CN116375048A - Nanometer flaky ZSM-5 molecular sieve and preparation method thereof - Google Patents

Nanometer flaky ZSM-5 molecular sieve and preparation method thereof Download PDF

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CN116375048A
CN116375048A CN202310433154.9A CN202310433154A CN116375048A CN 116375048 A CN116375048 A CN 116375048A CN 202310433154 A CN202310433154 A CN 202310433154A CN 116375048 A CN116375048 A CN 116375048A
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zsm
molecular sieve
temperature
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heat treatment
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张亚红
李贺
唐颐
杜可
高嵝
谭智超
王舒琪
余家玉
李婉宜
丁玲
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Fudan University
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
    • C01B39/02—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof
    • C01B39/36—Pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11
    • C01B39/38—Type ZSM-5
    • C01B39/40—Type ZSM-5 using at least one organic template directing agent
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  • Silicates, Zeolites, And Molecular Sieves (AREA)

Abstract

The invention provides a nano flaky ZSM-5 molecular sieve and a preparation method thereof, belonging to the technical field of molecular sieves. According to the invention, tetrapropylammonium hydroxide is used as a template agent, a microwave heating assisted synthesis method is adopted, ZSM-5 embryonic crystals with an MFI topological structure and uniform structure can be simply, quickly and efficiently obtained, a high-purity ZSM-5 embryonic crystal aqueous solution is obtained through dialysis purification, the ZSM-5 embryonic crystals have extremely high growth activity, directional aggregation and crystallization can be carried out through hydrothermal treatment within a wide pH range of pH=4-13, nano flaky ZSM-5 molecular sieve crystals with small particle size, good uniformity, large specific surface, stable morphology and high crystal face selectivity are obtained, and the b-axis direction of the ZSM-5 molecular sieve crystals has short and regular straight-line pore channels, so that shorter diffusion paths and more active sites can be provided, and the mass transfer efficiency and catalytic activity of the molecular sieve are effectively improved.

Description

Nanometer flaky ZSM-5 molecular sieve and preparation method thereof
Technical Field
The invention relates to the technical field of molecular sieves, in particular to a nano flaky ZSM-5 molecular sieve and a preparation method thereof.
Background
ZSM-5 molecular sieves have relatively small specific surface areas due to the lack of "cages" possessed by other types of molecular sieves, but possess relatively broad SiO' s 2 /Al 2 O 3 The range can be conveniently adjusted, the surface acidity and the polarity can be conveniently adjusted, and meanwhile, the ZSM-5 molecular sieve has higher SiO 2 /Al 2 O 3 The molecular sieve has stable structural characteristics, the internal structure is not collapsed at 1200 ℃, the original properties of the molecular sieve can be still maintained, the molecular sieve also has good shape selectivity, and the molecular sieve is widely applied to the oil refining industry and the petrochemical industry.
At present, the preparation method of the ZSM-5 molecular sieve mainly comprises a sol-gel method, an organic solvent method, a hydrothermal method and the like. Among them, the hydrothermal method has the advantages of convenience, high cost efficiency, easy amplification, and the like, and has the most wide application. ZSM-5 molecular sieves are typically synthesized hydrothermally in relatively high alkaline environments (pH > 9), while mineralizers (e.g., fluoride ions) are typically added to synthesize ZSM-5 molecular sieves in neutral and acidic environments. However, the ZSM-5 zeolite synthesized by the hydrothermal method in a neutral or acidic environment has large particles, so that the specific surface area is small, the mass transfer efficiency is low, and the practical application of catalysis and the like is limited.
Disclosure of Invention
In view of the above, the present invention aims to provide a nano flaky ZSM-5 molecular sieve and a preparation method thereof. The preparation method provided by the invention can prepare the nano flaky ZSM-5 molecular sieve in a wide pH range (pH=4-13), and the prepared nano flaky ZSM-5 molecular sieve has small and uniform particle size, large specific surface, high mass transfer efficiency and high catalytic activity.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a preparation method of a nano flaky ZSM-5 molecular sieve, which comprises the following steps:
mixing a silicon source, an aluminum source, a template agent and water, and sequentially carrying out microwave heat treatment and dialysis purification to obtain a ZSM-5 embryonic crystal solution; the template agent comprises tetrapropylammonium hydroxide;
and regulating the pH value of the ZSM-5 embryonic crystal solution to 4-13, and performing hydrothermal treatment to obtain the nano flaky ZSM-5 molecular sieve.
Preferably, the molar ratio of the silicon dioxide, the water, the aluminum isopropoxide and the template agent in the silicon source is 1:17.5 to 22.7: 0.002-0.03: 0.3 to 0.45.
Preferably, the aluminum source comprises one or more of aluminum isopropoxide, aluminum nitrate and aluminum chloride.
Preferably, the mixing is followed by aging the obtained mixture, wherein the aging temperature is room temperature, and the aging time is 4-48 hours.
Preferably, the microwave heat treatment comprises low-temperature microwave heat treatment and high-temperature microwave heat treatment in sequence; the temperature of the low-temperature microwave heat treatment is 70-100 ℃ and the time is 60-150 min; the high-temperature microwave heat treatment is carried out at the temperature of 120-160 ℃ for 10-50 min.
Preferably, the dialysis membrane for dialysis purification has a molecular weight cut-off of 1.5 to 6kDa.
Preferably, the dialysis purification comprises sequentially performing tetrapropylammonium hydroxide aqueous solution dialysis and water dialysis, wherein the concentration of the tetrapropylammonium hydroxide aqueous solution is 2-16 mmol/L.
Preferably, the pH value adjustment is performed by using an acid or a base, wherein the acid comprises one or more of hydrochloric acid, sulfuric acid and nitric acid, and the base comprises one or more of sodium hydroxide, potassium hydroxide and ammonia water.
Preferably, the temperature of the hydrothermal treatment is 80-180 ℃ and the time is 1-30 days, and the hydrothermal treatment is static hydrothermal treatment.
The invention provides the nano flaky ZSM-5 molecular sieve prepared by the preparation method, wherein the length of the nano flaky ZSM-5 molecular sieve is 100-400 nm, the width of the nano flaky ZSM-5 molecular sieve is 100-200 nm, and the thickness of the nano flaky ZSM-5 molecular sieve is 50-150 nm.
The invention provides a preparation method of a nano flaky ZSM-5 molecular sieve, which comprises the following steps: mixing a silicon source, an aluminum source, a template agent and water, and sequentially carrying out microwave heat treatment and dialysis purification to obtain a ZSM-5 embryonic crystal solution; the template agent comprises tetrapropylammonium hydroxide; and regulating the pH value of the ZSM-5 embryonic crystal solution to 4-13, and performing hydrothermal treatment to obtain the nano flaky ZSM-5 molecular sieve. According to the invention, tetrapropylammonium hydroxide is used as a template agent, a microwave heating assisted synthesis method is adopted, ZSM-5 crystals with uniform structure can be simply, quickly and efficiently obtained, redundant raw materials (such as free silicon) are removed after dialysis and purification, high-purity ZSM-5 crystal aqueous solution is obtained, ZSM-5 crystals have extremely high growth activity, directional aggregation can be carried out through hydrothermal treatment in a wide pH value environment with pH value of 4-13, ZSM-5 crystals are aggregated and crystallized in a layer-by-layer assembly mode, and then nano flaky ZSM-5 molecular sieve crystals with small particle size, good uniformity, large specific surface, stable morphology and high crystal face selectivity are obtained, meanwhile, the b-axis direction of the nano flaky ZSM-5 molecular sieve crystals prepared by the method has short and regular straight-line pore channels, so that a shorter diffusion path and more active sites can be provided, and the mass transfer efficiency and catalytic activity of the molecular sieve can be effectively improved. In addition, the preparation method provided by the invention has the advantages of simple process, low-cost and easily obtained raw materials, low energy consumption and low production cost, and is suitable for industrial production.
Further, the molar ratio of silicon dioxide, water, aluminum isopropoxide and template agent in the silicon source is controlled to be 1:17.5 to 22.7: 0.002-0.03: 0.3 to 0.45, which is beneficial to improving the yield of ZSM-5 embryonic crystals.
Further, the method promotes the formation of a large number of ZSM-5 crystals in the mixed solution of the silicon source, the template agent, the water and the aluminum source through low-temperature microwave heat treatment, and then enables the structure of the ZSM-5 crystals to develop to order through high-temperature microwave heat treatment, and the method is beneficial to the high order of the structure of the ZSM-5 crystals, has extremely high growth activity and is beneficial to the subsequent synthesis of the high-quality nano flaky ZSM-5 molecular sieve in a wide pH range through controlling the temperature and the time of the high-temperature microwave heat treatment.
Further, the invention is beneficial to improving the yield of ZSM-5 crystals by controlling the concentration of the tetrapropylammonium hydroxide aqueous solution for dialysis.
The invention provides the nano flaky ZSM-5 molecular sieve prepared by the preparation method, wherein the length of the nano flaky ZSM-5 molecular sieve is 100-400 nm, the width of the nano flaky ZSM-5 molecular sieve is 100-200 nm, and the thickness of the nano flaky ZSM-5 molecular sieve is 50-150 nm. The nano flaky ZSM-5 molecular sieve provided by the invention has the advantages of small particle size, good uniformity, large specific surface, stable morphology, high crystal plane selectivity, short and regular straight-line pore canal in the b-axis direction, shorter diffusion path and more active sites, can effectively improve the mass transfer efficiency and catalytic activity of the molecular sieve, and has good application prospect as a catalyst.
Drawings
FIG. 1 is a TEM image of the nanosheet ZSM-5 molecular sieve prepared in example 1;
FIG. 2 is an XRD pattern of the nano-platelet ZSM-5 molecular sieve prepared in example 1;
FIG. 3 is a TEM image of the nanosheet ZSM-5 molecular sieves prepared in examples 2-6;
FIG. 4 is an XRD pattern of the nano flaky ZSM-5 molecular sieves prepared in examples 2 to 6;
FIG. 5 is a TEM image of the nanosheet ZSM-5 molecular sieves prepared in examples 7-10;
FIG. 6 is an XRD pattern of the nanosheet ZSM-5 molecular sieves prepared in examples 7 to 10;
FIG. 7 is an XRD pattern of nano-platelet ZSM-5 molecular sieves prepared in example 1 and example 11;
FIG. 8 is a TEM image of the ZSM-5 molecular sieve prepared in comparative example 1;
FIG. 9 is a TEM image of a ZSM-5 molecular sieve prepared in comparative example 2;
FIG. 10 is a TEM image of a ZSM-5 molecular sieve prepared in comparative example 3;
FIG. 11 is an XRD pattern of the ZSM-5 molecular sieve prepared in comparative example 3;
FIG. 12 is a TEM image of a ZSM-5 molecular sieve prepared in comparative example 4;
FIG. 13 is a TEM image of the ZSM-5 molecular sieve prepared in comparative example 5;
FIG. 14 is a TEM image of the ZSM-5 molecular sieve prepared in comparative example 6;
FIG. 15 is a TEM image of a ZSM-5 molecular sieve prepared in comparative example 7.
Detailed Description
The invention provides a preparation method of a nano flaky ZSM-5 molecular sieve, which comprises the following steps:
mixing a silicon source, an aluminum source, a template agent and water, and sequentially carrying out microwave heat treatment and dialysis purification to obtain a ZSM-5 embryonic crystal solution; the template agent comprises tetrapropylammonium hydroxide;
and regulating the pH value of the ZSM-5 embryonic crystal solution to 4-13, and performing hydrothermal treatment to obtain the nano flaky ZSM-5 molecular sieve.
The raw materials adopted by the invention are all commercial products unless specified.
According to the invention, a silicon source, an aluminum source, a template agent and water are mixed, and microwave heat treatment and dialysis purification are sequentially carried out to obtain a ZSM-5 embryonic crystal solution.
In the present invention, the silicon source preferably includes one or more of white carbon black, silica sol, silica gel powder, tetraethyl orthosilicate and sodium silicate, and more preferably tetraethyl orthosilicate. In the present invention, the aluminum source preferably includes one or more of aluminum isopropoxide, aluminum nitrate and aluminum chloride, and more preferably aluminum isopropoxide. In the present invention, the templating agent includes tetrapropylammonium hydroxide (TPAOH). According to the invention, tetrapropylammonium hydroxide is used as a template agent to obtain ZSM-5 crystals with an MFI topological structure, and tetraethyl orthosilicate and TPAOH are used as raw materials, so that the sources of the raw materials are wide and the cost is lower. In the invention, the molar ratio of the silicon dioxide, the water, the aluminum isopropoxide and the template agent in the silicon source is preferably 1:17.5 to 22.7: 0.002-0.03: 0.3 to 0.45, more preferably 1:18 to 22:0.003 to 0.02:0.32 to 0.42, more preferably 1:19 to 21: 0.004-0.015: 0.35 to 0.4, most preferably 1:19.5:0.005:0.39. the invention controls the dosage ratio of the silicon source, the aluminum source, the template agent and the water in the range, thereby being beneficial to improving the yield of ZSM-5 embryonic crystals.
The mixing is not particularly limited, and the raw materials can be uniformly mixed, specifically, stirring and mixing are performed, and the stirring and mixing speed is preferably 100-400 rpm, more preferably 200-300 rpm; the temperature of the mixing is preferably room temperature.
After the mixing is completed, the invention preferably further comprises aging the obtained mixture, wherein the aging temperature is preferably room temperature; the aging time is preferably 4 to 48 hours, more preferably 20 to 24 hours; the aging is preferably carried out under stirring, and the stirring speed is preferably 100 to 400rpm, more preferably 200 to 300rpm. The invention can fully hydrolyze the silicon source and the aluminum source in the aqueous solution of the template agent by aging under the condition so as to facilitate the nucleation and the growth of the subsequent nano flaky ZSM-5 molecular sieve.
In the present invention, the microwave heat treatment preferably includes sequentially performing a low-temperature microwave heat treatment and a high-temperature microwave heat treatment; the microwave heat treatment is preferably performed in a microwave reactor, which is preferably a An Dongpa microwave reactor. In the present invention, the temperature of the low-temperature microwave heat treatment is preferably 70 to 100 ℃, more preferably 80 to 90 ℃; the time of the low-temperature microwave heat treatment is preferably 60 to 150 minutes, more preferably 80 to 120 minutes. In the present invention, the temperature of the high-temperature microwave heat treatment is preferably 120 to 160 ℃, more preferably 140 to 150 ℃; the high-temperature microwave heat treatment time is preferably 10 to 50 minutes, more preferably 20 to 30 minutes. The invention adopts a microwave heating assisted synthesis method, has the advantages of simple operation and high preparation speed of ZSM-5 embryonic crystals, can efficiently synthesize ZSM-5 zeolite embryonic crystals with uniform structure, and particularly promotes a large number of ZSM-5 embryonic crystals in a mixed solution of a silicon source, a template agent, water and an aluminum source through low-temperature microwave heat treatment, and enables the ZSM-5 embryonic crystal structure to develop orderly through high-temperature microwave heat treatment, and the ZSM-5 embryonic crystal structure is highly orderly, has extremely high growth activity and is conducive to subsequent synthesis of a high-quality nano flaky ZSM-5 molecular sieve in a wide pH range through control of the temperature and time of the high-temperature microwave heat treatment.
In the present invention, the dialysis membrane for dialysis purification is preferably a cellulose semipermeable membrane, and the molecular weight cut-off of the dialysis membrane is preferably 1.5 to 6kDa, more preferably 3.5 to 4kDa, and the present invention can remove particles having a size of 2.5nm or less by using the dialysis membrane. In the present invention, the temperature of the dialysis purification is preferably room temperature; the dialysis purification is preferably performed under low-speed stirring conditions, and the speed of the low-speed stirring is preferably 10 to 100rpm, more preferably 30 to 40rpm. In the present invention, the dialysis purification preferably comprises sequentially performing tetrapropylammonium hydroxide aqueous solution dialysis and water dialysis. In the present invention, the concentration of the tetrapropylammonium hydroxide aqueous solution is preferably 2 to 16mmol/L, more preferably 4 to 12mmol/L, still more preferably 6 to 8mmol/L; in the invention, the high concentration of the TPAOH aqueous solution can dissolve ZSM-5 rudiments, thereby affecting the yield of the ZSM-5 rudiments and also affecting the growth quality of the subsequent nano flaky ZSM-5 molecular sieve; the dialysis time of the tetrapropylammonium hydroxide aqueous solution is preferably 8 to 72 hours, more preferably 15 to 24 hours. In the present invention, the water for water dialysis is preferably pure water, more preferably distilled water of the chen type; preferably, the water is changed in the water dialysis process, and the interval time of the water is preferably 3-24 hours, more preferably 8-10 hours; the number of times of the water dialysis is not particularly limited, and the water dialysis is carried out until the pH value of the dialysis external liquid is 7-8. In a specific embodiment of the invention, the interval between water changes is 8 hours and the water dialysis time is 24 hours. The invention adopts a dialysis purification method, can realize the advantages of precise screening particles and more effective components, can obtain high-purity ZSM-5 embryonic crystal aqueous solution, and the obtained ZSM-5 embryonic crystal has uniform structure, high growth activity and high porosity, thereby providing high-quality raw materials for further synthesizing the nano-sheet ZSM-5 molecular sieve with stable morphology in a wide pH range. In the present invention, the ZSM-5 embryonic solution (dialysis inner solution) preferably has a pH of 8.5 to 9.
After obtaining ZSM-5 embryonic crystal solution, the pH value of the ZSM-5 embryonic crystal solution is adjusted to 4-13, and hydrothermal treatment is carried out to obtain the nano flaky ZSM-5 molecular sieve.
In the invention, the pH value adjustment is carried out by adopting acid or alkali; the acid is preferably hydrochloric acid, and the concentration of the hydrochloric acid is preferably 0.1-12 mol/L, more preferably 0.5-1 mol/L; the alkali is preferably sodium hydroxide, and the sodium hydroxide is preferably used in the form of an aqueous sodium hydroxide solution, and the concentration of the aqueous sodium hydroxide solution is preferably 0.5 to 2mol/L, more preferably 1 to 1.5mol/L.
In the present invention, the temperature of the hydrothermal treatment is preferably 80 to 180 ℃, more preferably 120 to 170 ℃, still more preferably 150 to 160 ℃; the time of the hydrothermal treatment is preferably 1 to 30 days, more preferably 5 to 10 days, and still more preferably 7 to 8 days; the hydrothermal treatment is preferably a static hydrothermal treatment; the device adopted by the hydrothermal treatment is not particularly limited, and the hydrothermal treatment device well known in the art can be adopted; in an embodiment of the present invention, the hydrothermal treatment is preferably: and (3) placing the ZSM-5 embryonic crystal solution with the pH value adjusted in a reaction kettle, sealing the reaction kettle, and placing the reaction kettle in a static constant-temperature oven for static hydrothermal treatment.
After the hydrothermal treatment, the method preferably further comprises the steps of cooling the system obtained after the hydrothermal treatment to room temperature, performing solid-liquid separation, washing the obtained solid material with water, and drying to obtain the nano flaky ZSM-5 molecular sieve. The cooling mode is not particularly limited, and cooling modes well known in the art, such as natural cooling, may be adopted. The solid-liquid separation mode is not particularly limited, and a solid-liquid separation mode well known in the art can be adopted, such as filtration, suction filtration or centrifugal separation; the rotational speed of the centrifugal separation is preferably 5000 to 15000rpm, more preferably 10000 to 12000rpm, and the time of the centrifugal separation is preferably 1 to 30min, more preferably 5 to 8min. In the present invention, the water washing is preferably centrifugal water washing, and the temperature of the centrifugal water washing is preferably room temperature; the rotation speed of the centrifugal water washing is preferably 5000-15000 rpm, more preferably 10000-12000 rpm; the number of times of the washing is preferably 1 to 6 times, more preferably 2 to 3 times; the time of the single water washing is preferably 1 to 60 minutes, more preferably 10 to 30 minutes; in the centrifugal water washing process, after water is added into the solid material, ultrasonic treatment is preferably performed firstly and then centrifugation is performed, the ultrasonic treatment is preferably performed in an ultrasonic cleaning machine, and the purpose of the ultrasonic treatment is to redisperse the solid material, so that the water is ensured to be washed cleanly. In the present invention, the drying temperature is preferably 25 to 140 ℃, more preferably 50 to 80 ℃; the drying time is preferably 1 to 48 hours, more preferably 5 to 12 hours.
The invention provides the nano flaky ZSM-5 molecular sieve prepared by the preparation method. In the invention, the length of the nano flaky ZSM-5 molecular sieve is 100-400 nm, preferably 200-300 nm; the width of the nano flaky ZSM-5 molecular sieve is 100-200 nm, preferably 120-180 nm; the thickness of the nano flaky ZSM-5 molecular sieve is 50-150 nm, preferably 80-120 nm.
The invention provides application of the nano flaky ZSM-5 molecular sieve as a catalyst. The nano flaky ZSM-5 molecular sieve prepared by the invention has the characteristics of small particle size, large specific surface area, uniform structure, high porosity, multiple effective components, high growth activity and high mass transfer efficiency, and has good application prospect as a catalyst.
The technical solutions of the present invention will be clearly and completely described in the following in connection with the embodiments of the present invention. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
Mixing 0.0441g of aluminum isopropoxide, 9g of tetraethyl orthosilicate, 13.7g of TPAOH and 4.893g of water uniformly at room temperature under the stirring condition of 300rpm, aging for 24 hours, transferring into a microwave reactor, carrying out low-temperature microwave heat treatment for 90 minutes at 90 ℃, carrying out high-temperature microwave heat treatment for 20 minutes at 140 ℃, transferring into a cellulose semipermeable membrane with the interception molecular weight of 3.5kDa, soaking in 1L of TPAOH water solution with the concentration of 6mmol/L, dialyzing and purifying for 24 hours at room temperature under the condition of 40rpm, and then placing in distilled water for dialysis and purification, wherein distilled water is replaced every 8 hours until the pH value of dialysis external liquid is 7.0, thus obtaining ZSM-5 embryonic solution (ZSM-5 embryonic yield is 32.4%), and the pH value of the embryonic solution is 8.5-9.0; wherein, the yield of the chicks = mass of silica in ZSM-5 chick solution/mass of silica in charged tetraethyl orthosilicate x 100%.
And (3) regulating the pH value of the ZSM-5 embryonic crystal solution to 9.0 by using a sodium hydroxide solution with the concentration of 1mol/L, placing the solution in a hydrothermal reaction kettle, sealing, then standing the solution in a preheated 160 ℃ constant temperature oven for carrying out standing hydrothermal treatment for 7 days, cooling to room temperature, transferring the obtained milky white solution into a centrifuge tube, placing the centrifuge tube in a centrifuge, centrifuging at room temperature and 10000rpm for 5min, pouring out supernatant, adding deionized water into the obtained solid material, uniformly distributing in an ultrasonic cleaner, centrifuging, pouring out supernatant, centrifuging for 3 times, and drying in an oven at 65 ℃ for 12h for the single-time centrifugal washing time of 30min to obtain the nano flaky ZSM-5 molecular sieve crystal. When the pH value of the embryonic solution=9, the operation of adjusting the pH value by the sodium hydroxide solution was omitted.
FIG. 1 is a Transmission Electron Microscope (TEM) image of the nanosheet ZSM-5 molecular sieve prepared in this example. As can be seen from fig. 1, the nano flaky ZSM-5 molecular sieve crystal prepared by the present invention has a length x width x thickness=300 nm x 180nm x 77nm, and is a nano flaky ZSM-5 molecular sieve crystal with high crystal plane selectivity in the short b axis direction, and has small size and good uniformity in size, and the flaky molecular sieve is more favorable for mass transfer.
FIG. 2 is an X-ray diffraction pattern of the nano flaky ZSM-5 molecular sieve prepared in this example. As can be seen from fig. 2, the nano flaky ZSM-5 molecular sieve prepared in this example has a highly crystalline MFI topology.
Example 2
A nanosheet ZSM-5 molecular sieve was prepared according to the method of example 1, except that "the pH of the ZSM-5 embryonic crystal solution was adjusted to 9.0 with a sodium hydroxide solution having a concentration of 1 mol/L" was replaced with "the pH of the ZSM-5 embryonic crystal solution was adjusted to 8.0 with a hydrochloric acid aqueous solution having a concentration of 0.5 mol/L".
Example 3
A nanosheet ZSM-5 molecular sieve was prepared according to the method of example 1, except that "the pH of the ZSM-5 embryonic crystal solution was adjusted to 9.0 with a sodium hydroxide solution having a concentration of 1 mol/L" was replaced with "the pH of the ZSM-5 embryonic crystal solution was adjusted to 7.0 with a hydrochloric acid aqueous solution having a concentration of 0.5 mol/L".
Example 4
A nanosheet ZSM-5 molecular sieve was prepared according to the method of example 1, except that "the pH of the ZSM-5 embryonic crystal solution was adjusted to 9.0 with a sodium hydroxide solution having a concentration of 1 mol/L" was replaced with "the pH of the ZSM-5 embryonic crystal solution was respectively adjusted to 6.0 with hydrochloric acid having a concentration of 0.5 mol/L".
Example 5
A nanosheet ZSM-5 molecular sieve was prepared according to the method of example 1, except that "the pH of the ZSM-5 embryonic crystal solution was adjusted to 9.0 with a sodium hydroxide solution having a concentration of 1 mol/L" was replaced with "the pH of the ZSM-5 embryonic crystal solution was respectively adjusted to 5.0 with hydrochloric acid having a concentration of 0.5 mol/L".
Example 6
A nanosheet ZSM-5 molecular sieve was prepared according to the method of example 1, except that "the pH of the ZSM-5 embryonic crystal solution was adjusted to 9.0 with a sodium hydroxide solution having a concentration of 1 mol/L" was replaced with "the pH of the ZSM-5 embryonic crystal solution was respectively adjusted to 4.0 with hydrochloric acid having a concentration of 0.5 mol/L".
FIG. 3 is a Transmission Electron Microscope (TEM) image of the nano-platelet ZSM-5 molecular sieve prepared in examples 2 to 6, and it is clear from FIG. 3 that the nano-platelet ZSM-5 molecular sieve crystals prepared in the invention have a length of 300 to 400nm, a width of 15 to 190nm, and a thickness of 50 to 110nm, and are all nano-platelet ZSM-5 molecular sieve crystals in the short b-axis direction.
Fig. 4 is an X-ray diffraction chart of the nano flaky ZSM-5 molecular sieves prepared in examples 2 to 6, and it can be confirmed from fig. 4 that the nano flaky molecular sieves prepared in the present invention have MFI topology.
Example 7
A nanosheet ZSM-5 molecular sieve was prepared according to the method of example 1, differing from example 1 only in that the pH of the ZSM-5 embryonic solution was adjusted to 10.0.
Example 8
A nanosheet ZSM-5 molecular sieve was prepared according to the method of example 1, differing from example 1 only in that the pH of the ZSM-5 embryonic solution was adjusted to 11.0.
Example 9
A nanosheet ZSM-5 molecular sieve was prepared according to the method of example 1, differing from example 1 only in that the pH of the ZSM-5 embryonic solution was adjusted to 12.0.
Example 10
A nanosheet ZSM-5 molecular sieve was prepared according to the method of example 1, differing from example 1 only in that the pH of the ZSM-5 embryonic solution was adjusted to 13.0.
FIG. 5 is a Transmission Electron Microscope (TEM) image of the nano-platelet ZSM-5 molecular sieve prepared in examples 7 to 10, and it is clear from FIG. 5 that the nano-platelet ZSM-5 molecular sieve crystals prepared in the invention have a length of 180 to 220nm, a width of 120 to 180nm, and a thickness of 70 to 120nm, and are all nano-platelet ZSM-5 molecular sieve crystals in the short b-axis direction.
Fig. 6 is an X-ray diffraction chart of the nano flaky ZSM-5 molecular sieves prepared in examples 7 to 10, and as can be seen from fig. 6, the nano flaky molecular sieves prepared in the present invention have MFI topology.
Example 11
A nano-platelet ZSM-5 molecular sieve was prepared as in example 1, differing from example 1 only in that the concentration of the aqueous solution of TPAOH for dialysis was 10mmol/L and the yield of ZSM-5 crystals was 29.1%. As is clear from a comparison of example 1 and example 11, the yield of ZSM-5 crystals obtained by dialysis with an aqueous solution of TPAOH having a concentration of 6mmol/L was higher than that of ZSM-5 crystals obtained by dialysis with an aqueous solution of TPAOH having a concentration of 10 mmol/L.
FIG. 7 is an X-ray diffraction chart of the nano flaky ZSM-5 molecular sieves prepared in example 1 and example 11. As can be seen from FIG. 7, the relative crystallinity of the nano flaky ZSM-5 molecular sieves grown by the ZSM-5 crystals obtained by the dialysis with the aqueous solution of TPAOH having a concentration of 10mmol/L is slightly lower than that obtained by the dialysis with the aqueous solution of TPAOH having a concentration of 6mmol/L.
Comparative example 1
The nano flaky ZSM-5 molecular sieve was prepared according to the method of example 1, except that the crystallization temperature was 80℃and the pH values of the ZSM-5 embryonic crystal solutions were adjusted to 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 and 13.0 using a sodium hydroxide solution having a concentration of 1mol/L or an aqueous solution of 0.5mol/L, respectively.
Fig. 8 is a Transmission Electron Microscope (TEM) image of a ZSM-5 molecular sieve formed by crystallization of the ZSM-5 crystals prepared in comparative example 1 in an environment at ph=4.0 to 13.0 and 80 ℃. As can be seen from FIG. 8, the ZSM-5 molecular sieves prepared at 80℃were larger than those prepared in examples 1 to 10.
Comparative example 2
44.44g TEOS and 0.596g aluminum isopropoxide are stirred for 3 hours at 25 ℃ and 300r/min, then 35.624g TPAOH is added and aged for 21 hours under the magnetic stirring condition of 25 ℃ and 300r/min, the clarified solution obtained after aging is transferred into a microwave reaction tube, and then the microwave reaction tube is placed in a microwave instrument. First, heat-treating at a low temperature of 90 ℃ for 1.5 hours, then immediately heating to 150 ℃ for 0.5 hour, transferring to a dialysis membrane with a molecular weight of 3.5kDa, immersing the dialysis membrane in 1000mL of an aqueous solution of TPAOH with a concentration of 6mmol/L, and then dialyzing at 25 ℃ and 40r/min for 1 day. The dialysis membrane is placed in 1000mL of distilled water for dialysis for 1 day, distilled water is replaced every 6-8 hours during the dialysis, the pH value of the dialysis external solution is between 7.0 and 8.0 after the dialysis is finished, the pH value of the obtained ZSM-5 embryonic crystal solution is respectively adjusted to 4.0-13.0 according to the method of examples 1-10, the ZSM-5 embryonic crystal solution is transferred into a hydrothermal reaction kettle, the hydrothermal reaction kettle is placed in a constant temperature oven at 160 ℃, and the static hydrothermal reaction is carried out for 7 days. Naturally cooling to room temperature, transferring the obtained milky white solution into a 10mL centrifuge tube, placing the centrifuge tube into a centrifuge, centrifuging for 5min at a rotating speed of 10000r/min, discarding supernatant, collecting a centrifugal substrate, placing the centrifugal substrate into the 10mL centrifuge tube, adding 8mL deionized water, ultrasonically washing in an ultrasonic dispersing instrument for 30min, centrifuging again, and repeating the ultrasonic washing step for three times. After the last centrifugation, the collected centrifugal substrate is placed in a constant temperature oven at 65 ℃ for drying for 12 hours, and crushed to obtain the powdery ZSM-5 molecular sieve with the silicon-aluminum ratio of 73.
FIG. 9 is a Transmission Electron Microscope (TEM) image of ZSM-5 molecular sieves prepared at different pH values in comparative example 2. As can be seen from fig. 9, the size of the ZSM-5 molecular sieve with a low silica to alumina ratio prepared in comparative example 2 was larger than that of the ZSM-5 molecular sieves (silica to alumina ratio 200) prepared in examples 1 to 10.
Comparative example 3
The preparation method of the microwave one-step method comprises the following specific steps: 0.0441g of aluminum isopropoxide, 9g of tetraethyl orthosilicate, 13.7g of TPAOH and 4.893g of water are added to a 100mL disposable test tube at room temperature under stirring at 300rpm, and after uniform mixing, the mixture is aged for 24 hours, and then the aged clear solution is transferred to a microwave reaction tube. Placing a microwave reaction tube in a microwave instrument, performing low-temperature microwave heat treatment for 90min at 90 ℃, performing high-temperature microwave heat treatment for 180min at 140 ℃, cooling to room temperature, transferring the obtained milky white solution into a centrifuge tube, placing the centrifuge tube in a centrifuge, centrifuging at room temperature and 10000rpm for 5min, pouring out supernatant, adding deionized water into the obtained solid material, performing ultrasonic distribution in an ultrasonic cleaner uniformly, centrifuging, pouring out supernatant, centrifuging for 3 times, performing single-time centrifugal washing for 5min, and drying in an oven at 65 ℃ for 12h to obtain the ZSM-5 molecular sieve.
FIG. 10 is a Transmission Electron Microscope (TEM) image of the ZSM-5 molecular sieve prepared in the microwave one-step method of comparative example 3, and it can be seen from FIG. 10 that the ZSM-5 molecular sieve prepared in the microwave one-step method has a morphology and a size which are not uniform, a shape which is similar to a sphere, and a size which is 150 to 300nm.
Fig. 11 is an X-ray diffraction chart of the ZSM-5 molecular sieve prepared by the microwave one-step method in comparative example 3, and as can be seen from fig. 11, the ZSM-5 molecular sieve prepared by the microwave one-step method has a highly crystalline MFI topology.
Comparative example 4
The preparation of the reaction kettle by a one-step method comprises the following specific steps: adding 0.0441g of aluminum isopropoxide, 9g of tetraethyl orthosilicate, 13.7g of TPAOH and 4.893g of water into a hydrothermal reaction kettle under stirring at room temperature and 300rpm, uniformly mixing and aging for 24h, transferring the reaction kettle into a 160 ℃ oven for crystallization for 7 days, cooling to room temperature, transferring the obtained milky white solution into a centrifuge tube, placing the centrifuge tube into a centrifuge, centrifuging for 5min at room temperature and 10000rpm, pouring out the supernatant, adding deionized water into the obtained solid material, uniformly distributing in an ultrasonic cleaner, centrifuging again, pouring out the supernatant, and carrying out centrifugal washing for 3 times, wherein the single centrifugal washing time is 5min, and then drying for 12h in the 65 ℃ oven to obtain the ZSM-5 molecular sieve.
FIG. 12 is a Transmission Electron Microscope (TEM) image of the ZSM-5 molecular sieve prepared in the one-step method in comparative example 4, and it is apparent from FIG. 12 that the size of the ZSM-5 molecular sieve prepared in the one-step method in the reaction kettle is 200 to 400nm, and the particle size of the ZSM-5 molecular sieve is large.
Comparative example 5
The one-step method for preparing ZSM-5 by using inorganic silicon source and aluminum source comprises the following specific steps: adding 0.0695g of aluminum isopropoxide, 8.64g of silica sol (40 wt%) and 18.27g of TPAOH into a 50mL disposable test tube under the stirring condition of room temperature and 300rpm, uniformly mixing, aging for 24 hours, transferring into a microwave reactor, carrying out low-temperature microwave heat treatment at 90 ℃ for 90 minutes, then carrying out high-temperature microwave heat treatment at 150 ℃ for 240 minutes, cooling to room temperature, transferring the obtained milky white solution into a centrifuge tube, placing the centrifuge tube into a centrifuge, centrifuging for 5 minutes at room temperature and 10000rpm, pouring out supernatant, adding deionized water into the obtained solid material, carrying out ultrasonic distribution uniformly, centrifuging again in an ultrasonic cleaner, pouring out supernatant, centrifuging and washing for 3 times, carrying out single centrifugation and washing time for 5 minutes, and then drying in an oven at 65 ℃ for 12 hours to obtain the ZSM-5 molecular sieve.
FIG. 13 is a Transmission Electron Microscope (TEM) image of a ZSM-5 molecular sieve prepared in one step by microwaves as in comparative example 5. As can be seen from FIG. 13, the ZSM-5 molecular sieve prepared from the inorganic silicon source and the aluminum source has a particle size of 100 to 300nm. It was demonstrated that varying the silicon and aluminum sources affected the size of the zeolite due to the non-uniform and larger size of the precursor formed after hydrolysis of the inorganic silicon and aluminum sources, resulting in the formation of larger ZSM-5 molecular sieve particles.
Comparative example 6
The preparation method for ZSM-5 crystals by aggregation growth of inorganic silicon source and aluminum source comprises the following specific steps: 0.0695g of aluminum isopropoxide, 8.64g of silica sol (40 wt%) and 18.27g of TPAOH are added into a 50mL disposable test tube under stirring at room temperature and 300rpm, the mixture is uniformly mixed and aged for 24 hours, then the mixture is transferred into a microwave reactor, the mixture is subjected to low-temperature microwave heat treatment at 90 ℃ for 90min and then high-temperature microwave heat treatment at 150 ℃ for 120min, and dialysis is carried out by adopting a dialysis mode of the embodiment 1, so as to obtain ZSM-5 embryonic solution (pH value is about 9.0). And placing the ZSM-5 embryonic crystal solution into a constant temperature oven at 80 ℃ for hydrothermal treatment for 7 days. Taking out the test tube, cooling to room temperature, transferring the obtained milky white solution into a centrifuge tube, placing the centrifuge tube into a centrifuge, centrifuging for 5min at room temperature and 10000rpm, pouring out supernatant, adding deionized water into the obtained solid material, uniformly distributing by ultrasonic in an ultrasonic cleaner, centrifuging again, pouring out supernatant, centrifuging for 3 times, centrifuging for 5min for a single centrifuging time, and drying in an oven at 65 ℃ for 12h to obtain the ZSM-5 molecular sieve.
FIG. 14 is a Transmission Electron Microscope (TEM) image of the ZSM-5 molecular sieve prepared in comparative example 6. As can be seen from FIG. 14, the ZSM-5 molecular sieve prepared from the inorganic silicon source and the aluminum source has a particle size of 500-700 nm and a large molecular sieve particle size.
Comparative example 7
The ZSM-5 molecular sieve was prepared in the same manner as in comparative example 6 except that the temperature of the hydrothermal treatment was 160 ℃.
FIG. 15 is a Transmission Electron Microscope (TEM) image of the ZSM-5 molecular sieve prepared in comparative example 7. As can be seen from FIG. 15, the ZSM-5 molecular sieve prepared from the inorganic silicon source and the aluminum source has a particle size of 600-1000 nm and a large molecular sieve size.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.

Claims (10)

1. The preparation process of nanometer flaky ZSM-5 molecular sieve includes the following steps:
mixing a silicon source, an aluminum source, a template agent and water, and sequentially carrying out microwave heat treatment and dialysis purification to obtain a ZSM-5 embryonic crystal solution; the template agent comprises tetrapropylammonium hydroxide;
and regulating the pH value of the ZSM-5 embryonic crystal solution to 4-13, and performing hydrothermal treatment to obtain the nano flaky ZSM-5 molecular sieve.
2. The method according to claim 1, wherein the molar ratio of silica, water, aluminum isopropoxide and template agent in the silicon source is 1:17.5 to 22.7: 0.002-0.03: 0.3 to 0.45.
3. The production method according to claim 1 or 2, wherein the aluminum source comprises one or more of aluminum isopropoxide, aluminum nitrate and aluminum chloride.
4. The method according to claim 1 or 2, wherein the mixing further comprises aging the obtained mixture at room temperature for 4 to 48 hours.
5. The production method according to claim 1 or 2, wherein the microwave heat treatment comprises sequentially performing a low-temperature microwave heat treatment and a high-temperature microwave heat treatment; the temperature of the low-temperature microwave heat treatment is 70-100 ℃ and the time is 60-150 min; the high-temperature microwave heat treatment is carried out at the temperature of 120-160 ℃ for 10-50 min.
6. The method according to claim 1, wherein the dialysis membrane for dialysis purification has a molecular weight cut-off of 1.5 to 6kDa.
7. The method according to claim 1 or 6, wherein the dialysis purification comprises sequentially performing dialysis with an aqueous tetrapropylammonium hydroxide solution having a concentration of 2 to 16mmol/L and water dialysis.
8. The method according to claim 1, wherein the pH adjustment is performed using an acid or a base, the acid including one or more of hydrochloric acid, sulfuric acid and nitric acid, and the base including one or more of sodium hydroxide, potassium hydroxide and aqueous ammonia.
9. The method according to claim 1, wherein the hydrothermal treatment is performed at a temperature of 80 to 180 ℃ for 1 to 30 days, and the hydrothermal treatment is a static hydrothermal treatment.
10. The nano flaky ZSM-5 molecular sieve prepared by the preparation method of any one of claims 1 to 9, wherein the length of the nano flaky ZSM-5 molecular sieve is 100 to 400nm, the width of the nano flaky ZSM-5 molecular sieve is 100 to 200nm, and the thickness of the nano flaky ZSM-5 molecular sieve is 50 to 150nm.
CN202310433154.9A 2023-04-21 2023-04-21 Nanometer flaky ZSM-5 molecular sieve and preparation method thereof Pending CN116375048A (en)

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