Cobalt molybdenum bimetallic nitride catalysts for ammonia synthesis Part 2. Kinetic study

New bimetallic molybdenum nitride catalysts were prepared and their kinetic analyses were done. The nitride catalysts were prepared by nitriding the corresponding oxide precursors with ammonia gas through a temperature-programmed reaction up to 973 K. The standard rate of ammonia synthesis was measured with a 0.4 g of catalyst at 588-673 K under 0.1-3.1 MPa with a flow rate of 60 ml min(-1) of N-2 + 3H(2). The rates over molybdenum nitride catalysts were increased with increasing the reaction pressure. The rates over Co-3 Mo3N at 673 K under 3.1 MPa (4.8 mmol h(-1) g-cat.(-1)) was much higher than the corresponding molybdenum bimetallic nitrides with nickel or iron prepared in a similar way to Co3Mo3N. Apparent activation energies of these catalysts (11-14 kcal mol(-1)) were on the same level. Alkali promoted Co3Mo3N catalysts and a doubly promoted iron catalyst were tested. The rate of ammonia synthesis over Co3Mo3N catalyst with 2 mol% Cs added was remarkably high under high pressure (15.0 mmol h(-1) g-cat.(-1) under 3.1 MPa). This catalyst gave higher productivity of ammonia than the doubly promoted iron catalyst (4.6 mmol h(-1) g-cat.(-1) under 3.1 MPa). The kinetic parameters for C03MO3N catalysts were similar to that of the iron catalyst, however, the rate on Co3Mo3N was more retarded by the product ammonia. Interestingly, the strong ammonia retardation on the Co3Mo3N surface was relieved by the alkali promoter addition. (C) 2001 Elsevier Science B.V. All rights reserved.