Nickel ferrites as heterogeneous catalyst for the β-O-4 cleavage and hydrodeoxygenation reactions of lignin: a model molecule approach

Maximizing the valorization of lignocellulosic biomass requires effective catalytic systems for converting lignin into monomeric phenolic compounds. In this context, heterogeneous catalysts applied in reductive catalytic fractionation (RCF) processes have emerged as particularly promising, achieving selective lignin depolymerization, producing valuable phenolic monomers, alongside the recovery of highly delignified cellulose-rich pulps. However, the structural complexity of lignin, characterized by diverse linkages and functional groups, poses significant challenges in achieving selective conversion to platform chemicals, typically resulting in complex product mixtures. Understanding reaction pathways through model compound studies offers a strategic approach to overcome these selectivity limitations and advance the technology toward the industrial scale up. In this work, a thorough model molecule study involving five spinel catalysts composed of Nickel and Iron: NiFe2O4 (SP1), NiFe1,8O4-x (SP2), Ni0,9Fe2O4-x (SP3), Ni0,8Fe2O4-x (SP4), and Ni0,5Fe2,5O4+x (SP5) and Ruthenium supported on the spinel NiFe2O4 (Ru/NiFe2O4) is conducted. The primary goal was to optimize the RCF process for lignocellulosic biomass valorization by examining various reaction conditions, such as the optimal temperature and the solvent quantity and composition, at which carry out the reactions. Additionally, this investigation establishes benchmarks for potential secondary conversion and advancement of the lignin fractions generated during RCF, with the final aim of increasing yield into fewer, highly desirable, aromatic compounds.