(245c) Understanding Nobel Metal Sulfation Using First Principles Computations

Hom N. Sharma¹, V. Sharma², and R. Ramprasad²

¹Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, CT

²Materials Science and Engineering, University of Connecticut, Storrs, CT

Sulfur poisoning augments catastrophic impacts to the noble metal based exhaust aftertreatment catalysts. Sulfur oxides (SO_x) chemisorb onto and react with the active catalyst sites, preventing reactant access and modifying the surface chemistry. Metal-sulfate formation due to the interactions with SO_x with the catalyst metals and supports are associated with changes in various structural, morphological, and electronic properties. In this work, we demonstrate molecular level understanding on sulfur poisoning, which is experimentally observed on Pd-based catalysts but not on Pt-based catalysts in realistic oxidizing/sulfating environment using first principles thermodynamics. In practically relevant temperature and O₂ and SO₃ chemical potentials (or partial pressures), Pt and Pd show significantly different behavior towards oxidation (metal oxide formation) and sulfation (metal sulfate formation). This study revealed a map with various stable phases involving the SO₃ and oxygen on the clean as well as oxidized surfaces and clearly showed the sulfation prone nature of Pd to form PdSO₄.