High-Coverage CO Adsorption and Dissociation on Ir(111), Ir(100), and Ir(110) from Computations

CO adsorption on the perfect Ir(111) as well as the unreconstructed Ir(100) and Ir(110) surfaces at different coverages has been computed at the level of periodic density functional theory. General agreement between theory and experiment is found in the top adsorption configuration at low coverage (vibrational frequencies) and adsorption patterns at a given coverage (low-energy electron diffraction) as well as saturation coverage (thermal desorption). At the lowest coverage, the computed CO adsorption energy on Ir(111) agrees very well with the experiment [-1.95 vs -1.91 +/- 0.09 eV], whereas large differences are found on Ir(100) [-2.22 vs -2.04 +/- 0.05 and -1.47 eV] and Ir(110) [-2.36 vs -1.61 eV]. The same trend is also found in the CO desorption temperature at the lowest coverage, that is, best agreement on Ir(111) [590 vs 560 K] and large differences on Ir(100) [620 vs 572 K] and Ir(110) [700 vs 620 K], while good agreement at high coverage on all surfaces. At the lowest coverage, CO dissociation has a very high effective barrier and is endothermic, in agreement with the experiment. Our results provide the basis for exploring CO activation and reaction on the Ir surfaces under real conditions.