Catalytic Oxidation of Methoxy Substituted Benzyl Alcohols as Model for Lignin Valorisation

Lignin contains around 50 wt% of aromatic hydrocarbons, which can be transformed in fuels and chemicals. Many processes convert lignin in phenols and alcohols, needing further oxidation to be converted in high-value products. This work reports a study on the catalytic oxidation of some model alcohols derived from lignin by bimetallic Au/Pd catalysts. The already proved beneficial synergistic effect between Au and Pd was investigated considering different Au:Pd ratios in the oxidation of benzyl alcohol, 4-methoxybenzyl alcohol and 3,4-dimethoxybenzyl alcohol, due to the importance of methoxy-substituents in lignin derivatives. The synergistic effect between Au and Pd on activated carbon was confirmed, being both the monometallic Au and Pd supported catalysts inactive for the oxidation of these alcohols under base-free conditions. Moreover, we proved that the position of the methoxy group on the aromatic ring played a crucial role, influencing the catalytic activity depending on the specific Au:Pd ratio. Results showed that Au-rich catalysts were not influenced by the substrate effect, on the contrary to the Pd-rich ones, where the specific Au:Pd ratio was crucial in determining the catalytic activity.