The purpose of this study is to analyze the localization of palladium nanoparticles within their silica support, in two heterogeneous catalysts synthesized by the sol-gel process, with different metal loadings. Electron tomography demonstrates that the palladium particles are localized deep inside the silica skeleton. The use of digital image analysis further shows that the dispersion of palladium is optimal in the sample with the lowest loading. The particles are regularly spaced in the middle of the silica skeleton, with a distance between them comparable to the diameter of the struts of silica.