Selective preparation of monomers from hydrotreatment of lignin using isopropanol over Ru-Pd/HZSM-5 catalysts

In this study, different bimetallic (Ru, Pd, and Pt) catalysts over a variety of supports (activity carbon, γ-Al 2 O 3 , TiO 2 , HZSM-5) were employed to improve the kraft lignin depolymerization process using isopropanol as in situ hydrogen source. The effect of catalysts was firstly investigated, which suggested that 1wt%Ru-1wt% Pd/HZSM-5 promoted the hydrogenolysis and hydrodeoxygenation effect on conversion of kraft lignin (95.86 wt%) and the selectivity of aliphatic alcohol (26.92 wt%) and hydrocarbon monomers (35.73 wt%), respectively. The effect of temperature and reaction time were also discussed, which indicated that the high temperature (250 to 310 °C) promoted the hydrogenolysis process; while the temperature is higher than 310 °C, the repolymerization process was appeared, leading to the decreasing yield of total monomers. For the influence of reaction time, it was noted that the optimal reaction time to acquired high yield and selectivity of aliphatic alcohol and hydrocarbon monomer was 120 min. It was also conducted FTIR and 2D HSQC NMR analysis to understand the effective depolymerization of the major linkages with attacked by the Ru-Pd/HZSM-5 catalyst, which was corresponding with the results with GC–MS. Graphical abstract