Theoretical Study on Adsorption and Dissociation of NO₂ Molecule on Fe(111) Surface

We applied periodic density-functional theory (DFT) to investigate the adsorption and dissociation of NO₂ on a Fe(111) surface. The most favorable adsorption configuration of NO₂/Fe(111) is the FeNO₂(S-μ₃-N,O,O′) configuration with NO₂ at the 3-fold-shallow site of the surface, which has an adsorption energy −64.59 kcal/mol. Of two geometries of NO₂/Fe(111) for the stepwise NO₂ deoxygenation, one is the most stable structure, FeNO₂(S-μ₃-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 FeNO₂(B-μ₂-N,O) has a smaller energy barrier (3.88 kcal/mol) to break the first ON−O bond. All these findings show that NO₂ 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, k_total (in units of cm³ molecule⁻¹ s⁻¹), can be represented by the equations k_total = 5.61 × 10⁻⁵T^−2.060 exp(−0.639 kcal mol⁻¹/RT) at T = 100−1000 K. To acquire insight into the great catalytic activity of the Fe(111) surface for the decomposition of NO₂, the nature of the interaction between the adsorbate and the substrate is subjected to a detailed electronic analysis.