Catalysis and Atom Probe Tomography: Recent Progresses and Future Developments towards the Analysis of Nanoporous Samples

Since the infancy of microscopy and surface science, many advanced techniques have been utilized to better understand catalytic systems. Previous studies focus either on the catalytic reaction (reactivity and selectivity) or on the catalyst itself, focusing on structural/morphological reconstructions as well as changes in the chemical composition of the catalyst. Atom probe tomography (APT) is a powerful tool for the characterization of both the three-dimensional structure and composition of catalysts at the atomic-scale. Alloys catalysts are of particular interest in applied catalysis because the synergistic effects between the different metals can drastically influence their activity as compared to their constituting pure metals [1]. At the microscopic scale, the surface composition of the very first atomic layers can differ from that of the bulk. The surface composition can be modified via physicochemical treatments, yielding different catalytic behaviours, which are highly dependent on the composition of the alloy, the temperature and duration of treatments, the crystallographic orientation, and the presence of surface or bulk defects. Among others, surface segregation/depletion, core-shell structure and formation of nano-islands can be studied by APT and can inform the nanoscale engineering of catalyst surface compositions (see [2] and references therein). For such studies, a needled shape catalyst is used, which can then be directly measured via APT. More recently, developments have been made regarding the sample preparation allowing the analysis of more realistic catalysts by atom probe tomography. Conventional tip samples used in APT can be used as a support for nanoparticles of catalysts using an electrophoresis method [3] and this method has been successfully used for the analysis of Pt, Pt-Co, Ir@Pt and Ag@Pd nanoparticles [1,3]. Eventually, embedding methods and FIB tip preparation can be used to study well-dispersed nanoparticles [4].