Manganese-doped silicon dioxide catalyst as well as preparation method and application thereof

Abstract

The invention discloses a manganese-doped silicon dioxide catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing a manganese-doped silicon dioxide catalyst by adopting a soft template method, namely dissolving a manganese source and a template agent in pure water, stirring and dissolving in a water bath, adding a small amount of alkali liquor into the solution for multiple times, stirring, then adding deionized water and ethanol, continuously stirring, and dropwise adding a silicon source for reaction through electrostatic force connection, so as to obtain the manganese-doped silicon dioxide catalyst. And washing, filtering, drying and calcining the obtained product to obtain the manganese-based catalyst. According to the invention, a soft template method is adopted, a surfactant is taken as a template, a one-step synthesized catalyst can form a hollow mesoporous structure after being calcined, and the catalyst has a large specific surface area and is beneficial to dispersion of reactants, so that the reactants are in full contact with active components to be degraded.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of pollution control technology, and particularly relates to a manganese-doped silicon dioxide catalyst and a preparation method and application thereof. BACKGROUND

[0002] Volatile organic compounds (VOCs) are a kind of atmospheric pollutants with a wide composition, which are mostly derived from industrial and commercial processes. Among all the VOCs, aromatic hydrocarbons have a more persistent benzene ring structure in the environment and are more difficult to degrade in catalytic combustion reaction than alkanes and alkenes. Therefore, the catalytic combustion of aromatic hydrocarbons has always been the focus of catalytic combustion degradation. Toluene is a typical aromatic volatile organic compound, which can exist stably in the environment, can be dispersed into the atmosphere to undergo photochemical reactions, and can also be settled on the soil or enter the water body to cause great harm to organisms and the environment, and even cause cancer.

[0003] At present, among the numerous VOCs control technologies, catalytic oxidation method is widely used. Catalytic oxidation refers to the chemical reaction of VOCs and oxygen on the surface of a catalyst at a specific temperature to produce water and carbon dioxide. This process can treat high content of VOCs, is simple to operate, has low energy consumption and no secondary pollution. The catalytic oxidation method usually uses metal as a catalyst. Among them, noble metals have high activity, but their composition is high and their resistance to poisoning is poor, while transition metals (such as manganese) have slightly lower activity, but their price is low and they are suitable for industrial application.

[0004] Soft templates are often aggregates of surfactant molecules. Such aggregates have a clear structural interface, and inorganic materials can be distributed in a specific direction through this interface to form nanomaterials with specific structures. Soft template method is simple and suitable for application in catalytic oxidation of VOCs. SUMMARY

[0005] In order to overcome the above shortcomings, the present application provides a manganese-doped silicon dioxide catalyst and a preparation method and application thereof.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: A preparation method of a manganese-doped silicon dioxide catalyst, wherein the catalyst has a spherical, leaf-shaped or rod-shaped morphology, and the specific preparation steps are as follows: Step one, dissolve a manganese source and a template agent in pure water and stir and dissolve under a water bath at 20-30℃ to obtain a colorless transparent uniform solution, wherein the template agent is polyacrylic acid; Step two, add a small amount of alkali solution to the solution in step one for multiple times and stir for 5-12h, then add deionized water and ethanol and continue to stir for 5-12h, and then add a silicon source drop by drop for reaction, and stir for 12-24h to obtain a white solution. Step three, the white solution in step two is washed, filtered, dried, and calcined to obtain the manganese-based catalyst.

[0007] Further optimization, the molar ratio of the template agent to the manganese source in step one is 1-10:1.

[0008] Further optimization, the manganese source is manganese nitrate.

[0009] Further optimization, the alkali solution in step two is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, ammonia, or sodium carbonate.

[0010] Further optimization, the silicon source in step two is one or more of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, or 3-aminopropyl triethoxysilane.

[0011] Further optimization, the washing in step three uses deionized water and is performed by suction filtration.

[0012] Further optimization, the calcination in step three is performed in a muffle furnace for 6 hours.

[0013] A manganese-doped silicon dioxide catalyst prepared by the above method.

[0014] The application of a manganese-doped silicon dioxide catalyst in treating toluene.

[0015] The beneficial effects of the present application are: The present application uses a soft template method to prepare a manganese-doped silicon dioxide catalyst, with polyacrylic acid as the template and manganese nitrate as the manganese source. The silicon source is added dropwise to the stirred solution through electrostatic force to form a silicon shell. The template polyacrylic acid is removed by calcination to form a hollow mesoporous structure catalyst. The soft template method uses a surfactant as the template, and the catalyst synthesized in one step can form a hollow mesoporous structure after calcination, has a large specific surface area, and is beneficial to the dispersion of reactants to fully contact the active components and be degraded. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The catalytic activity graph of the catalyst prepared in Examples 1-4 in the present application; Figure 2 The transmission electron microscope graph of the catalyst prepared in Example 2 in the present application; Figure 3 The XRD graph of the catalyst prepared in Examples 1-4 in the present application. DETAILED DESCRIPTION

[0017] In order to enable the above-mentioned objects, features and advantages of the present application to be more clearly understood, the present application will be described in detail below with reference to specific embodiments, the following embodiments are implemented on the premise of the technical scheme of the present application, a detailed implementation manner and specific operation process are given, but the present application can also be implemented in other ways different from those described herein, therefore the protection scope of the present application is not limited to the following embodiments.

[0018] A preparation method of a manganese-doped silicon dioxide catalyst, the catalyst has a spherical, leaf-shaped or rod-shaped morphology, and the specific preparation steps are as follows: Step one, dissolve the manganese source and the template agent in pure water and stir to dissolve under a water bath at 20-30℃ to obtain a colorless transparent uniform solution, the template agent is polyacrylic acid; Step two, add a small amount of lye to the solution in step one for multiple times and stir for 5-12h, then add deionized water and ethanol and continue to stir for 5-12h, then add the silicon source drop by drop for reaction, stir for 12-24h to obtain a white solution; Step three, wash, filter, dry and calcine the white solution in step two to obtain the manganese-based catalyst.

[0019] Further optimization, the molar ratio of the template agent to the manganese source in step one is 1-10:1.

[0020] Further optimization, the manganese source is manganese nitrate.

[0021] Further optimization, the lye in step two is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, ammonia water or sodium carbonate.

[0022] Further optimization, the silicon source in step two is one or more of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane or 3-aminopropyl triethoxysilane.

[0023] Further optimization, the washing in step three uses deionized water and is performed by suction filtration.

[0024] Further optimization, the calcination in step three is performed in a muffle furnace for 6h.

[0025] Example 1 Preparation of manganese-doped silicon dioxide catalyst Mn@SiO2(1:2) Step one, mix 0.39 mL manganese nitrate solution with 4 mL pure water, stir in a water bath at 25℃ for 30 min, then add 0.225 mL polyacrylic acid, stir for 30 min, then add 4.5 mL ammonia water, continue to stir for 8h, then add 45 mL pure water and 45 mL anhydrous ethanol and stir for 12h; Step two, 1.28 mL of tetraethoxysilane and 0.16 mL of 3-aminopropyl triethoxysilane were mixed and slowly added dropwise to the above solution under stirring at 25 °C for 24 h. The mixture was then filtered and washed with 200 mL of deionized water to obtain the filter cake; Step three, the filter cake was dried in an oven at 100 °C for 3 h and then calcined at 550 °C for 6 h in a muffle furnace to remove the template agent, thus obtaining the Mn@SiO2(1:2) catalyst.

[0026] Example 2 Preparation of manganese-doped silica catalyst Mn@SiO2(1:5) Step one, 0.195 mL of manganese nitrate solution was mixed with 2 mL of pure water and stirred in a water bath at 25 °C for 30 min, then 0.225 mL of polyacrylic acid was added, stirred for 30 min, then 4.5 mL of ammonia water was added, and the stirring was continued for 8 h. 45 mL of pure water and 45 mL of anhydrous ethanol were added and stirred for 12 h; Step two, 1.6 mL of tetraethoxysilane and 0.2 mL of 3-aminopropyl triethoxysilane were mixed and slowly added dropwise to the above solution under stirring at 25 °C for 24 h. The mixture was then filtered and washed with 200 mL of deionized water to obtain the filter cake; Step three, the filter cake was dried in an oven at 100 °C for 3 h and then calcined at 550 °C for 6 h in a muffle furnace to remove the template agent, thus obtaining the Mn@SiO2(1:5) catalyst.

[0027] Example 3 Preparation of manganese-doped silica catalyst Mn@SiO2(1:10) Step one, 0.195 mL of manganese nitrate solution was mixed with 2 mL of pure water and stirred in a water bath at 25 °C for 30 min, then 0.225 mL of polyacrylic acid was added, stirred for 30 min, then 4.5 mL of ammonia water was added, and the stirring was continued for 8 h. 45 mL of pure water and 45 mL of anhydrous ethanol were added and stirred for 12 h; Step two, 1.6 mL of tetraethoxysilane and 0.2 mL of 3-aminopropyl triethoxysilane were mixed and slowly added dropwise to the above solution under stirring at 25 °C for 24 h. The mixture was then filtered and washed with 200 mL of deionized water to obtain the filter cake; Step three, the filter cake was dried in an oven at 100 °C for 3 h and then calcined at 550 °C for 6 h in a muffle furnace to remove the template agent, thus obtaining the Mn@SiO2(1:5) catalyst.

[0028] Comparative example Preparation of manganese-impregnated silica catalyst Mn / SiO2(1:5) Step one, 0.225 mL polyacrylic acid was mixed with 2 mL pure water, stirred in a 25 °C water bath for 30 min, then 4.5 mL ammonia water was added, and stirring was continued for 8 h. 45 mL pure water and 45 mL anhydrous ethanol were added thereto and stirred for 12 h; Step two, 3.2 mL tetraethoxysilane was mixed with 0.4 mL 3-aminopropyltriethoxysilane, which was slowly added dropwise to the above solution under stirring, and stirred at 25 °C for 24 h. Then the mixture was suction filtered and washed with 200 mL deionized water to obtain a filter cake; Step three, the filter cake obtained was dried in an oven at 100 °C for 3 h, and then calcined at 550 °C in a muffle furnace for 6 h to remove the template, thereby obtaining a SiO2 carrier; Step four, 0.16 mL manganese nitrate solution was mixed with 10 mL anhydrous ethanol and ultrasonicated for 30 min. Then 0.45 g SiO2 carrier was added thereto and ultrasonicated for 1 h until complete dissolution; Step five, the above solution was stirred in a 65 °C water bath until it was evaporated to dryness, and then the dry solid was calcined at 500 °C in a muffle furnace for 6 h, thereby obtaining a Mn / SiO2(1:5) catalyst.

[0029] The activities of the catalysts prepared in Examples 1-3 and Comparative Examples were tested respectively, which were carried out on a fixed bed reactor device, and connected to a gas chromatograph equipped with a FID flame ion detector and a TCD thermal conductivity detector, and toluene target pollutants were used for activity testing.

[0030] The catalyst was pressed into a tablet and ground through a sieve, 0.05 g of the catalyst with a particle size of 40-60 mesh was mixed with quartz sand and loaded into a reaction tube, which was then placed in a reaction furnace, activated with oxygen at 250 °C for 1 h, and then toluene was introduced, and the activity of the catalyst was tested at 100, 150, 200, 225, 250, 275, 300 °C, respectively. The catalytic activity is shown in Figure 1 As shown in the table, Mn@SiO2(1:2), Mn@SiO2(1:5) and Mn@SiO2(1:10) prepared by soft template method in Examples 1-3 have the same activity trend, and the toluene conversion rate increases with the increase of temperature, and increases obviously after 225 °C. Compared with Mn@SiO2(1:2), Mn@SiO2(1:5) has more active components, and thus has better catalytic activity.

[0031] Although the Mn / SiO2(1:5) prepared by impregnation method in the comparative example has the same metal loading as the Mn@SiO2(1:5) prepared by soft template method in Example 2, the former has higher catalytic activity compared with the latter due to the high specific surface area of the soft template.

[0032] Therefore, by exploring the effects of different Mn / Si ratios and preparation methods on the catalytic oxidation of toluene, it is concluded that the Mn@SiO2(1:5) prepared by soft template method has the highest activity.

[0033] The above shows and describes the main features, use methods, basic principles and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made according to the actual situation, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a manganese-doped silica catalyst, characterized in that: The catalyst has a spherical, leaf-shaped or rod-shaped morphology, and the specific preparation steps are as follows: Step 1: dissolving a manganese source and a template in pure water and stirring in a water bath at 20-30° C. to obtain a colorless, transparent, and uniform solution, wherein the template is polyacrylic acid; Step 2: Add alkali solution to the solution in step 1 in small amounts and stir for 5-12 hours, then add deionized water and ethanol and continue stirring for 5-12 hours, then add silicon source dropwise to react, and stir for 12-24 hours to obtain a white solution; Step 3: Wash, filter, dry and calcine the white solution in step 2 to obtain a manganese-based catalyst.

2. The method for preparing a manganese-doped silica catalyst according to claim 1, wherein: In the step 1, the molar ratio of the template to the manganese source is 1 to 10:

1.

3. The method for preparing a manganese-doped silica catalyst according to claim 1, wherein: The manganese source is manganese nitrate.

4. The method for preparing a manganese-doped silica catalyst according to claim 1, wherein: The alkali solution in step 2 is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, ammonia water or sodium carbonate.

5. The method for preparing a manganese-doped silica catalyst according to claim 1, wherein: The silicon source in step 2 is one or more of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane or 3-aminopropyltriethoxysilane.

6. The method for preparing a manganese-doped silica catalyst according to claim 1, wherein: The washing in step 3 is performed with deionized water and is performed by suction filtration.

7. The method for preparing a manganese-doped silica catalyst according to claim 1, wherein: In the step 3, the mixture is calcined in a muffle furnace for 6 h.

8. A manganese-doped silica catalyst, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the manganese-doped silica catalyst according to claim 8 in treating toluene.

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