Highly selective production of gasoline-range hydrocarbons via hydroconversion of polyolefins over Ru/CeO2 and BEA hybrid catalysts

Abstract

To address the growing demand for sustainable plastic lifecycle, hydroconversion of polyolefins is a promising strategy for catalytic recycling of plastic wastes into fuel-range hydrocarbons. Ruthenium (Ru)-based hydrogenolysis catalysts exhibit high activity in the degradation of polyolefins, and bifunctional hydrocracking catalysts are much more beneficial for the selective production of gasoline-range hydrocarbons (C₄–C₁₂) than monofunctional hydrogenolysis catalysts. Herein, the Ru/CeO₂ and BEA zeolite hybrid catalyst demonstrated almost full conversion of low-density polyethylene (LDPE) with 95.4% gasoline selectivity, minimizing the production of low-value methane (<0.8%) in the hydroconversion of LDPE. Addition of BEA into Ru/CeO₂ switched the reaction pathway from hydrogenolysis to hydrocracking with a high fraction of branched hydrocarbons and efficient usage of hydrogen. The Ru/CeO₂ and BEA hybrid catalyst demonstrated the highest productivity of 3451 g_C5–C12 g_Ru⁻¹ h⁻¹ among the recently reported Ru-based hydroconversion catalysts, and this was even higher than that of Pt- and Ir-based hydrocracking catalysts. The effect of BEA addition on the high gasoline selectivity was validated at a reaction temperature of 250 °C, and it was found that among the various physicochemical properties of the zeolite, the three-dimensional pore structure with a sufficient amount of surface acidity in the zeolite is crucial for the selective production of gasoline via LDPE hydroconversion. This work provides fundamental groundwork for designing bifunctional catalysts in polyolefin recycling.