Spatio-temporal dynamics of the NO + NH3 reaction on polycrystalline platinum

Spontaneous reaction rate oscillations and spatio-temporal patterns have been observed by mass spectrometry and photoemission electron microscopy (PEEM) during the reduction of NO by NH3 on polycrystalline platinum at 1 × 10−4 Torr and temperatures from 460-520 K. The appearance of both oscillations and patterns was found to be strongly dependent on the gas phase composition and the temperature. In addition, the overall dynamics of the catalyst were found to be dominated by the nonlinear behavior of Pt(1 0 0) type grains, while other types of grains did not participate. In contrast to previous studies, a large number of complex multimodal oscillations were observed, particularly as the coupling between the surface and the gas phase was increased. The appearance of these complex oscillations demonstrates the importance of gas phase coupling to understanding catalytic reactions, even in high vacuum systems.