A nanosheet-shaped titanate / zeolite heterostructure catalyst and a preparation method thereof

Abstract

The application discloses a nanosheet titanic acid / zeolite heterostructure catalyst and a preparation method thereof. The nanosheet titanic acid is used as a hetero-nucleation aid, and the nanosheet titanic acid / zeolite heterostructure catalyst is quickly prepared through a hydrothermal reaction. The mass content of titanic acid in the nanosheet titanic acid dispersion liquid is 9-10 wt.%. The nanosheet titanic acid with the hetero-nucleation effect is introduced to quickly nucleate and grow the molecular sieve. The nanosheet titanic acid as the hetero-nucleation aid promotes the nucleation and growth of the molecular sieve and forms the coating of the molecular sieve to limit the micro size of the molecular sieve, so that the specific surface area of the nanosheet titanic acid / TS-2 molecular sieve heterostructure catalyst is ensured, and the silicon / titanium ratio of the heterostructure is significantly reduced.

Description

Technical Field

[0001] This invention belongs to the field of petrochemical catalysis technology, and relates to a nanosheet-like titanate / zeolite heterostructure catalyst and its preparation method. Background Technology

[0002] Nanosheet titanic acid (TA) is an important two-dimensional sheet material widely used in batteries, photocatalysis, and traditional industrial catalysis. Its structure consists of polycrystalline TiO2(B) titanium dioxide, where titanium-oxygen octahedral units are connected by sharing edges or vertices to form a two-dimensional layered structure. Zeolites (also known as molecular sieves) are framework-like hydrated aluminosilicates, aluminum phosphates, or other inorganic ordered porous materials. They possess unique adsorption, catalytic, and ion-exchange properties, ion selectivity, acid resistance, thermal stability, and multi-component characteristics, making them widely used in the petroleum and chemical industries, and even in other materials. Zeolites include two main categories: natural zeolites and synthetic zeolites. The latter are usually produced via a hydrothermal synthesis route and exist in nano- to micro-scale powder form. Due to the presence of a hydrothermal equilibrium system, the zeolite precursor dissolves in the hydrothermal system, leaving some residue. This phenomenon typically results in a yield of zeolite synthesized via hydrothermal systems remaining at 50-70%, rarely exceeding 80%. It is worth noting that nucleation and growth in hydrothermal synthesis systems have a certain energy barrier, resulting in a slow synthesis rate, typically requiring 24-72 hours. Currently, there is generally no correlation between nanosheet titanate and zeolite. Due to its nanoscale characteristics, nanosheet titanate usually exists in a solution-dispersed form, which limits its functional applications. In summary, zeolite currently faces technical bottlenecks in synthesis (synthesis yield and rate), while nanosheet titanate faces technical application bottlenecks. However, it is worth noting that both, as inorganic materials, possess similar ordered structures, thus endowing them with a certain degree of compatibility. Furthermore, nanosheet titanate, due to its layered structure, surface acidity, and polarization properties, can play a role in heterogeneous nucleation. Therefore, this paper proposes to synthesize a nanosheet titanate / zeolite heterostructure, that is, to combine nanosheet titanate onto nano- and micro-scale zeolite powders, and to achieve rapid zeolite synthesis.

[0003] This invention introduces nanosheet titanic acid into the hydrothermal synthesis system of zeolite, overcoming the technical bottlenecks of low zeolite synthesis yield and slow synthesis rate, and obtaining a nanosheet titanic acid / zeolite heterostructure. This form can also overcome the technical application bottleneck of nanosheet titanic acid. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a nanosheet-like titanate / zeolite heterostructure catalyst and its preparation method. This preparation method utilizes the heterogeneous nucleation-promoting effect of nanosheet-like titanate to hydrothermally crystallize zeolite precursors into zeolite in a hydrothermal synthesis system, thereby obtaining a nanosheet-like titanate / molecular sieve heterostructure catalyst, improving the zeolite synthesis yield and rate.

[0005] The technical solution adopted by the present invention to solve the aforementioned technical problem is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a nanosheet-like titanic acid / zeolite heterostructure catalyst, which uses nanosheet-like titanic acid as a heterostructure nucleation aid and rapidly prepares the nanosheet-like titanic acid / zeolite heterostructure catalyst via a hydrothermal reaction.

[0007] Under hydrothermal conditions, a certain amount of nanosheet titanic acid is used as a heterogeneous nucleation agent to promote the crystallization of zeolite precursors to form zeolite, while obtaining a nanosheet titanic acid / molecular sieve heterostructure.

[0008] The preparation method is as follows: obtaining nanosheet-shaped titanic acid and preparing it into a nanosheet-shaped titanic acid dispersion; the mass content of titanic acid in the nanosheet-shaped titanic acid dispersion, calculated as TiO2, is 9-10 wt.%.

[0009] Nanosheet-shaped titanic acid dispersion and zeolite nanocrystals are added to a synthesis system containing silicon source, titanium source, template agent and water. The mixture is then hydrothermally crystallized and separated, recovered and calcined to form a nanosheet-shaped titanic acid / zeolite heterostructure catalyst.

[0010] Secondly, the present invention provides a method for preparing a nanosheet-like titanic acid / TS-2 heterostructure catalyst, the specific process of which is as follows:

[0011] The first step is to prepare nanosheet-like titanic acid. The specific process is as follows: tetrabutyl titanate, isopropanol and triethanolamine are mixed in proportion and stirred thoroughly. Then, tetrabutylammonium hydroxide solution is added and stirred until homogeneous. Finally, hydrogen peroxide solution, a complexing agent, is slowly added and stirred until homogeneous. The mixture is then placed in a reactor for hydrothermal reaction. After hydrothermal reaction, the mixture is dialyzed with deionized water and evaporated and concentrated to obtain a concentrated colloidal solution of nanosheet-like titanic acid, which is then bottled for later use.

[0012] In the synthetic system for preparing nanosheet-like titanic acid, the molar ratio of the relevant reactants is: tetrabutylammonium hydroxide: tetrabutyl titanate: hydrogen peroxide: triethanolamine: isopropanol = 1.0: 2.0: 2.0: 6.0: 8.0;

[0013] The second step involves preparing nanosheet-like titanic acid / zeolite heterostructure catalysts via a hydrothermal method. The specific process is as follows: Tetrabutylammonium hydroxide solution is mixed with tetraethyl orthosilicate and stirred thoroughly at 60-80℃ to evaporate alcohol. During the evaporation process, ultrapure water is continuously added to the system. After complete hydrolysis, the concentrated colloidal solution of nanosheet-like titanic acid prepared in the first step is added, and after a complete reaction, a mixture A is obtained.

[0014] Tetrabutyl titanate and isopropanol were mixed evenly, and hydrogen peroxide solution was slowly added dropwise to the mixture. After the reaction was complete, mixture B was obtained.

[0015] Mix the two mixtures, A and B, thoroughly, then add TS-2 nanocrystals and stir until homogeneous. The mixture is then loaded into a reactor for hydrothermal reaction at 160-180℃ for 6-72 hours.

[0016] In the synthesis system for preparing nanosheet-like titanate / zeolite heterostructure catalysts, the molar ratio of the relevant reactants is: tetrabutyl orthosilicate: tetrabutylammonium titanate: hydrogen peroxide: ultrapure water = 1.0: 0.03: 0.23: 0.06: 2.0~10.0;

[0017] After repeated centrifugation and washing until neutral, the product was dried in a constant temperature oven to obtain a brown / white experimental product.

[0018] The experimental product was placed in a muffle furnace and calcined at 550°C for 5-6 hours to obtain a nanosheet-like titanic acid / TS-2 heterostructure catalyst.

[0019] The concentrated colloidal solution of nanosheet titanic acid contains 9-10 wt.% titanic acid as TiO2. In the second step, the amount of concentrated colloidal solution of nanosheet titanic acid added is 5-100 mL / 87 g tetraethyl orthosilicate. The mass fraction of tetrabutylammonium hydroxide in the methanol solution is 25%.

[0020] The tetrabutylammonium hydroxide solution used to prepare nanosheet titanic acid was an aqueous solution, while the tetrabutylammonium hydroxide solution used to prepare nanosheet titanic acid / zeolite heterostructure catalyst was a methanol solution; the mass percentage of tetrabutylammonium hydroxide in both template solutions was 25 wt.%; the particle size range of TS-2 nanocrystals was 120-300 nm.

[0021] The hydrothermal reaction temperature and the optimal time at that temperature in the second step are 175℃-12h, 160℃-24h, and 180℃-6h, respectively.

[0022] Nanosheet titanic acid plays a heterogeneous nucleation role in the hydrothermal synthesis of molecular sieves, enabling rapid synthesis of molecular sieves. During the hydrothermal synthesis process, nanosheet titanic acid lowers the nucleation energy barrier of molecular sieves, greatly shortens the nucleation process, and significantly improves the yield of molecular sieves, which ranges from 58% to 92%.

[0023] Thirdly, the present invention provides a nanosheet-like titanic acid / zeolite heterostructure catalyst, wherein the nanosheet-like titanic acid / zeolite heterostructure catalyst has a special heterostructure: a large number of nanosheet-like titanic acid spike-like structures are coated on the molecular sieve.

[0024] In the nanosheet-like titanate / zeolite heterostructure catalyst, titanium is concentrated at the edge of the heterostructure, while silicon is concentrated at the center. The silicon-to-titanium ratio Si / Ti is 1:0.06-0.4, preferably 1:0.15-0.4.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This invention creatively introduces nanosheet titanate with heterogeneous nucleation function to rapidly nucleate and grow molecular sieves. As a heterogeneous nucleation promoter, nanosheet titanate promotes the nucleation and growth of molecular sieves and forms a coating on the molecular sieve to restrict its micro-size during the hydrothermal reaction, thus ensuring the specific surface area of ​​the nanosheet titanate / TS-2 molecular sieve heterostructure catalyst and significantly reducing the silicon-to-titanium ratio of the heterostructure.

[0027] This invention incorporates nanosheet-like titanic acid into zeolite, thereby increasing the zeolite synthesis yield. Compared with conventional synthesis, it can significantly improve the synthesis rate. Compared with conventional titanium-silicon zeolite catalysts, it can increase the titanium content in the catalyst and form a heterostructure. The steps are simple and easy to implement, reducing the difficulty of synthesizing heterostructures of low silicon-to-titanium ratio molecular sieves. The obtained sheet-like titanic acid has a high specific surface area.

[0028] In this invention, TS-2 is prepared using tetraethyl orthosilicate, tetrabutyl titanate, and other raw materials via a hydrothermal process. All raw materials are added according to the steps and mixed thoroughly. The mixture is then subjected to a hydrothermal reaction at 175°C for 6-12 hours, allowing the TS-2 precursor to nucleate and grow under the heterogeneous nucleation of nanosheet titanate, ultimately yielding a nanosheet titanate / TS-2 molecular sieve heterostructure catalyst. This hydrothermal method ensures a low silicon-to-titanium ratio in the heterostructure, avoiding the drawbacks of long reaction times or high reaction temperatures. It is simple, easy to implement, and rapid.

[0029] In summary, this invention creatively proposes a novel technical route for synthesizing nanosheet-shaped titanate / zeolite heterostructure catalysts. These catalysts are porous materials with nanosheet-shaped titanate as the core raw material, which facilitates the rapid preparation of nanosheet-shaped titanate / zeolite heterostructure catalysts with a low silicon-to-titanium ratio. Attached Figure Description

[0030] Figure 1 This is a transmission electron microscope (TEM) image of nanosheet-like titanic acid.

[0031] Figure 2 This is the X-ray diffraction (XRD) pattern of the product from Example 1.

[0032] Figure 3 This is a scanning electron microscope (SEM) image of the product of Comparative Example 3.

[0033] Figure 4 This is the X-ray diffraction (XRD) pattern of the product from Example 9.

[0034] Figure 5 This is the X-ray diffraction (XRD) pattern of the product of Comparative Example 9.

[0035] Figure 6 This is an aberration-corrected transmission electron microscope (AC-TEM) image of the product from Example 9.

[0036] Figure 7 This is an aberration-corrected transmission electron microscope (AC-TEM) image of the product of Comparative Example 9.

[0037] Figure 8 This is a Si elemental distribution map of the product of Example 9 (mapped, magnification of 20k).

[0038] Figure 9 This is a Ti element distribution map of the product of Example 9 (mapped, magnification of 20k).

[0039] Figure 10 This is a Si elemental distribution map of the product of Example 9 (mapped, magnification of 100k).

[0040] Figure 11 This is a Ti element distribution map of the product of Example 9 (mapped, magnification of 100k).

[0041] Figure 12 This is the Si element distribution map of the product of Comparative Example 9 (mapped, magnification of 20k).

[0042] Figure 13 This is a Ti element distribution map of the product of Comparative Example 9 (Mapping, magnification of 20k).

[0043] Figure 14 This is the Si element distribution map of the product of Comparative Example 9 (Mapping, magnification of 100k).

[0044] Figure 15 This is a Ti element distribution map of the product of Comparative Example 9 (Mapping, magnification of 100k).

[0045] Figure 16 This is a scanning electron microscope (SEM) image of the product from Example 9.

[0046] Figure 17 This is a scanning electron microscope (SEM) image of the product of Comparative Example 9.

[0047] Figure 18 This is a transmission electron microscope (TEM) image of the product of Example 12. Detailed Implementation

[0048] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0049] The preparation method of the nanosheet-like titanate / zeolite heterostructure catalyst of the present invention includes the following steps:

[0050] Step 1: Preparation of nanosheet titanate. Nanosheet titanate is formed by reacting a titanium-containing precursor in a restricted synthesis medium to form a nanosheet titanate structure. Tetrabutyl titanate, isopropanol, and triethanolamine are mixed in a certain proportion and stirred thoroughly. Then, tetrabutylammonium hydroxide solution is added and stirred until homogeneous. Finally, hydrogen peroxide solution, a complexing agent, is slowly added and stirred until homogeneous. The mixture is then placed in a reactor for hydrothermal reaction. After hydrothermal reaction, the resulting solution is dialyzed against deionized water and concentrated by evaporation before being bottled for later use.

[0051] In the preferred synthesis system, the molar ratio of the five reactants—tetrabutylammonium hydroxide, tetrabutyl titanate, hydrogen peroxide, triethanolamine, and isopropanol—is 1.0:2.0:2.0:6.0:8.0. This synthesis system is then placed in a hydrothermal reactor and reacted at 80°C for 7 days. The specific process is as follows: 140g of tetrabutyl titanate, 100g of isopropanol, and 180g of triethanolamine are mixed and stirred thoroughly for 3 hours to obtain a slightly yellow, viscous liquid. This step requires ensuring the reaction vessel is absolutely dry and anhydrous.

[0052] Add 200g of 25wt.% tetrabutylammonium hydroxide solution and continue stirring for 12 hours;

[0053] Finally, slowly add 50g of hydrogen peroxide (30wt.%) solution as a complexing agent, and continue stirring for 1 hour. When the reaction system turns yellowish-brown, it can be loaded into a polytetrafluoroethylene-lined reactor for hydrothermal reaction.

[0054] The mixture after hydrothermal reaction was placed in a semi-permeable membrane dialysis bag and dialyzed with deionized water to remove alcohols, triethanolamine, and tetrabutylammonium hydroxide. The mixture was then evaporated and concentrated to obtain a concentrated colloidal solution of nanosheet titanic acid. The content of nanosheet titanic acid in the concentrated colloidal solution was 10 wt.%, which was then used for the synthesis of nanosheet titanic acid / zeolite heterostructure catalysts.

[0055] The second step involves the hydrothermal preparation of a nanosheet-like titanate / zeolite heterostructure catalyst. The zeolite is a MEL-structured titanium-silicon zeolite. In this embodiment, a nanosheet-like titanate / TS-2 heterostructure is preferably prepared. A concentrated colloidal solution of the aforementioned nanosheet-like titanate is added to a synthesis system containing a silicon source, a titanium source, a template agent, and water. Hydrothermal crystallization is then performed, followed by separation, recovery, and calcination to form the nanosheet-like titanate / zeolite heterostructure catalyst.

[0056] The specific process is as follows: 100g of tetrabutylammonium hydroxide methanol solution (TBAOH, 25wt.%) was mixed with 87g of tetraethyl orthosilicate (TEOS), and the mixture was stirred thoroughly at 80℃ to evaporate the alcohol, with ultrapure (UP) water continuously added during the process. After hydrolysis for three hours, 5-100mL of concentrated colloidal solution of nanosheet titanium acid prepared by hydrothermal method was added to the mixture, and the mixture was heated and stirred for another hour to hydrolyze it. After the reaction was complete, mixture A was obtained.

[0057] In addition, 4g of tetrabutyl titanate (TBOT) and 50g of isopropanol were mixed evenly, and 2.5g of hydrogen peroxide solution (H2O2, 30wt%) was slowly added dropwise to obtain mixture B after the reaction was complete.

[0058] Pour the mixture B (containing titanium) into the hydrolyzed system (mixture A), add 1g of nanocrystal seeds, and stir continuously for one hour to mix evenly. Then, put it into a stainless steel reactor lined with polytetrafluoroethylene, and place it in an oven to carry out a hydrothermal reaction at a hydrothermal reaction temperature of 175℃ for 6 to 12 hours.

[0059] In the hydrothermal synthesis system, the molar ratio of TEOS, TBOT, TBAOH, H2O2, and H2O is 1.00:0.03:0.23:0.06:2.0–10.0. The hydrothermal reaction temperature is 175℃, and the reaction time is 6–72 hours.

[0060] After the hydrothermal reaction is complete, the hydrothermal reaction product is stirred and centrifuged, washed until it is nearly neutral, and then dried in a 70°C constant temperature oven for 2 days. After calcination at 550°C for 5-6 hours, the white powdery target product—nanosheet titanate / zeolite heterostructure catalyst—is obtained.

[0061] The white product was identified as a MEL-type molecular sieve by XRD analysis, and the calculated product yields were all between 58% and 92%.

[0062] Yield calculation formula: n TiO2 n is the molar amount of TiO2. SiO2 M is the molar amount of SiO2; TiO2 M is the molar mass of TiO2, taken as 80 g / mol; SiO2 is the molar mass of SiO2, with a value of 60 g / mol; 0.85 is the average weight loss ratio after molecular sieve calcination.

[0063] In this invention, the nanocrystalline seeds and nanosheet titanate can be added together in the silicon-containing mixture, or they can be added separately, or the nanocrystalline seeds and nanosheet titanate can be added together after all the materials are mixed in sequence.

[0064] Example 1

[0065] Nanosheet-like titanic acid / TS-2 heterostructure catalysts were prepared by hydrothermal method. In the hydrothermal synthesis system, the molar ratio of TEOS, TBOT, TBAOH, H2O2 and H2O was 1.00:0.03:0.23:0.06:2.0 to 10.0.

[0066] 1) Mix 100g of TBAOH solution (25wt.%) with 87g of TEOS, then slowly add water in batches, adding a total of 100g UP of water throughout the mixing process. (Specifically, after mixing the TBAOH methanol solution with TEOS, the mixture will turn into a milky white liquid within a short time. At this point, heating and stirring are necessary. Heating is to remove alcohols from the system to prevent interference with the synthesis of molecular sieves, and to add water to promote hydrolysis while preventing evaporation.) Stir thoroughly at 80℃ for 6 hours to hydrolyze the mixture.

[0067] The TBAOH solution used here is a TBAOH / methanol solution with a TBAOH content of 25 wt.%. The TEOS used is an industrial grade product with a mass percentage of 90 wt.%.

[0068] 2) Take 5 mL of concentrated colloidal solution of nano-sheet titanic acid (based on the content of titanic acid converted to titanium dioxide, the TiO2 content is 10 wt.%, see Appendix). Figure 1 Add the mixture to the liquid obtained in step 1), and continue heating and stirring for 1 hour to hydrolyze and obtain a mixture A containing nanosheet titanium acid.

[0069] 3) Mix 50g isopropanol (IPA) and 4g TBOT evenly, place on a magnetic stirrer, and slowly add 2.5g H2O2 solution while stirring. The mixture is an orange-red transparent liquid. Continue stirring at 80℃ for 4 hours to obtain mixture B.

[0070] 4) Mix the two mixtures A and B evenly, add 1.0g of ordinary TS-2 seed crystals (particle size 120-300nm), continue heating and stirring for 1 hour, put it into a stainless steel reactor lined with polytetrafluoroethylene, and then place it in an oven, set the reaction temperature to 175℃, and carry out a hydrothermal reaction for 6 hours.

[0071] 5) Stir the hydrothermal reaction product and centrifuge it. Wash it until it is nearly neutral and then dry it in a constant temperature oven at 70℃ for 2 days. Then calcine it at 550℃ for 5-6 hours to obtain a white powder product with a mass of 18.71g.

[0072] The white product was analyzed by XRD (see attached). Figure 2 The product is a MEL-type molecular sieve, and the calculated product yield is 58%.

[0073] Comparative Example 1

[0074] The comparative example follows essentially the same procedure as Example 1, except that the synthesis solution for TS-2 zeolite prepared by hydrothermal method does not require the addition of nano-sheet titanic acid and seed crystals. The synthesis solution was placed in a stainless steel reactor lined with polytetrafluoroethylene, and then placed in an oven for a hydrothermal reaction at 175°C for 6 hours. The hydrothermal reaction product was stirred, centrifuged, washed until nearly neutral, and then dried in a 70°C oven for 2 days. It was then calcined at 550°C for 5-6 hours to remove the template agent from the zeolite, yielding a white powder product with a mass of 10.02 g. The calculated product yield was only 32%.

[0075] The white product was mainly composed of TS-2 molecular sieve, which was identified as a MEL-type molecular sieve by XRD analysis.

[0076] The difference between Comparative Example 1 and Example 1 lies in the fact that the former did not form a nanosheet-like titanic acid / TS-2 heterostructure, and the yield was significantly lower. This indicates that the addition of the nano-titanic acid dispersion helps to promote the synthesis of TS-2 zeolite.

[0077] Example 2

[0078] The implementation steps in this example are the same as in Example 1, except that 10 mL of nanosheet titanium acid (TiO2 content of 10 wt.%) and ordinary TS-2 seed crystals were added during the hydrothermal preparation of TS-2 molecular sieve. The mass of the obtained product was 19.84 g, and the calculated product yield was 60%. The main component of the obtained product was TS-2 molecular sieve, and the structure was a MEL-type molecular sieve, similar to that in Example 1.

[0079] Comparative Example 2

[0080] The comparative example follows essentially the same procedure as Example 2, except that the hydrothermal preparation of TS-2 molecular sieve does not require the addition of nano-sheet titanic acid; instead, only 1.0 g of ordinary TS-2 seed crystals are added, and the hydrothermal reaction time is 6 hours. The obtained product weighs 10.86 g, and the calculated yield is 31%. XRD analysis confirmed that the white product is a MEL-type molecular sieve.

[0081] This comparative example is basically the same as Example 2, except that ordinary seed crystals were added, but the yield was significantly lower than that of Example 2. This indicates that the nanosheet titanate in Example 2 can significantly promote the synthesis of TS-2 zeolite.

[0082] Example 3

[0083] The implementation steps in this embodiment are the same as in Example 1, except that 20 mL of nanosheet titanium acid and ordinary TS-2 seed crystals are added during the hydrothermal preparation of TS-2 molecular sieve. The mass of the obtained product is 21.79 g, and the calculated product yield is 64%. The main component of the obtained product is TS-2 molecular sieve, and the structure is a MEL-type molecular sieve, similar to that in Example 1.

[0084] Example 4

[0085] The implementation steps in this example are the same as in Example 1, except that 40 mL of nanosheet titanium acid and ordinary TS-2 seed crystals were added during the hydrothermal preparation of TS-2 molecular sieve. The mass of the obtained product was 25.69 g, and the calculated product yield was 71%. The main component of the obtained product was TS-2 molecular sieve, and the structure was a MEL-type molecular sieve, similar to that in Example 1.

[0086] Example 5

[0087] The implementation steps in this example are the same as in Example 1, except that the reaction time for preparing TS-2 molecular sieves by hydrothermal method is extended to 12 hours. The mass of the obtained product is 21.49 g, and the calculated product yield is 67%. The main component of the obtained product is TS-2 molecular sieve, and the structure is a MEL-type molecular sieve, similar to Example 1.

[0088] Example 6

[0089] The implementation steps in this example are the same as in Example 5, except that 10 mL of nanosheet titanium acid was added during the hydrothermal preparation of TS-2 molecular sieve. The mass of the obtained product was 26.02 g, and the calculated product yield was 79%. The main component of the obtained product was TS-2 molecular sieve, and the structure was a MEL-type molecular sieve, similar to Example 1.

[0090] Comparative Example 3

[0091] The comparative example follows essentially the same procedure as Example 6, except that 1.0 g of anatase nano-TiO2 (5-10 nm) was added during the hydrothermal preparation of TS-2 molecular sieve. The resulting product weighed 21.07 g. XRD analysis confirmed that the white product was a MEL-type molecular sieve, and the calculated yield was 64%.

[0092] SEM analysis (see appendix) Figure 3 As can be seen, in the comparative example group without the addition of nanosheet titanate dispersion, the product is a spherical aggregate with a significantly larger particle size than that of the example group with nanosheet titanate dispersion. This indicates that the nanosheet titanate dispersion has a significant effect on reducing the particle size of zeolite. Furthermore, although both Comparative Example 3 and Example 6 use TiO2 as the nucleation aid, the yield of the product obtained in this comparative example is significantly lower than that in Example 6. This indicates that, compared to anatase titanium dioxide, the structural characteristics of the nanosheet titanate in Example 6 are more conducive to heterogeneous nucleation.

[0093] Comparative Example 4

[0094] The comparative example follows essentially the same procedure as Example 6, except that 1.0 g of highly active TS-2 seed crystals (50-100 nm) is added instead of nanosheet titanium acid during the hydrothermal preparation of TS-2 molecular sieve. The resulting product weighed 25.27 g. XRD analysis confirmed that the white product was a MEL-type molecular sieve, and the calculated yield was 77%.

[0095] The difference between this comparative example and Example 6 lies in the nucleation agent. This comparative example uses highly active nano-TS-2 seed crystals, while Example 6 uses nano-sheet titanic acid. The yields of the obtained products are similar, indicating that nano-sheet titanic acid has high nucleation activity, consistent with that of the nano-seed crystals.

[0096] Comparative Example 5

[0097] The comparative example follows essentially the same procedure as Example 6, except that 1.0 g of ordinary TS-2 seed crystals were added instead of nanosheet titanium acid during the hydrothermal preparation of TS-2 molecular sieve. The obtained product weighed 12.65 g, with a calculated yield of 37%. XRD analysis confirmed that the white product was a MEL-type molecular sieve.

[0098] The difference between this comparative example and Example 6 lies in the nucleation agent. This comparative example uses ordinary TS-2 seed crystals, while Example 6 uses nanosheet titanium acid. The zeolite synthesis yield of this comparative example is significantly lower than the 79% in Example 6. This indicates that the nanosheet titanium acid in Example 6 can significantly improve the synthesis efficiency.

[0099] Comparative Example 6

[0100] The comparative example follows essentially the same steps as Example 6, except that nanosheet titanium acid is not required when preparing TS-2 molecular sieves via hydrothermal method, and the hydrothermal reaction time is 24 hours. The obtained product mass is 15.66 g, and the calculated product yield is 46%. XRD analysis of the white product indicates it to be a MEL-type molecular sieve.

[0101] Compared to Example 6, the synthesis yield of this comparative example was still significantly lower, while compared to Comparative Example 10, the synthesis yield was increased. This indicates that the nanosheet titanium acid in Example 6 can significantly improve the synthesis efficiency.

[0102] Comparative Example 7

[0103] The comparative example follows essentially the same steps as Example 6, except that nanosheet titanium acid is not required in the hydrothermal preparation of TS-2 molecular sieve, and the hydrothermal reaction time is 48 hours. The obtained product mass is 28.46 g, and the calculated product yield is 74%. XRD analysis of this white product indicates it to be a MEL-type molecular sieve.

[0104] Compared to Example 6, the synthesis yield of this comparative example is still relatively low, but it is higher than that of Comparative Example 6. This indicates that the nanosheet titanium acid in Example 6 can significantly improve the synthesis efficiency.

[0105] Comparative Example 8

[0106] The comparative example follows the same steps as Example 6, except that nanosheet titanium acid is not added during the hydrothermal preparation of TS-2 molecular sieve, and the hydrothermal reaction time is 72 hours. The obtained product weighs 32.04 g, and the calculated yield is 81%. XRD analysis confirmed that the white product is a MEL-type molecular sieve.

[0107] Compared to Example 6, the synthesis yield of this comparative example is similar, but the synthesis yield is increased. Under similar synthesis yield targets, the synthesis time in Example 6 was only 12 hours, while in this comparative example it was as long as 72 hours. This indicates that the nano-titanium sheet in Example 6 can significantly improve the synthesis efficiency, shortening the synthesis time from 72 hours to 12 hours.

[0108] Example 7

[0109] The implementation steps in this example are the same as in Example 5, except that 20 mL of nanosheet titanium acid was added during the hydrothermal preparation of TS-2 molecular sieve. The mass of the obtained product was 28.02 g, and the calculated product yield was 82%. The main component of the obtained product was TS-2 molecular sieve, and the structure was a MEL-type molecular sieve, similar to Example 1.

[0110] Example 8

[0111] The implementation steps in this example are the same as in Example 5, except that 40 mL of nanosheet titanium acid was added during the hydrothermal preparation of TS-2 molecular sieve. The mass of the obtained product was 31.21 g, and the calculated product yield was 85%. The main component of the obtained product was TS-2 molecular sieve, with a MEL-type molecular sieve structure, similar to Example 1.

[0112] Example 9

[0113] The implementation steps in this example are the same as in Example 5, except that 60 mL of nanosheet titanium acid was added during the hydrothermal preparation of TS-2 molecular sieve. The mass of the obtained product was 38.71 g, and the calculated product yield was 92%. The main component of the obtained product was TS-2 molecular sieve, similar to Example 1.

[0114] XRD characterization analysis showed that the product has good crystallinity and a MEL-type molecular sieve structure (see attached image). Figure 4 AC-TEM analysis revealed a nanosheet-like titanate / TS-2 heterostructure (see appendix). Figure 6 The elemental mapping results show the different distributions of titanium and silicon elements in the heterostructure: titanium elements are concentrated at the edges of the heterostructure, while silicon elements are concentrated at the center (see appendix). Figures 8-11 The XRF results confirmed the product's low silicon-to-titanium ratio (Si / Ti = 1:0.3), which met the research requirements.

[0115] Comparative Example 9

[0116] The procedures for this comparative example are basically the same as those for Comparative Example 1, except that the hydrothermal reaction time for preparing TS-2 molecular sieves is 12 hours. The procedures for this comparative example are basically the same as those for Example 5, except that nano-sheet titanium acid and seed crystals are not required when preparing TS-2 zeolite using the hydrothermal method. After the hydrothermal reaction, the product is centrifuged and thoroughly washed. The TS-2 product can be recovered after the pH drops to near neutral. The product is then slowly dried in a 70°C oven until it becomes pulverized. A white powder product with a mass of 11.53 g is obtained, and the calculated product yield is only 36%.

[0117] XRD characterization analysis showed that the product has good crystallinity and a MEL-type molecular sieve structure (see appendix). Figure 3 AC-TEM analysis revealed the structure of the TS-2 molecular sieve (see appendix). Figure 6 The elemental mapping results show that the titanium and silicon elements are basically distributed in the same position in the microstructure (see appendix). Figures 12-15 XRF results confirmed the product's high silicon-to-titanium ratio (Si / Ti = 1:0.05).

[0118] Comparative Example 10

[0119] The comparative example was carried out in accordance with the same procedures as Examples 5 and 9, except that the preparation of TS-2 zeolite by hydrothermal method did not require the addition of nano-sheet titanate and ordinary TS-2 seed crystals, and the hydrothermal reaction time for the preparation of TS-2 molecular sieve by hydrothermal method was 24 hours. The mass of the obtained product was 14.10 g, and the calculated product yield was 44%. The obtained white product was identified as a MEL-type molecular sieve by XRD analysis, and the silicon-to-titanium ratio was 1:0.05 by XRF analysis.

[0120] Comparative Example 11

[0121] The comparative example follows the same steps as Examples 5 and 9, except that nano-sheet titanate and ordinary TS-2 seed crystals are not added during the hydrothermal preparation of TS-2 zeolite, and the hydrothermal reaction time for TS-2 molecular sieve preparation is 48 hours. The obtained product mass is 28.01 g, and the calculated product yield is 74%.

[0122] Compared with Example 9, the synthesis time of this comparative example was extended to 48 hours, but the synthesis yield was still significantly lower.

[0123] Comparative Example 12

[0124] The comparative example follows the same steps as Examples 5 and 9, except that nano-sheet titanate and ordinary TS-2 seed crystals are not added during the hydrothermal preparation of TS-2 zeolite, and the hydrothermal reaction time for TS-2 molecular sieve preparation is 72 hours. The obtained product mass is 30.48 g, and the calculated product yield is 80%.

[0125] Compared with Example 9, the synthesis time of this comparative example was extended to 72 hours, but the synthesis yield was still significantly lower, significantly lower than 92% in Example 9.

[0126] Comparative Example 13

[0127] The comparative example follows the same steps as Examples 5 and 9, except that when preparing TS-2 zeolite via hydrothermal method, nano-sheet titanate and ordinary TS-2 seed crystals are not added; instead, 6g of ordinary TS-2 seed crystals are added. The obtained product mass is 29.79g, and the calculated product yield is 78%.

[0128] Compared to Example 9, this comparative example introduced the same mass of nucleation aid, but the synthesis yield of the former was significantly lower than that of the latter. This indicates that the promoting effect of ordinary TS-2 seeds in this comparative example on the synthesis is still lower than that of titanate nanosheets in Example 9.

[0129] Example 10

[0130] The procedures in this example are the same as in Example 1, except that 80 mL of nanosheet titanium acid was added during the hydrothermal preparation of TS-2 molecular sieve, and the reaction time was extended to 12 hours. The mass of the obtained product was 30.82 g, and the calculated product yield was 76%. The main component of the obtained product was TS-2 molecular sieve. The structure was a MEL-type molecular sieve, similar to that in Example 1.

[0131] Example 11

[0132] The implementation steps in this example are the same as in Example 1, except that 100 mL of nanosheet titanium acid was added during the hydrothermal preparation of TS-2 molecular sieve, and the reaction time was extended to 12 hours. The mass of the obtained product was 31.30 g, and the calculated product yield was 72%. The main component of the obtained product was TS-2 molecular sieve. The structure was a MEL-type molecular sieve, similar to that in Example 1.

[0133] Example 12

[0134] The implementation steps in this example are the same as in Example 9, but it is a scaled-up experiment (magnification of 10x). The mass of the obtained product is 345g, and the calculated product yield is 91%. The main component of the obtained product is TS-2 molecular sieve. The structure is a MEL-type molecular sieve, similar to that in Example 1. TEM analysis shows that the product sample of this scaled-up experiment has a nanosheet-like titanate / TS-2 heterostructure (see Appendix). Figure 18 This indicates that the heterostructure was well preserved during the scale-up experiment.

[0135] The experimental conditions and results for each embodiment and comparative example are shown in the table below:

[0136] The "dosage" column in the table means that x mL of nanosheet titanate was used in this example group / comparative group, which is equivalent to y g of TiO2.

[0137]

[0138] Based on the data in the table, it can be seen that the specific steps of Example 1 and Comparative Example 1 are the same, the difference being that Comparative Example 1 does not include the addition of nanosheet-shaped titanic acid nucleating agent. The comparative results show that the advantage of Example 1 lies in utilizing the nucleation effect of the nanosheet-shaped titanic acid, which can significantly improve the yield of molecular sieves. The nanosheet-shaped titanic acid plays a heterogeneous nucleation role in the hydrothermal synthesis of molecular sieves, leading to the rapid synthesis of molecular sieves. During the hydrothermal synthesis process, the nanosheet-shaped titanic acid lowers the nucleation energy barrier of the molecular sieves, greatly shortening the nucleation process and significantly increasing the yield of molecular sieves (58-92%).

[0139] The specific steps of Example 1 are the same as those of Examples 2, 3, and 4, the difference being the amount of nanosheet titanate used. A certain dosage gradient was used to analyze the product to investigate the effect of the amount of nanosheet titanate on the synthesis reaction. A comparison of Example 1 with Examples 2, 3, and 4 shows that, under a hydrothermal reaction time of six hours, increasing the amount of nanosheet titanate significantly promotes the crystallization of TS-2 molecular sieves and reduces the silicon-to-titanium ratio of the molecular sieve.

[0140] Examples 5 and 11 follow the same steps as Examples 6, 7, 8, 9, 10, and 11, differing only in the amount of nanosheet titanate used. Examples 5-11 not only extended the hydrothermal reaction time compared to Examples 1-4, but also further expanded the gradient in the amount of nanosheet titanate used. It was found that the yield of the examples with higher amounts reached 92% (Example 9), and the silicon-to-titanium ratio was also reduced. TEM and mapping images revealed a unique structure in the nanosheet titanate / TS-2 molecular sieve heterostructure: the surface of the TS-2 molecular sieve aggregates was coated with nanosheet titanate. Thanks to this heterostructure, the microstructure of the TS-2 aggregates was controlled, the titanium content was significantly increased, and there were no obvious byproducts or other impurities in the product. The above comparative results show that appropriately extending the hydrothermal reaction temperature and time is beneficial for the complete crystallization of the titanium-silicon molecular sieve and has a significant effect on reducing the silicon-to-titanium ratio.

[0141] Example 9 follows the same steps as Comparative Examples 3, 4, 9, and 13, except that Comparative Examples 3, 4, 9, and 13 do not include nanosheet-shaped titanate nucleating agents; instead, different heterogeneous nucleating agents are introduced (Comparative Example 9 is a blank control group). The comparative results show that, regardless of whether anatase titanium dioxide, nano-TS-2 seeds, or even an excessive amount of nano-TS-2 seeds are used, the synthesis yield and the titanium-to-silicon ratio of the product are both weaker than the experimental group with nanosheet-shaped titanate under the same conditions. The advantage of nanosheet-shaped titanate lies in its nanosheet structure, which plays a unique heterogeneous nucleation role, not only improving the synthesis yield and rate of molecular sieves but also significantly reducing the silicon-to-titanium ratio of the synthesized product. Furthermore, nanosheet-shaped titanate has a regulatory effect on the microstructure of TS-2.

[0142] Example 9 follows the same steps as Comparative Examples 1, 9, 10, 11, and 12, except that Comparative Examples 1, 9, 10, 11, and 12 do not include nanosheet titanate nucleating aids or ordinary TS-2 seed crystals. Instead, the effect of nanosheet titanate on the synthesis yield is verified by increasing the hydrothermal reaction time. The results show that in the comparative experimental group without nanosheet titanate and ordinary TS-2 seed crystals, the product yield gradually increases with increasing hydrothermal reaction time. At a hydrothermal reaction time of three days, the product yield is only close to that of Example 6 when 10 mL of nanosheet titanate was added. Furthermore, the increase in hydrothermal reaction time did not affect the silicon-to-titanium ratio of the product. This further demonstrates the superiority of nanosheet titanate for the rapid synthesis of TS-2 molecular sieves.

[0143] Example 9 follows the same steps as Comparative Examples 2, 5, 6, 7, and 8, except that Comparative Examples 2, 5, 6, 7, and 8 do not include nanosheet titanate nucleating agents. Instead, the effect of ordinary TS-2 seeds on the synthesis yield is verified by increasing the hydrothermal reaction time. The results show that in the control group without nanosheet titanate, the product yield gradually increases with increasing hydrothermal reaction time. At a hydrothermal reaction time of three days, the product yield is only close to that of Example 6 with 10 mL of nanosheet titanate. Furthermore, the increase in hydrothermal reaction time does not affect the silicon-to-titanium ratio of the product. No significant difference in yield was found compared to Comparative Examples 1, 2, 10, 11, and 12. This set of control experiments further demonstrates the superiority of nanosheet titanate for the rapid synthesis of TS-2 molecular sieves.

[0144] Through the above comparisons, two essential conditions were identified for the formation of high-purity nanosheet titanate / TS-2 molecular sieve heterostructures with low silicon-to-titanium ratios using the hydrothermal method: appropriate hydrothermal reaction time and the amount of nanosheet titanate used. These two conditions together determine the high yield of TS-2 molecular sieves. The amount of nanosheet titanate used controls the silicon-to-titanium ratio of the TS-2 molecular sieve during synthesis, while also regulating and limiting its microstructure and size.

[0145] The difference between Examples 1 and 5 lies in the hydrothermal reaction time, while both yielded similar nanosheet-like titanate / TS-2 molecular sieve heterostructures under the same hydrothermal reaction time. However, their yields differed significantly. This indicates that at a given reaction temperature, a longer hydrothermal reaction time results in a higher yield of the nanosheet-like titanate / TS-2 molecular sieve heterostructure at 175°C.

[0146] Examples 5, 6, 7, 8, 9, 10, 11, and 12, using the same hydrothermal reaction conditions, determined the optimal amount of nanosheet titanate required for preparing the nanosheet titanate / TS-2 molecular sieve heterostructure. Notably, adding 60 mL of nanosheet titanate resulted in a silicon-to-titanium ratio of 1:0.30 for the nanosheet titanate / TS-2 molecular sieve, a five-fold improvement compared to the experimental group without nanosheet titanate. Furthermore, Example 12, as a scale-up experiment, demonstrated the reproducibility of this experimental scheme and its feasibility for future industrialization.

[0147] The nanosheet-like titanate / zeolite heterostructure product obtained in this invention has a silicon-to-titanium ratio of no more than 1:0.04. Preferably, the silicon-to-titanium ratio of the product is less than 1:0.05. More preferably, the silicon-to-titanium ratio of the product is 1:0.06 to 1:0.34.

[0148] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0149] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for preparing a nanosheet-like titanic acid / TS-2 heterostructure catalyst, characterized in that, The specific process of this preparation method is as follows: The first step is to prepare nanosheet-like titanic acid. The specific process is as follows: tetrabutyl titanate, isopropanol and triethanolamine are mixed in proportion and stirred thoroughly. Then, tetrabutylammonium hydroxide solution is added and stirred until homogeneous. Finally, hydrogen peroxide solution, a complexing agent, is slowly added and stirred until homogeneous. The mixture is then placed in a reactor for hydrothermal reaction. After hydrothermal reaction, the mixture is dialyzed with deionized water and evaporated and concentrated to obtain a concentrated colloidal solution of nanosheet-like titanic acid, which is then bottled for later use. In the synthetic system for preparing nanosheet-like titanic acid, the molar ratio of the relevant reactants is: tetrabutylammonium hydroxide: tetrabutyl titanate: hydrogen peroxide: triethanolamine: isopropanol = 1.0: 2.0: 2.0: 6.0: 8.0; The second step involves preparing nanosheet-like titanic acid / zeolite heterostructure catalysts via a hydrothermal method. The specific process is as follows: Tetrabutylammonium hydroxide solution is mixed with tetraethyl orthosilicate and stirred thoroughly at 60-80℃ to evaporate alcohol. During the evaporation process, ultrapure water is continuously added to the system. After complete hydrolysis, the concentrated colloidal solution of nanosheet-like titanic acid prepared in the first step is added, and after a complete reaction, a mixture A is obtained. Tetrabutyl titanate and isopropanol were mixed evenly, and hydrogen peroxide solution was slowly added dropwise to the mixture. After the reaction was complete, mixture B was obtained. Mixtures A and B thoroughly, then add TS-2 nanocrystals and stir until homogeneous. The mixture is then placed in a reactor for hydrothermal reaction at 160-180℃ for 6-72 hours. In the synthesis system for preparing nanosheet-like titanate / zeolite heterostructure catalysts, the molar ratio of the relevant reactants is: tetrabutyl orthosilicate: tetrabutylammonium titanate: hydrogen peroxide: ultrapure water = 1.0:0.03:0.23:0.06:2.0~10.0; After repeated centrifugation and washing until neutral, the product was dried in a constant temperature oven to obtain a white experimental product. The experimental product was placed in a muffle furnace and calcined at 550°C for 5-6 hours to obtain a nanosheet-like titanic acid / TS-2 heterostructure catalyst. The tetrabutylammonium hydroxide solution used to prepare nanosheet titanic acid was an aqueous solution, while the tetrabutylammonium hydroxide solution used to prepare the nanosheet titanic acid / zeolite heterostructure catalyst was a methanol solution; the mass percentage of tetrabutylammonium hydroxide in both template solutions was 25 wt.%; the particle size range of TS-2 nanocrystals was 120-300 nm.

2. The preparation method according to claim 1, characterized in that, The concentrated colloidal solution of nanosheet titanic acid contains 9-10 wt.% titanic acid as TiO2. In the second step, the amount of concentrated colloidal solution of nanosheet titanic acid added is 5-100 mL / 87 g tetraethyl orthosilicate.

3. The preparation method according to claim 1, characterized in that, The hydrothermal reaction temperature and the optimal time at that temperature in the second step are 175℃-12h, 160℃-24h, and 180℃-6h, respectively.

4. A nanosheet-like titanate / zeolite heterostructure catalyst, characterized in that, The nanosheet titanic acid / zeolite heterostructure catalyst, obtained by any one of the preparation methods described in claims 1-3, possesses a unique heterostructure: a large number of nanosheet titanic acid spiky structures are coated around the molecular sieve.

5. The catalyst according to claim 4, characterized in that, In the nanosheet-like titanate / zeolite heterostructure catalyst, titanium is concentrated at the edge of the heterostructure, while silicon is concentrated at the center, with a silicon-to-titanium ratio of Si / Ti = 1:0.06-0.

4.

6. The catalyst according to claim 5, characterized in that, The silicon-to-titanium ratio is 1:0.15-0.4.

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