Reaction Mechanism of the Synthesis of Ammonia in the N2/H2/BeO and N2/H2/FeO Systems: A Theoretical Study

[[abstract]]Ab initio G2M(MP2)//MP2/6-31G** and density functional B3LYP/6-311+G(3df,2p)//B3LYP/6-31G** calculations for various reactions in the N2/H2/BeO and N2/H2/FeO systems show that beryllium and iron oxides can catalyze N2 hydrogenation and the reaction mechanism involves a facile addition of H2 to metal oxide to form HMOH, which reacts with nitrogen through N2 insertion into the M−H bond. The insertion barrier decreases from 125.2 kcal/mol for the N2 + H2 reaction to 68.9 and 45.3 kcal/mol for N2 + HBeOH and N2 + HFeOH, respectively. After the formation of η2-N2(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 + H2 + N2 → 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 N2 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 + H2 → N2H4BeO and N2H4BeO + H2 → 2NH3 + BeO reactions can be facile because they exhibit the highest barriers of 10.4 and 13.4 kcal/mol, respectively, relative to the reactants.[[notice]]補正完畢[[journaltype]]國