A manganese-cobalt composite oxide supported CeO2 denitration catalyst and its preparation method

Abstract

This invention belongs to the field of catalytic denitrification technology, specifically relating to a manganese-cobalt composite oxide-supported CeO2 denitrification catalyst and its preparation method. The invention first dissolves manganese and cobalt salts in a mixed solution of ethylene glycol and N-methylpyrrolidone, and then performs a solvothermal reaction to obtain a manganese-cobalt composite oxide precursor. Next, the obtained manganese-cobalt composite oxide precursor is dissolved in water with cerium ammonium nitrate, and then calcined at high temperature to obtain a CeO2-supported manganese-cobalt composite oxide denitrification catalyst. Compared with existing technologies, the CeO2-supported manganese-cobalt composite oxide material synthesized in this invention has better crystallinity, dispersibility, and thermal stability. As a selective catalytic reduction (SCR) denitrification catalyst, it has the advantages of high low-temperature denitrification activity and a wide activity temperature window. Furthermore, the synthesis route is simple and easy to implement, suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of catalytic denitrification technology, specifically relating to a manganese-cobalt composite oxide supported CeO2 denitrification catalyst and its preparation method. Background Technology

[0002] Vehicle exhaust from mobile sources and nitrogen oxides (NOx) emitted from industrial combustion of fossil fuels from stationary sources. x NO is considered one of the major air pollutants. Typically, NO... x It will cause serious environmental problems such as acid rain, photochemical smog, and PM2.5. Currently, the selective catalytic reduction of NO by NH3 is being utilized. x (NH3-SCR) becomes a method for removing NO. x One of the most effective methods is that this technology can remove NO through a denitrification catalyst. x It is reduced to non-toxic and harmless N2. As one of the most widely used traditional industrial NH3-SCR catalysts, V2O5-WO3 / TiO2 exhibits excellent catalytic activity in the medium-high temperature range, but its operating temperature generally needs to reach 300–400℃, while the temperature of diesel vehicle exhaust or ship exhaust is only 160–220℃. To meet the operating temperature requirements of vanadium-based catalysts, a significant increase in temperature is necessary for the reaction, which greatly increases the cost of denitrification. Therefore, developing novel environmentally friendly denitrification catalysts with catalytic activity under medium-low temperature conditions is crucial for controlling NO. x The key to emissions control is of great environmental significance in solving air pollution problems.

[0003] Compared with V₂O₅-WO₃(MoO₃) / TiO₂ catalysts, manganese-based catalysts have become a research hotspot in recent years due to their advantages such as variable valence state, excellent low-temperature redox ability, low cost, and easy availability (Chen et al., Appl Surf Sci 2022; 571:151285.). However, using manganese oxides as active centers also has some drawbacks, such as susceptibility to SO₂ poisoning and poor N₂ selectivity. Co doping can not only improve the performance of MnO₅-WO₃-MoO₃ catalysts, but also... x Ce can improve the thermal stability and sulfur / water resistance of manganese-based catalysts, enhance their redox performance and surface acid sites, promote NH3 adsorption, and facilitate NH3-SCR reactions (Yan et al., Appl Catal B 2018; 221:652-63., Meng et al., Environ Sci Tech 2020; 54(12):7697-705.). Simultaneously, Ce can also promote the structural stability and catalytic activity of manganese-based catalysts. Furthermore, through Ce… 4+ and Ce 3+The redox transfer between these components can store and release oxygen, promoting the oxidation of NO to NO2, thereby enhancing redox performance. Therefore, developing a manganese-based composite oxide denitrification catalyst suitable for medium and low temperature conditions based on Co and Ce would have significant application value for SCR denitrification. Summary of the Invention

[0004] To overcome the shortcomings of currently available commercial selective catalytic reduction (SCR) denitrification catalysts for nitrogen oxides, this invention provides a CeO2-supported manganese-cobalt composite oxide denitrification catalyst and its preparation method. This catalyst has the advantages of good thermal stability, high low-temperature denitrification activity, and a wide active temperature window, providing a highly efficient catalyst for SCR denitrification of nitrogen oxides in ship / vehicle exhaust under medium and low temperature conditions.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of this invention provides a method for preparing a manganese-cobalt composite oxide-supported CeO2 denitration catalyst, the method comprising the following steps:

[0007] S1. Manganese and cobalt salts are dissolved in a mixed solution of ethylene glycol and N-methylpyrrolidone, and after a solvothermal reaction, the manganese-cobalt composite oxide precursor is obtained by cooling and drying.

[0008] S2. Dissolve the manganese-cobalt composite oxide precursor of S1 and cerium ammonium nitrate in water, grind them into powder after stirring and drying, and then calcine them at high temperature to obtain the CeO2-supported manganese-cobalt composite oxide denitration catalyst.

[0009] This invention involves dissolving manganese and cobalt salts in a mixed solvent of ethylene glycol and N-methylpyrrolidone, followed by hydrolysis and condensation under high temperature and pressure via a solvothermal reaction to generate a manganese-cobalt composite oxide precursor; then, cerium ammonium nitrate is mixed with the precursor to allow Ce... 3+ / Ce 4+ During the preparation process, the metal valence state and interface structure of manganese and cobalt ions are dynamically controlled through a controlled redox reaction; finally, after drying and high-temperature calcination, a stable composite structure of CeO2 and manganese and cobalt oxide (MnCo2O4) is formed.

[0010] Compared with existing technologies, the CeO2-supported manganese-cobalt composite oxide material synthesized in this invention has better crystallinity, dispersibility and thermal stability. As a selective catalytic reduction (SCR) denitration catalyst, it has the advantages of high denitration activity at low temperature and wide activity temperature window. Moreover, the synthesis route is simple and easy to implement, and it is suitable for large-scale production.

[0011] The innovation of this invention lies in fully utilizing the superior low-temperature activity of manganese / cobalt and the strong oxygen storage capacity of cerium oxide to design a CeO2-supported manganese-cobalt composite oxide material. When the prepared CeO2-supported manganese-cobalt composite oxide material is used as an NH3-SCR denitration catalyst, it has the advantages of high low-temperature denitration activity, wide activity temperature window, and excellent thermal stability. Thus, it provides a CeO2-supported manganese-cobalt composite oxide denitration catalyst suitable for medium and low temperature conditions for denitration treatment.

[0012] Preferably, the manganese salt is Mn(NO3)2·4H2O or MnCl2·4H2O, and the cobalt salt is Co(NO3)2·6H2O or CoSO4·7H2O.

[0013] Preferably, in S1, the molar ratio of Mn:Co is 1:1 to 1:10.

[0014] Preferably, in S1, the concentration of the manganese salt is 1 mmol to 8 mmol / 10 mL.

[0015] Preferably, the volume ratio of ethylene glycol to N-methylpyrrolidone is 1-10:10-40.

[0016] Preferably, in S2, the molar ratio of Ce:Mn is 1:10 to 1:100.

[0017] Preferably, the temperature of the solvothermal reaction is 30–90°C and the time is 10–20 h.

[0018] Preferably, the high-temperature calcination is carried out in an air atmosphere at a temperature of 500–700°C for 2–4 hours, with a heating rate of 1–5°C / min.

[0019] Preferably, in step S2, the stirring is performed at room temperature for 1 to 4 hours.

[0020] The second aspect of the present invention provides a manganese-cobalt composite oxide supported CeO2 denitration catalyst prepared by the preparation method described in the first aspect.

[0021] The third aspect of this invention provides the application of the manganese-cobalt composite oxide supported CeO2 denitrification catalyst described in the second aspect in the NH3-SCR denitrification reaction.

[0022] As a selective catalytic reduction (SCR) denitrification catalyst, the CeO2-supported manganese-cobalt composite oxide provided by this invention has an ignition temperature of 50°C and a NO content in the range of 65–300°C. x The conversion rate is maintained above 90%, and it has the advantages of high low-temperature denitrification activity and a wide active temperature window.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] This invention discloses a method for preparing a CeO2 denitration catalyst supported on a manganese-cobalt composite oxide. First, manganese and cobalt salts are dissolved in a mixed solution of ethylene glycol and N-methylpyrrolidone, and a manganese-cobalt composite oxide precursor is obtained after a solvothermal reaction. Then, the obtained manganese-cobalt composite oxide precursor is dissolved in water with cerium ammonium nitrate, and subsequently calcined at high temperature to obtain a CeO2-supported manganese-cobalt composite oxide denitration catalyst. Specifically, this invention has the following advantages:

[0025] (1) The CeO2-supported manganese-cobalt composite oxide denitration catalyst provided by the present invention can be synthesized by a solvothermal method, and the synthesized CeO2-supported manganese-cobalt composite oxide material exhibits good crystallinity, dispersibility, and thermal stability. Moreover, the synthesis method of the present invention is simple and easy to implement, the product is stable and highly reproducible, and it is expected to be used for large-scale production.

[0026] (2) The CeO2-supported manganese-cobalt composite oxide provided by the present invention is used as an NH3-SCR denitration catalyst. Its ignition temperature is 50℃ and the conversion rate is maintained at more than 90% in the range of 65~300℃. It has good thermal stability and has the advantages of high low-temperature denitration activity and wide active temperature window. It provides a CeO2-supported manganese-cobalt composite oxide denitration catalyst suitable for medium and low temperature conditions for denitration treatment. Attached Figure Description

[0027] Figure 1 The X-ray diffraction pattern of CeO2-supported manganese-cobalt composite oxide and MnCo2O4 prepared in Example 1 is shown.

[0028] Figure 2 The image shows the SEM pattern of the CeO2-supported manganese-cobalt composite oxide prepared in Example 1.

[0029] Figure 3 The image shows the SEM pattern of MnCo2O4.

[0030] Figure 4 The graph shows a comparison of the denitrification performance of CeO2-supported manganese-cobalt composite oxides prepared with different Mn contents in Examples 1-3 for NH3-SCR.

[0031] Figure 5 Comparison of the denitrification performance of CeO2-supported manganese-cobalt composite oxides prepared with different Co contents in Examples 1, 4, and 5 for NH3-SCR.

[0032] Figure 6 Comparison chart of the denitrification performance of CeO2-supported manganese-cobalt composite oxides prepared with different Ce contents in Examples 1, 6, and 7 using NH3-SCR. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0035] Example 1: Preparation of a CeO2-supported manganese-cobalt composite oxide denitration catalyst

[0036] S1. Dissolve 1 mmol Mn(NO3)2·4H2O and 1 mmol Co(NO3)2·6H2O in 10 mL ethylene glycol and 20 mL N-methylpyrrolidone, and stir at room temperature for 30 min.

[0037] S2. The solution was placed in an oven and then aged at 90°C for 10 hours. After cooling and drying, the manganese-cobalt composite oxide precursor was obtained.

[0038] S3. Dissolve 0.4 mmol (NH4)2Ce(NO3)6 and 1 g of manganese-cobalt composite oxide precursor in 1 mL of deionized water and stir at room temperature for 2 h. Dry the product and grind it into a fine powder in a mortar. Then calcine it at 500 °C for 4 h in air atmosphere with a heating rate of 1 °C / min to obtain CeO2-supported manganese-cobalt composite oxide (5CeO2 / MnCo2O4) with a Ce molar ratio of 5%.

[0039] Example 2

[0040] The preparation method is the same as in Example 1, except that the amount of Mn(NO3)2·4H2O used is 3 mmol.

[0041] Example 3

[0042] The preparation method is the same as in Example 1, except that the amount of Mn(NO3)2·4H2O used is 6 mmol.

[0043] Example 4

[0044] The preparation method is the same as in Example 1, except that the amount of Co(NO3)2·6H2O used is 3 mmol.

[0045] Example 5

[0046] The preparation method is the same as in Example 1, except that the amount of Co(NO3)2·6H2O used is 6 mmol.

[0047] Example 6

[0048] The preparation method is the same as in Example 1, except that the amount of (NH4)2Ce(NO3)6 used is 0.2 mmol.

[0049] Example 7

[0050] The preparation method is the same as in Example 1, except that the amount of (NH4)2Ce(NO3)6 used is 0.1 mmol.

[0051] Experimental Example 1: Structural Characterization of CeO2-Supported Manganese-Cobalt Composite Oxide Materials

[0052] 1. X-ray diffraction (XRD)

[0053] The products obtained in Examples 1 to 7 were subjected to XRD tests.

[0054] The X-ray diffraction pattern of Example 1 is as follows: Figure 1 As shown, because cerium oxide is uniformly dispersed on the surface of MnCo2O4 and its relative content is low, the spectrum only shows the peaks of MnCo2O4. Furthermore, the X-ray diffraction patterns of Examples 2-7 are similar to... Figure 1 This approximates the results, indicating that the products of Examples 1 to 7 are all uniformly dispersed CeO2-supported manganese-cobalt composite oxide (MnCo2O4) materials.

[0055] 2. Scanning electron microscope (SEM)

[0056] The products obtained in Examples 1 to 7 were subjected to SEM testing.

[0057] The SEM image of Example 1 is as follows: Figure 2 As shown, MnCo2O4 is as Figure 3 As shown, it can be seen that metal oxides are clearly attached to the surface of 5CeO2 / MnCo2O4. Furthermore, the SEM images of Examples 2-7 are consistent with... Figure 1 This indicates that the CeO2 in the products of Examples 1-7 successfully supported manganese-cobalt composite oxide (MnCo2O4) materials, and that these materials are uniform spherical particles with rough surfaces. Experimental Example 2: NH3-SCR denitrification performance of CeO2-supported manganese-cobalt composite oxide materials.

[0058] 1. Performance Testing:

[0059] 20 mg of CeO2-supported manganese-cobalt composite oxide material (40-60 mesh) was placed in a quartz tube with an inner diameter of 8 mm and then placed in a fixed-bed reactor. The activity testing conditions were set as follows: [NO] = [NH3] = 500 ppm, [O2] = 5%, with argon as the balance gas. The total gas flow rate was 500 mL / min, the test temperature was 50–350 °C, the heating rate was 3 °C / min, and the space velocity was 40,000 h⁻¹. -1 .

[0060] 2. Experimental Results

[0061] The catalytic denitrification activity test results of Examples 1-3 are as follows: Figure 4 As shown, the catalytic denitrification activity test results of Examples 1, 4, and 5 are as follows: Figure 5 As shown, the catalytic denitrification activity test results of Examples 1, 6, and 7 are as follows: Figure 6 As shown in the figure, the CeO2-supported manganese-cobalt composite oxide material prepared by this invention can achieve a denitrification rate of over 90% at temperatures ranging from 65 to 300°C, and even 100% at temperatures ranging from 75 to 250°C, with the denitrification effect of Example 1 being the most significant. This indicates that the CeO2-supported manganese-cobalt composite oxide material prepared by this invention can be used to prepare selective catalytic reduction catalysts, providing a new material source for denitrification treatment.

[0062] In summary, the CeO2-supported manganese-cobalt composite oxide denitration catalyst prepared by the method of this invention has the advantages of good thermal stability, high low-temperature denitration activity, and wide activity temperature window. It can provide a highly efficient catalyst for SCR denitration treatment of nitrogen oxides in ship / vehicle exhaust under medium and low temperature conditions.

[0063] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. The application of a manganese-cobalt composite oxide supported CeO2 denitration catalyst in the NH3-SCR denitration reaction, characterized in that, The preparation method of the manganese-cobalt composite oxide supported CeO2 denitration catalyst includes the following steps: S1. Manganese and cobalt salts are dissolved in a mixed solution of ethylene glycol and N-methylpyrrolidone, and after a solvothermal reaction, the manganese-cobalt composite oxide precursor is obtained by cooling and drying. S2. The manganese-cobalt composite oxide precursor of S1 and cerium ammonium nitrate are dissolved in water, stirred and dried, then ground into powder and calcined at high temperature to obtain the manganese-cobalt composite oxide supported CeO2 denitration catalyst. In the manganese-cobalt composite oxide supported CeO2 denitration catalyst, the manganese-cobalt composite oxide is MnCo2O4, and cerium oxide is uniformly dispersed on the surface of MnCo2O4 with a relatively low content.

2. The application according to claim 1, characterized in that, The manganese salt is Mn(NO3)2·4H2O or MnCl2·4H2O, and the cobalt salt is Co(NO3)2·6H2O or CoSO4•7H2O.

3. The application according to claim 1, characterized in that, The volume ratio of ethylene glycol to N-methylpyrrolidone is 1-10:10-40.

4. The application according to claim 1, characterized in that, The solvothermal reaction is carried out at a temperature of 30–90 °C for a duration of 10–20 h.

5. The application according to claim 1, characterized in that, The high-temperature calcination is carried out in an air atmosphere at a temperature of 500–700 °C for 2–4 h, with a heating rate of 1–5 °C / min.

6. The application according to claim 1, characterized in that, In S2, the stirring is carried out at room temperature for 1 to 4 hours.

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