Selective hydrodeoxygenation of lignin to 4-ethylcyclohexanol catalyzed by Cu–Ni/MgCrOx spinel

Abstract

A novel approach is proposed for producing 4-ethylcyclohexanol, a versatile petrochemical in the polymer industry, from the renewable lignin in the presence of Cu–Ni/MgCrO_x spinel catalysts. Under the synergistic effect between the Ni⁰, Cu,⁺ and the balanced acidic and basic properties of MgO and MgCr₂O₄, an exceptional yield of monomer (30.1 wt%) with 59.5% selectivity of 4-ethylcyclohexanol (yield of 17.9 wt%) was achieved when the depolymerization of bamboo lignin was performed with Cu₆Ni₂₀/MgCr_0.5O_x (Cr:Mg = 0.5). Catalyst characterization illustrated that the formation of MgCr₂O₄ spinel, which restrained the generation of NiMgO₂ solid solution and increased the concentration of Ni⁰ species, along with the surface electron effect between Ni⁰ and Cu⁺, contributes to this superior hydrodeoxygenation performance of lignin. Mechanistic investigation further demonstrated that the conversion of lignin to 4-ethylcyclohexanol involves a tandem process of C_β–O bonds cleavage, demethoxylation, and saturated hydrogenation. Therefore, this work provides new insights on lignin utilization.