New insights into adsorption bonding of imidazole: A viable C2–H bond cleavage on copper surfaces

Abstract We show by means of density-functional-theory (DFT) calculations that dissociative adsorption bonding of imidazole is feasible on copper-oxide surfaces, but it differs considerably from that of 1,2,3-triazole and tetrazole (these three molecules can be seen as archetypal models of azole corrosion inhibitors). While for the latter two dissociative adsorption proceeds via the cleavage of the N–H bond leading to a strongly bonded molecule adsorbed upright on the surface with two N atoms, such a mode is unfavorable for imidazole due to its incompatible molecular geometry, because it has the two N atoms on opposite sides of the molecule. Instead, imidazole may adsorb dissociatively via either the cleavage of the C–H bond (in an upright adsorbed geometry) or the cleavage of the N–H bond in a lying down geometry; among the two possibilities, C–H dissociation is thermodynamically superior to the “lying down” N–H dissociation. Calculations further indicate that for triazole and tetrazole the C–H dissociative mode is also viable, because it is similar in stability to the N–H dissociative mode. However, there exists a notable difference between the two dissociation modes: while N–H dissociation of triazole and tetrazole is barrierless (or almost so) at oxygen vacancy sites on copper-oxide surfaces, the respective barrier for C–H dissociation of imidazole is 1.1 eV and is therefore kinetically hindered. We also investigate the C–H dissociation mode of imidazole on zinc and aluminum surfaces. We find that these are less reactive toward molecular C–H bond cleavage in most considered cases, with zinc being moderately less reactive and aluminum considerably less reactive than copper.