Platinum-supported catalyst with improved hydrogenation / dehydrogenation reversibility and liquid organic hydrogen carrier-based hydrogen storage and release method using the same

Abstract

This disclosure describes a hydrogenation / dehydrogenation catalyst based on a solid-phase method, in which platinum (Pt) metal in a mixed form of single atoms and clusters is supported on an alumina support as the active metal, and a technology that uses this catalyst to reversibly store and release hydrogen with high selectivity and high efficiency.

Description

[Technical Field]

[0001] The present disclosure relates to a platinum-supported catalyst with improved hydrogenation / dehydrogenation reversibility and a liquid organic hydrogen carrier-based hydrogen storage and release method using the same. More specifically, the present disclosure relates to a solid-phase-based hydrogenation / dehydrogenation catalyst in which platinum (Pt) metal, in the form of a mixture of single atoms and clusters, is supported on an alumina support as the active metal, and a technology for reversibly storing and releasing hydrogen with high selectivity and high efficiency using the same. [Background technology]

[0002] As environmental pollution issues, such as dwindling reserves of fossil fuels, pollutants generated during combustion, and global warming caused by carbon dioxide, become more serious, there has been an explosive increase in global interest and demand for the development of alternative energy sources.

[0003] New and renewable energy sources such as wind power, tidal power, geothermal power, hydrogen energy, and solar energy have been gaining attention as alternative energy sources, but each of these energy sources has its advantages and disadvantages. In this regard, since new and renewable energy sources are difficult to supply and demand due to the instability of energy sources depending on time and the natural environment, in order to effectively replace conventional fossil fuels, it is necessary to develop technology to store and supply surplus energy so as to ensure a stable energy supply.

[0004] From this perspective, hydrogen energy is attracting particular attention because (i) it has the highest energy efficiency per unit mass, (ii) it produces only water upon combustion with no other harmful by-products, (iii) water, the main source of hydrogen, is abundant in nature and is converted into water after use, making it easy to reuse, and (iv) it is a distributed power source that uses hydrogen as fuel and is suitable for ensuring the competitiveness of the precision and IT industries. Furthermore, hydrogen can be produced using other new and renewable energy sources such as solar energy and wind power, and can be widely applied not only to various energy sources but also to other industrial sectors (e.g., various petrochemical sectors), making it emerging as a key energy source of the future both in Korea and abroad.

[0005] Generally, research and development into hydrogen energy is broadly divided into the fields of hydrogen production, transportation, and storage. However, while hydrogen has excellent energy storage capacity per mass, it has low energy storage capacity per volume, making the technology to efficiently store hydrogen the biggest obstacle to the practical application of hydrogen energy. For example, while there are known materials with a mass storage density of 10% or more by weight at 77K, the volume storage density of these materials is 40g / L, which is too low for practical use as a hydrogen storage material. Therefore, active research is being conducted into technologies to store as much hydrogen as possible in a storage medium that is as light and small in volume as possible.

[0006] In this regard, countries have been investing a lot of money in research and development for several years, and the efficient hydrogen storage methods that have been researched and developed so far include the CGH2 method, which compresses hydrogen using a pressure of 700 bar, and the LH2 method, which stores liquid hydrogen by liquefying it at -253°C. However, these pressurization or liquefaction methods require maintaining low temperatures, and the density of liquid hydrogen is 71.2 kg / m 3 This is a low level.

[0007] As an alternative, materials with hydrogen storage capabilities, such as inorganic-organic frameworks (MOFs), porous organic or inorganic nanomaterials such as carbon nanotubes, zeolites, and activated carbon, and metal hydrides, have been attracting attention as materials for effectively storing hydrogen energy (Nature, 427, 523 (2004); J. Am. Chem. Soc., 127, 14904 (2005); JP 2008-95172 A; JP 2011-131120 A, etc.). However, in the case of room-temperature gas-phase hydrogen storage technology that relies on physical absorption by MOFs and porous nanomaterials, the energy storage density is relatively low and the energy required for storing and desorbing hydrogen is relatively large, making miniaturization and modularization difficult.

[0008] Recently, hydrogen storage technology based on reversible catalytic hydrogenation / dehydrogenation reactions using organic materials, specifically liquid organic hydrogen carriers (LOHCs), has been developed (see, e.g., U.S. Patent No. 7,901,491). LOHC technology has the advantages of being able to store more than 5% hydrogen by weight, as recommended by the U.S. Department of Energy (DOE), being able to operate at low pressures, and being able to easily regenerate storage materials. Furthermore, by leveraging the advantages of liquid fossil fuels, such as ease of handling and high energy density, it can provide a practical hydrogen storage system that can be efficiently transported and stored using existing liquid fuel transportation and storage infrastructure (Energy Rev., 6 (2002) 141; Energy Environ. Sci., 8 (2015) 1035-1045).

[0009] While techniques using π-conjugated substrate compounds as LOHC materials are known (e.g., U.S. Patent No. 7,351,395), it is difficult to ensure uniform reactivity due to π-conjugation, and most exist as solid phases, so they are used in the form of mixtures. To alleviate the above-mentioned difficulties, techniques using benzyltoluene and dibenzyltoluene as hydrogen storage materials are also known (e.g., Korean Patent Publication No. 2015-97558). These hydrogen carriers exist in a liquid phase at room temperature and have boiling points above 280°C, meaning there are few limitations in terms of their application. However, limitations in the hydrocarbon structure limit the efficiency of hydrogenation and dehydrogenation reactions.

[0010] Meanwhile, in order to commercialize hydrogen storage / release systems using LOHCs, various technological factors must be considered in addition to the development of hydrogen storage materials. Among these, the catalyst must be examined for its activity and reversibility in hydrogenation / dehydrogenation reactions, catalyst stability (reusability), and applicability of LOHCs to commercial processes.

[0011] In this regard, a LOHC-based hydrogen storage and release process using a platinum-supported catalyst, known for its excellent hydrogenation activity, can be considered. Platinum-supported catalysts generally easily dissociate hydrogen into hydrogen atoms, making them effective in reactions in which hydrogen gas is brought into contact with a reactant, such as hydrogenolysis or hydrogenation. In LOHC systems, such catalysts can also be effective in dehydrogenation reactions, acting as active sites for releasing hydrogen through cyclic compounds.

[0012] However, even when platinum-supported porous alumina catalysts are used in the hydrogenation / dehydrogenation reactions of LOHCs, the active metals are not highly dispersed, which can still result in insufficient dehydrogenation (hydrogen release) activity. Furthermore, platinum-supported alumina catalysts are typically manufactured by impregnation, which requires multiple steps to synthesize the alumina support and support the metal, resulting in a long catalyst manufacturing process and a disadvantage in terms of commercialization. While the inherent properties of alumina can ensure a certain degree of catalyst stability, there are limitations to achieving additional performance improvements.

[0013] In addition, while existing hydrogenation / dehydrogenation catalysts have shown relatively good hydrogen storage / release performance, mainly for LOHC systems with nitrogen-containing heterocycles, commercial companies are currently in high demand for technology that can provide good hydrogen storage / release performance even for LOHCs consisting only of hydrocarbons, such as decalin.

[0014] Therefore, there is a need for a catalyst that not only has better hydrogenation / dehydrogenation reaction activity and reversibility than conventionally known metal-supported catalysts, especially platinum-supported catalysts, but also provides good performance for various types of LOHC. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-095172 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-131120 [Patent Document 3] U.S. Patent No. 7,901,491 [Patent Document 4] U.S. Patent No. 7,351,395 [Patent Document 5] Korean Patent Publication No. 2015-97558 [Non-patent literature]

[0016] [Non-Patent Document 1] Nature, 427, 523 (2004) [Non-patent document 2] J.Am.Chem.Soc.,127,14904(2005) [Non-patent document 3] Energy Rev.,6(2002)141 [Non-patent document 4] Energy Environ.Sci.,8(2015)1035-1045 Summary of the Invention [Problem to be solved by the invention]

[0017] In one embodiment of the present disclosure, a catalyst having improved properties in terms of hydrogenation / dehydrogenation reaction efficiency and reversibility for a liquid organic hydrogen carrier, long-term stability, and scalability for a liquid organic hydrogen carrier, and a method for producing the same are provided.

[0018] According to another embodiment of the present disclosure, there is provided a liquid organic hydrogen carrier-based hydrogen storage / release process using the above-described catalyst. [Means for solving the problem]

[0019] According to the first aspect of the present disclosure, A catalyst for hydrogenation / dehydrogenation of a liquid organic hydrogen carrier, comprising: an alumina support; and Platinum, including monatomic and cluster forms, as the active metal supported on said alumina-containing support; Including, The platinum content (elemental basis) in the catalyst is 0.01% to 10% by weight. The catalyst is provided in which the content of platinum in cluster form in the supported platinum ranges from 10% to 55%.

[0020] According to a second aspect of the disclosure: A method for producing a hydrogenation / dehydrogenation catalyst for a liquid organic hydrogen carrier, comprising: a) carrying out a solid-state reaction in the absence of a solvent while applying external energy to a mixture containing at least one alumina precursor, at least one platinum precursor, and a base component to form a catalyst solid in the form of a gel; and b) heat-treating the catalytic solid in an oxygen-containing atmosphere to support platinum, including platinum in the form of monoatoms and clusters, on an alumina-containing support; Including, The platinum content (elemental basis) in the catalyst is in the range of 0.01% to 10% by weight. A method is provided in which the content of platinum in cluster form in the supported platinum ranges from 10% to 55%.

[0021] According to the third aspect of this disclosure: a hydrogenation step in which hydrogen is stored in a liquid organic hydrogen carrier in the presence of a catalyst; and a dehydrogenation step of releasing hydrogen from the hydrogenated liquid organic hydrogen carrier in the presence of a catalyst; The catalyst used in at least one of the hydrogenation step and the dehydrogenation step is an alumina support; and Platinum, including monatomic and cluster forms, as the active metal supported on said alumina-containing support; Including, The platinum content (element basis) in the catalyst is 0.01 wt% to 10 wt%, and the content of platinum in cluster form in the supported platinum is in the range of 10% to 55%. The hydrogenation and dehydrogenation steps are alternately performed to provide a method for storing and releasing hydrogen. [Effects of the Invention]

[0022] According to an embodiment of the present disclosure, platinum, including platinum in monoatomic and cluster forms, is supported as the active metal on an alumina support within the catalyst. This allows for excellent hydrogenation (hydrogen storage) / dehydrogenation (hydrogen release) activity for all liquid organic hydrogen carriers, including nitrogen-containing liquid organic hydrogen carriers, as well as hydrocarbon-based liquid organic hydrogen carriers. This catalyst offers the advantage of improved hydrogenation / dehydrogenation reversibility. Furthermore, in another embodiment of the present disclosure, a single-step reaction can be carried out without the use of a solvent by simply applying physical or mechanical external energy, such as milling, to a raw material mixture containing a platinum precursor and an alumina precursor. In particular, the unique properties of the platinum-supported alumina catalyst described above can be achieved by controlling the heat treatment or calcination conditions to affect the platinum morphology. The catalyst thus prepared not only overcomes the technical limitations of two-step catalyst preparation methods, such as the relatively high catalyst preparation cost and time-consuming impregnation method, but also offers multiple advantages, such as maintaining improved activity over a long period of time during the hydrogenation / dehydrogenation reaction of liquid organic hydrogen carriers. [Brief explanation of the drawings]

[0023] [Figure 1] 1 shows XRD patterns of a platinum-supported catalyst (MPtA) according to an example (solid phase method) and a platinum-supported catalyst (Pt / gA) according to a comparative example (impregnation method) each having various platinum contents (1 wt%, 2 wt%, 3 wt%, and 5 wt%) supported thereon. [Figure 2] 1 a and 1 b are dark-field HAADF-STEM images of a platinum-supported catalyst (MPtA) according to an example (solid phase method) and a platinum-supported catalyst (Pt / gA) according to a comparative example (impregnation method) with various platinum contents (1 wt%, 2 wt%, 3 wt%, and 5 wt%), respectively. [Figure 3]1 shows CO-DRIFT spectrum graphs of platinum-supported catalysts (MPtA) according to Examples (solid phase method; Pt loading: 1 wt%, 2 wt%, 3 wt%, and 5 wt%) and platinum-supported catalysts (Pt / gA) according to Comparative Examples (impregnation method; Pt loading: 1 wt%, 3 wt%, and 5 wt%), each carrying various platinum contents. [Figure 4] 1 is a graph showing the H2-TPD results for a platinum-supported catalyst (MPtA) according to an example (solid phase method) and a platinum-supported catalyst (Pt / gA) according to a comparative example (impregnation method) carrying various platinum contents (1 wt%, 2 wt%, 3 wt%, and 5 wt%) (the numerical values ​​in the figure are the amount of hydrogen adsorption (unit: mmol gPt-1)). [Figure 5] Graphs a and b show the EXAFS fitting results for a platinum-supported catalyst (MPtA) according to an example (solid phase method) and a platinum-supported catalyst (Pt / gA) according to a comparative example (impregnation method) with various platinum contents (1 wt%, 3 wt%, and 5 wt%), respectively (reference materials are Pt foil and PtO2). [Figure 6] Graphs a and b show a comparison of the hydrogenation and dehydrogenation reaction efficiencies using a platinum-supported catalyst (MPtA) according to an embodiment (solid phase method) and a platinum-supported catalyst (Pt / gA) according to a comparative example (impregnation method), each carrying various platinum contents (1 wt%, 2 wt%, 3 wt%, and 5 wt%). [Figure 7] 1 is a graph showing XRD patterns (a, b) and H2-TPD results (c, d) for Pt-supported catalysts (loading amounts: 1 wt % and 3 wt %) under different calcination conditions. [Figure 8] 1 shows HAADF-STEM photographs of Pt-supported catalysts under different calcination conditions (a and b show a loading of 3 wt %, and c and d show a loading of 1 wt %). [Figure 9] Figure 1 shows the hydrogen release curves over time for the dehydrogenation reaction of Pt-supported catalysts under different calcination conditions (a: 3 wt.% loading, b: 1 wt.% loading). (Reaction conditions: 250°C, 1 bar, 4 h, noble metal (mol) / reactant (mol) 0.1%). [Figure 10] FIG. 1 is a graph showing the results of a dehydrogenation reaction to evaluate the long-term stability of a platinum-supported catalyst (M3PtA) according to an example (solid phase method) and a platinum-supported catalyst (3Pt / gA) according to a comparative example (impregnation method) (reaction conditions: 250°C, 1 bar, 4 hours, precious metal (mol) / reactant (mol) 0.1%). [Figure 11] 1 shows XRD patterns (a, b) of a platinum-supported catalyst (M3PtA) according to an example (solid phase method) and a platinum-supported catalyst (3Pt / gA) according to a comparative example (impregnation method) before and after reaction, and HAADF-STEM photographs (c, d) of the catalysts after use. [Figure 12] Graphs a and b show the results of comparing the hydrogen storage and release efficiencies of H0-BT using a platinum-supported catalyst (M3PtA) according to an embodiment (solid phase method) and a platinum-supported catalyst (3Pt / gA) according to a comparative example (impregnation method) (hydrogenation reaction conditions: 150°C, 35 bar H2, 2 h; dehydrogenation reaction conditions: 250°C, 4 h). DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention can be achieved by the following description. The following description should be understood as describing a preferred embodiment of the present invention, and the present invention is not necessarily limited thereto. Furthermore, it should be understood that the attached drawings are for facilitating understanding, and the present invention is not limited thereto.

[0025] Terms used herein may be defined as follows:

[0026] A "heterogeneous catalyst" can refer to a catalyst that exists in a different phase from the reactants during a catalytic reaction, for example, a catalyst that is not dissolved in the reaction medium. In the case of a heterogeneous catalyst, for a reaction to occur, at least one reactant must diffuse onto and adsorb onto the surface of the heterogeneous catalyst, and after the reaction, the product must desorb from the surface of the heterogeneous catalyst.

[0027] "Support" may refer to a material (typically a solid phase material) having a high specific surface area to which catalytically active components are attached.

[0028] "Active metal in single atom form" may be understood as the active metal attached or fixed to the support being present in an isolated or individualized state in atomic form.

[0029] "Active metals in cluster form" 、2 nm less than The active metal (i.e., a collection of at least two active metal atoms) having a size of 1000 nm can be understood as being attached or fixed to the support.

[0030] "Hydrogenation" may refer to a reaction in which the hydrogen content in a compound is increased by contacting the compound with a catalyst in the presence of a supply of hydrogen to chemically add hydrogen to at least a portion of the compound.

[0031] "Dehydrogenation" may refer to a reaction in which hydrogen is removed from a compound and then the removed hydrogen is released from the compound.

[0032] The term "impregnation" refers to a method of preparing a catalyst by impregnating a separately synthesized support with a solution containing a catalyst precursor, followed by drying and / or calcination (or reduction) as necessary.

[0033] "Salt" may refer generically to a compound in which a metal cation is combined with an inorganic anion or an organic anionic species.

[0034] [Overall disclosure content] A specific example of the present disclosure can overcome technical limitations of platinum-supported alumina catalysts, which are known as conventional catalysts for hydrogenation / dehydrogenation reactions, when applied to hydrogen storage and release (i.e., hydrogenation and dehydrogenation) processes using liquid organic hydrogen carriers. These limitations include difficulty in ensuring good reversibility of the hydrogenation / dehydrogenation reaction, difficulty in repeatedly operating hydrogen storage and release systems due to reduced long-term catalyst stability, and limited applicability to hydrogen storage and release using limited types of liquid organic hydrogen carriers.

[0035] In general, the size of the active metal in a catalyst (especially nanometer-level metal particles) plays a significant role in determining reaction activity. That is, when the same amount of active metal is supported on a support with the same surface area, minimizing the size of the metal increases the number of metal active sites supported on the same support. Therefore, increasing the dispersion of the active metal and the ratio of coordinated surface atoms can enhance catalytic activity per metal atom.

[0036] In this regard, single atom catalysts (SACs), which are bound to a support in atomic units (single atom form), are effective in increasing the active sites of the catalyst, but their high surface energy can lead to aggregation at high temperatures, resulting in an increase in particle size. On the other hand, catalysts supported in cluster form have excellent catalytic stability because multiple metal atoms and ligands are bound to each other, forming an organized structure similar to other metal oxides. Compared to catalysts synthesized by conventional impregnation methods, the platinum-supported catalyst of this embodiment can enhance activity by uniformly dispersing the metal over a larger surface area. In particular, the catalyst supports platinum in a combined (mixed) form of single atoms and clusters, thereby simultaneously embodying the advantages of both single atoms and clusters and providing effects beyond those expected from either the single atom form or the cluster form. In particular, when prepared by the impregnation method, the catalyst is supported in the form of particles that are larger than clusters, which is an element that clearly differentiates the catalyst according to this embodiment from platinum-supported catalysts according to the prior art.

[0037] Thus, in the case of the platinum-supported catalyst according to this embodiment, platinum is supported in a form including a combination of single atoms and clusters through the catalyst synthesis method, and not only does it exhibit excellent catalytic activity for both gas-phase and liquid-phase hydrogenation and dehydrogenation reactions even in a single reactor, it also exhibits good reversibility and provides improved properties in terms of long-term catalyst stability. Particularly noteworthy is that when the ratio of platinum in cluster (or single atom) form in the supported active metal (platinum) is appropriately adjusted within a predetermined range, the hydrogen release efficiency of platinum-based catalysts, which is difficult to improve compared to the hydrogen storage efficiency, can be effectively increased in hydrogen storage / release reactions using a liquid organic hydrogen carrier.

[0038] [Hydrogenation / Dehydrogenation Catalyst] According to one embodiment of the present disclosure, a catalyst (i.e., a heterogeneous catalyst) suitable for storing / releasing hydrogen through hydrogenation / dehydrogenation reactions is provided, specifically for a wide range of liquid organic hydrogen carriers, specifically not only liquid organic hydrogen carriers having a nitrogen-containing heterocycle but also all liquid organic hydrogen carriers consisting solely of hydrocarbons.

[0039] In this regard, the hydrogenation / dehydrogenation catalyst is generally a supported catalyst containing platinum as an active metal on a porous alumina-containing support. In particular, platinum may be dispersed and supported on the support in a mixed form of single atoms and clusters, or may be in the form of crystallites. In this case, the platinum crystals may mainly contain the (111) plane. Furthermore, the platinum in the catalyst may be in an oxidized state and / or a reduced state (or in an elemental state or a partially reduced state), more specifically, in a reduced state. In this case, the reduced state can be achieved by reducing the oxidized (calcined) catalyst.

[0040] In exemplary embodiments, the platinum content (loading) in the catalyst can range, for example, from about 0.01% to 10% by weight, specifically from about 0.1% to 5% by weight, and more specifically from about 0.5% to 3% by weight, on an elemental basis.

[0041] According to an exemplary embodiment, the platinum in the catalyst is 2 nm Less than, Specifically, about 0.1 nm End 2nm less than It may be in the form of a combination of single atoms and clusters having a size in the range of 1 to 100. When the size of the platinum exceeds a certain level, the reaction efficiency decreases due to a decrease in the dispersion of the metal supported on the support, so it may be advantageous to adjust it within the above range, but it may be slightly changed within the above range depending on the reaction conditions, etc.

[0042] Meanwhile, in this embodiment, the support for the hydrogenation / dehydrogenation catalyst may be an alumina-containing support. Such alumina may be mesoporous alumina, typically exhibiting ink-bottle or channel-type pore connectivity, and therefore exhibiting a relatively high surface area, high packing density, thermal stability, physical strength, and regeneration ability in the hydrogenation / dehydrogenation reaction.

[0043] According to an exemplary embodiment, the BET specific surface area of ​​the support in the catalyst is, for example, at least about 300 m 2 / g, specifically about 320m 2 / g~400m 2 / g, more specifically, approximately 350m 2 / g~380m 2 This specific surface area is significantly higher than that of γ-alumina supports used in various conventional chemical reactions, and is therefore suitable for effectively dispersing platinum, an active metal.

[0044] According to an exemplary embodiment, the pore volume of the support within the catalyst may be, for example, about 0.4 cm 3 / g~0.55cm 3 / g, specifically about 0.42 cm 3 / g~0.5cm 3 / g, more specifically, approximately 0.45 cm 3 / g~0.49cm 3 The pore size of the support in the catalyst may be, for example, in the range of about 3 nm to 4.5 nm, specifically about 3.5 nm to 4.3 nm, and more specifically about 3.8 nm to 4.1 nm.

[0045] According to an exemplary embodiment, the shape of the catalyst is not particularly limited, but considering the stability and efficiency of the catalyst, structures such as balls, tablets, granules, pellets, etc. can be applied. In this case, the size (or diameter) of the catalyst can be, for example, in the range of about 0.1 mm to 10 mm, specifically about 0.5 mm to 5 mm, and more specifically about 1 mm to 3 mm, but this can be understood as an exemplary purpose.

[0046] The platinum-supported alumina catalyst according to this embodiment can enhance the hydrogenation / dehydrogenation reaction activity for a wide range of liquid organic hydrogen carriers, and in particular, can improve the reversibility of the hydrogenation / dehydrogenation reaction. Furthermore, due to the improved interaction between the metal components constituting the catalyst, the catalyst can maintain good catalytic activity (i.e., long-term stability) even under sustained repeated operation of the hydrogenation / dehydrogenation reaction, which distinguishes it from conventional platinum-supported catalysts (typically produced by impregnation methods).

[0047] [Catalyst Production] According to another embodiment of the present disclosure, there is provided a method for producing a hydrogenation / dehydrogenation catalyst for a liquid organic hydrogen carrier, in which platinum, an active metal, is supported on an alumina support in the form of a combination of single atoms and clusters.

[0048] In this regard, when a platinum / alumina-supported catalyst is prepared by the impregnation method commonly used in the prior art, platinum exists in the form of particles on the alumina support, and therefore a relatively high platinum content is required to exhibit a desired activity. However, in the catalyst preparation method according to this embodiment, the solvent required for preparing a metal precursor solution in the impregnation method (a method in which a liquid metal precursor solution is prepared and then contacted with a porous inorganic oxide support (e.g., alumina) to fix or attach the metal precursor to the pores of the support) is not used. Furthermore, the catalyst preparation method according to this embodiment does not use a solvent, which is required for preparing a metal precursor solution in the impregnation method. Furthermore, the catalyst preparation method according to this embodiment uses a simple method in which a platinum precursor and an alumina precursor are reacted in a single step, followed by a heat treatment (e.g., a heat treatment in an oxygen-containing atmosphere). This method selectively and uniformly disperses platinum in a mixture of monoatomic and cluster forms on the alumina-containing support, thereby improving the activity and reversibility of hydrogenation / dehydrogenation reactions. Furthermore, catalysts with excellent hydrogenation / dehydrogenation activity during liquid-phase or gas-phase reactions can be prepared not only for liquid organic hydrogen carriers having nitrogen-containing heterocycles but also for liquid organic hydrogen carriers consisting solely of hydrocarbons.

[0049] Furthermore, to improve the long-term stability of a catalyst, a strong interaction between the active metal and the support is required, and it is preferable to uniformly disperse and support the active metal on the support as much as possible. As a metal oxide-based support, alumina supports are generally known to be effective in terms of catalyst stability because they strongly bond with the active metal precursor. However, γ-alumina, which is widely used as an alumina support for impregnation, does not provide the properties (especially the specific surface area) necessary to uniformly disperse the active metal in fine sizes such as monoatomic particles and clusters. Furthermore, even when platinum is supported by impregnation using alumina, which has a relatively high specific surface area, there are limitations to dramatically increasing the specific surface area of ​​the final catalyst due to the characteristics of the manufacturing method, and it is still difficult to reduce the platinum size to the monoatomic level.

[0050] According to one embodiment, a precursor mixture is first prepared that includes at least one alumina precursor, at least one platinum precursor, and a base component.

[0051] For example, the precursor mixture may be prepared by mixing three components simultaneously. Alternatively, two of the three components may be mixed first, and then the remaining components may be added. For example, the alumina precursor and the base component may be mixed first, and then the platinum precursor may be added and mixed.

[0052] According to an exemplary embodiment, the platinum precursor may be an organic or inorganic salt of platinum, a complex, or a combination thereof, such as PtF6, PtF4, [PtF5]4, PtCl3, PtCl4, Pt6Cl. 12, PtBr3, PtBr4, PtI2, PtI3, PtI4, PtO, PtO2, PtO, PtS, PtS2, Pt(CO)4, [PtCl2(NH3)2], [PtCl 2(NH3)2], K2[PtCl6], K2[Pt(CN)4], PtCl4·5H2O, K[PtCl3(NH3)], Na2[PtBr6]·6H2O, (NH4) The platinum precursor may be, but is not necessarily limited to, at least one selected from the group consisting of K[PtBr6], K2[PtI6], (NH4)2[PtCl6], K2[Pt(CN)6], (NH4)2[PtCl4], K2[Pt(NO2)4], K[PtCl3(C2H4)]·H2O, [Pt(NH3)4](NO3)2, HPtCl6, etc. According to a particular embodiment, the platinum precursor may be [Pt(NH3)4](NO3)2.

[0053] The alumina precursor may be an organic or inorganic salt of aluminum, an alkoxide, a complex, or a combination thereof, and a representative example thereof may be at least one selected from the group consisting of aluminum acetate, aluminum acetylacetonate, aluminum bromide, aluminum t-butoxide, aluminum sec-butoxide, aluminum pentoxide, aluminum ethoxide, aluminum isopropoxide, aluminum tributoxide, aluminum chloride, aluminum iodide, aluminum sulfate, aluminum nitrate, and hydrates thereof. More specifically, aluminum nitrate and / or its hydrate may be used as the alumina precursor.

[0054] According to an illustrative example, the base component may be at least one selected from the group consisting of ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium oxalate, ammonium sulfate, ammonium hydroxide, ammonium nitrate, lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide, and more specifically, ammonium bicarbonate may be used. The reason for using a base in this manner is that, when a metal oxide is formed from an acidic metal precursor, a neutralization reaction occurs in which a metal salt and water are formed as the base component is added and precipitated.

[0055] According to illustrative examples, the molar ratio of platinum precursor to base component in the precursor mixture may be, for example, in the range of about 0.0001 to 0.1, specifically about 0.002 to 0.05, and more specifically about 0.008 to 0.02. However, if the amount of base used is too small or large, the time required for gel formation, the final synthesis step, may be shortened or lengthened, making it difficult to form a metal oxide having the desired crystalline phase. Furthermore, since the amount of base used may affect catalyst properties such as specific surface area, metal dispersion, and particle size, it may be advantageous to appropriately adjust the ratio within the above-mentioned range. However, this range may vary depending on the types of precursor and base. Furthermore, the mixing ratio between the platinum precursor and alumina precursor in the precursor mixture may be determined by the respective contents of the alumina support and platinum in the above-mentioned catalyst.

[0056] According to one embodiment, the reaction can be carried out by adding external energy during the preparation of the precursor mixture or after the physical mixture is formed. Unlike the impregnation method, the reaction between the precursors in solid phase is carried out without using a solvent. In this way, by inducing a stronger interaction between the metal precursors (platinum precursor and inorganic oxide (alumina) precursor) through the solid phase method, when the calcination or heat treatment conditions are adjusted after the solid phase reaction as described below, the aggregation (or agglomeration) of platinum can be significantly reduced. In particular, platinum can be supported on the alumina support in the form of a combination of single atoms and clusters.

[0057] According to one specific example, the external energy applied to carry out the solid-state reaction between the above-mentioned three components may typically be physical or mechanical energy, for example, in the form of frictional energy such as milling, grinding, or pulverization, specifically, frictional energy by a ball mill. However, this is merely exemplary, and any external energy may be used without particular limitation as long as it can induce a reaction between the platinum precursor and the alumina precursor under solvent-free conditions.

[0058] According to an exemplary embodiment, the solid-phase reaction under application of external energy may be carried out for, for example, about 5 to 40 minutes, specifically about 10 to 30 minutes, and more specifically about 13 to 25 minutes, but this can be understood as an exemplary purpose, and the reaction time can be changed depending on the reaction scale, etc.

[0059] In this case, a solid-state reaction between the precursors may occur, resulting in the formation of a gel-like solid catalyst. Specifically, during the solid-state reaction or during mixing under the application of external energy (e.g., frictional energy), the base component is partially or completely decomposed. If the metal precursor is in the form of a metal salt, anions or anionic species bound to the metal cations may be converted to hydroxide groups. During this process, gases derived from the precursors and the base may be released. For example, when ammonium bicarbonate is used as the base, a large amount of carbon dioxide may be generated. As the reaction proceeds under this gas release, the precursors first form a gel, then undergo solidification, which increases their hardness, and then they form a gel again, resulting in the formation of a gel-like solid catalyst.

[0060] The catalyst solid formed from the solid-state reaction may then be heat-treated, i.e., calcined, in an oxygen-containing atmosphere (e.g., air), to convert the gel-form catalyst solid into an oxide. Through this heat treatment, platinum may be uniformly dispersed within the pores of the alumina support. It should be noted that adjusting the heat treatment conditions can affect the crystallinity of platinum, allowing platinum monoatoms and clusters to be supported on the alumina support in an appropriate ratio. In this regard, shortening the heat treatment time or slowing the temperature rise rate tends to increase the proportion of platinum in monoatomic form.

[0061] However, as mentioned above, if only platinum in the form of a single atom is supported, while the activity resulting from the single atom catalyst is improved, the platinum aggregates under the elevated temperature conditions accompanying the hydrogenation / dehydrogenation reaction of the liquid organic hydrogen carrier, which is undesirable in terms of long-term stability. Therefore, in this example, by adjusting the heat treatment time and / or temperature increase rate during the catalyst preparation process using a solid-state method, platinum is supported in the form of a combination of single atoms and clusters, thereby maintaining good levels of catalytic activity and reversibility of the hydrogenation / dehydrogenation reaction, while also ensuring long-term stability even during repeated hydrogen storage / release operations. This represents an unexpected effect based on existing knowledge of catalysts.

[0062] According to an illustrative example, the content of cluster-form platinum in the supported catalyst can be determined, for example, through observation using HAADF-STEM (specifically, dark-field HAADF-STEM). In this regard, the respective numbers of monatoms and clusters in the supported platinum in the catalyst can be measured (although most of the supported platinum exists as monatoms and clusters, nanoparticles larger than clusters (e.g., about 2 nm to 8 nm, specifically about 2.5 nm to 6 nm, more specifically about 3 nm to 5 nm) may also be included, in which case the respective numbers of monatoms, clusters, and nanoparticles) can be measured to calculate the relative proportion (content) of cluster-form platinum. In this case, the content of nanoparticles larger than clusters in the platinum can be, for example, about 20% or less, specifically about 10% or less, more specifically about 5% or less.

[0063] According to one embodiment, the content of cluster form in platinum supported on an alumina support can be adjusted, for example, in the range of about 10% to 55%, specifically about 12% to 50%, and more specifically about 15% to 40%. According to a specific embodiment, the content of cluster form in platinum, which is the active metal, can be adjusted in the range of about 20% to 35%, specifically about 22% to 30%. In this regard, if the content of cluster form in platinum deviates from a certain range (i.e., if the content of monatomic atoms is excessively high or low), the dehydrogenation reaction activity decreases and it becomes difficult to improve the reversibility of the hydrogenation / dehydrogenation reaction. Therefore, it may be advantageous to set the heat treatment conditions so that the content of cluster form is adjusted within the above-mentioned range.

[0064] According to an illustrative example, the heat treatment may be performed at a temperature of, for example, about 300° C. to 800° C., specifically about 400° C. to 750° C., and more specifically about 500° C. to 700° C. In this case, it may be advantageous to appropriately adjust the temperature rise rate, for example, about 1° C. / min to 15° C. / min (specifically, about 1.5° C. / min to 12° C. / min, more specifically, about 2° C. / min to 10° C. / min), and the heat treatment time, for example, within a range of about 3 hours to 60 hours (specifically, about 5 hours to 50 hours, more specifically, about 10 hours to 40 hours), taking into consideration the desired ratio of monatoms and clusters.

[0065] On the other hand, after the heat treatment under an oxygen atmosphere, a reduction treatment can be additionally carried out to activate the catalyst for the final use in a hydrogenation / dehydrogenation reaction. According to an exemplary embodiment, hydrogen, carbon monoxide, methane, or a combination thereof can be used as the reduction gas, and the reduction treatment can be carried out more typically under a hydrogen atmosphere.

[0066] For example, the reduction temperature may be in the range of about 300°C to 600°C (specifically, about 350°C to 550°C, more specifically, about 400°C to 500°C). The heating rate may be, for example, about 1°C / min to 10°C / min, specifically about 4°C / min to 6°C / min. The reduction time may be, for example, about 1 hour to 10 hours, specifically about 2 hours to 5 hours. The pressure (partial pressure of the reducing gas) during the reduction is not particularly limited, but may be, for example, about 1 bar to 5 bar, specifically about 1.5 bar to 4 bar, more specifically about 2 bar to 3 bar. The above-described reduction conditions are merely illustrative and are not necessarily limited thereto. Through the above-described reduction process, a catalyst may be prepared in which platinum, the active metal, is supported on the alumina support in a fully reduced (i.e., elemental) state or a partially reduced (or oxidized) state, specifically, in a fully reduced state.

[0067] [Hydrogenation / Dehydrogenation Reactions (Storage and Release of Hydrogen) Using Liquid Organic Hydrogen Carrier Compounds] According to an embodiment of the present disclosure, a liquid organic hydrogen carrier (LOHC) can be used as a hydrogen storage material. Such a liquid organic hydrogen carrier system is composed of hydrogen-lean and hydrogen-rich organic compounds and can store and release hydrogen through repeated liquid or gas phase catalytic hydrogenation and dehydrogenation cycles. In particular, handling hydrogen in the form of a liquid organic hydrogen carrier can utilize existing fuel equipment. Unlike hydrogen storage through the hydrogenation of gases (e.g., carbon dioxide or nitrogen), releasing hydrogen from a liquid organic hydrogen carrier can produce pure hydrogen after condensation of the carrier compound, which has a relatively high boiling point.

[0068] According to this example, a catalyst in which platinum is supported on an alumina support in the form of a combination of single atoms and clusters can be used to carry out reversible hydrogenation / dehydrogenation reactions of liquid organic hydrogen carriers (LOHCs).

[0069] According to an exemplary embodiment, the above-described platinum-supported catalyst can be effectively applied to a wide range of liquid organic hydrogen carriers, including nitrogen-containing heterocyclic liquid organic hydrogen carriers and hydrocarbon-based liquid organic hydrogen carriers (specifically, aromatic hydrocarbon-based liquid organic hydrogen carriers such as dibenzyltoluene). Such compounds typically have at least one conjugated bond in the molecule.

[0070] According to one embodiment, the liquid organic hydrogen carrier may be at least one (hydrogen-lean form) selected from the compounds represented by the following general formulas 1 to 9:

[0071] [ka]

[0072] [ka]

[0073] [ka]

[0074] [ka]

[0075] [ka]

[0076] [ka]

[0077] [ka]

[0078] [ka]

[0079] [ka]

[0080] In the above formula, R, R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 each is hydrogen or a C1 to C6 alkyl group, and X is -(CHR 19 ) n - (n is an integer from 1 to 3, R 19 is H, OH, or a C1 to C6 alkyl group; and Y is CH or N.

[0081] The liquid organic hydrogen carrier compounds exemplified above may have a melting point of, for example, about 100° C. or less, specifically about 0° C. to 80° C., more specifically about 10° C. to 60° C., and therefore can maintain a liquid phase at room temperature, and a boiling point of about 380° C. or less, specifically about 130° C. to 350° C., more specifically about 180° C. to 300° C. Due to these melting and boiling point characteristics, a hydrogen storage and release system using a liquid organic hydrogen carrier has the advantage that it can omit the use of a separate solvent and / or additive for improving reactivity.

[0082] As described above, a catalyst in which platinum as an active metal is supported on an alumina support in the form of a mixture of single atoms and clusters is suitable for storing and releasing hydrogen by repeating the hydrogenation / dehydrogenation cycle of a liquid organic hydrogen carrier.

[0083] A method for storing and releasing hydrogen according to an exemplary embodiment may involve contacting an organic compound (e.g., in a liquid phase) serving as a liquid organic hydrogen carrier with the platinum-supported alumina catalyst described above in a reaction system. For example, the active metal (Pt) / LOHC ratio (M / R) in the catalyst may be set to, for example, about 0.05 mol% to 0.4 mol%, specifically about 0.07 mol% to 0.35 mol%, and more specifically about 0.1 mol% to 0.3 mol%. The M / R ratio may be differentiated between hydrogenation and dehydrogenation reactions. For example, the M / R ratio may be set relatively high for hydrogenation reactions and relatively low for dehydrogenation reactions. In this regard, an excessively low M / R ratio may result in insufficient reaction activity due to limitations in reducing the activation energy of the reaction. On the other hand, if the M / R ratio is too high, the solid-phase catalyst will significantly increase in volume compared to the liquid-phase reactants, forming an excessively slurried state, making stirring during the reaction difficult and causing diffusion limitations, which may lead to insufficient utilization of the catalyst's active sites. Therefore, it may be advantageous to appropriately adjust the M / R ratio within the above range. However, this ratio may vary depending on the type of hydrogen storage compound used.

[0084] As an example, the M / R ratio in the hydrogenation reaction (hydrogen storage) can be adjusted, for example, in the range of about 0.1 mol% to 0.4 mol% (specifically, about 0.15 mol% to 0.35 mol%, more specifically, about 0.2 mol% to 0.3 mol%), while the M / R ratio in the dehydrogenation reaction (hydrogen release) can be adjusted, for example, in the range of about 0.05 mol% to 0.15 mol% (specifically, about 0.07 mol% to 0.13 mol%, more specifically, about 0.09 mol% to 0.12 mol%).

[0085] In this regard, a hydrogenation reaction can be performed to store hydrogen in a hydrogen storage material (liquid organic hydrogen carrier). The hydrogenation reaction temperature can be, for example, about 50°C to 250°C, specifically about 80°C to 220°C, and more specifically about 100°C to 190°C. The hydrogenation reaction pressure can be, for example, about 5 bar to 100 bar, specifically about 20 bar to 80 bar, more specifically about 25 bar to 70 bar, and particularly specifically about 30 bar to 50 bar. The hydrogenation reaction time is not particularly limited, and can be, for example, about 0.5 hours to 24 hours, specifically about 1 hour to 12 hours, and more specifically about 1.5 hours to 6 hours.

[0086] According to an illustrative embodiment, by using the above-described platinum / alumina supported catalyst, the hydrogenation reaction efficiency (defined as the number of moles of hydrogen actually stored by the hydrogenation reaction relative to the number of moles of hydrogen that can theoretically be stored in one mole of the dehydrogenation reactant) can be, for example, at least about 62%, specifically at least about 90%, and more specifically at least about 96%, and the selectivity to the hydrogenation product corresponding to the hydrogen storage compound can be, for example, at least about 58%, specifically at least about 90%, and more specifically at least about 99%.

[0087] Meanwhile, a dehydrogenation reaction may be performed to release hydrogen from a hydrogen storage material (liquid organic hydrogen carrier). Because this dehydrogenation reaction is an endothermic reaction, it may be performed at a higher reaction temperature (e.g., a temperature range about 50°C to 150°C, specifically about 60°C to 120°C, and more specifically about 80°C to 100°C higher than the hydrogenation reaction temperature) than the hydrogenation reaction (exothermic reaction) of the same hydrogen storage material. According to an exemplary embodiment, the dehydrogenation reaction temperature may be, for example, about 100°C to 350°C, specifically about 150°C to 320°C, and more specifically about 180°C to 290°C. Unlike the reaction temperature, the dehydrogenation reaction pressure may be lower than the pressure conditions of the hydrogenation reaction, for example, about 1 bar to 10 bar, specifically about 1 bar to 5 bar, and more specifically, atmospheric pressure. The dehydrogenation reaction time is not particularly limited, but can be set, for example, in the range of about 0.5 hours to 24 hours, specifically about 2 hours to 12 hours, and more specifically about 3 hours to 8 hours.

[0088] According to illustrative embodiments, by using the above-described catalysts, the dehydrogenation reaction efficiency (defined as the number of moles of hydrogen actually produced by the dehydrogenation reaction relative to the number of moles of hydrogen that can theoretically be released per mole of hydrogenation reactant) can be, for example, at least about 50%, specifically at least about 60%, and more specifically at least about 86%.

[0089] Meanwhile, according to one embodiment, the hydrogenation / dehydrogenation reaction can be carried out using a conventional reactor known in the art, such as a batch reactor, a continuous reactor, or a semi-continuous reactor. In particular, in the case of liquid organic hydrogen carriers, especially liquid organic hydrogen carrier compounds having relatively high boiling points, the hydrogenation and dehydrogenation reactions can occur in the liquid phase, so the reactor can be equipped with an agitator. According to an exemplary embodiment, the reaction can be carried out in a fixed-bed reactor using a particulate catalyst.

[0090] The present invention can be more clearly understood from the following examples, which are for illustrative purposes only and are not intended to limit the scope of the invention. [Example]

[0091] In the examples and comparative examples, the catalysts prepared were analyzed by the following methods.

[0092] [Transmission electron microscope (TEM, HAADF-STEM) analysis] Using a transmission electron microscope (TEM, HAADF-STEM, JEOL, TEM2100F), a sample dispersed in methanol was dropped onto a Cu grid test piece, and then dried in a vacuum oven at 60°C for more than 20 hours, and the size of the metal particles supported on the carrier was measured.

[0093] [Crystalline State Analysis of Pt Metal (CO-DRIFT)] For CO-DRIFT (chemisorbed diffuse reflectance infrared Fourier transform) spectroscopy, a Nicolet 6700 FT-IR (equipped with a Harrick Praying Mantis high temperature reaction chamber) was used. Prior to the measurement, 30 mg of sample was heated at 500 °C for 1 h in 5% H2 / Ar (100 cm3). 3 min -1 After reduction, the temperature was lowered to 50°C and the atmosphere was replaced with Ar gas to remove the substances physically adsorbed on the surface of the sample. 3 min -1 The sample was exposed to a flow of CO for 30 minutes, and then the adsorbed CO was desorbed through a process of evacuation for 30 minutes, followed by IR analysis.

[0094] [Example] [Production of platinum / alumina catalyst by solid phase method] First, 21.84g of Al precursor (Al(NO3)3·9H2O), 13.88g of ammonium bicarbonate (NH4HCO3), and 0.182g of Pt metal precursor [Pt(NH3)4](NO3) were added to a mortar without a solvent and physically mixed. The physical mixture was then stirred for 20 minutes to apply frictional heat. During this time, the solid precursors were mixed a total of three times, generating a large amount of CO2 and forming a gel. 10 minutes after mixing, the mixture hardened and solidified again in gel form, and then softened again after 6 minutes.

[0095] The gel solid was then mixed for 20 minutes and placed in a crucible and calcined at 600°C for 5 hours (heating rate: 2°C / min). After calcination, reduction treatment using hydrogen was performed (500°C, 5°C / min, 3 hours). The reaction activity in the presence of the reduced catalyst was compared (the platinum / alumina catalyst prepared in the example was represented as M3PtA x_y (x: calcination temperature, y: calcination time)) (platinum loading: 3 wt%). Platinum / alumina catalysts with various platinum loadings (1 wt%, 2 wt%, and 5 wt%) were also prepared using the same procedure and their activity was evaluated.

[0096] Comparative Example [Production of platinum / alumina catalyst by impregnation method] 3 g of commercial γ-Al2O3(gA) was homogeneously mixed with 0.182 g of a 3 wt% Pt metal precursor solution ([Pt(NH3)4](NO3)2) and 2 ml of distilled water) via impregnation. The catalyst was then dried in an oven at 100 °C and placed in a crucible and calcined for 5 hours (600 °C, 2 °C / min). This was followed by hydrogen reduction (500 °C, 3 hours, heating rate 5 °C / min) to obtain the 3Pt / gA x_y (x: calcination temperature, y: calcination time) catalyst (platinum loading 3 wt%). Platinum / alumina catalysts with various platinum loadings (1 wt%, 2 wt%, and 5 wt%) were also prepared using the same procedure and their activity was evaluated.

[0097] [A. Analysis of catalyst properties and reaction activity by synthesis method] [Catalyst physical property analysis] FIG. 1 shows the XRD patterns of the platinum-supported catalyst (MPtA) according to the example (solid phase method) and the platinum-supported catalyst (Pt / gA) according to the comparative example (impregnation method) with various platinum contents (1 wt%, 2 wt%, 3 wt%, and 5 wt%).

[0098] As can be seen from the figure, even with the same platinum content, the size of the platinum crystals varied depending on the synthesis method. In the catalyst prepared by the impregnation method (comparative example), even with a low platinum content of 1 wt%, the crystal sizes of Pt(111), (200), and (220) were large. On the other hand, in the catalyst prepared by the solid-phase method (example), only Pt(111) crystals were formed even with a platinum loading of 5 wt%, indicating that platinum was more uniformly dispersed in the catalyst according to the example compared to the comparative example.

[0099] Meanwhile, dark-field HAADF-STEM photographs of the platinum-supported catalyst (MPtA) according to the example (solid phase method) and the platinum-supported catalyst (Pt / gA) according to the comparative example (impregnation method), which carried various platinum contents (1 wt%, 2 wt%, 3 wt%, and 5 wt%), are shown in Figures 2a and 2b, respectively.

[0100] As can be seen in the figure, platinum single atoms and clusters are distributed relatively unevenly in the catalysts according to the examples, while in the catalysts according to the comparative examples, platinum has a particle form even when supported at a low content of 1 wt %.

[0101] FIG. 3 shows CO-DRIFT spectra of the platinum-supported catalyst (MPtA) according to the example (solid phase method) and the platinum-supported catalyst (Pt / gA) according to the comparative example (impregnation method) with various platinum loadings.

[0102] According to the figure, in the case of the catalyst according to the embodiment, 2090 cm -1 , 2070cm -1 and 2040cm-1 On the other hand, the catalyst according to the comparative example showed a peak at 2070 cm -1 2060cm corresponding to the peak -1 The peak at 2090 cm corresponding to a single atom was formed relatively larger. -1 The peak was barely observed even when 1 wt % of platinum was supported.

[0103] FIG. 4 is a graph showing the H2-TPD results for the platinum-supported catalyst (MPtA) of the Example (solid phase method) and the platinum-supported catalyst (Pt / gA) of the Comparative Example (impregnation method) with various platinum contents (1 wt%, 2 wt%, 3 wt%, and 5 wt%).

[0104] Referring to the figure, the degree of hydrogen desorption depending on the platinum content was compared using H2-TPD. As a result, the hydrogen desorption peak of the catalyst according to the example tended to shift from 500°C to around 200°C as the platinum content increased, while the catalyst according to the comparative example showed almost no change in the desorption range.

[0105] To analyze the platinum morphology more accurately, EXAFS analysis was performed, and the results are shown in Table 1 below and FIG.

[0106] According to the tables and figures, when compared with the fitting results of the reference materials Pt foil and PtO2, the catalysts according to the examples showed patterns almost similar to PtO2 even when the platinum content increased, while the catalysts according to the comparative examples showed patterns similar to Pt foil.

[0107] [Table 1]

[0108] According to the table, many Pt-Pt bonds were observed in the catalysts according to the comparative examples, whereas many Pt-O, Pt-O-Pt, and Pt-O-Al bonds were present in the catalysts according to the examples at low platinum contents, and a tendency was observed that the number of Pt-Pt bonds increased as the platinum content increased.

[0109] [Reaction activity analysis] The efficiencies of the hydrogenation (reaction conditions: M / R 0.22 mol%, 35 bar, 150°C, and 2 hours) and dehydrogenation (reaction conditions: M / R 0.1 mol%, 250°C, and 4 hours) reactions of the catalysts prepared in the Examples and Comparative Examples are compared in Tables 2 and 3 below and FIG. 6.

[0110] [Table 2]

[0111] a : Calculation results through GC analysis. b Hydrogen storage efficiency = (full hydrogenation product [mol] × 6H2 + single-ring hydrogenation product [mol] × 3H2) / (reactant [mol] × 6H2) × 100%

[0112] [Table 3]

[0113] a : Calculation results through GC analysis. b : Hydrogen release efficiency = (full dehydrogenation product [mol] × 6H2 + single-ring dehydrogenation product [mol] × 3H2) / (reactant [mol] × 6H2) × 100%

[0114] Based on the above results, the catalysts according to the examples, which carried 3 wt% platinum, showed the best activity in both hydrogenation and dehydrogenation reactions. On the other hand, the catalysts according to the comparative examples, which carried 1 wt% platinum, showed the best activity. This is believed to be due to the increase in platinum size as the platinum loading increased. In particular, this difference in activity is believed to be due to the difference in the size of platinum particles supported on the alumina support depending on the catalyst manufacturing method.

[0115] [B. Analysis of catalyst properties and reaction activity depending on calcination conditions] [Catalyst physical property analysis] The calcination conditions were changed from 600°C for 5 hours (heating rate: 2°C / min) to 5 hours (heating rate: 10°C / min), 20 hours (heating rate: 2°C / min), and 40 hours (heating rate: 2°C / min). The size change of the platinum catalysts loaded at 1 wt% and 3 wt% was also observed. The XRD patterns, H2-TPD results, and HAADF-STEM images of the Pt-loaded catalysts (loading amounts: 1 wt% and 3 wt%) under different calcination conditions are shown in Figures 7 and 8, respectively.

[0116] In the figure, XRD analysis confirmed that when the calcination temperature (600°C) and calcination time (5 h) were fixed and the heating rate was changed from 2°C / min to 10°C / min, the Pt(111) peak increased for all platinum catalysts loaded with 1 wt% and 3 wt% platinum. Additionally, when the calcination temperature (600°C) and heating rate (2°C / min) were fixed and the calcination time was changed from 5 h to 20 h and 40 h, respectively, the Pt(111) peak increased for all platinum catalysts loaded with 1 wt% and 3 wt%, although the increase was smaller than the change in heating rate. Furthermore, H2-TPD analysis confirmed that the hydrogen desorption peak shifted to lower temperatures as the platinum size increased.

[0117] On the other hand, as confirmed by the HAADF-STEM results in Figure 8, in the case of the M1PtA (same as M1PtA c6005 h_2) catalyst in Figure 2, platinum single atoms were mainly observed, while when the calcination time was increased to 40 h and the heating rate to 10 °C / min, the proportion of clusters increased and particle morphology was also observed. Considering the above results, it is suggested that the calcination conditions affect the crystallinity of the metal, which is the main variable that can adjust the size of the platinum.

[0118] [Reaction activity analysis] The hydrogenation and dehydrogenation activity of the Pt-supported catalyst was measured under different calcination conditions. The results are shown in Table 4 (hydrogenation conditions: M / R 0.22 mol%, 35 bar, 150°C, 2 hours) and Table 5 (dehydrogenation conditions: M / R 0.1 mol%, 250°C, 4 hours) and in Figure 9.

[0119] [Table 4]

[0120] a : Calculation results through GC analysis. b Hydrogen storage efficiency = (full hydrogenation product [mol] × 6H2 + single-ring hydrogenation product [mol] × 3H2) / (reactant [mol] × 6H2) × 100%

[0121] [Table 5]

[0122] a : Calculation results through GC analysis. b: Hydrogen release efficiency = (full dehydrogenation product [mol] × 6H2 + single-ring dehydrogenation product [mol] × 3H2) / (reactant [mol] × 6H2) × 100%

[0123] Referring to the table and the figure, the M1PtA c600 5h_2 catalyst, which has a high platinum monoatomic ratio, showed a storage efficiency of 62.5% and a desorption efficiency of 33.7% in hydrogenation and dehydrogenation reactions, respectively. On the other hand, the M1PtA c600 40h_2 catalyst, which was prepared by increasing the calcination time during catalyst preparation, showed improved storage efficiency of 75.2% and desorption efficiency of 83.5%.

[0124] [C. Catalyst stability analysis using synthetic methods] [Evaluation of dehydrogenation reaction activity and changes in catalyst properties after use] To evaluate the long-term stability of the catalyst, a dehydrogenation activity evaluation was performed. The dehydrogenation reaction results for the platinum-supported catalyst (M3PtA) according to the example (solid-phase method) and the platinum-supported catalyst (3Pt / gA) according to the comparative example (impregnation method) are shown in Figure 10. The XRD patterns before and after the reaction for the platinum-supported catalyst (M3PtA) according to the example and the platinum-supported catalyst (3Pt / gA) according to the comparative example, as well as HAADF-STEM photographs of the catalysts after use, are shown in Figure 11.

[0125] Referring to the figure, the catalytic activity of the comparative catalyst (3Pt / gA) decreased rapidly after five reuses. Furthermore, after the reaction, the metal particle state of the catalyst was observed using XRD and HAADF-STEM. For the example catalyst (M3PtA), the XRD patterns were nearly identical before and after use. STEM analysis also revealed that platinum single atoms and clusters were still relatively unevenly distributed. This is believed to be due to the strong interaction between platinum and the alumina support in the example catalyst (M3PtA). Meanwhile, for the 3Pt / gA catalyst, the initial hydrogen desorption efficiency (55.7%) decreased by approximately twofold to 27.4% after five reuses. This is believed to be due to a weakening of the interaction between platinum and the alumina support and an increase in particle size due to platinum sintering.

[0126] [Evaluation of reversibility of hydrogenation / dehydrogenation reactions] Because platinum exhibits activity in both hydrogenation and dehydrogenation reactions, it is possible to achieve high hydrogen storage and release efficiencies even when using the same type of catalyst in a single reactor. Since the interaction between the active metal and the support varies depending on the synthesis method, we assumed that this would also affect the sequential reversible reactions. Therefore, we conducted experiments in which three sets of hydrogenation and dehydrogenation reactions were performed consecutively. In this regard, we measured and compared the hydrogen storage and release efficiencies of the HO-BT catalyst (M3PtA) according to the example and the catalyst (3Pt / gA) according to the comparative example. The results are shown in Figure 12.

[0127] Referring to the figure, under the same hydrogenation and dehydrogenation reaction conditions, the catalyst according to the example (M3PtA) consistently maintained its initial hydrogen storage and release efficiency, while the catalyst according to the comparative example (3Pt / gA) consistently decreased its hydrogen storage and release efficiency.

[0128] [D. Evaluation of dehydrogenation reaction activity depending on the type of liquid organic hydrogen carrier] Dehydrogenation reactions were carried out using various types of pyridine-based and bipyridine-based liquid organic hydrogen carriers, and the results are shown in Table 6 below.

[0129] [Table 6]

[0130] As can be seen from the table, the catalyst according to the embodiment (M3PtA 600 5h) showed improved reaction efficiency compared to the catalyst according to the comparative example (3Pt / gA 600 5h), regardless of the liquid organic hydrogen carrier.

[0131] [E. Evaluation of dehydrogenation reaction activity based on the cluster content (ratio) of platinum in the catalyst] Platinum-supported catalysts were prepared by the solid-state method while varying the heat treatment conditions (heat treatment temperature, time, and heating rate) (platinum loading: 1 wt%, 3 wt%, and 5 wt%). The number of single atoms and clusters (and additionally nanoparticles larger than clusters) was measured using dark-field HAADF-STEM images, and the content of clusters in the supported platinum was calculated. The results are shown in Table 7 below (reaction conditions: 250°C, 1 bar, 4 hours, precious metal (mol) / reactant (mol) 0.1%).

[0132] [Table 7]

[0133] In the table, the firing conditions corresponding to a are 600°C, 5 hours (heating rate 2°C / min), the firing conditions corresponding to b1 are 600°C, 40 hours (heating rate 2°C / min), and the firing conditions corresponding to b2 are 600°C, 5 hours (heating rate 10°C / min).

[0134] According to the table above, when the cluster content in the supported platinum is too low (M1PtA a :4.8%), or when the cluster content is excessively high (M5PtA b2The hydrogen desorption efficiencies of the M3PtA and M3PtA were low at 36.2% and 35.2%, respectively. On the other hand, when the cluster content was adjusted within an appropriate range, good hydrogen desorption efficiencies could be obtained, especially for the M3PtA b1 The catalyst (cluster content: 22.6%) achieved a high hydrogen release efficiency of 86.9%.

[0135] Simple variations and modifications of the present invention are readily accessible to those skilled in the art, and all such variations and modifications are to be considered as falling within the scope of the present invention.

Claims

1. A catalyst for hydrogenation / dehydrogenation of a liquid organic hydrogen carrier, comprising: an alumina support; and Platinum, including monatomic and cluster forms, as the active metal supported on the alumina support; Including, the clusters are groups of at least two platinum atoms and have a size of less than 2 nm; The platinum content (elemental basis) in the catalyst is 0.01% to 10% by weight, A catalyst in which the content of platinum in cluster form in the supported platinum is in the range of 10% to 55%.

2. The alumina support in the catalyst is at least 300 m ２ BET specific surface area of ​​0.4 cm ３ / g~0.55cm ３ Catalyst according to claim 1, characterized in that it has a pore volume of 0.1g / g and a pore size of 3nm to 4.5nm.

3. 2. The catalyst according to claim 1, wherein the content of platinum in cluster form in the supported platinum is in the range of 22% to 30%.

4. 10. The catalyst of claim 1, wherein the catalyst contains platinum crystals having a (111) face and is in a reduced state.

5. A method for producing a hydrogenation / dehydrogenation catalyst for a liquid organic hydrogen carrier, comprising: a) carrying out a solid-state reaction in the absence of a solvent while applying external energy to a mixture containing at least one alumina precursor, at least one platinum precursor, and a base component to form a catalyst solid in the form of a gel; and b) heat-treating the catalytic solid in an oxygen-containing atmosphere to form a heat-treated catalytic solid, thereby supporting platinum, including platinum in the form of monoatoms and clusters, on an alumina support; Including, the clusters are groups of at least two platinum atoms and have a size of less than 2 nm; The platinum content (elemental basis) in the catalyst is in the range of 0.01 wt % to 10 wt %. The method wherein the content of platinum in the cluster form in the supported platinum is in the range of 10% to 55%.

6. 6. The method of claim 5, wherein the heat treatment temperature in step b) is adjusted to 300° C. to 800° C., the temperature increase rate is adjusted to 1° C. / min to 15° C. / min, and the heat treatment time is adjusted to 3 hours to 60 hours.

7. c) further comprising a step of reducing the heat-treated catalytic solid to convert platinum to a fully reduced state or a partially reduced state; 6. The method according to claim 5, wherein the reduction treatment temperature is adjusted in the range of 300 to 600°C, the temperature increase rate is adjusted in the range of 1 to 10°C / min, and the reduction treatment time is adjusted in the range of 1 to 10 hours.

8. 6. The method of claim 5, wherein the platinum precursor / base component molar ratio in step a) is in the range of 0.0001 to 0.

1.

9. a hydrogenation step in which hydrogen is stored in a liquid organic hydrogen carrier in the presence of a catalyst; and a dehydrogenation step of releasing hydrogen from the hydrogenated liquid organic hydrogen carrier in the presence of a catalyst; The catalyst used in at least one of the hydrogenation step and the dehydrogenation step is an alumina support; and Platinum, including monatomic and cluster forms, as the active metal supported on the alumina support; Including, the clusters are groups of at least two platinum atoms and have a size of less than 2 nm; A catalyst in which the platinum content (element basis) in the catalyst is 0.01 wt% to 10 wt%, and the content of platinum in cluster form in the supported platinum is in the range of 10% to 55%, The hydrogenation step and the dehydrogenation step are alternately performed to store and release hydrogen.

10. The method according to claim 9, wherein the liquid organic hydrogen carrier is at least one selected from the compounds represented by the following general formulas 1 to 9: 【Chemistry 1】 【Chemistry 2】 【Transformation 3】 【Chemistry 4】 【Transformation 5】 【Transformation 6】 【Transformation 7】 【Transformation 8】 【Chemistry 9】 In the above formula, R, R １ , R ２ , R ３ , R ４ , R ５ , R ６ , R ７ , R ８ , R ９ , R １０ , R １１ , R １２ , R １３ , R １４ , R １５ , R １６ , R １７ and R １８ Each of １ ~C ６ and X is an alkyl group represented by -(CHR １９ ) ｎ - (n is an integer from 1 to 3, R １９ is H, OH, or C １ ~C ６ ) and Y is CH or N.

11. 11. The method of claim 10, wherein the liquid organic hydrogen carrier has a melting point of 100°C or less and a boiling point of 380°C or less.

12. 10. The method of claim 9, wherein the ratio (M / R) of the active metal (Pt) to the liquid organic hydrogen carrier in the catalyst is adjusted in the range of 0.05 mol % to 0.4 mol %.

13. 13. The method according to claim 12, wherein the ratio of M / R in the hydrogenation step is adjusted in the range of 0.1 mol% to 0.4 mol%, while the ratio of M / R in the dehydrogenation step is adjusted in the range of 0.05 mol% to 0.15 mol%.

14. The hydrogenation step is carried out at a temperature of 50°C to 250°C and a pressure of 5 bar to 100 bar; 14. The method according to claim 13, wherein the dehydrogenation step is carried out at a temperature of 100 to 350°C and a pressure of 1 to 10 bar.

15. 10. The method of claim 9, wherein the hydrogenation step has a hydrogenation reaction efficiency of at least 62% and the dehydrogenation step has a dehydrogenation reaction efficiency of at least 50%.

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