Engineering Fe Species on USY Zeolite Support for the Oxidative Cleavage of Lignin to Bio-Based Diethyl Maleate

The development of sustainable routes for polymer monomers is crucial for the chemical industry. Herein, we report a highly efficient and selective oxidative depolymerization strategy for converting lignin into diethyl maleate (DEM), a valuable precursor for polyaspartic polyurea resins. A series of iron oxide catalysts supported on commercial USY zeolites via a simple impregnation-calcination method were developed. Notably, the catalyst prepared using iron sulfate (Fe2(SO4)3) as the precursor exhibited superior performance, achieving a maximum DEM yield of 53.0 wt % and a selectivity of 72.4% from organosolv bagasse lignin, outperforming the iron nitrate- and chloride-derived catalysts by 29.2 and 31.9 wt % in yield, respectively. Comprehensive characterizations revealed that the unique highly dispersed Fe(SO4)x phases significantly increased the proportion of Fe3+ species and facilitated electron transfer across the support-iron interface. The synergistic interplay between sulfur-induced Brønsted acid sites and isolated octahedral iron sites was identified as the key factor driving the efficient cleavage of lignin linkages and subsequent oxidative ring-opening. By combining commercially available supports and earth-abundant metals, this work offers an environmentally viable pathway for lignin depolymerization into polymer monomers, demonstrating significant potential for industrial scalability.