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

[Display omitted] •Supported molybdenum oxide catalysts effectively transform m-cresol into toluene under mild conditions.•Highest HDO activity and stability is obtained for catalysts that stabilize Mo5+ and Mo3+ species.•HDO reactivity is inversely correlated to support cation electronegativity, with the exception of MoO3/CeO2.•Catalyst deactivation is reversible. The vapor-phase hydrodeoxygenation (HDO) of m-cresol is investigated at 593K and H2 pressures ⩽1bar for supported catalysts comprised of 10wt% MoO3 dispersed over SiO2, γAl2O3, TiO2, ZrO2, and CeO2. Reactivity data show that all catalysts selectively cleave CO bonds without saturating the aromatic ring, thus effectively transforming m-cresol into toluene at moderate to high conversions. MoO3/ZrO2 and MoO3/TiO2 feature the highest initial site time yields (23.4 and 13.9h−1, respectively) and lowest first-order deactivation rate constants (0.013 and 0.006h−1, respectively) of all catalysts tested after ca. 100h 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 (Mo5+ and Mo3+). In contrast, the catalysts with lower reactivity show different oxidation states: bulk MoO3 features mostly Mo4+ and metallic Mo species, while MoO3/CeO2 features a high proportion of Mo6+ 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 MoO3/CeO2).