3‐D X‐ray Nanotomography Reveals Different Carbon Deposition Mechanisms in a Single Catalyst Particle

Abstract

Catalyst deactivation involves a complex interplay of processes taking place at different length and time scales. Understanding this phenomenon is one of the grand challenges in solid catalyst characterization. A process contributing to deactivation is carbon deposition (i. e., coking), which reduces catalyst activity by limiting diffusion and blocking active sites. However, characterizing coke formation and its effects remains challenging as it involves both the organic and inorganic phase of the catalytic process and length scales from the atomic scale to the scale of the catalyst body. Here we present a combination of hard X-ray imaging techniques able to visualize in 3-D the distribution, effect and nature of carbon deposits in the macropore space of an entire industrially used catalyst particle. Our findings provide direct evidence for coke promoting effects of metal poisons, pore clogging by coke, and a correlation between carbon nature and its location. These results provide a better understanding of the coking process, its relation to catalyst deactivation and new insights into the efficiency of the industrial scale process of fluid catalytic cracking.

Hard X‐Ray Nanotomography for 3D Analysis of Coking in Nickel‐Based Catalysts

“…It should be noted that this comparison is of qualitative nature based on the N e and the resolution is not high enough to clearly identify single voxels of coking. A similar gradient of the N e during coke formation was also found in FCC catalysts particles studied with X‐ray holotomography [26] . However, further detailed experiments at different coking stages are required to validate this conclusion.…”

“…However, the differential contrast approach shown was sensitive to relative changes in N e in an arbitrary unit scale, without providing a physical unit for N e . Furthermore, PXCT greatly exceeds the maximum resolution so far shown with holotomography [26] …”

“…A similar gradient of the N e during coke formation was also found in FCC catalysts particles studied with X‐ray holotomography. [26] However, further detailed experiments at different coking stages are required to validate this conclusion.…”

Harte Röntgen‐Nanotomographie zur 3D‐Analyse der Verkokung in Nickel‐basierten Katalysatoren

“…vorgeschlagen möglich, da z. B. graphitischer Koks oder Aktivkohle verschiedene N e aufweisen [26] . Für solch genaue Unterscheidung ist eine höhere räumliche Auflösung jedoch unerlässlich, um die N e innerhalb der 3D‐Probenstruktur genau zuzuordnen.…”

“…Jedoch war dieser andere Kontrastansatz nur sensitiv bezüglich relativer Änderungen der N e in einer Skala beliebiger Einheit ohne echte physikalische Einheit. Außerdem übersteigt die bisher gezeigte mögliche maximale Auflösung von PXCT die der Holotomographie [26] …”