At the 22nd annual fall meeting of the American Chemical Society, a team of researchers led by the Pacific Northwest National Laboratory presented an innovative approach to plastics recycling that increases the conversion rate to useful products while reducing the use of the precious metal ruthenium. This research gives scientists the opportunity to develop more efficient, selective and versatile catalysts for plastic recycling.

The new method is more efficient at converting plastics into valuable commodity chemicals, a process known as "upcycling. In addition, this method produces much less methane as a byproduct than other reported methods.

Petroleum-based plastic waste is an untapped source of carbon-based chemicals that can be used as starting materials for making useful durable materials and fuels.

The addition of hydrogen (a reaction called hydrogenolysis) to hard-to-recycle plastics such as polypropylene and polyethylene is known to be a promising strategy for converting waste plastics into hydrocarbons. This process requires catalysts with high efficiency and selectivity to be economically viable.

The team found that reducing the amount of the precious metal ruthenium actually improved the upcycling efficiency and selectivity of the polymer. A recent study they published in ACS Catalysis showed that efficiency increased when a low ratio of metal to carrier structure resulted in a structural shift from an ordered array of particles to a disordered raft of atoms.

Based on these findings, the team observed the disordered transition at the molecular level and then used established theory to demonstrate that single atoms were actually more efficient catalysts in this experimental work.

The researchers said they have investigated cheaper and more readily available carrier materials to replace cerium oxide. The study also found that chemically modified titanium dioxide may provide a more efficient and selective pathway for upcycling polypropylene.

Chlorine from PVC and other sources is present in industrial upcycling processes when clean sources of plastics are not available. Chlorine can contaminate the upcycling reaction of plastics. To make the new approach applicable to mixed plastic recycling lines, the research team is now exploring how the presence of chlorine can affect the efficiency of chemical conversion or help convert waste plastics, which normally lead to environmental contamination, into useful products.

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