(360f) Redox Behavior of Single Atom Catalysts for the Upgrading of Plastic Waste-Derived Species

Within the last few decades, the production of plastics has exploded on a global scale. A vast majority of these plastics are disposed of in landfills or incinerated, while only 9% of the plastics ever made since 1950 have been recycled¹. Efforts to redirect more plastic waste from landfill have led to a recent interest to find catalysts suitable to upgrade plastic waste-derived species to value-added products via selective hydrogenation reactions. Single atom catalysts, with active metals dispersed atomically rather than as extended clusters, are promising candidates due to their ability to hydrogenate specific functionalities to selectively form high value-added products. However, fundamental knowledge relating the electronic character of these systems with the energetics of selective hydrogenation elementary reactions remains lacking. Understanding the redox environment during catalytic upgrading reactions will ultimately guide the rational design of highly active and selective single atom catalysts.

Here, we use density functional theory (DFT) to elucidate how Cu or Ag single atoms on anatase TiO₂ can be selective for the hydrogenation of plastic waste-derived carboxylic acids. Specifically, we examine the electronic structure progression of benzoic acid redox processes on these catalysts. We study how the extent of reduction on the support will differentially stabilize species that aid in the selective formation of hydrogenation products. We also propose calibration schemes that quantify the extent of reduction along these elementary steps and how it ultimately relates to the selectivity of value-added products. Finally, a global optimization workflow is proposed that uses graphical representations of the surface and DFT to elucidate the morphology of these systems and how it directly affects redox behavior and catalyst performance.

1. Ritchie, H., and Roser, M. “Plastic Pollution” 2018. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/plastic-pollution’.