CO2-assisted ethane oxidative dehydrogenation over MoOx catalysts supported on reducible CeO2–TiO2

Abstract

Supported MoO_x on mixed CeO₂–TiO₂ was investigated for the oxidative dehydrogenation of ethane (ODHE) using CO₂ as a mild oxidant. Raman spectroscopic characterization of the synthesized catalysts under dehydrated conditions suggested that surface MoO_x species prefer to anchor on the crystalline domains of TiO₂. Upon increasing the amount of CeO₂ in the mixed oxide support, significant spectral changes were observed, especially in the ∼900–950 cm⁻¹ region where Mo–O–M bonds are expected. The catalytic behaviors of Mo as opposed to pure support materials were distinct. As the ceria content in the support increased, MoO_x catalysts promoted oxidative dehydrogenation pathways via the Mars–van Krevelen mechanism, while pure supports appeared to favor ethane direct dehydrogenation. Investigation of structure–function relationships via in situ Raman spectroscopic efforts revealed that adding ceria not only changed the redox properties of the support but also improved those of the deposited amorphous MoO_x species. We also show that upon incorporation of ceria into the support, CO₂ directly participates in the reoxidation of the dispersed MoO_x species during catalysis. This effect was distinct from the participation of CO₂ in the reverse water gas shift reaction. Operando Raman spectra revealed that the presence of CO₂ prolonged the existence of the 930 cm⁻¹ feature which appears to correlate well with the relative contribution of the oxidative versus non-oxidative pathway in ethane dehydrogenation.