A General Method for Aluminum Incorporation into High-Silica Zeolites Prepared in Fluoride Media

The fluoride method of zeolite synthesis yields materials with unique characteristics such as high Si/Al ratio, large crystal size, and hydrophobic properties, and it has been advantageous for the synthesis of new pure-silica or high-silica zeolites. It is often difficult, however, to incorporate aluminum—and thus bring about useful catalytic properties—in materials prepared through the fluorite method. In this report, we show that FAU-type zeolites are an effective source of aluminum to the growing crystals in the high-silica LTA-type zeolite synthesis (ITQ-29). A key advantage of using aluminosilicate zeolite crystals as aluminum source in fluoride media was the high reproducibility and easy control of the Si/Al ratio of the product. The broad applicability of this methodology was demonstrated in the synthesis of several high-silica zeolites in fluoride media: we report the synthesis of aluminosilicate ITQ-12 (ITW-type zeolite). Other more conventional aluminosilicate zeolites (CHA-, *BEA-, and STT-type) were also synthesized by using this methodology. The Si/Al ratio of the final products was controlled by the amount of aluminosilicate zeolite added to the synthesis gel. All the products obtained had the typical features of a fluoride mediated synthesis, and it was found that the thermochemical stability of the aluminum source and seed crystals was an important factor. This simple methodology could be useful for aluminum incorporation into many novel siliceous zeolites, broadening their potential as catalytic materials.