Catalytic NH 3 Decomposition by Topotactic Molybdenum Oxides and Nitrides: Effect on Temperature Programmed γ-Mo 2N Synthesis

The extent of NH 3 decomposition during temperature-programmed synthesis of high surface area γ-Mo 2N from MoO 3 is reported. It was found that the flowing NH 3 feed gas is up to 99.88% decomposed at the elevated temperatures of the synthesis reaction. Kinetic data were used in a two-dimensional coupled heat and mass transfer model of the reactor to calculate bed temperatures from measured furnace temperature data. At the highest reaction temperatures, the endothermic NH 3 decomposition reaction strongly affects the bed temperatures, even in the small (0.1 g) bed used in the kinetic study. Local temperature ramps twice as high as the furnace ramping rate were found. Models of large reactant beds show that scale-up of the NH 3/MoO 3 reaction is difficult because of hindered heat transfer. It is proposed that N 2/H 2 mixtures be used in large-scale syntheses of topotactic γ-Mo 2N to reduce heat transfer problems.