Demethoxylation of guaiacol and methoxybenzenes over carbon-supported Ru-Mn catalyst

Hydrodeoxygenation of methoxybenzenes such as guaiacol over Ru catalyst was studied. Guaiacol was demethoxylated and then hydrogenated over carbon black supported Ru-MnO_x catalyst (Ru-MnO_x/C) forming cyclohexanol and methanol in good yield (81% and 86%, respectively) under relatively mild conditions (433K, H₂ 1.5MPa). Over Ru-MnO_x/C, yield of demethoxylated products (cyclohexanol and cyclohexane) was almost the same as that of methanol, suggesting that the methoxy group is eliminated by demethoxylation to form methanol. Other methoxybenzenes such as 2,6-dimethoxyphenol and anisole were also converted to demethoxylated saturated compounds such as cyclohexanol and cyclohexane. The reaction scheme was proposed where demethoxylation and total hydrogenation of aromatic ring from partially-hydrogenated adsorbed guaiacol proceeded in parallel. Lower H₂ pressure and higher reaction temperature were advantageous to demethoxylation. Addition of MnO_x species slowed down the reaction rate of total hydrogenation of aromatic ring, which increased the relative rate of the elimination of methoxy group to that of total hydrogenation before the elimination. The catalyst can be reused without significant loss of activity. The nanoparticles of Ru and Mn were highly dispersed, and the state of Mn species on Ru-MnO_x/C during the reaction was weakly basic MnO.