Preparation and application of cerium-manganese-based material

Abstract

The invention discloses preparation and application of a cerium-manganese-based material, and the preparation method specifically comprises the following steps: (1) prefabricating a reaction solution, and mixing a redox agent, a cerium salt, a manganese salt and a precipitant to obtain a mixed solution; (2) putting the mixed solution obtained in the step (1) on a constant-temperature stirrer, and continuously stirring at 50-60 DEG C; (3) adjusting the pH value of the solution to 6-11, and stirring for 2 hours; (4) aging for 2-4 hours, washing the solution with distilled water for 6-8 times, and then drying at 110-120 DEG C for 12-16 hours; and (5) putting the dried sample into a muffle furnace, and calcining at 400-500 DEG C for 6-8 hours to obtain the target product cerium-manganese-based material CeMnOx. The preparation method is short in reaction period, mild in reaction condition, simple in subsequent treatment step and low in cost, the prepared material has a very strong synergistic effect between metals, formation of lattice defects and oxygen vacancies is facilitated, and the activity in the aspect of catalytic oxidation of VOCs is greatly improved.

Description

Technical Field

[0001] The invention relates to preparation of a material and application thereof, in particular to preparation of a cerium-manganese-based material and application thereof to catalytic oxidation of VOCs, belonging to the technical field of catalyst material preparation. Background Art

[0002] Air pollution is an inevitable problem in social development. With the acceleration of mechanization, VOCs emissions have increased significantly. In addition to the negative impact on the environment and human health, they also produce secondary pollution, further threatening the ecosystem. Among various elimination technologies, catalytic oxidation is a promising candidate technology. Supported precious metal catalysts usually show excellent catalytic activity. However, due to high cost, poor thermal stability, and toxicity sensitivity, the large-scale application of such catalysts is severely limited. Generally speaking, transition metal oxides (FeO x , MnO x , CoO x , NiO x , CuO x ) and rare earth oxides (CeO x , SmO x , GdO x ) are used to degrade VOCs. Studies have shown that composite metal oxides are generally considered to be the most effective way to optimize the catalytic performance of non-precious metal catalysts. The synergistic effect of different metals improves the degradation activity and stability of the catalyst.

[0003] Cerium manganese-based catalysts are highly competitive among various composite metal oxide catalysts. Manganese oxides have open pore structures, high oxygen mobility, and a large number of surface active oxygen species, which have irreplaceable advantages in degrading VOCs. 2 It has high oxygen affinity and excellent oxygen storage capacity. 2 When combined with variable valence ions, the redox cycle efficiency and oxygen mobility are greatly improved. Cerium-manganese-based bimetallic catalysts deserve further study. Studies have shown that the catalytic activity of composite metal oxides with an amorphous phase is higher than that of catalysts with a highly crystalline phase. The interaction between different metals in solid solution catalysts is stronger, and the mutual integration between the lattices is conducive to the generation of more structural defects.

[0004] There are many methods for synthesizing composite metal oxides. Hydrothermal method, citric acid combustion method, template method, sol-gel method and precipitation method are representative methods. In comparison, precipitation method has the advantages of short reaction cycle, mild reaction conditions, simple subsequent processing steps and low cost. It is an attractive preparation method and is increasingly widely used.

[0005] Currently, patent

CN110801829A

CN111282571A

[0006] The technical problem to be solved by the present invention is, aiming at the above-mentioned defects existing in the prior art, to provide a preparation and application of a cerium-manganese-based material. The preparation method has a short reaction cycle, mild reaction conditions, simple subsequent treatment steps, and low cost. The prepared material has a strong synergistic effect between metals, is conducive to the formation of lattice defects and oxygen vacancies, and greatly improves the activity in the catalytic oxidation of VOCs.

[0007] The technical solution of the present invention to solve the above technical problems is as follows: A preparation method of a cerium-manganese-based material specifically includes the following steps: (1) Prepare a reaction solution by mixing an oxidation-reduction agent, a cerium salt, a manganese salt and a precipitating agent to obtain a mixed solution; (2) Place the mixed solution obtained in step (1) on a constant-temperature stirrer and continuously stir at 50 - 60 °C; (3) Adjust the pH of the solution to 6 - 11 and stir for 2 h; (4) After aging for 2 - 4 h, wash the solution with distilled water 6 - 8 times, and then dry it at 110 - 120 °C for 12 - 16 h; (5) Place the dried sample in a muffle furnace and calcine it at 400 - 500 °C for 6 - 8 h to obtain the target product cerium-manganese-based material CeMnO x.

[0008] The technical solution further defined in the present invention is: Furthermore, in the above-mentioned method for preparing cerium-manganese-based materials, the target product cerium-manganese-based material CeMnO x The x value is controlled between 2.5-4.

[0009] In the above-mentioned method for preparing the cerium-manganese-based material, the redox agent is potassium permanganate or hydrogen peroxide.

[0010] In the above-mentioned method for preparing the cerium-manganese-based material, the cerium salt is cerium nitrate or cerium sulfate.

[0011] In the above-mentioned preparation method of cerium-manganese-based material, the manganese salt is one of manganese nitrate, manganese acetate and manganese sulfate.

[0012] In the above-mentioned method for preparing the cerium-manganese-based material, the precipitant is potassium hydroxide or potassium carbonate.

[0013] The present invention also provides an application of a cerium-manganese-based material, and the cerium-manganese-based material is used for catalytic oxidation of VOCs.

[0014] The beneficial effects of the present invention are: At present, there are many methods for synthesizing composite metal oxides, such as hydrothermal method, citric acid combustion method, template method, sol-gel method and precipitation method. x The materials' technologies all require steps such as adding HCl, citric acid or mesoporous carbon CMK-3 reflux reaction. In these preparation technologies, it is inevitable to completely and effectively remove the additives, which may have a negative impact on the catalytic application of the materials. In comparison, the redox precipitation method used in the present invention has the advantages of short reaction cycle, mild reaction conditions, simple subsequent processing steps, low cost, etc., and is an attractive preparation method. In addition, the materials prepared by the redox precipitation method have a strong synergistic effect between metals, which is conducive to the formation of lattice defects and oxygen vacancies, and greatly improves the activity in the catalytic oxidation of VOCs.

[0015] The catalytic material of the present invention can completely oxidize VOCs at a relatively low reaction temperature (below 300°C), which indicates that the prepared CeMnO x The material can be directly used as a catalyst to carry out reactions and has relatively excellent catalytic properties.

[0016] The present invention can accurately adjust the CeMnO by controlling the pH value during preparation. x The influence of material structure and VOCs degradation performance, suitable pH value can make the material show excellent CeMnO x Structural dispersion, large specific surface area (133-154m 2 / g), abundant binding defects and rich Ce 3+ (Ce 3+ / Ce 4+ =0.15-0.18) and Mn 3+ (Mn 3+ / (Mn 2+ +Mn 3+ +Mn 4 + ) = 0.69-0.86), is a solid solution material with coexistence of polycrystalline and amorphous. Finally, VOCs can be completely oxidized at a lower temperature, and CeMnO synthesized by a one-pot method is used in the preparation process. x The material is easy to operate, low in cost, and can also control the morphology and structure of the material well.

[0017] The addition of the precipitant in the present invention has a great influence on the structural properties of the material, and also determines whether the introduction of the manganese salt can successfully prepare a Ce-Mn catalyst without a heterocrystalline phase. The precipitant combines the manganese salt with the cerium salt evenly during the preparation process to form a Ce-Mn catalyst without a heterocrystalline phase. In the material preparation process, the raw materials often contain impurities, unreacted monomers, etc. By adding an appropriate amount of precipitant, these components can react chemically or physically with the main body, thereby achieving effective separation. This separation effect helps to improve the purity and uniformity of the material.

[0018] The present invention strictly controls the pH value during preparation. By adjusting the pH value, the precipitation conditions of the metal ions can be controlled to ensure that the cerium and manganese metal ions can form stable precipitation. Adjusting the pH value can promote the formation of hydroxide precipitation by the cerium and manganese metal ions, thereby removing impurity ions. The pH value will affect the nucleation rate and growth rate of the precipitation, thereby affecting the particle size and morphology of the precipitation. Therefore, by controlling the pH value, an ideal precursor morphology and particle size distribution can be obtained.

[0019] The present invention adopts aging during preparation. During the aging process, fine crystal particles gradually gather and grow to form larger crystals. This process helps to improve the uniformity and integrity of the crystals, thereby improving the performance of the material. In addition, it also helps to remove impurities adsorbed on the surface of the precipitate and impurities hidden inside, making the precipitate purer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the XRD characterization diagram of the cerium-manganese-based material prepared in Example 1 of the present invention; Figure 2 The SEM photo and EDS-Mapping diagram of the cerium-manganese-based material prepared in Example 1 of the present invention; Figure 3This is a performance diagram of the catalytic oxidation of VOCs by the cerium-manganese-based material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be described clearly and completely below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Example 1

[0023] This embodiment provides a method for preparing a cerium-manganese-based material, specifically, preparing 120 ml of 0.01 mol KMnO 4 、0.02mol Ce(NO 3 ) 3 6H 2 O, 0.01 mol Mn(NO 3 ) 2 , 0.01mol 50wt.% KOH mixed solution, the mixed solution was placed in a constant temperature stirrer, and stirred continuously at 50°C for 1 hour, the pH of the solution was adjusted to 6, stirred again for 2 hours, and then aged for 2 hours. The obtained solution was washed with distilled water for several times, and then placed in a vacuum drying oven at 120°C for 12 hours. Finally, the dried sample was placed in a muffle furnace and calcined at 400°C for 6 hours to obtain the target material CeMnO x Sample 1.

[0024] Figure 1 This is the XRD characterization diagram of the material prepared in Example 1. It can be seen from the figure that there are 6 obvious diffraction peaks near 28.6°, 33.04°, 47.4°, 56.4°, 69.8° and 77.2°, which are respectively related to the CeO2 on the (1 1 1), (2 0 0), (2 2 0), (3 1 1), (4 0 0) and (3 3 1) crystal planes. 2 The peaks at 28.7°, 37.5°, 42.9°, 56.8° and 76.5° are attributed to MnO 2 The characteristic XRD diffraction peaks of CeMnO x Material.

[0025] In this embodiment, the pH is controlled to be 6. At pH = 6, cerium ions (Ce 4+) exists mainly in the form of hydrated ions under acidic conditions, but cerium (IV) ions have stronger oxidizing properties and will react with the reducing agent added in the present invention to generate other compound precipitations; manganese ions are not easy to precipitate directly under acidic conditions, but manganese ions usually exist in the form of low-valent states. Under acidic conditions, they can be oxidized to higher-valent states by the oxidant of the present invention, thereby promoting precipitation; the control of pH value in the present invention can control the precipitation conditions of metal ions, ensure that cerium and manganese metal ions can form stable precipitation, thereby removing impurity ions.

[0026] Under lower pH conditions, due to the low metal ion concentration, the growth rate of the precipitate will also be slower, and the growth rate of hydroxide crystals is limited by the concentration of hydroxide ions. Therefore, at low pH, the growth rate is usually lower; at higher pH values, hydroxide precipitation is relatively rapid, and the crystal growth rate of the precipitate is usually faster. With the increase of hydroxide ion concentration, the formation of the precipitate and the growth rate of the crystal will also accelerate accordingly; the pH value will affect the nucleation rate and growth rate of the precipitate, thereby affecting the particle size and morphology of the precipitate. Therefore, by controlling the pH value, the ideal precursor morphology and particle size distribution can be obtained.

[0027] Figure 2 The SEM photo and EDS-Mapping diagram of the material obtained in Example 1 show a relatively uniform block structure, and through EDS-Mapping, it can be concluded that the Ce and Mn elements are evenly distributed on the material, indicating that under appropriate reaction conditions of the present invention, this synthesis method can effectively obtain a solid solution material with a relatively uniform distribution of active components.

[0028] The above-mentioned cerium-manganese-based material is applied to the catalytic oxidation of VOCs, and the activity evaluation test of the material is carried out on a fixed bed reactor.

[0029] Weigh 0.5g of the cerium-manganese-based material sample 1 and place it in the center of a 20mm quartz tube in a tube furnace. The vaporized toluene gas is mixed evenly with air. The mixed gas contains 5000ppm toluene gas (20vol.%O 2 ), the total flow rate of the mixed gas is 200 mL / min. A gas chromatograph equipped with an existing flame ionization detector is used to detect the gas before and after the reaction.

[0030] Figure 3 The performance diagram of the material obtained in Example 1 for catalytic oxidation of VOCs is evaluated. As can be seen from the figure, the material obtained in Example 1 can achieve a 100% VOCs conversion rate at a reaction temperature of 280°C and completely oxidize VOCs.

[0031] Example 2

[0032] This embodiment provides a method for preparing a cerium-manganese-based material. The steps of Example 1 are repeated, except that the pH is adjusted to 8.5 to prepare CeMnO x Sample 2.

[0033] Example 3

[0034] This embodiment provides a method for preparing a cerium-manganese-based material. The steps of Example 1 are repeated, except that the pH is adjusted to 10 to obtain CeMnO x Sample 3.

[0035] CeMnO prepared in Example 1-3 x The x value in the sample is controlled at 2.5-4.

[0036] The samples obtained in the above Examples 1-3 were subjected to H 2 -TPR experiment, the specific reduction peak temperature area data are shown in Table 1; Table 1 According to H 2 -Reduction peak temperature region obtained by TPR sample Reduction peak I temperature (℃) Reduction peak II temperature (℃) Sample 1 255 338 Sample 2 280 369 Sample 3 293 352 The catalytic activity of the material is usually positively correlated with the low-temperature reduction of the sample, which can be 2 -TPR is used to reflect the H of different examples of materials. 2 -TPR data, as shown in Table 1, the reduction peak of the cerium-manganese bimetallic oxide catalyst appears in a lower temperature region, indicating that there is an obvious synergistic effect between the oxides containing cerium and manganese, and the reduction peak of sample 1 appears in the lowest temperature region, indicating that it exhibits the strongest intermetallic interaction among the three samples.

[0037] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for preparing a cerium-manganese-based material, characterized in that: The specific steps include: (1) Preparing a reaction solution, mixing a redox agent, a cerium salt, a manganese salt and a precipitant to obtain a mixed solution; (2) placing the mixed solution obtained in step (1) on a thermostatic stirrer and stirring continuously at 50-60° C.; (3) Adjust the pH of the solution to 6-11 and stir for 2 hours; (4) After aging for 2-4 hours, the solution was washed with distilled water 6-8 times and then dried at 110-120°C for 12-16 hours; (5) The dried sample is placed in a muffle furnace and calcined at 400-500°C for 6-8 hours to obtain the target product, cerium-manganese-based material CeMnO x .

2. The method for preparing the cerium-manganese-based material according to claim 1, characterized in that: The target product is cerium-manganese-based material CeMnO x The x value is controlled between 2.5-4.

3. The method for preparing the cerium-manganese-based material according to claim 1, characterized in that: The redox agent is potassium permanganate or hydrogen peroxide.

4. The method for preparing the cerium-manganese-based material according to claim 1, characterized in that: The cerium salt is cerium nitrate or cerium sulfate.

5. The method for preparing the cerium-manganese-based material according to claim 1, characterized in that: The manganese salt is one of manganese nitrate, manganese acetate and manganese sulfate.

6. The method for preparing the cerium-manganese-based material according to claim 1, characterized in that: The precipitant is potassium hydroxide or potassium carbonate.

7. An application of the cerium-manganese-based material prepared according to any one of claims 1 to 5, characterized in that: The cerium-manganese-based material is used for catalytic oxidation of VOCs.

Images