阅读说明：本技术 氨合成催化剂结构体及其制造方法、氨合成装置以及氨的合成方法 (Ammonia synthesis catalyst structure, method for producing same, ammonia synthesis apparatus, and method for synthesizing ammonia ) 是由 增田隆夫 中坂佑太 吉川琢也 加藤祯宏 福岛将行 高桥寻子 马场祐一郎 关根可织 于 2018-05-31 设计创作，主要内容包括：本发明提供一种能抑制催化活性降低而实现寿命延长的氨合成催化剂结构体及其制造方法、氨合成装置以及氨的合成方法。氨合成催化剂结构体(1)具备：多孔质结构的载体(10),由沸石型化合物构成；以及至少一种包含金属的平均粒径为0.7nm～5nm的氨合成催化剂物质,存在于所述载体(10)内,所述载体(10)具有相互连通的、平均内径为0.50nm～0.64nm的通道(11),所述氨合成催化剂物质存在于所述载体(10)的至少所述通道(11)。(The invention provides an ammonia synthesis catalyst structure which can inhibit the reduction of catalytic activity and prolong the service life, a manufacturing method thereof, an ammonia synthesis device and an ammonia synthesis method. An ammonia synthesis catalyst structure (1) is provided with: a porous support (10) composed of a zeolite-type compound; and at least one ammonia synthesis catalyst substance comprising a metal and having an average particle diameter of 0.7nm to 5nm, present in the support (10), the support (10) having interconnected channels (11) having an average inner diameter of 0.50nm to 0.64nm, the ammonia synthesis catalyst substance being present in at least the channels (11) of the support (10).)

1. An ammonia synthesis catalyst structure comprising:

a porous support composed of a zeolite-type compound; and

at least one metal-containing ammonia synthesis catalyst material having an average particle diameter of 0.7nm to 5nm, present in the support,

the carrier is provided with channels which are mutually communicated and have the average inner diameter of 0.50nm to 0.64nm,

the ammonia synthesis catalyst species is present in at least the channels of the support.

2. The ammonia synthesis catalyst structure according to claim 1,

the channel has: any one of one-dimensional pores, two-dimensional pores, and three-dimensional pores defined by the framework structure of the zeolite-type compound; and a diameter expanding portion that is different from any of the one-dimensional hole, the two-dimensional hole, and the three-dimensional hole, and that expands the diameter of the hole

The ammonia synthesis catalyst substance is present at least in the diameter-enlarged portion.

3. The ammonia synthesis catalyst structure according to claim 2,

the diameter expanding portion communicates a plurality of holes constituting any one of the one-dimensional hole, the two-dimensional hole, and the three-dimensional hole with each other.

4. The ammonia synthesis catalyst structure according to claim 2 or 3,

the ammonia synthesis catalyst material is a metal particulate.

5. The ammonia synthesis catalyst structure according to claim 4,

the metal fine particles are at least one metal selected from the group consisting of Mo, W, Re, Fe, Co, Ru, Os, Cr, Mn, Tc, and Rh.

6. Ammonia synthesis catalyst structure according to claim 4 or 5,

the metal element (M) of the metal fine particles is contained in an amount of 0.5 to 2.5 mass% relative to the ammonia synthesis catalyst structure.

7. The ammonia synthesis catalyst structure according to any one of claims 4 to 6,

the metal fine particles have an average particle diameter not larger than the inner diameter of the enlarged diameter portion.

8. Ammonia synthesis catalyst structure according to any one of claims 4 to 7,

the ratio of the average particle diameter of the metal fine particles to the average inner diameter of the channel is 1.2 to 10.

9. The ammonia synthesis catalyst structure according to claim 8,

the ratio of the average particle diameter of the metal fine particles to the average inner diameter of the channel is 1.3 to 8.

10. The ammonia synthesis catalyst structure according to claim 9,

the ratio of the average particle diameter of the metal fine particles to the average inner diameter of the channel is 1.4 to 3.6.

11. The ammonia synthesis catalyst structure according to any one of claims 2 to 10,

the inner diameter of the diameter-expanded portion is 0.7nm to 50 nm.

12. The ammonia synthesis catalyst structure according to any one of claims 1 to 11,

further comprising at least one other ammonia synthesis catalyst material retained on the outer surface of the support.

13. The ammonia synthesis catalyst structure according to claim 12,

the at least one ammonia synthesis catalyst species is present in the support in an amount greater than the amount of the at least one other ammonia synthesis catalyst species retained on the outer surface of the support.

14. The ammonia synthesis catalyst structure according to any one of claims 1 to 13,

the zeolite-type compound is a silicate compound.

15. An ammonia synthesis apparatus comprising the ammonia synthesis catalyst structure according to any one of claims 1 to 14.

16. A method for producing an ammonia synthesis catalyst structure, comprising:

a firing step of firing a precursor material (B) obtained by impregnating a precursor material (a) with a metal-containing solution, the precursor material (a) being used for obtaining a support having a porous structure made of a zeolite-type compound;

a hydrothermal treatment step of subjecting a precursor material (C) obtained by firing the precursor material (B) to hydrothermal treatment; and

and a step of subjecting the precursor material (C) after the hydrothermal treatment to a reduction treatment.

17. The method of producing an ammonia synthesis catalyst structure according to claim 16,

before the firing step, 50 to 500 mass% of a nonionic surfactant is added to the precursor material (A).

18. The method of producing an ammonia synthesis catalyst structure according to claim 16 or 17,

the metal-containing solution is added to the precursor material (a) in a plurality of portions before the firing step, whereby the precursor material (a) is impregnated with the metal-containing solution.

19. The method for producing an ammonia synthesis catalyst structure according to any one of claims 16 to 18,

when the precursor material (A) is immersed in the metal-containing solution before the firing step, the amount of the metal-containing solution added to the precursor material (A) is adjusted so that the atomic ratio Si/M, which is the ratio of silicon (Si) constituting the precursor material (A) to the metal element (M) contained in the metal-containing solution added to the precursor material (A), is 10 to 1000.

20. The method of producing an ammonia synthesis catalyst structure according to claim 16,

in the hydrothermal treatment step, the precursor material (C) is mixed with a structure-directing agent.

21. The method of producing an ammonia synthesis catalyst structure according to claim 16,

the hydrothermal treatment step is performed in an alkaline environment.

22. A method for synthesizing ammonia, characterized in that ammonia is synthesized from nitrogen and hydrogen using a catalyst,

the catalyst comprises an ammonia synthesis catalyst structure,

the ammonia synthesis catalyst structure comprises:

a porous support composed of a zeolite-type compound; and

at least one ammonia synthesis catalyst species present within the support,

the carrier has channels that are in communication with each other,

the ammonia synthesis catalyst substance is present in at least the expanded diameter portion of the channels of the carrier.

23. A method for synthesizing ammonia is characterized in that,

ammonia is synthesized from nitrogen and water using the ammonia synthesis catalyst structure of any one of claims 1 to 14.

24. A method for synthesizing ammonia is characterized in that,

use of the ammonia plant of claim 15 to convert nitrogen and hydrogen to ammonia.

Technical Field

The present invention relates to an ammonia synthesis catalyst structure including a porous support and an ammonia synthesis catalyst substance such as metal fine particles, a method for producing the ammonia synthesis catalyst structure, an ammonia synthesis apparatus, and a method for synthesizing ammonia.

Background

Ammonia is an essential compound for grain production as a raw material for artificial fertilizers such as ammonium sulfate and urea fertilizers. As a method for synthesizing ammonia, a Haber-Bosch (Haber-Bosch) method is known. The haber-bosch method directly reacts a mixed gas of nitrogen and hydrogen at 400 to 600 ℃ and 20 to 100 MPa. In addition, in the Haber-Bosch process, Fe is used₃O₄An iron-based catalyst as a main component. In order to satisfy the above-mentioned high-temperature and high-pressure conditions required by the Haber-Bosch process, the ammonia synthesis apparatus is required to have heat resistance and pressure resistance, becauseThis ammonia synthesis apparatus is complicated. In order to avoid the complication of the ammonia synthesis apparatus, an ammonia synthesis process capable of being carried out under low-temperature and low-pressure conditions is required.

Therefore, as an ammonia synthesis method that can be performed under low-temperature and low-pressure conditions, there have been proposed: one metal selected from the group consisting of Mo, W, Re, Fe, Co, Ru, and Os or a combination of metals selected from the group consisting of Fe and Ru, Ru and Re, and Fe and Mo is used as an ammonia synthesis catalyst (patent document 1).

Further, patent document 1 discloses: in an ammonia synthesis process which can be carried out under low temperature and low pressure conditions, an ammonia synthesis catalyst is also carried out in combination with a carrier to enhance the activity. As the above-mentioned vector, for example, there can be used: magnesium oxide, aluminum oxide, graphite, cerium, magnesia (magnesia), and the like.

Disclosure of Invention

Problems to be solved by the invention

However, in the catalyst structure described above, since the catalyst particles are supported on the surface of the carrier or in the vicinity of the surface of the carrier, the catalyst particles move in the carrier due to the influence of force, heat, and the like received from the fluid containing the raw material in ammonia synthesis, and aggregation (sintering) between the catalyst particles is likely to occur. When the aggregation of the catalyst particles occurs, the effective surface area of the catalyst decreases to lower the catalytic activity, and the life is shorter than usual, and therefore, the catalyst structure itself must be replaced and regenerated in a short period of time, which causes a problem that the replacement operation is complicated and the resource saving cannot be achieved.

An object of the present invention is to provide an ammonia synthesis catalyst structure, a method for producing the same, an ammonia synthesis apparatus, and a method for synthesizing ammonia, which can suppress a decrease in catalytic activity and prolong the life.

Technical scheme

As a result of intensive studies to achieve the above object, the present inventors have found the following facts, and have completed the present invention based on the findings, and have obtained an ammonia synthesis catalyst structure comprising: a porous support composed of a zeolite-type compound; and at least one metal-containing ammonia synthesis catalyst substance present in the carrier, the carrier having mutually communicating channels, the ammonia synthesis catalyst substance being present in at least the channels of the carrier, whereby a decrease in catalytic activity of the ammonia synthesis catalyst substance can be suppressed, and a prolonged life can be achieved.

That is, the gist of the present invention is as follows.

[1] An ammonia synthesis catalyst structure comprising: a porous support composed of a zeolite-type compound; and at least one metal-containing ammonia synthesis catalyst substance having an average particle diameter of 0.7nm to 5nm, which is present in the carrier, the carrier having mutually communicating channels having an average inner diameter of 0.50nm to 0.64nm, the ammonia synthesis catalyst substance being present in at least the channels of the carrier.

[2] The ammonia synthesis catalyst structure according to [1], wherein the channels have: any one of one-dimensional pores, two-dimensional pores, and three-dimensional pores defined by the framework structure of the zeolite-type compound; and an expanded diameter portion that is different from any of the one-dimensional pores, the two-dimensional pores, and the three-dimensional pores, and in which the ammonia synthesis catalyst substance is present at least in the expanded diameter portion.

[3] The ammonia synthesis catalyst structure according to [2], wherein the diameter-enlarged portion connects a plurality of pores constituting any one of the one-dimensional pores, the two-dimensional pores, and the three-dimensional pores to each other.

[4] The ammonia synthesis catalyst structure according to [2] or [3], wherein the ammonia synthesis catalyst substance is a fine metal particle.

[5] The ammonia synthesis catalyst structure according to [4], wherein the fine metal particles are at least one metal selected from the group consisting of Mo, W, Re, Fe, Co, Ru, Os, Cr, Mn, Tc and Rh.

[6] The ammonia synthesis catalyst structure according to [4] or [5], wherein the metal element (M) of the metal fine particles is contained in an amount of 0.5 to 2.5 mass% based on the ammonia synthesis catalyst structure.

[7] The ammonia synthesis catalyst structure according to any one of [4] to [6], wherein the average particle diameter of the fine metal particles is equal to or smaller than the inner diameter of the enlarged diameter portion.

[8] The ammonia synthesis catalyst structure according to any one of [4] to [7], wherein a ratio of an average particle diameter of the fine metal particles to an average inner diameter of the channels is 1.2 to 10.

[9] The ammonia synthesis catalyst structure according to item [8], wherein the ratio of the average particle diameter of the fine metal particles to the average inner diameter of the channels is 1.3 to 8.

[10] The ammonia synthesis catalyst structure according to item [9], wherein the ratio of the average particle diameter of the fine metal particles to the average inner diameter of the channels is 1.4 to 3.6.

[11] The ammonia synthesis catalyst structure according to any one of [2] to [10], wherein the inside diameter of the expanded diameter portion is 0.7nm to 50 nm.

[12] The ammonia synthesis catalyst structure according to any one of [1] to [11], further comprising at least one other ammonia synthesis catalyst substance held on the outer surface of the carrier.

[13] The ammonia synthesis catalyst structure according to [12], wherein the at least one ammonia synthesis catalyst substance is present in the carrier in a larger amount than the at least one other ammonia synthesis catalyst substance retained on the outer surface of the carrier.

[14] The ammonia synthesis catalyst structure according to any one of [1] to [13], wherein the zeolite-type compound is a silicate compound.

[15] An ammonia synthesis apparatus having the ammonia synthesis catalyst structure according to any one of [1] to [14 ].

[16] A method for producing an ammonia synthesis catalyst structure, comprising: a firing step of firing a precursor material (B) obtained by impregnating a precursor material (a) with a metal-containing solution, the precursor material (a) being used for obtaining a support having a porous structure made of a zeolite-type compound; a hydrothermal treatment step of subjecting a precursor material (C) obtained by firing the precursor material (B) to hydrothermal treatment; and a step of subjecting the precursor material (C) after the hydrothermal treatment to a reduction treatment.

[17] The method for producing an ammonia synthesis catalyst structure according to item [16], wherein 50 to 500 mass% of a nonionic surfactant is added to the precursor material (A) before the firing step.

[18] The method of producing an ammonia synthesis catalyst structure according to any one of [16] and [17], wherein the metal-containing solution is added to the precursor material (A) a plurality of times before the firing step, thereby impregnating the precursor material (A) with the metal-containing solution.

[19] The method for producing an ammonia synthesis catalyst structure according to any one of [16] to [18], wherein, when the metal-containing solution is impregnated into the precursor material (A) before the firing step, the amount of the metal-containing solution added to the precursor material (A) is adjusted so that the ratio (atomic ratio Si/M) of silicon (Si) constituting the precursor material (A) to a metal element (M) contained in the metal-containing solution added to the precursor material (A) is 10 to 1000 in terms of the ratio.

[20] The method for producing an ammonia synthesis catalyst structure according to item [16], wherein the precursor material (C) is mixed with a structure-directing agent in the hydrothermal treatment step.

[21] The method of producing an ammonia synthesis catalyst structure according to item [16], wherein the hydrothermal treatment step is performed in an alkaline environment.

[22] A method for synthesizing ammonia, which is a method for synthesizing ammonia by synthesizing ammonia from nitrogen and hydrogen using a catalyst comprising an ammonia synthesis catalyst structure, the ammonia synthesis catalyst structure comprising: a porous support composed of a zeolite-type compound; and at least one ammonia synthesis catalyst substance present in the carrier, the carrier having channels communicating with each other, the ammonia synthesis catalyst substance being present in at least expanded diameter portions of the channels of the carrier.

[23] A method for synthesizing ammonia, characterized in that ammonia is synthesized from nitrogen and water using the ammonia synthesis catalyst structure according to any one of [1] to [14 ].

[24] A method for synthesizing ammonia, characterized in that nitrogen and hydrogen are converted into ammonia using the ammonia synthesizing apparatus according to [15 ].

Advantageous effects

According to the present invention, it is possible to provide an ammonia synthesis catalyst structure, a method for producing the same, an ammonia synthesis apparatus, and a method for synthesizing ammonia, which can suppress a decrease in catalytic activity and prolong the life.

Drawings

Fig. 1 is a schematic view showing an internal structure of an ammonia synthesis catalyst structure according to an embodiment of the present invention, fig. 1(a) is a perspective view (partially shown in cross section), and fig. 1(b) is a partially enlarged sectional view.

Fig. 2 is a partially enlarged cross-sectional view for explaining an example of the function of the ammonia synthesis catalyst structure of fig. 1, fig. 2(a) is a view for explaining the sieve function, and fig. 2(b) is a view for explaining the catalytic ability.

Fig. 3 is a flowchart showing an example of a method for producing the ammonia synthesis catalyst structure of fig. 1.

Fig. 4 is a schematic diagram showing a modification of the ammonia synthesis catalyst structure of fig. 1.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[ constitution of Ammonia Synthesis catalyst Structure ]

Fig. 1 is a view schematically showing the structure of an ammonia synthesis catalyst structure according to an embodiment of the present invention, fig. 1(a) is a perspective view (partially shown in cross section), and fig. 1(b) is a partially enlarged sectional view. The ammonia synthesis catalyst structure shown in fig. 1 is an example thereof, and the shape, size, and the like of each component of the present invention are not limited to fig. 1.

As shown in fig. 1(a), an ammonia synthesis catalyst structure 1 includes: a porous support 10 made of a zeolite-type compound; and at least one metal fine particle 20 as an ammonia synthesis catalyst substance, present in the carrier 10.

In the ammonia synthesis catalyst structure 1, the plurality of metal fine particles 20 and 20 … … are included in the porous structure of the support 10. The fine metal particles 20 as the ammonia synthesis catalyst substance may be those having ammonia synthesis catalytic ability (catalytic activity), and details of the fine metal particles 20 will be described later.

The carrier 10 has a porous structure, and preferably has channels 11 communicating with each other by forming a plurality of holes 11a and 11a … …, as shown in fig. 1 (b). Here, the metal particles 20 are present in at least the channels 11 of the carrier 10, preferably retained in at least the channels 11 of the carrier 10.

With this configuration, the movement of the fine metal particles 20 in the carrier 10 is restricted, and the fine metal particles 20 and 20 are effectively prevented from being aggregated. As a result, the decrease in the effective surface area of the fine metal particles 20 can be effectively suppressed, and the catalytic activity of the fine metal particles 20 as the ammonia synthesis catalyst substance can be maintained for a long period of time. That is, according to the ammonia synthesis catalyst structure 1, the decrease in the catalytic activity due to the aggregation of the fine metal particles 20 can be suppressed, and the life of the ammonia synthesis catalyst structure 1 can be extended. Further, by extending the life of the ammonia synthesis catalyst structure 1, the frequency of replacement of the ammonia synthesis catalyst structure 1 can be reduced, the amount of waste ammonia synthesis catalyst structure 1 after use can be greatly reduced, and resources can be saved.

In general, when the ammonia synthesis catalyst structure is used in a fluid containing a raw material substance for ammonia synthesis, an external force may be applied from the fluid. In this case, if the fine metal particles 20 as the ammonia synthesis catalyst substance are held only in an attached state on the outer surface of the carrier 10, there is a problem that the fine metal particles are easily detached from the outer surface of the carrier 10 under the influence of an external force from the fluid. In contrast, in the ammonia synthesis catalyst structure 1, the fine metal particles 20 are present in at least the channels 11 of the support 10, and therefore, even when the fine metal particles 20 are affected by an external force by a fluid, the fine metal particles 20 are less likely to be detached from the support 10. Namely, it is considered that: when the ammonia synthesis catalyst structure 1 is in a fluid, the fluid flows into the channels 11 from the pores 11a of the carrier 10, and therefore the velocity of the fluid flowing in the channels 11 is lower than the velocity of the fluid flowing on the outer surface of the carrier 10 due to the flow path resistance (frictional force). Due to the influence of such flow path resistance, the metal particles 20 held in the passages 11 are subjected to a lower pressure from the fluid than the metal particles are subjected to from the fluid at the outside of the carrier 10. Therefore, the separation of the fine metal particles 20 present in the carrier 10 can be effectively suppressed, and the catalytic activity of the fine metal particles 20 can be stably maintained for a long period of time. It should be noted that: the more the channels 11 of the carrier 10 have a plurality of bends and branches, the more complicated and three-dimensional structure is inside the carrier 10, and the larger the flow path resistance as described above is.

Furthermore, the channel 11 preferably has: any one of one-dimensional pores, two-dimensional pores, and three-dimensional pores defined by the framework structure of the zeolite-type compound; and an enlarged diameter portion 12 different from any of the one-dimensional hole, the two-dimensional hole, and the three-dimensional hole, in which case, the metal fine particles 20 are preferably present at least in the enlarged diameter portion 12, and more preferably are included at least in the enlarged diameter portion 12. Further, the enlarged diameter portion 12 preferably communicates a plurality of holes 11a, 11a constituting any one of the one-dimensional hole, the two-dimensional hole, and the three-dimensional hole. Thus, since another channel different from the one-dimensional hole, the two-dimensional hole, or the three-dimensional hole is provided in the carrier 10, the fine metal particles 20 can further function. The one-dimensional hole referred to herein is a tunnel-type or cage-type hole in which one-dimensional channels are formed, or a plurality of holes (a plurality of one-dimensional channels) in which a plurality of one-dimensional channels are formed. In addition, the two-dimensional hole refers to a two-dimensional hole formed by two-dimensionally connecting a plurality of one-dimensional holes, and the three-dimensional hole refers to a three-dimensional hole formed by three-dimensionally connecting a plurality of one-dimensional holes. This further restricts the movement of the fine metal particles 20 in the carrier 10, and thus, the separation of the fine metal particles 20 and the aggregation of the fine metal particles 20 and 20 can be more effectively prevented. Inclusion means a state in which the metal fine particles 20 are enclosed in the carrier 10. In this case, the fine metal particles 20 and the carrier 10 do not necessarily need to be in direct contact with each other, and the fine metal particles 20 may be indirectly held on the carrier 10 in a state where another substance (for example, a surfactant or the like) is interposed between the fine metal particles 20 and the carrier 10.

Fig. 1(b) shows a case where the fine metal particles 20 are enclosed in the enlarged diameter portion 12, but the present invention is not limited to this configuration, and the fine metal particles 20 may be held in the passage 11 in a state where a part thereof protrudes to the outside of the enlarged diameter portion 12. The fine metal particles 20 may be partially embedded in a portion of the channel 11 other than the enlarged diameter portion 12 (for example, an inner wall portion of the channel 11), or may be held by adhesion or the like in a portion of the channel 11 other than the enlarged diameter portion 12 (for example, an inner wall portion of the channel 11).

Further, it is preferable that the channel 11 is three-dimensionally formed inside the carrier 10 so as to include a branching portion or a merging portion, and the diameter-expanding portion 12 is provided in the branching portion or the merging portion of the channel 11.

The average inner diameter D of the channel 11 formed in the carrier 10_FThe average value of the minor axis and major axis of the pores 11a constituting any one of the one-dimensional pores, two-dimensional pores, and three-dimensional pores is 0.50nm to 0.64nm, preferably 0.55nm to 0.61. Further, the inner diameter D of the enlarged diameter portion 12_EFor example, 0.7nm to 50nm, preferably 1.1nm to 40nm, and more preferably 1.1nm to 3.3 nm. Inner diameter D of enlarged diameter portion 12_EFor example, the pore diameter of the precursor (A) and the average particle diameter D of the enclosed metal fine particles 20_C. Inner diameter D of enlarged diameter portion 12_EIs of a size capable of encapsulating the intermetallic particles 20.

The support 10 is composed of a zeolite-type compound. Examples of the zeolite-type compound include: silicate compounds such as zeolite (aluminosilicate), cation-exchanged zeolite, and silicalite (silicalite); zeolite-like compounds such as aluminoborate, aluminoarsenate, germanate and the like; phosphate-based zeolite-like substances such as molybdenum phosphate; and the like. Among them, the zeolite-type compound is preferably a silicate compound.

The framework structure of the zeolite-type compound is selected from FAU type (Y type or X type), MTW type, MFI type (ZSM-5), FER type (ferrierite), LTA type (A type), MWW type (MCM-22), MOR type (mordenite), LTL type (L type)) And BEA type (. beta. -type), etc., preferably MFI type, more preferably ZSM-5. In the zeolite-type compound, a plurality of pores having pore diameters corresponding to respective framework structures are formed, and for example, the maximum pore diameter of MFI type is 0.636nm

Average pore diameter of 0.560nm

The metal fine particles 20 as the ammonia synthesis catalyst substance will be described in detail below.

There are: the case where the fine metal particles 20 are primary particles; and the fine metal particles 20 are secondary particles formed by aggregating the primary particles, the fine metal particles 20 having an average particle diameter D_CPreferably greater than the average internal diameter D of the channel 11_FAnd is not more than the inner diameter D of the enlarged diameter part 12_E(D_F<D_C≤D_E). Such fine metal particles 20 are preferably present in the enlarged diameter portion 12 in the channel 11, and restrict the movement of the fine metal particles 20 in the carrier 10. Thus, even when the fine metal particles 20 are subjected to an external force from a fluid, the fine metal particles 20 are prevented from moving in the carrier 10, and the fine metal particles 20, 20 … … present in the respective diameter-enlarged portions 12, 12 … … of the channels 11 dispersedly arranged in the carrier 10 can be effectively prevented from contacting each other.

Further, the average particle diameter D of the fine metal particles 20_CIn both cases of the primary particles and the secondary particles, the particle size is 0.7 to 5nm, more preferably 0.8nm or more and less than 4nm, and still more preferably 1.2 to 2.6 nm. Further, the average particle diameter D of the fine metal particles 20_CRelative to the mean internal diameter D of the channel 11_FRatio (D)_C/D_F) Preferably 1.2 to 10, more preferably 1.3 to 8, and particularly preferably 1.4 to 3.6. By adjusting the average particle diameter D of the fine metal particles 20_CThe particle size is 0.7 nm-5 nm, and excellent catalytic activity can be obtained. Further, the metal element (M) of the fine metal particles 20 is preferably contained in an amount of 0.5 to 2.5 mass% with respect to the ammonia synthesis catalyst structure 1, and more preferably contained in an amount of 0.5 to 2.5 mass% with respect to the ammonia synthesis catalyst structure 1The metal element (M) of the metal fine particles 20 is contained in an amount of 0.5 to 1.5 mass%. For example, in the case where the metal element (M) is Co, the content (mass%) of the Co element is represented by { (mass of Co element)/(mass of all elements of the ammonia synthesis catalyst structure 1) } × 100.

The fine metal particles 20 may be composed of a metal that is not oxidized, and may be composed of a single metal or a mixture of two or more metals, for example. In the present specification, "metal" (as a material) constituting the metal fine particles 20 means a single metal containing one metal element (M) and a metal alloy containing two or more metal elements (M), and is a generic term for metals containing one or more metal elements.

Such a metal is not particularly limited as long as it has a catalytic ability as an ammonia synthesis catalyst, and examples thereof include: at least one metal selected from the group consisting of molybdenum (Mo), tungsten (W), rhenium (Re), iron (Fe), cobalt (Co), ruthenium (Ru), osmium (Os), chromium (Cr), manganese (Mn), technetium (Tc), and rhodium (Rh); or combinations of the above metals such as Fe and Ru, Ru and Re, Fe and Mo, etc.; and the like. In particular, from the viewpoint of ammonia synthesis under low temperature conditions and low pressure conditions, at least one metal selected from the group consisting of Fe, Co, Ru, Os, and Rh is preferable.

The ratio (atomic ratio Si/M) of silicon (Si) constituting the carrier 10 to the metal element (M) constituting the fine metal particles 20 is preferably 10 to 1000, and more preferably 50 to 200. If the above ratio is more than 1000, the activity is low, and the like, and the function as an ammonia synthesis catalyst substance may not be sufficiently obtained. On the other hand, if the ratio is less than 10, the ratio of the fine metal particles 20 is too large, and the strength of the carrier 10 tends to decrease. The fine metal particles 20 referred to herein are particles held or carried in the carrier 10, and do not include fine metal particles adhering to the outer surface of the carrier 10.

[ function of Ammonia Synthesis catalyst Structure ]

As described above, the ammonia synthesis catalyst structure 1 includes: a support 10 having a porous structure; and at least one metal fine particle 20 as an ammonia synthesis catalyst substance, present in the carrier 10. In the ammonia synthesis catalyst structure 1, the fine metal particles 20 present in the carrier 10 come into contact with the fluid, whereby the fine metal particles 20 exert catalytic ability. Specifically, the fluid that contacts the outer surface 10a of the ammonia synthesis catalyst structure 1 flows into the inside of the carrier 10 from the pores 11a formed in the outer surface 10a, is guided into the channels 11, moves through the channels 11, and flows out of the ammonia synthesis catalyst structure 1 through the other pores 11 a. In the path of the fluid moving through the inside of the channel 11, it comes into contact with the metal particles 20 existing in the channel 11, whereby a catalytic reaction corresponding to the ammonia synthesis catalytic ability of the metal particles 20 occurs. Further, the ammonia synthesis catalyst structure 1 has a molecular sieve ability because the support 10 has a porous structure.

First, the molecular sieve capacity of the ammonia synthesis catalyst structure 1 will be described by taking, as an example, a case where a fluid is a gas containing a starting material 14 (for example, nitrogen molecules, hydrogen molecules, and the like) as a raw material for ammonia synthesis, with reference to fig. 2 (a). As shown in fig. 2(a), the starting material 14 having a size equal to or smaller than the pore diameter of the pores 11a, in other words, equal to or smaller than the inner diameter of the channels 11 can flow into the carrier 10. On the other hand, the non-starting material 15, which is not a raw material for ammonia synthesis, having a size larger than the pore diameter of the pores 11a cannot flow into the carrier 10. In this way, when the fluid contains a plurality of compounds, the reaction of the compounds that cannot flow into the carrier 10 is limited, and the compounds that can flow into the carrier 10 can be reacted.

Among the compounds generated in the carrier 10 by the reaction, only a compound composed of molecules having a size not larger than the pore diameter of the pores 11a can be obtained as a reaction product by flowing out of the carrier 10 through the pores 11 a. On the other hand, if the compound that cannot flow out of the carrier 10 through the pores 11a is converted into a compound composed of molecules having a size that can flow out of the carrier 10, the compound can flow out of the carrier 10. By using the ammonia synthesis catalyst structure 1 in this manner, a specific reaction product can be selectively obtained.

In the ammonia synthesis catalyst structure 1, as shown in FIG. 2(b), the diameter-enlarged portions 12 of the channels 11Metal fine particles 20 as a catalyst material for ammonia synthesis are included. The average particle diameter D of the fine metal particles 20_CGreater than the average internal diameter D of the channel 11_FAnd is smaller than the inner diameter D of the diameter-expanded portion 12_EIn the case of (D)_F<D_C<D_E) Small channels 13 are formed between the fine metal particles 20 and the enlarged diameter portion 12. Therefore, as shown by the arrows in fig. 2(b), the fluid flowing into the small channel 13 comes into contact with the metal particles 20. Since the metal microparticles 20 are present in the enlarged diameter portion 12, the movement of the metal microparticles in the carrier 10 is restricted, and the metal microparticles are prevented from being aggregated although being micronized. This prevents the fine metal particles 20, 20 in the carrier 10 from agglomerating with each other. As a result, a large contact area between the fine metal particles 20 and the fluid containing the starting material 14 flowing into the channel 11 can be stably maintained, and excellent catalytic activity can be obtained.

Then, when the starting material 14 that has permeated the channel 11 comes into contact with the metal fine particles 20, ammonia is synthesized by the oxidative decomposition reaction caused by the metal fine particles 20. Further, the ammonia synthesis apparatus may be formed using the ammonia synthesis catalyst structure 1. By using the ammonia synthesis catalyst structure 1 exemplified in the above embodiment, an ammonia synthesis apparatus can be obtained which exhibits the same effects as described above.

[ Process for producing Ammonia Synthesis catalyst Structure ]

Fig. 3 is a flowchart showing a method for producing the ammonia synthesis catalyst structure 1 of fig. 1. Hereinafter, an example of a method for producing an ammonia synthesis catalyst structure will be described, taking as an example a case where the ammonia synthesis catalyst substance present in the carrier is a fine metal particle.

(step S1: preparation Process)

As shown in fig. 3, first, a precursor material (a) for obtaining a support having a porous structure made of a zeolite-type compound is prepared. The precursor material (a) is preferably a regular mesoporous substance, and may be appropriately selected depending on the type (composition) of the zeolite-type compound constituting the support of the ammonia synthesis catalyst structure.

In the case where the zeolite-type compound constituting the support of the ammonia synthesis catalyst structure is a silicate compound, the regular mesoporous material is preferably a compound having a Si — O skeleton in which pores having pore diameters of 1 to 50nm are uniform in one-dimensional, two-dimensional or three-dimensional size and regularity develops. Such a regular mesoporous material is obtained as various compositions according to synthesis conditions, and specific examples of the compositions include: SBA-1, SBA-15, SBA-16, KIT-6, FSM-16, MCM-41 and the like, wherein MCM-41 is preferred. The fine pore diameter of SBA-1 is 10-30 nm, the fine pore diameter of SBA-15 is 6-10 nm, the fine pore diameter of SBA-16 is 6nm, the fine pore diameter of KIT-6 is 9nm, the fine pore diameter of FSM-16 is 3-5 nm, and the fine pore diameter of MCM-41 is 1-10 nm. Examples of such a regular mesoporous material include: mesoporous silica, mesoporous aluminosilicates, mesoporous metallosilicates, and the like.

The precursor (a) may be any of commercially available products and synthetic products. In the case of synthesizing the precursor material (a), it can be carried out by a known method for synthesizing a mesoporous substance having regularity. For example, a mixed solution containing a raw material containing a constituent element of the precursor material (a) and a template agent for specifying the structure of the precursor material (a) is prepared, and hydrothermal treatment (hydrothermal synthesis) is performed by adjusting the pH as necessary. Then, the precipitate (product) obtained by the hydrothermal treatment is recovered (e.g., filtered), washed and dried as necessary, and further fired, whereby the precursor material (a) as a powdery regular mesoporous substance can be obtained. Here, as the solvent of the mixed solution, for example, an organic solvent such as water or alcohol, or a mixed solvent thereof can be used. The raw material is selected depending on the kind of the carrier, and examples thereof include: silica agents (silica agents) such as Tetraethoxysilane (TEOS), fumed silica, and silica sand. Further, as the template agent, various surfactants, block copolymers and the like can be used, and it is preferably selected according to the kind of the composition of the ordered mesoporous substance, and for example, in the case of producing MCM-41, a surfactant such as cetyltrimethylammonium bromide is preferred. The hydrothermal treatment may be carried out, for example, in a closed vessel under the treatment conditions of 80 to 800 ℃ for 5 to 240 hours and 0 to 2000 kPa. The firing treatment can be performed, for example, in air at 350 to 850 ℃ for 2 to 30 hours.

(step S2: impregnation step)

Next, the prepared precursor material (a) is immersed in a metal-containing solution to obtain a precursor material (B).

The metal-containing solution may be a solution containing a metal component (for example, metal ions) corresponding to the metal element (M) constituting the metal fine particles of the ammonia synthesis catalyst structure, and may be prepared, for example, by dissolving a metal salt containing the metal element (M) in a solvent. Examples of such metal salts include: metal salts such as chlorides, hydroxides, oxides, sulfates, nitrates, etc., among which nitrates are preferable. As the solvent, for example, an organic solvent such as water or alcohol, or a mixed solvent thereof can be used.

The method for immersing the metal-containing solution in the precursor material (a) is not particularly limited, and for example, it is preferable to add the metal-containing solution to the precursor material (a) in small amounts in a plurality of times while stirring the powdery precursor material (a) before the firing step described later. In addition, from the viewpoint that the metal-containing solution more easily penetrates into the inside of the pores of the precursor material (a), it is preferable to add a surfactant as an additive in advance before adding the metal-containing solution to the precursor material (a). Consider that: such an additive has an effect of covering the outer surface of the precursor material (a), and suppresses the metal-containing solution added later from adhering to the outer surface of the precursor material (a), so that the metal-containing solution more easily penetrates into the pores of the precursor material (a).

Examples of such additives include: nonionic surfactants such as polyoxyethylene oleyl ether, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether. Consider that: these surfactants have large molecular sizes and cannot penetrate into the pores of the precursor material (a), and therefore do not adhere to the inside of the pores and do not inhibit the metal-containing solution from penetrating into the pores. As a method of adding the nonionic surfactant, for example, it is preferable to add 50 to 500 mass% of the nonionic surfactant to the precursor material (a) before the firing step described later. If the amount of the nonionic surfactant added to the precursor material (a) is less than 50 mass%, the above-described inhibiting effect is hardly exhibited, and if the amount of the nonionic surfactant added to the precursor material (a) is more than 500 mass%, the viscosity is excessively increased, which is not preferable. Thus, the amount of the nonionic surfactant added to the precursor material (a) is set to a value within the above range.

The amount of the metal-containing solution added to the precursor material (a) is preferably adjusted as appropriate in consideration of the amount of the metal element (M) contained in the metal-containing solution to be impregnated into the precursor material (a) (that is, the amount of the metal element (M) to be present in the precursor material (B)). For example, the amount of the metal-containing solution added to the precursor material (a) before the firing step described later is preferably adjusted so that the ratio (atomic ratio Si/M) of silicon (Si) constituting the precursor material (a) to the metal element (M) contained in the metal-containing solution added to the precursor material (a) is 10 to 1000, more preferably 50 to 200. For example, when a surfactant is added as an additive to the precursor material (a) before the metal-containing solution is added to the precursor material (a), the metal element (M) of the metal fine particles can be contained in an amount of 0.5 to 2.5 mass% with respect to the catalyst structure by setting the amount of the metal-containing solution added to the precursor material (a) to 50 to 200 in terms of an atomic ratio Si/M. In the state of the precursor material (B), if the metal concentration of the metal-containing solution, the presence or absence of the additive, other conditions such as temperature and pressure are the same, the amount of the metal element (M) present in the pores thereof is substantially proportional to the amount of the metal-containing solution added to the precursor material (a). Further, the amount of the metal element (M) present in the precursor material (B) is in proportional relation to the amount of the metal element constituting the metal fine particles present in the support of the ammonia synthesis catalyst structure. Therefore, by controlling the amount of the metal-containing solution added to the precursor material (a) within the above range, the metal-containing solution can be sufficiently impregnated into the pores of the precursor material (a), and the amount of the metal fine particles to be present in the support of the ammonia synthesis catalyst structure can be adjusted.

After the precursor material (a) is immersed in the metal-containing solution, a cleaning treatment may be performed as needed. As the cleaning solution, water, an organic solvent such as alcohol, or a mixed solution thereof can be used. Further, it is preferable that the metal-containing solution is immersed in the precursor material (a) and, after a cleaning treatment is performed as necessary, a drying treatment is further performed. Examples of the drying treatment include natural drying at about evening and high-temperature drying at 150 ℃. When the firing treatment described later is performed in a state where a large amount of moisture contained in the metal-containing solution or moisture in the cleaning solution remains in the precursor (a), the skeleton structure of the ordered mesoporous material as the precursor (a) may be broken, and therefore, it is preferable to sufficiently dry the precursor (a).

(step S3: firing Process)

Next, a precursor material (B) obtained by impregnating a precursor material (a) for obtaining a support having a porous structure made of a zeolite-type compound with a metal-containing solution is fired to obtain a precursor material (C).

The firing treatment is preferably carried out in air at 350 to 850 ℃ for 2 to 30 hours. By the firing treatment, the metal component impregnated into the pores of the ordered mesoporous material is subjected to crystal growth to form fine metal particles in the pores.

(step S4: hydrothermal treatment Process)

Next, a mixed solution in which the precursor material (C) and the structure-directing agent are mixed is prepared, and the precursor material (C) obtained by firing the precursor material (B) is subjected to hydrothermal treatment to obtain an ammonia synthesis catalyst structure.

The structure-directing agent is a template agent for defining the framework structure of the support of the ammonia synthesis catalyst structure, and for example, a surfactant can be used. The structure-directing agent is preferably selected according to the skeletal structure of the support of the ammonia synthesis catalyst structure, and is preferably a surfactant such as tetramethylammonium bromide (TMABr), tetraethylammonium bromide (TEABr), tetrapropylammonium bromide (TPABr), or the like.

The mixing of the precursor material (C) and the structure directing agent may be performed during the hydrothermal treatment step, or may be performed before the hydrothermal treatment step. The method for preparing the mixed solution is not particularly limited, and the precursor material (C), the structure-directing agent, and the solvent may be mixed at the same time, or the precursor material (C) and the structure-directing agent may be dispersed in the solvent in the form of separate solutions, and then the respective dispersed solutions may be mixed. As the solvent, for example, an organic solvent such as water or alcohol, or a mixed solvent thereof can be used. The mixed solution is preferably adjusted in pH by using an acid or an alkali in advance before the hydrothermal treatment.

The hydrothermal treatment can be carried out by a known method, and is preferably carried out in a closed vessel under treatment conditions of 80 to 800 ℃ for 5 to 240 hours and 0 to 2000kPa, for example. Further, the hydrothermal treatment is preferably performed in an alkaline environment. Although the reaction mechanism is not necessarily clear here, when the precursor material (C) is used as a raw material and subjected to hydrothermal treatment, the framework structure of the fine pore substance in the regularity as the precursor material (C) is gradually destroyed, but the position of the metal fine particles inside the fine pores of the precursor material (C) is maintained substantially unchanged, and a new framework structure (porous structure) serving as a support of the ammonia synthesis catalyst structure is formed by the action of the structure-directing agent. The ammonia synthesis catalyst structure thus obtained comprises a support having a porous structure and metal fine particles present in the support, the support further has channels in which a plurality of pores are interconnected by the porous structure, and at least a part of the metal fine particles are present in the channels of the support. In the present embodiment, in the hydrothermal treatment step, a mixed solution in which the precursor material (C) and the structure directing agent are mixed is prepared, and the precursor material (C) is subjected to the hydrothermal treatment.

It is preferable that the precipitate (ammonia synthesis catalyst structure) obtained after the hydrothermal treatment is recovered (for example, filtered), and then washed, dried, and fired as necessary. As the cleaning solution, water, an organic solvent such as alcohol, or a mixed solution thereof can be used. Examples of the drying treatment include natural drying at about evening and high-temperature drying at 150 ℃. When the calcination treatment is performed in a state where a large amount of water remains in the precipitate, the skeleton structure of the support serving as the ammonia synthesis catalyst structure may be broken, and therefore, it is preferable to sufficiently dry the precipitate. The firing treatment may be performed, for example, in air at 350 to 850 ℃ for 2 to 30 hours. By such a firing treatment, the structure directing agent adhering to the ammonia synthesis catalyst structure is burned off. The ammonia synthesis catalyst structure may be used as it is without subjecting the recovered precipitate to firing treatment depending on the purpose of use. For example, when the environment in which the ammonia synthesis catalyst structure is used is a high-temperature environment such as an oxidizing environment, the structure-directing agent is burned off by exposure to the use environment for a certain period of time, and the same ammonia synthesis catalyst structure as in the case of the firing treatment can be obtained and therefore can be used as it is.

The above-described production method is an example of a case where the metal element (M) contained in the metal-containing solution to be impregnated into the precursor material (a) is a metal species (for example, a noble metal) that is not easily oxidized.

When the metal element (M) contained in the metal-containing solution to be impregnated into the precursor (a) is a metal species (for example, Fe, Co, Cu, or the like) that is easily oxidized, it is preferable to perform a reduction treatment on the precursor (C) after the hydrothermal treatment step. When the metal element (M) contained in the metal-containing solution is a metal species that is easily oxidized, the metal component is oxidized by the heat treatment in the steps (steps S3 to S4) after the impregnation treatment (step S2). Therefore, the metal oxide fine particles are present in the carrier formed by the hydrothermal treatment step (step S4). Therefore, in order to obtain an ammonia synthesis catalyst structure in which fine metal particles are present in the carrier, it is preferable that the collected precipitate is subjected to a calcination treatment after the hydrothermal treatment and further subjected to a reduction treatment in a reducing atmosphere such as hydrogen gas (step S5: reduction treatment step). By performing the reduction treatment, the metal oxide fine particles present in the carrier are reduced to form metal fine particles corresponding to the metal element (M) constituting the metal oxide fine particles. As a result, an ammonia synthesis catalyst structure in which fine metal particles are present in the carrier can be obtained. For example, when the environment in which the ammonia synthesis catalyst structure is used is a reducing environment, the metal oxide fine particles are reduced by exposure to the reducing environment for a certain period of time, and therefore the same ammonia synthesis catalyst structure as that obtained when the reduction treatment is performed can be obtained, and therefore the catalyst structure can be used as it is with the oxide fine particles present in the carrier.

[ modification of Ammonia Synthesis catalyst Structure 1]

Fig. 4 is a schematic diagram showing a modification of the ammonia synthesis catalyst structure 1 of fig. 1.

The ammonia synthesis catalyst structure 1 of fig. 1 is shown to include the carrier 10 and the fine metal particles 20 as the ammonia synthesis catalyst substance present in the carrier 10, but the present invention is not limited to this configuration, and for example, as shown in fig. 4, the ammonia synthesis catalyst structure 2 may further include other fine metal particles 30 as another ammonia synthesis catalyst substance held on the outer surface 10a of the carrier 10.

The other metal particles 30 are substances that exert one or more catalytic abilities. The other metal particles 30 may have the same or different catalytic ability as the metal particles 20. In the case where both the fine metal particles 20 and 30 have the same catalytic ability, the material of the other fine metal particles 30 may be the same as or different from the material of the fine metal particles 20. According to the present configuration, the content of the catalyst substance held in the ammonia synthesis catalyst structure 2 can be increased, and the catalytic activity of the catalyst substance can be further promoted.

In this case, it is preferable that the content of the metal fine particles 20 present in the carrier 10 is larger than the content of the other metal fine particles 30 held on the outer surface 10a of the carrier 10. Thus, the catalytic ability of the fine metal particles 20 held in the carrier 10 is dominant, and the catalytic ability of the ammonia synthesis catalyst substance is stably exhibited.

Further, in the present invention, there can be provided a method for synthesizing ammonia by synthesizing ammonia from nitrogen and hydrogen using a catalyst. Such a catalyst comprises an ammonia synthesis catalyst structure 1, and the ammonia synthesis catalyst structure 1 includes: a porous support 10 made of a zeolite-type compound; and at least one ammonia synthesis catalyst substance present in the carrier 10, the carrier 10 having channels 11 communicating with each other, the ammonia synthesis catalyst substance being present in at least the expanded diameter portions 12 of the channels 11 of the carrier 10. That is, the present invention can provide a method for synthesizing ammonia by synthesizing ammonia from nitrogen and hydrogen using the above-described ammonia synthesis catalyst structure. In particular, the metal fine particles 20 as the ammonia synthesis catalyst substance preferably have an average particle diameter of 0.7nm to 5nm, and the channels 11 preferably have an average particle diameter of 0.50nm to 0.64 nm.

The raw material for carrying out such a method for synthesizing ammonia is not particularly limited as long as it is a synthesis gas containing molecular nitrogen and hydrogen as main components, and the composition ratio is preferably N2: H2 ═ 1:3 in terms of a molar ratio. In addition, the reaction conditions are preferably such that the reaction temperature is in the range of 250 to 600 ℃ and the pressure is in the range of 0.1 to 100MPa (absolute pressure).

The synthesis of ammonia can be carried out by a known process for ammonia synthesis, for example, a fixed bed, a supercritical fixed bed, a slurry bed (slurry bed), a fluidized bed, or the like. Preferred processes include: fixed bed, supercritical fixed bed, slurry bed. In particular, a representative method for synthesizing ammonia is as follows: in the same manner as in the conventional Haber-Bosch method, a mixed gas of nitrogen and hydrogen as raw materials is directly reacted under heat and pressure to thereby pass N₂+3H₂→2NH₃The ammonia produced by the reaction of (3) is cooled or absorbed by water and separated.

In this manner, by using the ammonia synthesis catalyst structure of the present invention in a method for synthesizing ammonia from nitrogen and hydrogen, the same effects as those exhibited by the ammonia synthesis catalyst structure can be obtained in the above-described method for synthesizing ammonia.

Further, the present invention can also provide a method for synthesizing ammonia by converting nitrogen and hydrogen into ammonia using the above-described ammonia synthesis apparatus. Such an ammonia synthesis apparatus is not particularly limited as long as it is an apparatus capable of synthesizing ammonia by using the ammonia synthesis catalyst structure, and for example, a commonly used reaction apparatus such as a reactor, a reaction tube, or a reaction column can be used. By using an ammonia synthesis apparatus having an ammonia synthesis catalyst structure, the same effects as those exhibited by the above ammonia synthesis catalyst structure can be obtained.

The ammonia synthesis catalyst structure according to the embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment, and various modifications and changes can be made based on the technical idea of the present invention.