# Atom Probe Tomography for Catalysis Applications: A Review
## 2 Atom Probe Tomography
### Latest Developments: Environmental Cells for APT  
To extend the capabilities of APT, in situ reaction cells have been developed for catalysis applications and to study corrosion processes and aging. The role of these in situ reaction cells is to expose the specimen to different gaseous environments at high temperatures so as to mimic realistic reaction conditions, with the advantage of avoiding possible oxidation, surface contaminations and impurities from external sources due to the transfer between ex situ reaction cells and the APT. This is especially important for oxygen- and moisture-sensitive samples. The main requirements for such reaction cells are (1) ease of integration with existing instruments; (2) isolation of the specimen within an enclosed volume during gas exposure and heating treatments; and (3) the absence of interference with the regular operation of the APT. The general procedure consists of:  
* cleaning the specimen by field evaporation (with regular APT analysis);
* transferring, under UHV conditions, the specimen to the reaction cell;
* isolating the cell from the rest of the instrument;
* applying reactive conditions (gases, \(T\), time,... );
* pumping the reaction cell;
* transferring, under UHV conditions, the specimen back to the analysis chamber.  
Reactions cells designed for 3 DAP systems can expose specimens to gas pressures up to 1 bar and at temperatures up to 873 K [85]; for modern versions of the instrument, cells exist with operating conditions of a few tens of mbar and up to \(T\approx\) 723 K [86], and from \(10^{-6}\) to 1000 mbar and up to \(T\approx\) 723 K with cryogenic quenching capabilities for the most recent design [87]. The improvement of APT analysis due to the use of in situ reaction cells is presented in Figure 3, corresponding to the analysis of Al oxidation under the same reaction conditions, but performed in ex situ (top spectra) and in situ (bottom spectra) cells [86]. Experiments performed in the ex situ cell reveal the presence of additional unassigned peaks in the mass spectra, probably originating in contamination during the transfer from the cell to the LEAP. This highlights the improvement over time in the instrument, as well as the reduction of the contamination with in situ cells.  
Different systems have been studied with these cells: NO and CO/Pt, NO, CO, O\({}_{2}\), N\({}_{2}\)O, NO + CO and NO + O\({}_{2}\)/Pt-Rh [85; 88; 89], NO/Pt-Rh-Ir, NO/Pt-Rh-Ru [90], NO/Au-Pd [91; 92] and O\({}_{2}\), N\({}_{2}\)O and H\({}_{2}\)/Au-Ag [92] for the 3 DAP version of the cell; and O\({}_{2}\)/Al, O\({}_{2}\)/Pt-Ir, O\({}_{2}\)/Pt-Rh-Ir [86]; D\({}_{2}\)/Pd, O\({}_{2}\) and H\({}_{2}\)O/Mg [87] for the most recent cells.  
Further developments are under way in the field of cryogenic transfer systems [93]. Indeed, the temperature and the gaseous environment control during transfer between instruments is mandatory for samples sensitive to air or thermal exposure, preventing chemical or morphological changes prior to analysis [94]. Environmental transfer hub and ultra-high vacuum carry transfer suitcase have been successfully used to improve the mass resolution of organometallic molecules analysis [94] and to investigate the surface oxidation of pure Mg during cryogenic transfer [95].