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 CrOxFyAlF3 were compared. It was proved that at temperatures higher than 600 degrees C, the support undergoes to release of HF molecules and sintering phenomena correlated with the irreversible evolution to the thermally stable alpha-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. (c) 2007 Elsevier B. V. All rights reserved.