Boosting the catalytic performance of metal–zeolite catalysts in the hydrocracking of polyolefin wastes by optimizing the nanoscale proximity†

Abstract

Hydrocracking polyolefins using bifunctional metal–zeolite catalysts is a pivotal strategy for the catalytic upcycling of plastic waste to produce value-added fuels. However, the macro-molecular size and stable C–C bond of polyolefins impose major challenges on catalyst design based on noble metal and microporous zeolites. The lack of investigation into the nanoscale proximity between Pt and USY has hindered the development of an evolving generation of catalysts. Herein, we report Pt/USY prepared by colloid-immobilization method with Pt nanoparticles exclusively located on the surface of USY is a superior catalyst (>50% higher activity) compared to its analogues that have Pt inside or away from USY crystalline, reaching a selectivity to gasoline (C_5–12) over 90%. The formation rate of liquid products reaches 6122 g_liquid g_Pt⁻¹ h⁻¹ and 5048 g_liquid g_Pt⁻¹ h⁻¹ in hydrocracking polyethylene (PE) and polypropylene (PP) at 280 °C, respectively. The hydrocracking of model alkanes with different molecular sizes demonstrates the nanoscale Pt-USY proximity as a key criterion in optimizing the accessibility and acidic environment of Pt, and the diffusion distance between metal and acid sites. These findings comprise a significant step forward toward rational catalyst design aiming at upcycling plastic waste for sustainable fuel production.