Oscillatory behaviour of the reduction of NO by H2 over Rh

The NO reduction by H₂ on Rh has been studied by field emission microscopy (FEM). It has been observed that this reduction shows oscillatory behaviour at 460 K andP _NO = –1.5 ×10^–1 Torr andP _H2 =1×10^-6 Torr, Unique features of FEM are the very high spatial resolution and the presence of, in principle, an indefinite number of different crystal planes. The oscillatory behaviour is reflected by periodic changes in the emission current and in the images observed. The communication between different surfaces present on the field emitter is shown on a fluorescent screen. Diffusion and gas phase coupling seem to play a role. Many of the features reported earlier for the oscillatory behaviour of the NO-H₂ and NO-NH₃ reactions over Pt(100) are observed on Rh as well, including the surface explosion. The vacancy model proposed earlier for the oscillations over Pt(100), can be applied to the reactions described in this paper as well.