Methanol formation by catalytic hydrogenation of CO2 on a nitrogen doped zinc oxide surface: an evaluative study on the mechanistic pathway by density functional theory

An investigation of the nature of adsorption of H2O and CO2 on a nitrogen doped zinc oxide cluster surface and the resultant reaction between them has been performed using hybrid density functional theory (DFT) calculations at the B3LYP level of theory in a vacuum. The stable chemisorption modes of CO2 and H2O on metal, oxygen and nitrogen sites were examined. The calculated adsorption energies reveal that the formation of CO2- attached to N is the most favorable process for CO2 on the Zn18O17:N cluster surface, with a binding energy of -1.86 eV. The water molecule spontaneously dissociates on the same surface to produce chemisorbed H* and *OH with an interaction energy of -0.77 eV. The model calculations rationalize the hydrogenation of CO2 by H-2 generated from H2O on the cluster surface. Thermodynamically favorable reaction pathways for the formation of methanol on the catalytic surface in a vacuum were proposed. Among the three pathways, methanol formation follows the carbamate route. The carbamate formed undergoes hydrogenation to generate COOH* units, followed by its exothermic decomposition to *CO attached to N and *OH. Further hydrogenation of CO ultimately yields methanol. All of the above steps were computationally evaluated.