Revealing the Atomic Structure of Rh/γ-Al₂O₃ Catalysts Using Low Dose Rate Electron Microscopy

Abstract

Atomic resolution scanning/transmission electron microscopy (S/TEM) is nowadays a standard method used to reveal catalysts' nanostructures [1]. However, the active nature of catalysts renders them susceptible to alterations by high-energy electron beams. Resulting radiation effects, including heating, electrostatic charging, radiolysis, displacement damage, sputtering, and hydrocarbon contamination, might introduce structural artifacts and prevent interpreting the actual structure of these complex catalyst/support systems [2]. Electron-beam-assisted (de)activation of supported nanocatalysts (metalsupport interactions and interparticle interactions) needs to be considered. Hence, it is necessary to study and, ultimately, to minimize electron beam effects in order to characterize the pristine catalyst structure in these investigations.

Direct Observation of Rhodium Aluminate (RhAlOx) and Its Role in Deactivation and Regeneration of Rh/Al2O3 under Three-Way Catalyst Conditions

“…To enhance the atomic Low probe current (20 pA) with a dwell time of 4 μs was used to minimize the electron beam effects on the specimen. 16 Electron energy-loss spectroscopy (EELS) of Rh-M, O-K, and Al-L edges were recorded by using an FEI Titan 3 G2 TEM equipped with a gun monochromator and a Gatan Imaging Filter Quantum ERD (996) with accelerating voltage at 300 kV. EELS spectra were acquired in parallel mode with a convergence angle of 10 mrad and a collection angle of 18 mrad.…”

“…To enhance the atomic number ( Z ) contrast between Rh species (including nanoparticles and single atoms) ( Z Rh = 45) and the Al 2 O 3 substrate (with Z Al = 13), the high-resolution high-angle annular dark-field (HAADF) STEM images were collected with an annular detection angle of 60–300 mrad. Low probe current (20 pA) with a dwell time of 4 μs was used to minimize the electron beam effects on the specimen . Electron energy-loss spectroscopy (EELS) of Rh-M, O-K, and Al-L edges were recorded by using an FEI Titan 3 G2 TEM equipped with a gun monochromator and a Gatan Imaging Filter Quantum ERD (996) with accelerating voltage at 300 kV.…”

Phase Identification in Aged Catalysts Using STEM Depth Sectioning and Electron Energy-Loss Spectroscopy

“…With the collections of focus series using aberrationcorrected ThermoFisher Themis Z STEM microscope, three-dimensional representation of microstructure will facilitate the interpretation of Rh-alumina interacting species with high-spatial resolution. In the meantime, in order to avoid microstructure alteration of beam-sensitive gamma-alumina supports, the lowdose analysis will be carried out and show the optimal conditions due to the trade-off between high contrast and minimum beam effects [9].…”