This presentation reviews the recent progress made in imaging catalytic and non-catalytic surface reactions and in providing information on the local chemical composition of reactive layers. The methodical approach is based on video-Field Ion Microscopy (FIM) and atom-probe Pulsed Field Desorption Mass Spectrometry (PFDMS). The usefulness of the approach will be demonstrated in several case studies.
First, the carbonylation of Nickel to Ni(CO)₄ will be presented. This reaction involves subcarbonyls, Ni(CO)_2,3 as intermediates. Time-resolved PFDMS studies - in this method short field pulses of variable repetition frequency are used to field-desorb reactive species during the ongoing reaction - reveal Ni(CO)₂ formation to be the slowest step in the overall reaction. In FIM this process is seen to coincide with Ni kink sites detaching in a repetitive manner so that an originally hemispherical Ni crystal ("field emitter") is transformed into a polyhedral one. Second, we show that strong morphological changes do also occur during the reaction of CO and mixtures of CO/H₂ with Co crystals. In this latter case video-FIM allows mapping of the catalytic activity and revealing the competition between morphological reshaping and chemical restructuring due to carbon deposition. C_xH_y species are detected by PFDMS during the ongoing CO/hydrogen reaction. The ion intensities of these species depend on the reaction time (ms time scale at 450 K and 10^-3 mbar, H₂/CO=2) and methane is the first product of this hydrogenation. The data will be directly compared to transient kinetic build-up measurements using Co supported model catalysts.
Finally, video-FIM data on the interaction of ethylene with Ni and Co crystals will be shown. In both cases step sites cause a strong promotion of ethylene decomposition. In the Ni case, graphitic overlayers seem to form at intermediate temperatures (~600 K). These layers undergo an explosive clean-off reaction (with hydrogen) in which chemical fronts ignite in (001) planes before travelling in a self-accelerating manner toward the central (001) plane of the crystal. In a similar study, a Ni crystal is heated to ~1000 K in the presence of 10^-2 Pa ethylene. Subsequent in-situ quenching and FIM imaging at 500 K reveals string-like structures arranged in a concentric manner in the outskirts of the crystal. These structures point away from the crystal centre. A tentative explanation of this observation is based on the formation of carbon nanofibers and their repulsive interaction with the positive electric field present during imaging.

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