Process for the preparation of manganese oxide-based catalysts and use thereof

Abstract

This invention provides a method for preparing a manganese oxide-based catalyst, comprising the following steps: Step 1): Pre-treating attapulgite to obtain pre-treated attapulgite; Step 2): Coating the pre-treated attapulgite obtained in Step 1) with a first coating agent and drying to obtain dried first-coated attapulgite; Step 3): Coating the dried first-coated attapulgite obtained in Step 2) with a second coating agent and drying to obtain the manganese oxide-based catalyst; the first coating agent comprises carbon materials and nano-manganese dioxide composite iron oxide catalyst; the second coating agent is composed of nano-manganese dioxide composite iron oxide catalyst, COF-LZU1 covalent organic framework, and lanthanide perovskite compound in a mass ratio of 8:(0.5-1.5):(0.5-1.5). The manganese oxide-based catalyst prepared by this invention has good formaldehyde adsorption effect. This invention also provides an application of this manganese oxide-based catalyst in formaldehyde adsorption.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a method for preparing and applying a manganese oxide-based catalyst. Background Technology

[0002] Formaldehyde (HCHO) is a colorless volatile organic compound (VOC) with a strong, pungent odor, and is one of the main pollutants in indoor air. Indoor formaldehyde primarily originates from the continuous release of decorative and building materials such as engineered wood products, furniture, paints, adhesives, and textiles, with a release period of 3-15 years. Due to the extensive use of these materials and insufficient ventilation, formaldehyde concentrations in newly renovated homes often exceed safety standards, posing a threat to human health. Long-term exposure to low doses of formaldehyde can cause chronic respiratory diseases, nasopharyngeal carcinoma, colon cancer, brain tumors, menstrual disorders, and gene mutations in cell nuclei. It can also have adverse effects on newborns and adolescents, such as memory loss and intellectual decline.

[0003] Currently, indoor formaldehyde purification technologies mainly include physical adsorption, chemical decomposition, photocatalytic oxidation, biodegradation, and plasma technology. Physical adsorption primarily utilizes the high specific surface area and abundant pore structure of porous materials (such as activated carbon, activated carbon fiber, zeolite molecular sieves, silica gel, attapulgite, etc.) to adsorb and fix formaldehyde molecules onto the material surface through van der Waals forces. This method is simple to operate and low in cost, but it has significant drawbacks: firstly, physical adsorption is a reversible process, and desorption is easily caused by adsorption saturation, resulting in secondary pollution; secondly, it has poor selectivity for low-concentration formaldehyde adsorption and is easily interfered with by water molecules and other VOCs in complex indoor environments; and thirdly, its adsorption capacity is limited, requiring frequent material replacement. Photocatalytic oxidation utilizes photogenerated electron-hole pairs generated by semiconductor materials (such as TiO2, ZnO, g-C3N4, etc.) under ultraviolet or visible light irradiation to catalytically oxidize formaldehyde into CO2 and H2O. TiO2 has been widely studied due to its good chemical stability, non-toxicity, and low cost. However, this method has significant limitations: first, it requires a specific wavelength of light source for excitation, and its efficiency drops sharply in the absence of light or in low light environments; second, the recombination rate of photogenerated carriers is high, resulting in low quantum efficiency; and third, it may produce harmful intermediate products (such as CO and formic acid). Therefore, photocatalysis technology is difficult to apply alone to all-weather indoor formaldehyde purification. Biodegradation methods utilize microorganisms or plant enzymes to metabolize formaldehyde, but they suffer from low processing efficiency, are greatly affected by environmental conditions, and are prone to microbial inactivation. Plasma technology can efficiently decompose formaldehyde, but it consumes a lot of energy and may produce byproducts such as ozone, making it unsuitable for long-term use in home environments.

[0004] Manganese dioxide (MnO2), as an environmentally friendly metal oxide, has attracted widespread attention in the field of room-temperature catalytic oxidation of formaldehyde due to its rich crystalline structures (α, β, γ, δ, ε types, etc.), high redox activity, low cost, and good stability. Formaldehyde molecules are first adsorbed onto active sites on the MnO2 surface (such as Mn...). 4+ / Mn 3+ The redox pairs, surface hydroxyl groups, oxygen vacancies, etc., are subsequently oxidized by lattice oxygen or surface-adsorbed oxygen to formate intermediates, and finally decompose into CO2 and H2O. Mn in MnO2 4+ Formaldehyde is reduced to Mn 3+ Meanwhile, formaldehyde is oxidized; subsequently, Mn 3+ It is re-oxidized to Mn by O2 in the air. 4+ The catalytic cycle is completed. However, single MnO2 materials still face technical bottlenecks in practical applications: insufficient density of active sites; powdered MnO2 is prone to agglomeration and has a large pressure drop, making it difficult to apply directly.

[0005] Therefore, it is necessary to develop efficient and practical manganese oxide-based formaldehyde purification materials. Summary of the Invention

[0006] The present invention aims to at least partially solve one of the technical problems existing in the prior art. Therefore, in a first aspect, the present invention provides a method for preparing a manganese oxide-based catalyst, comprising the following steps: Step 1): Pre-treat the attapulgite soil to obtain pre-treated attapulgite soil; Step 2): Coat the pretreated attapulgite obtained in Step 1) with the first coating agent, and dry it to obtain the dried first coated attapulgite. Step 3): Coat the dried first coated attapulgite obtained in Step 2) with the second coating agent, and dry to obtain the manganese oxide-based catalyst; The first coating agent comprises carbon materials and nano-manganese dioxide composite iron oxide catalyst; the second coating agent is composed of nano-manganese dioxide composite iron oxide catalyst, COF-LZU1 covalent organic framework, and lanthanide perovskite compound in a mass ratio of 8:(0.5-1.5):(0.5-1.5).

[0007] Through the above technical solution, in the outer second coating agent, COF-LZU1, due to its high specific surface area and pore structure, rapidly adsorbs and enriches formaldehyde within its pores, contacting the nano-manganese dioxide composite iron oxide catalyst and lanthanide perovskite compounds. Partial formaldehyde is initially oxidized. In this process, COF-LZU1 enrichment, nano-manganese dioxide composite iron oxide catalyst catalytic oxidation, and lanthanide perovskite compound oxidation achieve a good relay mode. Formaldehyde enters the COF-LZU1 pores through van der Waals forces and pore confinement, and is adsorbed... Formaldehyde diffuses and migrates from the pores of COF-LZU1 to the surface of the nano-manganese dioxide composite iron oxide catalyst. As a result, low-concentration formaldehyde is highly enriched on the surface of the catalyst, significantly increasing the local reactant concentration and driving the catalytic reaction forward. During catalysis, after the active oxygen on the surface of the nano-manganese dioxide composite iron oxide catalyst is consumed, perovskite replenishes the active oxygen at the interface through lattice oxygen overflow, rapidly repairing oxygen vacancies and enabling the catalytic cycle to proceed continuously and efficiently. COF-LZU1 and lanthanide perovskite compounds exhibit a synergistic effect in purifying low-concentration formaldehyde using the nano-manganese dioxide composite iron oxide catalyst system. In the first coating agent of the inner layer, unoxidized formaldehyde intermediates or unreacted formaldehyde continue to diffuse inward and enter the inner layer composed of carbon materials and nano-manganese dioxide composite iron oxide catalyst. The high specific surface area of ​​the carbon materials further adsorbs and enriches formaldehyde. With the help of the stable interface and good mass transfer channels formed by the inner layer manganese dioxide composite iron oxide and attapulgite carrier, rapid electron transfer and deep catalytic degradation of formaldehyde are achieved. The inner and outer layers thus form a continuous synergistic effect of "selective enrichment and preliminary catalytic oxidation in the outer layer, and efficient adsorption enhancement and deep catalytic oxidation in the inner layer", thereby promoting the further conversion of formaldehyde and some intermediates and reducing the risk of formaldehyde re-release after adsorption saturation.

[0008] Preferably, the method for preparing lanthanide perovskite compounds includes: a: will La 3+ Ca 2+ and Mn 2+ Add the first mixed solvent and disperse it evenly to obtain a mixed solution. Add citric acid to the second mixed solvent and mix evenly to obtain a citric acid solution. b: Add the citric acid solution obtained in step a to the mixed solution obtained in step a, stir and react at 20-30 ℃ for 10-14 h, raise the temperature to 40-60 ℃, stir and react for 8-12 h, after forming a gel, dry, grind, sinter, cool, grind, to obtain the lanthanide perovskite compound.

[0009] Preferably, La 3+ and Ca 2+ The sum of the molar amounts of Mn 2+ The molar amounts of La are equal.3+ Ca 2+ and Mn 2+ The ratio of the total molar amount to the molar amount of citric acid is 1:(1.2-1.8).

[0010] Preferably, in step a, La 3+ and Ca 2+ The molar ratio is (2.3-9):1.

[0011] Preferably, the carbon material includes at least one of graphene quantum dots and nitrogen-doped carbon materials.

[0012] Preferably, the preparation method of the nano-manganese dioxide composite iron oxide catalyst includes: dissolving manganese sulfate, potassium permanganate, and ferric sulfate in water to obtain a precursor solution, heating to 40-50℃ and stirring for 8-12 hours; heating to 140-180℃ for hydrothermal reaction for 10-20 hours, cooling, filtering, washing, and drying to obtain the nano-manganese dioxide composite iron oxide catalyst; wherein the molar ratio of manganese sulfate, potassium permanganate, and ferric sulfate is 1:(1.5-2.5):(0.2-0.8).

[0013] Preferably, both the first mixed solvent and the second mixed solvent are mixed solvents composed of ethanol and water in a volume ratio of 1:1.

[0014] Preferably, the first coating agent is composed of nano-manganese dioxide composite iron oxide catalyst and carbon material in a mass ratio of 10:(0.5-1.5).

[0015] Preferably, the method for preparing the nitrogen-doped carbon material includes the following steps: Step 1): Add sodium carboxymethyl cellulose to water and stir to obtain sodium carboxymethyl cellulose hydrogel. Then add NH4Cl and sonicate to obtain NH4Cl / sodium carboxymethyl cellulose gel. Step 2): Dry the NH4Cl / sodium carboxymethyl cellulose gel obtained in Step 1), transfer it to a tube furnace, purge the air from the tube with nitrogen, calcine, and cool to obtain nitrogen-doped carbon material; In step 1), the mass ratio of sodium carboxymethyl cellulose to NH4Cl is 1:(1.8-2.2).

[0016] Preferably, the carbon material is composed of graphene quantum dots and nitrogen-doped carbon material in a ratio of 3:(6-8). More preferably, the carbon material is composed of graphene quantum dots and nitrogen-doped carbon material in a ratio of 3:7. In this way, the graphene quantum dots have abundant edge defects and oxygen-containing functional groups, which can provide a large number of highly active adsorption sites for precise capture of formaldehyde molecules; the nitrogen-doped carbon material, by utilizing the electron-rich sites and polar defects introduced by nitrogen atoms, enhances the electrostatic and chemical adsorption of formaldehyde, while constructing a continuous conductive network and porous channels. The combination of the two not only improves the overall adsorption capacity and adsorption rate, but also strengthens the adsorption stability, achieving more efficient and longer-lasting adsorption and capture of formaldehyde.

[0017] Preferably, in step 1), the pretreatment is acid treatment; in step 2), the mass ratio of the pretreated attapulgite to the first coating agent is 5:(1.5-2.5); in step 3), the mass ratio of the dried first coated attapulgite to the second coating agent is 5:(1.5-2.5).

[0018] Secondly, the present invention provides an application of the manganese oxide-based catalyst prepared by the above-described method in the adsorption of formaldehyde.

[0019] The beneficial effects of this invention are as follows: 1. This invention provides a method for preparing a manganese oxide-based catalyst, the prepared manganese oxide-based catalyst having good formaldehyde adsorption effect.

[0020] 2. This invention provides an application of the manganese oxide-based catalyst prepared by the above method in the adsorption of formaldehyde. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments. However, the following embodiments are only for illustrative purposes and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the methods used are conventional methods known in the art, and the consumables and reagents used are commercially available. Unless otherwise stated, the technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be applied to the present invention. The COF-LZU1 covalent organic framework was purchased from Shanghai Kaishu Chemical Technology Co., Ltd., CAS: 1242082-12-7; attapulgite clay was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd., CAS: 1337-76-4, catalog number PA97668; graphene quantum dots (GQDs) were purchased from Changzhou Huada Nanomaterials Technology Co., Ltd.

[0022] Preparation Example 1 The preparation method of lanthanide perovskite compounds includes the following steps: a: Add 0.008 mol of lanthanum nitrate hexahydrate, 0.002 mol of calcium nitrate tetrahydrate and 0.01 mol of manganese nitrate tetrahydrate to 60 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and disperse evenly to obtain a mixed solution. Add 0.03 mol of citric acid monohydrate to 40 mL of a mixed solvent of ethanol and water in a volume ratio of 1:1, and mix evenly to obtain a citric acid solution. b: The citric acid solution obtained in step a was added dropwise to the mixed solution obtained in step a under stirring. The mixture was stirred at 25 °C for 12 h, then heated to 50 °C and stirred for 10 h to form a gel. After gel formation, the gel was vacuum dried at 100 °C and 0.07 MPa for 10 h, ground, and then sintered in a two-stage heating process under a high-purity oxygen atmosphere. First, the temperature was increased to 480 °C at a rate of 5 °C / min and sintered for 6 h. Then, the temperature was increased to 750 °C at a rate of 5 °C / min and sintered for 12 h. After cooling to room temperature, the mixture was ground to obtain the lanthanide perovskite compound La. 0.8 Ca 0.2 MnO3.

[0023] Preparation Example 2 The difference between Preparation Example 2 and Preparation Example 1 is that the amounts of lanthanum nitrate hexahydrate and calcium nitrate tetrahydrate used in step a are different. In Preparation Example 2, the amount of lanthanum nitrate hexahydrate used is 0.009 mol and the amount of calcium nitrate tetrahydrate used is 0.001 mol. Correspondingly, Preparation Example 2 yields the lanthanide perovskite compound La. 0.9 Ca 0.1 MnO3.

[0024] Preparation Example 3 The difference between Preparation Example 3 and Preparation Example 1 is that the amounts of lanthanum nitrate hexahydrate and calcium nitrate tetrahydrate used in step a are different. In Preparation Example 3, the amount of lanthanum nitrate hexahydrate used is 0.007 mol and the amount of calcium nitrate tetrahydrate used is 0.003 mol. Correspondingly, Preparation Example 3 yields the lanthanide perovskite compound La. 0.7 Ca 0.3 MnO3.

[0025] Preparation Example 4 0.01 mol manganese sulfate, 0.02 mol potassium permanganate, and 0.005 mol ferric sulfate were dissolved in 100 mL of water, and the pH was adjusted to 5-7. The mixture was stirred thoroughly to form a precursor solution, heated to 45 °C, and stirred for 10 h. The solution was then placed in a reaction vessel and heated to 160 °C for hydrothermal reaction for 16 h. After cooling, the solution was filtered, washed, and dried at 140 °C for 2 h to obtain a nano-manganese dioxide composite iron oxide catalyst.

[0026] Comparative Preparation Example 1 The difference between Comparative Preparation Example 1 and Preparation Example 2 is that the amounts of lanthanum nitrate hexahydrate and calcium nitrate tetrahydrate used in step a are different. In Comparative Preparation Example 1, the amount of lanthanum nitrate hexahydrate used is 0.005 mol and the amount of calcium nitrate tetrahydrate used is 0.005 mol. Correspondingly, Comparative Preparation Example 1 yields the lanthanide perovskite compound La. 0.5 Ca 0.5 MnO3.

[0027] Comparative Preparation Example 2 The difference between Comparative Preparation Example 2 and Preparation Example 1 is that the amount of lanthanum nitrate hexahydrate used in step a is different, and calcium nitrate tetrahydrate is not used. In Comparative Preparation Example 2, the amount of lanthanum nitrate hexahydrate used is 0.01 mol, and the amount of calcium nitrate tetrahydrate used is 0. Correspondingly, Comparative Preparation Example 2 yields the lanthanide perovskite compound LaMnO3.

[0028] Comparative preparation example 3 The difference between Preparation Example 3 and Preparation Example 1 is that, in step a, an equimolar amount of manganese nitrate tetrahydrate was replaced with cobalt nitrate hexahydrate. Correspondingly, Preparation Example 3 yielded the lanthanide perovskite compound La. 0.8 Ca 0.2 CoO3.

[0029] Example 1 The preparation method of manganese oxide-based catalyst includes the following steps: Step 1): Weigh attapulgite, add deionized water, stir evenly to prepare a mixture with an attapulgite mass fraction of 10wt%, add 1mol / L HCl to adjust the pH to 3-4, stir for 1h, centrifuge, wash until neutral, dry, and obtain the pretreated attapulgite.

[0030] Step 2): Add the pretreated attapulgite to the fluidized bed silo, close the silo door, and introduce inert gas to stabilize and suspend the pretreated attapulgite. Feed the ethanol dispersion of the first coating agent into the fluidized bed through a dual-fluid nozzle, disperse it with the airflow, and deposit it on the surface of the attapulgite to obtain the first coated attapulgite. Dry the first coated attapulgite at 100°C for 0.5 hours under argon protection to obtain the dried first coated attapulgite.

[0031] The first coating agent was prepared by mixing the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4 and graphene quantum dots at a mass ratio of 10:1. The first coating agent was added to ethanol, and polyethylene glycol PEG-6000 was added as a dispersant. The mixture was then dispersed to obtain an ethanol dispersion of the first coating agent. The mass-to-volume ratio of the first coating agent to ethanol was 0.2 g / mL, and the mass ratio of polyethylene glycol PEG-6000 to the first coating agent was 1:100. The mass ratio of the pretreated attapulgite clay to the first coating agent was 5:2.

[0032] Step 3): Add the dried first-coated attapulgite to the fluidized bed silo, close the silo door, and introduce inert gas to stabilize the first-coated attapulgite in suspension. Feed the ethanol dispersion of the second coating agent into the fluidized bed through a dual-fluid nozzle, disperse it with the airflow, and deposit it on the surface of the dried first-coated attapulgite to obtain the second-coated attapulgite. Dry the second-coated attapulgite at 100°C for 0.5 h under argon protection to obtain the manganese oxide-based catalyst.

[0033] The second coating agent was prepared by mixing the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4, the COF-LZU1 covalent organic framework, and the lanthanide perovskite compound prepared by the method of Preparation Example 1 in a mass ratio of 8:1:1. During mixing, the COF-LZU1 covalent organic framework and the lanthanide perovskite compound prepared by the method of Preparation Example 1 were first ball-milled until homogeneous, and then the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4 was added and mixed until homogeneous. The second coating agent was added to ethanol, and polyethylene glycol PEG-6000 was added as a dispersant. The mixture was then ultrasonically dispersed to obtain an ethanol dispersion of the second coating agent. The mass-to-volume ratio of the second coating agent to ethanol was 0.2 g / mL, and the mass ratio of polyethylene glycol PEG-6000 to the second coating agent was 1:100. The mass ratio of the dried first-coated attapulgite to the second coating agent was 5:2.

[0034] Example 2 The difference between Example 2 and Example 1 is that, in step 3), the lanthanide perovskite compound obtained in Preparation Example 1 is replaced by an equal mass of the lanthanide perovskite compound prepared by the method of Preparation Example 2.

[0035] Example 3 The difference between Example 3 and Example 1 is that, in step 3), the lanthanide perovskite compound prepared by the preparation method of Example 1 is replaced by the lanthanide perovskite compound prepared by the preparation method of Example 3.

[0036] Example 4 The difference between Example 4 and Example 1 is that, in step 3), the second coating agent is obtained by mixing the nano-manganese dioxide composite iron oxide catalyst prepared in Preparation Example 4, the COF-LZU1 covalent organic framework, and the lanthanide perovskite compound prepared by the preparation method of Preparation Example 1 in a mass ratio of 8:0.5:1.5.

[0037] Example 5 The difference between Example 5 and Example 1 is that, in step 3), the second coating agent is obtained by mixing the nano-manganese dioxide composite iron oxide catalyst prepared in Preparation Example 4, the COF-LZU1 covalent organic framework, and the lanthanide perovskite compound prepared by the preparation method of Preparation Example 1 in a mass ratio of 8:1.5:0.5.

[0038] Example 6 The difference between Example 6 and Example 1 is that in step 2), graphene quantum dots are replaced with nitrogen-doped carbon material. The preparation of nitrogen-doped carbon material includes the following steps: Step 1): Add 5g of sodium carboxymethyl cellulose to 200mL of ultrapure water and stir to obtain sodium carboxymethyl cellulose hydrogel. Then add 10g of NH4Cl and sonicate for 40min to obtain NH4Cl / sodium carboxymethyl cellulose gel. Step 2): Dry the NH4Cl / sodium carboxymethyl cellulose gel obtained in Step 1), transfer it to a tube furnace, purge the air from the tube with nitrogen, then heat the tube furnace to 900℃ at a heating rate of 5℃ / min and calcine it for 2 hours. Allow it to cool naturally to room temperature to obtain nitrogen-doped carbon material.

[0039] Example 7 The difference between Example 7 and Example 6 is that, in step 2), the first coating agent is obtained by mixing the nano-manganese dioxide composite iron oxide catalyst prepared in Example 4, graphene quantum dots, and nitrogen-doped carbon material in a mass ratio of 10:0.3:0.7. The preparation method of the nitrogen-doped carbon material is the same as in Example 6.

[0040] Example 8 The difference between Example 8 and Example 7 is that, in the preparation process of the carbon material, NH4Cl and other substances are replaced by urea.

[0041] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that, in step 3), the lanthanide perovskite compound prepared by the preparation method of Preparation Example 1 is replaced by the lanthanide perovskite compound prepared by the preparation method of Comparative Example 1 in equal mass.

[0042] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that, in step 3), the lanthanide perovskite compound prepared by the preparation method of Example 1 is replaced by the lanthanide perovskite compound prepared by the preparation method of Comparative Example 2.

[0043] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that, in step 3), the lanthanide perovskite compound prepared by the preparation method of Example 1 is replaced by the lanthanide perovskite compound prepared by the preparation method of Comparative Example 3 in equal mass.

[0044] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that, in step 3), the second coating agent is obtained by mixing the nano-manganese dioxide composite iron oxide catalyst prepared in Preparation Example 4 and the COF-LZU1 covalent organic framework in a mass ratio of 8:2.

[0045] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that, in step 3), the second coating agent is obtained by mixing the nano-manganese dioxide composite iron oxide catalyst prepared in Preparation Example 4 and the lanthanide perovskite compound prepared by the preparation method of Preparation Example 1 in a mass ratio of 8:2.

[0046] Comparative Example 6 The preparation method of manganese oxide-based catalyst includes the following steps: Step 1): Weigh attapulgite, add deionized water, stir evenly to prepare a mixture with an attapulgite mass fraction of 10wt%, add 1mol / L HCl to adjust the pH to 3-4, stir for 1h, centrifuge, wash until neutral, dry, and obtain the pretreated attapulgite.

[0047] Step 2): Add the pretreated attapulgite to the fluidized bed silo, close the silo door, and introduce inert gas to stabilize and suspend the pretreated attapulgite. Feed the ethanol dispersion of the second coating agent into the fluidized bed through a dual-fluid nozzle, disperse it with the airflow, and deposit it on the surface of the attapulgite to obtain the first coated attapulgite. Dry the first coated attapulgite at 100°C for 0.5 hours under argon protection to obtain the dried first coated attapulgite.

[0048] The second coating agent was prepared by mixing the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4, the COF-LZU1 covalent organic framework, and the lanthanide perovskite compound prepared by the method of Preparation Example 1 in a mass ratio of 8:1:1. During mixing, the COF-LZU1 covalent organic framework and the lanthanide perovskite compound prepared by the method of Preparation Example 1 were first ball-milled until homogeneous, and then the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4 was added and mixed until homogeneous. The second coating agent was added to ethanol, and polyethylene glycol PEG-6000 was added as a dispersant. The mixture was then dispersed to obtain an ethanol dispersion of the second coating agent. The mass-to-volume ratio of the second coating agent to ethanol was 0.2 g / mL, and the mass ratio of polyethylene glycol PEG-6000 to the second coating agent was 1:100. The mass ratio of the pretreated attapulgite to the second coating agent was 5:2.

[0049] Step 3): Add the dried first-coated attapulgite to the fluidized bed silo, close the silo door, and introduce inert gas to stabilize and suspend the dried first-coated attapulgite. Feed the ethanol dispersion of the first coating agent into the fluidized bed through a dual-fluid nozzle, disperse it with the airflow, and deposit it on the surface of the dried first-coated attapulgite to obtain the second-coated attapulgite. Dry the second-coated attapulgite at 100°C for 0.5 h under argon protection to obtain the manganese oxide-based catalyst.

[0050] The first coating agent was prepared by mixing the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4 with graphene quantum dots at a mass ratio of 10:1. The first coating agent was added to ethanol, and polyethylene glycol PEG-6000 was added as a dispersant. The mixture was then dispersed to obtain an ethanol dispersion of the first coating agent. The mass-to-volume ratio of the first coating agent to ethanol was 0.2 g / mL, and the mass ratio of polyethylene glycol PEG-6000 to the first coating agent was 1:100. The mass ratio of the dried first-coated attapulgite to the first coating agent was 5:2.

[0051] Comparative Example 7 The preparation method of manganese oxide-based catalyst includes the following steps: Step 1): Weigh attapulgite, add deionized water, stir evenly to prepare a mixture with an attapulgite mass fraction of 10wt%, add 1mol / L HCl to adjust the pH to 3-4, stir for 1h, centrifuge, wash until neutral, dry, and obtain the pretreated attapulgite.

[0052] Step 2): Add the pretreated attapulgite to the fluidized bed silo, close the silo door, and introduce inert gas to stabilize and suspend the pretreated attapulgite. Feed the ethanol dispersion of the second coating agent into the fluidized bed through a dual-fluid nozzle, disperse it with the airflow, and deposit it on the surface of the attapulgite to obtain the first coated attapulgite. Dry the first coated attapulgite at 100°C for 0.5 hours under argon protection to obtain the dried first coated attapulgite.

[0053] The second coating agent was prepared by mixing the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4, the COF-LZU1 covalent organic framework, and the lanthanide perovskite compound prepared by the method of Preparation Example 1 in a mass ratio of 8:1:1. During mixing, the COF-LZU1 covalent organic framework and the lanthanide perovskite compound prepared by the method of Preparation Example 1 were first ball-milled until homogeneous, and then the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4 was added and mixed until homogeneous. The second coating agent was added to ethanol, and polyethylene glycol PEG-6000 was added as a dispersant. The mixture was then ultrasonically dispersed to obtain an ethanol dispersion of the second coating agent. The mass-to-volume ratio of the second coating agent to ethanol was 0.2 g / mL, and the mass ratio of polyethylene glycol PEG-6000 to the second coating agent was 1:100. The mass ratio of the pretreated attapulgite to the second coating agent was 5:2.

[0054] Step 3): Add the dried first-coated attapulgite to the fluidized bed silo, close the silo door, and introduce inert gas to stabilize and suspend the dried first-coated attapulgite. Feed the ethanol dispersion of the second coating agent into the fluidized bed through a dual-fluid nozzle, disperse it with the airflow, and deposit it on the surface of the dried first-coated attapulgite to obtain the second-coated attapulgite. Dry the second-coated attapulgite at 100°C for 0.5 h under argon protection, then pulverize it to obtain the manganese oxide-based catalyst.

[0055] The second coating agent was prepared by mixing the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4, the COF-LZU1 covalent organic framework, and the lanthanide perovskite compound prepared by the method of Preparation Example 1 in a mass ratio of 8:1:1. During mixing, the COF-LZU1 covalent organic framework and the lanthanide perovskite compound prepared by the method of Preparation Example 1 were first ball-milled until homogeneous, and then the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4 was added and mixed until homogeneous. The second coating agent was added to ethanol, and polyethylene glycol PEG-6000 was added as a dispersant. The mixture was then ultrasonically dispersed to obtain an ethanol dispersion of the second coating agent. The mass-to-volume ratio of the second coating agent to ethanol was 0.2 g / mL, and the mass ratio of polyethylene glycol PEG-6000 to the second coating agent was 1:100. The mass ratio of the dried first-coated attapulgite to the second coating agent was 5:2.

[0056] Comparative Example 8 The preparation method of manganese oxide-based catalyst includes the following steps: Step 1): Weigh attapulgite, add deionized water, stir evenly to prepare a mixture with an attapulgite mass fraction of 10wt%, add 1mol / L HCl to adjust the pH to 3-4, stir for 1h, centrifuge, wash until neutral, dry, and obtain the pretreated attapulgite.

[0057] Step 2): Add the pretreated attapulgite to the fluidized bed silo, close the silo door, and introduce inert gas to stabilize and suspend the pretreated attapulgite. Feed the ethanol dispersion of the first coating agent into the fluidized bed through a dual-fluid nozzle, disperse it with the airflow, and deposit it on the surface of the attapulgite to obtain the first coated attapulgite. Dry the first coated attapulgite at 100°C for 0.5 hours under argon protection, then pulverize it to obtain the dried first coated attapulgite.

[0058] The first coating agent was prepared by mixing the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4 with graphene quantum dots at a mass ratio of 10:1. The first coating agent was added to ethanol, and polyethylene glycol PEG-6000 was added as a dispersant. The mixture was then dispersed to obtain an ethanol dispersion of the first coating agent. The mass-to-volume ratio of the first coating agent to ethanol was 0.2 g / mL, and the mass ratio of polyethylene glycol PEG-6000 to the first coating agent was 1:100. The mass ratio of the pretreated attapulgite to the first coating agent was 5:2.

[0059] Step 3): Add the dried first-coated attapulgite to the fluidized bed silo, close the silo door, and introduce inert gas to stabilize and suspend the dried first-coated attapulgite. Feed the ethanol dispersion of the first coating agent into the fluidized bed through a dual-fluid nozzle, disperse it with the airflow, and deposit it on the surface of the dried first-coated attapulgite to obtain the second-coated attapulgite. Dry the second-coated attapulgite at 100°C for 0.5 h under argon protection to obtain the manganese oxide-based catalyst.

[0060] The first coating agent was prepared by mixing the nano-manganese dioxide composite iron oxide catalyst obtained in Preparation Example 4 with graphene quantum dots at a mass ratio of 10:1. The first coating agent was added to ethanol, and polyethylene glycol PEG-6000 was added as a dispersant. The mixture was then dispersed to obtain an ethanol dispersion of the first coating agent. The mass-to-volume ratio of the first coating agent to ethanol was 0.2 g / mL, and the mass ratio of polyethylene glycol PEG-6000 to the first coating agent was 1:100. The mass ratio of the dried first-coated attapulgite to the first coating agent was 5:2.

[0061] test: At 25°C and RH=80%, 0.05g of the manganese oxide-based catalysts obtained in Examples 1-8 and Comparative Examples 1-8 were placed in petri dishes, covered, and placed in a 16.5L reactor. Formaldehyde gas was added to make the initial concentration of formaldehyde in the reactor 10ppm. The lid of the petri dish was opened, and timing was started. After 3 hours, the formaldehyde concentration was detected, and the formaldehyde removal rate was calculated as follows: Formaldehyde removal rate = (C1V1 - C2V2) / C1V1 × 100%, where C1 is the initial concentration of formaldehyde in the reactor, i.e., 10ppm, C2 is the concentration of formaldehyde in the reactor after 3 hours, and V1 and V2 are both 16.5L. The results are shown in Table 1.

[0062] Table 1

[0063] Comparing Comparative Examples 1 and 2 with Example 1, it can be seen that the ratio of La to Ca sources used in the preparation of lanthanide perovskite compounds significantly affects the adsorption effect of manganese oxide-based catalysts on formaldehyde. This may be because when the ratio of La to Ca sources is too high, there are fewer oxygen vacancies, resulting in lower adsorption capacity and catalytic activity; when the ratio is too low, the crystal lattice is unstable, adsorption is too strong, and byproducts such as formate are difficult to desorb and occupy sites.

[0064] Comparing Comparative Example 3 with Example 1, it can be seen that when replacing the manganese source with an equimolar amount of cobalt source in the preparation of lanthanide perovskite compounds, the adsorption effect of the manganese oxide-based catalyst on formaldehyde significantly deteriorates. This may be because the La2+ content of the cobalt source... 0.8 Ca 0.2 The lattice mismatch between CoO3 and the nano-manganese dioxide composite iron oxide catalyst results in low interfacial electron transfer efficiency and weak synergistic effect.

[0065] Comparing Comparative Example 4 with Example 1, it can be seen that when the lanthanide perovskite compound prepared by the preparation method of Example 1 in the second coating agent is replaced by an equal mass of COF-LZU1 covalent organic framework, the adsorption effect of manganese oxide-based catalyst on formaldehyde is significantly worse.

[0066] Comparing Comparative Example 5 with Example 1, it can be seen that when the COF-LZU1 covalent organic framework in the second coating agent is replaced by an equal mass of the lanthanide perovskite compound prepared by the preparation method of Example 1, the adsorption effect of the manganese oxide-based catalyst on formaldehyde is significantly worse.

[0067] Comparing Comparative Example 6 with Example 1, it can be seen that when the first and second coating agents are interchanged, the adsorption effect of the manganese oxide-based catalyst on formaldehyde significantly deteriorates. This may be because when the second coating agent is coated first and then the first coating agent is coated, the pores of the COF-LZU1 covalent organic framework may be blocked by the outer carbon material, etc. In addition, the interfacial bonding is weak, mass transfer is hindered, and active sites are covered, which is not conducive to the enrichment and catalytic oxidation of formaldehyde.

[0068] Comparing Comparative Example 7 with Example 1, it can be seen that when the first coating agent is replaced by an equal mass of the second coating agent, the adsorption effect of the manganese oxide-based catalyst on formaldehyde is significantly worse.

[0069] Comparing Comparative Example 8 with Example 1, it can be seen that when the second coating agent is replaced by the first coating agent at the same mass, the adsorption effect of the manganese oxide-based catalyst on formaldehyde is significantly worse.

[0070] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention, all of which should be included within the protection scope of the present invention.

Claims

1. A method for preparing a manganese oxide-based catalyst, characterized by, The method comprises the following steps: Step 1): pretreating the attapulgite to obtain pretreated attapulgite; Step 2): coating the pretreated attapulgite obtained in step 1) with a first coating agent, and drying to obtain dried first-coated attapulgite; Step 3): coating the dried first-coated attapulgite obtained in step 2) with a second coating agent, and drying to obtain the manganese oxide-based catalyst; The first coating agent comprises a carbon material and a nano-manganese dioxide composite iron oxide catalyst; and the second coating agent is composed of a nano-manganese dioxide composite iron oxide catalyst, a COF-LZU1 covalent organic framework, and a lanthanide perovskite compound at a mass ratio of 8: (0.5-1.5): (0.5-1.5).

2. The method for producing a manganese oxide-based catalyst according to claim 1, characterized by, The preparation method of the lanthanide perovskite compound comprises: a: La 3+ , Ca 2+ and Mn 2+ are added into the first mixed solvent, uniformly dispersed to obtain a mixed solution, and citric acid is added into the second mixed solvent, uniformly mixed to obtain a citric acid solution; b: adding the citric acid solution obtained in step a into the mixed solution obtained in step a, stirring at 20-30 ℃ for 10-14 h, increasing the temperature to 40-60 ℃, stirring for 8-12 h, drying after the gel is formed, grinding, sintering, cooling, and grinding to obtain the lanthanide perovskite compound.

3. The method for producing a manganese oxide-based catalyst according to claim 2, characterized by, La 3+ and Ca 2+ The sum of the molar amounts of Mn 2+ The molar amounts of La are equal. 3+ Ca 2+ and Mn 2+ The ratio of the total molar amount to the molar amount of citric acid is 1:(1.2-1.8).

4. The method for producing a manganese oxide-based catalyst according to claim 2, characterized by, The molar ratio of La 3+ and Ca 2+ is (2.3-9):

1.

5. The method of producing a manganese oxide-based catalyst according to claim 1, characterized by, The carbon material comprises at least one of graphene quantum dots and nitrogen-doped carbon material; the preparation method of the nano-manganese dioxide composite iron oxide catalyst comprises: dissolving manganese sulfate, potassium permanganate, and iron sulfate in water, adjusting the pH to 5-7 to obtain a precursor solution, heating to 40-50 ℃ and stirring for 8-12 h; heating to 140-180 ℃ for hydrothermal reaction for 10-20 h, cooling, filtering, washing, and drying to obtain the nano-manganese dioxide composite iron oxide catalyst; and the molar ratio of the manganese sulfate, the potassium permanganate, and the iron sulfate is 1: (1.5-2.5): (0.2-0.8).

6. The method of producing a manganese oxide-based catalyst according to claim 1, characterized by, The first coating agent is composed of the nano-manganese dioxide composite iron oxide catalyst and the carbon material at a mass ratio of 10: (0.5-1.5).

7. The method of producing a manganese oxide-based catalyst according to claim 5, characterized by, The preparation method of the nitrogen-doped carbon material comprises the following steps: Step 1): adding sodium carboxymethyl cellulose into water, stirring to prepare a sodium carboxymethyl cellulose hydrogel, and then adding NH4Cl and ultrasonicating to obtain an NH4Cl / sodium carboxymethyl cellulose gel; Step 2): drying the NH4Cl / sodium carboxymethyl cellulose gel obtained in step 1), transferring to a tube furnace, introducing nitrogen to discharge air in the tube, calcining, and cooling to obtain the nitrogen-doped carbon material; In step 1), the mass ratio of the sodium carboxymethyl cellulose to the NH4Cl is 1: (1.8-2.2).

8. The method of producing a manganese oxide-based catalyst according to claim 5, characterized by, The carbon material is composed of the graphene quantum dots and the nitrogen-doped carbon material at a ratio of 3: (6-8).

9. The method of producing a manganese oxide-based catalyst according to claim 1, characterized by, In step 1), the pretreatment is acid treatment; in step 2), the mass ratio of the pretreated attapulgite to the first coating agent is 5: (1.5-2.5); and in step 3), the mass ratio of the dried first-coated attapulgite to the second coating agent is 5: (1.5-2.5).

10. Use of the manganese oxide-based catalyst prepared by the preparation method of any one of claims 1-9 in adsorbing formaldehyde.

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