Yunchao Feng

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.

Liquid organic hydrogen carriers (LOHCs) are considered promising carriers for large-scale H₂ storage and transportation, among which the toluene-methylcyclohexane cycle has attracted great attention from industry and academia because of the low cost and its compatibility with the current infrastructure facility for the transportation of chemicals. The large-scale deployment of the H₂ storage/transportation plants based on the toluene-methylcyclohexane cycle relies on the use of high-performance catalysts, especially for the H₂ release process through the dehydrogenation of methylcyclohexane. In this work, we have developed a highly efficient catalyst for MCH dehydrogenation reaction by incorporating subnanometer PtFe clusters with precisely controlled composition and location within a rigid zeolite matrix. The resultant zeolite-encapsulated PtFe clusters exhibit the up-to-date highest reaction rate for dehydrogenation of methylcyclohexane to toluene, very high chemoselectivity to toluene (enabling the production of H₂ with purity >99.9%), remarkably high stability (>2000 h) and regenerability over consecutive reaction-regeneration cycles.

A fundamental understanding of the active sites in working catalysts can guide the rational design of new catalysts with improved performances. In this work, we have followed the evolution of homogeneous and heterogeneous Pd catalysts under the reaction conditions for aerobic oxidative coupling of toluene for the production of 4,4′-bitolyl. We have found that subnanometer Pd clusters made with a few Pd atoms are the working active sites in both homogeneous and heterogeneous catalytic systems. Moreover, water can promote the activity of Pd clusters by nearly one-order magnitude for oxidative coupling reaction by facilitating the activation of O₂. These new insights lead to the preparation of a catalyst made with Pd clusters supported on a two-dimensional zeolite, which expands the scope of the oxidative coupling of aromatics to larger substrates.