# Atom Probe Tomography for Catalysis Applications: A Review
## 3 Case Studies
### Catalysts as Porous Materials--Zeolites
Using SAPO-34 instead of H-ZSM-5 catalysts also showed that coke formation during the methanol-to-hydrocarbons reaction correlates with the presence of acid sites, with differences in the cluster number, cluster size, and number of coke-depleted regions between the two catalysts [194]. Similar experiments were performed regarding the ethanol-to-hydrocarbon reaction [195] run for a longer time (72 h) to assess the industrial relevance of the analysis. Similarly to [191], a non-uniform distribution of Al and the formation of C-rich region can be observed after reaction, showing the usefulness of the APT methodology to study the coke formation in zeolites. With its unique spatial resolution, a homogeneous distribution of P after impregnation of a HZSM-5 zeolite, without significant removal of Al, can also be probed by APT [196]. Another type of zeolite studied by APT is the SSZ-13 for selective catalytic reduction [187]. The analysis of Fe-SSZ-13 after hydrothermal aging demonstrates that the Fe distribution remains homogeneous, but the authors mentioned that the results should be treated with caution since the size of the APT specimen is smaller than an individual SSZ-13 zeolite particle [197]. Cu-exchanged zeolite catalysts are also used for selective catalytic reduction systems due to their high activity and stability [198; 199; 200]. Cu-ZSM-5 and Cu-SSZ-13 zeolites were aged using industry standard protocol to  
Figure 15: Towards the analysis of zeolites by APT. (**a**) Helium Ion Microscope image of a ZSM-5 sample (scale bar: 20 \(\upmu\)m); (**b**) sample preparation by FIB lift-out (scale bar: 25 \(\upmu\)m); (**c**) and (**d**) TEM of the APT specimen highlighting the damage suffered during sample preparation: the crystalline structure is embedded in an amorphous shell due to Ga implantation (scale bars: (**c**) 100 nm and (**e**) 20 nm); 3D atom map of the Al distribution within a ZSM-5 specimen (**e**) before any treatment, representing a homogeneous distribution and (**f**) after steam treatment, where the formation of Al clusters is apparent, as well as segregation to a grain boundary; (**g**) coke formation on a ZSM-5 zeolite after methanol-to-hydrocarbon reaction using \({}^{13}\)C label. The red dots correspond to \({}^{13}\)C atoms, and the black regions correspond to \({}^{13}\)C-clusters, with possible coke species produced (consistent with the cluster size, even though APT do not provide such detailed molecular fingerprints). Panels (**a**–**f**): reprinted from [18977] under the terms of the Creative Commons Attribution License. Panel (**g**): reprinted from [191] under the terms of the Creative Commons Attribution License. simulate 135,000 miles of vehicle use and then analyzed by APT [201; 202]. In both cases, some material destruction occurred after aging due to Al removal from the framework. The difference in deNOx reactivity between Cu-SSZ-13 and Cu-ZSM-5 can be assigned to the changes in both Cu and Al spatial distribution between fresh and aged catalysts. Some Cu and Al clustering occurs in the Cu-SSZ-13 catalyst, whereas a strong segregation of Cu and Al in the form of CuAl\({}_{2}\)O\({}_{4}\) spinel phase takes place in the Cu-ZSM-5 catalysts. It is thus possible to correlate the activity and stability of zeolites with the formation of heterogeneities and/or the formation of inactive phases at the nanoscale level by APT.