A gadolinium-doped lanthanum manganese perovskite modified by coupling acid etching, a preparation method and applications thereof

Abstract

The application discloses a Gd-doped lanthanum-manganese perovskite modified by coupling acid etching, a preparation method and application, and belongs to the technical field of volatile organic compound purification, and comprises the following steps: dissolving a lanthanum-containing compound, a gadolinium-containing compound and a manganese nitrate solution in water, and performing ultrasonic treatment to obtain a precursor mixed solution; adding oxalic acid to the precursor mixed solution, stirring until the oxalic acid is dissolved, and then performing a heating reaction, performing suction filtration, and drying until the weight is constant to obtain a solid substance; performing high-temperature calcination on the solid substance, placing a product obtained in a nitric acid solution to perform acid etching treatment, and after being taken out, performing rinsing and drying to obtain the Gd-doped lanthanum-manganese perovskite modified by coupling acid etching. The catalyst presents excellent low-temperature catalytic oxidation removal VOCs performance, and provides a high-performance and low-cost catalyst solution for industrial VOCs treatment.

Description

Technical Field

[0001] This invention belongs to the field of volatile organic compound (VOCs) purification technology, and particularly relates to a Gd-doped coupled acid-etched modified lanthanum manganese perovskite, its preparation method, and its application. Background Technology

[0002] In recent years, dust, sulfur dioxide (SO2), and nitrogen oxides (NOx) have become increasingly prominent. x The effectiveness of controlling traditional air pollutants such as carbon dioxide (VOCs) has been widely recognized. However, as the focus of environmental governance shifts, VOCs have gradually become a key factor affecting air quality and a core area of ​​focus in the current field of air pollution prevention and control.

[0003] The harm of VOCs to human health and the ecological environment is highly insidious and destructive. From a health risk perspective, most VOCs are toxic, irritating, and even carcinogenic. They can enter the human body through inhalation and skin contact. Long-term exposure can induce respiratory diseases, damage to the nervous system, and even increase the risk of malignant tumors such as lung cancer, posing a serious threat to human health. From an ecological impact perspective, VOCs are responsible for the formation of ozone (O3) and fine particulate matter (PM2.5). 2.5 It is an important precursor to NO. x Under the sun's ultraviolet radiation, complex photochemical reactions occur, generating more toxic secondary aerosols, which in turn cause a series of environmental problems such as photochemical smog, exacerbate the greenhouse effect, and damage the ozone layer, seriously hindering the continuous improvement of the ecological environment quality.

[0004] Given the significant hazards of VOCs, they have been explicitly included in the key control scope, and VOCs have officially replaced SO2 as one of the core indicators for urban air quality assessment. However, current VOCs control still faces significant shortcomings: on the one hand, VOCs emission sources are complex (involving multiple industries such as chemicals, printing, and coating), and the management system is not yet fully mature; on the other hand, existing pollution control facilities often suffer from problems such as simple technology and low treatment efficiency, making it difficult to meet increasingly stringent emission requirements. Therefore, the urgency and necessity of VOCs control are becoming increasingly prominent.

[0005] Currently, VOCs treatment technologies are mainly divided into two categories: recycling and disposal. Recycling technologies include adsorption, absorption, condensation, and membrane separation. Among these, adsorption is the most widely used in industry due to its relatively simple operation. However, this technology has significant limitations: the adsorption capacity of the adsorption material is limited, requiring frequent regeneration or replacement, resulting in high treatment costs; and if the adsorbed VOCs are not properly treated, they can easily be released back into the environment, causing secondary pollution, making complete treatment difficult.

[0006] In contrast, catalytic oxidation, with its significant advantages, is considered a highly promising green and environmentally friendly VOCs treatment technology. This technology, through the action of a catalyst, can completely degrade VOCs into pollution-free carbon dioxide (CO2) and water (H2O). It not only boasts a simple operation process and high conversion efficiency but also low energy consumption and no secondary pollution, fundamentally solving the VOCs emission problem. In catalytic oxidation technology, the catalyst is the core element. It can significantly accelerate the reaction rate by altering the reaction pathway and lowering the activation energy of the VOCs oxidation reaction, directly determining the efficiency and stability of the catalytic oxidation process. Therefore, the development of high-performance catalysts is crucial for promoting the industrial application of this technology.

[0007] Currently, catalysts used for the catalytic oxidation of VOCs are mainly divided into two categories: noble metal catalysts and non-noble metal catalysts. Noble metal catalysts (such as Pt and Pd-based catalysts) have the advantages of excellent low-temperature activity, low ignition temperature, and high product selectivity, but their disadvantages are also very prominent: noble metal resources are scarce and expensive, resulting in high catalyst preparation costs; moreover, under high-temperature reaction conditions, noble metals are prone to sintering and agglomeration, and they are also sensitive to impurities such as sulfur and chlorine in flue gas, with weak resistance to poisoning, which seriously limits their large-scale application in industrial settings.

[0008] Non-precious metal catalysts (represented by rare earth / transition metal oxides) have gradually become a research hotspot in the field of VOCs catalytic oxidation due to their low cost, strong thermal stability, outstanding oxygen storage capacity, and excellent redox performance. Among them, perovskite oxide (ABO3) catalysts have shown great application potential due to their unique crystal structure and performance advantages. In their crystal structure, the A site is usually a rare earth metal or alkaline earth metal cation (such as La). 3+ The B site is a transition metal cation (such as Mn). 3+ Co 3+ This structure endows the catalyst with the core advantages of high stability and low cost.

[0009] However, traditional ABO3-type perovskite catalysts still suffer from performance bottlenecks: on the one hand, their active site distribution is relatively random and their specific surface area is small, resulting in low catalytic activity; on the other hand, their sulfur resistance is unsatisfactory, making them difficult to adapt to the complex environment of industrial flue gas. It is worth noting that the perovskite structure possesses excellent "tunability," as both A-site and B-site cations can be partially substituted by other elements, while still maintaining the original perovskite crystal structure. This characteristic can be significantly improved by controlling the number of active oxygen sites, optimizing the valence state distribution of metal ions, and constructing surface micro-defects, thereby enhancing the low-temperature catalytic activity and sulfur and water resistance of the catalyst, providing a feasible path to address the performance shortcomings of traditional perovskite catalysts.

[0010] Further research revealed that the catalytic activity of perovskite catalysts mainly depends on the valence and dispersion state of B-site transition metal ions (such as Mn ions), while A-site elements can indirectly affect catalytic performance by modulating the chemical environment of B-site ions through electronic interactions. However, during the preparation of perovskite catalysts, the high-temperature calcination step easily leads to the enrichment of A-site metal ions on the catalyst surface, thereby masking a large number of B-site active metal sites. This significantly reduces the utilization rate of active sites and severely restricts catalytic performance. Summary of the Invention

[0011] To overcome existing technological bottlenecks, this invention proposes a Gd-doped coupled acid-etched modified lanthanum manganese perovskite, its preparation method, and its application. The aim is to precisely control the catalyst's defect structure, oxygen vacancy concentration, Mn ion valence and dispersion state, and the number of exposed active Mn sites by doping the A-sites of LaMnO3 perovskite with rare earth metal Gd, combined with nitric acid etching treatment. Ultimately, this significantly enhances the catalyst's low-temperature catalytic oxidation activity for VOCs and its resistance to sulfur and water, providing a high-performance, low-cost catalyst solution for industrial VOCs treatment.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A method for preparing Gd-doped coupled acid-etched modified lanthanum manganese perovskite includes the following steps:

[0014] A lanthanum-containing compound, a gadolinium-containing compound, and a manganese nitrate solution were dissolved in water and subjected to ultrasonic treatment to obtain a precursor mixed solution.

[0015] Oxalic acid was added to the precursor mixture solution, stirred until dissolved, heated to react, filtered, and dried to constant weight to obtain a solid.

[0016] The solid was calcined at high temperature, and the resulting product was placed in a nitric acid solution for acid etching. After removal, it was rinsed and dried to obtain Gd-doped coupled acid-etched modified lanthanum manganese perovskite.

[0017] This invention leverages the advantages of ABO3-type perovskite catalysts, such as the ability to dope A and B sites, low cost, good thermal stability, and catalytic activity. It also considers the unique electronic structures of rare earth metals La and Gd. The invention employs a defect engineering strategy involving Gd doping of LaMnO3 perovskite catalysts. By controlling the valence and dispersion state of active Mn through Gd doping, defects and oxygen vacancies are induced, promoting electron transfer and redox performance, enhancing the activity and mobility of oxygen species, and thus improving low-temperature catalytic activity. Lanthanum-containing compounds, gadolinium-containing compounds, and manganese nitrate solution are used as precursors for La, Gd, and Mn, respectively. These precursors are mixed in appropriate proportions, and a suitable amount of oxalic acid is added. The two bendable and rotatable carboxyl groups of oxalic acid chelate the heteroatoms La, Gd, and Mn in situ, forming a uniformly distributed lanthanum-gadolinium-manganese-oxalic acid composite precursor. A topological phase transition occurs at a suitable calcination temperature, enhancing the activity of Mn. 3+ The quantity and dispersion of these elements increase the number of lattice defects and oxygen vacancies, forming highly active Gd-doped LaMnO3 perovskite catalysts, with the aim of achieving low-temperature catalytic oxidation removal of VOCs.

[0018] The high-temperature calcination process during the preparation of ABO3 perovskite catalysts leads to the enrichment of A-site metals on the catalyst surface, masking many B-site active metals and resulting in less exposed B-site active metals and poor catalytic performance. This invention employs nitric acid etching to alter the physicochemical structure of the catalyst surface, exposing more Mn active metals and enhancing Mn activity. 3+ The quantity and dispersion of active metals increase the reactants and Mn 3+ On the one hand, it can facilitate contact between active sites; on the other hand, it can induce changes in catalyst surface stress and lattice distortion, increase the concentration of oxygen active sites and active oxygen, and thus enhance low-temperature catalytic activity.

[0019] This invention employs Gd doping coupled with nitric acid etching to comprehensively modify LaMnO3 perovskite catalysts. Acid etching, along with different atomic doping and orbital hybridization, alters the catalyst's physicochemical properties to a certain extent, inducing lattice distortion, deformation, and charge imbalance in the metal, generating numerous lattice defects, oxygen vacancies, and active sites. This enhances the electron migration ability between different atoms and their different valence states, increases the quantity and mobility of surface active oxygen, and increases the exposure of active Mn. 3+ The quantity and dispersion of Gd enhance its redox performance and catalytic oxidation activity, thus facilitating the deep oxidation and complete degradation of VOCs under low-temperature conditions. Furthermore, Gd doping coupled with nitric acid etching optimizes its surface / interface properties, improves the diffusion and mass transfer capabilities of reactants and products, enhances the catalyst's thermal stability and resistance to sulfur and water, and increases its potential for industrial applications.

[0020] Further, the molar ratio of the lanthanum-containing compound, the gadolinium-containing compound, and the manganese nitrate solution is 0.8:0.2:1; the molar ratio of the total molar amount of the lanthanum-containing compound and the gadolinium-containing compound to the manganese nitrate solution is 1:1; and / or,

[0021] The lanthanum-containing compound is lanthanum nitrate hexahydrate (La(NO3)3·6H2O); and / or,

[0022] The gadolinium-containing compound is gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O); and / or,

[0023] The concentration of the manganese nitrate (Mn(NO3)2) solution is 50 wt.%.

[0024] The ultrasonic treatment lasted for 1 hour.

[0025] Furthermore, the molar amount of oxalic acid is 1.2 times the sum of the molar amounts of lanthanum nitrate hexahydrate, gadolinium nitrate hexahydrate, and manganese nitrate solutions in the precursor mixture solution.

[0026] Furthermore, the stirring speed is 800-1200 r / min; the heating temperature is 75-85℃, and the heating time is 40-100 min.

[0027] Furthermore, the temperature at which the material is dried to constant weight is 90-120°C.

[0028] Furthermore, the conditions for the high-temperature calcination are: a temperature of 600-800℃, a heating rate of 3-10℃ / min, and a time of 4-8h.

[0029] Furthermore, the concentration of the nitric acid solution is 0.05-0.15 mol / L.

[0030] Furthermore, the acid etching treatment time is 0.5-12 hours.

[0031] This invention also provides a Gd-doped, acid-etched modified lanthanum manganese perovskite catalyst prepared using the above-described method. This catalyst exhibits a three-dimensional porous structure with a specific surface area of ​​278.965 m². 2 / g, pore volume reaches 0.388cm³ 3 / g, Mn 3+ / Mn n+ The percentage was 86.8%, and the average pore size was 5.564 nm.

[0032] This invention also provides an application of the Gd-doped coupled acid-etched modified lanthanum manganese perovskite for VOC removal in flue gas, wherein the reaction temperature for the catalytic removal of VOCs by the Gd-doped coupled acid-etched modified lanthanum manganese perovskite in flue gas is 60-380℃. This catalyst can catalytically oxidize toluene and other VOCs at relatively low temperatures, completely degrading them into harmless CO2 and H2O.

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

[0034] (1) Microscopic defect control level: The defect engineering strategy of heterogeneous rare earth atom Gd doping and acid etching synergistic modification of LaMnO3 is adopted to induce lattice distortion and charge imbalance, significantly improve the lattice defect and oxygen vacancy concentration of the catalyst system, increase the number and mobility of active oxygen, and the synergistic effect of the three metals constructs the "generation-migration-consumption-replenishment" cycle channel of active oxygen, improves the migration and conversion rate of surface active oxygen species, reduces the catalytic reaction energy barrier, improves the redox performance, and enhances the low-temperature catalytic oxidation degradation ability of VOCs such as toluene;

[0035] (2) Electronic structure optimization: The two bendable and rotatable carboxyl groups of oxalic acid are used to chelate the heteroatoms La, Gd and Mn in situ. At the same time, the unique electronic structure of rare earth metals La and Gd, especially their empty 5d orbitals, can act as channels for electron transfer. La, Gd and Mn improve the electron transfer rate between different atoms and different valence states of each atom through orbital hybridization, thereby enhancing the redox ability of the catalyst and improving its low-temperature catalytic activity.

[0036] (3) Enhanced reaction kinetics: Gd doping coupled with nitric acid etching can not only induce lattice defects, but also increase the exposure of active Mn 3+ The quantity and distribution of Gd provide more types and quantities of catalytic active sites and more reactive oxygen species, reducing the catalytic efficiency reduction caused by competition for active sites and reactive oxygen species in the catalytic oxidation of VOCs such as toluene. Gd doping coupled with nitric acid etching can optimize the physicochemical properties of the three-dimensional porous structure on the catalyst surface, greatly increasing the specific surface area and pore volume, and reducing the average pore size. It can not only expose more active sites and reactive oxygen species, but also promote the diffusion and mass transfer of reactants and products, which is more conducive to the contact between reactants and active sites, thereby greatly improving its ability to catalytically oxidize VOCs such as toluene at low temperatures. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0038] Figure 1 La with different Gd doping levelsx Gd 1-x Results of the catalytic performance of MnO3 catalyst on toluene (C7H8) at different temperatures;

[0039] Figure 2 Figure 1 shows the nitrogen adsorption-desorption process for different catalysts.

[0040] Figure 3 The results show the catalytic performance of different catalysts on C7H8 at different temperatures;

[0041] Figure 4 The effect of flue gas components (O2, H2O(g) and SO2) on La 0.8 Gd 0.2 The effect of MnO3(n) on the catalytic oxidation performance of C7H8;

[0042] Figure 5 SEM images of different catalysts; among them, a-La 0.8 Gd 0.2 MnO3(n); b-La 0.8 Gd 0.2 MnO3; c-LaMnO3; d-MnO x ;

[0043] Figure 6 H2 temperature-programmed reduction (H2-TPR) diagrams for different catalysts;

[0044] Figure 7 X-ray photoelectron spectra (XPS, La 3d) of different catalysts;

[0045] Figure 8 X-ray photoelectron spectra (XPS, Gd 4d) of different catalysts.

[0046] Figure 9 X-ray photoelectron spectra (XPS, Mn 2p) of different catalysts;

[0047] Figure 10 X-ray photoelectron spectra (XPS, O 1s) of different catalysts. Detailed Implementation

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0052] 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.

[0053] This invention provides a method for preparing La by Gd-doped coupled nitric acid etching. x Gd 1-x MnO3(n) catalyst, which exhibits a three-dimensional porous structure and has a specific surface area of ​​278.965 m². 2 / g, pore volume reaches 0.388cm³ 3 / g, Mn 3+ / Mn n+ The percentage was 86.8%, and the average pore size was 5.564 nm.

[0054] This invention provides a method for preparing Gd-doped coupled acid-etched modified lanthanum manganese perovskite, comprising the following steps:

[0055] S1. Dissolve a lanthanum-containing compound, a gadolinium-containing compound, and a manganese nitrate solution in water, and then sonicate the solution to obtain a mixed precursor solution;

[0056] S2. Oxalic acid is added to the precursor mixture solution obtained in step S1 and stirred in a magnetic stirrer until dissolved. Then, the reaction is carried out under stirring and heated. The solution after the reaction is filtered by a vacuum filter to separate the solid and liquid. It is dried to constant weight to obtain a solid.

[0057] S3. The solid obtained in step S2 is calcined at high temperature to obtain Gd-doped LaMnO3 perovskite catalyst, which is La x Gd 1-x MnO3;

[0058] S4. The Gd-doped LaMnO3 perovskite catalyst obtained in step S3 is subjected to acid etching in nitric acid solution. After removal, it is rinsed and dried to obtain Gd-doped coupled acid-etched modified lanthanum manganese perovskite, which is La... x Gd 1-x MnO3(n).

[0059] This invention employs a defect engineering strategy of heterogeneous rare earth atom Gd coupled with acid etching for synergistic modification of LaMnO3. Lanthanum nitrate hexahydrate (La(NO3)3·6H2O) is used as the precursor for La, gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O) is used as the precursor for heterogeneous rare earth atom Gd, and manganese nitrate aqueous solution (50 wt.%) is used as the precursor for Mn. The above precursors are prepared into a mixed solution, and an appropriate amount of oxalic acid is added. The two bendable and rotatable carboxyl groups of oxalic acid are used to chelate La, Gd, and Mn in situ, constructing a lanthanum-gadolinium-manganese-oxalic acid composite precursor with a three-dimensional atomically uniform dispersion structure. This precursor undergoes a topological phase transition at the critical decomposition temperature, forming a Gd-doped, acid-etched synergistically modified LaMnO3 (La... x Gd 1-x MnO3(n)), where x∶(1-x) is the molar ratio of La∶Gd, and the molar ratio of La∶Gd can be 0.75∶0.25, 0.8∶0.2, 0.85∶0.15, 0.9∶0.1 or 0.95∶0.05, preferably 0.8∶0.2.

[0060] In the following preferred embodiments of the present invention, in step S1, the lanthanum-containing compound is lanthanum nitrate hexahydrate (La(NO3)3·6H2O); the gadolinium-containing compound is gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O); and the manganese nitrate solution itself has a mass concentration of 50 wt.%.

[0061] Specifically, take a beaker, add an appropriate amount of deionized water, then weigh an appropriate amount of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) and gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O) using an analytical balance, take an appropriate amount of 50wt.% manganese nitrate aqueous solution using a pipette, stir thoroughly until the sample is completely dissolved, form a homogeneous solution, and sonicate for 0.5-2 hours (preferably 1 hour).

[0062] In the following preferred embodiments of the present invention, in step S2, the molar amount of oxalic acid is 1.2 times the sum of the molar amounts of lanthanum nitrate hexahydrate, gadolinium nitrate hexahydrate, and manganese nitrate solutions in the precursor mixed solution.

[0063] Specifically, a beaker containing the aforementioned precursor mixture solution is placed in a constant-temperature heating magnetic stirrer and continuously stirred at a speed of 800-1200 r / min (preferably 850 r / min). Oxalic acid, which is 1.2 times the sum of the molar amounts of the lanthanum-containing compound, the gadolinium-containing compound, and the manganese nitrate solution, is added to the above solution. After stirring until the sample is completely dissolved, the system is heated to 75-85℃ (preferably 80℃) and reacted for 40-100 min (preferably 60 min). The solution after the reaction is filtered through a vacuum filtration device to separate the solid and liquid phases, and then dried at 90-120℃ (preferably 95℃) to constant weight.

[0064] In the following preferred embodiments of the present invention, the conditions for high-temperature calcination in step S3 are: temperature of 600-800℃, heating rate of 3-10℃ / min, and time of 4-8h.

[0065] Specifically, the solid material dried in step S1 is transferred to a tube furnace for programmed temperature-controlled heat treatment. Heating is performed in a flowing air atmosphere at a constant heating rate of 3-10℃ / min (preferably 5℃ / min). Once the system temperature reaches the preset calcination temperature of 600-800℃ (preferably 700℃), the reaction is maintained at this temperature for 4-8 hours (preferably 6 hours), thus obtaining a three-dimensional porous catalyst of Gd-doped LaMnO3, named La. x Gd 1-x MnO3.

[0066] In the following preferred embodiments of the present invention, in step S4, the acid etching time with nitric acid solution is 0.5-12 hours.

[0067] Specifically, the La prepared in step S3 x Gd 1-x MnO3 is placed in a 0.05-0.15 mol / L nitric acid solution for acid etching for 0.5-12 hours (preferably 6 hours), rinsed, and dried to obtain La after nitric acid etching. x Gd 1-xMnO3 catalyst, labeled as La x Gd 1-x MnO3(n).

[0068] The prepared Gd-doped coupled acid-etched modified lanthanum manganese perovskite can be used for VOCs removal from flue gas. Toluene (C7H8) was selected as a representative of simulated VOCs molecules, and the reaction temperature ranged from 60 to 380 °C. Specifically, in a gas-solid reactor with programmed temperature rise, an appropriate amount of Gd-doped coupled acid-etched modified lanthanum manganese perovskite (La... x Gd 1-x MnO3(n) catalytically oxidizes toluene (C7H8) to completely degrade it into CO2 and H2O in the presence of a mixed gas of 300 ppm toluene (C7H8), 6% O2 and 94% N2.

[0069] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0070] All raw materials used in this invention were purchased from the market.

[0071] The technical solution of the present invention will be further illustrated by the following embodiments.

[0072] Comparative Example 1

[0073] A La 0.8 Gd 0.2 The preparation method of MnO3 is as follows:

[0074] S1. Dissolve 0.8 mmol lanthanum nitrate hexahydrate, 0.2 mmol gadolinium nitrate hexahydrate, and 1 mmol manganese nitrate solution (mass concentration of 50 wt.%) in 50 mL of water and sonicate for 1 h to form a precursor mixed solution;

[0075] S2. Add 2.4 mmol of oxalic acid to the precursor mixture obtained in step S1, place it in a magnetic stirrer, stir at a stirring rate of 850 r / min until the sample is completely dissolved, then heat to 80°C, continue stirring at this temperature for 60 min, filter the reaction solution through a vacuum filter to separate the solid and liquid, and dry the obtained solid at 95°C to constant weight to obtain a solid product.

[0076] S3. The solid obtained in step S2 is transferred to a tube furnace for programmed temperature-controlled heat treatment. Heating is performed at a constant heating rate of 5°C / min in a flowing air atmosphere. After the system temperature reaches the preset calcination temperature of 700°C, calcination is carried out at this temperature for 6 hours to obtain a three-dimensional porous catalyst of Gd-doped LaMnO3, named La. 0.8 Gd 0.2 MnO3.

[0077] Comparative Example 2

[0078] A method for preparing La by Gd-doped coupling with LaMnO3 0.95 Gd 0.05 The method using MnO3 perovskite catalysts comprises the following steps:

[0079] S1. Dissolve 0.95 mmol lanthanum nitrate hexahydrate, 0.05 mmol gadolinium nitrate hexahydrate, and 1 mmol manganese nitrate solution (mass concentration of 50 wt.%) in 50 mL of water and sonicate for 1 h to form a precursor mixed solution;

[0080] S2. Add 2.4 mmol of oxalic acid to the precursor mixture obtained in step S1, place it in a magnetic stirrer, stir at a stirring rate of 850 r / min until the sample is completely dissolved, then heat to 80°C, continue stirring at this temperature for 60 min, filter the reaction solution through a vacuum filter to separate the solid and liquid, and dry the obtained solid at 95°C to constant weight to obtain a solid product.

[0081] S3. The solid obtained in step S2 is transferred to a tube furnace for programmed temperature-controlled heat treatment. Heating is performed at a constant heating rate of 5°C / min in a flowing air atmosphere. After the system temperature reaches the preset calcination temperature of 700°C, calcination is carried out at this temperature for 6 hours to obtain a three-dimensional porous catalyst of Gd-doped LaMnO3, named La. 0.95 Gd 0.05 MnO3.

[0082] Comparative Example 3

[0083] A method for preparing La by Gd-doped coupling with LaMnO3 0.9 Gd 0.1 The method using MnO3 perovskite catalysts comprises the following steps:

[0084] S1. Dissolve 0.9 mmol lanthanum nitrate hexahydrate, 0.1 mmol gadolinium nitrate hexahydrate, and 1 mmol manganese nitrate solution (mass concentration of 50 wt.%) in 50 mL of water and sonicate for 1 h to form a precursor mixed solution;

[0085] S2. Add 2.4 mmol of oxalic acid to the precursor mixture obtained in step S1, place it in a magnetic stirrer, stir at a stirring rate of 850 r / min until the sample is completely dissolved, then heat to 80°C, continue stirring at this temperature for 60 min, filter the reaction solution through a vacuum filter to separate the solid and liquid, and dry the obtained solid at 95°C to constant weight to obtain a solid product.

[0086] S3. The solid obtained in step S2 is transferred to a tube furnace for programmed temperature-controlled heat treatment. Gradient heating is performed at a constant heating rate of 5℃ / min in a flowing air atmosphere. After the system temperature reaches the preset calcination temperature of 700℃, it is calcined at this temperature for 6 hours to obtain a three-dimensional porous catalyst of Gd-doped LaMnO3, named La. 0.9 Gd 0.1 MnO3.

[0087] Comparative Example 4

[0088] A method for preparing La by Gd-doped coupling with LaMnO3 0.85 Gd 0.15 The method using MnO3 perovskite catalysts comprises the following steps:

[0089] S1. Dissolve 0.85 mmol lanthanum nitrate hexahydrate, 0.15 mmol gadolinium nitrate hexahydrate, and 1 mmol manganese nitrate solution (mass concentration of 50 wt.%) in 50 mL of water and sonicate for 1 h to form a precursor mixed solution;

[0090] S2. Add 2.4 mmol of oxalic acid to the precursor mixture obtained in step S1, place it in a magnetic stirrer, stir at a stirring rate of 850 r / min until the sample is completely dissolved, then heat to 80°C, continue stirring at this temperature for 60 min, filter the reaction solution through a vacuum filter to separate the solid and liquid, and dry the obtained solid at 95°C to constant weight to obtain a solid product.

[0091] S3. The solid obtained in step S2 is transferred to a tube furnace for programmed temperature-controlled heat treatment. Gradient heating is performed at a constant heating rate of 5℃ / min in a flowing air atmosphere. After the system temperature reaches the preset calcination temperature of 700℃, it is calcined at this temperature for 6 hours to obtain a three-dimensional porous catalyst of Gd-doped LaMnO3, named La. 0.85 Gd 0.15 MnO3.

[0092] Comparative Example 5

[0093] A method for preparing La by Gd-doped coupling with LaMnO3 0.75 Gd 0.25 The method using MnO3 perovskite catalysts comprises the following steps:

[0094] S1. Dissolve 0.75 mmol lanthanum nitrate hexahydrate, 0.25 mmol gadolinium nitrate hexahydrate, and 1 mmol manganese nitrate solution (mass concentration of 50 wt.%) in 50 mL of water and sonicate for 1 h to form a precursor mixed solution;

[0095] S2. Add 2.4 mmol of oxalic acid to the precursor mixture obtained in step S1, place it in a magnetic stirrer, stir at a stirring rate of 850 r / min until the sample is completely dissolved, then heat to 80°C, continue stirring at this temperature for 60 min, filter the reaction solution through a vacuum filter to separate the solid and liquid, and dry the obtained solid at 95°C to constant weight to obtain a solid product.

[0096] S3. The solid obtained in step S2 is transferred to a tube furnace for programmed temperature-controlled heat treatment. Gradient heating is performed at a constant heating rate of 5℃ / min in a flowing air atmosphere. After the system temperature reaches the preset calcination temperature of 700℃, it is calcined at this temperature for 6 hours to obtain a three-dimensional porous catalyst of Gd-doped LaMnO3, named La. 0.75 Gd 0.25 MnO3.

[0097] Comparative Example 6

[0098] Similar to Comparative Example 1, the difference is that the raw materials do not contain Gd, that is, the 0.2 mmol gadolinium nitrate hexahydrate is replaced with lanthanum nitrate hexahydrate to prepare LaMnO3.

[0099] Comparative Example 7

[0100] Similar to Comparative Example 1, the difference is that the raw materials do not contain La and Gd, that is, gadolinium nitrate hexahydrate and lanthanum nitrate hexahydrate are not added, and the product obtained is MnO. x .

[0101] Comparative Example 8

[0102] Similar to Comparative Example 1, the difference is that the raw material does not contain La, that is, the 0.8 mmol lanthanum nitrate hexahydrate is replaced with gadolinium nitrate hexahydrate to prepare GdMnO3.

[0103] Experimental Example 1

[0104] La prepared using 0.10 g of comparative examples 1-5 respectively 0.8 Gd 0.2 MnO3, La 0.95 Gd 0.05 MnO3, La 0.9 Gd 0.1 MnO3, La 0.85 Gd 0.15 MnO3, La 0.75 Gd 0.25 Using MnO3 as the experimental subject, within a temperature range of 60-380℃, a normal simulated flue gas atmosphere (SFG) included 300 ppm toluene (C7H8), 6 vol.% O2, and 94 vol.% N2. The test results are as follows: Figure 1 As shown.

[0105] from Figure 1 It can be seen that the influence of reaction temperature on the catalytic oxidation performance of all samples follows a roughly consistent trend, except for La. 0.95 Gd 0.05 In addition to MnO3, its catalytic activity for the oxidation of toluene increases with increasing reaction temperature under low-temperature conditions, achieving a good catalytic effect at around 260℃. Subsequently, as the reaction temperature continues to rise, the catalytic performance for C7H8 fluctuates and even decreases slightly.

[0106] In all Gd-doped samples, La 0.8 Gd 0.2 MnO3 exhibits the best catalytic degradation performance of toluene, mainly because appropriate Gd metal doping gives the catalyst the strongest synergistic effect and the best physicochemical properties. It can promote the dispersion of metal oxides, inhibit their aggregation, and provide sufficient adsorption and catalytic active sites for the catalytic reaction, thus exhibiting the best C7H8 catalytic oxidation performance.

[0107] Therefore, the La:Gd ratio of Comparative Example 1 was selected as the basis for catalyst preparation.

[0108] Example 1

[0109] A method for preparing LaMnO3 by Gd doping coupled with nitric acid etching synergistic modification 0.8 Gd 0.2 The method for using MnO3(n) perovskite catalysts, the steps are as follows:

[0110] S1. Dissolve 0.8 mmol lanthanum nitrate hexahydrate, 0.2 mmol gadolinium nitrate hexahydrate, and 1 mmol manganese nitrate solution (mass concentration of 50 wt.%) in 50 mL of water and sonicate for 1 h to form a precursor mixed solution;

[0111] S2. Add 2.4 mmol of oxalic acid to the precursor mixture obtained in step S1, place it in a magnetic stirrer, stir at a stirring rate of 850 r / min until the sample is completely dissolved, then heat to 80°C, continue stirring at this temperature for 60 min, filter the reaction solution through a vacuum filter to separate the solid and liquid, and dry the obtained solid at 95°C to constant weight to obtain a solid product.

[0112] S3. The solid obtained in step S2 is transferred to a tube furnace for programmed temperature-controlled heat treatment. Heating is performed at a constant heating rate of 5°C / min in a flowing air atmosphere. After the system temperature reaches the preset calcination temperature of 700°C, calcination is carried out at this temperature for 6 hours to obtain a three-dimensional porous catalyst of Gd-doped LaMnO3, named La. 0.8 Gd 0.2 MnO3;

[0113] S4. The La obtained in step S3 0.8 Gd 0.2 MnO3 was acid-etched in 0.1 mol / L nitric acid solution for 6 h, then rinsed and dried to obtain Gd-doped coupled acid-etched modified lanthanum manganese perovskite, named La. 0.8 Gd 0.2 MnO3(n).

[0114] Experimental Example 2

[0115] La in Example 1 0.8 Gd 0.2 MnO3(n) and La in Comparative Example 1 0.8 Gd 0.2 MnO3, LaMnO3 in Comparative Example 6, and MnO in Comparative Example 7 x A comparison of specific surface area and pore size distribution was performed, and the results are shown in Table 1 and 2. Figure 2 .

[0116] Table 1. Comparison results of products from Example 1 and Comparative Examples 1, 6, and 7.

[0117]

[0118] From Table 1 and Figure 2 It can be seen that La in Comparative Example 1 0.8 Gd 0.2 Compared to LaMnO3 in Comparative Example 6, MnO3 has a larger specific surface area and higher pore volume, indicating that Gd doping can not only increase the active metal Mn 3+ The quantity and distribution of La can also optimize the interfacial properties of the catalyst, increasing its specific surface area and pore volume; in Example 1, La 0.8 Gd 0.2 MnO3(n) compared with La in Example 1 0.8 Gd 0.2 MnO3 possesses a significantly larger specific surface area and higher pore volume, along with a smaller average pore size. This indicates that nitric acid etching can greatly improve the physicochemical properties of the catalyst, resulting in a significantly larger specific surface area and higher pore volume. This provides more catalytically active interfaces, exposes more active metal sites and reactive oxygen species, and is more conducive to increasing the number of accessible active sites and reactive oxygen species, as well as the timely mass transfer and diffusion of reactants and products. In summary, Gd doping coupled with nitric acid etching synergistically regulates the physicochemical properties of modified LaMnO3, inducing more lattice defects and oxygen vacancies, and providing more active MnO3. 3+ This improves the electron mobility and redox properties of La, promotes lattice oxygen activation, and enhances its low-temperature catalytic oxidation and degradation activity against VOCs such as toluene. Therefore, La... 0.8 Gd0.2 MnO3(n) exhibits higher performance than La under different temperature conditions. 0.8 Gd 0.2 Catalytic activity of MnO3 and LaMnO3.

[0119] Using 0.1g of La from Example 1 0.8 Gd 0.2 MnO3(n), La in Comparative Example 1 0.8 Gd 0.2 MnO3, LaMnO3 in Comparative Example 6, and MnO in Comparative Example 7 x As the experimental subject, within a temperature range of 60-380℃, a normal simulated flue gas atmosphere (SFG) included 300 ppm toluene (C7H8), 6 vol.% O2, and 94 vol.% N2. The test results are as follows... Figure 3 As shown.

[0120] from Figure 3 It can be seen that La in Example 1 0.8 Gd 0.2 MnO3(n) exhibits significantly better catalytic oxidation performance for C7H8 than La in Comparative Example 1. 0.8 Gd 0.2 MnO3, LaMnO3 in Comparative Example 6, and MnO in Comparative Example 7 x .

[0121] Experimental Example 3

[0122] While maintaining the reaction temperature at 260°C, the effects of flue gas components (O2, H2O(g), and SO2) on the La prepared in Example 1 were investigated. 0.8 Gd 0.2 The influence of MnO3(n) on the low-temperature catalytic oxidation performance of C7H8. A normal simulated flue gas atmosphere (SFG) includes: 300 ppm toluene (C7H8), 6 vol.% O2, and 94 vol.% N2. Different systems were set up by changing the SFG composition, as follows:

[0123] (1) SFG-6%O2 group: 300ppm toluene (C7H8) and 94%N2;

[0124] (2) SFG+6%O2 group: 300ppm toluene (C7H8), 12 Vol.%O2 and 94 Vol.%N2;

[0125] (3) SFG+200ppmSO2 group: 300ppm toluene (C7H8), 6 Vol.%O2, 94 Vol.%N2 and 200ppmSO2;

[0126] (4) SFG+400ppmSO2 group: 300ppm toluene (C7H8), 6 Vol.%O2, 94 Vol.%N2 and 400ppmSO2;

[0127] (5) SFG+600ppmSO2 group: 300ppm toluene (C7H8), 6 Vol.%O2, 94 Vol.%N2 and 600ppmSO2;

[0128] (6) SFG+3%H2O group: 300ppm toluene (C7H8), 6Vol.%O2, 94Vol.%N2 and 3Vol.%H2O;

[0129] (7) SFG+5%H2O group: 300ppm toluene (C7H8), 6Vol.%O2, 94Vol.%N2 and 5Vol.%H2O;

[0130] (8) SFG + 400ppm SO2 + 5% H2O group: 300ppm toluene (C7H8), 6 Vol.% O2, 94 Vol.% N2, 400ppm SO2 and 5 Vol.% H2O;

[0131] (9) SFG group: 300 ppm toluene (C7H8), 6 Vol.% O2 and 94 Vol.% N2.

[0132] Test results are as follows Figure 4 As shown.

[0133] from Figure 4 As can be seen from La 0.8 Gd 0.2 MnO3(n) exhibits a toluene conversion efficiency of 78.1% under an SFG-6% O2 atmosphere. When 6% O2 is added to the reaction system, La... 0.8 Gd 0.2 The toluene conversion rate of MnO3(n) was increased to 94.3%. Further addition of 6% O2 to the system resulted in La... 0.8 Gd 0.2 The toluene conversion rate of MnO3(n) only increased to 94.8%. This shows that O2 has a significant effect on the conversion of La... 0.8 Gd 0.2 MnO3(n) significantly promotes the catalytic oxidation of C7H8, as it can promptly replenish consumed reactive oxygen species, thus enhancing the performance of La. 0.8 Gd 0.2 MnO3(n) is a necessary condition for maintaining sustained and efficient catalytic oxidation of C7H8, and 6% O2 is sufficient to meet this requirement; water vapor is essential for the oxidation of La 0.8 Gd 0.2MnO3(n) exhibits a slight inhibitory effect on the catalytic oxidation of C7H8. Although the hydroxyl groups (-OH) generated by H2O dissociation can promote the oxidation reaction, this slight inhibitory effect may stem from the fact that the inhibitory effect caused by the competition between water vapor and reactants for active sites outweighs the promoting effect of the generated hydroxyl groups; SO2 has a slight inhibitory effect on La. 0.8 Gd 0.2 The catalytic oxidation of C7H8 by MnO3(n) exhibits a certain degree of inhibition. This may be because SO2 not only competes with reactants for active sites but also reacts with active metal oxides to produce metal sulfates or sulfites, leading to coverage of active sites, pore blockage, and a decrease in specific surface area, thus reducing its catalytic oxidation performance of C7H8. 0.8 Gd 0.2 MnO3(n) still exhibits good catalytic oxidation performance of C7H8 under the conditions of simultaneous presence of SO2 and water vapor, demonstrating good resistance to water and sulfur, and has good potential for industrial application.

[0134] Test Example 4

[0135] To investigate the mechanism by which Gd doping coupled with nitric acid etching synergistically modifies LaMnO3 and enhances its VOCs removal performance, the LaMnO3 in Example 1 was used as an example. 0.8 Gd 0.2 MnO3(n), La in Comparative Example 1 0.8 Gd 0.2 MnO3, LaMnO3 in Comparative Example 6, and MnO in Comparative Example 7 x The experimental subject was characterized using scanning electron microscopy (SEM), and the results are shown in [Figure number missing]. Figure 5 Where a, b, c, and d correspond to La respectively 0.8 Gd 0.2 MnO3(n), La 0.8 Gd 0.2 MnO3, LaMnO3, MnO x .

[0136] Depend on Figure 5 It can be known that La 0.8 Gd 0.2 The three-dimensional porous structure of MnO3(n) is superior to that of La. 0.8 Gd 0.2 MnO3, LaMnO3 and MnO x . LaMnO3 and MnO x Metal aggregation is more pronounced in La 0.8 Gd 0.2MnO3(n) has a better pore structure, better dispersion of active metals, and larger pore volume and specific surface area, which is more conducive to exposing more active sites and to the reaction of O2 and C7H8 at the active sites, as well as their mass transfer and diffusion. Therefore, La 0.8 Gd 0.2 MnO3(n) exhibits good performance in the low-temperature catalytic oxidation of VOCs such as toluene.

[0137] Experimental Example 5

[0138] To investigate the mechanism by which Gd doping coupled with nitric acid etching synergistically modifies LaMnO3 and enhances its VOCs removal performance, the LaMnO3 in Example 1 was used as an example. 0.8 Gd 0.2 MnO3(n), La in Comparative Example 1 0.8 Gd 0.2 MnO3 and LaMnO3 in Comparative Example 6 were used as experimental subjects, and their H2 temperature-programmed reduction (H2-TPR) characterization was performed. The results are shown in [Figure 1]. Figure 6 .

[0139] like Figure 6 As shown, both Gd doping and nitric acid etching shift the corresponding reduction peaks toward lower temperatures. This indicates that both Gd doping and nitric acid etching can induce lattice defects, enhance redox performance, generate higher density surface oxygen vacancies, construct richer active oxygen and electron migration channels, and promote the performance of low-temperature catalytic oxidation of C7H8.

[0140] Experimental Example 6

[0141] To investigate the mechanism by which Gd doping coupled with nitric acid etching synergistically modifies LaMnO3 and enhances its VOCs removal performance, the LaMnO3 in Example 1 was used as an example. 0.8 Gd 0.2 MnO3(n), La in Comparative Example 1 0.8 Gd 0.2 MnO3, LaMnO3 in Comparative Example 6, and MnO in Comparative Example 7 x Using GdMnO3 from Comparative Example 8 as the experimental subject, X-ray photoelectron spectroscopy (XPS) characterization was performed, and the results are shown in [Figure 8]. Figure 7-10 .

[0142] Depend on Figure 7 It is known that both Gd doping and nitric acid etching can lead to the migration of the corresponding peak in La, indicating that electrons migrate and the environment in which the electrons are located changes. This will promote the migration of active oxygen and improve its redox properties to a certain extent, which will help improve the low-temperature catalytic activity of the catalyst for VOCs such as toluene.

[0143] Depend on Figure 8It is known that both Gd doping and nitric acid etching can lead to the migration of the corresponding peak of Gd, indicating that electrons migrate and the environment in which these electrons reside changes. This can promote the migration of reactive oxygen species and enhance their redox properties to some extent, which helps to improve the efficiency of La. 0.8 Gd 0.2 Low-temperature catalytic activity of MnO3(n) on VOCs such as toluene.

[0144] Depend on Figure 9 It can be seen that Gd doping promotes Mn 3+ / Mn n+ (Mn) n+ =Mn 3+ +Mn 4+ The percentage of Mn increased from 83.5% to 85.5% due to nitric acid etching. 3+ / Mn n+ The increase from 85.5% to 86.8% indicates that both Gd doping and nitric acid etching can improve the activity of Mn. 3+ The proportion of La 0.8 Gd 0.2 Mn in MnO3(n) 3+ The highest content of oxygen vacancies corresponds to the highest oxygen vacancy concentration, giving it excellent redox properties. This helps in the adsorption and activation of gaseous oxygen molecules, which is beneficial for the low-temperature catalytic oxidation of VOCs such as C7H8.

[0145] Depend on Figure 10 It can be known that La 0.8 Gd 0.2 The relative proportion of chemisorbed oxygen in MnO3(n) is significantly higher than that in LaMnO3. Generally speaking, the low-temperature catalytic activity of a catalyst is related to the proportion of chemisorbed oxygen, because chemisorbed oxygen is the most active oxygen species with a high mobility, which is beneficial to the adsorption and activation of C7H8. Therefore, LaMnO3... 0.8 Gd 0.2 MnO3(n) exhibits good performance in the low-temperature catalytic oxidation of VOCs.

[0146] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention 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 the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. Application of Gd-doped coupling acid-etching modified lanthanum manganese perovskite in removal of VOCs in flue gas, characterized in that, In a temperature programmed gas-solid reactor, the Gd-doped lanthanum manganese perovskite modified by coupling acid etching is loaded, and catalytic oxidation of toluene is carried out in the presence of 300 ppm toluene, 6 Vol.% O2 and 94 Vol.% N2 mixed gas; The preparation method of the Gd-doped lanthanum manganese perovskite modified by coupling acid etching comprises the following steps: A lanthanum-containing compound, a gadolinium-containing compound and a manganese nitrate solution are dissolved in water, and ultrasonic treatment is performed to obtain a precursor mixed solution; the molar ratio of La in the lanthanum-containing compound to Gd in the gadolinium-containing compound is 0.8:0.2; Oxalic acid is added to the precursor mixed solution, and after stirring to dissolve, heating reaction is performed, and then filtration, drying to constant weight are performed to obtain a solid substance; The solid substance is subjected to high-temperature calcination, and the obtained product is placed in a nitric acid solution for acid etching treatment, and after being taken out, rinsing and drying are performed to obtain the Gd-doped lanthanum manganese perovskite modified by coupling acid etching.

2. Use according to claim 1, characterized in that, The total molar amount of the lanthanum-containing compound and the gadolinium-containing compound is 1:1 of the molar amount of the manganese nitrate solution; and / or The lanthanum-containing compound is lanthanum nitrate hexahydrate; and / or The gadolinium-containing compound is gadolinium nitrate hexahydrate.

3. Use according to claim 1, characterized in that, The molar amount of the oxalic acid is 1.2 times of the sum of the molar amounts of the lanthanum-containing compound, the gadolinium-containing compound and the manganese nitrate solution.

4. Use according to claim 1, characterized in that, The stirring speed is 850 r / min; and / or The temperature of the heating reaction is 80℃, and the time is 60 min.

5. The use according to claim 1, characterized in that, The temperature during drying to constant weight is 95℃.

6. Use according to claim 1, characterized in that, The high-temperature calcination condition is that the temperature is 700℃, the temperature rising rate is 5℃ / min, and the time is 6 h.

7. The use according to claim 1, characterized in that, The concentration of the nitric acid solution is 0.1 mol / L.

8. The use according to claim 1, characterized in that, The acid etching treatment time is 6 h. 9.A Gd-doped lanthanum manganese perovskite modified by coupling acid etching prepared by the preparation method in the application of any one of claims 1-8.

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