Example 1, and a uniform type ammonia decomposition catalyst (Ru / Nd ₂ O ₃ / θAl ₂ O ₃ ) in which ruthenium and neodymium oxide were supported on a θ alumina support. Obtained.

(Example 11)
In the same manner as in Example 10, a θ-alumina carrier (Nd ₂ O ₃ / θAl ₂ O ₃ ) on which neodymium oxide was supported was obtained.
The carrier was cooled to room temperature, then added to 0.80 mL of an aqueous ruthenium chloride solution (containing 0.09 g of ruthenium content), and 1.2 mL of an aqueous sodium carbonate solution was further added, and the mixture was allowed to stand overnight. Then, after removing the liquid using a Pasteur pipette, washing with water and drying at 100 to 110 ° C. in an air atmosphere, an ammonia decomposition catalyst precursor (RuO ₂ / R) on which ruthenium oxide and neodymium oxide are supported. Nd ₂ O ₃ / θAl ₂ O ₃ ) was obtained. 3 mL of this precursor was reduced in the same manner as in Example 1, and an egg shell type ammonia decomposition catalyst (Ru / Nd ₂ O ₃ / θAl ₂ O ₃ ) in which ruthenium and neodymium oxide were supported on a θ alumina support. Got.

Example 12
The θ alumina support (Nd ₂ O ₃ / θAl) was changed in the same manner as in Example 11 except that the amount of the θ alumina support was changed to 2.49 g and the amount of neodymium nitrate hexahydrate was changed to 1.09 g. After obtaining ₂ O ₃ ), an ammonia decomposition catalyst (Ru / Nd ₂ O ₃ / θAl ₂ O ₃ ) carrying ruthenium and neodymium oxide was obtained.
This catalyst is added to 0.80 mL of an aqueous solution of 0.16 g of potassium carbonate (in which the amount of potassium contained in 1 mol of ruthenium is 2.6 mol), and dried at 100 to 110 ° C. in an air atmosphere to carry potassium carbonate. Thus, a potassium carbonate-treated ammonia decomposition catalyst (K ₂ CO ₃ / Ru / Nd ₂ O ₃ / θAl ₂ O ₃ ) carrying ruthenium and neodymium oxide was obtained. 3 mL of this catalyst was reduced in the same manner as in Example 1, and an egg shell type potassium-treated ammonia decomposition catalyst (K / Ru / Nd ₂ O ₃₎ in which potassium, ruthenium, and neodymium oxide were supported on a θ-alumina support. / ΘAl ₂ O ₃ ). The thickness of the shell portion of this catalyst was 100 to 200 μm (see Table 2 below).

(Example 13)
In Example 12, the operation procedure was changed so that potassium was loaded before loading ruthenium, and ruthenium, potassium and neodymium oxide were loaded on the θ alumina support in the same manner as in Example 12 except that. An egg shell type ammonia decomposition catalyst (Ru / K / Nd ₂ O ₃ / θAl ₂ O ₃ ) was obtained.

(Examples 14 to 18)
Egg shell type ammonia decomposition catalysts were prepared in the same manner as in Example 12 except that the blending raw materials were changed so as to obtain the component compositions of the catalysts shown in Table 1 below.

(Comparative Example 5)
As a support, 2.91 g of cerium oxide, which is a rare earth oxide, was used. On this support, 8.9 mL of ruthenium chloride aqueous solution (containing 0.09 g of ruthenium content) was supported in the same manner as in Example 1, and an ammonia decomposition catalyst precursor (RuCl ₃ / CeO ₂ ) supporting ruthenium chloride. Got. A uniform in which 3 mL of this precursor is charged into a reactor and reduced in a mixed gas stream of hydrogen gas and nitrogen gas for 1 hour at 300 ° C. and further for 1 hour at 500 ° C., and ruthenium is supported on a cerium oxide support. A type of ammonia decomposition catalyst (Ru / CeO ₂ ) was obtained.

(Comparative Example 6)
In Comparative Example 5, the compounding amount of cerium oxide was changed to 2.43 g, and the ammonia decomposition catalyst precursor (Ru / CeO ₂ ) on which ruthenium was supported was prepared in the same manner as in Comparative Example 5 except that.
This precursor is mixed with 0.48 g of α-alumina (2) support, and an ammonia decomposition catalyst (Ru / CeO ₂ + αAl ₂ O ₃ ) composed of a mixed powder of cerium oxide and α-alumina (2) on which ruthenium is supported. Obtained.

(Comparative Example 9)
To 2.91 g of the γ-alumina (2) support, 0.80 mL of ruthenium chloride aqueous solution (containing 0.09 g of ruthenium content) was added, and further 2.4 mL of sodium carbonate aqueous solution was added and allowed to stand overnight. Then, after removing the liquid using a Pasteur pipette, washing with water, drying at 100 to 110 ° C. in an air atmosphere, and an ammonia decomposition catalyst precursor (RuO ₂ / γAl ₂ O carrying ruthenium oxide) ₃ ) got. 3 mL of this precursor was reduced in the same manner as in Example 1 to obtain an egg shell type ammonia decomposition catalyst (Ru / γAl ₂ O ₃ ) in which ruthenium was supported on a γ alumina support. The thickness of the shell portion of this catalyst was 100 to 200 μm (see Table 2 below).

[Ammonia decomposition reaction]
Using each ammonia decomposition catalyst obtained in the above examples and comparative examples, a cylindrical reactor (Examples 1 to 7 and Comparative Examples 1 to 5: inner diameter) of an ammonia decomposition apparatus (flow type / fixed bed type) Space velocity (SV) at 0.1 MPa (atmospheric pressure) for 3 mL of catalyst packed in 0.75 cm, length 40 cm, Examples 8-18 and Comparative Examples 6-9: inner diameter 1.1 cm, length 40 cm) Ammonia was circulated at 10,000 h ⁻¹ (flow rate 500 mL / min), the temperature at the lower end of the catalyst packed portion was 500 ° C., an ammonia decomposition reaction was performed, and the ammonia decomposition rate was determined.
In addition, about Example 6 and Comparative Example 4, since it did not reach the ammonia decomposition rate measurable with an infrared spectrophotometer at 500 ° C., the temperature was set to 600 ° C. Further, in Examples 5 and 6 and Comparative Example 5, in consideration of the difference from the density of the ammonia decomposition catalyst of Example 1, the circulation amount of ammonia per mass of ruthenium is approximately the same as that of Example 1. The space velocity (SV) was adjusted to the values shown in Table 1.
The decomposition rate is an index representing the magnitude of the ammonia decomposition rate, that is, the degree of catalytic activity of the ammonia decomposition catalyst. The closer the decomposition rate is to 100%, the higher the catalytic activity of the ammonia decomposition catalyst.
These results are shown together in Table 1 together with the component composition of the catalyst.

From the results shown in Table 1, when a catalyst supporting ruthenium and 0.1 to 30.0% by mass of a rare earth oxide was used on a carrier made of a metal oxide other than the rare earth oxide (Examples 1 to 18). ) Was found to exhibit high catalytic activity in the ammonia decomposition reaction.
From the comparison between Examples 1 to 4 and Comparative Examples 1 and 2, the comparison between Example 5 and Comparative Example 3, and the comparison between Example 6 and Comparative Example 4, the rare earth oxide is supported at a predetermined content. It has been confirmed that the catalytic activity is improved by the treatment.
Further, from the comparison between Example 7 and Example 1 and the comparison between Examples 12 to 18 and Example 11, it was confirmed that the catalytic activity was further improved by further supporting an alkali metal. . In addition, when the alkali metal was supported, the catalyst supported after the ruthenium (Example 12) was higher in catalytic activity than the catalyst previously supported (Example 13).
When α-alumina or θ-alumina was used as the support (Examples 8 to 10), it was confirmed that sufficient catalytic activity could be obtained even if the amount of rare earth oxide supported was reduced. In particular, when α-alumina was used (Examples 8 and 9), sufficient catalytic activity could be maintained with a smaller amount of rare earth oxide supported.
In addition, when an egg shell type catalyst was used (Examples 11 to 18), it was confirmed that the catalytic activity was improved.

Claims

An ammonia decomposition catalyst in which ruthenium and a rare earth oxide are supported on a carrier made of a metal oxide other than the rare earth oxide, and the content of the rare earth oxide is 0.1 to 30.0 mass%.
The ammonia decomposition catalyst according to claim 1, wherein the metal oxide is at least one selected from alumina, zirconia and titania.
The ammonia decomposition catalyst according to claim 1 or 2, wherein the metal oxide is alumina.
The ammonia decomposition catalyst according to claim 2 or 3, wherein the alumina is α-alumina.
The ammonia decomposition catalyst according to any one of claims 1 to 4, wherein the rare earth oxide is one or more selected from lanthanum oxide, cerium oxide, neodymium oxide, and samarium oxide.
The ammonia decomposition catalyst according to any one of claims 1 to 5, wherein the rare earth oxide is neodymium oxide.
The ammonia decomposition catalyst according to any one of claims 1 to 6, wherein the ruthenium content is 0.1 to 10.0 mass%.
The ammonia decomposition catalyst according to any one of claims 1 to 7, further comprising one or more metals selected from alkali metals and alkaline earth metals supported on the carrier.
The ammonia decomposition catalyst according to claim 8, wherein the content of the metal is 0.1 to 10.0 mol per 1 mol of the ruthenium.
The ammonia decomposition catalyst according to any one of claims 1 to 9, wherein the ruthenium is supported in an egg shell type.
11. The ammonia decomposition catalyst according to claim 10, wherein in the egg shell type, the thickness of the shell part, which is a ruthenium distribution region, is 10 to 300 μm.
The ammonia decomposition catalyst according to claim 11, wherein the concentration of ruthenium in the shell part is 0.1 to 15.0% by mass with respect to 100% by mass of the constituent atoms of the shell part.
A method for producing an ammonia decomposition catalyst according to any one of claims 1 to 12,
Step 1 for supporting a rare earth oxide on the carrier;
A process for producing an ammonia decomposition catalyst, comprising the step 2 of supporting the ruthenium on the support on which the rare earth oxide is supported obtained in the step 1.
14. The method for producing an ammonia decomposition catalyst according to claim 13, wherein the step 2 includes a step of immersing the carrier carrying the rare earth oxide in an aqueous solution of ruthenium salt and then bringing the carrier into contact with a basic aqueous solution.
The carrier obtained by supporting the rare earth oxide obtained in the step 1 or the carrier obtained by supporting the rare earth oxide and ruthenium obtained by the step 2 may be further added with alkali metal and alkaline earth. The method for producing an ammonia decomposition catalyst according to claim 13 or 14, further comprising a step of supporting one or more metals selected from among similar metals.
A method for producing hydrogen gas, wherein ammonia is decomposed to produce hydrogen gas in the presence of the ammonia decomposition catalyst according to any one of claims 1 to 12.