CHEMICAL WAVE-PROPAGATION AND RATE OSCILLATIONS DURING THE NO2 H-2 REACTION OVER PT/

We have studied the catalytic reduction of NO, with hydrogen on Pt tip s by means field ion microscopy (FIM) and have observed kinetic instab ilities like explosive ignitions of the reaction as well as self-susta ined rate oscillations under certain conditions of temperature and pre ssure. These phenomena were found to occur at the apex of a Pr tip tha t resembled a top-and edge-truncated pyramid rather than a hemisphere. The pacemakers of the oscillations were identified to be the ''corner '' {0 1 2} planes which were most likely reconstructed under reaction conditions. Clear evidence was obtained that the communication mechani sm between successively igniting {0 1 2} planes is based on surface re action/diffusion. One-dimensional wavefronts were observed to move alo ng the [2 1 1] zone lines. For increasing hydrogen pressures and decre asing temperatures rate oscillations took also place on Pt(0 0 1). Rea ction waves were triggered by defects or small Pt clusters atop of thi s plane. While the frequency of the oscillations(f = 1.1 Hz) was stabl e over hundreds of cycles, the amplitudes were found to vary quite str ongly even on a short time scale. (C) 1998 Elsevier Science B.V, All r ights reserved.