CN113213505B

CN113213505B - SSZ-13 molecular sieve, preparation method thereof and Cu-SSZ-13 molecular sieve

Info

Publication number: CN113213505B
Application number: CN202110698018.3A
Authority: CN
Inventors: 于吉红; 陈梦阳; 白璞; 闫文付; 李延峰; 李庆硕; 薛海霞
Original assignee: Luoyang Jianlong Micro Nano New Materials Co ltd; Jilin University
Current assignee: Luoyang Jianlong Micro Nano New Materials Co ltd; Jilin University
Priority date: 2021-06-23
Filing date: 2021-06-23
Publication date: 2022-07-19
Anticipated expiration: 2041-06-23
Also published as: CN113213505A

Abstract

The invention provides an SSZ-13 molecular sieve, a preparation method thereof and a Cu-SSZ-13 molecular sieve, belonging to the technical field of catalysts. The invention takes the diatomite as a silicon source, and because the diatomite contains Fe element, the Fe can be directly introduced into the SSZ-13 molecular sieve in the crystallization process³⁺Avoiding the introduction of Fe by the subsequent ion exchange method³⁺The operation is simpler; meanwhile, diatomite is used as a silicon source, and Fe is introduced in the crystallization process³⁺Can avoid Fe³⁺Fe in the SSZ-13 molecular sieve as extra framework Fe³⁺In the form of ions. The Cu-SSZ-13 molecular sieve catalyst prepared by the SSZ-13 molecular sieve has good high-temperature catalytic activity, and solves the defect of the reduction of the high-temperature activity of the traditional Cu-SSZ-13.

Description

SSZ-13 molecular sieve, preparation method thereof and Cu-SSZ-13 molecular sieve

Technical Field

The invention relates to the technical field of catalysts, and particularly relates to an SSZ-13 molecular sieve, a preparation method thereof and a Cu-SSZ-13 molecular sieve.

Background

Nitrogen oxides are one of the main pollutants of the atmosphere, the main sources of which are motor vehicle exhaust emissions and the combustion of fossil fuels in power plants. With the increasing strictness of the national standards for the exhaust gas of automobiles, especially diesel vehicles, it is important to develop a denitration catalyst with high activity and high hydrothermal stability. The denitration catalyst most widely studied at present is a Cu-SSZ-13 molecular sieve catalyst.

In order to ensure the catalytic activity and hydrothermal stability of the Cu-SSZ-13 molecular sieve catalyst, Fe needs to be introduced into the Cu-SSZ-13 molecular sieve³⁺Ions. The traditional Cu-SSZ-13 molecular sieve adopts an ion exchange or impregnation method to introduce Fe³⁺Complicated steps, easy to make Fe³⁺Aggregation, which results in a decrease in the high temperature activity of the Cu-SSZ-13 molecular sieve catalyst.

Disclosure of Invention

In view of the above, the present invention aims to provide an SSZ-13 molecular sieve, a preparation method thereof, and a Cu-SSZ-13 molecular sieve. The method provided by the invention is simple to operate and can avoid Fe³⁺And (4) aggregating.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of an SSZ-13 molecular sieve, which comprises the following steps:

mixing diatomite, NaOH, N, N, N-trimethyl-1-adamantyl ammonium hydroxide, aluminum hydroxide and water to obtain a mixed solution;

and heating and crystallizing the mixed solution to obtain the SSZ-13 molecular sieve.

Preferably, the mass ratio of the diatomite, NaOH, N, N, N-trimethyl-1-adamantyl ammonium hydroxide and aluminum hydroxide is (2-3.6): (0.2-0.4): (2-4): 0.156.

Preferably, the particle size of the diatomite is 1-3 μm.

Preferably, the heating crystallization temperature is 140-160 ℃, and the time is 60-72 h.

The invention provides the SSZ-13 molecular sieve prepared by the preparation method.

Preferably, the SSZ-13 molecular sieve has an aluminum-silicon ratio of 8-11, an iron-aluminum ratio of 0.14-0.16 and a specific surface area of 446-466 m²Per g, the volume of the micro-pores is 0.20-0.22 cm³/g。

The invention provides a preparation method of a Cu-SSZ-13 molecular sieve, which comprises the following steps:

(1) preparing the SSZ-13 molecular sieve according to the preparation method;

(2) soaking the SSZ-13 molecular sieve in a soluble ammonium salt solution for first ion exchange, then soaking a solid subjected to the first ion exchange in a soluble copper salt solution for second ion exchange to obtain a Cu-SSZ-13 molecular sieve precursor;

(3) and calcining the precursor of the Cu-SSZ-13 molecular sieve to obtain the Cu-SSZ-13 molecular sieve.

Preferably, the soluble ammonium salt is ammonium nitrate and/or ammonium chloride, and the concentration of the soluble ammonium salt solution is 0.1-1 mol/L;

the soluble copper salt is one or more of copper nitrate, copper acetate and copper sulfate, and the concentration of the soluble copper salt is 0.002-0.1 mol/L.

The invention provides the Cu-SSZ-13 molecular sieve prepared by the preparation method.

The invention provides an application of the Cu-SSZ-13 molecular sieve in selective catalytic reduction of ammonia.

The invention provides a preparation method of an SSZ-13 molecular sieve, which comprises the following steps: mixing diatomite, NaOH, N, N, N-trimethyl-1-adamantyl ammonium hydroxide, aluminum hydroxide and water to obtain a mixed solution; and heating and crystallizing the mixed solution to obtain the SSZ-13 molecular sieve. The invention takes the diatomite as a silicon source, and because the diatomite contains Fe element, the Fe element can be directly introduced into the SSZ-13 molecular sieve in the crystallization process³⁺Avoiding the introduction of Fe by the subsequent ion exchange method³⁺The operation is simpler; meanwhile, diatomite is used as a silicon source, and Fe is introduced in the crystallization process³⁺Can avoid Fe³⁺Fe in the SSZ-13 molecular sieve as extra framework Fe³⁺In the form of ions.

Furthermore, the heating crystallization time is 60-72 h, and compared with the traditional preparation method of the SSZ-13 molecular sieve (the crystallization time is 120-144 h), the crystallization time is greatly reduced.

The invention provides a preparation method of a Cu-SSZ-13 molecular sieve, which comprises the steps of firstly preparing the SSZ-13 molecular sieve according to the method and then respectively mixing with NH⁴⁺、Cu²⁺And carrying out ion exchange, and calcining to obtain the Cu-SSZ-13 molecular sieve. In the Cu-SSZ-13 molecular sieve, Cu²⁺And Fe³⁺Respectively used as active centers at low temperature (less than or equal to 400 ℃) and high temperature (more than 400 ℃), because the invention takes the diatomite as the silicon source, the Fe is introduced in the crystallization process³⁺Fe in the obtained Cu-SSZ-13 molecular sieve³⁺The aggregation is avoided, so that the Cu-SSZ-13 molecular sieve catalyst has good high-temperature catalytic activity, and the defect of reduced high-temperature activity of the traditional Cu-SSZ-13 is overcome; meanwhile, the SSZ-13 molecular sieve contains Fe³⁺，Fe³⁺Has the inhibition of Cu²⁺The Cu-SSZ-13 molecular sieve has good low-temperature catalytic activity due to the aggregation effect. The results of the examples show that the NO conversion rate of the Cu-SSZ-13 molecular sieve provided by the invention is still higher than 95% at 400-500 ℃.

Drawings

FIG. 1 is an XRD diffractogram of the product obtained in example 1 at various times;

FIG. 2 is a graph showing the degree of crystallization of the product obtained in example 1 at various times;

FIG. 3 is an IR spectrum of a product obtained in example 1 at different crystallization times;

FIG. 4 is an XPS spectrum of SSZ-13 molecular sieve obtained after crystallization for 60 hours;

FIG. 5 is an infrared spectrum of the SSZ-13 molecular sieve obtained after 60h of crystallization;

FIG. 6 is an EPR spectrum of the SSZ-13 molecular sieve obtained after 60h of crystallization;

FIG. 7 is an XRD diffractogram of the resulting product for different Si/Al ratios in example 2;

FIG. 8 shows N of SSZ-13 molecular sieve having a Si/Al ratio of 8 to 10₂Adsorption-desorption curves;

FIG. 9 is an XRD diffractogram of the product obtained in comparative example 1 at various times;

FIG. 10 is a graph showing the degree of crystallization of the product obtained in comparative example 1 at various times;

FIG. 11 is a scanning electron micrograph of SSZ-13 molecular sieve sample 3 from example 2;

FIG. 12 is a scanning electron micrograph of the SSZ-13 molecular sieve obtained in comparative example 1;

FIG. 13 shows the NO conversion at different times for the catalysts obtained in the present invention and comparative examples.

Detailed Description

The invention mixes diatomite, NaOH, N, N, N-trimethyl-1-adamantyl ammonium hydroxide, aluminum hydroxide and water to obtain mixed solution. The present invention does not require any particular source for the above raw materials, and any commercially available raw materials can be used.

In the invention, the mass ratio of the diatomite, NaOH, N, N, N-trimethyl-1-adamantyl ammonium hydroxide and aluminum hydroxide is (2-3.6): (0.2-0.4): (2-4): 0.156, more preferably 3: 0.2: 3: 0.156.

in the present invention, the particle size of the diatomaceous earth is preferably 1 to 3 μm, and more preferably 1.5 to 2 μm.

In the present invention, the N, N, N-trimethyl-1-adamantyl ammonium hydroxide functions as a template.

In the present invention, the mixing is preferably performed in the following manner: firstly, mixing NaOH, N, N, N-trimethyl-1-adamantyl ammonium hydroxide and water, then adding aluminum hydroxide into the mixed solution for first stirring, then adding diatomite into the mixed solution for second stirring. In the present invention, the time of the first stirring is preferably 1 hour, and the time of the second stirring is preferably 3 hours. In the present invention, the first stirring and the second stirring are preferably 400 to 600rpm, and more preferably 500rpm, independently.

After the mixed liquid is obtained, the invention heats and crystallizes the mixed liquid to obtain the SSZ-13 molecular sieve. In the present invention, the heat crystallization is preferably performed in a reaction vessel. In the invention, the heating crystallization temperature is preferably 140-160 ℃, and more preferably 150-160 ℃; the time is preferably 60 to 72 hours, and more preferably 60 to 65 hours.

The invention provides the SSZ-13 molecular sieve prepared by the preparation method. In the invention, the ratio of aluminum to silicon of the SSZ-13 molecular sieve is preferably 8-11, and more preferably 9-10; the iron-aluminum ratio is preferably 0.14-0.16, and more preferably 0.15-0.16; the specific surface area is preferably 446 to 466m²(iv)/g, more preferably 450 to 460m²(iv) g; the preferable micropore volume is 0.20-0.22 cm³A concentration of 0.21 to 0.22cm³/g。

(1) preparing the SSZ-13 molecular sieve according to the preparation method;

The SSZ-13 molecular sieve is prepared according to the preparation method. The preparation method is the same as above, and is not described herein again.

The method comprises the steps of immersing the SSZ-13 molecular sieve in a soluble ammonium salt solution for first ion exchange, then immersing the solid after the first ion exchange in a soluble copper salt solution for second ion exchange, and obtaining a Cu-SSZ-13 molecular sieve precursor.

In the invention, the soluble ammonium salt solution is preferably an ammonium nitrate solution, and the concentration of the soluble ammonium salt solution is preferably 0.1-1 mol/L, and more preferably 0.5-1 mol/L. In the invention, the temperature of the first ion exchange is preferably 60-80 ℃, and more preferably 80 ℃; the time is preferably 4 to 8 hours, and more preferably 5 to 6 hours. The present invention enables removal of Na from the initially prepared SSZ-13 molecular sieve by the first ion exchange⁺。

In the present invention, after the first ion exchange, the present invention preferably centrifuges the solution of the soluble ammonium salt impregnated with the SSZ-13 molecular sieve, and dries the resulting solid after the centrifugation. The present invention does not require any particular way of centrifugation and drying, and may be carried out using the procedures described above, which are well known to those skilled in the art.

In the invention, the soluble copper salt solution is preferably a copper nitrate solution, and the concentration of the soluble copper salt is preferably 0.002-0.1 mol/L, and more preferably 0.05 mol/L. In the invention, the temperature of the second ion exchange is preferably 60-80 ℃, and more preferably 80 ℃; the time is preferably 1 to 3 hours, and more preferably 2 hours. According to the invention, Cu ions are introduced into the SSZ-13 molecular sieve through the second ion exchange to obtain a Cu-SSZ-13 molecular sieve precursor.

After the precursor of the Cu-SSZ-13 molecular sieve is obtained, the precursor of the Cu-SSZ-13 molecular sieve is calcined to obtain the Cu-SSZ-13 molecular sieve. In the invention, the calcining temperature is preferably 500-600 ℃, and more preferably 550 ℃; the time is preferably 4-6 h, and more preferably 5 h. The present invention enables removal of NH from SSZ-13 by the calcination₄ ⁺And promote Cu²⁺Migrate to the ion exchange sites.

After the calcination, the Cu-SSZ-13 molecular sieve is preferably tableted, ground and sieved to obtain Cu-SSZ-13 molecular sieve powder. The present invention does not require any particular means for tabletting and grinding, as would be known to those skilled in the art. In the invention, the screening is preferably 40-60 mesh.

The invention provides the Cu-SSZ-13 molecular sieve prepared by the preparation method. In the invention, the particle size of the Cu-SSZ-13 molecular sieve is preferably 40-60 meshes.

The invention provides an application of the Cu-SSZ-13 molecular sieve in selective catalytic reduction of ammonia. In the invention, the Cu-SSZ-13 molecular sieve is preferably used as a denitration catalyst for catalyzing nitrogen oxides to be converted into nitrogen, and the reaction formula is 4NH₃+4NO+O₂＝4N₂+6H₂O。

The following examples are provided to illustrate the SSZ-13 molecular sieve and the preparation method thereof, and the Cu-SSZ-13 molecular sieve in detail, but they should not be construed as limiting the scope of the present invention.

Example 1

First, 0.2g of NaOH (Beijing chemical) and 3g of N, N, N-trimethyl-1-adamantyl ammonium hydroxide (TMADAOH, Beijing YinuoKai) were dissolved in 6.65g of secondary water. Then, 0.156g of aluminum hydroxide (Tianjin Corp.) was added to the above solution and stirred for 1 hour. And finally, adding 3g of diatomite (Tianjin plain) with the particle size of 1-3 mu m, and stirring for 3 hours. The element proportion in the obtained suspension system is Al₂O₃：SiO₂：NaOH：TMAdaOH：H₂O＝0.5:11:2.5:1.8:250。

Transferring the obtained suspension into a reaction kettle, crystallizing at 160 ℃ for different times, wherein XRD diffraction patterns of the obtained product at different times are shown in figure 1, and a crystallization degree curve is shown in figure 2. As can be seen from FIGS. 1 and 2, the SSZ-13 molecular sieve can be completely crystallized within 60 hours.

The IR spectra of the products obtained at different crystallization times are shown in FIG. 3. As can be seen from fig. 3, the diatomite sample contains a six-membered ring structure (6 silicon and 6 oxygen ring structures) which can promote crystallization of the SSZ-13 molecular sieve.

The XPS spectrum of the SSZ-13 molecular sieve obtained after 60h of crystallization is shown in FIG. 4. As can be seen from FIG. 4, Fe is present in the SSZ-13 molecular sieve³⁺And Fe²⁺Two forms.

The infrared spectrum of the SSZ-13 molecular sieve obtained after 60h of crystallization is shown in FIG. 5. As can be seen from FIG. 5, at 700 ℃ &710cm^-1There is no peak indicating that Fe is not present as framework Fe, but as additional framework Fe.

The EPR spectrum of the SSZ-13 molecular sieve obtained after 60h of crystallization is shown in FIG. 6. In fig. 6, g-4.3 indicates the presence of isolated four-coordinate Fe³⁺And g-2.0 indicates the presence of isolated hexa-coordinated Fe³⁺。

From the comprehensive graphs of FIGS. 4-6, it can be determined that Fe in the finally obtained SSZ-13 sample is added as extra framework Fe³⁺In the form of ions.

Example 2

SSZ-13 molecular sieves were prepared using different masses of diatomaceous earth and aluminum hydroxide, the amounts used being shown in Table 1. Wherein the mass of NaOH is 0.2g, the mass of N, N, N-trimethyl-1-adamantyl ammonium hydroxide is 3g, and the mass of water is 6.65 g; the crystallization temperature is 160 ℃ and the crystallization time is 60 hours.

TABLE 1 SSZ-13 molecular sieve raw material dosage

The XRD diffraction patterns of the products obtained at different Si/Al ratios are shown in figure 7, and from figure 7, it can be seen that the addition of small amount or excessive amount of diatomite can cause the existence of cristobalite in the products, wherein pure phase of SSZ-13 molecular sieve is obtained in the range of 8-11 of initial gel Si/Al.

N of SSZ-13 molecular sieve with silicon-aluminum ratio of 8-11₂The adsorption-desorption curve is shown in fig. 8. As can be seen in FIG. 8, the resulting SSZ-13 molecular sieve is typically microporous in structure.

The comparative area and micropore volume of the SSZ-13 molecular sieve with the silicon-aluminum ratio of 8-11 are shown in Table 2.

TABLE 2 comparative area and micropore volume for SSZ-13 molecular sieves of different Al-Si ratios

Sample (I)	Si/Al	Fe/Al	Comparative area (BET, m)²/g)	Micropore volume (cm)³/g)
					1	8	0.14	446	0.21
2	9	0.14	459	0.20
					3	10	0.16	466	0.22
4	11	0.15	448	0.20

As can be seen from Table 2, the SSZ-13 molecular sieve provided by the present invention has a high specific surface area and micropore volume.

Comparative example 1

The preparation method of the traditional silicon source comprises the following steps: first 0.3g NaOH (Beijing chemical) and 3g N, N, N-trimethyl-1-adamantyl ammonium hydroxide (TMADAOH, Beijing Yinuoka) were dissolved in 6g of secondary water. Then, 0.05 to 0.1 g of aluminum hydroxide (Alfa) was added to the above solution, and stirred for 1 hour. Finally, 2g of silica sol (Sigma) was added and stirred for 3 hours. And (3) transferring the suspension into a 25ml reaction kettle, crystallizing at 160 ℃ for different time (0-144 hours), wherein XRD diffraction patterns of the obtained product at different time are shown in figure 9, and a crystallization degree curve is shown in figure 10. As can be seen from FIGS. 9 and 10, the SSZ-13 molecular sieve obtained by the conventional preparation method takes 120 hours to be completely crystallized.

The SEM of the SSZ-13 molecular sieve of sample 3 in example 2 is shown in FIG. 11, and the SEM of the SSZ-13 molecular sieve obtained in comparative example 1 is shown in FIG. 12. As can be seen by comparing FIG. 11 with FIG. 12, the SSZ-13 molecular sieve obtained by the present invention has smoother morphology and better crystallinity.

Example 3

Using sample 3 of example 2 as a carrier, ion-exchanged with 1M ammonium nitrate at 80 ℃ for 5 hours, twice exchanged, centrifuged several times with water twice and then dried, after which the dried sample was ion-exchanged with 0.05M copper nitrate at 80 ℃ for 1 hour, then centrifuged and dried, and calcined at 550 ℃ for 5 hours. And tabletting the calcined sample, and screening to 40-60 meshes to obtain the Cu-SSZ-13 molecular sieve.

Comparative example 2

The Cu-SSZ-13 molecular sieve was prepared by using the SSZ-13 molecular sieve of comparative example 1 as a carrier. The method comprises the following steps:

the SSZ-13 of comparative example 1 was first calcined at 600 ℃ for 8 hours to remove the organic templating agent, then ion-exchanged with 1M ammonium nitrate at 80 ℃ for 5 hours, twice exchanged, centrifuged several times with two times of water and then dried, and then the dried sample was ion-exchanged with 0.05M copper nitrate at 80 ℃ for 1 hour, then centrifuged and dried, and calcined at 550 ℃ for 5 hours. And tabletting the calcined sample, and screening to 40-60 meshes to obtain the Cu-SSZ-13 molecular sieve.

Performance testing

The Cu-SSZ-13 molecular sieve obtained in example 3 and comparative example 2 is used for denitration catalytic reaction, and the reaction condition is 500ppmNH₃，500ppmNO，5％O₂，N₂As balance gas, the space velocity is 200000h^-1。

The conversion rate of NO at different time is shown in FIG. 13, and it can be seen from FIG. 13 that the conversion rate of NO is still higher than 95% at 400-500 ℃ in the Cu-SSZ-13 molecular sieve provided by the present invention, while the conversion rate of NO starts to decrease significantly at a temperature higher than 400 ℃ in the Cu-SSZ-13 molecular sieve of comparative example 2, and the conversion rate of NO is lower than 90% at a temperature higher than 450 ℃. The Cu-SSZ-13 molecular sieve provided by the invention has excellent catalytic activity.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a Cu-SSZ-13 molecular sieve comprises the following steps:

(1) mixing diatomite, NaOH, N, N, N-trimethyl-1-adamantyl ammonium hydroxide, aluminum hydroxide and water to obtain a mixed solution;

heating and crystallizing the mixed solution to obtain the SSZ-13 molecular sieve;

2. The preparation method according to claim 1, wherein the soluble ammonium salt is ammonium nitrate and/or ammonium chloride, and the concentration of the soluble ammonium salt solution is 0.1-1 mol/L;

3. The method according to claim 1, wherein the mass ratio of the diatomaceous earth to NaOH to the N, N, N-trimethyl-1-adamantyl ammonium hydroxide to the aluminum hydroxide is (2-3.6) to (0.2-0.4) to (2-4) to 0.156.

4. The method according to claim 1, wherein the diatomaceous earth has a particle size of 1 to 3 μm.

5. The preparation method according to claim 1, wherein the temperature for heating crystallization is 140-160 ℃ and the time is 60-72 hours.

6. The preparation method according to claim 1, wherein the SSZ-13 molecular sieve has an Al/Si ratio of 8 to 11, an Fe/Al ratio of 0.14 to 0.16, and a specific surface area of 446 to 466m²The volume of the micro pores is 0.20-0.22 cm³/g。

7. The Cu-SSZ-13 molecular sieve prepared by the preparation method of any one of claims 1 to 6.

8. Use of the Cu-SSZ-13 molecular sieve of claim 7 for selective catalytic reduction of ammonia.