There is a growing awareness of the negative effects of plastic waste on the environment, leading to a shift towards a more sustainable “circular plastic economy.” However, current recycling methods are limited by being primarily mechanical based, hindering the full realization of a truly circular plastics economy. In this paper, we explore a promising catalytic chemical recycling process that can convert polyolefins into olefins, offering new pathways for upcycling and contributing to the goal of a circular plastics economy.

Abstract

The dehydrogenation of alkanes is a critical process to enable olefin upcycling in a circular economy. A suitable selective catalyst is required in order to avoid demanding reaction conditions and ensure the activation of the C−H bond rather than breaking the C−C bond, which is the weaker of the two. Herein, using periodic density functional theory, we have investigated the dehydrogenation of n-pentane (as a model compound) on Pt and Ru surface catalysts. The results show that the first dehydrogenation occurs through the dissociative adsorption of the C−H bond, resulting in pentyl and H intermediates on the metal surfaces. A successive dehydrogenation creates pentene via a hydride di-σ state, leaving the abstracted hydrogen atoms on the metal surfaces. In agreement with recent experiments, Pt and Ru catalysts show a similar reactivity trend: pentane dehydrogenation yields pent-1-ene and pent-2-ene. The simulations reveal that the 1^st C−H dissociation is the rate-determining step, whereas the double-bonded alkenes (pent-1-ene and pent-2-ene) are formed due to fast successive dehydrogenation processes. Pt favors the formation of pent-1-ene, whereas Ru favors the formation of pent-2-ene.