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

Abstract

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.

Imaging spatiotemporal evolution of molecules and active sites in zeolite catalyst during methanol-to-olefins reaction

“…In addition, as shown in Fig. 4c, d , though propylene and C 4+ are almost completely trapped inside the crystal, the further reactions with HCP species to form coke precursors still occur 33 , 54 . This can explain that, even the methanol conversion significantly declines or even cutting off the inlet flow, the formation of coke precursors still continues for a while 33 , 46 .…”

Multifunctional Catalyst Combination for the Direct Conversion of CO2 to Propane

“…The latter also presents an evident shoulder at higher Raman shifts, roughly centered at 1420 cm –1 . All these features relate to species trapped in the zeotype cages, identifiable as fingerprints of alkenes (1630 and 1420 cm –1 modes) − and polycyclic aromatic hydrocarbons (1383 cm –1 peak, typical for naphthalene) . TGA analysis was further employed on the spent hybrid system to quantify the amount of coke, showing a 2.96 wt % weight loss in the 300–600 °C region that can be attributed to coke (see Figure b).…”

Directed transforming of coke to active intermediates in methanol-to-olefins catalyst to boost light olefins selectivity

“…4c . Normally the bands at 1630, 1415, and 1360 cm −1 are related to PAHs (e.g., naphthalene, phenanthrene, and pyrene) 39 – 42 , while the band at 1600 cm −1 corresponds to the intense G band of amorphous carbon 39 and is overlapped with the band at 1630 cm −1 . As can be seen, during steam cracking the intensities of peaks at 1630, 1415, and 1360 cm −1 decrease, indicating the elimination of PAHs.…”