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

In this study, the complete reaction mechanism of methanol decomposition on metallic Mo 2 C(001) and Mo/C-mixed Mo 2 C(101) hexagonal Mo 2 C crystalline phases was systematically investigated using plane-wave-based periodic density functional theory (DFT). The main reaction route for Mo 2 C(001) is as follows: CH 3 OH → CH 3 O + H → CH 2 O + 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 Mo 2 C(001) surface was too active to be easily oxidized or carburized. The optimal reaction pathway for Mo 2 C(101) is as follows: CH 3 OH → CH 3 O + H → CH 2 O + 2H → CH 2  + O + 2H → CH 3  + O + H → CH 4  + O. Therefore, CH 4 is the major product. The hydrogenation of CH 3 leading to CH 4 showed the highest energy barrier and the lowest rate constant and should be the rate-determining step. In addition, the formation of CO + 2H 2 was competitive on Mo 2 C(101), and the optimal path was CH 3 OH → CH 3 O + H → CH 2 O + 2H → CH 2  + O + 2H → CH + O + 3H → C + O + 4H → CO + 2H 2 . 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 Mo 2 C-catalyzed decomposition of methanol and other side reactions.