(638b) Modeling of the Kinetics of Tandem Chain Scission/Aromatization

The catalytic depolymerization of polyethylene (PE) to alkylaromatics using bifunctional catalysts such as Pt/SiO₂ -Al₂ O₃ offers a promising pathway for sustainable plastic upcycling. The tandem reactions of C-C bond scission and aromatization occur without external hydrogen under mild conditions by redistributing PE-derived hydrogen. However, external hydrogen pressures (P_H2 ) significantly influence both the reaction kinetics and product selectivity. At moderate pressures, P_H2 enhances the depolymerization rate, increases alkylbenzene yield, and suppresses polyaromatic formation.

In this study, a kinetic model incorporating the quasi-equilibria of dehydrogenation and aromatization was developed to describe the experimental observations. The model accounted for the competitive adsorption of aromatic products on active catalytic sites, elucidating a pseudo-zeroth-order dependence of aromatic yields and the non-monotonic dependence of C-C bond scission rates on P_H2 . Fitting the model to data yields rate constants and equilibrium constants from the experimental results. The insights provide a mechanistic understanding of the role of P_H2 in enhancing depolymerization rates while optimizing aromatics yield.