Insight into the effect of metal and support for mild hydrodeoxygenation of lignin-derived phenolics to BTX aromatics

Hydrodeoxygenation (HDO) of lignin-derived phenolics, including the reactions of hydrogenation and dehydration, is an efficient method for production of bio-based aromatic hydrocarbons. The purpose of this study was to explore the catalytic performance of different metals as hydrogenation active sites (Pd, Ru, Cu and Ni) and mild acidic supports (ZrO2, CeO2 and ZrCeO2) as dehydration promoter in order to enhance the HDO efficiency under mild reaction conditions (temperature <350 °C, pressure: 1 atm). Rhenium oxide was added to all catalysts to increase catalyst acidity for an enhanced dehydration activity. m-Cresol and guaiacol were used as phenolic lignin model compounds. Zirconia showed better performance than ceria as a result of its higher acid density. The hydrogenation activity order of metals was as follows: Pd > Ni > Ru > Cu. All the hydrogenation metals selectively promoted the hydrogenation of carbonyl group, and led to the selective formation of aromatic hydrocarbons. The catalyst of PdReOx/ZrO2 was used for HDO of m-cresol in the temperature range of 250–300 °C, and almost retained its entire catalytic activity by temperature reduction. This is due to the mild acid strength induced by zirconia support and rhenium oxide which do not cause phenolic adsorption and trapping at atmospheric pressure and low temperatures.