Abstract: : MnO_x–CeO₂ catalysts for the low-temperature selective catalytic reduction (SCR) of NO remain vulnerable to water and sulfur poisoning, limiting their practical applications. Herein, we report a hydrophobic-modified MnO_x–CeO₂ catalyst that achieves enhanced NO conversion rate and stability under harsh conditions. The catalyst was synthesized by decorating MnO_x crystals with amorphous CeO₂, followed by loading hydrophobic silica on the external surfaces. The hydrophobic silica allowed the adsorption of NH₃ and NO and diffusion of H, suppressed the adsorption of H₂O, and prevented SO₂ interaction with the Mn active sites, achieving selective molecular discrimination at the catalyst surface. At 120°C, under H₂O and SO₂ exposure, the optimal hydrophobic catalyst maintains 82% NO conversion rate compared with 69% for the unmodified catalyst. The average adsorption energies of NH₃, H₂O, and SO₂ decreased by 0.05, 0.43, and 0.52 eV, respectively. The NO reduction pathway follows the Eley-Rideal mechanism, NH₃* + * → NH₂* + H* followed by NH₂* + NO* → N₂* + H₂O*, with NH₃ dehydrogenation being the rate determining step. Hydrophobic modification increased the activation energy for H atom transfer, leading to a minor decrease in the NO conversion rate at 120°C. This work demonstrates a viable strategy for developing robust NH₃-SCR catalysts capable of efficient operation in water- and sulfur-rich environments.