Towards in situ Raman microscopy of single catalytic sites

We describe analytical techniques that allow an observation of heterogeneously catalyzed reactions, close to realistic chemical reaction conditions, with a spatial resolution down to 100 nm. Vibrational spectroscopy and scanning-force microscopy are combined to accomplish this goal. Raman microscopy is used for the investigation of the structural changes during heterogeneous catalytic reaction. This results already in a resolution of 1-2 mum, while in combination with scanning near-field optical microscopy (SNOM), a spatial resolution of even 100 nm has been achieved. Surface-enhanced Raman scattering (SERS) improves the sensitivity of Raman spectroscopy by many orders of magnitude and thus allows the study of a much broader range of reactions. As a model reaction system, the Pd catalyzed hydrogenation of benzene to cyclohexane was chosen. Spectra measured under reactive conditions differ significantly from reference spectra of the reactants and products measured under nonreactive conditions. This is explained by a structural change of the adsorbates on the activated surface but also by the possible formation of reaction intermediates.