KR20240154811A - Catalyst with improved durability, method for preparing the same, and method for dehydrogenating ammonia using the same - Google Patents

Abstract

The present invention relates to a catalyst having improved durability, a method for producing the same, and a method for dehydrogenating ammonia using the same. The catalyst comprises: a support; a transition metal supported on the support; and hexagonal boron nitride synthesized on the transition metal. The hexagonal boron nitride is synthesized from ammonia borane, and by applying an ammonia borane solution on the transition metal supported on the support and then heat-treating it under an ammonia atmosphere, there is provided a highly commercially available hexagonal boron nitride-based catalyst.

Description

Catalyst with improved durability, method for preparing the same, and method for dehydrogenating ammonia using the same

The present disclosure discloses a catalyst having improved durability, a method for producing the same, and a method for dehydrogenating ammonia using the same.

Ammonia has a hydrogen storage capacity of 17.7% by weight, and at the same time, it is easily liquefied under a relatively weak pressure of 8 bar, making it a key material that can solve the problems of hydrogen storage and transportation. When ammonia is decomposed at high temperatures, hydrogen can be produced, which is used as fuel for energy generation devices such as fuel cells and hydrogen turbines. To produce hydrogen from ammonia, an ammonia decomposition reactor and, if necessary, an adsorption process to remove unreacted ammonia are applied. The fields and scales that require hydrogen are gradually increasing, and in response, technology that can process large quantities of hydrogen from ammonia is required. In particular, transition metals such as Ru, Ni, Fe, Co, and Rh can be applied as catalysts in the reactor where the ammonia decomposition reaction is performed to lower the activation energy of the reaction.

In terms of the shape of the catalyst, catalysts in the shape of beads, pellets, monoliths, honeycombs, etc., rather than powders that cause pressure drops, can be practically applied to ammonia decomposition or synthesis processes. Recently, it has been reported that a Ru/h-BN catalyst using hexagonal boron nitride as a support is effective in ammonia decomposition activity due to the heteroepitaxy effect (metal particles grow while maintaining continuity with the lattice of the support) and the effect of increasing electron density. However, since this hexagonal boron nitride support is a powder, it has a disadvantage in that it is difficult to apply it to an actual large-scale ammonia decomposition reaction system. In particular, not only is it difficult to pelletize hexagonal boron nitride powder, but the method of physically coating the hexagonal boron nitride powder shows low adhesion, which reduces the compatibility of hexagonal boron nitride-based catalysts. Therefore, it is necessary to develop technology for hexagonal boron nitride-based catalysts to improve the compatibility of catalysts.

KR 2021-0028712 A

In one aspect, the present disclosure aims to provide a catalyst having improved durability.

In another aspect, the present disclosure aims to provide a method for producing a catalyst having improved durability.

In another aspect, the present disclosure aims at providing a method for synthesizing hexagonal boron nitride on transition metal particles supported on a support.

In another aspect, the present disclosure aims to provide a method for dehydrogenating ammonia using the catalyst having improved durability.

In one aspect, the present disclosure provides a catalyst having improved durability, comprising: a support; a transition metal supported on the support; and hexagonal boron nitride synthesized on the transition metal.

In an exemplary embodiment, the support may be at least one selected from the group consisting of carbon, silica, silicon carbide, silicon nitride, alumina, magnesium oxide, magnesium aluminate, calcium oxide, calcium aluminate, zeolite, zirconia, titania, ceria, lanthania, yttria, and rare earth oxides.

In an exemplary embodiment, the transition metal may be at least one selected from the group consisting of Mo, Ni, Fe, Co, Cu, Pd, Pt, Ru, Rh, Au, and Ir.

In an exemplary embodiment, the hexagonal boron nitride may be synthesized from ammonia borane.

In an exemplary embodiment, the hexagonal boron nitride may be synthesized by applying an ammonia borane solution on a transition metal supported on the support and then heat-treating it under an ammonia atmosphere.

In an exemplary embodiment, the ammonia borane solution may contain ammonia borane in a polar aprotic solvent.

In an exemplary embodiment, the polar aprotic solvent may include one or more selected from tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), dioxane (DXN), diethyleneglycoldimethylether (Diglyme), dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide (DMA), and hexamethyl phosphoramide (HMPA).

In an exemplary embodiment, the polar aprotic solvent may have a boiling point of 100° C. or less.

In an exemplary embodiment, the molar concentration of the ammonia borane solution may be greater than or equal to 0.2 mol/L.

In an exemplary embodiment, the mL unit volume of the polar aprotic solvent contained in the ammonia borane solution may be no more than 0.5 times the total g unit weight of the support and the transition metal.

In an exemplary embodiment, the hexagonal boron nitride may be included in less than 0.5 wt% based on the total weight of the support and the transition metal.

In another aspect, the present disclosure provides a method for preparing a catalyst having improved durability, the method comprising: (1) preparing a catalyst comprising a support and a transition metal supported on the support; (2) preparing an ammonia borane solution by adding ammonia borane to a polar aprotic solvent; and (3) applying the ammonia borane solution onto the prepared catalyst.

In an exemplary embodiment, the method may further include a step of applying an ammonia borane solution in step (3) and then heat-treating the catalyst under an ammonia atmosphere.

In an exemplary embodiment, the heat treatment may be performed at 600 to 700° C.

In an exemplary embodiment, the step (1) may be a process of obtaining a catalyst by impregnating a support with a transition metal precursor solution and calcining the support impregnated with the transition metal precursor solution.

In another aspect, the present disclosure provides a method for dehydrogenating ammonia using the catalyst with improved durability, the method comprising the steps of: (1) charging the catalyst with improved durability into a reactor and reducing it under a hydrogen atmosphere; and (2) injecting ammonia into the reactor and performing a heat treatment.

In one aspect, the technology disclosed in the present disclosure has the effect of providing a catalyst with improved durability.

In another aspect, the technology disclosed in the present disclosure has the effect of providing a method for producing a catalyst having improved durability.

In another aspect, the technology disclosed in the present disclosure has the effect of providing a method for synthesizing hexagonal boron nitride on transition metal particles supported on a support. The method uses ammonia borane as a synthesis material for hexagonal boron nitride, coats polyborazylene on transition metal particles supported on a support at room temperature, and then performs an additional ammonia heat treatment process to finally synthesize hexagonal boron nitride.

Hexagonal boron nitride powder is difficult to pelletize, and the method of physically coating the hexagonal boron nitride powder shows low adhesion, so that existing hexagonal boron nitride-based catalysts have the disadvantage of low compatibility. The present disclosure provides an effect of significantly improving the compatibility of hexagonal boron nitride-based catalysts by chemically coating boron nitride on the metal particles of the catalyst.

In another aspect, the technology disclosed in the present disclosure has the effect of providing a method for dehydrogenating ammonia using a catalyst with improved durability.

FIG. 1 is a flow chart illustrating a process for synthesizing hexagonal boron nitride on a catalyst according to one embodiment.
Figure 2 shows the results of room temperature coating of polyborazylene on a catalyst according to one embodiment. The left photo is of catalyst No. 3, and the right photo is of catalyst No. 9.
FIG. 3 illustrates a room temperature coating process of polyborazylene on a catalyst in the preparation of catalyst No. 9 according to one embodiment.
Figure 4 shows the results of coating hexagonal boron nitride on a catalyst according to one embodiment. The left photo is a catalyst of No. 1, and the right photo is a catalyst of No. 9.
Figure 5 shows the results of coating hexagonal boron nitride on a catalyst according to one embodiment. The photo on the left is catalyst No. 6, and the photo on the right is catalyst No. 7.
Figure 6 shows the XPS analysis results of a catalyst surface according to one embodiment.
Figure 7 shows the XPS analysis results of the catalyst surface of No. 7 according to one embodiment.
Figure 8 shows the XPS analysis results of the catalyst surface of No. 9 according to one embodiment.
Figure 9 shows the results of an ammonia decomposition reaction using a catalyst according to one embodiment.
Figure 10 shows the results of an ammonia decomposition reaction using a catalyst according to one embodiment.
Figure 11 shows the results of scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) analysis of the catalyst of No. 2 according to a comparative example.
Figure 12 shows the results of TEM-EDS mapping analysis for the catalyst No. 9 according to one embodiment.
Figure 13 shows the results of XRD analysis for a catalyst according to one embodiment.
Figure 14 shows the results of visually confirming the dispersion of an ammonia borane solution used in the manufacture of a catalyst according to one embodiment.
Figure 15 shows the results of coating hexagonal boron nitride on a catalyst according to one embodiment.

Hereinafter, the present disclosure is described in detail.

In one aspect, the present disclosure provides a catalyst having improved durability, comprising: a support; a transition metal supported on the support; and hexagonal boron nitride synthesized on the transition metal.

In an exemplary embodiment, the catalyst having improved durability may be one in which hexagonal boron nitride is grown directly on transition metal particles of a pre-synthesized catalyst.

In an exemplary embodiment, the catalyst with improved durability and/or the synthesized catalyst may have a bead, pellet, monolith or honeycomb form. Accordingly, there is an effect of providing a highly compatible catalyst.

In the catalyst according to the present disclosure, hexagonal boron nitride causes particle deformation of the metal, which provides an effect of offsetting deactivation due to agglomeration of the metal, thereby improving the durability of the catalyst.

In an exemplary embodiment, the catalyst may be a catalyst for an ammonia decomposition reaction.

In an exemplary embodiment, the catalyst may be a catalyst for the dehydrogenation reaction of ammonia.

In an exemplary embodiment, the catalyst may have improved durability for ammonia decomposition reaction and/or ammonia dehydrogenation reaction.

The catalyst according to the present disclosure not only has high ammonia decomposition reaction activity and/or ammonia dehydrogenation reaction activity, but also has the effect of providing high ammonia decomposition reaction activity and/or ammonia dehydrogenation reaction activity without deterioration of catalytic performance even over a long period of time.

In an exemplary embodiment, the support may be at least one selected from the group consisting of carbon, silica, silicon carbide, silicon nitride, alumina, magnesium oxide, magnesium aluminate, calcium oxide, calcium aluminate, zeolite, zirconia, titania, and rare earth oxides.

In an exemplary embodiment, the rare earth element may be at least one selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.

In an exemplary embodiment, the rare earth oxide may be one or more of ceria, lanthania, yttria, and gadolium oxide.

In an exemplary embodiment, the transition metal may be at least one selected from the group consisting of Mo, Ni, Fe, Co, Cu, Pd, Pt, Ru, Rh, Au, and Ir.

In an exemplary embodiment, the support may be alumina and the transition metal may be Ru or Ni.

In an exemplary embodiment, the transition metal may be supported in an amount of 10 wt% or less based on the total weight of the support and the transition metal.

In an exemplary embodiment, the hexagonal boron nitride may be synthesized from ammonia borane (H ₃ NBH ₃ ).

In an exemplary embodiment, the hexagonal boron nitride may be synthesized by applying an ammonia borane solution on a transition metal supported on the support and then heat-treating under an ammonia atmosphere. The ammonia borane solution is applied at room temperature and pressure.

In an exemplary embodiment, the ammonia borane solution may contain ammonia borane in a polar aprotic solvent for inducing a dehydrogenation reaction of ammonia borane.

In an exemplary embodiment, the ammonia borane solution may be ammonia borane dispersed by ultrasonic treatment. The high dispersion process by ultrasonic treatment has the effect of further improving the uniformity of the hexagonal boron nitride coating film.

In an exemplary embodiment, the polar aprotic solvent may include one or more selected from tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), dioxane (DXN), diethyleneglycoldimethylether (Diglyme), dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide (DMA), and hexamethyl phosphoramide (HMPA).

In the catalyst according to the present disclosure, the evaporation time of the solvent may vary depending on the boiling point and vapor pressure characteristics of the polar aprotic solvent itself during the room temperature coating process of a nitrogen-boron compound, such as polyborazylene, and therefore it may be preferable to use a polar aprotic solvent having a relatively low boiling point. For example, the boiling point of Diglyme is 162° C., which is higher than the boiling point (53° C.) of borazine, a substance that can change into hexagonal boron nitride among the products, and thus it may take a relatively long time to evaporate the solvent. Therefore, it may be preferable that the polar aprotic solvent is, for example, tetrahydrofuran (THF).

In an exemplary embodiment, the polar aprotic solvent may have a boiling point of 100 °C or less, 90 °C or less, 80 °C or less, 70 °C or less, 60 °C or less, or 50 °C or less. In another exemplary embodiment, the polar aprotic solvent may preferably have a boiling point of 40 to 80 °C, or 45 to 75 °C, or 50 to 70 °C.

In an exemplary embodiment, the molar concentration of the ammonia borane solution may be at least 0.2 mol/L. In another exemplary embodiment, the molar concentration of the ammonia borane solution may be at least 0.2 mol/L, at least 0.3 mol/L, at least 0.4 mol/L, or at least 0.5 mol/L, and at most 2.0 mol/L, at most 1.9 mol/L, at most 1.8 mol/L, at most 1.7 mol/L, at most 1.6 mol/L, at most 1.5 mol/L, at most 1.4 mol/L, at most 1.3 mol/L, at most 1.2 mol/L, at most 1.1 mol/L, at most 1.0 mol/L, at most 0.9 mol/L, at most 0.8 mol/L, at most 0.7 mol/L, or at most 0.6 mol/L. For example, in forming a uniform coating film without an additional solvent evaporation or removal process, the molar concentration of the ammonia borane solution may be preferably 0.3 to 0.7 mol/L or 0.4 to 0.6 mol/L.

In an exemplary embodiment, the mL unit volume of the polar aprotic solvent contained in the ammonia borane solution may be 0.5 times or less, 0.01 to 0.5 times, 0.05 to 0.5 times, 0.05 to 0.3 times, or 0.1 to 0.3 times the total g unit weight of the support and the transition metal. Accordingly, it provides the effect of forming a uniform coating film without an additional solvent evaporation or removal process.

In an exemplary embodiment, the hexagonal boron nitride may be included in an amount of less than 0.5 wt% based on the total weight of the support and the transition metal. If the content of hexagonal boron nitride in the catalyst according to the present disclosure is high, the catalytic activity may decrease or an uneven coating film may be formed. Therefore, the hexagonal boron nitride may be included in an amount of less than 0.5 wt%, less than or equal to 0.4 wt%, or less than or equal to 0.3 wt%, and preferably in an amount of 0.01 wt% or more, 0.05 wt% or more, 0.1 wt% or more, 0.15 wt% or more, 0.2 wt% or more, 0.25 wt% or more, or 0.3 wt% or more based on the total weight of the support and the transition metal.

In an exemplary embodiment, the catalyst with improved durability can be used in an ammonia dehydrogenation reaction and/or an ammonia synthesis reaction. In the case of a catalyst using hexagonal boron nitride as a support (e.g., Ru/h-BN), there is a disadvantage that the hexagonal boron nitride support is in the form of powder, making it difficult to apply to a large-scale ammonia decomposition reaction system, and in the case of a catalyst in which a metal is loaded onto a support physically coated with boron nitride (e.g., Ru/BN-paint/θ-Al ₂ O ₃ ), there is no durability enhancing effect, whereas a catalyst in which hexagonal boron nitride is formed on a transition metal supported on a support according to the present disclosure (e.g., BN-K-Ru/θ-Al ₂ O ₃ ) provides not only excellent ammonia decomposition reaction activity but also a durability enhancing effect.

In another aspect, the present disclosure provides a method for preparing a catalyst having improved durability, the method comprising: (1) preparing a catalyst comprising a support and a transition metal supported on the support; (2) preparing an ammonia borane solution by adding ammonia borane to a polar aprotic solvent; and (3) applying the ammonia borane solution onto the prepared catalyst.

In an exemplary embodiment, the method for preparing the catalyst with improved durability may be a method for synthesizing hexagonal boron nitride on a catalyst. In this aspect, the present disclosure provides a method for synthesizing hexagonal boron nitride on a catalyst, the method comprising the steps of: (1) preparing a catalyst including a support and a transition metal supported on the support; (2) preparing an ammonia borane solution by adding ammonia borane to a polar aprotic solvent; and (3) applying the ammonia borane solution on the prepared catalyst. The method can directly grow hexagonal boron nitride on transition metal particles of the catalyst.

The low-temperature synthesis method of hexagonal boron nitride according to the present disclosure comprises using ammonia borane as a synthesis material to coat polyborazylene at room temperature through a selective dehydrogenation reaction on metal particles, and then further heat treating under an ammonia atmosphere to finally synthesize hexagonal boron nitride.

In an exemplary embodiment, the step (3) may be to coat a nitrogen-boron compound, such as borazine or polyborazylene, on the catalyst by applying an ammonia borane solution at room temperature.

In an exemplary embodiment, the method may further include a step of applying an ammonia borane solution in step (3) and then heat-treating the catalyst under an ammonia atmosphere. For example, the method may include applying an ammonia borane solution in step (3) and then heat-treating the catalyst from which the solvent has been evaporated under an ammonia atmosphere to produce a catalyst with improved durability or synthesizing hexagonal boron nitride on the catalyst.

The method for producing a catalyst according to the present disclosure is such that when an ammonia borane solution comes into contact with a transition metal particle of a catalyst, a dehydrogenation reaction occurs to produce polyborazylene, and the solvent evaporates with the heat generated, so that no additional solvent removal process is required. Accordingly, the above-described method may not include a process for evaporating or removing the solvent of the ammonia borane solution, since the ammonia borane solution is immediately evaporated in about 1 second when dropped on the catalyst.

In an exemplary embodiment, the step of heat treating under an ammonia atmosphere may be performed in a dehydrogenation reaction of ammonia. That is, the step of heat treating under an ammonia atmosphere may be performed simultaneously with the dehydrogenation reaction of ammonia. Through the heat treatment process in the dehydrogenation reaction of ammonia, hexagonal boron nitride may be synthesized on the catalyst, and the catalyst on which the hexagonal boron nitride is formed may increase the efficiency of the dehydrogenation reaction of ammonia.

In an exemplary embodiment, the heat treatment may be performed by injecting ammonia gas at a gas hour space velocity (GHSV) of 60,000 mL/g _cat /h or less. In another exemplary embodiment, the heat treatment may be performed by injecting ammonia gas at a gas hour space velocity (GHSV) of 200 mL/min or less. In yet another exemplary embodiment, the heat treatment may be performed by injecting ammonia gas at a gas hour space velocity (GHSV) of 200 mL/min or less based on 0.2 g of catalyst.

In an exemplary embodiment, the heat treatment may be performed at 600° C. or higher, or from 600 to 700° C. The method can induce transformation of metal particles in a reducing atmosphere (including ammonia decomposition or synthesis process) at 600° C. or higher, thereby obtaining an effect of enhancing the activity and/or improving the durability of the catalyst.

In an exemplary embodiment, the heat treatment may be performed for one hour or more.

The method for producing a catalyst according to the present disclosure has the advantage of being able to mass-produce a catalyst based on hexagonal boron nitride with enhanced durability. Compared to the chemical vapor deposition process, which is a conventional coating method, hexagonal boron nitride synthesis is performed at a temperature about 400° C. lower, and since no vacuum device is required, large-scale synthesis is relatively very easy.

In an exemplary embodiment, the step (1) may be a process of obtaining a catalyst by impregnating a support with a transition metal precursor solution and calcining the support impregnated with the transition metal precursor solution.

In an exemplary embodiment, the transition metal precursor may be at least one selected from the group consisting of metal chlorides, metal chlorates, metal acetate compounds, metal halide compounds, metal nitrate compounds, metal hydroxide compounds, metal carbonyl compounds, metal sulfate compounds, and metal fatty acid salt compounds.

In an exemplary embodiment, the transition metal precursor may be a metal nitrate compound or a metal carbonyl chlorate.

In an exemplary embodiment, the firing in step (1) may be performed at 400 to 500°C.

In an exemplary embodiment, the firing in step (1) may be performed in an air atmosphere, an inert gas atmosphere such as nitrogen or argon, a hydrogen atmosphere, or a vacuum atmosphere.

In an exemplary embodiment, in step (3), the ammonia borane solution may be applied onto the catalyst at room temperature and pressure.

In an exemplary embodiment, the mL unit volume of the polar aprotic solvent contained in the ammonia borane solution applied on the catalyst in step (3) may be 0.5 times or less, 0.01 to 0.5 times, 0.05 to 0.5 times, 0.05 to 0.3 times, or 0.1 to 0.3 times the total g unit weight of the support and the transition metal.

In another aspect, the present disclosure provides a method for dehydrogenating ammonia using the catalyst with improved durability, the method comprising the steps of: (1) charging the catalyst with improved durability into a reactor and reducing it under a hydrogen atmosphere; and (2) injecting ammonia into the reactor and performing a heat treatment.

Hereinafter, the present disclosure will be described in more detail through examples. It will be apparent to those skilled in the art that these examples are intended only to illustrate the present disclosure, and that the scope of the present disclosure is not to be construed as being limited by these examples.

Comparative example.

A bead-shaped θ-Al ₂ O ₃ support was impregnated in a methanol solvent containing a ruthenium precursor, Ru ₃ (CO) ₁₂ , and potassium hydroxide, and the solvent was evaporated at a temperature of 45° C. using a vacuum rotary evaporator to prepare a catalyst loaded with 6 wt% ruthenium based on the total weight of the catalyst. The catalyst was calcined at 450° C. under a hydrogen atmosphere for 3 hours to prepare a K-Ru/θ-Al ₂ O ₃ catalyst.

In addition, according to Table 1 below, hexagonal boron nitride ( h -BN) powder was dispersed in a methanol solvent, and then the K-Ru/θ-Al ₂ O ₃ catalyst prepared above was impregnated, and the hexagonal boron nitride was physically coated using a vacuum rotary evaporator to prepare a catalyst No. 1 (BN-K-Ru/θ-Al ₂ O ₃ catalyst).

In addition, paint containing hexagonal boron nitride according to Table 1 below was diluted in water, and then hexagonal boron nitride was physically coated on a bead-shaped θ-Al ₂ O ₃ support. After that, the paint was calcined in air at a temperature of about 100°C for 2 hours to produce a catalyst No. 2 (Ru/BN-paint/θ-Al ₂ O ₃ catalyst) supporting ruthenium as a transition metal.

No. coating
method ingredient catalyst
Weight (g) Catalytic metal content (wt%) h-BN powder
Weight (g) Solvent volume
(mL, name) Catalytic BN
Content (wt%) 1 Physical
method h-BN
Powder 5.0 6 0.5 39
(mL,
Methanol) 10 2 Physical
method h-BN
paint 1.0 6 0.129 17.5 (mL, BN Paint 2.5 + DI water 15) 12.9

In the above Table 1, the catalyst weight refers to the total weight of the support and transition metal, and the catalyst phase content refers to the amount calculated based on the total weight of the support and transition metal.

Example.

Using the K-Ru/θ-Al ₂ O ₃ catalysts manufactured in the comparative examples above, catalysts Nos. 3-13 (BN-K-Ru/θ-Al ₂ O ₃ catalysts) were manufactured by chemically coating hexagonal boron nitride on transition metal particles according to Tables 2 and 3 below. Catalysts Nos. 6-7 were manufactured and used using a Ruthenium(III) nitrosyl nitrate solution as a ruthenium precursor, and catalysts loaded with 2 wt% of ruthenium were manufactured and used.

The above chemical coating method is divided into 1) a room-temperature polyborazylene coating step on a transition metal and 2) an ammonia heat treatment step (see Fig. 1). Nitrogen-boron compounds such as borazine and polyborazylene can be formed on the metal through a dehydrogenation reaction of ammonia borane, and can be converted into boron nitride materials through an additional ammonia heat treatment process. Specifically, a mixture in which ammonia borane (AB) is dispersed in a solvent is applied onto a catalyst to coat the nitrogen-boron compound at room temperature. Thereafter, about 100 mL/min of ammonia was supplied per 0.5 g of the catalyst, and the catalyst was heat-treated at 600°C for 1 hour to manufacture a catalyst chemically coated with hexagonal boron nitride.

No. coating
method ingredient catalyst
Weight (g) Catalytic metal content (wt%) AB
Weight (mg) Solvent volume
(mL, name) Molar concentration of ammonia borane solution (mol/L) Catalytic BN
Content (wt%) 3 Chemical
method Ammonia borane (AB) 0.5 6 64 4
(mL, Diglyme) 0.52 9.3 4 Chemical
method Ammonia borane (AB) 0.5 6 32 1
(mL, THF) 1.04 4.9 5 Chemical
method Ammonia borane (AB) 0.5 6 3.2 0.1
(mL, THF) 1.04 0.5 6 Chemical
method Ammonia borane (AB) 0.5 2 2.56 0.08
(mL, Diglyme) 1.04 0.4 7 Chemical
method Ammonia borane (AB) 0.5 2 1.92 0.06
(mL, Diglyme) 1.04 0.3 8 Chemical
method Ammonia borane (AB) 0.5 6 2.56 0.08
(mL, THF) 1.04 0.4 9 Chemical
method Ammonia borane (AB) 0.5 6 1.92 0.06
(mL, THF) 1.04 0.3

In Table 2 above, the catalyst weight refers to the total weight of the support and transition metal, and the catalyst phase content refers to the amount calculated based on the total weight of the support and transition metal.

No. coating
method ingredient catalyst
Weight (g) Catalytic metal content (wt%) AB
Weight (mg) Solvent volume
(mL, name) Molar concentration of ammonia borane solution (mol/L) Catalytic BN
Content (wt%) 10 Chemical
method Ammonia borane (AB) 0.2 6 0.77 0.192
(mL, THF) 0.13 0.3 11 Chemical
method Ammonia borane (AB) 0.2 6 0.77 0.048
(mL, THF) 0.52 0.3 12 Chemical
method Ammonia borane (AB) 0.2 6 0.77 0.024
(mL, THF) 1.04 0.3 13 Chemical
method Ammonia borane (AB) 0.2 6 0.77 0.016
(mL, THF) 1.56 0.3

In Table 3 above, the catalyst weight refers to the total weight of the support and transition metal, and the catalyst phase content refers to the amount calculated based on the total weight of the support and transition metal.

The catalyst of No. 3 was coated with hexagonal boron nitride so that the BN content in the catalyst phase was 9.3 wt% in an ammonia borane solution having a molar concentration of 0.52 mol/L. The catalysts of Nos. 4-9 were coated with hexagonal boron nitride so that the BN content in the catalyst phase was varied from 0.3 to 4.9 wt% in an ammonia borane solution having a molar concentration of 1.04 mol/L. The catalysts of Nos. 10-13 were coated with hexagonal boron nitride so that the BN content in the catalyst phase was 0.3 wt% in an ammonia borane solution having a molar concentration of 0.13 to 1.56 mol/L.

Figure 2 shows the results of room temperature coating of polyborazylene on a catalyst. The photo on the left is catalyst No. 3, and the photo on the right is catalyst No. 9.

For the catalyst No. 3, it was observed that the nitrogen-boron compound (white), which is a product of the ammonia borane dehydrogenation reaction, and the catalyst (black) existed in layers separated in the diglyme solvent phase. For the catalysts Nos. 4-5, it was also confirmed that the nitrogen-boron compound, which is a product, and the catalyst existed in layers separated in the THF solvent phase.

In the case of the catalyst of No. 9, since the boiling point of the solvent is about 66℃ and has the characteristic of high vapor pressure, when the solution was dropped, the dehydrogenation reaction of ammonia borane progressed and the solvent was vaporized and evaporated simultaneously, and it was observed that only the product was uniformly coated on the catalyst. Fig. 3 shows that when a part of the solution containing 1.92 mg of ammonia borane and 0.06 mL of THF was dropped onto 0.5 g of catalyst, the dehydrogenation reaction of ammonia borane progressed and THF evaporated simultaneously after about 1 second, resulting in the coating of polyborazylene on the surface of the catalyst over time. It is important to evenly disperse the ammonia borane solution and drop it so that it comes into contact with the surface of the catalyst.

Fig. 4 shows the results of coating hexagonal boron nitride on a catalyst. The left photo shows the physically coated catalyst No. 1, and the right photo shows the chemically coated catalyst No. 9. When hexagonal boron nitride powder was dispersed in a methanol solvent and physically coated on the bead-shaped catalyst, an uneven coating film and low adhesion characteristics were observed. On the other hand, the catalyst No. 9 formed a uniform and highly adhesive coating film, confirming that hexagonal boron nitride was synthesized on the bead-shaped catalyst. The catalysts Nos. 6-8 also showed uniform coating films, confirming that hexagonal boron nitride was formed on the bead-shaped catalyst.

Figure 5 shows the catalysts of Nos. 6-7 coated with hexagonal boron nitride on the catalyst using diglyme as a solvent, and it was confirmed that a uniform and highly adhesive coating film was formed, and that the solvent evaporated quickly, so that an additional drying process could be omitted. In addition, it was shown that the catalyst of No. 7 having a lower BN content on the catalyst layer formed a more uniform coating film.

Fig. 6 shows the XPS analysis results of the catalyst surfaces of Nos. 4, 5, 8, and 9. The surface XPS results of the catalysts that were subjected to the dehydrogenation reaction of ammonia borane and then heat-treated (600°C, 1 hour) in the same ammonia atmosphere were analyzed. In the N 1s XPS spectra of the catalysts of Nos. 8 and 9, a peak corresponding to the B-N bond was observed, confirming the formation of boron nitride. Considering that the B-N bond energy value gets closer to 398.4 to 398.0 eV as the crystal of hexagonal boron nitride is used among boron nitride, it was found that the catalyst of No. 9 showed the best hexagonal boron nitride synthesis result.

Figure 7 shows the XPS analysis results of the catalyst surface of No. 7. It was confirmed that a catalyst in which boron nitride was formed was obtained using diglyme as a polar aprotic solvent. It was confirmed that hexagonal boron nitride was well synthesized by showing a peak indicating a B-N bond (B-N bond energy value of 398.96 eV).

Figure 8 shows the XPS analysis results of the catalyst surface of No. 9. After ammonia heat treatment (or 168 hours after ammonia decomposition reaction), B-N bonds were observed in the XPS spectrum corresponding to B 1s and N 1s, confirming the formation of hexagonal boron nitride.

Figure 9 compares the results of ammonia decomposition reaction using K-Ru/θ-Al ₂ O ₃ bead-type catalyst and catalysts Nos. 2 and 9. A quartz reactor with a diameter of 1/2" was filled with a catalyst having a volume of 0.27 mL, ^and an ammonia decomposition reaction was performed at a reaction temperature of 500°C for up to 170 hours under gas hourly space velocity (GHSV) conditions of 21,000 h -1. The slope of the equation was utilized after linearly fitting the change in ammonia conversion rate with respect to time as a criterion for judging the performance deterioration of the catalyst. As a result, in the case of the catalyst without BN coating, a performance degradation of about -1.68% was observed for about 40 hours. On the other hand, the catalyst coated with BN according to the present disclosure showed a positive slope value despite the long-term experiment, confirming that it had improved durability. The catalyst in which BN was physically coated on Al ₂ O ₃ and then Ru was loaded showed a negative slope value as the evaluation time progressed, similar to the catalyst without BN coating.

Figure 10 compares the results of ammonia decomposition reaction using a K-Ru/θ-Al ₂ O ₃ bead-type catalyst and a catalyst coated with BN. Here, the BN-coated catalyst was manufactured using the same method as the catalyst of No. 9, but using a Ruthenium(III) nitrosyl nitrate solution as a ruthenium precursor. After filling a quartz reactor with a diameter of 1/2" with a catalyst volume of 0.27 mL, reduction was performed at a temperature of 550°C for 1 hour at a flow rate of 100 mL/min of _H2 , and ammonia was injected at a flow rate of 93.33 mL/min, and ammonia decomposition reaction was performed at a reaction temperature of 500°C for up to 100 hours under GHSV conditions of 21,000 h ^-1 . As a result, in the case of the catalyst without BN coating, a performance decrease of about -1.96% was observed for about 100 hours. On the other hand, it was confirmed that the catalyst coated with BN according to the present disclosure not only increased the ammonia conversion rate by 2.49% after 100 hours of evaluation, but also increased the catalytic activity by about 6%. Accordingly, it was found that low-temperature chemical BN coating is effective in enhancing the activity and/or durability of the catalyst for a transition metal, such as Ru-based catalyst. In addition, the catalyst by BN coating It was confirmed that the activation and/or durability enhancing effects can be implemented regardless of the type of metal precursor.

Fig. 11 shows the results of scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) analyses of the catalyst of No. 2. As a result, it was observed that Ru nanoparticles were concentrated on the Al ₂ O ₃ support rather than the BN, even though Ru ₃ (CO) ₁₂ (Triruthenium dodecacarbonyl) was used as a Ru precursor considering the hydrophobic nature of BN. Meanwhile, some rod-shaped Ru particles with a thickness of about 20 nm and a length of about 70 nm or triangular Ru particles with a size of about 20 nm were observed at the edge of BN. From the above results, it was found that the Al ₂ O ₃ composite support coated with BN is difficult to utilize as a support for Ru nanoparticles because Ru is not supported on BN.

Fig. 12 shows the results of TEM-EDS mapping analysis for the catalyst of No. 9. From the analysis results showing that B and N are simultaneously distributed in the area where Ru particles are distributed, it was confirmed that hexagonal boron nitride was successfully formed on the catalyst through the low-temperature synthesis method according to the present disclosure.

Fig. 13 shows the results of XRD analysis for the K-Ru/θ-Al ₂ O ₃ bead-type catalyst and catalyst No. 9. In catalyst No. 9, a peak corresponding to h -BN(002) was observed, indicating that hexagonal boron nitride was formed through a low-temperature synthesis method using ammonia borane. In addition, the ICDD card no. for the observed Ru particle peak was confirmed to be 04-018-8034 and 04-015-6086, respectively, and from the results, it was found that the density of the Ru particles increased from 11.854 g/cm ³ to 12.361 g/cm ³ .

Fig. 14 shows the results of visually confirming the dispersion of the ammonia borane solution used in the preparation of catalysts of Nos. 10-13. (a) The photo shows the appearance immediately after mixing ammonia borane and THF, and (b) The photo shows the appearance 1 minute after mixing. Mixing was performed by putting ammonia borane and THF in a glass vial, dispersing them for 10 minutes using an ultrasonic cleaner (AJC-5030, OMAX. Co., Ltd., Korea), and then mixing them for 1 minute using a vortex mixer (VM-10, DAIHAN Scientific, Korea). After mixing, the solution was left for 1 minute, and the glass vial was visually inspected to compare and observe the dispersion stability according to the molar concentration of the ammonia borane solution. It was confirmed that the ammonia borane solution exhibited excellent dispersion stability when the molar concentration was 0.3 to 0.7 mol/L, more specifically, 0.52 mol/L.

Fig. 15 shows the results of comparing and observing the hexagonal boron nitride coating of the catalysts of Nos. 10-13. The catalyst of No. 10 had a small amount of heat generated by the dehydrogenation reaction in the polyborazylene room-temperature coating process, so that the evaporation of the ammonia borane solution did not occur properly, requiring an additional drying process and causing an uneven coating layer during this process. Even when the hexagonal boron nitride was coated so that the BN content in the catalyst was less than 0.5 wt%, it was found that it was difficult to form a uniform and adhesive coating film when the molar concentration of the ammonia borane solution was lower than 0.2 mol/L. On the other hand, the catalysts of Nos. 11-13 were found to form a uniform coating film without an additional drying process. In addition, it was confirmed that the catalyst of No. 11 could further improve the uniformity of the coating film by using an ammonia borane solution with a high molar concentration and dispersion stability.

While the specific parts of the present disclosure have been described in detail, it will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the present disclosure. Accordingly, the substantial scope of the present disclosure is defined by the appended claims and their equivalents.

Claims (15)

support;
A transition metal supported on the support; and
A catalyst having improved durability, comprising hexagonal boron nitride synthesized on the above transition metal.
In paragraph 1,
A catalyst having improved durability, wherein the support is at least one selected from the group consisting of carbon, silica, silicon carbide, silicon nitride, alumina, magnesium oxide, magnesium aluminate, calcium oxide, calcium aluminate, zeolite, zirconia, titania, ceria, lanthania, yttria, and rare earth oxides.
In paragraph 1,
A catalyst having improved durability, wherein the transition metal is at least one selected from the group consisting of Mo, Ni, Fe, Co, Cu, Pd, Pt, Ru, Rh, Au and Ir.
In paragraph 1,
The above hexagonal boron nitride is a catalyst with improved durability, synthesized from ammonia borane.
In paragraph 4,
The above hexagonal boron nitride is a catalyst with improved durability, which is synthesized by applying an ammonia borane solution on a transition metal supported on the support and then heat-treating it under an ammonia atmosphere.
In paragraph 5,
The above ammonia borane solution is a catalyst with improved durability, wherein ammonia borane is contained in a polar aprotic solvent.
In paragraph 6,
A catalyst having improved durability, wherein the polar aprotic solvent comprises at least one selected from tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), dioxane (DXN), diethyleneglycoldimethylether (Diglyme), dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide (DMA), and hexamethyl phosphoramide (HMPA).
In paragraph 6,
The above polar aprotic solvent is a catalyst with improved durability having a boiling point of 100°C or less.
In paragraph 5,
A catalyst with improved durability, wherein the molar concentration of the ammonia borane solution is 0.2 mol/L or more.
In paragraph 6,
A catalyst with improved durability, wherein the mL unit volume of the polar aprotic solvent contained in the ammonia borane solution is 0.5 times or less relative to the total g unit weight of the support and the transition metal.
In paragraph 1,
A catalyst having improved durability, wherein the hexagonal boron nitride is contained in an amount of less than 0.5 wt% based on the total weight of the support and the transition metal.
A method for producing a catalyst with improved durability according to any one of claims 1 to 11, said method comprising:
(1) A step of preparing a catalyst including a support and a transition metal supported on the support;
(2) a step of preparing an ammonia borane solution by adding ammonia borane to a polar aprotic solvent; and
(3) A method for producing a catalyst with improved durability, comprising the step of applying an ammonia borane solution onto the prepared catalyst.
In Article 12,
A method for producing a catalyst with improved durability, wherein the method further comprises a step of applying an ammonia borane solution in step (3) and then heat-treating the catalyst in an ammonia atmosphere.
In Article 13,
A method for producing a catalyst with improved durability, wherein the above heat treatment is performed at 600 to 700°C.
A method for dehydrogenating ammonia using a catalyst having improved durability according to any one of claims 1 to 11, wherein the method
(1) A step of charging a catalyst with improved durability according to any one of claims 1 to 11 into a reactor and then reducing it under a hydrogen atmosphere; and
(2) A method for dehydrogenating ammonia using a catalyst with improved durability, comprising the step of injecting ammonia into the reactor and performing heat treatment.