CN112978748A

CN112978748A - TS-1 molecular sieve with macroporous-microporous composite pore channel structure, and preparation method and application thereof

Info

Publication number: CN112978748A
Application number: CN201911283725.5A
Authority: CN
Inventors: 张晓敏; 许磊; 李沛东; 赵晓炜
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2019-12-13
Filing date: 2019-12-13
Publication date: 2021-06-18
Anticipated expiration: 2039-12-13
Also published as: CN112978748B

Abstract

The application discloses a TS-1 molecular sieve with a macroporous-microporous composite pore channel structure, wherein macropores and micropores are embedded in the TS-1 molecular sieve, and the pore diameter of the macropores is 50-500 nm. The product obtained by the method has the advantages of excellent single crystal stability and a mutually-communicated macroporous-microporous composite pore channel structure, the titanium content of the product can be controllably adjusted in a wider range, the product shows excellent catalytic performance in olefin epoxidation reaction, and the defect of a single microporous system is relieved.

Description

TS-1 molecular sieve with macroporous-microporous composite pore channel structure, and preparation method and application thereof

Technical Field

The application relates to a TS-1 molecular sieve with a macroporous-microporous composite pore channel structure, a preparation method and application thereof, belonging to the technical field of catalyst synthesis.

Background

In 1983, Taramasso et al (U.S. Pat. No. 4,4410501,1983, 10, 18), the Italian scientist, for the first time, reported a method for preparing Titanium Silicalite molecular sieves of Titanium Silicalite-1(TS-1) having an MFI topology. The isolated four-coordinate titanium atom in the TS-1 molecular sieve framework structure has a unique catalytic oxidation function, and meanwhile, the TS-1 molecular sieve has high hydrothermal stability and certain hydrophobicity, so that the TS-1 molecular sieve has the characteristics of high activity and selectivity, easiness in separation of a catalyst and the like in a catalytic system in the presence of a water-soluble oxidant. The development and application of the TS-1 molecular sieve extend the application of the molecular sieve from the field of acid catalysis to the field of liquid phase selective oxidation, and therefore is called a milestone in the field of molecular sieve catalysis. The microporous pore channel of the traditional molecular sieve is small, so that the diffusion rate of materials in the pore channel of the molecular sieve is limited on one hand; on the other hand, guest molecules with larger molecular diameter cannot enter the molecular sieve pore channels to contact with the catalyst active center, resulting in poor catalytic activity of the molecular sieve in catalytic macromolecular reactions (chem.rev.,2006,106, 896-910).

In order to solve this problem, attempts have been made to introduce mesopores or macropores into the existing molecular sieve to improve its diffusion properties. Due to the combination of strong acidity, high hydrothermal stability, excellent shape selectivity and good diffusion performance of mesoporous/macroporous channels of microporous molecular sieves, the synthesis of hierarchical composite molecular sieves has become a current research hotspot (Nano Today,2009,4, 292-.

At present, the methods for synthesizing the hierarchical pore molecular sieve can be divided into a post-treatment method and a direct synthesis method. The direct synthesis method can be divided into a hard template method and a soft template method according to the template used. For example, Zhang et al prepared ZSM-5 materials with a micropore-mesopore diplopore distribution by heat treating a ZSM-5 molecular sieve at high temperature (micro. meso. mater.,2003,62, 157-. The post-treatment method is simple to operate and has obvious effect, but the method is only effective for the molecular sieve with a specific structure or composition. On the other hand, the crystallinity of the molecular sieve is reduced after treatment, and the catalytic active center can be damaged. The direct synthesis method is to add a secondary template agent in the process of synthesizing the molecular sieve and introduce a mesoporous or macroporous structure into the molecular sieve by utilizing the template agent. With the continuous expansion of the types of the template agents, the direct synthesis method becomes a more effective way for preparing the hierarchical pore molecular sieve at present. Xiao et al (Angew. chem. int. Ed.,2006,45, 3090-3093; Ind. Eng. chem. Res.,2014,53, 13903-13909; Chin. J. Catal.,2011,32,1656-1661) have achieved the synthesis of hierarchical pore Beta, ZSM-5 and TS-1 using mixed templating agents of cationic polymers and conventional quaternary ammonium salts. The Ryoo topic group synthesizes hierarchical pore molecular sieves with polyquaterniums having different numbers of quaternary ammonium groups (Nat. Mater.,2006,5, 718-723; Nature,2009,461, 246-250; Science,2011,333, 328-332). Most of the secondary template agents are difficult to obtain, and more manpower and material resources are needed to synthesize the secondary template before the hierarchical pore molecular sieve is synthesized, so that the production cost for preparing the hierarchical pore molecular sieve by a direct synthesis method is higher. On the other hand, most of the pore channel structures of the products obtained by the synthesis method are formed by compounding mesopores and micropores, the improvement of the molecular sieve diffusion performance is limited, and particularly in a liquid phase reaction system, the multi-level pore channel structure formed by compounding the mesopores and the micropores cannot effectively improve the diffusion efficiency of the guest molecules in the molecular sieve pore channels.

Therefore, it is necessary to provide a TS-1 molecular sieve having a macroporous-microporous composite pore channel structure and a corresponding preparation method thereof.

Disclosure of Invention

According to one aspect of the application, the TS-1 molecular sieve with the macroporous-microporous composite pore channel structure is provided, the TS-1 molecular sieve has micropores and interconnected macropores at the same time, and shows excellent catalytic performance in olefin epoxidation reaction, and the defect of a single microporous system is relieved.

The TS-1 molecular sieve with the macroporous-microporous composite pore channel structure is characterized in that mutually communicated macropores are embedded in the TS-1 molecular sieve, and the pore diameter of each macropore is 50-500 nm.

Optionally, the pores have a pore size of less than 2 nm.

Alternatively, the upper limit of the pore size of the macropores is 60nm, 80nm, 100nm, 120nm, 150nm, 200nm, 300nm, 350nm, 400nm, 450nm, 500 nm.

Alternatively, the lower limit of the pore size of the macropores is 50nm, 80nm, 100nm, 120nm, 150nm, 200nm, 300nm, 350nm, 400nm, 450 nm.

According to another aspect of the present application, there is also provided a method for preparing the TS-1 molecular sieve having a macroporous-microporous composite channel structure, the method comprising: 1) reacting a silicon source and a titanium source in an alkaline system to obtain a titanium dioxide/silicon composite material; 2) adding the titanium dioxide/silicon composite material obtained in the step 1) into a solution containing a structure directing agent II, and drying to obtain an initial synthesis mixture; 3) crystallizing the initial synthesis mixture of step 2) using a steam assisted process; 4) and (3) separating and roasting the reaction product obtained in the step 3) to obtain the TS-1 molecular sieve.

Optionally, in step 1), the order of adding the silicon source and the titanium source is: firstly, adding a silicon source into the alkaline system, and adding a titanium source after 5-240min of interval.

Optionally, the alkaline system in the step 1) contains a structure directing agent I, wherein the structure directing agent I is a cationic surfactant.

Optionally, the structural formula of the cationic surfactant is shown as formula I;

wherein R is₁，R₂，R₃Independently selected from C₁～C₅Alkyl groups of (a); r₄Is selected from C₈～C₂₀Alkyl groups of (a); x^-Is selected from Br^-、Cl^-Or OH^-。

Optionally, the structure directing agent i is selected from at least one of dodecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide or octadecyl trimethyl ammonium bromide.

Optionally, the alkaline system in step 1) contains at least one of ammonia or sodium hydroxide solution; the pH value of the alkaline system is between 9 and 12.

Optionally, the silicon source in step 1) is selected from at least one of methyl orthosilicate, ethyl orthosilicate, silica sol and sodium silicate; the titanium source is at least one selected from tetraethyl titanate, tetrabutyl titanate, isopropyl titanate, titanium trichloride and titanium tetrachloride.

Alternatively, the structure directing agent i: silicon source: the titanium source is 0.005-1.0:1: 0.001-0.05.

In the present application, the silicon source is in terms of moles of silicon element contained therein, the titanium source is in terms of moles of titanium element contained therein, and the structure directing agent I is in terms of moles of itself.

In the present application, the titanium dioxide/silicon composite material refers to homogeneous titanium silicon spheres.

Alternatively, structure directing agent i: the silicon source may have a molar ratio of 0.005:1.0, 0.006:1.0, 0.007:1.0, 0.008:1.0, 0.009:1.0, 0.01:1.0, 0.02:1.0, 0.03:1.0, 0.04:1.0, 0.05:1.0, 0.06:1.0, 0.07:1.0, 0.08:1.0, 0.09:1.0, 0.10:1.0, 0.11:1.0, 0.12:1.0, 0.13:1.0, 0.14:1.0, 0.15:1.0, 0.16:1.0, 0.17:1.0, 0.18:1.0, 0.19:1.0, 0.2:1.0, 0.3:1.0, 0.4:1.0, 0.5:1.0, 0.1.9: 1.0, 0.9:1.0, 0, and any ratio therebetween.

Optionally, the silicon source: the molar ratio of the titanium source is 1:0.001, 1:0.002, 1:0.003, 1:0.004, 1:0.005, 1:0.006, 1:0.007, 1:0.008, 1:0.009, 1:0.01, 1:0.011, 1:0.012, 1:0.013, 1:0.014, 1:0.015, 1:0.016, 1:0.017, 1:0.018, 1:0.019, 1:0.02, 1:0.022, 1:0.025, 1:0.028, 1:0.030, 1:0.04, 1:0.05 and ranges between any two ratios.

Optionally, the reaction temperature of the reaction in step 1) is 30-100 ℃; the reaction time is 1-12 h.

Optionally, the titanium dioxide/silicon composite material is spherical or ellipsoidal, and the average particle size is 100-500 nm.

Alternatively, the titanium dioxide/silicon composite has an average particle size of

Optionally, the structure directing agent ii is selected from at least one of tetraethylammonium hydroxide, tetrapropylammonium bromide and tetrapropylammonium chloride.

Optionally, the molar ratio of silicon in the titanium dioxide/silicon composite material in the step 2) to the structure directing agent II is 1: 0.05-0.5.

Optionally, the molar ratio of silicon in the titanium dioxide/silicon composite material in step 2) to the structure directing agent ii is 1:0.05, 1:0.1, 1:0.15, 1:0.20, 1:0.25, 1:0.30, 1:0.35, 1:0.40, 1:0.45, 1:0.50, and ranges between any two ratios.

Optionally, the molar ratio of silicon in the titanium dioxide/silicon composite material in the step 2) to the structure directing agent II is 1: 0.05-0.15.

Optionally, the step 1) further comprises filtering, drying and roasting the reaction product after the reaction.

Optionally, the crystallization reaction in step 3) comprises: placing the initial synthesis mixture in the step 2) into a closed reactor, and carrying out crystallization reaction on the initial synthesis mixture in the presence of water vapor.

Optionally, the temperature of the crystallization reaction is 100-.

Optionally, the temperature of the crystallization reaction is 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃,200 ℃ and a range between any two values.

Optionally, the crystallization reaction time is 12h, 20h, 24h, 30h, 40h, 50h, 60h, 70h, 72h, 80h, 90h, 96h, 100 h.

Optionally, the roasting temperature in the step 4) is 400-700 ℃, and the roasting time is 2-8 hours.

According to another aspect of the application, the application of the TS-1 molecular sieve with the macroporous-microporous composite pore channel structure as a catalyst in the epoxidation reaction of olefin is also provided.

The beneficial effects that this application can produce include:

1) firstly, synthesizing amorphous titanium dioxide/silicon nanospheres in an alkaline system, and solving the problems of difficult introduction of framework titanium and low content of framework titanium. In the synthesis step, the introduction amount of titanium can be adjusted in a wider range, and a foundation is laid for synthesizing TS-1 molecular sieves with different titanium contents.

2) The synthesis method provided by the invention uses mesoporous titanium dioxide/silicon with a specific morphology as a precursor, and directly converts the precursor into the macroporous-microporous composite TS-1 molecular sieve by using a steam assisted conversion method in a water vapor atmosphere through dipping a structure directing agent II. The method is simple and feasible, has low cost, can adjust the titanium content of the molecular sieve in a wide range, does not need expensive mesoporous or macroporous organic template agents, reduces the production cost of the hierarchical pore TS-1 molecular sieve, and lays a foundation for large-scale industrial application

3) The TS-1 molecular sieve with the macroporous-microporous composite pore channel structure has the characteristics of high activity, good shape selectivity and high hydrothermal stability of a microporous molecular sieve, and the mutually communicated macroporous channels of the molecular sieve have good heat and mass transfer capacity, are favorable for a reaction system with macromolecules participating, and have excellent catalytic performance when being used as a catalyst in olefin epoxidation reaction. The TS-1 molecular sieve prepared by the invention has micropores and mutually communicated macropores simultaneously, and the defect of a single micropore system is relieved.

4) The crystallization process adopted by the invention is a steam-assisted crystallization method, the titanium silicon precursor is not directly contacted with the aqueous solution in the crystallization process, the steam generated by the aqueous solution and the titanium silicon precursor are subjected to crystallization reaction in the crystallization kettle to further generate the TS-1 molecular sieve, the process is simple to operate, the using amounts of the template agent and the aqueous solvent are saved, and the aqueous solution can be recycled. The method can effectively utilize raw materials and save production cost.

5) The product obtained by the method has the advantages of excellent stability of single crystal and a mutually communicated macroporous-microporous composite pore channel structure, and the titanium content of the product can be controllably adjusted in a wider range.

6) Because the hydrolysis speeds of the titanium source and the silicon source are different, in the invention, the silicon source is added into the system at first, and the titanium source is added after the interval of 5-240min, so that the introduction amount of the titanium source can be increased, and the distribution of Ti species can be controlled.

Drawings

FIG. 1 is an SEM photograph of samples MTS-I to III prepared in example 1.

Fig. 2 is an XRD spectrum of samples HTS-1 to HTS-6 prepared in example 2.

Fig. 3 is an SEM image of samples HTS-1 to HTS-6 prepared in example 2.

Detailed Description

The present invention is further described with reference to the following drawings and examples, but the present invention is not limited to the following examples, and all similar structures and similar variations of the present invention are included in the scope of the present invention.

The raw material reagents used in the examples were all obtained commercially and used without any special treatment.

The product was subjected to morphological analysis using a scanning electron microscope (model: JSM-7800F).

The product was subjected to diffraction analysis using an X-ray diffractometer (model: PANalytical X' Pert Pro).

The Ti content of the product was measured on an ICP-OES (Optima8000 spectrometer).

EXAMPLE 1 preparation of amorphous mesoporous titanium oxide/silicon spheres MTS-I to MTS-V

Preparation of sample MTS-I:

under the condition of stirring at 50 ℃, 0.20g of hexadecyl trimethyl ammonium bromide (structure directing agent I) is dissolved in 60mL of deionized water and ethanol solution, then ammonia water is added into the solution to adjust the pH value of the solution, 1.0g of ethyl orthosilicate is added after stirring, 0.05g of tetrabutyl titanate is added after 30min, and the stirring is continued for 2 h. And (3) filtering, washing and drying the product, and then removing the structure directing agent I by roasting, wherein the roasting temperature is 550 ℃, and the roasting time is 6 hours, so that white powder is obtained. I.e. amorphous titanium dioxide/silicon spheres, labelled MTS-I.

Preparation of samples MTS-II, MTS-III, MTS-IV, MTS-V:

samples MTS-II and MTS-III were prepared according to the conditions listed in Table 1 below, respectively, in a manner substantially similar to that of sample MTS-I, except as listed in Table 1, and otherwise identical to that of sample MTS-I.

The correspondence between the sample numbers and the preparation conditions is shown in table 1.

TABLE 1 mesoporous Titania/Si Synthesis conditions and Performance parameter Table

SEM characterization of the samples was performed, as shown typically in FIG. 1, and FIG. 1 is a SEM image of samples MTS-I-III prepared in example 1. Wherein, I, II, III in FIG. 1 are SEM images of samples MTS-I, MTS-II, III, respectively.

SEM results show that the obtained product has uniform particle size and good dispersibility, and is a spherical material with the size between 100nm and 500 nm. Considering that the SEM pictures of the samples MTS-V, MTS-VI are substantially similar to the SEM pictures of the sample MTS-I, the sizes are all between 100nm and 500nm, and thus are not shown.

Example 2: preparation of samples HTS-1 to HTS-8

Firstly, adding the structure directing agent II into deionized water, and stirring and dissolving to obtain a mixed solution. A quantity of the above solution was taken to impregnate the amorphous titanium dioxide/silica spheres prepared in example 1, and the solid mixture was obtained after drying at room temperature for a period of time. And transferring the solid mixture to a flat disc at the upper part of a stainless steel high-pressure reaction kettle, and adding water into the bottom of the reaction kettle. Sealing the stainless steel reaction kettle, putting the stainless steel reaction kettle into an oven, and crystallizing the stainless steel reaction kettle for 12 to 100 hours at the temperature of 100 to 200 ℃. And after the reaction is finished, quickly cooling, separating a solid product, washing with deionized water, drying at 110 ℃ in an air atmosphere, and roasting at 550 ℃ for 6 hours to obtain the nano TS-1 molecular sieve. The samples were labeled HTS-1 to HTS-8. The types and proportions of raw materials, crystallization temperatures and crystallization times of the prepared samples HTS-1 to HTS-8, particle size of the prepared samples and Ti element content are respectively shown in Table 2.

TABLE 2 Table of synthetic ingredients, crystallization conditions and particle size of product for TS-1 molecular sieve

Note: the material ratio in table 2 refers to titanium dioxide/silicon-in-silicon: and (3) a structure directing agent II: molar ratio of deionized water

XRD characterization was performed on the prepared samples, and since the XRD patterns of HTS-7 and HTS-8 are similar to those of HTS-1, the main diffraction peak positions and shapes are the same, and the relative peak intensities fluctuate within ± 5% depending on the synthesis conditions, they are not shown. Typically, the result is shown in fig. 2, the XRD patterns of the samples HTS-1 to HTS-6 are consistent with the characteristic pattern of the standard MFI molecular sieve, the positions and shapes of the main diffraction peaks are the same, the intensity of the diffraction peaks is higher, and the crystallization is good, which indicates that the samples HTS-1 to HTS-6 are TS-1 molecular sieves.

Scanning electron microscope characterization is carried out on the prepared typical samples HTS-1 to HTS-6 by adopting a JSM-7800F type high resolution scanning electron microscope, and SEM images of HTS-7 and HTS-8 are similar to that of HTS-1 and are not shown. As shown in FIG. 3, all samples are crystal grains with uniform nano-size distribution, and have macroporous and microporous structures, and the size of each macroporous is 50-500 nm.

Example 3: evaluation of epoxidation reaction of 1-hexene

The TS-1 sample is synthesized by adopting the traditional hydrothermal method in the experiment, and the proportion of the synthesized gel is 1SiO₂:0.25TPAOH:0.02TiO₂:35H₂And O. The preparation method comprises the following specific gel preparation steps: firstly, adding tetrapropylammonium hydroxide (TPAOH) into deionized water at room temperature and stirring; slowly adding a certain amount of ethyl orthosilicate and butyl titanate after the materials are fully dissolved; stirring at room temperature for 24 hr, transferring the material to a stainless steel synthesis kettle, and crystallizing at 150 deg.C for 24 hr. The obtained solid product is centrifuged and washed, then dried at 110 ℃ overnight, and finally roasted at 550 ℃ for 6h to remove the organic template, which is named as conv-TS-1.

The prepared conv-TS-1 and the nano TS-1 molecular sieve prepared in the example 2 are subjected to the epoxidation evaluation of 1-hexene. The reaction evaluation comprises the following specific steps: 0.05g of the sample, 1.0g of 1-hexene, 0.375g of H were weighed₂O₂Was charged into a 50mL round-bottom flask, and then 10mL of acetonitrile solvent was added thereto. The reaction is carried out for 2h at the temperature of 60 ℃. After the reaction was stopped, the solid catalyst was filtered off, and the reaction solution was analyzed by gas chromatography. The conversion of 1-hexene and the selectivity to cyclohexene oxide are shown in table 3. Comparative conv-TThe results of the S-1 sample and the HTS-1 to HTS-8 samples show that the catalytic activity of the TS-1 molecular sieve prepared by the method for catalyzing the epoxidation reaction of 1-hexene is obviously higher than that of the TS-1 molecular sieve synthesized by the traditional hydrothermal method.

TABLE 3 result of epoxidation reaction of 1-hexene catalyzed by TS-1 molecular sieve

Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.

Claims

1. The TS-1 molecular sieve with the macroporous-microporous composite pore channel structure is characterized in that macropores and micropores are embedded in the TS-1 molecular sieve, and the pore diameter of the macropores is 50-500 nm.

2. The method for preparing the TS-1 molecular sieve with the macroporous-microporous composite pore channel structure according to claim 1, wherein the method comprises the following steps:

1) reacting a silicon source and a titanium source in an alkaline system to obtain a titanium dioxide/silicon composite material;

2) adding the titanium dioxide/silicon composite material obtained in the step 1) into a solution containing a structure directing agent II, and drying to obtain an initial synthesis mixture;

3) crystallizing the initial synthesis mixture in step 2) by using a steam-assisted crystallization method;

4) and (3) separating and roasting the reaction product obtained in the step 3) to obtain the TS-1 molecular sieve.

3. The method according to claim 1, wherein the silicon source and the titanium source are added in the order of step 1): firstly, adding a silicon source into the alkaline system, and adding a titanium source after 5-240min of interval.

4. The preparation method according to claim 1, wherein the alkaline system in step 1) contains a structure-directing agent I, wherein the structure-directing agent I is a cationic surfactant;

the structural formula of the cationic surfactant is shown as a formula I;

wherein R is₁，R₂，R₃Independently selected from C₁～C₅Alkyl groups of (a); r₄Is selected from C₈～C₂₀Alkyl groups of (a); x^-Is selected from Br^-、Cl^-Or OH^-；

Preferably, the structure directing agent I is selected from at least one of dodecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide or octadecyl trimethyl ammonium bromide.

5. The method of claim 1, wherein the alkaline system in step 1) comprises at least one of ammonia or sodium hydroxide solution;

the pH value of the alkaline system is between 9 and 12;

preferably, the silicon source in step 1) is selected from at least one of methyl orthosilicate, ethyl orthosilicate, silica sol and sodium silicate;

the titanium source is at least one selected from tetraethyl titanate, tetrabutyl titanate, isopropyl titanate, titanium trichloride and titanium tetrachloride.

6. The method of claim 2, wherein the structure directing agent i: silicon source: the titanium source is 0.005-1.0:1: 0.001-0.05.

7. The method according to claim 2, wherein the reaction temperature of the reaction in step 1) is 30 to 100 ℃; the reaction time is 1-12 h;

preferably, the titanium dioxide/silicon composite is spherical or ellipsoidal in shape, and has an average particle size of 100-500 nm.

8. The preparation method according to claim 2, wherein the structure directing agent II is at least one selected from tetraethylammonium hydroxide, tetrapropylammonium bromide and tetrapropylammonium chloride;

preferably, the molar ratio of silicon in the titanium dioxide/silicon composite material in the step 2) to the structure directing agent II is 1: 0.05-0.5;

preferably, the molar ratio of silicon in the titanium dioxide/silicon composite material in the step 2) to the structure directing agent II is 1: 0.05-0.15.

9. The method according to claim 2, wherein the step 1) further comprises filtering, drying, and calcining the reaction product after the reaction;

preferably, the crystallizing in step 3) includes: placing the initial synthesis mixture obtained in the step 2) in a closed reactor, and carrying out crystallization reaction on the initial synthesis mixture in the presence of water vapor;

preferably, the temperature of the crystallization reaction is 100-;

preferably, the roasting temperature in the step 4) is 400-700 ℃, and the roasting time is 2-8 hours.

10. The TS-1 molecular sieve with the macroporous-microporous composite pore channel structure according to claim 1 or the TS-1 molecular sieve with the macroporous-microporous composite pore channel structure prepared by the preparation method according to any one of claims 2 to 9 is applied as a catalyst in an olefin epoxidation reaction.