Nanoplasmonic Probes of Catalytic Reactions

Scientists from Sweden have recently published a report in Science, which discuss about their newly developed plasmonic sensing method for heterogeneous catalytic reactions based on arrays of nanofabricated gold disks, covered by a thin (~10 nanometer) coating (catalyst support) on which the catalyst nanoparticles are deposited.

In heterogeneous catalysis, reactants in gas or liquid phase are converted to desired product molecules on the surface of a solid catalyst, which is usually composed of catalytically active nanoparticles (1 to 10 nm) dispersed on a porous, high-surface-area support material. In order to understand and improve these systems, it is important to be able to monitor the catalyst’s state and to follow the reaction in real time. An important quantity is the surface coverage of reactants. However, experimental difficulties arise from the complexity of the catalyst and the atmospheric or higher pressures in which the reactions occur. Model systems (commonly single-crystal surfaces) and model reactions are frequently investigated at idealized ultrahigh vacuum (UHV) conditions, allowing use of powerful experimental probes (such as electrons, photons, or ions). A major challenge is to correlate results obtained by using the idealized and thoroughly scrutinized model catalysts in UHV with those of the less characterized real nanostructured catalysts at real reaction conditions.

This Report describe a method that, with a simple optical transmission (or reflection) measurement, can follow catalytic reactions in real time for both model and real supported catalysts. The principle is "nanoplasmonic" [localized surface plasmon resonance (LSPR)] sensing, currently intensely explored for biosensing, down toward single-molecule sensitivity. It is shown that LSPR can monitor changes in adsorbate coverages on "realistic" supported catalysts with a sensitivity corresponding to much less than 0.1 monolayer (ML).

The LSPR sensing structures are nanoscale disks of gold or platinum. The light transmitted through the sample has an intensity minimum (maximum extinction) at the wavelength at which the LSPR excitation in the sensing particles is strongest. The excitation creates a strongly enhanced electromagnetic near field, which acts as a probe of the nanoparticle’s surrounding.

For detailed experimental study please goto Science, Vol. 326. no. 5956, pp. 1091 - 1094