Chemisorption of oxygen and subsequent reactions on low index surfaces of β–Mo2C: Insights from first-principles thermodynamics and kinetics

• The (1 0 0), (0 0 1) (0 1 0), (1 1 0) and (1 1 1) surfaces can be fully oxidized by O2.
• With increasing O coverage, the portion of the (1 1 1) surface increased largest.
• CO desorption is more favorable at saturated oxygen coverage than low coverage.
• O diffusion to carbon vacancy is always favorable for the (0 1 1) and (1 0 1) surfaces.

Oxygen chemisorption on β–Mo2C surfaces, the subsequent CO/CO2 desorption and oxygen diffusion to the carbon vacancy have been investigated by density-functional theory. The most stable structures together with the energetics of oxygen stepwise adsorption, CO/CO2 desorption and oxygen diffusion to the carbon vacancy were identified. We examined the effect of oxygen coverage on the morphology of β–Mo2C by plotting the equilibrium crystal shape. Thermodynamic effect of temperature and reactant or product pressure on the CO/CO2 desorption were investigated. The CO/CO2 desorption is more favorable at the saturated oxygen coverage than the low oxygen coverage thermodynamically. The subsequent oxygen diffusion to the carbon vacancy after CO/CO2 desorption may happen depending on the surfaces and oxygen coverage.

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