CN111439756A - Preparation method of cascade pore heteroatom M-Beta molecular sieve - Google Patents

Abstract

The invention provides a preparation method of a stepped pore heteroatom M-Beta molecular sieve. Compared with the existing synthesis methods, this method can directly synthesize M-Beta molecular sieves through the "one-step steam-assisted method", breaking through the inherent defects of traditional hydrothermal synthesis. Compared with the existing method for synthesizing M-Beta, this method does not require either the nucleation promoter aluminum nor the highly corrosive crystallization assistant hydrofluoric acid, and can synthesize M-Beta with a stepped pore structure and regular morphology. Beta molecular sieve; the synthesis time is reduced to 48 hours, and the steps are simple, which can effectively reduce energy consumption; there is very little crystallization liquid, which can effectively avoid the pollution problem of a large amount of crystallization waste liquid; at the same time, it also gets rid of the traditional "secondary isomorphous substitution method" And aluminum-containing "one-step synthesis" must use strong acid pretreatment to bring about a large amount of waste acid emissions.

Description

A kind of preparation method of stepped pore heteroatom M-Beta molecular sieve

technical field

The invention relates to a preparation method for synthesizing skeleton heteroatom M-Beta molecular sieves, in particular to a preparation method for one-step synthesis of [Al,F]-Free heteroatom M-Beta nanocrystals by steam-assisted transformation.

Background technique

Beta molecular sieve is the only molecular sieve with 12-membered ring three-dimensional intersecting channels, with unique pore structure, acidity and good hydrothermal stability. The traditional Beta molecular sieve is a silica-alumina zeolite, but only relying on the traditional Al-Beta zeolite cannot greatly improve the application field of the BEA structure. The introduction of different transition metals (Ti, Fe, Co, Ga, etc.) into the zeolite framework can endow the silicon framework with separated, well-dispersed, and diverse catalytically active centers. The special pore structure of zeolite provides suitable habitation space for these metal atoms, so that it has both the redox properties of transition metals and the acidity and shape selectivity of molecular sieves. possible. At the same time, the introduction of some heteroatoms can also effectively improve the hydrophobicity and framework stability of the zeolite, thereby improving the thermal stability and thermal stability of the zeolite framework. These advantages bring about the synthesis of porous materials and the expansion of their catalytic applications. As a result, various types of heteroatom M-Beta zeolites have been developed one after another and have received great attention.

So far, the preparation methods of heteroatom molecular sieves are mainly divided into one-step hydrothermal synthesis method and secondary isomorphous substitution method.

Secondary isomorphic substitution method, that is, secondary synthesis (modification) method, firstly, the pre-synthesized silico-alumina-based H-Beta molecular sieve is dealuminated with concentrated nitric acid to expose the skeleton of the open silicon hydroxyl nest defect site. , and then post-process the treated Si-Beta carrier. T. Maschmeyer (Nature, 1995, 378, 159) et al. used a post-treatment method of "wet impregnation method" to introduce organometallic titanium into the framework, but this method requires a large amount of toxic organic solvents, and the effective grafting rate of titanium lower. Severino F. Oliveira et al. successfully introduced Cu _II and Co _II into the zeolite framework through a "chemical deposition method", but the experimental process of this method is complicated, the requirements for the experimental equipment are relatively high, and the deposition rate of metal precursors is easily affected. influence of many factors. In order to make up for the shortcomings of the "wet impregnation method", YCChai et al. (Micropor. Mesopor. Mater., 2018, 264, 230) recently developed a "dry impregnation method", which successfully introduced Pb with a larger ionic radius into the zeolite framework. . However, in the zeolite material prepared by this secondary isomorphous substitution method, the heteroatoms are mainly concentrated in the atomic layer on the surface of the pores (CN104445255A), and are easily deposited on the zeolite as non-framework heteroatom species, which are calcined. The corresponding heteroatom metal oxides are directly formed and deposited on the surface of zeolite.

Compared with the secondary synthesis method, the heteroatom zeolite synthesized by the one-step hydrothermal synthesis method has unique advantages. This direct isomorphous growth method makes the heteroatoms grow firmly in the zeolite framework and present a highly dispersed state, and this method is not easy to change the pore structure of the original zeolite, and the desired heteroatom zeolite can be directly synthesized (CN1171792C ). However, this method of realizing zeolite growth relying on the diffusion and mass transfer of a large amount of crystallization liquid will significantly reduce the concentration of "nutrients" available for zeolite growth and make zeolite nucleation difficult. Therefore, for the one-step hydrothermal method , the amount of template agent and the crystallization time will be greatly increased (TEAOH/SiO ₂ ≥0.55, 7-14 days, BR Wang, Micropor. Mesopor. Mater., 2019, 278, 30). In order to solve the problem of nucleation, aluminum source, boron source, etc., as a kind of nucleation promoter, are indispensable in the one-step hydrothermal synthesis of Beta zeolite, which is also the traditional synthesis of Beta zeolite has always been a silica-alumina system or a silica-boron system s reason. However, the presence of aluminum in the synthesis system not only preempts the growth sites of heteroatoms, but also makes Beta zeolite too acidic, thereby reducing the selectivity of some products (DPSerrano, Micropor. Mesopor. Mater. 200, 146, 35; JL Zhang, Chem.Eng.J., 2016, 291, 82). In order to make up for the defects of aluminum, Y.Naraki, H.Kessler (Y.Naraki,, Adv.Porous Mater., 2016, 2, 125; H. Kessler Stud. Surf. Sci. Catal. 1994, 85, 75) et al. A fluorine-containing crystallization aid was introduced into the hydrothermal system, but the introduction of HF significantly reduced the alkalinity of the crystallization system, slowed down the mass diffusion and nucleation rate in the mass transfer system, and easily formed large-grained zeolite. Secondly, as a highly corrosive and high-risk pollutant, HF will also cause great harm to the environment along with the massive discharge of crystallization liquid.

To sum up, both the one-step hydrothermal synthesis method and the secondary isomorphous substitution method belong to the category of hydrothermal crystallization, and the inherent drawbacks of hydrothermal synthesis, such as the large discharge of crystallization liquid, the waste of nutrients, Excessive crystallization time, excessive consumption of template agent, low single-pot yield, and high still pressure are unavoidable (L.M.Ren, J.Am.Chem.Soc., 2012, 134, 15173), therefore, the development of A new method for efficient, green and simple steps of heteroatom zeolite is particularly important.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a kind of preparation method of simple steps, short time consumption, less template consumption, no need of fluorine source and aluminum source, and one-step synthesis of heteroatom M-Beta molecular sieves with stepped pores by steam-assisted action.

The method includes the following steps:

1. Basic steps

1) The silicon source is calculated as SiO ₂ , the heteroatom metal is calculated as element M, and the alkali source is calculated as OH ⁻ , according to silicon source: heteroatom metal: alkali source: template agent: water=1:0～0.07:0.01～0.8: Mix well with a molar ratio of 0.05～0.5:20～80, then add pure silicon seeds equivalent to 0.001%～10% of the mass of the silicon source, and age at a temperature of 20～80℃ for 0.5～2 hours. The hydrogels were evaporated in an oil bath at 50-100 °C for 12-48 hours to obtain templated and seeded xerogels;

2) Grinding the xerogel obtained in step 1), placing it in a kettle and a small inner liner in a ratio of 0.01 to 1:1 according to the water: dry powder mass ratio, and crystallization at 120 to 170 ° C for 20 to 96 hours, the obtained The product was ion-exchanged in 1 mol/L ammonium salt solution for 2 hours, washed to neutrality and dried, and then calcined at 550°C for 6 hours to obtain M-Beta molecular sieve.

2. Wherein, the molar ratio of silicon source, heteroatom source, alkali source, template agent and water is silicon source: heteroatom metal: alkali source: template agent: water=1:0～0.04:0.2～0.5:0.1～0.25 : 30 to 60, and the amount of seed crystals added is 5% to 10% of the mass of the silicon source.

3. Wherein, the aging temperature is 30-60°C, and the time is 0.5-1 hour, and the drying temperature is 60-90°C, and the time is 20-40 hours.

4. The mass ratio of crystallized water to dry powder is 0.1 to 0.5:1.

5. The crystallization temperature is 140 to 160° C., and the crystallization time is 36 to 72 hours.

6. Wherein, the silicon source is one or more of silica, silica gel, water glass, and silica sol.

7. wherein, the described heteroatom metal source is a kind of in titanium sulfate, titanocene dichloride, ferric ammonium citrate, ferric ammonium ethylenediamine tetraacetate, cobalt acetate, cobalt nitrate, gallium chloride, gallium nitrate or several.

8. Wherein, the organic quaternary ammonium base substance is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

9. wherein, the alkali source is one or more of sodium hydroxide and potassium hydroxide.

10. Wherein, the ammonium salt is one or more of ammonium nitrate, ammonium chloride, ammonium fluoride and ammonium phosphate.

Compared with the existing technology for synthesizing heteroatom M-Beta molecular sieves, the method has the following significant advantages: (1) Steam assists nucleation and crystallization, and the crystallization efficiency is high. Compared with the traditional hydrothermal synthesis method, this method makes full use of the infiltration effect of steam, so that the dry powder "nutrients" are encapsulated in dense water vapor, so that the concentration of dry powder nutrients is greatly improved, and the nucleation efficiency and crystallization efficiency are remarkable. improve; (2) the synthesis steps are simple. Diversified heteroatom M-Beta molecular sieves with high crystallinity can be directly synthesized by the "one-step synthesis method", and the heteroatom metal source can be directly added during the synthesis process without additional pretreatment; (3) The synthesis time and The cost of synthesis is greatly reduced. The crystallization time of the method for synthesizing M-Beta molecular sieve provided by the present invention is only two days, which has an absolute advantage in time cost; (4) the synthesis cost is greatly reduced. The consumption of the template agent used in this method is low, and the silicon source and the heteroatom metal source used are inorganic substances, so that the material cost is greatly reduced; (5) the product is nanocrystalline grains with rich hierarchical pore structure. Generally speaking, the M-Beta samples in the hydrothermal system are mostly single microporous materials of micron level, while the M-Beta molecular sieves synthesized by the present invention are nanomaterials with rich hierarchical pore structure; (6) The whole synthesis process is free of aluminum, no The presence of fluorine; (7) high product yield. The crystallization process of traditional hydrothermal synthesis requires a large amount of solvent. After the crystallization is completed, some "nutrients" such as silicon species, titanium species, fluorides, and template agents still exist in the solvent, so the product yield is relatively low. However, the present invention The proposed "steam-assisted method" can use all the templated "nutrients" to synthesize M-Beta molecular sieve with nearly 100% product yield; (8) low pollution. Usually, the residual substances dissolved in the solvent under hydrothermal conditions are directly discharged as pollutants, but in the present invention, almost no residual crystallization waste liquid is discharged, and the synthesis process does not need to use highly corrosive hydrofluoric acid, fluoride, etc.

Based on the above analysis, the "one-step steam-assisted method" proposed by the present invention is a universal method for synthesizing heteroatom M-Beta molecular sieves, and has the characteristics of realizing large-scale industrialization of M-Beta molecular sieves, and the synthesis cost and environmental load are greatly reduced. , greatly improving the application field of BEA molecular sieves.

Description of drawings

Fig. 1 XRD patterns of M-Beta molecular sieves synthesized in Examples 1-4 of the present invention.

Fig. 2 UV-Vis and UV-Vis of M-Beta molecular sieve synthesized in Examples 1-4 of the present invention

FT-IR image.

Figure 3 TEM images of the M-Beta molecular sieves synthesized in Examples 1 to 4 of the present invention.

Detailed ways

The invention provides a method for preparing a stepped pore heteroatom M-Beta molecular sieve, characterized in that the method comprises the following steps:

1) The silicon source is calculated as SiO ₂ , the heteroatom metal is calculated as element M, and the alkali source is calculated as OH ⁻ , according to silicon source: heteroatom metal: alkali source: template agent: water=1:0～0.07:0.01～0.8: Mix well with a molar ratio of 0.05～0.5:20～80, then add pure silicon seeds equivalent to 0.001%～10% of the mass of the silicon source, and age at a temperature of 20～80℃ for 0.5～2 hours. The hydrogels were evaporated in an oil bath at 50-100 °C for 12-48 hours to obtain templated and seeded xerogels;

2) Grinding the xerogel obtained in step 1), placing it in a kettle and a small inner liner in a ratio of 0.01 to 1:1 according to the water: dry powder mass ratio, and crystallization at 120 to 170 ° C for 20 to 96 hours, the obtained The product was ion-exchanged in 1 mol/L ammonium salt solution for 2 hours, washed to neutrality and dried, and then calcined at 550°C for 6 hours to obtain M-Beta molecular sieve.

According to the method of the present invention, in step 1), the molar ratio of silicon source, heteroatom source, alkali source, template agent and water is preferably silicon source: heteroatom metal: alkali source: template agent: water=1:0～0.04 : 0.2 to 0.5: 0.1 to 0.25: 30 to 60, and the amount of seed crystals added is 5% to 10% of the mass of the silicon source.

According to the method of the present invention, the inorganic silicon source compound described in step 1) can be various high-quality and pure solid silicon sources or liquid silicon sources known in the art. Specifically, it can be one or more of white carbon black, silica gel, water glass, and silica sol, all of which can show good relative crystallinity. Preference is given to silica and silica sol.

According to the method of the present invention, the inorganic heteroatom metal source described in step 1) can be various solids of high quality and purity known in the art. Specifically, it can be one or more of titanium sulfate, titanocene dichloride, ferric ammonium citrate, ferric ammonium ethylenediaminetetraacetate, cobalt acetate, cobalt nitrate, gallium chloride, and gallium nitrate. Preferred are titanocene dichloride, ferric ammonium citrate, cobalt acetate, and gallium nitrate.

According to the method of the present invention, the alkali source described in step 1) is preferably sodium hydroxide.

According to the method of the present invention, the templating agent described in step 1) can be an organic quaternary ammonium base known in the art. Specifically, it can be one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide solution. A tetraethylammonium hydroxide solution is preferred.

According to the method of the present invention, the ammonium salt described in step 2) is one or more of ammonium nitrate, ammonium chloride, ammonium fluoride and ammonium phosphate. Ammonium nitrate is preferred.

According to the method of the present invention, the aging temperature in step 1) is preferably 30-60° C., and the time is 0.5-1 hour.

According to the method of the present invention, the drying temperature in step 1) is preferably 60-90° C., and the time is preferably 20-40 hours.

According to the method of the present invention, the aging method described in step 1) is a method known to those skilled in the art.

According to the method of the present invention, the drying method described in step 1) is a method known to those skilled in the art.

According to the method of the present invention, the ratio of crystallized water to dry powder in step 2) is preferably crystallized water: the mass of dry powder is 0.1-0.5:1.

According to the method of the present invention, in step 2), the crystallization temperature is preferably 140-160° C., and the crystallization time is preferably 36-72 hours, and the ion-exchanged product is washed to neutrality and dried, and then calcined at 550° C. 6 hours.

According to the method of the present invention, the washing, drying and roasting methods described in step 2) are methods known to those skilled in the art. For example, after washing three times with deionized water, it is dried at 110° C. for 2 to 10 hours.

According to the method of the present invention, the crystallization process in step 2) is a crystallization process known in the art, and the crystallization process is a static crystallization process.

The present invention will be described in detail below through specific examples, but the present invention is not limited to the following examples.

The reagents in the following examples, various silicon sources were purchased from Shanghai Shanbo Industrial Co., Ltd., organic template agents were purchased from West Asia Reagent Co., Ltd., and the remaining reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

In the following examples, the molar amount of the silicon source is calculated as SiO ₂ , the molar amount of the heteroatom source is calculated as the metal element, and the molar amount of the template agent is calculated as TEA ⁺ .

Example 1

This example is used to illustrate a preparation method of a heteroatom Ti-Beta molecular sieve.

First, the silicon source, titanium source, alkali source, template agent, and water are thoroughly mixed according to the molar ratio of silica: titanocene dichloride: NaOH: TEAOH: H ₂ O=1:0.015:0.1:0.15:50, and then Seed crystals equivalent to 10% of the mass of the silicon source were added and aged for 0.5 hours at a temperature of 30°C. The aged hydrogels were evaporated in an oil bath at 60 °C for 48 h to obtain templated and seeded xerogels. Grind the obtained xerogel to no graininess, take 10 g and place it in a small liner, then put it into a crystallization kettle filled with 1 g of water, seal the kettle, and crystallize at 145 ° C for 48 hours. After ion exchange in 1 mol/L ammonium nitrate solution for 2 hours, washed to neutrality and dried, calcined at 550° C. for 6 hours to obtain product a.

Example 2

This example is used to illustrate a preparation method of a heteroatom Fe-Beta molecular sieve.

First, the silicon source, iron source, alkali source, template agent and water are fully mixed according to the molar ratio of silica: ferric ammonium citrate: NaOH: TEAOH: H ₂ O=1:0.028:0.16:0.1:40, and then add Seed crystals equivalent to 1% of the mass of the silicon source were aged for 0.5 hours at a temperature of 30°C. The aged hydrogels were evaporated in an oil bath at 70 °C for 24 h to obtain templated and seeded xerogels. Grind the obtained xerogel to no graininess, take 10 g and place it in a small lining, then put it into a crystallization kettle containing 5 g of water, seal the kettle, and crystallize at 145 ° C for 48 hours. After ion exchange in 1 mol/L ammonium nitrate solution for 2 hours, after washing to neutrality and drying, calcined at 550° C. for 6 hours to obtain product b.

Example 3

This example is used to illustrate a preparation method of a heteroatom Co-Beta molecular sieve.

First, the silicon source, cobalt source, alkali source, template agent, and water are thoroughly mixed according to the molar ratio of silica gel: cobalt acetate: NaOH: TEAOH: H ₂ O=1:0.01:0.09:0.25:40, and then the equivalent silicon source is added. Seed crystals of 3% by mass were aged for 0.5 hours at a temperature of 50°C. The aged hydrogels were evaporated in an oil bath at 70 °C for 24 h to obtain templated and seeded xerogels. Grind the obtained xerogel to no graininess, take 10 g of it and put it in a small lining, put it into a crystallization kettle containing 1.5 g of water, seal the kettle, and crystallize at 145 ° C for 48 hours. The product was ion-exchanged in 1 mol/L ammonium nitrate solution for 2 hours, washed to neutrality and dried, and then calcined at 550° C. for 6 hours to obtain product c.

Example 4

This example is used to illustrate a preparation method of a heteroatom Ga-Beta molecular sieve.

First, the silicon source, gallium source, alkali source, template agent: water are fully mixed according to the molar ratio of silica sol: gallium nitrate: NaOH: TEAOH: H ₂ O = 1:0.005:0.16:0.06:50, and then the equivalent of silicon is added. Seed crystals with a source mass of 10% were aged for 0.5 hours at a temperature of 30°C. The aged hydrogels were evaporated in an oil bath at 50 °C for 40 h to obtain templated and seeded xerogels. Grind the obtained xerogel to no graininess, take 10g and put it in a small liner, then put it into a crystallization kettle containing 4g of water, seal the kettle, and crystallize at 140 ° C for 72 hours. After ion exchange in 1 mol/L ammonium nitrate solution for 2 hours, washed to neutrality and dried, calcined at 550° C. for 6 hours to obtain product d.

The XRD, UV-Vis and TEM images of product a (Ti-Beta), product b (Fe-Beta), product c (Co-Beta) and product d (Ga-Beta) obtained in Examples 1-4 are shown in the attached Figure 1, Figure 2, Figure 3, it can be seen that the heteroatom M-Beta molecular sieve synthesized by the "one-step steam-assisted method" provided by the present invention is a high-crystallinity nanocrystal with rich hierarchical pore structure. Based on the above analysis, the method for synthesizing heteroatom M-Beta molecular sieves by the "one-step steam-assisted method" proposed by the present invention is a universal synthesis method, which has the characteristics of realizing large-scale industrialization of M-Beta molecular sieves, and reduces the synthesis cost. And the environmental load is greatly reduced, which greatly expands the application field of Beta molecular sieve.

Claims (10)

1. A preparation method of a gradient pore heteroatom M-Beta molecular sieve is characterized by comprising the following steps:

1) silicon source of SiO₂Calculated as element M, the heteroatom metal is calculated as OH^－Counting according to silicon source: heteroatom metal: alkaliSource: template agent: fully mixing water in a molar ratio of 1: 0-0.07: 0.01-0.8: 0.05-0.5: 20-80, adding pure silicon seed crystals with the mass of 0.001-10% of that of a silicon source, aging at 20-80 ℃ for 0.5-2 hours, and evaporating the aged hydrogel in an oil bath at 50-100 ℃ for 12-48 hours to obtain a templated and seeded xerogel;

2) grinding the dried gel obtained in the step 1), respectively placing the dried gel in a kettle and a small liner according to the mass ratio of 0.01-1: 1 of water to the dried powder, crystallizing the dried gel for 20-96 hours at 120-170 ℃, ion exchanging the obtained product for 2 hours in 1 mol/L ammonium salt solution, washing the product to be neutral, drying the product, and calcining the product for 6 hours at 550 ℃ to obtain the M-Beta molecular sieve.

2. The method according to claim 1, wherein in step 1), the molar ratio of the silicon source, the heteroatom source, the alkali source, the template agent and the water is silicon source: heteroatom metal: alkali source: template agent: the ratio of water to silicon is 1: 0-0.04: 0.2-0.5: 0.1-0.25: 30-60, and the addition amount of the seed crystal is 5-10% of the mass of the silicon source.

3. The method according to claim 1, wherein in the step 1), the aging temperature is 30-60 ℃ for 0.5-1 hour, and the evaporation temperature is 60-90 ℃ for 20-40 hours.

4. The method as claimed in claim 1, wherein in the step 2), the mass ratio of the crystallized water to the dry powder is 0.1-0.5: 1.

5. the method as claimed in claim 1, wherein the crystallization temperature in step 2) is 140 to 160 ℃ and the crystallization time is 36 to 72 hours.

6. The method according to claim 1 or 2, wherein the silicon source is one or more of white carbon black, silica gel, water glass and silica sol.

7. The method of claim 1 or 2, wherein the heteroatom metal source is one or more of titanium sulfate, titanocene dichloride, ferric ammonium citrate, ferric ammonium ethylene diamine tetraacetate, cobalt acetate, cobalt nitrate, gallium chloride and gallium nitrate.

8. The method according to claim 1 or 2, wherein the organic quaternary ammonium base material is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

9. The method according to claim 1 or 2, wherein the alkali source is one or more of sodium hydroxide and potassium hydroxide.

10. The method according to claim 2, wherein the ammonium salt is one or more of ammonium nitrate, ammonium chloride, ammonium fluoride and ammonium phosphate.

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