(363t) Two-Dimensional (2D) Catalysts for Plastic Waste Conversion

The exponential increase in global plastic production has significantly outpaced our current waste management capabilities, leading to severe environmental, energy, and economic impacts. The reliance on landfilling and incineration as major methods of managing plastic waste does decrease the volume of discarded materials but creates substantial negative impacts in terms of energy utilization and greenhouse gas emissions. The alternative method of recycling is a promising solution, however the rate of utilization in the United States is dismally low at only 5-6%. Furthermore, the strong C-C backbone of polyolefins makes them particularly challenging to depolymerize and recycle with existing chemical recycling methods such as pyrolysis and gasification which have low product selectivity and high energy consumption. This situation underscores the critical need to develop sustainable recycling methods to address the rapid growth of plastic production and subsequent waste.

Recent advancements in the hydrogenolysis of plastic waste using ruthenium (i.e., Ru) have shown significant potential for upcycling polyolefins into valuable fuels. Due to their high activity, Ru nanoparticles have been extensively utilized in the plastic hydrogenolysis process, demonstrating the ability to rapidly break C-C bonds in polyolefins such as polyethylene. Despite these promising aspects, one major flaw of this process is the tendency of Ru-based catalysts to break terminal C-C bonds, leading to the formation of low-value methane gas which diminishes the overall yield of valuable hydrocarbon products. Additionally, the high density of polyolefin macromolecules creates significant external mass transport diffusion limitations which can adversely affect the efficiency of depolymerization reaction.

MXenes are a class of two-dimensional materials derived from MAX phases that exhibit exceptional chemical, physical, and mechanical properties, making them promising candidates for catalytic applications including plastic depolymerization. MXenes' high surface area in combination with the presence of functional groups on their nanosheets enable the dispersion of metal active sites as well as modification of their electronic charges, thereby enhancing catalytic activity. This structure allows for higher accessible active sites and the incorporation of ionic crosslinkers (like Ru) during synthesis can prevent MXene nanosheets from re-stacking or aggregating, further enhancing their catalytic capability. In this talk, we discuss an innovative approach to enhance the hydrogenolysis of plastic waste by leveraging the unique properties of MXene materials supported with Ru nanoclusters. To address the mass transfer diffusion problem of plastics, we modified the interlayer spacing of MXene nanosheets to enhance the efficient contact between polymer substrates and catalytic sites. The use of this material in polyolefins hydrogenolysis demonstrated a remarkable conversion rate and selectivity under mild conditions. These findings highlight the potential of MXene materials in addressing the challenges associated with the catalytic depolymerization of plastics.