The rapid accumulation of plastic waste in landfills, waterways, and our oceans is resulting in a poorly understood environmental crisis, which current recycling technologies are not capable of ameliorating. Recent proposed approaches in the depolymerization of waste plastics employ an Olefin-Intermediate Process (OIP), where feedstocks like polyolefin plastics are ‘activated,’ producing an olefin intermediate. This olefin can then be reacted with an orthogonal and tandem chemistry that results in new overall reaction pathways to alkanes or alkenes without the need for exogenous hydrogen. We investigate the role of the dehydrogenation catalyst on the reaction rate, kinetics, and product distribution in heterogeneous tandem dehydrogenation and olefin metathesis (Tandem D/OM) of three different alkane reactants in both the liquid and gas-phase. Our work demonstrates that a gamma-alumina supported Pd-based dehydrogenation catalyst shows four-fold higher activity (surface area basis) compared to Pt or Sn1Pt3 catalyst on the same support and is effective at depolymerizing linear polyethylene feedstocks. Uniquely, the method of catalyst preparation, prior to reaction, demonstrated in-situ synthesis of a bifunctional catalyst capable of facilitating both dehydrogenation and olefin metathesis. This Pd-based bifunctional catalyst displays reduced rates of deactivation compared to Pt-based catalysts and a surprising promotion of olefin metathesis activity.
Selena Moore is a master’s student in chemical engineering working in Dr. Ellis’ lab. She previously graduated from the University of Colorado Boulder with a B.S. in chemical engineering. Her research at OSU is focused on catalytic tandem chemistry for hydrocarbon rearrangement and polyethylene depolymerization.