CN111943222B - Fe-beta molecular sieve for removing NOx and synthetic method and application thereof - Google Patents
Fe-beta molecular sieve for removing NOx and synthetic method and application thereof Download PDFInfo
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- C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
- C01B39/02—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof
- C01B39/06—Preparation of isomorphous zeolites characterised by measures to replace the aluminium or silicon atoms in the lattice framework by atoms of other elements, i.e. by direct or secondary synthesis
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- B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
- B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
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- C01B39/44—Ferrierite type, e.g. types ZSM-21, ZSM-35 or ZSM-38
- C01B39/445—Ferrierite type, e.g. types ZSM-21, ZSM-35 or ZSM-38 using at least one organic template directing agent
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Abstract
The invention discloses a Fe-beta molecular sieve synthesis method for removing NOx, which comprises the following steps: dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and part of an iron source in water in sequence, and stirring to form a uniform initial gel mixture; placing the initial gel in a high-temperature high-pressure reaction kettle, heating to a required temperature for aging reaction, adding the rest iron source in situ through an online feeding device after aging is finished, and heating to a crystallization temperature for crystallization reaction; filtering and washing after crystallization until a filter cake is neutral, dispersing the filter cake into a solution containing oxalic acid or ammonium oxalate with a certain concentration again, and heating to the required temperature for reaction; and after the reaction is finished, separating the obtained mixture, washing, drying and roasting to obtain the Fe-beta molecular sieve. The Fe-beta molecular sieve for removing NOx, the synthesis method and the application thereof can improve the content of iron in the Fe-beta molecular sieve, and the iron species exist in the form of monomer iron, so that the formation of iron oxide clusters is reduced, and the prepared Fe-beta has excellent NOx denitration activity.
Description
Technical Field
The invention relates to a Fe-beta molecular sieve for removing NOx and a synthesis method and application thereof, belonging to the technical field of molecular sieve synthesis and application.
Background
Nitrogen oxide (NOx) emissions are one of the main causes of atmospheric pollutionAs the amount of mobile sources, particularly NOx emitted from diesel vehicles, increases with the amount of vehicles kept, NOx has become a major source of NOx emission, and strict NOx emission control regulations are being introduced in various countries around the world. NOx selective catalytic reduction technology (NH)3-SCR) becomes the most effective technical route to solve the control of exhaust emissions from diesel vehicles. The molecular sieve has a large specific surface area, a regular pore structure, high thermal stability and hydrothermal stability, and has good denitration performance when used as a carrier material and used for loading a catalyst prepared from components such as Fe, Cu and the like.
The beta molecular sieve has a three-dimensional twelve-membered ring channel structure, and a large number of researches show that the Fe-modified beta molecular sieve has a wider denitration activity window, high medium-high temperature activity and N2The catalyst has good selectivity and is an excellent denitration catalyst. Patent CN 107029781A discloses that Fe and Ce are introduced in a liquid ion exchange-impregnation mode to prepare modified beta, and the modified beta has the characteristics of high low-temperature denitration activity and good hydrothermal stability. Iwasaki (Applied Catalysis B-Environmental,2011,102(1-2):302-309) adopts a chemical vapor deposition method to prepare different molecular sieve supported Fe active component catalysts, and compared with ZSM-5, FER, ITL and MOR, Fe-beta has the highest denitration activity. Mauvezin (Catal. Lett.1999,62,41) found Fe modified beta catalyzed NH3Reduction of N2The O reaction activity is better than that of Fe-ZSM-5.
The method for modifying the metal of the molecular sieve mainly comprises liquid ion exchange (J.Catal.2001,202,156, Catal.Comm 3(2002)385-389), solid phase ion exchange, chemical vapor deposition and one-step synthesis of the metal modified molecular sieve. Different preparation methods affect the metal loading amount and the existence form of the active component, thereby affecting the performance of the catalytic reaction. Liquid phase ion exchange processes are somewhat less reproducible and have limited loading, typically less than 3% (call.lett.52 (1998)13, j.call.190 (2000)384), whereas chemical vapor deposition processes require the iron source to be an iron-containing organic compound. The Fe-beta is synthesized by a one-step method, and the Fe content actually entering the framework is usually low, or the iron content of the framework is increased by a fluorine-containing system. Patent CN 105253895A discloses a beta molecular sieve with high Fe content in framework and a preparation method thereof, wherein Fe-beta is synthesized by a one-step method by taking an iron complex as an iron source and tetraethylammonium hydroxide cation as a template agent, and the Fe content in the framework reaches 3-8 wt%.
In order to obtain Fe-beta with high NOx removal activity it is generally required that the iron content cannot be too low and that the iron species is present as monomeric iron, avoiding the formation of iron oxide clusters. The Fe-beta molecular sieve synthesis method in the prior art can not meet the requirements, so that a Fe-beta molecular sieve synthesis method is urgently needed to solve the technical problems.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide the Fe-beta molecular sieve for removing NOx and the synthesis method and application thereof, which can improve the content of iron in the Fe-beta molecular sieve, reduce the formation of iron oxide clusters due to the existence of iron species in a form of monomer iron and ensure that the prepared Fe-beta has excellent NOx denitration activity.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a Fe-beta molecular sieve synthesis method for removing NOx comprises the following steps:
dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and part of an iron source in water in sequence, and stirring to form a uniform initial gel mixture;
placing the initial gel mixture in a high-temperature high-pressure reaction kettle, heating to a required temperature for an aging reaction, adding the residual iron source in situ through an online feeding device after the aging reaction is finished, and heating to a crystallization temperature for a crystallization reaction;
after the crystallization reaction is finished, filtering and washing until a filter cake is neutral, dispersing the filter cake into a solution containing oxalic acid or ammonium oxalate with a certain concentration again, and heating to the required temperature for reaction;
after the reaction is finished, separating the obtained mixture, and then washing, drying and roasting the mixture.
The molar ratio of the raw materials in the initial gel mixture is aluminum source: silicon source: organic template agent: inorganic base: water 1: 20-40: 1-10: 0.5-5: 200 to 500 parts by weight; the aluminum source is Al2O3The silicon source is SiO2And (6) counting.
The adding amount of the iron source in the initial gel mixture accounts for 10-30% of the total iron source, after the aging reaction is finished, adding the rest iron source in situ, wherein the total amount of the two parts of iron source is calculated by molar ratio: 0.01 to 0.5 of aluminum source, and Fe as iron source2O3And (6) counting.
The aluminum source is one or a mixture of any more of alumina, sodium metaaluminate and alumina sol; the silicon source is one or a mixture of any more of silica sol, silica gel and gas-phase silica, and the inorganic base is one or a mixture of two of sodium hydroxide and potassium hydroxide; the iron source is one or a mixture of any more of water-soluble iron salt, iron-containing organic metal compounds and iron oxide; the organic templating agent includes tetraethylammonium hydroxide.
The high-temperature high-pressure reaction kettle is provided with a mechanical stirring and online feeding device, and the online feeding device is cut off from the reaction kettle system through a valve after the required iron source material is accurately added.
The aging reaction temperature is 80-150 ℃, the aging reaction time is 8-48 h, the crystallization reaction temperature is 150-200 ℃, and the crystallization reaction time is 12-72 h.
The reaction temperature of the filter cake and oxalic acid or ammonium oxalate solution is 65-85 ℃, the reaction time is 1-12 hours, and the concentration of oxalic acid or ammonium oxalate is 0.1-2 mol/L in terms of oxalate ions.
The roasting procedure is roasting for 1-3 h at 200-300 ℃, and the temperature is programmed to 550 ℃ at the temperature rise rate of 1-5 ℃/min, and roasting for 1-2 h.
The Fe-beta molecular sieve for removing NOx is prepared by the synthesis method.
The Fe-beta molecular sieve for removing NOx in NOxThe application of selective catalyst removal.
The invention has the beneficial effects that: the invention provides a Fe-beta molecular sieve synthesis method for removing NOx, which synthesizes Fe-beta molecular sieve with high Fe content by a one-step method, and controls the concentration of Fe source in different stages of synthesis reaction and the action of other reaction raw materials and intermediate products by adding the Fe source into a synthesis system step by step so as to ensure that iron species are more uniformDispersing into the framework and pore canal of the beta molecular sieve; the monodispersity of iron species is good, iron oxide clusters are few, and the content of NH is3Has high low-temperature activity, wide active window and N in selective reduction of NOx reaction2The selectivity is good; the Fe-beta molecular sieve synthesized by oxalic acid/ammonium oxalate weak acidic materials is adopted to improve the hydrothermal stability of Fe-beta; the Fe-beta molecular sieve synthesized by sectional roasting has the advantages that the organic template agent is pre-carbonized at a lower roasting temperature, and then slowly heated to a high temperature for roasting, so that the residual template agent is removed, and the crystallinity of the Fe-beta molecular sieve is kept to the maximum extent.
Drawings
FIG. 1 is an X-ray diffraction pattern of Fe-beta molecular sieves synthesized in practical example 1, practical example 2, practical example 3, comparative example 1 and comparative example 2 of the present invention;
FIG. 2 is a scanning electron microscope result diagram of the Fe-beta molecular sieve synthesized in the embodiment 1 of the present invention;
FIG. 3 shows NH of Fe-beta molecular sieves synthesized in embodiments 1 to 3 and comparative examples 1 and 2 of the present invention3-SCR reaction results;
FIG. 4 shows NH of Fe-beta molecular sieves synthesized in embodiments 1 to 3 and comparative examples 1 and 2 of the present invention3SCR reaction N2(ii) a selective outcome;
FIG. 5 shows NH of the H-Fe-beta molecular sieve synthesized in the embodiment 1 of the present invention after hydrothermal aging3-SCR reaction results.
Detailed Description
The present invention is further described with reference to the accompanying drawings, and the following examples are only for clearly illustrating the technical solutions of the present invention, and should not be taken as limiting the scope of the present invention.
Detailed description of the preferred embodiment 1
According to the molar ratio of the materials in the initial gel mixture, the aluminum source: silicon source: organic template agent: inorganic base: water: 1: 30: 1.13: 3.4: 300: and 0.3, weighing the materials. Wherein the aluminum source is Al2O3The silicon source is SiO2In terms of iron source Fe2O3And (6) counting. Wherein the organic template agent R is tetraethyl hydroxideAmmonium chloride (25 wt%), coarse-pore silica gel as silicon source, aluminium sol as aluminium source, iron trichloride as iron source and sodium hydroxide as inorganic alkali. Under the condition of stirring at room temperature, sequentially dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and a 10% iron source into water, and stirring to form uniform initial gel. And (3) putting the initial gel in a high-temperature high-pressure reaction kettle, heating to 120 ℃ for carrying out an aging reaction for 24 hours, adding the rest 90% of iron source in situ through an online feeding device after the aging reaction is finished, and heating to 150 ℃ for carrying out a crystallization reaction for 48 hours. Filtering and washing the mixture after crystallization till a filter cake is neutral, re-dispersing the filter cake into a solution containing 1mol/L oxalic acid, and stirring the mixture at 75 ℃ for reaction for 4 hours. And after the reaction is finished, separating the obtained mixture, washing and drying, and roasting the obtained filter cake in stages to remove the template agent, wherein the roasting condition is that the room temperature is 5 ℃/min to 300 ℃, roasting is carried out for 2h, and then the roasting is carried out for 1h at the temperature of 5 ℃/min to 550 ℃, so as to obtain the Fe-beta molecular sieve. Wherein, the mole ratio of silicon to aluminum: 29.6, Fe2O3The content was 4.3 wt%.
As shown in FIG. 1a, it can be seen that the synthesized Fe-Beta has significant Beta molecular sieve characteristic peaks 2 θ of 13.45 °, 21.41 °, 22.46 °, 25.40 °, 26.91 ° and 29.59 °, respectively. Wherein 22.46 degrees is a strong peak, and 21.41 degrees is a shoulder peak. FIG. 2 is the scanning electron microscope result image of the synthesized Fe-beta molecular sieve.
Comparative example 1
According to the molar ratio of the materials in the initial gel mixture, the aluminum source: silicon source: organic template agent: inorganic base: water: 1: 30: 1.13: 3.4: 300: and 0.3, weighing the materials. Wherein the aluminum source is Al2O3The silicon source is SiO2In terms of iron source Fe2O3And (6) counting. Wherein the organic template agent R is tetraethyl ammonium hydroxide (25 wt%), the silicon source is macroporous silica gel, the aluminum source is aluminum sol, the iron source is ferric trichloride, and the inorganic base is sodium hydroxide. Under the condition of stirring at room temperature, sequentially dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and a 100% iron source into water, and stirring to form uniform initial gel. And (3) putting the initial gel in a high-temperature high-pressure reaction kettle, heating to 120 ℃ for carrying out an aging reaction for 24 hours, and after the aging reaction is finished, heating to 150 ℃ at a speed of 5 ℃/min for carrying out a crystallization reaction for 48 hours. Filtering and washing after crystallization till the filter cake is neutral and heavyDispersing the mixture into a solution containing 1mol/L oxalic acid, and stirring the mixture at 75 ℃ for reaction for 4 hours. And after the reaction is finished, separating the obtained mixture, washing and drying, and roasting the obtained filter cake in stages to remove the template agent, wherein the roasting condition is that the room temperature is 5 ℃/min to 300 ℃, roasting is carried out for 2h, and then the roasting is carried out for 1h at the temperature of 5 ℃/min to 550 ℃, so as to obtain the Fe-beta molecular sieve. Wherein, the mole ratio of silicon to aluminum: 29.3, Fe2O3The content was 3.3 wt%.
As shown in FIG. 1b, the characteristic peaks 2 θ of the Beta zeolite are seen to be 13.30 °, 21.41 °, 22.43 °, 25.26 °, 26.81 ° and 29.48 °, respectively. Wherein 22.43 degrees is a strong peak, and 21.41 degrees is a shoulder peak.
Comparative example 2
According to the molar ratio of the materials in the initial gel mixture, the aluminum source: silicon source: organic template agent: inorganic base: water: 1: 30: 1.13: 3.4: 300: and 0.3, weighing the materials. Wherein the aluminum source is Al2O3The silicon source is SiO2In terms of iron source Fe2O3And (6) counting. Wherein the organic template agent R is tetraethyl ammonium hydroxide (35 wt%), the silicon source is macroporous silica gel, the aluminum source is aluminum sol, the iron source is ferric trichloride, and the inorganic base is sodium hydroxide.
Under the condition of stirring at room temperature, sequentially dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and a 10% iron source into water, and stirring to form uniform initial gel. And (3) putting the initial gel in a high-temperature high-pressure reaction kettle, heating to 120 ℃ for carrying out an aging reaction for 24 hours, adding the rest 90% of iron source in situ through an online feeding device after the aging reaction is finished, and heating to 150 ℃ for carrying out a crystallization reaction for 48 hours. And after crystallization, filtering and washing until a filter cake is neutral, and roasting the obtained filter cake in sections to remove the template agent, wherein the roasting condition is that the room temperature is 5 ℃/min to 300 ℃, roasting for 2h, and then, the temperature is 5 ℃/min to 550 ℃, and roasting for 1h to obtain the Fe-beta molecular sieve. Wherein, the mole ratio of silicon to aluminum: 26.8, Fe2O3The content was 4.5 wt%.
As shown in FIG. 1c, the characteristic peaks 2 θ of the Beta zeolite are seen to be 13.25 °, 21.39 °, 22.40 °, 25.26 °, 26.81 ° and 29.44 °, respectively. Wherein 22.40 degrees is a strong peak, and 21.39 degrees is a shoulder peak.
Specific example 2
According to the molar ratio of the materials in the initial gel mixture, the aluminum source: silicon source: organic template agent: inorganic base: water: 1: 30: 1.5: 2.3: 300: and 0.4, weighing the materials. Wherein the aluminum source is Al2O3The silicon source is SiO2In terms of iron source Fe2O3And (6) counting. Wherein the organic template agent R is tetraethyl ammonium hydroxide (35 wt%), the silicon source is macroporous silica gel, the aluminum source is aluminum sol, the iron source is ferric trichloride, and the inorganic base is sodium hydroxide.
Under the condition of stirring at room temperature, sequentially dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and a 30% iron source into water, and stirring to form uniform initial gel. And (3) putting the initial gel in a high-temperature high-pressure reaction kettle, heating to 120 ℃ for carrying out an aging reaction for 24 hours, adding the rest 70% of iron source in situ through an online feeding device after the aging reaction is finished, and heating to 150 ℃ for carrying out a crystallization reaction for 48 hours. Filtering and washing the mixture after crystallization till a filter cake is neutral, re-dispersing the filter cake into a solution containing 0.5mol/L oxalic acid, and stirring the mixture at 75 ℃ for reaction for 4 hours. And after the reaction is finished, separating the obtained mixture, washing and drying, and roasting the obtained filter cake in sections to remove the template agent, wherein the roasting condition is that the temperature is 5 ℃ per minute to 300 ℃ at room temperature for 2 hours, and then the roasting condition is that the temperature is 5 ℃ per minute to 550 ℃ for 1 hour to prepare the Fe-beta molecular sieve. Wherein, the mole ratio of silicon to aluminum: 29.8, Fe2O3The content was 5.2 wt%.
As shown in FIG. 1d, the characteristic peaks 2 θ of the Beta zeolite are seen to be 13.41 °, 21.46 °, 22.46 °, 25.36 °, 27.10 ° and 29.61 °, respectively. Wherein 22.46 degrees is a strong peak, and 21.46 degrees is a shoulder peak.
Specific example 3
According to the molar ratio of the materials in the initial gel mixture, the aluminum source: silicon source: organic template agent: inorganic base: water: 1: 30: 2.0: 1.3: 300: and 0.5 calculating and weighing the materials. Wherein the aluminum source is Al2O3The silicon source is SiO2In terms of iron source Fe2O3And (6) counting. Wherein the organic template agent R is tetraethyl ammonium hydroxide (35 wt%), the silicon source is macroporous silica gel, the aluminum source is aluminum sol, the iron source is ferric nitrate, and the inorganic alkali is sodium hydroxide.
Under the condition of stirring at room temperature, mixingAnd dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and a 30% iron source in water in sequence, and stirring to form uniform initial gel. And (3) putting the initial gel in a high-temperature high-pressure reaction kettle, heating to 120 ℃ for aging reaction for 36h, adding the rest 70% of iron source in situ through an online feeding device after the aging reaction is finished, and heating to 150 ℃ for crystallization reaction for 48 h. Filtering and washing the mixture after crystallization till a filter cake is neutral, re-dispersing the filter cake into a solution containing 0.5mol/L oxalic acid, and stirring the mixture at 75 ℃ for reaction for 4 hours. And after the reaction is finished, separating the obtained mixture, washing and drying, and roasting the obtained filter cake in stages to remove the template agent, wherein the roasting condition is that the room temperature is 5 ℃/min to 300 ℃, roasting is carried out for 2h, and then the roasting is carried out for 1h at the temperature of 5 ℃/min to 550 ℃, so as to obtain the Fe-beta molecular sieve. Wherein, the mole ratio of silicon to aluminum: 29.8, Fe2O3The content was 5.8 wt%.
As shown in FIG. 1e, the characteristic peaks 2 θ of the Beta zeolite are seen to be 13.28 °, 21.35 °, 22.39 °, 25.28 °, 26.82 ° and 29.48 °, respectively. Wherein 22.39 degrees is a strong peak, and 21.35 degrees is a shoulder peak.
Specific example 4
According to the molar ratio of the materials in the initial gel mixture, the aluminum source: silicon source: organic template agent: inorganic base: water: 1: 20: 1: 0.5: 200: and 0.01 calculating and weighing the materials. Wherein the aluminum source is Al2O3The silicon source is SiO2In terms of iron source Fe2O3And (6) counting. Wherein the organic template agent R is tetraethyl ammonium hydroxide (35 wt%), the silicon source is macroporous silica gel, the aluminum source is aluminum sol, the iron source is ferric nitrate, and the inorganic alkali is sodium hydroxide.
Under the condition of stirring at room temperature, sequentially dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and a 30% iron source into water, and stirring to form uniform initial gel. And (3) putting the initial gel in a high-temperature high-pressure reaction kettle, heating to 80 ℃ for carrying out an aging reaction for 48 hours, adding the rest 70% of iron source in situ through an online feeding device after the aging reaction is finished, and heating to 200 ℃ for carrying out a crystallization reaction for 12 hours. Filtering and washing the mixture after crystallization till a filter cake is neutral, re-dispersing the filter cake into a solution containing 0.1mol/L oxalic acid, and stirring the mixture at 65 ℃ for reaction for 12 hours. After the reaction is finished, separating the obtained mixture, washing and drying the mixture, and removing the obtained filter cake by roasting in sectionsThe template agent is roasted for 3h under the roasting condition that the room temperature is increased to 200 ℃ at the rate of 1 ℃/min, and then the template agent is roasted for 1.5h under the roasting condition that the room temperature is increased to 550 ℃ at the rate of 5 ℃/min to prepare the Fe-beta molecular sieve. Wherein, the mole ratio of silicon to aluminum: 19.4, Fe2O3The content was 0.12 wt%.
Specific example 5
According to the molar ratio of the materials in the initial gel mixture, the aluminum source: silicon source: organic template agent: inorganic base: water: 1: 40: 10: 5: 500: and 0.5 calculating and weighing the materials. Wherein the aluminum source is Al2O3The silicon source is SiO2In terms of iron source Fe2O3And (6) counting. Wherein the organic template agent R is tetraethyl ammonium hydroxide (35 wt%), the silicon source is macroporous silica gel, the aluminum source is aluminum sol, the iron source is ferric nitrate, and the inorganic alkali is sodium hydroxide.
Under the condition of stirring at room temperature, sequentially dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and a 30% iron source into water, and stirring to form uniform initial gel. And (3) putting the initial gel in a high-temperature high-pressure reaction kettle, heating to 150 ℃ for aging reaction for 8 hours, adding the rest 70% of iron source in situ through an online feeding device after the aging reaction is finished, and heating to 180 ℃ for crystallization reaction for 72 hours. Filtering and washing the mixture after crystallization till a filter cake is neutral, re-dispersing the filter cake into a solution containing 1.0mol/L oxalic acid, and stirring the mixture at 85 ℃ for reaction for 2 hours. And after the reaction is finished, separating the obtained mixture, washing and drying, and roasting the obtained filter cake in stages to remove the template agent, wherein the roasting condition is that the room temperature is increased to 250 ℃ at 3 ℃/min for roasting 1h, and then the roasting condition is increased to 550 ℃ at 5 ℃/min for roasting 2h to prepare the Fe-beta molecular sieve. Wherein, the mole ratio of silicon to aluminum: 36.8, Fe2O3The content was 5.5 wt%.
And (3) comparing catalytic reaction effects: the Fe-beta molecular sieves synthesized in the above specific examples 1 to 3 and comparative examples 1 and 2 contain a certain content of Na ions in the presence of NH3Ion exchange is required before evaluation of the SCR reaction, Na is added+Exchange for NH4 +And is roasted to become H-Fe-beta. The process conditions of the ion exchange are as follows: 0.5mol/LNH4And (3) exchanging Cl aqueous solution for 4H at 65-75 ℃, filtering, washing and drying to obtain the Na ion-free H-Fe-beta molecular sieve sample.
Will concretely be describedThe molecular sieve samples obtained in examples 1,2 and 3 and comparative examples 1 and 2 were used for fixed bed NH respectively3-SCR reaction. And tabletting and granulating the molecular sieve powder, screening out particles of 40-60 meshes, weighing 0.1g of the particles, placing the particles in a fixed bed reactor, and diluting the particles with 0.9g of quartz sand. Space velocity of reaction raw material gas is 600,000h-1The gas composition is as follows: 500ppmNO, 500ppmNH3，5％O2，3.5％H2O，8％CO2、N2And (4) balancing. The reaction product was analyzed by an infrared gas analyzer. As can be seen in FIG. 3, the Fe-beta molecular sieves synthesized according to examples 1-3 exhibited very high NOx conversion at low temperatures and high NOx conversion activity at high temperatures, as can be seen in FIG. 4, N2The selectivity is very high throughout the temperature interval.
Carrying out hydrothermal treatment on the H-Fe-beta molecular sieve synthesized in the specific example 1 under the condition of 10% H2O，90％N2Treating for 16h at 650 ℃ in the atmosphere to obtain a hydrothermal aged Fe-beta molecular sieve sample.
The aged Fe-beta molecular sieve sample is used for fixed bed NH3SCR reaction, it can be seen from FIG. 5 that the hydrothermally aged Fe-beta molecular sieve samples still have high NOx conversion.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (7)
1. A Fe-beta molecular sieve synthetic method for removing NOx is characterized in that: the method comprises the following steps: dispersing a silicon source, an organic template agent, an inorganic alkali, an aluminum source and part of an iron source in water in sequence, and stirring to form a uniform initial gel mixture;
placing the initial gel mixture in a high-temperature high-pressure reaction kettle, heating to a required temperature for an aging reaction, adding the residual iron source in situ through an online feeding device after the aging reaction is finished, and heating to a crystallization temperature for a crystallization reaction; filtering and washing the mixture after the crystallization reaction is finished until a filter cake is neutral,re-dispersing the mixture into oxalic acid or ammonium oxalate solution with certain concentration, and heating to the required temperature for reaction; after the reaction is finished, separating the obtained mixture, and then washing, drying and roasting the mixture; the molar ratio of the raw materials in the initial gel mixture is as follows: an aluminum source: silicon source: organic template agent: inorganic base: water = 1: 20-40: 1-10: 0.5-5: 200 to 500 parts by weight; the aluminum source is Al2O3The silicon source is SiO2Counting; the adding amount of an iron source in the initial gel mixture accounts for 10-30% of the total iron source, after the aging reaction is finished, adding the rest iron source in situ, wherein the total amount of the two parts of iron sources is calculated by molar ratio: the aluminum source = 0.01-0.5, and the iron source is Fe2O3Counting; the aging reaction temperature is 80-150 ℃, the aging reaction time is 8-48 h, the crystallization reaction temperature is 150-200 ℃, and the crystallization reaction time is 12-72 h.
2. The method for synthesizing the Fe-beta molecular sieve for removing the NOx of claim 1 is characterized in that: the aluminum source is one or a mixture of any more of alumina, sodium metaaluminate and alumina sol; the silicon source is one or a mixture of any more of silica sol, silica gel and gas-phase silica, and the inorganic base is one or a mixture of two of sodium hydroxide and potassium hydroxide; the iron source is one or a mixture of any more of water-soluble iron salt, iron-containing organic metal compounds and iron oxide; the organic templating agent includes tetraethylammonium hydroxide.
3. The method for synthesizing the Fe-beta molecular sieve for removing the NOx of claim 1 is characterized in that: the high-temperature high-pressure reaction kettle is provided with a mechanical stirring and online feeding device, and the online feeding device is cut off from the reaction kettle system through a valve after the required iron source material is accurately added.
4. The method for synthesizing the Fe-beta molecular sieve for removing the NOx of claim 1 is characterized in that: the reaction temperature of the filter cake and oxalic acid or ammonium oxalate solution is 65-85 ℃, the reaction time is 1-12 hours, and the concentration of oxalic acid or ammonium oxalate is 0.1-2 mol/L in terms of oxalate ions.
5. The method for synthesizing the Fe-beta molecular sieve for removing the NOx of claim 1 is characterized in that: the roasting procedure is roasting for 1-3 h at 200-300 ℃, and the temperature is programmed to 550 ℃ at the temperature rise rate of 1-5 ℃/min, and roasting for 1-2 h.
6. An Fe-beta molecular sieve for removing NOx prepared by the synthesis method of any one of claims 1 to 5.
7. The Fe-beta molecular sieve for removing NOx of claim 6 in NOxThe application of selective catalyst removal.
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