Insight into the effect of surface coverage and structure over different Co surfaces on the behaviors of H2 adsorption and activation

In this study, in order to identify the effect of surface coverage and structure over Co catalyst on the behaviors of H2 adsorption and activation, the adsorption, dissociation and desorption of H2 at different coverage over the periodic p(3 × 3) Co(0001) and (100) surfaces have been examined over Co catalyst, in which H2 adsorption with the parallel and vertical modes at different sites have been considered. Here, the results are obtained using density functional theory calculations. Our results that H2 adsorption from low to high coverage at the hollow sites over Co surfaces dominantly focus on the dissociative adsorption. Meanwhile, only H2 adsorption with the parallel mode at the top site is the molecular adsorption, which correspond to the saturated coverage of 4/9 and 7/9 ML over Co(0001) and (100) surfaces, respectively; moreover, the dissociations of these molecular adsorption H2 are much more easier to occur rather than their desorption. As a result, H2 dissociative adsorption and the dissociation of molecular adsorption H2 over Co(0001) and (100) surfaces are independent of its surface coverage and structure, namely, when there are the continuous supplies of H2 in syngas conversion, H2 will exist in the form of the dissociative H atoms from low to high coverage over Co surfaces under the realistic condition. Therefore, Co surfaces exhibit good catalytic activity towards the adsorption, activation and dissociations of H2. Our results give out the reasonable explanations for many catalytic systems related to H2 on Co surfaces, in which all studies related to H2 are in the form of H atoms rather than H2 molecule.