Ruthenium loss inhibition-type ruthenium-based ammonia synthesis catalyst and preparation method therefor

Abstract

The present invention provides a preparation method for a ruthenium catalyst complex for ammonia synthesis, and a ruthenium catalyst complex for ammonia synthesis, prepared by the preparation method, the preparation method comprising the steps of: (c) preparing a magnesium / aluminum calcined product by drying and primary heat-treating a magnesium / aluminum precursor; (d) preparing a magnesium / aluminum / barium calcined product by impregnating an aqueous barium precursor solution into the magnesium / aluminum calcined product, and then drying and secondary heat-treating same; and (e) preparing a ruthenium catalyst complex by impregnating a ruthenium precursor solution into the magnesium / aluminum / barium calcined product, and then drying and tertiary heat-treating same. Accordingly, the loss of ruthenium (Ru) due to the volatilization thereof may be blocked during the catalyst preparation and ammonia synthesis, and, by containing a very small amount of aluminum, the deterioration of catalytic activity caused by a high content of aluminum oxide may be solved.

Description

Ruthenium loss inhibition type ruthenium-based ammonia synthesis catalyst and method for preparing the same

[0001] The present invention relates to a ruthenium-based ammonia synthesis catalyst and a method for producing the same, and more specifically, to a ruthenium-based ammonia synthesis catalyst capable of suppressing loss due to ruthenium volatilization and a method for producing the same.

[0002] This invention was developed through a project (GTL24051-000) supported by the Ministry of Science and ICT of the Republic of Korea.

[0003] Precious metal elements are essential for use as catalysts in various industrially important reactions, including petroleum refining, pharmaceutical manufacturing, environmental remediation, and renewable energy conversion. To enhance the efficacy of precious metals in heterogeneous catalysts, precious metal particles can be formed to desired sizes, and their electronic structures can be adjusted using auxiliary components known as supports and promoters. These auxiliary components aim to improve activity, product selectivity, and durability while avoiding adverse effects. However, achieving these objectives is challenging due to the complex interactions between catalytic components and reaction intermediates.

[0004] Ruthenium (Ru) is an important catalytic component capable of maintaining various oxidation states and adsorbing and desorbing various molecules. Ruthenium is receiving significant attention for its use in the manufacture of electronic devices such as hard disks and as a catalyst for PEM water electrolysis. Recently, demand for it has been steadily increasing as a catalyst for the low-temperature, low-pressure ammonia (NH3) synthesis process, which is essential for decarbonization and the widespread adoption of renewable energy. Ruthenium-based catalysts are known to offer a much higher ammonia synthesis rate compared to commercial iron (Fe)-based catalysts, which are currently mostly applied in the Haber-Bosch process. Consequently, it is attracting considerable attention as a next-generation catalyst for ammonia synthesis reactions that can shift conventional process operating conditions to milder ones. However, as Ruthenium is the sixth rarest element in the Earth's crust, its widespread application is limited. To address this, there is a need to develop high-performance catalysts with a higher utilization rate of Ruthenium.

[0005] Heterogeneous ruthenium (Ru) catalysts are generally prepared by impregnating an ionic ruthenium precursor into a support and subjecting it to heat treatments such as calcination and reduction. During these catalyst preparation processes, intermediates such as ruthenium oxide (RuOx) may be formed. Ruthenium oxide is known to be a highly volatile substance. Consequently, under high-temperature conditions such as heat treatment, ruthenium may be lost from the catalyst surface due to volatilization, potentially limiting catalytic activity. Furthermore, when catalysts containing such highly volatile ruthenium are used in ammonia production, additional problems may arise, such as the deposition of ruthenium inside the reactor or contamination of the ammonia product.

[0006] [Prior Art Literature]

[0007] [Non-patent literature]

[0008] Journal of Catalysis Volume 434, June 2024, 115530

[0009] The objective of the present invention is to solve the above problems by providing a ruthenium (Ru)-based ammonia synthesis catalyst and a method for manufacturing a ruthenium (Ru)-based ammonia synthesis catalyst that can prevent the loss of ruthenium (Ru) due to volatilization during ammonia synthesis.

[0010] Another objective of the present invention is to provide a ruthenium-based ammonia synthesis catalyst that synthesizes ammonia with high efficiency by suppressing the loss of ruthenium (Ru) due to volatilization and prevents contamination of ammonia caused by ruthenium volatilization.

[0011] According to one aspect of the present invention,

[0012] (c) A step of manufacturing a magnesium / aluminum sintered product by drying and primary heat treating a magnesium / aluminum precursor;

[0013] (d) a step of impregnating the magnesium / aluminum calcined product with an aqueous barium precursor solution, followed by drying and secondary heat treatment to produce a magnesium / aluminum / barium calcined product; and

[0014] (e) a step of impregnating the magnesium / aluminum / barium calcined product with a ruthenium precursor solution, and then drying and tertiary heat treating to produce a ruthenium catalyst composite; a method for producing a ruthenium catalyst composite for ammonia synthesis is provided.

[0015] According to one embodiment of the present invention,

[0016] Prior to the above step (c),

[0017] (a) a step of preparing a mixed aqueous solution by mixing a magnesium precursor and an aluminum precursor with distilled water; and

[0018] (b) a step of obtaining a magnesium / aluminum precursor, which is a precipitate, by co-precipitating while adding a precipitating aqueous solution to the above-mentioned mixed aqueous solution; may be performed.

[0019] According to another embodiment of the present invention,

[0020] Before step (c),

[0021] (a') a step of preparing an aqueous solution of an aluminum precursor by mixing the aluminum precursor with distilled water; and

[0022] (b') A step of obtaining a magnesium / aluminum precursor by impregnating the above aluminum precursor aqueous solution into magnesium oxide (MgO); may be performed.

[0023] In step (a),

[0024] The above magnesium precursor may be any one selected from magnesium nitrate (Mg(NO3)2), magnesium bicarbonate (Mg(HCO3)2), magnesium chlorate (Mg(ClO3)2), magnesium chloride (MgCl2), magnesium bromide (MgBr2), magnesium iodide (MgI2) and magnesium sulfate (MgSO4) or a hydrate thereof.

[0025] In steps (a) and (a'),

[0026] The above aluminum precursor may be any one selected from aluminum nitrate (Al(NO3)3), aluminum bicarbonate (Al(HCO3)3), aluminum chlorate (Al(ClO3)3), aluminum chloride (AlCl3), aluminum bromide (AlBr3), aluminum iodide (AlI3) and aluminum sulfate (Al2(SO4)3) or a hydrate thereof.

[0027] In step (a),

[0028] In the above aqueous solution of magnesium and aluminum mixture, the Al / (Mg+Al) molar ratio may be 0.01 to 0.10.

[0029] The above aqueous solution of magnesium and aluminum mixture may be 20 to 100°C.

[0030] In step (b),

[0031] The above aqueous solution for precipitation may be any one of the following: ammonium carbonate ((NH4)2CO3), ammonium phosphate ((NH4)3PO4), ammonium chromate ((NH4)2CrO4), ammonium sulfide ((NH4)2S), and ammonium hydroxide (NH4OH).

[0032] In step (c),

[0033] The above precipitate may be additionally washed with distilled water until the pH reaches 7 before drying.

[0034] The above drying can be performed at 60 to 130°C.

[0035] The above first heat treatment can be performed at 400 to 800℃.

[0036] The above first heat treatment can be performed in an air atmosphere or an inert gas atmosphere.

[0037] In step (d),

[0038] The above barium precursor may be any one selected from barium nitrate (Ba(NO3)2), barium bicarbonate (Ba(HCO3)2), barium chlorate (Ba(ClO3)2), barium chloride (BaCl2), barium bromide (BaBr2), barium iodide (BaI2) and barium sulfate (BaSO4) or a hydrate thereof.

[0039] The above barium precursor can be impregnated so that the Ba / (Mg+Al) molar ratio is 0.02 to 0.10.

[0040] The above drying can be performed at 60 to 130°C.

[0041] The above secondary heat treatment can be performed at 400 to 800℃.

[0042] The above secondary heat treatment can be performed in a nitrogen atmosphere, a hydrogen atmosphere, or an inert gas atmosphere.

[0043] In step (e),

[0044] The above ruthenium precursor is triruthenium dodecacarbonyl (Ru3(CO)12 It may be any one selected from ), ruthenium chloride (RuCl3·xH2O), ruthenium carbonate (C3O9Ru2), and ruthenium nitrate (Ru(NO)(NO3)3).

[0045] The above ruthenium precursor solution may be a solution dissolved in any one of the organic solvents selected from tetrahydrofuran, diisopropyl ether, methyl t-butyl ether (MTBE), ethyl t-butyl ether, methyl t-pentyl ether (TAME), ethyl t-pentyl ether, 1,4-dioxane, ethylene glycol dimethyl ether or diethyl ether, diethylene glycol dimethyl ether, and diethyl ether.

[0046] The above ruthenium precursor solution can be impregnated so that the Ba / Ru molar ratio is 1.5 to 4.0.

[0047] The above drying can be performed at 60 to 130°C.

[0048] The above third heat treatment can be performed at 300 to 700℃.

[0049] The above third heat treatment can be performed in a hydrogen gas atmosphere.

[0050] According to another aspect of the present invention,

[0051] A ruthenium catalyst complex for ammonia synthesis manufactured according to the above manufacturing method is provided.

[0052] The above ruthenium catalyst composite for ammonia synthesis may have a magnesium (Mg) content of 40 to 50 wt%.

[0053] The above ruthenium catalyst composite for ammonia synthesis may have an aluminum (Al) content of 0.5 to 4.0 wt%.

[0054] The above ruthenium catalyst complex for ammonia synthesis may have a barium (Ba) content of 8 to 25 wt%.

[0055] The above ruthenium catalyst complex for ammonia synthesis is Al according to 27Al MAS-NMR analysis O / Al T The value can be 6 to 8.

[0056] The above ruthenium catalyst complex for ammonia synthesis may have a solid solution structure in which aluminum (Al) atoms are dispersed.

[0057] The ruthenium included in the above ruthenium catalyst complex for ammonia synthesis may have an average diameter of 1.5 to 2 nm.

[0058] According to another aspect of the present invention,

[0059] A method for synthesizing ammonia using a ruthenium catalyst complex for ammonia synthesis prepared according to the above manufacturing method is provided.

[0060] The method for manufacturing a ruthenium (Ru)-based catalyst for ammonia synthesis according to the present invention can prevent the loss of ruthenium (Ru) due to volatilization during catalyst manufacturing and ammonia synthesis. Unlike conventional catalysts, it implements a solid solution structure in which trace amounts of aluminum (Al) are uniformly dispersed in an atomic state within MgO and BaO. Furthermore, it includes BaO crystals with higher dispersion and ruthenium (Ru) particles with higher dispersion in small particles, and forms a spatially close structure between the active center, ruthenium (Ru), and the co-catalyst, barium (Ba), thereby maximizing the interface between the two components. Consequently, the ruthenium (Ru)-based catalyst for ammonia synthesis manufactured according to the method of the present invention can synthesize ammonia with high efficiency and possess high long-term stability. Moreover, it can prevent the secondary problem of ammonia products being contaminated due to ruthenium volatilization and resolve the issue of reduced catalytic activity caused by high aluminum oxide content by including a minute amount of aluminum.

[0061] FIG. 1 is a flowchart sequentially illustrating the process of manufacturing a ruthenium-based catalyst composite according to one embodiment of the present invention.

[0062] FIG. 2 is a flowchart sequentially illustrating the manufacturing process of a ruthenium-based catalyst composite according to another embodiment of the present invention.

[0063] Figure 3 shows the results of the ruthenium (Ru) volatility analysis (TPD-MS) at the final heat treatment according to Experimental Example 2.

[0064] FIG. 4 is according to Experimental Example 3 27 This is the result of Al MAS-NMR analysis.

[0065] Figure 5 shows the XRD analysis results of the ruthenium catalyst composite powder according to Experimental Example 4.

[0066] Figure 6 is an electron microscope analysis image according to Experimental Example 5.

[0067] Figure 7 is the result of comparing the catalytic activity of the ruthenium catalyst complex of the example and comparative example according to Experimental Example 6.

[0068] Figure 8 is the long-term evaluation result of an ammonia synthesis reaction using the ruthenium catalyst composite support of Example 1 according to Experimental Example 6.

[0069] Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.

[0070] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention.

[0071] However, the following description is not intended to limit the present invention to specific embodiments, and detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions could obscure the essence of the present invention.

[0072] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to indicate the presence of the features, numbers, steps, actions, components, 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, or combinations thereof.

[0073]

[0074] FIG. 1 is a flowchart sequentially illustrating a method for manufacturing a ruthenium (Ru) catalyst composite for ammonia synthesis according to one embodiment of the present invention. Hereinafter, a method for manufacturing a ruthenium (Ru) catalyst composite for ammonia synthesis according to one embodiment of the present invention will be described with reference to FIG. 1.

[0075] First, a mixed aqueous solution is prepared by mixing a magnesium precursor and an aluminum precursor with distilled water (step a).

[0076] The magnesium precursor is preferably magnesium nitrate (Mg(NO3)2), magnesium bicarbonate (Mg(HCO3)2), magnesium chlorate (Mg(ClO3)2), magnesium chloride (MgCl2), magnesium bromide (MgBr2), magnesium iodide (MgI2), or magnesium sulfate (MgSO4) and its hydrates, and more preferably magnesium nitrate (Mg(NO3)2) or its hydrates may be used. The magnesium precursor is characterized by being soluble in distilled water.

[0077] The above aluminum precursor is preferably aluminum nitrate (Al(NO3)3), aluminum bicarbonate (Al(HCO3)3), aluminum chlorate (Al(ClO3)3), aluminum chloride (AlCl3), aluminum bromide (AlBr3), aluminum iodide (AlI3), or aluminum sulfate (Al2(SO4)3) and their hydrates, and more preferably aluminum nitrate (Al(NO3)3) or its hydrates may be used. The above aluminum precursor is characterized by being soluble in distilled water.

[0078] In the mixed aqueous solution containing the magnesium precursor and the aluminum precursor, the Al / (Mg+Al) molar ratio is preferably 0.01 to 0.10, and more preferably 0.012 to 0.08. The ruthenium (Ru) catalyst composite for ammonia synthesis according to the present invention is characterized by having a very low aluminum (Al) content compared to conventional ruthenium-based catalysts, and if the upper or lower limit of the above range is exceeded, the stability of the catalyst may be significantly reduced, and in particular, the catalytic activity may be significantly increased when the Al / (Mg+Al) molar ratio is in the range of 0.03 to 0.05.

[0079] As will be explained later, barium oxide (BaO) requires maintaining strong basicity and necessitates a basic support, and magnesium oxide (MgO) is a component of the catalyst support suitable as a basic support. In contrast, acidic supports such as aluminum oxide (Al2O3) can inhibit the activity of the ruthenium (Ru) catalyst by counteracting the strong basicity of barium oxide (BaO). For example, according to prior research, Ru-Ba catalysts using a support with an MgO:Al2O3 ratio of 70:30 are known to exhibit significantly lower catalytic activity compared to Ru-Ba catalysts using pure magnesium oxide (MgO) as a support.

[0080] In the present invention, by using a minute amount of aluminum (Al), the aluminum in the final catalyst composite can form an atomicly dispersed solid solution structure without existing as an oxide (Al2O3). Therefore, the reduction in catalytic activity caused by the inclusion of conventional aluminum oxide in the catalyst composite can be prevented.

[0081] The above aqueous solution of magnesium and aluminum mixture may be at a temperature of 20 to 100°C, more preferably at 22 to 30°C, and even more preferably at 23 to 27°C.

[0082] Next, a precipitating aqueous solution is added to the above-mentioned mixed aqueous solution and co-precipitated to obtain a magnesium / aluminum precursor as a precipitate (step b).

[0083] The above aqueous solution for precipitation is preferably an aqueous solution of ammonium carbonate ((NH4)2CO3), ammonium phosphate ((NH4)3PO4), ammonium chromate ((NH4)2CrO4), ammonium sulfide ((NH4)2S), and ammonium hydroxide (NH4OH), and more preferably, it may be ammonium carbonate ((NH4)2CO3). The anions of the above aqueous solution for precipitation, such as carbonate ions, phosphate ions, chromate ions, sulfide ions, or hydroxide ions, may combine with magnesium and aluminum ions to form a precipitate when added to the mixed aqueous solution of the magnesium precursor and the aluminum precursor.

[0084] Subsequently, the magnesium / aluminum precursor, which is a precipitate, is dried and subjected to primary heat treatment to produce a magnesium / aluminum calcined product (step c).

[0085] It is preferable to wash the above precipitate with distilled water until the pH reaches 7 before drying.

[0086] The above drying can be performed at 60 to 130°C, more preferably at 80 to 125°C, and even more preferably at 100 to 120°C.

[0087] The above first heat treatment is preferably performed at 400 to 800°C, more preferably at 450 to 700°C, and even more preferably at 500 to 600°C.

[0088] In addition, it is preferable that the first heat treatment be performed in an air atmosphere or an inert gas atmosphere. By performing the sintering according to the first heat treatment at the above temperature in an air atmosphere or an inert gas atmosphere, magnesium oxide can be formed and an atomicly dispersed solid solution of aluminum can be formed. If the heat treatment is performed at a temperature below 400°C, oxidation and sintering may not be sufficiently achieved, and if performed at a temperature above 800°C, unnecessary process costs may be incurred.

[0089] Next, the magnesium / aluminum calcined product is impregnated with an aqueous barium precursor solution, and then dried and subjected to a second heat treatment to produce a magnesium / aluminum / barium calcined product (step d).

[0090] The above barium precursor may be any one selected from barium nitrate (Ba(NO3)2), barium bicarbonate (Ba(HCO3)2), barium chlorate (Ba(ClO3)2), barium chloride (BaCl2), barium bromide (BaBr2), barium iodide (BaI2) and barium sulfate (BaSO4) or a hydrate thereof.

[0091] It is preferable to impregnate the above barium precursor so that the Ba / (Mg+Al) molar ratio is 0.02 to 0.10, and more preferably 0.03 to 0.09. If the Ba / (Mg+Al) molar ratio is less than 0.02, the activity of the final catalyst composite may be significantly reduced, and if it exceeds 0.10, there is almost no increase in catalytic activity with increasing barium (Ba), and the content of other components is lowered, which may instead lead to a decrease in catalytic activity.

[0092] The above drying is preferably performed at 60 to 130°C, more preferably at 70 to 90°C, and even more preferably at 75 to 85°C.

[0093] The above secondary heat treatment is preferably performed at 400 to 800°C, more preferably at 450 to 700°C, and even more preferably at 500 to 600°C.

[0094] The above secondary heat treatment can be performed in a nitrogen atmosphere, a hydrogen atmosphere, or an inert gas atmosphere. Through such secondary heat treatment, barium oxide (BaO) is formed and added to the catalyst composite, and a magnesium / aluminum / barium calcined product can be firmly formed.

[0095] Finally, a ruthenium catalyst composite is prepared by impregnating the magnesium / aluminum / barium calcined product with a ruthenium precursor solution, followed by drying and a third heat treatment (step e).

[0096] The above ruthenium precursor is triruthenium dodecacarbonyl (Ru3(CO) 12 It is preferable that it be any one selected from ), ruthenium chloride (RuCl3·xH2O), ruthenium carbonate (C3O9Ru2), and ruthenium nitrate (Ru(NO)(NO3)3), and more preferably triruthenium dodecacarbonyl (Ru3(CO) 12 It may be ) or ruthenium chloride (RuCl3·xH2O), and more preferably triruthenium dodecacarbonyl (Ru3(CO) 12 It can be. Triruthenium dodecacarbonyl (Ru3(CO) 12 When using ), the final manufactured catalyst activity can be significantly improved.

[0097] The above ruthenium precursor solution may be a solution dissolved in any one of the organic solvents selected from tetrahydrofuran, diisopropyl ether, methyl t-butyl ether (MTBE), ethyl t-butyl ether, methyl t-pentyl ether (TAME), ethyl t-pentyl ether, 1,4-dioxane, ethylene glycol dimethyl ether or diethyl ether, diethylene glycol dimethyl ether, and diethyl ether.

[0098] It is preferable to impregnate the above ruthenium precursor solution such that the Ba / Ru molar ratio is 1.5 to 4.0, and more preferably 1.7 to 3.8. Catalytic activity can be maximized at such a molar ratio, and if it falls outside the above range, the catalytic activity may be significantly reduced.

[0099] The above drying is preferably performed at 60 to 130°C, more preferably at 70 to 90°C, and even more preferably at 75 to 85°C.

[0100] The above third heat treatment is preferably performed at 300 to 700°C, more preferably at 400 to 600°C, and even more preferably at 450 to 550°C. The above third heat treatment can be performed in a hydrogen gas atmosphere. Accordingly, ruthenium (Ru) particles can be evenly dispersed in the catalyst composite, and ruthenium (Ru), barium (Ba), and aluminum (Al) can be distributed in close spatial contact.

[0101] Even if a third heat treatment is performed under the same conditions, if the catalyst composite is manufactured under conditions excluding aluminum, the problem arises that the "Ru-BaO interface," which is the active site, becomes smaller because it is deposited in the co-catalyst barium oxide (BaO) layer or some parts are not in contact with barium (Ba), which can lead to a decrease in catalytic activity. Excellent catalytic activity can be exhibited as the ruthenium (Ru) and barium oxide (BaO) form a close interface. Barium oxide (BaO) acts as an electronic promoter, which can accelerate nitrogen gas (N2) activation of lutein (Ru), the active center, and alleviate hydrogen (H) poisoning.

[0102]

[0103] FIG. 2 is a flowchart sequentially illustrating a method for manufacturing a ruthenium (Ru) catalyst composite for ammonia synthesis according to another embodiment of the present invention. Hereinafter, a method for manufacturing a ruthenium (Ru) catalyst composite for ammonia synthesis according to another embodiment of the present invention will be described with reference to FIG. 2.

[0104] First, an aluminum precursor aqueous solution is prepared by mixing the aluminum precursor with distilled water (step a').

[0105] Since the aluminum precursor and aqueous solution temperature are the same as previously explained, specific details will be referred to above.

[0106] Next, the above aluminum precursor aqueous solution is impregnated into magnesium oxide (MgO) to obtain a magnesium / aluminum precursor (step b').

[0107] Subsequently, a catalyst composite can be prepared by sequentially performing steps (step c), (step d), and (step e) in the previously described embodiment. Therefore, specific details will be referred to above.

[0108] However, in (step e), the ruthenium precursor is triruthenium dodecacarbonyl (Ru3(CO) 12It is preferable that it be any one selected from ), ruthenium chloride (RuCl3·xH2O), ruthenium carbonate (C3O9Ru2), and ruthenium nitrate (Ru(NO)(NO3)3), and more preferably triruthenium dodecacarbonyl (Ru3(CO) 12 It may be ) or ruthenium chloride (RuCl3·xH2O), and more preferably, ruthenium chloride (RuCl3·xH2O) may be used. When ruthenium chloride (RuCl3·xH2O) is used, triruthenium dodecacarbonyl (Ru3(CO) 12 The final catalyst activity can be significantly improved compared to when using ).

[0109]

[0110] According to another embodiment of the present invention, a ruthenium catalyst complex for ammonia synthesis is provided according to a manufacturing method.

[0111] The above ruthenium catalyst composite for ammonia synthesis preferably has a magnesium (Mg) content of 40 to 50 wt%. Magnesium oxide (MgO) containing magnesium can serve as a basic support to maintain the strong basicity of barium oxide (BaO), which is a co-catalyst.

[0112] The above ruthenium catalyst composite for ammonia synthesis preferably has an aluminum (Al) content of 0.5 to 4.0 wt%, more preferably 0.6 to 3.8 wt%, and even more preferably 0.7 to 3.7 wt%. As the aluminum (Al) content is in a very small amount, oxide formation is difficult, and the decrease in catalytic activity seen in catalyst supports with a high aluminum oxide (Al2O3) content can be prevented. In addition, it can penetrate the crystal plane of barium oxide (BaO) to form a solid solution structure in which aluminum (Al) is dispersed as atoms. As a result, the "Ru-BaO interface" is increased, catalytic activity is improved, and the loss of ruthenium (Ru) due to volatilization can be suppressed.

[0113] The above ruthenium catalyst composite for ammonia synthesis preferably has a barium (Ba) content of 8 to 25 wt%, and more preferably 10 to 22 wt%. If the barium (Ba) content is less than 8 wt%, the activity of the final catalyst composite may be significantly reduced, and if it exceeds 25 wt%, the effect of increasing catalyst activity due to the increase in barium (Ba) is negligible, while the content of other components is lowered, which may actually reduce catalyst activity.

[0114] In addition, the above-mentioned ruthenium catalyst complex for ammonia synthesis Al according to 27Al MAS-NMR analysis O / Al T It is preferable that the value be 6 to 8, more preferably 6.5 to 7.7, and even more preferably 7 to 7.5. Here, Al T represents tetrahedral Al, and Al O represents hexahedral Al. That is, the ruthenium catalyst composite of the present invention is characterized by a much higher distribution of hexahedral aluminum (Al) species, and means that it is dispersed in the hexahedral structure of magnesium oxide (MgO) and barium oxide (BaO).

[0115] Thus, the above-described ruthenium catalyst complex for ammonia synthesis is characterized by having a solid solution structure in which aluminum (Al) atoms are dispersed.

[0116] The ruthenium included in the above ruthenium catalyst complex for ammonia synthesis is characterized by having an average diameter of 1.5 to 2 nm.

[0117]

[0118] According to another embodiment of the present invention, the present invention provides a method for synthesizing ammonia using a ruthenium catalyst complex for ammonia synthesis prepared according to a manufacturing method.

[0119] All known methods can be applied to the synthesis of ammonia.

[0120]

[0121] Hereinafter, the present invention will be examined in detail according to the embodiments.

[0122] [Example]

[0123] Example 1: Preparation of a catalyst containing Ru, Ba, Mg, and Al

[0124] 18.610 g of Mg(NO3)2·6H2O (Sigma Aldrich) and 0.908 g of Al(NO3)3·9H2O (Sigma Aldrich) (Mg / Al = 30 molar ratio) were added to 37.5 ml of distilled water and stirred at 25°C to prepare an aqueous solution of mixed Mg and Al. Additionally, 28.827 g of (NH4)2CO3 (Sigma Aldrich) was added to 122 ml of distilled water and stirred at 25°C to prepare an aqueous precipitate solution. Subsequently, the aqueous precipitate solution was co-precipitated by adding it to the aqueous solution of mixed Mg and Al at a rate of 1 ml / min using a burette.

[0125] The mixed suspension prepared accordingly was stirred at 60°C for 6 hours, and after the stirring process, the precipitate was obtained using a vacuum filtration device and washed with distilled water until the pH reached 7. The obtained product was dried in an oven at 110°C for 12 hours, and then calcined by primary heat treatment at 550°C for 1.5 hours under an air flow.

[0126] Subsequently, 0.588 g of Ba(NO3)2 (Sigma Aldrich) was dissolved in 40 ml of distilled water and impregnated into 1.5 g of the product. At this time, the solvent was evaporated at 50°C using a rotary vacuum evaporator. The product from which the solvent was removed was dried in an 80°C oven to remove moisture, and then subjected to a second heat treatment at 550°C for 1.5 hours under a nitrogen (N2) flow.

[0127] Next, Ru3(CO) 120.166 g of (Sigma Aldrich) was dissolved in 50 ml of tetrahydrofuran and impregnated into 1.5 g of the product containing Ba, Mg, and Al. The solvent was evaporated at 40°C using a rotary vacuum concentrator. The solvent-removed product was dried in an 80°C oven for 30 minutes, recovered, and reduced by tertiary heat treatment at 500°C for 1.5 hours under a hydrogen (H2) flow.

[0128]

[0129] Example 2: Ruthenium catalyst composite with lower aluminum content compared to Example 1

[0130] A catalyst was prepared in the same manner as in Example 1, except that 19.019 g of Mg(NO3)2·6H2O and 0.309 g of Al(NO3)3·9H2O (Mg / Al = 90 molar ratio) were added to 37.5 ml of distilled water and stirred at 25°C to prepare an aqueous solution mixed with Mg and Al.

[0131]

[0132] Example 3: Ruthenium catalyst composite with higher aluminum content compared to Example 1

[0133] A catalyst was prepared in the same manner as in Example 1, except that 18.029 g of Mg(NO3)2·6H2O and 1.758 g of Al(NO3)3·9H2O (Mg / Al = 15 molar ratio) were added to 37.5 ml of distilled water and stirred at 25°C to prepare an aqueous solution mixed with Mg and Al.

[0134]

[0135] Example 4: Ruthenium catalyst complex with low barium content compared to Example 1

[0136] A catalyst was prepared in the same manner as in Example 1, except that 20.392 g of Ba(NO3) was used in the Ba impregnation step.

[0137]

[0138] Example 5: Ruthenium catalyst complex with high barium content compared to Example 1

[0139] A catalyst was prepared in the same manner as in Example 1 above, except that 20.784 g of Ba(NO3) was used in the Ba impregnation step.

[0140]

[0141] Example 6: Ruthenium catalyst complex with a different aluminum input method from Example 1

[0142] A solution was prepared by dissolving 0.908 g of Al(NO3)3·9H2O in 15 ml of distilled water, and this was impregnated into 2.926 g of commercial MgO (Sigma Aldrich). The MgO impregnated with Al in this manner was dried in an oven at 110°C for 12 hours, and then calcined by heat treatment at 550°C for 1.5 hours under an airflow to produce a calcined product containing magnesium and aluminum. Except for this, the subsequent process was carried out in the same manner as in Example 1 to prepare the catalyst.

[0143]

[0144] Example 7: Ruthenium catalyst composite with lower aluminum content compared to Example 6

[0145] A catalyst was prepared in the same manner as in Example 6, except that an aqueous solution of 0.309 g of Al(NO3)3·9H2O was dissolved in 15 ml of distilled water and impregnated with 2.990 g of commercial MgO.

[0146]

[0147] Example 8: Ruthenium catalyst complex using a Ru precursor different from Example 1

[0148] Ru3(CO) in the Ru impregnation step 12 A catalyst was prepared in the same manner as in Example 1, except that 0.162 g of RuCl3·xH2O (~40 wt% Ru, Alfa Aesar) was used instead of 0.166 g.

[0149]

[0150] Comparative Example 1: Al-excluded ruthenium catalyst complex

[0151] A catalyst was prepared in the same manner as in Example 1, except that an Al precursor was not used in the initial solution, and only 19.231 g of Mg(NO3)2·6H2O was added to 37.5 ml of distilled water and stirred at 25°C to prepare an aqueous solution containing Mg.

[0152]

[0153] Comparative Example 2: Catalyst complex with Al excluded and low Ba content

[0154] A catalyst was prepared in the same manner as in Example 4, except that an Al precursor was not used in the initial solution, and only 19.231 g of Mg(NO3)2·6H2O was added to 37.5 ml of distilled water and stirred at 25°C to prepare an aqueous solution containing Mg.

[0155]

[0156] Comparative Example 3: Ruthenium catalyst complex with Al excluded and high Ba content

[0157] A catalyst was prepared in the same manner as in Example 5, except that no Al precursor was used in the initial solution, and only 19.231 g of Mg(NO3)2·6H2O was added to 37.5 ml of distilled water and stirred at 25°C to prepare an aqueous solution containing Mg.

[0158]

[0159] Comparative Example 4: Mg-excluded catalyst

[0160] A catalyst was prepared in the same manner as in Example 5, except that 28.135 g of Al(NO3)3·9H2O was added to 37.5 ml of distilled water without using an Mg precursor in the initial solution and stirred at 25°C to prepare an aqueous solution containing Mg.

[0161]

[0162] [Experimental Example]

[0163] Experimental Example 1: Elemental Analysis (ICP)

[0164] In Examples 1 to 8 and Comparative Examples 1 to 4 of the present invention, the Ru content was analyzed using inductively coupled plasma spectroscopy (ICP-OES) before and after the 'reduction' step performed after Ru precursor impregnation. The results regarding the Ru content in the catalyst measured accordingly are shown in Table 1 below.

[0165] Catalyst Ru content (wt%), Ru content before reduction (wt%), change in Ru content after reduction % Example 14.7 14.33-8.07 Example 24.8 54.66-3.92 Example 34.5 64.71+3.29 Example 44.9 24.58-6.91 Example 54.3 54.29-1.38 Example 64.4 24.55+2.94 Example 74.6 84.42-5.56 Example 84.1 43.89-6.04 Comparative Example 14.3 21.01-76.62 Comparative Example 24.5 02.01-55.33 Comparative Example 34.4 50.71-84.04 Comparative Example 44.8 94.78-2.25

[0166] According to this, the ruthenium catalyst composites of Examples 1 to 8 and Comparative Example 4 containing aluminum (Al) showed a change in ruthenium (Ru) content of -8.07 to +3.29% before and after reduction heat treatment, with almost no difference. However, the catalyst composites of Comparative Examples 1 to 3, which exclude aluminum (Al), showed a significant decrease in ruthenium (Ru) content after reduction, ranging from -84.04 to -55.33% compared to before reduction. In other words, it can be confirmed that the loss of ruthenium (Ru) is suppressed during reduction treatment in catalyst composites containing aluminum (Al).

[0167]

[0168] Meanwhile, the weight ratios of magnesium (Mg), aluminum (Al), and barium (Ba) in the ruthenium catalyst composites of Examples 1 to 8 and Comparative Examples 1 to 4 were analyzed, and the results are summarized in Table 2 below. In addition, the molar ratios among the constituent elements of magnesium (Mg), aluminum (Al), barium (Ba), and ruthenium (Ru) were analyzed, and the results are summarized in Table 3.

[0169] Catalyst Mg (wt%) Al (wt%) Ba (wt%) Example 1 45.8 6 2.09 17.57 Example 2 46.5 4 0.8 8 18.22 Example 3 43.9 9 3.6 6 16.25 Example 4 49.4 12.3 3 10.59 Example 5 42.2 2 1.7 7 2 1.81 Example 6 45.9 5 2.01 16.84 Example 7 46.6 9 0.7 2 17.22 Example 8 44.3 7 1.9 8 17.27 Comparative Example 1 48.6 70 16.37 Comparative Example 2 50.9 40 12.09 Comparative Example 3 45.9 50 20.18 Comparative Example 40 41.1 11 19.22

[0170] Catalyst Al / (Mg+Al)Ba / (Mg+Al)Ba / Ru Example 10.039 40.065 12.99 Example 20.0168 0.068 12.88 Example 30.069 70.060 92.54 Example 40.040 80.036 41.70 Example 50.036 40.088 13.74 Example 60.0379 0.062 42.72 Example 70.0137 0.064 42.87 Example 80.038 70.066 23.27 Comparative Example 100.059 511.9 Comparative Example 200.042 04.43 Comparative Example 300.077 720.9 41.0000.09192.96

[0171]

[0172] Experimental Example 2: Analysis of Ruthenium (Ru) Volatility upon Heat Treatment (TPD-MS)

[0173] The catalyst composites prepared according to Example 1 and Comparative Example 1, respectively, prior to the final heat treatment step, were subjected to a vacuum at a temperature range of 150 to 750°C for 20°C min -1 The mass spectrum (MS) was analyzed while heat-treating at a heating rate, and the results are shown in Figure 3.

[0174] According to this, the ruthenium catalyst composite of Comparative Example 1, which does not contain aluminum (Al), exhibited increasing mass spectrum (MS) signals at m / z = 101, 117, 133, 149, and 165 starting from approximately 250°C. These represent ionized Ru, RuO, RuO2, RuO3, and RuO4, respectively, and RuOx The presence of (x= 1~4) indicates that ruthenium (Ru) can volatilize and be lost from the catalyst in an oxidized form. On the other hand, the ruthenium catalyst complex of Example 1 did not show a mass spectrum (MS) signal at the corresponding m / z, which indicates that ruthenium (Ru) was not volatilized and was stably fixed on the catalyst surface.

[0175]

[0176] Experimental Example 3: 27 Al MAS-NMR

[0177] of the ruthenium catalyst complex of Example 1 and Comparative Example 4 27 The Al MAS-NMR (Magic angle spinning-nuclear magnetic resonance) pattern is shown in Fig. 4.

[0178] According to this, the chemical shift value appearing at 80–60 ppm is tetrahedral Al (Al T ) and the chemical shift value appearing at -10~20 ppm is hexahedral Al (Al O It represents ). The distribution of aluminum (Al) species within the catalyst was confirmed through a comparison of peak areas. That is, the ruthenium catalyst composite of Comparative Example 4 is Al O / Al T It showed a value of 1.7, indicating an aluminum (Al) distribution similar to typical gamma alumina. In contrast, the ruthenium catalyst composite of Example 1 Al O / Al T = 7.2, showing a much more dominant hexahedral aluminum (Al) distribution.

[0179] This is a unique property of the catalyst in the example, implying that most of the aluminum (Al) is dispersed in MgO and BaO having a cubic structure. Conventional mixtures of magnesium (Mg) and aluminum (Al) form an MgAl2O4 spinel structure (Journal of Materials Chemistry, 2011, 21, 8332-8337), and it can be confirmed that the ruthenium catalyst complex of Example 1 exhibits an NMR pattern that is distinctly different from the MgAl2O4 spinel structure. The Al appearing in the ruthenium catalyst complex of Example 1 O The peak splitting in this region indicates the structure of Al-O with various surrounding elements (Al, Mg, Ba) coordinated, and Al 3+ The Mg of this MgO and BaO 2+ and Ba 2+ It represents a solid solution structure formed by replacing positions.

[0180]

[0181] Experimental Example 4: X-ray Diffraction (XRD) Analysis

[0182] X-ray diffraction (XRD) patterns were measured for the ruthenium catalyst composite powders prepared according to Example 1 and Comparative Example 1, respectively, and the results are shown in Fig. 5.

[0183] According to Fig. 5(a), no characteristic peaks for ruthenium (Ru) and aluminum (Al) were found in both the ruthenium catalyst composites of Example 1 and Comparative Example 1, and characteristic peaks for BaO and MgO were observed. These results indicate that aluminum (Al) is very evenly distributed in the catalyst below the XRD detection limit.

[0184] Additionally, FIG. 5(b) is an enlarged view of the 2θ = 23–25° region showing characteristic peaks of the BaO (201) and BaO (211) crystal planes. The BaO (201) and BaO (211) peaks of Example 1 are observed at a higher 2θ than in Comparative Example 1, which indicates that Ba 2+Al having a smaller size compared to 3+ This indicates that it penetrated the BaO crystal plane and shifted toward a higher diffraction angle. In other words, it reconfirmed the atomicly dispersed solid solution structure of aluminum (Al).

[0185] Meanwhile, the crystal size of BaO was analyzed by analyzing the BaO (201) peak using the Scherrer equation, and it was confirmed that BaO in the ruthenium catalyst composite of Example 1 was 26 nm, and BaO in the ruthenium catalyst composite of Comparative Example 1 was 44 nm. That is, BaO in the ruthenium catalyst composite of Example 1 is evenly dispersed as relatively small crystals.

[0186]

[0187] Experimental Example 5: Electron Microscope Analysis

[0188] The ruthenium catalyst composites prepared according to Example 1 and Comparative Example 1, respectively, were analyzed using transmission electron microscopy (TEM), HAADF-STEM, and EDS elemental mapping, and the results are shown in Fig. 6. Here, (a) shows an image of the ruthenium catalyst composite of Example 1, and (b) shows an image of the ruthenium catalyst composite of Comparative Example 1.

[0189] According to this, it can be seen that the ruthenium catalyst composite of Example 1 has an average particle diameter of ruthenium (Ru) that is evenly dispersed at approximately 1.8 nm, and that ruthenium (Ru), barium (Ba), and aluminum (Al) are distributed in close spatial contact. In contrast, it can be seen that the ruthenium catalyst composite of Comparative Example 1 has an average particle diameter of ruthenium (Ru) that is evenly dispersed at approximately 7 nm, and that some of the ruthenium (Ru) is in close spatial contact with barium (Ba), while some is deposited in a thick layer of BaO or is not in contact with barium (Ba).

[0190] In other words, by adding a trace amount of aluminum (Al) to the catalyst, the present invention can reduce the average size of the active center, ruthenium (Ru), and induce a structure that is spatially closely distributed with the co-catalyst, BaO. Such a structure can induce the effect of maximizing the "Ru-BaO interface," commonly known as the active site.

[0191]

[0192] Experimental Example 6: Evaluation of Ammonia Synthesis Reactivity

[0193] The ammonia synthesis reactivity of the ruthenium catalyst composites prepared according to Examples 1 to 8 and Comparative Examples 1 to 4, respectively, was evaluated.

[0194] The ammonia synthesis reaction is carried out at 400°C, 50 bar, N₂ / H₂=1 / 3, and WHSV 18,000 cm⁻¹ 3 g cat. -1 h -1 The experiment was conducted under these conditions. The concentration of ammonia in the product stream was detected by gas chromatography, and the activity of the catalyst was calculated through the space velocity and the detected ammonia concentration.

[0195] The ammonia synthesis activity of ruthenium catalyst composites prepared according to Examples 1 to 8 and Comparative Examples 1 to 4, respectively, was compared and is shown in Figure 7.

[0196] According to this, the ruthenium catalyst complexes of Examples 1 to 8 have an activity of 0.97 g NH3 g cat. -1 h -1 Thus, the activity is 0.80 g NH3 g cat. -1 h -1 It exhibits significantly higher ammonia synthesis activity compared to the ruthenium catalyst complexes of Comparative Examples 1 to 4. In particular, in the case of Example 1, 1.73 g NH3 g cat. -1 h -1It exhibited high activity, showing more than twice the activity compared to the ruthenium catalyst complex of Comparative Example 2, which exhibited the highest activity among the comparative examples. Examples 1 to 5, prepared with the same method and precursor, showed similar values ​​of 1.36 to 1.73 g NH3 g cat. -1 h -1 It was confirmed that it exhibits catalytic activity. It was also confirmed that Examples 6 to 8, which used a different manufacturing method or a different ruthenium (Ru) precursor than Examples 1 to 5, exhibited superior activity compared to the comparative examples.

[0197] Meanwhile, when comparing the ruthenium catalyst composites using the same MgO as a support among the comparative examples, it can be confirmed that the catalytic activity is correlated with the ruthenium (Ru) content (Comparative Example 2 > Comparative Example 1 > Comparative Example 3). Therefore, it can be seen that the ruthenium (Ru) content plays an important role in catalytic activity. Furthermore, among the catalysts in the comparative examples, Comparative Example 4, which uses pure Al2O3 as a support instead of a mixed oxide of magnesium (Mg) and aluminum (Al), shows significantly lower catalytic activity despite having a high ruthenium (Ru) content. In other words, it can be seen that mixing Mg and Al in an appropriate ratio is very important for enhancing catalytic activity.

[0198] Figure 8 shows the results of long-term operation of an ammonia synthesis reaction for about 120 hours using the ruthenium catalyst support of Example 1, which had the highest catalytic activity. According to this, the ruthenium catalyst support of Example 1 maintained its activity for 120 hours, confirming that it has high durability in the ammonia synthesis reaction.

[0199]

[0200] Although embodiments of the present invention have been described above, those skilled in the art may modify and change the present invention in various ways by adding, changing, deleting, or adding components, etc., without departing from the spirit of the invention as described in the claims, and such modifications and changes are also to be included within the scope of the rights of the present invention.

Claims

1. (c) A step of manufacturing a magnesium / aluminum sintered product by drying and primary heat treating a magnesium / aluminum precursor; (d) a step of impregnating the magnesium / aluminum calcined product with an aqueous barium precursor solution, followed by drying and secondary heat treatment to produce a magnesium / aluminum / barium calcined product; and (e) a step of preparing a ruthenium catalyst composite by impregnating the magnesium / aluminum / barium calcined product with a ruthenium precursor solution, followed by drying and tertiary heat treatment; comprising a method for preparing a ruthenium catalyst composite for ammonia synthesis.

2. In Paragraph 1, Prior to the above step (c), (a) a step of preparing a mixed aqueous solution by mixing a magnesium precursor and an aluminum precursor with distilled water; and (b) a step of co-precipitating while adding a precipitating aqueous solution to the above-mentioned mixed aqueous solution to obtain a magnesium / aluminum precursor as a precipitate; characterized by performing the step of preparing a ruthenium catalyst composite for ammonia synthesis.

3. In Paragraph 1, Before step (c), (a') a step of preparing an aqueous solution of an aluminum precursor by mixing the aluminum precursor with distilled water; and (b') a step of impregnating the above aluminum precursor aqueous solution into magnesium oxide (MgO) to obtain a magnesium / aluminum precursor; characterized by performing a method for preparing a ruthenium catalyst composite for ammonia synthesis.

4. In Paragraph 2, In step (a), A method for preparing a ruthenium catalyst complex for ammonia synthesis, characterized in that the magnesium precursor is any one selected from magnesium nitrate (Mg(NO3)2), magnesium bicarbonate (Mg(HCO3)2), magnesium chlorate (Mg(ClO3)2), magnesium chloride (MgCl2), magnesium bromide (MgBr2), magnesium iodide (MgI2) and magnesium sulfate (MgSO4) or a hydrate thereof.

5. In Paragraph 1 or 2, In steps (a) and (a'), A method for preparing a ruthenium catalyst complex for ammonia synthesis, characterized in that the aluminum precursor is selected from aluminum nitrate (Al(NO3)3), aluminum bicarbonate (Al(HCO3)3), aluminum chlorate (Al(ClO3)3), aluminum chloride (AlCl3), aluminum bromide (AlBr3), aluminum iodide (AlI3) and aluminum sulfate (Al2(SO4)3) or a hydrate thereof.

6. In Paragraph 2, In step (a), A method for preparing a ruthenium catalyst composite for ammonia synthesis, characterized in that the Al / (Mg+Al) molar ratio in the above magnesium and aluminum mixed aqueous solution is 0.01 to 0.

10.

7. In Paragraph 1, In step (d), A method for preparing a ruthenium catalyst complex for ammonia synthesis, characterized in that the above barium precursor is any one selected from barium nitrate (Ba(NO3)2), barium bicarbonate (Ba(HCO3)2), barium chlorate (Ba(ClO3)2), barium chloride (BaCl2), barium bromide (BaBr2), barium iodide (BaI2) and barium sulfate (BaSO4) or a hydrate thereof.

8. In Paragraph 1, In steps (c) and (d), A method for manufacturing a ruthenium catalyst composite for ammonia synthesis, characterized in that the above first heat treatment and second heat treatment are performed at 400 to 800℃.

9. In Paragraph 1, In step (e), The above ruthenium precursor is triruthenium dodecacarbonyl (Ru3(CO) 12 A method for preparing a ruthenium catalyst complex for ammonia synthesis, characterized by being selected from any one of ), ruthenium chloride (RuCl3·xH2O), ruthenium carbonate (C3O9Ru2), and ruthenium nitrate (Ru(NO)(NO3)3).

10. In Paragraph 1, In step (e), A method for manufacturing a ruthenium catalyst composite for ammonia synthesis, characterized in that the above third heat treatment is performed at 300 to 700℃.

11. A ruthenium catalyst composite for ammonia synthesis manufactured according to the manufacturing method of any one of claims 1 to 3.

12. In Paragraph 11, The above ruthenium catalyst composite for ammonia synthesis is characterized by having an aluminum (Al) content of 0.5 to 4.0 wt%.

13. In Paragraph 11, The above ruthenium catalyst composite for ammonia synthesis is characterized by having a solid solution structure in which aluminum (Al) atoms are dispersed.

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