CO oxidation over defective and nonmetal doped MoS2 monolayers

Abstract

Defective (missing S atoms) and nonmetal (C- and N-) doped MoS2 monolayers in the 2H and 1T′ phases have been evaluated for catalyzing CO oxidation based on first-principles calculations. For the reaction 2CO + O2 → 2CO2, the oxidization of the first CO molecule is fairly easy and sometimes is even spontaneous, as the O2 molecule is highly activated or dissociates upon adsorption. However, for the defective (2H-), C-doped (1T′-), and N-doped (2H- and 1T′-) MoS2 monolayers, the remaining O* adatom often refuses to react with other CO molecules and is hard to be removed (barrier > 1.20 eV). Only when over the C-doped 2H- and defective 1T′-MoS2 monolayers, the removal of the second O* adatom requires to overcome moderate barriers (0.74 and 0.88 eV, respectively) by reacting with another CO molecule via the Eley–Rideal mechanism and the catalysts are recovered. The barriers can be further reduced by applying either tensile or compressive strain to the MoS2 nanosheet. In contrast, the Langmuir–Hinshelwood mechanism is followed over the metal-containing MoS2 nanosheets, as the bigger size of metal dopants allow the co-adsorption of CO and O2. Therefore, the C-doped 2H- and defective 1T′-MoS2 monolayers are promising nonmetal-doped catalysts for CO oxidation.