WO2024257923A1 - Carbon-based catalyst, for ammonia synthesis, which exhibits high activity under low-pressure and low-temperature conditions, and ammonia synthesis method using same - Google Patents

Abstract

The present invention relates to a promoter-containing catalyst for ammonia synthesis, and an ammonia synthesis method using same. According to the catalyst material of the present invention, and the method for preparing same, ammonia can be highly-efficiently synthesized at a lower temperature and pressure than in the conventional commercial Haber-Bosch process, and thus the present invention has the benefits of significantly reducing the process energy consumption and carbon dioxide emissions.

Description

Carbon-based catalyst for ammonia synthesis showing high activity under low pressure and low temperature conditions and method for synthesizing ammonia using the same

The present invention relates to a carbon-based catalyst for ammonia synthesis exhibiting high activity under low pressure and low temperature conditions and a method for synthesizing ammonia using the same.

Ammonia is a compound composed of nitrogen and oxygen, with a molecular formula of _NH3 , and exists as a gas with an irritating odor at room temperature. It is contained in small amounts in the atmosphere, and trace amounts are also contained in natural waters, and can exist in the soil as it is produced in the process of bacteria decomposing nitrogenous organic matter. Ammonia is used as a raw material for various chemical industries, in the production of ammonia water, and as a solvent for ionic substances.

The most common method for producing ammonia is the Haber-Bosch process, which synthesizes ammonia from hydrogen and nitrogen, and is performed at high pressure (over 200 atm) and high temperature (400–500°C) in the presence of an iron or ruthenium catalyst. This reaction consumes a huge amount of energy, about 30 GJ/ton NH ₃ , and has the problem of emitting a large amount of greenhouse gases equivalent to 1.8 ton CO ₂ /ton NH ₃ due to the fossil fuels used to supply this energy. In addition, the catalytic activity may be inhibited due to the characteristic of nitrogen and hydrogen molecules to be competitively adsorbed on the catalyst surface, and since nitrogen among the reactants has a very stable structure of a triple bond, the ammonia synthesis rate through the catalytic reaction is generally only 20%.

In addition, in order to transition to a hydrogen economy and society, the government is making a plan to procure at least 10-50% of the target green hydrogen supply from overseas at low prices from 2030 onwards in order to meet the target hydrogen supply amount (5.26 million tons/year) by 2040. However, green hydrogen still has low energy density when pressurized and liquefied for long-distance transport, and there is a problem that it is difficult to secure price competitiveness due to high hydrogen loss and energy consumption during transport. On the other hand, ammonia is evaluated as the most suitable hydrogen storage and transportation medium because it has a high hydrogen storage density and can be easily liquefied, so a technology is needed to convert overseas green hydrogen into ammonia and store and transport it.

Accordingly, through many technological developments and optimization of the Haber-Bosch process, the energy consumption has been reduced to 28 GJ/ton NH ₃ , which is close to the theoretical value. However, in order to reduce the production cost, the energy required for ammonia synthesis must be further reduced, and since existing commercial catalysts are designed to operate under high temperature and high pressure conditions, their ammonia synthesis performance is very low under the low pressure and low temperature conditions that we want, so it is necessary to develop and use a groundbreaking catalyst that can sufficiently synthesize ammonia at much lower pressure (100 atm or less) and temperature (400°C or less) than the existing process conditions (400–500°C and 200 atm or more).

The purpose of the present invention is to provide a novel catalyst material and a method for producing the same which exhibits a much higher ammonia synthesis rate than existing commercial ammonia synthesis catalysts at a lower pressure (less than 100 atm) and lower temperature (400°C) than the existing Haber-Bosch process for producing ammonia.

The present invention provides a catalyst for ammonia synthesis, comprising: a carbon-based support supporting a first metal catalyst; and a second metal cocatalyst additionally supported on the carbon-based support supporting the first metal catalyst.

In the ammonia synthesis catalyst of the present invention, the carbon-based support may be selected from the group consisting of low-grade coal, carbon black, nanocellulose, biochar, activated carbon, activated carbon fiber, carbon nanotube, and ketchen black, and the carbon-based support may contain 1 to 10 mass% of nitrogen or oxygen relative to the mass of the carbon-based support.

In the ammonia synthesis catalyst of the present invention, the first metal may be selected from the group consisting of iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), and osmium (Os), and the first metal catalyst may be included in an amount of 1 to 20 mass% relative to the mass of the carbon-based support.

In the ammonia synthesis catalyst of the present invention, the second metal may be selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and the second metal promoter may be included in an amount of 0.1 to 3 mmol/g relative to the mass of the carbon-based support.

The present invention provides a method for synthesizing ammonia at a temperature of 300 to 500°C and a pressure of 10 to 100 atm using the above-mentioned ammonia synthesis catalyst.

The present invention provides a method for producing a catalyst for ammonia synthesis, comprising the steps of: (a) supporting a first metal catalyst and a second metal promoter on a carbon-based support; and (b) treating the carbon-based support with acid.

In the method for producing an ammonia synthesis catalyst of the present invention, the carbon-based support may be selected from the group consisting of low-grade coal, carbon black, nanocellulose, biochar, activated carbon, activated carbon fiber, carbon nanotubes, and ketchen black.

In the method for producing an ammonia synthesis catalyst of the present invention, the first metal may be selected from the group consisting of iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), and osmium (Os), and the first metal catalyst may be included in an amount of 1 to 20 mass% relative to the mass of the carbon-based support.

In the method for producing an ammonia synthesis catalyst of the present invention, the second metal may be selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and the second metal promoter may be included in an amount of 0.1 to 3 mmol/g relative to the mass of the carbon-based support.

In the method for producing an ammonia synthesis catalyst of the present invention, the acid treatment may be performed at 20 to 100°C using an acid selected from the group consisting of sulfuric acid, hydrochloric acid, and nitric acid.

According to the catalyst material of the present invention and the method for manufacturing the same, ammonia can be synthesized with high efficiency at a lower temperature and pressure than the existing commercial Haber-Bosch process, thereby significantly reducing process energy consumption and carbon dioxide emissions.

Figure 1 is a TEM image of a catalyst for ammonia synthesis according to Example 1 of the present invention.

Figure 2 is an XRD graph of a catalyst for ammonia synthesis according to Example 5 of the present invention.

The ammonia synthesis catalyst of the present invention will be described in detail with reference to the attached drawings below.

The drawings introduced below are provided as examples so that the idea of the present invention can be sufficiently conveyed to those skilled in the art. Therefore, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated in order to clarify the idea of the present invention.

At this time, if there is no other definition in the technical and scientific terms used, they have the meaning commonly understood by a person of ordinary skill in the technical field to which this invention belongs, and the description of well-known functions and configurations that may unnecessarily obscure the gist of the present invention is omitted in the following description and the attached drawings.

Additionally, the singular forms used in the specification and the appended claims are intended to include the plural forms as well, unless the context clearly dictates otherwise.

In this specification and the appended claims, the terms first, second, etc. are not used in a limiting sense but are used to distinguish one component from another.

The terms “include” or “have” in this specification and the appended claims mean that a feature or component described in the specification is present, and unless specifically limited, do not preclude the possibility that one or more other features or components may be added.

In this specification and the appended claims, when a part such as a film (layer), region, component, etc. is said to be on or above another part, it includes not only the case where it is directly above and in contact with the other part, but also the case where another film (layer), another region, another component, etc. is interposed.

The ammonia synthesis catalyst of the present invention is characterized by comprising: a carbon-based support on which a first metal catalyst is supported; and a second metal cocatalyst additionally supported on the support on which the first metal catalyst is supported.

In one specific embodiment, the carbon-based support may include a one-dimensional carbon-based material or other carbon-based material, and preferably may be selected from the group consisting of low-grade coal, carbon black, nanocellulose, biochar derived from natural plants, activated carbon, activated carbon fibers, carbon nanotubes and ketchen black, and more preferably may include nitrogen-containing carbon black, carbon black or carbon nanotubes.

More specifically, the one-dimensional carbon-based material may be one or a combination of two or more selected from the group consisting of carbon nanotubes (CNTs), graphene nanoribbons (GNRs), carbon nanofibers, and carbon nanowires, and the carbon nanotubes may be single-walled carbon nanotubes (SWNTs) or multi-walled carbon nanotubes (MWNTs). Preferably, multi-walled carbon nanotubes may be used as the one-dimensional carbon-based material. Multi-walled carbon nanotubes have superior mechanical strength, superior structural retention upon repeated tensile stretching, and a wide tensile range compared to carbon nanotubes such as single-walled carbon nanotubes, and thus are advantageous in being used as a support.

In addition, the one-dimensional carbon-based material may have a diameter of 10 to 200 nm, preferably 20 to 150 nm, and a length of 10 to 100 μm, preferably 20 to 80 μm, but is not limited thereto.

The above other carbon-based materials may be one or a combination of two or more selected from the group consisting of low-grade coal, carbon black, nanocellulose, biochar, activated carbon, activated carbon fiber, and ketchen black.

The above carbon-based support may contain 1 to 10 mass% of nitrogen or oxygen relative to the mass of the carbon-based support, preferably 2 to 9 mass%, and more preferably 3 to 8 mass%.

By using the above carbon-based support, the specific surface area of the carbon-based support increases, so that the metal catalyst can be dispersed small and uniformly, thereby reducing the unit cost of the catalyst, and preventing sintering of the metal catalyst and cocatalyst when used for a long time. In addition, there is an advantage in that the high electrical conductivity of the carbon-based support can be used to rapidly supply electrons to nitrogen molecules, thereby promoting the nitrogen dissociation step, and the step in which the hydrogenation reaction proceeds and ammonia is generated can be promoted because it binds well to the dissociated nitrogen atoms.

In one specific example, non-limiting examples of the first metal include a metal selected from the group consisting of iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), molybdenum (Mo), and osmium (Os), and preferably ruthenium.

The first metal catalyst may be included in an amount of 1 to 20 mass% relative to the support mass, preferably 2 to 15 mass%, and most preferably 3 to 8 mass%.

The average particle diameter of the first metal catalyst may be 0.1 to 50 nm, preferably 0.1 to 20 nm, and most preferably 0.1 to 5 nm. When the first metal catalyst has an average particle diameter in the above range, the reaction site exposed to the surface area increases, thereby increasing the synthesis performance per unit mass of the first metal, and as the synthesis performance increases, the amount of the first metal used may be reduced, thereby reducing the unit cost of the catalyst.

In one specific example, the second metal may be an alkali metal or an alkaline earth metal, and non-limiting examples of the second metal include a metal selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and preferably barium.

The second metal cocatalyst may be included in an amount of 0.1 to 3.0 mmol/g relative to the mass of the support, preferably 0.5 to 2.0 mmol/g, and most preferably 0.7 to 1.5 mmol/g.

Due to the additional loading of the second metal promoter, there is an advantage in that the nitrogen bonding force is weakened by supplying electrons to nitrogen, a reactant of the ammonia synthesis reaction (Lewis base), and the reaction rate of the nitrogen dissociation step (the rate-determining step of the overall reaction) is accelerated, thereby allowing the reaction to proceed in the forward direction.

In one specific example, the average particle size of the ammonia synthesis catalyst may be 1 to 1,000 μm, preferably 2 to 900 μm, and most preferably 3 to 800 μm, but is not limited thereto.

In addition, the specific surface area of the ammonia synthesis catalyst as measured by the BET method may be 10 to 2,000 m ² /g, preferably 20 to 1,500 m ² /g, and most preferably 30 to 1,000 m ² /g. The ammonia synthesis catalyst having the above average particle size and specific surface area has the advantage that nitrogen molecules can be easily adsorbed on the surface of the catalyst.

The method for synthesizing ammonia using the ammonia synthesis catalyst of the present invention can be carried out at a temperature of 300 to 500°C, and preferably, ammonia can be synthesized at a temperature of 350 to 450°C. In addition, the method can be carried out at a pressure of 10 to 100 atm, and is characterized in that ammonia is synthesized at a pressure of preferably 30 to 80 atm.

The most common method for producing ammonia is the Haber-Bosch process, which synthesizes ammonia from hydrogen and nitrogen. It is performed at high pressure (over 200 atm) and high temperature (400–500°C) in the presence of a catalyst. This reaction consumes a huge amount of energy, emits a large amount of greenhouse gases, and the catalytic activity may be inhibited by the competitive nature of nitrogen and hydrogen molecules to be adsorbed on the catalyst surface. In addition, nitrogen among the reactants has a very stable structure of a triple bond, so the ammonia synthesis rate through the catalytic reaction is generally only 20%.

However, the method of synthesizing ammonia using the ammonia synthesis catalyst of the present invention has the effect of significantly reducing process energy consumption and carbon dioxide emissions because it shows a higher ammonia synthesis rate than existing commercial ammonia synthesis catalysts at lower pressure and lower temperature than the Haber-Bosch process.

The method for producing an ammonia synthesis catalyst of the present invention may include (a) a step of supporting a first metal catalyst and a second metal promoter on a carbon-based support; and (b) a step of acid-treating the carbon-based support.

In one specific example, the method for supporting the first metal catalyst may include dissolving the first metal catalyst precursor in a suitable solvent (water, alcohol, acetone, THF, DMF), impregnating the support through a simple wetness impregnation method, a wetness impregnation method, and then drying the solvent and performing a reduction treatment. A vapor deposition method may also be used, but there is no particular limitation as long as it is a general supporting method.

In one specific example, in the method for supporting the first metal catalyst, the first metal may be selected from the group consisting of iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), molybdenum (Mo), and osmium (Os), and preferably may be ruthenium, and at this time, precursors of the ruthenium catalyst may include ruthenium metal, ruthenium oxide (RuO ₂ ), ruthenium red, ruthenium acetylacetonate (Ru(acac) ₃ ), ruthenium chloride (RuCl ₃ ), ruthenocene (Bis(cyclopentadienyl) ruthenium), ruthenium nitrosyl nitrate, ruthenium iodide (RuI ₃ ), and triruthenium dodecacarbonyl (Ru ₃ (CO)). ₁₂ ; triruthenium dodecacarbonyl), ruthenium nitrate (Ru( _NO3 ) ₃ ; ruthenium nitrate), etc. can be used, but are not limited thereto. At this time, the first metal catalyst may be included in an amount of 1 to 20 mass% relative to the support mass, preferably 2 to 15 mass%, and most preferably 3 to 8 mass%.

In one specific example, before the step of supporting the first metal catalyst, the first metal catalyst may be additionally pretreated. The pretreatment step is a step of heating and calcining while flowing an inert gas such as nitrogen, argon, or helium; a reducing gas such as ammonia reaction synthesis gas (H ₂ +N ₂ ), hydrogen, diluted hydrogen (balance gas: an inert gas such as nitrogen, argon, or hydrogen); carbon monoxide, or diluted carbon monoxide (balance gas: an inert gas such as nitrogen, argon, or hydrogen); and the heating temperature varies depending on the component of the first metal, but is preferably heated at 250 to 700°C.

In one specific example, the method for supporting the second metal promoter may include dissolving the second metal promoter precursor in a suitable solvent (water, alcohol, acetone, THF, DMF), impregnating the support through a simple wetness impregnation method, a wetness impregnation method, and then drying the solvent and performing a reduction treatment. A vapor deposition method may also be used, but there is no particular limitation as long as it is a general supporting method.

In one specific example, in the method for supporting the second metal promoter, the second metal may be selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and preferably barium, and at this time, as the barium promoter precursor, barium nitrate (Ba(NO ₃ ) ₂ ; barium nitrate), barium hydroxide (Ba(OH) ₂ ; barium hydroxide), barium perchlorate (Ba(ClO ₄ ) ₂ ; barium perchlorate), barium isopropoxide (Ba(OCH(CH ₃ ) ₂ ) ₂ ; barium isopropoxide), barium fluoride (BaF ₂ ; barium fluoride), barium oxide (BaO; barium oxide), barium bromide (BaBr ₂ ; barium bromide), barium chloride (BaCl ₂ ; barium chloride), barium iodide (BaI ₂ ; barium iodide), barium acetate (Ba(CH ₃ COO) ₂ ; barium acetate), barium carbonate (BaCO ₃ ; barium carbonate), barium sulfate (BaSO ₄ ; barium sulfate), etc. can be used, but are not limited thereto. At this time, the second metal promoter may be included in an amount of 0.1 to 3.0 mmol/g relative to the mass of the support, preferably 0.5 to 2.0 mmol/g, and most preferably 0.7 to 1.5 mmol/g.

In one specific example, before the step of supporting the second metal promoter, the second metal promoter may be additionally pretreated. The pretreatment step is a step of heating and calcining while flowing an inert gas such as nitrogen, argon, or helium; a reducing gas such as ammonia reaction synthesis gas (H ₂ +N ₂ ), hydrogen, diluted hydrogen (balance gas: an inert gas such as nitrogen, argon, or hydrogen); carbon monoxide, or diluted carbon monoxide (balance gas: an inert gas such as nitrogen, argon, or hydrogen); and the heating temperature varies depending on the component of the first metal, but is preferably heated at 250 to 700°C.

In one specific example, the acid treatment in step (b) may be performed using a strong acid at 20 to 100°C, preferably using an acid selected from the group consisting of sulfuric acid, hydrochloric acid, and nitric acid. At this time, the concentration of the strong acid may be 0.05 to 1.0 M, preferably 0.1 to 0.9 M, and more preferably 0.3 to 0.8 M. When a strong acid having a concentration in the above range is used, there is an advantage in that impurities remaining on the catalyst surface can be removed without damaging the catalyst itself, and the degree of dispersion can be increased.

Hereinafter, the present invention will be described in detail through examples. However, these are provided to explain the present invention in more detail, and the scope of the present invention is not limited by the following examples.

<Example 1> Preparation of catalyst for ammonia synthesis

0.27 g of ruthenium chloride precursor (RuCl ₃ ·xH ₂ O, 37% Ru) is completely dissolved in 3 mL of water, and 2 g of carbon black is added to prepare a slurry. The slurry containing the ruthenium chloride and carbon black is allowed to stand in the air at a temperature of room temperature to 50°C for 20 minutes, and then a solution of 0.54 g of barium nitrate (Ba(NO ₃ ) ₂ ) dissolved in 2 mL of distilled water is mixed. Thereafter, the slurry is allowed to stand at room temperature for 20 minutes, dried in an oven at 100°C for 15 hours, and then treated with acid in a 0.6 M sulfuric acid solution to prepare the final catalyst.

<Example 2> Preparation of a catalyst having a ruthenium content of 9 wt%

The catalyst for ammonia synthesis was prepared using the same method as that for Example 1, except that 0.486 g of ruthenium chloride precursor (RuCl ₃ ·xH ₂ O, 37% Ru) was used instead of 0.27 g of ruthenium chloride precursor (RuCl ₃ ·xH ₂ O, 37% Ru).

<Example 3> Preparation of a catalyst having a ruthenium content of 3 wt%

The catalyst for ammonia synthesis prepared in Example 1 was prepared in the same manner as that for the catalyst for ammonia synthesis prepared in Example 1, except that 0.16 g of ruthenium chloride precursor (RuCl ₃ ·xH ₂ O, 37% Ru) was used instead of 0.27 g of ruthenium chloride precursor (RuCl ₃ ·xH ₂ O, 37% Ru), and 0.27 g of barium nitrate (Ba(NO ₃ ) ₂ ) was mixed instead of 0.54 g of barium nitrate (Ba(NO ₃ ) ₂ ).

<Example 4> Preparation of a catalyst having a barium content of 0.5 mmol/g

An ammonia synthesis catalyst was prepared using the same manufacturing method as that of Example 1, except that 0.27 g of barium nitrate (Ba( _NO3 ) ₂ ) was used instead of 0.54 g of barium nitrate (Ba( _NO3 ) ₂ ).

<Example 5> Preparation of a catalyst having a barium content of 2.0 mmol/g

An ammonia synthesis catalyst was prepared using the same manufacturing method as that of Example 1, except that 1.08 g of barium nitrate (Ba( _NO3 ) ₂ ) was used instead of 0.54 g of barium nitrate (Ba( _NO3 ) ₂ ).

<Example 6> Production of biochar-supported catalyst using soybean stover as raw material

The catalyst for ammonia synthesis was manufactured using the same manufacturing method as that of Example 1, except that biochar manufactured from soybeans was used as a support instead of carbon black.

<Example 7> Preparation of carbon black support catalyst with added nitrogen

A catalyst for ammonia synthesis was manufactured using the same manufacturing method as that of Example 1, except that carbon black doped with 2 wt% nitrogen was used as a support instead of the existing carbon black.

<Example 8> Preparation of a catalyst using carbon nanotubes as a support

0.069 g of ruthenium chloride precursor (RuCl ₃ ·xH ₂ O, 38% Ru) is completely dissolved in 2 mL of acetone, and 0.5 g of carbon nanotubes are added to prepare a slurry. The slurry is left in the air at room temperature to 50°C for 12 hours to remove the solvent, and then transferred to a calcination furnace and heat-treated at 200°C for 2 hours while flowing hydrogen. Thereafter, the temperature is increased to 350°C while flowing nitrogen gas, and heat-treated for 3 hours. After the heat-treated powder is impregnated with a solution of 0.14 g of barium nitrate (Ba(NO ₃ ) ₂ ) dissolved in 2 mL of distilled water, and then the solvent is removed by exposing it to the air in the same manner. The powder is subjected to acid treatment in a 0.6 M sulfuric acid solution to prepare the final catalyst.

<Comparative Example 1> Preparation of a catalyst not containing ruthenium

A catalyst for ammonia synthesis was prepared using the same manufacturing method as that of Example 1, except that a ruthenium chloride precursor (RuCl ₃ ·xH ₂ O, 37% Ru) was not used.

<Comparative Example 2> Production of a catalyst that does not contain barium

It was manufactured using the same manufacturing method as the ammonia synthesis catalyst manufactured in Example 1, except that barium nitrate (Ba(NO ₃ ) ₂ ) was not used.

<Comparative Example 3> Preparation of a catalyst with a ruthenium content of 2 wt%

The catalyst for ammonia synthesis was prepared using the same method as that for preparing the catalyst in Example 1, except that 0.108 g of ruthenium chloride precursor (RuCl ₃ ·xH ₂ O, 37% Ru) was used instead of 0.27 g of ruthenium chloride precursor (RuCl ₃ ·xH ₂ O, 37% Ru).

<Comparative Example 4> Preparation of a catalyst containing cesium as a cocatalyst

A catalyst for ammonia synthesis was prepared using the same manufacturing method as that of Example 1, except that cesium nitrate (CsNO ₃ ) was used instead of barium nitrate (Ba(NO ₃ ) ₂ ).

<Comparative Example 5> Preparation of a catalyst containing potassium as a cocatalyst

A catalyst for ammonia synthesis was prepared using the same manufacturing method as that of Example 1, except that potassium nitrate (KNO ₃ ) was used instead of barium nitrate (Ba(NO ₃ ) ₂ ).

<Comparative Example 6> Preparation of a catalyst using MgO as a support

A catalyst for ammonia synthesis was manufactured using the same manufacturing method as that of Example 1, except that a MgO series support (silica) was used instead of carbon black.

<Comparative Example 7> Preparation of a catalyst using CeO ₂ as a support

A catalyst for ammonia synthesis was manufactured using the same manufacturing method as that of Example 1, except that a CeO ₂ series support (ceria) was used instead of carbon black.

<Experimental Example 1> Structural Analysis of Catalyst for Ammonia Synthesis

First, the structure of the ammonia synthesis catalyst manufactured through the manufacturing method of Example 1 was observed using a transmission electron microscope (TEM).

Referring to Figure 1, it can be seen that the catalyst and cocatalyst components are finely dispersed.

Next, the structure of the ammonia synthesis catalyst manufactured through the manufacturing method of Example 5 was observed through X-ray diffraction analysis.

Referring to Figure 2, only diffraction peaks due to carbon nanotubes and cocatalyst components were analyzed, and no diffraction peaks for the ruthenium catalyst component were observed, which means that the catalyst component was very finely dispersed.

<Experimental Example 2> Analysis of ammonia synthesis rate using a catalyst for ammonia synthesis

Using the catalysts synthesized through the manufacturing methods of Examples 1 to 5 and Comparative Examples 1 to 7, ammonia was synthesized, and then the ammonia synthesis rate was evaluated. A mixed gas of H ₂ /N ₂ = 3 (molar ratio) was injected top-down into a high-pressure gas-phase fixed-bed reactor. The reaction was carried out at 50 atm and 400°C, and the reaction was carried out at a reaction flow rate (GHSV) of 5,000 h ^-1 , and the results are shown in Table 1.

catalyst
ingredient Catalyst content
(wt%) co-catalyst component Promoter content
(mmol/g) Type of support Ammonia synthesis rate
(g-NH ₃ /g-cat·hr) Example 1 Ru 5 Ba 1 Carbon black 1.0 Example 2 Ru 9 Ba 1 Carbon black 0.92 Example 3 Ru 3 Ba 0.5 Carbon black 1.0 Example 4 Ru 5 Ba 0.5 Carbon black 0.65 Example 5 Ru 5 Ba 2 Carbon black 0.85 Example 6 Ru 5 Ba 1 Soybean biochar 0.8 Example 7 Ru 5 Ba 1 Nitrogen doped carbon black 1.2 Example 8 Ru 5 Ba 1 Carbon nanotubes 1.35 Comparative Example 1 Ru 0 Ba 1 Carbon black ~0 Comparative Example 2 Ru 5 Ba 0 Carbon black 0.12 Comparative Example 3 Ru 2 Ba 1 Carbon black 0.25 Comparative Example 4 Ru 5 Cs 1 Carbon black 0.3 Comparative Example 5 Ru 5 K 1 Carbon black 0.2 Comparative Example 6 Ru 5 Ba 1 MgO 0.8 Comparative Example 7 Ru 5 Ba 1 _CeO2 0.25

Referring to Table 1 above, when ammonia was synthesized using the catalysts (support type: carbon-based material, first metal catalyst component: Ru, second metal promoter component: Ba) manufactured through the manufacturing methods of Examples 1 to 5, it was found that the ammonia synthesis rate was very excellent compared to the catalysts manufactured through the manufacturing methods of Comparative Examples 1 to 7. In particular, in the case of catalysts (Examples 1, 2, and 5) in which the content of the first metal catalyst was 3 to 8 wt% and the content of the second metal promoter was 0.7 to 1.5 mol/g, an ammonia synthesis rate of about 0.85 g-NH ₃ /g-cat hr or more was shown. In general, when an ammonia synthesis rate of 0.3 g-NH ₃ /g-cat hr or more is shown, it can be considered to be a higher level than the performance of existing commercial catalysts under the same low pressure conditions, and therefore, it was found that the ammonia synthesis rate was very excellent.

In comparison, in the case of a catalyst that did not include a first metal catalyst, such as in Comparative Example 1, or did not include a second metal promoter, such as in Comparative Example 2, it was found that almost no ammonia was synthesized under the conditions of 50 atm and 400°C.

In addition, in the case of catalysts having different contents of the first metal catalyst, such as Comparative Example 3, it was confirmed that the ammonia synthesis rate was significantly lower compared to the catalysts of Examples 1 and 2.

In addition, it was confirmed that the ammonia synthesis rate significantly decreased when the components of the promoter were different, such as in Comparative Examples 4 and 5, or when the types of the supports were different, such as in Comparative Examples 6 and 7. In particular, it was confirmed that the ammonia synthesis rate increased when a carbon-based support, such as carbon black or carbon nanotubes, was used, compared to when MgO was used as the support, such as in Comparative Example 6.

As described above, the ammonia synthesis catalyst according to the present invention exhibits an excellent ammonia synthesis rate even under low temperature and low pressure conditions, unlike the ammonia synthesis according to the general Haber-Bosch method, by using a specific support, catalyst, and cocatalyst.

Claims (15)

A carbon-based support supported with a first metal catalyst; and An ammonia synthesis catalyst, wherein a second metal promoter is additionally supported on a carbon-based support supporting the first metal catalyst. In the first paragraph, An ammonia synthesis catalyst, wherein the carbon-based support is selected from the group consisting of low-grade coal, carbon black, nanocellulose, biochar, activated carbon, activated carbon fiber, carbon nanotube, and ketchen black. In the first paragraph, A catalyst for ammonia synthesis, wherein the carbon-based support contains 1 to 10 mass% of nitrogen or oxygen relative to the mass of the carbon-based support. In the first paragraph, An ammonia synthesis catalyst, wherein the first metal is selected from the group consisting of iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), and osmium (Os). In the first paragraph, A catalyst for ammonia synthesis, wherein the first metal catalyst is included in an amount of 1 to 20 mass% relative to the mass of the carbon-based support. In the first paragraph, An ammonia synthesis catalyst, wherein the second metal is selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). In the first paragraph, A catalyst for ammonia synthesis, wherein the second metal promoter is contained in an amount of 0.1 to 3 mmol/g relative to the mass of the carbon-based support. A method for synthesizing ammonia at a temperature of 300 to 500°C and a pressure of 10 to 100 atm using an ammonia synthesis catalyst according to any one of claims 1 to 7. (a) a step of supporting a first metal catalyst and a second metal promoter on a carbon-based support; and (b) a step of acid-treating the carbon-based support; A method for producing a catalyst for ammonia synthesis. In Article 9, An ammonia synthesis catalyst, wherein the carbon-based support is selected from the group consisting of low-grade coal, carbon black, nanocellulose, biochar, activated carbon, activated carbon fiber, carbon nanotube, and ketchen black. In Article 9, A method for producing a catalyst for ammonia synthesis, wherein the first metal is selected from the group consisting of iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), and osmium (Os). In Article 9, A method for producing a catalyst for ammonia synthesis, wherein the first metal catalyst is included in an amount of 1 to 20 mass% relative to the mass of the carbon-based support. In Article 9, A method for producing a catalyst for ammonia synthesis, wherein the second metal is selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). In Article 9, A method for producing a catalyst for ammonia synthesis, wherein the second metal cocatalyst is included in an amount of 0.1 to 3 mmol/g relative to the mass of the carbon-based support. In Article 9, The above acid treatment is a method for producing an ammonia synthesis catalyst using an acid selected from the group consisting of sulfuric acid, hydrochloric acid and nitric acid at 20 to 100°C.

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