(435e) Surface Modification and Catalytic Activity of MoO3 during Hydrodeoxygenation (HDO) of Lignin-Derived Model Compounds

Hydrodeoxygenation (HDO) is a major route of upgrading bio-oil. MoO₃ has been shown to be active for HDO of bio-oil model compounds. Specifically, the catalyst is selective towards cleavage of C-O bonds at temperatures of 320-350^oC and H₂ pressures <= 1 bar. Importantly, this catalyst selectively cleaves stronger phenolic Ph-OMe over weaker PhO-Me bonds. Detailed reactivity studies were performed to gain insight into the nature of the active sites. An initial induction period was observed for the catalyst to achieve peak performance,which suggested a surface modification was required to render the catalyst active. The catalyst surface undergoes partial carburization as evidenced by the presence of oxycarbide- and oxycarbohydride-containing phases (i.e., MoO_xC_yH_z) at lower temperatures.  Mo⁵⁺ species are hypothesized to be responsible for the HDO chemistry on the catalyst. The transformation of bulk phases and the surface modification of MoO₃ by carbon/H₂ are also investigated to understand the role of surface carbon in the stabilization and enhanced activity of the partially reduced MoO₃ surface. The partial surface carburization during reaction was found to play a role in stabilizing Mo⁵⁺ state on the catalyst surface and slowing down over-reduction of MoO₃ into inactive MoO₂ phase.