De-NOx catalyst, method for producing the same, and use thereof

Abstract

The present application relates to the field of denitration catalyst, disclose a kind of low-temperature denitration catalyst and its preparation method and application.The low-temperature denitration catalyst of the present application contains the product of magnetite and spinel manganese oxide compound, the magnetite is gamma-Fe2O3, and the spinel manganese oxide is lambda-MnO2.The low-temperature denitration catalyst of the present application is not contained V, and N2 selectivity is high, and the denitration performance is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of denitration catalysts, in particular to a medium-low temperature denitration catalyst and a preparation method and application thereof. BACKGROUND

[0002] The key technology of medium-low temperature denitration is selective catalytic reduction (SCR), which essentially uses active catalysts to react NH3 and other reducing agents with NO x in flue gas to obtain green and non-polluting N2 and H2O. The key technology of medium-low temperature SCR is the catalyst.

[0003] The existing commercial medium-low temperature denitration catalysts are still mainly V2O5(-WO3) / TiO2. This catalyst formula is generally used for medium-high temperature flue gas denitration and has been widely used in coal-fired power plant denitration, steel blast furnace denitration and other fields. For example, CN112495369A discloses a medium-low temperature vanadium-tungsten-titanium-based SCR denitration catalyst and a preparation method thereof, which has certain medium-low temperature denitration activity and certain sulfur poisoning resistance. However, the activity of this catalyst is slightly low at a lower temperature, such as below 200℃, and the content of V element usually needs to be further increased to improve the catalytic activity. However, V element usually has certain toxicity, and a high content in the catalyst itself poses a certain risk. CN108465467A discloses a catalyst formula further adding Fe to the V-based catalyst, which has relatively ideal catalytic activity at medium-low temperature, but its disadvantage is still the large use of V.

[0004] In recent years, in order to further expand the denitration performance at lower temperature, active elements such as Mn are often added to the catalyst components. Such catalysts often have a series of problems, including low N2 selectivity. For example, CN102941083A discloses a core-shell type medium-low temperature denitration catalyst composed of Ti, Ce, Mn and other active components, which has good anti-poisoning ability and is a typical medium-low temperature denitration catalyst design strategy. However, the preparation scheme of the catalyst involved in this invention is complicated, a large amount of organic solvent is used, and the synthesis cost is high. CN113600206A discloses a cement kiln medium-low temperature SCR denitration catalyst containing Ti, Si, Ta, Mn, V and other elements, which can obtain high denitration activity in the medium-low temperature range. However, this invention uses more components, which brings certain difficulties to production control, and the formula still contains toxic V element. SUMMARY

[0005] The present application aims to overcome the problems of the prior art, such as the inability of the V component of the low-temperature denitration catalyst to reduce or increase the N2 selectivity after Mn is added, and provides a new low-temperature denitration catalyst without V, with high N2 selectivity and good denitration performance, and a preparation method and application thereof.

[0006] In order to achieve the above-mentioned purpose, the present application provides a denitration catalyst, wherein the denitration catalyst comprises a product compounded by magnetite and spinel manganese oxide, the magnetite is γ-Fe2O3, and the spinel manganese oxide is λ-MnO2.

[0007] Preferably, the content of the magnetite is 45-98 wt%, and the content of the spinel manganese oxide is 2-55 wt%; more preferably, the content of the magnetite is 50-98 wt%, and the content of the spinel manganese oxide is 2-50 wt%; more preferably, the content of the magnetite is 80-98 wt%, and the content of the spinel manganese oxide is 2-20 wt%; further preferably, the content of the magnetite is 95-98 wt%, and the content of the spinel manganese oxide is 2-5 wt%.

[0008] According to a second aspect of the present application, a preparation method of a denitration catalyst is provided, wherein the method comprises the following steps,

[0009] 1) contacting an acidic aqueous solution dissolving ferrous salt and ferric salt with an alkaline solution, then performing solid-liquid separation on the contacted product to obtain a hydrosol, performing first heat treatment on the hydrosol under the condition that the pH is 2-5, and performing first calcination to obtain a hematite γ-Fe2O3 matrix;

[0010] 2) performing second heat treatment on a divalent manganese salt aqueous solution and the magnetite γ-Fe2O3 matrix, then performing solid-liquid separation on the second heat treatment product, and performing second calcination.

[0011] Preferably, in step 1), the acidic aqueous solution dissolving ferrous salt and ferric salt is contacted with the alkaline solution in a dropwise manner.

[0012] Preferably, the acidic aqueous solution and the alkaline solution are respectively added dropwise in the reaction container to perform the contacting.

[0013] Preferably, in step 1), the Fe 3+ concentration in the acidic aqueous solution is 0.1-1 mol / L. 2+ The atomic ratio of Fe

[0014] Preferably, the H + concentration in the acidic aqueous solution is 0.1-1 mol / L.

[0015] The amount of the basic solution is such that the pH of the contact product is 11-12.

[0016] Preferably, in step 1), the ferrous salt is one or more of hydrochloride, sulfate and acetate, preferably one or more of ferrous chloride, ferrous sulfate and ferrous acetate, more preferably ferrous chloride.

[0017] Preferably, the ferric salt is one or more of hydrochloride, sulfate and acetate, preferably one or more of ferric chloride, ferric sulfate and ferric acetate, more preferably ferric chloride.

[0018] Preferably, the acid in the acidic aqueous solution is one or more of hydrochloric acid, sulfuric acid and acetic acid, preferably hydrochloric acid.

[0019] Preferably, the base in the basic solution is sodium hydroxide and / or potassium hydroxide.

[0020] Preferably, the method further comprises, before performing the first calcination, a step of first drying the first heat treatment product.

[0021] Preferably, the conditions of the contacting comprise that the temperature of the contacting is 5-40℃.

[0022] Preferably, the conditions of the first heat treatment comprise that the temperature of the heat treatment is 80-100℃ and the time of the heat treatment is 20-60 minutes.

[0023] Preferably, the conditions of the first drying comprise that the temperature of the drying is 50-150℃ and the time of the drying is 20-60 minutes.

[0024] Preferably, the first drying is performed under vacuum.

[0025] Preferably, the conditions of the first calcination comprise that the calcination is performed under air atmosphere at 200-300℃ for 2-10 hours.

[0026] Preferably, in step 2), the divalent manganese salt is one or more of nitrate, hydrochloride and acetate, preferably manganese nitrate.

[0027] Preferably, the amount of the divalent manganese salt is such that the Mn:Fe atomic ratio is 0.01-1:1, preferably 0.02-1:1.

[0028] Preferably, the method further comprises, before performing the second calcination, a step of second drying the solid phase obtained from the solid-liquid separation.

[0029] Preferably, the conditions of the second heat treatment comprise that the temperature of the heat treatment is 80-130℃ and the time of the heat treatment is 1-10h.

[0030] Preferably, the conditions of the second heat treatment include: the temperature of the heat treatment is 110-130℃, and the time of the heat treatment is 3-5h.

[0031] Preferably, the conditions of the second drying include: the temperature of the drying is 50-80℃.

[0032] More preferably, the second drying is performed under vacuum conditions.

[0033] Preferably, the conditions of the second calcination include: calcination under air atmosphere at 200-300℃ for 2-10h.

[0034] Preferably, the solid-liquid separation is performed by using a method of filtration, centrifugation or magnetic separation, preferably a method of magnetic separation.

[0035] According to a third aspect of the present application, there is provided a denitration catalyst prepared by the method for preparing the denitration catalyst according to the second aspect of the present application.

[0036] According to a fourth aspect of the present application, there is provided the denitration catalyst according to the first aspect or the third aspect of the present application for use in SCR flue gas denitration treatment.

[0037] By the above technical solution, the denitration catalyst of the present application can catalyze the removal of nitrogen oxides in a medium-low temperature range, has high selectivity, and exhibits excellent denitration performance, and the denitration catalyst does not contain toxic metal element V. DETAILED DESCRIPTION

[0038] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as exactly that endpoint. Any values that fall within the range of values along with the upper and lower limits on the range of values are contemplated. For values that are lesser than or greater than the range, endpoints are also contemplated, along with any values or sub-ranges therein. For values in ranges that are stated in fractions, it is intended that all fractions in the same range but with different numerators are also specifically stated. For values in ranges expressed in fractions, it is intended that all fractions in the same range but with different numerators are also specifically stated. Any narrower range, or value, disclosed herein is considered to be within the scope of what is disclosed herein as that value or range.

[0039] According to a first aspect of the present application, there is provided a denitration catalyst, wherein the denitration catalyst contains a product compounded by magnetic hematite and spinel manganese oxide, the magnetic hematite is γ-Fe2O3, and the spinel manganese oxide is λ-MnO2.

[0040] In order to further improve the selectivity and denitration performance, preferably, the content of the magnetite is 45-98% by weight, and the content of the spinel manganese oxide is 2-55% by weight; more preferably, the content of the magnetite is 50-98% by weight, and the content of the spinel manganese oxide is 2-50% by weight; more preferably, the content of the magnetite is 80-98% by weight, and the content of the spinel manganese oxide is 2-20% by weight; further preferably, the content of the magnetite is 95-98% by weight, and the content of the spinel manganese oxide is 2-5% by weight.

[0041] In a particularly preferred embodiment of the present application, the content of the magnetite is 95-98% by weight, and the content of the spinel manganese oxide is 2-5% by weight, thereby further improving the N2 selectivity and denitration performance.

[0042] According to the present application, by using the magnetite as the matrix, the stability of the spinel manganese oxide active material is improved by using the lattice similarity principle, and a stable active catalyst active component within 300°C can be obtained. The obtained catalyst can catalytically remove nitrogen oxides in the medium and low temperature range, has high selectivity, exhibits excellent denitration performance, and does not contain toxic metal element V.

[0043] According to the second aspect of the present application, a preparation method of a denitration catalyst is provided, wherein the method comprises the following steps,

[0044] 1) contacting an acidic aqueous solution dissolving ferrous salt and ferric salt with an alkaline solution, then performing solid-liquid separation on the contacted product to obtain a hydrosol, performing first heat treatment on the hydrosol under the condition that the pH is 2-5, and performing first calcination to obtain a hematite γ-Fe2O3 matrix;

[0045] 2) performing second heat treatment on the divalent manganese salt aqueous solution and the magnetite γ-Fe2O3 matrix, then performing solid-liquid separation on the second heat treatment product, and performing second calcination.

[0046] According to the method of the present application, in order to further improve the selectivity and denitration performance of the obtained denitration catalyst, preferably, in step 1), the acidic aqueous solution dissolving ferrous salt and ferric salt is contacted with the alkaline solution in a dropwise manner; more preferably, the acidic aqueous solution and the alkaline solution are respectively added dropwise in a reaction container to perform the contacting. The dropwise speed can only ensure that the temperature of the contacting is within the specified range.

[0047] In the present application, preferably, the conditions of the contacting include that the temperature of the contacting is 5-40℃ and the contacting time is 10-60 min; more preferably, the conditions of the contacting include that the temperature of the contacting is 20-30℃ and the contacting time is 20-40 min. In addition, it is preferred that the contacting is carried out under stirring.

[0048] According to the method of the present application, preferably, in step 1), the atomic ratio of Fe 3+ to Fe 2+ is 1.8-2.2:1; more preferably, in step 1), the atomic ratio of Fe 3+ to Fe 2+ is 1.9-2:1.

[0049] According to the method of the present application, preferably, the total Fe concentration in the acidic aqueous solution is 1.5-2 mol / L; more preferably, the total Fe concentration in the acidic aqueous solution is 1.7-1.9 mol / L, and particularly preferably 1.8 mol / L.

[0050] According to the method of the present application, preferably, the H + concentration in the acidic aqueous solution is 0.1-1 mol / L; more preferably, the H + concentration in the acidic aqueous solution is 0.3-0.5 mol / L, and particularly preferably 0.4 mol / L.

[0051] According to the method of the present application, the amount of the basic solution is such that the pH of the contacting product is kept in the range of 11-12. As the basic solution, for example, a basic solution having a concentration of 0.1-2 mol / L can be used, preferably a basic solution having a concentration of 0.5-1.6 mol / L, more preferably a basic solution having a concentration of 1.4-1.6 mol / L, and particularly preferably a basic solution having a concentration of 1.5 mol / L.

[0052] According to the method of the present application, preferably, in step 1), the ferrous salt is one or more of hydrochloride, sulfate and acetate; more preferably, the ferrous salt is one or more of ferrous chloride, ferrous sulfate and ferrous acetate; further preferably, the ferrous salt is ferrous chloride.

[0053] According to the method of the present application, preferably, in step 1), the ferric salt is one or more of hydrochloride, sulfate and acetate; more preferably, the ferric salt is one or more of ferric chloride, ferric sulfate and ferric acetate; further preferably, the ferric salt is ferric chloride.

[0054] According to the method of the present application, preferably, in step 1), the acid in the acidic aqueous solution is one or more of hydrochloric acid, sulfuric acid and acetic acid; more preferably, the acid in the acidic aqueous solution is hydrochloric acid.

[0055] According to the method of the present application, preferably, the base in the basic solution in step 1) is sodium hydroxide and / or potassium hydroxide.

[0056] According to the method of the present application, preferably, the solid-liquid separation can be performed using a method of filtration, centrifugation, magnetic separation, etc., preferably a method of magnetic separation.

[0057] According to the method of the present application, preferably, after the solid-liquid separation, the aqueous solvent is washed with deionized water several times until neutral.

[0058] According to the method of the present application, preferably, in step 1), the first heat treatment of the hydrosol is performed at a pH of 3.3-3.7; more preferably, in step 1), the first heat treatment of the hydrosol is performed at a pH of 3.4-3.6; particularly preferably, in step 1), the first heat treatment of the hydrosol is performed at a pH of 3.5.

[0059] According to the method of the present application, preferably, the method further comprises a step of performing a first drying of the first heat treatment product before performing the first calcination.

[0060] The above-mentioned first drying can be performed using a method of drying commonly used in the art. Preferably, the conditions of the first drying include a drying temperature of 50-150°C and a drying time of 20-60 minutes. In addition, the first drying can be performed under vacuum conditions.

[0061] According to the method of the present application, preferably, in step 1), the conditions of the first calcination include calcination at 200-300°C for 2-10 hours in an air atmosphere; more preferably, in step 1), the conditions of the first calcination include calcination at 230-270°C for 4-8 hours in an air atmosphere.

[0062] Preferably, in step 2), the divalent manganese salt is one or more of a nitrate, a chloride, and an acetate, preferably manganese nitrate.

[0063] According to the method of the present application, preferably, in step 2), the divalent manganese salt is added in an amount such that the Mn:Fe atomic ratio is 0.01-1:1; more preferably, in step 2), the divalent manganese salt is added in an amount such that the Mn:Fe atomic ratio is 0.02-1:1; more preferably, in step 2), the divalent manganese salt is added in an amount such that the Mn:Fe atomic ratio is 0.02-0.2:1.

[0064] According to the present application, preferably, the divalent manganese salt is used in the form of an aqueous solution, and the content of the divalent manganese salt in the aqueous solution can be 30-70% by weight, preferably 40-60% by weight, and particularly preferably 50% by weight.

[0065] According to the method of the present application, preferably, the method further comprises the step of subjecting the solid phase obtained by the solid-liquid separation to a second drying before the second calcination is performed.

[0066] The second drying can be performed by using a method commonly used in the art, such as drying. Preferably, the conditions of the second drying include a drying temperature of 50-80°C. The drying time is not particularly limited, and for example, can be 10-120 min. In addition, the second drying can be performed under vacuum conditions.

[0067] According to the method of the present application, in step 2), preferably, the conditions of the second heat treatment include a heat treatment temperature of 80-130°C and a heat treatment time of 1-10 h; more preferably, the conditions of the second heat treatment include a heat treatment temperature of 110-130°C and a heat treatment time of 3-5 h.

[0068] According to the method of the present application, in step 2), preferably, the conditions of the second calcination include calcination at 200-300°C for 2-10 h under an air atmosphere; more preferably, the conditions of the second calcination include calcination at 250-300°C for 4-8 h under an air atmosphere.

[0069] According to the third aspect of the present application, there is provided a denitration catalyst prepared by the method for preparing a denitration catalyst according to the second aspect of the present application.

[0070] According to the fourth aspect of the present application, there is provided the use of the denitration catalyst according to the first aspect or the third aspect of the present application in the SCR flue gas denitration treatment.

[0071] According to the above technical solution, the denitration catalyst of the present application can catalytically remove nitrogen oxides in a medium-low temperature range, has high selectivity, exhibits excellent denitration performance, and does not contain the toxic metal element V.

[0072] The present application will be described in detail below through examples, but the present application is not limited to the following examples.

[0073] The raw materials used in the examples and comparative examples are, if not particularly limited, publicly known in the art, for example, can be directly purchased or prepared according to the publicly known preparation method.

[0074] Example 1

[0075] 1) Preparation of Fe3O4 hydrosol

[0076] An acidic solution was prepared by mixing HCl with deoxygenated deionized water to dilute, and the dilution obtained 0.4 mol / L of the acidic solution. In the hydrochloric acid solution, FeCl3·6H2O and FeCl2 were added to ensure that the atomic ratio satisfies Fe(III): Fe(II) = 2:1, and the total Fe concentration is 1.8 mol / L. Then an alkaline solution was prepared by dissolving NaOH in deoxygenated deionized water to obtain a 1.5 mol / L alkaline solution. Subsequently, the acidic solution and the alkaline solution were added simultaneously to ensure that the pH of the mixed solution was maintained at 11-12 at all times, and the reaction was completed after 30 min of vigorous stirring. The product was then magnetically separated and washed with deionized water several times until it was neutral.

[0077] 2) Preparation of γ-Fe2O3

[0078] The Fe3O4 hydrosol obtained in step 1) was adjusted to pH 3.5 with hydrochloric acid, and air was blown at 100°C for condensation reflux for 30 min. At this time, a significant color change was observed in the solid material, and a γ-Fe2O3 hydrosol was obtained. The hydrosol was then further vacuum rotary evaporated at 60°C and calcined at 250°C in an air atmosphere in a tube furnace for 6 h to obtain γ-Fe2O3.

[0079] 3) Preparation of λ-MnO2 / γ-Fe2O3

[0080] γ-Fe2O3 and a deionized aqueous solution of Mn(NO3)2 (concentration of 50 wt%) were mixed in a ratio of Mn: Fe = 0.02:1 by atomic ratio, and the mixture was stirred uniformly and refluxed at 120°C for 4 h. Then, the product was magnetically separated and washed with water until the solid phase was neutral. The solid phase was then vacuum rotary evaporated at 60°C and calcined at 300°C in an air atmosphere in a tube furnace for 6 h.

[0081] The product was analyzed by X-ray diffraction spectrometer, and it was confirmed that it was composed of maghemite γ-Fe2O3 and spinel manganese oxide λ-MnO2, and the content of maghemite γ-Fe2O3 was 98 wt%, and the content of spinel manganese oxide λ-MnO2 was 2 wt%.

[0082] The performance of the catalyst was evaluated at a space velocity of 100,000 mL / (g·h) under the conditions of 500 ppm NO, 550 ppm NH3, and 2 vol.% O2, and the NO removal T 50 (NO removal rate was 50% when the temperature was 169°C, and the N2 selectivity was excellent, and the concentration of N2O generated within the test interval of 300°C was less than 8 ppm, which showed excellent low-temperature and high-selectivity denitration properties.

[0083] Example 2

[0084] The method of Example 1 was followed, except that in step 3), γ-Fe2O3 and Mn(NO3)2deionized aqueous solution were added according to the atomic ratio Mn:Fe = 0.04:1.

[0085] The product was analyzed using an X-ray diffractometer, and was confirmed to be composed of maghemite γ-Fe2O3 and spinel manganese oxide λ-MnO2, with the content of maghemite γ-Fe2O3 being 96% by weight and the content of spinel manganese oxide λ-MnO2 being 4% by weight.

[0086] The catalyst performance was evaluated under a space velocity of 100,000 mL / (g·h) in the presence of 500 ppm NO, 550 ppm NH3, and 2 vol.% O2, and the NO removal T 50 = 179°C, with excellent N2 selectivity, and N2O concentration less than 8 ppm within the test interval of 300°C, showing excellent low-temperature high-selectivity denitration properties.

[0087] Example 3

[0088] The method of Example 1 was followed, except that in step 3), γ-Fe2O3 and Mn(NO3)2deionized aqueous solution were added according to the atomic ratio Mn:Fe = 0.2:1.

[0089] The product was analyzed using an X-ray diffractometer, and was confirmed to be composed of maghemite γ-Fe2O3 and spinel manganese oxide λ-MnO2, with the content of maghemite γ-Fe2O3 being 82% by weight and the content of spinel manganese oxide λ-MnO2 being 17% by weight.

[0090] The catalyst performance was evaluated under a space velocity of 100,000 mL / (g·h) in the presence of 500 ppm NO, 550 ppm NH3, and 2 vol.% O2, and the NO removal T 50 = 184°C, with excellent N2 selectivity, and N2O concentration less than 10 ppm within the test interval of 300°C, showing excellent low-temperature high-selectivity denitration properties.

[0091] Example 4

[0092] The method of Example 1 was followed, except that in step 3), γ-Fe2O3 and Mn(NO3)2deionized aqueous solution were added according to the atomic ratio Mn:Fe = 1:1.

[0093] The product was analyzed using an X-ray diffractometer, and was confirmed to be composed of maghemite γ-Fe2O3 and spinel manganese oxide λ-MnO2, with the content of maghemite γ-Fe2O3 being 48% by weight and the content of spinel manganese oxide λ-MnO2 being 52% by weight.

[0094] The catalyst performance was evaluated at 100,000 mL / (g-h) space velocity under the conditions of 500 ppm NO, 550 ppm NH3, and 2 vol.% O2, and the NO removal T 50 = 194°C, and the N2 selectivity was excellent, and the N2O concentration was less than 13 ppm within the test interval of 300°C, showing excellent low-temperature high-selectivity denitration characteristics.

[0095] Comparative Example 1 (γ-Fe2O3 activity test without loaded λ-MnO2)

[0096] As in Example 1, γ-Fe2O3 was prepared, and denitration performance tests were performed according to Example 1. The test results showed that the NO removal T 50 = 227°C, and 100% denitration efficiency did not occur even when the test temperature was increased to 300°C. The denitration performance of this sample was poor, and the denitration conversion rate was only 68% at most in the 300°C temperature range, which did not reach 100% as in the example, and the performance was also poor, and the N2O concentration was as high as 20 ppm within the test interval of 300°C.

[0097] Comparative Example 2 (γ-Fe2O3 activity test with re-treated and unloaded λ-MnO2)

[0098] As in Example 1, γ-Fe2O3 was prepared, and the last step of synthesis was continued, but the difference was that Mn(NO3)2 was not added, and only the condensation reflux of the γ-Fe2O3 and H2O mixture, centrifugation, rotary evaporation, and calcination were performed.

[0099] Denitration performance tests were performed according to Example 1. The test results showed that the NO removal T 50 = 219°C, and the N2O concentration was as high as 20 ppm within the test interval of 300°C, and the low-temperature denitration performance was not as good as in Example 1-4.

[0100] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A denitration catalyst characterized by, The denitration catalyst contains a product compounded by magnetic hematite and spinel manganese oxide, wherein the magnetic hematite is γ-Fe2O3, and the spinel manganese oxide is λ-MnO2.

2. The de-NOx catalyst according to claim 1, wherein The content of the magnetic hematite is 45-98% by weight, and the content of the spinel manganese oxide is 2-55% by weight.

3. The de-NOx catalyst according to claim 2, wherein The content of the magnetic hematite is 50-98% by weight, and the content of the spinel manganese oxide is 2-50% by weight.

4. The de-NOx catalyst according to claim 3, wherein The content of the magnetic hematite is 80-98% by weight, and the content of the spinel manganese oxide is 2-20% by weight.

5. The de-NOx catalyst according to claim 4, wherein The content of the magnetic hematite is 95-98% by weight, and the content of the spinel manganese oxide is 2-5% by weight.

6. A method for producing a denitration catalyst, characterized by, The method Comprises the following steps, 1) After the acid aqueous solution dissolving ferrous salt and iron salt is contacted with the alkaline solution, the contacted product is subjected to solid-liquid separation to obtain a hydrosol, the hydrosol is subjected to first heat treatment under the condition that the pH is 2-5, and first calcination is performed to obtain a magnetic hematite γ-Fe2O3 matrix; 2) After the divalent manganese salt aqueous solution is subjected to second heat treatment with the magnetic hematite γ-Fe2O3 matrix, the second heat treatment product is subjected to solid-liquid separation and second calcination, The first heat treatment conditions include: the heat treatment temperature is 80-100℃, and the heat treatment time is 20-60 minutes, The first calcination conditions include: calcination under the air atmosphere at 200-300℃ for 2-10 hours, The second heat treatment conditions include: the heat treatment temperature is 80-130℃, and the heat treatment time is 1-10h, The second calcination conditions include: calcination under the air atmosphere at 200-300℃ for 2-10 hours.

7. The method of claim 6, wherein, In step 1), the acid aqueous solution dissolving ferrous salt and iron salt is contacted with the alkaline solution in a dropwise manner.

8. The method of claim 7, wherein, The acid aqueous solution and the alkaline solution are respectively dropped into the reaction container to perform the contact.

9. The method of claim 7, wherein, In step 1), the atomic ratio of Fe 3+ to Fe 2+ is 1.9-2:

1.

10. The method of claim 7, wherein, H in the acidic aqueous solution + concentration of 0.1-1 mol / L; The amount of the alkaline solution is such that the pH of the contact product is 11-12.

11. The method of any of claims 6-10, wherein, In step 1), the ferrous salt is one or more of hydrochloride, sulfate and acetate.

12. The method of claim 11, wherein, In step 1), the ferrous salt is one or more of ferrous chloride, ferrous sulfate and ferrous acetate.

13. The method of claim 12, wherein, In step 1), the ferrous salt is ferrous chloride.

14. The method of any one of claims 6-10, wherein, The iron salt is one or more of hydrochloride, sulfate and acetate.

15. The method of claim 14, wherein, The iron salt is one or more of ferric chloride, ferric sulfate and ferric acetate.

16. The method of claim 15, wherein, The iron salt is ferric chloride.

17. The method of any one of claims 6-10, wherein, The acid in the acid aqueous solution is one or more of hydrochloric acid, sulfuric acid and acetic acid.

18. The method of claim 17, wherein, The acid in the acid aqueous solution is hydrochloric acid.

19. The method of any one of claims 6-10, wherein, The base in the alkaline solution is sodium hydroxide and / or potassium hydroxide.

20. The method of any one of claims 6-10, wherein, The method further comprises the step of first drying the first heat treatment product before the first calcination.

21. The method of any one of claims 6-10, wherein, The contact conditions include: the contact temperature is 5-40℃.

22. The method of claim 20, wherein, The first drying conditions include: the drying temperature is 50-150℃, and the drying time is 20-60 minutes.

23. The method of claim 22, wherein, The first drying is performed under vacuum conditions.

24. The method of any one of claims 6-10, wherein, In step 2), the divalent manganese salt is one or more of nitrate, hydrochloride and acetate; The added amount of the divalent manganese salt is such that the Mn:Fe atomic ratio is 0.01-1:

1.

25. The method of claim 24, wherein, In step 2), the divalent manganese salt is manganese nitrate; The added amount of the divalent manganese salt is such that the Mn:Fe atomic ratio is 0.02-1:

1.

26. The method of any one of claims 6-10, wherein, The method further comprises a step of performing a second drying on the solid phase obtained by the solid-liquid separation before performing the second calcination.

27. The method of any one of claims 6-10, wherein, The conditions of the second heat treatment comprise a temperature of 110-130℃ and a time of 3-5h.

28. The method of claim 26, wherein, The conditions of the second drying comprise a temperature of 50-80℃.

29. The method of claim 28, wherein, The second drying is performed under vacuum.

30. The method of any one of claims 6-10, wherein, The solid-liquid separation is performed by filtration, centrifugation or magnetic separation.

31. The method of claim 30, wherein, The solid-liquid separation is performed by magnetic separation.

32. The denitration catalyst prepared by the preparation method of any one of claims 6-31.

33. The denitration catalyst of any one of claims 1-5 and 32 for use in the SCR flue gas denitration treatment.