JP7075794B2 - Manufacturing method of catalyst for ammonia synthesis - Google Patents

Description

The present invention relates to a method for producing a catalyst for synthesizing ammonia.

The Haber-Bosch method, which was developed in the early 20th century, is famous as a method for synthesizing ammonia, and this method is still used industrially in ammonia synthesis plants. Since the catalyst for ammonia synthesis is an important factor that affects the operating conditions and manufacturing efficiency of the plant, it is extremely important to improve its performance. As a catalyst for ammonia synthesis, an iron-based catalyst found by Mittasch is generally used, but in recent years, a ruthenium-based catalyst has also attracted attention (see Non-Patent Document 1).

For example, Patent Document 1 describes a step of mixing a carrier made of a semiconductor containing a transition element and a metal, and a step of firing the mixture obtained in the mixing step in the presence of air to obtain an ammonia synthesis catalyst. A method for producing an ammonia synthesis catalyst, which comprises the above, is disclosed, and in the examples, a ruthenium-based catalyst in which ruthenium is supported on barium titanate is also disclosed.

Patent Document 2 contains (1) ruthenium, an alloy containing ruthenium or a compound containing ruthenium, (2) a compound containing lanthanoid, and (3) a basic cocatalyst and / or a porous metal complex. Is disclosed, and in the examples, a ruthenium-based catalyst in which ruthenium is supported on cerium oxide is also disclosed.

In order to use these catalysts industrially in an ammonia synthesis plant, in addition to the high activity of the catalysts, it is also required to have high mechanical strength so that they can be used for a long period of time under harsh operating conditions. ..

JP-A-2017-148810 Japanese Unexamined Patent Publication No. 2013-11162

"Catalyst Utilization Dictionary" Editorial Committee, First Edition, Mining Research Association Co., Ltd., December 20, 2004, p. 534-535

As in Patent Documents 1 and 2 described above, various catalysts for ruthenium-based ammonia synthesis have been studied, but none have been obtained so far that exhibit satisfactory activity and mechanical strength at a practical level.

The present inventor has diligently studied catalysts containing ruthenium and cerium oxide. As a result, the present inventor has focused on the fact that cerium oxide has the ability to store and release oxygen, and that the crystal lattice of cerium oxide expands and contracts due to changes in the valence of cerium ions accompanying the storage or release of oxygen. It has been found that a catalyst having high mechanical strength can be obtained by producing the catalyst with the minimum expansion and contraction.

Specifically, it is a method for producing a catalyst for ammonia synthesis in which a carrier containing cerium oxide and a carrier containing ruthenium and ruthenium is unevenly distributed on the surface of the carrier containing ruthenium, in which a ruthenium compound is supported on a carrier containing cerium oxide. It has been found that the catalyst obtained through the steps of preparing the catalyst precursor and the step of firing the catalyst precursor in an atmosphere where the oxygen concentration is in the range of 10 to 3000 ppm has high mechanical strength. .. Furthermore, it was also found that when the catalyst obtained through the above steps was used as a catalyst for ammonia synthesis, it exhibited high activity, and the present inventor completed the invention.

The catalyst obtained by using the production method of the present invention has high mechanical strength and exhibits high activity when used as an ammonia synthesis catalyst.

It is a figure for demonstrating the outline of a catalyst. It is a figure for demonstrating the distribution of ruthenium in a catalyst. It is the result of SEM-EDS ray analysis (also called line analysis) which measured the distribution of ruthenium in a catalyst.

The production method of the present invention is a method for producing a catalyst for ammonia synthesis in which a carrier containing cerium oxide and ruthenium are contained and ruthenium is unevenly distributed on the surface of the carrier containing ruthenium, and a ruthenium compound is supported on the carrier containing cerium oxide. The step of preparing the catalyst precursor (hereinafter, also referred to as a precursor preparation step) and the step of calcining the catalyst precursor in the range of oxygen concentration of 10 to 3000 ppm (hereinafter, also referred to as a calcining step). include. The production method of the present invention will be described in detail below.

[material]
As the ruthenium compound used in the production method of the present invention, a conventionally known compound can be used as long as it is a compound containing ruthenium. For example, ruthenium nitrate, ruthenium nitrosyl nitrate, ruthenium chloride and the like can be used. In the production method of the present invention, it is preferable to use ruthenium nitrate such as ruthenium nitrate or ruthenium nitrosyl nitrate.

As the carrier containing cerium oxide used in the production method of the present invention, it is preferable to use a molded product having a size of 1 to 10 mm. In the present invention, the size of the molded body refers to the minor diameter of the molded body. Further, the shape is preferably spherical or columnar. In addition, the shape shall include those conforming to a spherical shape or a columnar shape. For example, even if it is a lotus root-shaped cylinder, it is included in the cylinder, and even if it is a slightly distorted spherical cylinder, it is included in the spherical shape.

The carrier containing cerium oxide in the production method of the present invention may contain a molding aid. For example, the molding aid may contain an organic binder, an inorganic binder, or both. However, such components other than cerium oxide are preferably 10% by mass or less. If the amount of components other than cerium oxide increases, the activity of the finally obtained catalyst may decrease.

The carrier containing cerium oxide can be obtained, for example, by kneading powdered cerium oxide and a molding aid, molding it into a spherical shape, a columnar shape or another shape, and then firing it in the air at a temperature of about 550 ° C. be able to.

[Precursor preparation step]
The precursor preparation step of the present invention is a step of supporting a ruthenium compound on a carrier containing cerium oxide to prepare a catalyst precursor. In the production method of the present invention, for example, an impregnation method can be used as a method for supporting the ruthenium compound on a carrier containing cerium oxide. Specifically, a method of immersing the impregnated solution in which the ruthenium compound is dissolved or dispersed in the solvent in the carrier, a method of spraying the impregnated solution on the carrier, and the like can be used. In the present invention, it is preferable to use the latter method capable of supporting the ruthenium compound on the surface of the carrier. When this method is used, it is easy to prepare a catalyst in which ruthenium is unevenly distributed on the surface of a carrier containing cerium oxide. In the present invention, whether or not ruthenium is unevenly distributed on the surface of the carrier containing cerium oxide can be determined by observing the cross section of the catalyst with an electron microscope. For example, in the case of a catalyst as shown in FIG. 1, when determining whether or not ruthenium is unevenly distributed on the surface of a carrier containing cerium oxide, first, the cross section of the catalyst is observed with an electron microscope. Next, a ruthenium ray analysis is performed with an electron beam microanalyzer so that the cross section of the catalyst is completely within the viewing angle and passes through the center of the catalyst. At this time, the distance from the surface of the catalyst to the center is r, the strength of the distance r from the surface (that is, the strength of the center) is I ₁ , and the strength of the distance 0.1 r from both surfaces is I ₂ and I ₃ respectively. If 2I ₁ ≤ I ₂ and 2I ₁ ≤ I ₃ , it can be determined that ruthenium is unevenly distributed on the surface of the carrier containing cerium oxide (FIG. 2). According to this criterion, if ruthenium is present only in the range of 0.1r or less from the surface of the catalyst, ruthenium will not be unevenly distributed. However, a catalyst in which ruthenium is extremely present only on the surface side of the catalyst is excluded from the technical scope of the present invention because its catalytic activity tends to decrease (for example, comparison). Example 4). A specific measurement method will be described later in Examples.

The amount of the ruthenium compound supported in this step is preferably such that the content of ruthenium is in the range of 1 to 10% by mass with respect to the total weight of the catalyst finally obtained. It is more preferable that the loading amount is in the range of 5% by mass. If the ruthenium content is too low relative to the total weight of the finally obtained catalyst, the activity may decrease when used as a catalyst for ammonia synthesis. Further, since ruthenium is an expensive precious metal, it is not preferable that the content of ruthenium is too large with respect to the total weight of the finally obtained catalyst because the cost of the catalyst is high.

When the impregnation method is used as a method for supporting the ruthenium compound, it is preferable to impregnate the carrier with an impregnating solution containing the ruthenium compound in the range of 10 to 70% by volume with respect to the water absorption amount of the carrier, preferably 20 to 60% by volume. It is more preferable to impregnate the carrier in the range. In the present invention, the water absorption amount of the carrier represents the volume of water that can be absorbed by the carrier per unit weight, and can be determined by the method of Examples described later. By impregnating the carrier with the impregnating liquid in a range lower than the water absorption of the carrier in this way, it becomes easier to support the ruthenium compound on the surface of the carrier. At this time, the concentration of the ruthenium compound contained in the impregnating solution may be appropriately adjusted according to the target loading amount of the ruthenium compound.

When the impregnation method is used as a method for supporting the ruthenium compound, the initial drying rate (drying rate from the start of drying to 5 minutes after the start of drying) is 0. It is preferable to dry under reduced pressure so that the solvent is removed from the impregnated carrier so as to be in the range of 05 to 0.3 ml / g-impregnated carrier / Hr, and 0.05 to 0.15 ml / g-impregnated carrier / Hr. It is more preferable to dry under reduced pressure so as to be within the range. In particular, if the initial drying rate is too fast, the ruthenium compound may aggregate and the ruthenium dispersity of the finally obtained catalyst may decrease, which is not preferable. By controlling the initial drying rate, the distribution state of the ruthenium compound can be controlled to some extent. For example, by increasing the initial drying rate, the ruthenium compound inside the impregnated carrier can be moved closer to the surface thereof. The initial drying rate can be controlled by the drying temperature and pressure as in the examples.

When a nitrate such as ruthenium nitrate or ruthenium nitrosyl nitrate is used as the raw material ruthenium compound, the drying temperature at the time of vacuum drying is preferably 100 ° C. or lower. If the drying temperature is 100 ° C. or lower, a large amount of nitrate-derived nitrogen can be left in the catalyst precursor. When such a catalyst precursor is calcined in the firing step described later, the dispersity of ruthenium in the finally obtained catalyst is increased, and the catalytic activity thereof is also improved. The amount of nitrate-derived nitrogen contained in the catalyst precursor is preferably 60% or more remaining with respect to the amount of nitrate contained in the raw material ruthenium compound.

[Baking process]
The firing step of the present invention is a step of firing the catalyst precursor prepared in the precursor preparation step in an atmosphere in which the oxygen concentration is in the range of 10 to 3000 ppm (volume basis, that is, ppmv). The purpose of this step is to calcin the catalyst precursor to decompose (oxidize) the ruthenium compound contained in the catalyst precursor into ruthenium oxide.

The atmosphere when the ruthenium compound is fired is generally, for example, an air atmosphere as in Patent Document 1 or an inert atmosphere such as He as in Patent Document 2. On the other hand, in the production method of the present invention, a catalyst precursor in which a ruthenium compound is supported on a carrier containing cerium oxide is prepared, and then the catalyst precursor is calcined in an atmosphere in which the oxygen concentration is in the range of 10 to 3000 ppm. This is intended to minimize the expansion and contraction of cerium oxide contained in the carrier, in addition to the above-mentioned purpose.

In general, cerium oxide absorbs oxygen in an oxidizing atmosphere because the difference in redox potential between Ce ³⁺ and Ce ⁴⁺ is relatively small at 1.61 V and the redox reaction occurs easily and reversibly. However, it is known that it exhibits an oxygen storage and release ability to release oxygen in an inert atmosphere without oxygen (formula (1) below).
CeO ₂ ⇔ CeO _(2-x) + x / 2O ₂ ... (1)
That is, cerium oxide releases oxygen with a change in the valence of Ce ⁴⁺ → Ce ³⁺ in an oxygen-free inert atmosphere, and changes in the valence of Ce ³⁺ → Ce ⁴⁺ in an oxygen-containing oxidizing atmosphere. Accompanied by storing oxygen. Here, it is considered that the crystal lattice of cerium oxide expands and contracts with the change in the valence of the above-mentioned cerium ion. According to the report of Shannon (Shannon et al., Acta A, 32 (1976) 751), the ionic radius (8 coordination) of Ce ⁴⁺ is 0.97 Å, whereas the ionic radius of Ce ³⁺ (Ce 3+ is The 8-coordination) is 1.143 Å, which is about 18% different between Ce ³⁺ and Ce ⁴⁺ . Comparing this in terms of volume, Ce ³⁺ and Ce ⁴⁺ are different by about 28%. When the crystal structure of cerium oxide expands and contracts due to such a change in the valence of cerium ions, the cerium oxide contained in the carrier also expands and contracts in the same manner. It is considered that the mechanical strength of the obtained catalyst is lowered. For example, when a carrier containing cerium oxide is fired in an inert atmosphere, the cerium oxide contained in the carrier releases oxygen and cerium ions change from Ce ⁴⁺ to Ce ³⁺ and expand. When this is suddenly exposed to an oxygen-rich atmosphere after the firing is completed, the cerium oxide contained in the carrier occludes oxygen, and Ce ³⁺ changes to Ce ⁴⁺ and contracts rapidly. It is considered that the catalyst finally obtained is stressed by such expansion and contraction of cerium oxide, and the mechanical strength is lowered. As a method of firing without desorbing oxygen from cerium oxide, it is effective to fire in an oxygen-rich atmosphere such as firing in air, but the ruthenium oxide as in the production method of the present invention. In addition, when a substance containing a ruthenium compound is fired in an oxygen-rich state, a problem such as a part of the ruthenium compound becoming RuO ₄ (boiling point: 40 ° C.) and volatilizing occurs. Therefore, in the production method of the present invention, it is important to fire the catalyst precursor containing the cerium oxide and the ruthenium compound in an atmosphere in which oxygen is present at a low concentration, that is, in an atmosphere in which the oxygen concentration is in the range of 10 to 3000 ppm. ..

Furthermore, it was also found that when the catalyst precursor containing cerium oxide and the ruthenium compound is fired under such conditions, the dispersity of ruthenium contained in the finally obtained catalyst is increased. This is because when the ligand is removed from the ruthenium compound in an atmosphere where oxygen is present at a low concentration, ruthenium and cerium oxide are bound to each other via oxygen released from cerium oxide, and ruthenium is fixed on the surface of cerium oxide. It is thought that this made it difficult for ruthenium to aggregate. Since oxygen needs to be appropriately present on the surface of cerium oxide in order to form such a bonded state, in the present invention, the ruthenium compound is segregated on the surface layer of a carrier having good oxygen diffusion.

The atmosphere in this step preferably has an oxygen concentration in the range of 200 to 3000 ppm, more preferably in the range of 500 to 3000 ppm. When the oxygen concentration is in such a range, the mechanical strength of the final catalyst tends to be higher. In the present invention, the oxygen concentration shall be analyzed using a zirconia oxygen concentration meter. In this step, in order to maintain such an atmosphere, it is preferable to bake while flowing a gas having an oxygen concentration in the above range, and the flow rate is adjusted to be 1000 to 10000 Hr ^-1 in terms of SV. Is preferable. In this way, by firing while flowing a gas having a constant oxygen concentration (oxygen partial pressure), excessive desorption of oxygen from cerium oxide is suppressed.

In this step, the firing temperature is preferably in the range of 200 to 500 ° C, more preferably in the range of 250 to 350 ° C. Within such a firing temperature range, even if oxygen is desorbed from cerium oxide, oxygen in the atmosphere is occluded, so that oxygen is not substantially desorbed from cerium oxide. On the other hand, if the firing temperature is too high, the amount of oxygen desorbed from cerium oxide may be larger than the amount of oxygen occluded from the atmosphere, which is not preferable, although it depends on the oxygen concentration in the atmosphere. Further, even if the firing temperature is too low, the ruthenium compound may not be decomposed into ruthenium oxide, which is not preferable.

The firing time is preferably in the range of about 1 to 24 hours, although it depends on the amount of the catalyst precursor charged. Further, the rate of temperature rise until the firing temperature is reached is preferably in the range of 50 to 200 ° C./Hr. If the temperature rise rate is too fast, the ruthenium compound is rapidly decomposed to generate gas, and the internal pressure may damage the catalyst. Further, if the temperature rise rate is too low, the productivity will be low, so it is preferable to raise the temperature within the range of the temperature rise rate described above.

[Catalyst for ammonia synthesis]
The finally obtained catalyst for ammonia synthesis is a state in which ruthenium oxide is supported on a carrier containing cerium oxide. However, since it does not function as a catalyst for ammonia synthesis in the state of ruthenium oxide, it is reduced to hydrogen at a temperature in the range of 100 to 500 ° C. and then used as a catalyst for ammonia synthesis. However, since ammonia synthesis is carried out at a high temperature in a hydrogen atmosphere, such hydrogen reduction treatment may be omitted. When ruthenium oxide is reduced, a part of Ce ⁴⁺ contained in cerium oxide is reduced to generate Ce ³⁺ and the catalyst expands, but Ce ³⁺ is changed to Ce ⁴ during the ammonia synthesis reaction. Since it is hardly oxidized to ⁺ and shrinks, it is considered that the mechanical strength of the catalyst during the reaction does not decrease.

Ammonia synthesis proceeds, for example, by bringing a raw material gas containing nitrogen gas and hydrogen gas into contact with the above-mentioned catalyst for ammonia synthesis. The reaction conditions are preferably a temperature in the range of 200 to 500 ° C. and a pressure in the range of 1 to 50 MPa. Further, the ratio (volume ratio) of nitrogen and hydrogen in the raw material gas is preferably in the range of 1:10 to 10: 1. Under such conditions, ammonia can be efficiently synthesized by using the above-mentioned catalyst for ammonia synthesis.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

The measurement and evaluation conditions performed in the examples of the present invention are shown below.
(Water absorption of carrier)
About 20 g of the carrier was immersed in 100 ml of pure water for 1 hour. Then, the carrier was taken out, the surface was wiped off, and the weight of the carrier after immersion was measured. Using this value, the water absorption of the carrier was calculated from the following equation (1). The weight per unit volume of pure water was 1 g / ml.
Water absorption of carrier [ml / g-carrier] = (weight of carrier after immersion-weight of carrier before immersion) / weight of carrier before immersion ... (1)

(Initial drying speed)
The weight of the impregnated carrier before vacuum drying and the weight of the impregnated carrier 5 minutes after the start of vacuum drying were measured, and the initial drying rate was calculated from the following equation (2).
Initial drying rate [ml / g-impregnated carrier / Hr] = (weight of impregnated carrier before vacuum drying-5 minutes after impregnated carrier weight) / weight of impregnated carrier before vacuum drying / (5/60) ... (2)

(Nitrogen content in catalyst precursor)
The catalyst precursor was suspended in ion-exchanged water and Devarda alloy to obtain a slurry. At this time, the nitrogen content contained in the catalyst precursor is reduced by the Devarda alloy to become ammonia, which is present in the slurry. Ammonia contained in this slurry was distilled with a distillation apparatus, and the separated ammonia was trapped with distilled water. The distilled water was diluted to an appropriate concentration and subjected to neutralization titration using hydrochloric acid having a known concentration. The content of nitrogen contained in the catalyst precursor was calculated from the weight of the catalyst precursor used and the neutralization titration value.

(Distribution of ruthenium in the catalyst)
After cutting the columnar catalyst into round slices, the cross section was observed using an electron microscope (S-5500, manufactured by Hitachi, Ltd.) and line-analyzed by EDS. This analysis was performed on at least 12 or more lines passing through the center of the catalyst. Taking the distance from the surface of the catalyst to the center as r, the intensities I ₁ at a distance r from the surface and the intensities I ₂ and I ₃ at a distance of 0.1 r from both surfaces were calculated.

(Ruthenium content)
The catalyst, sodium peroxide and sodium hydroxide ground in a mortar were mixed in a crucible and melted. Then, the melt in the crucible was dissolved with hydrochloric acid, diluted to an appropriate concentration, and then the ruthenium concentration was measured with an ICP emission spectroscopic analyzer. The ruthenium content of the catalyst was calculated from the weight of the catalyst used and the measured ruthenium concentration.

(Ruthenium dispersion)
T. Takeguchi, W.M. Measurements were carried out with reference to Ueda ,, Applied Catalysis A: General, 293 (2005), 91.
Specifically, about 0.2 g of the catalyst was precisely weighed and filled in the reaction tube. Then, the pretreatment was carried out by the following procedure.
It was kept at 300 ° C. for 30 minutes under 1st: O ₂ / He (O ₂ : 5 vol%) distribution.
It was held at 50 ° C. for 10 minutes under 2nd: He distribution.
It was kept at 400 ° C. for 10 minutes under 3rd: H ₂ / Ar (H ₂ : 15 vol%) distribution.
4th: Under He distribution, the mixture was kept at 50 ° C. for 10 minutes.
It was kept at 50 ° C. for 10 minutes under 5th: O ₂ / He (O ₂ : 5 vol%) distribution.
It was kept at 50 ° C. for 60 minutes under 6th: CO ₂ / He (He: 10vol%) distribution.
7th: Under He distribution, the mixture was kept at 50 ° C. for 5 minutes.
It was kept at 50 ° C. for 10 minutes under 8th: H ₂ / Ar (H ₂ : 15 vol%) distribution.
It was held at 50 ° C. for 20 minutes under 9th: He distribution.
Then, a gas having a CO concentration of 15 vol% was introduced into the reaction tube by a pulse, and the CO concentration at the outlet was measured by TPD-Mass (Nippon Bell Co., Ltd., BEL-CAT). The introduction of the pulse was terminated when there was no change in the CO concentration at the inlet and outlet. The amount of CO adsorbed on the catalyst is calculated from the difference between the CO concentration at the inlet and the CO concentration at the outlet for each pulse, and this is integrated until the introduction of the pulse is completed to calculate the amount of CO adsorbed on the catalyst. did. The ruthenium dispersity was calculated from the following equation (4) using the weight of the catalyst used, the ruthenium content, the ruthenium atomic weight, and the amount of CO adsorbed on the catalyst.
Ruthenium dispersion = (VCHEM x SF / 22414 x MW) / c x 100 ... (4)
VCHEM: CO adsorption amount [cm ³ ]
MW: Metal atomic weight [g / mol] (Ru = 101.07)
m: Sample weight [g]
SF: 1 (assuming that one molecule of CO is adsorbed for one Ru1 atom)
c: Metal weight (weight of metal supported on the sample) [g]
c = m × p / 100
p: Supported metal content [wt%]

(Mechanical strength)
Twenty grains were randomly sampled from the entire catalyst. Next, for this one catalyst grain, the fracture strength in the direction perpendicular to the diameter of the catalyst was measured using a load cell type fracture strength meter (model 3365 manufactured by Instron). This was repeated for 20 grains, and the average value of the strength was taken as the mechanical strength.

(Activity test)
The reaction tube was filled with 5.86 ml of the catalyst and set in a high pressure reaction test apparatus. The inside of the reaction tube was replaced with nitrogen, then replaced with hydrogen, and the temperature was raised to 460 ° C. with hydrogen flowing at GHSV = 6000 (1 / Hr), and pretreatment reduction of 60 Hr was carried out. After the pretreatment reduction was completed, the mixture was cooled to 400 ° C., and the pressure was increased to 3 MPa while circulating a gas of H ₂ : N ₂ = 3: 1 equivalent to GHSV = 3000 (1 / Hr). _When the temperature and pressure became stable, the H2 concentration of the gas at the inlet of the reaction tube and the H2 concentration of the gas at the outlet of the reaction tube _were measured with a gas chromatograph (GC3200 manufactured by GL Sciences). From this concentration and flow rate, the inlet hydrogen flow rate (InletH ₂ ) and the outlet hydrogen flow rate (OutletH ₂ ) were calculated. Using this value, the hydrogen conversion rate was calculated from the following equation (5), and this was used as an index of activity.
Hydrogen conversion rate [%] = (InletH ₂ [mmol / Hr] -OutletH ₂ [mmol / Hr]) / (InletH ₂ [mmol / Hr]) × 100 ... (5)

[Example 1]
After mixing the powder of cerium oxide (manufactured by Daiichi Rare Element Chemical Industry Co., Ltd., product number: Z-3117) and an organic binder, this was tablet-molded into a columnar shape of 3.2 mmφ-3.2 mmH. This was calcined in the air at a temperature of 550 ° C. to prepare a carrier containing cerium oxide. The water absorption of this carrier was 0.2 ml / g-carrier. An impregnated solution obtained by diluting a ruthenium nitrosyl nitrate solution (manufactured by Furuya Metal Co., Ltd.) with pure water on a carrier in a rolled state has a ruthenium content of 3 with respect to the total weight of the finally obtained catalyst. An impregnated carrier was obtained by spray impregnation so as to have a mass%. At this time, the volume of the impregnating liquid impregnated with the carrier by spraying was 50% with respect to the amount of water absorbed by the carrier. This impregnated carrier was dried under reduced pressure using a rotary evaporator while adjusting the pressure (vacuum degree) and the drying temperature so that the initial drying rate was 0.1 ml / g-impregnated carrier · Hr. At this time, the drying temperature was adjusted so as not to exceed 50 ° C., and the degree of vacuum was adjusted to be 5 kPa or less. Finally, when the weight loss of the impregnated carrier disappeared, the vacuum drying was completed. The content of nitrogen (derived from ruthenium nitrosyl nitrate) contained in the catalyst precursor obtained by vacuum drying was 81% with respect to the ratio of nitrogen contained in ruthenium nitrosyl nitrate charged as a raw material. Here, the amount of nitrogen contained in ruthenium nitrosyl nitrate charged as a raw material was calculated from the purity and chemical formula of ruthenium nitrosyl nitrate. This catalyst precursor was charged into a tube furnace and calcined at 300 ° C. for 5 hours while flowing a gas in which oxygen and nitrogen were mixed so that the oxygen concentration became 10 ppm. At this time, the rate of temperature rise was 100 ° C./Hr. The finally obtained catalyst was tested for ruthenium content, ruthenium dispersity and activity. In addition, the distribution of ruthenium in the catalyst was measured. The results are shown in Table 1. Further, FIG. 3 shows an electron micrograph when measuring the distribution state of ruthenium and the result of line analysis of ruthenium by EDS.

[Example 2]
A catalyst was prepared in the same manner as in Example 1 except that the catalyst was dried under reduced pressure while adjusting the degree of vacuum and the drying temperature so that the initial drying rate was 0.08 ml / g-impregnated carrier · Hr. The obtained catalyst was also evaluated by the same method as in Example 1.

[Example 3]
A catalyst was prepared in the same manner as in Example 1 except that the catalyst was dried under reduced pressure while adjusting the degree of vacuum and the drying temperature so that the initial drying rate was 0.13 ml / g-impregnated carrier · Hr. The obtained catalyst was also evaluated by the same method as in Example 1.

[Example 4]
A catalyst was prepared in the same manner as in Example 1 except that a gas in which oxygen and nitrogen were mixed was circulated so that the oxygen concentration became 3000 ppm when the catalyst precursor was calcined. The obtained catalyst was also evaluated by the same method as in Example 1.

[Example 5]
A catalyst was prepared in the same manner as in Example 1 except that ruthenium nitrate (manufactured by Furuya Metals Co., Ltd.) was used as a ruthenium compound. The obtained catalyst was also evaluated by the same method as in Example 1.

[Example 6]
A catalyst was prepared in the same manner as in Example 1 except that ruthenium chloride (manufactured by Furuya Metals Co., Ltd.) was used as a ruthenium compound. The obtained catalyst was also evaluated by the same method as in Example 1.

[Example 7]
A catalyst was prepared in the same manner as in Example 1 except that a gas in which oxygen and nitrogen were mixed was circulated so that the oxygen concentration became 1000 ppm when the catalyst precursor was calcined. The obtained catalyst was also evaluated by the same method as in Example 1.

[Example 8]
Using a blower-type dryer, the impregnated carrier was dried under normal pressure at 120 ° C. so that the initial drying rate was 0.17 ml / g-impregnated carrier · Hr, except that the impregnated carrier was dried by the same method as in Example 1. A catalyst was prepared. The obtained catalyst was also evaluated by the same method as in Example 1.

[Comparative Example 1]
A catalyst was prepared in the same manner as in Example 1 except that a gas in which oxygen and nitrogen were mixed was circulated so that the oxygen concentration became 1% (10000 ppm) at the time of firing the catalyst precursor. The obtained catalyst was also evaluated by the same method as in Example 1.

[Comparative Example 2]
A catalyst was prepared in the same manner as in Example 1 except that the catalyst precursor was circulated in the atmosphere at the time of firing. The obtained catalyst was also evaluated by the same method as in Example 1.

[Comparative Example 3]
A catalyst was prepared in the same manner as in Example 1 except that a gas in which oxygen and nitrogen were mixed was circulated so that the oxygen concentration became 5 ppm at the time of firing the catalyst precursor. The obtained catalyst was also evaluated by the same method as in Example 1.

[Comparative Example 4]
A catalyst was prepared in the same manner as in Example 1 except that the catalyst was dried under reduced pressure while adjusting the degree of vacuum and the drying temperature so that the initial drying rate was 0.4 ml / g-impregnated carrier · Hr. The obtained catalyst was also evaluated by the same method as in Example 1. In this catalyst, ruthenium was extremely unevenly distributed on the surface of the catalyst.

[Comparative Example 5]
A catalyst was prepared in the same manner as in Example 1 except that the volume of the impregnating solution impregnated with the carrier by spraying was 100% with respect to the water absorption of the carrier. The obtained catalyst was also evaluated by the same method as in Example 1.

Claims (3)

A beam analysis of ruthenium was performed with an electron beam microanalyzer so that ruthenium passes through the center of the catalyst at a magnification that allows the cross section of the catalyst to enter the viewing angle on the surface of the carrier containing cerium oxide and the carrier containing ruthenium. 2 I ₁ ≤ I when the distance from the surface of the catalyst to the center is r, the strength of the distance r from the surface is I ₁ , and the strength of the distance 0.1 r from both surfaces is I ₂ and I ₃ , respectively. It is a method for producing a catalyst for ammonia synthesis that is unevenly distributed so that ₂ and 2 I ₁ ≤ I ₃ are present.
After impregnating the carrier with an impregnating solution containing a ruthenium compound in the range of 10 to 70% by volume based on the water absorption of the carrier to prepare the impregnated carrier, the initial drying rate is 5 minutes after the start of drying. The ruthenium compound is supported on the carrier containing cerium oxide by drying under reduced pressure so that the solvent is removed from the impregnated carrier so that the drying rate is in the range of 0.05 to 0.3 ml / g-impregnated carrier / Hr. And the process of preparing the catalyst precursor
The step of calcining the catalyst precursor in an atmosphere where the oxygen concentration is in the range of 10 to 3000 ppm, and
A method for producing a catalyst for ammonia synthesis including. The method for producing a catalyst for ammonia synthesis according to claim 1, wherein in the step of preparing the catalyst precursor, the impregnated solution containing the ruthenium compound is spray-supported on the carrier containing cerium oxide to prepare the impregnated carrier. .. In the step of preparing the catalyst precursor, a nitrate of ruthenium is used as a raw material, and the content of nitrogen contained in the catalyst precursor is 60% or more with respect to the content of nitrogen contained in the nitrate of ruthenium used as a raw material. The method for producing a catalyst for ammonia synthesis according to claim 1 or 2.

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