Hydrogen production by ammonia decomposition using high surface area Mo2N and Co3Mo3N catalysts

Abstract

High surface area bulk molybdenum nitride catalysts were synthesized via temperature-programmed ammonolysis of an ammonium heptamolybdate and citric acid (CA) composite. The synthesized materials were tested for CO_x-free H₂ production via ammonia decomposition for fuel cell application. Cobalt was added at different loadings (1, 3, and 5 wt%) as a promoter for the bulk molybdenum nitrides. The chemical composition and surface morphology of the nitride catalysts were studied by means of XRD, XPS, SEM-EDAX and TEM techniques. Addition of cobalt increased the formation of the γ-Mo₂N phase and cobalt existed as the Co₃Mo₃N phase, which was uniformly distributed over Mo₂N as evidenced by TEM and SEM analyses. A drastic increase in Mo₂N crystal size was observed when the Co loading exceeded 3 wt%, which in turn decreased the catalyst activity for ammonia decomposition reaction. All catalysts exhibit higher activity than the reported nitride catalysts at low temperatures. All catalysts showed stable activity for 30 hours. The activation energy calculated for ammonia decomposition was decreased drastically from 131.2 to 99 kJ mol⁻¹ by the addition of cobalt (1 wt%) in Mo₂N preparation.