Multi-active-site manganese-based monolithic mixed VOCs catalyst and preparation method thereof

Abstract

The invention aims to provide a multi-active-site manganese-based monolithic mixed VOCs catalyst and a preparation method thereof, and belongs to the technical field of atmospheric pollutant governance, foamy copper on which Mn-MOFs-74 grows is used as a substrate, copper nitrate and a potassium permanganate aqueous solution are respectively dispensed on the substrate, and after calcination is performed for 1 hour at the temperature of 300 DEG C, the multi-active-site manganese-based monolithic mixed VOCs catalyst is obtained. The manganese-based monolithic metal oxide catalyst Cu-MnO2 / AMO is prepared from a manganese dioxide crystal phase coated manganese-based amorphous phase substance, an obvious interface structure is formed between the amorphous phase and the crystal phase, more defects are generated, and multiple active sites, including Mn < 3 + >, oxygen vacancies and lattice oxygen, for toluene and acetone are achieved. And higher catalytic oxidation performance of the VOCs mixed gas can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of atmospheric pollutant treatment, and specifically relates to a multi-active site manganese-based integral mixed VOCs catalyst and a preparation method thereof. Background Art

[0002] In a highly oxidizing environment, volatile organic pollutants (VOCs) can act as fine particulate matter (PM) 2.5 Toluene is an important precursor of ozone and poses great harm to the environment. Among the many VOCs, toluene not only has a wide range of sources (it is the main component of the exhaust gas from the petroleum industry, many organic chemical industries, gas stations and light gasoline vehicles), but also has a high ozone generation potential. Therefore, it is often used as one of the main pollutants in VOCs treatment. Currently, the commonly used treatment methods include adsorption, direct combustion, catalytic combustion, and biodegradation. Compared with other technologies, catalytic oxidation can completely oxidize toluene into carbon dioxide and water at lower temperatures. It has the advantages of low operating temperature, no secondary pollution, and thorough removal. Therefore, the development of low-temperature, high-efficiency and stable catalysts has become a hot research topic in this field.

[0003] At present, the catalysts in this field are mainly concentrated on precious metal catalysts and non-precious metal oxide catalysts. Among them, the high price of precious metal catalysts limits their large-scale application in industry. Therefore, non-precious metal oxides with low price, high high-temperature catalytic activity and stability have attracted widespread attention. Among them, manganese-based metal oxides show high activity in the catalytic oxidation of VOCs. However, most of the manganese-based catalysts currently developed are aimed at degrading a single type of VOCs, ignoring the actual situation that VOCs emitted by industry are of many types and complex components. The green and efficient degradation of mixed VOCs requires the synergistic effect of multiple active sites. In addition, traditional manganese-based catalysts are mostly powdered. Such catalysts have problems such as large pressure drop in the packed bed, low mass transfer rate, easy sintering, and unsuitable for industrial application. Summary of the Invention

[0004] In response to the above problems, the present invention provides a multi-active site manganese-based integral mixed VOCs catalyst and a preparation method thereof. Among the numerous VOCs, toluene and acetone are typical benzene ring and oxygen-containing VOCs, respectively. Both have high ozone generation potential and strong photochemical reaction activity, posing a great threat to the environment and human body. For the mixed gas of these two typical VOCs, the catalyst uses a foam copper with a special three-dimensional cross-channel structure and good shock resistance and heat resistance as an integral carrier, and is prepared by a two-step method of hydrothermal method and redox method. The preparation method is simple, and the obtained catalyst has a special structure of a crystalline phase encapsulating an amorphous phase. The interface structure of the crystalline phase / amorphous phase and defect structures such as amorphous phase work synergistically to promote the catalyst to produce multiple active sites, including Mn 3+, oxygen vacancies and lattice oxygen, which makes its catalytic performance high-efficiency at low temperature and good stability, and can be well applied to the catalytic oxidation of two-component mixed VOCs of toluene and acetone.

[0005] The present invention adopts the following technical solutions: A multi-active site manganese-based monolithic mixed VOCs catalyst is prepared. A copper foam substrate on which Mn-MOFs-74 is grown is used as a substrate. Copper nitrate and potassium permanganate aqueous solutions are drop-coated on the substrate, respectively. After calcination at 300°C for 1 hour, a manganese-based monolithic metal oxide catalyst Cu-MnO2 / AMO is prepared.

[0006] A method for preparing a multi-active site manganese-based monolithic mixed VOCs catalyst comprises the following steps: S1. The cut copper foam was ultrasonically treated in 0.1 M hydrochloric acid, anhydrous ethanol, and deionized water in sequence. After drying, it was immersed in a 30 mL aqueous solution of sodium hydroxide and ammonium persulfate for 2 hours. After the reaction, it was repeatedly rinsed with deionized water and dried and sealed for storage. It was recorded as CCF, where the molar ratio of sodium hydroxide to ammonium persulfate was 20:1. S2. Dissolve 2,5-dihydroxyterephthalic acid in a mixture of methanol / water / DMF in a volume ratio of 1 / 1 / 15, mix well, add 50 wt% manganese nitrate aqueous solution, transfer to a 100 ml reactor together with CCF, and react at 130°C for 12 hours. After cooling, ultrasonically treat the pellet with ethanol and water to remove impurities, dry and seal, and store, which is recorded as MCCF-MOF; S3. Dissolve copper nitrate trihydrate in 140 μL of deionized water to prepare liquid A; dissolve potassium permanganate in 710 μL of deionized water to prepare liquid B; use a pipette to draw liquid A and evenly apply it on the MCCF-MOF. After complete absorption, use a pipette to draw liquid B and add it on top. After uniform absorption, place it in a 120°C oven to react for 12 hours. After the reaction is completed, soak it in deionized water for 12 hours, then rinse it with deionized water and dry it. After drying, calcine it at 300°C in a muffle furnace for 1 hour, with a heating rate of 1°C / min and a cooling rate of 5°C / min. It is recorded as Cu-MnO2 / AMO.

[0007] Furthermore, the size of the copper foam cut out in S1 is 3.8 cm×2 cm.

[0008] Furthermore, the concentration of sodium hydroxide in the S1 mixed aqueous solution is 0.0833 mol / L, and the concentration of ammonium persulfate is 0.0042 mol / L.

[0009] Furthermore, the amount of 2,5-dihydroxyterephthalic acid used in S2 is 0.1189 g; the amount of the manganese nitrate aqueous solution used is 466 μL.

[0010] Furthermore, the amount of copper nitrate trihydrate used in S3 is 0.1088 g, and the amount of potassium permanganate used is 0.0474 g.

[0011] A multi-active site manganese-based monolithic mixed VOCs catalyst is used for the catalytic oxidation of toluene and acetone mixed gases.

[0012] The beneficial effects of the present invention are as follows: The present invention selects copper foam with a special three-dimensional cross-channel structure and good shock resistance and heat resistance as a monolithic carrier, and uses MOFs material with rich pore structure and huge specific surface area as an amorphous phase precursor. Copper nitrate and potassium permanganate aqueous solutions are respectively drop-coated on the copper foam substrate on which Mn-MOFs-74 is grown, and calcined at a certain temperature in a short time to obtain a manganese-based monolithic catalyst. This type of monolithic metal oxide is composed of a manganese-based amorphous phase material wrapped in a manganese dioxide crystal phase. A clear interface structure is formed between the amorphous phase and the crystalline phase, generating more defects, and having multiple active sites for toluene and acetone, including Mn 3+ , oxygen vacancies and lattice oxygen. In order to obtain higher catalytic oxidation performance of VOCs mixed gas.

[0013] The preparation method adopted by the present invention is simple. It only needs to calcine the MOFs obtained by the traditional hydrothermal method at a certain temperature for a short time to obtain the MOFs, which reduces the energy consumption in the preparation process to a certain extent and saves costs. A crystalline phase / amorphous phase interface is constructed on the monolithic substrate, providing a large number of defect sites, and improving the physical and chemical properties of the catalyst such as the pore structure and low-temperature reduction performance, forming multiple active sites for toluene and acetone. In addition, the monolithic catalyst solves the problems of large pressure drop, low mass transfer rate, and easy sintering of the powder catalyst bed, which greatly improves the possibility of industrial application of manganese-based catalysts. The Cu-MnO2 / AMO catalyst prepared by the present invention can completely catalyze the oxidation of toluene and acetone at a relatively low temperature, and can maintain high stability and hydrothermal stability for a long time, and has great application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The XRD patterns of the catalysts prepared in Example 1 and the comparative example are shown.

[0015] Figure 2 This is the HRTEM image of the catalyst Cu-MnO2 / AMO prepared in Example 1.

[0016] Figure 3 The graph shows the reaction activity of the catalysts prepared in Example 1 and the comparative example as a function of temperature.

[0017] Figure 4 This is a stability test diagram of the catalyst Cu-MnO2 / AMO in Example 1. DETAILED DESCRIPTION

[0018] Example 1 A method for preparing a multi-active site manganese-based monolithic mixed VOCs catalyst comprises the following steps: S1. Cut copper foam into a size of 3.8 cm × 2 cm and ultrasonically treat it in 0.1 M hydrochloric acid, anhydrous ethanol, and deionized water in sequence. After drying, soak it in 30 mL of an aqueous solution of sodium hydroxide and ammonium persulfate (molar ratio of 20:1) for 2 hours. After the reaction, rinse it repeatedly with deionized water and store it in a sealed container, which is recorded as CCF. S2. Dissolve 0.1189 g of 2,5-dihydroxyterephthalic acid in a mixture of methanol / water / DMF in a volume ratio of 1 / 1 / 15. After mixing evenly, add 466 μL of a 50 wt% aqueous solution of manganese nitrate. Transfer the mixture and CCF to a 100 mL reactor and react at 130°C for 12 hours. After cooling, ultrasonically treat the pellet with ethanol and water to remove impurities, dry and seal it for storage, and record it as MCCF-MOF. S3. Dissolve 0.1088 g of copper nitrate trihydrate in 140 μl of deionized water to prepare liquid A; dissolve 0.0474 g of potassium permanganate in 710 μl of deionized water to prepare liquid B; use a pipette to draw liquid A and evenly apply it on the MCCF-MOF. After complete absorption, use a pipette to draw liquid B and drop it on it. After uniform absorption, put it in a 120°C oven to react for 12 hours. After the reaction is completed, soak it in deionized water for 12 hours, then rinse it with deionized water and dry it. After drying, calcine it at 300°C in a muffle furnace for 1 hour, with a heating rate of 1°C / min and a cooling rate of 5°C / min. It is recorded as Cu-MnO2 / AMO.

[0019] Comparative Example When only liquid A is dripped (other steps are the same), the catalyst obtained is CuO / AMO; when only liquid B is dripped (other steps are the same), the catalyst obtained is R-MnO2 / AMO; the material without dripping liquid A or B (other steps are the same) is recorded as AMO.

[0020] The prepared catalyst was subjected to X-ray diffraction analysis to obtain the XRD pattern of the catalyst, such as Figure 1 As shown, all catalysts exhibit characteristic peaks of copper and copper oxide, which are caused by the copper substrate itself and the copper oxide generated in the oxidizing atmosphere. In the catalysts Cu-MnO2 / AMO and R-MnO2 / AMO, a characteristic peak belonging to Ramsdellite MnO2 was observed at 36.7°, indicating that crystalline R-MnO2 was successfully generated on the amorphous AMO surface using potassium permanganate as the manganese source via a simple drop coating method.

[0021] The prepared catalyst Cu-MnO2 / AMO was scanned by high-magnification transmission electron microscopy to obtain the HRTEM image of the catalyst, as shown in Figure 2. Figure 2 As shown. Figure 2 In (a), the amorphous phase region in the upper right corner and the region with lattice fringes in the lower right corner can be clearly observed. Four regions (colored boxes) are selected from the bottom to measure the lattice spacing by fast Fourier transform, as shown in Figure 2. Figure 2 (b1-b4) are respectively attributed to the (201), (210) and (301) crystal planes of MnO2. Figure 2 The element distribution diagram in (c) clearly shows that the outer layer of the spherical particles is richer in copper and manganese, and the structure and Figure 2 The linear scan of copper, manganese, and oxygen elements in (d) shows a valley shape, which further confirms the structural characteristics of the crystalline Cu-MnO2 coated amorphous phase AMO.

[0022] Example 2 The Cu-MnO2 / AMO catalyst prepared in Example 1, and the R-MnO2 / AMO and CuO / AMO catalysts prepared in the comparative example were rolled into a size suitable for loading into a fixed-bed reactor with a diameter of 6 mm. Before the reaction, nitrogen was introduced (at a flow rate of approximately 30 ml / min). The reaction tube was heated to 200°C and held for 1 hour to remove impurities on the catalyst surface. The temperature was then lowered to 150°C and programmed to rise to 150-260°C at a rate of 10°C / min for continuous catalytic oxidation of toluene and acetone. The reactant gas, bubbling through a bubbling device, consisted of 1000 ppm toluene, 1000 ppm acetone, or 1000 ppm toluene + 1000 ppm acetone. The balance gas was air at a space velocity of 12,000 h / min. -1 .

[0023] Catalyst reaction activity Figure 3 As shown in (a), catalysts Cu-MnO2 / AMO, R-MnO2 / AMO and CuO / AMO can achieve 90% toluene removal efficiency at 229℃, 245℃ and 248℃, respectively.

[0024] like Figure 3 As shown in (b), the catalyst Cu-MnO2 / AMO with the best toluene catalytic performance achieved a 90% conversion efficiency for acetone and toluene in the mixed gas at 183℃ and 231℃, respectively.

[0025] Example 3 The Cu-MnO2 / AMO catalyst prepared in Example 1 was subjected to stability testing and rolled into a size suitable for loading into a fixed-bed reactor. The catalyst was then loaded into a fixed-bed reactor (a reaction tube with an inner diameter of approximately 6 mm). Nitrogen was introduced prior to the reaction (at a flow rate of approximately 30 ml / min). The reaction tube was heated to 200°C and held for 1 hour to remove impurities from the catalyst surface. The temperature was then raised to 200°C at a rate of 10°C / min (toluene conversion was approximately 20% and acetone conversion was 96%), and the catalytic oxidation of toluene and acetone was carried out continuously at this temperature for 10 hours. The temperature was then raised to 260°C at a rate of 10°C / min (toluene conversion was approximately 91% and acetone conversion was 100%), and the catalytic oxidation of toluene was continued at this temperature for 62 hours. The reaction gas was bubbling through a bubbling device, consisting of 1000 ppm toluene + 1000 ppm acetone, with the balance being air, at a space velocity of 12,000 h / s. -1 During the stability test, 5 vol.% and 10 vol.% water vapor were introduced intermittently to test the hydrothermal stability of the catalyst. Figure 4 As shown, the catalyst maintains long-term stability at both 200°C and 260°C. The introduction of water vapor maintains no effect on the catalytic performance of acetone. However, the catalytic performance of toluene decreases somewhat after the introduction of 5 vol.% and 10 vol.% water vapor, but quickly recovers after the water vapor is removed. Overall, the catalyst exhibits excellent stability and has broad application prospects.

Claims

1. A multi-active site manganese-based monolithic hybrid VOCs catalyst, characterized by: The catalyst is based on a copper foam on which Mn-MOFs-74 is grown. Copper nitrate and potassium permanganate aqueous solutions are drop-coated on the substrate, respectively. After calcination at 300° C. for 1 hour, a manganese-based monolithic metal oxide catalyst Cu-MnO2 / AMO is prepared.

2. A method for preparing the multi-active site manganese-based monolithic hybrid VOCs catalyst according to claim 1, characterized in that: The steps include: S1. The cut copper foam was ultrasonically treated in 0.1 M hydrochloric acid, anhydrous ethanol, and deionized water in sequence. After drying, it was immersed in a 30 mL aqueous solution of sodium hydroxide and ammonium persulfate for 2 hours. After the reaction, it was repeatedly rinsed with deionized water and dried and sealed for storage. It was recorded as CCF, where the molar ratio of sodium hydroxide to ammonium persulfate was 20:

1. S2. Dissolve 2,5-dihydroxyterephthalic acid in a mixture of methanol / water / DMF in a volume ratio of 1 / 1 / 15, mix well, add 50 wt% manganese nitrate aqueous solution, transfer to a 100 ml reactor together with CCF, and react at 130°C for 12 hours. After cooling, ultrasonically treat the pellet with ethanol and water to remove impurities, dry and seal, and store, which is recorded as MCCF-MOF; S3. Dissolve copper nitrate trihydrate in 140 μL of deionized water to prepare liquid A; dissolve potassium permanganate in 710 μL of deionized water to prepare liquid B; use a pipette to draw liquid A and evenly apply it on the MCCF-MOF. After complete absorption, use a pipette to draw liquid B and add it on top. After uniform absorption, place it in a 120°C oven to react for 12 hours. After the reaction is completed, soak it in deionized water for 12 hours, then rinse it with deionized water and dry it. After drying, calcine it at 300°C in a muffle furnace for 1 hour, with a heating rate of 1°C / min and a cooling rate of 5°C / min. It is recorded as Cu-MnO2 / AMO.

3. The method for preparing a multi-active site manganese-based monolithic hybrid VOCs catalyst according to claim 2, characterized in that: The size of the copper foam cut out in S1 is 3.8 cm×2 cm.

4. The method for preparing a multi-active site manganese-based monolithic hybrid VOCs catalyst according to claim 2, characterized in that: The concentration of sodium hydroxide in the S1 mixed aqueous solution is 0.0833 mol / L, and the concentration of ammonium persulfate is 0.0042 mol / L.

5. The method for preparing a multi-active site manganese-based monolithic hybrid VOCs catalyst according to claim 2, characterized in that: The amount of 2,5-dihydroxyterephthalic acid used in S2 is 0.1189 g; the amount of the manganese nitrate aqueous solution used is 466 μL.

6. The method for preparing a multi-active site manganese-based monolithic hybrid VOCs catalyst according to claim 2, characterized in that: The amount of copper nitrate trihydrate used in S3 is 0.1088 g, and the amount of potassium permanganate used is 0.0474 g.

7. A multi-active site manganese-based monolithic mixed VOCs catalyst as claimed in claim 1, which is used for catalytic oxidation of a mixed gas of toluene and acetone.

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