Production of Branched Alkanes by Upcycling of Waste Polyethylene over Controlled Acid Sites of SO₄/ZrO₂‐Al₂O₃ Catalyst

Abstract

Branched alkanes, which enhance the octane number of gasoline, can be produced from waste polyethylene. However, achieving highly selective production of branched alkanes presents a significant challenge in the upcycling of waste polyethylene. Here, we report a one-pot process to convert polyethylene into gasoline-range hydrocarbons (C₄-C₁₃) with yield of 73.3 % over SO₄/ZrO₂-Al₂O₃ catalyst at 280 °C. The proportion of branched alkanes reaches 90.1 % within the C₄-C₁₃ fraction. Incorporation of sulfate group endows the catalyst with strong Lewis acid sites and weak and moderate Brønsted acid sites. In situ X-ray absorption, in situ infrared spectroscopy, in situ small angle neutron scattering, and DFT calculations reveal that polyethylene activation occurs through the synergy between sulfate groups and strong Lewis acid sites (Zr sites). The weak and moderate Brønsted acid sites preferentially catalyze the isomerization and type A β-scission processes, which favors the formation of branched alkanes, while suppressing competing reactions that produce straight-chain alkanes.