Low-temperature denitration catalyst based on mesoporous silica loaded ultra-small Mn-Fe-O nanoparticles as well as preparation method and application of low-temperature denitration catalyst

Abstract

The invention discloses a low-temperature denitration catalyst based on mesoporous silica loaded ultra-small Mn-Fe-O nanoparticles as well as a preparation method and application of the low-temperature denitration catalyst. The method comprises the following steps: preparing a mesoporous silica carrier rich in silicon hydroxyl by adopting a hydrothermal assembly and oxidation organic template removal method; preparing a manganese salt and ferric salt mixed solution by using deionized water, adding organic acid, and uniformly stirring and mixing; and adding mesoporous silica into the mixed solution, fully dipping, drying, grinding and roasting to obtain the catalyst. By means of the method, the ultra-small Mn-Fe-O nano-particles can be generated in the pore channels of the mesoporous silicon dioxide in an in-situ mode. Wherein the organic acid is used as a coordination agent to effectively limit the particle size increase of Mn-Fe-O, and the existence of silicon hydroxyl enhances the interaction between the carrier and the metal oxide, so that the migration of Mn-Fe-O nanoparticles is inhibited. The catalyst shows excellent low-temperature catalytic activity in an ammonia selective reduction denitration reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas denitration, and in particular to a catalyst based on mesoporous silica loaded Mn-Fe-O nanoparticles, and a preparation method and application thereof. Background Art

[0002] Power plants, waste incineration plants, motor vehicles and industrial boilers emit large amounts of toxic nitrogen oxides (NO) during production and daily operations. x (NO and NO2), which cause serious harm to the environment and human health. x In order to reduce emissions, my country has implemented a series of strict environmental protection policies, which has further promoted the development of low-temperature denitrification technology. Among them, ammonia selective catalytic reduction (NH3-SCR reaction) technology uses NH3 as a reducing agent and can efficiently convert NO to x It is reduced to nitrogen and water, so it is widely used in the purification of industrial flue gas. The development of efficient and stable NH3-SCR denitrification catalyst is the key to the application of this technology.

[0003] At present, commercial V2O5-WO3(MoO3) / TiO2 catalysts are widely used in the denitrification process of medium- and high-temperature flue gas (250-400℃) generated by industries such as petrochemicals and coal chemical industry. However, this type of catalyst still has many insurmountable defects, such as narrow operating temperature window, low N2 selectivity at high temperature, and biological toxicity of vanadium-based catalysts. Therefore, the development of efficient and environmentally friendly low-temperature denitrification catalysts has become a hot topic in industrial applications and scientific research.

[0004] In view of the problems of poor stability and insufficient low-temperature catalytic activity of existing catalysts in NH3-SCR reaction, the present invention proposes a hydrothermal assembly and oxidation removal of organic template method to prepare mesoporous silica rich in silanol as a carrier, and further prepares ultra-small Mn-Fe-O composite oxide nanoparticle catalysts with high dispersibility and large specific surface area. This series of catalysts exhibits excellent low-temperature catalytic activity and outstanding stability in NH3-SCR reaction. In addition, the preparation method is simple in process, has little impact on the environment, and has good application prospects. Summary of the invention

[0005] In view of the problems that existing catalyst materials have poor stability and insufficient low-temperature catalytic activity in NH3-SCR reactions, the present invention provides a catalyst based on mesoporous silica-loaded Mn-Fe-O nanoparticles, a preparation method and an application thereof.

[0006] The present invention adopts the following technical solutions:

[0007] A method for preparing a low-temperature denitration catalyst based on mesoporous silica loaded with ultra-small Mn-Fe-O nanoparticles comprises the following steps:

[0008] (1) Preparation of silanol-rich mesoporous silica by hydrothermal assembly and oxidative removal of organic templates;

[0009] (2) mixing manganese salt, iron salt and deionized water in a certain proportion to prepare a mixed metal salt solution;

[0010] (3) adding a certain amount of organic acid to the mixed metal salt solution obtained in step (2) to obtain an organic acid-metal salt solution;

[0011] (4) adding the silanol-rich mesoporous silica prepared in step (1) to the organic acid-metal salt solution obtained in step (3), heating and stirring to fully impregnate the solution, and obtaining a mixture;

[0012] (5) The mixture in step (4) is dried, ground and calcined to obtain a silica-based Mn-Fe-O catalyst.

[0013] Furthermore, in step (2), the manganese salt is one or more of manganese chloride (MnCl2), manganese sulfate (MnSO4) and manganese nitrate (Mn(NO3)2) or their salts containing crystal water.

[0014] Furthermore, in step (2), the iron salt is one or more of ferric sulfate (Fe2(SO4)3), ferric chloride (FeCl3), ferric nitrate (Fe(NO3)3) and ferric carbonate (Fe2(CO3)3).

[0015] Furthermore, in step (2), the molar ratio of the manganese salt to the iron salt is 0.01 to 100.

[0016] Furthermore, in step (3), the organic acid is one or more of acetic acid, citric acid, and oxalic acid, and the molar ratio of the organic acid to the metal in the organic acid-metal salt solution is 0.8-1.2:1.

[0017] Furthermore, in step (4), the heating and stirring temperature is 50-90° C. and the time is 4-8 h.

[0018] Furthermore, in step (5), the drying temperature is 60-100° C., the grinding particle size is 80-100 mesh, the roasting temperature is 200-600° C., and the calcination treatment time is 0.1-24 h.

[0019] Furthermore, in step (5), the total loading amount of manganese and iron in the obtained mesoporous silica-based Mn-Fe-O catalyst is 1-50 wt % based on the total weight of the catalyst.

[0020] The low-temperature denitration catalyst material of mesoporous silica loaded with ultra-small Mn-Fe-O nanoparticles obtained by the above preparation method has excellent conductivity and capacitance and has broad application prospects in the field of low-temperature denitration NH3-SCR.

[0021] The present invention uses mesoporous silica as a catalyst carrier and introduces Mn and Fe as active metal components. Mesoporous silica has a large specific surface area, a large pore volume, a uniform and adjustable pore size, and a stable skeleton structure, which not only helps to uniformly load the metal oxide, but also promotes the rapid progress of the catalytic reaction. Mn and Fe have excellent low-temperature catalytic activity and are more environmentally friendly than traditional vanadium-containing catalysts.

[0022] The key mechanisms of the present invention are as follows:

[0023] 1. Support modification: A mesoporous silica support rich in silanol was prepared by hydrothermal assembly and oxidative removal of organic templates. Silanol groups (Si-OH) can enhance the interaction between the support and the active metal during the in-situ growth of Mn-Fe-O nanoparticles, thereby limiting the migration of metal particles and improving the thermal stability of the catalyst. In addition, the nanopore confinement of mesoporous silica can effectively prevent metal oxides from aggregating in the pores, thereby avoiding crystal phase separation.

[0024] 2. Particle size control: Introducing organic acid as a ligand can effectively control the growth of Mn-Fe-O particles and improve the dispersion, specific surface area and surface active site concentration of the catalyst.

[0025] Compared with existing catalysts, the catalyst of the present invention has the following advantages:

[0026] 1. The preparation process is simple and environmentally friendly: Mn-Fe-O is loaded by solution impregnation method, which has a simple process and low cost, avoids the toxicity problem of traditional vanadium-containing catalysts, and has the potential to replace commercial catalysts.

[0027] 2. High specific surface area and excellent low-temperature catalytic activity: The Mn-Fe-O@SiO2 catalyst prepared by the present invention has a large specific surface area and high porosity, realizes efficient active metal dispersion, and exhibits excellent low-temperature catalytic activity and long-term stability in the NH3-SCR reaction.

[0028] 3. Wide temperature window and excellent low-temperature performance: The Mn-Fe-O@SiO2 catalyst prepared by the present invention exhibits a wide temperature window in the NH3-SCR reaction and can still maintain high catalytic activity in the low temperature range of 120-150°C, which is suitable for a wider range of industrial denitrification conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The N2 adsorption-desorption isotherms of the catalysts prepared for Example 1 and Comparative Example 1 are used to characterize the specific surface area and pore structure characteristics of the catalysts.

[0030] Figure 2 The powder X-ray diffraction (XRD) spectra of the catalysts prepared in Example 1 and Comparative Example 1 are used to analyze the crystal structure of the catalysts and the dispersion state of the metal oxides.

[0031] Figure 3 The powder X-ray diffraction (XRD) spectra of the catalysts prepared in Example 1 and Comparative Examples 2-4 are used to analyze the crystal structure of the catalysts and the dispersion state of the metal oxides.

[0032] Figure 4 Powder transmission electron microscopy (TEM) and elemental mapping (EDS) images of the catalyst prepared in Example 1 are used to analyze the morphology, crystal structure and dispersion state of the metal elements of the catalyst.

[0033] Figure 5 The NH3-SCR catalytic activity curves of the catalysts prepared in Example 1 and Comparative Example 1 are used to compare the denitration performance of the catalysts at different reaction temperatures.

[0034] Figure 6 The NH3-SCR catalytic activity curves of the catalysts prepared in Example 1 and Comparative Examples 2-4 are used to compare the denitration performance of the catalysts at different reaction temperatures.

[0035] Figure 7 This is the NH3-SCR water and sulfur resistance performance diagram of the catalyst prepared in Example 1, which is used to analyze the denitrification performance of the catalyst. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0037] Example 1

[0038] In this embodiment, hydrothermal assembly and oxidative removal of organic templates were used to prepare silanol-rich mesoporous silica SBA-15-OH, and Mn-Fe-O composite oxide was used as a catalytically active component to prepare Mn-Fe-O@SiO2-1 catalyst.

[0039] (1) Vector preparation

[0040] The hydrothermal assembly and oxidative removal of organic templates were used to synthesize mesoporous silica SBA-15-OH rich in silanols for loading active metal oxide components. The specific preparation method is as follows: 20.0g of the three-block copolymer PluronicP123 was added to a mixture of 650mL H2O and 100mL HCl (37wt.%), and continued to stir in a 38°C water bath until Pluronic P123 was completely dissolved, then 41.6g TEOS was added, and continued to stir for 24h, and the mixed solution was transferred to a hydrothermal autoclave and hydrothermally treated at 110°C for 24h. After cooling to room temperature, the solid suspension was filtered and dried overnight to obtain a mesoporous silica composition. The three-block copolymer was removed to open the cylindrical mesoporous channels of the surface functionalized SBA-15, 8.0g of the mesoporous silica composition was added to a round flask, and 120mL HNO3 (65wt.%) and 40mL H2O2 (35wt.%) solutions were added. The mixture was refluxed at 80°C for 3 hours. After cooling to room temperature, it was washed with ethanol and deionized water until neutral, and dried at 50°C overnight to obtain a mesoporous silica SBA-15-OH template rich in silanol groups.

[0041] (2) Catalyst preparation

[0042] Mn(NO3)2 aqueous solution and Fe(NO3)3·9H2O were weighed as manganese source and iron source, and dissolved in 20mL deionized water according to the molar ratio of Mn to Fe of 1:1. 0.5222g of citric acid monohydrate was added and stirred for 15 minutes to form a uniform solution. Subsequently, 1.0g of SBA-15-OH carrier was added and stirred in an 80℃ water bath for 5 hours to ensure that the metal ions were fully impregnated into the pores of mesoporous silica. The resulting mixture was dried in an 80℃ oven and then ground to 100 mesh. Finally, the Mn-Fe-O@SiO2-1 catalyst was obtained by calcining at 400℃ in a muffle furnace for 4 hours, in which the total loading of Mn and Fe was 20wt%.

[0043] (3) NH3-SCR reaction performance evaluation

[0044] The catalyst was tested for NH3-SCR reaction catalytic activity in a fixed bed reactor. The inlet gas mixture consisted of 500ppm NO, 500ppm NH3, 5vol% O2 and N2 as the balance gas, with a total flow rate of 200mL / min, corresponding to a mass hourly space velocity (WHSV) of 60000mL / g. cat ·h. Each time, 200 mg of catalyst was weighed and loaded into the reactor, heated to 300°C at a heating rate of 2°C / min, and the reaction gas was introduced after reaching the target temperature. The concentrations of reactants and products were monitored simultaneously using the Bruker Matrix-MG2. Nitrogen oxides (NO x) The conversion rate is calculated according to the following formula:

[0045]

[0046] Where [NO+N2O] in and [NO+N2O] out Represent the inlet and outlet gas nitrogen oxide concentrations respectively.

[0047] (4) Results analysis

[0048] Figure 5 The catalytic activity curves of the catalysts prepared in Example 1 and Comparative Example 1 for the NH3-SCR reaction are shown in Figure 1. The experimental results show that under the same conditions, the Mn-Fe-O@SiO2-1 catalyst exhibits excellent catalytic activity and a wide temperature window. x The conversion rate can reach 100%, and can still maintain 75% conversion rate in the low temperature area of ​​120℃.

[0049] Example 2

[0050] In this embodiment, hydrothermal assembly and oxidative removal of organic templates were used to prepare silanol-rich mesoporous silica SBA-15-OH, and Mn-Fe-O composite oxide was used as a catalytically active component to prepare Mn-Fe-O@SiO2-2 catalyst.

[0051] (1) Vector preparation

[0052] The hydrothermal assembly and oxidative removal of organic templates were used to synthesize mesoporous silica SBA-15-OH rich in silanol groups for loading active metal oxide components. The preparation method of the mesoporous silica SBA-15-OH template was the same as that of Example 1.

[0053] (2) Catalyst preparation

[0054] Mn(NO3)2 aqueous solution and Fe(NO3)3·9H2O were weighed as manganese source and iron source, and dissolved in 20mL deionized water according to the molar ratio of Mn to Fe of 10:1. 0.5040g of citric acid monohydrate was added and stirred for 15 minutes to form a uniform solution. Subsequently, 1.0g of SBA-15-OH carrier was added and stirred in an 80℃ water bath for 5 hours to ensure that the metal ions were fully impregnated into the pores of mesoporous silica. The resulting mixture was dried in an 80℃ oven and then ground to 100 mesh. Finally, the Mn-Fe-O@SiO2-2 catalyst was obtained by calcining at 400℃ in a muffle furnace for 4 hours, in which the total loading of Mn and Fe was 20wt%.

[0055] (3) NH3-SCR reaction performance evaluation

[0056] The evaluation of the catalytic activity of the catalyst for the NH3-SCR reaction was the same as that in Example 1. Figure 5 The test results show that under the same conditions, the NO x The conversion rate reaches 100% at 160°C, and it exhibits excellent catalytic activity (65%) in the low temperature region (120°C).

[0057] Example 3

[0058] In this embodiment, hydrothermal assembly and oxidative removal of organic templates were used to prepare silanol-rich mesoporous silica SBA-15-OH, and Mn-Fe-O composite oxide was used as a catalytically active component to prepare Mn-Fe-O@SiO2-3 catalyst.

[0059] (1) Vector preparation

[0060] The hydrothermal assembly and oxidative removal of organic templates were used to synthesize mesoporous silica SBA-15-OH rich in silanol groups for loading active metal oxide components. The preparation method of the mesoporous silica SBA-15-OH template was the same as that of Example 1.

[0061] (2) Catalyst preparation

[0062] Mn(NO3)2 aqueous solution and Fe(NO3)3·9H2O were weighed as manganese source and iron source, and dissolved in 20mL deionized water according to the molar ratio of Mn to Fe of 100:1. 0.7541g of citric acid monohydrate was added and stirred for 15 minutes to form a uniform solution. Subsequently, 1.0g of SBA-15-OH carrier was added and stirred in an 80℃ water bath for 5 hours to ensure that the metal ions were fully impregnated into the pores of mesoporous silica. The resulting mixture was dried in an 80℃ oven and then ground to 100 mesh. Finally, the Mn-Fe-O@SiO2-3 catalyst was obtained by calcining at 400℃ in a muffle furnace for 4 hours, in which the total loading of Mn and Fe was 20wt%.

[0063] (3) NH3-SCR reaction performance evaluation

[0064] The evaluation of the catalytic activity of the catalyst for the NH3-SCR reaction was the same as that in Example 1. Figure 5 The test results show that under the same conditions, the NO x The conversion rate reached 100% at 160°C, and it showed excellent catalytic activity (42%) in the low temperature region (120°C).

[0065] Comparative Example 1

[0066] In this comparative example, the V2O5-WO3-TiO2 catalyst was prepared by the impregnation method to compare the catalytic performance of the catalyst of the present invention.

[0067] (1) Preparation of catalyst

[0068] Weigh hydrated ammonium metatungstate and ammonium metacyanate, dissolve in deionized water at a mass ratio of 1:5, and stir evenly. Then, add an appropriate amount of TiO2 carrier and immerse for 1 hour to ensure that the active metal is fully adsorbed. The resulting mixture is dried in an oven at 80°C for 12 hours, heated to 400°C in a muffle furnace at a heating rate of 2°C / min and maintained for 4 hours to finally obtain a V2O5-WO3-TiO2 catalyst.

[0069] (2) NH3-SCR reaction performance evaluation

[0070] The evaluation of the catalytic activity of the catalyst for the NH3-SCR reaction was the same as that in Example 1.

[0071] (3) Results analysis

[0072] from Figure 5 It can be seen that under the same conditions, the NO x The conversion rate is generally lower than that of Mn-Fe-O@SiO2 series catalysts. x The conversion rate reaches 100% at 300°C, but the catalytic activity in the low temperature zone (120°C) is poor, only 32%, showing a narrow reaction temperature window.

[0073] Comparative Example 2

[0074] In this comparative example, an impregnation method was adopted to prepare a Mn-Fe-O-Bulk catalyst using a Mn-Fe-O composite oxide as a catalytically active component.

[0075] (1) Catalyst preparation

[0076] Mn(NO3)2 aqueous solution and Fe(NO3)3·9H2O were weighed as manganese source and iron source, and dissolved in 20mL deionized water according to the molar ratio of Mn to Fe of 1:1. 0.5222g of citric acid monohydrate was added and stirred for 15 minutes to form a uniform solution. The resulting mixture was dried in an oven at 80°C and then ground to 100 mesh. Finally, it was calcined at 400°C in a muffle furnace for 4 hours to obtain a Mn-Fe-O-Bulk catalyst, in which the total loading of Mn and Fe was 20wt%.

[0077] (2) NH3-SCR reaction performance evaluation

[0078] The evaluation of the catalytic activity of the catalyst for the NH3-SCR reaction was the same as that in Example 1.

[0079] (3) Results analysis

[0080] Figure 6 The test results show that under the same conditions, the NO x The conversion rate showed better activity at 100-140 °C, but its nitrogen selectivity was poor and the temperature window was narrow.

[0081] Comparative Example 3

[0082] This comparative example was prepared by impregnation method with Fe-O x Composite oxides were used as catalytic active components to prepare Fe-O x @SiO2 catalyst.

[0083] (1) Catalyst preparation

[0084] Weigh Mn(NO3)2 aqueous solution and Fe(NO3)3·9H2O as manganese source and iron source, and dissolve them in 20mL deionized water according to the molar ratio of Mn to Fe of 0:10. Add 0.5222g of citric acid monohydrate and stir for 15 minutes to form a uniform solution. Then, add 1.0g of SBA-15-OH carrier and stir in a water bath at 80℃ for 5 hours to ensure that the metal ions are fully impregnated into the pores of mesoporous silica. The resulting mixture is dried in an oven at 80℃ and then ground to 100 mesh. Finally, it is calcined at 400℃ in a muffle furnace for 4 hours to obtain Fe-O x @SiO2 catalyst, in which the total loading of Mn and Fe is 20wt%.

[0085] (2) NH3-SCR reaction performance evaluation

[0086] The evaluation of the catalytic activity of the catalyst for the NH3-SCR reaction was the same as that in Example 1.

[0087] (3) Results analysis

[0088] Figure 6 The test results show that under the same conditions, Fe-O x @SiO2 NO x The conversion rate showed better activity in the high temperature range (>220℃).

[0089] Comparative Example 4

[0090] This comparative example was prepared by impregnation method with Mn-O x Composite oxides were used as catalytic active components to prepare Mn-O x @SiO2 catalyst.

[0091] (1) Catalyst preparation

[0092] Weigh Mn(NO3)2 aqueous solution and Fe(NO3)3·9H2O as manganese source and iron source, and dissolve them in 20mL deionized water according to the molar ratio of Mn to Fe of 10:0. Add 0.5222g of citric acid monohydrate and stir for 15 minutes to form a uniform solution. Then, add 1.0g of SBA-15-OH carrier and stir in a water bath at 80℃ for 5 hours to ensure that the metal ions are fully impregnated into the pores of mesoporous silica. The resulting mixture is dried in an oven at 80℃ and then ground to 100 mesh. Finally, it is calcined at 400℃ in a muffle furnace for 4 hours to obtain Mn-O x @SiO2 catalyst, in which the total loading of Mn and Fe is 20wt%.

[0093] (2) NH3-SCR reaction performance evaluation

[0094] The evaluation of the catalytic activity of the catalyst for the NH3-SCR reaction was the same as that in Example 1.

[0095] (3) Results analysis

[0096] Figure 6 The test results show that under the same conditions, Mn-O x @SiO2 NO x Conversion rate of NO at 160℃ x The conversion rate reached 100%.

[0097] The microstructure of the above catalysts was further analyzed. Figure 1 The N2 adsorption-desorption isotherms of the catalysts prepared in Example 1 and Comparative Example 1 show that the calculated specific surface area and pore volume of the Mn-Fe-O@SiO2-1 catalyst are the highest, which are 587 m 2 / g and 1.01cm 3 / g. In contrast, the specific surface area and pore volume of the V2O5-WO3-TiO2 catalyst are only 50m 2 / g and 0.45cm 3 / g, the smaller pore volume and specific surface area may lead to lower dispersion of metal particles on the support surface, thus affecting its catalytic performance.

[0098] Figure 2The X-ray diffraction spectrum (XRD) analysis of the catalyst powder prepared for Example 1 and Comparative Example 1 shows that Mn-Fe-O@SiO2-1 has only one broadened diffraction peak in the range of 20-25°, corresponding to the superposition of the diffraction peaks of amorphous silica and metal oxides, indicating that the presence of the surface functionalized template with a high specific surface area effectively disperses the mixed metal oxide nanoparticles, which also indicates the successful introduction of the active metal oxide. However, no diffraction peaks attributed to the crystalline phase appear, indicating that the crystallinity of the metal oxide is low or the grain size is very small. Since the temperature conditions for catalyst preparation are sufficient to crystallize the metal oxide, it is indicated that the crystal size of the metal oxide is very small and is not enough to show a distinguishable diffraction peak on the XRD diffraction spectrum. Figure 3 The results showed that the characteristic reflections were attributed to MnO2 (PDF#44-0141), Mn2O3 (DF#41-1442) and Fe2O3 (PDF#39-0238). These results suggest that the high surface area supports with rich surface silanol groups stabilize the metal oxide nanoparticles and promote the formation of active catalytic sites.

[0099] Figure 4 Analysis of the powder transmission electron microscopy (TEM) and elemental mapping (EDS) images of the catalysts showed that the Mn-Fe-O@SiO2-1 catalysts exhibited a rod-like morphology, indicating that these catalysts maintained the morphological structure of the surface-functionalized mesoporous silica support. In addition, no visible mixed metal oxide nanoparticles were observed on the support surface, indicating that these nanoparticles were confined within the mesopores of the silica support. The TEM image along the

[001] direction clearly showed the periodic arrangement of the hexagonal hollow structure, indicating that the metal oxide nanoparticles did not block the mesopores. The corresponding elemental mapping demonstrated the uniform distribution of the Mn, Fe, O, and Si elements.

[0100] NH3-SCR catalyst water and sulfur resistance performance diagram ( Figure 7 ) analysis showed that the Mn-Fe-O@SiO2-1 catalyst maintained 100% NOx conversion both in the presence and absence of water vapor, indicating their strong water resistance compared to bulk catalysts. However, after the introduction of 5 Vol.% H2O and 100 ppm SO2, the NOx conversion of both catalysts dropped rapidly and stabilized at about 44% after 4 hours. This drop was attributed to the formation of sulfates (such as (NH4)2SO4, NH4HSO4 or metal sulfates), which blocked the active sites and inhibited the catalytic effect. After removing H2O and SO2, the NOx conversion of the Mn-Fe-O@SiO2-1 catalyst quickly recovered to 70%. The durability of NH3-SCR catalysts is crucial to their performance.

Claims

1. A method for preparing a low-temperature denitration catalyst based on mesoporous silica loaded with ultra-small Mn-Fe-O nanoparticles, characterized in that: The following steps are involved: (1) Preparation of silanol-rich mesoporous silica by hydrothermal assembly and oxidative removal of organic templates; (2) Mixing manganese salt, iron salt and deionized water to prepare a mixed metal salt solution; (3) adding an organic acid to the mixed metal salt solution obtained in step (2) to obtain an organic acid-metal salt solution; (4) adding the silanol-rich mesoporous silica prepared in step (1) to the organic acid-metal salt solution obtained in step (3), heating and stirring to fully impregnate the solution, and obtaining a mixture; (5) The mixture in step (4) is dried, ground and calcined to obtain a silica-based Mn-Fe-O catalyst.

2. The preparation method according to claim 1, characterized in that: In step (2), the manganese salt is one or more of manganese chloride MnCl2, manganese sulfate MnSO4 and manganese nitrate Mn(NO3)2 or their salts containing crystal water.

3. The preparation method according to claim 1, characterized in that: In step (2), the iron salt is one or more of iron sulfate Fe2(SO4)3, iron chloride FeCl3, iron nitrate Fe(NO3)3 and iron carbonate Fe2(CO3)3.

4. The preparation method according to claim 1, characterized in that: In step (2), the molar ratio of the manganese salt to the iron salt is 0.01 to 100:

1.

5. The preparation method according to claim 1, characterized in that: In step (3), the organic acid is one or more of acetic acid, citric acid, and oxalic acid; and the molar ratio of the organic acid to the metal in the organic acid-metal salt solution is 0.8-1.2:

1.

6. The preparation method according to claim 1, characterized in that: In step (4), the heating and stirring temperature is 50-90°C and the time is 4-8h.

7. The preparation method according to claim 1, characterized in that: In step (5), the drying temperature is 60-100° C., the grinding particle size is 80-100 mesh, the roasting temperature is 200-600° C., and the calcination treatment time is 0.1-24 h.

8. A low-temperature denitration catalyst based on mesoporous silica loaded with ultra-small Mn-Fe-O nanoparticles is prepared by the preparation method according to any one of claims 1 to 7.

9. The low-temperature denitration catalyst based on mesoporous silica loaded with ultra-small Mn-Fe-O nanoparticles according to claim 8, characterized in that: In the mesoporous silica-based Mn-Fe-O catalyst, the total loading amount of manganese and iron is 1-50wt% based on the total weight of the catalyst.

10. The low-temperature denitration catalyst based on mesoporous silica loaded with ultra-small Mn-Fe-O nanoparticles as claimed in claim 8 is used in low-temperature denitration NH3-SCR reaction.

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