SURFACE RESTRUCTURING DYNAMICS IN CO ADSORPTION, DESORPTION, AND REACTION WITH NO ON PT(100)

A detailed experimental molecular beam study of the CO-induced surface phase transition on Pt{100}, from the clean surface hex-RO.7-degrees structure of the bulk termination (1 X 1) structure, has recently been completed in our laboratory. In the present work a stepwise mechanistic scheme is presented which accounts for the observed sticking probability dependence on both coverage and substrate temperature, including a strong flux dependence in the net sticking probability, and the behaviour of the desorption spectra. The shift in the highest-temperature peak to lower temperatures with increasing coverage is reproduced, together with zero order desorption kinetics. The model is based on the observed dependence of the (1 X 1) island growth rate from the hex-R phase with an apparent reaction order of 4.1 in the local CO coverage on the hex-R phase, and reproduces the observed hysteresis in the surface phase transition when Pt{100} is heated or cooled in CO. Kinetic oscillations in the reaction between CO and NO to form CO2 and N2 are reproduced by the model within two temperature regimes, in close agreement with experiment. In the higher temperature regime the oscillations are assigned to a new mechanism involving the hex reversible (1 X 1) phase transition. As these transitions proceed surface defects are generated, and these defects are shown to play an important role in the time scale of the oscillations. All the major features of adsorbate-induced restructuring, desorption and the CO + NO oscillatory reaction are therefore successfully reproduced by this single mechanistic scheme.