CN107282101B - In-situ load modification method of SAPO-34 molecular sieve catalyst for diesel vehicle tail gas purification - Google Patents
In-situ load modification method of SAPO-34 molecular sieve catalyst for diesel vehicle tail gas purification Download PDFInfo
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- B01J29/00—Catalysts comprising molecular sieves
- B01J29/82—Phosphates
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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- B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
- B01J2229/10—After treatment, characterised by the effect to be obtained
- B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
- B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
Abstract
The invention relates to an in-situ load modification method of a SAPO-34 molecular sieve catalyst for purifying diesel vehicle tail gas, which takes SAPO-34 molecular sieve as a carrier and metal elements such as Cu, Mn, Fe and the like as active components, and activates Al on the surface of the SAPO-34 molecular sieve powder by pretreating the SAPO-34 molecular sieve powder on the premise of not damaging the framework structure of the SAPO-34 molecular sieve powder2O3And as an aluminum source, in-situ synthesizing a hydrotalcite-like precursor containing elements such as Cu, Mn, Fe and the like on the surface and in the pore canal, and roasting at 400-600 ℃ to obtain the SAPO-34 molecular sieve catalyst in which the corresponding metal oxide is loaded in situ. Powder samples of the catalyst were used for NH in a laboratory simulated atmosphere3SCR reaction, compared with the similar metal modified SAPO-34 molecular sieve prepared by simple dipping or aqueous solution ion exchange method, the denitration active temperature window is wider, and the hydrothermal aging resistance is greatly improved.
Description
Technical Field
The technical field of environmental protection and the technical field of motor vehicle pollutant emission control, in particular to an in-situ load modification method of an SAPO-34 molecular sieve catalyst for purifying tail gas of diesel vehicles.
Background
With the rapid development of the economy and automobile industry in China and the improvement of the living standard of residents, the automobile keeping quantity in China is continuously increased, and a considerable part of the automobile keeping quantity is diesel vehicles, including diesel passenger vehicles and commercial vehicles. The diesel vehicle has the advantages of more energy conservation, good economy, abundant power, less greenhouse gas emission and the like, not only plays an irreplaceable role in national production, but also is favored by consumers in the field of passenger vehicles. But the oxygen-enriched combustion characteristic of the diesel engine results in that of the diesel engineNitrogen Oxides (NO)X) The emission is high, and is one of important influencing factors causing haze climate. Therefore, the emission regulations at home and abroad are all for the NO of the motor vehicleXThe emission is limited, and with the stricter and stricter emission regulations in China, the emission requirements are difficult to meet by only in-cylinder optimization measures in the stages of the China V and the China VI, so that the reasonable application of a tail gas post-treatment technology and the combination of the tail gas post-treatment technology and in-cylinder purification measures become main technical means for solving the emission of the diesel engine in the future.
Among the currently common post-treatment techniques, NH3SCR technology is the most mature and can be perfectly coupled with Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) to achieve simultaneous reduction of PM emission and NOXThe purpose of discharging. The most widely used commercial SCR catalyst at home is mainly a vanadium-based SCR catalyst, and the main active component of the catalyst is V2O5/WO3/TiO2. But with the stricter emission regulations, NO in cold start stage of diesel engineXEmissions are tightly controlled due to the relatively narrow temperature window and V of vanadium-based SCR2O5Has high toxicity, so that the research on new alternative materials is necessary.
The metal modified molecular sieve SCR catalyst is considered to be the development direction of the SCR catalyst in the future, the main component of the molecular sieve is crystalline silicate or aluminosilicate with sieving property, including ZSM-5, SAPO-34, SSZ-13 and the like, the molecular sieve can be loaded with metal active species by an ion exchange method, and compared with a vanadium-based SCR catalyst, the molecular sieve SCR catalyst has excellent NOXLow temperature conversion efficiency and high space velocity flexibility. But poor hydrothermal stability is a major problem for the use of this series of catalysts in diesel vehicle aftertreatment systems. One of the main reasons that molecular sieve SCR catalysts deactivate under hydrothermal conditions is that their supported metal active species tend to agglomerate into metal oxide particles, thereby reducing their dispersancy leading to a decrease in catalytic activity. It is also believed by the scholars that the removal of metal species from the ionic sites, as well as the dealumination of the molecular sieve, is due. Under hydrothermal conditions, this dealumination and metal ion migration ultimately leads to destruction of the catalyst framework and active sites. To date, the above problems have been addressedThe solution of (2) is still under investigation.
Disclosure of Invention
In view of the above, in order to overcome the drawbacks of the prior art, the present invention aims to provide an in-situ modification method for a molecular sieve catalyst for diesel exhaust purification, which is not a simple ion exchange method, but grows a hydrotalcite-like nano-thin layer containing active metal elements (copper, manganese, and iron) on the surface of an SAPO-34 molecular sieve in situ, thereby improving the binding firmness of the active metal elements and a molecular sieve carrier, and simultaneously enables the active metal elements to maintain a high degree of uniform dispersion due to the hydrotalcite-like template effect. On the other hand, the hydrotalcite-like thin layer can also play a certain protection role on the molecular sieve framework, so that the hydrothermal stability and the catalytic activity of the hydrotalcite-like thin layer are improved, and a mesoporous-microporous composite structure is formed after roasting.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
an in-situ loading modification method of an SAPO-34 molecular sieve catalyst for purifying diesel vehicle tail gas is characterized by comprising the following steps of:
dissolving one of copper nitrate, manganese nitrate or ferric nitrate in water at normal temperature, stirring to form a transparent solution, adding ammonium nitrate, fully dissolving and mixing to obtain a mixed salt solution, wherein the molar ratio of metal nitrate to ammonium nitrate is 1: 0.3-0.7;
step two, adding a certain amount of SAPO-34 molecular sieve raw powder into the mixed salt solution obtained in the step one under the protection of nitrogen, and soaking for a certain time under the condition of continuous stirring at 50-80 ℃;
step three, standing the mixed slurry obtained in the step two until solid and liquid are layered, sucking out most of supernatant, and taking the slurry containing the molecular sieve raw powder at the lower layer for later use;
step four, adjusting the slurry obtained in the step three while stirring to a pH value of 7.5-8.0, and simultaneously carrying out the whole process under the protection of a nitrogen atmosphere;
step five, preparing a washing liquid by using ammonia water and an ammonium nitrate solution, wherein the pH value of the washing liquid is consistent with that of the slurry obtained in the step four;
step six, washing and filtering the serous fluid in the step four for 6-8 times by using the washing liquid prepared in the step five, and aging the obtained wet material for 1-5 hours at normal temperature in a nitrogen atmosphere;
washing the wet material obtained in the sixth step with deionized water until the wet material is neutral, filtering, putting the obtained solid material in an oven, and drying at 60-80 ℃ to obtain the SAPO-34 molecular sieve with the hydrotalcite-like nano thin layer synthesized on the surface of the SAPO-34 molecular sieve in situ;
and step eight, placing the SAPO-34 molecular sieve with the hydrotalcite-like nano thin layer obtained in the step seven into a tubular furnace, and roasting at 550 ℃ for 4-6 hours to obtain the mesoporous and microporous composite SAPO-34 molecular sieve SCR catalyst with the copper, manganese or iron metal oxide nano thin layer loaded on the surface in situ.
In the second and fourth steps, the protection of nitrogen atmosphere can prevent CO in the air2The interference of the catalyst can ensure that interlayer anions of the hydrotalcite-like compound are not formed by carbonate, the adhesion force of the hydrotalcite-like nano thin layer and the SAPO-34 molecular sieve can be improved, the pore channel of the SAPO-34 molecular sieve is prevented from being blocked, the specific surface area of the mesoporous and microporous composite SAPO-34 molecular sieve SCR catalyst with the copper, manganese or iron metal oxide nano thin layer loaded on the surface in situ is increased, and the catalytic performance of the molecular sieve is further improved.
Furthermore, the solvent and the washing water used in the modification process are deionized water, and the conductivity is less than 1 x 10-6S·cm-1。
Further, in the first step, the amount of water is 200 times of the total molar amount of nitrate;
preferably, in the first step, the molar ratio of the metal nitrate to the ammonium nitrate is 1: 0.5;
preferably, in the first step, the metal nitrate is diluted to a concentration of 0.01mol/L from a solution with a mass concentration of 50% at normal temperature, and then ammonium nitrate is added.
Further, in the second step, the molar ratio of the metal nitrate to the alumina in the SAPO-34 molecular sieve is 2-3: 1;
preferably, in the second step, the molar ratio of the metal nitrate to the alumina in the molecular sieve is 2.8: 1;
preferably, in the second step, the SAPO-34 molecular sieve raw powder is ground and then roasted in a muffle furnace at 500 ℃ for 1 hour, and then the SAPO-34 molecular sieve raw powder is added into the mixed salt solution obtained in the first step;
preferably, the mixed salt solution in the second step is soaked and stirred for 12-24 hours at the temperature of 50-80 ℃;
preferably, the mixed salt solution in the second step is immersed and stirred at 60 ℃ for 12 hours.
Further, in the third step, the retention amount of the supernatant is one third of the volume of the original supernatant;
preferably, in the third step, the mixed slurry in the second step is allowed to stand for 1 hour.
Further, in the fourth step, ammonia water is used for adjusting the pH value under the condition of vigorous stirring;
preferably, the concentration of the aqueous ammonia used is 2% by weight;
preferably, the pH value of the final slurry in the fourth step is 7.8 +/-0.1.
Further, a washing liquid is prepared in the fifth step, and the concentration of the ammonium nitrate solution is 0.5 mol/L.
Further, in the sixth step, the wet materials are washed by washing liquid until no turbidity is obvious in the supernatant;
preferably, the wet material in the sixth step is aged for 3 hours at normal temperature in a nitrogen atmosphere.
Further, in the seventh step, the solid materials are dried for 24 to 48 hours at a temperature of between 60 and 80 ℃;
preferably, in the seventh step, the solid material is dried for 36 hours at 70 ℃.
Further, step eight, nitrogen is introduced in the roasting process of the tubular furnace for atmosphere protection,
preferably, the solid material dried in the step eight is put into a tube furnace to be roasted for 4 hours at 500 ℃.
Compared with the prior art, the in-situ load modification method of the SAPO-34 molecular sieve catalyst for purifying the tail gas of the diesel vehicle has the following advantages:
the conversion efficiency of the nitrogen oxide of the fresh sample of the metal ion modified SAPO-34 molecular sieve catalyst prepared by the in-situ load modification method of the SAPO-34 molecular sieve catalyst for purifying the tail gas of the diesel vehicle can reach more than 60 percent within the temperature range of 150-550 ℃, and the conversion efficiency is higher than 95 percent within the temperature range of 200-450 ℃; after the sample is subjected to hydrothermal aging for 80 hours, the deterioration rate is not more than 5%.
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 is a graph showing the conversion efficiency of nitrogen oxides for a Cu-SAPO-34 molecular sieve SCR catalyst prepared according to the method of the present invention and a control Cu/SAPO-34 molecular sieve SCR catalyst prepared by a conventional impregnation method;
FIG. 2 is a schematic diagram of the conversion efficiency of nitrogen oxides after aging under the same test conditions for a Cu-SAPO-34 molecular sieve SCR catalyst prepared according to the method of the present invention and a control Cu/SAPO-34 molecular sieve SCR catalyst prepared by a conventional impregnation method.
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.
The present invention will be described in detail with reference to the following examples and accompanying drawings.
Example one
Dissolving copper nitrate in deionized water at normal temperature until the concentration of the copper nitrate is 0.01mol/L, adding ammonium nitrate, and fully dissolving and mixing to obtain a mixed salt solution, wherein the molar ratio of the copper nitrate to the ammonium nitrate is 1: 0.5;
adding a certain amount of SAPO-34 molecular sieve raw powder into the mixed salt solution under the protection of nitrogen, and dipping and stirring for 12 hours at the temperature of 60 ℃ to obtain mixed slurry; the molar ratio of copper nitrate to alumina in the SAPO-34 molecular sieve is 2.8: 1;
standing the mixed slurry for 1 hour under the protection of nitrogen, sucking out two thirds of the supernatant, and keeping the slurry containing the molecular sieve raw powder at the lower layer to adjust the pH value to 7.8 by using ammonia water; washing the slurry with a mixed solution of ammonia water and ammonium nitrate with the pH value of 7.8, which is prepared from ammonia water and ammonium nitrate solution with the concentration of 0.5mol/L, for 8 times, and aging for 3 hours in a nitrogen atmosphere at normal temperature;
repeatedly filtering the aged slurry, washing the slurry by using deionized water until the slurry is neutral, filtering out solid materials, and drying the solid materials in an oven at 80 ℃ for 48 hours; and (3) roasting the dried solid material in a tubular furnace at 450 ℃ for 4 hours to obtain the SAPO-34 molecular sieve SCR catalyst Cu-SAPO with copper loaded on the surface in situ.
0.5g of the catalyst was taken and NH was added at 500ppm3，500ppm NO，5％vol O2The balance gas is N2Under the condition of flue gas, the space velocity of the reaction volume is 450000h-1The conversion efficiency of the catalyst to NO in the temperature range of 150-550 ℃ is shown in Table 1 and FIG. 1.
And (3) aging the fresh sample in a hydrothermal aging furnace, wherein the aged sample is marked as Cu-SAPO-old. The water content of the aging atmosphere is 5 percent, and the aging is carried out for 80 hours at 400 ℃. The catalytic performance of the aged samples is shown in table 2 and fig. 2, consistent with the fresh samples tested.
Example two
Diluting a 50% manganese nitrate solution to a concentration of 0.01mol/L at normal temperature, taking a proper amount of manganese nitrate solution, adding ammonium nitrate, and mixing to obtain a mixed salt solution, wherein the molar ratio of manganese nitrate to ammonium nitrate is 1: 0.5; adding a certain amount of SAPO-34 molecular sieve raw powder into the mixed salt solution under the protection of nitrogen, and soaking and stirring for 24 hours at the temperature of 50 ℃; the molar ratio of the manganese nitrate to the alumina in the SAPO-34 molecular sieve is 3: 1;
standing the mixed slurry for 1 hour under the protection of nitrogen, sucking out two thirds of the supernatant, and keeping the slurry containing the molecular sieve raw powder at the lower layer to adjust the pH value to 8.0 by using ammonia water; washing the slurry for 6 times by using a mixed solution of ammonia water and ammonium nitrate with the pH value of 8.0, which is prepared by ammonia water and ammonium nitrate solution with the concentration of 0.5mol/L, and aging for 5 hours in a nitrogen atmosphere at normal temperature;
repeatedly filtering the aged slurry, washing the slurry by using deionized water until the slurry is neutral, filtering out solid materials, and drying the solid materials in an oven at 60 ℃ for 24 hours; and (3) roasting the dried solid material in a tubular furnace at 500 ℃ for 6 hours to obtain the SAPO-34 molecular sieve SCR catalyst Mn-SAPO with manganese loaded on the surface in situ.
The catalyst was used at 500ppm Nitric Oxide (NO), 500ppm ammonia (NH)3) 5% vol oxygen (O)2) And nitrogen (N)2) Under the condition of mixing as reaction gas, the loading of the catalyst is 0.5g, and the volume space velocity of the reaction is 45000h-1The conversion of NO by the catalyst in the temperature range of 150 ℃ and 550 ℃ is shown in Table 1.
And (3) carrying out aging treatment on the fresh sample in the second embodiment in a hydrothermal aging furnace, wherein the sample after aging is marked as Mn-SAPO-old. The water content of the aging atmosphere is 5 percent, and the aging is carried out for 80 hours at 400 ℃. The catalytic performance of the aged samples is shown in table 2, consistent with the fresh samples tested.
EXAMPLE III
Diluting a 50% ferric nitrate solution to a concentration of 0.01mol/L at normal temperature, taking a proper amount of the ferric nitrate solution, adding ammonium nitrate, and mixing to obtain a mixed salt solution, wherein the molar ratio of ferric nitrate to ammonium nitrate is 1: 0.5; adding a certain amount of SAPO-34 molecular sieve raw powder into the mixed salt solution under the protection of nitrogen, and soaking and stirring for 18 hours at the temperature of 80 ℃; the molar ratio of ferric nitrate to alumina in the SAPO-34 molecular sieve is 3: 1;
standing the mixed slurry for 1 hour under the protection of nitrogen, sucking out two thirds of the supernatant, and keeping the slurry containing the molecular sieve raw powder at the lower layer to adjust the pH value to 7.5 by using ammonia water; washing the slurry for 6 times by using a mixed solution of ammonia water and ammonium nitrate with the pH value of 7.5, which is prepared by ammonia water and ammonium nitrate solution with the concentration of 0.5mol/L, and aging for 1 hour in a nitrogen atmosphere at normal temperature;
repeatedly filtering the aged slurry, washing the slurry by using deionized water until the slurry is neutral, filtering out solid materials, and drying the solid materials in an oven at 70 ℃ for 36 hours; and (3) roasting the dried solid material in a tubular furnace at 550 ℃ for 6 hours to obtain the SAPO-34 molecular sieve SCR catalyst Fe-SAPO with iron loaded on the surface in situ.
The catalyst was used at 500ppm Nitric Oxide (NO), 500ppm ammonia (NH)3) 5% vol oxygen (O)2) And nitrogen (N)2) Under the condition of mixing as reaction gas, the loading of the catalyst is 0.5g, and the volume space velocity of the reaction is 45000h-1The conversion of NO by the catalyst in the temperature range of 150 ℃ and 550 ℃ is shown in Table 1.
And (3) ageing the fresh sample in the third example in a hydrothermal ageing furnace, wherein the aged sample is marked as Fe-SAPO-old. The water content of the aging atmosphere is 5 percent, and the aging is carried out for 80 hours at 400 ℃. The catalytic performance of the aged samples is shown in table 2, consistent with the fresh samples tested.
Control group sample
A Cu/SAPO-34 molecular sieve SCR catalyst prepared by a common ion exchange method was used as a control group, and performance comparison was performed under the same test conditions with samples prepared according to the proposed method of the present invention.
The control samples were prepared as follows:
grinding commercial SAPO-34 molecular sieve particles, adding the ground particles into a proper amount of deionized water, stirring to prepare a molecular sieve slurry, adding a copper nitrate solution into the molecular sieve slurry to obtain a mixed slurry, wherein the copper nitrate content of the mixed slurry is 0.01mol/L, and the molar ratio of the copper nitrate to the alumina in the SAPO-34 molecular sieve is 2.8: 1. The pH value of the mixed slurry was adjusted to about 7.8, and the slurry was immersed and stirred at 60 ℃ for 12 hours. Filtering the slurry after ion exchange to obtain filter cake, dispersing the filter cake into small blocks, and drying in an oven at 80 ℃ for 48 hours. And grinding the dried molecular sieve, and calcining the ground molecular sieve in a tubular furnace at 450 ℃ for 4 hours to obtain the Cu/SAPO-34 molecular sieve SCR catalyst Cu/SAPO. The nitrogen oxides conversion method of the fresh control group sample is the same as that of example 1, and the conversion efficiency is shown in table 1 and fig. 1.
And (3) aging the fresh sample of the control group in a hydrothermal aging furnace, wherein the sample after aging is marked as Cu/SAPO-old. The water content of the aging atmosphere is 5 percent, and the aging is carried out for 80 hours at 400 ℃. The catalytic performance of the aged samples is shown in table 2 and fig. 2, consistent with the fresh samples tested.
TABLE 1
As can be seen from the data in Table 1 and FIG. 1, compared with the similar catalyst prepared by the common ion exchange method, the Cu-SAPO molecular sieve catalyst prepared by the method of the invention has the advantages of significantly improved low-temperature performance, wider active temperature window and higher denitration efficiency than 95% in the temperature range of 200-450 ℃. The Mn-SAPO and Fe-SAPO prepared by the method of the invention have wider active temperature windows, and the denitration efficiency is higher than that of the corresponding catalyst prepared by the common ion exchange method.
As can be seen from the data in table 2 and fig. 2, the samples of example one and the control group were subjected to hydrothermal aging under the same conditions (the aging atmosphere had a water content of 5%, and the aging was carried out at 400 ℃ for 80 hours), and the samples of example were not significantly deteriorated and exhibited strong resistance to hydrothermal aging. The NO conversion efficiency of the control group sample is greatly reduced.
TABLE 2
As can be seen from the data in Table 2, after the samples in the first example and the control group are subjected to hydrothermal aging under the same conditions (the moisture content of the aging atmosphere is 5%, and the aging is carried out for 80 hours at 400 ℃), the samples in the first example are not obviously degraded, and show strong hydrothermal aging resistance, and the denitration efficiency is higher than 90% in the temperature range of 200 ℃ -450 ℃. The NO conversion efficiency of the control group sample is greatly reduced.
After hydrothermal aging of the samples (aging atmosphere with a water content of 5% and aging at 400 ℃ for 80 hours) in the second/third examples, the samples have no obvious deterioration and show strong resistance to hydrothermal aging.
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 (21)
1. An in-situ loading modification method of an SAPO-34 molecular sieve catalyst for purifying diesel vehicle tail gas is characterized by comprising the following steps of:
dissolving one of copper nitrate, manganese nitrate or ferric nitrate in water at normal temperature, stirring to form a transparent solution, adding ammonium nitrate, fully dissolving and mixing to obtain a mixed salt solution, wherein the molar ratio of metal nitrate to ammonium nitrate is 1: 0.3-0.7;
step two, adding a certain amount of SAPO-34 molecular sieve raw powder into the mixed salt solution obtained in the step one under the protection of nitrogen, and soaking for a certain time under the condition of continuous stirring at 50-80 ℃; in the second step, the molar ratio of the metal nitrate to the alumina in the SAPO-34 molecular sieve is 2-3: 1;
step three, standing the mixed slurry obtained in the step two until solid and liquid are layered, sucking out most of supernatant, and taking the slurry containing the molecular sieve raw powder at the lower layer for later use;
step four, adjusting the slurry obtained in the step three while stirring to a pH value of 7.5-8.0, and simultaneously carrying out the whole process under the protection of a nitrogen atmosphere;
step five, preparing a washing liquid by using ammonia water and an ammonium nitrate solution, wherein the pH value of the washing liquid is consistent with that of the slurry obtained in the step four;
step six, washing and filtering the serous fluid in the step four for 6-8 times by using the washing liquid prepared in the step five, and aging the obtained wet material for 1-5 hours at normal temperature in a nitrogen atmosphere;
washing the wet material obtained in the sixth step with deionized water until the wet material is neutral, filtering, putting the obtained solid material in an oven, and drying at 60-80 ℃ to obtain the SAPO-34 molecular sieve with the hydrotalcite-like nano thin layer synthesized on the surface of the SAPO-34 molecular sieve in situ;
and step eight, placing the SAPO-34 molecular sieve with the hydrotalcite-like nano thin layer obtained in the step seven into a tubular furnace, and roasting at 550 ℃ for 4-6 hours to obtain the mesoporous and microporous composite SAPO-34 molecular sieve SCR catalyst with the copper, manganese or iron metal oxide nano thin layer loaded on the surface in situ.
2. The modification method according to claim 1, characterized in that: the solvent and the washing water used in the modification process are deionized water, and the conductivity is less than 1 x 10-6S·cm-1。
3. The modification method according to claim 1, characterized in that: in the first step, the amount of water is 200 times of 100 times of the total molar amount of nitrate.
4. The modification method according to claim 1 or 3, characterized in that: in the first step, the molar ratio of the metal nitrate to the ammonium nitrate is 1: 0.5.
5. The modification method according to claim 4, characterized in that: in the first step, the metal nitrate is diluted to the concentration of 0.01mol/L at normal temperature by a solution with the mass concentration of 50%, and then ammonium nitrate is added.
6. The modification method according to claim 1, characterized in that: in the second step, the molar ratio of the metal nitrate to the aluminum oxide in the molecular sieve is 2.8: 1.
7. The modification method according to claim 1 or 6, characterized in that: and step two, grinding the SAPO-34 molecular sieve raw powder, roasting the ground SAPO-34 molecular sieve raw powder in a muffle furnace at 500 ℃ for 1 hour, and adding the SAPO-34 molecular sieve raw powder into the mixed salt solution obtained in the step one.
8. The modification method according to claim 7, characterized in that: soaking and stirring the mixed salt solution at 50-80 ℃ for 12-24 hours;
9. the modification method according to claim 8, characterized in that: and in the second step, the mixed salt solution is soaked and stirred for 12 hours at the temperature of 60 ℃.
10. The modification method according to claim 1, characterized in that: in the third step, the retention amount of the supernatant is one third of the volume of the original supernatant.
11. The modification method according to claim 1 or 10, characterized in that: in the third step, the mixed slurry in the second step is kept standing for 1 hour.
12. The modification method according to claim 1, characterized in that: in the fourth step, ammonia is used for adjusting the pH value under the condition of vigorous stirring.
13. The modification method according to claim 12, characterized in that: the concentration of the ammonia water used in the fourth step is 2 wt%.
14. The modification method according to claim 13, characterized in that: the pH value of the final slurry in the fourth step is 7.8 +/-0.1.
15. The modification method according to claim 1, characterized in that: and step five, preparing a washing liquid, wherein the concentration of the ammonium nitrate solution is 0.5 mol/L.
16. The modification method according to claim 1, characterized in that: in the sixth step, the wet material is washed by the washing liquid until no turbidity is obvious in the supernatant.
17. The modification method according to claim 1 or 16, characterized in that: and in the sixth step, the wet material is aged for 3 hours at normal temperature in a nitrogen atmosphere.
18. The modification method according to claim 1, characterized in that: in the seventh step, the solid material is dried for 24 to 48 hours at a temperature of between 60 and 80 ℃.
19. The modification method according to claim 1, characterized in that: in the seventh step, the solid material is dried for 36 hours at 70 ℃.
20. The modification method according to claim 1, characterized in that: and step eight, introducing nitrogen for atmosphere protection in the roasting process of the tubular furnace.
21. The modification method according to claim 1 or 20, characterized in that: and seventhly, putting the SAPO-34 molecular sieve with the hydrotalcite-like nano thin layer obtained in the step seven into a tubular furnace, and roasting for 4 hours at 500 ℃.
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| CN109399665B (en) * | 2018-09-29 | 2022-01-18 | 山东国瓷功能材料股份有限公司 | Composite structure SSZ-13@ Silicalite-1 molecular sieve and preparation method and application thereof |
| CN109433254B (en) * | 2018-11-09 | 2021-11-09 | 大连交通大学 | Confined molecular sieve denitration catalyst and preparation method thereof |
| CN110252392A (en) * | 2019-07-18 | 2019-09-20 | 付华 | A kind of cerium modified Cu-SAPO-34 molecular sieve catalyst and preparation method thereof |
| CN112439448B (en) * | 2019-08-30 | 2023-11-03 | 大连海事大学 | Copper-containing or iron-based SAPO molecular sieve SCR catalyst, and preparation method and application thereof |
| CN112960680B (en) * | 2021-04-09 | 2022-09-30 | 陕西延长石油（集团）有限责任公司 | Modification method for improving hydrothermal stability of ZSM-5 molecular sieve |
| CN114653397B (en) * | 2022-03-21 | 2024-03-22 | 南方科技大学 | Denitration sulfur-resistant catalyst with core-shell structure and preparation method and application thereof |
| CN114887649A (en) * | 2022-07-14 | 2022-08-12 | 中国汽车技术研究中心有限公司 | Coating-free integral type exhaust gas purification catalyst and preparation method thereof |
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