Dissociative adsorption of azoles on Cu(111) promoted by chemisorbed O and OH

Metal surfaces are usually either oxidized or at least covered with species such as O and OH under ambient conditions. We show by DFT calculations that chemisorbed O and OH species promote deprotonation of azole molecules on copper surfaces, as exemplified herein by imidazole, benzotriazole, and Cu(111). Deprotonation involves the N–H bond cleavage, although imidazole can also deprotonate via the C–H cleavage. Calculated deprotonation activation energies are considerably smaller for the cleavage of the N–H bond (0.01 eV for benzotriazole and about 0.1 eV for imidazole) than for the cleavage of the C–H bond (from 0.6 to 0.9 eV for imidazole), although the cleavage of C–H bond is thermodynamically preferred for imidazole. Deprotonation reaction energies do not depend strongly on the coverage of O and OH, and for coverages from 1/16 to 1/4 ML, reaction energies typically alter by about ±0.1 eV. The importance of molecular deprotonation upon adsorption is in higher stability of the resulting adsorption states, which increases the persistence of chemisorbed molecules. In particular, deprotonated benzotriazole molecules are by about 1 eV more stable on O/Cu(111) and OH/Cu(111) compared to an adsorbed intact molecule on bare Cu(111). In contrast, for imidazole, the magnitude of such stabilization is significantly weaker (from 0.3 to 0.7 eV).