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Back Cover: Characterization of a Fluidized Catalytic Cracking Catalyst on... cracking your back x rayA 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 ?m 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 ?m 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.[Show abstract] [Hide abstract]ABSTRACT: Full-field transmission X-ray microscopy has been used to determine the 3D structure of a whole individual fluid catalytic cracking (FCC) particle at high spatial resolution and in a fast, noninvasive manner, maintaining the full integrity of the particle. Using X-ray absorption mosaic imaging to combine multiple fields of view, computed tomography was performed to visualize the macropore structure of the catalyst and its availability for mass transport. We mapped the relative spatial distributions of Ni and Fe using multiple-energy tomography at the respective X-ray absorption K-edges and correlated these distributions with porosity and permeability of an equilibrated catalyst (E-cat) particle. Both metals were found to accumulate in outer layers of the particle, effectively decreasing porosity by clogging of pores and eventually restricting access into the FCC particle.[Show abstract] [Hide abstract]ABSTRACT: Porosity in catalyst particles is essential because it enables reactants to reach the active sites and it enables products to leave the catalyst. The engineering of composite-particle catalysts through the tuning of pore-size distribution and connectivity is hampered by the inability to visualize structure and porosity at critical-length scales. Herein, it is shown that the combination of phase-contrast X-ray microtomography and high-resolution ptychographic X-ray tomography allows the visualization and characterization of the interparticle pores at micro- and nanometer-length scales. Furthermore, individual components in preshaped catalyst bodies used in fluid catalytic cracking, one of the most used catalysts, could be visualized and identified.

The distribution of pore sizes, as well as enclosed pores, which cannot be probed by traditional methods, such as nitrogen physisorption and isotherm analysis, were determined.[Show abstract] [Hide abstract]ABSTRACT: Fluid catalytic cracking (FCC) particles account for 40 to 45% of worldwide gasoline production. The hierarchical complex particle pore structure allows access of long-chain feedstock molecules into active catalyst domains where they are cracked into smaller, more valuable hydrocarbon products (for example, gasoline). In this process, metal deposition and intrusion is a major cause for irreversible catalyst deactivation and shifts in product distribution. We used x-ray nanotomography of industrial FCC particles at differing degrees of deactivation to quantify changes in single-particle macroporosity and pore connectivity, correlated to iron and nickel deposition. Our study reveals that these metals are incorporated almost exclusively in near-surface regions, severely limiting macropore accessibility as metal concentrations increase.

Because macropore channels are highways of the pore network, blocking them prevents feedstock molecules from reaching the catalytically active domains. Consequently, metal deposition reduces conversion with time on stream because the internal pore volume, although itself unobstructed, becomes largely inaccessible.

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