Decomposition of polymers by heterogeneous catalysts presents a promising approach for reuse of waste plastics. We demonstrated non-hydrogenative decomposition of model polyolefins over proton-form and metal (Cu, Ni) ion-exchanged beta (BEA) zeolites at moderate temperatures (around 300 °C). Near complete polyolefin decomposition was observed in batch reactions monitored by thermogravimetric analysis, while decomposition at partial conversion was studied in flow reactions. Ni-exchanged zeolites produced H2 at substantially higher rates (>10x) than other catalysts while also uniquely resisting deactivation over time. Application of the delplot formalism offered insights into the reaction network for polyolefin decomposition over Ni/BEA most notably that H2 is solely a primary product. We deduce that H2 production is catalyzed by activation of C-H bonds at ionic Ni sites, and H2 prevents buildup of polyaromatic coke species in Ni-exchanged zeolites that deactivate Cu-exchanged and protonic zeolites.
Keywords: Deactivation; Heterogeneous catalysis; Plastics; Polyethylene; Zeolite.
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