In Situ-Formed Tridentate Pd–SOx Coordination for Sulfur-Tolerant CO Oxidation Catalysis

SO₂ impurity, widely existing in industrial exhaust, is a typical deactivator in many catalytic reactions. The poisoning mechanism of SO₂ on the active sites of catalysts has been well acknowledged, yet the role of support in sulfur-tolerant catalysis remains elusive. Herein, TiO₂, Al₂O₃, and CeO₂ carriers were selected to unveil the sulfur resistance mechanism of Pd-based catalysts in catalytic CO oxidation. We showed that Pd/TiO₂ effectively terminated continuous sulfidation, achieving 100% CO conversion at 175 °C for 200 h under SO₂ and H₂O exposure. This exceptional sulfur tolerance was attributed to the formation of a distinct tridentate sulfate structure on the PdO nanoparticles, facilitated by the moderate reducibility and strong acidity of Pd/TiO₂. In contrast, Pd/Al₂O₃ and Pd/CeO₂ remained only ∼70 and 5% efficiency, accompanied by the abundant formation of Pd-related bidentate and Ce-related tridentate sulfate species, respectively. Combined experimental and theoretical analyses revealed the distinct in situ-formed tridentate Pd-SO_x coordination over Pd/TiO₂ regulated the local electronic distribution, effectively mitigating the affinity of the catalyst to SO₂ while preserving the redox capability and reactivity of oxygen species. Our findings are crucial for advancing sulfur-tolerant catalysis, offering valuable strategies for rationally designing robust catalysts to overcome both economic and environmental challenges in industrial applications.