Alkali metal resistant rare earth doped iron-based core-shell denitration catalyst, preparation method and application thereof

Abstract

The application relates to an alkali metal-resistant rare earth-doped iron-based core-shell denitration catalyst and a preparation method and application thereof. Praseodymium-doped ferrous oxide microspheres are used as a core layer, titanium dioxide and silicon dioxide are used as a composite shell layer, and a core-shell structure is formed. The molar ratio of praseodymium, iron, titanium and silicon is (0.01-0.04):1:(0.1-0.8):(0.1-0.8). Iron sources, praseodymium sources, dispersants and sodium acetate are dissolved in a first solvent, a solvothermal reaction is carried out, praseodymium-doped ferrous oxide microspheres are obtained, the praseodymium-doped ferrous oxide microspheres and organic acids are dissolved in a second solvent, a third solvent is used for transfer, a precipitant is added for precipitation, and a microsphere solution is obtained. Titanium sources, silicon sources and pore-forming agents are dissolved in a fourth solvent, and a titanium-silicon solution is obtained. The microsphere solution and the titanium-silicon solution are mixed, a core-shell structure is assembled, calcination is carried out, and the catalyst is obtained. Compared with the prior art, the application can effectively improve the denitration efficiency and alkali resistance of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalytic materials technology, and relates to an alkali metal rare earth doped iron-based core-shell denitration catalyst, its preparation method, and its application. Background Technology

[0002] Nitrogen oxides (NO) x As a major byproduct of fossil fuel combustion, nitrogen oxides (NOx) cause environmental problems such as the greenhouse effect, acid rain, and ozone layer depletion. The need for treatment of emissions from industrial kilns, ship exhaust, and vehicle exhaust is particularly urgent. Against this backdrop, ammonia selective catalytic reduction (NH3-SCR) technology, with its economic and efficient characteristics, has become the mainstream solution for industrial denitrification. While the widely used V2O5-WO3 / TiO2 catalyst exhibits excellent denitrification performance, its operating temperature window is concentrated in the high-temperature range of 300–400 °C. Furthermore, the catalyst is often placed at the front end of desulfurization towers and electrostatic precipitators, making it susceptible to poisoning from high concentrations of sulfur dioxide (SO2) and alkali metal dust (such as potassium oxide (K2O) and sodium oxide (Na2O)) in the flue gas.

[0003] Studies have shown that gaseous alkali metal compounds cause catalyst performance degradation through three mechanisms: 1. Basic cations bind to acidic sites, weakening the acidity of the catalyst surface; 2. Electron migration alters the oxidation state of active centers, inhibiting redox capabilities; 3. They disrupt the thermal stability of the support, inducing high-temperature sintering and causing pore blockage. These factors collectively lead to a significant decrease in the denitrification activity, selectivity, and stability of the catalyst. Especially in flue gas environments containing biomass or high-alkali coal fuels, the catalyst lifetime is drastically shortened, severely restricting the widespread application of ammonia selective catalytic reduction technology.

[0004] To address the aforementioned issues, researchers have proposed various strategies to combat alkali metal poisoning: enhancing the competitive adsorption capacity of acidic sites through metal doping, achieving physical isolation using core-shell structures or hollow nanotubes, and constructing sacrificial sites through surface modifications such as sulfation and phosphorylation. These methods have improved the catalyst's resistance to poisoning to some extent, but common problems still remain to be solved.

[0005] Patent CN115739067A discloses a denitrification catalyst, its preparation method, and its application. The ammonia selective catalytic reduction denitrification catalyst is titanium oxide coated with samarium-doped iron oxide. However, the catalyst in this patent has poor low-temperature activity below 200 ℃, with a maximum denitrification activity of only 38% at 200 ℃, and it lacks alkali metal resistance.

[0006] Patent CN116809067A discloses a core-shell catalyst, its preparation method, and its application. The prepared core-shell catalyst uses iron(III) oxide (Fe3O4) as the core and titanium dioxide (TiO2) as the protective shell. This core-shell catalyst can be used in the field of flue gas catalytic oxidation denitrification. However, the catalyst preparation process of this patent uses acetonitrile, which is a toxic organic solvent and poses potential risks to the environment and operator health. It is not conducive to green synthesis and industrial scale-up. Furthermore, even under optimal operating conditions for denitrification, combined with alkaline absorption, the denitrification efficiency is only 88%, and the influence of common components in actual flue gas, such as fly ash and alkali metals, is not considered.

[0007] Patent CN117181231A discloses a catalyst that can improve the sulfur resistance of iron oxide catalysts and its preparation method. The catalyst has the molecular formula R. x FeO y In this context, R represents the rare earth element being doped. However, this patent simply involves doping with rare earth elements, which leads to alkali metal ions covering the catalyst surface, severely reducing the catalyst's denitrification activity. Summary of the Invention

[0008] The purpose of this invention is to overcome at least one defect of the existing technology, such as poor resistance to alkali metals of iron-based catalysts, and to provide an alkali metal-resistant rare earth-doped iron-based core-shell denitration catalyst, its preparation method, and its application. This invention can effectively improve the denitration efficiency and alkali metal resistance of the catalyst.

[0009] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of the present invention is to provide an alkali metal rare earth doped iron-based core-shell denitration catalyst, wherein the catalyst uses praseodymium (Pr) doped ferric oxide (Fe2O3) microspheres as the core layer and titanium dioxide (TiO2) and silicon dioxide (SiO2) as the composite shell layer to form a core-shell structure, wherein the molar ratio of praseodymium, iron (Fe), titanium (Ti) and silicon (Si) is (0.01~0.04):1:(0.1~0.8):(0.1~0.8).

[0010] As a preferred technical solution, the molar ratio of praseodymium, iron, titanium, and silicon is (0.01~0.04):1:(0.4~0.6):(0.2~0.4).

[0011] One of the technical solutions of the present invention is to provide a method for preparing the alkali metal rare earth doped iron-based core-shell denitration catalyst, the method comprising the following steps: S1. Iron source, praseodymium source, dispersant and sodium acetate are dissolved in the first solvent and subjected to a solvothermal reaction to obtain praseodymium-doped ferric oxide microspheres; S2. Praseodymium-doped ferric oxide microspheres and organic acids are dissolved in a second solvent to increase the acidity of the microsphere surface. The mixture is then transferred using a third solvent, and a precipitant is added to precipitate the microspheres, thus obtaining a microsphere solution. S3. Dissolve the titanium source, silicon source and pore-forming agent in a fourth solvent to obtain a titanium-silicon solution; S4, mixed microsphere solution and titanium silicon solution, assembled into core-shell structure, calcined to obtain alkali metal rare earth doped iron-based core-shell denitration catalyst.

[0012] As a preferred technical solution, the preparation of the microsphere solution and the titanium-silicon solution does not have a specific order.

[0013] Further, in step S1, the iron source is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate; the praseodymium source is selected from one or more of praseodymium chloride, praseodymium nitrate, and praseodymium sulfate; the dispersant is polyethylene glycol; and the first solvent is selected from one or more of ethanol, glycerol, and ethylene glycol.

[0014] Furthermore, in step S1, the molar / mass / volume ratio of iron in the iron source to the dispersant, sodium acetate, and the first solvent is 1 mol:(0.1~0.3 kg):(0.4~1 kg):(4~12 L).

[0015] Further, in step S2, the organic acid is selected from one or more of citric acid, acetic acid, and oxalic acid; the second solvent is selected from one or more of water and ethanol; the third solvent is selected from one or more of ethanol, glycerol, and ethylene glycol; the precipitant is selected from one or more of ammonia, ammonium bicarbonate solution, ammonium carbonate solution, and sodium hydroxide solution; and the concentration of the cation in the precipitant is 2~2.6 mol / L.

[0016] Further, in step S2, the mass / volume ratio of praseodymium-doped ferric oxide microspheres to organic acid and the second solvent is 1 g:(1~3 g):(0.1~0.3 L), and the mass / volume ratio of praseodymium-doped ferric oxide microspheres to the third solvent and the precipitant is 1 g:(0.1~0.3 L):(10~40 mL).

[0017] Further, in step S3, the titanium source is selected from one or more of tetrabutyl titanate, titanium tetrachloride, and titanium sulfate; the silicon source is selected from one or more of tetraethyl orthosilicate and silicon tetrachloride; the pore-forming agent is selected from one or more of hexadecyltrimethoxysilane, ammonium bicarbonate, and ammonium chloride; and the fourth solvent is selected from one or more of ethanol, glycerol, and ethylene glycol.

[0018] Furthermore, in step S3, the molar / volume ratio of titanium in the titanium source to the pore-forming agent and the fourth solvent is 1 mol:(0.01~0.4 L):(2~20 L).

[0019] Furthermore, the dissolution time in step S1 is 50-70 min. The temperature of the solvothermal reaction is 180~220 ℃, and the holding time is 6~10 h; The dissolution time in step S2 is 50-70 minutes. The settling time is 30-50 minutes; The dissolution time in step S3 is 20~40 min; The mixing time in step S4 is 100~140 min. The gas is calcined in an oxygen-containing gas atmosphere, which is selected from air, oxygen-containing nitrogen, or oxygen-containing argon. The calcination temperature is 400~500 ℃, and the holding time is 2~4 h.

[0020] As a preferred technical solution, the dissolution temperature in step S1 is 10~40 ℃; The dissolution temperature in step S2 is 10~40℃. The precipitation temperature is 10~40℃; The dissolution temperature in step S3 is 10~40℃; The mixing temperature in step S4 is 10~40 ℃.

[0021] As a preferred technical solution, in step S2, praseodymium-doped ferric oxide microspheres and organic acid are ultrasonically dissolved in a second solvent to increase the acidity of the microsphere surface. The frequency of ultrasound is 40~80 kHz.

[0022] As a preferred technical solution, the post-processing steps in each step of the preparation process include one or more of the following: transfer, centrifugation, washing, drying, and sieving. Transfer using one or more of water, ethanol, glycerol, and ethylene glycol. The centrifugation speed is 2000~4000 r / min, and the time is 2~4 min. Use one or more of water, ethanol, glycerol, and ethylene glycol for washing, and wash two to seven times. The drying temperature is 60~100 ℃, and the time is 6~12 h. Pass through a 40-80 mesh sieve.

[0023] One of the technical solutions of the present invention is to provide the application of the alkali metal rare earth doped iron-based core-shell denitration catalyst in selective catalytic reduction (SCR) denitration reaction.

[0024] As a preferred technical solution, the catalyst is applied to nitrogen oxides (NOx). x The ammonia selective catalytic reduction (NH3-SCR) denitrification reaction.

[0025] As a preferred technical solution, the catalyst is applied to the selective catalytic reduction denitrification reaction of flue gas containing nitrogen oxides and ammonia (NH3).

[0026] As a preferred technical solution, the flue gas includes nitrogen oxides, ammonia, oxygen (O2), and inert gases.

[0027] As a preferred technical solution, the reaction space velocity is 40,000~50,000 h⁻¹. -1 .

[0028] As a preferred technical solution, the concentration of nitrogen oxides is 400~600 ppm, the concentration of ammonia is 400~600 ppm, the concentration of oxygen is 4~6 vol%, and the inert gas is used as a balance gas, which is selected from argon (Ar), nitrogen (N2) or helium (He).

[0029] Compared with the prior art, the present invention has the following beneficial effects: (1) In the catalyst of the present invention, titanium dioxide and silicon dioxide are compositely coated with praseodymium-doped ferric oxide microspheres, presenting a core-shell structure. Praseodymium doping can effectively suppress the crystal transformation of ferric oxide as the temperature increases, reduce the grain size, increase the specific surface area, and improve the redox performance and the number of acidic sites. The titanium-silicon shell physically isolates alkali metal poisoning, which can protect the active sites inside the shell from alkali metal poisoning. The titanium dioxide in the shell increases Lewis acidic sites, thereby increasing the overall denitrification activity of the catalyst. The appropriate proportion of silicon dioxide is increased to increase the surface Brønsted acidic sites. The combined effect of the two increases the specific surface area of ​​the catalyst and the amount of adsorbed oxygen on the surface, so that the denitrification efficiency of the catalyst is significantly improved in a wider temperature window, the structure is stable, and the alkali metal resistance is excellent and the dispersibility is good. (2) The preparation method of the present invention has simple process requirements and low cost. Most of the preparation process can be carried out at room temperature, which reduces the limitations of specific temperature and specific equipment and provides convenience for actual production applications; (3) In the selective catalytic reduction denitrification of flue gas, the present invention has a wide activity window, a wide range of application types, and the raw materials are environmentally friendly and easy to be applied in a sustainable manner. Attached Figure Description

[0030] Figure 1 This is a transmission electron microscope (TEM) image at low magnification of the alkali metal rare earth doped iron-based core-shell denitration catalyst in Example 2 of the present invention; Figure 2 This is a transmission electron microscope (TEM) image at high magnification of the alkali metal rare earth doped iron-based core-shell denitration catalyst in Example 2 of the present invention. Figure 3 This is a transmission electron microscope (TEM) image at high magnification of the alkali metal rare earth doped iron-based core-shell denitration catalyst in Example 2 of the present invention. Figure 4 The X-ray diffraction (XRD) spectra of the denitrification catalysts in Comparative Examples 3, 4, 6, 8 to 10 of this invention are shown. Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0032] Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared by conventional methods in the art. In the following embodiments, unless otherwise described in detail, conventional experimental methods in the art can be used.

[0033] The grades and manufacturers of the reagents and gases used in the following examples and comparative examples are shown in Table 1.

[0034] Table 1. Grades and manufacturers of reagents and gases used in the examples and comparative examples. Unless otherwise specified, the following procedures are generally performed at room temperature and atmospheric pressure.

[0035] Example 1: A core-shell denitration catalyst resistant to alkali metal rare earth doped iron-based denitration and its preparation method are as follows: S1. Weigh 5.4 g ferric chloride hexahydrate, 0.174 g praseodymium nitrate hexahydrate, 4 g polyethylene glycol, and 14.4 g anhydrous sodium acetate. The molar ratio of praseodymium (Pr) to iron (Fe) is 0.02:1. Add the mixture to 160 mL of anhydrous ethylene glycol. The molar / mass / volume ratio of iron to polyethylene glycol, sodium acetate, and ethylene glycol is 1 mol:0.2 kg:0.7 kg:8 L. Dissolve the mixture by magnetic stirring at room temperature for 1 h. Transfer the resulting solution to a high-temperature reactor lined with polytetrafluoroethylene (PTFE). Incubate the reactor at 200 °C for 8 h for a solvothermal reaction. Then, pour off the supernatant from the reactor. Transfer the remaining black liquid to a centrifuge cup using deionized water. Centrifuge at 3500 r / min for 3 min. Wash the solution three times with deionized water and twice with anhydrous ethanol. Pour the solution into an evaporating dish and dry it in an oven at 80 °C for 8 hours. h, praseodymium-doped ferric oxide (Fe2O3) microspheres were obtained; S2. Weigh 0.4833 g of praseodymium-doped ferric oxide microspheres and 0.9605 g of anhydrous citric acid, add them to 100 mL of deionized water. The mass / volume ratio of praseodymium-doped ferric oxide microspheres to citric acid and water is 1 g:2 g:0.2 L. Stir appropriately with a glass rod at room temperature and sonicate at 50 kHz for 1 h to dissolve. Then transfer the solution to a centrifuge cup with anhydrous ethanol, centrifuge at 3500 r / min for 3 min, wash three times with anhydrous ethanol, and transfer the solution from the centrifuge cup to a magnetic conical flask with 100 mL of anhydrous ethanol and stir. Add a precipitant to the conical flask. The composite precipitant is a mixture of ammonia water and ammonium bicarbonate solution, with a volume ratio of ammonia water to ammonium bicarbonate solution of 1:4. The ammonium ion concentration of the ammonia water is 3.6 mol / L, and the ammonium ion concentration of the ammonium bicarbonate solution is 2 mol / L. The praseodymium-doped ferric oxide microspheres were mixed with ethanol and a composite precipitant at a mass / volume ratio of 1 g:0.2 L:25 mL. The mixture was magnetically stirred for 40 min at room temperature to precipitate the microspheres and obtain a microsphere solution. S3. Measure 35 mL of anhydrous ethanol, add 1.5 g of tetrabutyl titanate and 0.1304 g of tetraethyl orthosilicate using a dropper. The molar ratio of titanium (Ti) to silicon (Si) is 7:1, and the molar / volume ratio of titanium to ethanol is 1 mol:8 L. Add 0.5 mL of hexadecyltrimethoxysilane. The molar / volume ratio of titanium to hexadecyltrimethoxysilane is 1 mol:0.11 L. Shake well for 30 min to prevent hydrolysis and obtain a titanium-silicon solution. S4. Using a syringe, the titanium-silicon solution was slowly added dropwise to the microsphere solution while maintaining stirring. The molar ratio of iron to titanium was 1:0.7. The mixture was magnetically stirred at room temperature for 2 hours to assemble a core-shell structure. Then, the solution was transferred to a centrifuge cup with anhydrous ethanol and centrifuged at 3500 r / min for 3 min. After washing five times with anhydrous ethanol, the solution was poured into an evaporating dish and dried in an 80 ℃ forced-air drying oven for 8 hours. After passing through a 60-mesh sieve, the solution was calcined in a tube furnace at 450 ℃ in air atmosphere for 3 hours to obtain an alkali metal rare earth doped iron-based core-shell denitration catalyst, denoted as Pr / Fe2O3@Ti. 0.7 :Si 0.1 .

[0036] Comparative Example 1: An alkali metal poisoned rare earth doped iron-based core-shell denitration catalyst and its preparation method are disclosed below. Weigh 0.5 g of the catalyst from Example 1 and 0.005 g of potassium nitrate, potassium ions (K... +The catalyst, with a relative mass fraction of 0.4 wt%, was added sequentially to 25 mL of deionized water. The mixture was magnetically stirred at 50 ℃ for 4 h, then poured into an evaporating dish and dried in an 80 ℃ forced-air drying oven for 8 h. After passing through a 60-mesh sieve, the solution was calcined in a tube furnace at 450 ℃ in air atmosphere for 3 h to obtain an alkali metal poisoned rare earth-doped iron-based core-shell denitration catalyst, denoted as K-Pr / Fe2O3@Ti. 0.7 :Si 0.1 .

[0037] Comparative Example 2: A rare earth-doped iron-based core-shell denitration catalyst and its preparation method are basically the same as in Example 1, except that in step S3, the mass of tetrabutyl titanate is increased from 1.5 g to 1.7 g, while the mass of tetraethyl orthosilicate is decreased from 0.1304 g to 0 g. The molar ratio of titanium to ethanol is 1 mol:7 L, the molar ratio of titanium to hexadecyltrimethoxysilane is 1 mol:0.1 L, and the molar ratio of iron to titanium is 1:0.8. The obtained rare earth-doped iron-based core-shell denitration catalyst is designated as Pr / Fe2O3@Ti. 0.8 The specific steps are as follows: S1. Weigh 5.4 g ferric chloride hexahydrate, 0.174 g praseodymium nitrate hexahydrate, 4 g polyethylene glycol and 14.4 g anhydrous sodium acetate, with a molar ratio of praseodymium to iron of 0.02:1. Add to 160 mL anhydrous ethylene glycol, with a molar / mass / volume ratio of iron to polyethylene glycol, sodium acetate and ethylene glycol of 1 mol:0.2 kg:0.7 kg:8 L. Dissolve by magnetic stirring at room temperature for 1 h. Transfer the resulting solution to a high-temperature reactor lined with polytetrafluoroethylene and solvothermal reaction in a 200 ℃ oven for 8 h. Then pour out the supernatant from the high-temperature reactor and transfer the remaining black liquid to a centrifuge cup using deionized water. Centrifuge at 3500 r / min for 3 min, wash three times with deionized water and twice with anhydrous ethanol. Pour the solution into an evaporating dish and dry in an 80 ℃ oven for 8 h to obtain praseodymium-doped ferric oxide microspheres. S2. Weigh 0.4833 g of praseodymium-doped ferric oxide microspheres and 0.9605 g of anhydrous citric acid, add them to 100 mL of deionized water. The mass / volume ratio of praseodymium-doped ferric oxide microspheres to citric acid and water is 1 g:2 g:0.2 L. Stir appropriately with a glass rod at room temperature and sonicate at 50 kHz for 1 h to dissolve. Then transfer the solution to a centrifuge cup with anhydrous ethanol, centrifuge at 3500 r / min for 3 min, wash three times with anhydrous ethanol, and transfer the solution from the centrifuge cup to a magnetic conical flask with 100 mL of anhydrous ethanol and stir. Add a precipitant to the conical flask. The composite precipitant is a mixture of ammonia water and ammonium bicarbonate solution, with a volume ratio of ammonia water to ammonium bicarbonate solution of 1:4. The ammonium ion concentration of the ammonia water is 3.6 mol / L, and the ammonium ion concentration of the ammonium bicarbonate solution is 2 mol / L. The praseodymium-doped ferric oxide microspheres were mixed with ethanol and a composite precipitant at a mass / volume ratio of 1 g:0.2 L:25 mL. The mixture was magnetically stirred for 40 min at room temperature to precipitate the microspheres and obtain a microsphere solution. S3. Measure 35 mL of anhydrous ethanol, add 1.7 g of tetrabutyl titanate using a dropper, with a molar / volume ratio of titanium to ethanol of 1 mol: 7 L, add 0.5 mL of hexadecyltrimethoxysilane, with a molar / volume ratio of titanium to hexadecyltrimethoxysilane of 1 mol: 0.1 L, shake well for 30 min to prevent hydrolysis, and obtain a titanium-silicon solution. S4. Using a syringe, the titanium-silicon solution was slowly dripped into the microsphere solution while maintaining stirring. The molar ratio of iron to titanium was 1:0.8. The mixture was magnetically stirred at room temperature for 2 h to assemble a core-shell structure. Then, the solution was transferred to a centrifuge cup with anhydrous ethanol, centrifuged at 3500 r / min for 3 min, washed five times with anhydrous ethanol, poured into an evaporating dish, dried in an 80 ℃ forced-air drying oven for 8 h, passed through a 60-mesh sieve, and calcined in a tube furnace at 450 ℃ in air atmosphere for 3 h to obtain a rare earth-doped iron-based core-shell denitration catalyst.

[0038] Comparative Example 3: An alkali metal-poisoned rare earth-doped iron-based core-shell denitration catalyst and its preparation method are basically the same as those in Comparative Example 1, except that the catalyst in Example 1 is replaced with the catalyst in Comparative Example 2. The obtained alkali metal-poisoned rare earth-doped iron-based core-shell denitration catalyst is denoted as K-Pr / Fe2O3@Ti. 0.8 .

[0039] Example 2: An alkali metal rare earth doped iron-based core-shell denitration catalyst and its preparation method are basically the same as in Example 1, except that in step S3, the mass of tetrabutyl titanate is reduced from 1.5 g to 1.1 g, while the mass of tetraethyl orthosilicate is increased from 0.1304 g to 0.3912 g. The molar ratio of titanium to silicon is 5:3, the molar ratio of titanium to ethanol is 1 mol:11 L, the molar ratio of titanium to hexadecyltrimethoxysilane is 1 mol:0.15 L, and the molar ratio of iron to titanium is 1:0.5. The obtained alkali metal rare earth doped iron-based core-shell denitration catalyst is designated as Pr / Fe2O3@Ti. 0.5 :Si 0.3 The specific steps are as follows: S1. Weigh 5.4 g ferric chloride hexahydrate, 0.174 g praseodymium nitrate hexahydrate, 4 g polyethylene glycol and 14.4 g anhydrous sodium acetate, with a molar ratio of praseodymium to iron of 0.02:1. Add to 160 mL anhydrous ethylene glycol, with a molar / mass / volume ratio of iron to polyethylene glycol, sodium acetate and ethylene glycol of 1 mol:0.2 kg:0.7 kg:8 L. Dissolve by magnetic stirring at room temperature for 1 h. Transfer the resulting solution to a high-temperature reactor lined with polytetrafluoroethylene and solvothermal reaction in a 200 ℃ oven for 8 h. Then pour out the supernatant from the high-temperature reactor and transfer the remaining black liquid to a centrifuge cup using deionized water. Centrifuge at 3500 r / min for 3 min, wash three times with deionized water and twice with anhydrous ethanol. Pour the solution into an evaporating dish and dry in an 80 ℃ oven for 8 h to obtain praseodymium-doped ferric oxide microspheres. S2. Weigh 0.4833 g of praseodymium-doped ferric oxide microspheres and 0.9605 g of anhydrous citric acid, add them to 100 mL of deionized water. The mass / volume ratio of praseodymium-doped ferric oxide microspheres to citric acid and water is 1 g:2 g:0.2 L. Stir appropriately with a glass rod at room temperature and sonicate at 50 kHz for 1 h to dissolve. Then transfer the solution to a centrifuge cup with anhydrous ethanol, centrifuge at 3500 r / min for 3 min, wash three times with anhydrous ethanol, and transfer the solution from the centrifuge cup to a magnetic conical flask with 100 mL of anhydrous ethanol and stir. Add a precipitant to the conical flask. The composite precipitant is a mixture of ammonia water and ammonium bicarbonate solution, with a volume ratio of ammonia water to ammonium bicarbonate solution of 1:4. The ammonium ion concentration of the ammonia water is 3.6 mol / L, and the ammonium ion concentration of the ammonium bicarbonate solution is 2 mol / L. The praseodymium-doped ferric oxide microspheres were mixed with ethanol and a composite precipitant at a mass / volume ratio of 1 g:0.2 L:25 mL. The mixture was magnetically stirred for 40 min at room temperature to precipitate the microspheres and obtain a microsphere solution. S3. Measure 35 mL of anhydrous ethanol, add 1.1 g of tetrabutyl titanate and 0.3912 g of tetraethyl orthosilicate using a dropper. The molar ratio of titanium to silicon is 5:3, and the molar / volume ratio of titanium to ethanol is 1 mol:11 L. Add 0.5 mL of hexadecyltrimethoxysilane. The molar / volume ratio of titanium to hexadecyltrimethoxysilane is 1 mol:0.15 L. Shake well for 30 min to prevent hydrolysis and obtain a titanium-silicon solution. S4. Using a syringe, the titanium-silicon solution was slowly dripped into the microsphere solution while maintaining stirring. The molar ratio of iron to titanium was 1:0.5. The mixture was magnetically stirred at room temperature for 2 h to assemble a core-shell structure. Then, the solution was transferred to a centrifuge cup with anhydrous ethanol and centrifuged at 3500 r / min for 3 min. The solution was washed five times with anhydrous ethanol, poured into an evaporating dish, dried in an 80 ℃ forced-air drying oven for 8 h, passed through a 60-mesh sieve, and calcined in a tube furnace at 450 ℃ in air atmosphere for 3 h to obtain an alkali metal rare earth doped iron-based core-shell denitration catalyst.

[0040] like Figures 1 to 3 As shown, the microspheres in the embodiment are coated with a shell, which proves the formation of the core-shell structure of the denitration catalyst in the embodiment.

[0041] Comparative Example 4: An alkali metal-poisoned rare earth-doped iron-based core-shell denitration catalyst and its preparation method are basically the same as those in Comparative Example 1, except that the catalyst in Example 1 is replaced with the catalyst in Example 2. The obtained alkali metal-poisoned rare earth-doped iron-based core-shell denitration catalyst is denoted as K-Pr / Fe2O3@Ti. 0.5 :Si 0.3 .

[0042] Comparative Example 5: An iron-based denitration catalyst and its preparation method are basically the same as those in Example 1, except that praseodymium nitrate hexahydrate is not added in step S1, and ferric oxide microspheres are directly calcined in step S4 to obtain the iron-based denitration catalyst, denoted as Fe2O3. The specific steps are as follows: S1. Weigh 5.4 g of ferric chloride hexahydrate, 4 g of polyethylene glycol, and 14.4 g of anhydrous sodium acetate, and add them to 160 mL of anhydrous ethylene glycol. The molar / mass / volume ratio of iron to polyethylene glycol, sodium acetate, and ethylene glycol is 1 mol:0.2 kg:0.7 kg:8 L. Dissolve the mixture by magnetic stirring at room temperature for 1 h. Transfer the resulting solution to a high-temperature reactor lined with polytetrafluoroethylene and solvothermal reaction in an oven at 200 ℃ for 8 h. Then, pour out the supernatant from the high-temperature reactor and transfer the remaining black liquid to a centrifuge cup using deionized water. Centrifuge at 3500 r / min for 3 min, wash three times with deionized water, and wash twice with anhydrous ethanol. Pour the solution into an evaporating dish and dry it in an oven at 80 ℃ for 8 h to obtain ferric oxide microspheres. S4. Ferric oxide microspheres were calcined in a tubular furnace at 450 °C in air atmosphere for 3 h to obtain an iron-based denitrification catalyst.

[0043] Comparative Example 6: An alkali metal poisoned iron-based denitration catalyst and its preparation method are basically the same as those in Comparative Example 1, except that the catalyst in Example 1 is replaced with the catalyst in Comparative Example 5. The obtained alkali metal poisoned iron-based denitration catalyst is denoted as K-Fe2O3.

[0044] Comparative Example 7: A rare earth-doped iron-based denitration catalyst and its preparation method are basically the same as those in Example 1, except that the praseodymium-doped ferric oxide microspheres in step S1 are directly calcined in step S4 to obtain the rare earth-doped iron-based denitration catalyst, denoted as Pr / Fe2O3. The specific steps are as follows: S1. Weigh 5.4 g ferric chloride hexahydrate, 0.174 g praseodymium nitrate hexahydrate, 4 g polyethylene glycol and 14.4 g anhydrous sodium acetate, with a molar ratio of praseodymium to iron of 0.02:1. Add to 160 mL anhydrous ethylene glycol, with a molar / mass / volume ratio of iron to polyethylene glycol, sodium acetate and ethylene glycol of 1 mol:0.2 kg:0.7 kg:8 L. Dissolve by magnetic stirring at room temperature for 1 h. Transfer the resulting solution to a high-temperature reactor lined with polytetrafluoroethylene and solvothermal reaction in a 200 ℃ oven for 8 h. Then pour out the supernatant from the high-temperature reactor and transfer the remaining black liquid to a centrifuge cup using deionized water. Centrifuge at 3500 r / min for 3 min, wash three times with deionized water and twice with anhydrous ethanol. Pour the solution into an evaporating dish and dry in an 80 ℃ oven for 8 h to obtain praseodymium-doped ferric oxide microspheres. S4. Praseodymium-doped ferric oxide microspheres were calcined in a tubular furnace at 450 °C in air atmosphere for 3 h to obtain a rare earth-doped iron-based denitration catalyst.

[0045] Comparative Example 8: An alkali metal poisoned rare earth doped iron-based denitration catalyst and its preparation method are basically the same as those in Comparative Example 1, except that the catalyst in Example 1 is replaced with the catalyst in Comparative Example 7. The obtained alkali metal poisoned rare earth doped iron-based denitration catalyst is denoted as K-Pr / Fe2O3.

[0046] Comparative Example 9: An alkali metal poisoned iron-based core-shell denitration catalyst and its preparation method are basically the same as those in Comparative Example 3, except that praseodymium nitrate hexahydrate is not added in step S1. The obtained alkali metal poisoned iron-based core-shell denitration catalyst is denoted as K-Fe2O3@Ti. 0.8 The specific steps are as follows: S1. Weigh 5.4 g of ferric chloride hexahydrate, 4 g of polyethylene glycol, and 14.4 g of anhydrous sodium acetate, and add them to 160 mL of anhydrous ethylene glycol. The molar / mass / volume ratio of iron to polyethylene glycol, sodium acetate, and ethylene glycol is 1 mol:0.2 kg:0.7 kg:8 L. Dissolve the mixture by magnetic stirring at room temperature for 1 h. Transfer the resulting solution to a high-temperature reactor lined with polytetrafluoroethylene and solvothermal reaction in an oven at 200 ℃ for 8 h. Then, pour out the supernatant from the high-temperature reactor and transfer the remaining black liquid to a centrifuge cup using deionized water. Centrifuge at 3500 r / min for 3 min, wash three times with deionized water, and wash twice with anhydrous ethanol. Pour the solution into an evaporating dish and dry it in an oven at 80 ℃ for 8 h to obtain ferric oxide microspheres. S2. Weigh 0.4833 g of ferric oxide microspheres and 0.9605 g of anhydrous citric acid, add them to 100 mL of deionized water. The mass / volume ratio of ferric oxide microspheres to citric acid and water is 1 g:2 g:0.2 L. Stir appropriately with a glass rod at room temperature and sonicate at 50 kHz for 1 h to dissolve. Then transfer the solution to a centrifuge cup with anhydrous ethanol, centrifuge at 3500 r / min for 3 min, wash three times with anhydrous ethanol, and transfer the solution from the centrifuge cup to a magnetic conical flask with 100 mL of anhydrous ethanol. Add a precipitant to the conical flask. The composite precipitant is a mixture of ammonia and ammonium bicarbonate solution, with a volume ratio of ammonia to ammonium bicarbonate solution of 1:4. The ammonium ion concentration of ammonia is 3.6 mol / L, and the ammonium ion concentration of ammonium bicarbonate solution is 2 mol / L. The mass / volume ratio of ferric oxide microspheres to ethanol and composite precipitant is 1 g:0.2 L:25 L. mL, magnetically stirred at room temperature for 40 min to precipitate, yielding a microsphere solution; S3. Measure 35 mL of anhydrous ethanol, add 1.7 g of tetrabutyl titanate using a dropper, with a molar / volume ratio of titanium to ethanol of 1 mol: 7 L, add 0.5 mL of hexadecyltrimethoxysilane, with a molar / volume ratio of titanium to hexadecyltrimethoxysilane of 1 mol: 0.1 L, shake well for 30 min to prevent hydrolysis, and obtain a titanium-silicon solution. S4. Using a syringe, the titanium-silicon solution was slowly dripped into the microsphere solution while stirring. The molar ratio of iron to titanium was 1:0.8. The mixture was magnetically stirred at room temperature for 2 h to assemble a core-shell structure. Then, the solution was transferred to a centrifuge cup with anhydrous ethanol and centrifuged at 3500 r / min for 3 min. The solution was washed five times with anhydrous ethanol, poured into an evaporating dish, dried in an 80 ℃ forced-air drying oven for 8 h, passed through a 60-mesh sieve, and calcined in a tube furnace at 450 ℃ in air atmosphere for 3 h to obtain an iron-based core-shell denitration catalyst. Weigh 0.5 g of catalyst and 0.005 g of potassium nitrate, with a potassium ion mass fraction of 0.4 wt% relative to the catalyst, and add them to 25 mL of deionized water. Stir magnetically at 50 ℃ for 4 h, pour the solution into an evaporating dish, dry it in an 80 ℃ forced-air drying oven for 8 h, pass it through a 60-mesh sieve, and calcine it in a tube furnace at 450 ℃ in air atmosphere for 3 h to obtain an alkali metal poisoned iron-based core-shell denitration catalyst.

[0047] Comparative Example 10: An alkali metal poisoned iron-based core-shell denitration catalyst and its preparation method are basically the same as those in Comparative Example 4, except that praseodymium nitrate hexahydrate is not added in step S1. The obtained alkali metal poisoned iron-based core-shell denitration catalyst is denoted as K-Fe2O3@Ti. 0.5 :Si 0.3 The specific steps are as follows: S1. Weigh 5.4 g of ferric chloride hexahydrate, 4 g of polyethylene glycol, and 14.4 g of anhydrous sodium acetate, and add them to 160 mL of anhydrous ethylene glycol. The molar / mass / volume ratio of iron to polyethylene glycol, sodium acetate, and ethylene glycol is 1 mol:0.2 kg:0.7 kg:8 L. Dissolve the mixture by magnetic stirring at room temperature for 1 h. Transfer the resulting solution to a high-temperature reactor lined with polytetrafluoroethylene and solvothermal reaction in an oven at 200 ℃ for 8 h. Then, pour out the supernatant from the high-temperature reactor and transfer the remaining black liquid to a centrifuge cup using deionized water. Centrifuge at 3500 r / min for 3 min, wash three times with deionized water, and wash twice with anhydrous ethanol. Pour the solution into an evaporating dish and dry it in an oven at 80 ℃ for 8 h to obtain ferric oxide microspheres. S2. Weigh 0.4833 g of ferric oxide microspheres and 0.9605 g of anhydrous citric acid, add them to 100 mL of deionized water. The mass / volume ratio of ferric oxide microspheres to citric acid and water is 1 g:2 g:0.2 L. Stir appropriately with a glass rod at room temperature and sonicate at 50 kHz for 1 h to dissolve. Then transfer the solution to a centrifuge cup with anhydrous ethanol, centrifuge at 3500 r / min for 3 min, wash three times with anhydrous ethanol, and transfer the solution from the centrifuge cup to a magnetic conical flask with 100 mL of anhydrous ethanol. Add a precipitant to the conical flask. The composite precipitant is a mixture of ammonia and ammonium bicarbonate solution, with a volume ratio of ammonia to ammonium bicarbonate solution of 1:4. The ammonium ion concentration of ammonia is 3.6 mol / L, and the ammonium ion concentration of ammonium bicarbonate solution is 2 mol / L. The mass / volume ratio of ferric oxide microspheres to ethanol and composite precipitant is 1 g:0.2 L:25 L. mL, magnetically stirred at room temperature for 40 min to precipitate, yielding a microsphere solution; S3. Measure 35 mL of anhydrous ethanol, add 1.1 g of tetrabutyl titanate and 0.3912 g of tetraethyl orthosilicate using a dropper. The molar ratio of titanium to silicon is 5:3, and the molar / volume ratio of titanium to ethanol is 1 mol:11 L. Add 0.5 mL of hexadecyltrimethoxysilane. The molar / volume ratio of titanium to hexadecyltrimethoxysilane is 1 mol:0.15 L. Shake well for 30 min to prevent hydrolysis and obtain a titanium-silicon solution. S4. Using a syringe, the titanium-silicon solution was slowly dripped into the microsphere solution while stirring. The molar ratio of iron to titanium was 1:0.5. The mixture was magnetically stirred at room temperature for 2 h to assemble a core-shell structure. Then, the solution was transferred to a centrifuge cup with anhydrous ethanol and centrifuged at 3500 r / min for 3 min. The solution was washed five times with anhydrous ethanol, poured into an evaporating dish, dried in an 80 ℃ forced-air drying oven for 8 h, passed through a 60-mesh sieve, and calcined in a tube furnace at 450 ℃ in air atmosphere for 3 h to obtain an iron-based core-shell denitration catalyst. Weigh 0.5 g of catalyst and 0.005 g of potassium nitrate, with a potassium ion mass fraction of 0.4 wt% relative to the catalyst, and add them to 25 mL of deionized water. Stir magnetically at 50 ℃ for 4 h, pour the solution into an evaporating dish, dry it in an 80 ℃ forced-air drying oven for 8 h, pass it through a 60-mesh sieve, and calcine it in a tube furnace at 450 ℃ in air atmosphere for 3 h to obtain an alkali metal poisoned iron-based core-shell denitration catalyst.

[0048] like Figure 4As shown, praseodymium doping of the denitration catalyst in the examples inhibits the transformation of γ-Fe2O3 to α-Fe2O3. Also, under alkali metal poisoning, the diffraction peak intensity weakens, the crystallinity decreases, and the grain size decreases. This leads to an increase in the specific surface area of ​​the catalyst and an increase in active sites, which significantly improves its resistance to alkali metals.

[0049] The catalyst was subjected to the following tests or experiments, and the results were then analyzed.

[0050] Experimental example: The denitrification performance of the above-mentioned denitrification catalyst was tested, and the specific steps are as follows: The above-mentioned denitrification catalyst was placed in a fixed-bed quartz tube reactor, and simulated flue gas was subjected to denitrification treatment in the reactor. The simulated flue gas included nitric oxide (NO), ammonia (NH3), oxygen (O2), and argon (Ar), and the reaction space velocity was 45,000 h⁻¹. -1 The concentrations of nitric oxide, ammonia, and oxygen were 500 ppm and argon was used as the balance gas. The Testo-350 chemiluminescent nitric oxide / nitrogen oxide (NO) luminescence device was used. x The analyzer simultaneously monitors the nitric oxide concentration at the reactor inlet and outlet online, with a detection accuracy of 0.5 ppm; Data were collected 30 min after the ammonia selective catalytic reduction (NH3-SCR) denitrification reaction reached a steady state. The catalyst activity was evaluated by the denitrification rate (nitric oxide conversion rate). The activity evaluation temperature range was 150–450 °C. The nitric oxide conversion rate was calculated using the following formula: η NO =([NO]in-[NO]out) / [NO]in, In the formula, η NO denoted as nitric oxide conversion rate, and [NO]in and [NO]out as the nitric oxide concentrations at the reactor inlet and outlet under steady-state conditions, respectively. The activity evaluation of the catalysts in Examples 1 and 2 and Comparative Examples 1 to 8 is shown in Table 2.

[0051] Table 2. Activity evaluation of the catalysts in Examples 1 and 2 and Comparative Examples 1 to 8 As shown in Table 2, it can be seen that praseodymium doping in Comparative Example 7, compared to Comparative Example 5, can effectively improve the denitration efficiency and alkali metal resistance of the iron-based denitration catalyst. While the activity is improved across the entire temperature range, the activity decay is less after alkali metal poisoning. In Comparative Example 2, the titanium shell, compared to Comparative Example 7, can also effectively improve the denitration efficiency and alkali metal resistance of the iron-based denitration catalyst. While the activity is significantly improved across the entire temperature range, the activity decay after alkali metal poisoning is also relatively small. In Example 1, the titanium-silicon shell, compared to Comparative Example 2, can also effectively improve the denitration efficiency and alkali metal resistance of the iron-based denitration catalyst. While the activity is further improved in the low temperature range of 225 °C, the activity decay after alkali metal poisoning is also less. In Example 2, an appropriate proportion of silica was increased compared to Example 1. The iron-based denitration catalyst maintained good activity across the entire temperature range, while the activity decay after alkali metal poisoning almost disappeared, achieving optimal denitration efficiency and resistance to alkali metals.

[0052] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A core-shell denitration catalyst resistant to alkali metal rare earth doped iron, characterized in that, The catalyst has a core-shell structure with praseodymium-doped iron oxide microspheres as the core layer and titanium dioxide and silicon dioxide as the composite shell layer. The molar ratio of praseodymium, iron, titanium and silicon is (0.01~0.04):1:(0.1~0.8):(0.1~0.8).

2. A method for preparing the alkali metal rare earth doped iron-based core-shell denitration catalyst as described in claim 1, characterized in that, The method includes the following steps: S1. Iron source, praseodymium source, dispersant and sodium acetate are dissolved in the first solvent and subjected to a solvothermal reaction to obtain praseodymium-doped ferric oxide microspheres; S2. The praseodymium-doped ferric oxide microspheres and organic acid are dissolved in a second solvent, transferred using a third solvent, and a precipitant is added to precipitate, thus obtaining a microsphere solution. S3. Dissolve the titanium source, silicon source and pore-forming agent in a fourth solvent to obtain a titanium-silicon solution; S4, mixed microsphere solution and titanium silicon solution, assembled into core-shell structure, calcined to obtain alkali metal rare earth doped iron-based core-shell denitration catalyst.

3. The preparation method of the alkali metal rare earth doped iron-based core-shell denitration catalyst according to claim 2, characterized in that, In step S1, the iron source is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate; the praseodymium source is selected from one or more of praseodymium chloride, praseodymium nitrate, and praseodymium sulfate; the dispersant is polyethylene glycol; and the first solvent is selected from one or more of ethanol, glycerol, and ethylene glycol.

4. The preparation method of the alkali metal rare earth doped iron-based core-shell denitration catalyst according to claim 2, characterized in that, In step S1, the molar / mass / volume ratio of iron in the iron source to dispersant, sodium acetate, and the first solvent is 1 mol:(0.1~0.3 kg):(0.4~1 kg):(4~12 L).

5. The preparation method of the alkali metal rare earth doped iron-based core-shell denitration catalyst according to claim 2, characterized in that, In step S2, the organic acid is selected from one or more of citric acid, acetic acid, and oxalic acid; the second solvent is selected from one or more of water and ethanol; the third solvent is selected from one or more of ethanol, glycerol, and ethylene glycol; and the precipitant is selected from one or more of ammonia, ammonium bicarbonate solution, ammonium carbonate solution, and sodium hydroxide solution. The concentration of the cation in the precipitant is 2~2.6 mol / L.

6. The preparation method of the alkali metal rare earth doped iron-based core-shell denitration catalyst according to claim 2, characterized in that, In step S2, the mass / volume ratio of praseodymium-doped ferric oxide microspheres to organic acid and the second solvent is 1 g:(1~3 g):(0.1~0.3 L), and the mass / volume ratio of praseodymium-doped ferric oxide microspheres to the third solvent and the precipitant is 1 g:(0.1~0.3 L):(10~40 mL).

7. The preparation method of the alkali metal rare earth doped iron-based core-shell denitration catalyst according to claim 2, characterized in that, In step S3, the titanium source is selected from one or more of tetrabutyl titanate, titanium tetrachloride, and titanium sulfate; the silicon source is selected from one or more of tetraethyl orthosilicate and silicon tetrachloride; the pore-forming agent is selected from one or more of hexadecyltrimethoxysilane, ammonium bicarbonate, and ammonium chloride; and the fourth solvent is selected from one or more of ethanol, glycerol, and ethylene glycol.

8. The preparation method of the alkali metal rare earth doped iron-based core-shell denitration catalyst according to claim 2, characterized in that, In step S3, the molar / volume ratio of titanium in the titanium source to the pore-forming agent and the fourth solvent is 1 mol:(0.01~0.4 L):(2~20 L).

9. The preparation method of the alkali metal rare earth doped iron-based core-shell denitration catalyst according to claim 2, characterized in that, The dissolution time in step S1 is 50-70 minutes. The temperature of the solvothermal reaction is 180~220 ℃, and the holding time is 6~10 h; The dissolution time in step S2 is 50-70 minutes. The settling time is 30-50 minutes; The dissolution time in step S3 is 20~40 min; The mixing time in step S4 is 100~140 min. The gas is calcined in an oxygen-containing gas atmosphere, which is selected from air, oxygen-containing nitrogen, or oxygen-containing argon. The calcination temperature is 400~500 ℃, and the holding time is 2~4 h.

10. The application of the alkali metal rare earth doped iron-based core-shell denitration catalyst as described in claim 1 in selective catalytic reduction denitration reaction.

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