High-Efficiency Hydrocracking of Polyolefin Plastics by Controlling Intimacy between Pt Clusters and Zeolite Acid Sites.

Hydrocracking of polyolefins using metal-zeolite catalysts offers a promising route for upcycling plastic waste into valuable fuels. However, achieving high-efficiency hydrocracking remains a significant challenge due to the complex depolymerization mechanisms, which hinder the optimization of catalyst structures. Here, we present a novel catalyst design strategy that achieves precise spatial control of Pt and acid sites by strategically positioning Pt clusters on the external surfaces and within the channels of H-Beta (Hβ) zeolite. This synergistic dual-site architecture enables a stepwise reaction pathway: surface Pt-acid sites initiate isomerization and primary cracking to form branched intermediates, which then migrate into the channels, where internal Pt-acid sites drive secondary cracking. This design maximizes the reaction efficiency, achieving unprecedented hydrocracking rates of 30,000 gLDPE·gPt-1·h-1 for low-density polyethylene (LDPE) and 92,000 gPP·gPt-1·h-1 for polypropylene (PP) at 250 °C, surpassing state-of-the-art Pt-based catalysts by 5-fold. Remarkably, a 98% yield of short-chain alkanes is achieved even at a mild temperature of 180 °C, with C5-C12 selectivity about 80%, highlighting the advantage of the catalyst's low-temperature activity and industrial potential. By correlating reaction outcomes with the structural evolution of LDPE/PP, we propose a new isomerization-cracking mechanism that elucidates the critical roles of the surface and internal active sites. This work not only provides a rational design strategy for bifunctional metal-zeolite catalysts but also offers fundamental insights into polyolefin hydrocracking mechanisms, paving the way for scalable and sustainable plastic waste valorization.