Low-Temperature Aqueous Upgrading of Waste PET Plastics into Metal–Organic Frameworks with Confined PdNi Clusters for High-Performance Semihydrogenation of Alkynes

Abstract The selective semihydrogenation of alkynes to alkenes is an important industrial process for the production of bulk and fine chemicals. However, the activity and selectivity trade-off of alkyne hydrogenation has been a long-standing challenge, due to undesirable overhydrogenation or insufficient activity of the designed catalysts. Here, we report a sustainable route for high-performance alkyne hydrogenation using a metal–organic framework (MOF) confined PdNi cluster (PdcNi) catalyst, synthesized directly from waste polyethylene terephthalate (PET) plastics under low-temperature aqueous conditions. The PdcNi@UiO-66 catalyst with dispersed Pd clusters anchored on Ni clusters not only maximizes Pd utilization but also establishes a new pathway for the recycling of plastics. Importantly, when employed as a catalyst for phenylacetylene semihydrogenation, PdcNi@UiO-66 exhibited outstanding activity and selectivity, achieving a turnover frequency (TOF) of up to 67,470 h–1 at 65 °C. This performance significantly surpasses that of previously reported catalysts and is nearly 20 times higher than that of the commercial Lindlar catalyst. DFT calculations combined with experimental results reveal that the PdcNi cluster exhibits a moderate adsorption strength toward both reactants and target products, compared with its nanoparticle and single-atom counterparts. This balanced adsorption leads to a more favorable thermodynamic tendency for styrene desorption rather than overhydrogenation, ultimately contributing to the high activity and selectivity. This study demonstrates a direct route to transforming PET waste into high-performance MOF-based catalysts for selective hydrogenation, offering a cost-effective and sustainable solution for plastic recycling and the development of high-performance catalysts.