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(3) Structural modification
There are two types of structural modification: one is the modification of zeolite skeleton elements; the other is the modification of non-framework elements
① Modification of zeolite framework elements The modification of zeolite framework elements is mainly dealumination and aluminum supplementation.
a.
b.
c.
By changing the ratio of silicon to aluminum in the zeolite , the adsorption capacity of the zeolite for H 2 O, H 2 S, and NH 3 can be increased to a greater extent , and can be applied to remove H 2 S and NH 3 in industrial waste gas
②Modification of non-framework elements
a.
Commonly used aqueous solution modification methods include inorganic acid modification, inorganic salt modification and rare earth modification
I.
II.
I.
b.
The conventional solution exchange method requires a long exchange time, a large amount of salt solution needs to be processed after the exchange, and there are many ions that are insoluble in water or unstable in the aqueous solution, and cannot be introduced into the zeolite molecular sieve by the conventional solution exchange method
c.
Due to the very high activity of silanes, they can react with the surface hydroxyl groups of the zeolite to be grafted on the surface of the zeolite, and through subsequent treatments, a stable silica surface layer is finally formed
d.
The CVD method includes several processes such as adsorption deposition, chemical decomposition, hydrolysis and redox
.
The CVD method can be used for the preparation of highly dispersed, high-content metal or metal oxide supported catalysts
.
Karina Fodor et al.
used Si(OCH 3 ) 4 or Si(OC 2 H 5 ) 4 to modify the mesoporous MCM-41 molecular sieve.
By changing the deposition conditions, the pore size of MCM-41 can be reduced from 3nm to 2nm.
The pore size adjustment of pore molecular sieve provides an effective method
.
XSZhao et al.
used trimethylchlorosilane to modify the surface of zeolite.
The modified zeolite not only maintains a porous structure, but also has a good hydrophobic surface, so it can selectively adsorb and remove volatile organic compounds in the presence of water ( VOCs), have a certain value in air purification and wastewater treatment containing VOCs
.
However, the CVD method requires a vacuum device, requires a large investment, and is complicated to operate, which makes it difficult for industrial promotion and application
.