Monatomic catalyst for catalytic synthesis of sodium aluminum hydride, composite hydrogen storage system containing monatomic catalyst and preparation method

Abstract

The invention discloses a monatomic catalyst for catalytic synthesis of sodium aluminum hydride, a composite hydrogen storage system containing the monatomic catalyst and a preparation method, two-dimensional layered Ti3CN is used as a carrier, an active component monatomic zirconium is loaded, the catalyst Zr (SA) / Ti3CN is prepared, Zr stably exists on the surface of the Ti3CN carrier in an atomic-scale dispersion form, and the composite hydrogen storage system is used for catalytic synthesis of sodium aluminum hydride. According to the present invention, by using the single atom catalyst, the near 100% utilization rate of Zr atoms is achieved, the rich N atoms in the Ti3CN carrier and Zr form the strong coordination bond (Zr-N), the single atoms are effectively anchored, the migration and agglomeration of the single atoms are prevented, the initial hydrogen desorption temperature of the composite hydrogen storage system (containing 7 wt% (1 wt% Zr (SA)) / Ti3CN) prepared by using the single atom catalyst is significantly reduced to about 86 DEG C, and the hydrogen desorption amount at 300 DEG C is as high as 5.1 wt%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogen storage materials, and particularly relates to a single-atom catalyst for catalytically synthesizing sodium aluminum hydride, a composite hydrogen storage system containing the single-atom catalyst and a preparation method. BACKGROUND

[0002] Hydrogen energy is regarded as a future energy carrier due to its high energy density, cleanliness and other advantages. However, safe and efficient hydrogen storage technology is still a key bottleneck restricting its large-scale application. Solid-state hydrogen storage materials, especially sodium aluminum hydride (NaAlH4), have become a research hotspot due to their high theoretical hydrogen storage capacity (~7.4wt%) and potential reversibility. However, the thermodynamic stability of NaAlH4 is high, and its hydrogen release reaction needs to be carried out at a high temperature (>150℃), and the hydrogen absorption / release kinetics is slow, which seriously limits its practical application.

[0003] The introduction of catalysts is an effective way to improve the hydrogen storage performance of NaAlH4. Among them, the NaAlH4 composite system based on NaH and Al powder and in-situ catalytic synthesis has the advantages of low cost and uniform component mixing compared with directly doping NaAlH4. By ball milling the mixture of NaH and Al, mechanical force can induce particle nanocrystallization and generate defect sites, promoting the solid-phase reaction NaH+Al+H2→NaAlH4. However, the synthesis process has slow kinetics and low conversion rate, and usually requires ultra-long ball milling time and harsh conditions.

[0004] Existing catalysts mostly use nanoparticles or clusters of transition metals (such as Ti, Fe, Ni, Zr, etc.) and their compounds. However, these catalysts have significant limitations: (1) low utilization rate of active sites: only surface atoms of nanoparticles participate in catalysis; (2) poor high-temperature stability: nanoparticles are easy to sinter and agglomerate during the cycle process, leading to activity decline; (3) unclear catalytic mechanism: lack of in-depth understanding at atomic scale.

[0005] Single-atom catalysts (SACs) have shown great potential in the field of catalysis due to their maximum atomic utilization, unique electronic structure and potential high activity / selectivity, but their application faces the challenges of support selection and stability of single atoms. SUMMARY

[0006] In view of the problems of low utilization rate of active sites, poor high-temperature stability of existing NaAlH4 synthesis catalysts, and slow kinetics and low conversion rate of NaH / Al system for synthesizing NaAlH4, the application provides a monatomic catalyst for catalytically synthesizing sodium aluminum hydride, a composite hydrogen storage system containing the monatomic catalyst, and a preparation method.

[0007] To achieve the above object, the application provides the following technical solutions.

[0008] The application provides a monatomic catalyst for catalytically synthesizing sodium aluminum hydride (NaAlH4), wherein the carrier is two-dimensional layered Ti3CN (titanium nitride), and the active component is monatomic zirconium (Zr), and the loading amount of the monatomic zirconium is 0.1-3 wt%.

[0009] The nitride Ti3CN is a two-dimensional transition metal carbon / nitride, has a high specific surface area, rich surface functional groups, and excellent metal anchoring ability, Ti3CN has a higher nitrogen content than Ti3C2Tx, can provide stronger metal-support interaction (MSI), is beneficial to stabilizing monatomic atoms and preventing migration and agglomeration of the monatomic atoms. In addition, the good electrical conductivity of Ti3CN can promote charge transfer in the catalytic process. In the monatomic catalyst of the application, Zr is stably loaded on the two-dimensional layered Ti3CN material in an atomic dispersion form, the monatomic Zr has a highly unsaturated coordination environment (a large number of exposed active sites), which enables the Zr atoms to effectively adsorb and dissociate hydrogen molecules to generate active hydrogen atoms, which is essential for the synthesis of NaAlH4 (Na + , [AlH4] -The key step of the synthesis of NaAlH4 is the activation of H2 into active hydrogen species that can react with Al and Na, and monatomic Zr greatly promotes this process. The activated hydrogen atom needs to combine with Al to form an Al-H bond, and monatomic Zr not only provides active hydrogen, but also can weaken the bond of the metal Al surface or directly interact with Al through its unique electronic structure, thereby reducing the energy barrier of Al-H bond formation; the carrier Ti3CN itself has good conductivity and affinity with aluminum, which can synergistically promote the adsorption and activation of aluminum. Traditional NaAlH4 synthesis requires high temperature (~ 150-200℃) and high pressure hydrogen (~ 100bar), which is harsh, and the presence of the monatomic catalyst of the present application significantly reduces the activation energy of the entire reaction (especially the H2 activation and Al-H formation steps) by efficiently activating and providing an optimized reaction interface (the synergistic effect of monatomic Zr and Ti3CN carrier), which allows the reaction to be carried out at a lower temperature and lower hydrogen pressure, greatly improving the reaction conditions.

[0010] The present application also provides a preparation method of the monatomic catalyst for catalyzing the synthesis of sodium aluminum hydride, comprising the following steps:

[0011] Etching the Al layer in the Ti3AlCN precursor with HF solution to obtain a multilayer Ti3CN, dispersing the multilayer Ti3CN in deionized water for ultrasonic exfoliation, and centrifuging to collect the supernatant to obtain a Ti3CN nanosheet dispersion;

[0012] Mixing the zirconium monatomic precursor, the dispersant and the Ti3CN nanosheet dispersion, stirring at room temperature for coordination anchoring to obtain a mixture;

[0013] Adding NaOH solution to the mixture and stirring to react, so that the Zr species is precipitated; centrifuging to collect the precipitate and washing with water until neutral;

[0014] Freeze-drying the material washed with water until neutral to obtain a Zr / Ti3CN precursor powder;

[0015] Sintering the Zr / Ti3CN precursor powder in a reducing atmosphere to obtain the monatomic catalyst for catalyzing the synthesis of sodium aluminum hydride, denoted as Zr (SA) / Ti3CN catalyst.

[0016] Further, the zirconium monatomic precursor is selected from ZrOCl2·8H2O;

[0017] And / or, the dispersant is selected from sodium citrate.

[0018] Further, the reducing atmosphere is selected from H2 / Ar atmosphere;

[0019] And / or, the sintering temperature is 450 DEG C, and the time is 2h.

[0020] For example, the H2 / Ar atmosphere is a 5% H2 / Ar atmosphere, that is, in the above mixed atmosphere, the volume ratio of H2 is 5%.

[0021] Further, the preparation method of the monatomic catalyst for catalytically synthesizing sodium aluminum hydride comprises the following steps:

[0022] (1) Preparation of two-dimensional layered Ti3CN: etching the Al layer in the Ti3AlCN precursor (MAX phase) by using an HF solution to obtain multi-layered Ti3CN; dispersing the multi-layered Ti3CN in deionized water for ultrasonic exfoliation, and centrifuging to collect the supernatant to obtain a Ti3CN nanosheet dispersion;

[0023] (2) Precursor anchoring: mixing the Ti3CN nanosheet dispersion obtained in step (1), a zirconium (Zr) monatomic precursor (such as ZrOCl2·8H2O), and a dispersant (such as sodium citrate), and stirring at room temperature for 1h for coordination anchoring, so that the Zr 4+ is adsorbed on the surface of the Ti3CN;

[0024] (3) Precipitation and washing: adding a NaOH solution to the mixture obtained in step (2) and stirring to react, so that the Zr species is precipitated; centrifuging to collect the precipitate and washing with deionized water until neutral;

[0025] (4) Drying: freeze-drying the washed material obtained in step (3) to obtain a Zr / Ti3CN precursor powder;

[0026] (5) Pyrolysis reduction: sintering the Zr / Ti3CN precursor powder obtained in step (4) in a reducing atmosphere (such as 5% H2 / Ar) to reduce the Zr species and stably anchor it on the Ti3CN carrier in the form of a monatomic catalyst to obtain a Zr (SA) / Ti3CN catalyst.

[0027] The application also provides an application of the monatomic catalyst in a catalytic synthesis of a NaAlH4 composite hydrogen storage system.

[0028] The application also provides a preparation method of a NaAlH4 composite hydrogen storage system, comprising the following steps:

[0029] Mixing sodium hydride (NaH) and aluminum (Al), ball-milling to form a sodium hydride / aluminum NaH / Al mixture;

[0030] Mixing the monatomic catalyst with the sodium hydride / aluminum mixture to perform a hydrogen absorption reaction to obtain a sodium aluminum hydride composite hydrogen storage system.

[0031] Further, the molar ratio of sodium hydride and aluminum is 1:1.

[0032] Further, the parameters of the ball milling are as follows: the pressure is 1-6 MPa, the atmosphere is hydrogen, the ball-to-material ratio is (60-120):1, the rotation speed is 400-550 rpm, the intermittent ball milling mode is adopted, and the total ball milling time is 20-48 h.

[0033] Further, the intermittent ball milling mode is 15 min of ball milling and 10 min of stopping.

[0034] Further, the proportion of the monatomic catalyst in the NaAlH4 composite hydrogen storage system is 5-9 wt%.

[0035] Further, the preparation method of the NaAlH4 composite hydrogen storage system comprises the following steps:

[0036] (1) Raw material mixing: under the protection of an inert atmosphere (such as argon), NaH powder and Al powder with a molar ratio of 1:1 are uniformly mixed to form a NaH / Al mixture matrix; then, Zr (SA) / Ti3CN catalyst powder is added, the proportion of Zr (SA) / Ti3CN catalyst powder in the sodium aluminum hydride composite hydrogen storage system is 5-9 wt%, and the mixture is uniformly mixed;

[0037] (2) Ball milling activation: the mixture obtained in step (1) is placed in a ball milling tank, 1-6 MPa of high-purity hydrogen (purity ≥ 99.99%) is filled as a protection and reaction atmosphere, the ball milling tank is placed in a planetary ball mill, the ball-to-material ratio is set to (60-120):1, the rotation speed is 400-550 rpm, the intermittent ball milling mode (15 min of ball milling and 10 min of stopping) is adopted, and the total ball milling time is 20-48 h;

[0038] (3) Hydrogen absorption synthesis of NaAlH4: the sample after ball milling in step (2) is subjected to hydrogen absorption reaction at 80-110 bar of hydrogen pressure and 130-150℃ for 7-20 h, the in-situ catalytic synthesis of NaAlH4 is completed, and the NaAlH4 composite hydrogen storage system is obtained.

[0039] During the ball milling activation in step (2), stainless steel balls are used, and stainless steel balls with different diameters are mixed and used. For example, the diameters of the stainless steel balls are 5 cm, 8 cm and 10 cm, and the quantity ratio is 42:1.

[0040] The application also provides the application of the NaAlH4 composite hydrogen storage system prepared according to the above preparation method in solid-state hydrogen storage.

[0041] Compared with the prior art, the application has the following advantages and technical effects:

[0042] 1. Ultra-high activity and atom utilization: The catalyst Zr (SA) / Ti3CN in the present invention exists in an atomically dispersed form on the surface of the Ti3CN support, achieving nearly 100% utilization of Zr atoms. The abundant N atoms in the Ti3CN support form strong coordination bonds (Zr-N) with Zr, effectively anchoring the single atoms and preventing their migration and agglomeration. Compared to traditional nanoparticle catalysts, the single-atom structure provides more exposed high-activity sites.

[0043] 2. Excellent low-temperature catalytic synthesis and dehydrogenation performance: The composite hydrogen storage system prepared in the present invention (containing 7wt% Zr (SA) / Ti3CN) has a significantly reduced initial dehydrogenation temperature of about 86°C, and a dehydrogenation amount of up to 5.1wt% before 300°C. In contrast, the ball-milled NaH / Al system without catalyst has an initial dehydrogenation temperature of 163°C and a dehydrogenation amount of only 4.4wt% before 300°C; the system with an equal amount of Ti3CN support has a lower initial temperature (65°C), but a lower dehydrogenation amount (4.1wt%) than the system of the present invention, demonstrating that single-atom Zr is a highly efficient active center.

[0044] 3. Significantly improved reaction kinetics: The catalyst of the present invention significantly accelerates the dehydrogenation kinetics of NaAlH4. The composite hydrogen storage system releases 4.76wt% of hydrogen at 150°C in only 20 minutes, while the uncatalyzed NaH / Al system releases only 0.84wt% of hydrogen at the same temperature in 2 hours. Through the Kissinger equation, it is calculated that the two-step dehydrogenation activation energy of NaAlH4 catalyzed by Zr (SA) / Ti3CN is significantly reduced from 112.4kJ / mol and 92.3kJ / mol to 73.3kJ / mol and 70.3kJ / mol, respectively, with a decrease of 34.8% and 23.8%, respectively.

[0045] 4. Good reversibility and cycle stability: Thanks to the strong anchoring effect of Ti3CN support on single-atom Zr, the composite hydrogen storage system of the present invention exhibits excellent cycle stability. After 10 cycles of hydrogen absorption and release, the reversible hydrogen storage capacity remains above 4.2wt%, with a cycle retention rate of up to 91.3%, indicating that the catalytic system can effectively maintain structural stability and catalytic activity during the cycle process.

[0046] 5. Efficient in-situ one-step synthesis: The method of the present invention, by optimizing the ball milling conditions (hydrogen atmosphere, ball-to-material ratio, rotation speed, intermittent mode) combined with a subsequent mild hydrogen absorption step, uses the Zr (SA) / Ti3CN catalyst to achieve the in-situ one-step synthesis of NaAlH4 composite hydrogen storage material from NaH and Al powders under relatively mild conditions (≤150°C) with high efficiency and high conversion rate. BRIEF DESCRIPTION OF DRAWINGS

[0047] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application, illustrate preferred embodiments of the present application and assist in explaining the application. In the drawings:

[0048] Figure 1 XRD patterns and SEM images of (1 wt% Zr (SA) ) / Ti3CN catalyst prepared for Example 2 of the present application, wherein a is an XRD pattern, b is a SEM image, c is a HAADF-STEM image and element distribution Mapping image;

[0049] Figure 2 TPD dehydrogenation curves of NaAlH4 composite system catalyzed by (x wt% Zr (SA) ) / Ti3CN (x = 0.1, 1, 3) catalysts for Examples 4, 5 and 6 of the present application;

[0050] Figure 3 TPD dehydrogenation curves of NaH / Al mixture ball-milled (NaAlH4 ball-milled), NaH / Al mixture with 7 wt% Ti3CN added, and composite hydrogen storage systems containing x wt% (1 wt% Zr (SA) ) / Ti3CN (x = 5, 7, 9) prepared for Examples 5, 7 and 8 of the present application;

[0051] Figure 4 a is isothermal dehydrogenation curves of ball-milled NaH / Al mixture at 150°C and isothermal dehydrogenation curves of the composite hydrogen storage system of Example 9 at 90°C, 120°C and 150°C, b is XRD patterns of the composite hydrogen storage system of Example 9 after dehydrogenation at different temperatures;

[0052] Figure 5 DSC curves and two-step dehydrogenation activation energies calculated based on the Kissinger method of ball-milled NaH / Al mixture and the composite hydrogen storage system of Example 10, wherein a and b are DSC curves and two-step dehydrogenation activation energies calculated based on the Kissinger method of ball-milled NaH / Al mixture, respectively, and c and d are DSC curves and two-step dehydrogenation activation energies calculated based on the Kissinger method of the composite hydrogen storage system of Example 10, respectively;

[0053] Figure 6 TPD dehydrogenation curves of the composite hydrogen storage system prepared for Example 11 (containing 5 wt% Zr (SA) / Ti3CN) in 10 hydrogen absorption and release cycles. DETAILED DESCRIPTION

[0054] Various exemplary embodiments of the present application will now be described in detail, which should be considered in a descriptive sense only and not for purposes of limitation to the present application. Rather, it is understood that certain aspects, particular features and embodiments of the application are described for illustrative purposes only.

[0055] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. In addition, where particular ranges of values are given, understand that each intervening value, to the upper or lower limit of the ranges is also specifically included. Each smaller range that falls within the broader ranges is also specifically included in the present application. The upper and lower limits of these smaller ranges can independently be included or excluded in the range, and are also encompassed by the application, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of the limits are also included.

[0056] Unless defined otherwise, 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 application belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in further detail the methods and / or materials associated with the disclosure. In the event of conflict between the present specification and any incorporated document, the present specification controls.

[0057] Many modifications and variations of this application can be made in the light of the above teachings without departing from the spirit and scope thereof, and it is to be understood that all such modifications and variations warrant the patentable subject matter under the patent laws. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only.

[0058] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean including, but not limited to.

[0059] The embodiments of the present application provide a single-atom catalyst for catalytic synthesis of sodium aluminum hydride (NaAlH4), which has a two-dimensional layered Ti3CN (titanium nitride) as a carrier and single-atom zirconium (Zr) as an active ingredient, and the loading amount of the single-atom zirconium is 0.1-3 wt%.

[0060] Ti3CN nitrides are a class of two-dimensional transition metal carbides / nitrides with high specific surface area, abundant surface functional groups, and excellent metal anchoring ability. Compared with Ti3C2Tx, Ti3CN has a higher nitrogen content, which can provide stronger metal-support interaction (MSI), which is beneficial for stabilizing single atoms and preventing their migration and aggregation. In addition, the good conductivity of Ti3CN may promote charge transfer during the catalytic process. In the single-atom catalyst of this invention, Zr is stably supported on the two-dimensional layered Ti3CN material in an atomically dispersed form. The single-atom Zr has a highly unsaturated coordination environment (more exposed active sites), which allows Zr atoms to effectively adsorb and dissociate hydrogen molecules to generate active hydrogen atoms, which is the synthesis of NaAlH4 (essentially Na). + [AlH4] - The key step in the synthesis of NaAlH4 requires the activation of H2 into an active hydrogen species capable of reacting with aluminum (Al) and sodium (Na). Single-atom Zr greatly facilitates this process. The activated hydrogen atoms need to combine with Al to form Al-H bonds. Single-atom Zr not only provides active hydrogen but may also, through its unique electronic structure, weaken the bonds on the Al surface or interact directly with Al, lowering the energy barrier for Al-H bond formation. The support Ti3CN itself has good conductivity and affinity for aluminum, which can synergistically promote the adsorption and activation of aluminum. Traditional NaAlH4 synthesis requires high temperatures (~150-200℃) and high-pressure hydrogen (~100 bar), which are harsh conditions. The presence of the single-atom catalyst in this invention, through efficient activation and the provision of an optimized reaction interface (synergistic effect of single-atom Zr and Ti3CN support), significantly reduces the activation energy of the entire reaction (especially the H2 activation and Al-H formation steps). This allows the reaction to proceed at lower temperatures and lower hydrogen pressures, greatly improving the reaction conditions.

[0061] Embodiments of the present invention also provide a method for preparing a single-atom catalyst for the catalytic synthesis of sodium aluminum hydride, comprising the following steps:

[0062] (1) Preparation of two-dimensional layered Ti3CN: Weigh 1g of Ti3AlCN precursor powder, add 15mL of HF solution (mass fraction of 35%) to a Teflon container, pour the precursor powder into it under an ice-water bath and stir continuously; transfer the resulting mixed solution to a water bath, heat it in a 40℃ water bath and stir continuously for 24h, centrifuge the resulting solution, wash the precipitate with deionized water and centrifuge continuously until the pH value of the supernatant tends to be neutral (pH ~ 6), and obtain Ti3CN nanosheet dispersion;

[0063] (2) Precursor anchoring: The Ti3CN nanosheet dispersion obtained in step (1), zirconium (Zr) single-atom precursor (such as ZrOCl2·8H2O) and dispersant (such as sodium citrate) are mixed and stirred at room temperature for coordination anchoring;

[0064] (3) Precipitation and washing: NaOH solution was added to the mixture obtained in step (2), the reaction was stirred to make Zr species precipitate; the precipitate was collected by centrifugation and washed with deionized water until neutral;

[0065] (4) Drying: the washed material obtained in step (3) was freeze-dried to obtain Zr / Ti3CN precursor powder;

[0066] (5) Pyrolysis reduction: the Zr / Ti3CN precursor powder obtained in step (4) was sintered in a reducing atmosphere (such as 5% H2 / Ar) to reduce the Zr species and stabilize the single-atom form to anchor on the Ti3CN carrier, thereby obtaining a single-atom catalyst for catalyzing the synthesis of sodium aluminum hydride, denoted as Zr (SA) / Ti3CN catalyst.

[0067] In the embodiment of the present application, the sintering temperature is 450°C, the time is 2h, and the heating rate is 5°C / min.

[0068] The embodiment of the present application also provides an application of the above-mentioned single-atom catalyst in catalyzing the synthesis of NaAlH4 composite hydrogen storage system.

[0069] The embodiment of the present application also provides a preparation method of NaAlH4 composite hydrogen storage system, comprising the following steps:

[0070] (1) Raw material mixing: under the protection of inert gas (such as argon), NaH powder and Al powder with a molar ratio of 1:1 were uniformly mixed to form a NaH / Al mixture matrix; then Zr (SA) / Ti3CN catalyst powder was added, and the Zr (SA) / Ti3CN catalyst powder accounted for 5-9wt% in the sodium aluminum hydride composite hydrogen storage system, and was uniformly mixed;

[0071] (2) Ball milling activation: the mixture obtained in step (1) was placed in a ball milling tank, and high-purity hydrogen (purity ≥99.99%) with a pressure of 1-6MPa was filled as a protective and reaction atmosphere; the ball milling tank was placed in a planetary ball mill, the ball-to-material ratio was set to (60-120):1, the rotation speed was set to 400-550rpm, the intermittent ball milling mode (ball milling for 15min, and stopping for 10min) was adopted, and the total ball milling time was 20-48h;

[0072] (3) Hydrogen absorption synthesis of NaAlH4: the sample after ball milling in step (2) was subjected to hydrogen absorption reaction at a hydrogen pressure of 80-110bar and a temperature of 130-150°C for 7-20h, thereby completing the in-situ catalytic synthesis of NaAlH4, and obtaining a NaAlH4 composite hydrogen storage system.

[0073] In the following embodiments of the present application, during the ball milling activation process in step (2), stainless steel balls are used, and stainless steel balls with different diameters are mixed and used, the diameters of the stainless steel balls are 5 cm, 8 cm and 10 cm, and the quantity ratio is 4:2:1.

[0074] Unless otherwise specified, the room temperature in the present application is 25±2℃.

[0075] The raw materials used in the embodiments of the present application are all commercially available.

[0076] It should be noted that the parts not described in detail in the present application are all conventional operating means in the art, and are not the focus of the present application.

[0077] The technical solutions of the present application are further illustrated by the following examples.

[0078] Preparation of (0.1wt%Zr (SA) ) / Ti3CN catalyst

[0079] 3.5mg ZrOCl2·8H2O and 0.4mg sodium citrate were dissolved in 10mL deionized water, 150mL Ti3CN dispersion solution (1g) was added, and stirred at room temperature for 1h, and then centrifuged and washed, 10mL 0.5M NaOH solution was added and stirred for 10min. After washing to neutral, a Zr / Ti3CN suspension was obtained, and the precursor powder was obtained by freeze-drying for 24h; then sintered at 450℃ under 5%H2 / Ar atmosphere with a heating rate of 5℃ / min for 2h to prepare (0.1wt%Zr (SA) ) / Ti3CN catalyst.

[0080] Preparation of (1wt%Zr (SA) ) / Ti3CN catalyst

[0081] 35mg ZrOCl2·8H2O and 4mg sodium citrate were dissolved in 10mL deionized water, 150mL Ti3CN dispersion solution (1g) was added, and stirred at room temperature for 1h, and then centrifuged and washed, 10mL 0.5M NaOH solution was added and stirred for 10min. After washing to neutral, a Zr / Ti3CN suspension was obtained, and the precursor powder was obtained by freeze-drying for 24h; then sintered at 450℃ under 5%H2 / Ar atmosphere with a heating rate of 5℃ / min for 2h to prepare (1wt%Zr (SA) ) / Ti3CN catalyst.

[0082] Preparation of (3wt%Zr (SA) ) / Ti3CN catalyst

[0083] ZrOCl2·8H2O (105 mg) and Na citrate (12 mg) were dissolved in 10 mL deionized water, and stirred for 1 h at room temperature after adding 150 mL Ti3CN dispersion (1 g), and then washed by centrifugation. After washing to neutral, a Zr / Ti3CN suspension was obtained, and a precursor powder was obtained by freeze-drying for 24 h; then sintered at 5 °C / min to 450 °C under 5% H2 / Ar atmosphere for 2 h to prepare a (3wt% Zr (SA) ) / Ti3CN catalyst.

[0084] The (1wt% Zr (SA) ) / Ti3CN catalyst prepared in Example 2 was analyzed by XRD and SEM, and the results are shown in Figs. a and b in Figure 1 , respectively. The XRD pattern shows that the (002) diffraction peak shifts to a lower angle after etching, confirming that the Ti3AlCN MAX phase is successfully converted into layered Ti3CN MXene; the SEM photo shows that the layered Ti3CN has a two-dimensional sheet-like morphology after ultrasonic treatment. The HAADF-STEM photo and element distribution Mapping diagram of the (1wt% Zr (SA) ) / Ti3CN catalyst prepared in Example 2 are shown in Fig. c in Figure 1 . From the HAADF-STEM image, atomically dispersed zirconium monomers (bright spots) can be observed, and the EDS element distribution diagram confirms that Ti, Zr, C and N elements are uniformly distributed, verifying the successful preparation of the Zr (SA) / Ti3CN catalyst.

[0085] Preparation of NaAlH4 composite hydrogen storage system catalyzed by (0.1wt% Zr (SA) ) / Ti3CN in Example 4

[0086] In a glove box under an argon atmosphere, NaH and Al were mixed according to a molar ratio of 1:1, and NaH / Al and the (0.1wt% Zr (SA) ) / Ti3CN prepared in Example 1 were mixed according to the mass percentage of the chemical composition x(NaH / Al)-y((0.1wt% Zr (SA) ) / Ti3CN) (x = 93wt%, y = 7wt%), to obtain a mixture; the mixture was placed in a ball mill jar, filled with 4 MPa of hydrogen, and then placed in a planetary ball mill, with a ball-to-material ratio of 90:1, a rotation speed of 500 rpm, and a program setting of 15 min of ball milling and 10 min of stopping in between. After ball milling for 24 h, hydrogen absorption was carried out at 100 bar of hydrogen pressure and 150 °C for 15 h to obtain a Zr (SA) / Ti3CN catalyzed NaAlH4 composite hydrogen storage system.

[0087] Example 5 (1 wt% Zr (SA) Preparation of NaAlH4 composite hydrogen storage system catalyzed by (1 wt% Zr

[0088] In a glove box under argon atmosphere, NaH and Al were mixed in a molar ratio of 1:1, and NaH / Al and (1 wt% Zr (SA) ) / Ti3CN prepared in Example 1 were mixed in a mass percentage of x(NaH / Al)-y((1 wt% Zr (SA) ) / Ti3CN) according to the chemical composition (x = 93 wt%, y = 7 wt%), to obtain a mixture; the mixture was placed in a ball mill jar, filled with 4 MPa of hydrogen, and then placed in a planetary ball mill, with a ball-to-material ratio of 90:1, a rotation speed of 500 rpm, a program setting of 10 min of stop in every 15 min of ball milling, and ball milling for 24 h; hydrogen absorption was carried out at 100 bar of hydrogen pressure and 150 °C for 15 h, to obtain a Zr (SA) / Ti3CN catalyzed NaAlH4 composite hydrogen storage system.

[0089] Example 6 (3 wt% Zr (SA) Preparation of NaAlH4 composite hydrogen storage system catalyzed by (3 wt% Zr

[0090] In a glove box under argon atmosphere, NaH and Al were mixed in a molar ratio of 1:1, and NaH / Al and (3 wt% Zr (SA) ) / Ti3CN prepared in Example 1 were mixed in a mass percentage of x(NaH / Al)-y((wt% Zr (SA) ) / Ti3CN) according to the chemical composition (x = 93 wt%, y = 7 wt%), to obtain a mixture; the mixture was placed in a ball mill jar, filled with 4 MPa of hydrogen, and then placed in a planetary ball mill, with a ball-to-material ratio of 90:1, a rotation speed of 500 rpm, a program setting of 10 min of stop in every 15 min of ball milling, and ball milling for 24 h; hydrogen absorption was carried out at 100 bar of hydrogen pressure and 150 °C for 15 h, to obtain a Zr (SA) / Ti3CN catalyzed NaAlH4 composite hydrogen storage system.

[0091] To evaluate the catalytic effect of the three catalysts in Examples 1, 2, and 3, the hydrogen desorption performance of the composite materials in Examples 4, 5, and 6 was tested, and the ball milling hydrogen absorption conditions of the three systems were consistent with those in Example 2, and then the TPD was tested by heating from room temperature to 300 °C at a heating rate of 2 °C / min. The TPD test results are shown in Figure 2 NaH / Al-7wt%((0.1wt% Zr (SA)The () / Ti3CN) group begins to release hydrogen at 104℃, and its hydrogen release capacity is 4.2wt% at 300℃; NaH / Al-7wt% ((1wt% Zr) (SA) The () / Ti3CN) group begins to release hydrogen at 86℃, and its hydrogen release capacity is 5.1wt% at 300℃; NaH / Al-7wt%((3wt%Zr) (SA) The () / Ti3CN) mixture begins to release hydrogen at 83°C, and its hydrogen release capacity is 4.6 wt% at 300°C. In summary, the system in Example 5 exhibits the best hydrogen storage performance.

[0092] Example 7 (1wt% Zr) (SA) Preparation of NaAlH4 composite hydrogen storage system catalyzed by ) / Ti3CN

[0093] In a glove box under argon atmosphere protection, NaH and Al were mixed at a molar ratio of 1:1, and the NaH / Al mixture was combined with the 1wt% Zr prepared in Example 1. (SA) ) / Ti3CN according to chemical composition x(NaH / Al)-y((1wt%Zr) (SA) The mass percentages of 1 / Ti3CN were mixed (x = 95 wt%, y = 5 wt%) to obtain a mixture. This mixture was placed in a ball mill jar, filled with hydrogen gas at 4 MPa, and then placed in a planetary ball mill with a ball-to-material ratio of 90:1 and a rotation speed of 500 rpm. The program was set to mill for 15 minutes with a 10-minute pause, for a total of 24 hours. Hydrogen was then absorbed for 15 hours at a hydrogen pressure of 100 bar and a temperature of 150°C to obtain Zr. (SA) / Ti3CN-catalyzed NaAlH4 composite hydrogen storage system.

[0094] Example 8 (1wt% Zr) (SA) Preparation of NaAlH4 composite hydrogen storage system catalyzed by ) / Ti3CN

[0095] In a glove box under argon atmosphere protection, NaH and Al were mixed at a molar ratio of 1:1, and the NaH / Al mixture was combined with the 1wt% Zr prepared in Example 1. (SA) ) / Ti3CN according to chemical composition x(NaH / Al)-y((1wt%Zr) (SA) The mass percentages of 1 / Ti3CN were mixed (x = 91 wt%, y = 9 wt%) to obtain a mixture. This mixture was placed in a ball mill jar, filled with hydrogen gas at 4 MPa, and then placed in a planetary ball mill with a ball-to-material ratio of 90:1, a rotation speed of 500 rpm, and a program set to mill for 15 minutes with a 10-minute pause, for a total of 24 hours. Hydrogen was then absorbed for 15 hours at a hydrogen pressure of 100 bar and a temperature of 150°C to obtain Zr. (SA) / Ti3CN-catalyzed NaAlH4 composite hydrogen storage system.

[0096] To evaluate the optimal doping ratio of (1wt% Zr (SA) ) / Ti3CN catalyst, three groups of control experiments of examples 5, 7 and 8 were set up, all of which were heated from room temperature to 300℃ at a heating rate of 2℃ / min to test TPD. The TPD test results are shown in Figure 3 It can be seen that the pure NaH / Al system has a starting hydrogen release temperature of 163℃ and a hydrogen release amount of 4.4wt% at 300℃; the Ti3CN added system significantly reduces the starting temperature to 65℃, but the hydrogen release amount is slightly reduced to 4.1wt%; and the 7wt% (1wt% Zr (SA) ) / Ti3CN catalytic system of the present application has both low-temperature hydrogen release characteristics (starting temperature of 86℃) and high capacity advantages (hydrogen release amount of 5.1wt% at 300℃), which is 16% higher than the pure NaH / Al system in terms of hydrogen storage performance, and has the best catalytic effect.

[0097] Preparation of NaAlH4 composite hydrogen storage system catalyzed by (1wt% Zr (SA) ) / Ti3CN of example 9

[0098] In a glove box under argon atmosphere, NaH and Al were mixed in a molar ratio of 1:1, and NaH / Al and Zr (SA) / Ti3CN prepared in example 1 were mixed according to the chemical composition of x(NaH / Al)-y((1wt% Zr (SA) ) / Ti3CN) (x=93wt%, y=7wt%), to obtain a mixture; the mixture was placed in a ball mill jar, filled with 3MPa of hydrogen, and then placed in a planetary ball mill, with a ball-to-material ratio of 60:1, a rotation speed of 550rpm, a program setting of 15min of ball milling followed by 10min of stop, and ball milling for 48h, hydrogen absorption at 110bar hydrogen pressure and 130℃ for 10h, to obtain a Zr (SA) / Ti3CN catalyzed NaAlH4 composite hydrogen storage system.

[0099] Figure 4 a is the isothermal hydrogen release curve of ball-milled NaH / Al mixture (ball-milled NaAlH4 150℃) at 150℃ and the isothermal hydrogen release curves of the composite hydrogen storage system of the present example at 90℃, 120℃ and 150℃, and b is the XRD pattern of the composite hydrogen storage system of the present example after dehydrogenation at different temperatures. As Figure 4As shown in Figure a, the isothermal hydrogen release test demonstrates that the composite hydrogen storage system of Example 9 exhibits significantly improved kinetic performance at 150°C: it releases 4.76 wt% hydrogen in just 20 minutes, while the pure NaH / Al system releases only 0.84 wt% (black curve) in 2 hours at the same temperature. In-situ XRD characterization was also performed. Figure 4 b) reveals the phase transition mechanism of the dehydrogenation process: at 90℃, NaAlH4 first decomposes into Na3AlH6 and Al; after the temperature is raised to 120℃, Na3AlH6 further decomposes into NaH and Al; after hydrogen is released at 150℃, the characteristic peak of Na3AlH6 in the XRD spectrum completely disappears, and the second dehydrogenation reaction is finally completed.

[0100] Example 10 (1wt% Zr) (SA) Preparation of NaAlH4 composite hydrogen storage system catalyzed by ) / Ti3CN

[0101] In a glove box protected by an argon atmosphere, NaH and Al are mixed in a 1:1 molar ratio, and NaH / Al and Zr are then mixed. (SA) / Ti3CN is based on the chemical composition x(NaH / Al)-y(1wt%Zr) (SA) The following mixtures were prepared: (x = 93 wt%, y = 7 wt%) of Ti3CN were mixed to obtain a mixture; the mixture was placed in a ball mill jar, filled with hydrogen gas at 3 MPa, and then placed in a planetary ball mill with a ball-to-material ratio of 100:1, a rotation speed of 400 rpm, and a program set to mill for 15 minutes with a 10-minute pause in between, for a total of 36 hours; Zr was obtained by hydrogen absorption at 100 bar hydrogen pressure and 130°C for 20 hours. (SA) / Ti3CN-catalyzed NaAlH4 composite hydrogen storage system.

[0102] Kinetic analysis was performed on the ball-milled NaH / Al mixture and the composite hydrogen storage system in Example 10 of this invention using the Kissinger equation. The DSC curves of the ball-milled NaH / Al mixture and the composite hydrogen storage system in Example 4, and the two-step hydrogen desorption activation energies calculated based on the Kissinger method are shown below. Figure 5 As shown, Figure 5 As shown in a and b, (1wt% Zr (SA) The () / Ti3CN) catalytic system significantly reduced the reaction energy barrier. The activation energies for the two-step dehydrogenation in the uncatalyzed system were 112.4 kJ / mol (step one) and 92.3 kJ / mol (step two), respectively, while those for the system with 7 wt% Zr significantly decreased. (SA) After applying / Ti3CN, the activation energy decreased to 73.3 kJ / mol and 70.3 kJ / mol, respectively, representing reductions of 34.8% and 23.8%. This significant reduction in activation energy ( Figure 5The results of c and d) demonstrate the key role of Zr monatomic catalyst in optimizing the dehydrogenation kinetics of NaAlH4.

[0103] Example 11 (1 wt% Zr (SA) ) / Ti3CN catalyzed NaAlH4 composite hydrogen storage system

[0104] In a glove box under argon atmosphere, NaH and Al were mixed in a molar ratio of 1:1, and the mixture of NaH / Al and Zr (SA) / Ti3CN was mixed in a percentage of chemical composition x(NaH / Al)-y(1 wt% Zr (SA) / Ti3CN) (x=95 wt%, y=5 wt%), to obtain a mixture; the mixture was placed in a ball mill jar, filled with 3 MPa of hydrogen, and then placed in a planetary ball mill, with a ball-to-material ratio of 100:1, a rotation speed of 400 rpm, a program setting of 15 min of ball milling and 10 min of stop in between every 15 min, and ball milling for 36 h, hydrogen absorption at 90 bar hydrogen pressure and 130 °C for 10 h, to obtain a Zr (SA) / Ti3CN catalyzed NaAlH4 composite hydrogen storage system.

[0105] Figure 6 For the performance of the composite hydrogen storage system in this example in the 10-cycle test, it can be seen that the system undergoes a cycle process of isothermal hydrogen absorption at 130 °C / 90 bar and variable-temperature dehydrogenation at 30-150 °C, and the dehydrogenation capacity of NaAlH4-5 wt% Zr (SA) / Ti3CN decreases from 4.6 wt% in the first dehydrogenation to 4.2 wt% in the tenth dehydrogenation, with a capacity retention rate of 91.3%. This result fully demonstrates that the Zr (SA) / Ti3CN catalyst endows the NaAlH4 system with excellent cycle stability.

[0106] The above merely provides the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and should be encompassed within the protection scope of the present application.

Claims

1. A monatomic catalyst for catalytically synthesizing sodium aluminum hydride, characterized by, The carrier is two-dimensional layered Ti3CN, and the active ingredient is monatomic zirconium, and the loading amount of the monatomic zirconium is 0.1-3wt%.

2. A process for the preparation of a monatomic catalyst for catalytic synthesis of sodium aluminum hydride as claimed in claim 1, wherein, The method comprises the following steps: The monatomic zirconium precursor, the dispersant and the Ti3CN nanosheet dispersion liquid are mixed, and stirring is carried out at room temperature to obtain a mixture; NaOH solution is added to the mixture, and stirring reaction is carried out to precipitate Zr species; The precipitate is collected by centrifugation, and washed with water until neutral; The material washed with water until neutral is freeze-dried to obtain a Zr / Ti3CN precursor powder; The Zr / Ti3CN precursor powder is sintered in a reducing atmosphere to obtain the monatomic catalyst for catalyzing synthesis of sodium aluminum hydride.

3. The method for preparing a monatomic catalyst for catalytically synthesizing sodium aluminum hydride according to claim 2, characterized by, The monatomic zirconium precursor is selected from ZrOCl2·8H2O; And / or, the dispersant is selected from sodium citrate.

4. The method for preparing a single-atom catalyst for catalytically synthesizing sodium aluminum hydride according to claim 2, characterized in that, The reducing atmosphere is selected from H2 / Ar atmosphere; And / or, the sintering temperature is 450℃, and the time is 2h.

5. The monatomic catalyst according to claim 1 is applied in catalyzing synthesis of sodium aluminum hydride composite hydrogen storage system.

6. A method for preparing a sodium aluminum hydride composite hydrogen storage system, characterized in that, The method comprises the following steps: Sodium hydride and aluminum are mixed and ball-milled to form a sodium hydride / aluminum mixture; The monatomic catalyst according to claim 1 is mixed with the sodium hydride / aluminum mixture to carry out hydrogen absorption reaction to prepare a sodium aluminum hydride composite hydrogen storage system.

7. The method of claim 6, wherein the sodium aluminum hydride composite hydrogen storage system is prepared by the steps of: a) mixing sodium metal and aluminum metal in a solvent; b) adding a Lewis acid to the mixture; and c) adding a Lewis base to the mixture. The molar ratio of the sodium hydride and the aluminum is 1:

1.

8. The method of claim 6, wherein the sodium aluminum hydride composite hydrogen storage system is prepared by the steps of: a) mixing sodium metal and aluminum metal in a solvent; b) adding water to the mixture; and c) stirring the mixture until the sodium aluminum hydride composite hydrogen storage system is formed. The ball-milling parameters are as follows: the pressure is 1-6MPa, the atmosphere is hydrogen, the ball-to-material ratio is (60-120):1, the rotation speed is 400-550rpm, the intermittent ball-milling mode is adopted, and the total ball-milling time is 20-48h.

9. The method of claim 6, wherein the sodium aluminum hydride composite hydrogen storage system is prepared by the steps of: a) mixing sodium metal and aluminum metal in a solvent; b) adding a Lewis acid to the mixture; and c) adding a Lewis base to the mixture. The proportion of the monatomic catalyst in the sodium aluminum hydride composite hydrogen storage system is 5-9wt%.

10. The sodium aluminum hydride composite hydrogen storage system prepared by the preparation method according to any one of claims 6-9 is applied in solid-state hydrogen storage.

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