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The performance of zeolite-based catalyst extrudates can be largely influenced by the choice of binder material. To investigate these binder effects in zeolite-based catalyst extrudates in more detail, high spatiotemporal resolution techniques need to be further developed and employed. In this work, we present a new methodology to investigate binder effects in catalyst extrudates at different reaction pressures using operando UV-vis diffuse reflectance (DR) micro-spectroscopy coupled with on-line gas chromatography. We have studied mm-sized zeolite H-ZSM-5-containing extrudates with either Al2O3 or SiO2 binder material, during the transalkylation of toluene with 1,2,4-trimethylbenzene at 450 °C and at a pressure of either 1 or 5 bar. Using this technique, it was revealed that the binder material significantly influenced catalyst deactivation at different reaction pressures. By subsequent mapping of the cross sections of the cylindrical catalyst extrudates using UV-vis micro-spectroscopy, it was shown that the SiO2-bound extrudate formed poly-aromatic coke molecules homogeneously throughout the entire extrudate, whereas for the Al2O3-bound extrudate a coke ring formed that moved inwards with increasing reaction time. Notably, the developed methodology is not limited to the transalkylation reaction, and can also be used to gain more insight into binder effects during a variety of important catalytic reactions.

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 Al2O3‐bound extrudates. It was found that this was due to Al migration between the zeolite crystals and the Al2O3‐binder creating additional acid sites near the zeolite external surface. In contrast, minimal isomerization of 1,2,4‐TMB in the SiO2‐bound extrudate allowed greater access to the zeolite internal pore network, creating a more homogeneous coke distribution throughout the zeolite crystals.

The influence of the binder material in an industrial-type catalyst material is often neglected, although the addition of a binder can cause a significant change in the performance of the catalyst. It is difficult to visualize the effects of the different components in these multi-complex materials, and therefore, high spatiotemporal resolution techniques need to be employed. In this work, two complementary micro-spectroscopic techniques; operando UV-vis diffuse reflectance micro-spectroscopy (coupled to on-line mass spectrometry), and in situ confocal fluorescence microscopy were used to investigate the 1-hexene oligomerization reaction. The reaction was performed on both Al2O3- and SiO2-bound ZSM-5-containing extrudates at 250 °C and 300 °C. By employing operando UV-vis micro-spectroscopy, coupled with on-line mass spectrometry, Al2O3-bound catalysts were found to form larger reaction products, as well as more and larger hydrocarbon deposits, compared to the SiO2-bound catalysts. Furthermore, the extrudate containing Al2O3 deactivated slower than the extrudate containing SiO2 binder. Time-resolved chemical maps of the location of the reaction products were visualized using in situ confocal fluorescence microscopy. The maps show that, after reaction, the zeolite crystals contain different coke species than the Al2O3 binder.

Optical absorption and confocal fluorescence micro-spectroscopy were applied to investigate Brønsted acidity in millimetre-sized extrudates of Na(H)-ZSM-5 and SiO2 with varying ZSM-5 content. Partially (residual Na present) and fully proton-exchanged extrudates were employed, using thiophene oligomerization as a probe reaction. Time-resolved in situ optical absorption spectra and time dependent DFT calculations revealed several initial reaction pathways during the oligomerization reaction. In particular, it was found that protonated thiophene monomers reacted by either oligomerization (via reaction with un-reacted thiophene monomers) or ring-opening, depending on the Brønsted acid site density in each sample. Moreover, fully-exchanged extrudates not only have significantly higher reactivity than partially-exchanged samples, but they also favour the formation of ring-opening products, that are not formed on the partially-exchanged samples. Confocal fluorescence microscopy was employed to visualise non-invasively in 3D, the heterogeneity and homogeneity of thiophene oligomers on partially- and fully-exchanged extrudates, respectively. Furthermore, it was observed that extrudates with high binder content produce a higher relative amount of conjugated species, related with a higher quantity of available monomer in the binder, which is able to react further with intermediates adsorbed on active sites. Moreover, these conjugated species appear to form near the external surface of ZSM-5 crystals/agglomerates.