Mechanism of coverage dependent CO adsorption and dissociation on the Mo(100) surface.

The mechanism of coverage dependent CO adsorption and dissociation on the Mo(100) surface was investigated using periodic density functional theory. Structure optimization and frequency calculation were carried out using the GGA-PBE method and a p(3 × 3) supercell model. Energetic data have been obtained using the revised PBE method and the PBE optimized structures. CO adsorption prefers tilted adsorption configuration at the 4-fold hollow sites at low coverage and tilted and atop configurations at high coverage. The computed C-O stretching frequencies of the tilted and atop adsorbed CO molecules agree very well with the experimental results. Starting from the saturation coverage, five binding states have been found: two for molecular (α) CO adsorption and three for dissociative (β) CO adsorption, which are in agreement with the temperature-programmed desorption experiments. In addition, CO prefers dissociation with very low barriers in all coverages as long as free sites are available and is coverage independent; this nicely explains the observed CO dissociation at very low temperatures. All such agreements validate our computational methods and provide the basis of further studies.