Understanding of CO oxidation reaction by molecular and atomic oxygen on Cu19 cluster using the density functional theory

In this work, we present the CO oxidation by molecular and atomic oxygen on the Cu₃ site of the Cu₁₉ cluster employing the density functional theory (DFT)-PW91PW91/[LANL2DZ, 6-31G(d)] level. The computed results demonstrate that the O atom, O₂, and CO molecule adsorptions on the copper cluster are all chemical. For the CO oxidation by O₂ molecules that leads to the formation of C–O bonds and the dissociation of O–O bonds, the Langmuir–Hinshelwood (LH) mechanism is preferred. On the other hand, the Eley–Rideal (ER) mechanism is slightly favored by the oxidation of CO by atomic oxygen. According to the intrinsic reaction coordinate (IRC) calculation, the activation energy for CO oxidation is 4.02 kcal/mol for molecular oxygen and 3.17 kcal/mol for atomic oxygen. Therefore, molecular and atomic oxygen are very reactive for CO oxidation on the Cu₁₉ cluster. To check the applicability of the global hardness response (GHR) profile satisfying the maximum hardness principle along the IRC in the metal cluster reactions, the GHR profile for the oxidation reaction of CO with molecular oxygen and atomic oxygen was computed. The results indicate that this meets the principle of maximum hardness, effectively showcasing the use of DFT methods to analyze the global hardness profile using frontier molecular orbital energy in the context of metal cluster reaction pathways.

Graphical abstract

The CO oxidation by molecular and atomic oxygen on the Cu₃ site of the Cu₁₉ cluster employing the density functional theory has been studied. The results show that the CO oxidation by atomic oxygen slightly favors the Eley–Rideal (ER) mechanism, while the CO oxidation by molecular oxygen prefers the Langmuir–Hinshelwood (LH) mechanism. Both molecular and atomic oxygen are very reactive for CO oxidation. Furthermore, the global hardness profile along the intrinsic reaction coordinate follows the maximum hardness principle.