Mesoporous hollow sphere assembly structure catalyst, and preparation method and application thereof

Abstract

The application discloses a mesoporous hollow sphere assembly structure catalyst and a preparation method and application thereof, and belongs to the technical field of hydrogen production by methane decomposition. The preparation method comprises the following steps: dissolving Ni salt, Al salt and Ce salt in a solvent, and controlling the molar ratio of Ni, Al and Ce to be 7:(1-2.5):(0.5-2); obtaining atomized liquid drops through atomization, and performing a decomposition reaction on the atomized liquid drops at 400-500 DEG C; collecting reaction products, drying, and then calcining by heating to 550-700 DEG C to obtain a catalyst precursor; and performing reduction treatment on the catalyst precursor in a reducing atmosphere, and the mesoporous hollow sphere assembly catalyst with a cerium-doped regulated interface is obtained. The catalyst exhibits remarkable high mass space velocity long-term stability and anti-coking performance in the methane catalytic decomposition reaction.

Description

Technical Field

[0001] This invention relates to the field of methane decomposition for hydrogen production technology, and in particular to a mesoporous hollow sphere assembled structure catalyst, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Catalytic methane decomposition (CMD), as a sustainable hydrogen production route, can directly convert methane into high-purity hydrogen and value-added carbon materials. The process emits no greenhouse gases such as carbon dioxide, making it a promising technology. However, its practical application is severely hampered by the critical challenge of rapid catalyst deactivation.

[0004] The root cause of catalyst deactivation lies in the inherent contradiction of carbon deposition during the reaction. Methane molecules possess a highly stable tetrahedral structure with high CH bond energies, requiring activation and decomposition at high temperatures under the action of a catalyst. On transition metal catalysts such as nickel-based catalysts, the carbon atoms generated from methane dissociation can either dissolve and diffuse, eventually precipitating in an ordered manner as carbon nanotubes, or, due to the excessively rapid surface carbon formation rate, directly form a dense encapsulation layer on the active site surface. When the carbon formation rate exceeds its diffusion rate into the bulk metal phase or ordered structure, encapsulated carbon deposits will cover and block the active sites, leading to rapid catalyst deactivation. Therefore, optimizing the catalyst structure to precisely control and match the carbon formation and diffusion kinetics over a long period is the core challenge for suppressing active site encapsulation and improving catalyst lifetime.

[0005] Currently, research on improving the stability of nickel-based catalysts mainly revolves around two directions: modification of active components and innovation in preparation methods. For example, introducing a second metal component to modulate the electronic structure, or utilizing special synthetic pathways to obtain highly dispersed active sites. While these strategies can delay deactivation to some extent, they still have significant limitations: the modification effect on the active metal is often limited by the inherent tendency of carbon deposition during the reaction; and some synthetic methods that can create special microstructures often involve complex templates or lengthy processes, potentially leading to high costs, cumbersome steps, or potential impurity residues, thus restricting their practical application potential. Therefore, how to construct a catalyst system that can simultaneously achieve a persistent dynamic balance between carbon generation and diffusion through a simple and efficient strategy, working synergistically at both the chemical interface and physical structure levels, remains a pressing technical challenge in this field. Summary of the Invention

[0006] In view of this, the present invention provides a mesoporous hollow sphere assembled catalyst, its preparation method and application. The present invention prepares a Ni-Al-Ce-O mesoporous hollow sphere assembled catalyst with a cerium-doped regulated interface by a template-free aerosol-assisted self-assembly method. The catalyst exhibits significant long-term stability of high mass space velocity and anti-carbon deposition performance in the catalytic decomposition reaction of methane.

[0007] In a first aspect, the present invention provides a method for preparing a catalyst with a mesoporous hollow sphere assembly structure, comprising the following steps:

[0008] Ni, Al, and Ce salts are mixed and dissolved in a solvent, with the molar ratio of Ni, Al, and Ce controlled at 7:(1~2.5):(0.5~2). The mixture is atomized to obtain atomized droplets, which are then subjected to a decomposition reaction at 400~500℃. The reaction products are collected, dried, and calcined at 550~700℃ to obtain a catalyst precursor. The catalyst precursor is then reduced in a reducing atmosphere to obtain the mesoporous hollow sphere assembled structure catalyst. The reducing atmosphere is a mixture of hydrogen and an inert gas.

[0009] Preferably, the molar ratio of Ni, Al and Ce is 7 : (1.8~2.2) : (0.8~1.2).

[0010] Preferably, the Ni salt is selected from at least one of nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate; the Al salt is selected from at least one of aluminum nitrate, aluminum chloride, aluminum sulfate, and aluminum isopropoxide; and the Ce salt is selected from at least one of cerium nitrate, cerium ammonium nitrate, and cerium chloride.

[0011] Preferably, the solvent is selected from at least one of ethanol, methanol, isopropanol, and n-propanol.

[0012] Preferably, a carrier gas is used to carry the atomized droplets into a reactor at 400-500°C for decomposition reaction; the carrier gas is at least one of nitrogen and argon.

[0013] Preferably, in the step of heating to 550~700℃ for calcination, the heating rate is 1~5℃ / min, the calcination time is 3~6h, and the calcination is carried out in an oxygen-containing atmosphere.

[0014] Preferably, in the reducing atmosphere, the volume fraction of hydrogen is 2-10%; the reduction treatment time is 0.5-2 hours; and the reduction treatment temperature is 500-700°C.

[0015] Secondly, the present invention provides a mesoporous hollow sphere assembled structure catalyst, which is prepared by the above-described preparation method.

[0016] Thirdly, the present invention provides an application of the above-mentioned mesoporous hollow sphere assembled structure catalyst, wherein the application is: using the mesoporous hollow sphere assembled structure catalyst as a catalyst for the methane decomposition reaction.

[0017] Preferably, the reaction temperature of the methane decomposition reaction is 500~700℃, and the mass hourly space velocity is 24000~80000 mL·g. -1 ·h -1 .

[0018] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0019] (1) This invention achieves uniform composite of three metal oxides, namely nickel, aluminum, and cerium, at the atomic scale by limiting the specific molar ratio range of Ni, Al, and Ce. Among them, the introduction of cerium (Ce) effectively regulates the interfacial interaction between the active component nickel and the support alumina, enhances the metal-support interaction force, not only increases the concentration of oxygen vacancies in the catalyst to promote reactant activation, but also helps to maintain the high dispersion state of active nickel particles in the subsequent high-temperature reaction process, thereby chemically enhancing the catalyst's anti-sintering ability and intrinsic activity.

[0020] (2) This invention employs a preparation path involving the atomization of a precursor salt solution and rapid thermal decomposition at 400-500°C. This aerosol-assisted self-assembly process can directly and efficiently guide the formation of hollow sphere assemblies with mesoporous structures. This unique secondary structure generates a significant physical confinement effect through its cavities and channels. On the one hand, it prolongs the diffusion path of the reactant methane and dilutes the local concentration, thereby mitigating the instantaneous carbon generation rate. On the other hand, it provides directional space for the orderly growth of carbon nanotubes, effectively guiding carbon species to precipitate in a "bottom-end growth" mode. This structural confinement effect, combined with the aforementioned interfacial chemical regulation, synergistically achieves a dynamic balance between the carbon generation rate and the diffusion rate, fundamentally suppressing the problem of active sites being deactivated by disordered carbon deposition, and endowing the catalyst with excellent long-term operational stability.

[0021] (3) The preparation method of the present invention integrates two core steps: atomization pyrolysis and programmed temperature calcination. The process is simple and does not require the use of hard templates or structure directing agents. This method avoids the influence of complex post-processing steps and template residues on the intrinsic properties of the catalyst. It can controllably prepare mesoporous hollow sphere assembled catalysts with consistent structure and pure composition, and has good process repeatability and practicality. Attached Figure Description

[0022] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0023] Figure 1 The Ni7Al2Ce1O prepared in Example 1 of this invention x High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the precursor; where a represents Ni7Al2Ce1O x HAADF-STEM image of the precursor, b is a magnified HAADF-STEM image of a;

[0024] Figure 2 These are the X-ray diffraction (XRD) patterns of Example 1, Comparative Example 2, and Comparative Example 3 of the present invention, wherein a is the Ni7Al2Ce1O of Example 1. x Precursor, Ni7Al3O in Comparative Example 2 x Precursor and Comparative Example 3 Ni7Ce3O x XRD pattern of the precursor; b is Ni7Al2Ce1O from Example 1. x -H catalyst, Ni7Al3O (Comparative Example 2) x -H catalyst and Ni7Ce3O in Comparative Example 3 x XRD pattern of -H catalyst;

[0025] Figure 3 This is Ni7Al2Ce1O from Embodiment 1 of the present invention. x Quasi-in-situ X-ray photoelectron spectroscopy (XPS) spectrum of the -H catalyst, where a represents Ni 2 p XPS spectrum; b represents Ce 3d XPS spectrum;

[0026] Figure 4 This is Ni7Al2Ce1O from Embodiment 1 of the present invention. x -H catalyst and Ni7Al3O in Comparative Example 2 x High-resolution transmission electron microscopy (HRTEM) images of the -H catalyst after 300 min of methane decomposition reaction, where a is the HRTEM image of Example 1, b is the magnified HRTEM image of a and a schematic diagram of bottom growth; c is the HRTEM image of Comparative Example 2 and a schematic diagram of top growth.

[0027] Figure 5This is a comparison chart of methane conversion rate and carbon nanotube yield of the catalysts in Example 1, Comparative Examples 1-3, and Comparative Examples 5-6 of this invention, where a represents Ni7Al2Ce1O from Example 1. x -H catalyst and NiO catalyst of Comparative Example 1, Ni7Al3O of Comparative Example 2 x -H catalyst, Ni7Ce3O (Comparative Example 3) x -H catalyst, 50Ni / γ-Al2O3 catalyst of Comparative Example 5, and 50Ni / CeO2 catalyst of Comparative Example 6 were tested at a mass hourly space velocity (HHSV) of 60,000 mL·g. -1 ·h -1 Comparison of methane conversion rates at 0 min and 300 min under the specified conditions; b is the methane conversion rate of Ni7Al2Ce1O in Example 1. x -H catalyst and Ni7Al3O in Comparative Example 2 x -H catalyst, Ni7Ce3O (Comparative Example 3) x -H catalyst at a mass hourly space velocity (MHSV) of 30,000 mL·g -1 ·h -1 and 60000 mL·g -1 ·h -1 A comparison of carbon nanotube yields under different conditions;

[0028] Figure 6 This is Ni7Al2Ce1O from Embodiment 1 of the present invention. x -H catalyst, Ni7Al1Ce2O from Example 2 x -H catalyst, Ni7Al from Example 3 2.5 Ce 0.5 O x -H catalyst, NiO catalyst of Comparative Example 1, Ni7Al3O of Comparative Example 2 x -H catalyst, Ni7Ce3O (Comparative Example 3) x -H catalyst and Ni7Al of Comparative Example 4 2.95 Ce 0.05 O x -H catalyst at a mass hourly space velocity (MHSV) of 60,000 mL·g -1 ·h -1 Stability evaluation diagram under the given conditions;

[0029] Figure 7 This is Ni7Al2Ce1O from Embodiment 1 of the present invention. x -H catalyst, Ni7Al3O (Comparative Example 2) x -H catalyst, Ni7Ce3O (Comparative Example 3) x -H catalyst and Ni7Al2Ce1O of Comparative Example 7 x-C catalyst at a mass hourly space velocity (MHSV) of 60,000 mL·g -1 ·h -1 Stability evaluation diagram under the given conditions;

[0030] Figure 8 This is Ni7Al2Ce1O from Embodiment 1 of the present invention. x Stability evaluation diagram of the -H catalyst under pure methane atmosphere. Detailed Implementation

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] This invention provides a method for preparing a catalyst with a mesoporous hollow sphere assembly structure, comprising the following steps:

[0033] Ni, Al, and Ce salts are mixed and dispersed in a solvent, with the molar ratio of Ni, Al, and Ce controlled at 7:(1~2.5):(0.5~2). The mixture is atomized to obtain atomized droplets, which are then subjected to a decomposition reaction at 400~500℃. The reaction products are collected, dried, and then calcined at 550~700℃ to obtain a catalyst precursor. The catalyst precursor is then reduced in a reducing atmosphere to obtain the mesoporous hollow sphere assembled structure catalyst.

[0034] In this invention, the molar ratio of Ni, Al, and Ce is further preferably 7:(1.8~2.2):(0.8~1.2). Ni is the main catalytic active center; the introduction of Al aims to form an aluminum oxide matrix with a stable structure, serving as a "skeleton" for dispersing and anchoring Ni species; Ce, as a key promoter, plays a role that is not simply doping, but rather lies in its unique Ce content. 3+ / Ce 4+ It exhibits redox pairs and high oxygen migration capacity. At this ratio, Ce can effectively embed into the Ni-Al-O structure, significantly enhancing the strong metal-support interaction (SMSI) between Ni species and the aluminum oxide matrix, inducing abundant surface oxygen vacancies. These oxygen vacancies are potential active sites for activating methane CH bonds and can promote the transfer of carbon species generated in the reaction to the ordered structure. If the content of Al or Ce is too low, the framework support or interface regulation effect is insufficient; if it is too high, it may over-cover or dilute the active sites, leading to a decrease in activity. More preferably, the molar ratio of Ni, Al, and Ce is 7:(1.8~2.2):(0.8~1.2). Even more preferably, this molar ratio is 7:2:1, at which the synergistic effect of the three is optimal, and the catalyst activity and stability are most outstanding.

[0035] In this invention, the Ni salt is selected from at least one of nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate. Nickel nitrate is more preferred. The Al salt is selected from at least one of aluminum nitrate, aluminum chloride, aluminum sulfate, and aluminum isopropoxide; aluminum nitrate is more preferred. The Ce salt is selected from at least one of cerium nitrate, cerium ammonium nitrate, and cerium chloride; cerium nitrate is more preferred. The above metal salts can be anhydrous or hydrated, and this invention does not impose any special limitations on this.

[0036] The solvent selected in this invention must be able to dissolve the three metal salts mentioned above simultaneously and have a suitable evaporation rate to match the atomization process. The solvent is selected from at least one of ethanol, methanol, isopropanol, and n-propanol, with ethanol being more preferred. Ethanol has advantages such as low cost, rapid evaporation, and low toxicity. Its moderate surface tension is beneficial for forming uniform droplets during atomization, thereby obtaining a product with uniform size.

[0037] The mixing and dissolution time described in this invention is 10-50 min, more preferably 20-40 min. This process preferably employs stirring and / or ultrasonic treatment to ensure the formation of a homogeneous, stable, and precipitate-free clear precursor solution. For example, the mixture can be magnetically stirred for 10-20 min at room temperature, followed by ultrasonication for 5-15 min.

[0038] This invention transforms the precursor solution into micron-sized atomized droplets using an atomization device. The atomization device is not specifically limited; for example, an ultrasonic atomizer or a pressure atomizer can be used. Subsequently, these atomized droplets are carried by a carrier gas (such as nitrogen and / or argon) into a tubular furnace or other thermal reactor preheated to 400-500°C for rapid thermal decomposition. The atomized droplets undergo extremely rapid solvent evaporation and solute concentration in the high-temperature region, triggering evaporation-induced self-assembly. Metal salts preferentially concentrate and decompose on the droplet surface, forming a porous oxide shell, while the internal pressure generated by continuous solvent vaporization ultimately forms a hollow spherical structure. Multiple such hollow spheres further self-assemble into larger secondary aggregates with abundant mesopores and cavities during gas transport and collection.

[0039] The temperature of the decomposition reaction directly affects the decomposition rate of the metal salt and the crystallinity of the product. Too low a temperature may result in incomplete decomposition, leaving impurities such as nitrate ions; too high a temperature may lead to severe particle sintering, a decrease in specific surface area, and potential collapse of the hollow sphere structure. More preferably, the decomposition reaction temperature is 430–470 °C.

[0040] In this invention, the use of an inert carrier gas (such as high-purity nitrogen or argon) is to create an oxygen-free decomposition environment, prevent premature oxidation of the metal at high temperatures, and stabilize the delivery of the aerosol. The preferred carrier gas flow rate is 10~30 mL / min, which can be adjusted according to the atomization volume and reactor size to ensure that the droplets have sufficient residence time to complete the decomposition.

[0041] In this invention, after the decomposition reaction, the primary powder product obtained from the decomposition is collected from the rear end of the reactor. This product may contain a small amount of incompletely volatilized organic matter or moisture, and therefore needs to be dried. The drying method is preferably carried out in a forced-air drying oven or a vacuum drying oven, at a temperature preferably of 50-100°C, and for a time preferably of 6-15 hours, for example, drying overnight at 60°C.

[0042] In this invention, the dried primary powder product is calcined in an oxygen-containing atmosphere (air or oxygen atmosphere) at a programmed temperature rise, with a final calcination temperature of 550~700℃, more preferably 580~650℃. This step aims to further remove any trace carbonaceous species that may remain in the precursor, promote the crystallization and stabilization of the metal oxide phase, and strengthen the connection between hollow spheres, making the assembled structure more robust. For the Ni-Al-Ce-O system, calcination helps to form a more stable solid solution or composite oxide phase, allowing the interfacial regulation effect of Ce to be more fully realized.

[0043] In this invention, the heating rate is preferably 1~5℃ / min, more preferably 2~3℃ / min. A slower heating rate is beneficial for uniform heat transfer and reduces structural stress. The calcination time is preferably 3~6h, more preferably 4h. For example, the temperature is raised from room temperature to 600℃ at a rate of 2℃ / min, and then calcined at 600℃ for 4 hours.

[0044] In this invention, the reducing atmosphere is preferably a mixture of hydrogen and an inert gas (such as argon), wherein the volume fraction of hydrogen is controlled at 2-10%, more preferably 3-8%. The reduction treatment temperature is set at 500-700°C. If the temperature is too low, the reduction reaction rate is too slow and the efficiency is low; while if the temperature is too high, although reduction can be rapid, it will significantly aggravate the thermal migration and sintering tendency of nickel particles and may cause irreversible changes in the support structure, damaging its confinement effect. The reduction treatment time is 0.5-2 hours, which is sufficient to complete the reduction of the main NiO phase at the optimized temperature and hydrogen concentration. If the time is too short, the reduction may be incomplete; if the time is too long, the economy will decrease.

[0045] It is particularly noteworthy that the reduction process of this invention offers high operational flexibility. In practical applications, it is typically used as the final "activation" step before the catalyst is put into use, and is completed in situ within the reactor. The catalyst precursor can serve as a stable intermediate product that is easy to store and transport for extended periods. Users or manufacturers can, when needed, introduce a reducing gas and raise the temperature before the reaction begins, depending on the specific reaction system, to conveniently and reliably activate the stored catalyst precursor into a highly active final catalyst.

[0046] This invention also provides a mesoporous hollow sphere assembled structure catalyst, which is prepared by the above-described method. The chemical composition of this catalyst conforms to the general formula Ni. a Al b Ce c O x And it satisfies a:b:c = 7:(1~2.5):(0.5~2), its particle size is 50~500nm, and it presents an assembly structure of hollow spheres.

[0047] The hollow sphere assembly structure provided by this invention offers several advantages. First, high specific surface area and abundant pores: the packing voids between the mesoporous shell and the sphere provide an efficient pathway for reactant and product transport, exposing numerous active sites. Second, physical confinement effect: the cavities and tortuous channels within the hollow spheres extend the diffusion path of methane molecules, diluting their local concentration near the active sites, thereby physically slowing down the instantaneous carbon formation rate and allowing time for carbon atoms to diffuse into the bulk metallic phase and precipitate in an orderly manner. Third, structural stability: the assembled structure possesses good mechanical strength, better resisting the stress generated by carbon deposition during the reaction process and maintaining structural integrity.

[0048] The present invention also provides an application of the above-mentioned mesoporous hollow sphere assembled structure catalyst, wherein the application is: using the mesoporous hollow sphere assembled structure catalyst as a catalyst for methane decomposition reaction to efficiently and stably convert methane into hydrogen and carbon nanotubes.

[0049] The methane decomposition reaction described in this invention is preferably carried out in a fixed-bed reactor at a reaction temperature of 550-650°C, more preferably 600°C. If the temperature is too low, methane activation becomes difficult; if the temperature is too high, catalyst sintering may be accelerated. At this temperature, the catalyst can achieve both high activity and long lifespan.

[0050] Mass hourly space velocity (MHSV) is a crucial indicator for assessing the severity of a reaction and the processing capacity of a catalyst. One of the core advantages of the catalyst in this invention lies in its excellent stability even at high MHSVs. For application, the preferred MHSV for the catalyst is 24,000 to 80,000 mL·g. -1 ·h -1More preferably, the mass hourly space velocity (MSV) is 40,000 to 60,000 mL·g. -1 ·h -1 For example, at 60000 mL·g -1 ·h -1 At a high mass space velocity, the methane decomposition reaction catalyzed by the catalyst of this invention achieves a methane conversion rate of over 40% at 400 min, and the optimal catalyst can operate stably for over 1600 min, exhibiting excellent long-term stability.

[0051] Under the aforementioned preferred conditions, the catalyst of this invention can achieve efficient conversion of methane, and the generated carbon exists in the form of high-quality carbon nanotubes (CNTs). The growth mode is primarily bottom-end growth. Due to the strong interaction between the metal and the support, the metal nanoparticles do not detach from the support, and the carbon nanotubes grow outwards along the bottom end. This growth mode ensures that the active Ni particles are not encapsulated by CNTs, and the active sites are continuously exposed.

[0052] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0053] Example 1

[0054] This embodiment provides a mesoporous hollow sphere assembled structure catalyst Ni7Al2Ce1O x Preparation method of -H.

[0055] (1) Preparation of precursor solution: Accurately weigh Ni(NO3)2·6H2O, Al(NO3)3·9H2O and Ce(NO3)3·6H2O, wherein the molar ratio of Ni, Al and Ce is 7:2:1, and the total molar amount of the three nitrates is 8 mmol. Add the weighed three nitrates together to 120 mL of anhydrous ethanol, stir magnetically for 15 minutes at room temperature, and then sonicate for 10 minutes to form a homogeneous and clear precursor solution.

[0056] (2) Atomization and thermal decomposition: The precursor solution from step (1) was atomized into tiny droplets in small batches using an ultrasonic atomizer. Industrial nitrogen was used as the carrier gas to carry the atomized droplets into a high-temperature tubular furnace preheated to 450°C for rapid decomposition reaction. The decomposition reaction products were collected by a receiving device connected to the end of the reactor and equipped with a vacuum filtration pump to obtain primary powder.

[0057] (3) Drying and calcination: The collected primary powder was dried in an oven at 60°C for 12 hours. Then, the dried powder was transferred to a muffle furnace and heated to 600°C at a rate of 2°C / min in air, and calcined at this temperature for 4 hours. After natural cooling, the resulting sample was named Ni7Al2Ce1O. x Precursor.

[0058] (4) Reduction: Ni7Al2Ce1O x The precursor was reduced to 600℃ for 1 h in a 5% H2 / Ar atmosphere at a heating rate of 2℃ / min to obtain Ni7Al2Ce1O. x -H catalyst.

[0059] Figure 1 The high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image shows that the Ni7Al2Ce1O prepared in this embodiment... x The precursor exhibits spherical granular structure, with clearly visible lattice fringes spaced approximately 0.21 nm on its surface. Figure 1 b) corresponds to the (012) crystal plane of NiO, and the stripes with a spacing of about 0.32 nm correspond to the (111) crystal plane of CeO2, indicating that both NiO and CeO2 phases exist in the sample. However, no new information about Al2O3 was found, and Al2O3 may exist in an amorphous form.

[0060] Example 2

[0061] The difference between this embodiment and embodiment 1 is that the molar ratio of Ni, Al, and Ce in step (1) is 7:1:2, while the other steps and conditions remain unchanged. The precursor obtained in step (3) is named Ni7Al1Ce2O. x The precursor, the catalyst obtained in step (4), is named Ni7Al1Ce2O x -H catalyst.

[0062] Example 3

[0063] The difference between this embodiment and Embodiment 1 is that the molar ratio of Ni, Al, and Ce in step (1) is 7:2.5:0.5, while the other steps and conditions remain unchanged. The precursor obtained in step (3) is named Ni7Al. 2.5 Ce 0.5 O x The precursor, the catalyst obtained in step (4), is named Ni7Al. 2.5 Ce 0.5 O x -H catalyst.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 1 is that Al(NO3)3·9H2O and Ce(NO3)3·6H2O are not added in step (1) of this comparative example. Only 8 mmol of Ni(NO3)2·6H2O is weighed. The other steps and conditions remain unchanged. The precursor obtained is named NiO precursor and the catalyst obtained is named NiO-H catalyst.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 1 is that Ce(NO3)3·6H2O is not added in step (1) of this comparative example. Only Ni(NO3)2·6H2O and Al(NO3)3·9H2O are weighed out, with a total molar amount of 8 mmol. The molar ratio of Ni to Al is controlled at 7:3. The other steps and conditions remain unchanged. The precursor obtained in step (3) is named Ni7Al3O x The precursor, the catalyst obtained in step (4), is named Ni7Al3O x -H catalyst.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 1 is that Al(NO3)3·9H2O is not added in step (1) of this comparative example. Only Ni(NO3)2·6H2O and Ce(NO3)3·6H2O are weighed out, with a total molar amount of 8 mmol. The molar ratio of Ni to Ce is controlled at 7:3. The other steps and conditions remain unchanged. The precursor obtained in step (3) is named Ni7Ce3O. x The precursor, the catalyst obtained in step (4), is named Ni7Ce3O x -H catalyst.

[0070] Comparative Example 4

[0071] The difference between this comparative example and Example 1 is that the molar ratio of Ni, Al, and Ce in step (1) of this comparative example is 7:2.95:0.05, while the other steps and conditions remain unchanged. The precursor obtained in step (3) is named Ni7Al. 2.95 Ce 0.05 O x The precursor, the catalyst obtained in step (4), is named Ni7Al. 2.95 Ce 0.05 O x -H catalyst.

[0072] Comparative Example 5

[0073] This comparative example uses the traditional impregnation method to prepare a 50Ni / γ-Al2O3 catalyst, where "50" represents the theoretical mass percentage of Ni in γ-Al2O3. The specific preparation method is as follows:

[0074] First, 0.5 g of γ-Al₂O₃ powder was weighed and dispersed in 25 mL of high-purity water, then stirred and sonicated. Next, nickel nitrate solution was added dropwise to the γ-Al₂O₃ aqueous solution, controlling the mass of Ni element to be 50% of the mass of γ-Al₂O₃. The mixture was stirred in a 90℃ oil bath until dry to obtain the precursor, denoted as 50Ni / γ-Al₂O₃-UC. Finally, the precursor was calcined in a muffle furnace at 600℃ for 4 h, and the resulting product was denoted as the 50Ni / γ-Al₂O₃ catalyst.

[0075] Comparative Example 6

[0076] This comparative example uses the traditional impregnation method to prepare a 50Ni / CeO2 catalyst, where "50" represents the theoretical mass percentage of Ni in CeO2. The specific preparation method is as follows:

[0077] First, 0.5 g of CeO2 powder was weighed and dispersed in 25 mL of high-purity water, then stirred and sonicated. Next, nickel nitrate solution was added dropwise to the CeO2 aqueous solution, controlling the mass of Ni to be 50% of the CeO2 mass. The mixture was stirred in a 90℃ oil bath until dry to obtain the precursor, denoted as 50Ni / CeO2-UC. Finally, the precursor was calcined in a muffle furnace at 600℃ for 4 h, and the resulting product was denoted as the 50Ni / CeO2 catalyst.

[0078] Comparative Example 7

[0079] This comparative example provides Ni7Al2Ce1O x The preparation method of the -CH catalyst is as follows:

[0080] The Ni7Al2Ce1O prepared in Example 1 x The precursor was mechanically ball-milled in a planetary ball mill at 400 rpm for 240 min to break down its hollow sphere assembly structure. The resulting precursor was named Ni7Al2Ce1O. x -C precursor, the catalyst obtained by final reduction is named Ni7Al2Ce1O x -CH catalyst.

[0081] Test case

[0082] 1. Determination of specific surface area, pore volume, and average pore diameter

[0083] The test results of specific surface area, pore volume and average pore diameter of the precursors of Examples 1, 2, 3 and 7 are summarized in Table 1.

[0084] Table 1. Test results of specific surface area, pore volume, and average pore diameter.

[0085]

[0086] As can be seen from Table 1, the Ni7Al2Ce1O of Example 1 x After reduction, the precursor exhibits increased specific surface area and pore volume, with the average pore diameter changing from 3.02 nm to 2.98 nm, characteristic of a typical mesoporous structure. (Comparative Example 2: Ni7Al3O) x Precursor, Ni7Ce3O (Comparative Example 3) x Precursor and Comparative Example 7 Ni7Al2Ce1O x After reduction, the -C precursor has a smaller specific surface area and smaller pore volume, and it also belongs to a typical mesoporous structure.

[0087] 2. X-ray diffraction (XRD) measurement

[0088] Figure 2 In this context, 'a' refers to Ni7Al2Ce1O from Embodiment 1 of the present invention. x Precursor, Ni7Al3O in Comparative Example 2 x Precursor and Comparative Example 3 Ni7Ce3O x The X-ray diffraction (XRD) pattern of the precursor shows that Ni7Al2Ce1O x The precursor mainly consists of trigonal (rhombohedral) NiO (PDF#44-1159) and cubic CeO2 (PDF#34-0394). Notably, no obvious Al2O3 diffraction peaks were observed in the XRD pattern, indicating that the aluminum species mainly exist in an amorphous form. Figure 2 In this context, b represents Ni7Al2Ce1O from Example 1. x -H catalyst, Ni7Al3O (Comparative Example 2) x -H catalyst and Ni7Ce3O in Comparative Example 3 x The XRD pattern of the -H catalyst shows that after reduction treatment, three diffraction peaks belonging to the (111), (200), and (220) crystal planes of metallic Ni (PDF#4-850) appear. Furthermore, CeO doping is clearly observed. x This will broaden the diffraction peaks of metallic nickel and reduce their intensity. According to the Scherrer equation, the smaller the crystal size, the wider the diffraction peaks and the lower their intensity. In contrast, without CeO... x In the case of Al2O3, Ni7Al3Ox and Ni7Ce3O x The Ni diffraction peaks in the sample were significantly sharper. Meanwhile, the Ni7Al2Ce1O sample from Example 1 showed... x -H catalyst and Ni7Ce3O x Compared to the -H catalyst, the diffraction peaks of CeO2 disappeared significantly, indicating that it was in a highly dispersed state; while Al2O3 still maintained its amorphous structure.

[0089] 3. Quasi-in-situ X-ray photoelectron spectroscopy (XPS) determination

[0090] Figure 3 Ni7Al2Ce1O as described in Example 1 x Quasi-in-situ XPS spectra of -H catalysts; where a is Ce 3 d XPS spectrum; b represents Ni 2 p XPS spectrum. Figure 3 b in the text shows the source from Ni 2+ (854-856 eV) and Ni 0 A significant contribution from the (852.5 eV) species. Ni 2 p Quasi-in-situ XPS spectra show that Ni7Al2Ce1O x The -H catalyst exhibits significant Ni content at 852.5 eV. 0 Characteristic peaks, while Ni can still be observed 2+ Species, which may exist at the interface with CeO x Ni with a stable structure, or Al2O3. 2+ In addition, such as Figure 3 As shown in a, Ni7Al2Ce1O x Ce is present in the -H catalyst 3+ With Ce 4+ The mixed valence state.

[0091] 4. Catalyst application performance test

[0092] In a fixed-bed reactor, the atmospheric pressure catalytic performance of the catalyst was evaluated using a gas containing methane (CH4) as the reactant. First, 25 mg or 50 mg of the precursor powder from the examples or comparative studies were mixed with 2000 mg of inert SiO2 and packed into a quartz tube. Before the reaction, the mixture was reduced to 600 °C for 1 h at a programmed heating rate of 2 °C / min in a 5% H2 / Ar atmosphere, followed by testing in a catalytic methane decomposition (CMD) reaction environment. The gaseous products were analyzed using an online gas chromatograph equipped with a thermal conductivity detector (TCD).

[0093] The methane conversion rate is calculated using the following formula. and carbon nanotube production :

[0094] ;

[0095] ;

[0096] in This indicates the amount of CH4 in the intake air, while This indicates the amount of CH4 in the emitted gas. m C The mass m represents the actual mass of the carbon nanotubes after the reaction. Ni This indicates the mass of Ni in the catalyst.

[0097] (1) Morphological characterization of catalyst and carbon products

[0098] The test conditions are as follows: mass hourly space velocity (MHV) is 60,000 mL·g -1 ·h -1 Reactant gas: 20% CH4 / 80% N2; Gas flow rate: 25 mL / min; Fixed bed reactor inner diameter: 8 mm; Reaction temperature: 600℃; Catalyst dosage: 25 mg.

[0099] Figure 4 In this context, 'a' refers to Ni7Al2Ce1O from Example 1. x High-resolution transmission electron microscopy (HRTEM) image of the -H catalyst after 300 min of methane decomposition reaction; b is an enlarged HRTEM image of a and a schematic diagram of bottom growth; c is Ni7Al3O in Comparative Example 2. x HRTEM images and schematic diagrams of the top growth of the -H catalyst after 300 min of methane decomposition reaction. It can be seen that after 300 minutes of methane decomposition reaction, the Ni7Al2Ce1O catalyst in Example 1... x The -H catalyst retains its original hollow sphere assembly structure, and multi-directional carbon nanotubes (CNTs) are observed on its surface, exhibiting a bottom-end growth mode. Figure 4 The HRTEM image in Figure b shows that the lattice fringes of approximately 0.20 nm correspond to the (111) crystal plane of metallic Ni, while the lattice spacing of approximately 0.34 nm belongs to the (002) crystal plane of graphitic carbon, indicating the formation of graphitized carbon species during the reaction. In contrast, Ni7Al3O in Comparative Example 2... x The hollow sphere assembly structure of the -H catalyst underwent severe collapse, exhibiting a apical growth mode, and significant aggregation of metallic nickel particles was observed. These nickel particles were completely encapsulated by a dense carbon layer.

[0100] (2) Characterization of methane conversion rate and carbon nanotube yield

[0101] The test conditions are as follows: mass hourly space velocity (MHV) is 30,000 mL·g-1 ·h -1 Or 60000 mL·g -1 ·h -1 Reactant gas: 20% CH4 / 80% N2; Gas flow rate: 25 mL / min; Fixed bed reactor inner diameter: 40 mm; Reaction temperature: 600℃; Catalyst dosage: 25 mg.

[0102] Figure 5 In this context, 'a' refers to Ni7Al2Ce1O from Example 1. x -H catalyst and NiO catalyst of Comparative Example 1, Ni7Al3O of Comparative Example 2 x -H catalyst, Ni7Ce3O (Comparative Example 3) x -H catalyst, 50Ni / γ-Al2O3 catalyst of Comparative Example 5, and 50Ni / CeO2 catalyst of Comparative Example 6 were tested at a mass hourly space velocity (HHSV) of 60,000 mL·g. -1 ·h -1 A comparison of methane conversion rates at 0 min and 300 min under the specified conditions. It can be seen that the Ni7Al2Ce1O in Example 1... x The -H catalyst achieves an initial methane conversion of 55.1% at 600℃ and retains its initial activity after 300 min of reaction. Ni7Al3O x Ni7Ce3O x The initial activities of the CeO catalyst were 50.5%, 45.7%, and 4.7%, respectively. After 300 min of reaction, the methane conversion rates were only 5.7%, 7.1%, and 0.69%, respectively. This indicates that the CeO catalyst... x The addition of [a specific ingredient] significantly improved the stability of the catalyst; 50Ni / γ-Al2O3 and 50Ni / CeO2 were also almost completely deactivated after 300 min of reaction. The above data indicate that Ni7Al2Ce1O x -H catalysts combine high activity with excellent stability.

[0103] Further quantitative analysis was performed on the amount of carbon deposited on the catalyst, such as... Figure 5 As shown in b, Ni7Al2Ce1O in Example 1 x -H catalyst at a mass hourly space velocity (MHSV) of 30,000 mL·g -1 ·h -1 and 60000 mL·g -1 ·h -1 The yield of carbon nanotubes under the specified conditions reached 114.5 g. C / g Ni and 167.31 g C / g Ni It is significantly higher than that of Ni7Ce3O in Comparative Example 3.x -H catalyst and Ni7Al3O in Comparative Example 2 x -H catalyst.

[0104] Figure 6 Ni7Al2Ce1O as described in Example 1 x -H catalyst, Ni7Al1Ce2O from Example 2 x -H catalyst, Ni7Al from Example 3 2.5 Ce 0.5 O x -H catalyst, NiO catalyst of Comparative Example 1, Ni7Al3O of Comparative Example 2 x -H catalyst, Ni7Ce3O (Comparative Example 3) x -H catalyst and Ni7Al of Comparative Example 4 2.95 Ce 0.05 O x -H catalyst at a mass hourly space velocity (MHSV) of 60,000 mL·g -1 ·h -1 The stability evaluation chart under the given conditions shows that the catalysts in Examples 1-3 exhibit better stability, with the methane conversion rate remaining above 40% even after 400 min.

[0105] (3) Application performance under conditions of large inner diameter and high methane content

[0106] The test conditions are as follows: mass hourly space velocity (MHV) is 60,000 mL·g -1 ·h -1 Reactant gas: 20% CH4 / 80% N2; Gas flow rate: 25 mL / min; Fixed bed reactor inner diameter: 40 mm; Reaction temperature: 600℃; Catalyst dosage: 25 mg.

[0107] Figure 7 Ni7Al2Ce1O as described in Example 1 x -H catalyst, Ni7Al3O (Comparative Example 2) x -H catalyst, Ni7Ce3O (Comparative Example 3) x -H catalyst and Ni7Al2Ce1O of Comparative Example 7 x -C catalyst at a mass hourly space velocity (MHSV) of 60,000 mL·g -1 ·h -1 The stability evaluation diagram under the specified conditions shows that the catalysts of Comparative Examples 2, 3, and 7 were almost completely deactivated within 500 min, while the Ni7Al2Ce1O catalyst of Example 1... x The -H catalyst maintained a high methane conversion rate within 1600 min, decreasing only slightly from 50% to 44%, with a retention rate as high as 88%, demonstrating excellent long-term stability.

[0108] (4) Application performance under pure methane atmosphere

[0109] The test conditions are as follows: mass hourly space velocity (MHV) is 24000 mL·g -1 ·h -1 Reactant gas: 100% CH4; Gas flow rate: 20 mL / min; Fixed bed reactor inner diameter: 40 mm; Reaction temperature: 500℃; Catalyst dosage: 50 mg.

[0110] Figure 8 It is Ni7Al2Ce1O from Example 1 x The stability evaluation diagram of the -H catalyst under a pure methane atmosphere shows that even in a more demanding pure methane atmosphere, Ni7Al2Ce1O x It can still maintain a methane conversion rate of 13.1% within 1600 min.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a catalyst with a mesoporous hollow sphere assembly structure, characterized in that, Includes the following steps: Ni, Al, and Ce salts are mixed and dissolved in a solvent, with the molar ratio of Ni, Al, and Ce controlled at 7:(1~2.5):(0.5~2). The mixture is atomized to obtain atomized droplets, which are then carried into a reactor at 400~500℃ using a carrier gas, which is at least one of nitrogen and argon. The reaction products are collected, dried, and then calcined at 550~700℃ to obtain a catalyst precursor. The catalyst precursor is reduced in a reducing atmosphere to obtain the mesoporous hollow sphere assembled structure catalyst; the reducing atmosphere is a mixture of hydrogen and inert gas. The Al salt is selected from at least one of aluminum nitrate, aluminum chloride, aluminum sulfate, and aluminum isopropoxide; The solvent is selected from at least one of ethanol, methanol, isopropanol, and n-propanol; In the step of heating to 550~700℃ for calcination, the heating rate is 1~5℃ / min, the calcination time is 3~6h, and the calcination is carried out in an oxygen-containing atmosphere; In the reducing atmosphere, the volume fraction of hydrogen is 2-10%; the reduction treatment time is 0.5-2 hours; and the reduction treatment temperature is 500-700℃.

2. The preparation method according to claim 1, characterized in that, The molar ratio of Ni, Al and Ce is 7 : (1.8~2.2) : (0.8~1.2).

3. The preparation method according to claim 1, characterized in that, The Ni salt is selected from at least one of nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate; the Ce salt is selected from at least one of cerium nitrate, cerium ammonium nitrate, and cerium chloride.

4. A catalyst with a mesoporous hollow sphere assembly structure, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the mesoporous hollow sphere assembled structure catalyst as described in claim 4, characterized in that, The application is as follows: using the mesoporous hollow sphere assembled structure catalyst as a catalyst for the methane decomposition reaction.

6. The application as described in claim 5, characterized in that, The methane decomposition reaction is carried out at a temperature of 500–700 °C and a mass hourly space velocity (HHSV) of 24,000–80,000 mL·g. -1 ·h -1 .

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