Cobalt molybdenum bimetallic nitride catalysts for ammonia synthesis: Part 1. Preparation and characterization Original Research Article

Cesium-promoted cobalt molybdenum bimetallic nitride Co3Mo3N catalyst was found to give higher productivity of ammonia than a doubly promoted iron catalyst. Molybdenum nitride catalysts were prepared by nitridation of the corresponding oxide precursors with ammonia gas via a temperature-programmed reaction up to 973 K. The precursors were molybdenum trioxide or molybdenum bimetallic oxide prepared via a mixed solution of ammonium molybdate and metal (Co, Ni, and Fe) nitrate. Ammonia synthesis was carried out with a 0.4 g of catalyst at 673 K under 0.1 MPa with a flow rate of 60 ml min−1 of N2+3H2. The simple Mo2N was less active (35 μmol h−1 g-cat−1) and deactivated soon. Co3Mo3N prepared from cobalt molybdate hydrate was active (179 μmol h−1 g-cat−1) and stable. The activity of Co3Mo3N was increased (652 μmol h−1 g-cat−1) after being treated with the reactant gas at 873 K for 6 h after the passivation with 1% of O2 at 298 K. The corresponding molybdenum bimetallic nitrides with nickel or iron were also prepared; however, they were not as active as Co3Mo3N. The activity of Co3Mo3N was increased by the addition of alkali promoter. Cesium was a more effective promoter than potassium, suggesting an electronic effect. 2 mol% Cs addition was found to give the maximum activity after the reactant gas treatment at 873 K for 6 h (986 μmol h−1 g-cat−1).