The technique of scanning tunnelling microscopy has revolutionised our understanding of surface chemistry, due to its ability to image at the atomic and molecular scale, the very realm at which chemistry operates. This critical review focuses on its contribution to the resolution of various problems in heterogeneous catalysis, including surface structure, surface intermediates, active sites and spillover. In the article a number of images of surfaces are shown, many at atomic resolution, and the insights which these give into surface reactivity are invaluable. The article should be of interest to catalytic chemists, surface and materials scientists and those involved with nanotechnology/nanoscience. (129 references.)

The graphical abstract shows the reaction between gas phase methanol and oxygen islands on Cu(110), courtesy of Philip Davies of Cardiff University. The added-row island is shown as silver-coloured spheres (copper) and red (oxygen) on the copper surface. Methanol preferentially reacts with the terminal oxygen atoms in the island forming adsorbed methoxy and OH groups. Only the terminal oxygen atoms in the island are active sites for the reaction.