A ZSM-5 molecular sieve, its preparation method and application

Abstract

This invention discloses a ZSM-5 molecular sieve, its preparation method, and its applications. The ZSM-5 molecular sieve has an elongated plate morphology, with a uniform monolayer of nano-SiO2 particles covering the surface of the sieve crystals. The ZSM-5 molecular sieve exhibits good activity and selectivity in the toluene-methanol alkylation reaction.

Description

Technical Field

[0001] This invention relates to a ZSM-5 molecular sieve, its preparation method, and its application. Background Technology

[0002] ZSM-5 molecular sieve is a microporous silica-alumina molecular sieve, belonging to the MFI type. It has two intersecting channel systems: ten-membered ring cross-channels along the a-axis and ten-membered ring straight channels along the b-axis, with a pore size of (0.53 × 0.57 nm). The introduction of aluminum atoms gives the molecular sieve acidity, making it suitable for important applications in the petrochemical industry and the synthesis of fine chemicals. It is applicable to industrial catalytic processes such as selective dewaxing of petroleum, xylene isomerization, toluene disproportionation, methanol-to-olefins, esterification, and alkylation.

[0003] With the development of petrochemicals, extensive research has been conducted on the modification of zeolite molecular sieves to improve the selective properties of molecular sieve catalysts while reducing catalyst activity loss. Common modification methods include high-temperature steam treatment, acid dealumination, chemical modification, external surface organosilicon passivation, and epitaxial growth. Currently, catalysts prepared from core-shell molecular sieves exhibit good shape selectivity in aromatic hydrocarbon reactions. For ZSM-5 molecular sieves, a layer of silicon-aluminum ZSM-5 or an inert all-silica Silicate-1 molecular sieve shell is grown around the ZSM-5 molecular sieve as the core phase. This shell phase can modulate the acid properties of the outer surface without affecting the pore diffusion performance and acid properties of the core ZSM-5 zeolite. Patent US4868146 discloses a molecular sieve material with an inert outer surface, which, in a fluorine-containing system, uses a mesoporous ZSM-5 or ZSM-23 molecular sieve as the core phase, surrounded by a layer of silica-rich molecular sieve.

[0004] Patent CN107758689B discloses a method for synthesizing ZSM-5 / Silicalite-1 core-shell zeolite molecular sieves. This method uses microwaves as a heating source to crystallize and synthesize ZSM-5 / Silicalite-1 core-shell molecular sieves with high coverage. The crystallization time is short, and the shell coverage is high. Patent CN101723401B discloses ZSM-5 / ZSM-5 core-shell zeolite molecular sieves, where the ZSM-5 core phase is surrounded by a ZSM-5 shell layer with a thickness of 20–800 nm. Reference [Chem. Mater. 2006, 18, 4959-4966] lists several methods for preparing core-shell molecular sieve materials, including SOD-LTA, BEA-LTA, FAU-MFI, MFI-BEA, and MFI-MFI (ZSM-5-silicalite-1). These methods employ a seeding method to coat the outer layer of the molecular sieve with nanoparticles ranging from 50-200 nm in size, exhibiting varying sizes and uneven distribution on the surface of the molecular sieve crystals. Patent CN107649172B discloses a solid-phase method for synthesizing ZSM-5 / Silicalite-1 core-shell molecular sieves. These molecular sieves demonstrate good catalytic performance as catalysts in the alkylation of toluene and methanol to produce p-xylene.

[0005] The methods described above typically use a large number of organic structure-directing agents, have high alkalinity, and involve complex post-processing. Furthermore, the inert shell thickness of the synthesized molecular sieves is usually greater than 20 nm, and they are often multi-layered or unevenly dispersed. Therefore, developing a simple and convenient method for uniformly coating a single layer of inert material on the outer surface of a molecular sieve can effectively passivate the acidity of the outer surface of ZSM-5 molecular sieves, showing promising prospects for industrial applications. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a ZSM-5 molecular sieve, its preparation method, and its application. The ZSM-5 molecular sieve described herein exhibits good activity and selectivity in the toluene-methanol alkylation reaction.

[0007] The first aspect of the present invention provides a ZSM-5 molecular sieve, wherein the ZSM-5 molecular sieve has a long plate-shaped morphology and the surface of the molecular sieve crystal is uniformly covered with a single layer of nano-SiO2 particles.

[0008] In the above technical solution, the crystal size of the ZSM-5 molecular sieve is 1-3 μm in length, 160-300 nm in width, and 40-150 nm in thickness, preferably 1.1-2.9 μm in length, 165-290 nm in width, and 50-145 nm in thickness, and more preferably 1.2-2.8 μm in length, 170-280 nm in width, and 60-140 nm in thickness.

[0009] In the above technical solution, the particle size of the nano-SiO2 particles is 5-20 nm, preferably 5-18 nm, and more preferably 5-15 nm.

[0010] In the above technical solution, more than 90% of the nano-SiO2 particles covering the surface of the ZSM-5 molecular sieve crystal are monolayers.

[0011] In the above technical solution, the coverage rate of the nano-SiO2 particles on the surface of ZSM-5 molecular sieve crystals is more than 90%.

[0012] In the above technical solution, the specific surface area of ​​the ZSM-5 molecular sieve is 300-450 m². 2 / g.

[0013] In the above technical solution, the total pore volume of the ZSM-5 molecular sieve is 0.19–0.50 cm³. 3 / g, preferably 0.20~0.45cm 3 / g, with micropore volume of 0.05~0.18cm³ 3 / g, preferably 0.06~0.17cm 3 / g.

[0014] In the above technical solution, the bulk SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 80 to 500.

[0015] In the above technical solution, the ZSM-5 molecular sieve has a depth of 10nm within its outer surface that is essentially free of aluminum, and the SiO2 / Al2O3 molar ratio on the outer surface is greater than 2000.

[0016] A second aspect of this invention provides a method for preparing ZSM-5 molecular sieves, comprising the following steps:

[0017] A mixture of silicon source, aluminum source, tetrapropylammonium hydroxide, water and ZSM-5 molecular sieve seed crystals is subjected to a one-step heating crystallization treatment to obtain the ZSM-5 molecular sieve.

[0018] The silicon source is calculated as SiO2, the aluminum source as Al2O3, and the tetrapropylammonium hydroxide as TPA. + The mixture of water and SiO2, Al2O3, and TPA was prepared in a molar ratio of SiO2:Al2O3:TPA. + H2O = 1: 0.001~0.020: 0.015~0.045: 10~50; the silicon source is calculated as SiO2 and ZSM-5 molecular sieve seed crystals, with a mass ratio of 1: 0.03~0.25.

[0019] In the above technical solution, the silicon source is calculated as SiO2, the aluminum source as Al2O3, and the tetrapropylammonium hydroxide as TPA. +The mixture of water and SiO2, Al2O3, and TPA was prepared in a molar ratio of SiO2:Al2O3:TPA. + H2O = 1: 0.002~0.018: 0.020~0.040: 15~50; the silicon source is calculated as SiO2 and ZSM-5 molecular sieve seed crystals, with a mass ratio of 1: 0.05~0.2.

[0020] In the above technical solution, preferably, the method for preparing the ZSM-5 molecular sieve seed crystals is as follows: the molar ratio of silicon source TEOS (calculated as SiO2), aluminum source aluminum isopropoxide (calculated as Al2O3), tetrapropylammonium hydroxide, water, and urea is SiO2:Al2O3:TPA. + The mixture is prepared by heating H2O and Urea at 170-180°C for 2-3 days to obtain the ZSM-5 molecular sieve seed crystals.

[0021] In the above technical solution, the silicon source is tetraethyl orthosilicate and the aluminum source is aluminum hydroxide.

[0022] In the above technical solution, the pH value of the mixture is 7 to 8.5.

[0023] In the above technical solution, the crystallization process of the mixture is dynamic crystallization by rotation or stirring, with a rotation speed of 10-40 rpm and a stirring speed of 30-200 rpm; the crystallization conditions of the mixture are crystallization at 150-190℃ for 0.25-6 days, preferably at 155-185℃ for 0.5-5 days, and more preferably at 160-180℃ for 0.75-4 days.

[0024] In the above technical solution, after the crystallization step, the ZSM-5 molecular sieve can be separated from the obtained mixture by any conventionally known separation method. Examples of such separation methods include filtering, washing, and drying the mixture obtained after the crystallization step. Here, the filtration, washing, and drying can be performed in any manner conventionally known in the art. Specifically, for example, the filtration can be performed by simply vacuum filtering the obtained product mixture. For example, the washing can be performed using deionized water and / or ethanol, washing 1 to 2 times. For example, the drying temperature can be 40 to 110°C, and the drying time can be 4 to 24 hours. This drying can be carried out under normal pressure or under reduced pressure.

[0025] According to the present invention, the molecular sieve prepared according to the aforementioned method can also be calcined to remove organic structure-directing agents and any present moisture. The calcination can be carried out in any manner conventionally known in the art; for example, the calcination temperature is generally 300–800°C, preferably 400–650°C, and the calcination time is generally 1–10 hours, preferably 3–6 hours. Furthermore, the calcination is generally carried out in an oxygen-containing atmosphere, such as air or an oxygen atmosphere.

[0026] In the above technical solution, the yield of the ZSM-5 molecular sieve product synthesized by the preparation method is >60wt%.

[0027] A third aspect of the present invention provides a ZSM-5 molecular sieve obtained by the above preparation method.

[0028] In the above technical solution, the ZSM-5 molecular sieve has a long plate-shaped morphology, and the surface of the molecular sieve crystal is uniformly covered with a single layer of nano-SiO2 particles.

[0029] In the above technical solution, the crystal size of the ZSM-5 molecular sieve is 1-3 μm in length, 160-300 nm in width, and 40-150 nm in thickness, preferably 1.1-2.9 μm in length, 165-290 nm in width, and 50-145 nm in thickness, and more preferably 1.2-2.8 μm in length, 170-280 nm in width, and 60-140 nm in thickness.

[0030] In the above technical solution, the particle size of the nano-SiO2 particles is 5-20 nm, preferably 5-18 nm, and more preferably 5-15 nm.

[0031] In the above technical solution, more than 90% of the nano-SiO2 particles covering the surface of the ZSM-5 molecular sieve crystal are monolayers.

[0032] In the above technical solution, the coverage of the nano-SiO2 particles on the surface of ZSM-5 molecular sieve crystals exceeds 90%.

[0033] In the above technical solution, the specific surface area of ​​the ZSM-5 molecular sieve is 300-450 m². 2 / g.

[0034] In the above technical solution, the total pore volume of the ZSM-5 molecular sieve is 0.19–0.50 cm³. 3 / g, preferably 0.20~0.45cm 3 / g.

[0035] In the above technical solution, the micropore volume of the ZSM-5 molecular sieve is 0.05–0.18 cm³. 3 / g, preferably 0.06~0.17cm 3 / g.

[0036] In the above technical solution, the bulk SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 80 to 500.

[0037] In the above technical solution, the ZSM-5 molecular sieve has a depth of 10nm on its outer surface that is essentially free of aluminum, and the SiO2 / Al2O3 molar ratio is greater than 2000.

[0038] A fourth aspect of the present invention also provides a molecular sieve composition comprising a ZSM-5 molecular sieve provided according to the first aspect or the third aspect, and a binder.

[0039] The fifth aspect of the present invention also provides a ZSM-5 molecular sieve according to the first aspect, the third aspect, or the fourth aspect as a catalyst for the toluene-methanol alkylation reaction.

[0040] In the above technical solution, the catalyst is used for the toluene-methanol alkylation reaction, and the process conditions are: reaction temperature 350-500℃, preferably 380-480℃, molar ratio of toluene to methanol of the raw materials 1-6:1, preferably 1-4:1, and toluene mass hourly space velocity (HHSV) of 0.5-6 h⁻¹. -1 Preferably 0.5 to 4 hours -1 .

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] 1. The ZSM-5 molecular sieve provided by the present invention has a special morphology, which is a long plate shape, and the surface of the molecular sieve crystal is uniformly covered with a single layer of nano-SiO2 particles.

[0043] 2. This invention provides a simple and feasible method for preparing ZSM-5 molecular sieves. This method uses very little organic structure-directing agent. Through the proportioning and selection of various materials, the crystallization solution is weakly alkaline. The post-processing is very simple and environmentally friendly. Furthermore, it achieves the formation of elongated plate-like morphologies in one step while simultaneously covering the outer surface with a single layer of SiO2 nanoparticles. This method of coating the outer surface of ZSM-5 molecular sieves with a single layer of inert material can effectively passivate the acidity of the outer surface, showing good prospects for industrial application.

[0044] 3. The ZSM-5 molecular sieve provided by this invention, when used as a catalyst in the alkylation reaction of toluene and methanol, exhibits good activity and selectivity. Attached Figure Description

[0045] Figure 1 The X-ray diffraction pattern of the ZSM-5 molecular sieve seed crystals in Example 1;

[0046] Figure 2This is a scanning electron microscope (SEM) image of the ZSM-5 molecular sieve seed crystals in Example 1;

[0047] Figure 3 The X-ray diffraction pattern of the molecular sieve obtained in Example 1;

[0048] Figure 4 The image shows a scanning electron microscope (SEM) image of the molecular sieve obtained in Example 1.

[0049] Figure 5 The image shown is a TEM transmission electron microscope image of the molecular sieve obtained in Example 1.

[0050] Figure 6 The X-ray diffraction pattern of the molecular sieve obtained in Example 2;

[0051] Figure 7 This is a scanning electron microscope (SEM) image of the molecular sieve obtained in Example 2;

[0052] Figure 8 The image shown is a TEM transmission electron microscope image of the molecular sieve obtained in Example 2.

[0053] Figure 9 The X-ray diffraction pattern of the molecular sieve obtained in Example 3;

[0054] Figure 10 This is a scanning electron microscope (SEM) image of the molecular sieve obtained in Example 3;

[0055] Figure 11 The X-ray diffraction pattern of the molecular sieve obtained in Example 4;

[0056] Figure 12 This is a scanning electron microscope (SEM) image of the molecular sieve obtained in Example 4.

[0057] Figure 13 The image shows a scanning electron microscope (SEM) image of the molecular sieve obtained in Comparative Example 1.

[0058] Figure 14 The image shows a scanning electron microscope (SEM) image of the molecular sieve obtained in Comparative Example 2.

[0059] Figure 15 The image shows a scanning electron microscope (SEM) image of the molecular sieve obtained in Comparative Example 3.

[0060] Figure 16 The X-ray diffraction pattern of the sample obtained in Comparative Example 4;

[0061] Figure 17 The image shows a scanning electron microscope (SEM) image of the molecular sieve obtained in Comparative Example 5.

[0062] Figure 18 The image shows the X-ray diffraction pattern of the sample obtained in Comparative Example 6. Detailed Implementation

[0063] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims in the appendix.

[0064] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0065] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0066] In the context of this specification, except where expressly stated, any matters or issues not mentioned herein shall apply directly to those known in the art without any modification. Furthermore, any implementation described herein may be freely combined with one or more other implementations described herein, and any resulting technical solutions or concepts shall be considered part of the original disclosure or original record of this invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider such combination to be clearly unreasonable.

[0067] In the context of this specification, for a molecular sieve, the substances that fill the pores during the synthesis of the molecular sieve (such as organic structure-directing molecules, excluding water and metal ions) before they are removed are referred to as a "precursor".

[0068] In the context of this specification, the structure of the molecular sieve is determined by X-ray diffraction (XRD), which is measured using an X-ray powder diffractometer with a Cu-Kα ray source and a nickel filter. Before sample testing, the crystallinity of the molecular sieve sample is observed using a scanning electron microscope (SEM) to confirm that the sample contains only one type of crystal, i.e., the molecular sieve sample is a pure phase. XRD testing is then performed to ensure that there are no interfering peaks from other crystals in the diffraction pattern.

[0069] In the context of this specification, including in the following examples and comparative examples, the X-ray powder diffractometer used for the molecular sieves is a Panalytical X-PERPRO type X-ray powder diffractometer, used to analyze the phase composition of the samples, and a CuKα ray source. Nickel filter, 2θ scanning range 2~50°, operating voltage 40kV, current 40mA, scanning rate 10° / min.

[0070] In the context of this specification, including in the following examples and comparative examples, the scanning electron microscope (SEM) used for the molecular sieves is an S-4800II field emission scanning electron microscope. The method for measuring the crystal size of the molecular sieves is as follows: The molecular sieves are observed using this SEM at a magnification of 10,000x. A field of view is randomly selected, and the average sum of the crystal sizes in that field of view is calculated. This operation is repeated a total of 10 times. The average sum of the 10 averages is taken as the crystal size.

[0071] In the context of this specification, including in the following examples and comparative examples, the method for measuring the size of nano-SiO2 particles is as follows: the molecular sieve is observed at a magnification of 100,000 using a transmission electron microscope (FEI G2F30 transmission electron microscope, operating voltage 300kV, Netherlands). A field of view is randomly selected, and the average value of the sum of the sizes of all particles in that field of view is calculated. This operation is repeated a total of 10 times, and the average value of the sum of the 10 average values ​​is taken as the size of the nanoparticle.

[0072] In the context of this specification, including in the following examples and comparative examples, the X-ray photoelectron spectrometer (XPS) used for the molecular sieves is a Thermo ESCA LAB-250 X-ray photoelectron spectrometer, with C1s = 284.6 eV as the internal standard to correct the measured elemental signals, and the elemental content on the outer surface of the molecular sieves is measured using XPS.

[0073] In the context of this specification, including in the following examples and comparative examples, the molecular sieve was analyzed using an inductively coupled plasma atomic emission spectrometer (ICP) model Varian 725-ES. The elemental content of the analytical sample was determined by dissolving it in hydrofluoric acid. The bulk SiO2 / Al2O3 molar ratio of the molecular sieve was measured using ICP.

[0074] In the context of this specification, including in the following examples and comparative examples, the total pore volume of the molecular sieve includes micropore volume and mesopore / macropore volume, wherein the total pore volume, micropore volume, and specific surface area are measured by the nitrogen physical adsorption-desorption method (BET method): the nitrogen physical adsorption-desorption isotherm of the molecular sieve is measured using a physical adsorption instrument (such as a Micromeretic ASAP2020M physical adsorption instrument), and then calculated using the BET equation and t-plot equation. The experimental conditions for ZSM-5 molecular sieve are: measurement temperature -169℃, and before measurement, the molecular sieve is heat-treated at 550℃ in air atmosphere for 6 hours, and then pretreated in vacuum at 350℃ for 4 hours.

[0075] In the context of this specification, including in the following examples and comparative examples, the catalyst is used to carry out the toluene-methanol alkylation reaction:

[0076] Toluene conversion rate % = (molar amount of toluene in feed - molar amount of toluene in effluent) / (molar amount of toluene in feed) × 100%.

[0077] Selectivity of p-xylene % = (molar amount of p-xylene in the product) / (molar amount of xylene in the product) × 100%.

[0078] The present invention will be further described in detail below with reference to the embodiments, but the present invention is not limited to these embodiments.

[0079] Example 1

[0080] A mixture was prepared by thoroughly mixing 27.59 g of deionized water, 16.66 g of TPAOH solution (containing 25% by weight of TPAOH), 13.61 g of TEOS (containing 28.3% by weight of SiO2), 0.121 g of aluminum isopropoxide, and 2.013 g of urea. The mixture was stirred at room temperature for 12 hours to obtain a mixture with a molar ratio of SiO2:Al2O3:TPA + The ratio of H₂O to Urea was 1:0.005:0.32:35:0.5. The mixture was placed in a stainless steel reactor and allowed to crystallize at 175°C for 2 days. After crystallization, the mixture was centrifuged and washed until the pH was near neutral (pH = 7-8). The sample was then dried in an oven at 110°C. The XRD pattern of the sample is shown below. Figure 1 The image shown is of ZSM-5 molecular sieve; the SEM image of the molecular sieve is as follows. Figure 2 As shown, the crystal surface is smooth, free of SiO2 particles, and exhibits a long plate-like morphology with dimensions of 1.1 μm in length, 200 nm in width, and 80 nm in thickness. H-type ZSM-5 molecular sieve with a specific surface area of ​​408 m² was obtained after calcination at 550 °C for 6 hours. 2 / gram, micropore volume 0.13 cm³ 3 / gram, total pore volume is 0.22 cm³. 3 / g. The bulk silicon-aluminum molar ratio (SiO2 / Al2O3) of the sample was determined to be 81 using inductively coupled plasma atomic emission spectrometry (ICP). This molecular sieve was used as a seed crystal for subsequent synthesis.

[0081] 25.26 g of deionized water, 1.01 g of TPAOH solution (containing 25% by weight of TPAOH), 8.71 g of TEOS (containing 28.3% by weight of SiO2), 0.027 g of aluminum hydroxide, and 0.25 g of ZSM-5 molecular sieve seed crystals (accounting for 10% by weight of SiO2 in the raw materials) were mixed thoroughly and stirred at room temperature for 3 hours to obtain a mixture with a pH of 7.5. The final material ratio (molar ratio) was:

[0082] Al2O3 / SiO2 = 0.004

[0083] TPA + / SiO2=0.03

[0084] H2O / SiO2 = 35

[0085] The mixture was placed in a stainless steel reactor and crystallized at 175°C for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110°C. The XRD pattern of the sample is shown below. Figure 3 The image shown is of ZSM-5 molecular sieve with an MFI-type structure; the SEM and TEM images of the sample are as follows. Figure 4 and Figure 5 As shown, the crystal has a long plate-like morphology, with dimensions of 1.6 μm in length, 230 nm in width, and 110 nm in thickness. Nanoscale SiO2 particles are uniformly dispersed on the surface, with 95% of the SiO2 distributed in a monolayer. The SiO2 particle coverage on the surface is 90%, and the particle size is 12 nm. The specific surface area of ​​the sample is 398 m². 2 / gram, micropore volume 0.12 cm³ 3 / gram, total pore volume is 0.23 cm³ 3 / gram.

[0086] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was found to be greater than 2000, as measured by X-ray photoelectron spectroscopy (XPS).

[0087] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 261 using inductively coupled plasma atomic emission spectrometry (ICP).

[0088] Example 2

[0089] 35.84 g of deionized water, 1.68 g of TPAOH solution (containing 25% by weight of TPAOH), 12.42 g of TEOS (containing 28.3% by weight of SiO2), 0.051 g of aluminum hydroxide, and 0.35 g of ZSM-5 molecular sieve seed crystals from Example 1 (accounting for 10% by weight of SiO2 in the raw materials) were mixed evenly and stirred at room temperature for 3 hours to obtain a mixture with a pH of 7.6. The final material ratio (molar ratio) was:

[0090] Al2O3 / SiO2 = 0.006

[0091] TPA + / SiO2=0.035

[0092] H2O / SiO2 = 35

[0093] The mixture was placed in a stainless steel reactor and crystallized at 170℃ for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110℃. The XRD pattern of the sample is shown below. Figure 6 The image shown is of ZSM-5 molecular sieve with an MFI-type structure; the SEM and TEM images of the sample are as follows. Figure 7 and Figure 8 As shown, the crystal has a long plate-like morphology, with dimensions of 1.7 μm in length, 235 nm in width, and 115 nm in thickness. Nanoscale SiO2 particles are uniformly dispersed on the surface, with 95% of the SiO2 forming a monolayer. The SiO2 particle coverage on the surface is 91%, and the particle size is 13 nm. The sample has a specific surface area of ​​405 m². 2 / gram, micropore volume 0.12 cm³ 3 / gram, total pore volume is 0.20 cm³ 3 / gram.

[0094] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was found to be greater than 2000, as measured by X-ray photoelectron spectroscopy (XPS).

[0095] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 242 using inductively coupled plasma atomic emission spectrometry (ICP).

[0096] Example 3

[0097] 19.56 g of deionized water, 0.92 g of TPAOH solution (containing 25% by weight of TPAOH), 9.50 g of TEOS (containing 28.3% by weight of SiO2), 0.021 g of aluminum hydroxide, and 0.41 g of the above-mentioned ZSM-5 molecular sieve seed crystals (accounting for 15% by weight of SiO2 in the raw materials) were mixed evenly and stirred at room temperature for 3 hours to obtain a mixture with a pH of 7.5. The final material ratio (molar ratio) is as follows:

[0098] Al2O3 / SiO2 = 0.003

[0099] TPA + / SiO2=0.025

[0100] H2O / SiO2 = 25

[0101] The mixture was placed in a stainless steel reactor and crystallized at 175°C for one day by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110°C. The XRD pattern of the sample is shown below. Figure 9 The image shown is of ZSM-5 molecular sieve with an MFI-type structure; the SEM image of the sample is shown below. Figure 10 As shown, the TEM image and Figure 5Similarly, the crystals exhibit a long, plate-like morphology, with dimensions of 1.5 μm in length, 220 nm in width, and 110 nm in thickness. Nanoscale SiO2 particles are uniformly dispersed on the surface, with 94% of the SiO2 distributed in a monolayer. The SiO2 particle coverage on the surface is 90%, and the particle size is 11 nm. The sample has a specific surface area of ​​395 m². 2 / gram, micropore volume 0.12 cm³ 3 / gram, total pore volume is 0.22 cm³. 3 / gram.

[0102] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was found to be greater than 2000, as measured by X-ray photoelectron spectroscopy (XPS).

[0103] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 274 using inductively coupled plasma atomic emission spectrometry (ICP).

[0104] Example 4

[0105] 20.52 g of deionized water, 1.63 g of TPAOH solution (containing 25% by weight of TPAOH), 12.77 g of TEOS (containing 28.3% by weight of SiO2), 0.079 g of aluminum hydroxide, and 0.18 g of the above-mentioned ZSM-5 molecular sieve seed crystals (accounting for 10% by weight of SiO2 in the raw materials) were mixed evenly and stirred at room temperature for 3 hours to obtain a mixture with a pH of 8.0. The final material ratio (molar ratio) was:

[0106] Al2O3 / SiO2 = 0.008

[0107] TPA + / SiO2=0.033

[0108] H2O / SiO2 = 20

[0109] The mixture was placed in a stainless steel reactor and crystallized at 170℃ for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110℃. The XRD pattern of the sample is shown below. Figure 11 The image shown is of ZSM-5 molecular sieve with an MFI-type structure; the SEM image of the sample is shown below. Figure 12 As shown, the TEM image and Figure 5 Similarly, the crystal has a long plate-like morphology, with dimensions of 1.6 μm in length, 230 nm in width, and 120 nm in thickness. Nanoscale SiO2 particles are uniformly dispersed on the surface, with 96% of the SiO2 distributed in a monolayer. The SiO2 particle coverage on the surface is 92%, and the particle size is 12 nm. The sample has a specific surface area of ​​422 m². 2 / gram, micropore volume 0.11 cm³ 3 / gram, total pore volume is 0.23 cm³ 3 / gram.

[0110] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was found to be greater than 2000, as measured by X-ray photoelectron spectroscopy (XPS).

[0111] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 190 using inductively coupled plasma atomic emission spectrometry (ICP).

[0112] Example 5

[0113] 33.34 g of deionized water, 3.26 g of TPAOH solution (containing 25% by weight of TPAOH), 28.09 g of TEOS (containing 28.3% by weight of SiO2), 0.312 g of aluminum hydroxide, and 0.40 g of the above-mentioned ZSM-5 molecular sieve seed crystals (accounting for 5% by weight of SiO2 in the raw materials) were mixed evenly and stirred at room temperature for 3 hours to obtain a mixture. The pH value of the mixture was 8.0. The final material ratio (molar ratio) was:

[0114] Al2O3 / SiO2 = 0.015

[0115] TPA + / SiO2=0.030

[0116] H2O / SiO2 = 15

[0117] The mixture was placed in a stainless steel reactor and crystallized at 170℃ for 3 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110℃ to obtain the XRD pattern. Figure 3 Similarly, it is a ZSM-5 molecular sieve with an MFI-type structure; the SEM image of the sample is similar to... Figure 4 Similarly, TEM images and Figure 5 Similarly, the crystals exhibit a long, plate-like morphology, with dimensions of 1.6 μm in length, 220 nm in width, and 115 nm in thickness. Nanoscale SiO2 particles are uniformly dispersed on the surface, with 96% of the SiO2 distributed in a monolayer. The SiO2 particle coverage on the surface is 90%, and the particle size is 10 nm. The sample has a specific surface area of ​​389 m². 2 / gram, micropore volume 0.11 cm³ 3 / gram, total pore volume is 0.20 cm³ 3 / gram.

[0118] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was found to be greater than 2000, as measured by X-ray photoelectron spectroscopy (XPS).

[0119] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 101 using inductively coupled plasma atomic emission spectrometry (ICP).

[0120] Example 6

[0121] 44.55 g of deionized water, 1.87 g of TPAOH solution (containing 25% by weight of TPAOH), 13.46 g of TEOS (containing 28.3% by weight of SiO2), 0.121 g of aluminum hydroxide, and 0.31 g of the above-mentioned ZSM-5 molecular sieve seed crystals (accounting for 8% by weight of SiO2 in the raw materials) were mixed evenly and stirred at room temperature for 3 hours to obtain a mixture with a pH of 7.5. The final material ratio (molar ratio) was:

[0122] Al2O3 / SiO2 = 0.012

[0123] TPA + / SiO2=0.036

[0124] H2O / SiO2 = 40

[0125] The mixture was placed in a stainless steel reactor and crystallized at 165℃ for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110℃ to obtain the XRD pattern. Figure 3 Similarly, it is a ZSM-5 molecular sieve with an MFI-type structure; the SEM image of the sample is similar to... Figure 4 Similarly, TEM images and Figure 5 Similarly, the crystals exhibit a long, plate-like morphology, with dimensions of 1.8 μm in length, 240 nm in width, and 120 nm in thickness. Nanoscale SiO2 particles are uniformly dispersed on the surface, with 97% of the SiO2 forming a monolayer. The SiO2 particle coverage on the surface is 92%, and the particle size is 11 nm. The sample has a specific surface area of ​​382 m². 2 / gram, micropore volume 0.11 cm³ 3 / gram, total pore volume is 0.23 cm³ 3 / gram.

[0126] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was found to be greater than 2000, as measured by X-ray photoelectron spectroscopy (XPS).

[0127] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 116 using inductively coupled plasma atomic emission spectrometry (ICP).

[0128] Example 7

[0129] 13.55 g of deionized water, 0.86 g of TPAOH solution (containing 25% by weight of TPAOH), 5.55 g of TEOS (containing 28.3% by weight of SiO2), 0.041 g of aluminum hydroxide, and 0.08 g of the above-mentioned ZSM-5 molecular sieve seed crystals (accounting for 8% by weight of SiO2 in the raw materials) were mixed evenly and stirred at room temperature for 3 hours to obtain a mixture with a pH of 8.0. The final material ratio (molar ratio) is as follows:

[0130] Al2O3 / SiO2 = 0.01

[0131] TPA + / SiO2=0.04

[0132] H2O / SiO2 = 30

[0133] The mixture was placed in a stainless steel reactor and crystallized at 170°C for 1.5 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110°C to obtain the XRD pattern of the sample. Figure 3 Similarly, it is a ZSM-5 molecular sieve with an MFI-type structure; the SEM image of the sample is similar to... Figure 4 Similarly, TEM images and Figure 5 Similarly, the crystals exhibit a long, plate-like morphology, with dimensions of 2.0 μm in length, 235 nm in width, and 125 nm in thickness. Nanoscale SiO2 particles are uniformly dispersed on the surface, with 95% of the SiO2 distributed in a monolayer. The SiO2 particle coverage on the surface is 91%, and the particle size is 9 nm. The sample has a specific surface area of ​​379 m². 2 / gram, micropore volume 0.11 cm³ 3 / gram, total pore volume is 0.21 cm³ 3 / gram.

[0134] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was found to be greater than 2000, as measured by X-ray photoelectron spectroscopy (XPS).

[0135] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 124 using inductively coupled plasma atomic emission spectrometry (ICP).

[0136] Comparative Example 1

[0137] Except for the amount of TPAOH in the reactants, everything else was the same as in Example 2. The pH of the mixture was 9.0, and the final molar ratio was:

[0138] Al2O3 / SiO2 = 0.006

[0139] TPA + / SiO2=0.10

[0140] H2O / SiO2 = 35

[0141] The mixture was placed in a stainless steel reactor and crystallized at 170℃ for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110℃ to obtain the XRD pattern. Figure 3 Similarly, this is a ZSM-5 molecular sieve with an MFI-type structure; the SEM image of the sample is shown below. Figure 13As shown, the crystal has a long plate-like morphology, with dimensions of 2.0 μm in length, 240 nm in width, and 125 nm in thickness. The crystal surface is smooth, and no SiO2 particles were observed. The specific surface area of ​​the sample is 411 m². 2 / gram, micropore volume 0.11 cm³ 3 / gram, total pore volume is 0.20 cm³ 3 / gram.

[0142] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was measured to be 140 using X-ray photoelectron spectroscopy (XPS).

[0143] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 131 using inductively coupled plasma atomic emission spectrometry (ICP).

[0144] Comparative Example 2

[0145] Except for the amount of TPAOH in the reactants, everything else was the same as in Example 1. The pH of the mixture was 7.2, and the final molar ratio was:

[0146] Al2O3 / SiO2 = 0.006

[0147] TPA + / SiO2=0.01

[0148] H2O / SiO2 = 35

[0149] The mixture was placed in a stainless steel reactor and crystallized at 170℃ for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110℃ to obtain the XRD pattern. Figure 3 Similarly, this is a ZSM-5 molecular sieve with an MFI-type structure; the SEM image of the sample is shown below. Figure 14 As shown, the crystal has a long plate-like morphology with dimensions of 1.3 μm in length, 210 nm in width, and 95 nm in thickness. The surface of the crystal is covered with relatively few SiO2 particles, with a SiO2 particle coverage of less than 30%.

[0150] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was measured to be 268 using X-ray photoelectron spectroscopy (XPS).

[0151] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 193 using inductively coupled plasma atomic emission spectrometry (ICP).

[0152] Comparative Example 3

[0153] Except for replacing the aluminum source in the reactants with aluminum isopropoxide, the rest is the same as in Example 1.

[0154] The mixture was placed in a stainless steel reactor and crystallized at 175°C for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110°C to obtain the XRD pattern. Figure 3 Similarly, this is a ZSM-5 molecular sieve with an MFI-type structure; the SEM image of the sample is shown below. Figure 15 As shown, the crystal has a long plate-like morphology with dimensions of 2.0 μm in length, 260 nm in width, and 100 nm in thickness. The crystal surface is smooth, and no SiO2 particles were observed.

[0155] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was measured to be 226 using X-ray photoelectron spectroscopy (XPS).

[0156] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 203 using inductively coupled plasma atomic emission spectrometry (ICP).

[0157] Comparative Example 4

[0158] Except for replacing the aluminum source in the reactants with aluminum nitrate, everything else is the same as in Example 1.

[0159] The mixture was placed in a stainless steel reactor and crystallized at 175°C for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110°C. The XRD pattern of the sample is shown below. Figure 16 As shown, there are many amorphous structures, and the crystallization degree of the sample is poor.

[0160] Comparative Example 5

[0161] Except for replacing the silicon source in the reactants with gaseous SiO2, everything else is the same as in Example 1.

[0162] The mixture was placed in a stainless steel reactor and crystallized at 175°C for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110°C to obtain the XRD pattern. Figure 3 Similarly, this is a ZSM-5 molecular sieve with an MFI-type structure; the SEM image of the sample is shown below. Figure 17 As shown, the crystal has a long plate-like morphology, with crystal dimensions of 2.8 μm in length, 270 nm in width, and 110 nm in thickness. The crystal surface is relatively smooth, with a small amount of amorphous material on the ZSM-5 crystal surface.

[0163] The silicon-aluminum molar ratio (SiO2 / Al2O3) on the outer surface of the sample was measured to be 276 using X-ray photoelectron spectroscopy (XPS).

[0164] The molar ratio of SiO2 / Al2O3 in the calcined sample was determined to be 213 using inductively coupled plasma atomic emission spectrometry (ICP).

[0165] Comparative Example 6

[0166] Except that ZSM-5 seed crystals are not added to the reactants, everything else is the same as in Example 1.

[0167] The mixture was placed in a stainless steel reactor and crystallized at 175°C for 2 days by rotation. After crystallization, the sample was centrifuged, washed twice, and dried in an oven at 110°C. The XRD pattern of the sample is shown below. Figure 18 As shown, the sample has an amorphous structure and is essentially uncrystallized.

[0168] Example 8

[0169] The molecular sieve synthesized in Example 1 was calcined at 550°C for 6 hours to obtain H-type ZSM-5 molecular sieve.

[0170] The calcined H-type ZSM-5 molecular sieve powder sample was crushed and sieved to obtain 1.0 g of a 20-40 mesh particle size fraction, which was then placed in a fixed-bed reactor for toluene-methanol alkylation reaction. The reaction conditions were: a toluene to methanol molar ratio of 1:1, a reaction temperature of 400℃, a reaction pressure of atmospheric pressure, and a toluene weight hourly space velocity of 1.0 h⁻¹. -1 The products were analyzed using a Shimadzu GC-2014 gas chromatograph. The conversion rate of toluene was 23%, and the selectivity for p-xylene in the products was 85%.

[0171] Comparative Example 7

[0172] The molecular sieve synthesized in Comparative Example 1 was calcined at 550℃ for 6 hours to obtain H-type ZSM-5 molecular sieve.

[0173] The calcined H-type ZSM-5 molecular sieve powder sample was crushed and sieved to obtain 1.0 g of a 20-40 mesh particle size fraction, which was then placed in a fixed-bed reactor for toluene-methanol alkylation reaction. The reaction conditions were: a toluene to methanol molar ratio of 1:1, a reaction temperature of 400℃, a reaction pressure of atmospheric pressure, and a toluene weight hourly space velocity of 1.0 h⁻¹. -1 The products were analyzed using a Shimadzu GC-2014 gas chromatograph. The conversion rate of toluene was 25%, and the selectivity for p-xylene in the products was 32%.

Claims

1. A ZSM-5 molecular sieve, wherein the ZSM-5 molecular sieve has a long plate-shaped morphology and the surface of the molecular sieve crystal is uniformly covered with a single layer of nano-SiO2 particles; in, Of the nano-SiO2 particles covering the surface of the ZSM-5 molecular sieve crystal, more than 90% are monolayers; the coverage rate of the nano-SiO2 particles on the surface of the ZSM-5 molecular sieve crystal is more than 90%. The ZSM-5 molecular sieve has a crystal size of 1~3μm in length, 160~300nm in width, and 40~150nm in thickness. The particle size of the nano-SiO2 particles is 5~20nm.

2. The ZSM-5 molecular sieve according to claim 1, characterized in that, The ZSM-5 molecular sieve has crystal dimensions of 1.1~2.9μm in length, 165~290nm in width, and 50~145nm in thickness.

3. The ZSM-5 molecular sieve according to claim 1, characterized in that, The particle size of the nano-SiO2 particles is 5~18nm.

4. The ZSM-5 molecular sieve according to claim 1, characterized in that, The specific surface area of ​​the ZSM-5 molecular sieve is 300~450m². 2 / g; the total pore volume of the ZSM-5 molecular sieve is 0.19~0.50 cm³. 3 / g, with micropore volume of 0.05~0.18cm³. 3 / g.

5. The ZSM-5 molecular sieve according to claim 4, characterized in that, The total pore volume of the ZSM-5 molecular sieve is 0.20~0.45 cm³. 3 / g, with micropore volume of 0.06~0.17cm³ 3 / g.

6. The ZSM-5 molecular sieve according to claim 1, characterized in that, The bulk SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 80~500; the SiO2 / Al2O3 molar ratio on the outer surface of the ZSM-5 molecular sieve is >2000.

7. A method for preparing the ZSM-5 molecular sieve according to any one of claims 1-6, comprising the following steps: A mixture of silicon source, aluminum source, tetrapropylammonium hydroxide, water and ZSM-5 molecular sieve seed crystals is subjected to a one-step heating crystallization treatment to obtain the ZSM-5 molecular sieve. The silicon source is calculated as SiO2, the aluminum source as Al2O3, and the tetrapropylammonium hydroxide as TPA. + The mixture of water and SiO2, Al2O3, and TPA was prepared in a molar ratio of SiO2:Al2O3:TPA. + H2O = 1: 0.001~0.020: 0.015~0.045: 10~50; the silicon source is calculated as SiO2 and ZSM-5 molecular sieve seed crystals, with a mass ratio of 1: 0.03~0.

25.

8. The preparation method according to claim 7, characterized in that, The silicon source is calculated as SiO2, the aluminum source as Al2O3, and the tetrapropylammonium hydroxide as TPA. + The mixture of water and SiO2, Al2O3, and TPA was prepared in a molar ratio of SiO2:Al2O3:TPA. + H2O = 1: 0.002~0.018: 0.020~0.040: 15~50; the silicon source is calculated as SiO2 and ZSM-5 molecular sieve seed crystals, with a mass ratio of 1: 0.05~0.

2.

9. The preparation method according to claim 7, characterized in that, The silicon source is tetraethyl orthosilicate, and the aluminum source is aluminum hydroxide.

10. The preparation method according to claim 7, characterized in that, The pH value of the mixture is 7 to 8.

5.

11. The preparation method according to claim 7, characterized in that, The crystallization process of the mixture is dynamic crystallization by rotation or stirring, with a rotation speed of 10~40 rpm and a stirring speed of 30~200 rpm; the crystallization conditions of the mixture are crystallization at 150~190℃ for 0.25~6 days.

12. The preparation method according to claim 11, characterized in that, The crystallization conditions for the mixture are 155~185℃ for 0.5~5 days.

13. The preparation method according to claim 12, characterized in that, The crystallization conditions for the mixture are 160~180℃ for 0.75~4 days.

14. A molecular sieve composition comprising the ZSM-5 molecular sieve according to any one of claims 1 to 6 or the ZSM-5 molecular sieve prepared by the preparation method according to any one of claims 7 to 13, and a binder.

15. The use of a ZSM-5 molecular sieve according to any one of claims 1 to 6, a nano ZSM-5 molecular sieve prepared by the preparation method according to any one of claims 7 to 13, or a molecular sieve composition according to claim 14 as a catalyst in organic conversion reactions.

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