A catalyst for synthesizing biomass propylene, its preparation method and application

Abstract

This invention provides a catalyst for synthesizing biomass propylene, its preparation method, and its application. The catalyst comprises: a) 1-20 parts of at least one oxide selected from Zn, In, Ga, W, and Mo; b) 0.5-10 parts of at least one oxide selected from P and rare earth elements; c) 30-98.5 parts of an Al-Beta@Si-Beta composite molecular sieve; and d) 0-68 parts of a matrix. When used in the synthesis of biomass propylene, the catalyst exhibits the advantages of high propylene yield and excellent hydrothermal stability.

Description

Technical Field

[0001] This invention belongs to the field of bio-propylene catalyst technology, specifically relating to a catalyst for synthesizing biomass propylene, its preparation method, and its application. Background Technology

[0002] Propylene is an important organic chemical raw material, widely used in the preparation of chemicals such as propylene oxide, acrylonitrile, polypropylene, and polyethers. Currently, propylene is mainly derived from steam cracking and catalytic cracking processes. Essentially, these propylene preparation processes still belong to the category of producing low-carbon olefins from fossil fuels. However, the processing of fossil fuels is accompanied by large amounts of CO2 emissions, a major cause of global warming. Global warming has led to frequent extreme weather events, attracting widespread attention from countries around the world. How to reduce the use of fossil fuels and reduce CO2 emissions is a crucial issue that must be addressed in the process of global economic development.

[0003] In recent years, with the rapid development of biochemical technology, significant progress has been made in the technology of producing ethanol from biomass (such as lignin and cellulose). Using biomass as a raw material results in almost zero carbon emissions. Therefore, utilizing bioethanol as a raw material to produce biopropylene is of great practical significance for reducing CO2 emissions from existing propylene production processes and ensuring national energy security.

[0004] CN105148897A discloses a catalyst for the catalytic production of low-carbon olefins from bioethanol, its preparation method, and its application. The method includes the following steps: mixing a zirconium source and a yttrium source, then adding a precipitant to co-precipitate the zirconium and yttrium sources. The precipitate is then dried and calcined to obtain a ZrO2 / Y2O3 catalyst, which can be used to catalyze the conversion of ethanol to propylene, exhibiting good selectivity and stability, with a propylene yield of approximately 44.0% and an ethylene yield of approximately 31.3%. However, the catalyst prepared by this method suffers from low selectivity and yield of propylene in the reaction.

[0005] CN112958066A discloses a catalyst for the catalytic production of low-carbon olefins from bioethanol and its application. This method synthesizes a Ga-doped zirconium-based composite metal oxide (ZrO2 / Ga2O3) catalyst with both acid and base properties via co-precipitation. This catalyst is used to catalyze the conversion of ethanol to low-carbon olefins, achieving an ethylene yield of approximately 2.5%, a propylene yield of approximately 29.8%, and an optimal isobutylene yield of approximately 40.0%. However, this process still suffers from a low propylene yield, and no data on the hydrothermal stability of the catalyst is provided.

[0006] In summary, existing technologies suffer from low propylene yield and poor catalyst stability to varying degrees. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a novel catalyst for synthesizing biomass propylene, its preparation method, and its applications. The catalyst, when used in the synthesis of biomass propylene, exhibits the advantages of high propylene yield and excellent hydrothermal stability.

[0008] The first aspect of this invention provides a catalyst for synthesizing biomass propylene, wherein the catalyst comprises, by weight parts:

[0009] a) 1 to 20 parts selected from at least one oxide of Zn, In, Ga, W, and Mo;

[0010] b) 0.5 to 10 parts of at least one selected from oxides of P and rare earth elements;

[0011] c) 30–98.5 parts of Al-Beta@Si-Beta composite molecular sieve;

[0012] d) 0-68 parts of matrix.

[0013] According to the present invention, preferably, component a) is 4 to 12 parts selected from at least one oxide of Zn, In, Ga, W, and Mo.

[0014] According to the present invention, preferably, component b) is 1.5 to 7.5 parts selected from at least one of P and rare earth element oxides.

[0015] According to the present invention, the matrix in component d) is at least one selected from silicon dioxide, aluminum oxide, zirconium oxide, titanium dioxide, and clay. The clay includes at least one selected from kaolin, bentonite, diatomaceous earth, attapulgite, and kaolin.

[0016] According to the present invention, the Al-Beta@Si-Beta composite molecular sieve described in component c) is a core-shell composite molecular sieve with Al-Beta as the core phase and Si-Beta as the shell phase. The core-shell weight ratio is 70–99:1–30. Wherein, Si-Beta is an all-silica Beta molecular sieve. Al-Beta is an aluminum-containing Beta molecular sieve. The silicon-aluminum molar ratio (SiO2 / Al2O3) of the Al-Beta molecular sieve is 10–400.

[0017] According to the present invention, the Al-Beta@Si-Beta composite molecular sieve has a specific surface area of ​​580–720 m². 2 / g, with an external surface activity index of less than or equal to 10%, preferably 0.01% to 10%, and further less than or equal to 5%.

[0018] A second aspect of the present invention provides a method for preparing the above-mentioned catalyst. The catalyst is prepared by an impregnation method. Specifically, the Al-Beta@Si-Beta composite molecular sieve is impregnated with an impregnation solution containing component a), component b), and optionally component d), and then aged and calcined to obtain the catalyst.

[0019] According to the present invention, the source a) is a salt containing component a), preferably a nitrate.

[0020] According to the present invention, the source of b) is a salt containing component b), preferably a nitrate.

[0021] According to the present invention, the aging time is 2 to 48 hours, and the aging temperature is 10 to 35°C.

[0022] According to the present invention, the roasting time is 1 to 72 hours, and the roasting temperature is 500 to 700°C. Preferably, drying can be performed before roasting, with a drying temperature of 60 to 200°C and a drying time of 2 to 48 hours.

[0023] According to the present invention, the preparation method of the Al-Beta@Si-Beta composite molecular sieve includes:

[0024] 1) Mix the silicon source, template agent R, and water, and age them to obtain mixture I;

[0025] 2) Take a portion of mixture I and perform hydrothermal crystallization to obtain mixture II;

[0026] 3) Impregnate Al-Beta molecular sieve with impregnation solution containing mixture II, and obtain precursor III after aging and first calcination;

[0027] 4) Take another portion of mixture I and precursor III, hydrothermally crystallize and second calcinate to obtain Al-Beta@Si-Beta composite molecular sieve.

[0028] According to the present invention, in the preparation method of the Al-Beta@Si-Beta composite molecular sieve, the feed ratio of silicon source, template agent R, and water in step 1) is SiO2:R:H2O = 10:1 to 10:100 to 1000, in molar terms. The silicon source includes at least one of silica, silica sol, silica gel, and organosilicone grease. The template agent includes at least one of tetraethylammonium hydroxide and tetraethylammonium bromide.

[0029] According to the present invention, in the preparation method of the Al-Beta@Si-Beta composite molecular sieve, the aging temperature in step 1) is 10-50°C and the aging time is 24-96h.

[0030] According to the present invention, in the preparation method of the Al-Beta@Si-Beta composite molecular sieve, the hydrothermal crystallization temperature in step 2) is 80-150°C, and the crystallization time is 24-196 h. The mixture II is transparent or translucent.

[0031] According to the present invention, in the preparation method of the Al-Beta@Si-Beta composite molecular sieve, Al-Beta in step 3) is a conventional Beta molecular sieve. The silicon-aluminum molar ratio (SiO2 / Al2O3) of the Al-Beta molecular sieve is 10–400.

[0032] According to the present invention, in the preparation method of the Al-Beta@Si-Beta composite molecular sieve, in step 3), the mass ratio of SiO2 to Al-Beta molecular sieve in the impregnation solution containing mixture II is 1:100 to 10:100. Preferably, after impregnation, the aging and first calcination are carried out directly, without filtration or washing.

[0033] According to the present invention, in the preparation method of the Al-Beta@Si-Beta composite molecular sieve, the aging temperature in step 3) is no more than 35°C, preferably 10–35°C, and the aging time is 1–48 h. The first calcination temperature is 500–650°C, and the calcination time is 1–48 h. Drying can also be performed before calcination, with a drying temperature of 60–200°C and a drying time of 2–48 h.

[0034] According to the present invention, in the preparation method of the Al-Beta@Si-Beta composite molecular sieve, the liquid-to-solid ratio of the crystallization raw material in step 4) is 2:1 to 20:1 by weight. As a non-limiting example, the liquid-to-solid ratio can be any value among 3:1, 5:1, 8:1, 10:1, 12:1, 15:1, 17:1, etc.

[0035] According to the present invention, in the preparation method of the Al-Beta@Si-Beta composite molecular sieve, the crystallization equipment in step 4) is preferably a crystallization kettle. The crystallization conditions are: crystallization at 100-180℃ for 24-96 hours.

[0036] According to the present invention, in the preparation method of the Al-Beta@Si-Beta composite molecular sieve, the second calcination conditions in step 4) are: temperature 500–650°C, time 1–48 h. Washing and drying can be performed before calcination. The drying conditions are: temperature 60–200°C, time 2–72 h.

[0037] The third aspect of the present invention provides the application of the above-described catalyst or the catalyst prepared by the above-described preparation method in the preparation of biomass propylene reaction.

[0038] According to the present invention, in the aforementioned application, biomass ethanol is used as a raw material, wherein the ethanol weight content is 10% to 100%, preferably 30% to 100%.

[0039] According to the present invention, in the aforementioned application, the ethanol-containing material reacts with a catalyst to produce a propylene-containing stream.

[0040] According to the present invention, the reaction conditions are as follows: absolute reaction pressure of 0.1–2.0 MPa, and ethanol feed weight hourly space velocity of 0.5–10 h⁻¹. -1 The reaction temperature is 400–600℃.

[0041] According to the present invention, preferably, the reaction conditions are: an absolute reaction pressure of 0.1–0.8 MPa and an ethanol feed weight hourly space velocity of 1.0–4 h⁻¹. -1 The reaction temperature is 430–550℃.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] (1) The reaction pathway for the production of propylene from ethanol is very complex. Along with the production of propylene, byproducts such as CO2, methane, ethylene, and C4 are also generated. Suppressing the formation of these side reactions and improving the relative selectivity of propylene in the product is a crucial way to enhance the economic efficiency of this process. In the catalyst of this invention, Al-Beta@Si-Beta modified with composite oxides is used as the catalyst. This reduces the acidity of the catalyst's outer surface, suppresses the activity of non-selective acidic sites on the outer surface, and maintains the unobstructed pores, thus inhibiting selective side reactions such as polymerization and coking on the outer surface. This improves the selectivity and yield of the catalyst for propylene.

[0044] (2) In the catalyst preparation method of the present invention, the method of covering Al-Beta molecular sieve with crystallized precursor species and then crystallizing it again can make Si-Beta more uniformly covered on the surface of Al-Beta molecular sieve, covering the acidity of the outer surface of Al-Beta molecular sieve, which is beneficial to suppressing the occurrence of non-selective polymerization and carbon deposition side reactions on the outer surface.

[0045] (3) In the application of the present invention, the novel composite oxide modified Al-Beta@Si-Beta of the present invention is used as a catalyst in the reaction of ethanol to propylene, which has the advantage of high propylene yield. Attached Figure Description

[0046] Figure 1 The image shows the XRD patterns of Al-Beta@Si-Beta and Al-Beta in Example 1. Detailed Implementation

[0047] The present invention will be further illustrated by the following embodiments, but the scope of protection of the present invention is not limited by the embodiments.

[0048] In this invention, XRD was performed using a Rigaku D / MAX-1400X polycrystalline X-ray diffractometer. The test conditions were: graphite monochromator, Cu K-rays, tube voltage 40kV, tube current 40mA, and scanning speed 15° / min.

[0049] In this invention, the silicon-to-aluminum ratio was determined by XRF spectroscopy. The testing equipment was a Philips Magix X-ray fluorescence spectrometer, and the testing conditions were a rhodium-coated X-ray tube with a tube voltage of 60 kV and a tube current of 40 mA.

[0050] In this invention, the specific surface area of ​​the sample was measured by N2 physical adsorption, and the analysis was performed on a Micromeritics TriStar3000 multichannel physical adsorption instrument at an operating temperature of -196℃.

[0051] In this invention, the external surface activity index of the sample is used to characterize the catalytic activity of the non-selective acidic sites on the outer surface of the catalyst. A higher activity index indicates a higher degree of non-selective side reactions. The external surface activity index of the sample is characterized by the ratio of the conversion activity of the test sample to that of the reference Beta molecular sieve catalyst for triisopropylbenzene. The reference catalyst is a commercially available Beta molecular sieve (SiO2 / Al2O3 molar ratio of 25, commercial model NKF-6-25H) from Nankai University Catalyst Factory. Evaluation steps and conditions: The sample was pressed into tablets and pulverized to 20–40 mesh; catalyst loading was 2.0 g; reaction temperature was 480 °C; reaction pressure was atmospheric pressure; and the triisopropylbenzene WHSV was 1.05 h⁻¹. -1 The N2 partial pressure was 50%. The reaction products were analyzed online using an HP 7890B chromatograph.

[0052] In this invention, the conversion rate of ethanol, the yield of propylene, and the selectivity are all calculated based on hydrocarbon groups as 100%, that is, based on one molecule of ethanol minus one molecule of "CH2" from "H2O".

[0053] Example 1

[0054] Preparation of composite molecular sieves:

[0055] (1) Mix 416.7 g of tetraethyl orthosilicate, 353.4 g of tetraethylammonium hydroxide (25 wt%) and 815 g of water according to the molar ratio of 10SiO2:3R:300H2O, and age at 25°C for 30 h to obtain mixture I.

[0056] (2) Take 400g of mixture I and crystallize it at 90℃ for 96h to obtain mixture II.

[0057] (3) Take 100g of Al-Beta molecular sieve (silicon-aluminum molar ratio SiO2 / Al2O3 is 60), impregnate it with 60g of aqueous solution containing 30g of mixture II, age it at 25℃ for 6h, dry it at 100℃ for 12h, and then calcine it at 550℃ for 6h to obtain 102.8g of precursor III.

[0058] (4) 257g of mixture I and precursor III were mixed at a liquid-solid weight ratio of 2.5:1 and placed in a crystallization vessel for crystallization at 130℃ for 48h. After washing with distilled water, drying at 120℃ for 12h and calcining at 550℃ for 4h, Al-Beta@Si-Beta composite molecular sieve was obtained, wherein the weight ratio of Si-Beta to Al-Beta was 1:10.

[0059] Catalyst preparation:

[0060] Al-Beta@Si-Beta was compressed into tablets and pulverized to 20-40 mesh. The pulverized Al-Beta@Si-Beta particles were then impregnated with an aqueous solution containing 5 parts of zinc nitrate hexahydrate (ZnO), 2 parts of lanthanum nitrate hexahydrate (La2O3), and 3 parts of phosphoric acid (P2O5) for 90 parts of the composite molecular sieve Al-Beta@Si-Beta. The mixture was then aged at 25°C for 24 hours, dried at 120°C for 12 hours, and calcined at 550°C for 4 hours to obtain catalyst a.

[0061] Two grams of catalyst were reacted in a fixed-bed microreactor at a reaction temperature of 500°C, an ethanol concentration of 20 wt%, and an ethanol feed space velocity of 1.5 h⁻¹. -1 The pressure was atmospheric pressure. Reaction data and the external surface activity of the catalyst are listed in Table 2.

[0062] Example 2

[0063] The preparation of the composite molecular sieve is the same as in Example 1.

[0064] Seventy parts of Al-Beta@Si-Beta sample were mixed with 20 parts of kaolin, then pressed into tablets to 20-40 mesh. The Al-Beta@Si-Beta composite molecular sieve was then impregnated with a phosphoric acid aqueous solution containing 5 parts ZnO, 2 parts La2O3, lanthanum nitrate hexahydrate, and 3 parts P2O5. The mixture was then aged at 25°C for 24 hours, dried at 120°C for 12 hours, and calcined at 550°C for 4 hours to obtain catalyst b. The evaluation conditions for the catalyst were the same as in Example 1.

[0065] Example 3

[0066] Preparation of composite molecular sieves:

[0067] (1) Mix 416.7 g of tetraethyl orthosilicate, 353.4 g of tetraethylammonium hydroxide (25 wt%) and 815 g of water in a molar ratio of 10SiO2:3R:300H2O and age at 25°C for 30 h to obtain mixture I.

[0068] (2) Take 200g of mixture I and crystallize it at 105℃ for 60h to obtain mixture II.

[0069] (3) Take 100g of Al-Beta molecular sieve (silicon-aluminum molar ratio SiO2 / Al2O3 is 40), impregnate it with 60g of aqueous solution containing 30g of mixture II, age it at 25℃ for 6h, dry it at 100℃ for 12h, and then calcine it at 550℃ for 6h to obtain 102.8g of precursor III.

[0070] (4) 412g of mixture I and precursor III were mixed at a liquid-solid weight ratio of 4.0:1 and placed in a crystallization vessel for crystallization at 120℃ for 72h. After washing with distilled water, drying at 120℃ for 12h and calcining at 600℃ for 4h, Al-Beta@Si-Beta composite molecular sieve was obtained, wherein the weight ratio of Si-Beta to Al-Beta was 1.8:10.

[0071] Al-Beta@Si-Beta was compressed into tablets and pulverized to 20-40 mesh. 98.5 parts of the pulverized Al-Beta@Si-Beta particles were impregnated with a composite molecular sieve using an aqueous solution containing 1 part Ga₂O₃ (gallium nitrate), 0.1 part CeO₂ (cerium nitrate), and 0.4 parts P₂O₅ (phosphoric acid). The mixture was then aged at 25°C for 24 hours, dried at 120°C for 12 hours, and calcined at 550°C for 4 hours to obtain catalyst c. The evaluation conditions for the catalyst were the same as in Example 1.

[0072] Example 4

[0073] Preparation of composite molecular sieves:

[0074] (1) Mix 416.7 g of tetraethyl orthosilicate, 129.6 g of tetraethylammonium hydroxide (25 wt%) and 3503 g of water at 25 °C according to the molar ratio 10SiO2:1.1R:1000H2O, and age at 25 °C for 30 h to obtain mixture I.

[0075] (2) Take 400g of solution I and crystallize it at 90℃ for 96h to obtain mixture II.

[0076] (3) Take 100g of Al-Beta molecular sieve (silicon-aluminum molar ratio SiO2 / Al2O3 is 30), impregnate it with 120g of mixture II, age it at 25℃ for 10h, dry it at 100℃ for 12h, and then calcine it at 550℃ for 6h to obtain 103.8g of precursor III.

[0077] (4) Mix 1040g of mixture I with precursor III at a liquid-solid weight ratio of 10:1, place them in a crystallization kettle and crystallize at 130℃ for 48h. After washing with distilled water, drying at 120℃ for 12h and calcining at 550℃ for 4h, Al-Beta@Si-Beta composite molecular sieve is obtained, wherein the weight ratio of Si-Beta to Al-Beta is 2.8:10.

[0078] Al-Beta@Si-Beta was compressed into tablets and pulverized to 20-40 mesh. 80 parts of the pulverized Al-Beta@Si-Beta particles were impregnated with an aqueous solution containing 10 parts ZnO in zinc nitrate hexahydrate and 10 parts P2O5 in phosphoric acid. The catalyst was then aged at 25°C for 24 hours, dried at 120°C for 12 hours, and calcined at 550°C for 4 hours to obtain catalyst d. The evaluation conditions for the catalyst were the same as in Example 1.

[0079] Comparative Example 1

[0080] The only difference from Example 1 is that Al-Beta was used instead of the composite molecular sieve in Comparative Example 1. The specific preparation method is as follows.

[0081] Al-Beta zeolite (SiO2 / Al2O3 molar ratio of 60) was compressed into tablets and pulverized to 20-40 mesh. The pulverized Al-Beta zeolite particles were then impregnated with an aqueous solution of 5 parts zinc nitrate hexahydrate of ZnO, 2 parts lanthanum nitrate hexahydrate of La2O3, and 3 parts phosphoric acid of P2O5. The mixture was then aged at 25°C for 24 h, dried at 120°C for 12 h, and calcined at 550°C for 4 h to obtain catalyst x. The evaluation conditions for the catalyst were the same as in Example 1.

[0082] Comparative Example 2

[0083] The only difference from Example 1 is that in Comparative Example 2, Al-Beta@amorphous SiO2 was used to replace the composite molecular sieve in Example 1. The specific preparation method is as follows.

[0084] The preparation method of Al-Beta@amorphous SiO2 is as follows: 100g of Al-Beta zeolite (SiO2 / Al2O3 molar ratio of 60) is impregnated with 70g of an aqueous solution containing 25g of silica sol (40wt% SiO2), aged at 25℃ for 6h, dried at 100℃ for 12h, and then calcined at 550℃ for 4h to obtain SiO2@Al-Beta zeolite. The weight ratio of SiO2 to Al-Beta is 1:10.

[0085] SiO2@Al-Beta zeolite was pressed into tablets and pulverized to 20-40 mesh. The pulverized SiO2@Al-Beta zeolite particles were then impregnated with an aqueous solution of 5 parts ZnO (zinc nitrate hexahydrate), 2 parts La2O3 (lanthanum nitrate hexahydrate), and 3 parts P2O5 (phosphoric acid). The mixture was then aged at 25°C for 24 hours, dried at 120°C for 12 hours, and calcined at 550°C for 4 hours to obtain catalyst y. The catalyst evaluation conditions were the same as in Example 1.

[0086] Comparative Example 3

[0087] The only difference from Example 1 is that 10 grams of commercially available Si-Beta zeolite and 100 grams of Al-Beta zeolite synthesized according to Example 1 were used and mixed evenly at a weight ratio of Si-Beta:Al-Beta = 1:10 to obtain mechanically and physically mixed zeolite HB.

[0088] HB tablets were crushed to 20-40 mesh. 18 g of the crushed HB zeolite particles were impregnated with an aqueous solution containing 5 parts ZnO (zinc nitrate), 2 parts La2O3 (lanthanum nitrate hexahydrate), and 3 parts P2O5 (phosphoric acid) for 90 parts HB. The mixture was then aged at 25°C for 24 h, dried at 120°C for 12 h, and calcined at 550°C for 4 h to obtain catalyst z. The evaluation conditions for the catalyst were the same as in Example 1.

[0089] Comparative Example 4

[0090] The only difference from Example 1 is that Si-Beta was used instead of the composite molecular sieve in Comparative Example 4.

[0091] The preparation method of Si-Beta is as follows: 416.7 g of tetraethyl orthosilicate, 353.4 g of tetraethylammonium hydroxide (25 wt%) and 815 g of water are mixed evenly according to the molar composition of 10 SiO2:3R:300H2O. The mixture is aged at 25℃ for 30 h to obtain mixture I. After crystallizing mixture I at 130℃ for 30 h, it is washed with distilled water, dried at 130℃ for 12 h and calcined at 550℃ for 4 h to obtain Si-Beta zeolite.

[0092] Si-Beta zeolite was compressed into tablets and pulverized to 20-40 mesh. The pulverized Si-Beta zeolite particles were then impregnated with an aqueous solution containing 5 parts ZnO (zinc nitrate hexahydrate), 2 parts La2O3 (lanthanum nitrate hexahydrate), and 3 parts P2O5 (phosphoric acid). The mixture was then aged at 25°C for 24 hours, dried at 120°C for 12 hours, and calcined at 550°C for 4 hours to obtain catalyst u. The catalyst evaluation conditions were the same as in Example 1.

[0093] Table 1

[0094]

[0095] Table 2

[0096]

[0097] Table 3 shows the results obtained from Examples 1, 6-8 using catalyst a with varying process conditions for 2 hours.

[0098]

[0099]

[0100] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A catalyst for synthesizing biomass propylene, characterized in that, The catalyst comprises, by weight parts: a) 1 to 20 parts selected from at least one oxide of Zn, In, Ga, W, and Mo; b) 0.5 to 10 parts of at least one selected from oxides of P and rare earth elements; c) 30~98.5 parts of Al-Beta@Si-Beta composite molecular sieve; d) 0-68 parts of matrix; The Al-Beta@Si-Beta composite molecular sieve described in component c) is a core-shell composite molecular sieve with Al-Beta as the core phase and Si-Beta as the shell phase; the core-shell weight ratio is 70~99:1~30. Si-Beta is an all-silicon Beta molecular sieve; Al-Beta is an aluminum-containing Beta molecular sieve with a silicon-to-aluminum molar ratio of SiO2 / Al2O3 of 10~400.

2. The catalyst according to claim 1, characterized in that, The Al-Beta@Si-Beta composite molecular sieve has a specific surface area of ​​580~720 m². 2 / g; and / or, the external surface activity index is less than or equal to 10%.

3. A method for preparing a catalyst according to any one of claims 1 to 2, comprising the steps of: The Al-Beta@Si-Beta composite molecular sieve is impregnated with an impregnation solution containing source a), source b), and optionally source d), and then aged and calcined to obtain the catalyst.

4. The preparation method according to claim 3, characterized in that, The preparation method of the Al-Beta@Si-Beta composite molecular sieve includes: 1) Mix the silicon source, template agent R, and water, and age them to obtain mixture I; 2) Take a portion of mixture I and perform hydrothermal crystallization to obtain mixture II; 3) Impregnate Al-Beta molecular sieve with impregnation solution containing mixture II, and obtain precursor III after aging and first calcination; 4) Take another portion of mixture I and precursor III, hydrothermally crystallize and second calcinate to obtain Al-Beta@Si-Beta composite molecular sieve.

5. The preparation method according to claim 4, characterized in that, In step 1), the ratio of silicon source, template agent R, and water is SiO2:R:H2O = 10:1~10:100~1000, in molar terms.

6. The preparation method according to claim 4, characterized in that, The silicon source mentioned in step 1) includes at least one of silica, silica sol, silica gel, and organosilicone grease; And / or, the template agent includes at least one of tetraethylammonium hydroxide and tetraethylammonium bromide.

7. The preparation method according to claim 4, characterized in that, The hydrothermal crystallization temperature in step 2) is 80~150℃, and the crystallization time is 24~196h.

8. The preparation method according to claim 4, characterized in that, In step 3), the first roasting temperature is 500~650℃ and the roasting time is 1~48h.

9. The preparation method according to claim 4, characterized in that, In step 4), the liquid-to-solid ratio of the crystallization raw material is 2:1 to 20:1 by weight.

10. The preparation method according to claim 4, characterized in that, The crystallization conditions for step 4) are: crystallization at 100~180℃ for 24~96h.

11. The use of a catalyst according to any one of claims 1 to 2 or a catalyst prepared by any one of claims 3 to 10 in the preparation of biomass propylene.

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