Selective production of guaiacol from lignin via catalytic transfer hydrogenolysis using Ru-Cu/Zirconia

•Maximum lignin conversion of 52.4% and liquid yield of 32.4 wt.% were recorded.•The optimum reaction condition was 270 °C and 3 h with 2-propanol.•The major products were guaiacol (12.7 wt.%), 4-methyl guaiacol (8.0 wt.%) and 4-ethyl guaiacol (6.2 wt.%).•Due to strong metal-support interaction, Ru-Cu on ZrO2 calcined at 800 °C exhibited best catalytic activity.•The yield of monomeric phenols was stable until two catalyst regeneration cycles.