Aging investigation on catalysts for hydrofluorocarbons synthesis

This study aims to verify whether the thermal effects occurring during catalyst oxidative regeneration may have to do with the irreversible
catalyst deactivation industrially observed for CrOxFy-AlF3-based catalysts. Deactivation phenomena can be due to modifications occurring on
both the active phase and the support; therefore, the aging treatment effects on the support (AlF3) and fresh and stabilized catalysts CrOxFy/AlF3
were compared. It was proved that at temperatures higher than 600 8C, the support undergoes to release of HF molecules and sintering phenomena
correlated with the irreversible evolution to the thermally stable a-phase. The presence of Cr ions has an inhibiting effect on the support crystals
growth, but strongly catalyses the surface area decrease at a relatively low temperature. In addition, the evolution of HF from chromium-containing
catalysts starts at a very low temperature and is related to the formation of the crystalline Cr2O3 phase. Moreover, UV-vis and TPR analysis
demonstrated that, due to aging treatments, chromium ions tend to interact with the support, and lead to the formation of less reducible chromium
species, which are probably responsible for the irreversible catalytic activity degradation observed in commercial processes.