Molded catalyst for ammonia decomposition and manufacturing method therefor

Abstract

The present invention relates to a molded catalyst for ammonia decomposition and a manufacturing method therefor and, more specifically, to an economical method for manufacturing a molded catalyst for ammonia decomposition and a molded catalyst manufactured thereby, wherein a catalyst carrier is prepared by coating various molded bodies such as beads, pellets, honeycombs, and the like with lanthanum and cerium and then ruthenium is supported on the catalyst carrier to produce an ammonia decomposition catalyst as a catalyst with superior activity in an ammonia decomposition reaction, whereby the strength of the coating can be sufficiently expressed, the catalytic activity can be improved or maintained even with a small amount of a catalytically active material (ruthenium), the loss of a coating solution can be reduced during a catalyst coating process, and the molded catalyst can be manufactured without a separate powder catalyst manufacturing process.

Description

Title of Invention: MOLDED CATALYST FOR AMMONIA DECOMPOSITION AND MANUFACTURING METHOD THEREFOR Technical Field [1] The present disclosure relates generally to a molded catalyst for ammonia decomposition and a manufacturing method therefor. More particularly, the present disclosure relates to an economical method for manufacturing a molded catalyst for ammonia decomposition and a molded catalyst manufactured thereby, in which a catalyst support is prepared by coating various molded bodies, such as beads, pellets, and honeycombs, with one or more metals or metal oxides and then supporting a catalytically active material thereon to produce a catalyst having excellent activity for an ammonia decomposition reaction. This improves or maintains catalytic activity even with a small amount of catalytically active material while achieving sufficient coating strength, reduces the loss of coating solution during the catalyst coating process, and enables the molded catalyst to be manufactured without a separate process for preparing a powder catalyst. Background Art [2] Hydrogen has attracted considerable attention as a next-generation clean energy source due to its high gravimetric energy density and carbon emission-free nature. However, the industrial and commercial utilization of hydrogen as an energy source has been limited by its low volumetric energy density, low boiling point, and difficulties in handling (transportation and storage). [3] These limitations may be overcome through the use of a hydrogen carrier, which enables hydrogen to be readily transported to the point of consumption and subsequently released on-site through reforming or decomposition. Among various hydrogen carriers, ammonia is known as a promising candidate because of its low production cost, high volumetric and gravimetric energy densities, ease of liquefaction, ability to serve as a clean molecular hydrogen-storage medium, and capability of being catalytically decomposed to produce carbon-free hydrogen. [4] Currently, catalytic decomposition of ammonia has emerged as one of the promising approaches for hydrogen production, and extensive efforts have been devoted to the development of highly efficient catalysts for this reaction. Commonly used catalysts for ammonia decomposition consist mainly of a catalyst support and catalytically active metals supported on the surface of the catalyst support. Such catalysts are designed and optimized to provide appropriate selectivity and reactivity suitable for a desired process. [5] Such catalysts for ammonia decomposition are typically prepared in powder form by combining a catalyst support and catalytically active metals through various methods such as impregnation, co-precipitation, ion-exchange, hydrothermal synthesis, and fusion. The prepared powder catalyst is subsequently mixed with various additives and extruded into different shapes through a multi-stage injection molding method. However the drawbacks of the injection molding process lie in that the manufacturing process is highly complicated, a large volume of powdered catalyst is required, and a significant amount of dust generated during the process makes production, installation, and maintenance operations difficult. [6] Recently, in order to reduce pressure drop within a catalyst layer and to increase the surface area of the catalyst, there has been proposed a technology in which catalyst-containing materials are applied onto the internal channel surfaces of ceramic or metallic molded bodies having a bead or honeycomb shape using methods including dip coating, wash coating, and spray coating. In such coated catalysts based on ceramic or metallic molded bodies, the adhesion between the catalyst layer and the molded body is critical. Key factors influencing this adhesion include surface treatment methods of the molded body, preparation methods of catalyst coating solution, coating techniques, and drying and calcination conditions. [7] Korean Patent No. 10-0807730 discloses a method for improving the adhesion between a molded body and a catalyst by forming an interfacial adhesion layer on the surface of the molded body using atomic layer deposition (ALD) or chemical vapor deposition (CVD). In this approach, a material identical to the catalyst or having surface properties similar to those of the catalyst is deposited at the interface between the molded body and the catalyst. Korean Patent No. 10-1403698 discloses a method for manufacturing a metallic structured catalyst in which a metallic molded body is brought into contact with a mixed solution containing a precursor of a metal catalyst and a precipitant so that metal precipitates are formed on the surface of the metallic molded body, followed by heat treatment. Through this process, uniformly dispersed metal nanoparticles are supported on the surface of the metallic molded body, with enhanced bonding strength between the catalyst support layer and the surface of the metallic molded body. [8] Additionally, Korean Patent Application Publication No. 2023-0103587 provides a method in which a catalyst coating solution is deeply infiltrated into the surface of a molded body using an ultrasonic technique so that the catalyst coating solution can be uniformly distributed over the surface of the molded body. Subsequently, the catalyst coating solution is fixed onto the surface of the molded body at a constant and uniform thickness using an air knife combined with an infrared lamp. [9] However, the aforementioned conventional technologies suffer from the following problems. That is, they require expensive reaction equipment or vacuum environments, thereby limiting the ease of practical application and commercial feasibility of the technology. Additionally, it is difficult to uniformly disperse the catalyst coating solution over the surface of the molded body to obtain a uniform and consistent coating layer. Moreover, the adhesive strength between the catalyst coating layer and the molded body remains insufficient, and a significant loss of the catalyst coating solution may occur.

[10] Due to these problems, when one or more metals or metal oxides are directly coated onto molded bodies such as beads, pellets, or honeycombs, a weak bond with the surface of the molded body may lead to coating failure, or even when a coating layer is successfully formed, it may easily detach from the molded body. As a result, the catalytic activity and physical durability of the catalyst may be deteriorated. This phenomenon tends to become more pronounced when using composite metal oxides or metals composed of two or more components chemically bonded to each other.

[11] In order to address the above-described problems, the present disclosure provides a manufacturing method for a molded catalyst, and a molded catalyst manufactured thereby. The manufacturing method includes coating various molded bodies, such as beads, pellets, and honeycombs, with lanthanum and cerium and then supporting a catalytically active material thereon to produce a catalyst having excellent activity for an ammonia decomposition reaction. This approach enables lanthanum and cerium to be directly formed on the molded body without separately preparing a metal oxide or metal powder, while achieving sufficient coating strength. Additionally, it enables catalytic activity to be improved or maintained even with a small amount of catalytically active material, while reducing the loss of catalyst coating solution, thereby increasing economic feasibility.

[12] [Documents of Related Art]

[13] [Patent Documents]

[14] (Patent Document 1)  Korean Patent No.  10-0807730 (Publication Date: 2007.10.01.)

[15] (Patent Document 2)  Korean Patent No.  10-1403698 (Publication Date: 2013.02.07.)

[16] (Patent Document 3) Korean Patent Application Publication No. 2023-0103587 (Publication Date: 2023.07.07.) Disclosure Technical Problem

[17] Accordingly, the present disclosure has been made keeping in mind the above problems occurring in the related art, and one objective of the present disclosure is to provide a manufacturing method for a molded catalyst for ammonia decomposition and a molded catalyst manufactured thereby, in which various molded bodies, such as beads, pellets, and honeycombs, are coated with a coating component including lanthanum and cerium and then a catalytically active material is supported thereon to produce an ammonia decomposition catalyst. This improves catalytic activity for ammonia decomposition even with a small amount of catalytically active material while achieving sufficient coating strength, and minimizes the amount of catalyst coating solution used while reducing the loss of catalyst coating solution. Technical Solution

[18] In order to accomplish the above objective, the present disclosure provides a manufacturing method for a molded catalyst for ammonia decomposition, the manufacturing method including: (a) immersing a molded body in a coating solution containing a coating component including lanthanum and cerium and a first additive, thereby forming a wet layer containing the coating component on a surface of the molded body; (b) immersing the molded body having the wet layer formed thereon in a fixation solution in which an alkali metal hydroxide is dissolved, thereby fixing the wet layer on the surface of the molded body; (c) subjecting the molded body having the wet layer fixed thereon to heat treatment, thereby forming a coating layer containing the coating component on the surface of the molded body; (d) supporting ruthenium, as a catalytically active material, on the coating layer of the molded body; and (e) subjecting the molded body having the catalytically active material supported thereon to drying and optional calcination, thereby preparing a catalytically active material-supported molded body, in which the first additive may include at least one selected from the group consisting of methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, purified starch, dextrin, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyethylene glycol, and silica sol.

[19] In one embodiment of the present disclosure, the molded body of step (a) may be made of alumina.

[20] In one embodiment of the present disclosure, the molded body of step (a) may be surface-treated with acid and / or base.

[21] Additionally, in one embodiment of the present disclosure, the acid may include at least one selected from the group consisting of HCl, HNO3, H2SO4, HF, H3PO4, and organic acid, and the base may include at least one selected from the group consisting of LiOH, NaOH, KOH, NH4OH, and NaBH4.

[22] Additionally, in one embodiment of the present disclosure, the coating solution of step (a) may include 0.5 to 10 parts by weight of the first additive based on 100 parts by weight of the coating component.

[23] Additionally, in one embodiment of the present disclosure, the coating solution of step (a) may further include at least one second additive selected from the group consisting of polyhydric alcohols, waxes, and lubricants.

[24] Additionally, in one embodiment of the present disclosure, the coating solution of step (a) may include 5 to 90 parts by volume of the second additive based on 100 parts by volume of the coating component.

[25] Additionally, in one embodiment of the present disclosure, the fixation solution of step (b) may include at least one alkali metal hydroxide selected from the group consisting of LiOH, NaOH, and KOH.

[26] Additionally, in one embodiment of the present disclosure, step (b) may include immersing the molded body having the wet layer formed thereon in the fixation solution for 0.5 to 4 hours to fix the wet layer on the surface of the molded body.

[27] The present disclosure further provides a molded catalyst for ammonia decomposition, in which ruthenium is supported on a support having a coating layer containing lanthanum and cerium formed on an alumina molded body.

[28] The present disclosure further provides a molded catalyst for ammonia decomposition, the molded catalyst being manufactured by the manufacturing method according to the present disclosure.

[29] The present disclosure further provides an ammonia decomposition method, including: bringing ammonia into contact with the molded catalyst according to the present disclosure. Advantageous Effects

[30] According to the present disclosure, in manufacturing a molded catalyst for ammonia decomposition, a catalyst support is prepared by coating various molded bodies, such as beads, pellets, and honeycombs, with one or more metals or metal oxides and then supporting a catalytically active material thereon to produce a molded catalyst for ammonia decomposition. Accordingly, catalytic activity can be improved or maintained even with a small amount of catalytically active material, and the molded catalyst for ammonia decomposition can be manufactured without a separate process for preparing a powder catalyst.

[31] Additionally, according to the present disclosure, in coating the surface of a molded body with metals or metal oxides as described above, the incorporation of a first additive, or a combination of first and second additives, into a coating solution can improve adhesion between the molded body and a coating layer, thereby providing the resulting molded catalyst with sufficient mechanical strength.

[32] Furthermore, in coating the surface of the molded body with metals or metal oxides as described above, the incorporation of the first additive, or the combination of the first and second additives, into the coating solution can minimize the amount of coating solution used while allowing the coating solution remaining after the coating process to be reused. During fixation of the coating layer by immersing the coated molded body in a fixation solution, the components of the coating layer can be also prevented from leaching into the fixation solution, thereby allowing the fixation solution to be reused. As a result, unnecessary material loss during the manufacture of the molded catalyst can be reduced. Moreover, a high catalytic activity can be achieved using only small amounts of expensive catalytically active material and components constituting the coating layer, thereby enabling the economical mass production of molded catalysts for ammonia decomposition. Description of Drawings

[33] FIG. 1 is a flowchart schematically illustrating a manufacturing method for a molded catalyst for ammonia decomposition according to an embodiment of the present disclosure. Best Mode

[34] Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Generally, the nomenclature used herein is well known in the art and is the nomenclature normally used.

[35] It will be further understood that the terms “comprise”, “include”, “have”, etc. when used in this specification, specify the presence of stated features, numerical values, steps, operations, elements, components, and / or combinations thereof but do not preclude the presence or addition of one or more other features, numerical values, steps, operations, elements, components, and / or combinations thereof.

[36] Unless otherwise specified, the reactions and mixing processes described hereinafter may be carried out at room temperature and atmospheric pressure, and may be performed under conventional reaction and mixing conditions without additional modifications. However, the present disclosure should not be interpreted in a manner that departs from what would be clearly understood by those skilled in the art.

[37] The present disclosure relates to a manufacturing method for a molded catalyst for ammonia decomposition, the manufacturing method including: (a) immersing a molded body in a coating solution containing a coating component including lanthanum and cerium and a first additive, thereby forming a wet layer containing the coating component on a surface of the molded body; (b) immersing the molded body having the wet layer formed thereon in a fixation solution in which an alkali metal hydroxide is dissolved, thereby fixing the wet layer on the surface of the molded body; (c) subjecting the molded body having the wet layer fixed thereon to heat treatment, thereby forming a coating layer containing the coating component on the surface of the molded body; (d) supporting ruthenium, as a catalytically active material, on the coating layer of the molded body; and (e) subjecting the molded body having the catalytically active material supported thereon to drying and optional calcination, thereby preparing a catalytically active material-supported molded body. The present disclosure further relates to a molded catalyst for ammonia decomposition manufactured by the manufacturing method.

[38] Hereinafter, a manufacturing method for a molded catalyst for ammonia decomposition according to the present disclosure and a molded catalyst for ammonia decomposition manufactured thereby will be described in detail with reference to the accompanying drawings.

[39] FIG. 1 is a flowchart schematically illustrating a manufacturing method for a molded catalyst for ammonia decomposition according to an embodiment of the present disclosure.

[40] As illustrated in FIG. 1, in the manufacturing method for the molded catalyst for ammonia decomposition according to the present disclosure, first, a molded body is immersed in a coating solution containing a coating component including lanthanum and cerium so that a wet layer containing lanthanum and cerium is formed on a surface of the molded body [step (a)].

[41] The coating component including lanthanum and cerium contained in the coating solution may include at least one selected from a support material capable of supporting a catalytically active material (ruthenium) and a precursor of the support material, and may include metallic forms or metal oxide forms of lanthanum and cerium.

[42] In this case, the combined concentration of lanthanum and cerium in the coating solution may be 1 to 100 mmol mL-1, and preferably 5 to 10 mmol mL-1.

[43] With respect to the relative amounts of lanthanum and cerium, the number of moles of lanthanum may be 0.2 to 0.5 times the total number of moles of lanthanum and cerium, and preferably 0.25 to 0.45 times the total number of moles of lanthanum and cerium.

[44] In the resulting catalyst, lanthanum and cerium may be present in the form of metals or metal oxides, and preferably in the form of metal oxides.

[45] As a precursor of lanthanum or cerium, at least one selected from an oxide, chloride, hydroxide, bromide, iodide, nitrate, sulfate, carbonate, acetate, oxalate, fluoride, isopropoxide, and organometallic complex of lanthanum or cerium may be used.

[46] In the coating solution, the coating component may be present in a dissolved or dispersed state in a solvent. The solvent may be used without limitation as long as it is a solvent capable of dissolving or dispersing the coating component. Examples thereof include water such as distilled water and purified water; alcohols such as methanol, ethanol, and isopropanol; and glycols. Among these, preferred is water.

[47] The wet layer is formed via a dip coating method in which the molded body is immersed in the coating solution, allowing the coating solution to infiltrate into the molded body. In this process, dip coating is performed by dipping the molded body into the coating solution to form the wet layer 200 containing components of the coating solution on the surface of the molded body. The coating temperature and coating time may be controlled depending on the type, concentration, and amount of the coating solution and the molded body. For example, the temperature of the coating solution during dipping (immersion) may be 20°C to 40°C, and the coating time may be 0.5 to 4 hours. Additionally, the coating process may be repeated multiple times so that the coating layer having a desired thickness and strong adhesion is formed on the surface of the molded body.

[48] Additionally, the coating solution may include a first additive to bind the coating component to the surface of the molded body and impart cohesion and viscosity to the coating component. The first additive prevents the coating component contained in the wet layer formed on the surface of the molded body from being leached into a fixation solution during a fixation step which will be described later.

[49] The first additive is not particularly limited as long as it is an organic binder capable of improving adhesion of the coating component to the surface of the molded body and preventing the coating component in the wet layer from being leached into the fixation solution during the fixation step. Examples thereof include at least one selected from the group consisting of methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, purified starch, dextrin, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyethylene glycol, and silica sol. From the viewpoint of forming a uniform wet layer, the first additive may preferably be at least one selected from the group consisting of methyl cellulose, polyvinyl alcohol, polyethylene glycol, and silica sol, and more preferably methyl cellulose and / or polyvinyl alcohol.

[50] Due to the addition of the first additive, when performing the fixation step in which the molded body on which the wet layer has been formed is immersed in the fixation solution, the coating component contained in the wet layer may be prevented from being leached into the fixation solution. Accordingly, the loss of the coating component may be prevented, and contamination of the fixation solution may also be avoided. As a result, the manufacturing method for the molded catalyst becomes more economical and simpler.

[51] The first additive may be added to the coating solution in an amount of 0.5 to 10 parts by weight, and preferably 1 to 3 parts by weight, based on 100 parts by weight of the coating component. When the amount of the first additive is less than 0.5 parts by weight based on 100 parts by weight of the coating component, the first additive may not sufficiently function as a binder. On the other hand, when the amount of the first additive exceeds 10 parts by weight based on 100 parts by weight of the catalyst support component, the excessive amount of the first additive may reduce the relative content of the coating component and may cause problems during the fixation step.

[52] Meanwhile, the coating solution may further include a second additive for suppressing shrinkage or delamination of the coating layer that may occur during a drying process which will be described later. The second additive may include at least one selected from polyhydric alcohols, such as glycerol, ethylene glycol, and propylene glycol, or waxes and lubricants.

[53] The second additive may be added in an amount of 5 to 90 parts by volume based on 100 parts by volume of the coating component. Within the above content range, the second additive functions to form a uniform coating layer without deteriorating the catalyst properties.

[54] The molded body onto which the coating solution is applied may have various shapes depending on a reaction to which the molded catalyst is applied. Specifically, the molded body may be in the form of a bead, pellet, felt, mat, mesh, foam, foil, honeycomb, and fin, and preferably in the form of a bead or honeycomb. Additionally, the molded body is preferably made of alumina.

[55] Additionally, the molded body may undergo a chemical surface treatment using a surface treatment agent such as an acid and / or a base in order to form polar functional groups such as hydroxyl groups and to create an unstable surface state. This surface modification facilitates uniform dispersion of the coating component on the surface of the molded body. In this case, the acid used for surface treatment of the molded body may include at least one selected from the group consisting of HCl, HNO3, H2SO4, HF, H3PO4, and organic acid. The organic acid is not particularly limited, and examples thereof include acetic acid, formic acid, lactic acid, citric acid, acrylic acid, sulfonic acid, and carboxylic acid. The base may include at least one selected from the group consisting of base solutions containing LiOH, NaOH, KOH, NH4OH, and NaBH4, and preferably KOH or NH4OH.

[56] As described above, in the present disclosure, by applying the dip coating method to form a coating layer on the surface of the molded body, even a molded body having a complex structure may be provided with a uniform and thin coating layer on the surface thereof, and the coating amount may be easily controlled. Additionally, through the use of the first additive and / or the second additive, the loss of the coating solution may be minimized while enabling continuous use of the coating solution, thereby making economical mass production of the molded catalyst possible.

[57] Furthermore, in the present disclosure, after immersion of the molded body in the coating solution, excess coating solution remaining in the wet layer on the surface of the molded body may be removed so as to improve the strength of the coating layer while securing an appropriate thickness of the coating layer. In this case, the intensity and duration of an air blow for removing the excess coating solution may be controlled, or the viscosity of the coating solution may be controlled according to the content of the additives.

[58] Subsequently, the molded body on which the wet layer has been formed by dip coating is immersed in a fixation solution in which an alkali metal hydroxide is dissolved to perform fixation of the wet layer [step (b)].

[59] In step (b), the wet layer formed on the surface of the molded body in step (a) is fixed using the fixation solution, thereby enabling the coating component contained in the wet layer to be strongly bound to the surface of the molded body.

[60] The fixation solution is not particularly limited as long as it is a solution in which an alkali metal hydroxide capable of fixing the wet layer containing the coating component contained in the coating solution onto the surface of the molded body is dissolved in a solvent. Specifically, the alkali metal hydroxide may include at least one selected from the group consisting of LiOH, NaOH, and KOH. From the viewpoint of fixation and cost efficiency, preferred is NaOH and / or KOH.

[61] The solvent of the fixation solution is not particularly limited as long as it is capable of dissolving the alkali metal hydroxide, such as LiOH, NaOH, or KOH. Examples thereof include water, such as distilled water and purified water; alcohols, such as methanol, ethanol, and isopropanol; and glycols, and preferably water.

[62] The concentration of the alkali metal hydroxide in the fixation solution may be 0.5 to 4 mol L-1, and preferably 0.75 to 1.25 mol L-1.

[63] In this case, the fixation may be carried out by immersing the molded body on which the wet layer has been formed in the fixation solution at a temperature of 20°C to 60°C for 0.5 to 4 hours, and preferably for 1 to 3 hours. When the fixation is performed within the above temperature and time ranges, a coating layer having uniformity and strong adhesion may be obtained. Additionally, problems such as insufficient formation of the coating layer due to excessive exposure of the wet layer to the reaction solution and leaching of components contained in the wet layer, as well as contamination of the reaction solution that makes reuse difficult, may be prevented.

[64] Subsequently, the molded body on which the wet layer has been fixed is subjected to heat treatment to form a support coating layer on the surface of the molded body [step (c)].

[65] In step (c), the molded body on which the wet layer has been fixed by immersion in the fixation solution in step (b) is removed from the fixation solution, and the fixed wet layer is subjected to heat treatment. The heat treatment may further include, in detail, a drying step. That is, through the drying step, the solvent present in the fixation solution may be completely removed. The drying may be performed, for example, at 40°C to 120°C for a predetermined period of time, specifically for 4 to 48 hours, using a conventional method such as hot-air drying or constant-temperature constanthumidity drying. When the drying temperature falls within the above range, sufficient drying of the fixed wet layer may be achieved, while preventing excessive drying or delamination of the dried wet layer due to abrupt reactions of components contained in the wet layer.

[66] Thereafter, the heat treatment of the molded body may be variously modified in consideration of the glass transition temperature specific to the molded body or the catalyst support component. However, in order to obtain a molded body in which a support coating layer is formed without cracks, the heat treatment is preferably performed by calcination at 350°C to 700°C for a predetermined time period in an oxidizing atmosphere. The heat treatment time may vary depending on conditions such as the calcination temperature, coating amount, and the size and quantity of the molded body, but may be, for example, 2 to 6 hours.

[67] When the heat treatment temperature falls below 350°C, removal of additives contained in the dried wet layer may not be sufficiently achieved due to a low sintering temperature. On the other hand, when the temperature exceeds 700°C, excessive deformation of the coating layer and the molded body may occur due to an excessively high sintering temperature. Additionally, during the heat treatment process, a rapid temperature change may cause abrupt combustion and oxidation reactions of the additives, thereby generating cracks and delamination in the coating layer and significantly deteriorating the strength of the coating layer. Therefore, it is preferable that the temperature is gradually increased at a rate of equal to or less than 5°C per minute.

[68] Subsequently, ruthenium is supported as a catalytically active material on the coating layer of the molded body [step (d)].

[69] In step (d), the supporting of ruthenium is not particularly limited as long as it is a method capable of supporting the ruthenium on the molded body on which the coating layer has been formed. Specifically, the method may include a hydrothermal synthesis method, a co-precipitation method, an impregnation method, a mechanical mixing method, or a deposition method, and is preferably an impregnation method.

[70] In one embodiment, among the supporting methods, the impregnation may be performed by dissolving a catalytically active material or a precursor thereof in a solvent, and then uniformly distributing the resulting solution over the support coating layer, followed by evaporation of the solvent. In this case, the solvent is not particularly limited as long as it can uniformly disperse the precursor of the catalytically active material. Examples thereof include water, methanol, ethanol, propanol, butanol, and acetone. The amount of the solvent is not particularly limited as long as it allows uniform dispersion of the catalytically active material.

[71] The amount of ruthenium supported may vary depending on the reaction type, but may be 0.1 to 40 wt.% based on the total weight of the molded body, and preferably 0.1 to 10 wt.%.

[72] Subsequently, the molded body on which the catalytically active material has been supported is subjected to drying and optional calcination to prepare a catalytically active material-supported molded body [step (e)].

[73] The drying in step (e) may be performed at 50°C to 120°C for 2 to 48 hours using a conventional method, such as oven drying, hot-air drying, or constant-temperature constant-humidity drying.

[74] Although the drying condition may vary depending on circumstances, when the drying temperature falls below 50°C, the solvent used in the supporting process may not be sufficiently removed due to the low drying temperature. On the other hand, when it exceeds 120°C, rapid volatilization of the solvent may cause collapse of the coating layer. Therefore, it is preferable to maintain the drying temperature within the above range.

[75] The dried molded body may be further subjected to calcination. In order to obtain a molded catalyst without cracks, the calcination is preferably performed at 300°C to 500°C for a predetermined period of time in an oxidizing atmosphere. The calcination time may vary depending on conditions such as the calcination temperature, loading amount, and the size and quantity of the molded body, but may be, for example, 1 to 4 hours.

[76] The above calcination temperature range is preferred in order to avoid problems in which the catalytically active material is not sufficiently stabilized due to a low sintering temperature, or in which dispersion of the catalytically active material is deteriorated and deformation of the molded body occurs due to an excessively high sintering temperature. Additionally, during the calcination process, a rapid temperature change may cause cracks and pores in the molded body and in the coating layer formed on the surface thereof, thereby significantly reducing the strength of the coating layer. Therefore, it is preferable that the temperature is gradually increased at a rate of equal to or less than 10°C per minute.

[77] Additionally, the present disclosure provides a molded catalyst for ammonia decomposition, the molded catalyst being manufactured by a manufacturing method including: (a) immersing a molded body in a coating solution containing a coating component including lanthanum and cerium and a first additive, thereby forming a wet layer containing the coating component on a surface of the molded body; (b) immersing the molded body having the wet layer formed thereon in a fixation solution in which an alkali metal hydroxide is dissolved, thereby fixing the wet layer on the surface of the molded body; (c) subjecting the molded body having the wet layer fixed thereon to heat treatment, thereby forming a coating layer containing the coating component on the surface of the molded body; (d) supporting ruthenium, as a catalytically active material, on the coating layer of the molded body; and (e) subjecting the molded body having the catalytically active material supported thereon to drying and optional calcination, thereby preparing a catalytically active material-supported molded body.

[78] Detailed descriptions of the manufacturing method including steps (a) to (e) remain the same as those described above, and therefore will not be repeated herein.

[79] The molded catalyst for ammonia decomposition manufactured by the manufacturing method according to the present disclosure exhibits improved adhesion between the molded body and the coating layer, thereby achieving sufficient coating strength. Additionally, by using the first additive and / or the second additive, the loss of the catalyst coating solution may be reduced while improving the uniformity of the coating layer. Additionally, in the molded catalyst for ammonia decomposition manufactured by the manufacturing method according to the present disclosure, ruthenium is supported as a catalytically active material on the coating layer, so that catalytic activity for ammonia decomposition may be significantly improved even with a relatively small amount of the catalytically active material.

[80] Additionally, the present disclosure provides a molded catalyst for ammonia decomposition, or a molded catalyst for ammonia decomposition manufactured by the manufacturing method according to the present disclosure, in which ruthenium is supported on a support having a coating layer containing lanthanum and cerium formed on an alumina molded body.

[81] Additionally, the present disclosure provides an ammonia decomposition method in which ammonia is brought into contact with the molded catalyst for ammonia decomposition according to the present disclosure.

[82] An ammonia-containing gas to be treated in the ammonia decomposition method of the present disclosure is not particularly limited, but may be ammonia gas or an ammonia-containing gas, or may be a gas containing a substance, such as urea, that generates ammonia through thermal decomposition.

[83] The ammonia-containing gas may further contain other components as long as the components are present in amounts that do not cause catalyst poisoning. The reaction temperature is preferably 300°C to 600°C. The reaction pressure is preferably 0.002 to 2 MPa in terms of absolute pressure, and more preferably 0.004 to 1 MPa.

[84]

[85] Hereinafter, the present disclosure will be described in more detail with reference to preferred examples to aid understanding. However, the following examples are merely illustrative of the present disclosure, and the scope of the present disclosure is not limited thereto.

[86]

[87]        <Example 1>

[88] A solution was prepared by dissolving 4 mmol (1.7544 g) of Ce(NO3) 3 • 6H2O (Sigma, 99%) and 2 mmol (0.8661 g) of La(NO3) 3 • 6H2O (Sigma, 99%) as coating components in 10 mL of deionized water. Separately, a solution was prepared by dissolving 1 g of methyl cellulose as a first additive in 10 mL of deionized water and 30 mL of ethanol (99.9%), and 11 mL of the solution was taken and added to the above coating component solution. Thereafter, 5 mL of glycerol was additionally mixed to prepare a coating solution.

[89] Subsequently, 15 g of alumina beads (average diameter: 3 mm) were dip-coated in the prepared coating solution at room temperature for 60 minutes. The coated beads were then immersed in 20 mL of a 1 M KOH fixation solution at room temperature for 30 minutes so as to undergo fixation.

[90] After completion of fixation, the fixed alumina beads were dried in an oven at 60°C for 24 hours, followed by heat treatment at 600°C (heating rate: 5°C / min) for 6 hours.

[91] Thereafter, 12 g of the heat-treated alumina beads were suspended in a solution prepared by diluting 15.2586 mL of 1.5 wt.% ruthenium nitrosyl nitrate solution with 50 mL of deionized water, followed by solvent evaporation at 80°C under 400 mbar. The resulting material was dried in an oven at 100°C for 24 hours, and subsequently calcined at 350°C (heating rate: 10°C / min) for 2 hours. Thus, a Ru / La-Ce / Al2O3 molded catalyst was obtained.

[92]

[93] <Examples 2 to 4>

[94] Ru / La-Ce / Al2O3 molded catalysts were manufactured in the same manner as in Example 1, except that fixation was performed by immersion for 1 hour, 2 hours, and 3 hours in Examples 2, 3, and 4, respectively.

[95]

[96] <Examples 5 to 7>

[97] Ru / La-Ce / Al2O3 molded catalysts were manufactured in the same manner as in Example 1, except that polyvinyl alcohol (manufacturer: Sigma-Aldrich; average molecular weight: 89,000 to 98,000), polyethylene glycol (manufacturer: Sigma-Aldrich; average molecular weight: 400), and silica sol (manufacturer: Sigma-Aldrich; model name: LUDOX®-AS40) were used as the first additive instead of methyl cellulose in Examples 5, 6, and 7, respectively.

[98]

[99]        <Example 8>

[100] A Ru / La-Ce / Al2O3 molded catalyst was manufactured in the same manner as in Example 1, except that the alumina beads were surface-treated by immersion in 1 M KOH for 1 hour before being immersed in the coating solution.

[101]

[102]      <Comparative Example 1>

[103] 12 g of alumina beads having an average diameter of 3 mm were suspended in a solution prepared by diluting 15.2586 mL of a 1.5 wt.% ruthenium nitrosyl nitrate solution with 50 mL of deionized water, followed by solvent evaporation at 80°C under 400 mbar. The resulting material was dried in an oven at 100°C for 24 hours, and subsequently calcined at 350°C (heating rate: 10°C / min) for 2 hours. Thus, a Ru / Al2O3 molded catalyst was obtained.

[104]

[105]      <Comparative Example 2>

[106] A solution was prepared by dissolving 3.202 g of La(NO3) 3 • 6H2O and 6.4865 g of Ce(NO3) 3 • 6H2O in 100 mL of deionized water, followed by suspending 15 g of alumina beads (average diameter: 3 mm) therein. The solvent was evaporated at 80°C under 400 mbar. The resulting molded body on which the coating components have been supported was dried in an oven at 100°C for 24 hours, followed by heat treatment at 500°C for 3 hours. Thereafter, 12 g of the heat-treated alumina beads were suspended in a solution prepared by diluting 15.2586 mL of 1.5 wt.% ruthenium nitrosyl nitrate solution with 50 mL of deionized water, followed by solvent evaporation at 80°C under 400 mbar. The resulting material was dried in an oven at 100°C for 24 hours, and subsequently calcined at 350°C (heating rate: 10°C / min) for 2 hours. Thus, a Ru / La-Ce / Al2O3 molded catalyst was obtained.

[107]

[108] <Comparative Example 3>

[109] A solution was prepared by dissolving 4 mmol (1.7544 g) of Ce(NO3) 3 • 6H2O (Sigma, 99%) and 2 mmol (0.8661 g) of La(NO3) 3 • 6H2O (Sigma, 99%) as coating components in 10 mL of deionized water. Separately, a solution was prepared by dissolving 1 g of methyl cellulose as a first additive in 10 mL of deionized water and 30 mL of ethanol (99.9%), and 11 mL of the solution was taken and added to the above coating component solution. Thereafter, 5 mL of glycerol was additionally mixed to prepare a coating solution.

[110] Subsequently, 15 g of alumina beads (average diameter: 3 mm) were dip-coated in the prepared coating solution at room temperature for 60 minutes. The coated alumina beads were then dried in an oven at 60°C for 24 hours, followed by heat treatment at 600°C (heating rate: 5°C / min) for 6 hours.

[111] Thereafter, 12 g of the heat-treated alumina beads were suspended in a solution prepared by diluting 15.2586 mL of 1.5 wt.% ruthenium nitrosyl nitrate solution with 50 mL of deionized water, followed by solvent evaporation at 80°C under 400 mbar. The resulting material was dried in an oven at 100°C for 24 hours, and subsequently calcined at 350°C (heating rate: 10°C / min) for 2 hours. Thus, a Ru / La-Ce / Al2O3 molded catalyst was obtained.

[112]

[113] <Comparative Example 4>

[114] A Ru / La-Ce / Al2O3 molded catalyst was manufactured in the same manner as in Example 3, except that fixation was performed using 20 mL of deionized water instead of the fixation solution.

[115]

[116] <Comparative Example 5>

[117] A Ru / La-Ce / Al2O3 molded catalyst was manufactured in the same manner as in Example 3, except that NH4OH was used instead of KOH in the fixation solution.

[118]

[119] Table 1 below shows the preparation conditions for the molded catalysts of Examples 1 to 11 and Comparative Examples 1 to 5. 5

[120] Table 1 Classif Mol Coat Coatin Surf First Seco Fixa Fixa Catalyt ication ded ing g ace additi nd tion tion ically bod y comp onen t a) method trea tmen t agen t for mold ed body ve addi tive solu tion time (h) active materia l Example 1 Al2 O3 La Ce Dip coatin g - Methyl cellul ose Glyc erol KOH 0.5 Ru Example 2 Al2 O3 La Ce Dip coatin g - Methyl cellul ose Glyc erol KOH 1 Ru Example 3 Al2 03 La Ce Dip coatin g - Methyl cellul ose Glyc erol KOH 2 Ru Example 4 Al2 O3 La Ce Dip coatin g - Methyl cellul ose Glyc erol KOH 3 Ru Example 5 Al2 O3 La Ce Dip coatin g - Polyvi nyl alcoho l Glyc erol KOH 0.5 Ru Example 6 Al2 O3 La Ce Dip coatin g - Polyet hylene glycol Glyc erol KOH 0.5 Ru Example 7 Al2 O3 La Ce Dip coatin g - Silica sol Glyc erol KOH 0.5 Ru Example 8 Al2 O3 La Ce Dip coatin g KOH Methyl cellul ose Glyc erol KOH 0.5 Ru Compara tive Example 1 Al2 O3 - - - - - - - Ru Compara tive Example 2 Al2 O3 La Ce Impreg nation - - - - - Ru Compara tive Example 3 Al2 O3 La Ce Dip coatin g - Methyl cellul ose Glyc erol - - Ru Compara tive Example 4 Al2 O3 La Ce Dip coatin g - Methyl cellul ose Glyc erol H2O 2 Ru Compara tive Example 5 Al2 O3 La Ce Dip coatin g - Methyl cellul ose Glyc erol NH4O H 2 Ru a) For coating components, only metal elements derived from precursor compounds are listed. metal

[121]      <Experimental Example 1: Evaluation of Catalytic Performance for Ammonia Decomposition>

[122] Ammonia decomposition reactions were carried out using each of the molded catalysts manufactured in the 5 Examples and Comparative Examples, and the ammonia conversion rate was measured. The measurement was conducted under atmospheric pressure at an ammonia space velocity of 3,000 mL / gcat. / h, and at reaction temperatures of 350°C,  400°C, 450°C, 500°C, and 550°C. The gaseous products generated after the ammonia decomposition reaction, including hydrogen, nitrogen, and unreacted ammonia, were analyzed using gas 5 chromatography (GC). The ammonia conversion rate was calculated according to the following equation:

[123] Ammonia conversion rate = {(Flow rate of ammonia introduced-Flow rate of ammonia discharged) / flow rate of ammonia introduced} x 100 10   

[124]

[125]      <Effect of Molded Body Coating Method>

[126] In order to investigate the effect of the molded body coating method, the catalysts manufactured in Example 1 and Comparative Examples 1 to 3, which were manufactured using 15 the same procedure except that the molded body was either not coated or was coated using different methods, were subjected to the ammonia decomposition reaction of Experimental Example 1. The results are summarized in Table 2 below.

[127] Table 2 Classification Coating method Ammonia conversion rate (%) 350°C 400°C 450°C 500°C 550°C Example 1 Dip coating / fixation 17.3 39.3 70.8 96.5 99.8 Comparative Example 1 No coating 10.9 27.2 51.9 82.3 99.0 Comparative Example 2 Impregnation 13.2 31.1 57.7 85.0 98.9 Comparative Example 3 Dip coating / no fixation 13.8 32.3 58.8 89.6 99.6

[128] Referring to Table 2, it can be seen that the molded catalyst manufactured in Example 1 exhibited a higher ammonia conversion rate than Comparative Example 1, in which the molded body was not coated with lanthanum and cerium. This indicates 5 that coating the molded body with lanthanum and cerium is advantageous for improving catalytic activity for ammonia decomposition. Furthermore, in Example 1 employing the dipcoating method, the amount of the cerium and lanthanum precursors contained in the coating solution were only 10 approximately 27% of that used in Comparative Example 2 employing the impregnation method. Additionally, since the coating layer was also formed by the dip-coating method, the consumption of the coating solution was significantly reduced (less than 10% per one coating cycle), resulting in a 15 substantially lower usage of cerium and lanthanum compared to Comparative Example 2. Accordingly, it would be expected that the La-Ce coating layer of Comparative Example 2 would have a relatively higher specific surface area, and thus, under the condition of the same loading amount of Ru, Comparative Example 2 would exhibit a higher ammonia conversion rate due to better dispersion of Ru. However, contrary to this expectation, the experimental results demonstrated that Example 1 exhibited a higher ammonia conversion rate. From these results, it can be found that the manufacturing method of the present disclosure enables the manufacture of a highly efficient catalyst while reducing the amounts of relatively expensive coating components such as La and Ce, due to a synergistic effect arising from the interaction between the La-Ce mixed oxide layer and alumina.

[129] Additionally, the results indicate that, even when a La-Ce coating layer is formed on the molded body by the dipcoating method, omission of the fixation step, as in Comparative Example 3, can result in detachment of the coating material and a consequent decrease in catalytic activity.

[130]

[131] <Effect of Fixation Solution Type>

[132] In order to investigate the effect of the type of fixation solution, the catalysts manufactured in Example 3 and Comparative Examples 3 to 5, which were manufactured using the same procedure except for the fixation solution used, were subjected to the ammonia decomposition reaction described in Experimental Example 1. The results are summarized in Table 3 below.

[133] Table 3 Classification Fixation solution Ammonia conversion rate (%) 350°C 400°C 450°C 500°C 550°C Example 3 KOH 20.3 45.0 75.6 95.8 100 Comparative Example 3 No fixation 13.8 32.3 58.8 89.6 99.6 Comparative Example 4 H2O 12.2 28.6 51.7 82.7 99.1 Comparative Example 5 NH4OH 13.7 31.4 59.3 88.6 100

[134] Referring to Table 3, it can be seen that Example 3, in which an alkali metal hydroxide such as KOH was used in the fixation solution of the present disclosure, exhibited the highest catalytic activity. Comparative Example 4, in which 5 water was used instead of the fixation solution of the present disclosure, and Comparative Example 5, in which aqueous ammonia was used, exhibited lower catalytic activity for ammonia decomposition than Example 3, in which an alkali metal hydroxide was used. Similarly, Comparative Example 3, in which 10 the fixation step was omitted, also exhibited lower catalytic activity for ammonia decomposition. From these results, it can be found that, in the manufacture of a molded catalyst for ammonia decomposition, a fixation step using a fixation solution containing an alkali metal hydroxide is required. 15

[135]

[136] <Effect of Fixation Time>

[137] In order to investigate the effect of fixation time, the catalysts manufactured in Examples 1 to 4 and Comparative Example 1, which were manufactured using the same procedure except for the fixation time, were subjected to the ammonia 5 decomposition reaction described in Experimental Example 1. The results are summarized in Table 4 below.

[138] Table 4 Classification Fixation time (h) Ammonia conversion rate (%) 350°C 400°C 450°C 500°C 550°C Example 1 0.5 17.3 39.3 70.8 96.5 99.8 Example 2 1 20.6 43.6 74.1 96.9 99.3 Example 3 2 20.3 45.0 75.6 95.8 100 Example 4 3 17.5 41.4 72.5 96.3 100 Comparative Example 1 No fixation 13.8 32.3 58.8 89.6 99.6

[139] Referring to Table 4, it can be seen that the catalysts manufactured in Examples 1 to 4, in which the fixation 10 step was performed, exhibited substantially higher ammonia conversion rates than the catalyst manufactured in Comparative Example 1, in which the fixation step was omitted. As described above, these results indicate that, even when a coating layer is formed, omission of the fixation step can result in 15 detachment of the coating material and a consequent decrease in catalytic activity. Additionally, the catalysts subjected to fixation for 1 to 2 hours exhibited further improved catalytic activity for ammonia decomposition.

[140]

[141]      <Effect of First Additive Type> 5

[142] In order to investigate the effect of the type of first additive, the catalysts manufactured in Examples 1 and 5 to 7, which were manufactured using the same procedure except for the type of first additive, were subjected to the ammonia decomposition reaction described in Experimental Example 1. 10 The results are summarized in Table 5 below.

[143] Table 5 Classification First additive type Ammonia conversion rate (%) 350°C 400°C 450°C 500°C 550°C Example 1 Methyl cellulose 17.3 39.3 70.8 96.5 99.8 Example 5 Polyvinyl alcohol 17.6 40.8 72.7 95.8 99.6 Example 6 Polyethylene glycol 14.7 36.3 66.3 92.0 100 Example 7 Silica sol 15.9 36.8 65.6 91.5 99.2

[144] Referring to Table 5, it can be seen that the catalysts manufactured using polyvinyl alcohol, polyethylene glycol, or silica sol as the first additive, in addition to 15 methyl cellulose, also exhibited improved catalytic activity for ammonia decomposition. This indicates that the use of polyvinyl alcohol, polyethylene glycol, or silica sol can prevent the coating components from leaching during the fixation step, thereby allowing a sufficient amount of the 5 catalytically active material to be supported on the coating layer.

[145]

[146]      <Effect of Molded Body Pretreatment>

[147] In order to investigate the effect of molded body 10 pretreatment, the catalysts manufactured in Examples 1 and 8, which were manufactured using the same procedure except for the presence or absence of pretreatment of the molded body, were subjected to the ammonia decomposition reaction described in Experimental Example 1. The results are summarized in Table 6 15 below.

[148] Table 6 Classification Surface treatment agent for molded body Ammonia conversion rate (%) 350°C 400°C 450°C 500°C 550°C Example 1 - 17.3 39.3 70.8 96.5 99.8 Example 8 KOH 25.1 50.9 82.0 98.1 100

[149] Referring to Table 6, it can be seen that, at a relatively low reaction temperature of 350°C, the molded catalyst of Example 8, in which the molded body was subjected to surface treatment with 1 M KOH prior to coating, exhibited an ammonia conversion rate approximately 1.45 times that of the molded catalyst of Example 1, in which no surface treatment was performed. From these results, it can be found that pretreating the surface of the molded body with an acid or a base in advance during the manufacture of the molded catalyst can improve catalytic activity for ammonia decomposition.

[150] Although the preferred embodiments of the present disclosure have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the disclosure.

[151] It is thus well known to those skilled in that art that the present disclosure is not limited to the specific embodiments disclosed in the detailed description, and the patent right of the present disclosure should be defined by the scope and spirit of the disclosure as defined in the accompanying claims.

[152] Industrial Applicability

[153] The present disclosure relates to a molded catalyst for ammonia decomposition and a manufacturing method therefor. The present disclosure can improve or maintain catalytic activity even with a small amount of a catalytically active material, and enable the manufacture of a molded catalyst for ammonia decomposition without requiring a separate process for preparing a powder catalyst. Additionally, improved adhesion between a molded body and a coating layer enables the molded catalyst to exhibit sufficient mechanical strength. 5 Furthermore, the coating solution for the molded body and the fixation solution can be reused, thereby reducing unnecessary material loss during the manufacture of the molded catalyst. Accordingly, the present disclosure can be widely utilized in industrial fields in which catalytic ammonia decomposition 10 technology is required.

Claims

1. A manufacturing method for a molded catalyst for ammonia decomposition, the manufacturing method comprising:(a) immersing a molded body in a coating solution containing a coating component including lanthanum and cerium and a first additive, thereby forming a wet layer containing the coating component on a surface of the molded body;(b) immersing the molded body having the wet layer formed thereon in a fixation solution in which an alkali metal hydroxide is dissolved, thereby fixing the wet layer on the surface of the molded body;(c) subjecting the molded body having the wet layer fixed thereon to heat treatment, thereby forming a coating layer containing the coating component on the surface of the molded body;(d) supporting ruthenium, as a catalytically active material, on the coating layer of the molded body; and(e) subjecting the molded body having the catalytically active material supported thereon to drying and optional calcination, thereby preparing a catalytically active material-supported molded body,wherein the first additive includes at least one selected from the group consisting of methyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, purified starch,dextrin, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyethylene glycol, and silica sol.

2. The manufacturing method of claim 1, wherein the molded body of step (a) is made of alumina.

3. The manufacturing method of claim 1, wherein the molded body of step (a) is surface-treated with acid and / or base.

4. The manufacturing method of claim 3, wherein the acid includes at least one selected from the group consisting of HCl, HNO3, H2SO4, HF, H3PO4, and organic acid, and the base includes at least one selected from the group consisting of LiOH, NaOH, KOH, NH4OH, and NaBH4.

5. The manufacturing method of claim 1, wherein the coating solution of step (a) includes 0.5 to 10 parts by weight of the first additive based on 100 parts by weight of the coating component.

6. The manufacturing method of claim 1, wherein the coating solution of step (a) further includes at least one second additive selected from the group consisting of polyhydric alcohols, waxes, and lubricants.

7. The manufacturing method of claim 6, wherein the coating solution of step (a) includes 5 to 90 parts by volume of the second additive based on 100 parts by volume of the coating component.

8. The manufacturing method of claim 1, wherein the fixation solution of step (b) includes at least one alkali metal hydroxide selected from the group consisting of LiOH, NaOH, and KOH.

9. The manufacturing method of claim 1, wherein step (b) includes immersing the molded body having the wet layer formed thereon in the fixation solution for 0.5 to 4 hours to fix the wet layer on the surface of the molded body.

10. A molded catalyst for ammonia decomposition, wherein ruthenium is supported on a support having a coating layer containing lanthanum and cerium formed on an alumina molded body.

11. A molded catalyst for ammonia decomposition, the molded catalyst being manufactured by the manufacturing method of any one of claims 1 to 9.

12. An ammonia decomposition method, comprising:bringing ammonia into contact with the molded catalyst manufactured by the manufacturing method of any one of claims 1 to 9, or with the molded catalyst of claim 10.5

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