阅读说明：本技术 具有mfi结构的纳米雏晶催化剂及其制备方法和应用 (Nano-sized crystal catalyst with MFI structure and preparation method and application thereof ) 是由 张亚红 盛治政 唐颐 展裕璐 高嵝 会映双 杜可 于 2020-12-18 设计创作，主要内容包括：本发明提供了具有MFI结构的纳米雏晶催化剂的制备方法,本发明先通过微波加热使分子筛晶体从硅源和四丙基氢氧化铵水溶液的混合液中成核与生长,再通过微波加热使金属无机盐中的金属离子与分子筛结合,之后通过透析进行浓缩,通过冷冻干燥去除水分,最后通过煅烧去除模板剂四丙基氢氧化铵,进而得到了颗粒尺寸小、催化活性高的具有MFI结构的纳米雏晶催化剂。实施例的结果显示,本发明制备的具有MFI结构的纳米雏晶催化剂的粒径分布为6～10nm,外比表面积为104cm～3g～(-1),微孔比表面积为640cm～3g～(-1)。(The invention provides a preparation method of a nanometer crystal catalyst with MFI structure, which firstly heats a molecular sieve by microwaveThe crystal nucleates and grows from the mixed solution of a silicon source and tetrapropylammonium hydroxide aqueous solution, metal ions in metal inorganic salt are combined with a molecular sieve through microwave heating, then the mixture is concentrated through dialysis, moisture is removed through freeze drying, and finally the template agent tetrapropylammonium hydroxide is removed through calcination, so that the nanometer crystal catalyst with an MFI structure, small particle size and high catalytic activity is obtained. The results of the examples show that the particle size distribution of the nano-sized crystal catalyst with MFI structure prepared by the invention is 6-10 nm, and the external specific surface area is 104cm 3 g ‑1 The specific surface area of the micropore is 640cm 3 g ‑1 。)

1. The preparation method of the nano-sized crystal catalyst with the MFI structure comprises the following steps:

(1) mixing a silicon source and a tetrapropyl ammonium hydroxide aqueous solution, and carrying out microwave heating to obtain a pure silicon MFI molecular sieve precursor solution;

(2) mixing the pure silicon MFI molecular sieve precursor solution obtained in the step (1) with metal inorganic salt, and performing microwave heating to obtain an MFI molecular sieve dispersion liquid;

(3) dialyzing the MFI molecular sieve dispersion liquid obtained in the step (2) to obtain an MFI molecular sieve aqueous solution;

(4) and (4) sequentially carrying out freeze drying and calcination on the MFI molecular sieve aqueous solution obtained in the step (3) to obtain the nano-sized crystal catalyst with the MFI structure.

2. The method according to claim 1, wherein the ratio of the amount of the silicon source to the amount of the tetrapropylammonium hydroxide in the aqueous tetrapropylammonium hydroxide solution in step (1) is 1 (0.2 to 0.39).

3. The production method according to claim 1, wherein the microwave heating in the step (1) includes low-temperature microwave heating and high-temperature microwave heating which are performed in this order; the low-temperature microwave heating temperature is 60-90 ℃, and the high-temperature microwave heating temperature is 110-130 ℃.

4. The method according to claim 1, wherein the metal inorganic salt in the step (2) comprises one or more of aluminum nitrate, aluminum chloride, tin nitrate and tin chloride.

5. The preparation method according to claim 1, wherein the ratio of the amount of the metal ions in the metal inorganic salt in the step (2) to the amount of the silicon atoms in the pure silicon MFI molecular sieve precursor is 1 (20-200).

6. The method according to claim 1, wherein the microwave heating in step (2) is carried out at a temperature of 130 to 180 ℃ for 60 to 300 min.

7. The preparation method according to claim 1, wherein the temperature of the freeze-drying in the step (4) is-50 to-20 ℃, and the time of the freeze-drying is 36 to 48 hours.

8. The production method according to claim 1, wherein the calcination in the step (4) includes a low-temperature calcination and a high-temperature calcination which are sequentially performed; the low-temperature calcination temperature is 200-250 ℃, and the low-temperature calcination time is 1-2 h; the high-temperature calcination temperature is 500-600 ℃, and the high-temperature calcination time is 4-8 h.

9. The nano-sized crystallite catalyst with an MFI structure prepared by the preparation method of any one of claims 1 to 8, wherein the nano-sized crystallite catalyst with the MFI structure has micropores with the MFI structure.

10. Use of the nanocrystalline catalyst with MFI structure according to claim 9 in macromolecular organic matter cracking reactions and sugar conversion reactions.

Technical Field

The invention relates to the technical field of catalysts, in particular to a nanometer crystal catalyst with an MFI structure, and a preparation method and application thereof.

Background

Molecular sieves refer to a class of materials having uniform micropores and pore sizes comparable to the size of a typical molecule. The molecular sieve has wide application, can be used as a high-efficiency drying agent, a selective adsorbent, a catalyst, an ion exchanger and the like, and plays more and more important roles in petroleum processing, petrochemical industry, fine chemical industry and daily chemical industry.

When the molecular sieve is used as a catalyst, the catalytic activity of the molecular sieve is closely related to the microporous structure, the type and the distribution of active sites and the like. The traditional molecular sieve has the characteristics of large micropore diameter, long pore channel and mainly distributed acid sites in a framework, so that the traditional molecular sieve has the defects of low mass transfer efficiency, easy pore channel blockage, insufficient exposed active sites and the like, and further limits the application of the traditional molecular sieve in reactions such as macromolecular catalytic cracking, conversion of biomass platform compounds and the like. The particle size of the nano molecular sieve is only dozens to hundreds of nanometers, the external surface area is large, and the nano molecular sieve has short and regular pore channels, so that a shorter diffusion path and more contactable active sites can be provided, the mass transfer efficiency and the catalytic activity can be improved, and if the particle size of the nano ZSM-5 molecular sieve with the MFI structure is 100-300 nm, the nano ZSM-5 molecular sieve has good catalytic activity in catalytic cracking reaction of naphtha and butene. However, the above-mentioned nano ZSM-5 molecular sieve still has a large particle size, and when it is used as a catalyst for catalytic cracking reaction, it still has the defects of low catalytic activity and further high reaction temperature. Therefore, there is a need to provide a molecular sieve catalyst with smaller particle size and better catalytic activity.

Disclosure of Invention

The nanometer crystal catalyst with the MFI structure is small in particle size, can be used as a catalyst to be applied to macromolecular organic matter cracking reaction and saccharide conversion reaction, and is high in catalytic activity.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of a nanometer crystal catalyst with an MFI structure, which comprises the following steps:

(1) mixing a silicon source and a tetrapropyl ammonium hydroxide aqueous solution, and carrying out microwave heating to obtain a pure silicon MFI molecular sieve precursor solution;

(2) mixing the pure silicon MFI molecular sieve precursor solution obtained in the step (1) with metal inorganic salt, and performing microwave heating to obtain an MFI molecular sieve dispersion liquid;

(3) dialyzing the MFI molecular sieve dispersion liquid obtained in the step (2) to obtain an MFI molecular sieve aqueous solution;

(4) and (4) sequentially carrying out freeze drying and calcination on the MFI molecular sieve aqueous solution obtained in the step (3) to obtain the nano-sized crystal catalyst with the MFI structure.

Preferably, the ratio of the silicon source to the amount of tetrapropylammonium hydroxide in the aqueous tetrapropylammonium hydroxide solution in step (1) is 1 (0.2 to 0.39).

Preferably, the microwave heating in step (1) includes low-temperature microwave heating and high-temperature microwave heating which are sequentially performed; the low-temperature microwave heating temperature is 60-90 ℃, and the high-temperature microwave heating temperature is 110-130 ℃.

Preferably, the metal inorganic salt in step (2) includes one or more of aluminum nitrate, aluminum chloride, tin nitrate and tin chloride.

Preferably, the ratio of the metal ions in the metal inorganic salt in the step (2) to the silicon atoms in the pure silicon MFI molecular sieve precursor is 1 (20-200).

Preferably, the microwave heating temperature in the step (2) is 130-180 ℃, and the microwave heating time is 60-300 min.

Preferably, the temperature of the freeze drying in the step (4) is-50 to-20 ℃, and the time of the freeze drying is 36 to 48 hours.

Preferably, the calcination in the step (4) includes a low-temperature calcination and a high-temperature calcination which are sequentially performed; the low-temperature calcination temperature is 200-250 ℃, and the low-temperature calcination time is 1-2 h; the high-temperature calcination temperature is 500-600 ℃, and the high-temperature calcination time is 4-8 h.

The invention also provides the nano-sized crystal catalyst with the MFI structure, which is prepared by the preparation method in the technical scheme, and the nano-sized crystal catalyst with the MFI structure has micropores with the MFI structure.

The invention also provides the application of the nano-sized crystal catalyst with the MFI structure in the cracking reaction of macromolecular organic matters and the conversion reaction of saccharides.

The invention provides a preparation method of a nanometer crystal catalyst with an MFI structure, which comprises the following steps: mixing a silicon source and a tetrapropyl ammonium hydroxide aqueous solution, and carrying out microwave heating to obtain a pure silicon MFI molecular sieve precursor solution; mixing pure silicon MFI molecular sieve precursor solution with metal inorganic salt, and performing microwave heating to obtain MFI molecular sieve dispersion liquid; dialyzing the MFI molecular sieve dispersion liquid to obtain an MFI molecular sieve aqueous solution; and sequentially carrying out freeze drying and calcination on the MFI molecular sieve aqueous solution to obtain the nano-sized crystal catalyst with the MFI structure. The invention firstly leads the molecular sieve crystal to nucleate and grow from the mixed solution of a silicon source and tetrapropyl ammonium hydroxide aqueous solution by microwave heating, then leads the metal ions in the metal inorganic salt to be combined with the molecular sieve by microwave heating, then carries out concentration by dialysis, and freezesDrying to remove water, and finally removing the template agent tetrapropylammonium hydroxide by calcining to obtain the nano-sized rudimental catalyst with small particle size and high catalytic activity and MFI structure. By adopting a microwave heating method, the method has the advantages of rapid reaction and uniform heating, can obtain rich crystal nuclei on the premise of keeping the system uniform, and is favorable for obtaining the catalyst with small and uniform particle size; the template agent is removed by calcination, so that micropores with MFI structures can be formed in the catalyst, the catalytic activity of the catalyst can be improved, and the reaction temperature can be reduced. The results of the examples show that the particle size distribution of the nano-sized crystal catalyst with MFI structure prepared by the invention is 6-10 nm, and the external specific surface area is 104cm³g^-1The specific surface area of the micropore is 640cm³g^-1(ii) a The nanometer crystal catalyst with MFI structure prepared by the invention can initiate reaction at 260 ℃ when being used as a catalyst for low-density polyethylene cracking reaction, can completely crack low-density polyethylene at 800 ℃, can initiate reaction at 220 ℃ when being used as a catalyst for polypropylene cracking reaction, and can completely crack polypropylene at 360 ℃.

Drawings

FIG. 1 is a transmission electron microscope image of a nanocrystalline catalyst with MFI structure prepared in example 1 of the present invention;

FIG. 2 is an X-ray diffraction pattern of the nano-sized crystal catalyst with MFI structure and the nano-ZSM-5 molecular sieve prepared in example 1 of the present invention;

FIG. 3 is a graph showing the Ar gas adsorption and desorption curves of the nanocrystal catalyst with MFI structure prepared in example 1 of the present invention;

FIG. 4 is a graph of the pore size distribution of the nanocrystalline catalyst with MFI structure prepared in example 1 of the present invention;

FIG. 5 is a potentiometric titration curve of the nano-sized catalyst with MFI structure and the nano-sized ZSM-5 molecular sieve prepared in example 1 of the present invention;

FIG. 6 shows NH of the nano-sized catalyst with MFI structure and the nano-sized ZSM-5 molecular sieve prepared in example 1 of the present invention₃Adsorption and desorption curve graphs;

FIG. 7 is a graph showing the catalytic performance of the nano-sized catalyst with MFI structure and the nano-sized ZSM-5 molecular sieve and ZSM-5 molecular sieve in catalyzing the cracking reaction of low density polyethylene prepared in example 1 of the present invention;

FIG. 8 is a graph of the catalytic performance of the nano-sized catalyst with MFI structure and the nano-sized ZSM-5 molecular sieve and ZSM-5 molecular sieve in catalyzing the polypropylene cracking reaction prepared in example 1 of the present invention;

fig. 9 is a graph of the cycle performance of the nano-sized crystallite catalyst with MFI structure prepared in example 1 of the present invention in the polypropylene cracking reaction.

Detailed Description

The invention provides a preparation method of a nanometer crystal catalyst with an MFI structure, which comprises the following steps:

(1) mixing a silicon source and a tetrapropyl ammonium hydroxide aqueous solution, and carrying out microwave heating to obtain a pure silicon MFI molecular sieve precursor solution;

(2) mixing the pure silicon MFI molecular sieve precursor solution obtained in the step (1) with metal inorganic salt, and performing microwave heating to obtain an MFI molecular sieve dispersion liquid;

(3) dialyzing the MFI molecular sieve dispersion liquid obtained in the step (2) to obtain an MFI molecular sieve aqueous solution;

(4) and (4) sequentially carrying out freeze drying and calcination on the MFI molecular sieve aqueous solution obtained in the step (3) to obtain the nano-sized crystal catalyst with the MFI structure.

According to the invention, a silicon source is mixed with a tetrapropyl ammonium hydroxide aqueous solution, and microwave heating is carried out to obtain a pure silicon MFI molecular sieve precursor solution.

In the present invention, the silicon source preferably includes tetraethyl orthosilicate, water glass, silica sol, or white carbon black, and more preferably tetraethyl orthosilicate or water glass. The invention uses silicon source and tetrapropylammonium hydroxide as raw materials to prepare the pure silicon MFI molecular sieve, and the raw materials have wide sources.

In the present invention, the mass concentration of the tetrapropylammonium hydroxide aqueous solution is preferably 20 to 40%, and more preferably 25 to 35%. The invention takes tetrapropylammonium hydroxide as the template agent, which is beneficial to obtaining the nano-sized crystal catalyst with MFI structural characteristic micropores.

In the present invention, the ratio of the silicon source to the amount of tetrapropylammonium hydroxide in the tetrapropylammonium hydroxide aqueous solution is preferably 1 (0.2 to 0.39), and more preferably 1 (0.25 to 0.39). In the invention, the ratio of the silicon source to the amount of the tetrapropylammonium hydroxide in the tetrapropylammonium hydroxide aqueous solution is preferably controlled within the above range, which is favorable for the nucleation and growth of the molecular sieve.

The operation of mixing the silicon source and the tetrapropylammonium hydroxide aqueous solution is not particularly limited in the present invention, and a mixing technical scheme known to those skilled in the art may be adopted. In the present invention, the mixing of the silicon source and the aqueous tetrapropylammonium hydroxide solution is preferably performed under stirring. In the invention, the stirring speed is preferably 50-300 r/min, and more preferably 100-200 r/min; the stirring time is preferably 10-30 min, and more preferably 15-25 min.

After obtaining the mixed solution, the present invention preferably ages the mixed solution. In the invention, the aging time is preferably 12-24 h, and more preferably 24 h. In the present invention, the aging of the mixed solution is preferably performed under stirring. In the invention, the stirring speed is preferably 50-300 r/min, and more preferably 100-200 r/min. In the invention, the silicon source and the tetrapropyl ammonium hydroxide aqueous solution are preferably uniformly mixed by aging so as to facilitate the nucleation and growth of the subsequent molecular sieve.

After the aging is finished, the invention carries out microwave heating on the aged product to obtain pure silicon MFI molecular sieve precursor solution. According to the invention, the aged product is heated by microwave, so that molecular sieve crystals nucleate and grow from the mixed solution of a silicon source and a tetrapropylammonium hydroxide aqueous solution, the microwave heating has the advantages of rapid reaction and uniform heating, abundant crystal nuclei can be obtained on the premise of keeping the system uniform, and the catalyst with small and uniform particle size can be obtained.

In the present invention, the microwave heating after mixing the silicon source and the aqueous tetrapropylammonium hydroxide solution preferably includes low-temperature microwave heating and high-temperature microwave heating performed in this order. Preferably, the molecular sieve crystal is nucleated from the mixed solution of the silicon source and the tetrapropyl ammonium hydroxide aqueous solution by low-temperature microwave heating, and then the molecular sieve crystal is grown by high-temperature microwave heating. In the present invention, the microwave heating device is preferably a microwave synthesizer.

In the invention, the temperature of the low-temperature microwave heating is preferably 60-90 ℃, and more preferably 80-90 ℃; the time for low-temperature microwave heating is preferably 90-180 min, and more preferably 90-120 min. In the present invention, the temperature and time of the low-temperature microwave heating are preferably controlled within the above ranges, which is advantageous for improving the yield of the catalyst.

In the invention, the high-temperature microwave heating temperature is preferably 110-130 ℃, and more preferably 120-130 ℃; the time for high-temperature microwave heating is preferably 50-90 min, and more preferably 50-70 min. The temperature and time of the high-temperature microwave heating are preferably controlled within the above range, and the excessive high-temperature microwave heating temperature or the excessive high-temperature microwave heating time easily causes the excessive particle size of the catalyst and influences the catalytic activity of the catalyst.

After obtaining the pure silicon MFI molecular sieve precursor solution, mixing the pure silicon MFI molecular sieve precursor solution with metal inorganic salt, and carrying out microwave heating to obtain the MFI molecular sieve dispersion liquid. The invention makes metal ions in the metal inorganic salt adsorbed into the molecular sieve by microwave heating, and further forms bonds with oxygen atoms in the molecular sieve to be retained in a molecular sieve framework, thereby being beneficial to improving the catalytic activity of the catalyst.

In the present invention, the metal inorganic salt preferably includes one or more of aluminum nitrate, aluminum chloride, tin nitrate and tin chloride, and more preferably aluminum nitrate and/or aluminum chloride.

In the present invention, the ratio of the amount of metal ions in the metal inorganic salt to the amount of silicon atoms in the pure silicon MFI molecular sieve precursor is preferably 1 (20-200), and more preferably 1 (30-200). The invention preferably controls the quantity ratio of metal ions in the metal inorganic salt to silicon atoms in the pure silicon MFI molecular sieve precursor in the range, and is favorable for obtaining the nano-sized crystal catalyst with high catalytic activity and an MFI structure.

In the invention, the microwave heating temperature of the mixed pure silicon MFI molecular sieve precursor solution and the metal inorganic salt is preferably 130-180 ℃, and more preferably 130-150 ℃; the time for microwave heating is preferably 60 to 300min, and more preferably 100 to 210 min.

After obtaining the MFI molecular sieve dispersion liquid, the invention dialyzes the MFI molecular sieve dispersion liquid to obtain an MFI molecular sieve aqueous solution.

In the present invention, the dialysis preferably comprises: dialyzed with tetrapropylammonium hydroxide aqueous solution and then with deionized water. In the present invention, the dialysis is preferably performed under a stirring condition, and the stirring speed is preferably 20 to 50rpm, more preferably 30 to 50 rpm.

In the present invention, the dialysis membrane used for dialysis is preferably a cellulose semipermeable membrane; the cellulose semipermeable membrane preferably has a molecular weight cut-off of 3.5 to 10kDa, more preferably 3.5 to 6 kDa.

In the present invention, the concentration of the tetrapropylammonium hydroxide aqueous solution is preferably 6 to 10mmol/L, and more preferably 6 to 8 mmol/L. In the present invention, the concentration of the aqueous tetrapropylammonium hydroxide solution is preferably controlled within the above range, which is advantageous for improving the yield of the catalyst, and an excessively high concentration of the aqueous tetrapropylammonium hydroxide solution may dissolve part of the catalyst, thereby reducing the yield of the catalyst. In the invention, the dialysis time of the tetrapropylammonium hydroxide aqueous solution is preferably 24-48 h, and more preferably 24-36 h.

In the invention, the time for the deionized water dialysis is preferably 12-24 h, and more preferably 12-18 h. In the invention, when the deionized water is used for dialysis, the deionized water is preferably replaced every 12 hours until the pH of the dialysis external liquid is 7.0-8.0.

After obtaining the MFI molecular sieve aqueous solution, the invention sequentially carries out freeze drying and calcination on the MFI molecular sieve aqueous solution to obtain the nano-sized crystal catalyst with the MFI structure. The invention removes the water in the MFI molecular sieve water solution by freeze drying, and removes the template agent tetrapropylammonium hydroxide by calcining to form micropores of an MFI structure in the catalyst.

After obtaining the MFI molecular sieve aqueous solution, the invention preferably freezes the MFI molecular sieve aqueous solution to obtain the MFI molecular sieve ice cubes. In the present invention, the temperature of the freezing is preferably-20 to-25 ℃, more preferably-20 ℃.

In the present invention, the temperature of the freeze-drying is preferably-50 to-20 ℃, more preferably-50 to-40 ℃; the freeze drying time is preferably 36-48 h, and more preferably 48 h. In the present invention, the freeze-drying device is preferably a freeze dryer.

In the present invention, the calcination preferably includes low-temperature calcination and high-temperature calcination, which are sequentially performed. According to the invention, the structure of the catalyst is further shrunk stably by preferably calcining at low temperature, so that the structural damage in the high-temperature calcining process is prevented; and then removing the template agent through high-temperature calcination to form micropores with an MFI structure.

In the invention, the temperature of the low-temperature calcination is preferably 200-250 ℃, and more preferably 200-220 ℃; the time of the low-temperature calcination is preferably 1-2 h, and more preferably 2 h. In the invention, the temperature and time of the low-temperature calcination are preferably controlled within the ranges, which is beneficial to stabilizing the structure of the catalyst and further obtaining the catalyst with high catalytic activity.

In the invention, the high-temperature calcination temperature is preferably 500-600 ℃, and more preferably 500-550 ℃; the high-temperature calcination time is preferably 4-8 h, and more preferably 6-8 h. The invention preferably controls the temperature and time of the high-temperature calcination within the above range, which is beneficial to completely removing the tetrapropylammonium hydroxide, and further obtains the catalyst with high catalytic activity.

In the invention, the heating rate of the low-temperature calcination and the high-temperature calcination is preferably 1-2 ℃/min independently. In the present invention, the atmosphere of the low-temperature calcination and the high-temperature calcination is independently preferably an air atmosphere.

The method comprises the steps of firstly, nucleating and growing molecular sieve crystals from a mixed solution of a silicon source and a tetrapropylammonium hydroxide aqueous solution by microwave heating, then combining metal ions in metal inorganic salt with a molecular sieve by microwave heating, then concentrating by dialysis, removing moisture by freeze drying, and finally removing a template agent tetrapropylammonium hydroxide by calcining, thereby obtaining the nano-sized crystal catalyst with a small particle size and high catalytic activity and an MFI structure.

The invention provides the nanometer embryonic crystal catalyst with the MFI structure, which is prepared by the preparation method in the technical scheme, and the nanometer embryonic crystal catalyst with the MFI structure has micropores with the MFI structure.

In the invention, the specific surface area of the micropores is preferably 400-650 cm³g^-1More preferably 490 to 650cm³g^-1。

In the invention, the particle size of the nano-sized crystal catalyst with the MFI structure is preferably 6-20 nm, and more preferably 6-10 nm.

In the invention, the external specific surface area of the nano-sized crystal catalyst with the MFI structure is preferably 90-120 cm³g^-1More preferably 100 to 115cm³g^-1。

The invention provides application of the nano-sized crystal catalyst with the MFI structure in macromolecular organic matter cracking reaction and saccharide conversion reaction.

In the invention, the nanometer crystal catalyst with MFI structure can be used as a catalyst to be applied to the cracking reaction of macromolecular organic matters, and the macromolecular organic matters preferably comprise low-density polyethylene and polypropylene. In the invention, the application of the nano-sized crystal catalyst with the MFI structure in the cracking reaction of macromolecular organic matters preferably comprises the following steps: mixing the macromolecular organic matter with the nanometer crystal catalyst with MFI structure, heating and cracking reaction.

In the invention, the mass ratio of the macromolecular organic matter to the nano-sized crystal catalyst with the MFI structure is preferably 10: 1-15: 1, and more preferably 10: 1.

In the invention, the temperature of the cracking reaction is preferably 800-900 ℃, and more preferably 800 ℃.

In the invention, the rate of raising the temperature to the temperature of the cracking reaction is preferably 10-15 ℃/min, and more preferably 10 ℃/min.

In the present invention, the atmosphere of the cleavage reaction is preferably a nitrogen atmosphere.

In the invention, the nano-sized crystal catalyst with the MFI structure can be used as a catalyst for saccharide conversion reaction. In the present invention, the saccharide preferably includes fructose and glucose. In the present invention, the application of the nanocrystalline catalyst with MFI structure in the conversion reaction of saccharides preferably comprises the following steps: mixing saccharide with deionized water and catalyst, and heating for conversion reaction.

In the present invention, the mass ratio of the saccharide to the catalyst is preferably 10:1 to 15:1, and more preferably 10: 1. In the present invention, the ratio of the mass of the saccharide to the volume of the deionized water is preferably 500 mg: 10 mL.

In the invention, the temperature of the conversion reaction is preferably 170-190 ℃; the time of the conversion reaction is preferably 1-2 h.

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

1) 4.5686g of a 25 wt% aqueous solution of tetrapropylammonium hydroxide were added to 1.631g H₂O, stirring for 15min at the rotating speed of 100rpm, adding 3g of tetraethyl orthosilicate, continuously stirring and aging for 24h (the mass ratio of the silicon source to the tetrapropyl ammonium hydroxide in the tetrapropyl ammonium hydroxide aqueous solution is 1:0.39), transferring to a microwave synthesizer, heating for 90min at 90 ℃, and then heating for 50min at 130 ℃ to obtain pure silicon MFI molecular sieve precursor solution;

2) mixing the pure silicon MFI molecular sieve precursor solution with 0.087g of AlCl₃·6H₂O (the mass ratio of metal ions in the metal inorganic salt to silicon atoms in the pure silicon MFI molecular sieve precursor is 1:40), aging for 24h, placing in a microwave synthesizer, and heating at 150 ℃ for 210min to obtain an MFI molecular sieve dispersion liquid;

3) placing the MFI molecular sieve dispersion liquid into a cellulose semipermeable membrane with the molecular weight cutoff of 3.5kDa, then soaking the cellulose semipermeable membrane into 1L of tetrapropyl ammonium hydroxide aqueous solution with the molecular weight cutoff of 6mmol/L, stirring and dialyzing the mixture for 24 hours at the speed of 30rpm, then replacing the tetrapropyl ammonium hydroxide aqueous solution with deionized water for dialysis, and replacing the deionized water every 12 hours until the pH value of the dialyzed external solution is close to 7.0, so as to obtain the MFI molecular sieve aqueous solution;

4) and (2) freezing the MFI molecular sieve aqueous solution at-20 ℃ to form ice blocks, then freezing and drying the ice blocks in a freeze dryer at-50 ℃ for 48 hours to obtain white powder, and finally calcining the white powder at 200 ℃ for 2 hours and 550 ℃ for 6 hours under the air condition, wherein the heating rate is 1 ℃/min, so that the nano-sized crystal catalyst with the MFI structure is obtained and is marked as SC-Al (40).

The particle size distribution of the nanometer crystal catalyst with the MFI structure obtained in the embodiment is 6-10 nm, and the specific surface area of the micropore is 640cm³g^-1The external specific surface area is 104cm³g^-1The yield was 49%.

Fig. 1 is a transmission electron microscope image of the nano-sized crystallite catalyst with MFI structure prepared in this example. It can be seen that the particle size distribution of the nanocrystal catalyst prepared by the embodiment is 6-10 nm.

Fig. 2 is an X-ray diffraction pattern of the nano-sized catalyst with MFI structure and the nano ZSM-5 molecular sieve prepared in this example. It can be seen that the nano-sized crystal catalyst prepared by the invention does not have long-range order equivalent to that of the nano ZSM-5 molecular sieve.

Fig. 3 is a graph showing the adsorption and desorption curves of Ar gas for the nano-sized crystal catalyst with MFI structure prepared in this example. It can be seen that the amount of Ar gas adsorbed and desorbed by the nano-sized crystal catalyst prepared by the invention is higher in the range of low relative pressure, which indicates that the nano-sized crystal catalyst prepared by the invention has a very rich microporous structure.

Fig. 4 is a pore size distribution diagram of the nano-sized crystallite catalyst with MFI structure prepared in this example. The peaks at 0.52nm and 0.64nm are visible from the figure, indicating that the nanocrystalline catalyst prepared according to the invention has characteristic micropores of MFI structure.

Fig. 5 is a potentiometric titration curve of the nano-sized crystallite catalyst with MFI structure and the nano ZSM-5 molecular sieve prepared in this example. It can be seen that the contactable acid number of macromolecules of the nano-sized crystal catalyst prepared by the invention in a liquid phase is higher than that of the nano ZSM-5 molecular sieve.

FIG. 6 shows NH of the nano-sized catalyst with MFI structure and the nano-sized ZSM-5 molecular sieve prepared in this example₃Adsorption and desorption curve diagrams. It can be seen that the overall acid amount of the nano-sized crystal catalyst prepared by the invention is three times that of the nano ZSM-5 molecular sieve.

Example 2

The same raw materials and preparation method as those of example 1 are adopted, and AlCl in the step 2) is added₃·6H₂The mass of O is changed to 0.0174g (the mass ratio of metal ions in the metal inorganic salt to silicon atoms in the pure silicon MFI molecular sieve precursor is 1:200), the microwave heating temperature is changed from 150 ℃ to 140 ℃, and the time is changed from 210min to 180 min.

The particle size of the nanometer crystal catalyst with the MFI structure obtained in the embodiment is 6-8 nm, and the specific surface area of the micropore is 457cm³g^-1External specific surface area of 114cm³g^-1The yield was 31%.

Example 3

The same preparation method as that of example 1 is adopted, and AlCl in the step 2) is added₃·6H₂Changing O to Al (NO)₃)₃·9H₂O, the mass is 0.270g (the mass ratio of metal ions in the metal inorganic salt to silicon atoms in the pure silicon MFI molecular sieve precursor is 1:30), the aging time is changed to 48h, the microwave heating temperature is changed from 150 ℃ to 180 ℃, and the time is changed from 210min to 300 min.

The particle size of the nanometer crystal catalyst with MFI structure obtained in the embodiment is 8-15 nm, and the specific surface area of micropores is 420cm³g^-1External specific surface area of 101cm³g^-1The yield was 57%.

Example 4

1) 4.5686g of 25 wt% tetrapropyl ammonium hydroxide aqueous solution and 3g of tetraethyl orthosilicate are mixed, stirred and aged for 24h at the rotating speed of 100rpm (the mass ratio of the silicon source to the tetrapropyl ammonium hydroxide in the tetrapropyl ammonium hydroxide aqueous solution is 1:0.39), transferred to a microwave synthesizer, heated at 90 ℃ for 90min and then at 130 ℃ for 70min to obtain pure silicon MFI molecular sieve precursor solution;

2) mixing the pure silicon MFI molecular sieve precursor solution with 0.1305g AlCl₃·6H₂Mixing O, aging for 30h, placing in a microwave synthesizer, and heating at 170 deg.C for 240min to obtain MFI molecular sieve dispersion;

step 3) and step 4) are the same as in example 1.

The particle size distribution of the nanometer crystal catalyst with the MFI structure obtained in the embodiment is 6-10 nm, and the specific surface area of the micropore is 490cm³g^-1The external specific surface area is 110cm³g^-1The yield was 60%.

Example 5

The same preparation method as that of example 1 is adopted, and AlCl in the step 2) is added₃·6H₂Changing O to 0.1g SnCl₄·5H₂O。

The particle size of the nanometer crystal catalyst with the MFI structure obtained in the embodiment is 6-8 nm, and the specific surface area of micropores is 565cm³g^-1External specific surface area of 98cm³g^-1The yield was 41%.

Application example 1

15mg of low-density polyethylene was mixed with 1.5mg of the SC-Al (40) nanocrystalline catalyst, the nano ZSM-5 (noted as nanoZSM-5), and the ZSM-5 prepared in example 1, respectively, and a control example without the catalyst was set, placed in a thermogravimetric analyzer, purged with nitrogen gas and heated to 50 ℃ for 30min, and then heated to 800 ℃ at a rate of 10 ℃/min. The catalytic performance of each catalyst in catalyzing the cracking reaction of the low density polyethylene was evaluated by using the temperature and weight loss data, and the results are shown in fig. 7.

As can be seen from fig. 7, the nano-sized crystal catalyst prepared by the present invention can initiate the cracking of the low density polyethylene at a lower temperature, and achieve the effect of lower temperature required for the loss of the same quality of the low density polyethylene. Wherein the temperature for initiating cracking is as follows in sequence: SC-Al (40) (260 ℃) < nanoZSM-5(290 ℃) < ZSM-5(350 ℃) < no catalyst (400 ℃), the temperatures at which the low density polyethylene loses 20% of mass are in the order: SC-Al (40) (345 ℃ C.) < NanoZSM-5(377 ℃ C.) < ZSM-5(393 ℃ C.) < No catalyst (462 ℃ C.). Therefore, the SC-Al (40) nano-crystal catalyst prepared by the invention has quite excellent catalytic activity in the cracking reaction of low-density polyethylene.

Application example 2

15mg of polypropylene was mixed with 1.5mg of the SC-Al (40) nanocrystalline catalyst, the nano ZSM-5, and the ZSM-5 prepared in example 1, respectively, and a control example without the catalyst was set, placed in a thermogravimetric analyzer, purged with nitrogen gas and heated to 50 ℃ for 30min, and then heated to 800 ℃ at a rate of 10 ℃/min. The catalytic performance of each catalyst in the catalytic polypropylene cracking reaction was evaluated by using the temperature and weight loss data, and the results are shown in fig. 8.

As can be seen from FIG. 8, the nano-sized crystal catalyst prepared by the invention can initiate polypropylene cracking at a lower temperature, the temperature required by polypropylene with the same mass loss is lower, and the cracking of polypropylene can be promoted to be completed at a lower temperature. Wherein the temperature for initiating cracking is as follows in sequence: SC-Al (40) (220 ℃) < nanoZSM-5(320 ℃) < ZSM-5(320 ℃) < no catalyst (350 ℃), the temperatures at which the polypropylene loses 20% mass are in the order: SC-Al (40) (280 ℃) < nanoZSM-5(396 ℃) < ZSM-5(410 ℃) < no catalyst (426 ℃), the temperature at which polypropylene is completely cracked (i.e. mass loss 100%) is in turn SC-Al (40) (360 ℃) < nanoZSM-5(440 ℃) < ZSM-5(455 ℃) < no catalyst (485 ℃). Therefore, the SC-Al (40) nanocrystal catalyst prepared by the invention has quite excellent catalytic activity in the cracking reaction of polypropylene.

Application example 3

Mixing 15mg of polypropylene and 1.5mg of the SC-Al (40) nanocrystal catalyst prepared in example 1, placing the mixture in a thermogravimetric analyzer, introducing nitrogen, heating to 50 ℃, purging for 30min, heating to 800 ℃ at a speed of 10 ℃/min, and collecting a test data mark as 1; closing a nitrogen gas circuit, introducing air, heating and roasting, wherein the roasting temperature is 800 ℃, weighing the roasted and cooled catalyst, adding 10 times of the mass of polypropylene, reusing a test gas circuit and a program for reaction, collecting test data and marking as 2, carrying out the same operation in subsequent cyclic experiments, and testing the cyclic use effect of the SC-Al (40) nanocrystal catalyst prepared in the example 1 in the polypropylene cracking reaction, wherein the result is shown in figure 9.

As can be seen from fig. 9, the cracking curve of polypropylene remains unchanged after the nano-sized crystal catalyst prepared by the present invention is catalytically cycled for 10 times, which indicates that the nano-sized crystal catalyst prepared by the present invention has excellent cycle stability.

Application example 4

500mg of the saccharide substrate is dissolved in 10mL of deionized water, then is mixed with 50mg of the catalyst prepared in the example 5, then is placed in a microwave reaction tube, is heated to 170-190 ℃, and is reacted for 1-2 hours, and after the reaction is finished, the catalytic activity of the catalyst is tested by high performance liquid chromatography, and the results are shown in Table 1.

Table 1 reaction conditions and catalytic activity of catalyst in application example 4

BottomArticle (A)	Catalytic converterTransformingDosage/mg	Temperature of /℃	Time/h	Transformation ofRate of change /％	MilkAcid(s)Selectivity is /％
						FruitCandy	0	170	1	59	0
FruitCandy	50	170	1	98.1	13.6
						FruitCandy	50	170	2	98.9	14.9
GrapeGrape with water-soluble coreCandy	50	170	1	75.8	13.4
						GrapeGrape with water-soluble coreCandy	50	170	2	91.6	12.8
FruitCandy	50	190	1	100	14.5
						FruitCandy	50	190	2	100	15.6

As can be seen from table 1, the nanocrystal catalyst with MFI structure prepared by the present invention has excellent catalytic activity in the conversion reaction of saccharides, can promote the conversion of saccharides, and has a certain selectivity to lactic acid.

The embodiment shows that the nano-sized crystal catalyst with the MFI structure prepared by the invention has small particle size, high catalytic activity and high micropore specific surface area; when the catalyst is used as a catalyst for the cracking reaction of macromolecular organic matters, the reaction can be initiated at a lower temperature, and meanwhile, the macromolecular organic matters can be completely cracked at the lower temperature; when the catalyst is used as a catalyst for saccharide conversion reaction, the conversion rate of saccharide is high, and the catalyst also has certain selectivity on lactic acid.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.