Low-frequency Raman modes and atomic force microscopy for the size determination of catalytic gold clusters supported on iron oxide

A new method is proposed to measure the grain size of gold nanoparticles supported on iron oxide used as catalysts. These particles, particularly active in the oxidative reactions of carbon monoxide and methanol have been characterized by employing a multi-technique approach based on the application of low-frequency Raman (LFR) modes and microscopy techniques. Atomic force microscopy and scanning electron microscopy showed a surface constituted by almost spherical Fe2O3 and Au nanoparticles having a size of 9–17 and 7–30 nm, respectively. LFR was proved to be a very useful technique to selectively probe gold clusters, since no acoustic mode was revealed for Fe2O3 nanoparticles. Furthermore, LFR specifically probed particles around 10 nm in size, which are particularly active in the catalytic process.