KR102467320B1 - A hydrogen generation catalyst comprising a nickel-aluminum intermetallic compound and the method for producing the same - Google Patents

Abstract

In the present specification, a nickel-based structure; and a nickel-aluminum intermetallic compound, wherein the nickel-aluminum intermetallic compound includes at least one alloy phase of NiAl ₃ , Ni ₂ Al ₃ , NiAl, Ni ₃ Al, and Ni, and has pores on the surface of the catalyst. A hydrogen evolution catalyst having a porous structure is provided.

Description

Hydrogen generation catalyst comprising nickel-aluminum intermetallic compound and method for producing the same

Disclosed herein is a hydrogen generation catalyst comprising a nickel-aluminum intermetallic compound and a method for preparing the same.

Precious metals (Pt, Ru, Pd, Rh) have high activity in various hydrogen generation reactions (ammonia decomposition, sodium borohydride hydrolysis, electrochemical water decomposition), but are expensive, so research to replace them with cheaper metals is in progress Nickel, cobalt, iron, and molybdenum are inexpensive compared to noble metals and are known as reactive metals. (e.g. nickel and ruthenium price comparison ($14/kg _Ni vs. $7,909/kg _Ru as of 2019). However, these metals have lower intrinsic activity than noble metals, which results in a porous nature on the surface of the material. can be improved by giving

Aluminum alloying/dealloying process can be applied as a method to make the surface of nickel porous As such, it is widely applied.

On the other hand, existing nickel-aluminum alloy manufacturing methods can be largely divided into two methods: a method for manufacturing alloy powder and a method for coating an alloy layer on a structure, depending on the purpose. These two methods have the following problems.

i) alloy powder manufacturing process

Existing methods for manufacturing alloy powder are mainly cast-and-crush process, rapid solidification, and mechanical alloying with ball-milling process. Each of these processes has advantages and disadvantages. A high temperature at which both metals can be melted is required, or a hydrogen gas atmosphere is required to prevent oxidation of the metal during the process. In addition, a cost-consuming grinding process is additionally required to make the alloy obtained in the form of a block into a powder form. In addition, there is a disadvantage in that it is difficult to control the nickel-aluminum alloy phase due to the inherent characteristics of the material in the process of melting and cooling. In addition, it is a problem of the prior art that the size distribution of the alloy phase powder produced is wide.

ii) Structure alloy layer coating process

It is a common aluminizing technology to apply aluminide coating by applying a pack cementation process to structures (eg turbine blades) that require high temperature oxidation resistance. This pack cementation process requires a high temperature of at least 800°C and a hydrogen atmosphere to prevent oxidation. In addition, since aluminum powder with a melting point of 660°C melts during the process, the non-uniformity of the coating layer can be intensified. As a result, through this process, an alloy phase having a relatively high content of Ni, such as Ni ₃ Al and NiAl, is formed with a thickness of tens to hundreds of μm. When this process is applied to powder or a thin nickel support, there is a problem in that the shape cannot be maintained due to the sintering effect. For example, if the existing method is applied to nickel foam with a strut wall thickness of 20 um or less, the entire structure may change to NiAl ₃ due to the too fast aluminum diffusion rate, and the structure shape may change due to the characteristics of NiAl ₃ with weak mechanical strength. It is not maintained and crumble. For this reason, in order to activate the thin nickel foam as a catalyst, more detailed process control is required than in the prior art.

In addition, there may be various problems in the existing structural catalyst synthesis technology as well as the above problems in the nickel-aluminum alloy formation process. When a metal structure is used as a catalyst support for the purpose of reducing the thermal gradient due to endothermic/exothermic characteristics of chemical reactions, wash coating, sol-gel coating, ink jet coating, and aerosol are methods for imparting catalytic function to the structure. Methods such as coating and physical/chemical vapor deposition are applied. However, when the catalyst layer is formed on the surface of the structure using such a coating method and then applied to the reaction, the catalyst layer may be detached due to a difference in thermal expansion characteristics between the support and the catalyst material. This problem is especially noticeable when the catalyst is applied to a three-phase reaction in which hydrogen is vigorously produced (eg hydrolysis of sodium borohydride). Separation of the catalyst layer may lead to deterioration in durability of the catalyst, which may shorten the replacement cycle of the catalyst and thus increase system operating costs.

One aspect of the present invention is to solve the problem of difficulty in controlling the nickel-aluminum alloy phase due to the inherent characteristics of the material in the melting and cooling process of the alloy in the conventional alloy forming method.

In addition, in the conventional aluminizing method, the entire structure may be changed to NiAl ₃ due to an excessively fast aluminum diffusion rate, and the structure shape is not maintained due to the characteristics of NiAl ₃ having weak mechanical strength.

In addition, in the case of using the conventional structural catalyst coating method, the separation phenomenon of the catalyst layer occurs due to the difference in thermal expansion characteristics of the support and the catalyst material, thereby solving the problem of deterioration in durability of the catalyst.

In one embodiment of the present invention to achieve the above object, a nickel-based structure; and a nickel-aluminum intermetallic compound, wherein the nickel-aluminum intermetallic compound includes at least one alloy phase of NiAl ₃ , Ni ₂ Al ₃ , NiAl, Ni ₃ Al, and Ni, and has pores on the surface of the catalyst. A hydrogen evolution catalyst having a porous structure is provided.

In one embodiment, the nickel-aluminum intermetallic compound may include at least one alloy phase of NiAl, Ni ₃ Al, and Ni.

In one embodiment, the weight ratio of Ni:Al in the hydrogen generating catalyst may be 1:9 to 9:1.

In one embodiment, the weight ratio of Ni:Al in the hydrogen generating catalyst may be 4:6 to 6:4.

In one embodiment, the nickel-based structure may have one or more shapes selected from the group consisting of powder, foam, plate, wire, strip, and tube.

In one embodiment, it may have a core-shell structure of a core including a nickel-based structure of nickel powder and a shell including a nickel-aluminum intermetallic compound.

In one embodiment, the nickel-based structure is nickel powder, and the nickel-aluminum intermetallic compound may have a single alloy phase.

In one embodiment, alumina present in the surface and pores of the hydrogen generating catalyst; may further include.

In one embodiment, the hydrogen generating catalyst may have a BET specific surface area of 40 to 150 m ² /g.

In another embodiment of the present invention, mixing the nickel-based structure and aluminum powder; heat-treating the mixture to form a nickel-aluminum intermetallic compound including at least one alloy phase of NiAl ₃ , Ni ₂ Al ₃ , NiAl, Ni ₃ Al, and Ni; And a step of leaching with a basic aqueous solution; a method for preparing a hydrogen generating catalyst is provided.

In one embodiment, the manufacturing method may further include heat-treating the nickel-aluminum intermetallic compound.

In one embodiment, in the mixing step, the nickel-based structure:aluminum powder may be mixed in a weight ratio of 1:9 to 9:1.

In one embodiment, aluminum chloride may be added together in the mixing step.

In one embodiment, the composition and distribution of the alloy phase included in the nickel-aluminum intermetallic compound may be changed in the heat treatment step.

In one embodiment, heat treatment may be performed at a temperature of 400 to 600 ° C in the heat treatment step.

In one embodiment, heat treatment may be performed for 30 to 1200 minutes in the heat treatment step.

In one embodiment, pores may be formed by selectively leaching aluminum from the alloy phase included in the nickel-aluminum intermetallic compound in the leaching step.

The hydrogen generating catalyst according to an embodiment of the present invention is a nickel-aluminum alloy body from aluminum and aluminum chloride powder to a nickel structure in various forms (powder, foam, plate, wire, tube, etc.) in a large amount at low temperature simply without deformation of the structure can lead to nickel-aluminum alloys having various types and distributions.

In addition, through dealloying, porous nickel having performance and durability for various hydrogen generation reactions can be obtained, which can be easily synthesized as a metal-based structure catalyst that can be applied to chemical reactions requiring thermal management.

In addition, various Ni-Al alloy phases can be formed on the catalyst surface by controlling the temperature and time of heat treatment and post-treatment conditions, and through the subsequent heat treatment process, mutual diffusion between the surface alloy layer and the substrate forms an alloy phase with strong mechanical strength. Thus, the durability of the catalyst can be secured.

Figure 1a shows the results of SEM analysis on the cross-section of the nickel aluminum alloy powder of Example 1 prepared through temperature and time control of low-temperature aluminizing under conditions of Ni-50wt.% Al weight ratio.
Figure 1b shows the results of EDS-line scanning analysis on the cross section of the powder prepared by controlling the temperature and time of low-temperature aluminizing under the condition of Ni-50wt.% Al weight ratio of the nickel aluminum alloy powder of Example 1.
Figure 2a shows the results of XRD analysis of the nickel aluminum alloy powder of Example 1.
Figure 2b shows the results of particle size analysis of the nickel aluminum alloy powder of Example 1.
Figure 3a shows the results of SEM surface analysis of the nickel aluminum alloy powder of Example 1.
Figure 3b shows the results of cross-sectional analysis of the nickel-aluminum alloy powder of Example 1.
Figure 4a shows the results of XRD analysis of the nickel aluminum alloy powder of Example 1 prepared under high Al conditions.
Figure 4b shows the results of SEM analysis of the nickel aluminum alloy powder of Example 1 prepared under high Al conditions.
Figure 4c shows the results of particle size analysis of the nickel aluminum alloy powder of Example 1 prepared under high Al conditions.
Figure 4d shows the results of cross-sectional analysis of the nickel-aluminum alloy powder of Example 1 prepared under high Al conditions.
Figure 5a shows the time-dependent BET surface area change trend after aluminum leaching of the porous nickel-aluminum alloy powder of Example 2 prepared under high Al conditions.
Figure 5b shows the particle size change trend after aluminum leaching of the porous nickel-aluminum alloy powder of Example 2 prepared under high Al conditions.
Figure 6a shows the result of applying the ammonia decomposition reaction after aluminum leaching of the porous nickel-aluminum alloy powder of Example 2 prepared under high Al conditions.
Figure 6b shows the result of applying the ammonia decomposition reaction according to the aluminum leaching time of the porous nickel-aluminum alloy powder of Example 2 prepared under Ni-50wt% Al conditions.
Figure 7a shows a schematic diagram of the manufacturing method of the nickel-aluminum alloy structure of Example 3.
Figure 7b shows the XRD analysis results of the nickel aluminum alloy structure of Example 3.
Figure 7c shows the results of SEM and EDS analysis of the nickel aluminum alloy structure of Example 3.
Figure 8a shows the results of activity measurement for the boron hydroxide hydrolysis reaction after aluminum leaching of the nickel-aluminum alloy structure of Example 3.
Figure 8b shows the activity measurement results for the boron hydroxide hydrolysis reaction after an accelerated simulation experiment for 1 hour with ultrasound of the nickel aluminum alloy structure of Example 3.
Figure 8c shows the change in the surface area of the catalyst before and after the acceleration simulation experiment for 1 hour with ultrasound of the nickel-aluminum alloy structure of Example 3.
Figure 8d shows a graph of the hydrogen evolution rate according to the catalyst surface area in the nickel aluminum alloy structure of Example 3.
Figure 9a shows a schematic diagram of the manufacturing method of the nickel-aluminum alloy structure of Example 3 according to the heat treatment time.
Figure 9b shows the results of SEM and EDS analysis of the cross-sectional structure of the nickel-aluminum alloy structure of Example 3 according to the heat treatment time.
Figure 9c shows the results of XRD analysis of the cross-sectional structure of the nickel-aluminum alloy structure of Example 3 according to the heat treatment time.
Figure 10a is a result of measuring the activity of the ammonia decomposition reaction of the nickel-aluminum alloy structure of Example 3, and is a result of evaluating the ammonia characteristics by temperature for each sample.
Figure 10b shows the ammonia conversion rate at 500 ℃ for each sample as a result of measuring the activity of the ammonia decomposition reaction of the nickel aluminum alloy structure of Example 3.
Figure 10c shows the ammonia conversion rate by GHSV for the 20h-L sample as a result of measuring the activity of the nickel aluminum alloy structure of Example 3 for the ammonia decomposition reaction.
Figure 10d shows the result of evaluating the catalyst durability at 600 ° C for the 20h-L sample as a result of measuring the activity of the nickel aluminum alloy structure of Example 3 for the ammonia decomposition reaction.
11A shows H-NMR measurement results of reactants used in the LOHC (liquid phase organic compound-based hydrogen storage material) hydrogenation reaction.
Figure 11b shows the results of reactor operation over time in Experimental Example 3.

Hereinafter, embodiments of the present invention will be described in more detail.

The embodiments of the present invention disclosed in the text are illustrated for purposes of explanation only, and the embodiments of the present invention may be implemented in various forms and should not be construed as being limited to the embodiments described in the text. .

The present invention can have various changes and can have various forms, the embodiments are not intended to limit the present invention to a specific disclosed form, and all changes, equivalents or substitutes included in the spirit and technical scope of the present invention It will be understood to include.

hydrogen evolution catalyst

In one embodiment of the present invention to achieve the above object, a nickel-based structure; and a nickel-aluminum intermetallic compound, wherein the nickel-aluminum intermetallic compound includes at least one alloy phase of NiAl ₃ , Ni ₂ Al ₃ , NiAl, Ni ₃ Al, and Ni, and has pores on the surface of the catalyst. A hydrogen evolution catalyst having a porous structure is provided.

In one embodiment, the nickel-aluminum intermetallic compound may include at least one alloy phase of NiAl, Ni ₃ Al, and Ni. The surface of the nickel-aluminum intermetallic compound may be leached to have pores by eluting aluminum. At this time, in the case of an alloy phase in which nickel is dominant (for example, an alloy phase such as NiAl or Ni ₃ Al), structural stability is high, and leaching may be difficult to achieve. On the other hand, in the case of an alloy phase in which aluminum is dominant (eg, NiAl ₃ , Ni ₂ Al ₃ ), only Al can be selectively leached from a strong alkali solution, and through this, porous characteristics can be imparted to the catalyst surface. Accordingly, the nickel-aluminum intermetallic compound subjected to the leaching process may have a porous structure while including at least one alloy phase of NiAl, Ni ₃ Al, and Ni.

In one embodiment, the weight ratio of Ni:Al in the hydrogen generating catalyst may be 1:9 to 9:1. Preferably, the weight ratio of Ni:Al may be 4:6 to 6:4. In the case of using the low-temperature aluminizing method, various types of nickel-aluminum alloys can be formed through the change in aluminum content during alloying. For example, when the weight ratio of Ni:Al is less than 1:9 (that is, when an excessive amount of Al is contained), the aluminum content is dominant in the alloy phase, such as NiAl ₃ and Ni ₂ Al ₃ , but durability may be poor, 9 If it exceeds : 1 (that is, contains an excessive amount of Ni), the shape may not be maintained due to the sintering effect, and catalytic efficiency may decrease due to poor Al leaching.

In one embodiment, the nickel-based structure may have one or more shapes selected from the group consisting of powder, foam, plate, wire, strip, and tube. The low-temperature aluminizing method can form a nickel-aluminum alloy layer on all nickel-based materials by gas-phase chemical reaction of aluminum chloride, so it may not be limited by the shape of the substrate. In particular, it is possible to form a robust alloy layer between the surface layer and the structure through control of heat treatment and subsequent heat treatment conditions, and through this, a catalyst having durability even in a three-phase reaction in which hydrogen is vigorously generated can be manufactured.

For example, among the structures, a foam-type structure with a relatively large surface area can be used to increase the contact area between the catalyst and the reactant in the reactor. . In the catalyst according to an embodiment of the present invention, since alloying proceeds at a low temperature by applying low-temperature aluminizing, it may be easy to control the formation of a coating layer for a thin structure.

In one embodiment, it may have a core-shell structure of a core including a nickel-based structure of nickel powder and a shell including a nickel-aluminum intermetallic compound. Specifically, when the hydrogen generating catalyst is synthesized in the Ni:Al weight ratio range that does not have a single alloy phase in the Ni-Al phase equilibrium, it may have the core-shell structure, for example, the Ni:Al weight ratio is 5 :5, core-shell alloy powder may be formed. At this time, an alloy containing more Al than the shell may be located in the core.

In one embodiment, the nickel-based structure is nickel powder, and the nickel-aluminum intermetallic compound may have a single alloy phase. As described above, the alloy phase may be determined by the ratio between the weight of aluminum powder and the weight of nickel powder introduced in aluminizing. At this time, if the weight ratio is controlled to match a specific alloy phase, it is possible to manufacture a single alloy phase. In particular, in the case of NiAl ₃ alloy powder, it is difficult to form a single alloy phase due to peritectic transformation (L→Ni ₂ Al ₃ +NiAl ₃ ) characteristics in the process of solidification after melting, but it is difficult to form an alloy through chemical reaction and diffusion. If a low-temperature aluminizing method is applied, it may be possible to manufacture a single alloy phase.

In one embodiment, alumina present in the surface and pores of the hydrogen generating catalyst; may further include. The alumina may be formed from residual aluminum after leaching, and since it may exist between nanostructured nickel catalysts, aggregation of the catalyst may be prevented when applied to high temperature ammonia decomposition reaction, and thus high activity catalytic activity may be maintained.

In one embodiment, the hydrogen generating catalyst may have a BET specific surface area of 40 to 150 m ² /g. Preferably, it may have a BET specific surface area of 80 to 120 m ² /g. The BET specific surface area may vary depending on the content of aluminum contained in the catalyst, because the porous structure formed through the leaching process may vary depending on the content of aluminum. Accordingly, the hydrogen generating catalyst may exhibit excellent catalytic efficiency by having a wide BET specific surface area within the above range.

In one embodiment, the hydrogen generating catalyst can be applied to various fields. Exemplary fields in which the hydrogen generating catalyst can be used as a catalyst and an electrode are as follows:

1) Hydrogen extraction reaction from hydrocarbons (methane steam reforming, biogas reforming, dry reforming, etc.)

2) Chemical hydrogen generation reaction (ammonia decomposition, sodium borohydride hydrolysis)

3) Electrochemical hydrogen generation reaction (water electrolysis)

4) LOHC (liquid phase organic compound-based hydrogen storage material) hydrogenation reaction

5) CO ₂ hydrogenation reaction (can be converted to FA, a hydrogen storage material)

Method for producing hydrogen generating catalyst

In another embodiment of the present invention, mixing the nickel-based structure and aluminum powder; heat-treating the mixture to form a nickel-aluminum intermetallic compound including at least one alloy phase of NiAl ₃ , Ni ₂ Al ₃ , NiAl, Ni ₃ Al, and Ni; And a step of leaching with a basic aqueous solution; a method for preparing a hydrogen generating catalyst is provided. A specific manufacturing method will be described with reference to FIGS. 7A and 9A.

First, a nickel-based structure and aluminum powder may be mixed.

Aluminum chloride may be added together in the mixing step. The added aluminum chloride is in the form of powder at room temperature, but the form supplied is not particularly limited, and may be evaporated in advance in an evaporator and introduced into the reactor together with other high-purity hydrogen, nitrogen, or helium carrier gases. In this case, it may be introduced after exhausting air to sufficiently remove moisture and oxygen inside the reactor before introduction, and in this case, a vacuum process may be unnecessary.

Subsequently, the mixture may be introduced into the reactor and subjected to vacuum treatment, for example, under a vacuum condition of 10 ⁻¹ Torr or less.

In one embodiment, in the mixing step, the nickel-based structure:aluminum powder may be mixed in a weight ratio of 1:9 to 9:1. Preferably, the weight ratio of the nickel-based structure to the aluminum powder may be 4:6 to 6:4. In the case of using the low-temperature aluminizing method, various types of nickel-aluminum alloys can be formed through the change in aluminum content during alloying. For example, when the weight ratio of nickel-based structure: aluminum powder is less than 1:9 (that is, when an excessive amount of Al is contained), the content of aluminum is dominant in the alloy phase, such as NiAl ₃ and Ni ₂ Al ₃ , but durability may be poor. If the ratio exceeds 9:1 (that is, if Ni is contained in excess), the shape may not be maintained due to the sintering effect, and the Al leaching may not be smooth, resulting in a decrease in catalyst efficiency.

Subsequently, the mixture may be aluminized to form a nickel-aluminum intermetallic compound including at least one alloy phase of NiAl ₃ , Ni ₂ Al ₃ , NiAl, Ni ₃ Al, and Ni. For example, the reactor may be rotated to prevent sintering of nickel powders during the aluminizing process.

On the other hand, when raw material powders having a narrow size distribution are applied to the low temperature aluminizing method, alloy powders having almost similar sizes can be produced without powder sintering. At this time, the weight of aluminum powder and the weight of nickel powder The alloy phase can be determined by the ratio of

Next, the nickel-aluminum intermetallic compound may be heat treated.

In one embodiment, the composition and distribution of the alloy phase included in the nickel-aluminum intermetallic compound may be changed in the heat treatment step. The alloying reaction proceeding in the heat treatment step is known as follows.

[Scheme 1]

AlCl ₃ + Al(s) ↔ AlCl(g) + AlCl ₂ (g)

[Scheme 2]

Ni(s) + 2AlCl(g) ↔ 2NiAl + Cl ₂ (g)

[Scheme 3]

2AlCl ₂ + Cl ₂ (g) ↔ 2AlCl ₃ (g)

As shown in Reaction Scheme 1, aluminum metal and vaporized aluminum chloride (AlCl ₃ ) react to produce AlCl or AlCl ₂ and directly react with nickel as shown in Reaction Scheme 2 to produce a nickel-aluminum intermetallic compound. and the reaction gradually spreads. At this time, the reaction time and reaction temperature should be set for the diffusion described above. Also, as shown in Scheme 3, AlCl ₂ and Cl ₂ gas react to form AlCl ₃ again, and the reaction may continue until the reactants are exhausted.

In one embodiment, the composition and distribution of at least one of NiAl ₃ , Ni ₂ Al ₃ , NiAl, Ni ₃ Al, and Ni may be changed in the nickel-aluminum intermetallic compound through the heat treatment step.

For example, the NiAl ₃ alloy phase is an alloy phase that can be easily used as a catalyst due to easy aluminum leaching, but has a weak mechanical strength. In particular, if the NiAl ₃ phase is formed on the structure substrate without an intermediate layer, when applied as a catalyst after aluminum leaching, the catalyst layer may be detached and the durability of the catalyst may be reduced.

In order to solve this problem, a subsequent heat treatment process was introduced between the low-temperature aluminizing process and the aluminum leaching process, and through this heat treatment, a Ni ₂ Al ₃ phase with strong mechanical strength can be formed between the NiAl ₃ alloy layer and the nickel substrate. .

In addition, the composition of the surface alloy layer may be changed to Ni ₂ Al ₃ , NiAl, or Ni ₃ Al by changing the temperature and time conditions of the subsequent heat treatment process. In particular, when the subsequent heat treatment process at 600 ° C is performed, a NiAl and Ni ₃ Al alloy layer having a relatively high nickel content is formed on the surface, which is an alloy layer that requires a high temperature of 1000 ° C or more in the prior art. Subsequent heat treatment can be said to be an energy-saving method compared to conventional methods in this respect.

In one embodiment, heat treatment may be performed at a temperature of 400 to 600 ° C in the heat treatment step. Specifically, since the heat treatment temperature of 400 to 600 ° C is a temperature below the melting point of aluminum and a temperature at which aluminum chloride can react in the gas phase, it can be applied to the manufacture of various nickel structures. However, at a temperature of less than 400 ° C, the alloy layer may not be smoothly formed.

On the other hand, the alloy layer formation process at a high temperature of 600 ° C or higher may cause sintering and coating layer non-uniformity due to melting of aluminum. In particular, when the powder is used as a structure, the sintering phenomenon may be further promoted, resulting in a product having a wide size distribution or a lumpy product, or the internal alloy phase composition may be disturbed during the sintering process. In addition, due to the fast aluminum diffusion rate, it is difficult to control the composition and thickness of the alloy layer, so there are restrictions on the applicable structure shape (especially thin structures with a thickness of several tens of microns).

In one embodiment, heat treatment may be performed for 30 to 1200 minutes in the heat treatment step. Specifically, the alloy alloy phase formed may vary according to the heat treatment time, for example, NiAl ₃ may be formed in the initial stage of heat treatment, and the thickness of the alloy phase and the composition of the NiAl ₃ and Ni ₂ Al ₃ alloy phase by adjusting the process time You can control the ratio.

Next, a leaching process may be performed with a basic aqueous solution. For example, the basic aqueous solution may include a strong alkali aqueous solution having a pH greater than 13, such as NaOH or KOH. In addition, the basic aqueous solution may include a chelating agent such as KNaC ₄ H ₄ O ₆ , which may increase the solubility of Al by chelating Al(OH) ₃ . This leaching process is a dealloying process, and generally aluminizing is a method widely applied as a method for increasing high-temperature oxidation resistance of nickel- or iron-based materials. At this time, the main purpose is to form an alloy phase (Ni ₃ Al, NiAl) containing a relatively large amount of nickel. However, if aluminum forms relatively many alloy phases (Ni ₂ Al ₃ , NiAl ₃ ), it is possible to selectively leach only Al from the strong alkali solution, and through this operation, porous characteristics can be imparted to the surface.

In one embodiment, pores may be formed by selectively leaching aluminum from the alloy phase included in the nickel-aluminum intermetallic compound in the leaching step.

Therefore, through the manufacturing method according to the embodiment of the present invention, it is possible to achieve an excellent simplification of the powder / structure catalyst synthesis method, which plays a large role in lowering the cost of hydrogen emission system production, which will be used as a key technology that can advance the commercialization of hydrogen energy. can

Example

Hereinafter, the configuration and effects of the present invention will be described in more detail by way of examples. However, these examples are provided only for illustrative purposes to aid understanding of the present invention, and the scope and scope of the present invention are not limited by the following examples.

Example 1: Preparation of nickel aluminum alloy powder

Nickel powder (2.2-2.8um, Hart materials), aluminum powder (23.0um, Ecka granules), and AlCl ₃ (Junsei Chemistry) were mixed in a quartz ampoule. The weight of the mixture of Ni powder and Al powder was 10 to 20 g, and the content of AlCl ₃ was kept constant at 0.6 to 1.8 wt%, while Ni-x wt% Al (x = 0, 5, 15, 30, 40, 50 and 60), various types of nickel-aluminum alloys were formed through changes in the Al content ratio. After mixing the materials, the vacuum was reached to 10 ^-3 Torr or less using a vacuum pump, and then sealed. The prepared quartz ampoule was heat-treated for 0h, 5h, and 20h at heat treatment temperatures of 450°C and 500°C, respectively, to prepare nickel-aluminum alloy powder.

Experimental Example 1: Nickel Aluminum Alloy Powder Characteristics

1a and 1b show the results of SEM and EDS-line scanning analysis by preparing the nickel-aluminum alloy powder of Example 1 through temperature and time control of low-temperature aluminizing under the condition of Ni-50 wt% Al weight ratio. Compared to the sample synthesized by raising the temperature to 450 ° C, in the case of the sample synthesized by raising the temperature to 500 ° C, the alloy phase of the powder surface is different, and it can be seen that the composition of this surface changes according to the heat treatment time. In addition, the diffusion rate of Al into the nickel can be controlled by controlling the heat treatment temperature, and the alloy composition and structure of the nickel powder can be changed by controlling the heat treatment time.

Figure 2a shows the results of XRD analysis of the nickel aluminum alloy powder of Example 1. It can be seen that there is a change in the composition of the prepared nickel aluminum alloy powder when heat treatment is performed at 500 ° C. for 20 hours and the Al content is changed to 5 wt%, 15 wt%, 30 wt%, and 50 wt%, respectively. Through this, it can be seen that the composition of the alloy phase changes not only according to the synthesis temperature conditions (aluminizing, heat treatment) in FIG. 1 but also according to the contents of nickel and aluminum contained.

Figure 2b shows the results of particle size analysis of the nickel aluminum alloy powder of Example 1. Depending on the Al content change, it can be seen that the particle size analysis results are generally similar, and in the case of Ni-30wt%, it can be seen that the average diameter and deviation of the nickel aluminum alloy powder appear larger.

3a and 3b show the results of SEM surface and cross-section analysis of the nickel-aluminum alloy powder of Example 1 prepared by heat treatment at 500 ° C. for 20 hours. Through this, it can be confirmed that not only the surface composition of the nickel-aluminum alloy powder produced as the Al content changes, but also the internal structure and composition change. On the other hand, after the alloying process, the alloy exists in a thermodynamic equilibrium state and may exist in a single alloy phase or core-shell structure corresponding to the weight ratio composition of the starting material in the phase equilibrium diagram.

Figures 4a and 4b show the results of XRD analysis and SEM analysis of the nickel-aluminum alloy powder of Example 1 prepared under high Al conditions, respectively. Even when the Al content is high, it can be confirmed that the composition of the alloy phase changes according to the change in the content, as in the previous results. In particular, in the case of the Ni-60wt% AL sample, it was confirmed that it had a single alloy phase of NiAl ₃ .

Figure 4c shows the results of particle size analysis of the nickel aluminum alloy powder of Example 1 prepared under high Al conditions. As a result, it was confirmed that the diameter of the alloy powder according to the embodiment of the present invention was significantly smaller than that of the general commercial Ni-Al powder ('Commercial Ni-Al powder') to be compared. In addition, it can be seen that the alloy powder according to the embodiment has a size similar to or slightly increased in size to that of the Ni powder, which is the starting material, and through this, the Ni-Al alloy phase is formed with the size deformation of the template minimized. have.

Figure 4d shows the results of cross-sectional analysis of the nickel-aluminum alloy powder of Example 1 prepared under high Al conditions. As in the previous results, it can be confirmed that the composition of the alloy phase changes according to the change in the content, as in the previous results, even when the Al content is high. In particular, it was confirmed that the Ni-40wt% AL sample had a single alloy phase of Ni ₂ Al ₃ and the Ni-60wt% AL sample had a single alloy phase of NiAl ₃ .

Example 2: Preparation of Porous Nickel Aluminum Alloy Powder

Porosity was imparted to the nickel-aluminum alloy powder prepared in Example 1 through a leaching process.

Alkali containing 30 wt.% potassium hydroxide (KOH, Sigma Aldrich, ≥85%) and 10 wt.% sodium potassium tartrate (KNaC ₄ H ₄ O ₆ 4H ₂ O, Sigma Aldrich, 99%) The solution was used as a leaching agent. A specific Al leaching process can be expressed by the chemical formula below, and was performed at 80° C. by varying the leaching time from 5 to 240 minutes, and the leached sample was rinsed several times with deionized water.

2 Al + 2 NaOH + 6 H ₂ O → 2 Na[Al(OH) ₄ ] + 3 H ₂

Al(OH) ^- ₄ → Al(OH) ₃ + OH ^-

Al(OH) ^- ₄ + n(C ₄ H ₄ O ₆ ) _n ^{2 -} → Al(OH) ₃ (C ₄ H ₄ O ₆ ) _n ^{2 -} + OH ^-

Experimental Example 2: Characteristics of Porous Nickel Aluminum Alloy Powder

Figure 5a shows the BET surface area change trend after aluminum leaching of the porous nickel-aluminum alloy powder of Example 2 prepared under high Al conditions. As a result, it was confirmed that the degree of increase in the specific surface area was determined according to the alloy phase of the material before leaching, and that the BET surface area changed according to the aluminum content. As a result, it was confirmed that the BET specific surface area of the prepared catalyst was increased.

In addition, as the leaching time increases, the BET specific surface area also increases, and it was confirmed that the BET specific surface area does not increase any more when leaching for a certain period of time or more, and this is indicated as the 'optimal point'. Table 1 below shows specific BET specific surface area values according to the leaching time.

leaching time
(minute) BET Surface area (m ² /g) Ni-40wt% Al Ni-50wt% Al Ni-60wt% Al 5 15.49 51.87 90.90 30 22.02 56.75 104.25 60 31.40 76.17 111.25 120 44.22 89.26 109.38 240 49.93 87.47 115.77

Figure 5b shows the particle size change trend after aluminum leaching of the porous nickel-aluminum alloy powder of Example 2 prepared under high Al conditions. As a result of fitting the change trend, it was confirmed that the trend of decreasing the particle size due to leaching became larger as the Al content increased.

Experimental Example 3: Measurement of ammonia decomposition reaction and LOHC hydrogenation activity

First, the ammonia decomposition activity of the porous nickel aluminum alloy powder of Example 2 was measured.

Figures 6a and 6b show the result of applying the ammonia decomposition reaction after aluminum leaching of the porous nickel-aluminum alloy powder of Example 2 prepared under high Al conditions. As a result, it was confirmed that the catalyst prepared by leaching for about 120 minutes as a sample prepared with a Ni-50wt% Al content had the best catalytic efficiency.

Next, the LOHC hydrogenation activity of the porous nickel aluminum alloy powder of Example 2 was measured. Porous nickel aluminum alloy powder was used for samples leached for 240 minutes.

As the LOHC reactant, 20.0 g of a eutectic mixture in which biphenyl and diphenylmethane were mixed in a weight ratio of 35:65 was used, and the H-NMR result of the used LOHC reactant is shown in FIG. 11a.

Under the reaction conditions (temperature: 120 °C, H ₂ pressure: 50 bar, reactor: batch type, duration: about 66 h, conversion rate: 100%), the LOHC hydrogenation reaction was performed as shown in FIG. 11b.

Example 3: Fabrication of a nickel aluminum alloy structure

Nickel foam (#12, Alantum, nominal cell size: 1200 μm, strut thickness: 16 μm), aluminum powder (23.0um, Ecka granules), and AlCl ₃ (Junsei Chemistry) were mixed in a quartz ampoule. While keeping the AlCl ₃ content constant at 0.6-1.8 wt%, various types of A nickel-aluminum alloy was formed. After mixing the materials, the vacuum was reached to 10 ^-3 Torr or less using a vacuum pump, and then sealed. The prepared quartz ampoule was heat-treated for 5h, 10h, and 20h at a heat treatment temperature of 400° C., respectively, to prepare nickel-aluminum alloy powder.

Example 4: Fabrication of a porous nickel aluminum alloy structure

A porous nickel-aluminum alloy structure was prepared by Al leaching in the same manner as in Example 2, except that the nickel-aluminum alloy structure of Example 3 was etched at 80° C. for 1 hour.

Experimental example 4: Nickel-aluminum alloy structure and porous nickel-aluminum alloy structure properties

7b and 7c show XRD analysis results, SEM and EDS analysis results of the nickel-aluminum alloy structure of Example 3. Through this, it can be confirmed that the composition of the alloy phase formed on the surface of the structure can be changed by heat-treating the nickel-aluminum alloy structure synthesized by aluminizing.

Figure 8a shows the results of activity measurement for the boron hydroxide hydrolysis reaction immediately after aluminum leaching of the nickel-aluminum alloy structure of Example 3.

Figure 8b shows the activity measurement results for the boron hydroxide hydrolysis reaction after an accelerated simulation experiment for 1 hour with ultrasound of the nickel aluminum alloy structure of Example 3.

Figure 8c shows the change in the surface area of the catalyst before and after the acceleration simulation experiment for 1 hour with ultrasound of the nickel-aluminum alloy structure of Example 3.

Figure 8d shows a graph of the hydrogen evolution rate according to the catalyst surface area in the nickel aluminum alloy structure of Example 3.

9b and 9c show the results of XRD, SEM and EDS analysis of the cross-sectional structure of the nickel-aluminum alloy structure of Example 3 according to the heat treatment time. Through this, it can be confirmed that the composition ratio of the alloy phase formed on the surface of the structure can be changed in the alloy phase by heat-treating the synthesized nickel-aluminum alloy structure according to the aluminizing time.

Experimental Example 5: Measurement of ammonia decomposition reaction activity

Figure 10a is a result of measuring the activity of the ammonia decomposition reaction of the nickel-aluminum alloy structure of Example 4, and is a result of evaluating the ammonia characteristics by temperature for each sample.

Figure 10b shows the ammonia conversion rate at 500 ℃ for each sample as a result of measuring the activity of the ammonia decomposition reaction of the nickel aluminum alloy structure of Example 4.

Figure 10c shows the ammonia conversion rate by GHSV for the 20h-L sample leached after 20h heat treatment, as a result of measuring the activity of the nickel aluminum alloy structure of Example 4 for the ammonia decomposition reaction.

Figure 10d is a result of measuring the activity of the ammonia decomposition reaction of the nickel aluminum alloy structure of Example 4, and shows the results of evaluating the catalyst durability at 600 ° C for the 20h-L sample leached after 20h heat treatment.

The embodiments of the present invention described above should not be construed as limiting the technical spirit of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those skilled in the art can improve and change the technical idea of the present invention in various forms. Therefore, these improvements and modifications will fall within the protection scope of the present invention as long as they are obvious to those skilled in the art.

Claims (18)

a core comprising a nickel-based structure; And a shell containing a nickel-aluminum intermetallic compound; having a core-shell structure including,
The nickel-aluminum intermetallic compound is composed of at least one alloy phase of Ni ₂ Al ₃ , NiAl, and Ni ₃ Al and has a porous structure having pores on the surface of the catalyst,
The hydrogen evolution catalyst, wherein the weight ratio of Ni:Al in the hydrogen evolution catalyst is 4:6 to 6:4. delete According to claim 1,
Wherein the porous structure is formed by leaching a nickel-aluminum intermetallic compound. delete delete According to claim 1,
The nickel-based structure has at least one form selected from the group consisting of powder, foam, plate, wire, strip, and tube, hydrogen generating catalyst. delete delete According to claim 1,
Alumina present in the surface and pores of the hydrogen generating catalyst; further comprising a hydrogen generating catalyst. According to claim 1,
The hydrogen generating catalyst has a BET specific surface area of 40 to 150 m ² /g. Mixing a nickel-based structure and aluminum powder;
forming a nickel-aluminum intermetallic compound including a NiAl ₃ alloy phase by aluminizing the mixture under vacuum conditions;
converting all of the NiAl ₃ alloy phase into at least one alloy phase of Ni ₂ Al ₃ , NiAl, and Ni ₃ Al by subsequent heat treatment of the formed nickel-aluminum intermetallic compound; and
A step of leaching the subsequent heat-treated nickel-aluminum intermetallic compound with a basic aqueous solution;
In the mixing step, the weight ratio of nickel-based structure: aluminum powder is mixed at 4:6 to 6:4,
Heat treatment at a temperature of 500 to 600 ℃ in the subsequent heat treatment step, hydrogen generating catalyst manufacturing method. delete delete According to claim 11,
A method for producing a hydrogen generating catalyst in which aluminum chloride is added together in the mixing step. delete delete According to claim 11,
In the subsequent heat treatment step, heat treatment for 30 to 1200 minutes, hydrogen generating catalyst manufacturing method. According to claim 11,
In the leaching step, the hydrogen generation catalyst manufacturing method of forming pores by selectively leaching aluminum from the alloy phase included in the nickel-aluminum intermetallic compound.

Images