A 3D nanoflower-like MnO 2 Catalyst and its preparation method and application

Abstract

The present invention provides a 3D nano-flower-shaped MnO2-based catalyst and its preparation method and application, which relates to the field of air pollution control. A preparation method of a 3D nano-flower-shaped MnO2-based catalyst comprises: mixing a reducing agent, an oxidizing agent and a morphology directing agent, then heating to react, and then sequentially cooling, filtering, washing and drying, and then calcining to obtain a reducing agent; the reducing agent comprises Mn 2+ Compounds and / or Ce 3+ Compound. The 3D nanoflower-like MnO2-based catalyst is prepared according to the preparation method; the catalyst has a 3D flower-like structure in the form of staggered nanosheets; the 3D nanoflower-like MnO2-based catalyst is used for catalytic oxidation of ethane. The present invention uses a simple hydrothermal method to prepare a 3D flower-like MnO2-based catalyst, and the catalyst is used for catalytic oxidation of ethane. The synthesis process is simple, the raw material source is abundant and cheap, and it is easy to mass produce. The obtained catalyst has high activity and strong stability, and is especially used for catalytic oxidation of ethane, and a conversion rate of 90% can be achieved at 310°C.

Description

Technical Field

[0001] The invention belongs to the field of air pollution control, and in particular relates to a 3D nano-flower-shaped MnO2-based catalyst and a preparation method and application thereof. Background Art

[0002] Volatile organic compounds (VOCs) usually refer to organic compounds with a boiling point of 50-260°C under normal pressure, such as alkanes, aromatic hydrocarbons, alcohols, aldehydes, ketones and esters. Among them, olefins, aromatic hydrocarbons, alkanes, etc. have a high potential to generate ozone, which can lead to the formation of photochemical smog and secondary organic aerosols, which not only harm the atmospheric environment, but also affect human health and induce a series of diseases. Therefore, it is urgent to find effective control technologies for VOCs to reduce VOCs emissions.

[0003] VOCs come from a wide range of sources, involving many ways such as production and life. The Chinese anthropogenic VOCs emission inventory and on-site observations show that industrial sources are one of the largest sources. The emission of large-volume, low-concentration organic waste gas is more common in industrial production. When the waste gas recovery value is low or does not need to be recovered, adsorption concentration or catalytic combustion technology is often used for treatment. Among them, the catalytic oxidation method has the advantages of a wide range of applications, high purification efficiency, and no secondary pollution. It can oxidize VOCs into environmentally friendly CO2 and H2O at a relatively low temperature (250℃-500℃), so it has received widespread attention. The core of this method is the catalyst, which is mainly divided into two categories: precious metals and non-precious metals. The advantages of precious metal catalysts are good low-temperature activity, long service life, and good selectivity, but their application is limited by their high price, easy sintering, weak anti-poisoning ability, and easy generation of chlorinated by-products. Non-precious metal catalysts, because of their abundant reserves and low prices, have catalytic activity that is not as good as that of precious metal catalysts, but their catalytic activity can be optimized by adjusting their crystal structure, morphology, and surface properties during the synthesis process. MnO2-based materials are widely used to remove VOCs, NO due to their unique characteristics such as high abundance, low price, low toxicity, good redox ability, and variable valence state. x, CO, ozone, soot and other pollutants. Among VOCs, low-carbon alkanes usually require higher temperatures to activate because of their stable structure, so the development of low-temperature catalysts for deep oxidation of low-carbon alkanes is full of challenges. CN106582269A discloses a method for catalytic oxidation of ethane with a modified iron catalyst, but the catalyst preparation procedure is complicated and time-consuming, and the preparation process also involves the discharge of a large amount of waste alkali liquid, and most importantly, the efficiency of ethane conversion is not high. CN111266100A discloses an integral catalyst for catalytic combustion of ethane and a preparation method thereof, including a cordierite honeycomb ceramic carrier, a transition coating, an active coating and an active component, the main components of which are SiO2, γ-Al2O3, Pd and samarium oxide. However, the catalyst preparation process is cumbersome and has high energy consumption. The Pt-Nb / ZrO2 catalyst reported in the literature (Chin J Catal 2021, 42 (12), 2287) exhibits excellent ethane oxidation activity. However, as precious metal catalysts, they have common problems such as high application cost, easy sintering at high temperatures and weak resistance to poisoning.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a 3D nanoflower-shaped MnO2-based catalyst and a preparation method and application thereof to solve the above problems.

[0006] In order to achieve the above objectives, the present invention particularly adopts the following technical solutions:

[0007] A method for preparing a 3D nanoflower-shaped MnO2-based catalyst comprises: mixing a reducing agent, an oxidizing agent and a morphology directing agent, then heating the mixture for reaction, and then sequentially cooling, filtering, washing and drying the mixture, and then calcining the mixture to obtain the catalyst;

[0008] The reducing agent includes Mn 2+ Compounds and / or Ce 3+ Compound.

[0009] Optionally, the oxidant comprises persulfate and / or permanganate.

[0010] Optionally, the persulfate includes any one or more of ammonium persulfate, potassium persulfate or potassium hydrogen persulfate;

[0011] Preferably, the permanganate includes any one or more of lithium permanganate, sodium permanganate, potassium permanganate, ammonium permanganate, calcium permanganate, barium permanganate, zinc permanganate, magnesium permanganate, mercuric permanganate, cadmium permanganate or rubidium permanganate.

[0012] Optionally, the morphology directing agent includes Ce 3+ Compounds;

[0013] Preferably, the Ce 3+ The compound includes any one or more of cerous sulfate, ammonium cerous sulfate, ammonium cerous nitrate or cerous nitrate.

[0014] Optionally, the Mn 2+ The compound includes any one or more of manganese sulfate, manganese nitrate, manganese acetate, manganese carbonate, manganese gluconate, manganese oxalate, manganese formate or manganese citrate.

[0015] Optionally, the blending comprises: adding the reducing agent to a mixed system of the oxidizing agent and the morphology directing agent under stirring;

[0016] Preferably, the stirring temperature is 10-40°C;

[0017] Preferably, the stirring time is 10-60 min.

[0018] Optionally, the heating rate is 0.5-5°C / min;

[0019] Preferably, the target temperature of the heating is 90-150°C; preferably, the heating also includes keeping the temperature for 0.5-24h after heating to the target temperature.

[0020] Optionally, the calcination includes: calcining at a temperature of 300-500° C. for 1-8 hours at a rate of 0.1-5° C. / min.

[0021] During the process of adding the reducing agent to the oxidizing agent during blending, if the direct mixing or dropwise acceleration is too fast, the size of the formed nanoparticles will become larger, the specific surface area will decrease, the exposed active sites will become fewer, and the catalytic performance will decrease. If the stirring temperature is too low or too high, the size of the nanoparticles will exceed the size range of the catalyst provided by the present invention. A heating rate that is too fast will affect the growth direction of the nanoparticles, and ultimately the morphological characteristics of the catalyst provided by the present invention cannot be obtained. If the target temperature for heating and calcining exceeds the range, the catalyst crystal form will be converted into α and / or γ crystal form instead of the required β crystal form. Using the holding time at the target temperature will make the size and morphology of the formed nanoparticles more regular.

[0022] The present invention provides a method for preparing a 3D flower-shaped MnO2-based catalyst, using Mn 2+ Salt, Ce 3+ Salt is used as a reducing agent, and persulfate or permanganate is used as an oxidant to generate MnO2 material composed of [MnO6] octahedral structure. 3+ The morphology-guided effect in the redox reaction of salt and oxidant makes the final MnO2-based catalyst a 3D flower-like structure in the form of staggered nanosheets.

[0023] Ce 3+Salt acts as a reducing agent and also a morphology guiding agent. Without adding other template agents, a 3D flower-like structure composed of staggered nanosheets is formed. This structural feature is conducive to the generation of defects on the catalyst surface, exposing more active sites; strengthening the mass transfer of reactants / products and reducing carbon deposition. In short, this structural feature can not only improve the inherent catalytic activity of the catalyst, but also promote the improvement of overall performance.

[0024] The present invention provides a 3D nano-flower-shaped MnO2-based catalyst, which is prepared according to the preparation method; the catalyst has a 3D flower-shaped structure in the form of staggered stacking of nanosheets.

[0025] The present invention also provides an application of the 3D nanoflower-shaped MnO2-based catalyst, wherein the catalyst is applied to catalytic oxidation of ethane.

[0026] The 3D nanoflower-shaped MnO2-based catalyst provided by the present invention is applied to the catalytic oxidation of ethane, and has excellent performance, which is attributed to the CeO2-MnO2 solid solution formed after Ce incorporation not only inhibits grain growth, but also increases the specific surface area of ​​the catalyst, thereby exposing more active sites and enhancing the adsorption and activation of ethane. More importantly, Ce incorporation increases oxygen vacancies on the catalyst surface, thereby enhancing the mobility of lattice oxygen. In the oxidation process of alkanes, CH bond cleavage is the rate-controlling step, and lattice oxygen is the key species for activating CH bonds. Therefore, the highly mobile lattice oxygen will greatly promote the dissociation of ethane, and will also enhance the adsorption of O2 and weaken the influence of H2O competitive adsorption, so that the 3D nanoflower-shaped MnO2-based catalyst can maintain excellent ethane catalytic oxidation performance even in the presence of H2O.

[0027] Beneficial effects of the present invention:

[0028] The preparation method provided by the present invention uses cheap and readily available raw materials, has a simple preparation process, good controllability, and is convenient for industrial scale-up production. 2+ Salt is used as a reducing agent, and persulfate or permanganate is used as an oxidant to generate MnO2 material composed of [MnO6] octahedral structure. 3+ The morphology-guided effect in the redox reaction of salt and oxidant makes the final MnO2-based catalyst a 3D flower-like structure in the form of staggered nanosheets, which improves the overall performance of the catalyst.

[0029] The 3D nano-flower-shaped MnO2-based catalyst provided by the present invention has a CeO2-MnO2 solid solution formed after Ce is doped, which inhibits grain growth and increases the specific surface area of ​​the catalyst, thereby exposing more active sites. At the same time, it increases the oxygen vacancies on the catalyst surface, enhances the mobility of lattice oxygen, and further improves the catalytic oxidation performance. The catalyst provided by the present invention not only has high catalytic oxidation activity, but also has strong stability and good water resistance. It has been verified by experiments that it maintains excellent catalytic oxidation performance under dry or water-containing conditions.

[0030] The 3D nanoflower-shaped MnO2-based catalyst provided by the present invention is applied to the catalytic oxidation of ethane, and a 90% conversion rate of ethane can be achieved at 310°C; experimental verification shows that even in the presence of water, at 350°C, the conversion rate of ethane always remains at a high level. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 The 3D flower-shaped MnO2-based catalyst Ce prepared in Example 1 0.5 SEM image of Mn1;

[0033] Figure 2 The 3D flower-shaped MnO2-based catalyst Ce prepared in Example 1 0.5 HRTEM image of Mn1;

[0034] Figure 3 The 3D flower-shaped MnO2-based catalyst Ce prepared in Example 1 0.5 XPS full spectrum of Mn1;

[0035] Figure 4 The XRD diffraction patterns of the products obtained in Examples 1-4 and Comparative Examples 1-2;

[0036] Figure 5 The performance diagram of catalytic oxidation of ethane by the products obtained in Examples 1-4 and Comparative Examples 1-2;

[0037] Figure 6 The catalyst Ce prepared in Example 1 0.5 Schematic diagram of CO2 yield from Mn1-catalyzed oxidation of ethane;

[0038] Figure 7 The catalyst Ce under dry conditions 0.5Performance diagram of Mn1 catalytic oxidation of ethane at 350°C;

[0039] Figure 8 The catalyst Ce under the condition of H2O 0.5 Performance diagram of Mn1 catalytic oxidation of ethane at 350℃. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] Example 1

[0042] According to the preparation method provided by the present invention, 3D nanoflower-shaped MnO2-based catalyst is produced, and the specific steps are as follows:

[0043] S1: Dissolve 8.684 g of Ce(NO3)3·6H2O and 4.564 g of (NH4)2S2O8 in 60 mL of deionized water and stir until completely dissolved, which is referred to as solution 1;

[0044] S2: Dissolve 6.921 g of Mn(C2H3O2)2 in 60 mL of deionized water and stir until completely dissolved, which is called solution 2.

[0045] S3: Under magnetic stirring, add the solution 2 obtained from S2 dropwise into the solution 1 obtained from S1. After the addition is complete, continue stirring for 60 minutes. Keep the temperature at 25°C during the whole process.

[0046] S4: The blended solution obtained in S3 was transferred to a stainless steel reactor equipped with a 100 mL polytetrafluoroethylene liner, heated to 120°C at a heating rate of 2°C / min, and maintained for 60 min;

[0047] S5: After the reaction is completed, wait until the temperature of the S4 reactor drops to room temperature, filter the obtained sample, wash it three times with deionized water, and dry it in an oven at 80°C;

[0048] S6: The obtained powder was placed in a muffle furnace and heated to 400°C at a heating rate of 1°C / min, maintained for 4 h, and cooled naturally to room temperature to obtain a 3D flower-shaped MnO2-based catalyst, denoted as Ce 0.5 Mn1.

[0049] Example 2

[0050] The difference from Example 1 is that the amount of Ce(NO3)3·6H2O used in S1 is 0.868 g.

[0051] The obtained product is recorded as Ce 0.05 Mn1.

[0052] Example 3

[0053] The difference from Example 1 is that the amount of Ce(NO3)3·6H2O used in S1 is 1.737 g.

[0054] The obtained product is recorded as Ce 0.1 Mn1.

[0055] Example 4

[0056] The difference from Example 1 is that the amount of Ce(NO3)3·6H2O used in S1 is 2.953 g.

[0057] The obtained product is recorded as Ce 0.17 Mn1.

[0058] Comparative Example 1

[0059] When synthesizing MnO2, no Ce is added 3+ The amount and preparation steps of salt, (NH4)2S2O8 and Mn(C2H3O2)2 are the same as those in Example 1. The specific steps are as follows:

[0060] 4.564g of (NH4)2S2O8 and 6.921g of Mn(C2H3O2)2 were dissolved in 60mL of deionized water respectively and stirred until completely dissolved; under magnetic stirring, the Mn(C2H3O2)2 solution was added to the (NH4)2S2O8 solution, and after the addition was completed, stirring was continued for 60min, and the whole process was kept at 25°C; the mixed solution was transferred to a stainless steel reactor equipped with 100mL of polytetrafluoroethylene lining, heated to 120°C at a heating rate of 2°C / min, and maintained for 60min; when the temperature of the reactor dropped to room temperature, the obtained sample was filtered, washed repeatedly three times with deionized water, and placed in an 80°C oven for drying; the obtained powder was placed in a muffle furnace, heated to 400°C at a heating rate of 1°C / min, maintained for 4h, and after natural cooling, a MnO2 catalyst was obtained, recorded as MnO2.

[0061] Comparative Example 2

[0062] When synthesizing CeO2, no Mn is added 2+ The amounts of salt, (NH4)2S2O8 and Ce(NO3)3·6H2O and the preparation steps are the same as those in Example 1. The specific steps are as follows:

[0063] 0.456g of (NH4)2S2O8 and 1.737g of Ce(NO3)3·6H2O were dissolved in 60mL of deionized water respectively and stirred until completely dissolved; under magnetic stirring, Ce(NO3)3 solution was added to (NH4)2S2O8 solution, and after the addition was completed, stirring was continued for 60min, and the whole process was kept at 25°C; the blended solution was transferred to a stainless steel reactor equipped with 100mL of polytetrafluoroethylene lining, heated to 120°C at a heating rate of 2°C / min, and maintained for 60min; when the temperature of the reactor dropped to room temperature, the obtained sample was filtered, washed repeatedly three times with deionized water, and placed in an 80°C oven for drying; the obtained powder was placed in a muffle furnace, heated to 400°C at a heating rate of 1°C / min, maintained for 4h, and naturally cooled to room temperature to obtain a CeO2 catalyst, recorded as CeO2.

[0064] The structures of the products obtained in Examples 1-4 and Comparative Examples 1-2 were analyzed as follows:

[0065] 3D flower-shaped MnO2-based catalyst Ce prepared in Example 1 0.5 The surface scanning electron microscope (SEM) image of Mn1 is as follows Figure 1 As shown by Figure 1 It can be seen that the catalyst Ce 0.5 Mn1 presents a 3D nanoflower structure formed by stacking nanosheets, with a diameter of 0.1-4 μm and a thickness of 5-30 nm. 0.5 The HRTEM image of Mn1 is shown in Figure 2 As shown by Figure 2 It can be seen that Ce 0.5 Mn1 shows β-MnO2 lattice fringes.

[0066] For catalyst Ce 0.5 Mn1 was tested by XPS, and the XPS full spectrum is shown as follows Figure 3 As shown by Figure 3 The signal of cerium element can be seen, proving that cerium element is doped into the 3D flower-like MnO2-based catalyst.

[0067] Figure 4 The XRD diffraction patterns of the products obtained in Examples 1-4 and Comparative Examples 1-2 are shown in FIG. Figure 4 It can be seen that the catalysts prepared in Example 1 and Example 4 show the β-MnO2 crystal structure, and the catalysts prepared in Example 2 and Example 3 show both α-MnO2 and β-MnO2 crystal structures. No diffraction peak of CeO2 appears in Examples 1-4, indicating that the cerium element is doped into the MnO2 lattice or CeO2 is uniformly distributed.

[0068] The properties of the products obtained from Examples 1-4 and Comparative Examples 1-2 were tested:

[0069] (1) Activity test:

[0070] The catalyst prepared in Examples 1-4 was pelletized and 40-60 mesh particles were taken for evaluation of ethane catalytic oxidation activity in a fixed bed microreactor with an inner diameter of 6 mm. The reaction conditions were: catalyst dosage 0.2 g, O2 concentration 5 vol.%, space velocity 40000 mL h -1 g cat -1 , the test results are as follows Figure 5 and Figure 6 shown.

[0071] Figure 5 The performance diagram of the catalytic oxidation of ethane by the products obtained in Examples 1-4 and Comparative Examples 1-2 is shown in FIG. Figure 5 It can be seen that the 3D flower-shaped MnO2-based catalyst Ce obtained in Examples 1-4 0.5 Mn1、Ce 0.05 Mn1、Ce 0.1 Mn1 and Ce 0.17 The overall effect of Mn1 on catalytic oxidation of ethane is significantly better than that of MnO2 and CeO2 provided in Comparative Examples 1-2. 0.5 Mn1 exhibited the best ethane oxidation activity, with a temperature of 310 °C for 90% ethane conversion. Figure 6 For Ce 0.5 Schematic diagram of CO2 yield from Mn1 catalytic oxidation of ethane. It can be seen that ethane is mainly catalytically oxidized to CO2 and H2O, with no other by-products generated.

[0072] (2) Stability test:

[0073] The 3D flower-shaped MnO2-based catalyst Ce provided by the present invention was tested under dry and H2O-containing conditions. 0.5 The stability of Mn1 for ethane catalytic oxidation at 350°C is as follows:

[0074] The reaction gas composition under dry conditions is: 0.05 vol.% C2H6, 5 vol.% O2 / Ar, mass space velocity: 40000 mLh - 1 g cat -1 ; Test results such as Figure 7 shown.

[0075] The reaction gas composition under H2O-containing conditions is: 0.05 vol.% C2H6, 5 vol.% O2 / Ar, 2 vol.% H2O, mass space velocity: 40000 mLh -1 g cat -1 , the test results are as follows Figure 8 shown.

[0076] according to Figure 7 and Figure 8 It can be seen that, whether dry or containing H2O, the catalyst Ce 0.5 Mn1 always maintains excellent ethane conversion performance and strong stability.

[0077] The 3D flower-shaped MnO2-based catalyst provided by the present invention is used for ethane catalytic oxidation reaction. 3+ and Mn 2+ When the addition ratio is 0.5, the catalyst exhibits the best ethane catalytic oxidation performance, and can achieve 90% ethane conversion rate at 310°C. The products are CO2 and H2O, and no other by-products are generated. It has good stability and strong water resistance. The preparation method is simple, low-cost, and has good controllability, and is easy to prepare on a large scale.

[0078] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. Application of a 3D nanoflower-shaped MnO2-based catalyst, characterized in that: The 3D nanoflower-shaped MnO2-based catalyst is applied to catalytic oxidation of ethane; The preparation method of the 3D nanoflower-shaped MnO2-based catalyst comprises the following steps: S1: Ce 3+ The compound and the oxidant are dissolved in deionized water and stirred until completely dissolved to obtain solution 1; S2: Mn 2+ The compound was dissolved in deionized water and stirred until completely dissolved to obtain solution 2; S3: under magnetic stirring, add the solution 2 obtained from S2 dropwise into the solution 1 obtained from S1. After the addition is complete, continue stirring for 10-60 minutes. Keep the temperature at 10-40°C during the whole process to obtain a blended solution. S4: Transfer the blended solution obtained in S3 to a stainless steel reactor lined with polytetrafluoroethylene, heat to 90-150°C at a heating rate of 0.5-5°C / min, and maintain for 0.5-24h; S5: After the reaction in S4 is completed and the temperature of the reactor drops to room temperature, the obtained sample is filtered, washed three times with deionized water, and dried in an oven at 80°C to obtain a solid powder; S6: calcining the solid powder obtained in S5 at 300-500°C for 1-8h at a rate of 0.1-5°C / min, and cooling naturally to room temperature to obtain the 3D nanoflower-shaped MnO2-based catalyst, wherein the molar ratio of Ce to Mn in the catalyst is 0.5:1; The oxidant is selected from any one or more of ammonium persulfate, potassium persulfate, potassium hydrogen persulfate, lithium permanganate, sodium permanganate, potassium permanganate, ammonium permanganate, calcium permanganate, barium permanganate, zinc permanganate, magnesium permanganate, mercuric permanganate, cadmium permanganate or rubidium permanganate; The Ce 3+ The compound is selected from any one or more of cerous sulfate, cerous ammonium sulfate, cerous ammonium nitrate or cerous nitrate; The Mn 2+ The compound is selected from any one or more of manganese sulfate, manganese nitrate, manganese acetate, manganese carbonate, manganese gluconate, manganese oxalate, manganese formate or manganese citrate.

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