Origin of the spatiotemporal oscillations observed during the NO + H2 reaction on a Rh field emitter

The main purpose of the study described in the present paper was to obtain more detailed information on the mechanism of the spatiotemporal oscillations found recently by field emission microscopy for the NO + H₂ reaction on a Rh tip. These oscillations are related to the kinetics of the reaction over a Rh wire. There are two kinetic regions of the steady-state reaction. The oscillations are attributed to the reversible transition between these kinetic regions. The observed sharp moving wave can be ascribed to the hydrogenation of a nitrogen layer, followed by fast combination and/or decomposition of the adsorbed intermediate NH and restoring of its surface coverage by the NO + H₂ interaction. Surface defects and, probably, grain boundaries are responsible for the initiation of the chemical waves in the course of the sustained oscillations.