Highly Selective Upgrading of Polyethylene into Light Aromatics via a Low-Temperature Melting-Catalysis Strategy

The selective upgrading of polyethylene waste into light aromatics is hampered by relatively high C-C bond cleavage temperatures and low product selectivity. Herein, we report a low-temperature melting-catalysis strategy that directly upgrades low-density polyethylene (LDPE) into light aromatics over commercial ZSM-5 zeolite under mild conditions, eliminating the need for precious metals, solvent, or external H-2. Experimental results combined with DFT calculations and molecular dynamics simulations revealed that the molten LDPE microenvironment facilitates intimate LDPE-catalyst contact, promoting primary C-C cleavage while suppressing olefin intermediates diffusion out of pores. This feature increases the residence time for subsequent direct olefin cyclization within the confined micropores. Moreover, online mass spectra confirmed that the in situ generated hydrogen from cyclization and dehydroaromatization reactions plays a vital role in C-C bond scission. By optimizing the reaction conditions, a light aromatic yield of 50.6 wt % with an impressive selectivity of 90.9% toward benzene, toluene, and xylenes was achieved at 280 degrees C for 1 h. This strategy is not limited to the model polyethylene but also demonstrates remarkable efficiency in the depolymerization of various widely used polyethylene-rich plastics, enabling an economically viable and environmentally benign chemical recycling path for plastic wastes.