Density Functional Study of the Reaction of SO2 on Ir(111)

Abstract

The reaction of SO2 on Ir(111) has been systematically studied using self-consistent periodic density functional theory. Adsorptions of the reactants, intermediates, and products involved are calculated. In all possible adsorption modes of SO2, the parallel adsorption (η1(S)-η1(O)-η1(O)) is found to be the most favorable. Intermediate SO is also preferable for parallel adsorption. S and O are exclusively adsorbed at 3-fold sites. The oxidation product SO3 has two stable adsorption modes without any preference, i.e., η1(O)-η1(O)-η1(O) (crown) and η1(S)-η1(O)-η1(O) (chair). In the absence of oxygen, the disproportionated reaction, 3SO2 → S + 2SO3, is initiated by SO2 dissociation into SO and atomic O; then SO quickly decomposes into S and O; and lastly, the O atoms formed in the SO2 and SO dissociation are rapidly exhausted by other SO2. The fast reductions of SO and O accord well with the fact that they were not detected in the experiment [Fujitani, Nakamura, Kobayashi, Takahashi, Haneda, Hamada Surf. Sci. 2007, 601, 1615]. Further reaction of SO3 is expected to take place at high temperatures because of the high energy barriers involved (at least 2.06 eV), also in agreement with the experimental finding.