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 ${}^{\circ }$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 $\Delta m$ for end-group identification. At 90 ${}^{\circ }$C without catalyst, the spectrum shows PS fragments between $m/z=888$–4618, consistent with thermal depolymerization. With catalyst at 90 ${}^{\circ }$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 ${}^{\circ }$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 $\Delta m$ include alkenes (C${}_3$–C${}_7$), alkanes (C${}_4$, C${}_7$), cyclic C${}_6$–C${}_7$ 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.