Kinetic instabilities in the NO/H2 reaction on platinum

We have studied the catalytic reduction of nitric oxide (NO) with hydrogen (H-2) on platinum using both field ion microscopy (FIM) and pulsed field desorption mass spectrometry (PFDMS). Under certain conditions of temperature and gas pressure this reaction exhibits non-linear behaviour, i.e. hysteresis effects and rate oscillations occur. Ensembles of kink sites of the <100> zones are found to act as pacemakers, which is in line with earlier studies demonstrating {012} planes to ignite in a quasi-concerted manner. 1,2 Experiments with tips of varying radius of curvature always lead to the same sequence of image patterns. Large variations in the H-2 partial pressure has little influence on the frequency of the rate oscillations. Using PFDMS under the reaction conditions we show that NO+ rather than H2O+/H3O+ (the neutrals are formed during the reaction process) is the imaging species in FIM. Interestingly, PtOxn+ (x less than or equal to 3) are seen X in the mass spectra, indicating that the reaction is controlled by a vacant site mechanism with the inclusion of partial oxidation of the Pt surface. Copyright (C) 2004 John Wiley Sons, Ltd.