A pure phase alkaline earth metal mn-based perovskite catalyst and a preparation method thereof

Abstract

This disclosure presents a pure-phase alkaline earth metal Mn-based perovskite catalyst and its preparation method, belonging to the field of catalytic material preparation technology. The preparation method includes: weighing the A-site ion raw material corresponding to the product and manganese acetate, adding deionized water and stirring until completely dissolved, then continuing stirring for a first time to obtain a metal ion solution; adding a complexing agent to the metal ion solution, stirring until glycine is completely dissolved, then continuing stirring for a second time to form a stable complex solution; evaporating the complex solution under water bath conditions to a viscous liquid, and then heating the viscous liquid to obtain a powdered precursor; calcining the powdered precursor, and cooling to obtain a pure-phase AMnO3 perovskite catalyst powder free of impurities. By optimizing the complexation process and calcination parameters, stable preparation of pure-phase AMnO3 perovskite with Mg, Ca, Sr, and Ba at the A-site is achieved, while ensuring excellent catalytic performance of the catalyst.

Description

Technical Field

[0001] This disclosure belongs to the field of catalytic material preparation technology, specifically relating to a pure-phase alkaline earth metal Mn-based perovskite catalyst and its preparation method. Background Technology

[0002] With the acceleration of industrialization, volatile organic compound (VOC) pollution has become increasingly prominent. Toluene, as a typical VOC, is characterized by its high toxicity and difficulty in degradation, necessitating efficient treatment technologies. Catalytic oxidation technology is the core technology for end-of-pipe treatment of VOCs, and its performance depends on high-quality catalysts. Perovskite catalysts (ABO3) have become a research hotspot for non-precious metal catalysts due to their structural stability and excellent redox performance. Among them, the regulation of alkaline earth metal ions at the A-site is crucial to catalyst performance.

[0003] However, existing methods for preparing Mn-based perovskites with Mg, Ca, Sr, or Ba at the A-site generally suffer from the problem of "impure phase formation." Due to the difference in bonding ability between alkaline earth metal ions and Mn ions at the A-site, independent oxide impure phases such as MgO, CaO, SrO, BaO, or MnO2 and Mn2O3 are easily formed during calcination. These impure phases not only occupy the active sites of the catalyst but may also hinder the contact between reactants and active centers, significantly reducing catalytic performance. Simultaneously, the presence of impure phases also leads to a decrease in catalyst structural stability, affecting its lifespan. Therefore, developing a method for the stable preparation of impure phase-free alkaline earth metal Mn-based perovskites is crucial for promoting the industrial application of this type of catalyst. Summary of the Invention

[0004] This disclosure aims to at least solve one of the technical problems existing in the prior art, namely, the easy generation of impurity phases and the difficulty in obtaining pure phase materials when preparing Mn-based perovskites with Mg, Ca, Sr, and Ba at the A site, and to provide a pure phase alkaline earth metal Mn-based perovskite catalyst and its preparation method.

[0005] One aspect of this disclosure provides a method for preparing a pure-phase alkaline earth metal Mn-based perovskite catalyst, comprising: Weigh the A-site ion raw material and manganese acetate corresponding to the product, add deionized water and stir until completely dissolved, then continue stirring for a period of time to obtain a metal ion solution. A complexing agent is added to the metal ion solution, and the mixture is stirred until the glycine is completely dissolved. Stirring is continued for a second time to form a stable complex solution. The complex solution was evaporated into a viscous liquid under water bath conditions, and the viscous liquid was then heated to obtain a powdered precursor. The powdered precursor was calcined and cooled to obtain a pure phase AMnO3 perovskite catalyst powder without impurities.

[0006] Optionally, the A-site ion raw material is any one of calcium acetate, magnesium acetate, strontium acetate, and barium acetate.

[0007] Optionally, the molar ratio of the A-site ion raw material to the manganese acetate is 1:1.

[0008] Optionally, the first time and the second time are 10-20 minutes.

[0009] Optionally, the complexing agent is glycine; The amount of glycine added is 1.0 times the total number of moles of metal ions in the metal ion solution.

[0010] Optionally, the temperature at which the complex solution is evaporated under water bath conditions is 75-85 °C.

[0011] Optionally, the viscous liquid is heated to a temperature of 250-350°C for a time of 0.5-1.5 hours.

[0012] Optionally, the powdered precursor is calcined at a temperature of 600-700℃, a heating rate of 2℃ / min, and a calcination time of 3-5h.

[0013] In another aspect of this disclosure, a pure-phase alkaline earth metal Mn-based perovskite catalyst is provided, which is prepared by the preparation method described above.

[0014] Optionally, the catalyst has a porous network structure with pores and gaps on the surface of the catalyst particles, and the A, Mn and O elements are evenly distributed without obvious segregation.

[0015] This disclosure presents a pure-phase alkaline earth metal Mn-based perovskite catalyst and its preparation method. The preparation method includes: weighing the A-site ion raw material corresponding to the product and manganese acetate, adding deionized water and stirring until completely dissolved, then continuing stirring for a first time to obtain a metal ion solution; adding a complexing agent to the metal ion solution, stirring until glycine is completely dissolved, then continuing stirring for a second time to form a stable complex solution; evaporating the complex solution under water bath conditions to a viscous liquid, and then heating the viscous liquid to obtain a powdered precursor; calcining the powdered precursor, and cooling to obtain a pure-phase AMnO3 perovskite catalyst powder free of impurities. The above method of this disclosure uses A-site alkaline earth metal acetate and manganese acetate as raw materials, and glycine as a complexing agent. Through a "complexation-evaporation-precision calcination" process, the generation of impurities is suppressed, and a pure-phase perovskite with the chemical formula AMnO3 (free of A-site metal oxides and MnO3) is stably prepared. x (Impure phase). Secondly, when the pure phase catalyst of this disclosure is used for the catalytic combustion of toluene, the pure phase CaMnO3 performs best, with an ignition temperature (T).10 225℃, complete conversion temperature (T) 100 351℃. Attached Figure Description

[0016] Figure 1 A flowchart illustrating the preparation method of a pure-phase alkaline earth metal Mn-based perovskite catalyst according to a specific embodiment of this disclosure. Figure 2 The XRD patterns of the AMnO3 catalysts in Examples 1-4 of this disclosure are shown below. Figure 3 This is the SEM image of the MgMnO3 catalyst of Example 1 of this disclosure; Figure 4 This is the SEM image of the CaMnO3 catalyst in Example 2 of this disclosure; Figure 5 The SEM image of the SrMnO3 catalyst in Example 3 of this disclosure is shown below. Figure 6 This is the SEM image of the BaMnO3 catalyst in Example 4 of this disclosure; Figure 7 The following are elemental distribution diagrams of the AMnO3 catalysts in Examples 1, 2, and 4 of this disclosure; wherein, Figure 7 (A) in the text refers to the MgMnO3 catalyst of Example 1; Figure 7 (B) in the example is the CaMnO3 catalyst of Example 2; Figure 7 (C) in the text refers to the BaMnO3 catalyst from Example 4; Figure 8 The H2-TPR spectra of the AMnO3 catalysts in Examples 1-4 of this disclosure are shown below. Figure 9 The images show the toluene catalytic combustion activity curves of the AMnO3 catalysts in Examples 1-4 of this disclosure. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain this disclosure and represent a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the protection scope of this disclosure.

[0018] As shown in Figure 1, one aspect of this disclosure provides a method S100 for preparing a pure-phase alkaline earth metal Mn-based perovskite catalyst, specifically including the following steps S110~S140: S110. Raw material ratio and dissolution: Weigh the corresponding A-site ion precursor and manganese acetate, add deionized water to 100 mL, stir at room temperature until completely dissolved, and continue stirring for 10-20 min to ensure uniform dispersion of metal ions, and obtain a metal ion solution.

[0019] In step S110, the A-site ion precursor is an alkaline earth metal ion (Mg). 2+ / Ca 2+ / Sr 2+ / Ba 2+ The numbers ), corresponding to magnesium acetate, calcium acetate, strontium acetate, and barium acetate, respectively, mean that magnesium acetate is used as the A-site ion precursor in the preparation of MgMnO3 perovskite catalyst, calcium acetate can be used as the A-site ion precursor in the preparation of CaMnO3 perovskite catalyst, strontium acetate can be used as the A-site ion precursor in the preparation of SrMnO3 perovskite catalyst, and barium acetate can be used as the A-site ion precursor in the preparation of BaMnO3 perovskite catalyst.

[0020] In step S110, alkaline earth metal ions (Mg) at site A... 2+ / Ca 2+ / Sr 2+ / Ba 2+ The molar ratio of ions to Mn ions is 1:1.

[0021] It should be understood that the first time mentioned above, which is the stirring time after adding deionized water and stirring until completely dissolved in step S110 and continuing to stir for 10-20 minutes, refers to the stirring time after the A-site ion principle and the dissolution of manganese acetate and deionized water.

[0022] S120, Complexation reaction: Add a complexing agent to the metal ion solution, stir until glycine is completely dissolved, and continue stirring for 10-20 minutes to form a stable complex solution.

[0023] In step S120, the complexing agent is glycine, and the amount of glycine added is 1.0 times the total number of moles of metal ions in the metal ion solution.

[0024] In step S120, glycine can form stable chelates with A-site metal ions and Mn ions respectively, forming a uniform metal-glycine complex system, which inhibits the A-site metal and Mn from forming oxide impurities independently in subsequent processes from the source; stirring is continued after glycine is completely dissolved to ensure that the complexation reaction is sufficient.

[0025] It should be understood that the step S120 above, in which the complexing agent is added to the metal ion solution and the stirring continues for 10-20 minutes after the glycine is completely dissolved, is the second time mentioned above. That is, the second time refers to the time after the complexing agent is added to the metal ion solution and the stirring continues after the glycine is completely dissolved.

[0026] S130, Evaporation and Aging: Place the complexation solution in a 75-85 ℃ constant temperature water bath and evaporate it into a gel state (about 2~3h) with continuous stirring to avoid local agglomeration. Then transfer the gel to a muffle furnace and heat it at 250-350 ℃ for 0.5-1.5h to obtain a loose powder precursor.

[0027] S140, Calcination and Molding: The precursor is placed in a crucible and placed in a muffle furnace; the temperature is increased to 600-700 ℃ at 2 ℃ / min under air atmosphere, and calcined at a constant temperature for 3.5-4.5h, and then naturally cooled to room temperature to obtain AMnO3 perovskite catalyst.

[0028] In step S140, a slow heating rate of 2 °C / min and a calcination temperature of 650 °C ensure that the precursor is fully decomposed and promotes the complete formation of the perovskite crystal phase, avoiding the formation of impurity phases due to excessively rapid heating or improper calcination temperature.

[0029] The preparation method of this embodiment can stably produce pure-phase, porous alkaline earth metal Mn-based perovskite catalysts, that is, obtain a pure-phase alkaline earth metal Mn-based perovskite with Mg, Ca, Sr, and Ba at the A site. In addition, during the preparation process, the redox performance of the product can be significantly improved through the synergistic effect of A-site ion regulation and process optimization. This core characteristic not only ensures its high activity in the catalytic combustion of toluene, but also highly matches the reaction mechanism of carbon monoxide catalytic oxidation, providing a solid theoretical and structural basis for expanding to multi-pollutant treatment scenarios.

[0030] The catalyst preparation process disclosed herein is simple and controllable, low in cost, and exhibits excellent catalytic performance. The prepared catalyst can be widely used for the synergistic purification or individual treatment of VOCs and carbon monoxide in industrial exhaust gases, demonstrating significant environmental and economic benefits. It solves the technical pain point of existing methods for preparing this type of perovskite, which easily generates impurity phases. The process is simple, low in cost, and scalable. The prepared pure-phase catalyst has high activity and is suitable for the efficient treatment of toxic and harmful substances such as VOCs and carbon monoxide in industrial waste gases.

[0031] In another aspect of this disclosure, a pure-phase alkaline earth metal Mn-based perovskite catalyst is proposed. This pure-phase alkaline earth metal Mn-based perovskite catalyst is prepared by the preparation method described above. For details of the method, please refer to the above description, which will not be repeated here.

[0032] In this embodiment, the catalyst has a porous network structure with pores and gaps on the particle surface. The A, Mn and O elements are evenly distributed without obvious segregation. X-ray diffraction (XRD) tests show that 2θ only has characteristic diffraction peaks corresponding to the perovskite structure in the range of 10° to 80°, without any impurity phase diffraction peaks.

[0033] The AMnO3 perovskite catalyst will be further explained below with reference to specific embodiments: Example 1 This example illustrates the preparation and performance testing of a MgMnO3 perovskite catalyst: 1. Raw material weighing: Weigh manganese acetate and magnesium acetate according to the Mg to Mn molar ratio of 1:1, and add 100 mL of ultrapure water; 2. Solution preparation: Stir magnetically until the raw materials are completely dissolved, continue stirring for 15 min, add glycine at 1.0 times the total number of metal ions, stir until dissolved, and then stir for another 15 min; 3. Gel preparation: Evaporate in an 80 ℃ constant temperature water bath until gel-like, then heat in a 300 ℃ muffle furnace for 1 h to obtain a powdered precursor; 4. Calcination and shaping: The precursor is crushed, placed in a crucible, heated to 650 °C in a muffle furnace at 2 °C / min, calcined for 4 h, and then cooled to obtain MgMnO3 catalyst; 5. Performance Testing: A fixed-bed reactor was used, with 21% O2 + 79% N2 + 1000 ppm toluene, a total flow rate of 30 mL / min, a catalyst dosage of 60 mg, and a space velocity of 30000 mL / (h). g). Test results show that the catalyst T 10 =278℃, T 40 =351 ℃, T 70 =380 ℃, T 100 =432 ℃.

[0034] Example 2 This example illustrates the preparation and performance testing of a CaMnO3 perovskite catalyst: Following the preparation method of Example 1, magnesium acetate was replaced with calcium acetate, while the remaining steps remained unchanged, to obtain the CaMnO3 catalyst. Performance test results showed that the catalyst T 10 =225℃, T 40 =273℃, T 70 =305℃, T 100 =351℃.

[0035] Example 3 This example illustrates the preparation and performance testing of a SrMnO3 perovskite catalyst: Following the preparation method of Example 1, magnesium acetate was replaced with strontium acetate, while the remaining steps remained unchanged, to obtain the SrMnO3 catalyst. Performance test results showed that the catalyst T 10 =253℃, T 40 =324℃, T 70 =318℃, T 100 =373℃.

[0036] Example 4 This example illustrates the preparation and performance testing of a BaMnO3 perovskite catalyst: Following the preparation method of Example 1, magnesium acetate was replaced with barium acetate, while the remaining steps remained unchanged, to obtain the BaMnO3 catalyst. Performance test results showed that the catalyst T 10 =316℃, T 40 =352℃, T 70 =388℃, T 100 =472℃.

[0037] like Figure 2 As shown, the XRD spectra of the AMnO3 (MgMnO3, CaMnO3, SrMnO3, BaMnO3) samples prepared in Examples 1-4 all show typical perovskite structure (ABO3 type) characteristic diffraction peaks.

[0038] like Figure 3 As shown in the SEM image, the MgMnO3 catalyst exhibits a porous network structure with uniform particle size distribution and obvious pores and gaps on the surface, which is beneficial for the adsorption and mass transfer of reactants.

[0039] like Figure 4 As shown in the SEM image, the CaMnO3 catalyst exhibits a more developed porous structure with dense and uniform pore distribution, rough particle surface, and a larger specific surface area, which helps to improve catalytic activity.

[0040] like Figure 5 As shown in the SEM image, the SrMnO3 catalyst exhibits a similar porous network structure, but the pore size and distribution are slightly different. The particle morphology is relatively regular and there is no obvious agglomeration.

[0041] like Figure 6 As shown in the SEM image, the BaMnO3 catalyst exhibits a relatively obvious porous structure, but the particle size is relatively large, and the surface pores are evenly distributed.

[0042] like Figure 7 As shown in the figure, the elements such as Mg, Ca, Ba, Mn, and O are uniformly distributed in the catalyst, with no obvious elemental segregation or agglomeration, further proving the formation of a pure-phase perovskite structure.

[0043] like Figure 8 As shown, all samples exhibited obvious reduction peaks, indicating that the catalysts have good redox properties. CaMnO3 had the lowest reduction peak temperature and the largest peak area, indicating that it had the strongest redox ability.

[0044] like Figure 9 As shown, the four curves correspond to the catalytic activities of MgMnO3, CaMnO3, SrMnO3, and BaMnO3, respectively. Among them, the curve of CaMnO3 is furthest to the left, indicating that it has the lowest ignition temperature and achieves 100% toluene conversion at 351℃. The activities of the other catalysts are in the following order: SrMnO3 > MgMnO3 > BaMnO3.

[0045] In summary, the AMnO3 catalysts prepared in Examples 1-4 were confirmed by XRD characterization to be high-purity ABO3 perovskite structures with no impurity oxide peaks. SEM characterization showed that the catalysts had obvious porous network structures with pores and gaps on the particle surface. The elemental distribution diagram showed that Mg, Ca, Sr, Ba, Mn, O and other elements were uniformly distributed without obvious agglomeration or segregation, further proving the stable formation of the high-purity ABO3 perovskite structure. H2-TPR characterization showed that the product had good redox properties.

[0046] This disclosure presents a pure-phase alkaline earth metal Mn-based perovskite catalyst and its preparation method, which has the following advantages compared to the prior art: 1. The raw materials used in the catalyst preparation process are conventional chemical reagents, without the need for expensive template agents or special equipment. The preparation process only involves water bath evaporation, oven aging, and muffle furnace calcination. The operation is easy to control, the cost is low, and it is suitable for large-scale industrial production. 2. Pure-phase structure ensures the presence of Mn active sites in the catalyst (Mn 4+ / Mn 3+ / Mn 2+ ) and reactive oxygen species (adsorbed oxygen O) ads , lattice oxygen O latt Uniformly distributed, with no impurities occupying the active centers; 3. The catalysts exhibit good structural stability and uniform elemental distribution, and their porous network structure enhances the adsorption and mass transfer efficiency of reactants; among them, the CaMnO3 catalyst demonstrates the best catalytic combustion activity for toluene, with an ignition temperature (T0). 10 It can achieve 100% conversion of toluene at only 225℃ and 351℃, which is significantly better than some existing non-precious metal catalysts; 4. The redox ability of the catalyst can be regulated by A-site ions. CaMnO3 exhibits the strongest redox ability and the most reactive oxygen species, providing ample active sites for the catalytic reaction. Furthermore, it contains no precious metal components, avoiding excessively high costs and demonstrating significant industrial application value. It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of this disclosure; however, this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A method for preparing a pure-phase alkaline earth metal Mn-based perovskite catalyst, characterized in that, include: Weigh the A-site ion raw material and manganese acetate corresponding to the product, add deionized water and stir until completely dissolved, then continue stirring for a period of time to obtain a metal ion solution. A complexing agent is added to the metal ion solution, and the mixture is stirred until the glycine is completely dissolved. Stirring is continued for a second time to form a stable complex solution. The complex solution was evaporated into a viscous liquid under water bath conditions, and the viscous liquid was then heated to obtain a powdered precursor. The powdered precursor was calcined and cooled to obtain a pure phase AMnO3 perovskite catalyst powder without impurities.

2. The preparation method according to claim 1, characterized in that, The A-site ion raw material is any one of calcium acetate, magnesium acetate, strontium acetate, and barium acetate.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the A-site ion raw material to the manganese acetate is 1:

1.

4. The preparation method according to claim 1, characterized in that, The first time and the second time are 10-20 minutes.

5. The preparation method according to claim 1, characterized in that, The complexing agent is glycine; The amount of glycine added is 1.0 times the total number of moles of metal ions in the metal ion solution.

6. The preparation method according to claim 1, characterized in that, The complex solution is evaporated in a water bath at a temperature of 75-85 °C.

7. The preparation method according to claim 1, characterized in that, The viscous liquid is heated to a temperature of 250-350℃ for a time of 0.5-1.5h.

8. The preparation method according to claim 1, characterized in that, The powdered precursor is calcined at a temperature of 600-700℃, a heating rate of 2℃ / min, and a calcination time of 3-5h.

9. A pure-phase alkaline earth metal Mn-based perovskite catalyst, characterized in that, The pure-phase alkaline earth metal Mn-based perovskite catalyst is prepared by the preparation method described in any one of claims 1 to 8.

10. The pure-phase alkaline earth metal Mn-based perovskite catalyst according to claim 9, characterized in that, The catalyst has a porous network structure with pores and gaps on the surface of the catalyst particles, and the A, Mn and O elements are evenly distributed without obvious segregation.

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