A core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst, its preparation method and application

Abstract

The present invention relates to a hydrodesulfurization catalyst, specifically to a core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst and its preparation method and application. The catalyst has multiple types of active centers and shows a core-shell gradient distribution. The active centers include a hydrogenation active center, a desulfurization active center, and a catalytic cracking active center. Compared with the prior art, the present invention solves the problems of few active sites and poor catalytic effect in the prior art, realizes the core-shell gradient distribution of metal and acid active centers, shows excellent hydrodesulfurization and hydrocracking performances, and has a wide application range.

Description

Technical Field

[0001] The present invention relates to a hydrodesulfurization catalyst, and particularly to a core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst and its preparation method and application. Background Art

[0002] With the increasingly serious environmental pollution and the improvement of people's environmental protection awareness, various countries have introduced strict policies to limit the sulfur content in fuel oils. Therefore, the development of inexpensive and easily available high-efficiency hydrodesulfurization catalysts for producing ultra-clean fuel oils has become a research hotspot. Transition metal sulfides, especially molybdenum disulfide, have been widely used due to their special layered structure and physicochemical properties. Hydrotalcite (LDH) is a kind of two-dimensional nanomaterial, and its general composition formula can be expressed as [M 1-x 2+ M x 3+ (OH) 2 x+ (An - ) x / n ·mH 2 O, where M 2+ refers to divalent metal cations, M 3+ refers to trivalent metal cations, An - is an anion that can stably exist between layers. The elemental composition, charge density of its lamellae can be adjusted. The existence of interlayer anions and the narrow space between layers provide conditions for embedding molybdate precursors and confinement, and it shows good application prospects in many fields such as photocatalysis, electrocatalysis and environmental protection.

[0003] In current heavy oil hydrotreating processes, hydrocracking is required while performing desulfurization refining to convert heavy oil into light oil or other chemical products, making the process flow complex and costly.

[0004] Chinese Patent CN201610568683.X discloses a MoS 2 / LDHS hydrodesulfurization catalyst, which obtains MoS 2 -loaded hydrotalcite-like material LDHS by the method of ionic liquid. In the MoS 2 / LDHS, MoS 2 forms a close-packed monolayer on the surface of the hydrotalcite-like carrier; the MoS 2 / LDHS has a porous structure, and is a nanomaterial with a nanoparticle diameter of 20 - 80 nm and a specific surface area of 450 - 600 m 2 / g. However, in this catalyst, the hydrotalcite-like material can only act as a carrier, resulting in a planar distribution of active sites, a single active center, and poor catalytic effect.

[0005] ​Therefore, there is an urgent need to synthesize a multifunctional catalyst with excellent selectivity to achieve the lightening of heavy oil while achieving deep desulfurization, so as to achieve the goal of reducing processing costs and producing ultra-clean fuels. Summary of the Invention

[0006] The object of the present invention is to provide a core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst, its preparation method and application to solve at least one of the above problems, so as to solve the problems of few active sites and poor catalytic effect in the prior art, realize the gradient distribution of metal and acid active centers in a core-shell shape, exhibit excellent hydrodesulfurization and hydrocracking performances, and have a wide range of applications.

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

[0008] In the first aspect of the present invention, a core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst is disclosed. The catalyst has multiple types of active centers and shows a core-shell gradient distribution. The active centers include hydrogenation active centers, desulfurization active centers, and catalytic cracking active centers.

[0009] Preferably, the shell phase is one of cobalt-aluminum hydrotalcite, nickel-aluminum hydrotalcite, magnesium-aluminum hydrotalcite, and zinc-aluminum hydrotalcite, and a few layers of molybdenum disulfide are dispersed in the interlayer of the hydrotalcite; the core phase is USY zeolite with a silica-alumina ratio not exceeding 20.

[0010] In the second aspect of the present invention, a method for preparing the above-mentioned core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst is disclosed, including the following steps:

[0011] S1: Disperse USY@LDH in distilled water, add ammonium tetrathiomolybdate, adjust the pH and stir to carry out anion exchange, then centrifuge to obtain a precipitate, wash and dry the precipitate to obtain a precursor;

[0012] S2: Calcinate the precursor obtained in step S1 under an inert atmosphere and naturally cool it to room temperature to obtain the core-shell USY@MoS 2 / LDH catalyst.

[0013] Preferably, the ammonium tetrathiomolybdate is used as the ammonium tetrathiomolybdate.

[0014] Preferably, the mass ratio of the ammonium tetrathiomolybdate to USY@LDH is 0.1-10.

[0015] Preferably, the conditions for the anion exchange are: pH value is 6-11, temperature is 20-80 °C, and time is 6-48 h.

[0016] Preferably, the inert atmosphere is an argon atmosphere or a nitrogen atmosphere.

[0017] Preferably, the heating rate of the roasting is 1-20 °C / min, the temperature is 300-900 °C, and the roasting time is 3-12 h.

[0018] The third aspect of the present invention discloses an application of the core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst as described above in hydrodesulfurization of heavy oil.

[0019] Preferably, the reaction conditions for the hydrodesulfurization are: the temperature is 240-360 °C, and the pressure is 2-10 MPa.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The catalyst of the present invention uses hydrotalcite-coated ultrastable Y zeolite (USY@LDH) as a carrier, and a precursor containing thio molybdate anions in the interlayer confined space of the shell-phase hydrotalcite is prepared by the anion exchange method of thio molybdate, and a single-particle "graded pore" multifunctional core-shell catalyst is obtained by roasting in an inert atmosphere.

[0022] The formed catalyst retains the core-shell morphology of the original carrier, has a high specific surface area and a developed pore structure. The core phase is ultrastable Y zeolite (USY), and the shell phase is a single-particle core-shell structure of hydrotalcite with highly dispersed few-layer molybdenum disulfide embedded in the interlayer confined space, having multiple types of active centers of USY, molybdenum disulfide and hydrotalcite and showing a core-shell gradient distribution.

[0023] Transition metal sulfides with hydrodesulfurization activity are distributed in the shell layer, and the MoS in the interlayer of the shell-phase hydrotalcite 2 has a morphology with few short boards; the divalent transition metal in the lamellae of the shell-phase hydrotalcite acts as an assistant and is in close contact with MoS 2 to achieve the in-situ and highly dispersed introduction of the assistant; zeolites with hydrocracking ability are distributed in the core, forming a core-shell gradient distribution with coexistence of multiple active centers. The core phase and the shell phase have a connected developed pore system, which can meet the increasing performance requirements of catalysts in the petroleum refining industry, showing excellent hydrodesulfurization and hydrocracking performances and having a wide application range. Description of the Drawings

[0024] Figure 1 is the XRD spectrum of the product prepared in Example 1;

[0025] Figure 2 is the transmission electron micrograph of the product prepared in Example 1. Detailed Description of the Invention

[0026] The present invention will be described in detail below with reference to the drawings and specific examples.

[0027] In the following examples, if not otherwise specified, commercially available products that can be routinely purchased by those skilled in the art can be used, and the methods used can be the technical means commonly used in the art.

[0028] As a whole, the present invention uses hydrotalcite-coated ultrastable Y zeolite (USY@LDH) as a carrier. Through the ion exchange method, the anion between the layers of the hydrotalcite shell phase is thio molybdate anion, and then the catalyst is obtained by calcination in an inert gas.

[0029] Example 1

[0030] Take 0.8 g of USY, 1.45 g of Co(NO 3 ) 2 ·6H 2 O and 2.4 g of NH 4 NO 3 Add them to 50 mL of distilled water in sequence. After stirring evenly, gradually add 10 wt% dilute ammonia water until the pH value of the solution is 8. After stirring at room temperature for 20 min, transfer the mixed reaction solution into a 100 mL high-pressure reaction kettle lined with polytetrafluoroethylene, and react at 80 °C for 12 h. After the reaction, cool it to room temperature with water, separate the brown precipitate by centrifugation, wash it three times with water, and dry it overnight at 80 °C. The obtained precursor powder is hydrotalcite-coated ultrastable Y zeolite (USY@LDH), denoted as P1.

[0031] Take 0.6 g of the above-synthesized precursor P1 and disperse it in 50 mL of distilled water by ultrasonic dispersion for 30 min. Then add 0.5 g of ammonium tetrathiomolybdate, stir for 24 h at 25 °C and pH 8, and then separate the black precipitate by centrifugation. Wash it three times with water and ethanol respectively, and dry it overnight at 80 °C under vacuum. The obtained precursor powder is denoted as P2.

[0032] Take the synthesized P2 precursor, grind it and place it in a tubular furnace. Calcinate it at 550 °C for 5 hours in an argon atmosphere, with a heating rate of 5 °C / min, and finally cool it to room temperature naturally to prepare the catalyst, which is named USY@MoS 2 / Co-AlLDH.

[0033] Figure 1 The XRD spectrum of 2 shows that the catalyst prepared by the present invention has a composite structure of FAU and Co-Al LDH, and no obvious MoS Figure 2 diffraction peak is observed, which proves the high dispersion of molybdenum disulfide in the catalyst;

[0034] Example 2

[0035] The catalyst synthesis process is basically the same as that of Example 1, except that Co(NO 3 ) 2 ·6H 2 O is changed to Ni(NO 3 ) 2 ·6H 2 O, and other conditions are the same as those in Example 1. The obtained catalyst is USY@MoS 2 / Ni-Al LDH.

[0036] Example 3

[0037] The catalyst synthesis process is basically the same as that of Example 1, except that Co(NO 3 ) 2 ·6H 2 O is changed to Mg(NO 3 ) 2 ·6H 2 O, and other conditions are the same as those in Example 1. The obtained catalyst is USY@MoS 2 / Mg-Al LDH.

[0038] Example 4

[0039] The catalyst synthesis process is basically the same as that of Example 1, except that Co(NO 3 ) 2 ·6H 2 O is changed to Zn(NO 3 ) 2 ·6H 2 O, and other conditions are the same as those in Example 1. The obtained catalyst is USY@MoS 2 / Zn-Al LDH.

[0040] Example 5

[0041] The catalyst synthesis process is basically the same as that of Example 1, except that the calcination conditions are adjusted to: the heating rate is 10 °C / min, the temperature is 700 °C, and the calcination time is 4 h.

[0042] Example 6

[0043] The catalyst synthesis process is basically the same as that of Example 1, except that the calcination conditions are adjusted to: the heating rate is 20 °C / min, the temperature is 900 °C, and the calcination time is 3 h.

[0044] Example 7

[0045] The catalyst synthesis process is basically the same as that of Example 1, except that the calcination conditions are adjusted to: the heating rate is 1 °C / min, the temperature is 300 °C, and the calcination time is 12 h.

[0046] Example 8

[0047] The catalyst synthesis process is basically the same as that of Example 1, except that the conditions for anion exchange are adjusted to: pH = 6, temperature = 80 °C, and time = 6 h.

[0048] Example 9

[0049] The catalyst synthesis process is basically the same as that of Example 1, except that the conditions for anion exchange are adjusted to: pH = 11, temperature = 40 °C, and time = 48 h.

[0050] Example 10

[0051] Take 1 g of USY, 1.3 g of Co(NO 3 ) 2 ·6H 2 O and 2.4 g of NH 4 NO 3 Add them successively to 30 mL of distilled water and stir evenly, then gradually add 2.5 M sodium hydroxide solution until the pH value of the solution is 10. After stirring at room temperature for 20 min, transfer the mixed reaction solution into a 50 mL autoclave lined with polytetrafluoroethylene and react at 140 °C for 10 h. After the reaction is completed, cool it to room temperature with water, separate the brown precipitate by centrifugation, wash it three times with water, and dry it at 80 °C overnight. The obtained precursor powder is denoted as P3.

[0052] Disperse 0.6 g of the above-synthesized precursor P3 into 50 mL of distilled water and ultrasonically disperse it for 30 min, then add 0.5 g of ammonium tetrathiomolybdate. After stirring at 25 °C and pH = 8 for 24 h, separate the black precipitate by centrifugation, wash it three times with water and ethanol respectively, and dry it under vacuum at 80 °C overnight. The obtained precursor powder is denoted as P4.

[0053] Place the synthesized P4 precursor in a tubular furnace, calcine it at 550 °C for 5 hours under an argon atmosphere with a heating rate of 5 °C / min, and finally cool it naturally to room temperature to prepare the catalyst, which is named USY@MoS 2 / Co-Al LDH-2.

[0054] Comparative Example 1

[0055] Use commercial molybdenum disulfide as a comparative sample, denoted as MoS 2 .

[0056] Application Example

[0057] The catalyst USY@MoS 2 / Co-Al LDH and MoS 2Hydrodesulfurization performance comparison. A decalin solution of dibenzothiophene with a sulfur content of 300 ppm was used as the model oil to evaluate the performance of the catalyst. The hydrodesulfurization of dibenzothiophene was carried out in a 100 mL batch reactor at a reaction pressure of 6 MPa, a reaction temperature of 320 °C, and a reaction time of 9 h. The reaction evaluation results of various catalysts are shown in Table 1.

[0058] Table 1 Hydrodesulfurization performance of the catalysts in Example 1 and Comparative Example 1

[0059] sample Conversion rate (%) <![CDATA[USY@MoS 2 / Co-Al LDH]]> 94.8 <![CDATA[MoS 2 > 25.9

[0060] The application examples and the results in Table 1 show that the single-particle "graded pore" multifunctional core-shell catalyst prepared by the present invention exhibits good catalytic performance in the hydrodesulfurization reaction of dibenzothiophene.

[0061] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst, Characterized in that, The catalyst has multiple types of active centers and shows a core-shell gradient distribution. The active centers include hydrogenation active centers, desulfurization active centers, and catalytic cracking active centers; The shell phase of the catalyst is one of cobalt-aluminum hydrotalcite, nickel-aluminum hydrotalcite, magnesium-aluminum hydrotalcite, and zinc-aluminum hydrotalcite, and a few layers of molybdenum disulfide are dispersed between the layers of the hydrotalcite; the core phase of the catalyst is USY zeolite with a silica-alumina ratio not exceeding 20; The catalyst: using USY@LDH as a carrier, preparing a precursor containing thio molybdate anions in the confined space between the layers of the shell-phase hydrotalcite by the anion exchange method of thio molybdate, and calcining at 300-900 °C in an inert atmosphere.

2. A method for preparing the core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst as claimed in claim 1, Characterized in that, It includes the following steps: S1: Disperse USY@LDH in distilled water and add thio molybdate, adjust the pH and stir for anion exchange, then centrifuge to obtain a precipitate, wash and dry the precipitate to obtain a precursor; S2: Calcinate the precursor obtained in step S1 under an inert atmosphere and naturally cool it to room temperature to obtain the core-shell USY@MoS 2 / LDH catalyst.

3. A method for preparing a core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst according to claim 2, Characterized in that, The thio molybdate is ammonium tetrathiomolybdate.

4. A method for preparing a core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst according to claim 3, Characterized in that, The mass ratio of the thio molybdate to USY@LDH is 0.1-10.

5. A method for preparing a core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst according to claim 2, Characterized in that, The conditions for the anion exchange are: pH value is 6-11, temperature is 20-80 °C, and time is 6-48 h.

6. A method for preparing a core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst according to claim 2, Characterized in that, The inert atmosphere is an argon atmosphere or a nitrogen atmosphere.

7. A method for preparing a core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst according to claim 2 or 6, Characterized in that, The heating rate of the calcination is 1-20 °C / min, and the calcination time is 3-12 h.

8. An application of the core-shell graded structure USY@molybdenum disulfide / hydrotalcite catalyst as claimed in claim 1 in the hydrodesulfurization of heavy oil.

9. The application according to claim 8, Characterized in that, The reaction conditions for the hydrodesulfurization are: temperature is 240-360 °C, and pressure is 2-10 MPa.

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