JP7328549B2 - Ammonia dehydrogenation reaction catalyst, method for producing ammonia dehydrogenation reaction catalyst, and method for producing hydrogen using ammonia dehydrogenation reaction catalyst - Google Patents

Description

The present invention relates to an ammonia dehydrogenation catalyst for producing hydrogen from a gas containing ammonia, a method for producing an ammonia dehydrogenation catalyst, and a method for producing hydrogen using the ammonia dehydrogenation catalyst.

In view of recent global warming, full-scale efforts have been made to realize a hydrogen-based society by focusing on the use of hydrogen as a fuel source. As methods for producing hydrogen, in addition to methods for reforming fossil resources such as natural gas, petroleum, and coal, methods such as electrolysis of water are also being studied. However, all of these methods have the problem of generating a large amount of CO ₂ because they require heat and electric power in addition to using hydrocarbons as raw materials.

Under these circumstances, efforts are being made to produce hydrogen by dehydrogenation from various hydrogen-containing compounds, and in particular, attention is focused on ammonia, which has a large hydrogen content per unit volume and per unit mass. Since ammonia is composed only of hydrogen atoms and nitrogen atoms, the gas after the decomposition reaction does not contain CO ₂ at all, so unused exhaust heat is used to decompose ammonia with high efficiency. If it can be done, it will be an extremely ideal hydrogen production method with zero CO ₂ generation and no environmental load.

Regarding the dehydrogenation reaction from ammonia that has been worked on so far, hydrogen is currently produced by thermal decomposition in a furnace at a high temperature of around 900 ° C without using a catalyst, Although it is used for annealing of cold-rolled coils, it requires a high temperature of 900° C., so the problem is that the power cost for raising the temperature is high.

On the other hand, the dehydrogenation reaction from ammonia using a catalyst, which can be expected to lower temperatures, has been studied for a long time because it is inextricably linked with the ammonia synthesis reaction, and the catalyst components (that is, active metals and catalyst supports) are diverse. are being considered throughout. Ruthenium, nickel, iron and cobalt are known as active metals, and alumina, silica, magnesia, zirconia, titania, ceria and the like are known as catalyst carriers. (Patent Documents 1 to 4)

Ammonia-containing gases referred to here include synthetic high-purity ammonia used as a raw material for basic chemicals and fertilizers, as well as industrial exhaust gases (e.g., coke oven gas, urea manufacturing plants, semiconductor-related processing processes, nitrile manufacturing plants). etc.) and purified gas of ammonia separated and recovered.

An example of separated and recovered ammonia is ammonia separated and recovered in the refining process of coke oven gas. Coke oven gas (COG) generated from a coke oven contains about 8 to 10 g/ ^Nm3 of ammonia derived from nitrogen atoms contained in raw material coal. Since it causes the generation of NOx when burned as fuel, it is collected in advance. As a method for removing ammonia from COG, an ammonium sulfate recovery method is generally employed in which COG is washed with dilute sulfuric acid and ammonium sulfate (ammonium sulfate) is recovered. However, in this method, the demand for ammonium sulfate tends to be greatly influenced by market conditions. Therefore, as other ammonia treatment methods, for example, the Fossum method for producing high-purity liquid ammonia, the Coppers method for directly burning ammonia after separation, and the Karlstil method for burning in the presence of a catalyst have been adopted. Some factories use the collected ammonia as fertilizer such as ammonium sulfate, but other factories use it insufficiently, such as burning the ammonia and releasing it into the atmosphere after denitrification.

The separated and recovered ammonia is also a useful source of hydrogen.

JP 2010-094668 A JP 2011-056488 A JP 2016-159209 A JP 2016-198720 A JP 2011-078888 A

The dehydrogenation reaction from ammonia can be economically carried out by using a catalyst at a relatively low temperature of about 700° C. or lower. Further, the dehydrogenation reaction from ammonia can be carried out more economically by utilizing the unused waste heat of medium temperature of 300 to 700° C. in the ironworks. Therefore, in the dehydrogenation reaction from ammonia, it is desired to obtain a high ammonia decomposition rate (conversion rate) in the temperature range of 300 to 700°C. It is reported that some conventional ammonia dehydrogenation reaction catalysts, such as the ammonia dehydrogenation reaction catalysts disclosed in Patent Documents 1 to 3, can achieve a high ammonia decomposition rate in a relatively low temperature range such as 500 ° C. is done. However, there are few studies in the lower temperature range of 300°C or higher and lower than 500°C, and the activity of the ammonia dehydrogenation reaction catalyst is low at 300°C or higher and lower than 500°C.

In addition, there are cases in which the ammonia decomposition rate of these catalysts is measured under long contact time conditions with ammonia as the standard, and the catalytic performance is not necessarily high. In other words, in the dehydrogenation reaction using a conventional catalyst, there were cases where the contact time had to be lengthened in order to obtain a high ammonia decomposition rate.

Some catalysts, such as the catalyst described in Patent Document 4, exhibit high activity, but such catalysts have another problem in that a large amount of waste liquid containing HCl is produced in the reduction process. .

Although the catalyst described in Patent Document 5 also exhibits high activity, it is essential to add an alkali metal or an alkaline earth metal as a co-catalyst to the catalyst component. A co-catalyst may be used, but it is desirable not to have one from the viewpoint of economy.

Therefore, the present invention has been made in view of the above problems, and in order to utilize the unused intermediate temperature exhaust heat in the steelworks, ammonia dehydration is performed at a high ammonia conversion rate even at a temperature of about 300 to 700 ° C. An object of the present invention is to provide an ammonia dehydrogenation reaction catalyst capable of causing an elementary reaction, a method for producing an ammonia dehydrogenation reaction catalyst, and a method for producing hydrogen using the ammonia dehydrogenation reaction catalyst.

As a result of intensive studies by the inventors, it was found that an ammonia dehydrogenation reaction catalyst that exhibits excellent activity even at relatively low temperatures by using a ceria-based carrier manufactured by an organic acid method as a carrier that supports a ruthenium compound. I found what I got.
In this way, the inventors have found that an ammonia dehydrogenation reaction catalyst that exhibits high activity even at a low reaction temperature can be obtained, leading to the present invention.

The gist of the present invention is as follows.
<1> a carrier containing ceria as a main component;
Ruthenium supported on the carrier;
and wherein the Ce ³⁺ /Ce ⁴⁺ ratio on the surface of the carrier is 0.50 to 1.20.
<2> The method for producing the ammonia dehydrogenation reaction catalyst according to <1>,
an impregnation supporting step of supporting a ruthenium compound as a precursor of an active metal of a catalyst on a carrier mainly composed of ceria produced by an organic acid method;
A calcining step of calcining the catalyst carrier after the impregnating and supporting step to produce a catalyst;
A method for producing an ammonia dehydrogenation reaction catalyst comprising
<3> The method for producing an ammonia dehydrogenation reaction catalyst according to <2>, further including a reduction treatment step of reducing the catalyst after the baking step with a hydrogen-containing gas.
<4> The ammonia dehydrogenation reaction catalyst according to <1> above or the ammonia dehydrogenation reaction catalyst produced by the production method according to <2> above is reduced with a hydrogen-containing gas, and then ammonia is removed. A method for producing hydrogen, which comprises contacting with a gas containing hydrogen to produce hydrogen.
<5> A method for producing hydrogen, comprising bringing the ammonia dehydrogenation reaction catalyst produced by the production method according to <3> into contact with a gas containing ammonia to produce hydrogen.
<6> The method for producing hydrogen according to <4> or <5> above, wherein the gas containing ammonia is a gas recovered after being separated in a refining process of coke oven gas.

In the present invention, a catalyst is defined as one in which an active metal is supported on a catalyst carrier. A co-catalyst may be included as necessary. A co-catalyst is a third component added for the purpose of further improving activity, and is not necessarily a necessary component in the present invention.

According to the present invention, an ammonia dehydrogenation reaction catalyst capable of causing an ammonia dehydrogenation reaction at a high ammonia conversion rate even at a temperature of about 300 to 700° C., a method for producing an ammonia dehydrogenation reaction catalyst, and an ammonia dehydrogenation reaction. A method for producing hydrogen using a catalyst can be provided.

It is the figure which showed the manufacturing flow of the ammonia dehydrogenation reaction catalyst which concerns on embodiment of this invention. 1 is a schematic diagram showing a hydrogen production facility according to an embodiment of the present invention; FIG. FIG. 4 is a diagram showing an example of the result of separating peaks into Ce ³⁺ -derived peaks and Ce ⁴⁺ -derived peaks by performing peak separation after XPS measurement.

Hereinafter, embodiments of the present invention will be described with examples.

In this specification, the numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.

<Overview of this embodiment>
In the method for producing an ammonia dehydrogenation reaction catalyst according to the present embodiment, a mixed solution in which a ruthenium compound is dissolved as a precursor of ruthenium, which is an active metal, is impregnated with a catalyst carrier mainly composed of ceria produced by an organic acid method. , an impregnation-supporting step of supporting the metal compound on the catalyst carrier; and a calcining step of calcining the catalyst carrier after the impregnation-supporting step.

Further higher activity can be obtained by adding an alkali metal or alkaline earth metal as a cocatalyst to the ammonia dehydrogenation reaction catalyst according to the present embodiment. do not have to. When a cocatalyst is added to the ammonia dehydrogenation reaction catalyst, for example, potassium, sodium, cesium and the like are preferably used as the cocatalyst element.

According to this embodiment, it is possible to obtain an ammonia dehydrogenation reaction catalyst that exhibits high activity even when the temperature of the ammonia-containing gas (reaction gas) is low.

The present catalyst exhibits high activity not only at low temperatures but also at high temperatures exceeding 700°C.

The ammonia-containing gas (hereinafter also referred to as "ammonia-containing gas") includes an ammonia-containing gas recovered after being separated in the refining process of coke oven gas. Ammonia can be separated and recovered by the ammonium sulfate recovery method, the Fossum method, the Coppers method, the Karlstil method, and the like.

Ammonia dehydrogenation reaction is an endothermic reaction that decomposes ammonia into hydrogen and nitrogen, proceeding with 2NH ₃ →N ₂ +3H ₂ , and is an extremely ideal hydrogen production method that generates zero CO ₂ and has no environmental load.

<Method for producing ammonia dehydrogenation reaction catalyst>
In the production method of the present embodiment, a catalyst (ammonia dehydrogenation reaction catalyst) for producing hydrogen from ammonia-containing gas is produced. The ammonia dehydrogenation reaction catalyst obtained by this embodiment contains ruthenium as an active component, and uses ceria produced by an organic acid method as a catalyst carrier for supporting this active component.

An example of the method for producing the catalyst according to the present embodiment is shown below. FIG. 1 shows the manufacturing flow.

- Catalyst carrier As the catalyst carrier used in the production method of the present embodiment, a catalyst carrier containing ceria as a main component produced by an organic acid method (hereinafter also referred to as "ceria-based carrier") is used. The term "main component" as used herein refers to a component that accounts for 50% by mass or more in terms of oxide, and components other than the main component are preferably elements that do not inhibit the effects of the present embodiment.

In the organic acid method, first, an organic acid is dissolved in a solution of a cerium precursor reagent to form a metal complex. As a result, a gel uniformly containing the metal elements is synthesized, and the obtained gel is fired and decomposed by combustion. As a result, a ceria-based carrier in which ceria, which is the main component of the ceria-based carrier, is uniformly mixed can be synthesized. Organic acids that can be used include lactic acid, malic acid, citric acid, tartaric acid, glycolic acid, glycine, and the like. Among these, it is particularly preferable to use malic acid and citric acid. Since malic acid and citric acid are less expensive than other organic acids, the use of malic acid and citric acid makes it possible to synthesize a ceria-based carrier at low cost.

In addition, in the ceria-based carrier produced by the organic acid method, the presence ratio of trivalent cerium on the surface of the ceria-based carrier increases. That is, the Ce ³⁺ /Ce ⁴⁺ ratio, which will be described later, can be 0.50 to 1.20. In the ammonia dehydrogenation reaction, when the active metal is in a cationic state, the bond energy between the metal and nitrogen atoms increases, and desorption of the product N ₂ becomes rate-limiting. Here, by using a highly basic oxide as a support, the ruthenium particles, which are the active metal, are kept in an electron-rich state close to that of the metal, and electron transfer to the product, _N2 , promotes desorption. It is assumed that Therefore, it is speculated that the higher the ratio of Ce ³⁺ to Ce ⁴⁺ on the surface of the ceria-based support, the more accelerated the desorption of N ₂ . Under the reaction atmosphere (reduction) in the present embodiment, oxygen defects tend to occur on the surface of the ceria-based carrier, and Ce ³⁺ exists at a constant concentration and is considered to be stable. Here, the ceria-based carrier prepared by the organic acid method originally has a large proportion of Ce ³⁺ . Therefore, since it is not necessary to increase Ce ³⁺ by supplying electrons from ruthenium to the ceria-based carrier, it becomes easier for ruthenium to maintain an electron-rich state. For this reason, it is presumed that desorption of the product _N2 is promoted and high decomposition activity is exhibited.

Although the cerium precursor reagent used in the organic acid method is not particularly limited, for example, nitrates, chlorides, acetates, carbonates, sulfides, hydroxides and the like can be suitably used.

Here, the molar ratio between the organic acid and the metal ion can be selected at any value. When the ratio is up to 4:1, it is easy to obtain the expected catalyst, and it is particularly preferable to make the organic acid:metal ion ratio 1 to 3:1. That is, the Ce ³⁺ /Ce ⁴⁺ ratio on the surface of the ceria-based carrier can be easily adjusted to 0.50 to 1.20. If the amount of the organic acid is too small, the formation of the metal complex becomes insufficient, and cerium in the ceria-based carrier tends to become uneven. On the other hand, if the amount of the organic acid is too large, the cost increases, and the decomposition reaction of the organic acid during firing becomes excessively vigorous, which may cause problems such as scattering of the ceria-based carrier.

The atmosphere during gel firing may be a gas atmosphere containing a sufficient amount of oxygen to decompose the organic acid, and the firing can be easily carried out using air. At this time, if the firing atmosphere is not sufficiently ventilated, the combustion decomposition of the organic acid may not proceed sufficiently, and carbides such as cerium carbide may be partially formed. Therefore, it is preferable to ventilate sufficiently during gel firing. The maximum temperature during calcination is preferably set to a temperature equal to or higher than the reaction temperature at which the actual catalytic reaction (that is, ammonia dehydrogenation reaction) is performed. However, if the temperature is rapidly raised, the decomposition reaction of the organic acid proceeds rapidly, which may cause the ceria-based carrier to scatter. Therefore, specifically, the rate of temperature increase is preferably 5° C./min or less, more preferably 3° C./min or less, further preferably 1° C./min or less. Also, the firing temperature is preferably 400 to 750°C, more preferably 500 to 700°C, further preferably 550 to 600°C. The firing time is preferably 3 hours or more. It should be noted that the Ce ³⁺ /Ce ⁴⁺ ratio can be adjusted by adjusting the sintering temperature of the sintering treatment.

- Impregnation supporting step -
In the impregnation-supporting step, a ceria-based carrier produced by an organic acid method is impregnated with a solution in which a ruthenium compound is dissolved as a precursor of the active metal of the catalyst, so that the ceria-based carrier supports the metal compound.

・Precursor (metallic compound)
In the impregnation-supporting step, a ruthenium compound is supported on the ceria-based carrier as a precursor of ruthenium, which is an active metal. As the ruthenium compound (precursor) used in this case, counter ions (for example, in the case of ruthenium nitrate salt, (NO ₃ ) ⁻ in Ru(NO ₃ ) ₂ ) are generated during firing treatment and reduction treatment after supporting. Volatile ruthenium compounds such as nitrates, carbonates, acetates, chlorides, acetylacetonates, ammonium salts, etc. can be used. However, it is preferable to use a water-soluble ruthenium compound that can be used in an aqueous solution when performing the impregnation-supporting step, in order to reduce production costs and ensure a safe production work environment. A ruthenium compound that easily changes to an oxide state or a metal state during firing is also preferred. Specifically, nitrates and chlorides are preferred.

When a promoter element is added, nitrates, carbonates, acetates, chlorides, acetylacetonate, ammonium salts, etc. of promoter elements are prepared together with the ruthenium compound.

- Precursor solution The precursor solution used in the impregnation supporting step is a solution in which a ruthenium compound is dissolved. In addition, a co-catalyst solution in which a co-catalyst element is dissolved is prepared as necessary.
Solvents used for the precursor solution include, for example, water (aqueous solution), ethanol, methanol, ethylene glycol, propanol, etc. Among them, water is preferable.
Also, the solid content concentration in the precursor solution is not particularly limited, but is adjusted, for example, in the range of 1 to 5% by mass.

- Impregnation method The impregnation method of the precursor solution may be a conventional impregnation method such as an incipient wetness method, an ion exchange method, or the like. When the cocatalyst element is supported on the ceria-based carrier, the ceria-based carrier may be impregnated with the precursor solution and the cocatalyst solution by these impregnation methods.

- Support rate The support rate of the ruthenium metal in the ammonia dehydrogenation reaction catalyst is preferably 0.1 to 50% by mass, although activity can be obtained even with a small amount. When it is 0.1% by mass or more, the activity can be sufficiently expressed. In addition, when the content is 50% by mass or less, a decrease in the degree of dispersion is suppressed, the utilization efficiency of the supported ruthenium is enhanced, and economic efficiency is improved. More preferably, it is 0.5 to 20% by mass. In the production process, it is preferable to adjust the amount of the ruthenium compound (such as ruthenium nitrate) contained in the mixed solution so as to achieve the proper loading ratio.
Here, the loading rate is obtained by using the mass of the ammonia dehydrogenation reaction catalyst (more strictly, the mass of the sample for mass % measurement) as the denominator, and the ruthenium metal element as the numerator is calculated as the metal-equivalent mass. Moreover, in order to adjust the content of the supported metal to be within the above range, it is preferable to calculate and prepare each starting material in advance. Once the desired component composition of the catalyst has been achieved, it may be prepared according to the composition at that time.
The Ce ³⁺ /Ce ⁴⁺ ratio can be adjusted by adjusting the loading ratio.

-Drying process-
A drying treatment may be applied to the ceria-based carrier after the impregnation-supporting step and before the calcination step.
The drying treatment is preferably performed at 80 to 120°C. More preferably, it is 90 to 110°C. The drying time is preferably 1 to 10 hours, for example. Drying may be performed, for example, in an air atmosphere, and any device capable of reaching a sufficient temperature, such as a dryer, may be used.

- Baking process -
In this embodiment, the ceria-based carrier after the impregnation and supporting step is subjected to a calcination treatment (calcination step).
The baking treatment is preferably performed at 400 to 700°C. More preferably 450 to 600°C, more preferably 500 to 550°C. The firing time is preferably 3 to 8 hours, for example. Firing is performed, for example, in an air atmosphere, and may be performed in an apparatus capable of reaching a sufficient temperature, such as a muffle furnace.

- Granulation process -
The prepared ammonia dehydrogenation catalyst may be a powder or a molded body. Therefore, the granulation step may or may not be performed, but when the ammonia dehydrogenation reaction catalyst is used in a fixed bed, granulation is desirable in order to improve air permeability. The particle diameter and surface area of the ammonia dehydrogenation reaction catalyst should be appropriately adjusted in the case of a powder, and the pore volume, pore diameter, shape, etc. of the ammonia dehydrogenation reaction catalyst should be appropriately adjusted in consideration of the balance between surface area and strength in the case of a molded body. is preferred. The size of the granulated ammonia dehydrogenation reaction catalyst is 0.1 to 50 mm, preferably 0.5 to 40 mm, more preferably 1 to 30 mm. Examples of granulation methods include extrusion molding and compression molding. The shape of the molding may be spherical, cylindrical, ring-shaped, wheel-shaped, granular, or the like. The size of the ammonia dehydrogenation catalyst is, for example, when the ammonia dehydrogenation catalyst is produced by extrusion molding (for example, a cylindrical catalyst), the size of the mold used for extrusion molding (more specifically, , diameter of the opening). Moreover, it is possible to arrange the size of the ammonia dehydrogenation reaction catalyst within a certain range by classifying with a sieve. For example, when the ammonia dehydrogenation reaction catalyst is applied to a sieve with openings of X1 mm and X2 mm (X1<X2), the particles that fall from the sieve with openings of X2 mm and remain on the sieve with openings of X1 have a size of X1 to X2 mm. can be determined. Further, the ammonia dehydrogenation reaction catalyst may be, for example, a honeycomb substrate made of metal or ceramics coated with catalyst components.

-Reduction treatment process-
A hydrogen-containing gas may be used to reduce the ammonia dehydrogenation reaction catalyst after the baking step. When the manufactured catalyst is not used immediately and is to be temporarily stored, it is preferable to perform reduction treatment immediately before use without hydrogen reduction.
In the reduction treatment, the reaction gas containing 20% by volume or more of hydrogen (% by volume relative to the total volume of the reaction gas (more strictly, the total volume of the gas used for measurement)) is heated to 300 to 600 ° C. (more preferably 400 to 500° C.) for 1 to 4 hours (more preferably 1 to 2 hours) to proceed the reduction. Moreover, it is desirable that the gas components contained in addition to hydrogen be inert gases such as helium and argon.

The reduction treatment can be performed, for example, after a tubular reaction tube is filled with a catalyst.

In one example of the reduction treatment step, the contact time of the mixed gas containing hydrogen when reducing the ruthenium compound is 0.01 to 1 g·h/L, preferably 0.1 to 0.5 g·h/L, based on hydrogen. is.

By increasing the hydrogen concentration in the reducing gas, the active metal is efficiently reduced, the performance is improved, the reduction treatment process time is shortened, and the treatment cost is reduced. Therefore, it is preferable that the hydrogen concentration in the reduction treatment step is high.

The active metal of the catalyst prepared by the usual impregnation method is carried on the surface of the ceria-based carrier. The presence of ruthenium metal in the catalyst can be confirmed by X-ray diffraction (XRD). For XRD measurement, the catalyst sample is thoroughly ground in an agate mortar and placed on a sample stage using, for example, Rigaku's SmartLab so that the sample and the holder surface are horizontal, and then the measurement is performed. X-ray source is CuKα ray, X-ray output: 30 mA, 40 kV, divergence slit: 0.2 mm, length limiting slit: 0.5 mm, scan speed: 4 deg/min, scan step: 0.01 deg. The presence of ruthenium metal in the catalyst can be evaluated from the peak position and intensity.

Fluorescent X-ray (X-ray Fluorescence, XRF) analysis can be used as a method for measuring the content of ruthenium metal that constitutes the catalyst prepared above. XRF analysis can be performed by the glass bead method, for example, using ZSX Primus II manufactured by Rigaku. When performing XRF analysis, it is preferable to reduce the ignition weight of the powder sample to be analyzed at 1000 ° C. for 1 hour in advance so that the ratio between the melting agent and the sample does not change during glass bead production. Glass beads are prepared by weighing 1 g of lithium tetraborate as a flux for 0.2 g of a powder sample and blending them in an agate mortar, then adding lithium iodide as a release agent and heating and dissolving them at 1300° C. for a total of 8 minutes. You can do it.

At this time, it is converted to an oxide that is stable under standard conditions, and if there are multiple stable oxides, it is converted to the oxide with the highest oxidation number among them. In particular, for the lanthanide series elements, cerium is converted to cerium (IV) oxide, other elements are converted to trivalent oxides, and the total nitride content is calculated as the sum of these converted values. do.

In this way, each element is converted to an oxide, and furthermore, by converting to a mass ratio using the atomic weight described in the periodic table created by the Chemical Society of Japan, it is possible to determine the total composition of the catalyst, and the molar ratio display and mass Any composition ratio in the ratio display can be calculated. As a result, the content of ruthenium metal can be measured, and from the content of ruthenium metal, the supporting rate of ruthenium metal and the like can be calculated.

By the above production method, an ammonia dehydrogenation catalyst according to the present embodiment, that is, an ammonia dehydrogenation catalyst having a ceria-based carrier produced by an organic acid method and an active metal supported on the ceria-based carrier is obtained. be done.

XPS (X-ray photoelectron spectroscopy) can be used to measure the surface valence of the ceria-based carrier (that is, the valence of cerium present on the surface of the ceria-based carrier) constituting the catalyst prepared above. In XPS measurement, the catalyst sample is thoroughly ground in an agate mortar and evaluated using, for example, JPS-9200 manufactured by JEOL. A sample powder was placed on an indium chip and fixed using a glass plate to prevent scattering, and only the surface was measured. In this measurement, only a portion of the surface of the catalyst particles of several nanometers or less (that is, the depth at which electrons can be emitted by irradiation with X-rays) is measured, but there is no problem in applying the measurement results to the entire surface. X-ray source is AlKα, detection angle: 45°, X-ray output: 15 kV, 25 W, degree of vacuum: 2.6 × 10 ^-9 torr, measurement area: 300 μm square, number of times of integration (for example, 2 times). Then, the surface valence of the ceria-based carrier can be evaluated from the peak position and intensity.

The Ce ³⁺ /Ce ⁴⁺ ratio can be calculated after separating the peaks to clarify the Ce ³⁺ -derived peak and the Ce ⁴⁺ -derived peak. An example of peak separation is shown in FIG. The amount of Ce ⁴⁺ can be calculated using the peak area around 915-916 eV, and the amount of Ce ³⁺ can be calculated using the peak area around 902-903 eV. Note that peak separation can be performed using, for example, Spec Surf (Analysis). Peak fitting may be performed in performing peak separation. Peak fitting may be performed, for example, in the following steps. (1) subtract the background by the Shirley method (background processing), (2) align the carbon 1S spectrum to 285.0 eV (alignment), (3) Gauss-Lorentz (mixed function of Gaussian function and Lorentzian function) Select and perform peak fitting. Also, the Ce ³⁺ /Ce ⁴⁺ ratio in this embodiment is defined below. In the examples described later, the Ce ³⁺ /Ce ⁴⁺ ratio was measured by the method described above.
(Ce ³⁺ /Ce ⁴⁺ ratio) = (Ce ³⁺ peak area)/(Ce ⁴⁺ peak area)

The Ce ³⁺ /Ce ⁴⁺ ratio in this embodiment is 0.50 to 1.20. If the Ce ³⁺ /Ce ⁴⁺ ratio is less than 0.50, it is difficult for ruthenium to maintain an electron-rich state, and desorption of adsorbed N ₂ is not promoted. On the other hand, it is difficult to make the Ce ³⁺ /Ce ⁴⁺ ratio over 1.20. Therefore, the Ce ³⁺ /Ce ⁴⁺ ratio in this embodiment is set to 0.50 to 1.20.

<Method for producing hydrogen>
The thus-obtained ammonia dehydrogenation reaction catalyst according to the present embodiment is suitably used in a hydrogen production method for producing hydrogen from an ammonia-containing gas (reaction gas) by an ammonia dehydrogenation reaction. An ammonia dehydrogenation reaction catalyst that has not been subjected to reduction treatment is preferably subjected to reduction treatment before being used in the reaction. In the reduction treatment, a reaction gas containing 20% by volume or more of hydrogen is passed at 300 to 600° C. (more preferably 400 to 500° C.) for 1 to 4 hours (more preferably 1 to 2 hours) to proceed the reduction. is desirable. Moreover, it is desirable that the gas components contained in addition to hydrogen be inert gases such as helium and argon.
The ammonia dehydrogenation reaction is performed by bringing the ammonia-containing gas into contact with an ammonia dehydrogenation reaction catalyst. The reaction can be carried out in a fluidized bed if the ammonia dehydrogenation reaction catalyst is a powder granulated to less than 1 mm in the granulation step, and in a fixed bed if it is a molded body granulated to 1 mm or more. The reaction is desirably carried out at 300-700°C. It is preferably 400 to 700°C. FIG. 2 shows an example reactor. The reactor comprises a thermocouple 1 , an electric furnace 2 and a glass tube (glass reaction tube) 5 . When using this reactor, the sample 3 of the ammonia dehydrogenation reaction catalyst is inserted into the glass tube 5, the top and bottom of the sample 3 are fixed with quartz wool 4, and the tube is filled. Then, while heating the sample 3 in the electric furnace 2 and measuring the temperature of the sample 3 with the thermocouple 1 , an ammonia-containing gas is passed through the glass tube 5 . This allows the ammonia dehydrogenation reaction to proceed.
Thus, an ammonia dehydrogenation reaction catalyst can be produced which exhibits high activity even at a relatively low temperature of about 300 to 700° C., especially at a temperature of 500° C. or less.

The ammonia-containing gas used for the production of hydrogen is not particularly limited. A gas that is vol%) or more relative to the total volume) is preferred from the standpoint of productivity. For example, in addition to synthesized high-purity ammonia, ammonia-containing gas separated and recovered in the refining process of coke oven gas such as the ammonium sulfate recovery method, Fossum method, Coppers method, Karlstil method, etc. is preferably used. may include hydrocarbons such as methane, _H2 , CO, _CO2 , _N2 , _H2S , HCN, HSCN, and the like. Incidentally, the ammonia-containing gas may be produced by any route, not limited to synthesis or separation.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Evaluation of catalytic activity was carried out as follows.
Ruthenium nitrate was supported as a precursor on a ceria-based carrier by an incipient wetness method. Then, after drying treatment and calcination treatment, a tubular glass reaction tube having an inner diameter of 6 mm was filled with a catalyst carrier, and a reduction treatment was performed to obtain a catalyst. After that, catalytic activity was evaluated using a flow-type microreactor apparatus.
Specifically, an ammonia-containing gas was passed through a fixed-bed flow reactor, and changes in gas flow rates at the inlet and outlet of the catalyst layer were measured. Then, the ammonia conversion rate was calculated based on the measurement results, and the catalytic activity was evaluated based on this ammonia conversion rate. A predetermined amount of each gas was introduced from a liquefied ammonia cylinder and a helium cylinder using a mass flow controller and mixed to obtain an ammonia-containing gas. The composition of the ammonia-containing gas was NH ₃ /He = 1/2 (flow rate ratio), the ammonia-based contact time was 0.167 g·h/L, and the temperatures were 300°C, 400°C, and 600°C. An evaluation test was performed. The ammonia conversion rate was measured based on the results of determining the composition of the feed gas and the gas at the outlet of the glass reaction tube by gas chromatography.

Ammonia conversion shall be defined below.
(Ammonia conversion rate (%)) = {(flow rate of _NH3 before reaction) - (flow rate of _NH3 after reaction)}/(flow rate of _NH3 before reaction) x 100
Main conditions and results of Examples and Comparative Examples are summarized in Tables 1A and 1B (hereinafter also simply referred to as "Table 1"). The "calcination temperature" in Table 1 is the calcination temperature during the preparation of the ceria-based carrier, that is, the calcination temperature during gel calcination, and the "reduction temperature" is the reduction temperature during reduction treatment of the ammonia dehydrogenation reaction catalyst. indicates

(Example 1: Ceria-based carrier (citric acid method))
In Example 1, a ceria-based carrier was prepared by the citric acid method. Specifically, 5.0452 g of cerium (III) nitrate hexahydrate (Kanto Kagaku, purity>99.5%) was weighed and dissolved in 100 ml of pure water. 4.4655 g of citric acid monohydrate (Wako Pure Chemical Industries, purity>99.5%) was further dissolved in the resulting solution, and the solution was stirred with a magnetic stirrer for 15 minutes. At this time, the molar ratio of cerium ions and citric acid was adjusted to 1:2. After confirming that the solution became transparent and had no undissolved residue, aqueous ammonia (Wako Pure Chemical Industries, concentration 28% by mass) was added dropwise to the solution to adjust the pH to 7.0. The solution was stirred for an additional hour and the resulting solution was rotary evaporated to reduce the volume of the solution and transferred to an alumina crucible. The solution was heated to 100° C. on a hot plate to evaporate the water content in the solution over 2 hours and dry up the solid content in the solution. The resulting solid was crushed in an agate mortar to a powder and then returned to the alumina crucible. The sample was placed in an electric furnace together with the alumina crucible, and fired in an air atmosphere. Specifically, the sample was dried at 110° C. for 3 hours, heated to 600° C. over 2 hours, and fired at 600° C. for 5 hours. A sample of the ceria-based carrier was prepared through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. An XPS measurement of the calcined Ru/CeO ₂ catalyst gave a Ce ³⁺ /Ce ⁴⁺ ratio of 0.83. The conversion of ammonia was 33.8% at a reaction temperature of 300°C, 95.6% at 400°C, and 99.9% at 600°C.

(Example 2)
In Example 1, the reduction temperature was changed.
Specifically, using the ceria-based carrier prepared in Example 1, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by an incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 300° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. The conversion of ammonia was 31.4% at a reaction temperature of 300°C, 97.7% at 400°C, and 99.9% at 600°C.

(Example 3)
In Example 1, the reduction temperature was changed.
Specifically, using the ceria-based carrier prepared in Example 1, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by an incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After the Ru/CeO ₂ catalyst was calcined at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 600° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. The conversion of ammonia was 17.5% at a reaction temperature of 300°C, 89.3% at 400°C, and 99.9% at 600°C.

(Example 4)
In Example 1, the sintering temperature during preparation of the ceria-based carrier was changed.
Specifically, in Example 1, the ceria-based carrier was adjusted by changing the sintering temperature during preparation of the ceria-based carrier to 400°C. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. As a result of XPS measurement of the calcined catalyst, the Ce ³⁺ /Ce ⁴⁺ ratio was 0.61. The conversion of ammonia was 24.0% at a reaction temperature of 300°C, 89.2% at 400°C, and 99.9% at 600°C.

(Example 5)
In Example 1, the sintering temperature during preparation of the ceria-based carrier was changed.
Specifically, in Example 1, the ceria-based carrier was adjusted by changing the sintering temperature during the production of the ceria-based carrier to 700°C. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. As a result of XPS measurement of the catalyst after calcination, the Ce ³⁺ /Ce ⁴⁺ ratio was 0.67. The conversion of ammonia was 25.5% at a reaction temperature of 300°C, 94.3% at 400°C, and 99.9% at 600°C.

(Comparative example 1)
In Example 1, the sintering temperature during preparation of the ceria-based carrier was changed.
Specifically, in Example 1, the ceria-based carrier was adjusted by changing the sintering temperature during the preparation of the ceria-based carrier to 800°C. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. As a result of XPS measurement of the calcined catalyst, the Ce ³⁺ /Ce ⁴⁺ ratio was 0.49. The conversion of ammonia was 14.0% at a reaction temperature of 300°C, 84.1% at 400°C, and 99.8% at 600°C.

(Example 6)
In Example 1, the ruthenium loading was changed.
Specifically, ruthenium nitrate was used as a ruthenium precursor, and 0.5% by mass of ruthenium was supported on the ceria-based carrier prepared in Example 1 by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. As a result of XPS measurement of the calcined catalyst, the Ce ³⁺ /Ce ⁴⁺ ratio was 0.66. The conversion of ammonia was 21.2% at a reaction temperature of 300°C, 85.4% at 400°C, and 99.9% at 600°C.

(Example 7)
In Example 1, the ruthenium loading was changed.
Specifically, ruthenium nitrate was used as a ruthenium precursor, and 3% by mass of ruthenium was supported on the ceria carrier prepared in Example 1 by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. As a result of XPS measurement of the calcined catalyst, the Ce ³⁺ /Ce ⁴⁺ ratio was 0.75. The conversion of ammonia was 28.1% at a reaction temperature of 300°C, 90.3% at 400°C, and 99.9% at 600°C.

(Example 8)
In Example 1, the ruthenium loading was changed.
Specifically, ruthenium nitrate was used as a ruthenium precursor, and 10% by mass of ruthenium was supported on the ceria carrier prepared in Example 1 by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. As a result of XPS measurement of the calcined catalyst, the Ce ³⁺ /Ce ⁴⁺ ratio was 0.96. The conversion of ammonia was 38.8% at a reaction temperature of 300°C, 97.6% at 400°C, and 99.9% at 600°C.

(Example 9)
In Example 1, the ruthenium loading was changed.
Specifically, using ruthenium nitrate as a ruthenium precursor, 20% by mass of ruthenium was supported on the ceria carrier prepared in Example 1 by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was subjected to reduction treatment at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. As a result of XPS measurement of the calcined catalyst, the Ce ³⁺ /Ce ⁴⁺ ratio was 1.12. The conversion of ammonia was 51.6% at a reaction temperature of 300°C, 98.5% at 400°C, and 99.9% at 600°C.

(Example 10)
In Example 1, the ammonia-containing gas to be used was changed to the ammonia-containing gas separated and recovered by the ammonium sulfate recovery method in the refining process of coke oven gas.
Specifically, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria carrier prepared in Example 1 by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. After that, He is mixed with the ammonia-containing gas separated and recovered by the ammonium sulfate recovery method in the process of refining the coke oven gas, and the composition of the mixed gas is NH ₃ /He = 1/2 (the ammonia gas in the mixed gas flow ratio with He gas).
Then, using this mixed gas, the ammonia conversion rate was measured under conditions of a contact time of 0.167 g·h/L and a temperature of 300°C, 400°C, or 600°C. The conversion of ammonia was 25.8% at a reaction temperature of 300°C, 85.7% at 400°C and 99.9% at 600°C.

(Example 11 (Examples 11-1 to 11-5))
In Example 1, ceria-based carriers were prepared by changing the molar ratio of cerium ions to citric acid to 1:0.5, 1:1.5, 3, and 4.
Specifically, 5.0452 g of cerium (III) nitrate hexahydrate (Kanto Kagaku, purity>99.5%) was weighed and dissolved in 100 ml of pure water. To the resulting solution, citric acid monohydrate (Wako Pure Chemical Industries, purity >99.5%) was added to a predetermined ratio (that is, the molar ratio of cerium ions to citric acid was 1:0. 5, 1, 1.5, 3, 4) and the solution was stirred with a magnetic stirrer for 15 minutes. After confirming that the solution became transparent and had no undissolved residue, aqueous ammonia (Wako Pure Chemical Industries, concentration 28% by mass) was added dropwise to the solution to adjust the pH to 7.0. The solution was stirred for an additional hour and the resulting solution was rotary evaporated to reduce the volume of the solution and transferred to an alumina crucible. The solution was heated to 100° C. on a hot plate to evaporate the water content in the solution over 2 hours and dry up the solid content in the solution. The resulting solid was crushed in an agate mortar to a powder and then returned to the alumina crucible. The sample was placed in an electric furnace together with the alumina crucible, and fired in an air atmosphere. Specifically, the sample was dried at 110° C. for 3 hours, heated to 600° C. over 2 hours, and fired at 600° C. for 5 hours. A sample of the ceria-based carrier was prepared through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the prepared ceria carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. As a result of XPS measurement of the calcined catalyst, the Ce ³⁺ /Ce ⁴⁺ ratio was as shown in Table 1 for Examples 11-1 to 11-5. Ammonia conversion showed high activity at each reaction temperature as shown in Examples 11-1 to 11-5 in Table 1.

(Example 12: Ceria-based carrier (malic acid method) (Examples 12-1 to 12-6))
In Example 12, a ceria-based carrier was prepared by the malic acid method. Specifically, 5.0452 g of cerium (III) nitrate hexahydrate (Kanto Kagaku, purity>99.5%) was weighed and dissolved in 100 ml of pure water. To the resulting solution, DL-malic acid (Kanto Kagaku, Shika special grade) was added so that the molar ratio of cerium ions and malic acid was 1:0.5, 1, 1.5, 2, 3, or 4. and the solution was magnetically stirred for 15 minutes. After confirming that the solution became transparent and had no undissolved residue, aqueous ammonia (Wako Pure Chemical Industries, concentration 28% by mass) was added dropwise to the solution to adjust the pH to 7.0. The solution was stirred for an additional hour and the resulting solution was rotary evaporated to reduce the volume of the solution and transferred to an alumina crucible. The solution was heated to 100° C. on a hot plate to evaporate the water content in the solution over 2 hours and dry up the solid content in the solution. The resulting solid was crushed in an agate mortar to a powder and then returned to the alumina crucible. The sample was placed in an electric furnace together with the alumina crucible, and fired in an air atmosphere. Specifically, the sample was dried at 110° C. for 3 hours, heated to 600° C. over 2 hours, and fired at 600° C. for 5 hours. A sample of the ceria-based carrier was prepared through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/ _CeO2 catalyst at 500°C for 5 hours, the Ru/ _CeO2 catalyst was reduced at 450°C for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. . As a result of XPS measurement of the calcined Ru/CeO ₂ catalyst, the Ce ³⁺ /Ce ⁴⁺ ratio was as shown in Table 1 for Examples 12-1 to 12-6. As shown in Examples 12-1 to 12-6 in Table 1, the ammonia conversion rate showed high activity at each reaction temperature.

(Example 13: Ceria-based carrier (malic acid method) (Examples 13-1 to 13-2))
In Example 12-3, the sintering temperature of the ceria-based carrier prepared so that the molar ratio of cerium ions to malic acid was 1:1.5 was changed to 400°C or 700°C. Specifically, a solid obtained by using malic acid was crushed in an agate mortar to make powder, and then returned to the alumina crucible. After the sample was dried at 110° C. for 3 hours, it was heated to 400° C. over 1 hour or 700° C. over 2 hours, and fired at 400° C. or 700° C. for 5 hours. A sample of the ceria-based carrier was prepared through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/ _CeO2 catalyst at 500°C for 5 hours, the Ru/ _CeO2 catalyst was reduced at 450°C for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. . As a result of XPS measurement of the calcined Ru/CeO ₂ catalyst, the Ce ³⁺ /Ce ⁴⁺ ratio was as shown in Table 1 for Examples 13-1 to 13-2. As shown in Examples 13-1 and 13-2 in Table 1, the ammonia conversion rate showed high activity at each reaction temperature.

(Comparative example 2)
In Example 13-2, the firing temperature of the ceria-based carrier was changed to 800°C. Specifically, a solid obtained by using malic acid was crushed in an agate mortar to make powder, and then returned to the alumina crucible. After drying the sample at 110° C. for 3 hours, the temperature was raised to 800° C. over 2.5 hours, and calcination treatment was performed at 800° C. for 5 hours. A sample of the ceria-based carrier was prepared through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/ _CeO2 catalyst at 500°C for 5 hours, the Ru/ _CeO2 catalyst was reduced at 450°C for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. . XPS measurement of the calcined Ru/CeO ₂ catalyst gave a Ce ³⁺ /Ce ⁴⁺ ratio of 0.49. The conversion of ammonia was 15.4% at a reaction temperature of 300°C, 70.2% at 400°C, and 99.7% at 600°C.

(Example 14: Ceria carrier (tartaric acid method))
In Example 14, a ceria-based carrier was prepared by the tartaric acid method. Specifically, 5.0452 g of cerium (III) nitrate hexahydrate (Kanto Kagaku, purity>99.5%) was weighed and dissolved in 100 ml of pure water. 3.4881 g of DL-tartaric acid (Kanto Kagaku, Shika special grade) was further dissolved in the resulting solution, and the solution was stirred with a magnetic stirrer for 15 minutes. At this time, the molar ratio of cerium ions and tartaric acid was adjusted to 1:2. After confirming that the solution became transparent and had no undissolved residue, aqueous ammonia (Wako Pure Chemical Industries, concentration 28% by mass) was added dropwise to the solution to adjust the pH to 7.0. The solution was stirred for an additional hour and the resulting solution was rotary evaporated to reduce the volume of the solution and transferred to an alumina crucible. The solution was heated to 100° C. on a hot plate to evaporate the water content in the solution over 2 hours and dry up the solid content in the solution. The resulting solid was crushed in an agate mortar to a powder and then returned to the alumina crucible. The sample was placed in an electric furnace together with the alumina crucible, and fired in an air atmosphere. Specifically, the sample was dried at 110° C. for 3 hours, heated to 600° C. over 2 hours, and fired at 600° C. for 5 hours. A sample of the ceria-based carrier was prepared through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. XPS measurement of the calcined Ru/CeO ₂ catalyst gave a Ce ³⁺ /Ce ⁴⁺ ratio of 0.84. The conversion of ammonia was 35.2% at a reaction temperature of 300°C, 91.4% at 400°C, and 99.9% at 600°C.

(Example 15: Ceria carrier (lactic acid method))
In Example 15, the catalyst was prepared by the lactic acid method. Specifically, 5.0452 g of cerium (III) nitrate hexahydrate (Kanto Kagaku, purity>99.5%) was weighed and dissolved in 100 ml of pure water. 2.0935 g of lactic acid (Kanto Kagaku, special grade) was further dissolved in the resulting solution, and the solution was stirred with a magnetic stirrer for 15 minutes. At this time, the molar ratio of cerium ions and lactic acid was adjusted to 1:2. After confirming that the solution became transparent and had no undissolved residue, aqueous ammonia (Wako Pure Chemical Industries, concentration 28% by mass) was added dropwise to the solution to adjust the pH to 7.0. The solution was stirred for an additional hour and the resulting solution was rotary evaporated to reduce the volume of the solution and transferred to an alumina crucible. The solution was heated to 100° C. on a hot plate to evaporate the water content in the solution over 2 hours and dry up the solid content in the solution. The resulting solid was crushed in an agate mortar to a powder and then returned to the alumina crucible. The sample was placed in an electric furnace together with the alumina crucible, and fired in an air atmosphere. Specifically, the sample was dried at 110° C. for 3 hours, heated to 600° C. over 2 hours, and fired at 600° C. for 5 hours. A sample of the ceria-based carrier was prepared through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. XPS measurement of the calcined Ru/CeO ₂ catalyst gave a Ce ³⁺ /Ce ⁴⁺ ratio of 0.78. The conversion of ammonia was 34.2% at a reaction temperature of 300°C, 90.5% at 400°C, and 99.9% at 600°C.

(Example 16: Ceria carrier (glycolic acid method))
In Example 16, the catalyst was prepared by the glycolic acid method. Specifically, 5.0452 g of cerium (III) nitrate hexahydrate (Kanto Kagaku, purity>99.5%) was weighed and dissolved in 100 ml of pure water. 1.7674 g of glycolic acid (Kanto Kagaku, special grade) was further dissolved in the obtained solution, and the solution was stirred with a magnetic stirrer for 15 minutes. At this time, the molar ratio of cerium ions and glycolic acid was adjusted to 1:2. After confirming that the solution became transparent and had no undissolved residue, aqueous ammonia (Wako Pure Chemical Industries, concentration 28% by mass) was added dropwise to the solution to adjust the pH to 7.0. The solution was stirred for an additional hour and the resulting solution was rotary evaporated to reduce the volume of the solution and transferred to an alumina crucible. The solution was heated to 100° C. on a hot plate to evaporate the water content in the solution over 2 hours and dry up the solid content in the solution. The resulting solid was crushed in an agate mortar to a powder and then returned to the alumina crucible. The sample was placed in an electric furnace together with the alumina crucible, and fired in an air atmosphere. Specifically, the sample was dried at 110° C. for 3 hours, heated to 600° C. over 2 hours, and fired at 600° C. for 5 hours. A sample of the ceria-based carrier was prepared through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of ruthenium was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. XPS measurement of the calcined Ru/CeO ₂ catalyst gave a Ce ³⁺ /Ce ⁴⁺ ratio of 0.84. The conversion of ammonia was 37.1% at a reaction temperature of 300°C, 93.0% at 400°C, and 99.9% at 600°C.

(Comparative Example 3)
In Example 1, a reference catalyst CEO-5 (prepared by a precipitation method) distributed by Catalysis Society of Japan was used as a ceria-based carrier.
Specifically, using ruthenium nitrate as a ruthenium precursor, 5% by mass of ruthenium was supported on the reference catalyst CEO-5 by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. XPS measurement of the calcined Ru/CeO ₂ catalyst showed a Ce ³⁺ /Ce ⁴⁺ ratio of 0.42. The ammonia conversion rate was 13.8% at a reaction temperature of 300°C, 83.2% at 400°C, and 99.9% at 600°C.

(Comparative Example 4: Ceria-based carrier (precipitation method))
In Comparative Example 4, a ceria-based carrier was prepared by a precipitation method.
Specifically, 0.2088 g of cerium (III) nitrate hexahydrate (Kanto Kagaku, purity>99.5%) was weighed and dissolved in 100 ml of pure water. After stirring the solution for 30 minutes and confirming that it is uniform, aqueous ammonia (Wako Pure Chemical Industries, concentration 28% by mass) was added dropwise to the solution while stirring to adjust the pH to 10.0. The solution was stirred for 1 hour and allowed to stand for 30 minutes. The resulting precipitate was subjected to suction filtration using a membrane filter and washed with pure water. The obtained precipitate was transferred to an alumina crucible and then heated to 100° C. on a hot plate. Further, the water in the precipitate was evaporated over 2 hours, and the precipitate was dried. The resulting solid was crushed in an agate mortar to a powder and then returned to the alumina crucible. The sample was placed in an electric furnace together with the alumina crucible, and fired in an air atmosphere. Specifically, the sample was dried at 110° C. for 3 hours, heated to 600° C. over 2 hours, and fired at 600° C. for 5 hours. A sample of the ceria-based carrier was prepared through the above steps. Then, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of Ru was supported on the ceria-based carrier by the incipient wetness method. This prepared a Ru/CeO ₂ catalyst. After calcining this Ru/CeO ₂ catalyst at 500° C. for 5 hours, the Ru/CeO ₂ catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. XPS measurement of the calcined Ru/CeO ₂ catalyst gave a Ce ³⁺ /Ce ⁴⁺ ratio of 0.44. The conversion of ammonia was 12.4% at a reaction temperature of 300°C, 79.0% at 400°C, and 99.9% at 600°C.

(Comparative Example 5: Magnesia-based carrier (citric acid method))
In Comparative Example 5, a magnesia-based carrier was prepared by the citric acid method.
Specifically, 5.0452 g of magnesium nitrate hexahydrate (Kanto Kagaku, purity>99.0%) was weighed and dissolved in 100 ml of pure water. 4.4655 g of citric acid monohydrate (Wako Pure Chemical Industries, purity>99.5%) was further dissolved in the resulting solution, and the solution was stirred with a magnetic stirrer for 15 minutes. At this time, the molar ratio of magnesium ions and citric acid was adjusted to 1:2. After confirming that the solution became transparent and had no undissolved residue, aqueous ammonia (Wako Pure Chemical Industries, concentration 28% by mass) was added dropwise to the solution to adjust the pH to 7.0. The solution was stirred for an additional hour and the resulting solution was rotary evaporated to reduce the volume of the solution and transferred to an alumina crucible. The solution was heated to 100° C. on a hot plate to evaporate the water content in the solution over 2 hours and dry up the solid content in the solution. The resulting solid was crushed in an agate mortar to a powder and then returned to the alumina crucible. The sample was placed in an electric furnace together with the alumina crucible, and fired in an air atmosphere. Specifically, after drying at 110° C. for 3 hours, the temperature was raised to 600° C. over 2 hours, and firing treatment was performed at 600° C. for 5 hours. A sample of the magnesia-based carrier was produced through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of Ru was supported on the magnesia-based carrier by the incipient wetness method. A Ru/MgO catalyst was thus prepared. After calcining this Ru/MgO catalyst at 500° C. for 5 hours, the Ru/MgO catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. The conversion of ammonia was 15.9% at a reaction temperature of 300°C, 76.3% at 400°C, and 99.9% at 600°C.

(Comparative Example 6: Magnesia-based carrier (precipitation method))
In Comparative Example 6, a magnesia-based carrier was prepared by a precipitation method.
Specifically, 12.1986 g of magnesium nitrate hexahydrate (Kanto Kagaku, purity>99.0%) was weighed and dissolved in 100 ml of pure water. After stirring the solution for 30 minutes and confirming that it is uniform, aqueous ammonia (Wako Pure Chemical Industries, concentration 28% by mass) was added dropwise to the solution while stirring to adjust the pH to 10.0. The solution was stirred for 1 hour and allowed to stand for 30 minutes. The resulting precipitate was subjected to suction filtration using a membrane filter and washed with pure water. The obtained precipitate was transferred to an alumina crucible and then heated to 100° C. on a hot plate. Further, the water in the precipitate was evaporated over 2 hours, and the precipitate was dried. The resulting solid was crushed in an agate mortar to a powder and then returned to the alumina crucible. The sample was placed in an electric furnace together with the alumina crucible, and fired in an air atmosphere. Specifically, after drying at 110° C. for 3 hours, the temperature was raised to 600° C. over 2 hours, and firing treatment was performed at 600° C. for 5 hours. A sample of the magnesia-based carrier was produced through the above steps. Next, ruthenium nitrate was used as a ruthenium precursor, and 5% by mass of Ru was supported on the magnesia-based carrier by the incipient wetness method. A Ru/MgO catalyst was thus prepared. After calcining this Ru/MgO catalyst at 500° C. for 5 hours, the Ru/MgO catalyst was reduced at 450° C. for 1 hour with hydrogen gas set to a contact time of 0.0334 g·h/L. The conversion of ammonia was 16.2% at a reaction temperature of 300°C, 48.3% at 400°C, and 99.8% at 600°C.

As shown in Table 1, the ammonia dehydrogenation reaction catalyst produced by the production method according to the present embodiment exhibits high activity even at relatively low temperatures of 300 to 700°C. Since the conversion rate at 600°C is sufficiently high, it is presumed that a high conversion rate can be obtained even at 700°C.

Claims (6)

a carrier containing ceria as a main component;
Ruthenium supported on the carrier;
and wherein the Ce ³⁺ /Ce ⁴⁺ ratio on the surface of the carrier is 0.50 to 1.20. A method for producing an ammonia dehydrogenation reaction catalyst according to claim 1,
an impregnation supporting step of supporting a ruthenium compound as a precursor of an active metal of the catalyst on a catalyst carrier containing ceria as a main component produced by an organic acid method;
A calcining step of calcining the catalyst carrier after the impregnating and supporting step to produce a catalyst;
A method for producing an ammonia dehydrogenation reaction catalyst comprising 3. The method for producing an ammonia dehydrogenation reaction catalyst according to claim 2, further comprising a reduction treatment step of reducing said catalyst after said baking step with a hydrogen-containing gas. The ammonia dehydrogenation reaction catalyst according to claim 1 or the ammonia dehydrogenation reaction catalyst produced by the production method according to claim 2 is subjected to a reduction treatment with a hydrogen-containing gas, and then brought into contact with an ammonia-containing gas. A method for producing hydrogen, wherein hydrogen is produced by A method for producing hydrogen, comprising contacting an ammonia dehydrogenation reaction catalyst produced by the production method according to claim 3 with a gas containing ammonia to produce hydrogen. 6. The method for producing hydrogen according to claim 4 or 5, wherein the gas containing ammonia is a gas recovered after being separated in a refining process of coke oven gas.

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