CN1281315C - Molecular sieve containing secondary structure unit of beta zeolite and its preparing process - Google Patents

Abstract

The invention relates to a new type of catalytic material of mesopore molecular sieve or mesopore composite molecular sieve containing beta zeolite secondary structure unit and its preparation method. The present invention introduces the secondary structural unit of zeolite beta into the framework of mesoporous molecular sieve by pretreating the synthetic mixture, and then using it as an inorganic precursor to use surfactant supramolecular self-assembly, and successfully designs and synthesizes SBU -MCM-41, SBU-MCM-48 and mesoporous composite molecular sieves. The above novel molecular sieve catalytic material containing the secondary structural unit of zeolite beta has good catalytic reaction performance and high thermal and hydrothermal stability.

Description

Preparation method of mesoporous molecular sieve containing beta zeolite secondary structural unit

technical field

The invention relates to the design and preparation method of a class of mesoporous molecular sieve or mesoporous composite molecular sieve novel catalytic material containing beta zeolite secondary structural unit.

Background technique

Since the researchers of Mobil Corporation synthesized M41S series mesoporous molecular sieves by using supramolecular self-assembly of surfactants in 1992, the mesoporous materials (MCM-41 and MCM-48) have been characterized by their adjustable regular channels, large ratio The characteristics of surface area and good thermal stability have become a hot topic in the research of catalytic materials. It is hoped that mesoporous molecular sieves can be used in macromolecular catalytic reactions. However, compared with traditional microporous zeolite molecular sieves, there are obvious differences in the framework structure of mesoporous molecular sieves. Mesoporous molecular sieves have no repeating unit cell structure units in microporous zeolites, and their internal unit structures are similar to amorphous oxides, do not contain crystal structure regions, and only have local ordered structures. Therefore, aluminum-containing mesoporous molecular sieves and amorphous Similar to aluminosilicates, they have weak and moderate acidity, coupled with poor hydrothermal stability, which largely limits the industrial application of mesoporous molecular sieves. At present, people mostly use methods such as synthesizing Al-MCM-41 with high aluminum content and post-synthesis aluminization to improve the acidity of mesoporous molecular sieves, but these methods only change the distribution of aluminum in the mesoporous molecular sieve framework, and have not fundamentally changed Due to the amorphous skeleton structure of mesoporous molecular sieves, it is difficult to effectively improve the acidity.

Some important microporous molecular sieves, such as β zeolite, have achieved important industrial applications due to their unique topological structure, good thermal and hydrothermal stability, and excellent catalytic activity, but their pore size belongs to the micropore range (< 0.8nm=, can not satisfy the requirement of macromolecular reaction.We know that in the synthetic process of microporous zeolite molecular sieve, organic template agent molecule can arrange inorganic oxide species into the secondary structural unit with zeolite structure feature, secondary structural unit (Secondary Building Unit) referred to as SBU, these secondary structural units can be detected by IR spectrum and do not appear on the XRD pattern. The secondary structural unit of zeolite beta is composed of two single four-membered rings and a double 5-3 ring , its largest one-dimensional geometric size is much smaller than the pore wall thickness of the mesoporous molecular sieve. If the secondary structural unit of zeolite beta is introduced into the mesoporous molecular sieve framework structure, the amorphous framework structure performance of the mesoporous molecular sieve can be improved, and To effectively increase the acidity of mesoporous molecular sieves, no such work has been reported so far.

Contents of the invention

The purpose of the present invention is to develop a new type of mesoporous molecular sieve or mesoporous composite molecular sieve catalytic material containing beta zeolite secondary structural unit, wide application range and excellent performance, and to provide its preparation method.

The novel molecular sieve catalytic material of the present invention is a class of mesoporous molecular sieves or mesoporous composite molecular sieves containing β zeolite secondary structural units, and they have the following characteristics:

(1) The mesoporous pore wall contains the secondary structural unit of zeolite beta, and the thickness of the pore wall is 32% to 58% higher than that of the traditional mesoporous molecular sieve; (2) The mesoporous molecular sieve containing the secondary structural unit of zeolite beta includes hexagonal phase The SBU-MCM-41 of the cubic phase and the SBU-MCM-48 of the cubic phase are two kinds; (3) the mesoporous composite molecular sieve is composed of the mesoporous molecular sieve containing the secondary structural unit of β zeolite and the two phases of β microporous zeolite; (4) Good thermal and hydrothermal stability, after calcination at 800-1000°C or treatment in boiling water for 24-48 hours (h), the skeleton structure will not be destroyed All have good catalytic performance.

In the present invention, the preparation of the mesoporous molecular sieve containing the secondary structural unit of zeolite beta is realized in the following way: the reaction mixture capable of forming zeolite beta is pretreated under certain temperature and stirring conditions, and the pretreatment time is strictly controlled; When the reaction mixture has zeolite beta secondary structural units that can be detected by FT-IR and no zeolite beta crystals are formed, the pretreatment process is terminated immediately; The inorganic species of the inorganic species guide the inorganic species containing the secondary structural unit of zeolite β into a mesoporous molecular sieve with a regular pore structure through the interface action, and the pore wall of this SBU mesoporous material thus has the structural characteristics of zeolite β. When preparing, first dissolve a certain amount of aluminum source such as pseudo-boehmite in tetraethylammonium hydroxide (TEAOH) aqueous solution, then add fumed silica, stir evenly and put it into a liner with a polytetrafluoroethylene In a stainless steel reaction kettle, stir and react at 130-150°C for 20-140h. The above pretreated sol is dropped into a certain concentration of cetyltrimethylammonium bromide (CTAB) solution and the pH is adjusted to 9.6-12.5, and then the crystallization is continued at 100-150° C. for 24-72 hours. After the crystallization, the solid product was suction filtered, washed until neutral, and dried at 100°C. The dried sample was first calcined at 550°C for one hour under nitrogen flow, and then calcined at the same temperature for 6 hours in an air atmosphere to obtain a calcined sample.

When preparing mesoporous molecular sieves containing secondary structural units of zeolite beta, the materials used should reach the following molar ratio ranges: SiO ₂ /Al ₂ O ₃ =20-150, (TEA) ₂ O/SiO ₂ =0.15-0.30, CTAB/SiO ₂ =0.20-0.49, H ₂ O/SiO ₂ =30-100.

In the above preparation method, the preferred pretreatment temperature of the reaction mixture is 135-145° C., and the pretreatment time is 21-135 hours. The requirement for pretreatment is the presence of beta zeolite secondary structural units detectable by FT-IR in the reaction mixture without the formation of beta zeolite crystals.

In the above preparation method, the preferred molar ratio range of the materials used is: SiO ₂ /Al ₂ O ₃ =25-100, (TEA) ₂ O/SiO ₂ =0.22-0.28, CTAB/SiO ₂ =0.25-0.41, H ₂ O/SiO ₂ =39-96.

In the preparation method of the mesoporous molecular sieve containing the secondary structural unit of zeolite beta, the preparation process is completed in two steps: firstly, the synthetic gel containing the secondary structural unit of zeolite beta is prepared, and then the synthetic gel is used as the surface of the inorganic precursor Active agent CTAB supramolecular self-assembly into mesoporous molecular sieves.

In the present invention, the preparation method of the mesoporous composite molecular sieve containing the secondary structural unit of zeolite beta is to dissolve a certain amount of aluminum source such as NaAlO ₂ , silicon source such as fumed silica, etc. in tetraethylammonium hydroxide aqueous solution Stir evenly and put it into the reaction kettle, and crystallize it at 120-160°C for 36-240 hours; take out the reaction kettle, drop the gel in the kettle into the CTAB solution, adjust the pH to 9.6-10.5, and then in 90 Continue crystallization at ~110°C for 24~72h, and the molar ratio range of the synthesis mixture is: SiO ₂ /Al ₂ O ₃ =20~60, (TEA) ₂ O/SiO ₂ =0.10~0.20, CTAB/SiO ₂ =0.12~0.25 , H ₂ O/SiO ₂ =20-50. After the crystallization was completed, the solid sample was obtained by suction filtration, washing, and drying at 100°C. The dried sample was slowly heated to 550°C for one hour under nitrogen flow, then transferred to a muffle furnace, and then fired at 550°C for 6 hours to obtain a fired sample.

In the above preparation method, after uniformly mixing the aluminum source, silicon source, tetraethylammonium hydroxide and water, the preferred crystallization temperature is 130-150° C., and the crystallization time is 48-192 hours.

In the above preparation method, the preferred molar ratio range of the synthetic mixture is: SiO ₂ /Al ₂ O ₃ =25-40, (TEA) ₂ O/SiO ₂ =0.12-0.16, CTAB/SiO ₂ =0.14-0.20, H ₂ O/SiO ₂ =25-35.

In the above preparation method, the preparation process of the mesoporous composite molecular sieve containing the secondary structural unit of zeolite beta is realized in two steps: firstly, the synthetic gel containing the secondary structural unit of zeolite beta is prepared, and then the synthetic gel is used as the inorganic precursor Supramolecular Self-Assembly of Surfactant CTAB for Body into Microporous Composite Molecular Sieves.

The mesoporous molecular sieve or mesoporous composite molecular sieve containing beta zeolite secondary structural unit of the present invention is a kind of catalytic material. The introduction of the secondary structural unit of zeolite β has improved the amorphous framework structure performance of the mesoporous molecular sieve, and the acid content of SBU-MCM-41, SBU-MCM-48 and mesoporous composite molecular sieve has been greatly improved, thus showing good catalytic performance. Compared with the corresponding mesoporous molecular sieve, the acidity of SBU-MCM-41 is enhanced, and the cumene cracking activity is increased by more than 68%. Much higher (increased by more than 148%), and more than 13% higher than SBU-MCM-41 with the same gel-silica-alumina ratio. Compared with the mechanical mixture, the mesoporous composite molecular sieve has more strong acid content, especially the strong B acid content, thus showing better catalytic cracking activity (n-heptane cracking activity increased by 30%).

Description of drawings

The novel molecular sieve catalytic material of the present invention has the typical characterization results shown in Figures 1-5.

Fig. 1 is the XRD patterns (a) 25; (b) 50; (c) 100 of calcined SBU-MCM-41 mesoporous molecular sieves with different synthetic gel silica-aluminum ratios. It can be seen from the figure that the XRD patterns of SBU-MCM-41 with different synthetic gel silica-alumina ratios are similar, showing a strong hexagonal mesopore phase characteristic diffraction peak at (100), while (110) and (200) etc. The characteristic diffraction peaks with weaker intensity representing the fine structure of the hexagonal mesoporous phase cannot be distinguished, and appear as hill cell peaks in the 4°-5° diffraction interval of the XRD pattern.

Figure 2 is the XRD spectrum of the calcined SBU-MCM-48 mesoporous molecular sieve. The figure shows several characteristic diffraction peaks of a typical cubic mesoporous phase, namely: 211, 220, 400, 420 and 332.

Fig. 3 is the XRD patterns of calcined mesoporous composite molecular sieves with different crystallinity (S1) 16%; (S2) 19%; (S3) 28%; (S4) 39%. In the mesopore diffraction area, the diffraction peaks at 2θ between 1.9° and 2.3° are the unique hexagonal arrangement diffraction peaks of MCM-41, and in the micropore diffraction area, the diffraction peaks at 2θ near 7.8° and 22.4° are characteristic of zeolite beta Diffraction peaks.

Figure 4 is the IR backbone vibrational spectra of (a) SBU-MCM-41 and (b) mesoporous control. In the IR spectrum of SBU-MCM-41, it can be seen that there are two unique double-ring vibration absorption bands of zeolite β at 569cm ^-1 and 520cm ^-1 , indicating that there are β The secondary building blocks that characterize the structure of zeolites. However, no characteristic absorption band related to the vibration of the zeolite framework was observed in the IR spectrum of the mesoporous control object in the vibration range of 650-500cm ^-1 , showing the characteristics of an amorphous framework structure.

Fig. 5 is the ¹²⁹ XeNMR spectrum of (a) medium microporous composite molecular sieve; (b) β zeolite and MCM-41 mechanical mixture. It can be seen from the figure that under the similar equilibrium adsorption pressure, both the composite molecular sieve and the mechanical mixture have an unadsorbed Xe gas peak near the chemical shift of 0 ppm. The adsorption peak with a chemical shift of 119.2ppm in the composite molecular sieve corresponds to the adsorption peak with a chemical shift of 120.8ppm in the mechanical mixture, which is attributed to the adsorption of Xe in the β microporous phase. The peak with a chemical shift of 96.3ppm in the mechanical mixture corresponds to the adsorption peak of the mesoporous phase of MCM-41, while the chemical shift of the corresponding adsorption peak of the composite molecular sieve is at 109.1ppm, which is 12.8ppm higher, indicating that there is a strong adsorption of Xe, It can be seen that the mesoporous composite molecular sieve has a mesoporous channel structure different from that of the mechanical mixture. This is because there are secondary structural units of β zeolite on the mesoporous framework of the composite molecular sieve, which shows a strong Xe adsorption capacity.

Detailed ways

Example 1

Dissolve 0.067g of pseudo-boehmite (51wt% Al ₂ O ₃ ) in 10.0g of tetraethylammonium hydroxide solution (25wt%), then add 2.0g of fumed silica, stir well and load Stir the reaction at 140° C. for 22 h in a stainless steel reactor with a tetrafluoroethylene liner. The above pretreated sol was dropped into the CTAB solution with a concentration of 15.8wt%. At this time, the molar composition of the synthesis mixture was: SiO ₂ : 0.01Al ₂ O ₃ : 0.25(TEA) 2 _O : 0.28CTAB : 39H ₂ O . Then the pH was adjusted to 10.5 with dilute sulfuric acid, and crystallized at 100°C for 48 hours to obtain SBU-MCM-41 mesoporous molecular sieve (SiO ₂ /Al ₂ O ₃ =91.1).

Example 2

Weigh 0.1g of pseudo-boehmite (51wt% Al ₂ O ₃ ), dissolve it in 7.0g of tetraethylammonium hydroxide solution (25wt%), then add 1.5g of fumed silica, stir evenly and load it into the Stir the reaction at 135°C for 56h in a stainless steel reactor with a polytetrafluoroethylene liner. The above pretreated sol was dropped into the CTAB solution with a concentration of 14.1wt%. At this time, the molar composition of the synthesis mixture was: SiO ₂ : 0.02Al ₂ O ₃ : 0.23(TEA) _{2 O} : 0.25CTAB : 53H ₂ O . Then the pH was adjusted to 10.0 with dilute sulfuric acid, and crystallized at 95°C for 60 hours to obtain SBU-MCM-41 mesoporous molecular sieve (SiO ₂ /Al ₂ O ₃ =47.7).

Example 3

Dissolve 0.133g of pseudo-boehmite (51wt% Al ₂ O ₃ ) in 5.0g of tetraethylammonium hydroxide solution (25wt%), then add 1.0g of fumed silica, stir well and load Stir the reaction at 145° C. for 124 h in a stainless steel reactor with a tetrafluoroethylene liner. The above pretreated sol was dropped into the CTAB solution with a concentration of 16.2wt%. At this time, the molar composition of the synthesis mixture was: SiO ₂ : 0.04Al ₂ O ₃ : 0.25(TEA) _{2 O} : 0.29CTAB : 61H ₂ O . Then the pH was adjusted to 10.5 with dilute sulfuric acid, and crystallized at 105° C. for 72 hours to obtain SBU-MCM-41 mesoporous molecular sieve (SiO ₂ /Al ₂ O ₃ =22.4).

Example 4

Weigh 0.033g of pseudo-boehmite (51wt% Al ₂ O ₃ ), dissolve it in 5.0g of tetraethylammonium hydroxide solution (25wt%), then add 1.0g of fumed silica, stir well and put it into the Stir the reaction at 140° C. for 23 h in a stainless steel reactor with a polytetrafluoroethylene liner. The above pretreated sol was dropped into the CTAB solution with a concentration of 9.1wt%. At this time, the molar composition of the synthesis mixture was: SiO ₂ : 0.01Al ₂ O ₃ : 0.25(TEA) _{2 O} : 0.41CTAB : 94H ₂ O . Then adjust the pH to 11.8 with dilute sulfuric acid, and crystallize at 135° C. for 36 hours to obtain SBU-MCM-48 mesoporous molecular sieve (SiO ₂ /Al ₂ O ₃ =82.1).

Claims (3)

1, a kind of preparation method who contains the mesoporous molecular sieve of secondary structure unit of beta zeolite, it is characterized in that the reactant mixture of when mesoporous molecular sieve prepares aerosil, aluminium source, tetraethyl ammonium hydroxide and water being formed stirs, 130～150 ℃ of stirring reaction preliminary treatment 20～140 hours, then it is joined in the softex kw solution, reaction system has following mole and forms: SiO ₂/ Al ₂O ₃=20～150, (TEA) ₂O/SiO ₂=0.15～0.30, CTAB/SiO ₂=0.20～0.49, H ₂O/SiO ₂=30～100; Then at 100--150 ℃, pH is a crystallization 24～72 hours under 9.6～12.5 the condition, makes the molecular sieve that contains secondary structure unit of beta zeolite, and its pore wall thickness exceeds the molecular sieve 32～58% that does not contain secondary structure unit of beta zeolite.

2, the preparation method who contains the mesoporous molecular sieve of secondary structure unit of beta zeolite according to claim 1 is characterized in that reactant mixture was 135～145 ℃ of stirring reaction preliminary treatment 21～135 hours.

3, the preparation method who contains the mesoporous molecular sieve of secondary structure unit of beta zeolite according to claim 1 is characterized in that the reaction system molar ratio range is: SiO ₂/ Al ₂O ₃=25～100, (TEA) ₂O/SiO ₂=0.22～0.28, CTAB/SiO ₂=0.25～0.41, H ₂O/SiO ₂=39～96.

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