A platinum-manganese composite monolithic metal substrate catalyst, its preparation method and application

Abstract

This invention discloses a method for preparing a platinum-manganese composite monolithic metal substrate catalyst, comprising the following steps: A. Surface treatment of the metal substrate; B. Preparation of a manganese-containing precursor solution; C. Immersion of the surface-treated metal substrate in the manganese-containing precursor solution to obtain a metal substrate with a thin active layer of manganese oxide; D. Immersion of the metal substrate with the manganese oxide active layer first in a platinum ethylenediaminetetraacetic acid complex solution, and then in a sodium borohydride solution I to obtain a metal substrate with platinum seed crystals deposited on its surface; E. Preparation of a platinum-containing precursor solution; F. Immersion of the metal substrate with platinum seed crystals deposited on its surface in the platinum-containing precursor solution, adding sodium borohydride solution II dropwise during the immersion process to obtain the platinum-manganese composite monolithic metal substrate catalyst. The catalyst prepared by the method of this invention exhibits high decomposition catalytic activity, long service life, and high cost-effectiveness.

Description

Technical Field

[0001] This invention relates to the field of metal catalyst technology, and in particular to a platinum-manganese composite monolithic metal substrate catalyst, its preparation method, and its application. Background Technology

[0002] Volatile organic compounds (VOCs) mainly include alkanes, aromatics, esters, alkenes, carboxylic acids, and alcohols. Existing technologies for removing VOCs mainly include the following categories: (1) Adsorption method, which improves the adsorption capacity of VOCs by improving the specific surface area, pore capacity, surface chemical functional groups, and reducing pore size of the adsorption material. At the same time, the adsorption material and VOCs can be recovered and reused. However, it has the disadvantages of low adsorption capacity and the need for frequent replacement; (2) Biofiltration method, which utilizes the ability of microorganisms to adsorb and decompose organic matter to degrade VOCs. However, this method can only be used to remove low-concentration VOCs and cannot be used to remove high-concentration VOCs. It also requires backwashing of the filter bed regularly, which has the disadvantages of complex operation and poor adaptability. Compared with the above treatment methods, catalytic decomposition method can oxidize VOCs into silica, water, and other relatively less harmful substances at lower temperatures. It is considered to be an efficient and economical VOCs removal method with high VOCs treatment efficiency.

[0003] The catalysts used in the catalytic decomposition method in the prior art are mainly divided into the following two categories: (1) noble metal catalysts, which have high catalytic efficiency and long catalytic life, but their large-scale industrial application is limited by their high price and the fact that the catalyst is prone to sintering and poisoning; (2) catalysts containing transition metal oxides, the key point is that it is difficult to screen suitable transition metal oxides, and the low-temperature decomposition efficiency of transition metal oxide catalysts is low.

[0004] To overcome the drawbacks of high cost of precious metal catalysts and low low-temperature decomposition efficiency of transition metal oxide catalysts, manganese-containing catalysts have emerged in existing technologies. Manganese-containing catalysts are mainly classified into two types based on their macroscopic morphology: particulate and monolithic. Particulate catalysts suffer from high bed pressure drop, making them unsuitable for treating VOCs gases with high reaction space velocities. Monolithic catalysts, on the other hand, often use activated carbon honeycomb, metal, or ceramic honeycomb as the structured matrix. For example, Chinese invention patent CN109261164A discloses the preparation of a copper-cobalt co-doped manganese-based catalyst and its application in the decomposition of low-concentration ozone. This method involves first preparing catalyst powder, then formulating a catalyst slurry, and finally loading the catalyst slurry onto a honeycomb carrier using ultrasonic impregnation to create a shaped monolithic catalyst. This effectively reduces bed pressure drop during use, enabling effective removal of target gases under low temperature, high space velocity, and high humidity conditions. However, this method only provides a simple coating loading method between the catalyst and the support, and it is difficult to load the catalyst on a smooth metal substrate. In addition, the preparation method of coating adhesion by immersion generally requires the preparation of manganese-containing active component powder in advance, and then the manganese-containing active component powder is physically loaded and bound to the honeycomb support by coating, which easily increases the difficulty of preparation.

[0005] Furthermore, Chinese invention patent CN113477246A discloses a manganese-containing monolithic electro-assisted metal honeycomb catalyst. Although this catalyst can be directly grown in situ on a honeycomb support via hydrothermal reaction to form a shaped monolithic manganese-containing catalyst, and its catalytic decomposition efficiency is improved compared to catalysts containing transition metal oxides, the improvement is limited and cannot meet the practical application requirements for high catalytic decomposition efficiency. In addition, this preparation method is a hot water reaction method, which requires high temperature and high pressure, making the preparation conditions too harsh for industrialization.

[0006] In summary, the preparation of existing catalysts generally suffers from problems such as harsh preparation conditions, low decomposition catalytic activity, short service life, and low cost-effectiveness. Summary of the Invention

[0007] One of the objectives of this invention is to propose a method for preparing a platinum-manganese composite monolithic metal substrate catalyst. First, a mesh-like manganese oxide active thin layer is grown in situ on a metal substrate. Then, platinum particles are uniformly distributed on the mesh-like manganese oxide active thin layer to form a platinum-manganese composite monolithic metal substrate catalyst. The preparation conditions are mild, easy to scale up, and the obtained platinum-manganese composite monolithic metal substrate catalyst has high decomposition catalytic activity, long service life, and high cost performance, thus overcoming the shortcomings of the prior art.

[0008] The second objective of this invention is to provide a platinum-manganese composite monolithic metal substrate catalyst prepared by the above-mentioned method, which has high decomposition catalytic activity, long service life, high cost performance, and good application prospects.

[0009] The third objective of this invention is to propose the application of a platinum-manganese composite monolithic metal substrate catalyst in the catalytic decomposition of VOCs, which is beneficial to improving the catalytic decomposition efficiency of VOCs gas.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] 1. A method for preparing a platinum-manganese composite monolithic metal substrate catalyst, comprising the following steps:

[0012] A. Prepare the metal substrate and perform surface treatment on the metal substrate;

[0013] B. Add potassium permanganate to water and stir until homogeneous to obtain a manganese-containing precursor solution;

[0014] C. Immerse the metal substrate after surface treatment in step A in the manganese precursor solution in step B, take it out and rinse it with clean water, and dry it to obtain a metal substrate with a mesh-like manganese oxide active thin layer.

[0015] D. The metal substrate with the mesh-like manganese oxide active thin layer in step C is first immersed in a platinum complex solution of ethylenediaminetetraacetic acid, and then immersed in sodium borohydride solution I to obtain a metal substrate with platinum seeds deposited on the surface of the mesh-like manganese oxide active thin layer.

[0016] E. Mix chloroplatinic acid, sodium hydroxide, ethylenediamine, ethylenediaminetetraacetic acid and water, and stir until homogeneous to obtain a platinum-containing precursor solution;

[0017] F. The metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin film in step D is immersed in the platinum-containing precursor solution in step E, and sodium borohydride solution II is added dropwise during the immersion process to deposit platinum nanoparticles and obtain a platinum-manganese composite monolithic metal substrate catalyst.

[0018] Further, in step B, the concentration of potassium permanganate in the manganese-containing precursor solution is 0.01–0.03 g / L, and the pH value of the manganese-containing precursor solution is 6–7.

[0019] Further, in step D, the concentration of the platinum ethylenediaminetetraacetic acid complex solution is 0.1–0.3 g / L, and the pH value of the platinum ethylenediaminetetraacetic acid complex solution is 9–10; the metal substrate having a mesh-like manganese oxide active thin film is immersed in the platinum ethylenediaminetetraacetic acid complex solution for 0.15–0.25 h;

[0020] The concentration of sodium borohydride solution I is 0.05–0.2 g / L, and the metal substrate with a mesh-like manganese oxide active thin film is immersed in sodium borohydride solution I for 0.25–0.75 h.

[0021] Furthermore, in step E, the pH value of the platinum-containing precursor solution is 9-10;

[0022] In step F, the metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin film is immersed in the platinum-containing precursor solution at a immersion temperature of 60-80°C for 3-5 hours.

[0023] The platinum content in the platinum-manganese composite monolithic metal substrate catalyst is 0.05–0.3% by mass percentage.

[0024] Further, in step F, the metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin layer in step D is placed in the platinum-containing precursor solution in step E and soaked at 60-70°C for 2 hours, with 3 mL of sodium borohydride solution II added dropwise every 0.25 hours during the soaking process; then soaked at 80°C for 3-4 hours, with 5 mL of sodium borohydride solution II added dropwise every 0.5 hours during the soaking process; and the concentration of the sodium borohydride solution II is 0.05-0.20 g / L.

[0025] Further, in step E, the concentrations of chloroplatinic acid, sodium hydroxide, ethylenediamine, and ethylenediaminetetraacetic acid in the platinum-containing precursor solution are 0.226–0.340 mmol / L, 16–24 mmol / L, 46.4–69.6 mmol / L, and 118.96–178.44 mmol / L, respectively.

[0026] Furthermore, in step C, the surface-treated metal substrate is immersed in the manganese-containing precursor solution for 12 to 36 hours; and the drying temperature in the drying step is 80 to 100°C, and the drying time is 2 to 3 hours.

[0027] In step C, the manganese content in the metal substrate with the mesh-like manganese oxide active thin layer is 0.01 to 0.05% by mass percentage.

[0028] Further, in step A, a metal substrate is prepared and placed in detergent water for degreasing treatment. After soaking for 0.5 to 1 hour, it is taken out and rinsed with clean water. The degreased metal substrate is placed in a mixed acid solution of hydrofluoric acid and nitric acid and soaked at 35 to 45°C for 0.03 to 0.08 hours. After soaking, it is taken out and rinsed with clean water to obtain a surface-treated metal substrate.

[0029] The mixed acid solution of hydrofluoric acid and nitric acid includes the following raw materials: hydrogen fluoride, nitric acid and water, and the mixing ratio of hydrogen fluoride, nitric acid and water is (0.4~0.6):5:(44~45) by mass.

[0030] A platinum-manganese composite monolithic metal substrate catalyst is prepared using the above-described preparation method for platinum-manganese composite monolithic metal substrate catalysts.

[0031] An application of a platinum-manganese composite monolithic metal substrate catalyst in the catalytic decomposition of VOCs is described. The application method involves placing the platinum-manganese composite monolithic metal substrate catalyst in a reaction tube, and then introducing a catalyst with a concentration of 1 g / m³ into the reaction tube. 3 The reaction space velocity is 10000 h⁻¹ -1 The VOCs gas was detected online. The outlet of the reaction tube was connected to the inlet of the gas chromatograph. The residual VOCs gas in the reaction tube was detected online using the gas chromatograph. The decomposition catalytic temperature of the catalyst was recorded when the concentration of residual VOCs gas in the reaction tube was 90% and 10%, respectively.

[0032] The technical solutions provided in this application embodiment may include the following beneficial effects:

[0033] 1. In this technical solution, the metal substrate is first subjected to surface treatment, which helps to remove grease and passivation film from the surface of the metal substrate, exposing the metal substrate and making it easier to utilize the reducing properties of the metal substrate itself in subsequent processing to reduce and precipitate the manganese-containing precursor from the manganese-containing precursor solution in situ.

[0034] 2. A manganese-containing precursor solution is prepared, and a surface-treated metal substrate is immersed in the manganese-containing precursor solution. Utilizing the reducing properties of the metal substrate itself as an inducing agent, the manganese-containing precursor solution preferentially reduces and precipitates on the metal substrate surface, forming manganese oxide nuclei. Guided by these preferentially precipitated manganese oxide nuclei, the manganese-containing precursor continuously reduces, precipitates, and grows, ultimately forming active manganese oxide particles with specific crystal forms and morphologies on the metal substrate surface. By using the preferentially formed manganese oxide nuclei on the metal substrate surface as the basis for subsequent growth, the newly formed active manganese oxide particles can not only be uniformly distributed on the metal substrate surface but also firmly bonded to the metal substrate surface, forming a grid-like active manganese oxide thin layer with a regular array structure.

[0035] 3. In this technical solution, before depositing platinum nanoparticles, the metal substrate with the mesh-like manganese oxide active thin layer from step C is first immersed in a platinum ethylenediaminetetraacetic acid complex solution. Utilizing the complexing properties of the platinum ethylenediaminetetraacetic acid complex, the platinum ethylenediaminetetraacetic acid complex is adsorbed onto the surface of the mesh-like manganese oxide active thin layer. Then, it is immersed in sodium borohydride solution I. Utilizing the reducing properties of sodium borohydride solution I, the platinum ethylenediaminetetraacetic acid complex is reduced in situ, thereby achieving the deposition of a small amount of platinum seed crystals on the surface of the mesh-like manganese oxide active thin layer, ensuring the smooth and uniform deposition of platinum nanoparticles subsequently.

[0036] 4. By using platinum seed crystals as the basis for subsequent growth, the newly formed platinum nanoparticles can not only be uniformly distributed in a dotted pattern in the grid-like array of active thin layers of manganese oxide under the constraint of the grid-like thin layer, ensuring their catalytic activity; but also can be firmly bound to the grid-like active thin layer of manganese oxide, preventing them from falling off and causing catalytic performance failure. Detailed Implementation

[0037] This technical solution provides a method for preparing a platinum-manganese composite monolithic metal substrate catalyst, including the following steps:

[0038] A. Prepare the metal substrate and perform surface treatment on the metal substrate;

[0039] B. Add potassium permanganate to water and stir until homogeneous to obtain a manganese-containing precursor solution;

[0040] C. Immerse the metal substrate after surface treatment in step A in the manganese precursor solution in step B, take it out and rinse it with clean water, and dry it to obtain a metal substrate with a mesh-like manganese oxide active thin layer.

[0041] D. The metal substrate with the mesh-like manganese oxide active thin layer in step C is first immersed in a platinum complex solution of ethylenediaminetetraacetic acid, and then immersed in sodium borohydride solution I to obtain a metal substrate with platinum seeds deposited on the surface of the mesh-like manganese oxide active thin layer.

[0042] E. Mix chloroplatinic acid, sodium hydroxide, ethylenediamine, ethylenediaminetetraacetic acid and water, and stir until homogeneous to obtain a platinum-containing precursor solution;

[0043] F. The metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin film in step D is immersed in the platinum-containing precursor solution in step E, and sodium borohydride solution II is added dropwise during the immersion process to deposit platinum nanoparticles and obtain a platinum-manganese composite monolithic metal substrate catalyst.

[0044] To overcome the problems of harsh preparation conditions, low catalytic activity, short service life, and low cost-effectiveness in existing technologies, this technical solution proposes a method for preparing a platinum-manganese composite monolithic metal substrate catalyst, including six steps: A (surface treatment of the metal substrate), B (preparation of manganese-containing precursor solution), C (preparation of a mesh-like manganese oxide active thin layer), D (deposition of platinum seed crystals), E (preparation of platinum-containing precursor solution), and F (deposition of platinum nanoparticles). This method yields a platinum-manganese composite monolithic metal substrate catalyst with high decomposition catalytic activity, long service life, and high cost-effectiveness. Furthermore, the preparation conditions of this technical solution are mild and easy to scale up for production.

[0045] Specifically, existing technologies utilize immersion methods to achieve coating adhesion, loading catalyst slurry onto a honeycomb support to create a monolithic catalyst. However, this method is difficult to load catalysts onto smooth metal substrates and easily increases the difficulty of preparation. Additionally, existing technologies also employ hydrothermal reactions to directly grow monolithic manganese-containing catalysts on a honeycomb support in situ, but the improvement in catalytic decomposition efficiency is limited, and the preparation conditions are demanding, making industrialization difficult.

[0046] In this technical solution, the surface of the metal substrate is first treated to remove grease and passivation film, increasing the exposed surface of the metal. The reducing properties of the metal substrate are fully utilized to reduce and precipitate the manganese precursor in situ from the manganese precursor solution, resulting in the in-situ growth of a well-structured, grid-like active layer of manganese oxide on the metal substrate surface. This grid-like active layer of manganese oxide is then immersed in a platinum ethylenediaminetetraacetic acid (EDTA) complex solution. Utilizing the complexing properties of the platinum EDTA complex, the complex is adsorbed onto the surface of the metal substrate with the grid-like active layer of manganese oxide. Finally, the substrate is immersed in a sodium borohydride solution. In step I, the reducing properties of sodium borohydride solution I are used to reduce the platinum complex of ethylenediaminetetraacetic acid, thereby depositing a small amount of platinum seed crystals on the surface of a mesh-like manganese oxide active thin layer. Under the induction of the pre-activated platinum seed crystals, the platinum-containing precursor solution simultaneously undergoes precipitation, reduction, and growth to form platinum nanoparticles. These platinum nanoparticles are not only uniformly distributed in a dotted pattern within the mesh-like array of the manganese oxide active thin layer, ensuring catalytic activity, but also firmly bonded to the surface of the mesh-like manganese oxide active thin layer, preventing detachment and catalytic performance failure. Furthermore, the resulting platinum-manganese composite monolithic metal substrate catalyst utilizes not only the catalytic activity of manganese oxide but also the highly efficient catalytic activity of the noble metal platinum nanoparticles, significantly improving the decomposition catalytic efficiency. Simultaneously, due to the long lifespan of platinum nanoparticles, compared to a single manganese-containing catalyst, the platinum-manganese composite monolithic metal substrate catalyst obtained by this technique has a longer lifespan and higher decomposition catalytic efficiency. In addition, this preparation method does not require high temperature and high pressure conditions, the preparation conditions are mild, and it is easy to scale up for production. Meanwhile, this technical solution only requires the deposition of precious metal platinum nanoparticles on the surface, which greatly reduces the manufacturing cost compared with precious metal catalysts, and has extremely high cost performance.

[0047] More specifically, when an untreated metal substrate is directly immersed in the manganese-containing precursor solution in step B, the surface of the metal substrate is covered with grease and a passivation film formed by various metal oxides, preventing the metal substrate from being exposed. Utilizing the reducing properties of the metal substrate itself, the manganese-containing precursor solution is reduced and precipitated in situ, resulting in the in-situ growth of a well-structured, grid-like active thin layer of manganese oxides on the metal substrate surface. Therefore, in this technical solution, surface treatment of the metal substrate is performed first. This helps remove the grease and passivation film from the metal substrate surface, exposing the metal substrate and facilitating the subsequent processing by utilizing the reducing properties of the metal substrate itself to reduce and precipitate the manganese-containing precursor from the manganese-containing precursor solution in situ.

[0048] Secondly, a manganese-containing precursor solution is prepared, and a surface-treated metal substrate is immersed in the manganese-containing precursor solution. Utilizing the reducing properties of the metal substrate itself as an inducing agent, the manganese-containing precursor solution preferentially reduces and precipitates manganese oxide nuclei on the metal substrate surface. Guided by these preferentially precipitated manganese oxide nuclei, the manganese-containing precursor continuously reduces, precipitates, and grows, ultimately forming active manganese oxide particles with specific crystal forms and morphologies on the metal substrate surface. By using the preferentially generated manganese oxide nuclei on the metal substrate surface as the basis for subsequent growth, the newly formed active manganese oxide particles can not only be uniformly distributed on the metal substrate surface but also firmly bonded to the surface, forming a grid-like active manganese oxide thin layer with a regular array structure. Furthermore, this process requires no high temperature or high pressure conditions, nor does it require the addition of a reducing agent such as acetic acid to the manganese-containing precursor solution; it allows for in-situ reduction growth of a grid-like active manganese oxide thin layer with a regular array structure. The preparation conditions are simple and mild, which is conducive to large-scale application. It should be noted that in this step, the soaked metal substrate can also be removed and rinsed with water to remove the manganese-containing precursor solution remaining on the surface of the metal substrate. This avoids the reaction between the residual manganese-containing precursor solution with oxidizing properties and the reducing sodium borohydride solution I in subsequent steps, which would affect the reducing properties of sodium borohydride solution I and thus affect the subsequent deposition of platinum nanoparticles.

[0049] Furthermore, if the metal substrate with the mesh-like manganese oxide active thin layer from step C is directly placed into the platinum-containing precursor solution, platinum nanoparticles will grow disorderly on the mesh-like manganese oxide active thin layer, leading to the deactivation of the prepared platinum-manganese composite monolithic metal substrate catalyst. Therefore, in this technical solution, before depositing platinum nanoparticles, the metal substrate with the mesh-like manganese oxide active thin layer from step C is first immersed in a platinum ethylenediaminetetraacetic acid (EDTA) complex solution. Utilizing the complexing properties of the platinum ethylenediaminetetraacetic acid complex, the platinum ethylenediaminetetraacetic acid complex is adsorbed onto the surface of the mesh-like manganese oxide active thin layer. Then, it is immersed in sodium borohydride solution I. Utilizing the reducing properties of sodium borohydride solution I, the platinum ethylenediaminetetraacetic acid complex is reduced in situ, achieving the deposition of a small amount of platinum seed crystals on the surface of the mesh-like manganese oxide active thin layer, ensuring the smooth and uniform deposition of platinum nanoparticles. It should be noted that this step also includes cleaning the metal substrate with platinum seed crystals deposited on its surface to remove the sodium borohydride solution I.

[0050] Secondly, a platinum-containing precursor solution is first prepared. Then, a metal substrate with platinum seeds deposited on the surface of a mesh-like manganese oxide active thin film is immersed in the platinum-containing precursor solution. Under the induction of the platinum seeds, the platinum precursor in the precursor solution precipitates around the platinum seeds. During the immersion process, sodium borohydride solution II is added dropwise. Utilizing the reducing property of sodium borohydride solution II, the precipitated platinum-containing precursor is reduced in situ and continuously grows, eventually forming platinum nanoparticles on the surface of the mesh-like manganese oxide active thin film. In other words, the platinum precursor solution simultaneously precipitates, reduces, and grows to form platinum nanoparticles during this process. Furthermore, by using platinum seeds as the base point for subsequent growth, the newly formed platinum nanoparticles are not only uniformly distributed in a dotted pattern within the mesh-like array of the manganese oxide active thin film under the constraint of the mesh-like thin film, ensuring their catalytic activity, but they are also firmly bound to the mesh-like manganese oxide active thin film, preventing them from detaching and causing catalytic performance failure.

[0051] Preferably, in step A, the metal substrate includes any one of aluminum honeycomb, iron-chromium-aluminum, and nickel-chromium-aluminum.

[0052] In a preferred embodiment of this technical solution, the metal substrate is made of any one of aluminum honeycomb, iron-chromium-aluminum, and nickel-chromium-aluminum. Aluminum honeycomb, iron-chromium-aluminum, and nickel-chromium-aluminum all have weak reducing properties. By utilizing their own weak reducing properties, the manganese-containing precursor precipitated in the manganese-containing precursor solution can be reduced to active manganese oxide without the need to add additional reducing agents, thus saving manufacturing costs, simplifying the preparation process, and improving production efficiency.

[0053] To further clarify, in step B, the concentration of potassium permanganate in the manganese-containing precursor solution is 0.01–0.03 g / L, and the pH value of the manganese-containing precursor solution is 6–7.

[0054] If the concentration of potassium permanganate in the manganese-containing precursor solution is higher than 0.03 g / L, too much manganese oxide is formed, which is prone to agglomeration and does not easily form a uniformly distributed mesh-like thin layer. The specific surface area of ​​the mesh-like thin layer is low, making it difficult for the noble metal platinum nanoparticles to be uniformly distributed in the mesh-like manganese oxide active thin layer to obtain the desired high catalytic activity catalyst. If the concentration of potassium permanganate in the manganese-containing precursor solution is lower than 0.01 g / L, too little manganese oxide is formed, and the manganese oxide is only distributed in a dotted manner on the surface of the metal substrate, making it difficult to form a mesh-like thin layer. This causes the platinum nanoparticles, which are no longer constrained by the mesh array, to easily agglomerate and grow, leading to catalyst deactivation. Therefore, in a preferred embodiment of this technical solution, the concentration of potassium permanganate in the manganese precursor solution is limited to 0.01-0.03 g / L, so that the manganese oxide precipitated by in-situ reduction forms a uniformly distributed mesh-like thin layer, which increases the specific surface area of ​​the metal substrate. This is more conducive to the uniform distribution of platinum nanoparticles in the mesh-like array of the active thin layer formed by manganese oxide, avoiding the agglomeration and growth of platinum nanoparticles after the loss of mesh array constraint, which would lead to catalyst deactivation and ensure the catalytic effect of the catalyst.

[0055] Furthermore, limiting the pH of the manganese precursor solution to 6-7 can prevent corrosion and loss of the metal substrate under near-neutral conditions of pH 6-7, and is also more conducive to the formation of a uniform mesh-like active thin layer of manganese oxide during the in-situ reduction process.

[0056] To further clarify, in step D, the concentration of the ethylenediaminetetraacetic acid platinum complex solution is 0.1–0.3 g / L, and the pH value of the ethylenediaminetetraacetic acid platinum complex solution is 9–10; the immersion time of the metal substrate with the mesh-like manganese oxide active thin film in the ethylenediaminetetraacetic acid platinum complex solution is 0.15–0.25 h.

[0057] The concentration of sodium borohydride solution I is 0.05–0.2 g / L, and the metal substrate with a mesh-like manganese oxide active thin film is immersed in sodium borohydride solution I for 0.25–0.75 h.

[0058] In a preferred embodiment of this technical solution, the concentration of the ethylenediaminetetraacetic acid platinum complex solution, the immersion time of the metal substrate in the ethylenediaminetetraacetic acid platinum complex solution, the concentration of sodium borohydride solution I, and the immersion time of the metal substrate in sodium borohydride solution I are limited. On the one hand, this controls the particle size of the platinum seed crystals to below 1 nm, preventing the platinum seed crystals from becoming too large and easily detaching, thus failing to adhere to the surface of the manganese oxide active layer and thus failing to act as seed crystals. On the other hand, this helps to control the loading of platinum seed crystals to below 0.01 wt.%, ensuring that the platinum seed crystals are uniformly distributed in a dotted pattern in the mesh-like manganese oxide active thin layer. This controls the rate of in-situ precipitation of the platinum precursor solution under the induction of platinum seed crystals and the reduction effect of sodium borohydride solution II, allowing the formed platinum nanoparticles to be uniformly deposited and distributed on the surface of the mesh-like manganese oxide active thin layer, ensuring the decomposition catalytic activity of the obtained platinum-manganese composite monolithic metal substrate catalyst.

[0059] Furthermore, since active manganese oxides readily react in acidic environments, making the resulting mesh-like thin layer unstable, in a preferred embodiment of this technical solution, the pH of the ethylenediaminetetraacetic acid platinum complex solution is limited to a weakly alkaline environment of 9-10. This effectively prevents the active manganese oxides from reacting in acidic environments, ensuring the stability of the formed mesh-like thin layer. This provides conditions for the subsequent uniform distribution of platinum nanoparticles within the mesh-like array of the active thin layer formed by the manganese oxides, thus ensuring its catalytic activity.

[0060] To further clarify, in step E, the pH value of the platinum-containing precursor solution is 9-10;

[0061] In step F, the metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin film is immersed in the platinum-containing precursor solution at a immersion temperature of 60-80°C for 3-5 hours.

[0062] The platinum content in the platinum-manganese composite monolithic metal substrate catalyst is 0.05–0.3% by mass percentage.

[0063] In a preferred embodiment of this technical solution, the pH value of the platinum-containing precursor solution is 9-10. On the one hand, this avoids the reaction of active manganese oxides in an acidic environment, ensuring the stability of the formed mesh-like thin layer; on the other hand, in a weakly alkaline environment with a pH value of 9-10, the platinum-containing precursor solution can exist stably, improving the stability of the platinum-containing precursor solution deposition process.

[0064] The immersion temperature of the metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin layer is limited to 60–80 °C in a platinum-containing precursor solution. This allows for better control of the in-situ reduction and precipitation rate of the platinum-containing precursor, thereby controlling the size and distribution of platinum particles. The resulting platinum nanoparticles are kept within the range of 10–100 nm in size, ensuring that all platinum nanoparticles are uniformly distributed in a dotted pattern within the mesh-like array of the manganese oxide active thin layer. Furthermore, platinum nanoparticles that are too large or too small are prone to detaching from the mesh-like array of the manganese oxide active thin layer. Without the constraint of the mesh array, the platinum nanoparticles easily aggregate and grow, leading to catalyst deactivation.

[0065] Furthermore, the immersion time of the metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin layer in the platinum precursor solution is limited to 3-5 hours. This helps to ensure that all platinum ions in the platinum precursor solution are completely reduced and precipitated into platinum nanoparticles, so that the actual platinum loading in the catalyst is consistent with the theoretical amount of platinum precursor added in the electroless platinum plating solution, thereby improving the decomposition catalytic activity of the catalyst.

[0066] Furthermore, if the platinum content in the platinum-manganese composite monolithic metal substrate catalyst is less than 0.05%, the resulting catalyst exhibits low decomposition catalytic activity; conversely, if the platinum content exceeds 0.3%, production costs are easily increased. Therefore, in a preferred embodiment of this technical solution, the platinum content in the platinum-manganese composite monolithic metal substrate catalyst is limited to 0.05–0.3%, resulting in a high-performance catalyst at a lower cost.

[0067] To further explain, in step F, the metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin layer in step D is placed in the platinum-containing precursor solution in step E and soaked at 60-70°C for 2 hours, with 3 mL of sodium borohydride solution II added dropwise every 0.25 hours during the soaking process; then soaked at 80°C for 3-4 hours, with 5 mL of sodium borohydride solution II added dropwise every 0.5 hours during the soaking process; and the concentration of the sodium borohydride solution II is 0.05-0.20 g / L.

[0068] Because the concentration of the platinum-containing precursor solution is high in the initial stage of soaking and low in the later stage, the soaking temperature is lower and the amount of sodium borohydride solution II added is relatively higher in the early stage of soaking, while the soaking temperature is higher and the amount of sodium borohydride solution II added is relatively lower in the later stage of soaking. This ensures that the deposition rate of platinum nanoparticles remains consistent, which is more conducive to confining the platinum nanoparticles in the mesh-like array thin layer and ensuring the activity of the catalyst.

[0069] To further clarify, in step E, the concentrations of chloroplatinic acid, sodium hydroxide, ethylenediamine, and ethylenediaminetetraacetic acid in the platinum-containing precursor solution are 0.226–0.340 mmol / L, 16–24 mmol / L, 46.4–69.6 mmol / L, and 118.96–178.44 mmol / L, respectively.

[0070] In a preferred embodiment of this technical solution, the concentrations of chloroplatinic acid, sodium hydroxide, ethylenediamine, and ethylenediaminetetraacetic acid in the platinum-containing precursor solution are limited to 0.226–0.340 mmol / L, 16–24 mmol / L, 46.4–69.6 mmol / L, and 118.96–178.44 mmol / L, respectively, so that the molar ratio of platinum ions to ethylenediaminetetraacetic acid is limited to 1:(520–530), which allows the platinum-containing precursor solution to exist stably and improves the stability of the platinum-containing precursor solution deposition process.

[0071] To further explain, in step C, the immersion time of the surface-treated metal substrate in the manganese-containing precursor solution is 12 to 36 hours; and the drying temperature of the drying step is 80 to 100°C, and the drying time is 2 to 3 hours.

[0072] In step C, the manganese content in the metal substrate with the mesh-like manganese oxide active thin layer is 0.01 to 0.05% by mass percentage.

[0073] In a preferred embodiment of this technical solution, the immersion time of the surface-treated metal substrate in the manganese-containing precursor solution is limited to 12-36 hours. This preset time is a suitable reduction growth time for active manganese oxides, which is more conducive to the formation of a uniform mesh-like active manganese oxide thin layer during the in-situ reduction process.

[0074] Furthermore, if the drying temperature is too low and the drying time is too short, the moisture in the manganese oxide active thin layer cannot be completely removed; if the drying temperature is too high and the drying time is too long, the formed mesh-like manganese oxide active thin layer will agglomerate or deform due to overheating. Therefore, in a preferred embodiment of this technical solution, the drying temperature of the drying step is limited to 80-100°C, and the drying time is limited to 2-3 hours to ensure that the formed manganese oxide mesh-like thin layer can be completely dried without deformation, which is beneficial for the subsequent uniform deposition of platinum nanoparticles on its surface.

[0075] Furthermore, if the manganese content in the metal substrate with the mesh-like manganese oxide active thin layer is less than 0.01%, the low manganese content affects the uniformity of the mesh structure of the formed manganese oxide active thin layer, leading to uneven distribution of platinum nanoparticles and affecting the decomposition catalytic activity of the resulting catalyst. If the manganese content in the metal substrate with the mesh-like manganese oxide active thin layer is higher than 0.05%, the active manganese oxide is prone to agglomeration, making it difficult to form a mesh-like array thin layer, which can easily cause catalyst deactivation. Therefore, in this technical solution, the manganese content in the metal substrate with the mesh-like manganese oxide active thin layer is 0.01–0.05%, which helps to ensure the formation of a uniformly distributed mesh-like manganese oxide active thin layer and ensure the catalytic activity of the catalyst.

[0076] To further explain, in step A, a metal substrate is prepared and placed in detergent water for degreasing treatment. After soaking for 0.5 to 1 hour, it is taken out and rinsed with clean water. The degreased metal substrate is placed in a mixed acid solution of hydrofluoric acid and nitric acid and soaked at 35 to 45°C for 0.03 to 0.08 hours. After soaking, it is taken out and rinsed with clean water to obtain a surface-treated metal substrate.

[0077] The mixed acid solution of hydrofluoric acid and nitric acid includes the following raw materials: hydrogen fluoride, nitric acid and water, and the mixing ratio of hydrogen fluoride, nitric acid and water is (0.4~0.6):5:(44~45) by mass.

[0078] In a preferred embodiment of this technical solution, the metal substrate is soaked in detergent water for 0.5–1 hour, then removed and rinsed thoroughly with clean water to ensure complete removal of grease from the surface of the metal substrate. The degreased metal substrate is then immersed in a mixed acid solution of hydrofluoric acid and nitric acid to remove the passivation film on the surface of the metal substrate, exposing it. This facilitates subsequent processing by utilizing the reducing properties of the metal substrate itself to reduce and precipitate the manganese precursor from the manganese precursor solution in situ, resulting in the in-situ growth of a well-structured, grid-like active thin layer of manganese oxide on the surface of the metal substrate. Furthermore, when hydrofluoric acid or nitric acid is used alone, both can only remove a portion of the passivation film on the surface of the metal substrate, and the removal effect is relatively poor. Therefore, this technical solution uses a mixed acid solution of hydrofluoric acid and nitric acid to remove the passivation film on the surface of the metal substrate. The mixing ratio of hydrogen fluoride, nitric acid, and water is limited to (0.4-0.6):5:(44-45). The strong oxidizing power of nitric acid and the strong coordination properties of hydrofluoric acid work synergistically to rapidly and efficiently remove the passivation film from the metal substrate surface. Simultaneously, the soaking temperature and soaking time are limited to prevent excessive pickling, which could lead to a redox reaction between the acid solution and the metal substrate, consuming the metal substrate.

[0079] A platinum-manganese composite monolithic metal substrate catalyst is prepared using the above-described preparation method for platinum-manganese composite monolithic metal substrate catalysts.

[0080] This scheme also proposes a platinum-manganese composite monolithic metal substrate catalyst, which has high decomposition catalytic activity, long service life and high cost performance, and has good application prospects.

[0081] An application of a platinum-manganese composite monolithic metal substrate catalyst in the catalytic decomposition of VOCs is described. The application method involves placing the platinum-manganese composite monolithic metal substrate catalyst in a reaction tube, and then introducing a catalyst with a concentration of 1 g / m³ into the reaction tube. 3 The reaction space velocity is 10000 h⁻¹ -1 The VOCs gas was detected online. The outlet of the reaction tube was connected to the inlet of the gas chromatograph. The residual VOCs gas in the reaction tube was detected online using the gas chromatograph. The decomposition catalytic temperature of the catalyst was recorded when the concentration of residual VOCs gas in the reaction tube was 90% and 10%, respectively.

[0082] This technical solution also proposes the application of a platinum-manganese composite monolithic metal substrate catalyst in the catalytic decomposition of VOCs. The specific application method is as follows: place the platinum-manganese composite monolithic metal substrate catalyst in a reaction tube, and then introduce a catalyst with a concentration of 1 g / m³ into the reaction tube. 3 The reaction space velocity is 10000 h⁻¹ -1 The VOCs gas was removed; the outlet of the reaction tube was connected to the inlet of a gas chromatograph, and the residual VOCs gas in the reaction tube was detected online using gas chromatography. The decomposition catalytic temperature of the catalyst was recorded when the concentration of residual VOCs gas in the reaction tube was 90% and 10%, respectively. The results showed that the catalyst prepared by this technical method required a low decomposition catalytic temperature to decompose the same concentration of VOCs gas, and could effectively improve the activity of the catalyst in decomposing VOCs gas.

[0083] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0084] Example 1

[0085] A. Prepare a metal substrate and soak it in detergent water for 0.5 hours to remove oil. Then, remove it and rinse it with clean water to obtain a degreased metal substrate. Soak the degreased metal substrate in a mixed acid solution of hydrofluoric acid and nitric acid at 35°C for 0.08 hours. Then, remove it and rinse it with clean water to obtain a surface-treated metal substrate. The mixed acid solution of hydrofluoric acid and nitric acid includes hydrogen fluoride, nitric acid, and water, and the mixing ratio of hydrogen fluoride, nitric acid, and water is 0.5:5:44.5 by mass. The metal substrate is aluminum honeycomb.

[0086] B. Add potassium permanganate to water and stir until homogeneous to obtain a manganese precursor solution with a pH of 6 and a concentration of 0.02 g / L;

[0087] C. After surface treatment in step A, the metal substrate is immersed in the manganese precursor solution in step B for 24 hours, then removed and rinsed with clean water. After drying at 90°C for 2 hours, a metal substrate with a mesh-like manganese oxide active thin layer is obtained. The manganese content in the metal substrate with the mesh-like manganese oxide active thin layer is 0.01% by mass percentage.

[0088] D. The metal substrate with the mesh-like manganese oxide active thin layer in step C is first immersed in a platinum complex solution of ethylenediaminetetraacetic acid with a pH of 9 for 0.15 h, and then immersed in sodium borohydride solution I for 0.50 h to obtain a metal substrate with platinum seeds deposited on the surface of the mesh-like manganese oxide active thin layer.

[0089] E. Chloroplatinic acid, sodium hydroxide, ethylenediamine, ethylenediaminetetraacetic acid, and water were mixed and stirred until homogeneous to obtain a platinum-containing precursor solution with a pH of 9; wherein the concentrations of chloroplatinic acid, sodium hydroxide, ethylenediamine, and ethylenediaminetetraacetic acid in the platinum-containing precursor solution were 0.226 mmol / L, 24 mmol / L, 69.6 mmol / L, and 178.44 mmol / L, respectively.

[0090] F. The metal substrate with platinum seeds deposited on the surface of the mesh-like manganese oxide active thin layer in step D is placed in the platinum-containing precursor solution in step E. After soaking at 70°C for 2 hours, 3 mL of 0.05 g / L sodium borohydride solution II is added dropwise every 0.25 hours during the soaking process. Then, it is soaked at 80°C for 4 hours, with 5 mL of 0.05 g / L sodium borohydride solution II added dropwise every 0.5 hours during the soaking process. Platinum nanoparticles are deposited to obtain a platinum-manganese composite monolithic metal substrate catalyst. The platinum content in the platinum-manganese composite monolithic metal substrate catalyst is 0.1% by mass.

[0091] Example 2

[0092] A. Prepare a metal substrate and soak it in detergent water for 1 hour. Then, remove it and rinse it with clean water to obtain a degreased metal substrate. Soak the degreased metal substrate in a mixed acid solution of hydrofluoric acid and nitric acid at 40°C for 0.05 hours. Then, remove it and rinse it with clean water to obtain a surface-treated metal substrate. The mixed acid solution of hydrofluoric acid and nitric acid includes the following raw materials: hydrogen fluoride, nitric acid, and water. The mixing ratio of hydrogen fluoride, nitric acid, and water is 0.4:5:45 by mass. The metal substrate is iron-chromium-aluminum.

[0093] B. Add potassium permanganate to water and stir until homogeneous to obtain a manganese precursor solution with a pH of 7 and a concentration of 0.01 g / L;

[0094] C. The metal substrate after surface treatment in step A is immersed in the manganese precursor solution in step B for 12 hours, then removed and rinsed with clean water. After drying at 100°C for 3 hours, a metal substrate with a mesh-like manganese oxide active thin layer is obtained; wherein, the manganese content in the metal substrate with the mesh-like manganese oxide active thin layer is 0.03% by mass percentage.

[0095] D. The metal substrate with the mesh-like manganese oxide active thin layer in step C is first immersed in a platinum complex solution of ethylenediaminetetraacetic acid with a pH of 9 for 0.20 h, and then immersed in sodium borohydride solution I for 0.75 h to obtain a metal substrate with platinum seeds deposited on the surface of the mesh-like manganese oxide active thin layer.

[0096] E. Chloroplatinic acid, sodium hydroxide, ethylenediamine, ethylenediaminetetraacetic acid, and water were mixed and stirred until homogeneous to obtain a platinum-containing precursor solution with a pH of 10; wherein the concentrations of chloroplatinic acid, sodium hydroxide, ethylenediamine, and ethylenediaminetetraacetic acid in the platinum-containing precursor solution were 0.340 mmol / L, 16 mmol / L, 46.4 mmol / L, and 118.96 mmol / L, respectively.

[0097] F. The metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin film in step D is placed in the platinum-containing precursor solution in step E. After soaking at 60°C for 2 hours, 3 mL of 0.01 g / L sodium borohydride solution II is added dropwise every 0.25 hours during the soaking process; then it is soaked at 80°C for 3 hours, and 5 mL of 0.10 g / L sodium borohydride solution II is added dropwise every 0.5 hours during the soaking process; platinum nanoparticles are deposited to obtain a platinum-manganese composite monolithic metal substrate catalyst. The platinum content in the platinum-manganese composite monolithic metal substrate catalyst is 0.2% by mass percentage.

[0098] Example 3

[0099] A. Prepare a metal substrate and soak it in detergent water for 0.8 hours. Then, remove it and rinse it with clean water to obtain a degreased metal substrate. Soak the degreased metal substrate in a mixed acid solution of hydrofluoric acid and nitric acid at 45°C for 0.03 hours. Then, remove it and rinse it with clean water to obtain a surface-treated metal substrate. The mixed acid solution of hydrofluoric acid and nitric acid includes the following raw materials: hydrogen fluoride, nitric acid, and water. The mixing ratio of hydrogen fluoride, nitric acid, and water is 0.6:5:45 by mass. The metal substrate is nickel-chromium-aluminum.

[0100] B. Add potassium permanganate to water and stir until homogeneous to obtain a manganese precursor solution with a pH of 6 and a concentration of 0.03 g / L;

[0101] C. The metal substrate after surface treatment in step A is immersed in the manganese precursor solution in step B for 36 hours, then removed and rinsed with clean water. After drying at 80°C for 2 hours, a metal substrate with a mesh-like manganese oxide active thin layer is obtained; wherein, the manganese content in the metal substrate with the mesh-like manganese oxide active thin layer is 0.05% by mass percentage.

[0102] D. The metal substrate with the mesh-like manganese oxide active thin layer in step C is first immersed in a platinum complex solution of ethylenediaminetetraacetic acid with a pH of 10 for 0.25 h, and then immersed in sodium borohydride solution I for 0.25 h to obtain a metal substrate with platinum seeds deposited on the surface of the mesh-like manganese oxide active thin layer.

[0103] E. Chloroplatinic acid, sodium hydroxide, ethylenediamine, ethylenediaminetetraacetic acid, and water were mixed and stirred until homogeneous to obtain a platinum-containing precursor solution with a pH of 9; wherein the concentrations of chloroplatinic acid, sodium hydroxide, ethylenediamine, and ethylenediaminetetraacetic acid in the platinum-containing precursor solution were 0.310 mmol / L, 20 mmol / L, 55.7 mmol / L, and 160.30 mmol / L, respectively.

[0104] F. The metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin film in step D is placed in the platinum-containing precursor solution in step E. After soaking at 60–70°C for 2 hours, 3 mL of 0.20 g / L sodium borohydride solution II is added dropwise every 0.25 hours during this soaking process. Then, it is soaked at 80°C for 3 hours, with 5 mL of 0.20 g / L sodium borohydride solution II added dropwise every 0.5 hours during this soaking process. Platinum nanoparticles are deposited to obtain a platinum-manganese composite monolithic metal substrate catalyst. The platinum content in the platinum-manganese composite monolithic metal substrate catalyst is 0.3% by mass percentage.

[0105] Comparative Example 1

[0106] The preparation method and raw materials used in Comparative Example 1 are the same as those in the Example, except that Comparative Example 1 lacks steps D, E and F.

[0107] Comparative Example 2

[0108] The preparation method and raw materials used in Comparative Example 2 are the same as those in the examples. The difference is that Comparative Example 2 lacks steps B and C, that is, Comparative Example 2 only deposits platinum nanoparticles on a metal substrate.

[0109] The platinum-manganese composite monolithic metal substrate catalysts prepared in the examples and comparative examples were placed in a reaction tube, and then a reaction atmosphere with a concentration of 1 g / m3 and a reaction space velocity of 10000 h⁻¹ was introduced into the reaction tube. -1 Toluene gas was detected; the outlet of the reaction tube was connected to the inlet of a gas chromatograph, and the residual toluene gas in the reaction tube was detected online using gas chromatography. The decomposition catalytic temperature of the catalyst was recorded when the concentration of residual toluene gas in the reaction tube was 90% and 10%, respectively. The specific test results are shown in Table 1 below:

[0110] Table 1. Catalytic performance test results of different catalysts in the examples and comparative examples.

[0111] sample <![CDATA[T 10 / ℃]]> <![CDATA[T 90 / ℃]]> Example 1 160 190 Example 2 120 150 Example 3 110 130 Comparative Example 1 230 390 Comparative Example 2 190 240 Blank control (metallic nickel-chromium-aluminum substrate) 410 500

[0112] As can be seen from the performance test results in Table 1, the catalyst prepared by the method of platinum-manganese composite monolithic metal substrate catalyst has a lower decomposition catalytic temperature required to decompose toluene gas of the same concentration compared with Comparative Example 1 and Comparative Example 2. It can effectively improve the catalyst activity for decomposing toluene gas. That is, the catalyst obtained by this technical solution has better catalytic performance, and the higher the content of platinum element in the platinum-manganese composite monolithic metal substrate catalyst, the higher its catalytic activity.

[0113] It should be noted that T 10 / ℃ refers to the catalytic decomposition temperature of the catalyst when the concentration of residual VOCs gas in the reaction tube is 90%, i.e., T. 10 / ℃ refers to the decomposition catalytic temperature of the catalyst when the VOCs removal rate in the reaction tube is 10%; T 90 / ℃ refers to the catalytic decomposition temperature of the catalyst when the concentration of residual VOCs gas in the reaction tube is 10%, i.e., T. 90 / ℃ refers to the decomposition catalytic temperature of the catalyst when the VOCs removal rate in the reaction tube is 90%.

[0114] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a platinum-manganese composite monolithic metal substrate catalyst, characterized by, Includes the following steps: A. Prepare a metal substrate and immerse it in detergent water for degreasing treatment. After soaking for 0.5 to 1 hour, remove it and rinse it with clean water. Then, immerse the degreased metal substrate in a mixed acid solution of hydrofluoric acid and nitric acid at 35 to 45°C for 0.03 to 0.08 hours. Remove it and rinse it with clean water to obtain a surface-treated metal substrate. The metal substrate includes any one of aluminum honeycomb, iron-chromium-aluminum, and nickel-chromium-aluminum. The mixed acid solution of hydrofluoric acid and nitric acid includes the following raw materials: hydrogen fluoride, nitric acid and water, and the mixing ratio of hydrogen fluoride, nitric acid and water is (0.4~0.6):5:(44~45) by mass. B. Add potassium permanganate to water and stir until homogeneous to obtain a manganese-containing precursor solution; C. Immerse the metal substrate after surface treatment in step A in the manganese precursor solution in step B, take it out and rinse it with clean water, and dry it to obtain a metal substrate with a mesh-like manganese oxide active thin layer. D. The metal substrate with the mesh-like manganese oxide active thin layer from step C is first immersed in a platinum ethylenediaminetetraacetic acid complex solution, and then immersed in sodium borohydride solution I to obtain a metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin layer; wherein, the pH value of the platinum ethylenediaminetetraacetic acid complex solution is 9-10. E. Chloroplatinic acid, sodium hydroxide, ethylenediamine, ethylenediaminetetraacetic acid and water are mixed and stirred until homogeneous to obtain a platinum-containing precursor solution; wherein the pH value of the platinum-containing precursor solution is 9-10; F. The metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin film in step D is immersed in the platinum-containing precursor solution in step E, and sodium borohydride solution II is added dropwise during the immersion process to deposit platinum nanoparticles and obtain a platinum-manganese composite monolithic metal substrate catalyst.

2. The method of making a platinum-manganese composite monolithic metal-based catalyst according to claim 1, wherein, In step B, the concentration of potassium permanganate in the manganese-containing precursor solution is 0.01–0.03 g / L, and the pH value of the manganese-containing precursor solution is 6–7.

3. The method of making a platinum-manganese composite monolithic metal substrate catalyst according to claim 1, wherein, In step D, the concentration of the platinum ethylenediaminetetraacetic acid complex solution is 0.1–0.3 g / L; the immersion time of the metal substrate with the mesh-like manganese oxide active thin layer in the platinum ethylenediaminetetraacetic acid complex solution is 0.15–0.25 h; The concentration of sodium borohydride solution I is 0.05–0.2 g / L, and the metal substrate with a mesh-like manganese oxide active thin film is immersed in sodium borohydride solution I for 0.25–0.75 h.

4. The method of making a platinum-manganese composite monolithic metal substrate catalyst according to claim 1, wherein, In step F, the metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin film is immersed in the platinum-containing precursor solution at a immersion temperature of 60-80°C for 3-5 hours. The platinum content in the platinum-manganese composite monolithic metal substrate catalyst is 0.05–0.3% by mass percentage.

5. The method of making a platinum-manganese composite monolithic metal substrate catalyst according to claim 4, wherein, In step F, the metal substrate with platinum seed crystals deposited on the surface of the mesh-like manganese oxide active thin layer in step D is placed in the platinum-containing precursor solution in step E and soaked at 60-70°C for 2 hours, with 3 mL of sodium borohydride solution II added dropwise every 0.25 hours during the soaking process; then soaked at 80°C for 3-4 hours, with 5 mL of sodium borohydride solution II added dropwise every 0.5 hours during the soaking process; and the concentration of sodium borohydride solution II is 0.05-0.20 g / L.

6. The method of making a platinum-manganese composite monolithic metal substrate catalyst according to claim 1, wherein, In step E, the concentrations of chloroplatinic acid, sodium hydroxide, ethylenediamine, and ethylenediaminetetraacetic acid in the platinum-containing precursor solution are 0.226–0.340 mmol / L, 16–24 mmol / L, 46.4–69.6 mmol / L, and 118.96–178.44 mmol / L, respectively.

7. The method of making a platinum-manganese composite monolithic metal substrate catalyst according to claim 1, wherein, In step C, the surface-treated metal substrate is immersed in the manganese-containing precursor solution for 12 to 36 hours; and the drying temperature in the drying step is 80 to 100°C, and the drying time is 2 to 3 hours. In step C, the manganese content in the metal substrate with the mesh-like manganese oxide active thin layer is 0.01 to 0.05% by mass percentage.

8. A platinum-manganese composite monolithic metal-based catalyst characterized in that, It was prepared using the preparation method of the platinum-manganese composite monolithic metal substrate catalyst according to any one of claims 1 to 7.

9. Use of a platinum-manganese composite monolithic metal-based catalyst in the catalytic decomposition of VOCs, characterized in that, The platinum-manganese composite monolithic metal base catalyst as claimed in claim 8 is used in the following way: the platinum-manganese composite monolithic metal base catalyst is placed in a reaction tube, and then 1 g / m 3 of VOCs gas with a concentration of 1 g / m -1 and a reaction space velocity of 10000 h -1 is introduced into the reaction tube; the outlet of the reaction tube is connected to the inlet of a gas chromatograph, and the residual VOCs gas in the reaction tube is detected on line by the gas chromatograph, and the decomposition catalytic temperature of the catalyst when the concentration of the residual VOCs gas in the reaction tube is 90% and 10% respectively is recorded.