MXene-based sulfur high-value catalyst and preparation method and application thereof

Abstract

The application discloses a MXene-based sulfur high-value catalyst and a preparation method and application thereof, and belongs to the technical field of material preparation and environmental catalysis. Carbon titanium aluminum is used as a raw material, and anhydrous copper chloride is used as an etching agent. After ball milling, calcination, suction filtration and drying treatment, the ammonium persulfate is used to disperse active sites, so that the MXene material with the layered structure and the highly dispersed copper active sites is obtained. The synthesis method is green, clean, safe and reliable. The copper generated in the melting etching process is fully utilized. The catalyst is prepared by the oxidation dispersion method. The method not only saves the cost and reduces the harm to the environment, but also realizes the regulation and optimization of the electronic structure and dispersity of the catalyst. The catalyst exhibits good catalytic activity and target product selectivity in the reaction of reducing aromatic nitro compounds into aromatic amine compounds by H2S. Compared with traditional catalysts such as bulk metal oxides and carbon materials, the catalyst has better catalytic performance, is not easy to be poisoned and inactivated, can be recycled, has wide substrate applicability, and has a large application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material preparation and environmental catalysis, and particularly relates to a MXene-based sulfur high-value catalyst, a preparation method and application thereof. BACKGROUND

[0002] Hydrogen sulfide (H2S) is a colorless, irritating-smelling gas with strong toxicity and high flammability. As a toxic gas associated with the production of coal, petroleum and natural gas, H2S not only causes downstream catalysts to be poisoned and deactivated, but also seriously pollutes the ecological environment. The Claus method is commonly used to treat sulfur-containing waste gas, but the reaction needs to be carried out at a high temperature, and due to the limitation of reaction thermodynamic equilibrium, about 5% of H2S is difficult to remove. At the same time, the reaction can only recover sulfur resources in H2S, while hydrogen resources are oxidized to waste water and discharged. Therefore, green economic use of H and S elements in H2S and conversion into high-value chemical products not only can ensure the safe production of chemical processes, but also can generate huge economic benefits. It is a frontier topic and a key development direction in the field of desulfurization industry catalysis.

[0003] Aromatic aniline and its derivatives are an important class of organic compounds, which have important application value in the fields of chemical industry, pharmaceutical field, material science, dye industry and the like. At the same time, since nitro compounds are generally low in price, the preparation of aromatic amines from nitro compounds by reduction is a common scheme in industry. The methods for preparing aromatic amines from nitro compounds by reduction mainly include hydrogen reduction method, metal reduction method, sulfidation alkali reduction method, metal hydride reduction method, electrochemical reduction method and photochemical reduction method. For the common hydrogen reduction method, on the one hand, it needs to use relatively dangerous hydrogen, and on the other hand, it needs to ensure a large temperature and pressure, which requires high equipment and large investment, and is often accompanied by dehalogenation. The metal reduction method and the sulfidation alkali reduction method also have problems of environmental pollution and post-treatment due to the generation of a large amount of waste water and waste residue in the process. The metal hydride reduction method is limited by the fact that the metal hydride itself is a flammable and explosive reducing agent, and it is difficult to carry out large-scale utilization. The electrochemical reduction method and the photochemical reduction method are only used in small scale, and have high requirements on the process and equipment.

[0004] Catalytic hydrogen transfer reduction is a common method of organic synthesis, widely used in organic reactions. It uses catalysts and hydrogen sources to achieve hydrogen transfer and reduction reactions between compounds. In this method, the catalyst plays a role in promoting the reaction, making it more efficient and low-consumption. Catalytic hydrogen transfer reduction can achieve the conversion of a variety of organic substances, which greatly reduces the requirements of equipment. In the reaction, the catalyst can provide active sites, adsorb reactants and promote hydrogen transfer. H2S has reducing properties and can be used as a hydrogen source to participate in the reaction, reducing nitro groups or other hydrogen acceptors into the corresponding groups. This not only realizes the recovery of sulfur resources, but also makes efficient use of hydrogen resources, and the key to achieving the above process is to develop high-performance catalysts.

[0005] MXene is a new type of carbon / nitride two-dimensional layered material, which is generally obtained by selectively etching the A atom layer in the precursor MAX phase by chemical etching. Its general formula can be represented as M n+1 X n T x , where M represents a pre-transition metal, X represents carbon and / or nitrogen, and T x represents the functional groups (-OH, =O, etc.) attached to the surface of MXene during the etching process. The special layered structure of MXene brings good loading performance and mass transfer capacity, and at the same time the surface has rich functional groups, which makes it an ideal carrier for catalytic hydrogen transfer catalyst. Due to the unique chemical stability and loading capacity of MXene, it is often used as an environmentally friendly two-dimensional catalyst carrier with strong surface activity, which has excellent adsorption effect on active components and reactants in the reaction system. At the same time, MXene not only shows excellent adsorption performance in solution, but also can adsorb a large amount of gas, which meets the requirements of H2S catalytic hydrogen transfer reduction method.

[0006] However, the traditional MXene synthesis method relies on highly corrosive etchants such as hydrogen fluoride to etch the Al layer, which can cause serious instrument corrosion and environmental pollution, and hydrogen fluoride itself is expensive and difficult to store. Based on this, the application creatively develops a green method to prepare layered MXene catalysts and applies them to the reduction of aromatic nitro by H2S to prepare amine. We use carbon titanium aluminum as raw material, anhydrous copper chloride as etchant, through grinding, calcination, stirring, drying treatment, we get MXene intermediate product in the process of melting etching, and get a large amount of Cu species. Because the Cu site has high activity and stable catalytic performance in hydrogen transfer, we disperse the above intermediate product by ammonium persulfate solution oxidation, realize the high dispersion of Cu active component on the MXene carrier, and finally get the MXene catalyst with layered structure. The application provides a reference for the green preparation of MXene catalyst, has far-reaching research significance, and the prepared catalyst can efficiently realize the reduction of aromatic nitro by H2S to amine, which further expands the application field of MXene catalyst. SUMMARY

[0007] In view of the shortcomings of the prior art, the application provides a synthesis method of layered MXene material and its application, which solves the problems of low H2S desulfurization catalytic activity and low atomic utilization rate in the prior art. Compared with hydrogen fluoride etching, the MXene material prepared by melting can not only reduce environmental pollution, but also adjust the carrier performance and increase the catalytic ability of the material, while retaining the characteristics of high loading performance and strong cycle stability. By adjusting the oxidation dispersion time, the electronic structure and dispersion degree of the active site can be adjusted, so that more active sites are exposed in the layered structure, which exhibits excellent catalytic activity and stability in the reaction of catalyzing H2S to convert nitroarenes.

[0008] To achieve the above object, the application adopts the following technical scheme:

[0009] A preparation method of MXene sulfur high-value catalyst comprises the following steps:

[0010] a. The carbon titanium aluminum, potassium chloride, sodium chloride and anhydrous copper chloride are mixed and placed in a ball mill at 400-600 rpm for 30 min, and then the powder is collected for standby;

[0011] b. The powder obtained in step a is moved into a tube furnace, and after high-temperature calcination under the condition of argon gas for 30-36 h, the powder is taken out and ground through a 200 mesh sieve for standby;

[0012] c. The powder in step b is transferred to a magnetic stirrer, and ethanol water is used for stirring and washing, and then the powder is dried by suction filtration to obtain a layered MXene material intermediate;

[0013] d. 100~300 ml oxidant solution is measured, then 0.1~0.2 g of the intermediate obtained in step c is added, after stirring reaction, ethanol water is used for washing, then dry treatment is carried out by suction filtration, and a layered MXene material, i.e. a MXene-based sulfur high-value catalyst, is obtained;

[0014] Further, the molar ratio of the carbon titanium aluminum, potassium chloride, sodium chloride, anhydrous copper chloride in step a is 1:2:2:3~4.

[0015] Further, the heating rate of the calcination in step b is 3~5 ℃ / min, the calcination temperature is 650~750 ℃, and the calcination time is 30 h.

[0016] Further, the drying in step c is vacuum drying at 60~80 ℃ for 4~8 h.

[0017] Further, the oxidant in step d is an aqueous solution of ammonium persulfate, the concentration is 0.1 M, and the stirring time is 30~120 min.

[0018] Further, the drying in step d is vacuum drying at 60~80 ℃ for 8~10 h.

[0019] Further, the obtained layered MXene material is washed by a sulfuric acid ethanol solution, and can be used in the reaction of converting H2S into aryl nitro compounds, and the reaction temperature is 90 ℃.

[0020] Further, the specific conditions of the layered MXene for catalyzing the conversion of H2S into nitroaromatics are as follows: the reaction substrate is nitrobenzene 102 μL; 40 mL N,N-dimethylacetamide is used as a dispersion medium; the stirring rate is 180 rpm; the reactor volume is 100 ml; the catalyst dosage is 50 mg, and the adjuvant is potassium carbonate 20 mg; the raw gas is 5 wt% H2S / N2; the reaction pressure is 1.5 MPa; the reaction time is 2 h; and the reaction temperature is 90 ℃.

[0021] The beneficial effects of the present application are as follows:

[0022] (1) The layered MXene prepared by the present application can synthesize a better copper active component by regulating the oxidation dispersion time, improve the catalytic activity, and the layered structure has a large specific surface area, which is beneficial to the desorption of the product and improves the cycle stability of the material.

[0023] (2) The prepared MXene is dispersed on a larger specific surface area by a melting etching method and oxidation dispersion, so that copper elements are more dispersed, which is beneficial to sufficient exposure of active components and further improves catalytic activity. The high-activity catalyst metal doping amount is less, the preparation process is green and environmentally friendly, industrialized production is easy to realize, and has a wide application prospect.

[0024] (3) The MXene obtained in the application can adjust the adsorption and activation degree of the active center to H2S, which can prevent the active site from being poisoned on one hand, and make the sulfur intermediate quickly desorb and release hydrogen atoms to participate in the reduction reaction of aromatic nitro, so as to obtain the target product aromatic amine.

[0025] (4) The MXene-based sulfur high-value catalyst provided by the application has good catalytic activity and selectivity, can be recycled, and is better than BCN, Fe2O3, CuO, Si / Al molecular sieve and other materials. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 X-ray powder diffraction spectra of M-X min prepared in examples 1-4 of the application and precursor carbon titanium aluminum;

[0027] Figure 2 N2 physical adsorption-desorption curve (A) and pore size distribution graph (B) of M-X min prepared in examples 1-4 of the application;

[0028] Figure 3 SEM images of M-30 min (A) and M-90 min (B) prepared in example 3 of the application;

[0029] Figure 4 EDS element mapping spectrum of M-90 min prepared in example 3 of the application;

[0030] Figure 5 X-ray photoelectron spectrogram of M-90 min prepared in example 3 of the application, which is total spectrum (A), Ti2p spectrum (B), C 1s spectrum (C), metal Cu 2p spectrum (D), O 1s spectrum (E) and total spectrum (F) of the precursor carbon titanium aluminum;

[0031] Figure 6 Cu LMM spectrum of M-90 min X-ray photoelectron spectrogram prepared in examples 1-4 of the application;

[0032] Figure 7 Fourier infrared spectrogram of M-X min prepared in examples 1-4 of the application;

[0033] Figure 8H2-TPR spectra of M-X min prepared for Examples 1-4 of the present invention;

[0034] Figure 9 CO2-TPD spectra of M-X min prepared for Examples 1-4 of the present invention;

[0035] Figure 10 Aniline conversion, selectivity and yield of M-X min prepared for Examples 1-4 of the present invention at 2 h of reaction time for catalytic H2S conversion of nitroarenes;

[0036] Figure 11 Activity plot of M-90 min prepared for Example 3 of the present invention in five cycles of regeneration testing. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention is described in detail below in combination with examples and drawings, and the described examples are further descriptions of the present invention, rather than limitations on the content of the present invention.

[0038] Example 1

[0039] A method for synthesizing a layered MXene material: 1 g of aluminum titanium carbide, 2.76 g of anhydrous copper chloride, 0.76 g of potassium chloride, and 0.6 g of sodium chloride were mixed and added to a ball mill jar, and the mixture was ball milled at 400 rpm for 30 min by a ball mill, and then the mixture was placed in a tube furnace and heated to 700 °C at a rate of 4 °C / min under an argon stream for a total of 30 h. The product was washed and suction filtered with ethanol and water, and then the obtained precipitate was vacuum dried at 80 °C for 8 h. The product was stirred and soaked with 0.1 mol / L ammonium persulfate for 30 min, and then washed with ethanol and water and suction filtered and centrifuged. Finally, the obtained precipitate was vacuum dried at 80 °C for 8 h, and the obtained product was named M-30 min according to the treatment time.

[0040] Example 2

[0041] A method of synthesizing a layered MXene material: 1 g of aluminum titanium carbide, 2.76 g of anhydrous copper chloride, 0.76 g of potassium chloride, and 0.6 g of sodium chloride were mixed and added to a ball mill jar, and milled by a ball mill at 400 rpm for 30 min, and then the mixture was placed in a tube furnace, and the powder mixture was heated to 700 °C at a rate of 4 °C / min in an argon stream for a total of 30 h. The product was washed by ethanol and water and suction filtered, and then the obtained precipitate was vacuum dried at 80 °C for 8 h, the product was stirred and soaked with 0.1 mol / L ammonium persulfate for 60 min, and then washed by ethanol and water and suction filtered and centrifuged. Finally, the obtained precipitate was vacuum dried at 80 °C for 8 h, and the obtained product was named as M-60 min according to the treatment time.

[0042] Example 3

[0043] A method of synthesizing a layered MXene material: 1 g of aluminum titanium carbide, 2.76 g of anhydrous copper chloride, 0.76 g of potassium chloride, and 0.6 g of sodium chloride were mixed and added to a ball mill jar, and milled by a ball mill at 400 rpm for 30 min, and then the mixture was placed in a tube furnace, and the powder mixture was heated to 700 °C at a rate of 4 °C / min in an argon stream for a total of 30 h. The product was washed by ethanol and water and suction filtered, and then the obtained precipitate was vacuum dried at 80 °C for 8 h, the product was stirred and soaked with 0.1 mol / L ammonium persulfate for 90 min, and then washed by ethanol and water and suction filtered and centrifuged. Finally, the obtained precipitate was vacuum dried at 80 °C for 8 h, and the obtained product was named as M-90 min according to the treatment time.

[0044] Example 4

[0045] A method of synthesizing a layered MXene material: 1 g of aluminum titanium carbide, 2.76 g of anhydrous copper chloride, 0.76 g of potassium chloride, and 0.6 g of sodium chloride were mixed and added to a ball mill jar, and milled by a ball mill at 400 rpm for 30 min, and then the mixture was placed in a tube furnace, and the powder mixture was heated to 700 °C at a rate of 4 °C / min in an argon stream for a total of 30 h. The product was washed by ethanol and water and suction filtered, and then the obtained precipitate was vacuum dried at 80 °C for 8 h, the product was stirred and soaked with 0.1 mol / L ammonium persulfate for 120 min, and then washed by ethanol and water and suction filtered and centrifuged. Finally, the obtained precipitate was vacuum dried at 80 °C for 8 h, and the obtained product was named as M-120 min according to the treatment time.

[0046] X-ray powder diffraction (XRD): The phase characterization of the sample was performed by X’pert Pro MPD of Panalytical Company. 3X-ray powder diffractometer (XRD): The XRD patterns were measured on a PANalytical X'Pert PRO powder diffractometer with a PIXcel detector, Cu target (Cu Ka, l = 0.154 nm) as the excitation source, and an operating voltage of 45 KV and an operating current of 40 mA.

[0047] X-ray photoelectron spectroscopy (XPS): An EscaLab 250Xi X-ray photoelectron spectrometer from Thermo Fisher Scientific was used with an aluminum target (Al Ka 1486.6 eV) X-ray source. During the XPS measurement, a neutralization gun was used to compensate for surface charges, and in addition, the binding energy of the C-C bond was corrected to 284.8 eV. The base pressure in the analysis chamber was 2.5 x 10 −8 mbar.

[0048] Inductively coupled plasma emission spectroscopy (ICP): An OPTIMA 8000 inductively coupled plasma emission spectrometer from Perkin-Elmer was used, with an analysis range of 165-850 nm and a sensitivity of 0.1-10 ppb.

[0049] N2physical adsorption: An ASAP 2020 analyzer from Micrometric was used to measure the specific surface area and pore size of the samples at liquid nitrogen temperature (77 K). The samples were first vacuum pretreated at 473 K, then degassed for 3 h at a pressure of less than 10 - 5 torr, and the specific surface area of the samples was calculated using the BET (Brunauer-Emmett-Teller) method, and the pore size distribution curve was obtained using the BJH (Barrett-Joyner-Halenda) method.

[0050] Field emission scanning electron microscope (SEM): The SEM images of the samples were observed on an S-4800 scanning electron microscope, with a test current and voltage of 7 μA and 5 kV, respectively.

[0051] X-ray energy dispersive spectrometer (EDS): The EDS images of the samples were observed on an S-4800 scanning electron microscope equipped with an X-ray energy dispersive spectrometer from EDAX, with a test current and voltage of 15 μA and 15 kV, respectively.

[0052] Fourier transform infrared spectrometer (FTIR): A Nicolet 6700 Fourier transform infrared spectrometer from Thermo Fisher Scientific was used to detect the spectrum in the mid-infrared region (4000-500 cm -1 ).

[0053] Chemisorption (H2-TPR and CO2-TPD): All samples were pretreated at 573 K. The TPD sample was first adsorbed with CO2 at 323 K for 30 min, and then desorbed at 20 ℃ / min to 873 K in a helium stream. The TPR sample was reduced at 20 ℃ / min to 873 K in an argon atmosphere after standing for 30 min.

[0054] Figure 1 X-ray powder diffraction spectra of the catalysts prepared in Examples 1-4 and carbon titanium aluminum. As shown in FIG. 1, the peaks at 7.8 ° and 15.9 ° represent the (0 0 2) and (0 0 4) crystal planes of MXene, respectively. The peaks at 27.4 °, 36.0 °, 40.5 °, and 54.3 ° identified by triangles in the figure represent Ti-O generated by Ti-Cl on the surface of the catalyst when water is encountered. The disappearance of the diffraction peak at 38.7 ° of carbon titanium aluminum indicates that Al atoms are selectively etched from carbon titanium aluminum. The diffraction peaks at 43.3 ° and 50.4 ° of Examples 1-4 samples significantly decrease in intensity as the oxidation dispersion time increases, which may be due to the oxidation and dispersion of copper species on the surface of MXene, resulting in dispersed copper active sites. Figure 1

[0055] Figure 2 Physical adsorption spectrum of MXene prepared in Example 2 of the present application. Figure 2 (A) shows that all samples exhibit type IV adsorption isotherms with a clear H3 hysteresis loop. This belongs to mesoporous adsorbent materials, and the H3 hysteresis loop is commonly found in aggregates with layered structures, corresponding to slit-shaped mesoporous or macroporous materials, which is consistent with the layered structure of MXene. The catalyst prepared in Example 4 has the highest specific surface area, which is calculated to be 137.5 m 2 / g. Large specific surface area is beneficial to the mass transfer and diffusion process of catalytic reaction. Figure 2 (B) shows that the pore distribution of the material is relatively concentrated at about 4 nm, indicating that the MXene material has a large amount of mesopores (2-50 nm), and the total pore volume gradually increases and the average pore size slightly decreases with the soaking of ammonium persulfate.

[0056] Figure 3 SEM images of M-30 min and M-90 min prepared in Examples 1 and 3 of the present application. As can be seen from the figure, the MXene prepared in Examples 1 and 3 has a layered morphology. With the increase of dispersion time, the Cu species on the surface of M-30 min is uniformly dispersed on the surface of the catalyst.

[0057] ​Figure 4 The EDS spectrum of M-90 min prepared in Example 3 of the present application shows the distribution of Ti, C and Cu in the material, indicating that these elements are uniformly distributed in the whole system.

[0058] Figure 5 The X-ray photoelectron spectrum (XPS) of M-90 min prepared in Example 3 of the present application. Compared with the total spectrum of carbon titaniumized aluminum and MXene, the Al 2p binding energy spectrum peak area is obviously reduced, indicating that Al atoms are selectively etched from carbon titaniumized aluminum, and the Ti 2p is obviously increased, which also indicates that etching can expose more Ti layers. From the Ti 2p spectrum of Example 3, it can be found that the material surface contains Ti 4+ (Ti-O), Ti 3+ (Ti-Cl) and Ti 2+ (Ti 2+ -C) and Ti + (Ti + -C, Ti-Cu), and the more abundant Ti-C species and Figure 3 The conclusion that the material can still ensure the integrity of the layered skeleton after etching is consistent. In addition, as shown in the C 1s spectrum, the C-C bond characteristic spectrum peak accounts for a high proportion in the catalyst, indicating that the graphite layer structure in the material is basically maintained, and contains a certain content of C-Ti-T x , indicating that the surface groups of the material are rich, which can provide more active sites. The metal Cu 2p XPS spectrum shows that the material contains Cu + , Cu 0 and Cu 2+ metallic copper species, which provides rich active sites for catalysis. These results prove that MXene is composed of layered Ti and C layers, not only has rich surface active groups, but also has different types of copper species. From the O 1s spectrum, it can be seen that the oxygen in the catalyst exists in the form of surface oxygen in addition to a small amount of Cu-O lattice oxygen.

[0059] Figure 6 The Cu LMM spectrum of the X-ray photoelectron spectrum of M-X min prepared in Examples 1-4 of the present application. It can be found that the total content of Cu in the material gradually decreases with the extension of the oxidation dispersion time, and the proportion of Cu 0 , Cu 2+ gradually decreases, and the proportion of Cu + gradually increases, which indicates that the large Cu species fixed by the material in the catalyst is gradually washed out, and part of it is dispersed again in the form of Ti-O-Cu. At the same time, with the oxidation dispersion, the surface fixed Cu is gradually exposed and exists in the form of Ti-Cu-O.

[0060] Table 1 is the copper content of the corresponding catalysts determined by ICP at different dispersion times. It can be found that the copper content decreases obviously with the increase of dispersion time, which is consistent with the XPS characterization results.

[0061]

[0062] Figure 7 The Fourier infrared spectrum of M-X min prepared for examples 1-4 of the present application. From FTIR, it can be found that on the one hand, there is a considerable amount of-Ti-O on the surface of the catalyst, and at the same time, with the immersion of the solution, -C=O, -OH gradually increases, which shows that the immersion changes the species composition distribution of MXene.

[0063] Figure 8 The H2-TPR spectrum of M-X min prepared for examples 1-4 of the present application. From the H2-TPR curve, the hydrogen consumption peak between 250-350 ℃ corresponds to Cu 2+ reduction peak of CuO, and the hydrogen consumption peak at 450 ℃ is the Cu + reduction peak. From the Cu 2+ reduction peak area, with the extension of the stirring immersion time of ammonium persulfate, the CuO species is stripped and re-dispersed, the interaction force with the support surface is enhanced, the reduction peak moves to high temperature, the species distribution is more uniform, and the reduction peak gradually widens and narrows. And between 90 min and 120 min of immersion time, there is an inflection point. From the Cu + peak, due to the fixation of Ti-O-Cu and Ti-Cu-O, Cu 1+ is mainly distributed in the position close to the surface of the catalyst, which makes its reduction peak position remain at 450 ℃ without much change. Due to the stripping of CuO species close to the surface of Ti-Cu-O, and the re-dispersion of part of the stripped copper on the surface in the form of Ti-O-Cu, the Cu + reduction peak gradually rises, and then with the continuous increase of the immersion time, the Cu content gradually decreases, Ti-O-Cu and Ti-Cu-O are removed, which is reflected in the H2-TPR as the reduction peak first increases and then decreases.

[0064] Figure 9 The carbon dioxide temperature programmed desorption spectrum of M-X min prepared for examples 1-4 of the present application.

[0065] In the CO2-TPD of the catalyst, there are three kinds of basic sites, respectively (1) 100-200 ℃ weak basic site CO2 desorption peak generated by CuO. (2) 200-350 ℃ medium-strong basic site (HCO3 −) pyrolytic desorption peak. (3) 300~450 ℃ pyrolytic desorption peak of strong basic sites carbonate (CO3 2- ) formed by Ti-Cu-O combination. It can be found that the M-90 min provides the most strong basic sites, which may be conducive to the adsorption and activation of H2S, thereby improving the activity of the catalyst.

[0066] Reaction test of H2S converting nitrobenzene: the M-X min materials prepared in examples 1~4 can be used for the evaluation of the reaction activity of converting nitrobenzene after simple grinding. The test conditions are as follows: the catalyst loading is 50 mg, the promoter is potassium carbonate 20 mg, the stirring rate is 180 rpm, the reactor volume is 100 mL, the reaction substrate is nitrobenzene 102 μL with 40 mL N,N-dimethylacetamide as the dispersion medium, the raw gas is 5 wt % H2S / N2, the reaction pressure is 1.5 MPa, the reaction temperature is 90 ℃, and the reaction time is 2 h.

[0067] The catalyst prepared in each example is applied to the catalytic reaction of H2S converting nitrobenzene, and quantitative analysis is carried out by gas chromatography. The peak area at the corresponding retention time of the organic phase product at the end of the reaction and the aniline solution with a known prepared concentration is calculated to obtain the aniline yield I a of the reaction, and then the peak area I0 corresponding to 100 % conversion of the reactant nitrobenzene aniline at the retention time is calculated to obtain the yield of aniline in the reaction.

[0068] The yield calculation formula of aniline is as follows:

[0069]

[0070] Figure 10 The aniline conversion rate, selectivity and yield of M-X min prepared in examples 1~4 in the reaction of catalyzing H2S to convert nitroaromatic hydrocarbons for 2 h. The conversion rate and selectivity of the M-90 min sample prepared in example 3 reached 86.4 % and 82.3 % respectively at 1.5 Mpa and 90 ℃, which are better than the BCN, Fe2O3, CuO, Si / Al molecular sieve materials reported in the literature (Table 2).

[0071] Table 2 Statistical table of H2S reducing aromatic nitro to aromatic amine activity of examples 1~4 of the present application and BCN, Fe2O3, CuO, Si / Al molecular sieve

[0072]

[0073] In addition, the MXene catalyst synthesized in the present application has good catalytic activity and selectivity, and can be recycled. After five cycles of regeneration test, the activity does not decrease obviously (I Figure 11). More importantly, the catalyst can be applied to different aromatic nitro substrates and exhibits good amine preparation activity, and the substrate applicability is wide (Table 3).

[0074]

[0075] As can be seen from Table 3, the catalyst can be expanded to aromatic nitro substrates with different substituents. When the para-position group is -F or -Cl group, the nitro group at the para-position is more easily activated to generate a nitroso intermediate on the surface of the catalyst due to the conjugation effect of the benzene ring, thereby improving the reaction conversion rate. When the para-position group is a nucleophilic group such as -NH2 or -CH3, the reaction selectivity is improved by attracting H2S during the catalytic process. When the para-position group is -OH, the catalytic activity is reduced due to the acidity of the catalyst system itself and the acidity of the phenol itself, which inhibits the dissolution of H2S. In summary, for different aromatic nitro substrates, the conversion rate and selectivity are also good and have certain applicability, and the industrial application prospect is good.

[0076] In summary, the MXene catalysts prepared by the present application with different oxidation dispersion times have different catalytic properties in the H2S conversion nitrobenzene catalytic reaction, and the catalytic activity of the M-90 min sample is the highest. The prepared MXene material has a layered morphology, a mesoporous structure and a high dispersion of active sites, and a small amount of copper is loaded, which can effectively catalyze the reaction of H2S conversion nitrobenzene and has great application potential.

[0077] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. Application of a MXene-based sulfur high-value catalyst in catalyzing the reaction of converting aromatic nitro compounds by H2S, characterized in that: The preparation method of the MXene-based sulfur high-value catalyst comprises the following steps: a. Mix the precursors, potassium salt, sodium salt and metal salt, ball mill and mix uniformly; b. High-temperature calcination of the powder obtained in step a in an argon environment and natural cooling; c. Sieving the powder obtained in step b, washing with ethanol solution, suction filtration and drying to obtain the MXene material intermediate; d. Mixing the oxidizing agent and the MXene material intermediate, stirring and reacting, then drying by suction filtration to obtain the MXene-based sulfur high-value catalyst; In step a, the precursor is carbon titanium aluminum, the potassium salt is potassium chloride, the sodium salt is sodium chloride, and the metal salt is anhydrous copper chloride; the molar ratio of the precursor, potassium salt, sodium salt and metal salt is 1:2:2:3~4; In step a, the ball milling time is 30 min and the ball milling speed is 400~600 rpm; In step b, the calcination temperature is 650~750 ℃, the heating rate is 4~6 ℃ / min, and the time is 30~36 h; In step c, sieve through a 200-mesh sieve and vacuum dry at 60~80 ℃ for 6~8 h; In step d, the oxidizing agent is ammonium persulfate solution with a concentration of 0.1 mol / L; In step d, the reaction time is 30~120 min; and the drying is vacuum drying at 60~80 ℃ for 8~10 h.

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