In-situ confinement catalytic hydrogenation method of magnesium nanoparticles

Abstract

The invention provides an in-situ confinement catalytic hydrogenation method of magnesium nanoparticles. The in-situ confinement catalytic hydrogenation method comprises the following steps: S1, premixing treatment: uniformly mixing the magnesium nanoparticles and three-dimensional fold structure MXene nanosheets under the protection of an inert atmosphere; s2, confinement assembly: carrying out mechanical treatment on the mixture obtained in the step S1 to form an Mg / MXene composite precursor; s3, in-situ catalytic hydrogenation: putting the Mg / MXene composite precursor into a high-pressure hydrogenation reaction device, introducing hydrogen, increasing the pressure of the high-pressure hydrogenation reaction device to 3.0-8.0 Mpa, increasing the temperature to 180-280 DEG C, and carrying out heat-preservation and pressure-maintaining reaction for 2-10 hours; and S4, cooling and collecting: after the reaction is finished, cooling and releasing the pressure, and collecting a product under the protection of an inert atmosphere to obtain the MgH2 / MXene nano composite material. According to the method, the MXene nanosheet with the three-dimensional fold structure is utilized, the magnesium nanoparticles are effectively isolated and stabilized and prevented from being agglomerated in the hydrogenation process, meanwhile, an active catalytic phase is generated in situ to improve the hydrogenation reaction efficiency, and rapid and almost complete hydrogenation of magnesium can be achieved under the mild condition.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials and nanotechnology, specifically relating to an in-situ confined catalytic hydrogenation method for magnesium nanoparticles. Background Technology

[0002] Magnesium metal is considered a highly promising solid-state hydrogen storage material due to its high theoretical hydrogen storage density of 7.6 wt%, excellent reversible hydrogen absorption and desorption, abundant resources, and low cost, attracting significant attention in applications such as portable power supplies and on-board hydrogen storage. However, bulk magnesium exhibits poor hydrogenation kinetics, with effective reactions typically requiring high temperatures (generally exceeding 300°C) and high hydrogen pressures. This is mainly attributed to the formation of a dense and stable magnesium hydride (MgH2) surface layer during the initial hydrogenation stage. This layer severely hinders the further diffusion of hydrogen atoms into the magnesium matrix, resulting in a slow overall hydrogenation reaction rate that fails to meet the demands of rapid hydrogen charging and decharging in practical applications.

[0003] To improve the hydrogenation performance of magnesium, existing technologies mainly focus on two approaches: one is to nanoscale magnesium through high-energy ball milling and other methods to increase the specific surface area and shorten the hydrogen diffusion path; the other is to introduce catalysts such as transition metals and metal oxides to lower the reaction energy barrier. However, these methods still have significant limitations: First, magnesium nanoparticles obtained by ball milling or gas-phase condensation have extremely high surface energy, making them prone to sintering and excessive grain growth during subsequent hydrogenation or heat treatment, leading to a rapid decrease in active surface area and a significant reduction in hydrogenation performance; second, catalysts added through mechanical mixing are often unevenly dispersed, with limited interfacial contact with the magnesium matrix, resulting in low catalytic efficiency and the potential introduction of impurities.

[0004] Therefore, achieving rapid and complete hydrogenation of magnesium nanoparticles under relatively mild conditions is the key to preparing high-performance nano-hydride magnesium materials. Summary of the Invention

[0005] In view of the above problems, the present invention provides an in-situ confined catalytic hydrogenation method for magnesium nanoparticles, which can achieve rapid and complete hydrogenation of magnesium nanoparticles under relatively mild conditions.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] The first aspect of the present invention provides a method for preparing high-purity nano-magnesium powder, comprising the following steps:

[0008] S1. Premixing treatment: Magnesium nanoparticles and three-dimensional wrinkled MXene nanosheets are uniformly mixed under an inert atmosphere; wherein the average particle size of the magnesium nanoparticles is ≤50nm; and the specific surface area of ​​the three-dimensional wrinkled MXene nanosheets is >100m². 2 / g;

[0009] S2. Confined assembly: The mixture obtained in step S1 is mechanically processed to physically confine magnesium nanoparticles in the interlayer voids and surface depressions of MXene, forming a Mg / MXene composite precursor.

[0010] S3. In-situ catalytic hydrogenation: The Mg / MXene composite precursor obtained in step S2 is placed in a high-pressure hydrogenation reactor, hydrogen gas is introduced, the pressure of the high-pressure hydrogenation reactor is increased to 3.0~8.0 MPa, and the temperature is increased to 180~280℃ at a heating rate of 1~5℃ / min. Under these conditions, the reaction is maintained at the same temperature and pressure for 2~10 hours to hydrogenate magnesium nanoparticles in-situ to MgH2.

[0011] S4. Cooling and Collection: After the reaction is complete, the mixture is cooled and the pressure is released. The product is collected under an inert atmosphere to obtain the MgH2 / MXene nanocomposite material.

[0012] Further, in step S1, the magnesium nanoparticles are prepared by vapor-phase condensation; in step S1, the three-dimensional wrinkled MXene nanosheets are Ti3C2T. x Its surface is rich in -O, -OH, and -F functional groups. This step involves uniformly mixing highly active, easily agglomerated magnesium nanoparticles with MXene, a three-dimensional wrinkled structure with high specific surface area and abundant surface functional groups, under an inert atmosphere to prevent spontaneous agglomeration of magnesium nanoparticles.

[0013] Furthermore, the three-dimensional wrinkled MXene nanosheets are prepared by the following method: etching and exfoliating Ti3AlC2MAX phase powder to obtain an MXene nanosheet colloidal solution, followed by intercalation treatment and controlled drying to obtain the three-dimensional wrinkled MXene nanosheets.

[0014] Furthermore, the mass ratio of the magnesium nanoparticles to the three-dimensional wrinkled MXene nanosheets is 1:1 to 1:4.

[0015] Optionally, in step S2, the mechanical treatment is performed under argon protection using a planetary ball mill at a speed of 200-400 rpm for 0.5-2 hours.

[0016] Optionally, in step S2, the mechanical processing is to use a drum mixer for low-speed mixing.

[0017] In step S2 of this invention, the magnesium nanoparticles initially mixed in step S1 are further mixed with MXene through controlled mechanical processing. By using mechanical forces such as shearing, extrusion, or rolling, the magnesium nanoparticles are embedded and firmly fixed in the interlayer gaps and surface depressions formed by the three-dimensional wrinkles of the MXene nanosheets, thereby achieving physical confinement of the magnesium particles. This fundamentally prevents the spontaneous migration and aggregation of highly active magnesium nanoparticles in subsequent processing, while establishing a larger area and tighter interfacial contact between magnesium and the MXene nanosheet carrier, thus constructing a stable reaction interface for the in-situ catalytic hydrogenation reaction in the subsequent step S3.

[0018] Further, in step S3, the heating program includes an intermediate holding plateau of 150~180℃, maintained for 0.5~1h; in step S3, during the hydrogenation process, the Ti on the surface of the MXene nanosheets is reduced or converted in situ by hydrogen gas to generate catalytically active nano-TiH. x This process catalyzes the hydrogenation reaction of the magnesium nanoparticles. This step is the core conversion step for achieving efficient hydrogen storage in this invention. Under mild temperature (180~280℃) and relatively high hydrogen pressure (3.0~8.0MPa), a controllable heating program (including an intermediate holding platform of 150~180℃ to promote hydrogen pre-diffusion and activation) drives the reaction between hydrogen and the physically confined magnesium nanoparticles, completely converting them into MgH2. More importantly, during this process, Ti on or near the surface of the MXene support is reduced in situ or converted into highly catalytically active nano-TiH in a hydrogen atmosphere. x These in-situ generated active sites are in close contact with the confined magnesium particles, achieving efficient and specific interfacial catalysis, thereby significantly reducing the reaction energy barrier of magnesium hydrogenation. Under conditions far below the temperature required for bulk magnesium hydrogenation, rapid and complete hydrogenation of magnesium nanoparticles is achieved, and the nanoscale stability of the product is ensured by the confined structure of MXene.

[0019] Furthermore, before step S3, the invention includes a step of evacuating the high-pressure hydrogenation reactor and replacing it with an inert gas. This invention completely removes air (especially oxygen and water vapor) from the reaction system by evacuating, and then replaces the residual atmosphere with an inert gas. This creates an absolutely pure, oxygen-free, and dry inert environment before the high-pressure hydrogenation reaction begins in step S3, thereby preventing the highly reactive magnesium nanoparticles and MXene nanosheets from being oxidized or undergoing uncontrollable side reactions during the heating process. It also eliminates the safety hazards that may arise from mixing hydrogen and air, ensuring that the subsequent in-situ catalytic hydrogenation reaction can be carried out in a controlled, efficient, and safe atmosphere.

[0020] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0021] This invention utilizes three-dimensional wrinkled MXene nanosheets as both a physical confinement framework and a catalyst precursor, effectively isolating and stabilizing magnesium nanoparticles to prevent aggregation during hydrogenation. Furthermore, the in-situ generated active catalytic phase significantly enhances the hydrogenation reaction efficiency. This method enables rapid and near-complete hydrogenation of magnesium under mild conditions of 180–280 °C, yielding a high-purity, structurally intact MgH₂ / MXene composite material with uniformly dispersed nanoparticles. Moreover, the entire process is simple, parameters are controllable, and it is easily integrated with upstream and downstream processes, demonstrating excellent scalability and industrialization potential. Therefore, it provides an efficient and stable new route for the preparation of high-performance solid-state hydrogen storage materials. Attached Figure Description

[0022] Figure 1 This is the XRD pattern of the MgH2 / MXene nanocomposite material prepared in Example 1 of this invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0024] The term "comprising" as used in this application is an open-ended inclusion, meaning "including but not limited to". The term "according to" means "at least in part according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment". Definitions of other terms will be given in the description below.

[0025] Example 1

[0026] This embodiment provides an in-situ confined catalytic hydrogenation method for magnesium nanoparticles, specifically including the following steps:

[0027] S1. Premixing treatment: In a glove box filled with high-purity argon, weigh 1.0 g of magnesium nanoparticles with an average particle size of 30 nm (prepared by gas-phase condensation) and a three-dimensional wrinkled Ti3C2T structure with a specific surface area of ​​185 m² / g. x 2.0 g of MXene nanosheets were placed in a ball mill jar;

[0028] S2. Confined assembly: Add 5 zirconia grinding balls with a diameter of 10 mm to the ball mill jar, seal it, remove it from the glove box, and install it on the planetary ball mill; under an argon atmosphere, ball mill and mix at a speed of 300 rpm for 1 h to obtain a uniform Mg / MXene composite precursor powder.

[0029] S3. In-situ catalytic hydrogenation: 0.5g of Mg / MXene composite precursor powder is loaded into the alumina crucible of a high-pressure differential scanning calorimeter (HP-DSC), or an appropriate amount of powder is loaded into a custom-made high-pressure reaction tube; the system is evacuated to 10... -2 After Pa, high-purity hydrogen gas (99.999%) of 5.0 MPa was introduced, and the temperature was raised to 220°C at a heating rate of 3°C / min. The reaction was then maintained at this temperature for 5 hours to hydrogenate magnesium nanoparticles in situ to MgH2.

[0030] S4. Cooling and Collection: After the reaction is complete, the sample is naturally cooled to 40°C and hydrogen is slowly released. The sample is then removed under argon protection to obtain a gray-black MgH2 / MXene nanocomposite material.

[0031] Example 2

[0032] The hydrogen pressure in the in-situ catalytic hydrogenation step S3 is set to 6.0 MPa, the temperature is increased to 250°C at a rate of 3°C / min, and the reaction is maintained at this temperature for 3 hours; the remaining conditions are the same as in Example 1.

[0033] Comparative Example 1 (without MXene nanosheet confinement support)

[0034] Take 1.0 g of magnesium nanoparticles with an average particle size of 30 nm, without adding any support, and place them directly in an HP-DSC crucible; under a hydrogen pressure of 5.0 MPa, heat to 350°C and hold for 5 h to perform hydrogenation.

[0035] Comparative Example 2 (using a non-catalytic, unconfined support)

[0036] The three-dimensional wrinkled MXene nanosheets in Example 1 were replaced with an equal mass of inert carbon black (specific surface area of ​​50 m²) that had been treated at high temperature to lose its surface functional groups and catalytic activity. 2 / g); the remaining conditions are the same as in Example 1.

[0037] Test method:

[0038] (1) Analyze the purity and phase composition of the product by X-ray diffraction (XRD);

[0039] (2) The hydrogenation reaction kinetics were analyzed by high-pressure differential scanning calorimetry (HP-DSC);

[0040] Results analysis:

[0041] (1) Phase analysis: such as Figure 1As shown, quantitative analysis by XRD revealed that the β-MgH2 main phase content in the product of Example 1 was 99.2 wt%, while the product of Comparative Example 2 contained approximately 10 wt% unreacted metallic magnesium and 5 wt% magnesium oxide impurities in addition to the main phase. This indicates that the purity of the product of the present invention is significantly higher than that of Comparative Example 2, fully demonstrating the advantages of the in-situ confined catalytic hydrogenation method of the present invention.

[0042] (2) Hydrogenation conversion rate: As shown in Table 1, the present invention achieved a hydrogenation conversion rate of over 99% at 220℃, while the hydrogenation conversion rate of Comparative Example 1 was only 78% at 350℃ and the conversion rate of Comparative Example 2 was only 85% at 220℃. This indicates that the present invention uses three-dimensional wrinkled MXene nanosheets as a carrier to carry out in-situ catalytic hydrogenation and nano-confinement effect, synergistically reducing the hydrogenation reaction energy barrier, thereby achieving more complete hydrogenation under relatively mild conditions.

[0043] (3) Initial hydrogenation temperature: As shown in Table 1, the initial hydrogenation temperature of this invention is 180℃, the initial hydrogenation temperature of Comparative Example 1 is 320℃, and the initial hydrogenation temperature of Comparative Example 2 is 280℃. This indicates that the present invention utilizes three-dimensional wrinkled MXene nanosheets as a carrier, which greatly reduces the initial hydrogenation temperature. This is attributed to the active species (such as TiH) generated in situ on the MXene surface. x This provides an efficient pathway for the dissociation of hydrogen molecules and the transfer of hydrogen atoms.

[0044] (4) Initial dehydrogenation temperature: As shown in Table 1, the initial dehydrogenation temperature of the present invention is 150°C, the initial dehydrogenation temperature of Comparative Example 1 is 300°C, and the initial dehydrogenation temperature of Comparative Example 2 is 260°C. This shows that the MgH2 prepared by the present invention is fine, which makes it easier to release hydrogen at low temperature.

[0045] (5) Cyclic stability: As shown in Table 1, the capacity retention rate of the material of the present invention after 100 hydrogen adsorption and desorption cycles is >98%, which is much higher than that of Comparative Example 1 (<70%) and Comparative Example 2 (82%). This indicates that the present invention increases the cycling stability by introducing three-dimensional wrinkled MXene nanosheets to prevent the migration and aggregation of particles during the cycling process.

[0046] Table 1. Data Comparison between Embodiments of the Invention and Comparative Examples

[0047] Hydrogenation conversion rate (%) Initial hydrogenation temperature (°C) Initial dehydrogenation temperature (°C) Capacity retention rate after 100 cycles (%) Example 1 ＞99 180 150 ＞98 Comparative Example 1 78 320 300 ＜70 Comparative Example 2 85 280 260 82

[0048] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for in situ confined catalytic hydrogenation of magnesium nanoparticles, characterized in that, The method comprises the following steps: S1. Pre-mixing treatment: uniformly mixing magnesium nanoparticles and three-dimensional corrugated structure MXene nanosheets under the protection of an inert atmosphere; wherein the average particle size of the magnesium nanoparticles is ≤ 50 nm; the specific surface area of the three-dimensional corrugated structure MXene nanosheets is > 100 m 2 / g; S2. Confined assembly: mechanically treating the mixture obtained in step S1 to physically confine the magnesium nanoparticles in the interlayer space and surface depressions of the MXene, thereby forming a Mg / MXene composite precursor; S3. In-situ catalytic hydrogenation: placing the Mg / MXene composite precursor obtained in step S2 in a high-pressure hydrogenation reaction device, introducing hydrogen, increasing the pressure of the high-pressure hydrogenation reaction device to 3.0-8.0 MPa, and increasing the temperature to 180-280℃ at a temperature increasing rate of 1-5℃ / min, and then reacting under the conditions of isothermal and pressure for 2-10 h, so that the magnesium nanoparticles are in-situ hydrogenated into MgH2; S4. Cooling and collection: after the reaction is completed, cooling and releasing the pressure, and collecting the product under the protection of an inert atmosphere to obtain a MgH2 / MXene nanocomposite.

2. The in situ confined catalytic hydrogenation of magnesium nanoparticles process according to claim 1, characterized in that, In step S1, the magnesium nanoparticles are prepared by a gas-phase condensation method.

3. The in situ confined catalytic hydrogenation of magnesium nanoparticles process according to claim 1, characterized in that, In step S1, the three-dimensional wrinkled structure MXene nanoplatelets are Ti3C2T x with a surface rich in -O, -OH, -F functional groups.

4. The in situ confined catalytic hydrogenation of magnesium nanoparticles process according to claim 3, characterized in that, The three-dimensional wrinkled structure MXene nanosheet is prepared by the following method: etching and exfoliating Ti3AlC2 MAX phase powder to obtain a MXene nanosheet colloidal solution, and then performing intercalation treatment and controllable drying to obtain the three-dimensional wrinkled structure MXene nanosheet.

5. The in situ confined catalytic hydrogenation of magnesium nanoparticles process according to claim 1, wherein, The mass ratio of the magnesium nanoparticles to the three-dimensional wrinkled structure MXene nanosheet is 1:1-1:

4.

6. The in situ confined catalytic hydrogenation of magnesium nanoparticles process according to claim 1, wherein, In step S2, the mechanical treatment is performed by using a planetary ball mill at a rotation speed of 200-400 rpm for 0.5-2 h under the protection of argon.

7. The in situ confined catalytic hydrogenation of magnesium nanoparticles process according to claim 1, wherein, In step S2, the mechanical treatment is performed by using a drum-type mixer for low-speed mixing.

8. The in situ confined catalytic hydrogenation of magnesium nanoparticles process according to claim 1, wherein, In step S3, the temperature increasing procedure comprises an intermediate isothermal platform of 150-180℃, which is maintained for 0.5-1 h.

9. The in situ confined catalytic hydrogenation of magnesium nanoparticles process according to claim 1, wherein, In step S3, during the hydrogenation process, the Ti on the surface of the MXene nanosheets is reduced or converted in situ by hydrogen gas to generate catalytically active nano-TiH x to catalyze the hydrogenation reaction of the magnesium nanoparticles.

10. The in situ confined catalytic hydrogenation of magnesium nanoparticles process according to claim 1, wherein, Before step S3 is performed, a step of vacuumizing the high-pressure hydrogenation reaction device and replacing it with an inert gas is further included.

Images