<p>Current catalytic materials and processes designed for water treatment face a significant challenge in balancing reactivity and stability. Catalysts with initially high reactivity often lack long-term stability under environmentally relevant conditions, limiting their advancement toward practical application. In this study, we demonstrate that spatial confinement of catalysts at angstrom scale can significantly enhance the stability of iron oxyfluoride (FeOF), a highly efficient catalyst for advanced oxidation. We fabricate a catalytic membrane by intercalating FeOF catalysts between layers of graphene oxides. In flow-through operation, the catalytic membrane maintains near-complete removal of model pollutants, neonicotinoids, for over two weeks by effectively activating H₂O₂ to generate ^•OH. Catalyst deactivation is significantly mitigated by spatially confining fluoride ions leached from the catalyst, which is identified as the primary cause of catalytic activity loss. The angstrom-scale membrane channels effectively reject the majority of natural organic matter via size exclusion, thereby preserving radical availability and sustaining pollutant degradation under practical conditions. This innovative strategy for enhancing catalyst stability can be potentially applied to other existing catalysts developed for water treatment applications.</p>