Kinetics and mechanism of NH3 oxidation

The kinetics of NH 3 oxidation at 1279 to 1323 K have been studied experimentally witha flow tube reactor and theoretically by computer modelling. It was observed that the rate of NH 3 oxidation was zero order in NH 3 , increased with increasing [O 2 ], was inhibited by the presence of initial water, and promoted by the addition of H 2 or NO. During NH 3 oxidation, [NO] increased rapidly initially and more slowly thereafter. The size of the initial rise was independent of the presence or absence of H 2 O, while the subsequent increase was reduced by H 2 O. These and other kinetic features including the rate of oxidation of a trace of CO (a monitor of [OH]) are all quantitatively explained by a computer model. The major features of this model are conversion of NH 3 to NH 2 via reaction with O and OH, the reaction of NH 2 with O 2 , O, and OH to ultimately form NO, and the concurrent reduction of NO by NH 2 to ultimately yield N 2 . The chain carrier concentration during the process is regulated by a balance between carrier formation via the chain branching reactions and their removal by reactions such as NH 2 +HNO→NH 3 +NO.