Fe single atom supported catalyst, preparation and application thereof

Abstract

The application discloses a Fe single-atom supported catalyst prepared by limiting an amorphous layer of BaTiO3, and a preparation and application thereof. The catalyst is prepared by taking BaTiO3 as a precursor, preparing Ov-BaTiO3 coated with a surface amorphous layer through high-temperature hydrothermal reduction of sodium borohydride, and then applying a bipyridyl iron modified calcination method to limit Fe single atoms by an amorphous layer, so that the single-atom Fe supported catalyst is prepared. The catalyst has high ammonia yield and high stability in a piezoelectric-photocatalytic nitrogen reduction process, and has wide prospects in solar energy-mechanical energy utilization and realization of double-energy-to-high-value-chemicals conversion.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of catalyst preparation and nitrogen reduction, and particularly relates to a Fe monatomic supported catalyst prepared by limiting BaTiO3 amorphous layer, a preparation method thereof and application of the catalyst in piezoelectric-photocatalytic nitrogen reduction. BACKGROUND

[0002] Ammonia is one of the most basic chemical raw materials in modern industrial and agricultural production, and is widely used in the synthesis of fertilizers, medicaments, explosives and resins. At the same time, due to its high hydrogen content, high volume energy density, low liquefaction pressure and transportation safety, it is also considered as a very potential carbon-free energy carrier. The conversion of abundant N2 in the atmosphere into ammonia is not only the key to maintaining life, but also plays an important role in the development of national economy and society. Although its raw materials are inexhaustible and readily available, due to the high stability of N≡N bond (the bond energy is as high as 940.95 KJ·mol -1 ), the process from nitrogen to ammonia (i.e. nitrogen fixation process (NRR)) is extremely difficult.

[0003] The nitrogen fixation process can be generally divided into natural nitrogen fixation (including biological nitrogen fixation and lightning nitrogen fixation) and artificial nitrogen fixation. Among them, biological nitrogen fixation is to obtain nitrogen compounds by catalyzing a plurality of proton and electron transfer processes under environmental conditions by nitrogenase. The process has mild conditions and high reaction efficiency, and consumes 6-24 ATP per mole of N2, which is the most ideal nitrogen fixation route. However, relying only on natural nitrogen fixation cannot meet the increasing demand for ammonia of human beings, and artificial nitrogen fixation emerges as the times require and has become the main source of practical application demand. At present, the industrial scale artificial nitrogen fixation technology is mainly the Haber-Bosch method, which has a conversion efficiency of 20 %, realizes the intensification and scaling development of artificial nitrogen fixation, and directly promotes the unprecedented growth of global food production and population. Although the technology has undergone more than a hundred years of development, it still needs to be carried out under high temperature and high pressure conditions (350-550 ℃, 200-300 atm), and the annual average energy consumption accounts for 1-2 % of the total world energy consumption, and the annual CO2 emission accounts for about 1.6 % of the total greenhouse gas, which undoubtedly aggravates environmental pollution and energy shortage. Therefore, developing green, low-consumption and efficient artificial nitrogen fixation technology is an inevitable requirement for realizing human sustainable development, and is also a hot spot and a great challenge for researchers.

[0004] Inspired by nitrogen fixation by microorganisms in nature, electrocatalytic nitrogen fixation has attracted much attention as a green and safe ammonia synthesis technology. However, this technology still faces problems such as low ammonia production rate, poor selectivity, low Faradaic efficiency, high external bias, etc. At the same time, the system needs to be connected to an external circuit and consume additional electrical energy, limiting the application of the system. Therefore, how to directly use green renewable energy to replace the additional consumption of electrical energy, while considering the inhibition of the competitive reaction of hydrogen reduction to hydrogen gas, and improving the efficiency and selectivity of nitrogen fixation, is a key bottleneck problem faced by current mild artificial nitrogen fixation technology. In the face of the above challenges, the present application effectively promotes the activation of nitrogen molecules and inhibits the occurrence of the side reaction of hydrogen reduction to hydrogen gas by a single atom modification method, realizing efficient use of solar energy and mechanical energy for nitrogen reduction to generate ammonia. SUMMARY

[0005] In view of the problems of low efficiency and selectivity of current artificial nitrogen fixation technology, the present application provides a Fe single atom supported catalyst prepared by limiting BaTiO3 amorphous layer and a preparation method and application thereof. The catalyst Fe-BaTiO3 obtained in the present application has high ammonia production rate and high selectivity in the process of piezoelectric-photocatalytic nitrogen reduction, and has broad prospects in the utilization of solar energy and mechanical energy and the realization of double energy conversion to high value-added chemicals.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A Fe single atom supported catalyst prepared by limiting BaTiO3 amorphous layer, which is prepared by taking BaTiO3 as a precursor, forming an amorphous layer, and then limiting the formation of Fe single atoms by the amorphous layer, so as to constitute a highly dispersed single atom supported catalyst with Fe single atoms and Ti in the amorphous layer as main active components.

[0008] Further, the content of Fe in the catalyst is 1.0-5.0 mol%.

[0009] The preparation method of the Fe single atom supported catalyst prepared by limiting BaTiO3 amorphous layer is that BaTiO3 is reduced by sodium borohydride at high temperature by hydrothermal reduction, Ov-BaTiO3 coated with a surface amorphous layer is synthesized, and single atom Fe supported Fe-BaTiO3 is obtained by using iron bipyridine modification calcination method. It specifically includes the following steps:

[0010] (1) Preparation of Ov-BaTiO3: sodium borohydride and BaTiO3 are added to a NaOH solution, stirred for 1 h, and then hydrothermally reacted at 180℃ for 24 h to obtain Ov-BaTiO3 coated with a surface amorphous layer;

[0011] (2) Preparation of the catalyst: first, prepare a ferric chloride methanol solution, then dilute 1-5 mL with anhydrous methanol to 40 mL, then add 2,2'-dipyridyl to the diluent and dissolve it, and then stir for 1 h to obtain a clear iron dipyridyl solution; then add the surface amorphous layer coated Ov-BaTiO3 obtained in step (1) to the iron dipyridyl solution and stir for 1 h, then remove the solvent by rotary evaporation, and then calcine at 350 DEG C under argon for 1 h to obtain the catalyst Fe-BaTiO3.

[0012] Further, the mass ratio of sodium borohydride to BaTiO3 used in step (1) is 1:1; the concentration of the NaOH solution used is 1 mol / L.

[0013] Further, the concentration of the ferric chloride methanol solution used in step (2) is 3.24 mg / mL; the molar ratio of the amount of 2,2'-dipyridyl added to the ferric chloride in the diluent is 3:1.

[0014] The Fe monatomic supported catalyst prepared by limiting BaTiO3 amorphous layer can be used as a UV-visible light-piezoelectric co-catalyst for piezoelectric-photocatalytic reduction of nitrogen to ammonia.

[0015] Further, the power of the light source used is 300 W, and the wavelength (lambda) range is 320-780 nm.

[0016] By introducing Fe monomers in a suitable proportion, and forming a bimetallic site with Ti in the amorphous layer, the nitrogen molecules are converted from end single nitrogen atom adsorption to double nitrogen atom adsorption. At the same time, the asymmetric local electron distribution in the hetero double site can promote the uneven distribution of the double nitrogen atom electron distribution in the nitrogen molecule, promote the activation and rupture of the N≡N bond in the nitrogen molecule, and the introduction of Fe monomers can effectively inhibit the occurrence of hydrogen evolution side reactions and improve the selectivity of the product ammonia. At the same time, the introduction of a piezoelectric field can efficiently promote the separation of photo-generated carriers, inhibit the recombination of photo-generated carriers and the aggregation of photo-generated electrons, and promote the nitrogen reduction multi-electron reaction, thereby maintaining a high ammonia generation rate and selectivity during the nitrogen reduction process.

[0017] The significant advantages of the present application are:

[0018] In view of the shortcomings of traditional nitrogen fixation technology, such as high energy consumption and heavy pollution, and the current bottleneck of mild artificial nitrogen fixation technology, such as low yield, poor selectivity and system limitations, the present application provides a Fe monatomic supported catalyst prepared by limiting BaTiO3 amorphous layer, which can realize nitrogen conversion under piezoelectric-photocatalytic conditions and has high ammonia generation rate and stability. Therefore, the present application provides a new efficient, green and mild nitrogen fixation technology, which provides a new idea for the application and development of renewable solar energy and mechanical energy.

[0019] The Fe-BaTiO3 obtained by the present application has high ammonia yield and high selectivity in the piezoelectric-photocatalytic nitrogen reduction process, and has broad prospects in solar-mechanical energy utilization and realization of dual-energy conversion into high value-added chemicals. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 XRD patterns of BaTiO3, Ov-BaTiO3, 1 mol% Fe-BaTiO3, 3 mol% Fe-BaTiO3, 5 mol% Fe-BaTiO3 obtained in Example 1.

[0021] Figure 2 SEM patterns of BaTiO3, Ov-BaTiO3, 1 mol% Fe-BaTiO3, 3 mol% Fe-BaTiO3, 5 mol% Fe-BaTiO3 obtained in Example 1.

[0022] Figure 3 Spherical aberration-Transmission Electron Microscope pattern of Ov-BaTiO3 obtained in Example 1.

[0023] Figure 4 Performance comparison chart of piezoelectric-photocatalytic nitrogen reduction of BaTiO3, Ov-BaTiO3, 1 mol% Fe-BaTiO3, 3 mol% Fe-BaTiO3, 5 mol% Fe-BaTiO3 in Example 2.

[0024] Figure 5 Selectivity comparison chart of piezoelectric-photocatalytic nitrogen reduction of Ov-BaTiO3, 3 mol% Fe-BaTiO3 under the conditions of Example 2. DETAILED DESCRIPTION

[0025] In order to make the content of the present application more convenient to understand, the technical solutions described in the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0026] Preparation of catalyst of Example 1

[0027] (1) First, 60 mL of 1M NaOH solution was prepared, then 233 mg of sodium borohydride was added thereto and stirred to dissolve, 233 mg of BaTiO3 was further added and stirred for 1 h, and then loaded into a reaction kettle, and hydrothermal treatment was carried out at 180℃ in a hydrothermal oven for 24 h to obtain Ov-BaTiO3 coated with an amorphous layer on the surface.

[0028] (2) First, 32.4 mg of iron chloride was dissolved in [U1] mL of anhydrous methanol, and then 1 mL, 3 mL and 5 mL were measured respectively and diluted to 40 mL with anhydrous methanol. Subsequently, 5 mg, 15 mg and 25 mg of 2,2'-bipyridine were added to the dilution solution, so that the molar ratio of iron chloride to the added 2,2'-bipyridine was 1:3, stirred for 1 h to obtain a clear iron bipyridine solution. 233 mg of the surface amorphous layer coated Ov-BaTiO3 obtained in step (1) was added to the above iron bipyridine solution and stirred for 1 h, and then the methanol was removed by rotary evaporation, and then calcined at 350 ℃ for 1 h under argon to obtain 1 mol% Fe-BaTiO3, 3 mol% Fe-BaTiO3, 5 mol% Fe-BaTiO3 respectively.

[0029] Figure 1 XRD patterns of BaTiO3, Ov-BaTiO3, 1 mol% Fe-BaTiO3, 3 mol% Fe-BaTiO3, 5 mol% Fe-BaTiO3 catalysts obtained in Example 1. As can be seen from the figure, the introduction of amorphous layer and Fe does not cause changes in the structure of BaTiO3. At the same time, no other assigned X-ray diffraction peaks were detected, indicating that the introduction of Fe is not in the form of metal or metal oxide, mainly in the form of single atom.

[0030] Figure 2 Scanning electron microscope images of BaTiO3, Ov-BaTiO3, 1 mol% Fe-BaTiO3, 3 mol% Fe-BaTiO3, 5 mol% Fe-BaTiO3 catalysts obtained in Example 1. As can be seen from the figure, the introduction of amorphous layer and Fe cannot cause changes in the morphology of the material.

[0031] Figure 3 HREM image of Ov-BaTiO3 obtained. As can be seen from the figure, there are disordered atomic layers on the outermost periphery of Ov-BaTiO3, proving that the surface of the prepared Ov-BaTiO3 has an amorphous structure, and the Ov-BaTiO3 is specifically an amorphous layer coated BaTiO3 material.

[0032] Performance evaluation of catalysts of Example 2

[0033] In the evaluation process of piezophotocatalytic nitrogen reduction to generate ammonia, the catalyst dosage was 20 mg, which was added to a quartz reactor (100 mL) and 60 mL of deionized water was added. Nitrogen was passed for 1 h under dark conditions, and the flow rate of nitrogen was controlled at 60 mL·min -1After the aeration, the performance evaluation of piezophotocatalytic nitrogen reduction to ammonia was carried out by using 300 W xenon lamp to control the wavelength (λ) range of 320-780 nm and 200 W ultrasonic vibration frequency of 40 kHz. During the period, the nitrogen flow rate was maintained at 60 mL·min -1 , the reaction temperature was controlled at 25 DEG C, and finally the liquid product ammonium concentration was detected by cation chromatography.

[0034] Figure 4 The performance comparison chart of piezophotocatalytic nitrogen reduction for BaTiO3, Ov-BaTiO3, 1 mol% Fe-BaTiO3, 3 mol% Fe-BaTiO3, 5 mol% Fe-BaTiO3 is shown in the figure. As can be seen from the figure, the ammonium generation rates of BaTiO3, Ov-BaTiO3, 1 mol% Fe-BaTiO3, 3 mol% Fe-BaTiO3, 5 mol% Fe-BaTiO3 are 11.3, 25.2, 58.6, 102.4, 84.8 μmol·g −1 ·h −1 . It is shown that the introduction of amorphous layer can expose more Ti sites to promote the adsorption and activation of nitrogen molecules, and the further introduction of Fe monatomic can form Ti and Fe bimetallic sites to change the adsorption mode of nitrogen molecules, which is more conducive to the activation and rupture of N≡N bond (5 mol% Fe-BaTiO3 activity decreases may be due to excessive Fe introduction covering the Ti sites in the amorphous layer, which cannot play the role of bimetallic sites).

[0035] Figure 5 The selectivity comparison chart of piezophotocatalytic nitrogen reduction for Ov-BaTiO3 and 3 mol% Fe-BaTiO3 is shown in the figure. As can be seen from the figure, with the introduction of Fe monatomic, the selectivity of reduction product ammonia is improved, which is mainly due to the introduction of Fe which can effectively inhibit the occurrence of hydrogen evolution side reaction.

[0036] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. An Fe single-atom supported catalyst prepared by confinement in a BaTiO3 amorphous layer, characterized by: The catalyst uses BaTiO3 as a precursor, which is hydrothermally reduced with sodium borohydride at high temperature to synthesize Ov-BaTiO3 coated with an amorphous layer on the surface. The amorphous layer is then used to confine Fe single atoms, thereby forming a highly dispersed single-atom supported catalyst. The catalyst can be used for piezoelectric-photocatalytic reduction of nitrogen to ammonia.

2. The Fe single-atom supported catalyst prepared by confinement of BaTiO3 amorphous layer according to claim 1, characterized in that: The Fe content in the catalyst is 1.0-5.0 mol%.

3. A method for preparing a Fe single-atom supported catalyst prepared by confinement of a BaTiO3 amorphous layer as claimed in claim 1, characterized in that: BaTiO3 was hydrothermally reduced with sodium borohydride at high temperature to synthesize Ov-BaTiO3 coated with a surface amorphous layer, and then single-atom Fe-loaded Fe-BaTiO3 was obtained by bipyridine iron modification calcination method.

4. The preparation method according to claim 3, wherein: The following steps are involved: (1) Preparation of Ov-BaTiO3: Sodium borohydride and BaTiO3 were added to NaOH solution, stirred for 1 h, and then hydrothermally reacted at 180 °C for 24 h to obtain Ov-BaTiO3 coated with an amorphous layer on the surface; (2) Preparation of the catalyst: First, prepare a ferric chloride methanol solution, then take 1-5 mL and dilute it to 40 mL with anhydrous methanol, then add 2,2'-bipyridine to the diluted solution and dissolve it, and then stir for 1 hour to obtain a clear bipyridine iron solution; then add the Ov-BaTiO3 coated with the surface amorphous layer obtained in step (1) to the bipyridine iron solution, and stir for 1 hour, then remove the solvent by rotary evaporation, and then calcine at 350 ° C for 1 hour under argon conditions to obtain the catalyst Fe-BaTiO3.

5. The preparation method according to claim 4, characterized in that: The mass ratio of sodium borohydride and BaTiO3 used in step (1) is 1:1; the concentration of the NaOH solution used is 1 mol / L.

6. The preparation method according to claim 4, wherein: The concentration of the ferric chloride methanol solution used in step (2) is 3.24 mg / mL; the molar ratio of the amount of 2,2'-bipyridine added to the ferric chloride in the diluent is 3:

1.

7. Use of the Fe single-atom supported catalyst prepared by confinement of BaTiO3 amorphous layer as claimed in claim 1 in piezoelectric-photocatalytic reduction of nitrogen to ammonia.

8. The use according to claim 7, characterized in that: The Fe single-atom supported catalyst prepared by confining the BaTiO3 amorphous layer is used as an ultraviolet-visible light-piezoelectric co-catalyst for piezoelectric-photocatalytic reduction of nitrogen to ammonia.

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