Single‐Site Molybdenum on Solid Support Materials for Catalytic Hydrogenation of N 2 ‐into‐NH 3

Very stable in operando and low‐loaded atomic molybdenum on solid‐support materials have been prepared and tested to be catalytically active for N 2 ‐into‐NH 3 hydrogenation. Ammonia synthesis is reported at atmospheric pressure and 400 °C with NH 3 rates of approximately 1.3×10 3  μmol h −1  g Mo −1 using a well‐defined Mo‐hydride grafted on silica (SiO 2‐700 ). DFT modelling on the reaction mechanism suggests that N 2 spontaneously binds on monopodal [(≡Si−O‐)MoH 3 ]. Based on calculations, the fourth hydrogenation step involving the release of the first NH 3 molecule represents the rate‐limiting step of the whole reaction. The inclusion of cobalt co‐catalyst and an alkali caesium additive impregnated on a mesoporous SBA‐15 support increases the formation of NH 3 with rates of circa 3.5×10 3  μmol h −1  g Mo −1 under similar operating conditions and maximum yield of 29×10 3  μmol h −1  g Mo −1 when the pressure is increased to 30 atm.