Method for preparing ammonia decomposition catalyst and ammonia decomposition catalyst prepared thereby

Abstract

The present invention relates to a method for preparing an ammonia decomposition catalyst, comprising the steps of: (A) preparing a basic aqueous solution having a predetermined pH within a range of pH 8.5 to pH 9.5 by adding a base dropwise to water; (B) forming La-Ce aggregation nuclei by adding a base and a precursor aqueous solution containing a La precursor and a Ce precursor to the basic aqueous solution, such that the pH of the basic aqueous solution is maintained within a range of ±0.2 of the predetermined pH; (C) forming La-Ce aggregates by additionally adding a base to the solution in which the La-Ce aggregation nuclei are formed; (D) forming a La-Ce-O carrier by sintering the La-Ce aggregates; and (E) supporting an active metal on the La-Ce-O carrier.

Description

Method for manufacturing an ammonia decomposition catalyst and an ammonia decomposition catalyst manufactured thereby

[0001] The present invention relates to a method for manufacturing an ammonia decomposition catalyst and an ammonia decomposition catalyst manufactured thereby.

[0002] One method for efficiently storing and transporting hydrogen is to use ammonia as a hydrogen source. Since the process of decomposing ammonia into hydrogen and nitrogen is endothermic, energy is required to obtain the products. Conventional catalytic decomposition reactions require a large amount of heat to produce a useful amount of hydrogen gas, resulting in high costs for hydrogen production.

[0003] Ammonia decomposition catalysts are catalysts that decompose ammonia into nitrogen and hydrogen; conventionally, however, there was a problem in that very high reaction temperatures were required when attempting to obtain high-purity hydrogen using the ammonia decomposition catalysts proposed so far.

[0004] To solve this problem, Korean Patent Publication No. 10-2021-0147910 (Patent Document 1) discloses an ammonia decomposition catalyst that uses a complex oxide solid solution composed of lanthanum oxide and cerium oxide as a catalyst support and uses ruthenium as a catalytic active component. The ammonia decomposition catalyst in Patent Document 1 discloses that a basic substance is injected until the pH of the reaction vessel reaches 9 to generate a precipitate, and the precipitate is calcined to form a catalyst support; however, this method has the problem that a catalyst support of very non-uniform size and shape is formed, and the dispersion of the active metal supported thereon is very poor.

[0005] Accordingly, the present invention aims to provide a manufacturing method that ensures uniformity in the size and performance of an ammonia decomposition catalyst.

[0006] [Prior Art Literature]

[0007] [Patent Literature]

[0008] Republic of Korea Published Patent Application No. 10-2021-0147910

[0009] The present invention aims to provide a method for manufacturing an ammonia decomposition catalyst and an ammonia decomposition catalyst manufactured thereby. Specifically, the invention aims to provide a method for manufacturing an ammonia decomposition catalyst in which the size and shape of the support are uniformly controlled and an active metal is supported on the support with a high degree of dispersion.

[0010] However, the technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0011] One embodiment of the present invention provides a method for manufacturing an ammonia decomposition catalyst, comprising: (A) adding a basic substance to water to prepare a basic aqueous solution having a predetermined pH within the range of pH 8.5 to pH 9.5; (B) adding a precursor aqueous solution containing a La precursor and a Ce precursor and a basic substance dropwise to the basic aqueous solution to maintain the pH of the basic aqueous solution within ±0.2 of the predetermined pH, thereby forming La-Ce aggregation nuclei; (C) adding a basic substance further to the solution in which the La-Ce aggregation nuclei are formed to form La-Ce aggregates; (D) calcining the La-Ce aggregates to form a La-Ce-O carrier; and (E) supporting an active metal on the La-Ce-O carrier.

[0012] Another embodiment of the present invention provides an ammonia decomposition catalyst produced by the above manufacturing method.

[0013] Another embodiment of the present invention provides a method for decomposing ammonia, comprising the step of decomposing ammonia into nitrogen and hydrogen in the presence of the ammonia decomposition catalyst.

[0014] The ammonia decomposition catalyst prepared according to the present invention supports an active metal with a high degree of dispersion, thereby enabling a high ammonia decomposition rate. Furthermore, the ammonia decomposition catalyst prepared according to the present invention can ensure uniform performance by uniformly controlling the size and shape of the support, and has the advantage of being easily applicable to mass production, allowing for the manufacture of an ammonia decomposition catalyst of uniform quality.

[0015] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by a person skilled in the art from the description below.

[0016] Figure 1 shows an SEM image of a La-Ce-O support prepared according to Example 1.

[0017] Figure 2 shows an SEM image of a La-Ce-O support prepared according to Example 2.

[0018] Figure 3 shows an SEM image of a La-Ce-O support prepared according to Comparative Example 1.

[0019] Figure 4 shows an SEM image of a La-Ce-O support prepared according to Comparative Example 2.

[0020] Figure 5 shows an enlarged SEM image of a La-Ce-O support prepared according to Example 1.

[0021] Figure 6 shows an enlarged SEM image of a La-Ce-O support prepared according to Example 2.

[0022] Figure 7 shows an enlarged SEM image of a La-Ce-O support prepared according to Comparative Example 1.

[0023] Figure 8 shows an enlarged SEM image of a La-Ce-O support prepared according to Comparative Example 2.

[0024] Figure 9 shows an SEM image of a La-Ce-O support prepared according to Example 3.

[0025] Figure 10 shows an enlarged SEM image of a La-Ce-O support prepared according to Example 3.

[0026] Figure 11 shows the adsorption-desorption curves according to BET analysis of a La-Ce-O support prepared according to Example 1.

[0027] Figure 12 shows the adsorption-desorption curves according to BET analysis of a La-Ce-O support prepared according to Example 2.

[0028] Figure 13 shows the adsorption-desorption curves according to BET analysis of a La-Ce-O support prepared according to Comparative Example 2.

[0029] Figure 14 shows an SEM image of a La-Ce-O support prepared according to Comparative Example 3.

[0030] Figure 15 shows an enlarged SEM image of a La-Ce-O support prepared according to Comparative Example 3.

[0031] Figure 16 shows an SEM image of a La-Ce-O support prepared according to Comparative Example 4.

[0032] Figure 17 shows an enlarged SEM image of a La-Ce-O support prepared according to Comparative Example 4.

[0033] In this specification, terms such as “comprising” or “having” are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0034] In this specification, when a member is described as being located "on" another member, this includes not only cases where a member is in contact with another member, but also cases where another member exists between the two members.

[0035] The inventors completed the present invention while conducting research on the mass production of an ammonia decomposition catalyst having high ammonia decomposition efficiency at low temperatures, confirming that controlling the physical properties of the support on which the active metal is supported has a significant effect on the performance stability and ammonia decomposition efficiency of the catalyst. Specifically, the present invention recognized that it is impossible to manufacture a catalyst of uniform quality and that it is unsuitable for a mass production process when reproducing an ammonia decomposition catalyst based on the method for manufacturing an ammonia decomposition catalyst disclosed in Korean Publication No. 10-2021-0147910. By researching means to solve this problem, the inventors arrived at the completion of the present invention. For reference, the contents disclosed in Korean Publication No. 10-2021-0147910 may be incorporated into the present invention, provided that they do not conflict with the content and purpose of the present invention.

[0036] The present invention will be described in detail below.

[0037] One embodiment of the present invention provides a method for manufacturing an ammonia decomposition catalyst, comprising: (A) adding a basic substance to water to prepare a basic aqueous solution having a predetermined pH within the range of pH 8.5 to pH 9.5; (B) adding a precursor aqueous solution containing a La precursor and a Ce precursor and a basic substance dropwise to the basic aqueous solution to maintain the pH of the basic aqueous solution within ±0.2 of the predetermined pH, thereby forming La-Ce aggregation nuclei; (C) adding a basic substance further to the solution in which the La-Ce aggregation nuclei are formed to form La-Ce aggregates; (D) calcining the La-Ce aggregates to form a La-Ce-O carrier; and (E) supporting an active metal on the La-Ce-O carrier.

[0038] The inventors have confirmed that in order to achieve a uniform particle size and mesoporous structure of a La-Ce-O carrier on which an active metal is supported, it is necessary to precisely control the pH during the formation of La-Ce aggregation nuclei through steps (A) and (B). Specifically, controlling the pH of the basic aqueous solution in step (A) to within the range of 8.5 to 9.5, and further maintaining it within ±0.2 of a predetermined pH set in step (B), enables a uniform shape and physical properties of the La-Ce-O carrier and further enables the realization of a high dispersion of the supported active metal. More specifically, if the pH of the basic aqueous solution in step (A) is controlled to within the range of 8.8 to 9.3, it may be possible to form a more homogeneous La-Ce-O carrier. If the pH of the basic aqueous solution is below the above range, the mesoporous structure of the manufactured La-Ce-O carrier is not effectively formed, and problems may occur where the particle size becomes non-uniform and aggregates with each other. In addition, if the pH of the above basic aqueous solution exceeds the above range, the surface structure of the manufactured La-Ce-O carrier is formed as a plate-like shape rather than a porous one, making it difficult to support the active metal and potentially causing a problem of reduced dispersion.

[0039] In addition, in step (B), an aqueous precursor solution containing La precursors and Ce precursors and a basic substance are added dropwise while maintaining the pH within ±0.2 of the aforementioned predetermined range, thereby inducing a reaction between the La precursors and Ce precursors and the hydroxyl groups of the basic substance under specific reaction conditions. Through this process, the La-Ce aggregation nuclei produced can be controlled to a uniform size, and aggregation phenomena can be minimized. Furthermore, when La-Ce aggregates are formed using the La-Ce aggregation nuclei produced in this manner, a mesoporous La-Ce-O carrier with very high porosity can be uniformly produced.

[0040] According to one embodiment of the present invention, steps (B) and (C) can be performed in a mixing reactor and an aging reactor, respectively. Specifically, steps (B) and (C) can be performed in separate reactors. That is, the process of forming La-Ce aggregation nuclei and the process of forming La-Ce aggregates can be performed in different reactors. Specifically, in the mixing reactor, La-Ce aggregation nuclei are formed by simultaneously adding an aqueous precursor solution and a basic substance dropwise under conditions where the change in pH is controlled, and in the aging reactor, after receiving the solution from the mixing reactor, an additional basic substance is added and stirred to form La-Ce aggregates. That is, unlike the mixing reactor, there is no need to control the change in pH in the aging reactor, and the reaction for the smooth formation of La-Ce aggregates can be induced. Through such a design of separate reactors, the advantages of forming more uniform particles and enabling mass production can be obtained.

[0041] According to one embodiment of the present invention, steps (A) through (C) may be performed in a continuous stirred tank reactor (CSTR) composed of the mixing reactor and the aging reactor. Specifically, the solution containing the precipitate generated in the mixing reactor may be transferred to the aging reactor at a rate equal to the flow rate of the precursor aqueous solution and the basic substance introduced into the mixing reactor. Furthermore, when all of the prepared precursor aqueous solution is introduced into the mixing reactor, all of the solution and precipitate from the mixing reactor may be transferred to the aging reactor, and then an additional basic substance may be introduced and stirred to form La-Ce aggregates.

[0042] In the production of particles using a conventional coprecipitation method, there is a problem in that reaction conditions are inconsistent due to continuous pH changes during the nucleation stage, which inevitably leads to the formation of increasingly non-uniform particles as the production scale increases. Furthermore, when nucleation and aggregate formation are performed within the same reactor, the nucleation and aggregation stages occur simultaneously, resulting in the problem of particle clumping and the inability to control physical properties. As described above, the present invention has the advantage of solving all the problems of the conventional coprecipitation method through pH control and reactor separation.

[0043] According to one embodiment of the present invention, the La precursor and the Ce precursor may each be an oxide, chloride, hydroxide, bromide, iodide, nitrate, sulfate, carbonate, acetate, oxalate, fluoride, isopropoxide, or organometallic complex of La and Ce.

[0044] According to one embodiment of the present invention, the total number of moles of hydroxyl groups contained in the basic substance used in steps (A), (B), and (C) may be 2 to 5 times the total number of moles of metal ions in the added precursor aqueous solution. Specifically, the total number of moles of hydroxyl groups contained in the basic substance added in steps (A) to (C) may be 2 to 5 times, 2.5 to 4.5 times, or 3 to 4 times the total number of moles of metal ions (La and Ce metal ions) in the added precursor aqueous solution. That is, the amount of the basic substance added can be calculated through the amount of hydroxyl groups within the basic substance. Specifically, the total amount of the basic substance may be determined by the total amount of hydroxyl groups mentioned above. For example, if the basic substance is ammonia water, the total amount of ammonia water added may vary depending on the concentration of the ammonia water.

[0045] The amount of basic substance added in step (C) may be the amount obtained by subtracting the amount of basic substance used in steps (A) and (B) from the predetermined total amount of basic substance. If the total amount of basic substance is less than the above range, it may cause particle clumping during the aging process of forming La-Ce aggregates in step (C), making it difficult to form homogeneous La-Ce aggregates. Furthermore, if the total amount of basic substance exceeds the above range, it may not provide additional assistance in forming homogeneous La-Ce aggregates, and may only result in a loss of raw material costs and manufacturing time.

[0046] According to one embodiment of the present invention, the basic substance may be an aqueous solution comprising at least one selected from the group consisting of ammonia water, sodium hydroxide, potassium hydroxide, hydrazine, and sodium carbonate. Specifically, the basic substance may be ammonia water.

[0047] According to one embodiment of the present invention, the step of filtering and washing the La-Ce aggregate obtained through step (C) may be further included. Furthermore, the step of drying the La-Ce aggregate obtained through step (C) may be included. The drying may be vacuum drying at a temperature of 80°C to 120°C.

[0048] According to one embodiment of the present invention, the firing in step (D) can be performed in an air atmosphere at a temperature of 300 ℃ to 700 ℃, specifically 400 ℃ to 600 ℃.

[0049] The above La-Ce-O carrier may be a complex oxide solid solution containing lanthanum oxide and cerium oxide. The molar ratio of La to Ce in the above La-Ce-O carrier may be 1:1 to 1:3, and specifically, 1:2.

[0050] The above La-Ce-O carrier may be particles with an average diameter of 10 μm to 15 μm. Additionally, the above La-Ce-O carrier may have a flower-like surface structure in which plate-shaped metal oxides with a thickness at the nm level are intertwined to form a large number of mesopores. Specifically, according to one embodiment of the present invention, the above La-Ce-O carrier may have a mesoporous surface that exhibits the shape of an H3 hysteresis curve during BET adsorption-desorption analysis. The shape of the H3 hysteresis curve may indicate a shape in which thin plate-shaped particles are intertwined to form a wedge-shaped mesoporous surface structure. Due to these morphological characteristics, the above La-Ce-O carrier can support a very large amount of active metal, which can be confirmed by the high dispersibility of the active metal.

[0051] According to one embodiment of the present invention, the active metal may be Ru.

[0052] According to one embodiment of the present invention, step (E) may involve mixing an aqueous solution of a Ru precursor with the La-Ce-O carrier, adding the basic substance to obtain a precipitate, and then reducing the precipitate. The aqueous solution of the Ru precursor may be obtained by dissolving a Ru precursor in water. The Ru precursor may be an oxide, chloride, hydroxide, bromide, iodide, nitrate, sulfate, carbonate, acetate, oxalate, fluoride, isopropoxide, or an organometallic complex of Ru.

[0053] The above reduction treatment is not particularly limited as long as it is capable of reducing the ruthenium compound in the precipitate to form ruthenium metal. Specifically, methods such as using a reducing gas, such as carbon monoxide, hydrocarbons, or hydrogen; or adding a reducing agent, such as hydrazine, lithium aluminum hydride, or tetramethyl borohydride, may be used. In addition, when using a reducing gas, the reducing gas may be diluted with other gases (e.g., nitrogen, carbon dioxide). Among these methods, a reduction treatment using hydrogen as the reducing gas is preferred.

[0054] In the above reduction treatment, if a reducing gas is used, it can be performed at a temperature of 300°C to 800°C, specifically 400°C to 600°C.

[0055] Through the above reduction treatment, the ruthenium compound in the precipitate is, in principle, converted into ruthenium metal exhibiting a metallic state with a valence of 0. If the reduction treatment is insufficient, the ruthenium compound is reduced only partially, and the catalyst exhibits low activity. However, even in such cases, since hydrogen is generated during the ammonia decomposition reaction, the reaction is continued to create an environment similar to that of the reduction treatment, thereby allowing the reduction treatment of the insufficiently reduced portion to proceed, resulting in a metallic state with a valence of 0, and the catalyst can exhibit high activity.

[0056] As described above, the La-Ce-O carrier can have a high dispersion of active metal due to its surface shape having a large amount of mesoporous structure. Specifically, the dispersion of the active metal supported on the La-Ce-O carrier can be at least 30%, specifically at least 35%, at least 40%, at least 45%, or at least 50%. A higher dispersion indicates a higher loading amount, and the upper limit thereof can be 100%. The dispersion of the active metal can be measured through CO-pulse chemisorption analysis using Micromeritics’ Autochem II 2920 instrument.

[0057] According to one embodiment of the present invention, the ammonia decomposition rate of the ammonia decomposition catalyst at 450°C may be at least 90%.

[0058] According to another embodiment of the present invention, an ammonia decomposition catalyst prepared by the above-described manufacturing method is provided. The ammonia decomposition catalyst may be one in which an active metal is supported on a La-Ce-O carrier having a uniform diameter and a large amount of mesoporous surface structure as described above. The ammonia decomposition catalyst has the advantage of being able to achieve a high ammonia decomposition rate at low temperatures.

[0059] Another embodiment of the present invention provides a method for decomposing ammonia, comprising the step of decomposing ammonia into nitrogen and hydrogen in the presence of the ammonia decomposition catalyst. The ammonia decomposition method may utilize known methods, except for using the ammonia decomposition catalyst described above.

[0060] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present invention to those with average knowledge in the art.

[0061] [Example 1]

[0062] Aqueous solutions of Ce and La precursors were prepared by mixing 75.7 g (0.175 mol) of cerium nitrate hydrate and 37.7 g (0.087 mol) of lanthanum nitrate hydrate with distilled water. Ammonia water was prepared as a basic substance such that the number of moles of hydroxyl groups in the ammonia water was four times the number of moles of metal ions in the Ce and La precursor aqueous solutions. Then, a mixed reaction vessel aqueous solution with a pH of 9 was prepared by injecting 200 ml of distilled water and a small amount of ammonia water into a 500 ml beaker. Using a peristaltic pump, the Ce and La precursor aqueous solutions and the ammonia aqueous solution were added dropwise to the mixed reaction vessel at a rate that maintained a pH of 9 (±0.2), and the mixture was vigorously stirred to form a precipitate. Once it was confirmed that the pH was maintained at 9, the precipitate was transferred to the aging reaction vessel using a peristaltic pump at a rate equal to the combined rate of the aqueous Ce and La precursor solutions and ammonia water being simultaneously introduced into the aging reaction vessel. Subsequently, a uniform aqueous mixture was maintained in the aging zone using a baffle-type stirrer. When the aqueous Ce and La precursor solutions introduced into the mixing reaction vessel were depleted, the entire precipitate was transferred to the aging reaction vessel, all unused aqueous ammonia solution was rapidly introduced, and the mixture was aged for approximately 18 hours. Afterward, the precipitate was filtered and washed with water, then placed in a vacuum oven and dried at approximately 100°C for approximately 10 hours. The dried precipitate was ground, placed in a calcinerator, and treated at approximately 500°C for 4 hours in an air atmosphere to obtain approximately 50g of La-Ce-O support.

[0063] To support 2 wt.% Ru, 1 g of the obtained La-Ce-O support was added to 50 mL of distilled water, followed by the addition of 0.04 g of ruthenium chloride hydrate and stirring. An aqueous ammonia solution was added dropwise to this aqueous solution to form a precipitate. The precipitate was filtered and washed with water, then placed in a vacuum oven and dried at approximately 100 °C for about 10 hours. The dried precipitate was ground into a powder and subjected to reduction treatment at approximately 500 °C in a 100% hydrogen gas atmosphere for about 2 hours to obtain a Ru / Ce-La-O catalyst.

[0064] [Example 2]

[0065] A Ru / Ce-La-O catalyst was obtained in the same manner as in Example 1, except that the pH of the mixing reaction vessel was maintained at 9.5 (±0.2).

[0066] [Example 3]

[0067] A Ru / Ce-La-O catalyst was obtained in the same manner as in Example 1, except that the total molar ratio of Ce precursor and La precursor to the ammonia aqueous solution was prepared in an amount of 1:2.

[0068] [Comparative Example 1]

[0069] A Ru / Ce-La-O catalyst was obtained in the same manner as in Example 1, except that the pH of the mixing reaction vessel was maintained at 9.75 (±0.2).

[0070] [Comparative Example 2]

[0071] A Ru / Ce-La-O catalyst was obtained in the same manner as in Example 1, except that the pH of the mixing reaction vessel was maintained at 9.8 (±0.2).

[0072] [Comparative Example 3]

[0073] In the same manner as the manufacturing method disclosed in the example of Korean Patent Publication No. 10-2021-0147910, an aqueous solution of Ce and La precursors, comprising 75.7 g of cerium nitrate hydrate and 37.7 g of lanthanum nitrate hydrate mixed with distilled water, was introduced into a batch reactor, and an ammonia solution was added while stirring the aqueous solution in the batch reactor until the pH reached 9 to obtain a precipitate. The total amount of ammonia solution used at this time was approximately 1.5 times the total moles of the Ce precursor and the La precursor.

[0074] Subsequently, a La-Ce-O support was obtained using the precipitate, and the process of supporting Ru was carried out in the same manner as in Example 1 to obtain a Ru / Ce-La-O catalyst.

[0075] [Comparative Example 4]

[0076] A Ru / Ce-La-O catalyst was obtained using the same method as Comparative Example 3, except that the total amount of ammonia water used was prepared and applied as four times the total moles of the Ce precursor and La precursor. At this time, as the amount of ammonia water added increased, the pH in the batch reactor rose to 10.5.

[0077] The reaction conditions and ammonia decomposition rates of the Ru / Ce-La-O catalysts of Examples 1 to 3 and Comparative Examples 1 to 4 were as shown in Table 1 below.

[0078] Measurement of pH during mixing of ammonia water molar ratio in reactor, ammonia decomposition rate (@450 ℃), mixing reaction, maturation of reaction vessel, Example 1 CSTR Type 49.8394.87 %, Example 2 CSTR Type 49.59.8493.74 %, Example 3 CSTR Type 29.6190.99 %, Comparative Example 1 CSTR Type 49.759.8982.76 %, Comparative Example 2 CSTR Type 49.810.1461.04 %, Comparative Example 3 Batch Type 1.53→976.5 %, Comparative Example 4 Batch Type 43→10.581.05 %

[0079] The ammonia decomposition rate according to Table 1 above was measured as follows. To measure the ammonia decomposition rate, 0.2 g of the prepared Ru / Ce-La-O catalyst was packed into a fixed-bed reactor, and pretreatment was carried out under a hydrogen atmosphere at a temperature of 600 °C for 2 hours. Then, the temperature was lowered to 300 °C, and 100% ammonia was injected to a space velocity of 6,000 h -1 An evaluation of the ammonia decomposition reaction was performed under these conditions, and the temperature was increased from 300 ℃ to 450 ℃, and the ammonia decomposition rate at 450 ℃ was measured.

[0080] Furthermore, to observe the shape change of the La-Ce-O support according to the pH change of the mixing reactor, SEM images of the La-Ce-O support prepared according to Examples 1 and 2 and Comparative Examples 1 and 2 were analyzed. Figures 1 to 4 show SEM images of the La-Ce-O support prepared according to Examples 1 and 2 and Comparative Examples 1 and 2, respectively. Referring to the SEM images in Figures 1 to 4, it was confirmed that as the pH of the mixing reactor increased, the size of the individual particles became smaller, and then, through a process in which small particles clumped together to form one large mass, the particles grew into a hard and sharp shape.

[0081] In addition, to observe the surface morphology of the La-Ce-O support according to the pH change of the mixing vessel, the La-Ce-O support prepared according to Examples 1 and 2 and Comparative Examples 1 and 2 was analyzed using magnified SEM images. Figures 5 to 8 show magnified SEM images of the La-Ce-O support prepared according to Examples 1 and 2 and Comparative Examples 1 and 2, respectively. Referring to the magnified SEM images in Figures 5 to 8, it was confirmed that as the pH increased, the surface of the mesoporous structure formed by the intertwining of thin plates was filled with small particles, forming a plate-like surface.

[0082] From the SEM images according to FIGS. 1 to 8, it was confirmed that the La-Ce-O supports according to Examples 1 and 2 had particles of relatively uniform size and a mesoporous surface structure. In contrast, in Comparative Examples 1 and 2, in which the pH of the mixing reactor was set to exceed 9.5, it was confirmed that a La-Ce-O support having a surface with a mesoporous structure like that of Examples 1 and 2 was not formed.

[0083] In addition, SEM images of the La-Ce-O support prepared according to Example 3, in which ammonia water was applied such that the molar ratio of the total moles of Ce precursor and La precursor to the ammonia aqueous solution was 1:2, were as shown in Figures 9 and 10. Referring to Figures 9 and 10, although a mesoporous structure was observed on the surface of the prepared La-Ce-O support, it was confirmed that the mesoporous structure was filled due to the aggregation of fine particles, and the particle size was not uniform. This is understood to have affected the uniformity and surface structure of the La-Ce-O support particles by the insufficient amount of ammonia water introduced into the aging reactor after the formation of La-Ce aggregation nuclei, which prevented the formation of particles of uniform size and caused the fine particles to aggregate together. That is, to achieve a more uniform particle size and surface shape as in Examples 1 and 2, it may be desirable for the molar amount of the ammonia aqueous solution to exceed twice the total molar amount of the Ce precursor and La precursor.

[0084] The BET surface area and Ru dispersion of the Ru / La-Ce-O catalysts according to Examples 1, 2 and Comparative Example 3 were as shown in Table 2 below.

[0085] pHBET surface area (m 2 / g)Ru Dispersion (%) Example 19 36.945 4.603 Example 29.54 1.58 38.475 Comparative Example 29.875 5.46 18.1484

[0086] The above Ru dispersion was measured through CO-pulse chemisorption analysis using Micromeritics’ Autochem II 2920 instrument. Specifically, the Ru dispersion was determined by pre-treating the Ru / La-Ce-O catalyst for 1 hour in a 10 vol% hydrogen atmosphere (10 vol% H2 / N2 balance) at a temperature of 600 ℃, then injecting an inert gas and lowering the temperature to 60 ℃ to stabilize it. Subsequently, carbon monoxide gas was injected in a pulse, the adsorbed carbon monoxide gas was measured, and the dispersion of the active metal was calculated based on the amount of carbon monoxide gas adsorbed.

[0087] In addition, the BET surface area was measured using the BELSORP-MAX instrument from MicrotracBEL. Specifically, the BET surface area was measured after pre-treating the sample at 150 °C for 6 hours under a vacuum atmosphere. At this time, the specific surface area of ​​the sample was calculated by the Brunauer-Emmett-Teller (BET) method at a relative pressure range of 0.05 to 0.2 and a temperature of 350 °C.

[0088] According to Table 2, the total surface area (BET analysis results) of the Ru / La-Ce-O catalyst according to Examples 1 and 2 was larger for the La-Ce-O support (plate-shaped small particles) with the pH of the mixed reaction vessel controlled above 9.5 than for the La-Ce-O support (large particles with a mesoporous surface structure) with the pH of the mixed reaction vessel controlled to 9 to 9.5. However, when the dispersibility of the active metal (Ru) was confirmed through CO-Chemisorption, it was confirmed that the dispersibility of the active metal was significantly influenced by the surface shape of the La-Ce-O support rather than the BET surface area.

[0089] Furthermore, the surface morphology of the La-Ce-O support was analyzed through the analysis of the adsorption-desorption curves according to BET analysis of the La-Ce-O support prepared according to Examples 1 and 2 and Comparative Example 2.

[0090] FIGS. 11 to 13 show the adsorption-desorption curves according to BET analysis of La-Ce-O supports prepared according to Examples 1 and 2 and Comparative Example 2, respectively. Referring to FIGS. 11 to 13, it was confirmed that the adsorption-desorption curves of the La-Ce-O supports prepared according to Examples 1 and 2 exhibited the shape of an H3 hysteresis curve. The shape of an H3 hysteresis curve may indicate a surface having a wedge-shaped mesoporous structure formed by thin plate-like particles intertwining with each other. In contrast, it was confirmed that the adsorption-desorption curve of the La-Ce-O support prepared according to Comparative Example 2 exhibited the shape of an H4 hysteresis curve. The shape of an H4 hysteresis curve may indicate a surface with elongated pores formed by thin plate-like particles clumping together, rather than a mesoporous shape of the catalyst surface.

[0091] Furthermore, SEM images of the La-Ce-O support prepared according to Comparative Example 3 are shown in FIGS. 14 and 15. Referring to FIGS. 14 and 15, it was confirmed that the size of the prepared La-Ce-O support particles was very irregular, and that the mesoporous structure on the surface of the La-Ce-O support was largely filled by fine particles. This is attributed to the fact that the pH changes significantly as the mixing and aging reactions are carried out in a single batch reactor, and furthermore, the formation of La-Ce aggregation nuclei and aging proceed simultaneously. Specifically, in the case of Comparative Example 3 using a general co-precipitation method, the pH of the precursor solution increases from an initial pH of about 3 to a final pH of 9. Since the shape of the La-Ce-O support prepared at this time changes sensitively with changes in pH, a La-Ce-O support with a very irregular shape is formed under a rapidly changing pH atmosphere, and consequently, a problem arises in which the active metal cannot be supported with a high distribution. In addition, in the case of Comparative Example 3, in which ammonia water was added until the pH reached 9, it was found that when the La-Ce-O support was formed, a sufficient supply of hydroxyl groups was not provided, causing the particles to clump together and form a La-Ce-O support with a low specific surface area.

[0092] In addition, SEM images of the La-Ce-O support prepared according to Comparative Example 4, in which a batch reactor was used but the amount of ammonia water was increased, are shown in Figs. 16 and 17. Referring to Figs. 16 and 17, it was confirmed that the results were similar to those of Comparative Example 3. This is attributed to the fact that when the mixing and aging reactions are carried out in a single batch reactor, the pH changes significantly during the formation of La-Ce aggregation nuclei even when the amount of ammonia water is increased. In other words, similar to Comparative Example 3, it was confirmed that the size and surface morphology of the La-Ce-O support were not controlled because the formation of a mesoporous structure and fine particles occurred simultaneously in Comparative Example 4.

Claims

1. (A) A step of preparing a basic aqueous solution having a predetermined pH within the range of pH 8.5 to pH 9.5 by adding a basic substance to water; (B) A step of forming La-Ce aggregation nuclei by adding dropwise a precursor solution containing a La precursor and a Ce precursor and a basic substance to the basic aqueous solution so that the pH of the basic aqueous solution is maintained within ±0.2 of the predetermined pH; (C) A step of additionally adding a basic substance to the solution in which the La-Ce aggregation nuclei are formed to form La-Ce aggregates; (D) a step of calcining the above La-Ce aggregates to form a La-Ce-O carrier; and (E) a step of supporting an active metal on the La-Ce-O carrier; comprising, Method for manufacturing an ammonia decomposition catalyst.

2. In Claim 1, A method for producing an ammonia decomposition catalyst, wherein the basic substance is an aqueous solution containing at least one selected from the group consisting of ammonia, sodium hydroxide, potassium hydroxide, hydrazine, and sodium carbonate.

3. In Claim 1, (B) Step and (C) Step are performed in a mixing reactor and an aging reactor, respectively, in a method for producing an ammonia decomposition catalyst.

4. In Claim 1, A method for producing an ammonia decomposition catalyst, wherein the total number of moles of hydroxyl groups contained in the basic material used in steps (A), (B), and (C) is 2 to 5 times the total number of moles of metal ions in the aqueous precursor solution added.

5. In Claim 1, A method for manufacturing an ammonia decomposition catalyst in which the active metal is Ru.

6. In Claim 1, A method for preparing an ammonia decomposition catalyst, wherein the dispersion of the active metal supported on the La-Ce-O carrier is at least 30%.

7. In Claim 1, A method for preparing an ammonia decomposition catalyst, wherein the above-mentioned La-Ce-O carrier has a mesoporous surface that exhibits the shape of an H3 hysteresis curve during BET adsorption-desorption analysis.

8. Ammonia decomposition catalyst produced by the method of claim 1.

9. A method for decomposing ammonia, comprising the step of decomposing ammonia into nitrogen and hydrogen in the presence of an ammonia decomposition catalyst according to claim 8.

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