Direct deoxygenation of lignin model compounds into aromatic hydrocarbons through hydrogen transfer reaction

A new route is reported for the direct deoxygenation of lignin model compounds to aromatic hydrocarbons via the catalytic hydrogen transfer reactions over Ru/Nb2O5-SiO2 catalyst with 2-PrOH as a hydrogen donor. It is found that Ru/Nb2O5-SiO2 catalyst is active for the hydrodeoxygenation of p-cresol with 98.5% conversion and 84.0% yield of toluene at 230 degrees C, owing to the significant promotion effect of NbOX species on C-O bond cleavage and the proper transfer hydrogenation activity of Ru. Furthermore, Ru/Nb2O5-SiO2 catalyst also shows excellent performances in the transfer hydrodeoxygenation of various lignin model compounds such as 2-methoxy-4-methyl phenol, benzyl phenyl ether (alpha-O-4 model compound), 2-(2-methoxyphenyl)oxy-l-phenethanol (beta-O-4 model compound) and even the real lignin extracted from birch, into aromatic hydrocarbons with 2-PrOH as the hydrogen donor. The reaction pathway studies of these model compounds demonstrate that the direct deoxygenation (DDO) is the main reaction route over Ru/Nb2O5-SiO2 catalyst in the presence of 2-PrOH. Here, using 2-PrOH as a hydrogen source is found to be more selective to aromatic hydrocarbons than using molecular hydrogen. This work provides a new way for the high selective production of aromatic hydrocarbons from renewable lignin via the catalytic hydrogen transfer reactions.