Density Functional Studies of the Adsorption and Dissociation of NO(x) (x=1, 2) Molecules on the W(111) Surface

Abstract

Adsorption and dissociation of NOx (x = 1, 2) molecules on the W(111) surface have been investigated by using the density functional theory (DFT) with the projector-augmentcd wave (PAW) approach in periodic boundary conditions. The adsorption structures, vibrational frequencies, and binding energies of NO(2), NO, N, and 0 on the W(111) surface were predicted. It was shown that the most favorable adsorption geometry of W(111)/NO(2) is the WNO(2) (IV-mu(3)-N2, OI, OI) configuration with NO(2) at the 3-fold-shallow site of the surface and has an adsorption energy of 79.4 kcal/mol. For W(111)NO, WNO(II-mu(2)-N1, O1) with NO at the bridge site is energetically the most favorable one and has an adsorption energy of 74.4 kcal/mol. The N and 0 atoms are bound preferentially at the bridge and top sites, respectively. The potential energy profiles for the decomposition of NO(2) on W(111) were constructed using the nudged elastic band (NEB) method. The barriers for the stepwise NO(2)-deoxygenation process to N((ads)) + 20((ads)) are calculated to be only 0.5-3.7 (for the first step of the reaction, ON-O bond activation) and 0.2-3.0 (for the second step of the reaction, N-O bond activation of the coordinated NO molecule) kcal/mol, with an overall exothermicity of 177.0-185.2 kcal/mol. These findings show that NO,) can easily decompose on the W(111) surface. The rate constants for NO(2) and NO dissociation on the surface were also predicted.