Coadsorption of CO and H on Fe(100)

A DFT model of the Fe(100) surface was used to study the coadsorption of CO and hydrogen. Various coverages of CO and hydrogen were considered with resulting H:CO ratios ranging from 0.25 to 4. Electrostatic repulsive interactions exist between the adsorbed CO and H as well as an electronic interaction which can have a stabilizing effect on the coadsorbed geometry. A number of geometries at both 0.25 and 0.5 ML of CO coverage are stable in a mixed coadsorbed state as opposed to island formation. This is due to the relative instability of the corresponding compressed CO and H islands. For these mixed states the optimal surface H:CO ratios for circle minus(CO) = 0.5 ML and circle minus(CO) = 0.25 ML are 1 and 3 respectively.