Catalytic Hydrogenation Removal of Typical Halophenol Odorous Substances by Palladium Catalysts Confined in UiO-66
Halophenols are highly toxic disinfection byproducts and common taste-and-odor pollutants in drinking water. In this study, a palladium catalyst confined within the pores of UiO-66 (Pd@UiO-66) was prepared via a double-solvent method and applied for the catalytic hydrodechlorination of 4-chlorophenol (4-CP). A surface-supported catalyst (Pd/UiO-66) was synthesized by deposition-precipitation as a benchmark. Comprehensive characterization using ICP-OES, XRD, TEM, EDX mapping, XPS, and in situ CO-IR revealed that Pd@UiO-66 exhibited smaller Pd particle sizes, higher Pd dispersion, and a greater proportion of cationic Pd species (Pdn+) compared to Pd/UiO-66. These features enhanced the activation and cleavage of the C–Cl bond. Catalytic tests demonstrated that Pd@UiO-66 achieved >90% removal of 4-CP within 15 minutes, with phenol as the sole degradation product, showing significantly lower predicted toxicity (ECOSAR) than the parent compound. The kinetics followed the Langmuir-Hinshelwood model. Pd@UiO-66 exhibited 2.1 times higher initial activity and 1.2 times higher turnover frequency than Pd/UiO-66. Moreover, the pore confinement effect imparted high stability, with no significant loss in initial activity (within 10%) after five reaction cycles. These results highlight the potential of confined Pd catalysts for efficient removal of halophenolic odorants from water.