F-@d4r, a New Type of Acidic Catalytic Site in Zeolite

As a solid acid, zeolite has been widely used in many fields such as tail gas treatment, petrochemical engineering, and the fine chemical industry. F- has been widely used in the synthesis of pure silica or high silica zeolites. To balance the charge of organic structure directing agents (OSDA), F- is often found located at the center of the double-4-rings (d4r) of the as-made zeolites. During calcination, fluorine ion is removed with the OSDA. We screened a series of composition building units and found that d4r is capable to retain F- in zeolite structure. We introduce the F- back after the calcination to create an unprecedented type of acid site, i.e., F-@d4r in pure silica zeolites ITQ-12. The F-@d4r species is thermal stable up to 300 degrees C. ITQ-12 with F-@d4r shows substantial catalytic activity in Biginelli reaction. Furthermore, the catalytic performance is proved to be positive correlated with the presence of F-@d4r, indicating the mild acid catalytic property of F-@d4r.