(705c) CO2 Assisted Oxidative Dehydrogenation of Ethane over Supported Metal Oxide Catalysts

Utilizing carbon dioxide as a mild oxidizing agent in the oxidative dehydrogenation (ODH) of ethane has been widely reported on different metal-oxide-based catalysts and is underscored as a promising alternative route ¹. The potential in-situ removal of coke via the reverse Boudouard reaction has been highlighted in the open literature² among the benefits of the CO₂ assisted ODH. While ODH in the presence of oxygen involves a classical Mars Van Krevelen (MvK) mechanism,³in ODH with CO₂ it is hypothesized that the olefin is primarily formed through the coupling of direct dehydrogenation and reverse water gas shift (RWGS) reactions⁴. However, the actual role of CO₂ on the mechanism for the formation of olefins is still in question as different reaction pathways involving CO₂ participation over supported metal oxides catalysts may occur.

In this study, supported MO_x (M= Mo, V) on TiO₂-CeO₂ were thoroughly investigated for ODH of ethane (ODHE) with CO₂. Raman characterization suggested that surface molybdena species prefer to anchor on crystalline domains of titania. Upon increasing of ceria in the mixed support phase, the prevalent species tended to be polymeric (MoOx)_n domains. However, in VO_X catalysts, Raman study indicated a plausible gradual anchoring of oxygen of the surface vanadia species on both TiO₂ and CeO₂. The aforementioned induced structural changes by ceria addition in the support directly resulted in distinct catalytic behaviors, in which, Mo catalysts promoted ODHE via MvK mechanism while V catalysts promoted DH. Likewise, from in-situ Raman studies, it was shown that adding ceria in support phase not only changed the redox property of this phase but also improved that of deposited phase. Specifically, upon ceria addition into the support phase, besides the RWGS path, CO₂ directly participated in the reoxidation of the dispersed MO_x species of the catalysts investigated.