KR102249231B1 - Method for Storing and Releasing Hydrogen Using Palladium Supported Catalysts - Google Patents

Abstract

In the present disclosure, a technique capable of reversibly storing and releasing hydrogen with high selective conversion and high efficiency using a catalyst in which a palladium (Pd) metal having a specific surface as an active metal is dispersed and supported on a mesoporous alumina support is described. .

Description

Method for Storing and Releasing Hydrogen Using Palladium Supported Catalysts}

The present disclosure relates to a hydrogen storage and release technology using a palladium (Pd) supported catalyst. More specifically, the present disclosure is capable of reversibly storing and releasing hydrogen with a high selective conversion rate and high efficiency by using a catalyst in which a palladium (Pd) metal having a specific surface as an active metal is dispersed and supported on a mesoporous alumina support. It's about technology.

As environmental pollution problems such as reduction of fossil fuel reserves, global warming caused by pollutants generated during combustion and carbon dioxide are seriously raised, global interest and demand for alternative energy development is exploding.

As alternative energy sources, renewable energy such as wind power, tidal power, geothermal heat, hydrogen energy, solar energy, and the like are in the spotlight, and each of the energy sources listed above has advantages and disadvantages. In this regard, since renewable energy is difficult to supply and demand smoothly due to instability of energy sources according to time and natural environment, in order to effectively replace conventional fossil fuels, excess energy is stored so that energy can be stably supplied. It is necessary to develop the technology to be supplied.

From this point of view, hydrogen energy is (i) the most energy efficient per unit mass, (ii) only water is produced during combustion, and there are no other harmful by-products, and (iii) water, the main source of hydrogen, is abundant in nature and used. Since it is converted to water, it is advantageous in terms of reuse, and (iv) it is attracting special attention because it is suitable for securing competitiveness in the precision industry and IT industry as a distributed power source that uses hydrogen as a fuel. Moreover, hydrogen can be produced using other renewable energy such as solar energy and wind power, and can be widely applied not only to various energy sources, but also to other industrial fields (eg, various petrochemical fields). It is emerging as a key energy source in the future.

In general, the research and development of hydrogen energy is largely divided into the field of manufacturing hydrogen, the field of transport (transport), and the field of storage. While hydrogen has an excellent energy storage capacity compared to mass, while its energy storage capacity compared to volume is low, hydrogen can be efficiently used. The storage technology is acting as the biggest obstacle to the practical use of hydrogen energy. For example, a material having a mass storage density of 10% by weight or more under 77 K condition is known, but the volume storage density of these materials is 40 g/L, which is relatively low in volume storage density for use as an actual hydrogen storage material. . Therefore, research on a technology for storing as much hydrogen as possible in a storage medium that is as light as possible and small in volume is actively being conducted.

In this regard, countries have invested a lot of R&D expenditures over the years, and the efficient storage methods for hydrogen that have been researched and developed so far are the CGH2 method that compresses hydrogen using a pressure of 700 bar, and LH2 that stores liquid hydrogen by liquefying it at -253 ℃ There is a way. However, this pressurization or liquefaction method must maintain a low temperature, and the density of liquid hydrogen is also low at 71.2 kg/㎥.

As an alternative to this, materials having hydrogen storage capacity, such as metal-organic frameworks (MOFs), carbon nanotubes, zeolites, porous organic or inorganic nanomaterials such as activated carbon, metal hydrides, etc. It is attracting attention as a material that effectively stores energy (Nature, 427, 523 (2004); J. Am. Chem. Soc., 127, 14904 (2005); Japanese Patent Publication No. 2008-95172, 2011- 131120, etc.). However, in the case of a room temperature gaseous hydrogen storage technology by physical absorption of MOFs and porous nanomaterials, the energy storage density is relatively low, and the energy required for storage and desorption of hydrogen is relatively large, making miniaturization and modularization difficult.

Recently, a hydrogen storage technology by reversible catalytic hydrogenation/dehydrogenation reaction using organic substances, specifically, a liquid organic hydrogen carrier (LOHC), has been developed (US Patent No. 7,901,491, etc.). LOHC technology has advantages such as being able to store more than 5% by weight of hydrogen, which is recommended by the US Department of Energy (DOE), can operate in a low pressure range, and can easily recycle the storage material. Due to its advantage of handling and high energy density, it is possible to provide a practical hydrogen storage system capable of efficient transport and storage using the existing liquid fuel transport and storage infrastructure (Energ. Rev., 6 (2002) 141, Energy Environ. Sci., 8 (2015) 1035-1045).

Although the technique of using a pi-conjugated base type compound as a LOHC material is known (for example, U.S. Patent No. 7,351,395, etc.), it is difficult to secure uniform reactivity due to pi-conjugation. do. In order to alleviate this problem, a technique of using benzyl toluene and dibenzyl toluene as hydrogen storage materials is also known (for example, Korean Patent Publication No. 2015-97558, etc.). The hydrogen carrier exists in a liquid state at room temperature and has a boiling point of 280° C. or higher, so there is no restriction in terms of utilization, but there is a limitation in enhancing the hydrogenation and dehydrogenation reaction efficiency due to the limitation of the hydrocarbon structure.

On the other hand, in order to commercialize a hydrogen storage/release system using LOHC, various technical factors must be considered in addition to the development of a hydrogen storage material. In the case of a double catalyst, (1) effective dehydrogenation reaction efficiency at low temperature, and (2) stability (reusability) of the catalyst must be considered.

Among the above-described requirements, requirement (1) can be implemented by using a pyridine-based cyclic compound as a hydrogen carrier, and thus dehydrogenation can be performed at a lower temperature than a carboxylic compound (ChemSusChem, 7 (2014)). ) 229-235).

In the case of requirement (2), the hydrogenation reaction (hydrogen storage reaction) is a typical exothermic reaction, whereas the dehydrogenation reaction is a typical endothermic reaction, so catalyst stability is a priority factor in the dehydrogenation reaction than in the hydrogenation reaction. Therefore, alumina, which is good in terms of thermal stability, physical strength, and long-term stability, can be used as a support. In particular, gamma-alumina (γ-Al ₂ O ₃ ) has been widely used as a catalyst or catalyst support for vehicles and petroleum fields. However, even if a metal-supported porous alumina support catalyst is used in the hydrogenation/dehydrogenation reaction of LOHC, it may still exhibit insufficient dehydrogenation activity because the dispersibility of the active metal is not high.

In addition, a metal (specifically, palladium)-supported alumina catalyst is typically manufactured according to an impregnation method.Since it involves a plurality of steps of synthesizing an alumina support and supporting the metal, it takes a long time to prepare the catalyst and is commercialized. It is disadvantageous in terms of In particular, the catalyst stability can be secured to some extent due to the inherent characteristics of alumina, but there is a limit to achieving additionally improved performance.

Accordingly, there is a need for a LOHC-based hydrogen storage/release system that exhibits good hydrogenation/dehydrogenation performance over a long period of time compared to the prior art.

Accordingly, in one embodiment of the present disclosure, it is intended to provide a method for improving reaction efficiency, long-term stability, regeneration potential, and the like in a catalytic reaction accompanying storage and release of hydrogen using a liquid organic hydrogen carrier.

According to another embodiment of the present disclosure, to provide a catalyst capable of improving the hydrogenation/dehydrogenation activity associated with storage/release of hydrogen using a liquid organic hydrogen carrier, and a method for preparing the same.

According to the first aspect of this disclosure,

A hydrogenation step of storing hydrogen on a liquid organic hydrogen carrier having an N-heterocycle 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,

Mesoporous alumina-containing support, and

Including palladium having a (111) facet as an active metal in the mesoporous alumina-containing support,

A method of storing hydrogen or releasing hydrogen is provided as the hydrogenation step and the dehydrogenation step are alternately performed.

According to the second aspect of this disclosure,

a) applying external energy to a mixture containing at least one alumina precursor, at least one palladium precursor, and a base component while performing a solid-phase reaction in the absence of a solvent to form a gel-like catalyst solid; And

b) thermally treating the catalyst solid material under an oxygen-containing atmosphere and a temperature condition of 300 to 800° C. to support palladium crystals having (111) facets on a mesoporous alumina-containing support;

A method for producing a catalyst for hydrogenation/dehydrogenation of a liquid organic hydrogen carrier is provided.

According to the third aspect of this disclosure,

As a hydrogenation/dehydrogenation catalyst,

Mesoporous alumina support, and

Palladium having a (111) facet as an active metal on the mesoporous alumina-containing support;

Including,

The palladium content is 0.1 to 10% by weight, based on the total weight of the catalyst, and

The catalyst is provided with a catalyst exhibiting the following physical properties:

(i) BET specific surface area of at least 300 m2/g, (ii) palladium dispersion of at least 30%, (iii) palladium particle size of 3.5 nm or less, and (iv) chemisorbed diffuse reflectance infrared fourier transform (CO-DRIFT) Based on the CO adsorption band peak by spectral analysis, the relative adsorption band intensity ratio expressed as (C+D)/B is in the range of 1.5 to 10 (where B is in the Pd (100) plane). Is the CO adsorption band peak at ^{1978 cm -1} with multiple bonds ^{, C is the CO adsorption band peak at 1918 cm -1} single bonded to the Pd (111) plane, and D is the triple bond at the Pd (111) plane. Is the CO adsorption band peak at 1860 cm ^{-1 ).}

According to an embodiment of the present disclosure, in the palladium-supported alumina catalyst, palladium having a (111) face corresponds to a factor that significantly affects the hydrogenation/dehydrogenation (especially dehydrogenation) reaction activity of a specific liquid organic hydrogen carrier. On the basis of the new discovery that it becomes, it is possible to realize good hydrogenation/dehydrogenation activity over a long period of time by applying a palladium/alumina catalyst.

In addition, in another embodiment of the present disclosure, the aforementioned hydrogenation/dehydration is performed by performing a single step reaction by applying a simple physical or mechanical external energy such as milling to the raw material mixture including the palladium precursor and the alumina precursor without the use of a solvent. The properties of the digestion catalyst can be realized. The prepared catalyst can overcome the technical limitations of a two-step catalyst manufacturing method such as a relatively high catalyst manufacturing cost and time-consuming impregnation method, and has been improved during the hydrogenation/dehydrogenation reaction of a specific liquid organic hydrogen carrier. It can provide multiple advantages, such as maintaining activity over a long period of time.

1 is a photograph showing a phase change of a precursor during a series of processes of preparing a hydrogenation/dehydrogenation catalyst according to an embodiment;
_{Fig. 2 is an adsorption and desorption N 2} isothermal curve and pore size distribution curve for each of Pd/gA, Pd/MA and MPdA catalysts and supports (MA and gA);
3 is a hydrogen evolution curve (reaction conditions: each) obtained while changing the reaction temperature in the dehydrogenation reaction of _{H 12} -MBP using Pd/gA, Pd/MA and MPdA (Pd content: 1% by weight). 230° C., 250° C. and 270° C.; 1 bar; 4 hours; metal (mol)/reactant (mol) 0.1%).
4 is a GC chromatogram analysis of the product obtained while varying the reaction time in the dehydrogenation reaction of _{H 12} -MBP using an MPdA (left) catalyst and a Pd/gA (right) catalyst (Pd content: 1% by weight) A graph showing the results (reaction conditions: 250° C.; 1 bar; 4 hours; metal (mol)/reactant (mol) 0.4%) graph;
5 is a graph of CODRIFT spectra of Pd/gA, Pd/MA, and MPdA (Pd content: 1% by weight);
6 is (a) MPdA (b) Pd/MA and (c) HRTEM photographs and SAED patterns for each of Pd/gA;
7 is a HAADFSTEM photograph ((a) before and (b) after reaction) of each reaction of MPdA, Pd/MA and Pd/gA (Pd content: 1% by weight);
Fig. 8 is a Pd particle size distribution chart of a new catalyst (left) and a used catalyst (right) of (a) MPdA, (b) Pd/MA and (c) Pd/gA, respectively;
9 is a HRTEM and SAED (selected area electron diffraction) photographs of the catalysts used for (a) MPdA, (b) Pd/MA, and (c) Pd/gA, respectively;
FIG. 10 is a graph of a dehydrogenation reaction experiment for evaluating long-term stability of MPdA, Pd/MA and Pd/gA catalysts (reactant H ₁₂ -MBP (left) and reactant H ₈ -MID (right); reaction conditions: 250° C., 1 bar, 4 hours, noble metal (mol)/reactant (mol) 0.4% and 0.6%), and
11 is a graph showing the results of comparing the dehydrogenation activity of the MPdA (Pd content: 1% by weight) catalyst in a powder form and a pellet form, and a photograph of the appearance of a pellet-type catalyst.

The present invention can all be achieved by the following description. The following description should be understood as describing preferred embodiments of the present invention, and the present invention is not necessarily limited thereto. In addition, it should be understood that the accompanying drawings are provided to aid understanding, and the present invention is not limited thereto.

Terms used in the present specification may be defined as follows.

The "heterogeneous catalyst" may mean a catalyst that exists in a phase different from that of the reactant during the catalytic reaction, for example, it may mean a catalyst that is not dissolved in the reaction medium. In the case of a heterogeneous catalyst, in order for the reaction to occur, at least one reactant must be diffused and adsorbed onto the surface of the heterogeneous catalyst, and after the reaction, the product needs to be desorbed from the surface of the heterogeneous catalyst.

"Support" can mean a material (typically a solid material) having a high specific surface area to which the catalytically active component is attached.

"Hydrogenation" may refer to a reaction of increasing the hydrogen content in the compound by chemically adding hydrogen to at least a portion of the compound by contacting the compound with a catalyst under the supply of hydrogen.

"Dehydrogenation" may refer to a reaction in which hydrogen in the compound is removed, and further, the removed hydrogen is released from the compound.

"Impregnation" may mean a method of preparing a catalyst by impregnating a solution in which a catalyst precursor is dissolved into a separately synthesized support, and then subjecting to drying and/or firing (or reduction) treatment if necessary. have.

“Salt” may generically mean a compound in which a metal cation is bonded to an inorganic anion or an organic anionic species.

Overall disclosure

In one embodiment of the present disclosure, a palladium-supported alumina catalyst conventionally known as a catalyst for hydrogenation/dehydrogenation reaction is a liquid organohydrogen carrier, in particular, hydrogen storage and release using a liquid organohydrogen carrier having an N-heterocycle (i.e. When applied to hydrogenation and dehydrogenation) reactions, the long-term stability of the catalyst is deteriorated, and it is possible to improve the fact that it is limitedly applied to the operation of repetitive hydrogen storage and release systems.

Specifically, the present inventors pointed out that in the case of a metal-supported catalyst, even in the case of the same dehydrogenation reaction, the preferred metal crystal plane is different depending on the structure of the reactant, and in the case of a palladium/alumina catalyst, the orientation characteristics of palladium, an active metal, The hydrogenation/dehydrogenation reaction of the liquid organic hydrogen carrier having this N-heterocycle, especially the dehydrogenation reaction (hydrogen storage reaction is an exothermic reaction, while the hydrogen release reaction is an endothermic reaction, so the catalyst is more effective in the dehydrogenation reaction than in the hydrogenation reaction. It was confirmed that the reaction activity (e.g., selectivity) and long-term stability were significantly affected.

For example, in the case of methanol dehydrogenation reaction, CHO, CO, and H exhibit a strong adsorption tendency on the Pd (100) side compared to the Pd (111) side, and when compared to the reaction on the Pd (100) side, Pd ( 111) can provide a relatively low energy barrier and a larger dehydrogenation rate constant. This point indicates that the more open Pd surface exhibits high activity and selectivity in the complete dehydrogenation reaction of methanol.

On the other hand, in the case of the hydrogenation/dehydrogenation reaction of a liquid organic hydrogen carrier having an N-heterocycle, the degree of adsorption of these cyclic compounds acts as a major factor in the reaction activity.At this time, palladium having a (111) plane is supported. It can show strong adsorption capacity in the state. In consideration of the above, in one embodiment of the present disclosure, only palladium having a crystal plane effective for hydrogen storage and release reaction using a liquid organic hydrogen carrier having an N-heterocycle is selectively alumina (specifically, mesoporous alumina ) A catalyst dispersed and supported on a support is used.

Hydrogenation/dehydrogenation catalyst

According to one embodiment of the present disclosure, hydrogenation/dehydrogenation reaction, specifically, storage/release of hydrogen through a hydrogenation/dehydrogenation reaction of a liquid organic hydrogen carrier, more specifically a liquid organic hydrogen carrier having an N-containing heterocycle. A catalyst suitable for (ie, a heterogeneous catalyst) is provided.

In this regard, the hydrogenation/dehydrogenation catalyst is a supported catalyst that largely contains palladium as an active metal on a mesoporous alumina-containing support. At this time, palladium is dispersed and supported on the support in the form of fine metal particles, that is, metal clusters, and may be in the form of crystallites. In this regard, palladium in the catalyst may be in an oxidized state or a reduced state, and more specifically, may be a reduced state or an elemental state. In this case, the reduced state may be implemented by reducing the catalyst in an oxidized state (calcined state).

As described above, in order to provide high reaction activity and long-term stability as a hydrogenation/dehydrogenation catalyst, it is required to support palladium (in crystalline form) having a (111) facet in an appropriate amount. In this regard, the supported amount of palladium may range from, for example, about 0.1 to 10% by weight, specifically about 0.5 to 5% by weight, and more specifically about 1 to 3% by weight, based on the element. However, the amount of palladium in the catalyst may be insufficient to quantify the amount of palladium having a (111) facet.

To this end, the relative ratio of the CO adsorption bands by CO-DRIFT (chemisorbed diffuse reflectance infrared fourier transform) spectrum analysis may be used. Specifically, the relative adsorption band intensity ratio expressed as (C+D)/B based on the peak of the CO adsorption band is, for example, about 1.5 to 10, specifically about 2 to 6, More specifically, it may range from about 3 to 4. ^{Here, B is the CO adsorption band peak at 1978 cm -1} multiple bonded to the Pd (100) plane, C is the CO adsorption band peak at ^{1918 cm -1} single bonded to the Pd (111) plane, and D Is the CO adsorption band peak at ^{1860 cm -1} triple bonded to the Pd (111) plane.

The range of the above-described (C+D)/B ratio is an index indicating the relative amount of Pd (111) plane that effectively acts on the hydrogenation/dehydrogenation reaction for a liquid organic hydrogen carrier having an N-heterocycle. It may be advantageous to be set within a range.

Although the present invention is not bound by a particular theory, the basis for effective action of palladium having a Pd (111) plane on the hydrogenation/dehydrogenation of liquid organic hydrogen carriers having an N-heterocycle can be explained as follows:

The Pd (111) plane has a structure in which Pd atoms are tightly packed, and the hydrogen (H) atom and Pd atom of the liquid organic hydrogen carrier molecule having an N-heterocycle are close to each other to form a geometric structure suitable for preferential adsorption, Compared with less packed Pd faces (eg, Pd (100) faces and Pd (110) faces), a faster dehydrogenation reaction can be induced.

As an example, when H ₁₂ -NEC is used as a liquid organic hydrogen carrier, three Pd surfaces such as Pd (100), Pd (110) and Pd (111) are used to study the structural sensitivity of the dehydrogenation reaction by DFT. As a result, in terms of geometry, the initial adsorption can be seen as equivalent to removing the first two hydrogen atoms from the five-point ring adjacent to the N-heteroatom. At this time, since the Pd (100) plane and the Pd (110) plane have a less packed structure than the Pd (111) plane, the remaining two hydrogen atoms are removed from the ring consisting of five vertices in the liquid organic hydrogen carrier molecule. For this, an additional adsorption step is required. As a result, it is judged that the Pd (111) plane can exhibit higher dehydrogenation activity than other Pd planes.

According to an exemplary embodiment, the palladium particle size in the catalyst may range from about 3.5 nm or less, specifically about 0.5 to 3 nm, and more specifically about 1 to 2.8 nm. When the active metal cluster size is too large, the reaction efficiency decreases due to the decrease in the dispersion degree of the metal supported on the composite support, while when the active metal cluster size is too small, the number of active spots to be adsorbed by the reactant decreases and the frequency of adsorption decreases. As much as this can be caused, it may be advantageous to be adjusted in the above range, but may be slightly changed in the above numerical range depending on reaction conditions and the like. In addition, the dispersion degree of the active metal (measured by the CO-chemical adsorption method) may be, for example, at least about 30%, specifically about 35 to 50%, and more specifically about 40 to 45%.

Meanwhile, in this embodiment, the support of the hydrogenation/dehydrogenation catalyst may be an alumina-containing support. Such alumina, as mesoporous alumina, can typically exhibit ink-bottle or channel-type pore (pore) connectivity, and thus relatively high surface area, high packing density, thermal stability, and physical stability in the hydrogenation/dehydrogenation reaction. It can show strength and regeneration.

According to an exemplary embodiment, the BET specific surface area of the support in the catalyst may be, for example, at least about 300 m2/g, specifically about 320 to 400 m2/g, more specifically about 350 to 380 m2/g. have. This specific surface area is significantly higher than that of the gamma-alumina support used in various chemical reactions in the related art, and is suitable for effectively dispersing palladium having a Pd(111) surface.

According to an exemplary embodiment, the pore volume of the support in the catalyst may range from, for example, about 0.4 to 0.55 cm 3 /g, specifically about 0.42 to 0.5 cm 3 /g, more specifically about 0.45 to 0.49 cm 3 /g. . In addition, the pore size (size) of the support in the catalyst may range from, for example, about 3 to 4.5 nm, specifically about 3.5 to 4.3 nm, and more specifically about 3.8 to 4.1 nm.

According to an exemplary embodiment, the shape of the catalyst is not particularly limited, but considering the stability and efficiency of the catalyst, it may be applied in a structure such as a ball shape, a tablet shape, a granule shape, and a pellet shape. At this time, the size (or diameter) of the catalyst may be, for example, about 0.1 to 10 mm, specifically about 0.5 to 5 mm, and more specifically about 1 to 3 mm, but this may be understood for illustrative purposes. .

As such, the catalyst according to the present embodiment is in a form in which the (111) plane of palladium, an active metal, is selectively and effectively supported on a mesoporous alumina-containing support having a large specific surface area. Since the palladium (Pd) atom is supported on the (111) plane, the liquid organohydrogen carrier compound having an N-heterocycle can be adsorbed in a thermodynamically stable state, and at this time, the Pd atom close to the hydrogen atom is in the Pd (111) plane. It is noteworthy that it provides improved dehydrogenation activity.

Preparation of catalyst

According to another embodiment of the present disclosure, there is provided a method for preparing a catalyst having good hydrogenation/dehydrogenation activity for a liquid organohydrogen carrier, specifically an N-containing heterocyclic liquid organohydrogen carrier, as described above.

In this regard, the present inventors have found that it is difficult to selectively form Pd (111) planes in the catalyst by the impregnation method most typically applied in the production of a metal/alumina supported catalyst in the prior art. In consideration of this, a specific surface (orientation) through a simple method of reacting the palladium precursor and the alumina precursor in a single step without using a solvent, and subsequently performing heat treatment (specifically, heat treatment in an oxygen-containing atmosphere). By uniformly dispersing palladium having a on an alumina-containing support, a catalyst capable of carrying out hydrogenation/dehydrogenation reactions, particularly dehydrogenation reactions, with high conversion and selectivity can be prepared.

Moreover, in order to improve the long-term stability of the 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 a metal oxide-based support, an alumina support is known to be effective in terms of catalytic stability because it is basically strongly bonded with a precursor of an active metal. However, in the case of gamma-alumina, which is widely used as an alumina support by impregnation method, Pd It is difficult to provide properties (especially, specific surface area) for effectively dispersing palladium having a (111) face. In addition, even when palladium is supported by the impregnation method using mesoporous alumina having a relatively high specific surface area as a support, there is a limitation in dramatically increasing the specific surface area of the final catalyst due to the characteristics of the manufacturing method. It is difficult to selectively support only palladium having a Pd (111) plane.

According to one embodiment, first, a precursor mixture including at least one alumina precursor, at least one palladium precursor, and a base component is prepared.

Illustratively, the precursor mixture may mix three components at the same time. Alternatively, it may be prepared by first mixing two of the three ingredients and then adding the remaining ingredients. For example, the alumina precursor and the base component may be first mixed, and then a palladium precursor may be added and mixed.

According to an exemplary embodiment, the palladium precursor may be an organic or inorganic acid salt of palladium, a complex, or a combination thereof. Examples of such a palladium precursor may be at least one selected from the group consisting of palladium acetate, palladium nitrate, palladium sulfate, palladium carbonate, palladium hydroxide, palladium halide, and hydrates thereof, which may be understood as illustrative. More typically, palladium precursors in the form of palladium nitrate and/or hydrates thereof may be used.

In addition, the alumina precursor may be an organic or inorganic acid salt of aluminum, an alkoxide, a complex, or a combination thereof, and representative examples thereof are aluminum acetate, aluminum acetylacetonate, aluminum bromide, aluminum t-butoxide, aluminum sec-butoxide , Aluminum pentoxide, aluminum ethoxide, aluminum isoproxide, aluminum tributoxide, aluminum chloride, aluminum bromide, aluminum iodide, aluminum sulfate, aluminum nitrate, and at least one selected from the group consisting of a hydrate thereof. . More specifically, aluminum nitrate and/or a hydrate thereof may be used.

According to an exemplary embodiment, the base component is ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium oxalate, ammonium sulfate, ammonium hydroxide, ammonium nitrate, lithium hydroxide, sodium hardoxide, potassium hydroxide , It may be at least one selected from the group consisting of calcium hydroxide and magnesium hydroxide, and more specifically, ammonium bicarbonate may be used. The reason for using a base is that, in forming a metal oxide from an acidic metal precursor, a neutralization reaction occurs in which a metal salt and water are formed while the base component is added and precipitated.

According to an exemplary embodiment, the molar ratio of the palladium precursor/base component in the precursor mixture may range from, for example, about 0.0001 to 0.1, specifically about 0.002 to 0.05, more specifically about 0.008 to 0.02, and the base When the amount of used is too small or too large, the time required to form the gel, which is the final step of synthesis, becomes shorter or longer, and as a result, it is difficult to form a metal oxide having a desired crystal phase, and furthermore, it is difficult to form a metal oxide having a specific surface area and a metal It may be advantageous to appropriately control within the above-described range as it may affect catalyst properties such as dispersion degree, particle size, and the like. However, the range can be changed according to the type of precursor and base.

In addition, the mixing ratio between the palladium precursor and the alumina precursor in the precursor mixture may be determined according to the amount of palladium supported on the alumina support of the catalyst described above.

According to one embodiment, the reaction may be performed while applying external energy in the process of preparing the above-described precursor mixture or after forming a physical mixture thereof. At this time, it should be noted that unlike a conventional loading method such as an impregnation method, only the reaction between the solid-state precursors is performed without using a solvent. In the case of adopting a solid-phase reaction in the catalyst synthesis step, metal precursors are compared to the method of fixing or attaching the metal precursor to the pores of the support by making a liquid metal precursor solution and then contacting it with a porous inorganic metal oxide support (specifically, alumina). It is possible to induce a stronger interaction between (a precursor of an active metal and a precursor of an inorganic metal oxide (aluminum)). As a result, the agglomeration (or aggregation) phenomenon of the metal particles is significantly reduced even after the solid phase reaction.

The solvent-free production method according to this embodiment is a hydrogenation/dehydrogenation reaction of a liquid organohydrogen carrier having an N-containing heterocycle on a mesoporous alumina support having a high specific surface area, in particular, palladium on a specific orientation surface, which is particularly effective for dehydrogenation reactions, Specifically, it is possible to support palladium on (111) cotton with a high degree of dispersion, and furthermore, good catalytic activity (i.e., long-term stability) even under continuous repetition of hydrogenation/dehydrogenation reaction due to improved interaction between metal components constituting the catalyst. ) Can be maintained as a point that is clearly distinguished from the existing method (especially, the impregnation method).

According to one embodiment, the external energy applied to perform the solid-phase reaction between the three components described above may be typically physical or mechanical energy, for example, in the form of friction energy such as milling, grinding or grinding, specifically a ball mill. Although it may be friction energy due to, this is exemplary, and any external energy may be used without particular limitation as long as it can induce a reaction between the palladium precursor and the alumina precursor under a solvent-free condition.

According to an exemplary embodiment, the solid-phase reaction under the application of external energy may be performed for, for example, about 5 to 40 minutes, specifically about 10 to 30 minutes, and more specifically about 13 to 25 minutes. At this time, as the solid-phase reaction between the precursors proceeds, a catalyst solid in a gel form may be formed. Specifically, in the process of solid-phase reaction or mixing under the application of external energy (for example, friction energy), the base component is partially or completely decomposed, and when the metal precursor is in the form of a metal salt, it is combined with a metal cation. The anion or anion species that have been formed may be substituted with a hydroxide group. In the process, gases derived from precursors and bases can be released. For example, when ammonium bicarbonate is used as a base, a large amount of carbon dioxide may be mainly generated. As the reaction proceeds under gas evolution, the precursors form a gel, and then the hardness increases by solidification and then undergoes a process of forming a gel again, and as a result, a catalyst solid in the form of a gel can be obtained.

Then, a step of converting the catalyst solid in the form of a gel into an oxide by heat treatment, that is, calcining, in an oxygen-containing atmosphere (specifically, an air atmosphere) may be performed on the catalyst solid formed from the solid-phase reaction. Through this heat treatment step, nanoparticles (or crystals) of palladium may be evenly dispersed in the pores (pores) of the mesoporous alumina support. At this time, palladium crystals (or nanoparticles) having a (111) facet may be mainly supported on a mesoporous alumina-containing support, and the palladium crystals or particles are typically in an oxide state by heat treatment in an oxygen-atmosphere. It can be supported. In addition, through heat treatment in an oxygen-atmosphere, a porous and pore-to-pore connection structure may be developed, and a mesoporous alumina with enhanced stability may be formed.

According to an exemplary embodiment, the heat treatment may be performed under a temperature condition of, for example, about 300 to 800°C, specifically about 350 to 750°C, and more specifically about 400 to 700°C. At this time, the temperature increase rate may be adjusted within the range of, for example, about 1 to 10° C./min, specifically about 1.5 to 5° C./min, and more specifically about 2 to 4° C./min. Illustratively, the heat treatment time may be adjusted within a range of, for example, about 1 to 24 hours, specifically about 3 to 10 hours, and more specifically about 4 to 6 hours.

On the other hand, after the heat treatment in an oxygen-atmosphere, a reduction treatment may be additionally performed in order to activate the catalyst for the hydrogenation/dehydrogenation reaction, which is the final use. According to an exemplary embodiment, as the gas for reduction treatment, hydrogen, carbon monoxide, methane, or a combination thereof may be used, and more typically, reduction treatment may be performed under a hydrogen atmosphere.

As an example, the reduction treatment temperature may be, for example, in the range of about 250 to 500 °C (specifically about 300 to 450 °C, more specifically about 320 to 400 °C). At this time, the rate of temperature increase may be, for example, in the range of about 1 to 10 °C/min, specifically about 4 to 6 °C/min. In addition, the reduction treatment time may be determined within a range of, for example, about 1 to 10 hours, specifically about 2 to 5 hours. In addition, the pressure during the reduction treatment (partial pressure of the reducing gas) is not particularly limited, for example, in the range of about 1 to 5 bar, specifically about 1.5 to 4 bar, and more specifically about 2 to 3 bar Can be The above-described reduction treatment conditions may be understood by way of example, and are not necessarily limited thereto. Through such reduction treatment, it is possible to prepare a catalyst in which palladium, that is, an active metal on the Pd (111) surface, is supported in a reduced form (ie, elemental form) on a mesoporous alumina support.

Hydrogenation/dehydrogenation reaction (storage and release of hydrogen) using a liquid organic hydrogen carrier compound having an N-containing heterocycle

According to an embodiment of the present disclosure, it is possible to use a liquid organic hydrogen carrier (LOHC) as the hydrogen storage material, and such a liquid organic hydrogen carrier system consists of hydrogen-lean and hydrogen-rich organic compounds, which are repeated catalysts. Hydrogen can be stored and released by appropriate hydrogenation and dehydrogenation cycles. In particular, by handling hydrogen in the form of a liquid organic hydrogen carrier, existing fuel facilities can be utilized, and unlike hydrogen storage by hydrogenation of gas (e.g., carbon dioxide or nitrogen), hydrogen can be released from the liquid organic hydrogen carrier. In this case, pure hydrogen can be produced after condensation of a carrier compound having a relatively high boiling point.

In this regard, according to one embodiment, it is possible to use a liquid organic hydrogen carrier having an N-containing heterocycle as the liquid organic hydrogen carrier, and such a compound is an N-containing heterocyclic compound having at least one conjugated bond in the molecule. Can be Since these liquid organic hydrogen carrier compounds have the property of lowering the enthalpy of dehydrogenation by the presence of nitrogen (N) atoms in the ring, they store hydrogen compared to conventional liquid organic hydrogen carriers such as aromatic hydrocarbon compounds such as dibenzyltoluene. It has the advantage of easy (or absorption of hydrogen) and/or release (desorption of hydrogen), and easy transport and reaction because the same phase is maintained in a liquid phase even after dehydrogenation and hydrogenation reactions.

According to one embodiment, the liquid organic hydrogen carrier having an N-containing heterocycle may be at least one selected from compounds represented by the following general formulas 1 to 6:

[General Formula 1]

[General Formula 2]

[General Formula 3]

[General Formula 4]

[General Formula 5]

[General Formula 6]

In the above formula, R, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ . Each of R ₈ , R ₉ and R ₁₀ is hydrogen or a C ₁ to C ₆ alkyl group, X is -(CHR ₁₁ ) _n -(n is an integer of 1 to 3, R ₁₁ is H, OH, or C ₁ To C ₆ is an alkyl group), and Y is CH or N.

The exemplified hydrogen carrier compound may exhibit a melting point in the range of, for example, about 100° C. or less, specifically about 0 to 80° C., more specifically about 10 to 60° C., and can maintain a liquid phase at room temperature, and The boiling point may be in the range of at least about 380°C, specifically about 130 to 350°C, and more specifically about 180 to 300°C. Due to such melting point and boiling point characteristics, it has the advantage of omitting the use of a separate solvent and/or additive for improving reactivity in a hydrogen storage and release system using a liquid organic hydrogen carrier.

As described above, the catalyst supported on the mesoporous alumina support using palladium having a (111) plane as an active metal stores hydrogen in a manner that repeats the hydrogenation/dehydrogenation cycle of a liquid organic hydrogen carrier having an N-containing heterocycle. It is suitable for carrying out the release.

The hydrogen storage and release method according to an exemplary embodiment may involve contacting a compound having an N-containing heterocycle (specifically in a liquid form) with the catalyst described above in a reaction system. At this time, the ratio (M/R) of the active metal (Pd)/N-containing heterocyclic compound in the catalyst is, for example, about 0.01 to 1 mol%, specifically about 0.05 to 0.7 mol%, more specifically about 0.1 to It may be in the range of 0.5 mol%. In this regard, when the M/R ratio is too low or high, there is a limit to lowering the activation energy of the reaction, so that insufficient reaction activity may be exhibited, whereas when the M/R ratio is too high, the solid catalyst is considerably higher than the liquid reactant in terms of volume. Increases, resulting in the formation of an excessive slurry state. As a result, since stirring becomes difficult during the reaction process and diffusion limitation is generated, a phenomenon in which the catalytic active point cannot be sufficiently utilized may be caused, so it may be advantageous to appropriately control within the above-described range. However, the ratio can be changed depending on the type of hydrogen storage compound used.

In this regard, a hydrogenation reaction can be performed to store hydrogen in the hydrogen storage material, and the hydrogenation reaction temperature is, for example, about 50 to 250°C, specifically about 80 to 220°C, more specifically about 100 to It may be in the range of 190°C. In addition, the hydrogenation reaction pressure may be, for example, about 5 to 100 bar, specifically about 20 to 80 bar, and more specifically about 30 to 70 bar. In addition, the hydrogenation reaction time is not particularly limited, but may be, for example, in the range of about 0.5 to 24 hours, specifically about 1 to 12 hours.

According to an exemplary embodiment, the hydrogenation reaction efficiency (the number of moles of hydrogen stored by the actual hydrogenation reaction compared to the number of moles of hydrogen that can theoretically be stored in 1 mole of the dehydrogenation reaction product) by using the aforementioned Pd(111)/mesoporous alumina catalyst. Is, for example, at least about 50%, specifically at least about 60%, and more specifically at least about 70%. In addition, the selectivity for the hydrogenation product corresponding to the hydrogen storage compound may be, for example, at least about 60%, specifically at least about 70%, and more specifically at least about 80%.

On the other hand, a dehydrogenation reaction may be performed to release hydrogen from the hydrogen storage material.Since this dehydrogenation reaction is an endothermic reaction, the reaction temperature is higher than that of the hydrogenation reaction (exothermic reaction) of the same hydrogen storage material (for example, It may be carried out at a temperature range of about 50 to 100° C., specifically about 60 to 80° C. higher than the hydrogenation reaction temperature. According to an exemplary embodiment, the dehydrogenation reaction temperature may range from, for example, about 100 to 350°C, specifically about 150 to 320°C, and more specifically about 180 to 290°C. Unlike the reaction temperature, the dehydrogenation reaction pressure may be at a lower level than the pressure condition of the hydrogenation reaction, for example, about 1 to 10 bar, specifically about 1 to 5 bar, and more specifically, it may be a normal pressure condition. In addition, the dehydrogenation reaction time is not particularly limited, but may be, for example, in the range of about 0.5 to 24 hours, specifically about 2 to 12 hours.

According to an exemplary embodiment, the efficiency of the dehydrogenation reaction (defined as the number of moles of hydrogen produced by the actual dehydrogenation reaction relative to the number of moles of hydrogen that can be theoretically released from 1 mole of the hydrogenation reactant) by using the above-described catalyst, For example, it may be at least about 50%, specifically at least about 75%, and more specifically at least about 80%.

On the other hand, according to one embodiment, the hydrogenation / dehydrogenation reaction may be carried out using a known reactor known in the art, such as a batch reactor, a continuous reactor, a semi-continuous reactor, and in particular, a liquid organic hydrogen carrier, particularly a relatively high boiling point. In the case of a liquid organohydrogen carrier compound having, as much as hydrogenation and dehydrogenation reactions can occur in a liquid phase, a stirrer may be provided in the reactor. According to an exemplary embodiment, the reaction may be carried out in a fixed bed reactor using a particulate catalyst.

As described above, according to the present embodiment, it is suitable for carrying out both hydrogenation/dehydrogenation reactions of the N-containing heterocyclic compound even with a single catalyst. Alternatively, the catalyst may be replaced with one of the two types of catalysts used in conventional hydrogen storage and release reactions. In particular, the hydrogenation/dehydrogenation catalyst used in this embodiment is an active metal that effectively acts on the dehydrogenation reaction for the liquid organic hydrogen carrier, and palladium having a (111) face is dispersed and supported on the mesoporous alumina support with a high degree of dispersion. have. Moreover, it has a high specific surface area compared to the palladium/alumina catalyst prepared by a conventional impregnation method (a support preparation step and a support step two-step production process), and even mesoporous alumina is used as a support instead of gamma-alumina. It can form a larger specific surface area than the catalyst prepared by the precipitation method. Therefore, compared to the existing catalyst, hydrogenation/dehydrogenation reaction efficiency is good, and long-term reaction stability is excellent. In addition, in the case of adopting a single-step solid-phase method to prepare a palladium/mesoporous alumina catalyst having a high (111) side of hydrogenation/dehydrogenation activity, it is more convenient and advantageous in terms of cost reduction.

The present invention may be more clearly understood by the following examples, and the following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

Example

In Examples and Comparative Examples, the prepared catalyst was performed according to the following analysis method.

-Analysis of specific surface area, pore volume and pore size

For analysis of the specific surface area and pore size of the support (BET, Micromeritics 3Flex), a 100 mg sample was pretreated at 200°C and vacuum for 2 hours, and then liquid nitrogen was injected and analyzed by adsorption and desorption at 77 K. I did.

-Measurement of metal dispersion (COchemisorption)

To measure the degree of dispersion, it was confirmed through the COchemisorption BELCATB instrument (BEL Japan, Inc.). Specifically, 70 mg of a sample was added and high purity H ₂ gas was injected at 30 sccm as a pretreatment process, and reduction was performed in-situ for 3 hours at 350° C. (heating rate 5° C./min), and then the He carrier gas was The temperature was lowered to 35° C. while flowing, and then increased to 350° C. and adsorbed while increasing the partial pressure of 10% CO. By physically desorbing this again, the degree of dispersion of the metal was measured through the amount of CO adsorbed on the metal.

-Transmission electron microscope (TEM, HAADFSTEM) analysis

After dropping a sample dispersed in methanol on a Cu grid specimen using a transmission electron microscope (TEM, HAADFSTEM, JEOL, TEM2100F), it was dried in a vacuum oven at 60° C. for 20 hours or more, and the size of metal particles supported on the support was measured. It was measured.

-Pd metal particle crystal state analysis (CODRIFT)

For the analysis of the CO-DRIFT (chemisorbed diffuse reflectance infrared fourier transform) spectrum, the Nicolet 6700 FT-IR (Harrick Praying Mantis high temperature reaction chamber) was used, and 30 mg of the sample was added to 5% H _{2 at 350 °C for 3 hours before the measurement.} /Ar (100 cm ³ min ^-1 ) The reduction was performed in an atmosphere. After reduction, the temperature was lowered to 50° C., and then exchanged with Ar gas to remove the substance physically adsorbed on the sample surface. IR analysis was performed by flowing 5% CO/Ar (50 cm ³ min ^-1 ) and exposing the sample for 30 min, and then desorbing the adsorbed CO through evacuation for 30 min.

Example 1

The method for preparing the catalyst according to this embodiment is as shown in FIG. 1.

Referring to the drawing, first Al precursor (Al(NO ₃ ) ₃ ·9H ₂ O) 22.291g, ammonium bicarbonate (NH ₄ HCO ₃ ) 14.235g, and Pd metal precursor ((Pd(NO ₃ ) ₂ ·6H ₂ O) 0.0784 g was added to a mortar without a solvent at a time and mixed physically. After that, frictional heat was applied by continuously stirring the physical mixture for 20 minutes. A gel was formed while generating an amount of CO _2. Specifically, after 10 minutes of mixing, the gel was solidified and cured again in the form of a gel, and after 6 minutes, a gel was formed and softened.

Then, the gel solid mixed for 20 minutes was put in a crucible, and calcined for 5 hours under a heat treatment temperature condition of 600° C. (heating rate: 2° C./min). After calcination, a reduction treatment using hydrogen was performed (350° C., 5° C./min, 3 hours), and the reaction activity was prepared for the reduction-treated catalyst (the palladium/mesoporous alumina catalyst prepared according to the example was M1PdA. And calcination temperature together). At this time, the content of palladium in all catalysts was fixed at 1% by weight in order to prepare catalyst activity based on the characteristics of the supported metal and the support.

Comparative example

-Preparation of palladium/gamma-alumina catalyst by impregnation method

A palladium-supported catalyst using a commercial γ-Al ₂ O _{3 as a support was prepared.} Specifically, γ-Al ₂ O ₃ (gA) 1% by weight Pd metal precursor solution to 2 g (gA) (Pd (NO ₃ ) ₂ · 6H ₂ O 75 mg, and 1.3 ml of distilled water are uniformly mixed) Was physically supported through an impregnation method ^{, dried in a 100°} C. oven, put into a crucible, and calcined for 5 hours (600° C., 2° C./min). Thereafter, hydrogen reduction treatment (350 ^o C, 3 hours, temperature increase rate 5 ^o C/min) was performed, and finally 1Pd/gA catalyst was obtained, and the calcination temperature was also included. At this time, the content of palladium in all catalysts was fixed at 1% by weight in order to prepare catalyst activity based on the characteristics of the supported metal and the support.

-Preparation of palladium/mesoporous-alumina catalyst by impregnation method

_{First, the mesoporous Al 2} O ₃ (MA) synthesized by the following method was used:

In mortar, Al(NO ₃ ) ₃ ·9H ₂ O and NH ₄ HCO ₃ were mixed at a molar ratio of 1: 3 and completely pulverized with a mortar at room temperature, and the pulverization process was maintained for 20 minutes. The obtained precursor was directly calcined at 600° C. for 5 hours (heating rate: 2° C./min _{) to obtain Al 2} O ₃ (mA).

A 1 wt% Pd metal precursor solution ( _{75 mg of Pd(NO 3} ) ₂ ·6H ₂ O and 1.3 ml of distilled water is uniformly mixed) in _{2 g of mesoporous Al 2} O ₃ (MA) synthesized by the above method through an impregnation method. Physically supported ^{, dried in a 100 °} C oven, put in a crucible and calcined for 5 hours (600 °C, 2 °C/min). Thereafter, hydrogen reduction treatment (350 ^o C, 3 hours, temperature increase rate 5 ^o C/min) was performed, and finally 1Pd/MA catalyst was obtained, and the calcination temperature was also included. At this time, the content of palladium in all catalysts was fixed at 1% by weight in order to prepare catalyst activity based on the characteristics of the supported metal and the support.

Catalyst analysis

The properties of each of the catalyst (Pd content: 1% by weight) and the support subjected to calcination and reduction are shown in Tables 1 and 2 below.

Catalyst (support) Specific surface area (m ² /g) Pore volume (cm 3 /g) Pore size (nm) Pd dispersion degree (%) Pd particle size (nm) gAl ₂ O ₃ 271 0.59 6.4 - - 1Pd/gA 600 5h 264.0 0.59 6.5 25.1 4.4 1Pd/MA 600 5h 316.0 0.43 4.1 34.0 3.3 MA 600 5h 420.0 0.57 4.1 - - M1PdA 600 5h 359.0 0.49 4.1 42.4 2.6

-The pore volume is calculated from the desorption branch of the BET isothermal curve.

-Pd particle size was measured from CO pulsed chemisorption experiment

According to the above table, the specific surface area of the catalyst (support) prepared according to the Example (solid phase method) is 420 m ² /g, which is about 150 m ² /g compared to commercial gamma alumina (271 m ^{2 /g).} The degree increased, and accordingly, the pore volume and pore size also changed. In addition, compared to the catalyst prepared according to the comparative example (1Pd/gA 600 5h and 1Pd/MA 600 5h), the support specific surface area value (359 m ² /g) of the catalyst prepared according to the example (M1PdA 600 5h) was significantly It can be seen that it has increased.

In addition, when comparing the degree of dispersion of Pd in the catalyst according to the comparative examples (1Pd/gA 600 5h and 1Pd/MA 600 5h) and the examples (M1PdA 600 5h), the dispersion degree of Pd differs according to the specific surface area of alumina. It was confirmed that there is (Pd content: 1% by weight). Specifically, in the case of Pd/gA 600 5h, the Pd dispersion degree was 25.1%, and the Pd particle size was 4.4 nm. In the case of Pd/MA 600 5h, since it was impregnated with porous alumina with a large specific surface area, the dispersion degree increased to 34%, whereas the Pd particle size was 3.3 nm, which was smaller than that of gamma-alumina. It was the level.

On the other hand, the Pd particle size of MPdA 600 5h, the catalyst according to the Example, was 2.6 nm, and Pd particles having a significantly smaller size than the catalyst according to the Comparative Example were supported, and accordingly, the Pd dispersion was also the highest at 42.4%.

Referring to FIG. 2, a specific surface area was analyzed by measuring pore size and volume by performing _{an N 2} physical adsorption test on each of the calcined catalyst and the support. 2A and 2B, the calcined catalyst MPdOA has a complex of H2 and H3 hysteresis loops showing typical mesoporous (pore size 4.1 nm) with ink-bottle or channel-like pore connectivity. Type IV isotherms are shown. The BET specific surface area and pore volume of MPdOA and PdO/MA were at a lower level compared to MA, which was found by the standard reflection of PdO (101) and (112) planes (confirmed by JCPDS #43-1024). It can be seen as a result of existence. MPdOA showed higher porosity compared to PdO/MA, which is believed to be due to the formation of a uniform solid solution by the one-step method adopted in Examples. On the other hand, the 1Pd/gA catalyst exhibited a low specific surface area and pore volume, and a high pore size compared to other catalysts, MPdOA and PdO/MA, because of the high crystallinity of the gamma phase in alumina.

Analysis of catalyst properties according to calcination temperature

The catalyst was prepared through the same procedure except that the calcination (heat treatment) temperature was changed to 400°C, 500°C, and 700°C in the Examples, and the change of the support in the analyzed catalyst was heat-treated at 600°C. Together with it is shown in Table 2 below.

catalyst Specific surface area (m ² /g) Pore volume (cm 3 /g) Pore size (nm) M1PdA 400 5h 532.0 0.59 3.5 M1PdA 500 5h 418.0 0.55 3.9 M1PdA 600 5h 359.0 0.49 4.1 M1PdA 700 5h 282.0 0.49 5.2

According to the above table, the specific surface area of the catalyst changed according to the calcination temperature, and among the four catalysts (M1PdA 400 5h, M1PdA 500 5h, M1PdA 600 5h and M1PdA 700 5h), the specific surface area of the catalyst calcined at 400 °C was the most. It was measured as high. In this regard, the alumina support in the catalyst has a function of dispersing palladium, which is an expensive active metal, widely using as wide a specific surface area as possible, thereby improving physical properties such as thermal and mechanical stability that are difficult to obtain with palladium alone. During the calcination process, as the calcination temperature increased, the specific surface area ^{decreased from about 532 m 2} /g to 282 m ² /g. However, in the process of mixing the aluminum precursor, the palladium precursor, and the base component (ammonium bicarbonate) during the catalyst production, CO ₂ and NO ₂ are generated. In addition, the remaining ammonium nitrate is completely Can be removed. Therefore, in this embodiment, it was determined that the optimum calcination temperature is approximately 500 to 600°C.

Analysis of catalyst properties according to calcination time

The results are shown in Table 3 below by comparing the properties of the catalyst according to the calcination time under the same temperature (600° C.) and temperature increase rate (2° C./min) conditions.

catalyst Specific surface area (m ² /g) Pore volume (cm 3 /g) Pore size (nm) M1PdA 600 3h 352.0 0.50 4.3 M1PdA 600 5h 359.0 0.49 4.1 M1PdA 600 1h 433.0 0.53 3.7

According to the above table, the specific surface area of the support in the catalyst decreased in the calcination time of 3 hours compared to the calcination time of 1 hour, which can be seen as the effect of the pore volume decrease as the pore size increased from 3.7 nm to 4.3 nm. However, in terms of the thermal stability of the catalyst, since the calcination time can secure long-term stability at a certain level or more, it is judged that it is optimal to control it to 5 hours.

Analysis of catalyst properties according to Pd content

A catalyst was prepared according to the same procedure as in Examples, except that the Pd content in the catalyst was changed, and the results are shown in Table 4 below.

catalyst Specific surface area (m ² /g) Pore volume (cm 3 /g) Pore size (nm) M1PdA 600 1h 433.0 0.53 3.7 M0.5PdA 600 1h 459.0 0.57 3.8 M3PdA 600 1h 427.0 0.50 3.6 M5PdA 600 1h 416.0 0.48 3.5

According to the above table, as the content of palladium increases, the specific surface area (from 459 m2/g to 416 m2/g), pore volume (from 0.57 cm3/g to 0.48 cm3/g), and pore size (from 3.8 nm to 3.5 nm) It was found to decrease.

Evaluation of dehydrogenation activity according to catalyst's Pd dispersion and particle size

For each of the catalysts prepared according to Examples and Comparative Examples, the dehydrogenation activity was measured according to the following procedure.

_{Dehydrogenation of H 12} -MBP was performed in a batch reactor (volume: 90 cm 3) for the reduced catalyst. _{In this experiment, 7.3 mmol of H 12} -MBP was added dropwise to the catalyst previously loaded on the bottom of the reactor vessel. At this time, the catalyst weight was changed to obtain a desired metal-to-reactant (M/R) ratio. Prior to the reaction, the reactor was purged for 10 minutes to remove internal moisture and oxygen. Then, the reaction mixture was heated to a desired temperature by heating the reaction mixture at a heating rate of 18°C/min using a commercial thermal medium oil. The volume of hydrogen released during the reaction was monitored by the volume of water transferred in the glass burette.

After completion of the reaction, the reactor was cooled to room temperature, and the reaction mixture was diluted with acetone (20 cm 3) and filtered through a syringe filter (0.1 μm). An aliquot of this solution was mixed with Nonane, a GC calibration solvent, and then analyzed by a Youngling YL6500 gas chromatograph (GC) equipped with an FID detector and an HP-5 column (30 m × 0.32 mm × 0.25 μm).

The analysis results are shown in Tables 5 and 6 and FIGS. 3 and 4 below.

catalyst Pd dispersion degree (%) Pd particle size (nm) Reaction efficiency (%) 1Pd/gA 600 5h 25.1 4.4 48.7 1Pd/MA 600 5h 34.0 3.3 60.6 M1PdA 600 5h 42.4 2.6 70.1

Reactant Reactant name Catalyst name M/R (%) Temperature (℃) Reaction time (h) Reaction efficiency (%)

H ₁₀ -quinolin M1PdA_600 5h 0.1 250 4 62.9 1Pd/gA_600 5h 0.1 250 4 47.8

H ₁₂ -MBP M1PdA_600 5h 0.1 250 4 70.1 1Pd/gA_600 5h 0.1 250 4 49.8

H ₁₀ -MNLH M1PdA_600 5h 0.1 250 4 75.4 1Pd/gA_600 5h 0.1 250 4 60.2

H ₁₂ -NEC M1PdA_600 5h 0.1 250 4 58.8 1Pd/gA_600 5h 0.1 250 4 40.2

H ₈ -indole ¹ M1PdA_600 5h 0.1 180 4 30.5 1Pd/gA_600 5h 0.1 180 4 20.0

H ₈ -MID M1PdA_600 5h 0.6 250 4 99.8 1Pd/gA_600 5h 0.6 250 4 68.6

¹ : When H ₈ -indole (octahydroindole) is used as a reactant, the boiling point is 222.7°C, so the test is performed at 180°C.

According to the above table, as described above, the dehydrogenation reaction efficiency was also different due to the difference in the Pd particle size (size) and the dispersion degree, as described above, 70.1% in MPdA 600 5h, 60.6% in Pd/MA 600 5h, and Pd It is noteworthy that at /gA 600 5h, the reaction efficiency was 48.7%.

In this regard, _{when the MPdA catalyst is used in the dehydrogenation reaction of H 12} -MBP, the temperature is increased to 270°C (0.1 mol% M/R), or when more catalyst is used (for example, 0.4 mol % M/R; 250° C.), it can be seen that the dehydrogenation efficiency exceeds 90% (see FIG. 3). For reference, the enthalpy of dehydrogenation of the N-containing heterocyclic compound is lower than that of the corresponding homocyclic compound, for example, H ₁₂ -MBP is 67.3 kJ/mol _H2 , H ₁₂ -NEC is 55 kJ/mol _H2 , octahydroindole is 57.5 kJ/mol _H2 , decahydroquinoline is 61.9 kJ/mol _H2 , and perhydro 2-methyl-6-(n-methylbenzyl)pyridine is 66.7 kJ/mol _H2 .

In addition, in _{the dehydrogenation reaction of H 12} -MBP, the intrinsic activity of each of MPdA 600 5h, Pd/MA 600 5h and Pd/gA 600 5h was measured, and the results are shown in Table 7 below (250°C, 0.1 mol% M/R, 4 hours).

catalyst First order rate constant
(min ^-1 g _cat ^-1 ) TOF(min ^-1 ) TON MPdA 0.031 98.9 23745 Pd/MA 0.020 78.8 18904 Pd/gA 0.014 75.0 18007

According to the above table, it can be seen that the MPdA catalyst exhibits a higher first order rate constant and TOF than the Pd/MA catalyst and the Pd/gA catalyst.

On the other hand, the activity test was performed over different times (0.5 hours, 1 hour and 4 hours) under conditions of 250° C. and 0.4 mol% M/R, and the results of gas chromatography analysis are shown in FIG. 4 (left: MPdA , Right: Pd/gA).

Referring to the figure, in the gas chromatogram of the product mixture carried out over an MPdA catalyst over 0.5 hours, a GC peak corresponding to _{H 0} -MBP along with the GC peak of unconverted _{H 12 -MBP was detected, 41.9} % H ₁₂ -MBP and 96.8% H ₀ -MBP selectivity were obtained. In the presence of the MPdA catalyst, as the reaction proceeded for up to 4 hours, the H ₁₂ -MBP conversion rate increased to a level of 94%, and the _{selectivity of H 0} -MBP was maintained around 97%. On the other hand, _{the GC peak of the intermediate product H 6} -MBP was observed in all product mixtures obtained from the Pd/gA catalyst. As the reaction proceeded up to 4 hours, _{the conversion rate of H 12} -MBP increased from 30.9% to 83.2%, and _{the selectivity for H 0} -MBP increased from 36.7% to 64.9%. According to the results of GC chromatography analysis of the product, it was confirmed that when a considerable catalyst was used in the comparative example, more intermediate products were present than the desired product after the reaction. These results suggest that the MPdA catalyst exhibits good selectivity in the dehydrogenation reaction of _{H 12 -MBP.}

As such, the above-described difference in activity is due to the crystal form of the Pd particles supported on the alumina support, and the catalyst preparation method has a significant influence on the conversion rate of the reactant and the selectivity of the product, and as a result, the final hydrogen generation efficiency (dehydrogenation Reaction activity).

Analysis of changes in physical properties according to the crystal form of Pd particles

The effect of the crystal form of Pd particles on the dehydrogenation reaction was evaluated through CO adsorption, and the results are shown in FIG. 5.

Referring to the figure, the CO-chemisorbent DRFT spectrum of the MPdA catalyst exhibits spectral features that are clearly distinct from those in Pd/MA and Pd/gA. Specifically, a total of 5 IR bands can be distinguished on the spectrum, and when the CO adsorption form is linear, CO adsorption peaks (A ₁ and A ₂ ) were observed at ^{2000 cm 1 or more.} In addition, in the case of a complex form rather than a one-to-one bond of Pd and CO, CO adsorption bands (B, C, and D) ^{of 2,000 cm 1 or less were observed. In the latter region, MPdA exhibited stronger bands at 1918 cm 1} and 1860 cm ¹ compared to Pd/gA and Pd/MA, and these bands each showed a single bond of Pd particles on the Pd (111) facet. This is due to the isolated-bridged CO adsorption and the tri-coordinated CO adsorption.

On the other hand, Pd/gA and Pd/MA ^{showed a stronger band at 1978 cm 1} than in MPdA, which is a multiple bond adsorbed on a structurally open crystal plane such as (100) or (110). -bridged) It is believed to be caused by CO. In this regard, it is noteworthy that the dehydrogenation reaction mainly proceeds on the thermodynamically stable Pd(111) surface of the Pd nanoparticles supported on alumina due to the tightly-packed Pd atoms.

In addition, MPdA showed ^{a maximum peak at 2064 cm 1} (A ₂ ), whereas Pd/MA and Pd/gA showed a band indicating linearly bound CO at ^{2086 cm 1} (A _{1) in contrast.} . This means that in the case of MPdA, the (111) plane, which is preferentially exposed to the reactant, is well dispersed at a high density.

Meanwhile, in order to clarify the correlation between the (111) plane and the dehydrogenation activity, the relative ratio of the adsorption bands was calculated based on the respective CO bands adsorbed in CO-DRIFT, and the results are shown in Table 8 below.

catalyst Adsorption band strength (a.u.) (C+D)/B
ratio B
(1978 cm ^-1 ) ^a C
(1918 cm ^-1 ) ^b D
(1860 cm ^-1 ) ^c M1PdA 600 5h 0.0039 0.0092 0.0056 3.8 1Pd/gA 600 5h 0.0115 0.0076 0.0039 1.0 1Pd/MA 600 5h 0.0041 0.0058 0.0039 2.4

^a : B (1978 cm ^-1 ) is the compressed-bridged CO adsorption band peak on the Pd (100) plane,

^b : C (1918 cm ^-1 ) is a single-bridged CO adsorption band peak on the Pd (111) plane,

^c : D (1860 cm ^-1 ) is the peak of the CO adsorption band tri-coordinated to the Pd (111) plane.

As shown in the table above, the relative adsorption band intensity ratio (i.e., (C+D)/B) in MPdA (3.8) was higher than that of Pd/MA (2.4) and Pd/gA (1.0), and , This suggests that the Pd (111) plane is mainly present in MPdA.

In addition, according to the HRTEM picture (left of Fig. 6) of the MPdA, Pd/MA and Pd/gA catalysts, the Pd particles are in a well protected state by the alumina layer, whereas Pd/MA and Pd/gA have such protection. It can be seen that the condition is lacking.

Referring to the SAED (selected area electron diffraction) pattern of FIG. 6 (right side of FIG. 6), two diffraction patterns corresponding to Pd(111) and Pd(200) appear in the case of Pd/MA and Pd/gA. In the case of the SAED pattern of Pd(111) showing d-spacing of 0.224 nm, it can be seen that it is captured around all positions of MPdA. From this, it can be seen that MPdA has a greater number of Pd (111) planes in the same region. As such, in the light of the SAED pattern analysis, Pd (111) planes exist in the order of MPdA> Pd/MA> Pd/gA, which is consistent with the CO-DRIFT results performed by pressure.

As a result, it is believed that the reason why the MPdA catalyst exhibits higher dehydrogenation ability is because there are a large number of Pd (111) planes compared to Pd/MA and Pd/gA.

Long-term stability evaluation of catalyst

As a long-term stability evaluation of the catalyst according to each of the Examples and Comparative Examples, a dehydrogenation test was performed, and the results are shown in FIGS. 7 to 10.

As shown in FIG. 7, the particle size of Pd in the catalyst was measured by HAADF-STEM (high angle annular dark field scanning transmission electron microscopy) photographs (FIGS. 7A and 7B each was a new catalyst (at 350° C. for 3 hours). Hydrogen reduction treatment) and the catalyst used ( _{representing the catalyst after H 12} -MBP dehydrogenation reaction at 250° C. for 4 hours)), and the average size was calculated from the particle size distribution chart shown in FIG. 8 (FIGS. 8A, 8B and FIG. 8c each indicates MPdA.Pd/MA. and Pd/gA, the new catalyst is shown on the left, and the used catalyst (5 cycles) is shown on the right).

According to Figure 7a, the average size of Pd particles in the new catalyst was MPdA (3.4 nm), Pd/MA (4.4 nm) and Pd/gA (5.3 nm). On the other hand, the average size of Pd particles in the catalyst after 5 cycles was MPdA (4.0 nm), Pd/MA (9.6 nm), and Pd/gA (11.5 nm). ) Was significantly lower than that of the catalysts of Comparative Example (Pd/MA and Pd/gA), and showed stable metal dispersion. This indicates that MPdA is excellent in characteristics (stability) of keeping the size of Pd particles small even if the hydrogen storage/release reaction process is repeated.

In addition, Figure 9 is a HRTEM and SAED (selected area electron diffraction) photographs of the catalyst used. According to the above drawing, it can be seen that the Pd particles in the new MPdA catalyst are well protected by the alumina layer (see FIG. 6) and are maintained in the used catalyst. On the other hand, the catalyst according to the comparative example, that is, Pd/MA and Pd/gA, not only has a relatively low degree of protection even in the initial state, but also the state of lack of protection in the catalyst used can be clearly confirmed.

Hydrogen storage/release tests were performed with 5 cycles for the catalysts according to Examples and Comparative Examples, and in particular _{, changes in the dehydrogenation activity of H 8} -MID including H ₁₂ -MBP were measured and shown in FIGS. 10A and 10B. . At this time, _{the hydrogen emission test of H 12} -MBP was performed under conditions of 250° C. and 0.4 mol% M/R. As shown in FIG. 10A, the dehydrogenation efficiency of each of Pd/gA and Pd/MA was 49.0 at the fifth cycle. % And 69.1%, while the initial efficiency of MPdA was maintained over the course of 5 cycles.

The hydrogen release test of H ₈ -MID (hydrogen storage capacity: 5.75% by weight) was conducted under conditions of 250℃ and 0.6 mol% M/R, and in the case of MPdA, the hydrogen release capacity was very stable as 5.70% by weight in the course of 5 cycles. Was. On the other hand, in the case of Pd/gA and Pd/MA, _{similarly to the hydrogen release test of H 12} -MBP, the stability was decreased compared to MPdA.

Evaluation of dehydrogenation activity according to the shape of the catalyst

In order to be commercially applied to catalytic reactions, a catalyst in a pellet form rather than a powder form is advantageous in terms of operation. In consideration of this, it was evaluated whether or not the catalyst (MPdA) according to the Example could be maintained in the form of pellets, and the results are shown in FIG. 11.

To this end, a powder sample was pressed with a PIKE CrushIR Hydraulic Press at 0.5 US ton using an in-house die to prepare pellets having a diameter of 3 mm and a length of 5 mm.

As shown in the figure, the pellet-type MPdA exhibited a hydrogen generation curve similar to that of the powder form, except that the dehydrogenation rate was slightly lower initially. In addition, as a result of successively performing three consecutive cycles, similar hydrogen generation results could be obtained. In this regard, it is believed that the slightly lower hydrogen generation rate at the initial stage is due to the diffusion limitation resulting from the pellet structure.

When the product mixture was analyzed by GC, the hydrogen yield was estimated to be 66.6%, which was at most 4% lower than that of the powder sample. Accordingly, it was confirmed that when the MPdA catalyst was prepared in the form of pellets, it not only maintained the dehydrogenation activity comparable to that of the powder form, but also maintained the same level in terms of long-term stability.

Simple modifications or changes of the present invention can be easily used by those of ordinary skill in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (18)

A hydrogenation step of storing hydrogen on a liquid organic hydrogen carrier having an N-heterocycle 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,
Mesoporous alumina as a support, and
Containing palladium having a (111) facet as an active metal in the support,
As the hydrogenation step and the dehydrogenation step are alternately performed, hydrogen is stored or hydrogen is released,
The palladium particle size in the catalyst is 3.5 nm or less, and
The catalyst has a relative adsorption band intensity ratio expressed as (C+D)/B based on the CO adsorption band peak by CO-DRIFT (chemisorbed diffuse reflectance infrared fourier transform) spectrum analysis from 1.5 to ^{A range of 10, where B is the CO adsorption band peak at 1978 cm -1} multiple bonded to the Pd (100) side, and C is the CO adsorption band peak at ^{1918 cm -1} single bonded to the Pd (111) side. And D is the CO adsorption band peak at ^{1860 cm -1} triple bonded to the Pd (111) plane). The method of claim 1, wherein the liquid organohydrogen carrier is a compound of a heterocyclic structure containing an N element having at least one conjugated bond, wherein the ring structure comprises C3 to C20. The method of claim 2, wherein the liquid organic hydrogen carrier is at least one selected from compounds represented by the following general formulas 1 to 6:
[General Formula 1]

[General Formula 2]

[General Formula 3]

[General Formula 4]

[General Formula 5]

[General Formula 6]

In the above formula, R, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ . Each of R ₈ , R ₉ and R ₁₀ is hydrogen or a C ₁ to C ₆ alkyl group, X is -(CHR ₁₁ ) _n -(n is an integer of 1 to 3, R ₁₁ is H, OH, or C ₁ To C ₆ is an alkyl group), and Y is CH or N. The method of claim 1, wherein the catalyst exhibits a BET specific surface area of at least 300 m 2 /g. delete The method of claim 1, wherein the content of palladium in the catalyst is in the range of 0.1 to 10% by weight. delete The method of claim 4, wherein the catalyst has a pore volume in the range of 0.4 to 0.55 cm 3 /g and a pore size in the range of 3 to 4.5 nm. The method of claim 1, wherein the hydrogenation reaction is performed at 50 to 250°C for 0.5 to 24 hours, while the dehydrogenation reaction is performed at 100 to 350°C for 0.5 to 24 hours. The method of claim 1, wherein the ratio (M/R) of the palladium/N-containing heterocyclic compound in the catalyst is in the range of 0.01 to 1 mol%. a) applying external energy to a mixture containing at least one alumina precursor, at least one palladium precursor, and a base component while performing a solid-phase reaction in the absence of a solvent to form a gel-like catalyst solid; And
b) heat treating the catalyst solid material under an oxygen-containing atmosphere and a temperature condition of 300 to 800° C. to support palladium crystals having (111) facets on mesoporous alumina as a support;
As a method for producing a hydrogenation/dehydrogenation catalyst for reversible conversion of a liquid organic hydrogen carrier having an N-heterocycle, comprising:
The palladium particle size in the catalyst is 3.5 nm or less,
The particle size of the catalyst ranges from 0.1 to 10 mm, and
The catalyst has a relative adsorption band intensity ratio expressed as (C+D)/B based on the CO adsorption band peak by CO-DRIFT (chemisorbed diffuse reflectance infrared fourier transform) spectrum analysis from 1.5 to ^{A range of 10, where B is the CO adsorption band peak at 1978 cm -1} multiple bonded to the Pd (100) side, and C is the CO adsorption band peak at ^{1918 cm -1} single bonded to the Pd (111) side. And D is the CO adsorption band peak at ^{1860 cm -1} triple bonded to the Pd (111) plane). The method according to claim 11, wherein the heat treatment is performed at a heating rate of 1 to 10°C/min. 12. The method of claim 11, further comprising: c) reducing the hydrogenation/dehydrogenation catalyst. The method of claim 11, wherein the palladium precursor is an organic or inorganic acid salt of palladium, a complex, or a combination thereof. The method of claim 11, wherein the alumina precursor is an organic or inorganic acid salt of aluminum, an alkoxide, a complex, or a combination thereof. The method of claim 11, wherein the base component is ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium oxalate, ammonium sulfate, ammonium hydroxide, ammonium nitrate, lithium hydroxide, sodium hardoxide, potassium hydroxide A method, characterized in that at least one selected from the group consisting of side, calcium hydroxide and magnesium hydroxide. The method according to claim 11, wherein the molar ratio of palladium precursor/base component in step a) is in the range of 0.0001 to 0.1. As a catalyst for reversible conversion of the hydrogenation/dehydrogenation reaction of a liquid organic hydrogen carrier having an N-heterocycle,
Mesoporous alumina as a support, and
Palladium having a (111) facet as an active metal on the support;
Including,
The palladium content is 0.1 to 10% by weight, based on the total weight of the catalyst, and
The catalyst is a catalyst exhibiting the following physical properties:
(i) BET specific surface area of at least 300 m2/g, (ii) palladium dispersion of at least 30%, (iii) palladium particle size of 3.5 nm or less, (iv) chemisorbed diffuse reflectance infrared fourier transform (CO-DRIFT) spectrum Based on the CO adsorption band peak by the analysis, the relative adsorption band intensity ratio expressed as (C+D)/B is in the range of 1.5 to 10 (where B is multiplexed on the Pd (100) plane). and CO adsorption band peak in the combined 1978 cm ^-1, C is a Pd (111) and the CO absorption band at 1918 cm ^-1 peak to the single-bonded surface, and D is a bond 3 to Pd (111) surface Is the CO adsorption band peak at 1860 cm ^-1 ), and the pore size of the mesoporous alumina support is in the range of 3 to 4.5 nm.

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