Operando UV‐Raman Spectroscopy Tracking the Evolving Intermediates in Hydrocarbon Conversion Over MFI Zeolites

ABSTRACT Zeolites are widely used as catalysts in olefin conversion, methanol‐to‐hydrocarbons (MTH), and aromatics production. Brønsted acid sites (BAS) confined within zeolite frameworks critically facilitate olefin isomerization, oligomerization, cracking, and aromatization via carbocation‐mediated mechanisms. However, the formation and evolution of intermediates, particularly under working conditions, remain challenging to observe. Here, we developed an operando system integrating 244‐nm UV‐Raman spectroscopy with gas chromatography and a multisampler, enabling simultaneous spectroscopic analysis and product quantification. We demonstrate that olefin adsorption mechanisms on zeolites depend on the Si/Al ratio and reaction temperature. Raman spectroscopy identified distinct adsorbed species: π‐complexes (1640 cm −1 ), olefinic carbocations (1615 cm −1 ), and aromatic carbocations (1605 cm −1 ). During 1‐butene and methanol conversion, the transition from olefinic to aromatic carbocations depends on temperature. This study presents a Raman‐based approach for the identification of BAS‐stabilized carbocations in zeolites, offering mechanistic insights essential for the optimization of zeolite‐catalyzed processes. The combination of Raman spectroscopy with online chromatography technology enables more comprehensive and reliable insights into the principles governing heterogeneous catalysis.