Cold plasma-assisted co-conversion of polyolefin wastes and CO2 into aromatics over hierarchical Ga/ZSM-5 catalyst

Abstract

Cold plasma-assisted catalytic upcycling of polyolefin wastes integrated with CO₂ into value-added chemicals is a promising solution for mitigating the global carbon emissions and fossil energy crisis, but still challenging due to the complexity of products and low energy efficiency. Given this, a novel one-stage process of cold plasma coupled with Ga-modified hierarchical H-ZSM-5 (Ga/Hie-ZSM-5) catalyst for polyolefins upgrading was designed with polyolefins followed by the catalysts within the plasma region, which facilitated the upcycling of polyolefins to light olefins and CO₂ activation by plasma, and thereby the enhanced synergy between cold plasma and catalysts for aromatics production. At an input power of ca. 45 W without external heating, the low-density polyethylene (LDPE) waste was completely converted with the assistance of CO₂ and the yield of oil products over the Ga/Hie-ZSM-5 catalyst was highly up to 62.2 wt%, with nearly 100% selectivity of aromatics. Meanwhile, the degradation efficiency of LDPE and the energy efficiency could reach 2.5 g_LDPE⋅g_cat⁻¹⋅h⁻¹ and 55.56 g_LDPE⋅g_cat⁻¹⋅kW⁻¹⋅h⁻¹, respectively. Mechanism investigation revealed that the plasma and CO₂ synergistically affect the primary cracking of LDPE, forming a primary product enriched in olefins and a small amount of CO. Subsequently, the produced olefins intermediates were further aromatized via cyclization-dehydrogenation route on the Ga/Hie-ZSM-5 catalyst with assistance of CO₂ under the synergistic effect of plasma-catalysis. This work offers a feasible strategy to improve the yield of aromatic products for the plasma-catalytic upcycling of polyolefins and CO₂ at ambient pressure without any external heating.