Preparation method for synthesizing framework-containing Ga-MFI molecular sieve without template agent

Abstract

The invention discloses a preparation method for synthesizing a framework-containing Ga-MFI molecular sieve without a template agent, which simplifies the traditional synthesis process, reduces the production cost and reduces the environmental pollution. According to the method, no organic template agent needs to be added, the introduction process of gallium is simplified, the production efficiency and environment friendliness are improved, and the integrity and stability of the molecular sieve are kept.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and in particular relates to a method for synthesizing a skeleton-containing catalyst without a template. Background Art

[0002] Molecular sieve is an inorganic microporous material with a regular pore structure, which is widely used in many fields. MFI molecular sieve has shown good application prospects in the fields of adsorption, separation, catalysis, etc. due to its unique three-dimensional pore structure, large specific surface area, suitable surface acidity and other advantages. The introduction of gallium (Ga) atoms into the MFI zeolite framework can further adjust the acidity and strength of the traditional silicon-aluminum MFI molecular sieve and introduce a certain Lewis acidity, thus broadening its application range.

[0003] Ga-MFI type molecular sieves have a wide range of applications in many fields, such as (1) Ga-MFI type molecular sieves are used in the catalytic cracking reaction of aviation fuel, which can effectively and selectively produce low-carbon olefins. (2) Ga-MFI type molecular sieve membranes are widely used in the separation of small molecule gases due to their unique pore structure and good adsorption properties. These molecular sieve membranes exhibit excellent separation performance under high temperature conditions and are suitable for the separation and purification of a variety of gases. (3) Methanol aromatization: Ga-MFI catalysts exhibit excellent catalytic stability in methanol aromatization reactions, and the best catalytic effect can be achieved by adjusting the size of Ga-MFI molecular sieves. In summary, Ga-MFI type molecular sieves have important research and practical application value in many fields such as catalytic cracking, gas separation and chemical catalysis.

[0004] However, there are usually some problems in the synthesis process of Ga-MFI molecular sieves with templates, mainly including the following aspects: (1) Organic structure directing agents (templates) are usually added during the synthesis process. Organic templates are often expensive, which will greatly increase the production cost. In addition, a large amount of organic wastewater will be generated during the washing process of the synthesized product, increasing environmental pollution. In addition, because the template is strongly bonded to the molecular sieve, the traditional high-temperature calcination process to remove the template often affects the molecular sieve crystal skeleton structure and the integrity of the molecular sieve membrane, which may cause large intercrystalline defects. (2) The process of introducing gallium into the molecular sieve is complicated: it usually requires post-processing, such as desiliconization and gallium supplementation, which is cumbersome and costly. The gallium introduced by the ordinary impregnation method often exists on the outer surface of the molecular sieve in the form of oxides, with poor dispersion and low catalytic activity. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a Ga-MFI molecular sieve containing a template-free synthesis.

[0008] In order to solve the above technical problems, the present invention provides the following technical solution: a preparation method for synthesizing a framework-containing Ga-MFI molecular sieve without a template, characterized in that: comprising:

[0009] Dissolve the alkali source and gallium source in water and stir evenly, then add the silicon source to obtain a reaction solution;

[0010] The reaction is liquid crystalized and then ground and calcined to obtain the template-free synthetic framework-containing Ga-MFI molecular sieve.

[0011] As a preferred embodiment of the preparation method of the present invention, the alkali source includes but is not limited to sodium hydroxide or potassium hydroxide.

[0012] As a preferred embodiment of the preparation method of the present invention, the gallium source includes but is not limited to a cationic salt or hydroxide of gallium.

[0013] As a preferred embodiment of the preparation method of the present invention, the silicon source includes but is not limited to silica sol, tetraethyl orthosilicate, and fumed silica.

[0014] As a preferred embodiment of the preparation method of the present invention, the molar ratio of the silicon source to the gallium source is 10-60.

[0015] As a preferred embodiment of the preparation method of the present invention, the molar ratio of the silicon source to the alkali source is 1-10.

[0016] As a preferred embodiment of the preparation method of the present invention, the crystallization temperature is 160-200° C. and the crystallization time is 24-100 h.

[0017] As a preferred embodiment of the preparation method of the present invention, the calcination time is 5 to 10 hours and the temperature is 500 to 600°C.

[0018] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of synthesizing a framework-containing Ga-MFI molecular sieve without a template.

[0019] Beneficial effects of the present invention:

[0020] (1) The present invention does not add a template to synthesize the MFI molecular sieve containing framework gallium. During the synthesis process, there is no need to add an organic structure directing agent (template). Organic templates are often expensive and will greatly increase the production cost. In addition, a large amount of organic wastewater will be generated during the washing process of the synthesized product, increasing environmental pollution. In addition, because the template is strongly bonded to the molecular sieve, the traditional high-temperature calcination process to remove the template often affects the molecular sieve crystal framework structure and the integrity of the molecular sieve membrane, which may cause larger intercrystalline defects.

[0021] (2) The process of introducing gallium into the molecular sieve is simple: the addition of templates usually requires post-processing, such as the method of removing silicon and supplementing gallium, which is cumbersome and costly. Gallium introduced by ordinary impregnation methods often exists on the outer surface of the molecular sieve in the form of oxides, with poor dispersion and low catalytic activity. The present invention does not require the above steps to synthesize the MFI molecular sieve containing skeleton gallium without adding templates. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0023] Figure 1 A flow chart of the preparation method of template-free Ga-MFI provided in an embodiment of the present invention;

[0024] Figure 2 The XRD diagram of extending the crystallization time of template-free Ga-MFI provided in an embodiment of the present invention;

[0025] Figure 3 XRD diagram of increasing and decreasing the crystallization temperature of template-free Ga-MFI provided for the implementation of the present invention

[0026] Figure 4 XRD diagrams of increasing and decreasing the amount of alkali in template-free Ga-MFI provided for the implementation of the present invention;

[0027] Figure 5 XRD patterns of different silicon-gallium ratios of template-free Ga-MFI provided for the implementation of the present invention

[0028] Figure 6 The template-free Ga-MFI provided by the present invention71 GaNMR graph. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0032] The raw materials used in the present invention are shown in Table 1.

[0033] Table 1

[0034] Serial number Company Name Drug Name Part Number 1 Shanghai Aladdin Biochemical Technology Co., Ltd. NaOH 1310-73-2 2 Shanghai MacLean Biochemical Technology Co., Ltd. <![CDATA[Ga(NO3)3]]> 69365-72-6 3 Shanghai Aladdin Biochemical Technology Co., Ltd. <![CDATA[SiO2]]> 112945-52-5

[0035] The instruments used in the embodiments of the present invention are: German Bruker AXS polycrystalline X-ray diffractometer, model: D8 Advance; German Bruker solid-state nuclear magnetic resonance spectrometer, model AVANCE III 400 MHz WB.

[0036] Example 1

[0037] See also Figure 1 , Figure 1 The following is a flow chart of a method for preparing a Ga-MFI molecular sieve without a template provided in an embodiment of the present invention. The method comprises the following steps:

[0038] (1) Dissolve 0.95 g of sodium hydroxide in 2 g of water while stirring.

[0039] (2) Gallium nitrate is mixed with the above sodium hydroxide solution at a molar ratio of 0.2. The purity of the sodium hydroxide is above 97%, and 32.25 water is added to dilute the above reaction solution.

[0040] (3) Add 4.91 g of silicon dioxide powder into the reaction solution and stir for 30 min.

[0041] (4) The above materials were placed in a Teflon-lined stainless steel reactor and crystallized at 170°C for 72 hours. The catalyst was then ground into powder and calcined in a muffle furnace for 6 hours at a temperature of 550°C.

[0042] Example 2

[0043] The difference between this embodiment and embodiment 1 is that the crystallization time in step (4) is replaced with 24 hours, and the remaining steps are the same as those in embodiment 1.

[0044] Comparative Example 1

[0045] The difference between this comparative example and Example 1 is that the crystallization time in step (4) is replaced with 48 hours, and the remaining steps are the same as in Example 1.

[0046] The XRD patterns of Ga-MFI at different crystallization times are shown in Figure 2 , Figure 2 The instrument used is: German Bruker AXS polycrystalline X-ray diffractometer. The Kα line (wavelength 0.154nm) excited by the Cu target is used as the X-ray source. The current and voltage of the instrument are 40mA / 40kV, and the primary and secondary slits are 1 and 1 / 2. Before testing, the sample needs to be ground, spread in the quartz glass tank and compacted. The scanning speed is 0.2min / °, and the diffraction pattern scanning range (2θ) is 5°-60°.

[0047] Through the characterization results of XRD, we can find that the samples with crystallization time of 2 days, 3 days, and 4 days all show the characteristic diffraction peaks of MFI zeolite, while the samples with crystallization time of 1 day have no characteristic diffraction peaks of MFI zeolite and have poor crystallinity.

[0048] Example 3

[0049] The difference between this embodiment and embodiment 1 is that the crystallization temperature in step (4) is replaced with 150° C., and the remaining steps are the same as those in embodiment 1.

[0050] Comparative Example 2

[0051] The difference between this comparative example and Example 1 is that the crystallization temperature in step (4) is replaced with 190° C., and the remaining steps are the same as in Example 1.

[0052] The XRD patterns of Ga-MFI at different crystallization temperatures are shown in Figure 3 , Figure 3The instrument used is: German Bruker AXS polycrystalline X-ray diffractometer. The Kα line (wavelength 0.154nm) excited by the Cu target is used as the X-ray source. The current and voltage of the instrument are 40mA / 40kV, and the primary and secondary slits are 1 and 1 / 2. Before testing, the sample needs to be ground, spread in the quartz glass tank and compacted. The scanning speed is 0.2min / °, and the diffraction pattern scanning range (2θ) is 5°-60°.

[0053] Through the characterization results of XRD, we can find that the diffraction peak characteristic of MFI zeolite is not displayed when the crystallization temperature is 150°, but the diffraction peak characteristic of MFI zeolite is still displayed when the crystallization temperature is 190°.

[0054] The XRD patterns of Ga-MFI under different alkali source addition amounts are shown in Figure 4 , Figure 4 The instrument used is: German Bruker AXS multi-crystal X-ray diffractometer. The Kα line (wavelength of 0.154nm) excited by the Cu target is used as the X-ray source. The current and voltage of the instrument are 40mA / 40kV, and the primary and secondary slits are 1 and 1 / 2. Before testing, the sample needs to be ground, spread in the quartz glass groove and compacted. The scanning speed is 0.2min / °, and the diffraction pattern scanning range (2θ) is 5°-60°. Through the characterization results of XRD, we can find that the samples with +1 / 4 alkali source and 1 / 2 alkali source both show diffraction peaks characteristic of MFI zeolite.

[0055] XRD patterns of Ga-MFI with different Si-Ga ratios are shown in Figure 5 , Figure 5 The instrument used is: German Bruker AXS polycrystalline X-ray diffractometer. The Kα line (wavelength of 0.154nm) excited by the Cu target is used as the X-ray source. The current and voltage of the instrument are 40mA / 40kV, and the primary and secondary slits are 1 and 1 / 2. Before testing, the sample needs to be ground, spread in the quartz glass groove and compacted. The scanning speed is 0.2min / °, and the diffraction pattern scanning range (2θ) is 5°-60°. Through the characterization results of XRD, we can find that the diffraction peak characteristic of MFI zeolite can be displayed when the silicon-gallium ratio is 12, while the silicon-gallium ratio of 60-300 has shown other crystalline phases.

[0056] Template-free Ga-MFI 71 Ga NMR diagram see Figure 6 , Figure 6 The instrument used was an AVANCE III 500MHz WB instrument produced by Bruker, Germany. 71 GaNMR spectrum. Laboratory probe 1.9mm, rotation rate 40kHz. 71The Ga chemical shift was referenced to 1 mol / LGa(NO3)3 aqueous solution (0 ppm). Broad peaks appeared at around 152 ppm on the catalysts with crystallization time of 2 days, 3 days, and 4 days, indicating that the gallium species mainly existed in the molecular sieve framework in the form of isolated four-coordinated species.

[0057] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the present invention.

Claims

1. A method for preparing a Ga-MFI molecular sieve without a template, characterized in that: include, Dissolve the alkali source and gallium source in water and stir evenly, then add the silicon source to obtain a reaction solution; The reaction is liquid crystalized and then ground and calcined to obtain the template-free synthetic framework-containing Ga-MFI molecular sieve.

2. The preparation method according to claim 1, characterized in that: The alkaline source includes but is not limited to sodium hydroxide or potassium hydroxide.

3. The preparation method according to claim 1, characterized in that: The gallium source includes, but is not limited to, a cationic salt or hydroxide of gallium.

4. The preparation method according to claim 1, characterized in that: The silicon source includes but is not limited to silica sol, tetraethyl orthosilicate, and fumed silica.

5. The preparation method according to claim 1, characterized in that: The molar ratio of the silicon source to the gallium source is 10-60.

6. The preparation method according to claim 1, characterized in that: The molar ratio of the silicon source to the alkali source is 1-10.

7. The preparation method according to claim 1, characterized in that: The crystallization process comprises a crystallization temperature of 150 to 200° C. and a crystallization time of 24 to 100 hours.

8. The preparation method according to claim 1, characterized in that: The calcination process has a calcination time of 5 to 10 hours and a temperature of 500 to 600°C.

9. Application of the template-free synthesized framework-containing Ga-MFI molecular sieve as claimed in claim 8 in the fields of catalytic cracking and chemical catalysis.

10. Use of the template-free synthesized framework-containing Ga-MFI molecular sieve as claimed in claim 8 in the field of gas separation.

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