Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 57: Surface Chemical Reactions and Heterogeneous Catalysis II

O 57.7: Talk

Thursday, March 29, 2007, 17:15–17:30, H38

Site specific analysis of CO dissociation on Ni(111) with STM — •Sebastian Horch, Martin Andersson, Frank Abild-Pedersen, and Jens Nørskov — Center for Atomic-scale Materials Design (CAMD), NanoDTU, Department of Physics, Technical University of Denmark, DK-2800 Lyngby, Denmark

One of the most important problems in heterogeneous catalysis is the analysis of the “active site” (cf. our contribution on the experimental identification of the active site on MoS₂). Only when this site and its relative abundance are known, it is –at least in principal– possible to determine e.g. turnover-rates per active site.

There are not many methods that can perform such site-specific measurements. While STM is the method of choice for atomic-scale visualization of the active site, it is much too slow for a real-time investigation of catalytic reactions at this site. If, however, the reaction leaves a clear footprint at the active site, one might use this to learn more about the reaction itself.

We have used this approach to investigate the dissociation of CO on Ni(111) using STM. The footprint is here the formation of carbide islands at the upper step edges. The steps provide the active site in this process, as can be shown e.g. by step blocking. By measuring the carbon uptake per step length for different temperatures and CO pressures, we can learn more about the processes involved and shed some more light onto the long-term debate about the barrier for CO dissociation on Ni surfaces.