Mixed Cu–Mn Oxide Catalysts for Solvolysis of Technical Lignin

With the rising demand for fuel and the societal shift toward sustainable resources, lignin emerges as a prime feedstock. Lignin is mainly composed of aromatic compounds linked within a complex matrix and holds significant potential as a source of renewable aromatics. Technical lignin, the most abundant form of lignin, is often degraded due to harsh biomass pretreatment processes. Cu₂₀MgAlO_x porous mixed oxide (CuPMO) is an efficient catalyst to help solvolyze technical lignin. Here, we demonstrate the promotion of such mixed oxides with Mn toward improving both the yield of monomers and solubilized lignin oil. The promotion was highest at a Cu/Mn ratio of unity, resulting in a 2-fold increase in monomer extraction compared to the benchmark CuPMO. The Mn-doped catalyst produced more saturated products. Simultaneously, solvent consumption decreased with increasing Mn content. X-ray diffraction (XRD) and X-ray photoelectron (XPS) analyses revealed the formation of a Cu–Mn spinel oxide. The proximity of Cu and Mn in this precursor facilitated the reduction of Mn through hydrogen spillover from Cu⁰ formed during catalyst reduction during heating in the reaction mixture. The observed increase in saturated products, coupled with enhanced lignin solvolysis, highlights the superior hydrogenation capability of the CuMnMgAlO_x catalyst for the solvolysis of technical lignin.

A Mn-doped Cu₂₀MgAlO_x catalyst in supercritical ethanol was found to boost lignin monomer yield and hydrogenation over a Cu-only catalyst.