A core-shell molecular sieve@transition metal doping-molybdenum disulfide / carbon composite catalyst and its preparation method and application

Abstract

The present invention relates to a hydrodesulfurization catalyst, specifically a core-shell molecular sieve@transition metal-doped molybdenum disulfide / carbon composite catalyst, its preparation method, and application, comprising: S1: dispersing the core phase material in water, adjusting the pH to a negative charge, adding a positively charged polymer, and centrifuging and washing; S2: dispersing the configured material in water, adding a molybdate solution, and centrifuging and washing; S3: repeating the electrostatic adsorption processes of S1 and S2 at least once, leaving the outermost layer as a molybdenum layer; S4: dispersing the precursor in water, stirring, and drying; S5: calcining the product under an inert atmosphere; when the core phase material is not doped with a transition metal, S4: dispersing the precursor, and then adding a transition metal salt additive and trithiocyanate. Compared with the prior art, the present invention solves the problem of the lack of a simple and suitable bonding pathway between the molybdenum-based / carbon-supported hydrodesulfurization catalyst and the acidic support in the prior art, thereby achieving a regional distribution of metal active centers in the shell phase and acid active centers in the core phase.

Description

Technical Field

[0001] The present invention relates to a hydrodesulfurization catalyst, in particular to a core-shell molecular sieve@transition metal doping-molybdenum disulfide / carbon composite catalyst and a preparation method and application thereof. Background Art

[0002] The presence of a carrier in a molybdenum-based hydrodesulfurization catalyst can improve the dispersion of active species, the diffusion performance of the catalyst, and thus improve the catalytic activity.

[0003] The support's pore structure, acidity, and interaction with the active metal influence the degree of sulfidation, size, and dispersion of the active phase, thus impacting catalytic performance. Carbon supports are common supports for hydrodesulfurization catalysts due to their high specific surface area, well-developed pore structure, good stability, and suitable support-metal interaction.

[0004] However, the lack of acidity in the carbon support limits the catalyst's ability to remove recalcitrant organosulfur compounds and subsequent hydrocracking. Hybridization of carbon materials with acidic materials such as alumina and zeolites can improve the catalyst's acidity, but large non-hydrocarbon molecules easily diffuse onto the molecular sieve surface, poisoning it and causing rapid catalyst deactivation.

[0005] Chinese patent CN202211640110.5 discloses a graded USY@hydrotalcite-molybdenum disulfide catalyst, its in-situ preparation method, and its application. The catalyst, which comprises USY as the core phase and a few-layered molybdenum disulfide hydrotalcite as the shell phase, is considered a representative catalyst for existing molybdenum-based hydrodesulfurization (HDS) catalysts. If it can be rationally combined with carbon materials, the reaction conversion rate and desulfurization rate can be further improved. However, the lack of relevant technologies in the prior art has hindered the development of more efficient HDS catalysts. Summary of the Invention

[0006] The present invention aims to address at least one of the aforementioned problems by providing a core-shell molecular sieve@transition metal-doped molybdenum disulfide / carbon composite catalyst, its preparation method, and its application. This approach addresses the lack of a simple and suitable bonding pathway between molybdenum-based / carbon-supported hydrodesulfurization catalysts and acidic supports in the prior art, resulting in a highly efficient hydrodesulfurization catalyst with metal active centers distributed in the shell phase and acid active centers in the core phase. The carbon material in the MoS2 / C shell of this catalyst achieves high MoS2 dispersion, promoting the hydrogenation reaction rate on the catalyst surface. It also effectively prevents non-hydrocarbon macromolecules from diffusing to the zeolite surface, slowing the poisoning of the catalyst by heteroatoms. The catalyst exhibits excellent hydrodesulfurization and hydrocracking performance, which is of great significance for practical applications.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention discloses a method for preparing a core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst, comprising the following steps:

[0009] S1: Disperse the core phase material in water, adjust the pH to make the surface of the core phase material negatively charged, add positively charged polymers to it for electrostatic adsorption, and centrifuge and wash;

[0010] S2: Re-dispersing the positively charged polymer-modified core phase material prepared in step S1 in water, adding molybdate solution thereto for electrostatic adsorption, and centrifuging and washing;

[0011] S3: Repeat the electrostatic adsorption process of steps S1 and S2 at least once, and make the outermost layer electrostatically adsorbed be the molybdenum layer;

[0012] S4: Dispersing the precursor obtained in step S3 in water and stirring, and drying the obtained dispersion overnight;

[0013] S5: calcining the product of step S4 under an inert atmosphere and naturally cooling it to room temperature to obtain the catalyst;

[0014] When the core phase material is not doped with transition metal, after the precursor is dispersed in step S4, a transition metal salt additive and thiocyanate are added.

[0015] Preferably, the core phase material is one or more of zeolite, alumina, silica, hydrotalcite, zeolite@alumina, zeolite@silica and zeolite@hydrotalcite.

[0016] Preferably, if the pH needs to be adjusted in step S1, ammonia water or dilute hydrochloric acid is used for adjustment.

[0017] Preferably, the positively charged polymer is one or both of polyethyleneimine (PEI) and polydiallyldimethylammonium chloride (PDDA); the solute molybdate in the molybdate solution is one or more of ammonium heptamolybdate, ammonium tetramolybdate, sodium molybdate and ammonium tetrathiomolybdate.

[0018] Preferably, the mass of the positively charged polymer accounts for 0.1 to 30 wt % of the total mass, and the mass ratio of molybdate to core phase material is 0.01 to 5:1.

[0019] Preferably, the electrostatic adsorption time is 10 minutes to 24 hours, the electrostatic adsorption temperature is 10 to 80° C., and stirring is performed during the electrostatic adsorption process.

[0020] Preferably, the transition metal is one or both of cobalt and nickel, the transition metal salt additive is one or both of cobalt nitrate and nickel nitrate, the molar ratio of the transition metal salt additive to molybdate is 0 to 1:1, and not zero; and the mass ratio of thiocyanuric acid to molybdate is 0 to 0.5:1. The transition metal salt as an additive imparts excellent hydrodesulfurization performance to the catalyst; thiocyanuric acid, a crosslinking agent and vulcanizing agent, can be selectively added depending on the preparation method and raw materials.

[0021] Preferably, the calcination temperature is 300-900° C., and the calcination time is 3-12 hours.

[0022] The second aspect of the present invention discloses a core-shell molecular sieve@transition metal doping-molybdenum disulfide / carbon composite catalyst obtained by any of the above preparation methods.

[0023] The third aspect of the present invention discloses the use of the core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst in a catalytic hydrodesulfurization reaction.

[0024] Preferably, the reaction temperature of the hydrodesulfurization reaction is 240-360° C., and the reaction pressure is 2-10 MPa.

[0025] The working principle of the present invention is:

[0026] By leveraging the electrostatic interactions between oppositely charged molecular sieves, water-soluble polymers, and transition metal salts, a core-shell structured, graded-pore molecular sieve and transition metal-doped MoS2 / C composite ternary material was constructed and finalized by calcination. By varying the number of adsorbed layers of the water-soluble polymer and transition metal salt, the composite's shell pore structure, shell thickness, and the size, number, and dispersion of the transition metal sulfide shell can be precisely controlled.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The synthesis method of the molecular sieve@transition metal doping-MoS2 / C composite ternary material prepared by the present invention is safe and simple, the raw materials are cheap and easily available, the amino groups (or quaternary ammonium cations) in the positively charged polymer achieve high dispersion of molybdenum species, improve metal utilization and dispersibility, and the shell pore structure, shell thickness, size, number of layers and dispersion of the composite material can be precisely controlled by simply changing the number of adsorption layers of the water-soluble polymer and the transition metal salt. The doping of the transition metal salt additive greatly alleviates the problem of low activity of a single molybdenum-based catalyst; the molecular sieve with acid active centers is distributed in the core, the non-acidic carbon material is distributed in the shell and delays the poisoning and deactivation of the molecular sieve, and the metal elements in the shell are highly dispersed to form a core-shell gradient distribution of active centers, showing excellent desulfurization performance and a wide range of applications.

[0029] In the catalyst structure of the present invention, the shell carbon material not only promotes the high dispersion of MoS2 and the hydrogenation reaction rate on the catalyst surface, but also slows down the poisoning of the catalyst by heteroatoms and protects the core phase material.

[0030] The preparation method of the present invention has universal applicability, is not limited by the types of core phase materials, water-soluble polymers with different charges or metal salts, and is suitable for large-scale industrial production.

[0031] This invention achieves a selective distribution of metal active centers in the shell phase and acid active centers in the core phase. The carbon material in the shell promotes the rate of hydrogenation reaction on the catalyst surface, which is of great significance for practical applications and future development. It effectively solves the existing problems of catalysts with single carbon supports lacking acidity and molecular sieve supports being easily poisoned and deactivated. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The XRD pattern of the catalyst obtained in Example 5;

[0033] Figure 2 This is a transmission electron microscope image of the catalyst obtained in Example 5. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to the accompanying drawings and specific examples, providing detailed implementation plans and specific operating procedures, but it should not be understood that the applicable scope of the present invention is limited thereto.

[0035] Unless otherwise specified, the materials and reagents used in the following examples were purchased from conventional commercial products; unless otherwise specified, the methods and operations used were conventional means in the art.

[0036] Example 1

[0037] (1) 1.0 g of USY zeolite was ultrasonically dispersed in 20 mL of a 1 wt% polyethyleneimine solution with a molecular weight of 600. The solution was stirred at room temperature for 4 h and then centrifuged. The precursor obtained by washing was recorded as P1.

[0038] (2) The precursor P1 synthesized above was dispersed in 20 mL of distilled water, and then 5 g of (NH4)6Mo7O was added. 24 ·4H2O and stirred at room temperature for 18 h. The precursor obtained by centrifugation and washing was recorded as P2.

[0039] (3) The precursor P2 synthesized above was taken and the electrostatic adsorption reaction of steps (1) and (2) was repeated four times. The obtained precursor was recorded as P3.

[0040] (4) The precursor P3 synthesized above was dispersed in 20 mL of distilled water, and then 0.15 g of Co(NO3)2·6H2O and 2.3 g of trithiocyanate were added, stirred for 2 h, and then dried in an oven at 50 °C overnight to obtain a bright yellow solid powder, which was recorded as P4.

[0041] (5) The synthesized P4 precursor was ground and placed in a tube furnace. It was calcined at 850 °C for 5 h under an argon atmosphere at a heating rate of 5 °C / min. Finally, it was naturally cooled to room temperature to prepare the catalyst, which was named USY@Co-MoS2 / C PEI -5.

[0042] Example 1-1

[0043] The catalyst synthesis process is basically the same as that in Example 1, except that the number of repetitions in step (3) is changed to one, and the other conditions are the same as those in Example 1. The obtained catalyst is USY@Co-MoS2 / C PEI -2.

[0044] Example 1-2

[0045] The catalyst synthesis process is basically the same as that in Example 1, except that the number of repetitions in step (3) is changed to two, the mass of Co(NO3)2·6H2O in step (4) is changed to 0.05g, and the other conditions are the same as those in Example 1. The obtained catalyst is USY@Co-MoS2 / C PEI -3.

[0046] Examples 1-3

[0047] The catalyst synthesis process is basically the same as that in Example 1, except that the number of repetitions in step (3) is changed to three times. Other conditions are the same as those in Example 1. The obtained catalyst is USY@Co-MoS2 / C PEI -4.

[0048] Example 2

[0049] The catalyst synthesis process is basically the same as that in Example 1, except that USY is replaced by USY@Co-LDH and Co(NO3)2·6H2O is not added in step (4). Other conditions are the same as those in Example 1. The obtained catalyst is USY@Co-LDH@MoS2 / C PEI -5.

[0050] The synthesis process of USY@Co-LDH is as follows:

[0051] 0.8g of USY, 1.45g of Co(NO₃)₂·6H₂O, and 2.4g of NH₄NO₃ were added sequentially to 50mL of distilled water and stirred thoroughly. Then, 10wt% dilute ammonia was gradually added dropwise until the pH of the solution reached 8. After stirring at room temperature for 20 minutes, the mixed reaction solution was transferred to a 100mL polytetrafluoroethylene-lined autoclave and reacted at 80°C for 12 hours. After the reaction, the mixture was cooled to room temperature and the brown precipitate was separated by centrifugation. The resulting powder was washed three times with water and dried at 80°C overnight.

[0052] Example 3

[0053] The catalyst synthesis process is basically the same as that in Example 1, except that USY is replaced by USY@SiO2. Other conditions are the same as those in Example 1. The obtained catalyst is USY@SiO2@Co-MoS2 / C PEI -5.

[0054] Example 4

[0055] The catalyst synthesis process is basically the same as that in Example 1, except that USY is replaced by USY@Al2O3. In step (1), USY@Al2O3 is first dispersed in 10 mL of distilled water, adjusted to neutrality with ammonia water, and then 10 mL of 2 wt% PEI solution is added. Other conditions are the same as those in Example 1. The obtained catalyst is USY@Al2O3@Co-MoS2 / C PEI -5.

[0056] Example 5

[0057] (1) 1.0 g of USY zeolite was ultrasonically dispersed in 20 mL of a 0.2 wt% polydiallyldimethylammonium chloride solution, stirred at room temperature for 20 min, and then centrifuged and washed to obtain a precursor denoted as P5.

[0058] (2) The precursor P5 synthesized above was dispersed in 20 mL of distilled water, and then 0.1 g of ammonium tetrathiomolybdate was added and stirred at room temperature for 40 min. The precursor was then centrifuged and washed to obtain a precursor designated as P6.

[0059] (3) The precursor P6 synthesized above was taken and the electrostatic adsorption process of steps (1) and (2) was repeated four times. The precursor powder was dried in an oven at 50°C overnight and was recorded as P7.

[0060] (4) The precursor P7 synthesized above was dispersed in 1 mL of distilled water, and then 0.1 g of Co(NO3)2·6H2O was added, stirred for two hours, and dried in a vacuum oven overnight to obtain a precursor powder designated as P8.

[0061] (5) The synthesized P8 precursor was ground and placed in a tube furnace. It was calcined at 550 °C for 5 h under an argon atmosphere at a heating rate of 5 °C / min. Finally, it was naturally cooled to room temperature to prepare the catalyst, which was named USY@Co-MoS2 / C PDDA -5.

[0062] Figure 1 The XRD spectrum of the synthesized sample shows that the only diffraction peak is FAU, indicating that the Co and Mo species have high dispersion in the shell; Figure 2 Transmission electron microscopy and elemental distribution showed that the synthesized sample had a core-shell morphology.

[0063] Example 6

[0064] The catalyst synthesis process is basically the same as that in Example 5, except that USY is replaced by USY@Co-LDH and step (4) is omitted. Other conditions are the same as those in Example 1. The obtained catalyst is USY@Co-LDH@MoS2 / C PDDA -5.

[0065] The preparation method of USY@Co-LDH in this example is consistent with that of USY@Co-LDH in Example 2.

[0066] Comparative Example 1

[0067] The catalyst synthesis process is basically the same as that in Example 1, except that the number of repetitions in step (3) is canceled. Other conditions are the same as those in Example 1. The catalyst obtained is USY@Co-MoS2 / C PEI -1.

[0068] Comparative Example 2

[0069] The catalyst synthesis process is basically the same as that in Example 1, except that the addition of Co(NO3)2·6H2O in step (4) is eliminated. Other conditions are the same as those in Example 1. The obtained catalyst is USY@MoS2 / C PEI -5.

[0070] Comparative Example 3

[0071] The catalyst synthesis process is basically the same as that in Example 5, except that step (4) is omitted. Other conditions are the same as those in Example 1. The catalyst obtained is USY@MoS2 / C PDDA -5.

[0072] Application Examples

[0073] Catalyst performance was evaluated using a decalin solution of dibenzothiophene with a sulfur content of 300 ppm as a model oil. Hydrodesulfurization of dibenzothiophene was carried out in a 100 mL batch reactor at a pressure of 6 MPa, a temperature of 320°C, and a reaction time of 9 hours. The reaction evaluation results for some of the catalysts are shown in Table 1.

[0074] Table 1 Hydrodesulfurization performance of each catalyst

[0075]

[0076] The results of the application examples and Table 1 show that with the increase in the number of adsorption times of water-soluble polymer and molybdenum layer, the shell thickness increases, accompanied by the improvement of active species content and dispersion (compared with USY@Co-MoS2 / C PEI -1~USY@Co-MoS2 / C PEI -5), the reaction performance increases accordingly. After the introduction of the auxiliary species, the catalyst performance is greatly improved. The core-shell hydrodesulfurization catalyst prepared by the present invention shows good catalytic performance in the hydrodesulfurization reaction of dibenzothiophene.

[0077] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst, characterized in that: The steps include: S1: Disperse the core phase material in water, adjust the pH to make the surface of the core phase material negatively charged, add positively charged polymers to it for electrostatic adsorption, and centrifuge and wash; S2: Re-dispersing the positively charged polymer-modified core phase material prepared in step S1 in water, adding molybdate solution thereto for electrostatic adsorption, and centrifuging and washing; S3: Repeat the electrostatic adsorption process of steps S1 and S2 at least once, and make the outermost layer electrostatically adsorbed be the molybdenum layer; S4: Dispersing the precursor obtained in step S3 in water and stirring, and drying the obtained dispersion overnight; S5: calcining the product of step S4 under an inert atmosphere and naturally cooling it to room temperature to obtain the catalyst; When the core phase material is not doped with a transition metal, after the precursor is dispersed in step S4, a transition metal salt additive and trithiocyanate are added; the positively charged polymer is one or both of polyethyleneimine and polydiallyldimethylammonium chloride; The catalyst has a core-shell structure: the metal active center is in the shell phase and the acid active center is in the core phase; by changing the number of adsorption layers of the polymer and the transition metal salt, the shell pore structure, shell thickness, size, number of layers and dispersion of the shell transition metal sulfide of the composite material can be precisely controlled.

2. The method for preparing a core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst according to claim 1, characterized in that: The core phase material is one or more of zeolite, alumina, silica, hydrotalcite, zeolite@alumina, zeolite@silica and zeolite@hydrotalcite.

3. The method for preparing a core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst according to claim 1, characterized in that: The solute molybdate in the molybdate solution is one or more of ammonium heptamolybdate, ammonium tetramolybdate, sodium molybdate and ammonium tetrathiomolybdate.

4. The method for preparing a core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst according to claim 3, characterized in that: The mass ratio of molybdate to core phase material is 0.01~5:

1.

5. The method for preparing a core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst according to claim 1, characterized in that: The electrostatic adsorption time is 10 minutes to 24 hours, and the electrostatic adsorption temperature is 10 to 80°C.

6. The method for preparing a core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst according to claim 1, characterized in that: The transition metal is one or both of cobalt and nickel, the transition metal salt additive is one or both of cobalt nitrate and nickel nitrate, the molar ratio of the transition metal salt additive to molybdate is 0-1:1 and not 0; and the mass ratio of thiocyanate to molybdate is 0-0.5:

1.

7. The method for preparing a core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst according to claim 1, characterized in that: The calcination temperature is 300-900° C., and the calcination time is 3-12 hours.

8. A core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the core-shell molecular sieve@transition metal doped-molybdenum disulfide / carbon composite catalyst as claimed in claim 8 in a catalytic hydrodesulfurization reaction.

10. The use according to claim 9, characterized in that The reaction temperature of the hydrodesulfurization reaction is 240-360° C., and the reaction pressure is 2-10 MPa.

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