An ammonia decomposition catalyst, its preparation method, and a method for producing hydrogen from ammonia decomposition.

Abstract

This invention discloses an ammonia decomposition catalyst and its preparation method, as well as a method for ammonia decomposition to hydrogen production, relating to the field of catalysis technology. The specific steps of the method are as follows: ammonium chloride, melamine, and pretreated nickel foam are sequentially and evenly filled into a sealed crucible in the order of bottom center to top. The crucible is covered, and the crucible is placed in a tube furnace and heated for a certain time to obtain the ammonia decomposition catalyst. This invention utilizes a one-pot method for catalyst preparation. NH4Cl first decomposes at high temperature to form gaseous HCl; subsequently, under an HCl atmosphere, the nickel foam is etched and stripped, causing the surface Ni metal to be continuously converted into gaseous NiCl2 with a low boiling point; finally, the gaseous NiCl2 pyrolyzes to generate metallic Ni particles, which in turn drive the pyrolysis of melamine to generate nanofibers, which are then uniformly dispersed and attached to its surface. The method of this invention is simple and controllable. Not only can the catalytic activity of the catalyst be optimized by adjusting the etching conditions, but the unique structural design of the generated ammonia decomposition catalyst can significantly improve the catalyst's activity and stability.

Description

Technical Field

[0001] This invention belongs to the field of industrial catalysis technology, specifically relating to an ammonia decomposition catalyst, its preparation method, and a method for producing hydrogen from ammonia decomposition. Background Technology

[0002] Ammonia (NH3) has attracted widespread attention in recent years as an ideal hydrogen carrier. In existing ammonia decomposition hydrogen production technologies, the design and modification of ammonia decomposition catalysts mainly focus on three aspects: regulation of active components, selection and optimization of the carrier, and improvement of preparation methods. Among these, the carrier is a crucial component of the catalyst. The metal-carrier interaction, acid-base properties, catalyst porosity, and the dispersion of active metals are strongly influenced by the basic characteristics of the carrier, thus affecting the catalytic performance of the catalyst. Ammonia decomposition catalyst carriers are mainly classified into metal oxides (including active metals and transition metals), carbon-based materials (including carbon nanotubes, graphene, and hard carbon), and nitrides (including metal nitrides, imides, and amides). Compared to metal oxides, carbon-based materials are often used as materials for thermocatalytic ammonia decomposition due to their larger specific surface area and higher electron transport capacity. Among these, carbon nanofibers (CNFs) possess various tunable graphene sheet-oriented nanostructures, and therefore, different CNF edge structures have always been considered good catalyst carriers. Due to their unique electron transport properties, they are frequently used as catalyst carriers for selective hydrogenation and dehydrogenation. However, although CNFs exhibit good dispersibility, different preparation conditions can lead to varying degrees of loading and dispersion. Furthermore, during high-temperature reactions, metal nanoparticles may sinter, reducing catalytic activity. Many studies have first prepared CNFs and then loaded metals such as Ru, Ni, and Co onto their surfaces using different methods. While this approach offers good structural tunability, the multi-step preparation process makes the structure uncontrollable. Moreover, the synthesis process presents certain challenges, making it difficult to precisely control the microstructure, which can, to some extent, damage the CNFs and consequently affect catalytic activity.

[0003] Therefore, it is necessary to develop a simpler and more controllable method for preparing ammonia decomposition catalysts, while the ammonia decomposition catalysts prepared by this method have high efficiency and stable ammonia decomposition catalytic performance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide an ammonia decomposition catalyst, its preparation method, and a method for producing hydrogen from ammonia decomposition. The method of the present invention is simple and controllable. Not only can the catalytic activity of the catalyst be optimized by adjusting the etching conditions, but the unique structural design of the generated ammonia decomposition catalyst can also significantly improve the activity and stability of the catalyst.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An ammonia decomposition catalyst includes a support and an active component supported on the support, wherein the support is carbon nanofibers (CNFs) and the active component is metallic nickel (Ni). The general formula for the ammonia decomposition catalyst is Ni / CNF. x， Where x is the mass ratio of active metal Ni to carbon nanofiber CNF, x = 1-5.

[0007] A method for preparing an ammonia decomposition catalyst, comprising the following specific steps:

[0008] Ammonium chloride (NH4Cl), melamine (C3H6N6), and pretreated nickel foam are sequentially laid and filled into a sealed crucible in the order of bottom center to top. The crucible is then covered and placed in a tube furnace for heating and calcination for a certain period of time to obtain the ammonia decomposition catalyst.

[0009] Preferably, the pretreatment method for nickel foam is as follows: the circular nickel foam sheets are ultrasonically cleaned with acetone and hydrochloric acid to remove residual organic impurities on the surface, then thoroughly rinsed with deionized water and vacuum dried.

[0010] Preferably, the circular nickel foam sheet has a mass of 1.2 g, a diameter of 8 mm, a thickness of 2.0 mm, and a porosity of 110 PPI; the ultrasonic cleaning time is 20 min, and the vacuum drying temperature is 80 °C.

[0011] Preferably, the mass ratio of NH4Cl, C3H6N6 and nickel foam is 5:1 to 5:1; more preferably, the mass ratio of NH4Cl, C3H6N6 and nickel foam is 5:3:1.

[0012] Preferably, the heating and calcination process involves heating to 550 °C at a heating rate of 10 °C / min and holding at that temperature for 0.5 hours; then heating to 900 °C at a heating rate of 5 °C / min and holding at that temperature for 3 hours.

[0013] Preferably, the calcination is carried out in an argon atmosphere at a flow rate of 10 mL / min.

[0014] The present invention also protects the method for producing hydrogen by ammonia decomposition, wherein the ammonia decomposition catalyst is brought into contact with ammonia gas to react.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] This invention utilizes a one-pot method to calcine a certain proportion of melamine (C3H6N6), ammonium chloride (NH4Cl), and nickel foam in a crucible. During this process, NH4Cl first decomposes at high temperature to form gaseous HCl. Subsequently, under an HCl atmosphere, the nickel foam is etched and stripped, causing the surface Ni metal to be continuously converted into gaseous NiCl2 with a low boiling point. Finally, the gaseous NiCl2 pyrolyzes to generate metallic Ni particles, which in turn drive the melamine to pyrolyze and generate nanofibers that are uniformly dispersed and attached to its surface.

[0017] In this invention, metallic Ni is directly loaded in situ onto the surface of CN during the CN formation process. By adjusting the proportion of additives, the content, morphology, and other characteristics of the active metallic Ni and CN compound support can be controlled. Furthermore, this method is simple and controllable. Not only can the catalytic activity of the catalyst be optimized by adjusting the etching conditions, but the unique structural design of the generated ammonia decomposition catalyst can also significantly improve the catalyst's activity and stability.

[0018] (3) The mass ratio of NH4Cl, C3H6N6 and foamed nickel in this invention is 5:1-5:1. The specific mass ratio of raw materials is limited to avoid the low content of CNFs carrier and the amount of active component Ni exceeding the amount that the carrier can support, resulting in weak interaction between metal Ni and the carrier, large particle agglomeration, which is not conducive to the adhesion and decomposition of ammonia. It also avoids the problem that the content of CNFs generated is too high, the carrier content increases and the content of active metal Ni per unit mass is reduced, resulting in a reduction of effective active sites and a decrease in ammonia decomposition efficiency. Attached Figure Description

[0019] Figure 1 These are TEM images of the ammonia decomposition catalysts prepared in Examples 1-3 of this invention, wherein... Figure 1 (a) is a TEM image of the ammonia decomposition catalyst in Example 1; Figure 1 (b) is a TEM image of the ammonia decomposition catalyst in Example 2; Figure 1 (c) is a TEM image of the ammonia decomposition catalyst in Example 3.

[0020] Figure 2 The graphs show the ammonia decomposition efficiency of the ammonia decomposition catalyst and nickel foam in Examples 1-3 of this invention at different temperatures. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, all products in this invention were purchased through market channels. Example 1

[0023] A method for preparing an ammonia decomposition catalyst, comprising the following specific steps:

[0024] (1) Pretreatment of raw material foamed Ni: Circular foamed nickel sheets (1.2 g, diameter 8 mm, thickness 2.0 mm, porosity 110 PPI) were obtained by shearing. Then, the circular foamed nickel sheets were ultrasonically cleaned for 20 min with appropriate amount of acetone and 1 mol / L hydrochloric acid to remove residual organic impurities on the surface. After being thoroughly rinsed with deionized water, they were vacuum dried at 80℃.

[0025] (2) Preparation of Ni / CNF: 5g of NH4Cl, 1g of C3H6N6 and 1g of treated nickel foam were sequentially spread and filled into a sealed crucible in the order of bottom center to top. The internal dimensions of the crucible were 54×24×17 mm. The crucible was covered with a lid with dimensions of 53.5×23.5×8 mm. The crucible was heated to 550 °C at a heating rate of 10 °C / min and held for 0.5 hours. Then, it was heated to 900 °C at a heating rate of 5 °C / min and held for 3 hours. A low argon flow rate of 10 mL / min was maintained throughout the calcination process. The Ni / CNF ammonia decomposition catalyst sample was obtained.

[0026] like Figure 1 As shown in (a), the microstructure of the ammonia decomposition catalyst sample prepared above was observed using TEM. Fibers with a diameter of approximately 500 nm and particles present on their surface were observed. HR-TEM revealed that the lattice spacing of the dark particles was 2.02 nm, corresponding to the (111) crystal plane of metallic Ni; the lattice stripe spacing of the fibers was 3.34 nm, corresponding to the (002) crystal plane of carbon, indicating that it was mainly composed of carbon fibers. In addition, the blue particles in the EDS elemental mapping diagram corresponded to Ni, further verifying the conclusion that the dark particles were Ni. Example 2

[0027] A method for preparing an ammonia decomposition catalyst, comprising the following specific steps:

[0028] (1) Pretreatment of raw material foamed Ni: Circular foamed nickel sheets (1.2 g, diameter 8 mm, thickness 2.0 mm, porosity 110 PPI) were obtained by shearing. Then, the circular foamed nickel sheets were ultrasonically cleaned for 20 min with appropriate amount of acetone and 1 mol / L hydrochloric acid to remove residual organic impurities on the surface. After being thoroughly rinsed with deionized water, they were vacuum dried at 80℃.

[0029] (2) Preparation of Ni / CNF: 5g NH4Cl, 3g C3H6N6 and 1g of treated nickel foam were sequentially spread and filled into a sealed crucible in the order of bottom center to top. The internal dimensions of the crucible were 54×24×17 mm. The crucible was covered with a lid with dimensions of 53.5×23.5×8 mm. The temperature was increased to 550 °C at a heating rate of 10 °C / min and held for 0.5 hours. Then the temperature was increased to 900 °C at a heating rate of 5 °C / min and held for 3 hours. A low argon flow rate of 10 mL / min was maintained throughout the calcination process. The Ni / CNF3 ammonia decomposition catalyst sample was obtained.

[0030] like Figure 1 As shown in (b), the microstructure of the ammonia decomposition catalyst sample prepared above was observed using TEM. Fibers with a diameter of approximately 500 nm and particles present on their surface were observed. HR-TEM revealed that the lattice spacing of the dark particles was 2.02 nm, corresponding to the (111) crystal plane of metallic Ni; the lattice stripe spacing of the fibers was 3.34 nm, corresponding to the (002) crystal plane of carbon, indicating that it was mainly composed of carbon fibers. In addition, the blue particles in the EDS elemental mapping diagram corresponded to Ni, further verifying the conclusion that the dark particles were Ni. Example 3

[0031] A method for preparing an ammonia decomposition catalyst, comprising the following specific steps:

[0032] (1) Pretreatment of raw material foamed Ni: Circular foamed nickel sheets (1.2 g, 54×24×0.5 mm, thickness 2.0 mm, porosity 110 PPI) were obtained by shearing. Then, the circular foamed nickel sheets were ultrasonically cleaned for 20 min with appropriate amount of acetone and 1 mol / L hydrochloric acid to remove residual organic impurities on the surface. After being thoroughly rinsed with deionized water, they were vacuum dried at 80℃.

[0033] (2) Preparation of Ni / CNF: 5g of NH4Cl, 5g of C3H6N6 and 1g of treated nickel foam were sequentially spread and filled into a sealed crucible in the order of bottom center to top. The internal dimensions of the crucible were 54×24×17 mm. The crucible was covered with a lid with dimensions of 53.5×23.5×8 mm. The crucible was heated to 550 °C at a heating rate of 10 °C / min and held for 0.5 hours. Then, it was heated to 900 °C at a heating rate of 5 °C / min and held for 3 hours. A low argon flow rate of 10 mL / min was maintained throughout the calcination process. The Ni / CNF5 ammonia decomposition catalyst sample was obtained.

[0034] like Figure 1As shown in (c), the microstructure of the ammonia decomposition catalyst sample prepared above was observed using TEM. Fibers with a diameter of approximately 500 nm and particles present on their surface were observed. HR-TEM revealed that the lattice spacing of the dark particles was 2.02 nm, corresponding to the (111) crystal plane of metallic Ni; the lattice stripe spacing of the fibers was 3.34 nm, corresponding to the (002) crystal plane of carbon, indicating that it was mainly composed of carbon fibers. In addition, the blue particles in the EDS elemental mapping diagram corresponded to Ni, further verifying the conclusion that the dark particles were Ni.

[0035] Test results are as follows Figure 2 As shown, using Ni / CNFx as an ammonia decomposition catalyst significantly improves the ammonia decomposition efficiency compared to using nickel foam as an ammonia decomposition catalyst. Among them, the moderately carbonized catalyst Ni / NF3 exhibits the highest ammonia decomposition efficiency. At 600 °C, the GHSV is 18000 mL gcat. -1 h -1 At that time, the ammonia decomposition efficiency was approximately 90.5%. Meanwhile, the stability of the Ni / NF3 catalyst was also tested over a long period. In a continuous ammonia decomposition reaction at 600℃ for 100 hours, the decomposition efficiency of the Ni / NF3 catalyst remained stable at approximately 91%, with fluctuations not exceeding ±2%. This result demonstrates that the Ni / NF3 catalyst not only possesses excellent ammonia decomposition activity but also exhibits outstanding thermal stability and long-term durability.

[0036] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ammonia decomposition catalyst, characterized in that, The catalyst comprises a support and an active component loaded on the support, wherein the support is carbon nanofibers and the active component is metallic nickel. The general formula for the ammonia decomposition catalyst is Ni / CNF. x， Where x is the mass ratio of active metal Ni to carbon nanofiber CNF, x = 1-5; The preparation method of the ammonia decomposition catalyst includes the following specific steps: Ammonium chloride, melamine, and pretreated nickel foam are sequentially and evenly filled into a sealed crucible in the order of bottom middle to top. The crucible is covered and placed in a tube furnace for heating and calcination for a certain period of time to obtain an ammonia decomposition catalyst. The mass ratio of ammonium chloride, melamine, and nickel foam is 5:1 to 5:

1.

2. A method for preparing the ammonia decomposition catalyst according to claim 1, characterized in that, The specific steps are as follows: Ammonium chloride, melamine, and pretreated nickel foam are sequentially laid and filled into a sealed crucible in the order of bottom center to top. The crucible is then covered and placed in a tube furnace for heating and calcination for a certain period of time to obtain the ammonia decomposition catalyst.

3. The preparation method according to claim 2, characterized in that, The pretreatment method for nickel foam is as follows: the circular nickel foam sheets are ultrasonically cleaned with acetone and hydrochloric acid to remove residual organic impurities on the surface, then thoroughly rinsed with deionized water and vacuum dried.

4. The preparation method according to claim 3, characterized in that, The circular nickel foam sheet has a mass of 1.2g, a diameter of 8mm, a thickness of 2.0mm, and a porosity of 110PPI; the ultrasonic cleaning time is 20min, and the vacuum drying temperature is 80℃.

5. The preparation method according to claim 2, characterized in that, The mass ratio of ammonium chloride, melamine, and nickel foam is 5:3:

1.

6. The preparation method according to claim 2, characterized in that, The heating and calcination process involves heating to 550°C at a heating rate of 10°C / min and holding at that temperature for 0.5 hours; then heating to 900°C at a heating rate of 5°C / min and holding at that temperature for 3 hours.

7. The preparation method according to claim 2, characterized in that, The calcination was carried out in an argon atmosphere at a flow rate of 10 mL / min.

8. A method for producing hydrogen by ammonia decomposition, characterized in that, The ammonia decomposition catalyst of claim 1 is brought into contact with ammonia gas to react.

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