The denitrification mechanisms of piperidine, 2-methylpiperidine (2-MP), and 2,6-dimethylpiperidine (2,6-DMP) on MoP(001) were studied using self-consistent periodic density functional theory (DFT). These molecules located at Mo top site via the N atom and the molecular planes parallel with MoP surface. The energy barrier of the C-N bond cleavage of piperidinium (protonated piperidine) was much lower than that of the direct C-N bond cleavage of piperidine, indicating of a promoting effect of the protonation on the C-N bond cleavage, and the same trend was also found for 2-MP and 2,6-DMP. Our calculations suggested that the alpha-position methylation would not facilitate the hydrogenolysis pathway (protonation and subsequent C-N bond cleavage) of piperidine, in accordance with the experimental results. Both the protonation and alpha-position methylation could promote the C-N bond cleavage of piperidine on MoP(001), and the positive effect of protonation on C-N bond activation was more significant than that of the methylation. Graphic