Structure–Property Relationships for Nickel Aluminate Catalysts in Polyethylene Hydrogenolysis with Low Methane Selectivity
Brandon C. Vance, Sean Najmi, Pavel A. Kots, Cong Wang, Seil Jeon, Eric A. Stach, Dmitri N. Zakharov, Nebojša Marinković, Steven N. Ehrlich, Lu Ma, Dionisios G. Vlachos
Abstract
High Resolution Image Download MS PowerPoint Slide Earth-abundant metals have recently been demonstrated as cheap catalyst alternatives to scarce noble metals for polyethylene hydrogenolysis. However, high methane selectivities hinder industrial feasibility. Herein, we demonstrate that low-temperature ex-situ reduction (350 °C) of coprecipitated nickel aluminate catalysts yields a methane selectivity of <5% at moderate polymer deconstruction (25–45%). A reduction temperature up to 550 °C increases the methane selectivity nearly sevenfold. Catalyst characterization (XRD, XAS, 27 Al MAS NMR, H 2 TPR, XPS, and CO-IR) elucidates the complex process of Ni nanoparticle formation, and air-free XPS directly after reaction reveals tetrahedrally coordinated Ni 2+ cations promote methane production. Metallic and the specific cationic Ni appear responsible for hydrogenolysis of internal and terminal C–C scissions, respectively. A structure-methane selectivity relationship is discovered to guide the design of Ni-based catalysts with low methane generation. It paves the way for discovering other structure–property relations in plastics hydrogenolysis. These catalysts are also effective for polypropylene hydrogenolysis.