Method for synthesizing Cu-SSZ-39 molecular sieve through synergistic regulation and control of microwave radiation and specific template and application of Cu-SSZ-39 molecular sieve

Abstract

The invention provides a method for synthesizing a Cu-SSZ-39 molecular sieve through synergistic regulation and control of microwave radiation and a specific template. The method provided by the invention comprises the following steps: mixing an alkali source, a silicon source, a template agent and deionized water to obtain a first mixed solution; adding an aluminum source into the first mixed solution, and adding a seed crystal to obtain a second mixed solution; and putting the second mixed solution into a microwave reactor, crystallizing by adopting stepped heating, washing, drying and roasting to obtain the SSZ-39 molecular sieve. According to the microwave synthesis method provided by the invention, the hydrothermal crystallization time of the SSZ-39 molecular sieve is shortened from conventional 72 hours to 4 hours, the grain size of the molecular sieve is about 200-400 nm, rapid and efficient synthesis of the catalyst is realized, and the finally obtained product has excellent NH3-SCR catalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieve synthesis, and in particular to a method for synthesizing Cu-SSZ-39 molecular sieve by coordinated regulation of microwave radiation and a specific template and an application thereof. Background Art

[0002] The global energy crisis and the greenhouse effect are intensifying. Diesel engines based on lean burn technology have shown unique advantages in terms of power and fuel economy. They can significantly reduce the emission of greenhouse gas CO2. However, the large amount of harmful substances such as nitrogen oxides emitted from diesel vehicle exhaust can cause a series of environmental problems such as photochemical smog, haze, acid rain, and ozone layer depletion. At present, the elimination of NO x The most effective and widely used technology is ammonia selective catalytic reduction (NH3-SCR). The key to this technology lies in developing denitrification catalysts with high activity, good selectivity, and strong water and sulfur resistance. Among various catalysts, Cu-based molecular sieves are considered ideal for the NH3-SCR reaction due to their excellent redox performance, suitable acidity, and high hydrothermal stability. Domestic and international studies have shown that copper-based small-pore molecular sieves with CHA structures (SSZ-13) and AEI structures (SSZ-39) exhibit excellent SCR catalytic activity and resistance to HC poisoning, demonstrating promising application prospects. The SSZ-39 molecular sieve, with its AEI structure featuring adjacent double six-membered rings arranged in a mirror-image arrangement, exhibits superior high-temperature hydrothermal stability compared to Cu-SSZ-13. Considering my country's future stringent vehicle emission standards, Cu-SSZ-39 molecular sieves hold broad application prospects.

[0003] The traditional hydrothermal synthesis of SSZ-39 requires a long time for crystallization (usually >72 hours), the product particle size is large and unevenly distributed, and the synthesized molecular sieve has certain limitations in the diffusion and mass transfer of reactants and products. In addition, the NH3-SCR window temperature of the hydrothermally synthesized copper-based SSZ-39 catalyst is mainly concentrated in 200℃~500℃, and the denitrification effect on low-temperature flue gas generated by cold start and long-term low-speed operation of mobile sources is not ideal. In view of the existence of the above problems, it is necessary to provide a method for the rapid and efficient synthesis of SSZ-39 catalyst, which has good performance in improving the low-temperature activity and hydrothermal stability of small-pore molecular sieves, which is crucial for the efficient denitrification of diesel vehicle exhaust. Summary of the Invention

[0004] The present invention aims to overcome the time-consuming and energy-intensive drawbacks of conventional hydrothermal synthesis methods by providing a method and application for synthesizing Cu-SSZ-39 molecular sieves using microwave radiation and a specific template. Currently, the hydrothermal method for crystallizing SSZ-39 molecular sieves takes 3-7 days, resulting in long crystallization times, low efficiency, and high energy consumption, which increases the cost of synthesizing the molecular sieve.

[0005] The present invention provides a microwave preparation method to achieve rapid and efficient synthesis of SSZ-39 molecular sieve. The method shortens the hydrothermal crystallization time of the molecular sieve from the conventional 72 hours to 4 hours. The molecular sieve has a grain size of 200-400 nm, a uniform size distribution, and a specific surface area of ​​>600 m 2 / g.

[0006] At the same time, the present invention provides a copper-based SSZ-39 molecular sieve catalyst, which has very excellent low-temperature denitrification activity and a NOx conversion rate of more than 90% within a wide temperature range of 175-550°C, which can meet the requirements of National VI diesel vehicle exhaust treatment catalysts.

[0007] A method for synthesizing Cu-SSZ-39 molecular sieve by synergistically regulating microwave radiation and a specific template comprises the following steps:

[0008] 1) Mixing an alkali source, a silicon source, a template, and deionized water, stirring in an oil bath at 70-90° C. for 0.5-2 h, and cooling to obtain a first mixed solution;

[0009] 2) adding a liquid aluminum source to the first mixed solution, adding SSZ-39 seed crystals accounting for 5% to 20% of the mass of the silicon source, and stirring for 0.5 to 2 hours in an oil bath heated at 70 to 90° C. to obtain a second mixed solution;

[0010] 3) placing the second mixed solution in a microwave reactor and crystallizing at 120-200° C., cooling after the reaction, washing, drying at 80-120° C. for 5-12 h, and then calcining at 550-750° C. for 4-8 h to obtain SSZ-39 molecular sieve;

[0011] 4) Immersing the obtained SSZ-39 molecular sieve in a copper ion solution, performing ion exchange at 70-90°C for 3-6 hours, with a mass ratio of copper ions to silicon source of (0.02-0.06):1, washing after exchange, drying at 80-120°C for 5-12 hours, and then calcining at 550°C-750°C for 4-8 hours to obtain a Cu-SSZ-39 molecular sieve catalyst.

[0012] The inventors of the present invention have discovered through extensive experimental research that, during the synthesis of SSZ-39 molecular sieves, by controlling the contents of appropriate silicon sources, aluminum sources, templates, and seed crystals, and by employing the aforementioned specific templates in combination with microwave heating equipment, SSZ-39 molecular sieves can be rapidly synthesized within a few hours. Further introduction of copper yields Cu-SSZ-39 molecular sieves with excellent NH3-SCR activity and high-temperature hydrothermal stability.

[0013] According to the present invention, preferably, in step 1), the template agent is N,N-dimethyl-3,5-dimethylpiperidinium hydroxide or N,N-diethyl-cis-2,6-dimethylpiperidinium hydroxide.

[0014] Preferably, according to the present invention, in step 1), the mass ratio of the template to the silicon source is (0.4-0.9):1.

[0015] According to the preferred embodiment of the present invention, in step 1), the silicon source is silica sol or tetraethyl orthosilicate.

[0016] Preferably according to the present invention, in step 1), the alkali source is sodium hydroxide or potassium hydroxide.

[0017] According to the preferred embodiment of the present invention, in step 1), the stirring temperature of the first mixed solution is 70-90° C., for example, 70° C., 80° C., 90° C. The stirring time of the first mixed solution is 0.5-5 h, for example, 0.5 h, 1 h, 1.5 h, 2 h.

[0018] According to a preferred embodiment of the present invention, in step 2), the aluminum source is USY molecular sieve, pseudo-boehmite or aluminum isopropoxide.

[0019] According to the preferred embodiment of the present invention, in step 2), the particle size of the seed crystal SSZ-39 is 50-200 nm, and the SiO2 / Al2O3 molar ratio thereof is (15-25):1.

[0020] According to the preferred embodiment of the present invention, in step 2), the stirring temperature of the second mixture is 70-90° C., for example, 70° C., 80° C., 90° C. The stirring time of the second mixture is 0.5-2 h, for example, 0.5 h, 1 h, 1.5 h, 2 h.

[0021] Preferably according to the present invention, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the mass ratio of the silicon source, aluminum source, alkali source, seed crystal, and deionized water is 1: (0.05-0.15): (0.1-0.25): (0.1-0.25): (2.0-3.5).

[0022] According to a preferred embodiment of the present invention, in step 3), microwave crystallization adopts a step-by-step temperature program: first react at 120-150° C. for 1-2 h, then heat to 160-200° C. for 1-2 h.

[0023] According to the preferred embodiment of the present invention, in step 3), during the microwave crystallization process, the heating rate is controlled to be 5-10° C. / min, accompanied by pulsed microwave radiation, and the working / rest time ratio is 3:1-5:1.

[0024] Preferably according to the present invention, in step 3), the microwave power is 400-600W.

[0025] In some embodiments, the microwave crystallization temperature is 120-200°C, for example, 125°C, 130, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, or 200°C.

[0026] In some embodiments, the microwave synthesis power is 400-600W, for example, 400W, 450W, 500W, 550W, 600W, preferably 400-500W.

[0027] In some embodiments, the microwave crystallization time is 1-4 h, such as 1 h, 2 h, 3 h, 4 h, preferably 3-4 h.

[0028] According to the preferred embodiment of the present invention, in step 3), the drying temperature is 80-120° C., for example, 80° C., 90° C., 100° C., 110° C., 120° C. The drying time is 5-12 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h.

[0029] According to the preferred embodiment of the present invention, in step 3), the calcination temperature is 550-750° C., for example, 550° C., 600° C., 650° C., 700° C., 750° C. The calcination time is 4-8 h, for example, 4 h, 5 h, 6 h, 7 h, 8 h.

[0030] According to the preferred embodiment of the present invention, in step 4), the copper source is copper nitrate or copper acetate, and the concentration of the copper ion solution is 0.1-0.5 mol / L. The specific surface area of ​​the product after ion exchange is 600-650 m 2 / g, and the grain size is 200-400nm.

[0031] In some embodiments, in step 4), the copper ion exchange temperature is 70-90° C., for example, 70° C., 80° C., or 90° C. The exchange time is 3-6 h, for example, 3 h, 4 h, 5 h, or 6 h.

[0032] In some embodiments, in step 4), the drying temperature is 80-120° C., for example, 80° C., 90° C., 100° C., 110° C., or 120° C. The drying time is 5-12 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, or 12 h.

[0033] In some embodiments, in step 4), the calcination temperature is 550° C.-750° C., for example, 550° C., 600° C., 650° C., 700° C., or 750° C. The calcination time is 4-8 h, for example, 4 h, 5 h, 6 h, 7 h, or 8 h.

[0034] The present invention also provides a molecular sieve, which is prepared by the above molecular sieve preparation method and has a particle size of 200-400 nm.

[0035] Cu loading is 2.0-4.5 wt%, and NOx conversion rate in NH3-SCR reaction is ≥95% (200℃, space velocity 200,000h -1 ).

[0036] The present invention also provides an application of a copper-based molecular sieve prepared by the molecular sieve preparation method in a denitration reaction.

[0037] In some embodiments, the Cu-SSZ-39 molecular sieve is used for the conversion of nitrogen oxides in stationary source flue gas and / or mobile source exhaust gas, such as diesel vehicle exhaust.

[0038] In some embodiments, the use comprises reacting nitrogen oxide in the presence of the Cu-SSZ-39 molecular sieve prepared by the method of the first aspect.

[0039] In some embodiments, the reaction temperature is 100-550°C.

[0040] In some embodiments, the reaction space velocity is 100,000-500,000 h -1 .

[0041] In some embodiments, the Cu loading is 2.0-4.5 wt %, and the NOx conversion rate in the NH3-SCR reaction is ≥95% (200°C, space velocity 200,000h -1 ).

[0042] In some embodiments, Cu-SSZ-39 molecular sieve is used for ammonia selective catalytic reduction of nitrogen oxides (NH3-SCR) in diesel vehicle exhaust treatment, with a NOx removal rate of ≥90% and N2 selectivity of ≥95% in the range of 175-550°C.

[0043] Beneficial effects of the present invention:

[0044] 1. The present invention adopts microwave method to shorten the hydrothermal crystallization time of molecular sieve from the conventional 72h to 4h. The molecular sieve grain size is about 200-400nm and the specific surface area is greater than 600m 2 / g, which is more conducive to the adsorption and diffusion of reactants, realizes the rapid and efficient synthesis of SSZ-39 molecular sieve and reduces energy consumption.

[0045] 2. The present invention discloses a copper-based SSZ-39 molecular sieve catalyst with excellent low-temperature denitrification activity and hydrothermal stability. The NOx conversion rate reaches over 90% in a wide temperature range of 175 to 550°C. The activity after hydrothermal aging reaches over 85% in a wide temperature range of 150 to 450°C. The catalyst obtained by this method has better NH3-SCR low-temperature activity and high-temperature hydrothermal stability than the Cu-SSZ-39 obtained by the traditional hydrothermal method, and can meet the requirements of the National VI diesel vehicle exhaust treatment catalyst.

[0046] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0048] Figure 1 Shown is a process flow chart of the microwave synthesis of SSZ-39 provided in Example 1;

[0049] Figure 2 1 is a comparison diagram of the X-ray diffraction patterns of Example 1 of the present invention and Comparative Example 1;

[0050] Figure 3 The SEM images of Example 1 and Comparative Example 1 are compared.

[0051] Figure 4 is the X-ray diffraction pattern of Examples 1-9 of the present invention;

[0052] Figure 5 X-ray diffraction patterns of Example 1 and Examples 10-11 of the present invention;

[0053] Figure 6 This is the SCR activity test of the catalysts of Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0054] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples. The following examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0055] Example 1

[0056] The preparation method of SSZ-39 molecular sieve by microwave synthesis comprises the following steps:

[0057] Take 0.2518g of sodium hydroxide solid and add 0.63g of water, stirring to dissolve. Add 4.064g of 25% N,N-diethyl-2,6-dimethylpiperidinium hydroxide template and stir until uniform. Add 2.5g of 40% silica sol dropwise and stir in an 80°C oil bath for 1 hour to obtain mixed solution 1. After cooling to room temperature, add 1.14g of USY molecular sieves and 0.25g of SSZ-39 seed crystals to mixed solution 1 and continue stirring for half an hour. Transfer the sample in the beaker to a microwave apparatus at 400W power. React at 150°C for 1 hour, then increase to 180°C for crystallization for 3 hours. After cooling to room temperature, remove the sample, rinse with water, and centrifuge three times until the centrifuge is clear. Oven dry at 100°C for 12 hours. Grind the dried sample into a powder and calcine in a crucible at 600°C for 4 hours (heating rate 5°C / min) in a muffle furnace. The prepared SSZ-39 molecular sieve was ion exchanged with 0.2 mol / L Cu(Ac)2 solution at 80°C for 3 h to obtain Cu-SSZ-39 catalyst.

[0058] Example 2

[0059] The only difference between Example 2 and Example 1 is that 0.5 g of 40% silica sol is added.

[0060] Example 3

[0061] The only difference between Example 3 and Example 1 is that 1.5 g of 40% silica sol is added.

[0062] Example 4

[0063] The only difference between Example 4 and Example 1 is that 2.0 g of 40% silica sol is added.

[0064] Example 5

[0065] The only difference between Example 5 and Example 1 is that 2.6 g of 40% silica sol is added.

[0066] Example 6

[0067] The only difference between Example 6 and Example 1 is that 2.7 g of 40% silica sol is added.

[0068] Example 7

[0069] The only difference between Example 7 and Example 1 is that 2.8 g of 40% silica sol is added.

[0070] Example 8

[0071] The only difference between Example 8 and Example 1 is that 2.9 g of 40% silica sol is added.

[0072] Example 9

[0073] The only difference between Example 9 and Example 1 is that 3.2 g of 40% silica sol is added.

[0074] Example 10

[0075] The only difference between Example 10 and Example 1 is that: in a microwave instrument, the temperature is 180°C, the power is 400W, the reaction is first carried out at 150°C for 1 hour, and then the temperature is raised to 180°C for reaction and crystallization for 1 hour.

[0076] Example 11

[0077] The only difference between Example 11 and Example 1 is that: in a microwave instrument, the temperature is 180°C, the power is 400W, the reaction is first carried out at 150°C for 1 hour, and then the temperature is raised to 180°C for reaction and crystallization for 2 hours.

[0078] Comparative Example 1

[0079] Take 0.2518g of sodium hydroxide solid and add 0.63g of water, stirring to dissolve. Add 4.064g of 25% N,N-diethyl-2,6-dimethylpiperidinium hydroxide template and stir until uniform. Add 2.5g of 40% silica sol dropwise and stir in an 80°C oil bath for 1 hour. After cooling to room temperature, add 1.14g of USY molecular sieves and 0.25g of SSZ-39 seed crystals and continue stirring for half an hour. Transfer the sample from the beaker to a hydrothermal reactor and hydrothermally crystallize at 180°C for 10 hours. After cooling, remove the sample, rinse with water, and centrifuge three times until the centrifuge is clear. Oven dry at 100°C for 12 hours. Grind the dried sample into a powder and calcine it in a crucible at 600°C for 4 hours (heating rate 5°C / min) in a muffle furnace. The prepared SSZ-39 molecular sieve was ion exchanged with 0.2 mol / LCu(Ac)2 solution at 80°C for 3 h to obtain Cu-SSZ-39 catalyst.

[0080] Comparative Example 2

[0081] Comparative Example 2 differs from Example 1 in that the hydrothermal synthesis time is extended to 72 hours, achieving complete formation of SSZ-39. The prepared SSZ-39 molecular sieve is ion-exchanged with a 0.2 mol / L Cu(Ac)2 solution at 80°C for 3 hours to obtain the comparative example Cu-SSZ-39 catalyst.

[0082] Activity evaluation

[0083] The Cu-SSZ-39 catalyst samples prepared in the Examples and Comparative Examples were pelletized and sieved, and the 40-60 mesh size catalyst was used for the experiment. The gas components in the NH3-SCR activity test were as follows: 500 ppm NH3, 500 ppm NO, 5 vol% O2 and N2 balance, temperature range 100-550°C, total flow rate 300 ml / min, space velocity 200,000 h -1 The SCR activity of the catalyst was tested by catalytic reaction under the conditions of Figure 5 ).

[0084] From the XRD data of Example 1 and Comparative Example 1 ( Figure 2 ) It can be seen that the embodiment has been completely converted into the SSZ-39 crystal structure under the conditions of microwave synthesis for 4 hours, while the hydrothermal method still retains a large amount of raw material USY after 10 hours, and only a weak SSZ-39 diffraction peak appears, indicating that microwave accelerates the crystallization process and shortens the synthesis time.

[0085] From the SEM data of Example 1 and Comparative Example 1 ( Figure 3 ) It can be seen that in the embodiment, cubic particles of 200-400 nm were obtained under microwave synthesis conditions for 4 hours, and the mixed particles of cubes and spheres obtained by the hydrothermal method were larger in size and unevenly distributed.

[0086] From the XRD of Examples 1-9 ( Figure 4 ) data show that SSZ-39 is affected by the ratio of silicon source to other components, and SSZ-39 can only be synthesized within a certain ratio range.

[0087] From the XRD of Examples 1, 10-11 ( Figure 5 ) data show that SSZ-39 crystals have been mostly converted as early as 2 hours in microwave and completely converted after 4 hours.

[0088] The SCR activity data from Example 1 and Comparative Example 2 demonstrate that the Cu-SSZ-39 molecular sieve catalyst prepared by the present invention exhibits excellent denitration activity in the NH3-SCR reaction, with particularly significant increases in low-temperature activity. NOx conversion rates exceed 90% over a wide temperature range of 175°C to 500°C.

[0089] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for synthesizing Cu-SSZ-39 molecular sieve by synergistically regulating microwave radiation and a specific template, comprising the following steps: 1) Mixing an alkali source, a silicon source, a template, and deionized water, stirring in an oil bath at 70-90° C. for 0.5-2 h, and cooling to obtain a first mixed solution; 2) adding a liquid aluminum source to the first mixed solution, adding SSZ-39 seed crystals accounting for 5% to 20% of the mass of the silicon source, and stirring for 0.5 to 2 hours in an oil bath heated at 70 to 90° C. to obtain a second mixed solution; 3) placing the second mixed solution in a microwave reactor and crystallizing at 120-200° C., cooling after the reaction, washing, drying at 80-120° C. for 5-12 h, and then calcining at 550-750° C. for 4-8 h to obtain SSZ-39 molecular sieve; 4) Immersing the obtained SSZ-39 molecular sieve in a copper ion solution, performing ion exchange at 70-90°C for 3-6 hours, with a mass ratio of copper ions to silicon source of (0.02-0.06):1, washing after exchange, drying at 80-120°C for 5-12 hours, and then calcining at 550°C-750°C for 4-8 hours to obtain a Cu-SSZ-39 molecular sieve catalyst.

2. The method according to claim 1, characterized in that In step 1), the template agent is N,N-dimethyl-3,5-dimethylpiperidinium hydroxide or N,N-diethyl-cis-2,6-dimethylpiperidinium hydroxide, and the mass ratio of the template agent to the silicon source is (0.4-0.9):

1.

3. The method according to claim 1, characterized in that In step 1), the silicon source is silica sol or tetraethyl orthosilicate, and the alkali source is sodium hydroxide or potassium hydroxide.

4. The method according to claim 1, wherein In step 2), the aluminum source is USY molecular sieve, pseudo-boehmite or aluminum isopropoxide, the seed crystal SSZ-39 has a particle size of 50-200 nm, and its SiO2 / Al2O3 molar ratio is (15-25):

1.

5. The method according to claim 1, characterized in that The silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the mass ratio of silicon source, aluminum source, alkali source, seed crystal and deionized water is 1: (0.05~0.15): (0.1~0.25): (0.1~0.25): (2.0~3.5).

6. The method according to claim 1, characterized in that In step 3), microwave crystallization adopts a step-by-step heating program: first react at 120-150°C for 1-2 hours, then rise to 160-200°C for 1-2 hours. During the microwave crystallization process, the heating rate is controlled at 5-10°C / min, accompanied by pulsed microwave radiation, the working / intermission time ratio is 3:1-5:1, and the microwave power is 400-600W.

7. The method according to claim 1, characterized in that In step 4), the copper source is copper nitrate or copper acetate, and the concentration of the copper ion solution is 0.1 to 0.5 mol / L.

8. A Cu-SSZ-39 molecular sieve catalyst, which is prepared by the preparation method of any molecular sieve according to claim 1, has a particle size of 200-400 nm, and a Cu loading of 2.0-4.5 wt%.

9. Use of the Cu-SSZ-39 molecular sieve catalyst according to claim 8 in a denitration reaction.

10. The use according to claim 9, wherein the Cu-SSZ-39 molecular sieve is used for the conversion of nitrogen oxides in fixed source flue gas and / or mobile source exhaust gas, such as diesel vehicle exhaust, at a reaction temperature of 100-550°C and a reaction space velocity of 100,000-500,000 h -1 , in the range of 175~550℃, the NOx removal rate is ≥90%, and the N2 selectivity is ≥95%.

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