(465c) Sulfur Deactivation Pathways in Cu-SSZ-13 Determined through First-Principle Modeling and X-Ray Spectroscopy
The interaction between Cu active sites and sulfur-containing species with variable O/H/N stoichiometry (SOxHyNz) was explored by thermodynamic phase diagrams. We used AIMD simulation to explore molecular configurations of the adsorbate and picked lowest energy snapshots for structure optimizations. The potential of mean force method was used to calculate adsorption entropies of SOxHyNz on Cu sites. The phase diagrams show that ammonium sulfate and ammonium bisulfate are thermodynamically favorable below 600 K for a range of experimental conditions. Two Cu-SSZ-13 samples, containing either Z2Cu or ZCuOH sites, were synthesized in lab  and exposed to dry SO2 and O2 at variable temperatures to simulate accumulated sulfur poisoning in actual catalytic converters. We performed ex situ and in situ X-ray spectroscopy on the sulfated samples and analyzed the near edge structure (XANES) region of the spectra. Oxidation states elucidated from both Cu K-edge XANES and S K-edge XANES were consistent with the conclusion from first-principle studies. The difference in poisoning species on the two types of Cu sites suggested the possibility of designing a more sulfur-resistant catalyst.
 Kumar, A., Smith, M., Kamasamudram, K., Currier, N.W., An, H., Yezerets, A.. Catal. Today. 231, 75 (2014).
 Paolucci, C., Parekh, A.A., Khurana, I., Di Iorio, J.R., Li, H., Albarracin Caballero, J.D., Shih, A.J., Anggara, T., Delgass, W.N., Miller, J.T., Ribeiro, F.H., J. Am. Chem. Soc. 138, 18 (2016).