The use of methane as one of the cleanest energy sources has attracted significant public awareness, and methane production processes with less environmental impact than fracking are receiving considerable attention. Catalytic hydrocracking of plastic materials has been considered a potential clean alternative. However, catalysts that convert heterogeneous plastic feeds into a single product under industrially relevant conditions are lacking. Here, we describe a Ru-modified zeolite that catalytically transforms polyethylene, polypropylene, and polystyrene into grid-compatible methane (>97% purity), at 300 degrees C-350 degrees C using near-stoichiometric amounts of H-2. Mechanistic studies reveal a chain-end initiation process with limited isomerization of plastic substrates. A Ru site-dominant mechanism is proposed based on these studies and density functional theory (DFT) computations. We foresee that such a plastic-to-methane process may increase the intelligent use of plastic waste via energy recovery. There is also the potential to accommodate emerging sustainable H-2 production into existing natural gas networks, while integrating waste management, fuel production, and energy storage.