A BETA / MOR symbiotic molecular sieve and its preparation method

Abstract

This invention discloses a BETA / MOR symbiotic molecular sieve and its preparation method. The BETA / MOR symbiotic molecular sieve contains surface aluminum S... SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 0.1 to 0.8, preferably 0.5 to 0.8. The molecular sieve provided by the present invention has the characteristics of strong tunability of phase composition ratio and rich silicon on the surface and rich aluminum inside, and can be used as a catalyst component for reactions such as alkyl transfer.

Description

Technical Field

[0001] This invention relates to the field of molecular sieves, specifically to a BETA / MOR symbiotic molecular sieve and its preparation method. Background Technology

[0002] Symbiotic molecular sieves are a class of composite molecular sieve materials with multiple components. Their pore structure and acid properties are an organic combination of the pore and acid properties of their constituent molecular sieves, exhibiting superior hierarchical pores and a more rational acid distribution compared to individual molecular sieves. When processing complex reactants with varying molecular diameters, they can exert a synergistic catalytic effect, thus demonstrating excellent catalytic performance. Furthermore, compared to simply mechanically mixed molecular sieves, symbiotic molecular sieves, due to the higher degree of integration of their pore structure and acid properties, often exhibit superior catalytic performance.

[0003] Currently, there are numerous reports on the synthesis of symbiotic molecular sieves. CN1397493A discloses a type of twelve-membered ring structure two-phase symbiotic molecular sieve and its synthesis method. This method involves mixing a silicon source, an aluminum source, an alkali source, a template agent, and water in a specific ratio and order, followed by hydrothermal crystallization to produce a symbiotic molecular sieve containing two components: BETA and MOR zeolite. CN1648046A discloses a method for preparing a mixed crystal material of MOR zeolite and BETA molecular sieves. This method involves mixing a silicon source, an aluminum source, an alkali source, a template agent, fluoride, water, and seed crystals in a specific ratio and order, followed by hydrothermal crystallization to produce a symbiotic molecular sieve containing two components: BETA and MOR zeolite. CN101177276A discloses a core-shell structure binary composite molecular sieve and its preparation method. This method involves two main steps: first, synthesizing a BETA molecular sieve using a template agent; then, adding aluminum, a template agent, and an alkali, followed by hydrothermal crystallization to produce a binary composite molecular sieve containing both BETA and mordenite. CN101514009A discloses a MOR zeolite / BETA molecular sieve / Y molecular sieve symbiotic material and its synthesis method. The method involves mixing a silicon source, an aluminum source, an alkali source, a template agent, water, and Y-type molecular sieve seed crystals in a specific ratio and order, followed by hydrothermal crystallization to produce a symbiotic molecular sieve containing MOR zeolite, BETA, and Y components. CN101514010A discloses a MOR zeolite / BETA molecular sieve / articulate porous symbiotic material and its preparation method. This method involves mixing a silicon source, an aluminum source, an alkali source, a template agent, and water in a specific ratio and order, followed by hydrothermal crystallization to produce a symbiotic molecular sieve containing MOR zeolite, BETA, and articulate molecular sieve components. CN101514011A discloses a three-phase symbiotic molecular sieve containing MOR zeolite / BETA molecular sieve / MCM-22 and its synthesis method. The method involves mixing a silicon source, an aluminum source, an alkali source, a template agent, water, and MCM-22 molecular sieve seed crystals in a specific ratio and order, followed by hydrothermal crystallization to produce a composite molecular sieve containing MOR zeolite, BETA, and MCM-22. CN101514024A discloses a symbiotic material containing BETA molecular sieve / Magadiite / MOR zeolite and its synthesis method. This method involves mixing a silicon source, an aluminum source, an alkali source, a template agent, water, and mordenite seed crystals in a specific ratio and order, followed by hydrothermal crystallization to produce a symbiotic molecular sieve containing BETA, Magadiite, and MOR zeolite.

[0004] Although the symbiotic molecular sieves synthesized by the above method exhibit better catalytic performance than mechanically mixed molecular sieves to some extent, further research is needed on how to further leverage the advantages of pore structure and acid properties of BETA / MOR symbiotic molecular sieves. Summary of the Invention

[0005] This invention provides a novel BETA / MOR symbiotic molecular sieve and its preparation method to address the problems of existing technologies. This molecular sieve features highly adjustable phase composition ratios and a silicon-rich surface with an aluminum-rich interior.

[0006] The first aspect of this invention provides a BETA / MOR symbiotic molecular sieve, wherein the symbiotic molecular sieve has a surface aluminum S SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 0.1 to 0.8, preferably 0.5 to 0.8.

[0007] Furthermore, the BETA / MOR symbiotic molecular sieve has the following illustrative chemical composition, in molar ratio: nSiO2 / Al2O3, wherein 10≤n≤100, preferably 20≤n≤50.

[0008] Furthermore, in the BETA / MOR symbiotic molecular sieve, the mass ratio of BETA / MOR is 10 / 90 to 90 / 10, preferably 25 / 75 to 75 / 25.

[0009] Furthermore, the specific surface area of ​​the BETA / MOR symbiotic molecular sieve is 400–550 m². 2 / g, pore volume 0.10~0.30cm³ 3 / g, preferably 0.20~0.30cm 3 / g.

[0010] A second aspect of this invention provides a method for preparing the above-mentioned BETA / MOR symbiotic molecular sieve, comprising:

[0011] (1) Mix silicon source, aluminum source, first template agent T1, second template agent T2, alkaline source and water, adjust pH to 9-13, and then add MOR seed crystals to obtain molecular sieve precursor;

[0012] (2) The molecular sieve precursor described in (1) is first subjected to a first-stage hydrothermal crystallization, and then heated to perform a second-stage hydrothermal crystallization to obtain the BETA / MOR symbiotic molecular sieve.

[0013] Further, the MOR seed crystal in step (1) is a MOR molecular sieve seed crystal with a silicon-aluminum molar ratio (SiO2 / Al2O3) of 15 to 25.

[0014] Further, the silicon source in step (1) is selected from water glass, preferably water glass containing 15-40 wt% SiO2 and a modulus of 3.0-3.5; the aluminum source is selected from at least one of sodium aluminate, aluminum sulfate, boehmite, sodium aluminate, aluminum nitrate, aluminum isopropoxide, and aluminum hydroxide, preferably sodium aluminate and / or aluminum sulfate; the alkali source is selected from ammonia and / or alkaline hydroxides, preferably NaOH; the first template agent is tetraethylammonium hydroxide (TEAOH) and / or tetraethylammonium bromide (TEABr); the second template agent is sodium fluoride.

[0015] Further, the silicon source, aluminum source, first template agent T1, second template agent T2, alkali source and water mentioned in step (1) are mixed in a molar ratio of (1-6) alkali source: (30-55) SiO2: Al2O3: (8-15) T1: (100-1000) H2O: (2-8) T2 to prepare a sol.

[0016] Furthermore, the mass content of MOR seeds in the molecular sieve precursor described in step (1) is 20% to 55%.

[0017] Further, in step (2), the hydrothermal crystallization conditions for the first stage are: hydrothermal crystallization at 100-130℃ for 24-48 hours; and the hydrothermal crystallization conditions for the second stage are: hydrothermal crystallization at 160-200℃ for 24-48 hours.

[0018] Furthermore, after the hydrothermal crystallization in the second stage of step (2), conventional washing and drying processes in the art can be performed.

[0019] The third aspect of this invention provides that the above-mentioned BETA / MOR symbiotic molecular sieve can be used in catalytic fields, such as alkyl transfer, heavy aromatic hydrocarbon lightening, toluene / benzyl alcohol methylation and other reactions.

[0020] Before use in the catalytic field, the BETA / MOR symbiotic molecular sieve is preferably subjected to ammonium exchange. Ammonium exchange can be performed using conventional methods in the field.

[0021] The preferred alkyl transfer reaction is a toluene-trimethylbenzene alkyl transfer reaction, with the following reaction conditions: temperature 250–450°C, reaction pressure 1–5 MPa, hydrogen-to-hydrocarbon molar ratio 1–5:1, toluene-to-trimethylbenzene molar ratio in the feed 0.1–10:1, and feed mass hourly space velocity (WHSV) of toluene-to-trimethylbenzene 1–6 h⁻¹. -1 .

[0022] In existing technologies, the acidic sites within the pores of molecular sieves exhibit a significant confined catalytic effect, offering a clear advantage in improving product selectivity and suppressing the formation of coking precursors. In contrast, the non-poreicy surfaces of the molecular sieve outer surface, lacking a significant confined catalytic effect, can lead to the formation of large molecular byproducts and even coking precursors, thereby reducing catalyst selectivity. The inventors have discovered that the difference in aluminum distribution between the inner and outer surfaces of molecular sieve materials is a key challenge in addressing this issue. While existing methods for synthesizing molecular sieves include those containing BETA and mordenite components in symbiotic molecular sieves, they all share a common drawback: the resulting BETA / MOR symbiotic molecular sieves exhibit a largely uniform silica-alumina distribution without a significant concentration gradient. Although these methods sometimes yield BETA / MOR symbiotic molecular sieves with better catalytic performance than mechanically mixed BETA and MOR molecular sieves, they do not offer a significant advantage in further enhancing the pore-confined catalytic effect. In addition, for the synthesis of symbiotic molecular sieve materials, the flexible and adjustable composition of the two phases is also an important direction for synthesis. Although existing synthesis methods can synthesize BETA / MOR symbiotic molecular sieves, the controllability of the composition ratio of BETA and MOR is insufficient.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] The BETA / MOR symbiotic molecular sieve provided by this invention can effectively adjust the BETA / MOR phase ratio, making the raw material more complex and applicable. The aluminum distribution characteristics of being silicon-rich on the surface and aluminum-rich inside can effectively reduce non-shape-selective catalytic reactions on the outer surface of the molecular sieve, inhibit the formation of macromolecular byproducts and colloids, and improve catalyst activity and selectivity. Attached Figure Description

[0025] Figure 1 The XRD pattern of the BETA / MOR symbiotic molecular sieve obtained in Example 1;

[0026] Figure 2 The image shows the SEM image of the BETA / MOR symbiotic molecular sieve obtained in Example 1.

[0027] Figure 3 The XRD pattern of the BETA molecular sieve containing a small amount of ZSM-5 impurities obtained in Comparative Example 3 is shown.

[0028] Figure 4 SEM image of the BETA molecular sieve containing a small amount of ZSM-5 impurities obtained in Comparative Example 3;

[0029] Figure 5 The XRD pattern of the pure MOR molecular sieve obtained in Comparative Example 5 is shown.

[0030] Figure 6The image shows a SEM image of the pure MOR molecular sieve obtained in Comparative Example 5. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0032] The raw materials used in the embodiments and comparative examples of this invention are commercially available and have an analytical grade (AR) purity.

[0033] In the context of this specification, the aluminum distribution value obtained by XPS-argon ion etching is S, where S is S SAR with I SAR The ratio; where S SAR I represents the atomic percentage of aluminum on the surface of the molecular sieve obtained directly by XPS measurement. SAR The atomic percentage of aluminum inside the molecular sieve is measured by XPS after argon ion etching, with an argon ion etching depth of 20–50 nm.

[0034] In the context of this specification, specific surface area refers to the total surface area per unit mass of a sample, including both internal and external surface areas. Non-porous samples only have external surface area, such as silicate cement and some clay mineral powders; porous and multi-porous samples have both external and internal surface areas, such as asbestos fibers, diatomaceous earth, and molecular sieves. In the context of this specification, pore volume refers to the volume of pores per unit mass of porous material. Total pore volume refers to the volume of all pores per unit mass of molecular sieve (generally only pores with a diameter less than 50 nanometers are included). The pore structure parameters of molecular sieves, such as total pore volume and total specific surface area, are obtained by measuring the nitrogen physical adsorption-desorption isotherms using a physical adsorption instrument (such as the TriStar 3000 physical adsorption instrument from Micron Instruments, Inc.), and then calculating using the BET method and t-plot method. The experimental conditions for molecular sieves are: measurement temperature -196℃, and pretreatment of the molecular sieve under vacuum at 300℃ for 10 hours before measurement.

[0035] In the context of this specification, including in the following examples and comparative examples, the scanning electron microscope (SEM) used for molecular sieves is a model S-4800II field emission scanning electron microscope.

[0036] In the context of this specification, the structure of the molecular sieve is determined by X-ray diffraction (XRD), which is measured by an X-ray powder diffractometer. In the examples and comparative examples below, the X-ray powder diffractometer used for the molecular sieve is a Panalytical X PERPRO type X-ray powder diffractometer. The phase of the sample was analyzed using a CuKα-ray source with a nickel filter. The 2θ scanning range was 5–50°, the operating voltage was 40 kV, the current was 40 mA, and the scanning rate was 10° / min.

[0037] In this invention, the overall reaction conversion rate and xylene selectivity are defined as follows:

[0038]

[0039]

[0040] Example 1

[0041] The synthesis method of BETA / MOR molecular sieve: MOR molecular sieve with a silicon-to-aluminum molar ratio (SiO2 / Al2O3) of 20 is used as the seed crystal; water glass (containing 28% SiO2, modulus 3.0-3.5) is used as the silicon source; sodium aluminate is used as the aluminum source; tetraethylammonium hydroxide (TEAOH) is used as the first template agent; sodium fluoride is used as the second template agent; and NaOH is used as the alkali source. The composition of the molecular sieve synthesis gel is: n(Na2O) / n(SiO2) / n(Al2O3) / n(TEAOH) / n(H2O) / n(NaF) = 1.5:40:1:10:700:5. The pH is adjusted to 12 with ammonia, then the MOR seed crystal is added, and the mixture is stirred evenly to prepare the molecular sieve precursor. The mass content of the MOR seed crystal in the molecular sieve precursor is 20%. The aforementioned precursor was first hydrothermally crystallized at 120℃ for 48 hours, and then hydrothermally crystallized at 180℃ for 48 hours to obtain a symbiotic molecular sieve, namely a BETA / MOR symbiotic molecular sieve. The mass ratio of the BETA / MOR phase was 35 / 65, and the surface aluminum S... SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 0.55, and the molar ratio of SiO2 / Al2O3 is 29.

[0042] The XRD pattern of the symbiotic molecular sieve in this example is shown below. Figure 1 ,Depend on Figure 1 It is evident that it exhibits typical characteristic peaks of BETA and MOR molecular sieves.

[0043] The SEM image of the symbiotic molecular sieve in this example is shown below. Figure 2 ,Depend on Figure 2 It is evident that the morphology exhibits a clear coexistence of large-particle MOR and small-particle BETA molecular sieves.

[0044] The specific surface area of ​​the BETA / MOR symbiotic molecular sieve in this example is 410 m². 2 / g, pore volume 0.25cm 3 / g.

[0045] The above molecular sieve, after ammonium exchange, was applied to the alkyl transfer reaction of toluene and trimethylbenzene. The reaction conditions were: temperature 350℃, reaction pressure 3.0 MPa, hydrogen-to-hydrocarbon molar ratio 3:1 mol / mol, toluene-to-trimethylbenzene molar ratio in the feed 1:1 mol / mol, and feed mass hourly space velocity (WHSV) of toluene and trimethylbenzene 3 h⁻¹. -1 The overall conversion rate was 48%, and the xylene selectivity was 97%.

[0046] Example 2

[0047] The synthesis method of BETA / MOR molecular sieve: MOR molecular sieve with a silicon-to-aluminum molar ratio (SiO2 / Al2O3) of 25 was used as the seed crystal; water glass (containing 28wt% SiO2, modulus 3.0-3.5) was used as the silicon source; aluminum sulfate was used as the aluminum source; tetraethylammonium bromide (TEABr) was used as the first template agent; sodium fluoride was used as the second template agent; and NaOH was used as the alkali source. The composition of the molecular sieve synthesis gel was: n(Na2O) / n(SiO2) / n(Al2O3) / n(TEABr) / n(H2O) / n(NaF) = 2.0:55:1:12:980:6. The pH was adjusted to 11 with ammonia, and then the MOR seed crystal was added and stirred evenly to prepare the molecular sieve precursor. The mass content of the MOR seed crystal in the molecular sieve precursor was 35%. The aforementioned precursor was first hydrothermally crystallized at 130℃ for 24 hours, and then hydrothermally crystallized at 170℃ for 48 hours to obtain a BETA / MOR symbiotic molecular sieve. The mass ratio of the BETA / MOR phase was 56 / 44, and the surface aluminum content was [missing information]. SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 0.60, and the molar ratio of SiO2 / Al2O3 is 31.

[0048] The XRD pattern of the symbiotic molecular sieve in this example is... Figure 1 Similarly, the SEM images of the symbiotic molecular sieve in this example are... Figure 2 Similarly, the specific surface area of ​​the BETA / MOR symbiotic molecular sieve in this example is 466 m². 2 / g, pore volume 0.27cm 3 / g.

[0049] The above molecular sieve, after ammonium exchange, was applied to the alkyl transfer reaction of toluene and trimethylbenzene. The reaction conditions were: temperature 350℃, reaction pressure 3.0 MPa, hydrogen-to-hydrocarbon molar ratio 3:1 mol / mol, toluene-to-trimethylbenzene molar ratio in the feed 1:1 mol / mol, and feed mass hourly space velocity (WHSV) of toluene and trimethylbenzene 3 h⁻¹. -1The overall conversion rate was 46%, and the xylene selectivity was 98%.

[0050] Example 3

[0051] The synthesis method of BETA / MOR molecular sieve: MOR molecular sieve with a silicon-to-aluminum molar ratio (SiO2 / Al2O3) of 20 is used as the seed crystal; water glass (containing 28wt% SiO2, modulus 3.0-3.5) is used as the silicon source; sodium aluminate is used as the aluminum source; tetraethylammonium hydroxide (TEAOH) is used as the first template agent; sodium fluoride is used as the second template agent; and NaOH is used as the alkali source. The composition of the molecular sieve synthesis gel is: n(Na2O) / n(SiO2) / n(Al2O3) / n(TEAOH) / n(H2O) / n(NaF) = 2.5:55:1:12:800:4.5. The pH is adjusted to 13 with ammonia, then the MOR seed crystal is added, and the mixture is stirred evenly to prepare the molecular sieve precursor. The mass content of the MOR seed crystal in the molecular sieve precursor is 40%. The aforementioned precursor was first hydrothermally crystallized at 100℃ for 48 hours, and then hydrothermally crystallized at 160℃ for 72 hours to obtain a BETA / MOR symbiotic molecular sieve. The mass ratio of the BETA / MOR phase was 72 / 28, and the surface aluminum content was [missing information]. SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 0.78, and the molar ratio of SiO2 / Al2O3 is 25.

[0052] The XRD pattern of the symbiotic molecular sieve in this example is... Figure 1 Similarly, the SEM images of the symbiotic molecular sieve in this example are... Figure 2 Similarly, the specific surface area of ​​the BETA / MOR symbiotic molecular sieve in this example is 538 m². 2 / g, pore volume is 0.29cm 3 / g.

[0053] The above molecular sieve, after ammonium exchange, was applied to the alkyl transfer reaction of toluene and trimethylbenzene. The reaction conditions were: temperature 350℃, reaction pressure 3.0 MPa, hydrogen-to-hydrocarbon molar ratio 3:1 mol / mol, toluene-to-trimethylbenzene molar ratio in the feed 1:1 mol / mol, and feed mass hourly space velocity (WHSV) of toluene and trimethylbenzene 3 h⁻¹. -1 The overall conversion rate was 49%, and the xylene selectivity was 97%.

[0054] Comparative Example 1

[0055] The synthesis method of BETA / MOR molecular sieve: MOR molecular sieve with a silicon-to-aluminum molar ratio (SiO2 / Al2O3) of 20 was used as the seed crystal; water glass (containing 28wt% SiO2, modulus 3.0-3.5) was used as the silicon source; sodium aluminate was used as the aluminum source; tetraethylammonium hydroxide (TEAOH) was used as the first template agent; sodium fluoride was used as the second template agent; and NaOH was used as the alkali source. The composition of the molecular sieve synthesis gel was: n(Na2O) / n(SiO2) / n(Al2O3) / n(TEAOH) / n(H2O) / n(NaF) = 1.5:40:1:10:700:5. The pH was adjusted to 12 with ammonia, and then the MOR seed crystal was added and stirred evenly to prepare the molecular sieve precursor, wherein the mass content of the MOR seed crystal in the molecular sieve precursor was 20%. The above precursor was hydrothermally crystallized at 180℃ for 48 hours to obtain the BETA / MOR symbiotic molecular sieve. The mass ratio of BETA / MOR phase is 18 / 82, and the surface aluminum S SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 0.90, and the molar ratio of SiO2 / Al2O3 is 22.

[0056] The specific surface area of ​​the BETA / MOR symbiotic molecular sieve in this example is 384 m². 2 / g, pore volume 0.14cm 3 / g.

[0057] The above molecular sieve, after ammonium exchange, was applied to the alkyl transfer reaction of toluene and trimethylbenzene. The reaction conditions were: temperature 350℃, reaction pressure 3.0 MPa, hydrogen-to-hydrocarbon molar ratio 3:1 mol / mol, toluene-to-trimethylbenzene molar ratio in the feed 1:1 mol / mol, and feed mass hourly space velocity (WHSV) of toluene and trimethylbenzene 3 h⁻¹. -1 The overall conversion rate was 47%, and the xylene selectivity was 93%.

[0058] Comparative Example 2

[0059] The synthesis method of BETA / MOR molecular sieve: MOR molecular sieve with a silicon-to-aluminum molar ratio (SiO2 / Al2O3) of 40 is used as the seed crystal; water glass (containing 28wt% SiO2, modulus 3.0-3.5) is used as the silicon source; sodium aluminate is used as the aluminum source; tetraethylammonium hydroxide (TEAOH) is used as the first template agent; sodium fluoride is used as the second template agent; and NaOH is used as the alkali source. The composition of the molecular sieve synthesis gel is: n(Na2O) / n(SiO2) / n(Al2O3) / n(TEAOH) / n(H2O) / n(NaF) = 1.5:40:1:10:700:5. The pH is adjusted to 12 with ammonia, and then the MOR seed crystal is added and stirred evenly to prepare the molecular sieve precursor. The mass content of the MOR seed crystal in the molecular sieve precursor is 20%. The above precursor was first hydrothermally crystallized at 120℃ for 48 hours, and then hydrothermally crystallized at 180℃ for 48 hours to obtain a BETA / MOR symbiotic molecular sieve. The BETA / MOR phase ratio was 20 / 80, and the surface aluminum S... SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 1.12, and the molar ratio of SiO2 / Al2O3 is 51.

[0060] The specific surface area of ​​the BETA / MOR symbiotic molecular sieve in this example is 389 m². 2 / g, pore volume 0.15cm 3 / g.

[0061] The above molecular sieve, after ammonium exchange, was applied to the alkyl transfer reaction of toluene and trimethylbenzene. The reaction conditions were: temperature 350℃, reaction pressure 3.0 MPa, hydrogen-to-hydrocarbon molar ratio 3:1 mol / mol, toluene-to-trimethylbenzene molar ratio in the feed 1:1 mol / mol, and feed mass hourly space velocity (WHSV) of toluene and trimethylbenzene 3 h⁻¹. -1 The overall conversion rate was 40%, and the xylene selectivity was 94%.

[0062] Comparative Example 3

[0063] BETA / MOR molecular sieve synthesis method: Water glass (containing 28wt% SiO2, modulus 3.0-3.5) was used as the silicon source, and sodium aluminate as the aluminum source; tetraethylammonium hydroxide (TEAOH) was used as the first template agent, sodium fluoride as the second template agent, and NaOH as the alkali source. A molecular sieve synthesis gel was prepared by using a molar ratio of (Na2O) / n(SiO2) / n(Al2O3) / n(TEAOH) / n(H2O) / n(NaF) of 1.5:40:1:10:700:5. The pH was adjusted to 12 with ammonia water, and the mixture was stirred evenly to obtain the molecular sieve synthesis precursor. The precursor was first hydrothermally crystallized at 120℃ for 48 hours, and then hydrothermally crystallized at 180℃ for 48 hours to obtain a BETA molecular sieve containing a small amount of ZSM-5 impurity crystals. The surface aluminum S...SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 1.02, and the molar ratio of SiO2 / Al2O3 is 37.

[0064] The XRD pattern of the BETA molecular sieve containing a small amount of ZSM-5 impurities in this example is shown below. Figure 3 ,Depend on Figure 3 As can be seen, it exhibits typical characteristic peaks of BETA and weak diffraction peaks of ZSM-5. The SEM image of the BETA molecular sieve containing a small amount of ZSM-5 impurities in this example is shown below. Figure 4 ,Depend on Figure 4 It can be seen that the morphology of the BETA molecular sieve with uniform small particles is present, while ZSM-5 cannot be observed due to its small quantity.

[0065] In this example, the specific surface area of ​​the BETA molecular sieve containing a small amount of ZSM-5 impurities is 579 m². 2 / g, pore volume 0.35cm 3 / g.

[0066] The above molecular sieve, after ammonium exchange, was applied to the alkyl transfer reaction of toluene and trimethylbenzene. The reaction conditions were: temperature 350℃, reaction pressure 3.0 MPa, hydrogen-to-hydrocarbon molar ratio 3:1 mol / mol, toluene-to-trimethylbenzene molar ratio in the feed 1:1 mol / mol, and feed mass hourly space velocity (WHSV) of toluene and trimethylbenzene 3 h⁻¹. -1 The overall conversion rate was 44%, and the xylene selectivity was 92%.

[0067] Comparative Example 4

[0068] The synthesis method of BETA / MOR molecular sieve: MOR molecular sieve with a silicon-to-aluminum molar ratio (SiO2 / Al2O3) of 20 was used as the seed crystal; silica sol (containing 30 wt% SiO2) was used as the silicon source; sodium aluminate was used as the aluminum source; tetraethylammonium hydroxide (TEAOH) was used as the first template agent; sodium fluoride was used as the second template agent; and NaOH was used as the alkali source. The composition of the molecular sieve synthesis gel was: n(Na2O) / n(SiO2) / n(Al2O3) / n(TEAOH) / n(H2O) / n(NaF) = 2.5:55:1:12:800:4.5. The pH was adjusted to 13 with ammonia, and then the MOR seed crystal was added. After stirring evenly, the molecular sieve synthesis precursor was obtained, wherein the mass content of the MOR seed crystal in the molecular sieve precursor was 40%. The above precursor was first hydrothermally crystallized at 100℃ for 48 hours, and then hydrothermally crystallized at 160℃ for 72 hours to obtain a BETA / MOR symbiotic molecular sieve. The BETA / MOR phase ratio was 71 / 29, and the surface aluminum S... SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 0.95, and the molar ratio of SiO2 / Al2O3 is 35.

[0069] The specific surface area of ​​the BETA / MOR symbiotic molecular sieve in this example is 455 m². 2 / g, pore volume is 0.38cm 3 / g.

[0070] The above molecular sieve, after ammonium exchange, was applied to the alkyl transfer reaction of toluene and trimethylbenzene. The reaction conditions were: temperature 350℃, reaction pressure 3.0 MPa, hydrogen-to-hydrocarbon molar ratio 3:1 mol / mol, toluene-to-trimethylbenzene molar ratio in the feed 1:1 mol / mol, and feed mass hourly space velocity (WHSV) of toluene and trimethylbenzene 3 h⁻¹. -1 The overall conversion rate was 45%, and the xylene selectivity was 91%.

[0071] Comparative Example 5

[0072] The synthesis method of BETA / MOR molecular sieves: MOR molecular sieve with a silicon-to-aluminum molar ratio (SiO2 / Al2O3) of 20 is used as the seed crystal; water glass (containing 28wt% SiO2, modulus 3.0-3.5) is used as the silicon source; sodium aluminate is used as the aluminum source; tetraethylammonium hydroxide (TEAOH) is used as the first template agent; sodium fluoride is used as the second template agent; and NaOH is used as the alkali source. The composition of the molecular sieve synthesis gel is: n(Na2O) / n(SiO2) / n(Al2O3) / n(TEAOH) / n(H2O) / n(NaF) = 1.5:20:1:10:700:5. The pH is adjusted to 12 with ammonia, and then the MOR seed crystals are added and stirred evenly to prepare the molecular sieve synthesis precursor. The mass content of the MOR seed crystals in the molecular sieve precursor is 20%. The above precursor was first hydrothermally crystallized at 120°C for 48 hours, and then hydrothermally crystallized at 180°C for 48 hours, yielding only pure MOR molecular sieves. Among these, the surface aluminum S... SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 1.01, and the molar ratio of SiO2 / Al2O3 is 18.

[0073] The XRD pattern of the MOR molecular sieve in this example is shown below. Figure 5 ,Depend on Figure 5 As can be seen, it exhibits typical characteristic peaks of MOR. The SEM image of the MOR molecular sieve in this example is shown below. Figure 6 ,Depend on Figure 6 It is evident that the MOR molecular sieve exhibits a morphology of large-particle pure phase.

[0074] The specific surface area of ​​the MOR molecular sieve in this example is 277 m². 2 / g, pore volume 0.12cm 3 / g.

[0075] The above molecular sieve, after ammonium exchange, was applied to the alkyl transfer reaction of toluene and trimethylbenzene. The reaction conditions were: temperature 350℃, reaction pressure 3.0 MPa, hydrogen-to-hydrocarbon molar ratio 3:1 mol / mol, toluene-to-trimethylbenzene molar ratio in the feed 1:1 mol / mol, and feed mass hourly space velocity (WHSV) of toluene and trimethylbenzene 3 h⁻¹. -1 The overall conversion rate was 47%, and the xylene selectivity was 89%.

[0076] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A BETA / MOR symbiotic molecular sieve, wherein the symbiotic molecular sieve contains surface aluminum S SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 0.1–0.8; among which, S SAR I represents the atomic percentage of aluminum on the surface of the molecular sieve obtained directly by XPS measurement. SAR The atomic percentage of aluminum inside the molecular sieve is measured by XPS after argon ion etching, with an argon ion etching depth of 20–50 nm. In the BETA / MOR symbiotic molecular sieve, the mass ratio of BETA / MOR is 10 / 90 to 90 / 10.

2. The BETA / MOR symbiotic molecular sieve according to claim 1, characterized in that, The symbiotic molecular sieve has surface aluminum S SAR With aluminum I inside the molecular sieve SAR The atomic ratio is 0.5 to 0.

8.

3. The BETA / MOR symbiotic molecular sieve according to claim 1, characterized in that, The BETA / MOR symbiotic molecular sieve has the following schematic chemical composition, in molar ratio: nSiO2 / Al2O3, where 10≤n≤100.

4. The BETA / MOR symbiotic molecular sieve according to claim 3, characterized in that, The BETA / MOR symbiotic molecular sieve has the following schematic chemical composition, in molar ratio: nSiO2 / Al2O3, where 20≤n≤50.

5. The BETA / MOR symbiotic molecular sieve according to claim 1, characterized in that, In the BETA / MOR symbiotic molecular sieve, the mass ratio of BETA / MOR is 25 / 75 to 75 / 25.

6. The BETA / MOR symbiotic molecular sieve according to claim 1, characterized in that, The specific surface area of ​​the BETA / MOR symbiotic molecular sieve is 400–550 m². 2 / g, pore volume 0.10~0.30cm³ 3 / g.

7. A method for preparing the BETA / MOR symbiotic molecular sieve according to any one of claims 1-6, comprising: (1) Mix silicon source, aluminum source, first template agent T1, second template agent T2, alkaline source and water, adjust pH to 9-13, and then add MOR seed crystals to obtain molecular sieve precursor; (2) The molecular sieve precursor described in step (1) is first subjected to a first stage of hydrothermal crystallization, and then heated to carry out a second stage of hydrothermal crystallization to obtain the BETA / MOR symbiotic molecular sieve. The SiO2 / Al2O3 molar ratio of the MOR seed crystals in step (1) is 15-25; The first template agent is tetraethylammonium hydroxide and / or tetraethylammonium bromide; the second template agent is sodium fluoride; In step (1), the silicon source, aluminum source, first template agent T1, second template agent T2, alkali source and water are mixed in a molar ratio of (1-6) alkali source: (30-55) SiO2: Al2O3: (8-15) T1: (100-1000) H2O: (2-8) T2 to prepare a sol. Step (2) The hydrothermal crystallization conditions for the first stage are: 100-130℃ for 24-48 hours; the hydrothermal crystallization conditions for the second stage are 160-200℃ for 24-48 hours.

8. The preparation method according to claim 7, characterized in that, In step (1), the silicon source is selected from water glass; the aluminum source is selected from at least one of sodium aluminate, aluminum sulfate, boehmite, aluminum nitrate, aluminum isopropoxide, and aluminum hydroxide; and the alkali source is selected from ammonia and / or alkaline hydroxides.

9. The preparation method according to claim 8, characterized in that, The aluminum source in step (1) is selected from sodium aluminate and / or aluminum sulfate; the alkali source is selected from NaOH.

10. The preparation method according to claim 8, characterized in that, The silicon source in step (1) is selected from water glass containing 15-40 wt% SiO2 and a modulus of 3.0-3.

5.

11. The preparation method according to claim 7, characterized in that, The mass content of MOR seeds in the molecular sieve precursor in step (1) is 20% to 55%.

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