Operando UV-Raman study of the methanol to olefins reaction over SAPO-34: Spatiotemporal evolution monitored by different reactor approaches

A molecular understanding of coke formation during the methanol to olefins (MTO) reaction is of great importance in order to adopt strategies that can improve the lifetime of the catalyst. UV-Raman has proven to be a valuable characterization tool, because of the favorable resonance conditions achieved towards key coke components, e.g. aromatic and olefinic compounds. Still, the applicability of UV-Raman in MTO is limited by the high risk of inducing sample damage under the exposure to the intense UV excitation laser. This drawback has been addressed by specific experimental setups, exploiting the concept of sample movement under the laser beam during the measurement, so that the laser-sample interaction is minimized by averaging over a wider sample surface. In this work, the impact of two different experimental setups, both relying on sample movement, are evaluated for the operando investigation of the MTO reaction over a SAPO-34. While in one case the whole catalytic bed is moved (fluidized bed), in the other case the sample is pressed into a pellet and rotated. Due to the peculiar spatial evolution of the reaction zone during MTO in a fixed-bed reactor, each method provides valuable information, but at very different spatiotemporal scales.