Improving the reaction selectivity and activity for challenging substrates such as nitroaromatics bearing two reducible functional groups is important in industry, yet remains a great challenge using traditional metal nanoparticle based catalysts. In this study, single metal atom doped M-C2N catalysts were theoretically screened for selective hydrogenation of 3-nitrostyrene to 3-vinylaniline with H2 as the H-source. Among 20 M-C2N catalysts, the non-noble Mn-C2N catalyst was found to have excellent reaction selectivity. Importantly, due to the solid frustrated Lewis pair sites in the pores of Mn-C2N, a low H2 activation energy is achieved on high-spin Mn-C2N and the rate-determining step for the hydrogenation reactions is the H diffusion from the metal site to the N site. The unraveled mechanism of the hydrogenation of 3-nitrostyrene using Mn-C2N enriches the applications of Mn based catalysts and demonstrates its excellent properties for catalyzing the challenging hydrogenation reaction of substrates with two reducible functional groups.