A catalyst for catalytic oxidation of volatile organic compounds using samarium-modified manganese oxide and a method for preparing the same

Abstract

The application discloses a catalyst for catalyzing volatile organic compounds by using a samarium modified manganese oxide and a preparation method thereof, relates to a catalyst for organic compounds and a preparation method thereof, and discloses a samarium (Sm) modified manganese oxide catalyst and a preparation method and application thereof. 4+ The catalyst is Sm2Mn8, the Sm element is introduced by using a hydrothermal synthesis method, a Sm-O-Mn coordination structure is formed, high-density oxygen vacancies are generated, and a recyclable double-oxygen storage system is constructed. The structure stably maintains Mn , enhances oxygen migration ability and O2 activation ability, realizes low-temperature catalytic oxidation of toluene and other volatile organic compounds (VOCs), and has the advantages of high low-temperature activity, high CO2 selectivity, good water resistance and outstanding long-term stability. The catalyst has significant catalytic oxidation performance on VOCs such as toluene at low temperature, and has excellent water resistance and long-term stability.

Description

Technical Field

[0001] This invention relates to an organic catalyst and its preparation method, and particularly to a samarium-modified manganese catalyst for the oxidation of volatile organic compounds and its preparation method. Background Technology

[0002] Volatile organic compounds (VOCs) are common pollutants in industrial waste gases and are important precursors to ozone and PM2.5 formation, posing a serious threat to the environment and human health. Catalytic oxidation technology has become an effective method for VOCs control due to its low operating temperature, high conversion efficiency, and lack of secondary pollution.

[0003] Manganese oxide (MnO) x MnO has been extensively studied due to its multiple valence states and abundant oxygen vacancies, but traditional MnO... x Catalysts suffer from problems such as insufficient activity at low temperatures, limited oxygen migration, and insufficient surface adsorption of oxygen. Although existing doping or modification methods can increase the oxygen vacancy concentration, they often lead to insufficient lattice oxygen reserves or unstable catalyst structures, making it difficult to simultaneously meet the requirements of high activity at low temperatures and long-term stability.

[0004] Therefore, a catalyst is needed that can simultaneously regulate oxygen vacancies and lattice oxygen to form a stable structure to ensure high-efficiency catalytic performance at low temperatures. Summary of the Invention

[0005] The purpose of this invention is to provide a samarium-modified manganese catalyst for the oxidation of volatile organic compounds and its preparation method. The method prepares a Sm2Mn8 catalyst with a Sm-O-Mn coordination structure and dual oxygen reservoir characteristics. By constructing the Sm-O-Mn coordination structure, a high-density oxygen vacancy is formed, while lattice oxygen is retained, realizing a dual oxygen reservoir of adsorbed oxygen and lattice oxygen. It has significant catalytic oxidation performance for VOCs such as toluene at low temperature, and has excellent water resistance and long-term stability.

[0006] The objective of this invention is achieved through the following technical solution: A samarium-modified manganese catalyst for the oxidation of volatile organic compounds, wherein the catalyst is Sm2Mn8, and its crystal structure forms an Sm-O-Mn coordination structure, inducing oxygen vacancy formation and reducing the oxygen vacancy formation energy; the catalyst also has surface adsorption of oxygen (O2). ads ) and lattice oxygen (O latt This forms a dynamically circulating dual-oxygen reservoir system; the Sm-O-Mn structure stabilizes Mn through electronic coupling. 4+ It enhances oxygen migration and O2 activation capabilities; the catalyst has a nanosheet structure with low crystallinity and defect enrichment characteristics; (1)O ads / O total =0.33; (2)Mn 4+ / (Mn 3+ +Mn 4+ ) = 0.47; (3) The oxygen vacancy concentration in the catalyst is higher than that in unmodified MnO. x ; (4) Raman spectrum at approximately 201 cm⁻¹ -1 Sm-O-Mn characteristic peaks appear at this location; (5) EPR showed a significant oxygen vacancy signal at g=2.003; (6) XPS displays Mn 4+ The proportion was higher than that of unmodified manganese oxides.

[0007] A method for preparing a samarium-modified manganese catalyst for the oxidation of volatile organic compounds, the method comprising the following preparation steps: Preparation of Sm2Mn8 catalyst: Sm(NO3)3·6H2O, Mn(NO3)2·4H2O and KMnO4 were dissolved in deionized water, the pH of the solution was adjusted to about 9, and hydrothermal reaction was carried out at 180 °C for 16 h. After filtration, washing and drying, the solution was calcined at 400 °C for 5 h. The solution was then treated with 0.2 M dilute nitric acid for 16 h, washed until neutral and dried to obtain Sm2Mn8 catalyst.

[0008] The present invention relates to a samarium-modified manganese catalyst for the oxidation of volatile organic compounds and its preparation method. The prepared catalyst is used for the catalytic oxidation of volatile organic compounds in a temperature range of 150-250 °C. During the catalytic process, oxygen vacancies capture O2 to generate O. ads O ads Used for low-temperature CH bond activation, O latt It participates in deep oxidation and oxygen vacancy recycling to maintain the oxygen reservoir.

[0009] The significant features and positive effects of this invention are: 1. The catalyst prepared by this invention has high efficiency in low-temperature oxidation: the Sm-O-Mn coordination structure promotes the activation of adsorbed oxygen and the migration of lattice oxygen, thereby achieving low-temperature and high-efficiency toluene oxidation; the catalyst is Sm2Mn8 (corresponding to a Sm / Mn molar ratio of 2:8 and a mass fraction of Sm of about 40.6%), and an Sm-O-Mn coordination structure is formed in its lattice; 2. The synergistic effect of the catalyst with oxygen reservoir prepared in this invention: O ads and O latt The catalyst synergistically participates in the catalytic reaction, ensuring continuous oxidation capacity; the catalyst also contains surface-adsorbed oxygen (O2). ads ) and lattice oxygen (O latt This forms a dynamically circulating oxygen storage tank. 3. The catalyst prepared by this invention exhibits strong stability: it has a stable structure, is resistant to moisture, and can withstand long-term operation; the Sm-O-Mn structure stabilizes Mn through electronic coupling. 4+ It reduces the oxygen vacancy formation energy and enhances oxygen migration and O2 activation capacity; 4. Byproduct inhibition of the catalyst prepared in this invention: significantly reduces the formation of phenolic byproducts and improves mineralization efficiency; high catalytic activity at low temperatures (T 50 =212 ℃, T 90 =228 ℃), high CO2 selectivity, inhibition of by-product formation, excellent water resistance, and strong long-term stability.

[0010] 5. The catalyst prepared in this invention has clear characterization features: Raman spectrum 201 cm⁻¹ -1 The characteristic peak at [location], EPR spectrum g=2.003 oxygen vacancy signal, XPS spectrum Mn 4+ The proportion has increased. Attached Figure Description

[0011] Figure 1 The graphs show the catalytic oxidation toluene conversion rates of the catalysts in Examples 1, 2, and 3 of this invention. Figure 2 The graph shows the stability and water resistance of the catalyst in Example 1 of this invention. Figure 3 The N2 adsorption-desorption spectra of the catalysts in Examples 1, 2, and 3 of this invention are shown below; Figure 4 The XRD patterns of the catalysts in Examples 1, 2, and 3 of this invention are shown below. Figure 5 The Raman spectra of the catalysts in Examples 1, 2, and 3 of this invention are shown below. Figure 6 XPS spectra of the catalysts in Examples 1, 2, and 3 of this invention: (a) Mn 2p, (b) Mn 3s, (c) O 1s; Figure 7 The ERP spectra are those of the catalysts in Examples 1, 2, and 3 of this invention. Detailed Implementation

[0012] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

[0013] Example 1 (Preparation method of Sm2Mn8) Weigh 1.3334 g of samarium nitrate hexahydrate (Sm(NO3)3·6H2O), 0.5689 g of potassium permanganate (KMnO4), and 2.0583 g of manganese nitrate tetrahydrate (Mn(NO3)2·4H2O), dissolve them in an appropriate amount of deionized water, and stir at room temperature for 1 hour. Adjust the pH of the solution to 9 with ammonia water, and continue stirring for 1 hour to make the solution homogeneous. Then transfer the homogeneous solution to a 100 mL high-pressure reactor and hydrothermally react at 180 °C for 16 hours. After the reaction is complete, filter the precipitate, wash it repeatedly with deionized water until neutral, and dry it at 80 °C. The dried solid is then separated at 2 °C·min. -1 The temperature was increased to 400°C in air and calcined for 5 hours. The calcined solid was etched with 0.2 M dilute nitric acid for 16 hours, washed until neutral, and dried to obtain Sm2Mn8.

[0014] Example 2 (Preparation methods of other SmxMny catalysts) Prepared according to the method of Example 1, only the molar ratio of Mn / Sm in the precursor solution needs to be adjusted. When Mn / Sm is 9:1, Sm1Mn9 is obtained, and when Mn / Sm is 7:3, Sm3Mn7 is obtained. The remaining steps are the same as in Example 1.

[0015] Example 3 (pure MnO) x (and the preparation method of Sm2O3) MnO was prepared according to the method in Example 1. x Without adding samarium nitrate hexahydrate (Sm(NO3)3·6H2O), the remaining steps are the same, and pure MnO is obtained. x When preparing Sm2O3 according to the method in Example 1, only samarium nitrate hexahydrate (Sm(NO3)3·6H2O) is used as a precursor, without adding any manganese salt, and the remaining steps are the same to obtain Sm2O3.

[0016] Test Example 1 To verify the catalytic performance of Sm2Mn8 catalyst on toluene under low-temperature conditions, 0.1 g of catalyst (40-60 mesh) was loaded into a fixed-bed quartz reactor. The reactor was purged with 500 ppm toluene and 20% O2 and N2 equilibrium gases at a total flow rate of 100 mL / min (space velocity 60,000 mL·g⁻¹). -1 ·h -1 The toluene conversion rate was calculated by real-time detection of the outlet gas using online gas chromatography (FID). Experimental results showed that the Tconversion of Sm2Mn8... 50 and T 90 The results were 212 ℃ and 228 ℃, respectively, which were significantly better than those of Sm1Mn9, Sm3Mn7, and MnO. x and Sm2O3 ( Figure 1).

[0017] Test Example 2 The long-term stability of the Sm2Mn8 catalyst under alternating dry and wet conditions was evaluated through a 50-hour continuous test. When water vapor was periodically introduced, the toluene conversion and CO2 selectivity of the Sm2Mn8 catalyst both slightly improved, gradually returning to their initial levels after the water vapor was removed. Crucially, after multiple dry and wet cycles over 50 hours, the catalyst showed no signs of deactivation, demonstrating excellent durability and water resistance. Figure 2 ).

[0018] Test Example 3 N2 adsorption-desorption tests revealed that the Sm2Mn8 catalyst exhibited a type IV isotherm and an H3 hysteresis loop, indicating the presence of a typical mesoporous structure. Calculations showed an average pore size of approximately 19 nm and a total pore volume of 0.33 cm³. 3 / g, specific surface area 67.2 m² 2 / g, significantly higher than unmodified MnO x (16.2 m) 2 / g). The pore structure is uniform and the pore size is moderate, which is conducive to mass transfer, diffusion and catalytic oxidation reactions. Figure 3 ).

[0019] Test Example 4 Powder XRD analysis of Sm2Mn8 revealed the coexistence of MnO2 and SmMn2O5. Increased peak width indicated lattice defects and low crystallinity, suggesting that Sm successfully formed an Sm-O-Mn coordination structure, which is conducive to oxygen vacancy formation. Figure 4 ).

[0020] Test Example 5 The Raman spectrum of the Sm2Mn8 catalyst shows a characteristic peak at approximately 201 cm⁻¹, corresponding to the Sm-O-Mn coordination structure, while a defect-related peak is observed at approximately 608 cm⁻¹. -1 This clearly indicates the presence of high-density defects and oxygen vacancies in the catalyst lattice. Figure 5 ).

[0021] Test Example 6 XPS testing revealed the presence of Mn on the surface of the Sm2Mn8 catalyst. 4+ / (Mn 3+ +Mn 4+ The proportion of O reached a maximum of 0.47 compared to other catalysts. ads / O total The ratio is also the maximum value of 0.33, indicating that there is abundant adsorbed oxygen and lattice oxygen on the catalyst surface. At the same time, the Sm element maintains the +3 oxidation state, confirming the formation of the Sm-O-Mn coordination structure and high-density adsorbed oxygen. Figure 6 ).

[0022] Test Example 7 The catalyst was characterized using EPR. The EPR spectrum showed a significant signal at g = 2.003. Compared with other catalysts, Sm2Mn8 showed the strongest signal, indicating the highest surface oxygen vacancy density, which is beneficial to improving the catalytic activity of the catalyst. Figure 7 ).

Claims

1. A samarium-modified manganese catalyst for the oxidation of volatile organic compounds, characterized in that, The catalyst is Sm2Mn8, which forms an Sm-O-Mn coordination structure in its crystal structure, inducing oxygen vacancy formation and reducing the oxygen vacancy formation energy; the catalyst also has surface adsorption of oxygen (O2). ads ) and lattice oxygen (O latt This forms a dynamically circulating dual-oxygen reservoir system; the Sm-O-Mn structure stabilizes Mn through electronic coupling. 4+ It enhances oxygen migration and O2 activation capabilities; the catalyst has a nanosheet structure with low crystallinity and defect enrichment characteristics; (1)O ads / O total =0.33; (2)Mn 4+ / (Mn 3+ +Mn 4+ )=0.47; (3) The oxygen vacancy concentration in the catalyst is higher than that in unmodified MnO. x ; (4) Raman spectrum at approximately 201 cm⁻¹ -1 Sm-O-Mn characteristic peaks appear at this location; (5) EPR showed a significant oxygen vacancy signal at g=2.003; (6) XPS displays Mn 4+ The proportion was higher than that of unmodified manganese oxides.

2. A method for preparing a samarium-modified manganese catalyst for the oxidation of volatile organic compounds, characterized in that, The method includes the following preparation process: Preparation of Sm2Mn8 catalyst: Sm(NO3)3·6H2O, Mn(NO3)2·4H2O and KMnO4 were dissolved in deionized water, the pH of the solution was adjusted to about 9, and hydrothermal reaction was carried out at 180 °C for 16 h. After filtration, washing and drying, the solution was calcined at 400 °C for 5 h. The solution was then treated with 0.2 M dilute nitric acid for 16 h, washed until neutral and dried to obtain Sm2Mn8 catalyst.

3. A samarium-modified manganese catalyst for the oxidation of volatile organic compounds according to claim 1 or 2, and its preparation method thereof, characterized in that, The prepared catalyst is used for the catalytic oxidation of volatile organic compounds in the temperature range of 150-250 °C; during the catalytic process, oxygen vacancies capture O2 to generate O. ads O ads Used for low-temperature CH bond activation, O latt It participates in deep oxidation and oxygen vacancy recycling to maintain the oxygen reservoir.

Images