Comparative DFT study of methanol decomposition on Mo 2 C(001) and Mo 2 C(101) surfaces

Abstract

Abstract In this study, the complete reaction mechanism of methanol decomposition on metallic Mo2C(001) and Mo/C-mixed Mo2C(101) hexagonal Mo2C crystalline phases was systematically investigated using plane-wave-based periodic density functional theory (DFT). The main reaction route for Mo2C(001) is as follows: CH3OH → CH3O + H → CH2O + 2H → CHO + 3H → CO + 4H → C + O + 4H. Hence, C,O, and H are the main products. It was found that the energy barrier for CO dissociation was low. Therefore, it was concluded that the Mo2C(001) surface was too active to be easily oxidized or carburized. The optimal reaction pathway for Mo2C(101) is as follows: CH3OH → CH3O + H → CH2O + 2H → CH2 + O + 2H → CH3 + O + H → CH4 + O. Therefore, CH4 is the major product. The hydrogenation of CH3 leading to CH4 showed the highest energy barrier and the lowest rate constant and should be the rate-determining step. In addition, the formation of CO + 2H2 was competitive on Mo2C(101), and the optimal path was CH3OH → CH3O + H → CH2O + 2H → CH2 + O + 2H → CH + O + 3H → C + O + 4H → CO + 2H2. The computed energy barrier and rate constant indicate that the rate-determining step is the last step in CO formation. In agreement with the experimental observations, the results provide insights into the Mo2C-catalyzed decomposition of methanol and other side reactions.