A manganese oxide monolithic metal foam catalyst and its preparation method and application

Abstract

The invention discloses a manganese oxide monolithic metal foam catalyst and a preparation method and application thereof, belonging to the technical field of air purification. The invention uses manganese acetate solution as an electrolyte, uses a three-electrode system to perform electrodeposition on a pretreated metal foam substrate, washes and dries the product obtained after the electrodeposition, and obtains a manganese oxide monolithic metal foam catalyst. The preparation method of the manganese oxide monolithic metal foam catalyst of the invention is simple to operate, not only suitable for metal substrates of any shape, but also can ensure that the manganese oxide active components are firmly loaded and evenly dispersed on the substrate, and has the advantages of excellent activity, good conductivity, and being conducive to industrial application. The manganese oxide monolithic metal foam catalyst of the invention still has excellent long-term use stability and water resistance under high humidity conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of air purification, and in particular relates to a manganese oxide integral metal foam catalyst and a preparation method and application thereof. Background Art

[0002] In the Earth's stratosphere, the ozone layer plays a key barrier role, absorbing most of the ultraviolet radiation from the sun and protecting the Earth's organisms from harmful ultraviolet radiation. However, ozone in the ground layer is considered a common air pollutant because of its strong oxidizing properties. Its main source is the action of ultraviolet rays in the atmosphere on oxygen (O 2 ) photochemical reaction that produces ozone. In addition, the photochemical reaction between volatile organic compounds (VOCs) and nitrogen oxides (NOx) is also one of the sources of ozone. At the same time, some electrical equipment, such as copiers and printers, ultraviolet sterilizers, etc., also produce ozone during use. Ozone is a strong oxidant that can cause damage to human respiratory tract and lung tissue. Exposure to high concentrations of ozone may cause respiratory problems, including coughing, lung inflammation, etc. Ozone can also react with VOCs in indoor environments to produce secondary organic aerosols (SOA) and ultrafine particles. These secondary aerosols are more harmful to human health and may increase the risk of respiratory diseases, cardiovascular diseases and other health problems by increasing exposure to fine particles and inducing inflammatory reactions. In addition, ozone can also have a negative impact on plants, leading to reduced crop yields. The hazards of ozone involve many aspects such as human health and plant growth. Therefore, eliminating ozone is of great significance to the natural environment and human health.

[0003] At present, common methods for ozone elimination include thermal decomposition, liquid absorption, plasma decomposition, catalytic decomposition, etc. However, compared with other methods, catalytic decomposition has more significant advantages, including low energy consumption, mild reaction conditions, no waste liquid, and significant elimination effect. Therefore, catalytic decomposition has been widely studied by researchers. The catalysts commonly used for ozone catalytic decomposition can be divided into precious metal catalysts and non-precious metal catalysts. The high cost of precious metal catalysts limits their development. Non-precious metal catalysts have become the focus of research because of their good catalytic performance and low cost. Among them, manganese oxide (MnOx) has the advantages of abundant sources, green and cheap, and excellent performance. In addition, manganese oxide also has a variety of crystal forms, such as α-, β-, γ-, δ-type, and manganese has a variety of valence states (2+, 3+ and 4+), which is considered to have excellent application prospects. However, manganese oxide catalysts have the problem of easy deactivation and inability to be used for a long time under high humidity conditions, which limits their application in catalytic decomposition of ozone. In the process of ozone catalytic decomposition, the oxygen vacancies of manganese oxide catalysts are considered to be the active sites of the reaction, and the occupation of oxygen vacancies is the root cause of catalyst deactivation. The peroxide intermediates generated in the ozone catalytic decomposition reaction will occupy the oxygen vacancies, resulting in catalyst deactivation. At the same time, under high humidity conditions, water molecules compete with ozone for adsorption on oxygen vacancies, exacerbating the deactivation of the catalyst. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a manganese oxide monolithic metal foam catalyst and a preparation method and application thereof. The preparation method of the manganese oxide monolithic metal foam catalyst of the present invention is simple to operate, not only suitable for metal substrates of any shape, but also can ensure that the manganese oxide active components are firmly loaded and evenly dispersed on the substrate, and has the advantages of excellent activity, good conductivity and being conducive to industrial application. The manganese oxide monolithic metal foam catalyst of the present invention still has excellent long-term use stability and water resistance under high humidity conditions.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention:

[0007] A method for preparing a manganese oxide monolithic metal foam catalyst comprises the following steps:

[0008] Using manganese acetate solution as an electrolyte, using a three-electrode system to perform electrodeposition on a pretreated metal foam substrate, washing and drying the product obtained after the electrodeposition, to obtain the manganese oxide monolithic metal foam catalyst;

[0009] The loading amount of manganese oxide in the manganese oxide monolithic metal foam catalyst is 8-45%.

[0010] The present invention adopts a one-step method to directly load manganese oxide on a metal foam substrate, and there is no need to prepare a powder catalyst in advance, and there are no strict requirements on the physical and chemical properties of the powder, high difficulty in configuring the slurry, and uneven loading. The manganese oxide monolithic metal foam catalyst of the present invention is prepared under normal temperature and pressure conditions, and no reducing agent is added, and no high-temperature calcination is required. The manganese oxide can be simply and quickly loaded on the metal foam substrate, and the loading is firm and uniformly dispersed. The manganese oxide monolithic metal foam catalyst prepared by the present invention can be directly used for direct current-assisted ozone catalytic decomposition, and its catalytic decomposition activity for high-humidity ozone can be effectively improved.

[0011] The ozone catalytic decomposition reaction requires a certain amount of active components (manganese oxides). If the loading is too low, insufficient active components will lead to poor catalyst activity. The catalyst loading should not be too high either. Too high a loading may cause the active components to stack on each other, and the active sites may be covered, resulting in a decrease in catalyst activity. Too high a loading may also lead to a deterioration in the bonding strength between the active components and the substrate, causing them to fall off, which is not conducive to the preservation and use of the catalyst.

[0012] Preferably, the pretreatment process of the metal foam substrate is: firstly, ultrasonically treating the metal foam substrate in hydrochloric acid (HCl), then ultrasonically treating the metal foam substrate in water and anhydrous ethanol in sequence, and then washing with water and drying.

[0013] When the metal foam substrate is stored in the air for a long time, an oxide film will form on the surface, which will reduce the specific surface area of ​​the substrate and is not conducive to the loading of manganese oxide. Using HCl to treat the metal foam substrate can remove the surface oxide layer, making the manganese oxide more firmly bonded to the substrate and reducing the impact of the oxide layer on the reaction.

[0014] Preferably, the concentration of the hydrochloric acid is 1-3 mol / L, and the ultrasonic treatment time is 10-600 s. If the hydrochloric acid concentration is too low and the ultrasonic treatment time is too short, the oxide layer of the metal foam substrate cannot be effectively removed, while if the hydrochloric acid concentration is too high and the ultrasonic treatment time is too long, the metal foam substrate will be corroded by the hydrochloric acid, resulting in a decrease in the mechanical strength of the metal foam substrate.

[0015] More preferably, the pretreatment process of the metal foam substrate is: firstly, the metal foam substrate is ultrasonically treated in a 1-3 mol / L HCl solution to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol in sequence to remove the oil, then rinsed with deionized water, and vacuum dried.

[0016] Preferably, the metal foam substrate comprises foam iron (Fe), foam nickel (Ni), foam copper (Cu), foam aluminum (Al) or foam aluminum alloy. The above-mentioned metal foam substrate has a porous structure with a porosity of 95 PPI. The above-mentioned metal foam substrate has good mechanical strength and electrical conductivity. A DC power supply will be connected to both ends of the catalyst to carry out a DC-assisted ozone catalytic decomposition reaction. The substrate needs to have certain mechanical strength and excellent electrical conductivity. The above-mentioned substrate meets the basic requirements as a catalyst substrate. Moreover, the above-mentioned substrates are already capable of industrial production, and the stability of the preparation can be guaranteed. The above-mentioned porosity is adopted to enable more manganese oxide active components to be deposited on the substrate, and to be evenly loaded.

[0017] Preferably, the drying temperature is 50-150° C. and the drying time is 3-12 hours.

[0018] More preferably, the drying temperature is 80-120°C and the time is 8-12h. After the electrodeposition is completed, the sample needs to be dried to remove moisture. The deposited layer (manganese oxide) of the dried sample is more stable, and the dried sample can be used for ozone catalytic decomposition reaction. The drying temperature and time cannot be too low or too short, otherwise there will be residual moisture in the sample, which will have a greater impact on the ozone catalytic decomposition reaction. The drying temperature and drying time cannot be too high or too long, otherwise the deposited layer (manganese oxide) will be sintered, and the reduction in specific surface area is not conducive to the ozone catalytic decomposition reaction. Moreover, it has been found through experiments that when the drying temperature is 80-120°C, the moisture in the sample can be effectively removed, and the properties of the active component (manganese oxide) of the sample will not change at this time, and it can be efficiently used for ozone catalytic decomposition reaction.

[0019] Preferably, the concentration of the manganese acetate solution is 0.2-0.3 mol / L. Manganese acetate is a common manganese salt with a wide range of sources and low cost. Manganese acetate is easily soluble in water and easily ionized in water to produce Mn 2+ As a manganese source. And manganese acetate is not prone to unnecessary side reactions or decomposition. This helps to improve the efficiency of the electrolysis process and the purity of the product. When the concentration of manganese acetate solution is too low, there is a lack of sufficient Mn in the electrolyte. 2+ , resulting in the inability to load a sufficient amount of manganese oxide on the working electrode (metal foam substrate); when the concentration is too high, the rate of generating manganese oxide on the working electrode is too fast, which may cause the manganese oxides to stack on each other, resulting in the active sites being covered.

[0020] Preferably, during the electrodeposition, the cyclic deposition voltage is 0.6-1.5V, the voltage increases from 0.6V to 1.5V at a rate of 0.05V / s, and then decreases to 0.6V at the same rate.

[0021] More preferably, during the electrodeposition, the number of deposition turns is 80 turns.

[0022] Preferably, in the three-electrode system of the present invention, the working electrode is a metal foam substrate, the counter electrode is a platinum sheet, and the reference electrode is a saturated calomel electrode. 2+ It moves to the working electrode, where it loses electrons and becomes Mn 4+ , and the product manganese oxide is generated on the working electrode. The three-electrode system is used to stably prepare manganese oxide, because the potential of the reference electrode is stable and can be used as a reference to accurately measure the potential change of the working electrode, which is beneficial to control the parameters of the deposition process. Platinum is used as the counter electrode because it has weak activity, is not easy to corrode, has stable chemical properties, has good conductivity, and has a large potential range that can be scanned. The saturated calomel electrode is very stable as a reference electrode, and potassium chloride only needs to be prepared into a saturated solution, which is easy to make. The electrode potential is 0.244V and basically does not change.

[0023] The second technical solution of the present invention:

[0024] The present invention also provides a manganese oxide integral metal foam catalyst prepared by the method.

[0025] The manganese oxide monolithic metal foam catalyst of the present invention has the characteristics of accelerating the release of oxygen vacancies and reducing water competitive adsorption to improve the activity and stability of the catalyst. At present, the research on manganese oxide catalysts mainly focuses on increasing the oxygen vacancies on the manganese oxide catalyst by doping other transition metal oxides to maintain its concentration. The present invention provides a manganese oxide monolithic metal foam catalyst, which provides external electrons through direct current to promote electron transfer on the catalyst, thereby maintaining the concentration of oxygen vacancies and increasing their number. The external electric field formed by direct current can also inhibit the adsorption of water molecules on the oxygen vacancies.

[0026] The third technical solution of the present invention:

[0027] The present invention also provides the use of the manganese oxide monolithic metal foam catalyst in catalytic decomposition of ozone. The manganese oxide monolithic metal foam catalyst catalytically decomposes ozone under the assistance of direct current.

[0028] At present, in the field of ozone decomposition and purification research, more research is still on manganese oxide powder catalysts, while manganese oxide monolithic catalysts, especially monolithic metal foam catalysts, are less studied. Compared with powder catalysts, the advantages of monolithic metal foam catalysts are low bed pressure drop, good mass transfer, and easy recovery. At the same time, the metal foam substrate has good conductivity, which is more conducive to direct current-assisted applications.

[0029] The direct current-assisted ozone catalytic decomposition of the present invention is carried out in a continuous fixed bed quartz tube reactor; a manganese oxide monolithic metal foam catalyst is placed in the center of a quartz reaction tube, two ends of the catalyst are welded with wires and connected to the positive and negative electrodes of a direct current power supply, the air inlet of the reactor is connected to an ozone generator, and the reaction outlet is connected to an ozone detector, and external electrons provided by a direct current power supply form an external electric field on the metal foam substrate, and the potential difference formed by this electric field between the substrate and the manganese oxide active component layer causes part of the electrons to flow through the manganese oxide layer. The external electrons flowing through the manganese oxide accelerate the desorption of the intermediate product peroxide and the reduction of oxygen vacancies, so that the oxygen vacancies complete the ozone decomposition cycle in a short time and maintain the concentration of the catalyst oxygen vacancies. At the same time, the external electric field can also inhibit the adsorption of water on the oxygen vacancies through the potential difference. Both improve the catalyst ozone catalytic decomposition performance.

[0030] Compared with the hydrothermal method, it has certain advantages under the preparation conditions. The hydrothermal method usually needs to be carried out under high temperature and high pressure conditions, which is often a challenge that the catalyst prepared by the hydrothermal method is difficult to apply on a large scale in industry. Compared with the impregnation-coating method, the present invention has the advantages of simple operation and strong applicability. The impregnation-coating method requires the preparation of manganese active component powder in advance, and has strict requirements on the physical and chemical properties of the powder. Because the surface of the metal foam substrate is relatively smooth and the specific surface area is small, the applicability of this method on the metal substrate is relatively low. The present invention uses electrochemical principles under mild conditions (normal temperature and pressure) to make metal ions lose electrons on the electrode surface and oxidize to metal oxides and grow uniformly, and finally obtain a monolithic metal foam catalyst with a firmly and evenly dispersed manganese oxide load on the metal foam substrate.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] (1) The manganese oxide active component in the catalyst prepared by the present invention is firmly loaded and evenly distributed on the surface of the metal foam;

[0033] (2) The catalyst prepared by the present invention has good electrical conductivity, and the performance and water resistance of the catalyst in ozone catalytic decomposition can be improved by direct current assistance;

[0034] (3) The preparation method of the catalyst prepared by the present invention is simple and mild, and is applicable to metal foam substrates of various shapes and sizes, and has strong applicability to different types of metal foam substrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0036] Figure 1This is a performance diagram of ozone catalytic decomposition of the manganese oxide monolithic metal foam catalyst in Example 1 without direct current assistance;

[0037] Figure 2 This is a graph showing the ozone catalytic decomposition performance of the manganese oxide monolithic metal foam catalyst in Example 1 when assisted by direct current;

[0038] Figure 3 This is a performance diagram of ozone decomposition when the manganese oxide monolithic metal foam catalyst in Example 1 is repeatedly involved in 40 times with the assistance of direct current;

[0039] Figure 4 This is a scanning electron microscope image of the manganese oxide monolithic metal foam catalyst in Example 1 at a magnification of 100k;

[0040] Figure 5 This is a scanning electron microscope image of the manganese oxide monolithic metal foam catalyst in Example 1 at a magnification of 50k;

[0041] Figure 6 This is a scanning electron microscope image of the manganese oxide monolithic metal foam catalyst in Example 1 at a magnification of 10k;

[0042] Figure 7 This is the EDS image of the Ni element of the manganese oxide monolithic metal foam catalyst in Example 1;

[0043] Figure 8 This is the EDS image of the Mn element of the manganese oxide monolithic metal foam catalyst in Example 1;

[0044] Fig. 9 This is the EDS image of the O element of the manganese oxide monolithic metal foam catalyst in Example 1;

[0045] Fig.10 is the XRD pattern of the manganese oxide monolithic metal foam catalyst in Example 1;

[0046] Fig.11 is a narrow scan XRD pattern of 10-40 degrees of the manganese oxide monolithic metal foam catalyst in Example 1;

[0047] Fig.12 is the nitrogen adsorption-desorption isotherm of the manganese oxide monolithic metal foam catalyst in Example 1;

[0048] Fig.13 This is the pore size distribution diagram of the manganese oxide monolithic metal foam catalyst in Example 1. DETAILED DESCRIPTION

[0049] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0050] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0051] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0052] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0053] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0054] In the present invention, normal temperature refers to 25±2° C., and normal pressure refers to 1 atmosphere (101.325 kPa).

[0055] All raw materials and reagents used in the examples of the present invention are purchased from commercial sources.

[0056] In the present invention, the metal foam substrate has a porous structure with a porosity of 95 PPI.

[0057] The technical solution of the present invention is further illustrated by the following embodiments.

[0058] Example 1

[0059] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in 2mol / L HCl for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a manganese acetate solution with a concentration of 0.25mol / L was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the heights of the Ni foam, platinum electrode and saturated calomel electrode were kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0060] The scanning electron microscope image of the manganese oxide monolithic metal foam catalyst in Example 1 at a magnification of 100k is shown in 4, and the scanning electron microscope image at a magnification of 50k is shown in Figure 5 , SEM images at 10k magnification are shown in Figure 6 It can be seen that a large number of nano-sheet-shaped manganese oxides are formed on the foamed Ni substrate in Example 1, and these manganese oxide nano-sheets are interconnected to form a network structure. Fig.12 This is the nitrogen adsorption-desorption isotherm of the manganese oxide monolithic metal foam catalyst in Example 1, which has an H3-type hysteresis loop, which is a typical feature of a type IV isotherm. It can be seen that the catalyst in Example 1 has many mesopores. Fig.13 : is the pore size distribution diagram of the manganese oxide monolithic metal foam catalyst in Example 1, and it can be seen that the catalyst in Example 1 has a large number of mesopores around 5 nm. Therefore, the manganese oxide nanosheets with a network structure have a higher specific surface area and a higher pore volume, providing more active sites for ozone decomposition.

[0061] Table 1 BET specific surface area and DFT calculated pore volume characteristics of the catalyst in Example 1

[0062] sample <![CDATA[S BET (m 2 / g)]]> <![CDATA[V pore (cm 3 / g)]]> Example 1 55.8 0.053

[0063] Figure 7 This is the EDS image of the Ni element of the manganese oxide monolithic metal foam catalyst in Example 1; Figure 8 This is the EDS image of the Mn element of the manganese oxide monolithic metal foam catalyst in Example 1; Fig. 9 : is the EDS image of the O element of the manganese oxide monolithic metal foam catalyst in Example 1, and it can be seen that the Ni, Mn, and O elements are evenly distributed on the manganese oxide monolithic metal foam catalyst in Example 1. The proportions of different elements in the catalyst in Example 1 are shown in Table 2.

[0064] Table 2 Proportions of different elements in the catalyst in Example 1

[0065]

[0066] Fig.10 This is the XRD pattern of the manganese oxide monolithic metal foam catalyst in Example 1. It can be seen that the peak of the foam Ni is too strong to observe the peak of the manganese oxide; Fig.11 This is a narrow scan XRD pattern of 10-40 degrees of the manganese oxide monolithic metal foam catalyst in Example 1, in which the peak of manganese oxide can be observed.

[0067] The catalyst obtained in this example was wrapped with quartz wool and placed in the center of a quartz tube reactor to perform ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0068] Example 2

[0069] The 3cm long and 2cm wide Cu foam was first ultrasonically treated in a 2mol / L HCl solution for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a 0.25mol / L manganese acetate solution was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0070] The catalyst obtained in this example was wrapped with quartz wool and placed in the center of a quartz tube reactor to perform ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0071] Example 3

[0072] The 3cm long and 2cm wide Fe foam was first ultrasonically treated in a 2mol / L HCl solution for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a 0.25mol / L manganese acetate solution was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0073] The catalyst obtained in this example was wrapped with quartz wool and placed in the center of a quartz tube reactor to perform ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0074] Example 4

[0075] The NiCrAl foam with a length of 3 cm and a width of 2 cm was first ultrasonically treated in a 2 mol / L HCl solution for 1 min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10 min to remove oil, then rinsed with deionized water, and vacuum dried for use; a manganese acetate solution with a concentration of 0.25 mol / L was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the number of deposition cycles was 80. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12 hours to obtain a manganese oxide integral metal foam catalyst.

[0076] The catalyst obtained in this example was wrapped with quartz wool and placed in the center of a quartz tube reactor to perform ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0077] Example 5

[0078] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in a 2mol / L HCl solution for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a 0.25mol / L manganese acetate solution was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 120°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0079] The catalyst obtained in this example was wrapped with quartz wool and placed in the center of a quartz tube reactor to perform ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0080] Comparative Example 1: The concentration of manganese acetate solution is too high

[0081] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in 2mol / L HCl for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a manganese acetate solution with a concentration of 0.40mol / L was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the heights of the Ni foam, platinum electrode and saturated calomel electrode were kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0082] The catalyst obtained in this comparative example was wrapped with quartz wool and placed in the center of a quartz tube reactor to carry out an ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0083] Comparative Example 2: The concentration of manganese acetate solution is too low

[0084] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in 2mol / L HCl for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a manganese acetate solution with a concentration of 0.15mol / L was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the heights of the Ni foam, platinum electrode and saturated calomel electrode were kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0085] The catalyst obtained in this comparative example was wrapped with quartz wool and placed in the center of a quartz tube reactor to carry out an ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0086] Comparative Example 3: The concentration of manganese acetate solution is too low

[0087] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in 2mol / L HCl for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a manganese acetate solution with a concentration of 0.10mol / L was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the heights of the Ni foam, platinum electrode and saturated calomel electrode were kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0088] The catalyst obtained in this comparative example was wrapped with quartz wool and placed in the center of a quartz tube reactor to carry out an ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0089] Comparative Example 4: The maximum voltage of the deposition cycle is too high

[0090] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in a 2mol / L HCl solution for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a 0.25mol / L manganese acetate solution was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.9-1.8V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0091] The catalyst obtained in this comparative example was wrapped with quartz wool and placed in the center of a quartz tube reactor to carry out an ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0092] Comparative Example 5 The lowest voltage of the cyclic deposition voltage is too low

[0093] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in a 2mol / L HCl solution for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a 0.25mol / L manganese acetate solution was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0-0.9V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0094] The catalyst obtained in this comparative example was wrapped with quartz wool and placed in the center of a quartz tube reactor to carry out an ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0095] Comparative Example 6 Electrolyte Non-acetic Acid Manganese Solution

[0096] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in a 2mol / L HCl solution for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a manganese sulfate solution with a concentration of 0.25mol / L was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0097] The catalyst obtained in this comparative example was wrapped with quartz wool and placed in the center of a quartz tube reactor to carry out an ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0098] Comparative Example 7 Electrolyte Non-acetic Acid Manganese Solution

[0099] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in a 2mol / L HCl solution for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a manganese chloride solution with a concentration of 0.25mol / L was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in an oven at 80°C for 12h to obtain a manganese oxide integral metal foam catalyst.

[0100] The catalyst obtained in this comparative example was wrapped with quartz wool and placed in the center of a quartz tube reactor to carry out an ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0101] Comparative Example 8 Drying temperature is too high

[0102] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in a 2mol / L HCl solution for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a manganese chloride solution with a concentration of 0.25mol / L was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in a muffle furnace at 200℃ for 12h to obtain a manganese oxide integral metal foam catalyst.

[0103] The catalyst obtained in this comparative example was wrapped with quartz wool and placed in the center of a quartz tube reactor to carry out an ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0104] Comparative Example 9 Drying temperature is too high

[0105] The 3cm long and 2cm wide Ni foam was first ultrasonically treated in a 2mol / L HCl solution for 1min to remove the oxide layer, then ultrasonically treated in deionized water and anhydrous ethanol solution for 10min to remove oil, then rinsed with deionized water, and vacuum dried for use; a 0.25mol / L manganese chloride solution was prepared as an electrolyte. The Ni foam, platinum electrode and saturated calomel electrode were immersed in a beaker of the electrolyte at the same time, and the height of the Ni foam, platinum electrode and saturated calomel electrode was kept uniform. The CV electrodeposition method was used, the deposition voltage was set to 0.6-1.5V, and the deposition cycle was 80 cycles. The deposited Ni foam was rinsed with deionized water until neutral, and placed in a muffle furnace at 250℃ for 12h to obtain a manganese oxide integral metal foam catalyst.

[0106] The catalyst obtained in this comparative example was wrapped with quartz wool and placed in the center of a quartz tube reactor to carry out an ozone catalytic decomposition reaction without direct current assistance. The reaction was carried out at room temperature and pressure, with an ozone inlet concentration of 20 ppm, a relative humidity of 90%, and a space velocity of 100,000 h -1 The test time is 2 hours, and the outlet concentration is detected using an ozone detector. The specific test results are shown in Table 3.

[0107] Table 3 Ozone conversion rate of catalysts of Examples 1-5 and Comparative Examples 1-9 under direct current assistance

[0108]

[0109] As shown in Table 3, the manganese acetate solution in Comparative Example 1 is relatively high, and a large number of manganese oxide nanosheets are generated on the foam Ni substrate in a short time. These nanosheets are stacked on each other, resulting in the active sites on the catalyst being covered, and the performance of ozone decomposition is reduced. The manganese acetate solution concentration in Comparative Examples 2 and 3 is relatively low, and manganese oxide grows slowly on the foam Ni substrate, and it is impossible to form a good nanosheet network structure, resulting in a low specific surface area of ​​the catalyst in Comparative Examples 2 and 3, and it is impossible to provide more active sites for ozone decomposition, resulting in a decrease in catalyst performance. The highest voltage of the cyclic deposition voltage in Comparative Example 4 is relatively high, and a large amount of manganese oxide is generated at a faster rate on the foam Ni substrate. The active components cover each other, resulting in a decrease in active sites, resulting in a decrease in catalyst performance in Comparative Example 4. The lowest voltage of the cyclic deposition voltage in Comparative Example 5 is relatively low, and side reactions occur during the electrodeposition process, resulting in a decrease in the manganese oxide loading on the foam Ni substrate and a decrease in active sites. Ultimately, the catalyst performance in Comparative Example 5 is reduced. Comparative Examples 6 and 7 use manganese sulfate solution and manganese chloride solution as electrolytes, respectively. Acidic solutions are formed during the electrodeposition process, while the formation of manganese oxides requires a suitable weakly acidic or nearly neutral environment. The use of manganese sulfate and manganese chloride solutions as electrolytes will result in a strong acidity of the solution during the reaction, which is not conducive to the deposition of manganese oxides on the foamed Ni, resulting in fewer active components on the catalysts in Comparative Examples 6 and 7 and poor catalyst performance. The drying temperature in Comparative Examples 8 and 9 is relatively high, and a higher drying temperature will cause the active components on the catalyst to sinter, resulting in a decrease in the specific surface area of ​​the catalyst and a reduction in active sites, thereby causing the performance of the catalyst to decline.

[0110] The catalyst obtained in Example 1 was wrapped with quartz wool and placed in the center of a quartz tube reactor. Both ends of the catalyst were welded to the positive and negative electrodes of a DC power supply with wires. While introducing ozone for reaction, a constant current was applied to the catalyst (constant currents of 1.0A, 1.5A, 2.0A, 2.5A and 3.0A were applied respectively), thereby realizing a DC-assisted reaction mode. The reaction was carried out at room temperature and pressure, with an inlet concentration of ozone of 20ppm, a relative humidity of 90%, and an air velocity of 100,000h -1 The test time was 2 hours, and the outlet concentration was detected using an ozone detector. The results are shown in Table 4.

[0111] Table 4 Ozone conversion rate of the catalyst of Example 1 under different current strengths

[0112]

[0113] It can be seen from Table 4 that, under the condition of applying DC power with a constant current intensity of 1-3A, 2.0A is the lowest current to achieve the optimal performance, and increasing the current to 2.5A and 3.0A does not help to further improve the catalyst performance.

[0114] The performance of ozone catalytic decomposition of the manganese oxide monolithic metal foam catalyst in Example 1 without direct current assistance is shown in FIG. Figure 1 . The results show that: the catalyst obtained in Example 1 has an ozone conversion rate of only 51.6% within 2 hours under the condition of 90% relative humidity without direct current assistance; the catalyst obtained in Example 2 has an ozone conversion rate of only 49.5% within 2 hours under the condition of 90% relative humidity without direct current assistance; the catalyst obtained in Example 3 has an ozone conversion rate of only 49.0% within 2 hours under the condition of 90% relative humidity without direct current assistance; the catalyst obtained in Example 4 has an ozone conversion rate of only 50.3% within 2 hours under the condition of 90% relative humidity without direct current assistance; the catalyst obtained in Example 5 has an ozone conversion rate of only 50.9% within 2 hours under the condition of 90% relative humidity without direct current assistance. In the absence of direct current assistance, the catalysts obtained in Examples 1-5 show that oxygen vacancies are quickly occupied by peroxides and water molecules, resulting in a decrease in performance, and the service life and water resistance of the catalysts are poor.

[0115] The performance of ozone catalytic decomposition of the manganese oxide monolithic metal foam catalyst in Example 1 with direct current assistance is shown in FIG. Figure 2 , it can be seen that the ozone decomposition performance of the catalyst obtained in Example 1 is maintained at more than 94% within 48 hours when assisted by direct current (2.0A). When the catalyst obtained in Example 1 is assisted by direct current (1.0A), under the condition of relative humidity of 90%, the conversion rate of ozone within 2 hours is still higher than 80.3%, and it remains stable. When the catalyst obtained in Example 1 is assisted by direct current (1.5A), under the condition of relative humidity of 90%, the conversion rate of ozone within 2 hours is still higher than 91.2%, and it remains stable. When the catalyst obtained in Example 1 is assisted by direct current (2.5A), under the condition of relative humidity of 90%, the conversion rate of ozone within 2 hours is still higher than 94.7%, and it remains stable. When the catalyst obtained in Example 1 is assisted by direct current (3.0A), under the condition of relative humidity of 90%, the conversion rate of ozone within 2 hours is still higher than 94.7%, and it remains stable. When assisted by direct current, the catalyst obtained in Example 1 exhibits better long-term stability and water resistance.

[0116] The catalyst obtained in Example 1 was subjected to 40 on-off cycles with the assistance of direct current under a relative humidity of 90% (the direct current assistance (2.0A) was turned on for 15 minutes and then turned off for 5 minutes as one cycle, and 40 cycles were performed). The conversion rate of ozone obtained in Example 1 with the assistance of direct current was able to recover to more than 94% in each cycle, showing that it has excellent stability for repeated use. It can be inferred that when direct current is used to assist the reaction, the catalyst prepared by the present invention still exhibits excellent long-term stability, repeated stability and water resistance even under high humidity conditions.

[0117] The catalyst loading firmness test was performed: the catalyst obtained in Example 1 was placed in 20 mL of deionized water and ultrasonicated in an ultrasonic cleaning machine for 30 minutes. The sample weight was weighed before and after ultrasonication, and the mass loss was calculated. The results are shown in Table 5.

[0118] Table 5 Catalyst loading firmness test

[0119]

[0120] Note: In Table 5, Example 1 refers to the catalyst in Example 1 without reaction; Example 1 without DC-assisted reaction refers to the catalyst in Example 1 without DC-assisted reaction; Example 1 with DC-assisted reaction refers to the catalyst in Example 1 with DC-assisted reaction.

[0121] After the ultrasonic vibration test, the mass loss of the catalyst was small, indicating that the manganese oxide was firmly loaded on the substrate. At the same time, the catalyst with or without direct current assistance in Example 1 was also subjected to the same test, indicating that direct current assistance would not affect the loading firmness of the manganese oxide, further indicating that the loading firmness of the manganese oxide was high.

[0122] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. Application of a manganese oxide monolithic metal foam catalyst in catalytic decomposition of ozone, characterized in that: The manganese oxide monolithic metal foam catalyst catalytically decomposes ozone under the assistance of direct current; The method for preparing the manganese oxide monolithic metal foam catalyst comprises the following steps: Using manganese acetate solution as an electrolyte, using a three-electrode system to perform electrodeposition on a pretreated metal foam substrate, washing and drying the product obtained after the electrodeposition, to obtain the manganese oxide monolithic metal foam catalyst; The concentration of the manganese acetate solution is 0.2-0.3 mol / L; The electrodeposition is cyclic electrodeposition, the cyclic deposition voltage is 0.6-1.5V, the voltage increases from 0.6V to 1.5V at a rate of 0.05V / s, and then decreases to 0.6V at the same rate; The loading amount of manganese oxide in the manganese oxide monolithic metal foam catalyst is 8-45%.

2. The use according to claim 1, characterized in that: The pretreatment process of the metal foam substrate is: firstly, the metal foam substrate is ultrasonically treated in hydrochloric acid, then ultrasonically treated in water and anhydrous ethanol in sequence, and then washed with water and dried.

3. The use according to claim 2, characterized in that: The metal foam substrate includes foamed iron, foamed nickel, foamed copper, foamed aluminum or foamed aluminum alloy.

4. The use according to claim 1, characterized in that: The drying temperature is 50-150° C. and the drying time is 3-12 hours.

5. The use according to claim 4, characterized in that: The drying temperature is 80-120° C. and the drying time is 8-12 hours.

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