Density Functional Calculations and IR Reflection Absorption Spectroscopy on the Interaction of SO2 with Oxide-Supported Pd Nanoparticles

A systematic study on the interaction of sulfur dioxide (SO 2 ) on BaO-supported Pd nanoparticles has been carried out using suitable models and state-of-the-art density functional (DF) calculations. Detailed information concerning the structure and energetics of the different conformations of adsorbed SO 2 is provided as a function of coverage together with calculated infrared reflection absorption spectroscopy (IRAS) spectra. SO 2 may adsorb on Pd(111) in several conformations, some active, η 2 -S b O a and η 1 -S b, and others inactive in IRAS, η 3 -S a O a O a . SO 2 is found to attach stronger to Pd nanoparticle edges and corners, a fact intimately related to catalyst poisoning by site blocking. On Pd nanoparticles, SO 2 is found to preferably adopt adsorption conformations that depend on the specific region on the nanoparticle, thus adding site specificity to vibrational recognition. Molecular beam experiments and IRAS have been performed on a single-crystal-based Pd/BaAl 2 x O 1+3 x /NiAl(110) model NO x storage and reduction catalyst and its individual components. SO x formation on the oxide components, evolution of a SO 2 multilayer, and adsorption of SO 2 on BaO or Pd nanoparticles is linked to DF calculations. The effect of cation intermixing in the oxide support and overlap of absorption bands on the unequivocal discrimination of signals are discussed.