Hydrocracking of Polyethylene to Gasoline-Range Hydrocarbons over a Ruthenium-Zeolite Bifunctional Catalyst System with Optimal Synergy of Metal and Acid Sites
Qing Du, Xin Shang, Yangyang Yuan, Xiong Su, Yanqiang Huang
Abstract
Chemical recycling of plastic waste, especially polyolefins, into valuable liquid fuels is of considerable significance to address the serious issues raised by their threat on environmental and human health. Nevertheless, the construction of efficient and economically viable catalytic systems remains a significant hurdle. Herein, we developed an efficient bifunctional catalyst system comprising γ-Al2O3-supported ruthenium nanoparticles (Ru/γ-Al2O3) and β-zeolite for the conversion of polyolefins into gasoline-range hydrocarbons. A yield of C5–12 paraffins up to 73.4% can be obtained with polyethene as the reactant at 250 °C in hydrogen. The Ru sites primarily activate the initial cleavage of C–H bonds of polymer towards the formation of olefin intermediates, which subsequently go through further cracking and isomerization over the acid sites in β-zeolite. Employing in situ infrared spectroscopy and probe–molecule model reactions, our investigation reveals that the optimized proportion and spatial distribution of the dual catalytic sites are pivotal in the tandem conversion process. This optimization synergistically regulates the cracking kinetics and accelerates intermediate transfer, thereby minimizing the production of side C1–4 hydrocarbons resulting from over-cracking at the Ru sites and enhancing the yield of liquid fuels. This research contributes novel insights into catalyst design for the chemical upgrading of polyolefins into valuable chemicals, advancing the field of plastic waste recycling and sustainable chemical production.