Ab initio G2M(MP2)HMP2/6-31G** and density functional B3LYP/6-311+G(3df,2p)//B3LYP/6-31G** calculations for various reactions in the N-2/H-2/BeO and N-2/H-2/FeO systems show that beryllium and iron oxides can catalyze N-2 hydrogenation and the reaction mechanism involves a facile addition of H-2 to metal oxide to form HMOH, which reacts with nitrogen through N-2 insertion into the M-H bond. The insertion barrier decreases from 125.2 kcal/mol for the N-2 + H-2 reaction to 68.9 and 45.3 kcal/mol for N-2 + HBeOH and N-2 + HFeOH, respectively. After the formation of eta(2)-N-2(H)MOH intermediates, H atom can migrate from O to N with barriers of 59.2 and 50.7 kcal/mol leading to the N2H2MO complexes of metal oxides with diazene. The MO + H-2 + N-2 --> N2H2MO reactions in the gas phase can easily occur providing that the chemically activated HMOH species formed at the first step do not dissipate their energy before they collide with the N-2 molecule. The second and third stages of nitrogen hydrogenation in the presence of a metal oxide have been investigated taking BeO as a model. The results indicate that the gas-phase N2H2BeO + H-2 --> N2H4BeO and N2H4BeO + H-2 --> 2NH(3) + BeO reactions can be facile because they exhibit the highest barriers of 10.4 and 13.4 kcal/mol, respectively, relative to the reactants.