Chemical recycling of polystyrene waste: theoretical-experimental study of the mechanism of catalytic transformation

Abstract

This study combines experimental and theoretical approaches to investigate the catalytic pyrolysis of polystyrene (PS) waste using CeO₂ and Co/CeO₂ catalysts. A laboratory-scale reactor was designed and optimized at 450 °C under a nitrogen atmosphere to maximize liquid product yield. The catalysts, synthesized via the combustion method and characterized by XRD, BET, and potentiometric titration, exhibited high surface areas (110 and 100 m² g⁻¹, respectively). Experimental results revealed that pure CeO₂ selectively promoted PS depolymerization toward styrene monomer formation through a β-scission mechanism, achieving 87.04% styrene selectivity. In contrast, cobalt incorporation altered the reaction pathway, reducing styrene yield but increasing overall liquid fraction and calorific value, indicating a more energy-efficient process. Density functional theory (DFT) calculations supported these findings, showing that styrene dimer adsorption and β-scission on the CeO₂(111) surface are energetically favorable, whereas Co modification raises the activation barrier and enhances dimer adsorption, suggesting a possible reduction in the accessibility of the catalyst's acid active sites. These combined results suggest that CeO₂ is well-suited for selective monomer recovery, while Co/CeO₂ offers a balanced route for both material and energy valorization of PS waste, thus advancing the development of catalytic systems for sustainable chemical recycling.