Preparation method and application of single-layer MoS2 / C3N4 catalyst

Abstract

The present invention discloses a single-layer MoS 2 / C 3 N 4 The preparation method of the catalyst comprises the following steps: dissolving a surfactant and carbon nitride in deionized water, stirring at a constant temperature of 38-42°C for 20-24 hours; adding ammonium tetrathiomolybdate and hydrazine hydrate, mixing, stirring and refluxing at 90-100°C for 7-9 hours; separating the solid from the liquid, washing and drying the solid, and calcining at a high temperature to obtain a single-layer MoS 2 / C 3 N 4 Catalyst; The single layer MoS 2 / C 3 N 4 The catalyst is used in catalytic degradation of sulfur-containing volatile organic compounds. Experimental results show that methyl mercaptan can be completely removed at normal pressure and 425°C. The catalyst exhibits excellent catalytic performance and stability. The catalyst of the invention is simple to prepare and is suitable for industrial production and market promotion and application.

Description

Technical Field

[0001] The invention relates to a method for preparing a single-layer MoS2 / C3N4 catalyst for catalytically degrading sulfur-containing VOCs gas, belonging to the technical field of malodorous organic sulfur pollutant treatment. Background Art

[0002] In the process of coal gasification, hydrogen sulfide and sulfur-containing volatile organic compounds (S-VOCs) such as mercaptans and sulfides are inevitably produced. The impact of S-VOCs on the environment and human health is mainly manifested in three aspects: first, it has strong photochemical activity, which aggravates the formation of photochemical smog and haze; second, it seriously corrodes equipment and easily causes catalyst poisoning; third, the odor and toxic effects seriously affect people's quality of life. In view of the fact that the hazards of S-VOCs cannot be underestimated, in the 1990s, the national "Emission Standards for Odor Pollutants" (GB-14554-93) had very strict regulations on their emissions. The first, second and third level factory boundary standards for methyl mercaptan (CH3SH) are one order of magnitude lower than the corresponding factory boundary standards for hydrogen sulfide (the first level factory boundary standards for methyl mercaptan and hydrogen sulfide are 0.004 mg / m 3 and 0.03 mg / m 3 ). Methyl mercaptan is a highly toxic volatile organic pollutant (VOCs) with a strong odor. Its acidity is lower than that of H2S and CO2, and it is difficult to dissolve in water. Therefore, the basic research on the application of methyl mercaptan treatment technology is imminent. The research work on the treatment of methyl mercaptan tail gas in industrial production and the removal of mercaptans in petroleum products has important practical significance.

[0003] At present, the basic methods for removing methyl mercaptan include alkaline solution absorption, adsorption, direct combustion, catalytic oxidation, photocatalytic degradation, biological method and catalytic decomposition, among which catalytic decomposition is one of the ways to achieve efficient removal of S-VOCs. Mo-based catalysts show good catalytic and sulfur resistance in systems such as hydrogenation / oxidative desulfurization and inorganic / organic sulfide decomposition. However, there are few studies on Mo-based catalysts for catalytic decomposition of mercaptan reaction systems, and the catalytic mechanism is not clear enough. Summary of the invention

[0004] The invention provides a method for preparing a single-layer MoS2 / C3N4 catalyst. The method comprises the following steps: dissolving a surfactant and carbon nitride in deionized water, stirring at a constant temperature of 38-42°C for 20-24 hours; adding ammonium tetrathiomolybdate and hydrazine hydrate, mixing well, stirring and refluxing at 90-100°C for 7-9 hours; performing solid-liquid separation, washing and drying the solid, and calcining at a high temperature to obtain the single-layer MoS2 / C3N4 catalyst.

[0005] The surfactant is hexadecyltrimethylammonium bromide, the molar ratio of the surfactant to ammonium tetrathiomolybdate is 0:15-0.2:1, the mass ratio of the surfactant to carbon nitride is 0.3-0.5:1, and the volume mass ratio of hydrazine hydrate to ammonium tetrathiomolybdate is 6-7:1 in mL:g.

[0006] The ammonium tetrathiomolybdate is a conventional commercial reagent or is prepared by a conventional method.

[0007] In the above method, drying is performed at 50-70°C in vacuum for 24 hours, and calcination is performed at 550-650°C in a nitrogen atmosphere for 2-3 hours.

[0008] Another object of the present invention is to apply the single-layer MoS2 / C3N4 catalyst prepared by the above method to the catalytic degradation of sulfur-containing volatile organic matter, specifically, the MoS2 / C3N4 catalyst is sieved to 40-60 mesh and then loaded into a fixed bed reactor, and then the gas to be treated containing methyl mercaptan is introduced to catalytically degrade methyl mercaptan at normal pressure and 250-550°C.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] (1) High activity. The catalyst can completely convert methyl mercaptan at a reaction temperature of 425°C, which is 100-200°C lower than that of other reported catalysts.

[0011] (2) The MoS2 / C3N4 catalyst prepared by the present invention realizes the directional conversion of methyl mercaptan into H2S, CS2, CH4 and a small amount of other simple hydrocarbons. Among them, the H2S treatment process has become mature and is mostly treated by the Claus process. Both CS2 and CH4 can be used as industrial raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 N2 adsorption-desorption diagram and pore size distribution diagram of the MoS2 / C3N4 catalyst prepared in Example 1 of the present invention;

[0013] Figure 2 The XRD pattern of the MoS2 / C3N4 catalyst prepared in Example 1 of the present invention;

[0014] Figure 3 XRD diagram of the catalyst im MoS2 / C3N4 prepared by the conventional impregnation method in comparative example;

[0015] Figure 4 The results of the comparison of the methyl mercaptan degradation activities of the MoS2 / C3N4 catalyst prepared by the method of the present invention and the catalyst im MoS2 / C3N4 prepared in the comparative example;

[0016] Figure 5The results are a comparison of the stability of the MoS2 / C3N4 catalyst prepared by the method of the present invention and the catalyst im MoS2 / C3N4 prepared in the comparative example in degrading methyl mercaptan. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the above contents. The methods in the examples are conventional methods unless otherwise specified, and the reagents are conventional reagents or reagents prepared according to conventional methods unless otherwise specified;

[0018] The ammonium tetrathiomolybdate in the following examples is prepared by mixing ammonium molybdate and ammonium sulfide at a molar ratio of S:Mo of 4, stirring at 50°C for 1 hour, cooling in an ice bath for 3 hours, filtering and washing the formed crystals with isopropanol, and drying in vacuo at 80°C. Example 1

[0019] 1. Weigh 1g of carbon nitride and 0.36g of hexadecyltrimethylammonium bromide (CTAB) and dissolve them in 200mL of deionized water. Stir at 40°C for 22h to completely disperse them to obtain a suspension. Weigh 1.3g of ammonium tetrathiomolybdate (ATTM) and dissolve them in 80mL of deionized water. Stir thoroughly and ultrasonicate in a water bath at 30°C for 5min. Then add 8mL of hydrazine hydrate and add the obtained solution to the above suspension and stir for 30min. Finally, transfer the mixed solution to a conical flask and reflux in an oil bath at 95°C for 8h. Centrifuge the reaction product, wash the solid with deionized water and ethanol three times respectively, and vacuum dry at 60°C for 24h. The obtained black solid powder is calcined at 600°C in a N2 atmosphere for 2h to obtain a single-layer MoS2 / C3N4 catalyst.

[0020] Figure 1 The N2 adsorption-desorption diagram and pore size distribution diagram of MoS2 / C3N4 catalyst show that its BET average pore size is 12.24nm and its specific surface area is 44.503m 2 / g; MoS2 / C3N4 catalyst was analyzed by X-ray diffraction. Figure 2 It can be seen that obvious MoS2 characteristic peaks appear at 2θ=33.5°, 39.5°, and 58.3°, indicating that the prepared material is MoS2, and there is no MoS2 characteristic peak at 2θ=14.4°, indicating that it is a single-layer structure;

[0021] At the same time, the catalyst im MoS2 / C3N4 was prepared by conventional impregnation method as a comparative example, specifically, 1.3 g of ammonium tetrathiomolybdate was weighed and dissolved in 2 mL of deionized water, and stirred until dissolved, and then 1 g of carbon nitride was added and stirred until uniform; after vacuum drying at 60°C for 24 h, the material was transferred to a tube furnace and calcined at 600°C for 2 h in N2 atmosphere; Figure 3It can be seen that the characteristic peak of MoS2 at 2θ=14.4° is obvious, and im MoS2 / C3N4 is a multilayer structure;

[0022] 2. The MoS2 / C3N4 catalyst and imMoS2 / C3N4 catalyst were sieved to 40-60 mesh respectively and loaded into a fixed bed reactor. The catalyst loading mass was 0.2 g. The treated gas (nitrogen) containing 5000 ppm methyl mercaptan was introduced. The total feed space velocity was 4280 h -1 The reaction system pressure is normal pressure, the reaction temperature is 300~500℃, and the catalytic activity evaluation experiment of catalytic degradation of methyl mercaptan is carried out. The results are as follows Figure 4 As shown, the conversion rate of methyl mercaptan catalytically degraded by MoS2 / C3N4 catalyst can reach 100% at 425℃, while the im MoS2 / C3N4 catalyst can only completely degrade methyl mercaptan at 500℃.

[0023] The MoS2 / C3N4 catalyst and imMoS2 / C3N4 catalyst were loaded into a fixed bed reactor with a catalyst loading mass of 0.2 g. The treated gas (nitrogen) containing 5000 ppm of methyl mercaptan was introduced at a total feed space velocity of 4280 h -1 The reaction system pressure was normal pressure, and the reaction temperature was 450℃. The results are shown in Figure 5 As can be seen from the figure, when the reaction temperature is 450°C, the im MoS2 / C3N4 catalyst prepared in the comparative example shows signs of deactivation after 180 minutes for decomposing methyl mercaptan, and the conversion rate of methyl mercaptan is only 88% when the reaction reaches 300 minutes, while the MoS2 / C3N4 catalyst still has a conversion rate of 100% at 300 minutes, indicating that the MoS2 / C3N4 catalyst prepared by the method of the present invention is greatly superior to the catalyst prepared by the traditional impregnation method in terms of stability.

Claims

1. Application of a single-layer MoS2 / C3N4 catalyst in catalytic degradation of methyl mercaptan, characterized in that: The single-layer MoS2 / C3N4 catalyst is prepared by dissolving a surfactant and carbon nitride in deionized water, stirring at a constant temperature of 38-42°C for 20-24 hours; adding ammonium tetrathiomolybdate and hydrazine hydrate, mixing well, stirring and refluxing at 90-100°C for 7-9 hours; separating the solid from the liquid, washing and drying the solid, and calcining at a high temperature.

2. The use according to claim 1, characterized in that: The surfactant is hexadecyltrimethylammonium bromide, the molar ratio of the surfactant to ammonium tetrathiomolybdate is 0:15-0.2:1, and the mass ratio of the surfactant to carbon nitride is 0.3-0.5:

1.

3. The use according to claim 1, characterized in that: The volume mass ratio of hydrazine hydrate to ammonium tetrathiomolybdate (mL:g) is 6-7:

1.

4. The use according to claim 1, characterized in that: Drying is carried out under vacuum at 50~70℃ for 24h.

5. The use according to claim 1, characterized in that: The calcination is carried out in a nitrogen atmosphere at 550-650°C for 2-3 hours.

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