Production of liquid fuels via catalytic transfer hydrogenation promoting lignin depolymerization on modified Y zeolite: Formic acid as a continuous hydrogen source

Efficient depolymerization of lignin to produce valuable liquid fuels and phenolic compounds is essential to improve the effective utilization and contribution towards energy sustainability. However, challenges arise due to its complex three-dimensional structure, the inclination of intermediates to condense, and the excessive dependence of depolymerization reaction on high-pressure hydrogen. Herein, a novel Ni- and Zn- modified Y-zeolite (Ni1Zn1/HYa) was prepared to attain effective lignin conversion under conditions devoid of exogenous hydrogen, by utilizing formic acid as an in situ hydrogen donor. Ni1Zn1/HYa selectively activated and decomposed formic acid, continuously releasing H2 for lignin depolymerization. It stabilized active intermediates and inhibited condensation through synergistic interactions between Lewis acid (L-acid) and hydrogenation active sites, resulting in a depolymerization rate that effectively competes with the condensation rate. Following a 24 h reaction at 290 °C, the yields of liquid products and petroleum ether soluble (PES) reached 91.70 % and 67.74 %, respectively, without any coke production. Further, the higher heating value increased from 25.41 MJ kg−1 to 32.47 MJ kg−1.