CN100424012C - A preparation method of mesoporous material mainly composed of silicon oxide - Google Patents

Abstract

The invention relates to a method for preparing a mesoporous material with high hydrothermal stability, uniform pore size, and silicon oxide as the main body. NaOH is mixed and refluxed, and then the pH value of the dissolved substance is adjusted with inorganic acid, and crystallized for a period of time under certain conditions to obtain a mesoporous material with high hydrothermal stability and a particle size of 20-500 nanometers. After being calcined at 550°C, the specific surface area of the material is 300-1500m ² /g, the pore volume is 0.1-1.5cm ³ /g, and the pore diameter is 2-10nm. After being treated with boiling water at 100°C for 312 hours, the material still maintains more than 90% of its specific surface area and pore volume.

Description

A preparation method of mesoporous material mainly composed of silicon oxide

technical field

The invention relates to a preparation method of a mesoporous material mainly composed of silicon oxide with high hydrothermal stability.

Background technique

In 1992, Mobil Corporation synthesized silica mesoporous materials (U.S. Patent 5057296, 1991; U.S. Patent 5098684, 1992). This material has high specific surface area and high thermal stability, orderly arrangement of pores, and adjustable pore size. It has broad application prospects in adsorption, separation, catalytic conversion of macromolecules, and assembly of nanomaterials. attention. However, the low hydrothermal stability of silica mesoporous materials limits its application. Although people have tried a variety of methods to improve the hydrothermal stability of silica mesoporous materials to a large extent, compared with traditional microporous molecular sieves, the hydrothermal stability of this material is still low, and it is still difficult to Meet the stringent requirements of industrial high-temperature catalytic processes (such as catalytic cracking).

Recently, Pinnavaia et al. (U.S.Patent 6702993B2, 2004; U.S.Patent 6706169B2, 2004; U.S.Patent 6770258B2, 2004) and Qiu Shilun et al. (CN1349929A, 2001) reported that a microporous molecular sieve seed solution was used instead of a commonly used silicon source to synthesize a high-water Thermally stable silica-alumina mesoporous material. The seed crystal solution they adopted refers to that when synthesizing microporous molecular sieves (such as ZSM-5, Y, Beta), when the microstructural units of molecular sieves appear in the synthesis system but crystal nuclei have not yet formed, by reducing the reaction pressure, temperature or Increase the pH value of the system to interrupt the crystallization process, and obtain a clear solution containing silicon, aluminum and other components. They believe that the primary and secondary structural units of microporous molecular sieves exist in the seed solution, and these structural units can interact with surfactants and enter the mesoporous framework through organic-inorganic self-assembly process, which is equivalent to that in amorphous Microcrystals similar to microporous molecular sieves are introduced into the walls of the mesopores, thus improving the stability of the product. The obtained silicon-based mesoporous material can be treated in boiling water for 300 hours, or in saturated water vapor at 800 °C for 2 hours without significant change in mesoporous characteristics. However, it should be noted that not all microporous molecular sieves are available as seed solutions. Therefore, the application range of the above method is limited.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a mesoporous material mainly composed of silicon oxide.

In order to achieve the above object, the technical solution of the present invention is: firstly synthesize the microporous molecular sieve crystal, dissolve the obtained microporous molecular sieve in template agent and inorganic alkali solution, adjust the pH value of the solution, and then crystallize for a period of time. The present invention is also characterized in that the hydrothermal stability of the obtained mesoporous material is much higher than that of the directly synthesized mesoporous material, and the particle size of the mesoporous material is small, reaching 20-500 nanometers.

The preparation method of the present invention is:

a) Prepare the initial gel reactant of Si:aAl:bNaOH:cNaCl:dH ₂ O:eHMI, wherein:

HMI is hexamethyleneimine, a is the molar ratio of Al source to silicon source, b is the molar ratio of NaOH to silicon source, c is the molar ratio of NaCl to silicon source, d is the molar ratio of _H2O to silicon source Ratio, e is the mol ratio of HMI and silicon source;

0≤a≤0.2, 0.05≤(b+c)≤0.5, 10≤d≤500, 0.2≤e≤2.0;

Preferably 0≤a≤0.05, 0.1≤(b+c)≤0.3, 20≤d≤50, 0.4≤e≤1.0;

Among them, the silicon source material is white carbon black, water glass, silica sol, ortho silicic acid and/or orthosilicate; the aluminum source material is aluminum chlorohydrate, aluminum nitrate hydrate, aluminum sulfate hydrate and/or sodium metaaluminate ;

b) Crystallize the reactant in step a at 100-160°C for 2-15 days (preferably the crystallization temperature is 135-150°C; the crystallization time is 4-10 days), and the crystallized product is washed and dried Finally, the microporous molecular sieve precursor was obtained, named P;

c) Mix the precursor P obtained in step b with a template, NaOH, and H ₂ O to prepare a compound of P:xR:yNaOH:zH ₂ O, wherein R represents a template, which is a block copolymer EO ₂₀ PO ₇₀ EO ₂₀ , cetyltrimethylammonium bromide (CTAB), cetylamine and/or octadecylamine; , x, y, z respectively R, NaOH, H ₂ O and precursor P molar ratio, wherein: 0.6≤x≤5.0, 0.8≤y≤5.0, 50≤z≤100, preferably, 0.6≤x≤5.0, 0.8≤y≤5.0, 50≤z≤100;

d) reflux the mixture obtained in step c at 80-120°C for 2-50 hours (preferably at 90-100°C for 6-24 hours), and cool down to room temperature;

e) Use a mineral acid solution to adjust the pH of the mixture obtained in step d to 0.5-11 (preferably pH 3-9), and then reflux at 10-80° C. for 2-100 hours (preferably 20-40 ℃ reflux for 6-50 hours), and finally the solid product is separated, washed and dried to obtain the original powder of the mesoporous material;

f) Calcining the raw powder obtained in step e at 350-850° C. for 6-20 hours to remove the template agent and obtain a mesoporous material with high order and high hydrothermal stability.

More specifically, its preparation method is:

1) Mix the silicon source material, the aluminum source material, NaOH, NaCl, H ₂ O and HMI uniformly under stirring in proportion to obtain the initial gel reactant. Transfer it to a stainless steel autoclave with a Teflon liner and crystallize under autogenous pressure. The rotation speed of the reactor is 10-150r/min, the crystallization temperature is 100-160°C, and the crystallization time is 2-15 days. The obtained solid product is separated from the mother liquor, washed, and then dried to obtain a microporous molecular sieve precursor.

2) Mixing the precursor with the template agent, NaOH, and H ₂ O in proportion, and refluxing the obtained mixture at 80-120° C. for 2-50 hours. After cooling the mixture to room temperature, adjust the pH value of the system to 0.5-11 with 0.1-10M inorganic acid, such as hydrochloric acid, sulfuric acid, phosphoric acid, etc., and then stir at 10-80°C for 2-100 hours. After solid-liquid separation, washing and drying, the original powder of the mesoporous sample was obtained. This sample contains a template agent, in order to remove the template agent, it is calcined at 350-850°C for 6-20 hours to obtain a mesoporous material mainly composed of silicon oxide with high hydrothermal stability and uniform pore size.

Description of drawings

Fig. 1 is the X-ray diffraction (XRD) pattern of the former powder of mesoporous material prepared in embodiment 1;

Curves A, B, C, D, and E in Fig. 2 are respectively the XRD figure of the mesoporous material raw powder prepared in Examples 2, 3, 4, 5, and 6;

Curves A, B, C, and D in Fig. 3 are respectively the XRD patterns of the mesoporous material raw powder prepared in Examples 7, 8, 9, and 10;

Fig. 4 is the XRD pattern of the mesoporous material prepared in Example 11;

Fig. 5 is the scanning electron micrograph of the former powder of mesoporous material prepared in embodiment 8;

FIG. 6 is the XRD pattern of the mesoporous materials prepared in Comparative Example 1 and Comparative Example 2.

Detailed ways

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

Example 1

After mixing 40 g of white carbon black, 0.5 g of sodium metaaluminate, 2.5 g of sodium hydroxide, 2.7 g of NaCl with 540 g of deionized water and 47.5 g of HMI and stirring at room temperature for 30 minutes, the formed gel was transferred to a polymer In a stainless steel reaction kettle lined with tetrafluoroethylene, it was crystallized at 150°C and 90r/min for 8 days. The solid product obtained was centrifuged, washed with deionized water and dried at 100°C to obtain the original precursor powder UTM-1. Its XRD See Figure 1 for the picture.

After mixing 40 g of silica, 2.5 g of NaOH, 2.7 g of NaCl with 540 g of deionized water and 40 g of HMI and stirring at room temperature for 30 min, the formed gel was transferred to a stainless steel Teflon-lined In the reaction kettle, it was crystallized at 150°C and 90r/min for 8 days. After the product was centrifuged, washed with deionized water and dried at 100°C, the precursor powder kenyaite was obtained. The XRD pattern is shown in Figure 1.

Example 2

Take 1.8 grams of UTM-1 raw powder, mix it with 4.5 grams of cetyltrimethylammonium bromide (CTAB) and 4 grams of NaOH, add 190 milliliters of deionized water, and place the resulting suspension in an oil bath at 100°C After refluxing for 8 hours, cool and add 2M HCl to pH = 9, then stir at room temperature for 12 hours, and finally wash and dry the XRD pattern of the obtained sample as shown in Figure 2A.

Example 3

Take 1.8 grams of UTM-1 raw powder, mix it with 4.5 grams of CTAB and 4 grams of NaOH, add 190 milliliters of deionized water, place the resulting suspension in an oil bath at 100 ° C for 8 hours, cool and add 2M HCl to pH = 7, then stirred at room temperature for 12 hours, and the XRD pattern of the sample obtained after washing and drying is shown in Fig. 2B.

Example 4

In Example 3, after the mixture was cooled, 2M HCl was added to pH=3, and other conditions were kept unchanged. The XRD pattern of the obtained sample is shown in FIG. 2C .

Example 5

In Example 3, the amount of CTAB was changed to 1.44 g, and the other conditions were kept unchanged. The XRD pattern of the obtained sample is shown in FIG. 2D.

Example 6

In Example 3, the amount of NaOH was changed to 1.82 g, and other conditions were kept unchanged, and the XRD pattern of the obtained sample is shown in FIG. 2E.

Example 7

Take 1.8 grams of kenyaite raw powder, mix it with 4.5 grams of CTAB and 4 grams of NaOH, add 190 milliliters of deionized water, place the resulting suspension in an oil bath at 100°C for 8 hours, cool and add 2M HCl to pH = 9. Stir at room temperature for another 12 hours, and finally wash and dry the sample to obtain an XRD pattern as shown in Figure 3A.

Example 8

In Example 7, after the mixture was cooled, 2M HCl was added to pH=7, and other conditions were kept unchanged. The XRD pattern of the obtained sample is shown in FIG. 3B .

Example 9

In Example 7, after the mixture was cooled, 2M HCl was added to pH=5, and other conditions were kept unchanged. The XRD pattern of the obtained sample is shown in FIG. 3C .

Example 10

In Example 7, after the mixture was cooled, 2M HCl was added to pH=3, and other conditions were kept unchanged. The XRD pattern of the obtained sample is shown in FIG. 3D .

Example 11

The sample obtained in Example 3 was roasted at 550° C. for 10 hours and mixed with H ₂ O (the ratio of water to solid was controlled to be 100 ml per gram), then placed in an oven at 100° C. for a period of time, and finally the solid was separated and Perform structural analysis. The XRD patterns of the samples after different treatment times are shown in Figure 4, and their typical structural parameters are listed in Table 1. The XRD results in Figure 4 show that the prepared material has a regular pore structure. Figure 4 also shows that the sample obtained in Example 3 can still maintain good long-range order after being treated with boiling water for 312 hours; Table 1 shows that the specific surface area of the sample is 922m ² /g, and the pore volume is 1.08cm ³ /g , were respectively 92% and 90% of those before boiling water treatment. XRD results and nitrogen adsorption results indicated that the obtained samples had high hydrothermal stability.

Example 12

The SEM results of Example 8 are shown in Fig. 5, and it can be seen from Fig. 5 that the sample has a uniform particle size, and its particle size is about 200nm.

Comparative example 1

MCM-41 was synthesized from tetraethyl orthosilicate (TEOS). The gel with a ratio of TEOS:Al ₂ O ₃ :CTAB:NaOH: _{H 2} O=1:0.01:0.12:0.2:100 was transferred to a stainless steel reactor with a polytetrafluoroethylene liner at 100°C After crystallization for 3 days, the obtained solid product was centrifuged, washed with deionized water and dried at 100°C to obtain the original powder of MCM-41. The XRD pattern after calcination at 550°C for 10 hours is shown in Figure 6.

Comparative example 2

The MCM-41 calcined at 550°C was mixed with H ₂ O (the ratio of water to solid was controlled to be 100 ml per gram), and placed in an oven at 100°C for a period of time, and finally the solid was separated for structural analysis. The XRD patterns of the samples after different treatment times are shown in Figure 6 (the vertical axis is the same as that of Figure 4), and their typical structural parameters are listed in Table 1. Figure 6 shows that the order of the MCM-41 material is greatly reduced after 24 hours of treatment. Table 1 shows that the specific surface area of the sample is 150m ² /g, and the pore volume is 0.35cm ³ /g, which are respectively 17% and 51% of those before boiling water treatment. Further prolonging the treatment time will cause the collapse of the mesoporous structure.

Table 1 Structural parameters of samples after calcination at 550°C

The values in parentheses represent the percentage of the parameters of the sample after boiling water treatment to its pre-treatment

Claims (9)

1. A preparation method of a mesoporous material with silicon oxide as the main body, first hydrothermally synthesizing a microporous molecular sieve precursor, then mixing the precursor with a template agent and NaOH and refluxing, and then using an inorganic acid to adjust the pH value of the dissolved product Post-crystallization; its specific steps are: a) Prepare the initial gel reactant of Si:aAl:bNaOH:cNaCl:dH ₂ O:eHMI, wherein: HMI is hexamethyleneimine, a is the molar ratio of Al source to silicon source, b is the molar ratio of NaOH to silicon source, c is the molar ratio of NaCl to silicon source, d is the molar ratio of _H2O to silicon source Ratio, e is the mol ratio of HMI and silicon source; 0≤a≤0.2, 0.05≤b+c≤0.5, 10≤d≤500, 0.2≤e≤2.0; b) crystallize the reactant in step a at 100-160°C for 2-15 days, wash and dry the crystallized product to obtain a microporous molecular sieve precursor, named P; c) Mix the precursor P obtained in step b with a template, NaOH, and H ₂ O to prepare a compound of P:xR:yNaOH:zH ₂ O, wherein R represents a template, which is a block copolymer EO ₂₀ PO ₇₀ EO ₂₀ , cetyltrimethylammonium bromide, cetylamine and/or octadecylamine; x, y, z are the molar ratios of R, NaOH, H ₂ O to precursor P, respectively , where: 0.6≤x≤5.0, 0.8≤y≤5.0, 50≤z≤100; d) reflux the mixture obtained in step c at 80-120°C for 2-50 hours, and drop to room temperature; e) using a mineral acid solution to adjust the pH of the mixture obtained after reflux in step d to 0.5-11, then reflux at 10-80°C for 2-100 hours, and finally separate, wash and dry the solid product to obtain the original powder of the mesoporous material; f) Calcining the raw powder obtained in step e at 350-850° C. for 6-20 hours to remove the template agent and obtain a mesoporous material with high order and high hydrothermal stability. 2. The preparation method according to claim 1, characterized in that the prepared mesoporous material particle diameter is 20 to 500 nanometers. 3. The preparation method according to claim 1, wherein the silicon source material is white carbon black, water glass, silica sol, ortho silicic acid and/or orthosilicate. 4. The preparation method according to claim 1, wherein the aluminum source material is aluminum chlorohydrate, aluminum nitrate hydrate, aluminum sulfate hydrate and/or sodium metaaluminate. 5. The preparation method according to claim 1, characterized in that, among the initial gel reactants of Si:aAl:bNaOH:cNaCl:dH ₂ O:eHMI, 0≤a≤0.05, 0.1≤b+c≤0.3, 20 ≤d≤50, 0.4≤e≤1.0. 6. The preparation method according to claim 1, characterized in that, the crystallization temperature in step b is 135-150°C; the crystallization time is 4-10 days. 7. The preparation method according to claim 1, characterized in that, in step d, the precursor is mixed with the template agent and NaOH and then refluxed at 90-100°C for 6-24 hours. 8. the preparation method as claimed in claim 1, is characterized in that, the pH in step e is 3～9. 9. The preparation method according to claim 1, characterized in that, the crystallization temperature in step e is 20-40°C, and the time is 6-50 hours.

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