Manganese-cobalt composite oxide loaded CeO2 denitration catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of catalytic denitration, and particularly relates to a manganese-cobalt composite oxide loaded CeO2 denitration catalyst and a preparation method thereof. The preparation method comprises the following steps: firstly, dissolving manganese salt and cobalt salt in a mixed solution of ethylene glycol and N-methyl pyrrolidone, and carrying out solvothermal reaction to prepare a manganese-cobalt composite oxide precursor; and dissolving the obtained manganese-cobalt composite oxide precursor and ceric ammonium nitrate in water, and carrying out high-temperature calcination to obtain the CeO2-loaded manganese-cobalt composite oxide denitration catalyst. Compared with the prior art, the CeO2-loaded manganese-cobalt composite oxide material synthesized by the method has better crystallinity, dispersity and thermal stability, has the advantages of high low-temperature denitration activity and wide active temperature window when being used as a selective catalytic reduction (SCR) denitration catalyst, and is simple and easy to implement in synthesis technical route and suitable for large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic denitration, and specifically relates to a manganese-cobalt composite oxide loaded CeO2 denitration catalyst and a preparation method thereof. Background Art

[0002] Nitrogen oxides (NO) emitted from automobile exhaust in mobile sources and from fossil fuels in stationary sources due to industrial combustion x ) is considered to be one of the main air pollutants. x It will cause serious environmental problems such as acid rain, photochemical smog, PM 2.5, etc. At present, the selective catalytic reduction of NO by NH3 is widely used. x (NH3-SCR) becomes NO removal x One of the most effective methods, this technology can convert NO x 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 and high temperature range, but its operating temperature generally needs to reach 300-400°C, while the temperature of diesel vehicle exhaust or ship exhaust is only 160-220°C. In order to meet the working temperature of vanadium-based catalysts, it is necessary to significantly increase the temperature before the reaction can proceed, which greatly increases the cost of denitrification. Therefore, the development of new environmentally friendly denitrification catalysts with catalytic activity under medium and low temperature conditions is the key to controlling NO x It is the key to emissions and has very important environmental significance for solving the problem of air pollution.

[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 price and easy availability (Chen et al., Appl Surf Sci 2022; 571: 151285.). However, manganese oxides as active centers also have some disadvantages, such as easy SO2 poisoning and poor N2 selectivity. Co doping can not only improve the MnO x The thermal stability and sulfur / water resistance of Ce can also be improved, and its redox performance and surface acid center can be improved, which can promote the adsorption of NH3 and benefit the NH3-SCR reaction (Yan et al., Appl Catal B 2018; 221: 652-63., Meng et al., Environ Sci Tech 2020; 54(12): 7697-705.). At the same time, Ce can also promote the structural stability and catalytic activity of manganese-based catalysts. In addition, Ce can be used to 4+ and Ce 3+The redox transfer between them can store and release oxygen, promote the oxidation of NO to NO2, and thus enhance the redox performance. Therefore, if a manganese-based composite oxide denitrification catalyst suitable for medium and low temperature conditions can be developed based on Co and Ce, it will have important application value for SCR denitrification treatment. Summary of the invention

[0004] In order to overcome the shortcomings of the currently commercially available SCR denitration catalysts for selective catalytic reduction of nitrogen oxides, the present invention provides a CeO2-loaded manganese-cobalt composite oxide denitration catalyst and a preparation method thereof. The catalyst has the advantages of good thermal stability, high low-temperature denitration activity, and a wide active temperature window, and provides an efficient catalyst for the SCR denitration treatment of nitrogen oxides in ship / automobile exhaust under medium and low temperature conditions.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

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

[0007] S1, dissolving manganese salt and cobalt salt in a mixed solution of ethylene glycol and N-methylpyrrolidone, subjecting the mixture to a solvent thermal reaction, and then cooling and drying to obtain a manganese-cobalt composite oxide precursor;

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

[0009] The method comprises dissolving manganese salt and cobalt salt in a mixed solvent of ethylene glycol and N-methylpyrrolidone, and then hydrolyzing and condensing the mixture under high temperature and high pressure through a solvent thermal reaction to generate a manganese-cobalt composite oxide precursor; and then mixing ammonium cerium nitrate with the precursor to make Ce 3+ / Ce 4+ During the preparation process, the metal valence state and interface structure are dynamically regulated through controllable redox reactions with manganese and cobalt ions; finally, a stable composite structure of CeO2 and manganese cobalt oxide (MnCo2O4) is formed after drying and high-temperature calcination.

[0010] Compared with the prior art, the CeO2-loaded manganese-cobalt composite oxide material synthesized in the present invention has good 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 active temperature window. The synthesis technology route is simple and easy to implement, and is suitable for large-scale production.

[0011] The innovation of the present invention lies in: making full use of the superior low-temperature activity of manganese / cobalt and the strong oxygen storage capacity of cerium oxide, designing CeO2-loaded manganese-cobalt composite oxide materials, so that the prepared CeO2-loaded manganese-cobalt composite oxide material, when used as an NH3-SCR denitrification catalyst, has the advantages of high low-temperature denitrification activity, wide active temperature window, and excellent thermal stability, thereby providing a CeO2-loaded manganese-cobalt composite oxide denitrification catalyst suitable for medium and low temperature conditions for denitrification 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 solvent thermal reaction is 30 to 90° C. and the time is 10 to 20 hours.

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

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

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

[0021] The third aspect of the present invention provides the use of the manganese-cobalt composite oxide-loaded CeO2 denitration catalyst described in the second aspect in the NH3-SCR denitration reaction.

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

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The invention discloses a preparation method of a CeO2 denitration catalyst supported by a manganese-cobalt composite oxide, wherein a manganese salt and a cobalt salt are first dissolved in a mixed solution of ethylene glycol and N-methylpyrrolidone, and a manganese-cobalt composite oxide precursor is obtained after a solvent thermal reaction; then the obtained manganese-cobalt composite oxide precursor and ammonium cerium nitrate are dissolved in water, and then a CeO2-supported manganese-cobalt composite oxide denitration catalyst is obtained after high-temperature calcination. Specifically, the 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 has good crystallinity, dispersibility and thermal stability. The synthesis method of the present invention is simple and easy to implement, the product is stable, and the repeatability is high, and it is expected to be used for large-scale production.

[0026] (2) The CeO2-loaded manganese-cobalt composite oxide provided by the present invention is used as an NH3-SCR denitrification catalyst, and its ignition temperature is 50°C, and the conversion rate is maintained at more than 90% in the range of 65 to 300°C. It has good thermal stability, high low-temperature denitrification activity, and a wide active temperature window. It provides a CeO2-loaded manganese-cobalt composite oxide denitrification catalyst suitable for medium and low temperature conditions for denitrification treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the X-ray diffraction pattern of CeO2-loaded manganese-cobalt composite oxide and MnCo2O4 prepared in Example 1.

[0028] Figure 2 This is the SEM spectrum of the CeO2-loaded manganese-cobalt composite oxide prepared in Example 1.

[0029] Figure 3 This is the SEM spectrum of MnCo2O4.

[0030] Figure 4 This is a comparison chart of the denitration performance of NH3-SCR using CeO2-loaded manganese-cobalt composite oxides prepared with different Mn contents in Examples 1 to 3.

[0031] Figure 5 This is a comparison chart of the denitration performance of NH3-SCR using CeO2-loaded manganese-cobalt composite oxides prepared with different Co contents in Examples 1, 4, and 5.

[0032] Figure 6 This is a comparison chart of the denitration performance of CeO2-loaded manganese-cobalt composite oxides prepared with different Ce contents in Examples 1, 6, and 7 when used for NH3-SCR. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, 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] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0035] Example 1: Preparation of a CeO2-loaded 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 h, and then cooled and dried to obtain a manganese-cobalt composite oxide precursor;

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

[0039] Example 2

[0040] The preparation method is the same as that of 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 that of 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 that of 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 that of 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 that 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 that 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-loaded Mn-Co Composite Oxide Materials

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

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

[0054] Among them, the X-ray diffraction pattern of Example 1 is as follows Figure 1 As shown in FIG. 1 , since cerium oxide is uniformly dispersed on the surface of MnCo2O4 and its relative content is low, the spectrum only shows the peak of MnCo2O4. In addition, the X-ray diffraction patterns of Examples 2 to 7 are similar to those of Figure 1 This indicates that the products of Examples 1 to 7 are all uniformly dispersed CeO2-loaded 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 tests respectively.

[0057] Among them, the SEM spectrum of Example 1 is as follows Figure 2 As shown, MnCo2O4 Figure 3 As shown in the figure, it can be seen that metal oxides are obviously attached to the surface of 5CeO2 / MnCo2O4. In addition, the SEM spectra of Examples 2 to 7 are similar to Figure 1 The results show that CeO2 in the products of Examples 1 to 7 successfully loaded manganese-cobalt composite oxide (MnCo2O4) materials, and they are uniform spherical particles with rough surfaces. Experimental Example 2: NH3-SCR Denitrification Performance of CeO2 Loaded Manganese-Cobalt Composite Oxide Materials

[0058] 1. Performance measurement:

[0059] Take 20mg of 40-60 mesh CeO2 loaded manganese-cobalt composite oxide material and put it into a quartz tube with an inner diameter of 8mm, and then put it into a fixed bed reactor. The activity test conditions are set as: [NO] = [NH3] = 500ppm, [O2] = 5%, argon as the balance gas. The total gas flow rate is 500mL / min, the test temperature is 50-350℃, the heating rate is 3℃ / min, and the space velocity is 40000h -1 .

[0060] 2. Experimental results

[0061] The catalytic denitrification activity test results of Examples 1 to 3 are as follows: Figure 4 As shown, the catalytic denitration activity test results of Examples 1, 4, and 5 are as follows Figure 5 As shown, the catalytic denitration activity test results of Examples 1, 6, and 7 are as follows Figure 6 As shown in the figure, it can be seen that the denitration rate of the CeO2-loaded manganese-cobalt composite oxide material prepared by the present invention can reach more than 90% at a temperature of 65-300°C, and can even reach 100% at a temperature of 75-250°C, among which the denitration effect of Example 1 is the most significant. It shows that the CeO2-loaded manganese-cobalt composite oxide material prepared by the present invention can be used to prepare a selective catalytic reduction catalyst, providing a new material source for denitration treatment.

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

[0063] The embodiments of the present invention are 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 of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A method for preparing a manganese-cobalt composite oxide-supported CeO2 denitration catalyst, characterized in that: The following steps are involved: S1, dissolving manganese salt and cobalt salt in a mixed solution of ethylene glycol and N-methylpyrrolidone, subjecting the mixture to solvent thermal reaction, and then cooling and drying to obtain a manganese-cobalt composite oxide precursor; S2. Dissolve the manganese-cobalt composite oxide precursor of S1 and ammonium cerium nitrate in water, grind into powder after stirring and drying, and then calcine at high temperature to obtain a CeO2-loaded manganese-cobalt composite oxide denitration catalyst.

2. The method for preparing a manganese-cobalt composite oxide-supported CeO2 denitration catalyst 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 method for preparing a manganese-cobalt composite oxide-supported CeO2 denitration catalyst according to claim 1, characterized in that: In S1, the molar ratio of Mn:Co is 1:1 to 1:

10.

4. The method for preparing a manganese-cobalt composite oxide-supported CeO2 denitration catalyst according to claim 1, characterized in that: The volume ratio of the ethylene glycol to the N-methylpyrrolidone is 1-10:10-40.

5. The method for preparing a manganese-cobalt composite oxide-supported CeO2 denitration catalyst according to claim 1, characterized in that: In S2, the molar ratio of Ce:Mn is 1:10 to 1:

100.

6. The method for preparing a manganese-cobalt composite oxide-supported CeO2 denitration catalyst according to claim 1, characterized in that: The temperature of the solvent thermal reaction is 30-90° C. and the time is 10-20 hours.

7. The method for preparing a manganese-cobalt composite oxide-supported CeO2 denitration catalyst 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 hours at a heating rate of 1-5° C. / min.

8. The method for preparing a manganese-cobalt composite oxide-supported CeO2 denitration catalyst according to claim 1, characterized in that: In S2, the stirring is carried out at room temperature for 1 to 4 hours.

9. A manganese-cobalt composite oxide-loaded CeO2 denitration catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the manganese-cobalt composite oxide-loaded CeO2 denitration catalyst according to claim 9 in NH3-SCR denitration reaction.

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