Hydrogenolysis\nof Polyethylene by Metal–Organic\nFramework Confined Single-Site Ruthenium Catalysts

Upcycling polyolefins into value-added hydrocarbons via\ncatalytic\nhydrogenolysis is challenging due to poor product selectivity, random\nC–C bond cleavage, and the formation of volatile alkanes. We\nhave developed two isoreticular porous aluminum metal–organic\nframework (MOF) node-supported mononuclear ruthenium dihydride catalysts\n(DUT-5-RuH<sub>2</sub> and MIL-53-RuH<sub>2</sub>), which are efficient\nin the hydrogenolysis of low-density polyethylene (LDPE) at 200 °C\ninto a narrow distribution of liquid hydrocarbons (C8-C24). By systematic\ntuning of the pore sizes of the MOFs, high yields of desirable liquid\nalkanes were afforded with varying degrees of branching, achieving\n80% selectivity. DUT-5-RuH<sub>2</sub> produced a C22-centered bell-shaped\nalkane distribution with a polyethylene conversion of 98%, while MIL-53-RuH<sub>2</sub>, being selective for shorter alkanes, produced a C9-centered\nbell-shaped alkane distribution. Based on our spectroscopic and theoretical\nstudies, the high catalytic activity and selectivity of these MOF\ncatalysts are primarily attributed to the stabilization of single-site\nmono-RuH<sub>2</sub> species at the MOF’s nodes via active-site\nisolation and the confinement of the active catalytic species within\nporous MOFs. Theoretical calculations suggest that RuH<sub>2</sub>-mediated polyolefin C–C bond cleavage primarily occurs via\nturnover-limiting σ-bond metathesis. This study underscores\nthe significance of MOFs in the rational design of heterogeneous catalysts\nfor the efficient upcycling of plastic waste.