This thesis explores a novel tomographic reconstruction method that utilizes high angle annular dark field (HAADF) images to reconstruct the 3D structure of convex nanoparticles with homogenous composition and demonstrated the reconstruction of Au and Pt catalyst nanoparticles at a resolution of ~0.004nm³ Catalyst nanoparticles play a significant role in so many applications that a thorough understanding of structure-related catalytic performance is required. 2D analysis of such small structures appears to be inadequate and hence an efficient 3D characterization technique at atomic resolution is essential.