A "sandwich" structure of molybdenum disulfide / graphene nanosheet catalyst and preparation and application thereof

Abstract

The application discloses a "sandwich" structure MoS2 / graphene nanosheet catalyst and a preparation and application thereof. The catalyst has a "sandwich" nanosheet structure in which two-layer MoS2 layers and single-layer graphene layers sandwiched therebetween are stacked in parallel. In the catalyst, the interlayer spacing of MoS2 is larger than that of pure MoS2, the nanosheet size is smaller, and the stacking layer number is less, which is beneficial to fully expose the catalytic hydrogenation active sites of MoS2 edge sites. The catalyst preparation method comprises the following steps: dissolving ammonium tetrathiomolybdate, a reducing agent and a saccharide material in water, fully mixing to form a transparent solution; crystallizing h; and after solid-liquid separation, solid washing and drying of the obtained product, roasting, and cooling, the "sandwich" structure MoS2 / graphene nanosheet catalyst is obtained. The saccharide material used in the method is cheap and easy to obtain, and the synthesis condition is easy to control, so that large-scale industrial application can be realized. The "sandwich" structure MoS2 / graphene nanosheet catalyst of the application has excellent catalytic hydrogenation activity and stability in a polycyclic aromatic hydrocarbon catalytic hydrogenation reaction.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, and more particularly to a "sandwich" structured MoS2 / graphene nanosheet catalyst and its preparation and application. Technical Background

[0002] Against the backdrop of a global shift towards heavier crude oil supply, refineries need to convert heavy oil into high-value-added light products to meet growing energy demands. Slurry-bed hydrotreating is a crucial pathway for this conversion, and a key challenge lies in developing highly efficient hydrotreating catalysts. In slurry-bed heavy oil hydrotreating, molybdenum-based catalysts are widely used due to their high hydrotreating activity. (See J. Ind. Eng. Chem., 2019, 76, 1)

[0003] MoS2, found in natural molybdenite, is a typical two-dimensional layered nanomaterial. The layers of MoS2 are held together by relatively weak van der Waals forces. A single layer of MoS2 consists of two sulfur atoms sandwiching a molybdenum atom, with each molybdenum atom covalently bonded to six sulfur atoms. MoS2 exists in three crystalline phases: 1T, 2H, and 3R, with the 2H phase being the most stable. In this phase, the molybdenum atoms are triangular prisms with six-coordinate structures. Due to its unique layered structure and physicochemical properties, molybdenum disulfide has numerous applications in catalysis, energy storage, and semiconductor manufacturing. (See Chem. Soc. Rev., 2015, 44, 2603)

[0004] According to the rim-edge model of MoS2, only the edge sites (rim sites) of the top and bottom layers of MoS2 exhibit hydrogenation activity when used for catalytic hydrogenation reactions, while the edge sites (edge ​​sites) of the middle layers do not. (See J. Catal., 1994, 149, 414) MoS2 has a graphene-like layered structure. Bulk MoS2 typically has a large number of stacked layers and large sheet sizes, making it difficult to expose catalytic hydrogenation active sites. Therefore, those skilled in the art have developed many graphene-intercalated MoS2 composite materials to increase the exposure of catalytic hydrogenation active sites at the edges of MoS2 by expanding the interlayer spacing. CN202110069197.4 discloses a method for preparing and applying graphene-intercalated MoS2 composite materials. This method involves exfoliating MoS2 with n-butyllithium to obtain a MoS2 dispersion, then adding a cationic surfactant and a monolayer graphene oxide dispersion to the dispersion to allow the MoS2 and graphene oxide layers to adsorb onto each other. Finally, a reducing agent is used to reduce the graphene oxide, yielding the graphene-intercalated MoS2 composite material. CN201610699082.2 discloses a method for preparing monolayer 2H-phase MoS2 / graphene composite materials. This method involves first synthesizing lithium-intercalated 2H-phase molybdenum sulfide bulk material, then hydrolyzing and exfoliating it into 2H-phase monolayer MoS2 nanosheets, and finally self-assembling them with graphene oxide to form a monolayer MoS2 / graphene composite material. CN201710137998.3 discloses a single-layer metal structure molybdenum disulfide / redox graphene composite and its preparation method. The method involves adding a single-layer graphene oxide aqueous solution to a precursor solution for synthesizing MoS2, and obtaining the composite material on a glass substrate and a graphite electrode with the mixed solution inserted.

[0005] In the above-mentioned synthesis method of graphene-intercalated MoS2 composite material, it is necessary to first exfoliate MoS2 to form monolayer nanosheets, and then intercalate them with monolayer graphene; or it is necessary to add monolayer graphene dispersion to the precursor solution of MoS2, so that MoS2 grows on the graphene surface for composite. The problems with this method are that the required monolayer graphene is not easy to prepare, and the raw material cost of the finished product is high; the composite process is prone to graphene-graphene and MoS2-MoS2 self-packing processes, and the synthesis conditions are difficult to control; the synthesized MoS2 / graphene nanosheets have large structure size and many stacked layers. In terms of catalytic hydrogenation reaction, this structure is prone to agglomeration under high temperature and high pressure reaction conditions, and the structure is unstable, with limited exposure of MoS2 edge active sites. Summary of the Invention

[0006] To address the aforementioned problems, this invention employs a one-step solution method. Ammonium tetrathiomolybdate, a reducing agent, and sugars are mixed into a homogeneous solution. Under hydrothermal conditions, ammonium tetrathiomolybdate simultaneously acts as both a sulfur and molybdenum source, reacting to generate MoS2. The sugars then carbonize between the two MoS2 layers to form a single-layer graphene. The resulting "sandwich" structure of MoS2-graphene-MoS2 nanosheets can be uniformly crystallized and grown. The sugar raw materials used in this method are inexpensive and readily available, and the synthesis conditions are easily controlled. The co-crystallized "sandwich" structure MoS2 / graphene nanosheet catalyst is a nanostructure composed of two layers of MoS2 and a single layer of graphene, maintaining structural stability even under high temperature and high pressure conditions. Graphene intercalation increases the interlayer spacing of MoS2 and reduces the sheet size, fully exposing the edge active sites of MoS2.

[0007] To reduce the number of stacked layers and the size of the MoS2 sheets, while simultaneously increasing the interlayer spacing of MoS2 to fully expose the catalytic hydrogenation active sites of MoS2 and maintain structural stability under high temperature and high pressure conditions, this invention provides a "sandwich" structured MoS2 / graphene nanosheet catalyst. This catalyst has a "sandwich" nanosheet structure consisting of two parallel stacked MoS2 layers sandwiched between a single-layer graphene sheet. In this structure, the interlayer spacing between the two MoS2 sheets on either side of the graphene sheet is 1.0–1.1 nm, the thickness of the single MoS2 sheet is 0.65–0.67 nm, the thickness of the single graphene sheet is 0.34–0.36 nm, and the distance between the two furthest points on any side of the MoS2-graphene-MoS2 composite nanosheet is 5–10 nm. Compared to pure MoS2, this catalyst has a larger interlayer spacing, smaller nanosheet size, and fewer stacked layers, which is beneficial for fully exposing the catalytic hydrogenation active sites at the MoS2 edges. The graphene between the two MoS2 layers can maintain the structural stability of the catalyst under high temperature and high pressure conditions, and avoid the agglomeration and accumulation of MoS2 under high temperature and high pressure conditions, which would reduce the exposure of the catalytic hydrogenation active sites at the edge.

[0008] This invention also provides a method for preparing a "sandwich" structured MoS2 / graphene nanosheet catalyst, comprising the following steps:

[0009] (1) Dissolve ammonium tetrathiomolybdate, a reducing agent, and a sugar in deionized water and mix thoroughly to form a uniform transparent solution. Crystallize the solution at 120–220°C for 3–72 h, preferably at 180–210°C for 12–24 h. The reducing agent is one or more of hydrazine hydrate, hydroxylamine hydrochloride, oxalic acid, sodium borohydride, and potassium borohydride. The sugar is one or more of dextrin, water-soluble starch, and soluble starch. The C:Mo molar ratio of the sugar to ammonium tetrathiomolybdate is 1–30, preferably 5–15. The molar ratio of the reducing agent to Mo is 5–10, preferably 6–8. The concentration of ammonium tetrathiomolybdate in water is in the range of 0.02 mmol / L to 0.15 mmol / L, preferably 0.05 mmol / L to 0.10 mmol / L.

[0010] (2) The above reaction products are separated by one of centrifugation, filtration, vacuum filtration, or sedimentation, washed, and dried to obtain a black product;

[0011] (3) The black product obtained in step (2) is calcined in nitrogen, argon or helium at 350-800°C for 1-24 hours, preferably at 500-600°C for 4-8 hours, to obtain a "sandwich" structured MoS2 / graphene nanosheet catalyst.

[0012] The crystallization reaction in step (1) is carried out in a hydrothermal reactor, a microwave reactor, or a round-bottom flask in an oil bath.

[0013] The "sandwich" structured MoS2 / graphene nanosheet catalyst prepared by the above method is used for the catalytic hydrogenation reaction of polycyclic aromatic hydrocarbons. The model compound for evaluating the hydrogenation reaction activity is one of naphthalene, anthracene, and phenanthrene. The content of the catalyst in the reaction system is 0.01 wt.% to 0.3 wt.% (calculated as MoS2), preferably 0.1 wt.% to 0.2 wt.%. The reaction temperature is 300 to 500 °C, preferably 350 to 450 °C. The initial hydrogen pressure is 6 to 18 MPa, preferably 8 to 14 MPa.

[0014] Compared to pure MoS2, the MoS2 in this catalyst has a larger interlayer spacing, smaller nanosheet size, and fewer stacked layers, which is beneficial for fully exposing the catalytic hydrogenation active sites at the MoS2 edge. The sugar raw materials used in the catalyst preparation method are inexpensive and readily available, and the synthesis conditions are easy to control, enabling large-scale industrial applications. The "sandwich" structured MoS2 / graphene nanosheet catalyst of this invention exhibits excellent catalytic hydrogenation activity and stability in the catalytic hydrogenation reaction of polycyclic aromatic hydrocarbons.

[0015] The "sandwich" structure MoS2 / graphene nanosheet catalyst of this invention has a nanostructure composed of two parallel stacked MoS2 layers sandwiched between a single-layer graphene sheet. The graphene crystallizes and grows between the MoS2 layers, reducing the number of stacked MoS2 layers and the sheet size while increasing the interlayer spacing, thus fully exposing the catalytic hydrogenation active sites at the MoS2 edges. The graphene between the two MoS2 layers helps stabilize the catalyst structure, preventing the aggregation and stacking of MoS2 under high temperature and high pressure reaction conditions, which would reduce the exposure of the catalytic hydrogenation active sites at the edges. The sugar raw materials used in this method are inexpensive and readily available, and the synthesis conditions are easy to control, enabling large-scale industrial applications.

[0016] The structural characterization and analysis of the "sandwich" structure MoS2 / graphene nanosheet catalyst prepared in this invention are as follows: Figure 1 As shown, compared with the 2H-MoS2 standard card, both the MoS2 synthesized under the same conditions in the comparative example and the MoS2 / graphene nanosheet catalyst with the "sandwich" structure of this invention are 2H-MoS2 phases. However, the (002) crystal plane diffraction peak of MoS2 in the catalyst of this invention disappears, indicating that MoS2 is a single-layer or few-layer structure with small nanosheet size. Meanwhile, the XRD pattern of the catalyst of this invention shows two new diffraction peaks at 8.1° and 16.1°. Calculations based on the Bragg equation show that their interplanar spacings are 1.1 nm and 0.55 nm, respectively, which can be attributed to the interlayer spacing between the two MoS2 layers on both sides of the graphene and the interlayer spacing between the graphene and one side of the MoS2 layer. Figure 2 HRTEM images show that the "sandwich" structure of MoS2-graphene-MoS2 nanosheets is a composite nanostructure consisting of two layers of MoS2 and a single layer of graphene. The interlayer spacing between the two MoS2 layers on both sides of the graphene is 1.1 nm, and the distance between the two furthest points on any side of the composite nanosheet is 5.1–7.4 nm, which is conducive to fully exposing the edge active sites of MoS2. The thickness of the single-layer graphene sheet is 0.36 nm. Figure 3HRTEM images show that the interlayer spacing of MoS2 in the comparative example 1 nanosheet is 0.65 nm, the distance between any two points in the nanosheet plane is 20–50 nm, and the number of MoS2 stacked layers is more than 10. Compared with existing technologies, this invention has the following advantages and effects: Existing methods for synthesizing graphene-intercalated MoS2 composite materials often involve first exfoliating MoS2 to obtain monolayer nanosheets and then intercalating them with monolayer graphene, or adding a monolayer graphene dispersion to a MoS2 precursor solution to allow MoS2 to grow on the graphene surface for composite formation. This method directly mixes the graphene precursor and the MoS2 precursor to form a solution, allowing MoS2 / nanosheets to grow in situ. Regarding the synthesis method, the graphene precursor used in this invention is a carbohydrate, resulting in lower raw material costs; this invention directly and uniformly mixes the graphene precursor and the MoS2 precursor solution and then crystallizes them, making the synthesis process simpler and the conditions easier to control. In terms of material structure, the MoS2 / graphene nanosheets grown by uniform crystallization in this invention have smaller size, fewer stacked layers, and more stable structure.

[0017] This invention provides a "sandwich" structured MoS2 / graphene nanosheet catalyst, which has a nanostructure composed of two layers of MoS2 and a single layer of graphene sandwiched between them. Compared with pure MoS2, the interlayer spacing of MoS2 in this catalyst is increased from 0.65 nm to 1.1 nm, and the distance between any two points in the nanosheet plane is reduced from 20-50 nm to 5-10 nm. This structure is beneficial for fully exposing the edge active sites of MoS2. The graphene sandwiched between the two MoS2 layers helps maintain the stability of the catalyst structure and avoids the aggregation and accumulation of MoS2 under high temperature and high pressure reaction conditions, which would reduce the exposure of the edge catalytic hydrogenation active sites.

[0018] The catalyst preparation method provided by this invention involves mixing ammonium tetrathiomolybdate, a reducing agent, and sugars into a homogeneous solution. Under hydrothermal conditions, ammonium tetrathiomolybdate simultaneously acts as both a sulfur and molybdenum source to react and generate MoS2. The sugars then carbonize between two MoS2 layers to form a single layer of graphene. The resulting "sandwich" structure of MoS2-graphene-MoS2 nanosheets can be uniformly crystallized and grown. The sugar raw materials used in this method are inexpensive and readily available, and the synthesis conditions are easy to control, enabling large-scale industrial applications. Attached Figure Description

[0019] Figure 1 The XRD pattern of the "sandwich" structure MoS2 / graphene nanosheet catalyst in Example 1;

[0020] Figure 2 HRTEM image of the "sandwich" structured MoS2 / graphene nanosheet catalyst from Example 1;

[0021] Figure 3The image shows an HRTEM image of a comparative 1MoS2 nanocatalyst. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments:

[0023] Example 1

[0024] Weigh 1.626g of ammonium tetrathiomolybdate, 1.56g of hydrazine hydrate and 5.05g of dextrin and dissolve them in 60mL of deionized water. Mix thoroughly to form a uniform red transparent solution. Crystallize the solution in a hydrothermal reactor at 200℃ for 12h.

[0025] The reaction product was centrifuged, washed three times with deionized water, and then dried in a vacuum oven at 60°C for 24 hours to obtain a black product. The obtained black product was calcined at 600°C for 2 hours under a nitrogen atmosphere to obtain a "sandwich" structured MoS2 / graphene nanosheet catalyst. Figure 1 The XRD pattern shows that the interlayer spacing between the two MoS2 layers is 1.1 nm; according to Figure 2 The HRTEM image shows that the thickness of the monolayer MoS2 is 0.65 nm, the thickness of the monolayer graphene is 0.36 nm, and the distance between the two furthest points on any side surface of the nanosheet is 5.1–7.4 nm.

[0026] The "sandwich" structured MoS2 / graphene nanosheet catalyst prepared by the above method was used for the catalytic hydrogenation of polycyclic aromatic hydrocarbons, and its catalytic hydrogenation activity was evaluated using naphthalene, anthracene and phenanthrene as model compounds.

[0027] 1) The amount of naphthalene used as reactant is 2g, the amount of n-heptane used as solvent is 30g, the catalyst content in the reaction system is 0.01wt.% (calculated as MoS2) relative to the solvent n-heptane, and the reaction is carried out for 4h at a reaction temperature of 300℃ and an initial hydrogen pressure of 6MPa.

[0028] 2) The amount of anthracene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.1wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 400℃ and an initial hydrogen pressure of 8MPa for 4h.

[0029] 3) The amount of phenanthrene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.3wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 500℃ and an initial hydrogen pressure of 8MPa for 4h.

[0030] After the reaction was completed and cooled to room temperature, the liquid sample in the reactor was taken for chromatographic analysis. The results of the catalytic activity evaluation are shown in Table 1.

[0031] Example 2

[0032] 1.626 g of ammonium tetrathiomolybdate, 1.51 g of sodium borohydride, and 1.69 g of dextrin were weighed and dissolved in 60 mL of deionized water. The mixture was thoroughly mixed to form a homogeneous, transparent red solution. The solution was transferred to a polytetrafluoroethylene (PTFE) liner and crystallized in a microwave reactor at 220 °C for 3 h. The reaction product was filtered and separated, washed three times with deionized water, and then dried in a vacuum oven at 60 °C for 6 h to obtain a black product. The obtained black product was calcined at 350 °C for 24 h in an argon atmosphere to obtain a "sandwich" structured MoS2 / graphene nanosheet catalyst. XRD and HRTEM analyses showed that its structure was identical to that of the product in Example 1, except that the interlayer spacing between the two MoS2 layers was 1.1 nm, the thickness of a single MoS2 layer was 0.65 nm, the thickness of a single graphene layer was 0.36 nm, and the distance between the two furthest points on any side of the nanosheet surface was 7.8–9.2 nm.

[0033] The "sandwich" structured MoS2 / graphene nanosheet catalyst prepared by the above method was used for the catalytic hydrogenation of polycyclic aromatic hydrocarbons, and its catalytic hydrogenation activity was evaluated using naphthalene, anthracene and phenanthrene as model compounds.

[0034] 1) The amount of naphthalene used as reactant is 2g, the amount of n-heptane used as solvent is 30g, the catalyst content in the reaction system is 0.01wt.% (calculated as MoS2) relative to the solvent n-heptane, and the reaction is carried out for 4h at a reaction temperature of 300℃ and an initial hydrogen pressure of 6MPa.

[0035] 2) The amount of anthracene reactant is 3g, the amount of tridecane solvent is 30g, and the amount of MoS2 is 0.1wt.% (calculated as MoS2) of catalyst content relative to tridecane solvent in the reaction system. The reaction is carried out at a reaction temperature of 400℃ and an initial hydrogen pressure of 8MPa for 4h.

[0036] 3) The amount of phenanthrene reactant is 3g, the amount of tridecane solvent is 30g, and the amount of MoS2 is 0.3wt.% (calculated as MoS2) of catalyst content relative to tridecane solvent in the reaction system. The reaction is carried out at a reaction temperature of 500℃ and an initial hydrogen pressure of 8MPa for 4h.

[0037] After the reaction was completed and cooled to room temperature, the liquid sample in the reactor was taken for chromatographic analysis. The results of the catalytic activity evaluation are shown in Table 1.

[0038] Example 3

[0039] 1.626 g of ammonium tetrathiomolybdate, 2.15 g of potassium borohydride, and 5.05 g of water-soluble starch were weighed and dissolved in 60 mL of deionized water. The mixture was thoroughly mixed to form a homogeneous, transparent red solution. The solution was transferred to a polytetrafluoroethylene (PTFE) liner and crystallized in a microwave reactor at 220 °C for 3 h. The reaction product was filtered and separated, washed three times with deionized water, and then dried in a vacuum oven at 60 °C for 6 h to obtain a black product. The obtained black product was calcined at 600 °C for 2 h in a helium atmosphere to obtain a "sandwich" structured MoS2 / graphene nanosheet catalyst. XRD and HRTEM analyses showed that its structure was identical to that of the product in Example 1, except that the interlayer spacing between the two MoS2 layers was 1.1 nm, the thickness of a single MoS2 layer was 0.66 nm, the thickness of a single graphene layer was 0.36 nm, and the distance between the two furthest points on any side of the nanosheet surface was 6.1–9.5 nm.

[0040] The "sandwich" structured MoS2 / graphene nanosheet catalyst prepared by the above method was used for the catalytic hydrogenation of polycyclic aromatic hydrocarbons, and its catalytic hydrogenation activity was evaluated using naphthalene, anthracene and phenanthrene as model compounds.

[0041] 1) The amount of naphthalene used as reactant is 2g, the amount of n-heptane used as solvent is 30g, the catalyst content in the reaction system is 0.01wt.% (calculated as MoS2) relative to the solvent n-heptane, and the reaction is carried out for 4h at a reaction temperature of 300℃ and an initial hydrogen pressure of 6MPa.

[0042] 2) The amount of anthracene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.1wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 400℃ and an initial hydrogen pressure of 8MPa for 4h.

[0043] 3) The amount of phenanthrene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.3wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 500℃ and an initial hydrogen pressure of 8MPa for 4h.

[0044] After the reaction was completed and cooled to room temperature, the liquid sample in the reactor was taken for chromatographic analysis. The results of the catalytic activity evaluation are shown in Table 1.

[0045] Example 4

[0046] 1.626 g of ammonium tetrathiomolybdate, 3.13 g of hydrazine hydrate, and 0.177 g of water-soluble starch were weighed and dissolved in 60 mL of deionized water. The mixture was thoroughly mixed to form a homogeneous, transparent red solution. The solution was then crystallized in a hydrothermal reactor at 180 °C for 36 h. The reaction product was separated by sedimentation, washed three times with deionized water, and then dried in a vacuum oven at 60 °C for 24 h to obtain a black product. The obtained black product was calcined at 600 °C for 1 h under a nitrogen atmosphere to obtain a "sandwich" structured MoS2 / graphene nanosheet catalyst. XRD and HRTEM analyses showed that its structure was identical to that of the product in Example 1, except that the interlayer spacing between the two MoS2 layers was 1.1 nm, the thickness of a single MoS2 layer was 0.65 nm, the thickness of a single graphene layer was 0.35 nm, and the distance between the two furthest points on any side of the nanosheet surface was 5.5–7.8 nm.

[0047] The "sandwich" structured MoS2 / graphene nanosheet catalyst prepared by the above method was used for the catalytic hydrogenation of polycyclic aromatic hydrocarbons, and its catalytic hydrogenation activity was evaluated using naphthalene, anthracene and phenanthrene as model compounds.

[0048] 1) The amount of naphthalene used as reactant is 2g, the amount of n-heptane used as solvent is 30g, the catalyst content in the reaction system is 0.01wt.% (calculated as MoS2) relative to the solvent n-heptane, and the reaction is carried out for 4h at a reaction temperature of 300℃ and an initial hydrogen pressure of 6MPa.

[0049] 2) The amount of anthracene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.1wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 400℃ and an initial hydrogen pressure of 8MPa for 4h.

[0050] 3) The amount of phenanthrene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.3wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 500℃ and an initial hydrogen pressure of 8MPa for 4h.

[0051] After the reaction was completed and cooled to room temperature, the liquid sample in the reactor was taken for chromatographic analysis. The results of the catalytic activity evaluation are shown in Table 1.

[0052] Example 5

[0053] 1.626 g of ammonium tetrathiomolybdate, 3.60 g of oxalic acid, and 1.8 g of soluble starch were weighed and dissolved in 60 mL of deionized water. The mixture was thoroughly mixed to form a homogeneous, transparent red solution. The solution was transferred to a round-bottom flask heated in an oil bath and crystallized at 160 °C for 48 h. The reaction product was filtered and separated, washed three times with deionized water, and then dried in a vacuum oven at 60 °C for 72 h to obtain a black product. The obtained black product was calcined at 700 °C for 4 h in an argon atmosphere to obtain a "sandwich" structured MoS2 / graphene nanosheet catalyst. XRD and HRTEM analysis showed that its structure was identical to that of the product in Example 1, except that the interlayer spacing between the two MoS2 layers was 1.1 nm, the thickness of a single MoS2 layer was 0.67 nm, the thickness of a single graphene layer was 0.34 nm, and the distance between the two furthest points on any side of the nanosheet surface was 6.1–8.8 nm.

[0054] The "sandwich" structured MoS2 / graphene nanosheet catalyst prepared by the above method was used for the catalytic hydrogenation of polycyclic aromatic hydrocarbons, and its catalytic hydrogenation activity was evaluated using naphthalene, anthracene and phenanthrene as model compounds.

[0055] 1) The amount of naphthalene used as reactant is 2g, the amount of n-heptane used as solvent is 30g, the catalyst content in the reaction system is 0.01wt.% (calculated as MoS2) relative to the solvent n-heptane, and the reaction is carried out for 4h at a reaction temperature of 300℃ and an initial hydrogen pressure of 6MPa.

[0056] 2) The amount of anthracene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.1wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 400℃ and an initial hydrogen pressure of 8MPa for 4h.

[0057] 3) The amount of phenanthrene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.3wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 500℃ and an initial hydrogen pressure of 8MPa for 4h.

[0058] After the reaction was completed and cooled to room temperature, the liquid sample in the reactor was taken for chromatographic analysis. The results of the catalytic activity evaluation are shown in Table 1.

[0059] Example 6

[0060] 1.626 g of ammonium tetrathiomolybdate, 2.78 g of hydroxylamine hydrochloride, and 5 g of soluble starch were weighed and dissolved in 60 mL of deionized water. The mixture was thoroughly mixed to form a homogeneous, transparent red solution. The solution was then crystallized in a microwave reactor at 120 °C for 72 h. The reaction product was filtered and separated, washed three times with deionized water, and then dried in a vacuum oven at 60 °C for 24 h to obtain a black product. The obtained black product was calcined at 800 °C for 2 h under a nitrogen atmosphere to obtain a "sandwich" structured MoS2 / graphene nanosheet catalyst. XRD and HRTEM analysis showed that its structure was identical to that of the product in Example 1, except that the interlayer spacing between the two MoS2 layers was 1.1 nm, the thickness of a single MoS2 layer was 0.65 nm, the thickness of a single graphene layer was 0.36 nm, and the distance between the two furthest points on any side of the nanosheet surface was 7.2–9.9 nm.

[0061] The "sandwich" structured MoS2 / graphene nanosheet catalyst prepared by the above method was used for the catalytic hydrogenation of polycyclic aromatic hydrocarbons, and its catalytic hydrogenation activity was evaluated using naphthalene, anthracene and phenanthrene as model compounds.

[0062] 1) The amount of naphthalene used as reactant is 2g, the amount of n-heptane used as solvent is 30g, the catalyst content in the reaction system is 0.01wt.% (calculated as MoS2) relative to the solvent n-heptane, and the reaction is carried out for 4h at a reaction temperature of 300℃ and an initial hydrogen pressure of 6MPa.

[0063] 2) The amount of anthracene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.1wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 400℃ and an initial hydrogen pressure of 8MPa for 4h.

[0064] 3) The amount of phenanthrene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.3wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 500℃ and an initial hydrogen pressure of 8MPa for 4h.

[0065] After the reaction was completed and cooled to room temperature, the liquid sample in the reactor was taken for chromatographic analysis. The results of the catalytic activity evaluation are shown in Table 1.

[0066] Comparative Example 1

[0067] 1.626 g of ammonium tetrathiomolybdate and 1.56 g of hydrazine hydrate were weighed and dissolved in 60 mL of deionized water, and thoroughly mixed to form a homogeneous, transparent red solution. The solution was then crystallized in a hydrothermal reactor at 200 °C for 24 h. The reaction product was filtered and separated, washed three times with deionized water, and then dried in a vacuum oven at 60 °C for 24 h to obtain a black product. The obtained black product was calcined at 600 °C for 2 h under a nitrogen atmosphere to obtain a MoS2 nanosheet catalyst. Figure 1 The XRD pattern analysis showed that the interlayer spacing between the two MoS2 layers was 0.65 nm. Figure 3 HRTEM images show that the distance between the two furthest points on any side of the MoS2 nanosheet is 20–50 nm, and the number of stacked layers is more than 10.

[0068] The MoS2 catalyst prepared by the above method was used for the catalytic hydrogenation of polycyclic aromatic hydrocarbons, and its catalytic hydrogenation activity was evaluated using naphthalene, anthracene and phenanthrene as model compounds.

[0069] 1) The amount of naphthalene used as reactant is 2g, the amount of n-heptane used as solvent is 30g, the catalyst content in the reaction system is 0.01wt.% (calculated as MoS2) relative to the solvent n-heptane, and the reaction is carried out for 4h at a reaction temperature of 300℃ and an initial hydrogen pressure of 6MPa.

[0070] 2) The amount of anthracene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.1wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 400℃ and an initial hydrogen pressure of 8MPa for 4h.

[0071] 3) The amount of phenanthrene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.3wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 500℃ and an initial hydrogen pressure of 8MPa for 4h.

[0072] After the reaction was completed and cooled to room temperature, the liquid sample in the reactor was taken for chromatographic analysis. The results of the catalytic activity evaluation are shown in Table 1.

[0073] Comparative Example 2

[0074] 1.626 g of ammonium tetrathiomolybdate and 1.56 g of hydrazine hydrate were weighed and dissolved in 60 mL of deionized water, and thoroughly mixed to form a homogeneous, transparent red solution. Then, 500 mg of graphene oxide was added to the solution and ultrasonically dispersed for 1 h. The mixture was transferred to a hydrothermal reactor and crystallized at 200 °C for 24 h. The reaction product was filtered and separated, washed three times with deionized water, and then dried in a vacuum oven at 60 °C for 24 h to obtain a black product. The obtained black product was calcined at 600 °C for 2 h under a nitrogen atmosphere to obtain a supported MoS2 / rGO nanosheet catalyst. In its structure, MoS2 is uniformly dispersed and supported on the surface of the rGO support, and the MoS2 is in the form of micron-sized rolled-up sheets.

[0075] The MoS2 catalyst prepared by the above method was used for the catalytic hydrogenation of polycyclic aromatic hydrocarbons, and its catalytic hydrogenation activity was evaluated using naphthalene, anthracene and phenanthrene as model compounds.

[0076] 1) The amount of naphthalene used as reactant is 2g, the amount of n-heptane used as solvent is 30g, the catalyst content in the reaction system is 0.01wt.% (calculated as MoS2) relative to the solvent n-heptane, and the reaction is carried out for 4h at a reaction temperature of 300℃ and an initial hydrogen pressure of 6MPa.

[0077] 2) The amount of anthracene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.1wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 400℃ and an initial hydrogen pressure of 8MPa for 4h.

[0078] 3) The amount of phenanthrene reactant is 3g, the amount of tridecane solvent is 30g, the catalyst content in the reaction system is 0.3wt.% (calculated as MoS2) relative to the solvent tridecane, and the reaction is carried out at a reaction temperature of 500℃ and an initial hydrogen pressure of 8MPa for 4h.

[0079] After the reaction was completed and cooled to room temperature, the liquid sample in the reactor was taken for chromatographic analysis. The results of the catalytic activity evaluation are shown in Table 1.

[0080] Table 1 Catalytic hydrogenation activity of the catalyst prepared in this invention and the comparative catalyst.

[0081]

[0082] The products of hydrogenation of naphthalene (NH) include tetrahydronaphthalene (NH4) and decahydronaphthalene (NH10), as well as trace amounts of other hydrocracking products.

[0083]

[0084] The conversion rate of naphthalene hydrogenation, Conv. (%) = ([NH]0 - [NH]) / [NH]0 × 100% ([NH]0 is the molar amount of naphthalene before the reaction, and [NH] is the molar amount of naphthalene after the reaction);

[0085] Product selectivity S NHX = [NHX] / ([NH4]+[NH10]+[others])×100% (NHX represents NH4 or NH10);

[0086] Hydrogenation rate HP (%) = (4S) NH4 +10S NH10 ) / 10×Conv.

[0087] The products of anthracene (AH) hydrogenation include dihydroanthracene (AH2), tetrahydroanthracene (AH4), octahydroanthracene (AH8), and perhydroanthracene (AH14), as well as trace amounts of other hydrocracking products.

[0088]

[0089] The conversion rate of anthracene hydrogenation, Conv. (%) = ([AH]0 - [AH]) / [AH]0 × 100% ([AH]0 is the molar amount of anthracene before the reaction, and [AH] is the molar amount of anthracene after the reaction);

[0090] Product selectivity S AHX = [AHX] / ([AH2]+[AH4]+[AH8]+[AH14]+[others])×100% (AHX represents AH2, AH4, AH8 or AH14);

[0091] Hydrogenation rate HP (%) = (2S) AH2 +4S AH4 +8S AH8 +14S AH14 ) / 14×Conv.

[0092] The products of phenanthrene (PH) hydrogenation include dihydrophenanthrene (PH2), tetrahydrophenanthrene (PH4), octahydrophenanthrene (PH8), and perhydrophenanthrene (PH14), as well as trace amounts of other hydrocracking products.

[0093]

[0094] The conversion rate of phenanthrene hydrogenation, Conv. (%) = ([PH]0 - [PH]) / [PH]0 × 100% ([PH]0 is the molar amount of phenanthrene before the reaction, and [PH] is the molar amount of phenanthrene after the reaction);

[0095] Product selectivity S PHX= [PHX] / ([PH2]+[PH4]+[PH8]+[PH14]+[others])×100% (PHX represents PH2, PH4, PH8 or PH14);

[0096] Hydrogenation rate HP (%) = (2S) PH2 +4S PH4 +8S PH8 +14S PH14 ) / 14×Conv.

[0097] The method utilizes inexpensive and readily available sugar raw materials, and the synthesis conditions are easy to control, enabling large-scale industrial applications. The "sandwich" structured MoS2 / graphene nanosheet catalyst of this invention exhibits excellent catalytic hydrogenation activity and stability in the catalytic hydrogenation reaction of polycyclic aromatic hydrocarbons.

Claims

1. A method for preparing a "sandwich" structured MoS2 / graphene nanosheet catalyst, characterized in that, The catalyst has a "sandwich" nanosheet structure in which two sheet-like MoS2 layers and a single-layer graphene sheet sandwiched between them are stacked in parallel. In this structure, the interlayer spacing between the two MoS2 sheets on both sides of the sheet-like graphene is 1.0~1.1 nm, the thickness of the single-layer MoS2 sheet is 0.65~0.67 nm, the thickness of the single-layer graphene sheet is 0.34~0.36 nm, and the distance between the two furthest points on any side surface of the MoS2-graphene-MoS2 composite nanosheet is 5~10 nm. Includes the following steps: 1) Dissolve ammonium tetrathiomolybdate, reducing agent and sugar in water, mix thoroughly to form a uniform transparent solution, and then crystallize the solution; 2) The above reaction product is separated into solid and liquid phases, the solid is washed and dried to obtain the product; 3) The product obtained in step (2) was calcined in an inert atmosphere and cooled to obtain a "sandwich" structured MoS2 / graphene nanosheet catalyst. The crystallization temperature in step (1) is 120~220℃; The crystallization time in step (1) is 3~72h; In step (3), the roasting temperature is 350~800℃ and the roasting time is 1~24 h; In step (1), the C:Mo molar ratio in the sugar and ammonium tetrathiomolybdate precursor in the mixed solution is 5-15; the molar ratio of reducing agent to Mo is 6-8. The concentration range of ammonium tetrathiomolybdate in water is 0.05 mmol / L to 0.10 mmol / L.

2. The preparation method according to claim 1, characterized in that, The carbohydrate substance mentioned in step (1) is one or more of dextrin, water-soluble starch, and soluble starch; The reducing agent is one or more of hydrazine hydrate, hydroxylamine hydrochloride, oxalic acid, sodium borohydride, and potassium borohydride.

3. The preparation method according to claim 1, characterized in that, The crystallization temperature in step (1) is 180~210℃.

4. The preparation method according to claim 1, characterized in that, The crystallization time in step (1) is 12~24h.

5. The preparation method according to claim 1, characterized in that, The separation method in step (2) is one or more of centrifugation, filtration, vacuum filtration or sedimentation.

6. The preparation method according to claim 1, characterized in that, The inert atmosphere gas in step (3) is one or more of nitrogen, argon, and helium, and the calcination temperature is 500~600℃; the calcination time is 4~8h.

7. The application of the "sandwich" structured MoS2 / graphene nanosheet catalyst prepared by the method of claim 1 in the catalytic hydrogenation reaction of polycyclic aromatic hydrocarbons.

8. The application according to claim 7, characterized in that: The catalyst can be used for the catalytic hydrogenation of polycyclic aromatic hydrocarbons; The polycyclic aromatic hydrocarbons undergoing hydrogenation are one or more of naphthalene, anthracene, and phenanthrene. The catalyst content in the reaction system, calculated as MoS2, is 0.01 wt.%~0.3 wt.%. The reaction temperature is 300~500℃; the initial hydrogen pressure is 6~18MPa.

9. The application according to claim 8, characterized in that: The catalyst content in the reaction system, calculated as MoS2, is 0.1 wt.%~0.2 wt.%; the reaction temperature is 350~450℃; and the initial hydrogen pressure is 8~14 MPa.

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