Spatial Evolution of Coke in ZSM-5 Catalysts During Methanol-to-Hydrocarbons Conversion Revealed by In Situ X-Ray Photoelectron Spectroscopy.

Along with assessing chemical pathways, understanding the spatial evolution of deactivating coke species in zeolites is essential for enhancing their catalytic efficiency in processes for chemical and fuel production. In this study, synchrotron-based in situ X-ray photoemission spectroscopy experiments provide insights into the coke deposition on ZSM-5 catalysts with different Si/Al ratios during methanol-to-hydrocarbons conversion, which is an industrially relevant reaction. Surface-sensitive C 1s X-ray photoemission spectroscopy with a probing depth ≈1 nm demonstrates that the less acidic ZSM-5 zeolites exhibit a more pronounced coke accumulation on crystal surfaces and promote the formation of highly condensed, graphite-like structures than the higher acidic ones. Analysis of coking kinetics, lattice deformation, and coke composition using Raman, in situ infrared, and operando UV-vis spectroscopies further supports enhanced surface coking in low-acidity, slowly deactivating catalysts and more prominent micropore coke formation in high-acidity, fast-deactivating catalysts. The results indicate that acid site density governs both the kinetics and the preferential location of coke, shedding light on the fundamental nanoscale processes underlying coke-induced deactivation of zeolite catalysts.