CN113244949B - High-durability BEA molecular sieve catalyst with core-shell structure, preparation method and application thereof - Google Patents

High-durability BEA molecular sieve catalyst with core-shell structure, preparation method and application thereof Download PDF

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CN113244949B
CN113244949B CN202110716496.2A CN202110716496A CN113244949B CN 113244949 B CN113244949 B CN 113244949B CN 202110716496 A CN202110716496 A CN 202110716496A CN 113244949 B CN113244949 B CN 113244949B
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molecular sieve
sieve catalyst
bea
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CN113244949A (en
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李凯祥
贾凌峰
李振国
刘坚
王建海
任晓宁
邵元凯
吕丛杰
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China Automotive Technology and Research Center Co Ltd
CATARC Automotive Test Center Tianjin Co Ltd
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Abstract

The invention provides a high-durability BEA molecular sieve catalyst with a core-shell structure, a preparation method and application thereof. The catalyst provided by the invention has excellent ammonia adsorption capacity, low-temperature activity, temperature operation window and N in Urea-SCR technology by virtue of the intrinsic activity of Sm element2Selectivity and structural stability, and the use of a high stability oxide shell to protect the core BEA molecular sieve catalyst from large amounts of SO2And high-temperature water vapor, on the other hand, the active components are inhibited from migrating at high temperature, and the durability is further improved.

Description

High-durability BEA molecular sieve catalyst with core-shell structure, preparation method and application thereof
Technical Field
The invention belongs to the technical field of catalyst preparation, and particularly relates to a high-durability BEA molecular sieve catalyst with a core-shell structure, a preparation method and application thereof.
Background
The motor vehicle output and sales volume of China is steadily at the top of the world for 11 years continuously, the motor vehicle keeping volume of 2020 breaks through 3.72 hundred million vehicles, and the problem of the emission of mobile source pollutants such as motor vehicles and the like is increasingly highlighted. According to annual report of environmental management of China Mobile resources (2020), the total emission of four pollutants of motor vehicles in the whole country in 2019 is preliminarily accounted to 1603.8 ten thousand tons. Wherein carbon monoxide (CO), Hydrocarbon (HC), and Nitrogen Oxide (NO)X) The emission amount of Particulate Matters (PM) is 771.6 ten thousand tons, 189.2 ten thousand tons, 635.6 ten thousand tons and 7.4 ten thousand tons respectively, which is one of the main sources of urban air pollution in China. NO, one of the main pollutants of motor vehicle exhaustXIs an excellent source for causing severe environmental problems such as haze, photochemical smog, acid rain and the like, and seriously harms the health of people.
As internationally recognized catalytic clean-up diesel NOXThe selective catalytic reduction (scr) technology is a main technical route for diesel engines to achieve national VI emission regulations, and the technology has been applied in various countries. The catalyst is the core and key of the SCR technology. The temperature range of the tail gas of the diesel vehicle under the normal working condition is wider (200 plus 500 ℃), and the temperature is generally lower than 200 ℃ during cold start, so that higher requirements are provided for the low-temperature activity of the catalyst. Meanwhile, instantaneous high temperature generated during DPF active regeneration reaches more than 750 ℃, and the catalyst is required to have better hydrothermal stability. In addition, the exhaust gas atmosphere of diesel vehicles contains a large amount of hydrocarbon, which provides a challenge to the hydrocarbon poisoning resistance of the catalyst. In the IV/V stage of China, a vanadium-based catalyst (V) taking titanium-tungsten powder as a carrier2O5-WO3/TiO2) The catalyst has wide application in China, but has high toxicity and low temperatureLow conversion rate, poor high-temperature selectivity and the like. Molecular sieve catalysts are of great interest because of their high activity, good selectivity, environmental friendliness, and the like. After transition metal exchanged ZSM-5 molecular sieve catalysts have been reported to have better SCR activity since the 90 s of the last century, copper-based molecular sieve catalysts such as FAU, CHA, BEA, LTA, etc. were successively investigated for the removal of NOx by SCR technology. The iron-based BEA structure molecular sieve has good low-temperature performance and nitrogen selectivity, and the catalytic material belongs to a green environment-friendly material. However, the actual exhaust gas atmosphere in practical applications is usually accompanied by a high temperature, high hydrothermal and sulfur-containing atmosphere, resulting in a material that is susceptible to deactivation.
The patent with publication number CN112536066A relates to a preparation method of a mesoporous Fe-Beta molecular sieve catalyst containing a core-shell structure, which constructs a Fe-C-Al precursor with the core-shell structure, and the prepared Fe-Beta molecular sieve catalyst has a mesoporous structure communicated with the core-shell structure, and has the advantages of high product crystallinity, high specific surface area, rich mesopores and uniform iron distribution. But SO2Molecules can enter the core through the mesopores, contact with the Fe/BETA catalyst and deactivate the catalyst, and the catalyst does not have the capability of resisting sulfur poisoning.
The patent with the publication number of CN107029782A relates to a core-shell catalyst for FCC regenerated flue gas denitration and a preparation method thereof, and the method has complicated steps including equal-volume impregnation and ultrasonic dispersion, and has long preparation period and can not be realized in the actual large-scale production process.
The patent with the publication number of CN105253895A relates to a Beta molecular sieve with high content of Fe in a framework and a preparation method thereof, and the method fixes Fe in the framework structure of the molecular sieve, thereby greatly improving the thermal stability, but being incapable of solving the problem of sulfur poisoning resistance.
Disclosure of Invention
In view of the above, the present invention aims to provide a BEA molecular sieve catalyst with a high durable core-shell structure, a preparation method and applications thereof, SO as to improve the SO resistance of the catalyst2Poisoning ability and high temperature hydrothermal resistance.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the high-durability BEA molecular sieve catalyst with the core-shell structure comprises an inner core and a shell layer wrapped on the inner core, wherein the inner core is a modified Sm-based BEA molecular sieve catalyst, and the shell layer is made of an oxide.
Preferably, the material of the shell layer is at least one of alumina, cerium oxide, titanium oxide, silicon oxide and zirconium oxide.
Preferably, the thickness of the shell layer is less than or equal to 20 nm.
A preparation method of a BEA molecular sieve catalyst with a high-durability core-shell structure comprises the following steps:
(1) preparing a modified Sm-based BEA molecular sieve catalyst;
(2) mixing the modified Sm-based BEA molecular sieve catalyst with an oxide to prepare a BEA molecular sieve catalyst precursor with a core-shell structure;
(3) centrifuging a precursor of the core-shell structure BEA molecular sieve catalyst to obtain a solid, and drying and roasting the solid to prepare the core-shell structure BEA molecular sieve catalyst; preferably, the roasting temperature is 400-600 ℃, and the roasting time is 2-5 h.
Preferably, the specific operation of step (1) comprises the following steps:
ion exchange, dissolving a soluble active component samarium precursor in deionized water, stirring until the soluble active component samarium precursor is completely dissolved, adding a BEA structure molecular sieve, adding an accelerant, heating and stirring to perform an ion exchange reaction, preparing an Sm/BEA molecular sieve catalyst precursor, adding a soluble auxiliary agent, heating and stirring to prepare a modified Sm/BEA molecular sieve catalyst precursor;
reducing the temperature of the modified Sm/BEA molecular sieve catalyst precursor to below 50 ℃, and starting negative pressure to evaporate the solvent to obtain powder;
soaking for multiple times, adding deionized water and soluble auxiliary agent into the powder, stirring for dissolving for soaking, reacting for 10-60 min, evaporating under reduced pressure again to obtain powder, and repeating for 2-3 times;
and (3) fine grinding, namely fine grinding the powder obtained after multiple soakings, drying and roasting to obtain the modified Sm-based BEA molecular sieve catalyst with the particle size of 100 nm.
Preferably, the soluble active component samarium precursor is samarium salt which is soluble in water and has a molecular weight of less than 1000, the BEA structure molecular sieve comprises at least one of Beta and CIT-6, the promoter comprises at least one of acetic acid, phosphoric acid, formic acid, nitric acid, carbonic acid, ammonium carbonate, ammonium nitrate, ammonium phosphate and ammonium acetate, the soluble auxiliary agent is a compound which is soluble in water and has a molecular weight of less than 1000 and contains metal elements, and the metal elements comprise at least one of Fe, Cu, Ce, Mn, Y, Pr, Ni, Co, Pt, Pd and Rh; preferably, the soluble active component samarium precursor is at least one of samarium nitrate and samarium chloride, the BEA structure molecular sieve is a Beta molecular sieve, and the metal elements are Fe, Cu, Ce and Mn.
Preferably, the reaction temperature of ion exchange is 60-140 ℃, the reaction time of ion exchange is 1-10h, the water content in the powder obtained by reduced pressure evaporation is less than 6.5 wt%, the molar ratio of the soluble active component samarium precursor to the soluble auxiliary agent is 1:0.01-10, the ratio of the mass sum of the soluble active component samarium precursor and the soluble auxiliary agent to the mass of the BEA structure molecular sieve is 0.001-0.2: 1, the mass ratio of the singly supplemented deionized water to the BEA structure molecular sieve is 0.5-10:1, finely grinding for 1-6h, drying at 80-100 ℃ after finely grinding for 6-24 h; preferably, the reaction temperature of ion exchange is 60-80 ℃, the reaction time of ion exchange is 4-8h, the molar ratio of the soluble active component samarium precursor to the soluble auxiliary agent is 1:0.1-3, the ratio of the mass sum of the soluble active component samarium precursor and the soluble auxiliary agent to the mass of the BEA structure molecular sieve is 0.02-0.05: 1, the mass ratio of the singly supplemented deionized water to the BEA structure molecular sieve is 1-2.5: 1, the time for fine grinding is 3-4 h.
Preferably, the specific operation of step (2) comprises the following steps:
performing ultrasonic dispersion, namely placing the modified Sm-based BEA molecular sieve catalyst in an organic alcohol solvent for ultrasonic dispersion to obtain a suspension;
performing electrostatic adsorption, namely adding ammonia water into the suspension to adjust the pH to 8-10, forming electrostatic adsorption charges on the surfaces of the modified Sm-based BEA molecular sieve catalyst powder particles, adding a shell oxide precursor, and stirring and dispersing to form a uniform mixed solution;
and (3) coating a shell layer, namely heating the mixed solution for reflux reaction, and coating the shell layer to obtain the BEA molecular sieve catalyst precursor with the core-shell structure.
Preferably, the organic alcohol solvent comprises at least one of ethanol, methanol, ethylene glycol, glycerol and isopropanol, and the modified Sm-based BEA molecular sieve catalyst comprises the following components in percentage by weight: the organic alcohol solvent has a mass concentration of 0.0001-10g/ml, and the shell oxide precursor comprises tetrabutyl titanate, titanium sol, aluminum sol, silica sol, water glass, tetraethyl silicate, titanic acid, and ZrO2、TiO2、Al2O3、SiO2、CeO2Cerium nitrate, sodium aluminate, sodium silicate, aluminum nitrate, cerous cyclohexylammonium, shell oxide precursor: the mass concentration of the organic alcohol solvent is 0.001-30g/ml, the temperature of the reflux reaction is 25-50 ℃, and the reflux reaction time is 8-24 h; preferably, the organic alcohol solvent is methanol or ethanol, and the modified Sm-based BEA molecular sieve catalyst is as follows: the mass concentration of the organic alcohol solvent is 0.005-2g/ml, and the mass concentration of the shell oxide precursor is as follows: the mass concentration of the organic alcohol solvent is 0.1-10 g/ml.
The application of the BEA molecular sieve catalyst with the high-durability core-shell structure in selective reduction elimination of nitrogen oxides in tail gas.
Compared with the prior art, the high-durability BEA molecular sieve catalyst with the core-shell structure, the preparation method and the application thereof have the following advantages:
(1) the high-durability BEA molecular sieve catalyst with the core-shell structure shows excellent ammonia adsorption capacity, low-temperature activity, temperature operation window and N in the Urea-SCR technology by virtue of the intrinsic activity of Sm element2Selectivity and structural stability;
(2) the preparation method of the high-durability BEA molecular sieve catalyst with the core-shell structure adopts multiple soakings, can obviously improve the enrichment condition of oxides on the surface of the molecular sieve carrier, and ensures the low-temperature performance and the temperature window of the molecular sieve SCR catalyst;
(3) the high-durability core-shell structure BEA molecular sieve catalyst utilizes a high-stability oxide shell layer to protect the core BEA molecular sieve catalyst from contacting a large amount of SO2High temperature water vapor, the other partyThe surface inhibition active component is migrated at high temperature, so that the durability is improved, meanwhile, the modified Sm/BEA catalyst serving as the kernel has high activity and high thermal stability, and the kernel and the shell are mutually cooperated;
(4) the shell layer and the inner core of the high-durability BEA molecular sieve catalyst with the core-shell structure can form a unique core-shell interface, the core-shell interface effect can provide a stable catalytic oxidation reduction circulation place, and meanwhile, the shell layer has strong HC poisoning resistance, so that the catalyst has a wide reaction temperature window and strong HC poisoning resistance;
(5) the preparation method of the high-durability BEA molecular sieve catalyst with the core-shell structure is continuous and easy to operate, the thickness of the prepared nano shell layer is uniform, the consistency of products with the core-shell structure is good, and the preparation method is suitable for large-scale production.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 shows Fe-Sm/Beta @ TiO in accordance with an embodiment of the present invention2Scanning electron micrographs of the sample and its EDS;
FIG. 2 shows Fe-Sm/Beta @ TiO in an embodiment of the present invention2X-ray diffraction patterns of three samples of Fe-Sm/Beta and H-Beta;
FIG. 3 shows 2.5Fe-0.5Sm/Beta @ TiO in accordance with an embodiment of the present invention2、2.5Fe-0.5Sm/Beta@TiO2-Δ、0.5Fe-2.5Sm/Beta@TiO2,0.5Cu-2.5Sm/Beta@TiO2、2.5Fe-0.5Sm/Beta@TiO2NO of-. DELTA.XAnd (4) a schematic diagram of removal efficiency.
Detailed Description
Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.
In the examples of the invention and comparative examples, NH3Simulated smoke composition used for SCR performance testing: 500 ppm NO, 500 ppm NH3,5% O2,N2For balancing gas, the total flow is 1000 ml/min, and the reaction space velocity is 30000 h-1
In the examples of the invention and comparative examples, the low temperature Performance index T50When NO is representedXThe temperature corresponding to the conversion rate of 50%; temperature window index T90When NO is representedXThe temperature range corresponding to a conversion of more than 90%. N is a radical of2Selectivity is the arithmetic mean of the nitrogen selectivity data at each test temperature point within the range of 175-525 ℃.
The present invention will be described in detail with reference to the following embodiments and drawings, it being understood that the preferred embodiments described herein are merely for the purpose of illustrating and explaining the present invention and are not intended to limit the present invention.
Unless otherwise indicated, all numbers expressing quantities such as temperature, time, and mass percent of slurry feed, as used in the specification and claims are to be understood as being modified in all instances by the term "about" and not necessarily by the term "about".
1. Preparation of Sm/Beta catalyst
Weighing 10g of samarium nitrate, stirring and dissolving the samarium nitrate in 250g of deionized water, adding a 5g H type Beta molecular sieve, adding acetic acid to adjust the pH to be about =3, heating to 80 ℃ to perform ion exchange reaction for 6 hours, performing high-speed centrifugation to realize solid-liquid separation, repeatedly washing the solid with 50ml of deionized water for 3 times until the filtrate is colorless, drying at 120 ℃ for 8 hours, testing the content of Sm element by ICP (inductively coupled plasma) and marking as a 2.5Sm/Beta catalyst.
Similarly, the sample with the mass fraction of 0.1-7.5% can be prepared by adjusting the adding amount of the samarium nitrate, and the sample is marked as 0.1-7.5 Sm/Beta catalyst.
2. Preparation of modified Sm/Beta catalyst
Selecting 10g of 0.5Sm/Beta catalyst powder, uniformly stirring and dispersing the powder in 300 ml of deionized water, adding 1.08 g of ferric nitrate into the solution according to the stoichiometric ratio (molar ratio) of Fe/Sm =5:1, stirring and dissolving, carrying out ion exchange reaction at the constant temperature of 80 ℃ for 6 hours, starting reduced pressure evaporation, evaporating on an optional evaporator until the water content in the dry powder is 6%, and stopping evaporation; supplementing 15 g of deionized water into the dry powder, fully mixing and wetting, then carrying out reduced pressure evaporation again, repeating the steps for 3 times, drying the obtained powder, testing the Fe element content by XRF (X-ray diffraction) for 2.5 wt%, finely grinding in a planetary ball mill for 2h, intensively distributing the particle size of laser particle size analysis particles to about 100nm, stopping grinding, filtering, washing and drying, and roasting at 550 ℃ for 5h under the protection of nitrogen to obtain catalyst powder which is marked as a 2.5Fe-0.5Sm/Beta catalyst.
In the same way, catalyst powders with different Sm contents are selected, and series (0.5-3.5) Fe- (0.1-3.5) Sm/Beta catalysts are prepared by adjusting the addition of ferric nitrate according to the stoichiometric ratio.
Similarly, different additive elements are selected, and the addition amounts of manganese nitrate, cerium nitrate, cobalt nitrate and copper nitrate are respectively adjusted according to the stoichiometric ratio to prepare series (0.5-3.5) Mn- (0.1-3.5) Sm/Beta, (0.5-3.5) Co- (0.1-3.5) Sm/Beta, (0.5-3.5) Ce- (0.1-3.5) Sm/Beta and (0.5-3.5) Cu (0.1-3.5) Sm/Beta catalysts.
Example 1
Weighing 0.15 g of 2.5Fe-0.5Sm/Beta sample as a core catalyst, ultrasonically dispersing in 150ml of absolute ethyl alcohol for 3 hours, adding 1g of PVP, and continuing to perform ultrasonic treatment for 1 hour until the PVP is completely dissolved. Adding 0.5ml ammonia water, stirring for 1 hr, adjusting pH =9, dripping 1ml tetrabutyl titanate, condensing and refluxing at 45 deg.C for 12 hr, centrifuging, washing, vacuum drying at 60 deg.C for 12 hr, and calcining at 500 deg.C under nitrogen atmosphere for 3 hr, wherein the mark is 2.5Fe-0.5Sm/Beta @ TiO2A core-shell catalyst.
Example 2
The conditions and flow of the catalyst preparation in this example were the same as in example 1 except that the amount of aqueous ammonia was 0.4ml and the amount of tetrabutyl titanate was 1.75 ml. The prepared core-shell catalyst is marked as 2.5Fe-0.5Sm/Beta @ TiO2
Example 3
The preparation conditions and preparation flow of the catalyst of this example were the same as in example 1, except thatThe core catalyst is 0.5Fe-2.5Sm/Beta, and the high-durability core-shell catalyst is prepared and is marked as 0.5Fe-2.5Sm/Beta @ TiO2
Example 4
The conditions and flow for the preparation of the catalyst of this example were the same as in example 1 except that the core catalyst was selected to be 0.5Cu to 2.5Sm/Beta, designated 0.5Cu to 2.5Sm/Beta @ TiO2
Comparative example 1
Referring to the preparation conditions and preparation flow of the Sm/Beta catalyst preparation examples, a 2.5Sm/Beta catalyst was prepared. Different from the example 1, the additive doping modification and the shell coating are not carried out, and the mark is Sm/Beta.
Comparative example 2
Referring to the preparation conditions and the preparation flow in the preparation examples of the Sm/Beta catalyst and the modified Sm/Beta catalyst, 2.5Fe-1.5Sm/Beta catalyst is prepared. Unlike example 1, no shell coating was performed and was labeled 2.5Fe-0.5 Sm/Beta.
Comparative example 3
The catalyst of this example was prepared under the same conditions and in the same manner as in example 1 except that tetrabutyl titanate was used in an amount of 5 ml. The prepared core-shell catalyst is marked as 2.5Fe-0.5Sm/Beta @ TiO2-ΔΔ
Fresh sample performance verification
The core-shell catalysts of examples 1 to 4 and comparative examples 1 to 3 of the invention are prepared into 40-60 mesh powder samples, and NH is carried out on the powder samples in a miniature fixed bed reactor3-SCR catalytic performance evaluation. The size of the quartz reaction tube used is 15mm, and the evaluation test temperature rise rate is 5 ℃/min. Simulated atmosphere composition: 500 ppm NO, 500 ppm NH3,5% O2,N2For balancing gas, the total flow rate is 1,000 ml/min, and the reaction space velocity is 30,000 h-1
The results of the performance tests on the fresh samples of examples 1 to 4 and comparative examples 1 to 3 are shown in Table 1.
TABLE 1
Figure 436474DEST_PATH_IMAGE001
Aging Performance verification
The core-shell catalysts of examples 1-4 and comparative examples 1-3 of the invention are prepared into 40-60 mesh powder samples, and the powder samples are prepared into high-temperature hydrothermal aging samples through high-temperature hydrothermal treatment in a tubular furnace, wherein the treatment conditions are as follows: 10 vol% of water vapor and air as balance gas, aging at 750 deg.C for 24h, total flow rate of 1000 ml/min, and space velocity of 20000 h-1
Preparing the core-shell catalysts of the examples 1-4 and the comparative examples 1-3 into a 40-60 mesh powder sample, performing sulfur poisoning treatment in a tubular furnace to prepare a sulfur aged sample, wherein the treatment conditions are as follows: 10 vol% of water vapor and air as balance gas, aging at 750 ℃ for 24h, with the total flow of 1,000 ml/min and the space velocity of 20,000 h-1
Respectively carrying out NH treatment on the high-temperature hydrothermal aging sample and the sulfur aging sample on a miniature fixed bed reactor3-SCR catalytic performance evaluation. The size of the quartz reaction tube used is 15mm, and the evaluation test temperature rise rate is 5 ℃/min. Simulated atmosphere composition: 500 ppm NO, 500 ppm NH3,5% O2,N2For balancing gas, the total flow rate is 1,000 ml/min, and the reaction space velocity is 30,000 h-1
The results of the aged sample performance test of examples 1 to 4 and comparative examples 1 to 3 are shown in Table 2.
TABLE 2
Figure 933708DEST_PATH_IMAGE002
Fe-Sm/Beta@TiO2The scanning electron microscope image and the EDS image of the sample are shown in figure 1, and the microstructure and element mapping of the core-shell structure BETA molecular sieve catalyst can be observed.
Fe-Sm/Beta@TiO2The X-ray diffraction patterns of the three samples Fe-Sm/Beta and H-Beta are shown in FIG. 2, and the crystal phase structures of the samples can be judged. As can be seen from the figure, the three samples showed the same crystal phase structure, and it was confirmed that the crystal phase structures of the molecular sieve catalyst and the BEA molecular sieve were not destroyed during the preparation of the core-shell structure, and a large amount of oxides were not generated.
Examples 1 to 4 and pairsSample to NO ratio 3XThe removal efficiency is shown in fig. 3.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (5)

1. The high-durability BEA molecular sieve catalyst with the core-shell structure is characterized in that: comprises a kernel and a shell layer wrapped on the kernel, wherein the kernel is a modified Sm-based BEA molecular sieve catalyst, the shell layer is made of oxide, and the shell layer is made of at least one of alumina, cerium oxide, titanium oxide, silicon oxide and zirconium oxide,
the preparation method of the high-durability BEA molecular sieve catalyst with the core-shell structure comprises the following steps:
(1) the preparation method of the modified Sm-based BEA molecular sieve catalyst comprises the following steps:
ion exchange, dissolving a soluble active component samarium precursor in deionized water, stirring until the soluble active component samarium precursor is completely dissolved, adding a BEA structure molecular sieve, adding an accelerant, heating and stirring to perform an ion exchange reaction to prepare the Sm/BEA molecular sieve catalyst precursor, adding a soluble auxiliary agent, heating and stirring to prepare the modified Sm/BEA molecular sieve catalyst precursor, wherein the soluble active component samarium precursor is samarium salt which is dissolved in water and has a molecular weight of less than 1000, the BEA structure molecular sieve comprises at least one of Beta and CIT-6, the accelerant comprises at least one of acetic acid, phosphoric acid, formic acid, nitric acid, carbonic acid, ammonium carbonate, ammonium nitrate, ammonium phosphate and ammonium acetate, the soluble auxiliary agent is a compound which is dissolved in water and has a molecular weight of less than 1000 and contains metal elements, and the metal elements comprise Fe, Cu, Ce, Mn, Y, Pr, Ni, Co, Pt, Pr, Fe, Pr, and Mn, At least one of Pd and Rh;
reducing the temperature of the modified Sm/BEA molecular sieve catalyst precursor to below 50 ℃, and starting negative pressure to evaporate the solvent to obtain powder;
soaking for multiple times, adding deionized water and soluble auxiliary agent into the powder, stirring for dissolving for soaking, reacting for 10-60 min, evaporating under reduced pressure again to obtain powder, and repeating for 2-3 times;
fine grinding, fine grinding the powder obtained after multiple soakings, drying and roasting to obtain the modified Sm-based BEA molecular sieve catalyst with the particle size of 100 nm;
(2) mixing the modified Sm-based BEA molecular sieve catalyst with a shell oxide precursor to prepare a BEA molecular sieve catalyst precursor with a core-shell structure, wherein the specific operation comprises the following steps:
performing ultrasonic dispersion, namely placing the modified Sm-based BEA molecular sieve catalyst in an organic alcohol solvent for ultrasonic dispersion to obtain a suspension;
performing electrostatic adsorption, namely adding ammonia water into the suspension to adjust the pH to 8-10, forming electrostatic adsorption charges on the surfaces of the modified Sm-based BEA molecular sieve catalyst powder particles, adding a shell oxide precursor, and stirring and dispersing to form a uniform mixed solution;
coating a shell layer, namely heating the mixed solution for reflux reaction, and coating the shell layer to obtain a BEA molecular sieve catalyst precursor with a core-shell structure;
(3) and centrifuging the precursor of the core-shell structure BEA molecular sieve catalyst to obtain a solid, and drying and roasting the solid to prepare the core-shell structure BEA molecular sieve catalyst.
2. The high-durability core-shell structure BEA molecular sieve catalyst according to claim 1, characterized in that: the thickness of the shell layer is less than or equal to 20 nm.
3. The high-durability core-shell structure BEA molecular sieve catalyst according to claim 1, characterized in that: the reaction temperature of ion exchange is 60-140 ℃, the reaction time of ion exchange is 1-10h, the water content in the powder obtained by reduced pressure evaporation is less than 6.5 wt%, the molar ratio of the soluble active component samarium precursor to the soluble auxiliary agent is 1:0.01-10, the mass ratio of the sum of the soluble active component samarium precursor and the soluble auxiliary agent to the BEA structure molecular sieve is 0.001-0.2: 1, the mass ratio of the deionized water to the BEA structure molecular sieve supplemented once is 0.5-10:1, the fine grinding time is 1-6h, the drying temperature after the fine grinding is 80-100 ℃, and the drying time is 6-24 h.
4. The high-durability core-shell structure BEA molecular sieve catalyst according to claim 1, characterized in that: the organic alcohol solvent comprises at least one of ethanol, methanol, glycol, glycerol and isopropanol, and the modified Sm-based BEA molecular sieve catalyst comprises the following components in percentage by weight: the mass concentration of the organic alcohol solvent is 0.0001-10g/mL, and the precursor of the shell oxide comprises tetrabutyl titanate, titanium sol, aluminum sol, silica sol, water glass, tetraethyl silicate, titanic acid and ZrO2、TiO2、Al2O3、SiO2、CeO2At least one of cerous nitrate, sodium aluminate, sodium silicate, aluminum nitrate and cerous hexamethylene tetramine, a precursor of the BEA molecular sieve catalyst with a core-shell structure: the mass concentration of the organic alcohol solvent is 0.001-30g/mL, the temperature of the reflux reaction is 25-50 ℃, and the reflux reaction time is 8-24 h.
5. Use of the high-durability core-shell structure BEA molecular sieve catalyst according to any one of claims 1 to 4 for selective reduction elimination of nitrogen oxides in exhaust gas.
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