Researchers in the US have developed a catalytic upcycling process using platinum nanoparticles supported on perovskites to convert single-use polyethylene (PE) (such as grocery bags) into value-added high-quality liquid products (such as motor oils and waxes). An open-access paper on their work is published in ACS Central Science.

Hundreds of millions of tons of plastic are produced worldwide each year, and the majority of these materials are discarded after a single use. Most end up in landfills or the environment. Because of technical challenges, even the plastic that does get recycled typically generates materials that are of lower quality and value than the original polymer.

The researchers dispersed Pt nanoparticles (NPs) on SrTiO₃ perovskite nanocuboids using atomic layer deposition. At moderate pressure and temperature, this catalyst cleaved carbon-carbon bonds in polyethylene to produce high-quality liquid hydrocarbons.

Hydrogenolysis of PE into high-quality liquid products. Credit: ACS, Celik et al.

Pt/SrTiO₃ completely converts PE (M_n = 8000–158,000 Da) or a single-use plastic bag (M_n = 31,000 Da) into high-quality liquid products, such as lubricants and waxes, characterized by a narrow distribution of oligomeric chains, at 170 psi H₂ and 300 °C under solvent-free conditions for reaction durations up to 96 h.

The binding of PE onto the catalyst surface contributes to the number averaged molecular weight (M_n) and the narrow polydispersity (Đ) of the final liquid product. Solid-state nuclear magnetic resonance of ¹³C-enriched PE adsorption studies and density functional theory computations suggest that PE adsorption is more favorable on Pt sites than that on the SrTiO₃ support. Smaller Pt NPs with higher concentrations of undercoordinated Pt sites over-hydrogenolyzed PE to undesired light hydrocarbons.

—Celik et al.

These liquids could be used as motor oil, lubricants or waxes, or further processed to make ingredients for detergents and cosmetics. The new catalyst preferentially bound and cleaved longer hydrocarbon chains, so that the products were all of a similar, intermediate size.

In contrast, a commercially available catalyst generated lower-quality products with a broader size range and many short hydrocarbons, limiting the products’ usefulness.

The authors acknowledge funding from the Catalysis Science Program, Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences at the US Department of Energy.

Resources

• Gokhan Celik, Robert M. Kennedy, Ryan A. Hackler, Magali Ferrandon, Akalanka Tennakoon, Smita Patnaik, Anne M. LaPointe, Salai C. Ammal, Andreas Heyden, Frédéric A. Perras, Marek Pruski, Susannah L. Scott, Kenneth R. Poeppelmeier, Aaron D. Sadow, and Massimiliano Delferro (2019) “Upcycling Single-Use Polyethylene into High-Quality Liquid Products” ACS Central Science doi: 10.1021/acscentsci.9b00722