(243b) Hydrocracking of PVC-Mixed Polyolefin (PO) over Bifunctional Tungsten-Carbide (WxC) Catalysts

Polyolefins (PO), including polypropylene (PP) and polyethylene (PE), make up > 50% of non-degradable plastic waste. Hydrocracking over bifunctional metal-acid catalysts is an efficient process to cleave the chemically inert C−C bonds and upcycle PO into small hydrocarbons. The process is challenged by 1) PVC impurities and heteroatom-containing additives in post-consumer PO feedstocks that deactivate metal-based catalysts; 2) the slow diffusion of PO chains between metal and Brønsted-acid sites (BAS) in micropores. Here we will present studies on PO hydrocracking over non-porous SiO₂-supported tungsten-carbide (W_xC) catalysts synthesized by carburizing WO₃. Carbide sites are known for metal-like catalytic activities, while −OH on residual WO₃ clusters act as BAS in close contact with the “metallic” sites, enabling hydrocracking (Fig. a). We will show that the kinetics of PO hydrocracking is dependent on the carburization temperature of W_xC (Fig. b), which determines the distribution of various W phases (Fig. c: XRD) on the catalysts, thus the balance between and properties of “metallic” sites and BAS (Fig. d: NH₃-TPD). W_xC catalysts are compatible with PVC impurity in the substrate of up to 10 wt% (Fig. e-f). In the case of BAS-limited catalysts, PVC enhances hydrocracking rate (Fig. f), preassembly by increasing the acidity. Detailed kinetic and spectroscopic investigations to compare reaction mechanisms without and without PVC impurity will also be presented. This work leverages the underexplored bifunctionality of W_xC surfaces for upcycling contaminated PO, while establishing the synthesis-structure-function relationship of the bifunctional catalysts.