阅读说明：本技术 Ssz-13分子筛、ssz-13分子筛的制备方法、nh3-scr反应催化剂 (SSZ-13 molecular sieve, preparation method of SSZ-13 molecular sieve and NH3-SCR reaction catalyst ) 是由 王倩 刘中清 赵峰 邓兆敬 于 2021-08-23 设计创作，主要内容包括：本发明提供了一种SSZ-13分子筛、SSZ-13分子筛的制备方法、NH-(3)-SCR反应催化剂。该SSZ-13分子筛的XPS结果是以剖析深度为横坐标、硅铝比为纵坐标的阶梯曲线,所述阶梯曲线具有两个以上的平台,相邻两级平台之间的纵向距离为5以上。本发明还提供了一种SSZ-13分子筛的制备方法。本发明进一步提供了包括上述SSZ-13分子筛的NH-(3)-SCR反应催化剂。本发明提供的上述SSZ-13分子筛的表面和内部的硅铝比具有明显的层级差别,分子筛内部的硅铝比水平与分子筛表面的硅铝比存在明显的梯级分层变化。上述制备方法可以有效调控分子筛的硅铝比分布情况,进而达到改变分子筛结构及其催化性能的效果。(The invention provides an SSZ-13 molecular sieve, a preparation method of the SSZ-13 molecular sieve and NH 3 -an SCR reaction catalyst. The XPS result of the SSZ-13 molecular sieve is a step curve with the analysis depth as an abscissa and the silicon-aluminum ratio as an ordinate, the step curve is provided with more than two platforms, and the longitudinal distance between every two adjacent platforms is more than 5. The invention also provides a preparation method of the SSZ-13 molecular sieve. The invention further provides NH comprising the SSZ-13 molecular sieve described above 3 -an SCR reaction catalyst. The silicon-aluminum ratio of the surface and the interior of the SSZ-13 molecular sieve provided by the invention has obvious level difference, and the silicon-aluminum ratio level of the interior of the molecular sieve and the silicon-aluminum ratio of the surface of the molecular sieve have obvious step layering change. The preparation method can effectively regulate and control the silicon-aluminum of the molecular sieveThe specific distribution condition further achieves the effect of changing the structure and the catalytic performance of the molecular sieve.)

1. An SSZ-13 molecular sieve, wherein the XPS result of the SSZ-13 molecular sieve is a step curve with a parsing depth as an abscissa and a silicon-aluminum ratio as an ordinate, the step curve is provided with more than two platforms, and the longitudinal distance between every two adjacent platforms is more than 5.

2. The SSZ-13 molecular sieve of claim 1, wherein in the step curve, the amplitude of longitudinal fluctuation of each stage of the platform is within 16%; the method for calculating the fluctuation amplitude n comprises the following steps:

wherein ai is the silicon-aluminum ratio corresponding to the ith analysis depth in each stage of platform, and i is more than 0;is the average silicon-aluminum ratio in the platform of each stage.

3. The SSZ-13 molecular sieve of claim 1 or 2, wherein the SSZ-13 molecular sieve has an average feed silica to alumina ratio of 5-180, preferably 5-100, more preferably 10-30;

preferably, the particle size of the SSZ-13 molecular sieve is 0.1-5 μm, the crystallinity of the SSZ-13 molecular sieve is more than or equal to 90 percent, and the specific surface area of the SSZ-13 molecular sieve is more than or equal to 550m²·g^-1。

4. A method of making an SSZ-13 molecular sieve, comprising:

mixing a silicon source, an aluminum source, an alkali source, an organic template agent and water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain synthetic gel A;

mixing a silicon source, an aluminum source, an alkali source and an organic template agent with water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain a synthesized gel B, wherein the silicon-aluminum ratio of the synthesized gel B is different from that of the synthesized gel A;

heating the synthetic gel A to 120-200 ℃ for crystallization for 40-120 h; then adding the synthetic gel B, continuously crystallizing for 0.1-70 h at 120-200 ℃, cooling, and performing post-treatment to obtain the SSZ-13 molecular sieve;

or:

mixing an SSZ-13 molecular sieve with water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain synthetic gel A;

mixing a silicon source, an aluminum source, an alkali source and an organic template agent with water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain a synthesized gel B, wherein the silicon-aluminum ratio of the synthesized gel B is different from that of the synthesized gel A;

mixing the synthetic gel A and the synthetic gel B, crystallizing at the temperature of 120-200 ℃ for 0.1-70 h, cooling, and performing post-treatment to obtain the SSZ-13 molecular sieve.

5. The preparation method according to claim 4, wherein the preparation method further comprises, after the crystallization of the synthetic gel B is completed and before the temperature is reduced: further adding a synthetic gel C into a mixture of the synthetic gel A and the synthetic gel B, and crystallizing for 0.1h-70h at 120-200 ℃, wherein the silicon-aluminum ratio of the synthetic gel C is different from that of the synthetic gel B, and the preparation method of the synthetic gel C comprises the steps of mixing a silicon source, an aluminum source, an alkali source, an organic template and water, and aging for 0.1h-100h at room temperature to 100 ℃ to obtain the synthetic gel C;

preferably, the chemical composition of the synthetic gel C satisfies the molar ratio range: SiO 2₂/Al₂O₃＝5-180；OH-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, R is organic template; more preferably SiO₂/Al₂O₃＝5-30；OH-/SiO₂＝0.01-0.5；H₂O/SiO₂＝5-40；R/SiO₂＝0.01-0.2；

Preferably, the mass ratio of the synthetic gel C to the synthetic gel B is 0.01-5:1, more preferably 0.05-2:1, and further preferably 0.1-1: 1;

preferably, the chemical composition of the mixture of synthetic gel a, synthetic gel B and synthetic gel C satisfies the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-180；OH^-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, R is organic template;

preferably, when the synthetic gel C is added to the synthetic gel B, the crystallinity of the synthetic gel B is 60% or more and less than 100%.

6. The production method according to claim 4 or 5, wherein the silicon source comprises one or a combination of two or more of silica, silicate, and tetraethoxysilane; preferably, the silica comprises silica sol.

7. The production method according to claim 4 or 5, wherein the aluminum source comprises one or a combination of two or more of sodium metaaluminate, aluminum hydroxide, pseudoboehmite, and aluminum isopropoxide; preferably, the aluminium source comprises sodium metaaluminate and/or aluminium hydroxide.

8. The production method according to claim 4 or 5, wherein the organic template agent comprises one or a combination of two or more of salts and/or bases of N, N, N-trimethyl-1-adamantylammonium ion, benzyltrimethylammonium ion, N, N, N-dimethylethylcyclohexylammonium bromide ion, tetraethylammonium hydroxide ion, choline chloride ion, and Cu-tetraethylenepentamine ion;

the alkali source comprises sodium hydroxide.

9. The production method according to claim 4 or 5, wherein when the synthetic gel B is added to the synthetic gel A, the crystallinity of the synthetic gel A is 60% or more and less than 100%;

preferably, when the synthetic gel A is obtained by mixing and aging the SSZ-13 molecular sieve and water, the crystallinity of the synthetic gel A is more than 90% and less than 100% when the synthetic gel B is added into the synthetic gel A.

10. The preparation method according to claim 4 or 5, wherein the chemical composition of the synthetic gel A satisfies the molar ratio range: SiO 2₂/Al₂O₃＝5-180；OH^-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, R is organic template;

the chemical composition of the synthetic gel B satisfies the following molar ratio ranges:SiO₂/Al₂O₃＝5-180；OH-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, R is organic template;

preferably, the chemical composition of the synthetic gel a satisfies the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-30；OH-/SiO₂＝0.01-0.5；H₂O/SiO₂＝5-40；R/SiO₂＝0.01-0.2；

Preferably, the chemical composition of the synthetic gel B satisfies the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-30；OH-/SiO₂＝0.01-0.5；H₂O/SiO₂＝5-40；R/SiO₂＝0.01-0.2；

Preferably, the absolute value of the difference between the silicon-aluminum ratio of the synthetic gel A and the synthetic gel B is more than or equal to 5.

11. The method according to claim 4 or 5, wherein the mass ratio of the synthetic gel B to the synthetic gel A is 0.01-5:1, preferably 0.05-2:1, and more preferably 0.1-1: 1.

12. The preparation method according to any one of claims 4, 5 and 11, wherein the chemical composition of the mixture of the synthetic gel A and the synthetic gel B satisfies the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-180；OH-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, and R is an organic template.

13. The preparation method according to claim 4 or 5, wherein, when the synthetic gel A is subjected to the single crystallization, the crystallization time is 50h to 100 h.

14. The preparation method according to claim 4 or 5, wherein the SSZ-13 molecular sieve used for preparing the synthetic gel A has a particle size of 0.1 to 10 μm, preferably 0.2 to 5 μm, more preferably 0.5 to 1.5 μm.

15. The production method according to claim 4 or 5, wherein the post-treatment includes treatment of filtering, washing, drying a solid sample, and baking;

preferably, the roasting temperature is 500-800 ℃, and the roasting time is 6-10 h; more preferably, the roasting temperature is 550-650 ℃, and the roasting time is 7-8 h.

16. NH (hydrogen sulfide)₃-an SCR reaction catalyst comprising the SSZ-13 molecular sieve of any of claims 1-3.

Technical Field

The invention relates to the technical field of molecular sieve synthesis, in particular to an SSZ-13 molecular sieve, a preparation method of the SSZ-13 molecular sieve and NH₃-an SCR reaction catalyst.

Background

SSZ-13 is a molecular sieve with the CHA topology, made of AlO₄And SiO₄The tetrahedrons are connected end to end through oxygen atoms and are orderly arranged into an ellipsoidal cage (0.73nm multiplied by 1.2nm) with an eight-membered ring structure and a three-dimensional crossed pore channel structure, and the pore channel size is 0.38nm multiplied by 0.38 nm. The SSZ-13 molecular sieve has the characteristics of ordered pore structure, high specific surface area, good hydrothermal stability, more surface proton acid centers, excellent cation exchangeability and the like, and is widely applied to a plurality of industrial catalytic processes in recent years. Wherein the Cu ion exchanged SSZ-13 molecular sieve is subjected to selective catalytic reduction reaction (NH) in ammonia₃SCR) with a wider active temperature window, higher N₂Selectivity and excellent hydrothermal stability have been achieved for commercial application in diesel exhaust treatment (Bull, I.et al. processes for Reducing Nitrogen Oxides Using Copper Cha Zeolite catalyst.U.S. patent 8404203.B2,3013-03-26; chem.Soc.Rev.2015,44,7371).

The literature (appl.Catal.A: Gen.2018,550,256) reports the SCR performance of Cu-SSZ-13 catalysts with different silicon to aluminum ratios, which are found to affect not only the properties of Cu species, but also the Cu species distribution (referring to the molar ratio of silica to alumina). Under the condition of the same Cu content, the CuO content is increased along with the increase of the silicon-aluminum ratio, and the Cu with high stability⁺Is reduced, thereby significantly affecting the catalytic performance and hydrothermal stability of Cu-SSZ-13. Meanwhile, the acidic property is also influenced by the silicon-aluminum ratio, and as the silicon-aluminum ratio is increased, the density of Lewis acid centers is reduced, but the strength of the acid centers is enhanced. In addition, ACS Catal.2017,7,8214 also reported Cu in CHA cages²⁺The central position of the six-membered ring Al is beneficial to improving the hydrothermal stability of the Cu-SSZ-13 molecular sieve, and the beta Phys, Chim, sin, 2015 and 31,2165 find that the B acid site on the eight-membered ring is beneficialIn NH₃The adsorption of (1) is activated. If the distribution and density of framework aluminum in the molecular sieve can be adjusted by adopting a proper method, so that the distribution of Cu and acid centers is adjusted, the method has important significance for adjusting and controlling the catalytic performance and hydrothermal stability of Cu-SSZ-13.

SSZ-13 molecular sieve in tail gas NH of diesel engine vehicle₃The SCR reaction has important application, and the catalytic performance of the SCR reaction is influenced by acidic property which is closely related to the content and distribution of silicon and aluminum. However, the existing synthesis technology generally adopts a one-pot method to prepare the SSZ-13 molecular sieve, the distribution of silicon and aluminum in the mesostructure of the obtained molecular sieve is uniform and fixed, and the performance improvement space is limited.

Disclosure of Invention

In order to solve the above problems, the present invention is directed to an SSZ-13 molecular sieve, a method for producing an SSZ-13 molecular sieve, and NH₃-an SCR reaction catalyst. The surface and internal silicon-aluminum ratio of the SSZ-13 molecular sieve has obvious hierarchical difference, and the silicon-aluminum ratio level in the molecular sieve and the silicon-aluminum ratio on the surface of the molecular sieve have obvious step layering change.

In order to achieve the above object, the present invention provides an SSZ-13 molecular sieve, wherein XPS (X-ray photoelectron spectroscopy) results of the SSZ-13 molecular sieve are a step curve having a dissecting depth as abscissa and a silicon-aluminum ratio as ordinate, the step curve has two or more plateaus, and a longitudinal distance between adjacent plateaus is 5 or more.

In the above step curve, the silica to alumina ratio refers to the silica to alumina mole ratio of the SSZ-13 molecular sieve. The platform refers to a level with basically consistent silicon-aluminum ratio, and the longitudinal fluctuation amplitude (namely the fluctuation amplitude of the silicon-aluminum ratio) of each level of platform is generally within 16%, namely the fluctuation amplitude of the silicon-aluminum ratio is 0-16%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16% and the like. As shown in fig. 1 to 4, the stepped curves of fig. 1 to 3 have two plateaus, respectively, and the stepped curve of fig. 4 has three plateaus. The longitudinal distance between the platforms is the absolute value of the difference of the average silicon-aluminum ratio of each platform, and the longitudinal distance between two adjacent platforms is more than 5, which means that the absolute value of the difference of the average silicon-aluminum ratio of two adjacent platforms is more than 5, for example, the absolute value of the difference of the average silicon-aluminum ratio of the platform 1 and the platform 2 in fig. 1 is more than 12.

In a specific embodiment of the invention, as the analysis depth increases, the silica alumina ratio of the SSZ-13 molecular sieve is distributed in a hierarchical manner (corresponding to the XPS result as a step curve), the SSZ-13 molecular sieve can be regarded as a multilayer structure (corresponding to a plurality of platforms in the step curve) formed by arranging according to different silica alumina ratios, the fluctuation range of the silica alumina ratio of each layer of structure is within 16%, the silica alumina ratio of two adjacent layers has obvious transition, and specifically, the absolute value of the silica alumina ratio difference between the two adjacent layers of structures is not less than 5.

The method for calculating the longitudinal fluctuation amplitude (fluctuation amplitude of silicon-aluminum ratio) n of each stage of platform comprises the following steps:

wherein ai is a silicon-aluminum ratio corresponding to a certain analysis depth in the step;is the average Si/Al ratio in the step.

For example, in FIG. 1, of platform 1The amplitude n of the fluctuation of the platform 1 is as followsFor baseline calculation, n at point A1 isThe n thus calculated is less than or equal to 16%, and the fluctuation width n of A2 is also calculated in the same manner. Of the platform 2The B1 and B2 fluctuation amplitude n of the platform 2 is as followsThe baseline is calculated as described above.

In a specific embodiment of the invention, the silica to alumina ratio of the adjacent two-layer structure of the SSZ-13 molecular sieve has a distinct transition. Taking FIG. 1 as an example, the Si/Al ratios of the right end point (A2) of the stage 1 and the left end point (B1) of the stage 2 are greatly different, and the average Si/Al ratios of the stage 1 and the stage 2 are also greatly different, exceeding the fluctuation range of 16% of the Si/Al ratios inside the stage 1 and the stage 2. The silicon-aluminum ratios of adjacent end points of the two platforms in fig. 2 and 3 are greatly different, and the average silicon-aluminum ratios of the two platforms are also obviously different (more than 16% of fluctuation range), the step curve in fig. 4 has three platforms, the silicon-aluminum ratios of the adjacent end points of the two adjacent platforms are greatly different, and the average silicon-aluminum ratio difference of the two adjacent platforms is also more than 16% of fluctuation range.

In a specific embodiment of the present invention, the above profiling depth refers to a depth at which the ion gun sputter-peels off the sample when the XPS test is performed, thereby obtaining a concentration variation of the specific element in the depth direction of the sample. The general conditions for XPS measurements are full element spectra of samples tested using AlK α (1486.6eV) anode targets in the range 0-1400eV with an excitation spot of 650 μm.

In the above SSZ-13 molecular sieve, preferably, the SSZ-13 molecular sieve has an average feed silica to alumina ratio of 5 to 180, e.g., 5 to 100, 10 to 30, etc. Wherein, the average feeding silicon-aluminum ratio refers to the silicon-aluminum ratio of all raw materials added in the preparation process of the SSZ-13 molecular sieve, and if the SSZ-13 molecular sieve is prepared by adding the raw materials step by step, the average feeding silicon-aluminum ratio refers to the silicon-aluminum ratio calculated by taking all the added raw materials as a whole. For example, when the SSZ-13 molecular sieve is prepared by adding the synthesis gel A and then adding the synthesis gel B, the average feeding silicon-aluminum ratio refers to the silicon-aluminum ratio of all the added components in the synthesis gel A + the synthesis gel B; when the SSZ-13 molecular sieve is prepared by adding the synthetic gel A, then adding the synthetic gel B and then adding the synthetic gel C, the average feeding silicon-aluminum ratio refers to the silicon-aluminum ratio of all the added components in the synthetic gel A, the synthetic gel B and the synthetic gel C. In some embodiments, the actual silica to alumina ratio of the SSZ-13 molecular sieve may be lower than the average feed silica to alumina ratio, since some of the silica will dissolve in the alkaline synthesis system.

In the specific embodiment of the invention, under the condition of the same feed ratio, the SSZ-13 molecular sieve provided by the invention is obtained by more than two times of crystallization, and the particle size of the obtained molecular sieve is larger than that of the molecular sieve which is subjected to only one time of crystallization. Specifically, the SSZ-13 molecular sieve of the present invention generally has a particle size of 0.1 μm to 5 μm, the SSZ-13 molecular sieve has a crystallinity of 90% or more, and the SSZ-13 molecular sieve has a specific surface area of 550m or more²·g^-1。

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

the method comprises the following steps: mixing a silicon source, an aluminum source, an alkali source, an organic template agent and water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain synthetic gel A;

mixing a silicon source, an aluminum source, an alkali source and an organic template agent with water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain a synthesized gel B, wherein the silicon-aluminum ratio of the synthesized gel B is different from that of the synthesized gel A;

heating the synthesized gel A to 120-200 ℃ for crystallization for 40-120 h; then adding the synthetic gel B, continuing crystallization for 0.1-70 h at the temperature of 120-;

or:

the second method comprises the following steps: mixing an SSZ-13 molecular sieve with water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain synthetic gel A;

mixing a silicon source, an aluminum source, an alkali source and an organic template agent with water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain a synthesized gel B, wherein the silicon-aluminum ratio of the synthesized gel B is different from that of the synthesized gel A;

and mixing the synthetic gel A and the synthetic gel B, crystallizing at 120-200 ℃ for 0.1-70 h, cooling, and performing post-treatment to obtain the SSZ-13 molecular sieve.

The SSZ-13 molecular sieve synthesis system or the SSZ-13 molecular sieve with sufficient crystallization time is used as a primary crystallization system, and the SSZ-13 molecular sieve with obvious hierarchical difference in silicon-aluminum ratio can be prepared by adding synthetic gel with different silicon-aluminum ratio into the primary crystallization system for continuous crystallization, namely by more than two times of crystallization, so that the regulation and control of the internal rule of the molecular sieve on the mesoscale are realized, and the property and catalytic performance of the molecular sieve are further changed.

In the above preparation method, the aged synthetic gel a is in an initial gel state, which needs to undergo a process of local dissolution to be converted into secondary gel recrystallization. The crystallization time of the synthetic gel A in the method is 40h-120h, which is enough to convert the synthetic gel A into a secondary gel state and recrystallize, and the addition of the synthetic gel B can enable the finally formed crystalline molecular sieve to have obvious silicon-aluminum ratio gradient.

The research of the invention finds that if the crystallization degree of the synthetic gel A is too low, most of silicon and aluminum in the synthetic gel A are in a secondary gel stage, after the synthetic gel B is added, the secondary gel in the synthetic gel A is still in a slow dissolving process, the silicon-aluminum ratio of the secondary gel can be continuously changed, and further silicon-aluminum ratio distribution with obvious level difference can not be formed; if the crystallization degree of the synthetic gel A is too high and reaches 100%, the solid molecular sieve formed by the synthetic gel A can be locally dissolved and re-form precipitate dissolution balance, and secondary crystallization is started by taking the surface of the solid molecular sieve as a substrate, so that the local chemical composition and crystal structure of the surface of the molecular sieve are reconstructed.

In the first method (i.e., the synthetic gel A is formed by mixing and aging a silicon source, an aluminum source, an alkali source, an organic template and water), the synthetic gel B is generally added to the synthetic gel A when the crystallinity of the synthetic gel A is generally more than 60% and less than 100%. The crystallinity refers to XRD crystallinity, which is calculated by taking a commercial SSZ-13 molecular sieve as a standard sample and accounting for 100 percent, and the method for calculating the crystallinity of a synthetic sample comprises the following steps: degree of crystallinity (%) - (area of XRD diffraction peak of synthetic sample/area of XRD diffraction peak of standard sample X100%; the XRD diffraction peak has a2 theta range of 5-35 degrees.

In the second preparation method (i.e., the synthesis gel A is formed by mixing and aging an SSZ-13 molecular sieve and water), the crystallinity of the synthesis gel A formed by the SSZ-13 molecular sieve is generally controlled to be more than 90% and less than 100%.

In a specific embodiment of the present invention, the first method and/or the second method may further include:

after the synthesis gel B is crystallized and before the temperature is reduced, adding the synthesis gel C into the mixture of the synthesis gel A and the synthesis gel B, and continuously crystallizing at the temperature of 120-; the silicon-aluminum ratio of the synthetic gel C is different from that of the synthetic gel B, and the synthetic gel C can be prepared by mixing a silicon source, an aluminum source, an alkali source, an organic template agent and water and aging for 0.1-100h at room temperature to 100 ℃.

In a specific embodiment of the present invention, the first method may include:

mixing a silicon source, an aluminum source, an alkali source, an organic template agent and water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain synthetic gel A;

mixing a silicon source, an aluminum source, an alkali source and an organic template agent with water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain a synthesized gel B, wherein the silicon-aluminum ratio of the synthesized gel B is different from that of the synthesized gel A;

mixing a silicon source, an aluminum source, an alkali source, an organic template agent and water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain synthetic gel C;

heating the synthesized gel A to 120-200 ℃ for crystallization for 40-120 h; then adding the synthetic gel B, and continuously crystallizing for 0.1-70 h at the temperature of 120-; then adding the synthetic gel C, and continuing crystallization for 0.21h-170h (e.g. 40h) at the temperature of 120-; and cooling and post-treating to obtain the SSZ-13 molecular sieve.

In a specific embodiment of the present invention, the second method may include:

mixing an SSZ-13 molecular sieve with water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain synthetic gel A;

mixing a silicon source, an aluminum source, an alkali source and an organic template agent with water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain a synthesized gel B, wherein the silicon-aluminum ratio of the synthesized gel B is different from that of the synthesized gel A;

mixing a silicon source, an aluminum source, an alkali source, an organic template agent and water, and aging for 0.1-100h at room temperature to 100 ℃ to obtain synthetic gel C;

mixing the synthetic gel A and the synthetic gel B, and crystallizing at the temperature of 120-200 ℃ for 0.1-70 h; then adding the synthetic gel C, and continuing crystallization for 0.1h-70h (e.g. 40h) at the temperature of 120-; and cooling and post-treating to obtain the SSZ-13 molecular sieve.

In a specific embodiment of the present invention, in the case where the first and/or second method further comprises an operation of adding the synthetic gel C, the synthetic gel B generally has a crystallinity of 60% or more and less than 100% when the synthetic gel C is added to the synthetic gel B.

In particular embodiments of the present invention, the silicon source may include one or a combination of two or more of silicon dioxide, silicate, ethyl orthosilicate, and the like. The silica can be added in any conventional form, for example, in the form of silica sol.

In particular embodiments of the present invention, the aluminum source may include one or a combination of two or more of sodium metaaluminate, aluminum hydroxide, pseudoboehmite, aluminum isopropoxide, and the like. For example, the aluminum source can be sodium metaaluminate, aluminum hydroxide, and the like.

In a specific embodiment of the present invention, the alkali source may be sodium hydroxide or the like.

In a specific embodiment of the present invention, the organic template may include one or a combination of two or more of salts and/or bases of N, N-trimethyl-1-adamantylammonium ion, benzyltrimethylammonium ion, N-dimethylethylcyclohexylammonium bromide ion, tetraethylammonium hydroxide ion, choline chloride ion, and Cu-tetraethylenepentamine ion.

In the specific embodiment of the present invention, the silicon source, the aluminum source, the alkali source and the organic template used for synthesizing gel a, synthesizing gel B and synthesizing gel C may be the same or different.

In the present inventionIn particular embodiments, the chemical composition of the synthetic gel a generally satisfies the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-180；OH-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, and R is an organic template. In some embodiments, the chemical composition of synthetic gel a may satisfy the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-30；OH-/SiO₂＝0.01-0.5；H₂O/SiO₂＝5-40；R/SiO₂＝0.01-0.2。

In a particular embodiment of the invention, the chemical composition of the synthetic gel B generally satisfies the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-180；OH-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, and R is an organic template. In some embodiments, the chemical composition of synthetic gel B may satisfy the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-30；OH-/SiO₂＝0.01-0.5；H₂O/SiO₂＝5-40；R/SiO₂＝0.01-0.2。

In a particular embodiment of the invention, the chemical composition of the synthetic gel C may satisfy the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-180；OH-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, and R is an organic template. In some embodiments, the chemical composition of the synthetic gel C may also satisfy the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-30；OH-/SiO₂＝0.01-0.5；H₂O/SiO₂＝5-40；R/SiO₂＝0.01-0.2。

In a specific embodiment of the present invention, the mass ratio of the synthetic gel B to the synthetic gel A is generally controlled to be 0.01 to 5:1, for example, 0.05 to 2:1, 0.1 to 1:1, etc.

In a specific embodiment of the present invention, the mass ratio of the synthetic gel C to the synthetic gel B is generally controlled to be 0.01 to 5:1, for example, 0.05 to 2:1, 0.1 to 1:1, etc.

In a particular embodiment of the invention, the chemical composition of the mixture of synthetic gel a and synthetic gel B generally satisfies the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-180；OH-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, and R is an organic template.

In a particular embodiment of the invention, the chemical composition of the mixture of synthetic gel a, synthetic gel B and synthetic gel C generally satisfies the following molar ratio ranges: SiO 2₂/Al₂O₃＝5-180；OH-/SiO₂＝0.01-1；H₂O/SiO₂＝3-80；R/SiO₂0.01-0.5, and R is an organic template.

In a particular embodiment of the invention, the SSZ-13 molecular sieve used to prepare the synthetic gel A typically has a particle size of from 0.1 μm to 10 μm, e.g., from 0.2 μm to 5 μm, from 0.5 μm to 1.5 μm, and the like.

In a specific embodiment of the present invention, when the synthetic gel a is subjected to crystallization alone (i.e., crystallization performed before the synthetic gel B is added), the crystallization time may be 50h to 100 h.

In the embodiment of the present invention, when adding the synthetic gel B to the synthetic gel a and adding the synthetic gel C to the synthetic gel B, the synthetic gels may be added by means of a high pressure pump, or by cooling an autoclave to room temperature and opening the autoclave.

In a specific embodiment of the present invention, the post-treatment generally comprises filtration, washing, drying of the solid sample, calcination, and the like. In some embodiments, the temperature of the calcination is generally from 500 ℃ to 800 ℃ (e.g., from 550 ℃ to 650 ℃) and the calcination time is from 6h to 10h (e.g., from 7h to 8 h).

In a specific embodiment of the present invention, the above preparation method may be to mix the soluble components first, and then add the solid components and mix them.

The invention also provides an SSZ-13 molecular sieve which is obtained by the preparation method.

The invention further provides NH₃-SCR reaction catalysisAn agent comprising the SSZ-13 molecular sieve described above. In some embodiments, at NH₃In the SCR reaction, the maximum conversion rate of the SSZ-13 molecular sieve to nitrogen oxides and the maximum nitrogen selectivity can reach more than 90 percent at the temperature of 150 ℃ and 550 ℃.

The invention has the beneficial effects that:

the SSZ-13 molecular sieve provided by the invention has obvious step layering change in silica-alumina ratio, has higher and controllable hydrothermal stability and is applied to NH₃The SCR reaction process has higher catalytic performance, for example, the conversion rate of nitrogen oxides and the selectivity of nitrogen can reach more than 90 percent at the temperature of 150 ℃ and 550 ℃. The preparation method provided by the invention can effectively regulate and control the silicon-aluminum ratio distribution of the SSZ-13 molecular sieve, thereby achieving the effect of regulating the structure and the catalytic performance of the molecular sieve.

Drawings

FIG. 1 is a graph of XPS profiling depth of SSZ-13 molecular sieve of example 1 as a function of silica to alumina ratio.

FIG. 2 is a graph of XPS profiling depth of SSZ-13 molecular sieve of example 2 as a function of silica to alumina ratio.

FIG. 3 is a graph of XPS profiling depth of SSZ-13 molecular sieve of example 3 as a function of silica to alumina ratio.

FIG. 4 is a graph of XPS profiling depth of SSZ-13 molecular sieve of example 4 as a function of silica to alumina ratio.

FIG. 5 is a graph of XPS profiling depth of SSZ-13 molecular sieve of comparative example 1 versus silica to alumina ratio.

FIG. 6 is a graph of XPS profiling depth of SSZ-13 molecular sieve of comparative example 2 as a function of silica to alumina ratio.

FIG. 7 is an SEM image of the SSZ-13 molecular sieve of example 1.

FIG. 8 is an SEM image of the SSZ-13 molecular sieve of comparative example 2.

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 following examples and comparative examples, the particle size of the molecular sieve product was measured by SEM micrographs, crystallinity was measured by XRD (2. theta. from 5 to 35 degrees), and specific surface area was determined according to Brunauer-Emmett-Teller (BET) model processing low temperature nitrogen adsorption curve data.

Example 1

This example provides an SSZ-13 molecular sieve, the preparation method of which comprises:

1. preparation of synthetic gel a:

fully mixing aqueous solution formed by sodium metaaluminate, pure water, sodium hydroxide, 25 wt% of N, N, N-trimethyl-1-adamantyl ammonium hydroxide (used as an organic template) and silicon dioxide to obtain a raw material composition with the following molar ratio, and aging for 10 hours at room temperature to obtain synthetic gel A:

SiO₂/Al₂O₃＝20

organic template agent (SDA)/SiO₂＝0.1

OH^-/SiO₂＝0.15

H₂O/SiO₂＝30。

2. Preparation of synthetic gel B:

fully mixing aqueous solution formed by sodium metaaluminate, pure water, sodium hydroxide, 25 wt% of N, N, N-trimethyl-1-adamantyl ammonium hydroxide (used as an organic template) and silicon dioxide to obtain a raw material composition with the following molar ratio, and aging at room temperature for 10 hours to obtain synthetic gel B:

SiO₂/Al₂O₃＝10

SDA/SiO₂＝0.1

OH^-/SiO₂＝0.15

H₂O/SiO₂＝30。

3. and (3) putting the synthesized gel A into an autoclave, and heating to 180 ℃ under a stirring state to crystallize for 60 hours.

4. And (3) putting the synthetic gel B into the autoclave in the step (3), and continuously crystallizing for 60 hours at 180 ℃ under the stirring state, wherein the mass ratio of the synthetic gel B to the synthetic gel A is 2: 1.

5. Stopping crystallization, cooling to below 60 ℃, filtering, washing, drying a solid sample, and roasting at 550 ℃ for 8 hours to obtain the SSZ-13 molecular sieve.

The SSZ-13 molecular sieve sample of this example was measured to have a particle size of about 5 μm, a crystallinity of 95%, and a specific surface area of 572. + -.11 m²·g^-1。

A Thermo escalab 250Xi type X-ray photoelectron spectrometer is matched with a brand automatic high-efficiency ion analysis source test sample. The test adopts a full element spectrogram of an AlK alpha (1486.6eV) anode target test sample in a range of 0-1400eV, and measures the relative spectral line intensity of Al2p and Si2p by using the spectral line intensity of a specific element as a reference standard through a sensitivity factor method to obtain the relative content of each element. Specifically, firstly, an Ar ion source is adopted to carry out conventional pretreatment on a sample, and an XPS full spectrum of the surface of the sample is tested; and then, carrying out sputtering treatment on the sample for a certain time T by adopting an Ar ion analyzing source, testing the depth d of the obtained sample pit by using a step profiler, and obtaining the sputtering rate d/T of the sample on the assumption that the sputtering rate of the sample is constant in the sputtering process. And (3) according to the obtained sputtering rate, sequentially treating for a certain time, and carrying out auxiliary measurement by using a step profiler until the depths of 0.25 mu m, 0.50 mu m, 0.75 mu m, 1 mu m, 1.25 mu m, 1.50 mu m, 2.00 mu m and 2.50 mu m are obtained, and testing XPS full spectrograms of samples with different depths.

FIG. 1 is a graph showing the relationship between the XPS analysis depth and the Si/Al ratio of the SSZ-13 molecular sieve sample of this example. As can be seen from FIG. 1, SiO calculated from the results of element quantification in the depth interval of 0.75 μm from the surface of the sample₂/Al₂O₃The molar ratio is maintained to be about 5 and basically matched with the feeding ratio of the synthetic gel B; when the dissection depth is increased to 1 μm, SiO₂/Al₂O₃The ratio is small and the amplitude is increased to 6; when the analysis depth is increased to more than 1.50 μm, SiO₂/Al₂O₃The proportion is changed rapidly to 19, and the silicon-aluminum ratio is basically stable and unchanged along with the increase of the depth, and is basically consistent with the feeding ratio of the synthetic gel A.

The above results indicate that the silica-alumina ratio distribution in the SSZ-13 molecular sieve sample of this example is a non-uniform hierarchical distribution with significant hierarchical differences.

Example 2

This example provides an SSZ-13 molecular sieve, the preparation method of which comprises:

1. preparation of synthetic gel a:

fully mixing sodium hydroxide, pure water, an aqueous solution of 25 wt% N, N, N-trimethyl-1-adamantyl ammonium hydroxide (as an organic template), silica sol (the mass content of silicon dioxide is 40%) and pseudo-boehmite to obtain a raw material composition with the following mole ratio, and aging for 2 hours at room temperature to obtain a synthetic gel A:

SiO₂/Al₂O₃＝5

organic template agent (SDA)/SiO₂＝0.2

OH^-/SiO₂＝0.23

H₂O/SiO₂＝20。

2. Preparation of synthetic gel B:

sodium hydroxide, pure water, an aqueous solution of 25 wt% N, N-trimethyl-1-adamantyl ammonium hydroxide (as an organic template), silica sol (silica mass content 40%) and pseudo-boehmite were thoroughly mixed to obtain a raw material composition having the following composition by mole ratio, and aged at room temperature for 2 hours to obtain a synthetic gel B:

SiO₂/Al₂O₃＝20

SDA/SiO₂＝0.2

OH^-/SiO₂＝0.23

H₂O/SiO₂＝20。

3. and (3) putting the synthesized gel A into an autoclave, and heating to 170 ℃ under a stirring state to crystallize for 100 hours.

4. And (3) filling the synthesized gel B into the autoclave in the step (3), and continuously crystallizing for 40 hours at 170 ℃ under the stirring state, wherein the mass ratio of the synthesized gel B to the synthesized gel A is 0.8: 1.

5. Stopping crystallization, cooling to below 60 ℃, filtering, washing, drying a solid sample, and roasting at 550 ℃ for 8 hours to obtain the SSZ-13 molecular sieve.

Measured byThe SSZ-13 molecular sieve sample of this example had a particle size of about 2.8 μm, a crystallinity of 98%, and a specific surface area of 582. + -.13 m²·g^-1. FIG. 2 is a graph showing the relationship between the XPS analysis depth and the Si/Al ratio of the SSZ-13 molecular sieve sample of this example, which is tested in the same manner as example 1. As can be seen from FIG. 2, SiO calculated from the results of element quantification in the depth interval of 0.6 μm from the surface of the sample₂/Al₂O₃The molar ratio is about 18 and is basically consistent with the feeding ratio of the synthetic gel B; when the dissection depth is increased to 0.8 μm, SiO₂/Al₂O₃The proportion is sharply reduced; when the analysis depth is increased to more than 1 μm, SiO₂/Al₂O₃The proportion is stabilized at about 5, and is basically consistent with the feeding ratio of the synthetic gel A.

The above results indicate that the silica-alumina ratio distribution in the SSZ-13 molecular sieve sample of this example is a non-uniform hierarchical distribution with significant hierarchical differences.

Example 3

This example provides an SSZ-13 molecular sieve, the preparation method of which comprises:

1. preparation of synthetic gel a:

mixing SiO₂/Al₂O₃SSZ-13 solid powder (particle size 5 μm) of 20 was dispersed in pure water to give a starting composition having the following molar ratio composition, and aged at room temperature for 1h to give a synthetic gel a:

SiO₂/Al₂O₃＝20

H₂O/SiO₂＝10。

2. preparation of synthetic gel B:

fully mixing aqueous solution formed by sodium metaaluminate, pure water, sodium hydroxide, 25 wt% of N, N, N-trimethyl-1-adamantyl ammonium hydroxide (used as an organic template) and silicon dioxide to obtain a raw material composition with the following molar ratio, and aging at room temperature for 8 hours to obtain synthetic gel B:

SiO₂/Al₂O₃＝50

SDA/SiO₂＝0.15

OH^-/SiO₂＝0.25

H₂O/SiO₂＝50。

3. and (3) putting the synthesized gel A into an autoclave, heating to 100 ℃ under a stirring state, and aging for 10 hours to fully mix and react the components.

4. And (3) filling the synthesized gel B into the autoclave in the step (3), and continuously crystallizing for 50 hours at 160 ℃ under the stirring state, wherein the mass ratio of the synthesized gel B to the synthesized gel A is 0.2: 1.

5. Stopping crystallization, cooling to below 60 ℃, filtering, washing, drying a solid sample, and roasting at 550 ℃ for 8 hours to obtain the SSZ-13 molecular sieve.

The SSZ-13 molecular sieve sample of this example was measured to have a particle size of about 1 μm, a crystallinity of 92%, and a specific surface area of 559. + -. 10m²·g^-1。

FIG. 3 is a graph showing the relationship between the XPS analysis depth and the Si/Al ratio of the SSZ-13 molecular sieve sample of this example, which is tested in the same manner as example 1. As can be seen from FIG. 3, SiO calculated from the results of the element quantification in the range from the surface of the sample to a depth of 100nm₂/Al₂O₃The molar ratio is about 40 and is slightly lower than the charging ratio 50 of the synthesized gel B, because a part of silicon source is dissolved in the alkaline synthesis system; when the profile depth is increased to 100-150nm, the SiO layer is formed₂/Al₂O₃The proportion is rapidly reduced; when the analysis depth is increased to over 300nm, SiO₂/Al₂O₃The proportion is stabilized at about 15, and is basically consistent with the feeding ratio of the synthetic gel A.

The above results indicate that the silica-alumina ratio distribution in the SSZ-13 molecular sieve sample of this example is a non-uniform hierarchical distribution with significant hierarchical differences.

Example 4

This example provides an SSZ-13 molecular sieve, the preparation method of which comprises:

1. preparation of synthetic gel a:

aluminum isopropoxide, sodium hydroxide, pure water, an aqueous solution of 25 wt% N, N-trimethyl-1-adamantyl ammonium hydroxide, an aqueous solution of 25 wt% tetraethylammonium hydroxide, and silica sol (silica mass content 40%) were thoroughly mixed to obtain a raw material composition having the following molar ratio composition, wherein N, N-trimethyl-1-adamantyl ammonium hydroxide and tetraethylammonium hydroxide were used together as an organic template in a molar ratio of 1: 1. Aging the raw material composition for 1h at room temperature to obtain a synthetic gel A:

SiO₂/Al₂O₃＝60

SDA/SiO₂＝0.4

OH^-/SiO₂＝0.3

H₂O/SiO₂＝50。

2. preparation of synthetic gel B:

fully mixing aluminum isopropoxide, sodium hydroxide, pure water, an aqueous solution of 25 wt% N, N, N-trimethyl-1-adamantyl ammonium hydroxide, an aqueous solution of 25 wt% tetraethylammonium hydroxide and silica sol (silica mass content 40%) to obtain a raw material composition with the following molar ratio, and aging at room temperature for 12 hours to obtain a synthetic gel B:

SiO₂/Al₂O₃＝25

SDA/SiO₂＝0.4

OH^-/SiO₂＝0.3

H₂O/SiO₂＝50。

3. preparation of synthetic gel C:

fully mixing aluminum isopropoxide, sodium hydroxide, pure water, an aqueous solution of 25 wt% N, N, N-trimethyl-1-adamantyl ammonium hydroxide, an aqueous solution of 25 wt% tetraethylammonium hydroxide and silica sol (silica mass content 40%) to obtain a raw material composition with the following molar ratio, and aging at room temperature for 12 hours to obtain a synthetic gel C:

SiO₂/Al₂O₃＝5

SDA/SiO₂＝0.4

OH^-/SiO₂＝0.3

H₂O/SiO₂＝20。

4. and (3) putting the synthesized gel A into an autoclave, and heating to 180 ℃ under a stirring state to crystallize for 40 hours.

5. And (3) putting the synthetic gel B into the autoclave in the step (4), and continuously crystallizing for 80 hours at 180 ℃ under the stirring state, wherein the mass ratio of the synthetic gel B to the synthetic gel A is 2: 1.

6. And (3) putting the synthetic gel C into the autoclave in the step (5), and continuously crystallizing for 40 hours at 180 ℃ under the stirring state, wherein the mass ratio of the synthetic gel C to the synthetic gel B is 2: 1.

7. Stopping crystallization, cooling to below 60 ℃, filtering, washing, drying a solid sample, and roasting at 550 ℃ for 8 hours to obtain the SSZ-13 molecular sieve.

The SSZ-13 molecular sieve sample of this example was measured to have a particle size of about 1.4 μm, a crystallinity of 93%, and a specific surface area of 560. + -.10 m²·g^-1。

FIG. 4 is a graph showing the relationship between the XPS analysis depth and the Si/Al ratio of the SSZ-13 molecular sieve sample of this example. As can be seen from FIG. 4, SiO calculated from the elemental quantitative results as the profiling depth gradually increases₂/Al₂O₃The molar ratio is in an ascending trend and is determined by SiO on the surface of the sample₂/Al₂O₃Increased to 5 to the middle (profile depth 200-₂/Al₂O₃When the final analysis depth is 500nm or more, 25 is stabilized at SiO₂/Al₂O₃About 58.

The above results indicate that the silica-alumina ratio distribution in the SSZ-13 molecular sieve sample of this example is a non-uniform hierarchical distribution with significant hierarchical differences.

Comparative example 1

This comparative example provides an SSZ-13 molecular sieve which differs from example 1 primarily in the crystallization time and the silica to alumina ratio distribution of the resulting molecular sieve from example 1. Specifically, the preparation method of the molecular sieve of the comparative example comprises the following steps:

1. preparation of synthetic gel a:

fully mixing an aqueous solution formed by aluminum isopropoxide, pure water, sodium hydroxide, 25 wt% of N, N, N-trimethyl-1-adamantyl ammonium hydroxide and 25 wt% of tetraethylammonium hydroxide (N, N, N-trimethyl-1-adamantyl ammonium hydroxide and tetraethylammonium hydroxide are used together as an organic template and are mixed according to a molar ratio of 1: 1) with silica sol (the mass content of silicon dioxide is 40%) to obtain a raw material composition with the following molar ratio, and aging for 1h at room temperature to obtain a synthetic gel A:

SiO₂/Al₂O₃＝15

SDA/SiO₂＝0.4

OH^-/SiO₂＝0.3

H₂O/SiO₂＝50。

2. preparation of synthetic gel B:

fully mixing an aqueous solution formed by aluminum isopropoxide, sodium hydroxide, pure water, 25 wt% of N, N, N-trimethyl-1-adamantyl ammonium hydroxide and silica sol (the mass content of silicon dioxide is 40%) to obtain a raw material composition with the following mole ratio, and aging at room temperature for 1h to obtain a synthetic gel B:

SiO₂/Al₂O₃＝10

SDA/SiO₂＝0.4

OH^-/SiO₂＝0.3

H₂O/SiO₂＝50。

3. and (3) putting the synthesized gel A into an autoclave, and heating to 180 ℃ under a stirring state for crystallization for 12 hours.

4. And (3) putting the synthesized gel B into the autoclave in the step (3), and continuously crystallizing for 40 hours at 180 ℃ under the stirring state, wherein the mass ratio of the synthesized gel B to the synthesized gel A is 0.5: 1.

5. Stopping crystallization, cooling to below 60 ℃, filtering, washing, drying a solid sample, and roasting at 550 ℃ for 8 hours to obtain the SSZ-13 molecular sieve.

The SSZ-13 molecular sieve sample of this comparative example was measured to have a particle size of about 1.2 μm, a crystallinity of 93%, and a specific surface area of 570. + -.12 m²·g^-1。

FIG. 5 is a graphical representation of the XPS profiling depth versus silica to alumina ratio for a sample of SSZ-13 molecular sieve of this comparative example. As can be seen from FIG. 5, SiO calculated from the elemental quantitative results as the profiling depth gradually increases₂/Al₂O₃The molar ratio is gradually increased from 8 to about 14, which shows that the grade difference of the ratio of silicon to aluminum in the molecular sieve sample prepared by the comparative example is not obvious. This is because the crystallization time of the synthetic gel a in this comparative example is only 12 hours, at which time the synthetic gel a, although having been transformed into a solid phase, has not been transformed into a crystalline molecular sieve, belongs to the initial gel, which needs to undergo further local dissolution processes to be transformed into a secondary gel for recrystallization. And adding the synthetic gel B when the synthetic gel A is crystallized for 12 hours, and mixing the synthetic gel B with the slowly-dissolved secondary gel A to cause the crystallized crystalline molecular sieve to form a slowly-changing silicon-aluminum ratio gradient. The above results show that only by controlling the crystallization time of the synthesized gel A in a proper range, the SSZ-13 molecular sieve with a significant level difference silicon-aluminum ratio can be obtained.

Comparative example 2

This comparative example provides an SSZ-13 molecular sieve prepared by a process comprising:

1. preparation of the synthetic gel:

fully mixing sodium metaaluminate, sodium hydroxide, pure water, an aqueous solution of 25 wt% N, N, N-trimethyl-1-adamantyl ammonium hydroxide, an aqueous solution of 25 wt% tetraethylammonium hydroxide and silicon dioxide to obtain a raw material composition with the following molar ratio, and aging at room temperature for 10 hours to obtain the synthetic gel:

SiO₂/Al₂O₃＝10

SDA/SiO₂＝0.1

OH^-/SiO₂＝0.15

H₂O/SiO₂＝30。

2. the synthesized gel is transferred to an autoclave and stirred and crystallized for 60 hours at 180 ℃.

3. Stopping crystallization, cooling to below 60 ℃, filtering, washing, drying a solid sample, and roasting at 550 ℃ for 8 hours to obtain the SSZ-13 molecular sieve.

The SSZ-13 molecular sieve sample of this comparative example was measured to have a particle size of about 3 μm, a crystallinity of 100%, and a specific surface area of 585. + -.10 m²·g^-1。

FIG. 6 is a graphical representation of the XPS profiling depth versus silica to alumina ratio for a sample of SSZ-13 molecular sieve of this comparative example. As can be seen in FIG. 6, SiO at different dissection depth positions₂/Al₂O₃All are about 10, which shows that the silica-alumina ratio distribution in the molecular sieve sample prepared by the comparative example is uniform and no obvious level difference exists.

Table 1 shows the silicon to aluminum ratios at different depths of cut for the molecular sieve samples prepared in examples 1 to 4 and comparative examples 1 to 2.

TABLE 1

The amplitude of the longitudinal fluctuation of the plateau of each stage in the step curve of the molecular sieve samples of the examples can be calculated according to table 1. Taking example 1 as an example, the silicon-aluminum ratio of the sample has a first-stage platform at the parsing depth of 0-1.25 μm, and the average silicon-aluminum ratio of the platform is 5.45, so that the fluctuation amplitudes of three data points in the platform are respectively 15.6%, 2.8%, 4.6%, 2.8%, 15.6%, 10.1%, and are all less than 16%; and the analysis depth is 1.5-2.5 μm, the second stage platform has an average Si/Al ratio of 18.6, and the fluctuation amplitudes of three data points in the platform are respectively 0.5%, 2.7% and 2.2%, and are all less than 16%. The silica-alumina ratio distribution of the molecular sieve samples of examples 2 to 4 is analyzed according to the same method, and the longitudinal fluctuation amplitude of each stage of platform in the step curve of each sample is below 16%.

Test example 1

The test example provides a NH3-SCR reaction performance test on SSZ-13 molecular sieve samples prepared in examples 1 to 4 and comparative examples 1 to 2, the specific test method including:

1. ammonium exchange of molecular sieve: the SSZ-13 molecular sieves prepared in examples 1 to 4 and comparative examples 1 to 2 were used as test samples, respectively, according to the ammonium nitrate: molecular sieve: water 1: 1: 10, adjusting the pH to 8-8.5 by ammonia water, performing ammonium exchange for 1h at 90 ℃ under a stirring state, filtering, washing, drying, and roasting for 2h at 550 ℃. Repeating the above process for 3 times until Na in the molecular sieve₂And the mass content of O is less than 0.1 percent, and the molecular sieve after ammonium exchange is obtained. Wherein, Na₂The mass content of O is determined by XRF or ICP determination of the molecular sieve composition.

2. Loading molecular sieve copper: cu (NO) with the loading of 5 percent corresponding to molecular sieve CuO₃)₂Dissolving in 50 times of water, adding ammonium exchanged molecular sieve under stirring, adjusting pH to 8-8.5 with ammonia water, filtering, washing, oven drying, and roasting at 550 deg.C for 4h to obtain copper-loaded molecular sieve, also known as Cu-SSZ-13 molecular sieve.

3. Tabletting the molecular sieve sample which is subjected to ammonium exchange and is loaded with Cu, forming, crushing, sieving, and adding 10% of H₂After hydrothermal aging for 100h at 650 ℃ in an O + 90% air atmosphere, 0.5g of a molecular sieve sample of 40-60 meshes is taken and used 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^-1And the reaction temperature is 200-600 ℃, and an MKS infrared gas analyzer is used for detecting the concentration of NOx in the tail gas on line. Tables 1 and 2 show the NOx conversion and N at different temperatures for each molecular sieve sample₂And (5) selecting a test result.

Among them, NOx conversion rate (C)_NOx) Is defined as:

N₂selectivity (S)_N2) Is defined as:

wherein [ NO ]]_{An inlet}The concentration of NO in the reaction mixture, [ NO ]]_{An outlet}Is the concentration of NO in the exhaust, [ NH ]₃]_{An inlet}For reacting NH in gas mixture₃Concentration of [ NH ], [ NH ]₃]_{An outlet}For NH in tail gas₃Concentration of (A) [ N ]₂O]_{An outlet}For N in the tail gas₂The concentration of O; [ NO ]₂]_{An outlet}As NO in the exhaust gas₂The concentration of (c).

TABLE 2 conversion (C) of nitrogen oxides in the reaction mixture at different temperatures (150 ℃ C. -_NOx) And N₂Selectivity (S)_N2)

TABLE 3 conversion of nitrogen oxides in the reaction mixture at different temperatures (400 ℃ C. and 550 ℃ C.) and N₂Selectivity is

As can be seen from the data in tables 2 and 3, the Cu-SSZ-13 composite molecular sieve obtained by ammonium exchange and copper loading of SSZ-13 prepared in the example of the invention has DeNOx activity and N in the temperature range of 200-550 DEG C₂The selectivity is obviously better than that of molecular sieve samples treated in the same way in the comparative example 1 and the comparative example 2 at different temperatures, and the higher the temperature is, the more obvious the performance advantage is. And, the catalytic performance of the Cu-SSZ-13 molecular sieve with the gradual silicon-aluminum ratio prepared in the comparative example 1 is slightly better than that of the Cu-SSZ-13 molecular sieve with the uniformly distributed silicon-aluminum ratio prepared in the comparative example 2.

Further comparing the catalytic performance of the molecular sieves of examples 1 to 4, it can be seen that the molecular sieves having a surface silicon to aluminum ratio lower than the internal silicon to aluminum ratio (i.e., surface rich in aluminum, such as in examples 1 and 4) have a better NOx conversion as catalysts in the temperature region of 200-450 ℃, but have a higher activity as catalysts at high temperatures (500-550 ℃) than the molecular sieves having an internal silicon to aluminum ratio (i.e., surface rich in silicon, such as in examples 2 and 3).

The above results are due to the fact that the silica to alumina ratio affects the distribution and state of the molecular sieve acidity and Cu species. The Lewis acid site is the main low-temperature DeNOx active site of the Cu-SSZ-13 composite molecular sieve, Cu²⁺More NOx adsorption sites can be provided for Cu/SSZ-13, being the primary high temperature DeNOx active sites. When the silicon-aluminum ratio is increased to a certain degree, a large amount of Lewis acid sites are lost, so that the low-temperature DeNOx activity of the catalyst is not advantageous; but because the density of the skeleton Al is lower, Al is not easy to lose under the high-temperature hydrothermal condition, the part with high silicon-aluminum ratio of the outer layer can well protect the Cu component in the molecular sieve from being aggregated into CuO, the high-temperature activity and selectivity are obviously improved, the silicon-aluminum ratio is an important parameter for ensuring the catalytic performance, and the improvement of the catalytic effect is not facilitated when the silicon-aluminum ratio in the molecular sieve is changed all the time. It can be seen that when there is a significant difference in the silica-alumina ratio within the crystals of the SSZ-13 molecular sieve, the effect on improving the DeNOx activity and selectivity of the catalyst is more significant.

Fig. 7 and 8 are SEM photographs of the molecular sieves prepared in example 1 and comparative example 2, respectively. As can be seen from fig. 7 and 8, comparative example 2 prepared a molecular sieve having a mesoscopic morphology of microspheres with a diameter of 3 μm formed by agglomeration of bulk primary particles through a primary crystallization process, while example 1 prepared a molecular sieve having a mesoscopic morphology substantially identical to that of comparative example 2 but with the diameter of the microspheres of the molecular sieve increased to 5 μm through a secondary crystallization process. The above results demonstrate that the molecular sieve prepared in example 1 is formed by crystallization of the molecular sieve formed in synthesis gel B around the inner molecular sieve already having a certain crystallinity (i.e., the molecular sieve crystallized in synthesis gel a).