Preparation method and application of a spherical structure CoMn spinel catalyst
By preparing spherical CoMn spinel catalysts via co-precipitation, the problems of high cost of noble metal catalysts and insufficient activity of transition metal oxides were solved, achieving efficient oxidation and deep mineralization of VOCs at low temperatures and significantly improving catalytic activity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-31
- Publication Date
- 2026-04-14
AI Technical Summary
In the existing technology, noble metal-based catalysts are expensive and difficult to replace, and transition metal oxide catalysts are not effective in oxidizing VOCs under low temperature conditions. In particular, CoMn spinel catalysts with special morphology and structure are complex to synthesize and have few reports on their use in VOCs oxidation.
A spherical CoMn spinel catalyst was prepared by coprecipitation. By controlling the solution pH, aging time, and calcination temperature, a regular spherical structure was formed, avoiding morphological damage caused by high-temperature sintering, and achieving efficient oxidation of various VOCs.
The preparation method is simple and low-cost, and can achieve deep mineralization of chlorobenzene and efficient oxidation of various VOCs at medium and low temperatures, avoiding the formation of polychlorinated byproducts and significantly improving catalytic activity.
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Figure CN120885234B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst technology, and particularly relates to a method for preparing a spherical CoMn spinel catalyst and its application. Background Technology
[0002] Chlorine-containing volatile organic compounds (Cl-VOCs) are important precursors to gaseous pollutants such as ozone (O3), photochemical smog, and fine particulate matter (PM2.5), posing a serious threat to human health and the ecological environment. Catalytic oxidation technology, as a green and efficient technique for treating Cl-VOCs, focuses on designing and preparing catalysts capable of degrading Cl-VOCs into non-toxic CO2, H2O, and soluble HCl at low temperatures. Although noble metal-based catalysts exhibit excellent catalytic activity, their high cost and limited availability have prompted researchers to seek alternatives. Meanwhile, transition metal oxides are attracting increasing attention due to their low cost, superior catalytic activity, and stability, and hold promise as a replacement for noble metal-based catalysts.
[0003] Extensive research has shown that manganese (Mn) and cobalt (Co)-based oxides exhibit excellent activity in VOCs oxidation reactions among transition metal oxide catalysts, including single-type metal oxides (δ-MnO2, Mn3O4, and Co3O4) and composite metal oxides (MnO2, Mn3O4, and Co3O4). x -CeO2, CuCoO x and CuMnCoO x Supported metal oxides (MnO) x / Al2O3, α-MnO2 / ZSM-5 and Co3O4@MnO x CoMn oxides, including perovskite (LaCoO3), mullite (SmMn2O5), and spinel (CoMn2O4), have attracted significant attention for low-temperature oxidation of VOCs due to their tunable structure and diverse chemical composition. Unlike perovskite / mullite oxides where the A-site metal primarily stabilizes the catalyst structure, metals at both the A and B sites in the tetrahedral and octahedral regions of spinel can serve as active sites. These sites can be adjusted through metal doping and geometric distribution, thereby influencing the electronic structure and acidity of the catalyst. However, CoMn spinels with unique morphologies and structures are rarely reported in VOCs oxidation due to the typically complex synthesis procedures and sophisticated equipment required. Summary of the Invention
[0004] To address the aforementioned technical problems, this invention proposes a method for preparing a spherical CoMn spinel catalyst and its application. This invention employs a simple co-precipitation method to prepare CoMn spinel with a regular spherical structure. The synthesized CoMn spinel catalyst can not only achieve efficient oxidation of various VOCs but also achieve deep mineralization of chlorobenzene. Furthermore, the preparation method provided by this invention is simple and requires no high-precision instruments.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] This invention provides a method for preparing a spherical CoMn spinel catalyst, comprising the following steps:
[0007] (1) Cobalt nitrate and manganese acetate were added to a mixed solution of ethanol and water. After stirring, ammonium bicarbonate was added dropwise to adjust the pH of the solution to alkaline. After aging, a white precipitate was obtained.
[0008] (2) The white precipitate obtained in step (1) is washed until neutral, and then dried and calcined to obtain the spherical CoMn spinel catalyst.
[0009] Technical principle:
[0010] First, the metal salt is uniformly dissolved in an alcohol-water mixed solvent. Ammonium bicarbonate is slowly added to create an alkaline environment, which causes Co and Mn ions to co-precipitate uniformly, forming amorphous / microcrystalline initial particles.
[0011] Next, the particle morphology was controlled through long-term aging at room temperature: via Ostwald ripening and dissolution-recrystallization processes, the initially irregular particles were reorganized and smoothed, ultimately evolving into thermodynamically stable, well-defined spherical precursor particles in a low-surface-tension alcohol-water environment. The Ostwald ripening process involves the dissolution of small particles (high solubility), followed by migration and redeposition onto the surface of larger particles (low solubility). This process narrows the particle size distribution and smooths the surface. The dissolution-recrystallization process involves the continuous dissolution and recrystallization of initially formed amorphous or microcrystalline basic carbonate particles in a weakly alkaline environment and an alcohol-water mixed solvent. This process tends to eliminate sharp edges, forming thermodynamically stable, well-defined spherical precursor particles.
[0012] Subsequently, impurities were thoroughly removed by alternating washing with deionized water and ethanol. Ethanol replacement significantly reduced capillary forces during the subsequent drying process, effectively preventing the agglomeration and deformation of the spherical precursor. Slow heating allowed the organic components in the precursor to decompose and volatilize gently, avoiding morphological damage. Holding at a suitable temperature for a sufficient time allowed the precursor to decompose and recrystallize into the CoMn spinel phase, while maximally inheriting the regular spherical structure of the precursor, avoiding morphological damage caused by high-temperature sintering, ultimately yielding CoMn spinel with a regular spherical structure.
[0013] Further, in step (1), the molar ratio of metal ions of cobalt nitrate and manganese acetate is 1:(1.5~2).
[0014] Further, in step (1), the volume ratio of ethanol to water is (1-3):1.
[0015] Further, in step (1), the stirring temperature is room temperature, the stirring rate is 300-500 r / min, and the stirring time is 1-2 h.
[0016] Further, in step (1), the concentration of ammonium bicarbonate is 1-2 mol / L; ammonium bicarbonate is added dropwise to adjust the pH of the solution to 8-9.
[0017] Furthermore, in step (1), the aging temperature is room temperature, and the aging time is 16 to 18 hours.
[0018] Furthermore, in step (2), the drying temperature is 90-120°C, and the drying time is 12-15 hours.
[0019] Further, in step (2), the calcination temperature is 500-550℃, the calcination time is 3-5h, and the rate of heating to the calcination temperature is 2-5℃ / min.
[0020] This invention provides a spherical CoMn spinel catalyst, which is prepared according to the preparation method described in the above technical solution.
[0021] The present invention also provides an application of the spherical CoMn spinel catalyst described above in the deep oxidation of VOCs.
[0022] Compared with the prior art, the present invention has the following advantages and technical effects:
[0023] The method for preparing the spherical CoMn spinel catalyst provided by this invention uses low-cost materials and is simple to manufacture. Regular spherical CoMn spinel can be synthesized without complicated operation steps or the assistance of precision instruments.
[0024] The spherical CoMn spinel prepared by this invention can achieve deep oxidation of chlorobenzene in the medium and low temperature range, effectively avoiding the generation of polychlorinated byproducts, and can also deeply oxidize a variety of VOCs (such as toluene and ethyl acetate). Attached Figure Description
[0025] 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:
[0026] Figure 1 The X-ray diffraction (XRD) pattern of the spherical CoMn spinel catalyst prepared in Example 1;
[0027] Figure 2 The images shown are scanning electron microscope (SEM) images of the spherical CoMn spinel catalyst prepared in Example 1, where a, b, c, and d are SEM images at different magnifications.
[0028] Figure 3 The image shows a transmission electron microscope (TEM) image of the spherical CoMn spinel catalyst prepared in Example 1, where a is 500 nm and b is 200 nm.
[0029] Figure 4 The image shows the energy dispersive X-ray spectral elemental distribution (EDX-Mapping) of the spherical CoMn spinel catalyst prepared in Example 1, where a is the full spectrum, b is the spectrum of Co, c is the spectrum of Mn, and d is the spectrum of O. Detailed Implementation
[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0032] This invention provides a method for preparing a spherical CoMn spinel catalyst, comprising the following steps:
[0033] (1) Cobalt nitrate and manganese acetate were added to a mixed solution of ethanol and water. After stirring, ammonium bicarbonate was added dropwise to adjust the pH of the solution to alkaline. After aging, a white precipitate was obtained.
[0034] (2) The white precipitate obtained in step (1) is washed until neutral, and then dried and calcined to obtain the spherical CoMn spinel catalyst.
[0035] In a preferred embodiment, in step (1), the molar ratio of cobalt nitrate to manganese acetate is 1:(1.5-2), more preferably 1:2. The reason for controlling the molar ratio of cobalt nitrate to manganese acetate within the above range is to obtain a catalyst with an AB2O4 spinel configuration.
[0036] In a preferred embodiment, in step (1), the ratio of the cobalt nitrate to the mixed solution of ethanol and water is 0.01 mol: 60 mL.
[0037] In a preferred embodiment, in step (1), the volume ratio of ethanol to water is (1-3):1, more preferably 2:1; the ethanol is anhydrous ethanol.
[0038] In a preferred embodiment, in step (1), the stirring temperature is room temperature, the stirring rate is 300-500 r / min, and the stirring time is 1-2 h.
[0039] In a preferred embodiment, in step (1), the concentration of ammonium bicarbonate is 1-2 mol / L; ammonium bicarbonate is added dropwise to adjust the pH of the solution to 8-9. This invention uses ammonium bicarbonate to adjust the pH of the solution without introducing other impurities, as the ammonium ions can volatilize upon heating; adding ammonium bicarbonate dropwise avoids excessively high local concentrations and drastic pH changes, preventing explosive nucleation and the generation of a large number of small, uneven crystal nuclei.
[0040] In a preferred embodiment, in step (1), the aging temperature is room temperature and the aging time is 16-18 hours.
[0041] In a preferred embodiment, in step (2), the washing reagents are anhydrous ethanol and deionized water; the washing method is centrifugal washing, and the centrifugal washing speed is 5000-7000 r / min. This invention thoroughly removes impurities by alternating washing with anhydrous ethanol and deionized water. Ethanol replacement reduces capillary forces during the subsequent drying process, effectively preventing the aggregation and deformation of the spherical precursor.
[0042] In a preferred embodiment, in step (2), the drying temperature is 90-120°C and the drying time is 12-15 hours.
[0043] In a preferred embodiment, in step (2), the calcination temperature is 500–550°C, the calcination time is 3–5 h, and the rate of heating to the calcination temperature is 2–5°C / min. The controlled heating rate in this invention avoids morphological damage caused by excessively rapid heating; and holding at a suitable temperature for a sufficient time effectively promotes the decomposition and recrystallization of the precursor into CoMn spinel, while maintaining the regular spherical structure of the precursor to the greatest extent, thus avoiding morphological damage caused by high-temperature sintering.
[0044] This invention provides a spherical CoMn spinel catalyst, prepared according to the preparation method described above. The CoMn spinel catalyst provided by this invention has a regular spherical structure.
[0045] The present invention also provides an application of the spherical CoMn spinel catalyst described above in the deep oxidation of VOCs.
[0046] In a preferred embodiment, the VOCs are selected from one or more of chlorobenzene, toluene, and ethyl acetate.
[0047] In a preferred embodiment, the process conditions for deep oxidation of VOCs include: an O2 concentration of 20 vol.% and a space velocity of 60,000 h⁻¹. -1 The reaction temperature is 150-400℃.
[0048] The performance testing process for the catalyst in the embodiments and comparative examples of this invention for catalytic oxidation of VOCs is as follows:
[0049] Catalytic performance evaluation was conducted in a fixed-bed reactor. 0.1 g of catalyst (40-60 mesh) was weighed and placed into a quartz reaction tube (inner diameter 10 mm), and then a reaction mixture was introduced at a flow rate of 100 mL / min. After the gas concentration stabilized, the changes in VOCs concentration before and after the reaction were recorded. The VOCs conversion rate was calculated using the following formula:
[0050] Conversion rate (%) = ([C]0 - [C]) t ) / [C]0*100%;
[0051] Among them, [C]0 and [C] t The values represent the concentrations of VOCs before and after the reaction, respectively.
[0052] In this embodiment of the invention, room temperature refers to "25±2℃".
[0053] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.
[0054] Example 1
[0055] A method for preparing a spherical CoMn spinel catalyst, comprising the following steps:
[0056] (1) Add 0.01 mol of cobalt nitrate and 0.02 mol of manganese acetate to a mixed solution of anhydrous ethanol and deionized water (the volume ratio of anhydrous ethanol and deionized water is 2:1, and the total volume is 60 mL). Stir at 500 r / min for 1 h. Then slowly add 1.5 mol / L of ammonium bicarbonate dropwise and check the pH value of the solution immediately. When the pH value of the solution is detected to be 8-9, stop adding ammonium bicarbonate. After stirring evenly, age at room temperature for 18 h to obtain a white precipitate.
[0057] (2) The white precipitate obtained in step (1) was washed with deionized water and anhydrous ethanol by alternating centrifugation (7000 r / min) until neutral, and then dried overnight (12 h) in a forced-air drying oven at 90 °C to obtain a white solid product. The white solid product was placed in a muffle furnace and calcined at 500 °C for 3 h at a heating rate of 5 °C / min to obtain a CoMn spinel catalyst with a regular spherical structure.
[0058] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the spherical CoMn spinel catalyst prepared in Example 1. Figure 1 It can be seen that the diffraction peaks of the spherical CoMn spinel catalyst prepared in Example 1 are basically consistent with ((Co,Mn)(Co,Mn)2O4), indicating that Example 1 successfully prepared a catalyst with the CoMn spinel configuration.
[0059] Figure 2 The images shown are scanning electron microscope (SEM) images of the spherical CoMn spinel catalyst prepared in Example 1, where a, b, c, and d are SEM images at different magnifications. Figure 2 It can be seen that the CoMn spinel catalyst prepared in Example 1 has a regular spherical structure.
[0060] Figure 3 The image shows a transmission electron microscope (TEM) image of the spherical CoMn spinel catalyst prepared in Example 1, where a is 500 nm and b is 200 nm. Figure 3 It can be seen that the particle size of the spherical CoMn spinel catalyst prepared in Example 1 is about 600-1000 nm.
[0061] Figure 4 The image shows the energy-dispersive X-ray spectral elemental distribution (EDX-Mapping) of the spherical CoMn spinel catalyst prepared in Example 1, where a is the full spectrum, b is the spectrum of Co, c is the spectrum of Mn, and d is the spectrum of O. Figure 4It can be seen that Co, Mn, and O elements are uniformly distributed on the catalyst surface, indicating that Example 1 successfully prepared a CoMn spinel catalyst.
[0062] Comparative Example 1
[0063] A method for preparing a conventional CoMn spinel catalyst (i.e., without a special morphology or structure), the specific steps of which are as follows:
[0064] (1) Dissolve 0.01 mol of cobalt nitrate in 20 mL of deionized water and stir until homogeneous at room temperature to obtain a cobalt nitrate solution;
[0065] (2) Dissolve 0.02 mol of manganese nitrate in 40 mL of deionized water and stir until homogeneous at room temperature to obtain a manganese nitrate solution;
[0066] (3) Add 20 mL of ammonium hydroxide solution with a concentration of 25 wt.% to the cobalt nitrate solution obtained in step (1), and then mix it evenly with the manganese nitrate solution obtained in step (2) at room temperature. Stir at 300 r / min for 2 h, centrifuge and filter to obtain a solid precipitate, and then dry it overnight in a forced-air drying oven at 90 °C to obtain a solid product. Place the above solid product in a muffle furnace and calcine it at 500 °C for 3 h with a heating rate of 5 °C / min to obtain a conventional CoMn spinel catalyst.
[0067] The chlorobenzene removal efficiency of the catalysts prepared in Example 1 and Comparative Example 1 is shown in Table 1. The reaction mixture was a mixture of chlorobenzene and oxygen, and the reaction temperature was 300°C.
[0068] Table 1
[0069] Catalyst type Chlorobenzene removal efficiency Conventional CoMn spinel (Comparative Example 1) 61.5％ Spherical CoMn spinel (Example 1) 92.9％
[0070] As can be seen from Table 1, the conventional CoMn spinel catalyst prepared in Comparative Example 1 has poor chlorobenzene oxidation performance, with a chlorobenzene removal efficiency of only 61.5% at 300℃; while the spherical CoMn spinel catalyst prepared in Example 1 of this invention can achieve a chlorobenzene removal efficiency of 92.9% at 300℃.
[0071] The catalytic performance of the spherical CoMn spinel prepared in Example 1 for removing different VOCs (chlorobenzene, toluene and ethyl acetate) at different temperatures is shown in Table 2.
[0072] Table 2
[0073]
[0074]
[0075] As can be seen from Table 2, the spherical CoMn spinel prepared by this invention exhibits excellent catalytic performance in the removal of different VOCs. The removal efficiency of chlorobenzene can reach 99.4% at 350℃, the removal efficiency of toluene can reach 99.7% at 270℃, and the removal efficiency of ethyl acetate can reach 99.7% at 210℃.
[0076] Examples 2-5
[0077] A method for preparing a spherical CoMn spinel catalyst differs from Example 1 in that, in step (1), the volume ratio of anhydrous ethanol to deionized water is 1:1 (Example 2), 1.5:1 (Example 3), 2.5:1 (Example 4), and 3:1 (Example 5), respectively, while the rest is the same as in Example 1.
[0078] The chlorobenzene removal efficiency of the spherical CoMn spinel catalysts prepared in Examples 1-5 is shown in Table 3. The reaction mixture was a mixture of chlorobenzene and oxygen, and the reaction temperature was 300℃.
[0079] Table 3
[0080] Volume ratio of anhydrous ethanol to deionized water Chlorobenzene removal efficiency 1:1 (Example 2) 79.5％ 1.5:1 (Example 3) 88.4％ 2:1 (Example 1) 92.9％ 2.5:1 (Example 4) 90.2％ 3:1 (Example 5) 87.6％
[0081] Table 3 shows that the removal efficiency of chlorobenzene is the highest at 92.9% when the volume ratio of anhydrous ethanol to deionized water is 2:1. This is because the appropriate ratio of anhydrous ethanol to water can effectively adjust the polarity of the solvent, control the precipitation rate and particle size distribution of metal ions, and thus achieve uniform spheroidization of the catalyst precursor. At the same time, it optimizes the mesoporous channels formed by the stacking of spherical particles. This structure can not only effectively expose more active sites, but also increase the adsorption of chlorobenzene molecules, thereby significantly improving the catalytic activity of the material.
[0082] 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.
Claims
1. The application of a spherical CoMn spinel catalyst in the deep oxidation of ethyl acetate, characterized in that, The preparation method of the spherical CoMn spinel catalyst includes the following steps: (1) Cobalt nitrate and manganese acetate are added to a mixed solution of ethanol and water. After stirring, ammonium bicarbonate is added dropwise to adjust the pH of the solution to alkaline. After aging, a white precipitate is obtained. The molar ratio of metal ions of cobalt nitrate and manganese acetate is 1:(1.5-2). The volume ratio of ethanol and water is (1-3):
1. (2) The white precipitate obtained in step (1) is washed until neutral, and then dried and calcined to obtain the spherical CoMn spinel catalyst; the calcination temperature is 500-550℃, the calcination time is 3-5h, and the rate of heating to the calcination temperature is 2-5℃ / min.
2. The application according to claim 1, characterized in that, In step (1), the stirring temperature is room temperature, the stirring rate is 300-500 r / min, and the stirring time is 1-2 h.
3. The application according to claim 1, characterized in that, In step (1), the concentration of ammonium bicarbonate is 1-2 mol / L; ammonium bicarbonate is added dropwise to adjust the pH of the solution to 8-9.
4. The application according to claim 1, characterized in that, In step (1), the aging temperature is room temperature and the aging time is 16-18 hours.
5. The application according to claim 1, characterized in that, In step (2), the drying temperature is 90-120°C and the drying time is 12-15 hours.