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

Abstract

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-SOx 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.