Insights into the catalytic activity and surface modification of MoO3 during the hydrodeoxygenation of lignin-derived model compounds into aromatic hydrocarbons under low hydrogen pressures

Abstract

MoO₃ is an effective catalyst for the hydrodeoxygenation (HDO) of lignin-derived oxygenates to generate high yields of aromatic hydrocarbons without ring-saturated products. The catalyst is selective for the C–O bond cleavage under low H₂ pressures (≤1 bar) and temperatures ranging from 593 to 623 K. A bond-dissociation energy analysis of relevant phenolic C–O bonds indicates that the bond strengths follow an order of Ph–OH > Ph–OMe > Ph–O–Ph > Ph–O–Me. However, for all model compounds investigated, the MoO₃ catalyst preferentially cleaves phenolic Ph–OMe bonds over weaker aliphatic Ph–O–Me bonds. Characterisation studies reveal that the catalyst surface undergoes partial carburisation as evidenced by the presence of oxycarbide- and oxycarbohydride-containing phases (i.e., MoO_xC_yH_z). The transformation of bulk phases and the surface modification of MoO₃ by carbon–H₂ are investigated to understand the role of surface carbon in the stabilisation and enhanced activity of the partially reduced MoO₃ surface.