In situ characterization of the adsorption and reaction of chemicals in aqueous systems over heterogeneous catalysts has been a long been a challenge. While methods such as electron energy loss spectroscopy have been used successfully to monitor to the adsorption of compounds to model catalyst sites, they rely on ultra high vacuum environments. While FTIR coupled with ATR techniques can offer more realistic conditions, the penetration depth of such spectroscopy is on the bulk level, and signals produced suffer from the strong absorption of the aqueous environment. Surface-enhanced Raman spectroscopy (SERS) using gold nanoshells, on the other hand, could provide the requisite sensitivity for analyzing aqueous-phase catalyzed reactions. Au nanoshells are a class of SERS substrates, whose surface plasmon resonance (SPR) can easily be tuned by modifying core particle size and shell thickness, resulting in signals up to 1014 times greater than normal Raman alone.

The aqueous-phase hydrodechlorination (HDC) of trichloroethylene (TCE) has been shown to be highly efficient using newly developed Pd-on-Au nanoparticles (Pd/Au NPs), leading to ethane and chloride ions. These materials also are highly effective for other chlorinated ethylenes. In this paper, we report the synthesis of Pd-decorated Au nanoshells to mimic the HDC catalytic behavior of Pd/Au NPs during SERS analysis and the development of the SERS cell chamber. Preliminary SERS spectral analysis indicates that chemisorption and HDC surface reaction events of dichloroethylene (DCE) probe molecule can be observed. It appears that 1,1-DCE adsorbs to the Pd catalyst via pi-bonding with Pd atoms on the surface, for example. The results of this study highlights the promising use of SERS spectroscopy of metal-catalyzed reactions in water in situ.

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