Reactive Oxygen Species on the (100) Facet of Cobalt Spinel Nanocatalyst and their Relevance in 16O2/18O2 Isotopic Exchange, deN2O, and deCH4 Processes—A Theoretical and Experimental Account

Abstract

Periodic spin unrestricted, gradient corrected DFT calculations joined with atomistic thermodynamic modeling and experiment were used to study the structure and stability of various reactive oxygen species (ROS) and oxygen vacancies produced on the most stable terminations of the cobalt spinel (100) surface. The surface state diagram of oxygen in a wide range of pressures and temperatures was constructed for coverage varying from ΘO = 1.51 atom·nm–2 to ΘO = 6.04 atom·nm–2. A large variety of the unraveled surface ROS includes diatomic superoxo (CoO–O2––CoO), peroxo (CoT–O22––CoO), and spin paired (CoO–O2–CoO) adducts along with monatomic metal-oxo (CoT–O+, CoO–O2+) species, where CoT and CoO stand for the tetrahedral and octahedral cobalt surface centers, respectively. There are also two kinds of peroxo species associated with surface oxygen ions connected with 3CoO or 2CoO and 1CoT cations ((O2O,1T–O)2– and (O3O–O)2–), respectively). The results revealed that in the oxygen pressure range of typical catal...