Ni modulates the coordination environment of cations in Fe3O4 to efficiently catalyze lignin depolymerization

Synergistic action of Ni-O-Fe structure promotes β-O-4 bond breaking for selective and efficient depolymerization of lignin. [Display omitted] •NiFe2O4 nanosphere catalyst with irregular slit porous structure was prepared.•Efficient conversion of alkali lignans to alkylphenols and alkylguaiacols under milder conditions.•The synergism of Ni-O-Fe is the key to the efficient depolymerization of lignin.•The Lewis acidic center of the catalyst was significantly improved by the introduction of Ni, which promoted the β-O-4 bond breaking in lignin. Lignin shows great potential for sustainable production of high-quality fuels and value-added chemicals. The development of efficient and highly stable multifunctional catalysts for the depolymerization of lignin into aromatic chemicals remains a great challenge. In this work, environmentally friendly NiFe2O4 spinel catalyst characterizing with rich oxygen vacancies and porous structures was constructed by introducing Ni to modulate the coordination environment of cations in Fe3O4. Under optimal conditions, the conversion of alkali lignin catalyzed by NiFe2O4 reached 91.0%, the yield of liquid product reached 83.6% and the yield of aromatic monomer products was 31.7%. Combined results from catalyst characterization, product analysis and density functional theory calculations showed that the Lewis acidic center of the catalyst was significantly improved by the introduction of Ni, which promoted the C-O bond breaking in lignin. The Ni-O-Fe structure facilitated the adsorption of lignin substrates and reaction intermediates, which resulted in the improved depolymerization efficiency of lignin. The present work provides valuable insights into the depolymerization of lignin by spinel catalysts, and offers ideas for the future design and development of binary or even ternary spinel catalysts for the depolymerization of lignin.