MXene-supported transition metal single-atom catalysts for nitrogen dissociation

Industrial ammonia production follows the Haber-Bosch process, whose rate-limiting step is the dissociation of the nitrogen molecule (N2), hence requiring suitable catalysts to break its triple bond. MXenes, a class of two-dimensional transition metal carbides and nitrides, have been proposed as very efficient catalysts for N2 dissociation. Here, by employing density functional theory-based calculations, we assess whether the deposition of one atom of a transition metal element (TM) on the Ti2C MXene surface further improves the catalytic potential of the MXene, serving as a single-atom catalyst. The results show that, for 21 of the 30 TMs considered, N2 can exothermically bind to the TM adatom, this bonding being favourable with respect to adsorption on the pristine Ti2C MXene surface for TMs of groups 3 to 6 of the Periodic Table. All the 21 TMs that successfully bind to N2 effectively reduce the N2 dissociation energy barrier when compared to the bulk Ti2C MXene by 18 to 84 %. Our results strongly indicate that doping the Ti2C MXene with atoms of transition metal elements significantly reduces the energy required to break the triple bond in N2, which may impact the nitrogen-to-ammonia process.