PVDF mediated fabrication of freestanding AlF3 sub-microspheres: Facile and controllable synthesis of α, β and θ-AlF3

With Al(NO 3 ) 3 ·9H 2 O as the Al precursor and PVDF as the fluorine source, freestanding AlF 3 sub-microspheres were fabricated following calcination , without the involvement of corrosive HF solution. With the varying of Al(NO 3 ) 3 ·9H 2 O to PVDF weight ratio, θ -AlF 3 and β -AlF 3 , α -AlF 3 were obtained respectively. The formation mechanism, morphology, surface properties and catalytic activities for the dehydrofluorination of 1,1,1,2-tetrafluoroethane to trifluoroethylene were investigated. During the fabrication process, Al(NO 3 ) 3 interacts with O=C bond in DMF. Meanwhile, DMF further interacts with CH 2 species in PVDF. Following calcination , PVDF decomposes to CO 2 and HF fluorinating Al species to AlF 3 . The growth of AlF 3 crystal and particle are confined by PVDF. Consequently, θ -AlF 3 , β -AlF 3 and α -AlF 3 are achieved. At 450 °C, HFC-134a conversion of 23% and reaction rate of 1.9 mmol g −1  h −1 are approached over θ -AlF 3 catalyst. The reaction rate is almost 3 times higher than that of β -AlF 3 and is 40% higher than that of high surface area α -AlF 3 prepared by sol-gel method. No significant deactivation is observed in time on stream of 40 h. The stability is attributed to the interaction of AlF 3 with carbon frame work. The present study provides a scalable and facile synthesis route for AlF 3 spheres with controllable phase structures.