Preparation method of monatomic iron catalyst and application of monatomic iron catalyst in nitrogen heterocyclic biological hydrogen storage material

Abstract

The invention relates to the technical field of catalyst preparation and biological hydrogen storage material synthesis, and discloses a preparation method of a monatomic iron catalyst, which comprises the following steps: firstly adding melamine into a ball milling tank, then adding L-alanine, finally adding 100mg of iron acetate, and carrying out ball milling treatment; the preparation method comprises the following steps: adding a hydrochloric acid ethanol solution into a nitrogen-doped carbon carrier, grinding, drying, pyrolyzing in an N2 atmosphere, pickling to obtain a monatomic iron catalyst FeN4, carrying out dehydrogenation reaction in the nitrogen-heterocyclic biological hydrogen storage material by using the monatomic iron catalyst FeN4, and representing that iron is dispersed in the nitrogen-doped carbon carrier in a monatomic form by using the monatomic iron catalyst to form FeN4 active sites. The catalyst is prepared by pyrolyzing an iron precursor and a nitrogen-carbon carrier and has high-dispersion monatomic iron active sites, in the presence of oxygen, FeN4 can activate oxygen molecules to form superoxide free radicals, dehydrogenation reaction energy barriers are remarkably reduced, efficient catalysis at room temperature is achieved, the catalysis cost is low, and the catalyst is environmentally friendly and has good application prospects. The catalyst is suitable for dehydrogenation reaction of nitrogen heterocyclic biological hydrogen storage materials.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of catalyst preparation and biological hydrogen storage material synthesis, in particular to a preparation method of a single-atom iron catalyst and application of the single-atom iron catalyst in nitrogen heterocyclic biological hydrogen storage material. BACKGROUND

[0002] Hydrogen energy is considered as an important carrier of future clean energy due to its high-quality energy density (120 MJ kg-1) and carbon-free characteristics of combustion products (only water). However, the low density and volatility of hydrogen make it difficult to store and transport efficiently at normal pressure. The traditional compressed hydrogen or liquefied hydrogen technology has problems such as high energy consumption and poor safety, which limits its large-scale application.

[0003] Biological hydrogen storage materials realize the fixation and release of hydrogen through reversible hydrogenation / dehydrogenation reactions. N-heterocyclic compounds (such as carbazole, indole, pyridine derivatives, etc.) have become the most promising liquid organic hydrogen carriers (LOHCs) due to their high hydrogen storage capacity (> 5wt%) and reversible reaction characteristics under mild conditions. However, the existing technology still faces many problems. On the one hand, the dehydrogenation of N-heterocycles usually requires high temperature (> 150℃) and high pressure (> 5MPa) conditions, and relies on noble metal catalysts (such as Pt, Pd), which is costly and leads to slow dehydrogenation kinetics. On the other hand, traditional transition metal catalysts (such as Fe nanoparticles or metal oxides) are prone to agglomeration in N-heterocycle synthesis, resulting in a decrease in active sites and poor selectivity.

[0004] Therefore, it is crucial to develop a new type of safe and effective, non-noble metal-dependent, and easy-to-release hydrogen under mild conditions N-heterocyclic oxidative dehydrogenation catalyst for hydrogen energy economy. SUMMARY

[0005] The application provides a preparation method of a single-atom iron catalyst and application of the single-atom iron catalyst in nitrogen heterocyclic biological hydrogen storage material. The catalyst is prepared by pyrolyzing an iron precursor and a nitrogen-carbon carrier, and has high-dispersed single-atom iron active sites. In the presence of oxygen, FeN4 can activate oxygen molecules to form superoxide radicals, significantly reducing the dehydrogenation reaction energy barrier, realizing room-temperature efficient catalysis, and being low in catalytic cost and environmentally friendly, and being suitable for dehydrogenation reaction applications of nitrogen heterocyclic biological hydrogen storage material.

[0006] The application provides a preparation method of a single-atom iron catalyst, which comprises the following steps: S1, 12g of melamine is first added into a ball mill jar, then 2g of L-alanine is added, finally 100mg of iron acetate is added, and ball milling treatment is performed; S2, after adding hydrochloric acid ethanol solution, grinding and drying, pyrolysis under N2 atmosphere, acid washing to obtain monatomic iron catalyst FeN4, using the monatomic iron catalyst FeN4 in the dehydrogenation reaction of nitrogen heterocyclic biological hydrogen storage material, the characterization of the monatomic iron catalyst shows that the iron is dispersed in the nitrogen-doped carbon carrier in the form of single atom, forming FeN4 active site.

[0007] Further, in the step S1, the ingredient ratio of melamine, L-alanine and iron acetate is 227.10:52.31:1, and is a molar ratio.

[0008] Further, in the step S1, the ball milling mixing condition is: rotating speed 300 rpm, ball milling for 240 minutes.

[0009] Further, in the step S2, the N2 atmosphere is 600℃, 2 hours or 900℃, 90 minutes.

[0010] Further, in the step S2, the acid washing process is: in a hydrochloric acid solution with a concentration of 3 mol / L, refluxing at 80℃ for 12h, washing out the surface Fe particles.

[0011] The application also provides an application of a monatomic iron catalyst in a nitrogen heterocyclic biological hydrogen storage material, based on the preparation method of the monatomic iron catalyst as described above, comprising: S1, dissolving a dehydrogenation substrate in a predetermined solvent to form a homogeneous or homogeneous dispersion system; wherein the dehydrogenation substrate is THQ; S2, using the monatomic iron catalyst FeN4, under predetermined mild conditions, and in a predetermined solvent with a dehydrogenation substrate, inert gas N2 is introduced to carry away hydrogen.

[0012] Further, in the step S1, the predetermined solvent is toluene or xylene, and the predetermined mild condition is 25-80℃, normal pressure.

[0013] Further, in the step S2, the dehydrogenation reaction path includes: S201, substrate adsorption THQ molecules are adsorbed on the FeN4 active center through aromatic ring or nitrogen atom, and Fe sites are coordinated with the nitrogen lone pair electrons of THQ to enhance the activity of the substrate; S202, C-H bond activation α-C-H bond breaking: Fe center cooperates with adjacent nitrogen ligand or base catalyst to capture the α-hydrogen of THQ, forming Fe-H intermediate and carbon radical intermediate: THQ→[Fe-H]+quinoline radical; wherein the α-hydrogen is the hydrogen on the carbon adjacent to nitrogen; S203, secondary dehydrogenation Another molecule THQ transfers its a-H to the Fe-H intermediate to generate H2 and regenerate the Fe active center: [Fe-H]+THQ→FeN4+quinoline+H2, or through the β-H elimination pathway when the intermediate is Fe-alkyl species; S204, H2 release Two Fe-H intermediates combine to release H2, or with oxidants to generate H2O.

[0014] Further, in the step S202, the base promoter is K2CO3, which is used to promote hydrogen transfer; in the step S204, the oxidant is O2 or DDQ, which is used for oxidative dehydrogenation.

[0015] Further, THQ is tetrahydroquinoline, in the reaction process, first oxygen is adsorbed on FeN4 and activated into superoxide radical •O 2 ⁻, so that the dehydrogenation reaction energy barrier is reduced from 1.65 eV to 1.1 eV, and due to the presence of oxygen in the air, dehydrogenation begins, and the dehydrogenation reaction converts tetrahydroquinoline into quinoline while releasing hydrogen.

[0016] The beneficial effects of the present application are: The present application realizes efficient catalysis under mild conditions (such as 25-80℃, normal pressure) through the synergistic effect of FeN4 monatomic sites and nitrogen-doped carbon carriers. The non-noble metal catalyst has high activity and long cycle life, and the iron single atom dispersion feature makes the iron utilization rate reach 100%, and the turnover frequency (TOF) is improved by more than 10 times (compared with Fe nanoparticles). When oxygen is used as a green oxidant, the reaction energy barrier can be significantly reduced, and it is suitable for the dehydrogenation reaction of N-heterocyclic compounds (such as THQ) and their derivatives (the reaction path includes THQ adsorption, C-H / N-H bond breaking, H2O2 generation, and finally dehydrogenation product formation), and the conversion rate and selectivity are both 100%. The single-atom iron catalyst FeN4 is used for catalysis, which is low in catalytic cost and environmentally friendly, and is suitable for the dehydrogenation reaction of nitrogen heterocyclic biological hydrogen storage materials. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 TEM, HAADF-STEM and element distribution map of FeN4 catalyst in the present application.

[0018] Figure 2 Reaction energy barrier path diagram of FeN4 catalyzing THQ dehydrogenation in the present application.

[0019] The implementation, functional characteristics and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0020] It should be understood that the specific embodiments described herein are merely intended to explain the present application, and are not intended to limit the present application.

[0021] The application discloses a single-atom iron catalyst (FeN4) and application thereof in acceptor-free dehydrogenation reaction of nitrogen heterocyclic biological hydrogen storage materials, in particular, application of a single-atom iron catalyst supported by nitrogen-doped graphite carbon in catalyzing acceptor-free dehydrogenation reaction under mild conditions, and especially application in efficient synthesis of N-heterocyclic biological hydrogen storage molecules (such as carbazole, indole and derivatives thereof) in the presence of oxygen.

[0022] The single-atom iron catalyst (FeN4) is prepared by pyrolysis of an iron precursor and a nitrogen-carbon carrier, and has high-dispersed single-atom iron active sites. In the presence of oxygen, the FeN4 can activate oxygen molecules to form superoxide radicals, significantly reduce the dehydrogenation reaction energy barrier, and realize room-temperature efficient catalysis. The preparation method is low in catalytic cost, environmentally friendly, and suitable for application in dehydrogenation reaction of nitrogen heterocyclic biological hydrogen storage materials.

[0023] In one embodiment, the application provides a preparation method of the single-atom iron catalyst, comprising: S1, 12 g of melamine is first added into a ball mill tank, then 2 g of L-alanine is added, and finally 100 mg of iron acetate is added, and ball milling treatment is performed (ball milling mixing conditions are 300 rpm of rotation speed and 240 minutes of ball milling); wherein the ingredient ratio of the melamine, the L-alanine and the iron acetate is 227.10:52.31:1 (molar ratio).

[0024] S2, after adding an ethanol hydrochloride solution, grinding and drying are performed, pyrolysis is performed under N2 atmosphere (600 DEG C for 2 hours or 900 DEG C for 90 minutes), and after acid washing (the acid washing process is: in a 3 mol / L hydrochloric acid solution, refluxing at 80 DEG C for 12 h, and washing out surface Fe particles), a single-atom iron catalyst FeN4 is obtained, as shown in FIG. 1, which is used for dehydrogenation reaction in nitrogen heterocyclic biological hydrogen storage materials by using the single-atom iron catalyst FeN4, and the single-atom iron catalyst is characterized in that iron is dispersed in a nitrogen-doped carbon carrier in a single-atom form, and forms FeN4 active sites. Figure 1

[0025] In one embodiment, the application further provides application of a single-atom iron catalyst in nitrogen heterocyclic biological hydrogen storage materials, based on the preparation method of the single-atom iron catalyst, comprising: S1, a dehydrogenation substrate is dissolved in a preset solvent (toluene, xylene) to form a homogeneous or homogeneous dispersion system; wherein the dehydrogenation substrate is THQ; S2, the single-atom iron catalyst FeN4 is used to pass in inert gas N2 to carry away hydrogen under preset mild conditions (25-80 DEG C, normal pressure) and in the preset solvent with the dehydrogenation substrate.

[0026] (1) Dehydrogenation reaction conditions​ Temperature: Mild conditions 25-80 °C.

[0027] Pressure: Normal pressure.

[0028] Solvent: Toluene, Xylene.

[0029] Additives: Base (e.g. K2CO3) can promote hydrogen transfer; oxidant (e.g. DDQ) for oxidative dehydrogenation.

[0030] Catalytic reaction: 10 mg FeN4, 0.5 mmol THQ and 3 mL solvent were added in a 5 mL glass bottle, stirred at room temperature for 10 hours, GC analysis showed 100% conversion and selectivity.

[0031] Characterization and verification: ESR detected superoxide radical signal (1070 cm⁻¹), DFT calculation confirmed that the O-O bond length was 1.29 Å, consistent with superoxide radical.

[0032] (2) Dehydrogenation reaction path includes THQ adsorption, C-H / N-H bond breaking, H2O2 generation and final dehydrogenation product formation, which is efficiently completed under mild conditions. Specifically includes the following steps: S201, substrate adsorption THQ molecules are adsorbed on the FeN4 active center through aromatic ring or nitrogen atom, and the Fe site is coordinated with the nitrogen lone pair electrons of THQ to enhance the activity of the substrate; S202, C-H bond activation α-C-H bond breaking: Fe center cooperates with adjacent nitrogen ligand or base co-catalyst (K2CO3, used to promote hydrogen transfer) to grab the α-hydrogen of THQ (hydrogen on carbon adjacent to nitrogen), forming Fe-H intermediate and carbon radical intermediate: THQ→[Fe-H]+quinoline radical; S203, secondary dehydrogenation Another molecule of THQ transfers α-H to the Fe-H intermediate to generate H2 and regenerate the Fe active center: [Fe-H]+THQ→FeN4+quinoline+H2, or through the β-H elimination path (if the intermediate is Fe-alkyl species).

[0033] S204, H2 release Two Fe-H intermediates release H2 (similar to a bimolecular mechanism), or combine with an oxidant (O2 or DDQ, used for oxidative dehydrogenation) to generate H2O (oxidative dehydrogenation).

[0034] Parameters The present invention Conventional Fe catalyst Dispersion Monatomic Nanoparticle Quinoline dehydrogenation yield ＞95% 70-80% Cyclic stability 30 times without deactivation 5 times 50% activity decrease The new monatomic iron catalyst and its N-heterocyclic hydrogen storage material synthesis application proposed in the application realize the following breakthroughs: 1. Through the synergy of FeN4 monatomic sites and nitrogen-doped carbon supports, high-efficiency catalysis under mild conditions (such as 25-80℃, normal pressure) is achieved.

[0035] 2. Non-noble metal catalysts are used, with high activity and long cycle life. The iron monatomic dispersion feature makes the iron utilization rate reach 100%, and the turnover frequency (TOF) is increased by more than 10 times (compared with Fe nanoparticles).

[0036] 3. Oxygen as a green oxidizing agent can significantly reduce the reaction energy barrier.

[0037] The present application is suitable for the dehydrogenation reaction of N-heterocyclic compounds (such as THQ) and their derivatives (the reaction path includes THQ adsorption, C-H / N-H bond breaking, H2O2 generation, and finally the formation of dehydrogenation products), with conversion and selectivity reaching 100%. The single-atom iron catalyst FeN4 is used, which is low in catalytic cost and environmentally friendly, and is suitable for the dehydrogenation reaction of nitrogen heterocyclic biological hydrogen storage materials.

[0038] It should be noted that in this article, the term "includes", "contains" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, device, article or method including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such process, device, article or method. Without more limitations, the element defined by the statement "includes a" does not exclude the presence of another identical element in the process, device, article or method including the element.

[0039] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the present application specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a monatomic iron catalyst, characterized by, The application relates to a preparation method of a single-atom iron catalyst. S1, 12g melamine is first added into a ball mill tank, 2g L-alanine is then added, 100mg iron acetate is finally added, and ball milling treatment is carried out; S2, after adding an ethanol hydrochloride solution, grinding and drying are carried out, pyrolysis is carried out under N2 atmosphere, and after acid washing, a single-atom iron catalyst FeN4 is obtained; the single-atom iron catalyst FeN4 is used in a dehydrogenation reaction in a nitrogen heterocyclic biological hydrogen storage material; the single-atom iron catalyst is characterized in that iron is dispersed in a nitrogen-doped carbon carrier in a single-atom form to form FeN4 active sites.

2. The method of claim 1, wherein the monatomic iron catalyst is prepared by, In the step S1, the ingredient ratio of melamine, L-alanine and iron acetate is 227.10:52.31:1, and the ingredient ratio is a molar ratio.

3. The method of claim 1, wherein the monatomic iron catalyst is prepared by, In the step S1, the ball milling mixing condition is that the rotating speed is 300rpm and the ball milling time is 240 minutes.

4. The method of claim 1, wherein the monatomic iron catalyst is prepared by, In the step S2, the N2 atmosphere is 600 DEG C for 2 hours or 900 DEG C for 90 minutes.

5. The method of claim 1, wherein the monatomic iron catalyst is prepared by, In the step S2, the acid washing process is that Fe particles on the surface are washed out in a 3mol / L hydrochloric acid solution at 80 DEG C for 12h.

6. Use of a monatomic iron catalyst in aza-cyclic biohydrogen storage material, characterized in that, The application further discloses a preparation method of a single-atom iron catalyst based on any one of claims 1-5, comprising: S1, dissolving a dehydrogenation substrate in a preset solvent to form a homogeneous or homogeneous dispersion system; wherein the dehydrogenation substrate is THQ; S2, using the single-atom iron catalyst FeN4, under preset mild conditions, and in the preset solvent with the dehydrogenation substrate, inert gas N2 is introduced to carry away hydrogen.

7. Use of the monatomic iron catalyst according to claim 6 in aza-cyclic biohydrogen storage material, characterized in that, In the step S1, the preset solvent is toluene or xylene, and the preset mild condition is 25-80 DEG C under normal pressure.

8. Use of the monatomic iron catalyst according to claim 7 in aza-cyclic biohydrogen storage material, characterized in that, In the step S2, the dehydrogenation reaction path comprises: S201, substrate adsorption THQ molecules are adsorbed on FeN4 active centers through aromatic rings or nitrogen atoms, Fe sites are coordinated with nitrogen lone pair electrons of THQ to enhance substrate activity; S202, C-H bond activation Alpha-C-H bond breaking: Fe centers cooperate with adjacent nitrogen ligands or base cocatalysts to capture alpha-hydrogen of THQ to form Fe-H intermediates and carbon radical intermediates: THQ -> [Fe-H]+ quinoline radical; wherein the alpha-hydrogen is hydrogen on the carbon adjacent to nitrogen; S203, secondary dehydrogenation Alpha-H of another molecule of THQ is transferred to the Fe-H intermediate to generate H2 and regenerate the Fe active center: [Fe-H]+THQ -> FeN4+quinoline+H2, or through a beta-H elimination path when the intermediate is a Fe-alkyl species; S204, H2 release Two Fe-H intermediates release H2 in combination, or generate H2O in combination with an oxidant.

9. Use of the monatomic iron catalyst according to claim 8 in aza-cyclic biohydrogen storage material, characterized in that, In the step S202, the base cocatalyst is K2CO3 and is used for promoting hydrogen transfer; in the step S204, the oxidant is O2 or DDQ and is used for oxidative dehydrogenation.

10. Use of the monatomic iron catalyst according to claim 9 in aza-cyclic biohydrogen storage material, characterized in that, THQ is tetrahydroquinoline, in the reaction process, first oxygen is adsorbed on FeN4 and activated as superoxide radical •O 2 ⁻, so that the dehydrogenation reaction energy barrier is reduced from 1.65 eV to 1.1 eV, and due to the presence of oxygen in the air, dehydrogenation begins, and the dehydrogenation reaction converts tetrahydroquinoline into quinoline while releasing hydrogen.

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