Nitridation of the metallic Mo2C(001) surface from NH3 dissociative adsorption-A DFT study

Adsorption and sequential decomposition of ammonia on the metallic Mo2C(001) surface have been systematically computed using periodic density functional theory under the consideration of van der Waals dispersion correction (PBE-D3). It is found that NH3 adsorption prefers the top sites from low to saturation coverage. For the adsorption of surface NH2, bridge and hollow sites are possible at low coverage and only bridge sites are preferred at high coverage up to saturation. The adsorption of surface NH and N prefers the hollow sites. Sequential decomposition of NH3 into surface NH2, NH and N has low barrier and is highly exothermic. On the basis of surface Mo atoms, the saturation coverage of surface NH3, NH2 , NH and N by using NH3 as nitridation agent is 0.75, 1.0, 1.0 and 0.5 monolayer, respectively. These results provide the basis for the study of surface properties and catalytic reaction of nitrided Mo2C surfaces. The dissociative adsorption of ammonia among others metals and molybdenum nitrides has been categorized and compared.