CN114870887A - Cu-SSZ-39 molecular sieve, preparation method thereof and DeNOx catalyst - Google Patents

Cu-SSZ-39 molecular sieve, preparation method thereof and DeNOx catalyst Download PDF

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CN114870887A
CN114870887A CN202210458254.2A CN202210458254A CN114870887A CN 114870887 A CN114870887 A CN 114870887A CN 202210458254 A CN202210458254 A CN 202210458254A CN 114870887 A CN114870887 A CN 114870887A
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molecular sieve
ssz
acid
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郭冬冬
刘中清
孟波
赵峰
邓兆敬
梁武洋
程从礼
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China Chemical Technology Research Institute
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Abstract

The invention provides a Cu-SSZ-39 molecular sieve, a preparation method thereof and a DeNOx catalyst. The preparation method comprises the following steps: pretreating the first molecular sieve and the second molecular sieve by using an acidic substance, and mixing the pretreated first molecular sieve, the pretreated second molecular sieve, a silicon source, an alkali source, an organic template and water to obtain gel; crystallizing and roasting the gel to obtain the SSZ-39 molecular sieve; and carrying out copper ion exchange on the SSZ-39 molecular sieve to obtain the Cu-SSZ-39 molecular sieve. The invention also provides the Cu-SSZ-39 molecular sieve obtained by the preparation method and a DeNOx catalyst containing the Cu-SSZ-39 molecular sieve. The Cu-SSZ-39 molecular sieve has good low-temperature DeNOx reaction activity.

Description

Cu-SSZ-39 molecular sieve, preparation method thereof and DeNOx catalyst
Technical Field
The invention relates to the technical field of catalytic materials, in particular to a Cu-SSZ-39 molecular sieve, a preparation method thereof and a DeNOx catalyst.
Background
With the development of economy and the advancement of society, people are increasingly unable to leave a vehicle (mobile source), wherein a motor vehicle is the most important vehicle at present. However, with the rapid increase of the number of vehicles, the problem of pollution of the exhaust gas of diesel vehicles is getting worse, and although the reserved amount of diesel vehicles is only 9.4% of the total amount of nationwide automobile reserves, the NOx discharged from diesel vehicles is close to 70% of the total amount of automobile discharges. With the deep advance of emission reduction work, the national six-emission regulation implemented in 2020 has a tightened NOx emission limit value of 42% compared with the national five-emission standard. Accordingly, methods of eliminating NOx in diesel vehicle engines are receiving increased attention.
The NOx formation pathway in the tail gas of the diesel vehicle is as follows: n is a radical of 2 And O 2 NO is generated under high temperature condition, and NO is gradually oxidized into NO after entering the atmosphere 2 。
The conventional Cu-SSZ-39 molecular sieve prepared by the prior art has lower silicon-aluminum ratio and lower acid strength, and is not beneficial to denitration of diesel vehicles at low temperature. There is a need to provide a solution to the problem of poor activity of low temperature DeNOx catalysts.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a Cu-SSZ-39 molecular sieve, a preparation method thereof and a DeNOx catalyst. The Cu-SSZ-39 molecular sieve provided by the invention has higher relative crystallinity, silicon-aluminum ratio, acidity and thermal stability, and has good low-temperature DeNOx reaction activity.
In order to achieve the above object, the present invention provides a preparation method of a Cu-SSZ-39 molecular sieve, the preparation method comprising:
s1, pretreating the first molecular sieve and the second molecular sieve by using an acidic substance, and mixing the pretreated first molecular sieve, the pretreated second molecular sieve, a silicon source, an alkali source, an organic template and water to obtain gel, wherein the chemical composition of the gel meets the following molar ratio: (10-100) MOH: al (Al) 2 O 3 ：(10-100)SiO 2 ：(500-1000)H 2 O: (5-20) R, wherein R is an organic template, and MOH is an alkali source; the first molecular sieve comprises a Y molecular sieve, the second molecular sieve comprises a Beta molecular sieve and/or a ZSM-5 molecular sieve, and the mass ratio of the first molecular sieve (without pretreatment) to the second molecular sieve (without pretreatment) is 1-50: 1;
s3, crystallizing and roasting the gel to obtain the SSZ-39 molecular sieve;
s5, carrying out copper ion exchange on the SSZ-39 molecular sieve to obtain the Cu-SSZ-39 molecular sieve.
In the above preparation method, MOH represents an alkali source, and cations and OH in MOH - The coordination number of the ions is determined according to the principle of chemical equilibrium, and the coordination numbers of the ions and the coordination numbers are not limited to 1. The alkali source MOH includes, but is not limited to, one or a combination of two or more of sodium hydroxide, potassium hydroxide, ammonia water, and the like.
In the preparation method, in S1, the first molecular sieve and the second molecular sieve are pretreated to introduce defect sites to induce and synthesize the high-performance SSZ-39 molecular sieve, so that copper ions are induced to be uniformly distributed in the subsequent copper ion exchange process, CuO agglomeration is avoided, exposed metal sites participating in redox reaction are increased, and high metal sites are enhanced.
In some embodiments, in S1, the ratio of the mass of the acidic substance to the total mass of the first molecular sieve and the second molecular sieve is (0.005-0.1): 1.
in a specific embodiment of the present invention, the first molecular sieve and the second molecular sieve may be mixed with an acidic substance at the same time for pretreatment, or may be mixed with an acidic substance separately for pretreatment. When the first molecular sieve and the second molecular sieve are mixed with the acidic substance for pretreatment, respectively, the ratio of the total mass of the acidic substance to the total mass of the first molecular sieve and the second molecular sieve (0.005 to 0.1): 1. and the dosage ratio between the first molecular sieve and the second molecular sieve, and determining the amounts of the acidic substances respectively used for treating the first molecular sieve and the second molecular sieve by means of equal proportion distribution.
In some embodiments, the mass ratio of the first molecular sieve (without pretreatment) to the second molecular sieve (without pretreatment) in S1 is generally controlled to be 1-50: 1, preferably 4 to 30: 1, e.g. 4-27: 1, etc.
In some embodiments, the temperature of the pretreatment in S1 may be controlled to be 0 ℃ to 85 ℃, e.g., 20 ℃ to 85 ℃, 25 ℃ to 85 ℃, 20 ℃ to 70 ℃, etc.
In some embodiments, the time of the pretreatment in S1 can be controlled to be 0.5h to 10h, for example, 1h to 7 h.
In some embodiments, in S1, the pretreatment process is generally performed under stirring conditions.
In some embodiments, the acidic material used for pretreatment in S1 generally comprises one or a combination of two or more of organic acids, inorganic acids, strong acid and weak base salts. Wherein, the organic acid can comprise oxalic acid, citric acid and the like; the inorganic acid may include one or a combination of two or more of hydrochloric acid, sulfuric acid, nitric acid, and the like; the strong acid and weak base salt may include one or a combination of two or more of aluminum sulfate, aluminum nitrate, aluminum chloride, and the like.
In some embodiments, SiO is used 2 And Al 2 O 3 In general, the Si/Al molar ratio of the Y molecular sieve is controlled to be more than or equal to 5.3: 1. for example, 5.5:1, the above molar ratio of Si to Al has a higher value than that of the Y molecular sieveHigh stability. The Y molecular sieve may be a molecular sieve commonly used in the art, such as NaY molecular sieve, and the like.
In some embodiments, SiO is used 2 And Al 2 O 3 In general, the mole ratio of silicon to aluminum of the Beta molecular sieve is controlled to be 15-50: the Beta molecular sieve with the mole ratio of silicon to aluminum described above has a high acid content.
In some embodiments, SiO is used 2 And Al 2 O 3 On the basis, the silica-alumina molar ratio of the ZSM-5 molecular sieve is generally controlled to be 30-60: the ZSM-5 molecular sieve having the above silica to alumina molar ratio has a large acid amount.
In some embodiments, the silicon source may include one or a combination of two or more of water glass, silica sol, white carbon, tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, and the like.
In some embodiments, the organic templating agent can include one or a combination of two or more of N, N-dimethyl-N, N-bicyclononane, 2,6, 6-tetramethyl N, N-dimethylpiperidine, N-cyclooctyl-pyridine, 2,6, 6-tetramethyl-N-ethylpiperidine, 2-ethyl-N, N-dimethylpiperidine, 3, 5-dimethyl-N, N-dimethylpiperidine, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide, tetraethylammonium bromide, N-butylamine, triethylamine, ethylenediamine, and the like.
In some embodiments, in S3, the crystallization process may be dynamic crystallization, and specifically, the crystallization process may be performed under stirring.
In some embodiments, in S3, the crystallization temperature is generally controlled to be 100-180 ℃, and the crystallization time is generally controlled to be 24-80 h.
In some embodiments, the temperature at which the crystallized product is calcined in S3 is generally controlled to 300 ℃ to 700 ℃ and the time is generally controlled to 1h to 10 h.
In a specific embodiment of the present invention, S5 specifically includes the following operations: and carrying out ammonium exchange and first roasting on the SSZ-39 molecular sieve, and carrying out copper ion exchange, second roasting and hydrothermal treatment on a product of the first roasting to obtain the Cu-SSZ-39 molecular sieve.
In the embodiment of the present invention, the ammonium exchange method used in the present invention may be a method which is conventional in the art, and the present invention is not particularly limited thereto. In some embodiments, the process of ammonium exchanging the SSZ-39 molecular sieve in S5 may comprise: mixing SSZ-39 molecular sieve, ammonium salt and water according to the weight ratio of 1: 0.4-2: 3-20, e.g. 1: 0.5-2: 5-20, and performing ammonium exchange under the condition that the pH value is 2.0-6.0. Wherein, the ammonium salt can comprise one or the combination of more than two of ammonium sulfate, ammonium chloride, ammonium nitrate, ammonium acetate, ammonium oxalate and ammonium phosphate.
In some embodiments, an acidic solution may be used to adjust the pH during the ammonium exchange. The acidic solution can be one or more of hydrochloric acid, sulfuric acid solution, nitric acid solution, acetic acid solution, oxalic acid solution, and carbonic acid solution.
In some embodiments, the temperature for the first calcination of the ammonium exchanged product in S5 is generally controlled to be 300 ℃ to 700 ℃, and the time for the first calcination is generally controlled to be 1h to 10 h.
In some embodiments, in S5, the copper ion exchange process is generally carried out by immersing the product after the ammonium exchange and the first calcination in a solution containing copper salt. The copper salt is soluble copper salt, such as copper nitrate, copper acetate, etc.
In some embodiments, the temperature of the second roasting of the copper ion-exchanged product in S5 is generally controlled to be 300 ℃ to 700 ℃, and the time of the second roasting is generally controlled to be 1h to 10 h.
In some embodiments, in S5, the hydrothermal treatment process may specifically include: and carrying out hydrothermal treatment on the SSZ-39 molecular sieve subjected to secondary roasting in a steam atmosphere, wherein the temperature of the hydrothermal treatment is generally controlled to be 400-850 ℃, such as 500-800 ℃, and the time of the hydrothermal treatment is generally controlled to be 0.5-100 h, such as 20-60 h.
In some specific embodiments, the temperature rise rate during the hydrothermal treatment is generally controlled to be 1 ℃/min-30 ℃/min, preferably 3 ℃/min-8 ℃/min, so as to ensure that the molecular sieve has higher crystallinity and avoid the damage of the molecular sieve structure caused by too high temperature rise rate.
In some embodiments, the water vapor atmosphere may be pure water vapor or a mixture of water vapor and air. The water vapor is generally present in the water vapor atmosphere in a volume content of from 5% to 100%, for example from 7% to 50%; the air content in the water vapor atmosphere is generally from 0% to 95%, for example from 60% to 95%.
According to a specific embodiment of the present invention, the preparation method of the Cu-SSZ-39 molecular sieve may comprise:
1. pretreating a first molecular sieve (generally a Y molecular sieve, wherein the Si/Al molar ratio of the Y molecular sieve is preferably more than or equal to 5.3: 1) and a second molecular sieve (a Beta molecular sieve and/or a ZSM-5 molecular sieve) at 0-85 ℃ for 0.5-10 h by using an acidic substance such as an organic acid, an inorganic acid, a strong acid, a weak base salt and the like, wherein the acidic substance is: (first molecular sieve + second molecular sieve) ═ 0.005 to 0.1: 1, the mass ratio of the first molecular sieve to the second molecular sieve is 1-50: 1.
2. mixing the pretreated first molecular sieve, the pretreated second molecular sieve, a silicon source, an alkali source, an organic template and water to obtain gel, wherein the chemical composition of the gel meets the following molar ratio: (10-100) MOH: al (Al) 2 O 3 ：(10-100)SiO 2 ：(500-1000)H 2 O: (5-20) R, wherein R is an organic template, and MOH is an alkali source;
3. crystallizing the gel at the temperature of 100-180 ℃ for 24-80 h, and roasting the crystallized product at the temperature of 300-700 ℃ for 1-10 h to obtain the SSZ-39 molecular sieve;
4. mixing SSZ-39 molecular sieve, ammonium salt and water according to the weight ratio of 1: 0.4-2: 3-20, performing ammonium exchange under the condition that the pH value is 2.0-6.0, and roasting the ammonium exchange product for the first time for 1-10 h at the temperature of 300-700 ℃;
5. and (3) carrying out copper ion exchange on the first-time roasting product obtained in the step (4), carrying out second roasting on the product subjected to copper ion exchange for 1h-10h at the temperature of 300-700 ℃, and carrying out hydrothermal treatment on the product subjected to second roasting for 0.5h-100h at the temperature of 400-850 ℃ in a water vapor atmosphere with the water vapor volume content of 5-100% and the air volume content of 0-95% to obtain the Cu-SSZ-39 molecular sieve.
The invention also provides a Cu-SSZ-39 molecular sieve which is obtained by the preparation method.
The Cu-SSZ-39 molecular sieve provided by the invention has a higher silicon-aluminum ratio, for example, the silicon-aluminum molar ratio can reach 10-25, for example, 12-20, and 14.9-16.7.
The Cu-SSZ-39 molecular sieve provided by the invention has higher relative crystallinity, specific surface area and pore volume. Specifically, the relative crystallinity of the Cu-SSZ-39 molecular sieve can reach more than 90 percent, and preferably can reach more than 95 percent or even more than 96 percent; the specific surface can reach 700m 2 /g-900m 2 G, e.g. up to 750m 2 /g-850m 2 /g，756m 2 /g-789m 2 (ii)/g; the pore volume can reach 0.2cm 3 /g-0.4cm 3 In g, e.g. 0.25cm 3 /g-0.35cm 3 /g、0.28cm 3 /g-0.29cm 3 /g。
The Cu-SSZ-39 molecular sieve also has higher acid content, and particularly, in the Cu-SSZ-39 molecular sieve, the medium-strength acid accounts for 50-70% of the total acid content.
In some embodiments, the Cu-SSZ-39 molecular sieve comprises, in weight percent, 85 to 99% SSZ-39 molecular sieve, 1% to 15% CuO. In some embodiments, the Cu-SSZ-39 molecular sieve preferably comprises CuO in a weight percentage of 3.0% to 8.0%.
The invention also provides a DeNOx catalyst which comprises the Cu-SSZ-39 molecular sieve. The DeNOx catalyst provided by the invention has high NOx conversion rate and N generation in ammonia selective catalytic reduction reaction catalysis 2 High selectivity of (2).
The invention has the beneficial effects that:
the Cu-SSZ-39 molecular sieve catalyst has the characteristics of high relative crystallinity and silicon-aluminum ratio, high acid strength and good hydrothermal stability, can complete reaction at a lower reaction temperature when used for DeNOx reaction, can improve reactant diffusion, enhances the accessibility of activity, can reduce the occurrence of side reaction, and has good activity and selectivity.
Drawings
FIG. 1 is an XRD pattern of Cu-SSZ-39 molecular sieves prepared in example 1 and comparative example 1.
FIG. 2 is an SEM image of the Cu-SSZ-39 molecular sieve prepared in example 1.
FIG. 3 is a graph of NH of Cu-SSZ-39 molecular sieves prepared in example 1 and comparative example 1 3 -TPD results.
FIG. 4 is a graph of H for Cu-SSZ-39 molecular sieves prepared in examples 1-3 and comparative examples 1-2 2 -TPR results.
Detailed Description
The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.
In the present invention, the terms "first", "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated.
In the following examples and comparative examples, the samples were characterized by the following methods:
XRD characterization adopts an X-ray powder diffractometer of Shimadzu Japan, and the test conditions are as follows: CuKalpha radiation, Ni filtering, tube voltage of 30KV, tube current of 40Ma, step width of 0.02, scanning range of 5-35 degrees and scanning speed of 5 degrees/min.
The relative crystallinity Xi of the molecular sieve is calculated by the following method: xi ═ Σ Ai/Σ AR;
sigma Ai is the sum of XRD peak areas of the samples to be measured, Sigma AR is the sum of XRD peak areas of the reference sample, and the reference sample is the SSZ-39 molecular sieve purchased in the market. In the following examples and comparative examples, SSZ-39 molecular sieve products produced by Mitsubishi corporation were used as reference samples.
The BET characterization adopts a physical and chemical union ipore600 analyzer, the pore volume of the molecular sieve is measured by a low-temperature nitrogen adsorption method, the total pore volume of the molecular sieve is measured according to an RIPP151-90 standard method (compiled by a petrochemical engineering analysis method (RIPP test method), Yangzui and the like, published by scientific publishing company in 1990) and an adsorption isotherm, then the micropore volume of the molecular sieve is measured according to a T-plot method from the adsorption isotherm, and the specific surface area is calculated by a BET method.
Infrared spectrum (IR): and (3) determining the type of the acid center on the surface of the sample by adopting a pyridine adsorption-desorption infrared spectroscopy under the high vacuum condition. The instrument is a Nicolet 870 type Fourier transform infrared spectrometer. The determination method comprises the following steps: taking 8-10 mg-cm -2 A Cu-SSZ-39 molecular sieve powder sample is pressed into a thin sheet and is firstly pressed into a thin sheet at 623K, 1X 10 -3 And (4) after pretreatment for 4 hours under Pa, cooling to room temperature, and scanning the infrared spectrum of the hydroxyl base region of the sample. After adsorption of pyridine at room temperature, the temperature was raised to the measurement temperature (200 ℃ C., 350 ℃ C.) at 10 DEG C -4 Desorbing for 1h under Pa, cooling to room temperature, and recording at 1300-1700 cm -1 Infrared spectrum of the range. The temperature corresponding to the amount of acid is well known in the industry.
The data processing method comprises the following steps: b (l) acid amount ═ a × S/m. In the formula: a is absorbance; m is the sample weight in g; s is the cross-sectional area of the sample in cm 2 . Thus, the amount of B (L) acid specified by this formula is calculated in units of: acm 2 g -1 。
NH 3 TPD characterization Using physical and chemical Co-ordination ichem700, by NH 3 Qualitative strong B acid amount (qualitative), NH, by TPD analysis 3 The specific operation of the TPD analysis method is: and tabletting, mashing and screening the Cu-SSZ-39 molecular sieve sample, and drying the 20-40 mesh particles for later use to obtain the sample to be detected. In the experiment, 0.15g of the dried sample to be tested was accurately weighed and placed in a quartz tube. The lower part of the zeolite bed layer is supported by a quartz sand bed layer, and the upper part of the zeolite bed layer is covered by the quartz sand bed layer, so that the zeolite bed layer is positioned at the position of a thermocouple. Heating the sample to 550 ℃ in He atmosphere, activating for 3h, cooling to room temperature, adsorbing 100% ammonia for 20min, heating to 100 ℃ for constancy, heating to 650 ℃ at the heating rate of 10 ℃/min when the baseline is stable, and collecting an ammonia desorption signal. The desorption temperature of ammonia can be used for reflecting the acid strength of the molecular sieve catalyst, and the higher the desorption temperature of ammonia is, the stronger the corresponding acid strength is.
Hydrogen program liter of zeolite samplesThe thermal reduction analysis is carried out on a physicochemical linkage ichem700 type temperature programming chemical adsorption instrument, 0.3g of a sample to be detected is filled in a reactor, and N is added 2 Purging at 400 deg.C for 1h in atmosphere, cooling to room temperature, and adding N (N) at 15ml/min 2 )/n(H 2 ) Temperature programmed reduction reaction is carried out in a gas flow of 9/1, the temperature is increased to 1100 ℃ at the speed of 10 ℃/min, and multichannel online sampling analysis is carried out by a TCD detector.
And (4) carrying out sample morphology analysis by adopting SEM. The model of the scanning electron microscope instrument is as follows: regulus8100 of HITACHI, Japan. Fixing the fully dried sample on a sample tray by using conductive adhesive, and vacuumizing to 10 DEG -4 And after Pa, performing physical gold plating for 7-10min, and then performing scanning test.
And analyzing the silicon-aluminum ratio of the molecular sieve body, the sodium content in the molecular sieve framework and the like by adopting fluorescence spectroscopy (XRF). Fixing the fully dried molecular sieve on a tabletting machine, tabletting under the pressure of 30MPa, and then carrying out scanning test after purging with an ear suction bulb, wherein the instrument model is as follows: japan science Smart lab.
The NaY molecular sieves used in the following examples and comparative examples had a Si/Al molar ratio of 5.8 and the Beta molecular sieves had a Si/Al molar ratio of 18.4.
Example 1
This example provides a method for preparing a Cu-SSZ-39 molecular sieve, which includes:
1. adding 150g of NaY molecular sieve and 30g of Beta molecular sieve into a beaker, placing the beaker in a water bath at 50 ℃ for stirring, dropwise adding 16.5g of 3mol/L sulfuric acid solution for pretreatment after 5min, stirring for 30min, standing and aging for 1h at 50 ℃, centrifuging, washing and drying to obtain the pretreated NaY molecular sieve and the Beta molecular sieve;
2. according to a 72 NaOH: al (Al) 2 O 3 ：47SiO 2 ：801H 2 O: 35R (R is an organic template, which is the case in the following examples and comparative examples), all of the NaY molecular sieves after pretreatment, all of the Beta molecular sieves after pretreatment, silica sol (silica mass content: 40 wt%), sodium hydroxide solution (solute mass concentration: 5 wt%), organic template agent 2,2,6,6 tetramethyl-N, N-dimethylpiperidine, deionized water were mixed and subjected to gelationReacting to obtain gel;
3. dynamically crystallizing the gel obtained in the step 2 at 160 ℃ for 42h, filtering and drying the gel, and roasting the gel at 480 ℃ for 6h to obtain the SSZ-39 molecular sieve;
4. taking 20g of the SSZ-39 molecular sieve obtained in the step 3, adding 100g of ammonium sulfate solution with the mass fraction of 10%, stirring at room temperature and under the condition that the pH value is 2-6, performing ammonium exchange for 3 times, wherein the ammonium exchange time is 10min each time, and drying the product at 100 ℃ after the ammonium exchange is finished; and roasting the ammonium exchange product by adopting a temperature programming mode, wherein the temperature rising rate is 2 ℃/min, and the temperature rises to 550 ℃ for 5H to obtain the H-SSZ-39 molecular sieve.
5. And (3) stirring the H-SSZ-39 molecular sieve obtained in the step (4) and 0.1mol/L copper nitrate solution at room temperature for 1H for ion exchange, roasting the ion exchange product at 550 ℃ for 4H, and finally carrying out hydrothermal treatment on the roasted sample at 800 ℃ for 50H in a water vapor atmosphere (the volume content of water vapor is 20% and the volume content of air is 80%) to obtain the Cu-SSZ-39 molecular sieve.
The Cu-SSZ-39 molecular sieve of the embodiment has the relative crystallinity of 96 percent, the mole ratio of silicon to aluminum of 14.9 and the specific surface area of 768m after being tested 2 G, pore volume 0.29cm 3 The CuO content is 3.8 wt.%, the relative crystallinity of the molecular sieve after hydrothermal aging at 800 ℃ for 50h is 80%, the grain size is 2-3 mu m, the CuO agglomeration is less, the distribution is uniform, and the Cu content is high 2+ An active site.
Comparative example 1
This comparative example provides a method of preparing a molecular sieve, comprising:
1. according to a 72 NaOH: al (Al) 2 O 3 ：47SiO 2 ：801H 2 O: mixing 150g of NaY molecular sieve, 30g of Beta molecular sieve, silica sol (the mass content of silica is 40 wt%), sodium hydroxide solution (the mass concentration of solute is 5 wt%), organic template agent 2,2,6,6 tetramethyl N, N-dimethyl piperidine and deionized water according to the molar ratio of 35R, and carrying out gelation reaction to obtain gel;
2. dynamically crystallizing the gel obtained in the step 1 at 160 ℃ for 42h, filtering and drying the gel, and roasting the gel at 480 ℃ for 6h to obtain the SSZ-39 molecular sieve;
3. taking 20g of the SSZ-39 molecular sieve obtained in the step 2, adding 100g of ammonium sulfate solution with the mass fraction of 10%, stirring at room temperature for 3 times of ammonium exchange, wherein the ammonium exchange time is 10min each time, and drying the product at 100 ℃ after the ammonium exchange is finished; and roasting the ammonium exchange product by adopting a temperature programming mode, wherein the temperature rising rate is 2 ℃/min, and the temperature rises to 550 ℃ for 5H to obtain the H-SSZ-39 molecular sieve.
4. And (3) stirring the H-SSZ-39 molecular sieve obtained in the step (3) and 0.1mol/L copper nitrate solution for 1H at room temperature and under the condition of pH (2-6) for ion exchange, roasting the ion exchange product at 550 ℃ for 4H, and finally carrying out hydrothermal treatment on the roasted sample at 800 ℃ for 50H in a water vapor atmosphere (the volume content of water vapor is 20% and the volume content of air is 80%) to obtain the Cu-SSZ-39 molecular sieve.
The Cu-SSZ-39 molecular sieve of the comparative example has the relative crystallinity of 66 percent, the mole ratio of silicon to aluminum of 12.3 and the specific surface area of 668m after being tested 2 G, pore volume 0.26cm 3 The CuO content is 3.5 wt.%, the relative crystallinity of the molecular sieve after hydrothermal aging at 800 ℃ for 50h is 55%, the CuO is more agglomerated, and the Cu is more 2+ Has few active sites.
Compared with the test results of the example 1, the invention can effectively improve the crystallinity, the silicon-aluminum ratio, the surface area, the pore volume and the CuO content of the prepared Cu-SSZ-39 molecular sieve and simultaneously effectively improve the hydrothermal stability by pretreating the Y molecular sieve and the Beta molecular sieve which are used as raw materials.
Example 2
This example provides a method for preparing a Cu-SSZ-39 molecular sieve, which includes:
1. adding 175g of NaY molecular sieve and 43g of Beta molecular sieve into a beaker, placing the beaker in a 70 ℃ water bath, stirring, dropwise adding 10.3g of 1mol/L oxalic acid after 5min for pretreatment, stirring for 30min, standing and aging at 70 ℃ for 2h, centrifuging, washing and drying to obtain the pretreated NaY molecular sieve and the Beta molecular sieve;
2. according to 84NH 4 OH：Al 2 O 3 ：52SiO 2 ：810H 2 O: 34.7R, all NaY molecular sieves after pretreatment, all Beta fractions after pretreatmentMixing a sub-sieve, white carbon black, 7 wt.% ammonia water solution, organic template agent 2,2,6, 6-tetramethyl-N-ethylpiperidine and deionized water, and carrying out a gelation reaction to obtain gel;
3. dynamically crystallizing the gel obtained in the step 2 at 150 ℃ for 38h, filtering and drying the gel, and roasting the gel at 540 ℃ for 4h to obtain the SSZ-39 molecular sieve;
4. taking 27g of the SSZ-39 molecular sieve obtained in the step 3, adding 270g of ammonium chloride solution with the mass fraction of 10%, performing ammonium exchange for 1 time under the stirring condition of room temperature and pH 2-6, wherein the ammonium exchange time is 30min each time, and drying the product at 100 ℃ after the ammonium exchange is finished; and roasting the ammonium exchange product by adopting a temperature programming mode, wherein the temperature rising rate is 3 ℃/min, and the temperature rises to 550 ℃ for 4H to obtain the H-SSZ-39 molecular sieve.
5. And (3) stirring the H-SSZ-39 molecular sieve obtained in the step (4) and 0.07mol/L copper acetate solution at room temperature for 3 hours to perform ion exchange. Roasting the ion exchange product at 520 ℃ for 6h, and finally carrying out hydrothermal treatment on the roasted sample at 750 ℃ for 66h in a water vapor atmosphere (the volume content of water vapor is 50% and the volume content of air is 50%), so as to obtain the Cu-SSZ-39 molecular sieve.
Through tests, the Cu-SSZ-39 molecular sieve prepared in the embodiment has the relative crystallinity of 98%, the mole ratio of silicon to aluminum of 15.7 and the specific surface area of 789m 2 G, pore volume 0.28cm 3 The CuO content is 3.3 wt.%, the relative crystallinity of the molecular sieve after hydrothermal aging at 750 ℃ for 66h is 82%, the CuO agglomeration is less, the distribution is uniform, and the Cu content is high 2+ An active site.
Comparative example 2
This comparative example provides a method of preparing a molecular sieve, comprising:
1. according to 84NH 4 OH：Al 2 O 3 ：52SiO 2 ：810H 2 O: 34.7R, mixing 175g of NaY molecular sieve, 43g of Beta molecular sieve, white carbon black, 7 wt.% of ammonia water solution, organic template agent 2,2,6, 6-tetramethyl-N-ethylpiperidine and deionized water, and carrying out a gelation reaction to obtain gel;
2. dynamically crystallizing the gel obtained in the step 1 at 150 ℃ for 38h, dynamically crystallizing the gel obtained in the step 2 at 140 ℃ for 45h, filtering, drying, and roasting at 540 ℃ for 4h to obtain an SSZ-39 molecular sieve to obtain the SSZ-39 molecular sieve;
3. taking 27g of the SSZ-39 molecular sieve obtained in the step 2, adding 270g of ammonium chloride with the mass fraction of 10%, stirring at room temperature and under the condition that the pH value is 2-6, performing ammonium exchange for 1 time, wherein the ammonium exchange time is 30min each time, and drying the product at 100 ℃ after the ammonium exchange is finished; and roasting the ammonium exchange product by adopting a temperature programming mode, wherein the temperature rising rate is 3 ℃/min, and the temperature rises to 550 ℃ for 4H to obtain the H-SSZ-39 molecular sieve.
4. And (3) stirring the H-SSZ-39 molecular sieve obtained in the step (3) and 0.07mol/L copper acetate solution at room temperature for 3 hours to perform ion exchange. Roasting the ion exchange product at 520 ℃ for 6h, and finally carrying out hydrothermal treatment on the roasted sample at 750 ℃ for 66h in a water vapor atmosphere (the volume content of water vapor is 50% and the volume content of air is 50%), so as to obtain the Cu-SSZ-39 molecular sieve.
Through tests, the Cu-SSZ-39 molecular sieve of the comparative example has the relative crystallinity of 59 percent, the mole ratio of silicon to aluminum of 12.8 and the specific surface area of 642m 2 Per g, pore volume 0.26cm 3 The CuO content is 3.9 wt.%, the relative crystallinity of the molecular sieve after hydrothermal aging at 750 ℃ for 66h is 52%, the CuO is more agglomerated, and the Cu content is higher 2+ Has few active sites.
Example 3
This example provides a method for preparing a Cu-SSZ-39 molecular sieve, which includes:
1. adding 1900g of NaY molecular sieve and 70g of Beta molecular sieve into a beaker, placing the beaker in a water bath at 90 ℃ for stirring, dropwise adding 20g of 0.5mol/L hydrochloric acid for pretreatment after 5min, stirring for 30min, standing and aging at 90 ℃ for 1.5h, centrifuging, washing and drying to obtain the pretreated NaY molecular sieve and the Beta molecular sieve;
2. according to 52 NaOH: al (Al) 2 O 3 ：47SiO 2 ：810H 2 O: 44R, mixing all the pretreated NaY molecular sieves, all the pretreated Beta molecular sieves, silica sol (the mass content of silica is 34wt percent), sodium hydroxide solution (the mass concentration is 0.7wt percent), organic template agent 2,2,6,6 tetramethyl N, N-dimethyl piperidine and deionized water, and carrying out gelationAnd reacting to obtain gel;
3. dynamically crystallizing the gel obtained in the step 2 at 140 ℃ for 45 hours, filtering and drying the gel, and roasting the gel at 520 ℃ for 5 hours to obtain the SSZ-39 molecular sieve;
4. taking 25g of the SSZ-39 molecular sieve obtained in the step 3, adding 100g of ammonium sulfate solution with the mass fraction of 10%, stirring at room temperature and under the condition that the pH value is 2-6, performing ammonium exchange for 3 times, wherein the ammonium exchange time is 10min each time, and drying the product at 100 ℃ after the ammonium exchange is finished; and roasting the ammonium exchange product by adopting a temperature programming mode, wherein the temperature rising rate is 2 ℃/min, and the temperature rises to 550 ℃ for 5H to obtain the H-SSZ-39 molecular sieve.
5. And (3) stirring the H-SSZ-39 molecular sieve obtained in the step (4) and 0.4mol/L copper nitrate solution at room temperature for 1H for ion exchange, roasting the ion exchange product at 500 ℃ for 8H, and finally carrying out hydrothermal treatment on the roasted sample at 700 ℃ for 60H in a water vapor atmosphere (the volume content of water vapor is 70% and the volume content of air is 30%) to obtain the Cu-SSZ-39 molecular sieve.
Through tests, the Cu-SSZ-39 molecular sieve prepared in the example has the relative crystallinity of 99 percent, the mole ratio of silicon to aluminum of 16.7 and the specific surface area of 756m 2 G, pore volume 0.29cm 3 The CuO content is 4.1 wt.%, the relative crystallinity of the molecular sieve after aging hydrothermal at 700 ℃ for 60 hours is 88 percent, the CuO agglomeration is less, the distribution is uniform, and the Cu content is high 2+ An active site.
Test example 1
Cu-SSZ-39 molecular sieves prepared in examples 1 to 3 and comparative examples 1 to 2 were applied to NH as catalysts 3 -in an SCR reaction. In the reaction gas, NO X And NH 3 The volume fractions are all 300ppm, O 2 10% by volume, 10% by volume of water vapor, and N 2 As a balance gas. The space velocity is 80000h -1 . The test results are summarized in table 1. NOx conversion and N 2 Selectivity was calculated according to equations (1) and (2), respectively:
Figure BDA0003621218080000111
Figure BDA0003621218080000112
in the above formula:
[NOx] in inlet volume fraction,%, of NOx; [ NOx ]] out Represents the outlet volume fraction,%, of NOx;
[NO] in is the inlet volume fraction of NO,%; [ NO ]] out Is the outlet volume fraction of NO,%;
[N 2 O] out is N 2 Outlet volume fraction of O,%;
[NO 2 ] out is NO 2 Outlet volume fraction of (d)%;
[NH 3 ] in is NH 3 Inlet volume fraction of (d)%;
[NH 3 ] out is NH 3 Outlet volume fraction of (d)%.
TABLE 1
Figure BDA0003621218080000121
As can be seen from table 1, the Cu-SSZ-39 molecular sieves prepared in examples 1 to 3 have higher low temperature activity as DeNOx catalysts.
FIG. 1 is an XRD pattern of Cu-SSZ-39 molecular sieves prepared in example 1 and comparative example 1, and the relative crystallinity of the two can be calculated from FIG. 1. FIG. 2 is an SEM photograph of the Cu-SSZ-39 molecular sieve prepared in example 1, and it can be seen from FIG. 2 that the particle size of the Cu-SSZ-39 molecular sieve is 2-3 μm. FIG. 3 is a graph of NH of Cu-SSZ-39 molecular sieves prepared in example 1 and comparative example 1 3 TPD plot, from which 3 the acid content of the molecular sieve can be calculated. FIG. 4 is a graph of H for Cu-SSZ-39 molecular sieves prepared in examples 1-3 and comparative examples 1-2 2 TPR graph, used to characterize the bound form of CuO in molecular sieves. As can be seen from fig. 4, CuO exists in two reduction modes at different temperatures. H at 200-400 ℃ and 500-750 DEG C 2 The reduction peaks correspond to the separated Cu respectively 2+ Two step reduction of ionsOriginal: from CuO to Cu + Reduction (500 ℃ C. and 750 ℃ C.) and reduction of the metal active site (200 ℃ C. and 400 ℃ C.). H for Cu-SSZ-39 molecular sieve catalysts of examples 1-3 2 The reduction peaks are mainly concentrated in the range of 300-350 ℃, which indicates that more CuO microcrystals and more metal active sites exist in the Cu-SSZ-39 of examples 1-3.
Test example 2
The molecular sieves of examples 1 to 3, comparative examples 1 to 2 were tested for acid sites by pyridine-infrared spectroscopy.
TABLE 2
Figure BDA0003621218080000131
Table 2 shows the results of the acid site test on the surfaces of the molecular sieves prepared in examples 1 to 3 and comparative examples 1 to 2 at a temperature of 200 c and 350 c. It can be seen that the acid amount on the surface of the molecular sieve prepared in the embodiment of the present invention is significantly higher than that of the molecular sieve in the comparative example, and the distribution ratio of the medium and strong acids (B acids) in the molecular sieve in the embodiment is higher than that of the strong acid in the molecular sieve in the comparative example, and the medium and strong acids (B acids) can still maintain higher distribution at high temperature, which indicates that the activity of the molecular sieve prepared in the embodiment of the present invention is greatly improved compared with the activity of the molecular sieve prepared in the comparative example.

Claims (10)

1. A preparation method of a Cu-SSZ-39 molecular sieve comprises the following steps:
s1, pretreating the first molecular sieve and the second molecular sieve by using an acidic substance, mixing the pretreated first molecular sieve, the pretreated second molecular sieve, a silicon source, an alkali source, an organic template and water to obtain gel, wherein the chemical composition of the gel meets the following molar ratio: (10-100) MOH: al (Al) 2 O 3 ：(10-100)SiO 2 ：(500-1000)H 2 O: (5-20) R, wherein R is an organic template, and MOH is an alkali source; the first molecular sieve comprises a Y molecular sieve, the second molecular sieve comprises a Beta molecular sieve and/or a ZSM-5 molecular sieve, and the mass ratio of the first molecular sieve to the second molecular sieve is1-50：1；
S3, crystallizing and roasting the gel to obtain the SSZ-39 molecular sieve;
s5, carrying out copper ion exchange on the SSZ-39 molecular sieve to obtain the Cu-SSZ-39 molecular sieve.
2. The production method according to claim 1, wherein the ratio of the mass of the acidic substance to the total mass of the first molecular sieve and the second molecular sieve in S1 is (0.005-0.1): 1;
preferably, the temperature of the pretreatment is 0 ℃ to 85 ℃, more preferably 20 ℃ to 85 ℃;
preferably, the time of the pretreatment is 0.5h to 10h, more preferably 1h to 7 h;
preferably, the mass ratio of the first molecular sieve to the second molecular sieve is 4-30: 1.
3. the preparation method according to claim 1, wherein in S1, the acidic substance comprises one or a combination of two or more of an organic acid, an inorganic acid, a strong acid and weak base salt;
preferably, the organic acid comprises oxalic acid and/or citric acid, the inorganic acid comprises one or a combination of more than two of hydrochloric acid, sulfuric acid and nitric acid, and the strong acid and weak base salt comprises one or a combination of more than two of aluminum sulfate, aluminum nitrate and aluminum chloride.
4. The method according to claim 1, wherein in S1, SiO is used as the material 2 And Al 2 O 3 And the silicon-aluminum molar ratio of the Y molecular sieve is not less than 5.3: 1, preferably ≥ 5.5: 1;
with SiO 2 And Al 2 O 3 The silicon-aluminum molar ratio of the Beta molecular sieve is 15-50: 1;
with SiO 2 And Al 2 O 3 The silica-alumina molar ratio of the ZSM-5 molecular sieve is 30-60: 1;
the silicon source comprises one or the combination of more than two of water glass, silica sol, white carbon black, tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate and tetrabutyl orthosilicate;
the organic template agent comprises one or the combination of more than two of N, N-dimethyl-N, N-bicyclononane, 2,6, 6-tetramethyl-N, N-dimethylpiperidine, N-cyclooctane-pyridine, 2,6, 6-tetramethyl-N-ethylpiperidine, 2-ethyl-N, N-dimethylpiperidine, 3, 5-dimethyl-N, N-dimethylpiperidine, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide, tetraethylammonium bromide, N-butylamine, triethylamine and ethylenediamine.
5. The preparation method as claimed in claim 1, wherein in S3, the crystallization temperature is 100-180 ℃, and the crystallization time is 24-80 h;
the roasting temperature is 300-700 ℃, and the roasting time is 1-10 h.
6. The preparation method of claim 1, wherein S5 comprises subjecting the SSZ-39 molecular sieve to ammonium exchange, first calcination, and then subjecting the first calcination product to copper ion exchange, second calcination, and hydrothermal treatment to obtain the Cu-SSZ-39 molecular sieve;
preferably, in S5, the temperature of the first roasting is 300-700 ℃, and the time of the first roasting is 1-10 h;
preferably, in S5, the temperature of the second roasting is 300-700 ℃, and the time of the second roasting is 1-10 h.
7. The method of claim 6, wherein the ammonium exchange process comprises: mixing SSZ-39 molecular sieve, ammonium salt and water according to the weight ratio of 1: 0.4-2: 3-20, and performing ammonium exchange under the condition that the pH value is 2.0-6.0;
preferably, the ammonium salt comprises one or a combination of two or more of ammonium sulfate, ammonium chloride, ammonium nitrate, ammonium acetate, ammonium oxalate and ammonium phosphate.
8. The preparation method of claim 6, wherein, in S5, the hydrothermal treatment process comprises: carrying out hydrothermal treatment on the SSZ-39 molecular sieve subjected to secondary roasting in a steam atmosphere;
preferably, the temperature of the hydrothermal treatment is 400-850 ℃, and the time of the hydrothermal treatment is 0.5-100 h; more preferably, the temperature of the hydrothermal treatment is 500-800 ℃, and the time of the hydrothermal treatment is 20-60 h;
more preferably, the temperature rise speed of the hydrothermal treatment is 1-30 ℃/min, more preferably 3-8 ℃/min;
preferably, in the water vapor atmosphere, the volume content of the water vapor is 5-100%, and the volume content of the air is 0-95%;
further preferably, in the water vapor atmosphere, the volume content of the water vapor is 7% -50%, and the volume content of the air is 60% -95%.
9. A Cu-SSZ-39 molecular sieve obtained by the production method according to any one of claims 1 to 8;
preferably, the Cu-SSZ-39 molecular sieve comprises 85-99% of SSZ-39 molecular sieve, 1-15% of CuO; more preferably, the Cu-SSZ-39 molecular sieve comprises 3.0% to 8.0% CuO;
preferably, the Cu-SSZ-39 molecular sieve has a silica to alumina molar ratio of 10-25, preferably 12-20;
preferably, the relative crystallinity of the Cu-SSZ-39 molecular sieve is 90% or more, preferably 95% or more;
preferably, the specific surface area of the Cu-SSZ-39 molecular sieve is 700-900m 2 /g, preferably 750-850m 2 /g；
Preferably, the pore volume of the Cu-SSZ-39 molecular sieve is 0.2-0.4cm 3 Per g, preferably 0.25 to 0.35cm 3 /g；
Preferably, in the Cu-SSZ-39 molecular sieve, the acid content of the medium strong acid accounts for 50% -70% of the total acid content.
10. A DeNOx catalyst comprising the Cu-SSZ-39 molecular sieve of claim 9.
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