Modified zsm-5 molecular sieves and their use in the hydration of cyclohexene to cyclohexanol

Abstract

The application relates to the technical field of cyclohexene hydration and catalysts, and discloses a modified ZSM-5 molecular sieve and application of the modified ZSM-5 molecular sieve in preparation of cyclohexanol through cyclohexene hydration; the modified ZSM-5 molecular sieve comprises a ZSM-5 molecular sieve core, the core is expanded and then subjected to sulfonation treatment, then SiO2 is coated on the surface of the core to form a core-shell structure; after the core-shell structure is subjected to hydrophobic modification, a zirconium oxide layer is deposited on the surface, and a ZrO2-SiO2@SO3H-ZSM-5 molecular sieve is obtained. The molecular sieve is used as a catalyst in a cyclohexene hydration reaction, the conversion rate is more than 25%, the selectivity is more than 99.5%, and the activity is stable after 6 cycles; the catalyst has excellent catalytic performance, provides a new idea for current two-phase catalytic reactions, and is expected to be applied to an industrialized device for cyclohexene hydration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cyclohexene hydration and catalyst technology, in particular to a modified ZSM-5 molecular sieve and its application in the catalysis of cyclohexene hydration for preparing cyclohexanol. BACKGROUND

[0002] Cyclohexanol is a core intermediate in the field of nylon 6 and nylon 66, and its demand is highly related to the development of global engineering plastics and chemical fiber industry. Among the three major routes for industrial production of cyclohexanol, the cyclohexene hydration method gradually becomes the mainstream process due to its low hydrogen consumption and fewer by-products. However, there are still some problems to be improved in this technology, such as insufficient catalyst activity, low mass transfer efficiency due to the limitation of microporous structure of traditional solid acid catalysts (such as HZSM-5 molecular sieve), and the single-pass conversion rate is generally less than 15%. In addition, the hydration reaction is a reversible exothermic process, and the equilibrium conversion rate is restricted by temperature. The conventional process needs to improve the efficiency through multi-stage reaction-separation coupling, which has problems such as high energy consumption. There are also problems such as catalyst deactivation and regeneration difficulty, acid sites easily covered by reaction intermediates, swelling of ion exchange resin catalysts, poor mechanical strength, and short service life.

[0003] In view of the above problems, in recent years, many researches have focused on catalyst structure regulation and reaction process optimization. CN117160522A discloses a modified ZSM-5 molecular sieve catalyst prepared by desiliconizing ZSM-5 molecular sieve with an alkali solution to change the pore structure, and then ion exchanging with a metal salt solution. The catalyst is simple to prepare, but the conversion rate is limited to less than 15% after improvement. CN111253217A discloses the preparation of a hierarchical pore ZSM 5 molecular sieve, which has a microporous ZSM-5 framework topological structure and a mesoporous channel of silicoaluminate material. The mesoporous channel makes the acid centers inside the molecular sieve more easily contact with the reactant molecules, thereby improving the reaction rate and conversion rate, but the conversion rate is still limited to less than 18%. The current catalyst modification research mainly focuses on ZSM-5 molecular sieve, although the catalytic performance has been improved to some extent, but the effect is still not ideal, and further improvement is needed. SUMMARY

[0004] The present application provides a modified ZSM-5 molecular sieve and its application in the hydration of cyclohexene to prepare cyclohexanol. The modified ZSM-5 molecular sieve has excellent catalytic performance and good stability, and is expected to be applied to the industrial production of cyclohexene hydration.

[0005] The technical scheme of the present application is to provide a modified ZSM-5 molecular sieve, which comprises a ZSM-5 molecular sieve core, the core is expanded and then subjected to sulfonic acid treatment, and then a SiO2 layer is coated on the surface of the core to form a core-shell structure; and then the core-shell structure is subjected to hydrophobic modification and a zirconium oxide layer is deposited on the surface, thereby obtaining a ZrO2-SiO2@SO3H-ZSM-5 molecular sieve.

[0006] Optionally, the mass ratio of the ZSM-5 molecular sieve core, the SiO2 shell structure and the ZrO2 layer is (80-90):(8-18):(2-6).

[0007] Optionally, the molar ratio of silicon to aluminum in the ZSM-5 molecular sieve is 60-150:1.

[0008] The present application also relates to a preparation method of the modified ZSM-5 molecular sieve, which comprises the following steps:

[0009] S1, the ZSM-5 molecular sieve is subjected to expansion treatment with an alkali solution, and then is washed, filtered, dried and calcined to obtain an expanded ZSM-5 molecular sieve;

[0010] S2, the expanded ZSM-5 molecular sieve is mixed with a solution containing mercapto silane, and then is filtered and washed after reaction, and then is added to a hydrogen peroxide solution for reaction, and then is filtered and washed to obtain a SO3H-ZSM-5 molecular sieve;

[0011] S3, the SO3H-ZSM-5 molecular sieve is mixed with a silica sol, and then is filtered, washed, dried and calcined to obtain a SiO2@SO3H-ZSM-5 molecular sieve;

[0012] S4, the SiO2@SO3H-ZSM-5 molecular sieve is subjected to surface hydrophobic modification, and then is immersed in a zirconium salt solution, and finally is filtered, washed, dried and calcined to obtain a ZrO2-SiO2@SO3H-ZSM-5 molecular sieve.

[0013] Optionally, the alkali in S1 is sodium hydroxide and / or potassium hydroxide; the treatment process is carried out under heating and reflux; and after the treatment, the process is sequentially subjected to water washing, acid washing and water washing, and the calcination temperature is 500-600 DEG C.

[0014] Optionally, in S2, the solvent in the solution containing mercapto silane is a mixture of toluene and water, and the mass ratio is 20-30:1; the mercapto silane is at least one of 3-mercaptopropyl trimethoxysilane, 3-mercaptopropyl triethoxysilane, trimethoxysilyl methyl mercaptan and 3-mercaptopropyl methyl dimethoxysilane; when the expanded ZSM-5 molecular sieve in S2 is mixed with the solution containing mercapto silane, the reaction temperature is 80-110 DEG C, and the reaction time is 3-5 h; the concentration of the hydrogen peroxide is 0.5-10 wt%, and the reaction temperature of the hydrogen peroxide is 30-50 DEG C, and the reaction time is 1-3 h.

[0015] Optionally, the silicon sol of S3 is prepared by mixing hexadecyl trimethyl ammonium bromide (CTAB) dissolved in water, ammonia water to adjust pH to 10-11, and tetraethyl orthosilicate (TEOS) dropwise.

[0016] Optionally, S4 meets at least one of the following conditions:

[0017] 1) When the surface is hydrophobically modified, SiO2@SO3H-ZSM-5 molecular sieve is added to an ethanol solution, ammonia water is added to adjust the pH to 10-11, and a long-chain silane reagent is added dropwise, and the reaction is carried out at 50-80℃, and after the reaction is completed, filtration, washing, drying and calcination are carried out to complete the modification;

[0018] 2) When impregnated with a zirconium salt solution, the zirconium salt is one of zirconium nitrate, zirconium chloride, zirconium acetate, zirconium citrate or zirconium carbonate, and the concentration is 0.5-5wt%.

[0019] The application also relates to the application of the modified ZSM-5 molecular sieve as a catalyst in the preparation of cyclohexanol by hydrating cyclohexene.

[0020] The application has the following beneficial effects:

[0021] In the preparation process of the modified ZSM-5 molecular sieve, the pore volume and pore size are larger after reaming and sulfonic acid group modification, which is beneficial to mass transfer, and the conversion rate and selectivity are higher; the microporous-mesoporous porous structure of the molecular sieve catalyst is also beneficial to the rapid removal of the product cyclohexanol, preventing the occurrence of side reactions. Since the molecular sieve is hydrophobically modified by a long-chain silane on the mesopore surface, the adsorption and diffusion performance of the hydrophobic cyclohexene in the pore channel is enhanced, a high-concentration environment of cyclohexene is created inside the catalyst, the reaction thermodynamic limit is broken, the reaction is further promoted to cyclohexanol, and the conversion rate is improved; and the ZrO2 loaded on the mesopore surface has rich oxygen vacancies, which can enhance the activation ability of water molecules, the ZrO2 as a Lewis acid and the sulfonic acid group as a B acid center synergistically catalyze and activate water and cyclohexene, and cyclohexanol is prepared by rapid reaction and removed from the mesopore channel inside the catalyst.

[0022] The modified ZSM-5 molecular sieve provided by the application is prepared by the following steps: firstly, ZSM-5 molecular sieve is subjected to pore expansion; secondly, the surface of the ZSM-5 molecular sieve is modified by sulfonation; thirdly, the surface of the ZSM-5 molecular sieve is modified by silanization; fourthly, the surface of the ZSM-5 molecular sieve is subjected to hydrophobic treatment; and finally, the ZSM-5 molecular sieve is subjected to impregnation and deposition of a zirconium oxide layer to obtain a nanoparticle with a porous composite structure of core-shell. The nanoparticle is used as a catalyst in the reaction of preparing cyclohexanol from cyclohexene hydration, and shows high conversion rate and selectivity, high catalytic activity, stable structure, easy separation, high recovery rate and reusability. DETAILED DESCRIPTION

[0023] In the following examples, the experimental methods are conventional methods unless otherwise specified. In the following examples, the materials used are commercially available products unless otherwise specified.

[0024] The modified ZSM-5 molecular sieve provided by the application is prepared by the following steps: firstly, ZSM-5 molecular sieve is subjected to pore expansion; secondly, the surface of the ZSM-5 molecular sieve is modified by sulfonation; thirdly, the surface of the ZSM-5 molecular sieve is modified by silanization; fourthly, the surface of the ZSM-5 molecular sieve is subjected to hydrophobic treatment; and finally, the ZSM-5 molecular sieve is subjected to impregnation and deposition of a zirconium oxide layer to obtain a nanoparticle with a porous composite structure of core-shell. The nanoparticle is used as a catalyst in the reaction of preparing cyclohexanol from cyclohexene hydration, and shows high conversion rate and selectivity, high catalytic activity, stable structure, easy separation, high recovery rate and reusability.

[0025] The specific operation steps are as follows:

[0026] 1) ZSM-5 molecular sieve is added to an alkali solution, heated and refluxed, then filtered, washed, transferred to an acid solution, acid washed, water washed to neutral, dried, calcined, and then ZSM-5 molecular sieve with expanded pores is obtained.

[0027] The molar ratio of silicon to aluminum of the ZSM-5 molecular sieve is 60-150:1, and more preferably 80-120:1. In a preferred embodiment, the alkali solution can be a sodium hydroxide or potassium hydroxide solution. The concentration of the alkali solution is preferably 0.1-2 mol / L. The acid solution is preferably a hydrochloric acid solution, and the concentration is preferably 0.5-2 mol / L. The calcination temperature is preferably 500-600°C, and more preferably 550°C.

[0028] 2) The ZSM-5 molecular sieve with expanded pores is added to a solvent, ultrasonically dispersed, then an appropriate amount of mercaptosilane is added, reacted for a period of time, filtered and separated, washed with ethanol, then transferred to 20 ml of a hydrogen peroxide solution for reaction, filtered and washed with water after reaction, and then SO3H-ZSM-5 molecular sieve is obtained.

[0029] The solvent is preferably a mixture of toluene and water, and the mass ratio of the two is preferably 20-30:1. The mercaptosilane is preferably at least one of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, trimethoxysilyl methyl mercaptan, and 3-mercaptopropylmethyldimethoxysilane. The reaction temperature is preferably 80-110°C, and the reaction time is preferably 3-5 h.

[0030] Preferably, the concentration of hydrogen peroxide is 0.5-10wt%, and the oxidation reaction temperature in the hydrogen peroxide is 30-50℃, and the reaction time is 1-3h.

[0031] 3) The SO3H-ZSM-5 molecular sieve is mixed with silica sol, and then filtered, washed, dried and calcined to obtain the SiO2@SO3H-ZSM-5 molecular sieve. The silica sol is preferably prepared by dissolving cetyltrimethylammonium bromide (CTAB) in water, adding ammonia water to adjust the pH to 10-11, and then adding tetraethyl orthosilicate (TEOS) dropwise.

[0032] 4) The SiO2@SO3H-ZSM-5 is subjected to surface hydrophobic modification treatment, preferably using long-chain silane for modification. The SiO2@SO3H-ZSM-5 particles are first added to ethanol, and then ammonia water is added to adjust the pH to 10-11. Under stirring, an appropriate amount of long-chain silane reagent is added dropwise. The reaction is carried out at 50-80℃ for 2h. After filtration and water washing, the SiO2@SO3H-ZSM-5 after surface hydrophobic modification is obtained. The long-chain silane is preferably triethoxyl octyl silane, perfluorodecyl triethoxyl silane or hydrogenated polydimethyl siloxane.

[0033] 5) The SiO2@SO3H-ZSM-5 particles after hydrophobic modification are added to a pre-prepared zirconium salt solution for impregnation, and then filtered, washed, dried, baked and calcined to obtain the porous ZrO2-SiO2@SO3H-ZSM-5 molecular sieve particles.

[0034] Preferably, the zirconium salt is one of zirconium nitrate, zirconium chloride, zirconium acetate, zirconium citrate or zirconium carbonate, and the concentration of the zirconium salt solution is 0.5-5wt%. Preferably, the impregnation is carried out at room temperature, and the time is 24h. The calcination temperature is preferably 500℃.

[0035] When the modified ZSM-5 molecular sieve prepared in the application is used in the hydration of cyclohexene to prepare cyclohexanol, it is used as a catalyst, and the addition amount is preferably 5% of the mass of cyclohexene. In the hydration reaction of cyclohexene, the mass ratio of cyclohexene to water is preferably 1:3. The reaction is carried out in a sealed reaction kettle. Nitrogen is used to replace 3 times, and then the temperature is raised. The reaction conditions are preferably 120℃, 0.6Mpa and 500r / min for 60min.

[0036] The embodiments of the application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the application, and should not be regarded as limiting the scope of the application.

[0037] Example 1:

[0038] The preparation steps of the modified ZSM-5 molecular sieve catalyst A1 are as follows:

[0039] Step one: 5g of ZSM-5 molecular sieve with a silicon-aluminum ratio of 80:1 is added to 30ml of 0.5mol / L sodium hydroxide solution, heated and refluxed for 6h, then filtered, washed, transferred to 20ml of 1mol / L HCl solution, acid washed, washed with water to neutral, dried, calcined at 550°C, and the expanded pore ZSM-5 molecular sieve is obtained;

[0040] Step two: 2g of the above expanded pore ZSM-5 molecular sieve is taken and added to 50ml of a mixed solution prepared by mixing toluene and water in a mass ratio of 20:1, ultrasonic treatment is performed for 10min, then 0.6ml of 3-mercaptopropyltrimethoxysilane is added to the solution, 90°C reaction is performed for 3h, filtration separation is performed, ethanol washing is performed, then the solution is transferred to 20ml of 0.5% hydrogen peroxide solution, 30°C reaction is performed for 1h, filtration is performed, and water washing is performed, and the SO3H-ZSM-5 molecular sieve is obtained;

[0041] Step three: 0.1g of cetyltrimethylammonium bromide (CTAB) is dissolved in 50ml of deionized water, ammonia water is added to adjust the pH to 11, 1.5g of ethyl silicate (TEOS) is slowly added dropwise, magnetic stirring is performed for 30min, a silica sol is formed, then the above SO3H-ZSM-5 molecular sieve is added, ultrasonic treatment is performed for 30min, 500rpm stirring is performed at 60~80°C for 5h, cooling is performed, filtration separation is performed, and the solution is sequentially washed with ethanol and deionized water until neutral, 60°C vacuum drying is performed for 12h, and 550°C calcination treatment is performed for 4h, and the surface silanized SiO2@SO3H-ZSM-5 particles are obtained;

[0042] Step four: the above SiO2@SO3H-ZSM-5 particles are added to 50ml of an ethanol solution, 28% ammonia water is added to adjust the pH to 11, 0.1ml of perfluorooctyltriethoxysilane is added dropwise under stirring, 60°C reaction is performed for 2h, filtration is performed, and water washing is performed, and the surface hydrophobically modified SiO2@SO3H-ZSM-5 is obtained;

[0043] Step five: the above hydrophobically modified SiO2@SO3H-ZSM-5 particles are further added to a pre-prepared 1%wt zirconium nitrate solution, normal temperature immersion is performed for 24h, then filtration, washing, drying, drying, and 500°C calcination are performed for 4h, and the porous ZrO2-SiO2@SO3H-ZSM-5 molecular sieve catalyst A1 is obtained.

[0044] The catalyst is used in the reaction of cyclohexene hydration to prepare cyclohexanol, and the steps are as follows: 10 g of cyclohexene, 30 g of water and 0.5 g of the catalyst are weighed and added into a closed reaction kettle, and then replaced by nitrogen for 3 times, and then heated to 120℃, 0.6Mpa, 500r / min for 60 min, and then cooled to room temperature, and then depressurized, and then the material in the kettle is taken out and centrifuged, and the catalyst is recycled for 6 times, and then the upper clear liquid is taken out and analyzed by gas chromatography, and the results are shown in Table 1.

[0045] Example 2:

[0046] In the preparation and application of the modified ZSM-5 molecular sieve catalyst A2, except that the silicon-aluminum ratio in step one is 60:1, the others are the same as in example 1, and the results are shown in Table 1.

[0047] Example 3:

[0048] In the preparation and application of the modified ZSM-5 molecular sieve catalyst A3, except that the silicon-aluminum ratio in step one is 120:1, the others are the same as in example 1, and the results are shown in Table 1.

[0049] Comparative Example 1:

[0050] In the preparation and application of the modified ZSM-5 molecular sieve catalyst B1, except that the silicon-aluminum ratio in step one is 30:1, the others are the same as in example 1, and the results are shown in Table 1.

[0051] Example 4:

[0052] In the preparation and application of the modified ZSM-5 molecular sieve catalyst A4, except that trimethoxysilane methyl mercaptan is used in step two, the others are the same as in example 1, and the results are shown in Table 1.

[0053] Example 5:

[0054] In the preparation and application of the modified ZSM-5 molecular sieve catalyst A5, except that 3-mercaptopropyl triethoxysilane is used in step two, the others are the same as in example 1, and the results are shown in Table 1.

[0055] Example 6:

[0056] In the preparation and application of the modified ZSM-5 molecular sieve catalyst A6, except that the mercapto silane reaction is 105℃ in step two, the others are the same as in example 1, and the results are shown in Table 1.

[0057] Comparative Example 2:

[0058] In the preparation and application of the modified ZSM-5 molecular sieve catalyst B1, the catalyst preparation step does not perform step two sulfonation treatment, but 2g of the ZSM-5 molecular sieve after hole expansion in step one is treated in step three, and the others are the same as in example 1, and the results are shown in Table 1.

[0059] Example 7:

[0060] The preparation and application of modified ZSM-5 molecular sieve catalyst A7, except that 2% hydrogen peroxide was used in step two, the others were the same as example 1, and the results are shown in Table 1.

[0061] Example 8:

[0062] The preparation and application of modified ZSM-5 molecular sieve catalyst A8, except that 9% hydrogen peroxide was used in step two, the others were the same as example 1, and the results are shown in Table 1.

[0063] Comparative Example 3:

[0064] The preparation and application of modified ZSM-5 molecular sieve catalyst B3, except that 20% hydrogen peroxide was used in step two, the others were the same as example 1, and the results are shown in Table 1.

[0065] Example 9:

[0066] The preparation and application of modified ZSM-5 molecular sieve catalyst A9, except that the amount of CTAB added in step three was 0.25 g, the others were the same as example 1, and the results are shown in Table 1.

[0067] Example 10:

[0068] The preparation and application of modified ZSM-5 molecular sieve catalyst A10, except that the amount of TEOS added in step three was 2.5 g, the others were the same as example 1, and the results are shown in Table 1.

[0069] Comparative Example 4:

[0070] The preparation and application of modified ZSM-5 molecular sieve catalyst B4, in the catalyst preparation step, step three silanization coating treatment was not carried out, but the SO3H-ZSM-5 molecular sieve prepared in step two was treated in step four, and the others were the same as example 1, and the results are shown in Table 1.

[0071] Example 11:

[0072] The preparation and application of modified ZSM-5 molecular sieve catalyst A11, except that triethoxyl octyl silane was used in step four, the others were the same as example 1, and the results are shown in Table 1.

[0073] Comparative Example 5:

[0074] The preparation and application of modified ZSM-5 molecular sieve catalyst B5, in the catalyst preparation step, step four hydrophobic modification treatment was not carried out, but the SiO2@SO3H-ZSM-5 particles prepared in step three were treated in step five, and the others were the same as example 1, and the results are shown in Table 1.

[0075] Example 12:

[0076] The preparation and application of modified ZSM-5 molecular sieve catalyst A12, except that zirconium acetate was used in step five, the others were the same as example 1, and the results are shown in table 1.

[0077] Example 13:

[0078] The preparation and application of modified ZSM-5 molecular sieve catalyst A13, except that zirconium nitrate with a concentration of 0.5%wt was used in step five, the others were the same as example 1, and the results are shown in table 1.

[0079] Comparative example 6:

[0080] The preparation and application of modified ZSM-5 molecular sieve catalyst B6, except that step five was not performed in the catalyst preparation step, the others were the same as example 1, and the results are shown in table 1.

[0081] Comparative example 7:

[0082] The preparation and application of modified ZSM-5 molecular sieve catalyst B7, except that zirconium nitrate with a concentration of 10%wt was used in the catalyst preparation step, the others were the same as example 1, and the results are shown in table 1.

[0083] Comparative example 8:

[0084] The preparation and application of modified ZSM-5 molecular sieve catalyst B8, except that ammonium titanate was used in step five, the others were the same as example 1, and TiO2-SiO2@SO3H-ZSM-5 was obtained, and the results are shown in table 1.

[0085] Comparative example 9:

[0086] The preparation and application of modified ZSM-5 molecular sieve catalyst B9, except that aluminum nitrate was used in step five, the others were the same as example 1, and Al2O3-SiO2@SO3H-ZSM-5 was obtained, and the results are shown in table 1.

[0087] Table 1

[0088]

[0089] From the table results, it can be found that in comparative example 1, when the silicon aluminum ratio is too low, the reaction conversion rate is low, and the stability is also poor. When the silicon aluminum ratio is low, the aluminum content is high, the molecular sieve structure stability is poor, the thermal stability is also poor, and the framework structure may collapse during the subsequent modification process, affecting the activity of the catalyst and the stability during the recycling process.

[0090] The conversion rate of the catalyst without sulfonation in Comparative Example 2 decreased obviously, which indicated that the B acid active site was provided to the catalyst after sulfonation, and the catalytic activity of the catalyst was obviously increased.

[0091] The catalytic activity of the catalyst in Comparative Example 3 decreased obviously, because hydrogen peroxide has strong oxidizing property and can generate hydroxyl radicals, which can destroy the active site or structure on the surface of the ZSM-5 molecular sieve, and the acid center is destroyed, which affects the catalytic performance. The low concentration of hydrogen peroxide can play a certain catalytic role in the sulfonation process of the mercaptosiloxane, accelerate the reaction, and help the crosslinking of the siloxane chain and the fixation of the sulfonic acid group.

[0092] The catalytic activity of the catalyst in Comparative Example 4 decreased obviously, and the surface of the catalyst in Example 1 was coated with a silica shell, which can improve the stability of the ZSM-5 core and provide a mesoporous layer on the surface, which is convenient for subsequent impregnation and hydrophobic modification, and improves the catalytic activity of the catalyst.

[0093] The surface of the catalyst in Comparative Example 5 was not subjected to hydrophobic modification, and a large amount of water molecules can also diffuse into the interior of the catalyst, which is not conducive to the formation of a high-concentration cyclohexene environment, and cannot break the thermodynamic equilibrium. After hydrophobic modification, the adsorption and diffusion performance of the hydrophobic cyclohexene in the pore can be enhanced, a high-concentration cyclohexene environment can be created in the interior of the catalyst, and the reaction thermodynamic limit can be broken, so as to promote the reaction further to the direction of cyclohexanol, and the conversion rate is improved.

[0094] The conversion rate of the reaction cannot be improved by adding no zirconium salt or adding a high concentration of zirconium salt in Comparative Example 6 and Comparative Example 7. The ZrO2 layer has rich oxygen vacancies, which can enhance the activation ability of water molecules, and can also form L acid and B acid with the internal sulfonic acid group to synergistically catalyze the catalyst. However, when a high concentration of zirconium salt is used for impregnation and deposition, the surface pores can be blocked or unevenly dispersed, which affects the catalytic activity of the catalyst.

[0095] The surface modification effect of titanium salt and aluminum salt in Comparative Example 8 and Comparative Example 9 is poor. Titanium atoms and aluminum atoms can be more easily aggregated or the structure can be damaged at high temperature. Zirconium has better high-temperature resistance, and zirconium ions form a strong Si-O-Zr bond with the hydroxyl groups on the surface of the silica, which promotes the dispersion of the metal and obtains a catalyst with higher activity.

[0096] The above examples describe the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other way. These simple modifications and combinations should also be considered as disclosed by the present application, and belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing a modified ZSM-5 molecular sieve, characterized by: The molecular sieve comprises a ZSM-5 molecular sieve core, the core is expanded, then subjected to sulfonation treatment, and then coated with SiO2 to form a core-shell structure; and then subjected to hydrophobic modification and deposition of a zirconium oxide layer, thereby obtaining the ZrO2-SiO2@SO3H-ZSM-5 molecular sieve. The preparation specifically comprises the following steps: S1, ZSM-5 molecular sieve is expanded by adding an alkali solution, and then washed, filtered, dried and calcined to obtain expanded ZSM-5 molecular sieve; S2, the expanded ZSM-5 molecular sieve is mixed with a solution containing mercapto silane, reacted, filtered and washed, and then added to a hydrogen peroxide solution to react, and filtered and washed to obtain SO3H-ZSM-5 molecular sieve; S3, the SO3H-ZSM-5 molecular sieve is mixed with silica sol, and then filtered, washed, dried and calcined to obtain SiO2@SO3H-ZSM-5 molecular sieve; S4, the SiO2@SO3H-ZSM-5 molecular sieve is added to an ethanol solution, ammonia water is added to adjust the pH to 10-11, a long-chain silane reagent is added dropwise, and the reaction is carried out at 50-80℃, and after the reaction is completed, the product is filtered, washed, dried and calcined to complete the surface hydrophobic modification; then the product is immersed in a zirconium salt solution, the zirconium salt is one of zirconium nitrate, zirconium chloride, zirconium acetate, zirconium citrate or zirconium carbonate ammonium, the concentration is 0.5-5wt%, and finally the product is filtered, washed, dried and calcined to obtain the ZrO2-SiO2@SO3H-ZSM-5 molecular sieve.

2. The method of claim 1, wherein: The mass ratio of the ZSM-5 molecular sieve core, the SiO2 shell structure and the ZrO2 layer is (80-90):(8-18):(2-6).

3. The method of claim 1, wherein: The molar ratio of silicon to aluminum in the ZSM-5 molecular sieve is (60-150):

1.

4. The method of claim 1, wherein: The alkali in S1 is sodium hydroxide and / or potassium hydroxide; the treatment process is carried out under heating reflux; and after the treatment, the product is sequentially subjected to water washing, acid washing and water washing, and the calcination temperature is 500-600℃.

5. The method of claim 1, wherein: In the solution containing mercapto silane in S2, the solvent is a mixture of toluene and water, and the mass ratio is (20-30):1; the mercapto silane is at least one of 3-mercaptopropyl trimethoxysilane, 3-mercaptopropyl triethoxysilane, trimethoxysilyl methyl mercaptan and 3-mercaptopropyl methyl dimethoxysilane.

6. The method of claim 1, wherein: In S2, when the expanded ZSM-5 molecular sieve is mixed with the solution containing mercapto silane, the reaction temperature is 80-110℃, and the reaction time is 3-5 h; the concentration of hydrogen peroxide is 0.5-10wt%, the reaction temperature in the hydrogen peroxide solution is 30-50℃, and the reaction time is 1-3h.

7. The method of claim 1, wherein: In S3, the silica sol is prepared by dissolving cetyltrimethylammonium bromide (CTAB) in water, adding ammonia water to adjust the pH to 10-11, and then adding dropwise tetraethyl orthosilicate (TEOS) for mixing; the molar ratio of CTAB:TEOS:water is (0.01-0.1):1:(200-500); when the silica sol is mixed with the SO3H-ZSM-5 molecular sieve, the reaction temperature is 60-80℃, and the reaction time is 4-6h.

8. Application of the modified ZSM-5 molecular sieve obtained by the preparation method in any one of claims 1-7 as a catalyst in the hydration of cyclohexene to prepare cyclohexanol.

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