Spatially orthogonal CeOx-Zn sites on diatomite-aerogel-derived hierarchical HZSM-5 enable gated dechlorination and BTX-selective upcycling of PVC/PET mixed plastics

Spatially orthogonal CeO x –Zn sites were integrated into aerogel-derived hierarchical HZSM-5. • CeO x shifted HCl release and chlorinated-intermediate conversion to lower temperatures. • Zn promoted BTX-selective aromatization of dechlorinated and oxygenated fragments. • Accessibility-weighted bifunctional catalysis enabled cleaner and higher-value PVC/PET upcycling. Catalytic upcycling of chlorine-containing mixed plastics remains limited by the intrinsic conflict between efficient dechlorination and high-selectivity aromatization. Here we report a spatially orthogonal CeO x –Zn/Aero-40 catalyst derived from a diatomite-aerogel-templated hierarchical HZSM-5 support, in which CeO x -rich outer mesopores and Zn-containing MFI channels are integrated into a gated tandem architecture. The hierarchized support decreased the mean particle size from 386 ± 42 nm for Conv-40–274 ± 31 nm for Aero-40 and retained a shortened crystallite length of 289 ± 24 nm after dual-site loading, while exposing 3.01 wt% surface Ce and 1.86 wt% surface Zn on CeO x –Zn/Aero-40. Under the optimized two-stage conditions, CeO x -Zn/Aero-40 affords a BTX yield of 64.0 wt% on the initial dry-polymer feed basis, a BTX selectivity of 90.0% within the quantified liquid aromatics, and a dechlorination efficiency of 98.9%. Product-family analysis showed that aromatics rose to 71% whereas organochlorines fell to 2%; chlorine balance further demonstrated that 88% of chlorine was released as gaseous HCl, with only 3% remaining as oil-phase organochlorine. Taken together, the time-resolved spectroscopic/thermal analyses, probe experiments and kinetic measurements are consistent with a functionally staged mechanism in which Ce-associated sites facilitate low-temperature HCl elimination and chlorine management, whereas Zn-associated acid environments favor downstream cyclization/dehydrogenation-aromatization toward BTX. The DFT calculations support the intrinsic feasibility of these site-specific elementary steps but do not, by themselves, establish dynamic inter-site kinetic coupling. Across ten independent parallel runs, the mean BTX yield was 63.9 wt% of the initial dry polymer feed (RSD 1.0%), while the mean dechlorination efficiency was 98.8% (RSD 0.2%), retained 96.3% Zn after five cycles, and maintained high dechlorination efficiency for model and real feeds. These results establish a hierarchical dual-site zeolite platform for chlorine-tolerant aromatics-oriented upcycling of PVC/PET mixed plastics. Download: Download high-res image (274KB) Download: Download full-size image