<p>Supported MO<sub>x</sub> (M= Mo, V) on
mixed CeO<sub>2</sub>-TiO<sub>2</sub> were investigated for the oxidative
dehydrogenation of ethane (ODHE) using CO<sub>2</sub> as a mild oxidant. Raman spectroscopic
characterization of the synthesized catalysts under dehydrated conditions
suggest that surface MoO<sub>x</sub> species prefer to anchor on the crystalline
domains of TiO<sub>2</sub>. Upon increasing the amount of CeO<sub>2</sub> in
the mixed oxide support, an intense and broad band at ~930cm<sup>-1</sup>
underscored that the prevalent species tend to be polymeric (MoO<sub>x</sub>)<sub>n</sub>
domains. On the other hand, in the case of VO<sub>x</sub> catalysts, a gradual
shift in the symmetric stretching of the vanadyl (V=O) Raman band with increasing
CeO<sub>2</sub> content was observed that points at the gradual anchoring of
the surface vanadia species on both TiO<sub>2</sub> and CeO<sub>2</sub> thus
highlighting the possible existence of the amorphous VO<sub>x</sub> to be
located at the interface of the two mixed oxides. The catalytic behavior of Mo
and V were distinct. As the ceria content in the support increased, MoO<sub>x</sub>
catalysts promoted the ODHE via Mars van Krevelen mechanism while VO<sub>x</sub>
catalysts 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 metal oxide. We also show that upon
incorporation of ceria into the support, CO<sub>2</sub> directly participates in
the reoxidation of the dispersed MoO<sub>x</sub> species during catalysis. This
effect was distinct from the reaction of CO<sub>2</sub> in the reverse water
gas shift reaction. Operando Raman spectra revealed that the presence of CO<sub>2</sub>
enhances the stability of the bridging Mo–O–Mo bond of polymeric molybdena
domains, which is proposed to affect the relative contribution of oxidative
versus non-oxidative pathways in ethane dehydrogenation.</p>
Oxidative dehydrogenation of isobutane over supported V-Mo mixed oxides
