CN103708488B - Method for preparing multilevel porous zeolite through microwave assisted decomposition of hydrogen peroxide - Google Patents

Abstract

The invention belongs to the technical field of material chemistry, and specifically relates to a method for preparing hierarchically porous zeolite by microwave-assisted decomposition of hydrogen peroxide. In this method, under the action of microwave irradiation, a certain concentration of hydrogen peroxide is used to quickly decompose and generate gas to produce instantaneous and violent impact on zeolite, thereby introducing secondary pores into beta zeolite. The invention has the advantages of simple equipment, convenient operation and rapid response. The introduction of the secondary pores increases the specific surface area and pore volume of the beta zeolite and at the same time reduces the crystal defects of the beta zeolite and thus makes the framework more perfect. This micro-explosion pore-forming zeolite material has great application value in some zeolite catalytic fields where macromolecules are limited, such as petroleum reforming and catalytic cracking.

Description

A method for preparing hierarchically porous zeolite by microwave-assisted hydrogen peroxide decomposition

technical field

The invention belongs to the technical field of material chemistry, and in particular relates to a method for preparing hierarchically porous zeolite by microwave-assisted decomposition of hydrogen peroxide.

Background technique

According to the classification of inorganic porous materials by IUPAC (International Union of Pure and Applied Chemistry), substances with pore sizes below 2 nm are called microporous compounds or molecular sieves, and substances with pore sizes ranging from 2 to 50 nm Mesoporous materials are called mesoporous materials, and substances with a pore size range larger than 50 nm are called macroporous materials. As an important member of inorganic microporous materials, zeolite molecular sieve has unique physical and chemical properties, such as large specific surface area, regular pore structure, controllable acid site and acid density, etc. domain plays an important role.

Traditional zeolite materials are powerless for many macromolecular reactions because their pore size is generally less than 1nm. Compared with traditional microporous materials, mesoporous materials have wider channels, but usually the pore walls of mesoporous materials are amorphous, so their thermal stability and hydrothermal stability are poor, which also limits their applications. widely used.

To sum up, microporous and mesoporous materials have their own advantages and disadvantages. How to learn from each other, how to combine the advantages of these two materials more reasonably, and give full play to their respective advantages has become a topic of concern to people. Hierarchical porous materials with micropores and mesopores have increasingly become a hot spot of concern. Zeolite hierarchical porous materials with high hydrothermal stability and high acid strength and larger pore size have attracted people's attention. There are four main methods for the preparation of hierarchically porous zeolite materials: 1) removal of skeleton building atoms (such as dealumination and desilication method) to form mesopores in zeolite crystals; 2) induction of nano-sized zeolites to introduce intercrystalline mesopores; 3 ) Nano-carbon is a hard template to control crystallization, embedding activated carbon inside the crystal to form intracrystalline mesopores; 4) Soft template synthesis method. These methods are relatively complicated to operate, and the template agent cannot be completely eliminated, which affects the performance and application of the hierarchical zeolite.

The method proposed by the invention has simple equipment and convenient operation, and the reagent used is hydrogen peroxide, and the decomposition products are water and oxygen, which is clean and efficient. The hydrogen-type zeolite can be used directly after treatment without the need for successive treatments such as exchange roasting, so it has excellent and wide application prospects.

Contents of the invention

The object of the present invention is to propose a method for preparing hierarchically porous zeolite that can completely digest the zeolite template agent in a short time and easily controllable to obtain nano zeolite with complete template elimination, good retention of inorganic framework structure and surface properties, and good dispersibility.

The present invention proposes a method for preparing multi-level pore zeolite, which is to decompose hydrogen peroxide under microwave irradiation, rapidly generate a large amount of gas in situ, and generate new secondary pores in the zeolite framework due to instantaneous impact. Specific steps are as follows:

(1) Add beta zeolite to an appropriate amount of hydrogen peroxide with a mass concentration of 30-50% (wt%), and shake well;

(2) Add an appropriate amount of distilled water; ultrasonic treatment, so that the zeolite is evenly dispersed in the hydrogen peroxide reaction system;

(3) Seal the system, put it into a microwave reactor, and carry out microwave irradiation;

(4) After the reaction, the product was dispersed in distilled water, ultrasonicated, washed and dried.

In the present invention, the mass fraction of the hydrogen peroxide reaction system can be 2-50%, and the amount of zeolite treated per gram is 2-200 ml.

In the present invention, the conditions for microwave irradiation may be: temperature 40-210 ^o C, microwave irradiation 2-120 minutes; power control at 200-1000W. The preferred conditions are: temperature 80-150 ^o C, microwave irradiation for 30-100 minutes; power controlled at 400-800W.

The hydrogen-type zeolite treated by the method of the invention can be used directly after being washed and dried.

The method of the present invention utilizes the rapid decomposition of hydrogen peroxide under microwave irradiation to produce a large amount of gas impacting on the pores of the zeolite to introduce secondary pores inside the zeolite. By controlling the reaction conditions, both ultramicropores and larger-sized mesoporous pores can be introduced. , and the hole size and relative quantity can be adjusted. Compared with the traditional method, the method of the present invention reacts quickly, is simple and easy to implement, is environmentally friendly and safe, and has strong operability. The reagents used are cheap and easy to obtain, and the whole process is clean and efficient. Catalytic properties of materials.

Description of drawings

Fig. 1 Transmission electron micrograph (TEM) of initial BEA zeolite.

Fig. 2 Transmission electron micrograph (TEM) of BEA zeolite after treatment.

Fig. 3 _N2 adsorption-desorption isotherms of BEA zeolite before and after treatment.

Fig. 4 NLDFT pore size distribution (PSD) of BEA zeolite before and after treatment.

Fig. 5 _N2 adsorption-desorption isotherms of BEA zeolite before and after treatment.

Fig. 6 BJH pore size distribution (PSD) of BEA zeolite before and after treatment.

Fig. 7 X-ray powder diffraction pattern (XRD) of BEA zeolite before and after treatment.

Fig. 8 Infrared spectra (FTIR) of BEA zeolite before and after treatment.

Detailed ways

The following example is a further description of the preparation of hierarchically porous BEA zeolite by decomposing hydrogen peroxide under microwave irradiation provided by the present invention.

Example 1 Add 50 mg of BEA zeolite to 3ml of 30% (wt%) hydrogen peroxide, shake well; then add 2ml of distilled water, and ultrasonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once, ie, 100 minutes, according to the irradiation program listed in Attached Table 1. After the reaction, cool to room temperature, centrifuge the obtained product at 1000 r/min, discard the supernatant, and then wash with distilled water repeatedly for 3 times. The TEM image of the product is shown in Figure 2, and the TEM image of the initial sample is shown in Figure 1. Comparing the two images, it can be clearly found that zeolite beta has produced secondary pores after treatment.

Example 2 Add 150 mg of BEA zeolite to 9 ml of 30% (wt%) hydrogen peroxide, shake well; then add 1 ml of distilled water, and sonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once for 100 minutes according to the irradiation program listed in Attached Table 1. After the reaction, cool to room temperature, centrifuge the obtained product at 1000 r/min, discard the supernatant, and then wash with distilled water repeatedly for 3 times. The _N2 isotherm adsorption-desorption curves of BEA zeolite before and after the reaction are shown in Fig. 3, and the pore size distribution obtained by NLDFT method is shown in Fig. 4. From Figure 3, it can be clearly found that the isothermal adsorption-desorption curve of zeolite β after treatment has obvious hysteresis loops, showing the obvious characteristics of mesoporous composite materials. It can be seen from Figure 4 that the main pore size distribution of zeolite β after treatment has a red shift, which is caused by the large number of secondary pores.

Example 3 Add the BEA zeolite produced in Example 2 into 4ml of 50% (wt%) hydrogen peroxide, shake well; add 2ml of distilled water, and sonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once for 60 minutes according to the irradiation program listed in Attached Table 2. After the reaction, cool to room temperature, centrifuge the obtained product at 1000r/min, discard the supernatant, and then wash repeatedly with distilled water for 2 times, repeat the previous operation process, and process it again, and finally cool to room temperature. The product obtained is centrifuged under the condition of 1000r/min, the supernatant is discarded, and then repeatedly washed with distilled water for ₃ times to obtain the BEA zeolite that has been processed multiple times. The BJH pore size distribution diagram is shown in Fig. 6. From Figure 5, it can be clearly found that the isothermal adsorption-desorption curve of zeolite β after treatment has obvious hysteresis loop in the higher pressure region, indicating that a large number of mesopores have been introduced. It can be seen from Figure 6 that after multiple treatments, zeolite beta produced a new distribution peak in the 10nm mesoporous region, fully demonstrating the effectiveness of this method for introducing mesoporous pores. It can be seen from Fig. 8 that the framework order degree of BEA zeolite increases after multiple treatments.

Example 4 Add 500mg of BEA zeolite to 10ml of 30% (wt%) hydrogen peroxide, shake well, and sonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once for 100 minutes according to the irradiation program listed in Attached Table 1. After the reaction, cool down to room temperature, centrifuge the obtained product at 1000 r/min, discard the supernatant, and then wash with distilled water repeatedly 3 times to obtain the BEA zeolite introduced into the secondary pores.

Example 5 Add 250 mg of BEA zeolite to 5ml of 50% (wt%) hydrogen peroxide, shake well; then add 3ml of distilled water, and sonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once for 15 minutes according to the irradiation program listed in Table 3. After the reaction, cool down to room temperature, centrifuge the obtained product at 1000 r/min, discard the supernatant, and then wash with distilled water repeatedly 3 times to obtain BEA zeolite introduced into the secondary pores.

Example 6 Add 150 mg of BEA zeolite to 5 ml of 30% (wt%) hydrogen peroxide, shake well; then add 3 ml of distilled water, and ultrasonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once for 60 minutes according to the irradiation program listed in Attached Table 2. After the reaction, cool down to room temperature, centrifuge the obtained product at 1000 r/min, discard the supernatant, and then wash with distilled water repeatedly 3 times to obtain BEA zeolite introduced into the secondary pores.

Example 7 Add 400 mg of BEA zeolite to 2ml of 30% (wt%) hydrogen peroxide, shake well; then add 8ml of distilled water, and ultrasonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once for 60 minutes according to the irradiation program listed in Attached Table 2. After the reaction, cool down to room temperature, centrifuge the obtained product at 1000 r/min, discard the supernatant, and then wash with distilled water repeatedly 3 times to obtain BEA zeolite introduced into the secondary pores.

Example 8 Add 200 mg of BEA zeolite to 2ml of 50% (wt%) hydrogen peroxide, shake well, and sonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once for 60 minutes according to the irradiation program listed in Attached Table 2. After the reaction, cool down to room temperature, centrifuge the obtained product at 1000 r/min, discard the supernatant, and then wash with distilled water repeatedly 3 times to obtain BEA zeolite introduced into the secondary pores.

Example 9 Add 250 mg of ZSM-5 zeolite to 6ml of 30% (wt%) hydrogen peroxide, shake well; then add 4ml of distilled water, and ultrasonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once for 100 minutes according to the irradiation program listed in Attached Table 1. After the reaction, cool to room temperature, centrifuge the obtained product at 1000 r/min, discard the supernatant, and then wash with distilled water for 3 times to obtain ZSM-5 zeolite introduced into the secondary pores.

Example 10 Add 150 mg of MOR zeolite to 5ml of 30% (wt%) hydrogen peroxide, shake well; then add 3ml of distilled water, and sonicate for 5 minutes. The system was sealed and transferred to a microwave reactor, and reacted once for 15 minutes according to the irradiation program listed in Table 3. After the reaction, cool down to room temperature, centrifuge the obtained product at 1000 r/min, discard the supernatant, and then wash with distilled water repeatedly for 3 times to obtain the MOR zeolite introduced into the secondary pores.

The method of the invention is simple, easy to implement, environmentally friendly and safe, can effectively introduce ultramicropores and mesopores under the premise of maintaining the structure and properties of the zeolite crystal framework, and can improve the order degree of the framework at the same time, so it has superior and extensive application prospects.

Schedule Notes

Table 1 Microwave irradiation program under temperature control: Mode 1

Table 2 Microwave irradiation program under temperature control: Mode 2

Table 3 Microwave irradiation program under temperature control: Mode 3

Table 4 Pore structure properties of BEA zeolite before and after microwave irradiation hydrogen peroxide treatment

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Claims (1)

1. A method for preparing hierarchically porous zeolite by microwave-assisted hydrogen peroxide decomposition is characterized in that hydrogen peroxide is decomposed under microwave irradiation, and a large amount of gas is produced rapidly in situ, and the instant impact causes the zeolite framework to produce new secondary pores, and the specific steps are as follows: (1) Add beta zeolite to an appropriate amount of hydrogen peroxide with a mass concentration of 30-50%, and shake well; (2) Add an appropriate amount of distilled water; ultrasonic treatment; make the zeolite evenly dispersed in the hydrogen peroxide reaction system; (3) Seal the system, put it into a microwave reactor, and carry out microwave irradiation; (4) After the reaction finishes, the product is dispersed in distilled water, ultrasonicated, washed, and dried; The mass fraction of the hydrogen peroxide reaction system is 2-50%, and the amount of processing per gram of zeolite is 2-200 ml; The conditions for microwave irradiation are: temperature 40-210°C, microwave irradiation 2-120 minutes; power control at 200-1000W.