Short c-axis sheet-like mordenite molecular sieve, method for preparing same, and use thereof

Abstract

The application discloses a short-c-axis sheet-like mordenite molecular sieve, a preparation method and application thereof, and belongs to the technical field of molecular sieves. a ·M b ·(Si x Al y )O2;R is a template tetraethylammonium ion; a is the number of moles of R in each mole of (Si x Al y )O2, 0.02<=a<=0.04; M is an alkali metal ion; b is the number of moles of M in each mole of (Si x Al y )O2, 0.02<=b<=0.06; x is the mole fraction of Si in each mole of (Si x Al y )O2, 0.9<=x<=0.97; y is the mole fraction of Al in each mole of (Si x Al y )O2, 0.03<=y<=0.1, and x+y=1; and the size thickness of the c-axis direction of the molecular sieve is 20-80 nm. The molecular sieve exhibits excellent catalytic performance in a catalytic reaction of dimethyl ether carbonylation for preparing methyl acetate.

Description

Technical Field

[0001] This application belongs to the field of molecular sieve technology, and in particular relates to a short c-axis plate-like mordenite molecular sieve, its preparation method and application. Background Technology

[0002] Mordenite zeolite molecular sieves are an important class of silica-alumina zeolite molecular sieve materials, widely used as important adsorbents and catalysts in petroleum processing and fine chemical industries. The framework structure of mordenite zeolite molecular sieves belongs to the orthorhombic crystal system, space group Cmcm. Its framework consists of 12-membered rings parallel to the c-axis. and the 8-yuan ring The channels are composed of two 8-membered rings along the b-axis. The side pockets are connected. In fact, because the 8-membered ring channels along the c-axis are too narrow to allow most molecules to pass through, MOR molecular sieves often exhibit the characteristics of one-dimensional channel zeolite molecular sieves in actual catalytic reactions. The unique channel structure and acid properties of mordenite molecular sieves make them widely used in catalytic reactions such as toluene disproportionation to xylene, methanol and ammonia to methylamine, and dimethyl ether carbonylation to methyl acetate.

[0003] However, the very small pore size of mordenite molecular sieves restricts the entry of reactant molecules with larger kinetic diameters into the sieve channels. This also increases diffusion resistance within the channels, leading to side reactions and carbon buildup, and severely shortening the sieve's lifespan. Therefore, research into preparing mordenite with a shortened c-axis dimension to improve molecule diffusion performance has attracted considerable attention.

[0004] The regulation of zeolite morphology usually requires the introduction of organic templates containing long chains. For example, patent CN107963637 synthesized lamellar zeolite with a thickness of 40 nm along the c-axis using hexadecyl N-dimethylethyl N,N-dimethylammonium bromide containing long chains as an organic template; Wu Peng et al. (Angew. Chem. Int. Ed. 2020, 59, 62586262.) synthesized lamellar zeolite with a thickness of 11 nm along the b-axis using hexadecyl N-dimethylbutyl N-dimethylbenzylamine as an organic structure directing agent; Ryoo et al. (Angew. Chem. Int. Ed. 2013, 52, 10014) used triquaternary ammonium salt C 18 H 37 N + (Me)2C6H 12 N + (Me)2C6H 12 N + (Me)2C 18 H 37 Rod-shaped mordenite zeolite with a diameter of 100–300 nm along the c-axis was synthesized using a bisquaternary ammonium salt C18 H 37 N + (Me)2C6H 12 N + (Me)2C 18 H 37 Morphite with a lamellar thickness of 10–20 nm was synthesized using a template agent. Patent CN102718231A synthesized morphite with a lamellar thickness of 50 nm using hexadecyltrimethyl-p-toluenesulfonate ammonium salt as an organic template agent; however, the crystal orientation of the morphite was unclear. The above methods for controlling the morphology of morphite require the addition of an additional long-chain organic template agent as a directing agent. This method necessitates the separate synthesis of the template agent, increasing production costs, and the process of organically synthesizing the template agent is environmentally unfriendly. Summary of the Invention

[0005] In view of this, this application provides a short c-axis plate-like mordenite molecular sieve, its preparation method and application, the main purpose of which is to solve the technical problem that it is difficult to synthesize short c-axis thin plate-like mordenite molecular sieve.

[0006] On the one hand, this application provides a short c-axis lamellar mordenite molecular sieve, the chemical composition of which is shown in Formula I:

[0007] R a ·M b ·(Si x Al y O2 formula I;

[0008] In Formula I, R is a template agent, which is selected from tetraethylammonium ions;

[0009] a is per mole (Si) x Al y The number of moles of R in O2, 0.02≤a≤0.04;

[0010] In Formula I, M is an alkali metal ion;

[0011] b represents the number of moles (Si) x Al y The number of moles of M in O2, 0.02≤b≤0.06;

[0012] x is the number of moles (Si) x Al y The mole fraction of Si in O2, 0.9 ≤ x ≤ 0.97;

[0013] y is per mole (Si) x Al y The mole fraction of Al in O2 is 0.03 ≤ y ≤ 0.1, and x + y = 1;

[0014] The thickness of the silicate zeolite molecular sieve along the c-axis is 20–80 nanometers.

[0015] Optionally, 'a' is selected from any value among 0.02, 0.025, 0.03, 0.035, and 0.04, or a range between any two.

[0016] b is selected from any value among 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, and 0.06, or a range between any two.

[0017] x is selected from any value among 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, and 0.97, or any value between any two.

[0018] y is selected from any value in 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any value in between.

[0019] Optionally, the template agent is one of tetraethylammonium hydroxide or a salt thereof.

[0020] Optionally, the length of the mordenite molecular sieve along the a-axis is 0.7 to 3 micrometers, and the length along the b-axis is 0.5 to 2 micrometers.

[0021] Optionally, the thickness of the silicate zeolite molecular sieve along the c-axis is 20–50 nanometers.

[0022] Optionally, the thickness of the c-axis dimension of the silicate zeolite molecular sieve is selected from any value of 30, 40, 50, 60, 70, 80 nanometers or any value between the two.

[0023] Optionally, the morphology of the silicate zeolite molecular sieve is sheet-like.

[0024] Optionally, the template agent R and the alkali metal ion M are located in the channels of the mordenite molecular sieve.

[0025] This application uses tetraethylammonium hydroxide or its salt as a template agent to synthesize mordenite nanosheets with a thickness of 20-100 mm along the c-axis, and the molar ratio of Si to Al in the framework is adjustable between 10 and 30. This application achieves efficient synthesis of short c-axis plate-like MOR molecular sieves by using only conventional tetraethylammonium hydroxide or its salt as a template agent without using special long-chain template agents.

[0026] The mordenite molecular sieve described in this application has a short c-axis (12 circular annular channels) nanosheet morphology, and the mordenite sheets form a card house morphology, which is beneficial for product separation. It also exhibits excellent catalytic performance in the dimethyl ether carbonylation reaction.

[0027] Optionally, the molar ratio x / y of Si and Al elements in the silicate zeolite molecular sieve framework is in the range of 10 ≤ x / y ≤ 30.

[0028] More preferably, the molar ratio x / y of Si and Al elements in the silicate zeolite molecular sieve framework is in the range of 12 ≤ x / y ≤ 25.

[0029] The X-ray diffraction pattern of the molecular sieve has characteristic peaks at the following locations:

[0030]

[0031]

[0032] Secondly, this application provides a method for preparing the above-mentioned short c-axis lamellar mordenite molecular sieve, the method comprising the following steps:

[0033] S1: Mix the raw materials containing silicon source, aluminum source, alkali metal M hydroxide, seed crystal, water and template agent to form an initial gel mixture with the following molar ratio:

[0034] SiO2 / Al2O3 = 20~100;

[0035] M2O / SiO2 = 0.05–0.20, where M is an alkali metal;

[0036] Template agent / SiO2 = 0.05–0.15;

[0037] H2O / SiO2 = 10-20;

[0038] Seed crystal mass / SiO2 solid mass fed = 0.5–10%;

[0039] Wherein, the number of moles of the silicon source is calculated as the number of moles of SiO2, the number of moles of the aluminum source is calculated as the number of moles of Al2O3, the number of moles of the hydroxide of the alkali metal M is calculated as the number of moles of M2O, and the number of moles of water is calculated as the number of moles of its own H2O.

[0040] S2: The initial gel mixture in step S1 is heated and crystallized under closed conditions. The crystallization temperature is 160-220°C and the crystallization time under autogenous pressure is 5-50 hours to obtain the crystallized product.

[0041] S3: The crystallized product in step S2 is separated, washed, and dried to obtain the mordenite molecular sieve.

[0042] Optionally, the template agent is one of tetraethylammonium hydroxide or a salt thereof.

[0043] Optionally, the molar ratio of the initial gel mixture is:

[0044] SiO2 / Al2O3 = 30-40;

[0045] M2O / SiO2 = 0.08–0.15;

[0046] Template agent / SiO2 = 0.05–0.12;

[0047] H2O / SiO2 = 10-20;

[0048] Seed crystal mass / SiO2 solid mass fed = 2-8%.

[0049] The technical problem to be solved by this application is to directly use tetraethyl ammonium hydroxide or its salt as a template agent, and combine it with seed crystals and silicon, aluminum and alkali sources used in the conventional synthesis of mordenite molecular sieves as raw materials, and synthesize pure phase mordenite molecular sieves under hydrothermal synthesis conditions by synergistically controlling low template agent dosage and high crystallization temperature, and the synthesized mordenite molecular sieves have a short c-axis nanosheet morphology.

[0050] This application achieves efficient synthesis of short c-axis plate-like MOR molecular sieves by synergistically controlling key factors such as template agent dosage, crystallization temperature, and seed crystals, without using special long-chain template agents, and using only conventional tetraethylammonium hydroxide as a template agent.

[0051] Optionally, in the molar ratio of the initial gel mixture, the molar ratio of SiO2 / Al2O3 is selected from any value or a range between any two of 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100.

[0052] The molar ratio of M2O / SiO2 is selected from any value of 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.20 or any value in between.

[0053] The molar ratio of template agent to SiO2 is selected from any value of 0.05, 0.08, 0.1, 0.12, 0.15 or any value in between.

[0054] The molar ratio of H2O / SiO2 is selected from any value of 10, 12, 15, 18, 20 or any range between the two.

[0055] Optionally, the mass ratio of the seed crystal mass to the mass of the fed SiO2 solid is selected from any value of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or any range between the two.

[0056] Optionally, the crystallization temperature is selected from any value or a range between 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, and 220℃.

[0057] The crystallization time is selected from any value of 5, 10, 15, 20, 30, 40, 50 h or a range between any two.

[0058] Optionally, the seed crystals are selected from mordenite and / or Beta molecular sieves.

[0059] Preferably, the seed crystal is mordenite.

[0060] Optionally, the silicon source is selected from at least one of silica sol, activated silica, orthosilicate, water glass, metakaolin, and silica.

[0061] Preferably, the silicon source is at least one of silica sol, silica fume, and activated silica.

[0062] Optionally, the aluminum source is selected from at least one of sodium aluminate, aluminum alkoxy, aluminum salts, and metakaolin.

[0063] Preferably, the aluminum source is sodium aluminate or an aluminum salt.

[0064] Optionally, the hydroxide of the alkali metal M is selected from sodium hydroxide and / or potassium hydroxide.

[0065] Preferably, the hydroxide of the alkali metal is sodium hydroxide.

[0066] Optionally, the crystallization temperature is 180–200°C, and the crystallization time is 10–20 hours.

[0067] Preferably, the crystallization temperature is 180–200°C.

[0068] Optionally, the crystallization process can be carried out statically or dynamically.

[0069] Thirdly, this application provides a catalyst comprising the above-mentioned short c-axis lamellar zeolite molecular sieve or a short c-axis lamellar zeolite molecular sieve prepared by the above method.

[0070] Optionally, the silicate zeolite molecular sieve is subjected to ammonium ion exchange and then calcined in air at 500-600°C to obtain the catalyst.

[0071] Optionally, the calcination conditions are: a temperature of 500–600°C and a time of 2–10 hours.

[0072] Fourthly, this application provides the application of the above-mentioned catalyst in the catalytic reaction of dimethyl ether carbonylation to methyl acetate.

[0073] Fifthly, this application provides a method for preparing methyl acetate; the method includes: reacting a feed gas containing dimethyl ether and carbon monoxide in the presence of a catalyst to obtain the methyl acetate;

[0074] The catalyst is selected from the above-described catalysts or catalysts prepared by the above-described method.

[0075] Optionally, in the feed gas, the volume ratio of dimethyl ether to carbon monoxide is 1:5 to 10;

[0076] Optionally, the space velocity of the gas mixture is 500–6000 ml g. -1 h -1 ;

[0077] Optionally, the reaction conditions are: temperature of 150–350°C and pressure of 0.5–4 MPa.

[0078] Compared with the prior art, this application has the following beneficial effects:

[0079] 1) In this application, tetraethylammonium hydroxide or its salt was used as a template agent to synthesize mordenite nanosheets with a thickness of 20 to 100 mm in the c-axis direction. The molar ratio of Si to Al in the framework was adjustable between 10 and 30.

[0080] 2) This application achieves the efficient synthesis of short c-axis plate-like MOR molecular sieves by using only conventional tetraethylammonium hydroxide or its salts as template agents without the use of special long-chain template agents.

[0081] 3) The mordenite molecular sieve prepared in this application exhibits excellent catalytic performance in the carbonylation of dimethyl ether to produce methyl acetate. Attached Figure Description

[0082] Figure 1 The X-ray diffraction pattern of sample 1 in Example 1 of this application;

[0083] Figure 2 This is a scanning electron microscope image of sample 1 in Example 1 of this application, with a scale bar of 2.00 μm;

[0084] Figure 3 This is a scanning electron microscope image of sample 1 in Example 1 of this application, with a scale bar of 1.00 μm;

[0085] Figure 4 The transmission electron microscope (TEM) and selected area electron diffraction (SED) patterns of the sample in Example 1 of this application are shown.

[0086] Figure 5 Images of HAADF (left) and iDPC (right) of the sample in Example 1 of this application;

[0087] Figure 6 The carbon NMR spectrum of the sample in Example 1 of this application;

[0088] Figure 7 This is a diagram showing the catalytic performance of the short c-axis lamellar zeolite prepared in Example 1 of this application in the dimethyl ether carbonylation reaction;

[0089] Figure 8 The graph shows the catalytic performance of the mordenite zeolite prepared in Comparative Example 3 in the dimethyl ether carbonylation reaction. Detailed Implementation

[0090] The present application is further illustrated below with reference to specific embodiments. The following descriptions are merely a few embodiments of the present application and are not intended to limit the present application in any way. Although the present application discloses preferred embodiments as follows, they are not intended to limit the present application. Any modifications or variations made by those skilled in the art without departing from the scope of the technical solution of the present application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

[0091] Unless otherwise specified, the raw materials used in the embodiments of this application are all purchased commercially and used directly without any special treatment.

[0092] This application discloses a short c-axis plate-like mordenite molecular sieve, the anhydrous chemical composition of which can be expressed as: R a ·M b ·(Si x Al y O2, where R is tetraethylammonium hydroxide or its salt, distributed in the twelve-membered ring channels of mordenite molecular sieve, and a is the number of moles of Si x Al y The number of moles of R in O2, 0.02≤a≤0.04; M is an alkali metal ion, b is the number of moles of (Si) x Al y The number of moles of M in O2, 0.02≤b≤0.06; x is the number of moles of (Si) per mole. x Al y The mole fraction of Si in O2, 0.9 ≤ x ≤ 0.97; y is the mole fraction of Si per mole (Six Al y The mole fraction of Al in O2 is 0.03 ≤ y ≤ 0.1; x + y = 1.

[0093] The mordenite molecular sieve provided in this application is plate-shaped, with a thickness of 20–100 nanometers along the c-axis (12 circular channels), exhibiting a thin plate morphology. The molar ratio x / y of Si and Al elements in the framework of this mordenite molecular sieve ranges from 10 ≤ x / y ≤ 30.

[0094] This application also provides a method for synthesizing the above-mentioned mordenite molecular sieve and its catalytic application in acid-catalyzed reactions, especially in the carbonylation of dimethyl ether to produce methyl acetate; the molecular sieve exhibits good catalytic performance in the reaction.

[0095] Example 1

[0096] The molar ratios of the raw materials in the initial gel and the crystallization conditions are shown in Table 1.

[0097] First, 0.51 g of sodium aluminate and 0.40 g of sodium hydroxide solid were dissolved in 9 g of deionized water. After the solution was mixed evenly, 17.5 g of silica sol (27 wt%) was slowly added dropwise to the solution while stirring. Then, 0.2 g of uncalcined mordenite seed crystals and 3.4 g of tetraethylammonium hydroxide (35 wt%) were added to the mixture in one step. The initial gel was then stirred at room temperature until homogeneous. The gel was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 190 °C under dynamic conditions for 12 h. The resulting solid product was centrifuged, washed with deionized water until neutral, and dried in air at 110 °C to obtain raw powder sample 1.

[0098] XRD analysis was performed on sample 1 obtained in Example 1. The XRD pattern is shown in the figure. Figure 1 As can be seen, the synthesized product only has the characteristics of mordenite molecular sieve. This mordenite molecular sieve is a pure phase mordenite molecular sieve, and the sharp and clear diffraction peaks indicate that the molecular sieve has high crystallinity.

[0099] Sample 1 obtained in Example 1 was characterized by scanning electron microscopy. The scanning electron microscope image of the sample is shown below. Figure 2 and Figure 3 As shown, the sample has a sheet-like morphology, and different molecular sieve sheets agglomerate to form a card house morphology.

[0100] Sample 1 obtained in Example 1 was characterized by transmission electron microscopy (TEM). The TEM images and corresponding selected area electron diffraction (SED) results are shown below. Figure 4 This proves that the minor axis of the sample is the c-axis.

[0101] Sample 1 obtained in Example 1 was characterized by spherical aberration-corrected electron microscopy. The HAADF-STEM image and corresponding iDPC-STEM image of Sample 1 are shown below. Figure 5 It can be clearly seen that the short axis of the sample is in the direction of the 12-ring channel.

[0102] Sample 1 of mordenite zeolite powder from Example 1 was subjected to... 13 ¹³C MAS NMR analysis, spectrum shown in [reference image] Figure 6 Only characteristic carbon resonance peaks belonging to tetraethylammonium hydroxide were found, indicating that tetraethylammonium hydroxide maintained structural integrity during the crystallization process and was encapsulated in the channels of the resulting mordenite molecular sieve as a template agent.

[0103] XRF elemental analysis, CHN elemental analysis, and thermogravimetric analysis were performed on sample 1 of the raw powder from Example 1. The anhydrous chemical composition of the mordenite molecular sieve from Example 1 was R. 0.033 ·M 0.050 ·(Si 0.933 Al 0.067 )O2.

[0104] Examples 2-12

[0105] The specific ingredient ratios and crystallization conditions for Examples 2-12 are shown in Table 1, and the specific ingredient preparation process is the same as in Example 1. XRD analysis was performed on the raw powder samples obtained from Examples 2-12. The X-ray diffraction patterns of the products show... Figure 1 The characteristics of the peaks, namely their similar peak positions and shapes, and the relative peak intensities fluctuating within ±10% depending on the synthesis conditions, prove that the synthesized products are all mordenite molecular sieves. CHN elemental analysis, thermogravimetric analysis, and XRF determination were performed on the raw powder samples of Examples 2–12. The obtained elemental compositions were normalized to obtain the anhydrous chemical composition (chemical formula I) and silicon-aluminum ratio of the mordenite molecular sieves of Examples 2–12, which are listed in Table 1.

[0106] Example 13

[0107] Take 3g of each of the synthesized samples from Examples 1-12 and place them in a plastic beaker. Add 3mL of 40% hydrofluoric acid solution to dissolve the molecular sieve framework under ice-water bath conditions, then add 15mL of chloroform to dissolve the organic matter. GC-MS analysis of the organic matter showed that all contained tetraethylammonium hydroxide.

[0108] Example 14

[0109] Sample 1 obtained in Example 1 was calcined at 600°C with dry air for 4 hours, sodium ions were removed by NH4NO3 ion exchange, and then calcined in air at 550°C for 4 hours. The resulting product was then tableted and crushed into catalyst particles with a particle size of 40–60 mesh. 1.0 g of catalyst particles was weighed and loaded into a fixed-bed reactor for evaluation of the dimethyl ether (DME) carbonylation reaction. The reaction was initially activated at 400°C with nitrogen for 1 hour, then cooled to 200°C for further reaction. The mixed gas (DME / CO / N2 = 5 / 35 / 60, volume ratio) had a gas hourly space velocity (GHSV) of 3600 ml / g. -1 h -1 (STP) was used, with a reaction pressure of 2.0 MPa. After a 5-hour induction period, the conversion rate of dimethyl ether reached a maximum of 47%, and the selectivity of methyl acetate was above 90% within 13 hours of reaction. The corresponding performance graph for the dimethyl ether carbonylation reaction is shown below. Figure 7 .

[0110] Table 1. Initial gel formulation, crystallization conditions, and bulk elemental composition and thickness along the c-axis of the molecular sieves in Examples 1-12*

[0111]

[0112]

[0113] Note * Silicon source: a silica sol b Activated silica.

[0114] Aluminum source: c Sodium aluminate, d Alkoxyaluminum, e Aluminum salts.

[0115] R: f Tetraethylammonium hydroxide, g Grade IV ammonium chloride, h Tetraethylammonium bromide

[0116] Seed crystals: I Siliceous zeolite, II Beta molecular sieve.

[0117] Crystallization conditions: α Dynamic crystallization β Static crystallization.

[0118] Comparative Example 1

[0119] The difference between Comparative Example 1 and Example 1 is that no organic template agent was added in Comparative Example 1; the other ingredient ratios, ingredient processes and crystallization conditions were the same as in Example 1; the resulting product was identified by XRD as a mixture of mordenite and ZSM-5.

[0120] Comparative Example 2

[0121] The difference between Comparative Example 2 and Example 1 is that no seed crystals were added in Comparative Example 2; the other ingredient ratios, ingredient processes and crystallization conditions were the same as in Example 1; the resulting product was identified by XRD as a mixture of mordenite and ZSM-5.

[0122] Comparative Example 3

[0123] The difference between Comparative Example 3 and Example 1 is that the crystallization temperature of Comparative Example 3 is 150°C; the other ingredient ratios, ingredient processes and crystallization conditions are the same as those of Example 1; the obtained product is identified by XRD as mordenite, but the crystal c-axis thickness is 900 nm.

[0124] Comparative Example 4

[0125] The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 increases the amount of template agent, so that template agent / SiO2 = 0.25; other ingredient ratios, ingredient process and crystallization conditions are the same as in Example 1; the obtained product is identified by XRD as mordenite zeolite, but the crystal c-axis thickness is 200 nm.

[0126] Comparative Example 5

[0127] Comparative Example 3 was calcined at 600℃ with dry air for 4 hours, sodium ions were removed by NH4NO3 ion exchange, and then calcined in air at 550℃ for 4 hours. The resulting catalyst particles were then compressed and crushed into particles with a size of 40–60 mesh. 1.0 g of catalyst particles were weighed and loaded into a fixed-bed reactor for evaluation of the dimethyl ether (DME) carbonylation reaction. The reaction was initially activated at 400℃ with nitrogen for 1 hour, then cooled to 200℃ for further reaction. The mixed gas (DME / CO / N2 = 5 / 35 / 60, volume ratio) had a gas hourly space velocity (GHSV) of 3600 ml / g. - 1 h -1 (STP) was used, with a reaction pressure of 2.0 MPa. After a 3-hour induction period, the conversion rate of dimethyl ether reached a maximum of 19%, and the selectivity of methyl acetate was only higher than 90% within 6 hours. The corresponding performance diagram for the dimethyl ether carbonylation reaction is shown below. Figure 8 .

[0128] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A short c-axis lamellar mordenite molecular sieve, characterized in that, The morphology of the silicate zeolite molecular sieve is sheet-like; The length of the mordenite molecular sieve along the a-axis is 0.7 to 3 micrometers, and the length along the b-axis is 0.5 to 2 micrometers. The chemical composition of the mordenite molecular sieve is shown in Formula I: R a ·M b ·(Si x Al y )O₂ of formula I; In Formula I, R is a template agent, which is selected from tetraethylammonium ions; a is per mole (Si) x Al y The number of moles of R corresponding to O2, 0.02≤a≤0.04; In Formula I, M is an alkali metal ion; b represents the number of moles (Si) x Al y The number of moles of M corresponding to O2, 0.02≤b≤0.06; x is the number of moles (Si) x Al y The mole fraction of Si in O2, 0.9 ≤ x ≤ 0.97; y is per mole (Si) x Al y The mole fraction of Al in O2 is 0.03 ≤ y ≤ 0.1, and x + y = 1; The c-axis thickness of the mordenite molecular sieve is 20 to 80 nanometers.

2. The short c-axis lamellar mordenite molecular sieve according to claim 1, characterized in that, The thickness of the silicate zeolite molecular sieve along the c-axis is 20 to 50 nanometers. The template agent R and the alkali metal ion M are located in the channels of the mordenite molecular sieve.

3. The short c-axis lamellar mordenite molecular sieve according to claim 1, characterized in that, The template agent is one of tetraethylammonium hydroxide or its salt.

4. The method for preparing a short c-axis lamellar mordenite molecular sieve according to any one of claims 1 to 3, characterized in that, The method includes the following steps: S1: Mix the raw materials containing silicon source, aluminum source, alkali metal M hydroxide, seed crystal, water and template agent to form an initial gel mixture with the following molar ratio: SiO2 / Al2O3 = 20~100; M2O / SiO2 = 0.05~0.20, where M is an alkali metal; Template agent / SiO2 = 0.05~0.15; H2O / SiO2 = 10~20; Seed crystal mass / SiO2 solid mass fed = 0.5~10%; Wherein, the number of moles of the silicon source is calculated as the number of moles of SiO2, the number of moles of the aluminum source is calculated as the number of moles of Al2O3, the number of moles of the hydroxide of the alkali metal M is calculated as the number of moles of M2O, and the number of moles of water is calculated as the number of moles of its own H2O. S2: The initial gel mixture from step S1 is heated and crystallized under sealed conditions at a crystallization temperature of 160-220°C and a crystallization time of 5-50 hours under autogenous pressure to obtain a crystallized product. S3: The crystallized product in step S2 is separated, washed, and dried to obtain the mordenite molecular sieve.

5. The method for preparing a short c-axis lamellar mordenite molecular sieve according to claim 4, characterized in that, The molar ratio of the initial gel mixture is: SiO2 / Al2O3 = 30~40; M2O / SiO2 = 0.08~0.15; Template agent / SiO2 = 0.05~0.12; Seed mass / SiO2 solid mass fed = 2~8%.

6. The method for preparing a short c-axis lamellar mordenite molecular sieve according to claim 4, characterized in that, The seed crystals are selected from mordenite zeolite and / or Beta molecular sieve.

7. The method for preparing a short c-axis lamellar mordenite molecular sieve according to claim 4, characterized in that, The silicon source is selected from at least one of silica sol, activated silica, orthosilicate, water glass, metakaolin, and silica.

8. The method for preparing a short c-axis lamellar mordenite molecular sieve according to claim 4, characterized in that, The aluminum source is selected from at least one of sodium aluminate, aluminum alkoxy, and metakaolin.

9. The method for preparing a short c-axis lamellar mordenite molecular sieve according to claim 4, characterized in that, The hydroxide of the alkali metal M is selected from sodium hydroxide and / or potassium hydroxide.

10. The method for preparing a short c-axis lamellar mordenite molecular sieve according to claim 4, characterized in that, The crystallization temperature is 180~200 ℃, and the crystallization time is 10~20 hours.

11. A catalyst, characterized in that, The catalyst includes a short c-axis lamellar zeolite molecular sieve as described in any one of claims 1 to 3, or a short c-axis lamellar zeolite molecular sieve prepared by the method described in any one of claims 4 to 10.

12. The catalyst according to claim 11, characterized in that, The mordenite molecular sieve is subjected to ammonium ion exchange and then calcined in air at 500-600 °C to obtain the catalyst.

13. The use of the catalyst according to claim 11 or 12 in the catalytic reaction of dimethyl ether carbonylation to methyl acetate.

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