Cobalt molybdenum bimetallic nitride catalysts for ammonia synthesis Part 1. Preparation and characterization

摘要

Cesium-promoted cobalt molybdenum bimetallic nitride CO_3MO_3N catalyst was found to give higher productivity of am- monia 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 molybde- num 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 60rnlmin-l of N_2 + 3H_2. The simple Mo2N was less active (35 #mu#molh~(-l) g-cat~(-1)) and deactivated soon. CO_3MO_3N pre- pared from cobalt molybdate hydrate was active (179 #mu#mol h~(-1) g-cat~(-l)) and stable. The activity of Co3Mo3N was increased (652 #mu#mol h~(-1) g-cat~(-l)) after being treated with the reactant gas at 873 K for 6 hafter the passivation with 1% of 0_2 at 298 K. The corresponding molybdenum bimetallic nitrides with nickel or iron were also prepared; however, they were not as active as CO_3MO_3N. The activity of Co3Mo3N was increased by the addition of alkali promoter. Cesium was a more effective promoter than potassium, suggesting an electronic effect. 2mol% Cs addition was found to give the maximum activity after the reactant gas treatment at 873 K for 6h (986 #mu#mol h~(-1) g-cat~(-l_ ).