Preparation and application of sulfur-vacancy-rich metal sulfide

Abstract

The invention discloses a preparation method of sulfur-vacancy-rich metal sulfide, and belongs to the technical field of catalyst preparation. According to the preparation method, a synergistic strategy of boron hydrothermal synthesis and sodium hydride ultrasonic reduction is adopted, and high-density sulfur vacancies are constructed on a base plane and edges of a three-dimensional metal sulfide through chemical reduction regulation and control, so that the bottleneck that a traditional sulfur vacancy modification technology is limited to a specific substrate is broken through. The method has the characteristics of simple process and large-scale production, a universal solution is provided for base plane activation of the transition metal chalcogenide catalyst, and the obtained sulfur-vacancy-rich metal sulfide shows good conversion rate and aniline selectivity in preparation of aniline by selective catalytic reduction of nitrobenzene, and has good application prospects. The cyclic stability of the catalyst is superior to that of a conventional supported catalyst, and the catalyst has important application value in the fields of green chemical synthesis and new energy devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method of sulfur-rich vacancy metal sulfide and its application in the catalytic reduction of nitrobenzene to aniline with H2S. Background Art

[0002] As an important chemical intermediate in the chemical industry, aniline can be further used to prepare more than 300 chemicals, covering multiple fields closely related to people's lives (such as organic pigments, pharmaceuticals, pesticides, etc.). In recent years, with the increasing demand for aniline, the synthesis of aniline has shown more important research value. Currently, the industrial production process of preparing aniline from nitrobenzene mainly adopts the catalytic hydrogenation method of nitrobenzene. However, this method must be carried out under high temperature and high pressure conditions, and the reaction conditions are relatively harsh.

[0003] H2S is a highly toxic and malodorous acidic gas, which is widely present in industrial gases and chemical waste gases. It is one of the common harmful gases. It will not only cause corrosion to pipeline equipment, etc., but also seriously pollute the environment. Therefore, how to effectively treat H2S gas is an urgent problem to be solved in the development process of the petroleum industry and the natural gas industry. Currently, the most commonly used technology for treating H2S is the Claus process, which can recover sulfur from sulfur-containing gases (2H2S + SO2 → 3S + 2H2O). However, due to the limitation of the Claus reaction by the thermodynamic equilibrium, about 3 - 5% of H2S still exists in the discharged tail gas. In addition, the Claus technology process has the problems of long process flow and high operating cost, which greatly limits its application in H2S removal. At the same time, using the Claus reaction to remove H2S can only obtain sulfur, and the H element combines with O to form H2O, wasting the hydrogen resources therein.

[0004] In order to achieve the comprehensive utilization of resources and improve the economy of the process, and further enhance the economic and environmental benefits, new ways to involve H2S as a reducing agent in chemical reactions have been explored. If H2S can be used as a reducing agent to react with nitrobenzene, not only sulfur can be generated, but also the reduction product aniline can be obtained, which can further improve the atom economy of the reaction and has the advantage of low energy consumption. However, at present, there is little research on effective catalysts for catalyzing this reaction process.

[0005] Currently, the catalysts used for the nitrobenzene hydrogenation reaction are mainly noble metal catalyst systems (Pt, Pd, Au, Ru) and non-metal catalyst systems mainly based on Ni-based catalysts. These supported noble metal catalysts can efficiently catalyze the hydrogenation of nitrobenzene to prepare aniline, and have the characteristics of long service life and high catalytic activity. However, noble metals are expensive, with high costs, and when H2S exists in the system, these metals are prone to form MS with poor activity. x; The Ni-based catalyst system is inexpensive and highly selective, but its catalytic activity is not ideal, and it is prone to sulfur poisoning. Therefore, new catalytic materials must be explored to efficiently promote the reduction of nitrobenzene by H2S to aniline while achieving the high-value conversion of H2S. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method and application of sulfur-vacancy-rich metal sulfides in view of the deficiencies of the prior art, which can solve the problems of low selectivity in the reaction between H2S and nitrobenzene and easy poisoning and inactivation of the catalyst in the prior art.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions: A sulfur-vacancy-rich metal sulfide, the preparation of which includes the following steps: (1) Dissolve a molybdenum source or an iron source and a sulfur source in distilled water and continuously stir for half an hour to obtain a metal mixture solution; (2) Pour the metal mixture solution obtained in step (1) into a hydrothermal autoclave for reaction; (3) After the temperature of the hydrothermal autoclave drops to room temperature, filter, wash, and dry the obtained precipitate to obtain a precursor; (4) Dissolve the precursor obtained in step (3) and a reducing agent in distilled water successively, and then perform ultrasonic treatment on the obtained mixed solution at room temperature; (5) Filter, wash, and dry the precipitate obtained in step (4) to obtain the sulfur-vacancy-rich metal sulfide.

[0008] Further, in step (1), the molybdenum source is ammonium molybdate tetrahydrate ((NH4)6(Mo7O 24 )·4H2O) or Na2MoO4·2H2O.

[0009] Further, in step (1), the iron source is Fe(NO3)3·9H2O.

[0010] Further, in step (1), the sulfur source is thiourea (CH4N2S) or thioacetamide (CH3CSNH2).

[0011] Further, the molar ratio of the molybdenum source or iron source to the sulfur source used in step (1) is 1:30.

[0012] Further, the temperature of the reaction in step (2) is 200 °C and the time is 12 to 24 hours.

[0013] Further, in step (4), the reducing agent is sodium borohydride, and its dosage is calculated according to 0.1 mol per gram of the precursor.

[0014] Further, the power of the ultrasonic treatment in step (4) is 40 Hz and the time is 0 to 6 h.

[0015] Further, in the operation, the washing is carried out by washing three times each with distilled water and absolute ethanol in turn.

[0016] Further, the temperature of the drying in the operation is 60 °C.

[0017] The sulfur vacancy-rich metal sulfide can be used as a catalyst to catalyze the reaction of reducing nitrobenzene to aniline under the condition of using H2S as a reducing agent.

[0018] Further, the temperature of the reaction is 90 °C, the pressure is 1.5 MPa, and the time is 3 hours.

[0019] The present invention successfully prepares a metal sulfide catalyst with a rich sulfur vacancy structure, which makes full use of the nanosheet morphology characteristics to expose more active sites to promote the full contact of H2S and nitrobenzene with the catalyst active sites; the rich sulfur vacancies can further improve the catalytic activity through the adsorption and activation effects on H2S and nitrobenzene. Therefore, it can significantly improve the catalytic performance of the selective hydrogenation of nitrobenzene mediated by H2S to aniline.

[0020] The layered MoS2 prepared in the present invention is formed by the stacking of S-Mo-S units through van der Waals forces, and has excellent electronic structure, chemical stability and environmental friendliness; the edges of its nanoclusters and the basal plane defects (such as S vacancies, unsaturated Mo sites) can specifically adsorb H2S molecules, so it shows superior performance to traditional catalysts in the hydrodesulfurization reaction. The prepared pyrite-type FeS2 nanosheets construct a three-dimensional conductive framework with a strong covalent bond Fe-S octahedral network. The sulfur vacancy defects in its lattice can not only enhance the H2S adsorption capacity, but also promote the electron transfer process through the Fe 2+ / Fe 3+ redox pair. By means of chemical reduction, high-temperature treatment, etc., sulfur vacancies can be controllably constructed to effectively regulate the electronic structure of the material (such as reducing the density of states near the Fermi level), and then optimize the H2S dissociation path and catalytic reaction kinetics, providing an important theoretical basis for the design of efficient desulfurization catalysts.

[0021] Compared with traditional catalysts, the materials prepared in the present invention have the following breakthrough advantages: First, through precisely regulated sulfur vacancy engineering, the present invention effectively exposes active sites and optimizes the reactant diffusion channels. Second, the abundant sulfur vacancies, as highly efficient active centers, can synchronously promote the activation and dissociation of H2S and the adsorption orientation of nitrobenzene. Sulfur vacancies can not only promote the cleavage of the S-H bond in H2S through the electron induction effect but also precisely anchor the aromatic ring of nitrobenzene through π-π interaction, reducing the energy barrier for the formation of intermediates. This strategy of combining defect engineering with structural regulation not only solves the technical bottlenecks of the traditional catalyst, such as the embedding of active sites and the easy loss of sulfur species, but also realizes the high-value utilization of waste H2S resources, providing an innovative solution with both atomic economy and industrial feasibility for the green synthesis of aniline. Description of the Drawings

[0022] Figure 1 X-ray powder diffraction patterns of MoS2 prepared in Examples 1-3 and Comparative Example 1 (a) and FeS2 prepared in Examples 4-6 and Comparative Example 7 (b).

[0023] Figure 2 Scanning electron micrographs of MoS2 prepared in Examples 1-3 and Comparative Example 1.

[0024] Figure 3 Raman spectra of MoS2 prepared in Examples 1-3 and Comparative Example 1.

[0025] Figure 4 EPR spectra of MoS2 prepared in Examples 1-3 and Comparative Example 1. Detailed Description of the Invention

[0026] A sulfur-rich vacancy metal sulfide, the preparation of which comprises the following steps: (1) Dissolve a molybdenum source or an iron source and a sulfur source in distilled water at a molar ratio of 1:30, and continuously stir for half an hour to obtain a metal mixture solution; (2) Pour the metal mixture solution obtained in step (1) into a hydrothermal reactor, and react at 200 °C for 12-24 hours; (3) After the temperature of the hydrothermal reactor drops to room temperature, filter, wash, and dry the obtained precipitate at 60 °C to obtain a precursor; (4) Dissolve 80-120 mg of the precursor obtained in step (3) and 80-120 mmol of the reducing agent sodium borohydride in distilled water successively, and then ultrasonically treat the obtained mixed solution at room temperature for 0-6 h (power is 40 Hz); (5) Filter, wash, and dry the precipitate obtained in step (4) at 60 °C to obtain the sulfur-rich vacancy metal sulfide.

[0027] Wherein, the molybdenum source is ammonium molybdate tetrahydrate ((NH4)6(Mo7O 24)·4H2O) or Na2MoO4·2H2O. The iron source is Fe(NO3)3·9H2O. The sulfur source is thiourea (CH4N2S) or thioacetamide (CH3CSNH2).

[0028] In the operation, the washing is carried out by washing three times each with distilled water and absolute ethanol in turn.

[0029] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0030] Example 1 Preparation of MoS2 Nanosheets Rich in Sulfur Vacancies Under vigorous stirring, 2 mmol of (NH4)6Mo7O 24 ·4H2O and 60 mmol of thiourea were dissolved in 60 mL of distilled water. After stirring for 30 minutes, a homogeneous mixed solution was formed. The mixed solution was transferred to a stainless steel autoclave equipped with a 200 mL polytetrafluoroethylene liner and maintained at 200 °C for 24 hours. Then the reaction system was naturally cooled to room temperature. The obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain MoS2 nanosheets. 10 mmol of NaBH4 was dissolved in 30 mL of distilled water, and then 100 mg of the above MoS2 nanosheets was added. After ultrasonic treatment at room temperature for 2 h, the obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain MoS2 nanosheets rich in sulfur vacancies, named MoS2-2h.

[0031] Example 2 Preparation of MoS2 Nanosheets Rich in Sulfur Vacancies Under vigorous stirring, 2 mmol of (NH4)6Mo7O 24 ·4H2O and 60 mmol of thiourea were dissolved in 60 mL of distilled water. After stirring for 30 minutes, a homogeneous mixed solution was formed. The mixed solution was transferred to a stainless steel autoclave equipped with a 200 mL polytetrafluoroethylene liner and maintained at 200 °C for 24 hours. Then the reaction system was naturally cooled to room temperature. The obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain MoS2 nanosheets. 10 mmol of NaBH4 was dissolved in 30 mL of distilled water, and then 100 mg of the above MoS2 nanosheets was added. After ultrasonic treatment at room temperature for 4 h, the obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain MoS2 nanosheets rich in sulfur vacancies, named MoS2-4h.

[0032] Example 3 Preparation of MoS2 Nanosheets Rich in Sulfur Vacancies Under vigorous stirring, 2 mmol of (NH4)6Mo7O 24 ·4H2O and 60 mmol of thiourea were dissolved in 60 mL of distilled water. After stirring for 30 minutes, a homogeneous mixed solution was formed. The mixed solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner and maintained at 200 °C for 24 hours. Then the reaction system was allowed to cool naturally to room temperature. The obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain MoS2 nanosheets. 10 mmol of NaBH4 was dissolved in 30 mL of distilled water, and then 100 mg of the above MoS2 nanosheets was added. After ultrasonic treatment at room temperature for 6 h, the obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain MoS2 nanosheets rich in sulfur vacancies, which were named MoS2-6h.

[0033] Example 4 Preparation of FeS2 Nanosheets Rich in Sulfur Vacancies Under vigorous stirring, 2 mmol of Fe(NO3)3·9H2O and 60 mmol of CH3CSNH2 were dissolved in 60 mL of distilled water. After stirring for 30 minutes, a homogeneous mixed solution was formed. The mixed solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner and maintained at 200 °C for 24 hours. Then the reaction system was allowed to cool naturally to room temperature. The obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain FeS2 nanosheets. 10 mmol of NaBH4 was dissolved in 30 mL of distilled water, and then 100 mg of the above FeS2 nanosheets was added. After ultrasonic treatment at room temperature for 2 h, the obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain FeS2 nanosheets rich in sulfur vacancies, which were named FeS2-2h.

[0034] Example 5 Preparation of FeS2 Nanosheets Rich in Sulfur Vacancies Under vigorous stirring, 2 mmol of Fe(NO3)3·9H2O and 60 mmol of CH3CSNH2 were dissolved in 60 mL of distilled water. After stirring for 30 minutes, a homogeneous mixed solution was formed. The mixed solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner and maintained at 200 °C for 24 hours. Then, the reaction system was naturally cooled to room temperature. The obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain FeS2 nanosheets. 10 mmol of NaBH4 was dissolved in 30 mL of distilled water, and then 100 mg of the above FeS2 nanosheets was added. After ultrasonic treatment at room temperature for 4 h, the obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain FeS2 nanosheets rich in sulfur vacancies, which were named FeS2-4h.

[0035] Example 6 Preparation of FeS2 Nanosheets Rich in Sulfur Vacancies Under vigorous stirring, 2 mmol of Fe(NO3)3·9H2O and 60 mmol of CH3CSNH2 were dissolved in 60 mL of distilled water. After stirring for 30 minutes, a homogeneous mixed solution was formed. The mixed solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner and maintained at 200 °C for 24 hours. Then, the reaction system was naturally cooled to room temperature. The obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain FeS2 nanosheets. 10 mmol of NaBH4 was dissolved in 30 mL of distilled water, and then 100 mg of the above FeS2 nanosheets was added. After ultrasonic treatment at room temperature for 6 h, the obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain FeS2 nanosheets rich in sulfur vacancies, which were named FeS2-6h.

[0036] Comparative Example 1 Preparation of MoS2 Nanosheets Under vigorous stirring, 2 mmol of (NH4)6Mo7O 24 ·4H2O and 60 mmol of thiourea were dissolved in 60 mL of distilled water. After stirring for 30 minutes, a homogeneous mixed solution was formed. The mixed solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner and maintained at 200 °C for 24 hours. Then, the reaction system was naturally cooled to room temperature. The obtained product was collected by centrifugation, washed three times each with distilled water and absolute ethanol in turn, and dried in vacuo at 60 °C to obtain MoS2 nanosheets, named MoS2-0h.

[0037] Comparative Example 2 Preparation of MoS2 Nanosheets Under vigorous stirring, 2 mmol of Na2MoO4·2H2O and 60 mmol of thiourea were dissolved in 60 mL of distilled water. After stirring for 30 minutes, a homogeneous mixed solution was formed. This mixed solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner and maintained at 200 °C for 24 hours. Then, the reaction system was naturally cooled to room temperature. The resulting product was collected by centrifugation, washed three times each with distilled water and anhydrous ethanol in turn, and dried in vacuo at 60 °C to obtain MoS2 nanosheets, named MoS2.

[0038] Preparation of MoS2 catalyst for Comparative Example 3 Weigh 0.88 g (0.714 mmol) of (NH4)6Mo7O 24 ·4H2O and 2.28 g (30 mmol) of thiourea were dissolved in 80 mL of distilled water, and then vigorously stirred for 30 minutes to obtain a clear and homogeneous mixed solution. 12 mol / L hydrochloric acid solution was added dropwise to this mixed solution to adjust the pH value of the mixed solution to 1. Then, the above solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner. After hydrothermal treatment at 200 °C for 24 h, it was naturally cooled to room temperature, filtered, and the precipitate was washed three times each with anhydrous ethanol and distilled water alternately, and dried in vacuo at 60 °C to obtain a MoS2 catalyst, named MoS2-0P.

[0039] Preparation of MoS2 composite catalyst for Comparative Example 4 Weigh 0.88 g (0.714 mmol) of (NH4)6Mo7O 24 ·4H2O, 2.28 g (30 mmol) of thiourea and 0.1 g of PEG 1000 were dissolved in 80 mL of distilled water, and then vigorously stirred for 30 minutes to obtain a clear and homogeneous mixed solution. 12 mol / L hydrochloric acid solution was added dropwise to this mixed solution to adjust the pH value of the mixed solution to 1. Then, the above solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner. After hydrothermal treatment at 200 °C for 24 h, it was naturally cooled to room temperature, filtered, and the precipitate was washed three times each with anhydrous ethanol and distilled water alternately, and dried in vacuo at 60 °C to obtain a MoS2 composite catalyst, named MoS2-0.1P.

[0040] Preparation of MoS2 composite catalyst for Comparative Example 5 Weigh 0.88 g (0.714 mmol) of (NH4)6Mo7O 242.28 g (30 mmol) of thiourea and 0.2 g of PEG 1000 were dissolved in 80 mL of distilled water, and then vigorously stirred for 30 minutes to obtain a clear and homogeneous mixed solution. 12 mol / L hydrochloric acid solution was added dropwise to the mixed solution to adjust the pH value of the mixed solution to 1. Then the above solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner, hydrothermally treated at 200 °C for 24 h, and then naturally cooled to room temperature. The precipitate was filtered, washed alternately with absolute ethanol and distilled water three times each, and vacuum dried at 60 °C to obtain the MoS2 composite catalyst, which was named MoS2-0.2P.

[0041] Preparation of MoS2 Composite Catalyst in Comparative Example 6 Weighed 0.88 g (0.714 mmol) of (NH4)6Mo7O 24 2.28 g (30 mmol) of thiourea and 0.4 g of PEG 1000 were dissolved in 80 mL of distilled water, and then vigorously stirred for 30 minutes to obtain a clear and homogeneous mixed solution. 12 mol / L hydrochloric acid solution was added dropwise to the mixed solution to adjust the pH value of the mixed solution to 1. Then the above solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner, hydrothermally treated at 200 °C for 24 h, and then naturally cooled to room temperature. The precipitate was filtered, washed alternately with absolute ethanol and distilled water three times each, and vacuum dried at 60 °C to obtain the MoS2 composite catalyst, which was named MoS2-0.4P.

[0042] Preparation of FeS2 Nanosheets in Comparative Example 7 2 mmol of Fe(NO3)3·9H2O and 60 mmol of thioacetamide were dissolved in 60 mL of distilled water under vigorous stirring, and a homogeneous mixed solution was formed after stirring for 30 minutes. The mixed solution was transferred to a stainless-steel autoclave with a 200 mL Teflon liner and maintained at 200 °C for 24 hours. Then the reaction system was naturally cooled to room temperature. The obtained product was collected by centrifugation, washed alternately with distilled water and absolute ethanol three times each, and vacuum dried at 60 °C to obtain FeS2 nanosheets, named FeS2-0h.

[0043] X-ray powder diffraction (XRD): The phase characterization of the samples was carried out using a Panalytical X'pert pro powder diffractometer. The detector was X'celerator, and the copper target (Cu Kα, λ = 0.154 nm) was used as the excitation radiation source. The working voltage was 45 KV and the working current was 40 mA.

[0044] The morphology of the catalyst was observed by an S-4800 field emission scanning electron microscope. The vacuum degree of the analysis chamber was less than 2.7×10 -6 Pa, and the scanning voltage and current were 5 kV and 7 μA respectively. The sample powder was adhered to the conductive adhesive and sputtered with gold before observation.

[0045] Information on the defects or sulfur vacancies of the samples could be obtained by an E-500 electron paramagnetic resonance spectrometer (Bruker). The test was carried out at room temperature, and the test frequency was 100 kHz. After the sample was placed in a quartz test tube, the test tube should be kept vertical, and the working environment of the instrument should be stable and the air circulation should be ensured.

[0046] Figure 1 X-ray powder diffraction patterns of MoS2 prepared in Examples 1 to 3 and Comparative Example 1 and FeS2 prepared in Examples 4 to 6 and Comparative Example 7. It can be seen from the figure that the diffraction peaks of the prepared MoS2 at 9.6°, 32.5° and 57.2° respectively belong to the (002), (100) and (110) crystal planes of molybdenum disulfide, which are consistent with the standard card pattern. The diffraction peaks of FeS2 at 28.5°, 33.1°, 37.1°, 56.3° and 59.0° coincide with the (111), (200), (210), (311) and (222) crystal planes of pyrite FeS2, indicating that the prepared samples are MoS2 and FeS2. In addition, no impurity peaks were observed in the metal sulfides rich in sulfur vacancies, indicating that the method of generating sulfur vacancies on the basal plane of the metal sulfide in this scheme will not generate other phases or change the crystal structure.

[0047] Figure 2 SEM images of MoS2 prepared in Examples 1 to 3 and Comparative Example 1. It can be seen from the figure that all 4 samples show a flower-like morphology composed of aggregated nanosheets with sharp edges, similar to petals, indicating that the introduction of sulfur vacancies on the basal plane of MoS2 nanosheets will not significantly affect the morphology of MoS2.

[0048] Figure 3 Raman images of MoS2 prepared in Examples 1 to 3 and Comparative Example 1. It can be seen from the figure that there are two characteristic peaks at 376 cm -1 and 404 cm -1 , which respectively correspond to the in-plane bending vibration E 1 2g of the Mo-S bond and the out-of-plane bending vibration A 1g mode. With the increase of the ultrasonic reduction reaction time with sodium borohydride, the ratio of E 1 2g / A 1gThe relative peak intensity first increases and then decreases, indicating that an appropriate reaction duration helps to induce the slip edge dislocation of the MoS2 crystal plane, that is, the number of line defects increases, which confirms that the present invention can successfully regulate the defect sites of the active component MoS2. Among them, the E 1 2g / A 1g of the example 2 sample is relatively large, making it exhibit relatively high catalytic activity. Moreover, the MoS2 nanosheets containing sulfur vacancies show characteristic peaks similar to those of the original MoS2 nanosheets, further confirming that the 2H crystal phase is not damaged after the introduction of sulfur vacancies.

[0049] Figure 4 are the EPR spectra of the MoS2 prepared in Examples 1 to 3 and Comparative Example 1. It can be seen from the figure that all three samples prepared in the examples have a certain amount of sulfur vacancies. By comparing the peak intensities, it is found that the peak intensity of the example 2 sample is the highest, indicating that the ultrasonic reduction with sodium borohydride can effectively regulate the sulfur vacancy concentration of the catalyst. And the abundant sulfur vacancies can promote the adsorption and further conversion of H2S and nitrobenzene.

[0050] Performance test of the reduction of nitrobenzene to aniline with H2S: The metal sulfides prepared in the examples and comparative examples were ground into powders for the performance evaluation of the reduction of nitrobenzene with H2S. The test conditions are as follows: the catalyst dosage is 50 mg; the concentration of H2S is 5%, and N2 is the balance gas; the reaction pressure is 1.5 MPa; the reaction time is 3 h; the reaction substrate composition is: 1 mmol nitrobenzene, 40 mL N,N-dimethylacetamide, 20 mg K2CO3. The results are shown in Table 1.

[0051] Table 1

[0052] As can be seen from Table 1, compared with the untreated metal sulfide (comparative example), the metal sulfide with sulfur vacancies introduced by ultrasonic treatment with sodium borohydride has a higher nitrobenzene conversion rate and aniline yield, and the metal sulfide obtained by ultrasonic treatment for 4 hours has the most sulfur vacancies and the best catalytic activity.

[0053] In order to investigate the universality of the catalyst for the reaction substrate, taking MoS2-4h and FeS2-4h as examples, the tests were carried out according to the above reaction conditions to study their catalytic performance for nitrobenzenes containing different functional groups (such as p-nitrochlorobenzene, p-nitroanisole, p-nitrotoluene, etc.). The results are shown in Tables 2 and 3.

[0054] Table 2 Catalytic effect of MoS2-4h on nitrobenzenes containing different functional groups

[0055] Table 3 Catalytic effect of FeS2-4h on nitrobenzenes containing different functional groups

[0056] As can be seen from the results in Tables 2 and 3, the prepared sulfur-rich vacancy metal sulfides show excellent catalytic efficiency for p-fluoronitrobenzene, p-chloronitrobenzene and o-chloronitrobenzene containing strong electron-withdrawing groups, and their conversion rates all exceed 97%. For the substrate system containing electron-donating groups, the product selectivities for p-methylnitrobenzene and p-nitroanisole still remain above 71%, proving that the prepared sulfur-rich vacancy metal sulfides have good universality for nitrobenzenes containing different functional groups.

[0057] To investigate the stability of the catalyst, taking MoS2-4h as an example, a cyclic test of catalytic reduction of nitrobenzene was carried out. Specifically, after the reaction was carried out under the above conditions, the catalyst was filtered and separated, and then washed thoroughly with an ethanol solution with a volume fraction of 95%, and then vacuum dried at 120 °C to remove the sulfur deposited on the surface. After that, the treated catalyst was re-introduced into the next round of reaction system, and a total of 5 cyclic experiments were completed. The results are shown in Table 4.

[0058] Table 4 Catalytic performance of MoS2-4h in cyclic stability test

[0059] The results in Table 4 show that after five cycles, the selectivities of the substrate nitrobenzene and the product aniline do not decrease significantly, proving that the catalyst has good stability.

[0060] In summary, the sulfur-rich vacancy metal sulfides prepared in the present invention have good catalytic performance in the reaction of reducing nitrobenzene to aniline with H2S. Among them, the catalytic activities of MoS2-4h and FeS2-4h samples are the highest, and they have great application potential.

[0061] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. A preparation method of sulfur-rich vacancy metal sulfide, characterized in that: It includes the following steps: (1) Dissolve the molybdenum source or iron source and the sulfur source together in distilled water and continuously stir for half an hour to obtain a metal mixture solution; (2) Pour the metal mixture solution obtained in step (1) into a hydrothermal reactor for reaction; (3) After the temperature of the hydrothermal reactor drops to room temperature, filter, wash, and dry the obtained precipitate to obtain a precursor; (4) Dissolve the precursor obtained in step (3) and the reducing agent successively in distilled water, and then perform ultrasonic treatment on the obtained mixed solution at room temperature; (5) Filter, wash, and dry the precipitate obtained in step (4) to obtain the sulfur-rich vacancy metal sulfide.

2. The preparation method of the sulfur-rich vacancy metal sulfide according to claim 1, wherein: In step (1), the molar ratio of the molybdenum source or iron source to the sulfur source used is 1:

30.

3. The preparation method of the sulfur-rich vacancy metal sulfide according to claim 1 or 2, wherein: The molybdenum source is (NH4)6(Mo7O 24 )·4H2O or Na2MoO4·2H2O, the iron source is Fe(NO3)3·9H2O, and the sulfur source is thiourea or thioacetamide.

4. The preparation method of the sulfur-rich vacancy metal sulfide according to claim 1, wherein: In step (2), the temperature of the reaction is 200 °C and the time is 12 to 24 hours.

5. The preparation method of the sulfur-rich vacancy metal sulfide according to claim 1, wherein: In step (4), the reducing agent is sodium borohydride, and its dosage is calculated according to 0.1 mol per gram of the precursor.

6. The preparation method of the sulfur-rich vacancy metal sulfide according to claim 1, wherein: In step (4), the time of the ultrasonic treatment is 0 to 6 h.

7. The preparation method of the sulfur-rich vacancy metal sulfide according to claim 1, wherein: In the operation, the washing is carried out by washing three times each with distilled water and absolute ethanol in turn.

8. A sulfur-rich vacancy metal sulfide prepared by the method according to claim 1.

9. Use of the sulfur-rich vacancy metal sulfide according to claim 8 in the reduction of nitrobenzene to aniline, characterized in that: Using the sulfur-rich vacancy metal sulfide as a catalyst and H2S as a reducing agent, carry out the reduction reaction of nitrobenzene.

10. The application according to claim 9, wherein: The temperature of the reaction is 90 °C, the pressure is 1.5 MPa, and the time is 3 hours.

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