Single‐Site Molybdenum on Solid Support Materials for Catalytic Hydrogenation of N2‐into‐NH3

Abstract

AbstractVery stable in operando and low‐loaded atomic molybdenum on solid‐support materials have been prepared and tested to be catalytically active for N2‐into‐NH3 hydrogenation. Ammonia synthesis is reported at atmospheric pressure and 400 °C with NH3 rates of approximately 1.3×103 μmol h−1 gMo−1 using a well‐defined Mo‐hydride grafted on silica (SiO2‐700). DFT modelling on the reaction mechanism suggests that N2 spontaneously binds on monopodal [(≡Si−O‐)MoH3]. Based on calculations, the fourth hydrogenation step involving the release of the first NH3 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 NH3 with rates of circa 3.5×103 μmol h−1 gMo−1 under similar operating conditions and maximum yield of 29×103 μmol h−1 gMo−1 when the pressure is increased to 30 atm.