Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo₂C (001) Surface: A Density Functional Theory Study

Density functional theory (DFT) calculations were used to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O∗) from the Mo-terminated (T_Mo) and C-terminated (T_C) Mo₂C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O∗ removal were compared among undoped and Ni-doped Mo₂C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such as Ni adsorbed on T_Mo and T_C Mo₂C(001) surfaces enable weaker binding of important reactive intermediates (O∗, OH∗) compared to the undoped counterparts, which is beneficial for the O∗ removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O∗ removal reaction on the T_Mo Mo₂C(001) and T_C Mo₂C(001) surfaces. This computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo₂C and Ni-doped Mo₂C catalysts, which had been passivated and stored in an oxygen environment.