Preparation method of manganese dioxide room temperature catalyst

Abstract

The invention relates to the technical field of preparation of catalytic materials, in particular to a preparation method of a manganese dioxide room-temperature catalyst, which comprises the following steps: dissolving a manganese-containing soluble salt in deionized water to form a solution A; adding an oxidizing agent F into the solution A to form a mixed solution B; s3, carrying out hydrothermal reaction on the mixed solution B to obtain a reaction product; washing the reaction product for multiple times, centrifuging, precipitating and drying to obtain a sample; and calcining the sample to obtain the manganese dioxide catalyst. According to the preparation method of the manganese dioxide room-temperature catalyst, the manganese dioxide phase structure is accurately regulated and controlled, and the manganese dioxide synthesized by the method for regulating and controlling the phase structure has high specific surface area and rich oxygen vacancies; meanwhile, accumulation of intermediate products such as formic acid and CO is effectively inhibited through high-density distribution of defect sites, and the formaldehyde removal rate at the room temperature (25 DEG C) can reach 90% or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation technology of catalytic materials, in particular to a preparation method of a manganese dioxide room temperature catalyst. BACKGROUND

[0002] Indoor air quality is closely related to people's health. Formaldehyde, as a major indoor air pollutant, is widely released from building decoration materials, furniture and daily consumer goods. It has the characteristics of long volatilization period and strong physiological toxicity, which can cause eye and respiratory tract irritation, headache, pneumonia, and even cancer. By developing efficient indoor formaldehyde purification technology, the formaldehyde content in the indoor environment can be reduced; Indoor air purification is suitable for catalytic oxidation of formaldehyde (HCHO) into harmless carbon dioxide (CO2) and water (H2O) at room temperature. Room temperature catalytic formaldehyde decomposition technology can continuously and completely degrade formaldehyde without additional energy input, which is an ideal formaldehyde removal technology. Compared with traditional thermal catalytic technology which requires high temperature conditions, room temperature catalytic oxidation technology has mild reaction conditions and does not require additional energy input such as heat source or light source to completely oxidize and mineralize pollutants, and is considered as the most promising formaldehyde treatment technology.

[0003] At present, the catalysts for room temperature catalytic oxidation of formaldehyde mainly include noble metal catalysts and transition metal oxide catalysts. Noble metal catalysts (such as Pt, Pd, Au-based catalysts) are considered as benchmarks due to their excellent low-temperature catalytic activity and stability. For example, Pt-based catalysts can realize efficient conversion of formaldehyde at room temperature through hydrogen overflow effect and synergistic effect with the carrier; a catalyst with a special design of low Pt loading (0.034wt%) can also achieve 80% formaldehyde removal rate. However, noble metal catalysts face great economic barriers in market large-scale popularization and application due to their high raw material cost and resource scarcity. In addition, such catalysts are easy to be deactivated due to competition for adsorption of water molecules in high humidity environment, and there are problems such as sintering and agglomeration of active components in long-term use, which challenges the service life and stability.

[0004] Transition metal oxides, especially manganese dioxide (MnO2) based catalysts, have become promising candidates to replace noble metals due to their variable valence, diverse crystal structure, environmental friendliness, resource abundance and low cost. The catalytic activity of MnO2 is closely related to its crystal structure (such as α, β, γ, δ phase), specific surface area, pore structure and number of surface active oxygen species. Among them, δ-MnO2 exhibits excellent room temperature catalytic potential due to its layered structure which can provide large specific surface area and abundant active sites.

[0005] Currently, there are various methods for preparing manganese dioxide catalysts, such as sol-gel method, flow phase reaction method, microemulsion method, chemical co-precipitation method, and solid phase synthesis method. However, these methods have their own limitations, which restrict the preparation and application of high-performance MnO2 room temperature catalysts: High requirements for synthesis process and poor repeatability: for example, the sol-gel method is prone to cracking during the drying stage and is difficult to scale up; the flow phase reaction method requires high equipment precision, and parameter fluctuations can easily affect product quality; the solid phase method is not uniform, easily introduces impurities, and the product is prone to agglomeration, with poor repeatability of particle size and crystal form.

[0006] Poor product properties: traditional methods are difficult to accurately control the crystal phase and micro-morphology of MnO2, which can easily produce impurities or amorphous products, resulting in low specific surface area, poor pore structure, and insufficient active site exposure.

[0007] Cost and post-processing issues: for example, the microemulsion method requires the use of a large amount of surfactant, which is costly and complicated to dispose of, and residual materials can block the pores and affect performance; the co-precipitation method easily introduces impurity ions, and the cost of treating wastewater from washing is high.

[0008] Insufficient catalytic performance: most manganese-based catalysts prepared by existing methods have low room temperature activity, low CO2 selectivity (insufficient mineralization ability), poor adaptability to high humidity environments, and poor long-term stability, making it difficult to achieve efficient and complete mineralization of formaldehyde at room temperature.

[0009] Therefore, there is an urgent need in the art to develop a method for preparing manganese dioxide catalysts that is low-cost, simple to operate, easy to scale up, and can accurately control the crystal phase and morphology, thereby obtaining manganese dioxide catalysts with high specific surface area, abundant oxygen vacancies, excellent room temperature activity, and stability. SUMMARY

[0010] The purpose of the present application is to address the problem of how to develop a method for preparing manganese dioxide catalysts that is low-cost, simple to operate, easy to scale up, and can accurately control the crystal phase and morphology, thereby obtaining manganese dioxide catalysts with high specific surface area, abundant oxygen vacancies, excellent room temperature activity, and stability.

[0011] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is: A method for preparing a manganese dioxide room temperature catalyst, comprising the following steps: S1, dissolving a manganese-soluble salt in deionized water, stirring to dissolve, to form a solution A with a concentration of U1; S2, adding an oxidizing agent F to the solution A, stirring to mix at room temperature, to form a mixed solution B; S3, the mixed solution B is subjected to a hydrothermal reaction, a reaction temperature is W degrees Celsius, a reaction time is X hours, after the reaction is completed, cooling to room temperature, to obtain a reaction product; S4, the reaction product is washed with deionized water and anhydrous ethanol, centrifuged, after the washing is completed, the precipitate is dried, to obtain a dried sample; S5, the dried sample is calcined, a calcination temperature is Y degrees Celsius, a calcination time is Z hours, to obtain the manganese dioxide catalyst; Wherein, by adjusting the concentration U1, the type and number of the oxidant F, the hydrothermal reaction temperature W and the reaction time X, the crystal phase structure of the manganese dioxide room temperature catalyst is controlled, and the crystal phase structure is alpha phase and / or delta phase.

[0012] Preferably, in the step S1, the manganese-containing soluble salt is manganese sulfate.

[0013] Preferably, in the step S1, the concentration U1 is 0.0286 mmol / mL to 0.388 mmol / mL.

[0014] Preferably, in the step S2, the oxidant F is one of potassium permanganate or ammonium persulfate.

[0015] Preferably, in the step S2, the mass ratio of manganese sulfate to potassium permanganate is 0.18 to 0.42.

[0016] Preferably, in the step S3, the temperature W can be 160 degrees Celsius to 240 degrees Celsius.

[0017] Preferably, in the step S3, the time X is 12 hours to 24 hours.

[0018] Preferably, in the step S4, the drying temperature is 80 degrees Celsius, and the drying time is 12 hours.

[0019] Preferably, in the step S5, the calcination temperature Y is 350 degrees Celsius, and the calcination time Z is 4 hours.

[0020] The application of a manganese dioxide room temperature catalyst in improving the room temperature catalytic formaldehyde purification efficiency, the manganese dioxide room temperature catalyst is prepared by the preparation method.

[0021] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present application are: 1. By accurately controlling the phase structure of manganese dioxide, manganese dioxide (MnO2) catalysts with different phase structures exhibit diverse characteristics in microstructure, surface chemical properties, and catalytic performance due to significant differences in their crystal frameworks, profoundly affecting their application potential in the room-temperature catalytic oxidation of formaldehyde. α-MnO2 has a unique tetragonal tunnel structure formed by the stacking of double-chain Mn-O octahedra, providing efficient adsorption and diffusion channels for formaldehyde molecules. In contrast, β-MnO2, although also belonging to the tetragonal crystal system, is a single-chain tunnel, resulting in significant mass transfer resistance due to its narrow channels. γ-MnO2 has an orthorhombic disordered tunnel structure, while δ-MnO2 has a layered naphthoic mineral structure, with [MnO6] octahedral layers and exchangeable interlayer cations (such as K+). + Na + The invention constructs a flexible framework. The manganese dioxide synthesized by the method of regulating phase structure has a high specific surface area and abundant oxygen vacancies, providing efficient adsorption and diffusion channels for formaldehyde molecules. At the same time, the high density distribution of defect sites effectively inhibits the accumulation of intermediate products such as formic acid and CO. The formaldehyde removal rate can reach more than 90% at room temperature (25℃). 2. By regulating the phase structure, the specific surface area of ​​the product is increased, the pore structure is enriched, and formaldehyde adsorption and mass transfer are enhanced. The catalytic performance of MnO2 with different phase structures varies significantly, following the rule δ-MnO2 > α-MnO2 > γ-MnO2 > β-MnO2: δ-MnO2 achieves a formaldehyde removal rate of over 96% and a CO2 yield of 60% after 60 minutes, making it the optimal catalyst. Its layered structure provides a large specific surface area and abundant surface adsorbed oxygen (Oads), while interlayer cations and water molecules synergistically promote formaldehyde adsorption and activation. α-MnO2, with its regular tunnel structure and high Mn content, also exhibits superior performance. 4+ The content showed a removal rate similar to δ-MnO2 (96%) at room temperature, but the CO2 yield was slightly lower (35%), attributed to the restriction of oxygen vacancy migration by the tunnel structure. β-MnO2 and γ-MnO2 exhibited significantly lower catalytic performance than the former two due to their large mass transfer resistance and insufficient active sites, confirming that crystal phase structure is a key factor determining catalytic performance. 3. By controlling the phase structure and optimizing the morphology, the catalytic mechanism of formaldehyde decomposition under different phase structures was revealed. The prepared layered manganese oxide room temperature catalyst has a large specific surface area, and the abundant oxygen vacancies on the surface are conducive to formaldehyde purification, exhibiting higher formaldehyde degradation performance and stability than traditional room temperature catalysts. The layered manganese oxide room temperature catalyst synthesized in this invention shows good performance in indoor formaldehyde removal and has a wide range of applications. This invention uses inexpensive manganese oxide room temperature catalysts to replace traditional precious metal catalysts (Au, Pd) for the catalytic degradation of formaldehyde at room temperature, achieving catalytic activity comparable to precious metal supported catalysts, while reducing catalyst preparation costs and system start-up costs. Attached Figure Description

[0022] Figure 1 is a flow chart of a preparation method of a manganese dioxide room temperature catalyst; Figure 2 is an XRD pattern of a manganese oxide room temperature catalyst of different phase structure provided by embodiments 1-4 of the present application; Figure 3 is an SEM pattern of a β-MnO2 manganese oxide room temperature catalyst synthesized under the condition that the precursor is MnSO4 and (NH4)2S2O3, the hydrothermal temperature is 140℃, and the time is 12h provided by embodiment 1; Figure 4 is an SEM pattern of a γ-MnO2 manganese oxide room temperature catalyst synthesized under the condition that the precursor is MnSO4 and (NH4)2S2O3, the hydrothermal temperature is 90℃, and the time is 24h provided by embodiment 2 of the present application; Figure 5 is an SEM pattern of an α-MnO2 manganese oxide room temperature catalyst synthesized under the condition that the precursor is MnSO4 and KMnO4, the hydrothermal temperature is 160℃, and the time is 12h provided by embodiment 3 of the present application; Figure 6 is an SEM pattern of a δ-MnO2 manganese oxide room temperature catalyst synthesized under the condition that the precursor is MnSO4 and KMnO4, the hydrothermal temperature is 240℃, and the time is 24h provided by embodiment 4 of the present application; Figure 7 is a TEM pattern of an α-MnO2 manganese oxide room temperature catalyst synthesized under the condition that the precursor is MnSO4 and KMnO4, the hydrothermal temperature is 160℃, and the time is 12h provided by embodiment 3 of the present application; Figure 8 is a TEM pattern of a δ-MnO2 manganese oxide room temperature catalyst synthesized under the condition that the precursor is MnSO4 and KMnO4, the hydrothermal temperature is 240℃, and the time is 24h provided by embodiment 4 of the present application.

[0023] Figure 9 is an activity comparison chart of room temperature catalytic formaldehyde purification of different phase MnO2 manganese oxide room temperature catalysts provided by embodiments 1-4 of the present application.

[0024] Figure 10 is an XPS pattern of α, δ-MnO2 manganese oxide room temperature catalysts provided by embodiments 3 and 4 of the present application. DETAILED DESCRIPTION

[0025] The present application will be described in detail below with reference to the accompanying drawings.

[0026] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0027] General embodiment The preparation method of the manganese dioxide room temperature catalyst provided by the present application comprises the following steps: S1, dissolving Mn-containing soluble salt in deionized water, stirring and dissolving to form solution A with a concentration of U1; S2, adding an oxidizing agent F to the solution A, stirring and mixing at room temperature to form a mixed solution B; S3, carrying out hydrothermal reaction on the mixed solution B, the reaction temperature is W ℃, the reaction time is X hours, after the reaction is completed, cooling to room temperature to obtain a reaction product; S4, washing the reaction product with deionized water and anhydrous ethanol for multiple times, centrifuging, after the washing is completed, precipitating and drying to obtain a dried sample; S5, calcining the dried sample, the calcination temperature is Y ℃, the calcination time is Z hours, to obtain the manganese dioxide catalyst; Wherein, by adjusting the concentration U1, the type and amount of the oxidizing agent F, the hydrothermal reaction temperature W and the reaction time X, the crystal phase structure of the manganese dioxide room temperature catalyst is controlled, and the crystal phase structure is alpha phase and / or delta phase.

[0028] Specifically, as shown in Figure 1 As a preferred embodiment, the preparation method of the manganese oxide room temperature catalyst with different phase structures provided by the embodiments of the present application specifically comprises the following steps: S101, dissolving Mn-containing soluble salt in deionized water to obtain solution A; S102, dissolving oxidizing agent F in solution A, stirring for 30 min at room temperature to obtain mixed solution B; S103, pouring the mixed solution into a reaction kettle and placing it in an oven to carry out reaction to obtain a reaction product; S104, washing, centrifuging and drying the reaction product, and calcining in a muffle furnace to prepare the manganese oxide room temperature catalyst with different phase structures.

[0029] Further, S1. Dissolving Mn-containing soluble salt in deionized water in a beaker, stirring vigorously to make the Mn-containing soluble salt fully and completely dissolved to form solution A with a concentration of U1 mmol / mL; S2. Dissolving oxidizing agent F in the above solution, stirring vigorously at room temperature to make it fully and completely dissolved to form solution B; S3. Pour the mixed reaction solution B into the four-chlorofluorine reactor inner liner and place it in a W℃ constant temperature water bath for reaction, react for Xh, after the reaction is completed, wait for it to drop to room temperature, and end the hydrothermal process; S4. Wash and centrifuge the solution after the reaction is completed with deionized water and ethanol multiple times, dry the precipitate after the last washing, and calcine in a muffle furnace to obtain a non-noble metal different phase structure MnO2 manganese oxide room temperature catalyst.

[0030] Further, in the step S1, the manganese-containing soluble salt is manganese sulfate.

[0031] Further, in the step S1, the concentration U1 is 0.0286 mmol / mL-0.388 mmol / mL.

[0032] Further, in the step S2, the oxidant F is one of potassium permanganate or ammonium persulfate.

[0033] Further, in the step S2, the mass ratio of manganese sulfate to potassium permanganate is 0.18-0.42.

[0034] Further, in the step S3, the temperature W can be 160℃-240℃.

[0035] Further, in the step S3, the time X is 12 hours or 24 hours.

[0036] Further, in the step S4, the drying temperature is 80℃, and the drying time is 12 hours.

[0037] Further, in the step S5, the calcination temperature Y is 350℃, and the calcination time Z is 4 hours.

[0038] The non-noble metal different phase structure MnO2 manganese oxide room temperature catalyst provided by the embodiment of the present application exists in a tunnel structure or a layered structure, increases the specific surface area, and enriches the surface active oxygen.

[0039] The preparation method of the phase-structure manganese dioxide room temperature catalyst provided by the application not only retains and utilizes the rich active oxygen on the surface, but also improves the activity of the active oxygen on the surface, enhances the activity and stability of the manganese oxygen compound room temperature catalyst, and realizes efficient, safe and stable purification of formaldehyde at room temperature. The application overcomes the problem of dependence on external energy in traditional catalytic technology, and the manganese oxygen compound room temperature catalyst can effectively remove indoor formaldehyde without additional energy input. The oxidation of formaldehyde catalyzed by MnO2 at room temperature follows the "adsorption-oxidation-regeneration" path: formaldehyde is adsorbed on the surface of the catalyst through hydrogen bonding, and is gradually oxidized into formic acid, carbonate and finally CO2 and H2O under the action of hydroxyl and active oxygen, and the hydroxyl is regenerated through the action of active oxygen and water vapor. Research has confirmed that the catalytic activity is closely related to the surface Oads concentration and low-valence Mn species, and the layered structure of δ-MnO2 greatly improves the adsorption and diffusion rate of the surface active site, and it performs best in formaldehyde oxidation.

[0040] Example 1 The preparation method of the β-MnO2 manganese oxide room temperature catalyst provided by the embodiment of the application specifically includes the following steps: MnSO4 soluble salt is dissolved in 70 mL of deionized water, and the MnSO4 is fully dissolved by vigorous stirring to form solution A with a concentration of 0.286 mmol / mL; 2.564 g of (NH4)2S2O3 is dissolved in the above solution, and the solution is fully dissolved by vigorous stirring at 25℃ to form solution B; the mixed reaction solution B is poured into a reaction kettle, and is placed in a 130-150℃ oven for 12 h of reaction. After the reaction is completed, the solution is cooled to room temperature, and the hydrothermal synthesis process is completed; the solution after the reaction is completed is washed and centrifuged 3-4 times with deionized water and ethanol, and the precipitate after the last washing is dried in an 80℃ oven for 12 h, and then is calcined in a 350℃ muffle furnace for 4 h to obtain the β-MnO2 manganese oxide room temperature catalyst.

[0041] Example 2 The preparation method of the γ-MnO2 manganese oxide room temperature catalyst provided by the embodiment of the application specifically includes the following steps: MnSO4 soluble salt is dissolved in 70 mL of deionized water, and MnSO4 is fully dissolved by vigorous stirring to form solution A with a concentration of 0.286 mmol / mL U1; 2.564 g of (NH4)2S2O3 is dissolved in the above solution, and fully dissolved by vigorous stirring at 25℃ to form solution B; the mixed reaction solution B is poured into a four-chlorofluorine reaction kettle, and placed in an oven at 80-100℃ for 24 h of reaction; after the reaction is completed, the solution is cooled to room temperature, and the hydrothermal synthesis process is completed; the solution after the reaction is completed is washed and centrifuged 3-4 times with deionized water and ethanol, the precipitate after the last washing is dried in an oven at 80℃ for 12 h, and then moved to a 350℃ muffle furnace for calcination for 4 h, so that the γ-MnO2 manganese oxide room temperature catalyst is obtained.

[0042] Example 3 The preparation method of the α-MnO2 manganese oxide room temperature catalyst provided by the embodiment of the present application specifically includes the following steps: MnSO4 soluble salt is dissolved in 70 mL of deionized water, and MnSO4 is fully dissolved by vigorous stirring to form solution A with a concentration of 0.286 mmol / mL U1; 2.564 g of (NH4)2S2O3 is dissolved in the above solution, and fully dissolved by vigorous stirring at 25℃ to form solution B; the mixed reaction solution B is poured into a four-chlorofluorine reaction kettle, and placed in an oven at 80-100℃ for 24 h of reaction; after the reaction is completed, the solution is cooled to room temperature, and the hydrothermal synthesis process is completed; the solution after the reaction is completed is washed and centrifuged 3-4 times with deionized water and ethanol, the precipitate after the last washing is dried in an oven at 80℃ for 12 h, and then moved to a 350℃ muffle furnace for calcination for 4 h, so that the γ-MnO2 manganese oxide room temperature catalyst is obtained.

[0043] Example 4 The preparation method of the δ-MnO2 manganese oxide room temperature catalyst provided by the embodiment of the present application specifically includes the following steps: MnSO4 soluble salt is dissolved in 70 mL of deionized water, and MnSO4 is fully dissolved by vigorous stirring to form solution A with a concentration of 0.286 mmol / mL U1; 2.564 g of (NH4)2S2O3 is dissolved in the above solution, and fully dissolved by vigorous stirring at 25℃ to form solution B; the mixed reaction solution B is poured into a four-chlorofluorine reaction kettle, and placed in an oven at 80-100℃ for 24 h of reaction; after the reaction is completed, the solution is cooled to room temperature, and the hydrothermal synthesis process is completed; the solution after the reaction is completed is washed and centrifuged 3-4 times with deionized water and ethanol, the precipitate after the last washing is dried in an oven at 80℃ for 12 h, and then moved to a 350℃ muffle furnace for calcination for 4 h, so that the γ-MnO2 manganese oxide room temperature catalyst is obtained.

[0044] Application Example As Figure 9Figure 1 shows the activity comparison of different phase MnO2 catalysts provided by embodiments 1-4 of the present application in catalyzing formaldehyde purification at room temperature. The catalytic activity of HCHO oxidation was tested using a fixed-bed quartz flow reactor under simulated indoor conditions, such as high reaction space velocity, low HCHO concentration, and typical working conditions containing water vapor in air purifiers. The test device is shown in the figure. The reactor was placed in a precisely controlled incubator at 25°C. The size of the catalyst sample used was 40-60 mesh, each weighing 0.4 grams. In order to generate gaseous HCHO, nitrogen was passed through a temperature-regulated container bottle containing solid formaldehyde. At the same time, water vapor was generated by directing the nitrogen stream through a container bottle filled with water. The feed gas composition consisted of 30 ppm HCHO, 21% O2, and 35% relative humidity, balanced with nitrogen. The total flow rate was maintained at 400 mL / min, and the corresponding space velocity (WHSV) was determined to be 60,000 mL / (g-h). The inlet and outlet gases were continuously monitored using a photoacoustic spectrometer (DKG-42A). Before the experiment, the test system was purged with dry nitrogen to clean the pipeline, and then the indoor atmosphere was simulated in the reference gas path without catalyst. After the gas concentrations were balanced, the mixed gas was reacted with the catalyst for a period of time. By comparing the HCHO and CO2 concentrations at the inlet and outlet of the reaction tube during the reaction, the dynamic HCHO removal efficiency and the conversion efficiency of HCHO to CO2 of the catalyst can be calculated. The results show that the manganese oxides obtained by regulating the phase structure in embodiments 3 and 4 have the performance of catalyzing formaldehyde purification at room temperature. In figure (a), both a-MnO2 and δ-MnO2 achieved a formaldehyde removal rate of more than 96% after 60 min, while the γ and β samples had almost no purification effect and did not show catalytic activity. In figure (b), the CO2 production rate during the test catalysis process, the HCHO mineralization rate under the catalysis of δ-MnO2 was 60%, that of a-MnO2 was 35%, that of β-MnO2 was 10%, and that of γ-MnO2 had no mineralization performance. Therefore, by regulating the phase structure from β-MnO2→ γ-MnO2→ a-MnO2→ δ-MnO2, a higher-activity MnO2 catalyst for room temperature catalysis was prepared, proving that the phase regulation technology is actually feasible.

[0045] The HCHO removal efficiency and HCHO-to-CO2 conversion efficiency formulas are as follows:

[0046]

[0047] In the formula, C initial-HCHO and C HCHO correspond to the initial average concentration of gaseous formaldehyde and the gaseous formaldehyde concentration at that time, respectively, and C CO2 is the CO2 concentration at the outlet.

[0048] Result analysis like Figure 2 As shown, the room-temperature catalysts of different phase structures of MnO2 manganese oxide synthesized in Examples 1-4 of this invention were characterized by XRD (extra-directional randomization) after varying the concentration of Mn-containing precursor and the oxidant, and at hydrothermal temperatures of 90, 140, 160, and 240 °C for 12 or 24 h. The XRD results showed that β, γ, α, and δ-MnO2 were all pure-phase manganese oxides. β, γ, and α-MnO2 exhibited obvious tunnel structures, while δ-MnO2 showed obvious layered structures. No other impurity phases were found.

[0049] like Figure 3 The image shown is a SEM image of the β-MnO2 manganese oxide room temperature catalyst synthesized in Example 1 of this invention under the conditions of MnSO4 and (NH4)2S2O3 as precursors, hydrothermal temperature of 140℃, and time of 12h. The scale bar is 100 nm. The results show that the β-MnO2 manganese oxide room temperature catalyst exhibits a dendritic nanostructure.

[0050] like Figure 4 The image shown is a SEM image of the γ-MnO2 manganese oxide room temperature catalyst synthesized in Example 2 of the present invention under the conditions of MnSO4 and (NH4)2S2O3 as precursors, hydrothermal temperature of 90℃ and time of 24h. The scale bar is 100nm. The results show that it exhibits a spherical nanostructure composed of nanoneedles. like Figure 5 The image shown is a SEM image of the α-MnO2 manganese oxide room temperature catalyst synthesized in Example 3 of this invention under the conditions of MnSO4 and KMnO4 as precursors, hydrothermal temperature of 160℃, and time of 12h. The scale bar is 100nm. The results show that it exhibits a dendritic nanostructure composed of uniform nanorods.

[0051] like Figure 6 The image shown is a SEM image of the δ-MnO2 manganese oxide room temperature catalyst synthesized in Example 4 of this invention under the conditions of MnSO4 and KMnO4 as precursors, hydrothermal temperature of 240℃, and time of 24h. The scale bar is 1μm. The results show that δ-MnO2 exhibits a spherical morphology with a diameter of 2.0-4.0μm, which is composed of many cotton-like structures made up of very thin nanowires.

[0052] like Figure 7The image shown is a TEM image of the α-MnO2 manganese oxide room temperature catalyst synthesized in Example 3 of this invention under the conditions of MnSO4 and KMnO4 as precursors, hydrothermal temperature of 160℃, and time of 12h. The scale bar is 100nm. The results show that α-MnO2 is a dendritic structure of interwoven nanorods, and clear lattice stripes of 0.69nm were found, confirming that the exposed crystal plane is the (110) crystal plane of α-MnO2.

[0053] like Figure 8 The image shown is a TEM image of the δ-MnO2 manganese oxide room temperature catalyst synthesized in Example 4 of this invention under the conditions of MnSO4 and KMnO4 as precursors, hydrothermal temperature of 240℃, and time of 24h. The scale bar is 5nm. The results show that δ-MnO2 has a spherical cluster structure, and clear lattice stripes of 0.70nm are found, confirming that the exposed crystal plane is the (001) crystal plane of δ-MnO2.

[0054] like Figure 10 The figure shows XPS images of the α- and δ-MnO2 manganese oxide room temperature catalysts provided in Embodiments 3 and 4 of this invention. The results indicate that the MnO2 of different phases... 3+ / Mn 4+ The ratios are in the order δ−MnO2 > α−MnO2. Generally, the presence of low-valence Mn species induces the Jahn-Teller distortion, requiring oxygen vacancies to maintain charge conservation, i.e., Mn... 3+ The presence of oxygen results in a large amount of unsaturated oxygen on the surface. Hydroxyl groups formed by the combination of unsaturated oxygen and H are present on the surface. An increase in oxygen vacancies may lead to more molecular oxygen dissociating into surface-active oxygen. Therefore, controlling the phase structure results in a higher concentration of δ−MnO2 surface-active oxygen.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a manganese dioxide catalyst at room temperature, characterized in that, Includes the following steps: S1. Dissolve a manganese-containing soluble salt in deionized water and stir to dissolve, forming a solution A with a concentration of U1; S2. Add oxidant F to solution A and stir at room temperature to form mixed solution B; S3. The mixture B is subjected to a hydrothermal reaction at a reaction temperature of W℃ for a reaction time of X hours. After the reaction is completed, it is cooled to room temperature to obtain the reaction product. S4. The reaction product is washed and centrifuged multiple times with deionized water and anhydrous ethanol. After washing, the precipitate is dried to obtain the dried sample. S5. The dried sample is calcined at a temperature of Y℃ for a time of Z hours to obtain the manganese dioxide catalyst. The crystal phase structure of the manganese dioxide room temperature catalyst is controlled by adjusting the concentration U1, the type and quantity of the oxidant F, the hydrothermal reaction temperature W, and the reaction time X. The crystal phase structure is α phase and / or δ phase.

2. The method for preparing a manganese dioxide room temperature catalyst according to claim 1, characterized in that, In step S1, the manganese-containing soluble salt is manganese sulfate.

3. The method for preparing a manganese dioxide room temperature catalyst according to claim 2, characterized in that, In step S1, the concentration U1 is 0.0286 mmol / mL to 0.388 mmol / mL.

4. The method for preparing a manganese dioxide room temperature catalyst according to claim 3, characterized in that, In step S2, the oxidant F is either potassium permanganate or ammonium persulfate.

5. The method for preparing a manganese dioxide room temperature catalyst according to claim 4, characterized in that, In step S2, the mass ratio of manganese sulfate to potassium permanganate is 0.18 to 0.

42.

6. The method for preparing a manganese dioxide room temperature catalyst according to claim 5, characterized in that, In step S3, the temperature W can be 160℃~240℃.

7. The method for preparing a manganese dioxide room temperature catalyst according to claim 6, characterized in that, In step S3, the time X is 12 to 24 hours.

8. The method for preparing a manganese dioxide room temperature catalyst according to claim 7, characterized in that, In step S4, the drying temperature is 80°C and the drying time is 12 hours.

9. The method for preparing a manganese dioxide room temperature catalyst according to claim 8, characterized in that, In step S5, the calcination temperature Y is 350℃ and the calcination time Z is 4 hours.

10. The application of a manganese dioxide room temperature catalyst in improving the efficiency of formaldehyde purification at room temperature, characterized in that, The manganese dioxide room temperature catalyst is prepared according to any one of claims 1-9.

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