Quantitative Polyethylene Upcycling to Liquid Olefins over Ru-Containing Layered Zeolites

Area of Science:

• Catalysis
• Materials Science
• Chemical Engineering

Background:

• Direct deconstruction of polyolefins to olefins is an ideal but challenging route for plastic upcycling.
• Existing methods face a trade-off between substrate conversion and product selectivity.
• A hydrogen-free deconstruction method is highly desirable for efficient polyolefin valorization.

Purpose of the Study:

• To develop an efficient catalyst for the quantitative upcycling of polyethylene into liquid olefins without an external hydrogen source.
• To investigate the catalytic mechanism and the role of catalyst structure in achieving high performance.
• To demonstrate the potential of the developed catalyst for practical applications in plastic waste management.

Main Methods:

• Synthesis of layered MEL zeolite with confined Ruthenium (Ru) species via a ligand-assisted hydrothermal route (Ru@MEL).
• Optimization of Ru@MEL catalyst for polyethylene upcycling.
• Characterization of catalyst structure and elucidation of the reaction mechanism using advanced techniques.
• Testing catalyst performance in terms of conversion, selectivity, stability, and scalability.

Main Results:

• The optimized Ru@MEL catalyst achieved >99% polyethylene conversion and 92% selectivity toward C5-C9 olefins at 270 °C within 4 hours.
• Ru incorporation induced aluminum migration within the MEL zeolite framework, creating proximity between Ru species and acid sites.
• Mechanism insights revealed a synergistic cycle involving Ru-mediated C-H activation, Brønsted acid-catalyzed β-scission, and Lewis acid-assisted hydrogen transfer.
• The catalyst demonstrated high efficiency, stability, and scalability using real-world plastic waste.

Conclusions:

• Ru@MEL is a highly efficient catalyst for the direct deconstruction of polyethylene into valuable liquid olefins.
• The catalyst's performance is attributed to the unique synergy between confined Ru species and the acidic sites within the MEL zeolite framework.
• The developed catalytic system shows significant potential for the practical upcycling of plastic waste into chemical feedstocks.