CN101323460B - Method for preparing high specific surface area three-dimensional mesoporous active aluminum oxide by hard template - Google Patents

Abstract

The invention relates to a method for utilizing a hard template to prepare three-dimensional mesoporous active aluminium oxide with high specific surface area, belonging to the technical field of the preparation of solid mesoporous material. The existing mesoporous active aluminium oxide has the problems of undeveloped pore canal structure and small specific surface area, etc.; the method provided by the invention adopts tetraethoxysilane as a raw material and uses triblock copolymer (EO106PO70EO106) and hexadecyl trimethyl ammonium bromidec as a soft-template agent; three-dimensional mesoporous SBA-16 with different shapes is synthesized by hydro-thermal reaction; then the three-dimensional mesoporous SBA-16 is used as the hard template and sucrose is used as a carbon source to prepare the three-dimensional mesoporous carbon; finally, the three-dimensional mesoporous carbon is used as the hard template, aluminium nitrate is used as an aluminium source, absolute ethyl alcohol is used as a solvent, the three-dimensional mesoporous active aluminium oxide with high specific surface area is synthesized by the processes of a plurality of times of dipping and ignition in the radiation of ultrasonic wave. The method of the invention has low cost and simple and convenient operation, and the prepared three-dimensional mesoporous active aluminium oxide has the advantages of narrow pore size distribution and large specific surface area, etc.

Description

A method for preparing three-dimensional mesoporous activated alumina with high specific surface area using hard template

technical field

The invention belongs to the technical field of preparation of solid mesoporous materials, and in particular relates to a method for preparing three-dimensional mesoporous activated alumina with high specific surface area by using three-dimensional mesoporous carbon as a hard template.

Background of the invention

V，et al.，Micropor.Mesopor.Mater.，2001，44-45：203；YangP，et al.，Chem.Mater.，1999，11：2813)、阴离子表面活性剂(Yada M，et al.，Chem.Commun.，1996：769；Vaudry F，et al.，Chem.Mater.，1996，8：1451；Valange S，et al.，Micropor.Mesopor.Mater.，2000，35-36：597)和阳离子表面活性剂(Cabrera S，et al.，Adv.Mater.，1999，11(5)：379；Deng W，et al.，Adv.Funct.Mater.，2003，13：61)为模板剂合成介孔氧化铝的方法，但是他们所制得的大多数介孔氧化铝均为无定形(即非晶态)粉末，热稳定性很差，从而大大地限制了其在催化反应中的应用。直至最近，人们才以胺、聚乙二醇或嵌段共聚物为模板剂成功地合成出具有一定结晶度的介孔γ-Al₂O₃(Hicks R W，et al.，Chem.Mater.，2003，15：78；Zhang Z，et al.，J.Am.Chem.Soc.，2002，124：1592；Bossière C，etal.，Chem.Mater.，2006，18：5238)。Liu等采用“纳米复制”法合成出具有规整孔道结构的γ-Al₂O₃晶体(Liu Q，et al.，Chem.Mater.，2006，18：5153)，即先以SBA-15为模板制得介孔碳(CMK-3)，再以CMK-3为模板制得介孔活性氧化铝。然而，该方法所使用的硬模板(介孔硅和介孔碳)均为二维结构且比表面积较低(小于1000m²/g)，使得所得介孔活性氧化铝的孔道呈二维结构且比表面积较低(小于400m²/g)，限制了其在吸附与催化中的应用。Activated alumina is widely used as a catalyst, carrier and adsorbent, etc., and it is extremely important to control its specific surface area, pore size and distribution. In recent years, with the establishment of nanofabrication technology, the controllable synthesis of porous solid materials has become possible. Mesoporous activated alumina has the advantages of high specific surface area and developed pore structure, which is beneficial to the dispersion of active components and the adsorption and diffusion of reactant molecules. However, most of the pore structure of mesoporous activated alumina is destroyed under high temperature conditions. , resulting in a significant decrease in the specific surface area and dispersion of the active components, thus greatly affecting its physicochemical properties. Therefore, thermal stability is an important indicator to measure whether mesoporous activated alumina is suitable as a catalyst or carrier. Activated alumina (ie, γ-Al ₂ O ₃ ) is one of many crystal forms of alumina, and is usually obtained by burning an aluminum precursor at 400°C to 600°C. In the past ten years, scholars at home and abroad have studied nonionic surfactants (Bagshaw S A, et al., Angew.Chem.Int.Ed., 1996,35:1102; Gonzá

V, et al., Micropor.Mesopor.Mater., 2001,44-45:203; YangP, et al., Chem.Mater., 1999,11:2813), anionic surfactant (Yada M, et al. , Chem.Commun., 1996: 769; Vaudry F, et al., Chem. Mater., 1996, 8: 1451; Valange S, et al., Micropor. Mesopor. Mater., 2000, 35-36: 597) And cationic surfactant (Cabrera S, et al., Adv. Mater., 1999, 11 (5): 379; Deng W, et al., Adv. Funct. Mater., 2003, 13: 61) as template methods for synthesizing mesoporous alumina, but most of the mesoporous alumina they produced are amorphous (that is, non-crystalline) powders with poor thermal stability, which greatly limits their application in catalytic reactions . Until recently, people have successfully synthesized mesoporous γ-Al ₂ O ₃ with certain crystallinity using amine, polyethylene glycol or block copolymer as template (Hicks R W, et al., Chem. Mater., 2003, 15: 78; Zhang Z, et al., J. Am. Chem. Soc., 2002, 124: 1592; Bossière C, et al., Chem. Mater., 2006, 18: 5238). Liu et al. synthesized γ-Al ₂ O ₃ crystals with regular pore structure by the "nano-replication" method (Liu Q, et al., Chem. Mater., 2006, 18: 5153), that is, SBA-15 was used as a template first Prepare mesoporous carbon (CMK-3), and then use CMK-3 as a template to prepare mesoporous activated alumina. However, the hard templates (mesoporous silicon and mesoporous carbon) used in this method are two-dimensional structure and low specific surface area (less than 1000m ² /g), so that the pores of the obtained mesoporous activated alumina are two-dimensional structure and The specific surface area is low (less than 400m ² /g), which limits its application in adsorption and catalysis.

So far, there are no literatures and patents about the synthesis of three-dimensional mesoporous activated alumina with high specific surface area using three-dimensional mesoporous silicon template SBA-16 and three-dimensional mesoporous carbon as templates.

Contents of the invention

The purpose of the present invention is to solve the problems in the prior art, and provide a method for synthesizing three-dimensional mesoporous activated alumina with developed pore structure and high specific surface area.

The method provided by the present invention uses three-dimensional mesoporous SBA-16 with high specific surface area as a hard template to synthesize three-dimensional mesoporous carbon with high specific surface area and developed pore structure, and then uses three-dimensional mesoporous carbon as a hard template to synthesize three-dimensional mesoporous carbon with high specific surface area. Porous activated alumina, the specific steps are as follows:

1) Using tetraethyl orthosilicate as raw material, triblock copolymer polyethylene glycol-polypropylene glycol-polyethylene glycol (EO ₁₀₆ PO ₇₀ EO ₁₀₆ ) and cetyltrimethylammonium bromide as soft template agent, synthesize three-dimensional mesoporous SBA-16 by hydrothermal reaction (see literature "Mesa M, et al., Solid State Sci., 2005, 7:990");

2) Using the three-dimensional mesoporous SBA-16 prepared in step 1) as a hard template and sucrose as a carbon source to prepare three-dimensional mesoporous carbon (see patent CN101117222);

3) Disperse the three-dimensional mesoporous carbon black powder in the ethanol solution of Al(NO ₃ ) ₃ under stirring conditions, wherein the molar ratio of mesoporous carbon powder to Al(NO ₃ ) ₃ is 1:0.24, and ultrasonically disperse After 2 hours to make the aluminum nitrate molecules fully enter the pores of the three-dimensional mesoporous carbon, heat to completely evaporate the ethanol, and burn the obtained solid at 300°C for 2 hours in a nitrogen atmosphere;

4) After repeating the dispersion and burning process in step 3) for 2-3 times, the obtained solid powder was washed with absolute ethanol, and then burned at 550°C for 2 hours in an air atmosphere to obtain a three-dimensional medium with a high specific surface area. Porous activated alumina.

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

The method provided by the present invention is low in cost, easy to operate, narrow in target product pore size distribution (pore volume is 0.92-0.99cm ³ /g, average pore size is 7.0-7.3nm), and specific surface area (504-564m ² /g), The morphology, pore structure and specific surface area of alumina particles can be controlled by adjusting the morphology and mesoporous structure of mesoporous carbon.

Description of drawings

Fig. 1A, 1B, 1C are respectively the small-angle XRD pattern of three-dimensional mesoporous SBA-16, _N Adsorption-desorption isotherm and pore size distribution curve, wherein, curve (a) corresponds to the polyhedral three-dimensional organic matter prepared in Example 1 Ordered mesoporous SBA-16, curve (b) corresponds to the spherical three-dimensional mesoporous SBA-16 prepared in Example 2; Figure 1D is a SEM photo of the polyhedral three-dimensional ordered mesoporous SBA-16 prepared in Example 1; Figure 1E is The SEM photograph of the spherical three-dimensional mesoporous SBA-16 prepared in Example 2; Figure 1F is the TEM photograph of the polyhedral three-dimensional ordered mesoporous SBA-16 prepared in Example 1; Figure 1G is the spherical three-dimensional mesoporous prepared in Example 2 TEM photo of SBA-16.

Figures 2A, 2B, and 2C are the small-angle XRD spectra, _N2 adsorption-desorption isotherms, and pore size distribution curves of three-dimensional mesoporous carbon, respectively, wherein curve (a) corresponds to the three-dimensional ordered mesoporous carbon prepared in Example 1 , curve (b) corresponds to the three-dimensional worm-like mesoporous carbon prepared in Example 2; Figure 2D is the SEM photo of the three-dimensional ordered mesoporous carbon prepared in Example 1; Figure 2E is the three-dimensional worm-like mesoporous carbon prepared in Example 2 SEM photo of porous carbon; FIG. 2F is a TEM photo of the three-dimensional ordered mesoporous carbon prepared in Example 1; FIG. 2G is a TEM photo of the three-dimensional wormhole-like mesoporous carbon prepared in Example 1.

Figures 3A, 3B, and 3C are the small-angle XRD spectrum, wide-angle XRD spectrum, and pore size distribution curves of wormhole-like three-dimensional mesoporous activated alumina, respectively, where curve (a) corresponds to the wormhole-like three-dimensional mesoporous activated alumina prepared in Example 1. Mesoporous activated alumina, curve (b) corresponds to the wormhole-shaped three-dimensional mesoporous activated alumina prepared in Example 2; Figure 3D is a TEM photo of the wormhole-shaped three-dimensional mesoporous activated alumina prepared in Example 1, the illustration is SAED Pattern; Figure 3E is a TEM photo of the wormhole-like three-dimensional mesoporous activated alumina prepared in Example 2, and the inset is the SAED pattern.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Detailed ways

In the following examples, the three-dimensional mesoporous SAB-16 is synthesized with reference to the method in the literature "Mesa M, et al., Solid State Sci., 2005, 7:990", and the specific steps are as follows:

(a) At room temperature, after adding the triblock copolymer EO ₁₀₆ PO ₇₀ EO ₁₀₆ and cetyltrimethylammonium bromide to the hydrochloric acid solution, under vigorous stirring, add ethyl orthosilicate;

(b) transfer the mixture obtained in the step (a) into an autoclave and conduct hydrothermal treatment at a constant temperature of 95°C for 5 days, filter and wash with deionized water, and then dry at 60°C for 12 hours;

(c) Put the solid powder obtained in step (b) in a muffle furnace, raise the temperature to 550° C. at a rate of 1° C./min and burn at this temperature for 3 hours to obtain three-dimensional mesoporous SBA-16.

Referring to the method disclosed in the patent CN101117222 to synthesize three-dimensional mesoporous carbon, the specific steps are as follows:

(a) Add the three-dimensional mesoporous SBA-16 into the mixed liquid composed of sucrose, deionized water and concentrated sulfuric acid with a mass fraction of 98%, and after the water in the mixed liquid is evaporated by magnetic stirring, put it into 80 ℃ and 160℃ oven for 6 hours respectively;

(b) repeat step (a) 2-3 times;

(c) heating the solid powder obtained in step (b) to 900° C. at a rate of 1° C./min in a nitrogen flow with a volume flow rate of 100 mL/min and burning at a constant temperature for 2 hours;

(d) washing the solid powder obtained in step (c) with 10% HF solution to remove the silicon template SBA-16, and drying to obtain three-dimensional mesoporous carbon.

Example 1

1) Synthesis of polyhedral three-dimensional ordered mesoporous SBA-16:

(a) At room temperature, after adding EO ₁₀₆ PO ₇₀ EO ₁₀₆ and cetyltrimethylammonium bromide to the hydrochloric acid solution of 0.4mol/L, under vigorous stirring, add tetraethyl orthosilicate, wherein, The molar ratio of ethyl orthosilicate, hydrochloric acid, EO ₁₀₆ PO ₇₀ EO ₁₀₆ and cetyltrimethylammonium bromide is 1: 3.5: 0.005: 0.0038;

(b) Transfer the mixture obtained in step (a) to an autoclave and heat-treat it at a constant temperature of 95°C for 5 days, filter and wash with deionized water, and then dry it at 60°C for 12 hours;

(c) Put the solid powder obtained in step (b) in a muffle furnace, heat up to 550°C at a rate of 1°C/min and burn at this temperature for 3 hours to obtain a polyhedral three-dimensional ordered mesoporous SBA -16, its specific surface area, average pore diameter and pore volume are shown in Table 1;

2) Synthesis of three-dimensional ordered mesoporous carbon:

(a) Add polyhedral three-dimensional ordered mesoporous SBA-16 to a mixture of sucrose, deionized water, and concentrated sulfuric acid with a mass fraction of 98%, wherein the three-dimensional mesoporous SBA-16, sucrose, and deionized water The molar ratio of concentrated sulfuric acid with a mass fraction of 98% is 1: 0.219: 20: 0.0875, and it is stirred continuously to evaporate the water in the mixed liquid, and then put it into ovens at 80°C and 160°C in turn to maintain the temperature respectively. 6 hours of processing;

(b) repeat step (a) 3 times;

(c) heating the solid powder obtained in step (b) to 900° C. at a rate of 1° C./min in a nitrogen flow with a volume flow rate of 100 mL/min and burning at a constant temperature for 2 hours;

(d) washing the solid powder obtained in step (c) with a mass fraction of 10% HF solution to remove the silicon template SBA-16, and then drying to obtain a three-dimensional ordered mesoporous carbon, its specific surface area, average pore diameter and pore volume See Table 1;

3) Synthesis of wormhole-like three-dimensional mesoporous activated alumina: Disperse 0.4g three-dimensional ordered mesoporous carbon powder in 16mL Al(NO ₃ ) ₃ absolute ethanol solution (0.5mol/L) under stirring conditions , ultrasonically dispersed for 2 hours to make Al(NO ₃ ) ₃ molecules fully enter the pores of the three-dimensional ordered mesoporous carbon, and heated at 40°C to completely evaporate the ethanol, then the obtained solid was dissolved in a nitrogen gas stream with a volume flow rate of 100mL/min at 1 Heat up to 300°C at a rate of ℃/min and burn for 2 hours;

4) After repeating the impregnation and burning process in step 3) for 3 times, the obtained solid was washed with absolute ethanol, dried, and heated to 550°C in a muffle furnace at a rate of 1°C/min and burned at a constant temperature for 2 hours, the wormhole-like three-dimensional mesoporous activated alumina was obtained, and its specific surface area, average pore diameter and pore volume are shown in Table 1.

Example 2

1) Synthesis of spherical three-dimensional mesoporous SBA-16:

(a) At room temperature, after adding EO ₁₀₆ PO ₇₀ EO ₁₀₆ and cetyltrimethylammonium bromide to the hydrochloric acid solution of 0.8mol/L, under vigorous stirring, add tetraethyl orthosilicate, wherein, The molar ratio of ethyl orthosilicate, hydrochloric acid, EO ₁₀₆ PO ₇₀ EO ₁₀₆ and cetyltrimethylammonium bromide is 1: 6.9: 0.002: 0.0038;

(b) with step 1)-(a) in embodiment 1;

(c) Place the solid powder obtained in step (b) in a muffle furnace, heat up to 550°C at a rate of 1°C/min and burn at this temperature for 3 hours to obtain spherical three-dimensional mesoporous SBA-16, Its specific surface area, average pore diameter and pore volume are shown in Table 1;

2) Synthesis of three-dimensional worm-like mesoporous carbon:

(a) with step 2)-(a) in embodiment 1;

(b) repeat step (a) 3 times;

(c) with step 2)-(c) in embodiment 1;

(d) washing the solid powder obtained in step (c) with a mass fraction of 10% HF solution to remove the silicon template SBA-16, and then drying to obtain a three-dimensional worm-like mesoporous carbon, its specific surface area, average pore diameter and pore size See Table 1;

3) Synthesis of wormhole three-dimensional mesoporous activated alumina: Disperse 0.4g three-dimensional wormhole mesoporous carbon powder in 16mL Al(NO ₃ ) ₃ absolute ethanol solution (0.5mol/L) under stirring conditions In this method, ultrasonic dispersion was performed for 2 hours to allow Al(NO ₃ ) ₃ molecules to fully enter the pores of the three-dimensional ordered mesoporous carbon, and after heating at 40°C to completely evaporate ethanol, the obtained solid was dissolved in a nitrogen gas stream with a volume flow rate of 100mL/min. Heat up to 300°C at a rate of 1°C/min and burn for 2 hours;

4) After repeating the impregnation and burning process in step 3) for 3 times, the obtained solid was washed with absolute ethanol, dried, and heated to 550°C in a muffle furnace at a rate of 1°C/min and burned at a constant temperature for 2 Hours, high specific surface area wormhole-like three-dimensional mesoporous activated alumina was obtained, and its specific surface area, average pore diameter and pore volume are shown in Table 1.

The resulting product was characterized by techniques such as X-ray diffractometer (XRD), _N2 adsorption-desorption, scanning electron microscope (SEM), transmission electron microscope (TEM), selected area electron diffraction (SAED), and the results are shown in Figure 1, 2 and 3 are shown.

samples Average pore size (nm) Specific surface area (m²/g) Pore volume (cm³/g) Polyhedral three-dimensional ordered mesoporous SBA-16 3.6 1011 1.00 Spherical three-dimensional mesoporous SBA-16 3.5 809 0.67 Three-dimensional ordered mesoporous carbon 3.1 1600 1.42 Three-dimensional wormhole-like mesoporous carbon 3.5 966 0.91 Wormhole-like three-dimensional mesoporous activated alumina 7.0 564 0.99

samples Average pore size (nm) Specific surface area (m²/g) Pore volume (cm³/g) Wormhole-like three-dimensional mesoporous activated alumina 7.3 504 0.92

Table 1. Specific surface area, average pore diameter and pore volume of three-dimensional mesoporous SBA-16, three-dimensional mesoporous carbon and three-dimensional mesoporous activated alumina prepared in the present invention.

Claims (1)

1. A method utilizing hard template to prepare three-dimensional mesoporous activated alumina with high specific surface area, is characterized in that, comprises the following steps: 1) Using tetraethyl orthosilicate as raw material, triblock copolymer polyethylene glycol-polypropylene glycol-polyethylene glycol EO ₁₀₆ PO ₇₀ EO ₁₀₆ and cetyltrimethylammonium bromide as soft templating agent, Synthesis of three-dimensional mesoporous SBA-16 by hydrothermal reaction; 2) using the three-dimensional mesoporous SBA-16 prepared in step 1) as a hard template and sucrose as a carbon source to prepare three-dimensional mesoporous carbon; 3) Disperse the three-dimensional mesoporous carbon powder prepared in step 2) in an ethanol solution of Al(NO ₃ ) ₃ under stirring conditions, wherein the molar ratio of the mesoporous carbon powder to Al(NO ₃ ) ₃ is 1:0.24, after ultrasonic dispersion for 2 hours, heat to evaporate ethanol completely, and burn the obtained solid at 300°C for 2 hours in a nitrogen atmosphere; 4) After repeating step 3) 2-3 times, the obtained solid powder was washed with absolute ethanol, and then burned at 550° C. for 2 hours in an air atmosphere to obtain a three-dimensional mesoporous activated alumina with high specific surface area.

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