Novel\nInsight into\nthe Synergistic Mechanism for Pd\nand Rh Promoting the Hydro-Defluorination of 4‑Fluorophenol\nover Bimetallic Rh–Pd/C Catalysts

This\nstudy explores the synergistic effect between the\nRh and Pd\nof bimetallic Rh–Pd/C catalysts for the catalytic hydro-defluorination\n(HDF) of 4-fluorophenol (4-FP). It was found that 4-FP could not be\nefficiently hydro-defluorinated over 6% Pd/C and 6% Rh/C due to the\ninherent properties of Pd and Rh species in the dissociation of H<sub>2</sub> and the activation of C–F bonds. Compared with 6%\nPd/C and 6% Rh/C, bimetallic Rh–Pd/C catalysts, especially\n1% Rh–5% Pd/C, exhibited much higher catalytic activity in\nthe HDF of 4-FP, suggesting that the synergistic effect between the\nRh and Pd of the catalyst was much more positive. Catalyst characterizations\n(BET, XRD, TEM, and XPS) were introduced to clarify the mechanism\nfor the synergistic effect between the Rh and Pd of the catalyst in\nthe HDF reaction and revealed that it was mainly attributed to the\nbifunctional mechanism: Pd species were favorable for the dissociation\nof H<sub>2</sub>, and Rh species were beneficial to the activation\nof C–F bonds in the HDF reaction. Meanwhile, the interaction\nbetween Rh and Pd species enabled Rh and Pd to exhibit a more positive\nsynergistic effect, which promoted the migration of atomic H* from\nPd to Rh species and thus enhanced the HDF of 4-FP. Furthermore, 1%\nRh–5% Pd/C prepared using 20–40 equiv NaBH<sub>4</sub> exhibited the best performance in the catalytic HDF of 4-FP. Catalysis\ncharacterizations suggested that appropriate Rh<sup>3+</sup>/Rh<sup>0</sup> and Pd<sup>2+</sup>/Pd<sup>0</sup> ratios were beneficial\nto the dissociation of H<sub>2</sub> and the activation of C–F\nbonds, which caused the more positive synergistic effect between the\nRh and Pd of Rh–Pd/C in the HDF reaction. This work offers\na valuable strategy for enhancing the performance of catalytic HDF\ncatalysts via promoting synergistic effects.