H2O and CO coadsorption on Co (0001): The effect of intermolecular hydrogen bond

The co-adsorption of CO and H2O on a Co(0001) surface at 100 K has been systematically studied using temperature programmed desorption (TPD) and density functional theory (DFT) calculations. While the TPD spectra of CO is almost not affected by the presence of H2O, the stabilization of H2O by co-adsorbed CO is found for the first time in a large coverage range (0.15 ML < theta(co) < 0.66 ML; 0.01 ML < theta(H2O) < 0.6 ML). When the coverage of predosed CO is lower than 0.27 ML, the formerly single desorption peak of H2O is gradually separated into three peaks at 0.6 ML coverage. Those at lower and higher temperatures may be attributed to the repulsive interaction between H2O molecules and the attractive interaction between H2O and CO molecules, respectively. With increasing the coverage of predosed CO, not only the position of the high temperature peak shifts toward higher temperature (by about 15 K), but the intensity is greatly strengthened until a maximum is achieved when theta(co) = 0.36 ML. DFT calculations suggest that the attractive interaction between H2O and CO on Co(0001) originates from the formation of intermolecular hydrogen bonds. This work not only provides insights into water gas shift reactions with H2O and CO as reactants, but opens new avenues for a volume of catalytic process of technological importance.