OSCILLATIONS IN THE REACTION-RATE OF NITRIC-OXIDE REDUCTION BY AMMONIA OVER POLYCRYSTALLINE PLATINUM FOIL CATALYSTS

Self-sustained oscillations were obtained in the NO + NH3 reaction at atmospheric pressure with reactant partial pressures of 133-600 Pa (1-4.5 Torr), in the temperature range of 603-673 K. The effects of reaction parameters, temperature, partial pressure, and reactant gas velocity were studied. The onset temperature of the oscillations (603 K) was slightly dependent on thc partial pressure of nitric oxide in the feed gas. Near this temperature the oscillations were uncontrolled (chaotic), while increasing the temperature resulted in periodic oscillations in the reaction rates. The oscillation phenomena were studied in both isothermic and adiabatic modes. The oscillations, when initiated by a temperature increase, start up only after an induction period during which the rates of NO consumption and N2 formation sharply increase as opposed to the slow enhancement of the rate of N2O formation. The two reaction branches found at the high- and low-temperature regimes in the batch model have product distributions which are similar to those found at the extremes of the amplitudes of rate oscillations.