CN113307285A - MFI structure molecular sieve with uniformly distributed heteroatoms and synthesis method thereof - Google Patents

MFI structure molecular sieve with uniformly distributed heteroatoms and synthesis method thereof Download PDF

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CN113307285A
CN113307285A CN202110493208.1A CN202110493208A CN113307285A CN 113307285 A CN113307285 A CN 113307285A CN 202110493208 A CN202110493208 A CN 202110493208A CN 113307285 A CN113307285 A CN 113307285A
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molecular sieve
heteroatoms
mfi structure
silicon
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刘月明
陈贞
张莲霖
余云开
方南
刘东旭
李芳�
徐德义
何鸣元
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East China Normal University
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Abstract

The invention discloses an MFI structure molecular sieve with uniformly distributed heteroatoms and a synthesis method thereof, wherein skeleton heteroatoms in the MFI structure heteroatom molecular sieve containing different heteroatoms (heteroatoms M, such as Al, B, Fe, Ga, Ti, Sn, Nb, Zn and the like) are uniformly distributed in a molecular sieve crystal, and the Si/M ratio on the surface of the molecular sieve is basically equivalent to the integral Si/M ratio of the molecular sieve, which is different from the property of silicon enrichment on the surface of the MFI structure heteroatom molecular sieve obtained by traditional hydrothermal synthesis. The MFI structure molecular sieve with uniformly distributed heteroatoms has good accessibility of the heteroatom active center and few surface defects, can realize uniform distribution of two or more heteroatoms in a molecular sieve crystal, and is beneficial to the cooperative play of controllable design and catalytic action of the active center; meanwhile, the synthesis method is simple and controllable, has good repeatability and is easy for industrial production and application.

Description

MFI structure molecular sieve with uniformly distributed heteroatoms and synthesis method thereof
Technical Field
The invention belongs to the technical field of chemical industry, and relates to an MFI structure molecular sieve with uniformly distributed heteroatoms and a synthesis method thereof, in particular to an MFI structure heteroatom molecular sieve with uniformly distributed heteroatoms in a molecular sieve crystal, wherein the Si/M ratio of the surface of the molecular sieve is basically equivalent to the integral Si/M ratio of the molecular sieve, and the MFI structure heteroatom molecular sieve is synthesized by a hydrothermal crystallization method.
Background
Heteroatom molecular sieves generally refer to molecular sieves in which heteroatoms replace silicon in the molecular sieve framework by isomorphous substitution. The heteroatom is implanted into a molecular sieve framework, so that the properties of the molecular sieve, such as catalytic activity, hydrophilicity and hydrophobicity, adsorption property and the like, can be adjusted, and the heteroatom molecular sieve becomes a brand new catalytic material through the adjustment and control of the heteroatom, and is widely applied to the fields of petroleum refining and chemical industry, fine chemical industry, C1 chemistry, environmental protection and the like.
The TS-1 molecular sieve (U.S. Pat. No. 4,410,501) is a Ti-containing heteroatom molecular sieve obtained by implanting heteroatom Ti into an MFI structure molecular sieve framework, and the ZSM-5 molecular sieve (U.S. Pat. No. 3,702,886) is an Al-containing heteroatom molecular sieve obtained by implanting heteroatom Al into an MFI structure molecular sieve framework. At present, heteroatom B, Fe, Ga, Ti, Sn, Nb, Zn and the like are successfully implanted into an MFI structure molecular sieve framework to obtain a corresponding MFI structure heteroatom molecular sieve. For heteroatomic molecular sieves, the distribution of the heteroatoms (M) in the molecular sieve crystals is substantially as shown inThe surface is rich in silicon, and the hetero atoms in the molecular sieve crystal are gradually enriched from the surface to the inside, and the Si/M ratio (Si/M) of the molecular sieve surfaceSurface of) Si/M ratio (Si/M) of molecular sieveBulk phase) The difference of (c) generally satisfies |. Si/MSurface of-Si/MBulk phase∣/(Si/MBulk phase) Not less than 60 percent. The literature (Applied Catalysis A: General,453, (2013)272-279) reports that the synthesized Ti-containing molecular sieve TS-1 with MFI structure, Si/MBulk phaseIs 48.97 and Si/MSurface of80.57, | Si/MSurface of-Si/MBulk phase∣/(Si/MBulk phase) The content was 64.5%. The position of the heteroatom in the heteroatom molecular sieve directly affects its catalytic properties. The literature (ACS Catalysis,2016,6,7311-7325) reports that the difference of Al position in ZSM-5 molecular sieve skeleton directly influences the reaction path and product distribution of catalytic MTO reaction. The document (Advanced Materials,2020,2000272) reports that the Y-type molecular sieve with the Al uniformly distributed in the molecular sieve crystal has higher macromolecule catalytic cracking activity than the traditional Y-type molecular sieve with silicon-rich surface. At present, the MFI structure heteroatom molecular sieve obtained by hydrothermal synthesis presents a heteroatom distribution characteristic similar to that of the traditional heteroatom molecular sieve, namely, the surface is rich in silicon.
Disclosure of Invention
One of the purposes of the invention is to provide an MFI structure molecular sieve with uniformly distributed heteroatoms, which is characterized in that: heteroatom M in MFI structure molecular sieve is uniformly distributed in molecular sieve crystal, and Si/M ratio (Si/M) of molecular sieve surfaceSurface of) Si/M ratio (Si/M) of molecular sieveBulk phase) Satisfies | Si/MSurface of-Si/MBulk phase∣/(Si/MBulk phase) At most 20 percent, and the heteroatom M in the MFI structure molecular sieve framework is at least one of Al, B, Fe, Ga, Ti, Sn, Nb and Zn.
The invention also aims to provide a synthesis method of the MFI structure molecular sieve with uniform heteroatom distribution. Research shows that in the crystallization process of synthesizing the MFI structure heteroatom molecular sieve by adopting a hydrothermal crystallization method, the distribution of heteroatoms in the molecular sieve crystal is determined by the condensed state structure of silicon species in a synthesis system. The technical scheme for synthesizing the MFI structure molecular sieve with uniformly distributed heteroatoms comprises the following operation steps: preparing a silicon-containing species solution, preparing a crystallization mixed solution and crystallizing.
The technical solution of the present invention will now be described in detail.
The synthesis method of the MFI structure molecular sieve with uniformly distributed heteroatoms comprises the following operation steps:
first step preparation of a solution of silicon-containing species
SiO in silicon source2OH in the alkali Source-Preparing a silicon-containing species solution with water according to a molar ratio of 1 (0.4-2) (10-100), mixing an alkali source with water, adding a silicon source, uniformly mixing, performing hydrothermal treatment at 100-190 ℃ for 0.5-24 hours, and cooling to obtain the silicon-containing species solution, wherein the silicon source is at least one of an inorganic silicon compound and an organic silicon compound, the inorganic silicon compound is a pure silicon molecular sieve, silica sol, silica gel and white carbon black, the organic silicon compound is tetraethyl silicate, tetrapropyl silicate and tetrabutyl silicate, the alkali source is at least one of inorganic alkali and organic alkali, the inorganic alkali is NaOH and KOH, and the organic alkali is tetrapropylammonium hydroxide;
second step preparation of crystallized mixed solution
Adding water-soluble inorganic salt or organic compound containing heteroatom M into the prepared silicon-containing solution according to the molar ratio Si/M of 20-500, and uniformly stirring to obtain a crystallized mixed solution; wherein the heteroatom M is Al, B, Fe, Ga, Ti, Sn, Nb, Zn;
the third step of crystallization
And carrying out hydrothermal crystallization on the crystallized mixed solution at the crystallization temperature of 120-190 ℃ for 2-72 hours to obtain a crystallized product, and carrying out conventional filtration, washing, drying and roasting to obtain the MFI structure molecular sieve with uniformly distributed heteroatoms.
Compared with the prior art, the invention has the following remarkable advantages:
1. the MFI structure molecular sieve with uniformly distributed heteroatoms has good accessibility of the heteroatom active center and few surface defects, can realize uniform distribution of two or more heteroatoms in a molecular sieve crystal, and is beneficial to the cooperative play of controllable design and catalytic action of the active center;
2. the technical scheme of the invention has good expansibility, and can realize synthesis to obtain other topological structure heteroatom molecular sieves with uniformly distributed heteroatoms, such as MEL structure heteroatom molecular sieves, BEA structure heteroatom molecular sieves and the like;
3. the synthesis method is simple and controllable, has good repeatability and is easy for industrial production and application.
Drawings
Fig. 1 is an XRD spectrum of the MFI structure Ti-containing molecular sieve with uniform heteroatom distribution synthesized in example 1.
Detailed Description
All the embodiments are operated according to the operation steps of the technical scheme.
The overall Si/M ratio (Si/M) of the molecular sieve in the synthesized MFI structure heteroatom molecular sieveBulk phase) The Si/M ratio (Si/M) of the surface of the molecular sieve is obtained by analyzing and detecting by adopting an inductively coupled plasma emission spectrometer (ICP)Surface of) And analyzing and detecting by an X-ray photoelectron spectrometer (XPS).
Example 1
And (3) synthesizing the MFI structure Ti-containing molecular sieve with uniformly distributed heteroatoms.
First step preparation of a solution of silicon-containing species
SiO in silicon source2OH in the alkali Source-Preparing a silicon-containing species solution with water according to a molar ratio of 1:1:30, mixing an alkali source with water, adding a silicon source, uniformly mixing, performing hydrothermal treatment at 170 ℃ for 3 hours, and cooling to obtain the silicon-containing species solution, wherein the silicon source is a pure silicon molecular sieve Silicalite-1, and the alkali source is 25% tetrapropylammonium hydroxide by mass concentration;
second step preparation of crystallized mixed solution
The titanium source is Ti (SO)4)2Ti (SO) is added in a molar ratio Si/Ti of 604)2Adding the solution into the prepared silicon-containing solution, and uniformly stirring to obtain a crystallized mixed solution;
the third step of crystallization
And carrying out hydrothermal crystallization on the crystallized mixed solution at the crystallization temperature of 170 ℃ for 24 hours to obtain a crystallized product, and carrying out conventional filtration, washing, drying and roasting to obtain the Ti-containing molecular sieve with the MFI structure and uniformly distributed heteroatoms.
The XRD spectrum of the MFI structure Ti-containing molecular sieve with uniform heteroatom distribution is shown in FIG. 1, and XRD measurement is carried out on a German Bruker axs type X-ray diffractometer by adopting CuK alpha. From the XRD spectrogram, the positions of diffraction peaks show strong diffraction peaks at 2 θ ═ 7.8 °, 8.8 °, 23.2 °, 23.8 °, 24.3 ° and the like, indicating that they have MFI topology; Si/Ti thereofBulk phaseIs 56, Si/TiSurface ofIs 59, - ] Si/TiSurface of-Si/TiBulk phase∣/(Si/TiBulk phase) The content was found to be 5.4%.
Example 2
And (3) synthesizing the MFI structure Al-containing molecular sieve with uniformly distributed heteroatoms.
The procedure was as in example 1 except for the following differences.
In the second step, the aluminum source is NaAlO2NaAlO is added according to a molar ratio of Si/Al of 902Adding the mixture into the prepared silicon-containing solution, and uniformly stirring to obtain a crystallized mixed solution.
Obtaining the MFI structure Al-containing molecular sieve with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/Al isBulk phaseIs 101, Si/AlSurface ofIs 94, | Si/AlSurface of-Si/AlBulk phase∣/(Si/AlBulk phase) The content was 6.9%.
Example 3
And (3) synthesizing the MFI structure Fe-containing molecular sieve with uniformly distributed heteroatoms.
The procedure was as in example 1 except for the following differences.
In the second step, the iron source is Fe (NO)3)3·9H2O, Fe (NO) at a Si/Fe molar ratio of 603)3·9H2And adding O into the prepared silicon-containing solution, and uniformly stirring to obtain a crystallized mixed solution.
Obtaining the MFI structure Fe-containing molecular sieve with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/Fe isBulk phaseIs 55, Si/FeSurface ofIs 64, | Si/FeSurface of-Si/FeBulk phase∣/(Si/FeBulk phase) The content was 16.4%.
Example 4
And (3) synthesizing the MFI structure Sn-containing molecular sieve with uniformly distributed heteroatoms.
The procedure was as in example 1 except for the following differences.
In the second step, the tin source is SnCl4·5H2O, SnCl at a molar ratio of Si/Sn of 1204·5H2And adding O into the prepared silicon-containing solution, and uniformly stirring to obtain a crystallized mixed solution.
Obtaining the MFI structure Sn-containing molecular sieve with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/SnBulk phaseIs 150, Si/SnSurface ofIs 141, | Si/SnSurface of-Si/SnBulk phase∣/(Si/SnBulk phase) The content was 6.0%.
Example 5
And (3) synthesizing the MFI structure Nb-containing molecular sieve with uniformly distributed heteroatoms.
The procedure was as in example 1 except for the following differences.
In the second step, the niobium source is C10H5NbO20C in a molar ratio Si/Sn of 6510H5NbO20Adding the mixture into the prepared silicon-containing solution, and uniformly stirring to obtain a crystallized mixed solution.
Obtaining the MFI structure Nb-containing molecular sieve with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/Nb isBulk phaseIs 59, Si/NbSurface ofIs 65, - ] Si/NbSurface of-Si/NbBulk phase∣/(Si/NbBulk phase) The content was 10.2%.
Example 6
Synthesizing the MFI structure molecular sieve containing Ti and Al and having uniformly distributed heteroatoms.
The procedure was as in example 1 except for the following differences.
In the second step, the titanium source is TiCl4The aluminum source is NaAlO2TiCl in a molar ratio Si/Ti of 60 and Si/Al of 504And NaAlO2Adding the solution into the prepared silicon-containing species solution,stirring evenly to obtain a crystallized mixed solution.
Obtaining the MFI structure molecular sieve containing Ti and Al with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/TiBulk phaseIs 55, Si/TiSurface ofIs 60, | Si/TiSurface of-Si/TiBulk phase∣/(Si/TiBulk phase) 9.1% of Si/AlBulk phaseIs 47, Si/AlSurface ofIs 53, - ] Si/AlSurface of-Si/AlBulk phase∣/(Si/AlBulk phase) The content was 12.8%.
Example 7
And (3) synthesizing the MFI structure Ti-containing molecular sieve with uniformly distributed heteroatoms.
The procedure was as in example 1 except for the following differences.
In the second step, the titanium source is TiCl4TiCl in a molar ratio Si/Ti of 1004Adding the mixture into the prepared silicon-containing solution, and uniformly stirring to obtain a crystallized mixed solution.
Obtaining the MFI structure Ti-containing molecular sieve with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/TiBulk phaseIs 83, Si/TiSurface ofIs 87, - ] Si/TiSurface of-Si/TiBulk phase∣/(Si/TiBulk phase) The content was 4.8%.
Example 8
And (3) synthesizing the MFI structure Ti-containing molecular sieve with uniformly distributed heteroatoms.
The procedure was as in example 1 except for the following differences.
In the first step, the silicon source is tetraethyl silicate;
and in the second step, the titanium source is tetrabutyl titanate, tetrabutyl titanate is added into the prepared silicon-containing solution according to the molar ratio of Si/Ti of 100, and the mixture is uniformly stirred to obtain a crystallized mixed solution.
Obtaining the MFI structure Ti-containing molecular sieve with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/TiBulk phaseIs 85, Si/TiSurface ofIs 88, - ] Si/TiSurface of-Si/TiBulk phase∣/(Si/TiBulk phase) The content was found to be 3.5%.
Example 9
And (3) synthesizing the MFI structure Al-containing molecular sieve with uniformly distributed heteroatoms.
The procedure was as in example 2 except for the following differences.
The first part alkali source is a mixture of NaOH and tetrapropylammonium hydride with a molar ratio of 1:9, and the silicon source is white carbon black;
in the second step, the aluminum source is Al2(SO4)3Al in a molar ratio Si/Al of 3502(SO4)3Adding the mixture into the prepared silicon-containing solution, and uniformly stirring to obtain a crystallized mixed solution.
Obtaining the MFI structure Al-containing molecular sieve with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/Al isBulk phase325, Si/AlSurface ofIs 340, | Si/AlSurface of-Si/AlBulk phase∣/(Si/AlBulk phase) The content was 4.6%.
Example 10
And (3) synthesizing the MFI structure Ti-containing molecular sieve with uniformly distributed heteroatoms.
The procedure was as in example 1 except for the following differences.
In the first step, SiO in the silicon source2OH in the alkali Source-Preparing a silicon-containing species solution with water according to a molar ratio of 1:0.5:20, and performing hydrothermal treatment at 150 ℃ for 24 hours;
the XRD spectrum of the MFI structure Ti-containing molecular sieve with uniformly distributed heteroatoms is shown in figure 1, and Si/Ti of the molecular sieveBulk phaseIs 57, Si/TiSurface ofIs 61, - ] Si/TiSurface of-Si/TiBulk phase∣/(Si/TiBulk phase) The content was found to be 7.0%.
Example 11
And (3) synthesizing the MFI structure Al-containing molecular sieve with uniformly distributed heteroatoms.
The procedure was as in example 2 except for the following differences.
The first part of the silicon source is silica sol;
in the second step, Al (NO) is used as aluminum source3)3Al (NO) is added in a molar ratio Si/Al of 303)3Adding the solution into the prepared silicon-containing species solution;
and thirdly, performing hydrothermal crystallization on the crystallized mixed solution at the crystallization temperature of 150 ℃ for 72 hours to obtain the MFI structure Al-containing molecular sieve with uniformly distributed heteroatoms.
Obtaining the MFI structure Al-containing molecular sieve with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/Al isBulk phaseIs 28, Si/AlSurface ofIs 31, - ] Si/AlSurface of-Si/AlBulk phase∣/(Si/AlBulk phase) The content was 10.7%.
Example 12
And synthesizing the MFI structure containing Al and B molecular sieves with uniformly distributed heteroatoms.
The procedure was as in example 2 except for the following differences.
In the second step, Al (NO) is used as aluminum source3)3The boron source is boric acid, and Al (NO) is added according to a molar ratio of Si/Al of 90 and a Si/B ratio of 903)3And boric acid to the prepared silicon species-containing solution;
and thirdly, performing hydrothermal crystallization on the crystallized mixed solution at the crystallization temperature of 150 ℃ for 48 hours to obtain the MFI structure containing Al and B molecular sieve with uniformly distributed heteroatoms.
Obtaining the MFI structure Al and B molecular sieve with uniform heteroatom distribution, wherein the XRD spectrogram is similar to that of figure 1, and the Si/Al isBulk phaseIs 103, Si/AlSurface ofIs 97,. | Si/AlSurface of-Si/AlBulk phase∣/(Si/AlBulk phase) 5.8% of Si/BBulk phaseIs 110, Si/BSurface of117, | Si/BSurface of-Si/BBulk phase∣/(Si/BBulk phase) The content was 6.4%.
Comparative example 1
The MFI structure Ti-containing molecular sieve (TS-1) is synthesized according to U.S. Pat. No. 4,410,501, wherein the Si/Ti ratio in the crystallized mixed solution is 60.
The XRD spectrum of the TS-1 molecular sieve is similar to that of figure 1, and Si/Ti thereofBulk phaseIs 57, Si/TiSurface ofIs 140, | Si/TiSurface of-Si/TiBulk phase∣/(Si/TiBulk phase) The content was 145.6%.
Comparative example 2
An Al-containing molecular sieve (ZSM-5) of MFI structure was synthesized according to U.S. Pat. No. 3,702,886, in which the Si/Al ratio in the crystallized mixed solution was 90.
The XRD pattern of the ZSM-5 molecular sieve is similar to that of FIG. 1, and Si/Al thereofBulk phaseIs 94, Si/AlSurface of254, | Si/AlSurface of-Si/AlBulk phase∣/(Si/AlBulk phase) The content was 170.2%.

Claims (3)

1. The MFI structure molecular sieve with uniformly distributed heteroatoms is characterized in that the heteroatoms M in the MFI structure molecular sieve are uniformly distributed in a molecular sieve crystal, and the Si/M ratio (Si/M) on the surface of the molecular sieveSurface of) Si/M ratio (Si/M) of molecular sieveBulk phase) Satisfies | Si/MSurface of-Si/MBulk phase∣/ (Si/MBulk phase) At most 20%.
2. An MFI structure molecular sieve with a uniform distribution of heteroatoms as in claim 1, wherein the heteroatoms M in the framework of the MFI structure molecular sieve are at least one of Al, B, Fe, Ga, Ti, Sn, Nb and Zn.
3. A method for synthesizing an MFI structure molecular sieve with uniform heteroatom distribution as claimed in claim 1 or 2, comprising the steps of:
first step preparation of a solution of silicon-containing species
SiO in silicon source2OH in the alkali Source-Preparing a silicon-containing species solution with water according to a molar ratio of (0.4-2): (10-100), mixing an alkali source with water, adding a silicon source, uniformly mixing, performing hydrothermal treatment at 100-190 ℃ for 0.5-24 hours, and cooling to obtain the silicon-containing species solution, wherein the silicon source is at least one of an inorganic silicon compound and an organic silicon compound, the inorganic silicon compound is a pure silicon molecular sieve, silica sol, silica gel and white carbon black, and the organic silicon compound is tetraethyl silicate, tetrapropyl silicate and tetrabutyl silicate; the alkali source is at least one of inorganic alkali and organic alkali, the inorganic alkali is NaOH and KOH, and the organic alkali is tetrapropyl ammonium hydroxide;
second step preparation of crystallized mixed solution
Adding water-soluble salt or organic compound containing heteroatom M into the prepared silicon-containing solution according to the molar ratio Si/M of 20-500, and uniformly stirring to obtain a crystallized mixed solution; wherein the heteroatom M is Al, B, Fe, Ga, Ti, Sn, Nb, Zn;
the third step of crystallization
And carrying out hydrothermal crystallization on the crystallized mixed solution at the crystallization temperature of 120-190 ℃ for 2-72 hours to obtain a crystallized product, and carrying out conventional filtration, washing, drying and roasting to obtain the MFI structure molecular sieve with uniformly distributed heteroatoms.
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