A three-dimensional view of structural changes caused by deactivation of fluid catalytic cracking catalysts

Abstract

Since its commercial introduction three-quarters of a century ago, fluid catalytic cracking has been one of the most important conversion processes in the petroleum industry. In this process, porous composites composed of zeolite and clay crack the heavy fractions in crude oil into transportation fuel and petrochemical feedstocks. Yet, over time the catalytic activity of these composite particles decreases. Here, we report on ptychographic tomography, diffraction, and fluorescence tomography, as well as electron microscopy measurements, which elucidate the structural changes that lead to catalyst deactivation. In combination, these measurements reveal zeolite amorphization and distinct structural changes on the particle exterior as the driving forces behind catalyst deactivation. Amorphization of zeolites, in particular, close to the particle exterior, results in a reduction of catalytic capacity. A concretion of the outermost particle layer into a dense amorphous silica–alumina shell further reduces the mass transport to the active sites within the composite.

Magnetophoretic Sorting of Single Catalyst Particles

“…[18,19] During the FCC process, the catalyst deactivates irreversibly due to dealumination and the accumulation of metals, mainly Fe, Ni, and V. While Ni and V decrease the yield by promoting for example, coke formation, Fe is supposed to deactivate the particles by creating a shell of reduced porosity on the particles outer surface, either via vitrification of the particle matrix in the presence of Fe and/or co-deposition of silica. [20][21][22][23][24][25][26][27][28][29] Therefore, during operation, to create a stable process efficiency, a fraction of catalyst is being replaced on a daily basis, resulting in a mixture called equilibrium catalyst (ECAT). To investigate their deactivation, FCC ECAT particles are often sorted based on their skeletal density, which is associated with metal loading and age.…”

“…[18] This deposited Fe, which originates from the feedstock or from reactor debris, is mainly held responsible for the deactivation of these catalysts due to pore blocking. [20,28,29,39] Furthermore, it was shown that these two types of Fe distributions have different oxidation states. Inside the clay, Fe is found as Fe 0 and as Fe II in the form of FeO and SiFeO 3 .…”

Correlative Multiscale 3D Imaging of a Hierarchical Nanoporous Gold Catalyst by Electron, Ion and X‐ray Nanotomography

“…Taking into account the available spatial resolution, field of view and sample preparation requirements, PXCT in particular is brought into focus as a powerful and rapidly developing technique with widespread potential applications in catalysis. While PXCT is a relatively young technique, it has already demonstrated unprecedented 3D isotropic spatial resolutions of 14.6 nm for an integrated circuit sample and 31 nm for catalyst particles . Here we present an isotropic spatial resolution of 23 nm using PXCT, a new record for a heterogeneous catalyst sample.…”

“…When applied to catalysis, analytical methods based on structural imaging or microscopy are therefore required to incorporate large fields of view, high spatial resolution, and to extend across multiple length scales . Ideally such techniques should also be non‐invasive, or cause minimal damage or interaction with the sample of interest …”

“…preparation of lamellae), which carries the risk of structural damage. In this context, non‐invasive three‐dimensional (3D) imaging methods based on computed tomography are beginning to receive significant attention for characterisation of heterogeneous catalysts, including nanoporous gold . By revealing both exterior and interior structural features, tomographic analysis can derive surface area, porosity and pore size distribution data from the sample together with pore network mapping in 3D, as demonstrated recently for nanoporous silver .…”