Catalytic Transfer Hydrogenolysis of Native Lignin to Monomeric Phenols over a Ni–Pd Bimetallic Catalyst

Direct hydrogenolysis of native lignin in biomass into monomeric phenols has received increasing attention. In this work, catalytic transfer hydrogenolysis of native lignin from birch, pine, and corn stalk was studied over a Ni–Pd bimetallic catalyst using isopropanol as the in situ hydrogen source. The bimetallic Ni50Pd50/SBA-15 exhibited higher activity than the monometallic counterparts in catalytic transfer hydrogenolysis of native birch lignin, affording 37.2 wt % monophenols at 245 °C after 4 h. 4-Propylsyringol had the highest yield of 18.9 wt % with a selectivity of 51%. Among the three biomass feedstocks, native lignin in birch gave the highest monophenol yield, which is 2.2 times that of native pine lignin (16.9 wt %) and 4.6 times that of native corn stalk lignin (8.1 wt %). FTIR and Py–GC MS analyses of the starting biomasses and the depolymerization solid products revealed that native birch lignin has the highest depolymerization efficiency with the least active lignin remaining.