MoS2 as well as preparation method and application thereof

Abstract

The invention discloses MoS2 as well as a preparation method and application thereof, and belongs to the technical field of MoS2 preparation. The invention provides a preparation method of MoS2, which comprises the following steps: dissolving 2, 5-diamino-1, 4-benzenedithiol dihydrochloride in a first solvent to obtain a solution 1; dissolving a molybdenum source in a second solvent to obtain a solution 2; in a continuous stirring state, dropwise adding the solution 2 into the solution 1, stirring and mixing, standing, filtering, washing and drying to obtain a precursor; and carrying out carbonization treatment on the precursor in an inert gas atmosphere to obtain the MoS2. The precursor is obtained through a coordination effect between a specific organic ligand and a molybdenum source, MoS2 with few layers of high defects is successfully prepared through a strategy of carrying out controllable surface exposure on MoS2 through confinement growth, and the FL-MoS2 catalyst shows incomparable activity and excellent stability in a reverse water gas shift reaction at a high temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular, to a MoS2 and its preparation method and application. Background Art

[0002] The excessive emission of carbon dioxide (CO2) has caused serious environmental pollution. It is crucial to develop a technology for the economical and sustainable utilization of CO2. The reverse water-gas shift (RWGS) reaction can convert CO2 into CO, and the product CO can be further converted into various high-value-added liquid fuels and chemicals through Fischer-Tropsch synthesis. For the RWGS reaction, noble metals (such as Pt, Ru, Ir, Pd, etc.) usually have excellent performance, but due to their extremely high cost, they are greatly restricted; transition metals (such as Fe, Co, Ni, etc.) will produce a lot of methane by-products, which require further downstream separation and cannot be directly applied. At present, there is an urgent need to develop a catalyst system with high activity, high selectivity and stability to implement the RWGS reaction on a large scale to convert carbon dioxide.

[0003] Two-dimensional materials have received extensive attention due to their characteristics such as large specific surface area and high percentage of surface atoms exposed. Extensive experimental and theoretical studies have shown that MoS2 has prospects in RWGS catalysis due to its electronic properties similar to those of Pt-group noble metals. In addition, the interlayer distance connected by weak van der Waals forces is an effective channel for the diffusion of CO2 and protons. Recent studies have shown that the d orbitals of the edge unsaturated Mo atoms in MoS2 can receive the lone electron pairs of small molecules (such as CO2 and N2), thereby achieving strong adsorption. Two adjacent unsaturated Mo sites located at the edge of MoS2 can easily coordinate with oxygen to form a bidentate chelate configuration, which helps to break the linear symmetry of CO2. However, the catalytic activity of the reported MoS2 catalysts still lags far behind that of platinum-based catalysts, which may be due to the low structural control of the MoS2 catalysts and the insufficient active sites on the basal plane caused by the synthesis methods applied so far.

[0004] Defect engineering has been widely used to optimize the catalytic activity of MoS2. Defects can induce strain fields and regulate the electronic structure of adsorption sites to improve the interaction between adsorbed intermediates and adsorption sites. Wang et al. systematically evaluated various structural defects on the basal plane of MoS2. The Gibbs free energy calculated by first-principles shows that the HER catalytic efficiency of MoS2 can be greatly improved by introducing dislocations into MoS2. Creating sulfur vacancies can activate a high proportion of the inactive basal plane of MoS2 by generating new energy gap states near the Fermi level to achieve hydrogen binding. However, MoS2 usually exists in stacked blocks composed of S-Mo-S layered structures due to self-accumulation and aggregation caused by high surface energy and interlayer van der Waals forces. This spontaneous thermodynamic process leads to a sharp decrease in the specific surface area, hinders the construction of heterointerfaces, and the thickened stacked layers reduce the occupancy of surface atoms. Compared with monolayer MoS2, multilayer MoS2 expands the band gap, resulting in a decrease in conductivity. The reduction in the occupancy of surface atoms in multilayer MoS2 weakens the adsorption and activation of carbon dioxide. Unfortunately, few studies have focused on controlling the surface atom occupancy to solve these problems. Customizing the available MoS2 catalysts with a specific structure remains a considerable challenge. Summary of the Invention

[0005] To solve the above problems, the present invention provides a MoS2, a preparation method thereof, and an application.

[0006] In a first aspect, the present invention provides a preparation method of MoS2, and the preparation method includes the following steps:

[0007] Dissolve 2,5-diamino-1,4-benzenedithiol dihydrochloride in a first solvent to obtain solution 1;

[0008] Dissolve a molybdenum source in a second solvent to obtain solution 2;

[0009] Under continuous stirring, drop solution 2 into solution 1 for stirring and mixing, then let it stand, filter, wash, and dry to obtain a precursor;

[0010] Carry out carbonization treatment on the precursor under an inert gas atmosphere to obtain the MoS2.

[0011] Further, the molar ratio of the molybdenum source to 2,5-diamino-1,4-benzenedithiol dihydrochloride is (1-5):5, preferably 1:5.

[0012] Further, the first solvent includes at least one of water, methanol, ethanol, and DMF, preferably DMF.

[0013] Further, the working condition parameters of the carbonization treatment include: the temperature is 600-900 °C, preferably 800 °C; the time is 1-3 h, preferably 2 h.

[0014] Further, the second solvent is water.

[0015] Further, the molybdenum source is ammonium heptamolybdate tetrahydrate.

[0016] In a second aspect, based on the same inventive concept, the present invention provides a MoS2, which is prepared by the preparation method of MoS2 according to any one of the first aspect.

[0017] Further, the microscopic characteristic parameters of the MoS2 include: the microstructure of the MoS2 is composed of nanoparticles; preferably, the average particle size of the MoS2 is 104.06 nm; preferably, the length of the MoS2 is 2.00-5.26 nm.

[0018] In a third aspect, based on the same inventive concept, the present invention provides an application of the MoS2 according to any one of the second aspect in the reverse water gas shift reaction.

[0019] Further, at a medium gas hourly space velocity of 60000 mL / g cat / h, at 600 °C, when the above-prepared MoS2 is used in the reverse water gas shift reaction, the CO2 conversion rate reaches 59.9%, approaching the thermodynamic equilibrium limit, and the product CO selectivity is 100%.

[0020] The present invention has at least the following advantages compared with the prior art:

[0021] The present invention provides a MoS2, its preparation method and application. A precursor is obtained through the coordination effect between a specific organic ligand and a molybdenum source, and a strategy of controllable surface exposure of MoS2 is carried out through confined growth. A few-layer high-defect MoS2 (denoted as FL-MoS2) is successfully prepared. This FL-MoS2 catalyst exhibits unparalleled activity and excellent stability in the reverse water gas shift reaction at high temperature.

[0022] The present invention develops a strategy for controllable surface exposure of MoS2 through confined growth to optimize the performance of RWGS. A precursor is obtained through the coordination effect between a specific mercapto-containing organic monomer (2,5-diamino-1,4-benzenedithiol dihydrochloride) and ammonium heptamolybdate tetrahydrate, creating a confined space for the growth of MoS2 nanosheets with controllable layer numbers during subsequent annealing. Compared with the original MoS2 nanoblocks, the number of layers of FL-MoS2 can even be reduced to a single layer. Through the confined growth strategy, a large number of dislocation strain structures and sulfur vacancies can be introduced on the inert basal plane of MoS2 nanosheets, thus promoting the activation of H2 and the dissociation of CO2. Therefore, the confined growth of MoS2 with moderate surface atom exposure exhibits excellent RWGS performance, with a CO2 conversion rate reaching 59.9% and a CO selectivity reaching 100% at a reaction temperature of 600 °C. The catalyst shows high durability of more than 156 h in the stability test, without any attenuation of its activity and CO selectivity, and thus has great application potential in the large-scale synthesis of CO from CO2 reduction. Brief Description of the Drawings

[0023] The drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present invention and used together with the specification to explain the principles of the present invention.

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is a schematic diagram of the mechanism of the preparation process of FL-MoS2 in Example 1 provided by the present invention and ML-MoS2 disclosed in the prior art.

[0026] Figure 2 It is a comparative analysis diagram of the morphology and dislocation characterization of FL-MoS2 in Example 1 provided by the present invention and ML-MoS2 disclosed in the prior art; among them, Figure 2In: a) SEM image of FL-MoS2; b) HRTEM image of FL-MoS2 and a model diagram of FL-MoS2. The green stripes in the image represent FL-MoS2 nanosheets. The white parallel lines and white arrows indicate the lattice spacing of FL-MoS2. c) Aberration-corrected HAADF-STEM image of FL-MoS2. d) Dislocation analysis of the surface of FL-MoS2, with dislocations indicated by "T". e) SEM image of ML-MoS2. f) HRTEM image of ML-MoS2. g) Aberration-corrected HAADF-STEM image of ML-MoS2. h) Dislocation analysis of the surface of ML-MoS2. i) Particle size analysis of FL-MoS2 in a). j) Length analysis of FL-MoS2 in b). k) Length analysis of ML-MoS2 in f).

[0027] Figure 3 Figure showing the comparative analysis results of the structural characteristics of FL-MoS2 in Example 1 provided by the present invention and ML-MoS2 disclosed in the prior art; wherein, Figure 3 In: a) XRD pattern; b) N2 adsorption / desorption analysis of FL-MoS2 and ML-MoS2. The figure shows the corresponding pore size distribution, which is calculated from the adsorption branch of the isotherm according to the NLDFT model of cylindrical / spherical pores. c-d) Raman spectra.

[0028] Figure 4 Figure showing the comparative results of the catalytic performance of FL-MoS2 in Example 1 provided by the present invention and ML-MoS2 disclosed in the prior art for the hydrogenation of CO2 to CO; wherein, Figure 4 In: a) CO2 conversion rate and CO selectivity of different catalysts at different temperatures (test conditions: CO2:H2 = 1:3, 300°C - 600°C, GHSV = 60000 mL / g cat / h). b) Activity comparison of FL-MoS2 and other typical catalysts used in the RWGS reaction. c) Long-term stability test of FL-MoS2 at 600°C.

[0029] Figure 5 Figure showing the comparative results of the product structures obtained at different ratios of 2,5-diamino-1,4-benzenedithiol dihydrochloride and ammonium heptamolybdate tetrahydrate in the present invention; wherein, Figure 5 In: a-e correspond to the SEM images of ammonium heptamolybdate tetrahydrate and 2,5-diamino-1,4-benzenedithiol dihydrochloride with molar ratios of 1:5, 2:5, 3:5, 4:5, and 1:1, respectively.

[0030] Figure 6 Figure showing the comparative results of the product structures obtained at different degrees of protonation of 2,5-diamino-1,4-benzenedithiol dihydrochloride in the present invention; wherein,Figure 6 In the figure: a - e respectively correspond to the SEM images of the products obtained with the amounts of 1mol / L HCl being 0mL, 0.5mL, 1.0mL, 1.5mL, and 2.0mL in sequence.

[0031] Figure 7 This is the result comparison diagram of the product structures obtained under different solvent conditions in the present invention; among them, Figure 7 In the figure: a - d are respectively the SEM images of 2,5 - diamino - 1,4 - benzenedithiol dihydrochloride with solvents being water, methanol, ethanol, and DMF in sequence.

[0032] Figure 8 This is the result comparison diagram of the product performances obtained under different solvent conditions in the present invention; among them, Figure 8 In the figure: a) CO2 conversion rate, b) CO selectivity (test conditions: 69% H2, 23% CO2, 8% Ar, 100mg catalyst, space - time rate of 60000mL / g cat / h).

[0033] Figure 9 This is the raw material structure diagram under different organic ligand screening conditions in the present invention.

[0034] Figure 10 This is the XRD diffraction pattern of MoS2 calcined at different temperatures in the present invention.

[0035] Figure 11 This is the SEM image of MoS2 calcined at different temperatures in the present invention.

[0036] Figure 12 This is the CO yield result diagram of MoS2 calcined at different temperatures in the present invention at 500°C. Detailed implementation manners

[0037] 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 with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, rather than all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can all be obtained through market purchase or can be prepared by existing methods.

[0039] The present invention provides FL-MoS2 of Example 1 and ML-MoS2 disclosed in the prior art (prepared according to the reported literature: Advanced Materials, 2013, Defect-Rich MoS2 Ultrathin Nanosheets with Additional Active Edge Sites for Enhanced Electrocatalytic Hydrogen Evolution: Under vigorous stirring, 2.2836 g of (NH4)6Mo7O 24 ·4H2O and 1.2360 g of thiourea were dissolved in 35 mL of deionized water to form a homogeneous solution. Then, the solution was transferred to a 50 mL Teflon-lined stainless steel autoclave, maintained at 200 °C for 24 h, and naturally cooled to room temperature. The final product was washed several times with water and absolute ethanol and dried in vacuo at 60 °C. The obtained product was carbonized at 800 °C for 2 h in an argon atmosphere. The carbonized sample was named ML-MoS2, and the schematic diagram of the manufacturing process mechanism is as shown in Figure 1 :

[0040] Ammonium heptamolybdate tetrahydrate contains many functional groups and can serve as the anchoring sites for the loading of transition metal ions. First, molybdate ions are restricted around the organic monomer containing mercapto groups (2,5-diamino-1,4-benzenedithiol dihydrochloride) through coordination. After annealing in an Ar atmosphere, the benzene ring is transformed into a carbon skeleton, and a confined and customized MoS2 nanosheet is formed inside. The confinement effect plays an important role in regulating the growth size of MoS2 nanosheets. Different from the traditional bulk MoS2 material, the MoS2 grown in the carbon domain is not easily aggregated into a bulk, but shows the characteristics of nanosheets, such as small flakes, high dispersibility, and large specific surface area. These ultrafine nanosheets can expose abundant surface atoms, thus showing stronger CO2 adsorption and dissociation capabilities. ML-MoS2 is obtained by the coordination of ammonium heptamolybdate tetrahydrate and thiourea.

[0041] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0042] The main raw material information involved in the present invention is as follows:

[0043] Ammonium heptamolybdate tetrahydrate (NH4)6Mo7O 24·4H2O and 2,5-diamino-1,4-benzenedithiol dihydrochloride (CAS No. 75464-52-7) were obtained from Energy Chemical and Leyan, respectively. Thiourea, ethanol, and N,N-dimethylformamide (DMF) were purchased from Aladdin. Unless otherwise specified, all reagents were of analytical grade and used as received. All aqueous solutions were prepared with deionized water.

[0044] The main abbreviations involved in this invention are explained as follows:

[0045] RWGS: Reverse Water-Gas Shift Reaction, which is the reverse water-gas shift reaction in Chinese;

[0046] FL-MoS2: Few-Layer MoS2, which refers to few-layer (close to monolayer) MoS2 nanomaterials prepared by a confinement growth strategy, with high surface atom exposure and abundant sulfur vacancies.

[0047] ML-MoS2: Multi-Layer MoS2, which is the multi-layer molybdenum disulfide in Chinese.

[0048] HRTEM: High-Resolution Transmission Electron Microscopy, which is used to observe the atomic lattice structure of materials.

[0049] HAADF-STEM: High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy, which forms images through electron diffraction signals and can analyze the atomic column arrangement and defect structure of materials.

[0050] XRD: X-Ray Diffraction, which analyzes the crystal phase, layer number, and crystallinity of materials through crystal diffraction peaks;

[0051] BET: Brunauer-Emmett-Teller, which calculates the specific surface area and pore size distribution of materials through nitrogen adsorption isotherms;

[0052] FFT / IFFT: Fast Fourier Transform / Inverse Fast Fourier Transform, which converts an image from the spatial domain to the frequency domain and is used to analyze periodic structures or defects;

[0053] GHSV: Gas Hourly Space Velocity, which in Chinese is gas hourly space velocity, representing the gas flow rate passing through the unit catalyst volume per unit time (unit: mL / g cat / h);

[0054] I D / I G : The intensity ratio of the D band (disordered carbon) to the G band (graphite carbon) in Raman spectroscopy, reflecting the defect degree of the carbon material.

[0055] SEM: Scanning Electron Microscopy, which in Chinese is scanning electron microscope, used to observe the surface morphology of materials;

[0056] NLDFT: Non-Local Density Functional Theory, which in Chinese is non-local density functional theory, a model for calculating the pore size distribution of porous materials;

[0057] DMF: N,N-Dimethylformamide, which in Chinese is N,N-dimethylformamide, a polar solvent used to dissolve organic ligands;

[0058] rmp: Revolutions Per Minute, which in Chinese is revolutions per minute, representing the number of rotations of the device per minute. It is a unit for the rotational speed of a hard disk.

[0059] The main material characterization equipment and parameter conditions involved in the present invention are as follows:

[0060] Scanning electron microscope (SEM) images were obtained using a Hitachi Regulus 8220 (Japan) at 5 kV with a collection angle of 48 mrad. The SEM (scanning electron microscope) samples were prepared by directly attaching the catalyst powder onto the conductive carbon adhesive on an aluminum sample holder. Transmission electron microscope (TEM) and high-resolution TEM (HRTEM) images were taken on a Talos F200X S / TEM microscope (FEI Company, Ltd., USA). The HRTEM images were analyzed using free GMS software. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) was performed on a double-corrected ThermoFisher Scientific Spectra 300 microscope with a cold field emission gun, operating at 300 kV. TEM, HRTEM, and AC-HAADF-STEM samples were prepared by ultrasonically dispersing the catalyst powder in ethanol and then drop-casting onto ultra-thin copper grids. X-ray diffraction (XRD, DX-2700BH, Haoyuan Instruments, China) was used to analyze the crystal structure at 40 kV voltage with copper radiation on a multi-purpose X-ray diffractometer. The N2 adsorption / desorption isotherms were obtained using an Ankersmid-Belsorp Max, and the surface area and pore size distribution were evaluated based on Brunauer-Emmett-Teller (BET), respectively.

[0061] Example 1

[0062] This example provides a MoS2, and its preparation method includes the following steps:

[0063] Ammonium heptamolybdate tetrahydrate was used as the Mo-POM precursor, and 2,5-diamino-1,4-benzenedithiol dihydrochloride was selected as the organic ligand, and their molar ratio was 1:5. First, 0.1226 g of 2,5-diamino-1,4-benzenedithiol dihydrochloride was dissolved in 30 mL of DMF to obtain Solution 1. Then, 0.1236 g of (NH4)6Mo7O 24 ·4H2O was dissolved in 50 mL of H2O to obtain Solution 2. Under vigorous stirring (500 rpm), Solution 2 was slowly dropped into Solution 1, and stirring was continued for 2 h, followed by standing for 24 h. The product was collected by filtration, washed three times with H2O and ethanol, and vacuum-dried at 60 °C. The obtained product was carbonized at 800 °C for 2 h in an argon atmosphere, and the resulting carbonized sample was the final experimental sample, named FL-MoS2.

[0064] Comparative Example 1

[0065] This example provides an ML-MoS2, and its preparation method includes the following steps:

[0066] Under vigorous stirring, 2.2836 g of (NH4)6Mo7O 24 ·4H2O and 1.2360 g of thiourea were dissolved in 35 mL of deionized water to form a homogeneous solution. Then, the solution was transferred to a 50 mL Teflon-lined stainless steel autoclave and maintained at 200 °C for 24 h, and then naturally cooled to room temperature. The final product was washed several times with water and absolute ethanol and dried in vacuo at 60 °C. The obtained product was carbonized at 800 °C for 2 h in an argon atmosphere, and the obtained carbonized sample was named ML-MoS2.

[0067] Test Example 1

[0068] In this example, the morphology characterization and structural analysis of the FL-MoS2 obtained in the above Example 1 and the ML-MoS2 obtained in Comparative Example 1 were carried out.

[0069] The morphological features of FL-MoS2 and ML-MoS2 are as Figure 2 shown. FL-MoS2 shows a microstructure composed of aggregated but less well-defined nanoparticles ( Figure 2 a). In Figure 2 b, the lattice fringes of 0.627 and 0.269 nm correspond to the (002) and (101) crystal planes of FL-MoS2. After introducing the carbon skeleton, the growth of MoS2 shows an obvious confinement effect, with the thickness and length greatly reduced, and a large number of single-layer MoS2 nanosheets appear. Figure 2 c-d show that the surface of FL-MoS2 has a rich dislocation structure. The average particle size of FL-MoS2 is 104.06 nm ( Figure 2 i), and the length is 2.00 - 5.26 nm ( Figure 2 j). In contrast, ML-MoS2 shows a flower-like structure composed of nanosheets ( Figure 2 e). At the same time, the lattice fringes of 0.615, 0.269, 0.217, and 0.185 nm correspond to the (002), (101), (103), and (105) crystal planes of ML-MoS2 in Figure 2 f, and up to nine layers of MoS2 nanosheets can be observed. Figure 2 It can be seen from g-h that there is no dislocation structure on the basal plane of ML-MoS2. The average length of ML-MoS2 exceeds 36.10 nm ( Figure 2 k).

[0070] The structural characterization and analysis of FL-MoS2 and ML-MoS2 are as Figure 3 shown. Figure 3a shows the powder X-ray diffraction (XRD) patterns of FL-MoS2 and ML-MoS2. For FL-MoS2, the XRD pattern shows peaks at 2Theta of 33.5°, 39.5°, and 58.3°, which are consistent with the (101), (103), and (110) planes of MoS2 (PDF#37-1492). However, for ML-MoS2, in addition to the above three characteristic peaks, the XRD pattern shows peaks at 14.4°, 49.8°, 60.1°, and 69.0° at 2Theta, which are consistent with the (002), (105), (008), and (201) planes of MoS2. It is generally believed that the (002) plane of MoS2 is closely related to the stacking layers of MoS2. The XRD pattern of ML-MoS2 shows an obvious (002) characteristic peak, corresponding to its multi-layer structure. Due to the limitation of the carbon skeleton, the intensity of the corresponding peak of FL-MoS2 weakens or even disappears, which is attributed to the reduction of the layer thickness and length of MoS2. At Figure 3 b, the BET surface areas of FL-MoS2 and ML-MoS2 are 29.55 and 19.66 m 2 ·g cat -1 −1, respectively. The pore size distribution is calculated according to the adsorption branch of the isotherm by the NLDFT model of cylindrical / spherical pores. Raman spectroscopy also shows the same pattern in Figure 3 c-d. The two Raman peaks near 381 and 405 cm -1 −1 correspond to (in-plane displacement and shear force between Mo and S atoms) and A 1g mode (symmetric displacement and compression force between S atoms), confirming the MoS2 crystal structure in FL-MoS2 and ML-MoS2. In addition, FL-MoS2 and ML-MoS2 show two peaks near 1380 and 1610 cm -1 −1, which are consistent with the D and G bands of sp 2 2-bonded graphitic carbon, respectively. The D band represents the degree of disorder or defect of carbon, and the G band represents the degree of graphitization. Therefore, the value of I D D[ / I G G[ / I D D[ / I G G[ / I

[0071] Test Example 2

[0072] This example conducts a comparative analysis of the catalytic performance of FL-MoS2 obtained in the above Example 1 and ML-MoS2 obtained in Comparative Example 1 in RWGS.

[0073] For the RWGS reaction under harsh reaction conditions, supported catalysts containing active metals are prone to deactivation due to sintering of the active metals, although they may exhibit high initial activity. Due to its unique electronic structure and the absence of supported active metals, the FL-MoS2 catalyst is expected to achieve high activity and solid stability in the high-temperature RWGS reaction, as Figure 4 shown. As Figure 4 shown in a, at a moderate gas hourly space velocity (GHSV) of 60,000 mL / g cat / h, the FL-MoS2 catalyst exhibits very high activity and complete CO selectivity. At 600 °C, the CO2 conversion rate approaches the thermodynamic equilibrium limit. In addition, the CO selectivity of this catalyst is 100%, and no CH4 is detected during the entire activity evaluation process. Therefore, this catalyst effectively catalyzes the RWGS reaction rather than the methanation reaction. In Figure 4 b, the CO yield of FL-MoS2 is as high as 1.60 mol CO / g cat / h at 600 °C, which is undoubtedly a higher value compared to other reported traditional catalysts for the RWGS reaction. In addition, after running at 600 °C for 156 h, there is no downward trend in the CO2 conversion rate and CO selectivity rate ( Figure 4 c).

[0074] Test Example 3

[0075] This example elaborates in detail on the optimization process of the FL-MoS2 preparation method provided by the present invention, specifically as follows:

[0076] 1) Comparison of product structures obtained from different ratios of 2,5-diamino-1,4-benzenedithiol dihydrochloride and ammonium heptamolybdate tetrahydrate

[0077] Ammonium heptamolybdate tetrahydrate was selected as the Mo source, and 2,5-diamino-1,4-benzenedithiol dihydrochloride was used as the organic ligand, and their molar ratios were 1:5, 2:5, 3:5, 4:5, and 1:1, respectively. 2,5-Diamino-1,4-benzenedithiol dihydrochloride was dissolved in 30 mL of deionized water to obtain Solution 1. Then, (NH4)6Mo7O 24 ·4H2O was dissolved in 50 mL of H2O to obtain Solution 2. Under vigorous stirring (500 rpm), Solution 2 was slowly dropped into Solution 1, and stirring was continued for 2 h, and then left to stand for 24 h. The product was collected by filtration, washed three times with H2O and ethanol, and dried in vacuo at 60 °C. The obtained product was carbonized at 700 °C for 2 h in an argon atmosphere to obtain the product.

[0078] SEM images of ammonium heptamolybdate tetrahydrate and 2,5-diamino-1,4-benzenedithiol dihydrochloride with molar ratios of 1:5, 2:5, 3:5, 4:5, and 1:1 are as follows Figure 5 As shown, it can be seen from the SEM that when the molar ratio of ammonium heptamolybdate tetrahydrate to 2,5-diamino-1,4-benzenedithiol dihydrochloride is 1:5, the morphology of the obtained product is relatively uniform small particles; while the morphologies of the products obtained at other ratios are relatively disordered. Therefore, a ratio of 1:5 was selected for further experiments.

[0079] 2) Comparison of product structures obtained under different protonation degrees of 2,5-diamino-1,4-benzenedithiol dihydrochloride

[0080] Ammonium heptamolybdate tetrahydrate was selected as the Mo source, and 2,5-diamino-1,4-benzenedithiol dihydrochloride was used as the organic ligand, with a molar ratio of 1:5 between the two. 0.1226 g of 2,5-diamino-1,4-benzenedithiol dihydrochloride was dissolved in 30 mL of deionized water to obtain Solution 1. Then, 0.1236 g of (NH4)6Mo7O 24 ·4H2O was dissolved in 50 mL of H2O to obtain Solution 2. Under vigorous stirring (500 rpm), Solution 2 was slowly added dropwise to Solution 1. 1 mol / L HCl was added to control the protonation degree of the organic ligand (the amounts of 1 mol / L HCl used were 0 mL, 0.5 mL, 1.0 mL, 1.5 mL, and 2.0 mL), and stirring was continued for 2 h, then left standing for 24 h. The product was collected by filtration, washed three times with H2O and ethanol, and dried in vacuo at 60 °C. The obtained product was carbonized at 700 °C for 2 h in an argon atmosphere to obtain the product.

[0081] As Figure 6 shown, with the increase in the amount of hydrochloric acid used, the higher the protonation degree of 2,5-diamino-1,4-benzenedithiol dihydrochloride, the more uneven the obtained morphology, and the more serious the block stacking. The stacked and uneven morphology is not conducive to exposing active sites. Therefore, no HCl is added to adjust in this system.

[0082] 3) Comparison of product structures and properties obtained under different solvent conditions

[0083] Ammonium heptamolybdate tetrahydrate was selected as the Mo source, and 2,5-diamino-1,4-benzenedithiol dihydrochloride was used as the organic ligand, with a molar ratio of 1:5 between the two. 0.1226 g of 2,5-diamino-1,4-benzenedithiol dihydrochloride was dissolved in 30 mL of different solvents (water, methanol, ethanol, DMF) to obtain Solution 1. Then, 0.1236 g of (NH4)6Mo7O 24· 4H2O was dissolved in 50 mL of H2O to obtain Solution 2. Under vigorous stirring (500 rpm), Solution 2 was slowly added dropwise to Solution 1, and stirring was continued for 2 h, followed by standing for 24 h. The product was collected by filtration, washed three times with H2O and ethanol, and dried in vacuo at 60 °C. The obtained product was carbonized at 700 °C for 2 h in an argon atmosphere to obtain the product.

[0084] As Figure 7 shown, when 2,5-diamino-1,4-benzenedithiol dihydrochloride was dissolved in methanol, ethanol, and DMF, the obtained product morphologies were more uniform, being aggregates of small particles. As Figure 8 shown, when 2,5-diamino-1,4-benzenedithiol dihydrochloride was dissolved in 30 mL of DMF, the sample had the best performance, with a CO2 conversion rate of 27.4% and a CO selectivity of 100% at 500 °C.

[0085] 4) Analysis of the products obtained under different organic ligand conditions

[0086] Ammonium heptamolybdate tetrahydrate was selected as the Mo source, and three different small molecules, 2,5-diamino-1,4-benzenedithiol dihydrochloride, 2,5-dimercapto terephthalic acid, and trithiocyanuric acid, were used as organic ligands. The molar ratio of the Mo source to the organic ligand was 1:5. The organic ligand was dissolved in 30 mL of DMF to obtain Solution 1. Then, 0.1236 g of ammonium heptamolybdate tetrahydrate was dissolved in 50 mL of H2O to obtain Solution 2. Under vigorous stirring (500 rpm), Solution 2 was slowly added dropwise to Solution 1, and stirring was continued for 2 h, followed by standing for 24 h. The product was collected by filtration, washed three times with H2O and ethanol, and dried in vacuo at 60 °C. The obtained product was carbonized at 700 °C for 2 h in an argon atmosphere to obtain the product.

[0087] After replacing the organic ligand with 2,5-dimercapto terephthalic acid and trithiocyanuric acid, no precipitate was collected after standing for 24 h. Only when the organic ligand was 2,5-diamino-1,4-benzenedithiol dihydrochloride was a precipitate formed. Therefore, the coordination reaction has strict selectivity for the structure of organic monomers, and only with a suitable monomer structure can the product MoS2 be obtained. It is not the case that MoS2 can be obtained as long as the organic ligand contains "-SH-".

[0088] 5) Analysis of the products obtained under different carbonization temperature conditions

[0089] Ammonium heptamolybdate tetrahydrate was used as the Mo-POM precursor, and 2,5-diamino-1,4-benzenedithiol dihydrochloride was selected as the organic ligand, and the molar ratio of the two was 1:5. First, 0.1226 g of 2,5-diamino-1,4-benzenedithiol dihydrochloride was dissolved in 30 mL of DMF to obtain Solution 1. Then, 0.1236 g of (NH4)6Mo7O 24 ·4H2O was dissolved in 50 mL of H2O to obtain Solution 2. Under vigorous stirring (500 rpm), Solution 2 was slowly added dropwise to Solution 1, and stirring was continued for 2 h, and then left standing for 24 h. The product was collected by filtration, washed three times with H2O and ethanol, and dried in vacuo at 60 °C. The obtained product was carbonized at 600 °C, 700 °C, 800 °C, and 900 °C for 2 h in an argon atmosphere to obtain the product.

[0090] As Figure 10 , Figure 11 and Figure 12 (Test conditions: 69% H2, 23% CO2, 8% Ar, 100 mg of catalyst, space-time rate of 60000 mL / g cat / h) showed that the SEM images indicated that the morphologies of MoS2 calcined at different temperatures were basically the same, all being uniform small particles. The XRD results proved that the products obtained by calcination at different temperatures were all MoS2, but there were significant differences in crystallinity. With the increase of the calcination temperature, the crystallinity of MoS2 was also higher. When the calcination temperature was 800 °C, the obtained MoS2 had the best RWGS performance.

[0091] In summary, the present invention provides a MoS2 and its preparation method and application. By utilizing the coordination effect between 2,5-diamino-1,4-benzenedithiol dihydrochloride and ammonium heptamolybdate tetrahydrate, the present invention obtained few-layer or even single-layer MoS2. Different from bulk MoS2, the confined-growth MoS2 has high dispersibility and a large specific surface area. The ultrafine MoS2 nanosheets have rich heterojunction interfaces and unique surface electronic structures. The controllable exposure of surface atoms of MoS2 allows the adjustment of the dislocation strain structure, promotes the adsorption and dissociation of CO2, and improves the RWGS reaction performance of the catalyst. These results confirm the effectiveness of confined growth in regulating the exposure of surface atoms of materials to improve CO2 adsorption and dissociation. This new strategy provides a new way to develop engineering two-dimensional materials with unique morphologies and specific electronic structures.

[0092] The various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present invention; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any recited number (fraction or integer) within the indicated range.

[0093] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A preparation method of MoS2, characterized in that, The preparation method includes the following steps: Dissolve 2,5-diamino-1,4-benzenedithiol dihydrochloride in a first solvent to obtain Solution 1; Dissolve a molybdenum source in a second solvent to obtain Solution 2; Under continuous stirring, add Solution 2 dropwise to Solution 1 for stirring and mixing, then let it stand, filter, wash and dry to obtain a precursor; Carry out carbonization treatment on the precursor under an inert gas atmosphere to obtain the MoS2.

2. The preparation method of MoS2 according to claim 1, wherein, The molar ratio of the molybdenum source to 2,5-diamino-1,4-benzenedithiol dihydrochloride is (1-5):

5.

3. The preparation method of MoS2 according to any one of claims 1 to 2, characterized in that, The first solvent includes at least one of water, methanol, ethanol and DMF.

4. The preparation method of MoS2 according to any one of claims 1 to 3, characterized in that, The working condition parameters of the carbonization treatment include: the temperature is 600-900 °C; the time is 1-3 h.

5. The preparation method of MoS2 according to any one of claims 1 to 4, characterized in that, The second solvent is water.

6. The preparation method of MoS2 according to any one of claims 1 to 5, characterized in that, The molybdenum source is ammonium heptamolybdate tetrahydrate.

7. A MoS2, characterized in that, The MoS2 is prepared by the preparation method described in any one of claims 1-6.

8. The MoS2 according to claim 7, characterized in that, The microscopic characteristic parameters of the MoS2 include: the microstructure of the MoS2 is composed of nanoparticles; Preferably, the average particle size of the MoS2 is 104.06 nm; Preferably, the length of the MoS2 is 2.00-5.26 nm.

9. Use of the MoS2 according to claim 7 or 8 in the reverse water gas shift reaction.

10. The application according to claim 9, wherein At a medium gas hourly space velocity of 60000 mL / g cat When using MoS₂ as described in claim 7 or 8 in the reverse water-gas shift reaction at 600 °C and a medium gas hourly space velocity of 60000 mL / g, the CO₂ conversion rate reaches 59.9%, approaching the thermodynamic equilibrium limit, and the product CO selectivity is 100%.

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