Theoretical understanding on all-solid frustrated Lewis pair sites of C₂N anchored by single metal atom

The design of all-solid heterogeneous catalysts with frustrated Lewis pairs (FLPs) has attracted much attention recently because of their appealing low dissociation energy for H₂ molecules due to which a promotion of hydrogenation reaction is expected. The sterically encumbered Lewis acid (metal site) and base (nitrogen site) in the cavity of single transition metal atom-doped M/C₂N sheets make them potential candidates for the design of catalysts with FLPs, while a comprehensive understanding of their intrinsic property and reactivity is still lacking. Calculations show that the complete dissociation of the H₂ molecule into two H* states at the N sites requires two steps: heterolytic cleavage of the H₂ molecule and the transfer of H* from the metal site to the N site, which are strongly related to the acidity of the metal site. Ni/C₂N and Pd/C₂N, which outperform the other eight transition metal atom (M) anchored M/C₂N candidates, possess low energy barriers for the complete dissociation of H₂ molecules, with values of only 0.30 and 0.20 eV, respectively. Furthermore, both Ni/C₂N and Pd/C₂N catalysts can achieve semi-hydrogenation of C₂H₂ into C₂H₄, with overall barriers of 0.81 and 0.75 eV, respectively, which are lower than those reported for many other catalysts. It is speculated that M/C₂N catalysts with intrinsic FLPs may also find applications in other important hydrogenation reactions.