연구홍보포털

논문 초록 (Abstract)

Pyrolysis-based chemical recycling of plastics is promising because it converts mixed plastic waste into a liquid intermediate compatible with existing upgrading infrastructure without the need for complex sorting processes. However, chlorine (Cl) in pyrolysis oil, mainly originating from poly(vinyl chloride), causes reactor corrosion and catalyst deactivation in downstream processes, requiring its removal to below 10 ppm via hydrodechlorination (HDC). Trace-Pt-loaded γ-Al2O3 is highly effective for HDC because pentacoordinated Al sites in γ-Al2O3 activate C–Cl bonds while Pt activates H2. However, real pyrolysis oil contains not only chlorine compounds but also olefins and aromatics, leading to catalyst deactivation through complex reaction networks. Here, we identify coke formation as the primary cause of deactivation, promoted by the interplay between unsaturated hydrocarbons and in situ-generated Brønsted acid sites on chlorinated γ-Al2O3. The resulting coke evolves toward more dehydrogenated and condensed aromatic species with time-on-stream, and preferentially blocks pentacoordinated, Lewis acidic Al sites rather than Pt, thereby disrupting the bifunctional HDC mechanism. Based on this mechanistic insight, a two-step hydrotreating strategy was employed, in which pyrolysis oil was first hydrogenated over Pt/SiO2 under mild conditions, followed by HDC over Pt/γ-Al2O3 under more severe conditions. This strategy suppresses catalyst deactivation by mitigating coke formation, while reducing the Cl content from 550 ppm to <10 ppm over 6 days of continuous operation.