CN102424411A - Ordered mesoporous gamma-Al2O3Preparation method of (1) - Google Patents

Abstract

The invention discloses a method for preparing ordered mesoporous γ-Al ₂ O _3. The preparation method of the invention comprises synthesis reaction, aging, drying and calcination to obtain ordered mesoporous γ-Al ₂ O _3. The method of the invention is simple and easy to operate, safe to operate, and easy to industrialize. The obtained γ-Al ₂ O ₃ has the advantages of large specific surface and high thermal stability.

Description

A preparation method of ordered mesoporous γ-Al2O3

technical field

The invention relates to the technical field of preparation of mesoporous materials, in particular to a method for preparing ordered mesoporous γ-Al ₂ O ₃ .

Background technique

In 1992, the scientists of Mobil Corporation used alkyl quaternary ammonium salt cationic surfactants as templates for the first time to successfully synthesize M41S series silicon-based mesoporous molecular sieves under alkaline conditions. The materials industry attaches great importance to it. Various non-silicon-based mesoporous materials have been developed successively, including transition metal oxides, rare earth oxides and composite metal oxides. Due to the large pore size, specific surface area and pore volume of mesoporous materials, high thermal stability and hydrothermal stability, the pore size can be adjusted according to different experimental conditions. Therefore, it has a wide range of applications in macromolecular catalysis, biomolecular separation, adsorption, photoelectric nanomaterials and other fields.

Ordered mesoporous alumina is a new type of nanostructure material with large specific surface, pore size between 2-50nm, narrow pore size distribution and orderly pore size and shape. Alumina is an important catalyst carrier and adsorbent, and is widely used in industry. γ-Al ₂ O ₃ has a large specific surface area, a special pore structure, certain acidity, high thermal stability, and is the most widely used. The preparation of alumina as a mesoporous material is superior to traditional silica materials: it has higher hydrothermal stability, different isoelectric points, and is easy to uniformly load different metal species. Therefore, the research on the preparation, structure and properties of ordered mesoporous alumina, especially ordered mesoporous γ-Al ₂ O ₃ has become a hotspot in the field of current research.

At present, the commonly used method for preparing mesoporous alumina materials is to use surfactants as templates, and use physical and chemical processes such as solvothermal, sol-gel, precipitation, emulsification, etc., to self-assemble through the interface between organic and inorganic substances. For ordered mesoporous materials, neutral surfactants are the most used surfactants.

Chinese patent CN101024503A (application number 200710063718.5) uses aluminum nitrate as the aluminum source and ammonium carbonate as the precipitating agent to prepare ordered mesoporous alumina by using high gravity technology. The disadvantage is that the high gravity reactor needs to be used and the process is complicated. Chinese patent CN101597077A (Application No. 200910069671.2) provides a technology for preparing ordered mesoporous alumina using sodium lauroyl glutamate as a surfactant. The disadvantage is that the obtained mesoporous alumina has a small specific surface area and low thermal stability. Chinese patent CN101993102A (application number 200910091025.6) provides a synthesis of ordered mesoporous alumina using methyl cellulose as template, sodium aluminate and aluminum chloride as raw materials by acid-base pairing method. Its characteristic is that the prepared mesoporous alumina has a worm-like channel, relatively high thermal stability, but relatively small specific surface. Most of the products obtained by the above methods are amorphous mesoporous alumina with worm-like pore structure, small specific surface area and low thermal stability. Therefore, the application of mesoporous alumina in high temperature catalytic reaction and high temperature assembly is limited.

Contents of the invention

The object of the present invention is to provide a method for preparing ordered γ-Al ₂ O ₃ with large specific surface area and high thermal stability, which is simple in process, safe in operation and easy for industrial scale-up production.

The above-mentioned purpose of the present invention is achieved through the following technical solutions:

A preparation method of ordered mesoporous γ-Al ₂ O ₃ comprises the following steps:

(1) Synthesis reaction: Dissolve template agent in absolute ethanol, add mixed acid while stirring, add aluminum source after clarification, seal and stir;

(2) Aging: Aging the solution obtained in step (1) to obtain a transparent gel;

(3) Drying: Dry the transparent gel to obtain a white powder;

(4) Calcination: Calcining the white powder in an oxygen atmosphere to obtain ordered mesoporous γ-Al ₂ O ₃ .

As a preferred option, in the above preparation method, the template agent in step (1) is P123 or F127; the mixed acid is a mixture of concentrated hydrochloric acid, concentrated nitric acid, citric acid and acetic acid; the aluminum source is isopropyl Alcohol aluminum or anhydrous aluminum trichloride; the time of the sealed stirring is 5~10h.

As a preferred solution, in the above preparation method, the aging time in step (2) is 10-24 hours.

As a preferred solution, in the above preparation method, the drying temperature in step (3) is 60° C., and the drying time is 48 hours.

As a preferred option, in the above preparation method, the calcination conditions in step (4) are: heating up to 550°C at a rate of 1°C/min and holding for 6 hours, then raising the temperature to 700-1000°C at a rate of 10°C/min and holding the temperature 1 h.

Compared with the prior art, the present invention has the following beneficial effects:

The alumina prepared by the present invention has regular hexagonal pore structure, large specific surface area, and narrow pore size distribution. The order of mesoporous alumina can be adjusted by changing the content of acetic acid, and the ordered mesoporous structure can still be maintained after annealing at 1000°C.

Description of drawings

Fig. 1 is the small angle XRD figure of embodiment 1;

Fig. 2 is the TEM figure of embodiment 1;

Fig. 3 is the N of embodiment ₁ Adsorption-desorption curve and pore size distribution curve;

Fig. 4 is the small angle XRD figure of embodiment 2;

FIG. 5 is a TEM image of Example 4. FIG.

Detailed ways

The following connotations and examples are used to further explain the present invention, but the examples do not limit the present invention in any form.

Example 1

A． Synthesis reaction: Dissolve 1.0 g P123 in 20 mL absolute ethanol, add mixed acid (concentrated hydrochloric acid: citric acid: glacial acetic acid = 2:1:2) while stirring, and adjust the pH to 3~4. After clarification, add 10 mmol aluminum isopropoxide, seal with PE film, and continue stirring for 5 h.

B． Aging: Put the solution in step A into aging for 10 h to obtain a transparent gel.

C． Drying: transfer the gel in step B to an oven at 60 °C for 48 h to obtain a white powder.

D． Calcination: heat the white powder in step C to 550°C at 1°C/min in an oxygen atmosphere and keep it for 6 hours, then raise the temperature to 700°C at 10°C/min and hold it for 1 hour.

The product obtained by this method is ordered mesoporous γ-Al ₂ O ₃ . The small-angle XRD pattern (Fig. 1) and TEM (Fig. 2) of this product can be seen that the product channels are arranged in a two-dimensional regular hexagon, and the order Sex is very high. Figure 3 is the nitrogen adsorption-desorption curve and pore size distribution diagram of this product. It can be seen that the adsorption curve is a type VI curve, and then changed to a larger one, with obvious mesopore characteristics and narrow pore size distribution; other characteristics of the product: the specific surface area is 265.9 m ² /g, pore volume 0.46 m ³ /g, average pore diameter 5.7 nm.

Example 2

A． Synthesis reaction: Dissolve 1.0 g P123 in 20 mL absolute ethanol, add mixed acid (concentrated nitric acid: citric acid: glacial acetic acid = 2.5:1:1) while stirring, and adjust the pH to 3~4. After clarification, add 10 mmol aluminum isopropoxide, seal with PE film, and continue stirring for 5 h.

B． Aging: Put the solution in step A into aging for 10 h to obtain a transparent gel.

C． Drying: transfer the gel in step B to an oven at 60 °C for 48 h to obtain a white powder.

D． Calcination: heat the white powder in step C to 550°C at a rate of 1 ℃/min in an oxygen atmosphere for 6 hours, then raise the temperature to 700°C at a rate of 10 ℃/min and hold for 1 hour.

The prepared mesoporous γ-Al ₂ O ₃ has a specific surface area of 293.7 m ² /g, a pore volume of 0.49 m ³ /g, and an average pore diameter of 9.9 nm. The order of the product is better than that of Embodiment 1, as can be seen from the XRD pattern (Fig. 2).

Example 3

A． Synthesis reaction: Dissolve 1.0 g P123 in 20 mL absolute ethanol, add mixed acid (concentrated hydrochloric acid: citric acid: glacial acetic acid = 2:1:2) while stirring, and adjust the pH to 3~4. After clarification, add 10 mmol aluminum isopropoxide, seal with PE film, and continue stirring for 5 h.

B． Aging: Put the solution in step A into aging for 10 h to obtain a transparent gel.

C． Drying: transfer the gel in step B to an oven at 60 °C for 48 h to obtain a white powder.

D． Calcination: heat the white powder in step C to 550°C at 1°C/min in an oxygen atmosphere and keep it for 6 hours, then raise the temperature to 1000°C at 10°C/min and hold it for 1 hour.

The prepared mesoporous γ-Al ₂ O ₃ has a specific surface area of 181.23 m ² /g, a pore volume of 0.23 m ³ /g, and an average pore diameter of 7.3 nm. The ordered mesoporous structure is still maintained, and the order is lower than that of Embodiment 1.

Example 4

A． Synthesis reaction: Dissolve 1.0 g P123 in 20 mL absolute ethanol, add mixed acid (citric acid: glacial acetic acid = 1:1) while stirring to adjust the pH to 3~4. After clarification, add 10 mmol of anhydrous aluminum trichloride, seal with PE film, and continue to stir for 5 h.

B． Aging: Aging the solution in step A for 8 h to obtain a transparent gel.

C． Drying: transfer the gel in step B to an oven at 60 °C for 48 h to obtain a white powder.

D． Calcination: heat the white powder in step C to 550°C at 1°C/min in an oxygen atmosphere and keep it for 6 hours, then raise the temperature to 700°C at 10°C/min and hold it for 1 hour.

The prepared mesoporous γ-Al ₂ O ₃ has a specific surface area of 365.8 m ² /g, a pore volume of 0.59 m ³ /g, and an average pore diameter of 9.8 nm. The thermal stability and order are lower than those in Embodiment 1.

Example 5

A． Synthesis reaction: Dissolve 1.0 g F127 in 20 mL of absolute ethanol, add mixed acid (concentrated hydrochloric acid: citric acid: glacial acetic acid = 2:1:1.5) while stirring, and adjust the pH to 3~4. After clarification, add 10 mmol aluminum isopropoxide, seal with PE film, and continue stirring for 5 h.

B． Aging: aging the solution in step A for 10 h to obtain a transparent gel.

C． Drying: transfer the gel in step B to an oven at 60 °C for 48 h to obtain a white powder.

D． Calcination: heat the white powder in step C to 550°C at a rate of 1 ℃/min in an oxygen atmosphere for 6 hours, then raise the temperature to 700°C at a rate of 10 ℃/min and hold for 1 hour.

The prepared mesoporous γ-Al ₂ O ₃ has a specific surface area of 260.8 m ² /g, a pore volume of 0.23 m ³ /g, and an average pore diameter of 5.5 nm.

Claims (8)

1. A preparation method of ordered mesoporous γ-Al ₂ O ₃ is characterized in that comprising the steps: (1) Synthesis reaction: Dissolve template agent in absolute ethanol, add mixed acid while stirring, add aluminum source after clarification, seal and stir; (2) Aging: Aging the solution obtained in step (1) to obtain a transparent gel; (3) Drying: Dry the transparent gel to obtain a white powder; (4) Calcination: Calcining the white powder in an oxygen atmosphere to obtain ordered mesoporous γ-Al ₂ O ₃ . 2. The method for preparing ordered mesoporous γ-Al ₂ O ₃ according to claim 1, characterized in that the template agent in step (1) is P123 or F127. 3. The method for preparing ordered mesoporous γ-Al ₂ O ₃ according to claim 1, characterized in that the mixed acid in step (1) is a mixture of concentrated hydrochloric acid, concentrated nitric acid, citric acid and acetic acid. 4. The method for preparing ordered mesoporous γ-Al ₂ O ₃ according to claim 1, characterized in that the aluminum source in step (1) is aluminum isopropoxide or anhydrous aluminum trichloride. 5. The method for preparing ordered mesoporous γ-Al ₂ O ₃ according to claim 1, characterized in that the time for sealing and stirring in step (1) is 5-10 hours. 6. The method for preparing ordered mesoporous γ-Al ₂ O ₃ according to claim 1, characterized in that the aging time in step (2) is 10-24 hours. 7. The method for preparing ordered mesoporous γ-Al ₂ O ₃ according to claim 1, characterized in that the drying temperature in step (3) is 60° C., and the drying time is 48 hours. 8. The method for preparing ordered mesoporous γ-Al ₂ O ₃ according to claim 1, characterized in that the calcination conditions in step (4) are: heating up to 550°C at a rate of 1°C/min and holding for 6 hours, Then the temperature was raised to 700-1000°C at a speed of 10°C/min and kept for 1 h.

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