An integral conductive and thermally conductive manganese oxide catalyst, its preparation method and application

Abstract

This invention proposes a monolithic conductive and thermally conductive manganese oxide catalyst, its preparation method, and its applications, belonging to the field of nanomaterials technology. Combining pulsed deposition and electrodeposition methods, the ratio of potassium permanganate, manganese sulfate, and water is adjusted. By controlling the pulse voltage, frequency, duty cycle, and energizing time, the manganese oxide catalyst is uniformly grown on a conductive and thermally conductive support. After drying and calcination, the monolithic conductive and thermally conductive manganese oxide catalyst is obtained. The resulting monolithic catalyst exhibits advantages such as excellent conductivity, rapid heating, close contact between the surface manganese oxide and the support, and excellent stability; it has broad application prospects in petrochemical, fine chemical, and tail gas catalytic redox reactions.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, and particularly relates to an integral conductive and thermally conductive manganese oxide catalyst, its preparation method and application. Background Technology

[0002] Manganese oxide catalysts possess abundant lattice oxygen and surface oxygen, exhibiting excellent low-temperature catalytic performance. They demonstrate good catalytic purification capabilities for most volatile organic compounds and ozone, and are widely used in industrial air pollution control. However, powdered or granular manganese oxide catalysts face limitations in practical applications, hindering their effective catalytic performance. Furthermore, to further promote the activation of lattice oxygen and surface electron transfer capabilities on the manganese oxide surface, an electric current can be applied to the catalyst surface. Therefore, it is necessary to load manganese oxide onto a conductive support to prepare a monolithic conductive and thermally conductive manganese oxide catalyst, enabling uniform contact between air pollutants and the catalyst at high space velocities, resulting in high catalyst utilization and stability.

[0003] The main method used in industry to synthesize monolithic catalysts is the direct loading method. For example, patent CN105126822A uses an impregnation method to prepare a monolithic manganese oxide catalyst supported on a honeycomb ceramic. A cordierite honeycomb support is immersed in a manganese oxide catalyst and a boehmite slurry. After removal, excess slurry is purged with a high-pressure air gun, and the catalyst is dried to obtain the monolithic manganese oxide catalyst. This preparation method is simple, the reaction parameters are easy to control, the raw materials are widely available, the cost is low, and it is easy to popularize. However, the catalyst supported by the impregnation method has poor adhesion and is prone to detachment under high space velocities. Patent CN117960181A uses aluminum fiber as a substrate and grows a layer of boehmite in situ on the surface of the aluminum fiber using a hydrothermal method, thereby loading the active component and auxiliary components. This avoids the disadvantages of traditional coating methods, such as cumbersome steps, low loading of active components, and uneven distribution. It has the advantages of simple operation and less component detachment. However, this method has relatively harsh hydrothermal conditions and is not suitable for some metal supports.

[0004] In summary, the current methods for loading manganese oxide catalysts onto metals and other conductive supports suffer from problems such as low loading capacity, easy detachment, and harsh synthesis conditions. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes an integral conductive and thermally conductive manganese oxide catalyst, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the technical solutions of the present invention:

[0008] A method for preparing an integral conductive and thermally conductive manganese oxide catalyst includes the following steps:

[0009] A conductive and thermally conductive carrier is immersed in a mixed solution containing potassium permanganate and manganese sulfate. Then, manganese oxide is grown in situ on the conductive and thermally conductive carrier by pulse electrodeposition. After drying and calcination, a monolithic manganese oxide catalyst is prepared.

[0010] Beneficial effects: Applying pulsed voltage can significantly increase the migration and reduction rates of manganese ions on the conductive support surface, allowing more ions to be reduced and deposited on the conductive support in a short time, thereby accelerating the material growth rate. Simultaneously, the pulsed electrodeposition method, through the intermittent application of pulsed current, restores the ion concentration near the support surface, effectively reducing concentration polarization and ensuring the stability and uniformity of material growth. Furthermore, by changing the pulse frequency and duty cycle, crystal nucleation and growth can be adjusted, further controlling the grain size and enriching the material's microstructure and properties.

[0011] Preferably, the parameters in the pulse electrodeposition process are:

[0012] The pulse voltage is 10–220V, the pulse frequency is 2–300Hz, the duty cycle is 20–100%, and the power-on time is 1–6h.

[0013] Preferably, the conductive and heat-conducting carrier is one or more of the following: heating wire, conductive PTC heater, and electric heating rod.

[0014] Preferably, the conductive and thermally conductive carrier needs to undergo acid etching treatment for 2-4 hours before being immersed in the mixed solution;

[0015] The acid solution used in the acid etching is one or more of hydrochloric acid, sulfuric acid, oxalic acid, and acetic acid.

[0016] The volume concentration of the acid solution is 1-10%.

[0017] Beneficial effects: The present invention performs acid etching on the conductive and thermally conductive carrier for two reasons. First, it removes impurities and oxide layers from the carrier surface and increases its surface roughness, which is beneficial for the adhesion and growth of manganese ions during pulse electrodeposition, thereby increasing the contact area between the deposited layer and the carrier and improving the conductivity and thermal conductivity of the catalyst. Second, the microstructure of the carrier surface after acid etching changes, making the bond between the deposited layer and the carrier tighter. This helps to reduce peeling and cracking during pulse electrodeposition and improves the stability and durability of the catalyst.

[0018] Preferably, the mass ratio of potassium permanganate to manganese sulfate in the mixed solution is 1:0.5 to 1.

[0019] Beneficial effects: This invention selects manganese ions with different valence states, which can exhibit different electrochemical properties and reactivity during electrodeposition, providing the possibility of forming manganese oxides with specific crystal structures, morphologies, and properties. Furthermore, manganese ions with different valence states can form complex compound structures during electrodeposition, which promote electron transport and facilitate catalytic reactions.

[0020] Furthermore, the mass-to-volume ratio of potassium permanganate to deionized water in the mixed solution is 1g:100-120mL;

[0021] The mass-to-volume ratio of manganese sulfate to deionized water is 1g:150-170mL.

[0022] Preferably, the drying conditions are: a drying temperature of 105°C and a drying time of 8-16 hours.

[0023] Preferably, the calcination conditions are: calcination temperature of 250-450℃ and calcination time of 5-10h.

[0024] Furthermore, during the calcination process, the calcination temperature is increased from the drying temperature to 250–450°C at a heating rate of 1–5°C / min, and then held at this temperature for 5–10 hours.

[0025] The second technical solution of the present invention:

[0026] An integral conductive and thermally conductive manganese oxide catalyst is prepared by the above preparation method;

[0027] In the monolithic conductive and thermally conductive manganese oxide catalyst, the loading of manganese oxide is 1-3 wt.%, and the manganese oxide is in the nanoscale.

[0028] The third technical solution of this invention:

[0029] The above-mentioned monolithic conductive and thermally conductive manganese oxide catalyst is used in the selective catalytic oxidation of VOCs and ozone decomposition.

[0030] Preferably, the VOCs include one or more of toluene, formaldehyde, and ethyl acetate.

[0031] Preferably, the selective catalytic oxidation of VOCs employs a low-temperature electro-joule catalytic oxidation method.

[0032] Preferably, the ozone decomposition condition is room temperature catalysis.

[0033] Compared with the prior art, the present invention has the following advantages and technical effects:

[0034] This invention employs a pulsed in-situ growth method, which can enhance the temperature and surface electronic activity of the conductive and thermally conductive carrier by adjusting the pulse voltage and current frequency. This allows for the selective capture and growth of manganese ions on the carrier surface. The method is characterized by mild conditions, rapid surface catalyst growth rate, and high loading capacity, thereby improving its catalytic activity and stability.

[0035] The monolithic conductive and thermally conductive manganese oxide catalyst prepared by this invention can perform electrojoule catalytic oxidation of VOCs such as toluene, formaldehyde, and ethyl acetate at low temperatures, and can also perform highly active and stable catalytic decomposition of ozone at room temperature. Attached Figure Description

[0036] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0037] Figure 1 This is a scanning transmission electron microscope (SEM) image of the monolithic conductive and thermally conductive manganese oxide catalyst prepared in Example 1 of the present invention.

[0038] Figure 2 The X-ray diffraction (XRD) spectrum of the monolithic conductive and thermally conductive manganese oxide catalyst prepared in Example 2 of the present invention;

[0039] Figure 3 The diagram shows the activity comparison of the monolithic conductive and thermally conductive manganese oxide catalysts prepared in Examples 1 and 2 of this invention and the comparative samples 1-3 for catalytic ozone decomposition and toluene oxidation. Detailed Implementation

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0042] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0043] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0044] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0045] This invention discloses a method for preparing an integral conductive and thermally conductive manganese oxide catalyst, comprising the following steps:

[0046] a. Weigh a certain amount of potassium permanganate and manganese sulfate into a beaker, add deionized water, and stir with a magnetic stirrer until fully dissolved;

[0047] b. Slowly pour the manganese sulfate solution into the potassium permanganate solution, and continue stirring until the solution in the beaker gradually becomes cloudy, thus obtaining a mixed solution;

[0048] c. Immerse the acid-etched conductive and thermally conductive carrier into the mixed solution obtained in step b, and power the carrier with a pulse power supply, adjusting the pulse voltage, frequency, and duty cycle to allow manganese oxide to grow in situ on the carrier;

[0049] d. Place the product obtained in step c in a forced-air drying oven to dry it, and then calcine the dried product in a muffle furnace to obtain a monolithic manganese oxide catalyst.

[0050] In some preferred embodiments, in step a, the mass-to-volume ratio of potassium permanganate to deionized water is 1:100-120 mL, the mass ratio of manganese sulfate monohydrate to deionized water is 1:150-170 mL, and the mass ratio of potassium permanganate to manganese sulfate monohydrate is 1:0.5-1; the stirring speed of both the potassium permanganate solution and the manganese sulfate solution is 40-80 r / min, and the stirring time is 30-60 min.

[0051] In some preferred embodiments, in step b, the stirring speed of the mixed solution is 40-80 r / min, and the stirring time is 60-120 min.

[0052] In some preferred embodiments, in step c, the conductive heat carrier is one or more of the following: heating wire, conductive PTC heater, and electric heating rod;

[0053] The acid solution used for acid etching is one or more of hydrochloric acid, sulfuric acid, oxalic acid, and acetic acid.

[0054] The pulse voltage is 10–220V, the pulse frequency is 0–300Hz, the duty cycle is 20–100%, and the power-on time is 1–6h.

[0055] In some preferred embodiments, in step d, the drying temperature in the drying oven is 105°C, and the drying time is 8-16h; the calcination temperature range is 250-450°C, the calcination time is 5-10h, and the heating rate is 1-5°C / min.

[0056] All raw materials used in the embodiments of this invention were purchased commercially; potassium permanganate, manganese sulfate monohydrate and hydrochloric acid were purchased from Sinopharm Chemical Reagent Co., Ltd. and were of analytical grade; oxalic acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. and was of analytical grade.

[0057] Unless otherwise specified, the term "parts" used in the embodiments of this invention refers to "parts by weight".

[0058] The technical solution of the present invention will be further illustrated by the following embodiments.

[0059] Example 1

[0060] (1) Weigh 3.5g of potassium permanganate and 2.5g of manganese sulfate monohydrate into beakers, and then add 400mL of deionized water to each. Stir at 60r / min for 30min with a magnetic stirrer until fully dissolved.

[0061] (2) Slowly pour the manganese sulfate solution into the potassium permanganate solution and continue stirring at 60 r / min for 60 min until the solution in the beaker becomes turbid;

[0062] (3) Prepare a 5% (v / v) oxalic acid solution and etch the conductive PTC heater carrier for 4 hours. Afterward, immerse the carrier in the mixed turbid solution obtained in step (2) and power the carrier with a pulse power supply, adjusting the pulse voltage to 90V and the current density to 0.02A / mm. 2 The frequency was 100Hz, the duty cycle was 50%, and the power was applied for 4 hours to allow manganese oxide to grow in situ on the carrier.

[0063] (4) The obtained product was placed in a forced-air drying oven at 105°C for 12 hours. The dried product was then calcined in a muffle furnace at 350°C for 5 hours with a heating rate of 5°C / min. After cooling to room temperature, the monolithic manganese oxide catalyst was obtained.

[0064] Example 2

[0065] (1) Weigh 3.5g of potassium permanganate and 2.5g of manganese sulfate monohydrate into beakers, and then add 400mL of deionized water to each. Stir at 60r / min for 30min with a magnetic stirrer until fully dissolved.

[0066] (2) Slowly pour the manganese sulfate solution into the potassium permanganate solution and continue stirring at 60 r / min for 60 min until the solution in the beaker becomes turbid;

[0067] (3) Prepare a 1% (v / v) hydrochloric acid solution and etch the heating wire carrier for 2 hours. Then, immerse the carrier in the mixed turbid solution obtained in step (2) and power the carrier with a pulse power supply, adjusting the pulse voltage to 60V and the current density to 0.01A / mm. 2 The frequency was 200Hz, the duty cycle was 60%, and the power was applied for 1 hour to allow manganese oxide to grow in situ on the carrier.

[0068] (4) The obtained product was placed in a forced-air drying oven at 105°C for 12 hours. The dried product was then calcined in a muffle furnace at 450°C for 5 hours with a heating rate of 5°C / min. After cooling to room temperature, the monolithic manganese oxide catalyst was obtained.

[0069] Comparative preparation of control samples

[0070] Comparative Sample 1: An integral conductive and thermally conductive manganese oxide catalyst was prepared according to steps (1)-(4) in Example 1. The difference is that the conductive PTC heater carrier in step (3) was not acid-etched.

[0071] Comparative Sample 2: An integral conductive and thermally conductive manganese oxide catalyst was prepared according to steps (1)-(4) in Example 2. The difference is that the power supply in step (3) is DC power supply with a voltage of 60V and a power supply time of 1 hour.

[0072] Comparative Sample 3: An integral conductive and thermally conductive manganese oxide catalyst was prepared according to steps (1)-(4) in Example 2. The difference is that the power supply in step (3) is ordinary AC power supply with a voltage of 60V and a frequency of 50Hz, and the power is applied for 1 hour.

[0073] Effect verification

[0074] The monolithic conductive and thermally conductive manganese oxide catalysts prepared in Examples 1-2 and comparative samples 1-3 were subjected to catalytic effect tests on ozone decomposition and toluene oxidation, respectively. The specific catalytic test conditions were as follows:

[0075] (I) Catalytic Ozone Decomposition

[0076] [O3] = 100 ppm, N2 is the balance gas, total flow rate is 450 mL / min, and volumetric hourly space velocity is 60000 h⁻¹. -1 .

[0077] (II) Catalytic Toluene Oxidation

[0078] [C7H8] = 400 ppm, [O2] = 10%, N2 is the balance gas, total flow rate is 450 mL / min, and volumetric hourly space velocity is 60000 h⁻¹. -1 .

[0079] Since the catalytic effects of the monolithic conductive and thermally conductive manganese oxide catalyst on formaldehyde and ethyl acetate pollutants follow roughly the same pattern as those on toluene, only the experimental results of catalytic toluene oxidation are presented here.

[0080] Figure 1 This is a scanning transmission electron microscope (SEM) image of the monolithic conductive and thermally conductive manganese oxide catalyst prepared in Example 1 of this invention. From... Figure 1 As can be seen in the left figure, the synthesized manganese oxide catalyst has a distinct needle-like structure.

[0081] Figure 2 The image shows the X-ray diffraction (XRD) spectrum of the monolithic conductive and thermally conductive manganese oxide catalyst prepared in Example 2 of this invention. Figure 2 As can be seen from this, the present invention successfully synthesized a manganese oxide catalyst with high crystallinity.

[0082] Figure 3 This is a comparison of the catalytic ozone decomposition and toluene oxidation activities of the monolithic conductive and thermally conductive manganese oxide catalysts prepared in Examples 1 and 2 of this invention and comparative samples 1-3, where (a) represents catalytic ozone decomposition and (b) represents catalytic toluene oxidation. Figure 3 As can be seen from the above, the manganese oxide catalyst grown in situ by pulse electrolysis after acid etching exhibits superior catalytic performance. Specifically: (a) In this invention, the catalyst prepared in Examples 1-2 can achieve a near 100% catalytic effect on ozone at a temperature of around 70°C, while the ozone decomposition rate of Comparative Samples 1-3 is less than 80% at the same temperature, and Comparative Sample 2 is less than 50%, with its catalytic efficiency being far lower than that of Examples 1-2; (b) In this invention, the catalyst prepared in Examples 1-2 can achieve a near 100% catalytic effect on toluene oxidation at a temperature of around 250°C, while the catalytic effect of Comparative Samples 1-3 is only 50-60%. To achieve the same effect as Examples 1-2, the temperature needs to be increased to 400-500°C, further increasing the difficulty and complexity of the operation. Moreover, high temperature may also affect the structure and performance of the catalyst, further proving that the catalyst prepared in Examples 1-2 has low temperature, low energy consumption, high efficiency, and high stability.

[0083] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a monolithic electrically and thermally conductive manganese oxide catalyst, characterized by, The preparation method comprises the following steps: The conductive and heat-conductive carrier is immersed in a mixed solution containing potassium permanganate and manganese sulfate, and then manganese oxide is in-situ grown on the conductive and heat-conductive carrier by pulse electrodeposition, and then the whole manganese oxide catalyst is prepared by drying and calcining; The parameters in the pulse electrodeposition process are as follows: pulse voltage is 10-220 V, pulse frequency is 2-300 Hz, duty cycle is 20-100%, and power-on time is 1-6 h. The calcination conditions are as follows: calcination temperature is 250-450 ℃, and calcination time is 5-10 h.

2. The method for preparing an integral conductive and thermally conductive manganese oxide catalyst according to claim 1, characterized in that, The conductive and heat-conductive carrier is one or more of an electric heating wire, a conductive PTC heater, and an electric heating rod.

3. The method of claim 1, wherein the method further comprises the step of: The conductive and heat-conductive carrier needs to be subjected to acid etching treatment before being immersed in the mixed solution. ​ The acid solution used in the acid etching treatment is one or more of hydrochloric acid, sulfuric acid, oxalic acid, and acetic acid.

4. The method of claim 1, wherein the method further comprises the step of: The mass ratio of potassium permanganate to manganese sulfate in the mixed solution is 1:0.5-1. ​ 5. The method of claim 1, wherein the method further comprises the step of: The drying conditions are as follows: drying temperature is 105 ℃, and drying time is 8-16 h. ​ 6. The method of claim 1, wherein the method further comprises the step of: In the calcination process, the calcination temperature is increased from the drying temperature to 250-450 ℃ at a temperature increasing rate of 1-5 ℃ / min. ​ 7. A monolithic electrically and thermally conductive manganese oxide catalyst characterized by, The whole conductive and heat-conductive manganese oxide catalyst is prepared by the preparation method in any one of claims 1-6. The loading amount of manganese oxide in the whole conductive and heat-conductive manganese oxide catalyst is 1-3 wt.%.

8. Application of the whole conductive and heat-conductive manganese oxide catalyst in claim 7 in selective catalytic oxidation of VOCs and decomposition of ozone.

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