Ru nanoparticles encapsulated in defective UiO-66def for the hydrogenation of benzene rings in polyethylene terephthalate degraded chemicals

Abstract

Selective hydrogenation of polyethylene terephthalate (PET) degraded products is vital for the upcycling of waste PET to value-added products. In this work, a versatile Ru@UiO-66_def catalyst was synthesized via in situ growth of Ru nanoparticles (NPs) encapsulated in defective UiO-66_def, and tested in selective hydrogenation of PET-degraded dimethyl terephthalate (DMT) to dimethyl cyclohexane-1,4-dicarboxylate (DMCD). Characterization experiments disclosed that Ru@UiO-66_def possessed mesoporous channels (3.17 and 3.79 nm), enlarged surface area and pore volume (1050 m² g⁻¹ and 0.66 cm³ g⁻¹, respectively), sufficient acidity (480 μmol g⁻¹), strengthened interactions between Ru species and Zr–O nodes, and high dispersion of Ru NPs (38.8%). In particular, the conversion of DMT and selectivity of DMCD over Ru@UiO-66_def reached 96.1% and 98.3% at 150 °C, 3 MPa H₂ and n(DMT)/n(Ru) = 427 mol mol⁻¹ within 2 h. And, Ru@UiO-66_def could be recycled at least five times without obvious loss of activity. Moreover, Ru@UiO-66_def showed high efficiency for the hydrogenation of benzene rings in various PET-degraded products including bis(2-hydroxyethyl) terephthalate (BHET), diethyl terephthalate (DET), and terephthalic acid (TPA). The possible reaction mechanism was discussed based on the experiment results and density functional theory (DFT) calculations.