Selective Hydrocracking of Waste Polyolefins toward Gasoline-Range Liquid Fuels via Tandem Catalysis over a Cerium-Promoted Pt/HY Catalyst

Upcycling of waste plastics into value-added chemicals and fuels represents a promising orientation toward a more sustainable chemical industry. We present a selective process for hydrocracking waste polyolefins into a spectrum of branched gasoline-range C_5-12 hydrocarbons, utilizing a cerium-promoted Pt/HY as a metal-acid bifunctional catalyst. The HY zeolite was engineered with a hierarchical meso/microporosity and moderated acidity to alleviate the overcracking of intermediate hydrocarbons to light C_1-4 gas products. The cerium presented as a surface cerium oxide phase, which mitigated acidity and significantly improved Pt dispersion. Upon a proper metal-acid balance, an optimized yield of C_5-12 up to 85 wt % was achieved from the low-density polyethylene over a cerium-promoted Pt/HY catalyst at 280 °C and 2 MPa H₂ for 2 h. The tandem catalysis was proposed to proceed with an initial dehydrogenation of the polymer chain over Pt sites, with subsequent isomerization and cracking over the Brønsted acid sites and hydrogenation of the olefin intermediates over Pt sites. The strong Pt-O-Ce bridging structure inhibited the migration and agglomeration of Pt atoms, affording good stability and no distinct performance loss over three sequential runs. This process is applicable to the hydrocracking of other polyolefins such as high-density polyethylene, polypropylene, and daily plastic bags to gasoline-range fuels in desirable yields (60-80 wt %).