Catalytic hydrogenolysis of lignin in isopropanol as hydrogen donor over nickel-cobalt supported on zeolite to produce aromatic and phenolic monomers

Due to its high catalytic activity and good hydrogenating properties, bimetallic catalysts are gaining increasing attention for lignin valorization. Herein, transition bimetallic catalysts Ni-Co/HZSM-5 were proposed to investigate the catalytic hydrogenolysis reaction of lignin. The activity was demonstrated in an 80 mL stainless-steel reactor. At 250 ℃ temperature in 4 h of reaction using isopropanol as the hydrogen donor solvent. 45 wt% yields of total monomer products and 91% lignin conversion were obtained with Ni-Co/HZSM-5 catalysts. This is superior to the catalytic activity of Ni/HZSM-5 and Co/HZSM-5 monometallic catalysts. BET, SEM, XPS, and EDX techniques were used to characterize the catalysts. The results revealed that the synergistic effect between the two metal species (Ni-Co) was the major cause of their high catalytic activity, which resulted in better hydrogen transformation and better hydrogenolysis activity. The electronic interactions between Co and Ni enhanced the transfer of electrons and accelerated catalytic reactions. Also, well-dispersed Ni and Co on HZSM-5 support enhanced the surface area, providing more active sites for lignin to adsorb and participate in hydrogenolysis reactions. In addition, a series of measurements such as FT-IR, GPC, and GC-MS were performed to examine the hydrogenolysis reaction products. A total of 19 monomer products were successfully identified in GC-MS analysis. These results confirmed the great potential of bimetallic catalysts Ni-Co/HZSM-5 due to their synergistic effect.