Polyethylene Hydrogenolysis at Mild Conditions over Ruthenium on Tungstated Zirconia

Plastics waste has
become a major environmental threat, with polyethylene
being one of the most produced and hardest to recycle plastics. Hydrogenolysis
is potentially the most viable catalytic technology for recycling.
Ruthenium (Ru) is one of the most active hydrogenolysis catalysts
but yields too much methane. Here we introduce ruthenium supported
on tungstated zirconia (Ru-WZr) for hydrogenolysis of low-density
polyethylene (LDPE). We show that the Ru-WZr catalysts suppress methane
formation and produce a product distribution in the diesel and wax/lubricant
base-oil range unattainable by Ru-Zr and other Ru-supported catalysts.
Importantly, the enhanced performance is showcased for real-world,
single-use LDPE consumables. Reactivity studies combined with characterization
and density functional theory calculations reveal that highly dispersed
(WOx)n clusters store H as
surface hydroxyls by spillover. We correlate this hydrogen storage
mechanism with hydrogenation and desorption of long alkyl intermediates
that would otherwise undergo further C–C scission to produce
methane.