The structural properties of hollow sphere catalyst supports have been studied by neutron and X-ray tomography to visualize catalyst structures at different length scales by a non-destructive method. Neutron tomography has a lower spatial resolution compared to X-ray tomography (i.e. 100 vs. 10(-1) mu m), but allows investigating the entire catalyst structure, while X-ray tomography can be used to study the surface properties of single metallic spheres including the thickness of the washcoat layer. For neutron tomography, absorption contrast and phase contrast imaging are compared, the latter showing a significant improvement of the resolution and contrast. Neutron tomography showed differences in the packing density and in the interconnection of the individual spheres in different samples leading to open channels through the catalysts support structure, which affect the pressure drop and the efficiency of the catalyst packing.