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

Abstract

Nano-Cr2O3 was prepared via solution combustion synthesis (SCS) with Cr(NO3)3·9H2O 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. Cr2O3 samples were characterized by XRD, SEM, TEM, H2-TPR, and XPS. In addition, these catalysts were evaluated for the dehydrofluorination of 1,1-difluoroethane producing vinyl fluoride (VF, CH2=CHF). The results confirm that Cr2O3 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 m2 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 Cr2O3 at reaction temperatures below 300 °C. Compared with commercial Cr2O3, XPS, and H2-TPR reveal the higher CrO3 contents on the surface of Cr2O3 derived from SCS. It is suggested that CrO3 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 Cr2O3, 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 Cr2O3 declines with TOS. High surface area and much smaller size of Cr2O3 crystalline favors the formation of CrO x F y during reaction over Cr2O3-3.33 catalyst probably contribute to the high activity and stability.