Controlling Polyolefin Hydrogenolysis Selectivity by Engineering Single-Site Nickel(II) Hydride Active Catalytic Species

Hydrogenolysis of polyolefins using earth-abundant metal catalysts offers a viable route for upcycling plastic waste into value-added liquid hydrocarbons. We report the development of porous and isoreticular aluminium metal−organic frameworks (MOFs) supported well-defined heterogeneous nickel(II)-hydride catalysts (DUT-5-NiH and MIL-53-NiH) for efficient hydrogenolysis of polyethene and polypropylene into liquid hydrocarbons. The MOF’s metal-oxo-nodes supported coordinatively unsaturated and highly electrophilic mononuclear single-site nickel(II)-hydride active sites enable facile internal C−C bond cleavage in polyolefins, while the confinement of the Ni-species within the tunable porous framework of isoreticular MOFs facilitates precise control over narrow product distribution through shape-selective hydrogenolysis. The MOF-NiH catalyzed hydrogenolysis of single-use LDPE plastic bags, HDPE water bottle caps, and polypropylene at 250−285 °C afforded C9−C22 liquid alkanes up to 90% selectivity with minimal methane formation (<7%). The comparable mass-specific activity (77−104 mmol H 2 g Ni −1 h −1 ) of DUT-5-NiH and MIL-53-NiH for hydrogenolysis of LDPE, C 18 H 38, and C 24 H 50, suggests that the diffusion of polymer chains into catalyst pores is not a rate-limiting factor. Experimental, spectroscopic, kinetic, and computational studies reveal that the high activity and selectivity of these MOF catalysts stem from stabilizing mononuclear Ni(II)-hydride species at MOF nodes via active-site isolation and their confinement within pores, which efficiently cleave C–C bonds through σ-bond metathesis and β-alkyl transfer pathways. This work underscores the significance of active site engineering employing MOFs to develop highly active and well-defined abundant metal catalysts for the controlled hydrogenolysis of polyolefins.