Credit: © 2009 AAAS

Heterogeneous catalysts are often composed of metal nanoparticles dispersed across the surface of a support material. In a typical reaction, reactant molecules — supplied from the gas or liquid phase — will adsorb on the surface of the catalyst, where they will be converted into the desired products. To be able to analyse such reactions in situ is an important but challenging process. Elin Larsson and colleagues at Chalmers University of Technology have now developed a nanoplasmonic probe that allows catalytic reactions to be followed in real time1.

The approach uses optical transmission measurements taken through a quartz reactor containing a transparent sample. The sample is made up of arrays of gold disks, coated with a thin layer of catalyst support material on which catalytic nanoparticles are deposited. The gold disks act as localized surface plasmon resonance (LSPR) sensing structures. Light transmitted through the sample has an intensity minimum at the wavelength where the LSPR excitation in the sensing particles is strongest. The wavelength of maximum excitation is sensitive to changes in the dielectric properties near the sensing particles; by measuring shifts in wavelength, changes in the surface coverage of reactants on the catalytic nanoparticles can be followed.

The capabilities of the probe were demonstrated on common reactions with platinum catalysts, including the oxidation of carbon monoxide, and shown to be able to monitor changes in adsorbate coverages with a sensitivity of less than 0.1 monolayers.