An Experimental Study of Ammonia Dissociation in a Fixed-Bed Reactor Packed with Quartz Particles

Ammonia (NH3) dissociation over a bed of quartz particles of varying size was experimentally studied. A flow of 5%v/v NH3 in Ar was passed through the fixed-bed reactor and the exit stream was sampled and analysed using a gas chromatograph (GC) for measurement of H2 and N2 species concentrations.
A set of baseline experiments in the reactor without quartz particle packing were also run at various temperatures. The NH3 conversion, as well as H2 and N2 yields, were determined as a function of reaction temperature, gas-solid contact time, and quartz particle size fraction. The H2/N2 molar ratio in the reactor exit stream was found to be ~3 for all experimental runs, suggesting a robust
experimental measuring system. At a given temperature, the NH3 conversion monotonically increased with increasing contact time and decreasing particle size. Peculiarly, however, the effect of temperature was such that the NH3 conversion increased from 1000 K to 1100 K, decreased from 1100 K to 1250 K, and exponentially increased from 1250 K to 1400 K. The experimental data was
fitted with three kinetic rate laws assuming zeroth, first, and second orders of reaction. Possible reaction mechanisms were hypothesized and discussed, albeit requiring verifications with further independent experimentation and characterisation.