Catalytic Degradation of Polystyrene at Low Temperature over a Mo–W–Fe–Ni Carbide–Alloy Catalyst

In this study, we investigate the catalytic degradation of polystyrene (PS) in water at low temperature (90–110 °C, 1 atm) using a multiphase carbide–alloy catalyst obtained by mechanosynthesis. X-ray diffraction and scanning electron microscopy confirm a mixture of Mo–W carbides and Fe/Ni alloys, consistent with multiple types of active sites. High-resolution mass spectrometry (MS) is used to assign products by oligomer-series spacing (styrene repeat mass, 104.15 Da) and the residual mass Δm for end-group identification. At 90 °C without catalyst, the spectrum shows PS fragments between m/z=888–4618, consistent with thermal depolymerization. With catalyst at 90 °C, new lower-m/z peaks emerge and long-chain signals diminish, indicating enhanced chain scission under mild conditions. Increasing the temperature to 100 and 110 °C yields even lighter ions (e.g., m/z=307.59 and 247.88), confirming stronger cracking and a larger number of distinct products. End groups inferred from Δm include alkenes (C3–C7), alkanes (C4, C7), cyclic C6–C7 fragments, and alcohols, which are consistent with protolytic C–C bond cleavage (Haag–Dessau), oxidative dehydrogenation, and subsequent hydrogenation/hydration on metal/carbide sites. Overall, the results show that water-activated carbide–alloy catalysts can drive PS deconstruction at low temperature, shifting products toward shorter chains with useful functional groups, while a simple MS-based rule set provides a transparent and reproducible approach to product assignment.