Confinement of AlF3 in MOF derived structures for the formation of 4-fold coordinated Al and significantly improved dehydrofluorination activity

Dehydrofluorination is the major process for the production of fluorinated monomers and treatment of synthetic greenhouse gases. It is usually catalyzed by the Lewis acids, such as AlF3, MgF2 and fluorinated Cr2O3. The activity and stability remain the challenges of catalysts. For metal fluorides, Lewis acidic sites are derived from the unsaturated coordination of metal sites. This work reports the confinement of AlF3 into the cavity of quasi MOF structures. Due to the confinement effect and interaction of AlF3 with coordinatively unsaturated Cr-O nodes (oxygen vacancy), significant amounts of 4-fold coordinated Al in AlF3 can be achieved. Consequently, the Lewis acidity of AlF3 could be dramatically enhanced. As the catalyst of the gas-phase dehydrofluorination of HFC-245fa (1,1,1,3,3-pentafluoropropane) to tetrafluoropropene (HFO-1234ze, a new generation of green refrigerant) at 350 °C with the GHSV of 750 h−1, it exhibited the activity of 9 times higher than that of supported AlF3. After reaction of 35 h, no noticeable deactivation was detected. The present work provides a potential strategy for the preparation of metal fluoride Lewis acid catalysts with high efficiency.