Solution combustion synthesis of nano-chromia as catalyst for the dehydrofluorination of 1,1-difluoroethane

Nano-Cr 2 O 3 was prepared via solution combustion synthesis (SCS) with Cr(NO 3 ) 3 ·9H 2 O as the Cr precursor and glycine as the fuel. The effect of molar ratio of glycine to Cr in the feed during solution combustion was investigated. Cr 2 O 3 samples were characterized by XRD, SEM, TEM, H 2 -TPR, and XPS. In addition, these catalysts were evaluated for the dehydrofluorination of 1,1-difluoroethane producing vinyl fluoride (VF, CH 2 =CHF). The results confirm that Cr 2 O 3 is in relatively uniform flakes or flat particles via solution combustion synthesis with the particle size of 50–200 nm and composed by the aggregation of 58–77 nm nanoparticles. The specific surface area of higher than 30 m 2  g −1 is achieved, which is comparable to the values obtained by solvothermal route. For the dehydrofluorination of 1,1-difluoroethane, high conversion levels (83 % for commercial catalyst and 93 % for SCS catalyst) are achieved at 350 °C, and the activity of SCS catalyst is at least 2× higher than that of commercial Cr 2 O 3 at reaction temperatures below 300 °C. Compared with commercial Cr 2 O 3 , XPS, and H 2 -TPR reveal the higher CrO 3 contents on the surface of Cr 2 O 3 derived from SCS. It is suggested that CrO 3 plays a major role in the catalytic performance as high-valent Cr species such as Cr(VI) are vital for the reaction because they could be transformed to the active species such as CrO x F y . In addition to the high activity, compared with commercial Cr 2 O 3 , SCS catalyst also show higher stability. Following the reaction of 120 h at 300 °C, no noticeable deactivation is observed while the activity of commercial Cr 2 O 3 declines with TOS. High surface area and much smaller size of Cr 2 O 3 crystalline favors the formation of CrO x F y during reaction over Cr 2 O 3 -3.33 catalyst probably contribute to the high activity and stability.