Reactivity and stability investigation of supported molybdenum oxide catalysts for the hydrodeoxygenation (HDO) of m-cresol

Abstract The vapor-phase hydrodeoxygenation (HDO) of m-cresol is investigated at 593 K and H 2 pressures ⩽1 bar for supported catalysts comprised of 10 wt% MoO 3 dispersed over SiO 2 , γAl 2 O 3 , TiO 2 , ZrO 2 , and CeO 2 . Reactivity data show that all catalysts selectively cleave C O bonds without saturating the aromatic ring, thus effectively transforming m-cresol into toluene at moderate to high conversions. MoO 3 /ZrO 2 and MoO 3 /TiO 2 feature the highest initial site time yields (23.4 and 13.9 h −1 , respectively) and lowest first-order deactivation rate constants (0.013 and 0.006 h −1 , respectively) of all catalysts tested after ca. 100 h on stream. Characterization studies demonstrate that the supports play an important role in stabilizing partially reduced, coordinatively unsaturated (CU) sites in surface oligomeric Mo moieties. Post-reaction X-ray photoelectron spectroscopy shows that the catalysts with higher activity feature larger proportions of intermediate oxidation species (Mo 5+ and Mo 3+ ). In contrast, the catalysts with lower reactivity show different oxidation states: bulk MoO 3 features mostly Mo 4+ and metallic Mo species, while MoO 3 /CeO 2 features a high proportion of Mo 6+ species. An inverse correlation is established between the catalyst activity and both the maximum hydrogen consumption temperature obtained during temperature programmed reduction, and the support cation electronegativity (with the exception of MoO 3 /CeO 2 ).