The non‐linear behaviour of the NO‐H₂ reaction over Rh surfaces

Abstract

In this paper we describe the non-linearity of the NO-H, reaction over Rh surfaces. Rate oscillations have been observed over a stepped (1 1 1) surface with (100) steps, (Rh(533) at low pressures ( I @ Pa) below 500 K, while no oscillations could be observed under these conditions over a Rh( 100) surface and a stepped (1 00) surface with ( 1 1 I ) steps, Rh(71 I). The thermal stability of the N atoms formed during the reaction explains the observed structure sensitivity. Moreover, the results suggest that diffusion of N atoms is needed to synchronise the rate oscillations, a process that is absent on Rh (100) and Rh(71 I). Dans cet article, nous decrivons la non-linearite de la reaction NO-H, sur des surfaces de Rh. Des oscillations de vitesse ont ete observees sur une surface etagee (1 1 1) avec des etages (IOO), Rh(533) a de faibles pressions ( 1 fl Pa) en dessous de 500 K, tandis qu'aucune oscillation n'a pu &tre observee dans ces mCmes conditions sur une surface Rh( 100) et une surface etagee (100) avec des etages (1 1 I), Rh (711). La stabilite thermique des atomes de N formes lors de la reaction explique la sensibilite des structures observees. En outre, les resultats suggerent que la diffusion des atomes de N est necessaire pour synchroniser les oscillations de vitesse, un processus qui est absent sur le Rh(100) et le Rh (711).

Non-linear behaviour of nitric oxide reduction reactions over metal surfaces

“…Based on the FEM studies reported by van Tol et al a number of large Rh single-crystal surfaces (0.5 cm 2 ) consisting of ( 111) and (100) terraces were selected by Janssen et al [67,68,76] and Cobden et al [66].…”

“…TDS shows that N ads atoms start to combine and desorb between 450 and 600 K from Rh(533) [67]. In contrast, Rh(100) is deactivated in this temperature range due to the formation of a c(2 × 2)-N adlayer that is stable up to 700 K [67,76,77]. Strongly bound N ads atoms also form on the four-atom wide (100) terraces of Rh(410) and Rh(711) and, accordingly, no rate oscillations were observed over these surfaces either.…”