Heterogeneous tandem upcycling of polyoxymethylene into methanol and methylene derivatives

Abstract

The urgent need for sustainable polymer waste management has driven the development of efficient chemical recycling strategies. Polyoxymethylene (POM), a high-performance engineering plastic resistant to natural degradation, poses significant environmental challenges due to its stability and limited recyclability by conventional methods. Here, we present a heterogeneous tandem catalytic system that efficiently converts POM into methanol with up to 99% yield under mild conditions of 200 °C and 6 MPa H₂. This system synergistically combines Lewis-acidic Sn-Beta zeolite, which depolymerizes POM into formaldehyde, with oxalate gel-coprecipitation-derived Cu/Al₂O₃ (og-CuAl), selectively hydrogenating formaldehyde to methanol without producing CO₂ by-product. Sn-Beta, containing tetrahedral-coordinated Sn⁴⁺ species, exhibits optimal deploymerization activity due to excellent dispersion and strong Lewis acidity. Og-CuAl with a 50% Cu molar ratio shows exceptional hydrogenation, driven by high Cu dispersion and a balanced Cu⁺ to Cu⁰ ratio enabled by Cu–O–Al interfaces. Integration of these catalysts effectively shifts the equilibrium, preventing formaldehyde oligomerization and enabling complete, high-yield POM-to-methanol conversion. This dual catalytic approach offers a scalable, atom-efficient pathway to transform POM waste into high-value methanol, advancing circular-economy principles in polymer recycling and sustainable chemical production.