Theoretical Study on Adsorption and Dissociation of NO<sub>2</sub> Molecule on Fe(111) Surface

We applied periodic density-functional theory (DFT) to investigate the adsorption and dissociation of NO<sub>2</sub> on a Fe(111) surface. The most favorable adsorption configuration of NO<sub>2</sub>/Fe(111) is the FeNO<sub>2</sub>(S-μ<sub>3</sub>-N,O,O′) configuration with NO<sub>2</sub> at the 3-fold-shallow site of the surface, which has an adsorption energy −64.59 kcal/mol. Of two geometries of NO<sub>2</sub>/Fe(111) for the stepwise NO<sub>2</sub> deoxygenation, one is the most stable structure, FeNO<sub>2</sub>(S-μ<sub>3</sub>-N,O,O′), with activation barriers 10.38 and 19.36 kcal/mol to break the first (ON−O bond activation) and second (N−O bond activation) nitrogen−oxygen bonds, respectively; another configuration FeNO<sub>2</sub>(B-μ<sub>2</sub>-N,O) has a smaller energy barrier (3.88 kcal/mol) to break the first ON−O bond. All these findings show that NO<sub>2</sub> can readily decompose on the Fe(111) surface. The rate constants for the two aforementioned processes were also predicted by VTST and RRKM theory, and the predicted total rate constants, <i>k</i><sub>total</sub> (in units of cm<sup>3</sup> molecule<sup>−1</sup> s<sup>−1</sup>), can be represented by the equations <i>k</i><sub>total</sub> = 5.61 × 10<sup>−5</sup><i>T</i><sup>−2.060</sup> exp(−0.639 kcal mol<sup>−1</sup>/<i>RT</i>) at <i>T</i> = 100−1000 K. To acquire insight into the great catalytic activity of the Fe(111) surface for the decomposition of NO<sub>2</sub>, the nature of the interaction between the adsorbate and the substrate is subjected to a detailed electronic analysis.