Molybdenum modified hierarchical pore zsm-5 molecular sieve catalyst, preparation method and application thereof

Abstract

This invention relates to the field of catalyst technology, specifically a molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst, its preparation method, and its application. The molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst is obtained by the following method: First, a silicon source, a structure-directing agent, an alkali source, and water are mixed to obtain a mixed solution. Then, the mixed solution and an aluminum source are added to a molybdenum salt solution, stirred evenly, and subjected to a dynamic hydrothermal reaction to obtain a molecular sieve intermediate. Finally, the molecular sieve intermediate is separated, dried, and calcined. This invention's molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst is prepared in one step through a combination of molybdenum metal ligand protection and a dynamic hydrothermal reaction. It exhibits good thermal stability, uniform metal particle distribution and size, and high catalytic activity. The application of this molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst in the heavy oil catalytic cracking reaction for the production of low-carbon olefins (ethylene and propylene) demonstrates significant catalytic performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, and is a molybdenum-modified hierarchical pore ZSM-5 molecular sieve catalyst as well as a preparation method and application thereof. BACKGROUND

[0002] ZSM-5 molecular sieves exhibit excellent catalytic activity, shape selectivity and good carbon deposition resistance due to their unique pore structure, rich acid sites and good hydrothermal stability, and are commonly used for increasing production of low-carbon olefins and widely applied in the field of petroleum chemical industry. In industry, the method of modifying ZSM-5 molecular sieves with transition metals is usually adopted to fully combine the advantages of metals and molecular sieves, thereby improving the cracking performance.

[0003] The preparation methods of metal / molecular sieve bifunctional catalysts reported in the prior art are mainly obtained by using conventional impregnation, deposition and ion exchange methods, but these methods usually cause problems such as easy agglomeration of metal particles on the molecular sieve, uneven dispersion, uneven size, etc., resulting in poor catalyst stability. Moreover, the positions where metal particles can be distributed on the acid molecular sieve are the pore, supercage and external surface, but when metal particles are distributed in large quantities on the external surface of the molecular sieve, they are easy to migrate, agglomerate and flow out, resulting in poor catalytic performance.

[0004] Therefore, the existing metal / molecular sieve catalysts have the problem of poor catalytic performance due to poor catalyst stability, and how to construct a stable metal-supported molecular sieve catalyst is the key to solving this problem. SUMMARY

[0005] The present application provides a molybdenum-modified hierarchical pore ZSM-5 molecular sieve catalyst as well as a preparation method and application thereof, which overcomes the shortcomings of the prior art and effectively solves the problem of poor catalytic performance of the existing metal / molecular sieve catalysts due to poor stability.

[0006] One of the technical solutions of the present application is achieved by the following measures: a molybdenum-modified hierarchical pore ZSM-5 molecular sieve catalyst is obtained by the following method: S1, uniformly mixing a silicon source, a structure directing agent, an alkali source and water, and then obtaining a mixed solution after alcohol removal treatment; S2, uniformly stirring the mixed solution and an aluminum source in a molybdenum salt solution and performing a dynamic hydrothermal reaction to obtain a molecular sieve intermediate; S3, obtaining the molybdenum-modified hierarchical pore ZSM-5 molecular sieve catalyst by separating, drying and calcining the molecular sieve intermediate.

[0007] The following is a further optimization or / and improvement of one of the above technical solutions: In the above step S1, the silicon source is one or more of tetraethyl orthosilicate, water glass and silica sol.

[0008] In step S1 above, the structure directing agent is tetrapropylammonium hydroxide.

[0009] In step S1 above, the alkali source is one or more of sodium hydroxide and ammonia water.

[0010] In step S2 above, the aluminum source is one or more of aluminum nitrate, aluminum sulfate, and aluminum isopropoxide.

[0011] In step S1 above, the molar ratio of silicon source (calculated as SiO2), structure directing agent (calculated as TPAOH), alkali source (calculated as NaOH) and water is 1:(0.10 to 0.35):(0.10 to 0.15):(15 to 40).

[0012] In step S2 above, the molybdenum salt solution is one of the following: an aqueous solution of a molybdenum salt precursor and an aqueous solution of a molybdenum salt precursor containing an organic complex. The molar ratio of the organic complex to the molybdenum salt precursor in the aqueous solution of the molybdenum salt precursor containing an organic complex is (1:50):1. The concentration of the solute in both the aqueous solution of the molybdenum salt precursor and the aqueous solution of the molybdenum salt precursor containing an organic complex is 0.02 mol / L to 0.5 mol / L.

[0013] In step S2 above, the molybdenum salt precursor is one or more of sodium molybdate dihydrate, sodium phosphomolybdate hydrate, molybdenum chloride, and ammonium molybdate, and the organic complex is one or more of ethylenediamine, ethylenediaminetetraacetic acid, diethylenetriamine, and tetraethylenepentamine.

[0014] In step S2 above, the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3) and molybdenum salt solution (calculated as H8MoN2O4) is 1:(0.01 to 0.05):(0.005 to 0.05).

[0015] In step S1 above, the alcohol removal process is carried out at a temperature of 45°C to 50°C for 4.0 h to 4.5 h.

[0016] In step S2 above, during the dynamic hydrothermal reaction, the reaction temperature is 150℃ to 190℃, and the reaction time is 48h to 96h.

[0017] In step S3 above, during drying, the drying temperature is 90℃ to 120℃ and the drying time is 4h to 12h. During calcination, the calcination temperature is 500℃ to 600℃ and the calcination time is 4h to 10h.

[0018] The second technical solution of the present invention is achieved through the following measures: a molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst, carried out according to the following method: S1, mix silicon source, structure directing agent, alkali source and water, and then remove alcohol to obtain a mixed solution; S2, after adding a mixed solution and an aluminum source to a molybdenum salt solution, stirring until homogeneous, and carrying out a dynamic hydrothermal reaction, a molecular sieve intermediate is obtained; S3, after separating, drying and calcining the molecular sieve intermediate, a molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst is obtained.

[0019] The third technical solution of the present invention is achieved through the following measures: the application of a molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst in the catalytic cracking reaction of crude oil.

[0020] The molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst of this invention is prepared in one step by combining molybdenum metal ligand protection and dynamic hydrothermal reaction. It has the characteristics of good thermal stability, uniform metal particle distribution and size, and high catalytic activity. When the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst of this invention is applied to the heavy oil catalytic cracking reaction to produce more low-carbon olefins (ethylene and propylene), the catalytic performance is significant. Attached Figure Description

[0021] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention.

[0022] Figure 2 This is a scanning electron microscope (SEM) image of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of the present invention.

[0023] Figure 3 This is a transmission electron microscope (TEM) image of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of the present invention.

[0024] Figure 4 The average particle size diagram is shown for the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention.

[0025] Figure 5 This is a transmission electron microscope (TEM) image of the Mo / ZSM-5 molecular sieve catalyst prepared in Comparative Example 2 of this invention.

[0026] Figure 6 This is a nitrogen physical adsorption-desorption curve of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst of the present invention.

[0027] Figure 7 The catalytic performance diagrams are shown for the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention and Comparative Example 1.

[0028] Figure 8 The catalytic performance diagrams are shown for the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention and Comparative Example 2.

[0029] Figure 9 The figures show the catalytic performance of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalysts (with different silicon-to-aluminum ratios) prepared in Examples 13 to 15 of this invention.

[0030] Figure 10 The graph shows the catalytic performance of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalysts (with different metal loadings) prepared in Examples 13 and 16 of this invention. Detailed Implementation

[0031] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0032] The present invention will be further described below with reference to embodiments: Example 1: The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst was obtained by the following method: S1, mix silicon source, structure directing agent, alkali source and water, and then remove alcohol to obtain a mixed solution; S2, after adding a mixed solution and an aluminum source to a molybdenum salt solution, stirring until homogeneous, and carrying out a dynamic hydrothermal reaction, a molecular sieve intermediate is obtained; S3, after separating, drying and calcining the molecular sieve intermediate, a molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst is obtained.

[0033] In this invention, the silicon source (tetraethyl orthosilicate) will hydrolyze in the mixed solution into ethanol and silicon oxide. Ethanol will be generated in this process. Therefore, alcohol removal treatment is required in step S1. This alcohol removal treatment will improve the relative cleanliness of the molecular sieve.

[0034] Example 2: As an optimization of the above example, in step S1, the silicon source is one or more of tetraethyl orthosilicate, water glass and silica sol.

[0035] Example 3: As an optimization of the above example, in step S1, the structure directing agent is tetrapropylammonium hydroxide.

[0036] Example 4: As an optimization of the above example, in step S1, the alkaline source is one or more of sodium hydroxide and ammonia water.

[0037] Example 5: As an optimization of the above example, in step S2, the aluminum source is one or more of aluminum nitrate, aluminum sulfate and aluminum isopropoxide.

[0038] Example 6: As an optimization of the above example, in step S1, the molar ratio of silicon source (calculated as SiO2), structure directing agent (calculated as TPAOH), alkali source (calculated as NaOH) and water is 1:(0.10 to 0.35):(0.10 to 0.15):(15 to 40).

[0039] Example 7: As an optimization of the above embodiment, in step S2, the molybdenum salt solution is one of the aqueous solution of molybdenum salt precursor and the aqueous solution of molybdenum salt precursor containing organic complex. The molar ratio of organic complex to molybdenum salt precursor in the aqueous solution of molybdenum salt precursor containing organic complex is (1:50):1. The concentration of solute in both the aqueous solution of molybdenum salt precursor and the aqueous solution of molybdenum salt precursor containing organic complex is 0.02mol / L to 0.5mol / L. Preferably, the molar ratio of organic complex to molybdenum salt precursor in the aqueous solution of molybdenum salt precursor containing organic complex is (10:25):1.

[0040] Example 8: As an optimization of the above example, in step S2, the molybdenum salt precursor is one or more of sodium molybdate dihydrate, sodium phosphomolybdate hydrate, molybdenum chloride, and ammonium molybdate, and the organic complex is one or more of ethylenediamine, ethylenediaminetetraacetic acid, diethylenetriamine, and tetraethylenepentamine.

[0041] Example 9: As an optimization of the above example, in step S2, the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3) and molybdenum salt solution (calculated as H8MoN2O4) is 1:(0.01 to 0.05):(0.005 to 0.05).

[0042] Example 10: As an optimization of the above example, in step S1, the alcohol removal process is carried out at a temperature of 45°C to 50°C and a time of 4.0h to 4.5h.

[0043] Example 11: As an optimization of the above example, in step S2, during the dynamic hydrothermal reaction, the reaction temperature is 150°C to 190°C and the reaction time is 48h to 96h.

[0044] Example 12: As an optimization of the above example, in step S3, during drying, the drying temperature is 90°C to 120°C and the drying time is 4h to 12h; during calcination, the calcination temperature is 500°C to 600°C and the calcination time is 4h to 10h.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows: First, the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst of this invention is prepared in one step through a combination of molybdenum metal ligand protection and dynamic hydrothermal reaction. Its metal loading is between 0.5 wt% and 5.0 wt%, the metal nanoparticle size is between 1 nm and 10 nm, the silicon-aluminum molar ratio (SiO2 / Al2O3) is between 20 and 100, and the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst crystals are spherical with a diameter of 100 nm to 500 nm. It exhibits good thermal stability, uniform distribution, and consistent size. The molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst possesses both acid catalytic centers and metal active centers. This effectively solves the problems of easy agglomeration, uneven dispersion, and non-uniform size of metal particles on the molecular sieve, which exist in existing metal / molecular sieve catalysts obtained using conventional loading methods.

[0046] Secondly, the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst of this invention is obtained through a dynamic hydrothermal encapsulation method, i.e., through a dynamic hydrothermal reaction. This dynamic hydrothermal encapsulation method results in more uniform dispersion of the metal particles in the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst, while retaining the high specific surface area of ​​the ZSM-5 molecular sieve and good high-temperature stability. It avoids the problems of low encapsulation (loading) efficiency and partial pore blockage that occur in the existing static hydrothermal reaction encapsulation (loading) process. Furthermore, the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst obtained through the dynamic hydrothermal encapsulation method exhibits significant catalytic performance in the heavy oil catalytic cracking reaction that yields high levels of low-carbon olefins (ethylene and propylene). The conversion rate of the feedstock heavy oil and the yield of the reaction products low-carbon olefins (ethylene and propylene) are both higher than those of Mo / ZSM-5 molecular sieve catalysts prepared under the same reaction conditions by conventional wet impregnation and static hydrothermal encapsulation methods (static hydrothermal reaction).

[0047] Therefore, the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention achieves the dual-functional coupling of "dehydrogenation-cracking" through in-situ encapsulation and dynamic synthesis, thereby improving the cracking capacity of heavy oil.

[0048] Example 13: The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst was obtained by the following method: S1, a mixed solution is obtained by mixing silicon source (tetraethyl orthosilicate), structure directing agent (tetrapropylammonium hydroxide), alkali source (ammonia water) and water, and treating it at 45℃ to 50℃ for 4.0h to remove alcohol. The molar ratio of silicon source (calculated as SiO2), structure directing agent (calculated as TPAOH), alkali source (calculated as NaOH) and water is 1:0.3:0.1:35. S2, after slowly adding a mixed solution and an aluminum source (aluminum nitrate) to a molybdenum salt solution, stirring at 45°C for 4 hours, and then subjecting a rotary dynamic hydrothermal reaction at 170°C for 72 hours, a molecular sieve intermediate was obtained. The molar ratio of the silicon source (SiO2), aluminum source (Al2O3), and molybdenum salt solution (H8MoN2O4) was 1:0.025:0.02. The molybdenum salt solution was a water-soluble molybdenum salt precursor (ammonium molybdate) containing an organic complex (ethylenediamine). The solution, containing an organic complex, is prepared by dissolving the molybdenum salt precursor (ammonium molybdate) in deionized water, adding the organic complex (ethylenediamine), and stirring until homogeneous to form a transparent 0.3 mol / L aqueous solution containing the organic complex. The dynamic hydrothermal reaction involves placing the synthesis reactor in a rotary oven to conduct the dynamic hydrothermal reaction. S3. The molecular sieve intermediate was separated by centrifugation, dried at 105℃ for 6 hours, and then calcined at 550℃ for 6 hours to obtain the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst, which is denoted as A1.

[0049] The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared using Example 13 of the present invention has a silicon-to-aluminum ratio (SiO2 / Al2O3) of 40 and a Mo (wt%) loading of 1.97%.

[0050] Comparative Example 1: The Mo / ZSM-5 molecular sieve catalyst was prepared using a traditional wet impregnation method, as follows: The first step involves mixing the silicon source (tetraethyl orthosilicate), the structure directing agent (tetrapropylammonium hydroxide), the alkali source (ammonia), and water. After removing alcohol at 45°C to 50°C for 4.0 hours, a mixed solution is obtained. The molar ratio of the silicon source (as SiO2), the structure directing agent (as TPAOH), the alkali source (as NaOH), and water is 1:0.3:0.1:35. The second step involves adding an aluminum source (aluminum nitrate) to the mixed solution, stirring at 45°C for 4 hours, and then performing a dynamic hydrothermal reaction at 170°C for 72 hours to obtain a molecular sieve intermediate. The molar ratio of the silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), and molybdenum salt solution (calculated as H8MoN2O4) is 1:0.025:0.02. The third step involves centrifuging the molecular sieve intermediate, drying it at 105°C for 6 hours, and then calcining it at 550°C for 6 hours to obtain the hydrogen-form ZSM-5 molecular sieve. Fourth, the molybdenum salt precursor (ammonium molybdate) was dissolved in deionized water and stirred until dissolved to obtain a molybdenum salt solution with a concentration of 0.3 mol / L. Then, hydrogen-form ZSM-5 molecular sieve was added to the molybdenum salt solution and stirred at room temperature for 4 h. The resulting product was then dried, ground, and calcined at 550 °C for 4 h to obtain the Mo / ZSM-5 molecular sieve catalyst, labeled D1. The mass ratio of hydrogen-form ZSM-5 molecular sieve, molybdenum salt precursor (calculated as H8MoN2O4), and deionized water was 1:0.02:10.

[0051] The Mo / ZSM-5 molecular sieve catalyst prepared using Comparative Example 1 of the present invention has a silicon-to-aluminum ratio (SiO2 / Al2O3) of 40 and a Mo (wt%) loading of 2.03%.

[0052] Comparative Example 2: The Mo / ZSM-5 molecular sieve catalyst was prepared by a static hydrothermal method, as follows: S1, a mixed solution is obtained by mixing silicon source (tetraethyl orthosilicate), structure directing agent (tetrapropylammonium hydroxide), alkali source (ammonia water) and water, and treating it at 45℃ to 50℃ for 4.0h to remove alcohol. The molar ratio of silicon source (calculated as SiO2), structure directing agent (calculated as TPAOH), alkali source (calculated as NaOH) and water is 1:0.3:0.1:35. S2, after slowly adding a mixed solution and aluminum source (aluminum nitrate) to the molybdenum salt solution, stirring at 45℃ for 4 hours, and then carrying out a static hydrothermal reaction at 170℃ for 72 hours, a molecular sieve intermediate was obtained. The molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), and molybdenum salt solution (calculated as H8MoN2O4) was 1:0.025:0.02. The molybdenum salt solution was an aqueous solution of molybdenum salt precursor (ammonium molybdate) containing an organic complex (ethylenediamine). The molar ratio of the organic complex (ethylenediamine) to the molybdenum salt precursor (ammonium molybdate) in the aqueous solution of the molybdenum salt precursor containing the organic complex was 15:1. It was obtained by dissolving the molybdenum salt precursor (ammonium molybdate) in deionized water, then adding the organic complex (ethylenediamine), and stirring until homogeneous to form a transparent molybdenum salt solution with a concentration of 0.3 mol / L. In the static hydrothermal reaction, the synthesis reactor was placed in a conventional oven for static hydrothermal crystallization. S3. The molecular sieve intermediate was separated by centrifugation, dried at 105℃ for 6 hours, and then calcined at 550℃ for 6 hours to obtain the Mo / ZSM-5 molecular sieve catalyst, labeled as D2.

[0053] The Mo / ZSM-5 molecular sieve catalyst prepared using Comparative Example 1 of the present invention has a silicon-to-aluminum ratio (SiO2 / Al2O3) of 40 and a Mo (wt%) loading of 1.89%.

[0054] Example 14: The molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst differs from that in Example 13 of this invention in that the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), and molybdenum salt solution (calculated as H8MoN2O4) is 1:0.0167:0.02, while the other steps are the same. The resulting molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst is denoted as A2.

[0055] The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared using Example 14 of this invention has a silicon-to-aluminum ratio (SiO2 / Al2O3) of 60 and a Mo (wt%) loading of 2.04%.

[0056] Example 15: The molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst differs from that in Example 13 of this invention in that the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), and molybdenum salt solution (calculated as H8MoN2O4) is 1:0.0125:0.02, while the other steps are the same. The resulting molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst is denoted as A3.

[0057] The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared using Example 15 of the present invention has a silicon-to-aluminum ratio (SiO2 / Al2O3) of 80 and a Mo (wt%) loading of 2.06%.

[0058] Example 16: The molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst differs from that in Example 13 of this invention in that the molar ratio of silicon source (as SiO2), aluminum source (as Al2O3), and molybdenum salt solution (as H8MoN2O4) is 1:0.025:0.05, while the other steps are the same. The resulting molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst is denoted as A4.

[0059] The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared using Example 16 of the present invention has a silicon-to-aluminum ratio (SiO2 / Al2O3) of 40 and a Mo (wt%) loading of 4.65%.

[0060] Experimental Example 1: Structural characterization analysis of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst of the present invention.

[0061] Experimental methods: The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), average particle size, and N2 adsorption-desorption curves. X-ray diffraction (XRD) analysis was performed using an X'Pert PRO MPD diffractometer manufactured by Panalytical, Netherlands, with Cu target Kα radiation as the light source, tube voltage of 40 kV, tube current of 40 mA, and scanning step size of 0.0167. Diffraction patterns were recorded within the range of 2θ from 5° to 75°. Scanning electron microscopy (SEM) analysis was performed using an S-4800 scanning electron microscope manufactured by Hitachi, Japan, with magnification ranging from 30x to 800,000x and accelerating voltage from 0.5 kV to 30 kV. Transmission electron microscopy (TEM) analysis was performed using a JEM-2100UHR transmission electron microscope manufactured by JEOL, Japan, with an accelerating voltage of 200 kV. Average particle size analysis was performed on at least 200 particles in a random region of the statistical image. The sample was first ultrasonically dispersed in 1 mL of ethanol and then dropped onto a copper grid for testing. N2 adsorption-desorption curve analysis was performed using an ASAP micrometer manufactured by Micromeritics. The 2460 physical adsorption instrument was used. Before testing, the samples were degassed at 300℃ for 6 hours. Then, the adsorption-desorption isotherms were measured at -196.15℃ using high-purity nitrogen as the adsorption medium. Comparative Example 2 was used as a control.

[0062] Experimental Results: X-ray diffraction (XRD) of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention is as follows: Figure 1 As shown, from Figure 1 It can be seen that the X-ray diffraction (XRD) of the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst prepared in Example 13 of the present invention conforms to the structural characteristics of MFI type zeolite molecular sieves, and no impurity peaks such as metal Mo appear, indicating that the metal-modified hierarchical ZSM-5 type molecular sieve catalyst prepared by the preparation method of the present invention is an MFI type zeolite molecular sieve (ZSM-5 molecular sieve). The scanning electron microscope (SEM) image of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention is shown below. Figure 2 As shown, the transmission electron microscope (TEM) image of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention is as follows. Figure 3 As shown, the average particle size of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention is as follows: Figure 4 As shown, the transmission electron microscope (TEM) image of the Mo / ZSM-5 molecular sieve catalyst prepared in Comparative Example 2 of this invention is as follows. Figure 5 As shown, from Figure 5It can be seen that the Mo / ZSM-5 molecular sieve catalyst prepared in Comparative Example 2 (static hydrothermal reaction) exhibits clustered Mo metal, with poor dispersion and uneven size; from Figure 2 to 4 It can be seen that the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention has a uniform distribution of metallic Mo particles with a particle size of approximately 2 nm to 8 nm; the nitrogen physical adsorption-desorption curve of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention is shown in the figure below. Figure 6 As shown, from Figure 6 It can be seen that the synthesized molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst exhibits a typical microporous structure, and the specific surface area is as high as 582 m², as obtained from curve integration. 2 / g.

[0063] Experimental Example 2: Investigating the application of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst of the present invention in the catalytic cracking reaction of crude oil.

[0064] Experimental Methods: The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalysts prepared in Examples 13 to 16 of this invention and the Mo / ZSM-5 molecular sieve catalysts prepared in Comparative Examples 1 to 2 were pressed into tablets at 20 MPa, sieved into 20-40 mesh particles, and respectively loaded into a micro fixed-bed reactor for heavy oil cracking reaction evaluation. The reaction temperature of the heavy oil cracking reaction was 600℃, the reaction pressure was 0.1 MPa, and the reaction space velocity was 8 h⁻¹. -1 The conversion rate of the feedstock heavy oil and the yield of the reaction products (ethylene and propylene) were investigated. The properties of the feedstock crude oil (vacuum oil) are shown in Table 1.

[0065] Experimental Results: The catalytic performance of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention is as follows: Figure 7 As shown in the figure, A1 is the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of the present invention, and D1 is the Mo / ZSM-5 molecular sieve catalyst prepared in Comparative Example 1 of the present invention. Figure 7 As can be seen, the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention achieved a heavy oil conversion rate of 81.1 wt% and a product yield (ethylene and propylene) of 50 wt% in heavy oil cracking. In contrast, the Mo / ZSM-5 molecular sieve catalyst prepared in Comparative Example 1 (using the traditional wet impregnation method) only achieved a heavy oil conversion rate of 68.2 wt% and a product yield (ethylene and propylene) of 33.7 wt%. The catalytic performance of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of this invention is as follows: Figure 8As shown in the figure, A1 is the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of the present invention, and D2 is the Mo / ZSM-5 molecular sieve catalyst prepared in Comparative Example 2 of the present invention. Figure 8 As can be seen, compared with Example 13, the Mo / ZSM-5 molecular sieve catalyst prepared in Comparative Example 1 (static hydrothermal reaction) has a conversion rate of only 75.9 wt% for the feedstock heavy oil and a yield of only 44.5 wt% for the reaction products (ethylene and propylene). The Mo / ZSM-5 molecular sieve catalyst prepared in Comparative Example 1 has a lower conversion rate of feedstock heavy oil and a lower yield of reaction products (ethylene and propylene) in the catalytic cracking reaction of crude oil. The catalytic performance of the molybdenum-modified hierarchical ZSM-5 molecular sieve catalysts (with different silica-to-alumina ratios) prepared in Examples 13 to 15 of this invention is as follows: Figure 9 As shown in the figure, A1 is the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of the present invention, A2 is the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 14 of the present invention, and A3 is the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 15 of the present invention. Figure 9 It can be seen that with the increase of the silicon-aluminum ratio of the molecular sieve, the conversion rate of the feedstock heavy oil and the yield of the reaction products (ethylene and propylene) also decrease, indicating that the catalytic performance of the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst of this invention is optimal when the silicon-aluminum molar ratio (SiO2 / Al2O3) of the molecular sieve is around 40. The catalytic performance of the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalysts (with different metal loadings) prepared in Examples 13 and 16 of this invention is as follows: Figure 10 As shown in the figure, A1 is the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 13 of the present invention, and A4 is the molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 16 of the present invention. Figure 10 It can be seen that with the increase of the metal Mo loading, the conversion rate of the feedstock heavy oil and the yield of the reaction products (ethylene and propylene) also increase, indicating that the catalytic performance of the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst of the present invention is optimal when the metal Mo loading is around 4.65 wt%.

[0066] In summary, the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst of this invention is prepared in one step through a combination of molybdenum metal ligand protection and dynamic hydrothermal reaction. It has the characteristics of good thermal stability, uniform metal particle distribution and size, and high catalytic activity. When the molybdenum-modified hierarchical ZSM-5 molecular sieve catalyst of this invention is applied to the heavy oil catalytic cracking reaction to produce more low-carbon olefins (ethylene and propylene), the catalytic performance is significant.

[0067] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst, characterized in that... Obtained using the following method: S1, mix silicon source, structure directing agent, alkali source and water, and then remove alcohol to obtain a mixed solution; S2, after adding a mixed solution and an aluminum source to a molybdenum salt solution, stirring until homogeneous, and carrying out a dynamic hydrothermal reaction, a molecular sieve intermediate is obtained; S3, after separating, drying and calcining the molecular sieve intermediate, a molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst is obtained.

2. The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst according to claim 1, characterized in that... In step S1, the silicon source is one or more of tetraethyl orthosilicate, water glass, and silica sol; or / and, in step S1, the structure directing agent is tetrapropylammonium hydroxide.

3. The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst according to claim 1 or 2, characterized in that... In step S1, the alkali source is one or more of sodium hydroxide and ammonia water; or / and in step S2, the aluminum source is one or more of aluminum nitrate, aluminum sulfate and aluminum isopropoxide.

4. The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst according to claim 1, 2, or 3, characterized in that... In step S1, the molar ratio of silicon source, structure directing agent, alkali source and water is 1:0.10 to 0.35:0.10 to 0.15:15 to 40.

5. The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 1 to 4, characterized in that... In step S2, the molybdenum salt solution is one of the following: an aqueous solution of a molybdenum salt precursor and an aqueous solution of a molybdenum salt precursor containing an organic complex. The molar ratio of the organic complex to the molybdenum salt precursor in the aqueous solution of the molybdenum salt precursor containing an organic complex is 1:50:

1.

6. The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst according to claim 5, characterized in that... In step S2, the molybdenum salt precursor is one or more of sodium molybdate dihydrate, sodium phosphomolybdate hydrate, molybdenum chloride, and ammonium molybdate, and the organic complex is one or more of ethylenediamine, ethylenediaminetetraacetic acid, diethylenetriamine, and tetraethylenepentamine.

7. The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 1 to 6, characterized in that... In step S2, the molar ratio of silicon source, aluminum source and molybdenum salt solution is 1:0.01 to 0.05:0.005 to 0.05; or / and, in step S1, during the alcohol removal treatment, the treatment temperature is 45°C to 50°C and the treatment time is 4.0h to 4.5h.

8. The molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 1 to 7, characterized in that... In step S2, during the dynamic hydrothermal reaction, the reaction temperature is 150℃ to 190℃ and the reaction time is 48h to 96h; or / and in step S3, during drying, the drying temperature is 90℃ to 120℃ and the drying time is 4h to 12h, and during calcination, the calcination temperature is 500℃ to 600℃ and the calcination time is 4h to 10h.

9. A method for preparing a molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 2 to 8, characterized in that... Perform the following steps: S1, mix silicon source, structure directing agent, alkali source and water, and then remove alcohol to obtain a mixed solution; S2, after adding a mixed solution and an aluminum source to a molybdenum salt solution, stirring until homogeneous, and carrying out a dynamic hydrothermal reaction, a molecular sieve intermediate is obtained; S3, after separating, drying and calcining the molecular sieve intermediate, a molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst is obtained.

10. The application of a molybdenum-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 1 to 8 in the catalytic cracking reaction of crude oil.

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