阅读说明：本技术 一种具有核壳结构的复合分子筛及其合成方法 (Composite molecular sieve with core-shell structure and synthesis method thereof ) 是由 刘中清 王倩 赵峰 邓兆敬 于 2021-02-05 设计创作，主要内容包括：本发明提供了一种具有核壳结构的复合分子筛及其合成方法。该具有核壳结构的复合分子筛是以Cu-SSZ-39分子筛为核、以SSZ-39分子筛或者AFX分子筛为壳。本发明还提供了上述具有核壳结构的复合分子筛的合成方法。本发明通过构筑Cu-SSZ-39@SSZ-39或Cu-SSZ-39@AFX复合结构,以外壳SSZ-39或AFX为内核中向外迁移的Cu物种提供交换位点,能够抑制团聚CuO颗粒的产生,提高Cu-SSZ-39催化剂在苛刻反应条件下的水热稳定性,进而提高该类催化剂在高温区的催化性能。(The invention provides a composite molecular sieve with a core-shell structure and a synthesis method thereof. The composite molecular sieve with the core-shell structure takes a Cu-SSZ-39 molecular sieve as a core and takes an SSZ-39 molecular sieve or an AFX molecular sieve as a shell. The invention also provides a synthesis method of the composite molecular sieve with the core-shell structure. According to the invention, a Cu-SSZ-39@ SSZ-39 or Cu-SSZ-39@ AFX composite structure is constructed, and the shell SSZ-39 or AFX provides an exchange site for Cu species migrating outwards in the core, so that the generation of agglomerated CuO particles can be inhibited, the hydrothermal stability of the Cu-SSZ-39 catalyst under a severe reaction condition is improved, and the catalytic performance of the catalyst in a high-temperature region is further improved.)

1. The composite molecular sieve with a core-shell structure takes a Cu-SSZ-39 molecular sieve as a core and takes an SSZ-39 molecular sieve or an AFX molecular sieve as a shell.

2. The composite molecular sieve having a core-shell structure according to claim 1, wherein the CuO content in the Cu-SSZ-39 molecular sieve is 0.1 wt% to 20 wt%, preferably 1 wt% to 10 wt%.

3. The composite molecular sieve having a core-shell structure according to claim 1 or 2, wherein the Cu-SSZ-39 molecular sieve as the core accounts for 1 wt% to 99 wt%, preferably 10 wt% to 80 wt%, more preferably 20 wt% to 50 wt% of the total mass of the composite molecular sieve.

4. A method of synthesizing a composite molecular sieve having a core-shell structure according to any one of claims 1 to 3, wherein the method of synthesizing comprises the steps of:

mixing the molecular sieve, an alkali source, an organic template agent and water, and aging for 0.1-100 h at room temperature to 100 ℃ to obtain a gel for synthesizing the SSZ-39 molecular sieve;

adding the Cu-SSZ-39 molecular sieve into the gel for synthesizing the SSZ-39 molecular sieve, and then crystallizing for 10-100h at 120-200 ℃ in a high-pressure kettle;

cooling, filtering, washing, drying and roasting to obtain the composite molecular sieve with the core-shell structure;

alternatively, the first and second electrodes may be,

mixing the molecular sieve, an alkali source, an organic template agent and water, and aging for 0.1-100 h at room temperature to 100 ℃ to obtain a gel for synthesizing the SSZ-39 molecular sieve;

crystallizing the gel of the synthesized SSZ-39 molecular sieve in an autoclave at 120-200 ℃ for 0.1-40 h;

adding a Cu-SSZ-39 molecular sieve into an autoclave, and then crystallizing at 120-200 ℃ for 0.1-100 h;

and cooling, filtering, washing, drying and roasting to obtain the composite molecular sieve with the core-shell structure.

5. The synthesis method of claim 4, wherein the molecular sieves used in the feedstock for the synthesis of the SSZ-39 molecular sieve gel comprise USY molecular sieve, NaY molecular sieve and NH₄One or a combination of more than two of Y molecular sieves;

preferably, the starting material for the synthesis of the SSZ-39 molecular sieve gel further comprises a silicon source;

preferably, the silicon source comprises one or a combination of more than two of silicate, tetraethoxysilane, white carbon black and silica sol; silica sol is preferred.

6. The synthesis method according to claim 4, wherein the mass ratio of the gel of the synthesized SSZ-39 molecular sieve to the Cu-SSZ-39 molecular sieve is 80-0.8, preferably 40-1, more preferably 10-2.

7. The synthesis method of claim 4, wherein in the starting material for the synthesis of the gel of SSZ-39 molecular sieve, the SiO of the molecular sieve₂/Al₂O₃5-100, molar ratio.

8. The synthesis of claim 4, wherein the alkali source is sodium hydroxide and/or potassium hydroxide.

9. The synthetic method of claim 4, wherein the organic template comprises N, N-diethyl-2, 6-dimethylpiperidinium ion, 1,3, 5-tetramethylpiperidinium ion, 2, 6-dimethyl-5-azoniaspiro- [4.5] -decane ion, N-diethyl-2-ethylpiperidinium ion, N-ethyl-N-propyl-2, 6-dimethylpiperidinium ion, N-methyl-N-ethyl-2-ethylpiperidinium ion, 2, 5-dimethyl-N, N-diethylpyrrolium ion, 2, 6-dimethyl-N, n-dimethylpiperidinium ion, 3, 5-dimethyl-N, N-dimethylpiperidinium ion, 2-ethyl-N, N-dimethylpiperidinium ion, one or a combination of two or more of salts and/or bases of 2,2,6, 6-tetramethyl-N-methyl-N-ethylpiperidinium ion, N-cyclooctyl-pyridinium ion, 2,6, 6-tetramethyl-N, N-dimethylpiperidinium ion and N, N-dimethyl-N, N-bicyclononane ion, and preferably one or a combination of two or more of salts and/or bases of N, N-diethyl-2, 6-dimethylpiperidinium ion and/or 3, 5-dimethyl-N, N-dimethylpiperidinium ion.

10. The synthesis method according to claim 4 or 5, wherein, in the starting material for synthesizing the gel of SSZ-39 molecular sieve, the molar ratio of the molecular sieve, the alkali source, the organic template and the water satisfies the following condition:

SiO₂/Al₂O₃＝5-100，OH^-/SiO₂＝0.1-0.5，H₂O/SiO₂＝3-60，R/SiO₂＝0.01-0.5；

wherein R represents an organic template;

preferably, when the raw material for synthesizing the gel of the SSZ-39 molecular sieve further comprises a silicon source, the molar ratio of the silicon source, the molecular sieve, the alkali source, the organic template and the water satisfies the following condition:

SiO₂/Al₂O₃＝5-100，OH^-/SiO₂＝0.1-0.5，H₂O/SiO₂＝3-60，R/SiO₂＝0.01-0.5；

wherein R represents an organic template.

Technical Field

The invention relates to a composite molecular sieve with a core-shell structure and a synthesis method thereof, belonging to the technical field of molecular sieve preparation.

Background

SSZ-39 is a molecular sieve with an AEI topology made of AlO₄And SiO₄The tetrahedra are connected end to end via oxygen atoms and are arranged in order to form double six-membered rings (D6R), which are linked by partial four-membered rings to form a three-dimensional channel structure with a maximum of eight-membered rings. Currently, research on the application of SSZ-39 is primarily focused on ammonia-selective catalytic reduction (NH) to reduce nitrogen oxides (NOx) in diesel exhaust₃-SCR) reaction.

Studies have shown that SSZ-39 is via Cu²⁺After exchange, its active temperature window width and N₂The selectivity can be greatly improved, and the mechanism research proves that Cu²⁺Is the main active site in SCR (appl.catal.b: environ, 2020,264,118511). However, with the continued upgrading of diesel aftertreatment systems, particularly after upstream addition of a diesel particulate trap (DPF), the regeneration process for particulate matter can reach as high as 800 ℃, at which temperature Cu is isolated²⁺Is difficult to be stabilized at the initial position, and gradually migrates to the surface of the molecular sieve crystal and is agglomerated to form CuO particles. The formation of CuO not only causes the loss of SCR active sites, but also destroys the long-range ordered structure of the molecular sieve, directly causes the inactivation of the molecular sieve catalyst, so that the hydrothermal stability becomes NH₃Important evaluation criteria for SCR catalysts.

The hydrothermal treatment can obviously reduce the specific surface area and the pore volume of the Cu-SSZ-39 catalyst, and causes active site Cu²⁺Migrate to the outside of the molecular sieve to aggregate into CuO particles, so that NH₃-reduction of SCR activity. Thus, Cu is suppressed²⁺The agglomeration of CuO is the key for improving the hydrothermal stability of the Cu-SSZ-39 molecular sieve catalyst.

Disclosure of Invention

In order to solve the technical problems, the invention aims to provide a composite molecular sieve with a core-shell structure and a synthesis method thereof. The composite molecular sieve with the core-shell structure takes the Cu-SSZ-39 molecular sieve as a core and takes the SSZ-39 molecular sieve or the AFX molecular sieve as a shell, so that CuO agglomeration can be inhibited and the inactivation of a catalyst can be weakened in hydrothermal treatment.

In order to achieve the purpose, the invention provides a composite molecular sieve with a core-shell structure, wherein the composite molecular sieve takes a Cu-SSZ-39 molecular sieve as a core and takes an SSZ-39 molecular sieve or an AFX molecular sieve as a shell.

The composite molecular sieve ([email protected] SSZ-39 or [email protected] AFX) with the core-shell structure is a Cu-SSZ-39 molecular sieve which is a core layer material (the core layer material is solid particles) and is compounded with a SSZ-39 molecular sieve or an AFX molecular sieve without Cu to obtain the Cu-SSZ-39 molecular sieve with the copper-rich crystal core. The molecular sieve with the structure of [email protected] SSZ-39 or [email protected] AFX can be provided with the SSZ-39 or AFX shell of Cu when Cu species in the core Cu-SSZ-39 migrate to the outside of the molecular sieve under severe hydrothermal conditions²⁺A large number of exchange sites are provided, so that the generation of agglomerated CuO particles can be suppressed and the deactivation of the catalyst can be reduced.

According to a specific embodiment of the present invention, preferably, the Cu-SSZ-39 molecular sieve has a CuO content of 0.1 wt% to 20 wt%, more preferably 1 wt% to 10 wt%. The Cu-SSZ-39 molecular sieve may be prepared by any means.

According to a specific embodiment of the present invention, preferably, the Cu-SSZ-39 molecular sieve as the core layer accounts for 1 wt% to 99 wt%, more preferably 10 wt% to 80 wt%, and further preferably 20 wt% to 50 wt% of the total mass of the composite molecular sieve.

The invention also provides a synthesis method of the composite molecular sieve with the core-shell structure (taking the Cu-SSZ-39 molecular sieve as a core and the SSZ-39 molecular sieve as a shell), wherein the synthesis method comprises the following steps:

the first synthesis method comprises the following steps:

mixing the molecular sieve, an alkali source, an organic template agent and water, and aging for 0.1-100 h at room temperature to 100 ℃ to obtain a gel for synthesizing the SSZ-39 molecular sieve;

adding a Cu-SSZ-39 molecular sieve into the gel for synthesizing the SSZ-39 molecular sieve, and then crystallizing the gel in an autoclave at the temperature of 120-DEG C and 200 ℃ for 10-100 h;

cooling, filtering, washing, drying and roasting to obtain the composite molecular sieve with the core-shell structure;

and a second synthesis method comprises the following steps:

mixing the molecular sieve, an alkali source, an organic template agent and water, and aging for 0.1-100 h at room temperature to 100 ℃ to obtain a gel for synthesizing the SSZ-39 molecular sieve;

crystallizing the gel of the synthesized SSZ-39 molecular sieve in an autoclave at 120-200 ℃ for 0.1-40 h;

adding a Cu-SSZ-39 molecular sieve into an autoclave, and then crystallizing at 120-200 ℃ for 0.1-100 h;

and cooling, filtering, washing, drying and roasting to obtain the composite molecular sieve with the core-shell structure.

Wherein, the second synthesis method can shorten the soaking time of the Cu-SSZ-39 molecular sieve as the nuclear material in a strong alkaline crystallization system, and can reduce the dissolution and the damage of the nuclear material Cu-SSZ-39. In some embodiments, the gel of the synthesized SSZ-39 molecular sieve can be crystallized in an autoclave at 120 ℃ to 200 ℃ for 0.1h to 40h, and then the Cu-SSZ-39 molecular sieve is added into the autoclave and crystallized at 120 ℃ to 200 ℃ for 0.1h to 50 h.

In the above synthesis method, preferably, the molecular sieves used in the raw material of the gel for synthesizing the SSZ-39 molecular sieve include USY molecular sieve, NaY molecular sieve and NH₄One or a combination of two or more of the Y molecular sieves.

In the above synthesis method, preferably, the raw material for synthesizing the gel of the SSZ-39 molecular sieve further comprises a silicon source; more preferably, the silicon source includes but is not limited to one or a combination of two or more of silicate, tetraethoxysilane, white carbon black and silica sol, and more preferably silica sol.

In the above synthesis method, preferably, the mass ratio of the gel of the synthesized SSZ-39 molecular sieve to the Cu-SSZ-39 molecular sieve is 80 to 0.8, preferably 40 to 1, and more preferably 10 to 2.

In the above synthesis method, it is preferable that SiO of the molecular sieve used in the raw material for synthesizing the gel of the SSZ-39 molecular sieve₂/Al₂O₃5-100, molar ratio. The molecular sieve (e.g., USY molecular sieve) may be prepared by any means that functions to provide a source of aluminum and a source of silicon.

In the above synthesis method, preferably, the alkali source is sodium hydroxide and/or potassium hydroxide.

In the above synthesis method, preferably, the organic template includes N, N-diethyl-2, 6-dimethylpiperidine ion, 1,3, 5-tetramethylpiperidine ion, 2, 6-dimethyl-5-azoniaspiro- [4.5] -decane ion, N-diethyl-2-ethylpiperidine ion, N-ethyl-N-propyl-2, 6-dimethylpiperidine ion, N-methyl-N-ethyl-2-ethylpiperidine ion, 2, 5-dimethyl-N, N-diethylpyrrole ion, 2, 6-dimethyl-N, N-dimethylpiperidine ion, N-dimethyl-N, N-dimethylpiperidine ion, N-diethylpiperidine ion, N-diethyl, One or a combination of two or more of salts and/or bases of 3, 5-dimethyl-N, N-dimethylpiperidinium ion, 2-ethyl-N, N-dimethylpiperidinium ion, 2,6, 6-tetramethyl-N-methyl-ethylpiperidinium ion, N-cyclooctyl-pyridinium ion, 2,6, 6-tetramethyl-N, N-dimethylpiperidinium ion and N, N-dimethyl-N, N-bicyclononanium ion, and preferably one or a combination of two or more of salts and/or bases of N, N-diethyl-2, 6-dimethylpiperidinium ion and/or 3, 5-dimethyl-N, N-dimethylpiperidinium ion.

In the above synthesis method, preferably, in the raw material for synthesizing the gel of the SSZ-39 molecular sieve, the molar ratio of the molecular sieve, the alkali source, the organic template and water satisfies the following condition: SiO 2₂/Al₂O₃＝5-100，OH^-/SiO₂＝0.1-0.5，H₂O/SiO₂＝3-60，R/SiO₂0.01-0.5; wherein R represents an organic template.

In the above synthesis method, preferably, when the raw material for synthesizing the gel of the SSZ-39 molecular sieve further includes a silicon source, the molar ratio of the silicon source, the molecular sieve, the alkali source, the organic template, and water satisfies the following condition: SiO 2₂/Al₂O₃＝5-100，OH^-/SiO₂＝0.1-0.5，H₂O/SiO₂＝3-60，R/SiO₂0.01-0.5; wherein R represents an organic template.

In the above synthesis method, preferably, the temperature is reduced to 60 ℃ or lower.

When the AFX molecular sieve is used as the shell, the synthesis can be carried out by referring to the first synthesis method and the second synthesis method.

The Cu-SSZ-39 molecular sieve is taken as a core, mixed with the synthetic gel of the SSZ-39 molecular sieve or the AFX molecular sieve which does not contain copper, and crystallized to prepare the composite molecular sieve which only has the copper-rich inner core. Under a severe hydrothermal condition, when Cu species in the core Cu-SSZ-39 are migrated to the outside of the molecular sieve, the catalyst with the [email protected] SSZ-39 or [email protected] AFX structure provides a large number of exchange sites for the Cu species, so that the generation of agglomerated CuO particles can be inhibited, the inactivation of the catalyst is weakened, and the hydrothermal stability and the catalytic performance in a high-temperature region of the catalyst are improved.

Compared with the prior art, the invention provides an exchange site for Cu species migrating outwards in the core by constructing the [email protected] SSZ-39 and [email protected] AFX composite structures and using the shell SSZ-39 or AFX as the exchange site, so that the generation of agglomerated CuO particles can be inhibited, the hydrothermal stability of the Cu-SSZ-39 catalyst under severe reaction conditions is improved, and the catalytic performance of the catalyst in a high-temperature region is further improved.

Drawings

FIGS. 1-6 are X-ray diffraction patterns of the composite molecular sieve [email protected] SSZ-39 prepared in examples 1-6, respectively.

FIG. 7 is an XPS depth profile and a plot of surface copper atom concentration versus profile depth for the [email protected] SSZ-39 molecular sieve prepared in example 1.

FIG. 8 is an XPS depth profile and a plot of surface copper atom concentration versus profile depth for a [email protected] SSZ-39 molecular sieve prepared in a comparative example.

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.

Example 1

This example provides a composite molecular sieve [email protected] SSZ-39 having a core-shell structure, which was synthesized by:

1) taking USY molecular sieve, NaOH, N-diethyl-2, 6-dimethyl piperidine hydroxide and water as raw materials of the synthetic gel of the shell SSZ-39 molecular sieve according to the following raw material molar ratio:

SiO₂/Al₂O₃＝15，R/SiO₂＝0.2，OH^-/SiO₂＝0.4，H₂O/SiO₂20; r represents N, N-diethyl-2, 6-dimethyl piperidine hydroxide.

2) 1.20g of sodium hydroxide is dissolved in 40.81g of deionized water, 18.70g of an aqueous solution of N, N-diethyl-2, 6-dimethylpiperidine hydroxide with a mass fraction of 30% are added after complete dissolution, and 10g of SiO are added with rapid stirring₂/Al₂O₃The resulting mixture was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and aged at 80 ℃ for 12h to give a gel of synthetic SSZ-39 molecular sieve.

3) The content of CuO is 5 percent and SiO is used₂/Al₂O₃Taking commercial Cu-SSZ-39 of which the mass is 15 as a core layer material, adding 10g of the commercial Cu-SSZ-39 as a core layer material into the gel of the synthesized SSZ-39 molecular sieve prepared in the step 2), uniformly mixing, then putting into an autoclave, and heating to 190 ℃ under stirring for crystallization for 72 hours;

4) and (3) cooling to below 60 ℃ after crystallization is stopped, washing the product with deionized water, filtering and collecting, drying at 100 ℃ for 12h, and then placing in a muffle furnace to calcine at 550 ℃ for 8h to remove the structure directing agent, thus obtaining the composite molecular sieve [email protected] SSZ-39 with the core-shell structure.

The X-ray diffraction pattern of the composite molecular sieve [email protected] SSZ-39 is shown in figure 1. N is a radical of₂The result of physical adsorption shows that the specific surface area of the molecular sieve is 521m²/g。

Example 2

This example provides a method for preparing a [email protected] SSZ-39 core-shell molecular sieve, comprising the steps of:

1) preparation of SSZ-39 molecular sieve synthesis gel: substantially the same as in step (2) of example 1, except that no aging operation was conducted, an SSZ-39 molecular sieve synthesis gel was obtained.

2) The other preparation process is exactly the same as in example 1.

The X-ray diffraction pattern of the composite molecular sieve [email protected] SSZ-39 prepared in this example is shown in FIG. 2. N is a radical of₂The measurement result of a physical adsorption instrument shows that the specific surface area of the molecular sieve is 530m²/g。

Example 3

This example provides a method for preparing a [email protected] SSZ-39 core-shell molecular sieve, comprising the steps of:

1) preparation of SSZ-39 molecular sieve synthesis gel: the procedure was exactly the same as in step (2) of example 1.

2) SiO in the same CuO content of 5%₂/Al₂O₃Commercial Cu-SSZ-39 as a core layer material, 15 g, different from the example 1 step (3), in that the ratio of shell layer to core (i.e., the ratio of SSZ-39 to Cu-SSZ-39) was adjusted, 20.00g of Cu-SSZ-39 was added to the SSZ-39 molecular sieve synthesis gel, and the resulting mixture was transferred to a charge autoclave to be crystallized under the same conditions.

3) The other preparation process is exactly the same as in example 1.

The X-ray diffraction pattern of the composite molecular sieve [email protected] SSZ-39 prepared in this example is shown in FIG. 3. N is a radical of₂The result of physical adsorption shows that the specific surface area of the molecular sieve is 546m²/g。

Example 4

This example provides a composite molecular sieve [email protected] SSZ-39 having a core-shell structure, which was synthesized by:

1) taking USY molecular sieve, silica sol, NaOH, 1,3, 5-tetramethyl piperidine and water as raw materials of the synthetic gel of the shell SSZ-39 molecular sieve according to the following raw material molar ratio:

SiO₂/Al₂O₃＝50，R/SiO₂＝0.4，OH^-/SiO₂＝0.5，H₂O/SiO₂20; r represents 1,1,3, 5-tetramethyl piperidine.

2) Dissolving 0.44g of sodium hydroxide in 12.87g of deionized water, adding 28.36g of 25 mass percent 1,1,3, 5-tetramethylpiperidine aqueous solution after complete dissolution, then adding 10.00g of 40 mass percent silica sol under rapid stirring, adding 2.92g of SiO after uniform mixing₂/Al₂O₃The resulting mixture was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and aged at 80 ℃ for 12h to give a gel of synthetic SSZ-39 molecular sieve.

3) Putting the gel of the synthesized SSZ-39 molecular sieve prepared in the step 2) into an autoclave, and heating to 180 ℃ for crystallization for 40 hours under stirring.

4) The content of CuO is 5 percent and SiO is used₂/Al₂O₃3.46g of commercial Cu-SSZ-39 as a core layer material was added to the synthetic gel prepared in step 3), mixed well, charged into an autoclave, and crystallized at 180 ℃ for 60 hours with stirring.

5) And (3) cooling to below 60 ℃ after crystallization is stopped, washing the product with deionized water, filtering and collecting, drying at 100 ℃ for 12h, and then placing in a muffle furnace to calcine at 550 ℃ for 8h to remove the structure directing agent, thus obtaining the composite molecular sieve [email protected] SSZ-39 with the core-shell structure.

The X-ray diffraction pattern of the composite molecular sieve [email protected] SSZ-39 is shown in figure 4. N is a radical of₂The measurement result of a physical adsorption instrument shows that the specific surface area of the molecular sieve is 554m²/g。

Example 5

This example provides a composite molecular sieve [email protected] SSZ-39 having a core-shell structure, which was synthesized by:

1) taking a NaY molecular sieve, silica sol, NaOH, 1,3, 5-tetramethyl piperidine and water as raw materials of the synthetic gel of the shell SSZ-39 molecular sieve according to the following raw material molar ratio:

SiO₂/Al₂O₃＝75，R/SiO₂＝0.5，OH^-/SiO₂＝0.35，H₂O/SiO₂30; r represents 1,1,3, 5-tetramethyl piperidine.

2) At 21.47gAdding 28.96g of 25 mass percent 1,1,3, 5-tetramethylpiperidine aqueous solution into ionized water, then adding 10.00g of 40 mass percent silica sol under rapid stirring, and adding 1.59g of SiO after uniform mixing₂/Al₂O₃The resulting mixture was transferred to a stainless steel autoclave lined with teflon and aged at 80 ℃ for 12h to give a gel of synthetic SSZ-39 molecular sieve.

3) Putting the gel of the synthesized SSZ-39 molecular sieve prepared in the step 2) into an autoclave, and heating to 150 ℃ for crystallization for 80 hours under stirring.

4) The content of CuO is 8 percent and SiO is used₂/Al₂O₃Commercial Cu-SSZ-39 of 40 as a core layer material, 27.95g was added to the synthetic gel prepared in step 3), mixed well, charged into an autoclave, and crystallized at 150 ℃ for 80 hours with stirring.

5) And (3) cooling to below 60 ℃ after crystallization is stopped, washing the product with deionized water, filtering and collecting, drying at 100 ℃ for 12h, and then placing in a muffle furnace to calcine at 550 ℃ for 8h to remove the structure directing agent, thus obtaining the composite molecular sieve [email protected] SSZ-39 with the core-shell structure.

The X-ray diffraction pattern of the composite molecular sieve [email protected] SSZ-39 is shown in figure 5. N is a radical of₂The physical adsorption apparatus determination result shows that the specific surface area of the molecular sieve is 568m²/g。

Example 6

This example provides a composite molecular sieve [email protected] SSZ-39 having a core-shell structure, which was synthesized by:

1) taking USY molecular sieve, white carbon black, NaOH, 1,3, 5-tetramethyl piperidine, N-methyl-N-ethyl-2-ethyl piperidine and water as raw materials of the synthetic gel of the shell SSZ-39 molecular sieve according to the following raw material molar ratio:

SiO₂/Al₂O₃＝20，R/SiO₂＝0.1，OH^-/SiO₂＝0.25，H₂O/SiO₂10; r represents 1,1,3, 5-tetramethylpiperidine, N-methyl-N-ethyl-2-ethylpiperidine.

2) To 14.82g of deionized water was addedAdding 3.64g of 25 mass percent 1,1,3, 5-tetramethylpiperidine aqueous solution and 3.57g of 30 mass percent N, N-diethyl-2, 6-dimethylpiperidine aqueous solution, then adding 5.00g of white carbon black under rapid stirring, adding 2.55g of SiO after uniformly mixing₂/Al₂O₃The resulting mixture was transferred to a stainless steel autoclave lined with teflon and aged at 60 ℃ for 12h to give a gel of synthetic SSZ-39 molecular sieve.

3) Putting the gel of the synthesized SSZ-39 molecular sieve prepared in the step 2) into an autoclave, and heating to 200 ℃ for crystallization for 18 hours under stirring.

4) The content of CuO is 12 percent and SiO is used₂/Al₂O₃Commercial Cu-SSZ-39 of 40 as a core layer material, 30.20g was added to the synthetic gel prepared in step 3), mixed well, charged into an autoclave, and crystallized at 150 ℃ for 80 hours with stirring.

5) And (3) cooling to below 60 ℃ after crystallization is stopped, washing the product with deionized water, filtering and collecting, drying at 100 ℃ for 12h, and then placing in a muffle furnace to calcine at 550 ℃ for 8h to remove the structure directing agent, thus obtaining the composite molecular sieve [email protected] SSZ-39 with the core-shell structure.

The X-ray diffraction pattern of the composite molecular sieve [email protected] SSZ-39 is shown in figure 6. N is a radical of₂The measurement result of a physical adsorption instrument shows that the specific surface area of the molecular sieve is 526m²/g。

Comparative example

This comparative example a SSZ-39 molecular sieve was synthesized according to the method disclosed in US patent 5958370A, which preparation method included the steps of:

1) reacting NH₄Y molecular sieve, water glass (SiO)₂28-29 percent of content), NaOH, N-diethyl-2, 6-dimethyl piperidine hydroxide (concentration is 25 percent) and water are used as raw materials of the synthesis gel of the SSZ-39 molecular sieve according to the following raw material molar ratio:

SiO₂/Al₂O₃＝25，R/SiO₂＝0.152，OH^-/SiO₂＝0.682，H₂O/SiO₂43.3; r represents N, N-diethyl-2, 6-dimethyl piperidine hydroxide.

2) 0.27g of sodium hydroxide is dissolved in 342g of deionized water, 70.5g of an aqueous 25% by weight N, N-diethyl-2, 6-dimethylpiperidine hydroxide solution are added after complete dissolution, and 10.4g of NH are added with rapid stirring₄Y molecular sieve, transferring the obtained mixture into a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining, and crystallizing for 7 days at 135 ℃.

3) And (3) cooling to below 60 ℃ after crystallization is stopped, washing the product with deionized water, filtering and collecting, drying at 100 ℃ for 12h, and then placing in a muffle furnace for calcining at 550 ℃ for 8h to remove the structure directing agent to obtain the molecular sieve SSZ-39 with the core-shell structure.

N₂The result of physical adsorption shows that the specific surface area of the molecular sieve is 517m²/g。

[email protected] SSZ-39 core-shell molecular sieve catalyst activity test

The catalytic denitration performance of the molecular sieves prepared in the above examples and comparative examples is considered, and the specific operation is as follows:

ammonium exchange of molecular sieve: the molecular sieves prepared in examples 1-6 of the invention and comparative examples were prepared according to ammonium nitrate: molecular sieve: water (mass ratio) 1: 1: 10 mixing, exchanging for 1h at 90 ℃ under the stirring state, filtering, washing, drying and roasting for 2h at 550 ℃. Repeating the above process for 3 times until Na in the molecular sieve₂The O content is less than 0.1 mass%.

And (3) copper exchange of a molecular sieve: the ammonium exchanged comparative molecular sieve was prepared according to molecular sieve: water (mass ratio) 1: 10, adding a certain amount of copper acetate (5 percent of CuO loading according to a molecular sieve) under stirring, exchanging for 1 hour at 90 ℃, adjusting the pH value to 8-8.5 by ammonia water, filtering, washing, drying, and roasting for 2 hours at 550 ℃.

Respectively tabletting, grinding and sieving the molecular sieves of the examples 1-6 after ammonium exchange and the molecular sieves of the comparative examples after ammonium exchange and copper exchange, and taking 60-mesh samples as granules for standby; taking 0.5g of a granular sample for NH₃-SCR reaction, wherein the composition of the reaction mixture is: 1000ppmNO, 1100ppmNH₃、10Vol％O₂、10Vol％H₂O，N₂As balance gas, the volume space velocity is 120000h^-1The reaction temperature is 150-₂And N₂The O concentration. Conversion rate of nitrogen oxides in reaction mixed gas at different temperatures and N₂The selectivities are shown in tables 1 and 2.

NO_xThe conversion is defined as:

TABLE 1 conversion of nitrogen oxides in the reaction mixture at different temperatures and N₂Selectivity is

TABLE 2 conversion of nitrogen oxides in the reaction mixture at different temperatures and N₂Selectivity is

As can be seen from the data in tables 1 and 2, the [email protected] SSZ-39 core-shell molecular sieve prepared by the preparation method provided by the embodiment of the invention maintains higher catalytic activity in the temperature range of 200-550 ℃, and the conversion rate of nitrogen oxide is basically maintained above 90%, the Cu-SSZ-39 molecular sieve prepared by the comparative example only has higher catalytic activity in the temperature range of 200-400 ℃, and when the temperature exceeds 400 ℃, the conversion rate of nitrogen oxide is continuously reduced, and the high-temperature activity is poor.

The Cu-SSZ-39 molecular sieve prepared by the comparative example is subjected to hydrothermal treatment at high temperatureIsolated Cu²⁺The [email protected] SSZ-39 core-shell type molecular sieve prepared in examples 1-5 has isolated Cu in the core Cu-SSZ-39 molecular sieve under high temperature condition²⁺The shell SSZ-39 molecular sieve can be Cu when migrating to the outside of the molecular sieve²⁺And a large number of exchange sites are provided, so that the generation of agglomerated CuO particles can be inhibited, the inactivation of the catalyst is weakened, the [email protected] SSZ-39 core-shell type molecular sieve has high hydrothermal stability under severe reaction conditions, and the catalytic performance of the catalyst in a high-temperature zone is improved. However, when the mass of shell SSZ-39 is higher than the total weight of the molecular sieve, for example, the mass fraction of SSZ-39 in example 4 is 66.7%, the approach of gas molecules to the active sites of Cu-SSZ-39 is affected, and the catalytic activity of Cu-SSZ-39 is inhibited to some extent.

As can be seen from the data in tables 1 and 2, the [email protected] SSZ-39 core-shell molecular sieve prepared by the preparation method provided by the embodiment of the invention has excellent N in the whole temperature range₂And (4) selectivity.

Anti-aging performance test of [email protected] SSZ-39 core-shell type molecular sieve

The molecular sieves prepared in examples 1-6 of the present invention and comparative examples were aged at 800 ℃ with 10% H₂O pretreatment for 30h, taking 0.5g of aged granular sample for NH₃-SCR reaction, wherein the composition of the reaction mixture is: 1000ppmNO, 1100ppmNH₃、10Vol％O₂、10Vol％H₂O，N₂As balance gas, the volume space velocity is 120000h^-1The reaction temperature is 150 ℃, 300 ℃ and 550 ℃, and a Nicolet infrared gas analyzer is used for detecting NO and NO in the tail gas on line₂And N₂Concentration of O to obtain NO_xAnd (4) conversion rate. The conversion of nitrogen oxides in the reaction mixture at different temperatures is shown in table 3.

TABLE 3 conversion of nitrogen oxides in reaction mixture at different temperatures

	150℃	300℃	550℃
				Example 1	7％	94％	86％
Example 2	7％	92％	85％
				Example 3	9％	94％	82％
Example 4	10％	92％	85％
				Example 5	6％	93％	86％
Example 6	8％	94％	83％
				Comparative example	3％	75％	32％

The [email protected] SSZ-39 core-shell type molecular sieves prepared in the examples 1 to 6 are subjected to hydrothermal treatment at 800 ℃ for 30 hours, the conversion rate of nitrogen oxides at 300 ℃ is more than 90%, and the conversion rate of nitrogen oxides at 550 ℃ is more than 80%, which shows that the composite molecular sieve has high hydrothermal stability. And after the Cu-SSZ-39 molecular sieve prepared by the comparative example is subjected to hydrothermal treatment at 800 ℃ for 30 hours, the catalytic activity disappears at 150 ℃, the conversion rate of nitrogen oxides at 300 ℃ and 550 ℃ is less than 10%, and the hydrothermal stability is very poor.

FIG. 7 is an XPS depth profile and a plot of surface copper atom concentration versus profile depth for the [email protected] SSZ-39 molecular sieve prepared in example 1.

The results shown in FIG. 7 indicate that the molar concentration of Cu atoms is almost 0 in the depth range of 10nm from the surface of the sample, indicating that the shell contains no Cu element. And when the analysis depth is increased to more than 15nm, the Cu atomic concentration is gradually increased to 1.2 percent, which shows that the Cu element is distributed in the core. This result is favorable evidence for the synthesis of a [email protected] SSZ-39 core-shell molecular sieve with a heterogeneous Cu distribution. After hydrothermal aging, the molar concentration of Cu atoms in the depth range from the surface to 10nm is obviously improved, and the molar concentration of Cu atoms above 15nm is reduced, which indicates that part of Cu atoms migrate outwards in the hydrothermal aging process.

FIG. 8 is an XPS depth profile and a plot of surface copper atom concentration versus profile depth for a [email protected] SSZ-39 molecular sieve prepared in a comparative example.

The results shown in FIG. 8 are similar to those shown in FIG. 7, except that SSZ-39 has a low shell mass fraction and a thin shell, and thus has a weak effect of inhibiting core Cu atoms migrating after hydrothermal aging, and the surface Cu concentration increases more significantly.