CATALYTIC NH3 DECOMPOSITION BY TOPOTACTIC MOLYBDENUM OXIDES AND NITRIDES - EFFECT ON TEMPERATURE-PROGRAMMED GAMMA-MO2N SYNTHESIS

The extent of NH3 decomposition during temperature-programmed synthesis of high surface area γ-Mo2N from MoO3 is reported. It was found that the flowing NH3 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 NH3 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 NH3/MoO3 reaction is difficult because of hindered heat transfer. It is proposed that N2/H2 mixtures be used in large-scale syntheses of topotactic γ-Mo2N to reduce heat transfer problems. © 1994 Academic Press, Inc.