Using HAADF-STEM electron tomography and aberration-corrected TEM/STEM electron microscopy, 3D reconstructions and high resolution images have been recorded of heterogeneous catalysts consisting of gold nanoparticles supported on titanium dioxide (anatase); these catalysts have gained attention recently because of their potential for use in many reactions with both industrial and environmental importance. We will illustrate how through the combination of high resolution images and segmented 3D tomographic data, structural features of the supported phase can be revealed which are normally not accessible through conventional imaging. The location of the nanoparticles preferentially at the grain boundaries, confirmed by these studies, is likely to influence the stability of the nanoparticles and is a key step in understanding and facilitating the development of better catalysts. (C) 2010 Elsevier B.V. All rights reserved.