Phase-Tuning of Ru Nanostructures in Ru/ZrO ₂ Catalysts for Controlling Radical and Nonradical Pathways of Peroxymonosulfate-Based Oxidation and Defluorination of a Fluorinated Anticancer Drug

This study demonstrates that the catalytic performance of Ru catalysts is strongly influenced by the crystal facets and structures of Ru nanoparticles, with hexagonal close-packed (hcp)-Ru exhibiting superior activity (turnover frequency = 18.1 s⁻¹) compared to face-centered cubic (fcc)-Ru (5.27-10.6 s⁻¹). Notably, the crystalline phase of ZrO₂ (i.e., tetragonal (t-ZrO₂), monoclinic (m-ZrO₂), and mixed phase (mixed-ZrO₂)) preferentially directs the formation of distinct Ru nanostructures, resulting in fcc-Ru/t-ZrO₂, hcp-Ru/m-ZrO₂, and fcc-Ru/mixed-ZrO₂. These Ru nanostructures govern the dominant reaction mechanisms during peroxymonosulfate (PMS)-based oxidation of capecitabine, a fluorinated anticancer drug, where fcc-Ru favors a nonradical pathway involving direct electron transfer, while hcp-Ru mainly facilitates a radical pathway via PMS activation. This mechanistic variation between fcc-Ru and hcp-Ru led to different defluorination routes and degradation pathways. Among these catalysts, hcp-Ru/m-ZrO₂ exhibited a higher F⁻ selectivity (97.6 ± 1.42%) compared to fcc-Ru catalysts (40.9 ± 0.7-67.2 ± 1.2%). Density functional theory calculations further confirmed that the binding energy of Ru nanostructures toward PMS follows the order hcp-Ru > fcc-Ru, indicating that PMS interacts more strongly with hcp-Ru, thereby favoring the SO₄•--dominant pathway. Conclusively, these findings provide mechanistic insights to guide the rational design of catalysts with tailored reaction mechanisms and reactivity by controlling metal nanostructures through the specific crystallinity of the support material.