First-principles study of decomposition of NH3 on Ir(100)

The adsorption and dissociation of NH3 on Ir(100) have been investigated using the periodic density functional calculations. The recombination desorption of N-2 has also been studied. The corresponding reaction energies, the structure of the transition states and the activation energies were determined. The calculated activation barrier for NHx (x = 1-3) dehydrogenation is between 0.83 and 1.09 eV including the zero point energy correction. The NH3 desorption energy of 0.95 eV is close to the NH3 dehydrogenation barrier of 0.91 eV. which indicates that the desorption and dissociation of NH3 on Ir(100) is very competitive, consistent with the recent experimental results. The N-H bond cleavage in NH3 is found to be the rate limiting step. The activation energy for the recombinative desorption of N-2 is significantly lower than those for the NHx dehydrogenation. Moreover, it was found that the zero point energy has a large contribution to the reaction energies and activation barriers. (c) 2008 Elsevier B.V. All rights reserved.