A preliminary experimental investigation into ammonia oxidation in a fixed-bed

This paper reports the findings of a preliminary experimental investigation into NH3 oxidation in a quartz fixed-bed reactor. The reactor was filled with quartz sand of a size fraction of 1.0 ~ 2.0 mm to a bed height of 430 mm. NH3 and O2 were diluted with Ar, mixed and passed through the reactor at a constant total gas flowrate of 818 mL·min-1. The experiments were carried out at various reaction temperatures between 700 and 1450 K, corresponding to residence times ranging from 0.68 to 2.07 s and equivalence ratios of 0.5, 1.0, and 1.5. The reactor exit stream was sampled and analysed using a gas chromatograph (Shimadzu 2014) and an electrochemical analyser (Testo 340) for the concentrations of N2, O2, NO, and NO2. A set of comparative experiments without bed material (considered as an ‘empty bed reactor’) at identical residence times were also performed in order to appreciate the effect of quartz surface on NH3 oxidation and NOx formation. It was revealed that the lowest temperature to initiate noticeable NH3 oxidation was reduced from 1300-1350 K in the empty bed reactor, to 1050-1350 K in the quartz sand filled fixed-bed reactor. The presence of quartz sand significantly reduced NOx formation during NH3 oxidation. Additionally, the peak NO concentrations and the temperature to reach the peak were reduced from 578 to 191 ppm and ~1350 to ~1050 K, respectively. It is speculated that the active radicals such as NH* produced from the heterogeneous decomposition reaction of NH3 on the quartz surface may have promoted NH3 oxidation and NOx reduction.