posted on 2023-12-09, 14:06authored byManav Chauhan, Neha Antil, Bharti Rana, Naved Akhtar, Chhaya Thadhani, Wahida Begum, Kuntal Manna
Upcycling nonbiodegradable plastics such as polyolefins
is paramount
due to their ever-increasing demand and landfills after usage. Catalytic
hydrogenolysis is highly appealing to convert polyolefins into targeted
value-added products under mild reaction conditions compared with
other methods, such as high-temperature incineration and pyrolysis.
We have developed three isoreticular zirconium UiO-metal–organic
frameworks (UiO-MOFs) node-supported ruthenium dihydrides (UiO-RuH2), which are efficient heterogeneous catalysts for hydrogenolysis
of polyethylene at 200 °C, affording liquid hydrocarbons with
a narrow distribution and excellent selectivity via shape-selective
catalysis. UiO-66-RuH2 catalyzed hydrogenolysis of single-use
low-density polyethylene (LDPE) produced a C12 centered narrow bell-shaped
distribution of C8–C16 alkanes in >80% yield and 90% selectivity
in the liquid phase. By tuning the pore sizes of the isoreticular
UiO-RuH2 MOF catalysts, the distribution of the products
could be systematically altered, affording different fuel-grade liquid
hydrocarbons from LDPE in high yields. Our spectroscopic and theoretical
studies and control experiments reveal that UiO-RuH2 catalysts
enable highly efficient upcycling of plastic wastes under mild conditions
owing to their unique combination of coordinatively unsaturated single-site
Ru-active sites, uniform and tunable pores, well-defined porous structure,
and superior stability. The kinetics and theoretical calculations
also identify the C–C bond scission involving β-alkyl
transfer as the turnover-limiting step.