Binder Effects in SiO₂‐ and Al₂O₃‐Bound Zeolite ZSM‐5‐Based Extrudates as Studied by Microspectroscopy

Abstract

Microspectroscopic methods were explored to investigate binder effects occurring in ZSM‐5‐containing SiO2‐ and Al2O3‐bound millimetre‐sized extrudates. Using thiophene as a selective probe for Brønsted acidity, coupled with time‐resolved in situ UV/Vis and confocal fluorescence microspectroscopy, variations in reactivity and selectivity between the two distinct binder types were established. It was found that aluminium migration occurs in ZSM‐5‐containing Al2O3‐bound extrudates, forming additional Brønsted acid sites. These sites strongly influence the oligomer selectivity, favouring the formation of thiol‐like species (i.e., ring‐opened species) in contrast to higher oligomers, predominantly formed on SiO2‐bound ZSM‐5‐containing extrudates. Not only were the location and distribution of these oligomers visualised by 3 D analysis, it was also observed that more conjugated species appeared to grow off the surface of the zeolite ZSM‐5 crystals (containing less conjugated species) into the surrounding binder material. Furthermore, a higher binder content resulted in an increasing overall reactivity owing to the greater number of stored thiophene monomers available per Brønsted acid site.

An Overview on Zeolite Shaping Technology and Solutions to Overcome Diffusion Limitations

“…It could also be attributed to changes in the mesoporous structure during alkali treatment. Whiting et al [21] suggested that although SiO2 lacks acid sites able to take part in acid-catalyzed processes, its intimate contact with impregnated zeolite can induce solid-state ion exchange, with loss of Brønsted acidity as a result of zeolite framework dealumination.…”

A Facile Strategy to Prepare Shaped ZSM-5 Catalyst with Enhanced para-Xylene Selectivity and Stability for Toluene Methylation

“…Calculated from the saturation adsorption amounts, the adsorption ratio for Z5-bo increased from 1.8 to 1.9 after regeneration, whereas the adsorption ratio for Z5-atp decreased from 1.9 to 1.7 after regeneration. It means that the initial para-selectivity increment for regenerated Z5-bo was not only due to the reduced acidity but partially due to the more restricted pore opening which might be caused by the aluminium species migration in alumina-bound ZSM-5 extrudates [21,31]. In the Z5-atp case, the extent of pore opening reduction decreased after regeneration, which indicated that the continuously decreased acidity of Z5-atp was the main reason for para-selectivity increment.…”

“…As shown in Figure 6, the HZSM-5 catalyst exhibits three acid sites, i.e., weak (a low temperature peak at around 220 o C), medium (a medium temperature peak at around 300 o C) and strong (a high temperature peak at around 450 o C) acid sites. The amount of total acid sites of the zeolite extrudates Z5-atp and Z5-bo are much less than HZSM-5, showing the diluting effect of binders [31]. Compared with Z5-Bo, Z5-atp exhibited a lower total acidity and weaker acid strength.…”

“…Prior studies have reported that extra-framework aluminum species catalyze the formation of coke (and methane) in methanol to olefins (MTO) conversion [17,29]. Moreover, aluminum in alumina-bound extrudates can migrate to the zeolite surface, forming additional Brønsted acid sites [21,31]. These extra Brønsted acid sites facilitate coking, resulting a higher coke formation rate.…”

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

“…However, when zeolites are employed in an industrial reactor, they are usually combined with a binder material and shaped into catalyst bodies, such as extrudates. [27][28][29][30] It is however not known where such additional acid sites are located and how the additional acid sites affect the performance. [24] The addition of a binder material can have a large effect on the catalytic activity, as it can, for example, influence the overall acidity of the catalyst.…”