Secondary Synthesis of Titanium-containing Zeolites Gas-Solid Isomorphous Substitution Technique

2 Secondary Synthesis of Titanium-containing Zeolites - Gas-Solid Isomorphous Substitution Technique 

In 1999, Krijnen et al.[36] proposed another approach for the preparation of an effective Ti-/3 epoxidation catalyst. This approach is similar to the gas-solid isomorphous substitution technique, and two steps are involved. The first step is the deahimination, that is, to generate vacancies such as hydroxyl vacancies, and the second step is titanation 

Catalyst number Si/Ti (AAS) Si/Ti (XPS) Ti/unit cell (in product) Al/unit cell (after dealumination) Ti02 Raman signal 

3 Demetallation of Heteroatom Zeolites through High-temperature Vapor-phase Treatment 

The structures and properties of heteroatom zeolites vary due to the introduction of heteroatoms in the zeolite frameworks. When treated in high-temperature water vapor, zeolites Y, mordenite, and ZSM-5 are dealuminated to be ultra-stabilized, whereas heteroatom zeolites undergo demetallation that is, the heteroatoms are removed from the frameworks to form extraframework species, and the resulting zeolites become catalytically active for special reactions. For instance, when treated in water vapor at 

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