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This paper reviews some of the recent progress made in local probing of catalytic and non-catalytic surface reactions using relaxation-type pulsed field desorption mass spectrometry (PFDMS) in combination with video-field ion microscopy (FIM). First, the carbonylation of nickel to Ni(CO)4 is shown to involve surface Ni subcarbonyls as intermediates. Time-resolved PFDMS studies reveal Ni(CO)2 formation to be the slowest step in the overall reaction. Based on repetitive Ni(CO)2 formation in kink sites, a model is presented to explain morphological reshaping of Ni 3D field emitter crystals as observed previously by FIM. Second, we show that Co subcarbonyls, Co(CO)2,3, are formed during the interaction of CO and mixtures of CO/H2 with Co 3D crystals. CO dissociation and build-up of CxHy species are followed in real-time. Methane is the first product of hydrogenation, longer-chain hydrocarbons are detected by field pulses under steady reaction conditions. Finally, video-FIM data are presented for the ethylene reaction with Ni 3D crystals at elevated temperatures. Subsequent treatment of the Ni specimen with hydrogen, oxygen or by applying high electric fields in the absence of these gases results in the observation of non-linear reaction phenomena which are interpreted as being due to a clean-off titration of carbon. Chemical fronts seem to ignite in (0 0 1) planes and eventually travel to the central (1 1 1) plane. |
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