Shape-Selective Conversion of High-Density Polyethylene into Benzene with Zeolite-Encapsulated Subnanometer Pt Catalysts.

Selective conversion of polyolefins into a single value-added chemical can greatly improve the techno-economy of the upcycling process. However, to date, most reported catalytic processes can convert polyolefins into only mixed hydrocarbon or oxygenate compounds. Herein, we have developed a shape-selective catalytic route for converting high-density polyethylene (HDPE) into benzene through a two-step process based on zeolite-confined subnanometer Pt catalysts, including the conversion of HDPE to mixed alkanes through hydrocracking and the subsequent conversion of mixed alkanes to benzene through dehydroaromatization. By constructing neighboring subnanometer Pt clusters and acid sites within β-zeolite, we can achieve the highest specific activity in the hydrocracking of HDPE at a very low Pt loading (∼300 ppm) and high selectivity to liquid alkanes. Furthermore, the liquid alkanes are selectively converted into benzene with ∼45% yield by a PtSn@MFI catalyst in which subnanometer bimetallic PtSn clusters are confined in the MFI zeolite.