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Discerning the Location and Nature of Coke Deposition from Surface to Bulk of Spent Zeolite Catalysts

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ABSTRACT

The formation of carbonaceous deposits (coke) in zeolite pores during catalysis leads to temporary deactivation of catalyst, necessitating regeneration steps, affecting throughput, and resulting in partial permanent loss of catalytic efficiency. Yet, even to date, the coke molecule distribution is quite challenging to study with high spatial resolution from surface to bulk of the catalyst particles at a single particle level. To address this challenge we investigated the coke molecules in HZSM-5 catalyst after ethanol conversion treatment by a combination of C K-edge X-ray absorption spectroscopy (XAS), 13C Cross polarization-magic angle spinning nuclear magnetic resonance (CP-MAS NMR) spectroscopy, and atom probe tomography (APT). XAS and NMR highlighted the aromatic character of coke molecules. APT permitted the imaging of the spatial distribution of hydrocarbon molecules located within the pores of spent HZSM-5 catalyst from surface to bulk at a single particle level. 27Al NMR results and APT results indicated association of coke molecules with Al enriched regions within the spent HZSM-5 catalyst particles. The experimental results were additionally validated by a level-set–based APT field evaporation model. These results provide a new approach to investigate catalytic deactivation due to hydrocarbon coking or poisoning of zeolites at an unprecedented spatial resolution.

No MeSH data available.


Level-set simulation.(a) framework for porous material, (b) the reconstructed simulated APT result showing the non-uniform distribution of ions, (c) the simulation framework for the same material with pores filled with a high electric field material, and (d) the reconstruction from the material with filled pores.
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f6: Level-set simulation.(a) framework for porous material, (b) the reconstructed simulated APT result showing the non-uniform distribution of ions, (c) the simulation framework for the same material with pores filled with a high electric field material, and (d) the reconstruction from the material with filled pores.

Mentions: The reconstruction results in Fig. 6(a) show the simulated geometry of material with unfilled pores where the atoms at the periphery of pores are highlighted in blue. The reconstructed simulated APT data of the same material are shown in Fig. 6(b) in which considerable presence of edge atoms inside the pores is observable. This can be attributed to trajectory crossing events during evaporation of porous material39. In spite of the local distortions in ion trajectory, based on Fig. 6(b) it is clear that there can be a non-uniform density of atom distribution in the location of pores.


Discerning the Location and Nature of Coke Deposition from Surface to Bulk of Spent Zeolite Catalysts
Level-set simulation.(a) framework for porous material, (b) the reconstructed simulated APT result showing the non-uniform distribution of ions, (c) the simulation framework for the same material with pores filled with a high electric field material, and (d) the reconstruction from the material with filled pores.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120296&req=5

f6: Level-set simulation.(a) framework for porous material, (b) the reconstructed simulated APT result showing the non-uniform distribution of ions, (c) the simulation framework for the same material with pores filled with a high electric field material, and (d) the reconstruction from the material with filled pores.
Mentions: The reconstruction results in Fig. 6(a) show the simulated geometry of material with unfilled pores where the atoms at the periphery of pores are highlighted in blue. The reconstructed simulated APT data of the same material are shown in Fig. 6(b) in which considerable presence of edge atoms inside the pores is observable. This can be attributed to trajectory crossing events during evaporation of porous material39. In spite of the local distortions in ion trajectory, based on Fig. 6(b) it is clear that there can be a non-uniform density of atom distribution in the location of pores.

View Article: PubMed Central - PubMed

ABSTRACT

The formation of carbonaceous deposits (coke) in zeolite pores during catalysis leads to temporary deactivation of catalyst, necessitating regeneration steps, affecting throughput, and resulting in partial permanent loss of catalytic efficiency. Yet, even to date, the coke molecule distribution is quite challenging to study with high spatial resolution from surface to bulk of the catalyst particles at a single particle level. To address this challenge we investigated the coke molecules in HZSM-5 catalyst after ethanol conversion treatment by a combination of C K-edge X-ray absorption spectroscopy (XAS), 13C Cross polarization-magic angle spinning nuclear magnetic resonance (CP-MAS NMR) spectroscopy, and atom probe tomography (APT). XAS and NMR highlighted the aromatic character of coke molecules. APT permitted the imaging of the spatial distribution of hydrocarbon molecules located within the pores of spent HZSM-5 catalyst from surface to bulk at a single particle level. 27Al NMR results and APT results indicated association of coke molecules with Al enriched regions within the spent HZSM-5 catalyst particles. The experimental results were additionally validated by a level-set–based APT field evaporation model. These results provide a new approach to investigate catalytic deactivation due to hydrocarbon coking or poisoning of zeolites at an unprecedented spatial resolution.

No MeSH data available.