Metal composite catalyst for ammonia decomposition reaction and method for producing the same

Abstract

The present invention provides a metal composite catalyst for ammonia decomposition reaction, which comprises a metal-containing support and metal nanoparticles dispersed on the surface or in the pores of the metal-containing support, the metal nanoparticles having a particle size of 1.5 to 7 nm. More specifically, the metal composite catalyst according to one embodiment of the present invention is prepared by a polyol process and has a significant advantage in ammonia decomposition efficiency.

Description

[Technical Field]

[0001] The present invention relates to a metal composite catalyst for an ammonia decomposition reaction, and more particularly to a metal composite catalyst produced by a polyol process and a method for producing the same. [Background technology]

[0002] Recently, abnormal weather has been occurring around the world, causing many difficulties in all industries. The main cause of this abnormal weather is global warming caused by the continued use of fossil fuels. In particular, in East Asia, there was no significant change in average temperature between 1996 and 2005, but a rapid rise has been observed since the mid-21st century, and it has been confirmed that the global average temperature rose by approximately 0.85°C over the 133 years from 1880 to 2012.

[0003] If the Earth's temperature rises by 2 degrees Celsius, approximately 15 to 40% of species could become extinct. To prevent this, countries around the world have proposed measures such as halving greenhouse gas emissions by 2030, and are gradually implementing them (IPCC Sixth Assessment Report).

[0004] Alternative energy sources are needed to curb the use of fossil fuels, and currently, technological development and practical application of renewable energy sources is underway. However, with renewable energy sources, there is a possibility that energy supply problems may arise due to geographical or natural factors.

[0005] Recently, hydrogen has been attracting attention as an alternative energy source, and numerous related research and demonstration projects are underway. Hydrogen is known as an environmentally friendly power generation method because it does not emit harmful gases during power generation. However, hydrogen is mainly stored and transported as high-pressure gas hydrogen, which has disadvantages such as the risk of explosion, high costs, and limited storage capacity.

[0006] In the case of hydrogen, the thickness of the insulation increases, so a fuel storage tank about 7.6 times larger than that of conventional fossil fuels is required. On the other hand, the volumetric hydrogen energy density of ammonia is 121 kg / m3 and liquefied hydrogen 70.8 kg / m 3 Because hydrogen has a larger molecular weight than ammonia, it is used in a variety of industries. Specifically, when considering the cost of transporting hydrogen by pipeline, it costs approximately $1.87, while ammonia costs $0.19, which is about 10% of the cost. Furthermore, from the perspective of storage, when storing hydrogen for six months, the production, transportation, and storage costs are $19.82 for hydrogen and $4.53 for ammonia, making the storage cost of hydrogen approximately 4.3 times higher.

[0007] Ruthenium (Ru) is an active metal widely used in the field of ammonia decomposition (NH3 → 1 / 2N2 + 3 / 2H2), and it is known that the main active site in the ammonia decomposition reaction using Ru is the flat Ru(0001) surface. The Ru(0001) surface is highly temperature-dependent, and is one of the sites where N atoms easily attach in the rate-determining step of N2 desorption.

[0008] Ruthenium is significantly affected by particle shape and size, with the B5 site, which is the active site of Ru, functioning as the main active site. Therefore, in the production of ammonia decomposition catalysts, a manufacturing method that allows for free control of particle shape and size is required.

[0009] The main chemical synthesis methods are broadly divided into gas-phase and liquid-phase (colloidal) methods. However, since gas-phase methods using plasma or gas evaporation require expensive equipment, liquid-phase methods are primarily used, as they are inexpensive and produce uniform particles. A typical chemical liquid-phase method is the polyol synthesis method, which involves reduction using ethylene glycol or similar. Specifically, in the first step, a precursor metal salt is dissolved in a liquid polyol, and the dissolved salt is reduced with the polyol. Nano-sized particles are then produced from the solution through a nucleation and growth process of metal particles. The metal nanoparticles are then stabilized with a stabilizer.

[0010] However, in the case of conventional polyol processes, due to the stable polyol structure, synthesis methods mainly required reaction temperatures of 200°C or higher, and there was a risk of using explosive hazardous materials such as hydrazine derivatives to maximize reduction. Furthermore, the addition of substances such as PVP and PVA in addition to the polyol raw material to produce nanometal catalysts also posed a problem of reduced catalyst yield. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been conceived to solve the above problems, and one embodiment of the present invention provides a metal composite catalyst for an ammonia decomposition reaction.

[0012] Another embodiment of the present invention provides a method for preparing a metal composite catalyst for ammonia decomposition reaction.

[0013] The technical problems that the present invention aims to solve are not limited to the above-mentioned technical problems, and other technical problems not mentioned will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Means for solving the problem]

[0014] As a technical means for achieving the above-mentioned technical object, in one aspect of the present invention, Provided is a metal composite catalyst for an ammonia decomposition reaction, which comprises a metal-containing support and metal nanoparticles dispersed on the surface or inside the pores of the metal-containing support, characterized in that the particle size of the metal nanoparticles is 1.5 to 7 nm.

[0015] The metal composite catalyst may be characterized in that the content of the metal nanoparticles is 2.0 to 2.5 parts by weight relative to 100 parts by weight of the metal composite catalyst, and the metal dispersion of the metal nanoparticles in the metal composite catalyst is 23 to 50%.

[0016] The BET surface area of ​​the metal composite catalyst is 119.5 to 150 m 2 / g.

[0017] The total pore volume of the metal composite catalyst is greater than 0.56 to 0.75 cm 3 / g or less.

[0018] The metal nanoparticles may be at least one nanoparticle selected from the group consisting of ruthenium (Ru), rhodium (Rh), platinum (Pt), and gold (Au).

[0019] The metal-containing support may be characterized as being an oxide of at least one transition metal selected from the group consisting of magnesium, aluminum, iron, manganese, nickel, cobalt, titanium, and zinc.

[0020] The metal nanoparticles may be characterized as being composed of hemispherical particles having a particle size of 2 to 5 nm, or particles having a shape including a flat surface having a particle size of 1.5 to 7 nm.

[0021] The metal composite catalyst may be characterized as being self-reducing.

[0022] In another aspect of the present invention, Provided is a method for producing a metal composite catalyst for an ammonia decomposition reaction, comprising the steps of preparing an active metal precursor solution, mixing the active metal precursor solution with a polyol to obtain a mixture, heating the mixture to synthesize metal nanoparticles, and adding a metal-containing support to the heated mixture to form a composite.

[0023] The polyol may be at least one selected from the group consisting of ethylene glycol, propylene glycol, and butylene glycol.

[0024] The polyol may be characterized as comprising two hydroxy groups (-OH), the two hydroxy groups being substituted on adjacent carbons.

[0025] The active metal precursors include Ru(NO)(NO)3 (Ruthenium(III) nitrosyl nitrate), Ru(C5H7O2)3 (Ruthenium(III) acetylacetonate), C6H9O6Ru (Ruthenium(III) acetate), C 10 H 10 Ru(ruthenocen), C7H9RuC7H9 (bis(ethylcyclopentadienyl)ruthenium(II)), C 10 H 10 Ru (bis(cyclopentadienyl)ruthenium(II)), Ru(CH 11 )2(Bis(2,4-dimethylpentadienyl)ruthenium(II); Bis(2,4-dimethylpentadienyl)ruthenium(II)), C 14 H 10 The compound may be characterized as being at least one selected from the group consisting of O4Ru2 (bis(cyclopentadienylruthenium dicarbonyl) dimer), and mixtures thereof.

[0026] The step of heating the mixture to synthesize metal nanoparticles may be performed at a temperature of 195° C. or less.

[0027] The method may be characterized in that in the step of heating the mixture to synthesize metal nanoparticles, the mixture is stirred at a speed of 150 to 500 rpm.

[0028] The method may further include the steps of: adding a metal-containing carrier to the heated mixture to form a composite; and thereafter, washing the composite metal composite catalyst; drying the metal composite catalyst; and calcining the metal composite catalyst. [Effects of the Invention]

[0029] According to an embodiment of the present invention, a self-reducing metal composite catalyst is produced by a polyol reduction process, which prevents sintering, which occurs in the prior art when particles aggregate together at temperatures above 500°C, resulting in larger particles.

[0030] Furthermore, according to one embodiment of the present invention, a metal composite catalyst containing metal nanoparticles with controlled nanosize and shape can be prepared by utilizing the properties of polyol itself in the polyol process without adding a stabilizer such as PVP or PVA.

[0031] The effects of the present invention are not limited to these, and include all effects that can be inferred from the configuration of the invention described in the description of the present invention or the claims. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a flowchart showing a method for producing a metal composite catalyst according to an embodiment of the present invention. [Figure 2] 1 shows images obtained by analyzing a metal composite catalyst according to an embodiment of the present invention and a metal composite catalyst according to a comparative example using a transmission electron microscope (TEM). [Figure 3] 1 shows data comparing the ammonia decomposition activity of the metal composite catalysts of Examples 1 to 3 according to an embodiment of the present invention and Comparative Examples 1 and 2. [Figure 4] FIG. 1 is a graph showing the results of a comparison of ammonia decomposition reaction temperatures between an example and a comparative example according to a catalyst production method according to an embodiment of the present invention. [Figure 5] FIG. 1 is a diagram showing the results of a comparative test of ammonia decomposition activity with and without a catalytic reduction process according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention may, however, be embodied in many different forms and is not limited to the examples set forth herein, but is defined only by the appended claims.

[0034] It should be noted that the terms used in the present invention are merely used to describe specific embodiments and are not intended to limit the present invention. The singular expression includes the plural expression unless otherwise specified. Throughout the specification of the present invention, the term "comprises" a certain component does not mean that other components are excluded, but that other components may also be included, unless otherwise specified.

[0035] In a first aspect of the present application, Provided is a metal composite catalyst for an ammonia decomposition reaction, which comprises a metal-containing support and metal nanoparticles dispersed on the surface or inside the pores of the metal-containing support, characterized in that the particle size of the metal nanoparticles is 1.5 to 7 nm.

[0036] The metal composite catalyst for ammonia decomposition reaction according to the first aspect of the present specification will be described in detail below.

[0037] In one embodiment of the present specification, the metal-containing support may be selected from the group consisting of metal oxides, metal-organic frameworks, and rassiling. In particular, the metal oxide may be an oxide of a metal selected from the group consisting of lanthanum group metals, transition metals, such as magnesium, aluminum, zinc, gallium, cadmium, manganese, indium, iron, nickel, cobalt, tin, mercury, titanium, lead, bismuth, polonium, and alloys thereof. Among the metals, the oxide of a metal selected from the group consisting of lanthanum group metals, transition metals, aluminum, and alloys thereof is particularly preferred. The metal-containing support may be an oxide of at least one transition metal selected from the group consisting of magnesium, aluminum, iron, manganese, nickel, cobalt, titanium, and zinc. Preferably, the metal oxide may be at least one selected from the group consisting of alumina, silica, titanium dioxide, and MgAl2O4, and more preferably MgAl2O4. In particular, a highly basic metal-containing carrier is suitable, and a carrier to which a basic metal has been added supplies electrons to the active metal, thereby increasing the desorption rate by providing electrons during N2 binding and desorption, which are the rate-determining steps of the ammonia decomposition reaction.

[0038] In one embodiment of the present specification, the metal nanoparticles may be a metal selected from the group consisting of alkali metals, alkaline earth metals, and mixtures thereof, preferably at least one selected from the group consisting of ruthenium (Ru), rhodium (Rh), platinum (Pt), and gold (Au), more preferably ruthenium nanoparticles.

[0039] In one embodiment of the present specification, the BET surface area of ​​the metal composite catalyst is 119.25 m 2 / g or more, 119.5m 2 / g or more, 120m 2 / g or more, 125m 2 / g or more, 130m 2 / g or more, 135m 2 / g or more, and 2 / g or less, 157.5m 2 / g or less, 155m 2 / g or less, 152.5m 2 / g or less, or 150m 2 If the content exceeds the above range, the volume of the metal composite catalyst may be unnecessarily large, or the required strength may not be ensured, whereas if the content is below the above range, the ammonia decomposition efficiency may be reduced.

[0040] In one embodiment of the present specification, the metal composite catalyst may have a porous structure, specifically, may contain both micropores and mesopores. The total pore volume of the metal composite catalyst may be defined as the sum of the volume of the micropores and the volume of the mesopores, and may further include other pore volumes. Specifically, the total pore volume of the metal composite catalyst is 0.56 cm 3 / g or more, 0.57cm 3 / g or more, 0.58cm 3 / g or more, 0.60cm 3 / g or more, 0.63cm 3 / g or more, or 0.65cm 3 / g or more, and 3 / g or less, or 0.80 cm 3 / g or less, or 0.75cm 3 If the content exceeds the above range, the volume of the metal composite catalyst may be unnecessarily large, or the required strength may not be ensured, whereas if the content is below the above range, the ammonia decomposition efficiency may be reduced.

[0041] In one embodiment of the present specification, the particle size of the metal nanoparticles may be 0.5 nm or more, 0.75 nm or more, 1.0 nm or more, 1.25 nm or more, or 1.5 nm or more; 7 nm or less, 6.75 nm or less, 6.5 nm or less, 6.25 nm or less, 6.0 nm or less, 5.75 nm or less, 5.5 nm or less, 5.25 nm or less, or 5.0 nm or less, preferably 1.5 to 7 nm. If the particle size exceeds this range, the metal particles become too large, resulting in insufficient ammonia decomposition activity or difficulty in uniform dispersion. If the particle size is below this range, it is difficult to consider the nanoparticles as uniformly dispersed nanoparticles within a controllable range of overall particle size and shape.

[0042] In one embodiment of the present specification, the shape of the metal nanoparticles may be at least one selected from the group consisting of spherical, hemispherical, plate-like, cylindrical, and polyhedral with flat surfaces, and preferably may be hemispherical, polyhedral with flat surfaces, or a combination thereof.

[0043] In one embodiment of the present specification, if the metal nanoparticles are hemispherical in shape, they may have a particle size of 2 to 5 nm, and if the metal nanoparticles are polyhedral in shape, they may be characterized as being composed of particles with a shape including flat surfaces and a particle size of 1.5 to 7 nm. When this range is satisfied, if the metal is ruthenium, the B5 site, which is the active site for ammonia decomposition activity, can be present at a maximum concentration.

[0044] In one embodiment of the present specification, the content of metal nanoparticles may be 2.0 to 2.5 parts by weight per 100 parts by weight of the metal composite catalyst. The content of such supported metal nanoparticles can be measured by inductively coupled plasma (ICP) analysis. If the content is below or above the above range, it may be difficult to achieve the desired level of catalytic performance, and an excessive amount of expensive noble metal catalyst may be used, which is uneconomical. According to the inventors' research, it is important to satisfy the above range, considering the problem that using metal nanoparticles in an amount exceeding 3 parts by weight has conventionally made it difficult to ensure dispersion and was uneconomical.

[0045] In one embodiment of the present specification, the metal dispersion of the metal nanoparticles in the metal composite catalyst can be measured by CO2-chemisorption analysis and may be 23% or more, 26% or more, or 30% or more, or 70% or less, 65% or less, 60% or less, 55% or less, or 50% or less. If the metal dispersion exceeds this range, the process for uniform dispersion may be unnecessarily long, which may be inefficient from the viewpoint of energy, etc. If the metal dispersion is below this range, the ammonia decomposition activity of the metal composite catalyst may not be ensured at a required level due to insufficient uniform dispersion.

[0046] In one embodiment of the present specification, the metal composite catalyst may be self-reducing. Here, the term "self-reducing" means that the metal composite catalyst has ammonia decomposition activity without undergoing a reduction reaction in a hydrogen and / or nitrogen environment prior to the ammonia decomposition reaction, whereas catalysts prepared by conventional techniques require such a reduction reaction. In the case of a metal composite catalyst prepared by a method for preparing a metal composite catalyst according to one embodiment of the present specification, which will be described later, the particle shape and particle size are controlled during the polyol process, and a reduction reaction partially occurs during the synthesis process using the polyol, so that the metal composite catalyst can have ammonia decomposition activity without undergoing a reduction reaction in a subsequent process.

[0047] A metal composite catalyst according to an embodiment of the present specification may have high ammonia decomposition activity at lower temperatures. Specifically, the metal composite catalyst may have a temperature of 460°C or lower, preferably 350 to 460°C, at which an ammonia conversion rate of 50% is achieved. In an embodiment of the present specification, the metal composite catalyst may have a temperature of 520°C or lower, preferably 400 to 520°C, at which an ammonia conversion rate of 90% is achieved. In an embodiment of the present specification, the metal composite catalyst may have a temperature of 600°C or lower, preferably 490 to 600°C, at which an ammonia conversion rate of 100% is achieved. As demonstrated in the examples described below, these characteristics enable 100% ammonia conversion to be achieved at temperatures up to 60°C lower than those of metal composite catalysts containing ruthenium metal nanoparticles produced by conventional impregnation or vapor deposition precipitation methods.

[0048] In a second aspect of the present application, Provided is a method for producing a metal composite catalyst for an ammonia decomposition reaction, comprising the steps of preparing an active metal precursor solution, mixing the active metal precursor solution with a polyol to obtain a mixture, heating the mixture to synthesize metal nanoparticles, and adding a metal-containing support to the heated mixture to form a composite.

[0049] Detailed explanations of parts that overlap with the first aspect of this specification will be omitted, but the contents explained for the first aspect of this specification can be applied in the same way to the second aspect even if the explanations are omitted.

[0050] Hereinafter, the method for producing the metal composite catalyst for ammonia decomposition reaction according to the second embodiment of the present specification will be described with reference to the flow chart of FIG.

[0051] First, in one implementation example of the present specification, a step (S100) of preparing an active metal precursor solution may be included.

[0052] In one embodiment of the present disclosure, the active metal precursor is selected from the group consisting of Ru(NO)(NO)3 (Ruthenium(III) nitrosyl nitrate), Ru(C5H7O2)3 (Ruthenium(III) acetylacetonate), C6H9O6Ru (Ruthenium(III) acetate), C 10 H 10 Ru(ruthenocen), C7H9RuC7H9 (bis(ethylcyclopentadienyl)ruthenium(II)), C 10 H 10 Ru (bis(cyclopentadienyl)ruthenium(II)), Ru(CH 11 )2(Bis(2,4-dimethylpentadienyl)ruthenium(II); Bis(2,4-dimethylpentadienyl)ruthenium(II)), C 14 H 10 The compound may be characterized as being at least one selected from the group consisting of O4Ru2 (bis(cyclopentadienylruthenium dicarbonyl) dimer), and mixtures thereof.

[0053] Next, in one embodiment of the present specification, the method may include a step (S200) of mixing the active metal precursor solution with a polyol to obtain a mixture. The polyol is a substance having at least two OH groups in its molecule. The polyol not only acts as a solvent and stabilizer during the synthesis process, but also prevents particle growth and agglomeration. In addition, the polyol solvent creates a reducing atmosphere at its boiling point, thereby playing an important role in maintaining the oxidation state of the transition metal.

[0054] In one embodiment of the present specification, the polyol may be at least one selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol, and may be preferably propylene glycol or butylene glycol. The polyol may be characterized by including two hydroxy groups (-OH), and preferably the two hydroxy groups are substituted on adjacent carbons.

[0055] Next, in one implementation example of the present specification, a step (S300) of heating the mixture to synthesize metal nanoparticles may be included.

[0056] In one embodiment of the present specification, the step of heating the mixture to synthesize metal nanoparticles may be performed at a temperature of 195°C or less. Although the nucleation rate may vary depending on the mixing temperature, which may affect the particle size, there is no significant limit to the temperature. However, the boiling point at which the nucleation rate is fastest is preferred, and most preferably 185 to 195°C.

[0057] In one embodiment of the present specification, the step of heating the mixture to synthesize metal nanoparticles may be characterized by stirring at a speed of 150 to 500 rpm. While there are no significant limitations on the shape of the impeller, controlling the mixing speed can control particle size and shape. If the mixing speed is less than 150 rpm, it is difficult to achieve appropriate catalytic activity due to particle agglomeration. If the mixing speed is more than 500 rpm, it may be difficult to achieve the desired morphology of the active metal due to the high nucleation and vaporization rates, making it difficult to condense the gas. Preferably, the stirring speed may be 200 to 300 rpm.

[0058] In one embodiment of the present specification, the stirring method in the mixing process is not limited, but the mixing method used in this patent is a method using a magnetic bar, and there is no significant limitation on the shape of the impeller, but various mixers such as a propeller type may be used.

[0059] Next, in one embodiment of the present specification, a step (S400) may be provided in which a metal-containing support is added to the heated mixture to form a composite.

[0060] In one embodiment of the present specification, the compounding may be carried out by stirring at a high temperature for a predetermined period of time, preferably at a temperature of 60 to 150°C, and for 3 to 24 hours.

[0061] Next, in one embodiment of the present specification, a step of washing the composite metal composite catalyst may be provided, and the washing may be performed using an organic solvent or deionized water, preferably alcohol, more preferably ethanol.

[0062] Next, in one embodiment of the present specification, a step of drying the metal composite catalyst may be provided. The drying temperature is preferably 60 to 100°C. If the temperature exceeds this range, rapid evaporation of water will affect the pore size and volume of the metal composite catalyst. Furthermore, the drying is preferably performed for 3 to 6 hours.

[0063] Next, in one embodiment of the present specification, a step of calcining the metal composite catalyst may be provided. The calcination temperature is preferably 400 to 700°C. If the temperature is below this range, there is a risk that the catalytic activity will be reduced due to a portion of the polyol remaining in the active metal, and if the temperature is above this range, there is a risk that it will be difficult to maintain appropriate ammonia decomposition activity due to aggregation of the active metal.

[0064] The calcination is preferably carried out for 1 to 3 hours. If the time exceeds this range, it may become difficult to maintain appropriate ammonia decomposition activity due to aggregation of the active metal, or it may become inefficient from the viewpoint of energy consumption. If the time is shorter than this range, the calcination step itself becomes meaningless.

[0065] The manufacturing method according to one embodiment of the present specification is a polyol process that can control the particle size of metal nanoparticles to preferably 5 nm or less, and can improve the ammonia decomposition reaction activity and low-temperature activity during catalyst production.

[0066] The present invention will now be described in detail with reference to exemplary embodiments so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in various different forms and should not be construed as being limited to the exemplary embodiments described below.

[0067] [Example 1] Production of metal composite catalysts A 1 mM solution of Ru precursor (Ruthenium nitrosyl nitrate) was mixed with 300 mL of ethylene glycol and then stirred at 195°C. The MgAl2O4 support was added to the mixed solution and stirred at 100°C for 12 hours. After that, it was washed with ethanol, dried, and calcined at 400°C to produce a metal composite catalyst.

[0068] [Example 2] Production of metal composite catalysts A 2 mM Ru precursor (Ruthenium nitrosyl nitrate) solution was mixed with 300 mL of propylene glycol and then stirred at 185°C. The MgAl2O4 support was added to the mixed solution and stirred at 100°C for 12 hours. The mixture was then washed with ethanol, dried, and calcined at 400°C to produce a metal composite catalyst.

[0069] [Example 3] Production of metal composite catalysts A 3 mM solution of Ru precursor (Ruthenium nitrosyl nitrate) was mixed with 200 mL of butylene glycol and then stirred at 190°C. The MgAl2O4 support was added to the mixed solution and stirred at 100°C for 12 hours. The mixture was then washed with ethanol, dried, and calcined at 400°C to produce a metal composite catalyst.

[0070] [Comparative Example 1] Preparation of metal composite catalysts by impregnation. The MgAl2O4 support was prepared by impregnation, a well-known method in the prior art, with a Ru precursor (Ruthenium nitrosyl nitrate) solution added, and then calcined at 400°C.

[0071] Comparative Example 2 Preparation of metal composite catalysts by deposition-precipitation A Ru precursor (Ruthenium nitrosyl nitrate) solution was added to the MgAl2O4 support, and the catalyst was prepared by deposition-precipitation, a method well known in the prior art, and then calcined at 400°C.

[0072] [Experimental Example 1] Transmission electron microscope (TEM) analysis of metal composite catalysts FIG. 2 shows images of a metal composite catalyst according to an example of the present invention and a metal composite catalyst according to a comparative example analyzed by a transmission electron microscope (TEM).

[0073] 2, in the case of the metal composite catalyst of Example 3 according to one embodiment of the present specification, hemispherical particles having a particle size of about 1 to 2.5 nm are highly dispersed to a uniform size, and it is also observed that the metal particles are dispersed very uniformly.

[0074] On the other hand, in Comparative Example 1 using the impregnation method and Comparative Example 2 using the vapor deposition precipitation method, relatively coarse particle sizes exceeding 5 nm or up to 9 to 10 nm were observed, and the dispersion of the metal particles was also observed to be less uniform than in Example 3.

[0075] [Experimental Example 2] Inductively Coupled Plasma (ICP) and BET Analysis The catalyst particle characteristics such as the ruthenium metal content, particle size, and metal dispersion of the metal composite catalysts of the examples and comparative examples were observed by inductively coupled plasma analysis in Table 1. Specifically, the particle size and dispersion of the Ru catalyst dispersed on the catalyst surface after reduction at 600°C were confirmed by measurement using a chemical adsorption method.

[0076] [Table 1]

[0077] Referring to Table 1, it was confirmed that the metal composite catalysts produced by the polyol process of Examples 1 to 3 could control the Ru catalyst particle size to 5 nm or less, improving Ru metal dispersion. On the other hand, the metal composite catalysts produced by the impregnation method had problems such as too coarse particle size and insufficient metal dispersion, and Comparative Example 2 produced by the vapor deposition precipitation method provided insufficient data compared to the metal composite catalysts of the Examples in terms of characteristics such as ruthenium content and pore volume. The differences in the results shown in the above experimental data may indicate differences in effects such as ammonia decomposition efficiency, as described below.

[0078] [Experimental Example 3] Ammonia decomposition reaction activity experiment The Ru catalyst prepared for the ammonia decomposition activity experiment was pelletized to 60-100 mesh. The catalyst was then mixed with a diluent and packed into the center of a quartz reactor. A thermocouple (TCD) was inserted into the center of the packed catalyst to measure the temperature at the center of the catalyst. The catalyst reduction was carried out at 650°C in a 20% H2 / N2 atmosphere, and the reaction experiment was carried out at a high space velocity (GHSV) of 30,000 mL / g. cat The reaction was carried out at 350-650°C for 1 min.

[0079] FIG. 3 shows data comparing the ammonia decomposition activity of the metal composite catalysts of Examples 1 to 3 and Comparative Examples 1 and 2 of the present specification.

[0080] 3, it can be seen that the metal composite catalysts prepared by the polyol process in Examples 1 to 3 have higher ammonia decomposition activity than the catalyst samples in Comparative Examples 1 and 2. In particular, it was confirmed that the catalyst in Example 3 exhibited the highest ammonia decomposition activity and had excellent low-temperature reaction activity.

[0081] Figure 4 and the following Table 2 show the results of comparing the ammonia decomposition reaction temperatures for the catalyst production methods. Specifically, for each example and comparative example, the temperatures at which the NH3 conversion rates reached 50, 90, and 100% were measured. Hereinafter, X represents the ammonia conversion rate (%).

[0082] [Table 2]

[0083] 4 and Table 2, it was confirmed that the metal composite catalysts of Examples 1 to 3 prepared by the polyol method were able to achieve high conversion rates at low temperatures, with overall improved low-temperature activity compared to the catalysts of Comparative Examples 1 and 2. In particular, it was found that Example 3 had the best low-temperature activity required for ammonia decomposition. The catalyst of Example 3 was able to achieve 100% ammonia conversion at a temperature approximately 60°C lower than the catalyst of Comparative Example 2.

[0084] [Experimental Example 4] Self-reduction experiments of metal composite catalysts In order to confirm the self-reduction type, which is the greatest technical feature of the metal composite catalyst of this specification, Figure 5 shows the results of a comparative test of ammonia decomposition activity with and without a catalytic reduction process for the catalyst of Example 3.

[0085] 5, while catalysts prepared by impregnation or vapor deposition precipitation methods require H2 reduction prior to the ammonia decomposition reaction, the catalyst prepared by the polyol method in Example 3 exhibits the same reaction activity regardless of whether or not it was subjected to reduction prior to the reaction, confirming that it is a self-reducing catalyst. Furthermore, this reaction activity indicates that the physical properties of the composite catalyst, such as the metal dispersion described above, are maintained regardless of whether or not it was subjected to reduction.

[0086] The above description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention may be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. Therefore, the above-described embodiments are merely illustrative and not limiting. For example, components described as being single may be implemented in a distributed form, and similarly, components described as being distributed may be implemented in a combined form.

[0087] The scope of the present invention is defined by the claims, and all modifications and variations that fall within the meaning and scope of the claims, as well as equivalent concepts, are intended to be encompassed in the present invention. [Industrial Applicability]

[0088] According to an embodiment of the present invention, A self-reducing metal composite catalyst is produced through a polyol reduction process, which prevents sintering, which occurs when particles aggregate together at temperatures above 500 degrees, as occurs in conventional technology, and causes the particles to become larger.

[0089] Furthermore, according to one embodiment of the present invention, a metal composite catalyst containing metal nanoparticles with controlled size and shape can be prepared by utilizing the properties of polyol itself without adding stabilizers such as PVP or PVA in the polyol process, and therefore, it is considered to have industrial applicability.

Claims

1. a metal-containing support; and metal nanoparticles dispersed on the surface or inside the pores of the metal-containing support, The particle size of the metal nanoparticles is 1.5 to 7 nm. A metal composite catalyst for an ammonia decomposition reaction, characterized in that

2. The content of the metal nanoparticles is 2.0 to 2.5 parts by weight relative to 100 parts by weight of the metal composite catalyst; The metal dispersion of the metal nanoparticles in the metal composite catalyst is 23 to 50%. The metal composite catalyst for ammonia decomposition reaction according to claim 1.

3. The BET surface area of ​​the metal composite catalyst is 119.5 to 150 m ２ / g The metal composite catalyst for ammonia decomposition reaction according to claim 1.

4. The total pore volume of the metal composite catalyst is more than 0.56 to 0.75 cm ３ / g or less The metal composite catalyst for ammonia decomposition reaction according to claim 1.

5. The metal nanoparticles are at least one nanoparticle selected from the group consisting of ruthenium (Ru), rhodium (Rh), platinum (Pt), and gold (Au). The metal composite catalyst for ammonia decomposition reaction according to claim 1.

6. The metal-containing support is an oxide of at least one transition metal selected from the group consisting of magnesium, aluminum, iron, manganese, nickel, cobalt, titanium, and zinc. The metal composite catalyst for ammonia decomposition reaction according to claim 1.

7. The metal nanoparticles are hemispherical particles having a particle size of 2 to 5 nm, or It consists of particles with a diameter of 1.5 to 7 nm and a shape including flat surfaces. The metal composite catalyst for ammonia decomposition reaction according to claim 1.

8. The metal composite catalyst is a self-reducing catalyst. The metal composite catalyst for ammonia decomposition reaction according to claim 1.

9. A method for producing a metal composite catalyst for an ammonia decomposition reaction, comprising: providing an active metal precursor solution; mixing the active metal precursor solution with a polyol to obtain a mixture; heating the mixture to synthesize metal nanoparticles; and adding a metal-containing carrier to the heated mixture to form a composite.

1. A method for producing a metal composite catalyst for an ammonia decomposition reaction, comprising:

10. The polyol is at least one selected from the group consisting of ethylene glycol, propylene glycol, and butylene glycol. A method for producing the metal composite catalyst for ammonia decomposition reaction according to claim 9.

11. the polyol contains two hydroxy groups (—OH); The two hydroxy groups are substituted on adjacent carbon atoms. A method for producing the metal composite catalyst for ammonia decomposition reaction according to claim 9.

12. The active metal precursor is Ru(NO)(NO) ３ (Ruthenium (III) nitrosyl nitrate; Ruthenium (III) nitrosyl nitrate), Ru(C ５ H ７ O ２ ) ３ (Ruthenium acetylacetonate; Ruthenium (III) acetylacetonate), C ６ H ９ O ６ Ru (Ruthenium (III) acetate), C １０ H １０ Ru (Ruthenocen), C ７ H ９ RuC ７ H ９ (Bis(ethylcyclopentadienyl)ruthenium(II); Bis(ethylcyclopentadienyl)ruthenium(II)), C １０ H １０ Ru (bis(cyclopentadienyl)ruthenium(II)), Ru(C ７ H １１ ) ２ (Bis(2,4-dimethylpentadienyl)ruthenium(II); Bis(2,4-dimethylpentadienyl)ruthenium(II)), C １４ H １０ O ４ Ru ２ (bis(cyclopentadienylruthenium dicarbonyl) dimer; Bis(cyclopentadienylruthenium dicarbonyl) dimer), and at least one selected from the group consisting of mixtures thereof A method for producing the metal composite catalyst for ammonia decomposition reaction according to claim 9.

13. and heating the mixture to synthesize metal nanoparticles, said step being carried out at a temperature of 195° C. or less. A method for producing the metal composite catalyst for ammonia decomposition reaction according to claim 9.

14. heating the mixture to synthesize metal nanoparticles; Stir at a speed of 150-500 rpm A method for producing the metal composite catalyst for ammonia decomposition reaction according to claim 9.

15. adding a metal-containing support to the heated mixture to composite it; and Washing the composite metal catalyst; drying the metal composite catalyst; and calcining the metal composite catalyst. A method for producing the metal composite catalyst for ammonia decomposition reaction according to claim 9.

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