CN110882718B - Metal modified MFI @ MFI core-shell type molecular sieve catalyst and preparation thereof - Google Patents

Metal modified MFI @ MFI core-shell type molecular sieve catalyst and preparation thereof Download PDF

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CN110882718B
CN110882718B CN201911232183.9A CN201911232183A CN110882718B CN 110882718 B CN110882718 B CN 110882718B CN 201911232183 A CN201911232183 A CN 201911232183A CN 110882718 B CN110882718 B CN 110882718B
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molecular sieve
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CN110882718A (en
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孙玉坤
刘亚圣
翟岩亮
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Dalian Haixin Chemical Industrial Co ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
    • B01J29/48—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing arsenic, antimony, bismuth, vanadium, niobium tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
    • B01J29/405—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing rare earth elements, titanium, zirconium, hafnium, zinc, cadmium, mercury, gallium, indium, thallium, tin or lead
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
    • B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
    • B01J29/46—Iron group metals or copper
    • B01J35/396—
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
    • C07C1/20—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon starting from organic compounds containing only oxygen atoms as heteroatoms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
    • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2529/00—Catalysts comprising molecular sieves
    • C07C2529/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites, pillared clays
    • C07C2529/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • C07C2529/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2529/00—Catalysts comprising molecular sieves
    • C07C2529/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites, pillared clays
    • C07C2529/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • C07C2529/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11
    • C07C2529/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11 containing iron group metals, noble metals or copper
    • C07C2529/46—Iron group metals or copper
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2529/00—Catalysts comprising molecular sieves
    • C07C2529/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites, pillared clays
    • C07C2529/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • C07C2529/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11
    • C07C2529/48—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11 containing arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Abstract

The invention provides a metal modified MFI @ MFI core-shell type molecular sieve catalyst and a preparation method thereof. The method comprises the following steps: (1) carrying out metal oxide modification on the ZSM-5 molecular sieve by adopting a nano metal oxide through a solvothermal method to obtain a modified ZSM-5 molecular sieve; the metal is selected from one or more of Mn, Ce, Fe, Co, Ni, La, Ga and W; (2) and (2) carrying out secondary hydrothermal synthesis on the modified ZSM-5 molecular sieve obtained in the step (1) in a crystalline liquid of a Silicalite-1 molecular sieve or a B-ZSM-5 molecular sieve to obtain the metal modified MFI @ MFI core-shell type molecular sieve catalyst. The metal modified MFI @ MFI core-shell type molecular sieve catalyst can greatly reduce the carbon deposition rate of the reaction of preparing propylene from methanol, improve the selectivity of propylene and prolong the catalytic life, and the modification effect is improved more than that of the traditional mode.

Description

Metal modified MFI @ MFI core-shell type molecular sieve catalyst and preparation thereof
Technical Field
The invention relates to the field of chemical industry, in particular to the field of catalysts for preparing propylene from methanol, and more particularly relates to a metal modified MFI @ MFI core-shell type molecular sieve catalyst and a preparation method thereof.
Background
Propylene is an extremely important basic raw material in the field of petrochemical industry, has very wide application, such as production of polypropylene, acrylonitrile, butanol, octanol, propylene oxide and other products, and the world demand thereof is rapidly increased. The traditional propylene production route relies too much on petroleum resources and cannot meet the global propylene demand, so countries around the world are beginning to focus on the development of non-petroleum route propylene preparation technology, wherein Methanol To Propylene (MTP) technology is receiving more and more extensive attention. The source of the raw material methanol is very wide, and the methanol can be prepared from coal, natural gas or biomass through synthesis gas, so that the pressure of using petroleum resources is relieved. In order to improve the propylene yield of the MTP process, researchers have devoted a lot of efforts to research and develop core catalysts of the MTP process. For fixed bed reaction processes, ZSM-5 molecular sieves are the most well-established MTP reaction catalyst. A fixed bed MTP process successfully developed in 1996 by Lurgi Germany adopts a ZSM-5 molecular sieve developed by chemical companies in southern Germany as a catalyst, takes propylene as a target product, and simultaneously obtains byproducts such as liquefied gas, gasoline, fuel gas and the like with high added value. At present, a lot of catalysts are reported for preparing propylene from methanol, for example, in U.S. Pat. No. 9738570B1 and chinese patent CN102059137B, the selectivity of low-carbon olefin of these molecular sieve catalysts is improved to a certain extent, but the catalytic performance of the molecular sieve catalysts still has a larger promotion space, and the poor carbon deposition resistance of the catalysts is also a major problem of the existing catalysts, so a more suitable catalyst for preparing propylene from methanol needs to be found out to improve the selectivity of propylene and reduce the carbon deposition rate of the catalyst.
At present, the research on the process for preparing propylene from methanol at home and abroad is in a primary stage, and the core of the process is still the design and preparation of a catalyst. In order to improve the yield of the low-carbon olefin, from 2008, people begin to use a metal modified ZSM-5 molecular sieve catalyst, and find that the selectivity of a target product propylene of the ZSM-5 molecular sieve catalyst modified by metals such as Ce, W, Mn, Fe and the like is improved to a certain extent. The modification method usually employed is an impregnation method or an ion exchange method. The propylene selectivity of the metal modified ZSM-5 catalyst is usually 35-45% under different reaction raw materials and reaction temperatures.
Although the molecular sieve catalyst has many advantages, the catalyst has a short service life for a high-temperature hydrothermal reaction, and the disadvantage of quick carbon deposition makes the catalyst to be further perfected on industrial production. On one hand, reactants, intermediates and product molecules (such as olefin and aromatic hydrocarbon products) are not easy to diffuse in the reaction process, so that carbon deposit is caused by secondary reaction, in addition, the pore blocking or acid site covering of the molecular sieve caused by the carbon deposit in the reaction process, and the framework dealumination caused by high-temperature hydrothermal in the reaction process are all the reasons for causing the inactivation of the molecular sieve. Generally, the acid property of the molecular sieve is regulated and controlled, the grain size of the molecular sieve is reduced in combination, and the ZSM-5 molecular sieve with the mesoporous structure is synthesized, so that the reaction and diffusion performance of the molecular sieve is improved, and the comprehensive reaction performance of the catalyst is improved. However, the multistage pore structure ZSM-5 molecular sieve such as nanocrystal stacking ZSM-5, nano thin layer ZSM-5, small crystal ZSM-5 and the like has a very high external surface area, a short diffusion pore channel and excellent diffusion performance, and is beneficial to smooth progress of the reaction of preparing propylene from methanol, but the external surface of the multistage pore molecular sieve has high strong acid density, and carbon deposition preferentially occurs near the external surface, so that deactivation is fast. In view of the reasons, the invention provides a novel preparation method of a metal oxide modified MFI @ MFI core-shell type molecular sieve catalyst, wherein the internal acidity and inert shell layer covering are regulated and controlled through the modification of the metal oxide, the microstructure of the molecular sieve can be regulated and controlled by combining the internal acidity and inert shell layer covering, the density of strong acid on the outer surface of the catalyst can be greatly reduced, and the properties of the acid on the inner surface and the outer surface of the catalyst can be reasonably regulated, so that the carbon deposition rate of the reaction for preparing propylene from methanol is reduced, and the selectivity of a target product propylene is improved.
Disclosure of Invention
One purpose of the invention is to provide a metal modified MFI @ MFI core-shell type molecular sieve catalyst; the molecular sieve has a core-shell structure with a metal oxide modified Al-ZSM-5 molecular sieve as a core phase and a Silicalite-1 or B-ZSM-5 molecular sieve as a shell phase, has gradient acid distribution with more and less cores and strong and weak cores, and reasonably modulates the acid properties of the inner surface and the outer surface; the core-shell molecular sieve has a hierarchical pore structure with a core phase rich in mesopores and a shell phase rich in micropores;
the invention also aims to provide a preparation method of the metal modified MFI @ MFI core-shell type molecular sieve catalyst; compared with the traditional impregnation method and the like, the metal modification method can reduce the addition amount of modified metal species, improve the utilization rate of the metal species and modulate the surface acid property of the molecular sieve; in addition, the metal oxide clusters can be encapsulated inside the molecular sieve by adopting the microporous MFI molecular sieve shell layer grown by epitaxy, so that the loss of the metal oxide is slowed down, the preparation process is simple and controllable, and the catalytic performance is obviously improved after modification;
the invention also aims to provide application of the metal modified MFI @ MFI core-shell type molecular sieve catalyst.
In order to achieve the above object, in one aspect, the present invention provides a preparation method of a metal modified MFI @ MFI core-shell type molecular sieve catalyst, wherein the method comprises the following steps:
(1) Carrying out metal oxide modification on the ZSM-5 molecular sieve by adopting a nano metal oxide through a solvothermal method to obtain a modified ZSM-5 molecular sieve; the metal is selected from one or more of Mn, Ce, Fe, Co, Ni, La, Ga and W;
(2) and (2) carrying out secondary hydrothermal synthesis on the modified ZSM-5 molecular sieve obtained in the step (1) in a crystalline liquid of the Silicalite-1 molecular sieve or the B-ZSM-5 molecular sieve to obtain the metal modified MFI @ MFI core-shell type molecular sieve catalyst.
According to some embodiments of the present invention, the ZSM-5 molecular sieve is a small-grained ZSM-5 molecular sieve, a nanocrystalline stacking ZSM-5 molecular sieve, a nano-thin-layer ZSM-5 molecular sieve, or the like.
Wherein, the preparation method of the small crystal grain ZSM-5 molecular sieve is disclosed in patent CN104787777A, and the silicon-aluminum ratio of the small crystal grain ZSM-5 molecular sieve is 100-600 in some embodiments of the invention;
the preparation method of the nanocrystalline stacking ZSM-5 molecular sieve is disclosed in patent CN104525245A, and the silica-alumina ratio of the nanocrystalline stacking ZSM-5 molecular sieve is 100-600 in some specific embodiments of the invention;
the preparation method of the nano thin layer ZSM-5 molecular sieve is disclosed in patent CN106673007A, and the silica-alumina ratio of the nano thin layer ZSM-5 molecular sieve is 100-600 in some embodiments of the invention.
According to some embodiments of the present invention, in the step (1), the nano metal oxide has a particle diameter of 10 to 500 nm.
According to some embodiments of the present invention, in the step (1), the diameter of the nano metal oxide particles is 10 to 150 nm.
According to some embodiments of the invention, wherein the nano metal oxide has a particle diameter distribution within a range of ± 30 nm.
According to some embodiments of the invention, wherein the nano metal oxide has a particle diameter distribution within a range of ± 10 nm.
According to some specific embodiments of the invention, wherein the nanometal oxide is selected from MnO2、Mn2O3、Mn3O4、CeO2、Ce2O3、FeO、Fe2O3、Fe3O4、CoO、Co2O3、Co3O4、NiO、Ni2O3、La2O3、Ga2O3、WO2And WO3Any combination of one or more of the above.
According to some specific embodiments of the present invention, step (1) comprises adding the nano metal oxide, the organosilane and the ZSM-5 molecular sieve into a solvent to perform metal oxide modification to obtain a modified ZSM-5 molecular sieve; wherein the mass of the metal oxide for modification is 0.01-20% of that of the ZSM-5 molecular sieve, the mass of the solvent is 1-10 times of that of the ZSM-5 molecular sieve, and the mass of the organosilane is 0-30% of that of the ZSM-5 molecular sieve, wherein the mass of the ZSM-5 molecular sieve is 100%.
According to some embodiments of the invention, the organosilane is an amino-containing organosiloxane.
According to some embodiments of the invention, the organosilane is selected from the group consisting of aminopropyltriethoxysilane, N-aminoethyl-3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, and combinations of one or more thereof.
According to some embodiments of the invention, the solvent is selected from one or a mixture of any two of methanol, ethanol, n-hexane, cyclohexane, n-heptane and toluene.
According to some specific embodiments of the invention, the step (1) comprises adding the nano metal oxide, the organosilane and the ZSM-5 molecular sieve into the solvent, fully stirring for 1-12h, then treating at 100-300 ℃ (transferring into a high-temperature reaction kettle) for 6-48h, and drying to obtain the modified ZSM-5 molecular sieve.
According to some embodiments of the present invention, step (1) comprises adding the nano metal oxide, the organic silane and the ZSM-5 molecular sieve into the solvent, fully stirring for 2-6h, and then treating at 100-300 ℃.
According to some embodiments of the present invention, after the nano metal oxide, the organic silane and the ZSM-5 molecular sieve are put into the solvent in step (1) and sufficiently stirred, the treatment is performed at 180 ℃ and 270 ℃.
According to some embodiments of the present invention, step (1) is performed at 100-300 ℃ for 10-24 h.
According to some embodiments of the invention, the temperature of the drying in step (1) is in the range of 50-150 ℃.
According to some embodiments of the invention, the drying time in step (1) is 2h to 20 h.
According to some embodiments of the invention, step (1) is drying the treated product without filtration.
According to some embodiments of the present invention, the modified ZSM-5 molecular sieve in step (2) accounts for SiO in the crystallization liquid210-100% of the mass.
According to some specific embodiments of the present invention, the step (2) includes mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source, a boron source, a template agent and deionized water to form a secondary crystallized gel, then crystallizing, and performing post-treatment to obtain the metal modified MFI @ MFI core-shell molecular sieve catalyst.
According to some specific embodiments of the present invention, wherein the silicon source in step (2) is selected from one or more of water glass, silica sol, silicic acid, tetraethoxysilane, coarse silica gel and white carbon black.
According to some specific embodiments of the present invention, wherein the boron source of step (2) is selected from the group consisting of boric acid, sodium metaborate and sodium tetraborate.
According to some specific embodiments of the present invention, the template agent in step (2) is selected from one or more of tetrapropylammonium bromide and tetrapropylammonium hydroxide in any combination.
According to some embodiments of the present invention, in the step (2), the molar ratio of the silicon source, the boron source, the template agent and the deionized water gel is 1: (0-0.05): (0.05-0.5): (5-75).
According to some embodiments of the present invention, the crystallizing in step (2) comprises crystallizing at 100-200 ℃ for 2-96 h.
According to some embodiments of the present invention, the crystallizing in step (2) comprises crystallizing at 140 ℃ to 180 ℃ for 24 to 72 hours.
According to some embodiments of the present invention, the post-treatment in step (2) comprises filtering, washing, drying and ion-exchanging the product after crystallization.
According to some specific embodiments of the present invention, the step (2) includes mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source, a boron source, a template agent and deionized water, and stirring for 60-300min to form a secondary crystallized gel.
According to some specific embodiments of the present invention, step (2) comprises mixing the modified ZSM-5 molecular sieve obtained in step (1) with a silicon source, a boron source, a template and deionized water, and stirring for 180min to form a secondary crystallized gel.
According to some embodiments of the invention, the stirring speed in step (2) is 60 to 500 r/min.
According to some embodiments of the present invention, the stirring speed in step (2) is 120-300 r/min.
According to some embodiments of the present invention, the washing in step (2) comprises washing with one or two of deionized water, methanol and ethanol as a solvent; the drying temperature range is 50-150 ℃, and the drying time is 2-24 h.
According to some specific embodiments of the invention, the ion exchange in the step (2) comprises preparing a mixed solution of a molecular sieve and 0.5-2 mol/L ammonium chloride solution in a mass ratio of 1: 5-1: 20, performing ion exchange at 90 ℃, performing suction filtration, washing, drying, and roasting at 500-600 ℃ for 4-24 hours.
According to some specific embodiments of the present invention, the ion exchange in step (2) includes preparing a mixed solution of a molecular sieve and 1mol/L ammonium chloride solution in a mass ratio of 1:10, performing ion exchange at 90 ℃, performing suction filtration, washing, drying, and calcining at 550 ℃ for 6 hours.
According to some embodiments of the invention, the ion exchange process of step (2) is repeated 2 times.
It is understood that the "ion exchange process is repeated 2 times" in the present invention means that the step of repeating the ion exchange with ammonium chloride is repeated 2 times.
On the other hand, the invention also provides a metal modified MFI @ MFI core-shell type molecular sieve catalyst prepared by the preparation method.
On the other hand, the invention also provides a method for preparing propylene by methanol conversion, wherein the method comprises the step of carrying out catalytic reaction on a mixture of methanol and water serving as a raw material by using the metal modified MFI @ MFI core-shell type molecular sieve catalyst to obtain the propylene.
The method of the invention can obtain propylene and higher butene, and the catalyst can make the sum of trienes of ethylene, propylene and butene higher, and typically the selectivity of the trienes reaches more than 83%.
According to some embodiments of the invention, wherein the reaction conditions comprise: the reaction temperature is 450-500 ℃; the space velocity is 0.5-15h-1。
According to some embodiments of the invention, the reaction conditions further comprise: the pressure is normal pressure.
In conclusion, the invention provides a metal modified MFI @ MFI core-shell type molecular sieve catalyst and a preparation method thereof. The catalyst of the invention has the following advantages:
through the thermal modification of a metal oxide solvent, under the high-temperature and high-pressure thermal condition of the solvent and the synergistic effect of organosilane, the metal oxide can enter the inside of a molecular sieve pore channel, is bonded with a molecular sieve and hydroxyl of the organosilane, is stable in the molecular sieve, and can properly reduce the density of a strong acid in the molecular sieve; meanwhile, the optimized sample has a multi-stage pore channel structure with a core phase rich in mesopores and a shell phase rich in micropores, and the oxidation-reduction property of the metal oxide can oxidize carbon deposition into CO or CO 2And (4) removing and further delaying the carbon deposition rate. Due to the advantages, the metal oxide modified MFI @ MFI type core-shell molecular sieve catalyst can greatly reduce the carbon deposition rate of the reaction of preparing propylene from methanol, improve the selectivity of propylene and prolong the catalytic life, and the modification effect is improved more than that of the traditional mode.
Drawings
FIG. 1 is an X-ray diffraction (XRD) pattern of each of the inventive and comparative examples.
FIG. 2 is a Scanning Electron Microscope (SEM) image of a catalyst prepared according to example 1. It can be seen from the figure that the core-shell molecular sieve particles have uniform size and are distributed in the range of 300-500nm, and the scanning electron microscope images of the core-shell molecular sieves prepared in other examples also have the morphology similar to that of FIG. 2.
FIG. 3 shows MnO in example 22The SEM images of the nanoparticles show that the metal oxide particles are uniform in size and distributed in the range of 20-60nm, and the electron microscope images of the metal oxide particles of other examples also have similar particle sizes and distributions to those of FIG. 3.
Fig. 4 is a Transmission Electron Microscope (TEM) image of the catalyst prepared in example 1. The figure shows that the core-shell molecular sieve has a hierarchical pore channel structure with a core phase rich in mesopores and a shell phase rich in micropores. Transmission electron micrographs of the core-shell molecular sieves prepared in the other examples also have morphologies and channel structures similar to those of fig. 4.
FIG. 5 is a hydroxyl radical infrared (OH-IR) plot for comparative example 3 and example 1. The difference between comparative example 3 and example 1 is that example 1 was solvothermally modified with a metal oxide, whereas comparative example 3 was not solvothermally modified with a metal oxide, as can be seen in the figure, example 1 is 3740cm relative to comparative example 3-1、3725cm-1And 3610cm-1The peak intensity is obviously reduced, which shows that the metal oxide can enter the inside of the molecular sieve pore channel through the solvent thermal modification of the metal oxide, and is stably bonded with the molecular sieve and the hydroxyl of organosilane, so that the content of the silicon hydroxyl and the bridged hydroxyl on the inner and outer surfaces is reduced.
FIG. 6 shows temperature programmed desorption (NH) of ammonia gas in comparative example 3 and example 13-TPD) map. As can be seen from the figure, the amount of strong acid in example 1 is significantly reduced relative to comparative example 3, indicating that solvothermal modification of the metal oxide can reduce the strong acid density of the molecular sieve.
Fig. 7 is a bar graph showing the conversion of triisopropylbenzene cracking reaction in comparative example 1 and example 1. As can be seen from the figure, the TIPB conversion rate of example 1 is greatly reduced relative to comparative example 1, indicating that the density of the strong acid on the outer surface of the molecular sieve is greatly reduced relative to comparative example 1, and the inert MFI molecular sieve shell coating can greatly reduce the density of the strong acid on the outer surface of the molecular sieve.
Detailed Description
The following detailed description is provided for the purpose of illustrating the embodiments and the advantageous effects thereof, and is not intended to limit the scope of the present disclosure.
Example 1
0.2g of Mn having a particle size of 20. + -.10 nm2O3Adding nanometer metal oxide, 2g N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, 10g of hydrogen type ZSM-5 molecular sieve with the crystal grain size of 200 to 20g of methanol, fully stirring for 3h, transferring to a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment for 12h at 270 ℃, and drying for 10h at 140 ℃ to obtain Mn2O3Modified small crystal grain ZSM-5 molecular sieve. To a beaker were added 0.12g of boric acid, 12.18g of tetrapropylammonium hydroxide (25)%), 47.82g of deionized water, 2.2g of Mn2O3Modifying a small-crystal ZSM-5 molecular sieve and 20g of tetraethoxysilane, stirring for 180min at the stirring speed of 180r/min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 72h at 180 ℃, and performing suction filtration and drying on the obtained product to obtain catalyst powder. The obtained catalyst has XRD pattern as shown in FIG. 1, SEM pattern as shown in FIG. 2, TEM pattern as shown in FIG. 4, and OH-IR pattern as shown in FIG. 5.
Example 2
0.3g of MnO having a particle size of 30. + -.10 nm2Adding nanometer metal oxide (SEM figure is shown in figure 3), 1g N-aminoethyl-3-aminopropylmethyldimethoxysilane, 10g hydrogen type aluminum-silicon ratio 300 nanometer thin ZSM-5 molecular sieve into 40g n-hexane, stirring for 2h, transferring into high temperature resistant stainless steel kettle, performing solvent heat treatment at 220 deg.C for 8h, and drying at 100 deg.C for 20h to obtain MnO2Modified nanometer thin layer ZSM-5 molecular sieve. To a beaker were added 16.24g tetrapropylammonium hydroxide (25%), 36.62g deionized water, 3.2g MnO2Modified nano thin layer ZSM-5 molecular sieve, 20g of silica Sol (SiO)240 percent) and stirring for 300min at the stirring speed of 120r/min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 48h at 170 ℃, and carrying out suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1.
Example 3
0.4g of CeO with a particle size of 40. + -. 20nm2Adding nanometer metal oxide, 1g N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, 10g of hydrogen type silicon-aluminum ZSM-5 molecular sieve stacked in 400 nanometer crystal into 30g of toluene, fully stirring for 4h, transferring into a high temperature resistant stainless steel kettle, carrying out solvothermal treatment at 210 ℃ for 24h, and drying at 120 ℃ for 20h to obtain CeO 2The modified nanocrystal piles up ZSM-5 molecular sieve. 6.48g of tetrapropylammonium bromide, 36.62g of deionized water and 3g of CeO were added to a beaker2Stacking ZSM-5 molecular sieve and 10g of coarse silica gel on the modified nanocrystal, stirring for 240min at a stirring speed of 360r/min, transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 96h at 160 ℃, and performing suction filtration and drying on the obtained product to obtain the nano-crystalline silica gelA catalyst powder. The XRD pattern of the obtained catalyst is shown in FIG. 1.
Example 4
1.0g of CeO with a particle size of 60. + -.30 nm2Adding nano metal oxide, 3g aminopropyl methyl dimethoxy silane and 10g hydrogen type ZSM-5 molecular sieve stacked by nano crystal with silicon-aluminum ratio of 300 into 20g ethanol, fully stirring for 1h, then transferring into a high temperature resistant stainless steel kettle, carrying out solvent heat treatment at 280 ℃ for 20h, then drying at 50 ℃ for 20h to obtain CeO2The modified nanocrystal is stacked with the ZSM-5 molecular sieve. To a beaker was added 0.06g of sodium metaborate, 24.36g of tetrapropylammonium hydroxide (25%), 24.12g of deionized water, 1.1g of CeO2And stacking the ZSM-5 molecular sieve and 20g of tetraethoxysilane by the modified nanocrystal, stirring for 120min at the stirring speed of 240r/min, transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 48h at 180 ℃, and performing suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1.
Example 5
0.001g of Fe having a particle size of 200. + -.30 nm2O3Putting nano metal oxide, 2g N- (2-aminoethyl) -3-aminopropyltrimethoxysilane and 10g of hydrogen type silicon-aluminum into 10g of cyclohexane than a 100-nano thin-layer ZSM-5 molecular sieve, fully stirring for 12h, transferring into a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment for 48h at 300 ℃, and drying for 20h at 80 ℃ to obtain Fe2O3Modified nanometer thin layer ZSM-5 molecular sieve. To a beaker were added 5.36g tetrapropylammonium bromide, 47.82g deionized water, 0.56g Fe2O3And (2) stirring the modified nano thin layer ZSM-5 molecular sieve and 20g of tetraethoxysilane for 240min at a stirring speed of 400r/min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing at 120 ℃ for 72h, and performing suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1.
Example 6
2.0g of Fe having a particle size of 10. + -.5 nm2O3Adding nanometer metal oxide, 2g N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, 10g of hydrogen type silicon-aluminum 100 nanometer thin layer ZSM-5 molecular sieve into 100g of tolueneFully stirring for 6h, then transferring into a high-temperature resistant stainless steel kettle, carrying out solvent heat treatment for 6h at 100 ℃, and then drying for 2h at 150 ℃ to obtain Fe 2O3Modified nanometer thin layer ZSM-5 molecular sieve. To a beaker was added 5.36g tetrapropylammonium bromide, 95.64g deionized water, 8g Fe2O3Stirring the modified nano thin layer ZSM-5 molecular sieve and 10g of silicic acid for 60min at the stirring speed of 120r/min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing at 200 ℃ for 2h, and performing suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1.
Example 7
1.0g of Co having a particle size of 100. + -.30 nm2O3Adding nanometer metal oxide, 1g N-aminoethyl-3-aminopropylmethyldimethoxysilane and 10g of hydrogen-type ZSM-5 molecular sieve with the silicon-aluminum ratio of 200 small crystal grains into 50g of toluene, fully stirring for 6h, transferring into a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment for 16h at 150 ℃, and drying for 10h at 140 ℃ to obtain Co2O3Modified small crystal grain ZSM-5 molecular sieve. To a beaker were added 22.09g of tetrapropylammonium bromide, 24.82g of deionized water, 1g of Co2O3And (3) modifying the small-grain ZSM-5 molecular sieve and 10g of white carbon black, stirring for 120min at a stirring speed of 240r/min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 96h at 100 ℃, and carrying out suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1.
Example 8
0.5g of Ni having a particle size of 500. + -.30 nm2O3Adding nano metal oxide, 2g N- (2-aminoethyl) -3-aminopropyltrimethoxysilane and 10g of hydrogen type ZSM-5 molecular sieve with the silicon-aluminum ratio of 300 small crystal grains into 60g of methanol, fully stirring for 2h, transferring into a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment for 8h at 250 ℃, and drying for 20h at 140 ℃ to obtain Ni2O3Modified small crystal grain ZSM-5 molecular sieve. To a beaker was added 0.08g of sodium tetraborate, 4.24g of tetrapropylammonium bromide, 60.24g of deionized water, 0.8g of Ni2O3Modified small-grain ZSM-5 molecular sieve, 40g of water glass (SiO)219.82 percent) and stirring for 240min at the stirring speed of 180r/min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 12h at 180 ℃, and carrying out suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1.
Example 9
1.5g of La having a particle size of 300. + -.30 nm2O3Adding nano metal oxide, 2g N-aminoethyl-3-aminopropylmethyldimethoxysilane and 10g of hydrogen type silicon-aluminum to 100 nano crystal stacked ZSM-5 molecular sieve into 80g of n-heptane, fully stirring for 12h, transferring into a high temperature resistant stainless steel kettle, carrying out solvothermal treatment for 24h at 190 ℃, and drying for 10h at 130 ℃ to obtain La 2O3The modified nanocrystal piles up ZSM-5 molecular sieve. To a beaker were added 2.21g of tetrapropylammonium bromide, 15.00g of deionized water, 10g of La2O3And stacking the ZSM-5 molecular sieve and 10g of coarse silica gel by using the modified nanocrystal, stirring for 300min at a stirring speed of 60r/min, transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 72h at 140 ℃, and performing suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1.
Example 10
0.005g of La having a particle size of 30. + -.10 nm2O3Adding nano metal oxide, 2g N-aminoethyl-3-aminopropylmethyldimethoxysilane and 10g of hydrogen type silicon-aluminum ZSM-5 molecular sieve stacked in 100 nano crystals into 20g of n-hexane, fully stirring for 1h, transferring into a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment for 10h at 290 ℃, and drying for 15h at 90 ℃ to obtain La2O3The modified nanocrystal is stacked with the ZSM-5 molecular sieve. To a beaker were added 5.30g of tetrapropylammonium bromide, 224.00g of deionized water, 5g of La2O3And stacking the ZSM-5 molecular sieve and 10g of white carbon black in the modified nanocrystal, stirring for 240min at a stirring speed of 500r/min, transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 72h at 190 ℃, and performing suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1.
Example 11
0.002g of Ga having a particle size of 80. + -. 20nm2O3Putting nano metal oxide, 3g N- (2-aminoethyl) -3-aminopropyltrimethoxysilane and 10g of hydrogen type silicon-aluminum molecular sieve with a ratio of 500 nano thin layers of ZSM-5 into 80g of toluene, fully stirring for 2h, transferring into a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment for 18h at 180 ℃, and drying for 2h at 140 ℃ to obtain WO3Modified nanometer thin layer ZSM-5 molecular sieve. To a beaker was added 0.286g of sodium tetraborate, 6.36g of tetrapropylammonium bromide, 48.82g of deionized water, 4g of WO3Modified nano thin layer ZSM-5 molecular sieve, 20g of silica Sol (SiO)240 percent) and stirring for 120min at the stirring speed of 300r/min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 96h at the temperature of 150 ℃, and carrying out suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1.
Example 12
2.0g of WO having a particle size of 70. + -.10 nm3Putting nano metal oxide, 3g N- (2-aminoethyl) -3-aminopropyltrimethoxysilane and 10g of hydrogen type thin-layer ZSM-5 molecular sieve with the silica-alumina ratio of 500 nm into 50g of cyclohexane, fully stirring for 2h, transferring into a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment for 12h at 260 ℃, and drying for 4h at 140 ℃ to obtain WO 3Modified nanometer thin layer ZSM-5 molecular sieve. To a beaker was added 0.512g of boric acid, 11.05g of tetrapropylammonium bromide, 112.05g of deionized water, 1.6g of WO3Stirring the modified nano thin layer ZSM-5 molecular sieve and 10g of silicic acid for 60min at the stirring speed of 120r/min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 96h at 110 ℃, and performing suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in FIG. 1.
Comparative example 1
Putting 10g of a hydrogen type ZSM-5 molecular sieve with small crystal grain size of 200 Si/Al into 20g of methanol, fully stirring for 3h, then transferring into a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment at 280 ℃ for 12h, and then drying at 140 ℃ for 10h to obtain the solvothermal modified small crystal grain ZSM-5 molecular sieve. The XRD pattern of the obtained molecular sieve is shown in figure 1.
Comparative example 2
0.2g of Mn2O3Putting nano metal oxide and 10g of hydrogen type ZSM-5 molecular sieve with crystal grains smaller than 200 in proportion to 20g of methanol, fully stirring for 3h, transferring into a high-temperature resistant stainless steel kettle, carrying out solvent heat treatment at 280 ℃ for 12h, and drying at 140 ℃ for 10h to obtain Mn2O3Modified small crystal grain ZSM-5 molecular sieve. The XRD pattern of the obtained molecular sieve is shown in figure 1.
Comparative example 3
Putting 10g of a hydrogen type ZSM-5 molecular sieve with small crystal grain size of 200 Si/Al into 20g of methanol, fully stirring for 3h, then transferring into a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment at 280 ℃ for 12h, and then drying at 140 ℃ for 10h to obtain the solvothermal modified small crystal grain ZSM-5 molecular sieve. Adding 12.18g of tetrapropylammonium hydroxide (25%), 47.82g of deionized water, 2.2g of solvent thermal modified small-crystal ZSM-5 molecular sieve and 20g of ethyl orthosilicate into a beaker, stirring vigorously for 180min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing at 180 ℃ for 72h, and carrying out suction filtration and drying on the obtained product to obtain catalyst powder. The XRD pattern of the obtained catalyst is shown in figure 1. The OH-IR diagram is shown in FIG. 5.
Comparative example 4
0.2g of Mn2O3Adding nanometer metal oxide and 10g of hydrogen type ZSM-5 molecular sieve with the grain size of 200 g and the silica alumina ratio into 20g of methanol, fully stirring for 3h, transferring into a high-temperature resistant stainless steel kettle, carrying out solvothermal treatment at 280 ℃ for 12h, and drying at 140 ℃ for 10h to obtain Mn2O3Modified small crystal ZSM-5 molecular sieve. To a beaker were added 0.12g boric acid, 12.18g tetrapropylammonium hydroxide (25%), 47.82g deionized water, 2.2g Mn2O3And accumulating the ZSM-5 molecular sieve and 20g of tetraethoxysilane by the modified nanocrystal, violently stirring for 180min, then transferring the prepared crystallization liquid into a high-pressure stainless steel kettle, crystallizing for 72h at 180 ℃, and carrying out suction filtration and drying on the obtained product to obtain the catalyst powder. The XRD pattern of the obtained catalyst is shown in FIG. 1.
Examples of the experiments
The molecular sieve raw powder in examples 1-12 and comparative examples 1-4 is exchanged for 2h at 90 ℃ by using L mol/L ammonium nitrate solution, and the solid-liquid mass ratio is 1: 10, and roasting at 550 ℃ for 6 hours, and repeating the process twice to obtain a hydrogen type catalyst sample.
NH3Temperature programmed desorption (NH)3TPD) characterization was performed using an Tianjin priority TP-5080 full-automatic multipurpose adsorption apparatus in combination with a thermal conductivity cell detector (TCD). The specific method comprises the following steps: taking 0.1g of a 20-40-mesh sample, purging and activating the sample in a nitrogen atmosphere for 1h, then cooling to 100 ℃, adsorbing ammonia gas for 30min to saturation, then purging for 1h in the nitrogen atmosphere, heating from 100 ℃ to 600 ℃ at a speed of 10 ℃/min to perform ammonia desorption, analyzing and recording a desorption signal by TCD (temperature-dependent control device), wherein a desorption peak at 100-300 ℃ corresponds to NH (NH) adsorbed by a weak acid center 3Peak, desorption peak at 300-600 ℃ corresponds to NH adsorbed by strong acid center3And (4) peak. The results are shown in FIG. 6.
Performing triisopropylbenzene cracking reaction on a miniature fixed bed reactor, weighing a certain amount of 20-40 meshes of catalyst sample, loading the catalyst sample into the middle section of a quartz reaction tube with the inner diameter of 8mm, filling equal amount of quartz cotton at two ends of the catalyst, wherein the reaction temperature is 300-450 ℃, and the airspeed of triisopropylbenzene is 1-20 h-1、N2The flow rate is 20-200 ml/min. The product was analyzed on-line on an Agilent7890A gas chromatograph equipped with a hydrogen flame detector (FID) and an HP-5 capillary column (30 m.times.0.32 mm). The level of the tri-isopropyl benzene conversion rate can reflect the level of the strong acid density on the outer surface of the ZSM-5 molecular sieve catalyst. The results are shown in FIG. 7.
And (3) observing the catalytic performance of the catalyst in the reaction of preparing propylene from methanol by adopting a continuous fixed bed reactor. The reaction tube is a stainless steel tube with the diameter of 10mm multiplied by 530mm, the loading amount of the catalyst is 1.0g, the reaction temperature is 450 ℃ and 500 ℃, and the space velocity is 3.0h-lThe system pressure is 1 atm. The analysis was carried out on-line by means of an Agilent model 7890A gas chromatography, and the product composition was analyzed by means of an HP-PLOT Q capillary column (30 m.times.0.53 mm).
Catalyst life data were referenced from the start of feed to the time at which conversion dropped to 90%. The results are shown in Table 1. Nitrogen adsorption-desorption characterization of examples 1-12 and comparative examples 1-4 after degassing at 350 ℃ and 1.33Pa for 4h, N was carried out at-196 ℃ 2And (4) performing adsorption and desorption testing. Calculation of the specific surface area, P/P, by the BET method0Adsorbed N when equal to 0.992The total pore volume is calculated. Calculating the total specific surface area using the BET equation, and calculating the internal surface area, external surface area and micropore volume, P/P, by the t-plot method0Adsorbed N when equal to 0.992The total pore volume is calculated by volume, and the mesoporous volume is calculated by BJH method. The results are shown in Table 2.
TABLE 1 reaction results of examples and comparative examples
Figure BDA0002303863050000131
TABLE 2 texture Properties of examples and comparative examples
Figure BDA0002303863050000141

Claims (15)

1. A preparation method of a metal modified MFI @ MFI core-shell type molecular sieve catalyst comprises the following steps:
(1) the method comprises the steps of adopting a nano metal oxide to carry out metal oxide modification on a ZSM-5 molecular sieve by a solvothermal method to obtain a modified ZSM-5 molecular sieve, wherein the modified ZSM-5 molecular sieve comprises the steps of putting the nano metal oxide, amino-containing organosiloxane and the ZSM-5 molecular sieve into a solvent, fully stirring for 1-12h, then reacting for 6-48h at the temperature of 100-; the metal is selected from one or more of Mn, Ce, Fe, Co, Ni, La, Ga and W; wherein the mass of the metal oxide for modification is 0.01-20% of that of the ZSM-5 molecular sieve, the mass of the solvent is 1-10 times of that of the ZSM-5 molecular sieve, and the mass of the amino-containing organosiloxane is more than 0 and less than or equal to 30% of that of the ZSM-5 molecular sieve, based on 100% of the mass of the ZSM-5 molecular sieve;
(2) Performing secondary hydrothermal synthesis on the modified ZSM-5 molecular sieve obtained in the step (1) in a crystallization liquid for preparing a Silicalite-1 molecular sieve or a B-ZSM-5 molecular sieve to obtain the metal modified MFI @ MFI core-shell type molecular sieve catalyst, wherein the metal modified MFI @ MFI core-shell type molecular sieve catalyst is obtained by mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source, a boron source, a template agent and deionized water to form secondary crystallization gel, then crystallizing at the temperature of 100-200 ℃ for 2-96 hours, and performing post-treatment to obtain the metal modified MFI @ MFI core-shell type molecular sieve catalyst; wherein the silicon source is selected from one or more of water glass, silica sol, silicic acid, ethyl orthosilicate, coarse pore silica gel and white carbon black; the boron source is selected from the group consisting of boric acid, sodium metaborate, and sodium tetraborate; the template is selected from one or more of tetrapropylammonium bromide and tetrapropylammonium hydroxide in any combination; the molar ratio of the silicon source to the boron source to the template agent to the deionized water is 1: (0-0.05): (0.05-0.5): (5-75).
2. The method according to claim 1, wherein the nano metal oxide of step (1) has a particle diameter of 10 to 500 nm.
3. The preparation method according to claim 1, wherein the solvent of step (1) is selected from one or a mixture of any two of methanol, ethanol, n-hexane, cyclohexane, n-heptane and toluene.
4. The method according to claim 1, wherein the drying temperature in step (1) is in the range of 50 to 150 ℃ and the drying time is in the range of 2 to 20 hours.
5. The preparation method according to claim 1, wherein the amino group-containing organosiloxane of step (1) is selected from one or more of N-aminoethyl-3-aminopropylmethyldimethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane.
6. The preparation method according to claim 1, wherein the post-treatment of the step (2) comprises suction filtration, washing, drying and ion exchange of the product after the crystallization is continued.
7. The preparation method of claim 1, wherein the step (2) comprises mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source, a boron source, a template agent and deionized water, and stirring for 60-300min to form a secondary crystallized gel.
8. The preparation method of claim 1, wherein the step (2) comprises mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source, a boron source, a template agent and deionized water, and stirring at a stirring rate of 60-500 r/min for 60-300min to form the secondary crystallized gel.
9. The preparation method according to claim 6, wherein the washing in step (2) comprises washing with one or two of deionized water, methanol and ethanol as a solvent; the drying temperature range is 50-150 ℃, and the drying time is 2-24 h.
10. The preparation method of claim 6, wherein the ion exchange in the step (2) comprises preparing a mixed solution of a molecular sieve and 0.5-2 mol/L ammonium chloride solution in a mass ratio of 1: 5-1: 20, performing ion exchange at 90 ℃, performing suction filtration, washing, drying, and roasting at 500-600 ℃ for 4-24 hours.
11. The method of claim 10, wherein the ion exchange process is repeated 2 times.
12. The metal modified MFI @ MFI core-shell type molecular sieve catalyst prepared by the preparation method of any one of claims 1 to 11.
13. A method for preparing propylene by methanol conversion, wherein the method comprises the step of carrying out catalytic reaction on a mixture of methanol and water as a raw material by using the metal modified MFI @ MFI core-shell type molecular sieve catalyst as defined in claim 12 to obtain the propylene.
14. The method of claim 13, wherein the conditions of the reaction comprise: the reaction temperature is 450-500 ℃; the space velocity is 0.5-15 h-1。
15. The method of claim 14, wherein the conditions of the reaction comprise: the pressure is normal pressure.
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