A nitrogen-doped carbon modified Ni / MgAlO catalyst, a preparation method and application thereof

Abstract

The application discloses a kind of nitrogen-doped carbon modified Ni / MgAlO catalyst and its preparation method and application, belong to catalytic technology field.The present application is with magnesium source, aluminium source, nickel source and hexamethylene tetramine as raw material, by hydrothermal reaction and calcination preparation NiO / MgAlO, then with hydrochloric acid dopamine as carbon source to its surface modification, again carbonization treatment under nitrogen atmosphere, preparation Ni / MgAlO catalyst.Carbonization introduced carbon modifier and nickel exist strong electronic interaction, and through the same kind of repulsion effect mechanism accelerates the migration rate of carbon produced by methane cracking on the surface of nickel particle, reduce the formation of coated carbon, enhance the catalytic activity and hydrogen selectivity of catalyst;Carbon modifier on the surface of catalyst prevents methane cracking generated carbon from directly covering the surface of nickel particle, while inhibiting nickel particle sintering agglomeration at high temperature, enhances the catalytic stability of nickel.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and particularly relates to a nitrogen-doped carbon-modified Ni / MgAlO catalyst, its preparation method, and its application. Background Technology

[0002] Despite the promising prospects of methane cracking for hydrogen production, several pressing technical challenges remain in practical applications. While existing nickel catalysts possess good activity, low cost, and abundant reserves, making them the preferred catalysts for methane cracking to hydrogen production, they exhibit several significant drawbacks in actual operation. First, the reaction temperature is excessively high, increasing energy consumption and placing higher demands on the high-temperature resistance of equipment, thus increasing equipment costs and operational risks. Second, nickel catalysts are prone to deactivation during the reaction, primarily due to carbon deposition and sintering, which reduces the number of active sites, significantly shortening catalyst lifespan and increasing replacement frequency and cost. This severely restricts the large-scale and industrial application of methane cracking for hydrogen production. Therefore, reducing the reaction temperature of nickel catalysts and improving their stability during methane cracking for hydrogen production has become a crucial technical problem that needs to be solved in this field. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a nitrogen-doped carbon-modified Ni / MgAlO catalyst, its preparation method, and its applications.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst, comprising the following steps:

[0006] (1) After mixing magnesium source, aluminum source, nickel source and hexamethylenetetramine with water, a hydrothermal reaction was carried out, followed by drying and calcination to obtain NiO / MgAlO;

[0007] (2) Add the NiO / MgAlO and tris(hydroxymethyl)aminomethane from step (1) to water and stir, then add dopamine hydrochloride and continue stirring to obtain a black suspension; centrifuge and wash the black suspension to obtain a black precipitate; dry the black precipitate and then carbonize it under a nitrogen atmosphere to obtain the nitrogen-doped carbon-modified Ni / MgAlO catalyst.

[0008] Technical Principle: This invention first prepares NiO / MgAlO from magnesium, aluminum, nickel, and hexamethylenetetramine as raw materials through hydrothermal reaction and calcination. Then, it modifies the surface of the Ni / MgAlO catalyst using dopamine hydrochloride as a carbon source, followed by carbonization under an N2 atmosphere. Furthermore, the carbon modifier introduced by carbonization exhibits strong electronic interactions with Ni, accelerating the migration rate of carbon generated from methane cracking on the surface of nickel particles through a homogeneous repulsion mechanism. This reduces the formation of coated carbon, enhancing the catalytic activity and selectivity of the catalyst for hydrogen production from methane cracking. Simultaneously, the carbon modifier on the surface of the Ni / MgAlO catalyst provides spatial shielding protection for the Ni nanoparticles, preventing carbon generated from methane cracking from directly covering the Ni particle surface and inhibiting the sintering and agglomeration of Ni particles at high temperatures, thus enhancing the catalytic stability of the Ni particles. Dopamine hydrochloride contains nitrogen, which, after polymerization and carbonization, forms nitrogen-doped carbon that coats the surface of Ni / MgAlO. Nitrogen-doped carbon, acting as a semiconductor, forms a Mott-Schottky interaction (i.e., strong electronic interaction) upon contact with the conductor metal Ni, significantly reducing the deposition rate of carbon on the nickel surface during methane cracking and thus enhancing catalytic stability. Furthermore, the addition of Mg and Al sources is for the preparation of Mg and Al bimetallic oxides. The addition of Mg increases the Lewis basicity of the Al oxide, which can appropriately weaken the methane cracking rate to some extent, balancing carbon deposition formation and migration, and achieving the overall optimal effect of "moderate rate and extended lifetime".

[0009] Further, in step (1), the mass ratio of the magnesium source, aluminum source, nickel source and hexamethylenetetramine is 1:0.75:0.3:2.5.

[0010] Further, in step (1), the magnesium source is selected from magnesium nitrate hexahydrate; the aluminum source is selected from aluminum nitrate nonahydrate; and the nickel source is selected from nickel nitrate hexahydrate.

[0011] Furthermore, in step (1), the hydrothermal reaction is carried out at a temperature of 150°C for 24 hours.

[0012] Furthermore, in step (1), the roasting temperature is 700°C and the time is 2 hours.

[0013] Further, in step (2), the mass ratio of NiO / MgAlO, tris(hydroxymethyl)aminomethane and dopamine hydrochloride is 1:0.1:0.3.

[0014] Furthermore, in step (2), the stirring speed is 150 r / min and the time is 1-8 h.

[0015] Furthermore, in step (2), the carbonization temperature is 600-800℃ and the time is 2h.

[0016] This invention provides a nitrogen-doped carbon-modified Ni / MgAlO catalyst, which is prepared according to the preparation method described above.

[0017] The present invention also provides the application of the nitrogen-doped carbon-modified Ni / MgAlO catalyst as described above in the catalytic cracking of methane.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] This invention optimizes the structure, preparation process, and reaction conditions of the Ni catalyst, thereby reducing the reaction temperature and improving the catalyst's activity, stability, and resistance to carbon deposition. It achieves highly efficient catalytic conversion of nickel-based catalysts in the methane cracking hydrogen production reaction, providing an efficient and low-cost hydrogen solution for the fiberglass marine hydrogen fuel cell industry and promoting the development of green ships and related industries. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0021] Figure 1 The XRD patterns of the catalysts prepared in Examples 1-3 and Comparative Example 1 are shown below.

[0022] Figure 2 The methane conversion and hydrogen selectivity of the catalysts prepared in Examples 1-5 and Comparative Examples 1-4 in the methane cracking hydrogen production reaction;

[0023] Figure 3 The hydrogen yield of the catalysts prepared in Examples 1-5 and Comparative Examples 1-4 in the methane cracking hydrogen production reaction;

[0024] Figure 4 The results show the stability of the nitrogen-doped carbon-modified Ni / MgAlO catalyst prepared in Example 2. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] This invention provides a method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst, comprising the following steps:

[0028] (1) After mixing magnesium source, aluminum source, nickel source and hexamethylenetetramine with water, a hydrothermal reaction was carried out, followed by drying and calcination to obtain NiO / MgAlO;

[0029] (2) Add the NiO / MgAlO and tris(hydroxymethyl)aminomethane from step (1) to water and stir, then add dopamine hydrochloride and continue stirring to obtain a black suspension; centrifuge and wash the black suspension to obtain a black precipitate; dry the black precipitate and then carbonize it under a nitrogen atmosphere to obtain the nitrogen-doped carbon-modified Ni / MgAlO catalyst.

[0030] In a preferred embodiment, in step (1), the mass ratio of the magnesium source, aluminum source, nickel source and hexamethylenetetramine is 1:0.75:0.3:2.5.

[0031] In a preferred embodiment, in step (1), the magnesium source is selected from magnesium nitrate hexahydrate; the aluminum source is selected from aluminum nitrate nonahydrate; and the nickel source is selected from nickel nitrate hexahydrate.

[0032] In a preferred embodiment, in step (1), the amount of magnesium source used is 1g, and the amount of water used is 50mL.

[0033] In a preferred embodiment, in step (1), the magnesium source, aluminum source, nickel source and hexamethylenetetramine are mixed with water by stirring; the stirring temperature is room temperature, the stirring speed is 150 r / min, and the stirring time is 1 h.

[0034] In a preferred embodiment, in step (1), the hydrothermal reaction temperature is 150°C and the time is 24 hours; the equipment for the hydrothermal reaction is a stainless steel hydrothermal synthesis reactor with a polytetrafluoroethylene liner. During the hydrothermal reaction, hexamethylenetetramine first undergoes a hydrolysis reaction, and the generated ammonia gradually forms a weakly alkaline environment in the system. Mg from the magnesium source, aluminum source, and nickel source dissociates... 2+ Al 3 + Ni 2+ In a weakly alkaline environment, it gradually hydrolyzes to generate hydroxide or hydroxyl oxide precursors such as Al(OH)3, Mg(OH)2, and Ni(OH)2. Then, under high temperature and high pressure, it undergoes dehydration or ion recrystallization to form a more stable structure.

[0035] In a preferred embodiment, in step (1), the drying temperature is 100°C, the time is 12 hours, and the equipment is a drying oven.

[0036] In a preferred embodiment, in step (1), the calcination temperature is 700°C and the time is 2 hours; the calcination equipment is a muffle furnace. The hydroxide or hydroxyl oxide precursors obtained by hydrothermal reaction are mainly amorphous structures or metastable phases. During calcination, driven by high temperature, the precursors will further dehydrate, undergo solid-phase reactions or lattice rearrangement, and transform into more stable crystalline metal oxides.

[0037] In a preferred embodiment, in step (2), the mass ratio of NiO / MgAlO, tris(hydroxymethyl)aminomethane, and dopamine hydrochloride is 1:0.1:0.3. When dopamine hydrochloride is used as a carbon source, tris(hydroxymethyl)aminomethane needs to be added to the aqueous solution to maintain a weakly alkaline environment. Under these conditions, dopamine hydrochloride undergoes an oxidative polymerization reaction and forms a network polymer structure, which then uniformly coats the surface of NiO / MgAlO. The more dopamine hydrochloride is added, the more dopamine polymerizes on the surface of NiO / MgAlO, and the more nitrogen-doped carbon modifiers are generated on its surface after subsequent carbonization treatment. However, excessive carbon modifiers will hinder the effective contact between the reactants and the active sites, thus reducing the catalytic reaction efficiency. Conversely, if the amount of dopamine hydrochloride added is too small, the nitrogen-doped carbon modifiers on the surface of NiO / MgAlO will be insufficient, failing to fully exert their protective effect on the nickel active sites and making it difficult to effectively slow down the deposition rate of carbon on the nickel surface during methane cracking, which will also affect the catalytic reaction efficiency.

[0038] In a preferred embodiment, in step (2), the amount of water used is 70 mL, with the amount of NiO / MgAlO being 1 g.

[0039] In a preferred embodiment, in step (2), the stirring temperature is room temperature, the stirring speed is 150 r / min, and the stirring time is 1 h.

[0040] In a preferred embodiment, in step (2), the stirring speed is 150 r / min and the stirring time is 1-8 h, more preferably 3-8 h. During stirring, dopamine hydrochloride undergoes a polymerization reaction and forms a network structure, which then coats the NiO / MgAlO surface. As the stirring time increases, the amount of dopamine polymerized on the NiO / MgAlO surface gradually increases, and after subsequent carbonization treatment, the amount of nitrogen-doped carbon modification generated on its surface will also increase accordingly. Insufficient stirring time will lead to insufficient nitrogen-doped carbon modification, thus failing to fully exert its protective effect on nickel active sites and making it difficult to effectively inhibit the deposition rate of carbon on the nickel surface during methane cracking; while excessive stirring will cause too much nitrogen-doped carbon modification to coat the NiO / MgAlO surface, hindering the effective contact between reactants and active centers and reducing the catalytic reaction efficiency.

[0041] In a preferred embodiment, in step (2), the drying temperature is 100°C, the time is 12 hours, and the equipment is an oven.

[0042] In a preferred embodiment, step (2) further includes a grinding step after drying; the grinding equipment is an agate grinding jar, and the particle size of the product obtained by grinding is 300-500 mesh.

[0043] In a preferred embodiment, in step (2), the flow rate of nitrogen is 30 mL / min.

[0044] In a preferred embodiment, in step (2), the carbonization temperature is 600-800℃, and the time is 2 hours; the rate of heating to the carbonization temperature is 5℃ / min; the carbonization equipment is a tube furnace. The carbonization temperature has a significant impact on the activity of the Ni / MgAlO catalyst. If the carbonization temperature is too low, the polydopamine carbonization reaction will be incomplete, and the insufficiently carbonized polydopamine will remain and deposit on the catalyst surface, reducing the catalyst activity; conversely, if the carbonization temperature is too high, it is easy to cause high-temperature sintering of nickel particles, resulting in a reduction in the number of active sites, which will also cause a decrease in catalyst activity.

[0045] This invention provides a nitrogen-doped carbon-modified Ni / MgAlO catalyst, which is prepared according to the preparation method described above.

[0046] The present invention also provides the application of the nitrogen-doped carbon-modified Ni / MgAlO catalyst as described above in the catalytic cracking of methane.

[0047] In this embodiment of the invention, room temperature refers to "25±2℃".

[0048] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0049] Example 1

[0050] A method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst, comprising the following steps:

[0051] (1) Take 1g magnesium nitrate hexahydrate, 0.75g aluminum nitrate nonahydrate, 0.3g nickel nitrate hexahydrate and 2.5g hexamethylenetetramine, put them into 50mL of deionized water, stir at room temperature for 1h to obtain a mixed solution. Put the obtained mixed solution into a stainless steel hydrothermal synthesis reactor with a polytetrafluoroethylene liner, and hydrothermally react at 150℃ for 24h. Then put it into a drying oven at 100℃ for 12h, and then put it into a muffle furnace and calcine at 700℃ for 2h to obtain NiO / MgAlO.

[0052] (2) Take 1g NiO / MgAlO and 0.1g tris(hydroxymethyl)aminomethane and add them to 70mL of deionized water. Stir at room temperature and 150r / min for 1h, then add 0.3g dopamine hydrochloride and continue stirring at 150r / min for 1h to obtain a black suspension. After centrifugation and washing, a black precipitate is obtained. The black precipitate is placed in an oven and dried at 100℃ for 12h. It is then ground thoroughly in an agate grinding jar until the particle size is 300-500 mesh and placed in a porcelain boat. In a tube furnace under nitrogen atmosphere protection (nitrogen flow rate is 30mL / min), the temperature is raised to 700℃ at a heating rate of 5℃ / min for 2h to obtain a nitrogen-doped carbon-modified Ni / MgAlO catalyst, denoted as Ni / MgAlO-C1-700.

[0053] Example 2

[0054] A method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst, comprising the following steps:

[0055] Step (1) is the same as in Example 1.

[0056] (2) Take 1g NiO / MgAlO and 0.1g tris(hydroxymethyl)aminomethane and add them to 70mL of deionized water. Stir at room temperature and 150r / min for 1h, then add 0.3g dopamine hydrochloride and continue stirring at 150r / min for 3h to obtain a black suspension. After centrifugation and washing, a black precipitate is obtained. The black precipitate is placed in an oven and dried at 100℃ for 12h. It is then ground thoroughly in an agate grinding jar to a particle size of 300-500 mesh and placed in a porcelain boat. In a tube furnace under nitrogen atmosphere protection (nitrogen flow rate of 30mL / min), the temperature is raised to 700℃ at a heating rate of 5℃ / min for 2h to obtain a nitrogen-doped carbon-modified Ni / MgAlO catalyst, denoted as Ni / MgAlO-C3-700.

[0057] Example 3

[0058] A method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst, comprising the following steps:

[0059] Step (1) is the same as in Example 1.

[0060] (2) Take 1g NiO / MgAlO and 0.1g tris(hydroxymethyl)aminomethane and add them to 70mL of deionized water. Stir at room temperature and 150r / min for 1h, then add 0.3g dopamine hydrochloride and continue stirring at 150r / min for 8h to obtain a black suspension. After centrifugation and washing, a black precipitate is obtained. The black precipitate is placed in an oven and dried at 100℃ for 12h. It is then ground thoroughly in an agate grinding jar to a particle size of 300-500 mesh and placed in a porcelain boat. In a tube furnace under nitrogen atmosphere protection (nitrogen flow rate of 30mL / min), the temperature is raised to 700℃ at a heating rate of 5℃ / min for 2h to obtain a nitrogen-doped carbon-modified Ni / MgAlO catalyst, denoted as Ni / MgAlO-C8-700.

[0061] Example 4

[0062] A method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst, comprising the following steps:

[0063] Step (1) is the same as in Example 1.

[0064] (2) Take 1g NiO / MgAlO and 0.1g tris(hydroxymethyl)aminomethane and add them to 70mL of deionized water. Stir at room temperature and 150r / min for 1h, then add 0.3g dopamine hydrochloride and continue stirring at 150r / min for 3h to obtain a black suspension. After centrifugation and washing, a black precipitate is obtained. The black precipitate is placed in an oven and dried at 100℃ for 12h. It is then ground thoroughly with an agate grinding jar to a particle size of 300-500 mesh and placed in a porcelain boat. In a tube furnace under nitrogen atmosphere protection (nitrogen flow rate of 30mL / min), the temperature is raised to 600℃ at a heating rate of 5℃ / min for 2h to obtain a nitrogen-doped carbon-modified Ni / MgAlO catalyst, denoted as Ni / MgAlO-C3-600.

[0065] Example 5

[0066] A method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst, comprising the following steps:

[0067] Step (1) is the same as in Example 1.

[0068] (2) Take 1g NiO / MgAlO and 0.1g tris(hydroxymethyl)aminomethane and add them to 70mL of deionized water. Stir at room temperature and 150r / min for 1h, then add 0.3g dopamine hydrochloride and continue stirring at 150r / min for 3h to obtain a black suspension. After centrifugation and washing, a black precipitate is obtained. The black precipitate is placed in an oven and dried at 100℃ for 12h. It is then ground thoroughly in an agate grinding jar to a particle size of 300-500 mesh and placed in a porcelain boat. In a tube furnace under nitrogen atmosphere protection (nitrogen flow rate of 30mL / min), the temperature is raised to 800℃ at a heating rate of 5℃ / min for 2h to obtain a nitrogen-doped carbon-modified Ni / MgAlO catalyst, denoted as Ni / MgAlO-C3-800.

[0069] Comparative Example 1

[0070] A method for preparing a NiO / MgAlO catalyst, comprising the following specific steps:

[0071] Take 1g of magnesium nitrate hexahydrate, 0.75g of aluminum nitrate nonahydrate, 0.3g of nickel nitrate hexahydrate and 2.5g of hexamethylenetetramine, put them into 50mL of deionized water, and stir at room temperature for 1h to obtain a mixed solution; put the obtained mixed solution into a stainless steel hydrothermal synthesis reactor with a polytetrafluoroethylene liner, and hydrothermally react at 150℃ for 24h, then put it into a drying oven at 100℃ for 12h, and then put it into a muffle furnace and calcine at 700℃ for 2h to obtain NiO / MgAlO catalyst.

[0072] Comparative Example 2

[0073] A method for preparing a NiO / MgO catalyst, comprising the following steps:

[0074] Take 1g of magnesium nitrate hexahydrate, 0.3g of nickel nitrate hexahydrate and 2.5g of hexamethylenetetramine, put them into 50mL of deionized water, and stir at room temperature for 1h to obtain a mixed solution; put the obtained mixed solution into a stainless steel hydrothermal synthesis reactor with a polytetrafluoroethylene liner, and hydrothermally react at 150℃ for 24h, then put it into a drying oven at 100℃ for 12h, and then put it into a muffle furnace and calcine at 700℃ for 2h to obtain NiO / MgO catalyst.

[0075] Comparative Example 3

[0076] A method for preparing a NiO / Al2O3 catalyst, the specific steps of which are as follows:

[0077] Take 0.75g of aluminum nitrate nonahydrate, 0.3g of nickel nitrate hexahydrate and 2.5g of hexamethylenetetramine, put them into 50mL of deionized water, and stir at room temperature for 1h to obtain a mixed solution; put the obtained mixed solution into a stainless steel hydrothermal synthesis reactor with a polytetrafluoroethylene liner, and hydrothermally react at 150℃ for 24h, then put it into a drying oven at 100℃ for 12h, and then put it into a muffle furnace and calcine at 700℃ for 2h to obtain NiO / Al2O3 catalyst.

[0078] Comparative Example 4

[0079] A method for preparing a nitrogen-doped carbon-modified Ni / Al2O3 catalyst, the specific steps of which are as follows:

[0080] (1) Take 0.75g aluminum nitrate nonahydrate, 0.3g nickel nitrate hexahydrate and 2.5g hexamethylenetetramine, put them into 50mL of deionized water, and stir at room temperature for 1h to obtain a mixed solution; put the obtained mixed solution into a stainless steel hydrothermal synthesis reactor with a polytetrafluoroethylene liner, and hydrothermally react at 150℃ for 24h, then put it into a drying oven at 100℃ for 12h, and then put it into a muffle furnace and calcine at 700℃ for 2h to obtain NiO / Al2O3 catalyst.

[0081] (2) Take 1g of NiO / Al2O3 catalyst and 0.1g of tris(hydroxymethyl)aminomethane and add them to 70mL of deionized water. Stir at room temperature and 150r / min for 1h, then add 0.3g of dopamine hydrochloride and continue stirring at 150r / min for 3h to obtain a black suspension. After centrifugation and washing, a black precipitate is obtained. The black precipitate is placed in an oven and dried at 100℃ for 12h. After thorough grinding, it is placed in a porcelain boat and carbonized at 700℃ for 2h in a tube furnace under nitrogen atmosphere protection (nitrogen flow rate is 30mL / min) at a heating rate of 5℃ / min to obtain a nitrogen-doped carbon-modified Ni / Al2O3 catalyst, denoted as Ni / Al2O3-C3-700.

[0082] The catalyst activity evaluation was carried out in a fixed-bed reactor, and the specific process is as follows:

[0083] Weigh 0.05g of 40-60 mesh catalyst and 1g of quartz sand, mix thoroughly, and then pack the mixture into a quartz tube reactor with an inner diameter of 8mm, an outer diameter of 10mm, and a length of 45cm. Both ends of the catalyst bed are filled with quartz sand. The reaction outlet gas (containing H2 and CH4) is detected and analyzed by online gas chromatography.

[0084] The catalysts prepared in Examples 1-5 and Comparative Example 4 do not require H2 pre-reduction before the reaction. The catalytic reaction process for methane cracking to produce hydrogen is as follows: under N2 protection (nitrogen flow rate of 30 mL / min), the catalyst bed is heated to 800°C, and then methane (methane flow rate of 6 mL / min) is introduced to carry out the catalytic reaction for methane cracking to produce hydrogen. The reaction time is 4 h.

[0085] The catalysts prepared in Comparative Examples 1-3 require H2 pre-reduction before the reaction. The catalytic reaction process for methane cracking to produce hydrogen is as follows: the catalyst bed is heated to 500℃ under H2 atmosphere and pre-reduced for 2 hours, then cooled to room temperature (H2 pre-reduction), switched to N2 atmosphere and heated to the target temperature of 800℃, and then switched to a mixed reaction gas of methane and nitrogen (methane flow rate of 6 mL / min and nitrogen flow rate of 30 mL / min) to carry out the catalytic reaction for methane cracking to produce hydrogen, with a reaction time of 4 hours.

[0086] X-ray diffraction (XRD) analysis was performed on the catalysts prepared in Examples 1-3 and the catalyst prepared in Comparative Example 1 after H2 pre-reduction. The results are shown in the figure. Figure 1 The Ni / MgAlO reduced by hydrogen in the figure is the catalyst prepared by Comparative Example 1 after pre-reduction by H2. Figure 1 This confirms that in Examples 1-3 of the present invention, metallic Ni was formed by high-temperature carbonization, while in Comparative Example 1, after the catalyst was reduced at 500°C for 2 hours in H2 atmosphere, some NiO species were converted into metallic Ni.

[0087] The methane conversion and hydrogen selectivity of the catalysts prepared in Examples 1-5 and Comparative Examples 1-4 in the methane cracking to hydrogen production reaction are shown in the figures. Figure 2 The hydrogen yields of the catalysts prepared in Examples 1-5 and Comparative Examples 1-4 in the methane cracking hydrogen production reaction are shown in the figure. Figure 3 The catalytic activity data of the catalysts prepared in Examples 1-5 and Comparative Examples 1-4 in the methane cracking hydrogen production reaction are shown in Table 1.

[0088] Table 1 Catalytic activity data in methane cracking for hydrogen production.

[0089]

[0090] Combination Figure 2-3As shown in Table 1, the catalysts without nitrogen doping and carbon modification, i.e., the catalysts prepared in Comparative Examples 1-3, exhibited relatively low catalytic activity at 800℃. The methane conversion rate of the NiO / MgAlO catalyst prepared in Comparative Example 1 was 9.5%, that of the NiO / MgO catalyst prepared in Comparative Example 2 was 14.7%, and that of the NiO / Al2O3 catalyst prepared in Comparative Example 3 was 6.7%. In contrast, the activity of NiO / MgAlO significantly increased after nitrogen doping and carbon modification. The Ni / MgAlO-C3-700 catalyst prepared in Example 2 achieved the highest methane conversion rate of 42.1%, which was higher than the 20.8% methane conversion rate of the Ni / MgAlO-C1-700 catalyst prepared in Example 1 and the 36.3% methane conversion rate of the Ni / MgAlO-C8-700 catalyst prepared in Example 3. Furthermore, the nitrogen-doped carbon-modified Ni / MgAlO catalyst prepared in this invention exhibits almost 100% hydrogen selectivity, and the hydrogen yield increases with increasing methane conversion and hydrogen selectivity.

[0091] Figure 4 The stability results are for the nitrogen-doped carbon-modified Ni / MgAlO catalyst prepared in Example 2. From... Figure 4 It can be seen that the catalytic activity of the nitrogen-doped carbon-modified Ni / MgAlO catalyst prepared in Example 2 did not decrease and maintained good catalytic stability even after the methane cracking hydrogen production reaction lasted for 10 hours.

[0092] Comparing the catalytic activity results of the above examples and comparative examples, it can be seen that carbon modification plays an important role in enhancing the catalytic activity of the catalyst. This is mainly due to the fact that carbon modifiers can effectively regulate the electronic structure of metallic Ni and construct a spatial protective layer. This not only effectively shields the carbon generated in the methane cracking hydrogen production reaction from being directly deposited on the Ni active sites, but also accelerates the migration rate of carbon on the surface of Ni particles, reduces the formation of coated carbon, and thus enhances the catalytic activity and stability of the catalyst, achieving efficient catalytic conversion of nickel-based catalysts in the methane cracking hydrogen production reaction.

[0093] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst, characterized by, The preparation method comprises the following steps: (1) mixing a magnesium source, an aluminum source, a nickel source and hexamethylenetetramine with water, and then performing a hydrothermal reaction, and then drying and calcining to obtain a NiO / MgAlO; (2) adding the NiO / MgAlO obtained in step (1) and trimethylol aminomethane into water and stirring, and then adding dopamine hydrochloride and continuing to stir to obtain a black suspension; centrifuging and washing the black suspension to obtain a black precipitate; drying the black precipitate, and then performing carbonization under a nitrogen atmosphere to obtain the nitrogen-doped carbon-modified Ni / MgAlO catalyst.

2. The method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst according to claim 1, characterized by, In step (1), the mass ratio of the magnesium source, the aluminum source, the nickel source and the hexamethylenetetramine is 1:0.75:0.3:2.

5.

3. The method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst according to claim 2, characterized by, In step (1), the magnesium source is selected from magnesium nitrate hexahydrate; the aluminum source is selected from aluminum nitrate nonahydrate; and the nickel source is selected from nickel nitrate hexahydrate.

4. The method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst according to claim 1, characterized by, In step (1), the temperature of the hydrothermal reaction is 150 DEG C, and the time is 24 h.

5. The method of preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst according to claim 1, characterized by, In step (1), the temperature of the calcination is 700 DEG C, and the time is 2 h.

6. The method of preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst according to claim 1, characterized by, In step (2), the mass ratio of the NiO / MgAlO, the trimethylol aminomethane and the dopamine hydrochloride is 1:0.1:0.

3.

7. The method of preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst according to claim 1, characterized by, In step (2), the stirring speed is 150 r / min, and the time is 1-8 h.

8. The method for preparing a nitrogen-doped carbon-modified Ni / MgAlO catalyst according to claim 1, characterized by, In step (2), the temperature of the carbonization is 600-800 DEG C, and the time is 2 h.

9. A nitrogen-doped carbon-modified Ni / MgAlO catalyst characterized in that, The nitrogen-doped carbon-modified Ni / MgAlO catalyst is prepared by the preparation method according to any one of claims 1-8.

10. Use of the nitrogen-doped carbon-modified Ni / MgAlO catalyst according to claim 9 in catalyzing methane cracking.

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