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 NO(2) on a Fe(111) surface. The most favorable adsorption configuration of NO(2)/Fe(111) is the FeNO(2)(S-mu(3)-N,O,O') configuration with NO(2) at the 3-fold-shallow site of the surface, which has an adsorption energy -64.59 kcal/mol. Of two geometries of NO(2)/Fe(111) for the stepwise NO(2) deoxygenation, one is the most stable structure, FeNO(2)(S-mu(3)-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(2)(B-mu(2)-N,O) has a smaller energy barrier (3.88 kcal/mol) to break the first ON-O bond. All these findings show that NO(2) 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 cm(3) molecule(-1) s(-1)), can be represented by the equations k(total) = 5.61 x 10(-5)T(-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 NO(2), the nature of the interaction between the adsorbate and the substrate is subjected to a detailed electronic analysis.