The formation mechanisms of CH3O by CH3OH on clean and oxygen-precovered CuO(1 1 1) surface are studied using density functional theory within the generalized gradient approximation. Possible reaction paths including the geometry and the activation barriers are determined. The calculations demonstrate that the specific structure of oxygen on CuO(1 1 1) plays an important role in the formation of CH3O. Comparing with clean CuO(1 1 1) surface, the introduction of oxygen atom reduces the activation barrier of O-H bond-cleavage. The calculated results show that the O-H bond-cleavage path has the lowest activation barrier 29.97 kJ mol(-1). But the activation barriers of the C-O bond cleavage on oxygen-precovered CuO(1 1 1) surface is 272.86 kJ mol(-1), which indicated that the O-H bond cleavage on the oxygen-precovered CuO(1 1 1) surface is the most possible pathway. Meanwhile, the calculated results give a clear illustration about the formation mechanism of CH3O in the presence of oxygen and the role of oxygen at the microscopic level. (C) 2014 Elsevier B.V. All rights reserved.