CN115025770A - MnO (MnO) 2 /γ-Al 2 O 3 Low-dimensional nano composite material and preparation method and application thereof - Google Patents
MnO (MnO) 2 /γ-Al 2 O 3 Low-dimensional nano composite material and preparation method and application thereof Download PDFInfo
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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
Technical Field
The invention relates to a low-dimensional manganese-based nanocomposite, in particular 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.
Background
Ozone is generated primarily by the photochemical reaction of Volatile Organic Compounds (VOCs) and NOx under solar illumination. In order to reduce the concentration of ozone, the precursor VOCs is controlled, and it is necessary to reduce the use of raw and auxiliary materials of the VOCs from the source and reduce the discharge of the VOCs. However, it is difficult to achieve complete zero emission of low concentrations of VOCs due to process technology and product performance requirements. Therefore, end treatment remains an important component of VOCs treatment.
High-efficiency treatment technologies such as combustion, catalytic combustion and the like are widely applied to large spraying and chemical enterprises in China, but the high-efficiency treatment technologies of the VOCs are expensive, the operation cost and the later maintenance cost are high, most enterprises are difficult to bear, the VOCs can be treated only by a simple process of activated carbon adsorption, and the problem that the removal efficiency is not high or is negative is difficult to avoid in the mode. Therefore, aiming at the problem of treatment of small-air-quantity low-concentration VOCs in part of enterprises, the development of a catalyst capable of removing VOCs at a lower temperature is imperative, external energy supply can be greatly reduced, and energy consumption is reduced.
However, most of the current commercial catalysts are mainly noble metals, so that the cost is high, the resource waste is serious, and the research and development of replaceable non-noble metal catalysts are focuses and hot spots of concern in the field of environmental catalysis. In a single-component bulk metal oxide, metal ion oxidation-reduction cycle electron transfer is slow, the activation energy of lattice oxygen diffusing along the direction from a bulk phase to a surface is high, and the activation processes of reactant molecules on the metal oxide and the activation process of gas-phase oxygen can only be alternately carried out on the same metal position, so that the reaction activity of the metal oxide is low. The carrier in the supported catalyst can improve the performance of the catalyst by increasing the electron density, providing a dispersed phase nucleation center, regulating and controlling the surface acidity and alkalinity and the like.
Disclosure of Invention
In view of the above, in order to solve the problems of low-temperature activity and low reaction rate of VOCs (volatile organic compounds) purified by using a metal oxide catalyst in a catalytic combustion technology, the invention develops MnO which has adjustable carrier acidity and high exposure degree of oxygen vacancy active sites, and can efficiently and synergistically adsorb and activate organic waste gas and oxygen molecules and enable the organic waste gas and the oxygen molecules to rapidly react 2 /γ-Al 2 O 3 A low dimensional nanocomposite.
In particular, in a first aspect, the invention provides a MnO 2 /γ-Al 2 O 3 A low dimensional nanocomposite. 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 crystal 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%.
Preferably, the grain size of the manganese oxide nano crystal grain is 3-8 nm, and the gamma-Al is 2 O 3 The length of the nanosheet carrier is 350-400 nm, and the thickness of the nanosheet carrier is 8-15 nm; the MnO 2 /γ-Al 2 O 3 The specific surface area of the low-dimensional nano composite material is 200-220m 2 /g。
In a second aspect, the present invention provides a MnO as defined above 2 /γ-Al 2 O 3 The preparation method of the low-dimensional nano composite material comprises the following steps:
(1) mixing gamma-Al 2 O 3 Dispersing the nano-sheet carrier in water, adding a reducing agent and making the nano-sheet carrier fully adsorbed on gamma-Al 2 O 3 A nanosheet carrier surface;
(2) adding potassium permanganate solution to react with reductant to produce MnO 2 In-situ deposition of nanocrystalline particles on gamma-Al 2 O 3 The surface of a nanosheet carrier;
(3) centrifuging, washing, drying, grinding and roasting to obtain the MnO 2 /γ-Al 2 O 3 Low-dimensional nano compoundAnd (5) mixing the materials.
Preferably, the gamma-Al 2 O 3 The preparation method of the nanosheet carrier comprises the following steps: adding a weak alkaline solution and a dispersing agent into the sodium metaaluminate solution to form a mixed solution;
carrying out hydrothermal reaction on the mixed solution, and then carrying out centrifugation, washing, drying and grinding to obtain a gamma-AlOOH nanosheet precursor; calcining and grinding the gamma-AlOOH nanosheet precursor to obtain gamma-Al 2 O 3 A nanosheet carrier.
Preferably, the weak alkaline solution is ammonia water or urea solution, and the dispersing agent is sodium polyacrylate.
Preferably, the molar ratio of sodium metaaluminate to urea is 1: 8 to 12.
Preferably, the temperature of the hydrothermal reaction is 100-160 ℃, and the reaction time is 8-12 h.
Preferably, the temperature for calcining the gamma-AlOOH nanosheet is 400-700 ℃, preferably 500 ℃; the calcination time is 2-5 h.
Preferably, the reducing agent is ascorbic acid.
Preferably, the gamma-Al 2 O 3 The mass ratio of the nanosheet carrier to the reducing agent is 1: (0.5 to 1.2); the molar ratio of the potassium permanganate to the reducing agent is 1: (0.5 to 1).
Preferably, the MnO is 2 In-situ deposition of nanocrystalline particles on gamma-Al 2 O 3 The temperature of roasting the surface of the nanosheet carrier is 200-350 ℃, the time is 2-5 hours, and the atmosphere is air.
In a third aspect, the present invention provides a MnO as defined above 2 /γ-Al 2 O 3 Use of low dimensional nanocomposites for the removal of volatile organic compounds, VOCs, including toluene.
Advantageous effects
MnO provided by the invention 2 /γ-Al 2 O 3 The low-dimensional nano composite material has larger specific surface area, abundant weak acid sites and poor chemical binding property with product carbon dioxide, and is beneficial to the adsorption and activation of VOCs molecules such as toluene and the like on the surface of the material to produceDesorption of carbon dioxide molecules and catalytic oxidation reaction. The composite material can realize the treatment of medium and small air volume low concentration VOCs waste gas (mainly aiming at toluene, benzene and the like), has high purification efficiency (more than or equal to 99 percent), low ignition point temperature and lasting stability, can reduce the optimal catalytic temperature of the catalyst to be below 200 ℃, reduces the supply of external energy during reaction and reduces energy consumption. The method has great application potential in the aspect of small-air-volume low-concentration VOCs treatment in small coating enterprises.
Drawings
FIG. 1 shows MnO in the present invention 2 /γ-Al 2 O 3 Schematic diagram of the preparation process of the low-dimensional nano composite material;
FIG. 2 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) SEM, low power TEM, high power TEM, HAADF, HRTEM, and mapping profiles of low dimensional nanocomposites;
FIG. 3 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite with MnO prepared in comparative example 1 2 / γ-Al 2 O 3 (c) XRD characterization patterns of low dimensional nanocomposites;
FIG. 4 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite and MnO prepared in comparative example 1 2 / γ-Al 2 O 3 (c) NH of low dimensional nanocomposites 3 Temperature programmed desorption (NH) 3 -TPD) spectrum;
FIG. 5 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite with MnO prepared in comparative example 1 2 / γ-Al 2 O 3 (c) CO of low dimensional nanocomposites 2 Temperature programmed desorption (CO) 2 -TPD) spectrum;
FIG. 6 shows MnO prepared in comparative example 1 2 /γ-Al 2 O 3 (c) SEM and TEM characterization images of the nanocomposites;
FIG. 7 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite and MnO prepared in comparative example 1 2 / γ-Al 2 O 3 (c) Low vitamin nanoA nitrogen adsorption-desorption isothermal curve chart of the rice composite material;
FIG. 8 shows γ -Al prepared in example 1 2 O 3 (s) nanosheets and commercial alumina nanoparticles gamma-Al used in comparative example 1 2 O 3 (c) (ii) pyridine infrared spectrum of (a);
FIG. 9 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite with MnO prepared in comparative example 1 2 / γ-Al 2 O 3 (c) A spectrogram of the catalytic efficiency of the low-dimensional nano composite material changing along with the temperature when 600ppm of toluene is removed;
FIG. 10 shows MnO 2 /γ-Al 2 O 3 (s) a graphical representation of the results of a catalytic stability test of the material at elevated temperatures up to 200 ℃;
FIG. 11 shows MnO prepared in comparative example 2 2 /SiO 2 SEM and TEM characterization images of the nanocomposite;
FIG. 12 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite and MnO prepared in comparative example 1 2 / γ-Al 2 O 3 (c) MnO prepared in comparative example 2 2 /SiO 2 And MnO prepared in comparative example 3 2 A spectrogram of the catalytic efficiency of the/MgO low-dimensional nano composite material changing along with the temperature when 600ppm of methylbenzene is removed;
FIG. 13 shows MnO prepared in comparative example 3 2 SEM and TEM characterization of the/MgO nanocomposites.
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative, and not restrictive, of the invention.
The invention provides MnO applied to catalytic oxidation of Volatile Organic Compounds (VOCs) with low concentration (less than 1000ppm) 2 /γ-Al 2 O 3 A low-dimensional nano composite material and a preparation method thereof. The MnO 2 /γ-Al 2 O 3 The low dimensional nanocomposite is formed by fine manganese oxide nanocrystals adhered to an alumina nanoplate carrier.
In some embodiments, the manganese oxide nanocrystal particle may have a mass fraction of 10 to 15 wt% and the alumina nanosheet support may have a mass fraction of 85 to 90 wt%, based on 100 wt% of the total mass of the nanocomposite. Preferably, the size of the manganese oxide nanocrystal particle can be 3-8 nm; the length of the alumina nano-sheet carrier is 350-400 nm, and the thickness of the alumina nano-sheet carrier is 8-15 nm.
In the low-dimensional nano composite material, the carrier material is preferably gamma-phase alumina nano sheet, and the specific surface area of the carrier material can reach 200m 2 More than g, the specific surface area of the composite material can reach 200-220m 2 (ii) in terms of/g. The larger specific surface area of the carrier provides rich nucleation centers for the attachment of metal oxide particles, and the manganese oxide nano-crystalline particles in the composite material have high dispersity, small particle size and strong interaction with the carrier. At the same time, gamma-Al 2 O 3 The surface weak acidic sites of the nanosheet carrier are more (
The total amount of acid sites is high, and
the ratio of the acid sites to the Lewis acid sites is high), volatile organic compounds such as toluene and the like are easily adsorbed and activated, and the chemical bonding property between the volatile organic compounds and carbon dioxide is poor. In addition, MnO in the composite Material 2 The oxygen vacancy and the acid site on the alumina carrier can cooperate with each other to activate oxygen, toluene and other VOCs molecules and react, so that the realization of the low-temperature catalytic oxidation process is promoted.
Based on the characteristics, the MnO provided by the invention 2 /γ-Al 2 O 3 The low-dimensional nano composite material can be used as a catalyst for catalytic combustion of VOCs (volatile organic compounds) such as low-concentration methylbenzene at low temperature, and carbon dioxide generated in the catalytic oxidation process is easier to diffuse from the surface of the catalyst to the external environment.
The MnO of the present invention is exemplified below with reference to FIG. 1 2 /γ-Al 2 O 3 The preparation process of low dimensional nanometer composite material.
Preparation of gamma-AlOOH nanosheet precursor by hydrothermal method. Firstly, dissolving a proper amount of sodium metaaluminate in water completely, adding ammonia water or urea into the solution under magnetic stirring to adjust the pH value of the sodium metaaluminate aqueous solution to 7.5-10, and ensuring that AlO can be ensured under the condition of lower pH value by adding the ammonia water or the urea - Hydrolysis can also occur and hydroxide precipitates can be formed. The molar ratio of sodium metaaluminate to urea can be controlled to be 1: 8-12, so as to ensure the generation of the appropriate nanosheet morphology. Then, a proper amount of dispersing agents such as sodium polyacrylate and the like are added and completely dissolved in the solution, and the using amount of the dispersing agents can be 0.1-0.3 g. Stirring and mixing evenly at room temperature, transferring the solution into a high-pressure reaction kettle, and standing and reacting for 8-12 h at the temperature of 100-160 ℃. And after the reaction is finished, centrifuging, washing, freeze-drying and grinding to obtain a white powdery gamma-AlOOH nanosheet precursor.
Air calcination method for synthesizing gamma-Al 2 O 3 A nanosheet carrier. The precursor of the gamma-AlOOH nanosheet is paved in a square corundum crucible, the corundum crucible is placed in a muffle furnace to be calcined for 2-5 h, the calcination temperature is 400-700 ℃, the preferred temperature is 500 ℃, and the heating rate is 2-10 ℃/min. Grinding the calcined product to obtain white powdery gamma-Al with low crystallinity 2 O 3 A nanosheet carrier.
MnO synthesis by dip-in-situ surface deposition method 2 /γ-Al 2 O 3 A low dimensional nanocomposite. gamma-Al is mixed 2 O 3 Dispersing white powder in water, adding appropriate amount of reducing agent ascorbic acid, wherein the content of gamma-Al 2 O 3 The mass ratio to ascorbic acid may be 1: (0.5 to 1.2). Stirring and mixing evenly to make the ascorbic acid fully adsorbed on the surface of the alumina carrier. Then, potassium permanganate is added in the form of solution according to the molar ratio of potassium permanganate to ascorbic acid of 1: (0.5-1) is added into a mixed solution of ascorbic acid and an alumina carrier in a dropwise manner, the concentration of potassium permanganate can be 0.2-0.8mol/L, the dropwise adding speed can be 0.5-1.5 ml/min, and the mixture is stirred at room temperature for 2-4h to ensure that the reducing agent ascorbic acid and the potassium permanganate fully generate redox reaction, MnO 2 The crystal grains are in-situ deposited on the surface of the alumina carrier. After the reaction is finished, centrifuging, washing, freeze-drying, grinding the product, and roasting 2 at 200-350 ℃ in airAbout 5h (preferably, the temperature rising rate of roasting is 2-10 ℃/min), and brown black powdery MnO is obtained 2 /γ-Al 2 O 3 A low dimensional nanocomposite.
Use of the dip-in-situ surface deposition method in the present invention to favor MnO 2 In the presence of gamma-Al 2 O 3 Uniform distribution on the nano-sheet carrier and is beneficial to obtaining MnO with smaller size 2 And (4) crystal grains.
MnO obtained by the invention 2 /γ-Al 2 O 3 When the low-dimensional nano composite material is used as a catalyst for solving the problem of high-efficiency catalytic oxidation of medium-small air quantity low-concentration VOCs at low temperature, the low-dimensional nano composite material is added into a fixed bed continuous flow reactor for performance test, and the space velocity is 60000mL g -1 h -1 Reacting toluene C in the inlet and outlet gases 7 H 8 The concentration was measured on-line by gas chromatography. The invention provides a composite material (MnO) 2 /γ-Al 2 O 3 ) Has higher C 7 H 8 Catalytic oxidation activity: for 600ppm of C 7 H 8 The removal conversion rate of more than 90 percent can be realized under the low temperature condition of 153 ℃; the composite material can continue to achieve greater than 99% removal conversion for at least 24 hours when the temperature is raised to 200 ℃.
The invention uses air calcination method to prepare alumina carrier material with proper surface acidity and alkalinity, and uses dipping-in-situ surface deposition method to prepare MnO 2 /γ-Al 2 O 3 The low-dimensional nano composite material aims at the problem of treatment of medium and small air quantity and low concentration VOCs, and realizes feasibility of removing VOCs at a lower temperature. Moreover, the catalyst carrier material has larger specific surface area and provides abundant nucleation centers for metal oxide particles, thereby generating the catalyst with high dispersity, small particle size and strong interaction between the metal oxide and the carrier. Meanwhile, the acidic sites on the surface of the carrier are beneficial to the adsorption of VOCs molecules and CO products 2 Desorption of molecules further promotes the catalytic combustion of VOCs such as low-concentration toluene at low temperature.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., a person skilled in the art can make a selection within suitable ranges through the description herein, and are not limited to the specific values exemplified below.
Example 1
1g (0.012mol) of sodium metaaluminate are dissolved in 50mL of water and 6g (0.1mol) of urea and 0.20g of sodium polyacrylate are added to the solution with magnetic stirring. After stirring at room temperature for 1h, the solution was transferred to a reaction kettle and allowed to stand in an oven at 140 ℃ for 10 h. After reaction, the mixture is centrifuged, washed with water and freeze-dried in a freeze dryer. Grinding and collecting the product to obtain gamma-AlOOH white powder.
Then, 1g of gamma-AlOOH white powder sample is flatly paved in a square corundum crucible, the corundum crucible is placed in a muffle furnace to be calcined for 2 hours, the calcination temperature is 500 ℃, the heating rate is 5 ℃/min, and the gamma-Al is obtained by collection 2 O 3 White powder.
Finally, 0.3g of gamma-Al is added 2 O 3 The white powder was uniformly dispersed in 30mL of water, 0.176g (0.001mol) of ascorbic acid was added to the above solution, and after stirring at room temperature for 10 hours, the ascorbic acid was sufficiently adsorbed on the surface of the alumina carrier, and then 5mL of a potassium permanganate solution (0.4mol/L) was added dropwise to the above mixed solution, and stirring at room temperature for 2 hours. After the reaction is finished, centrifuging, washing, freeze-drying in a freeze dryer, grinding the product, transferring to a muffle furnace at 300 ℃ for calcining for 2h at the heating rate of 5 ℃/min to obtain the MnO 2 /γ-Al 2 O 3 Low dimensional nanocomposite, denoted MnO 2 /γ-Al 2 O 3 (s) low dimensional nanocomposites.
The mass fraction of the manganese oxide nanocrystal particles in the composite material prepared in the embodiment 1 is 13 wt%, and the gamma-Al is calculated by taking the total mass of the nanocomposite material as 100 wt% 2 O 3 The mass fraction of the nanosheet carrier is 87 wt%.
Scanning Electron microscopy, Transmission ElectronCharacterization of MnO by using mirror, X-ray diffraction, nitrogen adsorption-desorption and chemical adsorption 2 / γ-Al 2 O 3 (s) chemical composition and chemical microenvironment of the low dimensional nanocomposite.
FIG. 2 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) SEM, low power TEM, high power TEM, HAADF, HRTEM, and mapping characterization of the low dimensional nanocomposites. As can be seen from FIG. 2, Al 2 O 3 The length and thickness of the nano-sheet are respectively 360 nm and 10nm, and the composite material is formed by adhering a plurality of fine nano-particles with the particle size of about 5nm on an alumina nano-sheet carrier. The distribution of the Mn element in the small bright spots and mapping photographs shown in the HAADF graph both demonstrate that the fine manganese oxide nanoparticles are highly dispersed on the alumina nanosheet support.
FIG. 3 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) XRD characterization pattern of low dimensional nanocomposites. It can be seen that there are three weak and broad diffraction peaks at 37.76 °, 45.80 ° and 66.92 °, corresponding to the cubic system γ -Al 2 O 3 The (311), (400) and (440) crystal planes of (a) indicate that the support is a gamma-phase alumina material with lower crystallinity, but no distinct manganese oxide characteristic peak is identified, demonstrating that the manganese oxide crystal grain size is small and highly dispersed on the alumina nanosheet support.
FIG. 4 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite and MnO prepared in comparative example 1 2 /γ-Al 2 O 3 (c) NH of low dimensional nanocomposites 3 Temperature programmed desorption (NH) 3 -TPD) spectrum; FIG. 5 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite and MnO prepared in comparative example 1 2 /γ-Al 2 O 3 (c) CO of low dimensional nanocomposites 2 Temperature programmed desorption (CO) 2 -TPD) spectrum. From NH shown in FIG. 4 3 MnO can be seen in the TPD graph 2 /γ-Al 2 O 3 (s) a high and broad peak at 109 ℃ corresponding to a weakly acidic site; from CO shown in FIG. 5 2 As can be seen in the diagram of the TPD,MnO 2 /γ-Al 2 O 3 the carbon dioxide desorption temperature(s) was 118 ℃. The acid sites of the gamma-phase alumina nanosheets prepared in example 1 are mainly weak acid sites, and the stability of chemical bonding between the gamma-phase alumina nanosheets and carbon dioxide is low, so that carbon dioxide generated in the catalytic oxidation process of VOCs (volatile organic compounds) such as toluene is easier to diffuse from the surface of the catalyst to the external environment.
Example 2
Essentially the same as the protocol of example 1, with the main differences: in this example, gamma-AlOOH was converted into gamma-Al 2 O 3 The calcination temperature of the white powder was 600 ℃. The mass fraction of the manganese oxide nanocrystal particles in the composite material prepared in the embodiment is 13 wt%, and the gamma-Al is calculated by taking the total mass of the nanocomposite material as 100 wt% 2 O 3 The mass fraction of the nanosheet carrier is 87 wt%.
Example 3
Essentially the same as the protocol of example 1, with the main differences: in this example, gamma-AlOOH was converted into gamma-Al 2 O 3 The calcination temperature of the white powder was 700 ℃. The mass fraction of the manganese oxide nanocrystal particles in the composite material prepared in the embodiment is 12.8 wt%, and the gamma-Al is calculated by taking the total mass of the nanocomposite material as 100 wt% 2 O 3 The mass fraction of the nanosheet carrier is 87.2 wt%.
Example 4
Essentially the same as the protocol of example 1, with the main differences: the concentration of the potassium permanganate solution in this example was 0.2 mol/L. The mass fraction of the manganese oxide nanocrystal particles in the composite material prepared in the embodiment is 10 wt%, and the gamma-Al is calculated by taking the total mass of the nanocomposite material as 100 wt% 2 O 3 The mass fraction of the nanosheet carrier is 90 wt%.
Example 5
Essentially the same as the protocol of example 1, with the main differences that: the concentration of the potassium permanganate solution in this example was 0.8 mol/L. The mass fraction of the manganese oxide nanocrystal particles in the composite material prepared in the embodiment is 15 wt%, and the gamma-Al is calculated by taking the total mass of the nanocomposite material as 100 wt% 2 O 3 Material of nanosheet carrierThe amount fraction was 85 wt%.
Comparative example 1
Essentially the same as the protocol of example 1, with the main differences: in this comparative example, commercial alumina powder (Adamas reagent, 99%, gamma-phase Al) was used as it is 2 O 3 20nm) as a raw material to prepare the resulting MnO 2 /γ- Al 2 O 3 The low dimensional nanocomposite is denoted MnO 2 /γ-Al 2 O 3 (c) A low dimensional nanocomposite.
MnO is characterized by a scanning electron microscope, a transmission electron microscope, X-ray diffraction, nitrogen adsorption-desorption and chemical adsorption 2 / γ-Al 2 O 3 (c) Chemical composition and chemical microenvironment of low dimensional nanocomposites.
FIG. 6 shows MnO prepared in comparative example 1 2 /γ-Al 2 O 3 (c) SEM and TEM characterization of the nanocomposites. As can be seen from the figure, commercial Al 2 O 3 MnO with a particle size of 20nm and a smaller particle size 2 The nanoparticles simply pile up together.
FIG. 3 shows MnO prepared in comparative example 1 2 /γ-Al 2 O 3 (c) XRD characterization pattern of low dimensional nanocomposite. It can be seen from the figure that stronger diffraction peaks at 37.76 °, 39.44 °, 45.80 °, 61.06 ° and 66.92 ° correspond to the cubic system γ -Al 2 O 3 The (311), (222), (400), (511) and (440) crystal planes of (a) indicate that the material is a gamma-phase alumina material with higher crystallinity.
FIG. 7 shows MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite and MnO prepared in comparative example 1 2 /γ-Al 2 O 3 (c) Nitrogen adsorption-desorption isotherm graph of low dimensional nanocomposite. As can be seen from the figure, MnO prepared by adopting gamma-phase alumina nanosheet as carrier 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite to MnO prepared with commercial alumina nanoparticles as support 2 /γ-Al 2 O 3 (c) The specific surface area of the composite material is larger and is 209.8m respectively 2 G and 134.5m 2 (iv) g. The increased specific surface area of the two-dimensional nanosheet carrier is beneficial to the dispersion of manganese oxide nanoparticles and the catalytic reaction with VOCs gases such as toluene and the like.
FIG. 4 shows MnO prepared in comparative example 1 2 /γ-Al 2 O 3 (c) NH of low dimensional nanocomposites 3 Temperature programmed desorption (NH) 3 -TPD) spectrum. At NH 3 In TPD, MnO 2 /γ-Al 2 O 3 (c) At 94 ℃ and 274 ℃ there are two NH sites 3 Desorption peaks corresponding to weak acid and medium acid sites, respectively.
FIG. 5 shows MnO prepared in comparative example 1 2 /γ-Al 2 O 3 (c) CO of low dimensional nanocomposites 2 Temperature programmed desorption (CO) 2 -TPD) spectrum. In CO 2 In TPD, MnO 2 /γ-Al 2 O 3 (c) The desorption temperature of the carbon dioxide is 138 ℃ and 424 ℃, which proves that the acid sites of the alumina nano particles in the comparative example 1 are medium-strong acids, the chemical bonding with the carbon dioxide is strong, and the desorption of the carbon dioxide molecules is not facilitated, so that the activity of the catalyst is weakened.
FIG. 8 shows γ -Al prepared in example 1 2 O 3 (s) nanosheets and commercial alumina nanoparticles gamma-Al used in comparative example 1 2 O 3 (c) Pyridine infrared spectrum of (1). As can be seen from the figure, the γ -phase alumina nanosheets γ -Al prepared in example 1 2 O 3 (s) at the time of 423K,
acid/Lewis acid 0.55, 573K 0.63; commercial alumina nanoparticles gamma-Al 2 O 3 (c) At the time of 423K, the user can select the key,
the acid/Lewis acid ratio was 0.49 and 0.32 at 573K. The gamma phase alumina nano-plate prepared in the example 1 is proved to have higher total acid content and Lewis acid content ratio than the commercial alumina nano-particle
High acid content and gamma phaseAlumina nano-sheet gamma-Al 2 O 3 (s) on
Acid to acid ratio commercial alumina nanoparticle gamma-Al 2 O 3 (c) Is high.
MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite and MnO prepared in comparative example 1 2 /γ-Al 2 O 3 (c) The low-dimensional nano composite material is subjected to a toluene low-temperature degradation performance test experiment.
MnO prepared in example 1 2 /γ-Al 2 O 3 (s) Low dimensional nanocomposite and MnO prepared in comparative example 1 2 /γ- Al 2 O 3 (c) The toluene low-temperature degradation performance test of the low-dimensional nano composite material is carried out in a fixed bed continuous flow reactor, a quartz tube with the inner diameter of 8mm is used as the reactor, the filling amount of the catalyst is 0.1g, and the reaction gas inlet is as follows: c 7 H 8 Concentration 600ppm, O 2 Concentration 21% carrier gas N 2 The reaction temperature is 120-280 ℃, and the space velocity is 60000mL g -1 h -1 Reaction of C in the inlet and outlet gases 7 H 8 The concentration is detected on line by gas chromatography, and the catalyst reaction activity is detected by C 7 H 8 The results are shown in FIG. 9. As can be seen, MnO prepared in example 1 of the present invention 2 /γ-Al 2 O 3 (s) C of Low dimensional nanocomposite 7 H 8 The catalytic oxidation performance is obviously superior to MnO prepared by commercial alumina nano particles 2 /γ-Al 2 O 3 (c) Low dimensional nanocomposite, 600ppm of C 7 H 8 Over 90% removal conversion can be achieved at 153 ℃. FIG. 10 shows MnO 2 /γ-Al 2 O 3 (s) the results of the catalytic stability test of the material at a temperature increased to 200 ℃ are shown schematically, and it can be seen from the graph that it can achieve a toluene removal rate of 99% or more for at least 24 hours, and the activity of the material is hardly attenuated.
Comparative example 2
Same as in example 1The scheme of (2) is basically the same, and the main difference lies in that: in this comparative example, the obtained MnO was prepared by directly using the dendritic silica powder (note: nat. Commun.,2021,12,4968, doi. org/10.1038/s41467-021- 2 /SiO 2 A low dimensional nanocomposite.
FIG. 11 shows MnO prepared in comparative example 2 2 /SiO 2 SEM and TEM characterization of the nanocomposites. As can be seen from the figure, SiO 2 The carrier is a dendritic silicon dioxide nano material with a mesoporous structure with the diameter of about 30nm, and the micro MnO is 2 The nanoparticles are highly dispersed in the pores of the material.
MnO prepared in comparative example 2 2 /SiO 2 Toluene Low temperature degradation Performance test of Low dimensional nanocomposite passing toluene C 7 H 8 The results are shown in FIG. 12. As can be seen from the figure, 600ppm of C 7 H 8 Can realize the removal conversion rate of more than 90 percent at 211 ℃.
Comparative example 3
Essentially the same as the protocol of example 1, with the main differences: in this comparative example, the magnesium oxide powder (note: chem. Commun.,2013,49,6093-6095, DOI:10.1039/c3cc42504e) reported in the literature was directly used as the carrier raw material to prepare the obtained MnO 2 MgO low-dimensional nano composite material.
FIG. 13 shows MnO prepared in comparative example 3 2 SEM and TEM characterization of the/MgO nanocomposites. As can be seen from the figure, MgO is a flower-shaped structure assembled by nanosheets, and MnO is prepared by an in-situ dip deposition method 2 MgO and MnO of example 1 2 /Al 2 O 3 (s) similar morphology and structure, MnO 2 The nanoparticles are dispersed on the MgO nanosheets.
MnO prepared in comparative example 3 2 The toluene low-temperature degradation performance test of the/MgO low-dimensional nano composite material passes C 7 H 8 The results are shown in FIG. 12. As can be seen from the figure, 600ppm of C 7 H 8 When the reaction temperature is up to 260 ℃, the toluene conversion rate is still lower than 30 percent when the reaction temperature is tested under the conditions.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.
Claims (10)
1. MnO (MnO) 2 /γ-Al 2 O 3 A low dimensional nanocomposite material characterized in that said MnO is 2 /γ-Al 2 O 3 The low dimensional nanocomposite comprises gamma-Al 2 O 3 A nanosheet carrier, 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%.
2. The nanocomposite as claimed in claim 1, wherein the manganese oxide nanocrystal particle size is 3 to 8nm, and the γ -Al is 2 O 3 The length of the nanosheet carrier is 350-400 nm, and the thickness of the nanosheet carrier is 8-15 nm; the MnO 2 /γ-Al 2 O 3 The specific surface area of the low-dimensional nano composite material is 200-220m 2 /g。
3. The MnO of claim 1 or 2 2 /γ-Al 2 O 3 The preparation method of the low-dimensional nano composite material is characterized by comprising the following steps of:
(1) mixing gamma-Al 2 O 3 Dispersing the nano-sheet carrier in water, adding a reducing agent and making the nano-sheet carrier fully adsorbed on gamma-Al 2 O 3 The surface of a nanosheet carrier;
(2) adding potassium permanganate solution to react with reductant to produce MnO 2 In-situ deposition of nanocrystalline particles on gamma-Al 2 O 3 A nanosheet carrier surface;
(3) centrifuging, washing, drying, grinding and roasting to obtain the MnO 2 /γ-Al 2 O 3 A low dimensional nanocomposite.
4. The method of claim 3, wherein the γ -Al is 2 O 3 The preparation method of the nanosheet carrier comprises the following steps: adding a weak alkaline solution and a dispersing agent into the sodium metaaluminate solution to form a mixed solution;
carrying out hydrothermal reaction on the mixed solution, and then carrying out centrifugation, washing, drying and grinding to obtain a gamma-AlOOH nanosheet precursor; calcining and grinding the gamma-AlOOH nanosheet precursor to obtain gamma-Al 2 O 3 A nanosheet carrier.
5. The method according to claim 4, wherein the weakly alkaline solution is an aqueous ammonia or urea solution, and the dispersant is sodium polyacrylate; the molar ratio of the sodium metaaluminate to the urea is 1: 8-12.
6. The preparation method according to claim 4, wherein the hydrothermal reaction is carried out at a temperature of 100 to 160 ℃ for 8 to 12 hours.
7. The preparation method according to claim 4, wherein the temperature for calcining the gamma-AlOOH nanosheets is 400-700 ℃, preferably 500 ℃; the calcination time is 2-5 h.
8. The production method according to claim 3, wherein the reducing agent is ascorbic acid; the gamma-Al 2 O 3 The mass ratio of the nanosheet carrier to the reducing agent is 1: (0.5 to 1.2); the molar ratio of the potassium permanganate to the reducing agent is 1: (0.5 to 1).
9. The method of claim 3, wherein the MnO is 2 In-situ deposition of nanocrystalline particles on gamma-Al 2 O 3 The temperature of roasting the surface of the nanosheet carrier is 200-350 ℃, the time is 2-5 hours, and the atmosphere is air.
10. The MnO of claim 1 2 /γ-Al 2 O 3 Use of low dimensional nanocomposites for the removal of Volatile Organic Compounds (VOCs), wherein the VOCs comprise toluene.
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