Remarkable SO₂ and H₂S Resistant Ability on CO Oxidation by Unique Pd/WO₃ 3D Hollow Sphere Nanocatalyst: Correlating Structure–Activity Relationships on SO₂ Exposure

We report a simple inorganic route for synthesizing a Pd/WO 3 3D hollow sphere nanocatalyst, where Pd nanoparticles are encapsulated and well distributed on porous tungsten oxide nanospheres. The synthesis protocol has advantages, as it requires no surfactant or stabilizing agent, Pd loading is easily tuned, and the as-synthesized nanomaterials can be directly used as catalysts for the CO oxidation reaction. The synthesized nanocatalyst exhibited 100% CO to CO 2 conversion efficiency at 260 °C. In addition, the nanocatalyst demonstrated remarkable SO 2 (3 ppm) tolerance during the CO oxidation reaction for prolonged SO 2 sulfation of 1–21 h at 260–400 °C. This represents the longest SO 2 exposure time reported to date based on a single metal Pd/support-based nanocatalyst. No decrement in CO conversion efficiency was observed even after SO 2 (3 ppm) treatment for 21 h for the first time based on a single metal Pd-based nanocatalyst. Moreover, the synthesized nanocatalyst shows H 2 S (4 ppm), even in situ H 2 S tolerance during the CO oxidation reaction at 260 °C for 1–3 h and exhibited less sensitivity to prolonged and stringent sulfur exposure, with the highest H 2 S concentration and maximum 100% CO to CO 2 conversion efficiency obtained after H 2 S treatment for the first time based on a Pd-based nanocatalyst to the best of our knowledge. The composition and structure of the R-Pd/WO 3 nanocatalyst were not much influenced, even after the prolonged SO 2 and H 2 S exposure during the CO oxidation reaction, as verified from spent catalyst analysis. Finally, our DFT-based model provides insights into understanding the observed sulfur resistance on Pd/WO 3 by analyzing the underlying electronic structure. Therefore, our strategic synthesis methodology will open up many opportunities to select Pd/metal oxide-based nanomaterials for designing highly efficient, stable, and SO 2 /H 2 S-resistant nanocomposite catalyst.