# Atom Probe Tomography for Catalysis Applications: A Review
## 3 Case Studies
### Catalysts as Supported Nanoparticles
#### 3.4.2 Carbon-Supported Nanoparticles
(**a**) 3D reconstruction of the specimen presenting a complex morphology; 5 nm slice of the 3D map (from the grey arrow) representing the distribution of (**b**) Pt; and (**c**) C-based species and Na; mass spectra of a Pt-Rh tip sample (**d**) before any deposition where only Pt and Rh species are detected; (**e**) after deposition of C-support in methanol/water solution (in absence of Pt nanoparticles): only fragments of methanol (C\({}_{2}\)H\({}_{x}\)\({}^{1+}\), C\({}_{3}\)H\({}_{x}\)\({}^{1+}\), C\({}_{4}\)H\({}_{x}\)\({}^{1+}\)) and water (H\({}_{2}\)O\({}^{1+}\), H\({}_{3}\)O\({}^{1+}\)) are detected; (**f**) after deposition of C-supported Pt nanoparticles showing the presence of methanol and water fragment, as well as the expected Pt\({}^{1+}\) species and the non-expected Na\({}^{1+}\) from the synthesis. Reprinted with permission from [121]. Copyright (2014) American Chemical Society. only well-defined and isolated particles were taken into account, and the analysis reveals individual composition ranging from 0.7 to 23.2 at.% of Co (as compared to the nominal composition of 25.3 at.%), which composition distribution will undoubtedly affect the catalytic activity. The authors also emphasize that the magnetism of Pt/Co depends on the Co content, and that electrophoresis might selectively deposit certain compositions (although electrophoresis is not an inherently magnetic phenomenon). Additionally, supported core-shell Ir@Pt nanoparticles were probed revealing the presence of core-shell structure with significant intermixing of Pt and Ir within the layers, but also duplex structures, suggesting a relatively low control during the synthesis. Since detailed atomic-scale chemical information is vital to understanding the structure-activity relationship, the three examples presented prove that APT can be used for the quality control of synthesized nanoparticles, giving better insights into the presence of impurities, the size and concentration distribution, as well as the structure of the particles. However, the presence of porous carbon support, and more generally of porous materials, remains an issue for APT experiments. One more example is the study of graphite-supported Cu-based catalysts [153], graphite being used to minimize the presence of a porous support such as C black. After hydrogenation of the sample, the catalyst is present as isolated and dispersed nanoparticles (12-15 nm) and agglomerates (1-3 \(\upmu\)m). The dispersion being too low to ensure a statistical representation of nanoparticles within the APT specimen, an agglomerate was selected, transferred to a micro-post and then FIB milled into a sharp tip. Between every steps of the milling, e-beam assisted deposition of Pt was performed to ensure structural stability of the sample and fill the pores. The presence of nanoparticles within the agglomerate can be observed in the 3D reconstruction, proving that APT can be used for materials of increasing complexity. Powders of catalysts and the development of innovative sample preparation to analyze them by APT will be discussed in the next section.