Using a combination of spectromicroscopy at BESSY II and microscopic analyses at DESY's NanoLab, a team has gained new insights into the chemical behaviour of nanocatalysts during catalysis. The nanoparticles consisted of a platinum core with a rhodium shell. This image taken with a scanning electron microscope shows rhodium-coated platinum nanoparticles on a conductive substrate. Platinum core with Rhodium shell Platinum (Pt) is one of the best-known metal catalysts and is used in heterogeneous gas phase catalysis for emission control, for example to convert toxic carbon monoxide in car exhaust gases from combustion engines into non-toxic CO2 . The nanoparticles were first characterised and marked in their vicinity using scanning electron microscopy and atomic force microscopy at DESY NanoLab.