CN113797963A - High-alkali-resistance composite denitration powder and preparation method thereof - Google Patents

High-alkali-resistance composite denitration powder and preparation method thereof Download PDF

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CN113797963A
CN113797963A CN202111232196.3A CN202111232196A CN113797963A CN 113797963 A CN113797963 A CN 113797963A CN 202111232196 A CN202111232196 A CN 202111232196A CN 113797963 A CN113797963 A CN 113797963A
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CN113797963B (en
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刘雪松
杨亚萍
李佳盈
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University of Shaoxing
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Abstract

The high-alkali-resistance composite denitration powder is prepared by using a core-shell structure CHA/AEI molecular sieve modified by solid superacid and TiO2The carrier is loaded with denitration active ingredients and auxiliaries to obtain the denitration catalyst, the solid super acid is a shell, and the CHA/AEI molecular sieve is a core. The composite material powder has large specific surface area (200- & lt600 & gt m-)2Per g), uniform particle size (1-5 μm), large number of surface acid sites (greater than 40 μmol/g), small average pore size (less than13nm), high hydrothermal stability, strong alkali poisoning resistance and the like, meets the requirements of special SCR catalyst carriers, and is particularly suitable for solving the problem of flue gas denitration of cement kilns, biomass boilers and other dust containing a large amount of alkali metals or alkaline earth metals.

Description

High-alkali-resistance composite denitration powder and preparation method thereof
Technical Field
The invention belongs to the field of industrial waste gas purification, and particularly relates to high-alkali-resistance composite denitration powder and a preparation method thereof.
Background
Industrial exhaust emissions have become an important source of atmospheric pollution, among which strongly oxidizing Nitrogen Oxides (NO)x) Is the main factor for causing haze and ozone explosion. In 2020, the cement yield in China is 23.77 hundred million tons, which accounts for about 60% of the whole world. 85.12 million tons of nitrogen oxides discharged by cement industry in the last year of China are NO in the first major industry of China at presentxA source of emissions.
Currently, NH is mainly adopted for cement kiln denitration3The SNCR (selective non-catalytic reduction) technology has low denitration efficiency of 30-50%, high operation cost and serious ammonia escape. In order to meet the emission regulation of ' near zero ' in cement industry ', NH is adopted3The SCR (selective catalytic reduction) denitration purification technology will be a necessary trend. V2O5-WO3/TiO2The catalyst is used as a traditional commercial denitration catalyst, has the advantages of high denitration efficiency, wider temperature window, good sulfur resistance and the like, and is widely applied to the field of thermal power denitration. However, it cannot meet the requirements of cement and other industrial flue gas (such as biomass power generation and metal smelting) on alkali poisoning resistance, structural strength and the like. The high dust content of the flue gas of the cement kiln can cause the vanadium-tungsten-titanium catalyst to be worn by mechanical impact, and structural damage such as collapse, blockage and the like can occur. In addition, due to the particularity of the cement production process, the discharged smoke is rich in alkali (earth) metal oxides, so that the vanadium-tungsten-titanium catalyst is easy to cause the active species and alkali metal to be combined into inert compounds to be inactivated, and the service life of the vanadium-tungsten-titanium catalyst is shortened. The development of a denitration catalyst with high alkali dust resistance and structural strength is a major technical bottleneck at present.
Alkali metals (K, Na, etc.) and alkaline earth elements (Ca, Mg, etc.) can have a severe impact on the catalyst, causing catalyst poisoning, eventually leading to catalyst deactivation. The alkalosis is at present V2O5-WO3/TiO2The greatest threat to catalyst deactivation. The research shows that the degree of alkali poisoning is increased along with the increase of alkali concentration, and the degree of poisoning is K in the order of K under the condition of the same alkali concentration>Na>Ca>Mg, the stronger the basicity of the alkali element, the more obvious the poisoning effect. The poisoned catalyst is found by the characterization of the adsorption performance and the oxidation-reduction performance of the catalyst
Figure BDA0003316299550000011
The strength and stability of the acid sites are seriously reduced, the oxygen adsorption capacity of the surface chemistry is reduced, the oxidation reduction capacity is weakened, and finally the catalyst is poisoned. Among them, the decrease in the number and strength of acid sites on the surface of the catalyst is the most important cause of catalyst poisoning. Therefore, the development of a novel composite denitration powder having more acidic sites, a larger specific surface area and a more developed pore structure is the key to solve the above problems.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a high-alkali-resistance composite denitration powder, a preparation method and application thereof, wherein the composite denitration powder has a large specific surface area (200-2The catalyst has the characteristics of uniform granularity (1-5 mu m), large surface acid site number (more than 40 mu mol/g), small average pore diameter (less than 13nm), high hydrothermal stability, strong alkali poisoning resistance and the like, meets the requirements of special SCR catalyst carriers, is particularly suitable for solving the problem of flue gas denitration of cement kilns, biomass boilers and other dust containing a large amount of alkali metals or alkaline earth metals, and has the advantages of simple operation, simple and convenient equipment requirement and the like.
In order to achieve the purpose, the invention adopts the technical scheme that:
a high-alkali-resistance composite denitration powder is prepared from solid superacid modified core-shell CHA/AEI molecular sieve and TiO2The carrier is loaded with denitration active ingredients and auxiliaries to obtain the denitration catalyst, the solid super acid is a shell, and the CHA/AEI molecular sieve is a core.
The solid super acid is represented by SaO4a 2-/MO2Wherein a is between 1 and 2, M is Ti and/or Zr; examples of solid superacids includeIncluding but not limited to SO4 2-/TiO2、SO4 2-/ZrO2、S2O8 2-/TiO2、S2O8 2-/ZrO2At least one of (1).
Further, the high-alkali-resistance composite denitration powder comprises the following components in percentage by mass: 0.1-10 wt% of denitration active component, 1-15 wt% of assistant, 10-70 wt% of core-shell structure CHA/AEI molecular sieve, and the balance TiO2。
Preferably, the highly alkali-resistant TiO2-WO3The CHA/AEI composite denitration powder comprises the following components in percentage by mass: 1-5 wt% of denitration active component, 5-10 wt% of assistant, 30-55 wt% of core-shell structure CHA/AEI molecular sieve, and the balance TiO2。
More preferably, the content of the denitration active component in the composite denitration powder is 2-4 wt%.
The denitration active component is transition metal oxide, the transition metal is at least one of vanadium, gallium, germanium, tin, cobalt, cerium, lanthanum and iron, vanadium is preferred, and V is used as the transition metal oxide2O5(ii) a The auxiliary agent is selected from at least one of oxides of tungsten, iron, yttrium and copper, preferably tungsten, such as WO3。
The particle size of the composite denitration powder obtained by the invention is 1-5 mu m, and the specific surface area is 200-600m2The number of surface acid sites is more than 40 mu mol/g, and the average pore diameter is less than 13 nm.
The CHA/AEI molecular sieve with the core-shell structure is formed by that the inner core of the CHA/AEI molecular sieve comprises at least one of SSZ-13, SAPO-34, SSZ-16 and SSZ-39; the shell component is solid super acid and is expressed as SaO4a 2-/MO2。
The inventors have unexpectedly discovered that using a core-shell CHA/AEI molecular sieve as a support provides a plurality of acid sites as sacrificial agents for alkali poisoning by using a solid superacid shell and a molecular sieve core, wherein the solid superacid is mainly used to bind alkali metal, and the shell structure prevents the alkali metal in the dust from diffusing into the molecular sieve pores, thereby reducing the molecular weightLoss of active acid sites inside the sieve, while the shell structure of the solid superacid can be NH3Providing channels for diffusion into the molecular sieve. In addition, the CHA/AEI molecular sieve with the core-shell structure can provide a larger specific surface area, so that the dispersion of active components and the denitration performance of the catalyst are promoted, and the working temperature window of the catalyst is widened.
Further, in the CHA/AEI molecular sieve with the core-shell structure, S is in solid superacid as shellaO4a 2-1-10 wt%, preferably 3-7%, and the balance of MO2(ii) a The CHA/AEI molecular sieve accounts for 70-90 wt% of the CHA/AEI molecular sieve with the core-shell structure.
The CHA/AEI molecular sieve with the core-shell structure is prepared by the following steps:
(S1) adding the CHA/AEI molecular sieve into the first organic solvent to disperse, slowly adding a titanium source and/or a zirconium source to generate a precipitate, adding a mixed solution of a second organic solvent and water, performing ultrasonic treatment, washing, and drying;
(S2) adding the material dried in the step (S1) to H2SO4And/or H2S2O8And drying the solution, sequentially calcining for the first time in an inert atmosphere and calcining for the second time in an oxygen atmosphere to obtain the CHA/AEI molecular sieve with the core-shell structure.
Further, in the above method for preparing the CHA/AEI molecular sieve having the core-shell structure, the ratio of the total mass of the titanium source and/or the zirconium source to the mass of the CHA/AEI in the step (S1) is 1: 30-60, preferably 1: 40-50.
Further, in the step (S1), the first organic solvent is a mixed solvent of tetrahydrofuran and dimethylformamide, and the second organic solvent is selected from tetrahydrofuran; furthermore, the volume ratio of the tetrahydrofuran to the dimethylformamide is 4-6:1, and the dosage of the first organic solvent is 500 times of the mass of the molecular sieve; the volume ratio of the second organic solvent to the water is 10-20:1, the water is used for ensuring that the titanium source/the zirconium source are fully hydrolyzed, and in a specific embodiment of the invention, the water is used for 2-10 times of the total mass of the titanium source/the zirconium source.
Tetrahydrofuran (THF)A non-polar solvent in which the titanium/zirconium source is homogeneously dispersed but does not hydrolyze to form TiO2Or ZrO2. Dimethylformamide is a weakly polar solvent in which the titanium/zirconium source undergoes a small amount of hydrolysis to produce TiO2Or ZrO2. Adding a small amount of dimethylformamide into tetrahydrofuran, and slightly hydrolyzing a titanium source/zirconium source under the action of the dimethylformamide to generate a plurality of micro nano TiO2Or ZrO2. Then, under the condition of adding water, using micro nano TiO2Or ZrO2The titanium/zirconium source is completely hydrolyzed for nucleation and deposited on the surface of the SSZ-13 molecular sieve. The two-step hydrolysis can ensure that the titanium source/zirconium source generates TiO2Or ZrO2Dispersion and uniformity of the dispersion. Thereby forming a uniform mesoporous structure and increasing SaO4a 2-The dispersion degree lays a foundation.
In the step (S1), the sonication, hydrolysis, and drying are not particularly limited, and are well known in the art. In a specific embodiment of the invention, the washing is alcohol washing (at least one of methanol, ethanol and propanol) for a plurality of times, then water washing is carried out until the materials are neutral, and the materials are dried for 12 to 24 hours at 50 to 70 ℃ in a vacuum drying oven with the vacuum degree of-0.06 to 0.09Mpa, namely the materials with the acidified core-shell structure CHA/AEI @ meso-MO are obtained2。
Further, in step (S2), the dried material is added to H2SO4And/or H2S2O8Stirring the solution for 0.5 to 3 hours, drying and then carrying out two-section type calcination. The first stage of calcination is calcination at 350-450 ℃ for 4-6h under inert atmosphere, and the heating rate is 5-10 ℃/min; the second stage calcination is carried out in an oxygen atmosphere, such as air, at the temperature of 450-550 ℃ for 4-6h, and the heating rate is 2-5 ℃. Finally obtaining the CHA/AEI @ S with the core-shell structureaO4a 2-/MO2. The inventor finds that the core-shell structure obtained by the method can improve the specific surface area, the number of acid sites, the pore structure and the core-shell structure of the composite powder for the denitration powder prepared by taking the CHA/AEI molecular sieve as a carrier, has high dispersion degree of active components and high catalytic efficiency, and has excellent alkali poisoning resistance. The first step of inert atmosphere calcination is mainly to make the shell layer haveThe organic components are carbonized, and in order to prevent the organic components from igniting and ensure the organic components to be completely carbonized, the working procedure adopts inert atmosphere protection, low temperature and long-time calcination treatment. And the second step of calcination is to remove carbon particles in the shell layer by adopting an aerobic combustion mode, so that a residual space generates a mesoporous structure, and therefore, in order to prevent the mesoporous structure from collapsing caused by abrupt temperature rise and ensure that the carbon particles are completely burnt out, the process adopts calcination treatment at a high temperature and a slow temperature rise rate.
The invention also provides a preparation method of the composite denitration powder, which comprises the following steps:
and (2) fully dispersing an active component precursor, an auxiliary agent precursor and the CHA/AEI molecular sieve powder with the core-shell structure in the presence of a dispersing agent, drying, calcining and grinding to obtain the composite material.
Preferably, the composite denitration powder is prepared by adopting a sectional method of an auxiliary agent precursor and an active ingredient precursor, and the method comprises the following steps:
(P1) fully dispersing the additive precursor and the CHA/AEI molecular sieve powder with the core-shell structure in the presence of a dispersing agent, drying, calcining and grinding to obtain powder;
(P2) dispersing the powder obtained in the step (P1) in an aqueous solution of an active ingredient precursor, drying, and calcining to obtain the composite denitration powder.
The active component precursor, the auxiliary agent precursor and TiO2The mass ratio of the precursor to the CHA/AEI molecular sieve powder with the core-shell structure is 0.1-0.5:1-10:40-80: 20-50; preferably 0.2-0.4:4-10:45-70: 30-50.
The active ingredient precursors and adjuvant precursors are well known in the art and are typically aqueous solutions of their salts. For example, for vanadium oxide, the precursor is ammonium metavanadate; for tungsten oxide, the precursor is ammonium metatungstate; for titanium oxide precursor, ultra-fine low-sulfur TiO2And (3) powder.
Further preferably, ultra-fine low sulfur TiO2The specific surface area of the powder should be more than 300m2G, sulfate content less than 0.5 wt.%, D90The particle size is less than 1 μm, and the particle size distribution should be less than 0.5 μm.
The invention uses soluble ammonium metatungstate to replace insoluble ammonium paratungstate, and uses superfine low-sulfur titanium dioxide to replace metatitanic acid prepared by a sulfuric acid method, thereby improving the dispersion degree of tungsten on titanium and the quantity of titanium-tungsten solid solutions, and further improving the thermal stability and the oxidation-reduction performance of the composite powder.
The dispersant is at least one selected from perchloric acid, nitric acid, trichloroacetic acid, tripropylamine, triethylamine and dimethylamine, the dosage of the dispersant is not particularly limited, and the dispersant can fully disperse the system, and the dispersion is carried out by stirring for 2-6h at 40-80 ℃.
The drying method is not particularly limited, and is well known in the art, such as spray drying, wherein the spraying condition is 2-10 ml/min of liquid, the outlet of an air compressor is maintained at 0.5-3 atmospheric pressure, and the drying temperature is maintained at 90-280 ℃; or drying under the microwave vacuum condition, wherein the temperature is 40-150 ℃, the microwave power is 20-200W, and the vacuum degree is 200-500 Pa. The grinding method is not particularly limited, and examples thereof include ball grinding, gas stream grinding and rod-cut grinding
The temperature programming rate is 2-10 ℃/min, the calcining temperature is 300-600 ℃, and the constant-temperature calcining time is 2-6 hours.
The composite denitration powder has high specific surface area (200-600 m)2Per gram), uniform granularity (1-5 mu m), large surface acid site number (more than 40 mu mol/g), small average pore diameter (less than 13nm), high hydrothermal stability (after hydrothermal aging for 12-48 h at 500-700 ℃ in the air with water vapor concentration of 5-15 percent, the specific surface area of the composite powder is still more than 150m2(1-3 wt%) strong alkali poisoning resistance2After the forced alkalosis treatment of O, the acid site number of the composite powder is more than 30 mu mol/g, and the specific surface area is more than 160m2The catalyst has the advantages of low cost and meeting the requirements of high-alkali flue gas SCR denitration catalyst carriers.
Drawings
FIG. 1(a) SSZ-13 molecular sieve and FIG. 1(b) SSZ-13@ meso-SO in core-shell structure4 2-/TiO2TEM photograph of the molecular sieve;
FIG. 2 is a SSZ-13 molecular sieve and core-shell structure SSZ-13@ meso-SO4 2-/TiO2MoleculeAn XRD spectrogram of the sieve;
FIG. 3 shows V before and after alkalosis obtained in example 2 of the present invention2O5/TiO2-WO3-SSZ-13@SO4 2-/TiO2Novel catalyst and V2O5/TiO2-WO3NH of commercial catalysts3-SCR activity map;
FIG. 4 shows V before and after alkalosis obtained in example 2 of the present invention2O5/TiO2-WO3-SSZ-13@SO4 2-/TiO2Novel catalyst and V2O5/TiO2-WO3NH of commercial catalysts3-a TPD spectrum;
FIG. 5 shows V before and after alkalosis obtained in example 2 of the present invention2O5/TiO2-WO3-SSZ-13@SO4 2-/TiO2Novel catalyst and V2O5/TiO2-WO3H of commercial catalysts2-TPR spectrum.
Detailed Description
The following describes embodiments of the present invention in detail with reference to the drawings and examples, wherein the reagents used in the examples are analytical reagents.
Preparation of core-shell CHA/AEI molecular sieves
Preparation example 1
(S1) adding an SSZ-13 molecular sieve into a mixed solution of tetrahydrofuran and dimethylformamide (volume ratio is 4:1), wherein the solid-liquid mass ratio is 1:200, and performing ultrasonic oscillation for 2 hours to obtain a suspension. And then dissolving a tetrahydrofuran solution in which tetrabutyl titanate is dissolved, wherein the volume ratio of the tetrabutyl titanate to the tetrahydrofuran is 1:20, and the mass ratio of the tetrabutyl titanate to the SSZ-13 molecular sieve is 11: 500, the solution is added dropwise to the suspension while stirring, and a precipitate is gradually formed. Stirring for 2H after precipitation is complete, adding H2Mixture of O and tetrahydrofuran, H2The mass ratio of O to tetrahydrofuran is 1:10 to ensure complete hydrolysis of the tetrabutyl titanate precursor, wherein the water H2The mass ratio of O to tetrabutyl titanate is 1:2, and ultrasonic treatment is carried out for 2 hours after the dropwise addition is finished. Then washing the mixture with ethanol for 4 times, and then removingWashing the seed with water to neutrality, and drying in a vacuum drying oven at 50 deg.C under-0.06 MPa for 12 hr. After drying, the catalytic material is firstly N2Calcining for 10h at 350 ℃ under the protection of atmosphere, wherein the heating rate is 5 ℃/min. Then calcining for 4h at 450 ℃ in the air atmosphere, wherein the heating rate is 2 ℃/min. The obtained material is the non-acidified core-shell structure SSZ-13@ meso-TiO2。
(S2) the above SSZ-13@ meso-TiO2The material is added to 1mol/L of H2SO4The solution was stirred for 1h and then dried under rotary vacuum using a rotary evaporator at 70 ℃. Then the material after rotary drying is firstly processed by N2Calcining for 15h at 400 ℃ under the protection of atmosphere, wherein the heating rate is 6 ℃/min; then calcining for 4h at 500 ℃ in the air atmosphere, wherein the heating rate is 3 ℃/min. The obtained material is the core-shell structure SSZ-13@ meso-SO4 2-/TiO2In which SO4 2-The content of the molecular sieve is 6.3 percent of the total mass of the shell layer, and SSZ-13 accounts for 87.5 percent of the total molecular sieve with the core-shell structure. The obtained core-shell structure SSZ-13@ meso-SO4 2-/TiO2Specific surface area of 663m2The number of surface acid sites was 106. mu. mol/g. The obtained core-shell structure SSZ-13@ meso-SO4 2-/TiO2Respectively carrying out TEM and XRD characterization, and respectively observing SSZ-13 and core-shell structure SSZ-13@ meso-SO4 2-/TiO2The micro-morphology and the crystal structure of the crystal. SSZ-13@ meso-SO can be seen from the TEM transmission electron micrograph of FIG. 14 2-the/TiO 2 has an increased shell structure compared with SSZ-13. In FIG. 2, SSZ-13@ meso-SO4 2-/TiO2Is close to the characteristic diffraction peak of SSZ-13, no new diffraction peak appears, and the position of the characteristic peak is not changed, which indicates that the shell component is highly dispersed on the surface of SSZ-13 and the crystal structure of the SSZ-13 is not damaged.
Preparation example 2
The other conditions were the same as in preparation example 1 except that SSZ-13@ meso-TiO was used in step (S2)2Addition of materials to H2S2O8The solution was stirred for 1 h. Finally obtaining the core-shell structure SSZ-13@ meso-S2O8 2-/TiO2In which S is2O8 2-The content of the molecular sieve is 5.6 percent of the total mass of the shell layer, and SSZ-13 accounts for 89.3 percent of the total molecular sieve with the core-shell structure. The obtained core-shell structure SSZ-13@ meso-S2O8 2-/TiO2Has a specific surface area of 659m2The number of surface acid sites was 98. mu. mol/g.
Preparation example 3
The other conditions were the same as in preparation example 1, except that in the step (S1), the first organic solvent was replaced with a simple tetrahydrofuran solvent from a mixed solvent of tetrahydrofuran and dimethylformamide, and the resulting core-shell structure SSZ-13@ meso-SO4 2-/TiO2Specific surface area of 521m2The number of surface acid sites was 65. mu. mol/g. This indicates that one-step hydrolysis results in SO4 2-/TiO2The dispersity is reduced, and the specific surface area and the number of acid sites of the core-shell material are reduced.
Preparation example 4
The other conditions are the same as those in preparation example 1, except that the step (S2) is reduced to one-step air calcination, specifically, the temperature of the rotary dried material is raised to 500 ℃ at the temperature raising rate of 6 ℃/min in the air, and the material is calcined for 19h, SO that the core-shell structure SSZ-13@ meso-SO is obtained4 2-/TiO2Specific surface area of 285m2The number of surface acid sites was 42. mu. mol/g. This indicates that one calcination step results in SO4 2-/TiO2The shell layer agglomeration and the mesopores are reduced, thereby reducing the specific surface area and the acid site number of the core-shell material.
Preparation example 5
The other conditions were the same as in preparation example 1, except that in step (S1), tetrabutyl titanate was replaced with tetrabutyl zirconate, molecular sieve SSZ-13 was replaced with SAPO-34, and the mass ratio of tetrabutyl zirconate to molecular sieve SAPO-34 was 15: 500. finally obtaining SAPO-34@ SO with core-shell structure4 2-/ZrO2In which SO4 2-Accounting for 5.7 percent of the mass of the solid super acid, and the SAPO-34 accounting for 88.1 percent of all the molecular sieves with the core-shell structure. The obtained core-shell structure SAPO-34@ SO4 2-/ZrO2Has a specific surface area of 579m2The number of surface acid sites was 86. mu. mol/g.
Comparative preparation example 1
The other conditions were the same as in preparation example 1 except that in step (S2), the obtained SSZ-13@ meso-TiO was used2The material was dried under rotary vacuum using a rotary evaporator at 70 ℃. Then in N2Calcining for 15h at 400 ℃ under the protection of atmosphere, wherein the heating rate is 6 ℃/min; then calcining for 4h at 500 ℃ in the air atmosphere, wherein the heating rate is 3 ℃/min. The obtained material is SSZ-13@ meso/TiO2I.e. the molecular sieve has not been modified by solid superacid. The resulting SSZ-13@ meso/TiO2Has a specific surface area of 669m2However, the number of surface acid sites is only 25. mu. mol/g, so that the molecular sieve which is not modified by the solid super strong acid has a smaller number of acid sites, and is expected to have a weak anti-poisoning ability.
Example 1
Step 1: dissolving 0.55g of ammonium metatungstate in distilled water to obtain an ammonium metatungstate solution;
step 2: 8.5g of superfine low-sulfur TiO2Powder and 1g of SSZ-13@ SO obtained in production example 14 2-/TiO2Dispersing molecular sieve powder in ammonium metatungstate solution in an ultrasonic mode to obtain TiO2And SSZ-13@ SO4 2-/TiO2Molecular sieve suspension;
and step 3: adding 0.5ml of nitric acid into the obtained suspension, and then stirring for 2 hours at the temperature of 40 ℃;
and 4, step 4: performing microwave vacuum drying on the stirred product under the conditions of 50 ℃ of temperature, 50W of microwave power and 300Pa of vacuum degree;
and 5: calcining the dried product under the conditions that the temperature programming rate is 5 ℃/min, the calcining temperature is 500 ℃ and the constant-temperature calcining time is 4 hours;
step 6: ball-milling the calcined product in a ball mill to obtain TiO with the particle size of 1-5 mu m2-WO3-SSZ-13@SO4 2-/TiO2A composite powder having a surface area of 348m2A surface acid site number of 52. mu. mol/g, an average pore diameter of12.5 nm. In the obtained composite powder, WO35.7 wt.% of SSZ-13@ SO4 2-/TiO211.5 wt% of the balance TiO2。
1g of TiO2-WO3-SSZ-13@SO4 2-/TiO2And (3) putting the composite powder into a tubular furnace, introducing air with the water vapor concentration of 5%, and calcining at 650 ℃ for 18h to obtain a hydrothermal aging sample. Carrying out nitrogen adsorption and desorption experiments by utilizing physical adsorption, and then calculating by utilizing a BET formula to obtain the specific surface area of the hydrothermal aging sample, wherein the specific surface area of the hydrothermal aging sample is 253m2/g。
The TiO obtained in example 12-WO3-SSZ-13@SO4 2-/TiO2The composite powder was subjected to 1.5 wt% K2Forced alkalosis treatment of O: specifically, 1g of TiO2-WO3-SSZ-13@SO4 2-/TiO2The composite powder is put into agate mortar, slowly dropped with water solution containing 0.019gKOH, and then dried for 12h at 100 ℃ to obtain a forced alkalosis sample. Carrying out nitrogen adsorption and desorption experiments by utilizing physical adsorption, and then calculating by utilizing a BET formula to obtain the specific surface area of the alkalosis sample, wherein the specific surface area of the alkalosis sample is 266m2(ii) in terms of/g. At the same time, using NH3TPD test found that the number of acid sites on the surface of the sample subjected to alkali poisoning is 43. mu. mol/g.
Example 2
Step 1: dissolving 0.55g of ammonium metatungstate in distilled water to obtain an ammonium metatungstate solution;
step 2: 4.5g of ultrafine low-sulfur TiO2Powder and 5g of SSZ-13@ SO having a core-shell structure obtained in preparation example 14 2-/TiO2Dispersing molecular sieve powder in ammonium metatungstate solution in an ultrasonic mode to obtain TiO2And a suspension of SSZ-13 molecular sieve;
and step 3: adding 1ml of nitric acid into the obtained suspension, and then stirring for 4 hours at 50 ℃;
and 4, step 4: spray drying the stirred product under the conditions that the liquid flow rate is 3ml/min, the outlet of an air compressor is maintained at 1 atmosphere, and the drying temperature is maintained at 100 ℃;
and 5: calcining the dried product under the conditions that the temperature programming rate is 10 ℃/min, the calcining temperature is 550 ℃ and the constant-temperature calcining time is 3 hours;
step 6: ball-milling the calcined product in a ball mill to obtain TiO with the particle size of 1-5 mu m2-WO3-SSZ-13@SO4 2-/TiO2The surface area of the composite powder is 594m2The number of surface acid sites is 83. mu. mol/g, the average pore diameter is 10.1nm, WO35.3 wt.% of SSZ-13@ SO4 2-/TiO253.6 wt% and the balance TiO2。
And 7: 0.032g of ammonium metavanadate was dissolved in 100ml of water to obtain an aqueous solution thereof.
And 8: 1g of TiO obtained in step 62-WO3-SSZ-13@SO4 2-/TiO2Fully dispersing in the ammonium metavanadate aqueous solution, performing vacuum drying at 70 ℃ by using a rotary evaporator, calcining the dried product for 4 hours in an air atmosphere at 450 ℃ to finally obtain V2O5/TiO2-WO3-SSZ-13@SO4 2-/TiO2Denitration catalyst composite powder of V2O5In an amount of 2.4 wt.%, WO3The content is 5.2 wt%, and the CHA/AEI molecular sieve with a core-shell structure SSZ-13@ SO4 2-/TiO2The content was 52.3% by weight, and the surface area was 588m2The number of surface acid sites was 80. mu. mol/g, and the average pore diameter was 10.4 nm.
And step 9: v obtained in the step 82O5/TiO2-WO3-SSZ-13@SO4 2-/TiO2Denitration catalyst for 1.5 wt% K2Forced alkalosis treatment of O, surface area 581m2The number of surface acid sites was 77. mu. mol/g, and the average pore diameter was 10.5 nm.
Step 10: by means of NH3SCR Activity evaluation device, NH3TPD plant and H2TPR device for testing V before and after poisoning2O5/TiO2-WO3-SSZ-13@SO4 2-/TiO2And commercial V2O5/TiO2-WO3The denitration performance, the acid site number and the oxygen reduction performance of the catalyst are shown in the attached figures 3-5. It can be seen that example 2 produces V2O5/TiO2-WO3-SSZ-13@SO4 2-/TiO2The composite denitration powder has excellent catalytic denitration capability and alkali poisoning resistance, and the denitration powder is subjected to 1.5 wt% of K2After the forced alkali poisoning treatment of O, the denitration catalytic capability of the O is basically not reduced, and the requirement of high alkali poisoning resistance in cement and other industrial flue gas and the like can be met.
Example 3
The other conditions and operations were the same as in example 2 except that the molecular sieve of core-shell structure prepared in preparation example 1 in step 2 was replaced with the molecular sieve of core-shell structure prepared in preparation example 2 of the same mass.
Example 4
The other conditions and operations were the same as in example 2 except that the molecular sieve of core-shell structure prepared in preparation example 1 in step 2 was replaced with the molecular sieve of core-shell structure prepared in preparation example 3 of the same mass.
Example 5
The other conditions and operations were the same as in example 2 except that the molecular sieve of core-shell structure prepared in preparation example 1 in step 2 was replaced with the molecular sieve of core-shell structure prepared in preparation example 4 of the same mass.
Example 6
Step 1: dissolving 0.9g of ammonium metatungstate in distilled water to obtain an ammonium metatungstate solution;
step 2: mixing 6g of superfine low-sulfur TiO2Powder and 3g of SAPO-34@ SO having a core-shell structure prepared in preparation example 54 2-/ZrO2Dispersing molecular sieve powder in ammonium metatungstate solution in an ultrasonic mode to obtain TiO2And SAPO-34@ SO4 2-/ZrO2Molecular sieve suspension;
and step 3: adding 0.8ml of triethylamine into the obtained suspension, and then stirring for 6 hours at 70 ℃;
and 4, step 4: performing microwave vacuum drying on the stirred product under the conditions of 70 ℃ of temperature, 100W of microwave power and 200Pa of vacuum degree;
and 5: calcining the dried product under the conditions that the temperature programming rate is 8 ℃/min, the calcining temperature is 600 ℃ and the constant-temperature calcining time is 6 hours;
step 6: grinding the calcined product in an airflow grinder to obtain TiO with the particle size of 1-5 mu m2-WO3-SAPO-34@SO4 2-/ZrO2A composite powder having a surface area of 446m2The number of surface acid sites is 65. mu. mol/g, the average pore diameter is 11.8nm, WO3SAPO-34@ SO of 9.2 wt.% content4 2-/ZrO233.6 wt%, the balance being TiO2。
And 7: 0.04g of ammonium metavanadate was dissolved in 100ml of water to obtain an aqueous solution thereof.
And 8: 1g of TiO prepared in step 62-WO3-SAPO-34@SO4 2-/ZrO2Fully dispersing the composite powder in the ammonium metavanadate aqueous solution, performing vacuum drying at 70 ℃ by using a rotary evaporator, calcining the dried product for 4 hours in an air atmosphere at 450 ℃ to finally obtain V2O5/TiO2-WO3-SAPO-34@SO4 2-/ZrO2Denitration catalyst of wherein V2O5In an amount of 3.1 wt%, WO3SAPO-34@ SO in an amount of 9.0 wt%4 2-/ZrO2The content is 32.8 wt%, and the balance is TiO2。
And step 9: v obtained in the step 82O5/TiO2-WO3-SAPO-34@SO4 2-/ZrO2Denitration catalyst for 1.5 wt% K2And (4) performing forced alkali poisoning treatment on the O.
Comparative example 1
The other conditions and operation were the same as in example 2 except that the molecular sieve of core-shell structure obtained in preparation example 1 in step 2 was replaced with the molecular sieve SSZ-13@ meso/TiO prepared in comparative preparation example 1 of equal mass2。
Application example
The composite denitration powder obtained in the above examples and comparative examples was used as a catalyst to perform a denitration experiment under the following conditions, and the concentration (vol%) of each gas was controlled by a mass flow meter, and the ratio of NO: 500ppm, NH3：500ppm，O2：5％， N2For balance gas, the total gas flow is 1000mL/min, the catalyst dosage is 200mg, the temperature is 275 ℃, and the catalyst is divided into fresh catalyst and 1.5 wt% of K2After O-forced alkalosis, the results are shown in table 1 below:
the denitration efficiency is calculated by the formula of eta ═ C1-C2)/C1 x 100%, wherein C1 is NOxC2 is NOxThe concentration at the outlet of (2) is measured by a flue gas analyzer.
TABLE 1
Figure BDA0003316299550000101
The data in table 1 show that the composite denitration powder obtained by loading denitration active ingredients on the carrier of the CHA/AEI molecular sieve with the core-shell structure has beneficial alkali poisoning resistance and still has good catalytic activity even after forced alkali poisoning; the composite denitration powder disclosed by the invention is simple in preparation process, low in cost and easy to obtain raw materials, and is very suitable for being used as a denitration catalyst in an alkaline environment, particularly in a metal K alkaline environment, such as cement kiln denitration and other industrial flue gases.

Claims (10)

1. A high-alkali-resistance composite denitration powder is prepared from solid superacid modified core-shell CHA/AEI molecular sieve and TiO2The carrier is loaded with denitration active ingredients and auxiliaries to obtain the denitration catalyst, the solid super acid is a shell, and the CHA/AEI molecular sieve is a core.
2. The composite denitration powder of claim 1, wherein the CHA/AEI molecular sieve comprises at least one of SSZ-13, SAPO-34, SSZ-16, and SSZ-39;
the solid super acid is represented by SaO4a 2-/MO2Wherein a is between 1 and 2, M is Ti and/or Zr; examples of solid superacids include, but are not limited to, SO4 2-/TiO2、SO4 2-/ZrO2、S2O8 2-/TiO2、S2O8 2-/ZrO2At least one of (1).
3. The composite denitration powder of claim 1, wherein the high alkali-resistant composite denitration powder comprises the following components by mass: 0.1-10 wt% of denitration active component, 1-15 wt% of assistant, 10-70 wt% of core-shell structure CHA/AEI molecular sieve, and the balance TiO2。
4. The composite denitration powder of claim 3, wherein the high alkali-resistant composite denitration powder comprises the following components by mass: 1-5 wt% of denitration active component, 5-10 wt% of assistant, 30-55 wt% of core-shell structure CHA/AEI molecular sieve, and the balance TiO2。
5. The composite denitration powder of claim 1, wherein the denitration active component is a transition metal oxide, and the transition metal is at least one selected from vanadium, gallium, germanium, tin, cobalt, cerium, lanthanum and iron, preferably vanadium; the auxiliary agent is selected from at least one of oxides of tungsten, iron, yttrium and copper, and is preferably tungsten.
6. The composite denitration powder of claim 1, wherein the particle size of the composite denitration powder is 1 to 5 μm, and the specific surface area is 200 to 600m2The number of surface acid sites is more than 40 mu mol/g, and the average pore diameter is less than 13 nm.
7. The composite denitration powder of claim 1, wherein in the CHA/AEI molecular sieve with the core-shell structure, S is contained in solid super acid as a shellaO4a 2-1-10 wt%, preferably 3-7%, and the balance of MO2(ii) a CHA/AEI moleculesThe sieve accounts for 70-90 wt% of the CHA/AEI molecular sieve with the core-shell structure.
8. The composite denitration powder of claim 2, wherein the CHA/AEI molecular sieve with the core-shell structure is prepared by a preparation method comprising the following steps:
(S1) adding the CHA/AEI molecular sieve into the first organic solvent to disperse, slowly adding a titanium source and/or a zirconium source to generate a precipitate, adding a mixed solution of a second organic solvent and water, performing ultrasonic treatment, washing, and drying;
(S2) adding the material dried in the step (S1) to H2SO4And/or H2S2O8And drying the solution, sequentially calcining for the first time in an inert atmosphere and calcining for the second time in an oxygen atmosphere to obtain the CHA/AEI molecular sieve with the core-shell structure.
9. The composite denitration powder of claim 8, wherein in the step (S1), the total mass of the titanium source and/or the zirconium source and the mass ratio CHA/AEI are 1: 30-60, preferably 1: 40-50;
in the step (S1), the first organic solvent is a mixed solvent of tetrahydrofuran and dimethylformamide, and the second organic solvent is selected from tetrahydrofuran; furthermore, the volume ratio of the tetrahydrofuran to the dimethylformamide is 4-6:1, and the dosage of the first organic solvent is 500 times of the mass of the molecular sieve; the volume ratio of the second organic solvent to the water is 10-20: 1.
10. The method for preparing the composite denitration powder of any one of claims 1 to 9, comprising the steps of:
mixing active component precursor, assistant precursor and TiO2Fully dispersing the precursor and the CHA/AEI molecular sieve powder with the core-shell structure in the presence of a dispersing agent, drying, calcining and grinding to obtain the product;
preferably, an auxiliary agent precursor, TiO is adopted2The method for preparing the composite denitration powder by the segmented method of the precursor and the active component precursor comprises the following steps:
(P1) mixing the precursor of the auxiliary agent and TiO2Fully dispersing the precursor and the CHA/AEI molecular sieve powder with the core-shell structure in the presence of a dispersing agent, drying, calcining and grinding to obtain powder;
(P2) dispersing the powder obtained in the step (P1) in an aqueous solution of an active ingredient precursor, drying and calcining to finally obtain composite denitration powder;
the active component precursor, the auxiliary agent precursor and TiO2The mass ratio of the precursor to the CHA/AEI molecular sieve powder with the core-shell structure is 0.1-0.5:1-10:40-80: 20-50; preferably 0.2-0.4:4-10:45-70: 30-50.
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