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

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.