CN115025770A - MnO (MnO) 2 /γ-Al 2 O 3 Low-dimensional nano composite material and preparation method and application thereof - Google Patents

Abstract

The invention relates to MnO ₂ /γ‑Al ₂ O ₃ A low-dimensional nano composite material and a preparation method and application thereof belong to the field of environmental catalytic materials. The MnO ₂ /γ‑Al ₂ O ₃ The low dimensional nanocomposite comprises gamma-Al ₂ O ₃ Nanosheet support, and adhering to gamma-Al ₂ O ₃ Manganese oxide nanocrystal grains of a nanosheet carrier; the manganese oxide nano-crystalline particles account for 10-15 wt% of the total weight of the nano-composite material as 100 wt%, and the gamma-Al ₂ O ₃ The mass fraction of the nanosheet carrier is 85-90 wt%.

Description

A kind of MnO2/γ-Al2O3 low-dimensional nanocomposite material and its preparation method and application

technical field

The invention relates to a low-dimensional manganese-based nanocomposite material, in particular to a MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material, a preparation method and application thereof, and belongs to the field of environmental catalytic materials.

Background technique

Ozone is mainly produced by the photochemical reaction of volatile organic compounds (VOCs) and NOx under sunlight. In order to reduce the ozone concentration and control its precursor VOCs, it is extremely necessary to reduce the use of VOCs raw and auxiliary materials and reduce the emission of VOCs from the source. However, due to process technology and product performance requirements, it is difficult to completely achieve zero emission of low-concentration VOCs. Therefore, terminal treatment is still an important part of VOCs treatment.

High-efficiency treatment technologies such as combustion and catalytic combustion have been widely used in large-scale spraying and chemical enterprises in my country, but the high-efficiency treatment technology of VOCs is expensive, with high operating costs and post-maintenance costs, which are unbearable for most enterprises, and can only use activated carbon adsorption It is difficult to avoid problems such as low removal efficiency or negative value in the simple process of treating VOCs. Therefore, it is imperative to develop a catalyst that can remove VOCs at a lower temperature, which can greatly reduce external energy supply and reduce energy consumption in view of the problem of small air volume and low concentration VOCs treatment in some enterprises.

However, the current commercial catalysts are mostly precious metals, which are expensive and waste of resources. The research and development of alternative non-precious metal catalysts is the focus and hot spot in the field of environmental catalysis. In single-component bulk metal oxides, the electron transfer in the oxidation-reduction cycle of metal ions is slow, the activation energy of lattice oxygen diffusion along the bulk-to-surface direction is high, the activation of reactant molecules on the metal oxide and the gas-phase oxygen The activation process can only be carried out alternately on the same metal site, resulting in low reactivity of metal oxides. The carrier in the supported catalyst can improve the performance of the catalyst by increasing the electron density, providing the nucleation center of the dispersed phase, and regulating the acidity and alkalinity of the surface.

SUMMARY OF THE INVENTION

In view of this, in order to solve the problems of low low temperature activity and slow reaction rate of using metal oxide catalysts to purify VOCs in catalytic combustion technology, the present invention has developed a carrier with adjustable acidity, high exposure of oxygen vacancy active sites, and high efficiency. MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposites that synergistically adsorb and activate organic waste gas and oxygen molecules and make them react rapidly.

Specifically, in the first aspect, the present invention provides a MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material. The MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material comprises a γ-Al ₂ O ₃ nanosheet carrier, and manganese oxide nanocrystals adhered to the γ-Al ₂ O ₃ nanosheet carrier;

Based on the total mass of the nanocomposite material as 100 wt %, the mass fraction of the manganese oxide nanocrystal grains is 10-15 wt %, and the mass fraction of the γ-Al ₂ O ₃ nanosheet carrier is 85-90 wt %.

Preferably, the particle size of the manganese oxide nanocrystal grains is 3-8 nm, the length of the γ-Al ₂ O ₃ nanosheet carrier is 350-400 nm, and the thickness is 8-15 nm; the MnO ₂ /γ- The specific surface area of the Al ₂ O ₃ low-dimensional nanocomposite is 200-220 m ² /g.

In a second aspect, the present invention provides a method for preparing the above-mentioned MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material, comprising the following steps:

(1) Disperse the γ-Al ₂ O ₃ nanosheet carrier in water, add a reducing agent and make it fully adsorbed on the surface of the γ-Al ₂ O ₃ nanosheet carrier;

(2) adding potassium permanganate solution and reducing agent to undergo redox reaction, and the generated MnO ₂ nanocrystal grains are deposited in situ on the surface of γ-Al ₂ O ₃ nanosheet carrier;

(3) centrifugation, washing, drying, grinding and roasting to obtain the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material.

Preferably, the preparation method of the γ-Al ₂ O ₃ nanosheet carrier comprises: adding a weak alkaline solution and a dispersant to the sodium metaaluminate solution to form a mixed solution;

The mixed solution is subjected to a hydrothermal reaction, followed by centrifugation, washing, drying and grinding to obtain a γ-AlOOH nanosheet precursor; the γ-AlOOH nanosheet precursor is calcined and ground to obtain a γ-Al ₂ O ₃ nanosheet carrier .

Preferably, the weak alkaline solution is ammonia water or urea solution, and the dispersant is sodium polyacrylate.

Preferably, the molar ratio of the sodium metaaluminate to urea is 1:8-12.

Preferably, the temperature of the hydrothermal reaction is 100-160° C., and the reaction time is 8-12 h.

Preferably, the temperature for calcining the γ-AlOOH nanosheets is 400-700°C, preferably 500°C; the calcining time is 2-5h.

Preferably, the reducing agent is ascorbic acid.

Preferably, the mass ratio of the γ-Al ₂ O ₃ nanosheet carrier to the reducing agent is 1: (0.5-1.2); the molar ratio of the potassium permanganate to the reducing agent is 1: (0.5-1) .

Preferably, the MnO ₂ nanocrystal grains are deposited in-situ on the surface of the γ-Al ₂ O ₃ nanosheet carrier and then calcined at a temperature of 200-350° C. for 2-5 hours, and the atmosphere is an air atmosphere.

In a third aspect, the present invention provides an application of the above MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material in removing volatile organic compound VOCs, where the VOCs include toluene.

beneficial effect

The MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material provided by the present invention has a large specific surface area, abundant weak acid sites, and poor chemical bonding with the product carbon dioxide, which is beneficial for VOCs molecules such as toluene in the material. The adsorption and activation of the surface, the desorption of the product carbon dioxide molecules and the catalytic oxidation reaction. The composite material can realize the treatment of low-concentration VOCs exhaust gas with small and medium air volume (mainly for toluene, benzene, etc.), with high purification efficiency (≥99%), low light-off temperature, long-lasting stability, and can reduce the optimal catalytic temperature of the catalyst to 200 ℃ below, reduce the supply of external energy during the reaction and reduce the energy consumption. It has great application potential in the treatment of VOCs with small air volume and low concentration in small painting enterprises.

Description of drawings

FIG. 1 shows a schematic diagram of the preparation process of the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite according to the present invention;

2 shows the SEM, low-magnification TEM, high-magnification TEM, HAADF, HRTEM and mapping characterization diagrams of the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1;

3 shows the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 and the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1 XRD pattern of ;

4 shows the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 and the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1 The NH ₃ temperature programmed desorption (NH ₃ -TPD) spectrum;

5 shows the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 and the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1 The CO ₂ temperature programmed desorption (CO ₂ -TPD) spectrum;

6 shows the SEM and TEM characterization images of the MnO ₂ /γ-Al ₂ O ₃ (c) nanocomposite prepared in Comparative Example 1;

7 shows the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 and the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1 The nitrogen adsorption-desorption isotherm curve of ;

8 shows the pyridine infrared spectra of the γ-Al ₂ O ₃ (s) nanosheets prepared in Example 1 and the commercial alumina nanoparticles γ-Al ₂ O ₃ (c) used in Comparative Example 1;

9 shows the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 and the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1 Spectra of catalytic efficiency as a function of temperature when removing 600 ppm of toluene;

Figure 10 shows a schematic diagram of the catalytic stability test results of the MnO ₂ /γ-Al ₂ O ₃ (s) material when the temperature is increased to 200°C;

Figure 11 shows the SEM and TEM characterization images of the MnO ₂ /SiO ₂ nanocomposite prepared in Comparative Example 2;

Figure 12 shows the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 and the MnO ₂ /γ-Al ₂ O ₃ (c) prepared in Comparative Example 1 and Comparative Example 2 The spectra of the MnO ₂ /SiO ₂ and the MnO ₂ /MgO low-dimensional nanocomposites prepared in Comparative Example 3 in the removal of 600 ppm toluene as a function of temperature;

FIG. 13 shows the SEM and TEM characterization images of the MnO ₂ /MgO nanocomposite prepared in Comparative Example 3. FIG.

Detailed ways

The present invention is further described below through the embodiments, and it should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

The invention provides a MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material for catalytic oxidation of low-concentration (less than 1000 ppm) volatile organic compounds VOCs and a preparation method thereof. The MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material is formed by adhering fine manganese oxide nanocrystal grains to an alumina nanosheet carrier.

In some embodiments, based on the total mass of the nanocomposite material as 100 wt %, the mass fraction of the manganese oxide nanocrystal grains may be 10-15 wt %, and the mass fraction of the alumina nanosheet carrier may be 85-90 wt % %. Preferably, the size of the manganese oxide nanocrystal grains may be 3-8 nm; the length of the alumina nanosheet carrier is 350-400 nm, and the thickness is 8-15 nm.

酸性位点总量较高，且

酸性位点与Lewis酸性位点的比值较高)，易于吸附活化甲苯等可挥发性有机化合物，与二氧化碳之间的化学结合性较差。此外，复合材料中MnO₂上的氧空位与氧化铝载体上的酸性位点能够协同活化氧气和甲苯等VOCs分子并发生反应，促进低温催化氧化过程的实现。In the low-dimensional nanocomposite material, the carrier material is preferably γ-phase alumina nanosheets, the specific surface area of which can reach more than 200 m ² /g, and the specific surface area of the composite material can reach 200-220 m ² /g. The larger specific surface area of the carrier provides abundant nucleation centers for the attachment of metal oxide particles, and the manganese oxide nanocrystals in the composite have high dispersion, small particle size, and strong interaction with the carrier. At the same time, the surface of the γ-Al ₂ O ₃ nanosheet carrier has more weakly acidic sites (

The total amount of acidic sites is high, and

The ratio of acid sites to Lewis acid sites is higher), which is easy to adsorb and activate volatile organic compounds such as toluene, and has poor chemical bonding with carbon dioxide. In addition, the oxygen vacancies on _MnO2 in the composites and the acidic sites on the alumina support can synergistically activate and react with VOCs molecules such as oxygen and toluene, promoting the realization of the low-temperature catalytic oxidation process.

Based on the above characteristics, the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material provided by the present invention can be used as a catalyst for the catalytic combustion of VOCs such as low-concentration toluene at low temperature, and the carbon dioxide generated during the catalytic oxidation process is more easily diffused from the surface of the catalyst to the external environment.

The preparation process of the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material according to the present invention is exemplarily described below with reference to FIG. 1 .

Preparation of γ-AlOOH nanosheet precursors by hydrothermal method. First, dissolve an appropriate amount of sodium metaaluminate in water, and add ammonia or urea to the solution to adjust the pH of the sodium metaaluminate aqueous solution to 7.5-10 under magnetic stirring. AlO ^- can also be hydrolyzed under these conditions and form hydroxide precipitation. The molar ratio of sodium metaaluminate to urea can be controlled to be 1:8-12 to ensure the formation of suitable nanosheet morphology. Then, an appropriate amount of dispersing agent such as sodium polyacrylate is added to be completely dissolved in the solution, and the amount of the dispersing agent may be 0.1-0.3 g. After stirring and mixing at room temperature, the solution was transferred to an autoclave, and the reaction was allowed to stand at 100-160°C for 8-12 hours. After the reaction, centrifuge, wash, freeze-dry, and grind to obtain a white powdery γ-AlOOH nanosheet precursor.

Synthesis of γ-Al ₂ O ₃ nanosheet supports by air calcination. The γ-AlOOH nanosheet precursor is laid flat in a square corundum crucible, and the corundum crucible is placed in a muffle furnace for calcination for 2-5 hours. The calcination temperature is 400-700 °C, preferably 500 °C, and the heating rate is 2-10 °C. /min. The calcined product was ground to obtain a white powdery γ-Al ₂ O ₃ nanosheet carrier with low crystallinity.

Synthesis of MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposites by impregnation-in situ surface deposition method. The γ-Al ₂ O ₃ white powder is uniformly dispersed in water, and an appropriate amount of reducing agent ascorbic acid is added, wherein the mass ratio of γ-Al ₂ O ₃ to ascorbic acid can be 1:(0.5-1.2). Stir and mix evenly, so that the ascorbic acid is fully adsorbed on the surface of the alumina carrier. Then, potassium permanganate is added dropwise to the mixed solution of ascorbic acid and alumina carrier in the form of a solution according to the molar ratio of potassium permanganate to ascorbic acid as 1: (0.5～1), the concentration of potassium permanganate is It can be 0.2-0.8mol/L, and the dropping rate can be 0.5-1.5ml/min. Stir at room temperature for 2-4h, so that the reducing agent ascorbic acid and potassium permanganate fully undergo redox reaction, and the MnO ₂ grains are deposited in situ in the oxidation-reduction reaction. Aluminium carrier surface. After the reaction is completed, centrifuge, wash, freeze-dry and grind the product, and calcinate at 200-350° C. in air for 2-5h (preferably the heating rate of calcination is 2-10° C./min) to obtain brown-black powdery MnO ₂ / γ-Al ₂ O ₃ low-dimensional nanocomposites.

The use of the dip-in-situ surface deposition method in the present invention is beneficial to the uniform distribution of MnO ₂ on the γ-Al ₂ O ₃ nanosheet carrier, and is beneficial to obtain MnO ₂ crystal grains with smaller size.

When the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material obtained by the invention is used as a catalyst for solving the high-efficiency catalytic oxidation of VOCs at low temperature with medium and small air volume and low concentration, it is added into a fixed-bed continuous flow reactor for performance testing. The flow rate was 60000 mL g ^-1 h ^-1 , and the concentration of toluene C ₇ H ₈ in the reaction inlet and outlet gas was detected online by gas chromatography. The composite material (MnO ₂ /γ-Al ₂ O ₃ ) provided by the invention has high C ₇ H ₈ catalytic oxidation activity: 600 ppm of C ₇ H ₈ can be removed at a low temperature of 153° C. over 90% Conversion rate; when the temperature is raised to 200°C, the composite material can continuously achieve a removal conversion rate of more than 99% for at least 24 hours.

The invention uses the air calcination method to prepare the alumina carrier material with suitable surface acidity and alkalinity, and uses the impregnation-in-situ surface deposition method to prepare the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material, and the composite material is suitable for medium and small air volume and low The problem of concentration VOCs treatment realizes the feasibility of removing VOCs at lower temperature. Moreover, the catalyst carrier material has a large specific surface area, which provides abundant nucleation centers for the metal oxide particles, thereby producing a catalyst with high dispersion, small particle size, and strong interaction between the metal oxide and the carrier. At the same time, the acidic sites on the surface of the carrier are beneficial to the adsorption of VOCs molecules and the desorption of product _CO2 molecules, which further promotes the catalytic combustion of VOCs such as low-concentration toluene at low temperatures.

The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above content of the present invention belong to the present invention. scope of protection. The specific process parameters and the like in the following examples are only an example in the suitable range, that is, those skilled in the art can make selections within the suitable range through the descriptions herein, and are not intended to be limited to the specific values in the following examples.

Example 1

Dissolve 1 g (0.012 mol) of sodium metaaluminate in 50 mL of water, and add 6 g (0.1 mol) of urea and 0.20 g of sodium polyacrylate to the solution under magnetic stirring. After stirring at room temperature for 1 hour, the solution was transferred to the reaction kettle and left to react in a 140°C oven for 10 hours. After the reaction, it was centrifuged, washed with water, and lyophilized in a freeze dryer. The product was ground and collected to give γ-AlOOH white powder.

Then, 1 g of γ-AlOOH white powder sample was laid flat in a square corundum crucible, and the corundum crucible was calcined in a muffle furnace for 2 h at a calcination temperature of 500 °C and a heating rate of 5 °C/min, and collected to obtain γ-Al ₂ O ₃ white powder.

Finally, 0.3 g of γ-Al ₂ O ₃ white powder was uniformly dispersed in 30 mL of water, 0.176 g (0.001 mol) of ascorbic acid was added to the above solution, and after stirring at room temperature for 10 h, the ascorbic acid was fully adsorbed to the surface of the alumina carrier, and then 5 mL of permanganate was added to the solution. Potassium acid solution (0.4mol/L) was added dropwise to the above mixed solution and stirred at room temperature for 2h. After the reaction was completed, centrifuged, washed with water, freeze-dried in a freeze dryer, ground the product, transferred to a 300°C muffle furnace for calcination for 2h, and the heating rate was 5°C/min to obtain the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite, denoted as MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite.

Based on the total mass of the nanocomposite material as 100wt%, the mass fraction of manganese oxide nanocrystal grains in the composite material prepared in Example 1 is 13wt%, and the mass fraction of the γ-Al ₂ O ₃ nanosheet carrier is 87wt%.

The chemical composition and chemical microenvironment of MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption, and chemical adsorption.

2 shows the SEM, low-magnification TEM, high-magnification TEM, HAADF, HRTEM and mapping characterization images of the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1. It can be seen from Fig. 2 that the length and thickness of the Al ₂ O ₃ nanosheets are 360 and 10 nm, respectively, and the composite material is made by adhering many fine nanoparticles on the alumina nanosheet carrier with a particle size of about 5 nm. The small bright spots shown in the HAADF map and the distribution of Mn elements in the mapping photos both prove that the fine manganese oxide nanoparticles are highly dispersed on the alumina nanosheet support.

FIG. 3 shows the XRD characterization diagram of the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1. FIG. It can be seen from the figure that there are three weak and broad diffraction peaks at 37.76°, 45.80° and 66.92°, corresponding to the (311), (400) and (440) crystal planes of the cubic system γ-Al ₂ O ₃ , indicating that the carrier is a γ-phase alumina material with low crystallinity, but no obvious characteristic peaks of manganese oxide are identified, which proves that manganese oxide has small grain size and is highly dispersed on the alumina nanosheet carrier.

4 shows the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 and the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1 _The NH ₃ temperature _- programmed desorption (NH ₃ -TPD) spectrum _of CO ₂ temperature-programmed desorption (CO ₂ -TPD) spectra of ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposites. From the NH ₃ -TPD plot shown in Fig. 4, it can be seen that MnO ₂ /γ-Al ₂ O ₃ (s) has a high and broad peak at 109 °C, corresponding to the weakly acidic site; from Fig. 5 As can be seen from the CO ₂ -TPD diagram shown, the CO2 desorption temperature of MnO ₂ /γ-Al ₂ O ₃ (s) is at 118°C. It is proved that the acid sites of the γ-phase alumina nanosheets prepared in Example 1 are mainly weak acid sites, and the chemical bonding stability with carbon dioxide is low, so that the carbon dioxide generated during the catalytic oxidation of VOCs such as toluene can be easily removed from the carbon dioxide. The catalyst surface diffuses to the external environment.

Example 2

The scheme is basically the same as that of Example 1, the main difference is that: in this example, the calcination temperature for converting γ-AlOOH into γ-Al ₂ O ₃ white powder is 600°C. Based on the total mass of the nanocomposite material as 100 wt%, the mass fraction of manganese oxide nanocrystal grains in the composite material prepared in this example is 13 wt%, and the mass fraction of the γ-Al ₂ O ₃ nanosheet carrier is 87 wt %.

Example 3

The scheme is basically the same as that of Example 1, except that the calcination temperature for converting γ-AlOOH into γ-Al ₂ O ₃ white powder in this example is 700°C. Based on the total mass of the nanocomposite material as 100 wt %, the mass fraction of manganese oxide nanocrystals in the composite material prepared in this example is 12.8 wt %, and the mass fraction of the γ-Al ₂ O ₃ nanosheet carrier is 87.2 wt % .

Example 4

The scheme is basically the same as that of Example 1, and the main difference is that: in this example, the concentration of the potassium permanganate solution is 0.2 mol/L. Based on the total mass of the nanocomposite material as 100wt%, the mass fraction of manganese oxide nanocrystal grains in the composite material prepared in this example is 10wt%, and the mass fraction of the γ-Al ₂ O ₃ nanosheet carrier is 90wt%.

Example 5

The scheme is basically the same as that of Example 1, and the main difference is that: in this example, the concentration of the potassium permanganate solution is 0.8 mol/L. Based on the total mass of the nanocomposite material as 100wt%, the mass fraction of manganese oxide nanocrystal grains in the composite material prepared in this example is 15wt%, and the mass fraction of the γ-Al ₂ O ₃ nanosheet carrier is 85wt%.

Comparative Example 1

The scheme is basically the same as that of Example 1, the main difference is: in this comparative example, commercial alumina powder (Adamas Reagent Company, 99%, gamma-phase Al ₂ O ₃ , 20nm) is directly used as the raw material, and the prepared MnO ₂ The /γ-Al ₂ O ₃ low-dimensional nanocomposite is denoted as MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite.

The chemical composition and chemical microenvironment of the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption, and chemical adsorption.

FIG. 6 shows the SEM and TEM characterization images of the MnO ₂ /γ-Al ₂ O ₃ (c) nanocomposite prepared in Comparative Example 1. FIG. As can be seen from the figure, commercial _Al2O3 nanoparticles with a particle size of ₂₀ nm are simply stacked with _MnO2 nanoparticles of smaller particle size.

3 shows the XRD characterization diagram of the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1. It can be seen from the figure that the stronger diffraction peaks at 37.76°, _39.44 °, _45.80 °, 61.06° and 66.92° correspond to (311), (222), (400), (511) and (440) crystal planes, indicating that the material is a γ-phase alumina material with high crystallinity.

7 shows the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 and the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1 of nitrogen adsorption-desorption isotherms. It can be seen from the figure that the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared by using γ-phase alumina nanosheets as a carrier is better than the MnO ₂ /γ-Al prepared by using commercial alumina nanoparticles as a carrier. The specific surface area of the ₂ O ₃ (c) composite is larger, which are 209.8 m ² /g and 134.5 m ² /g, respectively. The increased specific surface area of the two-dimensional nanosheet support is not only conducive to the dispersion of manganese oxide nanoparticles, but also to the catalytic reaction with VOCs such as toluene.

4 shows the NH ₃ temperature programmed desorption (NH ₃ -TPD) spectrum of the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1. In NH ₃ -TPD, MnO ₂ /γ-Al ₂ O ₃ (c) has two NH ₃ desorption peaks at 94°C and 274°C, corresponding to weak acid and moderately strong acid sites, respectively.

5 shows the CO ₂ temperature-programmed desorption (CO ₂ -TPD) spectrum of the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1. In CO ₂ -TPD, the carbon dioxide desorption temperatures of MnO ₂ /γ-Al ₂ O ₃ (c) were at 138 °C and 424 °C, proving that the acid sites of alumina nanoparticles in Comparative Example 1 are moderately strong acids, which are not compatible with carbon dioxide. The chemical bonding between them is strong, which is not conducive to the desorption of the product carbon dioxide molecules and thus weakens the catalyst activity.

酸/Lewis酸为0.55，573K时为0.63；商业氧化铝纳米颗粒γ-Al₂O₃(c)在 423K时，

酸/Lewis酸为0.49，573K时为0.32。证明实施例1制备的γ相氧化铝纳米片比商业氧化铝纳米颗粒总酸量高，Lewis酸量比

酸量多，且γ相氧化铝纳米片γ-Al₂O₃(s)上的

酸酸量比商业氧化铝纳米颗粒γ-Al₂O₃(c)的高。8 shows the pyridine infrared spectra of the γ-Al ₂ O ₃ (s) nanosheets prepared in Example 1 and the commercial alumina nanoparticles γ-Al ₂ O ₃ (c) used in Comparative Example 1. It can be seen from the figure that the γ-phase alumina nanosheets γ-Al ₂ O ₃ (s) prepared in Example 1 are at 423K,

acid/Lewis acid 0.55, 0.63 at 573K; commercial alumina nanoparticles γ _{- Al2O3} (c) at 423K,

Acid/Lewis Acid 0.49, 0.32 at 573K. It is proved that the γ-phase alumina nanosheets prepared in Example 1 have higher total acid content than commercial alumina nanoparticles, and the Lewis acid content is higher than that of commercial alumina nanoparticles.

The acid content is large, and the γ-phase alumina nanosheets γ-Al ₂ O ₃ (s) on the

The amount of acid is higher than that of commercial alumina nanoparticles γ-Al ₂ O ₃ (c).

The MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 and the MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposite prepared in Comparative Example 1 are as follows The materials were tested for the low temperature degradation performance of toluene.

Toluene low temperature degradation performance of MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposites prepared in Example 1 and MnO ₂ /γ-Al ₂ O ₃ (c) low-dimensional nanocomposites prepared in Comparative Example 1 The test was carried out in a fixed-bed continuous flow reactor, a quartz tube with an inner diameter of 8 mm was used as the reactor, the catalyst filling amount was 0.1 g, and the reaction gas was: C ₇ H ₈ concentration of 600 ppm, O concentration of ₂₁ %, carrier gas N ₂ , the reaction temperature is 120-280 ℃, the space velocity is 60000mL g ^-1 h ^-1 , the C ₇ H ₈ concentration in the reaction inlet and outlet gas is detected online by gas chromatography, and the catalyst reaction activity is determined by the conversion rate of C ₇ H ₈ The results are shown in Figure 9. It can be seen that the C ₇ H ₈ catalytic oxidation performance of the MnO ₂ /γ-Al ₂ O ₃ (s) low-dimensional nanocomposite prepared in Example 1 of the present invention is significantly better than that of MnO ₂ /γ- Al ₂ O ₃ (c) low-dimensional nanocomposite, 600 ppm C ₇ H ₈ can achieve more than 90% removal conversion at 153 °C. Figure 10 shows the schematic diagram of the catalytic stability test results of the MnO ₂ /γ-Al ₂ O ₃ (s) material when the temperature is raised to 200°C. It can be seen from the figure that it can achieve a toluene concentration of more than 99% for at least 24 hours removal rate, and the material activity is almost not attenuated.

Comparative Example 2

The scheme is basically the same as that of Example 1, the main difference is: in this comparative example, the dendritic silica powder reported in the literature is directly used (Note: Nat. Commun., 2021, 12, 4968, doi.org/10.1038/ s41467-021-25226-x) as the carrier raw material, the obtained MnO ₂ /SiO ₂ low-dimensional nanocomposite was prepared.

11 shows the SEM and TEM characterization images of the MnO ₂ /SiO ₂ nanocomposite prepared in Comparative Example 2. It can be seen from the figure that the _SiO2 support is a dendritic silica nanomaterial with a mesoporous structure with a diameter of about 30 nm, and the tiny _MnO2 nanoparticles are highly dispersed in the pores of the material.

The toluene low-temperature degradation performance test of the MnO ₂ /SiO ₂ low-dimensional nanocomposite prepared in Comparative Example 2 is represented by the conversion rate of toluene C ₇ H ₈ , and the results are shown in FIG. 12 . It can be seen from the figure that 600 ppm of C ₇ H ₈ can achieve more than 90% removal conversion at 211 °C.

Comparative Example 3

The scheme is basically the same as that of Example 1, the main difference is: in this comparative example, the magnesium oxide powder reported in the literature is directly used (Note: Chem. Commun., 2013, 49, 6093-6095, DOI: 10.1039/c3cc42504e) As a carrier material, the obtained MnO ₂ /MgO low-dimensional nanocomposite was prepared.

FIG. 13 shows the SEM and TEM characterization images of the MnO ₂ /MgO nanocomposite prepared in Comparative Example 3. FIG. It can be seen from the figure that MgO is a flower-like structure assembled by nanosheets, and the morphology and structure of MnO ₂ /MgO prepared by in-situ dip deposition method are similar to that of MnO ₂ /Al ₂ O ₃ (s) in Example 1. , _MnO nanoparticles are dispersed on MgO nanosheets.

The toluene low-temperature degradation performance test of the MnO ₂ /MgO low-dimensional nanocomposite prepared in Comparative Example 3 is represented by the conversion rate of C ₇ H ₈ , and the results are shown in FIG. 12 . It can be seen from the figure that the toluene conversion rate is still lower than 30% when the reaction temperature is as high as 260°C when tested under the condition of 600ppm C ₇ H ₈ .

While the content of the present invention has been described in detail by way of the above preferred embodiments, it should be appreciated that the above description should not be construed as limiting the present invention. Various modifications and alternatives to the present invention will be apparent to those skilled in the art upon reading the foregoing. Accordingly, the scope of protection of the present invention should be defined by the appended claims.

Claims (10)

1. A MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material, wherein the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material comprises a γ-Al ₂ O ₃ nanosheet carrier, and manganese oxide nanocrystals adhered to the γ-Al ₂ O ₃ nanosheet carrier; Based on the total mass of the nanocomposite material as 100 wt%, the mass fraction of the manganese oxide nanocrystal grains is 10-15 wt%, and the mass fraction of the γ-Al ₂ O ₃ nanosheet carrier is 85-90 wt %. 2 . The nanocomposite material according to claim 1 , wherein the particle size of the manganese oxide nanocrystal grains is 3-8 nm, and the length of the γ-Al ₂ O ₃ nanosheet carrier is 350-400 nm. 3 . nm, the thickness is 8-15 nm; the specific surface area of the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material is 200-220 m ² /g. 3. A preparation method of the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material according to claim 1 or 2, characterized in that, comprising the following steps: (1) Disperse the γ-Al ₂ O ₃ nanosheet carrier in water, add a reducing agent and make it fully adsorbed on the surface of the γ-Al ₂ O ₃ nanosheet carrier; (2) Adding potassium permanganate solution and reducing agent for redox reaction, the generated MnO ₂ nano-grains are deposited in situ on the surface of γ-Al ₂ O ₃ nanosheet carrier; (3) centrifuging, washing, drying, grinding and calcining to obtain the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material. The preparation method according to claim 3, wherein the preparation method of the γ-Al ₂ O ₃ nanosheet carrier comprises: adding a weak alkaline solution and a dispersant to the sodium metaaluminate solution to form a mixed solution ; The mixed solution is subjected to a hydrothermal reaction, followed by centrifugation, washing, drying and grinding to obtain a γ-AlOOH nanosheet precursor; the γ-AlOOH nanosheet precursor is calcined and ground to obtain a γ-Al ₂ O ₃ nanosheet carrier . 5. preparation method according to claim 4 is characterized in that, described weak alkaline solution is ammoniacal liquor or urea solution, and described dispersant is sodium polyacrylate; The mol ratio of described sodium metaaluminate and urea is 1 : 8 to 12. 6 . The preparation method according to claim 4 , wherein the temperature of the hydrothermal reaction is 100-160° C., and the reaction time is 8-12 h. 7 . 7 . The preparation method according to claim 4 , wherein the temperature of calcining the γ-AlOOH nanosheets is 400-700° C., preferably 500° C.; the calcining time is 2-5 h. 8 . 8 . The preparation method according to claim 3 , wherein the reducing agent is ascorbic acid; the mass ratio of the γ-Al ₂ O ₃ nanosheet carrier to the reducing agent is 1: (0.5-1.2); the The molar ratio of the potassium permanganate to the reducing agent is 1:(0.5-1). 9 . The preparation method according to claim 3 , wherein the MnO ₂ nanocrystal grains are deposited in-situ on the surface of the γ-Al ₂ O ₃ nanosheet carrier and then calcined at a temperature of 200-350° C. and a time of 2 For ~5 hours, the atmosphere is air. 10 . The application of the MnO ₂ /γ-Al ₂ O ₃ low-dimensional nanocomposite material according to claim 1 in removing volatile organic compounds VOCs, wherein the VOCs comprise toluene. 11 .

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