[en] The adsorption of CH₂O at low-coordinated sites (edge and corner) of MgO (0 0 1) surface has been studied using cluster models in the framework of density functional theory. Two adsorption states of CH₂O, i.e. heterolytically dissociative adsorption and molecular adsorption were found. In the former case, the CH₂O adsorbed over Mg_3C-O_3C pair site was dissociated into two separate subspecies, 'CHO^-' and 'H⁺' through the C-H bond cleavage with rather low activation energy, 4.58 kcal/mol. Due to the quite similarity in adsorption energy, it can be expected that both two adsorption states, namely molecular and dissociative adsorption, should simultaneously exist for CH₂O over Mg_3C-O_3C pair site of MgO (0 0 1) surface. In analogy, for CH₄, C₂H₂ and CH₃OH, the edge and corner sites of MgO (0 0 1) surface exhibit the catalytic reactivity toward the C-H bond cleavage, thus leading to the dissociative subspecies, which was reinforced by the quantum chemical calculations and the respective experiments