Anchored dilacunary phosphotungstates on zeolite HY: synthesis and solvent free selective oxidation of levulinic acid to succinic acid using environmentally benign oxidant, H2O2

Abstract

The purpose of this research is to develop a highly efficient, atom-economical protocol for biomass valorization by targeting the challenging selective oxidation of levulinic acid into succinic acid. Addressing a long-standing challenge in biomass oxidation chemistry, this study outlines the design of an inorganic tungsten – oxygen rich dilacunary phosphotungstate anchored to zeolite HY, forming a redox-active heterogeneous catalyst. For the first time, complete selectivity toward succinic acid with a 42% yield was achieved using hydrogen peroxide as a green oxidant under mild, solvent-free conditions. The major innovation lies in utilizing the unique structural confinement and cooperative acidity of the faujasite supercages and phosphotungstates, which allowed the catalyst to significantly outperform the previously reported supports, opening new horizons towards dicarboxylic acid production. Comprehensive physicochemical characterization confirmed the successful incorporation of the active species and revealed the structural and acidic features responsible for catalytic performance. The reaction was carried out in a simple batch reactor, and systematic investigation of key reaction parameters enabled precise regulation of the reaction pathway, delivering a turnover number of 462. Mechanistic insights were gained through radical-scavenging and control experiments, elucidating the nature of the active oxidant and the reactive species involved. This highly controlled radical network precisely directs the oxidative cleavage at the C3–C4 bond of levulinic acid while completely suppressing over-oxidation pathways. The effectiveness of the developed system was highlighted through comparison with previously reported methods, and recycling experiments demonstrated catalyst stability up to 4 cycles. Overall, the developed methodology provides a blueprint for future inorganic materials design for the sustainable transformation of biomass-derived molecules into high-value chemical products.