Chemical Imaging of the Binder‐Dependent Coke Formation in Zeolite‐Based Catalyst Bodies During the Transalkylation of Aromatics

Abstract

The choice of binder material, added to a zeolite-based catalyst body, can significantly influence the catalyst performance during a reaction, i. e. its deactivation and selectivity. In this work the influence of the binder in catalyst extrudates on the formation of hydrocarbon deposits was explored during the transalkylation of toluene with 1,2,4-trimethylbenzene (1,2,4-TMB). Using in situ UV-vis micro-spectroscopy and ex situ confocal fluorescence microscopy approach, coke species were revealed to predominantly form on the rim of zeolite crystals within Al 2 O 3 -bound extrudates. It was found that this was due to Al migration between the zeolite crystals and the Al 2 O 3binder creating additional acid sites near the zeolite external surface. In contrast, minimal isomerization of 1,2,4-TMB in the SiO 2 -bound extrudate allowed greater access to the zeolite internal pore network, creating a more homogeneous coke distribution throughout the zeolite crystals.

The Known and Overlooked Sides of Zeolite‐Extrudate Catalysts

“…[19] The catalytic consequences of the migration of Al species and generation of new acid sites have been recently demonstrated in the transalkylation between 1,2,4-trimethylbenzene (TMB) and toluene. [22,23] Compared to the unbounded zeolite or SiO 2 -bonded ZSM-5 extrudate, the Al 2 O 3 -bonded extrudate displays distinct differences in the coking manners and side isomerization. [22,23] The spatiotemporal chemical imaging techniques demonstrate that more coke species are formed with a heterogeneous spatial distribution mode within the Al 2 O 3 -zeolite extrudates, which is highlighted by a predominant location in the rim/edge of ZSM-5 crystals.…”

High‐Pressure Operando UV‐Vis Micro‐Spectroscopy of Coke Formation in Zeolite‐based Catalyst Extrudates during the Transalkylation of Aromatics

“…Previously it was reported that under influence of an Al 2 O 3 binder, Al species can migrate between het H‐ZSM‐5 crystals and the binder, forming extra acid sites [13] . The increase in isomerization products can be attributed to the extra acid sites formed between the H‐ZSM‐5 crystals and the binder [41] …”

“…More specifically, a microscopy reactor system, which can go to higher pressures (e. g. 5 bar), was developed, and installed under an UV‐vis microscope in order to follow the deactivation of the catalyst extrudates and to investigate the influence of the binder material during the transalkylation of toluene and 1,2,4‐TMB at two different pressures, namely 1 and 5 bar. The catalytic reaction was performed on the same zeolite H‐ZSM‐5‐containing mm‐sized extrudates bound with either SiO 2 or Al 2 O 3 , as investigated in our previous study [41] . The SiO 2 ‐bound extrudate showed an increase in conversion at 5 bar, which caused the formation of more poly‐aromatic molecules that are homogeneously distributed throughout the extrudate.…”

“…Previously, we have investigated mm‐sized zeolite H‐ZSM‐5‐containing extrudates, with either SiO 2 or Al 2 O 3 as binder materials during the transalkylation reaction at atmospheric pressure. The different catalyst extrudates were compared using an in‐situ UV‐vis diffuse reflectance (DR) micro‐spectroscopic and ex‐situ confocal fluorescence microscopic approach [41] . Using these characterization techniques, coke species were revealed to predominantly form on the rim of zeolite H‐ZSM‐5 crystals within Al 2 O 3 ‐bound extrudates.…”

Tailoring Multiple Porosities of Hierarchical ZSM‐5 Zeolites by Carbon Dots for High‐Performance Catalytic Transformation

“…And the absorption peaks around 660 nm are likely due to the formation of large poly‐aromatic compounds on the surface of the catalysts. [ 64 ] As observed in Figure S4b, Supporting Information, for the hierarchical ZSM‐5 catalysts, there has been a considerable decrease in the formation amount of the large poly‐aromatic compounds compared with m‐ZSM‐5 catalyst. Especially, for the spent h‐ZSM‐5(M‐IEEE) catalyst, few poly‐aromatic compounds were detected.…”