Ruthenium modified mesoporous molecular sieve based catalyst and preparation method and application thereof

Abstract

The invention discloses a ruthenium-modified mesoporous molecular sieve-based catalyst and a preparation method and application thereof, and belongs to the technical field of polyethylene cracking catalysts.The ruthenium-modified mesoporous molecular sieve is used as a matrix, a silanol group of the ruthenium-modified mesoporous molecular sieve is replaced with Al atoms, the Al atoms are grafted to the ruthenium-modified mesoporous molecular sieve, and the ruthenium-modified mesoporous molecular sieve-based catalyst is obtained. And introducing an acidic site to the surface of the ruthenium-modified mesoporous molecular sieve to obtain the ruthenium-modified mesoporous molecular sieve-based catalyst. Al is introduced into the ruthenium-modified mesoporous molecular sieve through a post-grafting method, so that an acidic site is introduced, the catalytic reaction efficiency of the catalyst is effectively improved through introduction of the acidic site, the catalytic reaction time is shortened, and distribution of a catalytic product is improved through a mesoporous channel of the mesoporous molecular sieve. The catalytic reaction efficiency is further improved through the synergistic effect of metal ruthenium and acid sites.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene hydrocracking catalysts, and in particular to a ruthenium-modified mesoporous molecular sieve-based catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Plastics are widely used in daily life, but they have serious problems such as large production scale, low recycling rate, slow natural degradation rate, and great harm to the human body. How to efficiently recycle and reuse waste plastics is of great significance to environmental governance and human health.

[0003] Polyethylene (PE) accounts for a significant portion of waste plastics. Yosuke Nakaji et al. directly loaded Ru onto CeO2 for direct hydrogenolysis, demonstrating superior activity compared to other metal-supported catalysts in the hydrogenolysis of low-density polyethylene (LDPE). Kang et al. used a precise impregnation method to uniformly distribute Ru nanoparticles within the channels of an SBA-15 support, achieving significant improvements in the catalytic performance of polyethylene for conversion to high-value liquid fuels, particularly diesel. However, the resulting Ru nanoparticle-loaded SBA-15 catalyst exhibited low catalytic efficiency and a tendency to undergo methanation during polyethylene cracking. Summary of the Invention

[0004] The present invention provides a ruthenium-modified mesoporous molecular sieve-based catalyst, a preparation method and an application thereof, which effectively solve the technical problems of low catalytic reaction efficiency, poor product selectivity and easy methanation of existing polyethylene hydrocracking catalysts. The present invention introduces Al into the ruthenium-modified mesoporous molecular sieve by a grafting method, thereby introducing acidic sites, improving the catalytic reaction efficiency of the ruthenium-modified mesoporous molecular sieve, thereby shortening the catalytic reaction time, and simultaneously solving the problem of easy methanation in polyethylene hydrocracking caused by using ruthenium-modified mesoporous molecular sieve as a catalyst.

[0005] The first object of the present invention is to provide a method for preparing a ruthenium-modified mesoporous molecular sieve-based catalyst, comprising the following steps: Preparation of ruthenium-modified mesoporous molecular sieves.

[0006] The ruthenium modified mesoporous molecular sieve is used as a matrix and added to the soluble Al 3+ An alcohol solution of a salt is stirred for reaction at room temperature, and then filtered and dried to obtain a precursor. The precursor is calcined, and the silanol groups of the ruthenium-modified mesoporous molecular sieve are replaced with Al atoms. The Al atoms are grafted onto the ruthenium-modified mesoporous molecular sieve to obtain a ruthenium-modified mesoporous molecular sieve-based catalyst.

[0007] As a preferred embodiment, in the ruthenium-modified mesoporous molecular sieve-based catalyst, the molar ratio of Si to Al is 5 to 30:1.

[0008] As a preferred embodiment, the precursor is calcined at 500 °C to 550 °C for 5 h to 6 h.

[0009] As a preferred embodiment, the mesoporous molecular sieve is SBA-15.

[0010] As a preferred embodiment, the ruthenium-modified mesoporous molecular sieve and soluble Al 3+ The dosage ratio of the salt is 0.5 g: 0.3 mmol to 1.65 mmol.

[0011] As a preferred embodiment, the preparation method of the ruthenium-modified mesoporous molecular sieve comprises the following steps: Adding a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer to an aqueous hydrochloric acid solution, dissolving at 35 °C to 45 °C, and then adding tetraethyl orthosilicate to obtain a promoter; Mixing 3-mercaptopropyltrimethoxysilane, NaOH and water, and then adding soluble Ru 3+ salt to obtain a reaction solution.

[0012] Adding the reaction solution to the promoter, stirring and then standing, crystallizing at 100 °C to obtain a primary product, and calcining the primary product at 500 °C to 550 °C for 5 h to 6 h to obtain a ruthenium-modified mesoporous molecular sieve.

[0013] As a preferred embodiment, the mass ratio of sodium hydroxide, 3-mercaptopropyltrimethoxysilane and water is 1: 1 to 1.5: 10 to 50; the dosage ratio of 3-mercaptopropyltrimethoxysilane to the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer is 1: 33.3 to 50.

[0014] As a preferred embodiment, the mass ratio of 3-mercaptopropyltrimethoxysilane to soluble Ru 3+ salt is 1: 0.5 to 2.

[0015] As a preferred embodiment, cetyltrimethylammonium bromide is further added to the promoter, and the mass ratio of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer to cetyltrimethylammonium bromide is 5: 0.8 to 1.

[0016] The second object of the present invention is to provide a ruthenium-modified mesoporous molecular sieve-based catalyst prepared by the above preparation method.

[0017] The third object of the present invention is to provide an application of the above ruthenium-modified mesoporous molecular sieve-based catalyst in the catalytic hydrocracking of polyethylene.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a method for preparing a ruthenium-modified mesoporous molecular sieve-based catalyst. First, a ruthenium-modified mesoporous molecular sieve is prepared. Then, taking the ruthenium-modified mesoporous molecular sieve as the matrix, silicon hydroxyl groups of the ruthenium-modified mesoporous molecular sieve are replaced by Al atoms, and the Al atoms are grafted onto the ruthenium-modified mesoporous molecular sieve, thereby introducing acidic sites on the surface of the ruthenium-modified mesoporous molecular sieve to obtain a ruthenium-modified mesoporous molecular sieve-based catalyst. Based on the fact that mesoporous molecular sieves have a large specific surface area, pore volume, regular and ordered pore structure, and adjustable pore diameter, but lack acid sites, the present invention introduces Al into the ruthenium-modified mesoporous molecular sieve by a post-grafting method, thereby introducing acidic sites. The introduction of these acidic sites effectively improves the catalytic reaction efficiency of the catalyst, thereby shortening the catalytic reaction time, and improves the distribution of catalytic products through the mesoporous channels of the mesoporous molecular sieve. The present invention further improves the catalytic reaction efficiency through the synergistic effect of metal ruthenium and acidic sites.

[0019] The present invention synthesized three ruthenium-modified mesoporous molecular sieves with different morphologies. When the water bath temperature is controlled at 35 °C, the ruthenium-modified mesoporous molecular sieve will form columns; adding cetyltrimethylammonium bromide, i.e., CTAB, during the synthesis will promote the formation of spherical ruthenium-modified mesoporous molecular sieves. Description of the Drawings

[0020] Figure 1 SEM image of the spherical ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 1 of the present invention.

[0021] Figure 2 BET image of the spherical ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 1 of the present invention.

[0022] Figure 3 SEM image of the columnar ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 2 of the present invention.

[0023] Figure 4 BET image of the columnar ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 2 of the present invention.

[0024] Figure 5 SEM image of the short rod-shaped ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 3 of the present invention.

[0025] Figure 6 BET image of the short rod-shaped ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 3 of the present invention.

[0026] Figure 7 Distribution diagram of liquid products for catalytic hydrocracking of polyethylene using the spherical ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 1 of the present invention.

[0027] Figure 8The liquid product distribution diagram of catalytic polyethylene hydrocracking using the columnar ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 2 of the present invention.

[0028] Figure 9 The liquid product distribution diagram of catalytic polyethylene hydrocracking using the short rod-shaped ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 3 of the present invention. Detailed implementation manners

[0029] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the specific embodiments cited shall not be construed as limiting the present invention. The following test methods and detection methods are all conventional methods unless otherwise specified; the reagents and raw materials are all commercially available unless otherwise specified.

[0030] For the existing catalyst with Ru nanoparticles supported on SBA-15, there are technical problems such as low catalytic reaction efficiency, poor product selectivity, and easy methanation during the catalytic cracking of polyethylene. The present invention provides a ruthenium-modified mesoporous molecular sieve-based catalyst, its preparation method and application.

[0031] The technical solutions of the present invention will be described in detail below.

[0032] The present invention provides a preparation method of a ruthenium-modified mesoporous molecular sieve-based catalyst, including the following steps: S1, preparing a ruthenium-modified mesoporous molecular sieve.

[0033] S2, using the ruthenium-modified mesoporous molecular sieve as a matrix, adding it to an alcohol solution of a soluble Al 3+ salt, stirring and reacting at room temperature, then filtering and drying to obtain a precursor, and calcining the precursor to replace the silanol groups of the ruthenium-modified mesoporous molecular sieve with Al atoms, grafting the Al atoms onto the ruthenium-modified mesoporous molecular sieve to obtain a ruthenium-modified mesoporous molecular sieve-based catalyst.

[0034] In the above technical solution, Al is introduced into the ruthenium-modified mesoporous molecular sieve SBA-15 by the post-grafting method, thereby introducing acidic sites. The introduction of these acidic sites effectively improves the catalytic reaction efficiency of the catalyst, thereby shortening the catalytic reaction time, and improves the distribution of catalytic products through the mesoporous channels of SBA-15. The present invention further improves the catalytic reaction efficiency by the synergistic effect of metal ruthenium and acidic sites.

[0035] In order to introduce an appropriate amount of acidic sites onto the ruthenium-modified mesoporous molecular sieve, thereby maximizing the catalytic reaction activity of the catalyst, in the ruthenium-modified mesoporous molecular sieve-based catalyst, the molar ratio of Si to Al is 5 to 30:1. When the Al content is relatively high, that is, the silicon-aluminum ratio is relatively low, when the silicon-aluminum ratio is less than 5, the acidity is relatively strong, which may cause excessive cracking of the reactants and an increase in gas products. When the Al content is relatively low, that is, the silicon-aluminum ratio is relatively high, when the silicon-aluminum ratio is greater than 30, the acidity is relatively weak and the number of acidic sites is small, resulting in poor activity.

[0036] It should be noted that in the present invention, the precursor is calcined at 500 °C to 550 °C for 5 h to 6 h to obtain the ruthenium-modified mesoporous molecular sieve-based catalyst.

[0037] It should be noted that the molecular mesoporous sieve used in the present invention is SBA-15.

[0038] In order to control the molar ratio of Si to Al on the final product ruthenium-modified mesoporous molecular sieve-based catalyst to 5 to 30:1, the dosage ratio of the ruthenium-modified mesoporous molecular sieve to the soluble Al 3+ salt is 0.5 g: 0.3 mmol to 1.65 mmol.

[0039] The preparation method of the ruthenium-modified mesoporous molecular sieve adopted in the present invention includes the following steps: Adding a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer to an aqueous hydrochloric acid solution, dissolving it at 35 °C to 45 °C, and then adding tetraethoxysilane to obtain a promoting agent; Mixing 3-mercaptopropyltrimethoxysilane, NaOH and water, and then adding a soluble Ru 3+ salt to obtain a reaction solution.

[0040] Adding the reaction solution to the promoting agent, stirring and then standing, crystallizing at 100 °C to obtain a primary product, and calcining the primary product at 500 °C to 550 °C for 5 h to 6 h to obtain the ruthenium-modified mesoporous molecular sieve.

[0041] In the above preparation method of the ruthenium-modified mesoporous molecular sieve, the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer, that is, P123, plays a role of a structure-directing agent in the synthesis of the ruthenium-modified mesoporous molecular sieve. During the synthesis process of the ruthenium-modified mesoporous molecular sieve, P123 is used as a template agent to guide the structure of the ruthenium-modified mesoporous molecular sieve to be columnar. Dissolving P123 in an aqueous hydrochloric acid solution, the concentration and dosage of hydrochloric acid, as well as the stirring temperature, stirring speed and other surfactants will cause changes in the morphology of the ruthenium-modified mesoporous molecular sieve. If the stirring speed is too fast, the finally synthesized ruthenium-modified mesoporous molecular sieve will be bent, and if the temperature is too high, the ruthenium-modified mesoporous molecular sieve will change from columnar to short rod and long rod shapes.

[0042] When cetyltrimethylammonium bromide (CTAB) is further added to the promoting agent, the interfacial tension between the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer and silica can be reduced, enabling the ruthenium-modified mesoporous molecular sieve to exhibit a spherical morphology. The added mass of CTAB is 0.2 times the mass of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer.

[0043] In the preparation process of the above ruthenium-modified mesoporous molecular sieve, in order to obtain a ruthenium-modified mesoporous molecular sieve with the expected morphology, the mass ratio of the sodium hydroxide, 3-mercaptopropyltrimethoxysilane, and water is limited to 1:1 - 1.5:10 - 50; the mass ratio of the 3-mercaptopropyltrimethoxysilane to the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer is limited to 1:33.3 - 50.

[0044] In order to prepare a ruthenium-modified mesoporous molecular sieve and control the ruthenium loading amount, the present invention limits the mass ratio of the 3-mercaptopropyltrimethoxysilane to the soluble Ru 3+ salt to 1:0.5 - 2. Ruthenium is introduced into the mesoporous molecular sieve SBA-15 through mercapto-silane modification. A small amount of ruthenium will result in fewer metal sites and poor reaction performance; a high amount of ruthenium will result in less mercapto-silane and incomplete ligand formation, leading to more ruthenium loss.

[0045] The following specifically illustrates the content of the present invention through the following examples and comparative examples.

[0046] Example 1 A preparation method of a ruthenium-modified mesoporous molecular sieve-based catalyst includes the following steps: S1. Prepare the ruthenium-modified mesoporous molecular sieve: Add 2 g of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer and 0.4 g of cetyltrimethylammonium bromide to 45 g of hydrochloric acid with a concentration of 2 mol / L and 15 g of water, stir and dissolve at 40 °C in a water bath for 4 h, then add 5.8 g of tetraethoxysilane to obtain a promoting agent; Mix 0.04 g of sodium hydroxide, 0.05 g of 3-mercaptopropyltrimethoxysilane, and 2 g of water, then add 1.63 mL of RuCl3 with a concentration of 100 mM to obtain a reaction solution; Add the reaction solution to the promoting agent, stir for 5 min, stand at 40 °C for 24 h, then transfer to a crystallization kettle and crystallize at 100 °C for 24 h, filter and wash, dry at 80 °C for 12 h to obtain a preliminary product, and calcine the preliminary product at 550 °C for 5 h to obtain the ruthenium-modified mesoporous molecular sieve, denoted as spherical Ru-SBA-15.

[0047] S2. Dissolve 0.11 g of AlCl3 in 50 mL of ethanol solution to obtain an ethanol solution of AlCl3. Add 0.5 g of ruthenium-modified mesoporous molecular sieve to the ethanol solution of AlCl3, stir and react at room temperature for 12 h, filter and wash with ethanol, and dry at 100 °C for 12 h to obtain a precursor; heat the precursor to 550 °C and calcine for 6 h to obtain a ruthenium-modified mesoporous molecular sieve-based catalyst, denoted as spherical Al-Ru-SBA-15.

[0048] Example 2 A preparation method of a ruthenium-modified mesoporous molecular sieve-based catalyst, comprising the following steps: S1. Prepare ruthenium-modified mesoporous molecular sieve: Add 2 g of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer to 65 g of hydrochloric acid with a concentration of 2 mol / L, perform water bath at 35 °C, stir and dissolve for 4 h, then add 4.28 g of tetraethoxysilane to obtain a promoter; mix 0.04 g of sodium hydroxide, 0.05 g of 3-mercaptopropyltrimethoxysilane and 2 g of water, and then add 1.2 mL of RuCl3 with a concentration of 100 mM to obtain a reaction solution; add the reaction solution to the promoter, stir for 5 min, stand at 35 °C for 24 h, then transfer to a crystallization kettle and crystallize at 100 °C for 24 h, filter and wash, and dry at 80 °C for 12 h to obtain a primary product. Calcinate the primary product at 550 °C for 5 h to obtain a ruthenium-modified mesoporous molecular sieve, denoted as columnar Ru-SBA-15.

[0049] S2. Dissolve 0.11 g of AlCl3 in 50 mL of ethanol solution to obtain an ethanol solution of AlCl3. Add 0.5 g of ruthenium-modified mesoporous molecular sieve to the ethanol solution of AlCl3, stir and react at room temperature for 12 h, filter and wash with ethanol, and dry at 100 °C for 12 h to obtain a precursor; heat the precursor to 550 °C and calcine for 6 h to obtain a ruthenium-modified mesoporous molecular sieve-based catalyst, denoted as columnar Al-Ru-SBA-15.

[0050] Example 3 A preparation method of a ruthenium-modified mesoporous molecular sieve-based catalyst, comprising the following steps: S1. Preparation of ruthenium-modified mesoporous molecular sieve: Add 2 g of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer to 65 g of hydrochloric acid with a concentration of 2 mol / L, and stir and dissolve it in a water bath at 45 °C for 4 h. Then add 4.28 g of tetraethoxysilane to obtain a promoter; Mix 0.04 g of sodium hydroxide, 0.05 g of 3-mercaptopropyltrimethoxysilane and 2 g of water, and then add 1.2 mL of RuCl3 with a concentration of 100 mM to obtain a reaction solution; Add the reaction solution to the promoter, stir for 5 min, let it stand at 45 °C for 24 h, then transfer it to a crystallization kettle and crystallize at 100 °C for 24 h, filter and wash, and dry at 80 °C for 12 h to obtain a primary product. Calcinate the primary product at 550 °C for 5 h to obtain a ruthenium-modified mesoporous molecular sieve, denoted as short rod-shaped Ru-SBA-15.

[0051] S2. Add 0.11 g of AlCl3 to 50 mL of ethanol solution and dissolve it to obtain an ethanol solution of AlCl3. Add 0.5 g of ruthenium-modified mesoporous molecular sieve to the ethanol solution of AlCl3, stir and react at room temperature for 12 h, filter and wash with ethanol, and dry at 100 °C for 12 h to obtain a precursor; Heat the precursor to 550 °C and calcine it for 6 h to obtain a ruthenium-modified mesoporous molecular sieve-based catalyst, denoted as short rod-shaped Al-Ru-SBA-15.

[0052] The performance of the ruthenium-modified mesoporous molecular sieve-based catalysts provided in the above Examples 1 to 3 was detected, and the results are as follows.

[0053] Table 1 Parameter table of the catalysts prepared in Examples 1 to 3 of the present invention

[0054] Figure 1 、 Figure 3 and Figure 5 are the SEM images of the ruthenium-modified mesoporous molecular sieve-based catalysts prepared in Examples 1 to 3 of the present invention respectively. From Figure 1 、 Figure 3 and Figure 5 it can be seen that the ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 1 of the present invention is a spherical structure, while the ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 2 is a columnar structure, and the ruthenium-modified mesoporous molecular sieve-based catalyst prepared in Example 3 is a short rod shape.

[0055] Figure 2 、 Figure 4 and Figure 6 are the BET images of the ruthenium-modified mesoporous molecular sieve-based catalysts prepared in Examples 1 to 3 of the present invention respectively. From Figure 2 、 Figure 4 、 Figure 6As can be seen from Table 1, before and after the introduction of Al atoms, the surface area, pore volume, and pore diameter data of the ruthenium-modified mesoporous molecular sieve all decreased. Therefore, it can be proved that Al atoms were successfully incorporated into the ruthenium-modified molecular mesoporous sieve-based catalyst prepared in the present invention.

[0056] Figures 7 - 9 The following are the liquid product distribution diagrams of the catalytic hydrocracking of polyethylene using the ruthenium-modified mesoporous molecular sieve-based catalysts prepared in Examples 1 to 3 of the present invention. 0.5 g of low-density polyethylene and 0.1 g of the catalysts prepared in each example of the present invention were physically mixed and placed in a hydrocracking reactor. The reaction was carried out at 280 °C, 2 MPa, and H2 for 3 h. After the reaction, the gas products were collected and analyzed by gas chromatography; the liquid and solid products were extracted with dichloromethane, and n-hexadecane was used as an external standard for analysis by gas chromatography. As Figure 7 can be seen, the spherical Al-Ru-SBA-15 catalyst achieved complete conversion of low-density polyethylene, with the liquid product accounting for 87.71% and the C5-C7 products accounting for 47.04%. As Figure 8 can be seen, the columnar Al-Ru-SBA-15 catalyst had a conversion rate of 83.52% for low-density polyethylene, with the liquid product accounting for 50.68% and the C5-C7 products accounting for 41.65%. As Figure 9 can be seen, the short rod-shaped Al-Ru-SBA-15 catalyst had a conversion rate of 94.64% for low-density polyethylene, with the liquid product accounting for 74.22% and the C5-C7 products accounting for 43.21%. The catalytic performance of the spherical Al-Ru-SBA-15 was better than that of the columnar Al-Ru-SBA-15 because the spherical Al-Ru-SBA-15 catalyst had uniformly distributed mesoporous pore openings, while the pore channels of the columnar Al-Ru-SBA-15 catalyst were distributed at both ends of the catalyst.

[0057] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A preparation method of a ruthenium-modified mesoporous molecular sieve-based catalyst, characterized in that, It includes the following steps: Prepare ruthenium-modified mesoporous molecular sieve; Using the ruthenium-modified mesoporous molecular sieve as a matrix, adding it to an alcohol solution of a soluble Al 3+ salt, stirring and reacting at room temperature, then filtering and drying to obtain a precursor, calcining the precursor to replace the silanol groups of the ruthenium-modified mesoporous molecular sieve with Al atoms, and grafting the Al atoms onto the ruthenium-modified mesoporous molecular sieve to obtain a ruthenium-modified mesoporous molecular sieve-based catalyst.

2. The preparation method of the ruthenium-modified mesoporous molecular sieve-based catalyst according to claim 1, characterized in that, In the ruthenium-modified mesoporous molecular sieve-based catalyst, the molar ratio of Si to Al is 5-30:

1.

3. The preparation method of the ruthenium-modified mesoporous molecular sieve-based catalyst according to claim 1, characterized in that, The precursor is calcined at 500°C - 550°C for 5h - 6h.

4. The preparation method of the ruthenium-modified mesoporous molecular sieve-based catalyst according to claim 1, wherein, The mesoporous molecular sieve is SBA-15.

5. The preparation method of the ruthenium-modified mesoporous molecular sieve-based catalyst according to claim 1, wherein, The preparation method of the ruthenium-modified mesoporous molecular sieve includes the following steps: Add poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer into hydrochloric acid aqueous solution, dissolve it at 35°C - 45°C, and then add tetraethoxysilane to obtain a promoter; Mix 3-mercaptopropyltrimethoxysilane, NaOH and water, and then add a soluble Ru 3+ salt to obtain a reaction solution; Add the reaction solution into the promoter, stir, stand, and crystallize to obtain a primary product, and calcine the primary product at 500°C - 550°C for 5h - 6h to obtain the ruthenium-modified mesoporous molecular sieve.

6. The preparation method of the ruthenium-modified mesoporous molecular sieve-based catalyst according to claim 5, wherein The mass ratio of sodium hydroxide, 3-mercaptopropyltrimethoxysilane, and water is 1:1 - 1.5:10 - 50; the dosage ratio of 3-mercaptopropyltrimethoxysilane to poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer is 1:33.3 - 50.

7. The preparation method of the ruthenium-modified mesoporous molecular sieve-based catalyst according to claim 5, wherein, The mass ratio of the 3-mercaptopropyltrimethoxysilane to the soluble Ru 3+ salt is 1:0.5 to 2.

8. The preparation method of the ruthenium-modified mesoporous molecular sieve-based catalyst according to claim 5, characterized in that, Cetyltrimethylammonium bromide is also added to the promoter, and the mass ratio of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer to cetyltrimethylammonium bromide is 5:0.8 - 1.

9. A ruthenium-modified mesoporous molecular sieve-based catalyst, characterized in that Prepared by using the preparation method described in any one of claims 1 - 8.

10. Use of the ruthenium-modified mesoporous molecular sieve-based catalyst described in claim 9 in the catalytic hydrocracking of polyethylene.

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