Spectroscopic insights into the role of CO2 on the nature of Cr species in a CrOX/Al2O3 catalysts during ethane dehydrogenation with CO2

Abstract

The dehydrogenation of ethane with CO2 was studied on CrOx/Al2O3 catalysts (8 wt% of CrOx) in the 600–675 °C temperature range. The role of CO2 was determined by comparison with catalytic and spectroscopic data of ethane dehydrogenation without CO2. Characterization of fresh catalyst suggested an intimate interaction of Cr and support. Moreover, in situ Raman spectroscopic analysis combined with XPS studies done on reaction exposed samples indicated changes in both the nature of active Cr species and the reaction mechanism depending on the reaction conditions (i.e., presence/absence of CO2, and the reaction temperature). At lower temperatures (600–625 °C), CO2 promotes the re-oxidation of Cr3+ to Cr6+ favoring the oxidative dehydrogenation (ODH) route. While at higher temperatures (650–675 °C), the reaction occurs mainly via a catalytic dehydrogenation mechanism, as CO2 is no longer capable of re-oxidizing Cr3+ to Cr6+, with CO2 inhibiting partially the formation of coke.