The ammonia synthesis from N-2 is of vital importance, with imitating biological nitrogen fixation attracted much interest. Herein, we investigate the catalytic mechanisms of N-2-to-NH3 thermal conversion on the singly dispersed bimetallic catalyst Rh1Co3/CoO(011), and find that the preferred pathway is an associative mechanism analogous to the biological process, in which alternating hydrogenations of the N-2 occur, with H-2 activation on both metal sites. We propose that the singly dispersed bimetallic M(1)A(n) catalyst, in which the doped metal atom M substitutes an oxygen atom on the oxide surface of metal A, serves as a new surface single-cluster catalyst (SCC) design platform for the biomimetic N-2-to-NH3 thermal conversion. The catalytic ability of M(1)A(n) catalyst is attributed to both the charge buffer capacity of doped metal M and the complementary role of synergic metal A in catalysis. Our work provides insights and guidelines for further optimizing the M(1)A(n) catalyst.