Mn-Ce@NbOPO4 catalyst and preparation and application thereof

Abstract

The application belongs to the field of low-temperature SCR denitration technology, and particularly relates to a Mn-Ce@NbOPO4 catalyst and preparation and application thereof. The Mn-Ce@NbOPO4 catalyst provided by the application has a core-shell structure, the core is a Mn-Ce composite metal oxide, and the porous shell layer is a NbOPO4 solid acid material. The application grows the shell NbOPO4 solid acid material outside the core Mn-Ce composite metal oxide through a hydrothermal method, so as to obtain the Mn-Ce@NbOPO4 catalyst with a porous core-shell structure. The Mn-Ce@NbOPO4 catalyst provided by the application can efficiently remove nitrogen oxides at a low reaction temperature in the presence of alkali / alkaline earth metals, and still has high low-temperature denitration activity after poisoning of the catalyst, so that the problem of poisoning of NH3-SCR catalyst caused by flue gas of low-temperature non-electricity industry in the presence of alkali / alkaline earth metals can be well solved.

Description

Technical Field

[0001] This invention belongs to the field of low-temperature SCR denitrification technology, specifically relating to a Mn-Ce@NbOPO4 catalyst and its preparation and application. Background Technology

[0002] As one of the major air pollutants, nitrogen oxides (NOx) x This can lead to numerous environmental problems such as acid rain and photochemical smog. Currently, due to its advantages of high denitrification efficiency and low ammonia slip rate, the ammonia-based selective catalytic reduction (NH3-SCR) technology has been widely used in industrial stationary source flue gas denitrification. However, conventional low-temperature SCR catalysts have poor adaptability in non-power industry flue gas conditions such as cement kilns and waste incineration where flue gas temperatures are low and alkali / alkaline earth metals are present. This is mainly because the alkali / alkaline earth metals widely present in flue gas can poison the SCR denitrification catalyst. Generally speaking, their poisoning effects mainly include two aspects: first, physical effects, where alkali / alkaline earth metals deposited on the catalyst surface can block pores and reduce the specific surface area of ​​the catalyst; second, chemical effects, where the presence of alkali / alkaline earth metals can neutralize the catalyst's... Acidic sites weaken the adsorption capacity of NH3.

[0003] In recent years, common strategies for improving the resistance of catalysts to alkali / alkaline earth metals can be summarized as: protecting redox sites while increasing the acidity of the catalyst. Specific methods mainly include: introducing acidic promoters, acidifying the catalyst surface, and controlling the catalyst morphology. However, under the low-temperature flue gas conditions in non-electric industries where alkali / alkaline earth metals are present, current low-temperature SCR catalysts, represented by Mn-Ce, are still difficult to operate efficiently. Therefore, developing low-temperature SCR catalysts with high alkali / alkaline earth metal resistance has broad application prospects and development significance.

[0004] Chinese patent CN113522274A discloses a low-temperature manganese-based SCR denitration catalyst resistant to alkali metal poisoning and its preparation method. The catalyst undergoes surface acidification pretreatment in an SO2 atmosphere, which improves the catalyst's nitrogen oxide conversion rate while also providing some resistance to alkali metal poisoning and sulfur dioxide poisoning. However, this catalyst exhibits reduced NO2 conversion after alkali metal poisoning. x The conversion rate is still not ideal.

[0005] Chinese patent CN116251582A discloses a manganese-based low-temperature alkali metal poisoning-resistant SCR denitration catalyst and its preparation method. Acidification treatment of the sodium manganese ore catalyst with nitric acid slightly improves the catalyst's denitration activity while also significantly enhancing its resistance to alkali metal poisoning. However, this catalyst exhibits a significant decrease in low-temperature denitration activity after alkali metal poisoning.

[0006] Chinese Patent Publication No. CN116273044A discloses a low-temperature SCR denitration catalyst resistant to alkali metal poisoning and its preparation method. After alkali metal poisoning, the catalyst is subjected to low-temperature SCR denitration at 150–250 °C and 30,000 cm⁻¹. 3 g -1 h -1 It exhibits a denitrification efficiency of over 85% and an N2 selectivity of over 90% under space velocity conditions. However, this catalyst has limitations, including a narrow reaction temperature window and the need for further improvement in low-temperature denitrification activity. Summary of the Invention

[0007] The purpose of this invention is to provide a Mn-Ce@NbOPO4 catalyst, its preparation, and its application in NH3-SCR denitrification. The Mn-Ce@NbOPO4 catalyst provided by this invention can efficiently remove nitrogen oxides at lower reaction temperatures in the presence of alkali / alkaline earth metals, and still has high low-temperature denitrification activity after catalyst poisoning. It can effectively solve the problem of NH3-SCR catalyst poisoning caused by low-temperature non-electric industry flue gas in the presence of alkali / alkaline earth metals.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a Mn-Ce@NbOPO4 catalyst, wherein the Mn-Ce@NbOPO4 catalyst has a core-shell structure, the core being a Mn-Ce composite metal oxide and the shell being a NbOPO4 solid acid material, and the shell having a porous structure.

[0010] Preferably, the mass percentage of Mn-Ce composite metal oxide in the Mn-Ce@NbOPO4 catalyst is 5-15 wt.%.

[0011] This invention provides a method for preparing the Mn-Ce@NbOPO4 catalyst described above, comprising the following steps:

[0012] (1) Manganese salt, cerium salt, organic acid and water are mixed and the resulting mixture is calcined to obtain Mn-Ce composite metal oxide;

[0013] (2) The Mn-Ce composite metal oxide, niobium salt, water, hydrogen phosphate and cationic surfactant are mixed and subjected to hydrothermal reaction, wherein the molar amount of niobium ions in the niobium salt is equal to that of hydrogen phosphate ions in the hydrogen phosphate, to obtain hydrothermal reaction product; the hydrothermal reaction product is calcined to obtain the Mn-Ce@NbOPO4 catalyst.

[0014] Preferably, the manganese salt is manganese nitrate and the cerium salt is cerium nitrate; the molar ratio of the manganese salt to the cerium salt is 5:(1-10).

[0015] Preferably, the organic acid is citric acid; the molar ratio of the organic acid to the total molar ratio of manganese ions in the manganese salt and cerium ions in the cerium salt is 5:(1-5).

[0016] Preferably, the hydrogen phosphate is (NH4)2HPO4; the cationic surfactant is hexadecyltrimethylammonium bromide; and the molar ratio of the cationic surfactant to the hydrogen phosphate is (1-10):1.

[0017] Preferably, the hydrothermal reaction is carried out at a temperature of 120–200°C for 8–24 hours.

[0018] Preferably, the calcination temperature in step (1) and the calcination time in step (2) are independently 380-480°C and 2-5h respectively.

[0019] This invention provides the application of the Mn-Ce@NbOPO4 catalyst described in the above technical solution or the Mn-Ce@NbOPO4 catalyst prepared by the preparation method described in the above technical solution in NH3-SCR denitrification.

[0020] Preferably, the application conditions include: a reaction temperature of 150–350°C and a reaction space velocity of 20,000–100,000 h⁻¹. -1 .

[0021] This invention provides a Mn-Ce@NbOPO4 catalyst, which has a core-shell structure. The core is a Mn-Ce composite metal oxide, and the shell is a NbOPO4 solid acid material with a porous structure. In this invention, the Mn-Ce composite metal oxide core mainly performs efficient low-temperature activation of the reactants, while the porous NbOPO4 solid acid shell effectively reduces the influence of alkali / alkaline earth metals on the active sites. Specifically, manganese oxide (MnO4) is used. x The NbOPO4 solid acid porous shell possesses excellent redox properties. CeO2 exhibits excellent oxygen-carrying capacity, and the strong interaction between Mn and Ce promotes the redox cycle. These three factors ensure excellent low-temperature denitrification performance. In this invention, the NbOPO4 solid acid porous shell has abundant surface acidic sites and a large specific surface area. Its excellent surface acidity not only effectively anchors alkaline / alkaline earth metals carrying basic sites, avoiding the influence of alkaline / alkaline earth metals on internal nucleic acid sites, but also retains sufficient sites for NH3 adsorption after neutralizing the deposited alkaline / alkaline earth metals. Combined with the excellent redox sites on the Mn-Ce composite metal oxide, this achieves highly efficient and selective catalytic reduction of NO at low temperatures. x .

[0022] In addition, the large specific surface area of ​​the outer shell provides sufficient anchoring capacity for alkali / alkaline earth metals, preventing physical deactivation due to alkali / alkaline earth metal deposition. Therefore, the porous core-shell structured Mn-Ce@NbOPO4 catalyst provided by this invention not only exhibits high nitrogen oxide conversion rates at low temperatures but also demonstrates excellent resistance to alkali / alkaline earth metals. The results of the examples show that the Mn-Ce@NbOPO4 catalyst provided by this invention maintains a denitrification efficiency of over 95% and an N2 selectivity of over 92% at reaction temperatures of 150–350°C. Even with a potassium oxide loading of 0.5 wt.% (alkali metal poisoning), the catalyst's denitrification efficiency remains stable above 90%, and its N2 selectivity is still above 90%. The catalyst activity provided by this invention is not affected by the alkali metal K.

[0023] In summary, the beneficial effects of this invention compared to the prior art are as follows:

[0024] The porous core-shell structured Mn-Ce@NbOPO4 catalyst provided by this invention exhibits excellent low-temperature denitrification activity and can maintain good reactivity under alkaline / alkaline earth metal flue gas conditions.

[0025] The porous NbOPO4 shell of the catalyst provided by this invention has good resistance to alkali / alkaline earth metals, which improves the stability of the catalyst and can meet the complex working conditions under actual conditions.

[0026] The porous core-shell structured Mn-Ce@NbOPO4 catalyst provided by this invention uses transition metals and rare earth metals Mn and Ce as the main active materials, and can operate continuously at low temperatures, reducing energy consumption and the cost of nitrogen oxide removal. Detailed Implementation

[0027] This invention provides a Mn-Ce@NbOPO4 catalyst, wherein the Mn-Ce@NbOPO4 catalyst has a core-shell structure, the core being a Mn-Ce composite metal oxide and the shell being a NbOPO4 solid acid material, and the shell having a porous structure.

[0028] The Mn-Ce@NbOPO4 catalyst provided by this invention has a core-shell structure, with the core being a Mn-Ce composite metal oxide. In this invention, the mass percentage of the Mn-Ce composite metal oxide in the Mn-Ce@NbOPO4 catalyst is preferably 5-15 wt.%, specifically preferably 10 wt.%, 15 wt.%, or 5 wt.%. In this invention, the molar ratio of manganese to cerium in the Mn-Ce composite metal oxide is preferably 5:(1-10), specifically preferably 5:2, 5:1, or 5:5.

[0029] The Mn-Ce composite metal oxide core of the catalyst provided by this invention mainly completes the efficient low-temperature activation of the reactants. The strong interaction between Mn and Ce promotes the redox cycle, ensuring excellent low-temperature denitrification performance. Furthermore, the Mn-Ce composite metal oxide core of this invention exhibits optimal medium- and low-temperature denitrification performance and cannot be replaced by other composite metal oxides. Replacing it with other composite metal oxides would lead to poor medium- and low-temperature denitrification performance of the catalyst.

[0030] The Mn-Ce@NbOPO4 catalyst provided by this invention has a core-shell structure, with the shell being a solid NbOPO4 acid material, and the shell having a porous structure. In this invention, the average pore size of the shell is preferably 6–10 nm, and the pore volume is preferably 0.6–1.2 cm³. 3 / g, with a preferred specific surface area of ​​300–500 m² / g. 2 / g. The total acidity of the shell is preferably 1000-2200 μmol / g.

[0031] The porous NbOPO4 solid acid shell of the catalyst provided by this invention possesses abundant surface acidic sites and a large specific surface area. Its excellent surface acidity not only effectively anchors alkaline / alkaline earth metals carrying basic sites, avoiding the influence of these metals on internal nucleic acid sites, but also retains sufficient sites for NH3 adsorption after neutralizing the deposited alkaline / alkaline earth metals. Combined with the excellent redox sites on the Mn-Ce composite metal oxide, this enables highly efficient and selective catalytic reduction of NO at low temperatures. x .

[0032] The transition metal Nb in the shell layer of this invention cannot be replaced by other transition metals. Replacing it with other metals would cause the shell layer to become amorphous (a complex of metal oxides and phosphates), failing to form the optimal pore structure characteristics. Secondly, NbOPO4 exhibits superior acidity compared to other transition metal phosphates, which is one of the main reasons why the catalyst provided by this invention possesses excellent resistance to alkaline earth metal corrosion. Furthermore, compared to inorganic anions such as sulfate, nitrate, and chlorate, phosphate salts are chemically more stable, possessing better heat resistance and lower water solubility, allowing them to withstand long-term corrosion in the low-to-medium temperature SCR denitrification flue gas environment.

[0033] This invention provides a method for preparing the Mn-Ce@NbOPO4 catalyst described above, comprising the following steps:

[0034] (1) Manganese salt, cerium salt, organic acid and water are mixed and the resulting mixture is calcined to obtain Mn-Ce composite metal oxide;

[0035] (2) The Mn-Ce composite metal oxide, niobium salt, water, hydrogen phosphate and cationic surfactant are mixed and subjected to hydrothermal reaction, wherein the molar amount of niobium ions in the niobium salt is equal to that of hydrogen phosphate ions in the hydrogen phosphate, to obtain hydrothermal reaction product; the hydrothermal reaction product is calcined to obtain the Mn-Ce@NbOPO4 catalyst.

[0036] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0037] This invention involves mixing manganese salt, cerium salt, organic acid, and water, followed by calcination of the resulting mixture to obtain Mn-Ce composite metal oxide. In this invention, the manganese salt is preferably manganese nitrate, specifically hydrated manganese nitrate (Mn(NO3)2·xH2O). The cerium salt is cerium nitrate, specifically cerium nitrate hexahydrate (Ce(NO3)3·6H2O). The organic acid is preferably citric acid. The molar ratio of the manganese salt to the cerium salt is preferably 5:(1-10), specifically 5:2, 5:1, or 5:5, with 5:2 being the most preferred. The molar ratio of the organic acid to the total molar ratio of manganese ions in the manganese salt and cerium ions in the cerium salt is preferably 5:(1-5), specifically 5:2.5. This invention does not have specific requirements regarding the amount of water used, as long as the above raw materials are mixed evenly. The mixing preferably includes the following steps: dissolving the organic acid in water to obtain an aqueous solution of the organic acid; and mixing the manganese salt, cerium salt, and the aqueous solution of the organic acid. The mixing temperature is preferably room temperature, and the mixing is preferably carried out under stirring conditions. The mixing yields a mixture. Before calcination, the mixture is preferably dried. The drying temperature is preferably 80–160°C, more preferably 120°C; the drying time is preferably 10–24 h, more preferably 12 h. The drying is preferably carried out in an oven. The calcination temperature is preferably 380–480°C, more preferably 450°C; the calcination time is preferably 2–5 h, more preferably 4 h. The calcination is preferably carried out in an air atmosphere.

[0038] After obtaining the Mn-Ce composite metal oxide, the present invention mixes the Mn-Ce composite metal oxide, niobium salt, water, hydrogen phosphate and cationic surfactant to carry out a hydrothermal reaction, wherein the molar amount of niobium ions in the niobium salt is equal to that of hydrogen phosphate ions in the hydrogen phosphate, to obtain a hydrothermal reaction product; the hydrothermal reaction product is calcined to obtain the Mn-Ce@NbOPO4 catalyst.

[0039] In this invention, the niobium salt is preferably an organic niobium salt, specifically niobium tartrate. In this invention, the niobium tartrate is preferably prepared by dissolving Nb₂O₅·nH₂O in tartaric acid. In a specific embodiment of this invention, the preparation method of the niobium tartrate preferably includes: first, hydrolyzing NbCl₅ in deionized water to obtain a precipitate; then, filtering the precipitate and washing it thoroughly with deionized water to obtain niobic acid (Nb₂O₅·nH₂O); finally, slowly dissolving the niobic acid (Nb₂O₅·nH₂O) in an aqueous solution of tartaric acid while continuously stirring at 85°C to obtain a transparent aqueous solution of niobium tartrate. The molar ratio of niobic acid to tartaric acid is preferably 0.2.

[0040] In this invention, the hydrogen phosphate is preferably (NH4)2HPO4. The cationic surfactant is preferably hexadecyltrimethylammonium bromide (CTAB). Using CTAB as a surfactant in this invention yields a shell with superior pore structure characteristics. The molar ratio of the cationic surfactant to the hydrogen phosphate is preferably (1-10):1, specifically preferably 3:1. The amount of niobium salt and the Mn-Ce composite metal oxide is determined according to the mass percentage of the Mn-Ce composite metal oxide in the Mn-Ce@NbOPO4 catalyst. This invention does not have special requirements for the amount of water used; ensuring uniform mixing of the above raw materials is sufficient. The mixing preferably includes the following steps: dissolving the niobium salt in water to obtain a niobium salt aqueous solution; mixing the Mn-Ce composite metal oxide and the niobium salt aqueous solution, then adding the hydrogen phosphate, and finally adding the cationic surfactant. The mixing temperature is preferably room temperature, and the mixing is carried out under stirring. The hydrothermal reaction temperature is preferably 120-200°C, and the time is preferably 8-24 hours. After the hydrothermal reaction is completed, the solid obtained from the hydrothermal reaction is preferably washed with water and dried sequentially to obtain the hydrothermal reaction product. The drying temperature is preferably 80-160℃, more preferably 120℃; the drying time is preferably 10-24h, more preferably 12h. The drying is preferably carried out in an oven. The calcination temperature is preferably 380-480℃, more preferably 450℃; the calcination time is preferably 2-5h, more preferably 4h.

[0041] The preparation method provided by the present invention grows a core-shell NbOPO4 solid acid material on the outer shell of a core Mn-Ce composite metal oxide using a hydrothermal method, thereby obtaining a porous core-shell structured Mn-Ce@NbOPO4 catalyst.

[0042] This invention provides the application of the Mn-Ce@NbOPO4 catalyst described in the above technical solution or the Mn-Ce@NbOPO4 catalyst prepared by the preparation method described in the above technical solution in NH3-SCR denitrification.

[0043] In this invention, the application is preferably carried out in a fixed-bed reactor. Preferably, the Mn-Ce@NbOPO4 catalyst is loaded into the fixed-bed reactor for NH3-SCR denitrification. The Mn-Ce@NbOPO4 catalyst preferably has a mesh size of 40-60 mesh. In this invention, the preferred conditions for the application include: a reaction temperature of 150-350°C; and a reaction space velocity of 20,000-100,000 h⁻¹. -1 Specifically, in this example, it is 40000h. -1 The preferred initial gas volume concentrations are: NO = NH3 = 600 ppm, O2 = 3 vol.%, and N2 as the equilibrium gas. In a specific embodiment of the invention, the reaction tail gas is detected using a Testo350 flue gas analyzer.

[0044] The Mn-Ce@NbOPO4 catalyst provided by this invention is an alkali / alkaline earth metal resistant low-temperature SCR denitrification catalyst. The Mn-Ce@NbOPO4 catalyst provided by this invention can stably maintain high denitrification performance under low-temperature flue gas conditions with high alkali / alkaline earth metal content. The low-temperature denitrification activity of the Mn-Ce@NbOPO4 catalyst provided by this invention does not decrease significantly after alkali metal or alkaline earth metal poisoning, and still exhibits good low-temperature denitrification activity. That is, the Mn-Ce@NbOPO4 catalyst provided by this invention exhibits good low-temperature denitrification activity even after NO poisoning by alkali metal or alkaline earth metals. x The conversion rate remains high.

[0045] In this invention, the Mn-Ce@NbOPO4 catalyst poisoned by alkali metal or alkaline earth metal is a Mn-Ce@NbOPO4 catalyst supported on alkali metal oxides or alkaline earth metal oxides.

[0046] In the Mn-Ce@NbOPO4 catalyst poisoned with alkali metals or alkaline earth metals: the loading of alkali metals or alkaline earth metals, calculated as alkali metal oxides or alkaline earth metal oxides, is 0.5 wt.%. The loading is the mass percentage of the alkali metal oxides or alkaline earth metal oxides in the Mn-Ce@NbOPO4 catalyst.

[0047] The preferred alkali metal is K. The preferred alkaline earth metal is Ca. Alkali metal K exhibits stronger poisoning properties than alkaline earth metal Ca, mainly because the more basic alkali metal K has a stronger poisoning effect on the acidic sites of the catalyst. The porous core-shell structured low-temperature SCR catalyst provided by this invention not only has a high nitrogen oxide conversion rate at low temperatures, but also exhibits excellent resistance to alkali / alkaline earth metals.

[0048] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0049] In the following examples: The present invention uses an impregnation method to support potassium nitrate or calcium nitrate on a Mn-Ce@NbOPO4 catalyst, thereby obtaining an alkali / alkaline earth metal poisoned K / Ca-Mn-Ce@NbOPO4 catalyst to simulate the application environment of alkali metal poisoning.

[0050] The preferred method for preparing niobium tartrate in the following embodiments includes: first, hydrolyzing NbCl5 in deionized water to obtain a precipitate; then, filtering the precipitate and washing it thoroughly with deionized water to obtain niobic acid (Nb2O5·nH2O); finally, slowly dissolving the niobic acid (Nb2O5·nH2O) in an aqueous solution of tartaric acid (the molar ratio of niobic acid to tartaric acid is preferably 0.2), while continuously stirring at 85°C to obtain a transparent aqueous solution of niobium tartrate.

[0051] Example 1

[0052] Catalyst preparation:

[0053] (1) A certain molar amount of citric acid was dissolved in deionized water, and Mn(NO3)2·xH2O and Ce(NO3)3·6H2O were added under vigorous stirring {the molar ratio of Mn(NO3)2·xH2O to Ce(NO3)3·6H2O is 5:2, and the molar ratio of citric acid to (Mn+Ce) metal cation is 5:2.5}. After stirring and mixing, the mixture was dried in an oven at 120℃ for 12h and calcined in an air atmosphere at 450℃ for 4h to obtain a Mn-Ce composite metal oxide that can be used as a core.

[0054] (2) Disperse the Mn-Ce composite metal oxide obtained in step (1) in an aqueous solution containing a certain amount of niobium tartrate {the loading of the Mn-Ce composite metal oxide is 10 wt., and the niobium tartrate will form NbOPO4 (molar mass is 203.9) with phosphate after hydrothermal treatment. With the loading of Mn-Ce composite oxide at 10% (M), the mass percentage of NbOPO4 can be calculated to be 90% (9M). Furthermore, the amount of niobium tartrate (the molar amount of Nb in niobium tartrate is: 9M / 203.9) is determined. Then, an equimolar amount of (NH4)2HPO4 is added and stirred. Subsequently, an appropriate amount of CTAB is added (the molar ratio of CTAB to (NH4)2HPO4 is 3:1). After hydrothermal reaction (160℃, 24h), the solid is washed, dried in an oven at 120℃ for 12h, and calcined in air at 450℃ for 4h to obtain the alkali-resistant / alkaline earth metal type low-temperature SCR denitration catalyst.

[0055] Catalyst performance testing:

[0056] 2.3 mL of 40-60 mesh powdered catalyst was placed in a fixed-bed quartz tube reactor with an inner diameter of 1 cm. The initial gas volume concentrations were: NO = NH3 = 600 ppm, O2 = 3 vol.%, N2 as the equilibrium gas, and GHSV = 40,000 h⁻¹. -1 The reaction temperature was 150–350℃, and the reaction tail gas was analyzed using a Testo350 flue gas analyzer. Under these test conditions, the catalyst maintained a stable denitrification efficiency of over 95% and an N2 selectivity of over 92%.

[0057] The catalyst performance was tested in the reaction temperature range of 150 to 350°C. Within the temperature range of 150 to 350°C, the denitrification efficiency of the catalyst prepared in this embodiment was stable at over 95%, and the N2 selectivity was over 92%.

[0058] Alkali / Alkaline Earth Metal Resistance Test: A certain amount of potassium nitrate (KNO3), an alkali metal salt, was loaded onto a certain mass of catalyst using an impregnation method at a high concentration. The potassium oxide loading was 0.5 wt.%, and the catalyst was calcined at 350℃ for 4 hours, with other test conditions remaining unchanged. Under these test conditions, the catalyst's denitrification efficiency remained stable above 90%, and the N2 selectivity remained above 90%, demonstrating that the catalyst activity was not affected by the alkali metal K.

[0059] Example 2

[0060] The only difference between the catalyst preparation and Example 1 is that the molar ratio of Mn(NO3)2·xH2O to Ce(NO3)3·6H2O in step (1) is 5:1, and all other steps are the same.

[0061] Catalyst performance testing:

[0062] 2.3 mL of 40-60 mesh powdered catalyst was placed in a fixed-bed quartz tube reactor with an inner diameter of 1 cm. The initial gas volume concentrations were: NO = NH3 = 600 ppm, O2 = 3 vol.%, N2 as the equilibrium gas, and GHSV = 40,000 h⁻¹. -1 The reaction temperature was 150–350℃, and the reaction tail gas was analyzed using a Testo350 flue gas analyzer. Under these test conditions, the catalyst maintained a denitrification efficiency of over 97% and an N2 selectivity of over 82%.

[0063] Alkali / Alkaline Earth Metal Resistance Test: A certain amount of potassium nitrate (KNO3), an alkali metal salt, was loaded at a high concentration onto a certain mass of catalyst using an impregnation method. The potassium oxide loading was 0.5 wt.%, and the catalyst was calcined at 350℃ for 4 hours, with other test conditions remaining unchanged. Under these test conditions, the catalyst's denitrification efficiency remained stable at over 93%, and the N2 selectivity was over 80%, demonstrating that the catalyst activity was not affected by the alkali metal K.

[0064] Example 3

[0065] The catalyst preparation differs from that in Example 1 only in that the molar ratio of Mn(NO3)2·xH2O to Ce(NO3)3·6H2O in step (1) is 5:5, and all other steps are the same.

[0066] Catalyst performance testing:

[0067] 2.3 mL of 40-60 mesh powdered catalyst was placed in a fixed-bed quartz tube reactor with an inner diameter of 1 cm. The initial gas volume concentrations were: NO = NH3 = 600 ppm, O2 = 3 vol.%, N2 as the equilibrium gas, and GHSV = 40,000 h⁻¹. -1 The reaction temperature was 150–350℃, and the reaction tail gas was analyzed using a Testo350 flue gas analyzer. Under these test conditions, the catalyst maintained a stable denitrification efficiency of over 82% and an N2 selectivity of over 99%.

[0068] Alkali / Alkaline Earth Metal Resistance Test: A certain amount of potassium nitrate (KNO3), an alkali metal salt, was loaded onto a certain mass of catalyst using an impregnation method at a high concentration. The potassium oxide loading was 0.5 wt.%, and the catalyst was calcined at 350℃ for 4 hours, with other test conditions remaining unchanged. Under these test conditions, the catalyst's denitrification efficiency remained stable above 80%, and the N2 selectivity was above 95%, demonstrating that the catalyst activity was not affected by the alkali metal K.

[0069] Comparing the results of Examples 1 to 3, it can be seen that the optimal conditions are when the molar ratio of Mn(NO3)2·xH2O to Ce(NO3)3·6H2O is 5:2. An excessively high Mn / Ce ratio will lead to the over-oxidation of NH3 by the catalyst under high temperature conditions, which will reduce the N2 selectivity of the catalyst to a certain extent. On the other hand, an excessively low Mn / Ce ratio will make it difficult to activate NH3 under low temperature conditions, which will inhibit the activity of the catalyst to a certain extent.

[0070] Example 4

[0071] The catalyst preparation differs from that in Example 1 only in that the loading of Mn-Ce composite metal oxide in step (2) is 15 wt.%, while the rest are the same.

[0072] Catalyst performance testing:

[0073] 2.3 mL of 40-60 mesh powdered catalyst was placed in a fixed-bed quartz tube reactor with an inner diameter of 1 cm. The initial gas volume concentrations were: NO = NH3 = 600 ppm, O2 = 3 vol.%, N2 as the equilibrium gas, and GHSV = 40,000 h⁻¹. -1The reaction temperature was 150–350℃, and the reaction tail gas was analyzed using a Testo350 flue gas analyzer. Under these test conditions, the catalyst maintained a stable denitrification efficiency of over 99% and an N2 selectivity of over 70%.

[0074] Alkali / Alkaline Earth Metal Resistance Test: A certain amount of potassium nitrate (KNO3), an alkali metal salt, was loaded at a high concentration onto a certain mass of catalyst using an impregnation method. The potassium oxide loading was 0.5 wt.%, and the catalyst was calcined at 350℃ for 4 hours, with other test conditions remaining unchanged. Under these test conditions, the catalyst's denitrification efficiency remained stable above 95%, and the N2 selectivity was above 65%, demonstrating that the catalyst activity was not affected by the alkali metal K.

[0075] Example 5

[0076] The catalyst preparation differs from that in Example 1 only in that the loading of the Mn-Ce composite metal oxide in step (2) is 5 wt.%.

[0077] Catalyst performance testing:

[0078] 2.3 mL of 40-60 mesh powdered catalyst was placed in a fixed-bed quartz tube reactor with an inner diameter of 1 cm. The initial gas volume concentrations were: NO = NH3 = 600 ppm, O2 = 3 vol.%, N2 as the equilibrium gas, and GHSV = 40,000 h⁻¹. -1 The reaction temperature was 150–350℃, and the reaction tail gas was analyzed using a Testo350 flue gas analyzer. Under these test conditions, the catalyst maintained a stable denitrification efficiency of over 80% and an N2 selectivity of over 98%.

[0079] Alkali / Alkaline Earth Metal Resistance Test: A certain amount of potassium nitrate (KNO3), an alkali metal salt, was loaded onto a certain mass of catalyst using an impregnation method at a high concentration. The potassium oxide loading was 0.5 wt.%, and the catalyst was calcined at 350℃ for 4 hours, with other test conditions remaining unchanged. Under these test conditions, the catalyst's denitrification efficiency remained stable above 78%, and the N2 selectivity was above 95%, demonstrating that the catalyst activity was not affected by the alkali metal K.

[0080] Comparing the results of Examples 1, 4, and 5, it can be seen that the optimal condition is when the loading of Mn-Ce composite metal oxide is 10 wt.%. If the loading of Mn-Ce composite metal oxide is too high, the catalyst will over-oxidize NH3 under high temperature conditions, which will reduce the N2 selectivity of the catalyst to a certain extent. If the loading of Mn-Ce composite metal oxide is too low, it will be difficult to activate NH3 under low temperature conditions, which will inhibit the activity of the catalyst to a certain extent.

[0081] Example 6

[0082] The catalyst preparation process was the same as in Example 1.

[0083] Catalyst performance testing:

[0084] 2.3 mL of 40-60 mesh powdered catalyst was placed in a fixed-bed quartz tube reactor with an inner diameter of 1 cm. The initial gas volume concentrations were: NO = NH3 = 600 ppm, O2 = 3 vol.%, N2 as the equilibrium gas, and GHSV = 40,000 h⁻¹. -1 The reaction temperature was 150–350℃, and the reaction tail gas was analyzed using a Testo350 flue gas analyzer. Under these test conditions, the catalyst maintained a stable denitrification efficiency of over 95% and an N2 selectivity of over 92%.

[0085] Alkali / Alkaline Earth Metal Resistance Test: A certain amount of alkali metal salt calcium nitrate (Ca(NO3)2) was loaded onto a certain mass of catalyst at a high concentration using an impregnation method. The calcium oxide loading was 0.5 wt.%, and the catalyst was calcined at 350℃ for 4 hours, with other test conditions remaining unchanged. Under these test conditions, the catalyst's denitrification efficiency remained stable at over 93%, and the N2 selectivity was over 90%, demonstrating that the catalyst activity was not affected by the alkaline earth metal Ca.

[0086] Comparing the results of Example 1 and Example 6, it can be seen that alkali metal K exhibits stronger poisoning properties than alkaline earth metal Ca. This is mainly because alkali metal K, which has stronger basicity, has a stronger poisoning effect on the acidic sites of the catalyst.

[0087] Comparative Example 1

[0088] Catalyst preparation:

[0089] (1) Dissolve a certain molar amount of citric acid in deionized water, and add Mn(NO3)2·xH2O and Ce(NO3)3·6H2O under vigorous stirring {the molar ratio of Mn(NO3)2·xH2O to Ce(NO3)3·6H2O is 5:2, and the molar ratio of citric acid to (Mn+Ce) metal cation is 5:2.5}. After stirring and mixing, dry in an oven at 120℃ for 12h, and calcine in an air atmosphere at 450℃ for 4h to obtain a Mn-Ce composite metal oxide that can be used as the core.

[0090] (2) Dissolve an equimolar amount of (NH4)2HPO4 in an aqueous solution of niobium tartrate, then add an appropriate amount of CTAB (the molar ratio of CTAB to (NH4)2HPO4 is 3:1), after hydrothermal reaction, take the solid, wash it, dry it in an oven at 120℃ for 12h, and calcine it in an air atmosphere at 450℃ for 4h to obtain NbOPO4 solid acid material that can be used as a shell.

[0091] (3) Take an appropriate amount of Mn-Ce composite metal oxide and NbOPO4 solid acid material (the mass ratio of Mn-Ce composite metal oxide to NbOPO4 solid acid material is 1:9, that is, the mass percentage of Mn-Ce composite metal oxide in the final catalyst is 10wt.%) and place them in a mortar. After grinding them thoroughly, dry them in an oven at 120℃ for 12h and calcine them in an air atmosphere at 450℃ for 4h to obtain a non-core-shell structured Mn-Ce / NbOPO4 denitration catalyst.

[0092] Catalyst performance testing:

[0093] 2.3 mL of 40-60 mesh powdered catalyst was placed in a fixed-bed quartz tube reactor with an inner diameter of 1 cm. The initial gas volume concentrations were: NO = NH3 = 600 ppm, O2 = 3 vol.%, N2 as the equilibrium gas, and GHSV = 40,000 h⁻¹. -1 The reaction temperature was 150–350℃, and the reaction tail gas was analyzed using a Testo350 flue gas analyzer. Under these test conditions, the catalyst maintained a stable denitrification efficiency of over 80% and an N2 selectivity of over 87%.

[0094] Alkali / Alkaline Earth Metal Resistance Test: A certain amount of potassium nitrate (KNO3), an alkali metal salt, was impregnated onto a catalyst of a certain mass at a high concentration using an impregnation method. The potassium oxide loading was 0.5 wt.%, and the catalyst was calcined at 350℃ for 4 hours, with other test conditions remaining unchanged. Under these test conditions, the catalyst's denitrification efficiency was above 50%, and its N2 selectivity was above 75%, demonstrating that the activity of non-core-shell catalysts is severely affected by alkali / alkaline earth metals.

[0095] Comparative Example 2

[0096] The catalyst preparation differs from that in Example 1 only in that CTAB was not added in step (2), otherwise it is the same.

[0097] Catalyst performance testing:

[0098] 2.3 mL of 40-60 mesh powdered catalyst was placed in a fixed-bed quartz tube reactor with an inner diameter of 1 cm. The initial gas volume concentrations were: NO = NH3 = 600 ppm, O2 = 3 vol.%, N2 as the equilibrium gas, and GHSV = 40,000 h⁻¹. -1 The reaction temperature was 150–350℃, and the reaction tail gas was analyzed using a Testo350 flue gas analyzer. Under these test conditions, the catalyst maintained a stable denitrification efficiency of over 82% and an N2 selectivity of over 95%.

[0099] Alkali / alkaline earth metal resistance test: A certain amount of potassium nitrate (KNO3), an alkali metal salt, was loaded at a high concentration onto a certain mass of catalyst using an impregnation method. The potassium oxide loading was 0.5 wt.%, and the catalyst was calcined at 350℃ for 4 hours, with other test conditions remaining unchanged. Under these test conditions, the catalyst's denitrification efficiency was above 70%, and the N2 selectivity was above 83%, demonstrating that the activity of core-shell structured catalysts lacking good pore structure is affected by alkali / alkaline earth metals.

[0100] A comparison between Comparative Example 1 and Example 1 shows that the core-shell structure can effectively improve the low-temperature denitrification activity and resistance to alkali / alkaline earth metals in the catalyst. This is mainly because: Comparative Example 1 is merely a solid mixture of Mn-Ce composite metal oxide and NbOPO4 solid acid material, which cannot produce a core-shell structure catalyst. In contrast, the NbOPO4 solid acid shell material in Example 1 of this application, with its abundant surface acidic sites, can fully anchor the alkali / alkaline earth metals carrying basic sites, avoiding the influence of alkali / alkaline earth metals on the internal nucleic acid sites. Furthermore, after neutralizing the deposited alkali / alkaline earth metals, it still retains sufficient sites for NH3 adsorption. Combined with the excellent redox sites on the Mn-Ce composite metal oxide, this achieves highly efficient and selective catalytic reduction of NO at low temperatures. x Comparing Comparative Example 2 with Example 1, the absence of CTAB surfactant in Comparative Example 2 resulted in narrower pores in the shell, significantly reducing the specific surface area and pore volume. In Example 1, the NbOPO4 solid acid shell material possesses a large specific surface area and excellent pore structure, providing sufficient alkali / alkaline earth metal anchoring capacity and preventing physical deactivation due to alkali / alkaline earth metal deposition.

[0101] In summary, the porous core-shell structured low-temperature SCR catalyst of this invention not only exhibits high nitrogen oxide conversion rate at low temperatures, but also demonstrates excellent resistance to alkali / alkaline earth metals.

[0102] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A Mn-Ce@NbOPO4 catalyst, characterized in that, The Mn-Ce@NbOPO4 catalyst has a core-shell structure, with the core being a Mn-Ce composite metal oxide and the shell being a NbOPO4 solid acid material. The shell has a porous structure with an average pore size of 6–10 nm and a pore volume of 0.6–1.2 cm³. 3 / g, specific surface area of ​​300~500 m² 2 / g, wherein the total acidity of the shell is 1000~2200 μmol / g.

2. The Mn-Ce@NbOPO4 catalyst according to claim 1, characterized in that, In the Mn-Ce@NbOPO4 catalyst, the mass percentage of Mn-Ce composite metal oxide is 5~15 wt.%.

3. The method for preparing the Mn-Ce@NbOPO4 catalyst according to claim 1 or 2, characterized in that, Includes the following steps: (1) Manganese salt, cerium salt, organic acid and water are mixed and the resulting mixture is calcined to obtain Mn-Ce composite metal oxide; (2) The Mn-Ce composite metal oxide, niobium salt, water, hydrogen phosphate and cationic surfactant are mixed and subjected to hydrothermal reaction, wherein the molar amount of niobium ions in the niobium salt is equal to that of hydrogen phosphate ions in the hydrogen phosphate, and a hydrothermal reaction product is obtained; the hydrothermal reaction product is calcined to obtain the Mn-Ce@NbOPO4 catalyst.

4. The preparation method according to claim 3, characterized in that, The manganese salt is manganese nitrate, and the cerium salt is cerium nitrate; the molar ratio of the manganese salt to the cerium salt is 5:(1~10).

5. The preparation method according to claim 3 or 4, characterized in that, The organic acid is citric acid; the molar ratio of the organic acid to the total molar ratio of manganese ions in the manganese salt and cerium ions in the cerium salt is 5:(1~5).

6. The preparation method according to claim 3, characterized in that, The hydrogen phosphate is (NH4)2HPO4; the cationic surfactant is hexadecyltrimethylammonium bromide; the molar ratio of the cationic surfactant to the hydrogen phosphate is (1~10):

1.

7. The preparation method according to claim 3 or 6, characterized in that, The hydrothermal reaction is carried out at a temperature of 120~200℃ for 8~24 hours.

8. The preparation method according to claim 3, characterized in that, The calcination temperatures in step (1) and step (2) are independently 380~480℃, and the calcination times are independently 2~5h.

9. The application of the Mn-Ce@NbOPO4 catalyst according to claim 1 or 2 or the Mn-Ce@NbOPO4 catalyst prepared by the preparation method according to any one of claims 3 to 8 in NH3-SCR denitrification.

10. The application according to claim 9, characterized in that, The conditions for the application include a reaction temperature of 150~350℃.