A temporal analysis of products (TAP) reactor was used to study the mechanism of ammonia oxidation at high temperature (1073 K) over Fe₂O₃, Cr₂O₃, and CeO₂. The results were compared with those obtained over the industrially applied Pt95-Rh5 alloy. Analysis of characteristic times of the transient responses of N₂ and NO made it possible to gain insight into the sequence of their formation. A common feature of both metal oxide and noble metal catalysts is that NO is a primary product of NH₃ oxidation, whereas N₂ results mainly from secondary transformations of NO. The amount of N₂O formed over the oxides was minimal. Multipulse NH₃ experiments in the absence of gas-phase O₂ give unequivocal evidence of the participation of surface lattice oxygen of the metal oxides in the reaction of NH₃ to NO. The degree of reduction of the oxide surface determines the product distribution but does not alter the catalytic activity for NH₃ conversion. Greater reduction favors the reaction channel to N₂ over that to NO. The desired reaction follows a Mars-van Krevelen-type scheme involving the participation of lattice oxygen in the NH₃ conversion to NO and regeneration of the so-formed vacancies by gas-phase O₂ and bulk lattice oxygen. Replenishment of surface vacancies by the diffusion of bulk oxygen occurs to a significant extent over Fe₂O₃. However, when NH₃ and O₂ are fed together, dissociative adsorption of gas-phase oxygen can be considered the main mechanism for vacancy regeneration.