A combination of advanced characterization techniques: synchrotron X‐ray micro‐ and nanotomography, micro‐X‐ray fluorescence, and micro‐XRD have been used to characterize a commercial spent equilibrium fluid catalytic cracking catalyst (ECAT) at both the ensemble and individual particle level. At the ensemble level, X‐ray microtomography was used to determine the average size, shape, and respective distributions of over 1200 individual catalyst particles. This information is important to determine performance in commercial operation. It is shown that a large fraction of the particles contained large internal voids (5–80 μm diameter), and these voids likely aid the accessibility for large hydrocarbon molecules. At the individual particle level, by using X‐ray nanotomography, these voids were visualized at a much smaller scale (≈100 nm–12 μm in diameter). In addition, the individual phases that are present in the particle, for example, TiO2 and clay, are readily visualized in 3 D. Micro‐X‐ray fluorescence (XRF) was used to map, and semiquantitatively determine, both the contaminant (Ni, V, Fe) and inherent (La) catalyst elemental distributions. The distribution of zeolite Y in the ECAT particle was inferred from the La XRF map. Micro‐XRD determined the lattice constant of the zeolite Y at the individual catalyst particle level. This in‐depth characterization study at the ensemble and individual ECAT particle level presents a robust methodology that provides an understanding of the ECAT at both the micro‐ and nanometer scales.

The characterization of coke on spent catalysts is key to understanding deactivation mechanisms in hydrocarbon transformations. In this paper we report the comprehensive characterization (using laser Raman spectroscopy, 13C MAS NMR, temperature-programmed oxidation, XPS, and carbon K-edge NEXAFS) of coke on a series of spent Pt-Re re-forming catalysts as a function of time on stream and position in the catalytic bed. Laser Raman spectroscopy is shown to be rather insensitive to the carbon species present, while 13C MAS NMR finds that the carbon is present primarily as aromatic carbon. The TPO data are consistent with the coke being present on the alumina support and not to a large extent covering the metallic Pt-Re nanoclusters, but the data do suggest the presence of more than one type of coke present. The carbon K-edge NEXAFS data, however, clearly differentiate the types of coke species present. In the more coked samples the features ascribed to graphite become more pronounced, together with an increase in the aromaticity, as judged by the intensity of the π* peak. With increasing amounts of carbon on the catalyst there is also a concomitant decrease in the σ* C–H peak, indicating that the carbon is becoming less hydrogenated. By using a linear combination of C NEXAFS spectra for n-hexane, benzene, and broadened highly oriented pyrolytic graphite (HOPG), we estimate the compositional change on the coke species, verifying the aliphatic to aromatic conversion. The data indicate that a good model for the deposited coke is that of highly defected, medium-sized rafts with a short-range polycyclic aromatic structure which have a variety of points of contact with the alumina surface, in particular with the O atoms. In agreement with the NMR, there is evidence for the C–O functionality from the presence of a shoulder in the C NEXAFS spectra that is ascribed, as a result of DFT calculations, to a 1s → π* transition of the carbon atoms bound to the oxygen of a phenoxide-like species bound to the alumina surface. These data confirm earlier Soxhlet extraction studies and show that extraction process did not substantially change the character of the coke from what it was while still in contact with the catalyst surface.

The surface Si/Al ratio in a series of zeolite Y samples has been obtained using laboratory XPS, synchrotron (variable kinetic energy) XPS, and low energy ion scattering (LEIS) spectroscopy. The nondestructive depth profile obtained using variable kinetic energy XPS is compared to that from the destructive argon ion bombardment depth profile from the lab XPS instrument. All of the data indicate that the near surface region of both the ammonium form and steamed Y zeolites is strongly enriched in aluminum. It is shown that when the inelastic mean free path of the photoelectrons is taken into account that the laboratory XPS of aluminosilicates zeolites does not provide a true measurement of the surface stoichiometry while using variable kinetic energy XPS a more surface sensitive measurement can be made. A comprehensive Si/Al concentration profile as a function of depth is developed by combining the data from the three surface characterization techniques. The LEIS spectroscopy reveals that the topmost atomic layer is even further enriched in Al.

Many techniques, bigger pictureThe cover picture shows a combination of advanced characterization techniques: X-ray micro-and nanotomography and micro-X-ray fluorescence are used to characterize a commercial spent equilibrium fluid catalytic cracking catalyst at both the ensemble and individual particle level. In their Full Paper on p. 1427 ff., S. R. Bare et al. explain how the in-depth characterization study presents a robust methodology that provides an understanding of the equilibrium fluid catalytic cracking catalyst ECAT at both the micro-and nanometer scales.

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